Genetic analysis of the neurotrophin receptor p75 in neural development

描述（由申请人提供）：本项目的长期目标是了解神经营养因子受体p75在神经发育和再生中的作用。虽然最初被鉴定为具有结合神经营养因子的能力，但p75作为一种关键的辅助受体，在神经发育和功能中调节多种信号通路。例如，它是糖基-磷脂酰肌醇（GPI）连接的NgR和肝配蛋白A5的共受体。我们一直使用背根神经节（DRG）感觉神经元系统来了解p75在神经发育中的作用。DRG神经元通过多种标准分类，包括大小、神经肽、营养因子依赖性和感觉方式。感觉神经元的发育分为胚胎期和出生后两个阶段，受外在和内在因素的共同控制。我们以前的研究表明，在出生时，50%的DRG神经元在p75无效突变体中丢失。由于p75在神经元、雪旺氏细胞和参与DRG感觉系统发育的靶细胞中表达，我们通过Cre-LoxP系统产生p75条件突变小鼠（p75 floxed小鼠）以了解p75在这些单个细胞类型中的作用。为了删除神经元中的p75基因，我们将p75 floxed小鼠与在Islet 1启动子控制下表达Cre的小鼠杂交。与p75无效突变体相反，这些条件突变体在出生时没有DRG神经元损失。然而，20%的总DRG神经元在成年突变体中丢失，包括大量的胶质细胞源性神经营养因子（GDNF）依赖性c-Ret+ IB 4+伤害感受神经元。出生后p75缺陷的DRG神经元的GDNF依赖性存活显著降低，表明p75是GDNF信号传导所必需的。初步结果显示，p75和GPI连接的GDNF受体11/12（GFR 11）和c-Ret共定位于DRG神经元上，并形成GDNF依赖性复合物。此外，在转染的HEK 293细胞中，p75增加GDNF诱导的MAPK Erk 1/2活化的敏感性。为了进一步了解p75依赖的信号通路在神经发育中的细胞和分子机制，提出了三个具体的目标。目的1：探讨p75在胚胎脊髓感觉神经元发育过程中神经元、上皮细胞和雪旺细胞中的作用。目的2：研究p75在非肽能神经元发育中的作用。目的3：研究p75在GDNF信号转导中的作用。 公共卫生相关性：P75可能作为一个辅助受体整合多种信号通路来调节不同的细胞活动，并在外周和中枢神经系统的多种人类疾病中有牵连。本研究的结果将为设计治疗神经退行性疾病和周围神经病变（包括衰弱性阿尔茨海默病和慢性疼痛）的治疗策略提供见解。

DESCRIPTION (provided by applicant): The long-term goal of this project is to understand the role of the neurotrophin receptor p75 in neural development and regeneration. Although initially identified for its ability to bind neurotrophins, p75 serves as a critical co-receptor to transduce multiple signaling pathways in neural development and function. For example, it is a co-receptor for glycosyl-phosphophatidyl inositol (GPI)-linked NgR and ephrinA5. We have been using the dorsal root ganglion (DRG) sensory neuron system to understand the role of p75 in neural development. DRG neurons are classified by multiple criteria including sizes, neuropeptides, trophic factor-dependence and sensory modalities. Sensory neuron development has embryonic and postnatal phases and is controlled by both extrinsic and intrinsic factors. We previously showed that 50% of DRG neurons are lost in p75 null mutants at birth. Because p75 is expressed in neurons, Schwann and target cells involved in the development of DRG sensory system, we generated p75 conditional mutant mice via the Cre-LoxP system (p75 floxed mice) to understand the role of p75 in these individual cell types. To delete the p75 gene in neurons, we crossed p75 floxed mice with mice expressing Cre under the control of the Islet1 promoter. In contrast to p75 null mutants, there is no DRG neuronal loss in these conditional mutants at birth. However, 20% of total DRG neurons are lost in adult mutants, including a significant number of glial cell-derived neurotrophic factor (GDNF)-dependent c-Ret+IB4+ nociceptive neurons. GDNF-dependent survival of postnatal p75-deficient DRG neurons is markedly decreased, suggesting that p75 is required for GDNF signaling. Preliminary results showed that p75 and GPI-linked GDNF receptor 11/12 (GFR11) and c-Ret are co-localized on DRG neurons and form a GDNF- dependent complex. Furthermore, p75 increases sensitivity of GDNF-induced MAPK Erk1/2 activation in transfected HEK 293 cells. To further understand the cellular and molecular mechanisms of p75-dependent signaling pathways in neural development, three specific aims are proposed. Aim 1 is to determine the role of p75 in neurons, epithelial and Schwann cells during embryonic spinal sensory neuron development. Aim 2 is to determine the role of p75 in nonpeptidergic neuron development. Aim 3 is to determine the role of p75 in GDNF signaling. PUBLIC HEALTH RELEVANCE: P75 may serve as a co-receptor to integrate multiple signaling pathways to regulate diverse cellular activities and is implicated in multiple human diseases in both peripheral and central nervous systems. The results from the present study will provide insights into designing therapeutic strategies to treat neurodegenerative diseases and peripheral neuropathy, including debilitating Alzheimer's Disease and chronic pain.