The Role of the NLRP3 Inflammasome in Fibrosis

NLRP3 inflammasome in fibroblasts links tissue damage with inflammation in breast cancer progression and metastasis

Cancer-Associated Fibroblasts (CAFs) were shown to orchestrate tumour-promoting inflammation in multiple malignancies, including breast cancer. However, the molecular pathways that govern the inflammatory role of CAFs are poorly characterised. In this study we found that fibroblasts sense damage-associated molecular patterns (DAMPs), and in response activate the NLRP3 inflammasome pathway, resulting in instigation of pro-inflammatory signalling and secretion of IL-1β. This upregulation was evident in CAFs in mouse and in human breast carcinomas. Moreover, CAF-derived inflammasome signalling facilitated tumour growth and metastasis, which was attenuated when NLRP3 or IL-1β were specifically ablated. Functionally, CAF-derived inflammasome promoted tumour progression and metastasis by modulating the tumour microenvironment towards an immune suppressive milieu and by upregulating the expression of adhesion molecules on endothelial cells. Our findings elucidate a mechanism by which CAFs promote breast cancer progression and metastasis, by linking the physiological tissue damage response of fibroblasts with tumour-promoting inflammation.

Elevated serum levels of interleukin-1β and interleukin-33 in patients with systemic sclerosis in Chinese population

PURPOSE OF THE STUDY

Systemic sclerosis (SSc) is a multisystem autoimmune disease. Although the pathogenesis of the disease remains incompletely understood, some cytokines or growth factors which regulate SSc induction may be involved in the injury of endothelial cells and the modulation of leukocyte function. We aimed to perform this case-control study to determine serum levels of interleukin (IL)-1α, IL-1β, IL-18 and IL-33 and their associations with clinical manifestations in SSc patients.

MATERIALS AND METHODS

There were 56 patients with SSc and 56 healthy individuals who were recruited from local hospital between 2012 and 2014. Serum IL-1α, IL-1β, IL-18 and IL-33 levels were measured with specific enzyme-linked immunosorbent assay kits.

RESULTS

Univariate analysis revealed that serum IL-1β, IL-18 and IL-33 levels in SSc patients were significantly higher than that in healthy controls. After adjusting possible confounding factors (sex, age, smoking and drinking) by multivariable analyses, serum IL-1β levels (OR = 1.082; 95 % CI: 1.013-1.155) and serum IL-33 levels (OR = 1.100; 95 %CI: 1.022-1.185) were still related factors. There were interrelationships among the serum levels of IL-1α, IL-1β, IL-18 and IL-33 and these associations were not consistent in SSc patients and controls. No associations of serum IL-1α, IL-1β, IL-18 and IL-33 levels with clinical parameters were found.

CONCLUSION

IL-1β and IL-33 may contribute to the development of SSc. While there were no direct associations between these cytokines and disease manifestations, they still could be considered as serum markers of development of SSc. Further studies are required to validate this incipient data.

MicroRNAs as important regulators of the NLRP3 inflammasome

Inflammasomes are a group of cytosolic multi-protein signaling complexes that regulate maturation of the interleukin (IL)-1 family cytokines IL-1β and IL-18 through activation of inflammatory caspase-1. The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome is the best characterized and consists of several key components that are assembled and activated in response to different endogenous and exogenous signals. The NLRP3 inflammasome is common to a number of human inflammatory diseases and its targeting may lead to novel anti-inflammatory therapy. NLRP3 inflammasome activation is tightly regulated by different mechanisms especially post-transcriptional modulation via microRNAs (miRNA). MicroRNAs are small endogenous noncoding RNAs that are 21-23 nucleotides in length and control the expression of various genes through binding to the 3'-untranslated regions of the respective mRNA and subsequent post-transcriptional regulation. MicroRNAs have recently been recognized as crucial regulators of the NLRP3 inflammasome. In this review, we summarize the current understanding of the role of miRNAs in the regulation of NLRP3 inflammasome complexes and their impact on the pathogenesis of inflammatory disease processes.

Dual Role of Triptolide in Interrupting the NLRP3 Inflammasome Pathway to Attenuate Cardiac Fibrosis

In a previous paper, we reported that triptolide (TP), a commonly used immunomodulator, could attenuate cardiac hypertrophy. This present study aimed to further explore the inhibition of cardiac fibrosis by TP and the possible mechanism from the perspective of the NOD-like receptor protein 3 (NLRP3) inflammasome. Hematoxylin-eosin and Masson’s staining, immunohistochemistry, and immunofluorescence were performed to observe cardiac fibrotic changes in mice and mouse cardiac fibroblasts (CFs). The Western blot, colocalization, and immunoprecipitation were applied to detect protein expression and interactions. Results suggested that TP dose-dependently inhibited cardiac fibrosis induced by isoproterenol and collagen production of CFs induced by angiotensin II. TP exhibited an antifibrotic effect via inhibiting activation of the NLRP3 inflammasome, which sequentially decreased IL-1β maturation, myeloid differentiation factor 88 (MyD88)-related phosphorylation of c-Jun N-terminal kinase (JNK), extracellular regulated protein kinase 1/2 (ERK1/2), and TGF-β1/Smad signaling, and ultimately resulted in less collagen production. Moreover, TP showed no antifibrotic effect in Nlrp3-knockout CFs. Notably, TP inhibited the expression of NLRP3 and apoptosis-associated speck-like proteins containing a caspase recruitment domain (ASC) as well as inflammasome assembly, by interrupting the NLRP3-ASC interaction to inhibit inflammasome activation. Finally, TP indeed inhibited the NLRP3-TGFβ1-Smad pathway in vivo. Conclusively, TP was found to play a dual role in interrupting the activation of the NLRP3 inflammasome to attenuate cardiac fibrosis.

