Disturbed Laminar Blood Flow Vastly Augments Lipoprotein Retention in the Artery Wall

Annexin A8 deficiency delays atherosclerosis progression

BACKGROUND

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of lipids and leukocytes within the arterial wall. By studying the aortic transcriptome of atherosclerosis-prone apolipoprotein E (ApoE-/-) mice, we aimed to identify novel players in the progression of atherosclerosis.

METHODS

RNA-Seq analysis was performed on aortas from ApoE-/- and wild-type mice. AnxA8 expression was assessed in human and mice atherosclerotic tissue and healthy aorta. ApoE-/- mice lacking systemic AnxA8 (ApoE-/-AnxA8-/-) were generated to assess the effect of AnxA8 deficiency on atherosclerosis. Bone marrow transplantation (BMT) was also performed to generate ApoE-/- lacking AnxA8 specifically in bone marrow-derived cells. Endothelial-specific AnxA8 silencing in vivo was performed in ApoE-/- mice. The functional role of AnxA8 was analysed in cultured murine cells.

RESULTS

RNA-Seq unveiled AnxA8 as one of the most significantly upregulated genes in atherosclerotic aortas of ApoE-/- compared to wild-type mice. Moreover, AnxA8 was upregulated in human atherosclerotic plaques. Germline deletion of AnxA8 decreased the atherosclerotic burden, the size and volume of atherosclerotic plaques in the aortic root. Plaques of ApoE-/-AnxA8-/- were characterized by lower lipid and inflammatory content, smaller necrotic core, thicker fibrous cap and less apoptosis compared with those in ApoE-/-AnxA8+/+. BMT showed that hematopoietic AnxA8 deficiency had no effect on atherosclerotic progression. Oxidized low-density lipoprotein (ox-LDL) increased AnxA8 expression in murine aortic endothelial cells (MAECs). In vitro experiments revealed that AnxA8 deficiency in MAECs suppressed P/E-selectin and CD31 expression and secretion induced by ox-LDL with a concomitant reduction in platelet and leukocyte adhesion. Intravital microscopy confirmed the reduction in leukocyte and platelet adhesion in ApoE-/-AnxA8-/- mice. Finally, endothelial-specific silencing of AnxA8 decreased atherosclerosis progression.

CONCLUSION

Our findings demonstrate that AnxA8 promotes the progression of atherosclerosis by modulating endothelial-leukocyte interactions. Interventions capable of reducing AnxA8 expression in endothelial cells may delay atherosclerotic plaque progression.

KEY POINTS

This study shows that AnxA8 is upregulated in aorta of atheroprone mice and in human atherosclerotic plaques. Germline AnxA8 deficiency reduces platelet and leukocyte recruitment to activated endothelium as well as atherosclerotic burden, plaque size, and macrophage accumulation in mice. AnxA8 regulates oxLDL-induced adhesion molecules expression in aortic endothelial cells. Our data strongly suggest that AnxA8 promotes disease progression through regulation of adhesion and influx of immune cells to the intima. Endothelial specific silencing of AnxA8 reduced atherosclerosis progression. Therapeutic interventions to reduce AnxA8 expression may delay atherosclerosis progression.

Smooth muscle-specific deletion of cellular communication network factor 2 causes severe aorta malformation and atherosclerosis

AIMS

Cellular communication network factor 2 (CCN2) is a matricellular protein implicated in fibrotic diseases, with ongoing clinical trials evaluating anti-CCN2-based therapies. By uncovering CCN2 as abundantly expressed in non-diseased artery tissue, this study aimed to investigate the hypothesis that CCN2 plays a pivotal role in maintaining smooth muscle cell (SMC) phenotype and protection against atherosclerosis.

METHODS AND RESULTS

Global- and SMC-specific Ccn2 knockout mouse models were employed to demonstrate that Ccn2 deficiency leads to SMC de-differentiation, medial thickening, and aorta elongation under normolipidaemic conditions. Inducing hyperlipidaemia in both models resulted in severe aorta malformation and a 17-fold increase in atherosclerosis formation. Lipid-rich lesions developed at sites of the vasculature typically protected from atherosclerosis development by laminar blood flow, covering 90% of aortas and extending to other vessels, including coronary arteries. Evaluation at earlier time points revealed medial lipid accumulation as a lesion-initiating event. Fluorescently labelled LDL injection followed by confocal microscopy showed increased LDL retention in the medial layer of Ccn2 knockout aortas, likely attributed to marked proteoglycan enrichment of the medial extracellular matrix. Analyses leveraging data from the Athero-Express study cohort indicated the relevance of CCN2 in established human lesions, as CCN2 correlated with SMC marker transcripts across 654 transcriptomically profiled carotid plaques. These findings were substantiated through in situ hybridization showing CCN2 expression predominantly in the fibrous cap.

