Oxidized phosphatidylcholine induces the activation of NLRP3 inflammasome in macrophages.

The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome is a multiprotein complex consisting of a receptor, an adaptor protein, and procaspase-1 that induces the secretion of the mature form of IL-1β in response to microbial infection and danger signals. Activation of the NLRP3 inflammasome induced by endogenous danger signal molecules is closely linked to the development and progress of chronic inflammatory diseases. The oxidation of phospholipids occurs upon cellular stress and damage, resulting in the accumulation of oxidized phosphatidylcholines (oxPAPC) such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-phosphocholine (POVPC) at inflammatory sites. In this study, we investigated whether oxidized phosphatidylcholine induces the activation of NLRP3 inflammasome in macrophages, leading to the secretion of IL-1β. POVPC induced the degradation of procaspase-1 to caspase-1(p10), the cleavage of pro-IL-1β to IL-1β, and oligomerization of ASC in primary mouse bone marrow-derived macrophages. POVPC-induced production of caspase-1, and IL-1β was abolished in macrophages derived from NLRP3- or caspase-1-deficient mice. In an air pouch model and a peritonitis model in mice, POVPC injection resulted in the production of caspase-1(p10), IL-1β, and IL-18 in wild-type, but not in NLRP3-deficient, mice. POVPC-induced inflammasome activation was mediated by mitochondrial reactive oxygen species resulting from intracellular Ca2+ signaling and mitochondrial destabilization. Our results demonstrate that endogenously produced oxidized phosphatidylcholines such as POVPC induce the activation of NLRP3 inflammasome, leading to the production of IL-1β in macrophages. The results provide an insight to understand how the oxidized lipids endogenously produced upon cellular stress and tissue damage contribute to the inflammatory reaction at pathologic sites.

Yeon SH ，Yang G ，Lee HE ，Lee JY ... -  《-》

1'-Acetoxychavicol acetate inhibits NLRP3-dependent inflammasome activation via mitochondrial ROS suppression.

The nucleotide-binding oligomerization domain-like receptor (NLR) family pyrin domain containing (NLRP) 3 inflammasome is a multiprotein complex that triggers Caspase-1-mediated IL-1β production and pyroptosis, and its dysregulation is associated with the pathogenesis of inflammatory diseases. 1'-Acetoxychavicol acetate (ACA) is a natural compound in the rhizome of tropical ginger Alpinia species with anti-microbial, anti-allergic and anti-cancer properties. In this study, we found that ACA suppressed NLRP3 inflammasome activation in mouse bone marrow-derived macrophages and human THP-1 monocytes. ACA inhibited Caspase-1 activation and IL-1β production by NLRP3 agonists such as nigericin, monosodium urate (MSU) crystals, and ATP. Moreover, it suppressed oligomerization of the adapter molecule, apoptosis-associated speck-like protein containing a CARD (ASC), and Caspase-1-mediated cleavage of pyroptosis executor Gasdermin D. Mechanistically, ACA inhibited generation of mitochondrial reactive oxygen species (ROS) and prevented release of oxidized mitochondrial DNA, which trigger NLRP3 inflammasome activation. ACA also prevented NLRP3 inflammasome activation in vivo, as evidenced in the MSU crystal-induced peritonitis and dextran sodium sulfate-induced colitis mouse models accompanied by decreased Caspase-1 activation. Thus, ACA is a potent inhibitor of the NLRP3 inflammasome for prevention of NLRP3-associated inflammatory diseases.

Sok SPM ，Ori D ，Wada A ，Okude H ，Kawasaki T ，Momota M ，Nagoor NH ，Kawai T ... -  《-》

Activation of NLRP3 inflammasome in macrophages by mycoplasmal lipoproteins and lipopeptides.

The NLRP3 inflammasome, an intracellular sensor consisting of the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3), the adaptor protein apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), and procaspase-1, plays critical roles in host defense against microbial pathogens by inducing production of interleukin-1β (IL-1β) and IL-18. Mycoplasma salivarium and Mycoplasma pneumoniae cells activated murine bone marrow-derived macrophages (BMMs) to induce production of IL-1α, IL-1β, and IL-18. The IL-1β production-inducing activities of these mycoplasmas toward BMMs from Toll-like receptor 2 (TLR2)-deficient mice were significantly attenuated compared with those from C57BL/6 mice (B6BMMs). This result suggests the possibility that their lipoproteins as TLR2 agonists are involved in the activity. Lipoproteins of M. salivarium and M. pneumoniae (MsLP and MpLP), and the M. salivarium-derived lipopeptide FSL-1 induced IL-1β production by B6BMMs, but not by BMMs from caspase-1-, NLRP3- or ASC-deficient mice. The activities of MsLP and MpLP were not downregulated by the proteinase K treatment, suggesting that the active sites are their N-terminal lipopeptide moieties. B6BMMs internalized the mycoplasmal N-terminal lipopeptide FSL-1 at least 30 min after incubation, FSL-1-containing endosomes started to fuse with the lysosomes around 2 hours, and then FSL-1 translocated into the cytosol from LAMP-1+ endosomes. The artificial delivery of FSL-1 into the cytosol of B6BMMs drastically enhanced the IL-1β production-inducing activity. FSL-1 as well as the representative NLRP3 inflammasome activator nigericin induced the NLRP3/ASC speck, but FSL-1 located in a compartment different from the NLRP3/ASC speck.

Saeki A ，Sugiyama M ，Hasebe A ，Suzuki T ，Shibata K ... -  《-》

Inflammasome activation by mitochondrial oxidative stress in macrophages leads to the development of angiotensin II-induced aortic aneurysm.

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. 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. 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.

Usui F ，Shirasuna K ，Kimura H ，Tatsumi K ，Kawashima A ，Karasawa T ，Yoshimura K ，Aoki H ，Tsutsui H ，Noda T ，Sagara J ，Taniguchi S ，Takahashi M ... -  《-》

Caspase-1 autoproteolysis is differentially required for NLRP1b and NLRP3 inflammasome function.

Guey B ，Bodnar M ，Manié SN ，Tardivel A ，Petrilli V ... -  《-》