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.