Abstract 16: Progressive Alterations Of Mitochondrial Bioenergetics In The Kidney During The Development Of Salt-induced Hypertension

Abstract

Hypertension is a complex disease and a leading cause of morbidity and mortality globally. Although oxidative stress and mitochondrial dysfunction have been found in the kidney in various models of hypertension, progressive alteration of mitochondrial oxidative phosphorylation (OxPhos) in the kidney during the development of salt-sensitive hypertension has not been characterized. The present study determined changes of OxPhos in kidneys of Dahl salt-sensitive (SS) rats before (0.4% NaCl diet; LS) and after switching to a high salt diet (4.0% NaCl; HS) during the development of hypertension. Mitochondria were isolated from the outer medulla (OM) and cortex of the kidney of SS rats fed a LS diet since weaning and studied at days 3, 7, 14 & 21 of a HS diet feeding. Oxygen consumption rates (OCR) were measured in mitochondria energized with pyruvate + malate as substrates for three different respiratory states using an Oroboros Oxygraph-2k Instrument. This includes i) leak state (in the absence of ADP), ii) ADP-stimulated state, and iii) uncoupled state (in the presence of an uncoupler FCCP). A biphasic pattern of ADP-stimulated OCR with progressive uncoupling was observed in both the renal OM and cortex. Mitochondrial efficiency for ATP synthesis was increased in the early phases of hypertension (3 & 7 days) but was severely compromised in the established phases of hypertension (14 & 21 days). This decreased mitochondrial efficiency was associated with uncoupling of OxPhos and high levels of oxidative stress which we hypothesized were due to mitochondrial ROS stimulation of membrane NOXs. To test this, experiments were performed in SS rats with double knock out (DKO) of the cytosolic subunit of NOX2 (p67 phox ) and NOX4 (SS p67phox-/-/Nox4-/- ). DKO SS rats were fed a HS diet and OCR of renal cortical and OM mitochondria was determined at days 7 and 14. In contrast to SS rats, the DKO SS rats fed a HS diet showed no significant differences in mitochondrial OCR in the cortex or OM, nor to a control group maintained on a LS diet. HS diet in SS rats initially increases the efficiency of renal cortical and medullary mitochondrial ATP production (days 1-7) followed by an enhanced ROS production with mitochondrial uncoupling and reduced efficiency of ATP production by the third week.