Investigation of NLRP13 - driven innate immune responses

Abstract

NOD-like receptors are the key players of inflammasome activation. NLRP13 is a primate specific member of the NLR family containing PYRIN domain and its role in inflammation is still unknown. Since there is no published literature about NLRP13, our knowledge is restricted with the studies of former lab members. From these works, we know that NLRP13 weakly interacts with pro-Casp-1 and ASC and forms inflammasome-like structures with ASC-Casp-1 in an overexpression system. LPS and ATP are upstream activators of NLRP13 protein levels. On the other hand, NLRP13 levels are reduced when co-transfected with Casp-8 and Casp-9. In this the sis, we focus to find the roles of NLRP13 in inflammasome activation and macrophage differentiation through examination of upstream activators and downstream elements. Firstly, we showed that high levels of NLRP13 increases secretion of IL-1β and TNF-α, while decreases secretion of IL-10 upon LPS/ATP treatment. Then, we observed that NLRP13 shows a Pseudomonas aeruginosa-specific innate immune response. Infec tion of THP-1 monocytes with P. aeruginosa increases expression of NLRP13 sig nificantly. The increasing levels of NLRP13 enhanced expression and secretion of pro-inflammatory cytokines IL-1β, TNF-α and IL-6. The expression of IL-1β was diminished with NLRP13-knock down in THP-1 cells. Moreover, protein levels of inflammasome components including pro-IL-β and NLRP3 and maturation of both pro-Casp-1 and pro-Casp-8 were enhanced due to high levels of NLRP13 through ac tivation of NF-κB. NLRP13 positively regulated PMA-differentiation of THP-1 cells by activating AKT and ERK pathways. In addition, we showed that NLPR13 is post translationally cleaved by Casp-8 through stimulation with LPS/ATP and P. aerug inosa that is thought a driving force for the functions of NLRP13 in inflammasome activation and macrophage differentiation.