RAGE Mediates Cholesterol Efflux Impairment in Macrophages Caused by Human Advanced Glycated Albumin

We addressed the involvement of the receptor for advanced glycation end products (RAGE) in the impairment of the cellular cholesterol efflux elicited by glycated albumin. Albumin was isolated from type 1 (DM1) and type 2 (DM2) diabetes mellitus (HbA1c > 9%) and non-DM subjects (C). Moreover, albumin was glycated in vitro (AGE-albumin). Macrophages from Ager null and wild-type (WT) mice, or THP-1 transfected with siRNA-AGER, were treated with C, DM1, DM2, non-glycated or AGE-albumin. The cholesterol efflux was reduced in WT cells exposed to DM1 or DM2 albumin as compared to C, and the intracellular lipid content was increased. These events were not observed in Ager null cells, in which the cholesterol efflux and lipid staining were, respectively, higher and lower when compared to WT cells. In WT, Ager, Nox4 and Nfkb1, mRNA increased and Scd1 and Abcg1 diminished after treatment with DM1 and DM2 albumin. In Ager null cells treated with DM-albumin, Nox4, Scd1 and Nfkb1 were reduced and Jak2 and Abcg1 increased. In AGER-silenced THP-1, NOX4 and SCD1 mRNA were reduced and JAK2 and ABCG1 were increased even after treatment with AGE or DM-albumin. RAGE mediates the deleterious effects of AGE-albumin in macrophage cholesterol efflux.

RAGE impairs murine diabetic atherosclerosis regression and implicates IRF7 in macrophage inflammation and cholesterol metabolism

Despite advances in lipid-lowering therapies, people with diabetes continue to experience more limited cardiovascular benefits. In diabetes, hyperglycemia sustains inflammation and preempts vascular repair. We tested the hypothesis that the receptor for advanced glycation end-products (RAGE) contributes to these maladaptive processes. We report that transplantation of aortic arches from diabetic, Western diet-fed Ldlr-/- mice into diabetic Ager-/- (Ager, the gene encoding RAGE) versus WT diabetic recipient mice accelerated regression of atherosclerosis. RNA-sequencing experiments traced RAGE-dependent mechanisms principally to the recipient macrophages and linked RAGE to interferon signaling. Specifically, deletion of Ager in the regressing diabetic plaques downregulated interferon regulatory factor 7 (Irf7) in macrophages. Immunohistochemistry studies colocalized IRF7 and macrophages in both murine and human atherosclerotic plaques. In bone marrow-derived macrophages (BMDMs), RAGE ligands upregulated expression of Irf7, and in BMDMs immersed in a cholesterol-rich environment, knockdown of Irf7 triggered a switch from pro- to antiinflammatory gene expression and regulated a host of genes linked to cholesterol efflux and homeostasis. Collectively, this work adds a new dimension to the immunometabolic sphere of perturbations that impair regression of established diabetic atherosclerosis and suggests that targeting RAGE and IRF7 may facilitate vascular repair in diabetes.

Ager Deletion Enhances Ischemic Muscle Inflammation, Angiogenesis, and Blood Flow Recovery in Diabetic Mice

OBJECTIVE

Diabetic subjects are at higher risk of ischemic peripheral vascular disease. We tested the hypothesis that advanced glycation end products (AGEs) and their receptor (RAGE) block angiogenesis and blood flow recovery after hindlimb ischemia induced by femoral artery ligation through modulation of immune/inflammatory mechanisms.

