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.
The development of new treatments for pancreatitis had been hindered by the lack of physiologically relevant animal models. We have developed for the first time an animal model with a modified genetic background that develops chronic pancreatitis after manipulations that are physiologically relevant and which are not directly injurious. This new model will provide an opportunity to discover important new details about the mechanisms which initiate pancreatic disease.
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