Search

Rhabdomyolysis is a severe condition that commonly leads to acute kidney injury (AKI). While double-stranded DNA (dsDNA) released from injured muscle can be involved in its pathogenesis, the exact mechanism of how dsDNA contributes to rhabdomyolysis-induced AKI (RIAKI) remains obscure. A dsDNA sensor, absent in melanoma 2 (AIM2), forms an inflammasome and induces gasdermin D (GSDMD) cleavage resulting in inflammatory cell death known as pyroptosis. In this study using a mouse model of RIAKI, we found that Aim2-deficiency led to massive macrophage accumulation resulting in delayed functional recovery and perpetuating fibrosis in the kidney. While Aim2-deficiency compromised RIAKI-induced kidney macrophage pyroptosis, it unexpectedly accelerated aberrant inflammation as demonstrated by CXCR3

Calciprotein particles (CPPs) are nanoparticles composed of calcium phosphate crystals and fetuin-A and have been implicated in diseases associated with inflammation. In the current study, we investigated the molecular mechanisms underlying CPP-induced inflammation in mice. CPPs predominantly upregulated IL-1β and IL-1α and provided priming and activation signals for the NLRP3 inflammasome in murine macrophages. Pharmacological and genetic inhibition of the NLRP3 inflammasome revealed that CPPs induced the release of IL-1β and IL-1α via NLRP3 inflammasome-dependent and -independent mechanisms, respectively. CPPs also induced necrotic cell death, but gasdermin D was dispensable for CPP-induced IL-1β release and necrotic cell death. Although phagocytosis of CPPs was required for CPP-induced IL-1β/α release and necrotic cell death, lysosomal dysfunction and K+ efflux were mainly involved in CPP-induced NLRP3 inflammasome activation and subsequent IL-1β release but not in CPP-induced IL-1α release and necrotic cell death. In vivo experiments showed that CPP administration evoked acute inflammatory responses characterized by neutrophil accumulation via both IL-1β and IL-1α. In particular, CPP-induced neutrophil inflammation was mediated predominantly through an IL-1α–induced CXCL1/CXCR2 signaling pathway. These results provide new insights into the mechanism underlying CPP-induced inflammation and suggest that targeting both IL-1β and IL-1α is necessary to regulate the CPP-induced inflammatory response and to treat CPP-associated inflammatory disorders.

Recent evidence indicates that ferroptosis is implicated in the pathophysiology of various liver diseases; however, the mechanism of ferroptosis regulation in the liver is poorly understood. Here, using the whole-genome screening approach, we identified 7-dehydrocholesterol reductase (DHCR7), the terminal enzyme of cholesterol biosynthesis, as a novel regulator of ferroptosis in hepatocytes. Genetic and pharmacological inhibition (with AY9944) of DHCR7 suppressed lipid peroxidation and ferroptosis in human hepatocellular carcinoma Huh-7 cells. DHCR7 inhibition increased its substrate, 7-dehydrocholesterol (7-DHC), and extrinsic 7-DHC supplementation in turn suppressed ferroptosis. On the other hand, cholesterol deprivation had no effect on ferroptosis. A 7-DHC-derived oxysterol metabolite, 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), was increased by a ferroptosis inducer RSL-3 in DHCR7-deficient cells, suggesting that the ferroptosis-suppressive effect of DHCR7 inhibition was driven by intracellular 7-DHC as a radical scavenger. While extrinsic 7-DHC supplementation suppressed ferroptosis in various cancer cells, pharmacological DHCR7 inhibition by AY9944 showed cell-type specific effects, which could be explained by high DHCR7 expression in Huh-7 cells. We further showed that AY9944 suppressed ferroptosis in murine primary hepatocytes in vitro and systemic administration of AY9944 inhibited hepatic ischemia-reperfusion injury in vivo. These findings provide new insights into the regulatory mechanism of liver ferroptosis and suggest that DHCR7 inhibition is a potential therapeutic option for ferroptosis-related liver diseases.

Background Platelets are critical mediators of vascular homeostasis and thrombosis, and also contribute to the development of inflammation. NLRP3 inflammasome is a cytosolic multi-protein complex that consists of NLRP3, ASC and caspase-1, and regulates IL-1β-mediated inflammation. Method and Results Using two mouse models of thrombosis (i.e., occlusion of the middle cerebral artery and inferior vena cava), we found that thrombus formation was significantly enhanced in ASC-deficient (ASC−/−) mice, compared to that in wild-type (WT) and IL-1β−/− mice. ASC deficiency had no effects on blood coagulation parameters (i.e., prothrombin time [PT] and activated partial thromboplastin time [APTT]). Platelets from WT mice express ASC, but neither NLRP3 nor caspase-1. ASC deficiency significantly enhanced the expression of P-selectin and GPIIb/IIIa in response to a GPVI agonist (collagen-related peptide [CRP]), but not to thrombin, in platelets. CRP induced ASC speck formation in WT platelets. ASC deficiency also enhanced cytosolic Ca2+ elevation and phosphorylation of ERK1/2 and Akt in platelets. Conclusion Our results demonstrate that ASC negatively regulates GPVI signaling in platelets and enhances thrombus formation, independent of NLRP3 inflammasome and IL-1β, and provide novel insights into the link between inflammation and thrombosis.

