title: Rat testicular germ cells and Sertoli cells release different types of bioactive transforming growth factor beta in vitro.
abstract: Several in vivo studies have reported the presence of immunoreactive transforming growth factor-beta's (TGF-beta's) in testicular cells at defined stages of their differentiation. The most pronounced changes in TGF-beta1 and TGF-beta2 immunoreactivity occurred during spermatogenesis. In the present study we have investigated whether germ cells and Sertoli cells are able to secrete bioactive TGF-beta's in vitro, using the CCl64 mink lung epithelial cell line as bioassay for the measurement of TGF-beta. In cellular lysates, TGF-beta bioactivity was only observed following heat-treatment, indicating that within these cells TGF-beta is present in a latent form. To our surprise, active TGF-beta could be detected in the culture supernatant of germ cells and Sertoli cells without prior heat-treatment. This suggests that these cells not only produce and release TGF-beta in a latent form, but that they also release a factor which can convert latent TGF-beta into its active form. Following heat-activation of these culture supernatant's, total TGF-beta bioactivity increased 6- to 9-fold. Spermatocytes are the cell type that releases most bioactive TGF-beta during a 24 h culture period, although round and elongated spermatids and Sertoli cells also secrete significant amounts of TGF-beta. The biological activity of TGF-beta could be inhibited by neutralizing antibodies against TGF-beta1 (spermatocytes and round spermatids) and TGF-beta2 (round and elongating spermatids). TGF-beta activity in the Sertoli cell culture supernatant was inhibited slightly by either the TGF-beta1 and TGF-beta2 neutralizing antibody. These in vitro data suggest that germ cells and Sertoli cells release latent TGF-beta's. Following secretion, the TGF-beta's are converted to a biological active form that can interact with specific TGF-beta receptors. These results strengthen the hypothesis that TGF-beta's may play a physiological role in germ cell proliferation/differentiation and Sertoli cell function.
authors.affiliation: Department of Biochemistry and Cell Biology Faculty of Veterinary Medicine, Utrecht University, POBox 80,176, 3508 TD Utrecht, The Netherlands. haagmans@viro.fgg.eur.nl
authors.forename: Bart L
authors.initials: BL
authors.lastname: Haagmans
authors.forename: Jos W
authors.initials: JW
authors.lastname: Hoogerbrugge
authors.forename: Axel P N
authors.initials: AP
authors.lastname: Themmen
authors.forename: Katja J
authors.initials: KJ
authors.lastname: Teerds
mesh_terms: D000818:Animals; D001681:Biological Assay; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D008168:Lung; D008297:Male; D008907:Mink; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D017208:Rats, Wistar; D018125:Receptors, Transforming Growth Factor beta / Q000502:physiology; D012708:Sertoli Cells / Q000378:metabolism*; D013087:Spermatids / Q000378:metabolism; D013090:Spermatocytes / Q000378:metabolism; D013094:Spermatozoa / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2
chemical_list: D017077:Culture Media, Conditioned; D011498:Protein Precursors; D018125:Receptors, Transforming Growth Factor beta; C508962:Tgfb1 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2