Genetic analysis of the neurotrophin receptor p75 in neural development

描述（由申请人提供）：该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。尽管p75最初被认为是与神经营养因子结合的能力，但它在神经发育和功能中作为一个重要的共受体转导多种信号通路。例如，它是糖基磷脂酰肌醇（GPI）连接的NgR和ephrinA5的共受体。我们一直在使用背根神经节（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模式。感觉神经元的发育分为胚胎和出生后两个阶段，受外在因素和内在因素的双重控制。我们之前的研究表明，p75零突变体在出生时丢失了50%的DRG神经元。由于p75在参与DRG感觉系统发育的神经元、雪旺细胞和靶细胞中表达，我们通过Cre-LoxP系统生成了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捆绑小鼠与在Islet1启动子控制下表达Cre的小鼠杂交。与p75零突变体相比，这些条件突变体在出生时没有DRG神经元丢失。然而，在成年突变体中，总DRG神经元的20%丢失，包括大量胶质细胞源性神经营养因子（GDNF）依赖性c-Ret+IB4+伤害性神经元。出生后缺乏p75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与gpi连接的GDNF受体11/12 （GFR11）和c-Ret在DRG神经元上共定位并形成GDNF依赖性复合物。此外，p75在转染的HEK 293细胞中增加了gdnf诱导的MAPK Erk1/2激活的敏感性。为了进一步了解p75依赖性信号通路在神经发育中的细胞和分子机制，提出了三个具体目标。目的1是确定p75在胚胎脊髓感觉神经元发育过程中在神经元、上皮细胞和雪旺细胞中的作用。目的2是确定p75在非肽能神经元发育中的作用。目的3是确定p75在GDNF信号传导中的作用。

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.