Macrophages In Atherosclerotic Plaques Research Articles

A dynamical system framework for a mathematical model of atherosclerosis

Atherosclerosis is a chronic inflammatory disease occurs due to plaque accumulation in the inner artery wall. In atherosclerotic plaque formation monocytes and macrophages play a significant role in controlling the disease dynamics. In the present article, the entire biochemical process of atherosclerotic plaque formation is presented in terms of an autonomous system of nonlinear ordinary differential equations involving concentrations of oxidized low-density lipoprotein (LDL), monocytes, macrophages, and foam cells as the key dependent variables. To observe the capacity of monocytes and macrophages the model has been reduced to a two-dimensional temporal model using quasi steady state approximation theory. Linear stability analysis of the two-dimensional ordinary differential equations (ODEs) model has revealed the stability of the equilibrium points in the system. We have considered both one- and two-parameter bifurcation analysis with respect to parameters associated to the rate at which macrophages phagocytose oxidized LDL and the rate at which LDL enters into the intima. The bifurcation diagrams reveal the oscillating nature of the curves representing concentration of monocytes and macrophages with respect to significant model parameters. We are able to find the threshold values at which the plaque accumulation accelerates in an uncontrollable way. Further to observe the impact of diffusion, a spatiotemporal model has been developed. Numerical investigation of the partial differential equations (PDEs) model reveals the existence of travelling wave in the system which ensures the fact that the development of atherosclerotic plaque formation follows reaction–diffusion wave.

Human atherosclerotic plaque macrophages associate with clinical presentation and follow diverse lineage differentiation routes

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Research Council Veni grant. Netherlands Heart Foundation Atherosclerosis is characterized by inflammation and lipid accumulation, leading to complications such as stroke and myocardial infarction. Various macrophage subsets are present in human atherosclerotic plaques. However, it is unclear how subsets are interrelated and contribute to the disease process and its clinical outcomes. Here, we employed single-cell RNA-seq (scRNA-seq) on blood and plaque material from carotid endarterectomy patients enrolled in the AtheroExpress (AE) cohort to define regulatory pathways of macrophage recruitment, differentiation, and development. Additionally, we used these scRNA-seq data to deconvolute a large AE bulk RNA-seq cohort to allow correlating cellular subsets in plaques with clinical traits. Interestingly, we found that macrophages and their subsets are the only cell population significantly associated with major adverse cardiac events (MACE) during a 3-year follow-up period. Subsequently, we could divide plaque macrophages into 3 populations: inflammatory, tissue-resident / lipid-associated (TREM2 high), and foamy macrophages (TREM1 high). While the latter two are correlated with MACE, the inflammatory macrophages are inversely correlated with statin use. Cellular fate analyses revealed two major paths of macrophage development in the plaque. First, non-classical monocytes entering the plaque, turning into inflammatory cells before becoming foamy and eventually dying. Second, resident-like macrophages that turn into either inflammatory- or lipid-associated macrophages, before meeting their foamy demise. Together, these findings provide important insights on macrophages in atherosclerosis and suggest new leads to discover therapeutic targets for this disease.

Trem2 Agonist Reprograms Foamy Macrophages to Promote Atherosclerotic Plaque Stability-Brief Report.

Trem2 (triggering receptor on myeloid cells 2), a surface lipid receptor, is expressed on foamy macrophages within atherosclerotic lesions and regulates cell survival, proliferation, and anti-inflammatory responses. Studies examining the role of Trem2 in atherosclerosis have shown that deletion of Trem2 leads to impaired foamy macrophage lipid uptake, proliferation, survival, and cholesterol efflux. Thus, we tested the hypothesis that administration of a Trem2 agonist antibody (AL002a) to atherogenic mice would enhance macrophage survival and decrease necrotic core formation to improve plaque stability. To model a therapeutic intervention approach, atherosclerosis-prone mice (Ldlr [low-density lipoprotein receptor]-/-) were fed a high-fat diet for 8 weeks, then transitioned to treatment with AL002a or isotype control for an additional 8 weeks while continuing on a high-fat diet. AL002a-treated mice had increased lesion size in both the aortic root and whole mount aorta, which correlated with an expansion of plaque macrophage area. This expansion was due to increased macrophage survival and proliferation in plaques. Importantly, plaques from AL002a-treated mice showed improved features of plaque stability, including smaller necrotic cores, increased fibrous caps, and greater collagen deposition. Single-cell RNA sequencing of whole aorta suspensions from isotype- and AL002a-treated atherosclerotic mice revealed that Trem2 agonism dramatically altered foamy macrophage transcriptome. This included upregulation of oxidative phosphorylation and increased expression of collagen genes. In vitro studies validated that Trem2 agonism with AL002a promoted foamy macrophage oxidized low-density lipoprotein uptake, survival, and cholesterol efflux. Trem2 agonism expands atherosclerotic plaque macrophages by promoting cell survival and proliferation but improves features of plaque stability by rewiring foamy macrophage function to enhance cholesterol efflux and collagen deposition.

Ligand-dependent interactions between SR-B1 and S1PR1 in macrophages and atherosclerotic plaques

HDLs carry sphingosine-1-phosphate (S1P) and stimulate signaling pathways in different cells including macrophages and endothelial cells, involved in atherosclerotic plaque development. HDL signaling via S1P relies on the HDL receptor scavenger receptor class B, type I (SR-B1) and the sphingosine-1-phosphate receptor 1 (S1PR1), which interact when both are heterologously overexpressed in the HEK293 cell line. In this study, we set out to test if SR-B1 and S1PR1 interacted in primary murine macrophages in culture and atherosclerotic plaques. We used knock-in mice that endogenously expressed S1PR1 tagged with eGFP-(S1pr1eGFP/eGFP mice), combined with proximity ligation analysis to demonstrate that HDL stimulates the physical interaction between SR-B1 and S1PR1 in primary macrophages, that this is dependent on HDL-associated S1P and can be blocked by an inhibitor of SR-B1's lipid transfer activity or an antagonist of S1PR1. We also demonstrate that a synthetic S1PR1-selective agonist, SEW2871, stimulates the interaction between SR-B1 and S1PR1 and that this was also blocked by an inhibitor of SR-B1’s lipid transport activity. Furthermore, we detected abundant SR-B1/S1PR1 complexes in atherosclerotic plaques of S1pr1eGFP/eGFP mice that also lacked apolipoprotein E. Treatment of mice with the S1PR1 antagonist, Ex26, for 12 h disrupted the SR-B1-S1PR1 interaction in atherosclerotic plaques. These findings demonstrate that SR-B1 and S1PR1 form ligand-dependent complexes both in cultured primary macrophages and within atherosclerotic plaques in mice and provide mechanistic insight into how SR-B1 and S1PR1 participate in mediating HDL signaling to activate atheroprotective responses in macrophages.

Nalmefene, an opioid receptor modulator, aggravates atherosclerotic plaque formation in apolipoprotein E knockout mice by enhancing oxidized low-density lipoprotein uptake in macrophages

Nalmefene, an antagonist of mu- and delta-opioid receptors and a partial agonist of kappa-opioid receptors, has shown promise in reducing alcohol consumption among patients with alcohol dependence. Opioid receptors play pivotal roles in various physiological processes, including those related to peripheral inflammatory diseases such as colitis and arthritis, as well as functions in the immune system and phagocytosis. Atherosclerosis, a chronic inflammatory disease, progresses through the phagocytosis and uptake of oxidized low-density lipoprotein (oxLDL) by macrophages in atherosclerotic plaques. Despite this knowledge, it remains unclear whether nalmefene influences the formation of atherosclerotic plaques and increases the risk of serious cardiovascular events. This study aims to elucidate the impact of nalmefene on atherosclerosis in apolipoprotein E knockout (ApoE KO) mice and peritoneal macrophages in vitro.In this experiment, 8-week-old male ApoE KO mice were fed a high-fat diet intraperitoneally administered either vehicle (saline) or nalmefene (1 mg and 3 mg kg−1 day−1) for 21 days. Oil red O-staining and immunohistochemistry with an anti-MOMA2 (monocyte/macrophage) antibody showed that a dose-dependent increase in atherosclerotic plaque formation and augmentation of macrophage-rich plaque formation in ApoE-KO mice. Further investigations focused on the effects of nalmefene on the expression of scavenger receptor CD36 in RAW264.7 cells, conducted through western blotting analysis. Nalmefene demonstrated a significant increase in CD36 protein expression in RAW264.7 cells. To explore the impact on oxidized LDL uptake in peritoneal macrophages, cells were treated with nalmefene (300 μg/mL) for 24 h, followed by the addition of DiI-labeled oxLDL (DiI-oxLDL) for 4 h. Nalmefene significantly enhanced DiI-oxLDL uptake in macrophages. Additionally, treatment with nalmefene (300 μg/mL) for 24 h decreased the mRNA expression of mu-, delta-, and kappa-opioid receptors in RAW264.7 cells.In conclusion, nalmefene may augment oxLDL uptake by macrophages through increased CD36 expression and decreased opioid receptor, thereby contributing to atherosclerotic plaque formation and vulnerability. Consequently, the use of nalmefene may be associated with an elevated risk of cardiovascular events.

Follicle-Stimulating Hormone Exacerbates Cardiovascular Disease in the Presence of Low or Castrate Testosterone Levels

Low testosterone (T), common in aging men, associates with cardiovascular disease. We investigated whether follicle-stimulating hormone (FSH), which is affected by T, modulates the cardiovascular effects associated withlow T or castration. FSHβ-/-:low-density lipoprotein receptor (LDLR)-/- mice, untreated or castrated (orchiectomy, gonadotropin-releasing hormone agonist or antagonist), demonstrated significantly less atherogenesis compared with similarly treated LDLR-/- mice, but not following FSH delivery. Smaller plaque burden in LDLR-/- mice receiving gonadotropin-releasing hormone antagonists vs agonists were nullified in FSHβ-/-:LDLR-/- mice. Atherosclerotic and necrotic plaque size and macrophage infiltration correlated with serum FSH/T. In patients with prostate cancer, FSH/T following androgen-deprivation therapy initiation predicted cardiovascular events. FSH facilitates cardiovascular disease when T is low or eliminated.

Depletion of β-arrestin-1 in macrophages enhances atherosclerosis in ApoE−/− mice

Autophagy in atherosclerotic plaque macrophage contributes to the alleviation of atherosclerosis through the promotion of lipid metabolism. β-arrestins are multifunctional proteins participating various kinds of cellular signaling pathways. Here we aimed to determine the role of β-arrestin-1, an important member of β-arrestin family, in atherosclerosis, and whether autophagy was involved in this process. ApoE−/−β-arrestin-1fl/flLysM-Cre mice were created through bone marrow transplantation for the atherosclerosis model with conditional myeloid knocking out β-arrestin-1. Bone marrow-derived macrophages (BMDMs) were used for the in vitro studies. Oil red O staining was used to detect the lesional area. F4/80, Masson trichrome and picro-Sirius red staining were applied for the determination of plaque stability. Real-time PCR was used for the detection of levels of lipid metabolism-related receptors. Electron microscopy and tandem fluorescent mRFP-GFP-LC3 plasmid was applied to test autophagy level. We found that β-arrestin-1 was highly increased in expression in plaque macrophage on the occurrence of atherosclerosis. Conditional myeloid knocking out β-arrestin-1 largely promotes plaque formation and vulnerability. In murine macrophage with lipid loading, knocking down β-arrestin-1 enhanced foam cell formation and levels of plasma and cellular cholesterol, while overexpressing β-arrestin-1 led to the opposite effects. The alleviative effects induced by macrophage β-arrestin-1 in atherosclerosis were involved in autophagy, based on the reduction of autophagy level with the knocking down of macrophage β-arrestin-1 and administration of autophagy inhibitors which largely attenuated the decreasing effect on foam cell formation. Our results demonstrated for the first time that macrophage β-arrestin-1 protected against atherosclerosis through the induction of autophagy.

Preparation and evaluation of 111In-labeled liposomes containing phosphatidylglycerol for detection of macrophages in atherosclerotic plaques

Macrophage infiltration is a characteristic feature of atherosclerotic plaque progression. Since liposomes containing 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) are efficiently phagocytosed by macrophages, we deduced that radiolabeled liposomes containing DSPG could potentially be used for nuclear imaging of vulnerable atherosclerotic plaques. Indium-111 (111In)-labeled liposomes containing different ratios of DSPG were developed with a high labeling efficiency. 111In-labeled liposomes with higher DSPG content showed higher uptake by macrophage-like RAW264 cells. A biodistribution study demonstrated rapid blood clearance and selective accumulation in the liver and spleen, especially in normal mice injected with 111In-labeled liposomes with higher DSPG content. Accumulation in atherosclerotic plaques was evaluated using 111In-labeled DSPG liposomes, which had the highest DSPG content among the studied liposomes. 111In-labeled DSPG liposomes accumulated in the plaques and the radioactive regions were mostly consistent with the distribution of macrophages. The target-to-non-target ratio of 111In-labeled DSPG liposomes was higher than that of 111In-labeled control liposomes without DSPG. These results suggest that 111In-labeled liposomes containing DSPG are useful for nuclear medical diagnosis of atherosclerotic plaques.

Par3L, a polarity protein, promotes M1 macrophage polarization and aggravates atherosclerosis in mice via p65 and ERK activation.

Proinflammatory M1 macrophages are critical for the progression of atherosclerosis. The Par3-like protein (Par3L) is a homolog of the Par3 family involved in cell polarity establishment. Par3L has been shown to maintain the stemness of mammary stem cells and promote the survival of colorectal cancer cells. In this study, we investigated the roles of the polar protein Par3L in M1 macrophage polarization and atherosclerosis. To induce atherosclerosis, Apoe-/- mice were fed with an atherosclerotic Western diet for 8 or 16 weeks. We showed that Par3L expression was significantly increased in human and mouse atherosclerotic plaques. In primary mouse macrophages, oxidized low-density lipoprotein (oxLDL, 50 μg/mL) time-dependently increased Par3L expression. In Apoe-/- mice, adenovirus-mediated Par3L overexpression aggravated atherosclerotic plaque formation accompanied by increased M1 macrophages in atherosclerotic plaques and bone marrow. In mouse bone marrow-derived macrophages (BMDMs) or peritoneal macrophages (PMs), we revealed that Par3L overexpression promoted LPS and IFNγ-induced M1 macrophage polarization by activating p65 and extracellular signal-regulated kinase (ERK) rather than p38 and JNK signaling. Our results uncover a previously unidentified role for the polarity protein Par3L in aggravating atherosclerosis and favoring M1 macrophage polarization, suggesting that Par3L may serve as a potential therapeutic target for atherosclerosis.

A Lipid-Structured Model of Atherosclerotic Plaque Macrophages with Lipid-Dependent Kinetics

Atherosclerotic plaques are fatty growths in artery walls that cause heart attacks and strokes. Plaque formation is driven by macrophages that are recruited to the artery wall. These cells consume and remove blood-derived lipids, such as modified low-density lipoprotein. Ineffective lipid removal, due to macrophage death and other factors, leads to the accumulation of lipid-loaded macrophages and formation of a necrotic lipid core. Experimental observations suggest that macrophage functionality varies with the extent of lipid loading. However, little is known about the influence of macrophage lipid loads on plaque fate. Extending work by Ford et al. (J Theor Biol 479:48–63, 2019) and Chambers et al. (A lipid-structured model of atherosclerosis with macrophage proliferation, 2022), we develop a plaque model where macrophages are structured by their ingested lipid load and behave in a lipid-dependent manner. The model considers several macrophage behaviours, including recruitment to and emigration from the artery wall; proliferation and apotosis; ingestion of plaque lipids; and secondary necrosis of apoptotic cells. We consider apoptosis, emigration and proliferation to be lipid-dependent and we model these effects using experimentally informed functions of the internalised lipid load. Our results demonstrate that lipid-dependent macrophage behaviour can substantially alter plaque fate by changing both the total quantity of lipid in the plaque and the distribution of lipid between the live cells, dead cells and necrotic core. The consequences of macrophage lipid-dependence are often unpredictable because lipid-dependent effects introduce subtle, nonlinear interactions between the modelled cell behaviours. These observations highlight the importance of mathematical modelling in unravelling the complexities of macrophage lipid accumulation during atherosclerotic plaque formation.

Abstract P3189: Vcam-1-mediated Mitochondrial Biogenesis In Macrophages Exacerbates Inflammation And Atherosclerosis

Atherosclerotic cardiovascular disease is a leading cause of adult mortality worldwide. Macrophages play a key role in atherogenesis by sustaining the local inflammatory response, facilitating accumulation of immune cells in atheromas that contribute to plaque development. Mitochondrial metabolism plays a key role in governing inflammatory gene expression in macrophages. Yet, the role of mitochondrial biogenesis and mitochondrial DNA synthesis in regulating macrophage inflammation is not known. Vascular cell adhesion protein 1 (VCAM-1) expressed by endothelial cells mediates monocyte adhesion and extravasation in developing atherosclerotic plaques. We observed increased VCAM-1 expression in human and murine plaque macrophages. However, the function of this cell adhesion molecule expressed by macrophages is not known. Here, we evaluated if and how myeloid-VCAM-1 drive mitochondrial biogenesis, inflammation, and atherosclerosis pathology. Increased VCAM-1 expression in plaque macrophages correlated with oxidative DNA damage and mitochondrial volume. To understand the role of myeloid-Vcam1 in atherogenesis, we generated Apoe -/- LyzM cre/+ VCAM-1 fl/fl mice. Consistently, Apoe -/- mice lacking Vcam1 in macrophages exhibited reduced atherosclerosis severity and inflammation. Vcam1-deficient macrophages exhibited decreased inflammation, oxidative phosphorylation, mitochondrial biogenesis, and mitochondrial DNA synthesis genes, including Cmpk2. Cmpk2 deletion in macrophages after oxidized LDL treatment reduced inflammatory mediators that aggravate atherosclerosis. RNA sequencing analysis of Vcam-1 -deficient plaque macrophages and analysis of macrophages lacking Cmpk2 identified Fcor and Lyz1 as the target genes of Vcam1 and Cmpk2 . Interestingly, atherosclerotic plaque macrophages deficient of Sting , which mediates inflammatory signaling in response to oxidized mitochondrial DNA, had increased levels of Fcor and Lyz1 . Our data suggest that VCAM-1 in macrophages signals via CMPK2 and POLG to promote mitochondrial biogenesis, oxidation, and fragmentation, mediating atherogenesis.

