Pharmacological targeting of breast cancer stem cells (CSCs) is highly promising for the treatment of breast cancer, as the small population of CSCs appears responsible for tumor initiation and progression and also for resistance to conventional treatment. Here we report that the novel phosphosulindac (OXT-328, PS) selectively and effectively eliminates breast CSCs both in vitro and in vivo. PS reduced cell proliferation and induced apoptosis in various breast CSCs. Breast CSCs are resistant to conventional cancer drugs but are sensitive to PS. Long-term treatment with PS of mixtures of cultured breast CSCs with breast cancer cells preferentially eliminated the CSCs. PS impaired the ability of CSCs to form mammospheres and markedly suppressed the expression of CSC-related genes. More importantly, PS prevented by half (p=0.06) the formation of tumors initiated by CSCs in immunodeficient mice, and inhibited by 83% (p<0.05) the growth of already formed breast cancer xenografts, reducing the proportion of CSCs in them. PS suppressed the Wnt/β-catenin pathway by stimulating the degradation of β-catenin and its relocalization to the cell membrane; and also blocked the epithelial-mesenchymal transition (EMT) and the generation of breast CSCs. These results indicate that PS has a strong inhibitory effect against breast cancer, acting, at least in part, by targeting CSCs through a signaling mechanism involving Wnt signaling.

The efficiency of somatic cell reprogramming to pluripotency using defined factors is dramatically affected by the cell type of origin. Here we show that human keratinocytes, which can be reprogrammed at a higher efficiency than fibroblast¹, share more genes hypermethylated at CpGs with human ES cells than other somatic cells frequently used for reprogramming. Moreover, pluripotent cells reprogrammed from keratinocytes (KiPS) are more similar to ES cells that those reprogrammed from fibroblasts (FiPS) in regards to DNA methylation levels, mostly due to the presence of genes that fail to acquire high levels of DNA methylation in FiPS cells. We propose that higher reprogramming efficiency correlates with the hypermethylation of tissue specific genes, rather than with a more permissive pluripotency gene network.

Mutations in the survival of motor neuron gene (SMN1) are responsible for spinal muscular atrophy (SMA), a fatal neuromuscular disorder. Mice carrying a homozygous deletion of Smn exon 7 directed to skeletal muscle (HSA-Cre, Smn^F7/F7 mice) present clinical features of human muscular dystrophies for which new therapeutic approaches are highly warranted. Herein we demonstrate that tail vein transplantation of mouse amniotic fluid stem (AFS) cells enhances the muscle strength and improves the survival rate of the affected animals. Secondly, after cardiotoxin injury of the Tibialis Anterior, only AFS-transplanted mice efficiently regenerate. Most importantly, secondary transplants of satellite cells (SC) derived from treated mice show that AFS cells integrate into the muscle stem cell compartment, and have long term muscle regeneration capacity indistinguishable from that of wild type-derived SC. This is the first study demonstrating the functional and stable integration of AFS cells into the skeletal muscle, highlighting their value as cell source for the treatment of muscular dystrophies.

Blood transfusions have become indispensable to treat the anemia associated with a variety of medical conditions ranging from genetic disorders and cancer to extensive surgical procedures. In developed countries the blood supply is generally adequate. However, the projected decline in blood donor availability due to population ageing and the difficulty in finding rare blood types for alloimmunized patients indicate a need for alternative red blood cell (RBC) transfusion products. Increasing knowledge of processes that govern erythropoiesis has been translated into efficient procedures to produce RBC ex vivo using primary hematopoietic stem cells, embryonic stem cells or induced pluripotent stem cells. Although in vitro-generated RBC have recently entered clinical evaluation, several issues related to ex vivo RBC production are still under intense scrutiny: among those, are the identification of stem cell sources more suitable for ex vivo RBC generation, the translation of RBC culture methods into clinical grade production processes and the development of protocols to achieve maximal RBC quality, quantity and maturation. Data on size, hemoglobin and blood group antigen expression and phosphoproteomic profiling obtained on erythroid cells expanded ex vivo from a limited number of donors are presented as examples of the type of measurements which should be performed as part of the quality control to assess the suitability of these cells for transfusion. New technologies for ex vivo erythroid cell generation will hopefully provide alternative transfusion products to meet present and future clinical requirements.

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease that results from cell-mediated autoimmune destruction of insulin-producing cells. In T1DM animal models, it has been shown that the systemic administration of multipotent mesenchymal stromal cells (MSCs) results in the regeneration of pancreatic islets. Mechanisms underlying this effect are still poorly understood. Our aims were to assess whether donor MSCs (i) differentiate into pancreatic beta-cells and (ii) modify systemic and pancreatic pathophysiologic markers of T1DM. After the intravenous administration of 5x10⁵ syngeneic MSCs, we observed that mice with T1DM reverted their hyperglycemia and presented no donor-derived insulin-producing cells. In contrast, seven and 65 days post-transplantation, MSCs engrafted into secondary lymphoid organs. This correlated with a systemic and local reduction in the abundance of auto-aggressive T cells together with an increase in regulatory T cells. Additionally, in the pancreas of mice with T1DM treated with MSCs we observed a cytokine profile shift from pro-inflammatory to anti-inflammatory. MSC transplantation did not reduce pancreatic cell apoptosis but recovered local expression and increased the circulating levels of EGF, a pancreatic trophic factor. Therefore, the anti-diabetic effect of MSCs intravenously administered is unrelated to their trans-differentiation potential but to their capability to restore the balance between Th1 and Th2 immunological responses along with the modification of the pancreatic microenvironment. Our data should be taken into account when designing clinical trials aimed to evaluate MSC transplantation in patients with T1DM since the presence of endogenous precursors seems to be critical in order to restore glycemic control.

Neuronal precursor cells (NPCs) generated by stem cells in the subventricular zone (SVZ) migrate and differentiate into mature interneurons in the olfactory bulb (OB). The mechanisms responsible for the dynamic morphological changes in cells during this process are largely unknown. Wnt/Planar cell polarity (PCP) signaling regulates various developmental events, including neuronal migration and neurite formation. Here we studied the function of two components of the PCP pathway, Dishevelled2 and Van Gogh like-2, in the newborn neurons in the postnatal mouse OB. Electroporation- or lentivirus-mediated introduction of vectors carrying a knockdown or dominant-negative construct of these genes into the SVZ altered the distribution and dendrite formation of newborn neurons in the OB, suggesting that PCP signaling is involved in regulating the maturation of new neurons in the OB.

Induced pluripotent stem cells (iPSCs) generated from somatic cells of patients can be used to model different human diseases. They may also serve as sources of transplantable cells that can be used in novel cell therapies. Here, we analyzed neuronal properties of an iPSC line derived from a patient with a juvenile form of Huntington's disease (HD) carrying 72 CAG repeats (HD-iPSC). Although its initial neural inducing activity was lower than that of human ES cells, we found that HD-iPSC can give rise to GABAergic striatal neurons, i.e., the neuronal cell type that is most susceptible to degeneration in HD. We then transplanted HD-iPSC-derived neural precursors (HD-iPSC-NPC) into a rat model of HD with a unilateral excitotoxic striatal lesion, and observed a significant behavioral recovery in the grafted rats. Interestingly, during our in vitro culture and when the grafts were examined at 12 weeks after transplantation, no aggregate formation was detected. However, when the culture was treated with a proteasome inhibitor (MG132) or when the cells engrafted into neonatal brains were analyzed at 33 weeks, there were clear signs of HD pathology. Taken together, these results indicate that, although HD-iPSC carrying 72 CAG repeats can form GABAergic neurons and give rise to functional effects in vivo, without showing an overt HD phenotype, it is highly susceptible to proteasome inhibition and develops HD pathology at later stages of transplantation. These unique features of HD-iPSC will serve as useful tools to study HD pathology and develop novel therapeutics.

Phosphorylation of histone H2AX (γH2AX) is known to be the earliest indicator of DNA double-strand breaks (DSBs). Recently, it has been shown that mouse embryonic stem cells (mESCs) have very high basal levels of γH2AX, even when they have not been exposed to genotoxic agents. As the specialized role of high basal γH2AX levels in pluripotent stem cells is still debated, we investigated whether H2AX phosphorylation is important in maintaining self-renewal of these cells. Here we report that not only mESCs, but also mouse induced pluripotent stem cells (miPSCs), have high basal levels of γH2AX. We show that basal γH2AX levels decrease upon ESC and iPSC differentiation and increase when the cells are treated with self-renewal enhancing small molecules. We observe that self-renewal activity is highly compromised in H2AX-/- cells and that it can be restored in these cells through reconstitution with a wild-type, but not a phospho-mutated, H2AX construct. Taken together, our findings suggest a novel function of H2AX that expands the knowledge of this histone variant beyond its role in DNA damage and into a new specialized biological function in mouse pluripotent stem cells.

During embryogenesis, the endothelial and the hematopoietic lineages first appear during gastrulation in the blood island of the yolk sac. We have previously reported that an Ets variant gene 2 (Etv2/ER71) mutant embryo lacks hematopoietic and endothelial lineages, however, the precise roles of Etv2 in yolk sac development remains unclear. In the present study, we define the role of Etv2 in yolk sac blood island development using the Etv2 mutant and a novel Etv2-EYFP reporter transgenic line. Both the hematopoietic and the endothelial lineages are absent in the Etv2 mutant yolk sac. In the Etv2-EYFP transgenic mouse, the EYFP reporter is activated in the nascent mesoderm, expressed in the endothelial and blood progenitors, and in the Tie2⁺, c-kit⁺, CD41⁺ hematopoietic population. The hematopoietic activity in the E7.75 yolk sac was exclusively localized to the Etv2-EYFP⁺ population. In the Etv2 mutant yolk sac, Tie2⁺ cells are present but do not express hematopoietic or endothelial markers. In addition, these cells do not form hematopoietic colonies, indicating an essential role of Etv2 in the specification of the hematopoietic lineage. Forced overexpression of Etv2 during EB differentiation induces the hematopoietic and the endothelial lineages, and transcriptional profiling in this context identifies Lmo2 as a downstream target. Using EMSA, ChIP, transcriptional assays and mutagenesis, we demonstrate that Etv2 binds to the Lmo2 enhancer and transactivates its expression. Collectively, our studies demonstrate that Etv2 is expressed during and required for yolk sac hemato-endothelial development, and that Lmo2 is one of the downstream targets of Etv2.

Recent studies implicated the existence in adult human kidney of a population of renal progenitors with the potential to regenerate glomerular as well as tubular epithelial cells and characterized by co-expression of surface markers CD133 and CD24. Here, we demonstrate that CD133+CD24+ renal progenitors can be distinguished in distinct subpopulations from normal human kidneys based on the surface expression of Vascular Cell Adhesion Molecule 1 (VCAM1), also known as CD106. CD133+CD24+CD106+ cells were localized at the urinary pole of Bowman's capsule, while a distinct population of scattered CD133+CD24+CD106- cells was localized in the proximal tubule as well as in the distal convoluted tubule. CD133+CD24+CD106+ cells exhibited a high proliferative rate and could differentiate toward the podocyte as well as the tubular lineage. By contrast, CD133+CD24+CD106- cells showed a lower proliferative capacity and displayed a committed phenotype toward the tubular lineage. Both CD133+CD24+CD106+ and CD133+CD24+CD106- cells showed higher resistance to injurious agents in comparison to all other differentiated cells of the kidney. Once injected in SCID mice affected by acute tubular injury, both of these populations displayed the capacity to engraft within the kidney, generate novel tubular cells and improve renal function. These properties were not shared by other tubular cells of the adult kidney. Finally, CD133+CD24+CD106- cells proliferated upon tubular injury, becoming the predominating part of the regenerating epithelium in patients with acute or chronic tubular damage. These data suggest that CD133+CD24+CD106- cells represent tubular-committed progenitors that display resistance to apoptotic stimuli and exert regenerative potential for injured tubular tissue.

Hematopoietic stem cell (HSC) function is tightly regulated by cytokine signaling. Although phospho-flow cytometry allows us to study signaling in defined populations of cells, there has been tremendous hurdle to carry out this study in rare HSCs due to unrecoverable critical HSC markers, low HSC number, and poor cell recovery rate. Here, we overcame these difficulties and developed a “HSC phospho-flow” method to analyze cytokine signaling in murine HSCs at the single-cell level and compare HSC signaling profile to that of multipotent progenitors (MPPs), a cell type immediately downstream of HSCs, and commonly used Lin⁻ cKit⁺ cells (LK cells, enriched for myeloid progenitors). We chose to study signaling evoked from three representative cytokines, stem cell factor (SCF) and thrombopoietin (TPO) that are essential for HSC function, and granulocyte macrophage-colony stimulating factor (GM-CSF) that is dispensable for HSCs. HSCs display a distinct TPO and GM-CSF signaling signature from MPPs and LK cells, which highly correlates with receptor surface expression. In contrast, although majority of LK cells express lower levels of cKit than HSCs and MPPs, SCF-evoked ERK1/2 activation in LK cells shows a significantly increased magnitude for a prolonged period. These results suggest that specific cellular context plays a more important role than receptor surface expression in SCF signaling. Our study of HSC signaling at the homeostasis stage paves the way to investigate signaling changes in HSCs under conditions of stress, aging, and hematopoietic diseases.

Multipotent mesenchymal stromal cells (MSCs) have potential therapeutic benefit for the treatment of neurological diseases and injury. MSCs interact with and alter brain parenchymal cells by direct cell-cell communication and/or by indirect secretion of factors and thereby promote functional recovery. In this study, we found that MSC treatment of rats subjected to middle cerebral artery occlusion (MCAo) significantly increased microRNA 133b (miR-133b) level in the ipsilateral hemisphere. In vitro, miR-133b levels in MSCs and in their exosomes increased after MSCs were exposed to ipsilateral ischemic tissue extracts from rats subjected to MCAo. MiR-133b levels were also increased in primary cultured neurons and astrocytes treated with the exosome-enriched fractions released from these MSCs. Knockdown of miR-133b in MSCs, confirmed that the increased miR-133b level in astrocytes is attributed to their transfer from MSCs. Further verification of this exosome mediated intercellular communication was performed using a cel-miR-67 luciferase reporter system and an MSC-astrocyte co-culture model. Cel-miR-67 in MSCs was transferred to astrocytes via exosomes between 50 nm-100 nm in diameter. Our data suggest that the cel-miR-67 released from MSCs was primarily contained in exosomes. A gap junction intercellular communication (GJIC) inhibitor arrested the exosomal miRNA communication by inhibiting exosome release. Cultured neurons treated with exosome-enriched fractions from MSCs exposed to 72h post MCAo brain extracts significantly increased the neurite branch number and total neurite length. This study provides the first demonstration that MSCs communicate with brain parenchymal cells and may regulate neurite outgrowth by transfer of miR-133b to neural cells via exosomes.

There is increasing evidence that breast tumors are organized in a hierarchy, with a subpopulation of tumorigenic cancer cells, the cancer stem cells (CSCs), which sustain tumor growth. The characterization of protein networks that govern CSC behavior is paramount to design new therapeutic strategies targeting this subpopulation of cells. We have sought to identify specific molecular pathways of CSCs isolated from 13 different breast cancer cell lines of luminal or basal/mesenchymal subtypes. We compared the gene expression profiling of cancer cells grown in adherent conditions to those of matched tumorsphere cultures. No specific pathway was identified to be commonly regulated in luminal tumorspheres, resulting from a minor CSC enrichment in tumorsphere passages from luminal cell lines. However, in basal/mesenchymal tumorspheres, the enzymes of the mevalonate metabolic pathway were overexpressed compared to those in cognate adherent cells. Inhibition of this pathway with HMG-COA reductase blockers resulted in a reduction of breast CSC independent of inhibition of cholesterol biosynthesis and of protein farnesylation. Further modulation of this metabolic pathway demonstrated that protein geranylgeranylation (GG) is critical to breast CSC maintenance. A small molecule inhibitor of the geranylgeranyl transferase I (GGTI) enzyme reduced the breast CSC subpopulation both in vitro and in primary breast cancer xenografts. We found that the GGTI effect on the CSC subpopulation is mediated by inactivation of RHOA and increased accumulation of P27^kip1 in the nucleus. The identification of protein geranylgeranylation as a major contributor to CSC maintenance opens promising perspectives for CSC targeted therapy in basal breast cancer.

New neurons are continually produced after birth from neural stem/progenitor cells (NSCs/NPCs) in the hippocampal dentate gyrus (DG). Recent studies have reported that fatty acid binding protein 7 (Fabp7/BLBP) is required for the maintenance of embryonic NSCs/NPCs and have identified an association between the Fabp7 gene and behavioral paradigms that correlate with hippocampal functions. However, the specific roles of Fabps in postnatal neurogenesis remain unknown. Herein, we demonstrate the effects of Fabp7, and another Fabp, Fabp5, on postnatal neurogenesis. Fabp7 and Fabp5 were detected in the subgranular zone (SGZ) of the DG, and Fabp7+ cells were less differentiated than Fabp5+ cells. We analyzed the differentiation state of NSCs/NPCs in the SGZ of 4-week-old (4w) Fabp7 knockout (7KO), Fabp5 KO (5KO) and Fabp7/Fabp5 double KO (7/5KO) mice and found that the number of NSCs/NPCs was dramatically reduced compared with wild-type mice. Although the uptake of BrdU one day after injection was decreased in all KO mice, the survival of BrdU+ cells one month after injection was increased in the 7/5KO mice compared to other three genotypes. We also observed an enhancement of neuronal differentiation in all Fabp KO mice. In addition, the proliferation and survival of NSCs/NPCs differed along the anterior-posterior axis (A-P axis). A greater number of newborn cells in the posterior region became extinct, but this tendency was not apparent in the Fabps KO mice. These data suggest that Fabp7 and Fabp5 have differential roles for proliferation and survival of the NSCs/NPCs during postnatal DG neurogenesis.

We assessed the role of PAI-1 and MMP9 in wound healing process and in the BMMNC related effects on physiological and pathological wound healing.

A full thickness excision wound was created by removal of the skin on the midback of irradiated and non-irradiated animals. Angiogenesis and reepithelialization were markedly increased in PAI-1-/- mice compared to WT animals. We revealed high MMP activity in tissue of PAI-1-/- animals. Of interest, the wound healing process was reduced in PAI-1-/-:MMP9-/- animals compared to PAI-1-/- mice, suggesting a key role of MMP 9 in beneficial effect of PAI-1 deficiency on wound closure. To unravel the role of PAI-1 in BMMNC relative effects, mice were treated with or without local injection of BMMNC isolated from WT, PAI-1-/- and PAI-1-/-:MMP9-/- animals for 14 days (10⁶ cells, n=6 per group). In WT non-irradiated mice, transplantation of BMMNC isolated from PAI-1-/- animals, enhanced wound formation when compared to WT BMMNC. BMMNC differentiation into cells with endothelial phenotype was enhanced by PAI-1 deficiency. These effects were abrogated in PAI-1-/-:MMP9-/- and MMP 9 -/- BMMNC. In addition, using chimeric mice, we demonstrated that PAI-1 deficiency environment increased the BMMNC --GFP recruitment to the wound site, whereas this effect was abrogated when using PAI-1-/-:MMP9-/- BMMNC.

PAI-1 deficiency, at least through MMP9 up-regulation, enhanced wound healing and BMMNC therapeutic potential in irradiated and non irradiated animals.

