Caveolae and caveolin-1 mediate endocytosis and transcytosis of oxidized low density lipoprotein in endothelial cells

The long coiled-coil protein NECC2 regulates oxLDL-induced endothelial oxidative damage and exacerbates atherosclerosis development in apolipoprotein E -/- mice

Oxidized low density lipoprotein (oxLDL)-induced endothelial oxidative damage promotes the development of atherosclerosis. Caveolae play an essential role in maintaining the survival and function of vascular endothelial cell (VEC). It is reported that the long coiled-coil protein NECC2 is localized in caveolae and is associated with neural cell differentiation and adipocyte formation, but its role in VECs needs to be clarified. Our results showed NECC2 expression increased in the endothelium of plaque-loaded aortas and oxLDL-treated HUVECs. Down-regulation of NECC2 by NECC2 siRNA or compound YF-307 significantly inhibited oxLDL-induced VEC apoptosis and the adhesion factors expression. Remarkably, inhibition of NECC2 expression in the endothelium of apoE-/- mice by adeno-associated virus (AAV)-carrying NECC2 shRNA or compound YF-307 alleviated endothelium injury and restricted atherosclerosis development. The immunoprecipitation results confirmed that NECC2 interacted with Tyk2 and caveolin-1(Cav-1) in VECs, and NECC2 further promoted the phosphorylation of Cav-1 at Tyr14 b y activating Tyk2 phosphorylation. On the other hand, inhibiting NECC2 levels suppressed oxLDL-induced phosphorylation of Cav-1, uptake of oxLDL by VECs, accumulation of intracellular reactive oxygen species and activation of NF-κB. Our findings suggest that NECC2 may contribute to oxLDL-induced VEC injury and atherosclerosis via modulating Cav-1 phosphorylation through Tyk2. This work provides a new concept and drug target for treating atherosclerosis.

LOX-1 Receptor: A Diagnostic Tool and Therapeutic Target in Atherogenesis

Low-density lipoprotein (LDL) and oxidized LDL (oxLDL) are major contributors to atherogenesis, as endogenous antigens, via several receptors such as LOX 1. A PubMed search was conducted in order to identify relevant articles regarding LOX-1's role in the atherosclerosis, diagnosis, prognostic use and molecules that could be used for therapy. The references of the manuscripts obtained were also reviewed, in order to find additional relevant bibliography. LOX-1 is a lectin-like pattern recognition receptor, mostly expressed in endothelial cells (ECs) which can bind a variety of molecules, including oxLDL and C-reactive protein (CRP). LOX-1 plays a key role in oxLDL's role as a causative agent of atherosclerosis through several pathologic mechanisms, such as oxLDL deposition in the subintima, foam cell formation and endothelial dysfunction. Additionally, LOX-1 acts a scavenger receptor for oxLDL in macrophages and can be responsible for oxLDL uptake, when stimulated. Serum LOX-1 (sLOX-1) has emerged as a new, potential biomarker for diagnosis of acute coronary syndromes, and it seems promising for use along with other common biomarkers in everyday clinical practice. In a therapeutic perspective, natural as well as synthetic molecules exert anti-LOX-1 properties and attain the receptor's pathophysiological effects, thus extensive research is ongoing to further evaluate molecules with therapeutic potential. However, most of these molecules need further trials in order to properly assess their safety and efficacy for clinical use. The aim of this review is to investigate LOX-1 role in atherogenesis and explore its potential as diagnostic tool and therapeutic target.

Inflammatory Cell-Derived MYDGF Attenuates Endothelial LDL Transcytosis to Protect Against Atherogenesis

BACKGROUND

Inflammation contributes to the pathogenesis of atherosclerosis. But little is known about the potential benefits of inflammatory cells to atherosclerosis. The aim of this study was to investigate the function of inflammatory cells/endothelium axis and determine whether and how inflammatory cell-derived MYDGF (myeloid-derived growth factor) inhibited endothelial LDL (low-density lipoprotein) transcytosis.

METHODS

In in vivo experiments, both loss- and gain-of-function strategies were used to evaluate the effect of inflammatory cell-derived MYDGF on LDL transcytosis. We generated monocyte/macrophage-targeted MYDGF-null mice on an Ldlr (LDL receptor)-/- background in the loss-of-function strategy and restored the inflammatory cell-derived MYDGF by bone marrow transplantation and inflammatory cell-specific overexpression of MYDGF mice model in the gain-of-function strategy. In in vitro experiments, coculture experiments between primary mouse aortic endothelial cells and macrophages and mouse aortic endothelial cells supplemented with or without recombinant MYDGF were conducted.

RESULTS

Inflammatory cell-derived MYDGF deficiency aggravated endothelial LDL transcytosis, drove LDL uptake by artery wall, and thus exacerbated atherosclerosis in vivo. Inflammatory cell-derived MYDGF restoration by bone marrow transplantation and inflammatory cell MYDGF overexpression alleviated LDL transport across the endothelium, prevented LDL accumulation in the subendothelial space, and subsequently ameliorated atherosclerosis in vivo. Furthermore, in the in vitro study, macrophages isolated from MYDGF+/+ mice and recombinant MYDGF attenuated LDL transcytosis and uptake in mouse aortic endothelial cells. Mechanistically, MYDGF inhibited MAP4K4 (mitogen-activated protein kinase kinase kinase kinase isoform 4) phosphorylation, enhanced activation of Akt (protein kinase B)-1, and diminished the FoxO (forkhead box O) 3a signaling cascade to exert protective effects of MYDGF on LDL transcytosis and atherosclerosis.

CONCLUSIONS

The findings support a role for inflammatory cell-derived MYDGF served as a cross talk factor between inflammatory cells and endothelial cells that inhibits LDL transcytosis across endothelium. MYDGF may become a novel therapeutic drug for atherosclerosis, and the beneficial effects of inflammatory cell in atherosclerosis deserve further attention.

AGEs promote atherosclerosis by increasing LDL transcytosis across endothelial cells via RAGE/NF-κB/Caveolin-1 pathway

OBJECTIVE

To elucidate the mechanism whereby advanced glycation end products (AGEs) accelerate atherosclerosis (AS) and to explore novel therapeutic strategies for atherosclerotic cardiovascular disease.

METHODS AND RESULTS

The effect of AGEs on low-density lipoprotein (LDL) transcytosis across endothelial cells (ECs) was assessed using an in vitro model of LDL transcytosis. We observed that AGEs activated the receptor for advanced glycation end products (RAGE) on the surface of ECs and consequently upregulated Caveolin-1, which in turn increased caveolae-mediated LDL transcytosis and accelerated AS progression. Our molecular assessment revealed that AGEs activate the RAGE-NF-κB signaling, which then recruits the NF-κB subunit p65 to the RAGE promoter and consequently enhances RAGE transcription, thereby forming a positive feedback loop between the NF-κB signaling and RAGE expression. Increased NF-κB signaling ultimately upregulated Caveolin-1, promoting LDL transcytosis, and inhibition of RAGE suppressed AGE-induced LDL transcytosis. In ApoE-/- mice on a high-fat diet, atherosclerotic plaque formation was accelerated by AGEs but suppressed by EC-specific knockdown of RAGE.

CONCLUSION

AGEs accelerate the development of diabetes-related AS by increasing the LDL transcytosis in ECs through the activation of the RAGE/NF-κB/Caveolin-1 axis, which may be targeted to prevent or treat diabetic macrovascular complications.

