Mechanisms and functions of p75 neurotrophin receptor signaling in astrocytes

描述(申请人提供)：在中枢神经系统病理中，包括多发性硬化症、中风、脊髓和创伤，由反应性星形胶质细胞和细胞外基质沉积组成的瘢痕形成是组织修复的主要抑制因素。神经系统疾病中触发星形胶质细胞激活的分子机制尚不完全清楚。我们已经证明，神经营养素受体p75NTR通过抑制纤维蛋白降解和调节细胞分化来调节修复过程。我们的长期目标是确定p75NTR在神经系统发病机制中起作用的分子途径，作为开发特异性靶向p75NTR信号并减轻神经病理疾病过程的治疗方案的先决条件。我们的主要假设是p75NTR的膜内蛋白分解调节了转化生长因子-β信号，从而控制了星形胶质细胞在发育和疾病过程中的功能。我们的初步研究结果表明：a)p75NTR的胞内区(P75ICD)是星形胶质细胞核孔复合体的新成分；b)p75NTR直接与天然展开的核孔蛋白153(Nup153)的Fg区结合；c)转化生长因子β诱导p75NTR的3-分泌酶依赖的裂解导致其移位到核孔内；d)p75NTR调节Smad2的表达；e)p75NTR调节星形胶质细胞的分化和体内中枢神经系统中转化生长因子-β的功能。我们的具体目标是测试我们的工作模型，在该模型中，p75NTR的膜内切割导致核孔复合体重塑，从而允许Smad2的核质穿梭，并诱导星形胶质细胞的分化和激活。我们采用多阶段实验设计，包括转化生长因子β诱导星形胶质细胞激活的转基因模型、用于p75NTR表达细胞命运定位的新转基因小鼠的产生、原子力显微镜和三维电子断层扫描来确定切割的p75NTR在星形胶质细胞核孔复合体动态重塑中的作用，以及生化实验来确定p75NTR切割如何调节Smad2核质穿梭及其与转化生长因子β转录机制的偶联。确定p75NTR和转化生长因子信号通路之间的分子相互作用可能为以星形胶质细胞瘢痕形成和组织修复能力降低为特征的各种疾病的药物干预提供损伤特异性靶点。 公共卫生相关性：星形胶质细胞疤痕是中枢神经系统再生的主要抑制因素。研究p75NTR和转化生长因子信号通路之间的分子相互作用作为一种调节星形胶质细胞激活的新机制，可能为以星形胶质细胞瘢痕形成和组织修复能力降低为特征的各种疾病的药物干预提供损伤特异性靶点。

DESCRIPTION (provided by applicant): In central nervous system pathologies, including multiple sclerosis, stroke, spinal cord and traumatic injuries, scar formation consisting of reactive astrocytes and deposition of extracellular matrix is a major inhibitor of tissue repair. The molecular mechanisms that trigger astrocyte activation in nervous system disease remain incompletely characterized. We have shown that the neurotrophin receptor p75NTR regulates repair processes by inhibiting fibrin degradation and regulating cell differentiation. Our long-term goal is to characterize the molecular pathways that are responsible for the effects of p75NTR in nervous system pathogenesis, as a prerequisite for the development of therapeutic protocols that can specifically target p75NTR signaling and attenuate neuropathological disease processes. Our major hypothesis is that intramembrane proteolysis of p75NTR regulates TGF-¿ signaling to control astrocyte functions during development and disease. Our preliminary data demonstrate that a) the intracellular domain of p75NTR (p75ICD) is a novel component of the nuclear pore complex in astrocytes, b) p75NTR directly binds to the natively unfolded FG-domain of nucleoporin 153 (Nup153), c) TGF-¿ induces 3-secretase-dependant cleavage of p75NTR resulting in its translocation inside the nuclear pore, d) p75NTR regulates of Smad2, and e) p75NTR regulates astrocyte differentiation and TGF-¿ functions in the CNS in vivo. Our specific aims are designed to test our working model, in which intramembrane cleavage of p75NTR results in remodeling of the nuclear pore complex that allows nucleocytoplasmic shuttling of Smad2 and induces astrocyte differentiation and activation. We employ a multiphaceted experimental design that includes transgenic models of TGF¿-induced astrocyte activation, generation of new transgenic mice for cell-fate mapping of p75NTR - expressing cells, atomic force microscopy and three-dimensional electron tomography to determine the role of cleaved p75NTR in the dynamic remodeling of the nuclear pore complex in astrocytes, and biochemical experiments to define how p75NTR cleavage regulates Smad2 nucleocytoplasmic shuttling and its coupling to the TGF¿ transcriptional machinery. Identifying the molecular interplay between p75NTR and TGF¿ signaling pathways could potentially provide injury-specific targets for pharmacological intervention in a variety of diseases characterized by astrocyte scar formation and decreased capacity for tissue repair. PUBLIC HEALTH RELEVANCE: The astrocyte scar is a major inhibitor for regeneration in the CNS. Study of the molecular interplay between p75NTR and TGF¿ signaling pathways as a novel mechanism that regulates astrocyte activation could potentially provide injury-specific targets for pharmacological intervention in a variety of diseases characterized by astrocyte scar formation and decreased capacity for tissue repair.