Deletion of IRF8 (Interferon Regulatory Factor 8)-Dependent Dendritic Cells Abrogates Proatherogenic Adaptive Immunity

The Evolving Role of Dendritic Cells in Atherosclerosis

Atherosclerosis, a major contributor to cardiovascular morbidity and mortality, is characterized by chronic inflammation of the arterial wall. This inflammatory process is initiated and maintained by both innate and adaptive immunity. Dendritic cells (DCs), which are antigen-presenting cells, play a crucial role in the development of atherosclerosis and consist of various subtypes with distinct functional abilities. Following the recognition and binding of antigens, DCs become potent activators of cellular responses, bridging the innate and adaptive immune systems. The modulation of specific DC subpopulations can have either pro-atherogenic or atheroprotective effects, highlighting the dual pro-inflammatory or tolerogenic roles of DCs. In this work, we provide a comprehensive overview of the evolving roles of DCs and their subtypes in the promotion or limitation of atherosclerosis development. Additionally, we explore antigen pulsing and pharmacological approaches to modulate the function of DCs in the context of atherosclerosis.

Clonally expanded memory CD8+ T cells accumulate in atherosclerotic plaques and are pro-atherogenic in aged mice

Aging is a strong risk factor for atherosclerosis and induces accumulation of memory CD8+ T cells in mice and humans. Biological changes that occur with aging lead to enhanced atherosclerosis, yet the role of aging on CD8+ T cells during atherogenesis is unclear. In this study, using femle mice, we found that depletion of CD8+ T cells attenuated atherogenesis in aged, but not young, animals. Furthermore, adoptive transfer of splenic CD8+ T cells from aged wild-type, but not young wild-type, donor mice significantly enhanced atherosclerosis in recipient mice lacking CD8+ T cells. We also characterized T cells in healthy and atherosclerotic young and aged mice by single-cell RNA sequencing. We found specific subsets of age-associated CD8+ T cells, including a Granzyme K+ effector memory subset, that accumulated and was clonally expanded within atherosclerotic plaques. These had transcriptomic signatures of T cell activation, migration, cytotoxicity and exhaustion. Overall, our study identified memory CD8+ T cells as therapeutic targets for atherosclerosis in aging.

PLK1 inhibition dampens NLRP3 inflammasome-elicited response in inflammatory disease models

Unabated activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome is linked with the pathogenesis of various inflammatory disorders. Polo-like kinase 1 (PLK1) has been widely studied for its role in mitosis. Here, using both pharmacological and genetic approaches, we demonstrate that PLK1 promoted NLRP3 inflammasome activation at cell interphase. Using an unbiased proximity-dependent biotin identification (Bio-ID) screen for the PLK1 interactome in macrophages, we show an enhanced proximal association of NLRP3 with PLK1 upon NLRP3 inflammasome activation. We further confirmed the interaction between PLK1 and NLRP3 and identified the interacting domains. Mechanistically, we show that PLK1 orchestrated the microtubule-organizing center (MTOC) structure and NLRP3 subcellular positioning upon inflammasome activation. Treatment with a selective PLK1 kinase inhibitor suppressed IL-1β production in in vivo inflammatory models, including LPS-induced endotoxemia and monosodium urate-induced peritonitis in mice. Our results uncover a role of PLK1 in regulating NLRP3 inflammasome activation during interphase and identify pharmacological inhibition of PLK1 as a potential therapeutic strategy for inflammatory diseases with excessive NLRP3 inflammasome activation.

