Vascular wall growth control: the role of the endothelium

In vitro reendothelialization. Microfilament bundle reorganization in migrating porcine endothelial cells

An experimentally induced wound made in a confluent monolayer culture of porcine thoracic aortic endothelial cells (ECs) was studied 22 hours after wounding using 7-nitrobenz-2-oxa-1,3-diazole (NBD) phallacidin and immunofluorescence microscopy to localize actin and myosin containing microfilament (MF) bundles. ECs extending from the wound edge back toward the confluent monolayer showed a specific change in cell shape and in MF bundle distribution and orientation, which correlated with the cell migration behavior observed using time-lapse cinemicrophotography. The migrating ECs in the first zone, the leading zone, were polygonal to partially elongated in shape, and contained distinct central MF bundles oriented both parallel and perpendicular to the wound edge. The second zone, the elongated zone, was characterized by elongated cells with central MF bundles oriented parallel to the direction of migration. A third zone, the transitional zone, showed nonmigrating polygonal ECs containing prominent central and dense peripheral bands (DPB) of MF bundles. The central MF bundles were oriented randomly with respect to the wound edge. The MF bundles of the confluent resting monolayer were both centrally and peripherally located with the latter being more prominent. The results indicate that the reorientation of central MF bundles and reduction in the peripheral MF bundles are probably important in the reorganization of the cytoskeletal system during the conversion of stationary cells to migrating cells.

In vitro and in vivo effects of endothelial cell-derived growth factor

Endothelial cells in culture produce a growth factor with an apparent molecular weight of 10,000 to 30,000 daltons. This material, the endothelial cell-derived growth factor ( ECDGF ), can replace the requirement of 3T3 and smooth muscle cells for exogenous mitogens. ECDGF , added to plasma-derived serum, a platelet deficient preparation of plasma, supports growth of these cells to confluency. Lyophilized preparations of the ECDGF stimulate migration of smooth muscle cells into an in vitro wound. The same material induces an angiogenic response when implanted on the chick chorioallantoic membrane. Thus two requirements of an angiogenic response, migration and proliferation, are supplied by endothelial cell products.

Social instability and coronary artery atherosclerosis in cynomolgus monkeys

Epidemiologic research has increasingly implicated psychological factors in the emergence of atherosclerotic coronary heart disease in human beings. The study of behavioral influences on atherogenesis in man, however, is impeded by the difficulty of assessing coronary artery atherosclerosis in asymptomatic individuals and by the fact that significant arterial lesions typically develop only over relatively protracted intervals. Consequently, we have recently attempted development of an appropriate animal model for examining the atherogenic effects of psychosocial variables. In the first of two investigations, an experimental stressor--involving repeated reorganization of socially housed groups of adult, male cynomolgus monkeys (Macaca fascicularis) fed a moderately atherogenic diet--resulted in increased coronary artery atherosclerosis relative to control animals, though only among monkeys which retained dominant social status over the 22 months of the study. In the second investigation, which employed the same experimental procedures among monkeys fed a low cholesterol/low saturated fat diet, periodic social group reorganization similarly led to development of greater atherosclerosis in the coronary arteries. In neither experiment were psychosocial influences on coronary atherogenesis attributable to the concomitant effects of other physiologic variables commonly associated with atherosclerosis (e.g., serum lipids, blood pressure).

Factors influencing the expression of stress fibers in vascular endothelial cells in situ

The organization of actin and myosin in vascular endothelial cells in situ was studied by immunofluorescence microscopy. Examination of perfusion-fixed, whole mounts of normal mouse and rat descending thoracic aorta revealed the presence of axially oriented stress fibers containing both actin and myosin within the endothelial cells. In both species, the proportion of cells containing stress fibers varied from region to region within the same vessel. Some endothelial cells in mouse mesenteric vein and in rat inferior vena cava also contained stress fibers. Quantitative studies of the proportion of endothelial cells containing stress fibers in the descending thoracic aorta of age-matched normotensive and spontaneously hypertensive rats revealed significant differences. When animals of the same sex of the two strains were compared, the proportion was approximately two times greater in the spontaneously hypertensive rats. The proportion of endothelial cells containing stress fibers was about two times greater in males than in females of both strains. These observations suggest that multiple factors, including anatomical, sex, and hemodynamic differences, influence the organization of the endothelial cell cytoskeleton in situ.

