The vascular character of ovarian follicular granulosa cells: phenotypic and functional evidence for an endothelial-like cell population.

Ovarian follicular granulosa cells express temporally and spatially distinct functions throughout the follicle cycle. During the entire cycle, granulosa cells exhibit an unusually broad range of activities including the secretion of steroid hormones, enzymes, growth factors and cytokines. To date, the identity(ies) of these cells (lineage/cell type) remains unknown. We demonstrate expression of the Tie, Tek, cKit, Flt-1, CD-31 and vWF proteins and the ability to rapidly internalize acetylated low density lipoprotein among mural and cumulus subpopulations of human and murine follicular granulosa cells. In addition, we provide evidence that human and murine granulosa cells can engage in tube-forming activity in vitro. To the best of our knowledge, the six phenotypic and two functional markers examined during this study, as a group, are associated only with endothelial or endothelial-like cells. In total, the findings suggest that some granulosa cells may have the potential to actively participate in the vascularization of the corpus luteum, by way of an inherent capacity which is likely to be a characteristic of their unique identity and lineage. This inherent capacity of granulosa cells to behave and respond, at least to some extent, like endothelial cells may be of possible importance in the aetiology of certain follicular pathologies.