Systemic activation of NLRP3 inflammasome in patients with severe primary Sjögren's syndrome fueled by inflammagenic DNA accumulations

Abstract

Sjögren's syndrome (SS) patients manifest high cell-free DNA (cf-DNA) levels in serum, associated with impaired DNaseI activity. Undegraded DNA may accumulate in tissues and act as an inflammasome-activating signal. Herein, we investigated the occurrence of aberrant DNA build-up in various biologic compartments of SS patients and its correlation with the activity of NLRP3 and AIM2 inflammasomes. For this purpose, we evaluated sera, PBMC, circulating monocytes and salivary glands (SG) from different SS patient subgroups and controls. We found that SS patients at high risk for lymphoma and those with established lymphoma display high serum cf-DNA levels, substantial extranuclear DNA accumulations in PBMC and SG tissues, a unique NLRP3 inflammasome gene signature in PBMC, and significantly increased serum IL-18 and ASC levels. In these patients, the circulating monocytes manifested NLRP3 inflammasome activation and increased response to NLRP3 stimuli, whereas SG-infiltrating macrophages exhibited signs of NLRP3 activation and pyroptosis. Cell-free nucleic acids isolated from patients' sera competently primed the activation of both NLRP3 and AIM2 inflammasomes in healthy monocytes. SS patients also manifested diminished DNaseI activity in serum and DNaseII expression in PBMC, which inversely correlated with indices of inflammasome activation. DNaseII gene-silencing in healthy monocytes led to cytoplasmic DNA deposition and activation of inflammasome-related genes and of caspase1. Our data reveal the occurrence of systemic NLRP3 inflammasome activation in severe SS, which is associated with widespread extranuclear accumulations of inflammagenic DNA and impaired DNA degradation. These findings can provide novel biomarkers and new therapeutic targets for the management of SS patients with adverse outcomes.