Thyroid hormone regulation of myosin heavy chain isoform composition in young and old rats, with special reference to IIX myosin

Abstract

The effects of 4 weeks of thyroid hormone (3,5,3'-triiodothyronine, T3) treatment on the myosin heavy chain (MHC) composition were compared in the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles from young (3-6 months) and old (20-24 months) male albino rats. Four MHC isoforms were separated on silver-stained 6% sodium dodecyl sulphate polyacrylamide gel electrophoresis. According to immunoblotting experiments with specific MHC monoclonal antibodies, the four MHCs corresponded to types I, IIB, IIX and IIA. In the soleus, the type I MHC content was higher in the old than in the young animals, and the type IIA content lower. Type IIX myosin was observed in some young control soleus, but not in old ones. After T3 treatment, the content of type I MHC decreased substantially in both young and old animals and that of type IIA increased. After T3 treatment, type IIX myosin was observed in both young and old animals, with a slightly higher IIX myosin content in old age, but the age-related difference in the contents of types I and IIA was diminished. In EDL, the type IIX MHC content was significantly higher in the old animals, at the expense of a lower content of type IIB MHC. MHC composition was not affected significantly by T3 treatment in EDL, either in young or old animals. In conclusion, an age-related motor unit transformation is observed in both the slow-twitch soleus and the fast-twitch EDL and the capacity for MHC isoform switching in response to T3 treatment is not impaired in old age.

Fiber Types in Mammalian Skeletal Muscles

“…Rat skeletal muscles undergo a type 2B to 2X switching in aging fast muscles and a type 2A to type 1 switching in slow soleus (462)(463)(464). The histochemical fiber type profile does not appear to change with age in human skeletal muscle; however, the relative proportion of fast MyHCs is reduced in elderly subjects (423,733) due to greater atrophy of type 2 fibers (478).…”

Aberrant expression of myosin isoforms in skeletal muscles from mice lacking therev-erbAαorphan receptor gene

“…The total acrylamide and bis concentrations were 4% (wt/vol) in the stacking gel and 6% in the running gel, and the gel matrix included 30% glycerol (26). The ammonium persulfate concentrations were 0.4% and 0.029% in the stacking and separation gels, respectively, and the gel solutions were degassed (Ͻ100 mTorr) for 15 min at 18°C.…”

“…Immunoblotting experiments had been conducted previously in this laboratory to determine the migration order of the four MyHC isoforms separated by the type of gels used in this study. The migration order from slowest to fastest migrating MyHC isoform is as follows: IIa-IIx-IIb-I (26).…”

Regulation of troponin T expression during muscle development in sea breamSparus auratusLinnaeus: the potential role of thyroid hormones

“…It has been shown that in rats full differentiation of skeletal muscle phenotype is only achieved with appropriate thyroid hormone levels (Vadaszova et al, 2004). Moreover in rats, T3 treatment significantly changes the muscle contractile properties and myosin heavy chain (MHC) isoform expression in both fast and slow muscle types (Adams et al, 1999;Larsson et al, 1994;Larsson et al, 1995;Soukup and Jirmanova, 2000). In both thyroidectomised and thioureatreated chick embryos prolonged expression of slow MHC and myosin light chains (MLC) and inhibition of neonatal fast MHC isoforms occurs in the fast posterior latissimus dorsi muscle, whereas in the slow anterior latissimus dorsi muscle slow muscle differentiation is delayed and expression of embryonic fast MHC isoforms persist and there is induction of fast MLCs (Gardahaut et al, 1992).…”