CX3CR1 is required for monocyte homeostasis and atherogenesis by promoting cell survival

Pan-cancer mapping of single CD8+ T cell profiles reveals a TCF1:CXCR6 axis regulating CD28 co-stimulation and anti-tumor immunity

CD8+ T cells must persist and function in diverse tumor microenvironments to exert their effects. Thus, understanding common underlying expression programs could better inform the next generation of immunotherapies. We apply a generalizable matrix factorization algorithm that recovers both shared and context-specific expression programs from diverse datasets to a single-cell RNA sequencing (scRNA-seq) compendium of 33,161 CD8+ T cells from 132 patients with seven human cancers. Our meta-single-cell analyses uncover a pan-cancer T cell dysfunction program that predicts clinical non-response to checkpoint blockade in melanoma and highlights CXCR6 as a pan-cancer marker of chronically activated T cells. Cxcr6 is trans-activated by AP-1 and repressed by TCF1. Using mouse models, we show that Cxcr6 deletion in CD8+ T cells increases apoptosis of PD1+TIM3+ cells, dampens CD28 signaling, and compromises tumor growth control. Our study uncovers a TCF1:CXCR6 axis that counterbalances PD1-mediated suppression of CD8+ cell responses and is essential for effective anti-tumor immunity.

Classical monocyte ontogeny dictates their functions and fates as tissue macrophages

Classical monocytes (CMs) are ephemeral myeloid immune cells that circulate in the blood. Emerging evidence suggests that CMs can have distinct ontogeny and originate from either granulocyte-monocyte- or monocyte-dendritic-cell progenitors (GMPs or MDPs). Here, we report surface markers that allowed segregation of murine GMP- and MDP-derived CMs, i.e., GMP-Mo and MDP-Mo, as well as their functional characterization, including fate definition following adoptive cell transfer. GMP-Mo and MDP-Mo yielded an equal increase in homeostatic CM progeny, such as blood-resident non-classical monocytes and gut macrophages; however, these cells differentially seeded various other selected tissues, including the dura mater and lung. Specifically, GMP-Mo and MDP-Mo differentiated into distinct interstitial lung macrophages, linking CM dichotomy to previously reported pulmonary macrophage heterogeneity. Collectively, we provide evidence for the existence of two functionally distinct CM subsets in the mouse that differentially contribute to peripheral tissue macrophage populations in homeostasis and following challenge.

Dissecting and Visualizing the Functional Diversity of Cardiac Macrophages

Cardiac macrophages represent a functionally diverse population of cells involved in cardiac homeostasis, repair, and remodeling. With recent advancements in single-cell technologies, it is possible to elucidate specific macrophage subsets based on transcriptional signatures and cell surface protein expression to gain a deep understanding of macrophage diversity in the heart. The use of fate-mapping technologies and parabiosis studies have provided insight into the ontogeny and dynamics of macrophages identifying subsets derived from embryonic and adult definitive hematopoietic progenitors that include tissue-resident and bone marrow monocyte-derived macrophages, respectively. Within the heart, these subsets have distinct tissue niches and functional roles in the setting of homeostasis and disease, with cardiac resident macrophages representing a protective cell population while bone marrow monocyte-derived cardiac macrophages have a context-dependent effect, triggering both proinflammatory tissue injury, but also promoting reparative functions. With the increased understanding of the clinical relevance of cardiac macrophage subsets, there has been an increasing need to detect and measure cardiac macrophage compositions in living animals and patients. New molecular tracers compatible with positron emission tomography/computerized tomography and positron emission tomography/ magnetic resonance imaging have enabled investigators to noninvasively and serially visualize cardiac macrophage subsets within the heart to define associations with disease and measure treatment responses. Today, advancements within this thriving field are poised to fuel an era of clinical translation.

CX3CR1 deficiency promotes resolution of hepatic ischemia-reperfusion injury by regulating homeostatic function of liver infiltrating macrophages

Hepatic ischemia-reperfusion injury(HIRI) remains to be an unsolved risk factor that contributes to organ failure after liver surgery. Our clinical retrospective study showed that lower donor liver CX3-C chemokine receptor-1(CX3CR1) mRNA expression level were correlated with upregulated pro-resolved macrophage receptor MERTK, as well as promoted restoration efficiency of allograft injury in liver transplant. To further characterize roles of CX3CR1 in regulating resolution of HIRI, we employed murine liver partial warm ischemia-reperfusion model by Wt & Cx3cr1-/- mice and the reperfusion time was prolonged from 6 h to 4-7 days. Kupffer cells(KCs) were depleted by clodronate liposome(CL) in advance to focus on infiltrating macrophages, and repopulation kinetics were determined by FACS, IF and RNA-Seq. CX3CR1 antagonist AZD8797 was injected i.p. to interrogate potential pharmacological therapeutic strategies. In vitro primary bone marrow macrophages(BMMs) culture by LXR agonist DMHCA, as well as molecular and functional studies, were undertaken to dissect roles of CX3CR1 in modulating macrophages cytobiological development and resolutive functions. We observed that deficiency or pharmacological inhibition of CX3CR1 facilitated HIRI resolution via promoted macrophages migration in CCR1/CCR5 manner, as well as enhanced MerTK-mediated efferocytosis. Our study demonstrated the critical roles of CX3CR1 in progression of HIRI and identified it as a potential therapeutic target in clinical liver transplantation.

Mild Hypoxia Accelerates Cerebral Cavernous Malformation Disease Through CX3CR1-CX3CL1 Signaling

BACKGROUND

Heterogeneity in the severity of cerebral cavernous malformations (CCMs) disease, including brain bleedings and thrombosis that cause neurological disabilities in patients, suggests that environmental, genetic, or biological factors act as disease modifiers. Still, the underlying mechanisms are not entirely understood. Here, we report that mild hypoxia accelerates CCM disease by promoting angiogenesis, neuroinflammation, and vascular thrombosis in the brains of CCM mouse models.

METHODS

We used genetic studies, RNA sequencing, spatial transcriptome, micro-computed tomography, fluorescence-activated cell sorting, multiplex immunofluorescence, coculture studies, and imaging techniques to reveal that sustained mild hypoxia via the CX3CR1-CX3CL1 (CX3C motif chemokine receptor 1/chemokine [CX3C motif] ligand 1) signaling pathway influences cell-specific neuroinflammatory interactions, contributing to heterogeneity in CCM severity.

RESULTS

Histological and expression profiles of CCM neurovascular lesions (Slco1c1-iCreERT2;Pdcd10fl/fl; Pdcd10BECKO) in male and female mice found that sustained mild hypoxia (12% O2, 7 days) accelerates CCM disease. Our findings indicate that a small reduction in oxygen levels can significantly increase angiogenesis, neuroinflammation, and thrombosis in CCM disease by enhancing the interactions between endothelium, astrocytes, and immune cells. Our study indicates that the interactions between CX3CR1 and CX3CL1 are crucial in the maturation of CCM lesions and propensity to CCM immunothrombosis. In particular, this pathway regulates the recruitment and activation of microglia and other immune cells in CCM lesions, which leads to lesion growth and thrombosis. We found that human CX3CR1 variants are linked to lower lesion burden in familial CCMs, proving it is a genetic modifier in human disease and a potential marker for aggressiveness. Moreover, monoclonal blocking antibody against CX3CL1 or reducing 1 copy of the Cx3cr1 gene significantly reduces hypoxia-induced CCM immunothrombosis.

CONCLUSIONS

Our study reveals that interactions between CX3CR1 and CX3CL1 can modify CCM neuropathology when lesions are accelerated by environmental hypoxia. Moreover, a hypoxic environment or hypoxia signaling caused by CCM disease influences the balance between neuroinflammation and neuroprotection mediated by CX3CR1-CX3CL1 signaling. These results establish CX3CR1 as a genetic marker for patient stratification and a potential predictor of CCM aggressiveness.

Discrepant Phenotyping of Monocytes Based on CX3CR1 and CCR2 Using Fluorescent Reporters and Antibodies

Monocytes, as well as downstream macrophages and dendritic cells, are essential players in the immune system, fulfilling key roles in homeostasis as well as in inflammatory conditions. Conventionally, driven by studies on reporter models, mouse monocytes are categorized into a classical and a non-classical subset based on their inversely correlated surface expression of Ly6C/CCR2 and CX3CR1. Here, we aimed to challenge this concept by antibody staining and reporter mouse models. Therefore, we took advantage of Cx3cr1GFP and Ccr2RFP reporter mice, in which the respective gene was replaced by a fluorescent reporter protein gene. We analyzed the expression of CX3CR1 and CCR2 by flow cytometry using several validated fluorochrome-coupled antibodies and compared them with the reporter gene signal in these reporter mouse strains. Although we were able to validate the specificity of the fluorochrome-coupled flow cytometry antibodies, mouse Ly6Chigh classical and Ly6Clow non-classical monocytes showed no differences in CX3CR1 expression levels in the peripheral blood and spleen when stained with these antibodies. On the contrary, in Cx3cr1GFP reporter mice, we were able to reproduce the inverse correlation of the CX3CR1 reporter gene signal and Ly6C surface expression. Furthermore, differential CCR2 surface expression correlating with the expression of Ly6C was observed by antibody staining, but not in Ccr2RFP reporter mice. In conclusion, our data suggest that phenotyping strategies for mouse monocyte subsets should be carefully selected. In accordance with the literature, the suitability of CX3CR1 antibody staining is limited, whereas for CCR2, caution should be applied when using reporter mice.

