Proximal tubule-dominant transfer of AT1a receptors induces blood pressure responses to intracellular angiotensin II in AT1a receptor-deficient mice

The role of intracellular angiotensin II in proximal tubules of the kidney remains poorly understood. We tested the hypothesis that proximal tubule-dominant transfer of AT1a receptors in the cortex mediates intracellular ANG II-induced blood pressure responses in AT1a receptor-deficient (Agtr1a-/-) mice. A GFP-tagged AT1a receptor, AT1aR/GFP, and a cyan fluorescent intracellular ANG II fusion protein, ECFP/ANG II, were expressed in proximal tubules of Agtr1a-/- mouse kidneys via the adenoviral transfer using a sodium and glucose cotransporter 2 promoter. Transfer of AT1aR/GFP alone or with ECFP/ANG II induced proximal tubule-dominant expression of AT1aR/GFP and/or ECFP/ANG II with a peak response at 2 weeks. No significant AT1aR/GFP and/or ECFP/ANG II expression was observed in the glomeruli, medulla, or extrarenal tissues. Transfer of AT1aR/GFP alone, but not ECFP/ANG II, increased systolic blood pressure by 12 ± 2 mmHg by day 14 (n=9, p<0.01). However, co-transfer of AT1aR/GFP with ECFP/ANG II increased blood pressure by 18 ± 2 mmHg (n=12, p<0.01). 24 h urinary sodium excretion was decreased by day 7 with proximal tubule-dominant transfer of AT1aR/GFP alone (p<0.01) or with AT1aR/GFP and ECFP/ANG II cotransfer (p<0.01). These responses were associated with twofold increases in phosphorylated ERK1/2, lysate and membrane NHE-3 proteins in freshly isolated proximal tubules (p<0.01). By contrast, transfer of control CMV-GFP, ECFP/ANG II, or ECFP/ANG IIc alone in proximal tubules had no effect on all indices. These results suggest that AT1a receptors and intracellular ANG II in proximal tubules of the kidney play an important physiological role in blood pressure regulation.