Bruton's tyrosine kinase is essential for NLRP3 inflammasome activation and contributes to ischaemic brain injury

Protective effects of melatonin on the white matter damage of neonatal rats by regulating NLRP3 inflammasome activity

OBJECTIVE

The aim of the study was to investigate the protective effects and relevant mechanisms of melatonin on the white matter damage (WMD) caused by endotoxin and ischemic hypoxia in neonatal rats.

METHODS

Seventy-two female neonatal rats (postnatal day 3) were randomly divided into the sham, melatonin-treated, and control groups (n = 24 for each group). The periventricular white matter was collected to evaluate the WMD and apoptosis. In addition, the reactive oxygen species (ROS) level was measured. The expression levels of nucleotide-binding domain-like receptor protein 3 (NLRP3), interleukin (IL)-1β, IL-18, pink1, parkin, Toll-like receptor (TLR)-4, and nuclear factor (NF)-κB were detected.

RESULTS

Hematoxylin and eosin and terminal-deoxynucleoitidyl transferase mediated nick end labeling staining showed that the WMD, as well as cell degeneration, necrosis, and apoptosis in the control group, were more severe than those in the melatonin-treated group. Endotoxin and ischemic hypoxia upregulated the expression of NLRP3 and downstream inflammatory factors such as IL-1β and IL-18, which could be reversed by melatonin treatment. Melatonin increased mitochondrial autophagy marker (pink1 and parkin) expression in the white matter and reduced ROS production. Moreover, melatonin-reduced TLR4 and NF-κB expression.

CONCLUSIONS

Melatonin can inhibit the hyperactivity of NLRP3 inflammasomes by enhancing mitochondrial autophagy and inhibiting TLR4/NF-κB pathway activity. Thus, melatonin may be a promising treatment for alleviating the WMD caused by endotoxin and ischemic hypoxia in neonatal rats.

Ibrutinib does not prevent kidney fibrosis following acute and chronic injury

Recent studies suggested that ibrutinib, a Bruton tyrosine kinase (BTK) inhibitor, developed for the treatment of chronic lymphocytic leukemia, may prevent NLRP3 inflammasome activation in macrophages, IL-1β secretion and subsequent development of inflammation and organ fibrosis. The role of NLRP3 has been underlined in the various causes of acute kidney injury (AKI), a pathology characterized by high morbimortality and risk of transition toward chronic kidney disease (CKD). We therefore hypothesized that the BTK-inhibitor ibrutinib could be a candidate drug for AKI treatment. Here, we observed in both an AKI model (glycerol-induced rhabdomyolysis) and a model of rapidly progressive kidney fibrosis (unilateral ureteral obstruction), that ibrutinib did not prevent inflammatory cell recruitment in the kidney and fibrosis. Moreover, ibrutinib pre-exposure led to high mortality rate owing to severer rhabdomyolysis and AKI. In vitro, ibrutinib potentiated or had no effect on the secretion of IL-1β by monocytes exposed to uromodulin or myoglobin, two danger-associated molecule patterns proteins involved in the AKI to CKD transition. According to these results, ibrutinib should not be considered a candidate drug for patients developing AKI.

Aberrant NLRP3 Inflammasome Activation Ignites the Fire of Inflammation in Neuromuscular Diseases

Inflammasomes are molecular hubs that are assembled and activated by a host in response to various microbial and non-microbial stimuli and play a pivotal role in maintaining tissue homeostasis. The NLRP3 is a highly promiscuous inflammasome that is activated by a wide variety of sterile triggers, including misfolded protein aggregates, and drives chronic inflammation via caspase-1-mediated proteolytic cleavage and secretion of proinflammatory cytokines, interleukin-1β and interleukin-18. These cytokines further amplify inflammatory responses by activating various signaling cascades, leading to the recruitment of immune cells and overproduction of proinflammatory cytokines and chemokines, resulting in a vicious cycle of chronic inflammation and tissue damage. Neuromuscular diseases are a heterogeneous group of muscle disorders that involve injury or dysfunction of peripheral nerves, neuromuscular junctions and muscles. A growing body of evidence suggests that dysregulation, impairment or aberrant NLRP3 inflammasome signaling leads to the initiation and exacerbation of pathological processes associated with neuromuscular diseases. In this review, we summarize the available knowledge about the NLRP3 inflammasome in neuromuscular diseases that affect the peripheral nervous system and amyotrophic lateral sclerosis, which affects the central nervous system. In addition, we also examine whether therapeutic targeting of the NLRP3 inflammasome components is a viable approach to alleviating the detrimental phenotype of neuromuscular diseases and improving clinical outcomes.

Targeting Bruton's Tyrosine Kinase in Inflammatory and Autoimmune Pathologies

Bruton's tyrosine kinase (BTK) was discovered due to its importance in B cell development, and it has a critical role in signal transduction downstream of the B cell receptor (BCR). Targeting of BTK with small molecule inhibitors has proven to be efficacious in several B cell malignancies. Interestingly, recent studies reveal increased BTK protein expression in circulating resting B cells of patients with systemic autoimmune disease (AID) compared with healthy controls. Moreover, BTK phosphorylation following BCR stimulation in vitro was enhanced. In addition to its role in BCR signaling, BTK is involved in many other pathways, including pattern recognition, Fc, and chemokine receptor signaling in B cells and myeloid cells. This broad involvement in several immunological pathways provides a rationale for the targeting of BTK in the context of inflammatory and systemic AID. Accordingly, numerous in vitro and in vivo preclinical studies support the potential of BTK targeting in these conditions. Efficacy of BTK inhibitors in various inflammatory and AID has been demonstrated or is currently evaluated in clinical trials. In addition, very recent reports suggest that BTK inhibition may be effective as immunosuppressive therapy to diminish pulmonary hyperinflammation in coronavirus disease 2019 (COVID-19). Here, we review BTK's function in key signaling pathways in B cells and myeloid cells. Further, we discuss recent advances in targeting BTK in inflammatory and autoimmune pathologies.

The Role of NLRP3 Inflammasome in Cerebrovascular Diseases Pathology and Possible Therapeutic Targets

Cerebrovascular diseases are pathological conditions involving impaired blood flow in the brain, primarily including ischaemic stroke, intracranial haemorrhage, and subarachnoid haemorrhage. The nucleotide-binding and oligomerisation (NOD) domain-like receptor (NLR) family pyrin domain (PYD)-containing 3 (NLRP3) inflammasome is a protein complex and a vital component of the immune system. Emerging evidence has indicated that the NLRP3 inflammasome plays an important role in cerebrovascular diseases. The function of the NLRP3 inflammasome in the pathogenesis of cerebrovascular diseases remains an interesting field of research. In this review, we first summarised the pathological mechanism of cerebrovascular diseases and the pathological mechanism of the NLRP3 inflammasome in aggravating atherosclerosis and cerebrovascular diseases. Second, we outlined signalling pathways through which the NLRP3 inflammasome participates in aggravating or mitigating cerebrovascular diseases. Reactive oxygen species (ROS)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), ROS/thioredoxin-interacting protein (TXNIP) and purinergic receptor-7 (P2X7R) signalling pathways can activate the NLRP3 inflammasome; activation of the NLRP3 inflammasome can aggravate cerebrovascular diseases by mediating apoptosis and pyroptosis. Autophagy/mitochondrial autophagy, nuclear factor E2-related factor-2 (Nrf2), interferon (IFN)-β, sirtuin (SIRT), and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) reportedly alleviate cerebrovascular diseases by inhibiting NLRP3 inflammasome activation. Finally, we explored specific inhibitors of the NLRP3 inflammasome based on the two-step activation of the NLRP3 inflammasome, which can be developed as new drugs to treat cerebrovascular diseases.

Inflammation-Induced Tumorigenesis and Metastasis

Inflammation, especially chronic inflammation, plays a pivotal role in tumorigenesis and metastasis through various mechanisms and is now recognized as a hallmark of cancer and an attractive therapeutic target in cancer. In this review, we discuss recent advances in molecular mechanisms of how inflammation promotes tumorigenesis and metastasis and suppresses anti-tumor immunity in various types of solid tumors, including esophageal, gastric, colorectal, liver, and pancreatic cancer as well as hematopoietic malignancies.

