Targeted overexpression of PPARγ in skeletal muscle by random insertion and CRISPR/Cas9 transgenic pig cloning enhances oxidative fiber formation and intramuscular fat deposition

Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a master regulator of adipogenesis and lipogenesis. To understand its roles in fiber formation and fat deposition in skeletal muscle, we successfully generated muscle-specific overexpression of PPAR gamma in two pig models by random insertion and CRISPR/Cas9 transgenic cloning procedures. The content of intramuscular fat was significantly increased in PPAR gamma pigs while had no changes on lean meat ratio. PPAR gamma could promote adipocyte differentiation by activating adipocyte differentiating regulators such as FABP4 and CCAAT/enhancer-binding protein (C/EBP), along with enhanced expression of LPL, FABP4, and PLIN1 to proceed fat deposition. Proteomics analyses demonstrated that oxidative metabolism of fatty acids and respiratory chain were activated in PPAR gamma pigs, thus, gathered more Ca2+ in PPAR gamma pigs. Raising of Ca2+ could result in increased phosphorylation of CAMKII and p38 MAPK in PPAR gamma pigs, which can stimulate MEF2 and PGC1 alpha to affect fiber type and oxidative capacity. These results support that skeletal muscle-specific overexpression of PPAR gamma can promote oxidative fiber formation and intramuscular fat deposition in pigs.