Lactadherin deficiency leads to apoptotic cell accumulation and accelerated atherosclerosis in mice

Phytochemical-mediated efferocytosis and autophagy in inflammation control

Efferocytosis, the clearance of apoptotic cells, is a critical process that maintains tissue homeostasis and immune regulation. Defective efferocytosis is linked to the development of chronic inflammatory conditions, including atherosclerosis, neurological disorders, and autoimmune diseases. Moreover, the interplay between autophagy and efferocytosis is crucial for inflammation control, as autophagy enhances the ability of phagocytic cells. Efficient efferocytosis, in turn, regulates autophagic pathways, fostering a balanced cellular environment. Dysregulation of this balance can contribute to the pathogenesis of various disorders. Phytochemicals, bioactive compounds found in plants, have emerged as promising therapeutic agents owing to their diverse pharmacological properties, including antioxidant, anti-inflammatory, and immunomodulatory effects. This review aims to highlight the pivotal role of phytochemicals in enhancing efferocytosis and autophagy and explore their potential in the prevention and treatment of related disorders. This study examines how phytochemicals influence key aspects of efferocytosis, including phagocytic cell activation, macrophage polarization, and autophagy induction. The therapeutic potential of phytochemicals in atherosclerosis and neurological diseases is highlighted, emphasizing their ability to enhance efferocytosis and autophagy and reduce inflammation. This review also discusses innovative approaches, such as nanoformulations and combination therapies to improve the targeting and bioavailability of phytochemicals. Ultimately, this study inspires further research and clinical applications in phytochemical-mediated efferocytosis enhancement for managing chronic inflammatory and autoimmune conditions.

Defective macrophage efferocytosis in advanced atherosclerotic plaque and mitochondrial therapy

Atherosclerosis (AS) is a chronic inflammatory disease primarily affecting large and medium-sized arterial vessels, characterized by lipoprotein disorders, intimal thickening, smooth muscle cell proliferation, and the formation of vulnerable plaques. Macrophages (MΦs) play a vital role in the inflammatory response throughout all stages of atherosclerotic development and are considered significant therapeutic targets. In early lesions, macrophage efferocytosis rapidly eliminates harmful cells. However, impaired efferocytosis in advanced plaques perpetuates the inflammatory microenvironment of AS. Defective efferocytosis has emerged as a key factor in atherosclerotic pathogenesis and the progression to severe cardiovascular disease. Herein, this review probes into investigate the potential mechanisms at the cellular, molecular, and organelle levels underlying defective macrophage efferocytosis in advanced lesion plaques. In the inflammatory microenvironments of AS with interactions among diverse inflammatory immune cells, impaired macrophage efferocytosis is strongly linked to multiple factors, such as a lower absolute number of phagocytes, the aberrant expression of crucial molecules, and impaired mitochondrial energy provision in phagocytes. Thus, focusing on molecular targets to enhance macrophage efferocytosis or targeting mitochondrial therapy to restore macrophage metabolism homeostasis has emerged as a potential strategy to mitigate the progression of advanced atherosclerotic plaque, providing various treatment options.

Efferocytosis in atherosclerosis

Cardiovascular disease is the leading cause of death worldwide, and it commonly results from atherosclerotic plaque progression. One of the increasingly recognized drivers of atherosclerosis is dysfunctional efferocytosis, a homeostatic mechanism responsible for the clearance of dead cells and the resolution of inflammation. In atherosclerosis, the capacity of phagocytes to participate in efferocytosis is hampered, leading to the accumulation of apoptotic and necrotic tissue within the plaque, which results in enlargement of the necrotic core, increased luminal stenosis and plaque inflammation, and predisposition to plaque rupture or erosion. In this Review, we describe the different forms of programmed cell death that can occur in the atherosclerotic plaque and highlight the efferocytic machinery that is normally implicated in cardiovascular physiology. We then discuss the mechanisms by which efferocytosis fails in atherosclerosis and other cardiovascular and cardiometabolic diseases, including myocardial infarction and diabetes mellitus, and discuss therapeutic approaches that might reverse this pathological process.

Vascular smooth muscle cell phenotypic switching in atherosclerosis

Atherosclerosis (AS) is a complex pathology process involving intricate interactions among various cells and biological processes. Vascular smooth muscle cells (VSMCs) are the predominant cell type in normal arteries, and under atherosclerotic stimuli, VSMCs respond to altered blood flow and microenvironment changes by downregulating contractile markers and switching their phenotype. This review overviews the diverse phenotypes of VSMCs, including the canonical contractile VSMCs, synthetic VSMCs, and phenotypes resembling macrophages, foam cells, myofibroblasts, osteoblasts/chondrocytes, and mesenchymal stem cells. We summarize their presumed protective and pro-atherosclerotic roles in AS development. Additionally, we underscore the molecular mechanisms and regulatory pathways governing VSMC phenotypic switching, encompassing transcriptional regulation, biochemical factors, plaque microenvironment, epigenetics, miRNAs, and the cytoskeleton, emphasizing their significance in AS development. Finally, we outline probable future research directions targeting VSMCs, offering insights into potential therapeutic strategies for AS management.

Resveratrol and piceid enhance efferocytosis by increasing the secretion of MFG-E8 in human THP-1 macrophages

The process of apoptotic cell clearance by phagocytes, known as efferocytosis, plays an essential role in maintaining homeostasis. Defects in efferocytosis can lead to inflammatory diseases such as atherosclerosis and autoimmune disorders. Therefore, the maintenance and promotion of efferocytosis are considered crucial for preventing these diseases. In this study, we observed that resveratrol, a representative functional food ingredient, and its glycoside, piceid, promoted efferocytosis in both human THP-1 macrophages differentiated with phorbol 12-myristate 13-acetate and peritoneal macrophages from thioglycolate-elicited mice. Resveratrol and piceid significantly increased mRNA expression and protein secretion of MFG-E8 in THP-1 macrophages. Furthermore, the activation of efferocytosis and the increment in MFG-E8 protein secretion caused by resveratrol or piceid treatment were canceled by MFG-E8 knockdown in THP-1 macrophages. In conclusion, we have demonstrated for the first time that resveratrol and piceid promote efferocytosis through the upregulation of MFG-E8 excretion in human THP-1 macrophages.

TAG-FREE GLYCOSYLATED RHMFG-E8 AS A THERAPY FOR ACUTE KIDNEY INJURY

ABSTRACT

Background: Acute kidney injury (AKI) can result from renal ischemia and reperfusion (I/R) and often occurs during surgical procedures in cardiac, liver, kidney transplantation, and trauma-hemorrhage. Milk fat globule epidermal growth factor-factor VIII (MFG-E8) functions as a bridging molecule to promote the removal of dying cells by professional phagocytes. Because MFG-E8 promotes clearance of apoptotic cells, we have explored its therapeutic potential in various organ injury conditions. To develop human MFG-E8 as a potential therapy, we have generated a human cell-expressed, and thus glycosylated, tag-free recombinant human (rh) MFG-E8 and tested its safety and biological activity in vitro . We hypothesize that the tag-free glycosylated rhMFG-E8 is protective in I/R-induced AKI and it can be developed as an effective therapy for AKI. Methods: To assess the pharmacokinetic properties of the tag-free rhMFG-E8, Sprague-Dawley rats were either untreated or treated with a bolus dose of the tag-free rhMFG-E8, blood collected at various time points and the recovery of human MFG-E8 in the blood were measured by ELISA. Adult male C57BL6 mice underwent bilateral renal ischemia for 30 min, and immediately upon reperfusion, mice were treated intraperitoneally with either normal saline (vehicle) or 20 μg/kg human cell expressed, glycosylated tag-free rhMFG-E8. At either 24 h or 48 h after I/R, blood and kidneys were harvested for further analysis. In separate cohorts of mice after I/R and treatment, mice were observed for 10 days, and survival recorded. Results: AKI rats treated with the tag-free rhMFG-E8 had similar half-life as those in the treated control rats. At 48 h after I/R-induced AKI, renal function markers, blood urea nitrogen, and creatinine were increased and treatment with the tag-free rhMFG-E8 significantly decreased these markers. At both 24 h and 48 h after AKI, inflammatory cytokines, TNF-α, IL-6, and IL-1β were increased and treatment decreased these levels. The kidney mRNA expressions of these cytokines were also increased at 24 h after AKI and treatment significantly decreased those mRNA expressions. Histologically, at 48 h after AKI, tubular damage, and the number of TUNEL staining cells were increased and treatment markedly decreased these measurements. Administration of tag-free rhMFG-E8 at the time of reperfusion improved survival in a 10-day survival study. Conclusion: Our new human cell-expressed tag-free rhMFG-E8 is protective in I/R-induced AKI and it may have the potential to be further developed as a safe and effective therapy for AKI.