Sinomenine activation of Nrf2 signaling prevents inflammation and cerebral injury in a mouse model of ischemic stroke

Sinomenine (SINO), which is used clinically to treat rheumatoid arthritis and neuralgia, is derived from the root and stems of Sinomenium acutum. SINO has been reported to exert analgesic, sedative and anti-inflammatory effects, and provides a protective role against shock and organ damage. Studies have suggested that SINO primarily exerts it anti-inflammatory function by inhibiting NF-κB signaling. There is also evidence to indicate that SINO may regulate inflammation Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling. The present study aimed to investigate whether the anti-inflammatory and cerebral protective effects of SINO were induced through Nrf2 both in vitro and in vivo. The results revealed that SINO significantly upregulated Nrf2 protein expression levels, increased Nrf2 nuclear translocation and the upregulated the protein expression levels of downstream factors. The treatment of a middle cerebral artery occlusion model mice with SINO effectively reduced cerebral damage and inflammation, and restored the balance in cerebral oxidative stress. In addition, SINO treatment also promoted Nrf2-dependent microglia M1/M2 polarization and inhibited the phosphorylation of IκBα as well as NF-κB nuclear translocation. This revealed an important upstream event that contributed to its anti-inflammatory and cerebral tissue protective effects. In conclusion, the findings of the present study identified a novel pathway through which SINO may exert its anti-inflammatory and cerebral protective functions, and provided a molecular basis for the potential applications of SINO in the treatment of cerebral inflammatory disorders.

Btk knockout attenuates the liver inflammation in STZ-induced diabetic mice by suppressing NLRP3 inflammasome activation

Btk has pro-inflammatory role through a variety of signaling pathways. NLRP3 inflammasome plays a central role in liver inflammation for mediating the secretion of pro-inflammatory mediators. However, it is still unknown whether Btk could regulate NLRP3 inflammasome activation in diabetic liver. In this study, we used Btk knockout mice to establish the diabetic model by STZ. We found that Btk knockout could alleviate diabetic liver injury. This protection was due to reduced liver inflammation rather than lipid metabolism. Moreover, we found that macrophage infiltration and pro-inflammatory mediators were both significantly increased in diabetic mice liver. However, Btk deletion could reduce the activation of macrophage and secretion of pro-inflammatory cytokine, and reduced the liver inflammation through suppressing NLRP3 inflammasome activation. In conclusion, our study demonstrated that Btk knockout could significantly attenuate liver inflammation in diabetic mice by down-regulating NLRP3 inflammasome activation. Our finding has a broad prospect and provide a new idea for the treatment of diabetic liver injury.

An update on the regulatory mechanisms of NLRP3 inflammasome activation

The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is a multiprotein complex involved in the release of mature interleukin-1β and triggering of pyroptosis, which is of paramount importance in a variety of physiological and pathological conditions. Over the past decade, considerable advances have been made in elucidating the molecular mechanisms underlying the priming/licensing (Signal 1) and assembly (Signal 2) involved in NLRP3 inflammasome activation. Recently, a number of studies have indicated that the priming/licensing step is regulated by complicated mechanisms at both the transcriptional and posttranslational levels. In this review, we discuss the current understanding of the mechanistic details of NLRP3 inflammasome activation with a particular emphasis on protein-protein interactions, posttranslational modifications, and spatiotemporal regulation of the NLRP3 inflammasome machinery. We also present a detailed summary of multiple positive and/or negative regulatory pathways providing upstream signals that culminate in NLRP3 inflammasome complex assembly. A better understanding of the molecular mechanisms underlying NLRP3 inflammasome activation will provide opportunities for the development of methods for the prevention and treatment of NLRP3 inflammasome-related diseases.

Bruton's tyrosine kinase: an emerging targeted therapy in myeloid cells within the tumor microenvironment

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase belonging to the Tec family of kinases. The role of BTK in B cell receptor signaling is well defined and is known to play a key role in the proliferation and survival of malignant B cells. Moreover, BTK has been found to be expressed in cells of the myeloid lineage. BTK has been shown to contribute to a variety of cellular pathways in myeloid cells including signaling in the NLRP3 inflammasome, receptor activation of nuclear factor-κβ and inflammation, chemokine receptor activation affecting migration, and phagocytosis. Myeloid cells are crucial components of the tumor microenvironment and suppressive myeloid cells contribute to cancer progression, highlighting a potential role for BTK inhibition in the treatment of malignancy. The increased interest in BTK inhibition in cancer has resulted in many preclinical studies that are testing the efficacy of using single-agent BTK inhibitors. Moreover, the ability of tumor cells to develop resistance to single-agent checkpoint inhibitors has resulted in clinical studies utilizing BTK inhibitors in combination with these agents to improve clinical responses. Furthermore, BTK regulates the immune response in microbial and viral infections through B cells and myeloid cells such as monocytes and macrophages. In this review, we describe the role that BTK plays in supporting suppressive myeloid cells, including myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM), while also discussing the anticancer effects of BTK inhibition and briefly describe the role of BTK signaling and BTK inhibition in microbial and viral infections.

NLRP3 inflammasome and bruton tyrosine kinase inhibition interferes with upregulated platelet aggregation and in vitro thrombus formation in sickle cell mice

The nucleotide-binding domain leucine-rich repeat containing protein 3 (NLRP3) inflammasome is a critical inflammatory mechanism identified in platelets, which controls platelet activation and aggregation. We have recently shown that the platelet NLRP3 inflammasome is upregulated in sickle cell disease (SCD), which is mediated by Bruton tyrosine kinase (BTK). Here, we investigated the effect of pharmacological inhibition of NLRP3 and BTK on platelet aggregation and the formation of in vitro thrombi in Townes SCD mice. Mice were injected for 4 weeks with the NLRP3 inhibitor MCC950, the BTK inhibitor ibrutinib or vehicle control. NLRP3 activity, as monitored by caspase-1 activation, was upregulated in platelets from SCD mice, which was dependent on BTK. Large areas of platelet aggregates detected in the liver of SCD mice were decreased when mice were treated with MCC950 or ibrutinib. Moreover, platelet aggregation and in vitro thrombus formation were upregulated in SCD mice and were inhibited when mice were subjected to pharmacological inhibition of NLRP3 and BTK. Targeting the NLRP3 inflammasome might be a novel approach for antiplatelet therapy in SCD.

Gualou Guizhi Granule Protects against OGD/R-Induced Injury by Inhibiting Cell Pyroptosis via the PI3K/Akt Signaling Pathway

Pyroptosis is a proinflammatory form of regulated cell death that plays an important role in ischemic stroke. Gualou Guizhi granule (GLGZG) is a classic prescription that has been shown to exert neuroprotective effects against cerebral ischemia reperfusion injury. In the present study, we examined the involvement of pyroptosis and its associated mechanism in protecting nerve function. Methods. Primary neurons were exposed to oxygen-glucose deprivation and reperfusion (OGD/R) conditions in the presence or absence of GLGZG. Cellular viability was measured by the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazoliumbromide (MTT) assay. The number of apoptoic cells was detected by NeuN and NSE protein expression. The expression levels of the pyroptosis markers, namely, NOD-like receptor family pyrin domain-containing 3 (NLRP3), apoptosis-associated speck-like protein containing a CARD (ASC), caspase-1, interleukin-18 (IL-18), and IL-1β were determined by quantitative real-time PCR analysis, western blot, and ELISA analyses as appropriate. Moreover, the expression levels of the PI3K/Akt pathway key proteins were determined by quantitative real-time PCR analysis and western blot assays. To determine the PI3K/Akt pathway involvement in GLGZG-mediated neuroprotection, the PI3K inhibitor LY294002 (LY, 10 μM) was added. The expression levels of NeuN, Akt, and p-Akt were evaluated. Results. It was found that GLGZG could inhibit OGD/R-induced cell apoptosis, increase neuronal cell viability, decrease the production of IL-18 and IL-1β, and downregulate the expression levels of pyroptosis markers (NLRP3, ASC, and caspase-1). Furthermore, GLGZG could modulate the PI3K/Akt signaling pathway. Pharmacological inhibition of the PI3K pathway not only abrogated the effects of GLGZG on Akt but also neutralized its prosurvival and antipyroptotic actions. Conclusions. The findings indicated that GLGZG pretreatment effectively reduced OGD/R-induced injury by inhibiting cell pyroptosis and activating the PI3K/Akt pathway. These data provide important evidence for the therapeutic applications of this regimen in ischemic stroke.

