Endothelial cell-mediated type I collagen gel contraction is regulated by hemin

The contraction of three-dimensional type I collagen gels is regarded as a model of contraction during wound healing and tissue remodeling. Because su ch a process could contribute to vessel narrowing, we hypothesized that end othelial cells may be able to mediate gel contraction. To demonstrate this, type I collagen was extracted from rat tail tendon and used to prepare col lagen gels. Bovine arterial endothelial cells (BAECs) or human pulmonary ar tery endothelial cells (HPAECs) were then plated on the top of the gels in serum-free Ham's F-12 medium or 2% fetal calf serum-endothelium growth medi um-2 (FCS-EGM(2)), respectively. After 48 hours of attachment, gels were re leased and floated in 0.2% FCS-Ham's F-12 medium (BAECs) or 2% FCS-EGM(2) ( HPAECs). Gel size was measured with an image analyzer daily for 5 consecuti ve days. Gels were then digested with collagenase to quantify DNA and hydro xyproline. BAECs contracted the gels in a time-dependent manner over the 5 days. Contraction was dependent on cell density (gel size was 100% of initi al size after 5 days with no cells vs 66.4% +/- 0.5% with 0.9 x 10(4) cells /cm(2) and 22.1% +/- 0.3% with 7.5 x 10(4) cells/cm(2)) and was inversely r elated to collagen concentration (gel size was 22.3% +/- 0.05%, 46.4% +/- 0 .9%, 72.3% +/- 0.4%, and 87.4% +/- 0.3% of initial size for gels prepared w ith 0.5 mg/mL, 0.75 mg/mL, 1 mg/mL, and 2 mg/mL of collagen, respectively). Hemin (a precursor for CO) and cytochalasin D inhibited collagen gel contr action mediated by both bovine and human endothelial cells without changing cell number or hydroxyproline content. In contrast, prostaglandin E-2, an inhibitor, and transforming growth factor-beta 1, a stimulator of fibroblas t-mediated gel contraction, had no effect on endothelial cell-mediated cont raction. These findings demonstrate that endothelial cells are able to cont ract native type I collagen gels and that this process can be modulated by exogenous mediators. Such a capability may cause remodeling of subjacent ma trix of endothelial cells and may contribute to vessel narrowing.