Mechanism of efferocytosis in atherosclerosis

Atherosclerosis (AS) is a chronic inflammatory vascular disease that occurs in the intima of large and medium-sized arteries with the immune system's involvement. It is a common pathological basis for high morbidity and mortality of cardiovascular diseases. Abnormal proliferation of apoptotic cells and necrotic cells leads to AS plaque expansion, necrotic core formation, and rupture. In the early stage of AS, macrophages exert an efferocytosis effect to engulf and degrade apoptotic, dead, damaged, or senescent cells by efferocytosis, thus enabling the regulation of the organism. In the early stage of AS, macrophages rely on this effect to slow down the process of AS. However, in the advanced stage of AS, the efferocytosis of macrophages within the plaque is impaired, which leads to the inability of macrophages to promptly remove the apoptotic cells (ACs) from the organism promptly, causing exacerbation of AS. Moreover, upregulation of CD47 expression in AS plaques also protects ACs from phagocytosis by macrophages, resulting in a large amount of residual ACs in the plaque, further expanding the necrotic core. In this review, we discussed the molecular mechanisms involved in the process of efferocytosis and how efferocytosis is impaired and regulated during AS, hoping to provide new insights for treating AS.

Ferroptosis: a potential target for the treatment of atherosclerosis

Atherosclerosis (AS), the main contributor to acute cardiovascular events, such as myocardial infarction and ischemic stroke, is characterized by necrotic core formation and plaque instability induced by cell death. The mechanisms of cell death in AS have recently been identified and elucidated. Ferroptosis, a novel iron-dependent form of cell death, has been proven to participate in atherosclerotic progression by increasing endothelial reactive oxygen species (ROS) levels and lipid peroxidation. Furthermore, accumulated intracellular iron activates various signaling pathways or risk factors for AS, such as abnormal lipid metabolism, oxidative stress, and inflammation, which can eventually lead to the disordered function of macrophages, vascular smooth muscle cells, and vascular endothelial cells. However, the molecular pathways through which ferroptosis affects AS development and progression are not entirely understood. This review systematically summarizes the interactions between AS and ferroptosis and provides a feasible approach for inhibiting AS progression from the perspective of ferroptosis.

Macrophage mediators and mechanisms in cardiovascular disease

Macrophages are major players in myocardial infarction (MI) and atherosclerosis, two major cardiovascular diseases (CVD). Atherosclerosis is caused by the buildup of cholesterol-rich lipoproteins in blood vessels, causing inflammation, vascular injury, and plaque formation. Plaque rupture or erosion can cause thrombus formation resulting in inadequate blood flow to the heart muscle and MI. Inflammation, particularly driven by macrophages, plays a central role in both atherosclerosis and MI. Recent integrative approaches of single-cell analysis-based classifications in both murine and human atherosclerosis as well as experimental MI showed overlap in origin, diversity, and function of macrophages in the aorta and the heart. We here discuss differences and communalities between macrophages in the heart and aorta at steady state and in atherosclerosis or upon MI. We focus on markers, mediators, and functional states of macrophage subpopulations. Recent trials testing anti-inflammatory agents show a major benefit in reducing the inflammatory burden of CVD patients, but highlight a necessity for a broader understanding of immune cell ontogeny and heterogeneity in CVD. The novel insights into macrophage biology in CVD represent exciting opportunities for the development of novel treatment strategies against CVD.

Top Five Stories of the Cellular Landscape and Therapies of Atherosclerosis: Current Knowledge and Future Perspectives

Atherosclerosis (AS) is characterized by impairment and apoptosis of endothelial cells, continuous systemic and focal inflammation and dysfunction of vascular smooth muscle cells, which is documented as the traditional cellular paradigm. However, the mechanisms appear much more complicated than we thought since a bulk of studies on efferocytosis, transdifferentiation and novel cell death forms such as ferroptosis, pyroptosis, and extracellular trap were reported. Discovery of novel pathological cellular landscapes provides a large number of therapeutic targets. On the other side, the unsatisfactory therapeutic effects of current treatment with lipid-lowering drugs as the cornerstone also restricts the efforts to reduce global AS burden. Stem cell- or nanoparticle-based strategies spurred a lot of attention due to the attractive therapeutic effects and minimized adverse effects. Given the complexity of pathological changes of AS, attempts to develop an almighty medicine based on single mechanisms could be theoretically challenging. In this review, the top stories in the cellular landscapes during the initiation and progression of AS and the therapies were summarized in an integrated perspective to facilitate efforts to develop a multi-targets strategy and fill the gap between mechanism research and clinical translation. The future challenges and improvements were also discussed.

Extracellular vesicles in venous thromboembolism and pulmonary hypertension

Venous thromboembolism (VTE) is a multifactorial disease, and pulmonary hypertension (PH) is a serious condition characterized by pulmonary vascular remodeling leading with increased pulmonary vascular resistance, ultimately leading to right heart failure and death. Although VTE and PH have distinct primary etiologies, they share some pathophysiologic similarities such as dysfunctional vasculature and thrombosis. In both conditions there is solid evidence that EVs derived from a variety of cell types including platelets, monocytes, endothelial cells and smooth muscle cells contribute to vascular endothelial dysfunction, inflammation, thrombosis, cellular activation and communications. However, the roles and importance of EVs substantially differ between studies depending on experimental conditions and parent cell origins of EVs that modify the nature of their cargo. Numerous studies have confirmed that EVs contribute to the pathophysiology of VTE and PH and increased levels of various EVs in relation with the severity of VTE and PH, confirming its potential pathophysiological role and its utility as a biomarker of disease severity and as potential therapeutic targets.

Lactadherin's Multistate Binding Predicts Stable Membrane-Bound Conformations of Factors V and VIII's C Domains

Protein binding to negatively charged lipids is essential for maintaining numerous vital cellular processes where its dysfunction can lead to various diseases. One such protein that plays a crucial role in this process is lactadherin, which competes with coagulation factors for membrane binding sites to regulate blood clotting. Despite identifying key binding regions of these proteins through structural and biochemical studies, models incorporating membrane dynamics are still lacking. In this study, we report on the multimodal binding of lactadherin and use it to gain insight into the binding mechanisms of its C domain homologs, factor V and factor VIII. Molecular dynamics simulations enhanced with the highly mobile mimetic model enabled the determination of lactadherin's multimodal binding on membranes that revealed critical interacting residues consistent with prior NMR and mutagenesis data. The binding occurred primarily via two dynamic structural ensembles: an inserted state and an unreported, highly conserved side-lying state driven by a cationic patch. We utilized these findings to analyze the membrane binding domains of coagulation factors V and VIII and identified their preferred membrane-bound conformations. Specifically, factor V's C domains maintained an inserted state, while factor VIII preferred a tilted, side-lying state that permitted antibody binding. Insight into lactadherin's atomistically resolved membrane interactions from a multistate perspective can guide new therapeutic opportunities in treating diseases related to blood coagulation.

