ИСТИНА

Understanding of the cellular and molecular events involved in the formation of blood vessel network is very important for vascularized tissue engineering. In this study, we used a two-dimensional co-culture of human umbilical vein endothelial cells (HUVEC) with human adipose stromal cells (ASC) without exogenous matrix addition to study self-assembled network formation (SNF) by HUVEC. We have found that only co-culture of these cells in direct contact (but not out of contact co-culture in transwell) induced SNF by HUVEC. During this process, expression of urokinase receptor (uPAR) on the surface of co-cultured HUVEC was upregulated. uPAR was distributed mainly diffusely but we also observed spots of uPAR conglomerates. uPAR is essential for SNF, since blocking of uPAR by specific antibodies abrogated this process. Blocking of integrin subunit alpha v by antibodies decrease SNF in this model suggesting possible participation of uPA-uPAR system in this process through interaction with vitronectin and its integrin receptors. Importantly, HUVEC start network formation after 14 hours of co-culture with ASC that coincides with synthesis and secretion of extracellular matrix (ECM) by co-culturing cells. However, HUVEC seeded on decellularized ECM produced by co-cultured or monocultured cells did not form SNF in contrast to HUVEC seeded on Matrigel, which readily start formation of the tubular network after 4 hours. We have found that ASC produce fibronectin (FN) more intensively than HUVEC, and after 24 hours of co-culturing fibronectin cords are clearly visible, which creates the basis for ECM assembly through binding to other ECM proteins. After 48 hours of co-culture ASC were found inside formed ECM and HUVEC were placed on the upper surface of ECM. We also found that endocytosis machinery is important for SNF by HUVEC in presence of ASC because addition of the LRP antagonist RAP, inhibitor of intracellular protein transport - monensine, or inhibitor of microtubule polymerization - colhicine inhibited this process. Thus, our results suggest that ASC provide specific environment for migration of HUVEC and endothelial SNF, which includes ECM proteins, alpha v integrin, uPA-uPAR-LRP system. We found that direct contacts between ASC and HUVEC are necessary to maintain endothelial network.