title: Increased intramyocellular lipids but unaltered in vivo mitochondrial oxidative phosphorylation in skeletal muscle of adipose triglyceride lipase-deficient mice.
abstract: Adipose triglyceride lipase (ATGL) is a lipolytic enzyme that is highly specific for triglyceride hydrolysis. The ATGL-knockout mouse (ATGL(-/-)) accumulates lipid droplets in various tissues, including skeletal muscle, and has poor maximal running velocity and endurance capacity. In this study, we tested whether abnormal lipid accumulation in skeletal muscle impairs mitochondrial oxidative phosphorylation, and hence, explains the poor muscle performance of ATGL(-/-) mice. In vivo ¹H magnetic resonance spectroscopy of the tibialis anterior of ATGL(-/-) mice revealed that its intramyocellular lipid pool is approximately sixfold higher than in WT controls (P = 0.0007). In skeletal muscle of ATGL(-/-) mice, glycogen content was decreased by 30% (P < 0.05). In vivo ³¹P magnetic resonance spectra of resting muscles showed that WT and ATGL(-/-) mice have a similar energy status: [PCr], [P(i)], PCr/ATP ratio, PCr/P(i) ratio, and intracellular pH. Electrostimulated muscles from WT and ATGL(-/-) mice showed the same PCr depletion and pH reduction. Moreover, the monoexponential fitting of the PCr recovery curve yielded similar PCr recovery times (τPCr; 54.1 ± 6.1 s for the ATGL(-/-) and 58.1 ± 5.8 s for the WT), which means that overall muscular mitochondrial oxidative capacity was comparable between the genotypes. Despite similar in vivo mitochondrial oxidative capacities, the electrostimulated muscles from ATGL(-/-) mice displayed significantly lower force production and increased muscle relaxation time than the WT. These findings suggest that mechanisms other than mitochondrial dysfunction cause the impaired muscle performance of ATGL(-/-) mice.
authors.affiliation: Department of Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. P.Nunes@rad.umcn.nl
authors.forename: P M
authors.initials: PM
authors.lastname: Nunes
authors.forename: T
authors.initials: T
authors.lastname: van de Weijer
authors.forename: A
authors.initials: A
authors.lastname: Veltien
authors.forename: H
authors.initials: H
authors.lastname: Arnts
authors.forename: M K C
authors.initials: MK
authors.lastname: Hesselink
authors.forename: J F C
authors.initials: JF
authors.lastname: Glatz
authors.forename: P
authors.initials: P
authors.lastname: Schrauwen
authors.forename: C J
authors.initials: CJ
authors.lastname: Tack
authors.forename: A
authors.initials: A
authors.lastname: Heerschap
mesh_terms: D000818:Animals; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000648:ultrastructure; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D006614:Hindlimb; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008049:Lipase / Q000235:genetics / Q000378:metabolism*; D050356:Lipid Metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D008931:Mitochondria, Muscle / Q000378:metabolism* / Q000648:ultrastructure; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009129:Muscle Tonus; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000648:ultrastructure; D010085:Oxidative Phosphorylation; D000217:Acyltransferases
chemical_list: D008049:Lipase; C494445:PNPLA2 protein, mouse; D000217:Acyltransferases