Abstract 523: Regulation of Pancreatic β-cell Gene Expression and Function by ABCA1 and ABCG1

Abstract

Background: Loss-of-function mutations in the ABCA1 gene cause beta cell dysfunction in humans. Insulin secretion is impaired and glucose metabolism is adversely affected in mice with conditional deletion of ABCA1 in beta cells and in ABCG1 knockout mice. These effects are exacerbated in mice with conditional beta cell ABCA1 deletion plus global ABCG1 deficiency. To identify key beta cell pathways regulated by ABCA1 and ABCG1, we generated mice with beta cell-specific deletion of ABCA1 and ABCG1 (ABCA1 β-cell-/- /ABCG1 βcell-/- DKO mice). Aim: Identification of genes in key beta cell metabolic and signal transduction pathways that are regulated by ABCA1 and ABCG1. Methods: Islets were isolated from 16 week old chow fed ABCA1 β-cell-/- /ABCG1 β-cell-/- DKO mice. mRNA was extracted and subjected to Affymetrix GeneChip Mouse Gene ST 2.0 analysis, followed by Partek Genomics Suite and Ingeunity Pathway analysis. Islet cholesterol levels were determined by HPLC. Plasma and HDL cholesterol levels were measured enzymatically. Results: Total plasma cholesterol and HDL cholesterol levels in ABCA1 β-cell-/- /ABCG1 β-cell-/- DKO and Abca1fl/flAbcg1f/fl (control) mice were comparable. Islet cholesterol levels in the ABCA1 β-cell-/- /ABCG1 β-cell-/- DKO mice were increased relative to control (19.2±1.9 vs 8.7±1.0 μg cholesterol/μg protein, p<0.05). A total of 4216 genes were differentially expressed in the ABCA1 β-cell-/- /ABCG1 β-cell-/- DKO mouse islets compared to islets from control mice. Using more stringent criteria (1.2-fold change, p <0.05), 2617 down-regulated and 1599 up-regulated genes were identified in ABCA1 β-cell-/- /ABCG1 β-cell-/- DKO islets compared to control islets. Functional enrichment analysis of the differentially expressed genes revealed that ABCA1 and ABCG1 regulate pathways involved in cholesterol metabolism ( Hmgcr, Insing1, Ldlr, Srebf2 and ApoB ), insulin signaling/glucose metabolism ( Akt1, Fasn, Pik3r1, Irs1, Slc2a1 and Slc2a2 ) and inflammation ( Gbp11, Sftpd ) in beta cells. Differential expression of these genes was validated by real-time PCR. Conclusions: ABCA1 and ABCG1 regulate islet cholesterol levels as well as genes involved in insulin signaling, inflammation and glucose and cholesterol metabolism in beta cells.