APPROACH AND RESULTS

Wild-type mice rendered diabetic with streptozotocin and subjected to unilateral femoral artery ligation displayed increased accumulation and expression of AGEs and RAGE in ischemic muscle. In diabetic wild-type mice, femoral artery ligation attenuated angiogenesis and impaired blood flow recovery, in parallel with reduced macrophage content in ischemic muscle and suppression of early inflammatory gene expression, including Ccl2 (chemokine [C-C motif] ligand-2) and Egr1 (early growth response gene-1) versus nondiabetic mice. Deletion of Ager (gene encoding RAGE) or transgenic expression of Glo1 (reduces AGEs) restored adaptive inflammation, angiogenesis, and blood flow recovery in diabetic mice. In diabetes mellitus, deletion of Ager increased circulating Ly6C^hi monocytes and augmented macrophage infiltration into ischemic muscle tissue after femoral artery ligation. In vitro, macrophages grown in high glucose display inflammation that is skewed to expression of tissue damage versus tissue repair gene expression. Further, macrophages grown in high versus low glucose demonstrate blunted macrophage-endothelial cell interactions. In both settings, these adverse effects of high glucose were reversed by Ager deletion in macrophages.

CONCLUSIONS

These findings indicate that RAGE attenuates adaptive inflammation in hindlimb ischemia; underscore microenvironment-specific functions for RAGE in inflammation in tissue repair versus damage; and illustrate that AGE/RAGE antagonism may fill a critical gap in diabetic peripheral vascular disease.

Abstract 48: Role of Receptor for Advanced Glycation End Products (RAGE) in Regression of Diabetic Atherosclerosis

Atherosclerosis is a chronic inflammatory disorder. Both progression and regression of atherosclerosis are adversely affected by diabetes. A key player in these processes is Receptor for Advanced Glycation End Products (RAGE). RAGE is a multiligand cell surface macromolecule, which binds ligands enriched in atherosclerotic plaques, such as advanced glycation endproducts (AGEs). RAGE is expressed on a wide array of cell types implicated in cardiovascular disease, such as endothelial cells, and inflammatory cells such as macrophages. The cytoplasmic domain of RAGE binds to the formin molecule DIAPH1 and DIAPH1 is required for RAGE ligands to activate cell signaling responses. RAGE acts as a key mediator of oxidative and inflammatory signaling pathways that are involved in atherosclerosis. We tested mechanisms of impaired regression of atherosclerosis in a murine model of aorta transplantation and found that deletion of Ager or Diaph1 in diabetic mice recipients of Ldlr null mice atherosclerotic aortas accelerates atherosclerosis regression and significantly reduces the lesional macrophage content when compared to diabetic wild-type recipient mice. The antiatherosclerotic effects in diabetic Ager null mice and diabetic Diaph1 null mice include reduced RAGE ligand AGEs in transplanted aortas, with reduced expression of a range of proatherogenic factors, including reactive oxygen species and inflammatory cytokines implicated in leukocyte recruitment and activation. We employed RNA sequencing to identify the key transcriptional events by which RAGE mediates its effects in donor or recipient macrophages in diabetic regressing plaques. Our results suggest that critical gene expression profiles, including those genes involved in inflammation, endothelial dysfunction, oxidative stress, monocyte/macrophage fate (recruitment, differentiation, proliferation), signal transduction and lipid metabolism, are beneficially modulated, at least in part, via Ager deletion in atherosclerosis regression. Taken together, these data increase our understanding of the role of RAGE in diabetic atherosclerosis, particularly in macrophages, and may provide avenues for therapeutic strategies to accelerate regression of atherosclerosis in diabetes.

RAGE Suppresses ABCG1-Mediated Macrophage Cholesterol Efflux in Diabetes

Diabetes exacerbates cardiovascular disease, at least in part through suppression of macrophage cholesterol efflux and levels of the cholesterol transporters ATP binding cassette transporter A1 (ABCA1) and ABCG1. The receptor for advanced glycation end products (RAGE) is highly expressed in human and murine diabetic atherosclerotic plaques, particularly in macrophages. We tested the hypothesis that RAGE suppresses macrophage cholesterol efflux and probed the mechanisms by which RAGE downregulates ABCA1 and ABCG1. Macrophage cholesterol efflux to apolipoprotein A1 and HDL and reverse cholesterol transport to plasma, liver, and feces were reduced in diabetic macrophages through RAGE. In vitro, RAGE ligands suppressed ABCG1 and ABCA1 promoter luciferase activity and transcription of ABCG1 and ABCA1 through peroxisome proliferator-activated receptor-γ (PPARG)-responsive promoter elements but not through liver X receptor elements. Plasma levels of HDL were reduced in diabetic mice in a RAGE-dependent manner. Laser capture microdissected CD68(+) macrophages from atherosclerotic plaques of Ldlr(-/-) mice devoid of Ager (RAGE) displayed higher levels of Abca1, Abcg1, and Pparg mRNA transcripts versus Ager-expressing Ldlr(-/-) mice independently of glycemia or plasma levels of total cholesterol and triglycerides. Antagonism of RAGE may fill an important therapeutic gap in the treatment of diabetic macrovascular complications.

