Endothelial Transcytosis of Lipoproteins in Atherosclerosis

Modulation of FGF pathway signaling and vascular differentiation using designed oligomeric assemblies

Many growth factors and cytokines signal by binding to the extracellular domains of their receptors and driving association and transphosphorylation of the receptor intracellular tyrosine kinase domains, initiating downstream signaling cascades. To enable systematic exploration of how receptor valency and geometry affect signaling outcomes, we designed cyclic homo-oligomers with up to 8 subunits using repeat protein building blocks that can be modularly extended. By incorporating a de novo-designed fibroblast growth factor receptor (FGFR)-binding module into these scaffolds, we generated a series of synthetic signaling ligands that exhibit potent valency- and geometry-dependent Ca2+ release and mitogen-activated protein kinase (MAPK) pathway activation. The high specificity of the designed agonists reveals distinct roles for two FGFR splice variants in driving arterial endothelium and perivascular cell fates during early vascular development. Our designed modular assemblies should be broadly useful for unraveling the complexities of signaling in key developmental transitions and for developing future therapeutic applications.

Reversal of atherosclerosis by restoration of vascular copper homeostasis

Atherosclerosis has traditionally been considered as a disorder characterized by the accumulation of cholesterol and thrombotic materials within the arterial wall. However, it is now understood to be a complex inflammatory disease involving multiple factors. Central to the pathogenesis of atherosclerosis are the interactions among monocytes, macrophages, and neutrophils, which play pivotal roles in the initiation, progression, and destabilization of atherosclerotic lesions. Recent advances in our understanding of atherosclerosis pathogenesis, coupled with results obtained from experimental interventions, lead us to propose the hypothesis that atherosclerosis may be reversible. This paper outlines the evolution of this hypothesis and presents corroborating evidence that supports the potential for atherosclerosis regression through the restoration of vascular copper homeostasis. We posit that these insights may pave the way for innovative therapeutic approaches aimed at the reversal of atherosclerosis.

Insights from Murine Studies on the Site Specificity of Atherosclerosis

Atherosclerosis is an inflammatory reaction that develops at specific regions within the artery wall and at specific sites of the arterial tree over a varying time frame in response to a variety of risk factors. The mechanisms that account for the interaction of systemic factors and atherosclerosis-susceptible regions of the arterial tree to mediate this site-specific development of atherosclerosis are not clear. The dynamics of blood flow has a major influence on where in the arterial tree atherosclerosis develops, priming the site for interactions with atherosclerotic risk factors and inducing cellular and molecular participants in atherogenesis. But how this accounts for lesion development at various locations along the vascular tree across differing time frames still requires additional study. Currently, murine models are favored for the experimental study of atherogenesis and provide the most insight into the mechanisms that may contribute to the development of atherosclerosis. Based largely on these studies, in this review, we discuss the role of hemodynamic shear stress, SR-B1, and other factors that may contribute to the site-specific development of atherosclerosis.

Adaptive immunity and atherosclerosis: aging at its crossroads

Adaptive immunity plays a profound role in atherosclerosis pathogenesis by regulating antigen-specific responses, inflammatory signaling and antibody production. However, as we age, our immune system undergoes a gradual functional decline, a phenomenon termed "immunosenescence". This decline is characterized by a reduction in proliferative naïve B- and T cells, decreased B- and T cell receptor repertoire and a pro-inflammatory senescence associated secretory profile. Furthermore, aging affects germinal center responses and deteriorates secondary lymphoid organ function and structure, leading to impaired T-B cell dynamics and increased autoantibody production. In this review, we will dissect the impact of aging on adaptive immunity and the role played by age-associated B- and T cells in atherosclerosis pathogenesis, emphasizing the need for interventions that target age-related immune dysfunction to reduce cardiovascular disease risk.

Monocytic microRNAs-Novel targets in atherosclerosis therapy

Atherosclerosis is a chronic proinflammatory disease of the vascular wall resulting in narrowing of arteries due to plaque formation, thereby causing reduced blood supply that is the leading cause for diverse end-organ damage with high mortality rates. Monocytes/macrophages, activated by elevated circulating lipoproteins, are significantly involved in the formation and development of atherosclerotic plaques. The imbalance between proinflammatory and anti-inflammatory macrophages, arising from dysregulated macrophage polarization, appears to be a driving force in this process. Proatherosclerotic processes acting on monocytes/macrophages include accumulation of cholesterol in macrophages leading to foam cell formation, as well as dysfunctional efferocytosis, all of which contribute to the formation of unstable plaques. In recent years, microRNAs (miRs) were identified as factors that could modulate monocyte/macrophage function and may therefore interfere with the atherosclerotic process. In this review, we present effects of monocyte/macrophage-derived miRs on atherosclerotic processes in order to reveal new treatment options using miRmimics or antagomiRs.

The Role of Endothelial Cells in Atherosclerosis: Insights from Genetic Association Studies

Endothelial cells (ECs) mediate several biological functions that are relevant to atherosclerosis and coronary artery disease (CAD), regulating an array of vital processes including vascular tone, wound healing, reactive oxygen species, shear stress response, and inflammation. Although which of these functions is linked causally with CAD development and/or progression is not yet known, genome-wide association studies have implicated more than 400 loci associated with CAD risk, among which several have shown EC-relevant functions. Given the arduous process of mechanistically interrogating single loci to CAD, high-throughput variant characterization methods, including pooled Clustered Regularly Interspaced Short Palindromic Repeats screens, offer exciting potential to rapidly accelerate the discovery of bona fide EC-relevant genetic loci. These discoveries in turn will broaden the therapeutic avenues for CAD beyond lipid lowering and behavioral risk modification to include EC-centric modalities of risk prevention and treatment.

Endothelial Slc35a1 Deficiency Causes Loss of LSEC Identity and Exacerbates Neonatal Lipid Deposition in the Liver in Mice

BACKGROUND & AIMS

The functional maturation of the liver largely occurs after birth. In the early stages of life, the liver of a newborn encounters enormous high-fat metabolic stress caused by the consumption of breast milk. It is unclear how the maturing liver adapts to high lipid metabolism. Liver sinusoidal endothelial cells (LSECs) play a fundamental role in establishing liver vasculature and are decorated with many glycoproteins on their surface. The Slc35a1 gene encodes a cytidine-5'-monophosphate (CMP)-sialic acid transporter responsible for transporting CMP-sialic acids between the cytoplasm and the Golgi apparatus for protein sialylation. This study aimed to determine whether endothelial sialylation plays a role in hepatic vasculogenesis and functional maturation.

METHODS

Endothelial-specific Slc35a1 knockout mice were generated. Liver tissues were collected for histologic analysis, lipidomic profiling, RNA sequencing, confocal immunofluorescence, and immunoblot analyses.

RESULTS

Endothelial Slc35a1-deficient mice exhibited excessive neonatal hepatic lipid deposition, severe liver damage, and high mortality. Endothelial deletion of Slc35a1 led to sinusoidal capillarization and disrupted hepatic zonation. Mechanistically, vascular endothelial growth factor receptor 2 (VEGFR2) in LSECs was desialylated and VEGFR2 signaling was enhanced in Slc35a1-deficient mice. Inhibition of VEGFR2 signaling by SU5416 alleviated lipid deposition and restored hepatic vasculature in Slc35a1-deficient mice.

CONCLUSIONS

Our findings suggest that sialylation of LSECs is critical for maintaining hepatic vascular development and lipid homeostasis. Targeting VEGFR2 signaling may be a new strategy to prevent liver disorders associated with abnormal vasculature and lipid deposition.