Microglia have the ability to eliminate amyloid β (Aβ) by a cell-specific phagocytic mechanism, and bone marrow (BM) stem cells have shown a beneficial effect through endogenous microglia activation in the brains of Alzheimer's disease (AD) mice. However, the mechanisms underlying BM-induced activation of microglia have not been resolved. Here we show that BM-derived mesenchymal stem cells (MSCs) induced the migration of microglia when exposed to Aβ in vitro. Cytokine array analysis of the BM-MSC media obtained after stimulation by Aβ further revealed elevated release of the chemoattractive factor, CCL5. We also observed that CCL5 was increased when BM-MSCs were transplanted into the brains of Aβ-deposited AD mice, but not normal mice. Interestingly, alternative activation of microglia in AD mice was associated with elevated CCL5 expression following intracerebral BM-MSC transplantation. Furthermore, by generating an AD-green fluorescent protein (GFP) chimeric mouse, we ascertained that endogenous BM cells, recruited into the brain by CCL5, induced microglial activation. Additionally, we observed that neprilysin (NEP) and IL-4 derived from the alternative microglia were associated with a reduction in Aβ deposition and memory impairment in AD mice. These results suggest that the beneficial effects observed in AD mice after intracerebral BM-MSC transplantation may be explained by alternative microglia activation. The recruitment of the alternative microglia into the brain is driven by CCL5 secretion from the transplanted BM-MSCs, which itself is induced by Aβ deposition in the AD brain.

Retinal degeneration is a leading cause of irreversible blindness in the developed world. Differentiation of retinal cells, including photoreceptors, from both mouse and human ES and iPS cells, potentially provide a renewable source of cells for retinal transplantation. Previously, we have shown both the functional integration of transplanted rod photoreceptor precursors, isolated from the postnatal retina, in the adult murine retina, and photoreceptor cell generation by stepwise treatment of ES cells with defined factors. In this study we assessed the extent to which this protocol recapitulates retinal development and also evaluated differentiation and integration of ES cell-derived retinal cells following transplantation using our established procedures. Optimized retinal differentiation via isolation of Rax.GFP retinal progenitors recreated a retinal niche and increased the yield of Crx⁺ and Rhodopsin⁺ photoreceptors. Rod birth peaked at day 20 of culture and expression of the early photoreceptor markers Crx and Nrl increased until day 28. Nrl levels were low in ES cell-derived populations compared with developing retinae. Transplantation of early stage retinal cultures produced large tumors, which were avoided by prolonged retinal differentiation (up to day 28) prior to transplantation. Integrated mature photoreceptors were not observed in the adult retina, even when more than 60% of transplanted ES cell-derived cells expressed Crx. We conclude that exclusion of proliferative cells from ES cell-derived cultures is essential for effective transplantation. Despite showing expression profiles characteristic of immature photoreceptors, the ES cell-derived precursors generated using this protocol did not display transplantation competence equivalent to precursors from the postnatal retina.

During embryonic development, the emergence of hematopoiesis and vasculogenesis is tightly associated, with many transcription factors implicated in both developmental processes. Among those factors, ETV2 acts at the top of the hierarchy and controls the formation of both lineages. However, it is not known at which stage of mesoderm development ETV2 is acting and whether ETV2 activity is further required once mesodermal precursors have been specified to the hematopoietic and endothelial fates. In the present study, we characterize the developmental window during which ETV2 expression is required for hematopoietic and endothelial development. Using cre-mediated deletion of ETV2, we demonstrate that ETV2 is acting prior to or at the time of FLK1 expression in mesodermal precursors to initiate the hematopoietic and endothelial program. Using the in vitro differentiation of ES cells as a model system, we further show that ETV2 re-expression in Etv2^-/- Flk1-negative precursors drives hematopoiesis specification and switches on the expression of most genes known to be implicated in hematopoietic and endothelial development. Among the downstream targets of ETV2 we identify the transcription factors SCL, GATA2 and FLI1 known to operate a recursive loop controlling hematopoietic development. Surprisingly, SCL re-expression in Etv2^-/- cells fully rescues hematopoiesis, while the re-expression of FLI1 or GATA2 promotes only a very limited rescue. Altogether, our data establish that ETV2 is required very transiently to specify mesodermal precursors to hematopoiesis and vasculogenesis and that SCL is one of the key downstream targets of ETV2 in controlling hematopoietic specification.

Somatic cells can be reprogrammed to induced pluripotent stem (iPS) cells by ectopic expression of defined transcriptional factors. The efficiency of this process, however, is extremely low. Although inactivation of p53 has been recently shown to greatly enhance reprogramming efficiency, the underlying molecular mechanisms still remain largely unknown. Here we report that miR-199a-3p is upregulated by p53 at the post-transcriptional level. Induction of miR-199a-3p significantly decreases reprogramming efficiency, whereas miR-199a-3p inhibition greatly enhances it. Mechanistically, miR-199a-3p overexpression inhibits cell proliferation by imposing G1 cell cycle arrest. Conversely, miR-199a-3p inhibition results in a pronounced increase in cell proliferation. Furthermore, the enhancement in reprogramming of p53 knockdown cells is almost completely reversed with replacement of miR-199a-3p. Also, miR-199a-3p inhibition partially rescues iPS generation impaired by p53. These findings suggest miR-199a-3p as a novel p53 target that negatively regulates somatic cell reprogramming.

Glioblastoma contains a hierarchy of stem-like cancer cells, but how this hierarchy is established is unclear. Here we show that asymmetric Numb localization specifies glioblastoma stem-like cell fate in a manner that does not require Notch inhibition. Numb is asymmetrically localized to CD133-hi glioblastoma stem-like cells. The predominant Numb isoform, Numb4, decreases Notch and promotes a CD133-hi, radial glial-like phenotype. However, upregulation of a novel Numb isoform, Numb4d7, increases Notch and AKT activation while nevertheless maintaining CD133-hi fate specification. Numb knockdown increases Notch and promotes growth while favoring a CD133-lo, glial progenitor-like phenotype. We report the novel finding that Numb4 (but not Numb4d7) promotes SCF^Fbw7 ubiquitin ligase assembly and activation to increase Notch degradation. However, both Numb isoforms decrease EGF receptor (EGFR) expression, thereby regulating glioblastoma stem-like cell fate. Small molecule inhibition of EGFR activity phenocopies the effect of Numb on CD133 and Pax6. Clinically, homozygous NUMB deletions and low Numb mRNA expression occur primarily in a subgroup of proneural glioblastomas. Higher Numb expression is found in classical and mesenchymal glioblastomas and correlates with decreased survival. Thus, decreased Numb promotes glioblastoma growth, but the remaining Numb establishes a phenotypically diverse stem-like cell hierarchy that increases tumor aggressiveness and therapeutic resistance.

Recent studies reveal that the mechanical environment influences the behavior and function of various types of cells, including stem cells. However, signaling pathways involved in the mechanical regulation of stem cell properties remain largely unknown. Using polyacrylamide gels with varying Young's moduli as substrates, we demonstrate that mouse embryonic stem cells (mESCs) are induced to differentiate on substrates with defined elasticity, involving the Src-ShcA-MAP kinase pathway. While the dual inhibition of MAP kinase and GSK3, termed ‘2i’, was reported to sustain the pluripotency of mESCs, we find it to be substrate elasticity-dependent. In contrast, Src inhibition in addition to ‘2i’ allows mESCs to retain their pluripotency independent of substrate elasticity. The alternative dual inhibition of Src and GSK3 (‘alternative 2i’) retains the pluripotency and self-renewal of mESCs in vitro and is instrumental in efficiently deriving mESCs from preimplantation mouse embryos. In addition, the transplantation of mESCs, maintained under the ‘alternative 2i’ condition, to immunodeficient mice leads to the formation of teratomas that include differentiation into three germ layers. Furthermore, mESCs established with ‘alternative 2i’ contributed to chimeric mice production and transmitted to the germline. These results reveal a role for Src-ShcA-MAP kinase signaling in the mechanical regulation of mESC properties and indicate that ‘alternative 2i’ is a versatile tool for the maintenance of mESCs in serum-free conditions, as well as for the derivation of mESCs.

Mesenchymal stromal cells (MSCs) are explored as a novel treatment for a variety of medical conditions. Their fate after infusion is unclear, and long-term safety regarding malignant transformation and ectopic tissue formation has not been addressed in patients.

We examined autopsy material from 18 patients who had received HLA-mismatched MSCs, and 108 tissue samples from 15 patients were examined by PCR. No signs of ectopic tissue formation or malignant tumors of MSC-donor origin were found on macroscopic or histological examination. MSC donor DNA was detected in one or several tissues including lungs, lymph nodes, and intestine in 8 patients at levels from 1/100 to <1/1000. Detection of MSC donor DNA was negatively correlated with time from infusion to sample collection, as DNA was detected from 9 of 13 MSC infusions given within 50 days before sampling but from only 2 of 8 infusions given earlier. There was no correlation between MSC engraftment and treatment response. We conclude that MSCs appear to mediate their function through a “hit and run” mechanism. The lack of sustained engraftment limits the long-term risks of MSC therapy.

Pluripotent cells of the early embryo, to which embryonic stem (ES) cells correspond, give rise to all the somatic cells of the developing fetus. Any defects that occur in their genome or epigenome would have devastating consequences. Genetic and epigenetic change in human ES cells appears to be an inevitable consequence of long term culture, driven by selection of variant cells that have a higher propensity for self-renewal rather than either differentiation or death. Mechanisms underlying the potentially separate events of mutation and subsequent selection of variants are poorly understood. Here we show that human ES cells and their malignant counterpart, embryonic carcinoma (EC) cells, both fail to activate critical S-phase checkpoints when exposed to DNA replication inhibitors and commit to apoptosis instead. Human ES and EC cells also fail to form RPA, γH2AX or RAD51 foci or load TOPBP1 onto chromatin in response to replication inhibitors. Furthermore direct measurements of ssDNA show that these cells fail to generate the single-stranded DNA regions in response to replication stress that are necessary for the activation of checkpoints and the initiation of homologous recombination repair to protect replication fork integrity and restart DNA replication. Taken together our data suggest that pluripotent cells control genome integrity by the elimination of damaged cells through apoptosis rather than DNA repair, and therefore, mutations or epigenetic modifications resulting in an imbalance in cell death control could lead to genetic instability.

