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Inflammation plays a key role in the pathophysiology of hepatic ischemia–reperfusion (I/R) injury. However, the mechanism by which hepatic I/R induces inflammatory responses remains unclear. Recent evidence indicates that a sterile inflammatory response triggered by I/R is mediated through a multiple-protein complex called the inflammasome. Therefore, we investigated the role of the inflammasome in hepatic I/R injury and found that hepatic I/R stimuli upregulated the inflammasome-component molecule, nucleotide-binding oligomerization domain–like receptor (NLR) family pyrin domain–containing 3 (NLRP3), but not apoptosis-associated speck–like protein containing a caspase recruitment domain (ASC). NLRP3−/− mice, but not ASC−/− and caspase-1−/− mice, had significantly less liver injury after hepatic I/R. NLRP3−/− mice showed reduced inflammatory responses, reactive oxygen species production, and apoptosis in I/R liver. Notably, infiltration of neutrophils, but not macrophages, was markedly inhibited in the I/R liver of NLRP3−/− mice. Bone marrow transplantation experiments showed that NLRP3 not only in bone marrow–derived cells, but also in non-bone marrow–derived cells contributed to liver injury after I/R. In vitro experiments revealed that keratinocyte-derived chemokine–induced activation of heterotrimeric G proteins was markedly diminished. Furthermore, NLRP3−/− neutrophils decreased keratinocyte-derived chemokine–induced concentrations of intracellular calcium elevation, Rac activation, and actin assembly formation, thereby resulting in impaired migration activity. Taken together, NLRP3 regulates chemokine-mediated functions and recruitment of neutrophils, and thereby contributes to hepatic I/R injury independently of inflammasomes. These findings identify a novel role of NLRP3 in the pathophysiology of hepatic I/R injury.

NLRP3 inflammasomes recognize non-microbial danger signals and induce release of proinflammatory cytokine interleukin (IL)-1β, leading to sterile inflammation in cardiovascular disease. Because sterile inflammation is involved in doxorubicin (Dox)-induced cardiotoxicity, we investigated the role of NLRP3 inflammasomes in Dox-induced cardiotoxicity. Cardiac dysfunction and injury were induced by low-dose Dox (15 mg/kg) administration in NLRP3-deficient (NLRP3−/−) mice but not in wild-type (WT) and IL-1β−/− mice, indicating that NLRP3 deficiency enhanced the susceptibility to Dox-induced cardiotoxicity independent of IL-1β. Although the hearts of WT and NLRP3−/− mice showed no significant difference in inflammatory cell infiltration, macrophages were the predominant inflammatory cells in the hearts, and cardiac IL-10 production was decreased in Dox-treated NLRP3−/− mice. Bone marrow transplantation experiments showed that bone marrow-derived cells contributed to the exacerbation of Dox-induced cardiotoxicity in NLRP3−/− mice. In vitro experiments revealed that NLRP3 deficiency decreased IL-10 production in macrophages. Furthermore, adeno-associated virus-mediated IL-10 overexpression restored the exacerbation of cardiotoxicity in the NLRP3−/− mice. These results demonstrated that NLRP3 regulates macrophage IL-10 production and contributes to the pathophysiology of Dox-induced cardiotoxicity, which is independent of IL-1β. Our findings identify a novel role of NLRP3 and provided new insights into the mechanisms underlying Dox-induced cardiotoxicity.

Maternal obesity, a major risk factor for adverse pregnancy complications, results in inflammatory cytokine release in the placenta. Levels of free fatty acids are elevated in the plasma of obese human. These fatty acids include obesity-related palmitic acids, which is a major saturated fatty acid, that promotes inflammatory responses. Increasing evidence indicates that nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasomes mediate inflammatory responses induced by endogenous danger signals. We hypothesized that inflammatory responses associated with gestational obesity cause inflammation. To test this hypothesis, we investigated the effect of palmitic acid on the activation of NLRP3 inflammasomes and inflammatory responses in a human Sw.71 trophoblast cell line. Palmitic acid stimulated caspase-1 activation and markedly increased interleukin (IL)-1β secretion in Sw.71 cells. Treatment with a caspase-1 inhibitor diminished palmitic acid-induced IL-1β release. In addition, NLRP3 and caspase-1 genome editing using a CRISPR/Cas9 system in Sw.71 cells suppressed IL-1β secretion, which was stimulated by palmitic acid. Moreover, palmitic acid stimulated caspase-3 activation and inflammatory cytokine secretion (e.g., IL-6 and IL-8). Palmitic acid-induced cytokine secretion were dependent on caspase-3 activation. In addition, palmitic acid-induced IL-1β, IL-6, and IL-8 secretion was depended on reactive oxygen species (ROS) generation. In conclusion, palmitic acid caused activation of NLRP3 inflammasomes and inflammatory responses, inducing IL-1β, IL-6, and IL-8 secretion, which is associated with ROS generation, in human Sw.71 placental cells. We suggest that obesity-related palmitic acid induces placental inflammation, resulting in association with pregnancy complications.

