Cdx genes, inflammation, and the pathogenesis of intestinal metaplasia

Abstract

Intestinal metaplasia (IM) is a biologically interesting and clinically relevant condition in which one differentiated type of epithelium is replaced by another that is morphologically similar to normal intestinal epithelium. Two classic examples of this are gastric IM and Barrett's esophagus (BE). In both, a chronic inflammatory microenvironment, provoked either by Helicobacter pylori infection of the stomach or acid and bile reflux into the esophagus, precedes the metaplasia. The Caudal-related homeodomain transcription factors Cdx1 and Cdx2 are critical regulators of the normal intestinal epithelial cell phenotype. Ectopic expression of Cdx1 and Cdx2 occurs in both gastric IM as well as in BE. This expression precedes the onset of the metaplasia and implies a causal role for these factors in this process. We review the observations regarding the role of chronic inflammation and the Cdx transcription factors in the pathogenesis of gastric IM and BE.

Figure 1

Example of the considerable morphologic changes that can occur in tissues with the development of a metaplasia. In this example, a multi-layer squamous epithelium is converted to a simple columnar type epithelium. This type of metaplastic change is classically observed in Barrett’s esophagus.

Figure 2

Schematic of the domains critical for Cdx2 transcriptional activity including the DNA binding homeodomain and putative transactivating domain. Cdx1 has a similar structure (not shown). Phosphorylation sites at Serine 60 and Serine 281 are also indicated. Phosphorylation of Cdx2 at these sites reduces Cdx2 transcriptional activity (Serine 60) and protein stability (Serine 281).

Figure 3

The transcription factor Cdx2 regulates a number of functions critical to intestinal epithelial development, differentiation, and morphology. Best studied are Cdx2’s role in promoting the intestinal cell differentiation and the intestine-specific expression of genes who’s products support intestinal epithelial cell functions. Also well studied is the critical role played by Cdx2 at promoting cell to cell adhesion and the adoption of a polarized, columnar cell morphology. Less well understood are Cdx2’s regulation of intestinal cell apoptosis, proliferation, and chromosomal stability.

Figure 4

Histologic changes associated with metaplasia in Barrett’s esophagus. A. Hematoxylin & Eosin staining of normal esophagus demonstrating a uniform multilayered squamous epithelium. B. Hematoxylin & Eosin staining of tissue demonstrating intersection of Barrett’s esophagus with normal squamous epithelium. C. Higher-powered magnification of the Barrett’s epithelium stained with Hematoxylin & Eosin. Goblet cells are visible with blue inclusions. D. Alcian blue staining of Barrett’s esophagus tissue reveals expression of intestinal mucins.

Figure 5

Diagram illustrating anatomic location of Barrett’s esophagus. Endoscopic views of the gastroesophageal junction in a normal individual and a patient with Barrett’s esophagus. Endoscopic photos kindly provided by Nuzhat Ahmad M.D.

Figure 6

Endoscopic views of esophageal adenocarcinomas occurring at the gastroesophageal junction. Hematoxylin & Eosin staining of an esophageal adenocarcinoma (EAC) arising in the setting of Barrett’s esophagus (BE). Endoscopic photos kindly provided by Nuzhat Ahmad M.D.

Figure 7

Inflammatory microenvironment provokes metaplasia in Barrett’s esophagus by several mechanisms. Gastric acid and bile acid reflux in GERD injures the esophageal epithelium, inducing an inflammatory response. Cytokines expressed by both injured epithelial cells and infiltrating inflammatory cells contribute to metaplasia in a number of ways. 1. Induce cell proliferation and inhibit the tumor-suppressor apoptosis pathways in injured and damaged epithelial cells. 2. Proinflammatory cytokines stimulate ROS and eicosanoid production by phagocytic and non-phagocytic cells (including epithelial cells), increasing oxidative stresses and DNA mutagenesis. 3. Cytokines and chemokines are chemotactic and provoke inflammatory cell migration into the involved tissue. Moreover, cytokines influence the differentiation and activity of dendritic, macrophage, lymphocytic, and NK cells. 4. Cytokines signal to endothelial cells and stimulate angiogenesis. Within the epithelial cells, the combination of ROS damage, alterations in DNA methylation patterns, and activation of the NFKB signaling pathway (p50 subunit is especially important) by cytokines and the acid/bile refluxate contribute to activation of targets genes that further amplify the inflammation and ROS (Cox-2) and promote intestinal differentiation (Cdx2).

Figure 8

Histology of Barrett’s esophagus. A. Hematoxylin & Eosin staining of Barrett’s esophagus demonstrates a uniform columnar morphology with the presence of occasional goblet cells. B. Immunohistochemistry (IHC) staining for Keratin 20 labels all Barrett’s cells. C. IHC for Muc5AC labels both columnar and goblet cells. D. IHC for Muc2 localizes to the goblet cells. E. IHC for Cdx1 labels Barrett’s epithelium and not the adjacent squamous epithelium and localizes to the nucleus. F. IHC for Cdx2 labels the nuclei of Barrett’s cells.

Figure 9

Schematic model for the induction of metaplasia in Barrett’s esophagus, based on the ectopic expression of a number of developmentally important transcription factors that occurs in the setting of chronic inflammation due to acid and bile reflux into the esophagus in GERD patients.