Background and aims: Mesenchymal stem cells (MSCs) have been shown an immune modulatory properties and tissue repairing capability under inflammatory conditions. However, it is unknown how MSCs may affect immunity in liver inflammatory injury. This study was designed to dissect the molecular mechanisms of MSCs in regulating immune responses in ischemia and reperfusion (IR)-triggered liver inflammation. Methods: Bone marrow-derived MSCs were transfected with CRISPR/Cas9-mediated Notch1 or COX2 knockout vector (p-Notch1 KO and p-COX2 KO), and then co-cultured with bone marrow-derived macrophages followed by LPS (100 ng/ml) stimulation. Using liver IRI model, mice (n=6/gr) were injected with 1×10⁶ MSCs via the tail vein, 24 h prior to liver ischemia. Mice were sacrificed after 6 h of reperfusion. Results: MSCs upregulated the expression of Notch1, COX2, and PGE2 after LPS stimulation. MSCs co-cultured with macrophages reduced macrophage iNOS yet strongly augmented arginase-1, an M2 macrophage marker. Moreover, the expression of macrophage Notch1, RBP-J, p-JNK and p-P38 was reduced in the co-cultures, which accompanied by decreased TNF-α/IL-6 and increased IL-10/TGF-β. Interestingly, transfection of p-Notch1 KO in MSCs enhanced COX2 expression and PGE2 secretion, as well as increased macrophage arginase-1. Knockdown of COX2 by transfecting p-COX2 KO in MSCs diminished PGE2 production and inhibited macrophage arginase-1. Unlike in controls, adoptive transfer of MSCs in mice ameliorated IR-induced liver damage, increased liver macrophage arginase-1, and inhibited proinflammatory mediators. Administration of Notch1 KO MSCs further enhanced liver macrophage arginase-1 expression and decreased liver injury, whereas COX2 silencing in MSCs suppressed liver macrophage arginase-1 leading to diminishing MSC-mediated protection in liver IRI. Conclusion: This study demonstrates that MSCs can reprogram host macrophage differentiation towards an anti-inflammatory M2 phenotype via a Notch/COX2/PGE2-dependent manner. Our findings provide a novel therapeutic potential for the management of IR-triggered liver inflammatory injury.

CITATION INFORMATION: Li C, Yue S, Busuttil R, Kupiec-Weglinski J, Ke B. Mesenchymal Stem Cells Reprogram Macrophage Polarization and Attenuate Liver Ischemia and Reperfusion Injury by Regulating Notch/Cox2/PGE2 Signaling Pathway. Am J Transplant. 2016;16 (suppl 3).

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