The role of FGF signaling in suppressing astrogliosis

描述(申请人提供)：神经胶质增生症是对大脑损伤的一种反应，是许多神经疾病的显著特征，包括癫痫、神经退行性变、肿瘤生长、中风和创伤。对损伤的反应涉及中枢神经系统内的细胞类型，可能包括渗透的免疫细胞。反应的程度是不同的，并受许多秘密因素的调节(Sofroniew，2009；Kang和Hibert，2011)。然而，对于这些因素中的一些，它们在胶质细胞增生症中的需求和作用还没有明确的定义或在体内得到证实。成纤维细胞生长因子(FGFs)尤其如此。以前的免疫组织化学分析表明，星形胶质细胞对损伤的反应是核FGF2和至少一个受体上调(Eddleston和Mucke，1993；Ridet等人，1997)。然而，这些免疫标记的意义尚不清楚。此外，在正常情况下和损伤后的体内成熟星形胶质细胞中，成纤维细胞生长因子信号的作用仍未被阐明。这项建议的目的是为FGFs在正常情况下星形胶质细胞增生症和损伤反应中的作用提供确凿的证据。为了研究成纤维细胞生长因子信号在成人大脑中的功能，我们在FGFR3缺失的背景下有条件地删除了FGFR1和FGFR2的FGFR2等位基因。我们使用了NestinCreer小鼠品系，在该品系中，在他莫昔芬治疗后，Creer出人意料地在整个海马区和皮质实质(除了预期的神经源性区域之外)的星形胶质细胞中活跃。我们的初步数据表明，在成纤维细胞生长因子受体的三个突变体中，星形细胞GFAP、Vimentin和Nestin的表达显著增加，这表明星形胶质细胞增生。在携带NestinCreer的三苯氧胺处理的杂合子对照或只缺少一个或两个受体的突变体中，没有观察到中间丝的这种增加。在单突变体和双突变体中没有这种表型，这表明受体之间的功能代偿，这可能解释了为什么以前没有报道这种表型。在三个突变体中，胶质细胞标志物的增加并没有伴随着可检测到的组织损伤、细胞死亡或神经源性区域的明显变化。此外，我们的初步数据表明，突变体中具有反应性的星形胶质细胞是那些失去了成纤维细胞生长因子信号的星形胶质细胞，而邻近的非反应性星形胶质细胞保持了信号传递。这导致了我们的假设，即成纤维细胞生长因子受体在没有损伤的情况下自主地作用于细胞，以抑制星形胶质细胞增生。

DESCRIPTION (provided by applicant): Gliosis is a response to brain damage and is a prominent feature of many neurological disorders including epilepsy, neurodegeneration, tumor growth, stroke, and trauma. The response to damage involves cell types from within the CNS and can include infiltrating immune cells. The extent of the response varies and is modulated by a number of secreted factors (Sofroniew, 2009; Kang and Hibert, 2011). For some of these factors, however, their requirement and role in gliosis has not been clearly defined or demonstrated in vivo. This is particularly true for Fibroblast Growth Factors (FGFs). Previous immunohistochemical analyses suggested that nuclear FGF2 and at least one receptor are up-regulated in astrocytes in response to damage (Eddleston and Mucke, 1993; Ridet et al., 1997). However, the significance of these immunostains is unknown. Moreover the role of FGF signaling in mature astrocytes in vivo under normal conditions as well as after injury remains unaddressed. The goal of this proposal is to provide definitive evidence for the role of FGFs in astrogliosis under normal conditions and in response to damage. To address the function of FGF signaling in the adult cerebrum, we conditionally deleted floxed alleles of Fgfr1 and Fgfr2 in an Fgfr3 null background. We used a NestinCreER mouse line in which CreER, upon tamoxifen treatment, is unexpectedly active specifically in astrocytes throughout the hippocampal and cortical parenchyma (in addition to the expected neurogenic regions). Our preliminary data indicate that in FGF receptor triple mutants there is a tremendous increase in astrocytic GFAP, Vimentin, and Nestin expression, indicative of astrogliosis. This increase in intermediate filaments is not observed in tamoxifen-treated heterozygous littermate controls that carry NestinCreER or in mutants that lack only one or two receptors. The absence of the phenotype in single and double mutants suggests functional compensation between receptors and may explain why this phenotype has not previously been reported. The increase in gliotic markers in the triple mutant is not accompanied by detectable signs of tissue damage, cell death, or obvious changes in the neurogenic regions. Moreover, our preliminary data suggests that the astrocytes that are reactive in the mutants are the ones that have lost FGF signaling whereas neighboring non-reactive ones have maintained signaling. This leads us to the hypothesis that FGF receptors act cell autonomously in the absence of injury to suppress astrogliosis.