Regulates NLRP3 Inflammasome Activation Research Articles

Impaired autophagy in microglia aggravates dopaminergic neurodegeneration by regulating NLRP3 inflammasome activation in experimental models of Parkinson’s disease

Microglia-mediated inflammation plays an important role in the pathogenesis of several neurodegenerative diseases including Parkinson’s disease (PD). Recently, autophagy has been linked to the regulation of the inflammatory response. However, the potential role of microglial autophagy in the context of PD pathology has not been characterized. In the present study, we investigated whether impaired microglial autophagy would affect dopaminergic neurodegeneration and neuroinflammation both in vivo and in vitro. In vitro, BV2 microglial cells were exposed to LPS in the presence or absence of autophagy-related gene 5 (Atg5) small interference RNA (Atg5-siRNA). For in vivo study, microglial Atg5 conditional knockout (Atg5flox/flox; CX3CR1-Cre) mice and their wild-type littermates (Atg5flox/flox) were intraperitoneally injected with MPTP to induce experimental PD model. Our results revealed that disruption of autophagy by Atg5-siRNA aggravated LPS-induced inflammatory responses in BV2 cells and caused greater apoptosis in SH-SY5Y cells treated with BV2 conditioned medium. In mice, impaired autophagy in microglia exacerbated dopaminergic neuron loss in response to MPTP. The mechanism by which the deficiency of microglial autophagy promoted neuroinflammation and dopaminergic neurodegeneration was related to the regulation of NLRP3 inflammasome activation. These findings demonstrate that impairing microglial autophagy aggravates pro-inflammatory responses to LPS and exacerbates MPTP-induced neurodegeneration by modulating NLRP3 inflammasome responses. We anticipate that enhancing microglial autophagy may be a promising new therapeutic strategy for PD.

Phoenixin-20 Ameliorates Lipopolysaccharide-Induced Activation of Microglial NLRP3 Inflammasome.

Injury associated with neuroinflammation has been linked with several kinds of neurodegenerative diseases. The activation of the NLRP3 inflammasome plays an important role in microglia-mediated inflammation. Phoenixin (PNX)-20 is a newly discovered neuropeptide with pleiotropic effects involved in the regulation of reproductive and cognitive function, depression, and food uptake. This study investigated whether PNX-20 possesses a protective effect against lipopolysaccharide (LPS)-induced activation of the NLRP3 inflammasome in microglia. Firstly, our results show that the PNX-20 treatment significantly prevented LPS-induced expression of NADPH oxidase 4 (NOX-4) and the generation of reactive oxygen species (ROS). Secondly, PNX-20 mitigated LPS-induced upregulation of TxNIP, an upstream regulator of NLRP3 inflammasome activation. Thirdly, further evaluation of the major components of the NLRP3 inflammasome revealed that PNX-20 inhibited LPS-mediated upregulation of NLRP3, ASC, and cleaved caspase-1 (P10). Notably, based on our results, the inhibitory effect of PNX-20 on the NLRP3 inflammasome results in the inhibition of IL-1β and IL-18 secretions. Finally, we found that PNX-20 ameliorated the reduction in SIRT1 expression induced by LPS. When microglial SIRT1 was inhibited by nicotine, PNX-20 lost its suppressive effect on the expression of NLRP3, ASC, and caspase-1, as well as the secretion of IL-1β and IL-18. As a result of these findings, we draw the conclusion that the neuroprotective effect of PNX-20 is dependent on SIRT1. Collectively, the study shows that PNX-20 has a regulatory effect via modulation of neuroinflammation.

Low shear stress regulates vascular endothelial cell pyroptosis through miR-181b-5p/STAT-3 axis.

