Analysis of the role of Pellino2 in the Activation of the NLRP3 Inflammasome.

The innate immune system is the first line of defence against invading pathogens and is responsible for both initial pathogen recognition and mounting an effective immunological response. The recognition of conserved pathogen-associated molecular patterns can be carried out by a number of families of innate immune receptors, including Toll-like receptors. Toll-like receptors can respond to a diverse range of microbial signals and elicit a targeted immune response against the invading pathogen. A key regulator of inflammation is IL-1β, which can be secreted from activated cells and mediate a strong inflammatory response. The regulation of its release is a tightly controlled signalling event, as its dysregulation has been linked with the pathogenesis of a variety of diseases including Alzheimer’s disease and rheumatoid arthritis. The signalling complex which controls IL-1β release is known as the inflammasome, which requires two signals to facilitate its activation. The work in this thesis demonstrates a role for the E3 ubiquitin ligase Pellino2 in the specific activation of the NLRP3 inflammasome. Using a newly generated Pellino2-deficient mouse, it was determined that Pellino2 played no role during TLR induced NF-κB or MAPK signalling. However, Peli2-/- mice were more resistant to the lethal effects of LPS induced septic shock and this correlated with reduced serum IL-1β levels. Pellino2-deficient mice were shown to exhibit diminished NLRP3 inflammasome activation, correlating with reduced levels of NLRP3 ubiquitination and thus, lower levels of IL-1β secretion. While Pellino2 does not directly mediate the ubiquitination of NLRP3, it was observed that Pellino2-deficiency promoted the increased interaction of NLRP3 with hyperphosphorylated IRAK1. The data presented in this thesis defines for the first time a physiological role for Pellino2 in innate immune signalling with a particular function in mediating activation of the NLRP3 inflammasome