Vasopressin-Sensitive Aqp2 Regulation Mediated by the TAZ-NR4A1 Axis in Renal Collecting Duct Cells

Regulation of aquaporin-2 (Aqp2) gene is essential for body water homeostasis. This study investigated how TAZ (a transcriptional coactivator with PDZ-binding motif, Wwtr1) controls vasopressin-driven AQP2 expression. AQP2 expression was studied using collecting duct-specific TAZ-knockout (TAZ^f/f; HoxB7Cre) mice and siRNA-mediated knockdown of TAZ in vasopressin-responsive mpkCCDc11 cells. Downstream factors of TAZ were identified using transcriptomics and bioinformatics. The TAZ^f/f; HoxB7Cre mice demonstrated polyuria and a significant decrease in AQP2 abundance in the kidney cortex and the outer medulla. dDAVP treatment (10^-9 M, 24 h) on mpkCCDc11 cells significantly increased AQP2 mRNA and protein levels. However, siRNA-mediated TAZ knockdown (TAZ-KD) markedly attenuated these effects without affecting cAMP levels. Immunocytochemical analysis revealed a substantial decrease in AQP2 immunolabeling intensity in TAZ-KD cells following dDAVP stimulation. RNA sequencing analysis identified 1370 and 1985 differentially expressed genes in TAZ-KD cells under basal conditions and after dDAVP treatment, respectively. Among 17 previously identified transcription factor (TF) candidates, seven (Nr4a1, Cebpb, Mef2d, Elf3, Klf5, Junb, Stat3) were significantly upregulated by dDAVP in either control or TAZ-KD conditions. Among them, RT-qPCR analysis identified Nr4a1 as a TAZ-dependent TF, and immunoblotting revealed reduced NR4A1 protein levels in TAZ-KD cells upon dDAVP stimulation. This finding suggests its role as a TAZ-regulated target in dDAVP response pathway. Accordingly, Nr4a1-KD reduced the dDAVP-induced upregulation of Aqp2 mRNA and protein. KEGG pathway enrichment analysis revealed that HIF-1 signaling and glycolysis as central pathways affected by TAZ. TAZ-NR4A1 axis acts as a novel transcriptional regulatory mechanism in controlling vasopressin-mediated AQP2 expression.