Limb Immobilization Induces a Coordinate Down-Regulation of Mitochondrial and Other Metabolic Pathways in Men and Women

PLOS ONE, Aug 2009

Advancements in animal models and cell culture techniques have been invaluable in the elucidation of the molecular mechanisms that regulate muscle atrophy. However, few studies have examined muscle atrophy in humans using modern experimental techniques. The purpose of this study was to examine changes in global gene transcription during immobilization-induced muscle atrophy in humans and then explore the effects of the most prominent transcriptional alterations on protein expression and function. Healthy men and women (N = 24) were subjected to two weeks of unilateral limb immobilization, with muscle biopsies obtained before, after 48 hours (48 H) and 14 days (14 D) of immobilization. Muscle cross sectional area (∼5%) and strength (10–20%) were significantly reduced in men and women (∼5% and 10–20%, respectively) after 14 D of immobilization. Micro-array analyses of total RNA extracted from biopsy samples at 48 H and 14 D uncovered 575 and 3,128 probes, respectively, which were significantly altered during immobilization. As a group, genes involved in mitochondrial bioenergetics and carbohydrate metabolism were predominant features at both 48 H and 14 D, with genes involved in protein synthesis and degradation significantly down-regulated and up-regulated, respectively, at 14 D of muscle atrophy. There was also a significant decrease in the protein content of mitochondrial cytochrome c oxidase, and the enzyme activity of cytochrome c oxidase and citrate synthase after 14 D of immobilization. Furthermore, protein ubiquitination was significantly increased at 48 H but not 14 D of immobilization. These results suggest that transcriptional and post-transcriptional suppression of mitochondrial processes is sustained throughout 14 D of immobilization, while protein ubiquitination plays an early but transient role in muscle atrophy following short-term immobilization in humans.

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Limb Immobilization Induces a Coordinate Down-Regulation of Mitochondrial and Other Metabolic Pathways in Men and Women

et al. (2009) Limb Immobilization Induces a Coordinate Down-Regulation of Mitochondrial and Other Metabolic Pathways in Men and Women. PLoS ONE 4(8): e6518. doi:10.1371/journal.pone.0006518 Limb Immobilization Induces a Coordinate Down- Regulation of Mitochondrial and Other Metabolic Pathways in Men and Women Arkan Abadi 0 Elisa I. Glover 0 Robert J. Isfort 0 Sandeep Raha 0 Adeel Safdar 0 Nobuo Yasuda 0 Jan J. 0 Kaczor 0 Simon Melov 0 Alan Hubbard 0 Xiaoyan Qu 0 Stuart M. Phillips 0 Mark Tarnopolsky 0 Rodolfo Aramayo, Texas A&M University, United States of America 0 1 Department of Pediatrics & Medicine, McMaster University , Hamilton, Ontario , Canada , 2 Procter & Gamble Company, Mason, Ohio, United States of America, 3 Graduate School of Medicine, Juntendo University , Inba , Japan , 4 School of Medicine , Debinki 1, Gdansk , Poland , 5 Buck Institute for Age Research, Novato, California, United States of America, 6 School of Public Health, University of California, Berkeley, California, United States of America, 7 Department of Kinesiology, McMaster University , Hamilton, Ontario , Canada Advancements in animal models and cell culture techniques have been invaluable in the elucidation of the molecular mechanisms that regulate muscle atrophy. However, few studies have examined muscle atrophy in humans using modern experimental techniques. The purpose of this study was to examine changes in global gene transcription during immobilization-induced muscle atrophy in humans and then explore the effects of the most prominent transcriptional alterations on protein expression and function. Healthy men and women (N = 24) were subjected to two weeks of unilateral limb immobilization, with muscle biopsies obtained before, after 48 hours (48 H) and 14 days (14 D) of immobilization. Muscle cross sectional area (,5%) and strength (10-20%) were significantly reduced in men and women (,5% and 10-20%, respectively) after 14 D of immobilization. Micro-array analyses of total RNA extracted from biopsy samples at 48 H and 14 D uncovered 575 and 3,128 probes, respectively, which were significantly altered during immobilization. As a group, genes involved in mitochondrial bioenergetics and carbohydrate metabolism were predominant features at both 48 H and 14 D, with genes involved in protein synthesis and degradation significantly down-regulated and up-regulated, respectively, at 14 D of muscle atrophy. There was also a significant decrease in the protein content of mitochondrial cytochrome c oxidase, and the enzyme activity of cytochrome c oxidase and citrate synthase after 14 D of immobilization. Furthermore, protein ubiquitination was significantly increased at 48 H but not 14 D of immobilization. These results suggest that transcriptional and post-transcriptional suppression of mitochondrial processes is sustained throughout 14 D of immobilization, while protein ubiquitination plays an early but transient role in muscle atrophy following short-term immobilization in humans. - Funding: Funding for the current project was primarily from a grant-in aid from Proctor and Gamble to MAT and from NSERC (MAT). Dr. Tarnopolsky is partially supported through an Endowed Chair from the Childrens Hospital Celebration and Michael DeGroote. E.I. Glover was supported by a Canadian Institutes of Health Research Doctoral Research Award. A. Abadi is sponsored by a post-doctoral fellowship from Mr. Warren Lammert and Kathy Corkins. Infrastructure support was provided from grants and donations from the Canadian Foundation for Innovation, Mr. Warren Lammert and Kathy Corkins, and Giant Tiger Stores. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Skeletal muscle atrophy is associated with bed rest, corticosteroid use, denervation, chronic renal failure, limb immobilization, neuromuscular disorders, sarcopenia of aging, and arthritis [18]. Irrespective of the underlying cause of atrophy, reduced muscle activation/contractile activity (hypodynamia) is an invariant feature. Recently, strong interest has focused on characterizing the fundamental molecular mechanism(s) underlying muscle atrophy and numerous cellular processes are known to coalesce into the overall atrophy phenotype. These alterations include decreased protein synthesis, increased protein degradation, and suppression of bioenergetic pathways associated with mitochondrial function, and increased oxidative stress [9,10]. Upstream triggers that initiate atrophy are poorly understood and may vary depending on the pathological context; however, animal data suggests that disparate atrophic stimuli converge on the activation of protein degradation, particularly the ubiquitin (Ub)-26S proteasomal pathway [1,1114]. Two novel Ub-protein ligases, atrogin-1 (muscle atrophy F-box protein) and muscle ringfinger protein (MuRF-1), are (...truncated)


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Arkan Abadi, Elisa I. Glover, Robert J. Isfort, Sandeep Raha, Adeel Safdar, Nobuo Yasuda, Jan J. Kaczor, Simon Melov, Alan Hubbard, Xiaoyan Qu, Stuart M. Phillips, Mark Tarnopolsky. Limb Immobilization Induces a Coordinate Down-Regulation of Mitochondrial and Other Metabolic Pathways in Men and Women, PLOS ONE, 2009, 8, DOI: 10.1371/journal.pone.0006518