NLRP3-mediated dysfunction of mitochondria leads to cell death in CFT073-stimulated macrophages

Urinary tract infections (UTIs) are commonly caused by uropathogenic E coli (UPEC), which uses different mechanisms to invade and damage hosts. NLRP3 inflammasome activation is a double-edged sword, although beneficial in the clearance of dysfunctional cells or pathogens but results in severe pathologies, if unchecked. NLRP3 inflammasome plays a critical role in UPEC-mediated inflammatory cell death during UPEC infection, though the effects of its activation are not clearly understood yet. Inflammatory response usually involves Signal-I (MyD88, TRIF and NF-kappa B signalling) and Signal-II (Inflammasome oligomerization) which is induced by the pathogen-associated molecular patterns during infection. We observed that proIL-1 beta and mature IL-1 beta remained unchanged on inhibition of MyD88 and TRIF-dependent signalling in CFT073-insulted THP-1m. However, inhibition of NF-kappa B pathway resulted in concomitant reduction in both pro- and cleaved forms of IL-1 beta in cellular extracts but there was no change in IL-1 beta secretion. Interestingly, inhibition of NLRP3 completely abolished the maturation and release of cleaved form of IL-1 beta. Additionally, NLRP3-mediated mitochondrial dysfunction (increased mito-ROS and mitochondrial hyperpolarization) resulting in cell death was induced in CFT073-insulted THP-1m, which was rescued upon inhibition of NLRP3 activation. Therefore, we have concluded that UPEC uses a different signal-I pathway (other than MyD88 and TRIF), while NLRP3 inflammasome is the major signal-II for the induction of inflammatory response. Further, this study signifies the importance of NLRP3-mediated mitochondrial dysfunction in CFT073-induced inflammatory cell death of macrophages, which could be rescued through inhibition of NLRP3 activation.