Ninjurin1 Plays a Crucial Role in Pulmonary Fibrosis by Promoting Interaction between Macrophages and Alveolar Epithelial Cells

The transmembrane nerve injury-induced protein 1 (Ninjurin1 or Ninj1) is involved in progressing inflammatory diseases. In this study, we aimed to investigate a novel function of Ninj1 in pulmonary fibrosis. We found that the expression of Ninj1 in a patient cohort was upregulated in the lung specimens of idiopathic pulmonary fibrosis patients as well as mice with bleomycin-induced pulmonary fibrosis. In addition, the BLM-injected Ninj1 KO mice exhibited a mild fibrotic phenotype, as compared to WT mice. Therefore, we hypothesized that Ninj1 would play an important role in the development of pulmonary fibrosis. We discovered that Ninj1 expression increased in BLM-treated macrophages and alveolar epithelial cells (AECs). Interestingly, macrophages bound to BLM-treated AECs were activated. However, when Ninj1 expression was suppressed in either of AECs or macrophages, contact-dependent activation of macrophages with AECs was diminished. In addition, introduction of recombinant mouse Ninj1^1-50 to macrophages triggered an inflammatory response, but did not stimulate Ninj1-deficient macrophages. In conclusion, we propose that Ninj1 may contribute to activation of macrophages by enhancing interaction with AECs having elevated Ninj1 expression due to injury-inducing stimuli. Consequently, Ninj1 may be involved in the development of pulmonary fibrosis by enhancing inflammatory response of macrophages.

Salvianolate reduces atrial fibrillation through suppressing atrial interstitial fibrosis by inhibiting TGF-β1/Smad2/3 and TXNIP/NLRP3 inflammasome signaling pathways in post-MI rats

BACKGROUND

Salvianolate is the main water-soluble bioactive compound of Salvia Miltiorrhiza Bunge and is now clinically used in the treatment of cardiovascular diseases in China. However, its applications in the prevention of atrial interstitial fibrosis (AIF) and atrial fibrillation (AF) are not fully revealed.

PURPOSES

To investigate the preventive effect of salvianolate on the pathogenesis of AF in post-myocardial infarction (MI) rats and to elucidate the potential mechanisms.

MATERIALS AND METHODS

Rats underwent left anterior descending coronary artery ligation were randomized into four groups and administered intraperitoneally with vehicle (MI group, n = 13), or 10, 20 and 40 mg/kg salvianolate (Sal-L, Sal-M and Sal-H group, n = 13, 14 and 13 respectively) for totally five weeks. Rats underwent sham operation was used as control group (Sham, n = 10). Then, echocardiography and AF inducibility test were detected. Tissues and serum were collected for Sirius red and fast green counter stain or hematoxylin-eosin to assess atrial interstitial fibrosis and hypertrophy, or for western blot and ELISA analysis.

RESULTS

Salvianolate injection significantly improved cardiac function, reduced left atrial enlargement and P-wave duration, and decreased not only the vulnerability to AF but also AF duration. Histologic analysis showed that salvianolate mitigated AIF and atrial hypertrophy. Western blot analysis found that salvianolate inhibited the TGFβ1/Smad2/3 mediated-collagen deposition and inhibited the TXNIP/NLRP3 inflammasome /IL-1β and IL-18 signal pathway. ELISA analysis showed that salvianolate significantly reduced the serum concentrations of BNP, IL-6, CRP and TGFβ1.

CONCLUSIONS

Salvianolate may constitute a novel upstream therapy for AF by suppressing AIF. The underlying mechanism may be attributable to its inhibitory effects on TGF-β1/Smad2/3 and TXNIP/NLRP3 inflammasome signaling pathway.

Origin and Consequences of Necroinflammation

When cells undergo necrotic cell death in either physiological or pathophysiological settings in vivo, they release highly immunogenic intracellular molecules and organelles into the interstitium and thereby represent the strongest known trigger of the immune system. With our increasing understanding of necrosis as a regulated and genetically determined process (RN, regulated necrosis), necrosis and necroinflammation can be pharmacologically prevented. This review discusses our current knowledge about signaling pathways of necrotic cell death as the origin of necroinflammation. Multiple pathways of RN such as necroptosis, ferroptosis, and pyroptosis have been evolutionary conserved most likely because of their differences in immunogenicity. As the consequence of necrosis, however, all necrotic cells release damage associated molecular patterns (DAMPs) that have been extensively investigated over the last two decades. Analysis of necroinflammation allows characterizing specific signatures for each particular pathway of cell death. While all RN-pathways share the release of DAMPs in general, most of them actively regulate the immune system by the additional expression and/or maturation of either pro- or anti-inflammatory cytokines/chemokines. In addition, DAMPs have been demonstrated to modulate the process of regeneration. For the purpose of better understanding of necroinflammation, we introduce a novel classification of DAMPs in this review to help detect the relative contribution of each RN-pathway to certain physiological and pathophysiological conditions.

Silencing long non-coding RNA Kcnq1ot1 alleviates pyroptosis and fibrosis in diabetic cardiomyopathy

Diabetes cardiomyopathy (DCM) is a critical complication of long-term chronic diabetes mellitus and is characterized by myocardial fibrosis and myocardial hypertrophy. It has been suggested that DCM is related to pyroptosis, a programmed cell death associated with inflammation. The long non-coding RNA Kcnq1ot1 is involved in different pathophysiological mechanisms of multiple diseases, including acute myocardial damage and arrhythmia. Our previous study found that Kcnq1ot1 was elevated in left ventricular tissue of diabetic mice. However, whether Kcnq1ot1 is capable of regulating pyroptosis and fibrosis in high glucose-treated cardiac fibroblasts remains unknown. The aim of the study was to investigate the mechanisms of Kcnq1ot1 in DCM. Our study revealed that silencing Kcnq1ot1 by a lentivirus-shRNA improved cardiac function and fibrosis, ameliorated pyroptosis, and inhibited TGF-β1/smads pathway in C57BL/6 mice. In vitro, experiments revealed that Kcnq1ot1 and pyroptosis were activated in cardiac fibroblasts treated with 30 mmol/l glucose. Furthermore, Kcnq1ot1 knockdown by a small interfering RNA decreased caspase-1 expression. Bioinformatic prediction and luciferase assays showed that Kcnq1ot1 functioned as a competing endogenous RNA to regulate the expression of caspase-1 by sponging miR-214-3p. In addition, silencing Kcnq1ot1 promoted gasdermin D cleavage and the secretion of IL-1β, thus repressing the TGF-β1/smads pathway in high glucose-treated cardiac fibroblasts through miR-214-3p and caspase-1. Therefore, Kcnq1ot1/miR-214-3p/caspase-1/TGF-β1 signal pathway presents a new mechanism of DCM progression and could potentially be a novel therapeutic target.

Protective Effects of Nintedanib against Polyhexamethylene Guanidine Phosphate-Induced Lung Fibrosis in Mice

Nintedanib (NDN), a tyrosine kinase inhibitor, has been shown to have anti-tumor, anti-inflammatory, and anti-fibrotic effects in several reports. We investigated the protective effects of NDN against polyhexamethylene guanidine phosphate (PHMG)-induced lung fibrosis in mice. The following three experimental groups were evaluated: (1) vehicle control; (2) PHMG (1.1 mg/kg); and (3) PHMG & NDN (60 mg/kg). PHMG induced pulmonary inflammation and fibrosis by intratracheal instillation in mice. In contrast, NDN treatment effectively alleviated the PHMG induced lung injury, and attenuated the number of total cells and inflammatory cells in the bronchoalveolar lavage fluid, including the fibrotic histopathological changes, and also reduced the hydroxyproline content. NDN also significantly decreased the expression of inflammatory cytokines and fibrotic factors, and the activation of the NLRP3 inflammasome in lung tissues. These results suggest that NDN may mitigate the inflammatory response and development of pulmonary fibrosis in the lungs of mice treated with PHMG.

Saikosaponin‑d alleviates carbon‑tetrachloride induced acute hepatocellular injury by inhibiting oxidative stress and NLRP3 inflammasome activation in the HL‑7702 cell line

Saikosaponin‑d (SSd) the primary active component of triterpene saponin derived from Bupleurum falcatum L., possesses anti‑inflammatory and antioxidant properties. The present study aimed to examine the potential therapeutic effects of SSd on carbon tetrachloride (CCl4)‑induced acute hepatocellular injury in the HL‑7702 cell line and its underlying mechanisms. HL‑7702 cells were treated with SSd at different doses (0.5, 1 or 2 µmol/l). Cell viability was determined using an MTT assay. Injury was assessed by the levels of serum alanine aminotransferase (ALT) and aspartate transaminase (AST). Oxidative stress was assessed using malondialdehyde (MDA) content and total‑superoxide dismutase (T‑SOD) activity. The expression of nucleotide‑binding domain, leucine‑rich‑containing family, pyrin domain‑containing‑3 (NLRP3), apoptosis‑associated speck‑like protein (ASC), caspase‑1 and high mobility group protein B1 (HMGB1) was assessed by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blot analysis. Interleukin (IL)‑1β and IL‑18 were determined by RT‑qPCR and ELISA. SSd attenuated the inhibition of cell viability and the high AST and ALT levels induced by CCl4 in HL‑7702 cells. Oxidative stress was induced in HL‑7702 cells by CCl4, as demonstrated by the increase of MDA and the decrease of T‑SOD activity. These changes were reversed by SSd. SSd significantly downregulated the mRNA and protein expression of NLRP3, ASC, caspase‑1, IL‑1β, IL‑18 and HMGB1 induced by CCl4. In conclusion SSd alleviated CCl4‑induced acute hepatocellular injury, possibly by inhibiting oxidative stress and NLRP3 inflammasome activation in the HL‑7702 cell line.

Deletion of Thioredoxin-interacting protein ameliorates high fat diet-induced non-alcoholic steatohepatitis through modulation of Toll-like receptor 2-NLRP3-inflammasome axis: Histological and immunohistochemical study

Endemic prevalence of obesity is associated with alarming increases in non-alcoholic steatohepatitis (NASH) with limited available therapeutics. Toll-like receptor2 (TLR2) and Nod-like receptor protein 3 (NLRP3) Inflammasome are implicated in hepatic steatosis, inflammation and fibrosis; the histological landmark stages of NASH. TXNIP, a member of α-arrestin family activates NLRP3 in response to various danger stimuli. The aim of current work was to investigate the effect of TXNIP genetic deletion on histological manifestations of high fat diet-induced steatohepatitis and activation of TLR2-NLRP3-inflammasome axis. Wild-type mice (WT) and TXNIP knock out (TKO) littermates were randomized to normal diet (WT-ND and TKO-ND) or high fat diet (HFD, 60% fat) (WT-HFD and TKO-HFD). After 8-weeks, liver samples from all groups were evaluated by histological, immunohistochemical and western blot analysis. HFD resulted in significant induction of micro and macrovesicular hepatic steatosis, that was associated with increased inflammatory immune cell infiltration in WT-HFD compared with WT-ND and TKO-ND controls, but not in TKO-HFD group. In parallel, WT-HFD group showed significant fibrosis and α-SMA expression; a marker of pro-fibrotic stellate-cell activation, in areas surrounding the central vein and portal circulation, versus all other groups. Western blot revealed increased activation of TLR2-NLRP3 inflammasome pathway and downstream IL-1β and TNFα in WT-HFD group, but not in TKO-HFD group. IL-1β expression coincided within the same areas of steatosis, inflammatory cell infiltration, collagen deposition and α-SMA expression in WT-HFD mice, that was significantly reduced in TKO-HFD mice. In conclusion, TXNIP deletion ameliorates the HFD-induced steatosis, inflammatory and fibrotic response via modulation of TLR2-NLRP3 inflammasome axis. Targeting TXNIP-TLR2-NLRP3 pathway may provide potential therapeutic modalities for NASH treatment.

Mir-21 Mediates the Inhibitory Effect of Ang (1-7) on AngII-induced NLRP3 Inflammasome Activation by Targeting Spry1 in lung fibroblasts

MicroRNA-21 (mir-21) induced by angiotensin II (AngII) plays a vital role in the development of pulmonary fibrosis, and the NLRP3 inflammasome is known to be involved in fibrogenesis. However, whether there is a link between mir-21 and the NLRP3 inflammasome in pulmonary fibrosis is unknown. Angiotensin-converting enzyme 2/angiotensin(1-7) [ACE2/Ang(1-7)] has been shown to attenuate AngII-induced pulmonary fibrosis, but it is not clear whether ACE2/Ang(1-7) protects against pulmonary fibrosis by inhibiting AngII-induced mir-21 expression. This study's aim was to investigate whether mir-21 activates the NLRP3 inflammasome and mediates the different effects of AngII and ACE2/Ang(1-7) on lung fibroblast apoptosis and collagen synthesis. In vivo, AngII exacerbated bleomycin (BLM)-induced lung fibrosis in rats, and elevated mir-21 and the NLRP3 inflammasome. In contrast, ACE2/Ang(1-7) attenuated BLM-induced lung fibrosis, and decreased mir-21 and the NLRP3 inflammasome. In vitro, AngII activated the NLRP3 inflammasome by up-regulating mir-21, and ACE2/Ang(1-7) inhibited NLRP3 inflammasome activation by down-regulating AngII-induced mir-21. Over-expression of mir-21 activated the NLRP3 inflammasome via the ERK/NF-κB pathway by targeting Spry1, resulting in apoptosis resistance and collagen synthesis in lung fibroblasts. These results indicate that mir-21 mediates the inhibitory effect of ACE2/Ang(1-7) on AngII-induced activation of the NLRP3 inflammasome by targeting Spry1 in lung fibroblasts.

Identification of Optimal Mouse Models of Systemic Sclerosis by Interspecies Comparative Genomics

OBJECTIVE

Understanding the pathogenesis of systemic sclerosis (SSc) is confounded by considerable disease heterogeneity. Animal models of SSc that recapitulate distinct subsets of disease at the molecular level have not been delineated. We applied interspecies comparative analysis of genomic data from multiple mouse models of SSc and patients with SSc to determine which animal models best reflect the SSc intrinsic molecular subsets.

METHODS

Gene expression measured in skin from mice with sclerodermatous graft-versus-host disease (GVHD), bleomycin-induced fibrosis, Tsk1/+ or Tsk2/+ mice was mapped to human orthologs and compared to SSc skin biopsy-derived gene expression. Transforming growth factor β (TGFβ) activation was assessed using a responsive signature in mice, and tumor necrosis factor receptor superfamily member 12A (TNFRSF12A) expression was measured in SSc patient and mouse skin.

RESULTS

Gene expression in skin from mice with sclerodermatous GVHD and bleomycin-induced fibrosis corresponded to that in SSc patients in the inflammatory molecular subset. In contrast, Tsk2/+ mice showed gene expression corresponding to the fibroproliferative SSc subset. Enrichment of a TGFβ-responsive signature was observed in both Tsk2/+ mice and mice with bleomycin-induced skin fibrosis. Expression of TNFRSF12A (the TWEAK receptor/fibroblast growth factor-inducible 14) was elevated in skin from patients with fibroproliferative SSc and the skin of Tsk2/+ mice.

CONCLUSION

This study reveals similarities in cutaneous gene expression between distinct mouse models of SSc and specific molecular subsets of the disease. Different pathways underlie the intrinsic subsets including TGFβ, interleukin-13 (IL-13), and IL-4. We identify a novel target, Tnfrsf12a, with elevated expression in skin from patients with fibroproliferative SSc and Tsk2/+ mice. These findings will inform mechanistic and translational preclinical studies in SSc.

