Endocrine Abstracts

The activin-binding protein follistatin is produced by folliculostellate (FS) cells of the anterior pituitary. FS cells make numerous contacts with the classical endocrine cells of the anterior pituitary including gonadotrophs. Follistatin released from the FS cells could therefore play a role in the regulation of gonadotrophin secretion, in particular of FSH. We have previously shown by confocal microscopy (1) that annexin 1, which is also produced by FS cells, is secreted from FS cell lines (TtT/GF and TPitF1) at specific patches on the processes of the cells, and that these patches co-localize immunoreactive ABCA1; also, by western blotting, that the secretion of annexin 1 can be prevented by the ABC-transporter inhibitor glyburide.
To investigate the release of FS cell follistatin, TtT/GF and TPitF1 cells were cultured under standard conditions until the cells developed their characteristic processes. The cells were then either very lightly fixed and immunostained in order to reveal follistatin, ABCA1, and annexin 1 associated with the cell surface, or fixed more strongly in order to permeabilise the cells and reveal intracellular immunoreactivity. Confocal microscopy was used to assess the co-localisation of the three proteins. Within FS cells all three proteins were diffusely distributed in the cytoplasm. At the surface, follistatin and ABCA1 were colocalized in, and restricted to the patches of surface membrane on the processes of the cells where annexin 1 was also located.
These data strongly suggest that follistatin is released from FS cells at specific points on their surface by an ABCA1 transporter which also externalises annexin 1.
1. Christian, H.C. et al. Endocrine Abstracts 2002, 4: OC27