Caveolin-1 in endothelial cells: A potential therapeutic target for atherosclerosis

Atherosclerosis (AS) is a chronic vascular disease characterized by lipid accumulation and the activation of the inflammatory response; it remains the leading nation-wide cause of death. Early in the progression of AS, stimulation by pro-inflammatory agonists (TNF-α, LPS, and others), oxidized lipoproteins (ox-LDL), and biomechanical stimuli (low shear stress) lead to endothelial cell activation and dysfunction. Consequently, it is crucial to investigate how endothelial cells respond to different stressors and ways to alter endothelial cell activation in AS development, as they are the earliest cells to respond. Caveolin-1 (Cav1) is a 21-24-kDa membrane protein located in caveolae and highly expressed in endothelial cells, which plays a vital role in regulating lipid transport, inflammatory responses, and various cellular signaling pathways and has atherogenic effects. This review summarizes recent studies on the structure and physiological functions of Cav1 and outlines the potential mechanisms it mediates in AS development. Included are the roles of Cav1 in the regulation of endothelial cell autophagy, response to shear stress, modulation of the eNOS/NO axis, and transduction of inflammatory signaling pathways. This review provides a rationale for proposing Cav1 as a novel target for the prevention of AS, as well as new ideas for therapeutic strategies for early AS.

Caveolin-1 and Atherosclerosis: Regulation of LDLs Fate in Endothelial Cells

Caveolae are 50-100 nm cell surface plasma membrane invaginations observed in terminally differentiated cells. They are characterized by the presence of the protein marker caveolin-1. Caveolae and caveolin-1 are involved in regulating several signal transduction pathways and processes. It is well recognized that they have a central role as regulators of atherosclerosis. Caveolin-1 and caveolae are present in most of the cells involved in the development of atherosclerosis, including endothelial cells, macrophages, and smooth muscle cells, with evidence of either pro- or anti-atherogenic functions depending on the cell type examined. Here, we focused on the role of caveolin-1 in the regulation of the LDLs' fate in endothelial cells.

Caveolin-Mediated Internalization of Fmoc-FF Nanogels in Breast Cancer Cell Lines

INTRODUCTION

Hydrogel nanoparticles, also known as nanogels (NGs), have been recently proposed as alternative supramolecular vehicles for the delivery of biologically relevant molecules like anticancer drugs and contrast agents. The inner compartment of peptide based NGs can be opportunely modified according to the chemical features of the cargo, thus improving its loading and release. A full understanding of the intracellular mechanism involved in nanogel uptake by cancer cells and tissues would further contribute to the potential diagnostic and clinical applications of these nanocarriers, allowing the fine tuning of their selectivity, potency, and activity. The structural characterization of nanogels were assessed by Dynamic Light Scattering (DLS) and Nanoparticles Tracking Analysis (NTA) analysis. Cells viability of Fmoc-FF nanogels was evaluated by MTT assay on six breast cancer cell lines at different incubation times (24, 48, and 72 h) and peptide concentrations (in the range 6.25 × 10^-4 ÷ 5·10^-3 × wt%). The cell cycle and mechanisms involved in Fmoc-FF nanogels intracellular uptake were evaluated using flow cytometry and confocal analysis, respectively. Fmoc-FF nanogels, endowed with a diameter of ~130 nm and a zeta potential of ~-20.0/-25.0 mV, enter cancer cells via caveolae, mostly those responsible for albumin uptake. The specificity of the machinery used by Fmoc-FF nanogels confers a selectivity toward cancer cell lines overexpressing the protein caveolin1 and efficiently performing caveolae-mediated endocytosis.

Nucleic acid nanostructures for in vivo applications: The influence of morphology on biological fate

The development of programmable biomaterials for use in nanofabrication represents a major advance for the future of biomedicine and diagnostics. Recent advances in structural nanotechnology using nucleic acids have resulted in dramatic progress in our understanding of nucleic acid-based nanostructures (NANs) for use in biological applications. As the NANs become more architecturally and functionally diverse to accommodate introduction into living systems, there is a need to understand how critical design features can be controlled to impart desired performance in vivo. In this review, we survey the range of nucleic acid materials utilized as structural building blocks (DNA, RNA, and xenonucleic acids), the diversity of geometries for nanofabrication, and the strategies to functionalize these complexes. We include an assessment of the available and emerging characterization tools used to evaluate the physical, mechanical, physiochemical, and biological properties of NANs in vitro. Finally, the current understanding of the obstacles encountered along the in vivo journey is contextualized to demonstrate how morphological features of NANs influence their biological fates. We envision that this summary will aid researchers in the designing novel NAN morphologies, guide characterization efforts, and design of experiments and spark interdisciplinary collaborations to fuel advancements in programmable platforms for biological applications.

Lectin-Like Oxidized Low-Density Lipoprotein Receptor 1 Inhibition in Type 2 Diabetes: Phase 1 Results

Background Blockade of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a potentially attractive mechanism for lowering inflammatory and lipid risk in patients with atherosclerosis. This study aims to assess the safety, tolerability, and target engagement of MEDI6570, a high-affinity monoclonal blocking antibody to LOX-1. Methods and Results This phase 1, first-in-human, placebo-controlled study (NCT03654313) randomized 88 patients with type 2 diabetes to receive single ascending doses (10, 30, 90, 250, or 500 mg) or multiple ascending doses (90, 150, or 250 mg once monthly for 3 months) of MEDI6570 or placebo. Primary end point was safety; secondary and exploratory end points included pharmacokinetics, immunogenicity, free soluble LOX-1 levels, and change in coronary plaque volume. Mean age was 57.6/58.1 years in the single ascending doses/multiple ascending doses groups, 31.3%/62.5% were female, and mean type 2 diabetes duration was 9.7/8.7 years. Incidence of adverse events was similar among cohorts. MEDI6570 exhibited nonlinear pharmacokinetics, with terminal half-life increasing from 4.6 days (30 mg) to 11.2 days (500 mg), consistent with target-mediated drug disposition. Dose-dependent reductions in mean soluble LOX-1 levels from baseline were observed (>66% at 4 weeks and 71.61-82.96% at 10 weeks in the single ascending doses and multiple ascending doses groups, respectively). After 3 doses, MEDI6570 was associated with nonsignificant regression of noncalcified plaque volume versus placebo (-13.45 mm3 versus -8.25 mm3). Conclusions MEDI6570 was well tolerated and demonstrated dose-dependent soluble LOX-1 suppression and a pharmacokinetic profile consistent with once-monthly dosing. Registration URL: https://clinicaltrials.gov/; Unique identifier: NCT03654313.

Sphingolipids and Atherosclerosis: The Dual Role of Ceramide and Sphingosine-1-Phosphate

Sphingolipids are bioactive molecules that play either pro- and anti-atherogenic roles in the formation and maturation of atherosclerotic plaques. Among SLs, ceramide and sphingosine-1-phosphate showed antithetic properties in regulating various molecular mechanisms and have emerged as novel potential targets for regulating the development of atherosclerosis. In particular, maintaining the balance of the so-called ceramide/S1P rheostat is important to prevent the occurrence of endothelial dysfunction, which is the trigger for the entire atherosclerotic process and is strongly associated with increased oxidative stress. In addition, these two sphingolipids, together with many other sphingolipid mediators, are directly involved in the progression of atherogenesis and the formation of atherosclerotic plaques by promoting the oxidation of low-density lipoproteins (LDL) and influencing the vascular smooth muscle cell phenotype. The modulation of ceramide and S1P levels may therefore allow the development of new antioxidant therapies that can prevent or at least impair the onset of atherogenesis, which would ultimately improve the quality of life of patients with coronary artery disease and significantly reduce their mortality.

