Effects of TGF-betas and a specific antagonist on apoptosis of immature rat male germ cells in vitro.
Massive apoptosis of pubertal male germ cells is important for the development of functional spermatogenesis in the adult testis. Although the trigger(s) for male germ cell loss at puberty remain undefined, we have hypothesized that transforming growth factor-betas (TGF-betas) play an active role. Here we demonstrate that the three mammalian TGF-beta isoforms, TGF-beta1, TGF-beta2 and TGF-beta3, induce distinct apoptosis of pubertal spermatogonia and spermatocytes in a dose-dependent manner. Induction of male germ cell death by activation of caspase-3 was most pronounced with TGF-beta2 compared to TGF-beta1 and TGF-beta3. Furthermore, we found colocalization of activated caspase-3 with apoptotic protease-activating factor-1 (Apaf-1) in apoptotic germ cells, thus indicating the importance of the intrinsic mitochondrial pathway in TGF-beta-induced apoptosis. The specificity of the TGF-beta effects was proven by addition of recombinant latency-associated peptide against TGF-beta1 (rLAP-TGF-beta1) which completely abolished TGF-beta1-induced and TGF-beta3-induced germ cell apoptosis. Although TGF-beta2-triggered germ cell death also was significantly reduced by rLAP-TGF-beta1, inhibition was not maximal. Our results suggest that the three TGF-beta isoforms induce apoptosis of pubertal male germ cells via the mitochondrial pathway in vitro and are thus likely candidates involved in the excessive first wave of apoptosis of male germ cells during puberty.
Konrad
L
L
Department of Urology, Medical Faculty, 35033 Marburg, Germany. Konrad@med.uni-marburg.de
Keilani
M M
MM
Laible
L
L
Nottelmann
U
U
Hofmann
R
R
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D008297:Male; D009924:Organ Culture Techniques; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000378:metabolism; D013090:Spermatocytes / Q000187:drug effects; D013093:Spermatogonia / Q000187:drug effects; D013737:Testis / Q000166:cytology*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3
D020033:Protein Isoforms; D011994:Recombinant Proteins; C508962:Tgfb1 protein, rat; C509046:Tgfb3 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases