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Merg1a K⁺ channel induces skeletal muscle atrophy by activating the ubiquitin proteasome pathway

Xun Wang^*, Gregory H. Hockerman, Henry W. Green, III, Charles F. Babbs^*, Sulma I. Mohammad, David Gerrard^¶, Mickey A. Latour^¶, Barry London^||, Kevin M. Hannon^*,1 and Amber L. Pond^*,1,2

^* Department of Basic Medical Sciences, School of Veterinary Medicine;

Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy;

Department of Veterinary Clinical Sciences, School of Veterinary Medicine;

Department of Veterinary Pathobiology and Cancer Center; and

^¶ Department of Animal Sciences, College of Agriculture, Purdue University, West Lafayette, Indiana, USA; and

^|| Cardiovascular Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, USA

²Correspondence: School of Veterinary Medicine, Purdue University, 625 Harrison St., West Lafayette, IN 47907, USA. E-mail: pond{at}purdue.edu

ABSTRACT

Skeletal muscle atrophy results from an imbalance in protein degradation and protein synthesis and occurs in response to injury, various disease states, disuse, and normal aging. Current treatments for this debilitating condition are inadequate. More information about mechanisms involved in the onset and progression of muscle atrophy is necessary for development of more effective therapies. Here we show that expression of the mouse ether-a-go-go related gene (Merg1a) K⁺ channel is up-regulated in skeletal muscle of mice experiencing atrophy as a result of both malignant tumor expression and disuse. Further, ectopic expression of Merg1a in vivo induces atrophy in healthy wt-bearing mice, while expression of a dysfunctional Merg1a mutant suppresses atrophy in hindlimb-suspended mice. Treatment of hindlimb-suspended mice with astemizole, a known Merg1a channel blocker, inhibits atrophy in these animals. Importantly, in vivo expression of Merg1a in mouse skeletal muscle activates the ubiquitin proteasome pathway that is responsible for the majority of protein degradation that causes muscle atrophy, yet expression of a dysfunctional Merg1a mutant decreases levels of ubiquitin-proteasome proteolysis. Thus, expression of Merg1a likely initiates atrophy by activating ubiquitin-proteasome proteolysis. This gene and its product are potential targets for prevention and treatment of muscle atrophy.—Wang, X., Hockerman, G. H., Green, H. W. III, Babbs, C. F., Mohammad, S. I., Gerrard, D., Latour, M. A., London, B., Hannon, K. M., Pond, A. L. Merg1a K⁺ channel induces skeletal muscle atrophy by activating the ubiquitin proteasome pathway.

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