p22^phox in the macula densa regulates single nephron GFR during angiotensin II infusion in rats

Abstract

Angiotensin II (ANG II) infusion increases renal superoxide (O(2)(-)) and enhances renal vasoconstriction via macula densa (MD) regulation of tubuloglomerular feedback, but the mechanism is unclear. We targeted the p22(phox) subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) with small-interfering RNA (siRNA) to reduce NADPH oxidase activity and blood pressure response to ANG II in rats. We compared single nephron glomerular filtration rate (SNGFR) in samples collected from the proximal tubule (PT), which interrupts delivery to the MD, and from the distal tubule (DT), which maintains delivery to the MD, to assess MD regulation of GFR. SNGFR was measured in control and ANG II-infused rats (200 ng.kg(-1).min(-1) for 7 days) 2 days after intravenous injection of vehicle or siRNA directed to p22(phox) to test the hypothesis that p22(phox) mediates MD regulation of SNGFR during ANG II. The regulation of SNGFR by MD, determined by PT SNGFR-DT SNGFR, was not altered by siRNA in control rats (control + vehicle, 13 +/- 1, n = 8; control + siRNA, 12 +/- 2 nl/min, n = 8; not significant) but was reduced by siRNA in ANG II-treated rats (ANG II + vehicle, 13 +/- 2, n = 7; ANG II + siRNA, 7 +/- 1 nl/min, n = 8; P < 0.05). We conclude that p22(phox) and NADPH oxidase regulate the SNGFR during ANG II infusion via MD-dependent mechanisms.

Oxidative Stress in Hypertension: Role of the Kidney

“…This reflects NO bioinactivation by O 2 -in the JGA of the SHR. In other studies, systemic silencing of the p22 phox gene during ANG II infusion reduced renal ROS, and prevented progressive hypertension (191) and moderated the TGF responses (207). Fu et al (70) reported that activation of AT1R by ANG II mediated NOX2-dependent O 2 -production in the MD cells, whereas basal O 2 -generation was sustained by NOX4.…”

“…phox was required for salt-sensitive hypertension (62), p22 phox and p47 phox for ANG II-induced hypertension (103,153,191,207) and for genetic hypertension in spontaneously hypertensive rats (SHR) (29, 265), and Poldip2 for hypertension in models of chronic kidney disease (CKD) (150).…”

“…These likely contribute to enhanced preglomerular vasoconstriction and reduced glomerular filtration rate (GFR) that would restrict the rapid elimination of a salt load and predispose to salt sensitivity (70,165,207,312).…”

“…Wild-type mice and transgenic mice expressing the human SOD-2 isoform have high levels of SOD-2 immunoreactivity in the mitochondria of all tubular cells. However, only transgenic mice have prominent SOD-2 immunoreactivity in endothelial cells (ECs), VSMCs, and interstitial and glomerular cells (210 62,70,90,93,129,138,153,187,207,312). Other studies reported increased mitochondrial generation of H 2 O 2 by the medullary thick ascending limb (mTAL) cells in response to increased tubular flow that secondarily increased NADPH oxidase activity (213).…”

“…Oxidative stress leads to the elaboration of an EDCF that activates TP on VSMC whose activity also is enhanced by ROS. This is accompanied by blunted EDRF/NO (28, 79, 151, 293) and augmented TGF responses (207,310,312), all of which contribute to a renal vascular prohypertensive pathway activated during oxidative stress.…”