Cellular cholesterol modifies flow-mediated gene expression

Abstract

Downregulation of heme oxygenase-1 (HO-1), cyclooxygenase-2 (COX2), and nitric oxide synthase-2 (NOS2) in the kidneys of Dahl rodents causes salt sensitivity, while restoring their expression aids in Na+ excretion and blood pressure reduction. Loading cholesterol into collecting duct (CD) cells represses fluid shear stress (FSS)-mediated COX2 activity. Thus, we hypothesized that cholesterol represses flow-responsive genes necessary to effectuate Na+ excretion. To this end, CD cells were used to test whether FSS induces these genes and if cholesterol loading represses them. Mice fed either 0% or 1% cholesterol diet were injected with saline, urine volume and electrolytes were measured, and renal gene expression determined. FSS-exposed CD cells demonstrated increases in HO-1 mRNA by 350-fold, COX2 by 25-fold, and NOS2 by 8-fold in sheared cells compared with static cells ( P < 0.01). Immunoblot analysis of sheared cells showed increases in HO-1, COX2, and NOS2 protein, whereas conditioned media contained more HO-1 and PGE2 than static cells. Cholesterol loading repressed the sheared mediated protein abundance of HO-1 and NOS2 as well as HO-1 and PGE2 concentrations in media. In cholesterol-fed mice, urine volume was less at 6 h after injection of isotonic saline ( P < 0.05). Urinary Na+ concentration, urinary K+ concentration, and osmolality were greater, whereas Na+ excretion was less, at the 6-h urine collection time point in cholesterol-fed versus control mice ( P < 0.05). Renal cortical and medullary HO-1 ( P < 0.05) and NOS2 ( P < 0.05) mRNA were repressed in cholesterol-fed compared with control mice. Cholesterol acts to repress flow induced natriuretic gene expression, and this effect, in vivo, may contribute to renal Na+ avidity.

Fluid shear stress triggers cholesterol biosynthesis and uptake in inner medullary collecting duct cells, independently of nephrocystin-1 and nephrocystin-4

“…Cellular cholesterol composition has been shown to affect COX2 expression and shear stress-mediated PGE2 release via a p38-dependent mechanism ( Liu et al, 2015 ). Cholesterol can also repress the expression of genes involved in sodium and water regulation, leading to increased Na + and water retention ( Repetti et al, 2019 ). We show here for the first time the direct link between cholesterol biosynthesis and shear stress, in which NPHP1 and NPHP4 do not seem to be involved.…”

Shear Stress and Metabolic Disorders—Two Sides of the Same Plaque

“…On the one hand, lipids can modulate the impact of shear stress. For example, cholesterol loading repressed the shear stress-induced expression of heme oxygenase 1 and NOS2, prostaglandin E 2 , and cyclooxygenase-2 in both in vivo and in vitro studies (114,147). Hypercholesterolemia reduced NO production and vasodilatation in response to shear stress, thus promoting plaque formation in ApoE knockout mice (39,91).On the other hand, shear stress impacts lipid metabolism.…”

Unilateral Nephrectomy Stimulates ERK and Is Associated With Enhanced Na Transport

“…Though flow-mediated Na absorption prevents renal Na losses, flow mediated paracrine factors are stimulated to inhibit Na absorption and enhance Na excretion. These factors include nitric oxide (NO), endothelin-1 (ET1), nucleotides, prostanoids, and heme oxygenase-1 (HO1) ( Rieg et al, 2007 ; Lyon-Roberts et al, 2011 ; Flores et al, 2012 ; Liu et al, 2015 ; Pandit et al, 2015 ; Gao et al, 2018 ; Repetti et al, 2019 ). Therefore, net Na excretion from each segment represents a balance of flow-mediated Na absorption vs. flow-mediated paracrine molecules that antagonize Na transport ( Flores et al, 2012 ).…”