A role for the apoptosis inhibitory factor AIM/Spalpha/Api6 in atherosclerosis development

FFAR4 Deficiency Increases Necrotic Cores in Advanced Lesions of ApoE-/- Mice-Brief Report

BACKGROUND

FFAR4 (free fatty acid receptor 4) has emerged as a target for preventing cardiovascular disease through its ability to control macrophage inflammation and foam cell formation. Previous studies have shown that FFAR4 activation can protect against the accumulation of arterial plaque buildup in atherosclerotic animal models. The goal of our study is to test the hypothesis that FFAR4 deficiency will increase atherosclerotic plaque development in apoE-/- mice.

METHODS

Male and female apoE-/-/Ffar4-/- mice and their apoE-/- controls were fed a Western diet for 8 or 16 weeks to assess early and advanced atherosclerotic lesions, respectively. At the end of each study, atherosclerotic plaque severity was determined by analyzing the aortic sinus lesion area of the heart and the en face lesion area of the aortic arch.

RESULTS

Following 8 weeks of Western diet feeding, lesions from apoE-/-/Ffar4-/- male and female mice had 33% and 22% decreases, respectively, in the aortic sinus lesion area with no changes in the aortic arch lesion area. After 16 weeks of Western diet feeding, the lesions showed no changes in the area or volume of the aortic sinus between apoE-/-/Ffar4-/- mice and apoE-/- controls. However, male apoE-/-/Ffar4-/- mice had a 27% increase in the plaque lesion area in the aortic arch compared with apoE-/- controls. Despite similar sizes of lesions in the aortic sinus, apoE-/-/Ffar4-/- mice had larger necrotic cores compared with the apoE-/- control mice. In fact, male and female mice had 43% and 37% increases in the necrotic lesion area, respectively.

CONCLUSIONS

These data suggest a novel role for FFAR4 in reducing necrotic core lesion formation and support a protective role for FFAR4 in stabilizing atherosclerotic plaques.

Redefining Macrophage Heterogeneity in Atherosclerosis: A Focus on Possible Therapeutic Implications

Atherosclerosis is a lipid disorder where modified lipids (especially oxidized LDL) induce macrophage foam cell formation in the aorta. Its pathogenesis involves a continuum of persistent inflammation accompanied by dysregulated anti-inflammatory responses. Changes in the immune cell status due to differences in the lesional microenvironment are crucial in terms of plaque development, its progression, and plaque rupture. Ly6Chi monocytes generated through both medullary and extramedullary cascades act as one of the major sources of plaque macrophages and thereby foam cells. Both monocytes and monocyte-derived macrophages also participate in pathological events in atherosclerosis-associated multiple organ systems through inter-organ communications. For years, macrophage phenotypes M1 and M2 have been shown to perpetuate inflammatory and resolution responses; nevertheless, such a dualistic classification is too simplistic and contains severe drawbacks. As the lesion microenvironment is enriched with multiple mediators that possess the ability to activate macrophages to diverse phenotypes, it is obvious that such cells should demonstrate substantial heterogeneity. Considerable research in this regard has indicated the presence of additional macrophage phenotypes that are exclusive to atherosclerotic plaques, namely Mox, M4, Mhem, and M(Hb) type. Furthermore, although the concept of macrophage clusters has come to the fore in recent years with the evolution of high-dimensional techniques, classifications based on such 'OMICS' approaches require extensive functional validation as well as metabolic phenotyping. Bearing this in mind, the current review provides an overview of the status of different macrophage populations and their role during atherosclerosis and also outlines possible therapeutic implications.

Apolipoprotein A1 deficiency increases macrophage apoptosis and necrotic core development in atherosclerotic plaques in a Bim-dependent manner

In advanced atherosclerotic lesions, macrophage apoptosis contributes to plaque progression and the formation of necrotic cores, rendering plaques vulnerable to rupture. The proapoptotic protein B-cell lymphoma 2 [Bcl-2] interacting mediator of cell death (Bim) plays a crucial role in mediating apoptosis in macrophages under prolonged endoplasmic reticulum stress. HDL has been shown to suppress macrophage apoptosis induced by endoplasmic reticulum stressors. To investigate the impact of apolipoprotein A1 (ApoA1) deficiency, associated with reduced HDL levels, on necrotic core growth and plaque apoptosis, we introduced ApoA1 deficiency into low-density lipoprotein receptor (LDLR) knockout mice and fed them a high-fat diet for 10 weeks. ApoA1-deficient Ldlr KO mice developed advanced plaques characterized by large necrotic cores, increased apoptosis, and elevated Bim expression in macrophages within the plaques. To assess whether deletion of Bim could mitigate this development, mice underwent bone marrow transplantation with bone marrow from either Bim-deficient mice or from mice with a deletion of myeloid-derived Bim driven by LyzM-cre. Inhibiting Bim in all bone marrow-derived cells led to leukocytosis, reductions in plasma cholesterol and triglyceride levels, and decreased plaque apoptosis, necrotic core, and plaque sizes in ApoA1 and Ldlr double-KO mice but not in Ldlr KO mice. Likewise, conditional deletion of Bim in the myeloid compartment of ApoA1 and Ldlr double-KO mice also reduced apoptosis, necrotic core sizes, and plaque sizes, without inducing leukocytosis or lowering plasma cholesterol levels. These findings suggest that ApoA1 deficiency triggers apoptosis in myeloid cells through a Bim-dependent pathway, significantly contributing to the development of necrotic cores and the progression of atherosclerotic plaques.

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.

CD5L up-regulates the TGF-β signaling pathway and promotes renal fibrosis

Renal fibrosis is the common final pathway of progressive renal diseases, in which the macrophages play an important role. ELISA was used to detect CD5 antigen-like (CD5L) in serum samples from end-stage renal disease (ESRD), as well as in mice serum with unilateral ureteral occlusion (UUO). Recombinant CD5L was injected into UUO mice to assess renal injury, fibrosis, and macrophage infiltration. The expression of CD5L was significantly upregulated in the serum of patients with ESRD and UUO mice. Histological analysis showed that rCD5L-treated UUO mice had more severe renal injury and fibrosis. Furthermore, rCD5L promoted the phenotypic transfer of monocytes from Ly6Chigh to LyC6low. RCD5L promoted TGF-β signaling pathway activation by promoting Smad2/3 phosphorylation. We used Co-IP to identify HSPA5 interact with CD5L on cell membrane could inhibit the formation of the Cripto/HSPA5 complex, and promote the activation of the TGF-β signaling pathway. The CD5L antibody could reduce the degree of renal fibrosis in UUO mice.

CD5L associates with IgM via the J chain

CD5 antigen-like (CD5L), also known as Spα or AIM (Apoptosis inhibitor of macrophage), emerges as an integral component of serum immunoglobulin M (IgM). However, the molecular mechanism underlying the interaction between IgM and CD5L has remained elusive. In this study, we present a cryo-electron microscopy structure of the human IgM pentamer core in complex with CD5L. Our findings reveal that CD5L binds to the joining chain (J chain) in a Ca2+-dependent manner and further links to IgM via a disulfide bond. We further corroborate recently published data that CD5L reduces IgM binding to the mucosal transport receptor pIgR, but does not impact the binding of the IgM-specific receptor FcμR. Additionally, CD5L does not interfere with IgM-mediated complement activation. These results offer a more comprehensive understanding of IgM and shed light on the function of the J chain in the immune system.