Vascular Aging and Atherosclerosis: A Perspective on Aging

Vascular aging (VA) is recognized as a pivotal factor in the development and progression of atherosclerosis (AS). Although various epidemiological and clinical research has demonstrated an intimate connection between aging and AS, the candidate mechanisms still require thorough examination. This review adopts an aging-centric perspective to deepen the comprehension of the intricate relationship between biological aging, vascular cell senescence, and AS. Various aging-related physiological factors influence the physical system's reactions, including oxygen radicals, inflammation, lipids, angiotensin II, mechanical forces, glucose levels, and insulin resistance. These factors cause endothelial dysfunction, barrier damage, sclerosis, and inflammation for VA and promote AS via distinct or shared pathways. Furthermore, the increase of senescent cells inside the vascular tissues, caused by genetic damage, dysregulation, secretome changes, and epigenetic modifications, might be the primary cause of VA.

Deciphering the emerging landscape of HOX genes in cardiovascular biology, atherosclerosis and beyond (Review)

Atherosclerosis, a dominant driving force underlying multiple cardiovascular events, is an intertwined and chronic inflammatory disease characterized by lipid deposition in the arterial wall, which leads to diverse cardiovascular problems. Despite unprecedented advances in understanding the pathogenesis of atherosclerosis and the substantial decline in cardiovascular mortality, atherosclerotic cardiovascular disease remains a global public health issue. Understanding the molecular landscape of atherosclerosis is imperative in the field of molecular cardiology. Recently, compelling evidence has shown that an important family of homeobox (HOX) genes endows causality in orchestrating the interplay between various cardiovascular biological processes and atherosclerosis. Despite seemingly scratching the surface, such insight into the realization of biology promises to yield extraordinary breakthroughs in ameliorating atherosclerosis. Primarily recapitulated herein are the contributions of HOX in atherosclerosis, including diverse cardiovascular biology, knowledge gaps, remaining challenges and future directions. A snapshot of other cardiovascular biological processes was also provided, including cardiac/vascular development, cardiomyocyte pyroptosis/apoptosis, cardiac fibroblast proliferation and cardiac hypertrophy, which are responsible for cardiovascular disorders. Further in‑depth investigation of HOX promises to provide a potential yet challenging landscape, albeit largely undetermined to date, for partially pinpointing the molecular mechanisms of atherosclerosis. A plethora of new targeted therapies may ultimately emerge against atherosclerosis, which is rapidly underway. However, translational undertakings are crucially important but increasingly challenging and remain an ongoing and monumental conundrum in the field.

iPSC-Derived Endothelial Cells Reveal LDLR Dysfunction and Dysregulated Gene Expression Profiles in Familial Hypercholesterolemia

Defects in the low-density lipoprotein receptor (LDLR) are associated with familial hypercholesterolemia (FH), manifested by atherosclerosis and cardiovascular disease. LDLR deficiency in hepatocytes leads to elevated blood cholesterol levels, which damage vascular cells, especially endothelial cells, through oxidative stress and inflammation. However, the distinctions between endothelial cells from individuals with normal and defective LDLR are not yet fully understood. In this study, we obtained and examined endothelial derivatives of induced pluripotent stem cells (iPSCs) generated previously from conditionally healthy donors and compound heterozygous FH patients carrying pathogenic LDLR alleles. In normal iPSC-derived endothelial cells (iPSC-ECs), we detected the LDLR protein predominantly in its mature form, whereas iPSC-ECs from FH patients have reduced levels of mature LDLR and show abolished low-density lipoprotein uptake. RNA-seq of mutant LDLR iPSC-ECs revealed a unique transcriptome profile with downregulated genes related to monocarboxylic acid transport, exocytosis, and cell adhesion, whereas upregulated signaling pathways were involved in cell secretion and leukocyte activation. Overall, these findings suggest that LDLR defects increase the susceptibility of endothelial cells to inflammation and oxidative stress. In combination with elevated extrinsic cholesterol levels, this may result in accelerated endothelial dysfunction, contributing to early progression of atherosclerosis and other cardiovascular pathologies associated with FH.

Apolipoprotein C3: form begets function

Increased circulating levels of apolipoprotein C3 (APOC3) predict cardiovascular disease (CVD) risk in humans, and APOC3 promotes atherosclerosis in mouse models. APOC3's mechanism of action is due in large part to its ability to slow the clearance of triglyceride-rich lipoproteins (TRLs) and their remnants when APOC3 is carried by these lipoproteins. However, different pools and forms of APOC3 exert distinct biological effects or associations with atherogenic processes. Thus, lipid-free APOC3 induces inflammasome activation in monocytes whereas lipid particle-bound APOC3 does not. APOC3-enriched LDL binds better to the vascular glycosaminoglycan biglycan than does LDL depleted of APOC3. Patterns of APOC3 glycoforms predict CVD risk differently. The function of APOC3 bound to HDL is largely unknown. There is still much to learn about the mechanisms of action of different forms and pools of APOC3 in atherosclerosis and CVD, and whether APOC3 inhibition would prevent CVD risk in patients on LDL-cholesterol lowering medications.

Unraveling the Cave: A Seventy-Year Journey into the Caveolar Network, Cellular Signaling, and Human Disease

In the mid-1950s, a groundbreaking discovery revealed the fascinating presence of caveolae, referred to as flask-shaped invaginations of the plasma membrane, sparking renewed excitement in the field of cell biology. Caveolae are small, flask-shaped invaginations in the cell membrane that play crucial roles in diverse cellular processes, including endocytosis, lipid homeostasis, and signal transduction. The structural stability and functionality of these specialized membrane microdomains are attributed to the coordinated activity of scaffolding proteins, including caveolins and cavins. While caveolae and caveolins have been long appreciated for their integral roles in cellular physiology, the accumulating scientific evidence throughout the years reaffirms their association with a broad spectrum of human disorders. This review article aims to offer a thorough account of the historical advancements in caveolae research, spanning from their initial discovery to the recognition of caveolin family proteins and their intricate contributions to cellular functions. Furthermore, it will examine the consequences of a dysfunctional caveolar network in the development of human diseases.

In vitro microvascular engineering approaches and strategies for interstitial tissue integration

The increasing gap between clinical demand for tissue or organ transplants and the availability of donated tissue highlights the emerging opportunities for lab-grown or synthetically engineered tissue. While the field of tissue engineering has existed for nearly half a century, its clinical translation remains unrealised, in part, due to a limited ability to engineer sufficient vascular supply into fabricated tissue, which is necessary to enable nutrient and waste exchange, prevent cellular necrosis, and support tissue proliferation. Techniques to develop anatomically relevant, functional vascular networks in vitro have made significant progress in the last decade, however, the challenge now remains as to how best incorporate these throughout dense parenchymal tissue-like structures to address diffusion-limited development and allow for the fabrication of large-scale vascularised tissue. This review explores advances made in the laboratory engineering of vasculature structures and summarises recent attempts to integrate vascular networks together with sophisticated in vitro avascular tissue and organ-like structures. STATEMENT OF SIGNIFICANCE: The ability to grow full scale, functional tissue and organs in vitro is primarily limited by an inability to adequately diffuse oxygen and nutrients throughout developing cellularised structures, which generally results from the absence of perfusable vessel networks. Techniques to engineering both perfusable vascular networks and avascular miniaturised organ-like structures have recently increased in complexity, sophistication, and physiological relevance. However, integrating these two essential elements into a single functioning vascularised tissue structure represents a significant spatial and temporal engineering challenge which is yet to be surmounted. Here, we explore a range of vessel morphogenic phenomena essential for tissue-vascular co-development, as well as evaluate a range of recent noteworthy approaches for generating vascularised tissue products in vitro.

The Greatly Under-Represented Role of Smooth Muscle Cells in Atherosclerosis

PURPOSE OF REVIEW

This article summarizes previous and recent research on the fundamental role of arterial smooth muscle cells (SMCs) as drivers of initial and, along with macrophages, later stages of human atherosclerosis.

