GPR35 promotes neutrophil recruitment in response to serotonin metabolite 5-HIAA

Neutrophil and neutrophil extracellular trap involvement in neutrophilic asthma: A review

Asthma is a highly prevalent chronic inflammatory disease characterized by variable airflow obstruction and airway hyperresponsiveness. Neutrophilic asthma (NA) is classified as "type 2 low" asthma, defined as 65% or more neutrophils in the total cell count. There is no clear consensus on the pathogenesis of NA, and the accumulation of neutrophils and release of neutrophil extracellular traps (NETs) may be responsible for its development. A NET is a large extracellular meshwork comprising cell membrane and granule proteins. It is a powerful antimicrobial defence system that traps, neutralizes, and kills bacteria, fungi, viruses, and parasites and prevents the spread of microorganisms. However, dysregulation of NETs may lead to chronic airway inflammation, is associated with worsening of asthma, and has been the subject of major research advances in chronic lung diseases in recent years. NA is insensitive to steroids, and there is a need to find effective biomarkers as targets for the treatment of NA to replace steroids. This review analyses the mechanisms of action between asthmatic neutrophil recruitment and NET formation and their impact on NA development. It also discusses their possible therapeutic significance in NA, summarizing the advances made in NA agents and providing strategies for the treatment of NA, provide a theoretical basis for the development of new therapeutic drugs, thereby improving the level of diagnosis and treatment, and promoting the research progress in the field of asthma.

The Complex World of Kynurenic Acid: Reflections on Biological Issues and Therapeutic Strategy

It has been unequivocally established that kynurenic acid has a number of actions in a variety of cells and tissues, raising, in principle, the possibility of targeting its generation, metabolism or sites of action to manipulate those effects to a beneficial therapeutic end. However, many basic aspects of the biology of kynurenic acid remain unclear, potentially leading to some confusion and misinterpretations of data. They include questions of the source, generation, targets, enzyme expression, endogenous concentrations and sites of action. This essay is intended to raise and discuss many of these aspects as a source of reference for more balanced discussion. Those issues are followed by examples of situations in which modulating and correcting kynurenic acid production or activity could bring significant therapeutic benefit, including neurological and psychiatric conditions, inflammatory diseases and cell protection. More information is required to obtain a clear overall view of the pharmacological environment relevant to kynurenic acid, especially with respect to the active concentrations of kynurenine metabolites in vivo and changed levels in disease. The data and ideas presented here should permit a greater confidence in appreciating the sites of action and interaction of kynurenic acid under different local conditions and pathologies, enhancing our understanding of kynurenic acid itself and the many clinical conditions in which manipulating its pharmacology could be of clinical value.

LIFR regulates cholesterol-driven bidirectional hepatocyte-neutrophil cross-talk to promote liver regeneration

Liver regeneration is under metabolic and immune regulation. Despite increasing recognition of the involvement of neutrophils in regeneration, it is unclear how the liver signals to the bone marrow to release neutrophils after injury and how reparative neutrophils signal to hepatocytes to reenter the cell cycle. Here we report that loss of the liver tumour suppressor Lifr in mouse hepatocytes impairs, whereas overexpression of leukaemia inhibitory factor receptor (LIFR) promotes liver repair and regeneration after partial hepatectomy or toxic injury. In response to physical or chemical damage to the liver, LIFR from hepatocytes promotes the secretion of cholesterol and CXCL1 in a STAT3-dependent manner, leading to the efflux of bone marrow neutrophils to the circulation and damaged liver. Cholesterol, via its receptor ERRα, stimulates neutrophils to secrete hepatocyte growth factor to accelerate hepatocyte proliferation. Altogether, our findings reveal a LIFR-STAT3-CXCL1-CXCR2 axis and a LIFR-STAT3-cholesterol-ERRα-hepatocyte growth factor axis that form bidirectional hepatocyte-neutrophil cross-talk to repair and regenerate the liver.

The role of kynurenines in migraine-related neuroimmune pathways

Migraine, a primary headache disorder whose mechanism remains incompletely understood, appears to involve the activation of the trigeminovascular system (TS) during attacks. Research suggests that inflammatory processes mediated by the immune system may play a role in migraine pathophysiology. Neuroinflammation is often associated with migraine attacks, with cytokines serving as crucial mediators in the process. Elevated levels of pro-inflammatory cytokines, such as interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), have been observed in the blood and cerebrospinal fluid of individuals experiencing migraine attacks. These cytokines have the capacity to sensitize pain pathways in the brain, thereby increasing sensitivity to pain stimuli. This phenomenon, known as central sensitization, is believed to contribute to the intensity and persistence of migraine pain. Kynurenines, endogenous mediators of glutamatergic mechanisms, can significantly influence the pathophysiology of primary headache disorders. The kynurenine system is collectively known as the kynurenine pathway (KP), which can act on multiple receptors, such as glutamate receptors, aryl hydrocarbon receptors (AhRs), G protein-coupled receptors 35 (GPR35), and α-7 nicotinic acetylcholine (α7 nACh) receptors. These receptors are also found on various cells of the immune system, so the role of the KP in the pathomechanism of primary headaches may also be mediated through them. In this review, our goal is to show a possible link between the receptors of the KP and immune system in the context of inflammation and migraine. Migraine research in recent years has focused on neuropeptides, such as calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP) as potential pathogenic factors and possible therapeutic approaches. These peptides share many similarities in their characteristics and roles. For instance, they exhibit potent vasodilation, occur in both the peripheral and central nervous systems, and play a role in transmitting nociception and neurogenic inflammation. The investigation of potential connections between the aforementioned neuropeptides and the kynurenine pathway could play a significant role in uncovering the pathomechanism of migraine and identifying new drug candidates.

Gz Enhanced Signal Transduction assaY (GZESTY) for GPCR deorphanization

G protein-coupled receptors (GPCRs) are key pharmacological targets, yet many remain underutilized due to unknown activation mechanisms and ligands. Orphan GPCRs, lacking identified natural ligands, are a high priority for research, as identifying their ligands will aid in understanding their functions and potential as drug targets. Most GPCRs, including orphans, couple to Gi/o/z family members, however current assays to detect their activation are limited, hindering ligand identification efforts. We introduce GZESTY, a highly sensitive, cell-based assay developed in an easily deliverable format designed to study the pharmacology of Gi/o/z-coupled GPCRs and assist in deorphanization. We optimized assay conditions and developed an all-in-one vector employing novel cloning methods to ensure the correct expression ratio of GZESTY components. GZESTY successfully assessed activation of a library of ligand-activated GPCRs, detecting both full and partial agonism, as well as responses from endogenous GPCRs. Notably, with GZESTY we established the presence of endogenous ligands for GPR176 and GPR37 in brain extracts, validating its use in deorphanization efforts. This assay enhances the ability to find ligands for orphan GPCRs, expanding the toolkit for GPCR pharmacologists.

The dual roles of serotonin in antitumor immunity

Research has shown that a significant portion of cancer patients experience depressive symptoms, often accompanied by neuroendocrine hormone imbalances. Depression is frequently associated with decreased levels of serotonin with the alternate name 5-hydroxytryptamine (5-HT), leading to the common use of selective serotonin reuptake inhibitors (SSRIs) as antidepressants. However, the role of serotonin in tumor regulation remains unclear, with its expression levels displaying varied effects across different types of tumors. Tumor initiation and progression are closely intertwined with the immune function of the human body. Neuroimmunity, as an interdisciplinary subject, has played a unique role in the study of the relationship between psychosocial factors and tumors and their mechanisms in recent years. This article offers a comprehensive review of serotonin's regulatory roles in tumor onset and progression, as well as its impacts on immune cells in the tumor microenvironment. The aim is to stimulate further interdisciplinary research and discover novel targets for tumor treatment.

