Chronic
inflammation is fundamental for the induction of
insulin resistance in the muscle tissue of vertebrates. Although several
miRNAs are thought to be involved in the development of
insulin resistance, the role of
miRNAs in the association between
inflammation and
insulin resistance in muscle tissue is poorly understood. Herein, we investigated the aberrant expression of
miRNAs by conducting
miRNA microarray analysis of TNF-α-treated mouse C2C12 myotubes. We identified two
miRNAs that were upregulated and six that were downregulated by a >1.5-fold change compared to normal cells. Among the findings, qRT-PCR analysis confirmed that miR-494 is consistently upregulated by TNF-α-induced
inflammation. Overexpression of miR-494 in CHO(IR/IRS1) and C2C12 myoblasts suppressed
insulin action by down-regulating phosphorylations of GSK-3α/β, AS160 and
p70S6K, downstream of Akt. Moreover, overexpression of miR-494 did not regulate TNF-α-mediated
inflammation . Among genes bearing the seed site for miR-494, RT-PCR analysis showed that the expression of Stxbp5, an inhibitor of
glucose transport, was downregulated following miR-494 inhibition. In contrast, the expression of PTEN decreased in the cells analyzed, thus showing that both positive and negative regulators of
insulin action may be simultaneously controlled by miR-494. To investigate the overall effect of miR-494 on
insulin signaling, we performed a PCR array analysis containing 84 genes related to the
insulin signaling pathway, and we observed that 25% of genes were downregulated (P<0.05) and 11% were upregulated (P<0.05). These results confirm that miR-494 might contribute to
insulin sensitivity by positive and negative regulation of the expression of diverse genes. Of note, PCR array data showed downregulation of Slc2A4, a coding gene for Glut4. Altogether, the present study concludes that the upregulation of miR-494 expression by TNF-α-mediated
inflammation exacerbates
insulin resistance. Therefore, we suggest that miR-494 could prove an important target for the diagnosis and
therapy of
inflammation-mediated
insulin resistance in muscle.