核受体/miRNA通路在肌肉线粒体能量代谢中的功能和分子机制研究

This proposal focuses on unraveling the nuclear receptor/miRNA axis in the control of muscle mitochondria fuel metabolism. Muscle mitochondria malfunction is a critical component underlying the pathogenesis of many metabolic diseases such as obesity and type 2 diabetes. Nuclear receptors have been identified as key regulators of skeletal muscle fuel metabolism, and have been implicated in metabolic diseases.However,the mechanisms have not been yet fully understood. We have previously found that PPARb and ERRg function to activate transcription of miR-208b and miR-499, triggering a cascade of muscle slow-twitch contractile protein gene expression. Our preliminary data indicated that many energy metabolic genes could be regulated by miR-499. These results have led to the hypothesis of this proposal that, miR-499/208b are important downstream targets of PPARb/ERRg, miR-499/208b could mediate the broad control of muscle mitochondria fuel metabolism by PPARb/ERRg. We will delineate the nuclear receptor/miRNA axis and downstream targets involved in the control of mitochondria fuel metabolism in vivo, using muscle-specific transgenes or knockout mice, and in vitro, in primary muscle cell culture. The nuclear receptor/miRNA regulatory pathways unveiled in these studies will greatly enhance our understanding of the mechanisms that control muscle energy metabolism. A longterm goal is to identify novel targets for metabolic modulator therapies aimed at enhancing muscle fitness in a variety of disease states such as obesity and diabetes.

肌肉线粒体能量代谢的功能异常在肥胖症和II型糖尿病的发生发展中起着至关重要的作用。肌肉线粒体能量代谢基因主要由核受体调控，但其下游的效应分子及分子机制还不清楚。我们曾发现核受体PPARb/ERRg可调控肌肉特异性的miR-499/208b的表达，并对肌纤维的结构转变有影响。本课题的前期研究表明miR-499/208b可以调节肌肉线粒体能量代谢基因的表达。因此，我们提出：miR-499/208b可能是PPARb/ERRg调节肌肉线粒体能量代谢的关键通路。为证实这一假设，本课题将分别从整体水平、细胞水平和线粒体亚细胞水平阐明miRNA在线粒体能量代谢中的作用过程及其功能贡献，提出一个较系统的核受体/miRNA通路对线粒体能量代谢的调节模式。本课题的完成，将为探讨代谢性疾病的防治新途径提供实验依据。

骨骼肌线粒体能量代谢的功能异常在肥胖症和2型糖尿病的发生发展中起着至关重要的作用。核受体是调节肌肉线粒体能量代谢的关键因子，与代谢性疾病密切相关，但其下游的效应分子及分子机制还不清楚。本课题我们提出：miR-499/208b可能是核受体调节肌肉线粒体能量代谢的关键通路。为证实这一假设，本课题利用系列小鼠模型，分别从整体水平、细胞水平和线粒体亚细胞水平阐明核受体/miRNA通路在线粒体能量代谢中的作用过程及其功能贡献。我们发现，核受体靶基因miR-499可显著增强肌肉线粒体功能，从而提高小鼠的运动耐力，降低小鼠运动后的血乳酸水平；这些作用依赖于miR-499激活其下游的线粒体功能主调控因子PGC-1ɑ；进一步的分子细胞研究结果显示miR-499通过直接抑制FNIP1靶基因，从而激活AMPK/PGC-1ɑ信号通路以及线粒体功能；研究还发现，miR-499通路在Duchenne肌肉萎缩症（DMD）疾病模型mdx小鼠中显著下调；在mdx小鼠肌肉中重新激活miR-499不仅可以显著改善mdx小鼠的线粒体功能，而且还可以改善mdx小鼠的肌肉损伤症状，并且完全恢复mdx小鼠的运动耐力。此外，我们还发现了一个运动锻炼通过核受体ERR/Ldhb通路改善骨骼肌线粒体功能的新分子机制。这些研究不仅阐明了骨骼肌线粒体功能与肌纤维结构精准偶联的分子基础，还为防治肌肉线粒体代谢相关疾病提供了新的线索。

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