Molecular Mechanisms of Acute Pancreatitis

描述（由申请人提供）：胰腺炎是美国发病率和死亡率最高的疾病。目前还没有针对胰腺炎的特异性治疗方法，主要是由于缺乏对其发病机制的了解。我们最近观察到，由突变K-Ras过度表达产生的高水平Ras活性导致胰腺炎。这表明Ras激活的信号通路足以引发腺泡细胞的病理反应。然而，目前尚不清楚高水平的Ras突变表达是否代表一种生理模型。因此，我们在内源性水平上研究了突变K-Ras对腺泡细胞表达的影响。我们发现内源性突变的K-Ras水平在胰腺中没有引起明显的变化。然而，在腺泡细胞中K-Ras表达低突变的小鼠中，生理刺激如胰蛋白酶抑制剂喂养可诱导慢性胰腺炎。因此，我们已经制定了一个工作假设，即Ras信号通路整合了生理和病理刺激，当活动水平超过阈值时，就会启动病理反应。我们将通过追求以下具体目标来确定参与这些反应的重要机制：1)确定在内源性突变K-Ras水平存在的情况下产生病理反应的生理刺激。在这个目的中，我们将确定在低突变Ras的背景下，高脂肪或高蛋白质的饮食是否可以诱导胰腺炎，以及这种作用是否由CCK介导。我们还将研究分泌剂neuromedin b和secretin的作用，它们在对照动物中不会诱发胰腺炎，以确定它们的信号机制是否会在腺泡细胞中携带突变K-Ras的动物中与Ras整合。2)确定Ras下游启动胰腺炎症和纤维化的必要和/或充分机制。Ras直接与许多信号分子相互作用。然而，我们将重点关注三个已经有证据表明它们可能与胰腺炎有关的基因，Erks、PI3K和Src。我们将利用遗传和药理学方法的结合来确定这些信号通路对于观察到的病理效应是必要的还是充分的。3)确定p53在Ras活性诱导的胰腺炎相关炎症和纤维化中的作用。Ras活性水平升高导致p53激活。我们假设这是Ras活性变为病态的阈值。我们进一步认为p53通过诱导caspase 1的激活来介导炎症作用。我们将使用遗传学和药理学方法的结合来检验这些假设。总之，这些使用新模型的研究将为涉及急性和慢性胰腺炎的机制提供重要的新见解，并且一些观察结果可能与携带沉默Ras突变的人群部分直接相关。

DESCRIPTION (provided by applicant): Pancreatitis accounts for significant morbidity and mortality in the USA. Currently there are no specific treatments for pancreatitis, primarily due to are lack of mechanistic understanding. We have recently observed that high levels of Ras activity generated by over-expression of mutant K-Ras cause pancreatitis. This indicates that the signaling pathways activated by Ras are sufficient to initiate pathological responses in acinar cells. However, it is unclear that high levels of mutant Ras expression represent a physiologic model. Therefore, we investigated the influence of acinar cell expression of mutant K-Ras at an endogenous level. We found that endogenous levels of mutant K-Ras cause no obvious changes in the pancreas. However, in mice with low mutant K-Ras expression in acinar cells, physiologic stimuli such as trypsin inhibitor feeding induced chronic pancreatitis. Therefore, we have formulated a working hypothesis that the Ras signaling pathway integrates both physiologic and pathologic stimuli and when activity levels exceed a threshold pathological responses are initiated. We will identify the important mechanisms involved in these responses by pursuing the following specific aims: 1) Identify physiologic stimuli that generate pathological responses in the presence of endogenous levels of mutant K-Ras. In this aim, we will determine whether diets high in fat or protein can induce pancreatitis in a background of low mutant Ras and whether this effect is mediated by CCK. We will also investigate the effects of the secretagogues neuromedin b and secretin, which do not induce pancreatitis in control animals, to determine whether their signaling mechanisms will integrate with Ras in animals bearing mutant K-Ras in acinar cells. 2) Identify mechanisms down-stream of Ras which are necessary and/or sufficient to initiate pancreatic inflammation and fibrosis. Ras interacts directly with many signaling molecules. However, we will focus on three for which there is already evidence that they may be involved in pancreatitis, Erks, PI3K and Src. We will utilize a combination of genetic and pharmacological approaches to determine whether these signaling pathways are necessary or sufficient for the observed pathological effects. 3) Determine the role of p53 in the inflammation and fibrosis associated with Ras activity induced pancreatitis. Elevated levels of Ras activity lead to p53 activation. We hypothesize that this is the threshold at which Ras activity becomes pathological. We further suggest that p53 mediates inflammatory effects by inducing the activation of caspase 1. We will test these hypotheses using a combination of genetic and pharmacological approaches. Together these studies using novel models will provide important new insights into the mechanisms involved in acute and chronic pancreatitis and some observations may be directly relevant to a segment of the population which carries silent Ras mutations.