Transplantation of Mesenchymal Stem Cells Attenuates Acute Liver Failure in Mice via an Interleukin-4-dependent Switch to the M2 Macrophage Anti-inflammatory Phenotype

Background and Aims:Transplantation of mesenchymal stem cells(MSCs)derived from bone marrow(BM)is an alternative treatment of acute liver failure(ALF)mainly be-cause of the resulting anti-inflammatory activity.It is not known how MSCs regulate local immune responses and liver regeneration.This study explored the effects of MSCs on hepatic macrophages and the Wnt signaling pathway in ALF.Methods:MSCs were isolated from BM aspirates of C57BL/6J mice,and transplanted in mice with ALF induced by D-galactosamine(D-Gal).The proliferation of hepato-cytes was assayed by immunohistochemical(IHC)staining of Ki-67 and proliferating cell nuclear antigen(PCNA).The levels of key proteins in the Wnt signaling pathway were assayed by western blotting and cytokines were determined enzyme-linked immunosorbent assays(ELISAs).A mac-rophage polarization assay characterized the M1/M2 ratio.The potential role of interleukin-4(IL-4)in the biological ac-tivity of MSCs was determined by silencing of IL-4.Results:Transplantation of allogeneic MSCs significantly attenuated D-Gal-induced hepatic inflammation and promoted liver re-generation.MSC transplantation significantly promoted a phenotypic switch from proinflamatory M1 macrophages to anti-inflammatory M2 macrophages,leading to significant Wnt-3a induction and activation of the Wnt signaling path-way in mice with D-Gal-induced ALF.Of the paracrine fac-tors secreted by MSCs(G-CSF,IL-6,IL-1 beta,IL-4,and IL-17A),IL-4 was specifically induced following transplantation in the ALF model mice.The silencing of IL-4 significantly ab-rogated the phenotypic switch to M2 macrophages and the protective effects of MSCs in both the ALF model mice and a co-culture model in an IL-4 dependent manner.Conclu-sions:In vivo and in vitro studies showed that MSCs ame-liorated ALF through an IL-4-dependent macrophage switch toward the M2 anti-inflammatory phenotype.The findings may have clinical implications in that overexpression of IL-4 may enhance the therapeutic effects of allogeneic MSC transplantation in the treatment of ALF.