Critical role of claudin‐7 in maintaining intestinal crypt stem cell functions

Intestinal epithelial integrity and self‐renewal are two main features that maintain intestinal homeostasis. Tight junctions control epithelial integrity while intestinal crypt stem cells fuel epithelial self‐renewal. Claudin‐7 is a tight junction membrane protein present along the entire intestinal epithelium. Using our global (gCldn7 −/− ) and inducible intestinal‐specific (cCldn7 −/− ) claudin‐7 knockout mouse models, we found that claudin‐7 deletion induces rapid crypt stem cell loss and increases cell proliferation. We hypothesized that claudin‐7 regulates intestinal epithelial self‐renewal. To elucidate the underlying mechanism, we employed ex vivo organoid culture using Cldn7 +/+ and gCldn7 −/− small intestines. We found that claudin‐7 deletion not only decreases the survival of organoids and crypt stem cells, but also induces the formation of spheroids without villi compared to normal organoids with villi derived from Cldn7 +/+ small intestines. In addition, immunostaining of Cldn7 +/+ and gCldn7 −/− organoids demonstrated that claudin‐7 deletion increases the proliferative epithelial cells and decreases the number of enterocytes, Paneth cells, enteroendocrine cells, and tuft cells. Interestingly, the number of goblet cells was unaffected which comports with our in vivo findings. Western blotting analysis revealed that β‐catenin (a key molecule in the Wnt signaling pathway) is upregulated in claudin‐7‐deficient intestines. Furthermore, immunostaining revealed that β‐catenin localizes predominately to the epithelial cell cytoplasm. More importantly, we found that activation of the Wnt signaling pathway increases the size of the claudin‐7‐deficient spheroids compared to claudin‐7‐positive organoids. These findings suggest that claudin‐7 plays a novel, but as yet unidentified function in the regulation of epithelial cell renewal in intestines. Claudin‐7 is required for regeneration of intestinal epithelium, survival of crypt stem cells, and differentiation of intestinal epithelial cells. Claudin‐7 also maintains the balance of epithelial cell proliferation and suppresses Wnt signaling pathway during normal intestinal epithelial renewal. Support or Funding Information This study is supported by the National Institute of Health grant DK103166. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .