cytochalasin-b and Arteriosclerosis

Cultured human umbilical vein endothelial cells (EC) exposed to atherogenic low-density lipoprotein (LDL) levels for protracted periods demonstrated heightened endocytosis. Confluent EC were incubated with LDL 90 to 240 mg/dl cholesterol for 1 to 4 days and endocytosis was measured by 14C-sucrose uptake. Control EC and cells incubated with 90 mg/dl LDL cholesterol showed similar uptakes of 14C-sucrose during all measured time periods. In contrast, EC exposed to 240 mg/dl LDL cholesterol showed an increase in endocytosis beginning at 2 days, whereas 160 mg/dl LDL cholesterol promoted increased uptake by 4 days. The endocytotic activity of LDL-perturbed EC is reduced to levels seen in control cells by cytochalasin B, an actin polymerization inhibitor. This finding suggests a modulatory role for the cytoskeleton in endocytosis changes. Examination of LDL-perturbed EC cytoskeleton reveals structural remodeling resulting in a marked increase in stress fibers. Cytochalasin B exposure causes a loss of stress fibers with the formation of globular filamental aggregates. Such LDL-induced cellular functional changes may contribute mechanistically to endothelial dysfunction, which is widely held to be a major contributing factor in the pathogenesis of atherosclerosis.

Topics: Arteriosclerosis; Cells, Cultured; Cytochalasin B; Cytoskeleton; Endocytosis; Endothelium, Vascular; Humans; Lipoproteins, LDL; Osmolar Concentration; Thymidine

Although on the average aortic endothelium is a highly stable tissue, available data indicate that there are areas of high, spontaneous, focal cell turnover. This may be significant since the response to experimental endothelial denudation includes thrombosis and smooth muscle proliferation, both components of atherosclerosis lesion formation. Thus questions about mechanisms of endothelial injury and about the role of the repair process in maintenance of endothelial integrity are likely to be important in attempting to understand the pathogenesis of atherosclerosis. Our approach is to ask what factors control endothelial regeneration. Studies include both in vitro and in vivo data. Regeneration in vivo is strongly dependent on the geometry of the vessel; recovery is much more rapid along the vessel axis. This appears to explain the localization of smooth muscle lesions following mechanical removal of the endothelium, since rapidly recovered areas do not develop smooth muscle proliferation. In vitro, regeneration is independent of a requirement for growth factors, implying that the signal for this process is intrinsic to the monolayer. Cytochalasin B inhibits both movement and replication, implying that movement may be required for transition from G0 to G1. Finally, we have discovered that cultured endothelial cells themselves produce a growth factor. This is of potential importance for interactions between smooth muscle cells and endothelial cells in the vascular response to injury.

Topics: Animals; Aorta; Arteriosclerosis; Cell Movement; Cells, Cultured; Cytochalasin B; Endothelium; Microscopy, Electron, Scanning; Muscle, Smooth, Vascular; Rats; Regeneration; Wound Healing