Organization of actin cytoskeleton in normal and regenerating arterial endothelial cells.

Abstract

The distribution of actin stress fibers in normal and regenerating (after endothelial denudation by means of a balloon catheter) rabbit aortic endothelial cells has been studied by means of immunofluorescence with human actin autoantibodies on enface endothelial cell preparations. Our results show that: (i) under normal conditions actin is accumulated as a network at the periphery of endothelial cells. Stress fibers are present only in endothelial cells located immediately below intercostal artery branches; (ii) stress fibers develop in endothelial cells early during regeneration and persist after the end of endothelial mitotic and motile activities; and (iii) the orientation of stress fibers within the cytoplasm follows the direction of blood flow, with the exception of stress fibers situated in cells at the edge of the wound, when endothelial cell progression toward the denuded area as well as mitotic activity have ceased. We conclude that stress fibers are an organelle present in endothelial cells in vivo and that they reorganize during endothelial cell adaptation to unfavorable or pathological situations.Endothelial continuity depends on the maintenance of an extremely thin single cell layer. When arterial endothelium is removed by mechanical abrasion, the wound is repaired by endothelial cell replication and movement (1). When the endothelial cell loss is small (few cells in width) repair is accomplished essentially by movement without replication (2). Cell movement results probably from the activity of cytoskeletal and cytocontractile elements (3), among which actin is the most abundant. Cellular actin (4, 5) is organized in the form of G actin, a microfilamentous network, and microfilamentous bundles or stress fibers, which are typical of most adherent cultured cells, including endothelial cells. Stress fibers have been shown to contain actin, myosin, and regulatory proteins (6-9). Little information is presently available on the distribution of stress fibers in vivo (5).We have studied the organization of stress fibers in endothelial cells of rabbit aorta and carotid artery under normal conditions and during regeneration after ballooning-induced endothelial denudation (10). For this purpose, we have developed a technique of immunofluorescent staining with antiactin antibodies (AAAbs) on en face endothelial cell preparations. Our results show that under normal conditions stress fibers are present only in some aortic endothelial cells-namely, those submitted to high shear stress; they become common in regenerating endothelial cells and persist long after motile and mitotic activities have ceased. MATERIALS AND METHODSMale rabbits, -3 kg of body weight, were used for the experiments. The endothelium was removed from the thoracic aorta or the left carotid artery by using the technique originally described by Baumgartner and Studer (10) with minor modifications. Evans blue (4 ml of a 1% solution in 0.9% NaCI) was injected intravenously 20 min prior to sacrifice to label denuded areas (blue areas). Tw...

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