Abstract 532: The Receptor for Advanced Glycation End Products (RAGE) Suppresses Macrophage Cholesterol Transport in Diabetes

Diabetes is a leading cause of cardiovascular morbidity and mortality. In human subjects, diabetes suppresses macrophage cholesterol efflux capacity, at least in part via reduction in levels of the major cholesterol transporters, ABCA1 and ABCG1. We tested the hypothesis that the receptor for advanced glycation end products (RAGE) contributes to these processes. We report that ligand-RAGE interaction suppresses cholesterol efflux to ApoA1 and HDL in primary murine bone marrow-derived macrophages (BMDMs) and in human THP-1 cells, at least in part via downregulation of ABCA1 and ABCG1. In vivo, compared to cholesterol-loaded wild-type (WT) diabetic murine BMDMs, diabetic BMDMs devoid of Ager (gene encoding RAGE) displayed significantly higher reverse cholesterol transport (RCT) to plasma, liver and feces when injected into WT non-diabetic mice. In atherosclerotic plaques from mice devoid of both Ldlr and Ager and fed a high cholesterol diet, higher Abca1 and Abcg1 mRNA transcript levels were also observed compared to Ager-expressing LDL receptor null mice. RAGE ligand AGEs suppress ABCG1 promoter luciferase activity and transcription of ABCG1 through reduced binding of PPARgamma (PPARG) to PPARG-responsive elements in the ABCG1 promoter. These data reveal that RAGE contributes to dysregulation of macrophage cholesterol metabolism, particularly in diabetes. We infer that antagonism of RAGE may mitigate accelerated atherosclerosis in the diabetic state, at least in part due to modulation of impaired cholesterol transport.

Abstract 583: Receptor for Advanced Glycation End Products ( Ager ) and Diaphanous-1 ( Drf1) Suppress Macrophage Reverse Transendothelial Migration and Regression of Diabetic Atherosclerosis

Macrophages display complex trafficking properties in vivo , involving interaction with vascular endothelial cells. Macrophage migration is an important mechanism linked to the progression and regression of atherosclerosis. The underlying mechanisms involved in these processes are not fully defined. RAGE is a multiligand cell surface macromolecule, which binds distinct ligands. The RAGE cytoplasmic domain interacts with Diaphanous-1 ( Drf1 ), both in vitro and in vivo and this interaction is essential for RAGE ligand-mediated signaling in macrophages. We tested the hypothesis that RAGE and Diaphanous-1 suppress regression of diabetic atherosclerosis; at least in part by impaired reduction of plaque macrophage content in an AGE-enriched diabetic environment. In a aorta transplantation model, we examined the morphologic changes in LDLr-/- donor plaques found in Ager -/-, Drf1 -/- or WT recipient diabetic mice. After lipid normalization into Ager -/- recipient diabetic mice, we observed reduced plaque macrophage density (CD68 -46%;p<0.05), but increased plaque collagen (PSR+43%;p<0.06), compared to WT diabetic recipients. Oil Red O staining for fatty deposit suggests a decrease (-51%;p<0.05) in plaque area stained and lower AGE staining (-32%;p<0.05) in diabetic Drf1 -/- recipient mice compared to WT diabetic recipients. We employed a monocyte bead-tracking model in this in vivo aorta transplantation study. In WT recipient mice, when the donors were LDLr-/- mice fed a western diet, bead frequency per plaque section was reduced (22%;p< 0.05) on day 5 post-transplant compared with baseline. In contrast, bead frequency per plaque section was significantly reduced by (41%;p< 0.05) compared with baseline in the absence of Ager (gene encoding RAGE). In vitro, in a reverse transendothelial migration assay using primary aortic endothelial cells and Ager or Drf1 deficient bone marrow derived macrophages (BMDMs), revealed in the setting of treatment with RAGE ligand AGEs, deletion of Ager or Drf1 in BMDMs facilitated macrophage reverse migration vs. that observed in WT BMDMs. Therefore, we propose that deletion of Ager or Drf1 in recipient diabetic mice accelerates atherosclerotic plaque regression, via reduction in lesional macrophage content.

