CHIP mediates glucagon action on hepatic glucose production via regulating Smad3 ubiquitination.

AIMS

Excessive hepatic glucose production (HGP) driven by glucagon contributes to hyperglycaemia in obesity and type 2 diabetes (T2D), yet the molecular mechanisms underlying this dysregulation remain incompletely defined. This study investigates the role of Smad3 signaling and its regulation by CHIP (Carboxy-terminus of Hsc70-interacting protein) in modulating glucagon action on HGP.

MATERIALS AND METHODS

We examined glucagon signaling and HGP in primary hepatocytes and in high-fat diet (HFD)-induced obese (DIO) mice. Mechanistic studies included hepatic knockdown of CHIP and Smad3, assessment of Smad3 protein stability, ubiquitination assays, and quantification of gluconeogenic gene expression.

RESULTS

We identified Smad3 as a key mediator of glucagon-induced HGP, synergizing with TGF-β1 signaling to enhance gluconeogenic gene G6pc expression in a Foxo1-dependent manner. Glucagon elevated Smad3 protein levels by inhibiting CHIP-mediated ubiquitination, thereby increasing Smad3 stability. CHIP expression was downregulated in the livers of DIO mice. Hepatic CHIP knockdown augmented glucagon-stimulated HGP and increased Smad3 levels, whereas simultaneous knockdown of Smad3 reversed these effects.

CONCLUSIONS

Our findings reveal a novel CHIP-Smad3 regulatory axis that enhances glucagon action on HGP in obesity. Targeting this pathway may offer a new therapeutic strategy for improving glycaemic control in T2D.