Mesenchymal Stem Cell Attenuates Acute Liver Failure Via Prostaglandin E₂

BackgroundAs a clinical syndrome caused by drug toxicity or viral hepatitis,acute liver failure(ALF)is associated with high morbidity and mortality.Currently,liver transplantation is the only effective way to cure ALF.However,a shortage of liver donors greatly limits the application of this therapy.Recently,stem cell based therapy has been proved to be a potential treatment for liver diseases.Mesenchymal stem cell(MSC)are one of the most common stem cells.Accumulating evidence has revealed that various trophic factors secreted by MSC play key therapeutic roles in liver diseases by alleviating inflammation,apoptosis,and fibrosis as well as stimulating angiogenesis,modulating immune response and promoting tissue regeneration.Several clinical trials have confirmed the therapeutic ability of MSC on ALF,however the effect is not satisfied and the therapeutic mechanisms of MSC transplantation are still not fully characterized.Thus,to underlie the mechanism of therapeutic ability of MSC on ALF,might provide a new strategy to enhance the functionality of MSC and accelerate the process of clinical transformation.MethodsWe overexpressed or knocked down cyclooxygenase 2(COX2)in MSC via lentivirus and established ALF model by lipopolysaccharide(LPS)/D-galactosamine(D-Gal)via intraperitoneal injection in mice,to explore the therapeutic ability of MSC derived prostaglandin E2(PGE2)on ALF.Next we focused on the liver injury in ALF,to clarify the effects of MSC-derived PGE2 on liver inflammatory environment and macrophage polarization.Then,we investigated the effect of MSC-derived PGE2 on liver regeneration,the role of yes-associated protein(YAP)and mammalian target of rapamycin(mTOR)signaling on hepatocyte proliferation and the mechanism of MSCderived PGE2 on YAP regulation.Finally,we detected which prostaglandin E receptor(EP)played major role on the therapeutic ability of MSC-derived PGE2 on ALF via RTqPCR and administration of antagonist.Results1.We confirmed the role of MSC-derived PGE2 on attenuating ALF in animal model,and then we found that MSC-derived PGE2 could inhibit hepatocyte apoptosis and promote hepatocyte proliferation by immunohistochemistry.2.MSC-derived PGE2 could inhibit TAK1-NF-κB signaling and NLRP3 inflammasome activation in liver macrophages,thus to alleviate inflammatory response in liver.And administration of TAK1 inhibitor significantly suppressed liver injury.Meanwhile,MSC-derived PGE2 could also activate STAT6 and mTOR signaling in liver macrophages thus to induce M2 macrophages to secrete anti-inflammatory factors,like IL-10,to enhance tissue repair.3.MSC-derived PGE2 phosphorylated CREB then to activate YAP,and improve nuclear translocation of YAP,thus to increase expression of YAP related genes(like AREG and CTGF).In parallel,YAP increased levels of miR-29a-3p to suppress PTEN thus to activate mTOR signaling,establishing the corporation between YAP and mTOR pathways to enhance hepatocyte proliferation.4.EP4 played a core role in MSC-derived PGE2 on liver injury and liver regeneration.Administration of EP4 antagonist significantly inhibited the therapeutic ability of MSC on ALF.The effect of MSC on liver inflammatory and macrophage polarization was inhibited by EP4 antagonist.Also,YAP and mTOR signaling were also suppressed by EP4 antagonist.ConclusionMSC-derived PGE2 alleviated liver damage by inhibiting inflammatory response in liver and inducing M2 macrophages to promote tissue repair.On the other hand,MSC-derived PGE2 could also activate YAP and mTOR pathways,which coordinated to enhance hepatocyte proliferation.This study provided a new mechanism of therapeutic ability of MSC on ALF.