Sonic hedgehog and retinoic acid synergistically promote sensory fate specification from bone marrow-derived pluripotent stem cells

Mesenchymal stem cells enhance wound healing through differentiation and angiogenesis

Although chronic wounds are common, treatment for these disabling conditions remains limited and largely ineffective. In this study, we examined the benefit of bone marrow-derived mesenchymal stem cells (BM-MSCs) in wound healing. Using an excisional wound splinting model, we showed that injection around the wound and application to the wound bed of green fluorescence protein (GFP)(+) allogeneic BM-MSCs significantly enhanced wound healing in normal and diabetic mice compared with that of allogeneic neonatal dermal fibroblasts or vehicle control medium. Fluorescence-activated cell sorting analysis of cells derived from the wound for GFP-expressing BM-MSCs indicated engraftments of 27% at 7 days, 7.6% at 14 days, and 2.5% at 28 days of total BM-MSCs administered. BM-MSC-treated wounds exhibited significantly accelerated wound closure, with increased re-epithelialization, cellularity, and angiogenesis. Notably, BM-MSCs, but not CD34(+) bone marrow cells in the wound, expressed the keratinocyte-specific protein keratin and formed glandular structures, suggesting a direct contribution of BM-MSCs to cutaneous regeneration. Moreover, BM-MSC-conditioned medium promoted endothelial cell tube formation. Real-time polymerase chain reaction and Western blot analysis revealed high levels of vascular endothelial growth factor and angiopoietin-1 in BM-MSCs and significantly greater amounts of the proteins in BM-MSC-treated wounds. Thus, our data suggest that BM-MSCs promote wound healing through differentiation and release of proangiogenic factors. Disclosure of potential conflicts of interest is found at the end of this article.

Concise review: mesenchymal stem/multipotent stromal cells: the state of transdifferentiation and modes of tissue repair--current views

Mesenchymal stem cells or multipotent stromal cells (MSCs) isolated from the bone marrow of adult organisms were initially characterized as plastic adherent, fibroblastoid cells with the capacity to generate heterotopic osseous tissue when transplanted in vivo. In recent years, MSCs or MSC-like cells have been shown to reside within the connective tissue of most organs, and their surface phenotype has been well described. A large number of reports have also indicated that the cells possess the capacity to transdifferentiate into epithelial cells and lineages derived from the neuroectoderm. The broad developmental plasticity of MSCs was originally thought to contribute to their demonstrated efficacy in a wide variety of experimental animal models of disease as well as in human clinical trials. However, new findings suggest that the ability of MSCs to alter the tissue microenvironment via secretion of soluble factors may contribute more significantly than their capacity for transdifferentiation in tissue repair. Herein, we critically evaluate the literature describing the plasticity of MSCs and offer insight into how the molecular and functional heterogeneity of this cell population, which reflects the complexity of marrow stroma as an organ system, may confound interpretation of their transdifferentiation potential. Additionally, we argue that this heterogeneity also provides a basis for the broad therapeutic efficacy of MSCs.

Enhanced Survival of Bone???Marrow-Derived Pluripotent Stem Cells in an Animal Model of Auditory Neuropathy

OBJECTIVE

The loss of spiral ganglion neurons (SGNs) is one of the major causes of profound sensorineural hearing loss (SNHL). Stem cell replacement therapy, which is still in its infancy, has the potential to treat or cure those who suffer from an array of illnesses and degenerative neurologic disorders, including sensorineural deafness (SNHL). Little is known about the potentials of mesenchymal stem cells (MSCs) and their ability to take on properties of SGNs. The two main purposes of this study were to evaluate the survival of mouse MSCs transplanted into normal and ouabain-treated gerbil cochleae and to determine the migratory patterns of MSCs with two differing injection methods.

SUBJECTS

Thirty-two Mongolian gerbils, 3 to 4 months old, were used as recipients, and four 6-week-old TgN(ACTbEGFP) mice that ubiquitously express green fluorescent protein (GFP) were used as donors.

DESIGN

The animals were deafened by ouabain, which damaged SGNs while leaving hair cell systems intact. After 4 weeks of recovery, the animals received an intraperilymphatic transplantation of 1.0x10(6) GFP-positive undifferentiated MSCs via two different injection methods: scala tympani injection and modiolar injection. Seven days after the transplantation, the survival of MSCs was evaluated by microscopic examination of frozen sections cut through the cochleae of the recipient animals. The number of profiles was counted on the five most central modiolar sections. One-way analyses of variance (ANOVA) were used to determine any significantdifferences among mean profile counts across the experimental conditions.

