MicroRNA-27a inhibits porcine type I muscle fibre gene expression by directly targeting peroxisome proliferator-activated receptor-γ coactivator-1α.

MicroRNAs are one of the key determinants of muscle fibre development and phenotype in mammals. The preliminary experiment implied that microRNA-27a (miR-27a) might involve in regulation of muscle fibre type composition of pigs. Thereby, the present study aimed to confirm the regulatory effect of miR-27a on porcine type I muscle fibre-encoding gene (myosin heavy chain gene 7, MYH7) expression and its related mechanism. We firstly observed opposite expression patterns between miR-27a and MYH7 as well as between miR-27a and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) during differentiation of porcine skeletal muscle satellite cells. Through the subsequent transfection analysis in porcine myotubes, we found that miR-27a suppressed the expression of MYH7 and PGC-1α. Besides, miR-27a induced inhibition of PGC-1α downstream targets, namely myocyte enhancer factor-2C (MEF2C) along with mitochondrial biogenesis and oxidative metabolism-related factors such as nuclear respiratory factor 1 (NRF-1), mitochondrial transcription factor A (mtTFA), cytochrome c (Cytc) and cytochrome oxidase IV (COX Ⅳ) and succinodehydrogenase (SDH). Dual-luciferase reporter analysis revealed that miR-27a could bind to the predicted target site in the 3'-untranslated regions of PGC-1α mRNA, confirming a direct targeting of PGC-1α by miR-27a. Moreover, PGC-1α silencing abolished the promotive effects of miR-27a inhibitor on MYH7, PGC-1α and its downstream targets (MEF2C, NRF-1, mtTFA, COX Ⅳ, Cytc and SDH) in porcine myotubes. Collectively, miR-27a inhibits porcine MYH7 expression by negatively regulating PGC-1α and PGC-1α-controlled MEF2C expression as well as mitochondrial biogenesis and oxidative metabolism. Our findings may provide a molecular target for genetic or nutritional control of muscle fibre phenotype of pigs, probably having an important implication for regulating pork quality.