YAP-IRGM1 REGULATES HEPATIC INFLAMMATION IN ORTHOTOPIC LIVER TRANSPLANTATION

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PROJECT SUMMARY/ABSTRACT Hepatic ischemia and reperfusion injury (IRI) remains a common problem in liver transplant, hepatic resection, and shock. As it often leads to primary graft dysfunction (PGD), late chronic rejection, and contributes to the shortage of donor organs available for transplantation, liver IRI represents one of the most challenging yet understudied complications in clinical orthotopic liver transplantation (OLT). As intrinsic YAP expression negatively correlated with liver function and tissue damage in human OLT, treatment with YAP activator ameliorated liver IRI by depressing macrophage function and improving hepatocyte protection in a non-transplant model of hepatic “warm” IRI. Here, the function of distinct YAP signaling pathways is proposed to study in a clinically relevant mouse model of prolonged hepatic cold ischemia followed by OLT. Hypothesis: downregulated peri-transplant YAP expression is an important driver of graft injury and development of PGD, and that such reduced YAP expression in liver graft may be of prognostic and therapeutic significance. Cellular specific YAP distribution, has prompted to put forth a dissection that YAP signaling at the macrophage (innate immune) regulates inflammation (pathogenic), autophagic reprogramming (homeostatic) and cytoprotection (anti-oxidative) during IR-stress in cold-stored murine OLTs. The following three specific aims are proposed: Aim 1: Determine whether downregulated macrophage YAP expression is a risk factor for developing PGD in cold-stored murine OLTs? Based on preliminary data, genetically modified mice strain (YAPM-KO) will be used to evaluate pre-OLT and post-OLT YAP expression on residential and circulation macrophage in relation to PGD events in a clinically relevant mouse model of extended hepatic cold storage followed by OLT. Aim 2: Define regulatory mechanisms by which YAP signaling controls immunity-related GTPase family M member 1 (IRGM1)-dependent macrophage inflammation in IR-stressed OLTs. Hypothesis: YAP activation modulates macrophage IRGM1 in liver IRI by coupling cyclic GMP-AMP synthase (cGAS) and interferon regulatory factor 3 (IRF3), which in turn mitigates liver IRI by diminishing innate pro-inflammatory responses. YAP-mediated IRGM1 deprivation will be screened in IRI-OLTs. Then, a new model of liver IRI in CD11b-DTR mice in which adoptive transfer of distinctive macrophage populations (after conditional depletion of native CD11b+ cells) will be utilized to dissect YAP–IRGM1 cross-regulation in hepatic IR-inflammation. Aim 3: Define molecular mechanisms by which YAP controls IRGM1-dependent macrophage autophagy in IR-stressed OLTs. Hypothesis: YAP deficiency augments IRGM1-mediated macrophage autophagy and leads into hepatocellular deterioration in IRI-OLT. YAP–IRGM1 mediated major autophagosomal formation in governing macrophage M1/M2 balance, and the biological significance and mechanisms of IRGM1-derived macrophage polarization will be assessed in IR-stressed YAPnull OLTs.