Nlrp2 deletion ameliorates kidney damage in a mouse model of cystinosis

Cystinosis is a rare autosomal recessive disorder caused by mutations in the CTNS gene that encodes cystinosin, a ubiquitous lysosomal cystine/H+ antiporter. The hallmark of the disease is progressive accumulation of cystine and cystine crystals in virtually all tissues. At the kidney level, human cystinosis is characterized by the development of renal Fanconi syndrome and progressive glomerular and interstitial damage leading to end-stage kidney disease in the second or third decade of life. The exact molecular mechanisms involved in the pathogenesis of renal disease in cystinosis are incompletely elucidated. We have previously shown upregulation of NLRP2 in human cystinotic proximal tubular epithelial cells and its role in promoting inflammatory and profibrotic responses. Herein, we have investigated the role of NLRP2 in vivo using a mouse model of cystinosis in which we have confirmed upregulation of Nlrp2 in the renal parenchyma. Our studies show that double knock out Ctns-/- Nlrp2-/- animals exhibit delayed development of Fanconi syndrome and kidney tissue damage. Specifically, we observed at 4-6 months of age that animals had less glucosuria and calciuria and markedly preserved renal tissue, as assessed by significantly lower levels of inflammatory cell infiltration, tubular atrophy, and interstitial fibrosis. Also, the mRNA expression of some inflammatory mediators (Cxcl1 and Saa1) and the rate of apoptosis were significantly decreased in 4-6-month old kidneys harvested from Ctns-/- Nlrp2-/- mice compared to those obtained from Ctns-/-mice. At 12-14 months of age, renal histological was markedly altered in both genetic models, although double KO animals had lower degree of polyuria and low molecular weight proteinuria and decreased mRNA expression levels of Il6 and Mcp1. Altogether, these data indicate that Nlrp2 is a potential pharmacological target for delaying progression of kidney disease in cystinosis.

NLRP2 in health and disease

NLR family pyrin domain containing 2 (NLRP2) is a novel member of the Nod-like receptor (NLR) family. However, our understanding of NLRP2 has long been ambiguous. NLRP2 may have a role in the innate immune response, but its 'specific' functions remain controversial. Although NLRP2 can initiate inflammasome and promote inflammation, it can also downregulate inflammatory signals. Additionally, NLRP2 has been reported to function in the reproductive system and shows high expression in the placenta. However, the exact role of NLRP2 in the reproductive system is unclear. Here, we highlight the most current progress on NLRP2 in inflammasome activation, effector function and regulation of nuclear factor-κB. And we discuss functions of NLRP2 in inflammatory diseases, reproductive disorders and the potential implication of NLRP2 in human diseases.

"Other Than NLRP3" Inflammasomes: Multiple Roles in Brain Disease

Human neuroinflammatory and neurodegenerative diseases, whose prevalence keeps rising, are still unsolved pathobiological/therapeutical problems. Among others, recent etiology hypotheses stressed as their main driver a chronic neuroinflammation, which is mediated by innate immunity-related protein oligomers: the inflammasomes. A panoply of exogenous and/or endogenous harmful agents activates inflammasomes' assembly, signaling, and IL-1β/IL-18 production and neural cells' pyroptotic death. The underlying concept is that inflammasomes' chronic activation advances neurodegeneration while their short-lasting operation restores tissue homeostasis. Hence, from a therapeutic standpoint, it is crucial to understand inflammasomes' regulatory mechanisms. About this, a deluge of recent studies focused on the NLRP3 inflammasome with suggestions that its pharmacologic block would hinder neurodegeneration. Yet hitherto no evidence proves this view. Moreover, known inflammasomes are numerous, and the mechanisms regulating their expression and function may vary with the involved animal species and strains, as well as organs and cells, and the harmful factors triggered as a result. Therefore, while presently leaving out some little-studied inflammasomes, this review focuses on the "other than NLRP3" inflammasomes that participate in neuroinflammation's complex mechanisms: NLRP1, NLRP2, NLRC4, and AIM2. Although human-specific data about them are relatively scant, we stress that only a holistic view including several human brain inflammasomes and other potential pathogenetic drivers will lead to successful therapies for neuroinflammatory and neurodegenerative diseases.