RESULTS

Our findings indicated that undifferentiated MSCs were able to survive in the modiolus both in the control and the ouabain-treated cochleae. The average number of profiles found in the modiolus was greater in the ouabain-treated cochleae than in the control cochleae. This difference was statistically significant (P<.01) as determined using a one-way ANOVA and an ad hoc Tukey-Kramer's test. With the scala tympani injection, there were no profiles found in the modiolus either in the control or ouabain-treated cochleae. This finding may indicate that donor MSCs need to be directly injected into the modiolus to replace injured SGNs. Finally, there was no evidence of hyperacute rejection in any of the gerbils despite the use of xenotransplantation.

CONCLUSIONS

These findings may have important clinical implications as a means of delivering MSCs in the cochlea for stem-cell replacement therapy. Survival of transplanted MSCs into the modiolus of the cochlea may result in regeneration of damaged SGNs.

Altered localization of gene expression in both ectoderm and mesoderm is associated with a murine strain difference in retinoic acid-induced forelimb ectrodactyly

BACKGROUND

Defects in digit number or fusion as a teratogenic response are well documented in humans and intensively studied in various mouse models. Maternal exposure to excess levels of all-trans-retinoic acid (RA) at gestational day 9.5 induces postaxial ectrodactyly (digit loss) in the murine C57BL/6N strain but not in the SWV/Fnn strain.

METHODS

Whole-mount in situ hybridization was used to examine the differential expression of limb patterning genes at the transcriptional level between the two mouse strains following the maternal exposure to a teratogenic level of RA. The detection of a gene with altered expression was followed by either the evaluation of other genes that were synexpressed or with an assessment of downstream genes.

RESULTS

In the C57BL/6N limb bud following maternal RA administration, gene-specific perturbations were observed within hours of the RA injection in the posterior pre-AER (apical ectodermal ridge) (Fgf8, Dlx3, Bmp4, Sp8, but not Dlx2 or p63), whereas these genes were normally expressed in the SWV/Fnn limb bud. Furthermore, although RA caused comparable reductions of Shh expression between the strains in the 12 h after administration, some Shh downstream genes were differentially expressed (e.g., Gli1, Ptc, and Hoxd13), whereas others were not (e.g., Fgf4, Bmp4, and Gremlin).

CONCLUSIONS

It is proposed that altered gene expression in both pre-AER and mesoderm is involved in the pathogenesis of postaxial digit loss, and that because the alterations in the pre-AER occur relatively early in the temporal sequence of events, those changes are candidates for an initiating factor in the malformation.

Specification of a dopaminergic phenotype from adult human mesenchymal stem cells

Dopamine (DA) neurons derived from stem cells are a valuable source for cell replacement therapy in Parkinson disease, to study the molecular mechanisms of DA neuron development, and for screening pharmaceutical compounds that target DA disorders. Compared with other stem cells, MSCs derived from the adult human bone marrow (BM) have significant advantages and greater potential for immediate clinical application. We report the identification of in vitro conditions for inducing adult human MSCs into DA cells. Using a cocktail that includes sonic hedgehog and fibroblast growth factors, human BM-derived MSCs were induced in vitro to become DA cells in 12 days. Based on tyrosine hydroxylase (TH) expression, the efficiency of induction was determined to be approximately 67%. The cells develop a neuronal morphology expressing the neuronal markers NeuN and beta III tubulin, but not glial markers, glial fibrillary acidic protein and Olig2. As the cells acquire a postmitotic neuronal fate, they downregulate cell cycle activator proteins cyclin B, cyclin-dependent kinase 2, and proliferating cell nuclear antigen. Molecular characterization revealed the expression of DA-specific genes such as TH, Pitx3, Nurr1, DA transporter, and vesicular monoamine transporter 2. The induced MSCs also synthesize and secrete DA in a depolarization-independent manner. The latter observation is consistent with the low expression of voltage gated Na(+) and Ca(2+) channels in the induced MSCs and suggests that the cells are at an immature stage of development likely representing DA neuronal progenitors. Taken together, the results demonstrate the ability of adult human BM-derived MSCs to form DA cells in vitro.

