FAM3C activates HSF1 to suppress hepatic gluconeogenesis and attenuate hyperglycemia of type 1 diabetic mice.

FAM3C, a member of FAM3 gene family, has been shown to improve insulin resistance and hyperglycemia in obese mice. This study further determined whether FAM3C functions as a hepatokine to suppress hepatic gluconeogenesis of type 1 diabetic mice. In STZ-induced type 1 diabetic mouse liver, the FAM3C-HSF1-CaM signaling axis was repressed. Hepatic FAM3C overexpression activated HSF1-CaM-Akt pathway to repress gluconeogenic gene expression and ameliorate hyperglycemia of type 1 diabetic mice. Moreover, hepatic HSF1 overexpression also activated CaM-Akt pathway to repress gluconeogenic gene expression and improve hyperglycemia of type 1 diabetic mice. Hepatic FAM3C and HSF1 overexpression had little effect on serum insulin levels in type 1 diabetic mice. In cultured hepatocytes, conditioned medium of Ad-FAM3C-infected cells induced Akt phosphorylation. Moreover, Akt activation and gluconeogenesis repression induced by FAM3C overexpression were reversed by the treatment with anti-FAM3C antibodies. Treatment with recombinant FAM3C protein induced Akt activation in a HSF1- and CaM-dependent manner in cultured hepatocytes. Furthermore, recombinant FAM3C protein repressed gluconeogenic gene expression and gluconeogenesis by inactivating FOXO1 in a HSF1-dependent manner in cultured hepatocytes. In conclusion, FAM3C is a new hepatokine that suppresses hepatic gluconeogenic gene expression and gluconeogenesis independent of insulin by activating HSF1-CaM-Akt pathway.