Receptor-independent, direct membrane binding leads to cell-surface lipid sorting and Syk kinase activation in dendritic cells

Striking a balance: new perspectives on homeostatic dendritic cell maturation

Dendritic cells (DCs) are crucial gatekeepers of the balance between immunity and tolerance. They exist in two functional states, immature or mature, that refer to an information-sensing versus an information-transmitting state, respectively. Historically, the term DC maturation was used to describe the acquisition of immunostimulatory capacity by DCs following their triggering by pathogens or tissue damage signals. As such, immature DCs were proposed to mediate tolerance, whereas mature DCs were associated with the induction of protective T cell immunity. Later studies have challenged this view and unequivocally demonstrated that two distinct modes of DC maturation exist, homeostatic and immunogenic DC maturation, each with a distinct functional outcome. Therefore, the mere expression of maturation markers cannot be used to predict immunogenicity. How DCs become activated in homeostatic conditions and maintain tolerance remains an area of intense debate. Several recent studies have shed light on the signals driving the homeostatic maturation programme, especially in the conventional type 1 DC (cDC1) compartment. Here, we highlight our growing understanding of homeostatic DC maturation and the relevance of this process for immune tolerance.

Neutrophils and extracellular traps in crystal-associated diseases

Crystalline material can cause a multitude of acute and chronic inflammatory diseases, such as gouty arthritis, silicosis, kidney disease, and atherosclerosis. Crystals of various types are thought to cause similar inflammatory responses, including the release of proinflammatory mediators and formation of neutrophil extracellular traps (NETs), processes that further promote necroinflammation and tissue damage. It has become apparent that the intensity of inflammation and the related mechanisms of NET formation and neutrophil death in crystal-associated diseases can vary depending on the crystal type, amount, and site of deposition. This review details new mechanistic insights into crystal biology, highlights the differential effects of various crystals on neutrophils and extracellular trap (ET) formation, and discusses treatment strategies and potential future approaches for crystal-associated disorders.

Metabolite-derived damage-associated molecular patterns in immunological diseases

Damage-associated molecular patterns (DAMPs) are typically derived from the endogenous elements of necrosis cells and can trigger inflammatory responses by activating DAMPs-sensing receptors on immune cells. Failure to clear DAMPs may lead to persistent inflammation, thereby contributing to the pathogenesis of immunological diseases. This review focuses on a newly recognized class of DAMPs derived from lipid, glucose, nucleotide, and amino acid metabolic pathways, which are then termed as metabolite-derived DAMPs. This review summarizes the reported molecular mechanisms of these metabolite-derived DAMPs in exacerbating inflammation responses, which may attribute to the pathology of certain types of immunological diseases. Additionally, this review also highlights both direct and indirect clinical interventions that have been explored to mitigate the pathological effects of these DAMPs. By summarizing our current understanding of metabolite-derived DAMPs, this review aims to inspire future thoughts and endeavors on targeted medicinal interventions and the development of therapies for immunological diseases.

Cholesterol, Eukaryotic Lipid Domains, and an Evolutionary Perspective of Transmembrane Signaling

Transmembrane signaling is essential for complex life forms. Communication across a bilayer lipid barrier is elaborately organized to convey precision and to fine-tune strength. Looking back, the steps that it has taken to enable this seemingly mundane errand are breathtaking, and with our survivorship bias, Darwinian. While this review is to discuss eukaryotic membranes in biological functions for coherence and theoretical footing, we are obliged to follow the evolution of the biological membrane through time. Such a visit is necessary for our hypothesis that constraints posited on cellular functions are mainly via the biomembrane, and relaxation thereof in favor of a coordinating membrane environment is the molecular basis for the development of highly specialized cellular activities, among them transmembrane signaling. We discuss the obligatory paths that have led to eukaryotic membrane formation, its intrinsic ability to signal, and how it set up the platform for later integration of protein-based receptor activation.

Clec12a inhibits MSU-induced immune activation through lipid raft expulsion

Monosodium uric acid (MSU) crystal, the etiological agent of gout, has been shown to trigger innate immune responses via multiple pathways. It is known that MSU-induced lipid sorting on plasma membrane promotes the phosphorylation of Syk and eventually leads to the activation of phagocytes. However, whether this membrane lipid-centric mechanism is regulated by other processes is unclear. Previous studies showed that Clec12a, a member of the C-type lectin receptor family, is reported to recognize MSU and suppresses this crystalline structure-induced immune activation. How this scenario is integrated into the lipid sorting-mediated inflammatory responses by MSU, and particularly, how Clec12a intercepts lipid raft-originated signaling cascade remains to be elucidated. Here, we found that the ITIM motif of Clec12a is dispensable for its inhibition of MSU-mediated signaling; instead, the transmembrane domain of Clec12a disrupts MSU-induced lipid raft recruitment and thus attenuates downstream signals. Single amino acid mutagenesis study showed the critical role of phenylalanine in the transmembrane region for the interactions between C-type lectin receptors and lipid rafts, which is critical for the regulation of MSU-mediated lipid sorting and phagocyte activation. Overall, our study provides new insights for the molecular mechanisms of solid particle-induced immune activation and may lead to new strategies in inflammation control.

Asymptomatic hyperuricaemia in chronic kidney disease: mechanisms and clinical implications

Asymptomatic hyperuricaemia (HU) is considered a pathogenic factor in multiple disease contexts, but a causative role is only proven for the crystalline form of uric acid in gouty arthritis and urate nephropathy. Epidemiological studies document a robust association of HU with hypertension, cardiovascular disease (CVD) and CKD progression, but CKD-related impaired uric acid (UA) clearance and the use of diuretics that further impair UA clearance likely accounts for these associations. Interpreting the available trial evidence is further complicated by referring to xanthine oxidase inhibitors as urate-lowering treatment, although these drugs inhibit other substrates, so attributing their effects only to HU is problematic. In this review we provide new mechanistic insights into the biological effects of soluble and crystalline UA and discuss clinical evidence on the role of asymptomatic HU in CKD, CVD and sterile inflammation. We identify research areas with gaps in experimental and clinical evidence, specifically on infectious complications that represent the second common cause of death in CKD patients, referred to as secondary immunodeficiency related to kidney disease. In addition, we address potential therapeutic approaches on how and when to treat asymptomatic HU in patients with kidney disease and where further interventional studies are required.

Human dendritic cell maturation induced by amorphous silica nanoparticles is Syk-dependent and triggered by lipid raft aggregation

BACKGROUND

Synthetic amorphous silica nanoparticles (SAS-NPs) are widely employed in pharmaceutics, cosmetics, food and concretes. Workers and the general population are exposed daily via diverse routes of exposure. SAS-NPs are generally recognized as safe (GRAS) by the Food and Drug Administration, but because of their nanoscale size and extensive uses, a better assessment of their immunotoxicity is required. In the presence of immune "danger signals", dendritic cells (DCs) undergo a maturation process resulting in their migration to regional lymph nodes where they activate naive T-cells. We have previously shown that fumed silica pyrogenic SAS-NPs promote the two first steps of the adaptative immune response by triggering DC maturation and T-lymphocyte response, suggesting that SAS-NPs could behave as immune "danger signals". The present work aims to identify the mechanism and the signalling pathways involved in DC phenotype modifications provoked by pyrogenic SAS-NPs. As a pivotal intracellular signalling molecule whose phosphorylation is associated with DC maturation, we hypothesized that Spleen tyrosine kinase (Syk) may play a central role in SAS-NPs-induced DC response.

RESULTS

In human monocyte-derived dendritic cells (moDCs) exposed to SAS-NPs, Syk inhibition prevented the induction of CD83 and CD86 marker expression. A significant decrease in T-cell proliferation and IFN-γ, IL-17F and IL-9 production was found in an allogeneic moDC:T-cell co-culture model. These results suggested that the activation of Syk was necessary for optimal co-stimulation of T-cells. Moreover, Syk phosphorylation, observed 30 min after SAS-NP exposure, occurred upstream of the c-Jun N-terminal kinase (JNK) Mitogen-activated protein kinases (MAPK) and was elicited by the Src family of protein tyrosine kinases. Our results also showed for the first time that SAS-NPs provoked aggregation of lipid rafts in moDCs and that MβCD-mediated raft destabilisation altered Syk activation.