RECENT FINDINGS

Studies using human tissues and SMC lineage-tracing mice have reinforced earlier observations that SMCs drive initial atherogenesis in humans and contribute a multitude of phenotypes including foam cell formation hitherto attributed primarily to macrophages in atherosclerosis. Arterial smooth muscle cells (SMCs) are the primary cell type in human pre-atherosclerotic intima and are responsible for the retention of lipoproteins that drive the development of atherosclerosis. Despite this, images of atherogenesis still depict the process as initially devoid of SMCs, primarily macrophage driven, and indicate only relatively minor roles such as fibrous cap formation to intimal SMCs. This review summarizes historical and recent observations regarding the importance of SMCs in the formation of a pre-atherosclerotic intima, initial and later foam cell formation, and the phenotypic changes that give rise to multiple different roles for SMCs in human and mouse lesions. Potential SMC-specific therapies in atherosclerosis are presented.

Mapping the dynamic high-density lipoprotein synapse

BACKGROUND AND AIMS

Heterogeneous high-density lipoprotein (HDL) particles, which can contain hundreds of proteins, affect human health and disease through dynamic molecular interactions with cell surface proteins. How HDL mediates its long-range signaling functions and interactions with various cell types is largely unknown. Due to the complexity of HDL, we hypothesize that multiple receptors engage with HDL particles resulting in condition-dependent receptor-HDL interaction clusters at the cell surface.

METHODS

Here we used the mass spectrometry-based and light-controlled proximity labeling strategy LUX-MS in a discovery-driven manner to decode HDL-receptor interactions.

RESULTS

Surfaceome nanoscale organization analysis of hepatocytes and endothelial cells using LUX-MS revealed that the previously known HDL-binding protein scavenger receptor B1 (SCRB1) is embedded in a cell surface protein community, which we term HDL synapse. Modulating the endothelial HDL synapse, composed of 60 proteins, by silencing individual members, showed that the HDL synapse can be assembled in the absence of SCRB1 and that the members are interlinked. The aminopeptidase N (AMPN) (also known as CD13) was identified as an HDL synapse member that directly influences HDL uptake into the primary human aortic endothelial cells (HAECs).

CONCLUSIONS

Our data indicate that preformed cell surface residing protein complexes modulate HDL function and suggest new theragnostic opportunities.

Amplified Risk of Intracranial Artery Stenosis/Occlusion Associated With RNF213 p.R4810K in Familial Hypercholesterolemia

Background

The RNF213 p.R4810K variant is associated with moyamoya disease in East Asian individuals and increases the risk of developing intracranial major artery stenosis/occlusion (ICASO) that affects anterior circulation. Meanwhile, 0.5% to 2.5% of asymptomatic East Asian individuals also carry this variant. As such, additional factors are likely required to develop ICASO in variant carriers. Familial hypercholesterolemia (FH) is a common genetic disorder in Japan that has a significant associated risk of developing premature coronary atherosclerosis; however, the relationship between ICASO and FH remains unknown.

Objectives

This study aimed to determine if FH facilitates RNF213 p.R4810K carriers to develop ICASO.

Methods

We enrolled patients with FH who had undergone brain magnetic resonance angiography at our hospital from May 2005 to March 2020. The RNF213 p.R4810K variant, and LDLR and PCSK9 mutations were genotyped. ICASO lesions in the brain magnetic resonance angiogram were analyzed.

Results

Six RNF213 p.R4810K variant carriers were identified among 167 patients with FH (LDLR, n = 104; PCSK9, n = 22). Five of the carriers (83.3%) exhibited ICASO in the anterior circulation; a significant difference in ICASO frequency was observed between the variant carriers and noncarriers (P = 0.025). The median number of stenotic or occluded arteries in the anterior circulation was also significantly larger in the variant carriers (3 vs 1, P = 0.01); however, did not differ between patients with FH with LDLR and PCSK9 mutations.

Conclusions

Patients with FH exhibit increased prevalence and severity of ICASO associated with RNF213 p.R4810K. Gene mutations for FH may confer an increased risk of ICASO in RNF213 p.R4810K carriers.

The Beneficial Effect of Lomitapide on the Cardiovascular System in LDLr-/- Mice with Obesity

OBJECTIVES

Homozygous familial hypercholesteremia (HoFH) is a rare, life-threatening metabolic disease, mainly caused by a mutation in the LDL receptor. If untreated, HoFH causes premature death from acute coronary syndrome. Lomitapide is approved by the FDA as a therapy to lower lipid levels in adult patients with HoFH. Nevertheless, the beneficial effect of lomitapide in HoFH models remains to be defined. In this study, we investigated the effect of lomitapide on cardiovascular function using LDL receptor-knockout mice (LDLr-/-).

METHODS

Six-week-old LDLr-/- mice were fed a standard diet (SD) or a high-fat diet (HFD) for 12 weeks. Lomitapide (1 mg/Kg/Day) was given by oral gavage for the last 2 weeks in the HFD group. Body weight and composition, lipid profile, blood glucose, and atherosclerotic plaques were measured. Vascular reactivity and markers for endothelial function were determined in conductance arteries (thoracic aorta) and resistance arteries (mesenteric resistance arteries (MRA)). Cytokine levels were measured by using the Mesoscale discovery V-Plex assays.

RESULTS

Body weight (47.5 ± 1.5 vs. 40.3 ± 1.8 g), % of fat mass (41.6 ± 1.9% vs. 31.8 ± 1.7%), blood glucose (215.5 ± 21.9 vs. 142.3 ± 7.7 mg/dL), and lipid levels (cholesterol: 600.9 ± 23.6 vs. 451.7 ± 33.4 mg/dL; LDL/VLDL: 250.6 ± 28.9 vs. 161.1 ± 12.24 mg/dL; TG: 299.5 ± 24.1 vs. 194.1 ± 28.1 mg/dL) were significantly decreased, and the % of lean mass (56.5 ± 1.8% vs. 65.2 ± 2.1%) was significantly increased in the HFD group after lomitapide treatment. The atherosclerotic plaque area also decreased in the thoracic aorta (7.9 ± 0.5% vs. 5.7 ± 0.1%). After treatment with lomitapide, the endothelium function of the thoracic aorta (47.7 ± 6.3% vs. 80.7 ± 3.1%) and mesenteric resistance artery (66.4 ± 4.3% vs. 79.5 ± 4.6%) was improved in the group of LDLr-/- mice on HFD. This was correlated with diminished vascular endoplasmic (ER) reticulum stress, oxidative stress, and inflammation.

CONCLUSIONS

Treatment with lomitapide improves cardiovascular function and lipid profile and reduces body weight and inflammatory markers in LDLr-/- mice on HFD.

RNA-binding proteins in vascular inflammation and atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) remains the major cause of premature death and disability worldwide, even when patients with an established manifestation of atherosclerotic heart disease are optimally treated according to the clinical guidelines. Apart from the epigenetic control of transcription of the genetic information to messenger RNAs (mRNAs), gene expression is tightly controlled at the post-transcriptional level before the initiation of translation. Although mRNAs are traditionally perceived as the messenger molecules that bring genetic information from the nuclear DNA to the cytoplasmic ribosomes for protein synthesis, emerging evidence suggests that processes controlling RNA metabolism, driven by RNA-binding proteins (RBPs), affect cellular function in health and disease. Over the recent years, vascular endothelial cell, smooth muscle cell and immune cell RBPs have emerged as key co- or post-transcriptional regulators of several genes related to vascular inflammation and atherosclerosis. In this review, we provide an overview of cell-specific function of RNA-binding proteins involved in all stages of ASCVD and how this knowledge may be used for the development of novel precision medicine therapeutics.

