脑源性神经营养因子（BDNF）调控能量代谢的分子和环路研究

Brain-derived neurotrophic factor (BDNF) is a master gene controlling many different brain functions, possibly through its unique genomic structure: BDNF gene has 9 upstream promoters; each drives a small exon that is alternatively spliced onto a common exon 10 coding for BDNF protein. Thus, there are 9 BDNF mRNAs in the brain, all encode for the same BDNF protein! To investigate the role and regulation of individual promoters, we have generated four knock-in mouse lines in which four of the most commonly studied promoters, promoter I, II, IV, or VI, were individually mutated. ..The goal of this application is to investigate how different BDNF promoters differentially regulate the development and function of neuronal circuits that control energy metabolism. Our preliminary experiments show that the BDNF promoter I mutant mice were significantly overweight. Interestingly, the promoter I mutant mice exhibit a marked reduction in energy expenditure without affecting food intake. Thus, we hypothesize that BDNF promoter I can regulate the development and function of thermogenesis neural circuit through driving BDNF expression in specific brain regions and/or neuronal populations. In this project, we propose to systematically examine promoter mutant(s) that exhibit obesity, and identify their specific deficits in energy metabolism; to determine whether their obesity was due to an increase in food intake or a decrease in energy expenditure; to delineate the development and function of neural circuits for energy metabolism specifically controlled by BDNF promoter I; and to explore the molecular mechanisms underlying thermogenesis controlled by BDNF promoter I. These studies will not only answer the long-term puzzle – how BDNF could regulate some many brain functions, but also reveal new neural circuits and new mechanisms for energy expenditure control. Our study may also provide an animal model for obesity study and drug development.

神经营养因子（BDNF）具有种类繁多的调控功能，原因之一可能是其特有“多个启动子对应同一蛋白”的基因结构：9个启动子驱动9个BDNF mRNAs在不同脑区或细胞表达,但它们都编码同样的BDNF蛋白。本项目研究BDNF不同启动子调控代谢神经环路的形成和功能。我们建立了4个主要启动子I、II、IV和VI小鼠突变品系，初步研究发现启动子I突变小鼠呈明显肥胖，但进食正常，却显能量消耗下降。据此我们假说，启动子I驱动在特定脑区、特定神经元中表达BDNF，以调节控制热耗散的神经环路。我们将系统鉴定导致肥胖的启动子突变；确定其原因是能量摄入增加还是能量消耗减少；描绘启动子I调控代谢神经环路的形成和功能；探索其下游的分子机制和特异性修复的可能。本研究不仅将解答BDNF为何能调控如此众多的神经功能这一学术难题，也将揭示调控能量消耗的新的神经环路机制，还能为代谢研究提供新的动物模型和药物研发思路。

本项目主要研究了神经营养因子（Brain-derived neurotrophic factor, 简称 BDNF）在转录水平上对能量代谢中的神经环路的调控，建立 BDNF 在代谢调节过程中的“启动子——神经环路——代谢表型”的因果关系。Bdnf 基因有9个非编码性外显子, 它们由其各自特定的启动子来启动表达同一种BDNF蛋白。虽然表达同一种蛋白，但不同的启动子却可以在不同生理条件下启动转录，使得同一种BDNF蛋白可以在不同的生物学功能中发挥作用。.在这几年中，我们较为深入地探究了BDNF的不同启动子在代谢调控各个方面的参与和具体功能，发现了启动子I参与到能量消耗中，棕色脂肪组织（BAT）产热功能和交感神经投射在Bdnf-e1-/-小鼠中的缺损，详细描绘了启动子I调节BAT功能所涉及的核团-侧边下丘脑（lateral hypothalamus，LH），探索了Bdnf-e1/BAT-connected神经元的种类和功能，以及我们利用实验室自己开发的新型BDNF-TrkB信号通路激活工具，即TrkB激活性抗体（TrkB-agomab），挽救了Bdnf-e1-/-小鼠中的BAT产热功能的缺损。之后，我们又重点关注了BDNF在能量摄入中的功能机制，发现启动子II在能量摄入中起重要作用，进而围绕此功能展开一系列实验进行深入探究。通过对以上实验总结，并对结果进行了反复论证，撰写了科研论文，经过了同行评议，最终我们有六篇文章发表在相关领域重要期刊上。