The effects of soluble growth factors on embryonic stem cell differentiation inside of fibrin scaffolds

The goal of this research was to determine the effects of different growth factors on the survival and differentiation of murine embryonic stem cell-derived neural progenitor cells (ESNPCs) seeded inside of fibrin scaffolds. Embryoid bodies were cultured for 8 days in suspension, retinoic acid was applied for the final 4 days to induce ESNPC formation, and then the EBs were seeded inside of three-dimensional fibrin scaffolds. Scaffolds were cultured in the presence of media containing different doses of the following growth factors: neurotrophin-3 (NT-3), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF)-AA, ciliary neurotrophic factor, and sonic hedgehog (Shh). The cell phenotypes were characterized using fluorescence-activated cell sorting and immunohistochemistry after 14 days of culture. Cell viability was also assessed at this time point. Shh (10 ng/ml) and NT-3 (25 ng/ml) produced the largest fractions of neurons and oligodendrocytes, whereas PDGF (2 and 10 ng/ml) and bFGF (10 ng/ml) produced an increase in cell viability after 14 days of culture. Combinations of growth factors were tested based on the results of the individual growth factor studies to determine their effect on cell differentiation. The incorporation of ESNPCs and growth factors into fibrin scaffolds may serve as potential treatment for spinal cord injury.

The human fetal cochlea can be a source for auditory progenitors/stem cells isolation

The development of new stem cell-based technologies is creating new hopes in regenerative medicine. Hearing-impaired individuals should benefit greatly from the development of a cell-based regenerative strategy to treat deafness. An important achievement would be to develop a human-based system that could bring the advances made in animal models closer to clinical application. In this work, we have explored the suitability of the developing fetal cochlea to be used as a source for the extraction of auditory progenitor/stem cells. We have established cultures that express critical markers such as NESTIN, SOX2, GATA3 and PAX2. These cultures can be expanded in vitro for several months and differentiating markers such as ATOH1/HATH1 and POU4F3/BRN3C can be induced by manipulating the culture conditions using specific growth factors such as bFGF, EGF and retinoic acid.

Common molecular pathways involved in human CD133+/CD34+ progenitor cell expansion and cancer

Background

Uncovering the molecular mechanism underlying expansion of hematopoietic stem and progenitor cells is critical to extend current therapeutic applications and to understand how its deregulation relates to leukemia. The characterization of genes commonly relevant to stem/progenitor cell expansion and tumor development should facilitate the identification of novel therapeutic targets in cancer.

Methods

CD34+/CD133+ progenitor cells were purified from human umbilical cord blood and expanded in vitro. Correlated molecular changes were analyzed by gene expression profiling using microarrays covering up to 55,000 transcripts. Genes regulated during progenitor cell expansion were identified and functionally classified. Aberrant expression of such genes in cancer was indicated by in silico SAGE. Differential expression of selected genes was assessed by real-time PCR in hematopoietic cells from chronic myeloid leukemia patients and healthy individuals.

Results

Several genes and signaling pathways not previously associated with ex vivo expansion of CD133+/CD34+ cells were identified, most of which associated with cancer. Regulation of MEK/ERK and Hedgehog signaling genes in addition to numerous proto-oncogenes was detected during conditions of enhanced progenitor cell expansion. Quantitative real-time PCR analysis confirmed down-regulation of several newly described cancer-associated genes in CD133+/CD34+ cells, including DOCK4 and SPARCL1 tumor suppressors, and parallel results were verified when comparing their expression in cells from chronic myeloid leukemia patients

Conclusion

Our findings reveal potential molecular targets for oncogenic transformation in CD133+/CD34+ cells and strengthen the link between deregulation of stem/progenitor cell expansion and the malignant process.

