Calcium-sensing receptor activates the NLRP3 inflammasome in LS14 preadipocytes mediated by ERK1/2 signaling

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

TIMP2 facilitates CIRI through activating NLRP3-mediated pyroptosis

This study aimed to investigate the underlying mechanisms of cerebral ischemia-reperfusion injury (CIRI) in mice using CIR and hypoxia/reoxygenation (H/R) cell models. The study evaluated brain tissue weight, pathological injury, and changes in the expression levels of TIMP2, p-ERK1/2 and NLRP3-mediated pyroptosis-related proteins in brain tissues and hippocampal neurons of CIR mice using established methods such as dry/wet weight measurement, HE staining, qPCR, TUNEL assay, and Western blotting. The results demonstrated a significant increase in brain water content and neuronal apoptosis rate in the experimental groups compared with those in the control group. In particular, the I/R+TIMP2 group showed the highest increase. Additionally, the control group exhibited a clear brain tissue structure, neatly and densely arranged cells with normal morphology, and evenly stained and clear hippocampal tissues. However, the I/R group showed hippocampal structure disorders, interstitial edema, deep nuclear staining, karyopyknosis, and karyorrhexis in brain tissues. The study results further revealed that TIMP2 could aggravate the pathological damage of brain tissues in the I/R+TIMP2 group compared with the I/R group and significantly reduced it in the TIMP2-KD group. Furthermore, the Western blotting results demonstrated that the protein expression levels of TIMP2, p-ERK1/2, t-ERK1/2, NLRP3, IL-1β, IL-18, GSDMD, Caspase-1, and ASC in brain tissues and hippocampal neurons were significantly higher in the experimental groups than those in the control group. The I/R+TIMP2 group displaying the highest increase and the TIMP2-KD group showing a significant decrease. In conclusion, TIMP2 can contribute to the occurrence and progression of CIRI by activating NLRP3-mediated pyroptosis.

The calcium-sensing receptor modulates the prostaglandin E2 pathway in intestinal inflammation

Introduction: The prostaglandin E2 (PGE2) pathway is one of the main mediators of intestinal inflammation. As activation of the calcium-sensing receptor (CaSR) induces expression of inflammatory markers in the colon, we assessed the impact of the CaSR on the PGE2 pathway regulation in colon cancer cells and the colon in vitro and in vivo. Methods and Results: We treated CaSR-transfected HT29 and Caco-2 colon cancer cell lines with different orthosteric ligands or modulators of the CaSR and measured gene expression and PGE2 levels. In CaSR-transfected HT29CaSR-GFP and Caco-2CaSR-GFP cells, the orthosteric CaSR ligand spermine and the positive allosteric CaSR modulator NPS R-568 both induced an inflammatory state as measured by IL-8 gene expression and significantly increased the expression of the PGE2 pathway key enzymes cyclooxygenase (COX)-2 and/or prostaglandin E2 synthase 1 (PGES-1). Inhibition of the CaSR with the calcilytic NPS 2143 abolished the spermine- and NPS R-568-induced pro-inflammatory response. Interestingly, we observed cell-line specific responses as e.g. PGES-1 expression was affected only in HT29CaSR-GFP but not in Caco-2CaSR-GFP cells. Other genes involved in the PGE2 pathway (COX-1, or the PGE2 receptors) were not responsive to the treatment. None of the studied genes were affected by any CaSR agonist in GFP-only transfected HT29GFP and Caco-2GFP cells, indicating that the observed gene-inducing effects of spermine and R-568 were indeed mediated by the CaSR. In vivo, we had previously determined that treatment with the clinically approved calcimimetic cinacalcet worsened symptoms in a dextran sulfate sodium (DSS)-induced colitis mouse model. In the colons of these mice, cinacalcet significantly induced gene expression of PGES-2 and the EP3 receptor, but not COX-2; while NPS 2143 increased the expression of the PGE2-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Importantly, neither treatment had any effect on the colons of non-DSS treated mice. Discussion: Overall, we show that activation of the CaSR induces the PGE2 pathway, albeit with differing effects in vitro and in vivo. This may be due to the different microenvironment in vivo compared to in vitro, specifically the presence of a CaSR-responsive immune system. Since calcilytics inhibit ligand-mediated CaSR signaling, they may be considered for novel therapies against inflammatory bowel disease.

NLRP3 Inflammasome’s Activation in Acute and Chronic Brain Diseases—An Update on Pathogenetic Mechanisms and Therapeutic Perspectives with Respect to Other Inflammasomes

Increasingly prevalent acute and chronic human brain diseases are scourges for the elderly. Besides the lack of therapies, these ailments share a neuroinflammation that is triggered/sustained by different innate immunity-related protein oligomers called inflammasomes. Relevant neuroinflammation players such as microglia/monocytes typically exhibit a strong NLRP3 inflammasome activation. Hence the idea that NLRP3 suppression might solve neurodegenerative ailments. Here we review the recent Literature about this topic. First, we update conditions and mechanisms, including RNAs, extracellular vesicles/exosomes, endogenous compounds, and ethnic/pharmacological agents/extracts regulating NLRP3 function. Second, we pinpoint NLRP3-activating mechanisms and known NLRP3 inhibition effects in acute (ischemia, stroke, hemorrhage), chronic (Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, MS, ALS), and virus-induced (Zika, SARS-CoV-2, and others) human brain diseases. The available data show that (i) disease-specific divergent mechanisms activate the (mainly animal) brains NLRP3; (ii) no evidence proves that NLRP3 inhibition modifies human brain diseases (yet ad hoc trials are ongoing); and (iii) no findings exclude that concurrently activated other-than-NLRP3 inflammasomes might functionally replace the inhibited NLRP3. Finally, we highlight that among the causes of the persistent lack of therapies are the species difference problem in disease models and a preference for symptomatic over etiologic therapeutic approaches. Therefore, we posit that human neural cell-based disease models could drive etiological, pathogenetic, and therapeutic advances, including NLRP3’s and other inflammasomes’ regulation, while minimizing failure risks in candidate drug trials.

Secretory Factors from Calcium-Sensing Receptor-Activated SW872 Pre-Adipocytes Induce Cellular Senescence and A Mitochondrial Fragmentation-Mediated Inflammatory Response in HepG2 Cells

Adipose tissue inflammation in obesity has a deleterious impact on organs such as the liver, ultimately leading to their dysfunction. We have previously shown that activation of the calcium-sensing receptor (CaSR) in pre-adipocytes induces TNF-α and IL-1β expression and secretion; however, it is unknown whether these factors promote hepatocyte alterations, particularly promoting cell senescence and/or mitochondrial dysfunction. We generated conditioned medium (CM) from the pre-adipocyte cell line SW872 treated with either vehicle (CMveh) or the CaSR activator cinacalcet 2 µM (CMcin), in the absence or presence of the CaSR inhibitor calhex 231 10 µM (CMcin+cal). HepG2 cells were cultured with these CM for 120 h and then assessed for cell senescence and mitochondrial dysfunction. CMcin-treated cells showed increased SA-β-GAL staining, which was absent in TNF-α- and IL-1β-depleted CM. Compared to CMveh, CMcin arrested cell cycle, increased IL-1β and CCL2 mRNA, and induced p16 and p53 senescence markers, which was prevented by CMcin+cal. Crucial proteins for mitochondrial function, PGC-1α and OPA1, were decreased with CMcin treatment, concomitant with fragmentation of the mitochondrial network and decreased mitochondrial transmembrane potential. We conclude that pro-inflammatory cytokines TNF-α and IL-1β secreted by SW872 cells after CaSR activation promote cell senescence and mitochondrial dysfunction, which is mediated by mitochondrial fragmentation in HepG2 cells and whose effects were reversed with Mdivi-1. This investigation provides new evidence about the deleterious CaSR-induced communication between pre-adipocytes and liver cells, incorporating the mechanisms involved in cellular senescence.

The interplay of inflammation, exosomes and Ca2+ dynamics in diabetic cardiomyopathy

Diabetes mellitus is one of the prime risk factors for cardiovascular complications and is linked with high morbidity and mortality. Diabetic cardiomyopathy (DCM) often manifests as reduced cardiac contractility, myocardial fibrosis, diastolic dysfunction, and chronic heart failure. Inflammation, changes in calcium (Ca²⁺) handling and cardiomyocyte loss are often implicated in the development and progression of DCM. Although the existence of DCM was established nearly four decades ago, the exact mechanisms underlying this disease pathophysiology is constantly evolving. Furthermore, the complex pathophysiology of DCM is linked with exosomes, which has recently shown to facilitate intercellular (cell-to-cell) communication through biomolecules such as micro RNA (miRNA), proteins, enzymes, cell surface receptors, growth factors, cytokines, and lipids. Inflammatory response and Ca²⁺ signaling are interrelated and DCM  has been known to adversely affect many of these signaling molecules either qualitatively and/or quantitatively. In this literature review, we have demonstrated that Ca²⁺ regulators are tightly controlled at different molecular and cellular levels during various biological processes in the heart. Inflammatory mediators, miRNA and exosomes are shown to interact with these regulators, however how these mediators are linked to Ca²⁺ handling during DCM pathogenesis remains elusive. Thus, further investigations are needed to understand the mechanisms to restore cardiac Ca²⁺ homeostasis and function, and to serve as potential therapeutic targets in the treatment of DCM.

The calcium-sensing receptor in inflammation: Recent updates

The Calcium-Sensing Receptor (CaSR) is a member of the class C of G-proteins coupled receptors (GPCRs), it plays a pivotal role in calcium homeostasis by directly controlling calcium excretion in the kidneys and indirectly by regulating parathyroid hormone (PTH) release from the parathyroid glands. The CaSR is found to be ubiquitously expressed in the body, playing a plethora of additional functions spanning from fluid secretion, insulin release, neuronal development, vessel tone to cell proliferation and apoptosis, to name but a few. The present review aims to elucidate and clarify the emerging regulatory effects that the CaSR plays in inflammation in several tissues, where it mostly promotes pro-inflammatory responses, with the exception of the large intestine, where contradictory roles have been recently reported. The CaSR has been found to be expressed even in immune cells, where it stimulates immune response and chemokinesis. On the other hand, CaSR expression seems to be boosted under inflammatory stimulus, in particular, by pro-inflammatory cytokines. Because of this, the CaSR has been addressed as a key factor responsible for hypocalcemia and low levels of PTH that are commonly found in critically ill patients under sepsis or after burn injury. Moreover, the CaSR has been found to be implicated in autoimmune-hypoparathyroidism, recently found also in patients treated with immune-checkpoint inhibitors. Given the tight bound between the CaSR, calcium and vitamin D metabolism, we also speculate about their roles in the pathogenesis of severe acute respiratory syndrome coronavirus-19 (SARS-COVID-19) infection and their impact on patients' prognosis. We will further explore the therapeutic potential of pharmacological targeting of the CaSR for the treatment and management of aberrant inflammatory responses.

Olaparib, a PARP-1 inhibitor, protects retinal cells from ocular hypertension-associated oxidative damage

Glaucoma is the most common cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) and relative hypoxia in the retina stimulate the production of reactive oxygen species (ROS), which, in turn, puts the retina and optic nerve under chronic oxidative stress. Emerging evidence has shown that oxidative stress can trigger PARP-1 overactivation, mitochondrial-associated endoplasmic reticulum membrane (MAM) dysregulation, and NLRP3 activation. Oxidative damage can trigger inflammasome activation, and NLRP3 is the only inflammasome associated with MAM dysregulation. In addition, multiple transcription factors are located on the MAM. This study aimed to investigate the protective effects and underlying mechanisms of a PARP-1 inhibitor (olaparib) against chronic ocular hypertension-associated retinal cell damage. We also mimicked hypoxic stimulation of a retinal precursor cell line by exposing the cells to 0.2% O₂in vitro. We discovered that chronic ocular hypertension (COH) induces oxidative damage and MAM dysregulation in the retinal ganglion cells (RGCs). The protein levels of cleaved-PARP and NLRP3 were upregulated in the retinas of the COH rats. Olaparib, a PARP-1 inhibitor, alleviated COH-induced RGC loss, retinal morphological alterations, and photopic negative response amplitude reduction. Olaparib also relieved hypoxic stimulation-induced loss of cell viability and MAM dysregulation. Additionally, some indicators of mitochondrial performance, such as reactive oxygen species accumulation, mitochondrial Ca²⁺ influx, and mitochondrial membrane potential collapse, decreased after olaparib treatment. Olaparib attenuated the hypoxia-induced upregulation of NLRP3 protein levels as well as the phosphorylation of ERK1/2 and histone H2A.X. These results suggest that olaparib protects RGCs from chronic intraocular pressure elevation in vivo and alleviates the abnormal MAM dysregulation and mitochondrial dysfunction caused by hypoxia in vitro. This protection may be achieved by inhibiting PARP-1 overactivation, NLRP3 upregulation, and phosphorylation of ERK1/2.

Macrophages in obesity are characterised by increased IL-1β response to calcium-sensing receptor signals

Objective

Obesity is complicated by inflammatory activation of the innate immune system. Stimulation of the calcium-sensing receptor (CaSR) by extra-cellular calcium ions ([Ca²⁺]_ex) can trigger NLRP3 inflammasome activation and inflammation. We hypothesised, that this mechanism might contribute to the activation of adipose tissue (AT) in obesity, and investigated [Ca²⁺]_ex-induced, CaSR mediated IL-1β release by macrophages in obesity.

Methods

[Ca²⁺]_ex-induced IL-1β release was investigated in monocyte-derived macrophages (MDM) generated from peripheral blood of patients with obesity and from normal-weight controls. Visceral and subcutaneous AT biosamples were stimulated with [Ca²⁺]_ex, and IL-1β release, as well as expression of NLRP3 inflammasome and cytokine genes, was determined.

Results

Both MDM and AT readily responded with concentration-dependent IL-1β release already at low, near physiological concentrations to addition of [Ca²⁺]_ex, which was more than 80 fold higher than the LPS-induced effect. IL-1β levels induced by [Ca²⁺]_ex were significantly higher not only in MDM from patients with obesity compared to controls, but also in visceral versus subcutaneous AT. This fat-depot difference was also reflected by mRNA expression levels of inflammasome and cytokine genes.

Conclusions

Obesity renders macrophages more susceptible to [Ca²⁺]_ex-induced IL-1β release and pyroptosis. Increased susceptibility was independent of the response to LPS and circulating CRP arguing against mere pro-inflammatory pre-activation of monocytes. Instead, we propose that CaSR mediated signalling is relevant for the deleterious innate immune activation in obesity.

Inhibition of NLRP3 by Fermented Quercetin Decreases Resistin-Induced Chemoresistance to 5-Fluorouracil in Human Colorectal Cancer Cells

The drug resistance of colorectal cancer (CRC) cells against 5-fluorouracil (5-FU) therapy is a major challenge to successful cancer treatment. While previous studies have proposed several 5-FU resistance mechanisms, the effects of the adipokines on cancer cells remain unclear. Thus, this study investigated the effect of resistin on 5-FU-treated CRC cell lines. The upregulation of NLRP3 can regulate the inflammatory responses in cancer cells and then enhance cancer progression. This study investigated the expression level and the function of NLRP3 on 5-FU-induced cytotoxicity in CRC cells and found that resistin-induced ERK activation and increased NLRP3 expression in CRC HCT-116 and DLD-1 cells were mediated by Toll-like receptor 4 (TLR4). The inhibition of TLR4 and ERK by pharmacological inhibitors attenuated the resistin-induced NLRP3 mRNA and protein levels. In contrast, the knockdown of NLRP3 enhanced the cytotoxic effects of 5-FU. Furthermore, quercetin is an effective chemopreventive compound. This study showed that quercetin fermented by Lactobacillus could exhibit low cytotoxicity on normal mucosa cells and improve the function of inhibiting CRC cells. The treatment of CRC cells with fermented quercetin increased the cytotoxicity and enhanced cell death in the presence of resistin. In this study, fermented quercetin induced the cytotoxicity and cell death of 5-FU in resistin-treated CRC cells, which is associated with the downregulation of NLRP3 expression and ERK phosphorylation. These results indicate the role of NLRP3 in the development of drug resistance to 5-FU in CRC cells. Elucidating the mechanism regarding the cytotoxicity effect of quercetin may provide another vision for the development of a chemotherapy strategy for CRC in the future.

Myrtenal and β-caryophyllene oxide screened from Liquidambaris Fructus suppress NLRP3 inflammasome components in rheumatoid arthritis

Background

Liquidambaris Fructus (LF) is the infructescence of Liquidambar formosana. In Traditional Chinese Medicine, LF has been used to treat joint pain, a common symptom of arthritis and rheumatism; however, a lack of pharmacological evidence has limited its applications in modern clinics. Therefore, this study aims to explore the protective effect of LF on rheumatoid arthritis (RA) and to identify its active ingredients.

Methods

Rats with adjuvant-induced arthritis (AIA) were divided into 4 groups and administered petroleum ether extract of LF (PEL), ethyl acetate extract of LF (EEL), water extract of LF (WEL), or piroxicam (PIR) respectively for 3 weeks. Two additional groups were used as normal control (NC) and model control (MC) and administered distilled water as a placebo. The clinical scores for arthritis, bone surface, synovial inflammation and cartilage erosion were used to evaluate the therapeutic efficacy of each treatment. The serum IL-1β and TNF-α level and the expression of NLRP3, IL-1β and caspase-1 p20 in the synovial tissue of AIA rats were evaluated by ELISA and Western blot. The active ingredients of LF were investigated using network pharmacology and molecular docking methods, and their inhibition of NLRP3 inflammasome activation was verified in the human rheumatoid arthritis fibroblast-like synovial cells (RA-FLS) model.

Results

PEL could alleviate paw swelling, bone and joint destruction, synovial inflammation and cartilage erosion in the AIA rats, with significantly superior efficacy to that of EEL and WEL. PEL reduced IL-1β and TNF-α serum levels, and attenuated the upregulation of NLRP3, IL-1β and caspase-1 p20 expression in the synovial tissue of AIA rats. Network pharmacology and molecular docking results indicated that myrtenal and β-caryophyllene oxide were the main two active ingredients of PEL, and these two compounds showed significant inhibition on TNF-α, NLRP3, IL-1β and caspase-1 p20 expression in RA-FLS.

Conclusions

Myrtenal and β-caryophyllene oxide screened from PEL could suppress the activation of NLRP3 inflammasome, thereby alleviating RA symptoms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03410-2.

SCIMP is a spatiotemporal transmembrane scaffold for Erk1/2 to direct pro-inflammatory signaling in TLR-activated macrophages

Immune cells are armed with Toll-like receptors (TLRs) for sensing and responding to pathogens and other danger cues. The role of extracellular-signal-regulated kinases 1/2 (Erk1/2) in TLR signaling remains enigmatic, with both pro- and anti-inflammatory functions described. We reveal here that the immune-specific transmembrane adaptor SCIMP is a direct scaffold for Erk1/2 in TLR pathways, with high-resolution, live-cell imaging revealing that SCIMP guides the spatial and temporal recruitment of Erk2 to membrane ruffles and macropinosomes for pro-inflammatory TLR4 signaling. SCIMP-deficient mice display defects in Erk1/2 recruitment to TLR4, c-Fos activation, and pro-inflammatory cytokine production, with these effects being phenocopied by Erk1/2 signaling inhibition. Our findings thus delineate a selective role for SCIMP as a key scaffold for the membrane recruitment of Erk1/2 kinase to initiate TLR-mediated pro-inflammatory responses in macrophages.

A virulent Bacillus cereus strain from deep-sea cold seep induces pyroptosis in a manner that involves NLRP3 inflammasome, JNK pathway, and lysosomal rupture

Recent studies indicate that the Bacillus species is distributed in deep-sea environments. However, no specific studies on deep-sea Bacillus cereus have been documented. In the present work, we isolated a B. cereus strain, H2, from the deep-sea cold seep in South China Sea. We characterized the pathogenic potential of H2 and investigated H2-induced death of different types of cells. We found that H2 was capable of tissue dissemination and causing acute mortality in mice and fish following intraperitoneal/intramuscular injection. In vitro studies revealed that H2 infection of macrophages induced pyroptosis and activation of the NLRP3 inflammasome pathway that contributed partly to cell death. H2 infection activated p38, JNK, and ERK, but only JNK proved to participate in H2-triggered cell death. Reactive oxygen species (ROS) and intracellular Ca²⁺ were essential to H2-induced activation of JNK and NLRP3 inflammasome. In contrast, lysosomal rupture and cathepsins were required for H2-induced NLRP3 inflammasome activation but not for JNK activation. This study revealed for the first time the virulence characteristics of deep-sea B. cereus and provided new insights into the mechanism of B. cereus infection.

Calcium-Sensing Receptor (CaSR), Its Impact on Inflammation and the Consequences on Cardiovascular Health

The calcium Sensing Receptor (CaSR) is a cell surface receptor belonging to the family of G-protein coupled receptors. CaSR is mainly expressed by parathyroid glands, kidneys, bone, skin, adipose tissue, the gut, the nervous system, and the cardiovascular system. The receptor, as its name implies is involved in sensing calcium fluctuations in the extracellular matrix of cells, thereby having a major impact on the mineral homeostasis in humans. Besides calcium ions, the receptor is also activated by other di- and tri-valent cations, polypeptides, polyamines, antibiotics, calcilytics and calcimimetics, which upon binding induce intracellular signaling pathways. Recent studies have demonstrated that CaSR influences a wide variety of cells and processes that are involved in inflammation, the cardiovascular system, such as vascular calcification, atherosclerosis, myocardial infarction, hypertension, and obesity. Therefore, in this review, the current understanding of the role that CaSR plays in inflammation and its consequences on the cardiovascular system will be highlighted.

A New Hope in Spinal Degenerative Diseases: Piezo1

As a newly discovered mechanosensitive ion channel protein, the piezo1 protein participates in the transmission of mechanical signals on the cell membrane and plays a vital role in mammalian biomechanics. Piezo1 has attracted widespread attention since it was discovered in 2010. In recent years, studies on piezo1 have gradually increased and deepened. In addition to the discovery that piezo1 is expressed in the respiratory, cardiovascular, gastrointestinal, and urinary systems, it is also stably expressed in cells such as mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, chondrocytes, and nucleus pulposus cells that constitute vertebral bodies and intervertebral discs. They can all receive external mechanical stimulation through the piezo1 protein channel to affect cell proliferation, differentiation, migration, and apoptosis to promote the occurrence and development of lumbar degenerative diseases. Through reviewing the relevant literature of piezo1 in the abovementioned cells, this paper discusses the effect of piezo1 protein expression under mechanical stress stimuli on spinal degenerative disease, providing the molecular basis for the pathological mechanism of spinal degenerative disease and also a new basis, ideas, and methods for the prevention and treatment of this degenerative disease.

The NLRP3 inflammasome: Multiple activation pathways and its role in primary cells during ventricular remodeling

Inflammasomes are a group of multiprotein signaling complexes located in the cytoplasm. Several inflammasomes have been identified, including NLRP1, NLRP2, NLRP3, AIM2, and NLRC4. Among them, NLRP3 was investigated in most detail, and it was reported that it can be activated by many different stimuli. Increased NLRP3 protein expression and inflammasome assembly lead to caspase-1 mediated maturation and release of IL-1β, which triggers inflammation and pyroptosis. The activation of the NLRP3 inflammasome has been widely reported in studies of tumors and neurological diseases, but relatively few studies on the cardiovascular system. Ventricular remodeling (VR) is an important factor contributing to heart failure (HF) after myocardial infarction (MI). Consequently, delaying VR is of great significance for improving heart function. Studies have shown that the NLRP3 inflammasome plays an essential role in the process of VR. Here, we reviewed the latest studies on the activation pathway of the NLRP3 inflammasome, focusing on the effects of the NLRP3 inflammasome in primary cells during VR, and finally discuss future research directions in this field.

Exosomes Released from CaSR-Stimulated PMNs Reduce Ischaemia/Reperfusion Injury

Ischemia-reperfusion (I/R) injury caused by acute myocardial infarction (AMI) can initiate a strong inflammatory response. Polymorphonuclear cells (PMNs) are the most important inflammatory cells. Our previous studies found that the calcium-sensing receptor (CaSR) regulates the proinflammatory effects of PMNs. However, the role and mechanism of CaSR-regulated PMNs in I/R injury remain uncertain. A rat AMI model was developed in this study and showed that the expression of CaSR on PMNs increased in AMI; however, the levels of Bcl-xl and SOD in myocardial tissue decreased, while Bax and MDA levels increased. Then, after coculture with CaSR-stimulated PMNs, the expression of Bcl-xl in cardiomyocytes significantly increased, Bax expression and the apoptotic rate decreased, and ROS production was significantly inhibited. At the same time, the cardiomyocyte damage caused by hypoxia-reoxygenation was reduced. Furthermore, we found that exosomes derived from PMNs could be taken up by cardiomyocytes. Additionally, the exosomes secreted by CaSR-stimulated PMNs had the same effect on cardiomyocytes as CaSR-stimulated PMNs, while the increased phosphorylation level of AKT in cardiomyocytes could be revered by AKT transduction pathway inhibitors. Subsequently, we identified the exosomes derived from CaSR-stimulated PMNs by second-generation sequencing technology, and increased expression of lncRNA ENSRNOT00000039868 was noted. The data show that this lncRNA can prevent the hypoxia-reoxygenation injury by upregulating the expression of PDGFD in cardiomyocytes. In vivo, exosomes from CaSR-stimulated PMNs played a significant role against AMI and reperfusion injury in myocardial tissue. Thus, we propose that exosomes derived from CaSR-stimulated PMNs can reduce I/R injury in AMI, and this effect may be related to the AKT signaling pathway.

Inflammasome signaling could be used to sense and respond to endogenous damage in brown but not white adipose tissue of a hibernating ground squirrel

Small mammalian hibernators use metabolic suppression to enhance survival during the winter. Torpor is punctuated by periods of euthermia used to clear metabolic by-products and damaged cell components. The current study was performed to determine if the innate immune system, specifically NLRP and AIM2 inflammasome signaling, may detect and respond to cell stress during hibernation. Nlrp3, Casp1, and Il1b genes were significantly upregulated in brown adipose tissue (BAT) during arousal with respect to the euthermic control, suggesting increased NLRP3 inflammasome priming. NLRP3, IL-18, and gasdermin D protein levels increased during torpor, indicating a lag between inflammasome priming and formation. AIM2 and gasdermin D levels increased in BAT during arousal, as did caspase-1 activity. Thus, non-shivering thermogenesis may generate pro-inflammatory triggers of inflammasome signaling. This study is the first to support a role for inflammasome signaling in sensing cellular perturbations at various points of the torpor-arousal cycle, in metabolically-active BAT, but not white adipose tissue (WAT).

Prokineticin 2 via Calcium-Sensing Receptor Activated NLRP3 Inflammasome Pathway in the Testicular Macrophages of Uropathogenic Escherichia coli-Induced Orchitis

Reproductive tract infections contribute to the development of testicular inflammatory lesions, leading to male infertility. Previous research shows that the activation of the NLRP3 inflammasome in orchitis promotes the secretion and maturation of IL-1β and, thus, decreases male fertility. The calcium-sensing receptor (CaSR) is closely related to the secretion of proinflammatory cytokines. An increase in the CaSR level promotes the assembly and activation of the NLRP3 inflammasome. However, the role of CaSRs in orchitis is unknown. We first constructed a uropathogenic Escherichia Coli (UPEC) rat orchitis model and then detected the expression of CaSR and NLRP3 inflammatory pathway proteins in testicular macrophages (TM) through RT-PCR and WB, calcium levels in TM through flow cytometry, and proinflammatory factor IL-1β through ELISA. In addition, testosterone levels in the serum samples were detected using liquid chromatography–mass spectrometry (LC-MS). Here, we show that CaSR upregulation after infection in TM in a rat model of UPEC induces the activation of the NLRP3 inflammasome pathway and thereby enhances IL-1β secretion and reduces the testosterone level in the blood. Moreover, CaSR inhibitors can alleviate inflammatory impairment. After UPEC challenge in vitro, CaSR promoted NLRP3 expression and released IL-1β cleaved from TM into the supernatant. Overall, elevated CaSR levels in TM in testes with UPEC-induced orchitis may impair testosterone synthesis through the activation of the NLRP3 pathway and PK2 is an upstream regulatory protein of CaSR. Our research further shows the underlying mechanisms of inflammation-related male infertility and provides anti-inflammatory therapeutic targets for male infertility.

Calcium-Sensing Receptor in Adipose Tissue: Possible Association with Obesity-Related Elevated Autophagy

Autophagy is upregulated in adipose tissue (AT) from people with obesity. We showed that activation of the calcium-sensing receptor (CaSR) elevates proinflammatory cytokines through autophagy in preadipocytes. Our aim is to understand the role of CaSR on autophagy in AT from humans with obesity. We determined mRNA and protein levels of CaSR and markers of autophagy by qPCR and western blot in human visceral AT explants or isolated primary preadipocytes (60 donors: 72% female, 23-56% body fat). We also investigated their association with donors' anthropometric variables. Donors' % body fat and CaSR mRNA expression in AT were correlated (r = 0.44, p < 0.01). CaSR expression was associated with mRNA levels of the autophagy markers atg5 (r = 0.37, p < 0.01), atg7 (r = 0.29, p < 0.05) and lc3b (r = 0.40, p < 0.01). CaSR activation increased becn and atg7 mRNA expression in AT. CaSR activation also upregulated LC3II by ~50%, an effect abolished by the CaSR inhibitor. Spermine (CaSR agonist) regulates LC3II through the ERK1/2 pathway. Structural equation model analysis suggests a link between donors' AT CaSR expression, AT autophagy and expression of Tumor Necrosis Factor alpha TNF-α. CaSR expression in visceral AT is directly associated with % body fat, and CaSR activation may contribute to obesity-related disruption in AT autophagy.

Calcium-sensing receptor-mediated NLRP3 inflammasome response to calciprotein particles drives inflammation in rheumatoid arthritis

Increased extracellular Ca2+ concentrations ([Ca2+]ex) trigger activation of the NLRP3 inflammasome in monocytes through calcium-sensing receptor (CaSR). To prevent extraosseous calcification in vivo, the serum protein fetuin-A stabilizes calcium and phosphate into 70-100 nm-sized colloidal calciprotein particles (CPPs). Here we show that monocytes engulf CPPs via macropinocytosis, and this process is strictly dependent on CaSR signaling triggered by increases in [Ca2+]ex. Enhanced macropinocytosis of CPPs results in increased lysosomal activity, NLRP3 inflammasome activation, and IL-1β release. Monocytes in the context of rheumatoid arthritis (RA) exhibit increased CPP uptake and IL-1β release in response to CaSR signaling. CaSR expression in these monocytes and local [Ca2+] in afflicted joints are increased, probably contributing to this enhanced response. We propose that CaSR-mediated NLRP3 inflammasome activation contributes to inflammatory arthritis and systemic inflammation not only in RA, but possibly also in other inflammatory conditions. Inhibition of CaSR-mediated CPP uptake might be a therapeutic approach to treating RA.

Statins activate the NLRP3 inflammasome and impair insulin signaling via p38 and mTOR

Statins lower cholesterol and risk of cardiovascular disease. Statins can increase blood glucose and risk of new-onset diabetes. It is unclear why statins can have opposing effects on lipids versus glucose. Statins have cholesterol-independent pleiotropic effects that influence both insulin and glucose control. Statin lowering of isoprenoids required for protein prenylation promotes pancreatic β-cell dysfunction and adipose tissue insulin resistance. Protein prenylation influences immune function and statin-mediated adipose tissue insulin resistance involves the NLR family pyrin domain-containing 3 (NLRP3) inflammasome and IL-1β. However, the intracellular cues that statins engage to activate the NLRP3 inflammasome and those responsible for IL-1β-mediated insulin resistance in adipose tissue have not been identified. We hypothesized that stress kinases or components of the insulin signaling pathway mediated statin-induced insulin resistance. We tested the associations of p38, ERK, JNK, phosphatase, and tensin homolog (PTEN), and mTOR in statin-exposed adipose tissue from WT and IL-1β^-/- mice. We found that statins increased phosphorylation of p38 in WT and IL-1β^-/- mice. Statin activation of p38 upstream of IL-1β led to priming of this NLRP3 inflammasome effector in macrophages. We found that mTORC1 inhibition with low doses of rapamycin (2 or 20 nM) lowered macrophage priming of IL-1β mRNA and secretion of IL-1β caused by multiple statins. Rapamycin (20 nM) or the rapalog everolimus (20 nM) prevented atorvastatin-induced lowering of insulin-mediated phosphorylation of Akt in mouse adipose tissue. These results position p38 and mTOR as mediators of statin-induced insulin resistance in adipose tissue and highlight rapalogs as candidates to mitigate the insulin resistance and glycemic side effects of statins.

Piezo1 activates the NLRP3 inflammasome in nucleus pulposus cell-mediated by Ca2+/NF-κB pathway

Studying and understanding the mechanism of inflammation in nucleus pulposus is the key to understand and prevent intervertebral disc degeneration. We propose a model of mechanical sensitive ion channel Piezo1 mediated inflammation of nucleus pulposus cells. Piezo1 can up-regulate the level of interleukin-1β (IL-1β) in nucleus pulposus cells once it is activated. It is suggested that Piezo1 may mediate inflammation by activating Nod-like receptor protein 3 (NLRP3) inflammasome to accelerate the production and maturation of IL-1β. The primary objective of this study was to explore whether Piezo1 activates NLRP3 inflammasome in nucleus pulposus cells. Piezo1 sensitization was induced by mechanical stretch following which we analyzed the priming and assembly of NLRP3 inflammasome and also studied if the downstream Ca²⁺/NF-κB pathway mediated this activation in nucleus pulposus cells. The expression of Piezo1 and NLRP3 inflammasome increased in a time-dependent manner upon mechanical stretch. Piezo1 activation promoted NLRP3 inflammasome assembly, which was demonstrated by the upregulation of caspase-1 activation and IL-1β production. Transfection of Piezo1-siRNA reversed this process. The inhibition of Ca²⁺/NF-κB pathway reduced Piezo1-dependent activation of NLRP3 inflammasome. Thus, we propose that activation of NLRP3 inflammasome in nucleus pulposus cells mediated by Piezo1 through the Ca²⁺/NF-κB pathway is a novel pathogenesis for the progress of intervertebral disc degeneration. As per our knowledge this is the first study which has provided evidence linking Piezo1-mediated inflammation in nucleus pulposus cells with the production of NLRP3 inflammasome.

Does NLRP3 Inflammasome and Aryl Hydrocarbon Receptor Play an Interlinked Role in Bowel Inflammation and Colitis-Associated Colorectal Cancer?

Inflammation is a hallmark in many forms of cancer; with colitis-associated colorectal cancer (CAC) being a progressive intestinal inflammation due to inflammatory bowel disease (IBD). While this is an exemplification of the negatives of inflammation, it is just as crucial to have some degree of the inflammatory process to maintain a healthy immune system. A pivotal component in the maintenance of such intestinal homeostasis is the innate immunity component, inflammasomes. Inflammasomes are large, cytosolic protein complexes formed following stimulation of microbial and stress signals that lead to the expression of pro-inflammatory cytokines. The NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome has been extensively studied in part due to its strong association with colitis and CAC. The aryl hydrocarbon receptor (AhR) has recently been acknowledged for its connection to the immune system aside from its role as an environmental sensor. AhR has been described to play a role in the inhibition of the NLRP3 inflammasome activation pathway. This review will summarise the signalling pathways of both the NLRP3 inflammasome and AhR; as well as new-found links between these two signalling pathways in intestinal immunity and some potential therapeutic agents that have been found to take advantage of this link in the treatment of colitis and CAC.

Calcium sensing receptor activation in THP-1 macrophages triggers NLRP3 inflammasome and human preadipose cell inflammation

Excess adipose tissue (AT) associates with inflammation and obesity-related diseases. We studied whether calcium-sensing receptor (CaSR)-mediated NLRP3 inflammasome activation in THP-1 macrophages elevates inflammation in LS14 preadipocytes, modeling deleterious AT cell crosstalk. THP-1 macrophages exposed to cinacalcet (CaSR activator, 2 μM, 4 h) showed elevated proinflammatory marker and NLRP3 inflammasome mRNA, pro-IL-1β protein and caspase-1 activity, whereas preincubation with CaSR negative modulators prevented these effects. The key NLRP3 inflammasome component ASC was silenced (siRNA) in THP-1 cells, and inflammasome activation was evaluated (qPCR, Western blot, caspase-1 activity) or they were further cultured to obtain conditioned medium (CoM). Exposure of LS14 preadipocytes to CoM from cinacalcet-treated THP-1 elevated LS14 proinflammatory cytokine expression, which was abrogated by THP-1 inflammasome silencing. Thus, CaSR activation elevates THP-1-induced inflammation in LS14 preadipocytes, via macrophage NLRP3 inflammasome activation. Modulating CaSR activation may prevent deleterious proinflammatory cell crosstalk in AT, a promising approach in obesity-related metabolic disorders.

Calcium-Sensing Receptor on Neutrophil Promotes Myocardial Apoptosis and Fibrosis After Acute Myocardial Infarction via NLRP3 Inflammasome Activation

BACKGROUND

The infiltration of neutrophils aggravates inflammatory response in acute myocardial infarction (AMI), and the role of calcium-sensing receptor (CaSR) in neutrophil-associated inflammation is largely unknown. The aim of this study was to evaluate the regulatory effects of CaSR on nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome in neutrophils and to explore its role in AMI-related ventricular remodelling.

METHODS

The expression of CaSR, NLRP3 inflammasome, and interleukin 1β (IL-1β) in peripheral blood and infiltrating neutrophils in patients and rats with AMI was detected by western blotting and immunofluorescence. Cardiomyocyte apoptosis was detected by western blotting and transmission electron microscopy. The degree of fibrosis was evaluated by Masson staining and western blotting.

RESULTS

We found upregulation of CaSR, NLRP3 inflammasome, Caspase-1, and IL-1β in peripheral neutrophils from patients with AMI compared with matched healthy controls, peaking on day 1 and decreasing gradually till 7 days. Peripheral and infiltrating neutrophils from rats with AMI showed the same trend. Calindol enhanced NLRP3 inflammasome activation and IL-1β release in neutrophils from healthy volunteers, which was blocked by inhibitors of the PLC-IP₃ pathway and ER-Ca²⁺ release. Calhex-231 decreased NLRP3 inflammasome activation and IL-1β release in neutrophils from patients with AMI. The calindol-stimulated neutrophils from healthy rats promoted cardiomyocyte apoptosis and fibrosis of cardiac fibroblasts from healthy rats, which were inhibited by calhex-231.

CONCLUSION

The results suggest that CaSR activates NLRP3 inflammasome in neutrophils, contributing to ventricular remodelling after AMI. CaSR inhibition may be a potential therapeutic target for heart failure in AMI.

The role of NLRP3 in traumatic brain injury and its regulation by pioglitazone

OBJECTIVE

Perilesional edema is a predominant mechanism underlying secondary brain injury after traumatic brain injury (TBI). Perilesional edema is characterized by inflammation, production of proinflammatory cytokines, and migration of peripheral immune cells into the brain. The nucleotide-binding domain and leucine-rich repeat (NLR) family pyrin domain-containing 3 protein (NLRP3) is a key component of secondary injury. Pioglitazone regulates NLRP3 and other inflammatory cytokines. In the present study, the role of NLRP3 and the pharmacological effects of pioglitazone were investigated in animal TBI models.

METHODS

Brain contusion was induced in a weight drop model involving 3 groups of mice: C57 BL/6 (sham group), NLRP3 knockout (K/O group), and pioglitazone-treated mice (treatment group). The percentage of brain water content of the 3 groups of mice was compared over a period of time. Western blot, immunohistochemistry, and immunofluorescence analyses were conducted to investigate NLRP3-related inflammasomes and the effects of pioglitazone in the TBI models.