Activation of NLRP2 in Triple-Negative Breast Cancer sensitizes chemotherapeutic therapy through facilitating hnRNPK function

Nucleotide-binding oligomerization domain (NOD)-like receptor type 2 protein (NLRP2) was reported to inhibit NF-κB in response to inflammatory stimuli, but its role in tumors remains elusive. We screened out NLRP2 from mouse models of breast cancer metastasis. Bioinformatics analysis showed NLRP2 expression was positively correlated with survival rate and negatively correlated with the potential of cancer metastasis. Its significance in Triple-Negative Breast Cancer (TNBC) was investigated by gain- and loss-of-function studies in vivo and vitro. Re-expression of NLRP2 dramatically inhibited the growth and metastasis of the xenograft model of MDA-MB-231 cells. Mechanically, NLRP2 confined hnRNPK within cytoplasm, which in turn blocked vimentin mRNA production. Not only that, NLRP2 further enhanced the H2O2-induced high level of p53&Bax and hence dramatically increased the apoptosis rate (fivefold). Likewise, carboplatin-treated cells showed decreased cell viability, suggesting that patients of TNBC with high level of NLRP2 respond well to chemotherapeutics. Under the stimulus of H2O2, NLRP2-hnRNPK no longer stayed in the cytoplasm, but entered the nucleus to increase the expression of p53 and hence enhanced corresponding apoptosis effect, increasing Bax expression. It suggested that NLRP2 helps p53 enter the nucleus to induce apoptosis. This study revealed a novel function of NLRP2 that modulated oncogenic and anti-oncogenic characteristics of hnRNPK, and provided a new biomarker for TNBC chemotherapy.

Loss of the Maternal Effect Gene Nlrp2 Alters the Transcriptome of Ovulated Mouse Oocytes and Impacts Expression of Histone Demethylase KDM1B

The subcortical maternal complex (SCMC) is a multiprotein complex in oocytes and preimplantation embryos that is encoded by maternal effect genes. The SCMC is essential for zygote-to-embryo transition, early embryogenesis, and critical zygotic cellular processes, including spindle positioning and symmetric division. Maternal deletion of Nlrp2, which encodes an SCMC protein, results in increased early embryonic loss and abnormal DNA methylation in embryos. We performed RNA sequencing on pools of meiosis II (MII) oocytes from wild-type and Nlrp2-null female mice that were isolated from cumulus-oocyte complexes (COCs) after ovarian stimulation. Using a mouse reference genome-based analysis, we found 231 differentially expressed genes (DEGs) in Nlrp2-null compared to WT oocytes (123 up- and 108 downregulated; adjusted p < 0.05). The upregulated genes include Kdm1b, a H3K4 histone demethylase required during oocyte development for the establishment of DNA methylation marks at CpG islands, including those at imprinted genes. The identified DEGs are enriched for processes involved in neurogenesis, gland morphogenesis, and protein metabolism and for post-translationally methylated proteins. When we compared our RNA sequencing data to an oocyte-specific reference transcriptome that contains many previously unannotated transcripts, we found 228 DEGs, including genes not identified with the first analysis. Interestingly, 68% and 56% of DEGs from the first and second analyses, respectively, overlap with oocyte-specific hyper- and hypomethylated domains. This study shows that there are substantial changes in the transcriptome of mouse MII oocytes from female mice with loss of function of Nlrp2, a maternal effect gene that encodes a member of the SCMC.

NLRP2 inhibits cell proliferation and migration by regulating EMT in lung adenocarcinoma cells

Nucleotide-binding oligomerization domain-like receptors (NLRs) are crucial types of innate immune sensors and well known for their critical roles in the immune system. However, how NLRP2 functions in the progression of cancer is largely unknown. Here, we identified NLRP2 as an antioncogene in lung adenocarcinoma (LUAD) cells. Gain- and loss-of-function studies revealed that NLRP2 silencing promoted cell proliferation and migration by stimulating NF-kB signaling in the microenvironment, which induced epithelial-to-mesenchymal transition (EMT) phenotype and cytoskeleton reorganization in LUAD cells. The addition of the NF-kB inhibitor rescued the function of NLRP2 on EMT. Moreover, NLRP2 increased the level of cofilin phosphorylation and repressed subsequent F-actin reorganization. Consistently, the in vivo study showed that NLRP2 played an inhibitory role in forming metastasis foci. Taken together, NLRP2 inhibited cell proliferation and migration by regulating EMT in LUAD cells, demonstrating the essential function of NLRP2 in the development of LUAD.

NLRP2 Is Overexpressed in Spinal Astrocytes at the Peak of Mechanical Pain Sensitivity during Complete Freund Adjuvant-Induced Persistent Pain

Our earlier findings revealed that interleukin-1 receptor type-1 (IL-1R1) was overexpressed in spinal neurons, and IL-1R1-deficient mice showed significant attenuation of thermal and mechanical allodynia during the course of the Complete Freund adjuvant (CFA)-induced persistent pain model. In the present study, we found that a ligand of IL-1R1, termed interleukin-1β (IL-1β), is also significantly overexpressed at the peak of mechanical pain sensitivity in the CFA-evoked pain model. Analysis of cellular distribution and modeling using IMARIS software showed that in the lumbar spinal dorsal horn, IL-1β is significantly elevated by astrocytic expression. Maturation of IL-1β to its active form is facilitated by the formation of the multiprotein complex called inflammasome; thus, we tested the expression of NOD-like receptor proteins (NLRPs) in astrocytes. At the peak of mechanical allodynia, we found expression of the NLRP2 inflammasome sensor and its significantly elevated co-localization with the GFAP astrocytic marker, while NLRP3 was moderately present and NLRP1 showed total segregation from the astrocytic profiles. Our results indicate that peripheral CFA injection induces NLRP2 inflammasome and IL-1β expression in spinal astrocytes. The release of mature IL-1β can contribute to the maintenance of persistent pain by acting on its neuronally expressed receptor, which can lead to altered neuronal excitability.

Oxysterols Modify NLRP2 in Epithelial Cells, Identifying a Mediator of Ozone-induced Inflammation

Ozone (O₃) is a prevalent air pollutant causing lung inflammation. Previous studies demonstrate that O₃ oxidizes lipids, such as cholesterol, in the airway to produce oxysterols, such as secosterol-A (SecoA), which are electrophiles capable of forming covalent linkages preferentially with lysine residues and consequently modify protein function. The breadth of proteins modified by this oxysterol as well as the biological consequences in the lung are unknown. Using an alkynyl-tagged form of SecoA and shotgun proteomics, we identified 135 proteins to be modified bronchial epithelial cells. Among them was NLR Family Pyrin Domain Containing 2 (NLRP2) forming a SecoA-protein adduct at lysine (K1019) in the terminal leucine-rich-repeat, a known regulatory region for NLR proteins. NLRP2 expression in airway epithelial cells was characterized and CRISPR-Cas9 knockout and shRNA knockdown of NLRP2 was used to determine its function in O₃-induced inflammation. No evidence for NLPR2 inflammasome formation or NLRP2-dependent increase in caspase-1 activity in response to O₃ was observed. O₃-induced pro-inflammatory gene expression for CXCL2 and CXCL8/IL8 was further enhanced in NLRP2 knockout cells, suggesting a negative regulatory role. Reconstitution of NLRP2 KO cells with K1019R mutant NLRP2 partially blocked SecoA adduction and enhanced O₃-induced IL-8 release as compared to wild type NLRP2. Together, our findings uncover NLRP2 as a highly abundant, key component of pro-inflammatory signaling pathways in airway epithelial cells and as a novel mediator of O₃-induced inflammation.