Anti-CX3CL1 (fractalkine) monoclonal antibody attenuates lung and skin fibrosis in sclerodermatous graft-versus-host disease mouse model

BACKGROUND

Systemic sclerosis (SSc) is an autoimmune disease characterized by vascular injury and inflammation, followed by excessive fibrosis of the skin and other internal organs, including the lungs. CX3CL1 (fractalkine), a chemokine expressed on endothelial cells, supports the migration of macrophages and T cells that express its specific receptor CX3CR1 into targeted tissues. We previously reported that anti-CX3CL1 monoclonal antibody (mAb) treatment significantly inhibited transforming growth factor (TGF)-β1-induced expression of type I collagen and fibronectin 1 in human dermal fibroblasts. Additionally, anti-mouse CX3CL1 mAb efficiently suppressed skin inflammation and fibrosis in bleomycin- and growth factor-induced SSc mouse models. However, further studies using different mouse models of the complex immunopathology of SSc are required before the initiation of a clinical trial of CX3CL1 inhibitors for human SSc.

METHODS

To assess the preclinical utility and functional mechanism of anti-CX3CL1 mAb therapy in skin and lung fibrosis, a sclerodermatous chronic graft-versus-host disease (Scl-cGVHD) mouse model was analyzed with immunohistochemical staining for characteristic infiltrating cells and RNA sequencing assays.

RESULTS

On day 42 after bone marrow transplantation, Scl-cGVHD mice showed increased serum CX3CL1 level. Intraperitoneal administration of anti-CX3CL1 mAb inhibited the development of fibrosis in the skin and lungs of Scl-cGVHD model, and did not result in any apparent adverse events. The therapeutic effects were correlated with the number of tissue-infiltrating inflammatory cells and α-smooth muscle actin (α-SMA)-positive myofibroblasts. RNA sequencing analysis of the fibrotic skin demonstrated that cGVHD-dependent induction of gene sets associated with macrophage-related inflammation and fibrosis was significantly downregulated by mAb treatment. In the process of fibrosis, mAb treatment reduced cGVHD-induced infiltration of macrophages and T cells in the skin and lungs, especially those expressing CX3CR1.

CONCLUSIONS

Together with our previous findings in other SSc mouse models, the current results indicated that anti-CX3CL1 mAb therapy could be a rational therapeutic approach for fibrotic disorders, such as human SSc and Scl-cGVHD.

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.

Unraveling the enigma: housekeeping gene Ugt1a7c as a universal biomarker for microglia

Background

Microglia, brain resident macrophages, play multiple roles in maintaining homeostasis, including immunity, surveillance, and protecting the central nervous system through their distinct activation processes. Identifying all types of microglia-driven populations is crucial due to the presence of various phenotypes that differ based on developmental stages or activation states. During embryonic development, the E8.5 yolk sac contains erythromyeloid progenitors that go through different growth phases, eventually resulting in the formation of microglia. In addition, microglia are present in neurological diseases as a diverse population. So far, no individual biomarker for microglia has been discovered that can accurately identify and monitor their development and attributes.

Summary

Here, we highlight the newly defined biomarker of mouse microglia, UGT1A7C, which exhibits superior stability in expression during microglia development and activation compared to other known microglia biomarkers. The UGT1A7C sensing chemical probe labels all microglia in the 3xTG AD mouse model. The expression of Ugt1a7c is stable during development, with only a 4-fold variation, while other microglia biomarkers, such as Csf1r and Cx3cr1, exhibit at least a 10-fold difference. The UGT1A7C expression remains constant throughout its lifespan. In addition, the expression and activity of UGT1A7C are the same in response to different types of inflammatory activators' treatment in vitro.

Conclusion

We propose employing UGT1A7C as the representative biomarker for microglia, irrespective of their developmental state, age, or activation status. Using UGT1A7C can reduce the requirement for using multiple biomarkers, enhance the precision of microglia analysis, and even be utilized as a standard for gene/protein expression.

Transcription factor C/EBPα is required for the development of Ly6Chi monocytes but not Ly6Clo monocytes

Monocytes comprise two major subsets, Ly6Chi classical monocytes and Ly6Clo nonclassical monocytes. Notch2 signaling in Ly6Chi monocytes triggers transition to Ly6Clo monocytes, which require Nr4a1, Bcl6, Irf2, and Cebpb. By comparison, less is known about transcriptional requirements for Ly6Chi monocytes. We find transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα) is highly expressed in Ly6Chi monocytes, but down-regulated in Ly6Clo monocytes. A few previous studies described the requirement of C/EBPα in the development of neutrophils and eosinophils. However, the role of C/EBPα for in vivo monocyte development has not been understood. We deleted the Cebpa +37 kb enhancer in mice, eliminating hematopoietic expression of C/EBPα, reproducing the expected neutrophil defect. Surprisingly, we also found a severe and selective loss of Ly6Chi monocytes, while preserving Ly6Clo monocytes. We find that BM progenitors from Cebpa +37-/- mice rapidly progress through the monocyte progenitor stage to develop directly into Ly6Clo monocytes even in the absence of Notch2 signaling. These results identify a previously unrecognized role for C/EBPα in maintaining Ly6Chi monocyte identity.

BCG immunization induces CX3CR1hi effector memory T cells to provide cross-protection via IFN-γ-mediated trained immunity

After a century of using the Bacillus Calmette-Guérin (BCG) vaccine, our understanding of its ability to provide protection against homologous (Mycobacterium tuberculosis) or heterologous (for example, influenza virus) infections remains limited. Here we show that systemic (intravenous) BCG vaccination provides significant protection against subsequent influenza A virus infection in mice. We further demonstrate that the BCG-mediated cross-protection against influenza A virus is largely due to the enrichment of conventional CD4+ effector CX3CR1hi memory αβ T cells in the circulation and lung parenchyma. Importantly, pulmonary CX3CR1hi T cells limit early viral infection in an antigen-independent manner via potent interferon-γ production, which subsequently enhances long-term antimicrobial activity of alveolar macrophages. These results offer insight into the unknown mechanism by which BCG has persistently displayed broad protection against non-tuberculosis infections via cross-talk between adaptive and innate memory responses.

RBP-J regulates homeostasis and function of circulating Ly6Clo monocytes

Notch-RBP-J signaling plays an essential role in the maintenance of myeloid homeostasis. However, its role in monocyte cell fate decisions is not fully understood. Here, we showed that conditional deletion of transcription factor RBP-J in myeloid cells resulted in marked accumulation of blood Ly6Clo monocytes that highly expressed chemokine receptor CCR2. Bone marrow transplantation and parabiosis experiments revealed a cell-intrinsic requirement of RBP-J for controlling blood Ly6CloCCR2hi monocytes. RBP-J-deficient Ly6Clo monocytes exhibited enhanced capacity competing with wildtype counterparts in blood circulation. In accordance with alterations of circulating monocytes, RBP-J deficiency led to markedly increased population of lung tissues with Ly6Clo monocytes and CD16.2+ interstitial macrophages. Furthermore, RBP-J deficiency-associated phenotypes could be genetically corrected by further deleting Ccr2 in myeloid cells. These results demonstrate that RBP-J functions as a crucial regulator of blood Ly6Clo monocytes and thus derived lung-resident myeloid populations, at least in part through regulation of CCR2.

Resident Synovial Macrophages in Synovial Fluid: Implications for Immunoregulation in Infectious and Inflammatory Arthritis

Objectives

Resident synovial macrophages (RSM) provide immune sequestration of the joint space and are likely involved in initiation and perpetuation of the joint-specific immune response. We sought to identify RSM in synovial fluid (SF) and demonstrate migratory ability, in additional to functional changes that may perpetuate a chronic inflammatory response within joint spaces.

Methods

We recruited human patients presenting with undifferentiated arthritis in multiple clinical settings. We used flow cytometry to identify mononuclear cells in peripheral blood and SF. We used a novel transwell migration assay with human ex-vivo synovium obtained intra-operatively to validate flow cytometry findings. We used single cell RNA-sequencing (scRNA-seq) to further identify macrophage/monocyte subsets. ELISA was used to evaluate the bone-resorption potential of SF.

