Animal age, weight and estrus cycle stage impact the quality of in vitro grown follicles

BACKGROUND Ovarian tissue cryopreservation is an emerging fertility preservation option, and culturing follicles isolated from this tissue to obtain mature gametes may ultimately be the best solution for patients for whom transplantation is contraindicated. It is unclear, however, how patient-specific variables (including age, weight and menstrual cycle stage) impact follicle growth and quality during three-dimensional culture. METHODS We used a mouse model to systematically determine how these variables impact in vitro follicle growth. We characterized metabolic and hormonal profiles of mice at specific ages, weights and cycle stages and secondary follicles from these cohorts were isolated and cultured. We then assessed follicle survival, growth and function, as well as meiotic competence and spindle morphology of the resulting oocytes. RESULTS We found that older mice and mice with increased body weight had higher serum cholesterol, abnormal glucose tolerance and lower levels of circulating Anti-Müllerian hormone compared with younger and leaner controls. Secondary follicles isolated from different cohorts and grown in vitro had indistinguishable growth trajectories. However, the follicles isolated from older and heavier mice and those in diestrus had altered hormone profiles. These follicles contained oocytes with reduced meiotic competence and produced oocytes with greater spindle defects. CONCLUSIONS These results suggest that the original physical environment of the follicle within the ovary can impact its function when isolated and cultured. These findings are valuable as we begin to use in vitro follicle growth technology for a heterogeneous fertility preservation patient population.