Ibrutinib modulates Aβ/tau pathology, neuroinflammation, and cognitive function in mouse models of Alzheimer's disease

We previously demonstrated that ibrutinib modulates LPS‐induced neuroinflammation in vitro and in vivo, but its effects on the pathology of Alzheimer's disease (AD) and cognitive function have not been investigated. Here, we investigated the effects of ibrutinib in two mouse models of AD. In 5xFAD mice, ibrutinib injection significantly reduced Aβ plaque levels by promoting the non‐amyloidogenic pathway of APP cleavage, decreased Aβ‐induced neuroinflammatory responses, and significantly downregulated phosphorylation of tau by reducing levels of phosphorylated cyclin‐dependent kinase‐5 (p‐CDK5). Importantly, tau‐mediated neuroinflammation and tau phosphorylation were also alleviated by ibrutinib injection in PS19 mice. In 5xFAD mice, ibrutinib improved long‐term memory and dendritic spine number, whereas in PS19 mice, ibrutinib did not alter short‐ and long‐term memory but promoted dendritic spinogenesis. Interestingly, the induction of dendritic spinogenesis by ibrutinib was dependent on the phosphorylation of phosphoinositide 3‐kinase (PI3K). Overall, our results suggest that ibrutinib modulates AD‐associated pathology and cognitive function and may be a potential therapy for AD.

Targeting the NLRP3 Inflammasome via BTK

The NLRP3 inflammasome represents a critical inflammatory machinery driving pathology in many acute (e. g., myocardial infarction or stroke) and chronic (Alzheimer's disease, atherosclerosis) human disorders linked to the activity of IL-1 cytokines. Although the therapeutic potential of NLRP3 is undisputed, currently no clinically approved therapies exist to target the NLRP3 inflammasome directly. The recent discovery of BTK as a direct and positive regulator of the NLRP3 inflammasome has, however, raised the intriguing possibility of targeting the NLRP3 inflammasome via existing or future BTK inhibitors. Here, I review the mechanistic basis for this notion and discuss the molecular and cellular role of BTK in the inflammasome process. Specific attention will be given to cell-type dependent characteristics and differences that may be relevant for targeting approaches. Furthermore, I review recent (pre-)clinical evidence for effects of BTK inhibitors on NLRP3 activity and highlight and discuss open questions and future research directions. Collectively, the concept of targeting BTK to target NLRP3-dependent inflammation will be explored comprehensively at the molecular, cellular and therapeutic levels.

Inflammasome activation controlled by the interplay between post-translational modifications: emerging drug target opportunities

Controlling the activation of the NLRP3 inflammasome by post-translational modifications (PTMs) of critical protein subunits has emerged as a key determinant in inflammatory processes as well as in pathophysiology. In this review, we put into context the kinases, ubiquitin processing and other PTM enzymes that modify NLRP3, ASC/PYCARD and caspase-1, leading to inflammasome regulation, activation and signal termination. Potential target therapeutic entry points for a number of inflammatory diseases focussed on PTM enzyme readers, writers and erasers, leading to the regulation of inflammasome function, are discussed. Video Abstract.

Predicting Multi-Interfacial Binding Mechanisms of NLRP3 and ASC Pyrin Domains in Inflammasome Activation

NLRP3-PYD inflammasome activates an inflammatory pathway in response to a wide variety of cell damage or infections. Dysregulated NLRP3 inflammatory signaling has many chronic inflammatory and autoimmune disorders. NLRP3 and ASC have a PYD, a superfamily member of the Death Domain, which plays a key role in inflammatory assembly. The ASC interacts with NLRP3 through a homotypic PYD and recruits the procaspase-1 through a homotypic caspase recruitment domain interaction. Here, we used several computational approaches to reveal the interactions of the NLRP3 and ASC PYD domains that lead to the activation of the inflammasome complex. We have characterized ASC and NLRP3-PYD intermolecular interactions by protein-protein docking, and further molecular dynamics (MD) simulations were conducted to evaluate the stability of NLRP3/ASC-PYD complex. Subsequently, we have identified several residues that stabilize the NLRP3/ASC-PYD complex in different faces (i.e., Face-1 to Face-4). The research framework offers new insights into the molecular mechanisms of inflammasome and apoptosis signaling as well as the ease of the drug discovery process.

Recent Progress on the Discovery of NLRP3 Inhibitors and their Therapeutic Potential

BACKGROUND

Inflammation is the body's immune system's fast coordinating response to irritants caused by pathogens, external injuries, and chemical or radiation effects. The nucleotidebinding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is a critical component of the innate immune system. The dysfunction of NLRP3 inflammasome contributes to various pathogeneses of complex diseases, such as uncontrolled infection, autoimmune diseases, neurodegenerative diseases, and metabolic disorders. This review describes recent progress on the discovery of NLRP3 inflammasome inhibitors and their therapeutic potential.

METHODS

Based on the mechanism of NLRP3 activation, several types of NLRP3 inhibitors are described and summarized according to their origins, structures, bioactivity, and mechanism of action. Structure-Activity Relationship (SAR) is also listed for different scaffolds, as well as effective pharmacophore.

RESULTS

Over one-hundred papers were included in the review. The development of NLRP3 inhibitors has been described from the earliest glyburide in 2001 to the latest progress in 2019. Several series of inhibitors have been categorized, such as JC-series based on glyburide and BC-series based on 2APB. Many other small molecules such as NLRP3 inhibitors are also listed. SAR, application in related therapeutic models, and five different action mechanisms are described.

CONCLUSION

The findings of this review confirmed the importance of developing NLRP3 inflammasome inhibitors. Various NLRP3 inhibitors have been discovered as effective therapeutic treatments for multiple diseases, such as type II diabetes, experimental autoimmune encephalomyelitis, stressrelated mood disorders, etc. The development of a full range of NLRP3 inflammasome inhibitors is still at its foundational phase. We are looking forward to the identification of inhibitory agents that provide the most potent therapeutic strategies and efficiently treat NLRP3 inflammasome-related inflammatory diseases.

Different Roles of Mitochondria in Cell Death and Inflammation: Focusing on Mitochondrial Quality Control in Ischemic Stroke and Reperfusion

Mitochondrial dysfunctions are among the main hallmarks of several brain diseases, including ischemic stroke. An insufficient supply of oxygen and glucose in brain cells, primarily neurons, triggers a cascade of events in which mitochondria are the leading characters. Mitochondrial calcium overload, reactive oxygen species (ROS) overproduction, mitochondrial permeability transition pore (mPTP) opening, and damage-associated molecular pattern (DAMP) release place mitochondria in the center of an intricate series of chance interactions. Depending on the degree to which mitochondria are affected, they promote different pathways, ranging from inflammatory response pathways to cell death pathways. In this review, we will explore the principal mitochondrial molecular mechanisms compromised during ischemic and reperfusion injury, and we will delineate potential neuroprotective strategies targeting mitochondrial dysfunction and mitochondrial homeostasis.

Regulation of the NLRP3 Inflammasome by Post-Translational Modifications and Small Molecules

Inflammation is a host protection mechanism that eliminates invasive pathogens from the body. However, chronic inflammation, which occurs repeatedly and continuously over a long period, can directly damage tissues and cause various inflammatory and autoimmune diseases. Pattern recognition receptors (PRRs) respond to exogenous infectious agents called pathogen-associated molecular patterns and endogenous danger signals called danger-associated molecular patterns. Among PRRs, recent advancements in studies of the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome have established its significant contribution to the pathology of various inflammatory diseases, including metabolic disorders, immune diseases, cardiovascular diseases, and cancer. The regulation of NLRP3 activation is now considered to be important for the development of potential therapeutic strategies. To this end, there is a need to elucidate the regulatory mechanism of NLRP3 inflammasome activation by multiple signaling pathways, post-translational modifications, and cellular organelles. In this review, we discuss the intracellular signaling events, post-translational modifications, small molecules, and phytochemicals participating in the regulation of NLRP3 inflammasome activation. Understanding how intracellular events and small molecule inhibitors regulate NLRP3 inflammasome activation will provide crucial information for elucidating the associated host defense mechanism and the development of efficient therapeutic strategies for chronic diseases.

The NLRP3 inflammasome drives inflammation in ischemia/reperfusion injury after transient middle cerebral artery occlusion in mice

PURPOSE

Cerebral ischemia induces a profound neuro-inflammatory response, but the underlying molecular mechanisms are poorly understood. Inflammasomes (NLRP1, NLRP3, NLRC4, AIM2) are intracellular multi-protein complexes which can induce sets of pro-inflammatory cyto- and chemokines, and thereby guide inflammation. We, here, assessed the functional role of NLRP3 in ischemia/reperfusion (I/R) injury in a mouse model of transient cerebral ischemia.

