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

 描述（由申请人提供）：肥胖是一种与代谢紊乱（如2型糖尿病）相关的全球性健康流行病。当白色脂肪组织积累脂肪作为能量储存时，棕色脂肪组织（BAT）通过线粒体解偶联蛋白1（UCP 1）以热量形式耗散能量。对啮齿动物的研究表明，BAT中非颤抖性产热的激活增加了能量消耗并防止肥胖。成年人也具有功能性BAT，其产热能力随着冷暴露而增加，并随着年龄和体脂量而降低，这表明BAT的激活可能有助于治疗人类肥胖。通过电子传递链（ETC）进行的有效线粒体呼吸对BAT产热至关重要，因为它提供了UCP1介导的产热所需的能量。ETC由四个大亚基复合物（I-IV）组成。大多数ETC复合物亚基由核DNA编码并输入线粒体，但ETC复合物I、III和IV的11个必需亚基由线粒体DNA（mtDNA）编码。因此，协调调节细胞核和线粒体基因组响应冷是至关重要的功能ETC复合物的生物合成。虽然线粒体的基本转录机制已被确定和表征，但涉及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的一种短亚型（命名为NT-PGC-1a），它是由PGC-1a基因的选择性剪接产生的。NT-PGC-1a是一种功能性转录共激活因子，其表达受冷诱导。冷诱导的NT-PGC-1a易位到细胞核并驱动UCP1和许多线粒体基因的表达。令人惊讶的是，虽然PGC-1a存在于细胞核中，但一小部分NT-PGC-1a定位于线粒体并被募集到mtDNA中，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，我们的目标是测试我们的假设，即NT-PGC-1a在细胞核和线粒体中的同时定位是协调细胞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：研究NT-PGC-1a在线粒体DNA转录调控中的作用。目的2是确定冷胁迫期间核和线粒体中NT-PGC-1a活性增加的机制。目的3：研究NT-PGC-1a基因缺失对线粒体呼吸活性和适应性产热的影响。这项研究将揭示NT-PGC-1a在棕色脂肪细胞中调节线粒体转录的先前未被重视的作用，并将突出这一过程对BAT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.