Neutrophil-specific gain-of-function mutations in Nlrp3 promote development of cryopyrin-associated periodic syndrome

Gain-of-function mutations in NLRP3 are responsible for a spectrum of autoinflammatory diseases collectively referred to as “cryopyrin-associated periodic syndromes” (CAPS). Treatment of CAPS patients with IL-1–targeted therapies is effective, confirming a central pathogenic role for IL-1β. However, the specific myeloid cell population(s) exhibiting inflammasome activity and sustained IL-1β production in CAPS remains elusive. Previous reports suggested an important role for mast cells (MCs) in this process. Here, we report that, in mice, gain-of-function mutations in Nlrp3 restricted to neutrophils, and to a lesser extent macrophages/dendritic cells, but not MCs, are sufficient to trigger severe CAPS. Furthermore, in patients with clinically established CAPS, we show that skin-infiltrating neutrophils represent a substantial biological source of IL-1β. Together, our data indicate that neutrophils, rather than MCs, can represent the main cellular drivers of CAPS pathology.     

Helicobacter urease–induced activation of the TLR2/NLRP3/IL-18 axis protects against asthma

Inflammasome activation and caspase-1–dependent (CASP1-dependent) processing and secretion of IL-1β and IL-18 are critical events at the interface of the bacterial pathogen Helicobacter pylori with its host. Whereas IL-1β promotes Th1 and Th17 responses and gastric immunopathology, IL-18 is required for Treg differentiation, H. pylori persistence, and protection against allergic asthma, which is a hallmark of H. pylori–infected mice and humans. Here, we show that inflammasome activation in DCs requires the cytoplasmic sensor NLRP3 as well as induction of TLR2 signaling by H. pylori. Screening of an H. pylori transposon mutant library revealed that pro–IL-1β expression is induced by LPS from H. pylori, while the urease B subunit (UreB) is required for NLRP3 inflammasome licensing. UreB activates the TLR2-dependent expression of NLRP3, which represents a rate-limiting step in NLRP3 inflammasome assembly. ureB-deficient H. pylori mutants were defective for CASP1 activation in murine bone marrow–derived DCs, splenic DCs, and human blood-derived DCs. Despite colonizing the murine stomach, ureB mutants failed to induce IL-1β and IL-18 secretion and to promote Treg responses. Unlike WT H. pylori, ureB mutants were incapable of conferring protection against allergen-induced asthma in murine models. Together, these results indicate that the TLR2/NLRP3/CASP1/IL-18 axis is critical to H. pylori–specific immune regulation.     

In vivo regulation of interleukin 1β in patients with cryopyrin-associated periodic syndromes

