The transgenic expression of human follistatin-344 increases skeletal muscle mass in pigs.

Follistatin (FST), which was first found in the follicles of cattle and pigs, has been shown to be an essential regulator for muscle development. Mice that were genetically engineered to overexpress Fst specifically in muscle had at least twice the amount of skeletal muscle mass as controls; these findings are similar to earlier results obtained in myostatin-knockout mice. However, the role of follistatin in skeletal muscle development has yet to be clarified in livestock. Here, we describe transgenic Duroc pigs that exogenously express Fst specifically in muscle tissue. The transgenic pigs exhibited an increased proportion of skeletal muscle and a reduced proportion of body fat that were similar to those reported in myostatin-null cattle. The lean percentage of lean meat was significantly higher in the F1 generation of TG pigs (72.95 ± 1.0 %) than in WT pigs (69.18 ± 0.97 %) (N = 16, P < 0.05). Myofiber hypertrophy was also observed in the longissimus dorsi of transgenic pigs, possibly contributing to the increased skeletal muscle mass. Western blot analysis showed a significantly reduced level of Smad2 phosphorylation and an increased level of Akt phosphorylation in the skeletal muscle tissue of the transgenic pigs. Moreover, no cardiac muscle hypertrophy or reproductive abnormality was observed. These findings indicate that muscle-specific Fst overexpression in pigs enhances skeletal muscle growth, at least partly due to myofiber hypertrophy and providing a promising approach to increase muscle mass in pigs and other livestock.