Over 20 years ago, it was first proposed that autoinflammation underpins a handful of rare monogenic disorders characterized by recurrent fever and systemic inflammation. The subsequent ...identification of novel, causative genes directly led to a better understanding of how the innate immune system is regulated under normal conditions, as well as its dysregulation associated with pathogenic mutations. Early on, IL-1 emerged as a central mediator for these diseases, based on data derived from patient cells, mutant mouse models and definitive clinical responses to IL-1 targeted therapy. Since that time, our understanding of the mechanisms of autoinflammation has expanded beyond IL-1 to additional innate immune processes. However, the number and complexity of IL-1-mediated autoinflammatory diseases has also multiplied to include additional monogenic syndromes with expanded genotypes and phenotypes, as well as more common polygenic disorders seen frequently by the practising clinician. In order to increase physician awareness and update rheumatologists who are likely to encounter these patients, this review discusses the general pathophysiological concepts of IL-1-mediated autoinflammation, the epidemiological and clinical features of specific diseases, diagnostic challenges and approaches, and current and future perspectives for therapy.
Autoinflammatory diseases are conditions in which pathogenic inflammation arises primarily through antigen-independent hyperactivation of immune pathways. First recognized just over 2 decades ago, ...the autoinflammatory disease spectrum has expanded rapidly to include more than 40 distinct monogenic conditions. Related mechanisms contribute to common conditions such as gout and cardiovascular disease. Here, we review the basic concepts underlying the "autoinflammatory revolution" in the understanding of immune-mediated disease and introduce major categories of monogenic autoinflammatory disorders recognized to date, including inflammasomopathies and other IL-1-related conditions, interferonopathies, and disorders of nuclear factor kappa B and/or aberrant TNF activity. We highlight phenotypic presentation as a reflection of pathogenesis and outline a practical approach to the evaluation of patients with suspected autoinflammation.
Mitochondrial DNA (mtDNA) escaping stressed mitochondria provokes inflammation via cGAS-STING pathway activation and, when oxidized (Ox-mtDNA), it binds cytosolic NLRP3, thereby triggering ...inflammasome activation. However, it is unknown how and in which form Ox-mtDNA exits stressed mitochondria in non-apoptotic macrophages. We found that diverse NLRP3 inflammasome activators rapidly stimulated uniporter-mediated calcium uptake to open mitochondrial permeability transition pores (mPTP) and trigger VDAC oligomerization. This occurred independently of mtDNA or reactive oxygen species, which induce Ox-mtDNA generation. Within mitochondria, Ox-mtDNA was either repaired by DNA glycosylase OGG1 or cleaved by the endonuclease FEN1 to 500–650 bp fragments that exited mitochondria via mPTP- and VDAC-dependent channels to initiate cytosolic NLRP3 inflammasome activation. Ox-mtDNA fragments also activated cGAS-STING signaling and gave rise to pro-inflammatory extracellular DNA. Understanding this process will advance the development of potential treatments for chronic inflammatory diseases, exemplified by FEN1 inhibitors that suppressed interleukin-1β (IL-1β) production and mtDNA release in mice.
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•Ca2+ uptake via MCU triggers IMM mPTP opening to induce OMM VDAC oligomerization•Ox-mtDNA is repaired by OGG1 or cleaved by FEN1 to fragments that exit mitochondria•Cytosolic Ox-mtDNA activates NLRP3 inflammasome and cGAS-STING and escapes cells•mtOGG1 and FEN1 inhibitors suppress acute peritonitis and reduce circulating mtDNA
Ox-mtDNA enables NLRP3 inflammasome activation, but how Ox-mtDNA reaches the cytoplasm is unclear. In this issue of Immunity, Xian et al. show that Ox-mtDNA cleaved by FEN1 escapes mitochondria via mPTP and VDAC channels to activate NLRP3 inflammasome and STING.
CAPS and NLRP3 Booshehri, Laela M.; Hoffman, Hal M.
Journal of clinical immunology,
04/2019, Letnik:
39, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Cryopyrin-associated periodic syndrome (CAPS) is a rare inherited autoinflammatory disorder characterized by systemic, cutaneous, musculoskeletal, and central nervous system inflammation. ...Gain-of-function mutations in
NLRP3
in CAPS patients lead to activation of the cryopyrin inflammasome, resulting in the inappropriate release of inflammatory cytokines including IL-1β and CAPS-related inflammatory symptoms. Several mechanisms have been identified that are important for the normal regulation of the cryopyrin inflammasome in order to prevent uncontrolled inflammation. Investigators have taken advantage of some of these pathways to develop and apply novel targeted therapies, which have resulted in improved quality of life for patients with this orphan disease.
