Myometrial extracellular vesicles promoted endometrial mesenchymal stem/stromal cells to self-renewal via jag1-mediated notch signaling.

Background: In the human endometrium, studies show the importance of extracellular vesicles in mediating various physiological as well as pathological processes. We have demonstrated that the myometrial cells are candidate niche cells of the endometrial mesenchymal stem/stromal cells (eMSC) modulating their biological function. The Notch signaling pathway regulates the endometrial stem cell functions. Although classical Notch signaling relies on direct cell contract for actions, this pathway can also be activated at a distance by Notch ligands containing extracellular vesicles (EV). We hypothesized that certain Notch ligand(s) are packaged into the myometrial EV to mediate stem cell functions.

Methods: Endometrial samples were obtained from women undergoing total abdominal hysterectomy. Endometrial MSC (CD140b⁺CD146⁺ cells) were cocultured with myometrial EV and the percentage of eMSC was analysed by flow cytometry. Blockage of the secretion of EV was performed by transfection of RAB27 A siRNA. Western blot analysis and gene silencing approach were used to validate the role of Notch signaling in eMSC. The therapeutic features of transplanted eMSC/myometrial EV was determined using a mouse injured endometrium model.

Results: EV released from myometrial cells could be internalized by eMSC, leading to a significant stimulatory effect on the self-renewal and clonogenic activity of eMSC. Pharmacological inhibition of Notch signaling with DAPT or silencing of NOTCH 1 nullified the stimulatory effects. Myometrial EV contains a high amount of the Notch ligand - JAG1, thus inducing a strong Notch activity in eMSC. When JAG1 was silenced in the myometrial EV, the self-renewal and clonogenic activity was reduced. Combined transplantation of eMSC with myometrial EV improves the therapeutic effect of eMSC in endometrial regeneration in vivo. The observed therapeutic feature was potentially achieved by elevating the cell proliferation and suppressing apoptosis in the injured mouse endometrium.

Conclusions: This study identifies a novel EV mediated communication axis between the myometrial cells and the eMSC, providing new insights into endometrial regeneration. The findings highlight the potential of eMSC and myometrial EV as a therapeutic strategy for women with intrauterine adhesions and other endometrial disorders.