Xenobiotic Pregnane X Receptor (PXR) Regulates Innate Immunity via Activation of NLRP3 Inflammasome in Vascular Endothelial Cells*

Background: Xenobiotics activate nuclear receptor PXR for detoxification and clearance. However, a role of PXR in regulating innate immunity remains unknown. Results: PXR induced NLRP3 expression and triggered inflammasome activation in vascular ECs. Conclusion: PXR plays an important role in the activation of NLRP3 inflammasome in response to xenobiotics. Significance: Our findings revealed a novel mechanism of innate immunity. Pregnane X receptor (PXR) is a member of nuclear receptor superfamily and responsible for the detoxification of xenobiotics. Our previously study demonstrated that PXR is expressed in endothelial cells (ECs) and acts as a master regulator of detoxification genes to protect ECs against xenobiotics. Vascular endothelial cells are key sentinel cells to sense the pathogens and xenobiotics. In this study, we examined the potential function of PXR in the regulation of innate immunity in vasculatures. Treatments with PXR agonists or overexpression of a constitutively active PXR in cultured ECs increased gene expression of the key pattern recognition receptors, including Toll-like receptors (TLR-2, -4, -9) and NOD-like receptors (NOD-1 and -2 and NLRP3). In particular, PXR agonism triggered the activation of NLRP3 inflammasome and the ensuing cleavage and maturation of caspase-1 and interleukin-1β (IL-1β). Conversely, selective antagonism or gene silencing of PXR abrogated NLRP3 inflammasome activation. In addition, we identified NLRP3 as a transcriptional target of PXR by using the promoter-reporter and ChIP assays. In summary, our findings revealed a novel regulatory mechanism of innate immune by PXR, which may act as a master transcription factor controlling the convergence between the detoxification of xenobiotics and the innate immunity against them.