Immune Sensing of Cell Death through Recognition of Histone Sequences by C-Type Lectin-Receptor-2d Causes Inflammation and Tissue Injury

Single-cell RNA sequencing of peripheral blood links cell-type-specific regulation of splicing to autoimmune and inflammatory diseases

Alternative splicing contributes to complex traits, but whether this differs in trait-relevant cell types across diverse genetic ancestries is unclear. Here we describe cell-type-specific, sex-biased and ancestry-biased alternative splicing in ~1 M peripheral blood mononuclear cells from 474 healthy donors from the Asian Immune Diversity Atlas. We identify widespread sex-biased and ancestry-biased differential splicing, most of which is cell-type-specific. We identify 11,577 independent cis-splicing quantitative trait loci (sQTLs), 607 trans-sGenes and 107 dynamic sQTLs. Colocalization between cis-eQTLs and trans-sQTLs revealed a cell-type-specific regulatory relationship between HNRNPLL and PTPRC. We observed an enrichment of cis-sQTL effects in autoimmune and inflammatory disease heritability. Specifically, we functionally validated an Asian-specific sQTL disrupting the 5' splice site of TCHP exon 4 that putatively modulates the risk of Graves' disease in East Asian populations. Our work highlights the impact of ancestral diversity on splicing and provides a roadmap to dissect its role in complex diseases at single-cell resolution.

DAMPs in immunosenescence and cancer

Damage-associated molecular patterns (DAMPs) are endogenous molecules released by cells in response to injury or stress, recognized by host pattern recognition receptors that assess the immunological significance of cellular damage. The interaction between DAMPs and innate immune receptors triggers sterile inflammation, which serves a dual purpose: promoting tissue repair and contributing to pathological conditions, including age-related diseases. Chronic inflammation mediated by DAMPs accelerates immunosenescence and influences both tumor progression and anti-tumor immunity, underscoring the critical role of DAMPs in the nexus between aging and cancer. This review explores the characteristics of immunosenescence and its impact on age-related cancers, investigates the various types of DAMPs, their release mechanisms during cell death, and the immune activation pathways they initiate. Additionally, we examine the therapeutic potential of targeting DAMPs in age-related diseases. A detailed understanding of DAMP-induced signal transduction could provide critical insights into immune regulation and support the development of innovative therapeutic strategies.

Identification of molecular targets of Hypericum perforatum in blood for major depressive disorder: a machine-learning pharmacological study

BACKGROUND

Major depressive disorder (MDD) is one of the most common psychiatric disorders worldwide. Hypericum perforatum (HP) is a traditional herb that has been shown to have antidepressant effects, but its mechanism is unclear. This study aims to identify the molecular targets of HP for the treatment of MDD.

METHODS

We performed differential analysis and weighted gene co-expression network analysis (WGCNA) with blood mRNA expression cohort of MDD and healthy control to identify DEGs and significant module genes (gene list 1). Three databases, CTD, DisGeNET, and GeneCards, were used to retrieve MDD-related gene intersections to obtain MDD-predicted targets (gene list 2). The validated targets were retrieved from the TCMSP database (gene list 3). Based on these three gene lists, 13 key pathways were identified. The PPI network was constructed by extracting the intersection of genes and HP-validated targets on all key pathways. Key therapeutic targets were obtained using MCODE and machine learning (LASSO, SVM-RFE). Clinical diagnostic assessments (Nomogram, Correlation, Intergroup expression), and gene set enrichment analysis (GSEA) were performed for the key targets. In addition, immune cell analysis was performed on the blood mRNA expression cohort of MDD to explore the association between the key targets and immune cells. Finally, molecular docking prediction was performed for the targets of HP active ingredients on MDD.

RESULTS

Differential expression analysis and WGCNA module analysis yielded 933 potential targets for MDD. Three disease databases were intersected with 982 MDD-predicted targets. The TCMSP retrieved 275 valid targets for HP. Separate enrichment analysis intersected 13 key pathways. Five key targets (AKT1, MAPK1, MYC, EGF, HSP90AA1) were finally screened based on all enriched genes and HP valid targets. Combined with the signaling pathway and immune cell analysis suggested the effect of peripheral immunity on MDD and the important role of neutrophils in immune inflammation. Finally, the binding of HP active ingredients (quercetin, kaempferol, and luteolin) and all 5 key targets were predicted based on molecular docking.

CONCLUSIONS

The active constituents of Hypericum perforatum can act on MDD and key targets and pathways of this action were identified.

The goat pan-genome reveals patterns of gene loss during domestication

BACKGROUND

Unveiling genetic diversity features and understanding the genetic mechanisms of diverse goat phenotypes are pivotal in facilitating the preservation and utilization of these genetic resources. However, the total genetic diversity within a species can't be captured by the reference genome of a single individual. The pan-genome is a collection of all the DNA sequences that occur in a species, and it is expected to capture the total genomic diversity of the specific species.

RESULTS

We constructed a goat pan-genome using map-to-pan assemble based on 813 individuals, including 723 domestic goats and 90 samples from their wild relatives, which presented a broad regional and global representation. In total, 146 Mb sequences and 974 genes were identified as absent from the reference genome (ARS1.2; GCF_001704415.2). We identified 3,190 novel single nucleotide polymorphisms (SNPs) using the pan-genome analysis. These novel SNPs could properly reveal the population structure of domestic goats and their wild relatives. Presence/absence variation (PAV) analysis revealed gene loss and intense negative selection during domestication and improvement.

CONCLUSIONS

Our research highlights the importance of the goat pan-genome in capturing the missing genetic variations. It reveals the changes in genomic architecture during goat domestication and improvement, such as gene loss. This improves our understanding of the evolutionary and breeding history of goats.

Unraveling the interplay between inflammation and stem cell mobilization or homing: Implications for tissue repair and therapeutics

Inflammation and stem cell mobilization or homing play pivotal roles in tissue repair and regeneration. This review explores their intricate interplay, elucidating their collaborative role in maintaining tissue homeostasis and responding to injury or disease. While examining the fundamentals of stem cells, we detail the mechanisms underlying inflammation, including immune cell recruitment and inflammatory mediator release, highlighting their self-renewal and differentiation capabilities. Central to our exploration is the modulation of hematopoietic stem cell behavior by inflammatory cues, driving their mobilization from the bone marrow niche into circulation. Key cytokines, chemokines, growth factors, and autophagy, an intracellular catabolic mechanism involved in this process, are discussed alongside their clinical relevance. Furthermore, mesenchymal stem cell homing in response to inflammation contributes to tissue repair processes. In addition, we discuss stem cell resilience in the face of inflammatory challenges. Moreover, we examine the reciprocal influence of stem cells on the inflammatory milieu, shaping immune responses and tissue repair. We underscore the potential of targeting inflammation-induced stem cell mobilization for regenerative therapies through extensive literature analysis and clinical insights. By unraveling the complex interplay between inflammation and stem cells, this review advances our understanding of tissue repair mechanisms and offers promising avenues for clinical translation in regenerative medicine.

DAMP sensing and sterile inflammation: intracellular, intercellular and inter-organ pathways

Damage-associated molecular patterns (DAMPs) are endogenous molecules that are released from host cells as a result of cell death or damage. The release of DAMPs in tissues is associated with loss of tissue homeostasis. Sensing of DAMPs by innate immune receptors triggers inflammation, which can be beneficial in initiating the processes that restore tissue homeostasis but can also drive inflammatory diseases. In recent years, the sensing of intracellular DAMPs has received extensive attention in the field of sterile inflammation. However, emerging studies have shown that DAMPs that originate from neighbouring cells, and even from distal tissues or organs, also mediate sterile inflammatory responses. This multi-level sensing of DAMPs is crucial for intercellular, trans-tissue and trans-organ communication. Here, we summarize how DAMP-sensing receptors detect DAMPs from intracellular, intercellular or distal tissue and organ sources to mediate sterile inflammation. We also discuss the possibility of targeting DAMPs or their corresponding receptors to treat inflammatory diseases.