Objective Recent investigations have suggested that the inflammasome plays a role in the development of vascular inflammation and atherosclerosis; however, its precise role remains controversial. We produced double-deficient mice for apolipoprotien E (Apoe) and caspase-1 (Casp1), a key component molecule of the inflammasome, and investigated the effect of caspase-1 deficiency on vascular inflammation and atherosclerosis. Methods and results Atherosclerotic plaque areas in whole aortas and aortic root of Western diet (WD)-fed Apoe−/−Casp1−/− mice were significantly reduced compared to those in Apoe−/− mice. The amount of macrophages and vascular smooth muscle cells in the plaques was also reduced in Apoe−/−Casp1−/− mice. No significant differences in plasma lipid profiles and body weight change were observed between these mice. Expression of interleukin (IL)-1β in the plaques as well as plasma levels of IL-1β, IL-1α, IL-6, CCL2, and TNF-α, in Apoe−/−Casp1−/− mice were lower than those in Apoe−/− mice. In vitro experiments showed that calcium phosphate crystals induced caspase-1 activation and secretion of IL-1β and IL-1α in macrophages. Conclusion Our findings suggest that caspase-1 plays a critical role in vascular inflammation and atherosclerosis, and that modulation of caspase-1 could be a potential target for prevention and treatment of atherosclerosis.

F-box and WD repeat domain-containing 7α (Fbw7α) is the substrate recognition component of a ubiquitin ligase that controls the degradation of factors involved in cellular growth, including c-Myc, cyclin E, and c-Jun. In addition, Fbw7α degrades the nuclear form of sterol regulatory element-binding protein (SREBP)-1a, a global regulator of lipid synthesis, particularly during mitosis in cultured cells. This study investigated the in vivo role of Fbw7α in hepatic lipid metabolism. siRNA knockdown of Fbw7α in mice caused marked hepatosteatosis with the accumulation of triglycerides. However, inhibition of Fbw7α did not change the level of nuclear SREBP-1 protein or the expression of genes involved in fatty acid synthesis and oxidation. In vivo experiments on the gain and loss of Fbw7α function indicated that Fbw7α regulated the expression of peroxisome proliferator-activated receptor (PPAR) γ2 and its target genes involved in fatty acid uptake and triglyceride synthesis. These genes included fatty acid transporter Cd36, diacylglycerol acyltransferase 1 (Dgat1), and fat-specific protein 27 (Cidec). The regulation of PPARγ2 by Fbw7α was mediated, at least in part, by the direct degradation of the Krüppel-like factor 5 (KLF5) protein, upstream of PPARγ2 expression. Hepatic Fbw7α contributes to normal fatty acid and triglyceride metabolism, functions that represent novel aspects of this cell growth regulator.

Objective— Sterol regulatory element–binding protein-1 (SREBP-1) is nutritionally regulated and is known to be a key transcription factor regulating lipogenic enzymes. The goal of this study was to evaluate the roles of SREBP-1 in dyslipidemia and atherosclerosis. Methods and Results— Transgenic mice that overexpress SREBP-1c in the liver and SREBP-1-deficient mice were crossed with low-density lipoprotein receptor (LDLR)–deficient mice, and the plasma lipids and atherosclerosis were analyzed. Hepatic SREBP-1c overexpression in LDLR-deficient mice caused postprandial hypertriglyceridemia, increased very-low-density lipoprotein (VLDL) cholesterol, and decreased high-density lipoprotein cholesterol in plasma, which resulted in accelerated aortic atheroma formation. Conversely, absence of SREBP-1 suppressed Western diet–induced hyperlipidemia in LDLR-deficient mice and ameliorated atherosclerosis. In contrast, bone marrow-specific SREBP-1 deficiency did not alter the development of atherosclerosis. The size of nascent VLDL particles secreted from the liver was increased in SREBP-1c transgenic mice and reduced in SREBP-1-deficient mice, accompanied by upregulation and downregulation of phospholipid transfer protein expression, respectively. Conclusion— Hepatic SREBP-1c determines plasma triglycerides and remnant cholesterol and contributes to atherosclerosis in hyperlipidemic states. Hepatic SREBP-1c also regulates the size of nascent VLDL particles.

