The impact of the unfolded protein responses on steatosis

描述（由申请人提供）：估计有超过1亿的美国人患有脂肪肝（FLD）。这是糖尿病、病毒性肝炎和艾滋病毒感染总发病率的五倍。FLD的初期阶段可以通过改变生活方式来治愈。然而，即使目前的FLD患者中有一小部分进展到晚期，仅对这些患者的管理就会使诊所、肝移植等待名单和卫生保健预算不堪重负。目前迫切需要了解导致这种疾病的第一步，即肝细胞脂质积累（脂肪变性）的细胞途径，以便设计针对这些途径的有效治疗方法。此外，还需要体内模型来测试候选药物。我们用斑马鱼幼虫来研究导致脂肪变性的基因和途径。其中一个途径是未折叠蛋白反应（UPR）的激活，它在分泌途径中作为应激的测量仪。我们开发了几种诱导斑马鱼幼鱼脂肪变性的方法，发现UPR激活在所有这些方法中都发生。利用斑马鱼研究UPR与脂肪变性之间的联系的优势包括相对快速和廉价的遗传方法，样本量大，动物体积小以及与人类的遗传同源性。此外，斑马鱼脂肪肝的组织病理学与在患者身上看到的非常相似，很可能许多相同的病理生理机制会导致这种疾病。我们发现，虽然一个强大的UPR通常会导致脂肪变性，但在一个

DESCRIPTION (provided by applicant): More than 100 million Americans are estimated to have fatty liver disease (FLD). This is five times the combined incidence of diabetes, viral hepatitis and HIV infection. The initial stages of FLD can be cured with lifestyle changes. However, if even a small percentage of current FLD patients progress to advanced stages, the management of these patients alone will overwhelm clinics, liver transplant waiting lists and health care budgets. There is an urgent need to understand the cellular pathways that contribute to the first step of this disease, accumulation of lipid in hepatocytes (steatosis), so s to design effective therapies to target these pathways. Moreover, in vivo models are needed to test candidate drugs. We use zebrafish larvae to study the genes and pathways that lead to steatosis. One such pathway is the activation of the unfolded protein response (UPR) which serves as a meter for stress in the secretory pathway. We developed several means of inducing steatosis in zebrafish larvae discovered that UPR activation occurs in all of these. The advantage of using zebrafish for studying the link between the UPR and steatosis include the relatively rapid and inexpensive genetic approaches, large sample size, small animal size and genetic homology to humans. Also, the histopatholgy of fatty liver in zebrafish is very similar to what is seen in patients and it is likely that many of the same pathophysiological mechanisms will contribute to this disease. We found that while a robust UPR typically causes steatosis, in a moderate UPR does not, and instead, protects against it. The UPR is highly complex, and it is now clear that analysis of isolated metrics of UPR activation is not sufficient to understand how URP activation can alternatively cause or reduce steatosis. We will address this by integrating multiple metrics UPR activation into a system in order to understand their relationships to the outcome of steatosis. This systems biology approach in Aim 1 will allow us to generate a signature of molecular metrics that identify the stressed UPR that is associated with steatosis and the adaptive UPR that protects against it. Once we understand the complex and dynamic nature of the UPR then we can use this to determine how steatosis caused by chronic UPR activation is reduced when one of the key UPR players, Atf6, is depleted whereas steatosis caused by acute UPR activation worsens with Atf6 depletion. In Aim 2 the hypothesis that in chronic UPR activation, Atf6 depletion dials down a 'stressed UPR'. In Aim 3, we will analyze whether Atf6 depletion deprives hepatocytes of the complete reserve of protein folding capacity, accentuating a stressed UPR caused by an acute insult. This work will provide valuable information elucidating the mechanism by which individual UPR components may serve to treat fatty liver disease caused by different etiologies.