Pim-1对骨骼肌肌间脂肪生成的调控及其在肌少症发生中的作用机制研究

Frailty, as the intermediate stage between health ageing and disability, is manifested as sarcopenia in the early period. And the essential pathologic change of sarcopenia lies in the increased intermuscular fat (IMF) in ageing which also exists in non-obese subjects. However, the mechanism underlying the increased IMF remains incompletely understood, as well as the role of the increased IMF in sarcopenia. In this study, we will establish the aged PDGFRα+ mesenchymal progenitor cells model in vitro and explore the effects of Pim-1 gene overexpression and silencing on adipocyte differentiation in PDGFRα+ mesenchymal progenitor cells. Then, a co-culture system composed of PDGFRα+ mesenchymal progenitor cells and skeletal muscle satellite cells (C2C12 skeletal muscle cells) was used to examine whether the adipocyte differentiation in PDGFRα+ mesenchymal progenitor cells contributes to muscle regeneration and alters muscle fiber orientation. Finally, aged Pim-1-/- mouse model will be established to investigate the effects of Pim-1 gene knockout on the increased IMF and sarcopenia. We hypothesize that Pim-1/PPARgamma signaling pathway might contribute to the increased IMF and sarcopenia via the regulation of adipocyte differentiation in PDGFRα+ mesenchymal progenitor cells. Our findings will offer new ideas and therapeutic targets for comprehensive control of frailty and the alleviation of disability in ageing.

衰弱是正常老龄化和失能之间的过度阶段，肌少症是衰弱的早期表现，老年人肌间脂肪显著增加是肌少症的主要病理改变，即使非肥胖患者肌间脂肪仍显著增加。然而，肌间脂肪增加的具体机制以及如何诱导肌少症的发生尚不清楚。本课题以PDGFRα+间叶祖细胞为研究对象，探讨Pim-1基因干预对衰老PDGFRα+间叶祖细胞向脂肪细胞分化能力的影响，并与原代肌卫星细胞或成肌细胞株C2C12共培养，观察肌细胞分化、肌纤维表型的改变；体内建立衰老Pim-1-/-小鼠动物模型，进一步揭示Pim-1在衰老骨骼肌肌间脂肪增加、肌少症发生中的关键地位；提出了Pim-1/PPARgamma信号传导途径通过调控骨骼肌PDGFRα+间叶祖细胞向脂肪细胞分化，是导致衰老机体肌间脂肪增加、肌少症发生发展关键环节的假说，为老年衰弱的综合防治及减缓失能和部分失能的发生提供理论依据。

世界人口老龄化进展迅速，带来肌少症的大流行。肌间脂肪浸润增加是肌少症的重要病理改变，是导致肌细胞萎缩和肌肉功能减退的重要因素。但是，肌间脂肪增加的具体机制及其如何诱导肌少症的发生有待进一步研究。本项目应用分子生物学、细胞生物学、组织病理学等技术，以年轻和衰老的野生型和Pim-1-/-小鼠为研究对象，以PDGFRα+间叶祖细胞为切入点，对Pim-1介导的衰老PDGFRα+间叶祖细胞成脂分化能力改变在老年肌少症的发生发展中的作用进行了研究。结果显示：⑴衰老PDGFRα+间叶祖细胞高表达Pim-1；⑵衰老PDGFRα+间叶祖细胞成脂分化能力增强，且成脂过程中Pim-1表达上调；⑶Pim1抑制剂SGI-1776能够显著抑制衰老PDGFRα+间叶祖细胞的成脂分化能力；⑷Pim1抑制剂SGI1776能够显著降低衰老PDGFRα+间叶祖细胞衰老标志物表达，并显著抑制年轻细胞的增殖能力；⑸Pim1抑制通过抑制C/EBPδ通路进而减少衰老间叶祖细胞成脂分化；⑹Pim-1基因敲除通过下调C/EBPβ通路进而减轻衰老小鼠肌间脂肪沉积；⑺Pim-1基因敲除能够抑制肌萎缩通路；⑻Pim-1基因敲除降低衰老后基础状态下卫星细胞激活；⑼Pim-1基因敲除减轻衰老小鼠肌萎缩；⑽Pim-1基因敲除改善衰老小鼠运动能力和肌肉力量。结论：Pim1基因敲除能够通过抑制C/EBPδ通路而抑制衰老PDGFRα+间叶祖细胞成脂分化，降低肌间脂肪生成，进而抑制肌萎缩通路和基础状态下卫星细胞的持续激活，减轻肌细胞萎缩，从而延缓衰老相关运动能力的减退，在衰老相关肌少症中发挥保护作用。

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