IRF8: Mechanism of Action and Health Implications

Interferon regulatory factor 8 (IRF8) is a transcription factor of the IRF protein family. IRF8 was originally identified as an essentialfactor for myeloid cell lineage commitment and differentiation. Deletion of Irf8 leads to massive accumulation of CD11b⁺Gr1⁺ immature myeloid cells (IMCs), particularly the CD11b⁺Ly6C^hi/+Ly6G⁻ polymorphonuclear myeloid-derived suppressor cell-like cells (PMN-MDSCs). Under pathological conditions such as cancer, Irf8 is silenced by its promoter DNA hypermethylation, resulting in accumulation of PMN-MDSCs and CD11b⁺ Ly6G⁺Ly6C^lo monocytic MDSCs (M-MDSCs) in mice. IRF8 is often silenced in MDSCs in human cancer patients. MDSCs are heterogeneous populations of immune suppressive cells that suppress T and NK cell activity to promote tumor immune evasion and produce growth factors to exert direct tumor-promoting activity. Emerging experimental data reveals that IRF8 is also expressed in non-hematopoietic cells. Epithelial cell-expressed IRF8 regulates apoptosis and represses Osteopontin (OPN). Human tumor cells may use the IRF8 promoter DNA methylation as a mechanism to repress IRF8 expression to advance cancer through acquiring apoptosis resistance and OPN up-regulation. Elevated OPN engages CD44 to suppress T cell activation and promote tumor cell stemness to advance cancer. IRF8 thus is a transcription factor that regulates both the immune and non-immune components in human health and diseases.

Crosstalk between dendritic cells and T lymphocytes during atherogenesis: Focus on antigen presentation and break of tolerance

Atherosclerosis is a chronic disease resulting from an impaired lipid and immune homeostasis, where the interaction between innate and adaptive immune cells leads to the promotion of atherosclerosis-associated immune-inflammatory response. Emerging evidence has suggested that this response presents similarities to the reactivity of effector immune cells toward self-epitopes, often as a consequence of a break of tolerance. In this context, dendritic cells, a heterogeneous population of antigen presenting cells, play a key role in instructing effector T cells to react against foreign antigens and T regulatory cells to maintain tolerance against self-antigens and/or to patrol for self-reactive effector T cells. Alterations in this delicate balance appears to contribute to atherogenesis. The aim of this review is to discuss different DC subsets, and their role in atherosclerosis as well as in T cell polarization. Moreover, we will discuss how loss of T cell tolerogenic phenotype participates to the immune-inflammatory response associated to atherosclerosis and how a better understanding of these mechanisms might result in designing immunomodulatory therapies targeting DC-T cell crosstalk for the treatment of atherosclerosis-related inflammation.

The why and how of adaptive immune responses in ischemic cardiovascular disease

Atherosclerotic cardiovascular disease is a major cause of disability and death worldwide. Most therapeutic approaches target traditional risk factors but ignore the fundamental role of the immune system. This is a huge unmet need. Recent evidence indicates that reducing inflammation may limit cardiovascular events. However, the concomitant increase in the risk of lifethreatening infections is a major drawback. In this context, targeting adaptive immunity could constitute a highly effective and safer approach. In this Review, we address the why and how of the immuno-cardiovascular unit, in health and in atherosclerotic disease. We review and discuss fundamental mechanisms that ensure immune tolerance to cardiovascular tissue, and examine how their disruption promotes disease progression. We identify promising strategies to manipulate the adaptive immune system for patient benefit, including novel biologics and RNA-based vaccination strategies. Finally, we advocate for establishing a molecular classification of atherosclerosis as an important milestone in our quest to radically change the understanding and treatment of atherosclerotic disease.

How the immune system shapes atherosclerosis: roles of innate and adaptive immunity

Atherosclerosis is the root cause of many cardiovascular diseases. Extensive research in preclinical models and emerging evidence in humans have established the crucial roles of the innate and adaptive immune systems in driving atherosclerosis-associated chronic inflammation in arterial blood vessels. New techniques have highlighted the enormous heterogeneity of leukocyte subsets in the arterial wall that have pro-inflammatory or regulatory roles in atherogenesis. Understanding the homing and activation pathways of these immune cells, their disease-associated dynamics and their regulation by microbial and metabolic factors will be crucial for the development of clinical interventions for atherosclerosis, including potentially vaccination-based therapeutic strategies. Here, we review key molecular mechanisms of immune cell activation implicated in modulating atherogenesis and provide an update on the contributions of innate and adaptive immune cell subsets in atherosclerosis.

Dendritic cell-mediated chronic low-grade inflammation is regulated by the RAGE-TLR4-PKCβ1 signaling pathway in diabetic atherosclerosis

Background

The unique mechanism of diabetic atherosclerosis has been a central research focus. Previous literature has reported that the inflammatory response mediated by dendritic cells (DCs) plays a vital role in the progression of atherosclerosis. The objective of the study was to explore the role of DCs in diabetes mellitus complicated by atherosclerosis.

