Suppression of CRTC2-mediated hepatic gluconeogenesis by TRAF6 contributes to hypoglycemia in septic shock

Abstract

Although hypoglycemia has been documented as a major cause of high mortality in the setting of septic shock, the mechanism of hypoglycemia in infection has not been clearly determined. Hepatic gluconeogenesis serves as an important mechanism to maintain glucose levels under physiological conditions and CREB coactivator CRTC2 plays an important role in regulating gluconeogenic gene expression. Here, we show that triggering of the Toll-like receptor 4 pathway in response to endotoxin lipopolysaccharide (LPS) inhibits gluconeogenic gene expression and hepatic glucose output by blocking CRTC2 activation. Interleukin-1β (IL-1β) is found to disrupt gluconeogenic gene expression via the activation of the E3 ubiquitin ligase TRAF6, a key component of the Toll-like receptor 4 signaling pathway that associates with and ubiquitinates CRTC2. TRAF6 promotes the K63-linked ubiquitination of CRTC2, a modification that blocks binding of calcineurin at an adjacent calcineurin-binding site, thereby disrupting CRTC2 dephosphorylation in response to glucagon signals. Mutation of TRAF6-binding sites or ubiquitination site in CRTC2 rescues hepatic gluconeogenesis in LPS-challenged mice. These results suggest that pro-inflammatory signals intersect with the CRTC2 pathway in liver, thus contributing to hypoglycemia caused by infection.