Phagocytosis of apoptotic cells in homeostasis

Comprehensive analysis of hub mRNA, lncRNA and miRNA, and associated ceRNA networks implicated in cobia (Rachycentron canadum) scales under hypoosmotic adaption

Salinity plays a vital role in fish aquaculture, profoundly influencing the growth and development of fish. Scales, as the protective outer layer of fish, function as a critical defense against external factors. In this study, we employed transcriptome sequencing to analyze the ceRNA expression profiles to reveal the effect of salinity acclimation on transcriptional expression changes in the scales of cobia (Rachycentron canadum). The results revealed that after being exposed to a salinity level of 15 ‰ for just one day (1D), a total of 407 mRNAs/genes were significantly regulated; 66 miRNAs were respectively significantly regulated; and 109 target genes of the differentially expressed miRNAs were significantly regulated; a total of 185 differently expressed lncRNAs and 292 differently expressed target genes (DetGenes) of differently expressed lncRNAs were also identified. After 7 days (7D), a total of 2195 mRNAs/genes were found to be significantly regulated and 82 miRNAs were significantly regulated; among the target genes of the differentially expressed miRNAs, 245 were regulated. Moreover, 438 differently expressed lncRNAs and 681 DetGenes of these lncRNAs were identified. Subsequent analysis through GO, KEGG pathway, in 1D vs. CG (control group), DeGenes, which first respond to changes in salinity, are mainly involved in negative regulation of macrophage differentiation, negative regulation of granulocyte differentiation and negative regulation of phagocytosis, and are mainly related to biological processes related to the immune function of fish. After a 7-day process, DeGenes were enriched in the collagen fibril organization, regulation of nodal signaling pathway and cell recognition biology processes. These biological processes are not only related to the immune function of fish, but more importantly, to the physiological structure of fish. By analyzing the co down-regulated miRNAs of 1D vs. CG, as well as 7D vs. CG, the functions of these miRNAs are mainly related to bone differentiation and development. In addition，ceRNA network uncovered that the effect of salinity is temporal. The first competing lncRNAs mainly regulated genes related to physiological processes and biological development, while target genes related to immunity and body defense were less competitive. On the contrary, after a period of salinity treatment, the types of competing lncRNAs involved changed.

Prognostic implications of ERLncRNAs in ccRCC: a novel risk score model and its association with tumor mutation burden and immune microenvironment

INTRODUCTION/BACKGROUND

The specific role of efferocytosis-related long noncoding RNAs (ERLncRNAs) in Clear Cell Renal Cell Carcinoma (ccRCC) has not been thoroughly examined. This study aims to identify and validate a signature of ERLncRNAs for prognostic prediction and characterization of the immune landscape in individuals with ccRCC.

MATERIALS AND METHODS

Analysis of ccRCC samples was conducted by utilizing clinical and RNA sequencing information obtained from The Cancer Genome Atlas (TCGA). Pearson correlation analysis was utilized to identify lncRNAs associated with efferocytosis, which was then used to create a new prognostic model through univariate Cox regression, Least Absolute Shrinkage and Selection Operator (LASSO) regression, and stepwise multivariate Cox analysis. In order to investigate the biological significance, we performed a functional enrichment analysis to assess how well the model predicts outcomes. Differences in the immune landscape were observed through a comparison of immune cell infiltration, tumor mutational burden (TMB), and tumor microenvironment (TME) characteristics. Following this, drug sensitivity analysis was conducted.

RESULTS

This led to the identification of a unique signature consisting of seven ERLncRNAs (LINC01615, RUNX3-AS1, FOXD2-AS1, AC002070.1, LINC02747, LINC00944, and AC092296.1). Model performance was measured by Kaplan-Meier curves and receiver operating characteristic (ROC) curves. The nomogram and C-index provided additional validation of the strong correlation between the risk signature and clinical decision-making.

CONCLUSION

On the whole, our innovative signature exhibits potential for prognostic prediction and assessment of immunotherapeutic response in patients with ccRCC.

Unraveling the role of macrophages in diabetes: Impaired phagocytic function and therapeutic prospects

The rising aging population and changing lifestyles have led to a global increase in diabetes and its complications, making it one of the most prevalent diseases worldwide. Chronic inflammation is a key pathogenic feature of diabetes and its complications, yet the precise mechanisms remain unclear, impeding the development of targeted therapies. Recent studies have highlighted the β cell-macrophage crosstalk pathway as a crucial factor in chronic low-grade inflammation and glucose homeostasis imbalance in both type 1 and type 2 diabetes. Furthermore, impaired macrophage phagocytic functions, including pathogen phagocytosis, efferocytosis, and autophagy, play a significant role in diabetes complications. Given their high plasticity, macrophages represent a promising research target. This review summarizes recent findings on macrophage phagocytic dysfunction in diabetes and its complications, and explores emerging therapies targeting macrophage phagocytic function. We also discuss the current challenges in translating basic research to clinical practice, aiming to guide researchers in developing targeted treatments to regulate macrophage status and phagocytic function, thus preventing and treating metabolic inflammatory diseases.

Copper Chelate Targeting Externalized Phosphatidylserine Inhibits PD-L1 Expression and Enhances Cancer Immunotherapy

Inhibitors of the PD-1/PD-L1 immune checkpoint have revolutionized cancer treatment. However, the clinical response remains limited, with only 20% of patients benefiting from treatment and approximately 60% of PD-L1-positive patients exhibiting resistance. One key factor contributing to resistance is the externalization of phosphatidylserine (PS) on the surface of cancer cells, which suppresses immune responses and promotes PD-L1 expression, further hindering the efficacy of PD-L1 blockade therapies. Here, we introduce a copper chelate composed of a terpyridine-Cu complex with a farnesol tail designed to selectively target and cap the externalized PS on cancer cells. This approach not only promotes dendritic cell maturation and effector T-cell proliferation and tumor infiltration but also significantly inhibits PD-L1 expression, thereby amplifying T-cell-mediated immune responses. Our results demonstrate that this strategy induces robust immunological memory and leads to the eradication of tumors in over 70% of mice with colorectal and melanoma cancers. These findings highlight a promising, antibody-independent strategy for cancer immunotherapy where targeting externalized PS could overcome current limitations of checkpoint blockade therapies.

Elimination of apoptotic cells by non-professional embryonic phagocytes can be stimulated or inhibited by external stimuli

Active elimination of apoptotic cells is very important for maintaining homeostasis of early embryos. Recent observations on mouse blastocysts freshly isolated from healthy dams have shown that the majority of incidentally occurring apoptotic cells is eliminated by neighbouring embryonic cells. Some apoptotic cells escape phagocytosis, but the frequency of such processes usually does not exceed 10%. The aim of the current study was to evaluate whether the non-professional embryonic phagocytes can respond to experimentally induced increase in apoptosis by increasing the frequency of efferocytosis and whether their activity can be decreased by selective inhibition of specific component of efferoctosis machinery. Experiments were performed in vitro on cultured mouse blastocysts with a differentiated trophectoderm and inner cell mass and on the human trophoblast cell line Ac-1M88. Samples were assessed using fluorescence immunostaining: Apoptotic cells (TUNEL) internalised within the cytoplasm of non-professional embryonic phagocytes (phalloidin T membrane staining) were considered ingested; apoptotic cells co-localised with acidified phagosomes (LysoTracker) were considered digested. First, we tested the ability of embryonic phagocytes to respond to elevated incidence of apoptosis induced by actinomycin D (4 nM). The results showed that the increase in apoptosis was accompanied by a significant elevation of the phagocytosis and digestion of dead cells in both mouse blastocysts and human trophoblast cells. We then assessed the effect of selective inhibition of lysosomal acidification in embryonic phagocytes using a specific V-ATPase inhibitor bafilomycin A1. The results showed that the inhibitor at 0.1 and 0.2 nM was able to negatively affect the execution of both initiative and terminal phases of efferocytosis in mouse blastocysts, although the decrease was not as profound as expected. When compared to mouse trophectoderm cells, human hybrid cells displayed a very low sensitivity to bafilomycin A1. Higher concentrations of bafilomycin A1 had a more harmful impact on overall cell viability than on digestive activity. The results show that the ability of non-professional embryonic phagocytes to successfully execute all stages of efferocytosis is not limited by the frequency of apoptosis and is preserved even at elevated rates of the apoptotic process. The effectiveness of embryonic phagocytes can be partially decreased by selective inhibition of lysosomal acidification conducted via V-ATPase.

