HuR/HIF – SIRT1 Signaling Axis in Liver Transplant Rejuvenation

摘要 原位肝移植（奥尔特）是终末期肝病患者的金标准治疗， 肝源性肿瘤患者。然而，供体器官的稀缺促使使用扩展标准 “边缘”肝脏，特别容易受到缺血再灌注损伤（IRI）的影响， 急性/慢性排斥反应，可能需要再次移植。我们引入了器官的概念 “返老还童”，即，供体肝脏从IRI超敏状态转化为IRI超敏的稳态， 抗虹膜识别我们还提出SIRT 1脱乙酰酶作为连接IR应激与肝脏的变阻器 在小鼠和人类奥尔特中的年轻化。我们最近发现了新的肝阻力调节因子 对抗热与冷缺血应激反应，即，人类抗原R（HuR）与缺氧诱导因子 （HIF-1α）。我们还发现了Ikaros（IKZF 1），作为巨噬细胞活化标志物， 肝脏IRI。重要的是，我们还发现，在人类中， 奥尔特移植患者肝活检组织中HuR/HIF-1α水平升高，但Ikaros水平降低 样品我们假设肝细胞HuR / HIF-1α和巨噬细胞Ikaros之间的相互作用提供了一个新的途径。 调节供体肝脏对IR应激和再灌注介导的肝损伤的适应的新方法。 具体目标1：确定肝细胞HuR / HIF-1α与SIRT 1在IRI-OLT中相互作用的机制。 假设：肝细胞SIRT 1激活，由不同的缺氧/复氧（H/R）要求控制， HuR（热H/R）与HIF-1α（冷H/R），提供了新的手段来调节供体肝脏对IR应激的适应。 1.1：SIRT 1功能依赖于HuR信号传导，用于氧化应激中的抗炎反应。1.2： 小鼠肝缺血模型中的HuR/HIF-1α信号传导是温度应激依赖性的1.3：HIF-1α 控制冷诱导的IRI-OLT。1.4：HuR控制热诱导的IRI-OLT。 具体目标2：阐明IRI-OLT中巨噬细胞Ikaros与SIRT 1串扰的机制。 假设：巨噬细胞Ikaros信号通过抑制SIRT 1转录和M2加重IRI-OLT 巨噬细胞极化2.1：Ikaros-SIRT 1髓样轴影响肝HuR/HIF 1 α缺氧感知回路 在IRI-OLT中。2.2：巨噬细胞Ikaros信号传导依赖于SIRT 1转录用于M2极化。 具体目标3：确定低温机器保存下人肝再生的机制。 假设：在离体HMP过程中操纵HIF-1α /SIRT 1轴改善肝细胞功能， 再生的人类肝脏由于先前存在的质量差而拒绝用于移植。3.1：药理学 HIF-1α蛋白的稳定剂与SIRT 1协同改善人肝功能。3.2：预处理 激活/稳定HIF-1α的PHD抑制剂与增强的SIRT 1信号传导协同作用，改善 炎症，促进细胞保护，并使人类肝脏恢复活力。这些实验与以下方面高度相关： 优化供体肝脏捐献（DBD和DCD），以及改善当前器官供应的质量/规模。

ABSTRACT Orthotopic liver transplantation (OLT) is the gold standard of care in patients with end-stage liver disease and those with tumors of hepatic origin. However, the scarcity of donor organs prompted the use of extended criteria “marginal” livers, which are particularly susceptible to ischemia-reperfusion injury (IRI), which predispose to acute/chronic rejection, and may require re-transplantation. We have introduced the concept of organ “rejuvenation”, i.e., conversion of the donor liver from the state of IRI-hypersensitivity to the homeostatic state of IRI-resistance. We have also proposed that SIRT1 deacetylase serves as a rheostat linking IR-stress with liver rejuvenation in both, mouse and human OLT. We have recently identified new regulators of hepatic resistance against warm vs. cold ischemia stress responses, i.e., Human Antigen R (HuR) and Hypoxia-Inducible Factor (HIF-1α). We have also discovered Ikaros (IKZF1), acts as a macrophage activation marker and exacerbates liver IRI. Importantly, we also found that preserved hepatocellular function/improved clinical outcomes in human OLT patients were associated with increased HuR/HIF-1α but depressed Ikaros levels in the liver biopsy samples. We hypothesize that crosstalk between hepatocyte HuR / HIF-1α and macrophage Ikaros provides a new means to regulate the adaptation of donor livers to IR-stress and reperfusion-mediated hepatic damage. Specific Aim 1: Determine mechanisms of hepatocyte HuR / HIF-1α crosstalk with SIRT1 in IRI-OLT. Hypothesis: Hepatocyte SIRT1 activation, controlled by distinct hypoxia/reoxygenation (H/R) requirements for HuR (warm H/R) vs. HIF-1α (cold H/R), provide new means to regulate adaptation of donor livers to IR-stress. 1.1: SIRT1 function is dependent on HuR signaling for anti-inflammatory responses in oxidative stress. 1.2: HuR/HIF-1α signaling in a mouse model of hepatic ischemia is temperature stress-dependent. 1.3: HIF-1α controls cold-induced IRI-OLT. 1.4: HuR controls warm-induced IRI-OLT. Specific Aim 2: Delineate mechanisms of macrophage Ikaros crosstalk with SIRT1 in IRI-OLT. Hypothesis: Macrophage Ikaros signaling exacerbates IRI-OLT by repressing SIRT1 transcription and M2 macrophage polarization. 2.1: Ikaros-SIRT1 myeloid axis influences hepatic HuR/HIF1α hypoxia sensing circuit in IRI-OLT. 2.2: Macrophage Ikaros signaling depends on SIRT1 transcription for M2 polarization. Specific Aim 3: Define mechanism of human liver rejuvenation under hypothermic machine preservation. Hypothesis: Manipulation of HIF-1α / SIRT1 axis during ex-vivo HMP improves hepatocellular function to rejuvenate human livers declined for transplantation due to preexisting poor quality. 3.1: Pharmacological stabilizer of HIF-1α protein synergizes with SIRT1 to improve human liver function. 3.2: Preconditioning with PHD-inhibitor, which activates/stabilizes HIF-1α, synergizes with enhanced SIRT1 signaling to ameliorate inflammation, promote cytoprotection, and rejuvenate human livers. These experiments are of high relevance to refine donor liver donation (DBD and DCD) as well as to improve quality/size of the current organ supply.