BMAL1 regulates the initial step of embryo implantation by modulating endometrial cell adhesion and migration.

Embryo implantation is a critical and tightly regulated process essential for successful human reproduction. Although the role of endometrial receptivity is well established, the molecular mechanisms governing this process are not thoroughly understood. Circadian rhythm regulators, particularly brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1), have emerged as key modulators in reproductive biology. In this study, we investigated the role of BMAL1 in regulating endometrial receptivity and embryo implantation. Ishikawa cells were transfected with BMAL1-specific or control siRNA, followed by RT-qPCR, western blotting, and immunofluorescence analyses. Functional assays, including migration assays, co-culture with JEG-3 spheroids, cell viability, and cytotoxicity, were also performed. Our results demonstrated that BMAL1-knockdown in Ishikawa cells downregulated adhesion-related genes, including ITGAV, ITGB3, and ITGB5. Although total ITGB5 protein levels remained stable, its localized expression intensity was significantly reduced; the protein expression of ITGAV and ITGB3 was decreased, and cell migration was impaired. Notably, while BMAL1-knockdown compromised cellular motility, it had no significant effect on cell viability or cytotoxicity. A co-culture model with JEG-3 spheroids further demonstrated significantly decreased embryo adhesion following BMAL1-knockdown. In conclusion, BMAL1 is a critical regulator of integrin-mediated adhesion and endometrial receptivity, underscoring its potential as a therapeutic target for recurrent implantation failure.