Abstract 471: Receptor for Advanced Glycation End Products, Reverse Transmigration and Impaired Regression of Diabetic Atherosclerosis

Cellular migration is fundamental processes linked to diverse pathological states including atherosclerosis and diabetes. RAGE is a multiligand cell surface macromolecule, which binds ligands such as advanced glycation endproducts. In evaluating the relationship between impaired regression of atherosclerosis in diabetes and RAGE, we tested the hypothesis that RAGE contributes to impaired regression by suppression of reverse transmigration of macrophages in an AGE-enriched environment. We evaluated if the expression of RAGE modulates influx and/or egress of macrophages from the atherosclerotic lesions in the non-diabetic and diabetic states. We used a monocyte bead-tracking model in an aorta transplantation study with LDL-/-diabetic mice fed high-fat diet as a baseline (donors), and non-diabetic RAGE-/- or WT mice as recipient. Migration patterns evaluated by labeled monocytes showed a decrease in bead number in RAGE null recipients (23±0.05p<0.05) compared to WT (30±0.05p<0.05) indicating that monocyte-derived cell content in the diabetic state was lower in the absence of RAGE. In our surgical aorta transplant model, we also examined the morphologic changes in plaques found in RAGE-/- or WT recipient mice. After lipid normalization into RAGE-/- recipient mice we observed reduced plaque cells positive for macrophage marker CD68+ (-58%), but increased plaque collagen (+51%), compared to WT recipients. Our data indicate Oil Red O stains for fatty deposit in plaque suggest a decrease (-53%) in plaque area stained and lower AGEs staining (-22%) in RAGE-/- recipient mice compared to WT recipient. Therefore, the presence of RAGE hindered plaque regression in our atherosclerotic mouse model.

We performed our studies in vitro, a reverse transmigration assay, using primary murine aortic endothelial cells from wild-type C57BL6 mice and wild-type or RAGE deficient bone marrow derived macrophages. Our data show RAGE-AGEs impact macrophage-endothelial transmigration. Our studies suggest RAGE-AGEs action delays reverse transmigration of macrophages and augments pro-inflammatory gene expression. Therefore blockade of RAGE may be able to limit pathological acceleration of vascular diseases.

Radical roles for RAGE in the pathogenesis of oxidative stress in cardiovascular diseases and beyond

Oxidative stress is a central mechanism by which the receptor for advanced glycation endproducts (RAGE) mediates its pathological effects. Multiple experimental inquiries in RAGE-expressing cultured cells have demonstrated that ligand-RAGE interaction mediates generation of reactive oxygen species (ROS) and consequent downstream signal transduction and regulation of gene expression. The primary mechanism by which RAGE generates oxidative stress is via activation of NADPH oxidase; amplification mechanisms in the mitochondria may further drive ROS production. Recent studies indicating that the cytoplasmic domain of RAGE binds to the formin mDia1 provide further support for the critical roles of this pathway in oxidative stress; mDia1 was required for activation of rac1 and NADPH oxidase in primary murine aortic smooth muscle cells treated with RAGE ligand S100B. In vivo, in multiple distinct disease models in animals, RAGE action generates oxidative stress and modulates cellular/tissue fate in range of disorders, such as in myocardial ischemia, atherosclerosis, and aneurysm formation. Blockade or genetic deletion of RAGE was shown to be protective in these settings. Indeed, beyond cardiovascular disease, evidence is accruing in human subjects linking levels of RAGE ligands and soluble RAGE to oxidative stress in disorders such as doxorubicin toxicity, acetaminophen toxicity, neurodegeneration, hyperlipidemia, diabetes, preeclampsia, rheumatoid arthritis and pulmonary fibrosis. Blockade of RAGE signal transduction may be a key strategy for the prevention of the deleterious consequences of oxidative stress, particularly in chronic disease.

