A microcarrier-based cocultivation system for the investigation of factors and cells involved in angiogenesis in three-dimensional fibrin matrices in vitro.

Angiogenesis in situ includes coordinated interactions of various microvascular cell types, i.e., endothelial cells, pericytes and perivascular fibroblasts. To study the cellular interactions of microvascular cells in vitro, we have developed a microcarrier-based cocultivation system. The technical details of this method include seeding of endothelial cells on unstained cytodex-3 microcarriers and seeding of pericytes, fibroblasts or vascular smooth muscle cells on microcarriers which have been labeled by trypan blue staining. A mixture of both unstained and trypan blue-stained microcarriers was subsequently embedded in a three-dimensional fibrin clot. The growth characteristics of each cell type could be conveniently observed since the majority of cells left their supporting microcarriers in a horizontal direction to migrate into the transparent fibrin matrix. As differently stained microcarriers were randomly arranged in the fibrin matrix, the characteristic patterns of the microcarriers allowed location of particular points of interest at different developmental stages, facilitating the observation of cellular growth over the course of time. One further advantage of this microcarrier-based system is the possibility of reliably quantifying capillary growth by determination of average numbers of capillary-like formations per microcarrier. Thus, this model allows convenient evaluation of the effects of non-endothelial cells on angiogenesis in vitro. By using this coculture system, we demonstrate that endothelial capillary-like structures in vitro do not become stabilized by contacting vascular smooth muscle cells or pericytes during the initial stages of capillary formation.