CONCLUSION

This study identifies CCN2 as a major constituent of the normal artery wall, critical in regulating SMC differentiation and aorta integrity and possessing a protective role against atherosclerosis development. These findings underscore the need for further investigation into the potential effects of anti-CCN2-based therapies on the vasculature.

Endothelial-to-Mesenchymal Transition Contributes to Accelerated Atherosclerosis in Hutchinson-Gilford Progeria Syndrome

BACKGROUND

Atherosclerosis is the main medical problem in Hutchinson-Gilford progeria syndrome, a rare premature aging disorder caused by the mutant lamin-A protein progerin. Recently, we found that limiting progerin expression to vascular smooth muscle cells (VSMCs) is sufficient to hasten atherosclerosis and death in Apoe-deficient mice. However, the impact of progerin-driven VSMC defects on endothelial cells (ECs) remained unclear.

METHODS

Apoe- or Ldlr-deficient C57BL/6J mice with ubiquitous, VSMC-, EC- or myeloid-specific progerin expression fed a normal or high-fat diet were used to study endothelial phenotype during Hutchinson-Gilford progeria syndrome-associated atherosclerosis. Endothelial permeability to low-density lipoproteins was assessed by intravenous injection of fluorescently labeled human low-density lipoprotein and confocal microscopy analysis of the aorta. Leukocyte recruitment to the aortic wall was evaluated by en face immunofluorescence. Endothelial-to-mesenchymal transition (EndMT) was assessed by quantitative polymerase chain reaction and RNA sequencing in the aortic intima and by immunofluorescence in aortic root sections. TGFβ (transforming growth factor β) signaling was analyzed by multiplex immunoassay in serum, by Western blot in the aorta, and by immunofluorescence in aortic root sections. The therapeutic benefit of TGFβ1/SMAD3 pathway inhibition was evaluated in mice by intraperitoneal injection of SIS3 (specific inhibitor of SMAD3), and vascular phenotype was assessed by Oil Red O staining, histology, and immunofluorescence in the aorta and the aortic root.

RESULTS

Both ubiquitous and VSMC-specific progerin expression in Apoe-null mice provoked alterations in aortic ECs, including increased permeability to low-density lipoprotein and leukocyte recruitment. Atherosclerotic lesions in these progeroid mouse models, but not in EC- and myeloid-specific progeria models, contained abundant cells combining endothelial and mesenchymal features, indicating extensive EndMT triggered by dysfunctional VSMCs. Accordingly, the intima of ubiquitous and VSMC-specific progeroid models at the onset of atherosclerosis presented increased expression of EndMT-linked genes, especially those specific to fibroblasts and extracellular matrix. Aorta in both models showed activation of the TGFβ1/SMAD3 pathway, a major trigger of EndMT, and treatment of VSMC-specific progeroid mice with SIS3 alleviated the aortic phenotype.

CONCLUSIONS

Progerin-induced VSMC alterations promote EC dysfunction and EndMT through TGFβ1/SMAD3, identifying this process as a candidate target for Hutchinson-Gilford progeria syndrome treatment. These findings also provide insight into the complex role of EndMT during atherogenesis.

The LDL cumulative exposure hypothesis: evidence and practical applications

The trapping of LDL and other apolipoprotein B-containing lipoproteins within the artery wall causes atherosclerosis. As more LDL becomes trapped within the artery wall over time, the atherosclerotic plaque burden gradually increases, raising the risk of an acute cardiovascular event. Therefore, the biological effect of LDL on the risk of atherosclerotic cardiovascular disease (ASCVD) depends on both the magnitude and duration of exposure. Maintaining low levels of LDL-cholesterol (LDL-C) over time decreases the number of LDL particles trapped within the artery wall, slows the progression of atherosclerosis and, by delaying the age at which mature atherosclerotic plaques develop, substantially reduces the lifetime risk of ASCVD events. Summing LDL-C measurements over time to calculate cumulative exposure to LDL generates a unique biomarker that captures both the magnitude and duration of exposure, which facilitates the estimation of the absolute risk of having an acute cardiovascular event at any point in time. Titrating LDL-C lowering to keep cumulative exposure to LDL below the threshold at which acute cardiovascular events occur can effectively prevent ASCVD. In this Review, we provide the first comprehensive overview of how the LDL cumulative exposure hypothesis can guide the prevention of ASCVD. We also discuss the benefits of maintaining lower LDL-C levels over time and how this knowledge can be used to inform clinical practice guidelines as well as to design novel primary prevention trials and ASCVD prevention programmes.