Salvianolic Acid B: A Review of Pharmacological Effects, Safety, Combination Therapy, New Dosage Forms, and Novel Drug Delivery Routes

Salvianolic acid B is extracted from the roots and rhizomes of Danshen (Salvia miltiorrhiza Bge., family Labiatae). It is a water-soluble, weakly acidic drug that has demonstrated antitumor and anti-inflammatory effects on various organs and tissues such as the lung, heart, kidney, intestine, bone, liver, and skin and protective effects in diseases such as depression and spinal cord injury. The mechanisms underlying the protective effects of salvianolic acid B are mainly related to its anti-inflammatory, antioxidant, anti- or pro-apoptotic, anti- or pro-autophagy, anti-fibrotic, and metabolism-regulating functions. Salvianolic acid B can regulate various signaling pathways, cells, and molecules to achieve maximum therapeutic effects. This review summarizes the safety profile, combination therapy potential, and new dosage forms and delivery routes of salvianolic acid B. Although significant research progress has been made, more in-depth pharmacological studies are warranted to identify the mechanism of action, related signaling pathways, more suitable combination drugs, more effective dosage forms, and novel routes of administration of salvianolic acid B.

NOX2 inhibition stabilizes vulnerable plaques by enhancing macrophage efferocytosis via MertK/PI3K/AKT pathway

NADPH oxidases 2 (NOX2) is the main source of ROS in macrophages, which plays a critical role in the formation of atherosclerosis. However, effects of NOX2 inhibition on established vulnerable plaques and the potential role involved remain unclear. The purpose of this study is to investigate the latent mechanism of NOX2-triggered vulnerable plaque development. We generated a vulnerable carotid plaque model induced by carotid branch ligation and renal artery constriction, combined with a high-fat diet in ApoE^-/- mice. NOX2 specific inhibitor, GSK2795039 (10 mg/kg/day by intragastric administration for 8 weeks) significantly prevented vulnerable plaque, evaluated by micro-ultrasound imaging parameters. A profile of less intraplaque hemorrhage detection, increased collagen-lipid ratio, fibrous cap thickness and less necrotic core formation were also found in GSK2795039 treated group. Mechanistically, reduced 4-HNE, in situ lesional apoptosis and enhanced efferocytosis were involved in mice treated with NOX2 inhibitor. Further analysis in mouse macrophages confirmed the role of NOX2 inhibition in enhancing macrophage efferocytosis by regulating the MertK/PI3K/AKT pathway. In summary, our data defined previously few recognized roles of NOX2 in vulnerable plaque pathogenesis and an undescribed NOX2-ROS-MerTK axis acts involved in regulating macrophage efferocytosis in the formation of rupture-prone vulnerable plaques.

Elevated MFG-E8 in CSF in the Early Stage Indicates Rapid Recovery of Mild Aneurysmal SAH Patients

Background

Aneurysmal subarachnoid hemorrhage (aSAH) can impair blood perfusion in brain tissue and cause adverse effects. Microglia, which are the inherent immune cells of the brain, significantly activate and play a role in phagocytosis, anti-inflammatory, proinflammatory, and damage repair in this process. Milk fat globule epidermal growth factor 8 (MFG-E8) is the bridging molecule of this process and mediates the activation and biological effects of microglia.

Methods

We obtained cerebrospinal fluid (CSF) from patients with aSAH at various times (the third day, seventh day, and ninth day) as well as from patients in the control cohort. MFG-E8 protein levels in CSF were measured by enzyme-linked immunosorbent assay (ELISA). Meanwhile, we evaluated the GCS and GOS of aSAH patients on admission and on the third day, seventh day, ninth day, and at discharge. Then, we analyzed the association between the levels of MFG-E8 and the changes in GCS and GOS.

Results

MFG-E8 expression rose in the early stage on the third day and reached equilibrium around day 7 and day 9. The levels of MFG-E8 on the third day were associated with the change in GOS on the seventh day (r = 0.644, p = 0.018) and ninth day (r = 0.572, p = 0.041) compared with admission but were not correlated with the change on day 3 or at discharge. The levels of MFG-E8 were not correlated with any change in GCS.

Conclusions

We found that aSAH resulted in an upregulation of MFG-E8 in CSF. Moreover, high MFG-E8 levels in the early stage indicated a rapid recovery of mild aSAH patients.

The Impaired Mechanism and Facilitated Therapies of Efferocytosis in Atherosclerosis

ABSTRACT

Cardiovascular disease is responsible for the largest number of deaths worldwide, and atherosclerosis is the primary cause. Apoptotic cell accumulation in atherosclerotic plaques leads to necrotic core formation and plaque rupture. Emerging findings show that the progression of atherosclerosis appears to suppress the elimination of apoptotic cells. Mechanistically, the reduced edibility of apoptotic cells, insufficient phagocytic capacity of phagocytes, downregulation of bridging molecules, and dysfunction in the polarization of macrophages lead to impaired efferocytosis in atherosclerotic plaques. This review focuses on the characteristics of efferocytosis in plaques and the therapeutic strategies aimed at promoting efferocytosis in atherosclerosis, which would provide novel insights for the development of antiatherosclerotic drugs based on efferocytosis.

Inframe insertion and splice site variants in MFGE8 associate with protection against coronary atherosclerosis

Cardiovascular diseases are the leading cause of premature death and disability worldwide, with both genetic and environmental determinants. While genome-wide association studies have identified multiple genetic loci associated with cardiovascular diseases, exact genes driving these associations remain mostly uncovered. Due to Finland's population history, many deleterious and high-impact variants are enriched in the Finnish population giving a possibility to find genetic associations for protein-truncating variants that likely tie the association to a gene and that would not be detected elsewhere. In a large Finnish biobank study FinnGen, we identified an association between an inframe insertion rs534125149 in MFGE8 (encoding lactadherin) and protection against coronary atherosclerosis. This variant is highly enriched in Finland, and the protective association was replicated in meta-analysis of BioBank Japan and Estonian biobank. Additionally, we identified a protective association between splice acceptor variant rs201988637 in MFGE8 and coronary atherosclerosis, independent of the rs534125149, with no significant risk-increasing associations. This variant was also associated with lower pulse pressure, pointing towards a function of MFGE8 in arterial aging also in humans in addition to previous evidence in mice. In conclusion, our results suggest that inhibiting the production of lactadherin could lower the risk for coronary heart disease substantially.

Sphingosine 1-phosphate receptor 2 promotes erythrocyte clearance by vascular smooth muscle cells in intraplaque hemorrhage through MFG-E8 production

Intraplaque hemorrhage (IPH) accelerates atherosclerosis progression. To scavenge excessive red blood cells (RBCs), vascular smooth muscle cells (VSMCs) with great plasticity may function as phagocytes. Here, we investigated the erythrophagocytosis function of VSMCs and possible regulations involved. Based on transcriptional microarray analysis, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that genes up-regulated in human carotid atheroma with IPH were enriched in functions of phagocytic activities, while those down-regulated were enriched in VSMCs contraction function. Transcriptional expression of Milk fat globule-epidermal growth factor 8 (MFG-E8) was also down-regulated in atheroma with IPH. In high-fat diet-fed apolipoprotein E-deficient mice, erythrocytes were present in cells expressing VSMC markers αSMA in the brachiocephalic artery, suggesting VSMCs play a role in erythrophagocytosis. Using immunofluorescence and flow cytometry, we also found that eryptotic RBCs were bound to and internalized by VSMCs in a phosphatidylserine/MFG-E8/integrin α_Vβ₃ dependent manner in vitro. Inhibiting S1PR2 signaling with specific inhibitor JTE-013 or siRNA decreased Mfge8 expression and impaired the erythrophagocytosis of VSMCs in vitro. Partial ligation was performed in the left common carotid artery (LCA) followed by intra-intimal injection of isolated erythrocytes to observe their clearance in vivo. Interfering S1PR2 expression in VSMCs with Adeno-associated virus 9 inhibited MFG-E8 expression inside LCA plaques receiving RBCs injection and attenuated erythrocytes clearance. Erythrophagocytosis by VSMCs increased vascular endothelial growth factor-a secretion and promoted angiogenesis. The present study revealed that VSMCs act as phagocytes for RBC clearance through S1PR2 activation induced MFG-E8 release.

