MicroRNA-494 regulates mitochondrial biogenesis in skeletal muscle through mitochondrial transcription factor A and Forkhead box j3

Yamamoto H, Morino K, Nishio Y, Ugi S, Yoshizaki T, Kashiwagi A, Maegawa H. MicroRNA-494 regulates mitochondrial biogenesis in skeletal muscle through mitochondrial transcription factor A and Forkhead box j3. Am J Physiol Endocrinol Metab 303: E1419-E1427, 2012. First published October 9, 2012; doi:10.1152/ajpendo.00097.2012.-MicroRNAs (miRNAs) are important posttranscriptional regulators of various biological pathways. In this study, we focused on the role of miRNAs during mitochondrial biogenesis in skeletal muscle. The expression of miR-494 was markedly decreased in murine myoblast C2C12 cells during myogenic differentiation, accompanied by an increase in mtDNA. Furthermore, the expression of predicted target genes for miR-494, including mitochondrial transcription factor A (mtTFA) and Forkhead box j3 (Foxj3), was posttranscriptionally increased during myogenic differentiation. Knockdown of miR-494 resulted in increased mitochondrial content and upregulation of mtTFA and Foxj3 at the protein level. A 3'-untranslated region reporter assay revealed that miR-494 knockdown directly upregulated the luciferase activity of mtTFA and Foxj3. All of these observations were reversed by overexpression of miR-494. Furthermore, the miR-494 content significantly decreased after endurance exercise in C57BL/6J mice, accompanied by an increase in expression of mtTFA and Foxj3 proteins. These results suggest that miR-494 regulates mitochondrial biogenesis by downregulating mtTFA and Foxj3 during myocyte differentiation and skeletal muscle adaptation to physical exercise.