Although the intimate linkage between hypoxia and inflammation is well known, the mechanism underlying this linkage has not been fully understood. Nucleotide-binding oligomerization domain-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome is an intracellular multiprotein complex that regulates interleukin-1β (IL-1β) secretion and pyroptosis, and is implicated in the pathogenesis of sterile inflammatory diseases. Here, we investigated the regulatory mechanism of NLRP3 inflammasome activation in response to hypoxia in macrophages. Severe hypoxia (0.1% O2 ) induced the processing of pro-IL-1β, pro-caspase-1, and gasdermin D, as well as the release of IL-1β and lactate dehydrogenase in lipopolysaccharide (LPS)-primed murine macrophages, indicating that hypoxia induces NLRP3 inflammasome-driven inflammation and pyroptosis. NLRP3 deficiency and a specific caspase-1 blockade inhibited hypoxia-induced IL-1β release. Hypoxia-induced IL-1β release and cell death were augmented under glucose deprivation, and an addition of glucose in the media negatively regulated hypoxia-induced IL-1β release. Under hypoxia and glucose deprivation, hypoxia-induced glycolysis was not driven and subsequently, the intracellular adenosine triphosphates (ATPs) were depleted. Atomic absorption spectrometry analysis showed a reduction of intracellular K+ concentrations, indicating the K+ efflux occurring under hypoxia and glucose deprivation. Furthermore, hypoxia and glucose deprivation-induced IL-1β release was significantly prevented by inhibition of K+ efflux and KATP channel blockers. In vivo experiments further revealed that IL-1β production was increased in LPS-primed mice exposed to hypoxia (9.5% O2 ), which was prevented by a deficiency of NLRP3, an apoptosis-associated speck-like protein containing a caspase recruitment domain, and caspase-1. Our results demonstrate that NLRP3 inflammasome can sense intracellular energy crisis as a danger signal induced by hypoxia and glucose deprivation, and provide new insights into the mechanism underlying hypoxia-induced inflammation.

Acetaminophen (APAP) overdose is a common cause of drug-induced acute liver failure. Although hepatocyte cell death is considered to be the critical event in APAP-induced hepatotoxicity, the underlying mechanism remains unclear. Ferroptosis is a newly discovered type of cell death that is caused by a loss of cellular redox homeostasis. As glutathione (GSH) depletion triggers APAP-induced hepatotoxicity, we investigated the role of ferroptosis in a murine model of APAP-induced acute liver failure. APAP-induced hepatotoxicity (evaluated in terms of ALT, AST, and the histopathological score), lipid peroxidation (4-HNE and MDA), and upregulation of the ferroptosis maker PTGS2 mRNA were markedly prevented by the ferroptosis-specific inhibitor ferrostatin-1 (Fer-1). Fer-1 treatment also completely prevented mortality induced by high-dose APAP. Similarly, APAP-induced hepatotoxicity and lipid peroxidation were prevented by the iron chelator deferoxamine. Using mass spectrometry, we found that lipid peroxides derived from n-6 fatty acids, mainly arachidonic acid, were elevated by APAP, and that auto-oxidation is the predominant mechanism of APAP-derived lipid oxidation. APAP-induced hepatotoxicity was also prevented by genetic inhibition of acyl-CoA synthetase long-chain family member 4 or α-tocopherol supplementation. We found that ferroptosis is responsible for APAP-induced hepatocyte cell death. Our findings provide new insights into the mechanism of APAP-induced hepatotoxicity and suggest that ferroptosis is a potential therapeutic target for APAP-induced acute liver failure.

Maternal obesity is one of the major risk factors for pregnancy complications and is associated with low-grade chronic systemic inflammation due to higher levels of pro-inflammatory cytokines such as interleukin (IL)-1β. Pregnant women with obesity have abnormal lipid profiles, characterized by higher levels of free fatty acids, especially palmitic acid (PA). Previously, we reported that PA stimulated IL-1β secretion via activation of NLRP3 inflammasome in human placental cells. These observations led us to hypothesize that higher levels of PA induce NLRP3 inflammasome activation and placental inflammation, resulting in pregnancy complications. However, the effects of PA on NLRP3 inflammasome during pregnancy in vivo remain unclear. Therefore, PA solutions were administered intravenously into pregnant mice on day 12 of gestation. Maternal body weight was significantly decreased and absorption rates were significantly higher in PA-injected mice. The administration of PA significantly increased IL-1β protein and the mRNA expression of NLRP3 inflammasome components (NLRP3, ASC, and caspase-1) within the placenta. In murine placental cell culture, PA significantly stimulated IL-1β secretion, and this secretion was suppressed by a specific NLRP3 inhibitor (MCC950). Simultaneously, the number of macrophages/monocytes and neutrophils, together with the mRNA expression of these chemokines increased significantly in the placentas of PA-treated mice. Treatment with PA induced ASC assembling and IL-1β secretion in macrophages, and this PA-induced IL-1β secretion was significantly suppressed in NLRP3-knockdown macrophages. These results indicate that transient higher levels of PA exposure in pregnant mice activates NLRP3 inflammasome and induces placental inflammation, resulting in the incidence of absorption.

Cryopyrin-associated periodic syndrome (CAPS) is an autoinflammatory syndrome caused by mutations of NLRP3, which was originally identified as cryopyrin. Familial cold autoinflammatory syndrome (FCAS), the mildest form of CAPS, is characterized by cold-induced inflammation induced by the overproduction of IL-1β. However, the molecular mechanism of how mutated NLRP3 causes inflammasome activation in CAPS remains unclear. Here, we found that CAPS-associated NLRP3 mutants form cryo-sensitive aggregates that function as a scaffold for inflammasome activation. Cold exposure promoted inflammasome assembly and subsequent IL-1β release triggered by mutated NLRP3. While K+ efflux was dispensable, Ca2+ was indispensable for mutated NLRP3-mediated inflammasome assembly. Notably, Ca2+ influx was induced during mutated NLRP3-mediated inflammasome assembly. Furthermore, caspase-1 inhibition prevented Ca2+ influx and inflammasome assembly induced by the mutated NLRP3, suggesting a feed-forward Ca2+ influx loop triggered by mutated NLRP3. Thus, the mutated NLRP3 forms cryo-sensitive aggregates to promote inflammasome assembly distinct from canonical NLRP3 inflammasome activation.

