Oxidized low-density lipoproteins impair the pro-atherosclerotic effect of granulocyte-macrophage-colony-stimulating factor-producing T helper cells on macrophages

T cells contribute to the pathogenesis of atherosclerosis. However, the presence and function of granulocyte-macrophage-colony-stimulating factor (GM-CSF)-producing T helper (ThGM) cells in atherosclerosis development is unknown. This study aims to characterize the phenotype and function of ThGM cells in experimental atherosclerosis. Atherosclerosis was induced by feeding apolipoprotein E knockout (ApoE-/-) mice with a high-fat diet. Aortic ThGM cells were detected and sorted by flow cytometry. The effect of oxidized low-density lipoprotein (oxLDL) on ThGM cells and the impact of ThGM cells on macrophages were evaluated by flow cytometry, quantitative RT-PCR, oxLDL binding/uptake assay, immunoblotting and foam cell formation assay. We found that GM-CSF+IFN-γ- ThGM cells existed in atherosclerotic aortas. Live ThGM cells were enriched in aortic CD4+CCR6-CCR8-CXCR3-CCR10+ T cells. Aortic ThGM cells triggered the expression of interleukin-1β (IL-1β), tumour necrosis factor (TNF), interleukin-6 (IL-6) and C-C motif chemokine ligand 2 (CCL2) in macrophages. Besides, aortic ThGM cells expressed higher CD69 than other T cells and bound to oxLDL. oxLDL suppressed the cytokine expression in ThGM cells probably via inhibiting the signal transducer and activator of transcription 5 (STAT5) signalling. Furthermore, oxLDL alleviated the effect of ThGM cells on inducing macrophages to produce pro-inflammatory cytokines and generate foam cells. The nuclear receptor subfamily 4 group A (NR4A) members NR4A1 and NR4A2 were involved in the suppressive effect of oxLDL on ThGM cells. Collectively, oxLDL suppressed the supportive effect of ThGM cells on pro-atherosclerotic macrophages.

Foamy macrophages are proinflammatory and express TREM2 in eruptive xanthomas

The accumulation of dermal foam cells (lipid-laden macrophages) is the primary histopathological feature of eruptive xanthomas. Yet, an understanding of the activation and implications of foamy macrophages in eruptive xanthomas remains unknown. We investigated foamy macrophage activation and found that these cells are proinflammatory. Of note, foam cells in eruptive xanthomas express TREM2, a recently identified marker for lipid-laden macrophages in atherosclerosis and obesity.

In Vivo Fluorescent Labeling of Foam Cell-Derived Extracellular Vesicles as Circulating Biomarkers for In Vitro Detection of Atherosclerosis

Real-time monitoring of the development of atherosclerosis (AS) is key to the management of cardiovascular disease (CVD). However, existing laboratory approaches lack sensitivity and specificity, mostly due to the dearth of reliable AS biomarkers. Herein, we developed an in vivo fluorescent labeling strategy that allows specific staining of the foam cell-derived extracellular vesicles (EVs) in atherosclerotic plaques, which are released into the blood as circulating biomarkers for in vitro detection of AS. This strategy relies on a self-assembled nanoprobe that could recognize foam cells specifically, where the probe is degraded by the intracellular HClO to produce a trifluoromethyl-bearing boron-dipyrromethene fluorophore (termed B-CF3), a lipophilic dye that can be transferred to the exosomal membranes. These circulating B-CF3-stained EVs can be detected directly on a fluorescence spectrometer or microplate reader without resorting to any sophisticated analytical method. This liquid-biopsy format enables early detection and real-time differentiation of lesion vulnerability during AS progression, facilitating effective CVD management.

Scutellarin inhibits oleic acid induced vascular smooth muscle foam cell formation via activating autophagy and inhibiting NLRP3 inflammasome activation

Abnormalities in vascular smooth muscle cells (VSMCs) are pivotal in the pathogenesis of cardiovascular pathologies such as atherosclerosis and hypertension. Scutellarin (Scu), a flavonoid derived from marigold flowers, exhibits a spectrum of biological activities including anti-inflammatory, antioxidant, antitumor, immunomodulatory and antimicrobial effects. Notably, Scu has demonstrated the capacity to mitigate vascular endothelial damage and prevent atherosclerosis via its antioxidative properties. Nevertheless, the influence of Scu on the formation of VSMC-derived foam cells remains underexplored. In this study, Scu was evidenced to efficaciously attenuate oleic acid (OA)-induced lipid accumulation and the upregulation of adipose differentiation-associated protein Plin2 in a dose- and time-responsive manner. We elucidated that Scu effectively diminishes OA-provoked VSMC foam cell formation. Further, it was established that Scu pretreatment augments the protein expression of LC3B-II and the mRNA levels of Map1lc3b and Becn1, concurrently diminishing the protein levels of the NLRP3 inflammasome compared to the OA group. Activation of autophagy through rapamycin attenuated NLRP3 inflammasome protein expression, intracellular lipid droplet content and Plin2 mRNA levels. Scu also counteracted the OA-induced decrement of LC3B-II levels in the presence of bafilomycin-a1, facilitating the genesis of autophagosomes and autolysosomes. Complementarily, in vivo experiments revealed that Scu administration substantially reduced arterial wall thickness, vessel wall cross-sectional area, wall-to-lumen ratio and serum total cholesterol levels in comparison to the high-fat diet model group. Collectively, our findings suggest that Scu attenuates OA-induced VSMC foam cell formation through the induction of autophagy and the suppression of NLRP3 inflammasome activation.

The role of foam cells in spinal cord injury: challenges and opportunities for intervention

Spinal cord injury (SCI) results in a large amount of tissue cell debris in the lesion site, which interacts with various cytokines, including inflammatory factors, and the intrinsic glial environment of the central nervous system (CNS) to form an inhibitory microenvironment that impedes nerve regeneration. The efficient clearance of tissue debris is crucial for the resolution of the inhibitory microenvironment after SCI. Macrophages are the main cells responsible for tissue debris removal after SCI. However, the high lipid content in tissue debris and the dysregulation of lipid metabolism within macrophages lead to their transformation into foamy macrophages during the phagocytic process. This phenotypic shift is associated with a further pro-inflammatory polarization that may aggravate neurological deterioration and hamper nerve repair. In this review, we summarize the phenotype and metabolism of macrophages under inflammatory conditions, as well as the mechanisms and consequences of foam cell formation after SCI. Moreover, we discuss two strategies for foam cell modulation and several potential therapeutic targets that may enhance the treatment of SCI.

Hypertensive Pressure Mechanosensing Alone Triggers Lipid Droplet Accumulation and Transdifferentiation of Vascular Smooth Muscle Cells to Foam Cells

Arterial Vascular smooth muscle cells (VSMCs) play a central role in the onset and progression of atherosclerosis. Upon exposure to pathological stimuli, they can take on alternative phenotypes that, among others, have been described as macrophage like, or foam cells. VSMC foam cells make up >50% of all arterial foam cells and have been suggested to retain an even higher proportion of the cell stored lipid droplets, further leading to apoptosis, secondary necrosis, and an inflammatory response. However, the mechanism of VSMC foam cell formation is still unclear. Here, it is identified that mechanical stimulation through hypertensive pressure alone is sufficient for the phenotypic switch. Hyperspectral stimulated Raman scattering imaging demonstrates rapid lipid droplet formation and changes to lipid metabolism and changes are confirmed in ABCA1, KLF4, LDLR, and CD68 expression, cell proliferation, and migration. Further, a mechanosignaling route is identified involving Piezo1, phospholipid, and arachidonic acid signaling, as well as epigenetic regulation, whereby CUT&Tag epigenomic analysis confirms changes in the cells (lipid) metabolism and atherosclerotic pathways. Overall, the results show for the first time that VSMC foam cell formation can be triggered by mechanical stimulation alone, suggesting modulation of mechanosignaling can be harnessed as potential therapeutic strategy.

Cholesterol trafficking, lysosomal function, and atherosclerosis

Despite years of study and major research advances over the past 50 years, atherosclerotic diseases continue to rank as the leading global cause of death. Accumulation of cholesterol within the vascular wall remains the main problem and represents one of the early steps in the development of atherosclerotic lesions. There is a complex relationship between vesicular cholesterol transport and atherosclerosis, and abnormalities in cholesterol trafficking can contribute to the development and progression of the lesions. The dysregulation of vesicular cholesterol transport and lysosomal function fosters the buildup of cholesterol within various intracytoplasmic compartments, including lysosomes and lipid droplets. This, in turn, promotes the hallmark formation of foam cells, a defining feature of early atherosclerosis. Multiple cellular processes, encompassing endocytosis, exocytosis, intracellular trafficking, and autophagy, play crucial roles in influencing foam cell formation and atherosclerotic plaque stability. In this review, we highlight recent advances in the understanding of the intricate mechanisms of vesicular cholesterol transport and its relationship with atherosclerosis and discuss the importance of understanding these mechanisms in developing strategies to prevent or treat this prevalent cardiovascular disease.

Macrophage P2Y6 receptor deletion attenuates atherosclerosis by limiting foam cell formation through phospholipase Cβ/store-operated calcium entry/calreticulin/scavenger receptor A pathways

BACKGROUND AND AIMS

Macrophage-derived foam cells play a causal role during the pathogenesis of atherosclerosis. P2Y6 receptor (P2Y6R) highly expressed has been considered as a disease-causing factor in atherogenesis, but the detailed mechanism remains unknown. This study aims to explore P2Y6R in regulation of macrophage foaming, atherogenesis, and its downstream pathways. Furthermore, the present study sought to find a potent P2Y6R antagonist and investigate the feasibility of P2Y6R-targeting therapy for atherosclerosis.

METHODS

The P2Y6R expression was examined in human atherosclerotic plaques and mouse artery. Atherosclerosis animal models were established in whole-body P2Y6R or macrophage-specific P2Y6R knockout mice to evaluate the role of P2Y6R. RNA sequencing, DNA pull-down experiments, and proteomic approaches were performed to investigate the downstream mechanisms. High-throughput Glide docking pipeline from repurposing drug library was performed to find potent P2Y6R antagonists.

RESULTS

The P2Y6R deficiency alleviated atherogenesis characterized by decreasing plaque formation and lipid deposition of the aorta. Mechanically, deletion of macrophage P2Y6R significantly inhibited uptake of oxidized low-density lipoprotein through decreasing scavenger receptor A expression mediated by phospholipase Cβ/store-operated calcium entry pathways. More importantly, P2Y6R deficiency reduced the binding of scavenger receptor A to CALR, accompanied by dissociation of calreticulin and STIM1. Interestingly, thiamine pyrophosphate was found as a potent P2Y6R antagonist with excellent P2Y6R antagonistic activity and binding affinity, of which the pharmacodynamic effect and mechanism on atherosclerosis were verified.

CONCLUSIONS

Macrophage P2Y6R regulates phospholipase Cβ/store-operated calcium entry/calreticulin signalling pathway to increase scavenger receptor A protein level, thereby improving foam cell formation and atherosclerosis, indicating that the P2Y6R may be a potential therapeutic target for intervention of atherosclerotic diseases using P2Y6R antagonists including thiamine pyrophosphate.

Role of dysregulated macrophage subpopulation ratios and functional changes in the development of coronary atherosclerosis

Coronary heart disease is one of the most significant risk factors affecting human health worldwide. Its pathogenesis is intricate, with atherosclerosis being widely regarded as the leading cause. Aberrant lipid metabolism in macrophages is recognized as one of the triggering factors in atherosclerosis development. To investigate the role of macrophages in the formation of coronary artery atherosclerosis, we utilized single-cell data from wild-type mice obtained from the aortic roots and ascending aortas after long-term high-fat diet feeding, as deposited in GSE131776. Seurat software was employed to refine the single-cell data in terms of scale and cell types, facilitating the identification of differentially expressed genes. Through the application of differential expression genes, we conducted Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional enrichment analyses at 0, 8 and 16 weeks, aiming to uncover pathways with the most pronounced functional alterations as the high-fat diet progressed. The AddModuleScore function was employed to score the expression of these pathways across different cell types. Subsequently, macrophages were isolated and further subdivided into subtypes, followed by an investigation into intercellular communication within these subtypes. Subsequent to this, we induced THP-1 cells to generate foam cells, validating critical genes identified in prior studies. The results revealed that macrophages underwent the most substantial functional changes as the high-fat diet progressed. Furthermore, two clusters were identified as potentially playing pivotal roles in macrophage functional regulation during high-fat diet progression. Additionally, macrophage subtypes displayed intricate functionalities, with mutual functional counterbalances observed among these subtypes. The proportions of macrophage subtypes and the modulation of anti-inflammatory and pro-inflammatory functions played significant roles in the development of coronary artery atherosclerosis.

Bioengineered Vascular Model of Foam Cell Formation

Foam cell formation is a complex blood vessel pathology, which is characterized by a series of events, including endothelium dysfunction, inflammation, and accumulation of immune cells underneath the blood vessel walls. Novel bioengineered models capable of recapitulating these events are required to better understand the complex pathological processes underlying the development of foam cell formation and, consequently, advanced bioengineered platforms for screening drugs. Here, we generated a microfluidic blood vessel model, incorporating a three-dimensional (3D) extracellular matrix coated with an endothelial layer. This system enables us to perform experiments under a dynamic microenvironment that recapitulates the complexities of the native vascular regions. Using this model, we studied the effectors that regulate monocyte adhesion and migration, as well as foam cell formation inside vessel walls. We found that monocyte adhesion and migration are regulated by both the endothelium and monocytes themselves. Monocytes migrated into the extracellular matrix only when endothelial cells were cultured in the vessel model. In addition, the exposure of an endothelial layer to tumor necrosis factor α (TNF-α) and low shear stress both increased monocyte migration into the subendothelial space toward the matrix. Furthermore, we demonstrated the process of foam cell formation, 3 days after transmigration of peripheral blood mononuclear cells (PBMCs) into the vessel wall. We showed that pre-exposure of PBMCs to high shear rates increases their adhesion and migration through the TNF-α-treated endothelium but does not affect their capacity to form foam cells. The versatility of our model allows for mechanistic studies on foam cell formation under customized pathological conditions.

Possible roles of human mast cells in the formation of xanthelasma palpebrarum

Cutaneous xanthoma consist of foam cells that originate from monocytes or macrophages and accumulate in perivascular areas of the skin. The main component of these cells is oxidized low-density lipoprotein (oxLDL). In this study, we show that mast cells surround the accumulated foam cells, suggesting their involvement in xanthoma formation. Coculture of THP-1 or U937 monocytes with the human mast cell line LUVA upregulated their uptake of oxLDL. Positive staining for intracellular cell adhesion molecule-1 (ICAM-1) at the borders between mast cells and foam cells was seen in pathological specimens of the most common cutaneous xanthoma, xanthelasma palpebrarum, and in cocultures. In the latter, ICAM1 messenger RNA levels were upregulated. The administration of anti-ICAM-1 blocking antibody inhibited the increase in oxLDL uptake by THP-1 or U937 monocytes cocultured with LUVA. Taken together, these results suggest a role for mast cells in the formation of xanthelasma palpebrarum and the involvement of ICAM-1 in this process.

Endocytosis of red blood cell extracellular vesicles by macrophages leads to cytoplasmic heme release and prevents foam cell formation in atherosclerosis

Extracellular vesicles (EVs) can be produced from red blood cells (RBCs) on a large scale and used to deliver therapeutic payloads efficiently. However, not much is known about the native biological properties of RBCEVs. Here, we demonstrate that RBCEVs are primarily taken up by macrophages and monocytes. This uptake is an active process, mediated mainly by endocytosis. Incubation of CD14+ monocytes with RBCEVs induces their differentiation into macrophages with an Mheme-like phenotype, characterized by upregulation of heme oxygenase-1 (HO-1) and the ATP-binding cassette transporter ABCG1. Moreover, macrophages that take up RBCEVs exhibit a reduction in surface CD86 and decreased secretion of TNF-α under inflammatory stimulation. The upregulation of HO-1 is attributed to heme derived from haemoglobin in RBCEVs. Heme is released from internalized RBCEVs in late endosomes and lysosomes via the heme transporter, HRG1. Consequently, RBCEVs exhibit the ability to attenuate foam cell formation from oxidized low-density lipoproteins (oxLDL)-treated macrophages in vitro and reduce atherosclerotic lesions in ApoE knockout mice on a high-fat diet. In summary, our study reveals the uptake mechanism of RBCEVs and their delivery of heme to macrophages, suggesting the potential application of RBCEVs in the treatment of atherosclerosis.

A systematic review of the impact of Porphyromonas gingivalis on foam cell formation: Implications for the role of periodontitis in atherosclerosis

BACKGROUND

The current literature suggests the significant role of foam cells in the initiation of atherosclerosis through the formation of a necrotic core in atherosclerotic plaques. Moreover, an important periodontal pathogen called Porphyromonas gingivalis (P. gingivalis) is indicated to play a significant role in this regard. Thus, the aim of this systematic review was to comprehensively study the pathways by which P. gingivalis as a prominent bacterial species in periodontal disease, can induce foam cells that would initiate the process of atherosclerosis formation.

METHODS

An electronic search was undertaken in three databases (Pubmed, Scopus, and Web of Science) to identify the studies published from January 2000 until March 2023. The risk of bias in each study was also assessed using the QUIN risk of bias assessment tool.

RESULTS

After the completion of the screening process, 11 in-vitro studies met the inclusion criteria and were included for further assessments. Nine of these studies represented a medium risk of bias, while the other two had a high risk of bias. All of the studies have reported that P. gingivalis can significantly induce foam cell formation by infecting the macrophages and induction of oxidized low-density lipoprotein (oxLDL) uptake. This process is activated through various mediators and pathways. The most important factors in this regard are the lipopolysaccharide of P. gingivalis and its outer membrane vesicles, as well as the changes in the expression rate of transmembrane lipid transportation channels, including transient receptor potential channel of the vanilloid subfamily 4 (TRPV4), lysosomal integral protein 2 (LIMP2), CD36, etc. The identified molecular pathways involved in this process include but are not limited to NF-κB, ERK1/2, p65.

CONCLUSION

Based on the results of this study, it can be concluded that P. gingivalis can effectively promote foam cell formation through various pathogenic elements and this bacterial species can affect the expression rate of various genes and the function of specific receptors in the cellular and lysosomal membranes. However, due to the moderate to high level of risk of bias among the studies, further studies are required in this regard.

Lipid-laden foam cells in the pathology of atherosclerosis: shedding light on new therapeutic targets

INTRODUCTION

Lipid-laden foam cells within atherosclerotic plaques are key players in all phases of lesion development including its progression, necrotic core formation, fibrous cap thinning, and eventually plaque rupture. Manipulating foam cell biology is thus an attractive therapeutic strategy at early, middle, and even late stages of atherosclerosis. Traditional therapies have focused on prevention, especially lowering plasma lipid levels. Despite these interventions, atherosclerosis remains a major cause of cardiovascular disease, responsible for the largest numbers of death worldwide.

AREAS COVERED

Foam cells within atherosclerotic plaques are comprised of macrophages, vascular smooth muscle cells, and other cell types which are exposed to high concentrations of lipoproteins accumulating within the subendothelial intimal layer. Macrophage-derived foam cells are particularly well studied and have provided important insights into lipid metabolism and atherogenesis. The contributions of foam cell-based processes are discussed with an emphasis on areas of therapeutic potential and directions for drug development.

EXERT OPINION

As key players in atherosclerosis, foam cells are attractive targets for developing more specific, targeted therapies aimed at resolving atherosclerotic plaques. Recent advances in our understanding of lipid handling within these cells provide insights into how they might be manipulated and clinically translated to better treat atherosclerosis.

TRIM64 promotes ox-LDL-induced foam cell formation, pyroptosis, and inflammation in THP-1-derived macrophages by activating a feedback loop with NF-κB via IκBα ubiquitination

Atherosclerosis is a chronic inflammatory disease and the main pathology behind most cardiovascular diseases and the overactivation of macrophages initiates the development of atherosclerosis. However, the specific functions of oxidized low-density lipoprotein (ox-LDL) in macrophages remain elusive. Macrophages derived from monocyte (THP-1) were treated with ox-LDL and were used to generate atherosclerosis in an in vitro model. NLRP3 inflammasome markers were examined using quantitative RT-PCR and Western blotting. Cytokines were measured using ELISA. Chromatin immunoprecipitation (ChIP) was utilized to detect nuclear factor kappa B (NF-κB) and TRIM64 interactions. A fat-rich diet was applied to ApoE-/- mice for in vivo studies. ox-LDL promoted TRIM64 expression in a time-dependent manner. According to loss- and gain-of-function analyses, TRIM64 enhanced the activation of NLRP3 inflammasomes and the expression of downstream molecules. TRIM64 directly interacted with IκBα and promoted IκBα ubiquitination at K67 to activate NF-κB signaling. We detected direct binding between NF-κB and the TRIM64 promoter, as well as enhanced TRIM64 expression. Our study revealed an interaction between TRIM64 and NF-κB in the development of atherosclerosis. TRIM64 and NF-κB formed a positive feedback to activate NF-κB pathway. ox-LDL induces foam cell formation and TRIM64 expression TRIM64 regulates ox-LDL-induced foam cell formation, pyroptosis and inflammation via the NF-κB signaling TRIM64 activates NF-κB signaling by ubiquitination of IκBα NF-κB inhibition attenuates atherosclerosis in HFD-induced ApoE (-/-) mice.

MiR-146a encapsulated liposomes reduce vascular inflammatory responses through decrease of ICAM-1 expression, macrophage activation, and foam cell formation

Vascular insults can create an inflammatory cascade involving endothelial cell, smooth muscle cell, and macrophage activation which can eventually lead to vascular disease such as atherosclerosis. Several studies have identified microRNA 146a's (miR-146a) anti-inflammatory potential based on its role in regulating the nuclear factor kappa beta (NF-κβ) pathway. Therefore, in this study, we introduced exogenous miR-146a encapsulated by liposomes to lipopolysaccharide (LPS) stimulated vascular cells and macrophages to reduce inflammatory responses. First, the miR-146a encapsulated liposomes showed uniform size (radius 96.4 ± 4.22 nm) and round shape, long term stability (at least two months), high encapsulation efficiency (69.73 ± 0.07%), and were well transfected to human aortic endothelial cells (HAECs), human aortic smooth muscle cells (SMCs), and human differentiated monocytes (U937 cells). In addition, we demonstrated that miR-146a encapsulated liposomes reduced vascular inflammation responses in HAECs and SMCs through inhibition of ICAM-1 expression and decreased monocyte adhesion. In macrophages, miR-146a liposome treatment demonstrated decreased production of proinflammatory cytokines, tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β), as well as reduced oxidized low-density lipoprotein (ox-LDL) uptake and foam cell formation. Thus, based on these results, miR-146a encapsulated liposomes may be promising for reducing vascular inflammation by targeting its multiple associated mediators.

Differential Expression of Inflammarafts in Macrophage Foam Cells and in Nonfoamy Macrophages in Atherosclerotic Lesions-Brief Report

BACKGROUND

Reprogramming of monocytes and macrophage manifests in hyperinflammatory responses and chronification of inflammation in atherosclerosis. Recent studies focused on epigenetic, transcriptional, and metabolic alterations that characterize trained immunity. However, the underlying effector mechanisms driving the hyperinflammatory response of reprogrammed macrophages remain unclear. We hypothesized that the plasma membrane of atherosclerotic lesion macrophages undergoes reprogramming to maintain inflammarafts, enlarged lipid rafts (LR) serving as a platform for assembly of inflammatory receptor complexes.

METHODS

Single-cell suspensions from the aortae of Western diet-fed Ldlr-/- mice were gated for BODIPY-high foamy and BODIPY-low nonfoamy F4/80 macrophages by flow cytometry. Inflammarafts were characterized by increased levels of LR, TLR4 (toll-like receptor-4) localization to LR, TLR4 dimers, and the proximity between TLR2, TLR1, and CD36. In a cellular model of trained immunity, LR, TLR4 dimers, and the inflammatory response were measured in bone marrow-derived macrophages subjected to a 24-hour treatment with LPS (lipopolysaccharide) or OxLDL (oxidized low-density lipoprotein), followed by a 6-day wash-out period.

RESULTS

Nonfoamy macrophages, which constituted ≈40% of macrophages in atherosclerotic lesions, expressed significantly higher levels of LR and TLR4 dimers, as well as proximity ligation signals for TLR4-LR, TLR2-CD36, and TLR2-TLR1 complexes, compared with foamy macrophages. These inflammaraft measures associated, to a different degree, with plasma cholesterol and inflammatory cytokines, as well as the size of the atherosclerotic lesions and necrotic cores. The bone marrow-derived macrophages trained with LPS simulated nonfoamy atherosclerotic lesion macrophages and continued to express inflammarafts and inflammatory genes for 6 days after LPS removal and displayed a hyperinflammatory response to Pam3CSK4, a TLR2/TLR1 agonist. OxLDL-exposed, lipid-laden macrophages did not express inflammarafts.

CONCLUSIONS

Our data support the hypothesis that persistent inflammarafts in nonfoamy macrophages in atherosclerotic lesions serve as effectors of macrophage reprogramming into a hyperinflammatory phenotype.

Receptor-independent fluid-phase macropinocytosis promotes arterial foam cell formation and atherosclerosis

Accumulation of lipid-laden foam cells in the arterial wall plays a central role in atherosclerotic lesion development, plaque progression, and late-stage complications of atherosclerosis. However, there are still fundamental gaps in our knowledge of the underlying mechanisms leading to foam cell formation in atherosclerotic arteries. Here, we investigated the role of receptor-independent macropinocytosis in arterial lipid accumulation and pathogenesis of atherosclerosis. Genetic inhibition of fluid-phase macropinocytosis in myeloid cells (LysMCre+ Nhe1fl/fl) and repurposing of a Food and Drug Administration (FDA)-approved drug that inhibits macrophage macropinocytosis substantially decreased atherosclerotic lesion development in low-density lipoprotein (LDL) receptor-deficient and Apoe-/- mice. Stimulation of macropinocytosis using genetic (H-RASG12V) and physiologically relevant approaches promoted internalization of unmodified native (nLDL) and modified [e.g., acetylated (ac) and oxidized (ox) LDL] lipoproteins in both wild-type and scavenger receptor (SR) knockout (Cd36-/-/Sra-/-) macrophages. Pharmacological inhibition of macropinocytosis in hypercholesterolemic wild-type and Cd36-/-/Sra-/- mice identified an important role of macropinocytosis in LDL uptake by lesional macrophages and development of atherosclerosis. Furthermore, serial section high-resolution imaging, LDL immunolabeling, and three-dimensional (3D) reconstruction of subendothelial foam cells provide visual evidence of lipid macropinocytosis in both human and murine atherosclerotic arteries. Our findings complement the SR paradigm of atherosclerosis and identify a therapeutic strategy to counter the development of atherosclerosis and cardiovascular disease.

Curcumin attenuates inflammation of Macrophage-derived foam cells treated with Poly-L-lactic acid degradation via PPARγ signaling pathway

Poly-L-lactic acid (PLLA) is considered to be a promising candidate material for biodegradable vascular scaffolds (BVS) in percutaneous coronary intervention (PCI). But, PLLA-BVS also faces the challenge of thrombosis (ST) and in-stent restenosis (ISR) caused by in-stent neo-atherosclerosis (ISNA) associated with inflammatory reactions in macrophage-derived foam cells. Our previous studies have confirmed that curcumin alleviates PLLA-induced injury and inflammation in vascular endothelial cells, but it remains unclear whether curcumin can alleviate the effect of inflammatory reactions in macrophage-derived foam cells while treated with degraded product of PLLA. In this study, PLLA-BVS was implanted in the porcine coronary artery to examine increased macrophages and inflammatory cytokines such as NF-κb and TNF-α by histology and immunohistochemistry. In vitro, macrophage-derived foam cells were induced by Ox-LDL and observed by Oil Red Staining. Foam cells were treated with pre-degraded PLLA powder, curcumin and PPARγ inhibitor GW9662, and the expression of IL-6, IL-10, TNF-α, NF-κb, PLA2 and PPARγ were investigated by ELISA or RT-qPCR. This study demonstrated that the macrophages and inflammatory factors increased after PLLA-BVS implantation in vivo, and foam cells derived from macrophages promoted inflammation by products of PLLA degradation in vitro. This present study was found that the inflammation of foam cells at the microenvironment of PLLA degraded products were significantly increased, and curcumin can attenuate the inflammation caused by the PLLA degradation via PPARγ signal pathway. In addition, curcumin should be further studied experimentally in vivo experiments on animal models as a potential therapeutic to reduce ISNA of PLLA-BVS. Graphical abstract.

