Abstract 11704: NF-κβ Signaling Regulates Vasopressin Receptor 2 Promoter Activity

Abstract

Background: Arginine vasopressin, through vasopressin receptor 2 (AVP-V2R), regulates water reabsorption via aquaporin-2 and sodium reabsorption via several mechanisms. We recently implicated V2R, and its transcriptional downregulation, in a model of B-cell deficiency with increased sodium- and water-excretion and reduced blood pressure (BP). Here, we identify mechanisms underlying the immunoregulation of V2R transcription and evaluate the importance of V2R in BP regulation. Methods & Results: Using an Avpr2 promoter-luciferase reporter in an immortalized mouse inner medullary collecting duct cell line [mIMCD-3], we found that IL-6 (100ng/mL), a stimulator of NF-κβ signaling, increased promoter-reporter activity (10.4±3.2 vs 4.0±0.5 RLU; N=2-3/group); while PDTC (60μM), an inhibitor of NF-κβ signaling, reduced promoter-reporter activity (2.2 vs 4.0±0.5 RLU; N=1-3/group). Importantly, single point mutations in two putative NF-κβ binding sites in the proximal Avpr2 promoter also reduced promoter activity (2.3±0.6 vs 4.0±0.5 RLU; N=2-3/group), and blocked the stimulatory effect of IL-6 (2.4 vs 2.3±0.6 RLU; N=1-2/group). An anti-IL-6 receptor antibody (10μg/mL vs isotype, 10μg/mL) also abolished the stimulatory effect of IL-6 on promoter activity (3.2 vs 9.1 RLU; N=1/group). To determine the role of V2R in BP regulation, wild-type C57BL/6J mice (male and female; aged 10-wk) were randomized to (i) Tolvaptan (TOL), a selective V2R-antagonist or (ii) DMSO/glycerol control (50/50) via osmotic mini-pump (0.0375mg/d). Invasive hemodynamics 12-d post-implant revealed reduced mean arterial pressure (MAP) in TOL-treated mice (76±3 vs 86±3 mmHg; N=4-5/group; P<0.05), while metabolic cage studies 8-11-d post-implant showed higher 24-h urine volume/body weight (UV/BW; 0.07±0.00 vs 0.05±0.00 mL/g; N=4-5/group; P<0.05) and 24-h sodium excretion/BW (0.25±0.01 vs 0.17±0.01 mg/d/g; N=4-5/group; P<0.01). Correlation analyses revealed inverse relationships between MAP and 24-h UV/BW (r=-0.65; N=9 pairs; P<0.05) and 24-h sodium excretion/BW (r=-0.64; N=9 pairs; P<0.05). Conclusion: These studies suggest that the V2R promoter is responsive to NF-κβ signaling, and that V2R serves a role in BP homeostasis through sodium- and water-handling.