RESULTS

Brain edema was the highest on day 3 after TBI in the sham group. Brain edema in both the K/O and the treatment groups was lower than in the sham group. In Western blot, the expression of inflammasomes was higher after TBI in the sham group, but the expression of interleukin-1β, caspase-1, and NLRP3 was decreased significantly following treatment with pioglitazone. The expression of GFAP (glial fibrillary acidic protein) and Iba1 was decreased in both the K/O and treatment groups. In addition, confocal microscopy revealed a decrease in microglial cell and astrocyte activation following pioglitazone therapy.

CONCLUSIONS

The inflammasome NLRP3 plays a pivotal role in regulating cerebral edema and secondary inflammation. Interestingly, pioglitazone reduced cerebral edema and immune response after TBI by downregulating the effects of NLRP3. These results suggest that the clinical application of pioglitazone may be a neuroprotective strategy in TBI.

Glibenclamide alleviates inflammation in oleic acid model of acute lung injury through NLRP3 inflammasome signaling pathway

Background: Pulmonary fat embolism (PFE) is one of the important causes of acute lung injury (ALI), but its pathogenesis is unclear. In recent years, it has been found that the NLRP3 inflammasome is closely related to inflammatory response. However, there are no reports about the involvement of NLRP3 in PFE- associated ALI. Glibenclamide is a kind of hypoglycaemic drug with anti-inflammatory effect. It has been reported to have the anti-inflammatory effect related to inhibiting NLRP3. Objective: To determine whether NLRP3 inflammasome was involved in ALI induced by PFE or whether glibenclamide had therapeutic effects on such lung injury, we designed this experiment. Materials and methods: The rat model of intravenous injection of oleic acid (OA) was used to simulate PFE. Rats were divided into three groups: control, OA and glibenclamide treatment group. Blood free fatty acid (FFA) concentration was determined by ACS-ACOD. Histopathological examinations were taken to assess the severity of lung injury. The expression of NLRP3 pathway and its downstream products were analyzed by IHC, WB, qPCR and ELISA. Results: Four hours after intravenous OA injection, the typical pathological manifestations of ALI accompanied by elevated levels of plasma FFAs were found. The activity of NLRP3 inflammasomes increased in OA group, too. Pretreatment with glibenclamide partly inhibited the increase in NLRP3, caspase-1 and IL-1β expression induced by OA, simultaneously attenuated the lung injury. But it has little effect on the expression of Toll-like receptor 4 (TLR4) expression in this experiment. Conclusion: NLRP3 inflammasome, one of the main components of innate immune response, involved in ALI induced by OA. Glibenclamide can alleviate this kind of ALI by inhibiting rather the NLRP3/caspase-1/IL-1β signaling pathway than the levels of FFAs or TLR4 pathway.

Calcium-sensing receptor mediates interleukin-1β-induced collagen expression in mouse collecting duct cells

The mechanisms that underlie the profibrotic effect of interleukin (IL)-1β are complicated and not fully understood. Recent evidence has suggested the involvement of the calcium-sensing receptor (CaSR) in tubular injury. Therefore, the current study aimed to investigate whether CaSR mediates IL-1β-induced collagen expression in cultured mouse inner medullary collecting duct cells (mIMCD3) and to determine the possible downstream signaling effector. The results showed that IL-1β significantly upregulated the expression of type I and III collagens in a concentration- and time-dependent manner. Moreover, CaSR was expressed in mIMCD3 cells, and its expression was increased by increasing the concentrations and times of IL-1β treatment. Selective inhibitors (Calhex231 or NPS2143) or the siRNA of CaSR attenuated the enhanced expression of type I and III collagens. Furthermore, IL-1β increased nuclear β-catenin protein levels and decreased cytoplasmic β-catenin expression in cells. In contrast, blockage of CaSR by the pharmacological antagonists or siRNA could partially attenuate such changes in the IL-1β-induced nuclear translocation of β-catenin. DKK1, an inhibitor of β-catenin nuclear translocation, further inhibited the expression of type I and III collagens in cells treated with IL-1β plus CaSR antagonist. In summary, these data demonstrated that IL-1β-induced collagen I and III expressions in collecting duct cells might be partially mediated by CaSR and the downstream nuclear translocation of β-catenin.

Modulation of calcium signaling pathway by hepatitis C virus core protein stimulates NLRP3 inflammasome activation

Hepatitis C virus (HCV) infection remains a major cause of hepatic inflammation and liver disease. HCV triggers NLRP3 inflammasome activation and interleukin-1β (IL-1β) production from hepatic macrophages, or Kupffer cells, to drive the hepatic inflammatory response. Here we examined HCV activation of the NLRP3 inflammasome signaling cascade in primary human monocyte derived macrophages and THP-1 cell models of hepatic macrophages to define the HCV-specific agonist and cellular processes of inflammasome activation. We identified the HCV core protein as a virion-specific factor of inflammasome activation. The core protein was both necessary and sufficient for IL-1β production from macrophages exposed to HCV or soluble core protein alone. NLRP3 inflammasome activation by the HCV core protein required calcium mobilization linked with phospholipase-C activation. Our findings reveal a molecular basis of hepatic inflammasome activation and IL-1β release triggered by HCV core protein.

This study deciphers the molecular mechanism of Hepatitis C virus (HCV)-induced hepatic inflammation. HCV triggers NLRP3 inflammasome activation and IL-1β release from hepatic macrophages, thus driving liver inflammation. Using biochemical, virological, and genetic approaches we identified the HCV core protein as the specific viral stimulus that triggers intracellular calcium signaling linked with phospholipase-C activation to drive NLRP3 inflammasome activation and IL-1β release in macrophages.