Loss of Smad5 leads to the disassembly of the apical junctional complex and increased susceptibility to experimental colitis

Abstract

The regulation of intestinal epithelial cell adhesion and migratory properties is often compromised in inflammatory bowel disease (IBD). Despite an increasing interest in bone morphogenetic protein (Bmp) signaling in gut pathologies, little is known of the specific roles played by individual Smads in intestinal epithelial functions. In the present study, we generated a mouse model with deletion of Smad5 transcriptional effector of the Bmp signaling pathway exclusively in the intestinal epithelium. Proliferation, migration, and apical junctional complex (AJC) protein expression were analyzed by immunofluorescence and Western blot. Human intestinal biopsies from control and IBD patients were analyzed for SMAD5 gene transcript expression by quantitative PCR (qPCR). Smad5(ΔIEC) and control mice were subjected to dextran sulfate sodium (DSS)-induced experimental colitis, and their clinical and histological symptoms were assessed. Loss of Smad5 led to intestinal epithelial hypermigration and deregulation of the expression of claudin-1 and claudin-2. E-cadherin was found to be equally expressed but displaced from the AJC to the cytoplasm in Smad5(ΔIEC) mice. Analysis of SMAD5 gene expression in human IBD patient samples revealed a significant downregulation of the gene transcript in Crohn's disease and ulcerative colitis samples. Smad5(ΔIEC) mice exposed to experimental DSS colitis were significantly more susceptible to the disease and had impaired wound healing during the recovery phase. Our results support that Smad5 is partly responsible for mediating Bmp signals in intestinal epithelial cells. In addition, deficiency in epithelial Smad5 leads to the deregulation of cell migration by disassembling the AJC with increasing susceptibility to experimental colitis and impairment in wound healing.

BMP signaling in rats with TNBS-induced colitis following BMP7 therapy

“…During intestinal morphogenesis, BMPs are important mediators of numerous epithelial-mesenchymal interactions (57). Analysis of BMP gene expression in the colon revealed the presence of Bmp1, 2,5,7, and SMAD7 and BmprII in the top part of the colon crypt (37). Recent studies showed the perturbance of BMP signaling pathway in hereditary gastrointestinal diseases and the efficacy of growth factor therapy along with the conventional treatment of IBD (27,38).…”

“…Recently, researches have shown that BMPs act mainly as tumor suppressor factors in intestine tumorigenesis, as evidenced by the loss of BMP signaling pathway in the colorectal cancer (28,29,35). Smad5 gene downregulation was observed in human inflammatory bowel disease (IBD), which leads to higher susceptibility to experimental colitis (2). Conditional mutations of the BMPRII in mice lead to appearance of epithelial hyperplasia and hamartomatous polyps (5).…”

Mucosal healing in inflammatory bowel diseases: a systematic review

“…For instance, genetic targeting of Smad5, a protein partly responsible for mediating Bmp signals in IECs, led to the dysregulation of IEC migration, increasing susceptibility to colitis and impairment in wound healing 46. Furthermore, activation of protein kinase C (PKC) signalling resulted in protection from TNF-induced tight junction disruption and mucosal healing in experimental colitis,47 suggesting that induction of PKC activity may improve mucosal healing.…”

Loss of Sonic Hedgehog Leads to Alterations in Intestinal Secretory Cell Maturation and Autophagy

“…Digestive tracts from 180 to 210 day-old Shh ΔIEC mice and control littermates were fixed, sectioned and stained (H&E and Alcian blue) as previously described [25]–[28].…”