Administration of an antibody against apoptosis inhibitor of macrophage prevents aortic aneurysm progression in mice

Apoptosis inhibitor of macrophage (AIM) is known to induce apoptosis resistance in macrophages and to exacerbate chronic inflammation, leading to arteriosclerosis. The role of AIM in aortic aneurysm (AA) remains unknown. This study examined the effects of an anti-AIM antibody in preventing AA formation and progression. In apolipoprotein E-deficient mice, AA was induced by subcutaneous angiotensin II infusion. Mice were randomly divided into two groups: (i) AIM group; weekly anti-murine AIM monoclonal antibody injection (n = 10), and (ii) IgG group; anti-murine IgG antibody injection as control (n = 14). The AIM group, compared with the IgG group, exhibited reduced AA enlargement (aortic diameter at 4 weeks: 2.1 vs. 2.7 mm, respectively, p = 0.012); decreased loss of elastic lamellae construction; reduced expression levels of IL-6, TNF-α, and MCP-1; decreased numbers of AIM-positive cells and inflammatory M1 macrophages (AIM: 1.4 vs. 8.0%, respectively, p = 0.004; M1 macrophages: 24.5 vs. 55.7%, respectively, p = 0.017); and higher expression of caspase-3 in the aortic wall (22.8 vs. 10.5%, respectively, p = 0.019). Our results suggest that administration of an anti-AIM antibody mitigated AA progression by alleviating inflammation and promoting M1 macrophage apoptosis.

Accumulation of persistent organic pollutants in the kidneys of pet cats (Felis silvestris catus) and the potential implications for their health

Persistent organic pollutants (POPs), such as polychlorinated diphenyls (PCBs) and brominated diphenyl ethers (PBDEs), are ubiquitous in the pet cat's living environment and are ingested through dietary intake and environmental exposure such as house dust. Cats are known to be susceptible to chronic kidney disease (CKD) and exposure to POPs may be associated with CKD. However, no studies have been conducted on the renal accumulation and health effects of POPs in cats. The objective of this study was to elucidate the accumulation of PCBs, PBDEs, and organochlorine pesticides (OCPs) in the kidneys of domestic cats and discuss their potential impact on feline health. We report here that cats specifically accumulate POPs in their kidneys. Tissue samples were collected from the kidneys, livers, and muscles of cats and the concentrations of POPs in these tissues were analyzed in this study. The results showed that these compounds accumulated significantly higher in the kidney compared to other tissues. In addition, the ability to accumulate in the kidney was higher in cats than in other animals, suggesting that cats have a unique pattern of POPs accumulation in their kidneys, which is thought to occur because cats store a significant number of lipid droplets in the proximal tubules of the kidneys. This unique feature suggests that lipophilic POPs may accumulate in these lipid droplets during the excretory process. Accumulation of certain POPs in the kidneys causes necrosis and sloughing of renal tubular epithelial cells, which may be associated with CKD, a common disease in cats. This study provides valuable insight into understanding the renal accumulation and risk of POPs in cats and provides essential knowledge for developing strategies to protect the health and welfare of domestic cats.

CD5L as a promising biological therapeutic for treating sepsis

Sepsis results from systemic, dysregulated inflammatory responses to infection, culminating in multiple organ failure. Here, we demonstrate the utility of CD5L for treating experimental sepsis caused by cecal ligation and puncture (CLP). We show that CD5L's important features include its ability to enhance neutrophil recruitment and activation by increasing circulating levels of CXCL1, and to promote neutrophil phagocytosis. CD5L-deficient mice exhibit impaired neutrophil recruitment and compromised bacterial control, rendering them susceptible to attenuated CLP. CD5L-/- peritoneal cells from mice subjected to medium-grade CLP exhibit a heightened pro-inflammatory transcriptional profile, reflecting a loss of control of the immune response to the infection. Intravenous administration of recombinant CD5L (rCD5L) in immunocompetent C57BL/6 wild-type (WT) mice significantly ameliorates measures of disease in the setting of high-grade CLP-induced sepsis. Furthermore, rCD5L lowers endotoxin and damage-associated molecular pattern (DAMP) levels, and protects WT mice from LPS-induced endotoxic shock. These findings warrant the investigation of rCD5L as a possible treatment for sepsis in humans.

Sexual dimorphism in atherosclerotic plaques of aged Ldlr-/- mice

BACKGROUND

Atherosclerosis, the main underlying pathology of cardiovascular disease, is a chronic inflammatory disease characterized by lipid accumulation and immune cell responses in the vascular wall, resulting in plaque formation. It is well-known that atherosclerosis prevalence and manifestation vary by sex. However, sexual dimorphism in the immune landscape of atherosclerotic plaques has up to date not been studied at high-resolution. In this study, we investigated sex-specific differences in atherosclerosis development and the immunological landscape of aortas at single-cell level in aged Ldlr-/- mice.

METHODS

We compared plaque morphology between aged male and female chow diet-fed Ldlr-/- mice (22 months old) with histological analysis. Using single-cell RNA-sequencing and flow cytometry on CD45+ immune cells from aortas of aged Ldlr-/- mice, we explored the immune landscape in the atherosclerotic environment in males and females.

RESULTS

We show that plaque volume is comparable in aged male and female mice, and that plaques in aged female mice contain more collagen and cholesterol crystals, but less necrotic core and macrophage content compared to males. We reveal increased immune cell infiltration in female aortas and found that expression of pro-atherogenic markers and inflammatory signaling pathways was enriched in plaque immune cells of female mice. Particularly, female aortas show enhanced activation of B cells (Egr1, Cd83, Cd180), including age-associated B cells, in addition to an increased M1/M2 macrophage ratio, where Il1b+ M1-like macrophages display a more pro-inflammatory phenotype (Nlrp3, Cxcl2, Mmp9) compared to males. In contrast, increased numbers of age-associated Gzmk+CD8+ T cells, dendritic cells, and Trem2+ macrophages were observed in male aortas.

CONCLUSIONS

Altogether, our findings highlight that sex is a variable that contributes to immunological differences in the atherosclerotic plaque environment in mice and provide valuable insights for further preclinical studies into the impact of sex on the pathophysiology of atherosclerosis.

Programmed death of macrophages in atherosclerosis: mechanisms and therapeutic targets

Atherosclerosis is a progressive inflammatory disorder of the arterial vessel wall characterized by substantial infiltration of macrophages, which exert both favourable and detrimental functions. Early in atherogenesis, macrophages can clear cytotoxic lipoproteins and dead cells, preventing cytotoxicity. Efferocytosis - the efficient clearance of dead cells by macrophages - is crucial for preventing secondary necrosis and stimulating the release of anti-inflammatory cytokines. In addition, macrophages can promote tissue repair and proliferation of vascular smooth muscle cells, thereby increasing plaque stability. However, advanced atherosclerotic plaques contain large numbers of pro-inflammatory macrophages that secrete matrix-degrading enzymes, induce death in surrounding cells and contribute to plaque destabilization and rupture. Importantly, macrophages in the plaque can undergo apoptosis and several forms of regulated necrosis, including necroptosis, pyroptosis and ferroptosis. Regulated necrosis has an important role in the formation and expansion of the necrotic core during plaque progression, and several triggers for necrosis are present within atherosclerotic plaques. This Review focuses on the various forms of programmed macrophage death in atherosclerosis and the pharmacological interventions that target them as a potential means of stabilizing vulnerable plaques and improving the efficacy of currently available anti-atherosclerotic therapies.

