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 alpha/beta/gamma 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 alpha2 and gamma2 are constitutively expressed, while those for alpha1, beta1 and beta2 are undetectable in undifferentiated myoblasts but increasingly expressed with differentiation to myotubes. Although the gamma3 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 alpha subunit homologue MELK is expressed only in proliferating myoblasts, while the ARK5 alpha subunit homologue is increasingly expressed with differentiation. Myotubes displayed higher basal and stimulated alpha1/alpha2 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-alpha] 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.
Niesler
Carola U
CU
Hormone and Metabolic Research Unit, Christian de Duve Institute of Cellular Pathology, University of Louvain Medical School, ICP-UCL 7529, Avenue Hippocrate 75, B-1200 Brussels, Belgium.
Myburgh
Katherine H
KH
Moore
Frances
F
D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation; D002470:Cell Survival; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D032448:Myoblasts, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D012097:Repressor Proteins / Q000378:metabolism; D013997:Time Factors
D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D009840:Oligomycins; D011720:Pyrazoles; D011743:Pyrimidines; D012097:Repressor Proteins; C516138:dorsomorphin; C108524:Melk protein, mouse; C526221:Prkag3 protein, mouse; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase