Inhibtion of mTORC2 signaling prevents and reverses salt‐induced hypertension and kidney injury in Dahl salt‐sensitive rats

Abstract

IntroductionThe present study explored the mechanism of mTORC2 activation in Sprague Dawley (SD) rats and the protective effect of mTORC2 inhibition in salt‐induced hypertension and kidney injury in Dahl salt‐sensitive (SS) rats. Although there are evidences that the mTORC2 pathway contributes to renal podocyte homeostasis and tubular epithelial Na+ and K+ transport, this pathway has remained unexplored in hypertension. Since excess production of H2O2 in the kidney is the hallmark of salt‐induced hypertension in the SS rat, we hypothesized that H2O2 may stimulate mTORC2 and contributes to this salt‐sensitive form of hypertension.MethodsH2O2 (347 nmol/Kg/min) was chronically infused for 3 days into renal medullary interstitium of unilaterally nephrectomized (SD) rats to determine the in vivo consequence of H2O2 upon mTORC2 activity. To test the protective effect of PP242 (ATP competitive inhibitor of both mTORC1 and mTORC2), SS rats were divided in to four groups. Groups 1 and 2: vehicle (group 1) or PP242 (group 2) was administrated daily (i.p., 15 mg/Kg/day) for 4 days to SS rats fed a 0.4% NaCl diet (control), then switched to a 4.0% NaCl diet for 21 days. Groups 3 and 4: rats were fed 4.0 % NaCl for 7 days before being treated with vehicle (group 3) or PP242 (group 4) for next 14 days while maintained on the 4.0 % NaCl diet. Kidneys were harvested to measure the protein levels of pAKT S473 and AKT by Western blots. mTORC2 activity was determined by assessing the ratio pAKTS473 and AKT. Microalbuminuria was quantified and kidney sections were immunostained with antibody against anti‐CD3 to determine the renal T lymphocytes infiltration.ResultsA significant increase of mTORC2 (pAKT S473/AKT) activity was observed in the renal cortex of SD rats infused with H2O2 for 3 days compared to saline infused rats. PP242 treatment significantly reduced H2O2 stimulated mTORC2 activity in nephron segments isolated from SS rat kidneys in vitro. Daily adminsiration of PP242 significantly reduced salt‐induced blood pressure in SS rats which averaged 119 ± 2 mmHg in group 2 rats (n=7) compared to 168 ± 3 mmHg in group 1 rats (n=7). Importantly, PP242 reversed the hypertension from 143 ± 3 mmHg to the base line 126 ± 5 mmHg in 2 days and maintained it at similar levels over the next 12 days in the group 4 rats (n=7) compared with group 3 rats (n=6). Albuminuria was greatly reduced with urine albumin excretion (mg/day) averaging 32.8 ± 3 in group 2 rats compared to 256 ± 37 in group 1 rats. PP242 treatment notably reduced infiltration of T lymphocytes in the kidneys of SS rats fed a 4.0% NaCl diet. CD3+ cells/mm2 averaging 36.0 ± 11.0 compared to 157.0 ± 40.0 in the cortex and 24.0 ± 9.0 compared to 218.0 ± 24.0 in the outer medulla in group 2 versus group 1 rats.ConclusionThese data show that mTORC2 is required for the initiation of salt‐induced hypertension and therapeutic suppression of this pathway prevents and reverses the salt‐induced hypertension and and kidney injury in SS rats.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.