GENETIC ABLATION OF THE C-TYPE LECTIN RECEPTOR CLEC2D INCREASES PERITONITIS MORTALITY, INFLAMMATION, AND PHYSIOLOGY WITHOUT DIMINISHING ORGAN INJURY

ABSTRACT

Background: Sepsis accounts for substantial morbidity and mortality motivating investigators to continue the search for pathways and molecules driving the pathogenesis of the disease. The current study examined if the novel C-type lectin receptor (CLR), Clec2d, plays a significant role in the pathogenesis of sepsis. Methods: Clec2d knockout (KO) mice were fully backcrossed onto the C57/BL6 background. Acute endotoxemia was induced with an intraperitoneal injection of lipopolysaccharide (LPS). Sepsis was induced in two different models, cecal ligation and puncture (CLP) and Pseudomonas aeruginosa pneumonia. Both models were treated with antibiotics and fluid resuscitation. In the sepsis models, physiologic and hematologic measurements were measured at 24 h by collecting a small sample of peripheral blood. Mortality was followed for 14 days. Results : A total of 197 mice were studied, 58 wild type (WT) and 54 knock-out (KO) in the LPS model; 27 wild type and 21 KO mice in the CLP model; and 22 WT and 15 KO mice in the pneumonia model. Clec2d KO mice had greater mortality in the LPS and CLP studies but not the pneumonia model. There were significant differences in multiple parameters determined 24 h post sepsis between mice who subsequently died and those lived. Consistent with previous reports in the CLP model, higher concentrations of IL-6, increased numbers of peripheral blood lymphocytes and greater renal injury were found in the dying mice. In contrast, in the pneumonia model, IL-6 was higher in the surviving mice; however, the IL-6 levels in the pneumonia model (0.6 ± 0.3 ng/mL mean ± SEM) were less than 2% of the IL-6 levels of mice that died in the CLP model (41 ± 9 ng/mL, mean ± SEM). There were no differences in the lymphocyte count or renal injury between living and dying mice in the pneumonia model. In both sepsis models, dying mice had lower heart rates, respiratory rates, and body temperatures. These values were also lower in the KO mice compared to the WT in CLP, but the breath rate and body temperature were increased in the KO pneumonia mice. Conclusion: The C-type lectin receptor Clec2d plays a complicated role in the pathogenesis of sepsis, which varies with source of infection as demonstrated in the models used to study the disease. These data highlight the heterogeneity of the responses to sepsis and provide further evidence that a single common pathway driving sepsis organ injury and death likely does not exist.

Innate immune sensing of cell death in disease and therapeutics

Innate immunity, cell death and inflammation underpin many aspects of health and disease. Upon sensing pathogens, pathogen-associated molecular patterns or damage-associated molecular patterns, the innate immune system activates lytic, inflammatory cell death, such as pyroptosis and PANoptosis. These genetically defined, regulated cell death pathways not only contribute to the host defence against infectious disease, but also promote pathological manifestations leading to cancer and inflammatory diseases. Our understanding of the underlying mechanisms has grown rapidly in recent years. However, how dying cells, cell corpses and their liberated cytokines, chemokines and inflammatory signalling molecules are further sensed by innate immune cells, and their contribution to further amplify inflammation, trigger antigen presentation and activate adaptive immunity, is less clear. Here, we discuss how pattern-recognition and PANoptosome sensors in innate immune cells recognize and respond to cell-death signatures. We also highlight molecular targets of the innate immune response for potential therapeutic development.

Pyroptotic-Spatiotemporally Selective Delivery of siRNA against Pyroptosis and Autoimmune Diseases

Small-interfering RNAs (siRNAs) offer promising prospects for treating pyroptosis-related autoimmune diseases. However, poor stability and off-target effects during in vivo transportation hinder their practical clinical applications. Precision delivery and adaptive release of siRNAs into inflamed tissues and immune cells could unleash their full therapeutic potential. This study establishes a pyroptotic-spatiotemporally selective siRNA delivery system (PMRC@siGSDME) that selectively targets inflammatory tissues, responds to pyroptosis, and exhibits remarkable therapeutic efficacy against various autoimmune diseases. Novel hybrid nanovesicles (NVs) are designed as a combination of pyroptotic macrophage membranes (PMs) and R8-cardiolipin-containing nanovesicles (RC-NVs). Evidence provides that PM-derived proteins involved in cell-cell interactions and membrane trafficking may contribute to the specificity of NVs to inflammatory tissue. In addition, cardiolipin anchored in the hybrid NVs increases its affinity for activated gasdermin E (GSDME) and achieves pyroptosis-adaptive release of siGSDME for the spatiotemporally selective suppression of immune responses. More importantly, PMRC@siGSDME displays significant anti-inflammatory and therapeutic effects in multiple mouse autoimmune disease models, including arthritis and inflammatory bowel disease (IBD). Collectively, an innovative siRNA delivery strategy precisely tailored for pyroptotic cells has been developed, paving the way for new treatments for autoimmune inflammatory diseases with minimal side effects and wide clinical applicability.

Systemic mechanisms of necrotic cell debris clearance

Necrosis is an overarching term that describes cell death modalities caused by (extreme) adverse conditions in which cells lose structural integrity. A guaranteed consequence of necrosis is the production of necrotic cell remnants, or debris. Necrotic cell debris is a strong trigger of inflammation, and although inflammatory responses are required for tissue healing, necrotic debris may lead to uncontrolled immune responses and collateral damage. Besides local phagocytosis by recruited leukocytes, there is accumulating evidence that extracellular mechanisms are also involved in necrotic debris clearance. In this review, we focused on systemic clearance mechanisms present in the bloodstream and vasculature that often cooperate to drive the clearance of cell debris. We reviewed the contribution and cooperation of extracellular DNases, the actin-scavenger system, the fibrinolytic system and reticuloendothelial cells in performing clearance of necrotic debris. Moreover, associations of the (mis)functioning of these clearance systems with a variety of diseases were provided, illustrating the importance of the mechanisms of clearance of dead cells in the organism.

Extracellular histones promote TWIK2-dependent potassium efflux and associated NLRP3 activation in alveolar macrophages during sepsis-induced lung injury

BACKGROUND AND AIM

Sepsis-induced acute lung injury (ALI) is a complex and life-threatening condition lacking specific and efficient clinical treatments. Extracellular histones, identified as a novel type of damage-associated molecular patterns, have been implicated in the inflammatory process of ALI. However, further elucidation is needed regarding the precise mechanism through which extracellular histones induce inflammation. The aim of this study was to investigate whether extracellular histones can activate NLRP3 inflammasome-mediated inflammation in alveolar macrophages (AMs) by affecting TWIK2-dependent potassium efflux.

METHODS AND RESULTS

We conducted experiments using cecal ligation and puncture (CLP) C57BL/6 mice and extracellular histone-stimulated LPS-primed MH-S cells. The results demonstrated a significant increase in the levels of extracellular histones in the plasma and bronchoalveolar lavage fluid (BALF) of CLP mice. Furthermore, neutralizing extracellular histone mitigated lung injury and inflammation in CLP-induced ALI mice. In vitro studies confirmed that extracellular histones upregulated the expression of NLRP3 inflammasome activation-related proteins in MH-S cells, and this effect was dependent on increased potassium efflux mediated by the TWIK2 channel on the plasma membrane. Moreover, extracellular histones directly triggered a substantial influx of calcium, leading to increased Rab11 activity and facilitating the trafficking and location of TWIK2 to the plasma membrane.

CONCLUSION

These findings underscore the critical role of extracellular histone-induced upregulation of TWIK2 expression on the plasma membrane of alveolar macrophages (AMs). This upregulation leads to potassium efflux and subsequent activation of the NLRP3 inflammasome, ultimately exacerbating lung inflammation and injury during sepsis.

naRNA-LL37 composite DAMPs define sterile NETs as self-propagating drivers of inflammation

Neutrophil extracellular traps (NETs) are a key antimicrobial feature of cellular innate immunity mediated by polymorphonuclear neutrophils (PMNs). NETs counteract microbes but are also linked to inflammation in atherosclerosis, arthritis, or psoriasis by unknown mechanisms. Here, we report that NET-associated RNA (naRNA) stimulates further NET formation in naive PMNs via a unique TLR8-NLRP3 inflammasome-dependent pathway. Keratinocytes respond to naRNA with expression of psoriasis-related genes (e.g., IL17, IL36) via atypical NOD2-RIPK signaling. In vivo, naRNA drives temporary skin inflammation, which is drastically ameliorated by genetic ablation of RNA sensing. Unexpectedly, the naRNA-LL37 'composite damage-associated molecular pattern (DAMP)' is pre-stored in resting neutrophil granules, defining sterile NETs as inflammatory webs that amplify neutrophil activation. However, the activity of the naRNA-LL37 DAMP is transient and hence supposedly self-limiting under physiological conditions. Collectively, upon dysregulated NET release like in psoriasis, naRNA sensing may represent both a potential cause of disease and a new intervention target.