The investigation of interleukin 1β (IL-1β) in human inflammatory diseases is hampered by the fact that it is virtually undetectable in human plasma. We demonstrate that by administering the anti–human IL-1β antibody canakinumab (ACZ885) to humans, the resulting formation of IL-1β–antibody complexes allowed the detection of in vivo–produced IL-1β. A two-compartment mathematical model was generated that predicted a constitutive production rate of 6 ng/d IL-1β in healthy subjects. In contrast, patients with cryopyrin-associated periodic syndromes (CAPS), a rare monogenetic disease driven by uncontrolled caspase-1 activity and IL-1 production, produced a mean of 31 ng/d. Treatment with canakinumab not only induced long-lasting complete clinical response but also reduced the production rate of IL-1β to normal levels within 8 wk of treatment, suggesting that IL-1β production in these patients was mainly IL-1β driven. The model further indicated that IL-1β is the only cytokine driving disease severity and duration of response to canakinumab. A correction for natural IL-1 antagonists was not required to fit the data. Together, the study allowed new insights into the production and regulation of IL-1β in man. It also indicated that CAPS is entirely mediated by IL-1β and that canakinumab treatment restores physiological IL-1β production.IL-1α and β, which were originally described as leukocytic pyrogens (1), are important regulators of the response to tissue damage and infections and mediate symptoms of fever, fatigue, pain, arthritis, and the hepatic acute phase responses including synthesis of C-reactive protein (CRP) and serum amyloid A protein (SAA) (2). Although studies using recombinant IL-1 in cancer patients confirmed the causative role of IL-1 for many of these symptoms (3), its direct investigation in man is hampered by the inability to detect IL-1 in biological fluids. cryopyrin-associated periodic syndromes (CAPS) is a clinical disease syndrome resulting from heterozygous gain-of-function mutations in NLRP3, the gene encoding cryopyrin. These mutations are supposed to promote release of IL-1, thereby providing an excellent paradigm for studying human IL-1 in vivo (4, 5). CAPS patients present with a spectrum of autoinflammatory diseases (6–11) involving almost all organ systems. NLRP3 mutations result in overactivation of caspase 1, the enzyme which cleaves the precursors of IL-1β, IL-18, and IL-33, members of the IL-1 family of cytokines, into their active forms (12). Although pro–IL-1α is not a substrate of caspase 1, recent studies in mice indicate that secretion of bioactive IL-1α requires functional NLRP3 (13) and activated caspase-1 (14). The recombinant IL-1 receptor antagonist (IL-1Ra) anakinra and the IL-1 receptor type I (IL-1RI) fusion protein rilonacept (IL-1 trap) have both induced clinical response in CAPS, demonstrating that signaling via the IL-1RI is crucial for the pathogenesis of CAPS (15–17). This strongly implies that neither IL-18 nor IL-33 plays significant roles in the disease, as neither of these two cytokines signals via the IL-1RI, and suggests that the disease is caused by overproduction of IL-1. By administering the human anti–IL-1β antibody canakinumab to CAPS patients, we provide evidence in this paper that IL-1β is pivotal in the pathogenesis of CAPS. Treatment with the antibody allowed the detection of IL-β and the creation of a mathematical model, which indicates that the in vivo production rate of IL-1β is fivefold higher in CAPS as compared with healthy subjects. Furthermore, in vivo IL-β production could be completely restored in these patients after canakinumab treatment.     

Uropathogenic Escherichia coli strain CFT073 disrupts NLRP3 inflammasome activation

Successful bacterial pathogens produce an array of virulence factors that allow subversion of the immune system and persistence within the host. For example, uropathogenic Escherichia coli strains, such as CFT073, express Toll/IL-1 receptor–containing (TIR-containing) protein C (TcpC), which impairs TLR signaling, thereby suppressing innate immunity in the urinary tract and enhancing persistence in the kidneys. Here, we have reported that TcpC also reduces secretion of IL-1β by directly interacting with the NACHT leucin-rich repeat PYD protein 3 (NLRP3) inflammasome, which is crucial for recognition of pathogens within the cytosol. At a low MOI, IL-1β secretion was minimal in CFT073-infected macrophages; however, IL-1β release was markedly increased in macrophages infected with CFT073 lacking tcpC. Induction of IL-1β secretion by CFT073 and tcpC–deficient CFT073 required the NLRP3 inflammasome. TcpC attenuated activation of the NLRP3 inflammasome by binding both NLRP3 and caspase-1 and thereby preventing processing and activation of caspase-1. Moreover, in a murine urinary tract infection model, CFT073 infection rapidly induced expression of the NLRP3 inflammasome in the bladder mucosa; however, the presence of TcpC in WT CFT073 reduced IL-1β levels in the urine of infected mice. Together, these findings illustrate how uropathogenic E. coli use the multifunctional virulence factor TcpC to attenuate innate immune responses in the urinary tract.     

An NLRP3 inflammasome–triggered Th2-biased adaptive immune response promotes leishmaniasis

Leishmaniasis is a major tropical disease that can present with cutaneous, mucocutaneous, or visceral manifestation and affects millions of individuals, causing substantial morbidity and mortality in third-world countries. The development of a Th1-adaptive immune response is associated with resistance to developing Leishmania major (L. major) infection. Inflammasomes are key components of the innate immune system that contribute to host defense against bacterial and viral pathogens; however, their role in regulating adaptive immunity during infection with protozoan parasites is less studied. Here, we demonstrated that the NLRP3 inflammasome balances Th1/Th2 responses during leishmaniasis. Mice lacking the inflammasome components NLRP3, ASC, or caspase 1 on a Leishmania-susceptible BALB/c background exhibited defective IL-1β and IL-18 production at the infection site and were resistant to cutaneous L. major infection. Moreover, we determined that production of IL-18 propagates disease in susceptible BALB/c mice by promoting the Th2 cytokine IL-4, and neutralization of IL-18 in these animals reduced L. major titers and footpad swelling. In conclusion, our results indicate that activation of the NLRP3 inflammasome is detrimental during leishmaniasis and suggest that IL-18 neutralization has potential as a therapeutic strategy to treat leishmaniasis patients.     

UCP2-induced fatty acid synthase promotes NLRP3 inflammasome activation during sepsis

Cellular lipid metabolism has been linked to immune responses; however, the precise mechanisms by which de novo fatty acid synthesis can regulate inflammatory responses remain unclear. The NLRP3 inflammasome serves as a platform for caspase-1–dependent maturation and secretion of proinflammatory cytokines. Here, we demonstrated that the mitochondrial uncoupling protein-2 (UCP2) regulates NLRP3-mediated caspase-1 activation through the stimulation of lipid synthesis in macrophages. UCP2-deficient mice displayed improved survival in a mouse model of polymicrobial sepsis. Moreover, UCP2 expression was increased in human sepsis. Consistently, UCP2-deficient mice displayed impaired lipid synthesis and decreased production of IL-1β and IL-18 in response to LPS challenge. In macrophages, UCP2 deficiency suppressed NLRP3-mediated caspase-1 activation and NLRP3 expression associated with inhibition of lipid synthesis. In UCP2-deficient macrophages, inhibition of lipid synthesis resulted from the downregulation of fatty acid synthase (FASN), a key regulator of fatty acid synthesis. FASN inhibition by shRNA and treatment with the chemical inhibitors C75 and cerulenin suppressed NLRP3-mediated caspase-1 activation and inhibited NLRP3 and pro–IL-1β gene expression in macrophages. In conclusion, our results suggest that UCP2 regulates the NLRP3 inflammasome by inducing the lipid synthesis pathway in macrophages. These results identify UCP2 as a potential therapeutic target in inflammatory diseases such as sepsis.     

Mast cells mediate neutrophil recruitment and vascular leakage through the NLRP3 inflammasome in histamine-independent urticaria

