Exploring new regulators of innate immune signalling pathways with a particular focus on inflammasomes

Abstract

Inflammasomes are innate immune signalling complexes vital in the activation of caspase-1, inflammation and wound healing. The dysregulation of inflammasome activity has been linked to the development of autoinflammatory diseases. Recently, the role of post-translational modifications has been identified to play an important role in regulating inflammasome activity, in particular the process of ubiquitination. Therefore, it is of great value to identify ubiquitin ligases or complexes that may regulate inflammasome activity through ubiquitination. This study investigated the role of suppressor of cytokine signalling (SOCS) proteins, which promote proteasomal degradation through ubiquitination, in regulating inflammasome activity. In this study SOCS2 and SOCS3 deficiency did not impact the inflammatory response to inflammasome-activating stimuli, including the highly antibiotic-resistant and encapsulated bacterium Klebsiella pneumoniae (Kp), ex vivo and in vivo. This study employed two strains of Kp (Kp52145 and Kp43816) with differential expression of the capsule; Kp52145 has a thicker capsule than Kp43816. This study demonstrated the importance of the capsule in regulating immune responses as it was found that Kp43816 was more effective at colonising C57BL/6J mice and inducing an inflammatory response than Kp52415. Furthermore, Kp43816 induced a stronger inflammasome response and was phagocytosed more efficiently than Kp52415 by macrophages. The importance of inflammasome activity during Kp infection was investigated with the use of nucleotide-binding oligomerisation domain-like receptor 3 (NLRP3)- and caspase-1/11-deficient mice, in addition to the pharmacological inhibition of NLRP3 (with MCC950) and caspase (with
z-VAD-FMK) activity. This study found that Kp activated the NLRP3 inflammasome, as well as other caspase-1/11-dependent and independent pathways that contributed to the production and secretion of IL-1β, but that these did not impact the bactericidal activity of macrophages. These findings demonstrated that multiple inflammasomes and inflammatory signalling pathways can detect Kp and induce an inflammatory immune response to promote the elimination of Kp.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Queen's University Belfast
Supervisor	Adrien Kissenpfennig (Supervisor) & Paul Moynagh (Supervisor)