title: Controlling skeletal muscle CPT-I malonyl-CoA sensitivity: the importance of AMPK-independent regulation of intermediate filaments during exercise.
abstract: The obligatory role of carnitine palmitoyltransferase-I (CPT-I) in mediating mitochondrial lipid transport is well established, a process attenuated by malonyl-CoA (M-CoA). However, the necessity of reducing M-CoA concentrations to promote lipid oxidation has recently been challenged, suggesting external regulation on CPT-I. Since previous work in hepatocytes suggests the involvement of the intermediate filament fraction of the cytoskeleton in regulating CPT-I, we investigated in skeletal muscle if CPT-I sensitivity for M-CoA inhibition could be regulated by the intermediate filaments, and whether AMP-activated protein kinase (AMPK) could be involved in this process. Chemical disruption (3,3'-iminodipropionitrile, IDPN) of the intermediate filaments did not alter mitochondrial respiration or sensitivity for numerous substrates (palmitoyl-CoA, ADP, palmitoyl carnitine and pyruvate). In contrast, IDPN reduced CPT-I sensitivity for M-CoA inhibition in permeabilized muscle fibers, identifying M-CoA kinetics as a specific target for intermediate filament regulation. Importantly, exercise mimicked the effect of IDPN on M-CoA sensitivity, suggesting that intermediate filament disruption in vivo is physiologically important for CPT-I regulation. To ascertain a potential mechanism, since AMPK is activated during exercise, AMPK β1β2-KO mice were utilized in an attempt to ablate the observed exercise response. Unexpectedly, these mice displayed drastic attenuation in resting M-CoA sensitivity, such that exercise and IDPN could not further alter M-CoA sensitivity. These data suggest that AMPK is not required for the regulation of the intermediate filament interaction with CPT-I. Altogether, these data highlight that M-CoA sensitivity is important for regulating mitochondrial lipid transport. Moreover, M-CoA sensitivity appears to be regulated by intermediate filament interaction with CPT-I, a process that is important when metabolic homeostasis is challenged.
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Rd East, Guelph, Ontario, Canada N1G 2W1 pmiotto@uoguelph.ca ghollowa@uoguelph.ca.
authors.forename: Paula M
authors.initials: PM
authors.lastname: Miotto
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.|Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Steinberg
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Rd East, Guelph, Ontario, Canada N1G 2W1 pmiotto@uoguelph.ca ghollowa@uoguelph.ca.
authors.forename: Graham P
authors.initials: GP
authors.lastname: Holloway
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D007382:Intermediate Filaments / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008316:Malonyl Coenzyme A / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008931:Mitochondria, Muscle / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D010172:Palmitoylcarnitine / Q000378:metabolism; D010805:Physical Conditioning, Animal; D019289:Pyruvic Acid / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity
chemical_list: D009570:Nitriles; D010171:Palmitoyl Coenzyme A; D010172:Palmitoylcarnitine; C008110:3,3'-iminodipropionitrile; D008316:Malonyl Coenzyme A; D000244:Adenosine Diphosphate; D019289:Pyruvic Acid; C558401:CPT1B protein, mouse; D002334:Carnitine O-Palmitoyltransferase; D055372:AMP-Activated Protein Kinases
keywords: AMPK; CPT-I; intermediate filament; lipid metabolism; mitochondrial respiration; muscle metabolism