Stability of neural differentiation in human adipose derived stem cells by two induction protocols

There are some evidences for suggesting that adipose derived stem cells (ADSCs) can be differentiated to the fate of neural cell type. ADSCs can be expanded rapidly in vitro and can be obtained by a less invasive method. In this study, we attempted to compare the stability of neural differentiation in human ADSCs by using two induction protocols.Isolated ADSCs were induced into neural-like cells using diverse effects of two specific procedures. For protocol 1, ADSCs were induced by chemical induction. In protocol 2, ADSCs were treated for sphere formation. Then, the singled cells were cultured in neurobasal media supplemented with special components. Differentiated ADSCs were evaluated for Nestin, MAP2 and GFAP expression by immunocytochemistry and semi quantitative RT-PCR techniques. Moreover, MTT assay was employed to detect cell viability and proliferation.Immunocytochemical analysis of both protocols demonstrated that ADSCs had large expression of the neural-specific markers. In RT-PCR, protocol 1 showed the highest percentage of MAP2 expression, but with time passing, the neural like state was reversible. Protocol 2 found with express of Nestin at week 1, however MAP2 and GFAP expression increased after 3 weeks. The neural-like cells produced by protocol 1 led to the further cell death.Comparative analysis showed that neural-like cell differentiation of ADSCs in chemical induction protocol was rapid but transitory, while it was approximately steady in neurosphere formation protocol.     

Neural Stem-Like Cells Derived from Human Amnion Tissue are Effective in Treating Traumatic Brain Injury in Rat

Although human amnion derived mesenchymal stem cells (AMSC) are a promising source of stem cells, their therapeutic potential for traumatic brain injury (TBI) has not been widely investigated. In this study, we evaluated the therapeutic potential of AMSC using a rat TBI model. AMSC were isolated from human amniotic membrane and characterized by flow cytometry. After induction, AMSC differentiated in vitro into neural stem-like cells (AM-NSC) that expressed higher levels of the neural stem cell markers, nestin, sox2 and musashi, in comparison to undifferentiated AMSC. Interestingly, the neurotrophic factors, brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin 3 (NT-3), glial cell derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF) were markedly upregulated after neural stem cell induction. Following transplantation in a rat TBI model, significant improvements in neurological function, brain tissue morphology, and higher levels of BDNF, NGF, NT-3, GDNF and CNTF, were observed in the AM-NSC group compared with the AMSC and Matrigel groups. However, few grafted cells survived with minimal differentiation into neural-like cells. Together, our results suggest that transplantation of AM-NSC promotes functional rehabilitation of rats with TBI, with enhanced expression of neurotrophic factors a likely mechanistic pathway.     

Neural Differentiation of Rat Adipose-Derived Stem Cells in Vitro

It is reported that adipose-derived stem cells (ADSCs) had multilineage differentiation potential, and could differentiate into neuron-like cells induced by special induction media, which may provide a new idea for restoration of erectile dysfunction (ED) after cavernous nerve injury. The aim of this research was to explore the neuronal differentiation potential of ADSCs in vitro. ADSCs isolated from inguinal adipose tissue of rat were characterized by flow cytometry, and results showed that ADSCs were positive for mesenchymal stem cell markers CD90 and CD44, but negative for hematopoietic stem cell markers. ADSCs maintained self-renewing capacity and could differentiate into adipocytes and neurocytes under special culture condition. In this research, two methods were used to induce ADSCs. In method 1, ADSCs were treated with the preinduction medium including epithelium growth factor, basic fibroblast growth factor, and brain derived neurotrophic factor (BDNF) for 3?days, then with the neurogenic induction medium containing isobutylmethylxanthine, indomethacin, and insulin. While in method 2, BDNF was not used to treat ADSCs. After induction, neuronal differentiation of ADSCs was evaluated. Neuronal markers, glial fibrillary acidic protein (GFAP), and ??-tubulin III (Tuj-1) were detected by immunofluorescence and Western Blot analyses. The expressions of GFAP and Tuj-1 in method 1 were obviously higher then those in method 2. In addition, the positive rate of the neuron-like cells was higher in method 1. It suggested that ADSCs are able to differentiate into neural-like cells in vitro, and the administration of BDNF in the preinduction medium may provide a new way to modify the culture method for getting more neuron-like cells in vitro.     

