Anti-Inflammatory Effects of HDL (High-Density Lipoprotein) in Macrophages Predominate Over Proinflammatory Effects in Atherosclerotic Plaques Panagiotis Fotakis , Vishal Kothari , David G. Thomas , Marit Westerterp , Matthew M. Molusky , Elissa Altin , Sandra Abramowicz , Nan Wang , Yi He , Jay W. Heinecke , Karin E. Bornfeldt , Alan R. Tall Originally published3 Oct 2019https://doi.org/10.1161/ATVBAHA.119.313253Arteriosclerosis, Thrombosis, and Vascular Biology. 2019;39:e253–e272 Abstract Download figure Download PowerPoint Objective: HDL (high-density lipoprotein) infusion reduces atherosclerosis in animal models and is being evaluated as a treatment in humans. Studies have shown either anti- or proinflammatory effects of HDL in macrophages, and there is no consensus on the underlying mechanisms. Here, we interrogate the effects of HDL on inflammatory gene expression in macrophages. Approach and Results: We cultured bone marrow–derived macrophages, treated them with reconstituted HDL or HDL isolated from APOA1Tg;Ldlr−/− mice, and challenged them with lipopolysaccharide. Transcriptional profiling showed that HDL exerts a broad anti-inflammatory effect on lipopolysaccharide-induced genes and proinflammatory effect in a subset of genes enriched for chemokines. Cholesterol removal by POPC (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine) liposomes or β-methylcyclodextrin mimicked both pro- and anti-inflammatory effects of HDL, whereas cholesterol loading by POPC/cholesterol-liposomes or acetylated LDL (low-density lipoprotein) before HDL attenuated these effects, indicating that these responses are mediated by cholesterol efflux. While early anti-inflammatory effects reflect reduced TLR (Toll-like receptor) 4 levels, late anti-inflammatory effects are due to reduced IFN (interferon) receptor signaling. Proinflammatory effects occur late and represent a modified endoplasmic reticulum stress response, mediated by IRE1a (inositol-requiring enzyme 1a)/ASK1 (apoptosis signal-regulating kinase 1)/p38 MAPK (p38 mitogen-activated protein kinase) signaling, that occurs under conditions of extreme cholesterol depletion. To investigate the effects of HDL on inflammatory gene expression in myeloid cells in atherosclerotic lesions, we injected reconstituted HDL into Apoe−/− or Ldlr−/− mice fed a Western-type diet. Reconstituted HDL infusions produced anti-inflammatory effects in lesion macrophages without any evidence of proinflammatory effects. Conclusions: Reconstituted HDL infusions in hypercholesterolemic atherosclerotic mice produced anti-inflammatory effects in lesion macrophages suggesting a beneficial therapeutic effect of HDL in vivo. Highlights HDL (high-density lipoprotein) exerts anti- and proinflammatory effects that are mediated by cholesterol removal in cultured macrophages. Anti-inflammatory effects are associated with reduced TLR (Toll-like receptor) 4 levels and reduced interferon receptor signaling. Proinflammatory effects of reconstituted HDL represent a modified endoplasmic reticulum stress response that involves IRE1a (inositol-requiring enzyme 1a)/ASK1 (apoptosis signal-regulating kinase 1)/p38 MAPK (p38 mitogen-activated protein kinase) signaling and occurs under conditions of extreme cholesterol depletion. Reconstituted HDL infusions in mice produced anti-inflammatory effects in lesion macrophages suggesting a beneficial therapeutic effect of HDL in vivo. Introduction Epidemiological studies1 and experimental animal models2,3 suggest that HDL (high-density lipoprotein) protects against atherosclerosis. However, the causal relationship of HDL cholesterol levels to atherosclerosis has been challenged by Mendelian randomization studies4,5 and failure or mediocre success of HDL cholesterol elevating treatments in clinical trials of statin-treated subjects.6,7 To reconcile these findings, it has been suggested that evaluating the functionality of HDL, instead of the HDL cholesterol level, may provide a better biomarker of its ability to confer atheroprotection.8 HDL exerts a