Cells along all of those other crypt villous axis were positive for UEA1, and samples from the colon tested negative. types were identified by means of immunostaining and morphological characterization with transmission electron microscopy. Some differences in biomarker expression and antibody cross-reactivity were identified in equine tissue, compared with other species. However, each known type of mucosal epithelial cell was identified in equine tissue. CONCLUSIONS AND CLINICAL RELEVANCE The methodology used can enhance detection of stem cells and progenitor cells as well as postmitotic cell lineages in equine intestinal tissues. Results may have relevance to regenerative potential of intestinal mucosa and survival in horses with colic. Colic is a 11-hydroxy-sugiol major cause of morbidity and death in horses. In 2005, a USDA National Animal Health Monitoring System report1 indicated that colic was second only to old age as the leading cause of death in horses. The intestine is a complex organ composed of multiple layers including the outer serosa, 2 muscular layers (an inner circular layer and outer longitudinal layer separated by fascia that contains the myenteric nerve plexus), the submucosa, and an innermost mucosal layer.2 Death in cases of colic is associated with breakdown of the mucosal barrier, of which the intestinal epithelial cells are an important component. These cells create a single layer that simultaneously forms a barrier, transports nutrients, and undergoes self-renewal.3 The glandular epithelium is arranged in structures called crypts of Lieberkhn. The small intestine is additionally composed of villi which extend into the intestinal lumen. This anatomic arrangement is referred to as the crypt-villus axis.2 At the base of the crypts are undifferentiated stem cells flanked by Paneth cells.4 Immediately adjacent to these cells are progenitor cells, and collectively, this region of the crypts is termed the stem cell niche.4 This population of cells is responsible 11-hydroxy-sugiol for creating new 11-hydroxy-sugiol epithelium every 3 to 5 5 days. The remaining epithelium is made up of mature, postmitotic cell types that include absorptive enterocytes, goblet cells, and Paneth cells. Severe mucosal injury likely compromises the proliferative cell population that resides within the glandular crypts. A study5 has shown that intestinal ischemic injury that denudes 50% of the glandular epithelium, such as occurs with large colon volvulus, is associated with a poor prognosis for survival. However, research to explore this proliferative compartment of the intestinal mucosa in further detail has been lacking because, until recently, the technology to distinctly identify unique cell types did not exist. Protein biomarkers for intestinal epithelial stem cells have been identified and described in rodents since 20076 and Rabbit Polyclonal to HTR4 in pigs in 1 recent study.7 Additionally, in these species and in humans, protein biomarkers have been similarly used to identify mature cell lineages. 7C10 This is commonly based on a cells distinct function, although some cells are identified by use of uniquely expressed proteins whose role in cellular activity is incompletely understood. For example, epithelial cell adhesion molecule plays a role in cell-cell adhesion, is uniquely expressed by epithelial cells, and is therefore a useful target for cellular identification.11 Absorptive enterocytes in the small intestine and colon express digestive enzymes within the brush border that include sucrase isomaltase and carbonic anhydrase, respectively,12,13 allowing for targeted identification of these cell types. Finally, Paneth cells are a population of cells that exist only in the small intestine of certain mammalian species.7,14 These cells are commonly identified using lysozyme, an antibacterial enzyme, as the biomarker for identification.15 However, other biomarkers including c-KIT and UEA1 have also been used.14,16 To the authors knowledge, no study has fully characterized the equine intestinal epithelium by examination of protein biomarker expression and ultrastructural cellular appearance. Recent advances in the field of intestinal stem cell biology have enabled detailed study of the stem cell niche as the potential source of novel therapeutic targets to enhance intestinal mucosal regeneration.17,18 The objective of the study reported here was to characterize epithelial cells of the small intestine and colon in horses without clinical gastrointestinal abnormalities, with an emphasis on the stem cell niche constituents. Our aim was to distinguish stem cells, partially differentiated cells, and postmitotic or fully differentiated epithelial cells by means of histologic evaluation, immunofluorescence, and electron microscopy. Materials and Methods Animals and sample collection All animal experiments were approved by the Institutional Animal.