BDNF and TrkB-containing neuronal circuits mediating energy balance

描述（由申请人提供）：美国近三分之一的人口肥胖，超过60%的人超重。这是一个令人担忧的趋势，因为肥胖显著增加了对2型糖尿病、心血管疾病和其他医学疾病的易感性。越来越多的证据表明，脑源性神经营养因子（BDNF）/TrkB通路在能量平衡调节中起着关键作用，是一个有前途的新疗法的目标。因此，在小鼠和人类中减少的BDNF信号传导导致过度吞噬行为和显著的肥胖。目前尚不清楚支持神经元存活、分化和突触可塑性的脑源性神经营养因子是否充当成人大脑中所需的饱腹因子或喂养神经回路的发育促进剂。作为先前资助的项目的一部分，我们表明BDNF在成年动物中起促进饱腹感的作用，并且腹内侧下丘脑（VMH）是这种神经营养因子的重要来源。支持性证据包括能量状态对VMH中BDNF和TrkB表达的强大影响，以及通过选择性删除成年小鼠VMH中的BDNF引起的摄食过多和肥胖。BDNF在VMH中的促凋亡作用的细胞和分子机制仍有待阐明。我们最近的一项大规模人类研究中，对从中枢（BDNF 2L/2LCk-cre）或VMH特异性BDNF缺失小鼠VMH中激光捕获的细胞转录组进行了分析，结果显示a2 d-1和其他两个与肥胖易感性相关的基因的表达降低。我们的初步研究表明，BDNF的促凋亡作用是由a2 d-1介导的，a2 d-1是一种高电压门控钙通道亚单位，可增强钙电流并介导兴奋性突触发生。我们发现：i）通过慢性加巴喷丁输注到野生型VMH中的选择性a2 d-1抑制增加了食物摄入和体重，和ii）病毒介导的a2 d-1递送到BDNF 2L/2LCk-cre突变体的VMH改善了它们的摄食过多和体重增加。这项竞争性更新提案旨在通过确定BDNF和a2 d-1作用的细胞机制来建立这些发现。由于BDNF突变体的VMH细胞中的钙电流是正常的，a2 d-1的饱足效应可能与其以非钙依赖的方式诱导兴奋性突触发生的能力有关。因此，目的1将探讨BDNF和a2 d-1的作用，在动态变化的VMH兴奋性驱动的营养线索诱导的POMC神经元，使用解剖和电生理方法。在目的2中，我们将研究是否BDNF和a2 d-1也调节兴奋性驱动到致凋亡的VMH神经元。在目标3中，我们将测试BDNF突变体VMH中其他两个候选基因的表达减少是否有助于出现贪食行为和肥胖，以及它们是否与VMH中的a2 d-1共同作用于共同途径。这些研究将提供一个机制的理解BDNF的促肥胖作用，并揭示新的途径治疗肥胖。

DESCRIPTION (provided by applicant): Close to a third of the population in the United States is obese and over 60% is overweight. This is an alarming trend as obesity significantly increases susceptibility to type 2 diabetes, cardiovascular disease and other medical disorders. Mounting evidence indicates that the brain-derived neurotrophic factor (BDNF)/TrkB pathway plays a critical part in energy balance regulation and is a promising target for novel therapies. Accordingly, reduced BDNF signaling in mice and humans results in hyperphagic behavior and dramatic obesity. It remained unclear whether BDNF, which supports neuronal survival, differentiation and synaptic plasticity, acted as a required satiety factor in the adult brain or as a developmental facilitator of feeding neural circuits. As part of the previously funded project, we showed that BDNF acts in the adult animal to promote satiety and that the ventromedial hypothalamus (VMH) is a critical source of this neurotrophin. Supportive evidence includes the robust effects of energy status on expression of BDNF and TrkB in the VMH and the hyperphagia and obesity elicited by selectively deleting BDNF in the VMH of adult mice. The cellular and molecular mechanisms underlying the anorexigenic effects of BDNF in the VMH remain to be elucidated. Our recent analysis of the transcriptome of cells laser-captured from the VMH of mice with central (BDNF2L/2LCk-cre) or VMH-specific depletion of BDNF revealed decreased expression of a2d-1 and of two other genes associated with obesity susceptibility in a recent large-scale human study. Our preliminary studies show that BDNF's anorexigenic effects are mediated by a2d-1, a high voltage-gated calcium channel subunit that enhances calcium currents and mediates excitatory synaptogenesis. We found that: i) selective a2d-1 inhibition by chronic gabapentin infusion into wild type VMH increased food intake and body weight and ii) viral-mediated a2d-1 delivery to the VMH of BDNF2L/2LCk-cre mutants ameliorated their hyperphagia and body weight gain. This competitive renewal proposal seeks to build on these findings by ascertaining cellular mechanisms underlying the effects of BDNF and a2d-1. Because calcium currents in VMH cells of BDNF mutants are normal, the satiety effects of a2d-1 might be related to its ability to induce excitatory synaptogenesis in a calcium-independent manner. Thus, Aim 1 will investigate the role of BDNF and a2d-1 in dynamic changes in VMH excitatory drive onto anorexigenic POMC neurons induced by nutritional cues using anatomical and electrophysiological approaches. In Aim 2, we will investigate whether BDNF and a2d-1 also regulate excitatory drive onto anorexigenic VMH neurons. In Aim 3, we will test whether the reduced expression of two other gene candidates in the BDNF mutant VMH contributes to the emergence of hyperphagic behavior and obesity and whether they act in common pathways with a2d-1 in the VMH. These studies will provide a mechanistic understanding of anorexigenic actions of BDNF and reveal novel avenues for the treatment of obesity.