Possible mechanisms of type I collagen-induced vascular tube formation

We investigated the effect of type I collagen on endothelial behaviour following its contact with the apical versus basal surface of cultured human endothelial cells. When endothelial cells were plated onto type I collagen they attached via their basal surface and formed a confluent monolayer. However, when type I collagen (100 micrograms/ml) was added directly to the growth medium, so that it made contact with the apical surface of endothelial cells, it induced rapid capillary-like tube formation. Possible mechanisms were assessed using a) polyclonal (anti-VLA-2) and monoclonal (AK7) antibodies to different epitopes on the alpha 2 beta 1 integrin receptor for collagen and b) drugs (chlorpromazine and trifluoperazine) that inhibit protein kinase C activity. Both anti-VLA-2 and AK7 (1-50 micrograms/ml) showed a dose-dependent inhibition of tube formation and cell attachment. At 50 micrograms/ml, anti-VLA-2 completely inhibited tube formation whereas AK7 caused only partial inhibition (less than 50%). By contrast, AK7 was a more potent inhibitor of cell attachment than anti-VLA-2. Both chlorpromazine and trifluoperazine prevented tube formation.

1) The alpha 2 beta 1 integrin receptor plays a role in both endothelial cell attachment and the induction of tube formation by type I collagen. 2) Protein kinase C may be involved in collagen-induced tube formation.