Abstract P019: Renal Mitochondrial Bioenergetics In Salt-sensitive Hypertension Is Affected By ANP

Abstract

There are clinical data suggesting that low levels of Atrial Natriuretic Peptide (ANP) aggravate susceptibility to salt-sensitive (SS) hypertension. ANP is known to affect mitochondria in many tissues, however, little is known about the effects of ANP on renal mitochondrial function. According to our earlier studies, Dahl SS rats lacking ANP exhibit increased blood pressure and pronounced kidney injury. We hypothesized that in SS hypertension ANP deficiency affects renal mitochondrial bioenergetics and contributes to renal function impairment. SS hypertension was induced in male SS NPPA-/- ( Nppa knockout in Dahl SS background, KO) and SS WT (wild type, WT) rats by a high salt (HS) 4% NaCl diet administered for 21 days. Age-matched control animals were fed a normal (NS) 0.4% NaCl salt diet. A combination of in vivo studies, molecular biology and tests of mitochondria isolated from renal cortex (seahorse respiration and spectrofluorimetry assays using TMRM, Amplex Red and MCLA) were used to probe the role ANP in mitochondrial function. Data was analyzed with ANOVA followed by Holm-Sidak post hoc. We report a significant decrease in mitochondrial membrane potential in the SS NPPA-/- rats vs SS WT (25 ± 4% decrease in KO vs WT on NS, and a 16 ± 5% decrease in KO on HS). Furthermore, mitochondrial H 2 O 2 (57.7 ± 7.4 (WT) vs 57.6 ± 1.3 au (KO), p<0.0001) and superoxide (36.6± 1.8 au (WT) vs 67.9 ± 5.2 au (KO), p<0.0001) levels were increased in the KO on a HS diet. Next, we antioxidant capacity was elevated in the SS NPPA-/- rats on HS diet in comparison with SS WT , and increased SOD2 levels were observed in the KO animals. Furthermore, SS NPPA-/- rats exhibit higher MCU (mitochondrial calcium uniporter) activity than SS WT , implying an ANP-dependent effect on mitochondrial calcium influx. Seahorse assay revealed dramatic elevation of the basal, ATP-linked, maximal and spare oxygen consumption rate (OCR) in the cortical mitochondria of the knockout rats on HS, while in HS fed SS WT rats these OCR parameters were, as expected, reduced (vs NS). Therefore, deficiency of circulating ANP leads to significant changes of renal mitochondrial bioenergetics, potentially via effects on mitochondrial calcium uptake, which in turn affects respiratory chain activity leading to oxidative stress.