Neurotransmitters: Impressive regulators of tumor progression

In contemporary times, tumors have emerged as the primary cause of mortality in the global population. Ongoing research has shed light on the significance of neurotransmitters in the regulation of tumors. It has been established that neurotransmitters play a pivotal role in tumor cell angiogenesis by triggering the transformation of stromal cells into tumor cells, modulating receptors on tumor stem cells, and even inducing immunosuppression. These actions ultimately foster the proliferation and metastasis of tumor cells. Several major neurotransmitters have been found to exert modulatory effects on tumor cells, including the ability to restrict emergency hematopoiesis and bind to receptors on the postsynaptic membrane, thereby inhibiting malignant progression. The abnormal secretion of neurotransmitters is closely associated with tumor progression, suggesting that focusing on neurotransmitters may yield unexpected breakthroughs in tumor therapy. This article presents an analysis and outlook on the potential of targeting neurotransmitters in tumor therapy.

From orphan to oncogene: The role of GPR35 in cancer and immune modulation

G protein-coupled receptors (GPCRs) are well-studied and the most traceable cell surface receptors for drug discovery. One of the intriguing members of this family is G protein-coupled receptors 35 (GPR35), which belongs to the class A rhodopsin-like family of GPCRs identified over two decades ago. GPR35 presents interesting features such as ubiquitous expression and distinct isoforms. Moreover, functional and genome-wide association studies on its widespread expression have linked GPR35 with pathophysiological disease progression. Various pieces of evidence have been accumulated regarding the independent or endogenous ligand-dependent role of GPR35 in cancer progression and metastasis. In the current scenario, the relationship of this versatile receptor and its putative endogenous ligands for the activation of oncogenic signal transduction pathways at the cellular level is an active area of research. These intriguing features offered by GPR35 make it an oncological target, justifying its uniqueness at the physiological and pathophysiological levels concerning other GPCRs. For pharmacologically targeting receptor-induced signaling, few potential competitive antagonists have been discovered that offer high selectivity at a human level. In addition to its fascinating features, targeting GPR35 at rodent and human orthologue levels is distinct, thus contributing to the sub-species selectivity. Strategies to modulate these issues will help us understand and truly target GPR35 at the therapeutic level. In this article, we have provided prospects on each topic mentioned above and suggestions to overcome the challenges. This review discusses the molecular mechanism and signal transduction pathways activated by endogenous ligands or spontaneous auto-activation of GPR35 that contributes towards disease progression. Furthermore, we have highlighted the GPR35 structure, ubiquitous expression, its role in immunomodulation, and at the pathophysiological level, especially in cancer, indicating its status as a versatile receptor. Subsequently, we discussed the various proposed ligands and their mechanism of interaction with GPR35. Additionally, we have summarized the GPR35 antagonist that provides insights into the opportunities for therapeutically targeting this receptor.

CXCL17 is a proinflammatory chemokine and promotes neutrophil trafficking

CXCL17, a novel member of the CXC chemokine class, has been implicated in several human pathologies, but its role in mediating immune response is not well understood. Characteristic features of immune response include resident macrophages orchestrating successive and structured recruitment of neutrophils and monocytes to the insult site. Here, we show that Cxcl17 knockout (KO) mice, compared with the littermate wild-type control mice, were significantly impaired in peritoneal neutrophil recruitment post-lipopolysaccharide (LPS) challenge. Further, the KO mice show dysregulated Cxcl1, Cxcr2, and interleukin-6 levels, all of which directly impact neutrophil recruitment. Importantly, the KO mice showed no difference in monocyte recruitment post-LPS challenge or in peritoneal macrophage levels in both unchallenged and LPS-challenged mice. We conclude that Cxcl17 is a proinflammatory chemokine and that it plays an important role in the early proinflammatory response by promoting neutrophil recruitment to the insult site.

Long-term intravital subcellular imaging with confocal scanning light-field microscopy

Long-term observation of subcellular dynamics in living organisms is limited by background fluorescence originating from tissue scattering or dense labeling. Existing confocal approaches face an inevitable tradeoff among parallelization, resolution and phototoxicity. Here we present confocal scanning light-field microscopy (csLFM), which integrates axially elongated line-confocal illumination with the rolling shutter in scanning light-field microscopy (sLFM). csLFM enables high-fidelity, high-speed, three-dimensional (3D) imaging at near-diffraction-limit resolution with both optical sectioning and low phototoxicity. By simultaneous 3D excitation and detection, the excitation intensity can be reduced below 1 mW mm-2, with 15-fold higher signal-to-background ratio over sLFM. We imaged subcellular dynamics over 25,000 timeframes in optically challenging environments in different species, such as migrasome delivery in mouse spleen, retractosome generation in mouse liver and 3D voltage imaging in Drosophila. Moreover, csLFM facilitates high-fidelity, large-scale neural recording with reduced crosstalk, leading to high orientation selectivity to visual stimuli, similar to two-photon microscopy, which aids understanding of neural coding mechanisms.

Communications between Neutrophil-Endothelial Interaction in Immune Defense against Bacterial Infection

The endothelial barrier plays a critical role in immune defense against bacterial infection. Efficient interactions between neutrophils and endothelial cells facilitate the activation of both cell types. However, neutrophil activation can have dual effects, promoting bacterial clearance on one hand while triggering inflammation on the other. In this review, we provide a detailed overview of the cellular defense progression when neutrophils encounter bacteria, focusing specifically on neutrophil-endothelial interactions and endothelial activation or dysfunction. By elucidating the underlying mechanisms of inflammatory pathways, potential therapeutic targets for inflammation caused by endothelial dysfunction may be identified. Overall, our comprehensive understanding of neutrophil-endothelial interactions in modulating innate immunity provides deeper insights into therapeutic strategies for infectious diseases and further promotes the development of antibacterial and anti-inflammatory drugs.

Neutrophil Percentage as a Potential Biomarker of Acute Kidney Injury Risk and Short-Term Prognosis in Patients with Acute Myocardial Infarction in the Elderly

Objective

This study aimed to explore the association of preoperative neutrophil percentage (NEUT%) with the risk of acute kidney injury (AKI) in patients with acute myocardial infarction (AMI) having undergone coronary interventional therapy.

Methods

A single-center, retrospective and observational study was conducted. From December 2012 to June 2021, patients with AMI were enrolled and divided into AKI group and non-AKI group. The NEUT% in the two groups was compared. The association between NEUT% with the risk of post-AMI AKI was analyzed by univariate and multivariable logistic regression. Kaplan-Meier survival curve was drawn to evaluate the prognostic ability of NEUT% for short-term all-cause death following AMI.

Results

A total of 3001 consecutive patients were enrolled with an average age of 64.38 years. AKI occurred in 327 (10.9%) patients. The NEUT% was higher in the AKI group than in the non-AKI group ([76.65±11.43]% versus [73.22±11.83]%, P<0.001). NEUT% was also identified as an independent risk factor for AKI in AMI patients after adjustment (OR=1.021, 95% CI: 1.010-1.033, P < 0.001). Compared with those at the lowest quartile of NEUT%, the patients at quartiles 2-4 had a higher risk of AKI (P for trend = 0.003). The odds of AKI increased by 29.0% as NEUT% increased by 1 standard deviation (OR=1.290, 95% CI: 1.087-1.531, P = 0.004). After a median of 35 days follow-up, 93 patients died. Patients with a higher NEUT% presented a higher risk of all-cause death after AMI (Log rank: χ2 =24.753, P<0.001).