Matricellular proteins in atherosclerosis development

The extracellular matrix (ECM) is an intricate network composed of various multi-domain macromolecules like collagen, proteoglycans, and fibronectin, etc., that form a structurally stable composite, contributing to the mechanical properties of tissue. However, matricellular proteins are non-structural, secretory extracellular matrix proteins, which modulate various cellular functions via interacting with cell surface receptors, proteases, hormones, and cell-matrix. They play essential roles in maintaining tissue homeostasis by regulating cell differentiation, proliferation, adhesion, migration, and several signal transduction pathways. Matricellular proteins display a broad functionality regulated by their multiple structural domains and their ability to interact with different extracellular substrates and/or cell surface receptors. The expression of these proteins is low in adults, however, gets upregulated following injuries, inflammation, and during tumor growth. The marked elevation in the expression of these proteins during atherosclerosis suggests a positive association between their expression and atherosclerotic lesion formation. The role of matricellular proteins in atherosclerosis development has remained an area of research interest in the last two decades and studies revealed these proteins as important players in governing vascular function, remodeling, and plaque formation. Despite extensive research, many aspects of the matrix protein biology in atherosclerosis are still unknown and future studies are required to investigate whether targeting pathways stimulated by these proteins represent viable therapeutic approaches for patients with atherosclerotic vascular diseases. This review summarizes the characteristics of distinct matricellular proteins, discusses the available literature on the involvement of matrix proteins in the pathogenesis of atherosclerosis and suggests new avenues for future research.

Benzo[a]pyrene and a high-fat diet induce aortic injury and promote

Benzo[a]pyrene (BaP) is a ubiquitous environmental pollutant which mainly exposed though diet. High-fat diet (HFD) can induce atherosclerosis, as can BaP. Unhealthy dietary habits lead to high intake of both BaP and lipids. However, the combined effect of BaP and HFD on atherosclerosis and lipid accumulation in the arterial wall, the initial stage of atherosclerosis, is unclear. In this study, C57BL/6 J mice were subchronically exposed to BaP and a HFD, and the mechanism of lipid accumulation was investigated in EA.hy926 and HEK293 cells. Results showed that BaP and HFD increased blood lipids and damaged aortic wall synergistically. Meanwhile, LDL enhanced the toxicity of BaP, and BaP promoted the production of reactive oxygen species and malonaldehyde in EA.hy926 cells, which aggravated LDL-induced cell injury. Moreover, BaP and HFD/LDL induced LDL accumulation in the aortic wall of C57BL/6 J mice/EA.hy926, and the mechanism was by activating AHR/ARNT heterodimer to combine with the scavenger receptor BⅠ (SR-BⅠ) and activin receptor-like kinase 1 (ALK1) promoter regions to transcriptional upregulate its expression, which enhanced the uptake of LDL, and promoting the production of AGEs to inhibit reverse cholesterol transport by SR-BI. BaP and lipid synergistically promoted aortic and endothelial damage, and the health risk of their combined intake should be paid attention to.

Multiomic Analysis and CRISPR Perturbation Screens Identify Endothelial Cell Programs and Novel Therapeutic Targets for Coronary Artery Disease

Endothelial cells (EC) are an important mediator of atherosclerosis and vascular disease. Their exposure to atherogenic risk factors such as hypertension and serum cholesterol leads to endothelial dysfunction and many disease-associated processes. Identifying which of these multiple EC functions is causally related to disease risk has been challenging. There is evidence from in vivo models and human sequencing studies that dysregulation of nitric oxide production directly affects risk of coronary artery disease. Human genetics can help prioritize the other EC functions with causal relationships because germline mutations are acquired at birth and serve as a randomized test of which pathways affect disease risk. Though several coronary artery disease risk variants have been linked to EC function, this process has been slow and laborious. Unbiased analyses of EC dysfunction using multiomic approaches promise to identify the causal genetic mechanisms responsible for vascular disease. Here, we review the data from genomic, epigenomic, and transcriptomic studies that prioritize EC-specific causal pathways. New methods that CRISPR (clustered regularly interspaced short palindromic repeats) perturbation technology with genomic, epigenomic, and transcriptomic analysis promise to speed up the characterization of disease-associated genetic variation. We summarize several recent studies in ECs which use high-throughput genetic perturbation to identify disease-relevant pathways and novel mechanisms of disease. These genetically validated pathways can accelerate the identification of drug targets for the prevention and treatment of atherosclerosis.

Effects of Atherogenic Factors on Endothelial Cells: Bioinformatics Analysis of Differentially Expressed Genes and Signaling Pathways

(1) Background: Atherosclerosis is a serious medical condition associated with high morbidity and mortality rates. It develops over many years as a complex chain of events in the vascular wall involving various cells and is influenced by many factors of clinical interest. (2) Methods: In this study, we performed a bioinformatic analysis of Gene Expression Omnibus (GEO) datasets to investigate the gene ontology of differentially expressed genes (DEGs) in endothelial cells exposed to atherogenic factors such as tobacco smoking, oscillatory shear, and oxidized low-density lipoproteins (oxLDL). DEGs were identified using the limma R package, and gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, and protein-protein interaction (PPI) network analysis were performed. (3) Results: We studied biological processes and signaling pathways involving DEGs in endothelial cells under the influence of atherogenic factors. GO enrichment analysis demonstrated that the DEGs were mainly involved in cytokine-mediated signaling pathway, innate immune response, lipid biosynthetic process, 5-lipoxygenase activity, and nitric-oxide synthase activity. KEGG pathway enrichment analysis showed that common pathways included tumor necrosis factor signaling pathway, NF-κB signaling pathway, NOD-like receptor signaling pathway, lipid and atherosclerosis, lipoprotein particle binding, and apoptosis. (4) Conclusions: Atherogenic factors such as smoking, impaired flow, and oxLDL contribute to impaired innate immune response, metabolism, and apoptosis in endothelial cells, potentially leading to the development of atherosclerosis.

LDL Affects the Immunomodulatory Response of Endothelial Cells by Modulation of the Promyelocytic Leukemia Protein (PML) Expression via PKC

In addition to its function as an intravascular lipid transporter, LDL also triggers signal transduction in endothelial cells (ECs), which, among other things, trigger immunomodulatory cascades, e.g., IL-6 upregulation. However, the molecular mechanisms of how these LDL-triggered immunological responses in ECs are realized are not fully understood. Since promyelocytic leukemia protein (PML) plays a role in promoting inflammatory processes, we examined the relationship between LDL, PML, and IL-6 in human ECs (HUVECs and EA.hy926 cells). RT-qPCR, immunoblotting, and immunofluorescence analyses showed that LDL but not HDL induced higher PML expression and higher numbers of PML-nuclear bodies (PML-NBs). Transfection of the ECs with a PML gene-encoding vector or PML-specific siRNAs demonstrated PML-regulated IL-6 and IL-8 expression and secretion after LDL exposure. Moreover, incubation with the PKC inhibitor sc-3088 or the PKC activator PMA showed that LDL-induced PKC activity leads to the upregulation of PML mRNA and PML protein. In summary, our experimental data suggest that high LDL concentrations trigger PKC activity in ECs to upregulate PML expression, which then increases production and secretion of IL-6 and IL-8. This molecular cascade represents a novel cellular signaling pathway with immunomodulatory effects in ECs in response to LDL exposure.

Anti-inflammatory therapy of atherosclerosis: focusing on IKKβ

Chronic low-grade inflammation has been identified as a major contributor in the development of atherosclerosis. Nuclear Factor-κappa B (NF-κB) is a critical transcription factors family of the inflammatory pathway. As a major catalytic subunit of the IKK complex, IκB kinase β (IKKβ) drives canonical activation of NF-κB and is implicated in the link between inflammation and atherosclerosis, making it a promising therapeutic target. Various natural product derivatives, extracts, and synthetic, show anti-atherogenic potential by inhibiting IKKβ-mediated inflammation. This review focuses on the latest knowledge and current research landscape surrounding anti-atherosclerotic drugs that inhibit IKKβ. There will be more opportunities to fully understand the complex functions of IKKβ in atherogenesis and develop new effective therapies in the future.

