Mixed lineage kinase-like protein protects against Clostridium perfringens infection by enhancing NLRP3 inflammasome-extracellular traps axis

The pseudokinase MLKL contributes to host defense against Streptococcus pluranimalium infection by mediating NLRP3 inflammasome activation and extracellular trap formation

Host innate immunity plays a pivotal role in the early detection and neutralization of invading pathogens. Here, we show that pseudokinase mixed lineage kinase-like protein (MLKL) is required for host defence against Streptococcus pluranimalium infection by enhancing NLRP3 inflammasome activation and extracellular trap formation. Notably, Mlkl deficiency leads to increased mortality, increased bacterial colonization, severe destruction of organ architecture, and elevated inflammatory cell infiltration in murine models of S. pluranimalium pulmonary and systemic infection. In vivo and in vitro data provided evidence that potassium efflux-dependent NLRP3 inflammasome signalling downstream of active MLKL confers host protection against S. pluranimalium infection and initiates bacterial killing and clearance. Moreover, Mlkl deficiency results in defects in extracellular trap-mediated bactericidal activity. In summary, this study revealed that MLKL mediates the host defence response to S. pluranimalium, and suggests that MLKL is a potential drug target for preventing and controlling pathogen infection.

The protective effects of Bacillus licheniformis against inflammatory responses and intestinal barrier damage in broilers with necrotic enteritis induced by Clostridium perfringens

BACKGROUND

Bacillus licheniformis is a gram-positive bacterium that has strong environmental adaptability and can improve the growth performance, immunity, and antioxidant function of broilers. The current study aimed to elucidate the protective capability of B. licheniformis against inflammatory responses and intestinal barrier damage in broilers with necrotic enteritis (NE) induced by Clostridium perfringens (CP).

RESULTS

The results showed that B. licheniformis enhanced the final body weight in broilers compared with that of broilers in the CP group after the stress of infection (P < 0.05). Bacillus licheniformis reversed the decreased levels of serum and jejunum mucosa immunoglobulins and anti-inflammatory cytokines, reduced the values of villus height and the ratio of villus height to crypt depth, and mitigated the increased levels of serum d-lactic acid and diamine oxidase in CP-challenged broilers (P < 0.05). Moreover, B. licheniformis modulated the expression levels of genes involved in the TLR4/NF-κB signalling pathway, the NLRP3 inflammasome activation pathway, and the sirt 1/Parkin signalling pathway in CP-challenged broilers. Compared with the CP challenge group, the B. licheniformis-treated group exhibited reduced abundance values of Shuttleworthia and Alistipes and enhanced abundance values of Parabacteroides in the caecal contents (P < 0.05).

CONCLUSION

Bacillus licheniformis improved the final body weight and alleviated the inflammatory response and intestinal barrier function damage in birds with NE induced by CP by maintaining intestinal physiological function, enhancing immunity, regulating inflammatory cytokine secretion, modulating the mitophagy response, and increasing the abundance of beneficial intestinal flora. © 2023 Society of Chemical Industry.

The role of caspase-8 in inflammatory signalling and pyroptotic cell death

The programmed cell death machinery exhibits surprising flexibility, capable of crosstalk and non-apoptotic roles. Much of this complexity arises from the diverse functions of caspase-8, a cysteine-aspartic acid protease typically associated with activating caspase-3 and - 7 to induce apoptosis. However, recent research has revealed that caspase-8 also plays a role in regulating the lytic gasdermin cell death machinery, contributing to pyroptosis and immune responses in contexts such as infection, autoinflammation, and T-cell signalling. In mice, loss of caspase-8 results in embryonic lethality from unrestrained necroptotic killing, while in humans caspase-8 deficiency can lead to an autoimmune lymphoproliferative syndrome, immunodeficiency, inflammatory bowel disease or, when it can't cleave its substrate RIPK1, early onset periodic fevers. This review focuses on non-canonical caspase-8 signalling that drives immune responses, including its regulation of inflammatory gene transcription, activation within inflammasome complexes, and roles in pyroptotic cell death. Ultimately, a deeper understanding of caspase-8 function will aid in determining whether, and when, targeting caspase-8 pathways could be therapeutically beneficial in human diseases.

G Protein-Coupled Receptor 120 Mediates Host Defense against Clostridium perfringens Infection through Regulating NOD-like Receptor Family Pyrin Domain-Containing 3 Inflammasome Activation

Clostridium perfringens is a major cause of infectious foodborne disease, frequently associated with the consumption of raw and undercooked food. Despite intensive studies on clarifying C. perfringens pathogenesis, the molecular mechanisms of host-pathogen interactions remain poorly understood. In soft tissue and mucosal infection models, Gpr120^-/- mice, G protein-coupled receptor 120 (GPR120), are more susceptible to C. perfringens infection. Gpr120 deficiency leads to a low survival rate (30 and 10%, p < 0.01), more bacterial loads in the muscle (2.26 × 10⁸ ± 2.08 × 10⁸ CFUs/g, p < 0.01), duodenum (2.80 × 10⁷ ± 1.61 × 10⁷ CFUs/g, p < 0.01), cecum (2.50 × 10⁸ ± 2.05 × 10⁸ CFUs/g, p < 0.01), and MLN (1.23 × 10⁶ ± 8.06 × 10⁵ CFUs/g, p < 0.01), less IL-18 production in the muscle (8.54 × 10³ ± 1.20 × 10³ pg/g, p < 0.01), duodenum (3.34 × 10³ ± 2.46 × 10² pg/g, p < 0.01), and cecum (3.81 × 10³ ± 5.29 × 10² pg/g, p < 0.01), and severe organ injury. Obviously, GPR120 facilitates IL-18 production and pathogen control via potassium efflux-dependent NOD-like receptor family pyrin domain-containing 3 (NLRP3) signaling. Mechanistically, GPR120 interaction with NLRP3 potentiates the NLRP3 inflammasome assembly. Thus, this study uncovers a novel role of GPR120 in host protection and reveals that GPR120 may be a potential therapeutic target for limiting pathogen infection.

Inflammasome activation by Gram-positive bacteria: Mechanisms of activation and regulation

The inflammasomes are intracellular multimeric protein complexes consisting of an innate immune sensor, the adapter protein ASC and the inflammatory caspases-1 and/or -11 and are important for the host defense against pathogens. Activaton of the receptor leads to formation of the inflammasomes and subsequent processing and activation of caspase-1 that cleaves the proinflammatory cytokines IL-1β and IL-18. Active caspase-1, and in some instances caspase-11, cleaves gasdermin D that translocates to the cell membrane where it forms pores resulting in the cell death program called pyroptosis. Inflammasomes can detect a range of microbial ligands through direct interaction or indirectly through diverse cellular processes including changes in ion fluxes, production of reactive oxygen species and disruption of various host cell functions. In this review, we will focus on the NLRP3, NLRP6, NLRC4 and AIM2 inflammasomes and how they are activated and regulated during infections with Gram-positive bacteria, including Staphylococcus spp., Streptococcus spp. and Listeria monocytogenes.