The short isoform of PGC-1alpha in the control of brown adipose tissue thermogenesis

 描述(申请人提供)：肥胖是一种全球性的健康流行病，与代谢紊乱有关，如2型糖尿病。白色脂肪组织蓄积脂肪作为能量储存，而棕色脂肪组织(BAT)通过线粒体解偶联蛋白1(UCP1)将能量以热量的形式散失。对啮齿动物的研究表明，激活蝙蝠的非颤抖产热功能可以增加能量消耗，防止肥胖。成年人也有功能性的蝙蝠，其发热能力随着寒冷的暴露而增加，随着年龄和身体脂肪质量的增加而下降，这表明激活蝙蝠可能有助于治疗人类肥胖。有效的线粒体呼吸通过电子传递链(ETC)是蝙蝠产热所必需的，因为它提供了UCP1介导的热产生所需的能量。ETC由四个大的多亚基复合体(I-IV)组成。大多数ETC复合体亚基由核DNA编码并输入线粒体，而ETC复合体I、III和IV的11个必需亚基由线粒体DNA(MtDNA)编码。因此，协调调控核和线粒体基因组对寒冷的响应对于功能ETC复合体的生物发生至关重要。虽然线粒体的基本转录机制已经被识别和表征，但线粒体基因表达的调控机制仍然是一个悬而未决的问题。我们最近发现了PGC-1a的一个短亚型(命名为NT-PGC-1a)，它是通过PGC-1a基因的选择性剪接而产生的。NT-PGC-1a是一种功能性转录共激活因子，在蝙蝠体内受寒冷诱导高表达。冷诱导的NT-PGC-1a移位到细胞核，并驱动UCP1和一些线粒体基因的表达。令人惊讶的是，虽然PGC-1a位于细胞核，但一小部分NT-PGC-1a定位于线粒体并被招募到mtDNA，这增加了线粒体NT-PGC-1a直接调节mtDNA转录以增加mtDNA编码的ETC基因表达的可能性。在本研究项目中，我们旨在验证我们的假设，即NT-PGC-1a在细胞核和线粒体中的同时定位是协调核和线粒体基因表达的机制，有助于冷诱导的线粒体适应和产热。目的1探讨NT-PGC-1a在线粒体DNA转录调控中的作用。目的2确定冷应激时核内和线粒体中NT-PGC-1a活性升高的机制。目的3评价NT-PGC-1a缺失对线粒体呼吸活性和体内适应性产热的影响。这项研究将揭示以前未被认识的NT-PGC-1a在调节棕色脂肪细胞线粒体转录中的作用，并将强调这一过程对蝙蝠适应性产热和能量消耗的重要性。

 DESCRIPTION (provided by applicant): Obesity is a global health epidemic associated with metabolic disorders such as type 2 diabetes. While white adipose tissue accumulates fat as energy storage, brown adipose tissue (BAT) dissipates energy as heat by mitochondrial uncoupling protein 1 (UCP1). Studies in rodents have shown that activation of non-shivering thermogenesis in BAT increases energy expenditure and protects against obesity. Adult humans also have functional BAT whose thermogenic capacity increases with cold exposure and decreases with age and body fat mass, suggesting that activation of BAT might be useful for treating human obesity. Efficient mitochondrial respiration through the electron transport chain (ETC) is essential for BAT thermogenesis since it provides the energy required for UCP1-mediated heat production. The ETC consists of four large multisubunit complexes (I- IV). The majority of ETC complex subunits are encoded by nuclear DNA and are imported into mitochondria, but 11 essential subunits of ETC complexes I, III, and IV are encoded by mitochondrial DNA (mtDNA). Thus, coordinated regulation of nuclear and mitochondrial genomes in response to cold is critically important for the biogenesis of functional ETC complexes. Although the basal transcription machinery of mitochondria has been identified and characterized, the regulatory mechanisms involved in mitochondrial gene expression remains an open question. We recently discovered a short isoform of PGC-1a (designated NT-PGC-1a) that is produced by alternative splicing of the PGC-1a gene. NT-PGC-1a is a functional transcriptional coactivator and its expression is highly induced by cold in BAT. Cold-induced NT-PGC-1a translocates to the nucleus and drives the expression of UCP1 and a number of mitochondrial genes. Surprisingly, while PGC-1a resides in the nucleus, a small fraction of NT-PGC-1a localizes to mitochondria and is recruited to the mtDNA, raising the possibility that mitochondrial NT-PGC-1a directly regulates mtDNA transcription to increase mtDNA-encoded ETC gene expression in response to cold. In this research project, we aim to test our hypothesis that simultaneous localization of NT-PGC-1a in both nucleus and mitochondria is the mechanism that coordinates nuclear and mitochondrial gene expression, contributing to cold-induced mitochondrial adaptation and thermogenesis. Aim 1 is to evaluate the role of NT-PGC-1a in the regulation of mtDNA transcription. Aim 2 is to determine the mechanism by which NT-PGC-1a activity is increased in the nucleus and mitochondria during cold stress. Aim 3 is to evaluate the effects of NT-PGC-1a deletion on mitochondrial respiratory activity and adaptive thermogenesis in vivo. This research will uncover the previously unappreciated role of NT-PGC-1a in regulating mitochondrial transcription in brown adipocytes and will highlight the importance of this process for adaptive thermogenesis and energy expenditure in BAT.