High Levels of MFG-E8 Confer a Good Prognosis in Prostate and Renal Cancer Patients

Simple Summary

In the present study, we analyzed the distribution and prognostic impact of milk fat globule-epidermal growth factor-8 (MFG-E8) protein expression in patients with prostate and renal cancers. Our data highlighted MFG-E8 expression by tumor cells in the epithelium. Our results also showed that low levels of MFG-E8 in prostate and renal cancers were associated with worse clinical outcomes. Furthermore, higher numbers of CD206⁺ cells were found in the peripheral regions of renal clear cell carcinoma that expressed lower MFG-E8 levels. Globally, our results suggest that MFG-E8 expression could potentially be used as a prognostic marker in prostate and renal cancers.

Abstract

Milk fat globule-epidermal growth factor-8 (MFG-E8) is a glycoprotein secreted by different cell types, including apoptotic cells and activated macrophages. MFG-E8 is highly expressed in a variety of cancers and is classically associated with tumor growth and poor patient prognosis through reprogramming of macrophages into the pro-tumoral/pro-angiogenic M2 phenotype. To date, correlations between levels of MFG-E8 and patient survival in prostate and renal cancers remain unclear. Here, we quantified MFG-E8 and CD68/CD206 expression by immunofluorescence staining in tissue microarrays constructed from renal (n = 190) and prostate (n = 274) cancer patient specimens. Percentages of MFG-E8-positive surface area were assessed in each patient core and Kaplan–Meier analyses were performed accordingly. We found that MFG-E8 was expressed more abundantly in malignant regions of prostate tissue and papillary renal cell carcinoma but was also increased in the normal adjacent regions in clear cell renal carcinoma. In addition, M2 tumor-associated macrophage staining was increased in the normal adjacent tissues compared to the malignant areas in renal cancer patients. Overall, high tissue expression of MFG-E8 was associated with less disease progression and better survival in prostate and renal cancer patients. Our observations provide new insights into tumoral MFG-E8 content and macrophage reprogramming in cancer.

2021 Jeffrey M. Hoeg Award Lecture: Defining the Role of Efferocytosis in Cardiovascular Disease: A Focus on the CD47 (Cluster of Differentiation 47) Axis

A key feature of atherogenesis is the accumulation of diseased and dying cells within the lesional necrotic core. While the burden of intraplaque apoptotic cells may be driven in part by an increase in programmed cell death, mounting evidence suggests that their presence may primarily be dictated by a defect in programmed cell removal, or efferocytosis. In this brief review, we will summarize the evidence suggesting that inflammation-dependent changes within the plaque render target cells inedible and reduce the appetite of lesional phagocytes. We will present the genetic causation studies, which indicate these phenomena promote lesion expansion and plaque vulnerability, and the interventional data which suggest that these processes can be reversed. Particular emphasis is provided related to the antiphagocytic CD47 (cluster of differentiation 47) do not eat me axis, which has emerged as a novel antiatherosclerotic translational target that is predicted to provide benefit independent of traditional cardiovascular risk factors.

MFG-E8 promotes osteogenic transdifferentiation of smooth muscle cells and vascular calcification by regulating TGF-β1 signaling

Vascular calcification occurs in arterial aging, atherosclerosis, diabetes mellitus, and chronic kidney disease. Transforming growth factor-β1 (TGF-β1) is a key modulator driving the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs), leading to vascular calcification. We hypothesize that milk fat globule–epidermal growth factor 8 (MFG-E8), a glycoprotein expressed in VSMCs, promotes the osteogenic transdifferentiation of VSMCs through the activation of TGF-β1-mediated signaling. We observe that the genetic deletion of MFG-E8 prevents calcium chloride-induced vascular calcification in common carotid arteries (CCAs). The exogenous application of MFG-E8 to aged CCAs promotes arterial wall calcification. MFG-E8-deficient cultured VSMCs exhibit decreased biomineralization and phenotypic transformation to osteoblast-like cells in response to osteogenic medium. MFG-E8 promotes β1 integrin–dependent MMP2 expression, causing TGF-β1 activation and subsequent VSMC osteogenic transdifferentiation and biomineralization. Thus, the established molecular link between MFG-E8 and vascular calcification suggests that MFG-E8 can be therapeutically targeted to mitigate vascular calcification.

A molecular link between the milk fat globule–epidermal growth factor 8 (MFG-E8), activation of vascular calcification driver TGF-β1 and osteogenic differentiation of vascular smooth muscle cells suggests that MFG-E8 could be a therapeutic target for vascular calcification.

MFG-E8 Reduces Aortic Intimal Proliferation in a Murine Model of Transplant Vasculopathy

Transplant vasculopathy is characterized by endothelial apoptosis, which modulates the local microenvironment. Milk fat globule epidermal growth factor 8 (MFG-E8), which is released by apoptotic endothelial cells, limits tissue damage and inflammation by promoting anti-inflammatory macrophages. We aimed to study its role in transplant vasculopathy using the murine aortic allotransplantation model. BALB/c mice were transplanted with fully mismatched aortic transplants from MFG-E8 knockout (KO) or wild type (WT) C57BL/6J mice. Thereafter, mice received MFG-E8 (or vehicle) injections for 9 weeks prior to histopathological analysis of allografts for intimal proliferation (hematoxylin and eosin staining) and leukocyte infiltration assessment (immunofluorescence). Phenotypes of blood leukocytes and humoral responses were also evaluated (flow cytometry and ELISA). Mice receiving MFG-E8 KO aortas without MFG-E8 injections had the most severe intimal proliferation (p < 0.001). Administration of MFG-E8 decreased intimal proliferation, especially in mice receiving MFG-E8 KO aortas. Administration of MFG-E8 also increased the proportion of anti-inflammatory macrophages among graft-infiltrating macrophages (p = 0.003) and decreased systemic CD4+ and CD8+ T-cell activation (p < 0.001). An increase in regulatory T cells occurred in both groups of mice receiving WT aortas (p < 0.01). Thus, the analarmin MFG-E8 appears to be an important protein for reducing intimal proliferation in this murine model of transplant vasculopathy. MFG-E8 effects are associated with intra-allograft macrophage reprogramming and systemic T-cell activation dampening.

Crosstalk Between Macrophages and Vascular Smooth Muscle Cells in Atherosclerotic Plaque Stability

Most acute cardiovascular events are due to plaque rupture, with atheromas containing large necrotic cores and thin fibrous caps being more susceptible to rupture and lesions with small necrotic cores and thick fibrous caps being more protected from rupture. Atherosclerotic plaques are comprised various extracellular matrix proteins, modified lipoprotein particles, and cells of different origins, that is, vascular cells and leukocytes. Although much has been revealed about the mechanisms that lead to plaque instability, several key areas remain incompletely understood. This In-Focus Review highlights processes related to cellular crosstalk and the role of the tissue microenvironment in determining cell function and plaque stability. Recent advances highlight critical underpinnings of atherosclerotic plaque vulnerability, particularly impairments in the ability of macrophages to clear dead cells and phenotypic switching of vascular smooth muscle cells. However, these processes do not occur in isolation, as crosstalk between macrophages and vascular smooth muscle cells and interactions with their surrounding microenvironment play a significant role in determining plaque stability. Understanding these aspects of cellular crosstalk within an atherosclerotic plaque may shed light on how to modify cell behavior and identify novel approaches to transform rupture-prone atheromas into stable lesions.