Signaling pathways regulating the immune function of cochlear supporting cells and their involvement in cochlear pathophysiology

The inner ear, including the cochlea, used to be regarded as an immune-privileged site because of its immunologically isolated environment caused by the blood-labyrinthine barrier. Cochlear resident macrophages, which originate from the yolk sac or fetal liver during the embryonic stage and are maintained after birth, are distributed throughout various regions of the cochlear duct. Intriguingly, these cells are absent in the organ of Corti, where hair cells (HCs) and supporting cells (SCs) are located, except for a limited number of ionized calcium-binding adapter molecule 1 (Iba1)-positive cells. Instead, SCs exert glial functions varying from a quiescent to an emergency state. Notably, SCs acquire the nature of macrophages and begin to secrete inflammatory cytokines during viral infection in the organ of Corti, which is ostensibly unprotected owing to the lack of general resident macrophages. This review provides an overview of both positive and negative functions of SCs enabled to acquire macrophage phenotypes upon viral infection focusing on the signaling pathways that regulate these functions. The former function protects HCs from viral infection by inducting type I interferons, and the latter function induces HC death by necroptosis, leading to sensorineural hearing loss. Thus, SCs play contradictory roles as immune cells with acquired macrophage phenotypes; thereby, they are favorable and unfavorable to HCs, which play a pivotal role in hearing function.

Cordyceps as potential therapeutic agents for atherosclerosis

Atherosclerosis is a leading cause of mortality and morbidity worldwide. Despite the challenges in managing atherosclerosis, researchers continue to investigate new treatments and complementary therapies. Cordyceps is a traditional Chinese medicine that has recently gained attention as a potential therapeutic agent for atherosclerosis. Numerous studies have demonstrated the effectiveness of cordyceps in treating atherosclerosis through various pharmacological actions, including anti-inflammatory and antioxidant activities, lowering cholesterol, inhibiting platelet aggregation, and modulating apoptosis or autophagy in vascular endothelial cells. Notably, the current misuse of the terms cordyceps and Ophiocordyceps sinensis has caused confusion among researchers, and complicated the current academic research on cordyceps. This review focuses on the chemical composition, pharmacological actions, and underlying mechanisms contributing to the anti-atherosclerotic effects of cordyceps and the mycelium of Ophiocordyceps spp. This review provides a resource for the research on the development of new drugs for atherosclerosis from cordyceps. Please cite this article as: Zhang Y, Liu SJ. Cordyceps as potential therapeutic agents for atherosclerosis. J Integr Med. 2024; 22(2): 102-114.

Kupffer cells dictate hepatic responses to the atherogenic dyslipidemic insult

Apolipoprotein-B (APOB)-containing lipoproteins cause atherosclerosis. Whether the vasculature is the initially responding site or if atherogenic dyslipidemia affects other organs simultaneously is unknown. Here we show that the liver responds to a dyslipidemic insult based on inducible models of familial hypercholesterolemia and APOB tracing. An acute transition to atherogenic APOB lipoprotein levels resulted in uptake by Kupffer cells and rapid accumulation of triglycerides and cholesterol in the liver. Bulk and single-cell RNA sequencing revealed a Kupffer-cell-specific transcriptional program that was not activated by a high-fat diet alone or detected in standard liver function or pathological assays, even in the presence of fulminant atherosclerosis. Depletion of Kupffer cells altered the dynamic of plasma and liver lipid concentrations, indicating that these liver macrophages help restrain and buffer atherogenic lipoproteins while simultaneously secreting atherosclerosis-modulating factors into plasma. Our results place Kupffer cells as key sentinels in organizing systemic responses to lipoproteins at the initiation of atherosclerosis.

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

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

Apoptosis inhibitor of macrophages/CD5L enhances phagocytosis in the trabecular meshwork cells and regulates ocular hypertension

The trabecular meshwork (TM) cells of the eye are important for controlling intraocular pressure (IOP) and regulating outflow resistance in the aqueous humor. TM cells can remove particles and cellular debris by phagocytosis, decreasing both outflow resistance and IOP. However, the underlying mechanisms remain unclear. Here, we investigate whether apoptosis inhibitor of macrophages (AIM), which mediates the removal of dead cells and debris in renal tubular epithelial cells, regulates the phagocytic capacity of TM cells. In vitro experiments revealed that CD36, the main receptor for AIM, colocalized with AIM in human TM cells; additionally, phagocytosis was stimulated when AIM was provided. Furthermore, in a mouse model with transient IOP elevation induced by laser iridotomy (LI), removal of accumulated iris pigment epithelial cells or debris in the TM and recovery of IOP to baseline levels were delayed in AIM-/- mice, compared with control mice. However, treatment with AIM eyedrops rescued AIM-/- mice from the elevated IOP after LI. Since AIM is a protein known to inhibit macrophage apoptosis, we additionally verified its involvement in macrophage removal of cellular debris and IOP. There were no statistically significant differences in the number of macrophages between control mice and AIM-/- mice in the TM. Additionally, we confirmed the rescue effect of the rAIM eyedrops after macrophages had been removed by clodronate liposomes. Therefore, AIM plays an important role in regulating the phagocytic capacity of TM cells, thereby affecting outflow resistance. Our results suggest that drugs targeting the phagocytic capacity of TM cells via the AIM-CD36 pathway may be used to treat glaucoma.

Serum level of apoptosis inhibitor of macrophage in dogs with histiocytic sarcoma and its association with the disease

Histiocytic sarcoma (HS) is a rare neoplasm of macrophages or dendritic cells with a poor prognosis in dogs. As the apoptosis inhibitor of macrophage (AIM) is characteristically expressed in canine macrophages, we hypothesised that AIM is involved in the development or progression of HS in dogs. In this study, AIM expression in the tumour region and serum AIM levels in dogs with HS was assessed. Additionally, the effects of AIM overexpression on HS cell viability were investigated using a HS cell line that was selected from five validated HS cell lines. Immunohistochemistry showed that AIM expression was observed in the cytoplasm of the HS cells. CD36, a candidate AIM receptor, was also observed on the cell membrane of HS cells. When the serum AIM level was detected in 36 dogs with HS and 10 healthy dogs via western blot analysis, the AIM levels in the HS dogs were significantly higher than those in the controls. AIM mRNA expression in the 5 HS cell lines varied but was higher than that in the other tumour-derived lines. Among the five HS cell lines, DH82 originally had lower AIM and the highest CD36 expression. When AIM was overexpressed in DH82, therein cell growth speed and invasion, apoptosis inhibition and phagocytic activity were strongly upregulated. These data suggest that elevated intra-tumour expression of AIM could induce the progression of HS cells in dogs. Moreover, elevated serum AIM levels in dogs with HS could serve as a biomarker of HS.

Loss of Macrophage mTORC2 Drives Atherosclerosis via FoxO1 and IL-1β Signaling

BACKGROUND

The mTOR (mechanistic target of rapamycin) pathway is a complex signaling cascade that regulates cellular growth, proliferation, metabolism, and survival. Although activation of mTOR signaling has been linked to atherosclerosis, its direct role in lesion progression and in plaque macrophages remains poorly understood. We previously demonstrated that mTORC1 (mTOR complex 1) activation promotes atherogenesis through inhibition of autophagy and increased apoptosis in macrophages.

METHODS

Using macrophage-specific Rictor- and mTOR-deficient mice, we now dissect the distinct functions of mTORC2 pathways in atherogenesis.

RESULTS

In contrast to the atheroprotective effect seen with blockade of macrophage mTORC1, macrophage-specific mTORC2-deficient mice exhibit an atherogenic phenotype, with larger, more complex lesions and increased cell death. In cultured macrophages, we show that mTORC2 signaling inhibits the FoxO1 (forkhead box protein O1) transcription factor, leading to suppression of proinflammatory pathways, especially the inflammasome/IL (interleukin)-1β response, a key mediator of vascular inflammation and atherosclerosis. In addition, administration of FoxO1 inhibitors efficiently rescued the proinflammatory response caused by mTORC2 deficiency both in vitro and in vivo. Interestingly, collective deletion of macrophage mTOR, which ablates mTORC1- and mTORC2-dependent pathways, leads to minimal change in plaque size or complexity, reflecting the balanced yet opposing roles of these signaling arms.

