Cytoskeletal changes induced by excess extracellular matrix impair endothelial cell replication

Thickening of basement membranes is an early and characteristic feature of diabetic vessels, but its consequences on the properties of vascular cells remain undefined. We investigated whether and how excess extracellular matrix (ECM) alters the replication of vascular endothelial cells in vitro. To test the effects of endogenous excess matrix, human umbilical vein endothelial cells (HUVEC) were plated on ECM produced under culture conditions (high ambient glucose) that increase ECM synthesis. Four of six HUVEC isolates plated on such ECM yielded a lower cell number (68 +/- 18 %) than cells plated on control ECM. Growth inhibition was observed in HUVEC cultured on elevated concentrations (10 and 50 mu g/ml) of exogenous fibronectin, when compared with HUVEC plated on tissue culture plastic or 0.25, 1.0, and 5.0 mu g/ml fibronectin; the decreased replication was attributable to delayed transit through the G(1) phase of the cell cycle. HUVEC grown on both 1 and 10 mu g/ml fibronectin exhibited a modest upregulation of the fibronectin-specific integrin receptor alpha 5 beta 1, and increased attachment to fibronectin substratum. However, unique to the HUVEC plated on growth-inhibitory concentrations of fibronectin was a redistribution in situ of integrins and vinculin to form more numerous focal adhesions, and an increased polymerization of cytoskeletal actin to form stress fibers. Concentrations (0.01 mu g/ml) of cytochalasin D intended to prevent excess actin polymerization prevented the growth inhibition. Thus, excess ECM hampers endothelial cell replication in vitro through increased cell-ECM adhesion and attendant cytoskeletal rearrangements. These phenotypic changes provide probes to test whether cell-ECM interactions are altered in diabetic vessels in a direction that may compromise orderly endothelial cell renewal and its antithrombogenic function.