Diet and the Calcium Channel TRPV6 in Colon Hyperplasia

描述（由申请人提供）：炎症性肠病（IBD）增加结肠癌的风险。炎症性肠病的病因包括遗传背景和损害肠道微生物菌群的西方生活方式，如高脂肪、低纤维和低钙的饮食。这些因素结合起来会损害肠道的先天免疫，增加对细菌感染和慢性炎症的易感性。为了确定细胞事件和信号通路可能参与对增加恶性转化易感性的腔内因子的反应，我们采用了革兰氏阴性细菌（CR）诱导的传染性小鼠结肠增生（TMCH）模型。受感染的小鼠出现中度炎症反应，仅限于结肠远端和结肠隐窝的极度增生。这些反应通常是自限性的，但明显增加了致癌物治疗或基因改变（即肿瘤抑制基因Apc突变）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可能的解释，这些研究表明TMCH与两种强大的上皮增殖调节剂（-catenin和NF- B）的早期和持续升高有关。通过使用富含纤维（果胶）或高钙的饲料，我们发现两种饲料都抑制了增生。然而，富含果胶的饮食降低了2-catenin和NF-(B)的活性，但富含钙的饮食对这两个促生长和抗凋亡途径没有影响。这使我们得出结论，高钙饮食通过抑制第三种强大的生长促进途径起作用，该途径独立于NF-(B)和（-catenin）。对几种与肠道钙反应相关的基因产物的初步评估显示，在受感染小鼠的结肠中，钙通道TRPV6显著上调，并且在给予1%膳食钙的受感染小鼠的结肠中，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的表达升高，我们假设TRPV6过表达引起的钙信号传导中断有助于cr诱导的结肠增生，这种异常的细胞反应可以通过膳食钙下调TRPV6来预防。为了验证这一假设，我们提出了以下目的：1)使用WT和TRPV6消融（KO）小鼠来确定TRPV6基因产物对TMCH增生和炎症的贡献；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。这些研究将为膳食钙预防结肠肿瘤前期增生的机制提供深入的见解，并可能为降低结肠癌风险的饮食建议奠定基础。公共卫生相关性：本研究将关注膳食钙减缓结肠异常细胞生长的机制。这种异常细胞生长发生在细菌感染后，可能增加患结肠癌的易感性。通过确定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/活动，并逆转在结肠终身暴露于缺钙饮食中所造成的损害。

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.