Subcortical maternal complex (SCMC) expression during folliculogenesis is affected by oocyte donor age in sheep

PURPOSE

The age-associated decline in female fertility is largely ascribable to the decrease in oocyte quality. The subcortical maternal complex (SCMC) is a multiprotein complex essential for early embryogenesis and female fertility and functionally conserved across mammals. The present work evaluated expression dynamics of its components during folliculogenesis in relation to maternal age in sheep.

METHODS

The expression of the SCMC components (KHDC3/FILIA, NLRP2, NLRP5/MATER, OOEP/FLOPED, PADI6, TLE6 and ZBED3) was analyzed by real-time PCR in pools of growing oocytes (GO) of different diameters (70-90 μm (S), 90-110 μm (M), or 110-130 μm (L)) derived from non-hormonally treated adult (Ad; age < 4 years), prepubertal (Pr; age 40 days), or aged ewes (age > 6 years).

RESULTS

Specific expression patterns associated with donor age were observed during folliculogenesis for all genes, except ZBED3. In oocytes of adult donors, the synthesis of NLRP2, NLRP5, PADI6, and ZBED3 mRNAs was complete in S GO, while FILIA, TLE6, and OOEP were actively transcribed at this stage. Conversely, Pr GO showed active transcription of all mRNAs, except for ZBED3, during the entire window of oocyte growth. Notably, aged GO showed a completely inverse pattern, with a decrease of NLRP2, TLE6, FILIA, and PADI6 mRNA abundance during the latest stage of oocyte growth (L GO). Interestingly, MATER showed high expression variability, suggesting large inter-oocyte differences.

CONCLUSION

Our study describes the SCMC expression dynamics during sheep oogenesis and reports age-specific patterns that are likely involved in the age-related decline of oocyte quality.

NLRP2 Regulates Proinflammatory and Antiapoptotic Responses in Proximal Tubular Epithelial Cells

Nod-like Receptor Pyrin domain containing proteins (NLRPs) expressed by resident renal cells may contribute to the pathogenesis of multiple renal diseases. Cystinosis is a genetic disorder that affects kidney and particularly proximal tubular epithelial cells (PTEC). Here, we investigated the expression of NLRP family members in human control and cystinotic conditionally immortalized PTEC. Among all the NLRPs tested, we found that NLRP2 is highly expressed in cystinostic PTEC, but not in PTEC from healthy subjects. The NLRP2 overexpression was confirmed in primary PTEC and in kidney biopsies from cystinotic patients. In order to elucidate the role of NLRP2 in PTEC, we stably transfected control PTEC with an NLRP2-containing plasmid. We showed that NLRP2 markedly increases the production of several NF-κB regulated cytokines and chemokines. Accordingly, we demonstrated that NLRP2 interacts with IKKa and positively regulates the DNA-binding activity of p50 and p65 NF-κB, by modulating the p65 NF-κB phosphorylation status in Serine 536. Transcriptome analysis revealed that NLRP2 also upregulates the expression of profibrotic mediators and reduces that of several interferon-inducible genes. Finally, NLRP2 overexpression decreased the apoptotic cell rate. Consistently, silencing of NLRP2 by small-interfering RNA in cystinotic PTEC resulted in a significant decrease in cytokine and chemokine production as well as in an increase in the apoptosis rate. Altogether, our data reveals a previously unrecognized role for NLRP2 in regulating proinflammatory, profibrotic and antiapoptotic responses in PTEC, through NF-κB activation. Moreover, our findings unveil a novel potential mechanism involving NLRP2 overexpression in the pathogenesis of cystinosis.

Suppressing NLRP2 expression accelerates hepatic steatosis: A mechanism involving inflammation and oxidative stress

Nonalcoholic fatty liver disease (NAFLD) is characterized by lipid accumulation and inflammation in the liver, contributing to a broad spectrum of severe pathologies, such as metabolic syndrome and hepatocellular carcinoma. Presently, the pathogenesis that attributes to NAFLD has not been fully understood. NLRP2 has been shown to inhibit the NF-κB signaling, and thus may contribute to regulate the inflammatory response. However, its role in NAFLD is largely unclear. In the study, we found that NLRP2 was markedly decreased in liver tissues of individuals with severe steatosis, or in a genetic deficiency (ob/ob) mice. High fat diet (HFD) feeding also led to a significant reduction of NLRP2 in liver of mice. Then, the wild type (WT) and NLRP2 knockout (KO) mice were used to further explore the role of NLRP2 in the NAFLD progression. NLRP2 knockout mice exhibited severer metabolic syndrome and hepatic steatosis after HFD administration, as evidenced by the increased body weight, liver histological changes and lipid accumulation. Moreover, HFD feeding-induced inflammation was significantly accelerated by the loss of NLRP2, as evidenced by the increased expression of pro-inflammatory cytokines and activation of nuclear factor κB (NF-κB) pathway. In addition, oxidative stress triggered by HFD was further promoted by NLRP2 deletion through repressing NF-E2-related factor 2 (Nrf2) pathway. In vitro, we surprisingly found that promoting Nrf2 activation could attenuate NLRP2 knockout-accelerated inflammation and reactive oxygen species (ROS) generation. Therefore, our study indicated that NLRP2 might be a potential target for developing effective therapeutic strategy to prevent NAFLD progression.

NLRP2 negatively regulates antiviral immunity by interacting with TBK1

Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are intracellular pattern recognition receptors (PRRs) that regulate a variety of inflammatory and host defense responses. Unlike the well-established NLRs, the roles of NLRP2 are controversial and poorly defined. Here, we report that NLRP2 acts as a negative regulator of TANK-binding kinase 1 (TBK1)-mediated type I interferon (IFN) signaling. Mechanistically, NLRP2 interacted directly with TBK1, and this binding disrupted the interaction of TBK1 and interferon regulatory factor 3 (IRF3), which interfered with TBK1-induced IRF3 phosphorylation. IFNs induce a series of proteins that have well-known antiviral or immune-regulatory functions, and tight control of the IFN signaling cascade is critical for limiting tissue damage and preventing autoimmunity. Our studies indicate that the NLRP2-TBK1 axis may serve as an additional signaling cascade to maintain immune homeostasis in response to viral infection.

Maternal variants in NLRP and other maternal effect proteins are associated with multilocus imprinting disturbance in offspring

Background

Genomic imprinting results from the resistance of germline epigenetic marks to reprogramming in the early embryo for a small number of mammalian genes. Genetic, epigenetic or environmental insults that prevent imprints from evading reprogramming may result in imprinting disorders, which impact growth, development, behaviour and metabolism. We aimed to identify genetic defects causing imprinting disorders by whole-exome sequencing in families with one or more members affected by multilocus imprinting disturbance.

Methods

Whole-exome sequencing was performed in 38 pedigrees where probands had multilocus imprinting disturbance, in five of whom maternal variants in NLRP5 have previously been found.

Results

We now report 15 further pedigrees in which offspring had disturbance of imprinting, while their mothers had rare, predicted-deleterious variants in maternal effect genes, including NLRP2, NLRP7 and PADI6. As well as clinical features of well-recognised imprinting disorders, some offspring had additional features including developmental delay, behavioural problems and discordant monozygotic twinning, while some mothers had reproductive problems including pregnancy loss.

Conclusion

The identification of 20 putative maternal effect variants in 38 families affected by multilocus imprinting disorders adds to the evidence that maternal genetic factors affect oocyte fitness and thus offspring development. Testing for maternal-effect genetic variants should be considered in families affected by atypical imprinting disorders.

