Response of the porcine -promoter and -expressing myotubes to known anabolic and catabolic agents .

Unlabelled: Myosin heavy chain-IIB (MyHC-IIB; encoded by or ) expression is often associated with muscle hypertrophic growth. Unlike other large mammals, domestic pig breeds express MyHC-IIB at both the mRNA and protein level.

Aim: To utilise a fluorescence-based promoter-reporter system to test the influence of anabolic and catabolic agents on increasing porcine -promoter activity and determine whether cell hypertrophy was subsequently induced

Methods: C2C12 myoblasts were co-transfected with porcine promoter-driven ZsGreen and CMV-driven DsRed expression plasmids. At the onset of differentiation, treatments (dibutyryl cyclic-AMP (dbcAMP), Des(1-3) Insulin-Like Growth Factor-1 (IGF-I), triiodo-l-thyronine (T3) and dexamethasone (Dex)) or appropriate vehicle controls were added and cells maintained for up to four days. At day 4 of differentiation, measurements were collected for total fluorescence and average myotube diameter, as indicators of -promoter activity and cell hypertrophy respectively.

Results: Porcine -promoter activity increased during C2C12 myogenic differentiation, with a marked increase between days 3 and 4. -promoter activity was further increased following four days of dbcAMP treatment and average myotube diameter was significantly increased by dbcAMP. Porcine -promoter activity also tended to be increased by T3 treatment, but there were no effects of Des(1-3) IGF-I or Dex treatment, whereas average myotube diameter was increased by Des(1-3) IGF-I, but not T3 or Dex.

Conclusion: Porcine -promoter activity responded to dbcAMP, Des(1-3) IGF-I and T3 treatment as observed previously in reported studies. However, we report that increased -promoter activity was not always associated with muscle cell hypertrophy. The fluorescence-based reporter system offers a useful tool to study muscle cell hypertrophic growth.