Co-culture with neurotrophic factor secreting cells induced from adipose-derived stem cells: Promotes neurogenic differentiation

Adipose-derived stem cells (ADSCs) and bone marrow stem cells (BMSCs) can be equally proper in the treatment of neurodegenerative diseases. However, ADSCs have practical benefits. In this study, we attempted to induce the secretion of neurotrophic factors (NTF) in human ADSCs. We then evaluated the effects of co-culture with NTF secreting cells in neural differentiation of human ADSCs. Isolated human ADSCs were induced to neurotrophic factors secreting cells. To evaluate the in vitro effects of NTF-secreting ADSCs on neurogenic differentiation of ADSCs, we used neurogenic induction medium (control group), the combination of neurogenic medium and conditioned medium, or co-cultured NTF-secreting ADSCs which were encapsulated in alginate beads (co-culture) for 7 days. ELISA showed increased (by about 5 times) release of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in NTF-secreting ADSCs compared to human ADSCs. Real time RT-PCR analysis revealed that NTF-secreting ADSCs highly expressed NGF and BDNF. In addition, co-culture with NTF-secreting ADSCs could also promote neuronal differentiation relative to gliogenesis. Overall, NTF-secreting ADSCs secrete a range of growth factors whose levels in culture could promote neuronal differentiation and could support the survival and regeneration in a variety of neurodegenerative diseases.     

NT-3, BDNF, and NGF in the developing rat nervous system: parallel as well as reciprocal patterns of expression.

To obtain insight into the site and stage specificity of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) action in vivo, we compared the expression patterns of the genes for these three related neurotrophic factors as well as for the NGF receptor in developing and adult rats. Initial embryonic expression of these related neurotrophic factors approximately coincides with the onset of neurogenesis. However, the levels at which the three factors are expressed at this time and throughout the developing nervous system are dramatically different. NT-3 is by far the most highly expressed in immature regions of the CNS in which proliferation, migration, and differentiation of neuronal precursors is ongoing. NT-3 expression dramatically decreases with maturation of these regions. By contrast, BDNF expression is low in developing regions of the CNS and increases as these regions mature. NGF expression varies during the development of discrete CNS regions, but not in any consistent manner compared with NT-3 and BDNF. Despite the dramatic variations, NT-3, BDNF, and NGF do share one striking similarity--high level expression in the adult hippocampus. Our observations are consistent with the idea that NT-3, BDNF, and NGF have paralleled as well as reciprocal roles in vivo.     

Effects of Differentiated Versus Undifferentiated Adipose Tissue-derived Stromal Cell Grafts on Functional Recovery After Spinal Cord Contusion

Controversies exist concerning the need for mesenchymal stromal cells (MSCs) to be transdifferentiated prior to their transplantation. In the present study, we compared the results of grafting into the rat contused spinal cord undifferentiated, adipose tissue-derived stromal cells (uADSCs) versus ADSCs induced by two different protocols to form differentiated nervous tissue. Using Basso, Beattie, and Bresnahan scores and grid tests, we found that three cell-treated groups, including uADSCs-treated, dADSCs induced by Protocol 1 (dADSC-P1)-treated, and dADSCs induced by Protocol 2 (dADSC-P2)-treated groups, significantly improved locomotor functional recovery in SCI rats, compared with the saline-treated group. Furthermore, functional recovery was better in the uADSC-treated and dADSC-P2-treated groups than in the dADSC-P1-treated group at week 12 postinjury (P < 0.05 for dADSC-P1 group vs. uADSCs or dADSC-P2 groups). Although both protocols could induce high percentages of cells expressing neural markers in vitro, few BrdU-labeled cells survived at the injury sites in the three cell-treated groups, and only a small percentage of BrdU-positive cells expressed neural markers. On the other hand, the number of NF200-positive axons in the uADSC-treated and dADSC-P2-treated groups was significantly larger than those in the dADSC-P1-treated and saline-treated control groups. Our results indicate that ADSCs are able to differentiate into neural-like cells in vitro and in vivo. However, neural differentiated ADSCs did not result in better functional recovery than undifferentiated ones, following SCI. In vitro neural transdifferentiation of ADSCs might therefore not be a necessary pretransplantation step. Furthermore, cellular replacement or integration might not contribute to the functional recovery of the injured spinal cord.     

