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.