Results

We were able to identify a rare population of CD14dim, OPG+, ZO-1+ cells consistent with RSM in SF via flow cytometry. These cells were relatively enriched in the SF during infectious processes, but absolutely decreased compared to healthy controls. Similar putative RSM were identified using ex vivo migration assays when MCP-1 and LPS were used as migratory stimulus. scRNA-seq revealed a population consistent with RSM transcriptionally related to CD56+ cytotoxic dendritic cells and IDO+ M2 macrophages.

Conclusion

We identified a rare cell population consistent with RSM, indicating these cells are likely migratory and able to initiate or coordinate both acute (septic) or chronic (autoimmune or inflammatory) arthritis. RSM analysis via scRNA-seq indicated these cells are M2 skewed, capable of antigen presentation, and have consistent functions in both septic and inflammatory arthritis.

A Comprehensive Retrospective Study on the Mechanisms of Cyclic Mechanical Stretch-Induced Vascular Smooth Muscle Cell Death Underlying Aortic Dissection and Potential Therapeutics for Preventing Acute Aortic Aneurysm and Associated Ruptures

Acute aortic dissection (AAD) and associated ruptures are the leading causes of death in cardiovascular diseases (CVDs). Hypertension is a prime risk factor for AAD. However, the molecular mechanisms underlying AAD remain poorly understood. We previously reported that cyclic mechanical stretch (CMS) leads to the death of rat aortic smooth muscle cells (RASMCs). This review focuses on the mechanisms of CMS-induced vascular smooth muscle cell (VSMC) death. Moreover, we have also discussed the potential therapeutics for preventing AAD and aneurysm ruptures.

Identification and validation of immune and cuproptosis - related genes for diabetic nephropathy by WGCNA and machine learning

Background

As the leading cause of chronic kidney disease, diabetic kidney disease (DKD) is an enormous burden for all healthcare systems around the world. However, its early diagnosis has no effective methods.

Methods

First, gene expression data in GEO database were extracted, and the differential genes of diabetic tubulopathy were obtained. Immune-related genesets were generated by WGCNA and immune cell infiltration analyses. Then, differentially expressed immune-related cuproptosis genes (DEICGs) were derived by the intersection of differential genes and genes related to cuproptosis and immune. To investigate the functions of DEICGs, volcano plots and GO term enrichment analysis was performed. Machine learning and protein-protein interaction (PPI) network analysis helped to finally screen out hub genes. The diagnostic efficacy of them was evaluated by GSEA analysis, receiver operating characteristic (ROC) curve, single-cell RNA sequencing and the Nephroseq website. The expression of hub genes at the animal level by STZ -induced and db/db DKD mouse models was further verified.

Results

Finally, three hub genes, including FSTL1, CX3CR1 and AGR2 that were up-regulated in both the test set GSE30122 and the validation set GSE30529, were screened. The areas under the curve (AUCs) of ROC curves of hub genes were 0.911, 0.935 and 0.922, respectively, and 0.946 when taking as a whole. Correlation analysis showed that the expression level of three hub genes demonstrated their negative relationship with GFR, while those of FSTL1 displayed a positive correlation with the level of serum creatinine. GSEA was enriched in inflammatory and immune-related pathways. Single-nucleus RNA sequencing indicated the main distribution of FSTL1 in podocyte and mesangial cells, the high expression of CX3CR1 in leukocytes and the main localization of AGR2 in the loop of Henle. In mouse models, all three hub genes were increased in both STZ-induced and db/db DKD models.

Conclusion

Machine learning was combined with WGCNA, immune cell infiltration and PPI analyses to identify three hub genes associated with cuproptosis, immunity and diabetic nephropathy, which all have great potential as diagnostic markers for DKD and even predict disease progression.

A double-edged sword: interactions of CX3CL1/CX3CR1 and gut microbiota in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic chronic disease initiated by an abnormal immune response to self and can affect multiple organs. SLE is characterized by the production of autoantibodies and the deposition of immune complexes. In regard to the clinical observations assessed by rheumatologists, several chemokines and cytokines also contribute to disease progression. One such chemokine and adhesion molecule is CX3CL1 (otherwise known as fractalkine). CX3CL1 is involved in cell trafficking and inflammation through recognition by its receptor, CX3CR1. The CX3CL1 protein consists of a chemokine domain and a mucin-like stalk that allows it to function both as a chemoattractant and as an adhesion molecule. In inflammation and specifically lupus, the literature displays contradictory evidence for the functions of CX3CL1/CX3CR1 interactions. In addition, the gut microbiota has been shown to play an important role in the pathogenesis of SLE. This review highlights current studies that illustrate the interactions of the gut microbiota and CX3CR1 in SLE.

The cellular microenvironment regulates CX3CR1 expression on CD8+ T cells and the maintenance of CX3CR1+ CD8+ T cells

Expression levels of the chemokine receptor CX3CR1 serve as high-resolution marker delineating functionally distinct antigen-experienced T-cell states. The factors that influence CX3CR1 expression in T cells are, however, incompletely understood. Here, we show that in vitro priming of naïve CD8+ T cells failed to robustly induce CX3CR1, which highlights the shortcomings of in vitro priming settings in recapitulating in vivo T-cell differentiation. Nevertheless, in vivo generated memory CD8+ T cells maintained CX3CR1 expression during culture. This allowed us to investigate whether T-cell receptor ligation, cell death, and CX3CL1 binding influence CX3CR1 expression. T-cell receptor stimulation led to downregulation of CX3CR1. Without stimulation, CX3CR1+ CD8+ T cells had a selective survival disadvantage, which was enhanced by factors released from necrotic but not apoptotic cells. Exposure to CX3CL1 did not rescue their survival and resulted in a dose-dependent loss of CX3CR1 surface expression. At physiological concentrations of CX3CL1, CX3CR1 surface expression was only minimally reduced, which did not hamper the interpretability of T-cell differentiation states delineated by CX3CR1. Our data further support the broad utility of CX3CR1 surface levels as T-cell differentiation marker and identify factors that influence CX3CR1 expression and the maintenance of CX3CR1 expressing CD8+ T cells.

Reverse Onco-Cardiology: What Is the Evidence for Breast Cancer? A Systematic Review of the Literature

Breast cancer and cardiovascular diseases (CVD) represent significant global health challenges, with CVD being the leading cause of mortality and breast cancer, showing a complex pattern of incidence and mortality. We explore the intricate interplay between these two seemingly distinct medical conditions, shedding light on their shared risk factors and potential pathophysiological connections. A specific connection between hypertension (HTN), atrial fibrillation (AF), myocardial infarction (MI), and breast cancer was evaluated. HTN is explored in detail, emphasizing the role of aging, menopause, insulin resistance, and obesity as common factors linking HTN and breast cancer. Moreover, an attempt is made to identify the potential impact of antihypertensive medications and highlight the increased risk of breast cancer among those women, with a focus on potential mechanisms. A summary of key findings underscores the need for a multisystem approach to understanding the relationship between CVD and breast cancer is also explored with a highlight for all the gaps in current research, such as the lack of clinical observational data on MI and breast cancer in humans and the need for studies specifically designed for breast cancer. This paper concludes that there should be a focus on potential clinical applications of further investigation in this field, including personalized prevention and screening strategies for women at risk. Overall, the authors attempt to provide a comprehensive overview of the intricate connections between breast cancer and cardiovascular diseases, emphasizing the importance of further research in this evolving field of cardio-oncology.

Loss of function of ENT3 drives histiocytosis and inflammation through TLR-MAPK signaling

Histiocytoses are inflammatory myeloid neoplasms often driven by somatic activating mutations in mitogen-activated protein kinase (MAPK) cascade genes. H syndrome is an inflammatory genetic disorder caused by germ line loss-of-function mutations in SLC29A3, encoding the lysosomal equilibrative nucleoside transporter 3 (ENT3). Patients with H syndrome are predisposed to develop histiocytosis, yet the mechanism is unclear. Here, through phenotypic, molecular, and functional analysis of primary cells from a cohort of patients with H syndrome, we reveal the molecular pathway leading to histiocytosis and inflammation in this genetic disorder. We show that loss of function of ENT3 activates nucleoside-sensing toll-like receptors (TLR) and downstream MAPK signaling, inducing cytokine secretion and inflammation. Importantly, MEK inhibitor therapy led to resolution of histiocytosis and inflammation in a patient with H syndrome. These results demonstrate a yet-unrecognized link between a defect in a lysosomal transporter and pathological activation of MAPK signaling, establishing a novel pathway leading to histiocytosis and inflammation.