Inflammation Resolution: Implications for Atherosclerosis

Resolution is an active and highly coordinated process that occurs in response to inflammation to limit tissue damage and promote repair. When the resolution program fails, inflammation persists. It is now understood that failed resolution is a major underlying cause of many chronic inflammatory diseases. Here, we will review the major failures of resolution in atherosclerosis, including the imbalance of proinflammatory to pro-resolving mediator production, impaired clearance of dead cells, and functional changes in immune cells that favor ongoing inflammation. In addition, we will briefly discuss new concepts that are emerging as possible regulators of resolution and highlight the translational significance for the field.

Immune system and atherosclerosis: Hostile or friendly relationship

Coronary artery disease has remained a major health challenge despite enormous progress in prevention, diagnosis, and treatment strategies. Formation of atherosclerotic plaque is a chronic process that is developmentally influenced by intrinsic and extrinsic determinants. Inflammation triggers atherosclerosis, and the fundamental element of inflammation is the immune system. The immune system involves in the atherosclerosis process by a variety of immune cells and a cocktail of mediators. It is believed that almost all main components of this system possess a profound contribution to the atherosclerosis. However, they play contradictory roles, either protective or progressive, in different stages of atherosclerosis progression. It is evident that monocytes are the first immune cells appeared in the atherosclerotic lesion. With the plaque growth, other types of the immune cells such as mast cells, and T lymphocytes are gradually involved. Each cell releases several cytokines which cause the recruitment of other immune cells to the lesion site. This is followed by affecting the expression of other cytokines as well as altering certain signaling pathways. All in all, a mix of intertwined interactions determine the final outcome in terms of mild or severe manifestations, either clinical or subclinical. Therefore, it is of utmost importance to precisely understand the kind and degree of contribution which is made by each immune component in order to stop the growing burden of cardiovascular morbidity and mortality. In this review, we present a comprehensive appraisal on the role of immune cells in the atherosclerosis initiation and development.

Efferocytosis in multisystem diseases (Review)

Efferocytosis, the phagocytosis of apoptotic cells performed by both specialized phagocytes (such as macrophages) and non‑specialized phagocytes (such as epithelial cells), is involved in tissue repair and homeostasis. Effective efferocytosis prevents secondary necrosis, terminates inflammatory responses, promotes self‑tolerance and activates pro‑resolving pathways to maintain homeostasis. When efferocytosis is impaired, apoptotic cells that could not be cleared in time aggregate, resulting in the necrosis of apoptotic cells and release of pro‑inflammatory factors. In addition, defective efferocytosis inhibits the intracellular cholesterol reverse transportation pathways, which may lead to atherosclerosis, lung damage, non‑alcoholic fatty liver disease and neurodegenerative diseases. The uncleared apoptotic cells can also release autoantigens, which can cause autoimmune diseases. Cancer cells escape from phagocytosis via efferocytosis. Therefore, new treatment strategies for diseases related to defective efferocytosis are proposed. This review illustrated the mechanisms of efferocytosis in multisystem diseases and organismal homeostasis and the pathophysiological consequences of defective efferocytosis. Several drugs and treatments available to enhance efferocytosis are also mentioned in the review, serving as new evidence for clinical application.

Guanxinkang Decoction Attenuates the Inflammation in Atherosclerosis by Regulating Efferocytosis and MAPKs Signaling Pathway in LDLR-/- Mice and RAW264.7 Cells

Guanxinkang decoction (GXK), a traditional Chinese medicinal drug, is used to treat cardiovascular disease. The aim of the study was to investigate the effects of GXK on inflammation in LDLR^−/− mice and RAW264.7 cells. Fed with high fat diet for 12 weeks, the mice were randomly divided into six groups, then administered with oral 0.9% saline or GXK (7.24, 14.48, and 28.96 g/kg) or Atorvastatin (1.3 mg/kg) for 12 weeks. RAW 264.7 cells were induced with ox-LDL or ox-LDL plus different concentrations of GXK (1.25, 2.5, and 5 μg/ml), or ox-LDL plus GXK plus MAPKs activators. Serum lipid profiles and inflammatory cytokines were detected by ELISA, gene expression by RT-qPCR, plaque sizes by Oil Red O, α-SMA, caspase 3, NF-κB p65 and TNF-α production by immunofluorescence staining, and protein expression by Western Blot. The phagocytic ability of cells was determined by neutral red uptake assay. Efferocytosis-related proteins (AML, MERTK, TYRO3 and MFGE8) and MAPKs pathways were detected by Western Blot. Compared to mice fed with high fat diet, the mice with GXK showed lower cholesterol, triglyceride, low-density lipoprotein cholesterol, IL-1β, IL-6, and TNF-α, smaller plaque sizes, higher α-SMA, and lower caspase 3 and NF-κB p65 in aortic roots. RAW264.7 cells treated with ox-LDL plus GXK had lower IL-1β, IL-6, and TNF-α. GXK also increased the phagocytic ability of cells. High levels of AML, MERTK, TYRO3 and MFGE8, and decreased levels of iNOS, VCAM-1, LOX-1 and MCP-1, and phosphorylation of ERK1/2, JNK, p38, and NF-κB were detected in GXK-treated group. MAPKs activators reversed the effects of GXK in repressing inflammation and promoting phagocytosis. These results suggested that GXK could attenuate atherosclerosis and resolve inflammation via efferocytosis and MAPKs signaling pathways in LDLR^−/− mice and RAW264.7 cells.

Adoptive transfer of CX3CR1 transduced-T regulatory cells improves homing to the atherosclerotic plaques and dampens atherosclerosis progression

AIM

Loss of immunosuppressive response supports inflammation during atherosclerosis. We tested whether adoptive cell therapy (ACT) with Tregulatory cells (Tregs), engineered to selectively migrate in the atherosclerotic plaque, would dampen the immune-inflammatory response in the arterial wall in animal models of familial hypercholesterolaemia (FH).

METHODS AND RESULTS

FH patients presented a decreased Treg suppressive function associated to an increased inflammatory burden. A similar phenotype was observed in Ldlr -/- mice accompanied by a selective increased expression of the chemokine CX3CL1 in the aorta but not in other districts (lymph nodes, spleen, and liver). Treg overexpressing CX3CR1 were thus generated (CX3CR1+-Tregs) to drive Tregs selectively to the plaque. CX3CR1+-Tregs were injected (i.v.) in Ldlr -/- fed high-cholesterol diet (western type diet, WTD) for 8 weeks. CX3CR1+-Tregs were detected in the aorta, but not in other tissues, of Ldlr -/- mice 24 h after ACT, corroborating the efficacy of this approach. After 4 additional weeks of WTD, ACT with CX3CR1+-Tregs resulted in reduced plaque progression and lipid deposition, ameliorated plaque stability by increasing collagen and smooth muscle cells content, while decreasing the number of pro-inflammatory macrophages. Shotgun proteomics of the aorta showed a metabolic rewiring in CX3CR1+-Tregs treated Ldlr -/- mice compared to controls that was associated with the improvement of inflammation-resolving pathways and disease progression.

CONCLUSION

ACT with vasculotropic Tregs appears as a promising strategy to selectively target immune activation in the atherosclerotic plaque.

