Emerging mechanisms and functions of inflammasome complexes in teleost fish

The NLRP3 Inflammasome in inflammatory diseases: Cellular dynamics and role in granuloma formation

The innate immune system recognizes pathogen-associated molecular patterns (PAMPs) and damage associated molecular patterns (DAMPs) through pattern recognition receptors (PRRs). Inflammasomes, cytoplasmic protein complexes, are activated in response to PAMPs and DAMPs, leading to the release of inflammatory cytokines such as IL-1β and IL-18. NLRP3 inflammasome is one of the best characterized inflammasomes and recently its activation has been associated with granuloma formation, structures that aggregate immune cells in response to infections, such as those caused by bacteria, fungi and parasites, and autoinflammatory diseases, such as sarcoidosis. Activation of NLRP3 inflammasomes in macrophages induces the release of cytokines that recruit immune cells, such as monocytes and lymphocytes, to the site of infection. Neutrophils, monocytes, T and B lymphocytes are important in the formation and maintenance of granulomas. Although NLRP3 plays a key role in the immune response, cell recruitment and granuloma formation, many aspects of its function in different cell types remain to be elucidated. In this review, we aim to outline the NLRP3 inflammasome not only as a protein complex that aids innate immune cells in combating intracellular pathogens but also as a platform with broader implications in orchestrating immune responses. This underexplored aspect of the NLRP3 inflammasome presents a novel perspective on its involvement in immunity. Thus, we review the current understanding of the role of the NLRP3 inflammasome in immune cell infiltration and its significance in the organization and formation of granulomas in inflammatory diseases.

Analysis of Striped Bass (Morone saxatilis) and White Bass (M. chrysops) Splenic Transcriptome Following Streptococcus iniae Infection

Streptococcal disease results in major mortality events of both marine and freshwater fishes worldwide. Streptococcus iniae is among the prominent causative bacterial strains as it has been found to cause a higher incidence of mortality and act as a zoonotic pathogen. Here, we examine the susceptibility of two important aquaculture species in the USA, striped bass (Morone saxatilis) and white bass (Morone chrysops) to S. iniae. A high incidence of mortality was observed in both species, although striped bass succumbed more rapidly than white bass. Spleen gene expression at three time points following infection was analyzed to further elucidate the mechanisms underlying these observations. The down-regulation of gene transcripts associated with pathogen detection (tlr1, tlr8, tlr9), antigen processing (cd74a), immune cell recruitment and migration (ccr6b, ccr7), macrophage function (csf1ra), T-cell signaling, and NF-kB activation (card11, fyna, tirap) was detected in both species. These findings potentially indicate impairment in these critical early immune system processes such that both species were ultimately highly susceptible to S. iniae infection despite the detected up-regulation of transcripts typically associated with effective immune response, such as cytokines (il1β, il8, il12b2, il17rc, tnfα) and hepcidins (hamp, hamp2). The presented results collectively identify several candidate genes and associated pathways for further investigation to characterize the vulnerability of striped bass and white bass to S. iniae and that may be considered for selective breeding efforts, biotechnological intervention, and/or exploitation in the development of vaccines and alternative treatments.