Caveolar and non-Caveolar Caveolin-1 in ocular homeostasis and disease

Caveolae, specialized plasma membrane invaginations present in most cell types, play important roles in multiple cellular processes including cell signaling, lipid uptake and metabolism, endocytosis and mechanotransduction. They are found in almost all cell types but most abundant in endothelial cells, adipocytes and fibroblasts. Caveolin-1 (Cav1), the signature structural protein of caveolae was the first protein associated with caveolae, and in association with Cavin1/PTRF is required for caveolae formation. Genetic ablation of either Cav1 or Cavin1/PTRF downregulates expression of the other resulting in loss of caveolae. Studies using Cav1-deficient mouse models have implicated caveolae with human diseases such as cardiomyopathies, lipodystrophies, diabetes and muscular dystrophies. While caveolins and caveolae are extensively studied in extra-ocular settings, their contributions to ocular function and disease pathogenesis are just beginning to be appreciated. Several putative caveolin/caveolae functions are relevant to the eye and Cav1 is highly expressed in retinal vascular and choroidal endothelium, Müller glia, the retinal pigment epithelium (RPE), and the Schlemm's canal endothelium and trabecular meshwork cells. Variants at the CAV1/2 gene locus are associated with risk of primary open angle glaucoma and the high risk HTRA1 variant for age-related macular degeneration is thought to exert its effect through regulation of Cav1 expression. Caveolins also play important roles in modulating retinal neuroinflammation and blood retinal barrier permeability. In this article, we describe the current state of caveolin/caveolae research in the context of ocular function and pathophysiology. Finally, we discuss new evidence showing that retinal Cav1 exists and functions outside caveolae.

Caveolin-1 is a primary determinant of endothelial stiffening associated with dyslipidemia, disturbed flow, and ageing

Endothelial stiffness is emerging as a major determinant in endothelial function. Here, we analyzed the role of caveolin-1 (Cav-1) in determining the stiffness of endothelial cells (EC) exposed to oxidized low density lipoprotein (oxLDL) under static and hemodynamic conditions in vitro and of aortic endothelium in vivo in mouse models of dyslipidemia and ageing. Elastic moduli of cultured ECs and of the endothelial monolayer of freshly isolated mouse aortas were measured using atomic force microscopy (AFM). We found that a loss of Cav-1 abrogates the uptake of oxLDL and oxLDL-induced endothelial stiffening, as well as endothelial stiffening induced by disturbed flow (DF), which was also oxLDL dependent. Mechanistically, Cav-1 is required for the expression of CD36 (cluster of differentiation 36) scavenger receptor. Genetic deletion of Cav-1 abrogated endothelial stiffening observed in the DF region of the aortic arch, and induced by a high fat diet (4-6 weeks) and significantly blunted endothelial stiffening that develops with advanced age. This effect was independent of stiffening of the sub-endothelium layer. Additionally, Cav-1 expression significantly increased with age. No differences in elastic modulus were observed between the sexes in advanced aged wild type and Cav-1 knockout mice. Taken together, this study demonstrates that Cav-1 plays a critical role in endothelial stiffening induced by oxLDL in vitro and by dyslipidemia, disturbed flow and ageing in vivo.

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.

Protective role of Cav-1 in pneumolysin-induced endothelial barrier dysfunction

Pneumolysin (PLY) is a bacterial pore forming toxin and primary virulence factor of Streptococcus pneumonia, a major cause of pneumonia. PLY binds cholesterol-rich domains of the endothelial cell (EC) plasma membrane resulting in pore assembly and increased intracellular (IC) Ca2+ levels that compromise endothelial barrier integrity. Caveolae are specialized plasmalemma microdomains of ECs enriched in cholesterol. We hypothesized that the abundance of cholesterol-rich domains in EC plasma membranes confers cellular susceptibility to PLY. Contrary to this hypothesis, we found increased PLY-induced IC Ca2+ following membrane cholesterol depletion. Caveolin-1 (Cav-1) is an essential structural protein of caveolae and its regulation by cholesterol levels suggested a possible role in EC barrier function. Indeed, Cav-1 and its scaffolding domain peptide protected the endothelial barrier from PLY-induced disruption. In loss of function experiments, Cav-1 was knocked-out using CRISPR-Cas9 or silenced in human lung microvascular ECs. Loss of Cav-1 significantly enhanced the ability of PLY to disrupt endothelial barrier integrity. Rescue experiments with re-expression of Cav-1 or its scaffolding domain peptide protected the EC barrier against PLY-induced barrier disruption. Dynamin-2 (DNM2) is known to regulate caveolar membrane endocytosis. Inhibition of endocytosis, with dynamin inhibitors or siDNM2 amplified PLY induced EC barrier dysfunction. These results suggest that Cav-1 protects the endothelial barrier against PLY by promoting endocytosis of damaged membrane, thus reducing calcium entry and PLY-dependent signaling.

Salvianolic acid B attenuates the inflammatory response in atherosclerosis by regulating MAPKs/ NF-κB signaling pathways in LDLR-/- mice and RAW264.7 cells

Objectives: Salvianolic acid B (Sal B) is the main effective water-soluble component of Salvia miltiorrhiza. In this study, the anti-inflammatory effect of Sal B was explored in high-fat-diet (HFD)-induced LDLR-/- mice and oxidized low-density-lipoprotein (ox-LDL)-induced or lipopolysaccharide (LPS)-induced RAW264.7 cells. Methods: The LDLR-/- mice were randomly divided into four groups after 12 weeks of high-fat diet. Then, the mice were administrated with 0.9% saline or Sal B (25 mg/kg) or Atorvastatin (1.3 mg/kg) for 12 weeks. RAW 264.7 cells were induced with ox-LDL/LPS, or ox-LDL/LPS plus different concentrations of Sal B (1.25 μg/mL, 2.5 μg/mL, 5 μg/mL), or ox-LDL plus Sal B plus MAPKs activators. ELISA was used for detecting serum lipid profiles and inflammatory cytokines, RT-qPCR used for gene expression, Oil Red O used for plaque sizes, and immunofluorescence staining used for NF-κB p65 and TNF-α production. Inflammation-related proteins and MAPKs pathways were detected by Western Blot. Results: The results showed that Sal B decreased the levels of serum lipids (TC, TG, and LDL-C), attenuated inflammatory cytokines, and improved lipid accumulation in the aorta. Sal B also attenuated the elevation of inflammatory cytokines induced by ox-LDL or LPS in RAW264.7 cells, and the phosphorylation of MAPKs/NF-κB pathways in the aorta and RAW264.7 cells, resulting in a significant decrease in the contents of p-JNK, p-ERK 1/2, p-P38, p-IκB, and p-NF-κB p65. Conclusions: Sal B could exert anti-inflammatory effects on atherosclerosis via MAPKs/NF-κB signaling pathways in vivo and in vitro.

A New Hypothesis for Alzheimer’s Disease: The Lipid Invasion Model

This paper proposes a new hypothesis for Alzheimer’s disease (AD)—the lipid invasion model. It argues that AD results from external influx of free fatty acids (FFAs) and lipid-rich lipoproteins into the brain, following disruption of the blood-brain barrier (BBB). The lipid invasion model explains how the influx of albumin-bound FFAs via a disrupted BBB induces bioenergetic changes and oxidative stress, stimulates microglia-driven neuroinflammation, and causes anterograde amnesia. It also explains how the influx of external lipoproteins, which are much larger and more lipid-rich, especially more cholesterol-rich, than those normally present in the brain, causes endosomal-lysosomal abnormalities and overproduction of the peptide amyloid-β (Aβ). This leads to the formation of amyloid plaques and neurofibrillary tangles, the most well-known hallmarks of AD. The lipid invasion model argues that a key role of the BBB is protecting the brain from external lipid access. It shows how the BBB can be damaged by excess Aβ, as well as by most other known risk factors for AD, including aging, apolipoprotein E4 (APOE4), and lifestyle factors such as hypertension, smoking, obesity, diabetes, chronic sleep deprivation, stress, and head injury. The lipid invasion model gives a new rationale for what we already know about AD, explaining its many associated risk factors and neuropathologies, including some that are less well-accounted for in other explanations of AD. It offers new insights and suggests new ways to prevent, detect, and treat this destructive disease and potentially other neurodegenerative diseases.