Dead cell and debris clearance in the atherosclerotic plaque: Mechanisms and therapeutic opportunities to promote inflammation resolution

Phagocytic clearance of dead cells and debris is critical for inflammation resolution and maintenance of tissue homeostasis. Consequently, defective clearance of dead cells and debris is associated with initiation and exacerbation of several autoimmune disorders and chronic inflammatory diseases such as atherosclerosis. The progressive loss of dead cell clearance capacity within the atherosclerotic plaque leads to accumulation of necrotic cells, chronic non-resolving inflammation, and expansion of the necrotic core, which triggers atherosclerotic plaque rupture and clinical manifestation of acute thrombotic cardiovascular adverse events. In this review, we describe the fundamental molecular and cellular mechanisms of dead cell clearance and how it goes awry in atherosclerosis. Finally, we highlight novel therapeutic strategies that enhance dead cell and debris clearance within the atherosclerotic plaque to promote inflammation resolution and atherosclerotic plaque stabilization.

The mechanisms of vascular aging

Vascular senescence is one of the hotspots in current research. With global average life expectancy increasing, delaying or reducing aging and age-related diseases has become a pressing issue for improving quality of life. Vascular senescence is an independent risk factor for age-related cardiovascular diseases (CVD) and results in the deterioration of CVD. Nevertheless, the underlying mechanisms of the vascular senescence have not been expressly illustrated. In this review, we attempt to summarize the recent literature in the field and discuss the major mechanisms involved in vascular senescence. We also underline key molecular aspects of aging-associated vascular dysfunction in the attempt to highlight potential innovative therapeutic targets to delay the onset of age-related diseases.

MFG-E8 Regulates Vascular Smooth Muscle Cell Migration Through Dose-Dependent Mediation of Actin Polymerization

Background Migration of vascular smooth muscle cells (VSMCs) is the main contributor to neointimal formation. The Arp2/3 (actin-related proteins 2 and 3) complex activates actin polymerization and is involved in lamellipodia formation during VSMC migration. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a glycoprotein expressed in VSMCs. We hypothesized that MFG-E8 regulates VSMC migration through modulation of Arp2/3-mediated actin polymerization. Methods and Results To determine whether MFG-E8 is essential for VSMC migration, a model of neointimal hyperplasia was induced in the common carotid artery of wild-type and MFG-E8 knockout mice, and the extent of neointimal formation was evaluated. Genetic deletion of MFG-E8 in mice attenuated injury-induced neointimal hyperplasia. Cultured VSMCs deficient in MFG-E8 exhibited decreased cell migration. Immunofluorescence and immunoblotting revealed decreased Arp2 but not Arp3 expression in the common carotid arteries and VSMCs deficient in MFG-E8. Exogenous administration of recombinant MFG-E8 biphasically and dose-dependently regulated the cultured VSMCs. At a low concentration, MFG-E8 upregulated Arp2 expression. By contrast, MFG-E8 at a high concentration reduced the Arp2 level and significantly attenuated actin assembly. Arp2 upregulation mediated by low-dose MFG-E8 was abolished by treating cultured VSMCs with β1 integrin function-blocking antibody and Rac1 inhibitors. Moreover, treatment of the artery with a high dose of recombinant MFG-E8 diminished injury-induced neointimal hyperplasia and reduced VSMC migration. Conclusions MFG-E8 plays a critical role in VSMC migration through dose-dependent regulation of Arp2-mediated actin polymerization. These findings suggest that high doses of MFG-E8 may have therapeutic potential for treating vascular occlusive diseases.

Low-density lipoproteins cause atherosclerotic cardiovascular disease: pathophysiological, genetic, and therapeutic insights: a consensus statement from the European Atherosclerosis Society Consensus Panel

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Autoregulation of insulin receptor signaling through MFGE8 and the αvβ5 integrin

The role of integrins, in particular αv integrins, in regulating insulin resistance is incompletely understood. We have previously shown that the αvβ5 integrin ligand milk fat globule epidermal growth factor like 8 (MFGE8) regulates cellular uptake of fatty acids. In this work, we evaluated the impact of MFGE8 on glucose homeostasis. We show that acute blockade of the MFGE8/β5 pathway enhances while acute augmentation dampens insulin-stimulated glucose uptake. Moreover, we find that insulin itself induces cell-surface enrichment of MFGE8 in skeletal muscle, which then promotes interaction between the αvβ5 integrin and the insulin receptor leading to dampening of skeletal-muscle insulin receptor signaling. Blockade of the MFGE8/β5 pathway also enhances hepatic insulin sensitivity. Our work identifies an autoregulatory mechanism by which insulin-stimulated signaling through its cognate receptor is terminated through up-regulation of MFGE8 and its consequent interaction with the αvβ5 integrin, thereby establishing a pathway that can potentially be targeted to improve insulin sensitivity.

miR-33 Silencing Reprograms the Immune Cell Landscape in Atherosclerotic Plaques

[Figure: see text].

Immune responses against oxidized LDL as possible targets for prevention of atherosclerosis in systemic lupus erythematosus

Patients suffering from systemic lupus erythematosus (SLE) are at increased risk of developing cardiovascular disease (CVD) and traditional therapies including statins provide insufficient protection. Impaired removal of apoptotic material is a common pathogenic mechanism in both SLE and atherosclerosis and is considered to be a key factor in the development of autoimmunity. Since oxidized LDL and apoptotic material bind to the same receptors, we aimed to investigate if targeting the oxidized LDL autoimmunity can affect atherosclerosis in SLE. To investigate the possible role of oxidized LDL autoimmunity in the accelerated atherosclerosis associated with SLE we used a hypercholesterolemic SLE mouse model (B6.lpr.ApoE^-/- mice). Promoting LDL tolerance through mucosal immunization with an apolipoprotein B-100 peptide p45 (amino acids 661-680) and cholera toxin B-subunit fusion protein increased regulatory T cells and B cells in mesenteric lymph nodes and reduced plaque development in the aorta by 33%. Treatment with the oxidized LDL-specific antibody Orticumab reduced aortic atherosclerosis by 43%, subvalvular plaque area by 50% and the macrophage content by 31%. The present study provides support for oxLDL as a possible target for prevention of cardiovascular complications in SLE.

Metabolic Consequences of Efferocytosis and its Impact on Atherosclerosis

Billions of cells undergo apoptosis daily and are swiftly removed by macrophages through an evolutionarily conserved program termed "efferocytosis". Consequently, macromolecules within an apoptotic cell significantly burden a phagocyte with nutrients, such as lipids, oligonucleotides, and amino acids. In response to this nutrient overload, metabolic reprogramming must occur for the process of efferocytosis to remain non-phlogistic and to execute successive rounds of efferocytosis. The inability to undergo metabolic reprogramming after efferocytosis drives inflammation and impairs its resolution, often promoting many chronic inflammatory diseases. This is particularly evident for atherosclerosis, as metabolic reprogramming alters macrophage function in every stage of atherosclerosis, from the early formation of benign lesions to the progression of clinically relevant atheromas and during atherosclerosis regression upon aggressive lipid-lowering. This Review focuses on the metabolic pathways utilized upon apoptotic cell ingestion, the consequences of these metabolic pathways in macrophage function thereafter, and the role of metabolic reprogramming during atherosclerosis. Due to the growing interest in this new field, I introduce a new term, "efferotabolism", as a means to define the process by which macrophages break down, metabolize, and respond to AC-derived macromolecules. Understanding these aspects of efferotabolism will shed light on novel strategies to combat atherosclerosis and compromised inflammation resolution.