Target cell adhesion limits macrophage phagocytosis and promotes trogocytosis

Macrophage phagocytosis is an essential immune response that eliminates pathogens, antibody-opsonized cancer cells and debris. Macrophages can also trogocytose, or nibble, targets. Trogocytosis and phagocytosis are often activated by the same signal, including IgG antibodies. What makes a macrophage trogocytose instead of phagocytose is not clear. Using both CD47 antibodies and a Her2 Chimeric Antigen Receptor (CAR) to induce phagocytosis, we found that macrophages preferentially trogocytose adherent target cells instead of phagocytose in both 2D cell monolayers and 3D cancer spheroid models. Disrupting target cell integrin using an RGD peptide or through CRISPR-Cas9 knockout of the αV integrin subunit in target cells increased macrophage phagocytosis. Conversely, increasing cell adhesion by ectopically expressing E-Cadherin in Raji B cell targets reduced phagocytosis. Finally, we examined phagocytosis of mitotic cells, a naturally occurring example of cells with reduced adhesion. Arresting target cells in mitosis significantly increased phagocytosis. Together, our data show that target cell adhesion limits phagocytosis and promotes trogocytosis.

Neutrophil heterogeneity and plasticity: unveiling the multifaceted roles in health and disease

Neutrophils, the most abundant circulating leukocytes, have long been recognized as key players in innate immunity and inflammation. However, recent discoveries unveil their remarkable heterogeneity and plasticity, challenging the traditional view of neutrophils as a homogeneous population with a limited functional repertoire. Advances in single-cell technologies and functional assays have revealed distinct neutrophil subsets with diverse phenotypes and functions and their ability to adapt to microenvironmental cues. This review provides a comprehensive overview of the multidimensional landscape of neutrophil heterogeneity, discussing the various axes along which diversity manifests, including maturation state, density, surface marker expression, and functional polarization. We highlight the molecular mechanisms underpinning neutrophil plasticity, focusing on the complex interplay of signaling pathways, transcriptional regulators, and epigenetic modifications that shape neutrophil responses. Furthermore, we explore the implications of neutrophil heterogeneity and plasticity in physiological processes and pathological conditions, including host defense, inflammation, tissue repair, and cancer. By integrating insights from cutting-edge research, this review aims to provide a framework for understanding the multifaceted roles of neutrophils and their potential as therapeutic targets in a wide range of diseases.

Efferocytosis: The Janus-Faced Gatekeeper of Aging and Tumor Fate

From embryogenesis to aging, billions of cells perish daily in mammals. The multistep process by which phagocytes engulf these deceased cells without eliciting an inflammatory response is called efferocytosis. Despite significant insights into the fundamental mechanisms of efferocytosis, its implications in disorders such as aging and cancer remain elusive. Upon summarizing and analyzing existing studies on efferocytosis, it becomes evident that efferocytosis is our friend in resolving inflammation, yet it transforms into our foe by facilitating tumor development and metastasis. This review illuminates recent discoveries regarding the emerging mechanisms of efferocytosis in clearing apoptotic cells, explores its connections with aging, examines its influence on tumor development and metastasis, and identifies the regulatory factors of efferocytosis within the tumor microenvironment. A comprehensive understanding of these efferocytosis facets offers insights into crucial physiological and pathophysiological processes, paving the way for innovative therapeutic approaches to combat aging and cancer.

Santa-maria is a glial phagocytic receptor that acts with SIMU to recognize and engulf apoptotic neurons

The elimination of superfluous neurons via apoptosis and subsequent glial phagocytosis is crucial for the development of the central nervous system (CNS). In Drosophila, two glial phagocytic receptors, six-microns-under (SIMU) and Draper, mediate the phagocytosis of apoptotic neurons during embryogenesis. However, in simu;draper double-mutant embryos, some apoptotic neurons are still engulfed by the glia, suggesting the involvement of additional receptors. Here, we discover the Drosophila CD36 homolog Santa-maria, a transmembrane receptor, which is specifically expressed in embryonic phagocytic glia and plays a major role in the recognition and engulfment steps of phagocytosis. Our data demonstrate that santa-maria genetically interacts with simu and draper, while the protein product binds apoptotic cells and physically interacts with the SIMU protein. Moreover, we reveal that triple knockout of genes for all three glial phagocytic receptors (i.e., simu, draper, and santa-maria) causes partial lethality, thus illuminating their role in development, particularly in the developing nervous system.

Efferocytosis-related gene IL33 predicts prognosis and immune response and mediates proliferation and migration in vitro and in vivo of breast cancer

Background

Breast cancer (BRCA) has a high incidence among women, with poor prognosis and high mortality, which is increasing year by year. Efferocytosis is a process of phagocytosis of abnormal cells and is of great value in tumor research. Our study seeks to create a predictive model for BRCA using efferocytosis-related genes (ERGs) to explore the significance of efferocytosis in this disease.

Methods

In this research, Differential analysis, and univariate Cox regression were employed to identify genes linked to prognosis in BRCA patients. Then the BRCA patients were categorized into distinct groups using consensus clustering based on prognosis genes. Survival analysis, PCA, and t-SNE were performed to verify these groups. The enrichment of metabolic pathways within the detected clusters was evaluated using gene set variation analysis (GSVA) and gene set enrichment analysis (GSEA). Additionally, single-sample GSEA (ssGSEA) was used to examine changes in immune infiltration and enrichment. A risk prognostic model was constructed utilizing multivariable Cox regression and Least Absolute Shrinkage and Selection Operator (LASSO) analyses, and subsequently validated its predictive accuracy by stratifying patients according to the median risk score. Ultimately, some crucial independent prognostic genes were pinpointed and their expression, roles, and immune characteristics were explored in both laboratory and live models.

Results

Findings revealed 52 differentially expressed genes (DEGs), of which 21 were significantly linked to BRCA outcomes. These 21 genes were utilized for consensus clustering to categorize BRCA patients into two subtypes. Subtype B was linked to a worse prognosis compared to Subtype A, though both subtypes were distinguishable. The enriched pathways were mainly concentrated in Subtype A and were actively expressed in this group. Following this, a prognostic risk model was constructed using five risk genes, which was proven to possess significant predictive value. A significant link was identified between the immune microenvironment and the risk-associated genes and scores. IL33 was identified as an independent prognostic gene with important research value. Its in vivo expression results aligned with the data analysis findings, showing low expression in BRCA. Furthermore, overexpression of IL33 significantly inhibited BRCA growth and motility in vitro and in vivo, while also enhancing their vulnerability to destruction by activated CD8+ T cells.

Conclusion

The ERG-based risk model effectively predicts the prognosis of BRCA patients and shows a strong link with the immune microenvironment. IL33 stands out as a significant prognostic marker, crucial in the onset and advancement of BRCA. This highlights the necessity for additional studies and indicates that IL33 might be a potential target for BRCA treatment.

The sentinel against brain injury post-subarachnoid hemorrhage: efferocytosis of erythrocytes by leptomeningeal lymphatic endothelial cells

Rationale: The clearance of extravasated erythrocytes represents the most reasonable strategy against brain injury post-subarachnoid hemorrhage (SAH). There is little knowledge about the autologous clearance of extravasated erythrocytes post-SAH. The leptomeningeal lymphatic endothelial cells (LLECs) have been less studied functionally, which were firstly harvested and cultured in vitro by our group previously and are probably related to the clearance of extravasated erythrocytes post-SAH for they closely surround subarachnoid space. Methods: We established a SAH animal model, employed primary LLECs in vitro, mimicked the conditions of the SAH in vitro, performed RNA sequencing, and transfected LLECs with adenovirus and adeno-associated virus both in vivo and in vitro to reveal the molecular mechanisms of efferocytosis of erythrocytes by LLECs and its neuroprotection post-SAH. Results: Firstly, we demonstrated the eryptosis-initiated degradation of extravasated erythrocytes in vitro. Furthermore, we found LLECs preferentially adhered and engulfed apoptotic erythrocytes in vivo and in vitro while sparing from intact erythrocytes, suggesting their novel capacity in the efferocytosis of erythrocytes. Additionally, the efferocytosis of erythrocytes by LLECs plays a role on neuroprotection via improving neurological functions, maintaining neurostructural integrity, and alleviating neuropathological consequences post-SAH. During efferocytosis, phosphatidylserine (PS) and phosphatidylserine receptor (PSR) mediated the recognition of apoptotic erythrocytes by LLECs. We also confirmed that NHL repeat-containing 2 (NHLRC2) positively regulated the efferocytosis of erythrocytes by LLECs to serve as a central regulator in it mediated neuroprotection post-SAH. Conclusions: This study elucidated the efferocytosis of erythrocytes by LLECs and subsequently neuroprotection post-SAH. These findings highlight a prompt, efficient, and regulable pathway for the autologous clearance of extravasated erythrocytes that performs as a sentinel against brain injury post-SAH.

EOR-1/PLZF-regulated WAH-1/AIF sequentially promotes early and late stages of non-apoptotic corpse removal

Programmed cell death (PCD) is a crucial, genetically-encoded, and evolutionarily-conserved process required for development and homeostasis. We previously identified a genetically non-apoptotic, highly ordered, and stereotyped killing program called Compartmentalized Cell Elimination (CCE) in the C. elegans tail-spike epithelial cell (TSC). Here we identify the transcription factor EOR-1/PLZF as an important coordinator of CCE. Loss of EOR-1 results in a large, persisting, un-engulfed soma with enlarged nuclei. We find that EOR-1 and its partners positively regulate the transcription of the Apoptosis Inducing Factor AIF homolog, WAH-1/AIF. We report stereotyped and sequential spatiotemporal dynamics of WAH-1/AIF1 during phagocytosis, with defined roles acting early and late, within the dying cells. Mitochondria to plasma membrane translocation within the TSC soma is required its internalization by its phagocyte, and plasma membrane to nuclear translocation is required for DNA degradation and ultimately, corpse resolution. Our study suggests that EOR-1 serves as a master regulator for the transcriptional control of DNA degradation is essential for changes in nuclear morphology required for cellular dismantling and infers that tight spatiotemporal regulation of WAH-1/AIF is required for this function.

Macrophage-based pathogenesis and theranostics of vulnerable plaques

Vulnerable plaques, which are high-risk features of atherosclerosis, constitute critical elements in the disease's progression due to their formation and rupture. Macrophages and macrophage-derived foam cells are pivotal in inducing vulnerability within atherosclerotic plaques. Thus, understanding macrophage contributions to vulnerable plaques is essential for advancing the comprehension of atherosclerosis and devising novel therapeutic and diagnostic strategies. This review provides an overview of the pathological characteristics of vulnerable plaques, emphasizes macrophages' critical role, and discusses advanced strategies for their diagnosis and treatment. It aims to present a comprehensive macrophage-centered perspective for addressing vulnerable plaques in atherosclerosis.

Phytochemical-mediated efferocytosis and autophagy in inflammation control

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

Hypoxia-Mimicking Mediated Macrophage-Elimination of Erythrocytes Promotes Bone Regeneration via Regulating Integrin αvβ3/Fe2+-Glycolysis-Inflammation

Erythrocytes are the dominant component of a blood clot in terms of volume and number. However, longstanding compacted erythrocytes in blood clots form a physical barrier and make fibrin mesh more anti-fibrinolytic, thus impeding infiltration of mesenchymal stem cells. The necrosis or lysis of erythrocytes that are not removed timely can also lead to the release of pro-inflammatory toxic metabolites, interfering with bone regeneration. Proper bio-elimination of erythrocytes is essential for an undisturbed bone regeneration process. Here, hypoxia-mimicking is applied to enhance macrophage-elimination of erythrocytes. The effect of macrophage-elimination of erythrocytes on the macrophage intracellular reaction, bone regenerative microenvironment, and bone regeneration outcome is investigated. Results show that the hypoxia-mimicking agent dimethyloxalylglycine successfully enhances erythrophagocytosis by macrophages in a dose-dependent manner primarily by up-regulating the expression of integrin αvβ3. Increased phagocytosed erythrocytes then regulate macrophage intracellular Fe2+-glycolysis-inflammation, creating an improved bone regenerative microenvironment characterized by loose fibrin meshes with down-regulated local inflammatory responses in vivo, thus effectively promoting early osteogenesis and ultimate bone generation. Modulating macrophage-elimination of erythrocytes can be a promising strategy for eradicating erythrocyte-caused bone regeneration hindrance and offers a new direction for advanced biomaterial development focusing on the bio-elimination of erythrocytes.

Vascular injury derived apoptotic exosome-like vesicles trigger autoimmunity

According to a central tenet of classical immune theory, a healthy immune system must avoid self-reactive lymphocyte clones but we now know that B cells repertoire exhibit some level of autoreactivity. These autoreactive B cells are thought to rely on self-ligands for their clonal selection and survival. Here, we confirm that healthy mice exhibit self-reactive B cell clones that can be stimulated in vitro by agonists of toll-like receptor (TLR) 1/2, TLR4, TLR7 and TLR9 to secrete anti-LG3/perlecan. LG3/perlecan is an antigen packaged in exosome-like structures released by apoptotic endothelial cells (ApoExos) upon vascular injury. We demonstrate that the injection of ApoExos in healthy animals activates the IL-23/IL-17 pro-inflammatory and autoimmune axis, and produces several autoantibodies, including anti-LG3 autoantibodies and hallmark autoantibodies found in systemic lupus erythematosus. We also identify γδT cells as key mediators of the maturation of ApoExos-induced autoantibodies in healthy mice. Altogether we show that ApoExos released by apoptotic endothelial cells display immune-mediating functions that can stimulate the B cells in the normal repertoire to produce autoantibodies. Our work also identifies TLR activation and γδT cells as important modulators of the humoral autoimmune response induced by ApoExos.

Efferocytosis: the resolution of inflammation in cardiovascular and cerebrovascular disease

Cardiovascular and cerebrovascular diseases have surpassed cancer as significant global health challenges, which mainly include atherosclerosis, myocardial infarction, hemorrhagic stroke and ischemia stroke. The inflammatory response immediately following these diseases profoundly impacts patient prognosis and recovery. Efficient resolution of inflammation is crucial not only for halting the inflammatory process but also for restoring tissue homeostasis. Efferocytosis, the phagocytic clearance of dying cells by phagocytes, especially microglia and macrophages, plays a critical role in this resolution process. Upon tissue injury, phagocytes are recruited to the site of damage where they engulf and clear dying cells through efferocytosis. Efferocytosis suppresses the secretion of pro-inflammatory cytokines, stimulates the production of anti-inflammatory cytokines, modulates the phenotype of microglia and macrophages, accelerates the resolution of inflammation, and promotes tissue repair. It involves three main stages: recognition, engulfment, and degradation of dying cells. Optimal removal of apoptotic cargo by phagocytes requires finely tuned machinery and associated modifications. Key molecules in efferocytosis, such as 'Find-me signals', 'Eat-me signals', and 'Don't eat-me signals', have been shown to enhance efferocytosis following cardiovascular and cerebrovascular diseases. Moreover, various additional molecules, pathways, and mitochondrial metabolic processes have been identified to enhance prognosis and outcomes via efferocytosis in diverse experimental models. Impaired efferocytosis can lead to inflammation-associated pathologies and prolonged recovery periods. Therefore, this review consolidates current understanding of efferocytosis mechanisms and its application in cardiovascular and cerebrovascular diseases, proposing future research directions.

Cytomegalovirus Biology Viewed Through a Cell Death Suppression Lens

Cytomegaloviruses, species-specific members of the betaherpesviruses, encode an impressive array of immune evasion strategies committed to the manipulation of the host immune system enabling these viruses to remain for life in a stand-off with host innate and adaptive immune mechanisms. Even though they are species-restricted, cytomegaloviruses are distributed across a wide range of different mammalian species in which they cause systemic infection involving many different cell types. Regulated, or programmed cell death has a recognized potential to eliminate infected cells prior to completion of viral replication and release of progeny. Cell death also naturally terminates replication during the final stages of replication. Over the past two decades, the host defense potential of known programmed cell death pathways (apoptosis, necroptosis, and pyroptosis), as well as a novel mitochondrial serine protease pathway have been defined through studies of cytomegalovirus-encoded cell death suppressors. Such virus-encoded inhibitors prevent virus-induced, cytokine-induced, and stress-induced death of infected cells while also moderating inflammation. By evading cell death and consequent inflammation as well as innate and adaptive immune clearance, cytomegaloviruses represent successful pathogens that become a critical disease threat when the host immune system is compromised. This review will discuss cell death programs acquired for mammalian host defense against cytomegaloviruses and enumerate the range of modulatory strategies this type of virus employs to balance host defense in favor of lifelong persistence.

