Folliculostellate cell

A Folliculostellate (FS) cell is a type of non-endocrine cell found in the anterior lobe of the pituitary gland.

Rinehart and Farquhar first discovered FS cells through electron microscopy of the anterior pituitary gland. Vila-Porcile named these non-endocrine cells "folliculo-stellate" cells in 1972 due to their stellate (star) shape, and their location lining the lumen of small follicules in the anterior pituitary. Unlike the majority of cells in the anterior pituitary, they are non-endocrine and agranular. They have long cytoplasmic processes which interlock to form a mesh, within which the endocrine cells reside. They typically have a large number of microvilli on their apical side, and contain lysosomes, suggesting phagocytotic activity.Gap junctions can be seen between the FS cells and the adjacent endocrine cells when viewed under an electron microscope.

Using pituitary slices, studies have been conducted that have illustrated that FS cells are arranged into 3D networks which are able to communicate intracellularly through gap junction-mediated calcium wave propagation. Experiments using two main FS cell lines (TtT/GF and Tpit/F1), have hugely improved our knowledge of the functional relevance of these cells- it has been shown that FS cells play a part in three areas of pituitary use: /paracrine control of anterior pituitary cell function though the use of cytokines and growth factors, intrapituitary communication among various cell types, and modulation of inflammatory response feedback.

FS cells have similar properties to dendritic cells and macrophages, implying a phagocytic role. FS cells having a main role in moderating the neuro-immune/endocrine regulation of inflammation is backed up by data in conjunction with depicting C3a, C5a receptors (which are the main factors of the innate immune system, secreting IL-6 and MIF (inflammatory cytokines), and controlling the release of these cytokines via anti-inflammatory molecules. Experiments have been carried out to assess the protein markers they express, in order to determine their cell-type and thus exact function in the pituitary. The first marker protein discovered in FS cells was S-100b, which is a calcium-binding protein expressed by glial cells. Some populations of FS cells have also been found to express different cell markers, including GFAP (glial fibrillary acidic protein), cytokeratin, vimentin and fibronectin. S-100 protein and GFAP expression seem to be strongest in early, newly-formed FS cells, thus could be important in early FS cell development. GFAP expression implies these cells could be of a neuroectodermal origin, whereas keratin-positive FS cells express epithelial-like characteristics. The study of fibronectin expression in these cells suggests that FS cells may help regulate pituitary function, by interacting with hormone secreting cells through fibronectin. Furthermore, as FS cells express vimentin, an intermediate filament protein marker, this supports the theory that FS cells may be derived from glial neuroectodermic cells.

...
Wikipedia