Oxyntic Atrophy and Novel Gastric Lineages

描述(由申请人提供)： 胃腺癌仍然是全球癌症相关死亡的第二大常见原因。绝大多数胃癌发生在慢性萎缩性胃炎的胃部，通常与幽门螺杆菌感染有关。虽然幽门螺杆菌作为胃癌发生的直接原因已被证实，但导致癌前化生和进展为癌症的谱系变化的细胞学基础仍不清楚。正常的胃底粘膜是由一组负责正常分泌粘蛋白、胃蛋白酶原和盐酸的异质上皮细胞组成的。与幽门螺杆菌感染相关的慢性损伤导致胃上皮细胞成分的显著变化，表现为壁细胞丢失(氧合萎缩)、表面细胞扩张(小凹增生)和粘液细胞化生。在人类氧化性萎缩的背景下，目前公认有两种化生谱系：肠化生(特征是胃粘膜中存在肠杯状细胞)和痉挛多肽表达化生(SPEM；特征是胃体中存在胃窦型粘液细胞)。然而，小鼠体内的幽门螺杆菌感染只会导致SPEM。在过去的10年里，我们研究了在氧合萎缩的情况下导致SPEM发展的因素。利用壁细胞定向的原载体DMP-777诱导急性壁细胞丧失，我们定义了在啮齿动物对急性壁细胞丧失的反应中诱导SPEM的动力学。我们最近对小鼠的谱系图谱研究表明，SPEM不是来自专业的祖细胞，而是来自表达Mist1的成熟主细胞向粘液细胞化生的转分化。所有这些结果支持胃底黏膜壁细胞的丧失导致主细胞转分化形成SPEM的假说，以及粘膜内在因素调节SPEM的出现是胃肿瘤发生的中心步骤。因此，了解引起和控制SPEM出现的因素是至关重要的，因为它是胃肿瘤发生所需的关键初始事件。我们将通过两个特定的目标继续我们对化生起源的研究：第一，尽管我们的谱系图谱研究已经确定主细胞正在产生SPEM，这表明成熟的主细胞一般都有转分化为化生的能力。然而，仍然有可能存在主要细胞亚群，这些亚群是真正的隐匿的化生前体细胞。因此，我们将试图通过检测长寿的主细胞亚群是否可能作为假定的静止祖细胞存在来确定主细胞亚群是否对SPEM的发展负责。此外，我们将研究胃底表达Lgr5的主细胞是否代表可能有助于SPEM发展的静止的前体细胞群。其次，我们将利用我们在之前的资助期间开发的新的小鼠主细胞条件永生化细胞培养模型(ImHead)，寻找可能影响主细胞体外转分化为SPEM的因素。在ImGeneral细胞中，我们将确定主要细胞分化特异性转录因子Mist1的过度表达是否可以促进主要细胞特性的进一步成熟。此外，我们还将确定在诱导Mist1 KO小鼠急性壁细胞丧失后，Mist1的缺失是否促进了化生的发展，并靶向下调了ImGeneral细胞中Mist1的表达。最后，我们将检验在我们最近对小鼠SPEM模型进行的基因微阵列分析中确定的可能的化生转化调控因子是否可以促进主细胞在ImGeneral细胞中表达时向SPEM的转分化。)通过这些研究，我们将获得导致化生诱导的细胞过程的基本见解，作为胃癌发生的关键启动步骤。) 公共卫生相关性： 在退伍军人中，胃炎、胃酸消化和反流性疾病是发病率较高的疾病。此外，在第三世界国家部署全球军事力量，使人员越来越多地暴露在胃癌常见的地区。因此，了解胃粘膜中易患癌症的化生变化的机制是非常重要的。我们最近的研究导致了胃癌起源概念的范式转变，表明正常和分化良好的主细胞可以产生化生，在慢性炎症的影响下，可以发展出进一步的变化，从而导致癌症。越来越多的证据表明，慢性损伤和炎症反应的组合对上皮源性癌症的发展至关重要。因此，我们对导致胃癌的最早病变的进化的研究将为导致癌症的一般途径提供重要的线索。)

DESCRIPTION (provided by applicant): Gastric adenocarcinoma remains the second most common cause of cancer-related death worldwide. The vast majority of gastric cancer evolves in the stomach in the setting of chronic atrophic gastritis usually in association with Helicobacter pylori infection. While the role of H. pylori as the proximate cause of gastric carcinogenesis is well established, the cellular basis of lineage changes that lead to development of preneoplastic metaplasia and progression to cancer remain unclear. The normal gastric fundic mucosa is assembled from a heterogeneous group of epithelial lineages responsible for the normal secretion of mucins, pepsinogen and HCl. Chronic injury associated with H. pylori infection leads to prominent changes in the composition of the gastric epithelia, with loss of parietal cells (oxyntic atrophy), expansion of surface cells (foveolar hyperplasia) and mucous cell metaplasia. Two metaplastic lineages are now acknowledged in the setting of oxyntic atrophy in humans: intestinal metaplasia (characterized by the presence of intestinal goblet cells in the gastric mucosa) and Spasmolytic Polypeptide Expressing Metaplasia (SPEM; characterized by presence of antral type mucous cells in the body of the stomach). However, Helicobacter infection in mice leads only to SPEM. Over the past 10 years, we have investigated the factors that lead to the development of SPEM in the face of oxyntic atrophy. Using a parietal cell directed protonophore, DMP-777, that induces acute loss of parietal cells, we have defined the dynamics of the induction of SPEM in rodents in the response to acute loss of parietal cells. Our recent lineage mapping studies in mice have demonstrated that SPEM arises, not from professional progenitor cells, but from transdifferentiation of mature Mist1-expressing chief cells into mucous cell metaplasia. All of these results support the hypotheses that loss of parietal cells