The Regulatory Effect Of MyoD And Myogenin On Myosin Heavy Chain Under The Condition Of Hypoxia And Training

The purpose of this study was to explore the mechanism of myogenic regulatory factors on myosin heavy chain isoform. Hypoxia and endurance training, these two different conditions were established to observe the transition of MyoD and myogenin under condition of MHC isoform shifting in different way.Experiment program: 40 male Sprague-Dawley rats were divided into four groups randomly, normoxic control groups (NC), normoxic training groups (NT), hypoxic controls groups (HC) and hypoxic training groups (HT). HC and HT group rats were bred under hypoxic condition (simulated 4000 meters altitude), NC and NT groups rats were bred in normoxic conditions, NT and HT groups rats were performed treadmill running training on a motor-driven treadmill once daily, 1h/day and 6 days a week. The inclination of the treadmill was 10°.The running velocity was 20m/min. After 28 days, VI,sTA muscle in all groups and SOL muscle in NC were extracted. MyoD, myogenin mRNA and MHC mRNA were assayed by RT-PCR; MHC protein were determined by SDS-PAGE; Myosin Ca²⁺- ATPase were assayed by biochemical methods.Results: Normoxic endurance-training didn't influence the composition of all MHC isoform protein; MHC-â…¡x mRNA was decreased significantly, meanwhile MHC-â…¡a mRNA had a increased tendency; MyoD and myogenin mRNA decreased sharply; Myosin Ca²⁺- ATPase activity didn't change. Under the condition of hypoxia, MHC-â…¡a protein was decreased while the MHC-â…¡x and MHC-â…¡b protein improved significantly. MHC-â…¡a mRNA was increased significantly; MyoD and myogenin mRNA had no evident change; The activity of myosin Ca²⁺-ATPase raised; Under the condition of hypoxic endurance-training,the change of the MHC protein was same as the condition of hypoxia, and MHC-â…¡b mRNA was increased significantly. there was significant correlation between Myogenin and MHC-â… (r=0.6874, p=0), in addition, myogenin had significant positive correlation with MHC-â…¡b (r=0.4662, p=0.029).Conclusion:1. Hypoxia and endurance-training were different stimulus for MHC isoform transforming.2. As Myogenin had a positive correlation with MHC-â… ,Myogenin probably regulated MHC-â… in the transcriptional level.3. There was significant correlation between Myogenin and MHC-â…¡b,which had contradiction with the previous results.So, the regulation of MHC maybe more complicated.4. The alteration of myosin Ca2+-ATPase was always in line with the change of MHC, that meant the activity of myosin Ca2+- ATPase was determined by MHC composition .5. The level of Myogenin mRNA was always high in slow muscles,while the fast muscles had a high MyoD level.Innovation:1. This was the first time that by the training models did we observe the change of Myogenin and MyoD.2. This was the first time that we studied the correlation between MHC and Myogenin and MyoD under the condition of the training and hypoxia.3. This was the first time that we changed the composition of MHC in more than one way (normoxicendurance-training, hypoxia and hypoxic endurance-training )4. We distinguished fibre types by MHC composition determined by SDS-PAGE.