We have read with great interest the article by Abderrazak et al1 in which the authors found that arglabin, a natural product isolated from Artemisia glabella (wormwood), inhibited cholesterol crystal–induced activation of NLRP3 inflammasomes in macrophages and showed that its treatment significantly decreased plasma lipid levels and the development of atherosclerosis in high-fat diet–fed ApoE2.Ki mice. Recently, NLRP3 inflammasomes have received considerable attention because they have been shown to mediate sterile inflammatory responses in many types of disease. Indeed, we have recently …

Inflammation plays an important role in the development of obesity and metabolic disorders; however, it has not been fully understood how inflammation occurs and is regulated in their pathogenesis. Low-molecular mass protein-7 (LMP7) is a proteolytic subunit of the immunoproteasome that shapes the repertoire of antigenic peptides on major histocompatibility complex class I molecule. In this study, we investigated the role of LMP7 in the development of obesity and metabolic disorders using LMP7-deficient mice. LMP7 deficiency conveyed resistant to obesity and improved glucose intolerance and insulin sensitivity in mice fed with high-fat diet (HFD). LMP7 deficiency decreased pancreatic lipase expression, increased fecal lipid contents and inhibited the increase of plasma triglyceride levels upon oral oil administration or HFD feeding. Using bone marrow-transferred chimeric mice, we found that LMP7 in both bone marrow- and non-bone marrow-derived cells contributes to the development of HFD-induced obesity. LMP7 deficiency decreased inflammatory responses such as macrophage infiltration and chemokine expression while it increased serum adiponection levels. These findings demonstrate a novel role for LMP7 and provide new insights into the mechanisms underlying inflammation in the pathophysiology of obesity and metabolic disorders.

Rhabdomyolysis is one of the main causes of community-acquired acute kidney injury (AKI). Although inflammation is involved in the pathogenesis of rhabdomyolysis-induced AKI (RIAKI), little is known about the mechanism that triggers inflammation during RIAKI. Recent evidence has indicated that sterile inflammation triggered by tissue injury can be mediated through multiprotein complexes called the inflammasomes. Therefore, we investigated the role of NLRP3 inflammasomes in the pathogenesis of RIAKI using a glycerol-induced murine rhabdomyolysis model. Inflammasome-related molecules were upregulated in the kidney of RIAKI. Renal tubular injury and dysfunction preceded leukocyte infiltration into the kidney during the early phase of RIAKI and they were markedly attenuated in mice deficient in NLRP3, ASC, caspase-1 and interleukin (IL)-1β compared with those in wild-type mice. No difference in leukocyte infiltration was observed between wild-type and NLRP3-deficient mice. Furthermore, NLRP3 deficiency strikingly suppressed the expression of renal injury markers and inflammatory cytokines and apoptosis of renal tubular cells. These results demonstrated that NLRP3 inflammasomes contribute to inflammation, apoptosis and tissue injury during the early phase of RIAKI and provide new insights into the mechanism underlying the pathogenesis of RIAKI.

