Cell-matrix interactions of microvessel endothelial cells in response to basic fibroblast growth factor.

Abstract

Vertebrate tissues consist of parenchyma and vascular elements all of which are necessary for the specific form and function of these tissues. In a unique process termed angiogenesis, vessels invade forming tissues to provide for proper tissue perfusion. Much is known about the molecular and cellular elements of angiogenesis, however, it is not clear how these elements are coordinated to produce specific microvascular beds. In an effort to answer this question, the effects of basic fibroblast growth factor (bFGF) on human microvessel endothelial cell (HMVEC) interactions with collagen I were examined. HMVEC migration on collagen I was chosen as the model angiogenic response. Utilizing two distinct migration assays, bFGF either induced migration or had no effect. Examination of HMVEC adhesion with two separate assays revealed that HMVEC adhesion to collagen I was altered by bFGF treatment and depended on the density of HMVEC at the time of treatment. Adhesion of HMVEC with or without bFGF treatment was mediated entirely by β1 integrins as demonstrated with a blocking antibody studies. Experiments were performed to determine the mechanism by which bFGF can alter HMVEC adhesion and focused on low density HMVEC. The reduction in adhesion of low density HMVEC following bFGF treatment correlated with no change in β1 integrin surface expression, delayed cell spreading, altered organization of β1 integrin into substrate contacts, and serine/threonine phosphorylation of the β1 subunit. To evaluate the coordinated effects of bFGF on angiogenesis, an in vitro model simulating a microvascular environment was developed utilizing isolated microvessel fragments from rat adipose tissue cultured in three dimensional collagen I gels. The addition of crude basic fibroblast growth factor to the cultures resulted in the growth of significantly longer microvessels and the expression of an endothelial cell protein, von Willebrand factor. Based on this work, it is apparent that cellular responses to physiological signals during angiogenesis are multifactorial and are sensitive to many coincidental environmental factors such as cell density. The influence of these environmental factors is such as to substantially alter the effects of a signalling factor acting alone.