Methods

ApoE^−/− mice and bone marrow-derived DCs were used for in vivo and in vitro experiments, respectively. Masson’s staining and Oil-red-O staining were performed for atherosclerotic lesion assessment. The content of macrophages and DCs in plaque was visualized by immunohistochemistry. The expression of CD83 and CD86 were detected by flow cytometry. The fluctuations in the RNA levels of cytokines, chemokines, chemokine receptors and adhesions were analyzed by quantitative RT-PCR. The concentrations of IFN-γ and TNF-α were calculated using ELISA kits and the proteins were detected using western blot. Coimmunoprecipitation was used to detect protein–protein interactions.

Results

Compared with the ApoE^−/− group, the volume of atherosclerotic plaques in the aortic root of diabetic ApoE^−/− mice was significantly increased, numbers of macrophages and DCs were increased, and the collagen content in plaques decreased. The expression of CD83 and CD86 were significantly upregulated in splenic CD11c⁺ DCs derived from mice with hyperglycemia. Increased secretion of cytokines, chemokines, chemokine receptors, intercellular cell adhesion molecule (ICAM), and vascular cell adhesion molecule (VCAM) also were observed. The stimulation of advanced glycation end products plus oxidized low-density lipoprotein, in cultured BMDCs, further activated toll-like receptor 4, protein kinase C and receptor of AGEs, and induced immune maturation of DCs through the RAGE-TLR4-PKCβ₁ signaling pathway that was bound together by intrinsic structures on the cell membrane. Administering LY333531 significantly increased the body weight of diabetic ApoE^−/− mice, inhibited the immune maturation of spleen DCs, and reduced atherosclerotic plaques in diabetic ApoE^−/− mice. Furthermore, the number of DCs and macrophages in atherosclerotic plaques was significantly reduced in the LY333531 group, and the collagen content was increased.

Conclusions

Diabetes mellitus aggravates chronic inflammation, and promotes atherosclerotic plaques in conjunction with hyperlipidemia, which at least in part through inducing the immune maturation of DCs, and its possible mechanism of action is through the RAGE-TLR4-pPKCβ₁ signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00431-6.

IRF8-Dependent Type I Conventional Dendritic Cells (cDC1s) Control Post-Ischemic Inflammation and Mildly Protect Against Post-Ischemic Acute Kidney Injury and Disease

Post-ischemic acute kidney injury and disease (AKI/AKD) involve acute tubular necrosis and irreversible nephron loss. Mononuclear phagocytes including conventional dendritic cells (cDCs) are present during different phases of injury and repair, but the functional contribution of this subset remains controversial. Transcription factor interferon regulatory factor 8 (IRF8) is required for the development of type I conventional dendritic cells (cDC1s) lineage and helps to define distinct cDC1 subsets. We identified one distinct subset among mononuclear phagocyte subsets according to the expression patterns of CD11b and CD11c in healthy kidney and lymphoid organs, of which IRF8 was significantly expressed in the CD11b^lowCD11c^high subset that mainly comprised cDC1s. Next, we applied a Irf8-deficient mouse line (Irf8^fl/flClec9a^cre mice) to specifically target Clec9a-expressing cDC1s in vivo. During post-ischemic AKI/AKD, these mice lacked cDC1s in the kidney without affecting cDC2s. The absence of cDC1s mildly aggravated the loss of living primary tubule and decline of kidney function, which was associated with decreased anti-inflammatory Tregs-related immune responses, but increased T helper type 1 (T_H1)-related and pro-inflammatory cytokines, infiltrating neutrophils and acute tubular cell death, while we also observed a reduced number of cytotoxic CD8⁺ T cells in the kidney when cDC1s were absent. Together, our data show that IRF8 is indispensable for kidney cDC1s. Kidney cDC1s mildly protect against post-ischemic AKI/AKD, probably via suppressing tissue inflammation and damage, which implies an immunoregulatory role for cDC1s.