CONCLUSIONS

Our data provide the first mechanistic details of macrophage mTOR signaling in atherosclerosis and suggest that therapeutic measures aimed at modulating mTOR need to account for its dichotomous functions.

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

INTRODUCTION

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

AREAS COVERED

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

EXERT OPINION

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

The comprehensive role of apoptosis inhibitor of macrophage (AIM) in pathological conditions

CD5L/AIM (apoptosis inhibitor of macrophage), as an important component in maintaining tissue homeostasis and inflammation, is mainly produced and secreted by macrophages but partially dissociated and released from blood AIM-IgM. AIM plays a regulatory role in intracellular physiological mechanisms, including lipid metabolism and apoptosis. AIM not only increases in autoimmune diseases, directly targets liver cells in liver cancer and promotes cell clearance in acute kidney injury, but also causes arteriosclerosis and cardiovascular events, and aggravates inflammatory reactions in lung diseases and sepsis. Obviously, AIM plays a pleiotropic role in the body. However, to date, studies have failed to decipher the mechanisms behind its different roles (beneficial or harmful) in inflammatory regulation. The inflammatory response is a "double-edged sword," and maintaining balance is critical for effective host defense while minimizing the adverse side effects of acute inflammation. Enhancing the understanding of AIM function could provide the theoretical basis for new therapies in these pathological settings. In this review, we discuss recent studies on the roles of AIM in lipid metabolism, autoimmune diseases and organic tissues, such as liver cancer, myocardial infarction, and kidney disease.

Apoptosis Inhibitor of Macrophages Contributes to the Chronicity of Mycobacterium avium Infection by Promoting Foamy Macrophage Formation

In Mycobacterium avium infections, macrophages play a critical role in the host defense response. Apoptosis inhibitor of macrophage (AIM), also known as CD5L, may represent a novel supportive therapy against various diseases, including metabolic syndrome and infectious diseases. The mechanisms of AIM include modulating lipid metabolism in macrophages and other host cells. We investigated the role of AIM in M. avium infections in vitro and in vivo. In a mouse model of M. avium pneumonia, foamy macrophages were induced 6 wk after infection. The bacteria localized in these macrophages. Flow cytometric analysis also confirmed that the percentage of CD11chighMHCclassIIhigh interstitial and alveolar macrophages, a cell surface marker defined as foamy macrophages, increased significantly after infection. AIM in alveolar lavage fluid and serum gradually increased after infection. Administration of recombinant AIM significantly increased the number of bacteria in the lungs of mice, accompanied by the induction of inflammatory cytokine and iNOS expression. In mouse bone marrow-derived macrophages, the mRNA expression of AIM after M. avium infection and the amount of AIM in the supernatant increased prior to the increase in intracellular bacteria. Infected cells treated with anti-AIM Abs had fewer bacteria and a higher percentage of apoptosis-positive cells than infected cells treated with isotype control Abs. Finally, AIM in the sera of patients with M. avium-pulmonary disease was measured and was significantly higher than in healthy volunteers. This suggests that AIM production is enhanced in M. avium-infected macrophages, increasing macrophage resistance to apoptosis and providing a possible site for bacterial growth.

Macrophage-Derived 25-Hydroxycholesterol Promotes Vascular Inflammation, Atherogenesis, and Lesion Remodeling

BACKGROUND

Cross-talk between sterol metabolism and inflammatory pathways has been demonstrated to significantly affect the development of atherosclerosis. Cholesterol biosynthetic intermediates and derivatives are increasingly recognized as key immune regulators of macrophages in response to innate immune activation and lipid overloading. 25-Hydroxycholesterol (25-HC) is produced as an oxidation product of cholesterol by the enzyme cholesterol 25-hydroxylase (CH25H) and belongs to a family of bioactive cholesterol derivatives produced by cells in response to fluctuating cholesterol levels and immune activation. Despite the major role of 25-HC as a mediator of innate and adaptive immune responses, its contribution during the progression of atherosclerosis remains unclear.

METHODS

The levels of 25-HC were analyzed by liquid chromatography-mass spectrometry, and the expression of CH25H in different macrophage populations of human or mouse atherosclerotic plaques, respectively. The effect of CH25H on atherosclerosis progression was analyzed by bone marrow adoptive transfer of cells from wild-type or Ch25h-/- mice to lethally irradiated Ldlr-/- mice, followed by a Western diet feeding for 12 weeks. Lipidomic, transcriptomic analysis and effects on macrophage function and signaling were analyzed in vitro from lipid-loaded macrophage isolated from Ldlr-/- or Ch25h-/-;Ldlr-/- mice. The contribution of secreted 25-HC to fibrous cap formation was analyzed using a smooth muscle cell lineage-tracing mouse model, Myh11ERT2CREmT/mG;Ldlr-/-, adoptively transferred with wild-type or Ch25h-/- mice bone marrow followed by 12 weeks of Western diet feeding.

RESULTS

We found that 25-HC accumulated in human coronary atherosclerotic lesions and that macrophage-derived 25-HC accelerated atherosclerosis progression, promoting plaque instability through autocrine and paracrine actions. 25-HC amplified the inflammatory response of lipid-loaded macrophages and inhibited the migration of smooth muscle cells within the plaque. 25-HC intensified inflammatory responses of lipid-laden macrophages by modifying the pool of accessible cholesterol in the plasma membrane, which altered Toll-like receptor 4 signaling, promoted nuclear factor-κB-mediated proinflammatory gene expression, and increased apoptosis susceptibility. These effects were independent of 25-HC-mediated modulation of liver X receptor or SREBP (sterol regulatory element-binding protein) transcriptional activity.

CONCLUSIONS

Production of 25-HC by activated macrophages amplifies their inflammatory phenotype, thus promoting atherogenesis.

K-80003 Inhibition of Macrophage Apoptosis and Necrotic Core Development in Atherosclerotic Vulnerable Plaques

PURPOSE

Macrophage apoptosis coupled with a defective phagocytic clearance of the apoptotic cells promotes plaque necrosis in advanced atherosclerosis, which causes acute atherothrombotic vascular disease. Nonsteroidal anti-inflammatory drug sulindac derivative K-80003 treatment was previously reported to dramatically attenuate atherosclerotic plaque progression and destabilization. However, the underlying mechanisms are not fully understood. This study aimed to determine the role of K-80003 on macrophage apoptosis and elucidate the underlying mechanism.

METHODS

The mouse model of vulnerable carotid plaque in ApoE-/- mice was developed in vivo. Consequently, mice were randomly grouped into two study groups: the control group and the K-80003 group (30 mg/kg/day). Samples of carotid arteries were collected to determine atherosclerotic necrotic core area, cellular apoptosis, and oxidative stress. The effects of K-80003 on RAW264.7 macrophage apoptosis, oxidative stress, and autophagic flux were also examined in vitro.

RESULTS

K-80003 significantly suppressed necrotic core formation and inhibited cellular apoptosis of vulnerable plaques. K-80003 can also inhibit 7-ketocholesterol-induced macrophage apoptosis in vitro. Furthermore, K-80003 inhibited intraplaque cellular apoptosis mainly through the suppression of oxidative stress, which is a key cause of advanced lesional macrophage apoptosis. Mechanistically, K-80003 prevented 7-ketocholesterol-induced impairment of autophagic flux in macrophages, evidenced by the decreased LC3II and SQSTM1/p62 expression, GFP-RFP-LC3 cancellation upon K-80003 treatment.