Serum soluble TREM2 is an independent biomarker associated with coronary heart disease

BackgroundTriggering receptor expressed on myeloid cells 2 (TREM2) is a unique receptor expressed by macrophages in atherosclerotic plaque and is involved in the progression of atherosclerosis. Whether serum soluble TREM2 (sTREM2) levels has a relationship with coronary heart disease (CHD) remains unclear. MethodsThe cross-sectional study included 86 patients with CHD and 86 controls matched with age and sex. Demographic information, medication history, and laboratory data were collected. sTREM2 concentrations were detected by enzyme-linked immunosorbent assay. We compared the sTREM2 levels in two groups and constructed stepwise linear regression analysis for factors related to the sTREM2 level in patients with CHD; we further used the logistic regression model to evaluate the relationship between sTREM2 and CHD. The diagnostic value of sTREM2 and other biomarkers in CHD was evaluated by the receiver operating characteristic curve (ROC). ResultsThe serum level of sTREM2 in CHD patients is higher than that in controls. In CHD patients, the stepwise linear regression analysis found that sTREM2 levels were correlated with triglyceride (TG), high-density lipoprotein cholesterols (HDL-C), apolipoprotein B (ApoB) and smoking status. Logistic regression models showed that sTREM2 was associated independently with CHD after adjusted confounders. The ROC curve showed a sensitivity of 59.3% and specificity of 81.4% with an area under the curve of 0.781 (95% CI: 0.711–0.852) for the diagnosis of CHD with serum sTREM2 at a cut-off value of > 1104.894 pg/ml, indicating a higher diagnostic value than high sensitivity C reaction protein (hs-CRP) and apolipoprotein B (ApoB). ConclusionIn this study, we provide evidence that sTREM2 levels are elevated in CHD patients and are associated with various cardiovascular risk factors. Additionally, sTREM2 demonstrates better diagnostic performance compared to traditional indicators in identifying CHD. These findings suggest that sTREM2 may serve as a potential biomarker for coronary heart disease.

Abstract 695: Serine Hydroxymethyltransferase 2 Regulates Mitochondrial Function And Ceramide Metabolism In Macrophages During Atherosclerosis

Increasing evidence suggests a critical role for amino acid metabolism in cardiovascular disease, highlighting potential therapeutic targets and our need for further understanding. Plasma serine has been found to be a biomarker for cardiovascular disease, while glycine is negatively correlated with coronary artery disease. Furthermore, attenuated plasma glycine:serine is associated with unstable atherosclerotic plaques. Mitochondrial Serine hydroxymethyl transferase (SHMT) catalyzes the bulk formation of glycine from serine in most cell types and drives one-carbon metabolism in the cytosol (SHMT1) or mitochondria (SHMT2). SHMT2 is necessary for mitochondrial protein translation and critical in development since global knockout mice are nonviable. We found LPS-treated macrophages have reduced SHMT2 expression concomitant with attenuated intracellular glycine:serine. Deletion of macrophage SHMT2 in vitro enhanced intracellular serine, which contributes to the rate-limiting step of ceramide de novo biosynthesis. C16:0 ceramide is highly abundant in atherosclerotic plaques and is positively associated with plaque severity, and SHMT2-deleted macrophages treated with C16:0 fatty acid enhances intracellular ceramide. Furthermore, deletion of SHMT2 reduced mitochondrial respiration and enhanced glycolysis similar to LPS-treated macrophages. Moreover, we found SHMT2 is highly expressed in plaque-associated macrophages in both human and mouse atherosclerotic plaques. We therefore hypothesized that SHMT2 regulates macrophage inflammatory phenotype in atherosclerosis through alterations in mitochondrial function and ceramide biosynthesis. To determine whether macrophage-expressed SHMT2 contributes to atherosclerosis, we developed a novel Shmt2 -floxed mouse crossed with LysM-Cre ( Shmt2 MKO ) and Apoe -/- mice. After 12 weeks on Western diet, we observed no differences in plasma glycine:serine or circulating lipids. Nevertheless, Shmt2 MKO / Apoe -/- mice had significantly enhanced plaque area compared to littermate controls. Our findings, representing the first investigation of conditional SHMT2 knockout mice, suggest a novel immunometabolic role for SHMT2 in macrophages in atherosclerosis.