Macrophage beta2-adrenergic receptor is dispensable for the adipose tissue inflammation and function

OBJECTIVE

Neuroimmune interactions between the sympathetic nervous system (SNS) and macrophages are required for the homeostasis of multiple tissues, including the adipose tissue. It has been proposed that the SNS maintains adipose tissue macrophages (ATMs) in an anti-inflammatory state via direct norepinephrine (NE) signaling to macrophages. This study aimed to investigate the physiological importance of this paradigm by utilizing a mouse model in which the adrenergic signaling from the SNS to macrophages, but not to other adipose tissue cells, was disrupted.

METHODS

We generated a macrophage-specific B2AR knockout mouse (Adrb2ΔLyz2) by crossing Adrb2fl/fl and Lyz2Cre/+ mice. We have previously shown that macrophages isolated from Adrb2ΔLyz2 animals do not respond to NE stimulation in vitro. Herein we performed a metabolic phenotyping of Adrb2ΔLyz2 mice on either chow or high-fat diet (HFD). We also assessed the adipose tissue function of Adrb2ΔLyz2 animals during fasting and cold exposure. Finally, we transplanted Adrb2ΔLyz2 bone marrow to low-density lipoprotein receptor (LDLR) knockout mice and investigated the development of atherosclerosis during Western diet feeding.

RESULTS

We demonstrated that SNS-associated ATMs have a transcriptional profile indicative of activated beta-2 adrenergic receptor (B2AR), the main adrenergic receptor isoform in myeloid cells. However, Adrb2ΔLyz2 mice have unaltered energy balance on a chow or HFD. Furthermore, Adrb2ΔLyz2 mice show similar levels of adipose tissue inflammation and function during feeding, fasting, or cold exposure, and develop insulin resistance during HFD at the same rate as controls. Finally, macrophage-specific B2AR deletion does not affect the development of atherosclerosis on an LDL receptor-null genetic background.

CONCLUSIONS

Overall, our data suggest that the SNS does not directly modulate the phenotype of adipose tissue macrophages in either lean mice or mouse models of cardiometabolic disease. Instead, sympathetic nerve activity exerts an indirect effect on adipose tissue macrophages through the modulation of adipocyte function.

ApoB-Specific CD4+ T Cells in Mouse and Human Atherosclerosis

Atherosclerosis is a chronic inflammatory condition of the arterial wall that leads to the formation of vessel-occluding plaques within the subintimal space of middle-sized and larger arteries. While traditionally understood as a myeloid-driven lipid-storage disease, growing evidence suggests that the accumulation of low-density lipoprotein cholesterol (LDL-C) ignites an autoimmune response with CD4⁺ T-helper (T_H) cells that recognize self-peptides from Apolipoprotein B (ApoB), the core protein of LDL-C. These autoreactive CD4⁺ T cells home to the atherosclerotic plaque, clonally expand, instruct other cells in the plaque, and induce clinical plaque instability. Recent developments in detecting antigen-specific cells at the single cell level have demonstrated that ApoB-reactive CD4⁺ T cells exist in humans and mice. Their phenotypes and functions deviate from classical immunological concepts of distinct and terminally differentiated T_H immunity. Instead, ApoB-specific CD4⁺ T cells have a highly plastic phenotype, can acquire several, partially opposing and mixed transcriptional programs simultaneously, and transit from one T_H subset into another over time. In this review, we highlight adaptive immune mechanisms in atherosclerosis with a focus on CD4⁺ T cells, introduce novel technologies to detect ApoB-specific CD4⁺ T cells at the single cell level, and discuss the potential impact of ApoB-driven autoimmunity in atherosclerosis.

Dendritic Cells and T Cells, Partners in Atherogenesis and the Translating Road Ahead

Atherosclerosis is a chronic process associated with arterial inflammation, the accumulation of lipids, plaque formation in vessel walls, and thrombosis with late mortal complications such as myocardial infarction and ischemic stroke. Immune and inflammatory responses have significant effects on every phase of atherosclerosis. Increasing evidence has shown that both innate and adaptive “arms” of the immune system play important roles in regulating the progression of atherosclerosis. Accumulating evidence suggests that a unique type of innate immune cell, termed dendritic cells (DCs), play an important role as central instigators, whereas adaptive immune cells, called T lymphocytes, are crucial as active executors of the DC immunity in atherogenesis. These two important immune cell types work in pairs to establish pro-atherogenic or atheroprotective immune responses in vascular tissues. Therefore, understanding the role of DCs and T cells in atherosclerosis is extremely important. Here, in this review, we will present a complete overview, based on existing knowledge of these two cell types in the atherosclerotic microenvironment, and discuss some of the novel means of targeting DCs and T cells as therapeutic tactics for the treatment of atherosclerosis.