Pro-neuroinflammatory and neurotoxic potential of extracellular histones H1 and H3

Histones organize DNA within cellular nuclei, but they can be released from damaged cells. In peripheral tissues extracellular histones act as damage-associated molecular patterns (DAMPs) inducing pro-inflammatory activation of immune cells. Limited studies have considered DAMP-like activity of histones in the central nervous system (CNS); therefore, we studied the effects of extracellular histones on microglia, the CNS immunocytes, and on neuronal cells. Both the linker histone H1 and the core histone H3 induced pro-inflammatory activation of microglia-like cells by upregulating their secretion of NO and cytokines, including interferon-γ-inducible protein 10 (IP-10) and tumor necrosis factor-α (TNF). The selective inhibitors MMG-11 and TAK-242 were used to demonstrate involvement of toll-like receptors (TLR) 2 and 4, respectively, in H1-induced NO secretion by BV-2 microglia. H1, but not H3, downregulated the phagocytic activity of BV-2 microglia. H1 was also directly toxic to all neuronal cell types studied. We conclude that H1, and to a lesser extent H3, when released extracellularly, have the potential to act as a CNS DAMPs. Inhibition of the DAMP-like effects of extracellular histones on microglia and their neurotoxic activity represents a potential strategy for combating neurodegenerative diseases that are characterized by the adverse activation of microglia and neuronal death.

Targeting extranuclear histones to alleviate acute and chronic inflammation

Extracellular histones instigate an inflammatory triad - centered on cytotoxicity, immune cell stimulation, and coagulation - ultimately shaping the dynamics and outcome of various inflammatory pathologies. Given the virtual absence of beneficial functions of histones in the extracellular space, in recent years a number of interference strategies have emerged. In this review we summarize pathogenic functions of extracellular histones and highlight current developments of therapeutic interference. Finally, we elaborate on the current status of preclinical attempts to interfere with extracellular histones in the context of a focus on sepsis and cardiovascular diseases, both of which are leading causes of mortality worldwide.

Myeloid C-type lectin receptors in innate immune recognition

C-type lectin receptors (CLRs) expressed by myeloid cells constitute a versatile family of receptors that play a key role in innate immune recognition. Myeloid CLRs exhibit a remarkable ability to recognize an extensive array of ligands, from carbohydrates and beyond, and encompass pattern-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs), and markers of altered self. These receptors, classified into distinct subgroups, play pivotal roles in immune recognition and modulation of immune responses. Their intricate signaling pathways orchestrate a spectrum of cellular responses, influencing processes such as phagocytosis, cytokine production, and antigen presentation. Beyond their contributions to host defense in viral, bacterial, fungal, and parasitic infections, myeloid CLRs have been implicated in non-infectious diseases such as cancer, allergies, and autoimmunity. A nuanced understanding of myeloid CLR interactions with endogenous and microbial triggers is starting to uncover the context-dependent nature of their roles in innate immunity, with implications for therapeutic intervention.

DAMPs and DAMP-sensing receptors in inflammation and diseases

Damage-associated molecular patterns (DAMPs) are endogenous danger molecules produced in cellular damage or stress, and they can activate the innate immune system. DAMPs contain multiple types of molecules, including nucleic acids, proteins, ions, glycans, and metabolites. Although these endogenous molecules do not trigger immune response under steady-state condition, they may undergo changes in distribution, physical or chemical property, or concentration upon cellular damage or stress, and then they become DAMPs that can be sensed by innate immune receptors to induce inflammatory response. Thus, DAMPs play an important role in inflammation and inflammatory diseases. In this review, we summarize the conversion of homeostatic molecules into DAMPs; the diverse nature and classification, cellular origin, and sensing of DAMPs; and their role in inflammation and related diseases. Furthermore, we discuss the clinical strategies to treat DAMP-associated diseases via targeting DAMP-sensing receptors.

C-TYPE LECTIN-2D RECEPTOR CONTRIBUTES TO HISTONE-INDUCED VASCULAR BARRIER DYSFUNCTION DURING BURN INJURY

ABSTRACT

Severe burns are associated with massive tissue destruction and cell death where nucleus histones and other damage-associated molecular patterns are released into the circulation and contribute to the pathogenesis of multiple-organ dysfunction. Currently, there is limited information regarding the pathophysiology of extracellular histones after burns, and the mechanisms underlying histone-induced vascular injury are not fully understood. In this study, by comparing the blood samples from healthy donors and burn patients, we confirmed that burn injury promoted the release of extracellular histones into the circulation, evidenced by increased plasma levels of histones correlating with injury severity. The direct effects of extracellular histones on human endothelial monolayers were examined, and the results showed that histones caused cell-cell adherens junction discontinuity and barrier dysfunction in a dose-related manner. Like burn patients, mice subjected to a scald burn covering 25% total body surface area also displayed significantly increased plasma histones. Intravital microscopic analysis of mouse mesenteric microcirculation indicated that treatment with a histone antibody greatly attenuated burn-induced plasma leakage in postcapillary venules, supporting the pathogenic role of extracellular histones in the development of microvascular barrier dysfunction during burns. At the molecular level, intrigued by the recent discovery of C-type lectin domain family 2 member D (Clec2d) as a novel receptor of histones, we tested its potential involvement in the histone interaction with endothelial cells. Indeed, we identified abundant expression of Clec2d in vascular endothelial cells. Further proximity ligation assay demonstrated a close association between extracellular histones and endothelial expressing Clec2d. Functionally, in vivo administration of an anti-Clec2d antibody attenuated burn-induced plasma leakage across mesenteric microvessels. Consistently, Clec2d knockdown in endothelial cells partially inhibited histone-induced endothelial barrier dysfunction. Together, our data suggest that burn injury-induced increases in circulating histones contribute to microvascular leakage and endothelial barrier dysfunction via a mechanism involving the endothelial Clec2d receptor.

C-type lectin 2D (CLEC2D) is upregulated in clear cell renal cell carcinoma (ccRCC) tissues and predicts poor prognosis

Clear cell renal cell carcinoma (ccRCC) is known as the most common type of renal cancer. Recently, a series of advances have been made in targeted therapy for ccRCC. To combat this highly metastatic tumor, novel therapeutic targets still need to be developed. C-type lectins (CLECs) contain a characteristic C-type lectin-like domain and affect several physiological functions. The effects of C-type lectin 2D (CLEC2D) on cancer progression have been revealed in several types of cancers; however, its expression in ccRCC tissues, and the possible effects on the progression and metastasis of ccRCC, are still unclear. Herein, we found the high mRNA and protein levels of CLEC2D in ccRCC tissues. We further found that CLEC2D expression was correlated with the prognosis of ccRCC patients and correlated with the tumor size (p = 0.019*) of patients. In addition, CLEC2D affected tumor immune infiltration, confirmed by the further analysis. CLEC2D knockdown suppressed the proliferation of ccRCC cells in vitro and restrained ccRCC tumor growth and immune infiltration in mice. Therefore, we believe that CLEC2D has the potential to serve as a promising ccRCC therapeutic target.

Decoding immunogenic cell death from a dendritic cell perspective

Dendritic cells (DCs) are myeloid cells bridging the innate and adaptive immune system. By cross-presenting tumor-associated antigens (TAAs) liberated upon spontaneous or therapy-induced tumor cell death to T cells, DCs occupy a pivotal position in the cancer immunity cycle. Over the last decades, the mechanisms linking cancer cell death to DC maturation, have been the focus of intense research. Growing evidence supports the concept that the mere transfer of TAAs during the process of cell death is insufficient to drive immunogenic DC maturation unless this process is coupled with the release of immunomodulatory signals by dying cancer cells. Malignant cells succumbing to a regulated cell death variant called immunogenic cell death (ICD), foster a proficient interface with DCs, enabling their immunogenic maturation and engagement of adaptive immunity against cancer. This property relies on the ability of ICD to exhibit pathogen-mimicry hallmarks and orchestrate the emission of a spectrum of constitutively present or de novo-induced danger signals, collectively known as damage-associated molecular patterns (DAMPs). In this review, we discuss how DCs perceive and decode danger signals emanating from malignant cells undergoing ICD and provide an outlook of the major signaling and functional consequences of this interaction for DCs and antitumor immunity.

Acute ischemia induces spatially and transcriptionally distinct microglial subclusters

BACKGROUND

Damage in the ischemic core and penumbra after stroke affects patient prognosis. Microglia immediately respond to ischemic insult and initiate immune inflammation, playing an important role in the cellular injury after stroke. However, the microglial heterogeneity and the mechanisms involved remain unclear.

METHODS

We first performed single-cell RNA-sequencing (scRNA-seq) and spatial transcriptomics (ST) on middle cerebral artery occlusion (MCAO) mice from three time points to determine stroke-associated microglial subclusters and their spatial distributions. Furthermore, the expression of microglial subcluster-specific marker genes and the localization of different microglial subclusters were verified on MCAO mice through RNAscope and immunofluorescence. Gene set variation analysis (GSVA) was performed to reveal functional characteristics of microglia sub-clusters. Additionally, ingenuity pathway analysis (IPA) was used to explore upstream regulators of microglial subclusters, which was confirmed by immunofluorescence, RT-qPCR, shRNA-mediated knockdown, and targeted metabolomics. Finally, the infarct size, neurological deficits, and neuronal apoptosis were evaluated in MCAO mice after manipulation of specific microglial subcluster.

RESULTS

We discovered stroke-associated microglial subclusters in the brains of MCAO mice. We also identified novel marker genes of these microglial subclusters and defined these cells as ischemic core-associated (ICAM) and ischemic penumbra-associated (IPAM) microglia, according to their spatial distribution. ICAM, induced by damage-associated molecular patterns, are probably fueled by glycolysis, and exhibit increased pro-inflammatory cytokines and chemokines production. BACH1 is a key transcription factor driving ICAM generation. In contrast, glucocorticoids, which are enriched in the penumbra, likely trigger IPAM formation, which are presumably powered by the citrate cycle and oxidative phosphorylation and are characterized by moderate pro-inflammatory responses, inflammation-alleviating metabolic features, and myelinotrophic properties.

CONCLUSIONS

ICAM could induce excessive neuroinflammation, aggravating brain injury, whereas IPAM probably exhibit neuroprotective features, which could be essential for the homeostasis and survival of cells in the penumbra. Our findings provide a biological basis for targeting specific microglial subclusters as a potential therapeutic strategy for ischemic stroke.

Single-cell RNA Sequencing Reveals Novel Cellular Factors for Response to Immunosuppressive Therapy in Aplastic Anemia

Aplastic anemia (AA) is a lethal hematological disorder; however, its pathogenesis is not fully understood. Although immunosuppressive therapy (IST) is a major treatment option for AA, one-third of patients do not respond to IST and its resistance mechanism remains elusive. To understand AA pathogenesis and IST resistance, we performed single-cell RNA sequencing (scRNA-seq) of bone marrow (BM) from healthy controls and patients with AA at diagnosis. We found that CD34+ early-stage erythroid precursor cells and PROM1+ hematopoietic stem cells were significantly depleted in AA, which suggests that the depletion of CD34+ early-stage erythroid precursor cells and PROM1+ hematopoietic stem cells might be one of the major mechanisms for AA pathogenesis related with BM-cell hypoplasia. More importantly, we observed the significant enrichment of CD8+ T cells and T cell-activating intercellular interactions in IST responders, indicating the association between the expansion and activation of T cells and the positive response of IST in AA. Taken together, our findings represent a valuable resource offering novel insights into the cellular heterogeneity in the BM of AA and reveal potential biomarkers for IST, building the foundation for future precision therapies in AA.

C-type lectin receptor 2d forms homodimers and heterodimers with TLR2 to negatively regulate IRF5-mediated antifungal immunity

Dimerization of C-type lectin receptors (CLRs) or Toll-like receptors (TLRs) can alter their ligand binding ability, thereby modulating immune responses. However, the possibilities and roles of dimerization between CLRs and TLRs remain unclear. Here we show that C-type lectin receptor-2d (CLEC2D) forms homodimers, as well as heterodimers with TLR2. Quantitative ligand binding assays reveal that both CLEC2D homodimers and CLEC2D/TLR2 heterodimers have a higher binding ability to fungi-derived β-glucans than TLR2 homodimers. Moreover, homo- or hetero-dimeric CLEC2D mediates β-glucan-induced ubiquitination and degradation of MyD88 to inhibit the activation of transcription factor IRF5 and subsequent IL-12 production. Clec2d-deficient female mice are resistant to infection with Candida albicans, a human fungal pathogen, owing to the increase of IL-12 production and subsequent generation of IFN-γ-producing NK cells. Together, these data indicate that CLEC2D forms homodimers or heterodimers with TLR2, which negatively regulate antifungal immunity through suppression of IRF5-mediated IL-12 production. These homo- and hetero-dimers of CLEC2D and TLR2 provide an example of receptor dimerization to regulate host innate immunity against microbial infections.

Identification of a protective microglial state mediated by miR-155 and interferon-γ signaling in a mouse model of Alzheimer's disease

Microglia play a critical role in brain homeostasis and disease progression. In neurodegenerative conditions, microglia acquire the neurodegenerative phenotype (MGnD), whose function is poorly understood. MicroRNA-155 (miR-155), enriched in immune cells, critically regulates MGnD. However, its role in Alzheimer's disease (AD) pathogenesis remains unclear. Here, we report that microglial deletion of miR-155 induces a pre-MGnD activation state via interferon-γ (IFN-γ) signaling, and blocking IFN-γ signaling attenuates MGnD induction and microglial phagocytosis. Single-cell RNA-sequencing analysis of microglia from an AD mouse model identifies Stat1 and Clec2d as pre-MGnD markers. This phenotypic transition enhances amyloid plaque compaction, reduces dystrophic neurites, attenuates plaque-associated synaptic degradation and improves cognition. Our study demonstrates a miR-155-mediated regulatory mechanism of MGnD and the beneficial role of IFN-γ-responsive pre-MGnD in restricting neurodegenerative pathology and preserving cognitive function in an AD mouse model, highlighting miR-155 and IFN-γ as potential therapeutic targets for AD.

Single-cell analysis of cellular heterogeneity and interactions in the ischemia-reperfusion injured mouse intestine

Nine major cell populations among 46,716 cells were identified in mouse intestinal ischemia‒reperfusion (II/R) injury by single-cell RNA sequencing. For enterocyte cells, 11 subclusters were found, in which enterocyte cluster 1 (EC1), enterocyte cluster 3 (EC3), and enterocyte cluster 8 (EC8) were newly discovered cells in ischemia 45 min/reperfusion 720 min (I 45 min/R 720 min) group. EC1 and EC3 played roles in digestion and absorption, and EC8 played a role in cell junctions. For TA cells, after ischemia 45 min/reperfusion 90 min (I 45 min/R 90 min), many TA cells at the stage of proliferation were identified. For Paneth cells, Paneth cluster 3 was observed in the resting state of normal jejunum. After I 45 min/R 90 min, three new subsets were found, in which Paneth cluster 1 had good antigen presentation activity. The main functions of goblet cells were to synthesize and secrete mucus, and a novel subcluster (goblet cluster 5) with highly proliferative ability was discovered in I 45 min/R 90 min group. As a major part of immune system, the changes in T cells with important roles were clarified. Notably, enterocyte cells secreted Guca2b to interact with Gucy2c receptor on the membranes of stem cells, TA cells, Paneth cells, and goblet cells to elicit intercellular communication. One marker known as glutathione S-transferase mu 3 (GSTM3) affected intestinal mucosal barrier function by adjusting mitogen-activated protein kinases (MAPK) signaling during II/R injury. The data on the heterogeneity of intestinal cells, cellular communication and the mechanism of GSTM3 provide a cellular basis for treating II/R injury.

Comparative Characterization of Immune Response in Sheep with Caseous Lymphadenitis through Analysis of the Whole Blood Transcriptome

Caseous lymphadenitis (CL) is a chronic contagious disease that affects small ruminants and is characterized by the formation of pyogranulomas in lymph nodes and other organs. However, the pathogenesis of this disease and the response of the host genome to infection are not yet fully understood. This study aimed to investigate the whole blood transcriptome and evaluate differential gene expression during the later stages of CL in naturally infected ewes. The study included diseased, serologically positive (EP), exposed, serologically negative (EN) ewes from the same infected flock and healthy ewes (CN) from a different flock. RNA sequencing was performed using the Illumina NextSeq system, and differential gene expression was estimated using DESeq2 and Edge R approaches. The analysis identified 191 annotated differentially expressed genes (DEGs) in the EP group (102 upregulated and 89 downregulated) and 256 DEGs in the EN group (106 upregulated and 150 downregulated) compared to the CN group. Numerous immunoregulatory interactions between lymphoid and nonlymphoid cells were influenced in both EP and EN ewes. Immune DEGs were preferentially assigned to antigen presentation through the MHC complex, T lymphocyte-mediated immunity, and extracellular matrix interactions. Furthermore, the EP group showed altered regulation of cytokine and chemokine signaling and activation and recombination of B-cell receptors. Conversely, NF-kappa B signaling, apoptosis, and stress response were the main processes influenced in the EN group. In addition, statistically significant enrichment of the essential immune pathways of binding and uptake of ligands by scavenger receptors in EP and p53 signaling in the EN group was found. In conclusion, this study provides new insights into the disease course and host-pathogen interaction in naturally CL-infected sheep by investigating the blood transcriptome.

