Expression of Bcl-2 and Bax in rhesus monkey testis during germ cell apoptosis induced by testosterone undecanoate

Apoptosis occurs spontaneously during spermatogenesis and can be induced by androgen withdrawal. However, the molecular events governing apoptosis have not been characterized. To study the molecular mechanism of apoptosis induced by a high dose of testosterone undecanoate (TU), the authors examined the temporal changes in proapoptotic Bax and antiapoptotic Bcl-2 in TU-treated monkey testes. Apoptotic cells were identified in tissue sections by in situ end labeling of fragmented DNA. The results showed that a great deal of the apoptotic cells occurred in the testes on day 30 after TU injection and that the dominant apoptotic germ cells are spermatocytes and spermatids. The expression of Bcl-2 and Bax was assessed by immunohistochemical method and Western blot. As compared with that of normal testes, the levels of Bcl-2 protein increased significantly from 7 to day 14 while that of Bax protein was almost unchanged in the testes from day 7 up to day 60 after TU treatment. Bcl-2 was localized to the spermatids in the normal testes and temporarily distributed in both the cytoplasm and nucleus of those cell types susceptible to TU-induced apoptosis on day 14 after TU injection. Therefore, it is suggested that Bax may not play a role in initiating germ cell apoptosis induced by TU injection and that the evaluation in Bcl-2 expression may represent a survival mechanism for the remaining germ cell.