Tongmai Zhuke decoction restrains the inflammatory reaction of macrophages for carotid artery atherosclerosis by up-regulating lincRNA-Cox2

ABSTRACT To explore the mechanism of Tongmai Zhuke decoction for promoting blood circulation by taking carotid artery atherosclerosis (CAA) as an example, two sets of in-depth transcriptomic data as well as two sets of single-cell RNA sequencing data related to the macrophages in CAA were included. STAR and DCC software were used to process in-depth transcriptomic data in order to measure the expression level of LncRNAs as well as mRNA according to FPKM analysis. Single-cell RNA sequencing data from Illumina NovaSeq 6000 were further analyzed by CellRanger channel, CellRanger count, Seurat R package, DoubletFinder package, CCA algorithm, LogNormalize, principal-component analysis, t-SNE and ToppGene online tools. Based On unsupervised clustering, a total of four diverse cell populations with distinct transcriptional features were found in human carotid atherosclerotic plaques. The macrophages were further annotated as the “effector cell” in the pathologic process of CAA, based on the expression of CD68+/CD440-. A total of 84 up-regulated genes and 58 down-regulated linc-RNAs were identified in samples with carotid atherosclerotic plaques. Thereinto, lincRNA-Cox2 is the most down-regulated LincRNA. For the macrophages in carotid atherosclerotic plaques, expression level of Il6, Ccl3, Ccl4 Il10 and Tnfa were significantly up-regulated, while Timp1 significantly down-regulated comparing with healthy carotid sample. The expression level of lincRNA-Cox2 was significantly increased in macrophages after treated by Tongmai Zhuke decoction, while Cxcl10, Ccl3, Ccl4, Cxcl2, Ccl5, and Ccl19 were significantly decreased. Collectively, Tongmai Zhuke decoction could restrain the inflammatory reaction of macrophages for carotid artery atherosclerosis by up-regulating lincRNA-Cox2.

Transient increase in atherosclerotic plaque macrophage content following Streptococcus pneumoniae pneumonia in ApoE-deficient mice.

Despite epidemiological associations between community acquired pneumonia (CAP) and myocardial infarction, mechanisms that modify cardiovascular disease during CAP are not well defined. In particular, largely due to a lack of relevant experimental models, the effect of pneumonia on atherosclerotic plaques is unclear. We describe the development of a murine model of the commonest cause of CAP, Streptococcus pneumoniae pneumonia, on a background of established atherosclerosis. We go on to use our model to investigate the effects of pneumococcal pneumonia on atherosclerosis. C57BL/6J and ApoE-/- mice were fed a high fat diet to promote atherosclerotic plaque formation. Mice were then infected with a range of S. pneumoniae serotypes (1, 4 or 14) with the aim of establishing a model to study atherosclerotic plaque evolution after pneumonia and bacteremia. Laser capture microdissection of plaque macrophages enabled transcriptomic analysis. Intratracheal instillation of S. pneumoniae in mice fed a cholate containing diet resulted in low survival rates following infection, suggestive of increased susceptibility to severe infection. Optimization steps resulted in a final model of male ApoE-/- mice fed a Western diet then infected by intranasal instillation of serotype 4 (TIGR4) S. pneumoniae followed by antibiotic administration. This protocol resulted in high rates of bacteremia (88.9%) and survival (88.5%). Pneumonia resulted in increased aortic sinus plaque macrophage content 2 weeks post pneumonia but not at 8 weeks, and no difference in plaque burden or other plaque vulnerability markers were found at either time point. Microarray and qPCR analysis of plaque macrophages identified downregulation of two E3 ubiquitin ligases, Huwe1 and Itch, following pneumonia. Treatment with atorvastatin failed to alter plaque macrophage content or other plaque features. Without antibiotics, ApoE-/- mice fed a high fat diet were highly susceptible to mortality following S. pneumoniae infection. The major infection associated change in plaque morphology was an early increase in plaque macrophages. Our results also hint at a role for the ubiquitin proteasome system in the response to pneumococcal infection in the plaque microenvironment.