Conclusion

In AMI patients, the peripheral blood NEUT% was positively associated with the odds of AKI and short-term all-cause mortality. NEUT% may provide physicians with more information about disease development and prognosis.

Suppression of Mast Cell Activation by GPR35: GPR35 Is a Primary Target of Disodium Cromoglycate

Mast cell stabilizers, including disodium cromoglycate (DSCG), were found to have potential as the agonists of an orphan G protein-coupled receptor, GPR35, although it remains to be determined whether GPR35 is expressed in mast cells and involved in suppression of mast cell degranulation. Our purpose in this study is to verify the expression of GPR35 in mast cells and to clarify how GPR35 modulates the degranulation. We explored the roles of GPR35 using an expression system, a mast cell line constitutively expressing rat GPR35, peritoneal mast cells, and bone marrow-derived cultured mast cells. Immediate allergic responses were assessed using the IgE-mediated passive cutaneous anaphylaxis (PCA) model. Various known GPR35 agonists, including DSCG and newly designed compounds, suppressed IgE-mediated degranulation. GPR35 was expressed in mature mast cells but not in immature bone marrow-derived cultured mast cells and the rat mast cell line. Degranulation induced by antigens was significantly downmodulated in the mast cell line stably expressing GPR35. A GPR35 agonist, zaprinast, induced a transient activation of RhoA and a transient decrease in the amount of filamentous actin. GPR35 agonists suppressed the PCA responses in the wild-type mice but not in the GPR35-/- mice. These findings suggest that GPR35 should prevent mast cells from undergoing degranulation induced by IgE-mediated antigen stimulation and be the primary target of mast cell stabilizers. SIGNIFICANCE STATEMENT: The agonists of an orphan G protein-coupled receptor, GPR35, including disodium cromoglycate, were found to suppress degranulation of rat and mouse mature mast cells, and their antiallergic effects were abrogated in the GPR35-/- mice, indicating that the primary target of mast cell stabilizers should be GPR35.

Mast cells help organize the Peyer's patch niche for induction of IgA responses

Peyer's patches (PPs) are lymphoid structures situated adjacent to the intestinal epithelium that support B cell responses that give rise to many intestinal IgA-secreting cells. Induction of isotype switching to IgA in PPs requires interactions between B cells and TGFβ-activating conventional dendritic cells type 2 (cDC2s) in the subepithelial dome (SED). However, the mechanisms promoting cDC2 positioning in the SED are unclear. Here, we found that PP cDC2s express GPR35, a receptor that promotes cell migration in response to various metabolites, including 5-hydroxyindoleacetic acid (5-HIAA). In mice lacking GPR35, fewer cDC2s were found in the SED, and frequencies of IgA+ germinal center (GC) B cells were reduced. IgA plasma cells were reduced in both the PPs and lamina propria. These phenotypes were also observed in chimeric mice that lacked GPR35 selectively in cDCs. GPR35 deficiency led to reduced coating of commensal bacteria with IgA and reduced IgA responses to cholera toxin. Mast cells were present in the SED, and mast cell-deficient mice had reduced PP cDC2s and IgA+ cells. Ablation of tryptophan hydroxylase 1 (Tph1) in mast cells to prevent their production of 5-HIAA similarly led to reduced PP cDC2s and IgA responses. Thus, mast cell-guided positioning of GPR35+ cDC2s in the PP SED supports induction of intestinal IgA responses.

The dark sides of the GPCR tree - research progress on understudied GPCRs

A large portion of the human GPCRome is still in the dark and understudied, consisting even of entire subfamilies of GPCRs such as odorant receptors, class A and C orphans, adhesion GPCRs, Frizzleds and taste receptors. However, it is undeniable that these GPCRs bring an untapped therapeutic potential that should be explored further. Open questions on these GPCRs span diverse topics such as deorphanisation, the development of tool compounds and tools for studying these GPCRs, as well as understanding basic signalling mechanisms. This review gives an overview of the current state of knowledge for each of the diverse subfamilies of understudied receptors regarding their physiological relevance, molecular mechanisms, endogenous ligands and pharmacological tools. Furthermore, it identifies some of the largest knowledge gaps that should be addressed in the foreseeable future and lists some general strategies that might be helpful in this process.

Metabolic alterations in urine among the patients with severe fever with thrombocytopenia syndrome

BACKGROUND

The pathogenesis of severe fever with thrombocytopenia syndrome (SFTS) remained unclear. We aimed to profile the metabolic alterations in urine of SFTS patients and provide new evidence for its pathogenesis.

METHODS

A case-control study was conducted in the 154th hospital in China. Totally 88 cases and 22 controls aged ≥ 18 years were enrolled. The cases were selected from laboratory-confirmed SFTS patients. The controls were selected among SFTSV-negative population. Those with diabetes, cancer, hepatitis and other sexually transmitted diseases were excluded in both groups. Fatal cases and survival cases were 1:1 matched. Inter-group differential metabolites and pathways were obtained, and the inter-group discrimination ability was evaluated.

RESULTS

Tryptophan metabolism and phenylalanine metabolism were the top one important metabolism pathway in differentiating the control and case groups, and the survival and fatal groups, respectively. The significant increase of differential metabolites in tryptophan metabolism, including 5-hydroxyindoleacetate (5-HIAA), L-kynurenine (KYN), 5-hydroxy-L-tryptophan (5-HTP), 3-hydroxyanthranilic acid (3-HAA), and the increase of phenylpyruvic acid and decrease of hippuric acid in phenylalanine metabolism indicated the potential metabolic alterations in SFTSV infection. The increase of 5-HIAA, KYN, 5-HTP, phenylpyruvic acid and hippuric acid were involved in the fatal progress of SFTS patients.

CONCLUSIONS

Tryptophan metabolism and phenylalanine metabolism might be involved in the pathogenesis of SFTSV infection. These findings provided new evidence for the pathogenesis and treatment of SFTS.

Rural and urban exposures shape early life immune development in South African children with atopic dermatitis and nonallergic children

BACKGROUND

Immunological traits and functions have been consistently associated with environmental exposures and are thought to shape allergic disease susceptibility and protection. In particular, specific exposures in early life may have more significant effects on the developing immune system, with potentially long-term impacts.

METHODS

We performed RNA-Seq on peripheral blood mononuclear cells (PBMCs) from 150 children with atopic dermatitis and healthy nonallergic children in rural and urban settings from the same ethnolinguistic AmaXhosa background in South Africa. We measured environmental exposures using questionnaires.

RESULTS

A distinct PBMC gene expression pattern was observed in those children with atopic dermatitis (132 differentially expressed genes [DEGs]). However, the predominant influences on the immune cell transcriptome were related to early life exposures including animals, time outdoors, and types of cooking and heating fuels. Sample clustering revealed two rural groups (Rural_1 and Rural_2) that separated from the urban group (3413 and 2647 DEGs, respectively). The most significantly regulated pathways in Rural_1 children were related to innate activation of the immune system (e.g., TLR and cytokine signaling), changes in lymphocyte polarization (e.g., TH17 cells), and immune cell metabolism (i.e., oxidative phosphorylation). The Rural_2 group displayed evidence for ongoing lymphocyte activation (e.g., T cell receptor signaling), with changes in immune cell survival and proliferation (e.g., mTOR signaling, insulin signaling).

CONCLUSIONS

This study highlights the importance of the exposome on immune development in early life and identifies potentially protective (e.g., animal) exposures and potentially detrimental (e.g., pollutant) exposures that impact key immunological pathways.

