Exosomes derived from human umbilical cord mesenchymal stem cells accelerate growth of VK2 vaginal epithelial cells through MicroRNAs in vitro.

STUDY QUESTION: Could human umbilical cord mesenchymal stem cell-derived exosomes (hucMSC-Ex) accelerate vaginal epithelium cell (VK2) growth?

SUMMARY ANSWER: HucMSC-Ex play a significant role in promoting proliferation of VK2 cells by accelerating the cell cycle and inhibiting apoptosis through exosomal microRNAs in vitro.

WHAT IS KNOWN ALREADY: Numerous studies have reported that MSC-Ex play an important role in tissue injury repair.

STUDY DESIGN, SIZE, DURATION: hucMSC and exosomes isolated from their conditioned medium were used to treat a vaginal epithelial cell line (VK2). Normal human fibroblasts (HFF-1) were used as negative control to hucMSC.

PARTICIPANTS/MATERIALS, SETTING, METHODS: VK2 cells were co-cultured with hucMSC whose paracrine effect on the viability, cell cycle and cell apoptosis of VK2 vaginal epithelial cells was further assessed by the CCK-8 assay and flow cytometry. HucMSC-Ex isolated from culture medium by ultracentrifuge were characterized by transmission electron microscopy, nanoparticle tracking analysis and Western blot. HucMSC-Ex at different concentrations and HFF-1 exosomes were used to treat VK2 cells. High-throughput RNA sequencing was utilized to reveal the profile of microRNAs in hucMSC, hucMSC-Ex, HFF-1 and HFF-1 exosomes and GO analysis was applied to demonstrate their functions. To evaluate the function of these specific microRNAs in hucMSC-Ex, VK2 cells were treated with RNA-interfered-hucMSC-Ex (RNAi-hucMSC-Ex) and their proliferation was measured by Label-free Real-time Cellular Analysis System.

MAIN RESULTS AND THE ROLE OF CHANCE: The study showed that hucMSC stimulate VK2 cell growth possibly through a paracrine route by promoting cell cycle and inhibiting apoptosis. Compared with control and low dose groups, hucMSC-Ex of high concentration (more than 1000 ng/ml) significantly increased VK2's growth after treatment in a dose-depended manner (P < 0.05). HucMSC-Ex raised the proportion of cells in S-phase and reduced the percentage of apoptotic cells in VK2 cells in comparison with the HFF-1 exosomes and control groups (P < 0.05). microRNAs, including miR-100 (16.92%), miR-146a (9.21%), miR-21 (6.67%), miR-221 (6.39%) and miR-143 (4.63%), were found to be specifically enriched (P < 0.05) in hucMSC-Ex and their functions concentrated on cell cycle, development and differentiation. Collectively, our findings indicate that hucMSC-Ex may play a significant role in accelerating VK2's proliferation by promoting cell cycle and inhibiting apoptosis through exosomal microRNAs in vitro.

LARGE-SCALE DATA: N/A.

LIMITATIONS, REASONS FOR CAUTION: Our study did not confirm the function of hucMSC-Ex or specifically enriched exosomal microRNAs in vivo. miR-100 and miR-146a are well-known immunomodulatory miRNAs that participate in the regulation of inflammatory disorders and may enhance the therapeutic effect of hucMSC-Ex by promoting the surgical injury repair after vaginal reconstruction. But whether it acts through anti-inflammatory responses needs further study.

WIDER IMPLICATIONS OF THE FINDINGS: This finding supports the potential use of hucMSC-Ex as a cell-free therapy of Meyer-Rokitansky-Küster-Hauser syndrome (MRKHS) after vaginoplasty.

STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the Chinese National Nature Sciences Foundation (grant number 91440107, 81471416 and 81771524) and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB19040102). All authors state that there is no conflict of interest to disclose.