Regression of Atherosclerosis: The Journey From the Liver to the Plaque and Back

Development of Pro-resolving and Pro-efferocytic Nanoparticles for Atherosclerosis Therapy

Atherosclerosis is a major contributor to cardiovascular diseases with a high global prevalence. It is characterized by the formation of lipid-laden plaques in the arteries, which eventually lead to plaque rupture and thrombosis. While the current lipid-lowering therapies are generally effective in lowering the risk of cardiovascular events, they do not address the underlying causes of disease. Defective resolution of inflammation and impaired efferocytosis are the main driving forces of atherosclerosis. Macrophages recognize cells for clearance by the expression of "eat me" and "do not eat me" signals, including the CD47-SIRPα axis. However, the "do not eat me" signal CD47 is overexpressed in atherosclerotic plaques, leading to compromised efferocytosis and secondary necrosis. In this context, prophagocytic antibodies have been explored to stimulate the clearance of apoptotic cells, but they are nonspecific and impact healthy tissues. In macrophages, downstream of signal regulatory protein α, lie protein tyrosine phosphatases, SHP 1/2, which can serve as effective targets for selectively phagocytosing apoptotic cells. While increasing the efferocytosis targets the end stages of lesion development, the underlying issue of inflammation still persists. Simultaneously increasing efferocytosis and reducing inflammation can be effective therapeutic strategies for managing atherosclerosis. For instance, IL-10 is a key anti-inflammatory mediator that enhances efferocytosis via phosphoSTAT3 (pSTAT3) activation. In this study, we developed a combination nanotherapy by encapsulating an SHP-1 inhibitor (NSC 87877) and IL-10 in a single nanoparticle platform [(S + IL)-NPs] to enhance efferocytosis and inflammation resolution. Our studies suggest that (S + IL)-NPs successfully encapsulated both agents, entered the macrophages, and delivered the agents into intracellular compartments. Additionally, (S + IL)-NPs decreased inflammation by suppressing pro-inflammatory markers and enhancing anti-inflammatory mediators. They also exhibited the potential for improved phagocytic activity via pSTAT3 activation. Our nanomedicine-mediated upregulation of the anti-inflammatory and efferocytic responses in macrophages shows promise for the treatment of atherosclerosis.

Enhanced Akt3 kinase activity reduces atherosclerosis in hyperlipidemic mice in a gender-dependent manner

Akt3 is one of the three members of the serine/threonine protein kinase B (AKT) family, which regulates multiple cellular processes. We have previously demonstrated that global knockout of Akt3 in mice promotes atherogenesis in a macrophage-dependent manner. Whether enhanced Akt3 kinase activity affects atherogenesis is not known. In this study, we crossed atherosclerosis-prone ApoE-/- mice with a mouse strain that has enhanced Akt3 kinase activity (Akt3nmf350) and assessed atherosclerotic lesion formation and the role of macrophages in atherogenesis. Significant reduction in atherosclerotic lesion area and macrophage accumulation in lesions were observed in ApoE-/-/Akt3nmf350 mice fed a Western-type diet. Experiments using chimeric ApoE-/- mice with either ApoE-/-/Akt3nmf350 bone marrow or ApoE-/- bone marrow cells showed that enhanced Akt3 activity specifically in bone marrow-derived cells is atheroprotective. The atheroprotective effect of Akt3nmf350 was more pronounced in male mice. In line with this result, the release of the pro-inflammatory cytokines IL-6, MCP1, TNF-α, and MIP-1α was reduced by macrophages from male but not female ApoE-/-/Akt3nmf350 mice. Levels of IL-6 and TNF-α were also reduced in atherosclerotic lesions of ApoE-/-/Akt3nmf350 male mice compared to ApoE-/- mice. Macrophages from male ApoE-/-/Akt3nmf350 mice were also more resistant to apoptosis in vitro and in vivo and tended to have more pronounced M2 polarization in vitro. These findings demonstrated that enhanced Akt3 kinase activity in macrophages protects mice from atherosclerosis in hyperlipidemic mice in a gender-dependent manner.

The Role of Macrophages in Atherosclerosis: Pathophysiologic Mechanisms and Treatment Considerations

Atherosclerotic diseases are a leading cause of morbidity and mortality worldwide, despite the recent diagnostic and therapeutic advances. A thorough understanding of the pathophysiologic mechanisms is thus essential to improve the care of affected individuals. Macrophages are crucial mediators of the atherosclerotic cascade, but their role has not been fully elucidated. The two main subtypes, tissue-resident and monocyte-derived macrophages, have distinct functions that contribute to atherosclerosis development or regression. Since polarization of macrophages to an M2 phenotype and induction of macrophage autophagy have been demonstrated to be atheroprotective, targeting these pathways could represent an appealing approach. Interestingly, macrophage receptors could act as drug targets, as seen in recent experimental studies. Last but not least, macrophage-membrane-coated carriers have been investigated with encouraging results.

Xestospongia muta Fraction-7 and Linoleic Acid: Effects on SR-BI Gene Expression and HDL Cholesterol Uptake

Xestospongia muta is a marine sponge belonging to the family Petrosiidae. It is an important source of biologically active marine natural products, with different kinds of essential fatty acids. Scavenger receptor class B type I (SR-BI) is the main receptor for high-density lipoprotein (HDL) cholesterol, which plays a pivotal role in preventing atherosclerosis. It removes cholesterol from HDL cholesterol, returning lipid-poor lipoprotein into blood circulation. The present study investigated the effects of X. muta Fraction-7 and linoleic acid on SR-BI gene expression and HDL cholesterol uptake. In vitro studies of the activity of X. muta and linoleic acid against the therapeutic target for hypercholesterolemia were conducted using the HDL receptor SR-BI via luciferase assay and HepG2 cells. In the present study, Fraction-7 of X. muta showed the highest expression level of the SR-BI gene via luciferase assay. Profiling of Fraction-7 of X. muta by GC-MS revealed 58 compounds, comprising various fatty acids, particularly linoleic acid. The in vitro study in HepG2 cells showed that the Fraction-7 of X. muta and linoleic acid (an active compound in X. muta) increased SR-BI mRNA expression by 129% and 85%, respectively, compared to the negative control. Linoleic acid increased HDL uptake by 3.21-fold compared to the negative control. Thus, the Fraction-7 of X. muta and linoleic acid have the potential to be explored as adjuncts in the treatment of hypercholesterolemia to prevent or reduce the severity of atherosclerosis development.

