In vitro effects of angiopoietins and VEGF on hematopoietic and endothelial cells

To investigate the role of TIE-2/angiopoietins (Angs) in postnatal hematopo iesis, we cultured bone marrow cells in the presence of Ang-1 and -2 with o r without VEGF, While either Ang-1 or Ang-2 alone had hematopoietic effects on unseparated bone marrow cells and no effect on proliferation of endothe lial cells, both enhanced the growth of endothelial cells and hematopoietic progenitor cells in the presence of VEGF. FAGS analysis showed that Lin(-) TIE-2(+)Flk-1(+) cells cocultured with OP9 stromal cells gave rise to endot helial and hematopoietic cells in the presence of VEGF and Ang-1, Ang-1 pro moted the adhesion of sorted primary Lin(-)TIE-2(+) cells to fibronectin, a nd this adhesion enhanced proliferation of hematopoietic progenitor cells s ynergistically with stem cell factor (SCF). Our findings suggest that TIE-2 /angiopoietins may act as critical regulators of proliferation of hematopoi etic progenitors and endothelial cells in a synergistic manner. (C) 1999 Ac ademic Press.