Microbial-derived D-lactate and LPS shape growth and inflammatory signalling in endometrial glandular epithelium

The endometrium, the inner lining of the uterus, is a dynamic tissue that undergoes precise molecular and structural changes to achieve a receptive state capable of supporting embryo implantation. Although the uterine environment was long considered sterile, molecular studies have detected microbial signals and bioactive compounds that may influence endometrial function. Endometrial epithelial organoids (EEOs) provide a three-dimensional in vitro model that recapitulates the architecture, polarity, and hormonal responsiveness of native endometrial tissue. This study aimed to elucidate how bacterial-derived compounds, including D-lactate (D-lac), commonly associated with Lactobacillus communities, and lipopolysaccharides (LPS), a component of Gram-negative bacteria, affect the transcriptomic profile of the endometrial epithelium under a hormonally induced receptive state. EEOs were exposed to different concentrations of these compounds, and relative metabolic activity was monitored through resazurin-based assays, revealing no significant alterations across the conditions tested. Transcriptomics analysis of hormonally stimulated EEOs, mimicking the mid-secretory phase, revealed that D-lac modulated genes related to epithelial development, tissue remodelling and growth regulation, whereas LPS influenced genes associated with inflammatory signalling and immune response. While key markers of receptivity remained largely stable, small transcriptional changes suggest that microbial signals may modulate the functional balance of the receptive endometrium. These findings highlight a modulatory role of microbial signals on endometrial epithelial function and demonstrate that EEOs are a robust platform for exploring host-microbe interactions in the uterus, offering new insights into the mechanisms underlying uterine receptivity.