Thymocyte apoptosis and proliferation modeling during rat thymic involution is influenced by ovarian hormones in a thymocyte subset-specific manner

Abstract

The study was aimed to define the putative role of ovarian hormones in shaping thymocyte apoptosis and proliferation during thymic involution. Thymocytes from young adult and middle-aged rats ovariectomized (Ox) before puberty were examined for apoptosis and proliferation. Apoptosis and proliferation were measured in fresh thymocyte suspensions and in their 18-hour cultures, and fresh thymocyte suspensions, respectively. The thymocyte population and the major thymocyte subsets were analyzed following triple staining using anti-CD4 and anti-CD8 monoclonal antibodies and 7-AAD to label apoptotic or proliferating cells. The frequency of apoptotic cells was lower in thymocyte suspensions and cultures from Ox rats of both ages. This reflected in a diminished frequency of apoptotic cells amongst CD4+CD8+ double positive (DP) and CD4+CD8- single positive (SP), and DP cells in young and middle-aged Ox rats, respectively. Additionally, in thymocyte cultures from Ox rats the frequency of apoptotic cells amongst CD4+CD8- and CD4-CD8+ SP cells decreased with age, but increased within DP and CD4-CD8- double negative (DN) subsets, reaching in the former subset from middle-aged Ox rats higher values than in age-matched controls. The frequency of proliferating cells was also lower in Ox rats than in controls. This reflected the lower frequency of cycling cells amongst CD4+CD8- SP and CD4-CD8+ SP thymocytes in young rats, and DP and CD4-CD8+ SP thymocytes in middle-aged rats. Besides, in both SP and DP thymocyte subsets from Ox rats the frequency of proliferating cells declined with age. In conclusion, thymocyte apoptosis and proliferation exhibit ovarian hormone-dependent thymocyte subset specific alterations during thymic involution.

Cilj istraživanja je bio da se definiše značaj hormona ovarijuma za razvoj promena u apoptozi i proliferaciji timocita tokom involucije timusa. U tom cilju apoptoza i proliferacija timocita ispitivana je kod prepubertetno ovariektomisanih (Ox) mladih (uzrasta 2 meseca) i sredovečnih pacova (uzrasta 11 meseci). Apoptoza je određivana u suspenziji sveže izolovanih timocita i nakon njihove 18- časovne kultivacije, a proliferacija u suspenziji sveže izolovanih timocita. Procenat apoptotičnih i proliferišućih ćelija je određivan u celokupnoj populaciji timocita, i unutar glavnih subpopulacija ovih ćelija, koje su razdvojene na osnovu ekspresije CD4/CD8 molekula, metodom protočne fluorocitometrije, korišćenjem 7-aminoaktinomicina D (7-AAD). Procenat ćelija u apoptozi je bio značajno manji u suspenzijama svežih timocita koji su izolovani iz Ox životinja i u njihovim kulturama nego u onim izolovanim iz kontrolnih životinja. Ovaj nalaz je odražavao smanjenu učestalost ćelija u apoptozi u CD4+CD8+ dvostruko pozitivnoj (DP) i CD4+CD8- jednostruko pozitivnoj (JP) subpopulaciji timocita kod mladih i u DP subpopulaciji kod sredovečnih Ox pacova. U kulturama timocita koji su izolovani iz sredovečnih Ox pacova uočeno je smanjenje učestalosti ćelija u apoptozi unutar subpopulacija CD4+CD8- i CD4-CD8+ JP timocita, a povećanje unutar DP i CD4-CD8- dvostruko negativne (DN) subpopulacije ovih ćelija. Učestalost proliferišućih ćelija je takođe bila niža u suspenzijama timocita izolovanih iz Ox pacova nego u onim izolovanim iz kontrolnih životinja. Ovo je odražavalo smanjenu proliferaciju CD4+CD8- i CD4-CD8+ JP timocita kod mladih, a DP i CD4-CD8+ JP timocita kod sredovečnih pacova. Procentualna zastupljenost proliferišućih ćelija u subpopulacijama JP i DP timocita je bila veća kod mladih nego kod sredovečnih Ox pacova. U zaključku, tokom involucije timusa dolazi do promena u apoptozi i proliferaciji timocita koje su specifične za pojedine subpopulacije timocita i zavisne od prisustva hormona ovarijuma.