Low Potassium Triggers Tubular Epithelial NLR Family Pyrin Domain-Containing 3/Apoptosis-Associated Speck-Like Protein-Containing a CARD-Driven Kidney Inflammation Independently of Inflammasomes.

Abstract

Pathologic potassium (K⁺) deficiency causes kidney inflammation and injury, known as hypokalemic nephropathy (HN), the underlying pathogenesis of which is obscure. NLR family pyrin domain-containing 3 (NLRP3) inflammasomes are platforms that sense the reduction of intracellular K⁺, engaging inflammation and tissue injury. The present study investigated whether or not systemic K⁺ deficiency induces NLRP3 inflammasome activation in HN. Clinically diagnosed HN in humans manifested up-regulation of NLRP3 and apoptosis-associated speck-like protein-containing a CARD (ASC) in the kidney epithelia. A K⁺ depletion model in mice demonstrated that kidney-resident NLRP3 and ASC play key roles in triggering early inflammation in HN kidneys. Unexpectedly, the K⁺ depletion-induced kidney inflammation was not dependent on inflammasome activation. A single-cell RNA-sequencing analysis revealed ASC up-regulation, NF-κB activation, and an increased level of tumor necrosis factor-like weak inducer of apoptosis receptor fibroblast growth factor-inducible 14 (FN14) in the HN kidneys, primarily in the distal nephron/collecting duct epithelial cells. Although kidney epithelial cells did not drive NLRP3 inflammasomes, NLRP3 and ASC alternatively enhanced with-no-lysine kinase-dependent NF-κB signaling in response to tumor necrosis factor-like weak inducer of apoptosis under a low-K⁺ milieu. These findings indicate a unique proinflammatory cascade mediated by NLRP3 and ASC beyond the framework of inflammasomes, which broadens the understanding of electrolyte-associated immunity in the kidney.