Objectives Maternal systemic and placental inflammatory responses participate in the pathogenesis of hypertensive disorders of pregnancy including preeclampsia, a pregnancy-specific syndrome, although the role of inflammation remains unclear. The NLRP3 inflammasome has been implicated in the control of sterile inflammation involved in preeclampsia. In the present study, we hypothesized that S100A9, as major alarmin, are associated with the pathogenesis of preeclampsia and induction of a preeclampsia-like phenotype in pregnant mice. Methods Plasma were taken from normal pregnant women and preeclampsia patients. Human placental tissues, trophoblast cell line Sw.71 cells, and human umbilical vein endothelial cells (HUVEC) were treated with S100A9 with or without inhibitors associated with NLRP3 inflammasome. Pregnant mice were administered S100A9. Results S100A9 was elevated in plasma and released from placentas of preeclampsia patients. S100A9 activated the NLRP3 inflammasome, resulting in IL-1β secretion, by human placental tissues and trophoblasts. In addition, secretion of soluble endoglin, a main contributor to the pathogenesis of preeclampsia, is regulated via S100A9-stimulated NLRP3 inflammasome activation in the human placenta and HUVECs. S100A9 administration significantly elevated maternal blood pressure and neutrophil accumulation within the placentas of pregnant mice, and both were significantly decreased in Nlrp3-knock out pregnant mice. Conclusion The results of this study demonstrated that S100A9 acts as a danger signal to activate the NLRP3 inflammasome in the placenta, associating with hypertension during pregnancy.

The immune system contributes to the regulation of pregnancy, and the disruption of well-controlled immune functions leads to pregnancy complications. Recently, the nucleotide-binding oligomerization domain, leucine-rich repeat-, and pyrin domain-containing 3 (NLRP3) inflammasome mechanisms [(a protein complex of NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and caspase-1)] have been reported to play roles in controlling placental inflammation involved in pregnancy pathologies. The ketone body β-hydroxybutyrate (BHB) can suppress NLRP3 inflammasome activation and improve various inflammatory diseases. Therefore, we hypothesized that BHB could suppress activation of the NLRP3 inflammasome in the placenta, resulting in the improvement of pregnancy complications. In human placental tissue culture, treatment with BHB suppressed the secretion levels of inflammatory cytokines, such as interleukin (IL)-1β, IL-6, and IL-8, but did not affect the mRNA expression levels of NLRP3 inflammasome-associated factors. Treatment with BHB reduced IL-1β secretion and the amount of mature IL-1β protein induced by lipopolysaccharide (LPS) stimulation in the placenta. In human trophoblast cells, BHB reduced ASC and activated-caspase-1 expression, resulting in the inhibition of IL-1β secretion. To investigate the effect of BHB during pregnancy, we used an animal model of LPS (100 μg/kg intraperitoneally [i.p.] on gestational day 14)-induced pregnancy complications. Administration of BHB (100 mg/kg i.p.) clearly suppressed the absorption rate and IL-1β production in the placenta induced by LPS in pregnant mice. Moreover, LPS-induced pregnancy abnormalities were improved in NLRP3-deficient mice. These findings suggest that BHB play a role in reducing placental inflammation and pregnancy complications via inhibition of NLRP3 inflammasome activation.

Inflammation plays a pivotal role in the pathophysiology of gastric aspiration–induced acute lung injury (ALI). However, its mechanism remains unclear. In this study, we investigated the role of NLRP3 inflammasome–driven IL-1β production in a mouse model of acid aspiration–induced inflammation and ALI. Acid aspiration–induced inflammatory responses and ALI in wild-type mice were significantly attenuated in IL-1β−/− mice, but not NLRP3−/− mice. In vitro experiments revealed that severe acidic stress (pH 1.75) induced the processing of pro–IL-1β into its 18-kDa mature form (p18–IL-1β), which was different from the caspase-1–processed 17-kDa form (p17–IL-1β), in human THP-1 macrophages and primary murine macrophages. Deficiency of NLRP3 and caspase-1 had no effect on acidic stress–produced IL-1β. The production of IL-1β by severe acidic stress was prevented by inhibitors of serine proteases [4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride], but not of cysteine proteases (E-64), cathepsin G, or inflammasome. The cathepsin D inhibitor pepstatin A inhibited IL-1β production induced by mild acidic stress (pH 6.2) or lactic acid, but not severe acidic stress. Using mass spectrometry and processing-site mutants of pro–IL-1β, we identified D109 as a novel cleavage site of pro–IL-1β in response to severe acidic stress and calculated the theoretical molecular mass of the mature form to be 18.2 kDa. The bioactivity of acidic stress–produced IL-1β was confirmed by its ability to promote p38 phosphorylation and chemokine upregulation in alveolar epithelial cells. These findings demonstrate a novel mechanism of acid-induced IL-1β production and inflammation independent of NLRP3 inflammasome and provide new insights into the therapeutic strategies for aspiration pneumonitis and ALI.