There is urgent need to treat atherosclerotic cardiovascular disease risk earlier, more intensively, and with greater precision: A review of current practice and recommendations for improved effectiveness

Atherosclerotic cardiovascular disease (ASCVD) is epidemic throughout the world and is etiologic for such acute cardiovascular events as myocardial infarction, ischemic stroke, unstable angina, and death. ASCVD also impacts risk for dementia, chronic kidney disease peripheral arterial disease and mobility, impaired sexual response, and a host of other visceral impairments that adversely impact the quality and rate of progression of aging. The relationship between low-density lipoprotein cholesterol (LDL-C) and risk for ASCVD is one of the most highly established and investigated issues in the entirety of modern medicine. Elevated LDL-C is a necessary condition for atherogenesis induction. Basic scientific investigation, prospective longitudinal cohorts, and randomized clinical trials have all validated this association. Yet despite the enormous number of clinical trials which support the need for reducing the burden of atherogenic lipoprotein in blood, the percentage of high and very high-risk patients who achieve risk stratified LDL-C target reductions is low and has remained low for the last thirty years. Atherosclerosis is a preventable disease. As clinicians, the time has come for us to take primordial and primary prevention more serously. Despite a plethora of therapeutic approaches, the large majority of patients at risk for ASCVD are poorly or inadequately treated, leaving them vulnerable to disease progression, acute cardiovascular events, and poor aging due to loss of function in multiple visceral organs. Herein we discuss the need to greatly intensify efforts to reduce risk, decrease disease burden, and provide more comprehensive and earlier risk assessment to optimally prevent ASCVD and its complications. Evidence is presented to support that treatment should aim for far lower goals in cholesterol management, should take into account many more factors than commonly employed today and should begin significantly earlier in life.

Efferocytosis induces macrophage proliferation to help resolve tissue injury

Apoptotic cell clearance by macrophages (efferocytosis) promotes resolution signaling pathways, which can be triggered by molecules derived from the phagolysosomal degradation of apoptotic cells. We show here that nucleotides derived from the hydrolysis of apoptotic cell DNA by phagolysosomal DNase2a activate a DNA-PKcs-mTORC2/Rictor pathway that increases Myc to promote non-inflammatory macrophage proliferation. Efferocytosis-induced proliferation expands the pool of resolving macrophages in vitro and in mice, including zymosan-induced peritonitis, dexamethasone-induced thymocyte apoptosis, and atherosclerosis regression. In the dexamethasone-thymus model, hematopoietic Rictor deletion blocked efferocytosing macrophage proliferation, apoptotic cell clearance, and tissue resolution. In atherosclerosis regression, silencing macrophage Rictor or DNase2a blocked efferocyte proliferation, apoptotic cell clearance, and plaque stabilization. In view of previous work showing that other types of apoptotic cell cargo can promote resolution in individual efferocytosing macrophages, the findings here suggest that signaling-triggered apoptotic cell-derived nucleotides can amplify this benefit by increasing the number of these macrophages.

Xinnaokang improves cecal microbiota and lipid metabolism to target atherosclerosis

This study aims to explore the potential mechanisms of Xinnaokang in atherosclerosis treatment. Firstly, the active components of Xinnaokang were analysed by HPLC, which contains ginsenoside Rg1, puerarin, tanshinone, notoginsenoside R1, ammonium glycyrrhizate and glycyrrhizin. Network pharmacology analysis showed there were 145 common targets of Xinnaokang, including the chemical stress, lipid metabolite, lipopolysaccharide, molecules of bacterial origin, nuclear receptor and fluid shear stress pathways. Then, the animal experiment showed that Xinnaokang reduced the body weight and blood lipid levels of atherosclerotic mice. Vascular plaque formation was increased in atherosclerotic mice, which was markedly reversed by Xinnaokang. In addition, Xinnaokang reduced CAV-1 expression and increased ABCA1, SREBP-1 and LXR expressions in the vasculature. Xinnaokang promoted SREBP-2 and LDLR expressions in the liver but decreased IDOL and PCSK9 expressions, indicating that Xinnaokang regulated lipid transport-related protein expression. Cecal microbiota diversity was reduced in atherosclerotic mice but increased after Xinnaokang treatment. Xinnaokang treatment also improved gut microbiota communities by enriching Actinobacteria, Bifidobacteriales and Bifidobacteriaceae abundances. Metabolic profile showed that Xinnaokang significantly reduced homogentisate, phenylacetylglycine, alanine and methionine expressions in the liver of atherosclerotic mice. Xinnaokang effectively alleviated atherosclerosis, and this effect might be linked with the altered features of the liver metabolite profiles and cecal microbiota.

Cardiovascular disease in diabetes, beyond glucose

Despite the decades-old knowledge that diabetes mellitus is a major risk factor for cardiovascular disease, the reasons for this association are only partially understood. While this association is true for both type 1 and type 2 diabetes, different pathophysiological processes may be responsible. Lipids and other risk factors are indeed important, whereas the role of glucose is less clear. This lack of clarity stems from clinical trials that do not unambiguously show that intensive glycemic control reduces cardiovascular events. Animal models have provided mechanisms that link diabetes to increased atherosclerosis, and evidence consistent with the importance of factors beyond hyperglycemia has emerged. We review clinical, pathological, and animal studies exploring the pathogenesis of atherosclerosis in humans living with diabetes and in mouse models of diabetes. An increased effort to identify risk factors beyond glucose is now needed to prevent the increased cardiovascular disease risk associated with diabetes.

Reduction of TMAO level enhances the stability of carotid atherosclerotic plaque through promoting macrophage M2 polarization and efferocytosis

It has been demonstrated that trimethylamine N-oxide (TMAO) serves as a driver of atherosclerosis, suggesting that reduction of TMAO level might be a potent method to prevent the progression of atherosclerosis. Herein, we explored the role of TMAO in the stability of carotid atherosclerotic plaques and disclosed the underlying mechanisms. The unstable carotid artery plaque models were established in C57/BL6 mice. L-carnitine (LCA) and methimazole (MMI) administration were applied to increase and reduce TMAO levels. Hematoxylin and eosin (H&E) staining, Sirius red, Perl's staining, Masson trichrome staining and immunohistochemical staining with CD68 staining were used for histopathology analysis of the carotid artery plaque. M1 and M2 macrophagocyte markers were assessed by RT-PCR to determine the polarization of RAW264.7 cells. MMI administration for 2 weeks significantly decreased the plaque area, increased the thickness of the fibrous cap and reduced the size of the necrotic lipid cores, whereas 5-week of administration of MMI induced intraplate hemorrhage. LCA treatment further deteriorated the carotid atherosclerotic plaque but with no significant difference. In mechanism, we found that TMAO treatment impaired the M2 polarization and efferocytosis of RAW264.7 cells with no obvious effect on the M1 polarization. In conclusion, the present study demonstrated that TMAO reduction enhanced the stability of carotid atherosclerotic plaque through promoting macrophage M2 polarization and efferocytosis.

Changes in the profile of circulating HDL subfractions in severe obese adolescents following a weight reduction program

BACKGROUND AND AIMS

Epidemiological studies show that obese adolescents are candidates to suffer cardiovascular pathologies in adulthood. In order to detect subfractions with a diagnostic value for future cardiovascular disorders, we analyzed the complete lipoprotein profile of severely obese adolescents.

METHODS AND RESULTS

Twenty-eight obese adolescents free from comorbidities were admitted into a weight reduction program. Anthropometric parameters were monitored. The circulating lipoproteins and glycemia were measured at the beginning and at the end of the study by conventional blood analysis as well as by using lipoprotein electrophoresis. Twenty-one puberty-matched normal-weight adolescents were recruited as controls. After 4 months, participants improved anthropometric parameters. Blood analysis indicated that circulating lipoproteins were in the healthy range during intervention. Nevertheless, results obtained from lipoprotein electrophoresis showed a significant increase in the large high-density lipoprotein subfraction in the obese population at the end of intervention, but significantly lower than normal-weight counterparts. In addition, intermediate- and low-density lipoprotein subfractions were in the healthy range in controls and in obese adolescents during intervention.

CONCLUSIONS

Altogether, it seems that the obese adolescents with no comorbidities do not develop a clear dyslipidemia. However, low values of large high-density lipoprotein subfractions could be considered as candidate predictors to develop cardiovascular disease in the future. For this reason, diet and exercise are key tools to fight against this pathology.

REGISTRATION NUMBER FOR CLINICAL TRIALS

ISRCTN99414527.

Reshaping of the gastrointestinal microbiome alters atherosclerotic plaque inflammation resolution in mice

Since alterations in the intestinal microbiota may induce systemic inflammation and polarization of macrophages to the M1 state, the microbiome role in atherosclerosis, an M1-driven disease, requires evaluation. We aimed to determine if antibiotic (Abx) induced alterations to the intestinal microbiota interferes with atherosclerotic plaque inflammation resolution after lipid-lowering in mice. Hyperlipidemic Apoe^−/− mice were fed a western diet to develop aortic atherosclerosis with aortas then transplanted into normolipidemic wild-type (WT) mice to model clinically aggressive lipid management and promote atherosclerosis inflammation resolution. Gut microbial composition pre and post-transplant was altered via an enteral antibiotic or not. Post aortic transplant, after Abx treatment, while plaque size did not differ, compared to Apoe^−/− mice, Abx^– WT recipient mice had a 32% reduction in CD68-expressing cells (p = 0.02) vs. a non-significant 12% reduction in Abx⁺ WT mice. A trend toward an M1 plaque CD68-expresing cell phenotype was noted in Abx⁺ mice. By 16S rRNA sequence analysis, the Abx⁺ mice had reduced alpha diversity and increased Firmicutes/Bacteroidetes relative abundance ratio with a correlation between gut Firmicutes abundance and plaque CD68-expressing cell content (p < 0.05). These results indicate that in a murine atherosclerotic plaque inflammation resolution model, antibiotic-induced microbiome perturbation may blunt the effectiveness of lipid-lowering to reduce the content of plaque inflammatory CD68-expressing cells.

Inducible phospholipid transfer protein deficiency ameliorates atherosclerosis

BACKGROUND AND AIMS

Atherosclerosis progression and regression studies are related to its prevention and treatment. Although we have gained extensive knowledge on germline phospholipid transfer protein (PLTP) deficiency, the effect of inducible PLTP deficiency in atherosclerosis remains unexplored.

METHODS

We generated inducible PLTP (iPLTP)-knockout (KO) mice and measured their plasma lipid levels after feeding a normal chow or a Western-type diet. Adenovirus associated virus-proprotein convertase subtilisin/kexin type 9 (AAV-PCSK9) was used to induce hypercholesterolemia in the mice. Collars were placed around the common carotid arteries, and atherosclerosis progression and regression in the carotid arteries and aortic roots were evaluated.

RESULTS

On a normal chow diet, iPLTP-KO mice exhibited decreased cholesterol, phospholipid, apoA-I, and apoB levels compared with control mice. Furthermore, the overall amount of high-density lipoprotein (HDL) particles was reduced in these mice, but this effect was more profound for larger HDL particles. On a Western-type diet, iPLTP-KO mice again exhibited reduced levels of all tested lipids, even though the basal lipid levels were increased. Additionally, these mice displayed significantly reduced atherosclerotic plaque sizes with increased plaque stability. Importantly, inducible PLTP deficiency significantly ameliorated atherosclerosis by reducing the size of established plaques and the number of macrophages in the plaques without causing lipid accumulation in the liver.

CONCLUSIONS

Induced PLTP deficiency in adult mice reduces plasma total cholesterol and triglycerides, prevents atherosclerosis progression, and promotes atherosclerosis regression. Thus, PLTP inhibition is a promising therapeutic approach for atherosclerosis.

A new activator of esterase D decreases blood cholesterol level through ESD/JAB1/ABCA1 pathway

Excessively high cholesterol content in the blood leads to nonalcohol fatty liver disease (NAFLD) and arteriosclerosis. Although there are increasing publications and patent applications to lower blood cholesterol with small chemical molecules, limited effective drugs can be available in clinic. It is necessary to uncover new targets and drugs to alleviate high cholesterol. Esterase D (ESD) is abundant in liver and it remains unknown about its role in cholesterol metabolism. Here we reported that small chemical molecule fluorescigenic pyrazoline derivative 5 (FPD5), a new ESD activator, could effectively reverse high blood cholesterol level and prevent fatty liver and arteriosclerosis in apoE^-/- mice fed the high-fat diet. We also observed that FPD5 could reduce oxidized low density lipoprotein (oxLDL)-induced formation of foam cells. To further investigate the mechanism of FPD5 action on blood cholesterol modulation, we found that ESD trigged by FPD5 was aggregated in lysosome and interacted with Jun activation domain binding protein 1 (JAB1). ESD served as a deacetylase to remove Thr89 acetylation of JAB1 and increased its activity; thus, promoting the ATP-binding cassette transporters A1 (ABCA1) to accelerate cholesterol efflux. Our findings demonstrate that FPD5 decreases blood cholesterol level to ameliorate NAFLD and arteriosclerosis through ESD/JAB1/ABCA1 pathway, and ESD functions as a novel nonclassical deacetylase that hydrolyzes serine/threonine acetyl group. Our findings not only highlight that FPD5 may be a pioneer drug for alleviating blood cholesterol but also indicate that ESD is a potential drug target that promotes cholesterol metabolism.