Asbestos-Induced Mesothelial to Fibroblastic Transition Is Modulated by the Inflammasome

Despite the causal relationship established between malignant mesothelioma (MM) and asbestos exposure, the exact mechanism by which asbestos induces this neoplasm and other asbestos-related diseases is still not well understood. MM is characterized by chronic inflammation, which is believed to play an intrinsic role in the origin of this disease. We recently found that asbestos activates the nod-like receptor family member containing a pyrin domain 3 (NLRP3) inflammasome in a protracted manner, leading to an up-regulation of IL-1β and IL-18 production in human mesothelial cells. Combined with biopersistence of asbestos fibers, we hypothesize that this creates an environment of chronic IL-1β signaling in human mesothelial cells, which may promote mesothelial to fibroblastic transition (MFT) in an NLRP3-dependent manner. Using a series of experiments, we found that asbestos induces a fibroblastic transition of mesothelial cells with a gain of mesenchymal markers (vimentin and N-cadherin), whereas epithelial markers, such as E-cadherin, are down-regulated. Use of siRNA against NLRP3, recombinant IL-1β, and IL-1 receptor antagonist confirmed the role of NLRP3 inflammasome-dependent IL-1β in the process. In vivo studies using wild-type and various inflammasome component knockout mice also revealed the process of asbestos-induced mesothelial to fibroblastic transition and its amelioration in caspase-1 knockout mice. Taken together, our data are the first to suggest that asbestos induces mesothelial to fibroblastic transition in an inflammasome-dependent manner.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

Activation of the NLRP3 inflammasome by cellular labile iron

Cellular labile iron, which contains chelatable redox-active Fe(2+), has been implicated in iron-mediated cellular toxicity leading to multiple organ dysfunction. Iron homeostasis is controlled by monocytes/macrophages through their iron recycling and storage capacities. Furthermore, iron sequestration by monocytes/macrophages is regulated by pro-inflammatory cytokines including interleukin-1, highlighting the importance of these cells in the crosstalk between inflammation and iron homeostasis. However, a role for cellular labile iron in monocyte/macrophage-mediated inflammatory responses has not been defined. Here we describe how cellular labile iron activates the NLRP3 inflammasome in human monocytes. Stimulation of lipopolysaccharide-primed peripheral blood mononuclear cells with ferric ammonium citrate increases the level of cellular Fe(2+) levels in monocytes and induces production of interleukin-1β in a dose-dependent manner. This ferric ammonium citrate-induced interleukin-1β production is dependent on caspase-1 and is significantly inhibited by an Fe(2+)-specific chelator. Ferric ammonium citrate consistently induced interleukin-1β secretion in THP1 cells, but not in NLRP3-deficient THP1 cells, indicating a requirement for the NLRP3 inflammasome. Additionally, activation of the inflammasome is mediated by potassium efflux, reactive oxygen species-mediated mitochondrial dysfunction, and lysosomal membrane permeabilization. Thus, these results suggest that monocytes/macrophages not only sequestrate iron during inflammation, but also mediate inflammation in response to cellular labile iron, which provides novel insights into the role of iron in chronic inflammation.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

The role of P2X7 receptors in tissue fibrosis: a brief review

Many previous studies have demonstrated that P2X(7) receptors (P2X(7)Rs) have a pleiotropic function in different pathological conditions and could represent a novel target for the treatment of a range of diseases. In particular, recent studies have explored the role of P2X(7)R in fibrosis, the pathological outcome of most chronic inflammatory diseases. The aim of this review is to discuss the biological features of P2X(7)R and summarize the current knowledge about the putative role of the P2X(7)R in triggering fibrosis in a wide spectrum of organs such as the lung, kidney, liver, pancreas, and heart.

Blockage of P2X7 attenuates acute lung injury in mice by inhibiting NLRP3 inflammasome

NLRP3 inflammasome is engaged in the inflammatory response during acute lung injury (ALI). Purinergic receptor P2X7 has been reported to be upstream of NLRP3 activation. However, the therapeutic implication of P2X7 in ALI remains to be explored. The present study used lipopolysaccharide (LPS)-induced mouse model to investigate the therapeutic potential of P2X7 blockage in ALI. Our results showed that P2X7/NLRP3 inflammasome pathway was significantly upregulated in the lungs of ALI mice as compared with control mice. P2X7 antagonist A438079 suppressed NLRP3/ASC/caspase 1 activation, production of IL-1β, IL-17A and IFN-γ and neutrophil infiltration but not the production of IL-10, resulting in a significant amelioration of lung injury. Moreover, blockage of P2X7 significantly inhibited NLRP3 inflammasome activation and IL-1β production in bone marrow derived macrophages. Similar results were obtained using another P2X7 inhibitor brilliant blue G (BBG) in vivo. Thus, pharmacological blockage of P2X7/NLRP3 pathway can be considered as a potential therapeutic strategy in patients with ALI.

The NLRP3 inflammasome and stroke

Inflammasome pattern recognition receptors, which belong to the family of multi-meric proteins, play an important role in innate immunity, including NLRPs, NLRC, and NAIP. Among these receptors, NLRP3 (nucleotide-binding domain (NOD)-like receptor protein 3) inflammasome may activate the inflammation and participate in atherosclerosis, pathophysiology of myocardial infarction, resultin ischemia/reperfusion injury and stroke and other cardiovascular diseases. Effective regulation of NLRP3 may help prevent or even treat stroke. In recent years, the role of inflammation in stroke has attracted much attention, and the in-depth study of its mechanism of action is gradually clear. This mini-review focuses on the association of regulatory mechanisms of NLRP3 inflammasome with the development of stroke, which may supply some clues for future therapies and novel drug targets for stroke.

The expression of NLRP3, NLRP1 and AIM2 in the gingival tissue of periodontitis patients: RT-PCR study and immunohistochemistry

OBJECTIVE

Detecting the distribution and intensity of NLRP3, NLRP1 and AIM2 expression in different types of periodontitis gingival tissues.

MATERIALS AND METHODS

A total of 65 gingival tissues were collected from clinic and been divided into three groups: patients with chronic periodontitis (CP), patients with generalized aggressive periodontitis (G-AgP) and healthy control subjects. Real-time polymerase chain reaction (RT-PCR) was performed to detect mRNA expression of NLRP3, NLRP1 and AIM2 in full-thickness tissue. In the meanwhile, immunohistochemistry was used to detect distribution of NLRP3, NLRP1 and AIM2 in the periodontal epithelium and in the connective tissue cells.

RESULTS

The overall intensity of NLRP3 expression was significantly higher in CP or G-AgP than healthy tissue. A more significant difference was observed in the periodontal epithelium layer. NLRP1 was barely expressed in the healthy and periodontitis gingival tissues, whereas AIM2 was expressed at a higher level in the chronic periodontitis group than others.

CONCLUSION

The NLRP3, NLRP1 and AIM2 proteins were differentially expressed in gingival tissues from patients with CP and G-AgP and may play vital roles in the progression of periodontal inflammation to different degrees. Our studies may provide a new direction for personalized periodontal treatment.

Gene silencing of non-obese diabetic receptor family (NLRP3) protects against the sepsis-induced hyper-bile acidaemia in a rat model

The role of NOD-like receptor family (NLRP3) has been confirmed in various inflammatory diseases. The association between NLRP3 and hyper-bileacidaemia during the sepsis remains unclear. We aimed to investigate whether NLRP3 silencing protects against the sepsis-induced hyper-bileacidaemia. Sepsis was induced by caecum ligation and puncture (CLP). Gene silencing of NLRP3 was performed by injecting rats with NLRP3 short hairpin RNA plasmids (NLRP3 shRNA) 48 h before surgery. Rats were divided into four groups: group 1: sham; group 2: sepsis; group 3: NLRP3 shRNA + sepsis (called the 'NLRP3 shRNA' group); and group 4: scrambled shRNA + sepsis (called the 'scrambled shRNA' group). The serum levels of bile acids, hepatic expression of hepatocyte membrane transporters, hepatic cytokine levels and behaviours of immune cells were compared among the groups. Hepatic NLRP3 expression was increased dramatically during the sepsis, but was suppressed by pretreatment with NLRP3 shRNA. Compared with rats in the sepsis and the scrambled shRNA groups, rats in the NLRP3 shRNA group exhibited significantly decreased serum levels of glycine and taurine conjugated-bile acids, with rehabilitated expression of hepatocyte transporters, suppressed hepatic cytokine levels, decreased hepatic neutrophils infiltration and attenuated macrophages pyroptosis. Gene silencing of NLRP3 ameliorates sepsis-induced hyper-bileacidaemia by rehabilitating hepatocyte transporter expression, reducing hepatic cytokine levels, neutrophil infiltration and macrophages pyroptosis. NLRP3 may be a pivotal target for sepsis management.

Inflammasome Activity in Non-Microbial Lung Inflammation

The understanding of interleukin-1 (IL-1) family cytokines in inflammatory disease has rapidly developed, due in part to the discovery and characterization of inflammasomes, which are multi-subunit intracellular protein scaffolds principally enabling recognition of a myriad of cellular stimuli, leading to the activation of caspase-1 and the processing of IL-1β and IL-18. Studies continue to elucidate the role of inflammasomes in immune responses induced by both microbes and environmental factors. This review focuses on the current understanding of inflammasome activity in the lung, with particular focus on the non-microbial instigators of inflammasome activation, including inhaled antigens, oxidants, cigarette smoke, diesel exhaust particles, mineral fibers, and engineered nanomaterials, as well as exposure to trauma and pre-existing inflammatory conditions such as metabolic syndrome. Inflammasome activity in these sterile inflammatory states contribute to diseases including asthma, chronic obstructive disease, acute lung injury, ventilator-induced lung injury, pulmonary fibrosis, and lung cancer.

Tight Skin 2 Mice Exhibit Delayed Wound Healing Caused by Increased Elastic Fibers in Fibrotic Skin

Rationale: The Tight Skin 2 (Tsk2) mouse model of systemic sclerosis (SSc) has many features of human disease, including tight skin, excessive collagen deposition, alterations in the extracellular matrix (ECM), increased elastic fibers, and occurrence of antinuclear antibodies with age. A tight skin phenotype is observed by 2 weeks of age, but measurable skin fibrosis is only apparent at 10 weeks. We completed a series of wound healing experiments to determine how fibrosis affects wound healing in Tsk2/+ mice compared with their wild-type (WT) littermates. Method: We performed these experiments by introducing four 4 mm biopsy punched wounds on the back of each mouse, ventral of the midline, and observed wound healing over 10 days. Tsk2/+ mice showed significantly delayed wound healing and increased wound size compared with the WT littermates at both 5 and 10 weeks of age. We explored the potential sources of this response by wounding Tsk2/+ mice that were genetically deficient either for the NLRP3 inflammasome (a known fibrosis mediator), or for elastic fibers in the skin, using a fibulin-5 knockout. Conclusion: We found that the loss of elastic fibers restores normal wound healing in the Tsk2/+ mouse and that the loss of the NLRP3 inflammasome had no effect. We conclude that elastic fiber dysregulation is the primary cause of delayed wound healing in the Tsk2/+ mouse and therapies that promote collagen deposition in the tissue matrix in the absence of elastin deposition might be beneficial in promoting wound healing in SSc and other diseases.

Mitochondrial quality control and age-associated arterial stiffening

Stiffening of large elastic arteries with age increases the risk of cardiovascular diseases (CVD), but the underlying mechanisms are incompletely understood. We investigated the role of mitochondrial quality control (QC, i.e., mitophagy and biogenesis) in arterial stiffening with aging. In C57BL6 mice, aging was associated with impaired aortic expression of mitochondrial QC mediators, greater activation of the mitochondrial redox/stress sensor p66shc, elevated superoxide production and increased arterial stiffness-as indicated by ~25% higher aortic pulse wave velocity (aPWV). In old mice, supplementation with trehalose, a nutraceutical reported to enhance mitophagy, normalized mitochondrial QC markers, p66shc activation and superoxide production, and reduced aPWV and aortic collagen I (a structural protein that confers stiffness). In vitro experiments suggested that mitochondrial QC processes were enhanced in the aortas from old trehalose-treated mice, and in aortic rings studied ex vivo, both aging and treatment with the mitochondrial stressor rotenone were associated with increases in p66shc activation and intrinsic mechanical stiffness, whereas co-incubation with trehalose prevented these effects. Taken together, these findings suggest that mitochondrial stress/dysfunction as a result of impaired mitochondrial QC contributes to large elastic artery stiffening with age. Enhancing mitochondrial QC with agents such as trehalose may be a novel strategy for reducing age-associated arterial stiffness and CVD.

Inflammasomes in respiratory disease: from bench to bedside

The respiratory tract of human subjects is constantly exposed to harmful microbes and air pollutants. The immune system responds to these offenders to protect the host, but an unbalanced inflammatory response itself may promote tissue damage and ultimately lead to acute and chronic respiratory diseases. Deregulated inflammasome activation is emerging as a key modulator of respiratory infections and pathologic airway inflammation in patients with asthma, COPD, and pulmonary fibrosis. Assembly of these intracellular danger sensors in cells of the respiratory mucosa and alveolar compartment triggers a proinflammatory cell death mode termed pyroptosis and leads to secretion of bioactive IL-1β and IL-18. Here, we summarize and review the inflammasome and its downstream effectors as therapeutic targets for the treatment of respiratory diseases.

Interleukin-18 as a therapeutic target in acute myocardial infarction and heart failure

Interleukin 18 (IL-18) is a proinflammatory cytokine in the IL-1 family that has been implicated in a number of disease states. In animal models of acute myocardial infarction (AMI), pressure overload, and LPS-induced dysfunction, IL-18 regulates cardiomyocyte hypertrophy and induces cardiac contractile dysfunction and extracellular matrix remodeling. In patients, high IL-18 levels correlate with increased risk of developing cardiovascular disease (CVD) and with a worse prognosis in patients with established CVD. Two strategies have been used to counter the effects of IL-18:IL-18 binding protein (IL-18BP), a naturally occurring protein, and a neutralizing IL-18 antibody. Recombinant human IL-18BP (r-hIL-18BP) has been investigated in animal studies and in phase I/II clinical trials for psoriasis and rheumatoid arthritis. A phase II clinical trial using a humanized monoclonal IL-18 antibody for type 2 diabetes is ongoing. Here we review the literature regarding the role of IL-18 in AMI and heart failure and the evidence and challenges of using IL-18BP and blocking IL-18 antibodies as a therapeutic strategy in patients with heart disease.

Inflammasome activation in airway epithelial cells after multi-walled carbon nanotube exposure mediates a profibrotic response in lung fibroblasts

Background

In vivo studies have demonstrated the ability of multi-walled carbon nanotubes (MWCNT) to induce airway remodeling, a key feature of chronic respiratory diseases like asthma and chronic obstructive pulmonary disease. However, the mechanism leading to remodeling is poorly understood. Particularly, there is limited insight about the role of airway epithelial injury in these changes.

Objectives

We investigated the mechanism of MWCNT-induced primary human bronchial epithelial (HBE) cell injury and its contribution in inducing a profibrotic response.

Methods

Primary HBE cells were exposed to thoroughly characterized MWCNTs (1.5-24 μg/mL equivalent to 0.37-6.0 μg/cm²) and MRC-5 human lung fibroblasts were exposed to 1:4 diluted conditioned medium from these cells. Flow cytometry, ELISA, immunostainings/immunoblots and PCR analyses were employed to study cellular mechanisms.

Results

MWCNT induced NLRP3 inflammasome dependent pyroptosis in HBE cells in a time- and dose-dependent manner. Cell death and cytokine production were significantly reduced by antioxidants, siRNA to NLRP3, a caspase-1 inhibitor (z-WEHD-FMK) or a cathepsin B inhibitor (CA-074Me). Conditioned medium from MWCNT-treated HBE cells induced significant increase in mRNA expression of pro-fibrotic markers (TIMP-1, Tenascin-C, Procollagen 1, and Osteopontin) in human lung fibroblasts, without a concomitant change in expression of TGF-beta. Induction of pro-fibrotic markers was significantly reduced when IL-1β, IL-18 and IL-8 neutralizing antibodies were added to the conditioned medium or when conditioned medium from NLRP3 siRNA transfected HBE cells was used.

Conclusions

Taken together these results demonstrate induction of a NLRP3 inflammasome dependent but TGF-beta independent pro-fibrotic response after MWCNT exposure.

Surface interactions with compartmentalized cellular phosphates explain rare earth oxide nanoparticle hazard and provide opportunities for safer design

Growing international exploitation of rare earth oxides (REOs) for commercial and biological use has increased the possibility of human exposure and adverse health effects. Occupational exposure to rare earth materials in miners and polishers leads to a severe form of pneumoconiosis, while gadolinium-containing MRI contrast agents cause nephrogenic systemic fibrosis in patients with renal impairment. The mechanisms for inducing these adverse pro-fibrogenic effects are of considerable importance for the safety assessment of REO particles as well as presenting opportunities for safer design. In this study, using a well-prepared REO library, we obtained a mechanistic understanding of how REOs induce cellular and pulmonary damage by a compartmentalized intracellular biotransformation process in lysosomes that results in pro-fibrogenic growth factor production and lung fibrosis. We demonstrate that rare earth oxide ion shedding in acidifying macrophage lysosomes leads to biotic phosphate complexation that results in organelle damage due to stripping of phosphates from the surrounding lipid bilayer. This results in nanoparticle biotransformation into urchin shaped structures and setting in motion a series of events that trigger NLRP3 inflammasome activation, IL-1β release, TGF-β1 and PDGF-AA production. However, pretreatment of REO nanoparticles with phosphate in a neutral pH environment prevents biological transformation and pro-fibrogenic effects. This can be used as a safer design principle for producing rare earth nanoparticles for biological use.