Cigarette smoking is a major risk factor for aortic aneurysm and dissection; however, no causative link between smoking and these aortic disorders has been proven. In the present study, we investigated the mechanism by which cigarette smoke affects vascular wall cells and found that cigarette smoke extract (CSE) induced a novel form of regulated cell death termed ferroptosis in vascular smooth muscle cells (VSMCs). CSE markedly induced cell death in A7r5 cells and primary rat VSMCs, but not in endothelial cells, which was completely inhibited by specific ferroptosis inhibitors [ferrostatin-1 (Fer-1) and Liproxstatin-1] and an iron chelator (deferoxamine). CSE-induced VSMC death was partially inhibited by a GSH precursor ( N-acetyl cysteine) and an NADPH oxidase inhibitor [diphenyleneiodonium chloride (DPI)], but not by inhibitors of pan-caspases (Z-VAD), caspase-1 (Z-YVAD), or necroptosis (necrostatin-1). CSE also upregulated IL-1β, IL-6, TNF-α, matrix metalloproteinase (MMP)-2, MMP-9, and TIMP-1 (tissue inhibitor of metalloproteinase)in A7r5 cells, which was inhibited by Fer-1. Furthermore, CSE induced the upregulation of Ptgs2 mRNA, lipid peroxidation, and intracellular GSH depletion, which are key features of ferroptosis. VSMC ferroptosis was induced by acrolein and methyl vinyl ketone, major constituents of CSE. Furthermore, CSE caused medial VSMC loss in ex vivo aortas. Electron microscopy analysis showed mitochondrial damage and fragmentation in medial VSMCs of CSE-treated aortas. All of these manifestations were partially restored by Fer-1. These findings demonstrate that ferroptosis is responsible for CSE-induced VSMC death and suggest that ferroptosis is a potential therapeutic target for preventing aortic aneurysm and dissection. NEW & NOTEWORTHY Cigarette smoke extract (CSE)-induced cell death in rat vascular smooth muscle cells (VSMCs) was completely inhibited by specific ferroptosis inhibitors and an iron chelator. CSE also induced the upregulation of Ptgs2 mRNA, lipid peroxidation, and intracellular GSH depletion, which are key features of ferroptosis. CSE caused medial VSMC loss in ex vivo aortas. These findings demonstrate that ferroptosis is responsible for CSE-induced VSMC death.

Objective— ACAT1 (Acyl-CoA cholesterol acyltransferase 1) esterifies cellular free cholesterol, thereby converting macrophages to cholesteryl ester-laden foam cells in atherosclerotic lesions and cutaneous xanthoma. Paradoxically, however, loss of ACAT1 in bone marrow causes the aggravation of atherosclerosis and the development of severe cutaneous xanthoma in hyperlipidemic mice. Recently, it has been reported that cholesterol crystals activate NLRP3 (NACHT, LRR [leucine-rich repeats], and PYD [pyrin domain] domain-containing protein 3) inflammasomes, thereby contributing to the development of atherosclerosis. The present study aimed to clarify the role of NLRP3 inflammasomes in the worsening of atherosclerosis and cutaneous xanthoma induced by ACAT1 deficiency. Approach and Results— Ldlr -null mice were transplanted with bone marrow from WT (wild type) mice and mice lacking ACAT1, NLRP3, or both. After the 4 types of mice were fed high-cholesterol diets, we compared their atherosclerosis and skin lesions. The mice transplanted with Acat1 -null bone marrow developed severe cutaneous xanthoma, which was filled with numerous macrophages and cholesterol clefts and had markedly increased expression of inflammatory cytokines, and increased atherosclerosis. Loss of NLRP3 completely reversed the cutaneous xanthoma, whereas it improved the atherosclerosis only partially. Acat1 -null peritoneal macrophages showed enhanced expression of CHOP (C/EBP [CCAAT/enhancer binding protein] homologous protein) and TNF-α (tumor necrosis factor-α) but no evidence of inflammasome activation, after treatment with acetylated LDL (low-density lipoprotein). Conclusions— Elimination of ACAT1 in bone marrow-derived cells aggravates cutaneous xanthoma and atherosclerosis. The development of cutaneous xanthoma is induced mainly via the NLRP3 inflammasome activation.

BACKGROUND AND AIM Serum Mac-2 binding protein glycosylation isomer (M2BPGi) is a novel fibrosis marker for various chronic liver diseases. We investigated the ability of M2BPGi to predict liver fibrosis in liver transplant (LT) recipients. METHODS A total of 116 liver biopsies were performed in 113 LT recipients. The serum level of M2BPGi was also measured on the same day. The median age at LT and liver biopsy was 1.1 and 11.8 years, respectively. Serum M2BPGi levels and liver fibrosis status using METAVIR fibrosis score were compared. Immunohistological evaluation by anti-α-smooth-muscle actin (αSMA) was performed, and the relationship between αSMA positive rate and serum M2BPGi levels was investigated. RESULTS The median M2BPGi level was 0.78 (range, 0.22-9.50), and 65, 29, 16, 5, and 1 patient(s) had METAVIR fibrosis scores of F0, F1, F2, F3, and F4, respectively. In patients with F0 fibrosis, median M2BPGi level was 0.69 and was significantly lower than in patients with F1 (median 0.99, P F1: 0.716, > F2: 0.720, and > F3: 0.900. Three patients with acute cellular rejection showed high levels of M2BPGi, which decreased after the treatment. A positive correlation existed between M2BPGi levels and αSMA positive rate (r2 = 0.715, P

Accumulating evidence suggests that IL-1β plays a pivotal role in the pathophysiology of hepatic ischemia–reperfusion (I/R) injury; however, the mechanism by which I/R triggers IL-1β production in the liver remains unclear. Recent data have shown that neutrophils contribute to hepatic I/R injury independently of the inflammasomes regulating IL-1β maturation. Thus, we investigated the role of neutrophils in IL-1β maturation and tissue injury in a murine model of hepatic I/R. IL-1β was released from the I/R liver and its deficiency reduced reactive oxygen species generation, apoptosis, and inflammatory responses, such as inflammatory cell infiltration and cytokine expression, thereby resulting in reduced tissue injury. Depletion of either macrophages or neutrophils also attenuated IL-1β release and hepatic I/R injury. In vitro experiments revealed that neutrophil-derived proteinases process pro–IL-1β derived from macrophages into its mature form independently of caspase-1. Furthermore, pharmacological inhibition of serine proteases attenuated IL-1β release and hepatic I/R injury in vivo. Taken together, the interaction between neutrophils and macrophages promotes IL-1β maturation and causes IL-1β–driven inflammation in the I/R liver. Both neutrophils and macrophages are indispensable in this process. These findings suggest that neutrophil-macrophage interaction is a therapeutic target for hepatic I/R injury and may also provide new insights into the inflammasome-independent mechanism of IL-1β maturation in the liver.

