Direct actions of androgen, estrogen and anti-Müllerian hormone on primate secondary follicle development in the absence of FSH in vitro

Abstract

STUDY QUESTION: What are effects of androgen, estrogen and anti-Müllerian hormone (AMH), independent of FSH action, on the development and function of primate follicles from the preantral to small antral stage in vitro? SUMMARY ANSWER: Androgen and estrogen, but not AMH, promote follicle survival and growth in vitro, in the absence of FSH. However, their growth-promoting effects are limited to the preantral to early antral stage. WHAT IS KNOWN ALREADY: FSH supports primate preantral follicle development in vitro. Androgen and estrogen augment follicle survival and growth in the presence of FSH during culture. STUDY DESIGN SIZE, DURATION: Nonhuman primate model; randomized, control versus treatment groups. Rhesus macaque (n = 6) secondary follicles (n = 24 per animal per treatment group) were cultured for 5 weeks. PARTICIPANTS/MATERIALS, SETTING, METHODS: Follicles were encapsulated in 0.25% (w/v) alginate and cultured individually in modified alpha minimum essential media with (i) FSH (1 ng/ml; control), (ii) no FSH, (iii) no FSH + estradiol (E2; 100 pg/ml)/dihydrotestosterone (DHT; 50 ng/ml) and (iv) no FSH + AMH (50 ng/ml). In a second experiment, follicles were cultured with (i) FSH (1 ng/ml), (ii) no FSH, (iii) no FSH + E2 (1 ng/ml), (iv) no FSH + DHT (50 ng/ml) and (v) no FSH + E2/DHT. Follicle survival, antrum formation and growth pattern were evaluated. Progesterone (P4), E2 and AMH concentrations in culture media were measured. MAIN RESULTS AND THE ROLE OF CHANCE: In the first experiment, FSH deprivation significantly decreased (P < 0.05) follicle survival rates in the no FSH group (16 ± 5%), compared to CTRL (66 ± 9%). E2/DHT (49 ± 5%), but not AMH (27 ± 8%), restored follicle survival rate to the CTRL level. Similarly, antrum formation rates were higher (P < 0.05) in CTRL (56 ± 6%) and E2/DHT groups (54 ± 14%), compared to no FSH (0 ± 0%) and AMH (11 ± 11%) groups. However, follicle growth rate after antrum formation and follicle diameter at week 5 was reduced (P < 0.05) in the E2/DHT group (405 ± 25 μm), compared to CTRL (522 ± 29 μm). Indeed, the proportion of fastgrow follicles at week 5 was higher in CTRL (29% ± 5), compared to E2/DHT group (10 ± 3%). No fast-grow follicles were observed in no FSH and AMH groups. AMH levels at week 3 remained similar in all groups. However, media concentrations of P4 and E2 at week 5 were lower (P < 0.05, undetectable) in no FSH, E2/DHT and AMH groups, compared to CTRL (P4 = 93 ± 10 ng/ml; E2 = 4 ± 1 ng/ml). In the second experiment, FSH depletion diminished follicle survival rate (66 ± 8% in control versus 45 ± 9% in no FSH, P = 0.034). E2 plus DHT (31.5 ± 11%) or DHT alone (69 ± 9%) restored follicle survival rate to the control (FSH) level as expected. Also, E2 plus DHT or DHT alone improved antrum formation rate. However, in the absence of FSH, E2 plus DHT or DHT alone did not support growth, in terms of follicle diameter, or steroid (P4 or E2) production after the antral stage. LIMITATIONS REASONS FOR CAUTION: This study is limited to in vitro effects of E2, DHT and AMH during the interval from the secondary to small antral stage of macaque follicular development. In addition, the primate follicle pool is heterogeneous and differs between animals; therefore, even though only secondary follicles were selected, follicle growth and developmental outcomes might differ from one animal to another. WIDER IMPLICATIONS OF THE FINDINGS: This study provides novel information on the possible actions of estrogen and androgen during early follicular development in primates. Our results suggest that sequential exposure of preantral follicles to local factors, e.g. E2 and DHT, followed by gonadotropin once the follicle reaches the antral stage, may better mimic primate folliculogenesis in vivo.