Role Of NLRP3 Research Articles

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

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. 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. 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. 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.

Abstract 486: Deficiency of Myocardial miR-17-92 Cluster Exacerbates Ischemic Injury in Diabetic Mice

Background: Dysregulation of miRNAs is associated with the pathogenesis of cardiovascular diseases. miR-17-92 cluster has been identified as a negative regulator of inflammation in rheumatoid arthritis. In diabetes, the persistent activation of NLRP3 inflammasome contributes to cardiac dysfunction and the severity of I/R. NLRP3 inflammasome consists of cryopyrin, apoptosis-associated speck-like protein (ASC), and procaspase-1 protein. The inflammasome triggers caspase-1 induced programmed cell death known as pyroptosis. Considering the pivotal role of NLRP3 in diabetes, we investigated the anti-inflammatory role of miR-17-92 cluster against I/R injury. Methods and Results: Adult male wild type and cardiac-specific miR-17-92-deficient mice were fed high-fat-diet (HFD) for 16 weeks before subjecting the heart to ex vivo I (30 min)/R (1 h) in Langendorff mode. HFD-fed mice exhibited impaired glucose tolerance with increased body weight and blood glucose levels (Figs. A, B, C). Tamoxifen-treatment (20 mg/kg, i.p. for 5 days) significantly reduced cardiac miR-17 and miR-20a in HFD-fed miR-17-92-defient mice (Figs. D, E), which resulted in increased myocardial infarct size and cardiac dysfunction following myocardial I/R injury as compared to WT mice (Figs. F, G). ASC aggregation and caspase 1 activity following simulated ischemia/reoxygenation were increased in isolated adult cardiomyocytes from diabetic tamoxifen-inducible miR-17-92-deficient mice as compared to WT mice (Figs. H & I). Conclusion: miR-17-92 plays a critical role in attenuating exacerbated myocardial I/R injury in diabetic mice by regulating NLRP3 inflammasome.

Abstract 2358: Porphyromonas gingivalis promotes colorectal cancer development by regulating NLRP3 inflammasome signaling

Abstract Metagenomic analyses indicate that Porphyromonas spp. is associated with human colorectal carcinoma (CRC), however, whether this is an indirect or causal link remains unclear. We found that Porphyromonas gingivalis (P. gingivalis) were enriched in human stool or FFPE samples from colorectal carcinoma patients compared to colorectal adenoma or healthy subjects. Two colorectal cohort studies demonstrated that P. gingivalis infection was associated with poor prognosis of CRC. Moreover, in the ApcMin/+ mouse model of colorectal tumorigenesis, P. gingivalis increases tumor counts and in the orthotopic rectal MC38 carcinoma model increases tumor growth. Furthermore, tumors from orthotopic MC38 model exposed to P. gingivalis exhibited a tumor-infiltrating myeloid cells recruiting signature that was confirmed in human P.gingivalis-positive colorectal carcinomas. We next evaluated the role of NLRP3 in P. gingivalis promoting on CRC progression. When comparing with wild type mice, the increased tumor growth was subtracted in Nlrp3-/- mice by the same orthotopic MC38 model exposed to P. gingivalis. To determine relevant cell compartment responsible for NLRP3 function, we generated Nlrp3-/- chimeric mice with adoptive bone marrow transplantation by using the same orthotopic tumor model. The results showed the effect of NLRP3 on P. gingivalis pathogenesis was from both hematopoietic and non-hematopoietic sources. Additionally, we performed expression profile to show that NLRP3 attenuates multiple pathways associated with P. gingivalis promoting colorectal cancer development. Collectively, these data suggest that, through recruitment of tumor-infiltrating immune cells by regulating NLRP3 inflammasome activity, P. gingivalis generates a proinflammatory microenvironment that is conductive for colorectal neoplasia progression. Note: This abstract was not presented at the meeting. Citation Format: Zhi Wang, Xi Wang, Yiqun Jia. Porphyromonas gingivalis promotes colorectal cancer development by regulating NLRP3 inflammasome signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2358.