Low shear stress and pyroptosis both play an important role in the onset and development of atherosclerosis (AS). MicroRNAs (miRNAs) are a kind of short (18-22) nucleotide sequences that can bind to the 3'-untranslated region (3'-UTR) of messenger RNA, thereby regulating programmed cell death including pyroptosis. However, the function of miRNAs in cells subjected to shear stress conditions is unknown. Therefore, we conducted the current study to demonstrate the effect of low shear stress on pyroptosis and the underlying mechanism. Human umbilical vein endothelial cells (HUVECs) stimulated by undisturbed shear stress (5 dynes/cm2 ) were the experimental group while HUVECs without shear stress treatment were the control group in our experiments. We observed that shear stress can suppress mechanosensitive miR-181b-5p expression, accompanying the elevated expression of NLRP3 inflammasome-dependent pyroptosis. Introduction of miR-181b-5p could alleviate NLRP3 inflammasome-dependent pyroptosis. Luciferase assay showed specific binding of miR-181b-5p to the 3'-UTR of signal transduction and transcriptional activation factor 3 (STAT-3) gene. Inhibition of STAT-3 gene expression at the posttranscriptional level results in the alleviation of NLRP3 inflammasome-dependent pyroptosis. Besides, the silencing of STAT-3 reduced anti-miR-181b-5p-mediated HUVEC pyroptosis via regulating NLRP3 inflammasome activation. Given the role of mechanosensitive miR-181b-5p and STAT-3 in the shear stress-induced pyroptosis, regulation of their expression levels may be a promising strategy to control AS.

The role of HIF-1α in regulating NLRP3 inflammasome activation in bladder cancer.

e17028 Background: Bladder cancer is one of the most common malignancies of urinary system with the forth incidence rate and the eighth leading mortality rate in male genitourinary tumors. Hypoxia environment activates the hypoxia‐signalling pathway, principally via hypoxia‐inducible transcription factors (HIF) to activate numerous target genes which mediate embryonic vascularization, metabolism, tumor angiogenesis and the other processes to supply tissues with blood and oxygen. Inflammasomes are multiprotein signal responsible for the maturation of proinflammatory cytokines IL-1β and IL-18 as well as trigger the inflammatory cell pyroptosis. Recent study showed that HIF-1α promotes NLRP3 inflammasome activation in bleomycin-induced acute lung injury. However, the role of HIF1α in regulating the progression of bladder cancer has not been examined so far. The present study aimed to investigate the effect of HIF-1α on NLRP3 inflammasome activation in urothelial carcinoma. Methods: In this research, urothelial carcinoma cell lines were treated with NLRP3 inflammasome inducers, LPS/ATP, to induce NLRP3 inflammasome activation. Results: Our preliminary results showed that both T24 and 5637 bladder cancer cells can be induced NLRP3 inflammasome activation and IL-1β secretion. In addition, hypoxia also induces the secretion of IL-1β in T24 cells. We further investigated the effect of NLRP3 inflammasome activation in modulating EMT-related protein levels, migration and invasion in bladder cancer T24 cells. Our results demonstrated that NLRP3 inflammasome activation promotes tumor growth and metastasis in bladder cancer cells. Furthermore, knockdown of HIF1α reduces both inflammatory response and migratory activity in bladder cancer. Conclusions: Collectively, these results suggest that targeting NLRP3 inflammasome might offer potential to treat hypoxic malignant tumor in bladder carcinoma.

Annexin A1 Regulates NLRP3 Inflammasome Activation and Modifies Lipid Release Profile in Isolated Peritoneal Macrophages.

Annexin A1 (AnxA1) is a potent anti-inflammatory protein that downregulates proinflammatory cytokine release. This study evaluated the role of AnxA1 in the regulation of NLRP3 inflammasome activation and lipid release by starch-elicited murine peritoneal macrophages. C57bl/6 wild-type (WT) and AnxA1-null (AnxA1-/-) mice received an intraperitoneal injection of 1.5% starch solution for macrophage recruitment. NLRP3 was activated by priming cells with lipopolysaccharide for 3 h, followed by nigericin (1 h) or ATP (30 min) incubation. As expected, nigericin and ATP administration decreased elicited peritoneal macrophage viability and induced IL-1β release, more pronounced in the AnxA1-/- cells than in the control peritoneal macrophages. In addition, nigericin-activated AnxA1-/- macrophages showed increased levels of NLRP3, while points of co-localization of the AnxA1 protein and NLRP3 inflammasome were detected in WT cells, as demonstrated by ultrastructural analysis. The lipidomic analysis showed a pronounced release of prostaglandins in nigericin-stimulated WT peritoneal macrophages, while ceramides were detected in AnxA1-/- cell supernatants. Different eicosanoid profiles were detected for both genotypes, and our results suggest that endogenous AnxA1 regulates the NLRP3-derived IL-1β and lipid mediator release in macrophages.

Exercise Mitigates Bone Loss via ROS‐NLRP3 Inflammasome Axis In High Fat Diet Fed Mice

Emerging evidence suggests that western diet‐induced obesity is associated with chronic low‐grade inflammation. Chronic inflammation is also linked with increased bone loss and osteopenia phenotype. However, the mechanistic basis of obesity‐associated bone loss via induction of inflammasome is not yet well understood. The recent study also found that irisin is expressed by various tissue including skeletal muscle during exercise. It is also currently unknown whether irisin is secreted by bone tissue upon exercise and possible involvement in the regulation of NLRP3 inflammasome activation during obesity in mice. To test the hypothesis, we employed 8‐weeks age‐matched male/female C57BJ/L6 wild‐type (WT) mice were grouped as fellows according to their diet and exercise (Ex) category: standard nonfat diet NFD (6%); (ii) NFD+Ex; (iii) HFD (42%); (iv) HFD+Ex. A nonfat diet (6%) and a high‐fat diet (40%) were given for three months. The selected mice were exercised for this 12‐week duration on a treadmill, with controlled speeds of 7 meters/min for the first week, 9 meters/min for the second week and 11 meters/min the following weeks for a total of 330 meters every day. After every 110 meters reached, the mice were given rest of 10 minutes. We tested protein/mRNA expression of oxidative stress, inflammasome metabolic indicators Glucose Transporters 1 and 4 (GLUT‐1, GLUT‐4), irisin, IL‐6, and IL‐1β in primarily isolated bone marrow mesenchymal cells (BMMSCs), plasma and bone from all the groups by Western Blot, real‐time PCR, and Immunohistochemistry. The data demonstrated that high levels of irisin protein expression were induced in both plasma and murine femoral bone tissues of HFD+EX mice. The mechanistic study shows that cellular oxidative damage and NLR3 signaling was indeed down‐regulated and resulted in decreased secretion of IL‐6 and IL‐1β in bone marrow mesenchymal cells (BMMSCs) and plasma of HFD+EX mice. Interestingly, HFD+EX mice showed higher trabecular, cortical bone formation and bone strength in vivo in compared to HFD mice. Lentiviral FNDC5/recombinant irisin administration suppresses HFD induced ROS‐NLR3 inflammation and restores bone mass, whereas blockade of FNDC5/irisin by siRNA delivery prevents the physical exercise mediated bone formation in HFD mice. Further osteoblast‐specific FNDC5 (or Irisin) deficiency in mice completely blocks EX‐induced trabecular bone formation. In conclusion, our findings demonstrate that exercise‐induced irisin mitigates the bone loss in part via inhibiting ROS‐NLR3 signaling in HFD mice, and possibly provide a mechanism for therapeutic effect in metabolic osteoporosis.Support or Funding InformationAcknowledgmentThis work is financially supported by the National Institute of Health Grant AR‐067667‐NT is greatly acknowledged.

Oral treatment with glycyrrhizin inhibits NLRP3 inflammasome activation and promotes microglial M2 polarization after traumatic spinal cord injury