Atherosclerosis: Making a U Turn

The development of potent cholesterol-reducing medications in the last decade of the twentieth century has altered the approach to prevention and treatment of cardiovascular disease (CVD). Initial experience with statins, and more recently with the addition of PCSK9 inhibitors, has proven that human CVD, like that in animal models, can be halted and regressed. Available clinical data show that the lower the achieved level of low-density lipoprotein cholesterol, the greater the regression of disease. Investigative studies are now aimed to understand those factors that both accelerate and impede this healing process. Some of these are likely to be modifiable, and the future of atherosclerotic CVD treatment is likely to be early screening, use of measures to repair atherosclerotic arteries, and prevention of most CVD events.

GSK3 modulation in acute lung injury, myocarditis and polycystic kidney disease-related aneurysm

GSK3 are involved in different physical and pathological conditions and inflammatory regulated by macrophages contribute to significant mechanism. Infection stimuli may modulate GSK3 activity and influence host cell adaption, immune cells infiltration or cytokine expressions. To further address the role of GSK3 modulation in macrophages, the signal transduction of three major organs challenged by endotoxin, virus and genetic inherited factors are briefly introduced (lung injury, myocarditis and autosomal dominant polycystic kidney disease). As a result of pro-inflammatory and anti-inflammatory functions of GSK3 in different microenvironments and stages of macrophages (M1/M2), the rational resolution should be considered by adequately GSK3.

Regression of Atherosclerosis in ApoE-/- Mice Via Modulation of Monocyte Recruitment and Phenotype, Induced by Weekly Dosing of a Novel "Cytotopic" Anti-Thrombin Without Prolonged Anticoagulation

Background Anticoagulants induce atherosclerosis regression in animal models but exploiting this clinically is limited by bleeding events. Here we test a novel thrombin inhibitor, PTL060, comprising hirulog covalently linked to a synthetic myristoyl electrostatic switch to tether to cell membranes. Methods and Results ApoE-/- mice were fed chow or high-fat diets, before transplantation of congenic aortic segments or injection of PTL060, parental hirulog, control saline, or labeled CD11b positive cells. Aortic transplants from transgenic mice expressing anticoagulants on endothelium did not develop atherosclerosis. A single intravenous injection of PTL060, but not hirulog inhibited atheroma development by >50% compared with controls when assessed 4 weeks later. Mice had prolonged bleeding times for only one seventh of the time that PTL060 was biologically active. Repeated weekly injections of PTL060 but not hirulog caused regression of atheroma. We dissected 2 contributory mechanisms. First, the majority of CCR2+ (C-C chemokine receptor type 2+) monocytes recruited into plaques expressed CCR7 (C-C chemokine receptor type 7), ABCA1 (ATP-binding cassette transporter - 1), and interleukin-10 in PTL060 mice, a phenotype seen in <20% of CCR2+ recruits in controls. Second, after several doses, there was a significant reduction in monocyte recruits, the majority of which were CCR2-negative with a similar regression-associated phenotype. Regression equivalent to that induced by intravenous PTL060 was induced by adoptive transfer of CD11b+ cells pre-coated with PTL060. Conclusions Covalent linkage of a myristoyl electrostatic switch onto hirulog in PTL060 uncouples the pharmacodynamic effects on hemostasis and atherosclerosis, such that plaque regression, mediated predominantly via effects on monocytes, is accompanied by only transient anticoagulation.

Atheroprotective and atheroregressive potential of azapeptide derivatives of GHRP-6 as selective CD36 ligands in apolipoprotein E-deficient mice

BACKGROUND AND AIMS

Scavenger receptor class B member 3, also known as cluster of differentiation-36 (CD36) receptor, is involved in the uptake and accumulation of modified lipoprotein in macrophages, driving atherosclerosis progression. Azapeptide analogs of growth hormone-releasing peptide-6 (GHRP-6) have been developed as selective CD36 ligands and evaluated for their anti-atherosclerotic properties in apoe^-/- mice.

METHODS

From 4 to 19 weeks of age, male apoe^-/- mice were fed a high fat high cholesterol (HFHC) diet, then switched to normal chow and treated daily with 300 nmol/kg of MPE-001 ([aza-Tyr⁴]-GHRP-6) or MPE-003 ([aza-(N,N-diallylaminobut-2-ynyl)Gly⁴]-GHRP-6) for 9 weeks. In another protocol, mice were fed a HFHC diet throughout the study.

RESULTS

Azapeptides decreased lesion progression in the aortic arch and reduced aortic sinus lesion areas below pre-existing lesions levels in apoe^-/- mice which were switched to chow diet. In mice fed a HFHC throughout the study, azapeptides reduced lesion progression in the aortic vessel and sinus. The anti-atherosclerotic effect of azapeptides was associated with a reduced ratio of iNOS⁺/CD206⁺ macrophages within lesions, and lowered plasma inflammatory cytokine levels. Monocytes from azapeptide-treated mice showed altered mitochondrial oxygen consumption rates, consistent with an M2-like phenotype. These effects were dependent on CD36, and not observed in apoe^-/-cd36^-/- mice.

CONCLUSIONS

Azapeptides MPE-001 and MPE-003 diminished aortic lesion progression and reduced, below pre-existing levels, lesions in the aortic sinus of atherosclerotic mice. A relative increase of M2-like macrophages was observed in lesions, associated with reduced systemic inflammation. Development of CD36-selective azapeptide ligands merits consideration for treating atherosclerotic disease.

Strategies to alter the trajectory of atherosclerotic cardiovascular disease

PURPOSE OF REVIEW

Cardiovascular disease prevention trials of lipid lowering with statins have shown unexpected long-term benefits after the formal randomized treatment stopped. This finding needs further exploration because it raises the possibility that the trajectory of the disease can be modified.

RECENT FINDINGS

Extended follow up data are now available from further major primary prevention studies and from meta-analyses of the legacy effect of statin trials. New outcome studies have been proposed and launched to test the ability of early intervention to slow or regress atherosclerosis.

SUMMARY

Legacy effects are apparent in trials of LDL lowering in hypercholesterolemic and hypertensive patient cohorts. Over follow up periods of decades, both cardiovascular mortality and all-cause mortality are reduced in individuals who received 3 to 5 years of statin therapy. The phenomenon is observed also in studies of intensive glycemic control suggesting that it is possible to impact plaque development with long-term beneficial consequences. Novel strategies for primary prevention are being devised that include the early use of both prolonged-moderate and short-term aggressive LDL lowering.

Human amnion mesenchymal stem cells attenuate atherosclerosis by modulating macrophage function to reduce immune response

Mesenchymal stem cells (MSCs) show immunosuppressive activities and alleviate atherosclerosis (AS) formation in apolipoprotein E-knockout (apoE-KO) mice. Human amnion mesenchymal stem cells (hAMSCs), a particular population of mesenchymal stem cells, have been shown to have immunomodulatory abilities. The present study investigated the effects of hAMSCs treatment on early atherosclerotic plaque formation and the progression of established lesion in apoE-KO mice. In total, 36 mice were fed with a high-fat diet. Mice were subjected to hAMSCs-injection treatment simultaneously with high-fat diet (early treatment) or after 8 weeks of high-fat diet (delayed treatment). In each treatment, mice were divided into three groups: i) hAMSCs group with hAMSCs treatment; ii) PBS group injected with PBS; and iii) control group without injection. Histological results showed that the plaque area in the aortic arch of mice was significantly reduced after hAMSCs treatment in the early and delayed treatment groups. In addition, immunohistochemical analysis suggested that the accumulation of macrophages was significantly decreased after hAMSCs treatment. Similarly, the release of the pro-inflammatory cytokine tumor necrosis factor-α was also decreased, whereas the release of the anti-inflammatory cytokine interleukin-10 was increased. In addition, hAMSCs treatment suppressed the phosphorylation of p65 and inhibitor of κB-α, suggesting that NF-κB pathway was involved in the hAMSCs-mediated suppression of immune response. In conclusion, hAMSCs treatment was effective in reducing immune response, which is the one of the major causes of AS, eventually leading to a significant reduction in size of athero-sclerotic lesions.

Akt Signaling in Macrophage Polarization, Survival, and Atherosclerosis

The PI3K/Akt pathway plays a crucial role in the survival, proliferation, and migration of macrophages, which may impact the development of atherosclerosis. Changes in Akt isoforms or modulation of the Akt activity levels in macrophages significantly affect their polarization phenotype and consequently atherosclerosis in mice. Moreover, the activity levels of Akt signaling determine the viability of monocytes/macrophages and their resistance to pro-apoptotic stimuli in atherosclerotic lesions. Therefore, elimination of pro-apoptotic factors as well as factors that antagonize or suppress Akt signaling in macrophages increases cell viability, protecting them from apoptosis, and this markedly accelerates atherosclerosis in mice. In contrast, inhibition of Akt signaling by the ablation of Rictor in myeloid cells, which disrupts mTORC2 assembly, significantly decreases the viability and proliferation of blood monocytes and macrophages with the suppression of atherosclerosis. In addition, monocytes and macrophages exhibit a threshold effect for Akt protein levels in their ability to survive. Ablation of two Akt isoforms, preserving only a single Akt isoform in myeloid cells, markedly compromises monocyte and macrophage viability, inducing monocytopenia and diminishing early atherosclerosis. These recent advances in our understanding of Akt signaling in macrophages in atherosclerosis may have significant relevance in the burgeoning field of cardio-oncology, where PI3K/Akt inhibitors being tested in cancer patients can have significant cardiovascular and metabolic ramifications.

Sortilin promotes macrophage cholesterol accumulation and aortic atherosclerosis through lysosomal degradation of ATP-binding cassette transporter A1 protein

Sortilin is closely associated with hyperlipidemia and the risk of atherosclerosis (AS). The role of sortilin and the underlying mechanism in peripheral macrophage are not fully understood. In this study, we investigated the effect of macrophage sortilin on ATP-binding cassette transporter A1 (ABCA1) expression, ABCA1-mediated cholesterol efflux, and aortic AS. Macrophage sortilin expression was upregulated by oxidized low-density lipoproteins (ox-LDLs) in both concentration- and time-dependent manners. Its expression reached the peak level when cells were incubated with 50 μg/ml ox-LDL for 24 h. Overexpression of sortilin in macrophage reduced cholesterol efflux, leading to an increase in intracellular total cholesterol, free cholesterol, and cholesterol ester. Sortilin was found to bind with ABCA1 protein and suppress macrophage ABCA1 expression, resulting in a decrease in cholesterol efflux from macrophages. The inhibitory effect of sortilin in cholesterol efflux was partially reversed by treatment with chloroquine, a lysosomal inhibitor. On the contrary, the ABCA1 protein level and ABCA1-mediated cholesterol efflux is increased by sortilin short hairpin RNA transfection. The fecal and biliary cholesterol 3H-sterol from cholesterol-laden mouse peritoneal macrophage was reduced by sortilin overexpression through lentivirus vector (LV)-sortilin in low-density lipoprotein receptor knockout mice, which was prevented by co-treatment with chloroquine. Treatment with LV-sortilin reduced plasma high-density lipoprotein and increased plasma ox-LDL levels. Accordingly, aortic lipid deposition and plaque area were exacerbated, and ABCA1 expression was reduced in mice in response to infection with LV-sortilin alone. These effects of LV-sortilin were partially reversed by chloroquine. Sortilin enhances lysosomal degradation of ABCA1 protein and suppresses ABCA1-mediated cholesterol efflux from macrophages, leading to foam cell formation and AS development.

Specialized Pro-resolving Lipid Mediators: Modulation of Diabetes-Associated Cardio-, Reno-, and Retino-Vascular Complications

Diabetes and its associated chronic complications present a healthcare challenge on a global scale. Despite improvements in the management of chronic complications of the micro-/macro-vasculature, their growing prevalence and incidence highlights the scale of the problem. It is currently estimated that diabetes affects 425 million people globally and it is anticipated that this figure will rise by 2025 to 700 million people. The vascular complications of diabetes including diabetes-associated atherosclerosis and kidney disease present a particular challenge. Diabetes is the leading cause of end stage renal disease, reflecting fibrosis leading to organ failure. Moreover, diabetes associated states of inflammation, neo-vascularization, apoptosis and hypercoagulability contribute to also exacerbate atherosclerosis, from the metabolic syndrome to advanced disease, plaque rupture and coronary thrombosis. Current therapeutic interventions focus on regulating blood glucose, glomerular and peripheral hypertension and can at best slow the progression of diabetes complications. Recently advanced knowledge of the pathogenesis underlying diabetes and associated complications revealed common mechanisms, including the inflammatory response, insulin resistance and hyperglycemia. The major role that inflammation plays in many chronic diseases has led to the development of new strategies aiming to promote the restoration of homeostasis through the "resolution of inflammation." These strategies aim to mimic the spontaneous activities of the 'specialized pro-resolving mediators' (SPMs), including endogenous molecules and their synthetic mimetics. This review aims to discuss the effect of SPMs [with particular attention to lipoxins (LXs) and resolvins (Rvs)] on inflammatory responses in a series of experimental models, as well as evidence from human studies, in the context of cardio- and reno-vascular diabetic complications, with a brief mention to diabetic retinopathy (DR). These data collectively support the hypothesis that endogenously generated SPMs or synthetic mimetics of their activities may represent lead molecules in a new discipline, namely the 'resolution pharmacology,' offering hope for new therapeutic strategies to prevent and treat, specifically, diabetes-associated atherosclerosis, nephropathy and retinopathy.