Response to retention hypothesis as a source of targets for arterial wall-directed therapies to prevent atherosclerosis: A critical review

The subendothelial retention of circulating lipoproteins on extracellular matrix proteins and proteoglycans is one of the earliest events in the development of atherosclerosis. Multiple factors, including the size, type, composition, surrounding pH, and chemical modifications to lipoproteins, influence the electrostatic interactions between relevant moieties of the apolipoproteins on lipoproteins and the glycosaminoglycans of proteoglycans. The length and chemical composition of glycosaminoglycan chains attached to proteoglycan core proteins determine the extent of initial lipoprotein binding and retention in the artery wall. The phenomena of hyperelongation of glycosaminoglycan chains is associated with initial lipid retention and later atherosclerotic plaque formation. This review includes a summary of the current literature surrounding cellular mechanisms leading to GAG chain modification and lipid retention and discusses potential therapeutic strategies to target lipoprotein:proteoglycan interactions to prevent the development and progression of atherosclerosis.

Can CSL-112 revolutionize atherosclerosis treatment? A critical look at the evidence

CSL-112, a recombinant human apolipoprotein A-I, holds promise for treating atherosclerotic disease by promoting reverse cholesterol transport. This review evaluates the current evidence on CSL-112's impact on atherosclerotic disease. A search identified studies investigating the effect of CSL-112 on apolipoprotein A-I levels, cholesterol efflux capacity, clinical outcomes, safety profile, pharmacokinetics, pharmacodynamics, and subgroup analysis in patients with atherosclerotic disease. All nine studies consistently demonstrated a dose-dependent increase in apolipoprotein A-I levels following CSL-112 administration. Most studies also reported a corresponding rise in cholesterol efflux capacity. However, the AEGIS-II trial, the largest study to date, did not show a statistically significant reduction in major adverse cardiovascular events in patients with acute myocardial infarction treated with CSL-112 compared to placebo. While some smaller studies suggested potential benefits, particularly in stable atherosclerotic disease, their limitations in size and duration necessitate further investigation. CSL-112 appeared to be generally well-tolerated, with mostly mild or moderate adverse events reported. However, the AEGIS-II trial identified a higher incidence of hypersensitivity reactions in the CSL-112 group, requiring further exploration. CSL-112 demonstrates promise in raising apolipoprotein A-I levels and enhancing cholesterol efflux capacity, potentially promoting reverse cholesterol transport. However, its clinical efficacy for atherosclerotic disease remains unclear. Larger, well-designed trials with longer follow-up periods are necessary to definitively establish its clinical benefit and safety profile before widespread clinical use can be considered. Future research should also explore deeper into the pharmacokinetic and pharmacodynamic profile of CSL-112 and explore its efficacy and safety in different patient subgroups.

Role of Endothelial Regeneration and Overloading of Enterocytes with Lipids in Capturing of Lipoproteins by Basement Membrane of Rat Aortic Endothelium

Atherosclerosis is a complex non-monogenic disease related to endothelial damage in elastic-type arteries and incorrect feeding. Here, using cryodamage of endothelial cells (ECs) of rat abdominal aorta, we examined the role of the EC basement membrane (BM) for re-endothelization endothelial regeneration and its ability to capture low density lipoproteins (LDLs). Regeneration of endothelium induced thickening of the ECBM. Secretion of the BM components occurred in the G2-phase. Multiple regenerations, as well as arterial hypertension and aging, also led to the thickening of the BM. Under these conditions, the speed of re-endothelialization increased. The thick BM captured more LDLs. LDLs formed after overloading of rats with lipids acquired higher affinity to the BM, presumably due to the prolonged transport of chylomicrons through neuraminidase-positive endo-lysosomes. These data provide new molecular and cellular mechanisms of atherogenesis.

New insight into dyslipidemia‐induced cellular senescence in atherosclerosis

Atherosclerosis, characterized by lipid‐rich plaques in the arterial wall, is an age‐related disorder and a leading cause of mortality worldwide. However, the specific mechanisms remain complex. Recently, emerging evidence has demonstrated that senescence of various types of cells, such as endothelial cells (ECs), vascular smooth muscle cells (VSMCs), macrophages, endothelial progenitor cells (EPCs), and adipose‐derived mesenchymal stem cells (AMSCs) contributes to atherosclerosis. Cellular senescence and atherosclerosis share various causative stimuli, in which dyslipidemia has attracted much attention. Dyslipidemia, mainly referred to elevated plasma levels of atherogenic lipids or lipoproteins, or functional impairment of anti‐atherogenic lipids or lipoproteins, plays a pivotal role both in cellular senescence and atherosclerosis. In this review, we summarize the current evidence for dyslipidemia‐induced cellular senescence during atherosclerosis, with a focus on low‐density lipoprotein (LDL) and its modifications, hydrolysate of triglyceride‐rich lipoproteins (TRLs), and high‐density lipoprotein (HDL), respectively. Furthermore, we describe the underlying mechanisms linking dyslipidemia‐induced cellular senescence and atherosclerosis. Finally, we discuss the senescence‐related therapeutic strategies for atherosclerosis, with special attention given to the anti‐atherosclerotic effects of promising geroprotectors as well as anti‐senescence effects of current lipid‐lowering drugs.

