The Role of Neurotrophins in Oligodendrocyte Function

描述(申请人提供)：目前工作的总体假设是少突胶质细胞(OLG)，即中枢神经系统的髓鞘细胞，受到明确定义的营养因子-脑源性神经营养因子(BDNF)的严重影响。BDNF的作用是通过TrkB及其相关的MAP激酶、PI3激酶-Akt和PLC-Gamma通路来实现的。BDNF支持OLG在大脑发育和整个生命过程中的增殖和分化。在最初筹资期间开展的工作支持这一假设。利用基底前脑(BF)OLG培养，我们发现BDNF可使DNA合成和髓鞘碱性蛋白+(MBP)细胞数量增加2-3倍。利用体内研究，我们发现BDNF基因敲除动物表达的NG2少突胶质前体细胞比野生型少突胶质细胞前体细胞少38%，BDNF+/_成年小鼠MBP表达减少。免疫细胞化学分析显示，BDNF受体TrkB在成年小鼠成熟的APC+OLGs上表达。这些观察结果支持了OLG受BDNF严格调控的可能性。为了扩展这些研究，我们现在建议1)测试培养工作的体内相关性，以及(2)确定潜在的BDNF作用的信号机制。具体地说，我们将：(1)确定介导BDNF效应的受体和信号通路；(2)确定TrkB在OLG中的体内表达模式；(3)利用基因敲除小鼠确定BDNF和BDNF受体在体内的作用。这些研究探索了BDNF在体内OLGs的形成和维持中可能发挥的作用。我们认为，这项工作可能对髓鞘形成缺陷提供重要的新见解，这些髓鞘缺陷发生在以少突胶质细胞丢失和无法重新填充受损区域为特征的破坏性神经疾病中。

DESCRIPTION (provided by applicant): The overall hypothesis of the current work is that oligodendrocytes (OLGs), the myelinating cells of the central nervous system are critically influenced by the well-defined trophic factor, brain-derived neurotrophic factor (BDNF). The effects of BDNF are mediated through trkB and its associated MAP kinase, PI3 kinase-Akt, and PLC-gamma pathways. BDNF supports OLG proliferation and differentiation during brain development and throughout life. Work performed during the initial funding period supports this hypothesis. Using basal forebrain (BF) OLG cultures, we found that BDNF elicits 2-3 fold increases in DNA synthesis and numbers of myelin basic protein + (MBP) cells. Using in vivo studies we found that BDNF knockout animals express 38 percent fewer NG2 oligodendrocyte progenitor cells than wild-type littermates and that BDNF +/_ adult mice exhibit reduced MBP expression. Moreover, coimmunocytochemical analysis revealed that the BDNF receptor, trkB, is expressed on mature APC+ OLGs in adult mice. These observations support the possibility that OLGs are critically regulated by BDNF. To extend these studies we now propose to 1) test in vivo relevance of the culture work and (2) determine signaling mechanisms underlying BDNF actions. In particular, we will: (1) Identify receptors and signaling pathways mediating BDNF effects, (2) Define the in vivo expression pattern of trkB in OLGs and (3) Define the roles of BDNF and BDNF receptors in vivo by using knockout mice. These studies explore the role BDNF may play in the development and maintenance of OLGs in vivo. We suggest that this work may provide significant new insights into deficits in myelination that occur in devastating neural diseases characterized by the loss of oligodendrocytes and an inability to repopulate the lesioned area.