miR-182调控骨骼肌肌纤维分型和能源物质利用的机制研究

Growing evidence indicates that the ability to control the balance between glucose and lipid oxidation is impaired in skeletal muscle from type 2 diabetes (T2D) patients. Understanding the molecular mechanism for the regulation of fuel metabolism in skeletal muscle will help us to identify novel targets that could lead to new treatments for T2D. It has been shown that miR-182 expression was dysregulated in the muscle of diabetic rats, however, the physiological and pathological roles of miR-182 in muscle are largely unknown. Recently, we took advantage of miR-182 knockout mice and found that lacking miR-182 might lead to muscle atrophy and myofiber type switch. Moreover, we also found that FoxO1 expression was upregulated in the muscle of miR-182 knockout mice. FoxO1 is a key regulator of myofiber type determination and fuel usage. Since FoxO1 was reported as a target gene of miR-182, we speculated that miR-182 might control myofiber content and fuel usage in skeletal muscle by targeting FoxO1 and dysregulation of miR-182 might be involved in the pathogenesis of diabetes. However, all these data are preliminary and several key questions require further study and clarification. In this research proposal, we try to clarify the physiological and pathological roles of miR-182 in skeletal muscle. We plan to identify the upstream signaling that regulate miR-182 expression, verify the role of miR-182 in myofiber type determination and fuel usage, and discover the molecular mechanisms by identifying key target genes of miR-182. Lastly, we would like to test whether skeletal miR-182 could serve as a therapeutic target to improve metabolic function in mouse models.

2型糖尿病患者骨骼肌平衡葡萄糖和脂肪酸氧化的能力受损，因此阐明骨骼肌调控能源物质利用的分子机制将有助于发现治疗糖尿病的新靶点。糖尿病大鼠骨骼肌miR-182的表达发生异常，但相关机理不清楚。而我们研究发现，miR-182敲除小鼠出现肌萎缩，肌纤维类型转变，并伴随FoxO1表达水平上升。FoxO1是调控肌纤维分型以及能源物质利用的关键因子，也是miR-182的靶基因。由此，我们推测miR-182可通过调控FoxO1影响肌纤维分型和能源物质的利用，而骨骼肌miR-182表达异常可能参与了糖尿病的发生和发展。为全面解析骨骼肌miR-182的作用，本研究将探索miR-182的表达调控方式，明确其对肌纤维分型和能源物质利用的调控方式，寻找潜在的关键靶基因，阐明miR-182调节能量代谢的分子机制。最后，我们还将在小鼠水平探索miR-182作为干预靶点改善糖脂代谢的可行性，为糖尿病的防治提供实验证据。

骨骼肌是人体重要的能量代谢组织。骨骼肌肌纤维类型及代谢类型的改变对于机体的能量代谢具有重要的影响。miR-182在快肌中具有更高的表达水平，其表达水平与血糖呈现负相关性。MiR-182敲除小鼠的骨骼肌存在I型肌纤维增多、肌肉萎缩和能量代谢紊乱的现象。进一步的研究证实，骨骼肌FoxO1和PDK4是miR-182的靶基因。 miR-182可以通过FoxO1/PDK4调控丙酮酸脱氢酶复合体（PDHC）的活性，进而调控能源物质的选择。此外，研究还发现短时间的高脂饮食就能增加骨骼肌内TNFα的水平，而TNFα可以抑制骨骼肌中miR-182的表达。该发现提示，短时间的高脂饮食就能通过改变骨骼肌miR-182的表达来影响骨骼肌对能源物质的选择，从而导致代谢柔性下降，并最终引起代谢紊乱。通过对在骨骼肌中系统的研究，我们发现miR-182对于骨骼肌能源物质的选择和葡萄糖稳态的维持具有重要的作用，并揭示了调控过程的分子机制。研究还提示，骨骼肌往糖酵解表型及快肌表型转变也有利于糖尿病的血糖控制。