MiR-34a通过抑制Pgc-1β和线粒体生成促进小鼠骨骼肌脂肪异位沉积

过氧化物酶体增殖物激活受体γ辅激活因子-1β（peroxisome proliferative activated receptor γ coactivator 1 β，Pgc-1β）与线粒体生成相关。已有研究证明，miR-34a在肝组织脂肪异位沉积中发挥重要作用，但是否与骨骼肌的脂肪异位沉积相关尚不清楚。本研究以C57Bl/6J小鼠为研究对象，通过尾静脉注射miR-34a模拟物，探讨miR-34a过表达对小鼠骨骼肌脂肪沉积的影响。组织切片进行油红O染色及甘油三酯含量测定揭示，miR-34a过表达的小鼠骨骼肌组织中脂滴积累及甘油三酯含量显著增加。实时荧光定量PCR（qRT-PCR）显示，与对照鼠比较，miR-34a处理的小鼠骨骼肌组织中的脂肪酸合成酶(Fas）表达显著上调，而脂肪酸氧化分解相关基因产物肉毒碱棕榈酰基转移酶1α（Cpt 1α）表达显著下调，提示miR-34a调控骨骼肌内脂肪的沉积机制可能是通过促进脂肪酸生成和抑制脂肪酸分解实现的。qRT-PCR和Western印迹证明，miR-34a可抑制Pgc-1β蛋白的表达。CoxⅡ/28S比例（线粒体定量指标）测定提示，注射miR-34a模拟物导致小鼠骨骼肌线粒体数目显著下调。生物信息分析显示，Pgc-1β mRNA的3′-UTR存在 miR-34a的潜在识别位点，因此miR-34a可能通过靶向识别Pgc-1β的3′-UTR抑制Pgc-1β表达，从而抑制线粒体生成。上述结果证明，miR-34a能通过靶向抑制PGC-1β表达，抑制线粒体生成，继而减少脂肪酸氧化分解，导致骨骼肌脂肪沉积增加。此外，上调脂肪酸合成酶也可能是miR-34a导致骨骼肌脂肪沉积增加的另一原因，其作用机制需进一步研究。

MiR-34a Promotes Fat Ectopic Deposition in Skeletal Muscle in Mice by Inhibition of Pgc-1β Expression and Mitochondrial Biogenesis

Peroxisome proliferative activated receptor γ coactivator-1β (Pgc-1β) is related to mitochondrial biogenesis. Previous studies have revealed that miR-34a plays an important role in the fat deposition of liver, while it remains unknown whether it is involved in the fat ectopic deposition of skeletal muscle. This study aims at deciphering the effects of miR-34a overexpression on the fat ectopic deposition in skeletal muscle by tail vein injection of miR-34a mimics to C57BL/6J mice. The results of oil red O staining and triglyceride (TG) quantitation showed that the deposition of lipid and TG content were significantly increased in the skeletal muscle in treated groups. Meanwhile, compared with control, the expression of fatty acid synthase (Fas) was up-regulated while the gene related with oxidation-carnitine palmityl transferase-1α (Cpt-1α) was down-regulated, which suggested that miR-34a may regulate the ectopic deposition of skeletal muscle through promoting the synthesis of lipids and inhibiting the oxidation. Further, we found that miR-34a can inhibit the expression of Pgc-1β in protein level. The results of CoxⅡ/28S (mitochondria quantitative indicators) revealed that miR-34a decreased the mitochondrial content significantly in mouse skeletal muscle. The analysis by bioinformatics displayed that a miR-34a potential binding site was exits in the 3′ untranslated region (3′UTR) of Pgc-1β mRNA, which suggested that miR-34a likely inhibits the expression of Pgc-1β through target on the 3′UTR, and further, decreases mitochondrial content in skeletal muscle. In conclusion, this study provided evidence that miR-34a resulted in an increase of deposition of lipids in skeletal muscle probably through inhibition of the expression of Pgc-1β by target its 3′UTR. miR-34a decreased the mitochondria content and further inhibited the oxidation of fatty acid. In addition, miR-34a upregulated Fas expression may be another reason for the increase of lipids deposition in skeletal muscle. The detail mechanism needs further elucidation.