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

描述（由申请人提供）：脑水肿和相关的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。一般认为氨气是造成ALF水肿的主要原因，而这种水肿主要是由于星形胶质细胞肿胀引起的“细胞毒性”。然而，越来越多的证据表明，除了氨外，细胞因子和相关的败血症和炎症也有助于ALF的脑水肿。在研究alf相关星形胶质细胞肿胀/脑水肿的机制过程中，我们发现转录因子NF-kB是星形胶质细胞肿胀/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-kB的激活剂。因此，细胞因子和氨似乎参与了ALF中NF-kB的激活。我们获得的初步数据表明，在培养的星形胶质细胞中，NF-kB确实被氨和细胞因子激活，并且NF-kB抑制剂BAY 11-7082显著减少氨和细胞因子引起的星形胶质细胞肿胀。我们还发现，在大鼠的硫代乙醯胺介导的肝毒性模型中，NF-kB在包括星形胶质细胞在内的神经细胞中被激活，并且全身给药BAY 11-7082可以减轻ALF中的脑水肿。我们的假设是NF-kB的激活是氨导致星形胶质细胞肿胀/ alf相关脑水肿途径的中心因素，细胞因子与氨协同作用导致星形胶质细胞肿胀。目的1将建立氨和细胞因子在星形胶质细胞肿胀和NF-kB活化中的协同相互作用。Aim #2将研究小胶质细胞（大脑中介导炎症的主要细胞）对星形细胞NF-kB激活和细胞肿胀机制的潜在贡献。Aim #3将研究NF-kB导致细胞肿胀的机制。我们已经获得了初步的数据，Na-K-Cl共转运蛋白+ + - (NKCC)和水通道蛋白aquaporin-4 （AQP4）在氨处理的培养星形胶质细胞中都被激活；这种激活似乎是由NF-kB介导的，NKCC和AQP4的激活可能是导致星形胶质细胞肿胀的倒数第二个事件。NKCC和AQP4在细胞肿胀机制中的确切参与，以及它们与炎症酶的相互作用，包括NF-kB调节的诱导型一氧化氮合酶（iNOS）、磷脂酶A2 （PLA2）和环氧合酶2 (COX-2)，将被研究。Aim #4将(a)利用TAA大鼠ALF模型确定NF-kB激活是否在体内发生，以及抑制NF-kB激活是否会减轻脑水肿的严重程度，(b)研究TAA介导的ALF在表现出NF-kB星形细胞功能失活的转基因小鼠中的脑水肿状态。我们相信我们的研究将有助于更好地理解ALF相关脑水肿的机制，旨在为这种临床上危及生命的疾病开发新的治疗策略。

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.