In the present study, we investigated the effect of heat stress on disuse atrophy from changes in the muscle protein levels of desmin and calpain. Wistar strain female rats (6-8 months old) were randomly assigned to two experimental groups: control (C) and heat stress (H). One hindlimb of all animals was immobilized in plantar flexion with plaster. Before immobilization, animals in H group were placed in a heat chamber (42°C for 60 min). Following 6 days of immobilization, the soleus muscles were removed and analyzed. Although immobilization resulted in significant muscle atrophy in all experimental animals, the soleus weight-to-body weight ratio in immobilized limbs of H group was significantly higher compared to that of C group. Expression of desmin and HSP72 in the atrophied soleus muscle from C group was significantly lower compared with the contralateral muscle; but this was not the case in H group. Further, in C group, the ratio of autolyzed calpains I increased significantly in the atrophied muscle compared to the contralateral muscle. These results show that the effect of heat stress on disuse skeletal muscle atrophy is attributed to the decreasing degradation of desmin by suppressing the activation of calpain.

The purpose of this study was to examine the effects of combination of a heat stress and astaxanthin supplementation, known as a potent anti-oxidative nutrient, on muscle protein degradation and disuse muscle atrophy. Fifty-two male Wistar rats (261.7±1.17 g) were divided into five groups: control (Cont, n=10), suspension (Sus, n=11), heat stress and suspension (Heat, n=10), astaxanthin and suspension (Ax, n=10), and heat stress, astaxanthin and suspension (H+A, n=11). There were no significant differences in Cu,Zn-SOD, cathepsin L and caspase-3 levels among the Heat, Ax and H+A groups in the soleus and plantaris muscles. Although levels of calpain 2 and ubiquitinated protein in the myofibrillar fraction in the soleus muscle were not significantly different among the Heat, Ax and H+A groups, levels in the H+A group were significantly (p<0.05) lower than Sus. Concerning atrophied plantaris muscles, the H+A group significantly (p<0.05) suppressed the expression of calpain 1 in the myofibrillar fraction, but there were no marked changes of proteolytic indexes. These data indicate that the combination of the heat stress and astaxanthin supplementation could be effective in inhibiting muscle protein degradation in disuse atrophy of the soleus.

In this study, we aimed to investigate the effects of long-term voluntary running exercise and caloric restriction during development on the skeletal muscle mass and intracellular signaling in female rats. Four-week-old female Wistar rats (n = 23) were randomly divided into the sedentary (SED) and voluntary running exercise (EX) groups, and then acclimated to a new environment. At 5 weeks of age, the rats in both groups were further divided into the ad libitum (AD+SED or AD+EX, n = 6) and calorie-restricted (CR+SED or CR+EX, n = 5-6) groups. EX group underwent 12 weeks of voluntary running exercise. CR group was only fed 70% of the food fed to the AD + SED group. After 12 weeks of intervention, soleus and plantaris muscles were removed, and the levels of intracellular signal transduction proteins involved in protein synthesis and degradation were measured by Western blotting. Significant diet × condition interactions were observed in the body, soleus muscle, and plantaris muscle weights. Specifically, plantaris muscle weight in the CR + EX group was significantly lower than that in the other groups; however, their soleus muscle weight was similar to that in the CR + SED group. In the plantaris muscles, significant diet × condition interactions were observed in the phosphorylation levels of 4E-binding protein 1, UNC-51-like autophagy-activating kinase-1, and light chain 3-II/I. Moreover, these factors were significantly altered in the CR + EX group than in the other groups. Notably, no significant interactions were observed in the soleus muscles. Our data suggest that long-term voluntary running exercise and caloric restriction exacerbate skeletal muscle loss, possibly mediated by muscle type-specific intracellular signaling mechanisms involved in protein synthesis and degradation.

This study aimed to elucidate the effects of long-term high-fat diet (HFD) consumption and cage restriction-induced physical inactivity (IN) during youth on skeletal muscle autophagy in rats. Three-week-old male Wistar rats were randomly assigned to two dietary groups: the normal diet (ND) and HFD groups. Each group was further subdivided into control (CON) and IN conditions, resulting in four experimental groups (n = 7-8). The HFD group was provided with a diet containing approximately 60% of total calories from crude fat for 16 weeks, from 4 to 20 weeks of age. The ND group received a standard diet for the same duration. The physical inactivity intervention during youth involved restricting the rats’ range of activity by housing them in smaller cages for eight weeks. After 12 weeks of age, the behavioral restrictions were lifted, and all groups of rats were housed in normal-sized cages for eight weeks. The ‘diet group’ and ‘condition’ factors exerted significant effects on the relative muscle weight of the gastrocnemius muscle. The HFD groups exhibited a notable decline in relative muscle weight compared to their ND counterparts. While no significant alterations were observed in LC3-II or p62 expression levels, the ‘diet group’ factor significantly influenced LC3-II/I levels in the white gastrocnemius muscle. These levels were markedly reduced in the HFD group. Our findings suggest that 16 weeks of HFD consumption leads to a reduction in autophagy flux, specifically within the white portion of the gastrocnemius muscle, but this effect is not influenced by cage restriction-induced physical inactivity during youth.

We examined the effect of a combination of astaxanthin (AX) supplementation, repeated heat stress, and intermittent reloading (IR) on satellite cells in unloaded rat soleus muscles. Forty-nine male Wistar rats (8-week-old) were divided into control, hind-limb unweighting (HU), IR during HU, IR with AX supplementation, IR with repeated heat stress (41.0-41.5 °C for 30 min), and IR with AX supplementation and repeated heat stress groups. After the experimental period, the antigravitational soleus muscle was analyzed using an immunohistochemical technique. Our results revealed that the combination of dietary AX supplementation and heat stress resulted in protection against disuse muscle atrophy in the soleus muscle. This protective effect may be partially due to a higher satellite cell number in the atrophied soleus muscle in the IR/AX/heat stress group compared with the numbers found in the other groups. We concluded that the combination treatment with dietary AX supplementation and repeated heat stress attenuates soleus muscle atrophy, in part by increasing the number of satellite cells.
Animals ; Body Weight ; Dietary Supplements ; Fibrinolytic Agents/pharmacology* ; Heat-Shock Response ; Hindlimb ; Hot Temperature ; Immunohistochemistry ; Male ; Muscle, Skeletal ; Muscular Atrophy/drug therapy* ; Oxidative Stress ; Rats ; Rats, Wistar ; Satellite Cells, Skeletal Muscle/cytology* ; Xanthophylls/pharmacology*