Re-cryopreservation impairs blastocyst implantation potential via activated endoplasmic reticulum stress pathway and induced apoptosis

This study is led by Prof. Lei Jin and Dr. Lixia Zhu (Reproductive Medicine Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology). Assisted reproductive technology has been demonstrated to be an efficacious intervention for addressing fertility challenges among infertile populations. The advent of assisted reproductive technology has led to the occasional occurrence of re-cryopreservation in blastocysts in clinical practice. The impact of this phenomenon on embryo development and outcome remains to be elucidated. "A comprehensive understanding of it and to investigate the potential mechanisms is crucial for embryologists in embryo management, " Jin says.

Jin and Zhu, together with Meng Wang, a postdoctoral researcher at Tongji Hospital, sought to determine whether re-cryopreservation procedure affect clinical outcomes. The team conducted a propensity score matching study for confounding factors control to investigate the effect of re-cryopreservation on blastocyst outcomes, and utilized transcriptome sequencing to explore the possible underlying mechanism.

The team found that after matching, re-cryopreservation procedure in blastocysts results in impaired blastocyst developmental potential, including decreased implantation rate, reduced biochemical pregnancy rate, declined clinical pregnancy rate, higher early miscarriage rate and lower live birth rate. "This result supports the decrease of developmental potential of blastocysts after re-cryopreservation," Zhu says.

The researchers also explore the association between re-cryopreservation procedure and HCG (human chorionic gonadotropin), the increase of which after embryo transfer indicates the success in blastocyst implantation. The positive correlation between HCG level and blastocyst grade, as well as trophectoderm score, disappear after re-cryopreservation, prompting that re-cryopreservation procedure impaired trophectoderm function of blastocysts and HCG secretion.

The mechanism exploration showed that the expression of genes involved in cell adhesion, embryos development, and apoptosis were changed. The team performed immunofluorescence analyses on human blastocysts, and it was found that the signaling pathways of endoplasmic reticulum stress and apoptosis were activated.

"These new exciting results add to growing evidence that re-cryopreservation might impair blastocyst developmental potential via activated endoplasmic reticulum stress pathway and induced apoptosis. Although the application of recryo procedure avoids the wastage of embryos and facilitates emergency handling, it provides caution to embryologists about the potential risk of recryopreservation on embryos." Jin says.