Comparison of long-term retinoic acid-based neural induction methods of bone marrow human mesenchymal stem cells

The differentiation of human mesenchymal stem cells (hMSCs) into neural cells in vitro provides a potential tool to be utilized for cell therapy of neurodegenerative disorders. Although previous studies repeated different protocols for the induction of neural cells from hMSCs in vitro, the results were not in complete agreement. In this study, we have attempted to compare three of these neural induction methods; retinoic acid (RA) treatment, RA treatment in serum reduced conditions, and treatment using other chemical compounds (dimethyl sulfoxide and potassium chloride) along with RA by real-time cell analysis and immunofluorescent staining of neural markers. RA treatment led to a slow progression of cells into neural-like morphology with the expression of neural protein neurofilament whereas reducing serum during RA treatment caused a much more extended differentiation process. Additionally, neural-like morphology was persistent in the later periods of differentiation in RA treatment. On the other hand, chemical induction caused cell shrinkages mimicking neural-like morphology in a short time and loss of this morphology along with increased cell death in later periods. Among the three methods compared, RA treatment was the most reliable one in terms of stability of differentiation and neural protein expressions.     

Extracellular-Regulated Kinases and Phosphatidylinositol 3-Kinase Are Involved in Brain-Derived Neurotrophic Factor-Mediated Survival and neuritogenesis of the Neuroblastoma Cell Line SH-SY5Y

Retinoic acid (RA) induces the differentiation of many cell lines, including those derived from neuroblastoma. RA treatment of SH-SY5Y cells induces the appearance of functional Trk B and Trk C receptors. Acute stimulation of RA-predifferentiated SH-SY5Y cells with brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), or neurotrophin 4/5 (NT-4/5), but not nerve growth factor (NGF), induces Trk autophosphorylation, followed by phosphorylation of Akt and the extracellular signal-regulated kinases (ERKs) 1 and 2. In addition, BDNF, NT-3, or NT-4/5, but not NGF, promotes cell survival and neurite outgrowth in serum-free medium. The mitogen-activated protein kinase and ERK kinase (MEK) inhibitor PD98059 blocks BDNF-induced neurite outgrowth and growth-associated protein-43 expression but has no effects on cell survival. On the other hand, the phosphatidylinositol 3-kinase inhibitor LY249002 reverses the survival response elicited by BDNF, leading to a cell death with morphological features of apoptosis.     

神经营养因子与神经干细胞

生长因子在神经干细胞的增殖,分化和存活过程中有重要作用。神经营养因子是其中的一类,它包括神经生长因子（NGF）家族,胶质源性神经营养因子（GDNF）家族和其它神经营养因子。NGF家族包括NGF,BDNF,NT－3,NT－4／5和NT－6。这一家族可促进epidermic growth facter(EGF)反应 海马及前脑室管膜下区神经干细胞的存活和分化。GDNF家族包括GDNF,NTN,PSP和ART。GDNF家族促神经发育的作用主要在外周,它促进肠神经嵴前体细胞的存活和增殖,且对外周感觉神经的发育至关重要。其它生长因子如bFGF和EGF,它们能促进神经干细胞增殖和存活;CNTF和LIF等在神经干细胞的分化中也有重要作用。     

Growth factor synergism and antagonism in early neural crest development.

This review article focuses on data that reveal the importance of synergistic and antagonistic effects in growth factor action during the early phases of neural crest development. Growth factors act in concert in different cell lineages and in several aspects of neural crest cell development, including survival, proliferation, and differentiation. Stem cell factor (SCF) is a survival factor for the neural crest stem cell. Its action is neutralized by neurotrophins, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) through apoptotic cell death. In contrast, SCF alone does not support the survival of melanogenic cells (pigment cell precursors). They require the additional presence of a neurotrophin (NGF, BDNF, or NT-3). Fibroblast growth factor-2 (FGF-2) is an important promoter of proliferation in neuronal progenitor cells. In neural crest cells, fibroblast growth factor treatment alone does not lead to cell expansion but also requires the presence of a neurotrophin. The proliferative stimulus of the fibroblast growth factor - neurotrophin combination is antagonized by transforming growth factor beta-1 (TGFbeta-1). Moreover, TGFbeta-1 promotes the concomitant expression of neuronal markers from two cell lineages, sympathetic neurons and primary sensory neurons, indicating that it acts on a pluripotent neuronal progenitor cell. Moreover, the combination of FGF-2 and NT3, but not other neurotrophins, promotes expression or activation of one of the earliest markers expressed by presumptive sympathetic neuroblasts, the norepinephrine transporter. Taken together, these data emphasize the importance of the concerted action of growth factors in neural crest development at different levels and in several cell lineages. The underlying mechanisms involve growth-factor-induced dependence of the cells on other factors and susceptibility to growth-factor-mediated apoptosis.     