from the gastric fundic mucosa induces the development of SPEM from transdifferentiation of chief cells and that intrinsic mucosal factors regulate the emergence of SPEM as the central step for initiation of gastric neoplasia. Thus, it is essential to understand the factors that elicit and control the emergence of SPEM as the critical initial event required for the development of gastric neoplasia. We will continue our studies of the origin of metaplasia through the prosecution of two specific aims: First, although our lineage mapping studies have determined that chief cells are giving rise to SPEM, suggesting that mature chief cells in general have the capacity to transdifferentiate into metaplasia. Nevertheless, it remains possible that subpopulations of chief cells exist that are the true cryptic progenitor cells for metaplasia. Therefore, we will seek to determine whether subpopulations of chief cells are responsible for development of SPEM by examining whether long- lived chief cell subpopulations may exist as putative quiescent progenitor cells. Furthermore, we will examine whether Lgr5-expressing chief cells in the gastric fundus may represent a quiescent progenitor cell population that could contribute to the development of SPEM. Second, we will seek to identify factors that may influence chief cell transdifferentiation into SPEM in vitro using novel conditionally immortalized cell culture models for mouse chief cells (ImChief) that we have developed during the previous funding period. In ImChief cells, we will determine whether over-expression of the chief cell differentiation-specific transcription factor Mist1 can promote further maturation of chief cell properties. In addition, we will determine whether loss of Mist1 promotes the development of metaplasia following induction of acute parietal cell loss in Mist1 KO mice and in targeted knockdown of Mist1 expression in ImChief cells. Finally, we will examine whether putative regulators of metaplastic transition, identified in our recent gene microarray analysis of mouse SPEM models, may promote chief cell transdifferentiation into SPEM when expressed in ImChief cells.))Through these studies we will gain fundamental insights into the cellular processes that lead to the induction of metaplasia as the critical initiating step for gastric carcinogenesis. ) PUBLIC HEALTH RELEVANCE: Gastritis, acid peptic and reflux diseases account for significant morbidity in the Veteran population. In addition, global deployment of military forces in third world nations increasingly exposes personnel to regions where gastric cancer is common. Thus, an understanding of the mechanisms involved in metaplastic changes within the lining of the stomach that predispose to cancer is of significant importance. Our recent studies have led to a paradigm shift in the concepts for the origin of gastric cancer, suggesting that normal and well-differentiated chief cells can give rise to metaplasias that, under the influence of chronic inflammation, can develop further changes that lead to cancer. Increasing evidence suggests that a combination of chronic injury and inflammatory responses are critical for the development of epithelial-derived cancers. Thus, our investigations of the evolution of the very earliest lesions that lead to gastric cancer will shed important light on the general pathways leading to cancer. )