Atherosclerosis: Pathogenesis and Key Cellular Processes, Current and Emerging Therapies, Key Challenges, and Future Research Directions

Atherosclerosis is the principal cause of cardiovascular disease that continues to be a substantial drain on healthcare systems, being responsible for about 31% of all global deaths. Atherogenesis is influenced by a range of factors, including oxidative stress, inflammation, hypertension, and hyperlipidemia, and is ultimately driven by the accumulation of low-density lipoprotein cholesterol within the arterial wall of medium and large arteries. Lipoprotein accumulation stimulates the infiltration of immune cells (such as monocytes/macrophages and T-lymphocytes), some of which take up the lipoprotein, leading to the formation of lipid-laden foam cells. Foam cell death results in increased accumulation of dead cells, cellular debris and extracellular cholesterol, forming a lipid-rich necrotic core. Vascular smooth muscle cells from the arterial media also migrate into the intima layer and proliferate, taking up the available lipids to become foam cells and producing extracellular matrix proteins such as collagen and elastin. Plaque progression is characterized by the formation of a fibrous cap composed of extracellular matrix proteins and smooth muscle cells, which acts to stabilize the atherosclerotic plaque. Degradation, thinning, and subsequent rupture of the fibrous cap leads to lumen-occlusive atherothrombosis, most commonly resulting in heart attack or stroke. This chapter describes the pathogenesis of atherosclerosis, current and emerging therapies, key challenges, and future directions of research.

Dietary Neu5Ac Intervention Protects Against Atherosclerosis Associated With Human-Like Neu5Gc Loss-Brief Report

Objective

Species-specific pseudogenization of the CMAH gene during human evolution eliminated common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) biosynthesis from its precursor N-acetylneuraminic acid (Neu5Ac). With metabolic nonhuman Neu5Gc incorporation into endothelia from red meat, the major dietary source, anti-Neu5Gc antibodies appeared. Human-like Ldlr-/-Cmah-/- mice on a high-fat diet supplemented with a Neu5Gc-enriched mucin, to mimic human red meat consumption, suffered increased atherosclerosis if human-like anti-Neu5Gc antibodies were elicited.

Approach and Results

We now ask whether interventional Neu5Ac feeding attenuates metabolically incorporated Neu5Gc-mediated inflammatory acceleration of atherogenesis in this Cmah-/-Ldlr-/- model system. Switching to a Neu5Gc-free high-fat diet or adding a 5-fold excess of Collocalia mucoid-derived Neu5Ac in high-fat diet protects against accelerated atherosclerosis. Switching completely from a Neu5Gc-rich to a Neu5Ac-rich diet further reduces severity. Remarkably, feeding Neu5Ac-enriched high-fat diet alone has a substantial intrinsic protective effect against atherosclerosis in Ldlr-/- mice even in the absence of dietary Neu5Gc but only in the human-like Cmah-null background.

Conclusions

Interventional Neu5Ac feeding can mitigate or prevent the red meat/Neu5Gc-mediated increased risk for atherosclerosis, and has an intrinsic protective effect, even in the absence of Neu5Gc feeding. These findings suggest that similar interventions should be tried in humans and that Neu5Ac-enriched diets alone should also be investigated further.

Long Noncoding RNA MALAT1 Regulates the Progression of Atherosclerosis by miR-330-5p/NF-κB Signal Pathway

ABSTRACT

Long non-coding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) was reported to be related to atherosclerosis (AS) progression. However, the underlying mechanism of MALAT1 in AS remains unknown. Quantitative real-time polymerase chain reaction was performed to detect the expression of MALAT1 and miR-330-5p. Western blot was applied to assess the protein levels of cluster of differentiation 36, interleukin-1β, interleukin-6 and tumor necrosis factor-α, phosphorylation of nuclear factor kappa-B inhibitor alpha and phosphorylation of p65. Flow cytometry assay, cell counting kit 8 assay, triglyceride, and total cholesterol detection assays were used to detect the apoptosis, viability, and lipid indexes of THP-1 macrophages-derived foam cells. Online database starbasev2.0 was used to predict the binding sequences between MALAT1 and miR-330-5p and it was verified by dual-luciferase reporter system and RNA immunoprecipitation assay. Besides, an AS mice model was used to evaluate the effect of MALAT1 in vivo. As a result, MALAT1 was overexpressed, whereas miR-330-5p was downregulated in THP-1 macrophages-derived foam cells. MiR-330-5p was a target of MALAT1. MALAT1 depletion inhibited cell formation, apoptosis, and inflammation in THP-1 macrophages-derived foam cells. Besides, MALAT1 overexpression promoted the inflammation in AS mice model, which promoted the pathogenesis of AS. Furthermore, miR-330-5p regulated the nuclear factor kappa light chain enhancer of activated B cells (NF-κB) pathway in THP-1 macrophages-derived foam cells. Moreover, MALAT1 regulated NF-κB signal pathway to mediate the pathogenesis of AS by sponging miR-330-5p. MALAT1 sponges miR-330-5p to activate NF-κB signal pathway in THP-1 macrophages-derived foam cells. This finding may provide a novel biomarker for AS diagnosis.

Ganoderma lucidum triterpenoids and polysaccharides attenuate atherosclerotic plaque in high-fat diet rabbits

BACKGROUND AND AIMS

Atherosclerosis is characterized by lipid deposition, oxidative stress, and inflammation in the arterial intima. Ganoderma lucidum triterpenoids (GLTs) and polysaccharides (GLPs) are traditional Chinese medicines with potential cardiovascular benefits. We aimed to comprehensively evaluate the effect of GLTs and GLPs on atherosclerosis and the associated underlying mechanisms in vivo and in vitro.

METHODS AND RESULTS

Japanese big-ear white rabbits were randomly divided into three groups of blank, model, and treatment, and the treatment group was fed with GLSO and GLSP (0.3 g/kg body-weight/day) for 4 months. Serum levels of triglyceride (TG), total (TC), and low density lipoprotein cholesterol (LDL-C) in GL treatment group were significantly lower than those in the model group. The area of aortic plaques was significantly reduced in the treatment group. Further, GL administration in oxidized low-density lipoprotein (ox-LDL) stimulated human umbilical vein endothelial cells (HUVECs) reduced the generation of reactive oxygen species (ROS) and malondialdehyde (MDA) by inhibiting the upregulation of the nuclear transcription factor (NF)-κB p65 and the relative receptor LOX-1. In THP-1 cells treated with phorbol myristate acetate, GL inhibited the inflammatory polarization of macrophages (as evidenced by reduced TNF-α levels) via regulation of Notch1 and DLL4 pathways. Ox-LDL-stimulated THP-1 cells treated with GL showed an increase in the apoptosis of foam cells.

CONCLUSIONS

GLTs and GLPs attenuated the progression of atherosclerosis by alleviating endothelial dysfunction and inflammatory polarization of macrophages, thus promoting apoptosis of foam cells.

Loss of TIMP4 (Tissue Inhibitor of Metalloproteinase 4) Promotes Atherosclerotic Plaque Deposition in the Abdominal Aorta Despite Suppressed Plasma Cholesterol Levels

[Figure: see text].

Decidua basalis and acute atherosis: Expression of atherosclerotic foam cell associated proteins

INTRODUCTION

Uteroplacental acute atherosis is frequently observed in preeclampsia, and shares features with early atherosclerotic lesions, including artery wall foam cells. The lipid-associated proteins FABP4 (fatty acid binding protein 4), perilipin-2, and LOX-1 (lectin-like oxidized LDL-receptor 1) are involved in atherosclerotic foam cell formation. Increased levels of these proteins have been associated with preeclampsia systemically and in placental tissue. Their role in acute atherosis is yet unidentified. Our aim was to describe the presence of these proteins in acute atherosis, and compare our findings to what is known in early atherosclerotic lesions.

METHODS

Serial sections of decidua basalis tissue from 12 normotensive (4 with acute atherosis) and 23 preeclamptic pregnancies (16 with acute atherosis) were stained with HE and immunostained for CK7, CD68, FABP4, perilipin-2, and LOX-1. Artery wall and perivascular protein expression was assessed in 190 spiral artery sections; 55 with acute atherosis.

RESULTS

Acute atherosis foam cells were commonly positive for perilipin-2 (55%), less often for FABP4 (13%), and never for LOX-1. LOX-1 was frequently observed in intramural trophoblasts of normal spiral arteries. Perivascularly, LOX-1 positivity of decidual stromal cells surrounding arteries with acute atherosis was significantly increased as compared to arteries lacking acute atherosis (38% vs. 15%, p < 0.001).

DISCUSSION

We found that perilipin-2 and FABP4 are expressed by acute atherosis foam cells, similar to atherosclerosis, supporting possible shared pathways for foam cell generation. Unlike atherosclerosis, LOX-1 is not present in acute atherosis, possibly explained by pregnancy-specific routes to decidua basalis foam cell generation.

