A matrix-free 3D <i>in vitro</i> follicle culture system in mice exhibits enhanced oocyte meiotic and developmental competence compared to hydrogel encapsulation

In vitro follicle culture (IFC) is an emerging fertility preservation alternative for women and children with cancer. Because two-dimensional (2D) IFC results in oocytes of suboptimal quality in mice and cannot support follicle growth in humans, the search for an optimal three-dimensional (3D) method that preserves the follicular structure is ongoing, and both matrix-free and hydrogel encapsulation systems are being explored. Our aim was to compare several 3D mouse IFC systems, including matrix-free and hydrogel encapsulation approaches. Secondary follicles were cultured for 12 days in a matrix-free non-attachment (NA) system, a Poly-Ethylene-Glycol (PEG) hydrogel, an extracellular-matrix-derived soft hydrogel (ES), and a 2D attachment (AT) control. We assessed follicle growth, survival, hormone secretion, theca cell localization, oocyte meiotic competence and diameter, gene expression in oocytes and cumulus cells, as well as oocyte fertilization potential. Metaphase II oocyte rates were significantly higher in the NA (75 ± 12.4%, n = 79) and AT systems (77 ± 12.6%, n = 109) compared to the ES (33.4 ± 9.5%, n = 40, P < 0.01), while low antral follicle rates from the PEG system led to its exclusion from the comparison. Similarly, following IVF, 2-cell rates were significantly higher in the NA (47.7 ± 17.6%, n = 147, P < 0.01) and AT (40.2 ± 9.7%, n = 132, P < 0.05) systems compared to the ES (23.5 ± 9.3%, n = 63). Furthermore, cumulus cells from the NA condition displayed a more in vivo-like gene expression profile than other conditions. No differences were detected in follicle survival, oocyte diameter, blastocyst rate, or quality between conditions. Lastly, we observed major differences in theca cell localization and hormone secretion levels that require further investigation. Our findings demonstrate the efficiency of the NA system over complex encapsulation methodologies, as it enhanced oocyte meiotic and developmental competence compared to the ES. However, as the study is limited by the lack of human data and the use of Fetal Bovine Serum (FBS) in the culture medium, further research is required to translate our findings to humans.