Efficient generation of functional Schwann cells from adipose-derived stem cells in defined conditions

Schwann cells (SCs) are hitherto regarded as the most promising candidates for viable cell-based therapy to peripheral nervous system (PNS) injuries or degenerative diseases. However, the extreme drawbacks of transplanting autologous SCs for clinical applications still represent a significant bottleneck in neural regenerative medicine, mainly owing to the need of sacrificing a functional nerve to generate autologous SCs and the nature of slow expansion of the SCs. Thus, it is of great importance to establish an alternative cell system for the generation of sufficient SCs. Here, we demonstrated that adipose-derived stem cells (ADSCs) of rat robustly give rise to morphological, phenotypic and functional SCs using an optimized protocol. After undergoing a 3-week in vitro differentiation, almost all of treated ADSCs exhibited spindle shaped morphology similar to genuine SCs and expressed SC markers GFAP and S100. Most importantly, apart from acquisition of SC antigenic and biochemical features, the ADSC-derived SCs were functionally identical to native SCs as they possess a potential ability to form myelin, and secret nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glia-derived neurotrophic factor (GDNF). The current study may provide an ideal strategy for harvesting sufficient SCs for cell-based treatment of various peripheral nerve injuries or disorders.     

Anti-apoptotic action of nerve growth factor in mouse osteoblastic cell line

We investigated the potential role of nerve growth factor (NGF) in osteoblast survival in vitro. We found the expression of the mRNAs encoding NGF, brain-derived neurotrophic factor (BDNF), and trk-b, which is the receptor molecule of BDNF in mouse osteoblastic MC3T3-E1 cells. NGF high-affinity receptor trk-a was expressed continuously in the cells as visualized by Western blotting. A proinflammatory cytokine mixture stimulated NGF mRNA, and NGF protein release from MC3T3-E1 cells. When the effect of the nuclear factor-KB inhibitor pyrrolidine dithiocarbamate (PDTC) and activating protein-1 inhibitor curcumin were examined, a dose-dependent inhibition of cytokine-activated NGF expression occurred in the presence of PDTC or curcumin. Further, a specific inhibitor of p38 mitogen activated protein kinase (MAPK), i.e., SB203580, inhibited the induction of NGF in cytokines-treated cells in a dose-dependent manner whereas a specific inhibitor of classic MAPK, PD98059 had no effect on the induction of NGF. Treatment of anti-NGF IgG resulted in a potent increase of DNA fragmentation at a dose-dependent manner. NGF but not BDNF caused a dose-dependent reduction in the extent of apoptotic DNA breakdown under treatment with cytokines. Under similar conditions, the addition of NGF resulted in a potent reduction in bax protein but not in Fas, or bcl-xl. These findings demonstrated that NGF in non-neuronal osteoblastic cells may play an important role in cell survival as an anti-apoptotic factor.     

Developmental changes in the protective effect of exogenous brain-derived neurotrophic factor and neurotrophin-3 against ototoxic drugs in cultured rat vestibular ganglion neurons

We examine developmental changes in the responsiveness of rat vestibular ganglion neurons (VGNs) to two neurotrophic factors (NTFs), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) and investigate the protective effects of these NTFs against ototoxic drugs during postnatal development in dissociated cultures. VGNs were obtained from rats on postnatal days (P) 1, 3, 7 and 14. BDNF facilitated neuronal survival as well as neurite sprouting of VGNs obtained from younger rats (P1 and P3), whereas these effects were not observed in older rats (P7 and P14). BDNF was also effective in facilitating neurite extension in VGNs at each of the postnatal ages. NT-3 also facilitated neuronal survival and neurite extension of VGNs from younger rats but these effects were significantly smaller than those of BDNF (p?<?0.05). The protective effects of BDNF and NT-3 against ototoxic drugs, gentamicin and cisplatin, were also age-dependent: they were effective for neuronal survival, neurite sprouting and neurite extension in VGNs from younger rats, whereas these effects tended to disappear in VGNs from older rats. Analysis of the changes in the expression of the receptors of NTFs revealed that expression of TrkB and TrkC proteins and their mRNA did not change during the developmental period, whereas expression of p75^NTR protein was down-regulated together with that of p75^NTR mRNA during the developmental period. Developmental changes in the responsiveness to exogenous NTFs in VGNs, which is not caused by the changes of their receptors but probably caused by changes in the intracellular signaling pathways, should be taken into consideration in the prevention of neuronal degeneration caused by ototoxic drugs.     