CONCLUSIONS

We showed that SAS-NPs could act as an immune danger signal in DCs through a Syk-dependent pathway. Our findings revealed an original mechanism whereby the interaction of SAS-NPs with DC membranes promoted aggregation of lipid rafts, leading to a Src kinase-initiated activation loop triggering Syk activation and functional DC maturation.

Immunology of a unique biological structure: the Echinococcus laminated layer

The larval stages of the cestode parasites belonging to the genus Echinococcus grow within internal organs of humans and a range of animal species. The resulting diseases, collectively termed echinococcoses, include major neglected tropical diseases of humans and livestock. Echinococcus larvae are outwardly protected by the laminated layer (LL), an acellular structure that is unique to this genus. The LL is based on a fibrillar meshwork made up of mucins, which are decorated by galactose-rich O-glycans. In addition, in the species cluster termed E. granulosus sensu lato, the LL features nano-deposits of the calcium salt of myo-inositol hexakisphosphate (Insp6). The main purpose of our article is to update the immunobiology of the LL. Major recent advances in this area are (i) the demonstration of LL "debris" at the infection site and draining lymph nodes, (ii) the characterization of the decoy activity of calcium Insp6 with respect to complement, (iii) the evidence that the LL mucin carbohydrates interact specifically with a lectin receptor expressed in Kupffer cells (Clec4F), and (iv) the characterization of what appear to be receptor-independent effects of LL particles on dendritic cells and macrophages. Much information is missing on the immunology of this intriguing structure: we discuss gaps in knowledge and propose possible avenues for research.

Interactions between silica and titanium nanoparticles and oral and gastrointestinal epithelia: Consequences for inflammatory diseases and cancer

Engineered nanoparticles (NPs) composed of elements such as silica and titanium, smaller than 100 nm in diameter and their aggregates, are found in consumer products such as cosmetics, food, antimicrobials and drug delivery systems, and oral health products such as toothpaste and dental materials. They may also interact accidently with epithelial tissues in the intestines and oral cavity, where they can aggregate into larger particles and induce inflammation through pathways such as inflammasome activation. Persistent inflammation can lead to precancerous lesions. Both the particles and lesions are difficult to detect in biopsies, especially in clinical settings that screen large numbers of patients. As diagnosis of early stages of disease can be lifesaving, there is growing interest in better understanding interactions between NPs and epithelium and developing rapid imaging techniques that could detect foreign particles and markers of inflammation in epithelial tissues. NPs can be labelled with fluorescence or radioactive isotopes, but it is challenging to detect unlabeled NPs with conventional imaging techniques. Different current imaging techniques such as synchrotron radiation X-ray fluorescence spectroscopy are discussed here. Improvements in imaging techniques, coupled with the use of machine learning tools, are needed before diagnosis of particles in biopsies by automated imaging could move usefully into the clinic.

Monosodium urate crystals with controlled shape and aspect ratio for elucidating the pathological progress of acute gout

Gout is a self-limiting inflammatory arthritis mediated by the precipitation of monosodium urate (MSU) crystals that further activate the NLRP3 inflammasome and initiate a cascade of inflammatory events. However, the key physicochemical properties of MSU crystals that determine the acute phase of gout have not been fully identified. In this study, a library of engineered MSU crystals with well-controlled size and shape is designed to explore their proinflammatory potentials in mediating the pathological progress of gout. It is demonstrated that medium-sized long aspect ratio MSU crystals induce more prominent IL-1β production in vitro due to enhanced cellular uptake and the production of mitochondrial reactive oxygen species (mtROS). The characteristics of MSU crystals are also correlated with their inflammatory potentials in both acute peritonitis and arthritis models. Furthermore, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) is demonstrated to inhibit MSU-induced oxidative burst by removing plasma membrane cholesterol. As a result, it attenuates the inflammatory responses both in vitro and in vivo. Additionally, antioxidant N-acetylcysteine (NAC) is shown to alleviate acute gouty symptom by suppressing oxidative stress. This study identifies the key physicochemical properties of MSU crystals that mediate the pathogenesis of gout, which sheds light on novel design strategies for the intervention of gout.

Inflammatory Response to Regulated Cell Death in Gout and Its Functional Implications

Gout, a chronic inflammatory arthritis disease, is characterized by hyperuricemia and caused by interactions between genetic, epigenetic, and metabolic factors. Acute gout symptoms are triggered by the inflammatory response to monosodium urate crystals, which is mediated by the innate immune system and immune cells (e.g., macrophages and neutrophils), the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation, and pro-inflammatory cytokine (e.g., IL-1β) release. Recent studies have indicated that the multiple programmed cell death pathways involved in the inflammatory response include pyroptosis, NETosis, necroptosis, and apoptosis, which initiate inflammatory reactions. In this review, we explore the correlation and interactions among these factors and their roles in the pathogenesis of gout to provide future research directions and possibilities for identifying potential novel therapeutic targets and enhancing our understanding of gout pathogenesis.

Natural antibodies and CRP drive anaphylatoxin production by urate crystals

In gout, crystallization of uric acid in the form of monosodium urate (MSU) leads to a painful inflammatory response. MSU crystals induce inflammation by activating the complement system and various immune cell types, and by inducing necrotic cell death. We previously found that the soluble pattern recognition molecule C-reactive protein (CRP) recognizes MSU crystals, while enhancing complement activation. In the absence of CRP, MSU crystals still induced complement activation, suggesting additional CRP-independent mechanisms of complement activation. In the present study, we searched for additional MSU crystal-binding complement activators. We found that all healthy individuals, even unborn children, have MSU crystal-specific immunoglobulin M (IgM) in their blood. This indicates that innate IgM, also known as natural IgM, recognizes these crystals. In serum lacking IgM and CRP, MSU crystals showed negligible complement activation as assessed by the production of the anaphylatoxins C4a, C3a, and C5a (listed in order of production via the classical complement pathway). We show that IgM and CRP both activate the classical complement pathway on MSU crystals. CRP was more efficient at fixating active C1 on the crystals and inducing release of the most inflammatory anaphylatoxin C5a, indicating non-redundant functions of CRP. Notably, while CRP recognizes MSU crystals but not the related calcium pyrophosphate dihydrate (CPPD) crystals, natural IgM bound to both, suggesting common and distinct mechanisms of recognition of individual crystal types by complement activators.

The Interplay Between Brain Vascular Calcification and Microglia

Vascular calcifications are characterized by the ectopic deposition of calcium and phosphate in the vascular lumen or wall. They are a common finding in computed tomography scans or during autopsy and are often directly related to a pathological condition. While the pathogenesis and functional consequences of vascular calcifications have been intensively studied in some peripheral organs, vascular calcification, and its pathogenesis in the central nervous system is poorly characterized and understood. Here, we review the occurrence of vessel calcifications in the brain in the context of aging and various brain diseases. We discuss the pathomechanism of brain vascular calcification in primary familial brain calcification as an example of brain vessel calcification. A particular focus is the response of microglia to the vessel calcification in the brain and their role in the clearance of calcifications.

Guizhi-Shaoyao-Zhimu decoction attenuates monosodium urate crystal-induced inflammation through inactivation of NF-κB and NLRP3 inflammasome

ETHNOPHARMACOLOGICAL RELEVANCE

Guizhi-Shaoyao-Zhimu decoction (GSZD), a classical traditional Chinese medicine (TCM) prescription, is used empirically to treat various types of arthritis in TCM clinical practice. However, the underlying mechanisms of GSZD on gouty inflammation are not totally elucidated.

AIM OF STUDY

The purpose of this study is to investigate the effects of GSZD on peritoneal recruitment of neutrophils, production of proinflammatory mediators, activations of nuclear factor (NF)-κB and nucleotide oligomerization domain-like receptor protein-3 (NLRP3) inflammasome in mice with monosodium urate crystal (MSU)-induced peritonitis (MIP).