A new lipid-structured model to investigate the opposing effects of LDL and HDL on atherosclerotic plaque macrophages

Atherosclerotic plaques form in artery walls due to a chronic inflammatory response driven by lipid accumulation. A key component of the inflammatory response is the interaction between monocyte-derived macrophages and extracellular lipid. Although concentrations of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles in the blood are known to affect plaque progression, their impact on the lipid load of plaque macrophages remains unexplored. In this paper, we develop a lipid-structured mathematical model to investigate the impact of blood LDL/HDL levels on plaque composition, and lipid distribution in plaque macrophages. A reduced subsystem, derived by summing the equations of the full model, describes the dynamics of biophysical quantities relating to plaque composition (e.g. total number of macrophages, total amount of intracellular lipid). We also derive a continuum approximation of the model to facilitate analysis of the macrophage lipid distribution. The results, which include time-dependent numerical solutions and asymptotic analysis of the unique steady state solution, indicate that plaque lipid content is sensitive to the influx of LDL relative to HDL capacity. The macrophage lipid distribution evolves in a wave-like manner towards an equilibrium profile which may be monotone decreasing, quasi-uniform or unimodal, attaining its maximum value at a non-zero lipid level. Our model also reveals that macrophage uptake may be severely impaired by lipid accumulation. We conclude that lipid accumulation in plaque macrophages may serve as a partial explanation for the defective uptake of apoptotic cells (efferocytosis) often reported in atherosclerotic plaques.

Unbalanced Redox With Autophagy in Cardiovascular Disease.

Precise redox balance is essential for the optimum health and physiological function of the human body. Furthermore, an unbalanced redox state is widely believed to be part of numerous diseases, ultimately resulting in death. In this review, we discuss the relationship between redox balance and cardiovascular disease (CVD). In various animal models, excessive oxidative stress has been associated with increased atherosclerotic plaque formation, which is linked to the inflammation status of several cell types. However, various antioxidants can defend against reactive oxidative stress, which is associated with an increased risk of CVD and mortality. The different cardiovascular effects of these antioxidants are presumably due to alterations in the multiple pathways that have been mechanistically linked to accelerated atherosclerotic plaque formation, macrophage activation, and endothelial dysfunction in animal models of CVD, as well as in in vitro cell culture systems. Autophagy is a regulated cell survival mechanism that removes dysfunctional or damaged cellular organelles and recycles the nutrients for the generation of energy. Furthermore, in response to atherogenic stress, such as the generation of reactive oxygen species, oxidized lipids, and inflammatory signaling between cells, autophagy protects against plaque formation. In this review, we characterize the broad spectrum of oxidative stress that influences CVD, summarize the role of autophagy in the content of redox balance-associated pathways in atherosclerosis, and discuss potential therapeutic approaches to target CVD by stimulating autophagy.

Sterol-regulated transmembrane protein TMEM86a couples LXR signaling to regulation of lysoplasmalogens in macrophages

Lysoplasmalogens are a class of vinyl ether bioactive lipids that have a central role in plasmalogen metabolism and membrane fluidity. The liver X receptor (LXR) transcription factors are important determinants of cellular lipid homeostasis owing to their ability to regulate cholesterol and fatty acid metabolism. However, their role in governing the composition of lipid species such as lysoplasmalogens in cellular membranes is less well studied. Here, we mapped the lipidome of bone marrow–derived macrophages (BMDMs) following LXR activation. We found a marked reduction in the levels of lysoplasmalogen species in the absence of changes in the levels of plasmalogens themselves. Transcriptional profiling of LXR-activated macrophages identified the gene encoding transmembrane protein 86a (TMEM86a), an integral endoplasmic reticulum protein, as a previously uncharacterized sterol-regulated gene. We demonstrate that TMEM86a is a direct transcriptional target of LXR in macrophages and microglia and that it is highly expressed in TREM2+/lipid-associated macrophages in human atherosclerotic plaques, where its expression positively correlates with other LXR-regulated genes. We further show that both murine and human TMEM86a display active lysoplasmalogenase activity that can be abrogated by inactivating mutations in the predicted catalytic site. Consequently, we demonstrate that overexpression of Tmem86a in BMDM markedly reduces lysoplasmalogen abundance and membrane fluidity, while reciprocally, silencing of Tmem86a increases basal lysoplasmalogen levels and abrogates the LXR-dependent reduction of this lipid species. Collectively, our findings implicate TMEM86a as a sterol-regulated lysoplasmalogenase in macrophages that contributes to sterol-dependent membrane remodeling.

Human Macrophage Long Intergenic Noncoding RNA, SIMALR, Suppresses Inflammatory Macrophage Apoptosis via NTN1 (Netrin-1).

