Localization of the cystic fibrosis transmembrane conductance regulator to a distinct sub-population of enterocytes in the small intestine - abstract

Immunocytochemical studies have localized the cystic fibrosis transmembrane regulator (CFTR) to the apical domain of a variety of epithelial cell types. This distribution is consistent with an established function of CFTR as an apical membrane chloride channel. In the intestine, several studies have identified the apical domain of crypt epithelial cells as the predominant site of CFTR expression. In addition to crypt epithelial cells, we have identified a distinct sub-population of small intestinal epithelial cells with high levels of CFTR immunoreactivity. Cryosections of human and rat intestine were stained with an affinity-purified anti-CFTR antibody (q-1468) and examined by indirect immunofluorescent microscopy. In both species, intense staining of a sub-population of isolated intestinal mucosal epithelial cells was observed. This staining pattern is eliminated by preincubation of a-1468 with the C-terminal peptide against which it was raised. In the rat, these cells are most abundant in the villi of the proximal small intestine and comprise less than 2 percent of the total epithelial cell population. They are not seen in the terminal ileum or colon. A similar sub-population of CFTR-expressing cells was identified in the human small intestine. Within these cells from both species, staining is punctate and present throughout the cytoplasm, with the greatest intensity near the apical (luminal) pole. We have confirmed the specificity of this staining, using two other anti-CFTR antibodies. Using in-situ hybridization, other investigators have identified a similar subset of intestinal epithelial cells that exhibit high levels of CFTR mRNA expression. We performed immunoelectron microscopy to determine the morphological characteristics of these cells. The CFTR-labelled villus cells possess morphological features ofenterocytes. Within these enterocytes, CFTR labelling was detected in the apical brush border and in several small vesicles scattered throughout the cytoplasm. Thus, in the small intestine of the rat and human, CFTR is present in two mucosal cell populations. Apical staining of contiguous cells, characteristic of CFTR, is present in the crypts in both the small and the large intestine. In addition, a distinct sub-population of enterocytes with an apparent subcellular distribution for CFTR is present, predominantly in the villi of proximal small intestine. The relative contribution of these CFTR-expressing enterocytes to the pathogenesis of CF remains to be elucidated (AU)