NLRP2 is highly expressed in a mouse model of ischemic stroke

Nucleotide binding oligomerization domain (NOD)-like receptors (NLRs) are a class of cytoplasmic pattern-recognition receptors with a major role in innate immunity. Fourteen of the twenty-two human NLRs contain a pyrin domain and form the NLRP subfamily (NLRPs). Among NLRPs, NLRP2 is less well-understood in aspects of distribution and functions, especially in central nervous system (CNS). This study was the first to explore the expression of NLRP2 in central nervous system both under normal conditions and in ischemic stroke models. We found NLRP2 protein had a basal level of expression in CNS, mainly in astrocytes and was significantly elevated in ischemic brains in vivo or oxygen-glucose deprivation-treated cells in vitro. And silencing of NLRP2 genes could reduce the apoptotic rate of oxygen-glucose deprivation-treated cells. Thus high expression of NLRP2, especially in astrocytes, may play important roles in the pathophysiological process of ischemic stroke and has potential clinical value for the treatment of ischemic stroke.

No evidence for mutations in NLRP7, NLRP2 or KHDC3L in women with unexplained recurrent pregnancy loss or infertility

STUDY QUESTION

Are mutations in NLRP2/7 (NACHT, LRR and PYD domains-containing protein 2/7) or KHDC3L (KH Domain Containing 3 Like) associated with recurrent pregnancy loss (RPL) or infertility?

SUMMARY ANSWER

We found no evidence for mutations in NLRP2/7 or KHDC3L in unexplained RPL or infertility.

WHAT IS KNOWN ALREADY

Mutations in NLRP7 and KHDC3L are known to cause biparental hydatidiform moles (BiHMs), a rare form of pregnancy loss. NLRP2, while not associated with the BiHM pathology, is known to cause recurrent Beckwith Weidemann Syndrome (BWS).

STUDY DESIGN, SIZE, AND DURATION

Ninety-four patients with well characterized, unexplained infertility were recruited over a 9-year period from three IVF clinics in Sweden. Blood samples from 24 patients with 3 or more consecutive miscarriages of unknown etiology were provided by the Recurrent Miscarriage Clinic at St Mary's Hospital, London, UK.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were recruited into both cohorts following extensive clinical studies. Genomic DNA was isolated from peripheral blood and subject to Sanger sequencing of NLRP2, NLRP7 and KHDC3L. Sequence electropherograms were analyzed by Sequencher v5.0 software and variants compared with those observed in the 1000 Genomes, single nucleotide polymorphism database (dbSNP) and HapMap databases. Functional effects of non-synonymous variants were predicted using Polyphen-2 and sorting intolerant from tolerant (SIFT).

MAIN RESULTS AND THE ROLE OF CHANCE

No disease-causing mutations were identified in NLRP2, NLRP7 and KHDC3L in our cohorts of unexplained infertility and RPL.

LIMITATIONS, REASONS FOR CAUTION

Due to the limited patient size, it is difficult to conclude if the low frequency single nucleotide polymorphisms observed in the present study are causative of the phenotype. The design of the present study therefore is only capable of detecting highly penetrant mutations.

WIDER IMPLICATIONS OF THE FINDINGS

The present study supports the hypothesis that mutations in NLRP7 and KHDC3L are specific for the BiHM phenotype and do not play a role in other adverse reproductive outcomes. Furthermore, to date, mutations in NLRP2 have only been associated with the imprinting disorder BWS in offspring and there is no evidence for a role in molar pregnancies, RPL or unexplained infertility.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by the following sources: Estonian Ministry of Education and Research (Grant SF0180044s09), Enterprise Estonia (Grant EU30020); Mentored Resident research project (Department of Obstetrics and Gynecology, Baylor College of Medicine); Imperial NIHR Biomedical Research Centre; Grant Number C06RR029965 from the National Center for Research Resources (NCCR; NIH). No competing interests declared.