Inflammasomes are intracellular sensors that couple detection of pathogens and cellular stress to activation of Caspase-1, and consequent IL-1β and IL-18 maturation and pyroptotic cell death. Here, ...we show that the absent in melanoma 2 (AIM2) and nucleotidebinding oligomerization domain-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasomes trigger Caspase-1-dependent mitochondrial damage. Caspase-1 activates multiple pathways to precipitate mitochondrial disassembly, resulting in mitochondrial reactive oxygen species (ROS) production, dissipation of mitochondrial membrane potential, mitochondrial permeabilization, and fragmentation of the mitochondrial network. Moreover, Caspase-1 inhibits mitophagy to amplify mitochondrial damage, mediated in part by cleavage of the key mitophagy regulator Parkin. In the absence of Parkin activity, increased mitochondrial damage augments pyroptosis, as indicated by enhanced plasma membrane permeabilization and release of danger-associated molecular patterns (DAMPs). Therefore, like other initiator caspases, Caspase-1 activation by inflammasomes results in mitochondrial damage.
Increased hepatocyte death contributes to the pathology of acute and chronic liver diseases. However, the role of hepatocyte pyroptosis and extracellular inflammasome release in liver disease is ...unknown.
We used primary mouse and human hepatocytes, hepatocyte-specific leucine 351 to proline Nlrp3KICreA mice, and GsdmdKO mice to investigate pyroptotic cell death in hepatocytes and its impact on liver inflammation and damage. Extracellular NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes were isolated from mutant NLRP3-YFP HEK cells and internalisation was studied in LX2 and primary human hepatic stellate cells. We also examined a cohort of 154 adult patients with biopsy-proven non-alcoholic fatty liver disease (Sir Charles Gairdner Hospital, Nedlands, Western Australia).
We demonstrated that primary mouse and human hepatocytes can undergo pyroptosis upon NLRP3 inflammasome activation with subsequent release of NLRP3 inflammasome proteins that amplify and perpetuate inflammasome-driven fibrogenesis. Pyroptosis was inhibited by blocking caspase-1 and gasdermin D activation. The activated form of caspase-1 was detected in the livers and in serum from patients with non-alcoholic steatohepatitis and correlated with disease severity. Nlrp3KICreA mice showed spontaneous liver fibrosis under normal chow diet, and increased sensitivity to liver damage and inflammation after treatment with low dose lipopolysaccharide. Mechanistically, hepatic stellate cells engulfed extracellular NLRP3 inflammasome particles leading to increased IL-1β secretion and α-smooth muscle actin expression. This effect was abrogated when cells were pre-treated with the endocytosis inhibitor cytochalasin B.
These results identify hepatocyte pyroptosis and release of inflammasome components as a novel mechanism to propagate liver injury and liver fibrosis development.
Our findings identify a novel mechanism of inflammation in the liver. Experiments in cell cultures, mice, and human samples show that a specific form of cell death, called pyroptosis, leads to the release of complex inflammatory particles, the NLRP3 inflammasome, from inside hepatocytes into the extracellular space. From there they are taken up by other cells and thereby mediate inflammatory and pro-fibrogenic stress signals. The discovery of this mechanism may lead to novel treatments for chronic liver diseases in the future.
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•Human and murine hepatocytes undergo pyroptosis and release NLRP3 inflammasome proteins.•Pyroptotic cell death in hepatocytes is dependent on caspase-1 and gasdermin D activation.•Caspase-1 activity is increased in livers and serum from NASH patients.•Nlrp3KICreA mice develop fibrosis and show increased sensitivity to liver damage.•Human hepatic stellate cells internalise extracellular NLRP3-YFP oligomeric particles.•Extracellular NLRP3 oligomeric particles perpetuate inflammation and fibrogenesis.
Nuclear factor κB (NF-κB), a key activator of inflammation, primes the NLRP3-inflammasome for activation by inducing pro-IL-1β and NLRP3 expression. NF-κB, however, also prevents excessive ...inflammation and restrains NLRP3-inflammasome activation through a poorly defined mechanism. We now show that NF-κB exerts its anti-inflammatory activity by inducing delayed accumulation of the autophagy receptor p62/SQSTM1. External NLRP3-activating stimuli trigger a form of mitochondrial (mt) damage that is caspase-1- and NLRP3-independent and causes release of direct NLRP3-inflammasome activators, including mtDNA and mtROS. Damaged mitochondria undergo Parkin-dependent ubiquitin conjugation and are specifically recognized by p62, which induces their mitophagic clearance. Macrophage-specific p62 ablation causes pronounced accumulation of damaged mitochondria and excessive IL-1β-dependent inflammation, enhancing macrophage death. Therefore, the “NF-κB-p62-mitophagy” pathway is a macrophage-intrinsic regulatory loop through which NF-κB restrains its own inflammation-promoting activity and orchestrates a self-limiting host response that maintains homeostasis and favors tissue repair.
