Role of ?-adrenergic signaling in masseter muscle.

ABSTRACT: In skeletal muscle, the major isoform of ?-adrenergic receptor (?-AR) is ?2-AR and the minor isoform is ?1-AR, which is opposite to the situation in cardiac muscle. Despite extensive studies in cardiac muscle, the physiological roles of the ?-AR subtypes in skeletal muscle are not fully understood. Therefore, in this work, we compared the effects of chronic ?1- or ?2-AR activation with a specific ?1-AR agonist, dobutamine (DOB), or a specific ?2-AR agonist, clenbuterol (CB), on masseter and cardiac muscles in mice. In cardiac muscle, chronic ?1-AR stimulation induced cardiac hypertrophy, fibrosis and myocyte apoptosis, whereas chronic ?2-AR stimulation induced cardiac hypertrophy without histological abnormalities. In masseter muscle, however, chronic ?1-AR stimulation did not induce muscle hypertrophy, but did induce fibrosis and apoptosis concomitantly with increased levels of p44/42 MAPK (ERK1/2) (Thr-202/Tyr-204), calmodulin kinase II (Thr-286) and mammalian target of rapamycin (mTOR) (Ser-2481) phosphorylation. On the other hand, chronic ?2-AR stimulation in masseter muscle induced muscle hypertrophy without histological abnormalities, as in the case of cardiac muscle, concomitantly with phosphorylation of Akt (Ser-473) and mTOR (Ser-2448) and increased expression of microtubule-associated protein light chain 3-II, an autophagosome marker. These results suggest that the ?1-AR pathway is deleterious and the ?2-AR is protective in masseter muscle. These data should be helpful in developing pharmacological approaches for the treatment of skeletal muscle wasting and weakness.

SUBMITTER: Ito A 

PROVIDER: S-EPMC6464212 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature