Conclusions
These findings indicate the important role of IL-6 in the pathogenesis of insulin resistance and further implicate PTP1B as a potential therapeutic target in the treatment of type 2 diabetes.
Methods
We analyzed the impact of IL-6 on insulin action in murine primary myocytes, skeletal muscle cell lines, and mice (wild type and protein-tyrosine phosphatase 1B [PTP1B] deficient).
Objective
Cytokines are elevated in various insulin-resistant states, including type 2 diabetes and obesity, although the contribution of interleukin-6 (IL-6) in the induction of these diseases is controversial. Research design and
Results
IL-6 per se increased glucose uptake by activating serine/threonine protein kinase 11 (LKB1)/AMP-activated protein kinase/protein kinase B substrate of 160 kDa (AS160) pathway. A dual effect on insulin action was observed when myotubes and mice were exposed to this cytokine: additive with short-term insulin (increased glucose uptake and systemic insulin sensitivity) but chronic exposure produced insulin resistance (impaired GLUT4 translocation to plasma membrane and defects in insulin signaling at the insulin receptor substrate 1 [IRS-1] level). Three mechanisms seem to operate in IL-6-induced insulin resistance: activation of c-Jun NH(2)-terminal kinase 1/2 (JNK1/2), accumulation of suppressor of cytokine signaling 3 (socs3) mRNA, and an increase in PTP1B activity. Accordingly, silencing JNK1/2 with either small interfering RNA or chemical inhibitors impaired phosphorylation of IRS-1 (Ser307), restored insulin signaling, and normalized insulin-induced glucose uptake in myotubes. When using a pharmacological approach, liver X receptor agonists overcome IL-6-induced insulin resistance by producing downregulation of socs3 and ptp1b gene expression. Finally, the lack of PTP1B confers protection against IL-6-induced insulin resistance in skeletal muscle in vitro and in vivo, in agreement with the protection against the IL-6 hyperglycemic effect observed on glucose and insulin tolerance tests in adult male mice. Conclusions: These findings indicate the important role of IL-6 in the pathogenesis of insulin resistance and further implicate PTP1B as a potential therapeutic target in the treatment of type 2 diabetes.