The role of circulating cell-free DNA as an inflammatory mediator after stroke

Stroke is the second leading cause of death worldwide and a leading cause of disability. Clinical and experimental studies highlighted the complex role of the immune system in the pathophysiology of stroke. Ischemic brain injury leads to the release of cell-free DNA, a damage-associated molecular pattern, which binds to pattern recognition receptors on immune cells such as toll-like receptors and cytosolic inflammasome sensors. The downstream signaling cascade then induces a rapid inflammatory response. In this review, we are highlighting the characteristics of cell-free DNA and how these can affect a local as well as a systemic response after stroke. For this purpose, we screened literature on clinical studies investigating cell-free DNA concentration and properties after brain ischemia. We report the current understanding for mechanisms of DNA uptake and sensing in the context of post-stroke inflammation. Moreover, we compare possible treatment options targeting cell-free DNA, DNA-sensing pathways, and the downstream mediators. Finally, we describe clinical implications of this inflammatory pathway for stroke patients, open questions, and potential future research directions.

Activation of immune signals during organ transplantation

The activation of host's innate and adaptive immune systems can lead to acute and chronic graft rejection, which seriously impacts graft survival. Thus, it is particularly significant to clarify the immune signals, which are critical to the initiation and maintenance of rejection generated after transplantation. The initiation of response to graft is dependent on sensing of danger and stranger molecules. The ischemia and reperfusion of grafts lead to cell stress or death, followed by releasing a variety of damage-associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors (PRRs) of host immune cells to activate intracellular immune signals and induce sterile inflammation. In addition to DAMPs, the graft exposed to 'non-self' antigens (stranger molecules) are recognized by the host immune system, stimulating a more intense immune response and further aggravating the graft damage. The polymorphism of MHC genes between different individuals is the key for host or donor immune cells to identify heterologous 'non-self' components in allogeneic and xenogeneic organ transplantation. The recognition of 'non-self' antigen by immune cells mediates the activation of immune signals between donor and host, resulting in adaptive memory immunity and innate trained immunity to the graft, which poses a challenge to the long-term survival of the graft. This review focuses on innate and adaptive immune cells receptor recognition of damage-associated molecular patterns, alloantigens and xenoantigens, which is described as danger model and stranger model. In this review, we also discuss the innate trained immunity in organ transplantation.

Inflammatory cell death: how macrophages sense neighbouring cell infection and damage

Programmed cell death is a critical host defence strategy during viral infection. Neighbouring cells deal with this death in distinct ways depending on how the infected cell dies. While apoptosis is considered immunologically silent, the lytic pathways of necroptosis and pyroptosis trigger inflammatory responses by releasing inflammatory host molecules. All these pathways have been implicated in influenza A virus infection. Here, we review how cells sense neighbouring infection and death and how sensing shapes ensuing inflammatory responses.

THE ROLE OF NEUTROPHIL EXTRACELLULAR TRAPS (NETS) IN THE IMMUNOPATHOGENESIS OF SEVERE COVID-19: POTENTIAL IMMUNOTHERAPEUTIC STRATEGIES REGULATING NET FORMATION AND ACTIVITY

The role of neutrophil granulocytes (NG) in the pathogenesis of COVID-19 is associated with the recruitment of NG into inflammatory foci, activation of their functions and enhanced formation of neutrophil extracellular networks (NETs). In this review, we analyzed a fairly large volume of scientific literature devoted to the peculiarities of the formation of NETs, their role in the pathogenesis of COVID-19, participation in the occurrence of immunothrombosis, vasculitis, acute respiratory distress syndrome, cytokine storm syndrome, multi-organ lesions. Convincing data are presented that clearly indicate the significant involvement of NETs in the immunopathogenesis of COVID-19 and the associated severe complications resulting from the intensification of the inflammation process, which is key for the course of infection caused by the SARS-CoV-2 virus. The presented role of NG and NETs, along with the role of other immune system cells and pro-inflammatory cytokines, is extremely important in understanding the development of an overactive immune response in severe COVID-19. The obtained scientific results, available today, allow identifying the possibilities of regulatory effects on hyperactivated NG, on the formation of NETs at various stages and on limiting the negative impact of already formed NETs on various tissues and organs. All of the above should help in the creation of new, specialized immunotherapy strategies designed to increase the chances of survival, reduce the severity of clinical manifestations in patients with COVID-19, as well as significantly reduce mortality rates. Currently, it is possible to use existing drugs and a number of new drugs are being developed, the action of which can regulate the amount of NG, positively affect the functions of NG and limit the intensity of NETs formation. Continuing research on the role of hyperactive NG and netosis, as well as understanding the mechanisms of regulation of the phenomenon of formation and restriction of NETs activity in severe COVID-19, apparently, are a priority, since in the future the new data obtained could become the basis for the development of targeted approaches not only to immunotherapy aimed at limiting education and blocking negative effects already formed NETs in severe COVID-19, but also to immunotherapy, which could be used in the complex treatment of other netopathies, first of all, autoimmune diseases, auto-inflammatory syndromes, severe purulent-inflammatory processes, including bacterial sepsis and hematogenous osteomyelitis.

Neutrophil Extracellular Traps Induce Glomerular Endothelial Cell Dysfunction and Pyroptosis in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease. Neutrophil extracellular traps (NETs) are a network structure composed of loose chromatin and embedded with multiple proteins. Here, we observed increased NETs deposition in the glomeruli of DKD patients and diabetic mice (streptozotocin-induced or db/db mice). After NETs were degraded with DNase I, diabetic mice exhibited attenuated glomerulopathy and glomerular endothelial cells (GECs) injury. We also observed alleviated glomerulopathy and GECs injury in peptidylarginine deiminase 4-knockout mice with streptozotocin-induced diabetes. In vitro, NETs-induced GECs pyroptosis was characterized by pore formation in the cell membrane, dysregulation of multiple genes involved in cell membrane function, and increased expression of pyroptosis-related proteins. Strengthening the GECs surface charge by oleylamine significantly inhibited NETs-induced GECs pyroptosis. These findings suggest that the GECs charge-related pyroptosis is involved in DKD progression, which is promoted by NETs.

Histones: The critical players in innate immunity

The highly conserved histones in different species seem to represent a very ancient and universal innate host defense system against microorganisms in the biological world. Histones are the essential part of nuclear matter and act as a control switch for DNA transcription. However, histones are also found in the cytoplasm, cell membranes, and extracellular fluid, where they function as host defenses and promote inflammatory responses. In some cases, extracellular histones can act as damage-associated molecular patterns (DAMPs) and bind to pattern recognition receptors (PRRs), thereby triggering innate immune responses and causing initial organ damage. Histones and their fragments serve as antimicrobial peptides (AMPs) to directly eliminate bacteria, viruses, fungi, and parasites in vitro and in vivo. Histones are also involved in phagocytes-related innate immune response as components of neutrophil extracellular traps (NETs), neutrophil activators, and plasminogen receptors. In addition, as a considerable part of epigenetic regulation, histone modifications play a vital role in regulating the innate immune response and expression of corresponding defense genes. Here, we review the regulatory role of histones in innate immune response, which provides a new strategy for the development of antibiotics and the use of histones as therapeutic targets for inflammatory diseases, sepsis, autoimmune diseases, and COVID-19.