Effect of NLRP3 in liver tissues of mice with hepatic ischemia-reperfusion injury

Objective According investigate the expression of NLRP3 in liver tissues of mice with hepatic ischemia-reperfusion injury (HIRI), to determin the role of NLRP3 in the process of HIRI. Methods Established mice model of partial HIRI. Forty-two male C57BL/6 mice (aged 7 to 8 weeks, weight 20 to 25 g) were respectively divided into 7 groups: no-treatment control group, sham operation group, HIRI groups (2、6、12、24 h) and CY-09 group, 6 mice in each group. The injury of the hepatic tissues in the 7 groups was analyzed based on detecting the levels of alanine transaminase (ALT), aspartate transaminase (AST), interleukin-1β (IL-1β), interleukin-18 (IL-18), tumor necrosis factor-α (TNF-α) by ELISA. HE and TUNEL staining were used to observe the pathological changes of liver tissues after HIRI. Western blotting assay were carried out to detect the expressions of NLRP3 and Caspase-1. Measurement data were expressed as mean±standard deviation (Mean±SD), and one-way variance analysis was used for comparison between groups. If the variance was not uniform, Dunnett C test was used. Results Serum ALT, AST, IL-1β, IL-18 and TNF-α of mice detected in HIRI groups were higher than no-treatment control group and sham operation group at all endpoints (P<0.05). The relative expression of NLRP3 and Caspase-1 in the liver tissues of mice in the HIRI groups were significantly higher than that in the no-treatment control group and sham operation group. Serum ALT, AST, IL-1β, IL-18 and TNF-α of mice detected in CY-09 group were lower than HIRI groups at all endpoints (P<0.05). Less hepatocellular necrosis were exhibited in CY-09 group, comparing to HIRI groups. The hepatocyte apoptosis rate of mice in the CY-09 group was significantly lower than that in the 12 h HIRI group (P<0.05). The relative expression of NLRP3 in the liver tissues of mice in the CY-09 group was significantly lower than that in other groups. The relative expression of Caspase-1 in the liver tissues of mice in the CY-09 group was significantly lower than that in other groups except the no-treatment control group and sham operation group. Conclusions HIRI cause an increase in NLRP3 expression. The inhibition of NLRP3 can reduce HIRI. Key words: Liver diseases; Reperfusion injury; Ischemia; Mice; NLRP3

The Role of NLRP3 in Repairing Sciatic Nerve Injury

The Role of NLRP3 in Repairing Sciatic Nerve Injury

NLRP3 deletion inhibits inflammation-driven mouse lung tumorigenesis induced by benzo(a)pyrene and lipopolysaccharide

BackgroundInflammatory micro-environment has been proposed to play a critical role in lung tumorigenesis. NLRP3 is known as an intracellular receptor involving inflammation and has been reported which is increasingly associated with tumor development, but the role in inflammation-driven lung cancer has not been fully clarified. In this study, we investigated whether lipopolysaccharide (LPS)-induced pulmonary inflammation could contribute to lung tumorigenesis induced by benzo(a)pyrene [B(a)p] in C57BL/6J mice and the role of NLRP3 in the pathogenesis.MethodsNLRP3−/− mice and C57BL/6J mice (wide-type, WT) were instilled intratracheally with B(a)p (1 mg/mouse) once a week for 4 times [the week of the last time of B(a)p treatment named Week 0], and mice were then instilled intratracheally with LPS at Week 3, 2.5 μg/mouse, once every three weeks for 5 times. At Week 30, the incidence, number, size and histopathology of lung tumor were analyzed.ResultsMice exposed to B(a)p or B(a)p plus LPS could induce lung tumors, whereas LPS or vehicles treatment could not induce lung tumorigenesis. In WT mice, B(a)p plus LPS exposure significantly increased tumor incidence, mean tumor count and tumor size of visible tumors of lungs compared with B(a)p treatment alone, and NLRP3 deletion inhibited lung tumorigenesis induced by B(a)p or B(a)p plus LPS. Histopathological examination found LPS-induced pulmonary inflammatory changes enhanced lung tumorigenesis induced by B(a)p in WT mice, deletion of NLRP3 improved the inflammatory changes induced by LPS and the number and size of pathological tumor nests induced by B(a)p or B(a)p plus LPS. In addition, we found B(a)p treatment and B(a)p plus LPS treatment predominately induced the development of adenoma.ConclusionLPS enhanced B(a)p-induced lung tumorigenesis in WT and NLRP3−/− mice of C57BL/6J strain, and NLRP3 deletion inhibits lung tumorigenesis induced by B(a)p or B(a)p plus LPS.

