Expression levels of sarcolemmal membrane repair proteins following prolonged exercise training in mice.

Membrane repair is a conserved cellular process, where intracellular vesicles translocate to sites of plasma membrane injury to actively reseal membrane disruptions. Such membrane disruptions commonly occur in the course of normal physiology, particularly in skeletal muscles due to repeated contraction producing small tears in the sarcolemmal membrane. Here, we investigated whether prolonged exercise could produce adaptive changes in expression levels of proteins associated with the membrane repair process, including mitsugumin 53/tripartite motif-containing protein 72 (MG53/TRIM72), dysferlin and caveolin-3 (cav3). Mice were exercised using a treadmill running protocol and protein levels were measured by immunoblotting. The specificity of the antibodies used was established by immunoblot testing of various tissue lysates from both mice and rats. We found that MG53/TRIM72 immunostaining on isolated mouse skeletal muscle fibers showed protein localization at sites of membrane disruption created by the isolation of these muscle fibers. However, no significant changes in the expression levels of the tested membrane repair proteins were observed following prolonged treadmill running for eight weeks (30 to 80 min/day). These findings suggest that any compensation occurring in the membrane repair process in skeletal muscle following prolonged exercise does not affect the expression levels of these three key membrane repair proteins.

Modulation of the caveolin-3 localization to caveolae and STAT3 to mitochondria by catecholamine-induced cardiac hypertrophy in H9c2 cardiomyoblasts

We investigated the effect of phenylephrine (PE)- and isoproterenol (ISO)-induced cardiac hypertrophy on subcellular localization and expression of caveolin-3 and STAT3 in H9c2 cardiomyoblast cells. Caveolin-3 localization to plasma membrane was attenuated and localization of caveolin-3 to caveolae in the plasma membrane was 24.3% reduced by the catecholamine-induced hypertrophy. STAT3 and phospho-STAT3 were up-regulated but verapamil and cyclosporin A synergistically decreased the STAT3 and phospho-STAT3 levels in PE- and ISO-induced hypertrophic cells. Both expression and activation of STAT3 were increased in the nucleus by the hypertrophy. Immunofluorescence analysis revealed that the catecholamine-induced hypertrophy promoted nuclear localization of pY705-STAT3. Of interest, phosphorylation of pS727-STAT3 in mitochondria was significantly reduced by catecholamine-induced hypertrophy. In addition, mitochondrial complexes II and III were greatly down-regulated in the hypertrophic cells. Our data suggest that the alterations in nuclear and mitochondrial activation of STAT3 and caveolae localization of caveolin-3 are related to the development of the catecholamine-induced cardiac hypertrophy.

Exercise type and muscle fiber specific induction of caveolin-1 expression for insulin sensitivity of skeletal muscle

It is well known that exercise can have beneficial effects on insulin resistance by activation of glucose transporter. Following up our previous report that caveolin-1 plays an important role in glucose uptake in L6 skeletal muscle cells, we examined whether exercise alters the expression of caveolin-1, and whether exercise-caused changes are muscle fiber and exercise type specific. Fifity week-old Sprague Dawley (SD) rats were trained to climb a ladder and treadmill for 8 weeks and their soleus muscles (SOL) and extensor digitorum longus muscles (EDL) were removed after the last bout of exercise and compared with those from non-exercised animals. We found that the expression of insulin related proteins and caveolins did not change in SOL muscles after exercise. However, in EDL muscles, the expression of insulin receptor beta (IRbeta) and glucose transporter-4 (GLUT-4) as well as phosphorylation of AKT and AMPK increased with resistance exercise but not with aerobic exercise. Also, caveolin-1 and caveolin-3 increased along with insulin related proteins only in EDL muscles by resistance exercise. These results suggest that upregulation of caveolin-1 in the skeletal muscle is fiber specific and exercise type specific, implicating the requirement of the specific mode of exercise to improve insulin sensitivity.