The neutrophil extracellular traps in neurological diseases: an update

Neutrophil extracellular traps (NETs) released by neutrophils are web-like DNA structures adhered to granulin proteins with bactericidal activity and can be an important mechanism for preventing pathogen dissemination or eliminating microorganisms. However, they also play important roles in diseases of other systems, such as the central nervous system. We tracked the latest advances and performed a review based on published original and review articles related to NETs and neurological diseases. Generally, neutrophils barely penetrate the blood-brain barrier into the brain parenchyma, but when pathological changes such as infection, trauma, or neurodegeneration occur, neutrophils rapidly infiltrate the central nervous system to exert their defensive effects. However, neutrophils may adversely affect the host when they uncontrollably release NETs upon persistent neuroinflammation. This review focused on recent advances in understanding the mechanisms and effects of NETs release in neurological diseases, and we also discuss the role of molecules that regulate NETs release in anticipation of clinical applications in neurological diseases.

Protective role of aconitate decarboxylase 1 in neuroinflammation-induced dysfunctions of the paraventricular thalamus and sleepiness

Sleepiness is commonly associated with neuroinflammation; however, the underlying neuroregulatory mechanisms remain unclear. Previous research suggests that the paraventricular thalamus (PVT) plays a crucial role in regulating sleep-wake dynamics; thus, neurological abnormalities in the PVT may contribute to neuroinflammation-induced sleepiness. To test this hypothesis, we performed electroencephalography recordings in mice treated with lipopolysaccharide (LPS) and found that the mice exhibited temporary sleepiness lasting for 7 days. Using the Fos-TRAP method, fiber photometry recordings, and immunofluorescence staining, we detected temporary PVT neuron hypoactivation and microglia activation from day 1 to day 7 post-LPS treatment. Combining the results of bulk and single-cell RNA sequencing, we found upregulation of aconitate decarboxylase 1 (Acod1) in PVT microglia post-LPS treatment. To investigate the role of Acod1, we manipulated Acod1 gene expression in PVT microglia via stereotactic injection of short hairpin RNA adenovirus. Knockdown of Acod1 exacerbated inflammation, neuronal hypoactivation, and sleepiness. Itaconate is a metabolite synthesized by the enzyme encoded by Acod1. Finally, we confirmed that exogenous administration of an itaconate derivative, 4-octyl itaconate, could inhibit microglia activation, alleviate neuronal dysfunction, and relieve sleepiness. Our findings highlight PVT's role in inflammation-induced sleepiness and suggest Acod1 as a potential therapeutic target for neuroinflammation.

Myelin debris phagocytosis in demyelinating disease

Demyelinating diseases are often caused by a variety of triggers, including immune responses, viral infections, malnutrition, hypoxia, or genetic factors, all of which result in the loss of myelin in the nervous system. The accumulation of myelin debris at the lesion site leads to neuroinflammation and inhibits remyelination; therefore, it is crucial to promptly remove the myelin debris. Initially, Fc and complement receptors on cellular surfaces were the primary clearance receptors responsible for removing myelin debris. However, subsequent studies have unveiled the involvement of additional receptors, including Mac-2, TAM receptors, and the low-density lipoprotein receptor-related protein 1, in facilitating the removal process. In addition to microglia and macrophages, which serve as the primary effector cells in the disease phase, a variety of other cell types such as astrocytes, Schwann cells, and vascular endothelial cells have been demonstrated to engage in the phagocytosis of myelin debris. Furthermore, we have concluded that oligodendrocyte precursor cells, as myelination precursor cells, also exhibit this phagocytic capability. Moreover, our research group has innovatively identified the low-density lipoprotein receptor as a potential phagocytic receptor for myelin debris. In this article, we discuss the functional processes of various phagocytes in demyelinating diseases. We also highlight the alterations in signaling pathways triggered by phagocytosis, and provide a comprehensive overview of the various phagocytic receptors involved. Such insights are invaluable for pinpointing potential therapeutic strategies for the treatment of demyelinating diseases by targeting phagocytosis.

Immune modulation through secretory autophagy

Autophagy is a central mechanism of cellular homeostasis through the degradation of a wide range of cellular constituents. However, recent evidence suggests that autophagy actively provides information to neighboring cells via a process called secretory autophagy. Secretory autophagy couples the autophagy machinery to the secretion of cellular content via extracellular vesicles (EVs). EVs carry a variety of cargo, that reflect the pathophysiological state of the originating cells and have the potential to change the functional profile of recipient cells, to modulate cell biology. The immune system has evolved to maintain local and systemic homeostasis. It is able to sense a wide array of molecules signaling disturbed homeostasis, including EVs and their content. In this review, we explore the emerging concept of secretory autophagy as a means to communicate cellular, and in total tissue pathophysiological states to the immune system to initiate the restoration of tissue homeostasis. Understanding how autophagy mediates the secretion of immunogenic factors may hold great potential for therapeutic intervention.

PHLDA1 protects intestinal barrier function via restricting intestinal epithelial cells apoptosis in inflammatory bowel disease

The current approach to treating inflammatory bowel disease (IBD) primarily focuses on managing inflammation rather than maintaining the integrity of the intestinal barrier. In our study, we sought to investigate the potential role of PHLDA1 in preserving intestinal barrier function as a promising strategy for treating IBD. We observed a significant decrease in PHLDA1 expression in intestinal epithelial cells (IECs) of both IBD patients and mice with chemically induced colitis. This deficiency of PHLDA1 led to increased apoptosis of IECs, resulting in a compromised epithelial barrier and the invasion of commensal bacteria into the mucosa. Consequently, this microbial invasion substantially exacerbated colonic inflammation in mice with the specific knockout of PHLDA1 in IECs (Phlda1IEC-KO) compared to their control littermates. Mechanistically, we found evidence of PHLDA1 interacting with MCL1 to protect against K48-linked polyubiquitylation at the K40 lysine residue, thus preventing ubiquitin-proteasome degradation through the MCL1 ubiquitin ligase E3 (Mule). We further confirmed that the PHLDA1-MCL1-Mule signaling pathway plays a critical role in the development of IBD. Notably, our study demonstrated that enhancing MCL1 levels or reducing Mule expression using adeno-associated virus (AAV) attenuated experimental colitis in Phlda1IEC-KO mice. Collectively, our findings emphasize the significance of PHLDA1 in the pathogenesis of IBD and propose that targeting the PHLDA1-MCL1-Mule signaling pathway could be a viable approach for combating IBD.

Lymphocyte-Derived Engineered Apoptotic Bodies with Inflammation Regulation and Cartilage Affinity for Osteoarthritis Therapy

Apoptotic bodies as plentiful extracellular vesicles generated from apoptotic cells play a central role in signal transduction and homeostasis regulation and simultaneously switch death to regeneration to a certain extent. Herein, we designed engineered apoptotic bodies derived from T cells to have the capacity of inflammation regulation and cartilage affinity. The engineered apoptotic bodies as a natural anti-inflammation factor were encapsulated into lubricating hydrogel microspheres to achieve an injectable microsphere complex for the treatment of osteoarthritis (OA). In the above therapeutic system, the engineered apoptotic bodies acted as a biochemical cue to regulate the inflammatory microenvironment and promote chondrocyte cartilage homeostasis, whereas the lubricating hydrogel microspheres served as a biophysical stimulation to effectively reduce the friction of the cartilage surface, restore the cartilage stress, and control the slow delivery of the encapsulated engineered apoptotic bodies by friction degradation. Consequently, the current work creates an injectable and multifunctional therapeutic microsphere to advance cartilage remodeling and OA therapy.

