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Background: Previous research has suggested that curcumin potentially induces mitochondrial biogenesis in skeletal muscle via increasing cAMP levels. However, the regulatory mechanisms for this phenomenon remain unknown. The purpose of the present study was to clarify the mechanism by which curcumin activates cAMP-related signalling pathways that upregulate mitochondrial biogenesis and respiration in skeletal muscle. Methods: The effect of curcumin treatment (i.p., 100 mg/kg-BW/day for 28 days) on mitochondrial biogenesis was determined in rats. The effects of curcumin and exercise (swimming for 2 h/day for 3 days) on the cAMP signalling pathway were determined in the absence and presence of phosphodiesterase (PDE) or protein kinase A (PKA) inhibitors. Mitochondrial respiration, citrate synthase (CS) activity, cAMP content, and protein expression of cAMP/PKA signalling molecules were analysed. Results: Curcumin administration increased COX-IV protein expression, and CS and complex I activity, consistent with the induction of mitochondrial biogenesis by curcumin. Mitochondrial respiration was not altered by curcumin treatment. Curcumin and PDE inhibition tended to increase cAMP levels with or without exercise. In addition, exercise increased the phosphorylation of PDE4A, whereas curcumin treatment strongly inhibited PDE4A phosphorylation regardless of exercise. Furthermore, curcumin promoted AMPK phosphorylation and PGC-1α deacetylation. Inhibition of PKA abolished the phosphorylation of AMPK. Conclusion: The present results suggest that curcumin increases cAMP levels via inhibition of PDE4A phosphorylation, which induces mitochondrial biogenesis through a cAMP/PKA/AMPK signalling pathway. Our data also suggest the possibility that curcumin utilizes a regulatory mechanism for mitochondrial biogenesis that is distinct from the exercise-induced mechanism in skeletal muscle.

The skeletal muscle occupies about 40% of body mass, one of the largest organs in the body, and it has great plasticity in response to physiological stressors and then alters the contractile and metabolic properties of the muscles. Therefore, healthy status of muscle affects health status of whole body. Mitochondria are abundantly present in mammalian muscle cells, known as the power plants of the cell to generate adenosine triphosphate (ATP) with oxygen. The muscle health depends on the mitochondrial function. In aging and some of metabolic disease states, the mitochondrial function is defected. Some parts of this defect result from lower physical activity and nutritional status. The exercise is well-known as a major strategy to induce mitochondrial biogenesis and upregulation of the mitochondrial function. Recently some nutrients are also suggested as ligands for transcription of the mitochondrial proteins. We also recently found insight of protein interaction with mitochondria that will possibly augment mitochondrial respiratory potential. The present review article introduces some recent research evidences relating to mitochondrial quality control, mitochondrial biogenesis mediated by both exercise and nutrients and an interaction of protein with mitochondria to facilitate mitochondrial respiration.

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