Abstract 9110: Elevated Glucose Increases ATP-Binding Cassette Transporter A1 mRNA Expression in Human Leukocytes and Murine Bone Marrow-Derived Macrophages and Decreases Cholesterol Efflux

Abstract

Background: Individuals with diabetes are at increased CVD risk. Limited evidence suggests that this is partially attributed to hyperglycemic suppression of macrophage ATP-binding cassette (ABC) transporter mediated cholesterol efflux. The relationship between glucose concentrations and expression of ABC-transporters (ABCA1 and ABCG1) was assessed in human monocytes and leukocytes (study 1) and murine bone marrow-derived macrophages (BMDM) as well as cholesterol efflux in BMDM (study 2). Methods: Ten healthy subjects (4F/6M, 50-85 yrs, BMI 25-35 kg/m²) were recruited for study 1. At baseline, 1- and 2-hour post oral glucose challenge (50 g glucose), RNA was extracted from blood leukocytes (Paxgene RNA kit) and from monocytes isolated by magnetic cell sorting to assess ABC-transporter mRNA expression. For study 2, bone marrow cells were isolated from C57BL/6 mice and differentiated to BMDM with macrophage-colony stimulating factor. BMDM were stimulated with a 20mmol/L challenge of D- or L-glucose and/or 5mmol/L D-glucose (control), 16 hrs, followed by exposure to oxLDL (25 ug/mL, 24 hrs). Triglyceride (TG) and cholesteryl ester (CE) accumulation, ABC-transporter mRNA and protein expression, as well as HDL-mediated cholesterol efflux were evaluated. Results: A glucose challenge caused a 35% rise in human leukocyte ABCA1 mRNA expression after 1- (p=0.003) and 2- (p=0.020) hrs, but no significant effect on leukocyte ABCG1, or monocyte ABCA1 or ABCG1. Elevated glucose concentrations in BMDM culture media led to a 120% increase in ABCA1 mRNA (p=0.001) but no significant effects on expression of ABCG1 transcripts, ABCA1 or ABCG1 protein, or on intracellular TG or CE accumulation. Elevated glucose suppressed HDL-mediated cholesterol efflux by 10% (p=0.005). Conclusion: These results support the concept that hyperglycemia attenuates HDL-mediated cholesterol efflux from macrophages, potentially contributing to diabetes-associated CVD. Moreover, in the absence of altered ABC-transporter protein expression, our data suggest that hyperglycemia impairs HDL-mediated cholesterol efflux perhaps by attenuating transporter activity. Correspondingly, we found human monocyte ABC-transporter gene expression unresponsive to a glucose challenge.