Fatty Acid Transport and Signaling: Mechanisms and Physiological Implications

Long-chain fatty acids (FAs) are components of plasma membranes and an efficient fuel source and also serve as metabolic regulators through FA signaling mediated by membrane FA receptors. Impaired tissue FA uptake has been linked to major complications of obesity, including insulin resistance, cardiovascular disease, and type 2 diabetes. Fatty acid interactions with a membrane receptor and the initiation of signaling can modify pathways related to nutrient uptake and processing, cell proliferation or differentiation, and secretion of bioactive factors. Here, we review the major membrane receptors involved in FA uptake and FA signaling. We focus on two types of membrane receptors for long-chain FAs: CD36 and the G protein-coupled FA receptors FFAR1 and FFAR4. We describe key signaling pathways and metabolic outcomes for CD36, FFAR1, and FFAR4 and highlight the parallels that provide insight into FA regulation of cell function.

Co-culture models of endothelial cells, macrophages, and vascular smooth muscle cells for the study of the natural history of atherosclerosis

BACKGROUND

This work aims to present a fast, affordable, and reproducible three-cell co-culture system that could represent the different cellular mechanisms of atherosclerosis, extending from atherogenesis to pathological intimal thickening.

METHODS AND RESULTS

We built four culture models: (i) Culture model #1 (representing normal arterial intima), where human coronary artery endothelial cells were added on top of Matrigel-coated collagen type I matrix, (ii) Culture model #2 (representing atherogenesis), which demonstrated the subendothelial accumulation and oxidative modification of low-density lipoproteins (LDL), (iii) Culture model #3 (representing intimal xanthomas), which demonstrated the monocyte adhesion to the endothelial cell monolayer, transmigration into the subendothelial space, and transformation to lipid-laden macrophages, (iv) Culture model #4 (representing pathological intimal thickening), which incorporated multiple layers of human coronary artery smooth muscle cells within the matrix. Coupling this model with different shear stress conditions revealed the effect of low shear stress on the oxidative modification of LDL and the upregulation of pro-inflammatory molecules and matrix-degrading enzymes. Using electron microscopy, immunofluorescence confocal microscopy, protein and mRNA quantification assays, we showed that the behaviors exhibited by the endothelial cells, macrophages and vascular smooth muscle cells in these models were very similar to those exhibited by these cell types in nascent and intermediate atherosclerotic plaques in humans. The preparation time of the cultures was 24 hours.

CONCLUSION

We present three-cell co-culture models of human atherosclerosis. These models have the potential to allow cost- and time-effective investigations of the mechanobiology of atherosclerosis and new anti-atherosclerotic drug therapies.

Low density lipoprotein receptor endocytosis in cardiovascular disease and the factors affecting LDL levels

Cardiovascular disease (CVD) is the one of major global health issues with approximately 30% of the mortality reported in the mid-income population. Low-density lipoprotein (LDL) plays a crucial role in development of CVD. High LDL along with others forms a plaque and blocks arteries, resulting in CVD. The present chapter deals with the mechanism of receptor-mediated endocytosis of LDL and its management by drugs such as statins and PCSK9 inhibitors along with dietary supplementation for health improvements.

Endothelial dysfunction: developmental mechanisms and therapeutic strategies

Introduction: Every year the importance of the normal functioning of the endothelial layer of the vascular wall in maintaining the health of the body becomes more and more obvious.

The physiological role of the endothelium: The endothelium is a metabolically active organ actively involved in the regulation of hemostasis, modulation of inflammation, maintenance of hemovascular homeostasis, regulation of angiogenesis, vascular tone, and permeability.

Risk factors for the development of endothelial dysfunction: Currently, insufficient bioavailability of nitric oxide is considered the most significant risk factor for endothelial dysfunction.

Mechanisms of development of endothelial dysfunction: The genesis of endothelial dysfunction is a multifactorial process. Among various complex mechanisms, this review examines oxidative stress, inflammation, hyperglycemia, vitamin D deficiency, dyslipidemia, excess visceral fat, hyperhomocysteinemia, hyperuricemia, as well as primary genetic defect of endotheliocytes, as the most common causes in the population underlying the development of endothelial dysfunction.

Markers of endothelial dysfunction in various diseases: This article discusses the main biomarkers of endothelial dysfunction currently used, as well as promising biomarkers in the future for laboratory diagnosis of this pathology.

Therapeutic strategies: Therapeutic approaches to the endothelium in order to prevent or reduce a degree of damage to the vascular wall are briefly described.

Conclusion: Endothelial dysfunction is a typical pathological process involved in the pathogenesis of many diseases. Thus, pharmacological agents with endothelioprotective properties can provide more therapeutic benefits than a drug without such an effect.

Hypertriglyceridemia and Atherosclerotic Carotid Artery Stenosis

Both fasting and non-fasting hypertriglyceridemia have emerged as residual risk factors for atherosclerotic disease. However, it is unclear whether hypertriglyceridemia increases the risks of the progression of carotid artery stenosis. Statins are well known to prevent carotid plaque progression and improve carotid plaque instability. In addition, statin therapy is also known to reduce cerebrovascular events in patients with carotid artery stenosis and to improve clinical outcomes in patients undergoing revascularization procedures. On the other hand, there have been no randomized controlled trials showing that the combination of non-statin lipid-lowering drugs with statins has additional beneficial effects over statin monotherapy to prevent cerebrovascular events and stenosis progression in patients with carotid artery stenosis. In this article, the authors demonstrate the mechanisms of atherosclerosis formation associated with hypertriglyceridemia and the potential role of lipid-lowering drugs on carotid artery stenosis. The authors also review the articles reporting the relationships between hypertriglyceridemia and carotid artery stenosis.

Modulation of vascular endothelial inflammatory response by proprotein convertase subtilisin-kexin type 9

BACKGROUND AND AIMS

Endotoxins carried within LDL are cleared from the circulation via hepatic LDL receptor (LDLR)-mediated endocytosis. Proprotein convertase subtilisin-kexin type 9 (PCSK9) reduces this clearance by down-regulating LDLR density on hepatocytes. In addition to hepatocytes, vascular endothelial cells also express receptor targets of PCSK9, including LDLR. Therefore, we hypothesized that PCSK9 may regulate vascular endothelial cell uptake of lipopolysaccharide (LPS) and alter the vascular endothelial cell inflammatory response.

METHODS AND RESULTS

We found that LPS is internalized by human umbilical vein vascular endothelial cells (HUVECs) and LPS uptake dose-dependently increased with increasing LDL concentration. Intracellular LPS co-localized with LDL. PCSK9 and, separately, blocking antibodies against LDLR, dose-dependently decreased the vascular endothelial cell uptake of LPS and, furthermore, inhibition of endocytosis using Dynasore blocked LPS uptake. In contrast, blocking antibodies against TLR4 did not alter LPS uptake. PCSK9 decreased the LPS-induced proinflammatory response (IL-6 and IL-8 gene expression and protein secretion, and VCAM-1/ICAM-1 expression) in vascular endothelial cells. In addition, a decrease in PCSK9 and increase in LDLR, mediated by triciribine or siPCSK9, increased LPS uptake and the LPS-induced proinflammatory response. Similar results were also found in aortic vascular tissue from Pcsk9^-/- mice after LPS injection.

CONCLUSIONS

Our data suggest that, similar to PCSK9 treatment in hepatocytes, PCSK9 reduces vascular endothelial cell uptake of LPS via LDLR-mediated endocytosis. Consequently, PCSK9 decreases the LPS-induced proinflammatory response in vascular endothelial cells. These results raise the possibility that PCSK9 inhibition may have additional effects on vascular endothelial inflammation via this alternative pathway, beyond the known effects of PCSK9 inhibition on LDL lowering and hepatic endotoxin clearance.