METHODS

Ischemic stroke was induced in C57Bl/6 mice by 60 min transient middle cerebral artery occlusion (tMCAO) and 3, 7 or 23 h of reperfusion, a paradigm of I/R injury. The expression patterns of inflammasomes in the ischemic hemispheres were evaluated by semiquantitative real-time PCR and Western Blot analysis accompanied by protein localization using immunocytochemistry. Finally, animals were treated with the inflammasome inhibitors Sulforaphane, Genipin, MCC950 or vehicle, directly before or upon recanalization after tMCAO. Stroke outcome was assessed, including infarct size and functional deficits, local inflammatory response, neuronal survival as well as blood-brain barrier function on day 1 after tMCAO.

RESULTS

After tMCAO the relative gene expression levels of NLRP3 increased 20-30x within 1 day in the ischemic hemisphere which translated into an increased expression of NLRP3 in neurons. Accordingly, the gene expression levels of the NLRP3-modulator, Bruton's Tyrosine Kinase (BTK), and the NLRP3-inducible cytokine IL-1β significantly rose. Lesser or non-significant changes were seen for the other inflammasomes. Application of inflammasome inhibitors covering all inflammasomes or specifically NLRP3 significantly reduced infarct volumes when given before or after tMCAO and was accompanied by clear evidence for reduced activation of caspase 1. This stroke attenuating effect coincided with less immune cell infiltration in the ischemic hemisphere and preservation of the blood-brain barrier integrity.

CONCLUSIONS

Our data show that induction of the NLRP3 inflammasome in neurons drives neuroinflammation in acute ischemic stroke. Early blockade of NLRP3 protects from I/R injury by mitigating inflammation and stabilizing the blood-brain barrier.

Pomelo peel oil alleviates cerebral NLRP3 inflammasome activation in a cardiopulmonary resuscitation rat model

The NLR family pyrin domain-containing 3 (NLRP3) inflammasome, which is composed of NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC) and pro-caspase-1 protein complexes, is activated by the reactive oxygen species (ROS) that are associated with ischemia-reperfusion (I/R) and are involved in brain damage. Pomelo peel oil (PPO) exhibits antioxidant activity. However, it is unclear whether PPO is able to attenuate NLRP3 inflammasome-induced inflammation and pyroptosis. Healthy male Sprague-Dawley rats were subjected to 7 min of cardiac arrest via trans-esophageal electrical stimulation, followed by cardiopulmonary resuscitation (CPR). The rats were then treated with PPO prior to reperfusion for 24 h. Hematoxylin and eosin staining was used to evaluate brain tissue and cell damage. In the brain tissues, reactive oxygen species (ROS) were assayed, immunofluorescence was used to analyze the expression of NLRP3 and western blotting was performed to determine the expression levels of neuroenolase (NSE), NF-κB, interleukin-1β (IL-1β), gasdermin D (GSDMD) and the NLRP3 inflammasome. Treatment of the rats with PPO significantly decreased the pathological damage of the brain tissue and reduced the expression of NSE, production of ROS and secretion of NF-κB, NLRP3, IL-1β and GSDMD. In conclusion, these results demonstrate the ability of PPO to protect the brain against I/R injury in rats after CPR by a mechanism involving inhibition of the inflammation and pyroptosis mediated by NLRP3 inflammasome activation.

Observations on the use of Bruton's tyrosine kinase inhibitors in SAR-CoV-2 and cancer

Bruton's tyrosine kinase (BTK) inhibitors, drugs utilized in cancer, are being repurposed for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) (COVID-19). Recently, BTK inhibitors acalabrutinib and ibrutinib have been found to protect against pulmonary injury in a small group of patients infected with SARS-CoV-2. The high levels of pro-inflammatory cytokines found in the circulation of COVID-19 patients with severe lung disease suggest the involvement of the innate immune system in this process. Understanding the potential mechanism of action of BTK inhibition in SARS-CoV-2 is clearly of importance to determine how acalabrutinib, ibrutinib and possibly other BTK inhibitors may provide protection against lung injury.

Genetics and Pathogenetic Role of Inflammasomes in Philadelphia Negative Chronic Myeloproliferative Neoplasms: A Narrative Review

The last decade has been very important for the quantity of preclinical information obtained regarding chronic myeloproliferative neoplasms (MPNs) and the following will be dedicated to the translational implications of the new biological acquisitions. The overcoming of the mechanistic model of clonal evolution and the entry of chronic inflammation and dysimmunity into the new model are the elements on which to base a part of future therapeutic strategies. The innate immune system plays a major role in this context. Protagonists of the initiation and regulation of many pathological aspects, from cytokine storms to fibrosis, the NLRP3 and AIM2 inflammasomes guide and condition the natural history of the disease. For this reason, MPNs share many biological and clinical aspects with non-neoplastic diseases, such as autoimmune disorders. Finally, cardiovascular risk and disturbances in iron metabolism and myelopoiesis are also closely linked to the role of inflammasomes. Although targeted therapies are already being tested, an increase in knowledge on the subject is desirable and potentially translates into better care for patients with MPNs.

Enhanced Bruton's tyrosine kinase activity in the kidney of patients with IgA nephropathy

Purpose

Bruton’s tyrosine kinase (BTK) is a vital biological molecule that contributes to immune regulation. Previous studies have showed that BTK can be detected in patients with lupus nephritis and rheumatoid arthritis. However, the role of BTK in IgA nephropathy (IgAN) has not yet been elucidated. The purpose of this research was to investigate the role of BTK activation in macrophages in IgAN.

Methods

Peripheral blood and renal tissue samples were collected from 63 patients with IgAN, and peritumoral normal tissues were collected from 20 patients after surgical resection of renal tumor for use as control. Additionally, 20 healthy volunteers were recruited as control. The levels of BTK, CD68, phosphorylated BTK (pBTK), phosphorylated NF-κB (p-NF-κB p65), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and monocyte chemotactic protein (MCP)-1 were measured by immunohistochemistry (IHC), real-time polymerase chain reaction (RT-PCR), western blotting, and enzyme-linked immunosorbent assay (ELISA).

Results

Compared to peritumoral normal tissues, the expression levels of CD68 and BTK were significantly increased in IgAN group (p < 0.001) and the differences between M0 and M1, E0 and E1, S0 and S1, T0 and T1-2, C0 and C1-2 were statistically significant in the updated Oxford Classification (p < 0.05). Also, CD68 and BTK were positively correlated with Katafuchi semi-quantitative glomerular and tubulointerstitial scores (r = 0.580, 0.637 and 0.442, 0.489, respectively, p < 0.05). The expression of BTK was significantly higher in C3b- and C4d-positive renal tissues of patients with IgAN (p < 0.05). In addition, BTK was positively correlated with 24-h urine protein, serum creatinine levels (r = 0.456 and 0.453, respectively, p < 0.001), and negatively correlated with serum albumin (r = 0.357, p < 0.05). The intensity of expression of pBTK and p-NF-κB p65 was observably increased in renal tissues and monocytes of patients with IgAN compared to the control group. The results of IHC, RT-PCR, and ELISA indicated that the levels of TNF-ɑ, IL-1β, and MCP-1 were markedly increased in the IgAN group (p < 0.05).

Conclusion

The results of this study indicate that activation of BTK in macrophages may play an important role in promoting the progression of renal inflammation in IgAN.

INT-777 attenuates NLRP3-ASC inflammasome-mediated neuroinflammation via TGR5/cAMP/PKA signaling pathway after subarachnoid hemorrhage in rats

BACKGROUND

Inflammasome-mediated neuroinflammation plays an important role in the pathogenesis of early brain injury (EBI) following subarachnoid hemorrhage (SAH). The activation of the TGR5 receptor has been shown to be neuroprotective in a variety of neurological diseases. This study aimed to investigate the effects of the specific synthetic TGR5 agonist, INT-777, in attenuating NLRP3-ASC inflammasome activation and reducing neuroinflammation after SAH.

METHODS

One hundred and eighty-four male Sprague Dawley rats were used. SAH was induced by the endovascular perforation. INT-777 was administered intranasally at 1 h after SAH induction. To elucidate the signaling pathway involved in the effect of INT-777 on inflammasome activation during EBI, TGR5 knockout CRISPR and PKA inhibitor H89 were administered intracerebroventricularly and intraperitoneally at 48 h and 1 h before SAH. The SAH grade, short- and long-term neurobehavioral assessments, brain water content, western blot, immunofluorescence staining, and Nissl staining were performed.