Protein aggregate-containing neuron-like cells are differentiated from bone marrow mesenchymal stem cells from mice with neurofilament light subunit gene deficiency

Autologous bone marrow mesenchymal stem cell (MSC) transplantation has great potential in cell therapy used for the treatment of neurodegenerative disorders. Since many genetic deficiencies have been reported in pathogenesis of the diseases, genetic backgrounds of donor stem cells should be concerned. In this study, effects of neurofilament light subunit (NFL) gene deficiency on proliferation and neuronal differentiation of MSCs were studied in vitro. Lower proliferation rate was observed in NFL-/- MSCs. When exposed to retinoic acid (RA), both NFL-/- and normal MSCs could express several markers of neuronal lineage, such as Nestin, MAP-2, NeuN, O4 and GFAP. However, the NFL expression at mRNA and protein levels was observed only in normal MSCs but absent in NFL-/- MSCs. Significant reductions in amount of neurofilament heavy subunit (NFH) protein and number of neuron-like cells were detected in differentiated NFL-/- MSCs. Interestingly, NFH positive protein accumulations were observed in the neuron-like cells derived from NFL-/- MSCs. These accumulations were perinuclear and morphologically similar to protein aggregations in motoneurons of the spinal cord in NFL-/- mice. The results suggest that NFL gene deficiency could retard MSCs proliferation and neuronal generation, even though the capability of neuronal lineage differentiation of MSCs may not be deterred. Moreover, the NFL-/- MSCs differentiated neuron-like cells carried on the genetic and pathologic deficiency, suggesting that the genetic quality of donor cells must not only be tested, but also modified before transplantation. This also points towards the possibility of creating a stem cell-derived cell model for pathogenesis study.

Spontaneous expression of neural phenotype and NGF, TrkA, TrkB genes in marrow stromal cells

Marrow stromal cells (MSCs) have the ability to provide growth factors and differentiate into neural-like cells on treating with EGF, bFGF and other factors. We wanted to explore whether growth factors secreted by MSCs itself could induce self-differentiation into neural-like cells. Here, we show that even in the absence of inducing factors, rMSCs spontaneously differentiate into neural-like cells expressing neural markers, such as nestin, beta-tubulin III, Doublecortin (DCX), microtubule-associated protein 2 (MAP2) and neuron-specific enolase (NSE). Furthermore, some cells become neurosphere-like growing in suspension. Compared with control and neural-like rMSCs induced by epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), we found using real-time PCR that self-differentiating rMSCs (SDrMSCs) expressed significantly higher levels of neurotrophic high-affinity receptors (TrkA and TrkB). Coincident with neural marker expression, nerve growth factor (NGF) mRNA was significantly higher than controls despite lower protein levels in the supernatant. Our study suggests that rMSCs have the potential to differentiate into neural cells spontaneously in culture and may contribute towards the natural function of MSCs for neural system in vivo.

Engraftment and differentiation of embryonic stem cell-derived neural progenitor cells in the cochlear nerve trunk: growth of processes into the organ of Corti

Hearing loss in mammals is irreversible because cochlear neurons and hair cells do not regenerate. To determine whether we could replace neurons lost to primary neuronal degeneration, we injected EYFP-expressing embryonic stem cell-derived mouse neural progenitor cells into the cochlear nerve trunk in immunosuppressed animals 1 week after destroying the cochlear nerve (spiral ganglion) cells while leaving hair cells intact by ouabain application to the round window at the base of the cochlea in gerbils. At 3 days post transplantation, small grafts were seen that expressed endogenous EYFP and could be immunolabeled for neuron-specific markers. Twelve days after transplantation, the grafts had neurons that extended processes from the nerve core toward the denervated organ of Corti. By 64-98 days, the grafts had sent out abundant processes that occupied a significant portion of the space formerly occupied by the cochlear nerve. The neurites grew in fasciculating bundles projecting through Rosenthal's canal, the former site of spiral ganglion cells, into the osseous spiral lamina and ultimately into the organ of Corti, where they contacted hair cells. Neuronal counts showed a significant increase in neuronal processes near the sensory epithelium, compared to animals that were denervated without subsequent stem cell transplantation. The regeneration of these neurons shows that neurons differentiated from stem cells have the capacity to grow to a specific target in an animal model of neuronal degeneration.