Immature Vascular Smooth Muscle Cells in Healthy Murine Arteries and Atherosclerotic Plaques: Localization and Activity

The local development of atherosclerotic lesions may, at least partly, be associated with the specific cellular composition of atherosclerosis-prone regions. Previously, it was demonstrated that a small population of immature vascular smooth muscle cells (VSMCs) expressing both CD146 and neuron-glial antigen 2 is postnatally sustained in atherosclerosis-prone sites. We supposed that these cells may be involved in atherogenesis and can continuously respond to angiotensin II, which is an atherogenic factor. Using immunohistochemistry, flow cytometry, wound migration assay xCELLigence system, and calcium imaging, we studied the functional activities of immature VSMCs in vitro and in vivo. According to our data, these cells do not express nestin, CD105, and the leptin receptor. They are localized in atherosclerosis-prone regions, and their number increases with age, from 5.7% to 23%. Immature VSMCs do not migrate to low shear stress areas and atherosclerotic lesions. They also do not have any unique response to angiotensin II. Thus, despite the localization of immature VSMCs and the presence of the link between their number and age, our study did not support the hypothesis that immature VSMCs are directly involved in the formation of atherosclerotic lesions. Additional lineage tracing studies can clarify the fate of these cells during atherogenesis.

Assessment and management of the heightened risk for atherosclerotic cardiovascular events in patients with lupus erythematosus or dermatomyositis

For patients with lupus erythematosus (LE) or dermatomyositis (DM), there is an urgent need to address a heightened risk of clinical events, chiefly heart attacks and strokes, caused by atherosclerotic cardiovascular disease (ASCVD). Patients with LE or DM frequently exhibit high levels of conventional risk factors for ASCVD events, particularly dyslipoproteinemia and hypertension; an amplified burden of atherosclerotic plaques; and increased age- and sex-adjusted rates of ASCVD events compared with the general population. The rate of ASCVD events exceeds what would be expected from conventional risk factors, suggesting that disease-specific autoimmune processes exacerbate specific, known pathogenic steps in atherosclerosis. Importantly, despite their heightened risk, patients with LE or DM are often undertreated for known causative agents and exacerbators of ASCVD. Herein, we propose an approach to assess and manage the heightened risk of ASCVD events in patients with LE or DM. Our approach is modeled in large part on established approaches to patients with diabetes mellitus or stage 3 or 4 chronic kidney disease, which are well-studied conditions that also show heightened risk for ASCVD events and have been explicitly incorporated into standard clinical guidelines for ASCVD. Based on the available evidence, we conclude that patients with LE or DM require earlier and more aggressive screening and management of ASCVD. We suggest that physicians consider implementing multipliers of conventional risk calculators to trigger earlier initiation of lifestyle modifications and medical therapies in primary prevention of ASCVD events, employ vascular imaging to quantify the burden of subclinical plaques, and treat to lower lipid targets using statins and newer therapies, such as PCSK9 inhibitors, that decrease ASCVD events in nonautoimmune cohorts. More clinical vigilance is needed regarding surveillance, prevention, risk modification, and treatment of dyslipidemias, hypertension, and smoking in patients with LE or DM. All of these goals are achievable.

Trafficking of Mononuclear Phagocytes in Healthy Arteries and Atherosclerosis

Monocytes and macrophages play essential roles in all stages of atherosclerosis – from early precursor lesions to advanced stages of the disease. Intima-resident macrophages are among the first cells to be confronted with the influx and retention of apolipoprotein B-containing lipoproteins at the onset of hypercholesterolemia and atherosclerosis development. In this review, we outline the trafficking of monocytes and macrophages in and out of the healthy aorta, as well as the adaptation of their migratory behaviour during hypercholesterolemia. Furthermore, we discuss the functional and ontogenetic composition of the aortic pool of mononuclear phagocytes and its link to the atherosclerotic disease process. The development of mouse models of atherosclerosis regression in recent years, has enabled scientists to investigate the behaviour of monocytes and macrophages during the resolution of atherosclerosis. Herein, we describe the dynamics of these mononuclear phagocytes upon cessation of hypercholesterolemia and how they contribute to the restoration of tissue homeostasis. The aim of this review is to provide an insight into the trafficking, fate and disease-relevant dynamics of monocytes and macrophages during atherosclerosis, and to highlight remaining questions. We focus on the results of rodent studies, as analysis of cellular fates requires experimental manipulations that cannot be performed in humans but point out findings that could be replicated in human tissues. Understanding of the biology of macrophages in atherosclerosis provides an important basis for the development of therapeutic strategies to limit lesion formation and promote plaque regression.

