Cellular cholesterol modifies flow-mediated gene expression.

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 ( < 0.01). Immunoblot analysis of sheared cells showed increases in HO-1, COX2, and NOS2 protein, whereas conditioned media contained more HO-1 and PGE than static cells. Cholesterol loading repressed the sheared mediated protein abundance of HO-1 and NOS2 as well as HO-1 and PGE concentrations in media. In cholesterol-fed mice, urine volume was less at 6 h after injection of isotonic saline ( < 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 ( < 0.05). Renal cortical and medullary HO-1 ( < 0.05) and NOS2 ( < 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.