Non-classical monocytes promote neurovascular repair in cerebral small vessel disease associated with microinfarctions via CX3CR1

Cerebral small vessel disease (cSVD) constitutes a major risk factor for dementia. Monocytes play important roles in cerebrovascular disorders. Herein, we aimed to investigate the contribution of non-classical C-X3-C motif chemokine receptor (CX3CR)1 monocytes to cSVD pathobiology and therapy. To this end, we generated chimeric mice in which CX3CR1 in non-classical monocytes was either functional (CX3CR1GFP/+) or dysfunctional (CX3CR1GFP/GFP). cSVD was induced in mice via the micro-occlusion of cerebral arterioles, and novel immunomodulatory approaches targeting CX3CR1 monocyte production were used. Our findings demonstrate that CX3CR1GFP/+ monocytes transiently infiltrated the ipsilateral hippocampus and were recruited to the microinfarcts 7 days after cSVD, inversely associated with neuronal degeneration and blood-brain barrier (BBB) disruption. Dysfunctional CX3CR1GFP/GFP monocytes failed to infiltrate the injured hippocampus and were associated with exacerbated microinfarctions and accelerated cognitive decline, accompanied with an impaired microvascular structure. Pharmacological stimulation of CX3CR1GFP/+ monocyte generation attenuated neuronal loss and improved cognitive functions by promoting microvascular function and preserving cerebral blood flow (CBF). These changes were associated with elevated levels of pro-angiogenic factors and matrix stabilizers in the blood circulation. The results indicate that non-classical CX3CR1 monocytes promote neurovascular repair after cSVD and constitute a promising target for the development of new therapies.

CX3CL1 represses autophagy via CX3CR1/ CaMKIIδ/HDAC4/Rubicon axis and exacerbates chronic intermittent hypoxia induced Kupffer cell apoptosis

BACKGROUND

Nocturnal hypoxemia is an established factor in the pathogenesis and exacerbation of term metabolic (dysfunction) associated fatty liver disease (MAFLD). Kupffer cells (KCs) are resident macrophages in the liver, and their activity is closely related to the progress of MAFLD. KC insufficient autophagy is involved in MAFLD pathogenesis. Herein, the regulatory mechanism of KC autophagy under chronic intermittent hypoxia (CIH) condition was investigated.

METHODS

Primary KCs and hepatic stellate cells (HSCs) were isolated from mouse liver. Immunofluorescence was employed to detect immunofluorescence intensity of LC3 protein and HDAC4 distribution. KC apoptosis was measured by TUNEL staining. Dual-luciferase reporter and ChIP assays were performed to analyze the interactions between HDAC4, MEF2C and RUBCN.

RESULTS

Herein, our results revealed that CIH-induced increased CX3CL1 in HSCs inhibited KC autophagy and promoted cell apoptosis by interacting with CX3CR1. Meanwhile, CX3CL1 treatment inhibited KC autophagy (p < 0.001, fold change: 0.059) and promoted cell apoptosis (p < 0.001, fold change: 8.18). Rubicon knockdown promoted KC autophagy (p < 0.001, fold change: 2.90) and inhibited cell apoptosis (p < 0.05, fold change: 0.23), while these effects were reversed by CX3CL1 treatment (p < 0.01, fold change: 6.59; p < 0.001, fold change: 0.35). Our mechanistic experiments demonstrated that HDAC4 overexpression transcriptionally inhibited RUBCN expression by interacting with MEF2C, thereby promoting KC autophagy and inhibiting cell apoptosis. Moreover, CaMKIIδ inhibition promoted the translocation of HDAC4 from the cytosol to the nucleus to promote KC autophagy and inhibit the apoptosis.

CONCLUSION

Taken together, CIH-induced increased CX3CL1 expression in HSCs inhibited KC autophagy and promoted apoptosis by regulating the CX3CR1/ CaMKIIδ/HDAC4/Rubicon axis.

Commensal myeloid crosstalk in neonatal skin regulates long-term cutaneous type 17 inflammation

Early life microbe-immune interactions at barrier surfaces have lasting impacts on the trajectory towards health versus disease. Monocytes, macrophages and dendritic cells are primary sentinels in barrier tissues, yet the salient contributions of commensal-myeloid crosstalk during tissue development remain poorly understood. Here, we identify that commensal microbes facilitate accumulation of a population of monocytes in neonatal skin. Transient postnatal depletion of these monocytes resulted in heightened IL-17A production by skin T cells, which was particularly sustained among CD4+ T cells into adulthood and sufficient to exacerbate inflammatory skin pathologies. Neonatal skin monocytes were enriched in expression of negative regulators of the IL-1 pathway. Functional in vivo experiments confirmed a key role for excessive IL-1R1 signaling in T cells as contributing to the dysregulated type 17 response in neonatal monocyte-depleted mice. Thus, a commensal-driven wave of monocytes into neonatal skin critically facilitates long-term immune homeostasis in this prominent barrier tissue.

Monocytes as primary defenders against Toxoplasma gondii infection

Monocytes are recruited from the bone marrow to sites of infection where they release cytokines and chemokines, function in antimicrobial immunity, and differentiate into macrophages and dendritic cells to control infection. Although many studies have focused on monocyte-derived macrophages and dendritic cells, recent work has examined the unique roles of monocytes during infection to promote immune defense. We focus on the effector functions of monocytes during infection with the parasite Toxoplasma gondii, and discuss the signals that mobilize monocytes to sites of infection, their production of inflammatory cytokines and antimicrobial mediators, their ability to shape the adaptive immune response, and their immunoregulatory functions. Insights from other infections, including Plasmodium and Listeria are also included for comparison and context.

The Hepatic Nerves Regulated Inflammatory Effect in the Process of Liver Injury: Is Nerve the Key Treating Target for Liver Inflammation?

Liver injury is a common pathological basis for various liver diseases. Chronic liver injury is often an important initiating factor in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Currently, hepatitis A and E infections are the most common causes of acute liver injury worldwide, whereas drug toxicity (paracetamol overdose) in the USA and part of Western Europe. In recent years, chronic liver injury has become a common disease that harms human health. Meanwhile, the main causes of chronic liver injury are viral hepatitis (B, C) and long-term alcohol consumption worldwide. During the process of liver injury, massive inflammatory cytokines are stimulated by these hazardous factors, leading to a systemic inflammatory response syndrome, followed by a compensatory anti-inflammatory response, which causes immune cell dysfunction and sepsis, subsequent multi-organ failure. Cytokine release and immune cell infiltration-mediated aseptic inflammation are the most important features of the pathobiology of liver failure. From this perspective, diminishing the onset and progression of liver inflammation is of clinical importance in the treatment of liver injury. Although many studies have hinted at the critical role of nerves in regulating inflammation, there largely remains undetermined how hepatic nerves mediate immune inflammation and how the inflammatory factors released by these nerves are involved in the process of liver injury. Therefore, the purpose of this article is to summarize previous studies in the field related to hepatic nerve and inflammation as well as future perspectives on the aforementioned questions. Our findings were presented in three aspects: types of nerve distribution in the liver, how these nerves regulate immunity, and the role of liver nerves in hepatitis and liver failure.

Hemolysis dictates monocyte differentiation via two distinct pathways in sickle cell disease vaso-occlusion

Sickle cell disease (SCD) is a hereditary hemoglobinopathy characterized by painful vaso-occlusive crises (VOC) and chronic hemolysis. The mononuclear phagocyte system is pivotal to SCD pathophysiology, but the mechanisms governing monocyte/macrophage differentiation remain unknown. This study examined the influence of hemolysis on circulating monocyte trajectories in SCD. We discovered that hemolysis stimulated CSF-1 production, partly by endothelial cells via Nrf2, promoting classical monocyte (CMo) differentiation into blood patrolling monocytes (PMo) in SCD mice. However, hemolysis also upregulated CCL-2 through IFN-I, inducing CMo transmigration and differentiation into tissue monocyte-derived macrophages. Blocking CMo transmigration by anti-P selectin antibody in SCD mice increased circulating PMo, corroborating that CMo-to-tissue macrophage differentiation occurs at the expense of CMo-to-blood PMo differentiation. We observed a positive correlation between plasma CSF-1/CCL-2 ratios and blood PMo levels in patients with SCD, underscoring the clinical significance of these two opposing factors in monocyte differentiation. Combined treatment with CSF-1 and anti-P selectin antibody more effectively increased PMo numbers and reduced stasis compared with single-agent therapies in SCD mice. Altogether, these data indicate that monocyte fates are regulated by the balance between two heme pathways, Nrf2/CSF-1 and IFN-I/CCL-2, and suggest that the CSF-1/CCL-2 ratio may present a diagnostic and therapeutic target in SCD.

