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J. Cell Biol.,
Volume 143, Number 5, November 30, 1998 1341-1352
Cell Biology Laboratory, Department of Gynecology and Obstetrics, University of Göttingen Medical School, 37075 Göttingen,
Germany
Single endothelial cells (EC) seeded in suspension culture rapidly undergo apoptosis. Addition of
survival factors, such as VEGF and FGF-2, does not
prevent apoptosis of suspended EC. However, when
cells are allowed to establish cell-cell contacts, they become responsive to the activities of survival factors.
These observations have led to the development of a
three-dimensional spheroid model of EC differentiation. EC spheroids remodel over time to establish a differentiated surface layer of EC and a center of unorganized EC that subsequently undergo apoptosis. Surface
EC become quiescent, establish firm cell-cell contacts,
and can be induced to express differentiation antigens
(e.g., induction of CD34 expression by VEGF). In contrast, the unorganized center spheroid cells undergo apoptosis if they are not rescued by survival factors.
The responsiveness to the survival factor activities of
VEGF and FGF-2 was not dependent on cell shape
changes since it was retained after cytochalasin D treatment. Taken together, these findings characterize survival factor requirements of unorganized EC and indicate that polarized surface EC differentiate to become
independent of exogenous survival factors. Furthermore, they demonstrate that spheroid cell culture systems are useful not just for the study of tumor cells and
embryonic stem cells but also for the analysis of differentiated functions of nontransformed cells.
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