Targeting Inflammation With Nanosized Drug Delivery Platforms in Cardiovascular Diseases: Immune Cell Modulation in Atherosclerosis

Atherosclerosis (AS) is a disorder of large and medium-sized arteries; it consists in the formation of lipid-rich plaques in the intima and inner media, whose pathophysiology is mostly driven by inflammation. Currently available interventions and therapies for treating atherosclerosis are not always completely effective; side effects associated with treatments, mainly caused by immunodepression for anti-inflammatory molecules, limit the systemic administration of these and other drugs. Given the high degree of freedom in the design of nanoconstructs, in the last decades researchers have put high effort in the development of nanoparticles (NPs) formulations specifically designed for either drug delivery, visualization of atherosclerotic plaques, or possibly the combination of both these and other functionalities. Here we will present the state of the art of these subjects, the knowledge of which is necessary to rationally address the use of NPs for prevention, diagnosis, and/or treatment of AS. We will analyse the work that has been done on: (a) understanding the role of the immune system and inflammation in cardiovascular diseases, (b) the pathological and biochemical principles in atherosclerotic plaque formation, (c) the latest advances in the use of NPs for the recognition and treatment of cardiovascular diseases, (d) the cellular and animal models useful to study the interactions of NPs with the immune system cells.

Deletion of Macrophage Low-Density Lipoprotein Receptor-Related Protein 1 (LRP1) Accelerates Atherosclerosis Regression and Increases C-C Chemokine Receptor Type 7 (CCR7) Expression in Plaque Macrophages

BACKGROUND

We previously showed that mice lacking MΦLRP1-/- (low-density lipoprotein receptor-related protein 1 in macrophages) undergo accelerated atherosclerotic plaque formation due to changes in macrophages including increased apoptosis, decreased efferocytosis, and exaggerated transition to the inflammatory M1 phenotype. Here we sought to explore the role of macrophage low-density lipoprotein receptor-related protein 1 during regression of atherosclerosis since regressing plaques are characterized by transitioning of macrophages to M2 status as inflammation resolves.

METHODS

Apolipoprotein E-/- mice on a high-fat diet for 12 weeks were reconstituted with bone marrow from apolipoprotein E-producing wild-type or MΦLRP1-/- mice, and then placed on a chow diet for 10 weeks (n=9 to 11 mice/group). A cohort of apolipoprotein E-/- mice reconstituted with apolipoprotein E-/- bone marrow served as baseline controls (n=9).

RESULTS

Plaques of both wild-type and MΦLRP1-/- bone marrow recipients regressed compared with controls (11% and 22%, respectively; P<0.05), and plaques of MΦLRP1-/- recipients were 13% smaller than those of wild-type recipients ( P<0.05). Recipients of MΦLRP1-/- marrow had 36% fewer M1 macrophages ( P<0.01) and 2.5-fold more CCR7 (C-C chemokine receptor type 7)-positive macrophages in the plaque relative to wild-type mice ( P<0.01). Additionally, in vivo studies of cellular egress showed a 4.6-fold increase in 5-ethynyl-2´-deoxyuridine-labeled CCR7+ macrophages in mediastinal lymph nodes. Finally, in vivo studies of reverse cholesterol transport showed a 1.4-fold higher reverse cholesterol transport in MΦLRP1-/- recipient mice ( P<0.01).

CONCLUSIONS

Absence of macrophage low-density lipoprotein receptor-related protein 1 unexpectedly accelerates atherosclerosis regression, enhances reverse cholesterol transport, and increases expression of the motility receptor CCR7, which drives macrophage egress from lesions.

Liver X Receptor Nuclear Receptors Are Transcriptional Regulators of Dendritic Cell Chemotaxis

The liver X receptors (LXRs) are ligand-activated nuclear receptors with established roles in the maintenance of lipid homeostasis in multiple tissues. LXRs exert additional biological functions as negative regulators of inflammation, particularly in macrophages. However, the transcriptional responses controlled by LXRs in other myeloid cells, such as dendritic cells (DCs), are still poorly understood. Here we used gain- and loss-of-function models to characterize the impact of LXR deficiency on DC activation programs. Our results identified an LXR-dependent pathway that is important for DC chemotaxis. LXR-deficient mature DCs are defective in stimulus-induced migration in vitro and in vivo Mechanistically, we show that LXRs facilitate DC chemotactic signaling by regulating the expression of CD38, an ectoenzyme important for leukocyte trafficking. Pharmacological or genetic inactivation of CD38 activity abolished the LXR-dependent induction of DC chemotaxis. Using the low-density lipoprotein receptor-deficient (LDLR^-/-) LDLR^-/- mouse model of atherosclerosis, we also demonstrated that hematopoietic CD38 expression is important for the accumulation of lipid-laden myeloid cells in lesions, suggesting that CD38 is a key factor in leukocyte migration during atherogenesis. Collectively, our results demonstrate that LXRs are required for the efficient emigration of DCs in response to chemotactic signals during inflammation.

The Ins and Outs of Myeloid Cells in Atherosclerosis

Atherosclerosis is a chronic inflammation of the arterial vessel wall that arises from an imbalanced lipid metabolism. A growing body of literature describes leukocyte recruitment as a critical step in the initiation and progression of lesion development. By contrast, the role of leukocytes during plaque regression has been described in less detail. Leukocyte egress might be an important step to resolving chronic inflammation and therefore it may be a promising target for limiting advanced lesion development. This review aims to summarize our current knowledge of leukocyte recruitment to the arterial vessel wall. We will discuss mechanisms of leukocyte egress from the lesion site, as well as potential therapeutic strategies to promote atherosclerotic regression.

