Regulation of Hepatic Stellate Cells by Extracellular Nucleotides

描述（由申请人提供）：纤维发生，或瘢痕形成，是对几乎所有器官损伤的反应。尽管慢性肝病的治疗取得了进展，肝纤维化和随后的肝硬化仍然是美国和全世界的一个严重的健康问题。肝星状细胞（HSC）是肝脏的原发性纤维化细胞。尽管近年来对HSC功能的理解取得了重要进展，但调节HSC活性的关键信号机制尚未完全了解。P2Y受体是胞外ATP和其他核苷酸的G蛋白偶联受体。P2Y受体通过肌醇三磷酸（IP3）介导的钙信号诱导下游细胞效应。最近，我们报道了HSC表达P2Y受体，并且这些受体的激活诱导了HSC的纤维化。我们现在已经观察到HSC在不同的区域表达IP3受体（IP3R）：细胞核和细胞延伸。这种独特的IP3R表达模式允许由这两个细胞区室介导的P2Y受体激活的不同影响。我们还观察到，在整个动物中阻断P2Y受体可能会阻止肝纤维化的发展，这表明通过P2Y受体的信号传导是疾病状态下肝纤维化的重要介质。因此，我们提出P2Y受体激活通过HSC内不同亚细胞区室的多种下游效应诱导肝纤维化。我们将通过以下三个具体目标来检验这一假设：1。确定P2Y受体活化对细胞核内HSC功能的影响。2. 确定P2Y受体激活对HSC细胞扩展功能的影响。3. 确定阻断P2Y受体是否抑制肝纤维化。我们相信，这些实验的结果将导致对HSC功能的新认识，并可能最终导致肝纤维化治疗的新药理学方法的发展。

DESCRIPTION (provided by applicant): Fibrogenesis, or scar formation, occurs as a response to injury in almost all organs. Liver fibrosis and subsequent cirrhosis remains a critical health problem in the United States and worldwide despite advances in therapy of chronic liver disease. Hepatic stellate cells (HSC) are the primary fibrogenic cells of the liver. Although there have been important advances in the understanding of HSC function in recent years, critical signaling mechanisms regulating HSC activity have not been completely understood. P2Y receptors are G protein coupled receptors for extracellular ATP and other nucleotides. P2Y receptors induce downstream cellular effects through inositol triphosphate (IP3)-mediated calcium signals. Recently, we reported that HSC express P2Y receptors, and that activation of these receptors induces fibrogenesis in HSC. We have now observed that HSC express IP3 receptors (IP3R) at distinct regions within HSC: the nucleus and cell extensions. This unique pattern of IP3R expression allows for distinct effects of P2Y receptor activation mediated by these two cellular compartments. We have also observed that blockade of P2Y receptors in the whole animal may prevent development of liver fibrosis, suggesting that signaling via P2Y receptors is an important mediator of liver fibrosis in disease states. Thus we propose that P2Y receptor activation induces liver fibrosis via multiple downstream effects in distinct subcellular compartments within HSC. We will test this hypothesis through the following three Specific Aims: 1. Determine the effects of P2Y receptor activation on the function of HSC in the nucleus. 2. Determine the effects of P2Y receptor activation on the function of HSC in cell extensions. 3. Identify whether blockade of P2Y receptors inhibits liver fibrosis. We believe that the results of the proposed experiments will lead to novel understanding of HSC function and may ultimately lead to the development of new pharmacologic approaches to the treatment of liver fibrosis. Public Health Relevance: Advanced liver fibrosis, leading to cirrhosis, is the most important cause of liver failure, leading to death in the absence of liver transplantation. Multiple therapeutic approaches have been proposed to prevent or reverse liver fibrosis; however, these have been stymied due to incomplete understanding of the basic mechanisms of liver fibrosis. In the proposed work, we will identify novel pathways that are important in the pathogenesis of liver fibrosis, which should in turn lead to new approaches to prevent or liver fibrosis in patients.