title: Serum Amyloid A Induces Toll-Like Receptor 2-Dependent Inflammatory Cytokine Expression and Atrophy in C2C12 Skeletal Muscle Myotubes.
abstract: BACKGROUND
  Skeletal muscle wasting is an important comorbidity of Chronic Obstructive Pulmonary Disease (COPD) and is strongly correlated with morbidity and mortality. Patients who experience frequent acute exacerbations of COPD (AECOPD) have more severe muscle wasting and reduced recovery of muscle mass and function after each exacerbation. Serum levels of the pro-inflammatory acute phase protein Serum Amyloid A (SAA) can rise more than 1000-fold in AECOPD and are predictively correlated with exacerbation severity. The direct effects of SAA on skeletal muscle are poorly understood. Here we have examined SAA effects on pro-inflammatory cachectic cytokine expression (IL-6 and TNFα) and atrophy in C2C12 myotubes.
  
  
  RESULTS
  SAA increased IL-6 (31-fold) and TNFα (6.5-fold) mRNA levels compared to control untreated cells after 3h of SAA treatment, and increased secreted IL-6 protein at 24h. OxPAPC, a dual TLR2 and TLR4 inhibitor, reduced the response to SAA by approximately 84% compared to SAA alone, and the TLR2 neutralising antibody T2.5 abolished SAA-induced expression of IL-6, indicating that SAA signalling in C2C12 myotubes is primarily via TLR2. SAA also reduced myotube width by 10-13% and induced a 2.5-fold increase in the expression of the muscle atrophy gene Atrogin-1, suggesting direct effects of SAA on muscle wasting. Blocking of TLR2 inhibited the SAA-induced decrease in myotube width and Atrogin-1 gene expression, indicating that SAA induces atrophy through TLR2.
  
  
  CONCLUSIONS
  These data demonstrate that SAA stimulates a robust pro-inflammatory response in skeletal muscle myotubes via the TLR2-dependent release of IL-6 and TNFα. Furthermore, the observed atrophy effects indicate that SAA could also be directly contributing to the wasting and poor recovery of muscle mass. Therapeutic strategies targeting this SAA-TLR2 axis may therefore ameliorate muscle wasting in AECOPD and a range of other inflammatory conditions associated with loss of muscle mass.
authors.affiliation: Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia.|School of Health and Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, Australia.
authors.forename: Samantha L
authors.initials: SL
authors.lastname: Passey
authors.affiliation: Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia.|School of Health and Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, Australia.
authors.forename: Steven
authors.initials: S
authors.lastname: Bozinovski
authors.affiliation: Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia.|School of Health and Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, Australia.
authors.forename: Ross
authors.initials: R
authors.lastname: Vlahos
authors.affiliation: Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia.
authors.forename: Gary P
authors.initials: GP
authors.lastname: Anderson
authors.affiliation: Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia.
authors.forename: Michelle J
authors.initials: MJ
authors.lastname: Hansen
mesh_terms: D000818:Animals; D002460:Cell Line; D005786:Gene Expression Regulation; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000276:immunology / Q000473:pathology; D009124:Muscle Proteins / Q000378:metabolism; D009133:Muscular Atrophy / Q000276:immunology / Q000473:pathology*; D010713:Phosphatidylcholines / Q000494:pharmacology; D029424:Pulmonary Disease, Chronic Obstructive / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D000685:Serum Amyloid A Protein / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D015850:Interleukin-6; D009124:Muscle Proteins; D010713:Phosphatidylcholines; D000685:Serum Amyloid A Protein; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; D014409:Tumor Necrosis Factor-alpha; C472349:oxidized-L-alpha-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine; C486691:Fbxo32 protein, mouse; D044843:SKP Cullin F-Box Protein Ligases