Multi-omics approaches for revealing the complexity of cardiovascular disease

The development and progression of cardiovascular disease (CVD) can mainly be attributed to the narrowing of blood vessels caused by atherosclerosis and thrombosis, which induces organ damage that will result in end-organ dysfunction characterized by events such as myocardial infarction or stroke. It is also essential to consider other contributory factors to CVD, including cardiac remodelling caused by cardiomyopathies and co-morbidities with other diseases such as chronic kidney disease. Besides, there is a growing amount of evidence linking the gut microbiota to CVD through several metabolic pathways. Hence, it is of utmost importance to decipher the underlying molecular mechanisms associated with these disease states to elucidate the development and progression of CVD. A wide array of systems biology approaches incorporating multi-omics data have emerged as an invaluable tool in establishing alterations in specific cell types and identifying modifications in signalling events that promote disease development. Here, we review recent studies that apply multi-omics approaches to further understand the underlying causes of CVD and provide possible treatment strategies by identifying novel drug targets and biomarkers. We also discuss very recent advances in gut microbiota research with an emphasis on how diet and microbial composition can impact the development of CVD. Finally, we present various biological network analyses and other independent studies that have been employed for providing mechanistic explanation and developing treatment strategies for end-stage CVD, namely myocardial infarction and stroke.

Low-density lipoproteins cause atherosclerotic cardiovascular disease: pathophysiological, genetic, and therapeutic insights: a consensus statement from the European Atherosclerosis Society Consensus Panel

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Extracellular Vesicles: An Emerging Mechanism Governing the Secretion and Biological Roles of Tenascin-C

ECM composition and architecture are tightly regulated for tissue homeostasis. Different disorders have been associated to alterations in the levels of proteins such as collagens, fibronectin (FN) or tenascin-C (TnC). TnC emerges as a key regulator of multiple inflammatory processes, both during physiological tissue repair as well as pathological conditions ranging from tumor progression to cardiovascular disease. Importantly, our current understanding as to how TnC and other non-collagen ECM components are secreted has remained elusive. Extracellular vesicles (EVs) are small membrane-bound particles released to the extracellular space by most cell types, playing a key role in cell-cell communication. A broad range of cellular components can be transported by EVs (e.g. nucleic acids, lipids, signalling molecules and proteins). These cargoes can be transferred to target cells, potentially modulating their function. Recently, several extracellular matrix (ECM) proteins have been characterized as bona fide EV cargoes, exosomal secretion being particularly critical for TnC. EV-dependent ECM secretion might underpin diseases where ECM integrity is altered, establishing novel concepts in the field such as ECM nucleation over long distances, and highlighting novel opportunities for diagnostics and therapeutic intervention. Here, we review recent findings and standing questions on the molecular mechanisms governing EV–dependent ECM secretion and its potential relevance for disease, with a focus on TnC.

ECM deposition is driven by caveolin-1-dependent regulation of exosomal biogenesis and cargo sorting

The composition and physical properties of the extracellular matrix (ECM) critically influence tumor progression, but the molecular mechanisms underlying ECM layering are poorly understood. Tumor–stroma interaction critically depends on cell communication mediated by exosomes, small vesicles generated within multivesicular bodies (MVBs). We show that caveolin-1 (Cav1) centrally regulates exosome biogenesis and exosomal protein cargo sorting through the control of cholesterol content at the endosomal compartment/MVBs. Quantitative proteomics profiling revealed that Cav1 is required for exosomal sorting of ECM protein cargo subsets, including Tenascin-C (TnC), and for fibroblast-derived exosomes to efficiently deposit ECM and promote tumor invasion. Cav1-driven exosomal ECM deposition not only promotes local stromal remodeling but also the generation of distant ECM-enriched stromal niches in vivo. Cav1 acts as a cholesterol rheostat in MVBs, determining sorting of ECM components into specific exosome pools and thus ECM deposition. This supports a model by which Cav1 is a central regulatory hub for tumor–stroma interactions through a novel exosome-dependent ECM deposition mechanism.

