Received June 20, 2006
Revised August 4, 2006
Accepted after revision August 29, 2006

¹ Stellenbosch University
² University of Stellenbosch

^* To whom correspondence should be addressed. E-mail: frances.moore{at}horm.ucl.ac.be.

	Abstract

Abstract AMP-activated protein kinase (AMPK) functions as a // 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 2 and 2 are constitutively expressed while those for 1, 1 and 2 are undetectable in undifferentiated myoblasts but increasingly expressed with differentiation to myotubes. Although the 3 subunit is expressed at a low level in myoblasts it too is increasingly expressed with differentiation to myotubes. The p50 but not the p72 isoform of the embryonic subunit homologue MELK is expressed only in proliferating myoblasts while the ARK5 subunit homologue is increasingly expressed with differentiation. Myotubes displayed higher basal and stimulated 1/2 AMPK activation than myoblasts. Furthermore, serum starvation resulted in less apoptosis of differentiated myotubes than undifferentiated myoblasts. This reflects, in part, their increased expression of functional AMPK since specific inhibition of AMPK activity with Compound C exacerbated the apoptosis due to serum withdrawal. If these in vitro events also occur in vivo then they could have implications for pathologies such as muscle wasting where undifferentiated satellite stem cells may be easier apoptotic targets than their differentiated counterparts. Further, 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.

Key Words: Energy, Myoblast, Protein kinase