BDNF AND MeCP2 in Autonomic Dysfunction

描述（由申请人提供）：拟议研究的目的是确定导致 Rett 综合征 (Rett) 的基因 MeCP2 的遗传缺失如何破坏脑干孤束核 (nTS) 自主反射通路中的脑源性神经营养因子 (BDNF) 信号传导。 nTS 是内脏感觉输入在脑干中整合的主要部位，nTS 功能缺陷已被认为是 Rett 自主神经功能障碍的基础。正常情况下，位于结状-岩骨颅感觉神经节 (NPG) 的内脏感觉神经元合成并释放高水平的 BDNF，这是 MeCP2 的假定转录靶标。然而，我们最近发现 MeCP2 缺失小鼠的 NPG 神经元中 BDNF 的表达和分泌严重受损。特别是，与野生型细胞相比，突变型 NPG 神经元中 BDNF 蛋白的水平显着降低，尽管 BDNF mRNA 的水平正常。此外，突变细胞表现出异常高水平的组成型 BDNF 释放。因此，我们假设 nTS 中内脏感觉神经元的突触 BDNF 信号传导因 MeCP2 的遗传缺失而受到破坏。此外，我们实验室最近的研究表明，BDNF 可以有效调节 nTS 中二级中继神经元的兴奋性，并且这种调节在 MeCP2 null 小鼠中受到损害。基于这些发现，我们假设 NPG 神经元对 BDNF 信号传导的失调导致与 Rett 相关的危及生命的自主神经功能障碍。然而，对于 nTS 中 BDNF 信号转导的一般机制，特别是 MeCP2 的作用，我们几乎一无所知。因此，拟议的研究旨在阐明1）使用脑干切片制剂在nTS中BDNF调节突触的基本机制，2）MeCP2功能的丧失如何改变内脏感觉神经元的BDNF依赖性信号传导和nTS中的突触传递，3）BDNF在nTS介导的体内自主反射中的作用。此外，我们最近发现 MeCP2 null NPG 神经元中的 BDNF 缺陷在体外是可逆的。因此，拟议的研究还旨在开发潜在的策略，以增加或恢复体内 MeCP2 无效突变体中 BDNF 表达的正常水平。通过阐明 BDNF 和 MeCP2 在自主反射通路中的作用，拟议的研究旨在阐明与理解和改善雷特综合征和其他自主神经稳态疾病的治疗相关的细胞和分子机制。特别是，希望确定 MeCP2 如何通过内脏感觉神经元破坏 BDNF 依赖性信号传导，从而确定药物开发的新分子靶标，旨在改善 Rett 患者的自主神经功能。

DESCRIPTION (provided by applicant): The aim of the proposed research is to define how genetic loss of MeCP2, the gene responsible for Rett Syndrome (Rett), disrupts Brain Derived Neurotrophic Factor (BDNF) signaling in autonomic reflex pathways in the brainstem nucleus tractus solitarius (nTS). nTS is the principal site at which visceral sensory input is integrated in the brainstem and defects in nTS function have been proposed to underlie autonomic dysfunctions in Rett. Normally, visceral sensory neurons, located in the nodose-petrosal cranial sensory ganglia (NPG), synthesize and release high levels of BDNF, a putative transcriptional target of MeCP2. However, we recently found that expression and secretion of BDNF are severely impaired in NPG neurons of MeCP2 null mice. In particular, levels of BDNF protein are markedly depressed in mutant NPG neurons compared to wildtype cells, although levels of BDNF mRNA are normal. In addition, mutant cells exhibit abnormally high levels of constitutive BDNF release. As a result, we hypothesize that transynaptic BDNF signaling by visceral sensory neurons in nTS is disrupted by genetic loss of MeCP2. Moreover, recent studies in our laboratory indicate that BDNF can potently modulate the excitability of second order relay neurons in nTS and that this modulation is impaired in MeCP2 null mice. On the basis of these findings we hypothesize that dysregulation of BDNF signaling by NPG neurons contributes to the life-threatening autonomic dysfunctions associated with Rett. However, almost nothing is known about mechanisms of BDNF signaling in nTS in general and the role of MeCP2 in particular. The proposed studies are designed, therefore, to elucidate 1) basic mechanisms of synaptic modulation by BDNF in nTS, using brainstem slice preparations, 2) how loss of MeCP2 function alters BDNF dependent signaling by visceral sensory neurons and synaptic transmission in nTS and 3) the role of BDNF in nTS mediated autonomic reflexes in vivo. In addition, we have recently found that the BDNF deficit in MeCP2 null NPG neurons is reversible in vitro. Therefore, the proposed studies are also designed to develop potential strategies for increasing or restoring normal levels of BDNF expression in MeCP2 null mutants in vivo. By elucidating the roles of BDNF and MeCP2 in autonomic reflex pathways, the proposed research aims to shed light on cellular and molecular mechanisms relevant to understanding and improved management of Rett Syndrome and other disorders of autonomic homeostasis. In particular, it is hoped that defining how MeCP2 disrupts BDNF dependent signaling by visceral sensory neurons will lead to identification of new molecular targets for drug development aimed at improving autonomic function in Rett patients..