Increased retention of LDL from type 1 diabetic patients in atherosclerosis-prone areas of the murine arterial wall

BACKGROUND AND AIMS

Type 1 diabetes accelerates the development of atherosclerotic cardiovascular diseases. Retention of low-density lipoprotein (LDL) in the arterial wall is a causal step in atherogenesis, but it is unknown whether diabetes alters the propensity of LDL for retention. The present study investigated whether LDL from type 1 diabetic and healthy non-diabetic subjects differed in their ability to bind to the arterial wall in a type 1 diabetic mouse model.

METHODS

Fluorescently-labeled LDL obtained from type 1 diabetic patients or healthy controls was injected into mice with type 1 diabetes. The amount of retained LDL in the atherosclerosis-prone inner curvature of the aortic arch was quantified by fluorescence microscopy. Healthy control LDL was in vitro glycated, analyzed for protein glycation by LC-MS/MS, and tested for retention propensity.

RESULTS

Retention of LDL from type 1 diabetic patients was 4.35-fold higher compared to LDL from nondiabetic subjects. Nuclear magnetic resonance (NMR) spectroscopy analysis of LDL revealed no differences in the concentration of the atherogenic small dense LDL between type 1 diabetic and non-diabetic subjects. In vitro glycation of LDL from a non-diabetic subject increased retention compared to non-glycated LDL. LC-MS/MS revealed four new glycated spots in the protein sequence of ApoB of in vitro glycated LDL.

CONCLUSIONS

LDL from type 1 diabetic patients showed increased retention at atherosclerosis-prone sites in the arterial wall of diabetic mice. Glycation of LDL is one modification that may increase retention, but other, yet unknown, mechanisms are also likely to contribute.

ApoB-100 Lipoprotein Complex Formation with Intima Proteoglycans as a Cause of Atherosclerosis and Its Possible Ex Vivo Evaluation as a Disease Biomarker

Experimental and clinical data indicate that the initiation and progress of atherosclerosis and its clinical manifestations are first caused by circulating apoB-100 lipoproteins that enter and are retained in the arterial intima. Extracellular sulfated proteoglycans (PGs) of the intima are the retention agents. The PGs also initiate physical and biochemical lipoprotein degradation with the production of bioactive, lipid products that trigger an inflammatory response that leads to atherosclerosis. There are many simple methods for measuring abnormalities of circulating lipoproteins and their relation to atherosclerotic cardiovascular disease (ACVD). However, limited research aims to evaluate procedures that could report quantitatively about the contribution of the interaction of apoB-100 lipoprotein-arterial intima PGs to clinical manifestation of ACVD. In the present review we discuss observations indicating that simple ex vivo evaluation of the affinity of apoB-100 lipoproteins for arterial PGs and glycosaminoglycans (GAGs) can give an indication of its association with clinical manifestations of atherosclerosis. In addition, we discuss molecular and cellular aspects of the apoB-100 lipoproteins association with arterial PGs that are related to atherogenesis and that support the experimental framework behind the current “Response-to-Retention” hypothesis of atherosclerosis.

Human mast cell neutral proteases generate modified LDL particles with increased proteoglycan binding

BACKGROUND AND AIMS

Subendothelial interaction of LDL with extracellular matrix drives atherogenesis. This interaction can be strengthened by proteolytic modification of LDL. Mast cells (MCs) are present in atherosclerotic lesions, and upon activation, they degranulate and release a variety of neutral proteases. Here we studied the ability of MC proteases to cleave apoB-100 of LDL and affect the binding of LDL to proteoglycans.

METHODS

Mature human MCs were differentiated from human peripheral blood-derived CD34⁺ progenitors in vitro and activated with calcium ionophore to generate MC-conditioned medium. LDL was incubated in the MC-conditioned medium or with individual MC proteases, and the binding of native and modified LDL to isolated human aortic proteoglycans or to human atherosclerotic plaques ex vivo was determined. MC proteases in atherosclerotic human coronary artery lesions were detected by immunofluorescence and qPCR.

RESULTS

Activated human MCs released the neutral proteases tryptase, chymase, carboxypeptidase A3, cathepsin G, and granzyme B. Of these, cathepsin G degraded most efficiently apoB-100, induced LDL fusion, and enhanced binding of LDL to isolated human aortic proteoglycans and human atherosclerotic lesions ex vivo. Double immunofluoresence staining of human atherosclerotic coronary arteries for tryptase and cathepsin G indicated that lesional MCs contain cathepsin G. In the lesions, expression of cathepsin G correlated with the expression of tryptase and chymase, but not with that of neutrophil proteinase 3.