During neurogenesis, cell cycle regulators play a pivotal role in ensuring proper proliferation, cell cycle exit, and differentiation of neural precursors. However, the precise role of cyclin-dependent kinases (Cdks) in these processes is not well understood. We generated Cdk2 and Cdk4 double knockout (DKO) mice and found a striking ablation of the intermediate zone and cortical plate in the mouse embryonic brain. When neural stem cells (NSCs) were isolated and analyzed, DKO NSCs proliferated comparable to wild type as Cdk1 now binds to cyclin D1 and E1 and assumes the role vacated by the loss of Cdk2 and Cdk4 in phosphorylating Rb. Although compensation was sufficient for the maintenance of self-renewal and multi-lineage potential, DKO NSCs displayed an altered cell cycle profile and were more prone to neuronal differentiation. This was manifested in vivo as a marked reduction in S phase length and an increased tendency for neurogenic divisions that prevented proper expansion of the basal progenitor pool. Our data thus demonstrate the induction of neurogenic divisions in the absence of critical mediators of G1/S transition -- Cdk2 and Cdk4, and highlight their evolutionary importance in the determination of cortical thickness.

Highlight #1 Loss of Cdk2 & Cdk4 results in enhanced neuronal differentiation

Highlight #2 Cdk1 complexes compensate for the loss of Cdk2 and Cdk4 in NSCs

Highlight #3 Cdk2 and Cdk4 are not essential for the proliferation of NSCs

Highlight #4 Cdk2 and Cdk4 mediates the expansion of basal progenitors

The function of the proteasome is essential for maintenance of cellular homeostasis, and in pluripotent stem cells this has been extended to the removal of nascent proteins in a manner that restricts differentiation. In this study we show enhanced expression of genes encoding subunits of the 20s proteasome in human embryonic stem cells (hESCs) coupled to their downregulation as the cells progress into differentiation. The decrease in expression is particularly marked for the alternative catalytic subunits of the 20s proteasome variant known as the immunoproteasome indicating the possibility of a hitherto unknown function for this proteasome variant in pluripotent cells. The immunoproteasome is normally associated with antigen presenting cells where it provides peptides of an appropriate length for antibody generation: however our data suggests that it may be involved in maintaining the pluripotency in human embryonic stem cells (hESC). Selective inhibition of two immunoproteasome subunits (PSMB9 and PSMB8) results in downregulation of cell surface and transcriptional markers that characterise the pluripotent state, subtle cell accumulation in G1 at the expense of S phase and upregulation of various markers characterising the differentiated primitive and definitive lineages arising from hESC. Our data also support a different function for each of these two subunits in hESC that may be linked to their selectivity in driving proteasome mediated degradation of cell cycle regulatory components and/or differentiation inducing factors.

The transcription factor Elf5 functions downstream of the prolactin receptor signaling pathway and plays an important role in mammary gland development. Using conditional mouse knockouts, we have previously shown that Elf5-null mammary glands exhibit a complete failure of alveologenesis during pregnancy. The Elf5-null developmental phenotype is mediated through alteration in the expression of several critical genes involved in alveologenesis, particularly those belonging to the JAK/STAT pathway. Here, we demonstrate that in addition to regulating terminal differentiation of alveolar cells, Elf5 also plays a critical role in determining cell fate and in regulating the stem/progenitor function of the mammary epithelium. Targeted deletion of Elf5 in the mammary glands leads to accumulation of cell types with dual luminal/basal properties such as co-expression of K8 and K14 and an increase in CD61⁺ luminal progenitor population during pregnancy. Further interrogation suggests that the abnormal increase in K14⁺K8⁺ cells may represent the CD61⁺ luminal progenitors blocked in differentiation. Remarkably, Elf5 deficiency in mammary epithelium also triggers an increase of adult mammary stem activity as evidenced by the accumulation of MaSC enriched cell population in both pregnant and virgin mice and further confirmed by mammosphere and transplantation assays. Additional support for this phenotype comes from the enriched MaSC gene signature based on transcriptomic analysis of the Elf5-null mammary gland. Finally our biochemical studies suggest that Elf5 loss leads to hyper activation of the Notch signaling pathway, which might constitute in part, the underlying molecular mechanism for the altered cell lineage decisions in Elf5-null mammary epithelial cells.

Multipotent mesenchymal stromal cells (MSCs) are tested in numerous clinical trials. Questions have been raised concerning fate and function of these therapeutic cells after systemic infusion. We therefore asked whether culture expanded human MSCs elicit an innate immune attack, termed instant blood-mediated inflammatory reaction (IBMIR), which has previously been shown to compromise the survival and function of systemically infused islet cells and hepatocytes.

We found that MSCs expressed hemostatic regulators similar to those produced by endothelial cells, but displayed higher amounts of pro-thrombotic tissue/stromal factors on their surface, which triggered the IBMIR after blood exposure, as characterized by formation of blood activation markers. This process was dependent on the cell dose, the choice of MSC donor, and particularly the cell passage number. Short-term expanded MSCs triggered only weak blood responses in vitro, whereas extended culture and co-culture with activated lymphocytes increased their pro-thrombotic properties. After systemic infusion to patients, we found increased formation of blood activation markers, but no formation of hyper-fibrinolysis marker D-dimer or acute-phase reactants with the currently applied dose of 1.0 to 3.0 x 10⁶ cells/kg.

Culture expanded MSCs trigger the IBMIR in vitro and in vivo. Induction of IBMIR is dose-dependent and increases after prolonged ex vivo expansion. Currently applied doses of low passage clinical grade MSCs elicit only minor systemic effects, but higher cell doses and particularly higher passage cells should be handled with care. This deleterious reaction can compromise the survival, engraftment, and function of these therapeutic cells.

As TLRs are expressed by hematopoietic stem and progenitor cells, they may play a role in hematopoiesis in response to pathogens during infection. We show here that TLR2, TLR4 and TLR9 agonists (Pam3CSK4, LPS and ODN) induce the in vitro differentiation of purified murine linage negative cells (Lin^-) as well as hematopoietic stem and progenitor cells (HSPCs, identified as LKS cells: Lin^- c-Kit⁺ Sca-1⁺ IL-7Rα^-) towards macrophages, through a MyD88-dependent pathway. In order to investigate the possible direct interaction of soluble microorganism-associated molecular patterns (MAMPs) and TLRs on HSPCs in vivo, we designed a new experimental approach: purified Lin^- and LKS cells from bone marrow of B6Ly5.1 mice (CD45.1 alloantigen) were transplanted into TLR2^-/-, TLR4^-/- or MyD88^-/- mice (CD45.2 alloantigen), which were then injected with soluble TLR ligands (Pam3CSK4, LPS or ODN, respectively). As recipient mouse cells do not recognize the TLR ligands injected, interference by soluble mediators secreted by recipient cells is negligible. Transplanted cells were detected in the spleen and bone marrow of recipient mice, and in response to soluble TLR ligands cells differentiated preferentially to macrophages. These results show, for the first time, that HSPCs may be directly stimulated by TLR agonists in vivo, and that the engagement of these receptors induces differentiation towards macrophages. Therefore, HSPCs may sense pathogen or pathogen-derived products directly during infection, inducing a rapid generation of cells of the innate immune system.

Paternally-inherited inactivating mutations of the GNAS gene have been associated with a rare and disabling genetic disorder, progressive osseous heteroplasia (POH), in which heterotopic ossification (HO) occurs within extraskeletal soft tissues, such as skin, subcutaneous fat, and skeletal muscle. This ectopic bone formation is hypothesized to be caused by dysregulated mesenchymal progenitor cell differentiation that affects a bipotential osteogenic-adipogenic lineage cell fate switch. Interestingly, patients with paternally-inherited inactivating mutations of GNAS are uniformly lean. Using a mouse model of Gsα-specific exon 1 disruption, we examined whether heterozygous inactivation of Gnas affects adipogenic differentiation of mesenchymal precursor cells from subcutaneous adipose tissues (fat pad). We found that paternally-inherited Gsα inactivation (Gsα^+/p-) impairs adipogenic differentiation of adipose-derived stromal cells (ASCs). The Gsα^+/p- mutation in ASCs also decreased expression of the adipogenic factors C/EBPβ, C/EBPα, PPARγ, and aP2. Impaired adipocyte differentiation was rescued by an adenylyl cyclase activator, forskolin, and provided evidence that Gsα-cAMP signals are necessary in early stages of this process. Supporting a role for Gnas in adipogenesis in vivo, fat tissue weight and expression of adipogenic genes from multiple types of adipose tissues from Gsα^+/p- mice were significantly decreased. Interestingly, the inhibition of adipogenesis by paternally-inherited Gsα mutation also enhances expression of the osteogenic factors, Msx2, Runx2, and osteocalcin. These data support the hypothesis that Gsα plays a critical role in regulating the balance between fat and bone determination in soft tissues, a finding that has important implications for a wide variety of disorders of osteogenesis and adipogenesis.

Studies of human embryonic stem cells (hESCs) commonly describe the non-functional p53-p21 axis of the G1/S checkpoint pathway with subsequent relevance for cell cycle regulation and the DNA damage response (DDR). Importantly, p21 mRNA is clearly present and upregulated after the DDR in hESCs but p21 protein is not detectable. In this article, we provide evidence that expression of p21 protein is directly regulated by the microRNA pathway under standard culture conditions and after DNA damage. The DDR in hESCs leads to upregulation of tens of microRNAs, including hESC-specific microRNAs such as those of the miR-302 family, miR-371-372 family, or C19MC microRNA cluster. Most importantly, we show that the hESC-enriched microRNA family miR-302 (miR-302a, miR-302b, miR-302c, and miR-302d) directly contributes to regulation of p21 expression in hESCs and thus demonstrate a novel function for miR-302s in hESCS. The described mechanism elucidates the role of microRNAs in regulation of important molecular pathway governing the G1/S transition checkpoint before as well as after DNA damage.