MATERIALS AND METHODS

Mice were intragastrically administered with GSZD for 7 days. After the last administration, mice were intraperitoneally injected with MSU. Peritoneal exudates of mice were harvested, and total peritoneal cells were calculated. Levels of interleukin (IL)-1β, IL-6 and monocyte chemotactic protein (MCP)-1 in peritoneal exudates were tested by enzyme-linked immunosorbent assay. Expressions of IL-1β, NLRP3, cysteinyl aspartate specific proteinase (caspase)-1, apoptosis-associated speck-like protein containing the caspase activation and recruitment domain (ASC), phosphorylated (p)-p65, inhibitor of NF-κB (IκB)α, p-IκB kinase (IKK)β, nuclear p65, p-mitogen-activated protein kinases (MAPKs) in peritoneal cells were analyzed by Western blot. Binding activity of NF-κB to DNA was measured by a Trans AM™ kit for p65. Interaction between ASC and pro-caspase-1 was assessed by co-immunoprecipitation assay.

RESULTS

Total peritoneal cells, levels of IL-1β, IL-6 and MCP-1 were significantly reduced by GSZD treatment in peritoneal exudates of MIP mice. As for the activation of NF-κB, GSZD treatment significantly reduced the levels of p-p65, p-IKKβ, nuclear p65 and p-MAPKs, enhanced the level of IκBα and abated the binding ability of NF-κB to DNA in peritoneal cells of MIP mice. As for the activation of NLRP3 inflammasome, GSZD treatment significantly reduced the levels of IL-1β, NLRP3 and caspase-1, and alleviated the interaction between ASC and pro-caspase-1 in peritoneal cells of MIP mice. Nevertheless, GSZD didn't remarkably change the level of ASC.

CONCLUSIONS

These results suggest that GSZD attenuates the MSU-induced inflammation through inhibiting the activations of NF-κB and NLRP3 inflammasome.

STING-Mediated Interferon Induction by Herpes Simplex Virus 1 Requires the Protein Tyrosine Kinase Syk

The nature and the intensity of innate immune response to virus infection determine the course of pathogenesis in the host. Among the many pathogen-associated molecular pattern recognition receptors, STING, an endoplasmic reticulum (ER)-associated protein, plays a pivotal role in triggering responses to microbial or cellular cytoplasmic DNA. Herpes simplex virus 1 (HSV-1), a common human pathogen, activates STING signaling, and the resultant induction of type I interferon causes inhibition of virus replication. In this context, we have observed that phosphorylation of Tyr245 of STING by epidermal growth factor receptor kinase is necessary for interferon induction. Here, we report that phosphorylation of Tyr240 by the tyrosine kinase Syk is essential for all signaling activities of STING. Our analysis showed that upon ligand-binding, STING dimerizes and interacts with membrane-bound EGFR, which autophosphorylates and provides the platform for the recruitment of cytoplasmic Syk to the signaling complex and its activation. Activated Syk phosphorylates Tyr240 of STING, followed by phosphorylation of Tyr245 by epidermal growth factor receptor (EGFR). Pharmacological or genetic ablation of Syk activity resulted in an arrest of STING in the ER compartment and a complete block of gene induction. Consequently, in the absence of Syk, HSV-1 could not induce interferon, and it replicated more robustly. IMPORTANCE The innate immune response to virus infection leads to interferon production and inhibition of viral replication. STING, an ER-bound protein, mediates such a response to cytoplasmic cellular or microbial DNA. HSV-1, a DNA virus, activates STING, and it replicates more efficiently in the absence of STING signaling. We demonstrate that phosphorylation of Tyr240 of STING by the protein tyrosine kinase Syk is essential for STING-mediated gene induction. To signal, ligand-activated STING recruits two kinases, Syk and EGFR, which phosphorylate Tyr240 and Tyr245, respectively. The dependence of STING signaling on Syk has broad significance, because STING plays a major role in many microbial, mitochondrial, and autoimmune diseases as well as in cancer development and therapy.

Centrality of Myeloid-Lineage Phagocytes in Particle-Triggered Inflammation and Autoimmunity

Exposure to exogenous particles found as airborne contaminants or endogenous particles that form by crystallization of certain nutrients can activate inflammatory pathways and potentially accelerate autoimmunity onset and progression in genetically predisposed individuals. The first line of innate immunological defense against particles are myeloid-lineage phagocytes, namely macrophages and neutrophils, which recognize/internalize the particles, release inflammatory mediators, undergo programmed/unprogrammed death, and recruit/activate other leukocytes to clear the particles and resolve inflammation. However, immunogenic cell death and release of damage-associated molecules, collectively referred to as "danger signals," coupled with failure to efficiently clear dead/dying cells, can elicit unresolved inflammation, accumulation of self-antigens, and adaptive leukocyte recruitment/activation. Collectively, these events can promote loss of immunological self-tolerance and onset/progression of autoimmunity. This review discusses critical molecular mechanisms by which exogenous particles (i.e., silica, asbestos, carbon nanotubes, titanium dioxide, aluminum-containing salts) and endogenous particles (i.e., monosodium urate, cholesterol crystals, calcium-containing salts) may promote unresolved inflammation and autoimmunity by inducing toxic responses in myeloid-lineage phagocytes with emphases on inflammasome activation and necrotic and programmed cell death pathways. A prototypical example is occupational exposure to respirable crystalline silica, which is etiologically linked to systemic lupus erythematosus (SLE) and other human autoimmune diseases. Importantly, airway instillation of SLE-prone mice with crystalline silica elicits severe pulmonary pathology involving accumulation of particle-laden alveolar macrophages, dying and dead cells, nuclear and cytoplasmic debris, and neutrophilic inflammation that drive cytokine, chemokine, and interferon-regulated gene expression. Silica-induced immunogenic cell death and danger signal release triggers accumulation of T and B cells, along with IgG-secreting plasma cells, indicative of ectopic lymphoid tissue neogenesis, and broad-spectrum autoantibody production in the lung. These events drive early autoimmunity onset and accelerate end-stage autoimmune glomerulonephritis. Intriguingly, dietary supplementation with ω-3 fatty acids have been demonstrated to be an intervention against silica-triggered murine autoimmunity. Taken together, further insight into how particles drive immunogenic cell death and danger signaling in myeloid-lineage phagocytes and how these responses are influenced by the genome will be essential for identification of novel interventions for preventing and treating inflammatory and autoimmune diseases associated with these agents.

Mechanosensitive TRPV4 is required for crystal-induced inflammation

Crystal structures activate innate immune cells, especially macrophages and initiate inflammatory responses. We aimed to understand the role of the mechanosensitive TRPV4 channel in crystal-induced inflammation. Real-time RT-PCR, RNAscope in situ hybridisation, and Trpv4^eGFP mice were used to examine TRPV4 expression and whole-cell patch-clamp recording and live-cell Ca²⁺ imaging were used to study TRPV4 function in mouse synovial macrophages and human peripheral blood mononuclear cells (PBMCs). Both genetic deletion and pharmacological inhibition approaches were used to investigate the role of TRPV4 in NLRP3 inflammasome activation induced by diverse crystals in vitro and in mouse models of crystal-induced pain and inflammation in vivo. TRPV4 was functionally expressed by synovial macrophages and human PBMCs and TRPV4 expression was upregulated by stimulation with monosodium urate (MSU) crystals and in human PBMCs from patients with acute gout flares. MSU crystal-induced gouty arthritis were significantly reduced by either genetic ablation or pharmacological inhibition of TRPV4 function. Mechanistically, TRPV4 mediated the activation of NLRP3 inflammasome by diverse crystalline materials but not non-crystalline NLRP3 inflammasome activators, driving the production of inflammatory cytokine interleukin-1β which elicited TRPV4-dependent inflammatory responses in vivo. Moreover, chemical ablation of the TRPV1-expressing nociceptors significantly attenuated the MSU crystal-induced gouty arthritis. In conclusion, TRPV4 is a common mediator of inflammatory responses induced by diverse crystals through NLRP3 inflammasome activation in macrophages. TRPV4-expressing resident macrophages are critically involved in MSU crystal-induced gouty arthritis. A neuroimmune interaction between the TRPV1-expressing nociceptors and the TRPV4-expressing synovial macrophages contributes to the generation of acute gout flares.