Abstract 148: AGES, Receptor for Advanced Glycation End Products (RAGE), Reverse Transmigration of Macrophages & Polarization

Cellular migration is fundamental processes linked to diverse pathological states including atherosclerosis and diabetes. RAGE is a multiligand cell surface macromolecule, which binds ligands such as advanced glycation endproducts (AGEs) in diseased settings such as atherosclerosis. We tested the hypothesis that RAGE contributes to impaired regression of diabetic atherosclerosis by suppression of reverse transmigration of macrophages in an AGE-enriched environment. We performed our studies in vitro, a reverse transmigration assay, using primary murine aortic endothelial cells from wild-type C57BL6 mice and wild-type or RAGE deficient primary bone marrow derived macrophages (BMDMs). Our data is shown in the table.

We evaluate if the expression of RAGE modulates influx and/or egress of macrophages from the atherosclerotic lesions in the non-diabetic and diabetic states. We used a monocyte bead-tracking model in an aorta transplantation study with LDL-/-diabetic mice fed high-fat diet as a baseline (donors), and non-diabetic RAGE-/- or WT mice as recipient. Migration patterns evaluated by labeled monocytes, showed a decrease in bead number in RKO recipients (23±0.05 p<0.05) compared to WT (30±0.05 p<0.05) indicating emigration of monocyte- derived cells from the plaque in the diabetic state.

We also tested if RAGE plays roles in macrophage polarization. AGEs-RAGE axis increases M1 polarization (MCP 1, TNF alpha, iNos, p<0.05) and suppresses M2 polarization (Arg1, IL-10, p<0.05) in a manner prevented by deletion of RAGE in BMDMs. Our studies suggest AGEs-RAGE axis action delays reverse transmigration of macrophages and augments pro-inflammatory gene expression.

Formin mDia1 mediates vascular remodeling via integration of oxidative and signal transduction pathways

RATIONALE

The mammalian diaphanous-related formin (mDia1), governs microtubule and microfilament dynamics while functioning as an effector for Rho small GTP-binding proteins during key cellular processes such as adhesion, cytokinesis, cell polarity, and morphogenesis. The cytoplasmic domain of the receptor for advanced glycation endproducts binds to the formin homology 1 domain of mDia1; mDia1 is required for receptor for advanced glycation endproducts ligand-induced cellular migration in transformed cells.

OBJECTIVE

Because a key mechanism in vascular remodeling is the induction of smooth muscle cell migration, we tested the role of mDia1 in this process.

METHODS AND RESULTS

We report that endothelial denudation injury to the murine femoral artery significantly upregulates mDia1 mRNA transcripts and protein in the injured vessel, particularly in vascular smooth muscle cells within the expanding neointima. Loss of mDia1 expression significantly reduces pathological neointimal expansion consequent to injury. In primary murine aortic smooth muscle cells, mDia1 is required for receptor for advanced glycation endproducts ligand-induced membrane translocation of c-Src, which leads to Rac1 activation, redox phosphorylation of AKT/glycogen synthase kinase 3β, and consequent smooth muscle cell migration.

CONCLUSIONS

We conclude that mDia1 integrates oxidative and signal transduction pathways triggered, at least in part, by receptor for advanced glycation endproducts ligands, thereby regulating pathological neointimal expansion.