CONCLUSIONS

The present study suggests that cathepsin G in human atherosclerotic lesions is largely derived from MCs and that activated MCs may contribute to atherogenesis by enhancing LDL retention.

Vascular Smooth Muscle-Specific Progerin Expression Accelerates Atherosclerosis and Death in a Mouse Model of Hutchinson-Gilford Progeria Syndrome

Supplemental Digital Content is available in the text.

Background:

Progerin, an aberrant protein that accumulates with age, causes the rare genetic disease Hutchinson-Gilford progeria syndrome (HGPS). Patients who have HGPS exhibit ubiquitous progerin expression, accelerated aging and atherosclerosis, and die in their early teens, mainly of myocardial infarction or stroke. The mechanisms underlying progerin-induced atherosclerosis remain unexplored, in part, because of the lack of appropriate animal models.

Methods:

We generated an atherosclerosis-prone model of HGPS by crossing apolipoprotein E–deficient (Apoe^–/–) mice with Lmna^G609G/G609G mice ubiquitously expressing progerin. To induce progerin expression specifically in macrophages or vascular smooth muscle cells (VSMCs), we crossed Apoe^–/–Lmna^LCS/LCS mice with LysMCre and SM22αCre mice, respectively. Progerin expression was evaluated by polymerase chain reaction and immunofluorescence. Cardiovascular alterations were determined by immunofluorescence and histology in male mice fed normal chow or a high-fat diet. In vivo low-density lipoprotein retention was assessed by intravenous injection of fluorescently labeled human low-density lipoprotein. Cardiac electric defects were evaluated by electrocardiography.

Results:

Apoe^–/–Lmna^G609G/G609G mice with ubiquitous progerin expression exhibited a premature aging phenotype that included failure to thrive and shortened survival. In addition, high-fat diet–fed Apoe^–/–Lmna^G609G/G609G mice developed a severe vascular pathology, including medial VSMC loss and lipid retention, adventitial fibrosis, and accelerated atherosclerosis, thus resembling most aspects of cardiovascular disease observed in patients with HGPS. The same vascular alterations were also observed in Apoe^–/–Lmna^LCS/LCSSM22αCre mice expressing progerin specifically in VSMCs, but not in Apoe^–/–Lmna^LCS/LCSLysMCre mice with macrophage-specific progerin expression. Moreover, Apoe^–/–Lmna^LCS/LCSSM22αCre mice had a shortened lifespan despite the lack of any overt aging phenotype. Aortas of ubiquitously and VSMC-specific progerin-expressing mice exhibited increased retention of fluorescently labeled human low-density lipoprotein, and atheromata in both models showed vulnerable plaque features. Immunohistopathological examination indicated that Apoe^–/–Lmna^LCS/LCSSM22αCre mice, unlike Apoe^–/–Lmna^G609G/G609G mice, die of atherosclerosis-related causes.

Conclusions:

We have generated the first mouse model of progerin-induced atherosclerosis acceleration, and demonstrate that restricting progerin expression to VSMCs is sufficient to accelerate atherosclerosis, trigger plaque vulnerability, and reduce lifespan. Our results identify progerin-induced VSMC death as a major factor triggering atherosclerosis and premature death in HGPS.

Macrophage-derived foam cells impair endothelial barrier function by inducing endothelial-mesenchymal transition via CCL-4

Recently, endothelial-mesenchymal transition (EndMT) has been demonstrated to play an important role in the development of atherosclerosis, the molecular mechanisms of which remain unclear. In the present study, scanning electron microscopy directly revealed a widened endothelial space and immunohistofluorescence demonstrated that EndMT was increased in human aorta atherosclerotic plaques. M1 macrophage-derived foam cell (M1-FC) supernatants, but not M2 macrophage-derived foam cell (M2-FC) supernatants, induced EndMT. A protein array and enzyme-linked immunosorbent assay identified that the levels of several cytokines, including C-C motif chemokine ligand 4 (CCL-4) were increased in M1-FC supernatants, in which EndMT was promoted, accompanied by increased endothelial permeability and monocyte adhesion. Furthermore, anti-CCL-4 antibody abolished the effects of M1-FC supernatants on EndMT. At the same time, CCL-4 activated its receptor, C-C motif chemokine receptor-5 (CCR-5), and upregulated transforming growth factor-β (TGF-β) expression. Further experiments revealed that EndMT induced by CCL-4 was reversed by treatment with CCR-5 antagonist and the RNA-mediated knockdown of TGF-β. On the whole, the data of the present study suggest that M1-FCs induce EndMT by upregulating CCL-4, and increase endothelial permeability and monocyte adhesion. These data may help to elucidate the important role of EndMT in the development of atherosclerosis.