RESULTS

The expressions of endogenous TGR5, p-PKA, and NLRP3-ASC inflammasome were increased after SAH. INT-777 administration significantly decreased NLRP3-ASC inflammasome activation in microglia, reduced brain edema and neuroinflammation, leading to improved short-term neurobehavioral functions at 24 h after SAH. The administration of TGR5 CRISPR or PKA inhibitor (H89) abolished the anti-inflammation effects of INT-777, on NLRP3-ASC inflammasome, pro-inflammatory cytokines (IL-6, IL-1β, and TNF-a), and neutrophil infiltration at 24 h after SAH. Moreover, early administration of INT-777 attenuated neuronal degeneration in hippocampus on 28 d after SAH.

CONCLUSIONS

INT-777 attenuated NLRP3-ASC inflammasome-dependent neuroinflammation in the EBI after SAH, partially via TGR5/cAMP/PKA signaling pathway. Early administration of INT-777 may serve as a potential therapeutic strategy for EBI management in the setting of SAH.

Immunopathology of Hyperinflammation in COVID-19

The rapid spread of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), has resulted in an unprecedented public health crisis worldwide. Recent studies indicate that a hyperinflammatory syndrome induced by SARS-CoV-2 contributes to disease severity and mortality in COVID-19. In this review, an overview of the pathophysiology underlying the hyperinflammatory syndrome in severe COVID-19 is provided. The current evidence suggests that the hyperinflammatory syndrome results from a dysregulated host innate immune response. The gross and microscopic pathologic findings as well as the alterations in the cytokine milieu, macrophages/monocytes, natural killer cells, T cells, and neutrophils in severe COVID-19 are summarized. The data highlighted include the potential therapeutic approaches undergoing investigation to modulate the immune response and abrogate lung injury in severe COVID-19.

Targeting the pathways of regulated necrosis: a potential strategy for alleviation of cardio-cerebrovascular injury

Apoptosis, necrosis and autophagy-dependent cell death are the three major types of cell death. Traditionally, necrosis is thought as a passive and unregulated form of cell death. However, certain necrosis can also occur in a highly regulated manner, referring to regulated necrosis. Depending on the signaling pathways, regulated necrosis can be further classified as necroptosis, pyroptosis, ferroptosis, parthanatos and CypD-mediated necrosis. Numerous studies have reported that regulated necrosis contributes to the progression of multiple injury-relevant diseases. For example, necroptosis contributes to the development of myocardial infarction, atherosclerosis, heart failure and stroke; pyroptosis is involved in the progression of myocardial or cerebral infarction, atherosclerosis and diabetic cardiomyopathy; while ferroptosis, parthanatos and CypD-mediated necrosis participate in the pathological process of myocardial and/or cerebral ischemia/reperfusion injury. Thereby, targeting the pathways of regulated necrosis pharmacologically or genetically could be an efficient strategy for reducing cardio-cerebrovascular injury. Further study needs to focus on the crosstalk and interplay among different types of regulated necrosis. Pharmacological intervention of two or more types of regulated necrosis simultaneously may have advantages in clinic to treat injury-relevant diseases.

Bruton's tyrosine kinase inhibition attenuates oxidative stress in systemic immune cells and renal compartment during sepsis-induced acute kidney injury in mice

Sepsis is a life-threatening condition which affects multiple organs including the kidney. Sepsis-induced acute kidney injury (AKI) is a major health burden throughout the globe. Pathogenesis of sepsis-induced AKI is complex; however, it involves both innate and adaptive immune cells such as B cells, T cells, dendritic cells (DCs), macrophages, and neutrophils. Bruton's tyrosine kinase (BTK) is reportedly involved in inflammatory and oxidative signaling in different immune cells, however its contribution with respect to sepsis-induced AKI has not been delineated. This study attempted to investigate the role of BTK and its inhibition on oxidizing enzymes NADPH oxidase (NOX-2) and inducible nitric oxide synthase (iNOS) in DCs, neutrophils, and B cells during AKI. Our data reveal that BTK is activated in DCs, neutrophils, and B cells which causes an increase in AKI associated biochemical markers such as serum creatinine/blood urea nitrogen, renal myeloperoxidase activity, and histopathological disturbances in renal tubular structures. Activation of BTK causes upregulation of NOX-2/iNOS/nitrotyrosine in these immune cells and kidney. Treatment with BTK inhibitor, Ibrutinib causes attenuation in AKI associated dysfunction in biochemical parameters (serum creatinine/blood urea nitrogen, renal myeloperoxidase activity) and oxidative stress in immune cells and kidney (iNOS/NOX2/lipid peroxides/nitrotyrosine/protein carbonyls). In summary, the current investigation reveals a compelling role of BTK signaling in sepsis-induced AKI which is evident from amelioration of AKI associated renal dysfunction after its inhibition.

TP53-induced glycolysis and apoptosis regulator alleviates hypoxia/ischemia-induced microglial pyroptosis and ischemic brain damage

Our previous studies have demonstrated that TP53-induced glycolysis and apoptosis regulator (TIGAR) can protect neurons after cerebral ischemia/reperfusion. However, the role of TIGAR in neonatal hypoxic-ischemic brain damage (HIBD) remains unknown. In the present study, 7-day-old Sprague-Dawley rat models of HIBD were established by permanent occlusion of the left common carotid artery followed by 2-hour hypoxia. At 6 days before induction of HIBD, a lentiviral vector containing short hairpin RNA of either TIGAR or gasdermin D (LV-sh_TIGAR or LV-sh_GSDMD) was injected into the left lateral ventricle and striatum. Highly aggressively proliferating immortalized (HAPI) microglial cell models of in vitro HIBD were established by 2-hour oxygen/glucose deprivation followed by 24-hour reoxygenation. Three days before in vitro HIBD induction, HAPI microglial cells were transfected with LV-sh_TIGAR or LV-sh_GSDMD. Our results showed that TIGAR expression was increased in the neonatal rat cortex after HIBD and in HAPI microglial cells after oxygen/glucose deprivation/reoxygenation. Lentivirus-mediated TIGAR knockdown in rats markedly worsened pyroptosis and brain damage after hypoxia/ischemia in vivo and in vitro. Application of exogenous nicotinamide adenine dinucleotide phosphate (NADPH) increased the NADPH level and the glutathione/oxidized glutathione ratio and decreased reactive oxygen species levels in HAPI microglial cells after oxygen/glucose deprivation/reoxygenation. Additionally, exogenous NADPH blocked the effects of TIGAR knockdown in neonatal HIBD in vivo and in vitro. These findings show that TIGAR can inhibit microglial pyroptosis and play a protective role in neonatal HIBD. The study was approved by the Animal Ethics Committee of Soochow University of China (approval No. 2017LW003) in 2017.

Bruton tyrosine kinase deficiency augments NLRP3 inflammasome activation and causes IL-1β-mediated colitis

Bruton tyrosine kinase (BTK) is present in a wide variety of cells and may thus have important non-B cell functions. Here, we explored the function of this kinase in macrophages with studies of its regulation of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome. We found that bone marrow-derived macrophages (BMDMs) from BTK-deficient mice or monocytes from patients with X-linked agammaglobulinemia (XLA) exhibited increased NLRP3 inflammasome activity; this was also the case for BMDMs exposed to low doses of BTK inhibitors such as ibrutinib and for monocytes from patients with chronic lymphocytic leukemia being treated with ibrutinib. In mechanistic studies, we found that BTK bound to NLRP3 during the priming phase of inflammasome activation and, in doing so, inhibited LPS- and nigericin-induced assembly of the NLRP3 inflammasome during the activation phase of inflammasome activation. This inhibitory effect was caused by BTK inhibition of protein phosphatase 2A-mediated (PP2A-mediated) dephosphorylation of Ser5 in the pyrin domain of NLRP3. Finally, we show that BTK-deficient mice were subject to severe experimental colitis and that such colitis was normalized by administration of anti-IL-β or anakinra, an inhibitor of IL-1β signaling. Together, these studies strongly suggest that BTK functions as a physiologic inhibitor of NLRP3 inflammasome activation and explain why patients with XLA are prone to develop Crohn's disease.

TSPO Ligands PK11195 and Midazolam Reduce NLRP3 Inflammasome Activation and Proinflammatory Cytokine Release in BV-2 Cells

Neuroinflammation related to microglial activation plays an important role in neurodegenerative diseases. Translocator protein 18 kDa (TSPO), a biomarker of reactive gliosis, its ligands can reduce neuroinflammation and can be used to treat neurodegenerative diseases. Therefore, we explored whether TSPO ligands exert an anti-inflammatory effect by affecting the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome, thereby inhibiting the release of inflammatory cytokines in microglial cells. In the present study, BV-2 cells were exposed to lipopolysaccharide (LPS) for 6 h to induce an inflammatory response. We found that the levels of reactive oxygen species (ROS), NLRP3 inflammasome, interleukin-1β (IL-1β), and interleukin-18 (IL-18) were significantly increased. However, pretreatment with TSPO ligands inhibited BV-2 microglial and NLRP3 inflammasome activation and significantly reduced the levels of ROS, IL-1β, and IL-18. Furthermore, a combination of LPS and ATP was used to activate the NLRP3 inflammasome. Both pretreatment and post-treatment with TSPO ligand can downregulate the activation of NLRP3 inflammasome and IL-1β expression. Finally, we found that TSPO was involved in the regulation of NLRP3 inflammasome with TSPO ligands treatment in TSPO knockdown BV2 cells. Collectively, these results indicate that TSPO ligands are promising targets to control microglial reactivity and neuroinflammatory diseases.

Strategies for Targeting the NLRP3 Inflammasome in the Clinical and Preclinical Space

Inhibiting the NLRP3 inflammasome mediates inflammation in an extensive number of preclinical models. As excitement in this field has grown, several companies have recently initiated testing of direct NLRP3 inhibitors in the clinic. At the same time, the NLRP3 inflammasome is part of a larger pro-inflammatory pathway, whose modulation is also being explored. Multiple targets in this pathway are already impinged upon by molecules that have been through clinical trials. These data, informed by the growing mechanistic understanding of the NLRP3 inflammasome in the preclinical space, provide a rich backdrop to assess the current state of the field. Here we explore attempts to inhibit the NLRP3 inflammasome in light of clinical and preclinical data around efficacy and safety.

An overview of disease models for NLRP3 inflammasome over-activation

Introduction: Inflammatory reactions, including those mediated by the NLRP3 inflammasome, maintain the body's homeostasis by removing pathogens, repairing damaged tissues, and adapting to stressed environments. However, uncontrolled activation of the NLRP3 inflammasome tends to cause various diseases using different mechanisms. Recently, many inhibitors of the NLRP3 inflammasome have been reported and many are being developed. In order to assess their efficacy, specificity, and mechanism of action, the screening process of inhibitors requires various types of cell and animal models of NLRP3-associated diseases.Areas covered: In the following review, the authors give an overview of the cell and animal models that have been used during the research and development of various inhibitors of the NLRP3 inflammasome.Expert opinion: There are many NLRP3 inflammasome inhibitors, but most of the inhibitors have poor specificity and often influence other inflammatory pathways. The potential risk for cross-reaction is high; therefore, the development of highly specific inhibitors is essential. The selection of appropriate cell and animal models, and combined use of different models for the evaluation of these inhibitors can help to clarify the target specificity and therapeutic effects, which is beneficial for the development and application of drugs targeting the NLRP3 inflammasome.

Recent insights into the regulatory networks of NLRP3 inflammasome activation

The NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome is a fascinating cellular machinery endowed with the capacity for rapid proteolytic processing of the pro-inflammatory cytokine IL-1β and the cell death effector gasdermin D (GSDMD). Although its activity is essential to fight infection and support tissue homeostasis, the inflammasome complex, which consists of the danger sensor NLRP3, the adaptor apoptosis-associated speck-like protein containing a CARD (ASC; also known as PYCARD), caspase-1 and probably other regulatory proteins, also bears considerable potential for detrimental inflammation, as observed in human conditions such as gout, heart attack, stroke and Alzheimer's disease. Thus, multi-layered regulatory networks are required to ensure the fine balance between rapid responsiveness versus erroneous activation (sufficient and temporally restricted versus excessive and chronic activity) of the inflammasome. These involve multiple activation, secretion and cell death pathways, as well as modulation of the subcellular localization of NLRP3, and its structure and activity, owing to post-translational modification by other cellular proteins. Here, we discuss the exciting progress that has recently been made in deciphering the regulation of the NLRP3 inflammasome. Additionally, we highlight open questions and describe areas of research that warrant further exploration to obtain a more comprehensive molecular and cellular understanding of the NLRP3 inflammasome.

Leukotriene B4 licenses inflammasome activation to enhance skin host defense

The initial production of inflammatory mediators dictates host defense as well as tissue injury. Inflammasome activation is a constituent of the inflammatory response by recognizing pathogen and host-derived products and eliciting the production of IL-1β and IL-18 in addition to inducing a type of inflammatory cell death termed "pyroptosis." Leukotriene B4 (LTB4) is a lipid mediator produced quickly (seconds to minutes) by phagocytes and induces chemotaxis, increases cytokine/chemokine production, and enhances antimicrobial effector functions. Whether LTB4 directly activates the inflammasome remains to be determined. Our data show that endogenously produced LTB4 is required for the expression of pro-IL-1β and enhances inflammasome assembly in vivo and in vitro. Furthermore, LTB4-mediated Bruton's tyrosine kinase (BTK) activation is required for inflammasome assembly in vivo as well for IL-1β-enhanced skin host defense. Together, these data unveil a new role for LTB4 in enhancing the expression and assembly of inflammasome components and suggest that while blocking LTB4 actions could be a promising therapeutic strategy to prevent inflammasome-mediated diseases, exogenous LTB4 can be used as an adjuvant to boost inflammasome-dependent host defense.

Host-pathogen interaction in COVID-19: Pathogenesis, potential therapeutics and vaccination strategies

The current coronavirus pandemic, COVID-19, is the third outbreak of disease caused by the coronavirus family, after Severe Acute Respiratory Syndrome and Middle East Respiratory Syndrome. It is an acute infectious disease caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). This severe disease is characterised by acute respiratory distress syndrome, septic shock, metabolic acidosis, coagulation dysfunction, and multiple organ dysfunction syndromes. Currently, no drugs or vaccines exist against the disease and the only course of treatment is symptom management involving mechanical ventilation, immune suppressants, and repurposed drugs. The severe form of the disease has a relatively high mortality rate. The last six months have seen an explosion of information related to the host receptors, virus transmission, virus structure-function relationships, pathophysiology, co-morbidities, immune response, treatment and the most promising vaccines. This review takes a critically comprehensive look at various aspects of the host-pathogen interaction in COVID-19. We examine the genomic aspects of SARS-CoV-2, modulation of innate and adaptive immunity, complement-triggered microangiopathy, and host transmission modalities. We also examine its pathophysiological impact during pregnancy, in addition to emphasizing various gaps in our knowledge. The lessons learnt from various clinical trials involving repurposed drugs have been summarised. We also highlight the rationale and likely success of the most promising vaccine candidates.

ADP/P2Y1 aggravates inflammatory bowel disease through ERK5-mediated NLRP3 inflammasome activation

Inflammasomes are essential for inflammation and pathogen elimination in response to microbial infection and endogenous danger signals. However, the mechanism of inflammasome activation by endogenous danger signals mediated posttranslational modification and the connection between inflammasomes and inflammatory diseases remains elusive. In this study, we found that ADP was highly released from injured colonic tissue as a danger signal during inflammatory bowel disease. Consequently, extracellular ADP activated the NLRP3 inflammasome through P2Y₁ receptor-mediated calcium signaling, which led to the maturation and secretion of IL-1β and further aggravation of experimental colitis. Genetic ablation or pharmacological blockade of the P2Y₁ receptor significantly ameliorated DSS-induced colitis and endotoxic shock through reducing NLRP3 inflammasome activation. Moreover, ERK5-mediated tyrosine phosphorylation of ASC was essential for activation of the NLRP3 inflammasome. Thus, our study provides a novel theoretical basis for posttranslational modification of ASC in NLRP3 inflammasome activation and revealed that ADP/P2Y₁ is a potential drug target for inflammatory bowel disease.

