title: Lower expression of PKAα impairs insulin secretion in islets isolated from low-density lipoprotein receptor (LDLR(-/-)) knockout mice.
abstract: 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. Results indicate that the lower insulin secretion observed in islets from LDLR(-/-) mice at postprandial levels of glucose can be explained, at least in part, by the reduced expression of PKAα in these islets.
authors.affiliation: Centro de Ciências Biológicas e da Saúde, Universidade Estadual do Oeste do Paraná (UNIOESTE), 85810-119 Cascavel, PR, Brazil.
authors.forename: Maria Lúcia
authors.initials: ML
authors.lastname: Bonfleur
authors.forename: Rosane Aparecida
authors.initials: RA
authors.lastname: Ribeiro
authors.forename: Sandra Lucinei
authors.initials: SL
authors.lastname: Balbo
authors.forename: Emerielle Cristine
authors.initials: EC
authors.lastname: Vanzela
authors.forename: Everardo Magalhães
authors.initials: EM
authors.lastname: Carneiro
authors.forename: Helena Coutinho Franco
authors.initials: HC
authors.lastname: de Oliveira
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Boschero
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005215:Fasting / Q000378:metabolism; D005260:Female; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D051571:Protein Kinase C-alpha / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D007328:Insulin; D011973:Receptors, LDL; D017868:Cyclic AMP-Dependent Protein Kinases; D051571:Protein Kinase C-alpha; D002118:Calcium