Approaches to Visualising Endocytosis of LDL-Related Lipoproteins

Endocytosis is the process by which molecules are actively transported into cells. It can take on a variety of forms depending on the cellular machinery involved ranging from specific receptor-mediated endocytosis to the less selective and actin-driven macropinocytosis. The plasma lipoproteins, which deliver lipids and other cargo to cells, have been intensely studied with respect to their endocytic uptake. One of the first molecules to be visualised undergoing endocytosis via a receptor-mediated, clathrin-dependent pathway was low-density lipoprotein (LDL). The LDL molecule has subsequently been shown to be internalised through multiple endocytic pathways. Dissecting the pathways of lipoprotein endocytosis has been crucial to understanding the regulation of plasma lipid levels and how lipids enter cells in the arterial wall to promote atherosclerosis. It has also aided understanding of the dysregulation that occurs in plasma lipid levels when molecules involved in uptake are defective, as is the case in familial hypercholesterolemia (FH). The aim of this review is to outline the many endocytic pathways utilised for lipoprotein uptake. It explores the various experimental approaches that have been applied to visualise lipoprotein endocytosis with an emphasis on LDL and its more complex counterpart, lipoprotein(a) [Lp(a)]. Finally, we look at new developments in lipoprotein visualisation that hold promise for scrutinising endocytic pathways to finer detail in the future.

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.

Polystyrene nanoplastics exposure caused defective neural tube morphogenesis through caveolae-mediated endocytosis and faulty apoptosis

Growing evidence demonstrated that bioaccumulation of polystyrene nanoplastics (PS-NPs) in various organisms including human beings caused destructive effects on health. Nanoplastics may adversely affect fetal development potentially since they can pass through the placental barrier. However, very little has been known about the embryonic toxicity of polystyrene nanoplastics, especially in embryonic neurulation, the early developmental stage of the fetus, as well as the corresponding mechanisms. In this study, we first observed that 60- or 900-nm PS-NPs (especially 60-nm PS-NPs) could cross mouse placentas and affect developing mice fetuses. To avoid the indirect adverse effects derived from the restricted placenta, we employed early chick embryos as a developmental model to evaluate direct adverse effects of PS-NPs on embryo/fetal development, revealing suppressive effects on embryo development and an increased frequency of congenital abnormalities (especially in the nervous system), including neural tube defects. Thus, we focused on the potential negative effects of PS-NPs on neurulation, the earliest stage of nervous system development. Using caveolin-1 immunofluorescent staining of SH-SY5Y cells exposed to PS-NPs-GFP, we demonstrated that PS-NPs were internalized by SH-SY5Y cells via caveolae-mediated endocytosis. Transmission electron microscopy; LC3B immunofluorescent staining; and Atg7, Atg5, p62 and LC3B western blot results revealed that autophagy was activated in SH-SY5Y cells exposed to PS-NPs. However, PS-NPs were not degraded by the autophagic-lysosomal system given the lack of LAMP1 changes and minimal PS-NPs-GFP and LAMP1 colocalization. Furthermore, the cytoplasmic accumulation of PS-NPs caused faulty apoptotic cell death in SH-SY5Y cells and the developing neural tube as revealed by c-caspase3 immunofluorescent staining. Thus, defective neural tube morphogenesis, as demonstrated by neural tube defects, occurred during embryogenesis in the context of PS-NP exposure.

The endocytosis of oxidized LDL via the activation of the angiotensin II type 1 receptor

Arrestin-dependent activation of a G-protein-coupled receptor (GPCR) triggers endocytotic internalization of the receptor complex. We analyzed the interaction between the pattern recognition receptor (PRR) lectin-like oxidized low-density lipoprotein (oxLDL) receptor (LOX-1) and the GPCR angiotensin II type 1 receptor (AT1) to report a hitherto unidentified mechanism whereby internalization of the GPCR mediates cellular endocytosis of the PRR ligand. Using genetically modified Chinese hamster ovary cells, we found that oxLDL activates Gαi but not the Gαq pathway of AT1 in the presence of LOX-1. Endocytosis of the oxLDL-LOX-1 complex through the AT1-β-arrestin pathway was demonstrated by real-time imaging of the membrane dynamics of LOX-1 and visualization of endocytosis of oxLDL. Finally, this endocytotic pathway involving GPCR kinases (GRKs), β-arrestin, and clathrin is relevant in accumulating oxLDL in human vascular endothelial cells. Together, our findings indicate that oxLDL activates selective G proteins and β-arrestin-dependent internalization of AT1, whereby the oxLDL-LOX-1 complex undergoes endocytosis.

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The binding of oxidized LDL (oxLDL) to LOX-1 induces selective activation of AT1

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oxLDL and angiotensin II additively or competitively activate AT1 in different cells

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oxLDL promotes β-arrestin-dependent internalization of oxLDL-LOX-1-AT1 complex

Effect of PM10 on pulmonary immune response and fetus development

Despite numerous reports that ambient particulate matter is a key determinant for human health, toxicity data produced based on physicochemical properties of particulate matters is very lack, suggesting lack of scientific evidence for regulation. In this study, we sampled inhalable particulate matters (PM10) in northern Seoul, Korea. PM10 showed atypical- and fiber-type particles with the average size and the surface charge of 1,598.1 ± 128.7 nm and -27.5 ± 2.8, respectively, and various toxic elements were detected in the water extract. On day 90 after the first pulmonary exposure, total cell number dose-dependently increased in the lungs of both sexes of mice. PM10 induced Th1-dominant immune response with pathological changes in both sexes of mice. Meanwhile, composition of total cells and expression of proteins which functions in cell-to-cell communication showed different trends between sexes. Following, male and female mice were mated to identify effects of PM10 to the next generation. PM10 remained in the lung of dams until day 21 after birth, and the levels of IgA and IgE increased in the blood of dams exposed to the maximum dose compared to control. In addition, the interval between births of fetuses, the number of offspring, the neonatal survival rate (day 4 after birth) and the sex ratio seemed to be affected at the maximum dose, and particularly, all offspring from one dam were stillborn. In addition, expression of HIF-1α protein increased in the lung tissue of dams exposed to PM10, and level of hypoxia-related proteins was notably enhanced in PM10-exposed bronchial epithelial cells compared to control. Taken together, we suggest that inhaled PM10 may induce Th1-shifting immune response in the lung, and that it may affect reproduction (fetus development) by causing lung hypoxia. Additionally, we propose that further study is needed to identify particle-size-dependent effects on development of the next generation.

