expression closely correlates with muscle fiber types in porcine muscle and regulates myosin heavy chains mRNA expression in C2C12 cells.

Background: Irisin (a glycosylated protein) is cleaved from fibronectin type III domain-containing protein 5 (FNDC5), which is expressed mainly in animal muscle tissues and has multiple metabolic regulatory activities. However, their roles in controlling myofiber types in skeletal muscle remain unclear.

Methodology: Two different commercial hybridized pigs, LJH (a crossed pig containing Chinese native pig genotypes) and DLY (Duroc × Landrace × Yorkshire) were selected to analyze mRNA expression and the mRNA composition of four adult myosin heavy chain () isoforms (IIIaIIxIIb) in the (LD) muscle. C2C12 myoblasts were cultured to investigate the effects of on the four MyHCs mRNA expressive levels, using small interfering RNA for depletion and a eukaryotic expression vector carrying for overexpression. ZLN005 (a small molecule activator of FNDC5's upstream control gene ) or recombinant human irisin protein were also used.

Results: In LD muscle, LJH pigs had the higher mRNA level, and proportion than DLY pigs (). For C2C12 cells in vitro, small interfering RNA (si-592) silencing of expression markedly reduced mRNA levels (), while overexpression significantly increased mRNA levels (). Exogenous irisin increased the mRNA levels of (peroxisome proliferator-activated receptor gamma coactivator 1-alpha), , , , (nuclear respiratory factor 1), (vascular endothelial growth factor), and (mitochondrial transcription factor A,) (), and the enzyme activities of SDH (succinate dehydrogenase), CK (creatine kinase), and MDH (malate dehydrogenase) in C2C12 myotubes (). These results showed that mRNA expression had a significant association with the characteristics of myofiber types in porcine muscle, and participated in regulating mRNA expression of C2C12 myogenic differentiation cells in vitro. could be an important factor to control muscle fiber types, which provides a new direction to investigate pork quality via muscle fiber characteristics.