BDNF AND MeCP2 in Autonomic Dysfunction

描述（由申请人提供）：拟议研究的目的是确定MeCP2 （Rett综合征（Rett）的基因）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。nTS是内脏感觉输入在脑干中整合的主要部位，nTS功能缺陷被认为是Rett自主神经功能障碍的基础。正常情况下，位于结节-岩侧颅感觉神经节（NPG）的内脏感觉神经元合成并释放高水平的BDNF，这是MeCP2的一个假定的转录靶点。然而，我们最近发现MeCP2缺失小鼠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神经元中的BDNF蛋白水平明显下降，尽管BDNF mRNA水平正常。此外，突变细胞表现出异常高水平的组成性BDNF释放。因此，我们假设nTS中内脏感觉神经元的跨突触BDNF信号传导因MeCP2的遗传缺失而中断。此外，我们实验室最近的研究表明，BDNF可以有效地调节nTS中二级中继神经元的兴奋性，并且这种调节在MeCP2缺失的小鼠中受损。基于这些发现，我们假设NPG神经元BDNF信号的失调导致了Rett相关的危及生命的自主神经功能障碍。然而，关于BDNF信号在nTS中的一般机制，特别是MeCP2的作用，几乎一无所知。因此，本研究旨在阐明1)利用脑干切片制备BDNF在nTS中突触调节的基本机制；2)MeCP2功能的缺失如何改变内脏感觉神经元依赖BDNF的信号传导和nTS中的突触传递；3)BDNF在nTS介导的体内自主神经反射中的作用。此外，我们最近发现MeCP2缺失的NPG神经元的BDNF缺陷在体外是可逆的。因此，拟议的研究也旨在制定潜在的策略，以增加或恢复体内MeCP2零突变体中BDNF的正常表达水平。通过阐明BDNF和MeCP2在自主神经反射通路中的作用，本研究旨在阐明与理解和改善Rett综合征及其他自主神经稳态紊乱相关的细胞和分子机制。特别是，希望通过定义MeCP2如何破坏内脏感觉神经元依赖BDNF的信号传导，从而鉴定出旨在改善Rett患者自主神经功能的药物开发的新分子靶点。

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..