CONCLUSION

Inhibition of macrophage apoptosis and necrotic core formation by autophagy-mediated reduction of oxidative stress is one mechanism of the suppression of plaque progression and destabilization by K-80003.

Liver X Receptor: a potential target in the treatment of atherosclerosis

INTRODUCTION

Liver X receptors (LXRs) are master regulators of atherogenesis. Their anti-atherogenic potential has been attributed to their role in the inhibition of macrophage-mediated inflammation and promotion of reverse cholesterol transport. Owing to the significance of their anti-atherogenic potential, it is essential to develop and test new generation LXR agonists, both synthetic and natural, to identify potential LXR-targeted therapeutics for the future.

AREAS COVERED

This review describes the role of LXRs in atherosclerotic development, provides a summary of LXR agonists and future directions for atherosclerosis research. We searched PubMed, Scopus and Google Scholar for relevant reports, from last 10 years, using atherosclerosis, liver X receptor, and LXR agonist as keywords.

EXPERT OPINION

LXRα has gained widespread recognition as a regulator of cholesterol homeostasis and expression of inflammatory genes. Further research using models of cell type-specific knockout and specific agonist-targeted LXR isoforms is warranted. Enthusiasm for therapeutic value of LXR agonists has been tempered due to LXRα-mediated induction of hepatic lipogenesis. LXRα agonism and LXRβ targeting, gut-specific inverse LXR agonists, investigations combining LXR agonists with other lipogenesis mitigating agents, like IDOL antagonists and synthetic HDL, and targeting ABCA1, M2 macrophages and LXRα phosphorylation, remain as promising possibilities.

DIA-Based Proteomic Analysis of Plasma Protein Profiles in Patients with Severe Acute Pancreatitis

Acute pancreatitis (AP) is a pancreatic inflammatory disease that varies greatly in course and severity. To further the understanding of the pathology of AP, we carried out data-independent acquisition-based proteomic analyses using proteins extracted from the plasma of patients with severe acute pancreatitis (SAP) (experimental group) and healthy volunteers (control group). Compared to the control group, there were 35 differentially expressed proteins (DEPs) in the plasma of patients with SAP. Of those, the expression levels for 6 proteins were significantly increased, and 29 proteins were significantly decreased. Moreover, six candidate biomarkers—VWF, ORM2, CD5L, CAT, IGLV3-10, and LTF—were matched as candidate biomarkers of the disease severity of AP. The area under the receiver operating characteristic of 0.903 (95% CI: 0.839, 0.967) indicated that this combination of these six candidate biomarkers had a good prediction accuracy for predicting the severity of AP. Our study provides specific DEPs that may be useful in the diagnosis and prognosis of SAP, which suggests new theoretical bases for the occurrence and development of SAP and offers potential novel treatment strategies for SAP.

Macrophage SR-B1 in atherosclerotic cardiovascular disease

PURPOSE OF REVIEW

Scavenger receptor class B type 1 (SR-B1) promotes atheroprotection through its role in HDL metabolism and reverse cholesterol transport in the liver. However, evidence indicates that SR-B1 may impact atherosclerosis through nonhepatic mechanisms.

RECENT FINDINGS

Recent studies have brought to light various mechanisms by which SR-B1 affects lesional macrophage function and protects against atherosclerosis. Efferocytosis is efficient in early atherosclerotic lesions. At this stage, and beyond its role in cholesterol efflux, SR-B1 promotes free cholesterol-induced apoptosis of macrophages through its control of apoptosis inhibitor of macrophage (AIM). At more advanced stages, macrophage SR-B1 binds and mediates the removal of apoptotic cells. SR-B1 also participates in the induction of autophagy which limits necrotic core formation and increases plaque stability.

SUMMARY

These studies shed new light on the atheroprotective role of SR-B1 by emphasizing its essential contribution in macrophages during atherogenesis as a function of lesion stages. These new findings suggest that macrophage SR-B1 is a therapeutic target in cardiovascular disease.

The heart-brain axis: A proteomics study of meditation on the cardiovascular system of Tibetan Monks

Background

There have been mixed reports on the beneficial effects of meditation in cardiovascular disease (CVD), which is widely considered the leading cause of death worldwide.

Methods

To clarify the role of meditation in modulating the heart-brain axis, we implemented an extreme phenotype strategy, i.e., Tibetan monks (BMI > 30) who practised 19.20 ± 7.82 years of meditation on average and their strictly matched non-meditative Tibetan controls. Hypothesis-free advanced proteomics strategies (Data Independent Acquisition and Targeted Parallel Reaction Monitoring) were jointly applied to systematically investigate and target the plasma proteome underlying meditation. Total cholesterol, low-density lipoprotein cholesterol  (LDL-C), apolipoprotein B (Apo B) and lipoprotein (a) [Lp(a)] as the potential cardiovascular risk factors were evaluated. Heart rate variability (HRV) was assessed by electrocardiogram.

Findings

Obesity, hypertension, and reduced HRV is offset by long-term meditation. Notably, meditative monks have blood pressure and HRV comparable to their matched Tibetan controls. Meditative monks have a protective plasma proteome, related to decreased atherosclerosis, enhanced glycolysis, and oxygen release, that confers resilience to the development of CVD. In addition, clinical risk factors in plasma were significantly decreased in monks compared with controls, including total cholesterol, LDL-C, Apo B, and Lp(a).

Interpretation

To our knowledge, this work is the first well-controlled proteomics investigation of long-term meditation, which opens up a window for individuals characterized by a sedentary lifestyle to improve their cardiovascular health with an accessible method practised for more than two millennia.

Funding

See the Acknowledgements section.

Foam Cells in Atherosclerosis: Novel Insights Into Its Origins, Consequences, and Molecular Mechanisms

Foam cells play a vital role in the initiation and development of atherosclerosis. This review aims to summarize the novel insights into the origins, consequences, and molecular mechanisms of foam cells in atherosclerotic plaques. Foam cells are originated from monocytes as well as from vascular smooth muscle cells (VSMC), stem/progenitor cells, and endothelium cells. Novel technologies including lineage tracing and single-cell RNA sequencing (scRNA-seq) have revolutionized our understanding of subtypes of monocyte- and VSMC-derived foam cells. By using scRNA-seq, three main clusters including resident-like, inflammatory, and triggering receptor expressed on myeloid cells-2 (Trem2 hi ) are identified as the major subtypes of monocyte-derived foam cells in atherosclerotic plaques. Foam cells undergo diverse pathways of programmed cell death including apoptosis, autophagy, necroptosis, and pyroptosis, contributing to the necrotic cores of atherosclerotic plaques. The formation of foam cells is affected by cholesterol uptake, efflux, and esterification. Novel mechanisms including nuclear receptors, non-coding RNAs, and gut microbiota have been discovered and investigated. Although the heterogeneity of monocytes and the complexity of non-coding RNAs make obstacles for targeting foam cells, further in-depth research and therapeutic exploration are needed for the better management of atherosclerosis.

The Function, Regulation and Mechanism of Programmed Cell Death of Macrophages in Atherosclerosis

Atherosclerosis is a chronic progressive inflammatory vascular disease, which is an important pathological basis for inducing a variety of cardio-cerebrovascular diseases. As a kind of inflammatory cells, macrophages are the most abundant immune cells in atherosclerotic plaques and participate in the whole process of atherosclerosis and are the most abundant immune cells in atherosclerotic plaques. Recent studies have shown that programmed cell death plays a critical role in the progression of many diseases. At present, it is generally believed that the programmed death of macrophages can affect the development and stability of atherosclerotic vulnerable plaques, and the intervention of macrophage death may become the target of atherosclerotic therapy. This article reviews the role of macrophage programmed cell death in the progression of atherosclerosis and the latest therapeutic strategies targeting macrophage death within plaques.

