The changing AMPK expression profile in differentiating mouse skeletal muscle myoblast cells helps confer increasing resistance to apoptosis

AMP‐activated protein kinase (AMPK) functions as a α/β/γ heterotrimer to preserve ATP levels and so cell viability during stressful conditions. However, its role in aiding survival of adult skeletal muscle precursor cells is unclear. Using the differentiating mouse C2C12 postnatal skeletal muscle myoblast cell line, we have determined that proteins for the AMPK subunit isoforms α2 and γ2 are constitutively expressed, while those for α1, β1 and β2 are undetectable in undifferentiated myoblasts but increasingly expressed with differentiation to myotubes. Although the γ3 subunit is expressed at a low level in myoblasts, it too is expressed increasingly with differentiation to myotubes. The p50 but not the p72 isoform of the embryonic α subunit homologue MELK is expressed only in proliferating myoblasts, while the ARK5 α subunit homologue is increasingly expressed with differentiation. Myotubes displayed higher basal and stimulated α1/α2 AMPK activation than myoblasts. Furthermore, serum starvation resulted in less apoptosis of differentiated myotubes than of undifferentiated myoblasts. This reflects, in part, the increased expression of functional AMPK in the myotubes, since specific inhibition of AMPK activity with 6‐[4‐(2‐piperidin‐1‐ylethoxy)‐phenyl]‐3‐pyridin‐4‐ylpyrazolo[1,5‐α] pyrimidine (Compound C) exacerbated the apoptosis resulting from serum withdrawal. If these in vitro events can also occur in vivo, they could have implications for pathologies such as muscle wasting, in which undifferentiated satellite stem cells may be easier apoptotic targets than their differentiated counterparts. Furthermore, these results suggest that when interpreting results from in vitro or in vivo experiments on AMPK, the subunit expression profile should be taken into account.