2017 George Lyman Duff Memorial Lecture: Fat in the Blood, Fat in the Artery, Fat in the Heart: Triglyceride in Physiology and Disease

Cholesterol is not the only lipid that causes heart disease. Triglyceride supplies the heart and skeletal muscles with highly efficient fuel and allows for the storage of excess calories in adipose tissue. Failure to transport, acquire, and use triglyceride leads to energy deficiency and even death. However, overabundance of triglyceride can damage and impair tissues. Circulating lipoprotein-associated triglycerides are lipolyzed by lipoprotein lipase (LpL) and hepatic triglyceride lipase. We inhibited these enzymes and showed that LpL inhibition reduces high-density lipoprotein cholesterol by >50%, and hepatic triglyceride lipase inhibition shifts low-density lipoprotein to larger, more buoyant particles. Genetic variations that reduce LpL activity correlate with increased cardiovascular risk. In contrast, macrophage LpL deficiency reduces macrophage function and atherosclerosis. Therefore, muscle and macrophage LpL have opposite effects on atherosclerosis. With models of atherosclerosis regression that we used to study diabetes mellitus, we are now examining whether triglyceride-rich lipoproteins or their hydrolysis by LpL affect the biology of established plaques. Following our focus on triglyceride metabolism led us to show that heart-specific LpL hydrolysis of triglyceride allows optimal supply of fatty acids to the heart. In contrast, cardiomyocyte LpL overexpression and excess lipid uptake cause lipotoxic heart failure. We are now studying whether interrupting pathways for lipid uptake might prevent or treat some forms of heart failure.

Studying the effect of systemic and biological drugs on intima-media thickness in patients suffering from moderate and severe psoriasis

BACKGROUND

Psoriasis has been related to a large number of cardiovascular risk factors such as hypertension, diabetes mellitus and arteriosclerosis. The increased carotid intima-media thickness (IMT) could be considered to be a marker of generalized arteriosclerosis.

OBJECTIVE

To assess the effect of systemic and biological drugs on psoriatic patients' carotid IMT.

METHODS

A prospective study was performed. We studied 53 patients with moderate and severe psoriasis from our psoriasis dermatological unit, analysing lipid and glucose metabolism and performing a carotid IMT sonography before introduction of systemic and biological drugs. After that, we performed an 8-month closely analytic and sonographic follow-up.

RESULTS

The IMT of the patients with psoriasis treated with biological drugs tended to decrease, although this occurrence was not statistically significant (P = 0.086). The subgroup analysis revealed that patients treated with methotrexate (P = 0.045) and anti-IL-12/23 (P = 0.010) presented a decrease in their IMT levels. This analysis also showed a decrease in glycaemia and insulin levels in patients treated with TNF-alpha inhibitors and ustekinumab.

CONCLUSIONS

Our study suggests that the carotid IMT may benefit from treatment with biological drugs, particularly anti-IL-12/23 and methotrexate in patients suffering from moderate and severe psoriasis. However, larger longitudinal studies should be performed to fully confirm these results.

Novel Reversible Model of Atherosclerosis and Regression Using Oligonucleotide Regulation of the LDL Receptor

RATIONALE

Animal models have been used to explore factors that regulate atherosclerosis. More recently, they have been used to study the factors that promote loss of macrophages and reduction in lesion size after lowering of plasma cholesterol levels. However, current animal models of atherosclerosis regression require challenging surgeries, time-consuming breeding strategies, and methods that block liver lipoprotein secretion.

OBJECTIVE

We sought to develop a more direct or time-effective method to create and then reverse hypercholesterolemia and atherosclerosis via transient knockdown of the hepatic LDLR (low-density lipoprotein receptor) followed by its rapid restoration.

METHODS AND RESULTS

We used antisense oligonucleotides directed to LDLR mRNA to create hypercholesterolemia in wild-type C57BL/6 mice fed an atherogenic diet. This led to the development of lesions in the aortic root, aortic arch, and brachiocephalic artery. Use of a sense oligonucleotide replicating the targeted sequence region of the LDLR mRNA rapidly reduced circulating cholesterol levels because of recovery of hepatic LDLR expression. This led to a decrease in macrophages within the aortic root plaques and brachiocephalic artery, that is, regression of inflammatory cell content, after a period of 2 to 3 weeks.

CONCLUSIONS

We have developed an inducible and reversible hepatic LDLR knockdown mouse model of atherosclerosis regression. Although cholesterol reduction decreased early en face lesions in the aortic arches, macrophage area was reduced in both early and late lesions within the aortic sinus after reversal of hypercholesterolemia. Our model circumvents many of the challenges associated with current mouse models of regression. The use of this technology will potentially expedite studies of atherosclerosis and regression without use of mice with genetic defects in lipid metabolism.

Heat shock protein 27-derived atheroprotection involves reverse cholesterol transport that is dependent on GM-CSF to maintain ABCA1 and ABCG1 expression in ApoE-/- mice

Recently, we demonstrated that heat shock protein (HSP)-27 is protective against the development of experimental atherosclerosis, reducing plaque cholesterol content by more than 30%. Moreover, elevated HSP-27 levels are predictive of relative freedom from clinical cardiovascular events. HSP-27 signaling occurs via the activation of NF-κB, which induces a marked up-regulation in expression of granulocyte-monocyte colony-stimulating factor (GM-CSF), a cytokine that is known to alter ABC transporters involved in reverse cholesterol transport (RCT). Therefore, we hypothesized that HSP-27-derived GM-CSF has a potent role in impeding plaque formation by promoting macrophage RCT and sought to better characterize this pathway. Treatment of THP-1 cells, RAW-Blue cells, and primary macrophages with recombinant HSP-27 resulted in NF-κB activation via TLR-4 and was inhibited by various pharmacologic blockers of this pathway. Moreover, HSP-27-induced upregulation of GM-CSF expression was dependent on TLR-4 signaling. Recombinant (r)HSP-27 treatment of ApoE^-/- female (but not male) mice for 4 wk yielded reductions in plaque area and cholesterol clefts of 33 and 47%, respectively, with no effect on GM-CSF^-/-ApoE^-/- mice. With 12 wk of rHSP-27 treatment, both female and male mice showed reductions in plaque burden (55 and 42%, respectively) and a 60% reduction in necrotic core area but no treatment effect in GM-CSF^-/-ApoE^-/- mice. In vitro functional studies revealed that HSP-27 enhanced the expression of ABCA1 and ABCG1, as well as facilitated cholesterol efflux in vitro by ∼10%. These novel findings establish a paradigm for HSP-27-mediated RCT and set the stage for the development of HSP-27 atheroprotective therapeutics.-Pulakazhi Venu, V. K., Adijiang, A., Seibert, T., Chen, Y.-X., Shi, C., Batulan, Z., O'Brien, E. R. Heat shock protein 27-derived atheroprotection involves reverse cholesterol transport that is dependent on GM-CSF to maintain ABCA1 and ABCG1 expression in ApoE^-/- mice.