ISM1 protects lung homeostasis via cell-surface GRP78-mediated alveolar macrophage apoptosis

Alveolar macrophages (AMs) are critical for lung immune defense and homeostasis. They are orchestrators of chronic obstructive pulmonary disease (COPD), with their number significantly increased and functions altered in COPD. However, it is unclear how AM number and function are controlled in a healthy lung and if changes in AMs without environmental assault are sufficient to trigger lung inflammation and COPD. We report here that absence of isthmin 1 (ISM1) in mice (Ism1-/- ) leads to increase in both AM number and functional heterogeneity, with enduring lung inflammation, progressive emphysema, and significant lung function decline, phenotypes similar to human COPD. We reveal that ISM1 is a lung resident anti-inflammatory protein that selectively triggers the apoptosis of AMs that harbor high levels of its receptor cell-surface GRP78 (csGRP78). csGRP78 is present at a heterogeneous level in the AMs of a healthy lung, but csGRP78high AMs are expanded in Ism1-/- mice, cigarette smoke (CS)-induced COPD mice, and human COPD lung, making these cells the prime targets of ISM1-mediated apoptosis. We show that csGRP78high AMs mostly express MMP-12, hence proinflammatory. Intratracheal delivery of recombinant ISM1 (rISM1) depleted csGRP78high AMs in both Ism1-/- and CS-induced COPD mice, blocked emphysema development, and preserved lung function. Consistently, ISM1 expression in human lungs positively correlates with AM apoptosis, suggesting similar function of ISM1-csGRP78 in human lungs. Our findings reveal that AM apoptosis regulation is an important physiological mechanism for maintaining lung homeostasis and demonstrate the potential of pulmonary-delivered rISM1 to target csGRP78 as a therapeutic strategy for COPD.

The Pathogenic Role of Foam Cells in Atherogenesis: Do They Represent Novel Therapeutic Targets?

BACKGROUND

Foam cells, mainly derived from monocytes-macrophages, contain lipid droplets essentially composed of cholesterol in their cytoplasm. They infiltrate the intima of arteries, contributing to the formation of atherosclerotic plaques.

PATHOGENESIS

Foam cells damage the arterial cell wall via the release of proinflammatory cytokines, free radicals, and matrix metalloproteinases, enhancing the plaque size up to its rupture.

THERAPY

A correct dietary regimen seems to be the most appropriate therapeutic approach to minimize obesity, which is associated with the formation of foam cells. At the same time, different types of antioxidants have been evaluated to arrest the formation of foam cells, even if the results are still contradictory. In any case, a combination of antioxidants seems to be more efficient in the prevention of atherosclerosis.

Macrophage Polarity and Disease Control

Macrophages are present in most human tissues and have very diverse functions. Activated macrophages are usually divided into two phenotypes, M1 macrophages and M2 macrophages, which are altered by various factors such as microorganisms, tissue microenvironment, and cytokine signals. Macrophage polarity is very important for infections, inflammatory diseases, and malignancies; its management can be key in the prevention and treatment of diseases. In this review, we assess the current state of knowledge on macrophage polarity and report on its prospects as a therapeutic target.

Increase in CD5L expression in the synovial membrane of knee osteoarthritis patients with obesity

Introduction

Obesity appears to be a powerful risk factor for the development of knee osteoarthritis (KOA), but the mechanisms of this are not fully understood. CD5L is expressed in tissue macrophages and is increased in obese mice. We hypothesized that CD5L expression is increased in the synovial membrane (SM) of obese KOA patients. Here, we investigated CD5L expression in the SM of these patients.

Material and methods

Ninety KOA patients (26 males, 64 females) were allocated to one of three groups based on body mass index (BMI): normal weight (NW, < 25 kg/m²), overweight (OW, 25-29.99 kg/m²) and obese (OB, ≥ 30 kg/m²), according to the World Health Organization BMI classification (each n = 30). Expression of CD5L in SM among the groups was compared using real-time polymerase chain reaction. To investigate CD5L-expressing cells in SM, CD14⁺ (macrophage fraction) and CD14^- (fibroblast fraction) cells were separated from the SM.

Results

CD5L expression was significantly higher in the OB group than in the NW and OW groups (p < 0.001). CD5L expression was observed in the CD14⁺ fraction but not in the CD14^- fraction.

Conclusions

CD5L is highly expressed in the SM of KOA patients with obesity. Further investigation is required to identify the role of CD5L in the relationship between KOA pathology and obesity.

Stage-Dependent Impact of RIPK1 Inhibition on Atherogenesis: Dual Effects on Inflammation and Foam Cell Dynamics

Objective: Atherosclerosis is an arterial occlusive disease with hypercholesterolemia and hypertension as common risk factors. Advanced-stage stenotic plaque, which features inflammation and necrotic core formation, is the major reason for clinical intervention. Receptor interacting serine/threonine-protein kinase 1 (RIPK1) mediates inflammation and cell death and is expressed in atherosclerotic lesions. The role of RIPK1 in advanced-stage atherosclerosis is unknown.

Approach and Results: To investigate the effect of RIPK1 inhibition in advanced atherosclerotic plaque formation, we used ApoE^SA/SA mice, which exhibit hypercholesterolemia, and develop angiotensin-II mediated hypertension upon administration of doxycycline in drinking water. These mice readily develop severe atherosclerosis, including that in coronary arteries. Eight-week-old ApoE^SA/SA mice were randomized to orally receive a highly selective RIPK1 inhibitor (RIPK1i, GSK547) mixed with a western diet, or control diet. RIPK1i administration reduced atherosclerotic plaque lesion area at 2 weeks of treatment, consistent with suppressed inflammation (MCP-1, IL-1β, TNF-α) and reduced monocyte infiltration. However, administration of RIPK1i unexpectedly exacerbated atherosclerosis at 4 weeks of treatment, concomitant with increased macrophages and lipid deposition in the plaques. Incubation of isolated macrophages with oxidized LDL resulted in foam cell formation in vitro. RIPK1i treatment promoted such foam cell formation while suppressing the death of these cells. Accordingly, RIPK1i upregulated the expression of lipid metabolism-related genes (Cd36, Ppara, Lxrα, Lxrb, Srebp1c) in macrophage foam cells with ABCA1/ABCG1 unaltered. Furthermore, RIPK1i treatment inhibited ApoA1 synthesis in the liver and reduced plasma HDL levels.

Conclusion: RIPK1 modulates the development of atherosclerosis in a stage-dependent manner, implicating both pro-atherosclerotic (monocyte infiltration and inflammation) and anti-atherosclerotic effects (suppressing foam cell accumulation and promoting ApoA1 synthesis). It is critical to identify an optimal therapeutic duration for potential clinical use of RIPK1 inhibitor in atherosclerosis or other related disease indications.