Assessment of NK cytotoxicity and interactions with porcine endothelial cells by live-cell imaging in 2D static and 3D microfluidic systems

Natural Killer (NK) cells are pivotal in immune responses to viral infections, malignancies, autoimmune diseases, and transplantation. Assessment of NK cell adhesion, migration, and cytotoxicity is fundamental for in vitro studies. We propose a novel live-cell tracking method that addresses these three major aspects of NK cell function using human NK cells and primary porcine aortic endothelial cells (PAECs) in two-dimensional (2D) static assays and an in-house cylindrical 3D microfluidic system. The results showed a significant increase of NK cytotoxicity against pTNF-activated PAECs, with apoptotic cell death observed in the majority of dead cells, while no difference was observed in the conventional Delfia assay. Computed analysis of NK cell trajectories revealed distinct migratory behaviors, including trajectory length, diameter, average speed, and arrest coefficient. In 3D microfluidic experiments, NK cell attachment to pTNF-activated PAECs substantially increased, accompanied by more dead PAECs compared to control conditions. NK cell trajectories showed versatile migration in various directions and interactions with PAECs. This study uniquely demonstrates NK attachment and killing in a 3D system that mimics blood vessel conditions. Our microscope method offers sensitive single-cell level results, addressing diverse aspects of NK functions. It is adaptable for studying other immune and target cells, providing insights into various biological questions.

Mechanism of Efferocytosis in Determining Ischaemic Stroke Resolution-Diving into Microglia/Macrophage Functions and Therapeutic Modality

After ischaemic cerebral vascular injury, efferocytosis-a process known as the efficient clearance of apoptotic cells (ACs) by various phagocytes in both physiological and pathological states-is crucial for maintaining central nervous system (CNS) homeostasis and regaining prognosis. The mechanisms of efferocytosis in ischaemic stroke and its influence on preventing inflammation progression from secondary injury were still not fully understood, despite the fact that the fundamental process of efferocytosis has been described in a series of phases, including AC recognition, phagocyte engulfment, and subsequent degradation. The genetic reprogramming of macrophages and brain-resident microglia after an ischaemic stroke has been equated by some researchers to that of the peripheral blood and brain. Based on previous studies, some molecules, such as signal transducer and activator of transcription 6 (STAT6), peroxisome proliferator-activated receptor γ (PPARG), CD300A, and sigma non-opioid intracellular receptor 1 (SIGMAR1), were discovered to be largely associated with aspects of apoptotic cell elimination and accompanying neuroinflammation, such as inflammatory cytokine release, phenotype transformation, and suppressing of antigen presentation. Exacerbated stroke outcomes are brought on by defective efferocytosis and improper modulation of pertinent signalling pathways in blood-borne macrophages and brain microglia, which also results in subsequent tissue inflammatory damage. This review focuses on recent researches which contain a number of recently discovered mechanisms, such as studies on the relationship between benign efferocytosis and the regulation of inflammation in ischaemic stroke, the roles of some risk factors in disease progression, and current immune approaches that aim to promote efferocytosis to treat some autoimmune diseases. Understanding these pathways provides insight into novel pathophysiological processes and fresh characteristics, which can be used to build cerebral ischaemia targeting techniques.

Changes in conjunctival mononuclear phagocytes and suppressive activity of regulatory macrophages in desiccation induced dry eye

PURPOSE

To evaluate the effects of dry eye on conjunctival immune cell number and transcriptional profiles with attention to mononuclear phagocytes.

METHODS

Expression profiling was performed by single-cell RNA sequencing on sorted conjunctival immune cells from non-stressed and C57BL/6 mice subjected to desiccating stress (DS). Monocle 3 modeled cell trajectory, scATAC-seq assessed chromatin accessibility and IPA identified canonical pathways. Inflammation and goblet cells were measured after depletion of MRC1+ MΦs with mannosylated clodronate liposomes.

RESULTS

Mononuclear phagocytes (monocytes, MΦs, DCs) comprised 72 % of immune cells and showed the greatest changes with DS. Distinct DS induced gene expression patterns were seen in phagocytes classified by expression of Ccr2 and [Timd4, Lyve1, Folr2 (TLR)]. Expression of phagocytosis/efferocytosis genes increased in TLF+CCR2- MΦs. Monocytes showed the highest expression of Ace, Cx3cr1, Vegfa, Ifngr1,2, and Stat1 and TLF-CCR2+ cells expressed higher levels of inflammatory mediators (Il1a, Il1b, Il1rn, Nfkb1, Ccl5, MHCII, Cd80, Cxcl10, Icam1). A trajectory from monocyte precursors branched to terminate in regulatory MΦs or in mDCs via transitional MΦ and cDC clusters. Activated pathways in TLF+ cells include phagocytosis, PPAR/RXRα activation, IL-10 signaling, alternate MΦ activation, while inflammatory pathways were suppressed. Depletion of MRC1+ MΦs increased IL-17 and IFN-γ expression and cytokine-expressing T cells, reduced IL-10 and worsened goblet loss.

CONCLUSIONS

Dryness stimulates distinct gene expression patterns in conjunctival phagocytes, increasing expression of regulatory genes in TLF+ cells regulated in part by RXRα, and inflammatory genes in CCR2+ cells. Regulatory MΦs depletion worsens DS induced inflammation and goblet cell loss.

Caspase inhibitors: a review on recently patented compounds (2016-2023)

INTRODUCTION

Caspases are a family of protease enzymes that play a crucial role in apoptosis. Dysregulation of caspase activity has been implicated in various pathological conditions, making caspases an important focus of research in understanding cell death mechanisms and developing therapeutic strategies for diseases associated with abnormal apoptosis.

AREAS COVERED

It is a comprehensive review of caspase inhibitors that have been comprising recently granted patents from 2016 to 2023. It includes peptide and non-peptide caspase inhibitors with their application for different diseases.

EXPERT OPINION

This review categorizes and analyses recently patented caspase inhibitors on various diseases. Diseases linked to caspase dysregulation, including neurodegenerative disorders, and autoimmune conditions, are highlighted to accentuate the therapeutic relevance of the patented caspase inhibitors. This paper serves as a valuable resource for researchers, clinicians, and pharmaceutical developers seeking an up-to-date understanding of recently patented caspase inhibitors. The integration of recent patented compounds, structural insights, and mechanistic details provides a holistic view of the progress in caspase inhibitor research and its potential impact on addressing various diseases.

Collagen patches releasing phosphatidylserine liposomes guide M1-to-M2 macrophage polarization and accelerate simultaneous bone and muscle healing

Bilateral communication between bones and muscles is essential for healing composite bone-muscle injuries from orthopedic surgeries and trauma. However, these injuries are often characterized by exaggerated inflammation, which can disrupt bone-muscle crosstalk, thereby seriously delaying the healing of either tissue. Existing approaches are largely effective at healing single tissues. However, simultaneous healing of multiple tissues remains challenging, with little research conducted to date. Here we introduce collagen patches that overcome this overlooked issue by harnessing the plasticity of macrophage phenotypes. Phosphatidylserine liposomes (PSLs) capable of shifting the macrophage phenotype from inflammatory M1 into anti-inflammatory/prohealing M2 were coated on collagen patches via a layer-by-layer method. Original collagen patches failed to improve tissue healing under inflammatory conditions coordinated by M1 macrophages. In contrast, PSL-coated collagen patches succeeded in accelerating bone and muscle healing by inducing a microenvironment dominated by M2 macrophages. In cell experiments, differentiation of preosteoblasts and myoblasts was completely inhibited by secretions of M1 macrophages but unaffected by those of M2 macrophages. RNA-seq analysis revealed that type I interferon and interleukin-6 signaling pathways were commonly upregulated in preosteoblasts and myoblasts upon stimulation with M1 macrophage secretions, thereby compromising their differentiation. This study demonstrates the benefit of PSL-mediated M1-to-M2 macrophage polarization for simultaneous bone and muscle healing, offering a potential strategy toward simultaneous regeneration of multiple tissues. STATEMENT OF SIGNIFICANCE: Existing approaches for tissue regeneration, which primarily utilize growth factors, have been largely effective at healing single tissues. However, simultaneous healing of multiple tissues remains challenging and has been little studied. Here we demonstrate that collagen patches releasing phosphatidylserine liposomes (PSLs) promote M1-to-M2 macrophage polarization and are effective for simultaneous healing of bone and muscle. Transcriptome analysis using next-generation sequencing reveals that differentiation of preosteoblasts and myoblasts is inhibited by the secretions of M1 macrophages but promoted by those of M2 macrophages, highlighting the importance of timely regulation of M1-to-M2 polarization in tissue regeneration. These findings provide new insight to tissue healing of multiple tissues.