Urticarial rash observed in cryopyrin-associated periodic syndrome (CAPS) caused by nucleotide-binding oligomerization domain–leucine-rich repeats containing pyrin domain 3 (NLRP3) mutations is effectively suppressed by anti–interleukin (IL)-1 treatment, suggesting a pathophysiological role of IL-1β in the skin. However, the cellular mechanisms regulating IL-1β production in the skin of CAPS patients remain unclear. We identified mast cells (MCs) as the main cell population responsible for IL-1β production in the skin of CAPS patients. Unlike normal MCs that required stimulation with proinflammatory stimuli for IL-1β production, resident MCs from CAPS patients constitutively produced IL-1β. Primary MCs expressed inflammasome components and secreted IL-1β via NLRP3 and apoptosis-associated speck-like protein containing a caspase recruitment domain when stimulated with microbial stimuli known to activate caspase-1. Furthermore, MCs expressing disease-associated but not wild-type NLRP3 secreted IL-1β and induced neutrophil migration and vascular leakage, the histological hallmarks of urticarial rash, when transplanted into mouse skin. Our findings implicate MCs as IL-1β producers in the skin and mediators of histamine-independent urticaria through the NLRP3 inflammasome.Urticaria, or hives, is a common disease that can affect up to 20% of the general population (1). Chronic urticaria, defined as urticaria that persists for >6 wk, occurs in 0.1% of the population (2), and in a significant percentage of cases (∼40–80%), there is no identifiable cause (1, 3). H1 antihistamines have remained the first line of treatment because histamine release from cutaneous mast cells (MCs) plays an important role in the pathophysiology of urticaria development. However, only ∼55% of patients with chronic urticaria are responsive to antihistamines (4), suggesting that in a significant number of individuals, chronic urticaria is mediated via histamine-independent mechanisms.An urticarial rash developing in the neonatal or early infantile period is one of the clinical manifestations characteristic of cryopyrin-associated periodic syndrome (CAPS). CAPS consists of a spectrum of hereditary periodic fever disorders that comprise three phenotypically overlapping but relatively distinct syndromes: familial cold autoinflammatory syndrome (Mendelian inheritance in men number [MIM] 120100), Muckle-Wells syndrome (MWS; MIM 191900), and chronic infantile neurological cutaneous and articular syndrome (MIM 607115), which is also known as neonatal-onset multisystem inflammatory disease. Familial cold autoinflammatory syndrome and MWS are characterized by periodic attacks of urticarial rash, fever, and arthralgia, whereas patients with chronic infantile neurological cutaneous and articular syndrome, the most severe form of CAPS, exhibit chronic urticaria as well as fever, arthropathy, chronic meningitis, papilledema, growth and mental retardation, and hearing loss (5). The urticarial rash observed in CAPS is similar to that associated with common urticaria. However, unlike the latter disorder, the rash observed in most CAPS patients responds to therapy with IL-1 receptor antagonist rather than antihistamines, suggesting that urticaria in these patients is mediated by IL-1. However, the cellular mechanism responsible for urticaria in CAPS patients remains poorly understood.The mature form of IL-1β is produced by cleavage of the inactive pro–IL-1β precursor by caspase-1, a protease activated by a large multiprotein complex termed the inflammasome (6). CAPS is caused by missense mutations in the gene, nucleotide-binding oligomerization domain (NOD)–leucine-rich repeats (LRRs) containing pyrin domain 3 (NLRP3) (7), whose product is a component of the inflammasome that includes the adaptor protein, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and procaspase-1 (8, 9). NLRP3, a member of the NOD-like receptor family, is an intracellular receptor involved in the recognition of pathogen-associated molecular patterns (PAMPs). Although several microbial activators of NLRP3 have been reported, the precise mechanism by which the NLRP3 inflammasome is activated by PAMPs remains poorly understood. In the presence of ATP or pore-forming molecules, several PAMPs, including LPS, muramyl dipeptide, bacterial mRNA, and the antiviral compound R837, activate the NLRP3 inflammasome (10, 11). In addition to PAMPs, NLRP3 senses endogenous danger signals such as monosodium urate crystals and particulate matter including asbestos, silica (12), and aluminum salts (13, 14). Disease-associated NLRP3 mutations associated with CAPS localize to the centrally located NOD domain and constitutively activate caspase-1 to produce active IL-1β (8, 15). NLRP3 is predominantly expressed in monocytes, granulocytes, and chondrocytes (16, 17), but to date, no reports have investigated the cells in the skin that are involved in the development of urticarial rash associated with CAPS. Our study identifies resident MCs in the skin as a cell population capable of producing IL-1β via the NLRP3 inflammasome and provides evidence that MCs mediate urticarial rash via dysregulated IL-1β production in the skin of CAPS patients.     

