Diet and the Calcium Channel TRPV6 in Colon Hyperplasia

描述(申请人提供)：炎症性肠病(IBD)会增加患结肠癌的风险。炎症性肠病的病因包括破坏肠道微生物区系的遗传背景和西方生活方式，如高脂肪、低纤维和低钙的饮食。这些因素结合在一起会损害肠道的天然免疫力，增加对细菌感染和慢性炎症的易感性。我们采用革兰氏阴性杆菌罗氏柠檬酸杆菌(CR)诱导的小鼠可传播性结肠增生症(TMCH)模型，以确定细胞事件和信号通路可能参与对增加癌变易感性的管腔因子的反应。感染的小鼠出现中度炎症反应，局限于远端结肠和结肠隐窝的极度增生。这些反应通常是自我限制的，但明显增加了接受致癌物治疗或基因改变(即肿瘤抑制基因APC突变)的小鼠患结肠癌的易感性。最近的研究为这些发现提供了一个潜在的解释，这些研究表明，TMCH与两种强大的上皮增殖调节剂(-连环蛋白和核因子-B)的早期和持续升高有关。通过使用富纤维(果胶)或高钙饮食，我们发现这两种饮食都抑制了增殖。然而，富含果胶的饲料降低了2-连环素和核因子-B的活性，但富钙饲料不影响这两条促生长和抗凋亡途径。这使我们得出结论，高钙饮食通过抑制第三个强大的促生长途径发挥作用，该途径独立于核因子(B)和(-连环蛋白)。对肠道中与钙反应相关的几种基因产物的初步评估显示，在感染的结肠中，钙通道TRPV6显著上调，而在服用1%膳食钙的感染小鼠的结肠中，该基因显著抑制。由于在包括结肠癌在内的其他恶性肿瘤中也发现了TRPV6的高表达，我们推测，由于TRPV6的过度表达而导致的钙信号中断导致CR诱导的结肠增生，这种异常的细胞反应可以通过饮食中钙下调TRPV6来防止。为了验证这一假设，我们提出了以下目标：1)WT和TRPV6消融(KO)小鼠将被用来确定TRPV6基因产物在TMCH增殖和炎症中的作用；2)这些小鼠也将被用来确定高钙饮食对TMCH的抑制是否依赖于TRPV6的表达。这些研究应该能深入了解饮食钙预防结肠癌前病变的机制，并可能为降低结肠癌风险的饮食建议奠定基础。与公众健康相关：这项研究将集中在饮食钙抑制结肠异常细胞生长的机制上。这种异常的细胞生长在细菌感染后发生，可能会增加患结肠癌的易感性。通过识别钙保护作用的靶基因，我们可以设计药物来阻止它们的表达/活性，并逆转在终生暴露于缺钙饮食中的结肠损伤。

DESCRIPTION (provided by applicant): Inflammatory bowel disease (IBD) increases the risk of colon cancer. The etiologies of inflammatory bowel diseases include genetic background and western life style that impair the microbial flora in the gut, such as diets high in fat and low in fiber and calcium. These factors combine to compromise the innate immunity of the gut and to increase the susceptibility to bacterial infections and chronic inflammation. To determine the cellular events and signaling pathways that may be involved with response to luminal factors that increase susceptibility to malignant transformation, we have employed the model of transmissible murine colonic hyperplasia (TMCH) induced by the gram-negative bacterium citrobacter rodentium (CR). The infected mice develop a moderate inflammatory response restricted to the distal colon and extreme hyperplasia of the colonic crypts. These responses are generally self-limited, but clearly increase the susceptibility to develop colon cancer in either carcinogen-treated or genetically-altered (i.e., mutation in the tumor-suppressing gene, Apc) mice. A potential explanation for these findings is provided by recent studies, which have shown that TMCH is associated with an early and sustained elevation of two powerful modifiers of epithelial proliferation, (-catenin and NF-(B. By using either fiber-rich (pectin) or high calcium diets, we found that both diets inhibited the hyperplasia. However, the pectin-rich diet diminished the activities of 2-catenin and NF-(B, but the calcium-rich diet did not affect these two growth-promoting and anti-apoptotic pathways. This led us to conclude that high calcium diet acted by inhibiting a third, powerful growth-promoting pathway, which was independent of NF-(B and (-catenin. Preliminary assessment of several gene products associated with response to calcium in the gut has revealed a dramatic upregulation of the calcium channel TRPV6 in the infected colon and a significant repression of this gene in the colon of infected mice given 1% dietary calcium. Since elevated expression of TRPV6 was found in other malignancies, including colon cancer, we hypothesized that disrupted calcium signaling caused by over expression of TRPV6 contributes to CR-induced colonic hyperplasia and this abnormal cellular response can be prevented by downregulation of TRPV6 with dietary calcium. To test this hypothesis we propose the following aims: 1) WT and TRPV6-ablated (KO) mice will be used to determine the contribution of the TRPV6 gene product to the hyperplasia and the inflammation in TMCH; 2) these mice will be also used to determine if inhibition of TMCH by high calcium diet is dependent on TRPV6 expression. These studies should provide an insight into the mechanisms whereby dietary calcium prevents pre-neoplastic hyperplasia in the colon and might establish the basis for dietary recommendations that reduce the risk of colon cancer. PUBLIC HEALTH RELEVANCE: This study will focus on the mechanisms by which dietary calcium attenuates abnormal cell growth in the colon. Such abnormal cell growth occurs after bacterial infections and can increase susceptibility to develop colon cancer. By identifying the target genes for the protective actions of calcium we can design drugs that block their expression/activities and reverse damages that develop during life-long exposure of the colon to calcium-deficient diets.