TLR7/8 stress response drives histiocytosis in SLC29A3 disorders

Loss-of-function mutations in the lysosomal nucleoside transporter SLC29A3 cause lysosomal nucleoside storage and histiocytosis: phagocyte accumulation in multiple organs. However, little is known about the mechanism by which lysosomal nucleoside storage drives histiocytosis. Herein, histiocytosis in Slc29a3-/- mice was shown to depend on Toll-like receptor 7 (TLR7), which senses a combination of nucleosides and oligoribonucleotides (ORNs). TLR7 increased phagocyte numbers by driving the proliferation of Ly6Chi immature monocytes and their maturation into Ly6Clow phagocytes in Slc29a3-/- mice. Downstream of TLR7, FcRγ and DAP10 were required for monocyte proliferation. Histiocytosis is accompanied by inflammation in SLC29A3 disorders. However, TLR7 in nucleoside-laden splenic monocytes failed to activate inflammatory responses. Enhanced production of proinflammatory cytokines was observed only after stimulation with ssRNAs, which would increase lysosomal ORNs. Patient-derived monocytes harboring the G208R SLC29A3 mutation showed enhanced survival and proliferation in a TLR8-antagonist-sensitive manner. These results demonstrated that TLR7/8 responses to lysosomal nucleoside stress drive SLC29A3 disorders.

TLR7 activation at epithelial barriers promotes emergency myelopoiesis and lung antiviral immunity

Monocytes are heterogeneous innate effector leukocytes generated in the bone marrow and released into circulation in a CCR2-dependent manner. During infection or inflammation, myelopoiesis is modulated to rapidly meet the demand for more effector cells. Danger signals from peripheral tissues can influence this process. Herein we demonstrate that repetitive TLR7 stimulation via the epithelial barriers drove a potent emergency bone marrow monocyte response in mice. This process was unique to TLR7 activation and occurred independently of the canonical CCR2 and CX3CR1 axes or prototypical cytokines. The monocytes egressing the bone marrow had an immature Ly6C-high profile and differentiated into vascular Ly6C-low monocytes and tissue macrophages in multiple organs. They displayed a blunted cytokine response to further TLR7 stimulation and reduced lung viral load after RSV and influenza virus infection. These data provide insights into the emergency myelopoiesis likely to occur in response to the encounter of single-stranded RNA viruses at barrier sites.

Molecular and cellular mechanisms of inflammation in atherosclerosis

Atherosclerosis and its complications are a major cause of morbidity and mortality worldwide in spite of the improved medical and invasive treatment in terms of revascularization. Atherosclerosis is a dynamic, multi-step process in which inflammation is a ubiquitous component participating in the initiation, development, and entanglements of the atherosclerotic plaque. After activation, the immune system, either native or acquired, is part of the atherosclerotic dynamics enhancing the pro-atherogenic function of immune or non-immune cells, such as endothelial cells, smooth muscle cells, or platelets, through mediators such as cytokines or directly by cell-to-cell interaction. Cytokines are molecules secreted by the activated cells mentioned above that mediate the inflammatory component of atherosclerosis whose function is to stimulate the immune cells and the production of further cytokines. This review provides insights of the cell axis activation and specific mechanisms and pathways through which inflammation actuates atherosclerosis.

Fractalkine Signalling (CX3CL1/CX3CR1 Axis) as an Emerging Target in Coronary Artery Disease

Acute myocardial infarction (MI) is the most common and dramatic complication of atherosclerosis, which, despite successful reperfusion therapy, can lead to incident heart failure (HF). HF occurs when the healing process is impaired due to adverse left ventricular remodelling, and can be the result of so-called ischaemia/reperfusion injury (IRI), visualised by the development of intramyocardial haemorrhage (IMH) or microvascular obstruction (MVO) in cardiac MRI. Thus far, translation of novel pharmacological strategies from preclinical studies to target either IRI or HF post MI have been largely unsuccessful. Anti-inflammatory therapies also carry the risk of affecting the immune system. Fractalkine (FKN, CX3CL1) is a unique chemokine, present as a transmembrane protein on the endothelium, or following cleavage as a soluble ligand, attracting leukocyte subsets expressing the corresponding receptor CX3CR1. We have shown previously that the fractalkine receptor CX3CR1 is associated with MVO in patients undergoing primary PCI. Moreover, inhibition of CX3CR1 with an allosteric small molecule antagonist (KAND567) in the rat MI model reduces acute infarct size, inflammation, and IMH. Here we review the cellular biology of fractalkine and its receptor, along with ongoing studies that introduce CX3CR1 as a future target in coronary artery disease, specifically in patients with myocardial infarction.

Single-cell RNA-seq reveals alterations in peripheral CX3CR1 and nonclassical monocytes in familial tauopathy

BACKGROUND

Emerging evidence from mouse models is beginning to elucidate the brain's immune response to tau pathology, but little is known about the nature of this response in humans. In addition, it remains unclear to what extent tau pathology and the local inflammatory response within the brain influence the broader immune system.

METHODS

To address these questions, we performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from carriers of pathogenic variants in MAPT, the gene encoding tau (n = 8), and healthy non-carrier controls (n = 8). Primary findings from our scRNA-seq analyses were confirmed and extended via flow cytometry, droplet digital (dd)PCR, and secondary analyses of publicly available transcriptomics datasets.

RESULTS

Analysis of ~ 181,000 individual PBMC transcriptomes demonstrated striking differential expression in monocytes and natural killer (NK) cells in MAPT pathogenic variant carriers. In particular, we observed a marked reduction in the expression of CX3CR1-the gene encoding the fractalkine receptor that is known to modulate tau pathology in mouse models-in monocytes and NK cells. We also observed a significant reduction in the abundance of nonclassical monocytes and dysregulated expression of nonclassical monocyte marker genes, including FCGR3A. Finally, we identified reductions in TMEM176A and TMEM176B, genes thought to be involved in the inflammatory response in human microglia but with unclear function in peripheral monocytes. We confirmed the reduction in nonclassical monocytes by flow cytometry and the differential expression of select biologically relevant genes dysregulated in our scRNA-seq data using ddPCR.

CONCLUSIONS

Our results suggest that human peripheral immune cell expression and abundance are modulated by tau-associated pathophysiologic changes. CX3CR1 and nonclassical monocytes in particular will be a focus of future work exploring the role of these peripheral signals in additional tau-associated neurodegenerative diseases.

Monocyte-endothelial cell interactions in vascular and tissue remodeling

Monocytes are circulating leukocytes of innate immunity derived from the bone marrow that interact with endothelial cells under physiological or pathophysiological conditions to orchestrate inflammation, angiogenesis, or tissue remodeling. Monocytes are attracted by chemokines and specific receptors to precise areas in vessels or tissues and transdifferentiate into macrophages with tissue damage or infection. Adherent monocytes and infiltrated monocyte-derived macrophages locally release a myriad of cytokines, vasoactive agents, matrix metalloproteinases, and growth factors to induce vascular and tissue remodeling or for propagation of inflammatory responses. Infiltrated macrophages cooperate with tissue-resident macrophages during all the phases of tissue injury, repair, and regeneration. Substances released by infiltrated and resident macrophages serve not only to coordinate vessel and tissue growth but cellular interactions as well by attracting more circulating monocytes (e.g. MCP-1) and stimulating nearby endothelial cells (e.g. TNF-α) to expose monocyte adhesion molecules. Prolonged tissue accumulation and activation of infiltrated monocytes may result in alterations in extracellular matrix turnover, tissue functions, and vascular leakage. In this review, we highlight the link between interactions of infiltrating monocytes and endothelial cells to regulate vascular and tissue remodeling with a special focus on how these interactions contribute to pathophysiological conditions such as cardiovascular and chronic liver diseases.

Normal saline remodels the omentum and stimulates its receptivity for transcoelomic metastasis

The omentum contains immune cell structures called milky spots that are niches for transcoelomic metastasis. It is difficult to remove the omentum completely, and there are no effective strategies to minimize the risk of colonization of preserved omental tissues by cancer cells that circulate in the peritoneal fluid. Normal saline is commonly administered into the peritoneal cavity for diagnostic and intraoperative lavage. Here we show that normal saline, when administered into the peritoneal cavity of mice, is prominently absorbed by the omentum, exfoliates its mesothelium, and induces expression of CX3CL1, the ligand for CX3CR1, within and surrounding the omental vasculature. Studies using CX3CR1-competent and CX3CR1-deficient mice showed that the predominant response in the omentum following saline administration is an accumulation of CX3CR1+ monocytes/macrophages that expand milky spots and promote neoangiogenesis within these niches. Moreover, saline administration promoted the implantation of cancer cells of ovarian and colorectal origin onto the omentum. By contrast, these deleterious effects were not observed following i.p. administration of lactated Ringer's solution. Our findings suggest that normal saline stimulates the receptivity of the omentum for cancer cells and that the risk of colonization can be minimized by using a biocompatible crystalloid for lavage procedures.