Bile salt-dependent lipase promotes the barrier integrity of Caco-2 cells by activating Wnt/β-catenin signaling via LRP6 receptor

Bile salt-dependent lipase (BSDL) within intestinal lumen can be endocytosed by enterocytes and support the intestinal barrier function. However, the epithelial-supporting effect of this protein has not been verified in a human cell line and neither the direct signaling pathway nor the function of endocytosis in this process has been clearly identified. We sought to investigate the signaling pathway and the membrane receptor through which BSDL might exert these effects using intestinal epithelial cells. Caco-2 cells were treated with recombinant BSDL, and the barrier function, cell proliferation, and activation of the Wnt signaling pathway were assessed. The effect of Wnt signaling activation induced by BSDL and BSDL endocytosis was investigated in LRP6-silenced and non-silenced cells. Moreover, caveolae- and clathrin-dependent endocytosis inhibitors were also applied respectively to analyze their effects on Wnt signaling activation induced by BSDL. BSDL treatment increased the barrier function but not proliferation of Caco-2 cells. It also induced β-catenin nuclear translocation and activated Wnt target gene transcription. Moreover, in the Wnt pathway, BSDL increased the levels of non-phosphorylated-β-catenin (Ser33/37/Thr41) and phosphorylated-β-catenin (Ser552). Notably, the silencing of LRP6 expression impaired BSDL endocytosis and decreased BSDL-induced β-catenin nuclear translocation. The inhibition of BSDL endocytosis induced by caveolae-mediated endocytosis inhibitor was stronger than that by clathrin-mediated endocytosis inhibitor, and the Wnt signaling activation associated with its endocytosis was also most likely caveolae-dependent. Our findings suggested that LRP6, a canonical Wnt pathway co-receptor, can mediate BSDL endocytosis and then activate Wnt signaling in Caco-2 cells.

Imperatorin reduces the inflammatory response of atherosclerosis by regulating MAPKs signaling pathway in vivo and in vitro

Inflammation plays an important role in the process of atherosclerosis (AS). Inhibition of inflammation is an effective way to prevent AS. Imperatorin (IMP) is a kind of furan coumarin with various activities. In this study, the anti-inflammatory effect of IMP was explored in oxidized low-density lipoprotein (ox-LDL)-induced VSMCs and high fat diet (HFD)-induced ApoE^-/- mice. The results showed that IMP attenuated the elevation of TNF-α, IL-6, MCP-1 and NO induced by ox-LDL in supernatant of VSMCs. IMP has normalized the levels of serum lipids (TC, TG, LDL-C and HDL-C) and attenuated inflammatory cytokines in serum. IMP also improved pathological changes and lipid accumulation in aorta. Matrix metalloproteinase-2 (MMP-2) expression in aorta was down-regulated by IMP. IMP could inhibit the phosphorylation of MAPKs pathway in the aorta and VSMCs, resulting in a significant decrease in the contents of p-ERK 1/2, p-JNK and p-P38. Overall, IMP could exert anti-inflammatory effects in vivo and in vitro to interfere with AS.

Role of LOX-1 (Lectin-Like Oxidized Low-Density Lipoprotein Receptor 1) as a Cardiovascular Risk Predictor: Mechanistic Insight and Potential Clinical Use

Atherosclerosis, the underlying cause of cardiovascular disease (CVD), is a worldwide cause of morbidity and mortality. Reducing ApoB-containing lipoproteins-chiefly, LDL (low-density lipoprotein)-has been the main strategy for reducing CVD risk. Although supported by large randomized clinical trials, the persistence of residual cardiovascular risk after effective LDL reduction has sparked an intense search for other novel CVD biomarkers and therapeutic targets. Recently, Lox-1 (lectin-type oxidized LDL receptor 1), an innate immune scavenger receptor, has emerged as a promising target for early diagnosis and cardiovascular risk prediction and is also being considered as a treatment target. Lox-1 was first described as a 50 kDa transmembrane protein in endothelial cells responsible for oxLDL (oxidized LDL) recognition, triggering downstream pathways that intensify atherosclerosis via endothelial dysfunction, oxLDL uptake, and apoptosis. Lox-1 is also expressed in platelets, where it enhances platelet activation, adhesion to endothelial cells, and ADP-mediated aggregation, thereby favoring thrombus formation. Lox-1 was also identified in cardiomyocytes, where it was implicated in the development of cardiac fibrosis and myocyte apoptosis, the main determinants of cardiac recovery following an ischemic insult. Together, these findings have revealed that Lox-1 is implicated in all the main steps of atherosclerosis and has encouraged the development of immunoassays for measurement of sLox-1 (serum levels of soluble Lox-1) to be used as a potential CVD biomarker. Finally, the recent development of synthetic Lox-1 inhibitors and neutralizing antibodies with promising results in animal models has made Lox-1 a target for drug development. In this review, we discuss the main findings regarding the role of Lox-1 in the development, diagnosis, and therapeutic strategies for CVD prevention and treatment.

LDL receptors, caveolae and cholesterol in endothelial dysfunction: oxLDLs accomplices or victims?

Oxidized LDLs (oxLDLs) and oxysterols play a key role in endothelial dysfunction and the development of atherosclerosis. The loss of vascular endothelium function negatively impacts vasomotion, cell growth, adhesiveness and barrier functions. While for some of these disturbances, a reasonable explanation can be provided from a mechanistic standpoint, for many others, the molecular mediators that are involved are unknown. Caveolae, specific plasma membrane domains, have recently emerged as targets and mediators of oxLDL-induced endothelial dysfunction. Caveolae and their associated protein caveolin-1 (Cav-1) are involved in oxLDLs/LDLs transcytosis, mainly through the scavenger receptor class B type 1 (SR-B1 or SCARB1). In contrast, oxLDLs endocytosis is mediated by the lectin-like oxidized LDL receptor 1 (LOX-1), whose activity depends on an intact caveolae system. In addition, LOX-1 regulates the expression of Cav-1 and vice versa. On the other hand, oxLDLs may affect cholesterol plasma membrane content/distribution thus influencing caveolae architecture, Cav-1 localization and the associated signalling. Overall, the evidence indicate that caveolae have both active and passive roles in oxLDL-induced endothelial cell dysfunction. First, as mediators of lipid uptake and transfer in the subendothelial space and, later, as targets of changes in composition/dynamics of plasma membrane lipids resulting from increased levels of circulating oxLDLs. Gaining a better understanding of how oxLDLs interact with endothelial cells and modulate caveolae-mediated signalling pathways, leading to endothelial dysfunction, is crucial to find new targets for intervention to tackle atherosclerosis and the related clinical entities. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Transcriptional Activation of Matricellular Protein Spondin2 (SPON2) by BRG1 in Vascular Endothelial Cells Promotes Macrophage Chemotaxis

The matricellular protein SPON2 plays diverse roles in the development of cardiovascular diseases. SPON2 is expressed in endothelial cells, but its transcription regulation in the context of atherogenesis remains incompletely appreciated. Here we report that SPON2 expression was up-regulated by pro-atherogenic stimuli (oxLDL and TNF-α) in vascular endothelia cells. In addition, endothelial SPON2 was elevated in Apoe^–/– mice fed on a Western diet compared to the control mice. Induction of SPON2 in endothelial cells by pro-atherogenic stimuli was mediated by BRG1, a chromatin remodeling protein, both in vitro and in vivo. Further analysis revealed that BRG1 interacted with the sequence-specific transcription factor Egr-1 to activate SPON2 transcription. BRG1 contributed to SPON2 trans-activation by modulating chromatin structure surrounding the SPON2 promoter. Functionally, activation of SPON2 transcription by the Egr-1/BRG1 complex provided chemoattractive cues for macrophage trafficking. SPON2 depletion abrogated the ability of BRG1 or Egr-1 to stimulate endothelial derived chemoattractive cue for macrophage migration. On the contrary, recombinant SPON2 rescued endothelial chemo-attractability in the absence of BRG1 or Egr-1. In conclusion, our data have identified a novel transcriptional cascade in endothelial cells that may potentially promote macrophage recruitment and vascular inflammation leading to atherogenesis.