Monocytic Cell Adhesion to Oxidised Ligands: Relevance to Cardiovascular Disease

Atherosclerosis, the major cause of vascular disease, is an inflammatory process driven by entry of blood monocytes into the arterial wall. LDL normally enters the wall, and stimulates monocyte adhesion by forming oxidation products such as oxidised phospholipids (oxPLs) and malondialdehyde. Adhesion molecules that bind monocytes to the wall permit traffic of these cells. CD14 is a monocyte surface receptor, a cofactor with TLR4 forming a complex that binds oxidised phospholipids and induces inflammatory changes in the cells, but data have been limited for monocyte adhesion. Here, we show that under static conditions, CD14 and TLR4 are implicated in adhesion of monocytes to solid phase oxidised LDL (oxLDL), and also that oxPL and malondialdehyde (MDA) adducts are involved in adhesion to oxLDL. Similarly, monocytes bound to heat shock protein 60 (HSP60), but this could be through contaminating lipopolysaccharide. Immunohistochemistry on atherosclerotic human arteries demonstrated increased endothelial MDA adducts and HSP60, but endothelial oxPL was not detected. We propose that monocytes could bind to MDA in endothelial cells, inducing atherosclerosis. Monocytes and platelets synergized in binding to oxLDL, forming aggregates; if this occurs at the arterial surface, they could precipitate thrombosis. These interactions could be targeted by cyclodextrins and oxidised phospholipid analogues for therapy.

Macrophage-, Dendritic-, Smooth Muscle-, Endothelium-, and Stem Cells-Derived Foam Cells in Atherosclerosis

Atherosclerosis is an inflammatory disease depending on the buildup, called plaque, of lipoproteins, cholesterol, extracellular matrix elements, and various types of immune and non-immune cells on the artery walls. Plaque development and growth lead to the narrowing of the blood vessel lumen, blocking blood flow, and eventually may lead to plaque burst and a blood clot. The prominent cellular components of atherosclerotic plaque are the foam cells, which, by trying to remove lipoprotein and cholesterol surplus, also participate in plaque development and rupture. Although the common knowledge is that the foam cells derive from macrophages, studies of the last decade clearly showed that macrophages are not the only cells able to form foam cells in atherosclerotic plaque. These findings give a new perspective on atherosclerotic plaque formation and composition and define new targets for anti-foam cell therapies for atherosclerosis prevention. This review gives a concise description of foam cells of different pedigrees and describes the main mechanisms participating in their formation and function.

Brain Endothelial Cells in Contrary to the Aortic Do Not Transport but Degrade Low-Density Lipoproteins via Both LDLR and ALK1

The transport of low-density lipoprotein (LDL) through the endothelium is a key step in the development of atherosclerosis, but it is notorious that phenotypic differences exist between endothelial cells originating from different vascular beds. Endothelial cells forming the blood–brain barrier restrict paracellular and transcellular passage of plasma proteins. Here, we systematically compared brain versus aortic endothelial cells towards their interaction with LDL and the role of proteins known to regulate the uptake of LDL by endothelial cells. Both brain endothelial cells and aortic endothelial cells bind and internalize LDL. However, whereas aortic endothelial cells degrade very small amounts of LDL and transcytose the majority, brain endothelial cells degrade but do not transport LDL. Using RNA interference (siRNA), we found that the LDLR–clathrin pathway leads to LDL degradation in either endothelial cell type. Both loss- and gain-of-function experiments showed that ALK1, which promotes transcellular LDL transport in aortic endothelial cells, also limits LDL degradation in brain endothelial cells. SR-BI and caveolin-1, which promote LDL uptake and transport into aortic endothelial cells, limit neither binding nor association of LDL to brain endothelial cells. Together, these results indicate distinct LDL trafficking by brain microvascular endothelial cells and aortic endothelial cells.

Antagonism of miR-148a attenuates atherosclerosis progression in APOBTGApobec-/-Ldlr+/- mice: A brief report

OBJECTIVE

miR-148a-3p (miR-148a) is a hepatic and immune-enriched microRNA (miRNA) that regulates macrophage-related lipoprotein metabolism, cholesterol homeostasis, and inflammation. The contribution of miR-148a-3p to the progression of atherosclerosis is unknown. In this study, we determined whether miR-148a silencing mitigated atherogenesis in APOBTGApobec-/-Ldlr+/- mice.

METHODS

APOBTGApobec-/-Ldlr+/- mice were fed a typical Western-style diet for 22 weeks and injected with a nontargeting locked nucleic acid (LNA; LNA control) or miR-148a LNA (LNA 148a) for the last 10 weeks. At the end of the treatment, the mice were sacrificed, and circulating lipids, hepatic gene expression, and atherosclerotic lesions were analyzed.

RESULTS

Examination of atherosclerotic lesions revealed a significant reduction in plaque size, with marked remodeling of the lesions toward a more stable phenotype. Mechanistically, miR-148a levels influenced macrophage cholesterol efflux and the inflammatory response. Suppression of miR-148a in murine primary macrophages decreased mRNA levels of proinflammatory M1-like markers (Nos2, Il6, Cox2, and Tnf) and increased the expression of anti-inflammatory genes (Arg1, Retlna, and Mrc1).

CONCLUSIONS

Therapeutic silencing of miR148a mitigated the progression of atherosclerosis and promoted plaque stability. The antiatherogenic effect of miR-148a antisense therapy is likely mediated by the anti-inflammatory effects observed in macrophages treated with miR-148 LNA and independent of significant changes in circulating low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C).

Deciphering the relationship between caveolae-mediated intracellular transport and signalling events

The caveolae-mediated transport across polarized epithelial cell barriers has been largely deciphered in the last decades and is considered the second essential intracellular transfer mechanism, after the clathrin-dependent endocytosis. The basic cell biology knowledge was supplemented recently, with the molecular mechanisms beyond caveolae generation implying the key contribution of the lipid-binding proteins (the structural protein Caveolin and the adapter protein Cavin), along with the bulb coat stabilizing molecules PACSIN-2 and Eps15 homology domain protein-2. The current attention is focused also on caveolae architecture (such as the bulb coat, the neck, the membrane funnel inside the bulb, and the associated receptors), and their specific tasks during the intracellular transport of various cargoes. Here, we resume the present understanding of the assembly, detachment, and internalization of caveolae from the plasma membrane lipid raft domains, and give an updated view on transcytosis and endocytosis, the two itineraries of cargoes transport via caveolae. The review adds novel data on the signalling molecules regulating caveolae intracellular routes and on the transport dysregulation in diseases. The therapeutic possibilities offered by exploitation of Caveolin-1 expression and caveolae trafficking, and the urgent issues to be uncovered conclude the review.

HDL as Bidirectional Lipid Vectors: Time for New Paradigms

The anti-atherogenic properties of high-density lipoproteins (HDL) have been explained mainly by reverse cholesterol transport (RCT) from peripheral tissues to the liver. The RCT seems to agree with most of the negative epidemiological correlations between HDL cholesterol levels and coronary artery disease. However, therapies designed to increase HDL cholesterol failed to reduce cardiovascular risk, despite their capacity to improve cholesterol efflux, the first stage of RCT. Therefore, the cardioprotective role of HDL may not be explained by RCT, and it is time for new paradigms about the physiological function of these lipoproteins. It should be considered that the main HDL apolipoprotein, apo AI, has been highly conserved throughout evolution. Consequently, these lipoproteins play an essential physiological role beyond their capacity to protect against atherosclerosis. We propose HDL as bidirectional lipid vectors carrying lipids from and to tissues according to their local context. Lipid influx mediated by HDL appears to be particularly important for tissue repair right on site where the damage occurs, including arteries during the first stages of atherosclerosis. In contrast, the HDL-lipid efflux is relevant for secretory cells where the fusion of intracellular vesicles drastically enlarges the cytoplasmic membrane with the potential consequence of impairment of cell function. In such circumstances, HDL could deliver some functional lipids and pick up not only cholesterol but an integral part of the membrane in excess, restoring the viability of the secretory cells. This hypothesis is congruent with the beneficial effects of HDL against atherosclerosis as well as with their capacity to induce insulin secretion and merits experimental exploration.

Atherosclerosis: Recent developments

Atherosclerosis is an inflammatory disease of the large arteries that is the major cause of cardiovascular disease (CVD) and stroke. Here, we review the current understanding of the molecular, cellular, genetic, and environmental contributions to atherosclerosis, from both individual pathway and systems perspectives. We place an emphasis on recent developments, some of which have yielded unexpected biology, including previously unknown heterogeneity of inflammatory and smooth muscle cells in atherosclerotic lesions, roles for senescence and clonal hematopoiesis, and links to the gut microbiome.

