ExoS Effector inPseudomonas aeruginosaHyperactive Type III Secretion System Mutant Promotes Enhanced Plasma Membrane Rupture in Neutrophils

Abstract

AbstractPseudomonas aeruginosais an opportunistic bacterial pathogen responsible for a large percentage of airway infections that cause morbidity and mortality in immunocompromised patients, especially those with cystic fibrosis (CF). One importantP. aeruginosavirulence factor is a type III secretion system (T3SS) that translocates effectors into host cells. ExoS is a T3SS effector with ADP ribosyltransferase (ADPRT) activity. The ADPRT activity of ExoS promotesP. aeruginosavirulence by inhibiting phagocytosis and limiting the oxidative burst in neutrophils. TheP. aeruginosaT3SS also translocates flagellin, which can activate the NLRC4 inflammasome, resulting in: 1) gasdermin-D (GSDMD) pores, release of IL-1β and pyroptosis; and 2) histone 3 citrullination (CitH3) and decondensation and expansion of nuclear DNA into the cytosol. However, recent studies with theP. aeruginosalaboratory strain PAO1 indicate that ExoS ADPRT activity inhibits activation of the NLRC4 inflammasome in neutrophils. Here, an ExoS+CF clinical isolate ofP. aeruginosawith a hyperactive T3SS was identified. Variants of the hyperactive T3SS mutant or PAO1 were used to infect neutrophils from C57BL/6 mice or mice engineered to have a CF genotype or a defect in inflammasome assembly. Responses to NLRC4 inflammasome assembly or ExoS ADPRT activity were assayed, results of which were found to be similar for C57BL/6 or CF neutrophils. The hyperactive T3SS mutant had enhanced resistance to neutrophil killing, like previously identified hypervirulentP. aeruginosaisolates. ExoS ADPRT activity in the hyperactive T3SS mutant regulated inflammasome and nuclear DNA decondensation responses like PAO1 but promoted enhanced CitH3 and plasma membrane rupture (PMR). Glycine supplementation inhibited PMR caused by the hyperactive T3SS mutant, suggesting ninjurin-1 is required for this process. These results identify enhanced neutrophil PMR as a pathogenic activity of ExoS ADPRT in a hypervirulentP. aeruginosaisolate.