Doublecortin-like kinase 1-positive enterocyte - a new cell type in human intestine.

Doublecortin-like kinase 1 (DCLK1) is a microtubule-associated kinase. In murine intestine, DCLK1 marks tuft cells with characteristic microvilli, features of neuroendocrine cells and also quiescent stem cell-like properties. The occurrence and pathological role of DCLK1-positive cells in human intestinal mucosa is unknown. We analysed DCLK1 expression in healthy duodenal, jejunal and colorectal mucosa samples (n = 35), and in duodenal specimens from patients with coeliac disease (n = 20). The samples were immunohistochemically double-stained with DCLK1, and synaptophysin, chromogranin A and Ki-67. Ultrastructure of DCLK1-expressing duodenal cells was assessed using correlative light and electron microscopy. DCLK1 expression was seen in about 1% of epithelial cells diffusely scattered through the intestinal epithelium. Electron microscopy showed that the duodenal DCLK1-positive cells had short apical microvilli similar to neighbouring enterocytes and cytoplasmic granules on the basal side. DCLK1-positive cells were stained with synaptophysin. The number of DCLK1-positive cells was decreased in villus atrophy in coeliac disease. Our findings indicate that in human intestinal epithelium, DLCK1-positive cells form a subpopulation of non-proliferating neuroendocrine cells with apical brush border similar to that in enterocytes, and their number is decreased in untreated coeliac disease.