Mechanisms and functions of p75 neurotrophin receptor signaling in astrocytes

描述（由申请人提供）：在中枢神经系统病理学中，包括多发性硬化、中风、脊髓和创伤性损伤，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剂。在神经系统疾病中触发星形胶质细胞激活的分子机制仍不完全表征。我们已经表明，神经营养因子受体p75 NTR通过抑制纤维蛋白降解和调节细胞分化来调节修复过程。我们的长期目标是表征负责p75 NTR在神经系统发病机制中的作用的分子途径，作为开发可以特异性靶向p75 NTR信号传导和减弱神经病理性疾病过程的治疗方案的先决条件。我们的主要假设是，p75 NTR的膜内蛋白水解调节TGF-β信号，以控制星形胶质细胞在发育和疾病过程中的功能。我们的初步数据表明：a）p75 NTR的胞内结构域（p75 ICD）是星形胶质细胞核孔复合物的新组分; B）p75 NTR直接结合核孔蛋白153（Nup 153）天然未折叠的FG结构域;诱导p75 NTR的β-分泌酶依赖性切割，导致其在核孔内移位，d）p75 NTR调节Smad 2，和e）p75 NTR在体内调节CNS中的星形胶质细胞分化和TGF-β功能。我们的具体目标是测试我们的工作模型，其中p75 NTR的膜内裂解导致核孔复合物的重塑，允许Smad 2的核质穿梭，并诱导星形胶质细胞分化和激活。我们采用多阶段实验设计，包括TGF？- 诱导的星形胶质细胞活化，产生新的转基因小鼠用于表达p75 NTR的细胞的细胞命运作图，原子力显微镜和三维电子断层扫描以确定裂解的p75 NTR在星形胶质细胞中核孔复合物的动态重塑中的作用，和生物化学实验来确定p75 NTR切割如何调节Smad 2核质穿梭及其与TGF β转录机制的偶联。鉴定p75 NTR和TGF β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：星形胶质细胞瘢痕是中枢神经系统再生的主要抑制剂。研究p75 NTR和TGF？信号通路之间的分子相互作用作为调节星形胶质细胞活化的新机制，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.