Endometrial gland secretions induce metabolic reprogramming and immunomodulatory signalling in trophoblast

The implanting embryo and developing placenta interface with the endometrium through a multinuclear trophoblast layer, syncytiotrophoblast (STB), which plays critical barrier, transport, immunomodulatory and endocrine roles throughout pregnancy. Understanding trophoblast and endometrial biology has recently been accelerated through sophisticated stem cell and organoid models, however few studies have combined these models to explore maternal-embryo communication. Here, we combined organoid models of secretory phase and decidual endometrial glands with trophoblast stem cell-derived STB to investigate signalling from maternal glands to the developing placenta. Luminal secretions collected from endometrial organoids by centrifugation were added to STB cultures and transcriptome analysis revealed that both secretory phase and decidual organoid secretions had profound effects on STB gene expression, inducing 3279 and 2634 differentially expressed genes (DEG), respectively (padj<0.05, >50% ≥1 log2 fold change). Gene set enrichment analysis of shared DEG (1926 genes) suggested upregulation of immune signalling and downregulation of mitochondrial respiration. Secretory and decidual secretions led to increased basal and maximal respiration (p<0.01) but reduced respiratory spare capacity (p<0.05) in STB, while glycolytic activity was also increased (p<0.05) together with increased expression of rate-limiting glycolysis enzymes HK1, HK2, PFKP and PKM (padj<0.03). Integrating cytokine array analysis of organoid secretions with upstream regulator analysis of STB DEG identified VEGFA and CSF1 as secretory products that might regulate mitochondrial and glycolytic genes, respectively, whereas secreted LCN2 and IL1A were upstream of immunomodulatory genes. Regulation of both immunomodulatory and metabolic gene sets was predicted for secreted CSF1 and EGF. The findings suggest that STB is highly responsive to endometrial gland secretions, which induce metabolic reprogramming likely to result in a more glycolytic phenotype in vivo as well as stimulating STB to modulate maternal immune responses. Endometrial gland signals thus shape trophoblast development to support successful establishment of pregnancy.