The molecular basis underlying the clinical phenotype in bone diseases is customarily associated with abnormal extracellular matrix structure and/or properties. More recently, cellular malfunction has been identified as a concomitant causative factor, and increased attention has focused on stem cells differentiation. Classical osteogenesis imperfecta (OI) is a prototype for heritable bone dysplasias: it has dominant genetic transmission and is caused by mutations in the genes coding for collagen I, the most abundant protein in bone. Using the Brtl mouse, a well-characterized knock-in model for moderately severe dominant OI, we demonstrated an impairment in the differentiation of bone marrow progenitor cells towards osteoblasts. In mutant MSCs the expression of early (Runx2, Sp7) and late (Col1a1, Ibsp) osteoblastic markers was significantly reduced with respect to wild type. Conversely, mutant MSCs generated an increased number of Colony Forming Unit-Adipocytes compared to WT, with more adipocytes per colony, and increased number and size of triglyceride drops per cell. Autophagy up-regulation was also demonstrated in mutant adult MSCs differentiating towards osteogenic lineage as consequence of ER stress due to mutant collagen retention. Treatment of the Brtl mice with the proteasome inhibitor Bortezomib ameliorated both osteoblast differentiation in vitro and bone properties in vivo as demonstrated by CFU-O assay and pQCT analysis on long bones, respectively. This is the first report of impaired MSC differentiation to osteoblasts in osteogenesis imperfecta and it identifies a new potential target for the pharmacological treatment of the disorder.

Bone marrow mesenchymal stem/stromal cells (MSC) are a heterogeneous population of multipotent progenitors currently under investigation for a variety of applications in regenerative medicine. While self-renewal of stem cells in different tissues has been demonstrated to be regulated by specialized microenvironments called niches, it is still unclear whether a self-renewing niche also exists for MSC. Here we show that primary human bone marrow cultures contain a population of intrinsically non-adherent mesenchymal progenitors (NAMP) with features of more primitive progenitors than the initially adhering Colony Forming Units-fibroblast (CFU-f). In fact, NAMP could generate an adherent progeny: 1) enriched with early mesenchymal populations (CD146+, SSEA-1+ and SSEA-4+); 2) with significantly greater proliferation and multilineage differentiation potential in vitro; and 3) capable of 3-fold greater bone formation in vivo than the corresponding CFU-f. Upon serial replating, NAMP were able to regenerate and expand in suspension as non-adherent clonogenic progenitors, while also giving rise to an adherent progeny. This took place at the cost of a gradual loss of proliferative potential, shown by a reduction in colony size, which could be completely prevented when NAMP were expanded on the initially adhering bone marrow fraction. Mechanistically, we found that NAMP crucially depend on FGF-2 signaling through FGFR2c for their survival and expansion. Further, NAMP maintenance depends at least in part on humoral signals distinct from FGF-2. In conclusion, our data show a niche/progenitor organization in vitro, in which the bone marrow adherent fraction provides a self-renewing microenviroment for primitive non-adherent mesenchymal progenitors.

LIM homeobox transcription factor 1 alpha (Lmx1a) is required for development of midbrain dopaminergic neurons, roof plate formation and cortical hem development. We generated a reporter ESC line for Lmx1a and used it to track differentiation and extract neural progenitors from differentiating mouse ESCs. Lmx1a⁺ cells gave rise to functional cortical upper layer GABAergic neurons or dopaminergic neurons depending on the culture conditions employed for differentiation. Under chemically defined neurobasal conditions, ESC differentiation resulted in widespread and transient expression of Lmx1a, without the addition of exogenous factors such as sonic hedgehog (Shh), Wnts, and/or BMPs. Under neutral conditions Lmx1a-positve cells express genes known to be downstream of Lmx1a and cortical hem markers Wnt-3a and p73. The majority of these cells did not express the ventral midbrain dopaminergic marker Foxa2 or dorsal roof plate marker BMP-2. Lmx1a⁺-Foxa2⁻-cells were primed to become SatB2-positive GABAergic neurons and appeared to be resistant to dopaminergic patterning cues. PA6 co-culture produced a substantial population of Lmx1a⁺ progenitors that also expressed Foxa2 and on further differentiation gave rise to dopaminergic neurons at high frequency. We conclude that Lmx1a is a useful marker for the extraction of progenitors of GABAergic or dopaminergic neurons. We caution against the assumption that it indicates dopaminergic commitment during in vitro differentiation of ESCs. Indeed, in monolayer culture under neurobasal conditions, with or without addition of Shh and FGF8, Lmx1a⁺ cells were predominantly progenitors of forebrain GABAergic neurons. We obtained dopaminergic cells in large numbers only by co-culture with PA6 cells.

The basic helix-loop-helix (bHLH) proteins are a large family of transcription factors that regulate the formation and fate of tissue stem cells. In hematopoiesis, the two major bHLH factors are stem cell leukemia (SCL) and lymphoblastic leukemia-derived sequence 1 (LYL1), both identified more than 20 years ago in chromosomal translocations occurring in T-cell acute lymphoblastic leukemia. SCL was termed the master regulator of hematopoiesis following the observation that SCL knockout mice die from complete lack of blood formation. However, once established, SCL is no longer required for maintenance of hematopoiesis. Pull-down experiments together with add-back experiments in SCL-null embryonic stem cells and generation of mice carrying a germline DNA binding mutation of SCL demonstrates that most of SCL function is mediated through the formation of a large DNA binding multiprotein complex with both repressor and activator potential. Recent genome-wide binding studies in a hematopoietic stem progenitor cell line suggest that SCL and LYL1 preferentially bind target DNA sequences as components of a heptad of transcription factors. LYL1, a paralog of SCL has been the forgotten sibling until recent mouse studies demonstrated that LYL1 replaced the function of SCL in adult hematopoiesis. Why LYL1 can replace the function of SCL for the maintenance but not formation of hematopoiesis remains a fundamental question. This review will compare and contrast the roles of these two transcription factors in hematopoiesis focusing on recent functional and genome-wide binding studies. STEM CELLS2012;30:1053–1058

The cornea is a tough transparent tissue admitting and focusing light in the eye. More than 90% of the cornea is stroma, a highly organized, transparent connective tissue maintained by keratocytes, quiescent mesenchymal cells of neural crest origin. A small population of cells in the mammalian stroma displays properties of mesenchymal stem cells, including clonal growth, multipotent differentiation, and expression of an array of stem cell-specific markers. Unlike keratocytes, the corneal stromal stem cells (CSSCs) undergo extensive expansion in vitro without loss of the ability to adopt a keratocyte phenotype. Several lines of evidence suggest CSSCs to be of neural crest lineage and not from bone marrow. CSSCs are localized in the anterior peripheral (limbal) stroma near to stem cells of the corneal epithelium. CSSCs may function to support potency of the epithelial stem cells in their unique limbal niche. On the other hand, little information is available documenting a role for CSSCs in vivo in stromal wound healing or regeneration. In vitro CSSCs reproduce the highly organized connective tissue of the stroma, demonstrating a potential use of these cells in tissue bioengineering. Direct introduction of CSSCs into the corneal stroma generated transparent tissue in a mouse model of corneal opacity. Human CSSCs injected into mice corneas did not elicit immune rejection over an extended period of time. The CSSCs therefore appear offer an opportunity to develop cell- and tissue-based therapies for irreversible corneal blindness, conditions affecting more than 10 million individuals worldwide. STEM CELLS2012;30:1059–1063

Glioblastoma multiforme (GBM) ranks among the deadliest types of cancer and given these new therapies are urgently needed. To identify molecular targets, we queried a microarray profiling 467 human GBMs and discovered that polo-like kinase 1 (PLK1) was highly expressed in these tumors and that it clustered with the proliferative subtype. Patients with PLK1-high tumors were more likely to die from their disease suggesting that current therapies are inactive against such tumors. This prompted us to examine its expression in brain tumor initiating cells (BTICs) given their association with treatment failure. BTICs isolated from patients expressed 110-470 times more PLK1 than normal human astrocytes. Moreover, BTICs rely on PLK1 for survival because the PLK1 inhibitor BI2536 inhibited their growth in tumorsphere cultures. PLK1 inhibition suppressed growth, caused G₂/M arrest, induced apoptosis, and reduced the expression of SOX2, a marker of neural stem cells, in SF188 cells. Consistent with SOX2 inhibition, the loss of PLK1 activity caused the cells to differentiate based on elevated levels of glial fibrillary acidic protein and changes in cellular morphology. We then knocked glial fibrillary acidic protein (GFAP) down SOX2 with siRNA and showed that it too inhibited cell growth and induced cell death. Likewise, in U251 cells, PLK1 inhibition suppressed cell growth, downregulated SOX2, and induced cell death. Furthermore, BI2536 delayed tumor growth of U251 cells in an orthotopic brain tumor model, demonstrating that the drug is active against GBM. In conclusion, PLK1 level is elevated in GBM and its inhibition restricts the growth of brain cancer cells. STEM CELLS2012;30:1064–1075

Castration is the standard therapy for advanced prostate cancer (PC). Although this treatment is initially effective, tumors invariably relapse as incurable, castration-resistant PC (CRPC). Adaptation of androgen-dependent PC cells to an androgen-depleted environment or selection of pre-existing, CRPC cells have been proposed as mechanisms of CRPC development. Stem cell (SC)-like PC cells have been implicated not only as tumor initiating/maintaining in PC but also as tumor-reinitiating cells in CRPC. Recently, castration-resistant cells expressing the NK3 homeobox 1 (Nkx3-1) (CARNs), the other luminal markers cytokeratin 18 (CK18) and androgen receptor (AR), and possessing SC properties, have been found in castrated mouse prostate and proposed as the cell-of-origin of CRPC. However, the human counterpart of CARNs has not been identified yet. Here, we demonstrate that in the human PC xenograft BM18, pre-existing SC-like and neuroendocrine (NE) PC cells are selected by castration and survive as totally quiescent. SC-like BM18 cells, displaying the SC markers aldehyde dehydrogenase 1A1 or NANOG, coexpress the luminal markers NKX3-1, CK18, and a low level of AR (AR^low) but not basal or NE markers. These CR luminal SC-like cells, but not NE cells, reinitiate BM18 tumor growth after androgen replacement. The AR^low seems to mediate directly both castration survival and tumor reinitiation. This study identifies for the first time in human PC SC-/CARN-like cells that may represent the cell-of-origin of tumor reinitiation as CRPC. This finding will be fundamental for refining the hierarchy among human PC cancer cells and may have important clinical implications. STEM CELLS2012;30:1076–1086