Functional Neuronal Differentiation of Bone Marrow-Derived Mesenchymal Stem Cells

Recent results have shown the ability of bone marrow cells to migrate in the brain and to acquire neuronal or glial characteristics. In vitro, bone marrow-derived MSCs can be induced by chemical compounds to express markers of these lineages. In an effort to set up a mouse model of such differentiation, we addressed the neuronal potentiality of mouse MSCs (mMSCs) that we recently purified. These cells expressed nestin, a specific marker of neural progenitors. Under differentiating conditions, mMSCs display a distinct neuronal shape and express neuronal markers NF-L (neurofilament-light, or neurofilament 70 kDa) and class III beta-tubulin. Moreover, differentiated mMSCs acquire neuron-like functions characterized by a cytosolic calcium rise in response to various specific neuronal activators. Finally, we further demonstrated for the first time that clonal mMSCs and their progeny are competent to differentiate along the neuronal pathway, demonstrating that these bone marrow-derived stem cells share characteristics of widely multipotent stem cells unrestricted to mesenchymal differentiation pathways.

Bone marrow mesenchymal stem cells are progenitors in vitro for inner ear hair cells

Stem cells have been demonstrated in the inner ear but they do not spontaneously divide to replace damaged sensory cells. Mesenchymal stem cells (MSC) from bone marrow have been reported to differentiate into multiple lineages including neurons, and we therefore asked whether MSCs could generate sensory cells. Overexpression of the prosensory transcription factor, Math1, in sensory epithelial precursor cells induced expression of myosin VIIa, espin, Brn3c, p27Kip, and jagged2, indicating differentiation to inner ear sensory cells. Some of the cells displayed F-actin positive protrusions in the morphology characteristic of hair cell stereociliary bundles. Hair cell markers were also induced by culture of mouse MSC-derived cells in contact with embryonic chick inner ear cells, and this induction was not due to a cell fusion event, because the chick hair cells could be identified with a chick-specific antibody and chick and mouse antigens were never found in the same cell.

Combination of adenoviral vector-mediated neurotrophin-3 gene transfer and retinoic acid promotes adult bone marrow cells to differentiate into neuronal phenotypes

This study aims to investigate the effect of adenoviral vector-mediated neurotrophine-3 (NT-3) gene transfer and retinoic acid (RA) pretreatment on inducing neuronal differentiation of bone marrow mesenchymal stem cells (MSCs) in vitro. MSCs could be efficiently transduced by NT-3 gene via recombinant adenoviral vectors (Adv). Combination of AdvNT-3 and RA significantly promoted MSCs to differentiate into cell types associated with phenotypes of neural lineages, which included neural markers nestin, NF, MAP2 and PSD95 as detected by immunocytochemistry. But the expressions of GFAP in these cells were not obvious. RT-PCR analysis revealed that AdvNT-3 in combination with RA pretreatment could initiate the transcription of TrkC mRNA. These results demonstrate that the combination of AdvNT-3 and RA pretreatment may promote neuronal differentiation of MSCs, which may serve as ideal seed cells for the repair of spinal cord injury.

Lin−CD34− bone marrow cells from adult mice can differentiate into neural-like cells

Numerous studies have shown that some populations of bone marrow cells (BMCs) have the capacity to differentiate into neural cells, which is useful for repairing brain lesions. In this paper, we analyze neural differentiation features of lineage-negative/CD34-negative (Lin(-)CD34(-)) cells in the bone marrow of adult mice. The population of Lin(-)CD34(-) in BMCs was isolated by magnetic bead sorting and fluorescence-activated cell sorter (FACS) using specific lineage (CD4, CD8a, CD11b, CD45R, Gr-1 and TER-119) antibodies and CD34 antibody. First, we cultured Lin(-)CD34(-) BMCs in the presence of RNIF: vitamin A derivative retinoic acid (RA) and neural-inducing factors (platelet-derived growth factor BB (PDGF-BB), epidermal growth factor (EGF) and fibroblast growth factor-basic (FGF-b)). Analyses of RT-PCR and immunocytochemistry indicated that RNIF-treated Lin(-)CD34(-) BMCs expressed neural phenotypes as well as neurogenic transcription factors. When we implanted the Lin(-)CD34(-) BMCs isolated from enhanced green fluorescent protein (eGFP) transgenic mice into the subventricular zone (SVZ) of postnatal mice, eGFP-positive cells survived 3 weeks after the injection in the various brain regions, some of which expressed the neural phenotypes. Our data suggest that certain subsets in the CD34(-) populations of adult bone marrow could have the capacity to differentiate into neural cells in a suitable environment.