ATVB Distinguished Scientist Award: How Costimulatory and Coinhibitory Pathways Shape Atherosclerosis

OBJECTIVE

Immune cells play a critical role in atherosclerosis. Costimulatory and coinhibitory molecules of the tumor necrosis factor receptor and CD28 immunoglobulin superfamilies not only shape T-cell and B-cell responses but also have a major effect on antigen-presenting cells and nonimmune cells.

APPROACH AND RESULTS

Pharmacological inhibition or activation of costimulatory and coinhibitory molecules and genetic deletion demonstrated their involvement in atherosclerosis. This review highlights recent advances in understanding how costimulatory and coinhibitory pathways shape the immune response in atherosclerosis.

CONCLUSIONS

Insights gained from costimulatory and coinhibitory molecule function in atherosclerosis may inform future therapeutic approaches.

Roles of Vascular Oxidative Stress and Nitric Oxide in the Pathogenesis of Atherosclerosis

Major reactive oxygen species (ROS)–producing systems in vascular wall include NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase, xanthine oxidase, the mitochondrial electron transport chain, and uncoupled endothelial nitric oxide (NO) synthase. ROS at moderate concentrations have important signaling roles under physiological conditions. Excessive or sustained ROS production, however, when exceeding the available antioxidant defense systems, leads to oxidative stress. Animal studies have provided compelling evidence demonstrating the roles of vascular oxidative stress and NO in atherosclerosis. All established cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, and smoking enhance ROS generation and decrease endothelial NO production. Key molecular events in atherogenesis such as oxidative modification of lipoproteins and phospholipids, endothelial cell activation, and macrophage infiltration/activation are facilitated by vascular oxidative stress and inhibited by endothelial NO. Atherosclerosis develops preferentially in vascular regions with disturbed blood flow (arches, branches, and bifurcations). The fact that these sites are associated with enhanced oxidative stress and reduced endothelial NO production is a further indication for the roles of ROS and NO in atherosclerosis. Therefore, prevention of vascular oxidative stress and improvement of endothelial NO production represent reasonable therapeutic strategies in addition to the treatment of established risk factors (hypercholesterolemia, hypertension, and diabetes mellitus).

Apolipoprotein B-containing lipoproteins and atherosclerotic cardiovascular disease

Cholesterol-rich, apolipoprotein B (apoB)-containing lipoproteins are now widely accepted as the most important causal agents of atherosclerotic cardiovascular disease. Multiple unequivocal and orthogonal lines of evidence all converge on low-density lipoprotein and related particles as being the principal actors in the genesis of atherosclerosis. Here, we review the fundamental role of atherogenic apoB-containing lipoproteins in cardiovascular disease and several other humoral and parietal factors that are required to initiate and maintain arterial degeneration. The biology of foam cells and their interactions with high-density lipoproteins, including cholesterol efflux, are also briefly reviewed.

The central role of arterial retention of cholesterol-rich apolipoprotein-B-containing lipoproteins in the pathogenesis of atherosclerosis: a triumph of simplicity

PURPOSE OF REVIEW

Today, it is no longer a hypothesis, but an established fact, that increased plasma concentrations of cholesterol-rich apolipoprotein-B (apoB)-containing lipoproteins are causatively linked to atherosclerotic cardiovascular disease (ASCVD) and that lowering plasma LDL concentrations reduces cardiovascular events in humans. Here, we review evidence behind this assertion, with an emphasis on recent studies supporting the 'response-to-retention' model - namely, that the key initiating event in atherogenesis is the retention, or trapping, of cholesterol-rich apoB-containing lipoproteins within the arterial wall.

RECENT FINDINGS

New clinical trials have shown that ezetimibe and anti-PCSK9 antibodies - both nonstatins - lower ASCVD events, and they do so to the same extent as would be expected from comparable plasma LDL lowering by a statin. These studies demonstrate beyond any doubt the causal role of apoB-containing lipoproteins in atherogenesis. In addition, recent laboratory experimentation and human Mendelian randomization studies have revealed novel information about the critical role of apoB-containing lipoproteins in atherogenesis. New information has also emerged on mechanisms for the accumulation in plasma of harmful cholesterol-rich and triglyceride-rich apoB-containing remnant lipoproteins in states of overnutrition. Like LDL, these harmful cholesterol-rich and triglyceride-rich apoB-containing remnant lipoprotein remnants become retained and modified within the arterial wall, causing atherosclerosis.

SUMMARY

LDL and other cholesterol-rich, apoB-containing lipoproteins, once they become retained and modified within the arterial wall, cause atherosclerosis. This simple, robust pathophysiologic understanding may finally allow us to eradicate ASCVD, the leading killer in the world.