title: Diminished anabolic signaling response to insulin induced by intramuscular lipid accumulation is associated with inflammation in aging but not obesity.
abstract: The loss of skeletal muscle mass is observed in many pathophysiological conditions, including aging and obesity. The loss of muscle mass and function with aging is defined as sarcopenia and is characterized by a mismatch between skeletal muscle protein synthesis and breakdown. Characteristic metabolic features of both aging and obesity are increases in intramyocellular lipid (IMCL) content in muscle. IMCL accumulation may play a mechanistic role in the development of anabolic resistance and the progression of muscle atrophy in aging and obesity. In the present study, aged and high-fat fed mice were used to determine mechanisms leading to muscle loss. We hypothesized the accumulation of bioactive lipids in skeletal muscle, such as ceramide or diacylglycerols, leads to insulin resistance with aging and obesity and the inability to activate protein synthesis, contributing to skeletal muscle loss. We report a positive association between bioactive lipid accumulation and the loss of lean mass and muscle strength. Obese and aged animals had significantly higher storage of ceramide and diacylglycerol compared with young. Furthermore, there was an attenuated insulin response in components of the mTOR anabolic signaling pathway. We also observed differential increases in the expression of inflammatory cytokines and the phosphorylation of IκBα with aging and obesity. These data challenge the accepted role of increased inflammation in obesity-induced insulin resistance in skeletal muscle. Furthermore, we have now established IκBα with a novel function in aging-associated muscle loss that may be independent of its previously understood role as an NF-κB inhibitor.
authors.affiliation: Nutrition, Exercise Physiology and Sarcopenia Laboratory, Tufts University, Boston, Massachusetts; and donato.rivas@tufts.edu.
authors.forename: Donato A
authors.initials: DA
authors.lastname: Rivas
authors.affiliation: Nutrition, Exercise Physiology and Sarcopenia Laboratory, Tufts University, Boston, Massachusetts; and.
authors.forename: Devin J
authors.initials: DJ
authors.lastname: McDonald
authors.affiliation: Nutrition, Exercise Physiology and Sarcopenia Laboratory, Tufts University, Boston, Massachusetts; and.
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Rice
authors.affiliation: Nutrition, Exercise Physiology and Sarcopenia Laboratory, Tufts University, Boston, Massachusetts; and.
authors.forename: Prashanth H
authors.initials: PH
authors.lastname: Haran
authors.affiliation: Mass Spectrometry Unit; Jean Mayer U.S. Department of Agriculture, Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Dolnikowski
authors.affiliation: Nutrition, Exercise Physiology and Sarcopenia Laboratory, Tufts University, Boston, Massachusetts; and.
authors.forename: Roger A
authors.initials: RA
authors.lastname: Fielding
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D007328:Insulin / Q000008:administration & dosage; D007333:Insulin Resistance; D050356:Lipid Metabolism / Q000187:drug effects*; D008055:Lipids / Q000096:biosynthesis; D008297:Male; D008660:Metabolism / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009220:Myositis / Q000378:metabolism; D009765:Obesity / Q000378:metabolism*; D055948:Sarcopenia / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D007328:Insulin; D008055:Lipids
keywords: aging; ceramide; diacylglycerol; inflammation; insulin; intramuscular lipids; obesity; sarcopenia