Deferoxamine Preconditioning of Neural-Like Cells Derived from Human Wharton’s Jelly Mesenchymal Stem Cells as a Strategy to Promote Their Tolerance and Therapeutic Potential: An In Vitro Study

Transplantation of neural-like cells is considered as a promising therapeutic strategy developed for neurodegenerative disease in particular for ischemic stroke. Since cell survival is a major concern following cell implantation, a number of studies have underlined the protective effects of preconditioning with hypoxia or hypoxia mimetic pharmacological agents such as deferoxamine (DFO), induced by activation of hypoxia inducible factor-1 (HIF-1) and its target genes. The present study has investigated the effects of DFO preconditioning on some factors involved in cell survival, angiogenesis, and neurogenesis of neural-like cells derived from human Wharton’s jelly mesenchymal stem cells (HWJ-MSCs) in presence of hydrogen peroxide (H₂O₂). HWJ-MSCs were differentiated toward neural-like cells for 14 days and neural cell markers were identified using immunocytochemistry. HWJ-MSC-derived neural-like cells were then treated with 100 µM DFO, as a known hypoxia mimetic agent for 48 h. mRNA and protein expression of HIF-1 target genes including brain-derived neurotrophic factors (BDNF) and vascular endothelial growth factor (VEGF) significantly increased using RT-PCR and Western blotting which were reversed by HIF-1α inhibitor, while, gene expression of Akt-1, Bcl-2, and Bax did not change significantly but pAkt-1 was up-regulated as compared to poor DFO group. However, addition of H₂O₂ to DFO-treated cells resulted in higher resistance to H₂O₂-induced cell death. Western blotting analysis also showed significant up-regulation of HIF-1α, BDNF, VEGF, and pAkt-1, and decrease of Bax/Bcl-2 ratio as compared to poor DFO. These results may suggest that DFO preconditioning of HWJ-MSC-derived neural-like cells improves their tolerance and therapeutic potential and might be considered as a valuable strategy to improve cell therapy.     

Enhanced synthesis of brain-derived neurotrophic factor in the lesioned peripheral nerve: different mechanisms are responsible for the regulation of BDNF and NGF mRNA

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are molecules which regulate the development and maintenance of specific functions in different populations of peripheral and central neurons, amongst them sensory neurons of neural crest and placode origin. Under physiological conditions NGF is synthesized by peripheral target tissues, whereas BDNF synthesis is highest in the CNS. This situation changes dramatically after lesion of peripheral nerves. As previously shown, there is a marked rapid increase in NGF mRNA in the nonneuronal cells of the damaged nerve. The prolonged elevation of NGF mRNA levels is related to the immigration of activated macrophages, interleukin-1 being the most essential mediator of this effect. Here we show that transsection of the rat sciatic nerve also leads to a very marked increase in BDNF mRNA, the final levels being even ten times higher than those of NGF mRNA. However, the time-course and spatial pattern of BDNF mRNA expression are distinctly different. There is a continuous slow increase of BDNF mRNA starting after day 3 post-lesion and reaching maximal levels 3-4 wk later. These distinct differences suggest different mechanisms of regulation of NGF and BDNF synthesis in non-neuronal cells of the nerve. This was substantiated by the demonstration of differential regulation of these mRNAs in organ culture of rat sciatic nerve and Schwann cell culture. Furthermore, using bioassays and specific antibodies we showed that cultured Schwann cells are a rich source of BDNF- and ciliary neurotrophic factor (CNTF)-like neurotrophic activity in addition to NGF. Antisera raised against a BDNF-peptide demonstrated BDNF-immunoreactivity in pure cultured Schwann cells, but not in fibroblasts derived from sciatic nerve.     

Characterization of the Responses of Purkinje Cells to Neurotrophin Treatment

Abstract: The ability of the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) to promote neuronal survival and phenotypic differentiation was examined in dissociated cultures from embryonic day 16 rat cerebellum. BDNF treatment increased the survival of neuron-specific enolase-immunopositive cells by 250 and 400% after 8 and 10 days in culture, respectively. A subpopulation of these neurons, the Purkinje cells, identified by calbindin staining, was increased to an equivalent extent, ∼200%, following BDNF, NT-4/5, or NT-3 treatment. The number of GABAergic neurons, identified by GABA immunoreactivity, was greatly increased by treatment with BDNF (470%) and moderately by NT-4/5 (46%), whereas NT-3 was without effect. NGF failed to increase the number of either Purkinje cells or GABAergic neurons. Addition of BDNF within 48 h of cell plating was required to obtain a maximal increase in Purkinje cell number after 8 days. In contrast, the NT-3 responses were nearly equivalent even if treatment was delayed for 96 h after plating. BDNF, NT-4/5, and NT-3, but not NGF, induced the rapid expression of the immediate early gene c- fos . Immunocytochemical double-labeling with antibodies to c-fos and calbindin was used to identify Purkinje cells that responded to neurotrophin treatment by induction of c-fos. After 4 days in vitro, both BDNF and NT-3 induced the formation of c-fos protein in calbindin-immunopositive neurons, whereas NT-4/5 did not. The latter results suggest that although BDNF and NT-4/5 have been shown to act through a common receptor, TrkB, it appears that the effects of BDNF and NT-4/5 are not identical.     

