Inflammasome-Independent Role of NLRP3 and ASC in Kidney Inflammation Triggered by Potassium Deficiency

Background: Pathological potassium (K+) deficiency causes kidney inflammation and injury, known as hypokalemic nephropathy (HN), the underlying pathogenesis of which is obscure. NLRP3 inflammasomes are platforms that sense the reduction of intracellular K+, engaging inflammation and tissue injury. We investigated whether or not K+ deficiency induces NLRP3 inflammasome-dependent inflammation in HN. Methods: To evaluate the role of NLRP3 inflammasomes in HN, we analyzed human HN kidney biopsy samples and an experimental HN model of mice fed a low K+ diet. To analyze the contribution of inflammasomes to HN, we used genetic knockout mice of the NLRP3 inflammasome components Nlrp3, Asc, and Casp1/11, as well as ASC-Citrine reporter mice and bone marrow chimera mice. Single-cell RNA sequencing was conducted on non-leukocyte kidney cells from mice fed a normal or low K+ diet. Primary kidney tubular epithelial cells from humans and mice were subjected to in vitro experiments. Results: Clinically diagnosed HN in humans manifested as upregulation of NLRP3 and ASC in the kidney epithelia. A K+ depletion model in mice demonstrated that kidney-resident NLRP3 and ASC play a key role in triggering early inflammation in the HN kidneys. Unexpectedly, the low-K+-induced kidney inflammation was not dependent on inflammasome activation. A single-cell RNA sequencing analysis revealed ASC upregulation, NF-κB activation, and an increased level of the TWEAK receptor Fn14 in the HN kidneys, primarily in the distal nephron/collecting duct epithelial cells. In in vitro experiments, kidney epithelial cells did not drive NLRP3 inflammasomes. NLRP3 and ASC alternatively enhanced with-no-lysine (WNK) kinase-mediated NF-κB signaling in response to TWEAK. Conclusion: Kidney tissue K+ depletion does not engage NLRP3 inflammasome activation, but its components NLRP3 and ASC in kidney epithelia alternatively trigger kidney inflammation by modulating the NF-κB signaling in HN. Funding: Government Support – Non-U.S.