Improved liver function and regeneration with A20

描述（申请人提供）：肝脏具有显著的再生能力，可在损伤或切除后恢复。然而，足够的再生取决于维持健康的残余肝块，否则会导致暴发性肝衰竭。这个问题在肝移植中尤为重要，同种异体移植物面临严重的缺血、炎症和免疫损伤，这些损伤在使用“小尺寸”肝移植的成人活体肝移植中进一步加剧。了解保护肝细胞和促进其增殖的生理保护机制对于制定旨在改善肝移植预后的治疗策略至关重要。我们已经确定7-锌指蛋白A20是肝细胞保护和再生反应的关键组成部分，因为它通过改变启动物Caspase 8的表达来保护肝细胞免于凋亡；通过限制氧化损伤保护肝细胞免于缺血性坏死；通过抑制NFkB激活含有肝细胞炎症反应；并通过降低细胞周期蛋白依赖性激酶抑制剂p21waf1的表达来促进肝细胞增殖。A20的这些“肝保护”功能转化为显著的再生优势，在小鼠根治性致死性肝切除术或长期肝缺血后显著提高生存率。有趣的是，A20的转录在“小尺寸”肝移植物中减少，可能导致损伤增加和再生不足。我们最近在肝细胞中发现了A20的新靶点，这可能解释了它的有益作用：1)增加过氧化物酶体增殖物激活受体α (PPAR1)的表达，2)降低p21waf1的表达，3)通过降低细胞因子信号传导抑制因子(SOCS)-3的表达，在IL-6水平较低的情况下增强信号传感器和转录激活因子3 （STAT-3）的磷酸化。揭示A20依赖性保护肝细胞免于氧化损伤后坏死细胞死亡的分子基础，并探讨PPAR1在介导这一作用中的作用。特异性目的2：通过研究p21waf1和IL-6/STAT-3/SOCS3在肝细胞中支持A20促增殖功能的作用，探索A20促增殖功能的分子基础。特异性目的3：评价肝脏中A20表达对非最佳肝移植物（包括小尺寸肝移植物和长时间缺血肝移植物）存活和功能的影响。在我们的实验模型中证明A20的有益作用应该为将A20为基础的疗法转化为临床实践奠定基础。

DESCRIPTION (provided by applicant): The liver has remarkable regenerative capacity, allowing recovery following injury or resection. Adequate regeneration is, however, contingent upon maintenance of a healthy residual liver mass, otherwise fulminant hepatic failure ensues. This issue is of particular importance in liver transplantation where allografts face substantial ischemic, inflammatory, and immune insults that are further exacerbated in adult living donor liver transplants using "small-for-size" liver grafts. Understanding the physiologic protective mechanisms safeguarding hepatocytes and promoting their proliferation is critical for devising therapeutic strategies aimed at improving outcome of liver transplantation. We have identified the 7-Zinc finger protein A20 as a critical component of the protective and regenerative responses of hepatocytes in that it protects hepatocytes from apoptosis by altering the expression of the initiator Caspase 8; safeguards hepatocytes from ischemic necrosis by limiting oxidative damage; contains hepatocyte inflammatory responses by inhibiting NFkB activation; and promotes hepatocyte proliferation by decreasing the expression of the Cyclin Dependent Kinase Inhibitor p21waf1. These "hepatoprotective" functions of A20 translate into a dramatic regenerative advantage with greatly improved survival following radical lethal hepatectomy or prolonged liver ischemia in mice. Interestingly, transcription of A20 is decreased in "small-for-size" liver grafts, likely contributing to increased damage and inadequate regeneration. We have recently unraveled novel targets for A20 in hepatocytes that may account for its beneficial effects: 1) Increases the expression of Peroxisome Proliferator-Activated Receptor alpha (PPAR1), 2) Decreases the expression of p21waf1 and 3) Enhances Signal Transducer and Activator of Transcription 3 (STAT-3) phosphorylation despite lower IL-6 levels through decreasing Suppressor of Cytokine Signaling (SOCS)-3 expression We wish to: Specific Aim 1: Decipher the molecular basis for the A20 dependent protection of hepatocytes from necrotic cell death following oxidative damage and probe the involvement of PPAR1 in mediating this effect. Specific Aim 2: Explore the molecular basis for the pro-proliferative function of A20 in hepatocytes by investigating the role of p21waf1 and IL-6/STAT-3/SOCS3 in supporting this effect. Specific Aim 3: Evaluate the impact of A20 expression in the liver upon survival and function of non- optimal liver grafts, including small-for-size liver grafts and grafts with prolonged ischemia time. Demonstrating A20's beneficial effects in our experimental models should set the basis for translating A20- based therapies into clinical practice.