BRG1 Activates PR65A Transcription to Regulate NO Bioavailability in Vascular Endothelial Cells

Vascular endothelial cells contribute to the pathogenesis of cardiovascular diseases by producing and disseminating angiocrine factors. Nitric oxide (NO), catalyzed by endothelial NO synthase (eNOS), is one of the prototypical angiocrine factors. eNOS activity is modulated by site-specific phosphorylation. We have previously shown that endothelial-specific knockdown of BRG1 in Apoe^–/– mice attenuates the development of atherosclerosis, in which eNOS-dependent NO catalysis plays an antagonizing role. Here we report that attenuation of atherogenesis in mice by BRG1 knockdown was accompanied by partial restoration of NO biosynthesis by 44% in the arteries and a simultaneous up-regulation of eNOS serine 1177 phosphorylation by 59%. Indeed, BRG1 depletion or inhibition ameliorated oxLDL-induced loss of NO bioavailability and eNOS phosphorylation in cultured endothelial cells. Further analysis revealed that BRG1 regulated eNOS phosphorylation and NO synthesis by activating the transcription of protein phosphatase 2A (PP2A) structural subunit a (encoded by PR65A). BRG1 interacted with ETS1, was recruited by ETS1 to the PR65A promoter, and cooperated with ETS1 to activate PR65A transcription. Finally, depletion of ETS1, similar to BRG1, repressed PR65A induction, normalized eNOS phosphorylation, and rescued NO biosynthesis in endothelial cells treated with oxLDL. In conclusion, our data characterize a novel transcriptional cascade that regulates NO bioavailability in vascular endothelial cells.

Endocytosis of Connexin 36 is Mediated by Interaction with Caveolin-1

The gap junctional protein connexin 36 (Cx36) has been co-purified with the lipid raft protein caveolin-1 (Cav-1). The relevance of an interaction between the two proteins is unknown. In this study, we explored the significance of Cav-1 interaction in the context of intracellular and membrane transport of Cx36. Coimmunoprecipitation assays and Förster resonance energy transfer analysis (FRET) were used to confirm the interaction between the two proteins in the Neuro 2a cell line. We found that the Cx36 and Cav-1 interaction was dependent on the intracellular calcium levels. By employing different microscopy techniques, we demonstrated that Cav-1 enhances the vesicular transport of Cx36. Pharmacological interventions coupled with cell surface biotinylation assays and FRET analysis revealed that Cav-1 regulates membrane localization of Cx36. Our data indicate that the interaction between Cx36 and Cav-1 plays a role in the internalization of Cx36 by a caveolin-dependent pathway.

Effect of Minoxidil on Trabecular Outflow via the Paracellular Pathway

PURPOSE

To investigate the pathway and effects of minoxidil on trabecular outflow in cultured human trabecular meshwork (TM) cells.

METHODS

After exposing primarily cultured TM cells to 0, 10, 50, or 100 μM minoxidil sulfate (MS), trabecular outflow was assessed by measuring TM cell monolayer permeability to carboxyfluorescein and transepithelial electrical resistance. To assess the pathway of permeability changes, caveolin-1, occludin, and claudin-5 levels were measured via western blot. Generation of reactive oxygen species (ROS) was measured using the dichlorofluorescein diacetate assay. To assess the involvement of nitric oxide (NO) in minoxidil-induced permeability increase, the degrees of endothelial nitric oxide synthase mRNA expression and NO production were measured with reverse transcription polymerase chain reaction and Griess assays, respectively. Permeability was also measured with co-exposure to 50 μM N-acetyl cysteine.

RESULTS

MS significantly increased TM cell monolayer permeability (p < 0.05) and decreased transepithelial electrical resistance (p < 0.05). MS decreased the degree of endothelial nitric oxide synthase mRNA expression but did not affect NO production. MS decreased occludin and claudin-5 levels but did not affect caveolin-1 level. MS at 100 μM increased the generation of ROS, and MS-induced permeability increase was attenuated after co-exposure to 50 μM N-acetyl cysteine.

CONCLUSIONS

Minoxidil may preferentially increase trabecular permeability via a paracellular pathway by downregulation of tight junction proteins. This minoxidil-induced permeability through the TM may be mediated by generation of ROS.

Lung Endothelial Transcytosis

Transcytosis of macromolecules through lung endothelial cells is the primary route of transport from the vascular compartment into the interstitial space. Endothelial transcytosis is mostly a caveolae-dependent process that combines receptor-mediated endocytosis, vesicle trafficking via actin-cytoskeletal remodeling, and SNARE protein directed vesicle fusion and exocytosis. Herein, we review the current literature on caveolae-mediated endocytosis, the role of actin cytoskeleton in caveolae stabilization at the plasma membrane, actin remodeling during vesicle trafficking, and exocytosis of caveolar vesicles. Next, we provide a concise summary of experimental methods employed to assess transcytosis. Finally, we review evidence that transcytosis contributes to the pathogenesis of acute lung injury. © 2020 American Physiological Society. Compr Physiol 10:491-508, 2020.

Caveolin as a Novel Potential Therapeutic Target in Cardiac and Vascular Diseases: A Mini Review

Caveolin, a structural protein of caveolae, play roles in the regulation of endothelial function, cellular lipid homeostasis, and cardiac function by affecting the activity and biogenesis of nitric oxide, and by modulating signal transduction pathways that mediate inflammatory responses and oxidative stress. In this review, we present the role of caveolin in cardiac and vascular diseases and the relevant signaling pathways involved. Furthermore, we discuss a novel therapeutic perspective comprising crosstalk between caveolin and autophagy.

Caveolin-1 as a critical component in the pathogenesis of lung fibrosis of different etiology: Evidences and mechanisms

Caveolin is a structural protein of flask-shaped invaginations of the plasma membrane termed as caveolae and is widely expressed on the endothelial cells, smooth muscle cells and fibroblasts in the different parts of the body including the lung tissues. The expression of caveolin-1 in the lung tissues is important to prevent the fibrogenic actions of TGF-β1 in lung fibrosis of different etiology including idiopathic pulmonary fibrosis, systemic sclerosis-associated interstitial lung disease and allergen-induced airway remodeling. Caveolin-1-mediated internalization and degradation of TGF-β1 receptors may possibly account for the decreased actions of TGF-β1. Studies have shown that the deficiency of caveolin-1 is very important in inducing lung fibrosis and its upregulation is reported to prevent lung fibrosis. The biological actions of caveolin-1 involve signaling pathways including JNK signaling, IL-4, STAT-3, miR199a-5p, CXCR4⁺ and CXCL12. The present review discusses the key role of caveolin and associated signaling pathways in the pathogenesis of lung fibrosis of different etiology.

CAV1-CAVIN1-LC3B-mediated autophagy regulates high glucose-stimulated LDL transcytosis

Diabetes is a recognized high-risk factor for the development of atherosclerosis, in which macroautophagy/autophagy is emerging to play essential roles. The retention of low-density lipoprotein (LDL) particles in subendothelial space following transcytosis across the endothelium is the initial step of atherosclerosis. Here, we identified that high glucose could promote atherosclerosis by stimulating transcytosis of LDL. By inhibiting AMPK-MTOR-PIK3C3 pathway, high glucose suppresses the CAV-CAVIN-LC3B-mediated autophagic degradation of CAV1; therefore, more CAV1 is accumulated in the cytosol and utilized to form more caveolae in the cell membrane and facilitates the LDL transcytosis across endothelial cells. For a proof of concept, higher levels of lipids were accumulated in the subendothelial space of umbilical venous walls from pregnant women with gestational diabetes mellitus (GDM), compared to those of pregnant women without GDM. Our results reveal that high glucose stimulates LDL transcytosis by a novel CAV1-CAVIN1-LC3B signaling-mediated autophagic degradation pathway.

ABBREVIATIONS

3-MA: 3-methyladenine; ACTB: actin beta; AMPK: AMP-activated protein kinase; Bafi: bafilomycin A₁; CAV1: caveolin-1; CAVIN1: caveolae associated protein 1; CSD: the CAV1 scaffolding domain; GDM: gestational diabetes mellitus; IMD: intramembrane domain; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule- associated protein 1 light chain 3; MFI: mean fluorescence intensity; MTOR: mechanistic target of rapamycin kinase; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; SQSTM1/p62: sequestosome 1.

