G.P.203: IL-6- and calcineurin-mediated but not IGF-1-mediated mechanisms contribute to the upregulation of MHC I and HSP70 mRNA levels in C2C12 cells

Abstract

Skeletal muscle has been known to cause disuse atrophy during long-term recumbence and to recover by exercise. Although there are many studies about skeletal muscle regulatory factors, such as IGF-1 or IL-6, that are known to affect skeletal muscle mass, mechanism of muscle cell hypertrophy is still unclear. Our previous study using rat soleus muscle indicated that myosin heavy chain (MHC) and HSP70 proteins were significantly increased by the exercise after disuse atrophy, therefore we examined effects of IGF-1, IL-6, and La³⁺ on MHC I, HSP70, and IL-6 mRNA expression level using real-time PCR method in C2C12 skeletal myoblasts. The C2C12 cells which were differentiated into myocyte in D-MEM containing 2% FCS was incubated with chemicals in 24h. First, we examined the effect of IGF-1 on MHC I, HSP70, and IL-6 mRNA expression levels. MHC I and HSP70 mRNA levels were significantly decreased by the incubation with IGF-1, although IL-6 mRNA level was increased. Second, we examined the effect of IL-6 on MHC I, HSP70, and IL-6 mRNA expression levels. These mRNA levels were significantly increased by the incubation with IL-6. Third, we examined the effect of La³⁺ on MHC I, HSP70, and IL-6 mRNA expression levels. These mRNA levels were significantly increased by the incubation with La³⁺. The effects of La³⁺ on these mRNA levels are considered as a result of calcineurin activation, because it was well known that La³⁺ stimulate the activity of calcineurin. Therefore, we confirmed that effect of calcineurin inhibitor on La³⁺-induced increase in mRNA levels of IGF-1, IL-6, and HSP70. La³⁺-induced upregulation of these mRNA levels were significantly attenuated by the application of FK506. These results indicate that IL-6- and La³⁺/calcineurin-mediated but not IGF-1-mediated mechanisms contribute to the upregulation of MHC I and HSP70 mRNA levels in C2C12 cells.