Betatrophin expression is promoted in obese hyperinsulinemic type 2 but not type 1 diabetic mice

Regeneration of pancreatic β-cell mass benefits both type 1 and type 2 diabetic patients. A recent study identified betatrophin as a β-cell proliferation factor. However, the expressional regulation of betatrophin remains less defined. In this study, we aimed to clarify the regulation of betatrophin expression in obese type 2 vs. type 1 diabetes model animals. We experimented type 2 diabetes models, diet-induced-obesity (DIO) mice and db/db mice, and type 1 diabetes models, C57B6 mice receiving streptozotocin (STZ) or 70% pancreatectomy to destroy or remove β-cells. Serum betatrophin levels and betatrophin mRNA expressions in the liver, white adipose tissue (WAT) and brown adipose tissue (BAT) were measured. In DIO mice and db/db mice, serum betatrophin and betatrophin mRNA expressions in the liver, WAT and BAT were elevated in parallel with increases in body weight and plasma insulin. These elevated betatrophin mRNA expressions were not altered by treatment with SGLT2 inhibitor that ameliorated hyperglycemia. In pancreatectomized mice, betatrophin expression in WAT decreased in parallel with reductions in weight and insulin. In STZ-treated mice, betatrophin expressions in the liver, WAT and BAT were reduced. However, when the mouse liver slices were cultured with STZ, betatrophin expression was significantly reduced, indicating a direct action of STZ on the liver. These results indicate that the expression of betatrophin is upregulated in the liver, WAT and BAT in obese hyperinsulinemic type 2 diabetes but decreased in WAT in hypoinsulinemic type 1 diabetes, suggesting its positive correlation with body weight and plasma insulin but not blood glucose.