Summary Pyroptosis is a form of regulated cell death that is characterized by gasdermin processing and increased membrane permeability. Caspase-1 and caspase-11 have been considered to be essential for gasdermin D processing associated with inflammasome activation. In the present study, we found that NLRP3 inflammasome activation induces delayed necrotic cell death via ASC in caspase-1/11-deficient macrophages. Furthermore, ASC-mediated caspase-8 activation and subsequent gasdermin E processing are necessary for caspase-1-independent necrotic cell death. We define this necrotic cell death as incomplete pyroptosis because IL-1β release, a key feature of pyroptosis, is absent, whereas IL-1α release is induced. Notably, unprocessed pro-IL-1β forms a molecular complex to be retained inside pyroptotic cells. Moreover, incomplete pyroptosis accompanied by IL-1α release is observed under the pharmacological inhibition of caspase-1 with VX765. These findings suggest that caspase-1 inhibition during NLRP3 inflammasome activation modulates forms of cell death and permits the release of IL-1α from dying cells., Graphical Abstract, Highlights • NLRP3 inflammasome induces necrotic cell death in the absence of caspase-1/11 • ASC initiates GSDME-dependent pyroptosis via caspase-8 • IL-1α, but not IL-1β, is released during Casp1/11-independent pyroptosis • Pharmacological inhibition of caspase-1 permits IL-1α release during pyroptosis, Immunology; Cell Biology; Functional Aspects of Cell Biology

Kawasaki disease (KD) is a systemic febrile syndrome during childhood that is characterized by coronary arteritis. The etiopathogenesis of KD remains to be elucidated. NLRP3 inflammasome is a large multiprotein complex that plays a key role in IL-1β-driven sterile inflammatory diseases. In the present study, we investigated the role of NLRP3 inflammasome in a murine model of KD induced by Candida albicans water-soluble fraction (CAWS) and found that NLRP3 inflammasome is required for the development of CAWS-induced vasculitis. CAWS administration induced IL-1β production, caspase-1 activation, leukocyte infiltration, and fibrotic changes in the aortic root and coronary arteries, which were significantly inhibited by a deficiency of IL-1β, NLRP3, and ASC. In vitro experiments showed that among cardiac resident cells, macrophages, but not endothelial cells or fibroblasts, expressed Dectin-2, but did not produce IL-1β in response to CAWS. In contrast, CAWS induced caspase-1 activation and IL-1β production in bone marrow-derived dendritic cells (BMDCs), which were inhibited by a specific caspase-1 inhibitor and a deficiency of NLRP3, ASC, and caspase-1. CAWS induced NLRP3 and pro-IL-1β expression through a Dectin-2/Syk/JNK/NF-κB pathway, and caspase-1 activation and cleavage of pro-IL-1β through Dectin-2/Syk/JNK-mediated mitochondrial ROS generation, indicating that CAWS induces the priming and activation of NLRP3 inflammasome in BMDCs. These findings provide new insights into the pathogenesis of KD vasculitis, and suggest that NLRP3 inflammasome may be a potential therapeutic target for KD.

Hepatic ischemia-reperfusion (I/R) injury is a major problem in liver transplantation (LT). Although hepatocyte cell death is the initial event in hepatic I/R injury, the underlying mechanism remains unclear. In the present study, we retrospectively analyzed the clinical data of 202 pediatric living donor LT and found that a high serum ferritin level, a marker of iron overload, of the donor is an independent risk factor for liver damage after LT. Since ferroptosis has been recently discovered as an iron-dependent cell death that is triggered by a loss of cellular redox homeostasis, we investigated the role of ferroptosis in a murine model of hepatic I/R injury, and found that liver damage, lipid peroxidation, and upregulation of the ferroptosis marker Ptgs2 were induced by I/R, and all of these manifestations were markedly prevented by the ferroptosis-specific inhibitor ferrostatin-1 (Fer-1) or α-tocopherol. Fer-1 also inhibited hepatic I/R-induced inflammatory responses. Furthermore, hepatic I/R injury was attenuated by iron chelation by deferoxamine and exacerbated by iron overload with a high iron diet. These findings demonstrate that iron overload is a novel risk factor for hepatic I/R injury in LT, and ferroptosis contributes to the pathogenesis of hepatic I/R injury.

Long-term peritoneal dialysis (PD) therapy leads to peritoneal inflammation and fibrosis. However, the mechanism underlying PD-related peritoneal inflammation and fibrosis remains unclear. NLRP3 inflammasome regulates the caspase-1-dependent release of interleukin-1β and mediates inflammation in various diseases. Here, we investigated the role of NLRP3 inflammasome in a murine model of PD-related peritoneal fibrosis induced by methylglyoxal (MGO). Inflammasome-related proteins were upregulated in the peritoneum of MGO-treated mice. MGO induced parietal and visceral peritoneal fibrosis in wild-type mice, which was significantly reduced in mice deficient in NLRP3, ASC, and interleukin-1β (IL-1β). ASC deficiency reduced the expression of inflammatory cytokines and fibrotic factors, and the infiltration of macrophages. However, myeloid cell-specific ASC deficiency failed to inhibit MGO-induced peritoneal fibrosis. MGO caused hemorrhagic ascites, fibrin deposition, and plasminogen activator inhibitor-1 upregulation, but all of these manifestations were inhibited by ASC deficiency. Furthermore, in vitro experiments showed that MGO induced cell death via the generation of reactive oxygen species in vascular endothelial cells, which was inhibited by ASC deficiency. Our results showed that endothelial NLRP3 inflammasome contributes to PD-related peritoneal inflammation and fibrosis, and provide new insights into the mechanisms underlying the pathogenesis of this disorder.