GPR35 acts a dual role and therapeutic target in inflammation

GPR35 is a G protein-coupled receptor with notable involvement in modulating inflammatory responses. Although the precise role of GPR35 in inflammation is not yet fully understood, studies have suggested that it may have both pro- and anti-inflammatory effects depending on the specific cellular environment. Some studies have shown that GPR35 activation can stimulate the production of pro-inflammatory cytokines and facilitate the movement of immune cells towards inflammatory tissues or infected areas. Conversely, other investigations have suggested that GPR35 may possess anti-inflammatory properties in the gastrointestinal tract, liver and certain other tissues by curbing the generation of inflammatory mediators and endorsing the differentiation of regulatory T cells. The intricate role of GPR35 in inflammation underscores the requirement for more in-depth research to thoroughly comprehend its functional mechanisms and its potential significance as a therapeutic target for inflammatory diseases. The purpose of this review is to concurrently investigate the pro-inflammatory and anti-inflammatory roles of GPR35, thus illuminating both facets of this complex issue.

Microbiota-derived tryptophan metabolism: Impacts on health, aging, and disease

The intricate interplay between gut microbiota and the host is pivotal in maintaining homeostasis and health. Dietary tryptophan (TRP) metabolism initiates a cascade of essential endogenous metabolites, including kynurenine, kynurenic acid, serotonin, and melatonin, as well as microbiota-derived Trp metabolites like tryptamine, indole propionic acid (IPA), and other indole derivatives. Notably, tryptamine and IPA, among the indole metabolites, exert crucial roles in modulating immune, metabolic, and neuronal responses at both local and distant sites. Additionally, these metabolites demonstrate potent antioxidant and anti-inflammatory activities. The levels of microbiota-derived TRP metabolites are intricately linked to the gut microbiota's health, which, in turn, can be influenced by age-related changes. This review aims to comprehensively summarize the cellular and molecular impacts of tryptamine and IPA on health and aging-related complications. Furthermore, we explore the levels of tryptamine and IPA and their corresponding bacteria in select diseased conditions, shedding light on their potential significance as biomarkers and therapeutic targets.

CXCL17 binds efficaciously to glycosaminoglycans with the potential to modulate chemokine signaling

Introduction

CXCL17 is a mucosally secreted protein, and the most recently identified human chemokine, an assignment based on protein fold prediction and chemotactic activity for leukocytes. However, these credentials have been the subject of much recent discussion and no experimental evidence has been presented regarding the definitive structure of CXCL17. In this study, we evaluated the structural and chemoattractant credentials of CXCL17 to better characterize this molecule, and gain deeper insights into its functional role as a glycosaminoglycan (GAG) binding protein.

Methods

In the absence of structural information, in silico modeling techniques assessed the likelihood of CXCL17 adopting a chemokine fold. Recombinant CXCL17 was synthesized in mammalian and prokaryotic systems. Modified Boyden chamber and real-time chemotaxis assays assessed the ability of CXCL17 to promote chemotaxis of murine splenocytes, human neutrophils, and CXCR1 transfectants. The efficacy of CXCL17 binding to GAGs was quantified with solid-phase assays and bio-layer interferometry techniques.

Results

All modeling efforts failed to support classification of CXCL17 as a chemokine based on its predicted conformation. Recombinant CXCL17 was observed to dimerize as a function of concentration, a characteristic of several chemokines. Contrary to a previous report, CXCL17 was not chemotactic for murine splenocytes, although it was a low-potency chemoattractant for human neutrophils at micromolar concentrations, several orders of magnitude higher than those required for CXCL8. As anticipated owing to its highly basic nature, CXCL17 bound to GAGs robustly, with key C-terminal motifs implicated in this process. While inactive via CXCR1, CXCL17 was found to inhibit CXCR1-mediated chemotaxis of transfectants to CXCL8 in a dose-dependent manner.

Discussion

In summary, despite finding little evidence for chemokine-like structure and function, CXCL17 readily bound GAGs, and could modulate chemotactic responses to another chemokine in vitro. We postulate that such modulation is a consequence of superior GAG binding, and that C-terminal fragments of CXCL17 may serve as prototypic inhibitors of chemokine function.

The Deubiquitinase OTUD1 Suppresses Secretory Neutrophil Polarization And Ameliorates Immunopathology of Periodontitis

Tissue-infiltrating neutrophils (TINs) secrete various signaling molecules to establish paracrine communication within the inflammatory milieu. It is imperative to identify molecular mediators that control this secretory phenotype of TINs. The present study uncovers a secretory neutrophil subset that exhibits increased pro-inflammatory cytokine production and enhanced migratory capacity which is highly related with periodontal pathogenesis. Further analysis identifies the OTU domain-containing protein 1 (OTUD1) plays a regulatory role in this secretory neutrophil polarization. In human and mouse periodontitis, the waning of inflammation is correlated with OTUD1 upregulation, whereas severe periodontitis is induced when neutrophil-intrinsic OTUD1 is depleted. Mechanistically, OTUD1 interacts with SEC23B, a component of the coat protein II complex (COPII). By removing the K63-linked polyubiquitin chains on SEC23B Lysine 81, the deubiquitinase OTUD1 negatively regulates the COPII secretory machinery and limits protein ER-to-Golgi trafficking, thus restricting the surface expression of integrin-regulated proteins, CD9 and CD47. Accordingly, blockade of protein transport by Brefeldin A (BFA) curbs recruitment of Otud1-deficient TINs and attenuates inflammation-induced alveolar bone destruction. The results thus identify OTUD1 signaling as a negative feedback loop that limits the polarization of neutrophils with secretory phenotype and highlight the potential application of BFA in the treatment of periodontal inflammation.

Fasting-mimicking diet alleviates inflammatory pain by inhibiting neutrophil extracellular traps formation and neuroinflammation in the spinal cord

BACKGROUND

Neutrophil extracellular traps (NETs) promote neuroinflammation and, thus, central nervous system (CNS) disease progression. However, it remains unclear whether CNS-associated NETs affect pain outcomes. A fasting-mimicking diet (FMD) alleviates neurological disorders by attenuating neuroinflammation and promoting nerve regeneration. Hence, in this study, we explore the role of NETs in the CNS during acute pain and investigate the role of FMD in inhibiting NETs and relieving pain.

METHODS

The inflammatory pain model was established by injecting complete Freund's adjuvant (CFA) into the hind paw of mice. The FMD diet regimen was performed during the perioperative period. PAD4 siRNA or CI-amidine (PAD4 inhibitor) was used to inhibit the formation of NETs. Monoamine oxidase-B (MAO-B) knockdown occurred by AAV-GFAP-shRNA or AAV-hSyn-shRNA or was inhibited by selegiline (an MAO-B inhibitor). The changes in NETs, neuroinflammation, and related signaling pathways were examined by western blot, immunofluorescence, ELISA, and flow cytometry.

RESULTS

In the acute phase of inflammatory pain, NETs accumulate in the spinal cords of mice. This is associated with exacerbated neuroinflammation. Meanwhile, inhibition of NETs formation alleviates allodynia and neuroinflammation in CFA mice. FMD inhibits NETs production and alleviates inflammatory pain, which is enhanced by treatment with the NETs inhibitor CI-amidine, and reversed by treatment with the NETs inducer phorbol 12-myristate 13-acetate (PMA). Mechanistically, the neutrophil-recruiting pathway MAO-B/5-hydroxyindoleacetic acid (5-HIAA) / G-protein-coupled receptor 35 (GPR35) and NETs-inducing pathway MAO-B/ Reactive oxygen species (ROS) are significantly upregulated during the development of inflammatory pain. MAO-B is largely expressed in astrocytes and neurons in the spinal cords of CFA mice. However, knockdown or inhibition of MAO-B effectively attenuates CFA-induced inflammatory pain, NETs formation, and neuroinflammation in the spinal cord. Moreover, within rescue experiments, MAO-B inhibitors synergistically enhance FMD-induced pain relief, NETs inhibition, and neuroinflammation attenuation, whereas supplementation with MAO-B downstream molecules (i.e., 5-HIAA and PMA) abolished this effect.