Cross-talk between macrophages and gut microbiota in inflammatory bowel disease: a dynamic interplay influencing pathogenesis and therapy

Inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD), is a group of chronic immune-mediated gastrointestinal disorders. The etiology of IBD is multifactorial, involving genetic susceptibility, environmental factors, and a complex interplay between the gut microbiota and the host's immune system. Intestinal resident macrophages play an important role in the pathogenesis and progress of IBD, as well as in maintaining intestinal homeostasis and facilitating tissue repair. This review delves into the intricate relationship between intestinal macrophages and gut microbiota, highlighting their pivotal roles in IBD pathogenesis. We discuss the impact of macrophage dysregulation and the consequent polarization of different phenotypes on intestinal inflammation. Furthermore, we explore the compositional and functional alterations in gut microbiota associated with IBD, including the emerging significance of fungal and viral components. This review also examines the effects of current therapeutic strategies, such as 5-aminosalicylic acid (5-ASA), antibiotics, steroids, immunomodulators, and biologics, on gut microbiota and macrophage function. We underscore the potential of fecal microbiota transplantation (FMT) and probiotics as innovative approaches to modulate the gut microbiome in IBD. The aim is to provide insights into the development of novel therapies targeting the gut microbiota and macrophages to improve IBD management.

Transcripts of repetitive DNA elements signal to block phagocytosis of hematopoietic stem cells

Macrophages maintain hematopoietic stem cell (HSC) quality by assessing cell surface Calreticulin (Calr), an "eat-me" signal induced by reactive oxygen species (ROS). Using zebrafish genetics, we identified Beta-2-microglobulin (B2m) as a crucial "don't eat-me" signal on blood stem cells. A chemical screen revealed inducers of surface Calr that promoted HSC proliferation without triggering ROS or macrophage clearance. Whole-genome CRISPR-Cas9 screening showed that Toll-like receptor 3 (Tlr3) signaling regulated b2m expression. Targeting b2m or tlr3 reduced the HSC clonality. Elevated B2m levels correlated with high expression of repetitive element (RE) transcripts. Overall, our data suggest that RE-associated double-stranded RNA could interact with TLR3 to stimulate surface expression of B2m on hematopoietic stem and progenitor cells. These findings suggest that the balance of Calr and B2m regulates macrophage-HSC interactions and defines hematopoietic clonality.

Pro-efferocytic nanotherapies reduce vascular inflammation without inducing anemia in a large animal model of atherosclerosis

Atherosclerosis is an inflammatory disorder responsible for cardiovascular disease. Reactivation of efferocytosis, the phagocytic removal of cells by macrophages, has emerged as a translational target for atherosclerosis. Systemic blockade of the key 'don't-eat-me' molecule, CD47, triggers the engulfment of apoptotic vascular tissue and potently reduces plaque burden. However, it also induces red blood cell clearance, leading to anemia. To overcome this, we previously developed a macrophage-specific nanotherapy loaded with a chemical inhibitor that promotes efferocytosis. Because it was found to be safe and effective in murine studies, we aimed to advance our nanoparticle into a porcine model of atherosclerosis. Here, we demonstrate that production can be scaled without impairing nanoparticle function. At an early stage of disease, we find our nanotherapy reduces apoptotic cell accumulation and inflammation in the atherosclerotic lesion. Notably, this therapy does not induce anemia, highlighting the translational potential of targeted macrophage checkpoint inhibitors.

Apoptotic metabolites ameliorate bone aging phenotypes via TCOF1/FLVCR1-mediated mitochondrial homeostasis

Over 50 billion cells undergo apoptosis each day in an adult human to maintain tissue homeostasis by eliminating damaged or unwanted cells. Apoptotic deficiency can lead to age-related diseases with reduced apoptotic metabolites. However, whether apoptotic metabolism regulates aging is unclear. Here, we show that aging mice and apoptosis-deficient MRL/lpr (B6.MRL-Faslpr/J) mice exhibit decreased apoptotic levels along with increased aging phenotypes in the skeletal bones, which can be rescued by the treatment with apoptosis inducer staurosporine (STS) and stem cell-derived apoptotic vesicles (apoVs). Moreover, embryonic stem cells (ESC)-apoVs can significantly reduce senescent hallmarks and mtDNA leakage to rejuvenate aging bone marrow mesenchymal stem cells (MSCs) and ameliorate senile osteoporosis when compared to MSC-apoVs. Mechanistically, ESC-apoVs use TCOF1 to upregulate mitochondrial protein transcription, resulting in FLVCR1-mediated mitochondrial functional homeostasis. Taken together, this study reveals a previously unknown role of apoptotic metabolites in ameliorating bone aging phenotypes and the unique role of TCOF1/FLVCR1 in maintaining mitochondrial homeostasis.

Coupled single-cell and bulk RNA-seq analysis reveals the engulfment role of endothelial cells in atherosclerosis

The clearance of apoptotic cell debris, containing professional phagocytosis and non-professional phagocytosis, is essential for maintaining the homeostasis of healthy tissues. Here, we discovered that endothelial cells could engulf apoptotic cell debris in atherosclerotic plaque. Single-cell RNA sequencing (RNA-seq) has revealed a unique endothelial cell subpopulation in atherosclerosis, which was strongly associated with vascular injury-related pathways. Moreover, integrated analysis of three vascular injury-related RNA-seq datasets showed that the expression of scavenger receptor class B type 1 (SR-B1) was up-regulated and specifically enriched in the phagocytosis pathway under vascular injury circumstances. Single-cell RNA-seq and bulk RNA-seq indicate that SR-B1 was highly expressed in a unique endothelial cell subpopulation of mouse aorta and strongly associated with the reorganization of cellular adherent junctions and cytoskeleton which were necessary for phagocytosis. Furthermore, SR-B1 was strongly required for endothelial cells to engulf apoptotic cell debris in atherosclerotic plaque of both mouse and human aorta. Overall, this study demonstrated that apoptotic cell debris could be engulfed by endothelial cells through SR-B1 and associated with the reorganization of cellular adherent junctions and cytoskeleton.

Stem cells tightly regulate dead cell clearance to maintain tissue fitness

Billions of cells are eliminated daily from our bodies1-4. Although macrophages and dendritic cells are dedicated to migrating and engulfing dying cells and debris, many epithelial and mesenchymal tissue cells can digest nearby apoptotic corpses1-4. How these non-motile, non-professional phagocytes sense and eliminate dying cells while maintaining their normal tissue functions is unclear. Here we explore the mechanisms that underlie their multifunctionality by exploiting the cyclical bouts of tissue regeneration and degeneration during hair cycling. We show that hair follicle stem cells transiently unleash phagocytosis at the correct time and place through local molecular triggers that depend on both lipids released by neighbouring apoptotic corpses and retinoids released by healthy counterparts. We trace the heart of this dual ligand requirement to RARγ-RXRα, whose activation enables tight regulation of apoptotic cell clearance genes and provides an effective, tunable mechanism to offset phagocytic duties against the primary stem cell function of preserving tissue integrity during homeostasis. Finally, we provide functional evidence that hair follicle stem cell-mediated phagocytosis is not simply redundant with professional phagocytes but rather has clear benefits to tissue fitness. Our findings have broad implications for other non-motile tissue stem or progenitor cells that encounter cell death in an immune-privileged niche.

Development of betabodies: The next generation of phosphatidylserine targeting agents

Externalized phosphatidylserine (PS) is a phospholipid and a selective marker of the tumor microenvironment (TME). It is exposed on the outer leaflet of the plasma membrane of tumor-associated endothelial cells, apoptotic tumor cells, and some viable tumor cells, where it functions in part to suppress immune responses by binding to PS receptors expressed on tumor-infiltrating myeloid cells. PS has been targeted with antibodies, such as bavituximab, that bind the phospholipid via a cofactor, β2-glycoprotein 1 (β2GP1); these antibodies showed excellent specificity for tumor vasculature and induce an immune stimulatory environment. We have advanced this concept by developing the next generation of PS targeting agent, a fusion protein (betabody) constructed by linking PS-binding domain V of β2GP1 to the Fc of an IgG2a. Betabodies bind to externalized PS with high affinity (∼1 nM), without the requirement of a co-factor and localize robustly to the TME. We demonstrate that betabodies are a direct PS-targeting agent that has the potential to be used as anti-tumor therapy, drug delivery vehicles, and tools for imaging the TME.