Colchicine in ischemic heart disease: the good, the bad and the ugly

Inflammation is the main pathophysiological process involved in atherosclerotic plaque formation, progression, instability, and healing during the evolution of coronary artery disease (CAD). The use of colchicine, a drug used for decades in non-ischemic cardiovascular (CV) diseases and/or systemic inflammatory conditions, stimulated new perspectives on its potential application in patients with CAD. Previous mechanistic and preclinical studies revealed anti-inflammatory and immunomodulatory effects of colchicine exerted through its principal mechanism of microtubule polymerization inhibition, however, other pleiotropic effects beneficial to the CV system were observed such as inhibition of platelet aggregation and suppression of endothelial proliferation. In randomized double-blinded clinical trials informing our clinical practice, low doses of colchicine were associated with the significant reduction of cardiovascular events in patients with stable CAD and chronic coronary syndrome (CCS) while in patients with a recent acute coronary syndrome (ACS), early initiation of colchicine treatment significantly reduced major adverse CV events (MACE). On the other hand, the safety profile of colchicine and its potential causal relationship to the observed increase in non-CV deaths warrants further investigation. For these reasons, postulates of precision medicine and patient-tailored approach with regards to benefits and harms of colchicine treatment should be employed at all times due to potential toxicity of colchicine as well as the currently unresolved signal of harm concerning non-CV mortality. The main goal of this review is to provide a balanced, critical, and comprehensive evaluation of currently available evidence with respect to colchicine use in the setting of CAD.

Kidney organoid systems for studies of immune-mediated kidney diseases: challenges and opportunities

Acute and chronic kidney diseases are major contributors to morbidity and mortality in the global population. Many nephropathies are considered to be immune-mediated with dysregulated immune responses playing an important role in the pathogenesis. At present, targeted approaches for many kidney diseases are still lacking, as the underlying mechanisms remain insufficiently understood. With the recent development of organoids—a three-dimensional, multicellular culture system, which recapitulates important aspects of human tissues—new opportunities to investigate interactions between renal cells and immune cells in the pathogenesis of kidney diseases arise. To date, kidney organoid systems, which reflect the structure and closer resemble critical aspects of the organ, have been established. Here, we highlight the recent advances in the development of kidney organoid models, including pluripotent stem cell-derived kidney organoids and primary epithelial cell-based tubuloids. The employment and further required advances of current organoid models are discussed to investigate the role of the immune system in renal tissue development, regeneration, and inflammation to identify targets for the development of novel therapeutic approaches of immune-mediated kidney diseases.

MYO1F regulates antifungal immunity by regulating acetylation of microtubules

Each year, the global mortality rates for fungal diseases now exceed those for malaria and breast cancer and are currently comparable to those for tuberculosis and HIV. The limited scope of currently available antifungal drugs is the major factor underlying the observed high mortality rate. Here, we provide evidence that Myosin IF (MYO1F) plays a critical role in the mediating of signaling molecules “trafficking from membrane to cytoplasm,” and this process is essential for the antifungal signaling pathway activation. Moreover, we provide evidence that Sirt2 deacetylase inhibitors promote antifungal immunity and protect mice from lethal Candida albicans infection, which indicates that the Sirt2 could be a good therapeutic target for the antifungal drug development.

Opportunistic fungal infections have become one of the leading causes of death among immunocompromised patients, resulting in an estimated 1.5 million deaths each year worldwide. The molecular mechanisms that promote host defense against fungal infections remain elusive. Here, we find that Myosin IF (MYO1F), an unconventional myosin, promotes the expression of genes that are critical for antifungal innate immune signaling and proinflammatory responses. Mechanistically, MYO1F is required for dectin-induced α-tubulin acetylation, acting as an adaptor that recruits both the adaptor AP2A1 and α-tubulin N-acetyltransferase 1 to α-tubulin; in turn, these events control the membrane-to-cytoplasm trafficking of spleen tyrosine kinase and caspase recruitment domain-containing protein 9. Myo1f-deficient mice are more susceptible than their wild-type counterparts to the lethal sequelae of systemic infection with Candida albicans. Notably, administration of Sirt2 deacetylase inhibitors, namely AGK2, AK-1, or AK-7, significantly increases the dectin-induced expression of proinflammatory genes in mouse bone marrow–derived macrophages and microglia, thereby protecting mice from both systemic and central nervous system C. albicans infections. AGK2 also promotes proinflammatory gene expression in human peripheral blood mononuclear cells after Dectin stimulation. Taken together, our findings describe a key role for MYO1F in promoting antifungal immunity by regulating the acetylation of α-tubulin and microtubules, and our findings suggest that Sirt2 deacetylase inhibitors may be developed as potential drugs for the treatment of fungal infections.

Regulation of crystal induced inflammation: current understandings and clinical implications

Introduction: Accumulation of abnormal crystals in the body, derived from endogenous or exogenous materials can drive a wide spectrum of inflammatory disease states. It is well established that intra-articular deposition of monosodium urate (MSU) and calcium pyrophoshate (CPP) crystals contributes to joint destruction through pro-inflammatory processes.Areas covered: This review will focus on current understanding and recent novelty about the mechanisms and the clinical implications of the inflammation induced by MSU and CPP crystals.Expert opinion: Advances in molecular biology reveal that at the base of the inflammatory cascade, stimulated by MSU or CPP crystals, there are many complex cellular mechanisms mainly involving the NLRP3 inflammasome, the hallmark of autoinflammatory syndromes. The extensive studies carried out through in vitro and in vivo models along with a better clinical definition of the disease has led to an optimized use of existing drugs and the introduction of novel therapeutic strategies. In particular, the identification of IL-1 as the most important target in gout and pseudogout has made it possible to expand the pharmacological indications of anti-IL-1 biological drugs, opening new therapeutic perspectives for patients.

Binding of Macrophage Receptor MARCO, LDL, and LDLR to Disease-Associated Crystalline Structures

Endogenous and exogenous crystalline structures are involved in various pathologies and diseases in humans by inducing sterile inflammation, mechanical stress, or obstruction of excretory organs. The best studied of these diseases is gout, in which crystallization of uric acid in the form of monosodium urate (MSU) mainly in synovial fluid of the joints leads to sterile inflammation. Though some of these diseases have been described for centuries, little is known about if and how the immune system recognizes the associated crystals. Thus, in this study we aimed at identifying possible recognition molecules of MSU using liquid chromatography-mass spectrometry (LC-MS) analysis of MSU-binding serum proteins. Among the strongest binding proteins, we unexpectedly found two transmembrane receptors, namely macrophage receptor with collagenous structure (MARCO) and low-density lipoprotein (LDL) receptor (LDLR). We show that recombinant versions of both human and mouse MARCO directly bind to unopsonized MSU and several other disease-associated crystals. Recombinant LDLR binds many types of crystals mainly when opsonized with serum proteins. We show that this interaction is predominantly mediated by LDL, which we found to bind to all crystalline structures tested except for cholesterol crystals. However, murine macrophages lacking LDLR expression do neither show altered phagocytosis nor interleukin-1β (IL-1β) production in response to opsonized crystals. Binding of LDL to MSU has previously been shown to inhibit the production of reactive oxygen species (ROS) by human neutrophils. We extend these findings and show that LDL inhibits neutrophil ROS production in response to most crystals tested, even cholesterol crystals. The inhibition of neutrophil ROS production only partly correlated with the inhibition of IL-1β production by peripheral blood mononuclear cells (PBMCs): LDL inhibited IL-1β production in response to large MSU crystals, but not small MSU or silica crystals. This may suggest distinct upstream signals for IL-1β production depending on the size or the shape of the crystals. Together, we identify MARCO and LDLR as potential crystal recognition receptors, and show that LDL binding to diverse disease-associated crystalline structures has variable effects on crystal-induced innate immune cell activation.

