Regulation and function of Bone Morphogenetic Protein signaling in colonic injury and inflammation
AJP Gastrointestinal and Liver Physiology
Published online on November 17, 2016
Abstract
The bone morphogenetic proteins (BMPs) regulate gastrointestinal homeostasis. We investigated the expression of BMP-4 and the localization and function of BMP signaling during colonic injury and inflammation. Wild type mice and mice expressing the β-galactosidase (β-gal) gene under the control of a BMP responsive element (BRE), BMP-4-β-gal/+ mice, and animals generated by crossing villin-Cre mice to mice with floxed alleles of BMP receptor 1A (villin-Cre;Bmpr1aflox/flox), were treated with DSS to induce colonic injury and inflammation. Expression of BMP-4, β-gal, BMPR1A, IL-8, α-SMA, and phosphorylated Smad1-5-8, were assessed by X-Gal staining, QRT-PCR and immunohistochemistry. Morphology of the colonic mucosa was examined by staining with H&E. The effect of IFN-, TNF-α, IL-1β, and IL-6 on BMP-4 mRNA expression was investigated in human intestinal fibroblasts, while that of BMP-4 on IL-8 was assessed in human colonic organoids. BMP-4 was localized in α-SMA-positive mesenchymal cells while the majority of BMP-generated signals targeted the epithelium. DSS caused injury and inflammation, leading to reduced expression of BMP-4 and BMPR1A mRNAs, and to decreased BMP signaling. Deletion of Bmpr1a enhanced colonic inflammation and damage. Administration of anti-TNF-α antibodies to DSS-treated mice ameliorated colonic inflammation and increased the expression of BMP-4 and BMPR1A mRNAs. TNF-α and IL-1β inhibited both basal and IFN- stimulated BMP-4 expression, while IL-6 had no effect. BMP-4 reduced IL-8 mRNA expression in the organoids. Inflammation and injury inhibit BMP-4 expression and signaling, leading to enhanced colonic damage. These observations underscore the importance of BMP signaling in the regulation of intestinal inflammation and homeostasis.