AUTOCRINE ROLE OF INSULIN-LIKE GROWTH-FACTOR-II SECRETION BY THE RAT CHOROID-PLEXUS

Insulin-like growth factor II (IGF-II) is expressed and secreted by th e choroid plexus and has been suggested to act as a trophic factor in the adult mammalian central nervous system. The aim of the present stu dy was to investigate whether IGF-II has an autocrine role in the chor oid plexus. Using in situ hybridization we demonstrate that IGF-II is primarily expressed in the epithelium of adult rat choroid plexus. Con ditioned medium from primary cultures of purified rat choroid plexus e pithelial cells, intact choroid plexus tissue, as well as rat CSF, dis placed IGF-II binding to a 23 HMM melanoma cell line in an IGF-II radi oreceptor assay. The presence of IGF-II and IGF binding protein-2 in c onditioned medium was shown by Western immunoblot. The mitotic activit y in choroid plexus epithelial cell cultures was quantified by immunoh istochemical staining of bromodeoxyuridine incorporated into cell nucl ei. A monoclonal antibody towards IGF-II inhibited cell division by 35 %, while IGF-I increased the number of stained nuclei by 75%. Basic fi broblast growth factor stimulated cell division at low concentrations, but had no effect at high concentrations. Growth hormone had no effec t. We conclude that IGF-II in the choroid plexus could have an autocri ne role in the regulation of choroid plexus epithelial cell growth.