STIMULATORY EFFECTS OF INSULIN AND INSULIN-LIKE GROWTH FACTOR-I ON MIGRATION AND TUBE FORMATION BY VASCULAR ENDOTHELIAL-CELLS

The effects of insulin and insulin-like growth factor I (IGF-I) on migration, proliferation and tube-forming activity of endothelial cells were investigated, by using bovine carotid artery endothelial cells. Migration was assayed by a filter membrane technique and tube formation was assayed by a quantitative angiogenesis in vitro model which we have recently developed. In this model, endothelial cells are cultured between two layers of type I collagen gel and become organized into tube-like structures which mimic capillaries in vivo ultrastructurally. Insulin (50-1000-mu-units/ml) and IGF-I (10-200 ng/ml) significantly stimulated migration of endothelial cells in a dose-dependent manner with a maximal stimulation of 3.0-fold at 1000-mu-units/ml for insulin and 3.8-fold at 200 ng/ml for IGF-I (P < 0.01). Insulin at concentrations up to 1000-mu-units/ml and IGF-I up to 100 ng/ml did not affect proliferation of endothelial cells. When insulin or IGF-I was added in culture medium on collagen gels, tube-forming activity of endothelial cells was markedly stimulated. The specific lengths of tubes significantly increased with the increase in insulin concentration from 25 to 100-mu-units/ml (P < 0.01). At 100-mu-units/ml, the stimulation was 1.77-fold (P < 0.01). IGF-I (1-100 ng/ml) also stimulated the elongation of tubes dose-dependently with a maximal stimulation of 1.96-fold at 100 ng/ml (P < 0.01). Thus, insulin and IGF-I at pathophysiological concentrations stimulate migration and tube-forming activity of endothelial cells, suggesting that these polypeptides may stimulate repair of endothelial injury in cases such as atherosclerosis and may act as a stimulator of angiogenesis.