Background: This study aimed to investigate the role of nicotinamide adenine dinucleotide (NAD+) in endometrial decidualization prior to embryo implantation and to elucidate the underlying mechanism. Methods: In this study, primary human endometrial stromal cells (hEnSCs) were isolated and cultured in vitro. Decidualization was induced under three conditions: an experimental group (EG) treated with nicotinamide mononucleotide (NMN) alongside the standard decidualization cocktail to increase intracellular NAD+ levels; a control group (CG) that received only the standard decidualization cocktail; and a blank group (BG) that received no decidualization stimuli. Decidualization was evaluated by examining morphological changes and by measuring the secretion of specific markers, prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1) using an enzyme-linked immunosorbent assay (ELISA). To explore the underlying mechanisms, transcriptomic sequencing and bioinformatics analysis were performed on cells from all three groups, followed by experimental validation. Results: The results indicated that increased intracellular NAD+ enhanced endometrial decidualization, as evidenced by higher secretion of the decidual markers PRL and IGFBP-1. Transcriptomic analysis revealed significant differences between the decidualized groups (CG and EG) and the nondecidualized group (BG), which reflect major cellular reprogramming. However, transcriptomic differences between the EG and CG groups were minimal. This finding suggests that NAD+ elevation does not initiate decidualization via broad transcriptional reprogramming but instead provides a fine-tuning, supportive effect on the already induced decidual state. Gene Set Enrichment Analysis (GSEA) indicated that NAD+ supplementation may influence decidualization through modulating DNA replication and cell cycle pathways. In addition, NAD+ effectively reduced apoptotic activity in decidualizing hEnSCs compared with the CG. Conclusions: This study establishes that increasing intracellular NAD+ level promotes decidualization of hEnSCs. Rather than causing widespread changes in gene expression, NAD+ appears to refine and support the decidualization process, likely through effects on DNA replication and cell cycle pathways and by reducing apoptosis. These early findings provide insight into how cellular metabolism may regulate decidualization and suggest a potential supportive role for NAD+ modulation.
Liu et al. (Thu,) studied this question.