Linc-smad7 promotes myoblast differentiation and muscle regeneration via sponging miR-125b

Long noncoding RNAs (lncRNAs) are involved in the regulation of skeletal muscle development. In the present study, differentially expressed lncRNAs were identified from RNA-seq data derived from myoblasts and myotubes. We conducted studies to elucidate the function and molecular mechanism of action of Linc-smad7 during skeletal muscle development. Our findings show that Linc-smad7 is upregulated during the early phase of myoblasts differentiation. In <i>in vitro</i> studies, we showed that overexpression of Linc-smad7 promoted the arrest of myoblasts in G1 phase, inhibited DNA replication, and induced myoblast differentiation. Our <i>in vivo</i> studies suggest that Linc-smad7 stimulates skeletal muscle regeneration in cardiotoxin-induced muscle injury. Mechanistically, Linc-smad7 overexpression increased smad7 and IGF2 protein levels. On the contrary, overexpression of miR-125b reduced smad7 and IGF2 protein levels. Results of RNA immunoprecipitation analysis and biotin-labeled miR-125b capture suggest that Linc-smad7 could act as a competing endogenous RNA (ceRNA) for miRNA-125b. Taken together, our findings suggest that the novel noncoding regulator Linc-smad7 regulates skeletal muscle development.

长链非编码RNA（long noncoding RNAs，lncRNAs）参与骨骼肌发育的调控。本研究从成肌细胞与肌管的RNA测序（RNA-seq）数据中鉴定得到差异表达的lncRNAs，并围绕Linc-smad7在骨骼肌发育中的功能及作用分子机制展开研究。研究结果显示，Linc-smad7在成肌细胞分化早期呈现上调表达。体外（in vitro）实验表明，过表达Linc-smad7可促使成肌细胞发生G1期阻滞、抑制DNA复制，并诱导成肌细胞分化。体内（in vivo）实验则证实，Linc-smad7能够促进心脏毒素诱导的肌肉损伤后的骨骼肌再生。机制层面分析发现，过表达Linc-smad7可提升smad7与IGF2的蛋白水平；与之相反，过表达miR-125b则会降低这两种蛋白的表达量。RNA免疫沉淀分析与生物素标记的miR-125b捕获实验结果显示，Linc-smad7可作为miR-125b的内源竞争RNA（competing endogenous RNA，ceRNA）发挥作用。综上，本研究表明新型非编码调控因子Linc-smad7可调控骨骼肌发育。