Recurrent implantation failure severely impairs fertility in females of childbearing age, which poses a great challenge to assisted reproductive technology, and its etiology is still unclear. Several studies have demonstrated that endometrial autophagy takes an important part in human endometrial receptivity, but its role in recurrent implantation failure remains largely unknown. Here, we collected mid-secretory endometrial tissue from recurrent implantation failure patients and fertile controls during menstruation and early pregnancy. Immunohistochemistry, western blotting, and quantitative real-time PCR were performed to compare the expression of microtubule-associated protein 1 light chain 3B, sequestosome 1, NOTCH1 signaling pathway members, and endometrial receptivity markers between recurrent implantation failure and control groups. In addition, to assess endometrial autophagy, transmission electron microscopy was used to observe autophagosomes. By RNA interference, we further investigated the effects of NOTCH1 on autophagy in Ishikawa cells. We found that endometrial autophagy was upregulated in the mid-secretory and decidual phases than in the early-proliferative phase. Compared to the control group, more autophagosomes were observed in the mid-secretory endometrium of recurrent implantation failure patients, which was accompanied by the downregulation of NOTCH1 signaling pathway members and endometrial receptivity markers. Moreover, knockdown of NOTCH1 impaired the receptivity of Ishikawa cells via protein kinase B/mammalian target of rapamycin pathway-mediated autophagy activation. Our data suggested that abnormally elevated autophagy and decreased NOTCH1 signaling pathway activity were observed in the mid-secretory endometrium of patients with recurrent implantation failure, perhaps due to decreased NOTCH1 pathway-mediated autophagy activation in endometrial cells impairing receptivity.

Summary Sentence

Elevated autophagy and decreased NOTCH1 signaling pathway activity were displayed in the mid-secretory endometrium of patients with recurrent implantation failure, perhaps due to decreased NOTCH1 pathway-mediated autophagy activation in endometrial cells impairing receptivity.

Graphical Abstract