Microencapsulation and nanowarming enables vitrification cryopreservation of mouse preantral follicles
Published in Nanowarming.
Conghui Tian, Lingxiao Shen, Chenjia Gong, Yunxia Cao, Qinghua Shi & Gang Zhao
Preantral follicles are often used as models for cryopreservation and in vitro culture due to their easy availability. As a promising approach for mammalian fertility preservation, vitrification of preantral follicles requires high concentrations of highly toxic penetrating cryoprotective agents (up to 6 M). Here, we accomplish low-concentration-penetrating cryoprotective agent (1.5 M) vitrification of mouse preantral follicles encapsulated in hydrogel by nanowarming. We find that compared with conventional water bath warming, the viability of preantral follicles is increased by 33%. Moreover, the cavity formation rate of preantral follicles after in vitro culture is comparable to the control group without vitrification. Furthermore, the percentage of MII oocytes developed from the vitrified follicles, and the birth rate of offspring following in vitro fertilization and embryo transfer are also similar to the control group. Our results provide a step towards nontoxic vitrification by utilizing the synergistic cryoprotection effect of microencapsulation and nanowarming.
In recent years, an increasing number of malignant diseases (such as breast cancer and hematological diseases) have occurred in young women1. Although active chemo- and radiotherapy or bone marrow transplantation can cure 90% of girls and young women, these treatments still damage the gonadal glands and even lead to premature ovarian failure2,3,4,5. In addition, due to work or financial reasons, many women who postpone childbearing are affected by infertility6. As a result, the demand for fertility preservation in women is dramatically increasing7. At present, methods to preserve female fertility mainly include cryopreservation of embryos, unfertilized oocytes8 and ovarian tissue9,10. Among them, embryo cryopreservation requires women to have a male partner or use donated sperms, which may involve religious, moral, ethical and other issues11. Oocyte cryopreservation is mainly used by women who have reached adolescence and can withstand multiple rounds of ovarian stimulation12. For prepubescent girls and women in urgent need of cancer treatment, cryopreservation of ovarian tissue containing healthy follicles is the only option13. However, this method is not suitable for women with certain malignant diseases (such as acute leukemia) because malignant cells may migrate to the ovarian tissue to be transplanted in the future14. Even worse, many follicles may be lost due to delays and failures in vascular reconstruction15, and qualitative and quantitative assessment of follicles in ovarian tissue is almost impossible16. For these women, cryopreservation of isolated ovarian follicles and in vitro culture is an alternative and safe option17. Preantral follicles (PAFs) are the early stage of follicles, which are composed of an oocyte surrounded by one or few layers of granulosa cells18. PAFs were abundant and easily available in hormone-stimulated prepubertal mice or young adolescent female mice19. Therefore, mouse PAFs were often used as models for optimizing cryopreservation, in vitro culture conditions, and fertility preservation in fertility studies18,19.