Abstract 15518: The Effects of High Glucose and Lipoprotein Lipase on Macrophage Regulatory Function

Abstract

Introduction: Atherosclerosis has an established inflammatory, macrophage(MФ)-mediated component which can be exacerbated by uncontrolled diabetes. However, there are also protective, regulatory MФ processes that can help quell atherosclerosis. Lipoprotein Lipase (LPL) on the MФ surface hydrolyzes circulating triglyceride-rich lipoproteins into glycerol and free fatty acids to provide a non-glucose energy source. Hypothesis: We hypothesized that regulatory MФs have high LPL activity, which could promote fatty acid metabolism to drive inflammation-resolving functions, and that this LPL activity is inhibited by ambient glucose. Methods and 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). We also report on lipoxygenase expression and specialized pro-resolving mediator production as effector functions downstream of LPL activity in regulatory MФs. 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.