CONCLUSIONS

Neutrophil-released NETs in the spinal cord contribute to pain development. FMD inhibits NETs formation and NETs-induced neuroinflammation by inhibiting the MAO-B/5-HIAA/GPR35 and MAO-B/ROS pathways in astrocytes and neurons, thereby relieving pain progression. Video Abstract.

The gut microbiota-induced kynurenic acid recruits GPR35-positive macrophages to promote experimental encephalitis

The intricate interplay between gut microbes and the onset of experimental autoimmune encephalomyelitis (EAE) remains poorly understood. Here, we uncover remarkable similarities between CD4+ T cells in the spinal cord and their counterparts in the small intestine. Furthermore, we unveil a synergistic relationship between the microbiota, particularly enriched with the tryptophan metabolism gene EC:1.13.11.11, and intestinal cells. This symbiotic collaboration results in the biosynthesis of kynurenic acid (KYNA), which modulates the recruitment and aggregation of GPR35-positive macrophages. Subsequently, a robust T helper 17 (Th17) immune response is activated, ultimately triggering the onset of EAE. Conversely, modulating the KYNA-mediated GPR35 signaling in Cx3cr1+ macrophages leads to a remarkable amelioration of EAE. These findings shed light on the crucial role of microbial-derived tryptophan metabolites in regulating immune responses within extraintestinal tissues.

An agonistic anti-signal regulatory protein α antibody for chronic inflammatory diseases

Signal regulatory protein (SIRPα) is an immune inhibitory receptor expressed by myeloid cells to inhibit immune cell phagocytosis, migration, and activation. Despite the progress of SIRPα and CD47 antagonist antibodies to promote anti-cancer immunity, it is not yet known whether SIRPα receptor agonism could restrain excessive autoimmune tissue inflammation. Here, we report that neutrophil- and monocyte-associated genes including SIRPA are increased in inflamed tissue biopsies from patients with rheumatoid arthritis and inflammatory bowel diseases, and elevated SIRPA is associated with treatment-refractory ulcerative colitis. We next identify an agonistic anti-SIRPα antibody that exhibits potent anti-inflammatory effects in reducing neutrophil and monocyte chemotaxis and tissue infiltration. In preclinical models of arthritis and colitis, anti-SIRPα agonistic antibody ameliorates autoimmune joint inflammation and inflammatory colitis by reducing neutrophils and monocytes in tissues. Our work provides a proof of concept for SIRPα receptor agonism for suppressing excessive innate immune activation and chronic inflammatory disease treatment.

The double-edged role of neutrophil heterogeneity in inflammatory diseases and cancers

Neutrophils are important immune cells act as the body's first line of defense against infection and respond to diverse inflammatory cues. Many studies have demonstrated that neutrophils display plasticity in inflammatory diseases and cancers. Clarifying the role of neutrophil heterogeneity in inflammatory diseases and cancers will contribute to the development of novel treatment strategies. In this review, we have presented a review on the development of the understanding on neutrophil heterogeneity from the traditional perspective and a high-resolution viewpoint. A growing body of evidence has confirmed the double-edged role of neutrophils in inflammatory diseases and tumors. This may be due to a lack of precise understanding of the role of specific neutrophil subsets in the disease. Thus, elucidating specific neutrophil subsets involved in diseases would benefit the development of precision medicine. Thusly, we have summarized the relevance and actions of neutrophil heterogeneity in inflammatory diseases and cancers comprehensively. Meanwhile, we also discussed the potential intervention strategy for neutrophils. This review is intended to deepen our understanding of neutrophil heterogeneity in inflammatory diseases and cancers, while hold promise for precise treatment of neutrophil-related diseases.

GPR35 and mediators from platelets and mast cells in neutrophil migration and inflammation

Neutrophil recruitment from circulation to sites of inflammation is guided by multiple chemoattractant cues emanating from tissue cells, immune cells, and platelets. Here, we focus on the function of one G-protein coupled receptor, GPR35, in neutrophil recruitment. GPR35 has been challenging to study due the description of multiple ligands and G-protein couplings. Recently, we found that GPR35-expressing hematopoietic cells respond to the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA). We discuss distinct response profiles of GPR35 to 5-HIAA compared to other ligands. To place the functions of 5-HIAA in context, we summarize the actions of serotonin in vascular biology and leukocyte recruitment. Important sources of serotonin and 5-HIAA are platelets and mast cells. We discuss the dynamics of cell migration into inflamed tissues and how multiple platelet and mast cell-derived mediators, including 5-HIAA, cooperate to promote neutrophil recruitment. Additional actions of GPR35 in tissue physiology are reviewed. Finally, we discuss how clinically approved drugs that modulate serotonin uptake and metabolism may influence 5-HIAA-GPR35 function, and we speculate about broader influences of the GPR35 ligand-receptor system in immunity and disease.

B cell-derived IL-10 promotes the resolution of lipopolysaccharide-induced acute lung injury

Inflammation resolution is critical for acute lung injury (ALI) recovery. Interleukin (IL)-10 is a potent anti-inflammatory factor. However, its role in ALI resolution remains unclear. We investigated the effects of IL-10 during the ALI resolution process in a murine lipopolysaccharide (LPS)-induced ALI model. Blockade of IL-10 signaling aggravates LPS-induced lung injury, as manifested by elevated pro-inflammatory factors production and increased neutrophils recruitment to the lung. Thereafter, we used IL-10 GFP reporter mice to discern the source cell of IL-10 during ALI. We found that IL-10 is predominantly generated by B cells during the ALI recovery process. Furthermore, we used IL-10-specific loss in B-cell mice to elucidate the effect of B-cell-derived IL-10 on the ALI resolution process. IL-10-specific loss in B cells leads to increased pro-inflammatory cytokine expression, persistent leukocyte infiltration, and prolonged alveolar barrier damage. Mechanistically, B cell-derived IL-10 inhibits the activation and recruitment of macrophages and downregulates the production of chemokine KC that recruits neutrophils to the lung. Moreover, we found that IL-10 deletion in B cells leads to alterations in the cGMP-PKG signaling pathway. In addition, an exogenous supply of IL-10 promotes recovery from LPS-induced ALI, and IL-10-secreting B cells are present in sepsis-related ARDS. This study highlights that B cell-derived IL-10 is critical for the resolution of LPS-induced ALI and may serve as a potential therapeutic target.

Mast cells in colorectal cancer tumour progression, angiogenesis, and lymphangiogenesis

The characteristics of the tumour cells, as well as how tumour cells interact with their surroundings, affect the prognosis of cancer patients. The resident cells in the tumour microenvironment are mast cells (MCs), which are known for their functions in allergic responses, but their functions in the cancer milieu have been hotly contested. Several studies have revealed a link between MCs and the development of tumours. Mast cell proliferation in colorectal cancer (CRC) is correlated with angiogenesis, the number of lymph nodes to which the malignancy has spread, and patient prognosis. By releasing angiogenic factors (VEGF-A, CXCL 8, MMP-9, etc.) and lymphangiogenic factors (VEGF-C, VEGF-D, etc.) stored in granules, mast cells play a significant role in the development of CRC. On the other hand, MCs can actively encourage tumour development via pathways including the c-kit/SCF-dependent signaling cascade and histamine production. The impact of MC-derived mediators on tumour growth, the prognostic importance of MCs in patients with various stages of colorectal cancer, and crosstalk between MCs and CRC cells in the tumour microenvironment are discussed in this article. We acknowledge the need for a deeper comprehension of the function of MCs in CRC and the possibility that targeting MCs might be a useful therapeutic approach in the future.

