Abstract 14344: The Competing Roles of Glucose and Lipoprotein Lipase on Regulatory Macrophage Function

Abstract

Background: Atherosclerosis causes more death than any other pathophysiologic process. It has a well-established inflammatory, macrophage(MФ)-mediated component which can be stoked by uncontrolled diabetes. However, there are also protective, regulatory MФ processes that can help quell atherosclerosis. Lipoprotein Lipase (LPL) on the MФ surface can hydrolyze circulating triglyceride-rich lipoproteins into glycerol and free fatty acids to provide a non-glucose energy source. We hypothesized that regulatory MФs have high LPL activity, which would promote fatty acid metabolism to drive inflammation-resolving functions, and that this LPL activity is inversely related to ambient glucose. Results: MФs were cultured and differentiated from bone marrow harvested from wild-type mice aged 9-16 weeks. Two weeks after harvest, these MФs were polarized with (1) interferon-γ and lipopolysaccharide to stimulate classically-activated, inflammatory MФs or (2) interleukin-4 to stimulate alternatively-activated, regulatory MФs. The resulting phenotypes were validated by canonical transcript markers ( Tnfa / Nos2 for inflammatory MФs and Ym1 / Arg1 for regulatory MФs) and cell surface markers (CD86 and CD206, respectively). Using a triglyceride analog that fluoresces when cleaved by LPL, we found that regulatory MФs have far greater LPL activity than inflammatory macrophages at baseline (33 ± 2 vs 1 ± 0.2 a.u., p < 0.001, n=8). By varying glucose concentration during the polarization, this effect was most pronounced at normal, physiological concentrations of glucose (5 mM, ~90 mg/dL) and blunted at a high-glucose concentration that can be found in uncontrolled diabetes (25 mM). Each experiment was repeated across multiple batches of MФs (n≥4) and from multiple mice (n=15), male and female. Conclusions: Taken together, our findings support a model in which regulatory MФs are programmed to utilize LPL to drive the inflammation-resolving phenotype and that this process works best at low, physiologic glucose concentrations. Future translational work will investigate whether a lack of LPL-mediated regulatory MФ function is a reason why patients with uncontrolled diabetes have higher atherosclerotic burden and plaque instability.