Role of myeloid cells in system-level immunometabolic dysregulation during prolonged successful HIV-1 treatment

OBJECTIVE

Why people with HIV-1 on ART (PWH ART ) display convoluted metabolism and immune cell functions during prolonged suppressive therapy is not well evaluated. In this study, we aimed to address this question using multiomics methodologies to investigate immunological and metabolic differences between PWH ART and HIV-1 negative individuals (HC).

DESIGN

Cross-sectional study.

METHODS

Untargeted and targeted metabolomics was performed using gas and liquid chromatography/mass spectrometry, and targeted proteomics using Olink inflammation panel on plasma samples. The cellular metabolic state was further investigated using flow cytometry and intracellular metabolic measurement in single-cell populations isolated by EasySep cell isolation. Finally, flow cytometry was performed for deep-immunophenotyping of mononuclear phagocytes.

RESULTS

We detected increased levels of glutamate, lactate, and pyruvate by plasma metabolomics and increased inflammatory markers (e.g. CCL20 and CCL7) in PWH ART compared to HC. The metabolite transporter detection by flow cytometry in T cells and monocytes indicated an increased expression of glucose transporter 1 (Glut1) and monocarboxylate transporter 1 (MCT-1) in PWH ART . Single cell-type metabolite measurement identified decreased glucose, glutamate, and lactate in monocytic cell populations in PWH ART . Deep-immunophenotyping of myeloid cell lineages subpopulations showed no difference in cell frequency, but expression levels of CCR5 were increased on classical monocytes and some dendritic cells.

CONCLUSIONS

Our data thus suggest that the myeloid cell populations potentially contribute significantly to the modulated metabolic environment during suppressive HIV-1 infection.

Differential expression of chemokine receptors on monocytes in TB and HIV

In the present study, we defined multiple chemokine receptors expressed by classical, intermediate and non-classical monocyte subsets in TB, HIV and TB/HIV co-infection and associate it with the perturbation of monocyte subsets due to the diseases. Peripheral blood mononuclear cells from TB+ (n = 34), HIV+ (n = 35), TB + HIV+ (n = 12), as well as TB-HIV- healthy controls (n = 39), were tested for monocyte phenotyping by flow cytometry. Frequencies of intermediate and non-classical monocytes were significantly higher in TB and/or HIV disease relative to healthy controls. CCR2 and CX3CR1 were significantly higher on monocytes in TB disease, whereas CCR4 and CCR5 were present at higher levels in HIV disease. TB/HIV co-infected patients exhibited CCR2, CCR5 and CX3CR1 levels intermediate to TB and HIV subjects, while CCR4 was at a higher level than HIV. Despite the increase in the expression of chemokine receptors due to disease conditions, chemokine receptors maintained their original expression pattern on monocyte subsets. Our data provided new insight into the disease-specific but not monocyte subsets-specific modulation of chemokine receptors in TB and HIV.

Inflammatory cells dynamics control neovascularization and tissue healing after localized radiation induced injury in mice

Local overexposure to ionizing radiation leads to chronic inflammation, vascular damage and cachexia. Here we investigate the kinetics of inflammatory cells from day (D)1 to D180 after mouse hindlimb irradiation and analyze the role of monocyte (Mo) subsets in tissue revascularization. At D1, we find that Mo and T cells are mobilized from spleen and bone marrow to the blood. New vessel formation during early phase, as demonstrated by ~1.4- and 2-fold increased angiographic score and capillary density, respectively, correlates with an increase of circulating T cells, and Mo^hi and type 1-like macrophages in irradiated muscle. At D90 vascular rarefaction and cachexia are observed, associated with decreased numbers of circulating Mo^lo and Type 2-like macrophages in irradiated tissue. Moreover, CCR2- and CX3CR1-deficency negatively influences neovascularization. However adoptive transfer of Mo^hi enhances vessel growth. Our data demonstrate the radiation-induced dynamic inflammatory waves and the major role of inflammatory cells in neovascularization.

CX3CR1 modulates SLE-associated glomerulonephritis and cardiovascular disease in MRL/lpr mice

OBJECTIVE

Patients with systemic lupus erythematosus (SLE) often develop multi-organ damages including heart and kidney complications. We sought to better define the underlying mechanisms with a focus on the chemokine receptor CX3CR1.

METHODS

We generated Cx3cr1-deficient MRL/lpr lupus-prone mice through backcrossing. We then employed heterozygous intercross to generate MRL/lpr littermates that were either sufficient or deficient of CX3CR1. The mice were also treated with either Lactobacillus spp. or a high-fat diet (HFD) followed by assessments of the kidney and heart, respectively.

RESULTS

Cx3cr1-/- MRL/lpr mice exhibited a distinct phenotype of exacerbated glomerulonephritis compared to Cx3cr1+/+ littermates, which was associated with a decrease of spleen tolerogenic marginal zone macrophages and an increase of double-negative T cells. Interestingly, upon correction of the gut microbiota with Lactobacillus administration, the phenotype of exacerbated glomerulonephritis was reversed, suggesting that CX3CR1 controls glomerulonephritis in MRL/lpr mice through a gut microbiota-dependent mechanism. Upon treatment with HFD, Cx3cr1-/- MRL/lpr mice developed significantly more atherosclerotic plaques that were promoted by Ly6C+ monocytes. Activated monocytes expressed ICOS-L that interacted with ICOS-expressing follicular T-helper cells, which in turn facilitated a germinal center reaction to produce more autoantibodies. Through a positive feedback mechanism, the increased circulatory autoantibodies further promoted the activation of Ly6C+ monocytes and their display of ICOS-L.

CONCLUSIONS

We uncovered novel, Cx3cr1 deficiency-mediated pathogenic mechanisms contributing to SLE-associated glomerulonephritis and cardiovascular disease.

Monocyte chemokine receptors as therapeutic targets in cardiovascular diseases

Chemokine receptors are fundamental in many processes related to cardiovascular diseases, such as monocyte migration to vessel walls, cell adhesion, and angiogenesis, among others. Even though many experimental studies have shown the utility of blocking these receptors or their ligands in the treatment of atherosclerosis, the findings in clinical research are still poor. Thus, in the current review we aimed to describe some promising results concerning the blockade of chemokine receptors as therapeutic targets in the treatment of cardiovascular diseases and also to discuss some challenges that need to be overcome before using these strategies in clinical practice.

Mass Cytometry Reveals the Imbalanced Immune State in the Peripheral Blood of Patients with Essential Hypertension

Mounting evidence has confirmed that essential hypertension (EH) is closely related to low-grade inflammation, but there is still a lack of in-depth understanding of the state of immune cells in the circulating blood of patients with EH. We analyzed whether hypertensive peripheral blood immune cell balance was destroyed. The peripheral blood mononuclear cells (PBMCs) of all subjects were analyzed using time-of-flight cytometry (CyTOF) based on 42 kinds of metal-binding antibodies. CD45⁺ cells were categorized into 32 kinds of subsets. Compared with the health control (HC) group, the percentage of total dendritic cells, two kinds of myeloid dendritic cell subsets, one intermediate/nonclassical monocyte subset and one CD4⁺ central memory T cell subset in the EH group, was significantly higher; the percentage of low-density neutrophils, four kinds of classical monocyte subsets, one CD14^lowCD16^- monocyte subset, one naive CD4⁺ and one naive CD8⁺ T cell subsets, one CD4⁺ effector and one CD4⁺ central memory T cell subsets, one CD8⁺ effector memory T cell subset, and one terminally differentiated γδ T cell subset, decreased significantly in EH. What is more, the expression of many important antigens was enhanced in CD45⁺ immune cells, granulocytes, and B cells in patients with EH. In conclusion, the altered number and antigen expression of immune cells reflect the imbalanced immune state of the peripheral blood in patients with EH.

Differences in Prostate Cancer Transcriptomes by Age at Diagnosis: Are Primary Tumors from Older Men Inherently Different?

Older age at diagnosis is consistently associated with worse clinical outcomes in prostate cancer. We sought to characterize gene expression profiles of prostate tumor tissue by age at diagnosis. We conducted a discovery analysis in The Cancer Genome Atlas prostate cancer dataset (n = 320; 29% of men >65 years at diagnosis), using linear regressions of age at diagnosis and mRNA expression and adjusting for TMPRSS2:ERG fusion status and race. This analysis identified 13 age-related candidate genes at FDR < 0.1, six of which were also found in an analysis additionally adjusted for Gleason score. We then validated the 13 age-related genes in a transcriptome study nested in the Health Professionals Follow-up Study and Physicians' Health Study (n = 374; 53% of men >65 years). Gene expression differences by age in the 13 candidate genes were directionally consistent, and age at diagnosis was weakly associated with the 13-gene score. However, the age-related genes were not consistently associated with risk of metastases and prostate cancer-specific death. Collectively, these findings argue against tumor genomic differences as a main explanation for age-related differences in prostate cancer prognosis.

PREVENTION RELEVANCE

Older age at diagnosis is consistently associated with worse clinical outcomes in prostate cancer. This study with independent discovery and validation sets and long-term follow-up suggests that prevention of lethal prostate cancer should focus on implementing appropriate screening, staging, and treatment among older men without expecting fundamentally different tumor biology.

Macrophages in Skin Wounds: Functions and Therapeutic Potential

Macrophages regulate cutaneous wound healing by immune surveillance, tissue repair and remodelling. The depletion of dermal macrophages during the early and middle stages of wound healing has a detrimental impact on wound closure, characterised by reduced vessel density, fibroblast and myofibroblast proliferation, delayed re-epithelization and abated post-healing fibrosis and scar formation. However, in some animal species, oral mucosa and foetal life, cutaneous wounds can heal normally and remain scarless without any involvement of macrophages. These paradoxical observations have created much controversy on macrophages' indispensable role in skin wound healing. Advanced knowledge gained by characterising macrophage subsets, their plasticity in switching phenotypes and molecular drivers provides new insights into their functional importance during cutaneous wound healing. In this review, we highlight the recent findings on skin macrophage subsets, their functional role in adult cutaneous wound healing and the potential benefits of targeting them for therapeutic use.

Dorsal root ganglia CX3CR1 expressing monocytes/macrophages contribute to arthritis pain

Pain is a persistent symptom of Rheumatoid Arthritis, and the K/BxN serum transfer model recapitulates both association and dissociation between pain and joint inflammation in RA. Furthermore, this model features monocyte/macrophage infiltration in joints and lumbar dorsal root ganglia (DRG), where these immune cells are close to nociceptive neurons. We focussed on CX₃CR₁-monocyte/macrophage trafficking and show that at peak paw swelling associated with nociception, CX₃CR₁ deletion altered neither swelling nor macrophage infiltration/phenotype in paws. However, acute nociception and DRG non-classical monocyte numbers were reduced in CX₃CR₁^GFP/GFP (KO) compared to CX₃CR₁^+/GFP (WT). Nociception that persisted despite swelling had resolved was attenuated in KO and correlated with DRG macrophages displaying M2-like phenotype. Still in the DRG, neurons up-regulated neuropeptide CGRP and olcegepant treatment reduced acute swelling, nociception, and leukocyte infiltration in paws and DRG. We delineate in-vitro a signalling pathway showing that CGRP liberates the CX₃CR₁ ligand fractalkine (FKN) from endothelium, and in bone marrow-derived macrophages, FKN promotes activation of intracellular kinases, polarisation towards M1-like phenotype and release of pro-nociceptive IL-6. These data implicate non-classical CX₃CR₁-expressing monocyte and macrophage recruitment into the DRG in initiation and maintenance of arthritis pain.

Common molecular mechanism and immune infiltration patterns of thoracic and abdominal aortic aneurysms

BACKGROUND

Aortic disease (aortic aneurysm (AA), dissection (AD)) is a serious threat to patient lives. Little is currently known about the molecular mechanisms and immune infiltration patterns underlying the development and progression of thoracic and abdominal aortic aneurysms (TAA and AAA), warranting further research.

METHODS

We downloaded AA (includes TAA and AAA) datasets from the GEO database. The potential biomarkers in TAA and AAA were identified using differential expression analysis and two machine-learning algorithms. The discrimination power of the potential biomarkers and their diagnostic accuracy was assessed in validation datasets using ROC curve analysis. Then, GSEA, KEGG, GO and DO analyses were conducted. Furthermore, two immuno-infiltration analysis algorithms were utilized to analyze the common immune infiltration patterns in TAA and AAA. Finally, a retrospective clinical study was performed on 78 patients with AD, and the serum from 6 patients was used for whole exome sequencing (WES).

RESULTS

The intersection of TAA and AAA datasets yielded 82 differentially expressed genes (DEGs). Subsequently, the biomarkers (CX3CR1 and HBB) were acquired by screening using two machine-learning algorithms and ROC curve analysis. The functional analysis of DEGs showed significant enrichment in inflammation and regulation of angiogenic pathways. Immune cell infiltration analysis revealed that adaptive and innate immune responses were closely linked to AA progression. However, neither CX3CR1 nor HBB was associated with B cell-mediated humoral immunity. CX3CR1 expression was correlated with macrophages and HBB with eosinophils. Finally, our retrospective clinical study revealed a hyperinflammatory environment in aortic disease. The WES study identified disease biomarkers and gene variants, some of which may be druggable.

CONCLUSION

The genes CX3CR1 and HBB can be used as common biomarkers in TAA and AAA. Large numbers of innate and adaptive immune cells are infiltrated in AA and are closely linked to the development and progression of AA. Moreover, CX3CR1 and HBB are highly correlated with the infiltration of immune cells and may be potential targets of immunotherapeutic drugs. Gene mutation research is a promising direction for the treatment of aortic disease.

A novel monocyte differentiation pattern in pristane-induced lupus with diffuse alveolar hemorrhage

Pristane causes chronic peritoneal inflammation resulting in lupus, which in C57BL/6 mice is complicated by lung microvascular injury and diffuse alveolar hemorrhage (DAH). Mineral oil (MO) also causes inflammation, but not lupus or DAH. Since monocyte depletion prevents DAH, we examined the role of monocytes in the disease. Impaired bone marrow (BM) monocyte egress in Ccr2-/- mice abolished DAH, confirming the importance of monocyte recruitment to the lung. Circulating Ly6Chi monocytes from pristane-treated mice exhibited increased annexin-V staining in comparison with MO-treated controls without evidence of apoptosis, suggesting that pristane alters the distribution of phosphatidylserine in the plasma membrane before or shortly after monocyte egress from the BM. Plasma membrane asymmetry also was impaired in Nr4a1-regulated Ly6Clo/- 'patrolling' monocytes, which are derived from Ly6Chi precursors. Patrolling Ly6Clo/- monocytes normally promote endothelial repair, but their phenotype was altered in pristane-treated mice. In contrast to MO-treated controls, Nr4a1-regulated Ly6Clo/- monocytes from pristane-treated mice were CD138+, expressed more TremL4, a protein that amplifies TLR7 signaling, and exuberantly produced TNFα in response to TLR7 stimulation. TremL4 expression on these novel CD138+ monocytes was regulated by Nr4a1. Thus, monocyte CD138, high TremL4 expression, and annexin-V staining may define an activated/inflammatory subtype of patrolling monocytes associated with DAH susceptibility. By altering monocyte development, pristane exposure may generate activated Ly6Chi and Ly6Clo/- monocytes, contributing to lung microvascular endothelial injury and DAH susceptibility.

Plasma sICAM-1 as a Biomarker of Carotid Plaque Inflammation in Patients with a Recent Ischemic Stroke

18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) identifies carotid plaque inflammation and predicts stroke recurrence in patients with atherothrombotic stroke. The aim of the study was to identify plasma inflammatory biomarkers associated with plaque inflammation according to 18F-FDG uptake. We conducted a prospective study of consecutive adult patients with a recent (< 7 days) anterior circulation ischemic stroke and at least one atherosclerotic plaque in the ipsilateral internal carotid artery. We included 64 patients, 57.8% of whom showed a carotid stenosis ≥ 50%. All patients underwent an early (< 15 days from inclusion) 18F-FDG PET, and a blood sample was obtained at days 7 ± 1 from the stroke. The plasma concentration of 16 inflammation-related molecules was analyzed in a Luminex using xMAP technology. Multivariable linear regression was used to assess the association between plasma biomarkers and the standardized uptake value (SUV) of 18F-FDG uptake. Soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular adhesion molecule-1 (sVCAM-1), and fractalkine (FKN) were independently associated with plaque inflammation (β = 0.121, 95% CI 0.061-0.181, p < 0.001; β = 0.144, 95% CI 0.012-0.276, p = 0.033; β = 0.136, 95% CI 0.037-0.235, p = 0.008). In a multivariable logistic regression analysis, sICAM-1 was associated with SUVmax ≥ 2.85 (OR = 1.02, 95% CI 1.00-1.03, p = 0.020). Multivariable Cox regression was used to assess the association between biomarkers and stroke recurrence. sICAM-1 was associated with stroke recurrence (HR = 1.03, 95% CI 1.00-1.05, p = 0.002). In summary, elevated concentrations of sICAM-1 were associated with carotid plaque inflammation and an increased risk of stroke recurrence in patients with recent ischemic stroke and carotid atherosclerosis.

