Exosomes from mesenchymal stem cells induce the conversion of hepatocytes into progenitor oval cells

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Exosomes from mesenchymal stem cells induce the conversion of hepatocytes into progenitor oval cells Hao-Hsiang Wu1 and Oscar K. Lee1,2,3,4,5*

Abstract Background: We previously reported that mesenchymal stem cells (MSCs) possess therapeutic effects in a murine model of carbon tetrachloride-induced acute liver failure. In the study, we observed that the majority of repopulated hepatocytes were of recipient origin and were adjacent to transplanted MSCs; only a low percentage of repopulated hepatocytes were from transplanted MSCs. The findings indicate that MSCs guided the formation of new hepatocytes. Exosomes are important messengers for paracrine signaling delivery. The aim of this study is to investigate the paracrine effects, in particular, the effects of exosomes from MSCs, on hepatocytes. Methods: Mature hepatocytes were isolated from murine liver by a two-step perfusion method with collagenase digestion. MSCs were obtained from murine bone marrow, and conditioned medium (CM) from MSC culture was then collected. Time-lapse imaging was used for observation of cell morphological change induced by CM on hepatocytes. In addition, expression of markers for hepatic progenitors including oval cells, intrahepatic stem cells, and hepatoblasts were analyzed. Results: Treatment with the CM promoted the formation of small oval cells from hepatocytes; time-lapse imaging demonstrated the change from epithelial to oval cell morphology at the single hepatocyte level. Additionally, expression of EpCAM and OC2, markers of hepatic oval cells, was upregulated. Also, the number of EpCAMhigh cells was increased after CM treatment. The EpCAMhigh small oval cells possessed colony-formation ability; they also expressed cytokeratin 18 and were able to store glycogen upon induction of hepatic differentiation. Furthermore, exosomes from MSC-CM could induce the conversion of mature hepatocytes to EpCAMhigh small oval cells. Conclusions: In summary, paracrine signaling through exosomes from MSCs induce the conversion of hepatocytes into hepatic oval cells, a mechanism of action which has not been reported regarding the therapeutic potentials of MSCs in liver regeneration. Exosomes from MSCs may therefore be used to treat liver diseases. Further studies are required for proof of concept of this approach. Keywords: Mesenchymal stem cells, Paracrine signaling, Conditioned medium, Exosomes

Background Mesenchymal stem cells (MSCs) possess multilineage differential potential and have been shown to possess therapeutic effects in animal models [1, 2]. In our previous study, MSC transplantation restored liver function in mice with carbon tetrachloride (CCl4)-induced acute * Correspondence: [email protected] 1 Institute of Biophotonics, National Yang-Ming University, No.155, Sec.2, Linong Street, Taipei 112, Taiwan 2 Taipei City Hospital, No.145, Zhengzhou Road, Datong District, Taipei 10341, Taiwan Full list of author information is available at the end of the article

liver failure [3]. However, only a small percentage of