Lower Expression Of Pkaα Impairs Insulin Secretion In Islets Isolated From Low-density Lipoprotein Receptor (ldlr -/-) Knockout Mice

Hypercholesterolemic low-density lipoprotein receptor knockout mice (LDLR -/-) show normal whole-body insulin sensitivity, but impaired glucose tolerance due to a reduced insulin secretion in response to glucose. Here, we investigate the possible mechanisms involved in such a defect in isolated LDLR -/- mice islets. Low-fat chow-fed female and male mice aged 20 weeks, LDLR -/- mice, and wild-type (WT) mice were used in this study. Static insulin secretion, cytoplasmatic Ca 2+ analysis, and protein expression were measured in islets isolated from LDLR -/- and WT mice. At basal (2.8 mmol/L) and stimulatory (11.1 mmol/L) glucose concentrations, the insulin secretion rates induced by depolarizing agents such as KCl, l-arginine, and tolbutamide were significantly reduced in LDLR -/- when compared with control (WT) islets. In addition, KCl-induced Ca 2+ influx at 2.8 mmol/L glucose was lower in LDLR -/- islets, suggesting a defect downstream of the substrate metabolism step of the insulin secretion pathway. Insulin secretion induced by the protein kinase A (PKA) activators forskolin and 3-isobutyl-1-methyl-xanthine, in the presence of 11.1 mmol/L glucose, was lower in LDLR -/- islets and was normalized in the presence of the protein kinase C pathway activators carbachol and phorbol 12-myristate 13-acetate. Western blotting analysis showed that phospholipase Cβ 2 expression was increased and PKAα was decreased in LDLR -/- compared with WT islets. 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