The Evolution of NLR Inflammasome and Its Mediated Pyroptosis in Metazoa

Nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) inflammasomes are multiprotein signaling platforms that control the inflammatory response and coordinate antimicrobial defense. In the present study, the distribution of NLR, Caspase-1, and gasdermin (GSDM) homologues and their structural characteristics and evolutionary relationships were systematically analyzed in metazoa according to the genomes of species. In invertebrates, there were only NLRC and/or NLRD presented from sponge to amphioxus, and according to the evolutionary tree, NLR from sponge located in the most primitive position. Caspase-1 existed in some metazoan phyla (Brachiopoda, Ectoprocta, Arthropoda, Mollusca, Annelia, Nematoda, Platyelminthes, Coelenterate, and Porifera) and its activation sites were relatively conserved. The amino acid sequences and three-dimensional structures of N-terminal CARD/Death domain of NLR and Caspase-1 were similar in species from sponge to human. NLR and Caspase-1 co-existed in species of Brachiopoda, Mollusca, Annelia, Coelenterate, and Porifera. There was only GSDME or PJVK found in some phyla of invertebrates and their cleavage sites were conserved (DxxD). And it was predicted that the NLR inflammasome in inducing pyroptosis could occur in species of Brachiopoda, Mollusca, Annelia, and Coelenterate. These studies indicated that NLR inflammasome emerged early in sponges of metazoa, and NLR inflammasome in inducing pyroptosis first appeared in Coelenterate, suggesting that inflammasome and its mediated pyroptosis had existed in the early stage of metazoa, but they had been lost in many species during evolution.

In vitro analysis of the expression of inflammasome, antiviral, and immune genes in an Oreochromis niloticus liver cell line following stimulation with bacterial ligands and infection with tilapia lake virus

The inflammasome is a multimeric protein complex that plays a vital role in the defence against pathogens and is therefore considered an essential component of the innate immune system. In this study, the expression patterns of inflammasome genes (NLRC3, ASC, and CAS-1), antiviral genes (IFNγ and MX), and immune genes (IL-1β and IL-18) were analysed in Oreochromis niloticus liver (ONIL) cells following stimulation with the bacterial ligands peptidoglycan (PGN) and lipopolysaccharide (LPS) and infection with TiLV. The cells were stimulated with PGN and LPS at concentrations of 10, 25, and 50 µg/ml. For viral infection, 106 TCID50 of TiLV per ml was used. After LPS stimulation, all seven genes were found to be expressed at specific time points at each of the three doses tested. However, at even higher doses of LPS, NLRC3 levels decreased. Following TiLV infection, all of the genes showed significant upregulation, especially at early time points. However, the gene expression pattern was found to be unique in PGN-treated cells. For instance, NLRC3 and ASC did not show any response to PGN stimulation, and the expression of IFNγ was downregulated at 25 and 50 µg of PGN per ml. CAS-1 and IL-18 expression was downregulated at 25 µg of PGN per ml. At a higher dose (50 µg/ml), IL-1β showed downregulation. Overall, our results indicate that these genes are involved in the immune response to viral and bacterial infection and that the degree of response is ligand- and dose-dependent.

NLRP3 inflammasome and pyroptosis in cardiovascular diseases and exercise intervention

NOD-like receptor protein 3 (NLRP3) inflammasome is an intracellular sensing protein complex that possesses NACHT, leucine-rich repeat, and pyrin domain, playing a crucial role in innate immunity. Activation of the NLRP3 inflammasome leads to the production of pro-inflammatory cellular contents, such as interleukin (IL)-1β and IL-18, and induction of inflammatory cell death known as pyroptosis, thereby amplifying or sustaining inflammation. While a balanced inflammatory response is beneficial for resolving damage and promoting tissue healing, excessive activation of the NLRP3 inflammasome and pyroptosis can have harmful effects. The involvement of the NLRP3 inflammasome has been observed in various cardiovascular diseases (CVD). Indeed, the NLRP3 inflammasome and its associated pyroptosis are closely linked to key cardiovascular risk factors including hyperlipidemia, diabetes, hypertension, obesity, and hyperhomocysteinemia. Exercise compared with medicine is a highly effective measure for both preventing and treating CVD. Interestingly, emerging evidence suggests that exercise improves CVD and inhibits the activity of NLRP3 inflammasome and pyroptosis. In this review, the activation mechanisms of the NLRP3 inflammasome and its pathogenic role in CVD are critically discussed. Importantly, the purpose is to emphasize the crucial role of exercise in managing CVD by suppressing NLRP3 inflammasome activity and proposes it as the foundation for developing novel treatment strategies.