Arid1a is essential for intestinal stem cells through Sox9 regulation.

Abstract

Inactivating mutations of <i>Arid1a</i>, a subunit of the Switch/sucrose nonfermentable chromatin remodeling complex, have been reported in multiple human cancers. Intestinal deletion of <i>Arid1a</i> has been reported to induce colorectal cancer in mice; however, its functional role in intestinal homeostasis remains unclear. We investigated the functional role of Arid1a in intestinal homeostasis in mice. We found that intestinal deletion of <i>Arid1a</i> results in loss of intestinal stem cells (ISCs), decreased Paneth and goblet cells, disorganized crypt-villous structures, and increased apoptosis in adult mice. Spheroids did not develop from intestinal epithelial cells deficient for <i>Arid1a</i> Lineage-tracing experiments revealed that <i>Arid1a</i> deletion in Lgr5⁺ ISCs leads to impaired self-renewal of Lgr5⁺ ISCs but does not perturb intestinal homeostasis. The Wnt signaling pathway, including Wnt agonists, receptors, and target genes, was strikingly down-regulated in <i>Arid1a</i>-deficient intestines. We found that Arid1a directly binds to the <i>Sox9</i> promoter to support its expression. Remarkably, overexpression of <i>Sox9</i> in intestinal epithelial cells abrogated the above phenotypes, although <i>Sox9</i> overexpression in intestinal epithelial cells did not restore the expression levels of Wnt agonist and receptor genes. Furthermore, <i>Sox9</i> overexpression permitted development of spheroids from <i>Arid1a</i>-deficient intestinal epithelial cells. In addition, deletion of <i>Arid1a</i> concomitant with <i>Sox9</i> overexpression in Lgr5⁺ ISCs restores self-renewal in <i>Arid1a</i>-deleted Lgr5⁺ ISCs. These results indicate that Arid1a is indispensable for the maintenance of ISCs and intestinal homeostasis in mice. Mechanistically, this is mainly mediated by Sox9. Our data provide insights into the molecular mechanisms underlying maintenance of ISCs and intestinal homeostasis.