Milk Fat Globule-Epidermal Growth Factor-Factor 8 Improves Hepatic Steatosis and Inflammation

BACKGROUND AND AIMS

Milk fat globule-epidermal growth factor-factor 8 (MFGE8) has been shown to be a critical extracellular molecule that mediates apoptotic signaling in the pathological process of nonalcoholic fatty liver disease (NAFLD). MFGE8 is abundantly expressed in hepatocytes, but its function in the pathogenesis of NAFLD has not been characterized.

APPROACH AND RESULTS

In our current study, hepatic MFGE8 showed a protective role in the pathogenesis of NAFLD. Hepatic MFGE8 deletion largely exacerbated lipid accumulation and inflammatory responses in the liver in response to overnutrition. Mechanistically, intercellular MFGE8 was shown to directly bind to apoptosis signal-regulating kinase 1 (ASK1) and to inhibit its dimerization and phosphorylation under a normal diet. However, under metabolic challenges, decreased cytoplasmic MFGE8 facilitated the dimerization and phosphorylation of ASK1 and subsequent mitogen-activated protein kinase signaling in hepatocytes.

CONCLUSIONS

Hepatic MFGE8 is an endogenous inhibitor that halts the progression of hepatic steatosis and inflammation. Metabolic challenge-induced loss of intracellular MFGE8 facilitates ASK1 dimerization and phosphorylation. Therefore, maintaining hepatic MFGE8 levels may serve as an alternative strategy for the treatment of NAFLD.

Roles and mechanisms of MFG-E8 in vascular aging-related diseases

The aging of the vasculature plays a crucial role in the pathological progression of various vascular aging-related diseases. As endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are essential parts in the inner and medial layers of vessel wall, respectively, the structural and functional alterations of ECs and VSMCs are the major causes of vascular aging. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a multifunctional glycoprotein which exerts a regulatory role in the intercellular interactions involved in a variety of biological and pathological processes. Emerging evidence suggests that MFG-E8 is a novel and outstanding modulator for vascular aging via targeting at ECs and VSMCs. In this review, we will summarise the cumulative roles and mechanisms of MFG-E8 in vascular aging and vascular aging-related diseases with special emphasis on the functions of ECs and VSMCs. In addition, we also aim to focus on the promising diagnostic function as a biomarker and the potential therapeutic application of MFG-E8 in vascular aging and the clinical evaluation of vascular aging-related diseases.

Absence of the MFG-E8 gene prevents hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension (PH) is a chronic vascular disease characterized by elevated pulmonary arterial resistance and vascular remodeling, and chronic hypoxia plays an important role in PH. Milk fat globule‐EGF factor 8 (MFG‐E8) is a glycoprotein that regulates cell proliferation and apoptosis, but its role in hypoxia‐induced PH is unknown. The current study aimed to determine the function and fundamental mechanisms of MFG‐E8 in hypoxia‐induced PH. Herein, we exposed mice to hypoxia for 5 weeks, and MFG‐E8 was found to be elevated in mouse lung tissues, arteries, and plasma. Compared with wild‐type littermates, mice lacking MFG‐E8 showed a significant increase in the ratio of pulmonary artery acceleration time to ejection time (PAT/PET), while they showed decreases in right ventricular systolic pressure, the Fulton's Index, percent medial wall thickness (%WT), and vascular muscularization in pulmonary arteries. In addition, MFG‐E8 protein levels were also increased in the serum of patients with chronic PH. Similarly, we observed a higher expression of MFG‐E8 in human pulmonary artery smooth muscle cells (PASMCs) in the presence of hypoxic stimulation than MFG‐E8 in cells in normoxic conditions. Furthermore, MFG‐E8 silencing resulted in partial inhibition of proliferation, migration and cell cycle progression in human PASMCs, and the possible mechanisms might involve the interaction between MFG‐E8 and the p‐Akt/cyclin D1 pathway. Collectively, our study suggests that the absence of MFG‐E8 can attenuate the development of hypoxia‐induced PH and vascular remodeling. MFG‐E8 can be a potential therapeutic target or a biomarker for PH.

The role of phosphatidylserine recognition receptors in multiple biological functions

Apoptotic cells are rapidly engulfed and degraded by phagocytes through efferocytosis. Efferocytosis is a highly regulated process. It is triggered upon the activation of caspase-dependent apoptosis, which in turn promotes the expression of "eat me" signals on the surface of dying cells and the release of soluble "find me" signals for the recruitment of phagocytes. To date, many "eat me" signals have been recognized, including phosphatidylserine (PS), intercellular adhesion molecule-3, carbohydrates (e.g., amino sugars, mannose) and calreticulin. Among them, PS is the most studied one. PS recognition receptors are different functionally active receptors expressed by phagocytes. Various PS recognition receptors with different structure, cell type expression, and ability to bind to PS have been recognized. Although PS recognition receptors do not fall into a single classification or family of proteins due to their structural differences, they all share the common ability to activate downstream signaling pathways leading to the production of anti-inflammatory mediators. In this review, available evidence regarding molecular mechanisms underlying PS recognition receptor-regulated clearance of apoptotic cells is discussed. In addition, some efferocytosis-independent biological functions of PS recognition receptors are reviewed.

MFGE8 attenuates Ang-II-induced atrial fibrosis and vulnerability to atrial fibrillation through inhibition of TGF-β1/Smad2/3 pathway

Atrial fibrillation (AF) is characterized by potentiated growth of atrial fibroblasts and excessive deposition of the extracellular matrix. Atrial fibrosis has emerged as a hallmark of atrial structural remodeling linked to AF. Nonetheless, the specific mechanism underlying the progression of atrial fibrosis to AF is still largely unknown. MFGE8 (milk fat globule-EGF factor 8) is a soluble glycoprotein associated with many human diseases. Recently, a number of studies revealed that MFGE8 plays a crucial role in heart disease. Yet, MFGE8 regulation and function in the process of atrial fibrosis and vulnerability to AF remain unexplored. In this study, we found that the expression of MFGE8 was downregulated in the atriums of patients with AF compared with individuals without AF. In addition, the expression of MFGE8 was lower in atriums of angiotensin II (Ang-II)-stimulated rats as compared with the sham group. In vitro, silencing of MFGE8 by small interfering RNA significantly increased Ang-II-induced atrial fibrosis, whereas administration of recombinant human MFGE8 (rhMFGE8) attenuated the atrial fibrosis. Moreover, we found that the activated TGF-β1/Smad2/3 pathway after Ang-II treatment was significantly potentiated by the MFGE8 knockdown but inhibited by rhMFGE8 in vitro. Inhibition of integrin β3 which is the receptor for MFGE8, suppressed the TGF-β1/Smad2/3 activating effects of the MFGE8 knockdown in Ang-II-treated rat atrial fibroblasts. Finally, we administered rhMFGE8 to rats; it attenuated atrial fibrosis and remodeling and further reduced AF vulnerability induced by Ang-II, indicating that MFGE8 might have the potential both as a novel biomarker and as a therapeutic target in atrial fibrosis and AF.

Vascular smooth muscle cells in atherosclerosis

Vascular smooth muscle cells (VSMCs) are a major cell type present at all stages of an atherosclerotic plaque. According to the 'response to injury' and 'vulnerable plaque' hypotheses, contractile VSMCs recruited from the media undergo phenotypic conversion to proliferative synthetic cells that generate extracellular matrix to form the fibrous cap and hence stabilize plaques. However, lineage-tracing studies have highlighted flaws in the interpretation of former studies, revealing that these studies had underestimated both the content and functions of VSMCs in plaques and have thus challenged our view on the role of VSMCs in atherosclerosis. VSMCs are more plastic than previously recognized and can adopt alternative phenotypes, including phenotypes resembling foam cells, macrophages, mesenchymal stem cells and osteochondrogenic cells, which could contribute both positively and negatively to disease progression. In this Review, we present the evidence for VSMC plasticity and summarize the roles of VSMCs and VSMC-derived cells in atherosclerotic plaque development and progression. Correct attribution and spatiotemporal resolution of clinically beneficial and detrimental processes will underpin the success of any therapeutic intervention aimed at VSMCs and their derivatives.