The Role of NLRP3 and IL-1β in the Pathogenesis of Inflammatory Bowel Disease

It is logical to assume that a major pro-inflammatory mechanism, i.e., the NLRP3 inflammasome would play a prominent role in the pathogenesis of the Inflammatory Bowel Disease (IBD) in humans. However, while both studies of murine models of gut disease and patients provide data that the main cytokine product generated by this inflammasome, IL-1β, does in fact contribute to inflammation in IBD, there is no evidence that IL-1β plays a decisive or prominent role in “ordinary” patients with IBD (Crohn's disease). On the other hand, there are several definable point mutations that result in over-active NLRP3 inflammasome activity and in these cases, the gut inflammation is driven by IL-1β and is treatable by biologic agents that block the effects of this cytokine.

NLRP3 deficiency exacerbates enterovirus infection in mice.

The role for the NOD-like receptor (NLR) P3 inflammasome in enterovirus infection remains controversial. Available data suggest that the NLRP3 inflammasome is protective against enterovirus A71 but detrimental to the host during coxsackievirus B3 (CVB3) infection. CVB3 is a common etiologic agent associated with myocarditis and pancreatitis. Previous findings on the role of NLRP3 in CVB3 were based primarily on indirect evidence. Here, we utilized NLRP3 knockout mice as well as immune and cardiac cells to investigate the direct interplay between CVB3 infection and NLRP3 activation. We demonstrated that NLRP3 knockout mice exhibited more severe disease phenotype after CVB3 infection (significantly higher virus titers), increased myocardial, and pancreatic damage, as well as markedly impaired cardiac function compared to nontransgenic control mice. We further showed that NLRP3 activity was enhanced during early stage of CVB3 infection, as evidenced by increased gene expression and/or secretion of IL-1β and caspase-1. Finally, we demonstrated that CVB3 inactivates the NLRP3 inflammasome by degrading NLRP3 and its upstream serine/threonine-protein kinase receptor-interacting protein 1/3 via the proteolytic activity of virus-encoded proteinases. Taken together, our results reveal the functional significance of NLRP3 in host antiviral immunity against CVB3 infection and the mechanisms by which CVB3 has evolved to counteract the host defense response.-Wang, C., Fung, G., Deng, H., Jagdeo, J., Mohamud, Y., Xue, Y. C., Jan, E., Hirota, J. A., Luo, H. NLRP3 deficiency exacerbates enterovirus infection in mice.

NLRP3 in somatic non-immune cells of rodent and primate testes.

NLRP3 is part of the NLRP3 inflammasome and a global sensor of cellular damage. It was recently discovered in rodent Sertoli cells. We investigated NLRP3 in mouse, human and non-human primate (marmoset and rhesus macaque) testes, employing immunohistochemistry. Sertoli cells of all species expressed NLRP3, and the expression preceded puberty. In addition, peritubular cells of the adult human testes expressed NLRP3. NLRP3 and associated genes (PYCARD, CASP1, IL1B) were also found in isolated human testicular peritubular cells and the mouse Sertoli cell line TM4. Male infertility due to impairments of spermatogenesis may be related to sterile inflammatory events. We observed that the expression of NLRP3 was altered in the testes of patients suffering from mixed atrophy syndrome, in which tubules with impairments of spermatogenesis showed prominent NLRP3 staining. In order to explore a possible role of NLRP3 in male infertility, associated with sterile testicular inflammation, we studied a mouse model of male infertility. These human aromatase-expressing transgenic mice (AROM+) develop testicular inflammation and impaired spermatogenesis during aging, and the present data show that this is associated with strikingly elevated Nlrp3 expression in the testes compared to WT controls. Interference by aromatase inhibitor treatment significantly reduced increased Nlrp3 levels. Thus, throughout species NLRP3 is expressed by somatic cells of the testis, which are involved in testicular immune surveillance. We conclude that NLRP3 may be a novel player in testicular immune regulation.

Inflammasomes, the eye and anti-inflammasome therapy.

Inflammasomes, key molecular regulators that play an important role in inflammation, consist of a central protein, an adaptor protein ASC (apoptosis speck-like protein) and a caspase-1 protein. Upon activation, caspase-1 induces maturation of cytokines such as interleukin-1β (IL-1β) and interleukin-18 (IL-18). The release of these cytokines can result in inflammation. Inflammasomes are activated by a variety of factors and their activation involves complex signalling leading to resolution of infection, but can also contribute to the pathology of inflammatory, autoimmune, and infectious diseases. The role of NLRP1, NLRP3, NLRC4 and AIM2 inflammasomes in the pathogenesis of ocular diseases such as glaucoma, age related macular degeneration (AMD), diabetic retinopathy, dry eye and infections of the eye has been established over the past decade. In experimental studies and models, inhibition of inflammasomes generally helps to reduce the inflammation associated with these eye diseases, but as yet the role of these inflammasomes in many human eye diseases is unknown. Therefore, a need exists to study and understand various aspects of inflammasomes and their contribution to the pathology of human eye diseases. The goal of this review is to discuss the role of inflammasomes in the pathology of eye diseases, scope for anti-inflammasome therapy, and current research gaps in inflammasome-related eye disease.

BAY 11-7082 inhibits the NF-κB and NLRP3 inflammasome pathways and protects against IMQ-induced psoriasis.

BAY 11-7082 antagonizes I-κB kinase-β preventing nuclear translocation of nuclear factor-κB (NF-κB); it also inhibits NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation. NF-κB is involved in psoriasis, whereas the role of NLRP3 is controversial. We investigated BAY 11-7082 effects in an experimental model of psoriasis-like dermatitis. Psoriasis-like lesions were induced by a topical application of imiquimod (IMQ) cream (62.5mg/day) on the shaved back skin of C57BL/6 and NLRP3 knockout (KO) mice for 7 consecutive days. Sham psoriasis animals were challenged with Vaseline cream. Sham and IMQ animals were randomized to receive BAY 11-7082 (20mg/kg/i.p.) or its vehicle (100μl/i.p of 0.9% NaCl). Skin of IMQ animals developed erythema, scales, thickening and epidermal acanthosis. IMQ skin samples showed increased expression of pNF-κB and NLRP3 activation. BAY 11-7082 blunted epidermal thickness, acanthosis and inflammatory infiltrate. BAY 11-7082 reduced pNF-κB, NLRP3, tumour necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β expression, blunted the phosphorylation of signal transducer and activators of transcription 3 (STAT3) and decreased IL-23 levels. In addition, BAY 11-7082 reawakened the apoptotic machinery. NLRP3 KO animals showed a reduced total histological score but persistent mild acanthosis, dermal thickness and expression of pNF-κB and pSTAT3, following IMQ application. Our data suggest that BAY 11-7082 might represent an interesting approach for the management of psoriasis-like dermatitis depending on the dual inhibition of NF-κB and NLRP3.

Inflammasomes in Mycobacterium tuberculosis-Driven Immunity.

The development of effective innate and subsequent adaptive host immune responses is highly dependent on the production of proinflammatory cytokines that increase the activity of immune cells. The key role in this process is played by inflammasomes, multimeric protein complexes serving as a platform for caspase-1, an enzyme responsible for proteolytic cleavage of IL-1β and IL-18 precursors. Inflammasome activation, which triggers the multifaceted activity of these two proinflammatory cytokines, is a prerequisite for developing an efficient inflammatory response against pathogenic Mycobacterium tuberculosis (M.tb). This review focuses on the role of NLRP3 and AIM2 inflammasomes in M.tb-driven immunity.

Donor and recipient genetic variants in NLRP3 associate with early acute rejection following kidney transplantation.

NLRP3 (NOD-like receptor family, pyrin domain containing 3) is a member of the inflammasome family and is of special interest in renal disease. Experimental studies have shown that Nlrp3 plays a significant role in the induction of renal damage and dysfunction in acute and chronic renal injury. However, the role of NLRP3 in human renal disease is completely unknown. From a retrospective cohort study, we determined in 1271 matching donor and recipient samples if several NLRP3 single nucelotide polymorphisms (SNPs) were associated with primary non-function (PNF), delayed graft function (DGF), biopsy-proven acute rejection (BPAR) and death-censored graft and patient survival. NLRP3 gain-of-function SNP (rs35829419) in donors was associated with an increased risk of BPAR while NLRP3 loss-of-function SNP (rs6672995) in the recipient was associated with a decreased risk of BPAR in the first year following renal transplantation (HR 1.91, 95% CI 1.38–2.64, P < 0.001 and HR 0.73, 95% CI 0.55–0.97, P = 0.03 resp.). NLRP3 SNPs in both donor and recipient were not associated with PNF, DGF, graft survival or patient survival. We conclude that genetic variants in the NLRP3 gene affect the risk of acute rejection following kidney transplantation.

The role of NLRP3 and AIM2 in inflammasome activation during Brucella abortus infection.

The innate immune system is essential for the detection and elimination of bacterial pathogens. Upon inflammasome activation, caspase-1 cleaves pro-IL-1β and pro-IL-18 to their mature forms IL-1β and IL-18, respectively, and the cell undergoes inflammatory death termed pyroptosis. Here, we reviewed recent findings demonstrating that Brucella abortus ligands activate NLRP3 and AIM2 inflammasomes which lead to control of infection. This protective effect is due to the inflammatory response caused by IL-1β and IL-18 rather than cell death. Brucella DNA is sensed by AIM2 and bacteria-induced mitochondrial reactive oxygen species is detected by NLRP3. However, deregulation of pro-inflammatory cytokine production can lead to immunopathology. Nervous system invasion by bacteria of the genus Brucella results in an inflammatory disorder termed neurobrucellosis. Herein, we discuss the mechanism of caspase-1 activation and IL-1β secretion in glial cells infected with B. abortus. Our results demonstrate that the ASC inflammasome is indispensable for inducing the activation of caspase-1 and secretion of IL-1β upon infection of astrocytes and microglia with Brucella. Moreover, our results demonstrate that secretion of IL-1β by Brucella-infected glial cells depends on NLRP3 and AIM2 and leads to neurobrucellosis. Further, the inhibition of the host cell inflammasome as an immune evasion strategy has been described for bacterial pathogens. We discuss here that the bacterial type IV secretion system VirB is required for inflammasome activation in host cells during infection. Taken together, our results indicate that Brucella is sensed by ASC inflammasomes mainly NLRP3 and AIM2 that collectively orchestrate a robust caspase-1 activation and pro-inflammatory response.

Inflammasome-independent NLRP3 is required for epithelial-mesenchymal transition in colon cancer cells

Inflammasome NLRP3 plays a crucial role in the process of colitis and colitis­-associated colon cancer. Even though much is known regarding the NLRP3 inflammasome that regulates pro-inflammatory cytokine release in innate immune cells, the role of NLRP3 in non-immune cells is still unclear. In this study, we showed that NLRP3 was highly expressed in mesenchymal-like colon cancer cells (SW620), and was upregulated by tumor necrosis factors-α (TNF-α) and transforming growth factor-β1 (TGF-β1) respectively, during EMT in colon cancer epithelial cells HCT116 and HT29. Knockdown of NLRP3 retained epithelial spindle-like morphology of HCT116 and HT29 cells and reversed the mesenchymal characteristic of SW620 cells, indicated by the decreased expression of vimentin and MMP9 and increased expression of E-cadherin. In addition, knockdown of NLRP3 in colorectal carcinoma cells displayed diminished cell migration and invasion. Interestingly, during the EMT process induced by TNF-α or TGF-β1, the cleaved caspase-1 and ASC speck were not detected, indicating that NLRP3 functions in an inflammasome-independent way. Further studies demonstrated that NLRP3 protein expression was regulated by NF-κB signaling in TNF-α or TGF-β1-induced EMT, as verified by the NF-κB inhibitor Bay 11-7082. Moreover, NLRP3 knockdown reduced the expression of Snail1, indicating that NLRP3 may promote EMT through regulating Snail1. In summary, our results showed that the NLRP3 expression, not the inflammasome activation, was required for EMT in colorectal cancer cells.

ROS-Mediated NLRP3 Inflammasome Activation in Brain, Heart, Kidney, and Testis Ischemia/Reperfusion Injury.

Ischemia and reperfusion (I/R) causes a reduction in arterial blood supply to tissues, followed by the restoration of perfusion and consequent reoxygenation. The reestablishment of blood flow triggers further damage to the ischemic tissue through reactive oxygen species (ROS) accumulation, interference with cellular ion homeostasis, and inflammatory responses to cell death. In normal conditions, ROS mediate important beneficial responses. When their production is prolonged or elevated, harmful events are observed with peculiar cellular changes. In particular, during I/R, ROS stimulate tissue inflammation and induce NLRP3 inflammasome activation. The mechanisms underlying the activation of NLRP3 are several and not completely elucidated. It was recently shown that NLRP3 might sense directly the presence of ROS produced by normal or malfunctioning mitochondria or indirectly by other activators of NLRP3. Aim of the present review is to describe the current knowledge on the role of NLRP3 in some organs (brain, heart, kidney, and testis) after I/R injury, with particular regard to the role played by ROS in its activation. Furthermore, as no specific therapy for the prevention or treatment of the high mortality and morbidity associated with I/R is available, the state of the art of the development of novel therapeutic approaches is illustrated.

NLRP3 SIGNALING AND ITS ROLE IN ATHEROSCLEROSIS: REVIEW AND NEW INSIGHTS

Atherosclerosis is associated with high morbidity and mortality. Recently, the roleof inflammation in the cascade of events leading to the development ofatherosclerosis has been the center of attention. Inflammasomes are proteincomplexes that are required for the secretion and maturation of proinflammatorycytokines as well as activation of inflammatory caspases. Among theseinflammasomes, the NLRP3 inflammasome has gained more importance due toits implication in a number of metabolic diseases. The relation of NLRP3inflammasome to atherosclerosis is an emerging and exciting area of ongoingresearch. Despite major leaps in our research of the signaling pathways ofNLRP3 inflammasome, the entire assembly and activation process and itsclinical implications are still eluding our understanding. This article will reviewsome major aspects of the inflammasome signaling pathways. It will also reviewpast studies and highlight recent developments in understanding the role ofNLRP3 inflammasomes in relation to atherosclerosis.

Role of NLRP3 Inflammasomes in Hepatic Ischemia-reperfusion Injury

Increasing evidence indicates that inflammation plays an important role in the pathogenesis of hepatic ischemia-reperfusion (I/R) injury. However, it is still unclear how I/R stimuli induce inflammatory responses in the liver. NLRP3 is an intracellular pattern recognition receptor and a component of NLRP3 inflammasomes that can induce caspase-1 activation, and regulate the processing of a potent inflammatory cytokine, interleukin-1β (IL-1β). Several investigations have recently suggested that inflammatory responses are mediated through NLRP3 inflammasomes in hepatic I/R injury. On the other hand, we recently found that NLRP3 regulates neutrophil functions and contributes to hepatic I/R injury independently of inflammasomes. This review summarizes the basic information on NLRP3 inflammasomes and discusses inflammasome-dependent/independent roles of NLRP3 in the pathophysiology of hepatic I/R injury. Rec.12/21/2014, Acc.1/22/2015, pp61-68

Muramyl dipeptide activates human beta defensin 2 and pro-inflammatory mediators through Toll-like receptors and NLRP3 inflammasomes in human dental pulp cells.