Atomic Force Microscopy-Based Force Spectroscopy and Multiparametric Imaging of Biomolecular and Cellular Systems

During the last three decades, a series of key technological improvements turned atomic force microscopy (AFM) into a nanoscopic laboratory to directly observe and chemically characterize molecular and cell biological systems under physiological conditions. Here, we review key technological improvements that have established AFM as an analytical tool to observe and quantify native biological systems from the micro- to the nanoscale. Native biological systems include living tissues, cells, and cellular components such as single or complexed proteins, nucleic acids, lipids, or sugars. We showcase the procedures to customize nanoscopic chemical laboratories by functionalizing AFM tips and outline the advantages and limitations in applying different AFM modes to chemically image, sense, and manipulate biosystems at (sub)nanometer spatial and millisecond temporal resolution. We further discuss theoretical approaches to extract the kinetic and thermodynamic parameters of specific biomolecular interactions detected by AFM for single bonds and extend the discussion to multiple bonds. Finally, we highlight the potential of combining AFM with optical microscopy and spectroscopy to address the full complexity of biological systems and to tackle fundamental challenges in life sciences.

Heterogeneity in the initiation, development and function of type 2 immunity

Type 2 immune responses operate under varying conditions in distinct tissue environments and are crucial for protection against helminth infections and for the maintenance of tissue homeostasis. Here we explore how different layers of heterogeneity influence type 2 immunity. Distinct insults, such as allergens or infections, can induce type 2 immune responses through diverse mechanisms, and this can have heterogeneous consequences, ranging from acute or chronic inflammation to deficits in immune regulation and tissue repair. Technological advances have provided new insights into the molecular heterogeneity of different developmental lineages of type 2 immune cells. Genetic and environmental heterogeneity also contributes to the varying magnitude and quality of the type 2 immune response during infection, which is an important determinant of the balance between pathology and disease resolution. Hence, understanding the mechanisms underlying the heterogeneity of type 2 immune responses between individuals and between different tissues will be crucial for treating diseases in which type 2 immunity is an important component.

Inflammasome-Mediated Immunogenicity of Clinical and Experimental Vaccine Adjuvants

In modern vaccines, adjuvants can be sophisticated immunological tools to promote robust and long-lasting protection against prevalent diseases. However, there is an urgent need to improve immunogenicity of vaccines in order to protect mankind from life-threatening diseases such as AIDS, malaria or, most recently, COVID-19. Therefore, it is important to understand the cellular and molecular mechanisms of action of vaccine adjuvants, which generally trigger the innate immune system to enhance signal transition to adaptive immunity, resulting in pathogen-specific protection. Thus, improved understanding of vaccine adjuvant mechanisms may aid in the design of “intelligent” vaccines to provide robust protection from pathogens. Various commonly used clinical adjuvants, such as aluminium salts, saponins or emulsions, have been identified as activators of inflammasomes - multiprotein signalling platforms that drive activation of inflammatory caspases, resulting in secretion of pro-inflammatory cytokines of the IL-1 family. Importantly, these cytokines affect the cellular and humoral arms of adaptive immunity, which indicates that inflammasomes represent a valuable target of vaccine adjuvants. In this review, we highlight the impact of different inflammasomes on vaccine adjuvant-induced immune responses regarding their mechanisms and immunogenicity. In this context, we focus on clinically relevant adjuvants that have been shown to activate the NLRP3 inflammasome and also present various experimental adjuvants that activate the NLRP3-, NLRC4-, AIM2-, pyrin-, or non-canonical inflammasomes and could have the potential to improve future vaccines. Together, we provide a comprehensive overview on vaccine adjuvants that are known, or suggested, to promote immunogenicity through inflammasome-mediated signalling.

Toward a Membrane-Centric Biology

With advancements of modern biophysical tools and superresolution imaging, cell biology is entering a new phase of research with technological power fitting for membrane dynamics analyses. However, our current knowledge base of cellular signaling events is mostly built on a network of protein interactions, which is incompatible with the essential roles of membrane activities in those events. The lack of a theoretical platform is rendering biophysical analyses of membrane biology supplementary to the protein-centric paradigm. We hypothesize a framework of signaling events mediated by lipid dynamics and argue that this is the evolutionarily obligatory developmental path of cellular complexity buildup. In this framework, receptors are the late comers, integrating into the pre-existing membrane based signaling events using their lipid interface as the point of entry. We further suggest that the reason for cell surface receptors to remain silent at the resting state is via the suppression effects of their surrounding lipids. The avoidance of such a suppression, via ligand binding or lipid domain disruption, enables the receptors to autonomously integrate themselves into the preexisting networks of signaling cascades.

Activation of the NLRP3 Inflammasome by Particles from the Echinococcus granulosus Laminated Layer

The interaction of dendritic cells and macrophages with a variety of rigid noncellular particles triggers activation of the NLRP3 inflammasome and consequent secretion of interleukin 1β (IL-1β). Noncellular particles can also be generated in the context of helminth infection, since these large pathogens often shed their outermost structures during growth and/or molting. One such structure is the massive, mucin-based, soft, flexible laminated layer (LL), which protects the larval stages of cestodes of the genus Echinococcus.

The interaction of dendritic cells and macrophages with a variety of rigid noncellular particles triggers activation of the NLRP3 inflammasome and consequent secretion of interleukin 1β (IL-1β). Noncellular particles can also be generated in the context of helminth infection, since these large pathogens often shed their outermost structures during growth and/or molting. One such structure is the massive, mucin-based, soft, flexible laminated layer (LL), which protects the larval stages of cestodes of the genus Echinococcus. We show that particles from the Echinococcus granulosus LL (pLL) trigger NLRP3- and caspase-1-dependent IL-1β in lipopolysaccharide (LPS)-primed mouse bone marrow-derived dendritic cells (BMDC). This response can be elicited by pLL too large for phagocytosis and nonetheless requires actin dynamics, Syk, and phosphatidylinositol 3-kinase (PI3K). These three requirements had already been observed in our previous study on the alteration by pLL of CD86, CD40, IL-10, and IL-12 responses to LPS in BMDC; however, we now show that these alterations are independent of NLRP3 and caspase-1. In other words, an initial interaction with particles requiring actin dynamics, Syk, and PI3K, but not phagocytosis, elicits both NLRP3-dependent and NLRP3-independent responses. Intraperitoneal injection of pLL induced IL-1β, suggesting that contact with LL materials induces IL-1β in the E. granulosus infection setting. Our results extend our understanding of NLRP3 inflammasome activation by noncellular particulate materials both to helminth-derived materials and to flexible/soft materials.

EPS8 regulates an NLRP3 inflammasome-independent caspase-1 activation pathway in monosodium urate crystal-treated RAW264.7 macrophages

Gout is an inflammatory arthritis caused by the phagocytosis of monosodium urate (MSU) crystal deposition in joints. NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) inflammasome-dependent caspase-1 activation is implicated in the processing of interleukin-1β (IL-1β), which is the major effector cytokine in the acute inflammatory response of gout. Mechanisms underlying caspase-1 activation remain unclear. Epidermal growth factor receptor pathway substrate no. 8 (Eps8) is a signal transducer and actin filament organizer that plays a key role in lipopolysaccharide-stimulated phagocytosis in macrophages. Here, RAW264.7 macrophages that have no intact NLRP3 inflammasomes were used to investigate the role of Eps8 in MSU crystal-mediated caspase-1 activation. A kinetic study revealed that the induction of Eps8 expression by MSU crystals occurred before NLRP3, p46/p33 caspase-1, and mature IL-1β in RAW 264.7 cells. In addition, actin cytoskeleton dynamics was required for Eps8 induction and caspase-1 activation in MSU crystal stimulation. Silencing Eps8 had no effect on the basal expression of p46/p33 caspase-1 and NLRP3, but nearly abolished MSU crystal-induced NLRP3 expression and caspase-1 activation. Furthermore, MSU crystals induced Eps8-pro-caspase-1 complex formation and Eps8 formed a stable complex with p33 caspase-1, but not with NLRP3. In summary, our results demonstrated for the first time the importance of Eps8 in MSU crystal-mediated caspase-1 activation without the involvement of NLRP3 inflammasomes.

