Hydrocortisone decreases the internalization of low density lipoprotein in cultured human fibroblasts and arterial smooth muscle cells

Abstract

The effect of hydrocortisone on the cellular low density lipoprotein (LDL) pathway was studied in cultured human skin fibroblasts and arterial smooth muscle cells. Hydrocortisone decreased both uptake and degradation of 125I-LDL. LDL binding, measured at 4.degree. C, was not affected by the hormone. Physiological concentrations of hydrocortisone (4.1 .times. 10-8 mol/l) resulted in a 30% reduction of LDL uptake and degradation which could not be accounted for by an effect of the hormone on macromolecular synthesis, cell protein or cell number. To test whether the decrease in uptake and degradation of 125I-LDL was due to reduced internalization, the effect of hydrocortisone on the internalization of prebound LDL was determined and found to be decreased. Also, preincubation with unlabeled LDL in the presence of hydrocortisone resulted in less down regulation of LDL receptor activity than when no hydrocortisone was present. An effect of the hormone on bulk phase endocytosis was excluded, since hydrocortisone did not affect either LDL degradation by receptor negative cells or endocytosis of 14C-sucrose by normal skin fibroblasts. Hydrocortisone impairs LDL catabolism by decreasing the internalization of LDL normally bound to its cell surface receptor. These results may be relevant to the pathogenesis of atherosclerosis in conditions associated with reduced cellular LDL catabolism.