Modulation of transforming growth factor β receptor levels on microvascular endothelial cells during in vitro angiogenesis

Abstract

Microvascular endothelial cells (RFCs) cultured in two-dimensional (2D) cultures proliferate rapidly and exhibit an undifferentiated phenotype. Addition of transforming growth factor β1 (TGFβ1) increases fibronectin expression and inhibits proliferation. RFCs cultured in three-dimensional (3D) type I collagen gels proliferate slowly and are refractory to the anti- proliferative effects of TGFβ1. TGFβ1 promotes tube formation in 3D cultures. TGFβ1 increases fibronectin expression and urokinase plasminogen activator (uPA) activity and plasminogen activator inhibitor-1 (PAI-1) levels in 3D cultures. Since the TGFβ type I and II receptors have been reported to regulate different activities induced by TGFβ1, we compared the TGFβ receptor profiles on cells in 2D and 3D cultures. RFCs in 3D cultures exhibited a significant loss of cell surface type II receptor compared with cells in 2D cultures. The inhibitory effect of TGFβ1 on proliferation is suppressed in transfected 2D cultures expressing a truncated form of the type II receptor, while its stimulatory effect on fibronectin production is reduced in both 2D and 3D transfected cultures expressing a truncated form of the type I receptor. These data suggest that the type II receptor mediates the antiproliferative effect of TGFβ1 while the type I receptor mediates the matrix response of RFCs to TGFβ1 and demonstrate that changes in the matrix environment can modulate the surface expression of TGFβ receptors, altering the responsiveness of RFCs to TGFβ1.