Mitsutoshi Kurosaka

Elevation of body temperature is an essential factor for exercise-increased extracellular heat shock protein 72 level in rat plasma

This study examined whether the exercise-increased extracellular heat shock protein 72 (eHsp72) levels in rats was associated with body temperature elevation during exercise. In all, 26 female Sprague-Dawley rats (3 mo old) were assigned randomly to control (CON; n = 8), exercise under warm temperature (WEx; n = 9), or exercise under cold temperature (CEx; n = 9). The WEx and CEx were trained at 25 degrees C or 4 degrees C, respectively, for nine days using a treadmill. Before and immediately after the final exercise bout, the colonic temperatures were measured as an index of body temperature. The animals were subsequently anesthetized, and blood samples were collected and centrifuged. Plasma samples were obtained to assess their eHsp72 levels. Only the colonic temperature in WEx was increased significantly (P < 0.05) by exercise. The eHsp72 level in WEx was significantly higher (P < 0.05) than that of either the CON or CEx. However, no significant difference was found between CON and CEx. Regression analyses revealed that the eHsp72 level increased as a function of the body temperature. In another experiment, the eHsp72 level of animals with body temperature that was passively elevated through similar kinetics to those of the exercise was studied. Results of this experiment showed that mere body temperature elevation was insufficient to induce eHsp72 responses. Collectively, our results suggest that body temperature elevation during exercise is important for induction of exercise-increased eHsp72. In addition, the possible role of body temperature elevation is displayed when the exercise stressor is combined with it.

Provision of a voluntary exercise environment enhances running activity and prevents obesity in Snark-deficient mice

The present study was performed to investigate the involvement of SNARK in physical activity levels in mice. To examine the acute effect of SNARK deficiency on voluntary running, Snark-deficient mice (Snark(+/-): n = 16) and their wild-type counterparts (Snark(+/+): n = 16) were assigned to sedentary or exercise (1 wk voluntary wheel running) groups. In addition, to clarify the differences in voluntary running activity and its effect between genotypes, mice (Snark(+/+): n = 16; Snark(+/-): n = 16) were also kept in individual cages with/without a running wheel for 5 mo. Unexpectedly, in both voluntary running experiments, running distances were increased in Snark(+/-) mice compared with Snark(+/+) mice. Under sedentary conditions, body and white adipose tissue weights were increased significantly in Snark(+/-) mice. However, no significant differences were observed between the two genotypes under exercise conditions, and the values were significantly less than those under sedentary conditions in the long-term experiment. In the short-term experiment, serum interleukin-6 level in exercised Snark(+/+) mice was the same as that in sedentary Snark(+/+) mice, whereas that in sedentary Snark(+/-) mice was significantly lower than in the other groups. In contrast, serum leptin level was reduced significantly in exercised Snark(+/-) mice compared with sedentary Snark(+/-) mice. The results of this study demonstrated that exposure to an environment that allows voluntary exercise promotes increased running activity and prevents obesity in Snark-deficient mice.

Alpha-actinin-3 levels increase concomitantly with fast fibers in rat soleus muscle

Alpha (alpha)-actinin-3 is located in the skeletal muscle Z-line and forms actin-actin crosslinks. An interesting property of alpha-actinin-3 is its expression pattern, which is restricted to fast type II skeletal muscle fibers. However, little is known about the response of alpha-actinin-3 levels to changes in skeletal muscle such as fiber type transformation. This study examined alpha-actinin-3 levels in the soleus muscles of rats subjected to hindlimb unloading, which causes a slow-to-fast fiber transformation in the soleus muscle. After unloading, type II myosin heavy chain (MyHC) and fast myosin levels increased significantly (P<0.0001 for type II MyHC, P<0.005 for fast myosin). Along with these increases in fast fibers, alpha-actinin-3 expression levels increased significantly (P<0.0007) and dramatically. These results indicate that alpha-actinin-3 levels increase concomitantly with increases in skeletal muscle fast fibers.