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•NF-κB mediates LPS-induced p62/SQSTM1 expression in macrophages•NLRP3 agonists damage mitochondria and release inflammasome activating signals•Ubiquitinated damaged mitochondria are eliminated by p62-dependent mitophagy•p62 ablation prevents mitophagy and enhances NLRP3-inflammasome activation
NF-κB restrains its own inflammation-promoting activity in macrophages by promoting p62-mediated removal of mitochondria that have been damaged after macrophages encounter various NLRP3-inflammasome activators.
Inflammasome activation plays a central role in the development of drug‐induced and obesity‐associated liver disease. However, the sources and mechanisms of inflammasome‐mediated liver damage remain ...poorly understood. Our aim was to investigate the effect of NLRP3 inflammasome activation on the liver using novel mouse models. We generated global and myeloid cell‐specific conditional mutant Nlrp3 knock‐in mice expressing the D301N Nlrp3 mutation (ortholog of D303N in human NLRP3), resulting in a hyperactive NLRP3. To study the presence and significance of NLRP3‐initiated pyroptotic cell death, we separated hepatocytes from nonparenchymal cells and developed a novel flow‐cytometry–based (fluorescence‐activated cell sorting; FACS) strategy to detect and quantify pyroptosis in vivo based on detection of active caspase 1 (Casp1)‐ and propidium iodide (PI)‐positive cells. Liver inflammation was quantified histologically by FACS and gene expression analysis. Liver fibrosis was assessed by Sirius Red staining and quantitative polymerase chain reaction for markers of hepatic stellate cell (HSC) activation. NLRP3 activation resulted in shortened survival, poor growth, and severe liver inflammation; characterized by neutrophilic infiltration and HSC activation with collagen deposition in the liver. These changes were partially attenuated by treatment with anakinra, an interleukin‐1 receptor antagonist. Notably, hepatocytes from global Nlrp3‐mutant mice showed marked hepatocyte pyroptotic cell death, with more than a 5‐fold increase in active Casp1/PI double‐positive cells. Myeloid cell‐restricted mutant NLRP3 activation resulted in a less‐severe liver phenotype in the absence of detectable pyroptotic hepatocyte cell death. Conclusions: Our data demonstrate that global and, to a lesser extent, myeloid‐specific NLRP3 inflammasome activation results in severe liver inflammation and fibrosis while identifying hepatocyte pyroptotic cell death as a novel mechanism of NLRP3‐mediated liver damage. (Hepatology 2014;59:898–910)
Autoinflammatory diseases are disorders of the innate immune system, characterized by systemic inflammation often driven by inflammasomes, and independent of infection and autoreactive antibodies or ...antigen-specific T cells. These diseases are increasingly recognized as disorders of immune dysregulation, presenting with a constellation of fevers, rashes, and mucosal symptoms in many cases, which suggests that the allergist/immunologist is the appropriate specialist for these patients. However, many practicing physicians are unaware of these disorders in their pediatric and adult patient populations, leading to substantial delays in diagnosis. Recognizing autoinflammatory disease symptom patterns, performing appropriate diagnostic tests, and instituting early effective therapy are essential to reduce morbidity and mortality in these patients. This review will focus on understanding the molecular basis of inflammasomes, recognizing the distinguishing features of the classic autoinflammatory disorders, and appreciating the treatment modalities available.
Inflammation, a vital response of the immune system to infection and damage to tissues, can be initiated by various germline-encoded innate immune-signaling receptors. Among these, the inflammasomes ...are critical for activation of the potent proinflammatory interleukin-1 cytokine family. Additionally, inflammasomes can trigger and maintain inflammatory responses aimed toward excess nutrients and the numerous danger signals that appear in a variety of chronic inflammatory diseases. We discuss our understanding of how inflammasomes assemble to trigger caspase-1 activation and subsequent cytokine release, describe how genetic mutations in inflammasome-related genes lead to autoinflammatory syndromes, and review the contribution of inflammasome activation to various pathologies arising from metabolic dysfunction. Insights into the mechanisms that govern inflammasome activation will help in the development of novel therapeutic strategies, not only for managing genetic diseases associated with overactive inflammasomes, but also for treating common metabolic diseases for which effective therapies are currently lacking.
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