Molecular Pharmacology of Inflammation Resolution in Atherosclerosis

Atherosclerosis is one of the most important problems of modern medicine as it is the leading cause of hospitalizations, disability, and mortality. The key role in the development and progression of atherosclerosis is the imbalance between the activation of inflammation in the vascular wall and the mechanisms of its control. The resolution of inflammation is the most important physiological mechanism that is impaired in atherosclerosis. The resolution of inflammation has complex, not fully known mechanisms, in which lipid mediators derived from polyunsaturated fatty acids (PUFAs) play an important role. Specialized pro-resolving mediators (SPMs) represent a group of substances that carry out inflammation resolution and may play an important role in the pathogenesis of atherosclerosis. SPMs include lipoxins, resolvins, maresins, and protectins, which are formed from PUFAs and regulate many processes related to the active resolution of inflammation. Given the physiological importance of these substances, studies examining the possibility of pharmacological effects on inflammation resolution are of interest.

The Endothelium as a Hub for Cellular Communication in Atherogenesis: Is There Directionality to the Message?

Endothelial cells line every blood vessel and thereby serve as an interface between the blood and the vessel wall. They have critical functions for maintaining homeostasis and orchestrating vascular pathogenesis. Atherosclerosis is a chronic disease where cholesterol and inflammatory cells accumulate in the artery wall below the endothelial layer and ultimately form plaques that can either progress to occlude the lumen or rupture with thromboembolic consequences – common outcomes being myocardial infarction and stroke. Cellular communication lies at the core of this process. In this review, we discuss traditional (e.g., cytokines, chemokines, nitric oxide) and novel (e.g., extracellular vesicles) modes of endothelial communication with other endothelial cells as well as circulating and vessel wall cells, including monocytes, macrophages, neutrophils, vascular smooth muscle cells and other immune cells, in the context of atherosclerosis. More recently, the growing appreciation of endothelial cell plasticity during atherogenesis suggests that communication strategies are not static. Here, emerging data on transcriptomics in cells during the development of atherosclerosis are considered in the context of how this might inform altered cell-cell communication. Given the unique position of the endothelium as a boundary layer that is activated in regions overlying vascular inflammation and atherosclerotic plaque, there is a potential to exploit the unique features of this group of cells to deliver therapeutics that target the cellular crosstalk at the core of atherosclerotic disease. Data are discussed supporting this concept, as well as inherent pitfalls. Finally, we briefly review the literature for other regions of the body (e.g., gut epithelium) where cells similarly exist as a boundary layer but provide discrete messages to each compartment to govern homeostasis and disease. In this light, the potential for endothelial cells to communicate in a directional manner is explored, along with the implications of this concept – from fundamental experimental design to biomarker potential and therapeutic targets.

Atherogenesis, Transcytosis, and the Transmural Cholesterol Flux: A Critical Review

The recently described phenomenon of cholesterol-loaded low-density lipoproteins (LDL) entering the arterial wall from the lumen by transcytosis has been accepted as an alternative for the long-held concept that atherogenesis involves only passive LDL movement across an injured or dysfunctional endothelial barrier. This active transport of LDL can now adequately explain why plaques (atheromas) appear under an intact, uninjured endothelium. However, the LDL transcytosis hypothesis is still questionable, mainly because the process serves no clear physiological purpose. Moreover, central components of the putative LDL transcytosis apparatus are shared by the counter process of cholesterol efflux and reverse cholesterol transport (RCT) and therefore can essentially create an energy-wasting futile cycle and paradoxically be pro- and antiatherogenic simultaneously. Hence, by critically reviewing the literature, we wish to put forward an alternative interpretation that, in our opinion, better fits the experimental evidence. We assert that most of the accumulating cholesterol (mainly as LDL) reaches the intima not from the lumen by transcytosis, but from the artery's inner layers: the adventitia and media. We have named this directional cholesterol transport transmural cholesterol flux (TCF). We suggest that excess cholesterol, diffusing from the avascular (i.e., devoid of blood and lymph vessels) media's smooth muscle cells, is cleared by the endothelium through its apical membrane. A plaque is formed when this cholesterol clearance rate lags behind its rate of arrival by TCF.

The microsomal triglyceride transfer protein inhibitor lomitapide improves vascular function in mice with obesity

OBJECTIVE

In this study, the effect of lomitapide, a microsomal triglyceride transfer protein inhibitor, on the cardiovascular function in obesity was investigated.

METHODS

Eight-week-old C57BL/6 mice were fed with high-fat diet for 12 weeks in the presence and absence of lomitapide. Lomitapide was administered by gavage (1 mg/kg/d) during the last 2 weeks of high-fat feeding. Body weight, blood glucose, body composition, and lipid profile were determined. Vascular function and endothelial function markers were studied in the aorta and mesenteric resistance arteries.

RESULTS

Lomitapide treatment reduced body weight in mice with obesity. Blood glucose, percentage of fat mass, total cholesterol, and low-density lipoprotein levels were significantly reduced, and the percentage of lean mass was significantly increased after lomitapide treatment. The vascular response to sodium nitroprusside in the aorta and mesenteric arteries was similar among groups. However, the vascular response to acetylcholine was improved in the treated group. This was associated with decreased levels of vascular endoplasmic reticulum stress, inflammation, and oxidative stress.

CONCLUSIONS

Treatment with lomitapide attenuated the increase in body weight in mice with obesity and restored the lipid profile and vascular function. These effects were accompanied by a decrease in inflammation and oxidative stress.

Pathophysiology of Atherosclerosis

Atherosclerosis is the main risk factor for cardiovascular disease (CVD), which is the leading cause of mortality worldwide. Atherosclerosis is initiated by endothelium activation and, followed by a cascade of events (accumulation of lipids, fibrous elements, and calcification), triggers the vessel narrowing and activation of inflammatory pathways. The resultant atheroma plaque, along with these processes, results in cardiovascular complications. This review focuses on the different stages of atherosclerosis development, ranging from endothelial dysfunction to plaque rupture. In addition, the post-transcriptional regulation and modulation of atheroma plaque by microRNAs and lncRNAs, the role of microbiota, and the importance of sex as a crucial risk factor in atherosclerosis are covered here in order to provide a global view of the disease.

Targeting the vasculature in cardiometabolic disease

Obesity has reached epidemic proportions and is a major contributor to insulin resistance (IR) and type 2 diabetes (T2D). Importantly, IR and T2D substantially increase the risk of cardiovascular (CV) disease. Although there are successful approaches to maintain glycemic control, there continue to be increased CV morbidity and mortality associated with metabolic disease. Therefore, there is an urgent need to understand the cellular and molecular processes that underlie cardiometabolic changes that occur during obesity so that optimal medical therapies can be designed to attenuate or prevent the sequelae of this disease. The vascular endothelium is in constant contact with the circulating milieu; thus, it is not surprising that obesity-driven elevations in lipids, glucose, and proinflammatory mediators induce endothelial dysfunction, vascular inflammation, and vascular remodeling in all segments of the vasculature. As cardiometabolic disease progresses, so do pathological changes in the entire vascular network, which can feed forward to exacerbate disease progression. Recent cellular and molecular data have implicated the vasculature as an initiating and instigating factor in the development of several cardiometabolic diseases. This Review discusses these findings in the context of atherosclerosis, IR and T2D, and heart failure with preserved ejection fraction. In addition, novel strategies to therapeutically target the vasculature to lessen cardiometabolic disease burden are introduced.