Renal tubular epithelial cells response to injury in acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome characterized by a rapid and significant decrease in renal function that can arise from various etiologies, and is associated with high morbidity and mortality. The renal tubular epithelial cells (TECs) represent the central cell type affected by AKI, and their notable regenerative capacity is critical for the recovery of renal function in afflicted patients. The adaptive repair process initiated by surviving TECs following mild AKI facilitates full renal recovery. Conversely, when injury is severe or persistent, it allows the TECs to undergo pathological responses, abnormal adaptive repair and phenotypic transformation, which will lead to the development of renal fibrosis. Given the implications of TECs fate after injury in renal outcomes, a deeper understanding of these mechanisms is necessary to identify promising therapeutic targets and biomarkers of the repair process in the human kidney.

Broad-spectrum antibiotics disrupt homeostatic efferocytosis

The clearance of apoptotic cells, termed efferocytosis, is essential for tissue homeostasis and prevention of autoimmunity1. Although past studies have elucidated local molecular signals that regulate homeostatic efferocytosis in a tissue2,3, whether signals arising distally also regulate homeostatic efferocytosis remains elusive. Here, we show that large peritoneal macrophage (LPM) display impairs efferocytosis in broad-spectrum antibiotics (ABX)-treated, vancomycin-treated and germ-free mice in vivo, all of which have a depleted gut microbiota. Mechanistically, the microbiota-derived short-chain fatty acid butyrate directly boosts efferocytosis efficiency and capacity in mouse and human macrophages, and rescues ABX-induced LPM efferocytosis defects in vivo. Bulk messenger RNA sequencing of butyrate-treated macrophages in vitro and single-cell messenger RNA sequencing of LPMs isolated from ABX-treated and butyrate-rescued mice reveals regulation of efferocytosis-supportive transcriptional programmes. Specifically, we find that the efferocytosis receptor T cell immunoglobulin and mucin domain containing 4 (TIM-4, Timd4) is downregulated in LPMs of ABX-treated mice but rescued by oral butyrate. We show that TIM-4 is required for the butyrate-induced enhancement of LPM efferocytosis capacity and that LPM efferocytosis is impaired beyond withdrawal of ABX. ABX-treated mice exhibit significantly worse disease in a mouse model of lupus. Our results demonstrate that homeostatic efferocytosis relies on distal metabolic signals and suggest that defective homeostatic efferocytosis may explain the link between ABX use and inflammatory disease4-7.

Galectins induced from hemocytes bridge phosphatidylserine and N-glycosylated Drpr/CED-1 receptor during dendrite pruning

During neuronal pruning, phagocytes engulf shed cellular debris to avoid inflammation and maintain tissue homeostasis. How phagocytic receptors recognize degenerating neurites had been unclear. Here, we identify two glucosyltransferases Alg8 and Alg10 of the N-glycosylation pathway required for dendrite fragmentation and clearance through genetic screen. The scavenger receptor Draper (Drpr) is N-glycosylated with complex- or hybrid-type N-glycans that interact specifically with galectins. We also identify the galectins Crouching tiger (Ctg) and Hidden dragon (Hdg) that interact with N-glycosylated Drpr and function in dendrite pruning via the Drpr pathway. Ctg and Hdg are required in hemocytes for expression and function, and are induced during dendrite injury to localize to injured dendrites through specific interaction with exposed phosphatidylserine (PS) on the surface membrane of injured dendrites. Thus, the galectins Ctg and Hdg bridge the interaction between PS and N-glycosylated Drpr, leading to the activation of phagocytosis.

Structure and function of the human apoptotic scramblase Xkr4

Phosphatidylserine externalization on the surface of dying cells is a key signal for their recognition and clearance by macrophages and is mediated by members of the X-Kell related (Xkr) protein family. Defective Xkr-mediated scrambling impairs clearance, leading to inflammation. It was proposed that activation of the Xkr4 apoptotic scramblase requires caspase cleavage, followed by dimerization and ligand binding. Here, using a combination of biochemical approaches we show that purified monomeric, full-length human Xkr4 (hXkr4) scrambles lipids. CryoEM imaging shows that hXkr4 adopts a novel conformation, where three conserved acidic residues create an electronegative surface embedded in the membrane. Molecular dynamics simulations show this conformation induces membrane thinning, which could promote scrambling. Thinning is ablated or reduced in conditions where scrambling is abolished or reduced. Our work provides insights into the molecular mechanisms of hXkr4 scrambling and suggests the ability to thin membranes might be a general property of active scramblases.

Mitochondrial Dysfunction is a Crucial Immune Checkpoint for Neuroinflammation and Neurodegeneration: mtDAMPs in Focus

Neuroinflammation is a pivotal factor in the progression of both age-related and acute neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and stroke. Mitochondria, essential for neuronal health due to their roles in energy production, calcium buffering, and oxidative stress regulation, become increasingly susceptible to dysfunction under conditions of metabolic stress, aging, or injury. Impaired mitophagy in aged or injured neurons leads to the accumulation of dysfunctional mitochondria, which release mitochondrial-derived damage-associated molecular patterns (mtDAMPs). These mtDAMPs act as immune checkpoints, activating pattern recognition receptors (PRRs) and triggering innate immune signaling pathways. This activation initiates inflammatory responses in neurons and brain-resident immune cells, releasing cytokines and chemokines that damage adjacent healthy neurons and recruit peripheral immune cells, further amplifying neuroinflammation and neurodegeneration. Long-term mitochondrial dysfunction perpetuates a chronic inflammatory state, exacerbating neuronal injury and contributing additional immunogenic components to the extracellular environment. Emerging evidence highlights the critical role of mtDAMPs in initiating and sustaining neuroinflammation, with circulating levels of these molecules potentially serving as biomarkers for disease progression. This review explores the mechanisms of mtDAMP release due to mitochondrial dysfunction, their interaction with PRRs, and the subsequent activation of inflammatory pathways. We also discuss the role of mtDAMP-triggered innate immune responses in exacerbating both acute and chronic neuroinflammation and neurodegeneration. Targeting dysfunctional mitochondria and mtDAMPs with pharmacological agents presents a promising strategy for mitigating the initiation and progression of neuropathological conditions.

Perivascular Adipose Tissue and Perivascular Adipose Tissue-Derived Extracellular Vesicles: New Insights in Vascular Disease

Perivascular adipose tissue (PVAT) is a special deposit of fat tissue surrounding the vasculature. Previous studies suggest that PVAT modulates the vasculature function in physiological conditions and is implicated in the pathogenesis of vascular diseases. Understanding how PVAT influences vasculature function and vascular disease progression is important. Extracellular vesicles (EVs) are novel mediators of intercellular communication. EVs encapsulate molecular cargo such as proteins, lipids, and nucleic acids. EVs can influence cellular functions by transferring the carried bioactive molecules. Emerging evidence indicates that PVAT-derived EVs play an important role in vascular functions under health and disease conditions. This review will focus on the roles of PVAT and PVAT-EVs in obesity, diabetic, and metabolic syndrome-related vascular diseases, offering novel insights into therapeutic targets for vascular diseases.

Induction of osteoblast apoptosis stimulates macrophage efferocytosis and paradoxical bone formation

Apoptosis is crucial for tissue homeostasis and organ development. In bone, apoptosis is recognized to be a main fate of osteoblasts, yet the relevance of this process remains underexplored. Using our murine model with inducible Caspase 9, the enzyme that initiates intrinsic apoptosis, we triggered apoptosis in a proportion of mature osteocalcin (OCN+) osteoblasts and investigated the impact on postnatal bone development. Osteoblast apoptosis stimulated efferocytosis by osteal macrophages. A five-week stimulation of OCN+ osteoblast apoptosis in 3-week-old male and female mice significantly enhanced vertebral bone formation while increasing osteoblast precursors. A similar treatment regimen to stimulate osterix+ cell apoptosis had no impact on bone volume or density. The vertebral bone accrual following stimulation of OCN+ osteoblast apoptosis did not translate in improved mechanical strength due to disruption of the lacunocanalicular network. The observed bone phenotype was not influenced by changes in osteoclasts but was associated with stimulation of macrophage efferocytosis and vasculature formation. Phenotyping of efferocytic macrophages revealed a unique transcriptomic signature and expression of factors including VEGFA. To examine whether macrophages participated in the osteoblast precursor increase following osteoblast apoptosis, macrophage depletion models were employed. Depletion of macrophages via clodronate-liposomes and the CD169-diphtheria toxin receptor mouse model resulted in marked reduction in leptin receptor+ and osterix+ osteoblast precursors. Collectively, this work demonstrates the significance of osteoblast turnover via apoptosis and efferocytosis in postnatal bone formation. Importantly, it exposes the potential of targeting this mechanism to promote bone anabolism in the clinical setting.