Normal prostatic epithelium is composed of basal and luminal cells. Prostate cancer can be initiated in both benign basal and luminal stem cells, but because basal cell markers are not expressed in patient tumors, the former result was unexpected. Since the cells of origin of prostate cancer are important therapeutic targets, we sought to provide further proof that basal stem cells have tumorigenic potential. Prostatic basal cells were enriched based on α2β1integrin^hi expression and further enriched for stem cells using CD133 in nontumorigenic BPH-1 cells. Human embryonic stem cells (hESCs) were also used as a source of normal stem cells. To test their tumorigenicity, we used two alternate stromal-based approaches; (a) recombination with human cancer-associated fibroblasts (CAFs) or (b) recombination with embryonic stroma (urogenital mesenchyme) and treated host mice with testosterone and 17β-estradiol. Enriched α2β1integrin^hi basal cells from BPH-1 cells resulted in malignant tumor formation using both assays of tumorigenicity. Surprisingly, the tumorigenic potential did not reside in the CD133⁺ stem cells but was consistently observed in the CD133⁻ population. CAFs also failed to induce prostatic tumors from hESCs. These data confirmed that benign human basal cells include cells of origin of prostate cancer and reinforced their importance as therapeutic targets. In addition, our data suggested that the more proliferative CD133⁻ basal cells are more susceptible to tumorigenesis compared to the CD133⁺-enriched stem cells. These findings challenge the current dogma that normal stem cells and cells of origin of cancer are the same cell type(s). STEM CELLS2012;30:1087–1096

While experimentally induced arrest of human embryonic stem cells (hESCs) in G1 has been shown to stimulate differentiation, it remains unclear whether the unperturbed G1 phase in hESCs is causally related to differentiation. Here, we use centrifugal elutriation to isolate and investigate differentiation propensities of hESCs in different phases of their cell cycle. We found that isolated G1 cells exhibit higher differentiation propensity compared with S and G2 cells, and they differentiate at low cell densities even under self-renewing conditions. This differentiation of G1 cells was partially prevented in dense cultures of these cells and completely abrogated in coculture with S and G2 cells. However, coculturing without cell-to-cell contact did not rescue the differentiation of G1 cells. Finally, we show that the subset of G1 hESCs with reduced phosphorylation of retinoblastoma has the highest propensity to differentiate and that the differentiation is preceded by cell cycle arrest. These results provide direct evidence for increased propensity of hESCs to differentiate in G1 and suggest a role for neighboring cells in preventing differentiation of hESCs as they pass through a differentiation sensitive, G1 phase. STEM CELLS2012;30:1097–1108

Neural stem cells (NSCs) were directly induced from mouse fibroblasts using four reprogramming factors (Oct4, Sox2, Klf4, and cMyc) without the clonal isolation of induced pluripotent stem cells (iPSCs). These NSCs gave rise to both neurons and glial cells even at early passages, while early NSCs derived from clonal embryonic stem cells (ESCs)/iPSCs differentiated mainly into neurons. Epidermal growth factor-dependent neurosphere cultivation efficiently propagated these gliogenic NSCs and eliminated residual pluripotent cells that could form teratomas in vivo. We concluded that these directly induced NSCs were derived from partially reprogrammed cells, because dissociated ESCs/iPSCs did not form neurospheres in this culture condition. These NSCs differentiated into both neurons and glial cells in vivo after being transplanted intracranially into mouse striatum. NSCs could also be directly induced from adult human fibroblasts. The direct differentiation of partially reprogrammed cells may be useful for rapidly preparing NSCs with a strongly reduced propensity for tumorigenesis. STEM CELLS2012;30:1109–1119

Reprogramming of adult human somatic cells to induced pluripotent stem cells (iPSCs) is a novel approach to produce patient-specific cells for autologous transplantation. Whether such cells survive long-term, differentiate to functional neurons, and induce recovery in the stroke-injured brain are unclear. We have transplanted long-term self-renewing neuroepithelial-like stem cells, generated from adult human fibroblast-derived iPSCs, into the stroke-damaged mouse and rat striatum or cortex. Recovery of forepaw movements was observed already at 1 week after transplantation. Improvement was most likely not due to neuronal replacement but was associated with increased vascular endothelial growth factor levels, probably enhancing endogenous plasticity. Transplanted cells stopped proliferating, could survive without forming tumors for at least 4 months, and differentiated to morphologically mature neurons of different subtypes. Neurons in intrastriatal grafts sent axonal projections to the globus pallidus. Grafted cells exhibited electrophysiological properties of mature neurons and received synaptic input from host neurons. Our study provides the first evidence that transplantation of human iPSC-derived cells is a safe and efficient approach to promote recovery after stroke and can be used to supply the injured brain with new neurons for replacement. STEM CELLS2012;30:1120–1133

Human mesenchymal stem cells (hMSCs) have been shown to have potential in regenerative approaches in bone and blood. Most protocols rely on their in vitro expansion prior to clinical use. However, several groups including our own have shown that hMSCs lose proliferation and differentiation ability with serial passage in culture, limiting their clinical applications. Cellular prion protein (PrP) has been shown to enhance proliferation and promote self-renewal of hematopoietic, mammary gland, and neural stem cells. Here we show, for the first time, that expression of PrP decreased in hMSC following ex vivo expansion. When PrP expression was knocked down, hMSC showed significant reduction in proliferation and differentiation. In contrast, hMSC expanded in the presence of small molecule 3/689, a modulator of PrP expression, showed retention of PrP expression with ex vivo expansion and extended lifespan up to 10 population doublings. Moreover, cultures produced a 300-fold increase in the number of cells generated. These cells showed a 10-fold increase in engraftment levels in bone marrow 5 weeks post-transplant. hMSC treated with 3/689 showed enhanced protection from DNA damage and enhanced cell cycle progression, in line with data obtained by gene expression profiling. Moreover, upregulation of superoxide dismutase-2 (SOD2) was also observed in hMSC expanded in the presence of 3/689. The increase in SOD2 was dependent on PrP expression and suggests increased scavenging of reactive oxygen species as mechanism of action. These data point to PrP as a good target for chemical intervention in stem cell regenerative medicine. STEM CELLS2012;30:1134–1143

Advances in stem cell biology have generated intense interest in the prospect of transplanting stem cells into the nervous system for the treatment of neurodegenerative diseases. Here, we report the results of an ongoing phase I trial of intraspinal injections of fetal-derived neural stems cells in patients with amyotrophic lateral sclerosis (ALS). This is a first-in-human clinical trial with the goal of assessing the safety and tolerability of the surgical procedure, the introduction of stem cells into the spinal cord, and the use of immunosuppressant drugs in this patient population. Twelve patients received either five unilateral or five bilateral (10 total) injections into the lumbar spinal cord at a dose of 100,000 cells per injection. All patients tolerated the treatment without any long-term complications related to either the surgical procedure or the implantation of stem cells. Clinical assessments ranging from 6 to 18 months after transplantation demonstrated no evidence of acceleration of disease progression due to the intervention. One patient has shown improvement in his clinical status, although these data must be interpreted with caution since this trial was neither designed nor powered to measure treatment efficacy. These results allow us to report success in achieving the phase I goal of demonstrating safety of this therapeutic approach. Based on these positive results, we can now advance this trial by testing intraspinal injections into the cervical spinal cord, with the goal of protecting motor neuron pools affecting respiratory function, which may prolong life for patients with ALS. STEM CELLS2012;30:1144–1151

Pathologies characterized by lipomatous infiltration of craniofacial structures as well as certain forms of lipodystrophies suggest the existence of a distinct adipogenic program in the cephalic region of mammals. Using lineage tracing, we studied the origin of craniofacial adipocytes that accumulate both in cranial fat depots and during ectopic lipomatous infiltration of craniofacial muscles. We found that unlike their counterparts in limb muscle, a significant percentage of cranial adipocytes is derived from the neural crest (NC). In addition, we identified a population of NC-derived Lin⁻/α7⁻/CD34⁺/Sca-1⁺ fibro/adipogenic progenitors (NC-FAPs) that resides exclusively in the mesenchyme of cephalic fat and muscle. Comparative analysis of the adipogenic potential, impact on metabolism, and contribution to the regenerative response of NC-FAPs and mesoderm-derived FAPs (M-FAPs) suggests that these cells are functionally indistinguishable. While both NC- and M-FAPs express mesenchymal markers and promyogenic cytokines upon damage-induced activation, NC-FAPs additionally express components of the NC developmental program. Furthermore, we show that craniofacial FAP composition changes with age, with young mice containing FAPs that are almost exclusively of NC origin, while NC-FAPs are progressively replaced by M-FAPs as mice age. Based on these results, we propose that in the adult, ontogenetically distinct FAPs form a diffused system reminiscent of the endothelium, which can originate from multiple developmental intermediates to seed all anatomical locations. STEM CELLS2012;30:1152–1162

Because of their ability to self-renew, to differentiate into multiple lineages, and to migrate toward a damaged site, neural stem cells (NSCs), which can be derived from various sources such as fetal tissues and embryonic stem cells, are currently considered to be promising components of cell replacement strategies aimed at treating injuries of the central nervous system, including the spinal cord. Despite their efficiency in promoting functional recovery, these NSCs are not homogeneous and possess variable characteristics depending on their derivation protocols. The advent of induced pluripotent stem (iPS) cells has provided new prospects for regenerative medicine. We used a recently developed robust and stable protocol for the generation of long-term, self-renewing, neuroepithelial-like stem cells from human iPS cells (hiPS-lt-NES cells), which can provide a homogeneous and well-defined population of NSCs for standardized analysis. Here, we show that transplanted hiPS-lt-NES cells differentiate into neural lineages in the mouse model of spinal cord injury (SCI) and promote functional recovery of hind limb motor function. Furthermore, using two different neuronal tracers and ablation of the transplanted cells, we revealed that transplanted hiPS-lt-NES cell-derived neurons, together with the surviving endogenous neurons, contributed to restored motor function. Both types of neurons reconstructed the corticospinal tract by forming synaptic connections and integrating neuronal circuits. Our findings indicate that hiPS-lt-NES transplantation represents a promising avenue for effective cell-based treatment of SCI. STEM CELLS2012;30:1163–1173

