Improved liver function and regeneration with A20
Principal Investigator: Christiane Ferran
Affiliation: Harvard University
Abstract: 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. PUBLIC HEALTH RELEVANCE: Orthotopic liver transplantation is a life-saving measure for patients suffering from acute or chronic liver failure. However, demand exceeds organ availability by several orders of magnitude, causing a number of patients to die while on the waiting list. We have identified the A20 protein as an ideal "hepatoprotective" candidate. A20 combines anti-apoptotic, anti-necrotic, anti-inflammatory, anti-oxidative and pro-proliferative functions in hepatocytes, which translates into significant survival and regenerative advantages following radical lethal hepatectomy and severe ischemia reperfusion injury in mice. We wish to test the effectiveness of A20-based therapies in improving survival and function of sub-optimal liver grafts that are usually unsuitable for transplantation. Any beneficial effects of A20 in these models would expand the pool of liver donors and help ease the severe organ shortage in liver transplantation.
Funding Period: ----------------2003 - ---------------2014-
more information: NIH RePORT