C-reactive protein (CRP) recognizes uric acid crystals and recruits proteases C1 and MASP1

Gout is caused by crystallization of uric acid in the form of monosodium urate (MSU) crystals, which induce a sterile inflammatory response that is hardly distinguishable from microbe-induced inflammatory responses. It is unclear, if MSU crystals (like microbes) are recognized by specific pattern recognition receptors. To identify possible soluble pattern recognition molecules for MSU crystals, we purified MSU-binding proteins from human body fluids. We identified C-reactive protein (CRP) as a major MSU-binding protein. Binding of CRP was strong enough to specifically deplete CRP from human serum. We found that CRP was required for fixation of complement components C1q, C1r, C1s and MASP1. Thus, we have identified a pattern recognition molecule for MSU crystals that links to the activation of complement. Notably, CRP does not show an even binding to the complete surface of the crystals. It rather binds to edges or distinct faces of the crystals.

Urate crystals trigger B-cell receptor signal transduction and induce B-cell proliferation

Background Urate in its crystal form is a known danger-associated molecular pattern, which after its internalization activates cells of the innate immune system. However, by inducing lipid raft sequestration and clustering of membrane-bound proteins with immunoreceptor tyrosine-based activation motifs, urate crystals can also activate cells of the innate immune system without previous internalization. Also, urate crystals trigger T-cell receptor signal transduction and induce T-cell proliferation. In this study, we evaluated whether urate crystals can also initiate B-cell receptor (BCR) signal transduction and promote B-cell proliferation. Methods B cells were isolated from the blood of 10 individuals and cultured with or without urate at a concentration of 10 mg/dL, at which crystallization occurs. Phosphorylated Igα (CD79A) and c-Myc were assessed by Western blotting and B-cell proliferation with BrdU assay. Results Urate increased the level of phosphorylated Igα, a component of the BCR complex. Phosphorylation of Igα is the very proximal event in BCR signal transduction. Also, urate increased the expression of c-Myc, an essential transcription factor for BCR-induced B-cell proliferation. Finally, urate induces B-cell proliferation. Conclusions Urate crystals trigger BCR signal transduction and induce B-cell proliferation. The clinical significance of urate-induced B-cell activation remains to be elucidated.

A mouse model of MSU-induced acute inflammation in vivo suggests imiquimod-dependent targeting of Il-1β as relevant therapy for gout patients

Rationale: The role of Monosodium Urate (MSU) crystals in gout pathophysiology is well described, as is the major impact of IL-1β in the inflammatory reaction that constitutes the hallmark of the disease. However, despite the discovery of the NLRP3 inflammasome and its role as a Pattern Recognition Receptor linking the detection of a danger signal (MSU) to IL-1β secretion in vitro, the precise mechanisms leading to joint inflammation in gout patients are still poorly understood. Methods: Acute urate crystal inflammation was obtained by subcutaneous injections of MSU crystals in mice. Symptoms were followed by scoring, cytokine quantification by ELISA and western blot, gene expression by RT-qPCR and RNAseq; Magnetic Resonance Imaging was also used to assess inflammation. Results: We provide an extensive clinical, biological and molecular characterization of an acute uratic inflammation mouse model which accurately mimics human gout. We report the efficacy of topical imiquimod treatment and its impact on Interferon-dependent down modulation of Il-1β gene expression in this experimental model. Conclusion: Our work reveals several key features of MSU-dependent inflammation and identifies novel therapeutic opportunities for gout patients.

Innate immunity to malaria-The role of monocytes

Monocytes are innate immune cells essential for host protection against malaria. Upon activation, monocytes function to help reduce parasite burden through phagocytosis, cytokine production, and antigen presentation. However, monocytes have also been implicated in the pathogenesis of severe disease through production of damaging inflammatory cytokines, resulting in systemic inflammation and vascular dysfunction. Understanding the molecular pathways influencing the balance between protection and pathology is critical. In this review, we discuss recent data regarding the role of monocytes in human malaria, including studies of innate sensing of the parasite, immunometabolism, and innate immune training. Knowledge gained from these studies may guide rational development of novel antimalarial therapies and inform vaccine development.

A guide to crystal-related and nano- or microparticle-related tissue responses

Crystals and nano- and microparticles form inside the human body from intrinsic proteins, minerals, or metabolites or enter the body as particulate matter from occupational and environmental sources. Associated tissue injuries and diseases mostly develop from cellular responses to such crystal deposits and include inflammation, cell necrosis, granuloma formation, tissue fibrosis, and stone-related obstruction of excretory organs. But how do crystals and nano- and microparticles trigger these biological processes? Which pathomechanisms are identical across different particle types, sizes, and shapes? In addition, which mechanisms are specific to the atomic or molecular structure of crystals or to specific sizes or shapes? Do specific cellular or molecular mechanisms qualify as target for therapeutic interventions? Here, we provide a guide to approach this diverse and multidisciplinary research domain. We give an overview about the clinical spectrum of crystallopathies, about shared and specific pathomechanisms as a conceptual overview before digging deeper into the specialty field of interest.

Particles from the Echinococcus granulosus Laminated Layer Inhibit CD40 Upregulation in Dendritic Cells by Interfering with Akt Activation

The larval stage of the cestode Echinococcus granulosus causes cystic echinococcosis in humans and livestock. This larva is protected by the millimeter-thick, mucin-based laminated layer (LL), from which materials have to be shed to allow parasite growth. We previously reported that dendritic cells (DCs) respond to microscopic pieces of the mucin gel of the LL (pLL) with unconventional maturation phenotypes, in the absence or presence of Toll-like receptor (TLR) agonists, including lipopolysaccharide (LPS).

The larval stage of the cestode Echinococcus granulosus causes cystic echinococcosis in humans and livestock. This larva is protected by the millimeter-thick, mucin-based laminated layer (LL), from which materials have to be shed to allow parasite growth. We previously reported that dendritic cells (DCs) respond to microscopic pieces of the mucin gel of the LL (pLL) with unconventional maturation phenotypes, in the absence or presence of Toll-like receptor (TLR) agonists, including lipopolysaccharide (LPS). We also reported that the presence of pLL inhibited the activating phosphorylation of the phosphatidylinositol 3-kinase (PI3K) effector Akt induced by granulocyte-macrophage colony-stimulating factor or interleukin-4. We now show that the inhibitory effect of pLL extends to LPS as a PI3K activator, and results in diminished phosphorylation of GSK3 downstream from Akt. Functionally, the inhibition of Akt and GSK3 phosphorylation are linked to the blunted upregulation of CD40, a major feature of the unconventional maturation phenotype. Paradoxically, all aspects of unconventional maturation induced by pLL depend on PI3K class I. Additional components of the phagocytic machinery are needed, but phagocytosis of pLL particles is not required. These observations hint at a DC response mechanism related to receptor-independent mechanisms proposed for certain crystalline and synthetic polymer-based particles; this would fit the previously reported lack of detection of molecular-level motifs necessary of the effects of pLL on DCs. Finally, we report that DCs exposed to pLL are able to condition DCs not exposed to the material so that these cannot upregulate CD40 in full in response to LPS.

The uric acid crystal receptor Clec12A potentiates type I interferon responses

Viral infections are accompanied by the release of pathogen-associated molecular patterns (PAMPs) during the virus life-cycle and damage-associated molecular patterns (DAMPs) from collateral injured cells. The sensing of viral PAMPs by pattern recognition receptors (PRRs) such as Toll-like receptors RIG-I and cGAS is essential in initiating host antiviral responses, especially the type I interferon (IFN-I) response. Here, we report that the DAMP-sensing C-type lectin receptor Clec12A positively regulates the IFN-I response induced by RIG-I, providing a mechanism of cross-talk between PAMP- and DAMP-triggered signaling pathways. Moreover, this modulatory function of Clec12A has functional consequences in both acute and chronic viral infection in mice.