Atherosclerosis, a syndrome with abnormal arterial walls, is one of the major causes that lead to the development of various cardiovascular diseases. The key initiator of atherosclerosis is cholesterol accumulation. The uncontrolled cholesterol deposition, mainly involving low-density lipoprotein (LDL), causes atheroma plaque formation, which initiates chronic inflammation due to the recruitment of inflammatory cells such as macrophages. Macrophages scavenge excess peripheral cholesterol and transport intracellular cholesterol to high-density lipoprotein (HDL) for excretion or storage. Cholesterol-laden macrophage-derived foam cell formation is the main cause of atherogenesis. It is critical to understand the regulatory mechanism of cholesterol homeostasis in the macrophage in order to prevent foam cells formation and further develop novel therapeutic strategies against atherosclerosis. Here we identified a protein, RIP140 (receptor interacting protein 140), which enhances macrophage-derived foam cell formation by reducing expression of reverse cholesterol transport genes, A TP-binding membrane cassette transporter A-1 (ABCA1) and ATP-binding membrane cassette transporter G-1 (ABCG1). In animal models, we found that reducing RIP140 levels by crossing macrophage-specific RIP140 knockdown (MϕRIP140KD) mice with ApoE null mice effectively ameliorates high-cholesterol diet-induced atherosclerosis. Our data suggest that reducing RIP140 levels in macrophages significantly inhibits atherosclerosis, along with markers of inflammation and the number of macrophages in a western diet fed ApoE null mouse. This study provides a proof-of-concept for RIP140 as a risk biomarker of, and a therapeutic target for, atherosclerosis.

BACKGROUND: Type I interferons (IFNs), including IFN-alpha (IFNA) and IFN-beta (IFNB), have anti-inflammatory properties and are used to treat patients with autoimmune and inflammatory disorders. However, little is known of the role of IFN-tau (IFNT), a type I IFN produced by ruminant animals for inflammation. Because IFNB has recently been shown to inhibit nucleotide-binding oligomerization domain-like receptor, pyrin domain-containing 3 (NLRP3) inflammasome activation and subsequent secretion of the potent inflammatory cytokine interleukin (IL)-1β, we examined the effects of ruminant IFNT on NLRP3 inflammasome-mediated IL-1β secretion in human THP-1 macrophages. METHODS AND RESULTS: IFNT dose-dependently inhibited IL-1β secretion induced by nano-silica, a well-known activators of NLRP3 inflammasomes, in human macrophages primed with lipopolysaccharide (LPS, TLR4 agonist) and Pam3CSK4 (TLR1/2 agonist). IFNT also suppressed phagocytosis of nano-silica and reactive oxygen species (ROS) generation. Western blot analysis showed that IFNT inhibited both pro-IL-1β and mature IL-1β. In addition, real-time RT-PCR analysis showed that IFNT suppressed IL-1β mRNA expression induced by LPS and Pam3CSK4. Although nano-silica particles did not induce IL-10 secretion, IFNT induced IL-10 secretion in a dose-dependent manner. Furthermore, IFNT-suppressed IL-1β secretion was restored by anti-IL-10 neutralizing antibody. CONCLUSIONS: Ruminant IFNT inhibits NLRP3 inflammasome-driven IL-1β secretion in human macrophages via multiple pathways, including the uptake of nano-silica particles, generation of ROS, and IL-10-mediated inhibition of pro-IL-1β induction. It may be a therapeutic alternative to IFNA and IFNB.

Objective— Abdominal aortic aneurysm (AAA) is considered a chronic inflammatory disease; however, the molecular basis underlying the sterile inflammatory response involved in the process of AAA remains unclear. We previously showed that the inflammasome, which regulates the caspase-1–dependent interleukin-1β production, mediates the sterile cardiovascular inflammatory responses. Therefore, we hypothesized that the inflammasome is a key mediator of initial inflammation in AAA formation. Approach and Results— Apoptosis-associated speck-like protein containing a caspase recruitment domain is highly expressed in adventitial macrophages in human and murine AAA tissues. Using an established mouse model of AAA induced by continuous infusion of angiotensin II in Apoe –/– mice, NLR family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase recruitment domain, and caspase-1 deficiency in Apoe –/– mice were shown to decrease the incidence, maximal diameter, and severity of AAA along with adventitial fibrosis and inflammatory responses significantly, such as inflammatory cell infiltration and cytokine expression in the vessel wall. NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain, and caspase-1 deficiency in Apoe –/– mice also reduced elastic lamina degradation and metalloproteinase activation in the early phase of AAA formation. Furthermore, angiotensin II stimulated generation of mitochondria-derived reactive oxygen species in the adventitial macrophages, and this mitochondria-derived reactive oxygen species generation was inhibited by NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain, and caspase-1 deficiency. In vitro experiments revealed that angiotensin II stimulated the NLRP3 inflammasome activation and subsequent interleukin-1β release in macrophages, and this activation was mediated through an angiotensin type I receptor/mitochondria-derived reactive oxygen species–dependent pathway. Conclusions— Our results demonstrate the importance of the NLRP3 inflammasome in the initial inflammatory responses in AAA formation, indicating its potential as a novel therapeutic target for preventing AAA progression.

