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

Abstract

Mechanical unloading of skeletal muscles leads to the development of atrophic processes and a decrease in the total number of satellite cells (SCs) that are involved in muscle regeneration. In vitro studies revealed an increased differentiation of myoblasts derived from rat soleus muscle after an unloading-induced decrease in AMP-activated protein kinase (AMPK). AMPK is necessary for the activation of SCs and also participates in the regulation of myoblast proliferation and differentiation. It can be assumed that a decrease in the activity of AMPK after mechanical unloading can contribute to 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 rat soleus muscle 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 rat soleus muscle 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 soleus muscle there was a significant decrease in AMPK (Thr172) and ACC (Ser 79) phosphorylation levels, an increase in myotube differentiation index, myoblast fusion factors and the expression of 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 obtained from the unloaded soleus muscle prevented a decrease in AMPK and ACC phosphorylation, returned the expression levels of MRF and fast isoforms of MyHC to the control levels as well as maintained the expression of slow MyHC. Thus, abnormally accelerated differentiation of myoblasts isolated from atrophied rat soleus muscle can be compensated by maintaining the control levels of AMPK activity using AICAR.