Caspase-1 is a cysteine protease responsible for the processing of the proinflammatory cytokine interleukin-1β and activated by the formation of inflammasome complexes. Although several investigations have found a link between diet-induced obesity and caspase-1, the relationship remains controversial. Here, we found that mice deficient in caspase-1 were susceptible to high-fat diet-induced obesity with increased adiposity as well as normal lipid and glucose metabolism. Caspase-1 deficiency clearly promoted the infiltration of inflammatory macrophages and increased the production of C-C motif chemokine ligand 2 (CCL2) in the adipose tissue. The dominant cellular source of CCL2 was stromal vascular fraction rather than adipocytes in the adipose tissue. These findings demonstrate a critical role of caspase-1 in macrophage-driven inflammation in the adipose tissue and the development of obesity. These data provide novel insights into the mechanisms underlying inflammation in the pathophysiology of obesity.

Objective— Inhibition of HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase) is atheroprotective primarily by decreasing plasma LDL (low-density lipoprotein)-cholesterol. However, it is unknown whether inhibition of HMGCR in myeloid cells contributes to this atheroprotection. We sought to determine the role of myeloid HMGCR in the development of atherosclerosis. Approach and Results— We generated mice with genetically reduced Hmgcr in myeloid cells ( Hmgcr m− /m − ) using LysM (Cre) and compared various functions of their macrophages to those of Hmgcr fl/fl control mice. We further compared the extent of atherosclerosis in Hmgcr m −/ m − and Hmgcr fl/fl mice in the absence of Ldlr (LDL receptor). Hmgcr m −/ m − macrophages and granulocytes had significantly lower Hmgcr mRNA expression and cholesterol biosynthesis than Hmgcr fl/fl cells. In vitro, Hmgcr m −/ m − monocytes/macrophages had reduced ability to migrate, proliferate, and survive compared with Hmgcr fl/fl monocytes/macrophages. However, there was no difference in ability to adhere, phagocytose, store lipids, or polarize to M1 macrophages between the 2 types of macrophages. The amounts of plasma membrane–associated small GTPase proteins, such as RhoA (RAS homolog family member A), were increased in Hmgcr m −/ m − macrophages. In the setting of Ldlr deficiency, Hmgcr m −/ m − mice developed significantly smaller atherosclerotic lesions than Hmgcr fl/fl mice. However, there were no differences between the 2 types of mice either in plasma lipoprotein profiles or in the numbers of proliferating or apoptotic cells in the lesions in vivo. The in vivo migration of Hmgcr m −/ m − macrophages to the lesions was reduced compared with Hmgcr fl/fl macrophages. Conclusions— Genetic reduction of HMGCR in myeloid cells may exert atheroprotective effects primarily by decreasing the migratory activity of monocytes/macrophages to the lesions.

Inflammasome mechanisms are involved as some of the pathways of sterile inflammation. Inflammasomes are large multiprotein complexes in the cytosol and are a key system for the production of the pivotal inflammatory cytokines, interleukin (IL)-1β and IL-18, and inflammatory cell death called pyroptosis. Although a number of inflammasomes have been described, the nucleotide-binding oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing 3 (NLRP3) is the most extensively investigated inflammasome. Exogenous pathogen-associated molecular patterns released during infection and endogenous crystalline danger/damage-associated molecular patterns (DAMPs) are well-known activators of NLRP3 inflammasomes. In addition, nanoparticle-associated molecular patterns (NAMPs), which are mediated by synthetic materials, including nanomaterials and nanoparticles, are proposed to be new danger signals of NLRP3 inflammasomes. Importantly, NAMP- and DAMP-triggered inflammation, a defining characteristic in inflammatory diseases, is termed as sterile inflammation because it occurs in the absence of foreign pathogens. This review focuses on the role of inflammasomes in exogenous NAMP- and endogenous crystalline DAMP-mediated sterile inflammation. Moreover, many regulatory mechanisms have been identified to attenuate NLRP3 inflammasomes. Therefore, we also summarize endogenous negative regulators of NLRP3 inflammasome activation, particularly induced by NAMPs or crystalline DAMPs.

Kawasaki disease (KD), which is the leading cause of pediatric heart disease, is characterized by coronary vasculitis and subsequent aneurysm formation. Although intravenous immunoglobulin therapy is effective for reducing aneurysm formation, a certain number of patients are resistant to this therapy. Because interleukin-10 (IL-10) was identified as a negative regulator of cardiac inflammation in a murine model of KD induced by Candida albicans water-soluble fraction (CAWS), we investigated the effect of IL-10 supplementation in CAWS-induced vasculitis. Mice were injected intramuscularly with adeno-associated virus (AAV) vector encoding IL-10, then treated with CAWS. The induction of AAV-mediated IL-10 (AAV-IL-10) significantly attenuated the vascular inflammation and fibrosis in the aortic root and coronary artery, resulting in the improvement of cardiac dysfunction and lethality. The predominant infiltrating inflammatory cells in the vascular walls were Dectin-2+CD11b+ macrophages. In vitro experiments revealed that granulocyte/macrophage colony-stimulating factor (GM-CSF) induced Dectin-2 expression in bone marrow-derived macrophages and enhanced the CAWS-induced production of tumor necrosis factor-α (TNF-α) and IL-6. IL-10 had no effect on the Dectin-2 expression but significantly inhibited the production of cytokines. IL-10 also inhibited CAWS-induced phosphorylation of ERK1/2, but not Syk. Furthermore, the induction of AAV-IL-10 prevented the expression of TNF-α and IL-6, but not GM-CSF and Dectin-2 at the early phase of CAWS-induced vasculitis. These findings demonstrate that AAV-IL-10 may have therapeutic application in the prevention of coronary vasculitis and aneurysm formation, and provide new insights into the mechanism underlying the pathogenesis of KD.

