The Maintenance of AMPK Activity Eliminates Abnormally Accelerated Differentiation of Primary Myoblasts Isolated from Atrophied Rat Soleus Muscle.

Mechanical unloading of skeletal muscles leads to the development of atrophic processes and a decrease in the total number of myosatellite cells involved in muscle regeneration. In vitro studies revealed an accelerated differentiation of myoblasts derived from the rat m. soleus after an unloading-induced decrease in AMP-activated protein kinase (AMPK). AMPK is required for the activation of SCs and also participates in the regulation of myoblast proliferation and differentiation. It can be hypothesized that a decrease in AMPK activity after mechanical unloading promotes the acceleration of myoblast differentiation. The main purpose of this study was to elucidate a possible role of AMPK in the regulation of differentiation of myoblasts isolated from the rat m. soleus after mechanical unloading. To test this hypothesis, a specific AMPK activator, AICAR, was used to prevent a decrease in AMPK activity during differentiation of myoblasts isolated from the rat m. soleus after 7-day unloading. Immunocytochemistry, PCR-RT and Western blotting were used to assess changes during myoblast differentiation. In differentiating myoblasts derived from the unloaded m. soleus, there was a significant decrease in AMPK (Thr172) and ACC (Ser79) phosphorylation levels, an increase in myotube differentiation index, as well as in the expression of myoblast fusion factors and myogenic regulatory factors (MRF). Furthermore, there was a decrease in the expression of slow myosin heavy chains (MyHC) and an increase in the expression of fast MyHC isoforms. AICAR treatment of differentiating myoblasts derived from the unloaded m. soleus prevented a decrease in AMPK and ACC phosphorylation, returned the expression levels of MRF and fast MyHC isoforms to the control levels, as well as maintained the expression of slow MyHC. Thus, abnormally accelerated differentiation of myoblasts isolated from the atrophied rat m. soleus can be compensated by the AICAR-assisted maintenance of control AMPK activity levels. [ABSTRACT FROM AUTHOR]