title: Relative Contribution of Intramyocellular Lipid to Whole-Body Fat Oxidation Is Reduced With Age but Subsarcolemmal Lipid Accumulation and Insulin Resistance Are Only Associated With Overweight Individuals.
abstract: Insulin resistance is closely related to intramyocellular lipid (IMCL) accumulation, and both are associated with increasing age. It remains to be determined to what extent perturbations in IMCL metabolism are related to the aging process per se. On two separate occasions, whole-body and muscle insulin sensitivity (euglycemic-hyperinsulinemic clamp with 2-deoxyglucose) and fat utilization during 1 h of exercise at 50% VO2max ([U-(13)C]palmitate infusion combined with electron microscopy of IMCL) were determined in young lean (YL), old lean (OL), and old overweight (OO) males. OL displayed IMCL content and insulin sensitivity comparable with those in YL, whereas OO were markedly insulin resistant and had more than twofold greater IMCL in the subsarcolemmal (SSL) region. Indeed, whereas the plasma free fatty acid Ra and Rd were twice those of YL in both OL and OO, SSL area only increased during exercise in OO. Thus, skeletal muscle insulin resistance and lipid accumulation often observed in older individuals are likely due to lifestyle factors rather than inherent aging of skeletal muscle as usually reported. However, age per se appears to cause exacerbated adipose tissue lipolysis, suggesting that strategies to reduce muscle lipid delivery and improve adipose tissue function may be warranted in older overweight individuals.
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, The University of Nottingham, Nottingham, U.K.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Chee
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, The University of Nottingham, Nottingham, U.K.
authors.forename: Chris E
authors.initials: CE
authors.lastname: Shannon
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, The University of Nottingham, Nottingham, U.K.
authors.forename: Aisling
authors.initials: A
authors.lastname: Burns
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Medicine, The University of Nottingham, Nottingham, U.K.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Selby
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Medicine, The University of Nottingham, Nottingham, U.K.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wilkinson
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Medicine, The University of Nottingham, Nottingham, U.K.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Smith
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, The University of Nottingham, Nottingham, U.K.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Greenhaff
authors.affiliation: Medical Research Council/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, The University of Nottingham, Nottingham, U.K. francis.stephens@nottingham.ac.uk.
authors.forename: Francis B
authors.initials: FB
authors.lastname: Stephens
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D015309:Glucose Clamp Technique; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D050356:Lipid Metabolism / Q000502:physiology*; D008055:Lipids / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism*; D050177:Overweight / Q000378:metabolism; D010084:Oxidation-Reduction; D055815:Young Adult
chemical_list: D008055:Lipids