RAGE impairs murine diabetic atherosclerosis regression and implicates IRF7 in macrophage inflammation and cholesterol metabolism

Despite advances in lipid-lowering therapies, people with diabetes continue to experience more limited cardiovascular benefits. In diabetes, hyperglycemia sustains inflammation and preempts vascular repair. We tested the hypothesis that the receptor for advanced glycation end-products (RAGE) contributes to these maladaptive processes. We report that transplantation of aortic arches from diabetic, Western diet-fed Ldlr-/- mice into diabetic Ager-/- (Ager, the gene encoding RAGE) versus WT diabetic recipient mice accelerated regression of atherosclerosis. RNA-sequencing experiments traced RAGE-dependent mechanisms principally to the recipient macrophages and linked RAGE to interferon signaling. Specifically, deletion of Ager in the regressing diabetic plaques downregulated interferon regulatory factor 7 (Irf7) in macrophages. Immunohistochemistry studies colocalized IRF7 and macrophages in both murine and human atherosclerotic plaques. In bone marrow-derived macrophages (BMDMs), RAGE ligands upregulated expression of Irf7, and in BMDMs immersed in a cholesterol-rich environment, knockdown of Irf7 triggered a switch from pro- to antiinflammatory gene expression and regulated a host of genes linked to cholesterol efflux and homeostasis. Collectively, this work adds a new dimension to the immunometabolic sphere of perturbations that impair regression of established diabetic atherosclerosis and suggests that targeting RAGE and IRF7 may facilitate vascular repair in diabetes.

T cell subsets and functions in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall and the primary underlying cause of cardiovascular disease. Data from in vivo imaging, cell-lineage tracing and knockout studies in mice, as well as clinical interventional studies and advanced mRNA sequencing techniques, have drawn attention to the role of T cells as critical drivers and modifiers of the pathogenesis of atherosclerosis. CD4+ T cells are commonly found in atherosclerotic plaques. A large body of evidence indicates that T helper 1 (TH1) cells have pro-atherogenic roles and regulatory T (Treg) cells have anti-atherogenic roles. However, Treg cells can become pro-atherogenic. The roles in atherosclerosis of other TH cell subsets such as TH2, TH9, TH17, TH22, follicular helper T cells and CD28null T cells, as well as other T cell subsets including CD8+ T cells and γδ T cells, are less well understood. Moreover, some T cells seem to have both pro-atherogenic and anti-atherogenic functions. In this Review, we summarize the knowledge on T cell subsets, their functions in atherosclerosis and the process of T cell homing to atherosclerotic plaques. Much of our understanding of the roles of T cells in atherosclerosis is based on findings from experimental models. Translating these findings into human disease is challenging but much needed. T cells and their specific cytokines are attractive targets for developing new preventive and therapeutic approaches including potential T cell-related therapies for atherosclerosis.

Deletion of Ppard in CD11c+ cells attenuates atherosclerosis in ApoE knockout mice

Ppardδ, one of the lipid-activated nuclear receptor expressed in many cell types to activate gene transcription, also regulates cellular functions other than lipid metabolism. The mechanism regulating the function of antigen-presenting cells during the development of atherosclerosis is not fully understood. Here we aimed to study the involvement of PPARδ in CD11c⁺ cells in atherosclerosis. We used the Cre-loxP approach to make conditional deletion of Ppard in CD11c⁺ cells in mice on Apoe^-/- background, which were fed with high cholesterol diet to develop atherosclerosis. Ppard deficiency in CD11c⁺ cells attenuated atherosclerotic plaque formation and infiltration of myeloid-derived dendritic cells (DCs) and T lymphocytes. Reduced lesion was accompanied by reduced activation of dendritic cells, and also a reduction of activation and differentiation of T cells to Th1 cells. In addition, DC migration to lymph node was also attenuated with Ppard deletion. In bone marrow-derived DCs, Ppard deficiency reduced palmitic acid-induced upregulation of co-stimulatory molecules and pro-inflammatory cytokine IL12 and TNFα. Our results indicated PPARδ activation by fatty acid resulted in the activation of myeloid DCs and subsequent polarization of T lymphocytes, which contributed to atherosclerosis in Apoe^-/- mice. These findings also reveal the potential regulatory role of PPARδ in antigen presentation to orchestrate the immune responses during atherosclerosis.