TREM2 protects against inflammation by regulating the release of mito-DAMPs from hepatocytes during liver fibrosis

BACKGROUND

Liver fibrosis typically develops as a result of chronic liver injury, which involves inflammatory and regenerative processes. The triggering receptor expressed on myeloid cells 2 (TREM2), predominantly expressing in hepatic non-parenchymal cells, plays a crucial role in regulating the function of macrophages. However, its mechanism in liver fibrosis remains poorly defined.

METHODS

Experimental liver fibrosis models in wild type and TREM2-/- mice, and in vitro studies with AML-12 cells and Raw264.7 cells were conducted. The expression of TREM2 and related molecular mechanism were evaluated by using samples from patients with liver fibrosis.

RESULTS

We demonstrated that TREM2 was upregulated in murine model with liver fibrosis. Mice lacking TREM2 exhibited reduced phagocytosis activity in macrophages following carbon tetrachloride (CCl4) intoxication. As a result, there was an increased accumulation of necrotic apoptotic hepatocytes. Additionally, TREM2 knockout aggravated the release of mitochondrial damage-associated molecular patterns (mito-DAMPs) from dead hepatocytes during CCl4 exposure, and further promoted the occurrence of macrophage-mediated M1 polarization. Then, TREM2-/- mice showed more serious fibrosis pathological changes. In vitro, the necrotic apoptosis inhibitor GSK872 effectively alleviated the release of mito-DAMPs in AML-12 cells after CCl4 intoxication, which confirmed that mito-DAMPs originated from dead liver cells. Moreover, direct stimulation of Raw264.7 cells by mito-DAMPs from liver tissue can induce intracellular inflammatory response. More importantly, TREM2 was elevated and inflammatory factors were markedly accumulated surrounding dead cells in the livers of human patients with liver fibrosis.

CONCLUSION

Our study highlights that TREM2 serves as a negative regulator of liver fibrosis, suggesting its potential as a novel therapeutic target.

Weathered polyethylene microplastics induced immunomodulation in zebrafish

Microplastics are pollutants of emerging concern and the aquatic biota consumes microplastics (MPs), which has a range of toxicological and environmental effects on aquatic organisms that are not the intended targets. The current study looked into how weathered polyethylene (wPE) MPs affected Danio albolineatus immunological and haematological markers. In this experiment, fish of both sexes were placed in control and exposure groups, and they were exposed for 40 d at the sublethal level (1 μg L-1) of fragmented wPE, which contained 1074 ± 52 MPs per litre. Similarly, fish exposed to wPE MPs showed significant modifications in lysozyme, antimicrobial, and antiprotease activity, as well as differential counts. Results of the present study show that the male fish were more susceptible than female fish after 40 d of chronic exposure. Further studies are needed to ascertain how the innate and humoral immune systems of the fish respond to MPs exposure.

Identification of Key Efferocytosis-Related Genes and Mechanisms in Diabetic Retinopathy

This study aimed to explore the key efferocytosis-related genes in diabetic retinopathy (DR) and their regulatory mechanisms. Public DR-related gene expression datasets, GSE160306 (training) and GSE60436 (validation), were downloaded. Differentially expressed efferocytosis-related genes (DEERGs) were analyzed using differential expression analysis and weighted gene co-expression network analysis. Functional enrichment analysis was conducted. Moreover, efferocytosis-related signature genes were identified using machine learning analysis, and their expression levels and diagnostic value were analyzed. Furthermore, nomograms were constructed; immune cell infiltration was analyzed; and gene set enrichment analysis, transcriptional regulation analysis, and small-molecule drug (SMD) prediction of efferocytosis-related signature genes were performed. In total, 36 DEERGs were identified in DR, and were markedly enriched in multiple functions, such as visual system development. Through further machine learning analysis, two efferocytosis-related signature genes, Ferritin Light Chain (FTL) and Fc Gamma Binding Protein (FCGBP), were identified, and were found to be upregulated in DR samples and showed high diagnostic performance for DR. A nomogram constructed using FTL and FCGBP accurately predicted the risk of DR. Moreover, the level of infiltration of immature B cells was positively correlated with FTL and FCGBP expression levels. Multiple transcription factors (TFs), such as CCCTC-Binding Factor (CTCF) and KLF Transcription Factor 9 (KLF9), were found to interact with both FTL and FCGBP. In addition, FTL can be targeted by miRNAs, such as miR-22-3p, and FCGBP can be targeted by miR-7973. In addition, both FTL and FCGBP can be targeted by SMDs, such as bisphenol A. Key efferocytosis-related genes, such as FTL and FCGBP, may promote DR development. Detecting or targeting FTL and FCGBP may aid in the prevention, diagnosis, and treatment of DR.

Organo NHC catalyzed aqueous synthesis of 4β-isoxazole-podophyllotoxins: in vitro anticancer, caspase activation, tubulin polymerization inhibition and molecular docking studies

We present, for the first time, the organo-N-heterocyclic carbene (NHC) catalyzed 1,3-dipolar cycloaddition of 4β-O-propargyl podophyllotoxin (1) with in situ aromatic nitrile oxides to afford regioselective 4β-isoxazolepodophyllotoxin hybrids (6a-n) in benign aqueous-organic media. Preliminary anticancer activity results showed that compound 6e displayed superior activity against MCF-7, HeLa and MIA PaCa2 human cell lines compared with podophyllotoxin. Compounds 6j and 6n showed greater activity against the MCF-7 cell line than the positive control. Caspase activation studies revealed that compound 6e at 20 μg ml-1 concentration had greater caspase 3/7 activation in MCF-7 and MIAPaCa2 cells than podophyllotoxin. Furthermore, in vitro tubulin polymerization inhibition studies revealed that compound 6e showed comparable activity with podophyllotoxin. Finally, in silico molecular docking studies of compounds 6e, 6j, 6n and podophyllotoxin on α,β-tubulin (pdb id 1SA0) revealed that compound 6n showed excellent binding energies and inhibition constants compared with podophyllotoxin.

Microglial phagocytosis of single dying oligodendrocytes is mediated by CX3CR1 but not MERTK

Oligodendrocyte death is common in aging and neurodegenerative disease. In these conditions, dying oligodendrocytes must be efficiently removed to allow remyelination and to prevent a feedforward degenerative cascade. Removal of this cellular debris is thought to primarily be carried out by resident microglia. To investigate the cellular dynamics underlying how microglia do this, we use a single-cell cortical demyelination model combined with longitudinal intravital imaging of dual-labeled transgenic mice. Following phagocytosis, single microglia clear the targeted oligodendrocyte and its myelin sheaths in one day via a precise, rapid, and stereotyped sequence. Deletion of the fractalkine receptor, CX3CR1, delays the microglial phagocytosis of the cell soma but has no effect on clearance of myelin sheaths. Unexpectedly, deletion of the phosphatidylserine receptor, MERTK, has no effect on oligodendrocyte or myelin sheath clearance. Thus, separate molecular signals are used to detect, engage, and clear distinct sub-compartments of dying oligodendrocytes to maintain tissue homeostasis.

Consequence of alcohol intoxication-mediated efferocytosis impairment

Alcohol ingestion is a widespread habituation that evolved along with a growing population, altering physiological conditions through immunomodulatory function. There is much research that has reported that consumption of alcohol at low and heavy levels causes different biological impacts, including cellular injury, leading to systemic dysfunction and increased inflammatory markers. In the fate of professional phagocytic cells, efferocytosis is an inevitable mechanism activated by the apoptotic cells, thus eliminating them and preventing the accumulation of cell corpses/debris in the microenvironment. Subsequently, it promotes the tissue repair mechanism and maintains cellular homeostasis. Unfortunately, defective efferocytosis is widely found in several inflammatory and age-related diseases such as atherosclerosis, autoimmune diseases, lung injury, fatty liver disease, and neurodegenerative diseases. Alcohol abuse is one of the factors that provoke an immune response that increases the rate of morbidity and mortality in parallel in systemic disease patients. Information regarding the emergence of immunomodulation during alcoholic pathogenesis and its association with efferocytosis impairment remain elusive. Hence, here in this review, we discussed the mechanism of efferocytosis, the role of defective efferocytosis in inflammatory diseases, and the role of alcohol on efferocytosis impairment.