Disruption of primary ciliary prostaglandin E2 signaling by transforming growth factor-β1 impairs endometrial receptivity.

Abstract

Background: Infertility affects one in six individuals worldwide despite the advancement of assisted reproductive technologies. Successful embryo implantation is the first step of pregnancy, which relies on the establishment of a receptive uterine microenvironment. However, the mechanisms governing uterine receptivity and implantation failure remain incompletely characterized. Primary cilia serve as key cellular signaling hubs, yet their contribution to human decidualization and uterine receptivity remains largely unexplored.

Methods: Primary cultured human endometrial stromal cells (ESCs) were used to investigate the mechanisms of decidualization, functions of primary cilia, and effects of transforming growth factor-β (TGF-β) in inhibiting prostaglandin E₂ (PGE₂)-induced decidualization. Human endometrial tissues (n = 108) were used to evaluate the clinicopathological parameters. The percentage of ciliated cells and cilia length were determined by immunofluorescent staining and AI-assisted quantification. Pseudopregnancy and pregnancy mouse models were employed to assess the effects of TGF-β1 on uterine receptivity and implantation outcomes.

Results: Prostaglandin E₂, through binding to the EP4 receptor located at the primary cilium, stimulates ESC decidualization, which is augmented by 17β-estradiol and progesterone. Loss of ciliogenesis by genetic or pharmacological inhibition impairs decidualization. Proinflammatory cytokines such as TGF-β inhibit ciliogenesis and thus markedly attenuate PGE₂-mediated decidualization. Mechanistically, TGF-β1 suppressed chicken ovalbumin upstream promoter transcription factor II and its downstream effector kinesin family member 3B, thereby inhibiting ciliogenesis and PGE₂-EP4 signaling. In mice, intrauterine administration of TGF-β1 impaired implantation, while TGF-β receptor blockade restored ciliogenesis, decidualization, and fertility. In women with endometriosis, ESCs displayed shortened cilia and reduced decidual response, which are due to elevated uterine and peritoneal TGF-β1-mediated suppression of ciliogenesis. Finally, women who failed to conceive after in vitro fertilization-embryo transfer (IVF-ET) have shorter and fewer primary cilia in ESCs. Receiver operating characteristic curve analysis demonstrated that both cilia length (AUC = 0.86) and ciliation frequency (AUC = 0.79) can serve as biomarkers for endometrial receptivity, providing predictive value for reproductive outcomes independent of ovarian reserve.

Conclusions: Endometrial primary cilia are indispensable for decidualization and are potential biomarkers for predicting endometrial receptivity. Targeting TGF-β signaling to restore ciliated cell number and ciliary length may serve as a potential therapeutic strategy to improve fertility outcomes.