Living on the Edge: Efferocytosis at the Interface of Homeostasis and Pathology

Nearly every tissue in the body undergoes routine turnover of cells as part of normal healthy living. The majority of these cells undergoing turnover die via apoptosis, and then are rapidly removed by phagocytes by the process of efferocytosis that is anti-inflammatory. However, a number of pathologies have recently been linked to defective clearance of apoptotic cells. Perturbed clearance arises for many reasons, including overwhelming of the clearance machinery, disruptions at different stages of efferocytosis, and responses of phagocytes during efferocytosis, all of which can alter the homeostatic tissue environment. This review covers linkages of molecules involved in the different phases of efferocytosis to disease pathologies that can arise due to their loss or altered function.

MFG-E8 mediates arterial aging by promoting the proinflammatory phenotype of vascular smooth muscle cells

BACKGROUND

Among older adults, arterial aging is the major factor contributing to increased risk for cardiovascular disease-related morbidity and mortality. The chronic vascular inflammation that accompanies aging causes diffuse intimal-medial thickening of the arterial wall, thus increasing the vulnerability of aged vessels to vascular insults. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a biomarker for aging arteries. This integrin-binding glycoprotein, induced by angiotensin II, facilitates vascular smooth muscle cell (VSMC) proliferation and invasion in aging vasculatures. This study investigated whether MFG-E8 directly mediates the initial inflammatory responses in aged arteries or VSMCs.

METHODS

A model of neointimal hyperplasia was induced in the common carotid artery (CCA) of aged mice to exacerbate age-associated vascular remodeling. Recombinant MFG-E8 (rMFG-E8) was administered to the injured artery using Pluronic gel to accentuate the effect on age-related vascular pathophysiology. The MFG-E8 level, leukocyte infiltration, and proinflammatory cell adhesion molecule (CAM) expression in the arterial wall were evaluated through immunohistochemistry. By using immunofluorescence and immunoblotting, the activation of the critical proinflammatory transcription factor nuclear factor (NF)-κB in the injured CCAs was analyzed. Immunofluorescence, immunoblotting, and quantitative real-time polymerase chain reaction were conducted using VSMCs isolated from the aortas of young and aged mice to assess NF-κB nuclear translocation, NF-κB-dependent gene expression, and cell proliferation. The extent of intimal-medial thickening in the injured vessels was analyzed morphometrically. Finally, Transwell migration assay was used to examine VSMC migration.

RESULTS

Endogenous MFG-E8 expression in aged CCAs was significantly induced by ligation injury. Aged CCAs treated with rMFG-E8 exhibited increased leukocyte extravasation, CAM expression, and considerably increased NF-κB activation induced by rMFG-E8 in the ligated vessels. Exposure of early passage VSMCs from aged aortas to rMFG-E8 substantially increased NF-κB activation, proinflammatory gene expression, and cell proliferation. However, rMFG-E8 attenuated VSMC migration.

CONCLUSIONS

MFG-E8 promoted the proinflammatory phenotypic shift of aged VSMCs and arteries, rendering the vasculature prone to vascular diseases. MFG-E8 may constitute a novel therapeutic target for retarding the aging processes in such vessels.

The glycoproteins EDIL3 and MFGE8 regulate vesicle-mediated eggshell calcification in a new model for avian biomineralization

The avian eggshell is a critical physical barrier, which permits extra-uterine development of the embryo. Its formation involves the fastest known biomineralization process in vertebrates. The eggshell consists of proteins and proteoglycans that interact with the mineral phase to impart its specific microstructure and mechanical properties. In this study, we investigated the role of epidermal growth factor (EGF)-like repeats and discoidin-like domains 3 (EDIL3) and milk fat globule-EGF factor 8 (MFGE8), two glycoproteins that are consistently detected in eggshell proteomes. We verified their common evolutionary history and identified the timing of the duplication event giving rise to these two distinct proteins. Edil3/mfge8 chromosomal locations revealed a nested syntenous relationship with other genes (hapln1/hapln3 and vcan/acan) that are also involved in vertebrate calcification. EDIL3 and MFGE8 proteins possess EGF-like and coagulation factor 5/8 (F5/8C) domains, and their 3D structures predicted that they bind calcium and extracellular vesicles. In chicken, we confirmed the presence of EDIL3 and MFGE8 proteins in eggshell, uterine fluid, and uterus. We observed that only edil3 is overexpressed in tissues in which eggshell mineralization takes place and that this overexpression occurs only at the onset of shell calcification. We therefore propose a model in which EDIL3 and, to a lesser extent, MFGE8 proteins guide vesicles containing amorphous calcium carbonate to the mineralization site. This model was supported by the observation that extracellular vesicles accumulate in uterine fluid during eggshell calcification and that they contain high levels of calcium, carbon, and oxygen that correspond to calcium carbonate.

Allograft inflammatory factor-1 supports macrophage survival and efferocytosis and limits necrosis in atherosclerotic plaques

BACKGROUND AND AIMS

Allograft inflammatory factor-1 (AIF1) has been characterized as a pro-inflammatory molecule expressed primarily in the monocyte/macrophage (MP) lineage and positively associated with various forms of vascular disease, including atherosclerosis. Studies of AIF1 in atherosclerosis have relied on mouse models in which AIF1 was overexpressed in either myeloid or smooth muscle cells, resulting in increased atherosclerotic plaque burden. How physiologic expression of AIF1 contributes to MP biology in atherogenesis is not known.

METHODS

Effects of global AIF1 deficiency on atherosclerosis were assessed by crossing Aif1^-/- and ApoE^-/- mice, and provoking hyperlipidemia with high fat diet feeding. Atherosclerotic plaques were studied en face and in cross section. Bone marrow-derived MPs (BMDMs) were isolated from Aif1^-/- mice for study in culture.

RESULTS

Atherosclerotic plaques in Aif1^-/-;ApoE^-/- mice showed larger necrotic cores compared to those in ApoE^-/- animals, without change in overall lesion burden. In vitro, lack of AIF1 reduced BMDM survival, phagocytosis, and efferocytosis. Mechanistically, AIF1 supported activation of the NF-κB pathway and expression of related target genes involved in stress response, inflammation, and apoptosis. Consistent with this in vitro BMDM phenotype, AIF1 deficiency reduced NF-κB pathway activity in vivo and increased apoptotic cell number in atherosclerotic lesions from Aif1^-/-;ApoE^-/- mice.

CONCLUSIONS

These findings characterize AIF1 as a positive regulator of the NF-κB pathway that supports MP functions such as survival and efferocytosis. In inflammatory settings such as atherosclerosis, these AIF1-dependent activities serve to clear cellular and other debris and limit necrotic core expansion, and may oppose lesion destabilization.

Microparticles and cardiovascular diseases

Microparticles are a distinctive group of small vesicles, without nucleus, which are involved as significant modulators in several physiological and pathophysiological mechanisms. Plasma microparticles from various cellular lines have been subject of research. Data suggest that they are key players in development and manifestation of cardiovascular diseases and their presence, in high levels, is associated with chronic inflammation, endothelial damage and thrombosis. The strong correlation of microparticle levels with several outcomes in cardiovascular diseases has led to their utilization as biomarkers. Despite the limited clinical application at present, their significance emerges, mainly because their detection and enumeration methods are improving. This review article summarizes the evidence derived from research, related with the genesis and the function of microparticles in the presence of various cardiovascular risk factors and conditions. The current data provide a substrate for several theories of how microparticles influence various cellular mechanisms by transferring biological information.