Macrophages in vascular inflammation and atherosclerosis

Atherosclerosis is characterized by lipid accumulation and chronic inflammation of the arterial wall, and its main complications-myocardial infarction and ischemic stroke-together constitute the first cause of death worldwide. Accumulation of lipid-laden macrophage foam cells in the intima of inflamed arteries has long been recognized as a hallmark of atherosclerosis. However, in recent years, an unexpected complexity in the mechanisms of macrophage accumulation in lesions, in the protective and pathogenic functions performed by macrophages and how they are regulated has been uncovered. Here, we provide an overview of the latest developments regarding the various mechanisms of macrophage accumulation in lesion, the major functional features of lesion macrophages, and how the plaque microenvironment may affect macrophage phenotype. Finally, we discuss how best to apprehend the heterogeneous ontogeny and functionality of atherosclerotic plaque macrophages and argue that moving away from a rigid nomenclature of arbitrarily defined macrophage subsets would be beneficial for research in the field.

2016 Russell Ross Memorial Lecture in Vascular Biology: Molecular-Cellular Mechanisms in the Progression of Atherosclerosis

Atherosclerosis is initiated by the subendothelial accumulation of apoB-lipoproteins, which initiates a sterile inflammatory response dominated by monocyte-macrophages but including all classes of innate and adaptive immune cells. These inflammatory cells, together with proliferating smooth muscle cells and extracellular matrix, promote the formation of subendothelial lesions or plaques. In the vast majority of cases, these lesions do not cause serious clinical symptoms, which is due in part to a resolution-repair response that limits tissue damage. However, a deadly minority of lesions progress to the point where they can trigger acute lumenal thrombosis, which may then cause unstable angina, myocardial infarction, sudden cardiac death, or stroke. Many of these clinically dangerous lesions have hallmarks of defective inflammation resolution, including defective clearance of dead cells (efferocytosis), necrosis, a defective scar response, and decreased levels of lipid mediators of the resolution response. Efferocytosis is both an effector arm of the resolution response and an inducer of resolution mediators, and thus its defect in advanced atherosclerosis amplifies plaque progression. Preclinical causation/treatment studies have demonstrated that replacement therapy with exogenously administered resolving mediators can improve lesional efferocytosis and prevent plaque progression. Work in this area has the potential to potentiate the cardiovascular benefits of apoB-lipoprotein-lowering therapy.

Effects of Extracts from Tiaozhi Granule and Its Components on Expression of Scavenger Receptor Class B Type I

Sera from the rats with different drug treatments (atorvastatin, Tiaozhi granule, or its extracts) were collected. LO-2 cells or HepG2 cells were pretreated with different sera as the following groups randomly: (1) blank control group, (2) positive control group (atorvastatin group), (3) Tiaozhi granule water extract groups, (4) Tiaozhi granule alcohol extract groups, and (5) alcohol extracts for each component: Pollen Typhae Angustifoliae, Curcuma longa L., and Rhizoma Alismatis. LO-2 cells were cotransfected with plasmid carrying SR-BI and pRL-TK promoter genes. Promoter activity was measured by the luciferase reporter gene assay. The mRNA and protein expressions of SR-BI were examined using real-time PCR and western blot analyses. Our results show that promoter activity and mRNA and protein expression levels of the SR-BI were significantly upregulated by Tiaozhi granules alcohol or water extracts in a dose-dependent manner. Pollen Typhae Angustifoliae alcohol extract with a high dosage could also increase SR-BI activity and expression, but not the extracts from Curcuma longa L. and Rhizoma Alismatis. Both Tiaozhi granule alcohol and water extracts can upregulate SR-BI gene expression. Among the components, Pollen Typhae Angustifoliae are important for the regulatory effect coordinating with Curcuma longa L. and Rhizoma Alismatis.

Macrophage Apoptosis and Efferocytosis in the Pathogenesis of Atherosclerosis

Macrophage apoptosis and the ability of macrophages to clean up dead cells, a process called efferocytosis, are crucial determinants of atherosclerosis lesion progression and plaque stability. Environmental stressors initiate endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR). Unresolved ER stress with activation of the UPR initiates apoptosis. Macrophages are resistant to apoptotic stimuli, because of activity of the PI3K/Akt pathway. Macrophages express 3 Akt isoforms, Akt1, Akt2 and Akt3, which are products of distinct but homologous genes. Akt displays isoform-specific effects on atherogenesis, which vary with different vascular cell types. Loss of macrophage Akt2 promotes the anti-inflammatory M2 phenotype and reduces atherosclerosis. However, Akt isoforms are redundant with regard to apoptosis. c-Jun NH₂-terminal kinase (JNK) is a pro-apoptotic effector of the UPR, and the JNK1 isoform opposes anti-apoptotic Akt signaling. Loss of JNK1 in hematopoietic cells protects macrophages from apoptosis and accelerates early atherosclerosis. IκB kinase α (IKKα, a member of the serine/threonine protein kinase family) plays an important role in mTORC2-mediated Akt signaling in macrophages, and IKKα deficiency reduces macrophage survival and suppresses early atherosclerosis. Efferocytosis involves the interaction of receptors, bridging molecules, and apoptotic cell ligands. Scavenger receptor class B type I is a critical mediator of macrophage efferocytosis via the Src/PI3K/Rac1 pathway in atherosclerosis. Agonists that resolve inflammation offer promising therapeutic potential to promote efferocytosis and prevent atherosclerotic clinical events. (Circ J 2016; 80: 2259-2268).

Immune-mediated mechanisms of atherosclerosis and implications for the clinic

INTRODUCTION

A large body of evidence supports the inflammatory hypothesis of atherosclerosis, and both innate and adaptive immune responses play important roles in all disease stages. Areas covered: Here, we review our understanding of the role of the immune response in atherosclerosis, focusing on the pathways currently amenable to therapeutic modulation. We also discuss the advantages or undesirable effects that may be foreseen from targeting the immune response in patients at high cardiovascular risk, suggesting new avenues for research. Expert commentary: There is an extraordinary opportunity to directly test the inflammatory hypothesis of atherosclerosis in the clinic using currently available therapeutics. However, a more balanced interpretation of the experimental and translational data is needed, which may help address and identify in more detail the appropriate settings where an immune pathway can be targeted with minimal risk.