Cytokine Signaling Co-opts the CREB/CRTC Pathway in Obesity

Obesity stimulates the infiltration of adipose tissue by innate immune cells, which in turn promote insulin resistance via the NFkB mediated induction of pro-inflammatory cytokines, which interfere with triglyceride metabolism. The cAMP responsive factor CREB has also been implicated in adipose tissue inflammation and insulin resistance, although the underlying mechanism is unclear. Here, we show that high fat diet (HFD) feeding triggers activation of the CREB cofactors CRTC2 and CRTC3, which bind to CREB and mediate induction of CXCL1 and other cytokine genes in cooperation with NFkB. HFD feeding reduced adipocyte C/EBPa expression in adipose, leading to decreases in the expression of Salt Inducible Kinase 2 (SIK2), which otherwise phosphorylates and sequesters CRTCs in the cytoplasm. Depletion of SIK2 in adipose led to dephosphorylation of CRTC2 and CRTC3 (CRTC2/3) and to the induction of CXCL1 and other cytokine genes in adipocytes. Indeed, CRTC2/3 were found to stimulate the expression of a subset of cellular genes cooperatively with NF-kB in adipocytes. Knockout of both CRTC2 and CRTC3 in adipose decreased the expression of CXCL1/2 and thereby reduced neutrophil and macrophage infiltration. As depletion of CXCL1/2, with neutralizing antiserum or by KO of the CXCL1 gene restored glucose tolerance and insulin sensitivity in the setting of diet induced obesity, our results demonstrate that NF-kB and CREB/CRTC pathways modulate adipose tissue function in part via cooperative effects on target gene expression. Overall design: ChIP-seq for CRTC2, p65, Histone H3 Acetyl K27 in 3T3L1 adipocytes untreated or treated with 10 uM forskolin, TNFa or both.