Steroid hormone-treated endometrial organoids enhance implantation of in vitro-produced porcine embryos.

Importance: Embryo implantation is a hormone-regulated event requiring a receptive endometrium. In vitro models that simulate this process are essential for studying early embryonic development. Endometrial epithelial organoids (EEOs) provide a promising platform to model these interactions.

Objective: This study aimed to verify the response of porcine EEOs to steroid hormones and assess how steroid hormones affect embryonic attachment in a culture medium containing EEOs.

Methods: During a 7-day organoid in vitro culture mimicking the in vivo environment, estradiol (E₂) was administered from day 3, followed by progesterone (P₄) treatment on day 5. On day 7, porcine EEOs were harvested using a cell recovery solution. We compared the untreated control group with the hormone-treated groups and measured the expression levels of E₂ and P₄ receptors.

Results: The results demonstrated a higher receptor expression level in the hormone-treated groups than that in the control group. Additionally, the expression levels of genes associated with E₂ (fibroblast growth factor 7 and insulin-like growth factor 1) and P₄ (transforming growth factor β1) were higher in the hormone-treated group as compared to those in the control group. The efficiency of embryonic attachment was assessed through co-culture with EEOs harvested from both groups on the 7^th day and parthenogenetic embryos.

Conclusion and relevance: This study confirmed that porcine endometrial organoids respond to steroid hormones and support embryo attachment. These findings provide a translational basis for developing in vitro models to study implantation failure and infertility in reproductive medicine.