Engineering the ovarian cycle using in vitro follicle culture

STUDY QUESTION: Can cultured follicles model the ovarian cycle, including follicular-and luteal-phase hormone synthesis patterns and ovulation? SUMMARY ANSWER: Under gonadotrophin stimulation, murine follicles grown in an encapsulated three-dimensional system ovulate in vitro and murine and human follicle hormone synthesis mimics follicular and luteal phases expected in vivo. WHAT IS KNOWN ALREADY: Studies of the human ovary and follicle function are limited by the availability of human tissue and lack of in vitro models. We developed an encapsulated in vitro follicle growth (eIVFG) culture system, which preserves 3D follicular structure. Thus far, the alginate system has supported the culture of follicles from mice, dog, rhesus macaque, baboon and human. These studies have shown that cultured follicles synthesize steroid hormones similar to those observed during the follicular phase in vivo. STUDY DESIGN, SIZE, DURATION: Cultured murine follicles were treated with human chorionic gonadotrophin (hCG) and epidermal growth factor (EGF) and either assayed for luteinization or removed from alginate beads and assayed for ovulation. Human follicles were also cultured, treated with follicle-stimulating hormone (FSH), hCG and EGF to mimic gonadotrophin changes throughout the ovarian cycle, and culture medium was assayed for hormone production. PARTICIPANTS/MATERIALS, SETTING, METHODS: Murine and human follicles were cultured in alginate hydrogel and hormone production [17 beta-estradiol, progesterone, inhibin A, inhibin B, activin A and anti-Mullerian hormone (AMH)] was quantified in medium by enzyme-linked immuno assay (ELISA). Human ovarian tissue was acquired from females between 6 and 34 years of age with a cancer diagnosis. These participants were undergoing ovarian tissue cryopreservation at National Physicians Cooperative sites as part of the Oncofertility Consortium. MAIN RESULTS AND THE ROLE OF CHANCE: When grown in this system, 96% of mouse follicles ovulated in response to hCG and released meiotically competent eggs. Ovulated follicles recapitulated transcriptional, morphologic and hormone synthesis patterns post-luteinizing hormone (LH/hCG). In addition to rodent follicles, individual human follicles secreted steroid and peptide hormones that mimicked the patterns of serum hormones observed during the menstrual cycle. LIMITATIONS, REASONS FOR CAUTION: This was a descriptive study of an in vitro model of ovulation and the ovarian hormone cycle. The ovulation studies were limited to murine tissue and further studies are needed to optimize conditions using other species. WIDER IMPLICATIONS OF THE FINDINGS: The eIVFG system reliably phenocopies the in vivo ovarian cycle and provides a new tool to study human follicle biology and the influence of cycling female hormones on other tissue systems in vitro.