Expression of myosin heavy chain isoforms in the postnatal mouse masseter muscle

We investigated the properties of the masseter muscle in mice from five to seven weeks of age. Myosin heavy chain (MyHC) isoforms were measured in the masseter muscle. The three types of muscle fibers (Type I, strong reaction; Type IIA, intermediate reaction; and Type IIB, weak reaction) were all present in the masseter muscle in five-weeks-old mice and seven-weeks-old mice, the three types could be clearly distinguished by their enzyme activity. The percentage of Type IIB fibers (above 50%) was the highest among all fiber types both 5- and 7-weeks-old mice. The mRNA levels for myosin slow and myosin IIb increased significantly between 5 and 7 weeks. These observations suggest that muscle fiber size, muscle fiber types and mRNA levels of the MyHC isoforms all contribute to the diminished functional adaptability of enzyme activity in the masseter muscle.

Expression of respiratory chain enzyme mRNA and the morphological properties of mitochondria in the masseter muscles of klotho mutant mice

The activity of respiratory chain enzymes in a rat's masseter muscle changes as the animal ages; however, there is little information about the RNA transcript levels of mitochondrial enzymes in klotho mutant mice as they age. We measured the activities of NADH-ferricyanide oxidoreductase and NADH-O2 oxidoreductase, and the RNA transcript levels of NADH dehydrogenase, the mitochondrial isoform of ND1, the nuclear isoforms of the 51 kDa and 75 kDa subunits of Complex I, the nuclear isoform of cytochrome c, and the mitochondrial isoform of beta subunits of ATPase (Complex V). In addition, we measured the RNA transcript levels of catalase (CAT) and superoxide dismutase (SOD), which are associated with antioxidant proteins. Moreover, we measured ATP concentrations using a luciferin-luciferase assay, and we determined the amount of cytochrome c associated with mitochondria in both klotho mutant mice and wild-type mice. However, the mRNA levels of cytochrome c and Complex V components, the mRNA levels of CAT, SOD, and apoptosis-inducing factor (Aifm), and the protein level of cytochrome c remained constant as klotho mutant mice aged from 5 weeks to 7 weeks. In wild-type mice, these components (except for those of Complex I) increased over time. NADH-ferricyanide oxidoreductase and NADH-O2 oxidoreductase activities decreased in klotho mutant mice as they aged from 5 weeks to 7 weeks. A few large mitochondria were scattered between myofibrils, and 7-week-old klotho mutant mice displayed an increased number of irregular mitochondria with fewer cristae. Our results indicate that the klotho protein plays a role in the diminished functional adaptability of enzymes in the masseter muscle of klotho mutant mice throughout the aging process.

Effect of changes in food consistency on NADH-ubiquinone oxidoreductase activity and levels of mRNA for ND1, 51kDa, 75kDa and myosin heavy chain isoforms in two different portions of rat masseter muscle

We investigated the effect of a change in food consistency on properties of the masseter muscle in 3-week-old rats fed a soft diet for 9 weeks (Group S) and fed a soft diet for 5 weeks followed by a hard diet for 4 weeks (Group S-H). The NADH-O2 oxidoreductase activity, levels of mRNAs transcribed from genes encoding NADH-ubiquinone oxidoreductase (Complex I: ND1, 51kDa, and 75kDa) and myosin heavy chain (MyHC) isoforms and the phenotype of the muscle fibers were measured in the superficial and deep portions of the muscle. In the period from 8 weeks to 12 weeks of age, NADH-O2 oxidoreductase enzyme activity in both the superficial and deep portions of the muscle showed similar patterns in Group S and Group S-H. In contrast, the ND1, 51kDa and 75kDa mRNA levels in the superficial and deep portions of the masseter muscle in the Group S-H were higher than those of Group S in the 12-week-old rats, except for the 51kDa mRNA in the superficial portion of the masseter muscle. MyHC-IIa and MyHC-IId/x mRNA levels in the superficial portion of the masseter muscle were higher in the Group S-H than in the Group S. These observations suggest that short-term feeding stress such as the transition from a soft diet to a hard diet causes changes in oxidative metabolism, in mRNA levels for the Complex I components ND1 and 75kDa, and the mRNA levels for the MyHC isoforms IIa and IId/x in the superficial portion of rat masseter muscle, but no changes in the composition of muscle fiber types.