Multifaceted Protective Effects of Hesperidin by Aromatic Hydrocarbon Receptor in Endothelial Cell Injury Induced by Benzo[a]Pyrene

Benzo[a]pyrene (BaP) causes atherosclerosis by activating the aromatic hydrocarbon receptor (AHR) signaling pathway to trigger lipid peroxidation and inflammation, thereby promoting the development of atherosclerosis. Hesperidin (Hsd), one of the 60 flavonoids of citrus, exhibits therapeutic effects on atherosclerosis. However, its antagonistic function for BaP remains unclear. In this study, the EA.hy926 cell model was used to systematically examine the antagonistic effect of Hsd with BaP, especially in low-density lipoprotein (LDL) oxidation and transport. Results showed that Hsd could reduce BaP-induced AHR activation in mRNA and protein expression level, and reduce LDL accumulation by decreasing the BaP-induced expression of advanced glycation end products and enhancing the BaP-inhibited Adenosine Triphosphate-binding cassette transporter A1 (ABCA1) protein and mRNA expression in EA.hy926 cells. In addition, Hsd could antagonize BaP-induced interaction of reactive oxygen species and the subsequent generation of oxidized LDL and malondialdehyde. Finally, Hsd could alleviate BaP-induced inflammatory response by decreasing IL-1β and TNF-α expression. All these results suggest that Hsd suppresses LDL accumulation, oxidation, and inflammatory response, and thus strongly impedes the AHR pathway activated by BaP.

Local Accumulation of Lymphocytes in the Intima of Human Aorta Is Associated with Giant Multinucleated Endothelial Cells: Possible Explanation for Mosaicism of Atherosclerosis

Distribution of different types of atherosclerotic lesions in the arterial wall is not diffuse, but is characterized by mosaicism. The causes of such distribution remain to be established. At the early stages of atherogenesis, low-density lipoprotein (LDL) particles and immune cells penetrate into the intimal layer of the arterial wall through the endothelium. In adult humans, the luminal surface of the arterial wall is a heterogeneous monolayer of cells with varying morphology including typical endothelial cells (ECs) and multinucleated variant endothelial cells (MVECs). We hypothesized that distribution of MVECs in the endothelial monolayer can be related to the distribution pattern of early atherosclerotic lesions. We obtained en face preparations of intact adult (22–59 years old) aortic wall sections that allowed us to study the endothelial monolayer and the subendothelial layer. We compared the distribution of MVECs in the endothelial monolayer with the localization of early atherosclerotic lesions in the subendothelial layer, which were characterized by lipid accumulation and immune cell recruitment. In primary culture, MVECs demonstrated increased phagocytic activity compared to mononuclear ECs. Moreover, we have shown that unaffected aortic intima contained associates formed as a result of aggregation and/or fusion of LDL particles that are non-randomly distributed. This indicated that MVECs may be involved in the accumulation of LDL in the subendothelial layer through increased transcytosis. Interaction of LDL with subendothelial cells of human aorta in primary culture increased their adhesive properties toward circulating immune cells. Study of unaffected aortic intima revealed non-random distribution of leukocytes in the subendothelial layer and increased localization of CD45+ leukocytes in the subendothelial layer adjacent to MVECs. Together, our observations indicate that MVECs may be responsible for the distribution of atherosclerotic lesions in the arterial wall by participating in LDL internalization and immune cell recruitment.

Induction of Hypoxic Response in Caco-2 Cells Promote the Expression of Genes Involved in SARS-CoV-2 Endocytosis and Transcytosis

In the present manuscript we analyzed the influence of hypoxic response in Caco-2 cells on the expression of genes and miRNAs involved in the mechanisms of intracellular transport of SARS-CoV-2 viral particles, especially endocytosis and transcytosis. With the use of RNA sequencing of Caco-2 cells treated with hypoxia-inducing oxyquinoline derivative, we showed two-fold increase in the expression of the main SARS-CoV-2 receptor ACE2. Expression of the non-canonical receptor TFRC was also elevated. We also observed a significant increase in the expression levels of genes from the low-density lipoprotein (LDL) receptor family, which play a crucial role in the transcytosis: LDLR, LRP1, LRP4, and LRP5. Upregulation of LDLR was coupled with the downregulation of hsa-miR-148a-3p, which can directly bind to LDLR mRNA. Thus, the hypoxic response in Caco-2 cells includes upregulation of genes involved in the mechanisms of endocytosis and transcytosis of SARS-CoV-2 viral particles.

Detection of lipid efflux from foam cell models using a label-free infrared method

Synchrotron-based microFTIR spectroscopy was used to study the process of lipid efflux in a foam cell model. The anti-atherosclerotic drug, atorvastatin, removed low-density lipoprotein from the foam cells in a dose, and time dependent manner.

Dysfunctional Vascular Endothelium as a Driver of Atherosclerosis: Emerging Insights Into Pathogenesis and Treatment

Atherosclerosis, the chronic accumulation of cholesterol-rich plaque within arteries, is associated with a broad spectrum of cardiovascular diseases including myocardial infarction, aortic aneurysm, peripheral vascular disease, and stroke. Atherosclerotic cardiovascular disease remains a leading cause of mortality in high-income countries and recent years have witnessed a notable increase in prevalence within low- and middle-income regions of the world. Considering this prominent and evolving global burden, there is a need to identify the cellular mechanisms that underlie the pathogenesis of atherosclerosis to discover novel therapeutic targets for preventing or mitigating its clinical sequelae. Despite decades of research, we still do not fully understand the complex cell-cell interactions that drive atherosclerosis, but new investigative approaches are rapidly shedding light on these essential mechanisms. The vascular endothelium resides at the interface of systemic circulation and the underlying vessel wall and plays an essential role in governing pathophysiological processes during atherogenesis. In this review, we present emerging evidence that implicates the activated endothelium as a driver of atherosclerosis by directing site-specificity of plaque formation and by promoting plaque development through intracellular processes, which regulate endothelial cell proliferation and turnover, metabolism, permeability, and plasticity. Moreover, we highlight novel mechanisms of intercellular communication by which endothelial cells modulate the activity of key vascular cell populations involved in atherogenesis, and discuss how endothelial cells contribute to resolution biology - a process that is dysregulated in advanced plaques. Finally, we describe important future directions for preclinical atherosclerosis research, including epigenetic and targeted therapies, to limit the progression of atherosclerosis in at-risk or affected patients.

Emerging role of long non-coding RNAs in endothelial dysfunction and their molecular mechanisms

Long non-coding RNAs (lncRNAs) are the novel class of transcripts involved in transcriptional, post-transcriptional, translational, and post-translational regulation of physiology and the pathology of diseases. Studies have evidenced that the impairment of endothelium is a critical event in the pathogenesis of atherosclerosis and its complications. Endothelial dysfunction is characterized by an imbalance in vasodilation and vasoconstriction, oxidative stress, proinflammatory factors, and nitric oxide bioavailability. Disruption of the endothelial barrier permeability, the first step in developing atherosclerotic lesions is a consequence of endothelial dysfunction. Though several factors interfere with the normal functioning of the endothelium, intrinsic epigenetic mechanisms governing endothelial function are regulated by lncRNAs and perturbations contribute to the pathogenesis of the disease. This review comprehensively addresses the biogenesis of lncRNA and molecular mechanisms underlying and regulation in endothelial function. An insight correlating lncRNAs and endothelial dysfunction-associated diseases can positively impact the development of novel biomarkers and therapeutic targets in endothelial dysfunction-associated diseases and treatment strategies.

Diversity of Lipid Function in Atherogenesis: A Focus on Endothelial Mechanobiology

Atherosclerosis is one of the most important problems in modern medicine. Its high prevalence and social significance determine the need for a better understanding of the mechanisms of the disease's development and progression. Lipid metabolism and its disorders are one of the key links in the pathogenesis of atherosclerosis. Lipids are involved in many processes, including those related to the mechanoreception of endothelial cells. The multifaceted role of lipids in endothelial mechanobiology and mechanisms of atherogenesis are discussed in this review. Endothelium is involved in ensuring adequate vascular hemodynamics, and changes in blood flow characteristics are detected by endothelial cells and affect their structure and function.