Melatonin is important for oocyte maturation, fertilization, early embryonic development, and embryo implantation, but less knowledge is available regarding its role in decidualization. The present study found that melatonin did not alter the proliferation of human endometrial stromal cells (ESCs), as well as cell cycle progress, but suppressed stromal differentiation after binding to the melatonin receptor 1B (MTNR1B), which was visualized in decidualizing ESCs. Further analysis evidenced that application of melatonin resulted in the diminishment for NOTCH1 and RBPJ expression. Supplementation of recombinant NOTCH1 protein (rNOTCH1) counteracted the impairment of stromal differentiation conferred by melatonin, while the addition of the NOTCH signaling pathway inhibitor DAPT aggravated the differentiation progress. Meanwhile, melatonin might restrain the expression and transcriptional activity of nuclear factor erythroid 2-related factor 2 (NRF2), whose blockage accelerated the fault of stromal differentiation under the context of melatonin, but this restraint was subsequently ameliorated by rNOTCH1. Forkhead box O 1 (FOXO1) was identified as a downstream target of melatonin in decidualization. Repression of NRF2 antagonized the retrieval of rNOTCH1 due to aberrant FOXO1 expression elicited by melatonin. Moreover, melatonin brought about the occurrence of oxidative stress accompanied by an obvious accumulation of intracellular reactive oxygen species and a significant reduction in glutathione (GSH) content, as well as enzymatic activities of glutathione peroxidase and glutathione reductase, whereas supplementation of rNOTCH1 improved the above-mentioned effects. Nevertheless, this improvement was disrupted by the blockage of NRF2 and FOXO1. Furthermore, addition of GSH rescued the defect of stromal differentiation by melatonin. Collectively, melatonin might impair endometrial decidualization by restraining the differentiation of ESCs dependent on NOTCH1–NRF2–FOXO1–GSH pathway after binding to the MTNR1B receptor.

Summary Sentence

Melatonin impaired endometrial decidualization by restraining the differentiation of stromal cells dependent on the NOTCH1–NRF2–FOXO1–GSH pathway after binding to the MTNR1B receptor.

Graphical Abstract