#4695 LOSS OF NLRP6 INCREASES THE SEVERITY OF KIDNEY FIBROSIS

Abstract

Abstract Background and Aims The burden of chronic kidney disease (CKD) is growing worldwide, illustrating the need for better prevention and therapeutic approaches. Kidney fibrosis is a hallmark of CKD that is not specifically addressed by current therapeutic options. The nucleotide-binding oligomerization domain-like receptor (NLR) family has 22 members. The NLRP3 inflammasome has been most extensively studied in the context of kidney disease where it plays a pathogenic role. However, the role of NRLP6 during CKD and kidney fibrosis remains unexplored. The aim of the study was to explore the role for endogenous Nlrp6 in protecting from kidney fibrosis. Method A hypothesis-driven analysis of non-biased human kidney disease transcriptomics databases was performed to identify NLRs other than NLRP3 of potential therapeutic interest, based on differential gene expression during CKD and the relationship of gene expression to severity of CKD. We explored Nlrp6 expression in preclinical accelerated CKD and kidney fibrosis (UUO) and characterized the function of endogenous Nlrp6 by inducing UUO in Nlrp6-deficient mice and validated the results in a second model of kidney fibrosis. Once tubular cells were identified as the key cells expressing NLRP6 and regulating NLRP6 expression during UUO, we explored the drivers of Nlrp6 downregulation in tubular cells, as well as the consequences of Nlrp6 downregulation in these same cells. Results The role of Nlrp6 in experimental CKD was explored in wild-type and Nlrp6-deficient mice with unilateral ureteral obstruction (UUO). Whole kidney Nlrp6 mRNA and tubular cell Nlrp6 protein decreased following UUO. Low kidney Nlrp6 immunostaining was also observed in human CKD. Genetic Nlrp6 deficiency resulted in increased kidney p38 MAP kinase activation and more severe kidney inflammation and fibrosis, as assessed by kidney inflammatory gene expression, interstitial macrophage infiltration, expression of profibrotic cytokines and extracellular matrix encoding genes, Smad3 phosphorylation, Sirius red staining, collagen, and fibronectin deposition and myofibroblast numbers. Similar results were obtained in adenine-induced kidney fibrosis. Cytokines involved in the pathogenesis of kidney fibrosis, such as the profibrotic cytokine TGF-β1 and the proinflammatory cytokine TWEAK, decreased Nlrp6 expression in cultured tubular cells, while siRNA targeting Nlrp6 resulted in increased TGF-β1 and CTGF expression, which was limited by inhibiting p38 MAPK. Conclusion In conclusion, endogenous constitutive Nlrp6 dampens sterile kidney inflammation and fibrosis likely by dampening tubular cell responses. Loss of Nlrp6 expression may contribute to CKD progression.