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Mesenchymal stromal cells (MSCs) are attractive candidates for treating hepatic disorders given their potential to enhance liver regeneration and function. The paracrine paradigm may be involved in the mechanism of MSC-based therapy, and exosomes (Exo) play an important role in this paracrine activity. Hypoxia significantly improves the effectiveness of MSC transplantation. However, whether hypoxia preconditioned MSCs (Hp-MSCs) can enhance liver regeneration, and whether this enhancement is mediated by Exo, are unknown. In this study, mouse bone marrow-derived MSCs (BM-MSCs) and secreted Exo were injected through the tail vein. We report that Hp-MSCs promote liver regeneration after partial hepatectomy in mice through their secreted exosomes. Interestingly, MSC-Exo were concentrated in liver 6 h after administration and mainly taken up by macrophages, but not hepatocytes. Compared with normoxic MSC-Exo (N-Exo), hypoxic MSC-Exo (Hp-Exo) enhanced M2 macrophage polarization both in vivo and in vitro. Microarray analysis revealed significant enrichment of microRNA (miR)-182-5p in Hp-Exo compared with that in N-Exo. In addition, miR-182-5p knockdown partially abolished the beneficial effect of Hp-Exo. Finally, Hp-MSC-derived exosomal miR-182-5p inhibited theprotein expression of forkhead box transcription factor 1 (FOXO1) in macrophages, which inhibited toll-like receptor 4 (TLR4) expression and subsequently induced an anti-inflammatory response. These results highlight the therapeutic potential of Hp-Exo in liver regeneration and suggest that miR-182-5p from Hp-Exo facilitates macrophage polarization during liver regeneration by modulating the FOXO1/TLR4 signaling pathway.
Xu et al. (Fri,) studied this question.