Targeted intestinal deletion of Rho guanine nucleotide exchange factor 7, βPIX, impairs enterocyte proliferation, villus maturation, and mucosal defenses in mice

Rho guanine nucleotide exchange factors (RhoGEFs) regulate Rho GTPase activity and cytoskeletal and cell adhesion dynamics. bPix, a CDC42/RAC family RhoGEF encoded by ARHGEF7, is reported to modulate human colon cancer cell proliferation and postwounding restitution of rat intestinal epithelial monolayers. We hypothesized that beta Pix plays a role in maintaining intestinal epithelial homeostasis. To test this hypothesis, we examined bPix distribution in the human and murine intestine and created mice with intestinal epithelial-selective beta Pix deletion [beta(Pixflox/flox)/Tg(villin-Cre); Arhgef7 CKO mice]. Using Arhgef7 conditional knockout (CKO) and control mice, we investigated the consequences of beta Pix deficiency in vivo on intestinal epithelial and enteroid development, dextran sodium sulfate-induced mucosal injury, and gut permeability. In normal human and murine intestines, we observed diffuse cytoplasmic and moderate nuclear beta Pix immunostaining in enterocytes. Arhgef7 CKO mice were viable and fertile, with normal gross intestinal architecture but reduced small intestinal villus height, villus-to-crypt ratio, and goblet cells; small intestinal crypt cells had reduced Ki67 staining, compatible with impaired cell proliferation. Enteroids derived from control mouse small intestine were viable for more than 20 passages, but those from Arhgef7 CKO mice did not survive beyond 24 h despite addition of Wnt proteins or conditioned media from normal enteroids. Adding a Rho kinase (ROCK) inhibitor partially rescued CKO enteroid development. Compared with littermate control mice, dextran sodium sulfatetreated beta Pix-deficient mice lost more weight and had greater impairment of intestinal barrier function, and more severe colonic mucosal injury. These findings reveal beta Pix expression is important for enterocyte development, intestinal homeostasis, and resistance to toxic injury. NEW & NOTEWORTHY To explore the role of beta Pix, a guanine nucleotide exchange factor encoded by ARHGEF7, in intestinal development and physiology, we created mice with intestinal epithelial cell Arhgef7/beta Pix deficiency. We found beta Pix essential for normal small intestinal epithelial cell proliferation, villus development, and mucosal resistance to injury. Moreover, Rho kinase signaling mediated developmental arrest observed in enteroids derived from beta Pix-deficient small intestinal crypts. Our studies provide insights into the role Arhgef7/beta Pix plays in intestinal epithelial homeostasis.