Astragalin Retards Atherosclerosis by Promoting Cholesterol Efflux and Inhibiting the Inflammatory Response via Upregulating ABCA1 and ABCG1 Expression in Macrophages

ABSTRACT

Lipid metabolism disorder and inflammatory response are considered to be the major causes of atherosclerogenesis. Astragalin, the most important functional component of flavonoid obtained from persimmon leaves, has the hypolipidemic effects. However, it is unknown, how astragalin protects against atherosclerosis. The aim of this study was to observe the effects of astragalin on cholesterol efflux and inflammatory response and to explore the underlying mechanisms. Our results showed that astragalin upregulated the expression of ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1), promoted cholesterol efflux, and suppressed foam cell formation. Inhibition of the PPARγ/LXRα pathway abrogated the promotive effects of astragalin on both transporter expression and cholesterol efflux. In addition, treatment of astragalin markedly decreased the secretion of inflammatory factors, including interleukin 6, monocyte chemotactic protein 1, tumor necrosis factor α, and interleukin 1β. Mechanistically, astragalin upregulated ABCA1 and ABCG1 expression, which in turn reduced TLR4 surface levels and inhibited NF-κB nuclear translocation. Consistently, astragalin reduced atherosclerotic plaque area in apoE-/- mice. Taken together, these findings suggest that astragalin protects against atherosclerosis by promoting ABCA1- and ABCG1-mediated cholesterol efflux and inhibiting proinflammatory mediator release.

High Content Image Analysis as a Tool to Morphologically Distinguish Macrophage Activation and Determine Its Importance for Foamy Alveolar Macrophage Responses

Introduction

Lung diseases are an increasing global health burden affecting millions of people worldwide. Only a few new inhaled medicines have reached the market in the last 30 years, in part due to foamy alveolar macrophage (FAM) responses observed in pre-clinical rat studies. The induction mechanism and signaling pathways involved in the development of highly vacuolated 'foamy' phenotype is not known. Furthermore, it has not been determined if these observations are adaptive or adverse responses.

Aim

To determine if high content image analysis techniques can distinguish between alveolar macrophage activation (LPS/IFN-γ activated and IL-4 activated macrophages) and if this could be applied to understanding the generation of 'foamy' macrophage phenotypes.

Methods

NR8383 rat alveolar macrophages were stimulated with a mix of cytokines (LPS/IFN-γ or IL-4) for 24 h. The cells were further exposed to FAM inducing-compounds amiodarone and staurosporine. Following 24 h incubation, phagocytosis and lipid accumulation were measured using flow cytometry and high content image analysis techniques. The alveolar macrophages responses after exposure to cytokines were assessed by evaluation: (i) cell surface and biochemical markers such as: nitric oxide production, arginase-1 activity and MRC-1 receptor expression (ii) cellular morphology (iii) cellular functionality (phagocytic activity and lipids accumulation).

Results

Macrophages activated with LPS/IFN-γ showed distinct morphological (increased vacuolation) features and functionality (increased lipidosis, decreased phagocytic activity). Foamy macrophage phenotypes induced by amiodarone also displayed characteristics of proinflammatory macrophages (significantly increased nitric oxide production, increased vacuolation and lipidosis and decreased phagocytosis). In contrast, staurosporine treatment resulted in increased NO production, as well as arginase-1 activity.

Conclusion

High content image analysis was able to determine distinct differences in morphology between non-activated and LPS/IFN-γ activated macrophages, characterized by increased vacuolation and lipidosis. When exposed to compounds that induce a FAM phenotype, healthy non-activated macrophages displayed proinflammatory (amiodarone) or pro-apoptotic (staurosporine) characteristics but these responses were independent of a change in activation status. This technique could be applied in early drug discovery safety assessment to identify immune responses earlier and increase the understanding of alveolar macrophage responses to new molecules challenge in development of new inhalation therapies, which in turn will enhance decision-making in an early safety assessment of novel drug candidates.

An integrated approach to simulating the vulnerable atherosclerotic plaque

Analyses of individual atherosclerotic plaques are mostly descriptive, relying, for example, on histological classification by spectral analysis of ultrasound waves or staining and observing particular cellular components. Such passive methods have proved useful for characterizing the structure and vulnerability of plaques but have little quantitative predictive power. Our aim is to introduce and discuss a computational framework to provide insight to clinicians and help them visualize internal plaque dynamics. We use partial differential equations (PDEs) with macrophages, necrotic cells, oxidized lipids, oxygen concentration, and platelet-derived growth factor (PDGF) as primary variables coupled to a biomechanical model to describe vessel growth. The model is deterministic, providing mechanical, morphological, and histological characteristics of an atherosclerotic vessel at any desired future time point. We use our model to create computer-generated animations of a plaque evolution that are in qualitative agreement with published serial ultrasound images and hypothesize possible atherogenic mechanisms. A systems biology model consisting of five differential equations is able to capture the morphology of necrotic cores residing within vulnerable atherosclerotic plaque. In the context of the model, the distribution of oxidized low-density lipoprotein (Ox-LDL) particles, endothelial inflammation, plaque oxygenation (via the presence of vasa vasora), and intimal oxygenation are four important factors that drive changes in core morphology.NEW & NOTEWORTHY In this article, we propose a quantitative framework to describe the evolution of atherosclerotic plaque. We use partial differential equations (PDEs) with macrophages, necrotic cells, oxidized lipids, oxygen concentration, and PDGF as primary variables coupled to a biomechanical model to describe vessel growth. A feature of our method is that it outputs color-coded vessel sections corresponding to regions of the plaque that are necrotic and fibrous, qualitatively similar to images generated by enhanced intravascular ultrasound.

Structures and anti-atherosclerotic effects of 1,6-α-glucans from Fructus Corni

In this study, two homogeneous polysaccharides (PFC-1 and PFC-2) having anti-atherosclerotic activity were isolated from Fructus Corni. PFC-1 and PFC-2 were 1,6-α-glucans with the molecular weight of 4.4 kDa and 82.0 kDa, respectively. In the in vitro experiments, PFC-1 and PFC-2 showed significant inhibitory effects on the cholesterol accumulation in RAW264.7 macrophages induced by oxidized low-density lipoproteins (ox-LDL), and the inhibitory rate of PFC-2 was 81.62%. Apolipoprotein E-deficient (ApoE^-/-) mice fed high-fat diet (HFD) were used to evaluate the anti-atherosclerotic effects of PFC-2 in vivo. The aortic root lipid area decreased by 55.01% in the PFC-2-administered group as compared to the model group. PFC-2 decreased the levels of serum low-density lipoprotein cholesterol, total cholesterol, triglycerides, and malondialdehyde, increased the superoxide dismutase activity, and reduced the contents of lipid and macrophages in the aortic sinus plaque in ApoE^-/- mice fed with HFD. Furthermore, PFC-2 markedly inhibited the expression of type A1 scavenger receptor (SR-A1) and cluster of differentiation 36 (CD36) in ox-LDL-treated macrophages. Taken together, 1,6-α-glucans from Fructus Corni showed significant anti-atherogenic effect, and the mechanism is related to enhanced antioxidant activity of the ApoE^-/- mice and down-regulated the expression of SR-A1 and CD36 proteins in macrophages.

The Fungal Iron Chelator Desferricoprogen Inhibits Atherosclerotic Plaque Formation

Hemoglobin, heme and iron are implicated in the progression of atherosclerosis. Therefore, we investigated whether the hydrophobic fungal iron chelator siderophore, desferricoprogen (DFC) inhibits atherosclerosis. DFC reduced atherosclerotic plaque formation in ApoE^-/- mice on an atherogenic diet. It lowered the plasma level of oxidized LDL (oxLDL) and inhibited lipid peroxidation in aortic roots. The elevated collagen/elastin content and enhanced expression of adhesion molecule VCAM-1 were decreased. DFC diminished oxidation of Low-density Lipoprotein (LDL) and plaque lipids catalyzed by heme or hemoglobin. Formation of foam cells, uptake of oxLDL by macrophages, upregulation of CD36 and increased expression of TNF-α were reduced by DFC in macrophages. TNF-triggered endothelial cell activation (vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecules (ICAMs), E-selectin) and increased adhesion of monocytes to endothelium were attenuated. The increased endothelial permeability and intracellular gap formation provoked by TNF-α was also prevented by DFC. DFC acted as a cytoprotectant in endothelial cells and macrophages challenged with a lethal dose of oxLDL and lowered the expression of stress-responsive heme oxygenase-1 as sublethal dose was employed. Saturation of desferrisiderophore with iron led to the loss of the beneficial effects. We demonstrated that DFC accumulated within the atheromas of the aorta in ApoE^-/- mice. DFC represents a novel therapeutic approach to control the progression of atherosclerosis.

Diagnostic dilemma of an isolated inguinal clinical cold abscess - ? Suppurative,? EPTB, ? NTM infection- a rare and interesting case report

Cold abscess is an abscess without local pain and warmth and it usually accompanies Tuberculosis. The site varied depending upon the organ affected and cervical region is the commonly affected one. Cyto-morphology of cold abscess usually showed caseation type of necrosis, lymphocytes and granuloma with degenerated epithelioid cells. Here we presented an inguinal cold abscess in 9 years old girl with unique cyto-morphology of plenty of neutrophils, foam cells and lymphocytes in fine needle aspiration smear without caseation necrosis and epithelioid cells. Presence of Mycobacterium in the aspirated pus was proved by Ziehl-Neelsen as well as Auramine fluorescent staining. This characteristic cyto-morphology of mycobacterium infection mimicking pyogenic abscess emphasizes the importance of Ziehl-Neelsen staining in all abscess for early specific diagnosis and effective treatment.

Long non-coding RNA CDKN2B-AS1 contributes to atherosclerotic plaque formation by forming RNA-DNA triplex in the CDKN2B promoter

Background

Atherosclerosis involves a slow process of plaque formation on the walls of arteries, and comprises a leading cause of cardiovascular disease. Long non-coding RNAs (lncRNAs) have been implicated in the pathogenesis of atherosclerosis. In this study, we aim to explore the possible involvement of lncRNA ‘cyclin-dependent kinase inhibitor 2B antisense noncoding RNA’ (CDKN2B-AS1) and CDKN2B in the progression of atherosclerosis.