Objective— Elovl6, a long-chain fatty acid elongase, is a rate-limiting enzyme that elongates saturated and monounsaturated fatty acids and has been shown to be related to obesity-induced insulin resistance via modification of fatty acid composition. In this study, we investigated the roles of Elovl6 in foam cell formation in macrophages and atherosclerosis in mice. Methods and Results— To investigate the roles of Elovl6 in macrophages in the progression of atherosclerosis, we transplanted bone marrow cells of wild-type or Elovl6 −/− mice into irradiated LDL-R −/− mice that were fed a western diet. Aortic atherosclerotic lesion areas and infiltration of macrophages were significantly smaller in Elovl6 −/− bone marrow cells-transplanted LDL-R −/− mice than in wild-type. Accumulation of esterified cholesterol on exposure to acetylated-LDL was less severe in peritoneal macrophages from Elovl6 −/− mice than those from wild-type. Cholesterol efflux and expression of cholesterol efflux transporters were increased in Elovl6 −/− macrophages, although no difference in uptake of acetylated-LDL was found between the two groups. On analysis of fatty acid composition of the esterified cholesterol fraction in macrophages, n-6 polyunsaturated fatty acids were decreased by absence of Elovl6. Conclusion— These findings suggest that Elovl6 in macrophages may contribute to foam cell formation and progression of atherosclerosis.

Insulin resistance is often associated with obesity and can precipitate type 2 diabetes. To date, most known approaches that improve insulin resistance must be preceded by the amelioration of obesity and hepatosteatosis. Here, we show that this provision is not mandatory; insulin resistance and hyperglycemia are improved by the modification of hepatic fatty acid composition, even in the presence of persistent obesity and hepatosteatosis. Mice deficient for Elovl6, the gene encoding the elongase that catalyzes the conversion of palmitate to stearate, were generated and shown to become obese and develop hepatosteatosis when fed a high-fat diet or mated to leptin-deficient ob/ob mice. However, they showed marked protection from hyperinsulinemia, hyperglycemia and hyperleptinemia. Amelioration of insulin resistance was associated with restoration of hepatic insulin receptor substrate-2 and suppression of hepatic protein kinase C epsilon activity resulting in restoration of Akt phosphorylation. Collectively, these data show that hepatic fatty acid composition is a new determinant for insulin sensitivity that acts independently of cellular energy balance and stress. Inhibition of this elongase could be a new therapeutic approach for ameliorating insulin resistance, diabetes and cardiovascular risks, even in the presence of a continuing state of obesity.

Highlights • CARD16 is the most abundant CARD-only protein in hematopoietic cells. • Unlike CARD17, CARD16 oligomerizes to form a filament-like structure. • The filament-like structure formed by CARD16 promotes caspase 1 (CASP1) assembly. • CASP1-dependent IL-1β processing is enhanced by CARD16. • CARD16 colocalizes in ASC-speck by interacting with ASC., Increasing evidence indicates that caspase recruitment domain (CARD)-mediated caspase-1 (CASP1) assembly is an essential process for its activation and subsequent interleukin (IL)-1β release, leading to the initiation of inflammation. Both CARD16 and CARD17 were previously reported as inhibitory homologs of CASP1; however, their molecular function remains unclear. Here, we identified that oligomerization activity allows CARD16 to function as a CASP1 activator. We investigated the molecular characteristics of CARD16 and CARD17 in transiently transfected HeLa cells. Although both CARD16 and CARD17 interacted with CASP1CARD, only CARD16 formed a homo-oligomer. Oligomerized CARD16 formed a filament-like structure with CASP1CARD and a speck with apoptosis-associated speck-like protein containing a CARD. A filament-like structure formed by CARD16 promoted CASP1 filament assembly and IL-1β release. In contrast, CARD17 did not form a homo-oligomer or filaments and inhibited CASP1-dependent IL-1β release. Mutated CARD16D27G, mimicking the CARD17 amino acid sequence, formed a homo-oligomer but failed to form a filament-like structure. Consequently, CARD16D27G weakly promoted CASP1 filament assembly and subsequent IL-1β release. These results suggest that oligomerized CARD16 promotes CARD-mediated molecular assembly and CASP1 activation.