NFkB in the Astrocyte Swelling/Brain Edema with Acute Liver Failure

描述（由申请人提供）：脑水肿和相关颅内高压是急性肝衰竭（ALF）的主要并发症，其死亡率高，治疗选择主要限于紧急肝移植。通常认为氨是ALF水肿的原因，并且由于星形胶质细胞肿胀，水肿主要是“细胞毒性的”。然而，越来越多的证据表明，除了氨之外，细胞因子和相关的败血症和炎症也会导致ALF的脑水肿。在研究ALF相关的星形胶质细胞肿胀/脑水肿的机制的过程中，我们确定了转录因子NF-κ B作为星形胶质细胞肿胀/脑水肿的关键介质。值得注意的是，细胞因子是众所周知的NF-κ B激活剂。因此，细胞因子与氨一起似乎参与了ALF中NF-κ B的活化。我们已经产生了初步的数据表明，NF-kB确实是激活氨和细胞因子在培养的星形胶质细胞，和BAY 11-7082，NF-kB的抑制剂，显着减少星形胶质细胞肿胀氨和细胞因子。我们还发现，在ALF（硫代乙酰胺介导的肝毒性）大鼠模型中，NF-kB在神经细胞（包括星形胶质细胞）中被激活，并且全身给予BAY 11-7082可减轻ALF中的脑水肿。我们的假设是NF-kB的激活代表氨导致星形胶质细胞肿胀/ALF相关脑水肿的途径中的中心因子，并且细胞因子与氨协同相互作用以引起星形胶质细胞肿胀。目的#1将建立氨和细胞因子在星形胶质细胞肿胀和NF-κ B活化中的协同相互作用。目的#2将检查小胶质细胞（脑中介导炎症的主要细胞）对星形胶质细胞NF-κ B活化和细胞肿胀机制的潜在贡献。目的#3将研究NF-kB引起细胞肿胀的机制。我们已经产生了初步的数据，钠-钾-氯协同转运蛋白+ + -（NKCC），和水通道蛋白水通道蛋白-4（AQP 4）都激活氨处理培养的星形胶质细胞，这种激活似乎是由NF-κ B介导的，NKCC和AQP 4的激活可能代表倒数第二个事件，导致星形胶质细胞肿胀。将研究NKCC和AQP 4在细胞肿胀机制中的确切参与，沿着它们与炎性酶的相互作用，包括受NF-κ B调节的诱导型一氧化氮合酶（iNOS）、磷脂酶A2（PLA 2）和环氧合酶-2（考克斯-2）。目的#4将（a）使用ALF的TAA大鼠模型确定NF-k B的激活是否在体内发生，以及抑制NF-k B激活是否降低脑水肿的严重性，和（B）研究在表现出NF-k B的星形胶质细胞功能失活的转基因小鼠中TAA介导的ALF引起的脑水肿的状态。我们相信我们的研究将导致更好地了解与ALF相关的脑水肿机制，旨在为这种临床上危及生命的疾病开发新的治疗策略。 公共卫生相关性：严重的肝脏疾病会引起广泛的脑肿胀（脑水肿），可能导致不可逆的脑损伤，这种情况被称为急性肝衰竭（ALF）。这是一种危及生命的疾病，目前除了紧急肝移植外没有其他治疗方法。我们建议检查转录因子NF-：B作为一个重要的中介负责导致脑肿胀的ALF的作用。

DESCRIPTION (provided by applicant): Brain edema and associated intracranial hypertension are major complications of acute liver failure (ALF), which has a high mortality and for which therapeutic options are largely limited to an emergency liver transplantation. It is generally believed that ammonia is responsible for the edema in ALF, and that the edema is principally "cytotoxic", due to astrocyte swelling. Mounting evidence suggests, however, that in addition to ammonia, cytokines and related sepsis and inflammation also contribute to the brain edema in ALF. During the course of investigating mechanisms of ALF-related astrocyte swelling/brain edema, we identified the transcription factor NF-kB as a key mediator of astrocyte swelling/brain edema. It is notable that cytokines are well known activators of NF-kB. Thus, cytokines together with ammonia, appear to be involved in the activation of NF-kB in ALF. We have generated preliminary data indicating that NF-kB is indeed activated by ammonia and cytokines in cultured astrocytes, and that BAY 11-7082, an inhibitor of NF-kB, markedly diminished astrocyte swelling by ammonia and cytokines. We also found that in a rat model of ALF (thioacetamidemediated hepatotoxicity) NF-kB is activated in neural cells, including astrocytes, and that brain edema in ALF could be diminished by the systemic administration of BAY 11-7082. Our hypothesis is that activation of NF-kB represents a central factor in the pathway by which ammonia results in astrocyte swelling/ALF-related brain edema, and that cytokines synergistically interact with ammonia to bring about astrocyte swelling. Aim #1 will establish synergistic interactions between ammonia and cytokines in astrocyte swelling and NF-kB activation. Aim #2 will examine the potential contribution of microglia, the major cell in brain mediating inflammation, to the mechanism of astrocytic NF-kB activation and cell swelling. Aim #3 will examine the mechanisms by which NF-kB brings about cell swelling. We have generated preliminary data that Na-K-Cl cotransporter + + - (NKCC), and the water channel protein aquaporin-4 (AQP4) are both activated in ammonia-treated cultured astrocytes; that such activation appears to be mediated by NF-kB, and that the activation of NKCC and AQP4 may represent the penultimate events leading to astrocyte swelling. The precise involvement of NKCC and AQP4 in the mechanism of cell swelling, along with their interaction with inflammatory enzymes, including inducible nitric oxide synthase (iNOS), phospholipase A2 (PLA2), and cyclooxygenase-2 (COX-2) that are regulated by NF-kB, will be investigated. Aim #4 will (a) establish whether activation of NF-kB occurs in vivo using the TAA rat model of ALF, and whether inhibiting NF-kB activation diminishes the severity of brain edema, and (b) investigate the status of brain edema by TAA-mediated ALF in transgenic mice that exhibit an astrocytic functional inactivation of NF-kB. We believe our investigations will lead to a better understanding of mechanisms involved in the brain edema associated with ALF, with an aim at developing novel therapeutic strategies for this clinically life-threatening condition. PUBLIC HEALTH RELEVANCE: Severe liver disease can cause extensive brain swelling (brain edema) that may lead to irreversible brain damage, a condition referred to as acute liver failure (ALF). This is a life-threatening condition for which there is currently no treatment available other than an emergency liver transplantation. We propose to examine the role of the transcription factor NF-:B as a critical intermediary responsible for causing brain swelling in ALF.