Methods

Initially, we quantified the expression of CDKN2B-AS1 in atherosclerotic plaque tissues and, in THP-1 macrophage-derived, and human primary macrophage (HPM)-derived foam cells. Next, we established a mouse model of atherosclerosis using apolipoprotein E knockout (ApoE^−/−) mice, where lipid uptake, lipid accumulation, and macrophage reverse cholesterol transport (mRCT) were assessed, in order to explore the contributory role of CDKN2B-AS1 to the progression of atherosclerosis. RIP and ChIP assays were used to identify interactions between CDKN2B-AS1, CCCTC-binding factor (CTCF), enhancer of zeste homologue 2 (EZH2), and CDKN2B. Triplex formation was determined by RNA-DNA pull-down and capture assay as well as EMSA experiment.

Findings

CDKN2B-AS1 showed high expression levels in atherosclerosis, whereas CDKN2B showed low expression levels. CDKN2B-AS1 accelerated lipid uptake and intracellular lipid accumulation whilst attenuating mRCT in THP-1 macrophage-derived foam cells, HPM-derived foam cells, and in the mouse model. EZH2 and CTCF were found to bind to the CDKN2B promoter region. An RNA-DNA triplex formed by CDKN2B-AS1 and CDKN2B promoter was found to recruit EZH2 and CTCF in the CDKN2B promoter region and consequently inhibit CDKN2B transcription by accelerating histone methylation.

Interpretation

The results demonstrated that CDKN2B-AS1 promotes atherosclerotic plaque formation and inhibits mRCT in atherosclerosis by regulating CDKN2B promoter, and thereby could be a potential therapeutic target for atherosclerosis.

Blood miR-1275 is associated with risk of ischemic stroke and inhibits macrophage foam cell formation by targeting ApoC2 gene

Apolipoprotein C2 (ApoC2) is an important member of the apolipoprotein C family and functions as a major activator of lipoprotein lipase (LPL). In cardiovascular and cerebrovascular systems, the lipolytic activity of the LPL-ApoC2 complex is critical for the metabolism of triglyceride-rich lipoproteins and contributes to the pathogenesis of ischemic stroke (IS). However, the regulation of ApoC2 in IS development remains unclear. In this study, we first explored potential ApoC2-targeting microRNAs (miRNAs) by bioinformatics tool and compared the miRNA expression profiles in the blood cells of 25 IS patients and 25 control subjects by miRNA microarray. miR-1275 was predicted to bind with the 3' untranslated region of ApoC2, and a significant reduction of blood miR-1275 levels was observed in IS patients. Dual-luciferase reporter assay and quantitative RT-PCR confirmed the regulation of ApoC2 by miR-1275 in THP-1 derived macrophages. miR-1275 also inhibited cellular uptake of ox-LDL and suppressed formation of macrophage foam cell. Furthermore, the whole blood miR-1275 levels were validated in 279 IS patients and 279 control subjects by TaqMan assay. miR-1275 levels were significantly lower in IS cases and logistic regression analysis showed that miR-1275 level was negatively associated with the occurrence of IS (adjusted OR, 0.76; 95% CI, 0.69-0.85; p < 0.001). Addition of miR-1275 to traditional risk factors showed an additive prediction value for IS. Our study shows that blood miR-1275 levels were negatively associated with the occurrence of IS, and miR-1275 might exert an athero-protective role against the development of IS by targeting ApoC2 and blocking the formation of macrophage foam cells.

Resveratrol Derivative, Trans-3, 5, 4'-Trimethoxystilbene, Prevents the Developing of Atherosclerotic Lesions and Attenuates Cholesterol Accumulation in Macrophage Foam Cells

SCOPE

Recent studies have demonstrated that trans-3, 5, 4'-Trimethoxystilbene (TMS), a novel derivative of resveratrol, may suppress the foam cells formation and restrain atherosclerosis in vitro and in vivo. Herein, the molecular mechanisms underlying the protective effects of TMS against atherosclerosis are further delineated.

METHODS AND RESULTS

In the present study, the cholesterol-lowering effects of TMS in macrophage-derived foam cell by animal studies, Oil Red O staining, and lipid uptake as well as efflux analysis, are explored. Real-time PCR, western blotting analysis, luciferase reporter assay, electrophoretic mobility shift assay, and immunofluorescent staining are applied for investigating the mechanism involved in atherosclerosis prevention by TMS. Herein, it is revealed that TMS, at a dosage of 10 mg kg-1  day-1 , may suppress atherosclerotic plaques within the aorta and arterial intima in apolipoprotein Edeficient mice (ApoE)-/- mice by reducing cholesterol level and macrophages content. Exposure of macrophages to TMS (10 µM) can suppress foam cells formation via regulating oxidized low density lipoprotein and cholesterol content in human macrophages through inhibiting scavenger receptors expression and activator protein-1(AP-1) activity. In addition, TMS can activate ERK/Nrf2/HO-1 signaling which increases the expression of ATP-binding cassette transporters.

CONCLUSION

In conclusion, TMS may inhibit the progress of atherosclerosis through regulating cholesterol homeostasis and inhibiting macrophage-derived foam cells formation.

Role of Phagocytosis in the Pro-Inflammatory Response in LDL-Induced Foam Cell Formation; a Transcriptome Analysis

Excessive accumulation of lipid inclusions in the arterial wall cells (foam cell formation) caused by modified low-density lipoprotein (LDL) is the earliest and most noticeable manifestation of atherosclerosis. The mechanisms of foam cell formation are not fully understood and can involve altered lipid uptake, impaired lipid metabolism, or both. Recently, we have identified the top 10 master regulators that were involved in the accumulation of cholesterol in cultured macrophages induced by the incubation with modified LDL. It was found that most of the identified master regulators were related to the regulation of the inflammatory immune response, but not to lipid metabolism. A possible explanation for this unexpected result is a stimulation of the phagocytic activity of macrophages by modified LDL particle associates that have a relatively large size. In the current study, we investigated gene regulation in macrophages using transcriptome analysis to test the hypothesis that the primary event occurring upon the interaction of modified LDL and macrophages is the stimulation of phagocytosis, which subsequently triggers the pro-inflammatory immune response. We identified genes that were up- or downregulated following the exposure of cultured cells to modified LDL or latex beads (inert phagocytosis stimulators). Most of the identified master regulators were involved in the innate immune response, and some of them were encoding major pro-inflammatory proteins. The obtained results indicated that pro-inflammatory response to phagocytosis stimulation precedes the accumulation of intracellular lipids and possibly contributes to the formation of foam cells. In this way, the currently recognized hypothesis that the accumulation of lipids triggers the pro-inflammatory response was not confirmed. Comparative analysis of master regulators revealed similarities in the genetic regulation of the interaction of macrophages with naturally occurring LDL and desialylated LDL. Oxidized and desialylated LDL affected a different spectrum of genes than naturally occurring LDL. These observations suggest that desialylation is the most important modification of LDL occurring in vivo. Thus, modified LDL caused the gene regulation characteristic of the stimulation of phagocytosis. Additionally, the knock-down effect of five master regulators, such as IL15, EIF2AK3, F2RL1, TSPYL2, and ANXA1, on intracellular lipid accumulation was tested. We knocked down these genes in primary macrophages derived from human monocytes. The addition of atherogenic naturally occurring LDL caused a significant accumulation of cholesterol in the control cells. The knock-down of the EIF2AK3 and IL15 genes completely prevented cholesterol accumulation in cultured macrophages. The knock-down of the ANXA1 gene caused a further decrease in cholesterol content in cultured macrophages. At the same time, knock-down of F2RL1 and TSPYL2 did not cause an effect. The results obtained allowed us to explain in which way the inflammatory response and the accumulation of cholesterol are related confirming our hypothesis of atherogenesis development based on the following viewpoints: LDL particles undergo atherogenic modifications that, in turn, accompanied by the formation of self-associates; large LDL associates stimulate phagocytosis; as a result of phagocytosis stimulation, pro-inflammatory molecules are secreted; these molecules cause or at least contribute to the accumulation of intracellular cholesterol. Therefore, it became obvious that the primary event in this sequence is not the accumulation of cholesterol but an inflammatory response.

Quercetin Suppresses the Progression of Atherosclerosis by Regulating MST1-Mediated Autophagy in ox-LDL-Induced RAW264.7 Macrophage Foam Cells

Objective: To investigate the process by which quercetin suppresses atherosclerosis by upregulating MST1-mediated autophagy in RAW264.7 macrophages. Methods: An in vitro foam cell model was established by culturing RAW264.7 macrophages with oxidized low-density lipoprotein (ox-LDL). The cells were treated with quercetin alone or in combination with the autophagy inhibitor, 3-methyladenine, and autophagy agonist, rapamycin. Cell viability was detected with a CCK-8 kit. Lipid accumulation was detected by oil red O staining, senescence was detected by SA-β-gal (senescence-associated β-galactosidase) staining, reactive oxygen species were detected by ROS assay kit. Autophagosomes and mitochondria were detected by transmission electron microscope (TEM), and expression of MST1, LC3-II/I, Beclin1, Bcl-2, P21, and P16 were detected by immunofluorescence and Western blot. Results: Ox-LDL induced RAW264.7 macrophage-derived foam cell formation, reduced survival, aggravated cell lipid accumulation, and induced a senescence phenotype. This was accompanied by decreased formation of autophagosome; increased expression of P53, P21, and P16; and decreased expression of LC3-II/I and Beclin1. After intervention with quercetin, the cell survival rate was increased, and lipid accumulation and senescence phenotype were reduced. Furthermore, the expression of LC3-II/I and Beclin1 were increased, which was consistent with the ability of quercetin to promote autophagy. Ox-LDL also increased the expression of MST1, and this increase was blocked by quercetin, which provided a potential mechanism by which quercetin may protect foam cells against age-related detrimental effects. Conclusion: Quercetin can inhibit the formation of foam cells induced by ox-LDL and delay senescence. The mechanism may be related to the regulation of MST1-mediated autophagy of RAW264.7 cells.

