title: Omega-3 fatty acid EPA improves regenerative capacity of mouse skeletal muscle cells exposed to saturated fat and inflammation.
abstract: Sarcopenic obesity is characterised by high fat mass, low muscle mass and an elevated inflammatory environmental milieu. We therefore investigated the effects of elevated inflammatory cytokine TNF-α (aging/obesity) and saturated fatty acid, palmitate (obesity) on skeletal muscle cells in the presence/absence of EPA, a-3 polyunsaturated fatty acid with proposed anti-inflammatory, anti-obesity activities. In the present study we show that palmitate was lipotoxic, inducing high levels of cell death and blocking myotube formation. Cell death under these conditions was associated with increased caspase activity, suppression of differentiation, reductions in both creatine kinase activity and gene expression of myogenic factors; IGF-II, IGFBP-5, MyoD and myogenin. However, inhibition of caspase activity via administration of Z-VDVAD-FMK (caspase-2), Z-DEVD-FMK (caspase-3) and ZIETD-KMK (caspase 8) was without effect on cell death. By contrast, lipotoxicity associated with elevated palmitate was reduced with the MEK inhibitor PD98059, indicating palmitate induced cell death was MAPK mediated. These lipotoxic conditions were further exacerbated in the presence of inflammation via TNF-α co-administration. Addition of EPA under cytotoxic stress (TNF-α) was shown to partially rescue differentiation with enhanced myotube formation being associated with increased MyoD, myogenin, IGF-II and IGFBP-5 expression. EPA had little impact on the cell death phenotype observed in lipotoxic conditions but did show benefit in restoring differentiation under lipotoxic plus cytotoxic conditions. Under these conditions Id3 (inhibitor of differentiation) gene expression was inversely linked with survival rates, potentially indicating a novel role of EPA and Id3 in the regulation of apoptosis in lipotoxic/cytotoxic conditions. Additionally, signalling studies indicated the combination of lipo- and cyto-toxic effects on the muscle cells acted through ceramide, JNK and MAPK pathways and blocking these pathways using PD98059 (MEK inhibitor) and Fumonisin B1 (ceramide inhibitor) significantly reduced levels of cell death. These findings highlight novel pathways associated with in vitro models of lipotoxicity (palmitate-mediated) and cytotoxicity (inflammatory cytokine mediated) in the potential targeting of molecular modulators of sarcopenic obesity.
authors.affiliation: Department of Laboratory Medicine, Clinical Physiology, Karolinska Institutet, and Unit of Clinical Physiology, Karolinska University Hospital, 141 86, Stockholm, Sweden.
authors.forename: Amarjit
authors.initials: A
authors.lastname: Saini
authors.affiliation: Stem Cells, Ageing and Molecular Physiology (SCAMP) Unit, Exercise Metabolism and Adaptation Research Group, Research Institute for Sport & Exercise Sciences, School of Sport and Exercise Sciences, Liverpool John Moores University, Life Science Building, Byrom Street Campus, Liverpool, L3 3AF, UK. a.p.sharples@googlemail.com.
authors.forename: Adam P
authors.initials: AP
authors.lastname: Sharples
authors.affiliation: Neuromuscular and Skeletal Ageing Research Group, Healthcare Science Research Institute, Manchester Metropolitan University, Oxford Road, Manchester, M1 5GD, UK.
authors.forename: Nasser
authors.initials: N
authors.lastname: Al-Shanti
authors.affiliation: Stem Cells, Ageing and Molecular Physiology (SCAMP) Unit, Exercise Metabolism and Adaptation Research Group, Research Institute for Sport & Exercise Sciences, School of Sport and Exercise Sciences, Liverpool John Moores University, Life Science Building, Byrom Street Campus, Liverpool, L3 3AF, UK.
authors.forename: Claire E
authors.initials: CE
authors.lastname: Stewart
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002460:Cell Line; D015118:Eicosapentaenoic Acid / Q000008:administration & dosage*; D051379:Mice; D032446:Myoblasts / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D009220:Myositis; D010168:Palmitates / Q000008:administration & dosage; D012038:Regeneration / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage
chemical_list: D010168:Palmitates; D014409:Tumor Necrosis Factor-alpha; D015118:Eicosapentaenoic Acid
keywords: Cytokines; Palmitate; Sarcopenia; Sarcopenic obesity; TNF