title: Denervation atrophy is independent from Akt and mTOR activation and is not rescued by myostatin inhibition.
abstract: The purpose of our study was to compare two acquired muscle atrophies and the use of myostatin inhibition for their treatment. Myostatin naturally inhibits skeletal muscle growth by binding to ActRIIB, a receptor on the cell surface of myofibers. Because blocking myostatin in an adult wild-type mouse induces profound muscle hypertrophy, we applied a soluble ActRIIB receptor to models of disuse (limb immobilization) and denervation (sciatic nerve resection) atrophy. We found that treatment of immobilized mice with ActRIIB prevented the loss of muscle mass observed in placebo-treated mice. Our results suggest that this protection from disuse atrophy is regulated by serum and glucocorticoid-induced kinase (SGK) rather than by Akt. Denervation atrophy, however, was not protected by ActRIIB treatment, yet resulted in an upregulation of the pro-growth factors Akt, SGK and components of the mTOR pathway. We then treated the denervated mice with the mTOR inhibitor rapamycin and found that, despite a reduction in mTOR activation, there is no alteration of the atrophy phenotype. Additionally, rapamycin prevented the denervation-induced upregulation of the mTORC2 substrates Akt and SGK. Thus, our studies show that denervation atrophy is not only independent from Akt, SGK and mTOR activation but also has a different underlying pathophysiological mechanism than disuse atrophy.
authors: McKusick-Nathans Institute of Genetic Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors: Elizabeth M
authors: EM
authors: MacDonald
authors: Eva
authors: E
authors: Andres-Mateos
authors: Rebeca
authors: R
authors: Mejias
authors: Jessica L
authors: JL
authors: Simmers
authors: Ruifa
authors: R
authors: Mi
authors: Jae-Sung
authors: JS
authors: Park
authors: Stephanie
authors: S
authors: Ying
authors: Ahmet
authors: A
authors: Hoke
authors: Se-Jin
authors: SJ
authors: Lee
authors: Ronald D
authors: RD
authors: Cohn
mesh_terms: D030301:Activin Receptors, Type II / Q000378:metabolism; D000818:Animals; D001343:Autophagy / Q000187:drug effects; D015415:Biomarkers / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D008297:Male; D051379:Mice; D009121:Muscle Denervation; D009133:Muscular Atrophy / Q000201:enzymology* / Q000473:pathology*; D055435:Myostatin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D015415:Biomarkers; D055435:Myostatin; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C444640:serum-inducible kinase; D030301:Activin Receptors, Type II; C425584:activin receptor type II-B; D020123:Sirolimus
keywords: Denervation atrophy; Muscle atrophy pathophysiology; Myostatin; Skeletal muscle; TGF-β signaling