Mouse Ocilrp2/Clec2i negatively regulates LPS-mediated IL-6 production by blocking Dap12-Syk interaction in macrophage

C-type lectin Ocilrp2/Clec2i is widely expressed in dendritic cells, lymphokine-activated killer cells and activated T cells. Previous studies have shown that Ocilrp2 is an important regulator in the activation of T cells and NK cells. However, the role of Ocilrp2 in the inflammatory responses by activated macrophages is currently unknown. This study investigated the expression of inflammatory cytokines in LPS-induced macrophages from primary peritoneal macrophages silenced by specific siRNA target Ocilrp2. Ocilrp2 was significantly downregulated in macrophages via NF-κB and pathways upon LPS stimuli or VSV infection. Silencing Ocilrp2 resulted in the increased expression of IL-6 in LPS-stimulated peritoneal macrophages and mice. Moreover, IL-6 expression was reduced in LPS-induced Ocilrp2 over-expressing iBMDM cells. Furthermore, we found that Ocilrp2-related Syk activation is responsible for expressing inflammatory cytokines in LPS-stimulated macrophages. Silencing Ocilrp2 significantly promotes the binding of Syk to Dap12. Altogether, we identified the Ocilrp2 as a critical role in the TLR4 signaling pathway and inflammatory macrophages’ immune regulation, and added mechanistic insights into the crosstalk between TLR and Syk signaling.

Histones of Neutrophil Extracellular Traps Induce CD11b Expression in Brain Pericytes Via Dectin-1 after Traumatic Brain Injury

The brain pericyte is a unique and indispensable part of the blood-brain barrier (BBB), and contributes to several pathological processes in traumatic brain injury (TBI). However, the cellular and molecular mechanisms by which pericytes are regulated in the damaged brain are largely unknown. Here, we show that the formation of neutrophil extracellular traps (NETs) induces the appearance of CD11b+ pericytes after TBI. These CD11b+ pericyte subsets are characterized by increased permeability and pro-inflammatory profiles compared to CD11b- pericytes. Moreover, histones from NETs by Dectin-1 facilitate CD11b induction in brain pericytes in PKC-c-Jun dependent manner, resulting in neuroinflammation and BBB dysfunction after TBI. These data indicate that neutrophil-NET-pericyte and histone-Dectin-1-CD11b are possible mechanisms for the activation and dysfunction of pericytes. Targeting NETs formation and Dectin-1 are promising means of treating TBI.

Dysregulated miRNAs network in the critical COVID-19: An important clue for uncontrolled immunothrombosis/thromboinflammation

Known as a pivotal immunohemostatic response, immunothrombosis is activated to restrict the diffusion of pathogens. This beneficial intravascular defensive mechanism represents the close interaction between the immune and coagulation systems. However, its uncontrolled form can be life-threatening to patients with the critical coronavirus disease 2019 (COVID-19). Hyperinflammation and ensuing cytokine storm underlie the activation of the coagulation system, something which results in the provocation of more immune-inflammatory responses by the thrombotic mediators. This vicious cycle causes grave clinical complications and higher risks of mortality. Classified as an evolutionarily conserved family of the small non-coding RNAs, microRNAs (miRNAs) serve as the fine-tuners of genes expression and play a key role in balancing the pro/anticoagulant and pro-/anti-inflammatory factors maintaining homeostasis. Therefore, any deviation from their optimal expression levels or efficient functions can lead to severe complications. Despite their extensive effects on the molecules and processes involved in uncontrolled immunothrombosis, some genetic agents and uncontrolled immunothrombosis-induced interfering factors (e.g., miRNA-single nucleotide polymorphysms (miR-SNPs), the complement system components, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, and reactive oxygen species (ROS)) have apparently disrupted their expressions/functions. This review study aims to give an overview of the role of miRNAs in the context of uncontrolled immunothrombosis/thromboinflammation accompanied by some presumptive interfering factors affecting their expressions/functions in the critical COVID-19. Detecting, monitoring, and resolving these interfering agents mafy facilitate the design and development of the novel miRNAs-based therapeutic approaches to the reduction of complications incidence and mortality in patients with the critical COVID-19.

Microbe capture by splenic macrophages triggers sepsis via T cell-death-dependent neutrophil lifespan shortening

The mechanisms linking systemic infection to hyperinflammation and immune dysfunction in sepsis are poorly understood. Extracellular histones promote sepsis pathology, but their source and mechanism of action remain unclear. Here, we show that by controlling fungi and bacteria captured by splenic macrophages, neutrophil-derived myeloperoxidase attenuates sepsis by suppressing histone release. In systemic candidiasis, microbial capture via the phagocytic receptor SIGNR1 neutralizes myeloperoxidase by facilitating marginal zone infiltration and T cell death-dependent histone release. Histones and hyphae induce cytokines in adjacent CD169 macrophages including G-CSF that selectively depletes mature Ly6G^high neutrophils by shortening their lifespan in favour of immature Ly6G^low neutrophils with a defective oxidative burst. In sepsis patient plasma, these mediators shorten mature neutrophil lifespan and correlate with neutrophil mortality markers. Consequently, high G-CSF levels and neutrophil lifespan shortening activity are associated with sepsis patient mortality. Hence, by exploiting phagocytic receptors, pathogens degrade innate and adaptive immunity through the detrimental impact of downstream effectors on neutrophil lifespan.

Hyperinflammation and immune dysfunction are key drivers of immunopathology in sepsis. Here the authors show microbial exploitation of phagocytic receptors is linked to triggering of sepsis and the immune cell mediated reduction in neutrophil life span.

Inhibition of P2Y6 receptor expression in Kupffer cells alleviates alcoholic steatohepatitis in mice

Inflammation plays an important role in the progression of alcohol-related liver disease (ALD). UDP-P2Y₆ signaling is involved in many human diseases. The purinergic P2Y₆ receptor, an important regulator of inflammation and phagocytosis, has attracted attention, but its role in alcoholic steatohepatitis remains unclear. Here, we found that P2Y₆ levels were significantly elevated in Kupffer cells in the livers of mice with alcoholic steatohepatitis and ethanol (EtOH)-induced RAW264.7 cells. In this study, mice with alcoholic steatohepatitis were intraperitoneally injected with MRS2578, a specific inhibitor of the P2Y₆ receptor, and P2Y₆ was silenced in EtOH-induced RAW264.7 cells. We found a marked improvement in steatosis and inflammation in the livers of mice with alcoholic steatohepatitis and EtOH-induced RAW264.7 cells. However, P2Y₆ activation in vivo and overexpression in vitro showed contrasting results. In addition, the expression of phospho-p38 mitogen-activated protein kinase (p-p38 MAPK), a phosphorylated protein in the p38 MAPK signaling pathway, was significantly altered after P2Y₆ silencing or overexpression in vitro. P2Y₆ can induce the activation of the p38 MAPK signaling pathway by mediating the calcium influx, whereas inhibition of the expression of P2Y₆ can block the inflammatory process to some extent and thus improve the inflammatory response. The results of this study suggested that targeting P2Y₆ signaling may be a potentially effective strategy for the treatment of alcoholic steatohepatitis.

Inhibition of myeloid-derived suppressor cell arginase-1 production enhances T-cell-based immunotherapy against Cryptococcus neoformans infection

Cryptococcosis is a potentially lethal disease that is primarily caused by the fungus Cryptococcus neoformans, treatment options for cryptococcosis are limited. Here, we show glucuronoxylomannan, the major polysaccharide component of C. neoformans, induces the recruitment of neutrophilic myeloid-derived suppressor cells in mice and patients with cryptococcosis. Depletion of neutrophilic myeloid-derived suppressor cells enhances host defense against C. neoformans infection. We identify C-type lectin receptor-2d recognizes glucuronoxylomannan to potentiate the immunosuppressive activity of neutrophilic myeloid-derived suppressor cells by initiating p38-mediated production of the enzyme arginase-1, which inhibits T-cell mediated antifungal responses. Notably, pharmacological inhibition of arginase-1 expression by a specific inhibitor of p38, SB202190, or an orally available receptor tyrosine kinase inhibitor, vandetanib, significantly enhances T-cell mediated antifungal responses against cryptococcosis. These data reveal a crucial suppressive role of neutrophilic myeloid-derived suppressor cells during cryptococcosis and highlight a promising immunotherapeutic application by inhibiting arginase-1 production to combat infectious diseases.

Cryptococcus neoformans causes opportunistic infection and potentially lethal immunopathology but therapeutic options are limited. Here the authors implicate myeloid derived suppressor cells during C. neoformans infection and suggest targeting arginase-1 production as a potential therapeutic strategy.

