The role of blood vessel epicardial substance in the maintenance of intestinal epithelial integrity
Reddy, Vishruth Keesara
Blood Vessel Epicardial Substance (BVES/Popdc1) is a junctional-associated transmembrane protein that is underexpressed in a number of malignancies and regulates epithelial-to-mesenchymal transition. BVES is known to regulate junctional-associated Wnt signaling, a critical regulator of intestinal stem cell signaling, crypt proliferation, and regeneration. Furthermore, it has been shown to regulate junctional integrity in vitro. The fundamental hypothesis underlying these studies was that BVES regulates intestinal homeostasis and response to injury. Our findings indicate a previously-unrecognized role for BVES in maintaining intestinal epithelial integrity in vivo. At baseline, Bves–/– small intestine demonstrated increased crypt height, proliferation, and expression of the stem cell marker Lgr5 compared to wildtype (WT) mice. Intercross with Lgr5-EGFP reporter mice confirmed expansion of the stem cell compartment in Bves–/– small intestine. Ex vivo 3D-crypt cultures of Bves–/– enteroids demonstrated increased stemness compared to WT, along with increased proliferation, expression of crypt-base columnar “CBC” and “+4” stem cell markers, and amplified Wnt signaling. Bves expression was downregulated after radiation in WT small intestine. Moreover, after radiation, Bves–/– mice demonstrated significantly greater small intestinal crypt viability, proliferation, and amplified Wnt signaling in comparison to WT mice. Bves–/– mice also demonstrated elevations in Lgr5 and Ascl2 expression, and putative damage-responsive stem cell populations marked by Bmi1 and TERT. The deletion of BVES in the colon increased epithelial barrier permeability, as well as colonization and injury after inoculation with the pathogen Citrobacter rodentium. At baseline, Bves–/– colons demonstrated increased colonic proliferation, decreased apoptosis, altered intestinal lineage allocation, and increased permeability ex vivo. Bves–/– mice inoculated with C. rodentium exhibited significantly more edematous colons, greater injury and hyperplasia when assessed histologically, as well as increased bacterial colonization and amplified immune responses. Finally, BVES mRNA levels were underexpressed in human ulcerative colitis biopsy specimens, suggesting relevance to human disease. Overall, these studies have identified BVES as a key regulator of intestinal mucosal integrity.