NLRP3 inflammasome activation in D-galactosamine and lipopolysaccharide-induced acute liver failure: role of heme oxygenase-1

D-Galactosamine (GalN) and lipopolysaccharide (LPS) are commonly used to study mechanisms of hepatic malfunction that result in hepatic inflammation and subsequent fulminant hepatic failure. Inflammasomes are intracellular multiprotein complexes that in response to cellular danger signals trigger the biological maturation of proinflammatory cytokines. Heme oxygenase-1 (HO-1) is a cytoprotective enzyme that induces anti-inflammatory and antioxidant activity against oxidative cellular stress. This study examined activation of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome in GalN/LPS-induced hepatic injury and the role of HO-1 in the signaling pathways of inflammasome. Mice (C57BL/6) were pretreated twice with hemin (HO-1 inducer, 30 mg/kg) and zinc protoporphyrin (ZnPP; HO-1 inhibitor, 10mg/kg) at 12 and 2h before GalN (800 mg/kg)/LPS (40 μg/kg) administration. HO-1 induction with hemin reversed the lethality induced by GalN/LPS administration, and ZnPP pretreatment blocked this change. Lipid peroxidation markedly increased after GalN/LPS treatment, whereas glutathione content decreased in the GalN/LPS group. These changes were attenuated by hemin, but ZnPP reversed the effects of hemin. Serum levels of tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β increased after GalN/LPS treatment; these increases were attenuated by hemin. Hepatic mRNA levels of TNF-α, IL-1β, and NLRP3 increased after GalN/LPS treatment, and hemin attenuated increases in TNF-α and IL-1β. After GalN/LPS treatment, the hepatic expression of NLRP3, ASC, and caspase-1 (p10) was increased. In immunoprecipitation studies, hemin attenuated the interaction of NLRP3 with ASC and caspase-1. GalN/LPS induced expression of the thioredoxin-interacting protein (TXNIP) gene and the interaction between NLRP3 and TXNIP; again, hemin attenuated these effects. The effects of hemin were reversed by ZnPP. Our findings suggest that activation of the NLRP3 inflammasome leads to a GalN/LPS-induced inflammatory response through TXNIP-NLRP3 interaction. Furthermore, HO-1 overexpression may protect the liver against GalN/LPS-induced inflammation through suppression of the NLRP3 signaling pathway.

Nonmicrobial-mediated inflammatory airway diseases--an update

In lungs, airways are in constant contact with air, microbes, allergens, and environmental pollutants. The airway epithelium represents the first line of lung defense through different mechanisms, which facilitate clearance of inhaled pathogens and environmental particles while minimizing an inflammatory response. The innate immune system facilitates immediate recognition of both foreign pathogens and tissue damage through toll-like receptor, which acts as a gateway for all intracellular events leading to inflammation. In the absence of microbial stimulus, the immune system is capable of detecting a wide range of insults against the host. This review focuses on various molecular mechanisms involved in pathophysiology of airway inflammation mediated by environmental factors, cellular stress, and pharmacological and clinical agents.

Genes involved in innate immunity associated with asbestos-related fibrotic changes

Objectives

To determine whether genetic polymorphisms in several candidate genes related to innate immunity and protease–antiprotease balance modify individual susceptibility to develop asbestos-related fibrotic pleuropulmonary changes.

Methods

Sixteen polymorphisms from nine genes (NLRP3, CARD8, TNF, TGFB1, GC, MMP1, MMP9, MMP12 and TIMP2) were genotyped from 951 Finnish asbestos-exposed workers. The genotype/haplotype data were compared to signs of fibrosis and pleural thickenings using linear and logistic regression analysis adjusted for potential confounders.

Results

A functional polymorphism (Q705K; rs35829419) in the NLRP3 gene was associated with interstitial lung fibrosis (p=0.013), and the TGFB1 rs2241718 SNP with visceral pleural fibrosis (VPF) (p=0.044). In stratified analysis, the carriage of at least one NLRP3 variant allele conferred a 2.5-fold increased risk for pathological interstitial lung fibrosis (OR 2.44, 95% CI 0.97 to 6.14). Conversely, the carriage of at least one TGFB1 rs2241718 variant allele protected against VPF (OR 0.62, 95% CI 0.39 to 0.98). The TIMP2 rs2277698 SNP and a haplotype consisting of the TGFB1 rs1800469 and rs1800470 SNPs were associated with the degree of pleural thickening calcification (p=0.037 and p=0.035), and the CARD8 rs2043211 SNP with the greatest thickness of pleural plaques (p=0.015).

Conclusions

Our results support the hypothesis that the NLRP3 inflammasome is important in the development of fibrotic lung disease by associating the NLRP3 rs35829419 variant allele with increased risk of asbestos-related interstitial lung fibrosis, and the TGFB1 rs2241718 variant allele with decreased risk of asbestos-related VPF. Polymorphisms in CARD8 and TIMP2 are proposed to modify the development and/or calcification of pleural thickenings.