Matrix elasticity directs stem cell lineage specification

Microenvironments appear important in stem cell lineage specification but can be difficult to adequately characterize or control with soft tissues. Naive mesenchymal stem cells (MSCs) are shown here to specify lineage and commit to phenotypes with extreme sensitivity to tissue-level elasticity. Soft matrices that mimic brain are neurogenic, stiffer matrices that mimic muscle are myogenic, and comparatively rigid matrices that mimic collagenous bone prove osteogenic. During the initial week in culture, reprogramming of these lineages is possible with addition of soluble induction factors, but after several weeks in culture, the cells commit to the lineage specified by matrix elasticity, consistent with the elasticity-insensitive commitment of differentiated cell types. Inhibition of nonmuscle myosin II blocks all elasticity-directed lineage specification-without strongly perturbing many other aspects of cell function and shape. The results have significant implications for understanding physical effects of the in vivo microenvironment and also for therapeutic uses of stem cells.

Transdifferentiation and its applicability for inner ear therapy

During normal development, cells divide, then differentiate to adopt their individual form and function in an organism. Under most circumstances, mature cells cannot transdifferentiate, changing their fate to adopt a different form and function. Because differentiated cells cannot usually divide, the repair of injuries as well as regeneration largely depends on the activation of stem cell reserves. The mature cochlea is an exception among epithelial cell layers in that it lacks stem cells. Consequently, the sensory hair cells that receive sound information cannot be replaced, and their loss results in permanent hearing impairment. The lack of a spontaneous cell replacement mechanism in the organ of Corti, the mammalian auditory sensory epithelium, has led researchers to investigate circumstances in which transdifferentiation does occur. The hope is that this information can be used to design therapies to replace lost hair cells and restore impaired hearing in humans.

In vivo and in vitro characterization of bone marrow-derived stem cells in the cochlea

OBJECTIVES/HYPOTHESIS

Stem cell replacement therapy has the potential to treat or cure an array of degenerative neurologic disorders, including sensorineural deafness. However, little is known about the potential for marrow-derived stem cells (MSCs) to take on properties of spiral ganglion neurons. The main purpose of this prospective animal study was to evaluate the survival of MSCs transplanted into the gerbil cochlea.

METHODS

Eight 3- to 4-month-old Mongolian gerbils were used as recipients. The animals received an intraperilymphatic transplantation of 100,000 green fluorescent protein (GFP)-positive MSCs with scala tympani injection and modiolar injection. Seven days after transplantation, MSC survival was evaluated by microscopic examination of frozen sections cut through the cochleae of the recipient animals.

RESULTS

MSCs isolated from the TgN (ACTbEGFP) mouse line used in this study exhibited bright green florescence after five to seven passages in vitro. Seven days after postoperatively, most transplanted MSCs were found in the scala tympani and scala vestibule and only a small number located in the scala media in animals that received both forms of injection. There were no GFP-positive MSCs in the modiolus in animals with scala tympani injection. In contrast, the mean profile count in animals with modiolar injection was 28, which was the highest in all regions. Although MSCs have the potential to migrate, the anatomic barrier between the perilymphatic space and the modiolus might account for the absence of GFP-positive MSCs in this region.

CONCLUSION

These findings may have important clinical implications as a means of delivering MSCs in the cochlea for cell replacement therapy.

Contribution of bone marrow hematopoietic stem cells to adult mouse inner ear: mesenchymal cells and fibrocytes

Bone marrow (BM)-derived stem cells have shown plasticity with a capacity to differentiate into a variety of specialized cells. To test the hypothesis that some cells in the inner ear are derived from BM, we transplanted either isolated whole BM cells or clonally expanded hematopoietic stem cells (HSCs) prepared from transgenic mice expressing enhanced green fluorescent protein (EGFP) into irradiated adult mice. Isolated GFP(+) BM cells were also transplanted into conditioned newborn mice derived from pregnant mice injected with busulfan (which ablates HSCs in the newborns). Quantification of GFP(+) cells was performed 3-20 months after transplant. GFP(+) cells were found in the inner ear with all transplant conditions. They were most abundant within the spiral ligament but were also found in other locations normally occupied by fibrocytes and mesenchymal cells. No GFP(+) neurons or hair cells were observed in inner ears of transplanted mice. Dual immunofluorescence assays demonstrated that most of the GFP(+) cells were negative for CD45, a macrophage and hematopoietic cell marker. A portion of the GFP(+) cells in the spiral ligament expressed immunoreactive Na, K-ATPase, or the Na-K-Cl transporter (NKCC), proteins used as markers for specialized ion transport fibrocytes. Phenotypic studies indicated that the GFP(+) cells did not arise from fusion of donor cells with endogenous cells. This study provides the first evidence for the origin of inner ear cells from BM and more specifically from HSCs. The results suggest that mesenchymal cells, including fibrocytes in the adult inner ear, may be derived continuously from HSCs.