Defective efferocytosis of vascular cells in heart disease

The efficient phagocytic clearance of dying cells and apoptotic cells is one of the processes that is essential for the maintenance of physiologic tissue function and homeostasis, which is termed "efferocytosis." Under normal conditions, "find me" and "eat me" signals are released by apoptotic cells to stimulate the engulfment and efferocytosis of apoptotic cells. In contrast, abnormal efferocytosis is related to chronic and non-resolving inflammatory diseases such as atherosclerosis. In the initial steps of atherosclerotic lesion development, monocyte-derived macrophages display efficient efferocytosis that restricts plaque progression; however, this capacity is reduced in more advanced lesions. Macrophage reprogramming as a result of the accumulation of apoptotic cells and augmented inflammation accounts for this diminishment of efferocytosis. Furthermore, defective efferocytosis plays an important role in necrotic core formation, which triggers plaque rupture and acute thrombotic cardiovascular events. Recent publications have focused on the essential role of macrophage efferocytosis in cardiac pathophysiology and have pointed toward new therapeutic strategies to modulate macrophage efferocytosis for cardiac tissue repair. In this review, we discuss the molecular and cellular mechanisms that regulate efferocytosis in vascular cells, including macrophages and other phagocytic cells and detail how efferocytosis-related molecules contribute to the maintenance of vascular hemostasis and how defective efferocytosis leads to the formation and progression of atherosclerotic plaques.

The Fractalkine‐CX3CR1 axis regulates non‐inflammatory osteoclastogenesis by enhancing precursor cell survival

The chemokine fractalkine (FKN) is produced by various cell types, including osteoblasts and endothelial cells in bone tissue, and signals through a sole receptor, CX3CR1, which is expressed on monocytes/macrophages, including osteoclast precursors (OCPs). However, the direct effects of FKN signaling on osteoclast lineage cells under homeostatic noninflammatory conditions remain unclear. Here, we report that FKN regulates mouse OCP survival and primes OCPs for subsequent osteoclast differentiation. Wild‐type but not CX3CR1‐deficient OCPs grown on immobilized FKN showed enhanced osteoclast formation following receptor activator of NF‐κB ligand (RANKL) stimulation, with increased expression of osteoclast differentiation markers. Interestingly, the growth of OCPs on immobilized FKN increased the expression of Cx3cr1 and Tnfrsf11a (Rank) transcripts, but following RANKL stimulation, OCPs rapidly downregulated Cx3cr1 expression. Consistently, anti‐FKN monoclonal antibody (mAb) treatment attenuated RANKL‐induced osteoclast formation on immobilized FKN before, but not during, RANKL stimulation. CX3CR1 and RANK proteins were highly expressed on bone marrow‐derived CD11b^high CD115⁺ OCPs. Growth on immobilized FKN prior to RANKL stimulation also increased CD11b^high CD115⁺ OCP number and their survival and differentiation potential. In a RANKL‐based mouse model of bone loss, anti‐FKN mAb pretreatment significantly inhibited RANKL‐dependent bone loss. Thus, blocking the FKN‐CX3CR1 axis could represent a therapeutic option in noninflammatory bone loss diseases. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Topographical Distribution and Phenotype of Resident Meibomian Gland Orifice Immune Cells (MOICs) in Mice and the Effects of Topical Benzalkonium Chloride (BAK)

Meibomian gland orifices (MGOs) are located along the eyelid margin and secrete meibum into the tear film. The profile of resident innate immune cells (ICs) at this site is not well understood. The distribution and phenotype of resident ICs around MGOs in mice was investigated and herein defined as MGO-associated immune cells (MOICs). The effect of topical 0.1% benzalkonium chloride (BAK) on MOICs was also assessed. Eyelids from healthy CD11ceYFP and Cx3cr1gfp/gfp mice aged three or seven months were compared. ICs were identified as CD11c+, Cx3cr1+, and MHC-II+ using four-colour immunostaining and confocal microscopy. MOIC density was variable but clustered around MGOs. There were more CD11c+ MOICs in three-month-old compared with seven-month-old mice (three-month-old: 893 ± 449 cells/mm2 vs. seven-month-old: 593 ± 493 cells/mm2, p = 0.004). Along the eyelid margin, there was a decreasing gradient of CD11c+ MOIC density in three-month-old mice (nasal: 1003 ± 369 cells/mm2, vs. central: 946 ± 574 cells/mm2, vs. temporal: 731 ± 353 cells/mm2, p = 0.044). Cx3cr1-deficient mice had two-fold fewer MHC-II+ MOICs, suggesting a role for Cx3cr1 receptor signaling in meibomian gland surveillance. CD11c+ MOIC density was lower in BAK-exposed eyes compared to saline-treated controls, suggesting a change in homeostasis. This study provides novel insight into resident ICs located at MGOs, and their contribution to MG homeostasis.

Placental dysfunction influences fetal monocyte subpopulation gene expression in preterm birth

The placenta is the primary organ for immune regulation, nutrient delivery, gas exchange, protection against environmental toxins, and physiologic perturbations during pregnancy. Placental inflammation and vascular dysfunction during pregnancy are associated with a growing list of prematurity-related complications. The goal of this study was to identify differences in gene expression profiles in fetal monocytes - cells that persist and differentiate postnatally - according to distinct placental histologic domains. Here, by using bulk RNA-Seq, we report that placental lesions are associated with gene expression changes in fetal monocyte subsets. Specifically, we found that fetal monocytes exposed to acute placental inflammation upregulate biological processes related to monocyte activation, monocyte chemotaxis, and platelet function, while monocytes exposed to maternal vascular malperfusion lesions downregulate these processes. Additionally, we show that intermediate monocytes might be a source of mitogens, such as HBEGF, NRG1, and VEGFA, implicated in different outcomes related to prematurity. This is the first study to our knowledge to show that placental lesions are associated with unique changes in fetal monocytes and monocyte subsets. As fetal monocytes persist and differentiate into various phagocytic cells following birth, our study may provide insight into morbidity related to prematurity and ultimately potential therapeutic targets.

Smoking-, Alcohol-, and Age-Related Alterations of Blood Monocyte Subsets and Circulating CD4/CD8 T Cells in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) represents a heterogeneous malignant disease of the oral cavity, pharynx, and larynx. Although cigarette smoking, alcohol abuse, and aging are well-established associated factors for HNSCC, their respective influence on immunologic alterations of monocyte subsets or T-cell compositions in the peripheral blood has not yet been fully unveiled. Using flow cytometry, whole blood measurements of CD14/CD16 monocyte subsets and analyses of T-cell subsets in isolated PBMC fractions were carried out in 64 HNSCC patients in view of their tobacco and alcohol consumption, as well as their age, in comparison to healthy volunteers. Flow cytometric analysis revealed significantly increased expression of monocytic CD11b, as well as significantly decreased expression levels of CX3CR1 on classical and intermediate monocyte subsets in smoking-related and in alcohol-related HNSCC patients compared to healthy donors. Peripheral monocytes revealed an age-correlated significant decrease in PD-L1 within the entirety of the HNSCC cohort. Furthermore, we observed significantly decreased abundances of CD8+ effector memory T cells in active-smoking HNSCC patients and significantly increased percentages of CD8+ effector T cells in alcohol-abusing patients compared to the non-smoking/non-drinking patient cohort. Our data indicate an enhanced influence of smoking and alcohol abuse on the dynamics and characteristics of circulating monocyte subsets and CD4/CD8 T-cell subset proportions, as well as an age-related weakened immunosuppression in head and neck cancer patients.

Analysis of Mononuclear Phagocytes Disclosed the Establishment Processes of Two Macrophage Subsets in the Adult Murine Kidney

The interstitium of kidney involves a variety of components including resident immune cells, in particular mononuclear phagocytes. However, many proposed markers for distinguishing macrophages or dendritic cells are, in fact, shared by the majority of renal mononuclear phagocytes, which impedes the research of kidney diseases. Here, by employing a flow cytometry strategy and techniques of fate mapping, imaging and lineage depletion, we were able to demarcate renal monocytes, macrophages and dendritic cells and their subsets in mice. In particular, using this strategy, we found that even in steady state, the renal macrophage pool was continuously replenished by bone marrow-derived monocytes in a stepwise process, i.e., from infiltration of classical monocyte, to development of nonclassical monocyte and eventually to differentiation to macrophages. In mechanism, we demonstrated that the ligation of tissue-anchored CX3CL1 and monocytic CX3CR1 was required for promoting monocyte differentiation to macrophages in the kidney, but CX3CL1-CX3CR1 signaling was dispensable in monocyte infiltrating into the kidney. In addition to the bone marrow-derived macrophages, fate mapping in adult mice revealed another population of renal resident macrophages which were embryo-derived and self-maintaining. Thus, the dissecting strategies developed by us would assist in exploration of the biology of renal mononuclear phagocytes.