TLR13 contributes to skeletal muscle atrophy by increasing insulin resistance in chronic kidney disease.

objectivesInsulin resistance in chronic kidney disease (CKD) stimulates muscle wasting, but the molecular processes behind the resistance are undetermined. However, inflammation in skeletal muscle is implicated in the pathogenesis of insulin resistance and cachexia. Toll-like receptors (TLRs) are known to regulate local innate immune responses, and microarray data have shown that Tlr13 is upregulated in the muscles of mice with CKD, but the relevance is unknown. MATERIALS AND

methodsWe performed in vitro experiments in C2C12 myotubes and constructed a CKD murine model using subtotal nephrectomy to conduct experiments in vivo.

resultsTlr13 expression was stimulated in C2C12 myotubes treated with uremic serum. The expression of Tlr13 was also upregulated in the tibialis anterior muscles of mice with CKD. Tlr13 knockdown with siRNAs in skeletal muscle cells decreased insulin resistance despite the inclusion of uremic serum. This led to increased levels of p-AKT and suppression of protein degradation. Using immunofluorescence staining and coimmunoprecipitation assay, we found that TLR13 recruits IRF3, which activates Irf3 expression, resulting in decreased AKT activity. Moreover, insulin resistance and proteolysis are re-induced by Irf3 overexpression under Tlr13 deletion.

conclusionsOur results indicate that TLR13 is involved in CKD-mediated insulin resistance in muscle. In catabolic conditions where insulin signaling is impaired, targeting TLR13 may improve insulin sensitivity and prevent muscle atrophy.