Role of sonic hedgehog in maintaining a pool of proliferating stem cells in the human fetal epidermis

BACKGROUND

The mammalian epidermis is maintained by the ongoing proliferation of a subpopulation of keratinocytes known as epidermal stem cells. Sonic hedgehog (Shh) can regulate morphogenesis of hair follicles and several types of skin cancer, but the effect of Shh on proliferation of human putative epidermal stem cells (HPESCs) is poorly understood.

METHODS AND RESULTS

We first found that Shh, its receptors Patched1 (Ptc1) as well as Smoothened (Smo) and its downstream transcription factor Gli-1 were expressed in the basal layer of human fetal epidermis and freshly sorted HPESCs. Next, treatment of HPESCs with media conditioned by Shh-N-expressing cells promoted cell proliferation, whereas inhibition of Shh by cyclopamine, a specific inhibitor of Shh signalling, had an opposite effect. Interestingly, the mitogenic effect of epidermal growth factor (EGF) on HPESCs was efficiently abolished by cyclopamine. Finally, bone morphogenetic protein 4 (BMP-4), a potential downstream effector of Shh signalling, increased HPESC proliferation in a concentration-dependent manner.

CONCLUSIONS

Shh is an important regulator of HPESC proliferation in the basal layer of human fetal epidermis and modulates the cell responsiveness to EGF, which will assist to unravel the mechanisms that regulate stem cell proliferation and neoplasia in the human epidermis.

Skeletal muscle-derived progenitor cells exhibit neural competence

Skeletal muscle contains heterogenous progenitor cells that give rise to muscle, hematopoietic cells and bone. The exact phenotypic definition of skeletal muscle progenitor cells has not been fully elucidated nor the potential of these cells to differentiate into neurons. Here, we demonstrate that phenotypically homogenous skeletal muscle progenitor cells defined as Lin-CD45-CD117-CD90+ cells express neural stem cell markers and are responsive to neural induction signals. When exposed to neural induction medium containing basic fibroblast growth factor and brain-derived neurotrophic factor, skeletal muscle progenitor cells dramatically changed their cell morphology, became postmitotic and began expressing neuronal markers. These results reveal unexpected potentials of muscle progenitor cells and suggest that these cells may potentially be used in cell-based therapies to replace damaged neurons.

Induction of neuronal differentiation of adult human olfactory neuroepithelial-derived progenitors

Neurosphere forming cells (NSFCs) have been established from cultures of adult olfactory neuroepithelium obtained from patients and cadavers as described previously. They remained undifferentiated in serum or defined media with or without neurotrophic factors. Many factors affect the differentiation of stem cells along a neuronal pathway. Retinoic acid (RA), forskolin (FN), and sonic hedgehog (Shh) have been reported to act as growth promoters during neurogenesis of embryonic CNS in vivo. The effect of RA, FN, and Shh on NSFCs' neuronal lineage restriction has not been described. The application of RA, FN, and Shh to NSFCs induced the expression of motoneuronal transcription factors, tyrosine hydroxylase, an indicator of dopamine production, and neurite formation. These studies further heighten the potential for using olfactory neuroepithelial progenitors for future autologous cell replacement strategies in neurodegenerative conditions and trauma as well as for use in diagnostic evaluation.

Regeneration and replacement in the vertebrate inner ear

Deafness affects more than 40 million people in the UK and the USA, and many more world-wide. The primary cause of hearing loss is damage to or death of the sensory receptor cells in the inner ear, the hair cells. Birds can readily regenerate their cochlear hair cells but the mammalian cochlea has shown no ability to regenerate after damage. Current research efforts are focusing on gene manipulation, gene therapy and stem cell transplantation for repairing or replacing damaged mammalian cochlear hair cells, which could lead to therapies for treating deafness in humans.