Human-induced pluripotent stem cells (hiPSCs) may represent an ideal cell source for research and applications in regenerative medicine. However, standard culture conditions that depend on the use of undefined substrates and xenogeneic medium components represent a significant obstacle to clinical translation. Recently, we reported a defined culture system for human embryonic stem cells using a synthetic polymer coating, poly[2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide] (PMEDSAH), in conjunction with xenogeneic-free culture medium. Here, we tested the hypothesis that iPSCs could be maintained in an undifferentiated state in this xeno-free culture system and subsequently be differentiated into mesenchymal stem cells (iPS-MSCs). hiPSCs were cultured on PMEDSAH and differentiated into functional MSCs, as confirmed by expression of characteristic MSC markers (CD166+, CD105+, CD90+,CD73+, CD31−, CD34−, and CD45−) and their ability to differentiate in vitro into adipogenic, chondrogenic, and osteoblastic lineages. To demonstrate the potential of iPS-MSCs to regenerate bone in vivo, the newly derived cells were induced to osteoblast differentiation for 4 days and transplanted into calvaria defects in immunocompromised mice for 8 weeks. MicroCT and histologic analyses demonstrated de novo bone formation in the calvaria defects for animals treated with iPS-MSCs but not for the control group. Moreover, positive staining for human nuclear antigen and human mitochondria monoclonal antibodies confirmed the participation of the transplanted hiPS-MSCs in the regenerated bone. These results demonstrate that hiPSCs cultured in a xeno-free system have the capability to differentiate into functional MSCs with the ability to form bone in vivo. STEM CELLS2012;30:1174–1181

Skeletal muscle undergoes a progressive age-related loss in mass and function. Preservation of muscle mass depends in part on satellite cells, the resident stem cells of skeletal muscle. Reduced satellite cell function may contribute to the age-associated decrease in muscle mass. Here, we focused on characterizing the effect of age on satellite cell migration. We report that aged satellite cells migrate at less than half the speed of young cells. In addition, aged cells show abnormal membrane extension and retraction characteristics required for amoeboid-based cell migration. Aged satellite cells displayed low levels of integrin expression. By deploying a mathematical model approach to investigate mechanism of migration, we have found that young satellite cells move in a random “memoryless” manner, whereas old cells demonstrate superdiffusive tendencies. Most importantly, we show that nitric oxide, a key regulator of cell migration, reversed the loss in migration speed and reinstated the unbiased mechanism of movement in aged satellite cells. Finally, we found that although hepatocyte growth factor increased the rate of aged satellite cell movement, it did not restore the memoryless migration characteristics displayed in young cells. Our study shows that satellite cell migration, a key component of skeletal muscle regeneration, is compromised during aging. However, we propose clinically approved drugs could be used to overcome these detrimental changes. STEM CELLS2012;30:1182–1195

Although stem cell therapy is a promising strategy for cardiac restoration, the heterogeneity of transplanted cells has been hampering the precise understanding of the cellular and molecular mechanisms. Previously, we established a cardiovascular cell differentiation system from mouse pluripotent stem cells, in which cardiomyocytes (CMs), endothelial cells (ECs), and mural cells (MCs) can be systematically induced and purified. Combining this with cell sheet technology, we generated cardiac tissue sheets reassembled with defined cardiovascular populations. Here, we show the potentials and mechanisms of cardiac tissue sheet transplantation in cardiac function after myocardial infarction (MI). Transplantation of the cardiac tissue sheet to a rat MI model showed significant and sustained improvement of systolic function accompanied by neovascularization. Reduction of the infarct wall thinning and fibrotic length indicated the attenuation of left ventricular remodeling. Cell tracing with species-specific fluorescent in situ hybridization after transplantation revealed a relatively early loss of transplanted cells and an increase in endogenous neovascularization in the proximity of the graft, suggesting an indirect angiogenic effect of cardiac tissue sheets rather than direct CM contributions. We prospectively dissected the functional mechanisms with cell type-controlled sheet analyses. Sheet CMs were the main source of vascular endothelial growth factor. Transplantation of sheets lacking CMs resulted in the disappearance of neovascularization and subsequent functional improvement, indicating that the beneficial effects of the sheet were achieved by sheet CMs. ECs and MCs enhanced the sheet functions and structural integration. Supplying CMs to ischemic regions with cellular interaction could be a strategic key in future cardiac cell therapy. STEM CELLS2012;30:1196–1205

Bacterial meningitis (BM) frequently causes persisting neurofunctional sequelae. Autopsy studies in patients dying from BM show characteristic apoptotic brain injury to the stem cell niche in the subgranular zone of the hippocampal dentate gyrus (DG), and this form of brain damage is associated with learning and memory deficits in experimental BM. With an eye to potential regenerative therapies, the survival, migration, and differentiation of neuronal precursor cells (NPCs) were evaluated after engraftment into the injured hippocampus in vitro and in vivo in an infant rat model of pneumococcal meningitis. Green fluorescent protein (GFP)-expressing NPCs were grafted into the DG of organotypic hippocampal slice cultures injured by challenge with live Streptococcus pneumoniae. Seven days after engraftment, NPCs had migrated from the site of injection into the injured granular layer of the DG and electro-functionally integrated into the hippocampal network. In vivo, GFP-expressing NPCs migrated within 1 week from the injection site in the hilus region to the injured granular layer of the hippocampal DG and showed neuronal differentiation at 2 and 4 weeks after transplantation. Hippocampal injury induced by BM guides grafted NPCs to the area of brain damage and provides a microenvironment for neuronal differentiation and functional integration. STEM CELLS2012;30:1206–1215

Bone marrow stromal cells (BMSCs) have shown significant promise in the treatment of disease, but their therapeutic efficacy is often limited by inefficient homing of systemically administered cells, which results in low number of cells accumulating at sites of pathology. BMSC home to areas of inflammation where local expression of integrins and chemokine gradients is present. We demonstrated that nondestructive pulsed focused ultrasound (pFUS) exposures that emphasize the mechanical effects of ultrasound-tissue interactions induced local and transient elevations of chemoattractants (i.e., cytokines, integrins, and growth factors) in the murine kidney. pFUS-induced upregulation of cytokines occurred through approximately 1 day post-treatment and returned to contralateral kidney levels by day 3. This window of significant increases in cytokine expression was accompanied by local increases of other trophic factors and integrins that have been shown to promote BMSC homing. When BMSCs were intravenously administered following pFUS treatment to a single kidney, enhanced homing, permeability, and retention of BMSC was observed in the treated kidney versus the contralateral kidney. Histological analysis revealed up to eight times more BMSC in the peritubular regions of the treated kidneys on days 1 and 3 post-treatment. Furthermore, cytokine levels in pFUS-treated kidneys following BMSC administration were found to be similar to controls, suggesting modulation of cytokine levels by BMSC. pFUS could potentially improve cell-based therapies as a noninvasive modality to target homing by establishing local chemoattractant gradients and increasing expression of integrins to enhance tropism of cells toward treated tissues. STEM CELLS2012;30:1216–1227

Recent findings have demonstrated that stem cells can differentiate into mature tissue when supplied with a niche containing factors identical to those in the normal developmental program. A niche for the development of an organ can be provided by xenotransplantation of a similar developing organ. However, this process has many technical, safety, and ethical concerns. Here, we established xenotransplantation models that control endogenous mesenchymal stem cell (MSC) differentiation into mature erythropoietin (EPO)-producing tissue in a niche provided by a developing xenometanephros. Transplantation of rat metanephroi into mouse omentum, and similarly pig metanephroi into cat omentum, led to the recruitment of host cells and EPO production. EPO-expressing cells were not differentiated from integrating vessels because they did not coexpress endothelial markers (Tie-2 and VE-cadherin). Instead, EPO-expressing cells were shown to be derived from circulating host cells, as shown by enhanced green fluorescent protein (EGFP) expression in the grown transplants of chimeric mice bearing bone marrow from a transgenic mouse expressing EGFP under the control of the EPO promoter. These results suggest that donor cell recruitment and differentiation in a xenotransplanted developing organ may be consistent between species. The cells responsible for EPO expression were identified as MSCs by injecting human bone marrow-derived MSCs and endothelial progenitor cells into NOD/SCID mice. Furthermore, using metanephroi from transgenic ER-E2F1 suicide-inducible mice, the xenotissue component could be eliminated, leaving autologous EPO-producing tissue. Our findings may alleviate adverse effects due to long-lasting immunosuppression and help mitigate ethical concerns. STEM CELLS2012;30:1228–1235

Gap junctional coupling is important for functional integration of transplanted cells with host myocardium. However, the role of gap junctions in cardiomyogenic differentiation of transplanted cells has not been directly investigated. The objective of this work is to study the role of connexin43 (Cx43) in cardiomyogenic differentiation of human mesenchymal stem cells (hMSCs). Knockdown of Cx43 gene expression (Cx43↓) was established in naturally Cx43-rich fetal amniotic membrane (AM) hMSCs, while Cx43 was overexpressed (Cx43↑) in inherently Cx43-poor adult adipose tissue (AT) hMSCs. The hMSCs were exposed to cardiomyogenic stimuli by coincubation with neonatal rat ventricular cardiomyocytes (nrCMCs) for 10 days. Differentiation was assessed by immunostaining and whole-cell current clamping. To establish whether the effects of Cx43 knockdown could be rescued, Cx45 was overexpressed in Cx43↓ fetal AM hMSCs. Ten days after coincubation, not a single Cx43↓ fetal AM hMSC, control adult AT MSC, or Cx43↑ adult AT mesenchymal stem cell (MSC) expressed α-actinin, while control fetal AM hMSCs did (2.2% ± 0.4%, n = 5,000). Moreover, functional cardiomyogenic differentiation, based on action potential recordings, occurred only in control fetal AM hMSCs. Of interest, Cx45 overexpression in Cx43↓ fetal AM hMSCs restored their ability to undergo cardiomyogenesis (1.6% ± 0.4%, n = 2,500) in coculture with nrCMCs. Gap junctional coupling is required for differentiation of fetal AM hMSCs into functional CMCs after coincubation with nrCMCs. Heterocellular gap junctional coupling thus plays an important role in the transfer of cardiomyogenic signals from nrCMCs to fetal hMSCs but is not sufficient to induce cardiomyogenic differentiation in adult AT hMSCs. STEM CELLS2012;30:1236–1245