Bruton's Tyrosine Kinase Inhibitor Attenuates Warm Hepatic Ischemia/Reperfusion Injury via Modulation of the NLR Family Pyrin Domain Containing 3 Inflammasome

The NLR family pyrin domain containing 3 (NLRP3) inflammasome is a widely studied inflammasome that plays a critical role in inflammatory responses. Many triggers, including microbial pathogens (ie, bacteria and viruses) and other signals (ie, reactive oxygen species, adenosine triphosphate, urate, silicon, and asbestos), can stimulate the NLRP3 inflammasome. Liver ischemia/reperfusion (I/R) injury is a common pathologic process during liver surgery and shock and can induce severe liver damage. Although its pathogenesis is still unclear, oxidative stress and overproduction of the inflammatory response are likely to contribute to I/R injury. The NLRP3 inflammasome is activated during the I/R process, resulting in further recruitment and activation of caspase-1. Activated caspase-1 cleaves the pro-forms of interleukin-1β and interleukin-18 and results in their maturation, triggering a proinflammatory cytokine cascade and causing liver damage. Bruton's tyrosine kinase is a critical molecule involved in diverse cellular pathways, such as proliferation, apoptosis, inflammation, and angiogenesis. Intrahepatic Bruton's tyrosine kinase is mainly expressed on Kupffer cells and sinusoidal endothelial cells, and the inflammasome is activated in Kupffer cells. Our study found that inhibition of Bruton's tyrosine kinase effectively attenuated liver I/R injury by suppressing activation of the NLRP3 inflammasome in Kupffer cells.

Contradictory Effects of NLRP3 Inflammasome Regulatory Mechanisms in Colitis

The inflammasome is an intracellular molecular complex, which is mainly involved in innate immunity. Inflammasomes are formed in response to danger signals, associated with infection and injury, and mainly regulate the secretion of interleukin-1β and interleukin-18. Inflammasome dysregulation is known to be associated with various diseases and conditions, and its regulatory mechanisms have become of great interest in recent years. In the colon, inflammasomes have been reported to be associated with autophagy and the microbiota, and their dysregulation contributes to colitis and. However, the detailed role of inflammasomes in inflammatory bowel disease is still under debate because the mechanisms that regulate the inflammasome are complex and the inflammasome components and cytokines show seemingly contradictory multiple effects. Herein, we comprehensively review the literature on inflammasome functioning in the colon and describe the complex interactions of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome components with inflammatory cytokines, autophagy, and the microbiota in experimental colitis models and patients with inflammatory bowel disease.

NLRP3 Inflammasome: The Stormy Link Between Obesity and COVID-19

Several countries around the world have faced an important obesity challenge for the past four decades as the result of an obesogenic environment. This disease has a multifactorial origin and it is associated with multiple comorbidities including type 2 diabetes, hypertension, osteoarthritis, metabolic syndrome, cancer, and dyslipidemia. With regard to dyslipidemia, hypertriglyceridemia is a well-known activator of the NLRP3 inflammasome, triggering adipokines and cytokines secretion which in addition induce a systemic inflammatory state that provides an adequate scenario for infections, particularly those mediated by viruses such as HIV, H1N1 influenza, and SARS-CoV-2. The SARS-CoV-2 infection causes the coronavirus disease 2019 (COVID-19) and it is responsible for the pandemic that we are currently living. COVID-19 causes an aggressive immune response known as cytokine release syndrome or cytokine storm that causes multiorgan failure and in most cases leads to death. In the present work, we aimed to review the molecular mechanisms by which obesity-associated systemic inflammation could cause a more severe clinical presentation of COVID-19. The SARS-CoV-2 infection could potentiate or accelerate the pre-existing systemic inflammatory state of individuals with obesity, via the NLRP3 inflammasome activation and the release of pro-inflammatory cytokines from cells trough Gasdermin-pores commonly found in cell death by pyroptosis.

X-Linked Immunodeficient Mice With No Functional Bruton's Tyrosine Kinase Are Protected From Sepsis-Induced Multiple Organ Failure

We previously reported the Bruton's tyrosine kinase (BTK) inhibitors ibrutinib and acalabrutinib improve outcomes in a mouse model of polymicrobial sepsis. Now we show that genetic deficiency of the BTK gene alone in Xid mice confers protection against cardiac, renal, and liver injury in polymicrobial sepsis and reduces hyperimmune stimulation ("cytokine storm") induced by an overwhelming bacterial infection. Protection is due in part to enhanced bacterial phagocytosis in vivo, changes in lipid metabolism and decreased activation of NF-κB and the NLRP3 inflammasome. The inactivation of BTK leads to reduced innate immune cell recruitment and a phenotypic switch from M1 to M2 macrophages, aiding in the resolution of sepsis. We have also found that BTK expression in humans is increased in the blood of septic non-survivors, while lower expression is associated with survival from sepsis. Importantly no further reduction in organ damage, cytokine production, or changes in plasma metabolites is seen in Xid mice treated with the BTK inhibitor ibrutinib, demonstrating that the protective effects of BTK inhibitors in polymicrobial sepsis are mediated solely by inhibition of BTK and not by off-target effects of this class of drugs.

The NLRP3-inflammasome as a sensor of organelle dysfunction

Diverse pathogen- and damage-associated stresses drive inflammation via activation of the multimolecular NLRP3-inflammasome complex. How the effects of diverse stimuli are integrated by the cell to regulate NLRP3 has been the subject of intense research, and yet an accepted unifying hypothesis for the control of NLRP3 remains elusive. Here, we review the literature on the effects of NLRP3-activating stimuli on subcellular organelles and conclude that a shared feature of NLRP3-activating stresses is an organelle dysfunction. In particular, we propose that the endosome may be more important than previously recognized as a signal-integrating hub for NLRP3 activation in response to many stimuli and may also link to the dysfunction of other organelles. In addition, NLRP3-inflammasome-activating stimuli trigger diverse posttranslational modifications of NLRP3 that are important in controlling its activation. Future research should focus on how organelles respond to specific NLRP3-activating stimuli, and how this relates to posttranslational modifications, to delineate the organellar control of NLRP3.

Bruton's Tyrosine Kinase Inhibition Promotes Myelin Repair

Background:

Microglia are the resident macrophages of the central nervous system (CNS). In multiple sclerosis (MS) and related experimental models, microglia have either a pro-inflammatory or a pro-regenerative/pro-remyelinating function. Inhibition of Bruton’s tyrosine kinase (BTK), a member of the Tec family of kinases, has been shown to block differentiation of pro-inflammatory macrophages in response to granulocyte–macrophage colony-stimulating factor in vitro. However, the role of BTK in the CNS is unknown.

Methods:

Our aim was to investigate the effect of BTK inhibition on myelin repair in ex vivo and in vivo experimental models of demyelination and remyelination. The remyelination effect of a BTK inhibitor (BTKi; BTKi-1) was then investigated in LPC-induced demyelinated cerebellar organotypic slice cultures and metronidazole-induced demyelinated Xenopus MBP-GFP-NTR transgenic tadpoles.

Results:

Cellular detection of BTK and its activated form BTK-phospho-Y223 (p-BTK) was determined by immunohistochemistry in organotypic cerebellar slice cultures, before and after lysophosphatidylcholine (LPC)-induced demyelination. A low BTK signal detected by immunolabeling under normal conditions in cerebellar slices was in sharp contrast to an 8.5-fold increase in the number of BTK-positive cells observed in LPC-demyelinated slice cultures. Under both conditions, approximately 75% of cells expressing BTK and p-BTK were microglia and 25% were astrocytes. Compared with spontaneous recovery, treatment of demyelinated slice cultures and MTZ-demyelinated transgenic tadpoles with BTKi resulted in at least a 1.7-fold improvement of remyelination.

Conclusion:

Our data demonstrate that BTK inhibition is a promising therapeutic strategy for myelin repair.

Hematopoietic Cell Kinase (HCK) Is Essential for NLRP3 Inflammasome Activation and Lipopolysaccharide-Induced Inflammatory Response In Vivo

Activation of the NLRP3 inflammasome results in caspase 1 cleavage, which subsequently leads to IL-1β and IL-18 secretion, as well as pyroptosis, and aberrant activation of the inflammasome is involved in several diseases such as type 2 diabetes, atherosclerosis, multiple sclerosis, Parkinson's disease, and Alzheimer's disease. NLRP3 activity is regulated by various kinases. Genetic and pharmacological inhibition of the hematopoietic cell kinase (HCK), a member of the Src family of non-receptor tyrosine kinases (NRTKs) primarily expressed in myeloid cells, has previously been shown to ameliorate inflammation, indicating that it may be involved in the regulation of microglia function. However, the underlying mechanism is not known. Hence, in this study, we aimed to investigate the role of HCK in NLRP3 inflammasome activation. We demonstrated that HCK silencing inhibited NLRP3 inflammasome activation. Furthermore, the HCK-specific inhibitor, A419259, attenuated the release of IL-1β and caspase 1(P20) from the macrophages and microglia and reduced the formation of the apoptosis-associated speck-like protein with a CARD domain (ASC) oligomer. We also observed that HCK binds to full length NLRP3 and its NBD(NACHT) and LRR domains, but not to the PYD domain. In vivo, the HCK inhibitor attenuated the LPS-induced inflammatory response in the liver of LPS-challenged mice. Collectively, these results suggested that HCK plays a critical role in NLRP3 inflammasome activation. Our results will enhance current understanding regarding the effectiveness of HCK inhibitors for treating acute inflammatory diseases.

