ABSTRACT
Cultured endothelial cells isolated from fenestrated capillaries express many properties characteristic of their in vivo differentiated phenotype, including the formation of a limited number of fenestrae. In this study, we have investigated whether physiological factors that control cell differentiation might regulate the surface density of fenestrae in capillary endothelial cells. We have found that treatment of the cultures with retinoic acid (10μM) induces a more than threefold increase in the surface density of endothelial fenestrae, whereastransforming growth factor β (TGFβ) (2 ng ml−1) causes a sevenfold decrease in the surface density of these structures. These results show that the expression of endothelial fenestrae is susceptible to bidirectional modulation by physiological signals, and suggest that retinoids and TGFβ may participate in the regulation of fenestral density of capillary endothelium in vivo.
Throughout the entire series of experiments reported in this study, the surface density of fenestrae in control cultures was found to be considerably higher than that measured in a previous study (Lombardi et al. 1986). The reasons for this difference are not clear; the cells used in the two groups of experiments were, however, from different frozen stocks of endothelial cells originally derived from the same clonal population (cf. Furie et al. 1984).