The mammary epithelium comprises two major cell lineages: basal and luminal. Basal cells (BCs) isolated from the mammary epithelium and transplanted into the mouse mammary fat pad cleared from the endogenous epithelium regenerate the mammary gland, strongly suggesting that the basal epithelial compartment harbors a long-lived cell population with multipotent stem cell potential. The luminal cell layer is devoid of the regenerative potential, but it contains cells with clonogenic capacity, the luminal progenitors. Mammary BCs and luminal progenitors express high levels of the transcription factor Myc. Here, we show that deletion of Myc from mammary basal epithelial cells led to impaired stem cell self-renewal as evaluated by limiting dilution and serial transplantation assays. Luminal progenitor population was significantly diminished in mutant epithelium suggesting control by the BC layer. Colony formation assay performed with isolated BCs showed that clonogenic capacity was abolished by Myc deletion. Moreover, transplanted BCs depleted of Myc failed to produce epithelial outgrowths. Stimulation with ovarian hormones estrogen (E) and progesterone (P) partially rescued the repopulation capacity of Myc-depleted BCs; however, the Myc-deficient mammary epithelium developed in response to E/P treatment lacked stem and progenitor cells. This study provides the first evidence that in the mammary gland, Myc has an essential nonredundant function in the maintenance of the self-renewing multipotent stem cell population responsible for the regenerative capacity of the mammary epithelium and is required downstream from ovarian hormones, for the control of mammary stem and progenitor cell functions. STEM CELLS2012;30:1246–1254

In mice, CD49f^hi mammary stem cells (MaSCs) asymmetrically divide to generate CD49f⁺ committed progenitor cells that differentiate into CD49f⁻ phenotypes of the milk-secreting tissue at the onset of pregnancy. We show CD49f⁺ primary mammary epithelial cells (PMECs) isolated from lactating tissue uniquely respond to pregnancy-associated hormones (PAH) compared with CD49f⁺ cells from nonlactating tissue. Differentiation of CD49f⁺ PMEC in extracellular matrix produces CD49f⁻ luminal cells to form differentiated alveoli. The PAH prolactin and placental lactogen specifically stimulate division of CD49f⁻ luminal cells, while receptor activator of nuclear factor (NF)-κB ligand (RANKL) specifically stimulates division of basal CD49f⁺ cells. In nondifferentiating conditions, we observed a greater proportion of multipotent self-renewing cells, and RANKL treatment activated the RANK pathway in these cultures. Furthermore, we observed the deposition of calcium nodules in a proportion of these cells. These data imply that a MaSC unique to the lactating breast exists in humans, which generates progeny with discrete lineages and distinct response to PAH. STEM CELLS2012;30:1255–1264

Insulin-like growth factor (IGF)-I and IGF-II regulate brain development and growth through the IGF type 1 receptor (IGF-1R). Less appreciated is that IGF-II, but not IGF-I, activates a splice variant of the insulin receptor (IR) known as IR-A. We hypothesized that IGF-II exerts distinct effects from IGF-I on neural stem/progenitor cells (NSPs) via its interaction with IR-A. Immunofluorescence revealed high IGF-II in the medial region of the subventricular zone (SVZ) comprising the neural stem cell niche, with IGF-II mRNA predominant in the adjacent choroid plexus. The IGF-1R and the IR isoforms were differentially expressed with IR-A predominant in the medial SVZ, whereas the IGF-1R was more abundant laterally. Similarly, IR-A was more highly expressed by NSPs, whereas the IGF-1R was more highly expressed by lineage restricted cells. In vitro, IGF-II was more potent in promoting NSP expansion than either IGF-I or standard growth medium. Limiting dilution and differentiation assays revealed that IGF-II was superior to IGF-I in promoting stemness. In vivo, NSPs propagated in IGF-II migrated to and took up residence in periventricular niches while IGF-I-treated NSPs predominantly colonized white matter. Knockdown of IR or IGF-1R using shRNAs supported the conclusion that the IGF-1R promotes progenitor proliferation, whereas the IR is important for self-renewal. Q-PCR revealed that IGF-II increased Oct4, Sox1, and FABP7 mRNA levels in NSPs. Our data support the conclusion that IGF-II promotes the self-renewal of neural stem/progenitors via the IR. By contrast, IGF-1R functions as a mitogenic receptor to increase precursor abundance. STEM CELLS2012;30:1265–1276

The objective of this article is to assess the safety of intraspinal infusion of autologous bone marrow mononuclear cells (BMNCs) and, ultimately, to look for histopathological signs of cellular neurotrophism in amyotrophic lateral sclerosis (ALS) patients. We conducted an open single arm phase I trial. After 6 months observation, autologous BMNCs were infused into the posterior spinal cord funiculus. Safety was the primary endpoint and was defined as the absence of serious transplant-related adverse events. In addition, forced vital capacity (FVC), ALS-functional rating scale (ALS-FRS), Medical Research Council scale for assessment of muscle power (MRC), and Norris scales were assessed 6 and 3 months prior to the transplant and quarterly afterward for 1 year. Pathological studies were performed in case of death. Eleven patients were included. We did not observe any severe transplant-related adverse event, but there were 43 nonsevere events. Twenty-two (51%) resolved in ≤2 weeks and only four were still present at the end of follow-up. All were common terminology criteria for adverse events grade ≤2. No acceleration in the rate of decline of FVC, ALS-FRS, Norris, or MRC scales was observed. Four patients died on days 359, 378, 808, and 1,058 post-transplant for reasons unrelated to the procedure. Spinal cord pathological analysis showed a greater number of motoneurons in the treated segments compared with the untreated segments (4.2 ± 0.8 motoneurons per section [mns per sect] and 0.9 ± 0.3 mns per sect, respectively). In the treated segments, motoneurons were surrounded by CD90+ cells and did not show degenerative ubiquitin deposits. This clinical trial confirms not only the safety of intraspinal infusion of autologous BMNC in ALS patients but also provides evidence strongly suggesting their neurotrophic activity. STEM CELLS2012;30:1277–1285

The therapeutic goal in peripheral arterial disease (PAD) patients is to restore blood flow to ischemic tissue. Stem cell transplantation offers a new avenue to enhance arteriogenesis and angiogenesis. Two major problems with cell therapies are poor cell survival and the lack of visualization of cell delivery and distribution. To address these therapeutic barriers, allogeneic bone marrow-derived mesenchymal stem cells (MSCs) were encapsulated in alginate impregnated with a radiopaque contrast agent (MSC-Xcaps.) In vitro MSC-Xcap viability by a fluorometric assay was high (96.9% ± 2.7% at 30 days postencapsulation) and as few as 10 Xcaps were visible on clinical x-ray fluoroscopic systems. Using an endovascular PAD model, rabbits (n = 21) were randomized to receive MSC-Xcaps (n = 6), empty Xcaps (n = 5), unencapsulated MSCs (n = 5), or sham intramuscular injections (n = 5) in the ischemic thigh 24 hours postocclusion. Immediately after MSC transplantation and 14 days later, digital radiographs acquired on a clinical angiographic system demonstrated persistent visualization of the Xcap injection sites with retained contrast-to-noise. Using a modified TIMI frame count, quantitative angiography demonstrated a 65% improvement in hind limb perfusion or arteriogenesis in MSC-Xcap-treated animals versus empty Xcaps. Post-mortem immunohistopathology of vessel density by anti-CD31 staining demonstrated an 87% enhancement in angiogenesis in Xcap-MSC-treated animals versus empty Xcaps. MSC-Xcaps represent the first x-ray-visible cellular therapeutic with enhanced efficacy for PAD treatment. STEM CELLS2012;30:1286–1296

Novel therapeutic concepts against cerebral ischemia focus on cell-based therapies in order to overcome some of the side effects of thrombolytic therapy. However, cell-based therapies are hampered because of restricted understanding regarding optimal cell transplantation routes and due to low survival rates of grafted cells. We therefore transplanted adult green fluorescence protein positive neural precursor cells (NPCs) either intravenously (systemic) or intrastriatally (intracerebrally) 6 hours after stroke in mice. To enhance survival of NPCs, cells were in vitro protein-transduced with TAT-heat shock protein 70 (Hsp70) before transplantation followed by a systematic analysis of brain injury and underlying mechanisms depending on cell delivery routes. Transduction of NPCs with TAT-Hsp70 resulted in increased intracerebral numbers of grafted NPCs after intracerebral but not after systemic transplantation. Whereas systemic delivery of either native or transduced NPCs yielded sustained neuroprotection and induced neurological recovery, only TAT-Hsp70-transduced NPCs prevented secondary neuronal degeneration after intracerebral delivery that was associated with enhanced functional outcome. Furthermore, intracerebral transplantation of TAT-Hsp70-transduced NPCs enhanced postischemic neurogenesis and induced sustained high levels of brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, and vascular endothelial growth factor in vivo. Neuroprotection after intracerebral cell delivery correlated with the amount of surviving NPCs. On the contrary, systemic delivery of NPCs mediated acute neuroprotection via stabilization of the blood-brain-barrier, concomitant with reduced activation of matrix metalloprotease 9 and decreased formation of reactive oxygen species. Our findings imply two different mechanisms of action of intracerebrally and systemically transplanted NPCs, indicating that systemic NPC delivery might be more feasible for translational stroke concepts, lacking a need of in vitro manipulation of NPCs to induce long-term neuroprotection. STEM CELLS2012;30:1297–1310