The detrimental effect of asymmetric dimethylarginine on cholesterol efflux of macrophage foam cells: Role of the NOX/ROS signaling

BACKGROUND

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor and has been proposed to be an independent risk factor for cardiovascular diseases. However, little is known about its role in the regulation of lipid metabolism. In this study, we investigated the effect of ADMA on cholesterol metabolism and its underlying molecular mechanism.

METHODS

Oxidized low-density lipoprotein (oxLDL)-induced macrophage foam cells were used as an in vitro model. Apolipoprotein E-deficient (apoE^-/-) hyperlipidemic mice were used as an in vivo model. Western blot analysis was used to evaluate protein expression. Luciferase reporter assays were used to assess the activity of promoters and transcription factors. Conventional assay kits were used to measure the levels of ADMA, cholesterol, triglycerides, and cytokines.

RESULTS

Treatment with oxLDL decreased the protein expression of dimethylarginine dimethylaminohydrolase-2 (DDAH-2) but not DDAH-1. Incubation with ADMA markedly increased oxLDL-induced lipid accumulation in macrophages. ADMA impaired cholesterol efflux following oxLDL challenge and downregulated the expression of ATP-binding cassette transporter A1 (ABCA1) and ABCG1 by interfering with liver X receptor α (LXRα) expression and activity. Additionally, this inhibitory effect of ADMA on cholesterol metabolism was mediated through the activation of the NADPH oxidase/reactive oxygen species pathway. In vivo experiments revealed that chronic administration of ADMA for 4 weeks exacerbated systemic inflammation, decreased the aortic protein levels of ABCA1 and ABCG1, and impaired the capacity of reverse cholesterol transport, ultimately, leading to the progression of atherosclerosis in apoE^-/- mice.

CONCLUSION

Our findings suggest that the ADMA/DDAH-2 axis plays a crucial role in regulating cholesterol metabolism in macrophage foam cells and atherosclerotic progression.

Geniposide against atherosclerosis by inhibiting the formation of foam cell and lowering reverse lipid transport via p38/MAPK signaling pathways

Geniposide, the main medicinal ingredient of Gardenia jasminoides Ellis, is known to be a resistant agent to atherosclerosis. Some reports its mechanism against atherosclerosis remains completely unclear. Herein, we have investigated the protective effect of geniposide against atherosclerosis as well as clarified the mechanisms related with inhibiting the formation of foam cells and lowering reverse lipid transport via p38/MAPK signaling pathways. Macrophage Raw264.7 was induced by lysophosphatidic acid (LPA) to form foam cell as a cell model. ApoE^-/- mice were fed with a high-fat diet for 16 weeks to cause atherosclerosis in carotid artery. After treatment with geniposide, CCK-8, oil red O stain, qRT-PCR and western blot were carried out to explore the effect of geniposide. Morphological changes, histological analyses were used to evaluate atherosclerosis in ApoE^-/- mice. Geniposide significantly reduced serum total cholesterol (TC), triglyceride (TG) and LDL cholesterol levels in ApoE^-/- mice compared with vehicle control. Meanwhile, geniposide dose dependently inhibited the development of atherosclerosis in ApoE^-/- mice. Furthermore, geniposide observably inhibited the formation of foam cells induced by LPA, down-regulated the mRNA and protein levels of SR-A and up-regulated the mRNA and protein levels of ABCA1 or SR-B1 in vitro via inhibition of the p38MAPK and AKT signaling pathways. Our study shows that geniposide protected against atherosclerosis and inhibited the formation of foam cells by regulating the equilibrium on expression of diverse lipid transporters in cytomembrane which related with p38MAPK and AKT signaling pathways. Geniposide is a potential therapeutic drug for atherosclerosis.

Myeloid Tribbles 1 induces early atherosclerosis via enhanced foam cell expansion

Macrophages drive atherosclerotic plaque progression and rupture; hence, attenuating their atherosclerosis-inducing properties holds promise for reducing coronary heart disease (CHD). Recent studies in mouse models have demonstrated that Tribbles 1 (Trib1) regulates macrophage phenotype and shows that Trib1 deficiency increases plasma cholesterol and triglyceride levels, suggesting that reduced TRIB1 expression mediates the strong genetic association between the TRIB1 locus and increased CHD risk in man. However, we report here that myeloid-specific Trib1 (mTrib1) deficiency reduces early atheroma formation and that mTrib1 transgene expression increases atherogenesis. Mechanistically, mTrib1 increased macrophage lipid accumulation and the expression of a critical receptor (OLR1), promoting oxidized low-density lipoprotein uptake and the formation of lipid-laden foam cells. As TRIB1 and OLR1 RNA levels were also strongly correlated in human macrophages, we suggest that a conserved, TRIB1-mediated mechanism drives foam cell formation in atherosclerotic plaque and that inhibiting mTRIB1 could be used therapeutically to reduce CHD.

c-Kit suppresses atherosclerosis in hyperlipidemic mice

Atherosclerosis is the most common underlying cause of cardiovascular morbidity and mortality worldwide. c-Kit (CD117) is a member of the receptor tyrosine kinase family, which regulates differentiation, proliferation, and survival of multiple cell types. Recent studies have shown that c-Kit and its ligand stem cell factor (SCF) are present in arterial endothelial cells and smooth muscle cells (SMCs). The role of c-Kit in cardiovascular disease remains unclear. The aim of the current study is to determine the role of c-Kit in atherogenesis. For this purpose, atherosclerotic plaques were quantified in c-Kit-deficient mice (KitMut) after they were fed a high-fat diet (HFD) for 16 wk. KitMut mice demonstrated substantially greater atherosclerosis compared with control (KitWT) littermates (P < 0.01). Transplantation of c-Kit-positive bone marrow cells into KitMut mice failed to rescue the atherogenic phenotype, an indication that increased atherosclerosis was associated with reduced arterial c-Kit. To investigate the mechanism, SMC organization and morphology were analyzed in the aorta by histopathology and electron microscopy. SMCs were more abundant, disorganized, and vacuolated in aortas of c-Kit mutant mice compared with controls (P < 0.05). Markers of the "contractile" SMC phenotype (calponin, SM22α) were downregulated with pharmacological and genetic c-Kit inhibition (P < 0.05). The absence of c-Kit increased lipid accumulation and significantly reduced the expression of the ATP-binding cassette transporter G1 (ABCG1) necessary for lipid efflux in SMCs. Reconstitution of c-Kit in cultured KitMut SMCs resulted in increased spindle-shaped morphology, reduced proliferation, and elevated levels of contractile markers, all indicators of their restored contractile phenotype (P < 0.05).NEW & NOTEWORTHY This study describes the novel vasculoprotective role of c-Kit against atherosclerosis and its function in the preservation of the SMC contractile phenotype.

SCD1 activation impedes foam cell formation by inducing lipophagy in oxLDL-treated human vascular smooth muscle cells

The formation of fat-laden foam cells, which contributes to the fatty streaks in the plaques of atheromas, is an important process in atherosclerosis. Vascular smooth muscle cells (VSMCs) are a critical origin of foam cells. However, the mechanisms that underlie VSMC foam cell formation are not yet completely understood. Here, we demonstrated that oxidized low-density lipoprotein (oxLDL) inhibited lipophagy by suppressing lipid droplet (LD)-lysosome fusion and increased VSMC foam cell formation. Moreover, although oxLDL treatment inhibited lysosomal biogenesis, it had no significant effect on lysosomal proteolysis and lysosomal pH. Notably, through TMT-based quantitative proteomic analysis and database searching, 94 differentially expressed proteins were identified, of which 54 were increased and 40 were decreased in the oxLDL group compared with those in the control group. Subsequently, SCD1, a protein of interest, was further investigated. SCD1 levels in the VSMCs were down-regulated by exposure to oxLDL in a time-dependent manner and the interaction between SCD1 and LDs was also disrupted by oxLDL. Importantly, SCD1 overexpression enhanced LD-lysosome fusion, increased lysosomal biogenesis and inhibited VSMC foam cell formation by activating TFEB nuclear translocation and its reporter activity. Modulation of the SCD1/TFEB-mediated lipophagy machinery may offer novel therapeutic approaches for the treatment of atherosclerosis.

PM2.5 aggravates the lipid accumulation, mitochondrial damage and apoptosis in macrophage foam cells

Epidemiological evidence showed that the particulate matter exposure is associated with atherosclerotic plaque progression, which may be related to foam cell formation, but the mechanism is still unknown. The study was aimed to investigate the toxic effects and possible mechanism of PM_2.5 on the formation of macrophage foam cells induced by oxidized low density lipoprotein (ox-LDL). Results showed that PM_2.5 induced cytotoxicity by decreasing the cell viability and increasing the LDH level in macrophage foam cells. PM_2.5 aggravated the lipid accumulation in ox-LDL-stimulated macrophage RAW264.7 within markedly increasing level of intracellular lipid by Oil red O staining. The level of ROS increased obivously after co-exposure to PM_2.5 and ox-LDL than single exposure group. In addition, serious mitochondrial damage such as the mitochondrial swelling, cristae rupturing and disappearance were observed in macrophage foam cells. The loss of the mitochondrial membrane potential (MMP) further exacerbated the mitochondrial damage in PM_2.5-induced macrophage foam cells. The apoptotic rate increased more severely via up-regulated protein level of Bax, Cyt C, Caspase-9, Caspase-3, and down-regulated that of Bcl-2, indicating that PM_2.5 activated the mitochondrial-mediated apoptosis pathway. In summary, our results demonstrated that PM_2.5 aggravated the lipid accumulation, mitochondrial damage and apoptosis in macrophage foam cells, suggesting that PM_2.5 was a risk factor of atherosclerosis progression.

