Loss of MuRF1 in Duroc pigs promotes skeletal muscle hypertrophy

Muscle mass development depends on increased protein synthesis and reduced muscle protein degradation. Muscle ring-finger protein-1 (MuRF1) plays a key role in controlling muscle atrophy. Its E3 ubiquitin ligase activity recognizes and degrades skeletal muscle proteins through the ubiquitin-proteasome system. The loss of Murf1, which encodes MuRF1, in mice leads to the accumulation of skeletal muscle proteins and alleviation of muscle atrophy. However, the function of Murf1 in agricultural animals remains unclear. Herein, we bred F1 generation Murf1(+/-) and F2 generation Murf1(-/-) Duroc pigs from F0 Murf1(-/-) pigs to investigate the effect of Murf1 knockout on skeletal muscle development. We found that the Murf1(+/-) pigs retained normal levels of muscle growth and reproduction, and their percentage of lean meat increased by 6% compared to that of the wild type (WT) pigs. Furthermore, the meat color, pH, water-holding capacity, and tenderness of the Murf1(+/-) pigs were similar to those of the WT pigs. The drip loss rate and intramuscular fat decreased slightly in the Murf1(+/-) pigs. However, the cross-sectional area of the myofibers in the longissimus dorsi increased in the adult Murf1(+/-) pigs. The skeletal muscle proteins MYBPC3 and actin, which are targeted by MuRF1, accumulated in the Murf1(+/-) and Murf1(-/-) pigs. Our findings show that inhibiting muscle protein degradation in MuRF1-deficient Duroc pigs increases the size of their myofibers and their percentage of lean meat without influencing their growth or pork quality. Our study demonstrates that Murf1 is a target gene for promoting skeletal muscle hypertrophy in pig breeding.