Protein inhibitor of activated STAT1 (PIAS1) inhibits IRF8 activation of Epstein-Barr virus lytic gene expression

Epstein-Barr virus (EBV), a major human oncogenic pathogen, establishes life-long persistent infections. In latently infected B lymphocytes, the virus persists as an episome in the nucleus. Periodic reactivation of latent virus is controlled by both viral and cellular factors. Our recent studies showed that interferon regulatory factor 8 (IRF8) is required for EBV lytic reactivation while protein inhibitor of activated STAT1 (PIAS1) functions as an EBV restriction factor to block viral reactivation. Here, we show that IRF8 directly binds to the EBV genome and regulates EBV lytic gene expression together with PU.1 and EBV transactivator RTA. Furthermore, our study reveals that PIAS1 antagonizes IRF8/PU.1-mediated lytic gene activation through binding to and inhibiting IRF8. Together, our study establishes IRF8 as a transcriptional activator in promoting EBV reactivation and defines PIAS1 as an inhibitor of IRF8 to limit lytic gene expression.

An immunoevasive strategy through clinically-relevant pan-cancer genomic and transcriptomic alterations of JAK-STAT signaling components

BACKGROUND

Since its discovery almost three decades ago, the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway has paved the road for understanding inflammatory and immunity processes related to a wide range of human pathologies including cancer. Several studies have demonstrated the importance of JAK-STAT pathway components in regulating tumor initiation and metastatic progression, yet, the extent of how genetic alterations influence patient outcome is far from being understood.

METHODS

Focusing on 133 genes involved in JAK-STAT signaling, we investigated genomic, transcriptomic and clinical profiles of over 18,000 patients representing 21 diverse cancer types. We identified a core set of 28 putative gain- or loss-of-function JAK-STAT genes that correlated with survival outcomes using Cox proportional hazards regression and Kaplan-Meier analyses. Differential expression analyses between high- and low-expressing patient groups were performed to evaluate the consequences of JAK-STAT misexpression.

RESULTS

We found that copy number alterations underpinning transcriptional dysregulation of JAK-STAT pathway genes differ within and between cancer types. Integrated analyses uniting genomic and transcriptomic datasets revealed a core set of JAK-STAT pathway genes that correlated with survival outcomes in brain, renal, lung and endometrial cancers. High JAK-STAT scores were associated with increased mortality rates in brain and renal cancers, but not in lung and endometrial cancers where hyperactive JAK-STAT signaling is a positive prognostic factor. Patients with aberrant JAK-STAT signaling demonstrated pan-cancer molecular features associated with misexpression of genes in other oncogenic pathways (Wnt, MAPK, TGF-β, PPAR and VEGF). Brain and renal tumors with hyperactive JAK-STAT signaling had increased regulatory T cell gene (Treg) expression. A combined model uniting JAK-STAT and Tregs allowed further delineation of risk groups where patients with high JAK-STAT and Treg scores consistently performed the worst.

CONCLUSION

Providing a pan-cancer perspective of clinically-relevant JAK-STAT alterations, this study could serve as a framework for future research investigating anti-tumor immunity using combination therapy involving JAK-STAT and immune checkpoint inhibitors.

Impaired Autophagy in CD11b+ Dendritic Cells Expands CD4+ Regulatory T Cells and Limits Atherosclerosis in Mice

Supplemental Digital Content is available in the text.

Atherosclerosis is a chronic inflammatory disease. Recent studies have shown that dysfunctional autophagy in endothelial cells, smooth muscle cells, and macrophages, plays a detrimental role during atherogenesis, leading to the suggestion that autophagy-stimulating approaches may provide benefit.