Rationale: A hallmark of chronic inflammatory disorders is persistence of pro-inflammatory macrophages in diseased tissues. In atherosclerosis this is associated with dyslipidemia and oxidative stress, but mechanisms linking these phenomena to macrophage activation remain incompletely understood. Objective: To investigate mechanisms linking dyslipidemia, oxidative stress and macrophage activation through modulation of immunometabolism, and to explore therapeutic potential targeting specific metabolic pathways. Methods and Results: Using a combination of biochemical, immunological, and ex vivo cell metabolic studies, we report that CD36 mediates a mitochondrial metabolic switch from oxidative phosphorylation to superoxide production in response to its ligand, oxLDL. Mitochondrial-specific inhibition of superoxide inhibited oxLDL-induced NF-κB activation and inflammatory cytokine generation. RNAseq, flow cytometry, 3H-labeled palmitic acid uptake, lipidomic analysis, confocal and EM imaging, and functional energetics revealed that oxLDL upregulated effectors of long-chain fatty acid (FA) uptake and mitochondrial import, while downregulating FA oxidation and inhibiting ATP5A, an electron transport chain (ETC) component. The combined effect is long-chain FA accumulation, alteration of mitochondrial structure and function, repurposing of the ETC to superoxide production, and NF-κB activation. Apoe null mice challenged with high fat diet showed similar metabolic changes in circulating Ly6C+ monocytes and peritoneal macrophages, along with increased CD36 expression. Moreover, mitochondrial ROS was positively correlated with CD36 expression in aortic lesional macrophages. Conclusions: These findings reveal that oxLDL/CD36 signaling in macrophages links dys-regulated FA metabolism to oxidative stress from the mitochondria, which drives chronic inflammation. Thus, targeting to CD36 and its downstream effectors may serve as potential new strategies against chronic inflammatory diseases such as atherosclerosis.

Aims/hypothesis The cAMP-degrading phosphodiesterase 4 (PDE4) enzyme has recently been implicated in the regulation of glucagon-like peptide-1 (GLP-1), an incretin hormone with glucose-lowering properties. We investigated whether the PDE4 inhibitor roflumilast elevates GLP-1 levels in diabetic db/db mice and whether this elevation is accompanied by glucose-lowering effects. Methods Plasma GLP-1 was determined in db/db mice after single oral administration of roflumilast or its active metabolite roflumilast-N-oxide. Diabetes-relevant variables including HbA 1c , blood glucose, serum insulin, body weight, food and water intake, and pancreas morphology were determined in db/db mice treated daily for 28 days with roflumilast or roflumilast-N-oxide. Pharmacokinetic/pharmacodynamic analysis clarified the contribution of roflumilast vs its metabolite. In addition, the effect of roflumilast-N-oxide on insulin release was investigated in primary mouse islets.Results Single treatment of db/db mice with 10 mg/kg roflumilast or roflumilast-N-oxide enhanced plasma GLP-1 2.5-and fourfold, respectively. Chronic treatment of db/db mice with roflumilast or roflumilast-N-oxide at 3 mg/kg showed prevention of disease progression. Roflumilast-N-oxide abolished the increase in blood glucose, reduced the increment in HbA 1c by 50% and doubled fasted serum insulin compared with vehicle, concomitant with preservation of pancreatic islet morphology. Furthermore, roflumilast-N-oxide amplified forskolininduced insulin release in primary islets. Roflumilast-N-oxide showed stronger glucose-lowering effects than its parent compound, consistent with its greater effect on GLP-1 secretion and explainable by pharmacokinetic/pharmacodynamic modelling. Conclusions/interpretation Our results suggest that roflumilast and roflumilast-N-oxide delay the progression of diabetes in db/db mice through protection of pancreatic islet physiology potentially involving GLP-1 and insulin activities.

Objective: To investigate the role of adipocyte Pcpe2 (procollagen C-endopeptidase enhancer 2) in SR-BI (scavenger receptor class BI)–mediated HDL-C (high-density lipoprotein cholesterol) uptake and contributions to adipose lipid storage. Approach and Results: Pcpe2, a glycoprotein devoid of intrinsic proteolytic activity, is believed to participate in extracellular protein-protein interactions, supporting SR-BI– mediated HDL-C uptake. In published studies, Pcpe2 deficiency increased the development of atherosclerosis by reducing SR-BI–mediated HDL-C catabolism, but the biological impact of this deficiency on adipocyte SR-BI–mediated HDL-C uptake is unknown. Differentiated cells from Ldlr −/− / Pcpe2 −/− (Pcpe2 −/− ) and Ldlr −/− (control) mouse adipose tissue showed elevated SR-BI protein levels, but significantly reduced HDL-C uptake. SR-BI–mediated HDL-C uptake was restored by preincubation of cells with exogenous Pcpe2. In diet-fed mice lacking Pcpe2, significant reductions in visceral, subcutaneous, and brown adipose tissue mass were observed, despite elevations in plasma triglyceride and cholesterol concentrations. Significant positive correlations exist between adipose mass and Pcpe2 expression in both mice and humans. Conclusions: Overall, these findings reveal a novel and unexpected function for Pcpe2 in modulating SR-BI expression and function as it relates to adipose tissue expansion and cholesterol balance in both mice and humans.

While increased levels of high‐density lipoprotein (HDL)‐cholesterol correlate with protection against cardiovascular disease, recent findings demonstrate that HDL function, rather than HDL‐cholesterol levels, may be a better indicator of cardiovascular risk. One mechanism by which HDL function can be compromised is through modification by reactive aldehydes such as acrolein (Acro), 4‐hydroxynonenal, and malondialdehyde (MDA). In this study, we tested the hypothesis that modification of HDL with reactive aldehydes would impair HDL’s athero‐protective functions in macrophages. Compared to native HDL, Acro‐ and MDA‐modified HDL have impaired abilities to promote migration of primary peritoneal macrophages isolated from C57BL6/J mice. Incubation of macrophages with MDA‐HDL also led to an increased ability to generate reactive oxygen species. Our studies revealed that the changes in HDL function following aldehyde modification are likely not through activation of canonical nuclear factor‐kappa B signaling pathways. Consistent with this finding, treatment of either noncholesterol‐loaded macrophages or foam cells with modified forms of HDL does not lead to significant changes in expression levels of inflammatory markers. Importantly, our data also demonstrate that changes in HDL function are dependent on the type of modification present on the HDL particle. Our findings suggest that modification of HDL with reactive aldehydes can impair some, but not all, of HDL’s athero‐protective functions in macrophages.

The HDL (high-density lipoprotein) Workshop was established in 2009 as a forum for candid discussions among academic basic scientists, clinical investigators, and industry researchers about the role of HDL in cardiovascular disease. This ninth HDL Workshop was held on May 16 to 17, 2019 in Boston, MA, and included outstanding oral presentations from established and emerging investigators. The Workshop featured 5 sessions with topics that tackled the role of HDL in the vasculature, its structural complexity, its role in health and disease states, and its interaction with the intestinal microbiome. The highlight of the program was awarding the Jack Oram Award to the distinguished professor emeritus G.S. Getz from the University of Chicago. The tenth HDL Workshop will be held on May 2020 in Chicago and will continue the focus on intellectually stimulating presentations by established and emerging investigators on novel roles of HDL in cardiovascular and noncardiovascular health and disease states.