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Title: A novel amino acid and metabolomics signature in mice overexpressing muscle uncoupling protein 3

item AGUER, CELINE - University Of Ottawa
item PICCOLO, BRIAN - Arkansas Children'S Nutrition Research Center (ACNC)
item FIEHN, OLIVER - University Of California
item Ferruzzi, Mario
item HARPER, MARY-ELLEN - University Of Ottawa

Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2016
Publication Date: 11/10/2016
Citation: Aguer, C., Piccolo, B., Fiehn, O., Adams, S.H., Harper, M. 2016. A novel amino acid and metabolomics signature in mice overexpressing muscle uncoupling protein 3. Journal of Federation of American Societies for Experimental Biology. doi:10.1096/fj.201600914R.

Interpretive Summary: Obesity is a major health concern in the U.S. and the world, and obesity during pregnancy increases obesity and metabolic disease risk in offspring. Increasing physical activity and exercise, even without a change in body weight, can ameliorate many of the untoward health impacts of obesity, but the mechanisms by which increased muscle work and fat combustion improve health remain to be fully established. Skeletal muscle makes up at least 20% of total body weight, so factors within this tissue have the potential to contribute greatly toward total energy requirements and generation of signals that impact physiology body-wide. A protein called uncoupling protein 3 (UCP3) is primarily found in skeletal muscle and has been shown to alter how energy is used in that tissue; however, it is still not clearly understood how this happens. We used an animal model with increased muscle UCP3 to investigate hundreds of metabolites in the muscle, liver and blood to identify patterns that would suggest how UCP3 affects energy pathways in the muscle and beyond. The animals also went through endurance-training and underwent a bout of exercise in order to make sure that the UCP3 protein was adequately stimulated. Surprisingly, a bout of exercise resulted in a substantial decrease in muscle amino acids from animals that had more UCP3. This is noteworthy because UCP3 has always been shown to alter how fat is used for energy in muscle and no report had suggested that protein metabolism can be altered. We also found evidence that a major antioxidant that the body makes is altered in animals with more UCP3 in muscle. This is also noteworthy because one of the proposed mechanisms of UCP3 function is that it helps protect muscle from excessive oxidative stress. The novel results from this study provide point to UCP3 as an important protein that contributes to muscle energy regulation during exercise and at rest; this can have implications for optimizing exercise intervention to promote muscle fitness and promote health.

Technical Abstract: Uncoupling protein 3 (UCP3) is highly expressed in skeletal muscle and is known to lower mitochondrial reactive oxygen species and promote fatty acid oxidation; however, the global impact of UCP3 activity on skeletal muscle and whole body metabolism has not been extensively studied. We utilized untargeted metabolomics to identify novel metabolites that distinguish mice overexpressing UCP3 in muscle, both at rest and following exercise regimens that challenged muscle metabolism to potentially unmask subtle phenotypes. Male wildtype (WT) and muscle-specific UCP3-overexpressing transgenic (UCP3 Tg) C57BL/6J mice were compared with or without a 5-week endurance training protocol, at rest or following an acute exercise bout (EB). Skeletal muscle, liver, and plasma samples were analyzed by GC-QTOFMS. Discriminant metabolites were considered if within the top 99th percentile of variable importance measurements obtained from partial least squares-discriminant analysis models. A total of 80 metabolites accurately discriminated UCP3 Tg mice from WT when modeled within a specific exercise condition (i.e., untrained/rested, endurance-trained/rested, untrained/EB, and endurance-trained/EB). Major findings include, 1) several amino acids and amino acid derivatives in skeletal muscle and plasma of UCP3 Tg mice (e.g., Asp, Glu, Lys, Tyr, Ser, Met) were significantly reduced after an EB, 2) metabolites associated with skeletal muscle glutathione/Met/Cys metabolism (2-hydroxybutanoic acid, oxoproline, Gly, and Glu) were altered in UCP3 Tg mice across all training and exercise conditions, and 3) muscle metabolite indices of dehydrogenase activity were increased in UCP3 Tg mice, suggestive of a shift in tissue NADH/NAD+ ratio. The results indicate that mitochondrial UCP3 activity impacts metabolism well beyond fatty acid oxidation, regulating biochemical pathways associated with amino acid metabolism and redox status. That select metabolites were altered in livers of UCP3 Tg mice highlights that changes in muscle UCP3 activity can also impact other organ systems, presumably through changes in systemic metabolite trafficking.