Inflammasome signaling in human placental trophoblasts regulates immune defense against Listeria monocytogenes infection

The human placenta is a dynamic organ that modulates physiological adaptations to pregnancy. To define the immunological signature of the human placenta, we performed unbiased profiling of secreted immune factors from human chorionic villi isolated from placentas at mid and late stages of pregnancy. We show that placental trophoblasts constitutively secrete the inflammasome-associated cytokines IL-1β and IL-18, which is blocked by NLRP3 inflammasome inhibitors and occurs without detectable gasdermin D cleavage. We further show that placenta-derived IL-1β primes monocytes for inflammasome induction to protect against Listeria monocytogenes infection. Last, we show that the human placenta responds to L. monocytogenes infection through additional inflammasome activation and that inhibition of this pathway sensitizes villi to infection. Our results thus identify the inflammasome as an important mechanism by which the human placenta regulates systemic and local immunity during pregnancy to defend against L. monocytogenes infection.     

IL-1β–driven osteoclastogenic Tregs accelerate bone erosion in arthritis

IL-1β is a proinflammatory mediator with roles in innate and adaptive immunity. Here we show that IL-1β contributes to autoimmune arthritis by inducing osteoclastogenic capacity in Tregs. Using mice with joint inflammation arising through deficiency of the IL-1 receptor antagonist (Il1rn^–/–), we observed that IL-1β blockade attenuated disease more effectively in early arthritis than in established arthritis, especially with respect to bone erosion. Protection was accompanied by a reduction in synovial CD4⁺Foxp3⁺ Tregs that displayed preserved suppressive capacity and aerobic metabolism but aberrant expression of RANKL and a striking capacity to drive RANKL-dependent osteoclast differentiation. Both Il1rn^–/– Tregs and wild-type Tregs differentiated with IL-1β accelerated bone erosion upon adoptive transfer. Human Tregs exhibited analogous differentiation, and corresponding RANKL^hiFoxp3⁺ T cells could be identified in rheumatoid arthritis synovial tissue. Together, these findings identify IL-1β–induced osteoclastogenic Tregs as a contributor to bone erosion in arthritis.     

肌萎缩侧索硬化蛋白激活小胶质细胞NLRP3炎性体

小胶质细胞NLRP3炎症小体激活正在成为神经退行性变期间神经炎症的关键因素。β-淀粉样蛋白和α-突触核蛋白等致病蛋白的聚集体可触发小胶质细胞NLRP3激活,并导致半胱氨酸天冬氨酸酶激活和白介素-1β分泌。半胱氨酸天冬氨酸酶和白介素-1β均促进肌萎缩侧索硬化(ALS)小鼠SOD1G93A模型的疾病进展,这提示小胶质细胞NLRP3在该进程中起作用。然而,先前的研究表明SOD1G93A模型小鼠的小胶质细胞并不表达NLRP3,并且SOD1G93A蛋白在小胶质细胞中产生白介素-1β不依赖于NLRP3。本研究展示了使用Nlrp3-GFP基因敲入小鼠,在SOD1G93A小鼠中小胶质细胞表达NLRP3。结果表明,聚集和可溶性SOD1G93A均以剂量和时间依赖性方式激活小鼠原代小胶质细胞中的炎性体,导致半胱氨酸天冬氨酸酶和白介素-1β裂解、ASC斑点形成和白介素-1β分泌。重要的是,SOD1G93A不能诱导缺乏Nlrp3的小胶质细胞或用特异性NLRP3抑制剂MCC950预处理的小胶质细胞分泌白介素-1β,这证实NLRP3是介导SOD1诱导的小胶质细胞白介素-1β分泌的关键炎性体复合物。在TDP-43Q331K ALS小鼠模型中也观察到小胶质细胞NLRP3上调,并且TDP-43野生型和突变蛋白也能以NLRP3依赖性方式激活小胶质细胞炎症小体。从机制上,本研究确定活性氧簇和ATP的产生是SOD1G93A介导的NLRP3激活所需的关键事件。总之,本研究的数据表明ALS小胶质细胞表达NLRP3,病理性ALS蛋白激活了小胶质细胞NLRP3炎性体。因此,抑制NLRP3可能是阻止小胶质细胞神经炎症和ALS疾病进展的潜在治疗方法。     

NLRP3 tyrosine phosphorylation is controlled by protein tyrosine phosphatase PTPN22

