P149 DECREASED COLONIC ACTIVIN RECEPTOR-LIKE KINASE 1 DISRUPTS EPITHELIAL BARRIER INTEGRITY AND IS ASSOCIATED WITH A POOR CLINICAL OUTCOME IN CROHN’S DISEASE

Abstract

Abstract Background and Aims Intestinal epithelial cell (IEC) barrier dysfunction is critical to the development of Crohn’s disease (CD). Mechanisms controlling colonocyte differentiation and barrier defects are understudied in CD. We recently reported increased expression of microRNA-31-5p (miR-31-5p) in colonic IECs of CD patients compared to non-IBD (NIBD) controls. In this study we identify and characterize the miR-31-5p target gene Activin Receptor-Like Kinase 1 (ALK1) as a key regulator of colonocyte maturation and IEC barrier integrity, specifically the functional impact of aberrant ALK1 signaling on colonocyte differentiation, barrier integrity, and clinical disease outcomes in CD. Methods MiR-31-5p target genes were identified in CD patients by integrative analysis of RNA- and small RNA-sequencing data from colonic mucosa and confirmed by quantitative RT-PCR (qPCR) in isolated colonic IECs. Functional characterization of ALK1 in colonic IECs was performed ex vivo using 2- or 3-dimensional cultured human primary colonic IECs. The impact of altered colonic ALK1 signaling for the risk of surgery and endoscopic relapse was evaluated by a multivariate regression analysis and a Kaplan-Meier estimator among CD patients. Results Integrative analysis of RNA- and small RNA-sequencing and follow-up qPCR identified ALK1 as a candidate target of miR-31-5p in the colonic IECs of CD patients. A 3’-UTR reporter assay with site-directed mutagenesis confirmed the direct regulation of ALK1 expression by miR-31-5p in HEK293T cells. Increased activation of ALK1 restricted the proliferation of primary colonic IECs in an EdU proliferation assay and down-regulated the expression of stemness-related genes, such as LGR5 and ASCL2. Activated ALK1 signaling directed the fate of human colonic IEC differentiation toward colonocytes. Down-regulated ALK1 signaling was associated with increased stemness-related gene expression and decreased colonocyte-specific gene expression in the isolated colonic IECs of CD patients compared to non-IBD controls. Activation of ALK1 did not affect colonic IEC migration in a wound healing assay, but enhanced epithelial barrier integrity in a trans-epithelial electrical resistance (TEER)-based permeability assay. Lower colonic ALK1 expression was associated with higher risks of surgery and endoscopic relapse in CD patients. Conclusion Decreased colonic ALK1 signaling disrupts colonic IEC barrier integrity and is associated with a poor clinical outcome in CD patients.