Abstract P215: Role of Nox4 - H 2 O 2 Production in Cctivation of mTORC1 in Salt-Induced Hypertension and Kidney Injury in Dahl S Rats

Abstract

Nox4 is the most abundant NADPH-oxidase isoform in the kidney. It predominantly releases H 2 O 2 and has been shown to contribute importantly to hypertension and renal injury in Dahl salt-sensitive (SS) rats fed a high salt diet. Recently, we reported that systemic inhibition of mTORC1 with chronic rapamycin treatment reduces salt-induced hypertension and kidney injury in SS rats. In the present study, we hypothesized that elevations of H 2 O 2 would activate mTORC1 and that reduction of Nox4 related H 2 O 2 production would reduce the mTORC1 contribution to salt-induced hypertension in SS rats. We first examined the effect of H 2 O 2 on mTORC1 activity in vivo by comparing the activity of mTORC1 in SS rats which have high levels of H 2 O 2 to SS-Nox4 knockout (SS Nox4–/– ) rats which have low levels of renal H 2 O 2 . As analyzed by Western blot, pS6 S235/236 /S6 (index of mTORC1 activity) was found to be significantly lower (P<0.05) in the renal cortex of SS Nox4-/- rats indicating that Nox4 generated H 2 O 2 was upstream in the mTORC1 pathway. We then examined whether systemic inhibition of mTORC1 with chronic rapamycin treatment would fail to reduce salt-sensitivity and kidney injury in nine week old male SS Nox4-/- rats. It was found that mean arterial pressure (MAP) of SS Nox4-/- rats treated with rapamycin (I.P.,1.5 mg/kg/day) fed a high salt diet (4.0%NaCl) for 21 days was not significantly different to vehicle treated SS Nox4-/- rats on the final day 21 (150 ± 7; n=8; vs 145 ± 6 mmHg; n=5; P>0.05). Neither did rapamycin treatment have a significant effect on kidney injury in SS Nox4-/- rats compared to vehicle treated rats determined at day 21 as reflected by albumin excretion rate (8 ± 2 vs 20 ± 13 mg/day, respectively; P>0.05). Rapamycin treated SS Nox4-/- rats exhibited a slow rate of body weight gain (302 ± 14 g at control and 313 ± 12 g at 21 days; P>0.05) compared to vehicle treated rats (316 ± 9 g at control and 366 ± 15 g at 21 days; P<0.05), although average food intake did not differ significantly (P>0.05) between the two groups. We conclude that Nox4 - H 2 O 2 production contributes importantly to mTORC1 activation leading to blood pressure salt-sensitivity, and renal injury in SS rats.