The inflammatory response induced by traumatic spinal cord injury (SCI) involves the activation of NLRP3 inflammasomes, which are closely related to the activation of microglia. Microglial polarization between M1/M2 phenotypes is a pivotal regulatory factor in neuroinflammatory responses to traumatic SCI-induced secondary injuries, and altering this polarization could be beneficial. Glycyrrhizin is a neuroprotective agent with a potent anti-inflammatory property in different neurological disorders and could potentially be useful in SCI. In this study, we investigated the potency of oral treatment with glycyrrhizin to reduce inflammation and improve functional recovery after traumatic SCI by inhibiting NLRP3 inflammasome activation and promoting microglial M2 polarization. After inducing traumatic SCI by dropping a 10 g impactor on the T9 and T10 spinal segments of male Sprague-Dawley rats, the animals were given glycyrrhizin orally immediately after injury and every 12 h for the next 3 d. Behavioral scores improved in glycyrrhizin-treated animals compared to the SCI group. The functional improvement in glycyrrhizin-treated rats paralleled the decreased expression of NLRP3 inflammasome components, such as ASC, NLRP3, and cleaved caspase-1, as well as IL-1β and IL-18. At the histopathological level, oral treatment with glycyrrhizin diminished the SCI-enhanced production of Iba-1+CD86+ cells (M1 microglia) but improved the release of Iba-1+CD206+ cells (M2 microglia). Likewise, oral therapy with glycyrrhizin significantly enriched the protein expression levels of M2 microglia-related markers (CD206 and Arg-1) but reduced those of M1 microglia-related markers (CD86 and iNOS) in the injured spinal cord. These findings support and extend the knowledge on post-traumatic SCI glycyrrhizin-mediated neuroprotection. Glycyrrhizin’s regulation of NLRP3 inflammasome activation and microglial polarization might be a new approach to understanding the anti-inflammatory potency of glycyrrhizin.

Inhibiting Caspase-12 Mediated Inflammasome Activation protects against Oxygen-Glucose Deprivation Injury in Primary Astrocytes.

Stroke is one of the leading causes of death worldwide. Accumulating evidence suggests that NLRP3 inflammasome activation plays an important role in ischemic stroke injury. However, the existence of the NLRP3 inflammasome in astrocytes remains controversial. In this study, we demonstrated the presence of the NLRP3 inflammasome in primary mouse astrocytes and investigated the role of caspase-12 in NLRP3 inflammasome activation and cell injury in an in vitro astrocyte oxygen-glucose deprivation (OGD) model. Astrocytes exposed to 2, 3, and 4 h of OGD exhibited increased cell injury and apoptosis, and the protein levels of caspase-12, cleaved caspase-3, NLRP3 inflammasome components, and IL-1β were also significantly elevated. Interestingly, pretreatment with the caspase-12-specific inhibitor Z-ATAD-FMK attenuated cell injury and apoptosis and decreased the levels of NLRP3, caspase-1, IL-1β, and cleaved caspase-3 in the OGD group. In conclusion, Z-ATAD-FMK protected astrocytes against OGD-induced cell death and inhibited NLPR3-inflammasome activation. Our results indicate that caspase-12 and its potential regulation of NLRP3 inflammasome activation might be a promising target for treatment of ischemic stroke.

Vitamin D Receptor Inhibits NLRP3 Activation by Impeding Its BRCC3-Mediated Deubiquitination.

The NLRP3 inflammasome is a multiprotein oligomer responsible for activation of the inflammatory response by promoting the maturation and secretion of the pro-inflammatory cytokines IL-1β and IL-18. Dysregulation of this inflammasome has been linked to several autoimmune diseases, indicating that NLRP3 is tightly regulated to prevent aberrant activation. The regulation of NLRP3 activation remains unclear. Here, we report the identification of vitamin D receptor (VDR) as a negative regulator of NLRP3 oligomerization and activation. VDR can physically bind NLRP3 and block the association of NLRP3 with BRCC3. When BRCC3-mediated deubiquitination of NLRP3 is inhibited by VDR, NLRP3 activation is subsequently inhibited. In the absence of VDR, caspase-1 activation and IL-1β release are increased in response to LPS-induced inflammation or alum-induced peritoneal inflammation, indicating that VDR is a negative regulator of NLRP3 inflammasome activation in vivo. In addition, vitamin D negatively regulates the NLRP3 inflammasome via VDR signaling to effectively inhibit IL-1β secretion. These studies demonstrate that VDR signaling constrains NLRP3 inflammasome activation and might be a potential treatment target for NLRP3 inflammasome-related diseases.

EK7 Regulates NLRP3 Inflammasome Activation and Neuroinflammation Post-traumatic Brain Injury.

As one of the most common causes of mortality and disability, traumatic brain injury (TBI) is a huge psychological and economic burden to patients, families, and societies worldwide. Neuroinflammation reduction may be a favorable option to alleviate secondary brain injuries and ameliorate the outcome of TBI. The nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome, has been shown to be involved in TBI. NIMA-related kinase 7 (NEK7) has been verified as an essential mediator of NLRP3 inflammasome activation that is recruited upstream of the formation of inflammasomes in response to NLRP3 activators. However, the underlying mechanism by which NEK7 operates post-TBI remains undefined. In this study, we performed both in vivo and in vitro experiments. Using an in vivo mouse TBI model, mice were administered an intracerebroventricular injection of NEK7-shRNA virus. For the in vitro analysis, primary cortical neurons with NEK7-shRNA were stimulated with lipopolysaccharide (LPS)/ATP or potassium (K+). We evaluated the effects of NEK7 knock-down on neurological deficits, NLRP3 inflammasomes, caspase-1 activation, and neuronal injury. During the 0–168 h post-TBI period in vivo, NEK7 and NLRP3 inflammasome activation increased in what appeared to be a time-dependent manner. As well as pyroptosis-related markers, caspase-1 activation (p20) and interleukin-1β (IL-1β) activation (p17) were up-regulated. NEK7 down-regulation attenuated neurological deficits, NLRP3 inflammasomes, caspase-1 activation, and neuronal injury. The same phenomena were observed during the in vitro experiments. Furthermore, NEK7 knock-down suppressed NLRP3 inflammasome activation and pyroptosis, which were triggered by K+ efflux, and the LPS + ATP-triggered NEK7–NLRP3 complex was reversed in primary cortical neurons placed in 50 mM K+ medium. Collectively, the data demonstrated that NEK7, as a modulator, regulates NLRP3 inflammasomes and downstream neuroinflammation in response to K+ efflux, through NEK7–NLRP3 assembly, pro-caspase-1 recruitment, caspase-1 activation, and pyroptosis in nerve injuries, post-TBI. NEK7 may be a potential therapeutic target for attenuating neuroinflammation and nerve injury post-TBI.

The pore-forming subunit Kir6.1 of the K-ATP channel negatively regulates the NLRP3 inflammasome to control insulin resistance by interacting with NLRP3

Excessive activation of the NLRP3 inflammasome is a key component contributing to the pathogenesis of various inflammatory diseases. However, the molecular mechanisms underlying its activation and regulation remain poorly defined. The objective of this study was to explore the possible function of the K+ channel pore-forming subunit Kir6.1 in regulating NLRP3 inflammasome activation and insulin resistance. Here, we demonstrate that Kir6.1 depletion markedly activates the NLRP3 inflammasome, whereas enhanced Kir6.1 expression produces opposing effects both in mice in vivo and in primary cells in vitro. We also demonstrate that Kir6.1 controls insulin resistance by inhibiting NLRP3 inflammasome activation in mice. We further show that Kir6.1 physically associates with NLRP3 and thus inhibits the interactions between the NLRP3 inflammasome subunits. Our results reveal a previously unrecognized function of Kir6.1 as a negative regulator of the NLRP3 inflammasome and insulin resistance, which is mediated by virtue of its ability to inhibit NLRP3 inflammasome assembly. These data provide novel insights into the regulatory mechanism of NLRP3 inflammasome activation and suggest that Kir6.1 is a promising therapeutic target for inflammasome-mediated inflammatory diseases.

The effect of corylin in regulating NLRP3 inflammasome activation in macrophages

Chronic inflammation is associated with several diseases and cancers. The activation of inflammasomes has been indicated as a main role in chronic inflammation, which is a group of cytosolic protein complexes, classically consisting an NOD‐like protein (NLR), the adaptor apoptosis‐associated speck‐like protein containing a caspase recruitment domain (ASC), and caspase‐1. Activation of inflammasome results in assembly of the inflammasome, caspase‐1 activation as well as IL‐1β and IL‐18 secretion. A number of studies have reported that increased concentration of IL‐1β protein in tumor tissues is associated with poor prognosis for cancer patients.Corylin is a main compound isolated from Psoralea corylifloia L., a common Chinese herbal medicine. The Psoralea corylifloia L. has been used in the treatment of skin diseases and osteoporosis. The extracts of this plant has been found to have anti‐oxidative, anti‐bacterial, anti‐diabetic, neuroprotective and immunomodulatory effects. Our previous study demonstrated that corylin inhibits the production of TNF‐α, IL‐6 and NO by murine macrophages through inhibiting the activities of MAPKs and NF‐κB. In the present study, we will examine the effect of corylin in regulating NLRP3 inflammasome activation in macrophages. We used murine macrophages (J774A.1 cells) and human monocytes (THP‐1 cells), and treated with LPS/ATP to induce the activation of NLRP3 inflammasome, then gave different doses of corylin to investigate its effects. The supernatant is used to determine the level of IL‐1β by enzyme‐linked immunosorbent assay (ELISA), and the lysates is used to investigate the level of NLRP3 inflammasome associated protein by Western blot. Our experimental results indicated that corylin inhibits the activation of NLRP3 inflammasome in both murine and human macrophages. We will further examine the effect of corylin on the polarization of macrophages.Support or Funding InformationThis study was supported by the Ministry of Science and Technology, Taiwan, R.O.C. (Grant No. MOST 107‐2320‐B‐037‐019).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cutting Edge: G Protein Subunit β 1 Negatively Regulates NLRP3 Inflammasome Activation

The NLRP3 inflammasome has important roles in the pathogenesis of various inflammatory diseases. However, the regulatory mechanisms of the NLRP3 inflammasome are not fully understood. In this study, we attempted to identify molecules that interact with NLRP3 upon its activation. We identified G protein subunit β 1 (GNB1), a downstream molecule of G protein-coupled receptors (GPCRs), which regulates the NLRP3 inflammasome activation. GNB1 was physically associated with NLRP3 via the pyrin domain of NLRP3. Activation of the NLRP3 inflammasome was enhanced in GNB1-knockdown or GNB1-deficient murine macrophages, although a lack of GNB1 did not affect activation of the AIM2 inflammasome. ASC oligomerization induced by NLRP3 was enhanced by GNB1 deficiency. Conversely, NLRP3-dependent ASC oligomerization was inhibited by the overexpression of GNB1. This study indicates that GNB1 negatively regulates NLRP3 inflammasome activation by suppressing NLRP3-dependent ASC oligomerization, and it provides a regulatory mechanism of the NLRP3 inflammasome.

HSP70 is a negative regulator of NLRP3 inflammasome activation

The NOD-leucine rich repeat and pyrin containing protein 3 (NLRP3) inflammasome is a multi-protein complex, aimed at producing IL-1β in response to danger signals which must be tightly regulated. Here we investigated the importance of the stress sensor, Heat Shock Protein 70 (HSP70) on NLRP3 inflammasome activation. HSP70 deficiency leads to the worsening of NLRP3-dependent peritonitis in mice. HSP70 deficiency also enhances caspase-1 activation and IL-1β production in murine Bone Marrow-Derived Macrophages (BMDMs) under NLRP3 activator treatment in vitro. This observation is associated with an increased number and size of Apoptosis associated Speck-like protein containing a CARD domain (ASC)/NLRP3 specks. Conversely, the overexpression of HSP70 in BMDMs decreases caspase-1 activation and IL-1β production under NLRP3 activator treatment. HSP70 interacts with NLRP3 and this interaction is lost upon NLRP3 inflammasome activation. Heat shock inhibits NLRP3 inflammasome activation in vitro and inhibits peritonitis in mice. Therefore this study provides evidence on the inhibitory role of HSP70 on NLRP3 inflammasome and open the possibility of treating inflammatory diseases via HSP70 induction and/or by hyperthermia.

Interactions Between Enteroviruses and the Inflammasome: New Insights Into Viral Pathogenesis.

Enteroviruses (EVs) have emerged a substantial threat to public health. EVs infection range from mild to severe disease, including mild respiratory illness, diarrhea, poliomyelitis, hand, foot, and mouth disease, aseptic meningitis, and encephalitis. In the Asia-Pacific region, for example, one of the best studied enterovirus 71 (EV71) has been associated with pandemics of hand, foot, and mouth disease (HFMD) in children, particularly those under the age of five. Serious HFMD cases are associated with neurological complications, such as aseptic meningitis, acute flaccid paralysis, brainstem encephalitis, and have been associated with as many as 1000s of deaths in children and infants from 2008 to 2017, in China. More than 90% of laboratory confirmed deaths due to HMFD are associated with EV71. However, little is known about the pathogenesis of EVs. Studies have reported that EVs-infected patients with severe complications show elevated serum concentrations of IL-1β. The secretion of IL-1β is mediated by NLRP3 inflammasome during EV71 and CVB3 infection. Enteroviruses 2B and 3D proteins play an important role in activation of NLRP3 inflammasome, while 3C and 2A play important roles in antagonizing the activation of NLRP3 and the secretion of IL-1β. In this review, we summarize current knowledge regarding the molecular mechanisms that underlie the activation and regulation of the NLRP3 inflammasome, particularly how viral proteins regulate NLRP3 inflammasome activation. These insights into the relationship between the NLRP3 inflammasome and the pathogenesis of EVs infection may ultimately inform the development of novel antiviral drugs.

LINC00969 promotes the degeneration of intervertebral disk by sponging miR-335-3p and regulating NLRP3 inflammasome activation.

Long noncoding RNAs (LncRNAs) may serve as miRNA sponges to regulate the expressions of miRNA target genes. LncRNA LINC00969 has been indicated to be upregulated in intervertebral disk degeneration. However, the regulatory mechanism of LINC00969 in intervertebral disk degeneration progression remains unclear. Differently expressed LINC00969, miR-335-3p, and thioredoxin-interacting protein (TXNIP) were determined in nucleus pulposus (NP) tissues and cells isolated from patients with intervertebral disk degeneration. The interaction between LINC00969, miR-335-3p, and TXNIP was also assessed. In this study, we demonstrated that LINC00969 was highly expressed, whereas miR-335-3p was aberrantly downregulated in NP tissues and cells of intervertebral disk degeneration patients. In addition, our results suggested that LINC00969 enhanced NP cell apoptosis. More importantly, LINC00969 was identified to function as a competitive endogenous RNA (ceRNA) for miR-335-3p to positively regulate TXNIP expression in vitro. Our study provided evidence for the cross-talk between LINC00969, miR-335-3p, and TXNIP, shedding light on the therapy for intervertebral disk degeneration. © 2018 IUBMB Life, 71(5):611-618, 2019.

Salvianolic acid B abolished chronic mild stress-induced depression through suppressing oxidative stress and neuro-inflammation via regulating NLRP3 inflammasome activation.

This study was framed to investigate the molecular mechanism behind the anti-depressant effect of salvianolic acid B (SB) against unpredictable chronic mild stress (CMS) induced depression rat model. Control rats received only saline without CMS exposure, whereas CMS model rats were induced to several stress (CMS) for 6weeks. Treatment group rats were induced with CMS for 6weeks but received either 20 or 40mg/kg of SB or 20mg/kg imipramine (CMS+IMP) from the 4th week to 6th week. Treatment with SB or IMP significantly ameliorated body weight, sucrose consumption rate with shorter immobility time than the control group. Also, administration with SB or IMP could reverse the hyperactivity of hypothalamic-pituitary-adrenal axis as well as decreased inflammatory cytokines with improved antioxidant status. Furthermore, the protein expression of NLRP3 (inflammasome) was markedly downregulated upon treatment with SB (both 20 and 40mg) or IMP and thereby confirming its potent anti-depressant activity. PRACTICAL APPLICATIONS: Salvianolic acid B (SB) is a phenolic acid extracted from Salvia militiorrhiza Bunge, a popular Chinese herb, which has been prescribed for various pathological conditions. SB has been previously reported with anti-depressant activity but, the in-depth mechanism behind the anti-depressant effect of SB against CMS is still elusive. Hence, the current study was plotted to explore the in-depth mechanism behind the anti-depressant effect of SB against CMS model of depression in rats. The outcome of the current study has confirmed the anti-depressant activity by abolishing oxidative stress, and neuroinflammatory response in the hippocampus through inhibiting NLRP3 inflammasome activation. Hence, SB can be prescribed to major depression patients with standard anti-depressant agents to abolish oxidative stress, neuro-inflammatory response, and related neurological changes.