Immunoprotective Effects of Two Histone H2A Variants in the Grass Carp Against Flavobacterium columnare Infection

In teleost fish, the nucleotide polymorphisms of histone H2A significantly affect the resistance or susceptibility of zebrafish to Edwardsiella piscicida infection. Whether histone H2A variants can enhance the resistance of grass carp to Flavobacterium columnare infection remains unclear. Here, the effects of 7 previously obtained variants (gcH2A-1~gcH2A-7) and 5 novel histone H2A variants (gcH2A-11, gcH2A-13~gcH2A-16) in response to F. columnare infection were investigated. It was found that these histone H2A variants could be divided into type I and II. Among them, 5 histone H2A variants had no any effects on the F. columnare infection, however 7 histone H2A variants had antibacterial activity against F. columnare infection. The gcH2A-4 and gcH2A-11, whose antibacterial activity was the strongest in type I and II histone H2A variants respectively, were picked out for yeast expression. Transcriptome data for the samples from the intestines of grass carp immunized with the engineered Saccharomyces cerevisiae expressing PYD1, gcH2A-4 or gcH2A-11 revealed that 5 and 12 immune-related signaling pathways were significantly enriched by gcH2A-4 or gcH2A-11, respectively. For the engineered S. cerevisiae expressing gcH2A-4, NOD-like receptor and Toll-like receptor signaling pathways were enriched for up-regulated DEGs. Besides NOD-like receptor and Toll-like receptor signaling pathways, the engineered S. cerevisiae expressing gcH2A-11 also activated Cytosolic DNA-sensing pathway, RIG-I-like receptor signaling pathway and C-type lectin receptor signaling pathway. Furthermore, grass carp were immunized with the engineered S. cerevisiae expressing PYD1, gcH2A-4 or gcH2A-11 for 1 month and challenged with F. columnare. These grass carp immunized with gcH2A-4 or gcH2A-11 showed lower mortality and fewer numbers of F. columnare than did the control group. All these results suggest that gcH2A-4 and gcH2A-11 play important roles in evoking the innate immune responses and enhancing disease resistance of grass carp against F. columnare infection.

Extracellular Nucleosomes Accelerate Microglial Inflammation via C-Type Lectin Receptor 2D and Toll-Like Receptor 9 in mPFC of Mice With Chronic Stress

Damage-associated molecular patterns (DAMPs) are the primary promoter of progressive neuroinflammation and are associated with chronic stress-related emotional disorders. The present study investigated the role and mechanism of extracellular nucleosomes and histones, the newly defined DAMPs, in mice with chronic stress. C57BL/6 mice were exposed to chronic unpredictable mild stress (CUMS) and corticosterone drinking, respectively, for 4 weeks. Negative emotional behaviors were comprehensively investigated. Microglial morphology, oxidative stress, and inflammation, as well as C-type lectin receptor 2D (Clec2d) and Toll-like receptor 9 (TLR9) expression in medial prefrontal cortex (mPFC) were assessed with flow cytometer and cell sorting. Specifically, microglial pro-inflammatory activation and inflammation were further investigated with stereotactic injection of recombinant nucleosomes and histones in mPFC and further evaluated with AAV-Clec2d knocking-down, DNase I, and activated protein C (APC) pretreatment. Moreover, the rescue effect by AAV-Clec2d knocking-down was observed in mice with chronic stress. Mice with chronic stress were presented as obviously depressive- and anxiety-like behaviors and accompanied with significant microglial oxidative stress and inflammation, indicating by reactive oxygen species (ROS) production, primed nuclear factor-κB (NF-κB) signaling pathway, activated NACHT, LRR, and PYD domain–containing protein 3 (NLRP3) inflammasome, and upregulated Clec2d and TLR9 in mPFC, together with histones dictation in cerebrospinal fluid and extracellular trap formation. Stereotactic injection of nucleosomes was contributed to promote microglial inflammation rather than histones in mPFC, indicating that the pro-inflammatory role was derived from extracellular histones-bound DNA but not freely histones. AAV-Clec2d knocking-down, DNase I, and APC were all effective to inhibit nucleosome-induced microglial oxidative stress and inflammation. Moreover, AAV-Clec2d knocking-down in mice with chronic stress exhibited reduced microglial inflammation and improved negative emotional behaviors. Our findings reveal a novel mechanism of DAMP-associated inflammation that extracellular nucleosomes accelerate microglial inflammation via Clec2d and TLR9, and then contribute to chronic stress-induced emotional disorders.

Attenuating oxidized low density lipoprotein (ox-LDL)-induced macrophages damage via inhibiting C-type lectin domain family 2 (CLEC2) expression through janus kinase 1 (JAK1)/ signal transducers and activators of transcription-1 (STAT1) pathway

Our study aimed to explore the effect of C-type lectin-like receptor 2 (CLEC2) expression level on oxidized low-density lipoprotein (ox-LDL)-induced macrophage damage and the regulatory mechanism of macrophage foaming. Foam cells were derived from RAW264.7 by ox-LDL, and the cell viability was detected by cell counting kit-8 (CCK-8) assay. Enzyme-linked immunosorbent assay (ELISA) was applied to detect the levels of inflammatory cytokines tumor necrosis factor (TNF-α), Interleukin-6 (IL-6), and Interleulin-1β (IL-1β). Small interfering CLEC2 (si-CLEC2) was synthesized and transfected into RAW264.7, and the apoptosis rate was analyzed by flow cytometry. Western blotting was employed to detect the protein expressions of Janus kinase 1 (JAK1), Signal transducers and activators of transcription-1 (STAT1), phosphorylation-JAK1 (p-JAK1), phosphorylation-STAT1 (p-STAT1), CLEC2, and the apoptosis-related proteins. The levels of total cholesterol (TC) and free cholesterol (FC) were measured using colorimetric kits. Results showed that ox-LDL could activate the JAK1/STAT1 pathway of macrophages and up-regulate the expression of CLEC2. CLEC2 knockdown could reduce macrophage inflammation and lipid accumulation. Inactivating JAK1/STAT1 pathway with JAK1 inhibitor can significantly reduce the phosphorylation of STAT1 and alleviate the ox-LDL-induced damage in macrophages by regulating the expression of CLEC2. In conclusion, targeting JAK1/STAT1 to inhibit CLEC2 can attenuate ox-LDL-induced macrophage damage. This study enriched the pathogenesis of atherosclerosis and provided the possible treatment targets.

Nonresolving inflammation redux

Nonresolving inflammation contributes to many diseases, including COVID-19 in its fatal and long forms. Our understanding of inflammation is rapidly evolving. Like the immune system of which it is a part, inflammation can now be seen as an interactive component of a homeostatic network with the endocrine and nervous systems. This review samples emerging insights regarding inflammatory memory, inflammatory aging, inflammatory cell death, inflammatory DNA, inflammation-regulating cells and metabolites, approaches to resolving or modulating inflammation, and inflammatory inequity.

Organellar homeostasis and innate immune sensing

A cell is delimited by numerous borders that define specific organelles. The walls of some organelles are particularly robust, such as in mitochondria or endoplasmic reticulum, but some are more fluid such as in phase-separated stress granules. Either way, all organelles can be damaged at times, leading their contents to leak out into the surrounding environment. Therefore, an elegant way to construct an innate immune defence system is to recognize host molecules that do not normally reside within a particular compartment. Here, we provide several examples where organellar homeostasis is lost, leading to the activation of a specific innate immune sensor; these include NLRP3 activation owing to a disrupted trans-Golgi network, Pyrin activation due to cytoskeletal damage, and cGAS-STING activation following the leakage of nuclear or mitochondrial DNA. Frequently, organelle damage is observed downstream of pathogenic infection but it can also occur in sterile settings as associated with auto-inflammatory disease. Therefore, understanding organellar homeostasis is central to efforts that will identify new innate immune pathways, and therapeutics that balance organellar homeostasis, or target the breakdown pathways that trigger innate immune sensors, could be useful treatments for infection and chronic inflammatory diseases.

