Angiotensin II activates mTORC1 pathway in the kidneys through a pressor‐independent mechanism.

Abstract

BackgroundAngiotensin II (AngII) has been found in vitro to stimulate the mTORC1 pathway and we have observed that AngII treatment enhanced mTORC1 phosphorylation of the ribosomal protein S6 kinase (pS6/S6) in a dose related manner in the NRK cell line. However, the in vivo effects of chronic elevations of AngII upon kidney activity of mTORC1 or upon mTORC2 (pAKT/AKT) have not been determined.GoalTo determine the effects of chronic hypertensive elevations of AngII upon the kidney expression of mTORC1 and mTORC2 in Sprague‐Dawley (SD) rats. Since it would normally not be possible to separate the direct effects of AngII upon mTORC1 activation from the effects of arterial pressure, studies were carried out using a unique servo‐control system that enabled the renal perfusion pressure (RPP) to the left kidney to be maintained at normal levels while the contralateral right kidney was subjected to the elevated systemic pressure.MethodsMale SD rats (n = 15) were maintained on a 0.4% NaCl diet throughout the study. At 9 weeks of age, rats were instrumented with carotid and femoral arterial catheters for measuring blood pressure, a femoral venous catheter for AngII infusion and a balloon occluder cuff was placed around the abdominal aorta between the renal arteries. The carotid and the femoral mean arterial pressures were used as surrogates to the RPP of the right and left kidneys respectively. After 7 days of recovery, baseline blood pressure was measured for 3 days, then the n = 9 of rats were infused with AngII (50 ng/kg/min) for 7 days to induce hypertension. N = 6 of rats were infused with only saline (vehicle control) throughout the study. A computer‐driven servo‐control system was used to inflate the aortic cuff to maintain left RPP to baseline levels while right RPP was left uncontrolled. Following 7 days of Ang II infusion, kidneys were removed for molecular analysis.ResultsPrior to infusion of AngII, baseline RPP values to the right and left kidneys were similar (117.3±3.0 vs 112.2±3.4 mmHg). Following 7 days of AngII infusion, the right RPP was significantly higher than left RPP (162.4±9.0 vs 113.2±2.7 mmHg; p<0.05). Average 24 hr mean arterial pressures (MAP) remained unchanged in saline infused rats throughout the study. Western blot analysis of renal cortical tissue at day 7 found pS6/S6 was higher in both pressure‐uncontrolled and pressure‐controlled kidneys of AngII infused rats (2.25±0.21 vs 2.00±0.23) compared to saline infused rat kidneys (1.42±0.21; p<0.05). In contrast, pAKT/AKT was unchanged by either AngII or differences in RPP.ConclusionChronic elevations of circulating AngII activates mTORC1 pathway in the kidneys through a pressor‐independent mechanism but has little effect on activation of mTORC2.Support or Funding InformationP01 HL116264, RO1 HL137748