Islet Stellate Cells Regulate Insulin Secretion via Wnt5a in Min6 Cells

Abstract

Background. Type 2 diabetes mellitus is a serious public health problem worldwide. Accumulating evidence has shown that β-cell dysfunction is an important mechanism underlying diabetes mellitus. The changes in the physiological state of islet stellate cells (ISCs) and the effects of these cells on β cell function play an important role in the development of diabetes. This study aimed at elucidating the mechanism by which ISCs regulate insulin secretion from Min6 cells via the Wnt5a protein. Methods. Glucose-stimulated insulin secretion (GSIS) from Min6 cells was examined by estimating the insulin levels in response to high glucose challenge after culture with ISC supernatant or exogenous Wnt5a. Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) analyses were used to observe changes in the β-catenin, receptor tyrosine kinase-like orphan receptor 2 (Ror2), Ca (2+)/calmodulin (CaM)-dependent protein kinase II (CamKII), forkhead box O1 (FoxO1), pancreatic and duodenal homeobox 1 (PDX1), glucose transporter 2 (Glut2), insulin, and Cask mRNA and protein levels in the Wnt and insulin secretory pathways. Flow cytometry was used to confirm the intracellular Ca2+ concentration in Min6 cells. Results. We observed a significant increase in insulin secretion from Min6 cells cocultured in vitro with supernatant from db/m mouse ISCs compared to that from Min6 cells cocultured with supernatant from db/db mouse ISCs; The intracellular Ca2+ concentration in Min6 cells increased in cultured in vitro with supernatant from db/m mouse ISCs and exogenous Wnt5a compared to that from control Min6 cells. Culture of Min6 cells with exogenous Wnt5a caused a significant increase in pCamKII, pFoxO1, PDX-1, and Glut2 levels compared to those in Min6 cells cultured alone; this treatment further decreased Ror2 and Cask expression but did not affect β-catenin expression. Conclusion. ISCs regulate insulin secretion from Min6 cells through the Wnt5a protein-induced Wnt-calcium and FoxO1-PDX1-GLUT2-insulin signalling cascades.