Serum Mac-2 binding protein glycosylation isomer (M2BPGi) is a novel fibrosis marker for various chronic liver diseases. We investigated the ability of M2BPGi to predict liver fibrosis in liver transplant (LT) recipients.A total of 116 liver biopsies were performed in 113 LT recipients. The serum level of M2BPGi was also measured on the same day. The median age at LT and liver biopsy was 1.1 and 11.8 years, respectively. Serum M2BPGi levels and liver fibrosis status using METAVIR fibrosis score were compared. Immunohistological evaluation by anti-α-smooth-muscle actin (αSMA) was performed, and the relationship between αSMA positive rate and serum M2BPGi levels was investigated.The median M2BPGi level was 0.78 (range, 0.22-9.50), and 65, 29, 16, 5, and 1 patient(s) had METAVIR fibrosis scores of F0, F1, F2, F3, and F4, respectively. In patients with F0 fibrosis, median M2BPGi level was 0.69 and was significantly lower than in patients with F1 (median 0.99, P 0.01), F2 (median 1.00, P = 0.01), and F3 fibrosis (median 1.53, P 0.01). Area-under-the-curve analysis of the ability of M2BPGi level to predict liver fibrosis grade were F1: 0.716, F2: 0.720, and F3: 0.900. Three patients with acute cellular rejection showed high levels of M2BPGi, which decreased after the treatment. A positive correlation existed between M2BPGi levels and αSMA positive rate (rMac-2 binding protein glycosylation isomer is a novel liver fibrosis marker in LT recipients and is also increased in patients with acute liver injuries, especially acute cellular rejection, even when fibrosis is absent.

Preeclampsia is a pregnancy-specific syndrome characterized by elevated blood pressure, proteinuria, and intrauterine growth restriction (IUGR). Although sterile inflammation appears to be involved, its pathogenesis remains unclear. Recent evidence indicates that sterile inflammation is mediated through the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes, composed of NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and caspase-1. Here we investigated the role of the NLRP3 inflammasomes in the pathogenesis of preeclampsia using Nlrp3−/− and Asc−/− (Nlrp3 and Asc deficient) pregnant mice. During pregnancy in mice, continuous infusion of high-dose angiotensin II (AngII) induced hypertension, proteinuria, and IUGR, whereas infusion of low-dose AngII caused hypertension alone. AngII-induced hypertension was prevented in Nlrp3−/− mice but not in Asc−/−, indicating that NLRP3 contributes to gestational hypertension independently of ASC-mediated inflammasomes. Although NLRP3 deficiency had no effect on IUGR, it restored the IL-6 up-regulation in the placenta and kidney of AngII-infused mice. Furthermore, treatment with hydralazine prevented the development of gestational hypertension but not IUGR or IL-6 expression in the placenta and kidney. These findings demonstrate that NLRP3 contributes to the development of gestational hypertension independently of the inflammasomes and that IUGR and kidney injury can occur independent of blood pressure elevation during pregnancy.

Supplemental oxygen inhalation is frequently used to treat severe respiratory failure; however, prolonged exposure to hyperoxia causes hyperoxic acute lung injury (HALI), which induces acute respiratory distress syndrome and leads to high mortality rates. Recent investigations suggest the possible role of NLRP3 inflammasomes, which regulate IL-1β production and lead to inflammatory responses, in the pathophysiology of HALI; however, their role is not fully understood. In this study, we investigated the role of NLRP3 inflammasomes in mice with HALI. Under hyperoxic conditions, NLRP3(-/-) mice died at a higher rate compared with wild-type and IL-1β(-/-) mice, and there was no difference in IL-1β production in their lungs. Under hyperoxic conditions, the lungs of NLRP3(-/-) mice exhibited reduced inflammatory responses, such as inflammatory cell infiltration and cytokine expression, as well as increased and decreased expression of MMP-9 and Bcl-2, respectively. NLRP3(-/-) mice exhibited diminished expression and activation of Stat3, which regulates MMP-9 and Bcl-2, in addition to increased numbers of apoptotic alveolar epithelial cells. In vitro experiments revealed that alveolar macrophages and neutrophils promoted Stat3 activation in alveolar epithelial cells. Furthermore, NLRP3 deficiency impaired the migration of neutrophils and chemokine expression by macrophages. These findings demonstrate that NLRP3 regulates Stat3 signaling in alveolar epithelial cells by affecting macrophage and neutrophil function independent of IL-1β production and contributes to the pathophysiology of HALI.

