Background
Angiotensin-(1-7) [Ang-(1-7)] counteracts many actions of the renin-angiotensin-aldosterone system. Despite its renoprotective effects, extensive controversy exists regarding the role of Ang-(1-7) in obstructive nephropathy, which is characterized by renal tubulointerstitial fibrosis and apoptosis.
Conclusion
Ang-(1-7) prevents obstructive nephropathy by suppressing renal apoptosis and fibrosis, possibly by regulating TGF-β1/Smad signaling and cell cycle arrest via suppression of AT1R expression. In addition, Ang-(1-7) increased and decreased ACE2 and TACE expression, respectively, which could potentially mediate a positive feedback mechanism via the Mas receptor.
Methods
To examine the effects of Ang-(1-7) in unilateral ureteral obstruction (UUO), male Sprague-Dawley rats were divided into three groups: control, UUO, and Ang-(1-7)-treated UUO rats. Ang-(1-7) was continuously infused (24 μg/[kg·h]) using osmotic pumps. We also treated NRK-52E cells in vitro with Ang II (1 μM) in the presence or absence of Ang-(1-7) (1 μM), Mas receptor antagonist A779 (1 μM), and Mas receptor siRNA (50 nM) to examine the effects of Ang-(1-7) treatment on Ang II-stimulated renal injury via Mas receptor.
Results
Angiotensin II (Ang II) and angiotensin type 1 receptor (AT1R) protein expression was higher in UUO kidneys than in controls. Ang-(1-7) treatment also decreased proapoptotic protein expression in UUO kidneys. Ang-(1-7) also significantly ameliorated TUNEL positive cells in UUO kidneys. Additionally, Ang-(1-7) reduced profibrotic protein expression and decreased the increased tumor growth factor (TGF)-β1/Smad signaling present in UUO kidneys. In NRK-52E cells, Ang II induced the expression of TGF-β1/Smad signaling effectors and proapoptotic and fibrotic proteins, as well as cell cycle arrest, which were attenuated by Ang-(1-7) pretreatment. However, treatment with A779 and Mas receptor siRNA enhanced Ang II-induced apoptosis and fibrosis. Moreover, Ang II increased tumor necrosis factor-α converting enzyme (TACE) and decreased angiotensin-converting enzyme 2 (ACE2) expression in NRK-52E cells, while pretreatment with Ang-(1-7) or A779 significantly inhibited or enhanced these effects, respectively.