Estrogen Inhibits LDL (Low-Density Lipoprotein) Transcytosis by Human Coronary Artery Endothelial Cells via GPER (G-Protein-Coupled Estrogen Receptor) and SR-BI (Scavenger Receptor Class B Type 1)

Objective- The atheroprotective effects of estrogen are independent of circulating lipid levels. Whether estrogen regulates transcytosis of LDL (low-density lipoprotein) across the coronary endothelium is unknown. Approach and Results- Using total internal reflection fluorescence microscopy, we quantified transcytosis of LDL across human coronary artery endothelial cells from multiple donors. LDL transcytosis was significantly higher in cells from men compared with premenopausal women. Estrogen significantly attenuated LDL transcytosis by endothelial cells from male but not female donors; transcytosis of albumin was not affected. Estrogen caused downregulation of endothelial SR-BI (scavenger receptor class B type 1), and overexpression of SR-BI was sufficient to restore LDL transcytosis. Similarly, depletion of SR-BI by siRNA attenuated endothelial LDL transcytosis and prevented any further effect of estrogen. In contrast, treatment with estrogen had no effect on SR-BI expression by liver cells. Inhibition of estrogen receptors α and β had no effect on estrogen-mediated attenuation of LDL transcytosis. However, estrogen's effect on LDL transcytosis was blocked by depletion of the GPER (G-protein-coupled estrogen receptor). GPER was found to be enriched in endothelial cells compared with hepatocytes and is reported to signal via transactivation of the EGFR (epidermal growth factor receptor); inhibition of EGFR prevented the effect of estrogen on LDL transcytosis and SR-BI mRNA. Last, SR-BI expression was significantly higher in human coronary artery endothelial cells from male compared with premenopausal female donors. Conclusions- Estrogen significantly inhibits LDL transcytosis by downregulating endothelial SR-BI; this effect requires GPER.

The Role of (Modified) Lipoproteins in Vascular Function: A Duet Between Monocytes and the Endothelium

Over the last century, many studies have demonstrated that low-density lipoprotein (LDL) is a key risk factor of cardiovascular diseases (CVD) related to atherosclerosis. Thus, for these CVD patients, LDL lowering agents are commonly used in the clinic to reduce the risk for CVD. LDL, upon modification, will develop distinct inflammatory and proatherogenic potential, leading to impaired endothelial integrity, influx of immune cells and subsequent increased foam cell formation. LDL can also directly affect peripheral monocyte composition, rendering them in a more favorable position to migrate and accumulate in the subendothelial space. It has become apparent that other lipoprotein particles, such as triglyceride- rich lipoproteins or remnants (TRL) and lipoprotein(a) [Lp(a)] may also impact on atherogenic pathways. Evidence is accumulating that Lp(a) can promote peripheral monocyte activation, eventually leading to increased transmigration through the endothelium. Similarly, remnant cholesterol has been identified to play a key role in endothelial dysfunction and monocyte behavior. In this review, we will discuss recent developments in understanding the role of different lipoproteins in the context of inflammation at both the level of the monocyte and the endothelium.

Retracted Article: MicroRNA-135a alleviates lipid accumulation and inflammation of atherosclerosis through targeting lipoprotein lipase

MicroRNAs (miRNAs) have recently attracted increasing attention for their involvement in atherosclerosis (AS). The purpose of this study was to further explore the function and underlying mechanism of miR-135a in AS progression. The expression levels of miR-135a and lipoprotein lipase (LPL) mRNA were detected by qRT-PCR, and LPL protein expression was measured by western blotting. The levels of blood lipids and inflammatory cytokines, and LPL activity were assessed using corresponding Assay Kits, and an HPLC assay was used to determine the levels of free cholesterol (FC), total cholesterol (TC) and cholesterol ester (CE). A Dil-oxLDL binding assay was performed to evaluate the ability of cholesterol uptake. The direct interaction between miR-135a and LPL was confirmed by a dual-luciferase reporter assay and RNA immunoprecipitation assay. Our data indicated that miR-135a was downregulated in serum samples of AS patients and mice. Upregulation of miR-135a alleviated lipid metabolic disorders and inflammation in AS mice. Moreover, miR-135a negatively regulated lipid accumulation and inflammation in ox-LDL-treated THP-1 macrophages. Mechanistically, miR-135a directly targeted LPL and repressed LPL expression. LPL mediated the regulatory effect of miR-135a on lipid accumulation and inflammation in ox-LDL-treated THP-1 macrophages. In conclusion, our study indicated that miR-135a upregulation ameliorated lipid accumulation and inflammation at least partly by targeting LPL in THP-1 macrophages, highlighting miR-135a as a potential antiatherogenic agent.

MicroRNAs (miRNAs) have recently attracted increasing attention for their involvement in atherosclerosis (AS).

Ox-LDL induces endothelial cell apoptosis and macrophage migration by regulating caveolin-1 phosphorylation

Oxidative low-density lipoprotein (ox-LDL) is a risk factor for atherosclerosis. Ox-LDL leads to endothelial injury in the initial stage of atherosclerosis. In this study, we investigated the role of ox-LDL in endothelial injury and macrophage recruitment. We demonstrated that ox-LDL promoted a dose-dependent phosphorylation of caveolin-1 in human umbilical vein endothelial cells. Phosphorylated caveolin-1 increased ox-LDL uptake. Intracellular accumulation of ox-LDL induced NF-κB p65 phosphorylation, promoted HMGB1 translocation from nucleus to cytoplasm and cytochrome C release from mitochondria to cytoplasm, and activated caspase 3, resulting in cell apoptosis. NF-κB activation also facilitated cavolin-1 phosphorylation and HMGB1 expression. In addition, caveolin-1 phosphorylation favored HMGB1 release and nuclear translocation of EGR1. Nuclear translocation of EGR1 contributed to cytoplasmic translocation of HMGB1. The extracellular HMGB1 induced the migration of PMBC-derived macrophages toward HUVECs in a TLR4-dependent manner. Our results suggested that ox-LDL promoted HUVECs apoptosis and macrophage recruitment by regulating caveolin-1 phosphorylation.

Cavin-1 regulates caveolae-mediated LDL transcytosis: crosstalk in an AMPK/eNOS/ NF-κB/Sp1 loop

Caveolae are specialized lipid rafts structure in the cell membrane and critical for regulating endothelial functions, e.g. transcytosis of macromolecules like low density lipoprotein (LDL) etc. Specifically, the organization and functions of caveolae are mediated by structure protein (caveolin-1) and adapter protein (cavin-1). The pathogenic role of caveolin-1 is well studied; nevertheless, mechanisms whereby cavin-1 regulates signaling transduction remain poorly understood. The aim of this study was designed to explore the role of cavin-1 in caveolae-mediated LDL transcytosis across endothelial cells. We reported here that cavin-1 knockdown mediated by small interfering RNA (siRNA) caused a significant decrease of LDL transcytosis. Moreover, cavin-1 knockdown increased the activity of endothelial nitric oxide synthase (eNOS) and the production of nitric oxide (NO). Consequently, an eNOS inhibitor, N-Nitro-L-Arginine Methyl Ester (L-NAME), not only suppressed the activity of specificity protein (Sp1) and nuclear factor kappa B (NF-κB), but also inhibited both activities via activating adenosine 5‘-monophosphate- activated protein kinase (AMPK). In conclusion, we proposed an AMPK/eNOS/NF-κB/Sp1 circuit loop was formed to regulate caveolae residing proteins’ expression, e.g. LDL receptor (LDLR), caveolin-1, eNOS, thereby to regulate caveolae-mediated LDL transcytosis in endothelial cells.

