Effects of arachidonic acid and its major prostaglandin derivatives on bovine myoblast proliferation, differentiation, and fusion.

Many studies have shown positive effects of prostaglandins (PGs) on various steps of skeletal muscle formation such as myoblast proliferation and myotube hypertrophy. In animals, PGs are synthesized through the action of the rate-limiting enzymes cyclooxygenase (COX) -1 and COX-2 from arachidonic acid (AA), a conditionally essential fatty acid. As a step toward exploring the possibility of using dietary supplementation of AA to improve skeletal muscle growth in cattle, which are major meat-producing animals, we determined the effects of AA and its major PG derivatives PGE2, PGF2α, and PGI2 on proliferation, differentiation, and fusion of primary bovine myoblasts in vitro. In the proliferation experiment, myoblasts were cultured in a growth medium to which was added 10 µM AA, 1 µM PGE2, 1 µM PGF2α, 1 µM PGI2, or vehicle control for 24 h, and the proliferating cells were identified by 5-ethynyl-2'-deoxyuridine (EdU) labeling. This experiment revealed that AA, PGE2, PGF2α, and PGI2 each increased the number of proliferating cells by 13%, 24%, 16%, and 16%, respectively, compared to the control (n = 7, P < 0.05). In the differentiation and fusion test, myoblasts were induced to differentiate and fuse into myotubes in the presence of the aforementioned treatments for 0, 24, 48, and 72 h. Based on quantitative reverse transcription PCR analyses of mRNAs of myoblast differentiation and fusion markers (myogenin; myosin heavy chain 3; creatine kinase, muscle; myomaker) at 0, 24, and 48 h of differentiation, AA, PGE2, and PGF2α promoted myoblast differentiation (n = 6, P < 0.05). Based on Giemsa staining and counting the number of myotubes at 72 h of differentiation, PGE2 enhanced the number of formed myotubes by 14% (P < 0.05) compared to the control. Treating the myoblasts with AA and either the COX-1 and COX-2 common inhibitor indomethacin or the COX-2-specific inhibitor NS-398 reversed the stimulatory effect of AA on myoblast proliferation (n = 4, P < 0.05). Overall, this study demonstrates that exogenous AA stimulates bovine myoblast proliferation and differentiation in culture. The results of this study suggest that AA stimulates myoblast proliferation through its metabolites PGE2, PGF2α, or PGI2, and that AA stimulates myoblast differentiation through PGE2.