LAUSR

Significance Thin endometrium is the most common reason for uterine infertility and refractory gynecological diseases due to its complexity in pathogenesis and adverse pregnancy outcomes. Here, we profile cells from normal and thin endometrium at single-cell resolution to investigate the sophisticated alterations in the local microenvironment that occur in thin endometrium. Increased cellular senescence, collagen overdeposition, and significant down-regulation of gene expression related to cell proliferation are observed and confirmed. Moreover, we demonstrate aberrant activation of the SEMA3 pathway accompanied by dampened EGF, PTN, and TWEAK signaling pathways in thin endometrium. These findings aid in understanding the mechanisms of thin endometrium and provide new tools to rejuvenate the atrophic endometrium for female fertility preservation and successful pregnancy. Thin endometrium has been widely recognized as a critical cause of infertility, recurrent pregnancy loss, and placental abnormalities; however, access to effective treatment is a formidable challenge due to the rudimentary understanding of the pathogenesis of thin endometrium. Here, we profiled the transcriptomes of human endometrial cells at single-cell resolution to characterize cell types, their communications, and the underlying mechanism of endometrial growth in normal and thin endometrium during the proliferative phase. Stromal cells were the most abundant cell type in the endometrium, with a subpopulation of proliferating stromal cells whose cell cycle signaling pathways were compromised in thin endometrium. Both single-cell RNA sequencing and experimental verification revealed cellular senescence in the stroma and epithelium accompanied by collagen overdeposition around blood vessels. Moreover, decreased numbers of macrophages and natural killer cells further exacerbated endometrial thinness. In addition, our results uncovered aberrant SEMA3, EGF, PTN, and TWEAK signaling pathways as causes for the insufficient proliferation of the endometrium. Together, these data provide insight into therapeutic strategies for endometrial regeneration and growth to treat thin endometrium.