骨骼肌的慢肌纤维比例与机体运动耐力表现及糖脂代谢能力的关系非常密切。已有证据表明核受体PPARβ/δ对骨骼肌慢肌纤维形成及线粒体生物合成起着重要的调控作用；miR-499是骨骼肌纤维类型转换的重要信号通路。我们前期研究发现，杨梅素能增强大鼠的运动耐力，延长力竭跑步时间；同时明显上调骨骼肌中miR-499的表达水平。本项目提出研究假设“杨梅素通过激活PPARβ/δ调控miR-499/Sox6信号通路促进骨骼肌慢肌纤维形成和线粒体生物合成，进而增强骨骼肌氧化代谢能力、提升运动耐力”，拟采用体外细胞实验与体内动物实验相结合的方法深入论证该研究假设。本研究为以骨骼肌PPARβ/δ为靶点调控肌纤维表型和功能转换的策略研究奠定重要理论基础，同时也为应用杨梅素干预提升机体运动耐力和防治肥胖及相关代谢性疾病提供科学证据。

The ratio of slow-twitch muscle fiber has closely correlated with exercise performance and glucose/lipid metabolism. Nuclear receptor PPARβ/δ plays a crucial role in regulating skeletal myofiber-type switch and mitochondrial biogenesis. Meanwhile, research also found that miR-499 is an important signaling molecule to modulate myofiber-type switch. In our previous study, we have found that myricetin significantly improved exercise performance of rats and increased the expression of miR-499 in skeletal muscle. Taken together, in this project, we hypothesize that myricetin could induce skeletal muscle fiber type switching and improve endurance through activating PPARβ/δ to regulate miR-499/Sox6 pathway. We will use in vitro models of gene knockout/ over-expression in mouse skeletal muscle cells and in vivo model of C57BL/6 mice to confirm this hypothesis. This study will further clarify PPARβ/δ induced muscle fiber type transition as a potent target for endurance improvement. In addition, this study will reveal that promoting expression of slow-twitch muscle fibers as a new way for myricetin to improve exercise performance, therefore provide more experimental proofs for application of myricetin in endurance-building and improving metabolism in the future.