Function of Ret-GFL signaling in sensory neurons

描述(申请人提供)：感觉疼痛的小直径感觉神经元被归类为伤害性感受器。在胚胎发育期间，几乎所有的伤害性感受器都表达神经营养因子NGF的受体TrkA，并依赖NGF生存。在胚胎晚期和出生后早期，小直径无髓伤害性感受器(C纤维伤害性感受器)分化成数量大致相等的两个不同的亚群。有一个种群继续表达TrkA。另一个群体下调TrkA的表达，并表达属于GDNF家族的神经营养因子的受体Ret。除了营养因子受体的表达外，这两种C纤维伤害性感受器亚群还可以根据肽的表达、它们与植物凝集素、异凝素B4(IB4)的结合能力以及它们的中枢和外周投射的模式来区分。表达TrkA的伤害性感受器也表达CGRP和P物质，不与IB4结合，投射到背角的I、IIO层。表达Ret的伤害性感受器通常不表达这些神经肽，确实与凝集素IB4结合，并投射到背角的LIII。有证据表明，神经营养因子信号在出生后和成熟期调节感觉神经元的结构和功能特性。肾发育不全导致Ret缺失小鼠的围产期死亡限制了对Ret在出生后和成熟感觉神经元中功能的研究。为了克服这一局限性，我们创造了一种在IB4阳性伤害性感受器中唯一删除Ret的小鼠，方法是将一只带有Ret等位基因的小鼠(Ret条件鼠)与一只在伤害性感受器特异性启动子(钠通道a亚单位1.8启动子)下表达Cre重组酶的小鼠杂交。我们将使用解剖学和行为学的方法来确定Ret缺失对该小鼠IB4伤害性感受器结构和功能的影响。对这只小鼠的分析将使我们能够确定Ret信号在伤害性感觉神经元存活和维持伤害性感受器结构和功能中的作用。此外，这只小鼠可能提供有关伤害性感受器IB4亚群对疼痛转导的具体贡献的见解。慢性疼痛的治疗是一项尚未得到满足的主要医疗需求。我们创造了一种新型的小鼠，其中GDNF家族神经营养因子配体(GFLS)的受体Ret在伤害性感受器(感受疼痛的神经元)中缺失。这只新的小鼠将使我们能够确定GFLS在伤害性感受器生存和功能中的作用，并研究GFLS在治疗慢性疼痛综合征中的有效机制。

DESCRIPTION (provided by applicant): Small-diameter sensory neurons that sense pain are classified as nociceptors. During embryonic development virtually all nociceptors express TrkA, the receptor for the neurotrophic factor NGF, and depend on NGF for survival. During late embryonic and early postnatal life, small-diameter unmyelinated nociceptors (C-fiber nociceptors) diverge into two distinct subpopulations of roughly equal number. One population continues to express TrkA. The other population down-regulates TrkA expression and expresses Ret, the receptor for the neurotrophic factors belonging to the GDNF family. In addition to trophic factor receptor expression, these two subpopulations of C-fiber nociceptors can be distinguished based on peptide expression, their ability to bind the plant lectin, isolectin B4 (IB4), and the pattern of their central and peripheral projections. Nociceptors that express TrkA also express the peptides CGRP and substance P, do not bind IB4, and project to lamina I and IIo of the dorsal horn. Nociceptors that express Ret do not typically express these neuropeptides, do bind the lectin IB4, and project to LIIi of the dorsal horn. Evidence suggests that neurotrophic factor signaling modulates structural and functional properties of sensory neurons in the postnatal period and in maturity. Perinatal death of Ret-null mice because of kidney agenesis has limited the study of Ret function in postnatal and mature sensory neurons. To overcome this limitation, we have created a mouse in which Ret is deleted exclusively in IB4-positive nociceptors by crossing a mouse with floxed Ret alleles (Ret-conditional mouse) with a mouse expressing Cre recombinase under a nociceptor specific promoter (the sodium channel a subunit 1.8 promoter). We will use anatomical and behavioral methods to determine the effect of Ret deletion on the structure and function of IB4 nociceptors in this mouse. Analysis of this mouse will enable us to determine the role of Ret signaling in nociceptive sensory-neuron survival and in the maintenance of nociceptor structure and function. In addition, this mouse may provide insights into the specific contribution of the IB4 subpopulation of nociceptors to pain transduction. The treatment of chronic pain is a major unmet medical need. We have created a novel mouse in which Ret, the receptor for the GDNF family neurotrophic factor ligands (GFLs) is deleted in nociceptors (neurons that sense pain). This novel mouse will allow us to determine the role of the GFLs in nociceptor survival and function and to study mechanisms by which GFLs are effective in the treatment of chronic pain syndromes.