Circulating CD5L is associated with cardiovascular events and all-cause mortality in individuals with chronic kidney disease

This study assessed the association of CD5L and soluble CD36 (sCD36) with the risk of a cardiovascular event (CVE), including CV death and all-cause mortality in CKD. We evaluated the association of CD5L and sCD36 with a predefined composite CV endpoint (unstable angina, myocardial infarction, transient ischemic attack, cerebrovascular accident, congestive heart failure, arrhythmia, peripheral arterial disease [PAD] or amputation by PAD, aortic aneurysm, or death from CV causes) and all-cause mortality using Cox proportional hazards regression, adjusted for CV risk factors. The analysis included 1,516 participants free from pre-existing CV disease followed up for 4 years. The median age was 62 years, 38.8% were female, and 26.8% had diabetes. There were 98 (6.5%) CVEs and 72 (4.8%) deaths, of which 26 (36.1%) were of CV origin. Higher baseline CD5L concentration was associated with increased risk of CVE (HR, 95% CI, 1.17, 1.0–1.36), and all-cause mortality (1.22, 1.01–1.48) after adjusting for age, sex, diabetes, systolic blood pressure, dyslipidemia, waist circumference, smoking, and CKD stage. sCD36 showed no association with adverse CV outcomes or mortality. Our study showed for the first time that higher concentrations of CD5L are associated with future CVE and all-cause mortality in individuals with CKD.

The Role of Renal Macrophage, AIM, and TGF-β1 Expression in Renal Fibrosis Progression in IgAN Patients

Objective

To analyze the expression of macrophages, AIM, TGF-β1 in the kidney of IgAN patients, and to explore the role of macrophages, AIM, TGF-β1 in the progression of renal fibrosis in IgAN patients.

Methods

The paraffin specimens of renal tissue from 40 IgAN patients were selected as the observation group. At the same time, paraffin specimens of normal renal tissue from 11 patients treated by nephrectomy were selected as the normal control group. We observed the distribution of macrophages, the expression of AIM and TGF-β1 by immunohistochemical staining and/or immunofluorescence.

Result

The number of M0, M1, M2 macrophages could be found increased in IgAN patients. M0 macrophages are mainly polarized towards M2 macrophages. The expression of AIM and TGF-β1 were significantly higher in IgAN patients than in NC. M2 macrophage, AIM and TGF-β1 were positively correlated with serum creatinine and 24-hour proteinuria, but negatively correlated with eGFR. M2 macrophages, AIM, TGF-β1 were positively correlated with fibrotic area.

Conclusion

M2 macrophages, AIM and TGF-β1 play important roles in the process of IgAN fibrosis, and the three influence each other.

Raman microspectroscopy and Raman imaging reveal biomarkers specific for thoracic aortic aneurysms

Aortic rupture and dissection are life-threatening complications of ascending thoracic aortic aneurysms (aTAAs), and risk assessment has been largely based on the monitoring of lumen size enlargement. Temporal changes in the extracellular matrix (ECM), which has a critical impact on aortic remodeling, are not routinely evaluated, and cardiovascular biomarkers do not exist to predict aTAA formation. Here, Raman microspectroscopy and Raman imaging are used to identify spectral biomarkers specific for aTAAs in mice and humans by multivariate data analysis (MVA). Multivariate curve resolution-alternating least-squares (MCR-ALS) combined with Lasso regression reveals elastic fiber-derived (Ce1) and collagen fiber-derived (Cc6) components that are significantly increased in aTAA lesions of murine and human aortic tissues. In particular, Cc6 detects changes in amino acid residues, including phenylalanine, tyrosine, tryptophan, cysteine, aspartate, and glutamate. Ce1 and Cc6 may serve as diagnostic Raman biomarkers that detect alterations of amino acids derived from aneurysm lesions.

Label-free Raman imaging of human/murine ascending thoracic aortic aneurysm (aTAA)

Multivariate analysis of Raman spectra allows detection of aTAA molecular features

Identification of spectral biomarkers for aTAA in elastic and collagen fibers

Alterations in amino acid spectra correlate with aTAA formation

Multifaceted Roles of CD5L in Infectious and Sterile Inflammation

CD5L, a protein expressed and secreted mainly by macrophages, is emerging as a critical immune effector. In addition to its well-defined function as an anti-apoptotic protein, research over the last decade has uncovered additional roles that range from pattern recognition to autophagy, cell polarization, and the regulation of lipid metabolism. By modulating all these processes, CD5L plays a key role in highly prevalent diseases that develop by either acute or chronic inflammation, including several infectious, metabolic, and autoimmune conditions. In this review, we summarize the current knowledge of CD5L and focus on the relevance of this protein during infection- and sterile-driven inflammatory pathogenesis, highlighting its divergent roles in the modulation of inflammation.

Targeting macrophages using nanoparticles: a potential therapeutic strategy for atherosclerosis

Atherosclerosis is one of the leading causes of vascular diseases, with high morbidity and mortality worldwide. Macrophages play a critical role in the development and local inflammatory responses of atherosclerosis, contributing to plaque rupture and thrombosis. Considering their central roles, macrophages have gained considerable attention as a therapeutic target to attenuate atherosclerotic progression and stabilize existing plaques. Nanoparticle-based delivery systems further provide possibilities to selectively and effectively deliver therapeutic agents into intraplaque macrophages. Although challenges are numerous and clinical application is still distant, the design and development of macrophage-targeting nanoparticles will generate new knowledge and experiences to improve therapeutic outcomes and minimize toxicity. Hence, the review aims to discuss various strategies for macrophage modulation and the development and evaluation of macrophage targeting nanomedicines for anti-atherosclerosis.

Foam Cells as Therapeutic Targets in Atherosclerosis with a Focus on the Regulatory Roles of Non-Coding RNAs

Atherosclerosis is a major cause of human cardiovascular disease, which is the leading cause of mortality around the world. Various physiological and pathological processes are involved, including chronic inflammation, dysregulation of lipid metabolism, development of an environment characterized by oxidative stress and improper immune responses. Accordingly, the expansion of novel targets for the treatment of atherosclerosis is necessary. In this study, we focus on the role of foam cells in the development of atherosclerosis. The specific therapeutic goals associated with each stage in the formation of foam cells and the development of atherosclerosis will be considered. Processing and metabolism of cholesterol in the macrophage is one of the main steps in foam cell formation. Cholesterol processing involves lipid uptake, cholesterol esterification and cholesterol efflux, which ultimately leads to cholesterol equilibrium in the macrophage. Recently, many preclinical studies have appeared concerning the role of non-encoding RNAs in the formation of atherosclerotic lesions. Non-encoding RNAs, especially microRNAs, are considered regulators of lipid metabolism by affecting the expression of genes involved in the uptake (e.g., CD36 and LOX1) esterification (ACAT1) and efflux (ABCA1, ABCG1) of cholesterol. They are also able to regulate inflammatory pathways, produce cytokines and mediate foam cell apoptosis. We have reviewed important preclinical evidence of their therapeutic targeting in atherosclerosis, with a special focus on foam cell formation.

Impact of myeloid RIPK1 gene deletion on atherogenesis in ApoE-deficient mice

BACKGROUND AND AIMS

Targeting macrophage death is a promising strategy for stabilizing atherosclerotic plaques. Recently, necroptosis was identified as a form of regulated necrosis in atherosclerosis. Receptor-interacting serine/threonine-protein kinase (RIPK)1 is an upstream regulator of RIPK3, which is a crucial kinase for necroptosis induction. We aimed to investigate the impact of myeloid-specific RIPK1 gene deletion on atherogenesis.

METHODS

RIPK1^F/FLysM-Cre⁺ApoE^-/- and RIPK1^+/+LysM-Cre⁺ApoE^-/- mice were fed a western-type diet (WD) for 16 or 24 weeks to induce plaque formation.