Inflammasomes form as the result of the intracellular presence of danger-associated molecular patterns and mediate the release of active IL-1β, which influences a variety of inflammatory responses. Excessive inflammasome activation results in severe inflammatory conditions, but physiological IL-1β secretion is necessary for intestinal homeostasis. Here, we have described a mechanism of NLRP3 inflammasome regulation by tyrosine phosphorylation of NLRP3 at Tyr861. We demonstrated that protein tyrosine phosphatase non-receptor 22 (PTPN22), variants in which are associated with chronic inflammatory disorders, dephosphorylates NLRP3 upon inflammasome induction, allowing efficient NLRP3 activation and subsequent IL-1β release. In murine models, PTPN22 deficiency resulted in pronounced colitis, increased NLRP3 phosphorylation, but reduced levels of mature IL-1β. Conversely, patients with inflammatory bowel disease (IBD) that carried an autoimmunity-associated PTPN22 variant had increased IL-1β levels. Together, our results identify tyrosine phosphorylation as an important regulatory mechanism for NLRP3 that prevents aberrant inflammasome activation.     

Alpinumisoflavone attenuates lipopolysaccharide-induced acute lung injury by regulating the effects of anti-oxidation and anti-inflammation both in vitro and in vivo

Alpinumisoflavone (AIF) is a plant-derived pyranoisoflavone that exhibits a number of pharmacological activities, but the protective effects of AIF against pulmonary inflammation are still unknown. This study aimed to investigate the anti-inflammatory effects and possible molecular mechanisms of AIF in both lipopolysaccharide (LPS)-stimulated macrophages and mice. The results revealed that AIF dramatically suppressed the production of pro-inflammatory mediators [including tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, IL-17, intercellular adhesion molecule-1 (ICAM-1), and nitric oxide (NO)] and increased the levels of anti-oxidative enzymes [including catalase (CAT), heme oxygenase-1 (HO-1), glutathione peroxidase (GPx), and superoxide dismutase (SOD)] both in vitro and in vivo. Additionally, pre-treatment with AIF could not only significantly prevent histopathological changes and neutrophil infiltration but also decreased the expression levels of nuclear factor-kappa B (NF-κB), mitogen-activated protein kinases (MAPKs), and the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome, as well as IL-17 production in LPS-induced lung tissues. The anti-inflammatory effects of AIF were mediated by up-regulating anti-oxidative enzymes and suppressing the NF-κB, MAPK, NLRP3 inflammasome and IL-17 signaling pathways. This is the first study to reveal that AIF has a protective effect against LPS-induced lung injury in mice.

The present study demonstrated that alpinumisoflavone exerts the significant effects of anti-inflammatory and anti-oxidative in both LPS-induced RAW264.7 macrophages and a mouse model of acute lung injury.     

IL-21R is essential for epicutaneous sensitization and allergic skin inflammation in humans and mice

Atopic dermatitis (AD) is a common allergic inflammatory skin disease caused by a combination of intense pruritus, scratching, and epicutaneous (e.c.) sensitization with allergens. To explore the roles of IL-21 and IL-21 receptor (IL-21R) in AD, we examined skin lesions from patients with AD and used a mouse model of allergic skin inflammation. IL-21 and IL-21R expression was upregulated in acute skin lesions of AD patients and in mouse skin subjected to tape stripping, a surrogate for scratching. The importance of this finding was highlighted by the fact that both Il21r^–/– mice and WT mice treated with soluble IL-21R–IgG2aFc fusion protein failed to develop skin inflammation after e.c. sensitization of tape-stripped skin. Adoptively transferred OVA-specific WT CD4⁺ T cells accumulated poorly in draining LNs (DLNs) of e.c. sensitized Il21r^–/– mice. This was likely caused by both DC-intrinsic and nonintrinsic effects, because trafficking of skin DCs to DLNs was defective in Il21r^–/– mice and, to a lesser extent, in WT mice reconstituted with Il21r^–/– BM. More insight into this defect was provided by the observation that skin DCs from tape-stripped WT mice, but not Il21r^–/– mice, upregulated CCR7 and migrated toward CCR7 ligands. Treatment of epidermal and dermal cells with IL-21 activated MMP2, which has been implicated in trafficking of skin DCs. These results suggest an important role for IL-21R in the mobilization of skin DCs to DLNs and the subsequent allergic response to e.c. introduced antigen.     

The key role of NLRP3 and STING in APOL1-associated podocytopathy

Coding variants in apolipoprotein L1 (APOL1), termed G1 and G2, can explain most excess kidney disease risk in African Americans; however, the molecular pathways of APOL1-induced kidney dysfunction remain poorly understood. Here, we report that expression of G2 APOL1 in the podocytes of Nphs1rtTA/TRE-G2APOL1 (G2APOL1) mice leads to early activation of the cytosolic nucleotide sensor, stimulator of interferon genes (STING), and the NLR family pyrin domain–containing 3 (NLRP3) inflammasome. STING and NLRP3 expression was increased in podocytes from patients with high-risk APOL1 genotypes, and expression of APOL1 correlated with caspase-1 and gasdermin D (GSDMD) levels. To demonstrate the role of NLRP3 and STING in APOL1-associated kidney disease, we generated transgenic mice with the G2 APOL1 risk variant and genetic deletion of Nlrp3 (G2APOL1/Nlrp3 KO), Gsdmd (G2APOL1/Gsdmd KO), and STING (G2APOL1/STING KO). Knockout mice displayed marked reduction in albuminuria, azotemia, and kidney fibrosis compared with G2APOL1 mice. To evaluate the therapeutic potential of targeting NLRP3, GSDMD, and STING, we treated mice with MCC950, disulfiram, and C176, potent and selective inhibitors of NLRP3, GSDMD, and STING, respectively. G2APOL1 mice treated with MCC950, disulfiram, and C176 showed lower albuminuria and improved kidney function even when inhibitor treatment was initiated after the development of albuminuria.     