plethora of functions in vitro that are thought to be atheroprotective, such as cholesterol efflux, anti-inflammatory, antioxidant, and antithrombotic effects.9 Among these, the cholesterol efflux capacity of HDL has been shown to be a better predictor of coronary heart disease risk compared with HDL cholesterol levels.10,11 The central role of inflammatory responses in human coronary heart disease has been clearly shown by the positive outcome of the CANTOS trial (Canakinumab Anti-Inflammatory Thrombosis Outcome Study).12 Given the importance of macrophage inflammation in the initiation and progression of atherosclerosis,13 recent studies have directly evaluated the anti-inflammatory potential of HDL and its major apolipoprotein APOA1 (apolipoprotein A1) in macrophages,14–19 mainly in the context of lipopolysaccharide (LPS) stimulation and TLR (Toll-like receptor) 4 activation.14–17 These studies reported conflicting results indicating either anti- or proinflammatory effects and suggested distinct mechanisms. For example, anti-inflammatory effects were attributed to induction of ATF3 (activating transcription factor 3)—an inhibitor of TLR/NFκB (nuclear factor-κ light-chain enhancer of activated B cells) signaling by HDL15—or defective induction of type I IFNs (interferons), downstream of TRAM (TRIF-related adaptor molecule)/TRIF (TIR-domain-containing adapter-inducing interferon-β) signaling.14 Another study showed anti-inflammatory effects of HDL in IFNγ-stimulated macrophages.20 In contrast, proinflammatory effects were associated with increased activity of PKC (protein kinase C),17 enhancing TLR signaling or direct stimulation of TLRs by APOA1.16 Notably, despite the relation of HDL to atherosclerosis, only 2 of these studies examined its effects on lesion macrophages.18,19 Moreover, one of these HDL studies, showing proinflammatory effects, associated the observed changes with the ability of HDL to remove cholesterol.17 This contrasts with the notion that cholesterol accumulation in macrophages amplifies TLR signaling, and thus cholesterol removal dampens this response.21,22 Given the discrepancies concerning the effects of HDL on macrophage inflammation and the potential concern that reconstituted HDL (rHDL) infusion in humans could have adverse effects in plaque macrophages, we have performed a systematic examination of the inflammatory potential of reconstituted human and native mouse HDL (rHDL and native HDL [nHDL], respectively) in cultured macrophages and in plaque myeloid cells. Transcriptome analysis using RNA-Seq showed anti- and proinflammatory effects of rHDL; both effects are mediated by cholesterol removal. The anti-inflammatory effects are associated with reduced TLR4 expression and decreased IFNAR (IFN-α/β receptor) signaling, whereas the proinflammatory effects represent an endoplasmic reticulum (ER) stress response, involving activation of the IRE1a (inositol-requiring enzyme 1a)/ASK1 (apoptosis signal-regulating kinase 1)/p38 MAPK (p38 mitogen-activated protein kinases) signaling axis. Both pro- and anti-inflammatory effects of HDL were attenuated by prior macrophage cholesterol loading. Importantly, infusions of rHDL in hypercholesterolemic atherosclerotic mice led to reduced expression of inflammatory genes in aortic macrophages without any evidence of increased inflammatory gene expression.
Biological activity of high density lipoproteins (HDL). Rapovets V.A. Lechebnoe delo. -2017.-6.-p.43-45. CHD remains the leading cause of death and disability in Europe and the United States. Despite significant progress in the correction of atherogenic lipoproteins, it remains unresolved the question of the pharmacological effects on cholesterol levels of high density lipoprotein . Recent studies have revealed heterogeneity of structure, metabolism, biological activity of HDL particles. In atherogenesis conditions revealed a significant transformation of HDL, leading to a decrease in their sacrificial function. Keywords: cholesterol, high density lipoprotein, atherosclerosis.