Long noncoding RNAs (lncRNAs) have emerged as novel regulators of macrophage biology and inflammatory cardiovascular diseases. However, studies focused on lncRNAs in human macrophage subtypes, particularly human lncRNAs that are not conserved in rodents, are limited. Through RNA-sequencing of human monocyte-derived macrophages, we identified suppressor of inflammatory macrophage apoptosis lncRNA (SIMALR). Lipopolysaccharide/IFNγ (interferon γ) stimulated human macrophages were treated with SIMALR antisense oligonucleotides and subjected to RNA-sequencing to investigate the function of SIMALR. Western blots, luciferase assay, and RNA immunoprecipitation were performed to validate function and potential mechanism of SIMALR. RNAscope was performed to identify SIMALR expression in human carotid atherosclerotic plaques. RNA-sequencing of human monocyte-derived macrophages identified SIMALR, a human macrophage-specific long intergenic noncoding RNA that is highly induced in lipopolysaccharide/IFNγ-stimulated macrophages. SIMALR knockdown in lipopolysaccharide/IFNγ stimulated THP1 human macrophages induced apoptosis of inflammatory macrophages, as shown by increased protein expression of cleaved PARP (poly[ADP-ribose] polymerase), caspase 9, caspase 3, and Annexin V+. RNA-sequencing of control versus SIMALR knockdown in lipopolysaccharide/IFNγ-stimulated macrophages showed Netrin-1 (NTN1) to be significantly decreased upon SIMALR knockdown. We confirmed that NTN1 knockdown in lipopolysaccharide/IFNγ-stimulated macrophages induced apoptosis. The SIMALR knockdown-induced apoptotic phenotype was rescued by adding recombinant NTN1. NTN1 promoter-luciferase reporter activity was increased in HEK293T (human embryonic kidney 293) cells treated with lentiviral overexpression of SIMALR. NTN1 promoter activity is known to require HIF1α (hypoxia-inducible factor 1 subunit alpha), and our studies suggest that SIMALR may interact with HIF1α to regulate NTN1 transcription, thereby regulating macrophages apoptosis. SIMALR was found to be expressed in macrophages in human carotid atherosclerotic plaques of symptomatic patients. SIMALR is a nonconserved, human macrophage lncRNA expressed in atherosclerosis that suppresses macrophage apoptosis. SIMALR partners with HIF1α (hypoxia-inducible factor 1 subunit alpha) to regulate NTN1, which is a known macrophage survival factor. This work illustrates the importance of interrogating the functions of human lncRNAs and exploring their translational and therapeutic potential in human atherosclerosis.

Use of acidic nanoparticles to rescue macrophage lysosomal dysfunction in atherosclerosis

ABSTRACT Dysfunction in the macrophage lysosomal system including reduced acidity and diminished degradative capacity is a hallmark of atherosclerosis, leading to blunted clearance of excess cellular debris and lipids in plaques and contributing to lesion progression. Devising strategies to rescue this macrophage lysosomal dysfunction is a novel therapeutic measure. Nanoparticles have emerged as an effective platform to both target specific tissues and serve as drug delivery vehicles. In most cases, administered nanoparticles are taken up non-selectively by the mononuclear phagocyte system including monocytes/macrophages leading to the undesirable degradation of cargo in lysosomes. We took advantage of this default route to target macrophage lysosomes to rectify their acidity in disease states such as atherosclerosis. Herein, we develop and test two commonly used acidic nanoparticles, poly-lactide-co-glycolic acid (PLGA) and polylactic acid (PLA), both in vitro and in vivo. Our results in cultured macrophages indicate that the PLGA-based nanoparticles are the most effective at trafficking to and enhancing acidification of lysosomes. PLGA nanoparticles also provide functional benefits including enhanced lysosomal degradation, promotion of macroautophagy/autophagy and protein aggregate removal, and reduced apoptosis and inflammasome activation. We demonstrate the utility of this system in vivo, showing nanoparticle accumulation in, and lysosomal acidification of, macrophages in atherosclerotic plaques. Long-term administration of PLGA nanoparticles results in significant reductions in surrogates of plaque complexity with reduced apoptosis, necrotic core formation, and cytotoxic protein aggregates and increased fibrous cap formation. Taken together, our data support the use of acidic nanoparticles to rescue macrophage lysosomal dysfunction in the treatment of atherosclerosis. Abbreviations: BCA: brachiocephalic arteries; FACS: fluorescence activated cell sorting; FITC: fluorescein-5-isothiocyanatel; IL1B: interleukin 1 beta; LAMP: lysosomal associated membrane protein; LIPA/LAL: lipase A, lysosomal acid type; LSDs: lysosomal storage disorders; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MFI: mean fluorescence intensity; MPS: mononuclear phagocyte system; PEGHDE: polyethylene glycol hexadecyl ether; PLA: polylactic acid; PLGA: poly-lactide-co-glycolic acid; SQSTM1/p62: sequestosome 1