Related expression of MyoD and Myf5 with myosin heavy chain isoform types in bovine adult skeletal muscles

Skeletal muscles are characterized as fast and slow muscles, according to the expression pattern of myosin heavy chain (MyHC) isoforms in the muscle fibers. To investigate the relationships between MyHC isoforms and myogenic regulatory factors (MRFs) including MyoD, Myf5, myogenin, and MRF4 in adult skeletal muscles, expressions of these MRFs in the ten muscles of three cows were analyzed by a semi-quantitative RT-PCR. The results showed that MyoD expression was significantly lower in the lingual muscles (TN), masseter (MS) and diaphragm (DP), which lack MyHC-2x (fast glycolytic) expression and abound with MyHC-slow (slow oxidative) and/or MyHC-2a (fast oxidative), than it was in the pectoralis (PP), psoas major (PM), longissimus thoracis (LT), spinnalis (SP), semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF). In contrast, the Myf5 expression in TN, MS, and DP was significantly higher than in PM, LT, ST, SM, and BF. No significant difference was observed in myogenin and MRF4 expression among the muscles tested. The results suggest that MyoD and Myf5 influence the MyHC isoform expression, although the effects are not decisive in specifying the phenotypes of adult muscles.     

Endurance training affects myosin heavy chain phenotype in regenerating fast-twitch muscle

Bigard, Xavier A., Chantal Janmot, Danièle Merino,Françoise Lienhard, Yannick C. Guezennec, and Anne D'Albis.Endurance training affects myosin heavy chain phenotype inregenerating fast-twitch muscle. J. Appl.Physiol. 81(6): 2658-2665, 1996.The aim of thisstudy was to analyze the effects of treadmill training (2 h/day, 5 days/wk, 30 m/min, 7% grade for 5 wk) on the expression of myosinheavy chain (MHC) isoforms during and after regeneration of afast-twitch white muscle [extensor digitorum longus (EDL)]. Male Wistar rats were randomly assigned to a sedentary(n = 10) or an endurance-trained (ET;n = 10) group. EDL muscle degeneration and regeneration were induced by two subcutaneous injections of a snaketoxin. Five days after induction of muscle injury, animals were trainedover a 5-wk period. It was verified that ~40 days after venomtreatment, central nuclei were present in the treated EDL muscles fromsedentary and ET rats. The changes in the expression of MHCs in EDLmuscles were detected by using a combination of biochemical andimmunocytochemical approaches. Compared with contralateral nondegenerated muscles, relative concentrations of types I, IIa, andIIx MHC isoforms in ET rats were greater in regenerated EDL muscles(146%, P < 0.05; 76%,P < 0.01; 87%,P < 0.01, respectively). Their elevation corresponded to a decreasein the relative concentration of type IIb MHC (36%,P < 0.01). Although type I accountedfor only 3.2% of total myosin in regenerated muscles from the ETgroup, the cytochemical analysis showed that the proportion of positive staining with the slow MHC antibody was markedly greater in regenerated muscles than in contralateral ones. Collectively, these results demonstrate that the regenerated EDL muscle is sensitive to endurance training and suggest that the training-induced shift in MHC isoforms observed in these muscles resulted from an additive effect of regeneration and repeated exercise.

     

Training affects myosin heavy chain phenotype in the trapezius muscle of women

The aim of this investigation was to determine whether 10 weeks of three different types of training can alter the myosin heavy chain (MyHC) composition of the trapezius muscle. Twenty-one women were randomly assigned to three training groups that performed strength (n=9), endurance (n=7) or coordination training (n=5). Pre and post biopsies were taken from the upper part of the descending trapezius muscle and were analysed for MyHC isoform content using 5% gel electrophoresis. In addition, we have studied the expression of embryonic and neonatal MyHCs using double-immunofluorescence staining. In the strength-trained group, there was a significant increase in the amount of MyHC IIA and a significant decrease in the amount of MyHC IIB and MyHC I. In the endurance group, there was a significant decrease in the amount of MyHC IIB. MyHC composition in the coordination group was not altered. Following the training period, myotubes and individual small-sized muscle fibres were observed in the strength and endurance trained groups. These structures were stained with the markers for early myogenesis (MyHC embryonic and neonatal). These data suggest that specific shifts in MyHC isoforms occur in the trapezius muscle following strength and endurance training. The presence of small-sized muscle fibres expressing the developmental isoforms of MyHC suggests that strength and endurance training induced the formation of new muscle fibres. Accepted: 31 March 1999     

Myogenic programs of mouse muscle cell lines: expression of myosin heavy chain isoforms, MyoD1, and myogenin

Different mouse muscle cell lines were found to express distinct patterns of myosin heavy chain (MHC) isoforms, MyoD1, and myogenin, but there appeared to be no correlation between the pattern of MHC expression and the patterns of MyoD1 and myogenin expression. Myogenic cell lines were generated from unconverted C3H10T1/2 cells by 5-azacytidine treatment (Aza cell lines) and by stable transfection with MyoD1 (TD cell lines) or myogenin (TG cell lines). Myogenic differentiation of the newly generated cell lines was compared to that of the C2C12 and BC3H-1 cell lines. Immunoblot analysis showed that differentiated cells of each line expressed the embryonic and slow skeletal/beta-cardiac MHC isoforms though slow MHC was expressed at a much lower, barely detectable level in BC3H-1 cells. Differentiated cells of each line except BC3H-1 also expressed an additional MHC(s) that was probably the perinatal MHC isoform. Myogenin mRNA was expressed by every cell line, and, with the exception of BC3H-1 (cf., Davis, R. L., H. Weintraub, and A. B. Lassar. 1987. Cell. 51:987-1000), MyoD1 mRNA was expressed by every cell line. To determine if MyoD1 expression would alter the differentiation of BC3H-1 cells, cell lines (termed BD) were generated by transfecting BC3H-1 cells with MyoD1 under control of the beta-actin promoter. The MyoD1 protein expressed in BD cells was correctly localized in the nucleus, and, unlike the parental BC3H-1 cell line that formed differentiated MHC-expressing cells, which were predominantly mononucleated, BD cell lines formed long, multinucleated myotubes (cf., Brennan, T. J., D. G. Edmondson, and E. N. Olson. 1990. J. Cell. Biol. 110:929-938). Despite the differences in morphology and MyoD1 expression, BD myotubes and the parent BC3H-1 cells expressed the same pattern of sarcomeric MHCs.     

Slow myosin heavy chain expression in the absence of muscle activity

Innervation has been generally accepted to be a major factor involved in both triggering and maintaining the expression of slow myosin heavy chain (MHC-1) in skeletal muscle. However, previous findings from our laboratory have suggested that, in the mouse, this is not always the case (30). Based on these results, we hypothesized that neurotomy would not markedly reduced the expression of MHC-1 protein in the mouse soleus muscles. In addition, other cellular, biochemical, and functional parameters were also studied in these denervated soleus muscles to complete our study. Our results show that denervation reduced neither the relative amount of MHC-1 protein, nor the percentage of muscle fibers expressing MHC-1 protein (P > 0.05). The fact that MHC-1 protein did not respond to muscle inactivity was confirmed in three different mouse strains (129/SV, C57BL/6, and CD1). In contrast, all of the other histological, biochemical, and functional muscle parameters were markedly altered by denervation. Cross-sectional area (CSA) of muscle fibers, maximal tetanic isometric force, maximal velocity of shortening, maximal power, and citrate synthase activity were all reduced in denervated muscles compared with innervated muscles (P < 0.05). Contraction and one-half relaxation times of the twitch were also increased by denervation (P < 0.05). Addition of tenotomy to denervation had no further effect on the relative expression of MHC-1 protein (P > 0.05), despite a greater reduction in CSA and citrate synthase activity (P < 0.05). In conclusion, a deficit in neural input leads to marked atrophy and reduction in performance in mouse soleus muscles. However, the maintenance of the relative expression of slow MHC protein is independent of neuromuscular activity in mice.     

Chronic oral administration of beta-adrenoceptor agonist clenbuterol affects myosin heavy chain (MHC) expression in adult mouse heart

The aim of this study was to analyze the effects of chronic administration of the beta-adrenoceptor agonist clenbuterol (2 mg/kg body weight/day for a period of 30 days) on the major contractile protein (myosin) in the left ventricular muscle of the adult mouse heart. Separation of myosin heavy chain (MHC) isoforms on 7.5 % glycerol SDS-PAGE and subsequent quantification of the gels by laser densitometry showed a 6.5-fold increase in the beta-isoform of MHC in the clenbuterol-treated group. The alpha : beta ratio of these two isoforms in the control group was 98.16+/-0.14 %: 1.83+/-0.14 %, whereas in the treated group it was 88.05+/-1.15 % : 11.95+/-1.15 %. Actomyosin ATPase activity assay demonstrated a significant (20 %) decline in ATPase activity of the tissue in the beta-agonist-treated group. These results suggest that chronic clenbuterol treatment is capable to induced the transformation of MHC isoforms increasing the slow beta-MHC isoform, which may contribute to the altered contractile mechanics of clenbuterol-treated hearts.