RESULTS

After 16 weeks WD, plaque area and percentage necrosis in RIPK1^F/FLysM-Cre⁺ApoE^-/- mice were significantly decreased as compared to plaques of RIPK1^+/+LysM-Cre⁺ApoE^-/- mice. Moreover, plaques of RIPK1^F/FLysM-Cre⁺ApoE^-/- mice showed more apoptosis and a decreased macrophage content. After 24 weeks WD, plaque size and percentage necrosis were no longer different between the two groups. Free apoptotic cells strongly accumulated in plaques of RIPK1^F/FLysM-Cre⁺ApoE^-/- mice. In addition to apoptosis, necroptosis was upregulated in plaques of RIPK1^F/FLysM-Cre⁺ApoE^-/- mice. In vitro, TNF-α triggered apoptosis in RIPK1^F/FLysM-Cre⁺ApoE^-/-, but not in RIPK1^+/+LysM-Cre⁺ApoE^-/- macrophages. Moreover, RIPK1^F/FLysM-Cre⁺ApoE^-/- macrophages were not protected against RIPK3-dependent necroptosis.

CONCLUSIONS

The impact of myeloid RIPK1 gene deletion depends on the stage of atherogenesis. At 16 weeks WD, myeloid RIPK1 gene deletion resulted in increased apoptosis, thereby slowing down plaque progression. However, despite decreased macrophage content, plaque and necrotic core size were no longer reduced after 24 weeks of WD, most likely due to the accumulation of free apoptotic and necroptotic cells.

Contradictory regulation of macrophages on atherosclerosis based on polarization, death and autophagy

The main pathological feature of atherosclerosis is lipid metabolism disorder and inflammation. Macrophages, as the most important immune cells in the body, run through the beginning and end of disease development. After macrophages overtake the atherosclerosis-susceptible area apolipoprotein low-density lipoprotein ox-LDL, they transform into foam cells that adhere to blood vessels and recruit a large number of pro-inflammatory factors to initiate the disease. Promoting the outflow of lipids in foam cells and alleviating inflammation have become the basic ideas for the study of atherosclerosis treatment strategies. The polarization of macrophages refers to the estimation of the activation of macrophages at a specific point in space and time. Determining the proportion of different macrophage phenotypes in the plaque can help identify delay or prevent disease development. However, the abnormal polarization of macrophages and the accumulation of lipid also affect the growth state of cells to some extent, thus aggravate the influence on plaque area and stability. Besides, overactive or deficient autophagy of macrophages may also lead to cell death and participate in lipid metabolism and inflammation regression. In this paper, the role of macrophages in atherosclerosis was discussed from three aspects: polarization, death, and autophagy.

Pyroptosis is a critical immune-inflammatory response involved in atherosclerosis

Pyroptosis is a form of programmed cell death activated by various stimuli and is characterized by inflammasome assembly, membrane pore formation, and the secretion of inflammatory cytokines (IL-1β and IL-18). Atherosclerosis-related risk factors, including oxidized low-density lipoprotein (ox-LDL) and cholesterol crystals, have been shown to promote pyroptosis through several mechanisms that involve ion flux, ROS, endoplasmic reticulum stress, mitochondrial dysfunction, lysosomal rupture, Golgi function, autophagy, noncoding RNAs, post-translational modifications, and the expression of related molecules. Pyroptosis of endothelial cells, macrophages, and smooth muscle cells in the vascular wall can induce plaque instability and accelerate atherosclerosis progression. In this review, we focus on the pathogenesis, influence, and therapy of pyroptosis in atherosclerosis and provide novel ideas for suppressing pyroptosis and the progression of atherosclerosis.

Apoptosis inhibitor of macrophage (AIM) contributes to IL-10-induced anti-inflammatory response through inhibition of inflammasome activation

Apoptosis inhibitor of macrophage (AIM) modulates the signaling in inflammatory responses, including infection, cancer, or other immune diseases. Recent studies suggest that like interleukin-10 (IL-10), AIM is involved in alternatively activated (M2) macrophage polarization. We aimed to understand whether and how AIM is involved in IL-10-induced inhibition of inflammasome activation and resolution of inflammation. First, we demonstrated that IL-10 induced increases in mRNA and protein expression of AIM in murine bone marrow-derived macrophages (BMDM). In addition, genetic and pharmacologic inhibition of STAT3 (signal transducer and activator of transcription 3) reduced IL-10-induced AIM expression. We also found that IL-10-induced STAT3 activity enhanced the AIM promoter activity by directly binding the promoter of the AIM gene. Additionally, reduction of LPS/adenosine triphosphate (ATP)-induced IL-1β production and caspase-1 activation by IL-10 was reversed in BMDM from AIM^-/- mice. Treatment of BMDM from both wild type (WT) and IL-10^-/- mice with recombinant AIM showed the inhibitory effects on IL-1β and IL-18 production and caspase-1 activation. Endogenous and exogenous AIM inhibited apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC) speck formation. In LPS-induced acute peritonitis, inhibition of IL-1β and IL-18 production in peritoneal lavage fluid (PLF) and serum, reduction of caspase-1 activation in peritoneal macrophages, and reduction of numbers of neutrophils and peritoneal macrophages in PLF by administration of IL-10 were not evident in AIM^-/- mice. Our in vitro and in vivo data reveal a novel role of AIM in the inhibition of inflammasome-mediated caspase-1 activation and IL-1β and IL-18 production.

Up-regulation of circRNA-0003528 promotes mycobacterium tuberculosis associated macrophage polarization via down-regulating miR-224-5p, miR-324-5p and miR-488-5p and up-regulating CTLA4

Background: In this study, we selected several candidate miRNAs to study their possible relationships with tuberculosis.

Results: The expression of hsa_circ_0003528 was negatively correlated with the expression of miR-224-5p, miR-324-5p, miR-488-5p, miR-587, and miR-668, while the expression of hsa_circ_0003528 was positively correlated with the expression of miR-224-5p, miR-324-5p and miR-488-5p. No evident difference was observed between tuberculosis and healthy control groups in terms of the expression of miR-587 and miR-668.

Conclusion: The findings of this study demonstrated that miR-224-5p, miR-324-5p and miR-488-5p were all ceRNAs of circRNA-0003528 by sponging each other and CTLA4 was found to be a shared target gene of miR-224-5p, miR-324-5p and miR-488-5p. Furthermore, we found that up-regulation of circRNA-0003528 promoted tuberculosis associated macrophage polarization by promoting expression CTLA4, which was mediated by the down-regulation of miR-224-5p, miR-324-5p and miR-488-5p.

Methods: RT-qPCR and Western blot were conducted to observe the expression of hsa_circ_0003528, miRNAs and CTLA4 in different patient and cell groups to establish the potential molecular mechanisms underlying the effect of hsa_circ_0003528 on M1 to M2 macrophage polarization.

A macrophage-specific lncRNA regulates apoptosis and atherosclerosis by tethering HuR in the nucleus

Long non-coding RNAs (lncRNAs) are emerging regulators of pathophysiological processes including atherosclerosis. Using RNA-seq profiling of the intima of lesions, here we identify a macrophage-specific lncRNA MAARS (Macrophage-Associated Atherosclerosis lncRNA Sequence). Aortic intima expression of MAARS increases by 270-fold with atherosclerotic progression and decreases with regression by 60%. MAARS knockdown reduces atherosclerotic lesion formation by 52% in LDLR-/- mice, largely independent of effects on lipid profile and inflammation, but rather by decreasing macrophage apoptosis and increasing efferocytosis in the vessel wall. MAARS interacts with HuR/ELAVL1, an RNA-binding protein and important regulator of apoptosis. Overexpression and knockdown studies verified MAARS as a critical regulator of macrophage apoptosis and efferocytosis in vitro, in an HuR-dependent manner. Mechanistically, MAARS knockdown alters HuR cytosolic shuttling, regulating HuR targets such as p53, p27, Caspase-9, and BCL2. These findings establish a mechanism by which a macrophage-specific lncRNA interacting with HuR regulates apoptosis, with implications for a broad range of vascular disease states.