利用胰臟專一性NEMO基因剔除小鼠探討肥胖是如何增加胰管腺癌的發生

Abstract

根據美國全國癌症研究所公佈的數據，胰管腺癌是全美第四大癌症死因，在台灣則 是第八大癌症死因。胰管腺癌 (Pancreatic ductal adenocarcinoma; PDAC) 是一種生長在 胰臟外分泌性腺的惡性腫瘤。由於胰腺腫瘤生長過程中沒有明顯症狀，多數患者檢查出 罹病時已處晚期。因此，胰管腺癌是一個最致命且惡性程度相當高的疾病，患者的生存 期平均不超過 6 個月且 5 年生存率只有 3％至 5％，並且大約有 90％的胰管腺癌是經由 K-Ras 致癌基因的活化和變異所產生，但是如何造成或增加胰管腺癌發生的其他因素， 目前並沒有確切的研究證實。 許多的研究團隊包括我們的研究指出，除了遺傳、年齡、性別、抽煙 及酒精可能 的因素導致增加胰臟癌的發生機率外，肥胖是一個非常重要的因素造成增加胰臟癌的發 生且研究指出: 肥胖增加 2.6 倍的胰臟癌風險。肥胖可以導致活化許多的致癌訊號路 徑，包括 insulin/IGF1R/AKT/mTOR（TORC1）訊號路徑，IGF1/RAS/MAPK 訊號路徑 以及 STAT3 和 NF-κB 的活化。如果這些路徑失調，最終可能導致胰臟癌的發生和進展。 但肥胖究竟是如何增加胰臟癌的發生風險，從來沒有得到適當答案。這個計劃我們將使 用新的 IKKgamma/NEMO 小鼠模型去探討肥胖是透過何種致癌機制增加胰管腺癌的發生率。

NEMO 基因是一種抑癌基因。我們已經產製胰臟專一性 NEMO 基因剔除小鼠 (NEMO∆pan mice)，並餵食高脂食物 (high fat diet; HFD)。但是在餵食高脂食物後， NEMO∆pan 小鼠出現脂肪腹瀉及體重減輕的症狀並且在 4-6 個星期內死亡。因此，我們 使用 NEMO 雜合子小鼠 (NEMO + /∆pan mice) 研究肥胖究竟是如何增加胰管腺癌的發生 風險。在餵食 NEMO + /∆pan 小鼠 4 個月高脂食物後，表現出典型的癌前病變以及胰腺上 皮內瘤病變 (PanIN lesions)，腺泡，導管上皮化生（ADM），以及自噬能力缺陷 (defective autophagy)。因此，本研究的目的是使用 NEMO + /∆pan 小鼠探索肥胖與胰管腺癌的發生的 關係及機制。以期望達到的下列目標：（1）研究長時間餵食高脂食物的 NEMO + /∆pan 小 鼠如何誘導胰腺上皮內瘤病變 形成和導致胰管腺癌發展。（2）探索肥胖是藉由何種機 制誘導 NEMO + /∆pan 小鼠的胰腺上皮內瘤病變形成及加速導致發展成胰管腺癌。（3）確 定是否高脂飲食抑制細胞自噬能力可以誘導胰腺上皮內瘤病變的發展及惡性的進展。我 們相信這項研究應該能夠提供更多的訊息去了解胰管腺癌的發生的機制以便日後提供 做為藥物的發展。

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignant diseases with median survival of less than 6 months after conventional therapy and 5-year overall survival rate lower than 5%. Resistance to conventional therapy and aggressive nature make PDAC an incurable cancer. Approximately 90% of PDACs exhibit KRAS oncogenic mutations, but additional factors cause of PDAC development are still unknown. Several attempts including ours on etiology of PDAC have been investigated and suggested that obesity plays multiple roles in the pathogenesis of PDAC. Obesity, which increases PDAC risk by 2.6-fold causes activation of several oncogenic signaling pathways, including insulin/IGF1R/AKT/mTOR(TORC1) signaling, IGF1/RAS/MAPK signaling , STAT3 and NF-κB activation. Deregulation of these pathways could eventually lead to PDAC development and progression but exactly how obesity increases PDAC risk has never been properly investigated due to the absence of suitable mouse models. This project will refine a novel mouse model for understanding the etiology of human PDAC. We have generated the NEMO∆pan mouse strain and kept on HFD developed steatorrhea and weight loss due to exocrine pancreas deficiency and died within 4-6 weeks. We have therefore switched to examine how NEMO+/∆pan heterozygous mice, which are phenotypically normal, respond to HFD. Our preliminary data show that NEMO+/∆pan mice, in which one IKK gamma/NEMO allele has been ablated in pancreatic epithelial cells, develop typical pre-malignant PanIN lesions, acinar-ductal metaplasia (ADM), and defective autophagy after 4 months on high fat diet (HFD). Therefore, the aim of this study is to use NEMO+/∆pan mice to explore the mechanistic connection between overnutrition and PDAC, and expect to achieve the follow goals: (1) Determine how prolonged exposure of NEMO+/∆pan mice to HFD induces PanIN development and causes PanINs to PDAC progression. (2) To identify mechanisms by which obesity induces PanIN lesion formation in NEMO+/∆pan mice and accelerate their progression. (3) Determine whether HFD-induced suppression of autophagy is sufficient for inducing PanIN lesion development and malignant progression. We believe this study should be able to provide more information for insight into the pathogenesis of PDAC.