PP.28.13

Abstract

Objective: Oxidative stress plays an important role in the development of hypertension. It is reported that renal dopamine D1 receptor (D1R), a major contributor to sodium homeostasis and BP regulation, is negatively regulated by oxidative stress. Antioxidants can reduce BP and redox-sensitive transcription factor Nrf2 could provide important clues for antihypertensive properties of antioxidants. We investigated the signaling molecules responsible for redox-sensitive renal proximal tubular D1R dysfunction and the role of renal specific Nrf2 in preserving D1R function. Design and method: Wild type (WT) and renal proximal tubular specific Nrf2 knockout (KO) mice were treated with 10 mM L-buthionine-sulfoximine (BSO, a pro-oxidant) without and with sulforaphane (S, an antioxidant; 5 μM daily by gavage) for 5 weeks. Human kidney proximal tubular (HK2) cells were also treated with BSO with and without sulforaphane. Results: In WT mice, BSO treatment increased oxidative stress and BP, reduced renal tubular D1R expression and attenuated SKF38393 (a D1R agonist)-induced Na/K-ATPase inhibition and sodium excretion. BSO also activated transcription factors activator protein (AP) 1 and SP3. However, the onset and severity of hypertension as well as oxidative stress, activation of AP1 and SP3 and D1R dysfunction were more robust in BSO-treated Nrf2 KO compared to WT mice. Also, sulforaphane activated Nrf2, reduced oxidative stress, normalized AP1 and SP3 activation, rescued DIR function and lowered BP in BSO-treated WT mice but not in Nrf2 KO mice. BSO also caused oxidative stress and D1R dysfunction in HK2 cells. BSO-treated HK2 cells exhibited increased AP1 (c-fos) and SP3 nuclear expression. Sulforaphane per se had no effect on oxidative milieu or D1R expression, but it mitigated BSO-induced oxidative stress, AP1—SP3 up-regulation and D1R down-regulation and dysfunction. Down-regulation of SP3 had no effect on BSO-mediated AP1 activation, however, AP1 siRNA blocked BSO-dependent SP3 up-regulation. In cells transfected with Nrf2 siRNA, sulforaphane failed to block BSO-induced AP1—SP3 activation and D1R dysfunction. Conclusions: Oxidative stress via AP1-SP3 pathway down-regulates D1R expression and function which leads to sodium retention and hypertension. Antioxidants, via Nrf2 activation, reduce oxidative stress, normalize AP1-SP3 signaling, protect renal D1R function and prevent development of hypertension.