Regulation of blood vascular permeability in the skin

Regulation of blood vessel permeability is essential for the homeostasis of peripheral tissues. This regulation controls the trafficking of plasma contents, including water, vitamins, ions, hormones, cytokines, amyloids, lipoproteins, carrier proteins, and immunoglobulins. The properties of blood vessels vary among tissues based on their structural differences: continuous, fenestrated, or sinusoidal. These three types of blood vessels have different charge and size barrier properties. The anionic luminal glycocalyx layer on endothelial cells establishes the "charge barrier" that repels the attachment of negatively charged blood cells and plasma molecules. In contrast, the "size barrier" of blood vessels largely relies on the interendothelial junctions (IEJs) between endothelial cells, which define the paracellular permeability. As in most peripheral tissues, blood capillaries in the skin are composed of continuous and/or fenestrated blood vessels that have relatively tighter IEJs compared to those in the internal organs. Small vesicles in the capillary endothelium were discovered in the 1950s, and studies have since confirmed that blood endothelial cells transport the plasma contents by endocytosis and subsequent transcytosis and exocytosis-this process is called transcellular permeability. The permeability of blood vessels is highly variable as a result of intrinsic and extrinsic factors. It is significantly elevated upon tissue inflammations as a result of disabled IEJs and increased paracellular permeability due to inflammatory mediators. An increase in transcellular permeability during inflammation has also been postulated. Here, we provide an overview of the general properties of vascular permeability based on our recent observations of murine skin inflammation models, and we discuss its physiological significance in peripheral homeostasis.

Saccharomyces cerevisiae show low levels of traversal across human endothelial barrier in vitro

Background:   Saccharomyces cerevisiae is generally considered safe, and is involved in the production of many types of foods and dietary supplements. However, some isolates, which are genetically related to strains used in brewing and baking, have shown virulent traits, being able to produce infections in humans, mainly in immunodeficient patients. This can lead to systemic infections in humans. Methods: In this work, we studied S. cerevisiae isolates in an in vitro human endothelial barrier model, comparing their behaviour with that of several strains of the related pathogens Candida glabrata and Candida albicans. Results: The results showed that this food related yeast is able to cross the endothelial barrier in vitro. However, in contrast to C. glabrata and C. albicans, S. cerevisiae showed very low levels of traversal. Conclusions: We conclude that using an in vitro human endothelial barrier model with S. cerevisiae can be useful to evaluate the safety of S. cerevisiae strains isolated from foods.

Saccharomyces cerevisiae show low levels of traversal across the human blood brain barrier in vitro

BACKGROUND

  Saccharomyces cerevisiae is generally considered safe, and is involved in the production of many types of foods and dietary supplements. However, some isolates, which are genetically related to strains used in brewing and baking, have shown virulent traits, being able to produce infections in humans, mainly in immunodeficient patients. This can lead to systemic infections in humans.

METHODS

In this work, we studied S. cerevisiae isolates in an in vitro human blood brain barrier model, comparing their behaviour with that of several strains of the related pathogens Candida glabrata and Candida albicans.

RESULTS

The results showed that this food related yeast is able to cross the blood brain barrier in vitro. However, in contrast to C. glabrata and C. albicans, S. cerevisiae showed very low levels of traversal.

CONCLUSIONS

We conclude that using an in vitro human blood brain barrier model with S. cerevisiae can be useful to evaluate the safety of S. cerevisiae strains isolated from foods.

NS1619 regulates the expression of caveolin-1 protein in a time-dependent manner via ROS/PI3K/PKB/FoxO1 signaling pathway in brain tumor microvascular endothelial cells

NS1619, a calcium-activated potassium channel (Kca channel) activator, can selectively and time-dependently accelerate the formation of transport vesicles in both the brain tumor capillary endothelium and tumor cells within 15min of treatment and then increase the permeability of the blood-brain tumor barrier (BTB). However, the mechanism involved is still under investigation. Using a rat brain glioma (C6) model, the expression of caveolin-1, FoxO1 and p-FoxO1 protein were examined at different time points after intracarotid infusion of NS1619 at a dose of 30μg/kg/min. Internalization of Cholera toxin subunit (CTB) labeled fluorescently was monitored by flow cytometry. The expression of caveolin-1 and FoxO1 protein at tumor microvessels was enhanced and caveolae-mediated CTB endocytosis was increased by NS1619 infusion for 15min. Compared with the 15min group, the expression of caveolin-1 protein was significantly decreased and the level of phosphorylation of FoxO1 was significantly increased in the NS1619 2h group. In addition, inhibitors of reactive oxygen species (ROS) or PI3K or PKB significantly attenuated the level of FoxO1 phosphorylation and also increased the expression of caveolin-1 protein in Human Brain Microvascular Endothelial Cells (HBMECs) cocultured with human glioma cells (U87) 2h after NS1619 treatment. This led to the conclusion that NS1619-mediated transport vesicle increase is, at least partly, related to the ROS/PI3K/PKB/FoxO1 signaling pathway.

Effect of quercetin and its metabolite on caveolin-1 expression induced by oxidized LDL and lysophosphatidylcholine in endothelial cells

Oxidized low-density lipoprotein contributes to atherosclerotic plaque formation, and quercetin is expected to exert anti-atherosclerotic effects. We previously reported accumulation of conjugated quercetin metabolites in the aorta of rabbits fed high-cholesterol diets with quercetin glucosides, resulting in attenuation of lipid peroxidation and inhibition of lipid accumulation. Caveolin-1, a major structural protein of caveolae in vascular endothelial cells, plays a role in atherosclerosis development. Here we investigated effects of oxidized low-density lipoprotein, quercetin and its metabolite, quercetin 3-O-β-glucuronide, on caveolin-1 expression. Oxidized low-density lipoprotein significantly upregulated caveolin-1 mRNA expression. An oxidized low-density lipoprotein component, lysophosphatidylcholine, also induced expression of both caveolin-1 mRNA and protein. However, lysophosphatidylcholine did not affect the location of caveolin-1 proteins within caveolae structures. Co-treatment with quercetin or quercetin 3-O-β-glucuronide inhibited lysophosphatidylcholine-induced caveolin-1 expression. Quercetin and quercetin 3-O-β-glucuronide also suppressed expression of adhesion molecules induced by oxidized low-density lipoprotein and lysophosphatidylcholine. These results strongly suggest lysophosphatidylcholine derived from oxidized low-density lipoprotein contributes to atherosclerotic events by upregulating caveolin-1 expression, resulting in induction of adhesion molecules. Quercetin metabolites are likely to exert an anti-atherosclerotic effect by attenuating caveolin-1 expression in endothelial cells.

Interleukin-1β induces the upregulation of caveolin-1 expression in a rat brain tumor model

The aim of the present study was to investigate the expression of caveolin-1 in rat brain glioma tissue, and to determine whether interleukin-1β (IL-1β) has a role in this process. Using glioma cells, a tumor-burdened rat model was established, and the expression of caveolin-1 protein in the tumor sites was significantly increased following intracarotid infusion of IL-1β (3.7 ng/kg/min), as indicated by western blot analysis. The maximum value of the caveolin-1 expression was observed in tumor-burdened rats after 60 min of IL-1β perfusion, and which was significantly enhanced by vascular endothelial growth factor (VEGF). In addition, VEGF also significantly increased IL-1β-induced blood tumor barrier (BTB) permeability. The results suggest that the IL-1β-induced BTB permeability increase may be associated with the expression of caveolin-1 protein, and VEGF may be involved in this process.