Sema4D deficiency enhances glucose tolerance through GLUT2 retention in hepatocytes

The glucose transporter 2 (GLUT2) is constitutively expressed in pancreatic beta cells and hepatocytes of mice. It is the most important receptor in glucose-stimulated insulin release and hepatic glucose transport. The Sema4D is a signalin receptor on cell membranes. The correlation between Sema4D and GLUT2 has not been reported previously. We investigated whether knockdown of Sema4D could exert a hypoglycemic effect based on the increased GLUT2 expression in Sema4D -/- mice hepatocytes.

The glucose tolerance test and insulin tolerance test in sema4D -/- and sema4D +/+ mice were compared before and after streptozotocin (STZ) injection; the expression of GLUT2 content on the membrane surface of both groups was verified by Western blot. Then, the levels of insulin and C-peptide in the serum of the two groups of mice after STZ injection were measured by ELISA; the differentially expressed mRNAs in the liver of the two groups of mice were analyzed by transcriptomic analysis; then the differences in the expression of GLUT2, glycogen, insulin and glucagon in the two groups of mice were compared by tissue section staining. Finally, metabolomics analysis was performed to analyze the metabolites differentially expressed in the two groups of mice.

First, Sema4D -/- male mice exhibited significantly greater glucose tolerance than wild-type mice in a hyperglycemic environment. Secondly, Sema4D -/- mice had more retained GLUT2 in liver membranes after STZ injection according to an immunofluorescence assay. After STZ injection, Sema4D -/- male mice did not exhibit fasting hyperinsulinemia like wild-type mice. Finally, analysis of metabolomic and immunohistochemical data also revealed that Sema4D -/- mice produce hypoglycemic effects by enhancing the pentose phosphate pathway, but not glycogen synthesis.

Thus, Sema4D may play an important role in the regulation of glucose homeostasis by affecting GLUT2 synthesis.