The detection of microbes and damaged host cells by the innate immune system is essential for host defense against infection and tissue homeostasis. However, how distinct positive and negative regulatory signals from immune receptors are integrated to tailor specific responses in complex scenarios remains largely undefined. Clec12A is a myeloid cell-expressed inhibitory C-type lectin receptor that can sense cell death under sterile conditions. Clec12A detects uric acid crystals and limits proinflammatory pathways by counteracting the cell-activating spleen tyrosine kinase (Syk). Here, we surprisingly find that Clec12A additionally amplifies type I IFN (IFN-I) responses in vivo and in vitro. Using retinoic acid-inducible gene I (RIG-I) signaling as a model, we demonstrate that monosodium urate (MSU) crystal sensing by Clec12A enhances cytosolic RNA-induced IFN-I production and the subsequent induction of IFN-I–stimulated genes. Mechanistically, Clec12A engages Src kinase to positively regulate the TBK1-IRF3 signaling module. Consistently, Clec12A-deficient mice exhibit reduced IFN-I responses upon lymphocytic choriomeningitis virus (LCMV) infection, which affects the outcomes of these animals in acute and chronic virus infection models. Thus, our results uncover a previously unrecognized connection between an MSU crystal-sensing receptor and the IFN-I response, and they illustrate how the sensing of extracellular damage-associated molecular patterns (DAMPs) can shape the immune response.

Calcium crystal deposition diseases - beyond gout

The most common types of calcium-containing crystals that are associated with joint and periarticular disorders are calcium pyrophosphate dihydrate (CPP) and basic calcium phosphate (BCP) crystals. Several diverse but difficult-to-treat acute and chronic arthropathies and other clinical syndromes are associated with the deposition of these crystals. Although the pathogenic mechanism of calcium crystal deposition is partially understood, much remains to be investigated, as no drug is available to prevent crystal deposition, permit crystal dissolution or specifically target the pathogenic effects that result in the clinical manifestations. In this Review, the main clinical manifestations of CPP and BCP crystal deposition are discussed, along with the biological effects of these crystals, current therapeutic approaches and future directions in therapy.

Crystallized but not soluble uric acid elicits pro-inflammatory response in short-term whole blood cultures from healthy men

Several epidemiological studies have pointed at serum uric acid (SUA) as an independent risk factor for mortality, diabetes, hypertension, cardiovascular and kidney disease; however, no clear pathogenic pathway is established. Uric acid (UA) crystals show pro-inflammatory properties and can thus create or contribute to the state of chronic low-grade inflammation, a widely accepted pathogenic mechanism in several of the above-mentioned pathologies. On the other hand, soluble uric acid possesses antioxidant properties that might attenuate inflammatory responses. We aimed to explore the net effects of experimentally rising SUA in human whole blood cultures on several mediators of inflammation. Production of TNF-α, IL-1ß, IL-1RA, MCP-1 and IL-8 was assessed upon addition of 200 µM UA, 500 µM UA or monosodium urate (MSU) crystals in the presence or absence of 5 ng/ml lipopolysaccharide (LPS). RT-qPCR and multiplex bead based immunoassay were used to measure mRNA expression and cytokine release at 2 and 4 h of culture, respectively. ¹⁴C labeled UA was used to assess intracellular uptake of UA. We show that crystallized, but not soluble, UA induces production of pro-inflammatory mediators in human whole blood. Soluble UA is internalized in blood cells but does not potentiate or reduce LPS-induced release of cytokines.

Crystalline silica activates the T-cell and the B-cell antigen receptor complexes and induces T-cell and B-cell proliferation

Silicosis is an occupational fibrotic lung disease, which is associated with an increased incidence of autoimmune diseases. The effect of crystalline silica on the immune system is thought to be mediated by the antigen presenting cells. However, the direct effect of silica on T-cells and B-cells has not been evaluated adequately. For this purpose, CD4(+)T-cells and B-cells from 10 healthy individuals were isolated and cultured with or without Min-U-Sil 5. Cell proliferation was assessed with BrdU assay. In cell proliferation experiments, tacrolimus, an inhibitor of the signal transduction derived from the activation of the T-cell or the B-cell antigen receptor (BCR) complex, was also used. The levels of phosphorylated zeta and phosphorylated Igα, indicative of the T-cell and BCR complex activation respectively, and of the transcription factor c-Myc, required for cell proliferation, were assessed by Western blotting. Crystalline silica triggered CD4(+)T-cell and B-cell proliferation, while tacrolimus significantly decreased the silica-induced proliferation in both cell types. Crystalline silica enhanced the level of phosphorylated zeta and phosphorylated Igα in CD4(+)T-cells and B-cells, respectively. In both cell types, treatment with silica increased c-Myc expression. Thus, crystalline silica may induce T-cell and B-cell proliferation by activating T-cell and BCR complexes. It is likely that the direct activation of CD4(+)T-cells and B-cells by silica crystals detected in this study circumvents many self-tolerance check-points and offers a mechanistic explanation for the crystalline silica-induced autoimmune diseases.

Adsorption of Proteins on m-CPPD and Urate Crystals Inhibits Crystal-induced Cell Responses: Study on Albumin-crystal Interaction

The biological effects and cellular activations triggered by monosodium urate (MSU) and calcium pyrophosphate dihydrate (monoclinic: m-CPPD) crystals might be modulated by protein coating on the crystal surface. This study is aimed at: (i) Identifying proteins adsorbed on m-CPPD crystals, and the underlying mechanisms of protein adsorption, and (ii) to understand how protein coating did modulate the inflammatory properties of m-CPPD crystals. The effects of protein coating were assessed in vitro using primary macrophages and THP1 monocytes. Physico-chemical studies on the adsorption of bovine serum albumin (BSA) upon m-CPPD crystals were performed. Adsorption of serum proteins, and BSA on MSU, as well as upon m-CPPD crystals, inhibited their capacity to induce interleukin-1-β secretions, along with a decreased ATP secretion, and a disturbance of mitochondrial membrane depolarization, suggesting an alteration of NLRP3 inflammasome activation. Proteomic analysis identified numerous m-CPPD-associated proteins including hemoglobin, complement, albumin, apolipoproteins and coagulation factors. BSA adsorption on m-CPPD crystals followed a Langmuir-Freundlich isotherm, suggesting that it could modulate m-CPPD crystal-induced cell responses through crystal/cell-membrane interaction. BSA is adsorbed on m-CPPD crystals with weak interactions, confirmed by the preliminary AFM study, but strong interactions of BSA molecules with each other occurred favoring crystal agglomeration, which might contribute to a decrease in the inflammatory properties of m-CPPD crystals. These findings give new insights into the pathogenesis of crystal-related rheumatic diseases and subsequently may open the way for new therapeutic approaches.

Macrophage Phosphoproteome Analysis Reveals MINCLE-dependent and -independent Mycobacterial Cord Factor Signaling

Immune sensing of Mycobacterium tuberculosis relies on recognition by macrophages. Mycobacterial cord factor, trehalose-6,6'-dimycolate (TDM), is the most abundant cell wall glycolipid and binds to the C-type lectin receptor (CLR) MINCLE. To explore the kinase signaling linking the TDM-MINCLE interaction to gene expression, we employed quantitative phosphoproteome analysis. TDM caused upregulation of 6.7% and suppressed 3.8% of the 14,000 phospho-sites identified on 3727 proteins. MINCLE-dependent phosphorylation was observed for canonical players of CLR signaling (e.g. PLCγ, PKCδ), and was enriched for PKCδ and GSK3 kinase motifs. MINCLE-dependent activation of the PI3K-AKT-GSK3 pathway contributed to inflammatory gene expression and required the PI3K regulatory subunit p85α. Unexpectedly, a substantial fraction of TDM-induced phosphorylation was MINCLE-independent, a finding paralleled by transcriptome data. Bioinformatics analysis of both data sets concurred in the requirement for MINCLE for innate immune response pathways and processes. In contrast, MINCLE-independent phosphorylation and transcriptome responses were linked to cell cycle regulation. Collectively, our global analyses show substantial reprogramming of macrophages by TDM and reveal a dichotomy of MINCLE-dependent and -independent signaling linked to distinct biological responses.

