Exosomal Let-7i-5p from Three-Dimensional Cultured Human Umbilical Cord Mesenchymal Stem Cell S Inhibits the Activation of Fibroblasts Induced by Silica Through Targeting TGFBR1

Abstract

Background: Pulmonary fibrosis (PF) is related to long-term excessive inhalation of silica, and primarily mediated by activated fibroblasts. Exosomes derived from human umbilical cord mesenchymal stem cells (hucMSC-Exos) are considered to be a potential therapy of silica-induced PF, however, their exact mechanism remains unknown. Therefore, this study aims to explore whether hucMSC-Exos affect the activation of fibroblasts to alleviate PF. Methods: In this study, a three-dimensional (3D) method was applied to culture hucMSCs and MRC-5 cells (human embryonic lung fibroblasts), and exosomes were isolated from serum-free media, identified by nanoparticle tracking analysis (NTA), electron microscopy (TEM) and Western blotting analysis. Then, the study used an animal model of silica-induced PF to observe the effects of hucMSC-Exos and MRC-5-Exos on activation of fibroblasts. In addition, the activation of fibroblasts was analyzed by Western blotting analysis, wound healing, and migration assay with the treatment of hucMSC-Exos and MRC-5-Exos in NIH-3T3 cells (mouse embryonic fibroblasts). Furthermore, differential expression of microRNAs (DE miRNAs) was measured between hucMSCs-Exos and MRC-5-Exos by high throughput sequence. Findings: HucMSC-Exos inhibited the activation of fibroblasts in mice and NIH-3T3 cells. Let-7i-5p was significantly up-regulated in hucMSCs-Exos compared to MRC-5-Exos, which was related to silica-induced PF. Let-7i-5p of hucMSCs-Exos was responsible for the activation of fibroblasts by targeting TGFBR1. Meanwhile, Smad3 was also an important role in the activation of fibroblasts. Interpretation: The study demonstrates that hucMSCs-Exos act as a mediator that transfers let-7i-5p to inhibit the activation of fibroblasts, which alleviates P F through the TGFBR1/Smad3 signalling pathway. The mechanism has potential value for the treatment of silica-induced PF. Funding: This study was supported by the National Natural Science Foundation of China (81872595, 81472958, 81703197, 81472958). Declaration of Interest: None to declare. Ethical Approval: This study was approved by the Laboratory Animal Care and Use Committee at Capital Medical University (AEEI-2018-223).