Macrophage Migration Inhibitory Factor Regulates U1 Small Nuclear RNP Immune Complex–Mediated Activation of the NLRP3 Inflammasome

High-expression alleles of macrophage migration inhibitory factor (MIF) are linked genetically to the severity of systemic lupus erythematosus (SLE). The U1 small nuclear RNP (snRNP) immune complex containing U1 snRNP and anti-U1 snRNP antibodies, which are found in patients with SLE, activates the NLRP3 inflammasome, comprising NLRP3, ASC, and procaspase 1, in human monocytes, leading to the production of interleukin-1β (IL-1β). This study was undertaken to investigate the role of the snRNP immune complex in up-regulating the expression of MIF and its interface with the NLRP3 inflammasome. MIF, IL-1β, NLRP3, caspase 1, ASC, and MIF receptors were analyzed by enzyme-linked immunosorbent assay, Western blotting, quantitative polymerase chain reaction, and cytometry by time-of-flight mass spectrometry (CytoF) in human monocytes incubated with or without the snRNP immune complex. MIF pathway responses were probed with the novel small molecule antagonist MIF098. The snRNP immune complex induced the production of MIF and IL-1β from human monocytes. High-dimensional, single-cell CytoF analysis established that MIF regulates activation of the NLRP3 inflammasome, including findings of a quantitative relationship between MIF and its receptors and IL-1β levels in the monocytes. MIF098, which blocks MIF binding to its cognate receptor, suppressed the production of IL-1β, the up-regulation of NLRP3, which is a rate-limiting step in NLRP3 inflammasome activation, and the activation of caspase 1 in snRNP immune complex-stimulated human monocytes. The U1 snRNP immune complex is a specific stimulus of MIF production in human monocytes, with MIF having an upstream role in defining the inflammatory characteristics of activated monocytes by regulating NLRP3 inflammasome activation and downstream IL-1β production. These findings provide mechanistic insight and a therapeutic rationale for targeting MIF in subgroups of lupus patients, such as those classified as high genotypic MIF expressers or those with anti-snRNP antibodies.

Role and mechanism of ROS scavengers in alleviating NLRP3-mediated inflammation.

Inflammation, as a common immune response to various infections or injuries, can cause many dangerous and complicated diseases. Inflammasome is a protein complex playing a vital role in an inflammation process, and the nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) inflammasome has been the most-widely studied one. Recent evidence suggests the reactive oxygen species (ROS)-NLRP3 signaling pathway to be a possible NLRP3 inflammasome regulation model. Numerous recent preclinical reports indicate that application of antioxidants could scavenge excessive ROS and attenuate inflammatory responses through suppressing NLRP3 inflammasome activation. This article, at first, briefly overviews how ROS may mediate the regulation of NLRP3 inflammasome activation. Then, preclinical researches of various ROS scavengers for treating NLRP3 inflammasome-associated diseases are focused on and critically analyzed. Finally, the potential of antioxidant treatment as a therapy for inflammation is to be discussed, and perspectives on future research directions will be shared.

Targeting Peroxiredoxin 1 by a Curcumin Analogue, AI-44, Inhibits NLRP3 Inflammasome Activation and Attenuates Lipopolysaccharide-Induced Sepsis in Mice.

Aberrant activation of the NLRP3 inflammasome contributes to the onset and progression of various inflammatory diseases, making it a highly desirable drug target. In this study, we screened a series of small compounds with anti-inflammatory activities and identified a novel NLRP3 inflammasome inhibitor, AI-44, a curcumin analogue that selectively inhibited signal 2 but not signal 1 of NLRP3 inflammasome activation. We demonstrated that AI-44 bound to peroxiredoxin 1 (PRDX1) and promoted the interaction of PRDX1 with pro-Caspase-1 (CASP1), which led to the suppression of association of pro-CASP1 and ASC. Consequently, the assembly of the NLRP3 inflammasome was interrupted, and the activation of CASP1 was inhibited. Knockdown of PRDX1 significantly abrogated the inhibitory effect of AI-44 on the NLRP3 inflammasome. Importantly, AI-44 alleviated LPS-induced endotoxemia in mice via suppressing NLRP3 inflammasome activation. Taken together, our work highlighted PRDX1 as a negative regulator of NLRP3 inflammasome activation and suggested AI-44 as a promising candidate compound for the treatment of sepsis or other NLRP3 inflammasome-driven diseases.