Immune regulation through tryptophan metabolism

Amino acids are fundamental units of molecular components that are essential for sustaining life; however, their metabolism is closely interconnected to the control systems of cell function. Tryptophan (Trp) is an essential amino acid catabolized by complex metabolic pathways. Several of the resulting Trp metabolites are bioactive and play central roles in physiology and pathophysiology. Additionally, various physiological functions of Trp metabolites are mutually regulated by the gut microbiota and intestine to coordinately maintain intestinal homeostasis and symbiosis under steady state conditions and during the immune response to pathogens and xenotoxins. Cancer and inflammatory diseases are associated with dysbiosis- and host-related aberrant Trp metabolism and inactivation of the aryl hydrocarbon receptor (AHR), which is a receptor of several Trp metabolites. In this review, we focus on the mechanisms through which Trp metabolism converges to AHR activation for the modulation of immune function and restoration of tissue homeostasis and how these processes can be targeted using therapeutic approaches for cancer and inflammatory and autoimmune diseases.

Modulation of immunity by tryptophan microbial metabolites

Tryptophan (Trp) is an essential amino acid that can be metabolized via endogenous and exogenous pathways, including the Kynurenine Pathway, the 5-Hydroxyindole Pathway (also the Serotonin pathway), and the Microbial pathway. Of these, the Microbial Trp metabolic pathways in the gut have recently been extensively studied for their production of bioactive molecules. The gut microbiota plays an important role in host metabolism and immunity, and microbial Trp metabolites can influence the development and progression of various diseases, including inflammatory, cardiovascular diseases, neurological diseases, metabolic diseases, and cancer, by mediating the body's immunity. This review briefly outlines the crosstalk between gut microorganisms and Trp metabolism in the body, starting from the three metabolic pathways of Trp. The mechanisms by which microbial Trp metabolites act on organism immunity are summarized, and the potential implications for disease prevention and treatment are highlighted.

Recent advances in GPR35 pharmacology; 5-HIAA serotonin metabolite becomes a ligand

GPR35, an orphan receptor, has been waiting for its ligand since its cloning in 1998. Many endogenous and exogenous molecules have been suggested to act as agonists of GPR35 including kynurenic acid, zaprinast, lysophosphatidic acid, and CXCL17. However, complex and controversial responses to ligands among species have become a huge hurdle in the development of therapeutics in addition to the orphan state. Recently, a serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), is reported to be a high potency ligand for GPR35 by investigating the increased expression of GPR35 in neutrophils. In addition, a transgenic knock-in mouse line is developed, in which GPR35 was replaced with a human ortholog, making it possible not only to overcome the different selectivity of agonists among species but also to conduct therapeutic experiments on human GPR35 in mouse models. In the present article, I review the recent advances and prospective therapeutic directions in GPR35 research. Especially, I'd like to draw attention of readers to the finding of 5-HIAA as a ligand of GPR35 and lead to apply the 5-HIAA and human GPR35 knock-in mice to their research fields in a variety of pathophysiological conditions.

What defines a chemokine? - The curious case of CXCL17

Chemotactic cytokines (chemokines) are a group of around 40 small proteins which share a similar protein fold and are well known for their ability to direct the migration of leukocytes to a variety of tissue locations. CXCL17 was the last member of the chemokine family to be assigned and was admitted to the family based on theoretical modelling of the CXCL17 structure and chemotactic activity for monocytes and dendritic cells. Of Interest, CXCL17 expression appears to be restricted to mucosal tissues such as the tongue, stomach and lung, suggestive of specific roles at these locations. A putative CXCL17 receptor, GPR35 was reportedly identified and mice deficient in CXCL17 were generated and characterised. More recently, however, some apparent contradictions regarding aspects of CXCL17 biology have been raised by ourselves and others. Notably, GPR35 appears to be a receptor for the serotonin metabolite 5-hydroxyindoleacetic acid rather than for CXCL17 and modelling of CXCL17 using a variety of platforms fails to identify a chemokine-like fold. In this article, we summarize the discovery of CXCL17 and discuss key papers describing the subsequent characterisation of this protein. Ultimately, we pose the question, 'What defines a chemokine?' (185 words).

Mast Cell and Innate Immune Cell Communication in Cholestatic Liver Disease

Mast cells (MCs) contribute to the pathogenesis of cholestatic liver diseases (primary sclerosing cholangitis [PSC] and primary biliary cholangitis [PBC]). PSC and PBC are immune-mediated, chronic inflammatory diseases, characterized by bile duct inflammation and stricturing, advancing to hepatobiliary cirrhosis. MCs are tissue resident immune cells that may promote hepatic injury, inflammation, and fibrosis formation by either direct or indirect interactions with other innate immune cells (neutrophils, macrophages/Kupffer cells, dendritic cells, natural killer, and innate lymphoid cells). The activation of these innate immune cells, usually through the degranulation of MCs, promotes antigen uptake and presentation to adaptive immune cells, exacerbating liver injury. In conclusion, dysregulation of MC-innate immune cell communications during liver injury and inflammation can lead to chronic liver injury and cancer.

GPR35: from enigma to therapeutic target

The orphan G-protein-coupled receptor 35 (GPR35), although poorly characterised, is attracting considerable interest as a therapeutic target. Marked differences in pharmacology between human and rodent orthologues of the receptor and a dearth of antagonists with affinity for mouse and rat GPR35 have previously restricted the use of preclinical disease models. The development of improved ligands, novel transgenic knock-in mouse lines, and detailed analysis of the disease relevance of single-nucleotide polymorphisms (SNPs) have greatly enhanced understanding of the key roles of GPR35 and have stimulated efforts towards disease-targeted proof-of-concept studies. In this opinion article, new information on the biology of the receptor is considered, whilst insight into how GPR35 is currently being assessed for therapeutic utility - in areas ranging from inflammatory bowel diseases to nonalcoholic steatohepatitis and various cancers - is also provided.

Aminosalicylates target GPR35, partly contributing to the prevention of DSS-induced colitis

GPR35, a class A G-protein-coupled receptor, is considered an orphan receptor; the endogenous ligand and precise physiological function of GPR35 remain obscure. GPR35 is expressed relatively highly in the gastrointestinal tract and immune cells. It plays a role in colorectal diseases like inflammatory bowel diseases (IBDs) and colon cancer. More recently, the development of GPR35 targeting anti-IBD drugs is in solid request. Nevertheless, the development process is in stagnation due to the lack of a highly potent GPR35 agonist that is also active comparably in both human and mouse orthologs. Therefore, we proposed to find compounds for GPR35 agonist development, especially for the human ortholog of GPR35. As an efficient way to pick up a safe and effective GPR35 targeting anti-IBD drug, we screened Food and Drug Administration (FDA)-approved 1850 drugs using a two-step DMR assay. Interestingly, we found aminosalicylates, first-line medicine for IBDs whose precise target remains unknown, exhibited activity on both human and mouse GPR35. Among these, pro-drug olsalazine showed the most potency on GPR35 agonism, inducing ERK phosphorylation and β-arrestin2 translocation. In dextran sodium sulfate (DSS)-induced colitis, the protective effect on disease progression and inhibitory effect on TNFα mRNA expression, NF-κB and JAK-STAT3 pathway of olsalazine are compromised in GPR35 knock-out mice. The present study identified a target for first-line medicine aminosalicylates, highlighted that uncleaved pro-drug olsalazine is effective, and provided a new concept for the design of aminosalicylic GPR35 targeting anti-IBD drug.