Sprouty1 regulates neuritogenesis and survival of cortical neurons

In multicellular organisms, receptor tyrosine kinases (RTKs) control a variety of cellular processes, including cell proliferation, differentiation, migration, and survival. Sprouty (SPRY) proteins represent an important class of ligand-inducible inhibitors of RTK-dependent signaling pathways. Here, we investigated the role of SPRY1 in cells of the central nervous system (CNS). Expression of SPRY1 was substantially higher in neural stem cells than in cortical neurons and was increased during neuronal differentiation of cortical neurons. We found that SPRY1 was a direct target gene of the CNS-specific microRNA, miR-124 and miR-132. In primary cultures of cortical neurons, the neurotrophic factors brain-derived neurotrophic factor (BDNF) and Basic fibroblast growth factor (FGF2) downregulated SPRY1 expression to positively regulate their own functions. In immature cortical neurons and mouse N₂A cells, we found that overexpression of SPRY1 inhibited neurite development, whereas knockdown of SPRY1 expression promoted neurite development. In mature neurons, overexpression of SPRY1 inhibited the prosurvival effects of both BDNF and FGF2 on glutamate-mediated neuronal cell death. SPRY1 was also upregulated upon glutamate treatment in mature neurons and partially contributed to the cytotoxic effect of glutamate. Together, our results indicate that SPRY1 contributes to the regulation of CNS functions by influencing both neuronal differentiation under normal physiological processes and neuronal survival under pathological conditions.     

神经营养因子NGF、BDNF与围绝经期妇女认知功能关系的研究进展

神经营养因子(NTFs)是近几年神经科学研究的热点,研究显示它在神经系统中发挥独特的作用,尤其是神经生长因子(NGF)、脑源性神经营养因子(BDNF)在脑内功能及其表达调控方面具有重要作用。围绝经期妇女随着雌激素水平的降低会产生认知功能的减退,有研究发现去卵巢动物(OVX)雌激素水平降低可以导致某些NGF、BDNF的丢失。通过启动内源性NGF和BDNF的表达而实现对神经元的保护可能为雌激素替代治疗(ERT)脑保护作用的一种机制。本文就近几年的研究进展做一简要综述。     

Evidence for the participation of nerve growth factor and its low-affinity receptor (p75NTR) in the regulation of the myogenic program

We have studied expression and function of neurotrophins and their receptors during myogenic differentiation of C2C12 cells, a clonal cell line derived from mouse muscle that is capable of in vitro differentiation. The genes coding for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and their common low-affinity receptor p75^{neurotrophin receptor} (p75^NTR) were shown to be expressed in C2C12 myoblasts and downregulated during myogenic differentiation and fusion into myotubes. Cocultures with dorsal root ganglia from day 8 chick embryos revealed neurite-promoting activities of C2C12 cells that ceased with myogenic differentiation. These data suggest a temporal and developmental window for the effect of myogenic cell-derived neurotrophins on neuronal as well as on myogenic cell populations. NGF was shown to increase DNA synthesis and cell growth of C2C12 myoblasts and to enhance myogenic differentiation in this cell line. We present evidence that NGF-mediated processes take place at stages preceding myogenic differentiation. Enhanced muscle differentiation was also seen in p75^NTR-overexpressing C2C12 myoblasts which maintained high levels of receptors but ceased to produce NGF during differentiation. In contrast, when exogenous NGF was present at the onset of myogenic differentiation of receptor-overexpressing cells, muscle cell development was strongly repressed. This indicates that downregulation of p75^NTR is necessary for guiding myogenic cells towards terminal differentiation. Since none of the trk high-affinity neurotrophin receptors could be demonstrated in C2C12 cells, we conclude that NGF mediates its nonneurotrophic effect via its low-affinity receptor in an autocrine fashion. J. Cell. Physiol. 176:10–21, 1998. © 1998 Wiley-Liss, Inc.