An inherited mutation in NLRC4 causes autoinflammation in human and mice

Autoinflammatory syndromes cause sterile inflammation in the absence of any signs of autoimmune responses. Familial cold autoinflammatory syndrome (FCAS) is characterized by intermittent episodes of rash, arthralgia, and fever after exposure to cold stimuli. We have identified a missense mutation in the NLRC4 gene in patients with FCAS. NLRC4 has been known as a crucial sensor for several Gram-negative intracellular bacteria. The mutation in NLRC4 in FCAS patients promoted the formation of NLRC4-containing inflammasomes that cleave procaspase-1 and increase production of IL-1β. Transgenic mice that expressed mutant Nlrc4 under the invariant chain promoter developed dermatitis and arthritis. Inflammation within tissues depended on IL-1β–mediated production of IL-17A from neutrophils but not from T cells. Our findings reveal a previously unrecognized link between NLRC4 and a hereditary autoinflammatory disease and highlight the importance of NLRC4 not only in the innate immune response to bacterial infections but also in the genesis of inflammatory diseases.Autoinflammatory syndrome is characterized by inflammatory responses in the absence of autoimmunity or infections, and it is generally caused by hyperactivation of innate immune cells (Chen and Nuñez, 2010; Park et al., 2012). Several studies, including those from our group, have identified the causative genes for familial autoinflammatory syndromes (McDermott et al., 1999; Jéru et al., 2008; Masters et al., 2009; Agarwal et al., 2010; Kitamura et al., 2011; Liu et al., 2012; Park et al., 2012). Among these genes, mutations in NLRP3 cause autoinflammatory syndromes, including familial cold autoinflammatory syndrome (FCAS), Muckle-Wells syndrome (MWS), and neonatal onset multisystem inflammatory disease (NOMID; Hoffman et al., 2001; Jéru et al., 2008; Masters et al., 2009; Aksentijevich and Kastner, 2011; Park et al., 2012). These diseases are named cryopyrin-associated periodic syndromes (CAPS). FCAS, the mildest of the CAPS, is characterized by rash, fever, and arthralgia by exposure to cold stimuli. Patients with MWS have more frequent inflammatory episodes and they frequently develop progressive sensorineural hearing loss and systemic amyloidosis. NOMID is the most severe of the three syndromes and is characterized by severe chronic inflammation involving the joints and nervous system. However, there are still significant numbers of CAPS without any mutations in NLRP3 (Aksentijevich et al., 2007).Heterozygous mutations in NLRP3 result in overactivation of caspase 1. This enzyme cleaves the precursors of IL-1β and IL-18 (members of the IL-1 family of cytokines) into their active forms (Masters et al., 2009; Aksentijevich and Kastner, 2011). The recombinant IL-1 receptor antagonist anakinra, canakinumab, and the IL-1 receptor type I fusion protein rilonacept have induced clinical response in CAPS, demonstrating that signaling via the IL-1 receptor is crucial for the pathogenesis of CAPS (Aksentijevich and Kastner, 2011; Dinarello and van der Meer, 2013). Recent studies have provided evidence that heterozygous mutations in NLRP12 cause FCAS-like symptoms (Jéru et al., 2008). The mutations are reported to inhibit NF-κB or activate caspase 1, depending on the genetic variation (Jéru et al., 2008; Jéru et al., 2011).In the current study, we used exome resequencing to analyze candidate genes of patients in one Japanese family with cold-induced urticaria and arthritis but without mutations in NLRP3 or NLRP12. We identified a heterozygous missense mutation in NLRC4. The mutant NLRC4 activates caspase-1 and this activation results in increased production of IL-1β. Expression of the mutant Nlrc4 in mice causes severe dermatitis, arthritis, and splenomegaly with augmented infiltration of neutrophils as well as cold-induced exanthema. The inflammation depended on IL-1β and IL-17A produced by neutrophils but not T cells. These data indicate that NLRC4 is a causative gene for this disease and highlight the crucial roles of NLRC4 not only in the innate immune response to bacterial infections but also in the pathogenesis of human inflammatory diseases.     

IL-17 produced by neutrophils regulates IFN-γ–mediated neutrophil migration in mouse kidney ischemia-reperfusion injury

The IL-23/IL-17 and IL-12/IFN-γ cytokine pathways have a role in chronic autoimmunity, which is considered mainly a dysfunction of adaptive immunity. The extent to which they contribute to innate immunity is, however, unknown. We used a mouse model of acute kidney ischemia-reperfusion injury (IRI) to test the hypothesis that early production of IL-23 and IL-12 following IRI activates downstream IL-17 and IFN-γ signaling pathways and promotes kidney inflammation. Deficiency in IL-23, IL-17A, or IL-17 receptor (IL-17R) and mAb neutralization of CXCR2, the p19 subunit of IL-23, or IL-17A attenuated neutrophil infiltration in acute kidney IRI in mice. We further demonstrate that IL-17A produced by GR-1⁺ neutrophils was critical for kidney IRI in mice. Activation of the IL-12/IFN-γ pathway and NKT cells by administering α-galactosylceramide–primed bone marrow–derived DCs increased IFN-γ production following moderate IRI in WT mice but did not exacerbate injury or enhance IFN-γ production in either Il17a^–/– or Il17r^–/– mice, which suggested that IL-17 signaling was proximal to IFN-γ signaling. This was confirmed by the finding that IFN-γ administration reversed the protection seen in Il17a^–/– mice subjected to IRI, whereas IL-17A failed to reverse protection in Ifng^–/– mice. These results demonstrate that the innate immune component of kidney IRI requires dual activation of the IL-12/IFN-γ and IL-23/IL-17 signaling pathways and that neutrophil production of IL-17A is upstream of IL-12/IFN-γ. These mechanisms might contribute to reperfusion injury in other organs.