The expression levels of intracellular pyrin domain-containing 3 (NLRP3) and microbial pattern-recognition receptors, such as nucleotide-binding oligomerization domain 2 (NOD2), have been reported in human dental pulp cells (HDPCs) and inflamed dental pulp tissue, but the role of NLRP3 and Toll-like receptors (TLRs) in the production of human beta defensin 2 (hBD2) and inflammatory cytokines against invading pathogens remains poorly defined. The aim of this study was to determine whether the NOD2 ligand muramyl dipeptide (MDP) upregulates hBD2 and inflammatory cytokines and whether this response is dependent on TLRs and NLRP inflammasomes in HDPCs. The effects of MDP on the expression of hBD2, TLRs, inflammasomes, and pro-inflammatory mediators in HDPCs were examined using Western blotting and reverse transcription-polymerase chain reaction. Levels of pro-inflammatory cytokines, such as nitric oxide (NO) and prostaglandin E2 (PGE2), were determined by enzyme-linked immunosorbent assay. MDP upregulated hBD2, TLR2, and TLR4 mRNAs and protein levels in a dose- and time-dependent manner. TLR2 and TLR4 neutralizing blocking antibodies and NOD2- and hBD2-specific small interfering RNAs (siRNAs) attenuated the MDP-induced production of NO, PGE2, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-8 and upregulated inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX2) in HDPCs. Additionally, MDP activated inflammasome-related genes, such as NLRP3, caspase 1, apoptotic speck protein containing a caspase recruitment domain, and IL-1β. Furthermore, silencing of the NLRP3 gene using a siRNA significantly decreased the MDP-induced expression of hBD2 and cytokines, such as iNOS-derived NO, COX2, PGE2, TNF-α, IL-6, and IL-8. These results suggest that NOD2 activates the TLR2, TLR4, and NLRP3 inflammasome-signaling pathways in HDPCs to induce the production of multiple inflammatory mediators and antimicrobial peptides, which in turn promote pulp immune defense against microbial challenge. The TLR and NLRP3 inflammasome pathways may represent an important modulatory mechanism of immune defense responses during the progression of pulpitis. Our results suggest that local inhibition of NLRP3 and TLRs may reduce the impact of cytokine-mediated host destructive processes in pulpitis.

Enhanced NLRP3, caspase-1, and IL- 1β levels in degenerate human intervertebral disc and their association with the grades of disc degeneration.

The NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome plays an important role in a variety of diseases. However, the role of NLRP3 in the human intervertebral disc (IVD) degeneration remains unknown. In the present study, we assessed the expression levels of the NLRP3 inflammasome and its downstream targets caspase-1 and IL-1β in 45 degenerate and seven nondegenerate IVD samples. The correlation between the degeneration scores and expression levels of NLRP3, caspase-1, and IL-1β were also analyzed. The mRNA expression levels of the three molecules (NLRP3, caspase-1, and IL-1β) were higher in the degenerate IVDs group than the controls (nondegenerate IVDs group). Immunohistochemistry showed that the expression levels of all three molecules were markedly increased in the nucleus pulposus of degenerate IVDs compared with nondegenerate IVDs. There was a positive correlation between the degeneration scores and the expression levels of the NLRP3 inflammasome as well as its downstream targets caspase-1 and IL-1β. The findings suggest that excessive activation of the NLRP3 inflammasome results in overproduction of downstream IL-1β, which participates in the pathogenesis of human IVD degeneration. Therefore, the NLRP3 inflammasome might serve as a potential therapeutic target for the prevention and treatment of IVD degeneration.