Endothelial regeneration in hypertensive and genetically hypercholesterolemic rats

Endothelial regeneration after a narrow, superficial aortic injury was studied in rats with chronic Goldblatt hypertension, genetic hypercholesterolemia, or a combination of hypertension and genetic hypercholesterolemia. In all groups, endothelial continuity was restored within 24 to 36 hours by a combination of endothelial migration and proliferation. A line of increased endothelial density covering the previous wound was seen through 16 weeks after injury. Intimal thickening after injury did not occur in any of the groups. These results indicate that hypertension and hypercholesterolemia neither delay endothelial regeneration nor cause intimal thickening after a small injury in the rat.

Dialyzable factor in human serum of platelet origin stimulates endothelial cell replication and growth

Porcine aortic endothelial cells were isolated and maintained in Dulbecco's modified Eagle's medium (DME medium)/10% citrate-treated human plasma. They were stimulated by DME medium/10% human serum to grow from a density of 10,100 +/- 500 per well to a final density of 83,000 +/- 1,800 per well over a 9-day period. On the other hand these cells grew poorly (11% increase) in DME medium/10% human platelet-poor plasma prepared without chelating agents and containing platelet factor 4 at 18 ng/ml by radioimmunoassay. Dialysis of the human serum (M(r) cutoff, 3,500) eliminated all the stimulatory activity. The activity recovered from the dialysate stimulated growth when added to endothelial cultures in conjunction with either dialyzed serum or platelet-poor plasma alone. The dialyzable factor could be obtained directly from platelets; both acetic acid extracts and boiled NaCl extracts stimulated porcine aortic endothelial cell replication. Gel filtration chromatography on Sephadex G-15 showed that the endothelial growth factor had a molecular weight of 700. Partially purified material induced a concentration-dependent stimulation of porcine aortic endothelial cell replication in the presence of DME medium alone; however, simultaneous incubation with platelet-poor plasma resulted in a much greater response. Fibroblast growth factor isolated from bovine brain was found to be mitogenic only in the presence of nondialyzed serum or of the dialyzable factor together with plasma. In the absence of this serum factor, fibroblast growth factor had no effect. We conclude that human serum contains a potent endothelial cell mitogen of platelet origin. Human plasma that is devoid of platelet content does not stimulate endothelial cell growth. This growth factor may be an important stimulant of the endothelial cell response to vascular wall injury.

Glucose inhibits replication of cultured human endothelial cells

Diabetes is an important risk factor for atherosclerosis but the mechanism of the risk is unknown. As endothelial injury is considered to be an early event in the development of atherosclerosis, the effect of glucose on endothelial cell replication was studied. Concentrations of glucose of 11.2, 16.8 and 22.4 mmol/l inhibited DNA synthesis in cultured human umbilical venous endothelial cells by 8.1 +/- 10.8, 24.3 +/- 8.8 and 30.9 +/- 7.4%, respectively. Glucose also inhibited the proliferative response of endothelial cells to experimental wounds in the cell layer. Sorbitol (22.4 mmol/l) inhibited endothelial cell DNA synthesis by 50 +/- 13.6%, but mannitol (22.4 mmol/l) inhibited DNA synthesis by only 3 +/- 24.3%. It is suggested that in diabetic subjects, high blood glucose levels may cause endothelial injury, or inhibit its repair, and hence allow the exposure of the arterial media to plasma and its constituents.

Selective arterial medial injury fails to produce intimal hyperplasia in experimental animals

The hypothesis was tested, in rats and rabbits, that selective medial injury may lead to arterial intimal hyperplasia. Lesions were produced by passage of a micro-suture through the arterial wall without penetration to the lumen, or controls in which the suture did penetrate. Vessels were examined histologically at intervals up to 2 weeks after suturing. Only vessels with penetrating sutures developed intimal hyperplasia, suggesting that medial injury alone is insufficient for the production of arteriosclerosis.