Cholesterol reduction ameliorates glucose-induced calcium handling and insulin secretion in islets from low-density lipoprotein receptor knockout mice

Abstract Aims/hypothesis Changes in cellular cholesterol level may contribute to beta cell dysfunction. Islets from low density lipoprotein receptor knockout (LDLR −/− ) mice have higher cholesterol content and secrete less insulin than wild-type (WT) mice. Here, we investigated the association between cholesterol content, insulin secretion and Ca 2 + handling in these islets. Methods Isolated islets from both LDLR −/− and WT mice were used for measurements of insulin secretion (radioimmunoassay), cholesterol content (fluorimetric assay), cytosolic Ca 2 + level (fura-2AM) and SNARE protein expression (VAMP-2, SNAP-25 and syntaxin-1A). Cholesterol was depleted by incubating the islets with increasing concentrations (0–10 mmol/l) of methyl-beta-cyclodextrin (MβCD). Results The first and second phases of glucose-stimulated insulin secretion (GSIS) were lower in LDLR −/− than in WT islets, paralleled by an impairment of Ca 2 + handling in the former. SNAP-25 and VAMP-2, but not syntaxin-1A, were reduced in LDLR −/− compared with WT islets. Removal of excess cholesterol from LDLR −/− islets normalized glucose- and tolbutamide-induced insulin release. Glucose-stimulated Ca 2 + handling was also normalized in cholesterol-depleted LDLR −/− islets. Cholesterol removal from WT islets by 0.1 and 1.0 mmol/l MβCD impaired both GSIS and Ca 2 + handling. In addition, at 10 mmol/l MβCD WT islet showed a loss of membrane integrity and higher DNA fragmentation. Conclusion Abnormally high (LDLR −/− islets) or low cholesterol content (WT islets treated with MβCD) alters both GSIS and Ca 2 + handling. Normalization of cholesterol improves Ca 2 + handling and insulin secretion in LDLR −/− islets.