Molecular Mechanisms of Acute Pancreatitis

描述(由申请人提供)：在美国，胰腺炎是发病率和死亡率的主要原因。目前还没有针对胰腺炎的特效治疗方法，主要原因是对其发病机制缺乏了解。我们最近观察到，突变的K-RAS过度表达所产生的高水平的RAS活性会导致胰腺炎。这表明RAS激活的信号通路足以启动腺泡细胞的病理反应。然而，目前尚不清楚突变RAS的高水平表达是否代表一种生理模型。因此，我们从内源性水平研究了突变型K-RAS对腺泡细胞表达的影响。我们发现，内源性突变K-RAS的水平不会引起胰腺的明显变化。然而，在腺泡细胞低突变K-RAS表达的小鼠中，胰蛋白酶抑制剂等生理性刺激可诱发慢性胰腺炎。因此，我们提出了一个工作假说，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，病理反应就会启动。我们将通过追求以下特定目标来确定参与这些反应的重要机制：1)在内源性水平的突变K-RAS存在的情况下，识别产生病理反应的生理刺激。为此，我们将确定高脂或高蛋白饮食是否可以在低突变RAS的背景下诱发胰腺炎，以及这种影响是否由CCK介导。我们还将研究不会在对照动物中诱发胰腺炎的促分泌剂Neurmedin b和促胰液素的作用，以确定它们的信号机制是否会在腺泡细胞中携带突变的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所必需和/或充分的机制。RAS与许多信号分子直接相互作用。然而，我们将重点关注已有证据表明它们可能与胰腺炎、ERKS、PI3K和Src有关的三种疾病。我们将结合遗传学和药理学方法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足够的。3)明确P53在RAS活性诱导的胰腺炎炎症和纤维化中的作用。RAS活性的升高会导致P53的激活。我们假设这是RAS活性变得病理性的阈值。我们进一步认为，P53通过诱导caspase1的激活来介导炎症效应。我们将结合遗传学和药理学的方法来检验这些假说。总之，这些使用新模型的研究将为急性和慢性胰腺炎涉及的机制提供重要的新见解，一些观察结果可能与携带沉默的RAS突变的人群直接相关。

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.