LIFR recruits HGF-producing neutrophils to promote liver injury repair and regeneration

The molecular links between tissue repair and tumorigenesis remain elusive. Here, we report that loss of the liver tumor suppressor Lifr in mouse hepatocytes impairs the recruitment and activity of reparative neutrophils, resulting in the inhibition of liver regeneration after partial hepatectomy or toxic injuries. On the other hand, overexpression of LIFR promotes liver repair and regeneration after injury. Interestingly, LIFR deficiency or overexpression does not affect hepatocyte proliferation ex vivo or in vitro . In response to physical or chemical damage to the liver, LIFR from hepatocytes promotes the secretion of the neutrophil chemoattractant CXCL1 (which binds CXCR2 to recruit neutrophils) and cholesterol in a STAT3-dependent manner. Cholesterol, in turn, acts on the recruited neutrophils to secrete hepatocyte growth factor (HGF) to accelerate hepatocyte proliferation and regeneration. Altogether, our findings reveal a LIFR-STAT3- CXCL1-CXCR2 axis and a LIFR-STAT3-cholesterol-HGF axis that mediate hepatic damage- induced crosstalk between hepatocytes and neutrophils to repair and regenerate the liver.

The Tryptophan and Kynurenine Pathway Involved in the Development of Immune-Related Diseases

The tryptophan and kynurenine pathway is well-known to play an important role in nervous, endocrine, and immune systems, as well as in the development of inflammatory diseases. It has been documented that some kynurenine metabolites are considered to have anti-oxidative, anti-inflammatory, and/or neuroprotective properties. Importantly, many of these kynurenine metabolites may possess immune-regulatory properties that could alleviate the inflammation response. The abnormal activation of the tryptophan and kynurenine pathway might be involved in the pathophysiological process of various immune-related diseases, such as inflammatory bowel disease, cardiovascular disease, osteoporosis, and/or polycystic ovary syndrome. Interestingly, kynurenine metabolites may be involved in the brain memory system and/or intricate immunity via the modulation of glial function. In the further deliberation of this concept with engram, the roles of gut microbiota could lead to the development of remarkable treatments for the prevention of and/or the therapeutics for various intractable immune-related diseases.

IL-33-mediated activation of mast cells is involved in the progression of imiquimod-induced psoriasis-like dermatitis

BACKGROUND

Psoriasis is a chronic inflammatory dermatosis with an unclear pathogenesis. Mast cells (MCs) can serve as a bridge between innate and adaptive immunity and are involved in the regulation of the inflammatory state and immune homeostasis in diseases. MCs constitutively express interleukin-33 receptor T1/ST2 (IL-33R). IL-33 is a potent MCs activator that is actively secreted by keratinocytes in psoriasis. However, the regulatory role of MCs in psoriasis remains uncertain. Therefore, we hypothesised that IL-33 could promote MC activation to regulate psoriasis development.

METHODS

We performed experiments on wild-type (WT) and MC-deficient (Kit Wsh/Wsh) mice, established psoriasis-like mouse models using imiquimod (IMQ), and performed RNA sequencing and transcriptomic analysis of skin lesions. Exogenous administration was performed using recombinant IL-33. Validation and evaluation were performed using PSI scoring, immunofluorescence, immunohistochemistry, and qPCR.

RESULTS

We observed an upregulation in the number and activation of MCs in patients with psoriasis and in IMQ-induced psoriasis-like dermatitis. Deficiency of MCs ameliorates IMQ-induced psoriatic dermatitis at an early stage. IL-33 is increased and co-localized with MCs in the dermis of psoriasis-like lesions using immunofluorescence. Compared to WT mice, IMQ-induced Kit^Wsh/Wsh mice demonstrated a delayed response to exogenous IL-33.

CONCLUSIONS

MCs are activated by IL-33 in the early stages of psoriasis and exacerbate psoriasis-associated skin inflammation. The regulation of MC homeostasis may be a potential therapeutic strategy for psoriasis. Video Abstract.

Neutrophil, neutrophil extracellular traps and endothelial cell dysfunction in sepsis

Sepsis is a persistent systemic inflammatory condition involving multiple organ failures resulting from a dysregulated immune response to infection, and one of the hallmarks of sepsis is endothelial dysfunction. During its progression, neutrophils are the first line of innate immune defence against infection. Aside from traditional mechanisms, such as phagocytosis or the release of inflammatory cytokines, reactive oxygen species and other antibacterial substances, activated neutrophils also release web-like structures composed of tangled decondensed DNA, histone, myeloperoxidase and other granules called neutrophil extracellular traps (NETs), which can efficiently ensnare bacteria in the circulation. In contrast, excessive neutrophil activation and NET release may induce endothelial cells to shift toward a pro-inflammatory and pro-coagulant phenotype. Furthermore, neutrophils and NETs can degrade glycocalyx on the endothelial cell surface and increase endothelium permeability. Consequently, the endothelial barrier collapses, contributing to impaired microcirculatory blood flow, tissue hypoperfusion and life-threatening organ failure in the late phase of sepsis.

GPR35 antagonist CID-2745687 attenuates anchorage-independent cell growth by inhibiting YAP/TAZ activity in colorectal cancer cells

Background and purpose: GPR35, a member of the orphan G-protein-coupled receptor, was recently implicated in colorectal cancer (CRC). However, whether targeting GPR35 by antagonists can inhibit its pro-cancer role has yet to be answered. Experimental approach: We applied antagonist CID-2745687 (CID) in established GPR35 overexpressing and knock-down CRC cell lines to understand its anti-cell proliferation property and the underlying mechanism. Key results: Although GPR35 did not promote cell proliferation in 2D conditions, it promoted anchorage-independent growth in soft-agar, which was reduced by GPR35 knock-down and CID treatment. Furthermore, YAP/TAZ target genes were expressed relatively higher in GPR35 overexpressed cells and lower in GPR35 knock-down cells. YAP/TAZ activity is required for anchorage-independent growth of CRC cells. By detecting YAP/TAZ target genes, performing TEAD4 luciferase reporter assay, and examining YAP phosphorylation and TAZ protein expression level, we found YAP/TAZ activity is positively correlated to GPR35 expression level, which CID disrupted in GPR35 overexpressed cells, but not in GPR35 knock-down cells. Intriguingly, GPR35 agonists did not promote YAP/TAZ activity but ameliorated CID's inhibitory effect; GPR35-promoted YAP/TAZ activity was only partly attenuated by ROCK1/2 inhibitor. Conclusion and implications: GPR35 promoted YAP/TAZ activity partly through Rho-GTPase with its agonist-independent constitutive activity, and CID exhibited its inhibitory effect. GPR35 antagonists are promising anti-cancer agents that target hyperactivation and overexpression of YAP/TAZ in CRC.

Focus on mast cells in the tumor microenvironment: Current knowledge and future directions

Mast cells (MCs) are crucial cells participating in both innate and adaptive immune processes that play important roles in protecting human health and in the pathophysiology of various diseases, such as allergies, cardiovascular diseases, and autoimmune diseases. In the context of tumors, MCs are a non-negligible population of immune cells in the tumor microenvironment (TME). In most tumor types, MCs accumulate in both the tumor tissue and the surrounding tissue. MCs interact with multiple components of the TME, affecting TME remodeling and the tumor cell fate. However, controversy persists regarding whether MCs contribute to tumor progression or trigger an anti-tumor immune response. This review focuses on the context of the TME to explore the specific properties and functions of MCs and discusses the crosstalk that occurs between MCs and other components of the TME, which affect tumor angiogenesis and lymphangiogenesis, invasion and metastasis, and tumor immunity through different mechanisms. We also anticipate the potential role of MCs in cancer immunotherapy, which might expand upon the success achieved with existing cancer therapies.

