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常见原因。绝大多数胃癌发生在慢性萎缩性胃炎的胃中，通常与幽门螺杆菌感染有关。而H.幽门螺杆菌作为胃癌发生的近因已被公认，但导致癌前化生发展和进展为癌症的谱系变化的细胞基础仍不清楚。正常胃底粘膜由负责粘蛋白、胃蛋白酶原和HCl的正常分泌的上皮谱系的异质组组装而成。慢性损伤与H.幽门螺杆菌感染导致胃上皮组成的显著变化，伴随壁细胞的丧失（泌酸萎缩）、表面细胞的扩张（小凹增生）和粘液细胞化生。目前，在人类胃泌酸性萎缩的背景下确认了两种化生谱系：肠化生（以胃粘膜中存在肠杯状细胞为特征）和痉挛性多肽表达化生（SPEM;以胃体中存在胃窦型粘液细胞为特征）。然而，小鼠的螺杆菌感染仅导致SPEM。在过去的10年里，我们已经调查了导致SPEM在胃泌酸性萎缩中发展的因素。使用壁细胞定向的质子载体，ESTA-777，诱导急性壁细胞的损失，我们已经定义了动态的诱导SPEM在啮齿动物中的响应急性壁细胞的损失。我们最近在小鼠中进行的谱系作图研究表明，SPEM不是由专职祖细胞产生的，而是由表达Mist 1的成熟主细胞转分化为粘液细胞化生产生的。所有这些结果支持的假设，壁细胞从胃底粘膜的损失诱导的主细胞转分化的SPEM的发展和内在的粘膜因素调节SPEM的出现作为启动胃肿瘤的中心步骤。因此，必须了解诱发和控制SPEM出现的因素，SPEM是胃肿瘤发生所需的关键初始事件。我们将通过两个具体目标继续我们对化生起源的研究：第一，虽然我们的谱系作图研究已经确定主细胞引起SPEM，但这表明成熟的主细胞通常具有转分化为化生的能力。尽管如此，仍然可能存在主细胞亚群，它们是真正的化生隐蔽祖细胞。因此，我们将通过检查长寿命主细胞亚群是否可以作为推定的静止祖细胞存在来寻求确定主细胞亚群是否负责SPEM的发育。此外，我们将研究是否Lgr 5表达的主细胞在胃底可能代表一个静止的祖细胞群，可能有助于发展的SPEM。第二，我们将寻求确定可能影响主细胞转分化为SPEM的因素，在体外使用新的条件永生化细胞培养模型小鼠主细胞（ImChief），我们已经在以前的资助期间开发。在ImChief细胞中，我们将确定主细胞分化特异性转录因子Mist 1的过表达是否可以促进主细胞特性的进一步成熟。此外，我们将确定Mist 1基因敲除小鼠中Mist 1基因的缺失是否会促进诱导急性壁细胞缺失后的化生发展，以及在ImChief细胞中Mist 1基因表达的靶向敲低中是否会促进化生发展。最后，我们将研究在我们最近对小鼠SPEM模型的基因微阵列分析中鉴定的化生转变的假定调节因子在ImChief细胞中表达时是否可以促进主细胞转分化为SPEM。通过这些研究，我们将获得基本的见解，导致诱导化生的细胞过程作为胃癌发生的关键起始步骤。)

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. )