title: Adiponectin is sufficient, but not required, for exercise-induced increases in the expression of skeletal muscle mitochondrial enzymes.
abstract: Adiponectin (Ad) has been proposed to be a regulator of mitochondrial biogenesis in skeletal muscle, and necessary for exercise-induced increases in mitochondrial content. We first confirmed that Ad could acutely increase the expression of mitochondrial proteins during a 10 h incubation in isolated soleus and extensor digitorum longus (EDL) muscles. Next, we further examined the role of Ad as a regulator of mitochondrial content using Ad knockout (AdKO) mice. The AdKO animals showed no differences in resting VO2, respiratory exchange ratio, or in time to exhaustion during exercise when compared to wild-type (WT) mice. There was a reduction in resting palmitate oxidation in isolated soleus from AdKO animals (-23%, P < 0.05) but not EDL, and 5-aminoimidazole-4-carboxamide (AICAR)-stimulated palmitate oxidation was similar in both genotypes regardless of muscle. There were no differences in protein markers of mitochondrial content (COX4, CORE1, CS, PDHE1α) in red and white gastrocnemius between WT and AdKO animals. A single bout of treadmill running increased the phosphorylation of AMP-activated protein kinase (AMPK) and the mRNA expression of mitochondrial proteins in red and white gastrocnemius in both WT and AdKO animals, with no differences between genotypes. Finally, 8 weeks of chronic exercise training increased the protein content of mitochondrial markers similarly (∼25-35%) in red gastrocnemius from both WT and AdKO mice. Collectively, our results demonstrate that the absence of Ad is not accompanied by reductions in mitochondrial protein content, or a reduction in aerobic exercise capacity. We conclude that Ad is not required for the maintenance of mitochondrial content, or for exercise-induced increases in skeletal muscle mitochondrial proteins.
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada, N1G2W1.
authors.forename: Ian R W
authors.initials: IR
authors.lastname: Ritchie
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada, N1G2W1.
authors.forename: Tara L
authors.initials: TL
authors.lastname: MacDonald
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada, N1G2W1.
authors.forename: David C
authors.initials: DC
authors.lastname: Wright
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada, N1G2W1 ddyck@uoguelph.ca.
authors.forename: David J
authors.initials: DJ
authors.lastname: Dyck
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D052242:Adiponectin / Q000502:physiology*; D000818:Animals; D015870:Gene Expression / Q000187:drug effects; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000502:physiology*; D012420:Running / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D052242:Adiponectin; D024101:Mitochondrial Proteins; D048051:p38 Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases