BDNF AND MeCP2 in Autonomic Dysfunction

描述(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的遗传缺失如何扰乱脑干孤束核(NTS)自主神经反射通路中的脑源性神经营养因子(BDNF)信号。NTS是内脏感觉输入整合到脑干的主要部位，NTS功能缺陷被认为是RET自主神经功能障碍的基础。正常情况下，位于结状岩颅感觉神经节(NPG)的内脏感觉神经元合成并释放高水平的BDNF，这可能是MeCP2的转录靶点。然而，我们最近发现MeCP2基因缺失小鼠的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蛋白的水平明显降低，尽管BDNF mRNA的水平是正常的。此外，突变细胞表现出异常高水平的结构性BDNF释放。因此，我们假设NTS内脏感觉神经元的跨突触BDNF信号受MeCP2基因缺失的干扰。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基因缺失的小鼠中受到损害。在这些发现的基础上，我们假设NPG神经元对BDNF信号的失调导致了与Rett相关的危及生命的自主神经功能障碍。然而，对于BDNF在NTS中的信号转导机制，尤其是MeCP2的作用，我们几乎一无所知。因此，本研究旨在阐明1)脑干切片上BDNF对NTS突触调节的基本机制，2)MeCP2功能丧失如何改变NTS内脏感觉神经元的BDNF依赖信号和突触传递，以及3)BDNF在NTS介导的自主神经反射中的作用。此外，我们最近发现，在体外，MeCP2缺失的NPG神经元中BDNF的缺失是可逆的。因此，建议的研究还旨在开发潜在的策略，以提高或恢复体内MeCP2缺失突变体中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，这项拟议的研究旨在阐明与理解和改善Rett综合征和其他自主神经稳态紊乱的治疗相关的细胞和分子机制。特别是，人们希望，明确MeCP2如何通过内脏感觉神经元扰乱BDNF依赖的信号将导致识别旨在改善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..