Loss of NKCC1 Activates the NLRP3 Inflammasome in Intestinal Epithelia.

BACKGROUND & AIMS: Potassium and chloride efflux have been reported to regulate nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation. Aberrant activation of NLRP3 inflammasome causes autoimmune and chronic inflammatory diseases. The Na+-K+-2Cl- cotransporter (NKCC1) maintains the intracellular concentrations of sodium, potassium, and chloride. Here we ask whether NKCC1 modulates NLRP3 inflammasome activation. METHODS: Mice with intestinal epithelial-specific deletion of NKCC1, CRISPR-Cas9 NKCC1-deleted Caco-2 and HT-29 cells, and human fibroblasts expressing mutant NKCC1 were used to evaluate NLRP3 inflammasome activation. RESULTS: We found that deletion of NKCC1 in established intestinal epithelial cells (IECs) in culture causes increased pyroptosis and interleukin (IL)-1β and IL-18 secretion upon NLRP3 inflammasome activation. Similarly, organoids derived from mice with conditional NKCC1 knockout in IECs also exhibit increased IL-1β secretion when stimulated with adenosine triphosphate (ATP). Moreover, fibroblasts from a patient with NKCC1 mutant also showed increased pyroptosis and IL-1β and IL-18 secretion. Loss of NKCC1 sensitizes IECs to changes in intracellular concentration of K+ and decreases the threshold required for NLRP3 inflammasome activation. Finally, we showed that NKCC1ΔIEC mice have increased infiltration of innate immune cells in the colon mucosa and peritoneal cavity. CONCLUSIONS: NKCC1 functions as a negative regulator of NLRP3 inflammasome activation and this may explain why patients of loss-of-function mutations in NKCC1 are susceptible to inflammatory diseases.