Pathways of smooth muscle foam cell formation in atherosclerosis

PURPOSE OF REVIEW

Smooth muscle cells (SMCs) are the major cell type in human atherosclerosis-prone arteries and take up excess lipids, thereby contributing to luminal occlusion. Here we provide a focused review on pathways by which smooth muscle cells (SMCs) can become foam cells in atherosclerosis.

RECENT FINDINGS

A synthesis of recent and older investigations provides key mechanistic insights into SMC foam cell formation. LDL and other apoB-containing lipoproteins are modified by a diverse array of oxidative, enzymatic, and nonenzymatic processes present in the arterial intima. These modifications of LDL all promote the aggregation of LDL (agLDL), a key finding from analysis of arterial lesion particles. Scavenger receptor and phagocytic capacity of SMCs can vary greatly, perhaps related to differences in SMC phenotype or in-vitro cell culture environments, and can be increased with exposure to cytokines, growth factors, and cholesterol. Macrophages promote the formation of SMC foam cells in direct or indirect co-culture models.

SUMMARY

SMCs contribute significantly to the foam cell population in atherosclerosis. Further investigation and identification of key mechanisms of SMC foam cell formation will help drive new therapeutics to reduce cardiovascular disease.

LncRNA UCA1 sponges miR-206 to exacerbate oxidative stress and apoptosis induced by ox-LDL in human macrophages

Long noncoding RNA UCA1 has exerted a significant effect in cardiovascular disease. The biological role of UCA1 in atherosclerosis is unclear. Our study was to identify the potential mechanisms in the progression of atherosclerosis. Here, we observed that ox-LDL increased UCA1 expression greatly in THP-1 cells. Knockdown of UCA1 greatly inhibited CD36 expression, a crucial biomarker in atherosclerosis. Meanwhile, 20 μg/ml ox-LDL induced foam cell formation, which can be reversed by downregulation of UCA1. In addition, TC and TG levels induced by ox-LDL was rescued by UCA1 small interfering RNA. Accumulating studies have indicated that oxidative stress contributes to atherosclerosis progression. Here, we also found that reactive oxygen species, MDA, and THP-1 cell apoptosis were restrained by decreased of UCA1 with an increase of the superoxide dismutase activity. Moreover, miR-206 was predicted as a target of UCA1 and knockdown of UCA1 was able to repress miR-206 expression. Furthermore, overexpression of miR-206 inhibited oxidative stress process and it was reversed by UCA1 upregulation in vitro. In conclusion, we indicated that UCA1 sponged miR-206 to exacerbate atherosclerosis events induced by ox-LDL in THP-1 cells.

A novel antioxidant Mito-Tempol inhibits ox-LDL-induced foam cell formation through restoration of autophagy flux

A bulk of cholesteryl esters accumulation in macrophage foam cells drives the occurrence and development of atherosclerosis. Evidence now shows that autophagy plays key roles in the degradation of intracellular lipid droplets via autolysosome, and also in the release of intracellular lipids via cholesterol efflux. In this study, we identified that a mitochondria-targeted antioxidant, Mito-Tempol, has protective effects against cholesteryl esters accumulation by activating autophagy. Mito-Tempol was shown to ameliorate the lipid burden for atherosclerosis, both in vitro and in vivo. In the established in vitro foam cell formation system using oxidized low-density lipoprotein (ox-LDL)-loaded THP-1 macrophages, Mito-Tempol prevented intracellular oxidative stress and attenuated lipid accumulation. Mito-Tempol rescued ox-LDL-impaired autophagic flux, thereby facilitating autophagy-mediated lipid degradation in THP-1 macrophages. Meanwhile, Mito-Tempol also increased the efflux of cholesterol via autophagy-dependent ABCA1 and ABCG1 up-regulation. The classical autophagy pathway of mTOR may be one of the effector for the autophagy restoration of Mito-Tempol. Our findings give the first insight that cardiovascular system disease may benefits more from the treatment of Mito-Tempol for its impact of reversing atherosclerosis via autophagy.

Complement Factor H and Apolipoprotein E Participate in Regulation of Inflammation in THP-1 Macrophages

The alternative pathway (AP) of complement is constantly active in plasma and can easily be activated on self surfaces and trigger local inflammation. Host cells are protected from AP attack by Factor H (FH), the main AP regulator in plasma. Although complement is known to play a role in atherosclerosis, the mechanisms of its contribution are not fully understood. Since FH via its domains 5-7 binds apoliporotein E (apoE) and macrophages produce apoE we examined how FH could be involved in the antiatherogenic effects of apoE. We used blood peripheral monocytes and THP-1 monocyte/macrophage cells which were also loaded with acetylated low-density lipoprotein (LDL) to form foam cells. Binding of FH and apoE on these cells was analyzed by flow cytometry. High-density lipoprotein (HDL)-mediated cholesterol efflux of activated THP-1 cells was measured and transcriptomes of THP-1 cells using mRNA sequencing were determined. We found that binding of FH to human blood monocytes and cholesterol-loaded THP-1 macrophages increased apoE binding to these cells. Preincubation of fluorescent cholesterol labeled THP-1 macrophages in the presence of FH increased cholesterol efflux and cholesterol-loaded macrophages displayed reduced transcription of proinflammatory/proatherogenic factors and increased transcription of anti-inflammatory/anti-atherogenic factors. Further incubation of THP-1 cells with serum reduced C3b/iC3b deposition. Overall, our data indicate that apoE and FH interact with monocytic cells in a concerted action and this interaction reduces complement activation and inflammation in the atherosclerotic lesions. By this way FH may participate in mediating the beneficial effects of apoE in suppressing atherosclerotic lesion progression.

Homocysteine accelerates atherosclerosis via inhibiting LXRα-mediated ABCA1/ABCG1-dependent cholesterol efflux from macrophages

AIMS

Macrophage-derived foam-cell formation plays a crucial role in the development of atherosclerosis, and liver X receptor alpha (LXRα) is a key regulator of lipid metabolism in macrophages. Homocysteine (Hcy) is an independent risk factor of atherosclerosis; however, the regulation of lipid metabolism and role of LXRα induced by Hcy in macrophages is still unknown. The present study aimed to investigate the potential role of Hcy in disordered lipid metabolism and atherosclerotic lesions, especially the effects of Hcy on cholesterol efflux in macrophages and the possible mechanisms.

MAIN METHODS

In vitro, lipid accumulation and cholesterol efflux were evaluated in THP-1 macrophages with Hcy intervention. Real-time quantitative PCR and western blot analyses were used to assess mRNA and protein levels. In vivo, atherosclerotic lesions and lipid profiles were evaluated by methionine diet-induced hyperhomocysteinemia (HHcy) in ApoE^-/- mice. The LXRα agonist T0901317 was used to verify the role of LXRα in HHcy-accelerated atherosclerosis.

KEY FINDINGS

Hcy promoted lipid accumulation and inhibited cholesterol efflux in THP-1 macrophages. HHcy mice showed increased lesion area and lipid accumulation in plaque. Both studies in vitro and in vivo showed decreased expression of ATP binding cassette transporter A1 (ABCA1) and G1 (ABCG1). T0901317 treatment increased ABCA1 and ABCG1 levels; reversed macrophage-derived foam-cell formation in THP-1 macrophages and reduced atherosclerotic lesions in ApoE^-/- mice.

SIGNIFICANCE

Inhibition of LXRα-mediated ABCA1/ABCG1-dependent cholesterol efflux from macrophages is a novel mechanism in Hcy-accelerated atherosclerosis.

Roles for endothelial cell and macrophage Gch1 and tetrahydrobiopterin in atherosclerosis progression

Aims

GTP cyclohydrolase I catalyses the first and rate-limiting reaction in the synthesis of tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthases (NOS). Both eNOS and iNOS have been implicated in the progression of atherosclerosis, with opposing effects in eNOS and iNOS knockout mice. However, the pathophysiologic requirement for BH4 in regulating both eNOS and iNOS function, and the effects of loss of BH4 on the progression of atherosclerosis remains unknown.

Methods and results

Hyperlipidemic mice deficient in Gch1 in endothelial cells and leucocytes were generated by crossing Gch1fl/flTie2cre mice with ApoE-/- mice. Deficiency of Gch1 and BH4 in endothelial cells and myeloid cells was associated with mildly increased blood pressure. High fat feeding for 6 weeks in Gch1fl/flTie2CreApoE-/- mice resulted in significantly decreased circulating BH4 levels, increased atherosclerosis burden and increased plaque macrophage content. Gch1fl/flTie2CreApoE-/- mice showed hallmarks of endothelial cell dysfunction, with increased aortic VCAM-1 expression and decreased endothelial cell dependent vasodilation. Furthermore, loss of BH4 from pro-inflammatory macrophages resulted in increased foam cell formation and altered cellular redox signalling, with decreased expression of antioxidant genes and increased reactive oxygen species. Bone marrow chimeras revealed that loss of Gch1 in both endothelial cells and leucocytes is required to accelerate atherosclerosis.

Conclusion

Both endothelial cell and macrophage BH4 play important roles in the regulation of NOS function and cellular redox signalling in atherosclerosis.