Transcriptional regulation of metabolic genes in the liver is the key to maintaining systemic energy homeostasis during starvation. The membrane-bound transcription factor cAMP-responsive element-binding protein 3-like 3 (CREB3L3) has been reported to be activated during fasting and to regulate triglyceride metabolism. Here, we show that CREB3L3 confers a wide spectrum of metabolic responses to starvation in vivo. Adenoviral and transgenic overexpression of nuclear CREB3L3 induced systemic lipolysis, hepatic ketogenesis, and insulin sensitivity with increased energy expenditure, leading to marked reduction in body weight, plasma lipid levels, and glucose levels. CREB3L3 overexpression activated gene expression levels and plasma levels of antidiabetic hormones, including fibroblast growth factor 21 and IGF-binding protein 2. Amelioration of diabetes by hepatic activation of CREB3L3 was also observed in several types of diabetic obese mice. Nuclear CREB3L3 mutually activates the peroxisome proliferator-activated receptor (PPAR) α promoter in an autoloop fashion and is crucial for the ligand transactivation of PPARα by interacting with its transcriptional regulator, peroxisome proliferator-activated receptor gamma coactivator-1α. CREB3L3 directly and indirectly controls fibroblast growth factor 21 expression and its plasma level, which contributes at least partially to the catabolic effects of CREB3L3 on systemic energy homeostasis in the entire body. Therefore, CREB3L3 is a therapeutic target for obesity and diabetes.

Objective— Inflammation provoked by the imbalance of fatty acid composition, such as excess saturated fatty acids (SFAs), is implicated in the development of metabolic diseases. Recent investigations suggest the possible role of the NLRP3 (nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3) inflammasome, which regulates IL-1β (interleukin 1β) release and leads to inflammation, in this process. Therefore, we investigated the underlying mechanism by which SFAs trigger NLRP3 inflammasome activation. Approach and Results— The treatment with SFAs, such as palmitic acid and stearic acid, promoted IL-1β release in murine primary macrophages while treatment with oleic acid inhibited SFA-induced IL-1β release in a dose-dependent manner. Analyses using polarized light microscopy revealed that intracellular crystallization was provoked in SFA-treated macrophages. As well as IL-1β release, the intracellular crystallization and lysosomal dysfunction were inhibited in the presence of oleic acid. These results suggest that SFAs activate NLRP3 inflammasome through intracellular crystallization. Indeed, SFA-derived crystals activated NLRP3 inflammasome and subsequent IL-1β release via lysosomal dysfunction. Excess SFAs also induced crystallization and IL-1β release in vivo. Furthermore, SFA-derived crystals provoked acute inflammation, which was impaired in IL-1β–deficient mice. Conclusions— These findings demonstrate that excess SFAs cause intracellular crystallization and subsequent lysosomal dysfunction, leading to the activation of the NLRP3 inflammasome, and provide novel insights into the pathogenesis of metabolic diseases.

Inflammation with macrophage infiltration is a key feature of atherosclerosis. Although the mechanisms had been unclear, emerging evidence unveiled that NLRP3 inflammasomes, which regulate caspase-1 activation and subsequent processing of pro-IL-1β, trigger vascular wall inflammatory responses and lead to progression of atherosclerosis. NLRP3 inflammasomes are activated by various danger signals, such as cholesterol crystals, calcium phosphate crystals, and oxidized low-density lipoprotein in macrophages, to initiate inflammatory responses in the atherosclerotic lesion. Recent studies have further clarified the regulatory mechanisms and the potential therapeutic agents that target NLRP3 inflammasomes. In this study, we reviewed the present state of knowledge on the role of NLRP3 inflammasomes in the pathogenesis of atherosclerosis and discussed the therapeutic approaches that target NLRP3 inflammasomes.

The nucleotide-binding oligomerization domain–like receptor family pyrin domain containing 3 (NLRP3) inflammasome is a molecular platform that induces caspase-1 activation and subsequent IL-1β maturation, and is implicated in inflammatory diseases; however, little is known about the negative regulation of NLRP3 inflammasome activation. In this article, we identified an E3 ligase, Ariadne homolog 2 (ARIH2), as a posttranslational negative regulator of NLRP3 inflammasome activity in macrophages. ARIH2 interacted with NLRP3 via its NACHT domain (aa 220–575) in the NLRP3 inflammasome complex. In particular, we found that while using mutants of ARIH2 and ubiquitin, the really interesting new gene 2 domain of ARIH2 was required for NLRP3 ubiquitination linked through K48 and K63. Deletion of endogenous ARIH2 using CRISPR/Cas9 genome editing inhibited NLRP3 ubiquitination and promoted NLRP3 inflammasome activation, resulting in apoptosis-associated speck-like protein containing a caspase recruitment domain oligomerization, pro–IL-1β processing, and IL-1β production. Conversely, ARIH2 overexpression promoted NLRP3 ubiquitination and inhibited NLRP3 inflammasome activation. Our findings reveal a novel mechanism of ubiquitination-dependent negative regulation of the NLRP3 inflammasome by ARIH2 and highlight ARIH2 as a potential therapeutic target for inflammatory diseases.

Inflammation plays a crucial role in the pathophysiological characteristics of chronic kidney disease; however, the inflammatory mechanisms underlying the chronic kidney disease process remain unclear. Recent evidence indicates that sterile inflammation triggered by tissue injury is mediated through a multiprotein complex called the inflammasome. Therefore, we investigated the role of the inflammasome in the development of chronic kidney disease using a murine unilateral ureteral obstruction (UUO) model. Inflammasome-related molecules were up-regulated in the kidney after UUO. Apoptosis-associated speck-like protein containing a caspase recruitment domain deficiency significantly reduced inflammatory responses, such as inflammatory cell infiltration and cytokine expression, and improved subsequent renal injury and fibrosis. Furthermore, apoptosis-associated speck-like protein containing a caspase recruitment domain was specifically up-regulated in collecting duct (CD) epithelial cells of the UUO-treated kidney. In vitro experiments showed that extracellular adenosine triphosphate (ATP) induced inflammasome activation in CD epithelial cells through P2X 7 -potassium efflux and reactive oxygen species–dependent pathways. These results demonstrate the molecular basis for the inflammatory response in the process of chronic kidney disease and suggest the CD inflammasome as a potential therapeutic target for preventing chronic kidney disease progression.