The MicroRNA miR-696 is Regulated by SNARK and Reduces Mitochondrial Activity in Mouse Skeletal Muscle Through Pgc1α Inhibition. André L. Queiroz, Sarah J. Lessard, Amanda T. Ouchida, Hygor N. Araujo, Dawit A. Gonçalves, Dimitrius Santiago Simões Guimarães, Bruno G. Teodoro, Kawai So, Enilza M. Espreafico, Luciane C. Alberici, Isis Carmo Kettelhut, Laurie J. Goodyear, Leonardo R. Silveira.
MicroRNAs (miRNA) are known to regulate expression of genes involved in severalphysiological processes including metabolism, mitochondrial biogenesis, proliferation, differentiation, and cell death. Using “in silico” analyses, we identified 219 unique miRNAs that potentially bind to the 3’UTR region of a critical mitochondrial regulator, the peroxisome proliferator-activated receptor gamma coactivator (PGC) 1 alpha (Pgc1α). Out of the 219 candidate miRNAs, miR-696 had one of the highest interactions at the 3’UTR of Pgc1α, suggesting that miR-696 may be involved in the regulation of Pgc1α. Consistent with this hypothesis, we found that miR-696 was highly expressed in the skeletal muscle of both STZinduced diabetic mice and chronic high-fat fed mice. C2C12 muscle cells exposed to palmitic acid also exhibited higher expression of miR-696. This increased expression corresponded with reduced expression of oxidative metabolism genes and reduced mitochondrial respiration. Importantly, reduction of miR-696 reversed decreases in mitochondrial activity in response to palmitic acid. Using C2C12 cells treated with the AMP-activated protein kinase (AMPK) activator AICAR and skeletal muscle from AMPKα2 dominant negative (DN) mice, we found that the signaling mechanism regulating miR-696 does not involve AMPK. In contrast, overexpression of SNF1-AMPK-related kinase (SNARK) in C2C12 cells increased miR-696 transcription while the knockdown of SNARK significantly decreased miR-696. Moreover, muscle-specific transgenic mice overexpressing SNARK exhibited lower expression of Pgc1α, elevated levels of miR-696, and reduced amounts of spontaneous activity. Our findings demonstrate that metabolic stress increases miR-696 expression in skeletal muscle cells, which in turn inhibits Pgc1α, reducing mitochondrial function. SNARK plays a role in this process as a metabolic stress signaling molecule inducing the expression of miR-696.
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