Sterile particle-induced inflammation is mediated by macrophages releasing IL-33 through a Bruton's tyrosine kinase-dependent pathway

Initiation of the innate sterile inflammatory response that can develop in response to microparticle exposure is little understood. Here, we report that a potent type 2 immune response associated with the accumulation of neutrophils, eosinophils and alternatively activated (M2) macrophages was observed in response to sterile microparticles similar in size to wear debris associated with prosthetic implants. Although elevations in interleukin-33 (IL-33) and type 2 cytokines occurred independently of caspase-1 inflammasome signalling, the response was dependent on Bruton's tyrosine kinase (BTK). IL-33 was produced by macrophages and BTK-dependent expression of IL-33 by macrophages was sufficient to initiate the type 2 response. Analysis of inflammation in patient periprosthetic tissue also revealed type 2 responses under aseptic conditions in patients undergoing revision surgery. These findings indicate that microparticle-induced sterile inflammation is initiated by macrophages activated to produce IL-33. They further suggest that both BTK and IL-33 may provide therapeutic targets for wear debris-induced periprosthetic inflammation.

Suppression of Syk activation by resveratrol inhibits MSU crystal-induced inflammation in human monocytes

Monosodium urate (MSU) crystals are an endogenous sterile particulate that has been identified as a potent damage-associated molecular pattern (DAMP). In humans, the induction of IL-1β production through MSU-induced NLRP3 inflammasome activation in monocytes/macrophages is responsible for pathogenesis of gouty arthritis. It was recently reported that in a murine model of this disease, resveratrol decreases MSU-induced recurrent attacks of gouty arthritis. Despite its demonstrated anti-inflammatory effects, the mechanisms underlying resveratrol-mediated repression of IL-1β production in MSU-activated monocytes remain poorly understood. Here, we show that resveratrol suppresses secretion of active IL-1β by human primary monocytes stimulated with MSU crystals through suppression of Syk activation. Metabolic labeling and pull-down assays to investigate de novo protein synthesis clearly demonstrated that intracellular pro-IL-1β synthesis is rapidly repressed in monocytes after resveratrol treatment due to decreased phosphorylation of Syk and p38. Resveratrol also inhibited NLRP3 inflammasome activation in MSU-stimulated monocytes by suppressing oligomerization of ASC. Furthermore, resveratrol exerted a beneficial effect by reducing IL-1β production and inhibiting neutrophil recruitment in a mouse model of MSU-mediated peritonitis. Our findings suggest that resveratrol exerts anti-inflammatory effects via post-translational regulation of IL-1β production and, thus, may prove beneficial for the treatment of MSU crystal-mediated sterile inflammation. KEY MESSAGE: Resveratrol has negative effects on pro-IL-1β synthesis through Syk and p38. Resveratrol inhibits oligomerization of ASC. Resveratrol is beneficial in a mouse model of MSU-induced peritonitis.

A phosphatidylinositol 4,5-bisphosphate redistribution-based sensing mechanism initiates a phagocytosis programing

Phagocytosis is one of the earliest cellular functions, developing approximately 2 billion years ago. Although FcR-based phagocytic signaling is well-studied, how it originated from ancient phagocytosis is unknown. Lipid redistribution upregulates a phagocytic program recapitulating FcR-based phagocytosis with complete dependence on Src family kinases, Syk, and phosphoinositide 3-kinases (PI3K). Here we show that in phagocytes, an atypical ITAM sequence in the ancient membrane anchor protein Moesin transduces signal without receptor activation. Plasma membrane deformation created by solid structure binding generates phosphatidylinositol 4,5-bisphosphate (PIP2) accumulation at the contact site, which binds the Moesin FERM domain and relocalizes Syk to the membrane via the ITAM motif. Phylogenic analysis traces this signaling using PI3K and Syk to 0.8 billion years ago, earlier than immune receptor signaling. The proposed general model of solid structure phagocytosis implies a preexisting lipid redistribution-based activation platform collecting intracellular signaling components for the emergence of immune receptors.

Inflammatory Potential of Four Different Phases of Calcium Pyrophosphate Relies on NF-κB Activation and MAPK Pathways

Background: Calcium pyrophosphate (CPP) microcrystal deposition is associated with wide clinical phenotypes, including acute and chronic arthritis, that are interleukin 1β (IL-1β)-driven. Two CPP microcrystals, namely monoclinic and triclinic CPP dihydrates (m- and t-CPPD), have been identified in human tissues in different proportions according to clinical features. m-CPP tetrahydrate beta (m-CPPTβ) and amorphous CPP (a-CPP) phases are considered as m- and t-CPPD crystal precursors in vitro.

Objectives: We aimed to decipher the inflammatory properties of the three crystalline phases and one amorphous CPP phase and the intracellular pathways involved.

Methods: The four synthesized CPP phases and monosodium urate crystals (MSU, as a control) were used in vitro to stimulate the human monocytic leukemia THP-1 cell line or bone marrow-derived macrophages (BMDM) isolated from WT or NLRP3 KO mice. The gene expression of pro- and anti-inflammatory cytokines was evaluated by quantitative PCR; IL-1β, IL-6 and IL-8 production by ELISA; and mitogen-activated protein kinase (MAPK) activation by immunoblot analysis. NF-κB activation was determined in THP-1 cells containing a reporter plasmid. In vivo, the inflammatory potential of CPP phases was assessed with the murine air pouch model via cell analysis and production of IL-1β and CXCL1 in the exudate. The role of NF-κB was determined by a pharmacological approach, both in vivo and in vitro.

Results:In vitro, IL-1β production induced by m- and t-CPPD and m-CPPTβ crystals was NLRP3 inflammasome dependent. m-CPPD crystals were the most inflammatory by inducing a faster and higher production and gene expression of IL-1β, IL-6, and IL-8 than t-CPPD, m-CPPTβ and MSU crystals. The a-CPP phase did not show an inflammatory property. Accordingly, m-CPPD crystals led to stronger activation of NF-κB, p38, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) MAPKs. Inhibition of NF-κB completely abrogated IL-1β and IL-8 synthesis and secretion induced by all CPP crystals. Also, inhibition of JNK and ERK1/2 MAPKs decreased both IL-1β secretion and NF-κB activation induced by CPP crystals. In vivo, IL-1β and CXCL1 production and neutrophil infiltration induced by m-CPPD crystals were greatly decreased by NF-κB inhibitor treatment.

Conclusion: Our results suggest that the inflammatory potential of different CPP crystals relies on their ability to activate the MAPK-dependent NF-κB pathway. Studies are ongoing to investigate the underlying mechanisms.

Biomaterial-assisted targeted modulation of immune cells in cancer treatment

The past decade has witnessed the accelerating development of immunotherapies for cancer treatment. Immune checkpoint blockade therapies and chimeric antigen receptor (CAR)-T cell therapies have demonstrated clinical efficacy against a variety of cancers. However, issues including life-threatening off-target side effects, long processing times, limited patient responses and high cost still limit the clinical utility of cancer immunotherapies. Biomaterial carriers of these therapies, though, enable one to troubleshoot the delivery issues, amplify immunomodulatory effects, integrate the synergistic effect of different molecules and, more importantly, home and manipulate immune cells in vivo. In this Review, we will analyse thus-far developed immunomaterials for targeted modulation of dendritic cells, T cells, tumour-associated macrophages, myeloid-derived suppressor cells, B cells and natural killer cells, and summarize the promises and challenges of cell-targeted immunomodulation for cancer treatment.

The Role of Inhibitory Receptors in Monosodium Urate Crystal-Induced Inflammation

Inhibitory receptors are key regulators of immune responses. Aberrant inhibitory receptor function can either lead to an exacerbated or defective immune response. Several regulatory mechanisms involved in the inflammatory reaction induced by monosodium urate crystals (MSU) during acute gout have been identified. One of these mechanisms involves inhibitory receptors. The engagement of the inhibitory receptors Clec12A and SIRL-1 has opposing effects on the responses of neutrophils to MSU. We review the general concepts of inhibitory receptor biology and apply them to understand and compare the modulation of MSU-induced inflammation by Clec12A and SIRL-1. We also discuss gaps in our knowledge of the contribution of inhibitory receptors to the pathogenesis of gout and propose future avenues of research.