Tomentosin inhibit cerebral ischemia/reperfusion induced inflammatory response via TLR4/ NLRP3 signalling pathway - in vivo and in vitro studies

Stoke is a global threat, leading to 50 % of deaths worldwide and it causes permanent disability to about 5 million individuals globally each year. In this study, we assessed the potency of tomentosin to inhibit the neuroinflammation in in vivo and in vitro models. The Sprague Dawley rats were pretreated with 25 mg/kg bodyweight (b.wt) and 50 mg/kg b.wt of tomentosin for seven days followed by induction of cerebral ischemic reperfusion. The brain edema and cerebral infractions were analyzed. The levels of antioxidants and the interleukins were measured by standard methods. The NLRP3 signaling proteins expression was evaluated using qPCR analysis. In vitro studies were performed in SH-SY5Y-cells pretreated with tomentosin and subjected to OGD-R treatment. Our results depicts tomentosin scavenges the free radicals, enhances antioxidant system, inhibits the NLRP3 signaling. In vitro results substantiates with in vivo results. To conclude, our in vivo and in vitro results confirm tomentosin may be potent alternative for existing antistroke drugs.

Simultaneous targeting of mitochondria and monocytes enhances neuroprotection against ischemia-reperfusion injury

Ischemia-reperfusion injury impairs the efficacy of reperfusion therapy after ischemic stroke. Cyclophilin D (CypD)-mediated openings of mitochondrial permeability transition pore (mPTP) and subsequent monocyte-mediated inflammation are considered as major mechanisms of reperfusion injury. However, no medical therapies are currently available. Therefore, we have tested a hypothesis that simultaneous targeting of mPTP and inflammation confers substantial neuroprotection after cerebral ischemia-reperfusion. To address this point, we prepared CypD knockout mice, C-C chemokine receptor 2 (CCR2) knockout mice and CypD/CCR2 double knockout mice. These mice were subjected to 60 min transient cerebral ischemia by occluding middle cerebral arteries. Neurological deficits evaluated 3 days after reperfusion were significantly attenuated in CypD/CCR2 double knockout mice as compared to wild-type mice and other single knockout mice. Then, we have prepared polymeric nanoparticles containing cyclosporine A (CsA-NPs) and pitavastatin (Pitava-NPs), targeting mPTP opening and inflammation, respectively. Simultaneous administration of CsA-NP and Pitava-NP at the time of reperfusion also decreased infarct size and attenuated neurological deficits as compared to control nanoparticles and single administration of CsA-NPs or Pitava-NPs. These results indicate that simultaneous targeting of the mPTP opening and monocyte-mediated inflammation could be a novel strategy for better neurological outcomes in patients with ischemic stroke.

Inhibition of Bruton's TK regulates macrophage NF-κB and NLRP3 inflammasome activation in metabolic inflammation

BACKGROUND AND PURPOSE

There are no medications currently available to treat metabolic inflammation. Bruton's tyrosine kinase (BTK) is highly expressed in monocytes and macrophages and regulates NF-κB and NLRP3 inflammasome activity; both propagate metabolic inflammation in diet-induced obesity.

EXPERIMENTAL APPROACH

Using an in vivo model of chronic inflammation, high-fat diet (HFD) feeding, in male C57BL/6J mice and in vitro assays in primary murine and human macrophages, we investigated if ibrutinib, an FDA approved BTK inhibitor, may represent a novel anti-inflammatory medication to treat metabolic inflammation.

KEY RESULTS

HFD-feeding was associated with increased BTK expression and activation, which was significantly correlated with monocyte/macrophage accumulation in the liver, adipose tissue, and kidney. Ibrutinib treatment to HFD-fed mice inhibited the activation of BTK and reduced monocyte/macrophage recruitment to the liver, adipose tissue, and kidney. Ibrutinib treatment to HFD-fed mice decreased the activation of NF-κB and the NLRP3 inflammasome. As a result, ibrutinib treated mice fed HFD had improved glycaemic control through restored signalling by the IRS-1/Akt/GSK-3β pathway, protecting mice against the development of hepatosteatosis and proteinuria. We show that BTK regulates NF-κB and the NLRP3 inflammasome specifically in primary murine and human macrophages, the in vivo cellular target of ibrutinib.

CONCLUSION AND IMPLICATIONS

We provide "proof of concept" evidence that BTK is a novel therapeutic target for the treatment of diet-induced metabolic inflammation and ibrutinib may be a candidate for drug repurposing as an anti-inflammatory agent for the treatment of metabolic inflammation in T2D and microvascular disease.

Harmful and beneficial effects of inflammatory response on reproduction: sterile and pathogen-associated inflammation

In reproduction, inflammatory processes play important roles in the development of many pregnancy complications such as preterm labor/birth, recurrent pregnancy loss, recurrent implantation failure, and preeclampsia. Inflammation can be initiated by both microbial and non-microbial causes. Bacterial infection in the feto-maternal interface and uterus can provoke preterm labor/birth, miscarriage, and chronic endometritis. By contrast, inflammation without infection, or 'sterile inflammation,' can also lead to many kinds of complications, such as preterm labor/birth, miscarriage, or preeclampsia. Aberrant inflammation is facilitated by immune cells such as macrophages, dendritic cells, natural killer cells, and invariant natural killer T cells. In addition, cytokines, chemokines, and several kinds of inflammatory mediators are involved. On the other hand, appropriate inflammation is required for a successful offspring during the progression of the entire pregnancy. Herein, we discuss the relation between pregnancy and inflammation with immunological alterations. Understanding the role of inflammation in complications during pregnancy may establish new perspectives of the progress of normal pregnancy as well as treatments during pregnancy complications.

IL-37 Gene Modification Enhances the Protective Effects of Mesenchymal Stromal Cells on Intestinal Ischemia Reperfusion Injury

Background

Ischemia reperfusion injury (IRI) is the major cause of intestinal damage in clinic. Although either mesenchymal stromal cells (MSCs) or interleukin 37 (IL-37) shows some beneficial roles to ameliorate IRI, their effects are limited. In this study, the preventative effects of IL-37 gene-modified MSCs (IL-37-MSCs) on intestinal IRI are investigated.

Methods

Intestinal IRI model was established by occluding the superior mesenteric artery for 30 minutes and then reperfused for 72 hours in rats. Forty adult male Sprague-Dawley rats were randomly divided into the sham control, IL-37-MSC-treated, MSC-treated, recombinant IL-37- (rIL-37-) treated, and untreated groups. Intestinal damage was assessed by H&E staining. The levels of gut barrier function factors (diamine oxidase and D-Lactate) and inflammation cytokine IL-1β were assayed using ELISA. The synthesis of tissue damage-related NLRP3 inflammasome and downstream cascade reactions including cleaved caspase-1, IL-1β, and IL-18 was detected by western blot. The mRNA levels of proinflammatory mediators IL-6 and TNF-α, which are downstream of IL-1β and IL-18, were determined by qPCR. Data were analyzed by one-way analysis of variance (ANOVA) after the normality test and followed by post hoc analysis with the least significant difference (LSD) test.

Results

IL-37-MSCs were able to migrate to the damaged tissue and significantly inhibit intestinal IRI. As compared with MSCs or the rIL-37 monotherapy group, IL-37-MSC treatment both improved gut barrier function and decreased local and systemic inflammation cytokine IL-1β level in IRI rats. In addition, tissue damage-related NLRP3 and downstream targets (cleaved caspase-1, IL-1β, and IL-18) were significantly decreased in IRI rats treated with IL-37-MSCs. Furthermore, IL-1β- and IL-18-related proinflammatory mediator IL-6 and TNF-α mRNA expressions were all significantly decreased in IRI rats treated with IL-37-MSCs.

Conclusion

The results suggest that IL-37 gene modification significantly enhances the protective effects of MSCs against intestinal IRI. In addition, NLRP3-related signaling pathways could be associated with IL-37-MSC-mediated protection.