Adipocyte-Specific IKKβ Signaling Suppresses Adipose Tissue Inflammation through an IL-13-Dependent Paracrine Feedback Pathway

Adipose tissue inflammation is one pathway shown to mediate insulin resistance in obese humans and rodents. Obesity induces dynamic cellular changes in adipose tissue to increase proinflammatory cytokines and diminish anti-inflammatory cytokines. However, we have found that anti-inflammatory interleukin-13 (IL-13) is unexpectedly induced in adipose tissue of obese humans and high-fat diet (HFD)-fed mice, and the source of IL-13 is primarily the adipocyte. Moreover, HFD-induced proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha) and IL-1 beta mediate IL-13 production in adipocytes in an IKKb-dependent manner. In contrast, adipocyte- specific IKK beta-deficient mice show diminished IL-13 expression and enhanced inflammation after HFD feeding, resulting in a worsening of the insulinresistant state. Together these data demonstrate that although IKK beta activates the expression of proinflammatory mediators, in adipocytes, IKKb signaling also induces the expression of the anti-inflammatory cytokine IL-13, which plays a unique protective role by limiting adipose tissue inflammation and insulin resistance.