Role of Early Growth Response Factor-1 in Cholestatic Liver Injury

描述（由申请人提供）：本提案的总体目标是阐明胆汁淤积触发肝脏促炎介质产生的机制。胆汁淤积性肝病发生时，从肝脏的胆汁酸排泄被中断。这导致胆汁酸在肝脏中积聚，肝脏炎症和肝细胞损伤。胆汁淤积期间肝细胞损伤的发病机制部分取决于促炎介质的释放，促炎介质导致中性粒细胞在肝脏积聚并被激活以损害肝细胞。有趣的是，与胆汁淤积相关的炎症独立于肿瘤坏死因子-a或白介素-1发生，这表明这一过程是由一种新的、先前未描述的机制调节的。我们的初步研究表明，转录因子，早期生长反应因子-1 (Egr-1)，在这个过程中是至关重要的。在胆汁淤积期间，Egr-1在肝细胞中迅速上调。Egr-1的上调似乎是由胆汁酸直接介导的，因为原代小鼠肝细胞暴露于病理浓度的胆汁酸中会上调Egr-1。我们的研究进一步表明，在Egr-1基因敲除的胆汁淤积小鼠中，巨噬细胞炎症蛋白-2、细胞间粘附分子-1、中性粒细胞积累和肝细胞损伤的上调显著降低。这些初步结果表明，肝细胞中Egr-1的上调对于中性粒细胞依赖性炎症性肝损伤的发展至关重要。此外，这些研究表明，Egr-1在胆汁酸浓度升高和肝脏促炎介质的产生之间提供了关键联系。因此，本建议的主要假设是，在胆汁淤积的早期阶段，胆汁酸浓度升高上调肝细胞中的Egr-1，从而增加促炎介质的表达，导致中性粒细胞在肝脏积聚并被激活以损害肝细胞。本研究旨在通过：(1)阐明胆汁酸上调肝细胞Egr-1的分子机制，(2)确定Egr-1是否调节肝细胞促炎介质的表达，(3)确定胆汁酸是否通过Egr-1依赖机制增加肝细胞促炎介质的表达。更深入地了解Egr-1介导胆汁淤积过程中肝细胞损伤的分子机制，可以为治疗人类这种疾病提供新的思路。此外，由于胆汁酸浓度在人类几种肝脏疾病中升高，这一途径也可能被证明是肝脏炎症损伤的一个重要的一般机制。

DESCRIPTION (provided by applicant): The overall goal of this proposal is to elucidate the mechanism by which cholestasis triggers production of proinflammatory mediators in the liver. Cholestatic liver disease arises when excretion of bile acids from the liver is interrupted. This results in the accumulation of bile acids in the liver, hepatic inflammation, and hepatocyte injury. The pathogenesis of hepatocyte injury during cholestasis depends in part on the release of proinflammatory mediators that cause neutrophils to accumulate in the liver and become activated to damage hepatocytes. Interestingly, inflammation associated with cholestasis occurs independently of tumor necrosis factor-a or interteukin-1, suggesting that this process is regulated by a novel, previously undescribed mechanism. Our preliminary studies indicate that the transcription factor, early growth response factor-1 (Egr-1), is critical for this process. Egr-1 is rapidly upregulated in hepatocytes during cholestasis. Upregulation of Egr-1 appears to be mediated directly by bile acids, since exposure of primary mouse hepatocytes to pathological concentrations of bile acids upregulates Egr-1. Our studies show further that upregulation of macrophage inflammatory protein-2, intercellular adhesion molecule-1, neutrophil accumulation, and hepatocyte injury are dramatically reduced in Egr-1 knockout mice with cholestasis. These preliminary results suggest that upregulation of Egr-1 in hepatocytes is vital for the development of neutrophil-dependent inflammatory liver injury. Furthermore, these studies indicate that Egr-1 provides the critical link between elevated concentrations of bile acids and the production of proinflammatory mediators in liver. Therefore, the main hypothesis of this proposal is that during early stages of cholestasis, elevated concentrations of bile acids upregulate Egr-1 in hepatocytes, which increases expression of proinflammatory mediators that cause neutrophils to accumulate in the liver and become activated to damage hepatocytes. The studies in this proposal aim to test this hypothesis by: (1) elucidating the molecular mechanism(s) by which bile acids upregulate Egr-1 in hepatocytes, (2) determining whether Egr-1 regulates proinflammatory mediator expression by hepatocytes, and (3) determining whether bile acids increase proinflammatory mediator expression by hepatocytes through Egr-1-dependent mechanisms. A greater understanding of the molecular mechanism(s) by which Egr-1 mediates hepatocellular injury during cholestasis could provide insight into ways to treat this disease in humans. Furthermore, since bile acid concentrations are increased in several types of liver disease in humans, this pathway could also prove to be an important, general mechanism of inflammatory injury in the liver.