Neutrophil Extracellular Traps (NETs) and Covid-19: A new frontiers for therapeutic modality

Coronavirus disease 2019 (Covid-19) is a worldwide infectious disease caused by severe acute respiratory coronavirus 2 (SARS-CoV-2). In severe SARS-CoV-2 infection, there is severe inflammatory reactions due to neutrophil recruitments and infiltration in the different organs with the formation of neutrophil extracellular traps (NETs), which involved various complications of SARS-CoV-2 infection. Therefore, the objective of the present review was to explore the potential role of NETs in the pathogenesis of SARS-CoV-2 infection and to identify the targeting drugs against NETs in Covid-19 patients. Different enzyme types are involved in the formation of NETs, such as neutrophil elastase (NE), which degrades nuclear protein and release histones, peptidyl arginine deiminase type 4 (PADA4), which releases chromosomal DNA and gasdermin D, which creates pores in the NTs cell membrane that facilitating expulsion of NT contents. Despite of the beneficial effects of NETs in controlling of invading pathogens, sustained formations of NETs during respiratory viral infections are associated with collateral tissue injury. Excessive development of NETs in SARS-CoV-2 infection is linked with the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) due to creation of the NETs-IL-1β loop. Also, aberrant NTs activation alone or through NETs formation may augment SARS-CoV-2-induced cytokine storm (CS) and macrophage activation syndrome (MAS) in patients with severe Covid-19. Furthermore, NETs formation in SARS-CoV-2 infection is associated with immuno-thrombosis and the development of ALI/ARDS. Therefore, anti-NETs therapy of natural or synthetic sources may mitigate SARS-CoV-2 infection-induced exaggerated immune response, hyperinflammation, immuno-thrombosis, and other complications.

Neutrophil and remnant clearance in immunity and inflammation

Neutrophil-centred inflammation and flawed clearance of neutrophils cause and exuberate multiple pathological conditions. These most abundant leukocytes exhibit very high daily turnover in steady-state and stress conditions. Various armours including oxidative burst, NETs and proteases function against pathogens, but also dispose neutrophils to spawn pro-inflammatory responses. Neutrophils undergo death through different pathways upon ageing, infection, executing the intruder's elimination. These include non-lytic apoptosis and other lytic deaths including NETosis, necroptosis and pyroptosis with distinct disintegration of the cellular membrane. This causes release and presence of different intracellular cytotoxic, and tissue-damaging content as cell remnants in the extracellular environment. The apoptotic cells and apoptotic bodies get cleared with non-inflammatory outcomes, while lytic deaths associated remnants including histones and cell-free DNA cause pro-inflammatory responses. Indeed, the enhanced frequencies of neutrophil-associated proteases, cell-free DNA and autoantibodies in diverse pathologies including sepsis, asthma, lupus and rheumatoid arthritis, imply disturbed neutrophil resolution programmes in inflammatory and autoimmune diseases. Thus, the clearance mechanisms of neutrophils and associated remnants are vital for therapeutics. Though studies focused on clearance mechanisms of senescent or apoptotic neutrophils so far generated a good understanding of the same, clearance of neutrophils undergoing distinct lytic deaths, including NETs, are being the subjects of intense investigations. Here, in this review, we are providing the current updates in the clearance mechanisms of apoptotic neutrophils and focusing on not so well-defined recognition, uptake and degradation of neutrophils undergoing lytic death and associated remnants that may provide new therapeutic approaches in inflammation and autoimmunity.

Inhibition of Drug-Induced Liver Injury in Mice Using a Positively Charged Peptide That Binds DNA

Hepatic cell death occurs in response to diverse stimuli such as chemical and physical damage. The exposure of intracellular contents such as DNA during necrosis induces a severe inflammatory response that has yet to be fully explored therapeutically. Here, we sought means to neutralize the ability of extracellular DNA to induce deleterious tissue inflammation when drug-induced liver injury had already ensued. DNA exposure and inflammation were investigated in vivo in drug-induced liver injury using intravital microscopy. The necrotic DNA debris was studied in murine livers in vivo and in DNA debris models in vitro by using a positively charged chemokine-derived peptide (MIG30; CXCL9[74-103]). Acetaminophen-induced liver necrosis was associated with massive DNA accumulation, production of CXC chemokines, and neutrophil activation inside the injured tissue. The MIG30 peptide bound the healthy liver vasculature and, to a much greater extent, to DNA-rich necrotic tissue. Moreover, MIG30 bound extracellular DNA directly in vivo in a charge-dependent manner and independently of glycosaminoglycans and chemokines. Post-treatment of mice with MIG30 reduced mortality, liver damage, and inflammation significantly. These effects were not observed with a control peptide that does not bind DNA. Mechanistically, MIG30 inhibited the interaction between DNA and histones, and promoted the dissociation of histones from necrotic debris. MIG30 also inhibited the pro-inflammatory effect of CpG DNA, as measured by a reduction in CXCL8 production, indicating that MIG30 disturbs the ability of DNA to induce hepatic inflammation. Conclusion: The use of DNA-binding peptides reduces necrotic liver injury and inflammation, even at late timepoints.

Cis P-tau underlies vascular contribution to cognitive impairment and dementia and can be effectively targeted by immunotherapy in mice

Compelling evidence supports vascular contributions to cognitive impairment and dementia (VCID) including Alzheimer's disease (AD), but the underlying pathogenic mechanisms and treatments are not fully understood. Cis P-tau is an early driver of neurodegeneration resulting from traumatic brain injury, but its role in VCID remains unclear. Here, we found robust cis P-tau despite no tau tangles in patients with VCID and in mice modeling key aspects of clinical VCID, likely because of the inhibition of its isomerase Pin1 by DAPK1. Elimination of cis P-tau in VCID mice using cis-targeted immunotherapy, brain-specific Pin1 overexpression, or DAPK1 knockout effectively rescues VCID-like neurodegeneration and cognitive impairment in executive function. Cis mAb also prevents and ameliorates progression of AD-like neurodegeneration and memory loss in mice. Furthermore, single-cell RNA sequencing revealed that young VCID mice display diverse cortical cell type-specific transcriptomic changes resembling old patients with AD, and the vast majority of these global changes were recovered by cis-targeted immunotherapy. Moreover, purified soluble cis P-tau was sufficient to induce progressive neurodegeneration and brain dysfunction by causing axonopathy and conserved transcriptomic signature found in VCID mice and patients with AD with early pathology. Thus, cis P-tau might play a major role in mediating VCID and AD, and antibody targeting it may be useful for early diagnosis, prevention, and treatment of cognitive impairment and dementia after neurovascular insults and in AD.

Decoding Cell Death: From a Veritable Library of Babel to Vade Mecum?

Programmed cell death (PCD) is a requisite feature of development and homeostasis but can also be indicative of infections, injuries, and pathologies. In concordance with these heterogeneous contexts, an array of disparate effector responses occur downstream of cell death and its clearance-spanning tissue morphogenesis, homeostatic turnover, host defense, active dampening of inflammation, and tissue repair. This raises a fundamental question of how a single contextually appropriate response ensues after an event of PCD. To explore how complex inputs may together tailor the specificity of the resulting effector response, here we consider (a) the varying contexts during which different cell death modalities are observed, (b) the nature of the information that can be passed on by cell corpses, and (c) the ways by which efferocyte populations synthesize signals from dying cells with those from the surrounding microenvironment.

Tissue Homeostasis and Inflammation

There is a growing interest in understanding tissue organization, homeostasis, and inflammation. However, despite an abundance of data, the organizing principles of tissue biology remain poorly defined. Here, we present a perspective on tissue organization based on the relationships between cell types and the functions that they perform. We provide a formal definition of tissue homeostasis as a collection of circuits that regulate specific variables within the tissue environment, and we describe how the functional organization of tissues allows for the maintenance of both tissue and systemic homeostasis. This leads to a natural definition of inflammation as a response to deviations from homeostasis that cannot be reversed by homeostatic mechanisms alone. We describe how inflammatory signals act on the same cellular functions involved in normal tissue organization and homeostasis in order to coordinate emergency responses to perturbations and ultimately return the system to a homeostatic state. Finally, we consider the hierarchy of homeostatic and inflammatory circuits and the implications for the development of inflammatory diseases.

The Concept of Pathogenic TH2 Cells: Collegium Internationale Allergologicum Update 2021

T helper (TH) cells have evolved into distinct subsets that mediate specific immune responses to protect the host against a myriad of infectious and noninfectious challenges. However, if dysregulated, TH-cell subsets can cause inflammatory disease. Emerging evidence now suggests that human allergic disease is caused by a distinct subpopulation of pathogenic TH2 cells. Pathogenic TH2 cells from different type-2-driven diseases share a core phenotype and show overlapping functional attributes. The unique differentiation requirements, activating signals, and metabolic characteristics of pathogenic TH2 cells are just being discovered. A better knowledge of this particular TH2 cell population will enable the specific targeting of disease-driving pathways in allergy. In this review, we introduce a rational for classifying TH cells into distinct subsets, discuss the current knowledge on pathogenic TH2 cells, and summarize their involvement in allergic diseases.