Insights into divalent cation regulation and G13-coupling of orphan receptor GPR35

Endogenous ions play important roles in the function and pharmacology of G protein-coupled receptors (GPCRs) with limited atomic evidence. In addition, compared with G protein subtypes G_s, G_i/o, and G_q/11, insufficient structural evidence is accessible to understand the coupling mechanism of G_12/13 protein by GPCRs. Orphan receptor GPR35, which is predominantly expressed in the gastrointestinal tract and is closely related to inflammatory bowel diseases (IBDs), stands out as a prototypical receptor for investigating ionic modulation and G₁₃ coupling. Here we report a cryo-electron microscopy structure of G₁₃-coupled GPR35 bound to an anti-allergic drug, lodoxamide. This structure reveals a novel divalent cation coordination site and a unique ionic regulatory mode of GPR35 and also presents a highly positively charged binding pocket and the complementary electrostatic ligand recognition mode, which explain the promiscuity of acidic ligand binding by GPR35. Structural comparison of the GPR35-G₁₃ complex with other G protein subtypes-coupled GPCRs reveals a notable movement of the C-terminus of α5 helix of the Gα₁₃ subunit towards the receptor core and the least outward displacement of the cytoplasmic end of GPR35 TM6. A featured 'methionine pocket' contributes to the G₁₃ coupling by GPR35. Together, our findings provide a structural basis for divalent cation modulation, ligand recognition, and subsequent G₁₃ protein coupling of GPR35 and offer a new opportunity for designing GPR35-targeted drugs for the treatment of IBDs.

Toward manipulating serotonin signaling via the microbiota-gut-brain axis

It is now well established in humans that there is a bidirectional pathway of communication between the central and enteric nervous systems in which members of the microbiome participate. This microbiota-gut-brain axis (MGBA) is crucial for normal development and physiology, and its dysregulation has been implicated in a range of neurological and intestinal disorders. Investigations into the mechanistic underpinnings of the MGBA have identified serotonin as a molecule of particular interest. In this review, we highlight recent advances toward understanding the role of endogenous serotonin in microbial communities, how microbial communities bidirectionally interact with host serotonin, and potential future engineering opportunities to leverage these novel mechanisms for biomedical applications.

The role of platelet mediated thromboinflammation in acute liver injury

Acute liver injuries have wide and varied etiologies and they occur both in patients with and without pre-existent chronic liver disease. Whilst the pathophysiological mechanisms remain distinct, both acute and acute-on-chronic liver injury is typified by deranged serum transaminase levels and if severe or persistent can result in liver failure manifest by a combination of jaundice, coagulopathy and encephalopathy. It is well established that platelets exhibit diverse functions as immune cells and are active participants in inflammation through processes including immunothrombosis or thromboinflammation. Growing evidence suggests platelets play a dualistic role in liver inflammation, shaping the immune response through direct interactions and release of soluble mediators modulating function of liver sinusoidal endothelial cells, stromal cells as well as migrating and tissue-resident leucocytes. Elucidating the pathways involved in initiation, propagation and resolution of the immune response are of interest to identify therapeutic targets. In this review the provocative role of platelets is outlined, highlighting beneficial and detrimental effects in a spatial, temporal and disease-specific manner.

Neutrophils in ANCA-associated vasculitis: Mechanisms and implications for management

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of systemic autoimmune diseases, which is typified by inflammatory necrosis predominantly affecting the small vessels and often accompanied by positive ANCA. Clinically, AAV primarily includes microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA). It has been found that in AAV pathogenesis, both innate and adaptive immunity are related to neutrophil function mutually. Many proteins, such as myeloperoxidase (MPO) and proteinase 3 (PR3), in neutrophil cytoplasm lead to the production of proteins such as MPO-ANCA and PR3-ANCA by activating adaptive immunity. In addition, through the process of neutrophil extracellular trap (NET) formation, activation of an alternative complement pathway and the respiratory burst can stimulate the neutrophils close to vascular endothelial cells and will participate the vessel inflammation. This review aims to reveal the potential mechanisms regulating the association between the neutrophils and various types of AAVs and to emphasize the results of recent findings on these interactions. Moreover, multiple underlying signaling pathways involved in the regulation of neutrophils during AAV processes have also been discussed. The ultimate goal of this review is to identify novel biomarkers and therapeutic targets for AAV management in the future.

Isoforms of GPR35 have distinct extracellular N-termini that allosterically modify receptor-transducer coupling and mediate intracellular pathway bias

Within the intestine, the human G protein–coupled receptor (GPCR) GPR35 is involved in oncogenic signaling, bacterial infections, and inflammatory bowel disease. GPR35 is known to be expressed as two distinct isoforms that differ only in the length of their extracellular N-termini by 31 amino acids, but detailed insights into their functional differences are lacking. Through gene expression analysis in immune and gastrointestinal cells, we show that these isoforms emerge from distinct promoter usage and alternative splicing. Additionally, we employed optical assays in living cells to thoroughly profile both GPR35 isoforms for constitutive and ligand-induced activation and signaling of 10 different heterotrimeric G proteins, ligand-induced arrestin recruitment, and receptor internalization. Our results reveal that the extended N-terminus of the long isoform limits G protein activation yet elevates receptor–β-arrestin interaction. To better understand the structural basis for this bias, we examined structural models of GPR35 and conducted experiments with mutants of both isoforms. We found that a proposed disulfide bridge between the N-terminus and extracellular loop 3, present in both isoforms, is crucial for constitutive G₁₃ activation, while an additional cysteine contributed by the extended N-terminus of the long GPR35 isoform limits the extent of agonist-induced receptor–β-arrestin2 interaction. The pharmacological profiles and mechanistic insights of our study provide clues for the future design of isoform-specific GPR35 ligands that selectively modulate GPR35–transducer interactions and allow for mechanism-based therapies against, for example, inflammatory bowel disease or bacterial infections of the gastrointestinal system.

Sex differences at the platelet-vascular interface

Platelets are multifunctional cells that ensure the integrity of the vascular wall and modulate the immune response at the blood/vascular interface. Their pathological activation results in both thrombosis and inflammation and implicates them in the pathogenesis of vascular disease. Vascular diseases are sexually dimorphic in terms of incidence, clinical presentation, outcome, and efficacy of anti-platelet therapy. We here provide an overview of what is known about the role of platelets in the initiation and progression of vascular diseases and summarize what is known about the sex differences in platelet reactivity and in the thromboinflammatory mechanisms that drive these diseases, with a particular focus on atherosclerosis, obstructive and non-obstructive coronary artery disease, and ischemic stroke. Understanding the sex differences at the platelet-vascular interface is clinically relevant as it will enable: (1) to design new therapeutic strategies that prevent the detrimental effects of the immune-modulatory function of platelets taking sex into account, and (2) to evaluate if sex-specific anti-platelet drug regimens should be used to reduce the risk not only of thrombosis but also of vascular disease progression.

Nutritional and metabolic signalling through GPCRs

Deregulated metabolism is a well-known feature of several challenging diseases, including diabetes, obesity and cancer. Besides their important role as intracellular bioenergetic molecules, dietary nutrients and metabolic intermediates are released in the extracellular environment. As such, they may achieve unconventional roles as hormone-like molecules by activating cell-surface G-protein-coupled receptors (GPCRs) that regulate several pathophysiological processes. In this review, we provide an insight into the role of lactate, succinate, fatty acids, amino acids, ketogenesis-derived and β-oxidation-derived intermediates as extracellular signalling molecules. Moreover, the mechanisms by which their cognate metabolite-sensing GPCRs integrate nutritional and metabolic signals with specific intracellular pathways will be described. A better comprehension of these aspects is of fundamental importance to identify GPCRs as novel druggable targets.