Metabolic cooperation between vascular endothelial cells and smooth muscle cells in co-culture: changes in low density lipoprotein metabolism.

Abstract

A microcarrier co-culture system for aortic endothelial cells and smooth muscle cells (SMCs) was developed as a model for metabolic interactions between cells of the vessel wall. Low density lipoprotein (LDL) metabolism in SMCs was significantly influenced by coculture with endothelium. The numbers of high affinity receptors for LDL was increased more than twofold (range, 2.1-5.6), with concomitant increases in LDL receptor-mediated endocytosis and degradation. These effects reached a plateau at an endothelial celI/SMC ratio of 1. Kinetic analysis of the endocytic pathway for LDL in SMCs indicated that, in co-culture with endothelium, there was no alteration in the binding affinity of LDL to its receptors but that the internalization rate constant declined and the rate constant for degradation increased. This analysis suggested that the formation and migration of endocytic vesicles was the rate-limiting step of enhanced LDL metabolism under co-culture conditions. Two mechanisms by which endothelial cells influenced smooth muscle LDL metabolism were identified. First, mitogen(s) derived from endothelial cells stimulated entry of SMCs into the growth cycle, and the changes in LDL metabolism occurred as a consequence of G1-S transition. Second, SMC lipoprotein metabolism was stimulated in the absence of mitogens by a low molecular weight (<3,500) factor or factors. Co-culture was a required condition for the latter effect, suggesting that the mediator(s) may be unstable or that cell-cell communication was necessary for expression. These results (a) demonstrate that vascular cell interactions can modify LDL metabolism in SMCs, (b) provide some insights into the mechanisms responsible, and (c) identify co-culture as an experimental approach appropriate to certain aspects of vascular cell biology. (3)(4)(5) or by co-cultures in which endothelium and SMCs were plated together (3,6,7).In attempts to dissect such interactions, it is necessary to separate effects that may be mediated via cell-cell contact

Endothelial-Smooth Muscle Cell Interactions during Atherosclerosis

“…With respect to lysosomal CE hydrolysis, we observed decreased ACEH activity in smooth muscle cells co-cultured with endo thelial cells as compared to smooth muscle cells cultured alone (table V). These results are supported, in part, by the findings of Davies et al [57] who studied the catabolism of labeled LDL in smooth muscle cells co cultured with endothelial cells grown on mi crocarrier spheres. Their results suggest that the presence of endothelial cells enhances the uptake of LDL by co-cultured smooth muscle cells but inhibits LDL degradation.…”

“…Their results suggest that the presence of endothelial cells enhances the uptake of LDL by co-cultured smooth muscle cells but inhibits LDL degradation. Paradoxically, they also reported that endo thelial cell-derived conditioned medium (ECDM) had an inhibitory effect on LDL binding, internalization, and degradation in co-cultured smooth muscle cells [57], In our experiments, we were unable to demonstrate an effect with ECDM on cholesterol esterifi cation or CE hydrolysis (table V, VI).…”

Antiplatelet properties of protein S-nitrosothiols derived from nitric oxide and endothelium-derived relaxing factor.

“…21 Endothelial cells on beads (ECBs) were exposed to 30 /xM acetylsalicylic acid for 30 minutes, washed three times, and resuspended in PBS. The ECBs were placed in the thiol-containing solutions and stimulated to secrete EDRF by exposure to shear force as previously described.…”

Acetylated lipoproteins impair erythroid growth factor release from endothelial cells.

“…Human low density lipoproteins (LDL; density, 1.019-1.063) and very low density lipoproteins (VLDL; density, 0.94-1.006) were isolated by heparin-manganese precipitation from recovered plasma (American Red Cross, Needham, MA) as described previously (16), followed by assessment of purity by double radial immunodiffusion. The amino groups on the LDL were acetylated by reaction with acetic anhydride following the method of Fraenkel-Conrat (17), and the changed electrophoretic mobility of the AcLDL was verified on agarose gels (18).…”