Inflammasome-Independent NLRP3 Augments TGF-β Signaling in Kidney Epithelium

Abstract

Tubulointerstitial inflammation and fibrosis are strongly associated with the outcome of chronic kidney disease. We recently demonstrated that the NOD-like receptor, pyrin domain containing-3 (NLRP3) contributes to renal inflammation, injury, and fibrosis following unilateral ureteric obstruction in mice. NLRP3 expression in renal tubular epithelial cells (TECs) was found to be an important component of experimental disease pathogenesis, although the biology of NLRP3 in epithelial cells is unknown. In human and mouse primary renal TECs, NLRP3 expression was increased in response to TGF-β1 stimulation and associated with epithelial–mesenchymal transition (EMT) and the expression of α-smooth muscle actin (αSMA) and matrix metalloproteinase (MMP) 9. TGF-β1–induced EMT and the induction of MMP-9 and αSMA were significantly decreased in mouse Nlrp3−/− renal TECs, suggesting a role for Nlrp3 in TGF-β–dependent signaling. Although apoptosis-associated speck-like protein containing a CARD domain−/− TECs demonstrated a phenotype similar to that of Nlrp3−/− cells in response to TGF-β1, the effect of Nlrp3 on MMP-9 and αSMA expression was inflammasome independent, as IL-1β, IL-18, MyD88, and caspase-1 were dispensable. Smad2 and Smad3 phosphorylation in response to TGF-β1 was attenuated in Nlrp3−/− and apoptosis-associated speck-like protein containing a CARD domain−/− cells, accounting for the dampened EMT and TGF-β1 responsiveness in these cells. Consistent with these findings, overexpression of NLRP3 in 293T cells resulted in increased Smad3 phosphorylation and activity. Taken together, these data support a novel and direct role for NLRP3 in promoting TGF-β signaling and R-Smad activation in epithelial cells independent of the inflammasome.

A Tissue-Specific Role for Nlrp3 in Tubular Epithelial Repair after Renal Ischemia/Reperfusion

“…We show that TECs express Nlrp3 (this study), as macrophages do. 20 Current research shows a profibrotic role for Nlrp3 in renal epithelium 27 and a proinflammatory role in macrophages, 20 indicating cell typeespecific effects of Nlrp3 on cellular function. To differentiate leukocyte-from renalassociated Nlrp3, we generated Nlrp3KO chimeras.…”

“…These results are consistent with other reports showing noncanonical effects of Nlrp3 in the kidney. 15,16,27,29 Next to cytokines, renal function is influenced by tubular damage and repair. Interestingly, we observed that renal apoptosis was reduced in mice lacking Nlrp3 expression in leukocytes, suggesting that leukocyte-associated Nlrp3 influences tubular epithelial apoptosis and, thereby, renal dysfunction.…”

Les lymphocytes Th9

“…Les protéines SMAD2 (Sma and Mad related protein 2), SMAD3 et SMAD4 sont impliquées dans l'activation des cellules induite par le TGF-b [12,13]. Elles sont à l'origine de modifications de la structure de la chromatine, au niveau du locus de l'Il9, notamment en bloquant le recrutement des protéines comme EZH2 (enhancer of zeste 2), appartenant au complexe multi-protéique PRC2 (polycomb repressive complex 2) responsable de la méthylation de l'ADN [13].…”

“…Elles sont à l'origine de modifications de la structure de la chromatine, au niveau du locus de l'Il9, notamment en bloquant le recrutement des protéines comme EZH2 (enhancer of zeste 2), appartenant au complexe multi-protéique PRC2 (polycomb repressive complex 2) responsable de la méthylation de l'ADN [13]. SMAD2 et SMAD3 interagissent également avec IRF4 lui permettant une fixation optimale au promoteur de l'Il9 [12].…”

“…SMAD2 et SMAD3 interagissent également avec IRF4 lui permettant une fixation optimale au promoteur de l'Il9 [12]. Les SMAD favoriseraient également la différenciation Th9 en bloquant l'expression des gènes spécifiques du sous-type Th2 induits par l'IL-4 [13]. La stimulation des cellules par le TGF-b active également des voies de signalisation, indépendantes des SMAD, qui peuvent induire l'expression de PU.1, un facteur de transcription de la famille ETS (E26 transformation-specific).…”