Sa1750 Epithelial Notch-1 Signaling Modulates Regulatory/Effector T Cell Signature: A Role for the Epithelial Barrier

Abstract

BACKGROUND/AIMS: We previously reported that inhibition of Bone Morphogenetic Protein (BMP) signaling in vivo, leads to enhancement of Helicobacter-induced gastric inflammation suggesting that the BMPs exert anti-inflammatory actions in the gut. The aim of this study was to examine the expression of BMP-4 and the localization of BMP-generated signals during gastrointestinal (GI) inflammation. METHODS: 3 month-old transgenic (TG) mice expressing the β-galactosidase (gal) gene under the control of a BMP responsive element (BRE) and C57BL/6-BMP-4β-gal/+ mice were either infected with H. felis (HF) or given 3% DSS-containing water for 4 days, to induce gastric and colonic inflammation, respectively. Animals were analyzed 2 months after HF infection and 3 days after DSS administration. Expression of BMP-4, BRE-β-gal and BMP Receptor 1A (BMPR1A) were assessed by X-Gal staining, IHC with anti-β-gal antibodies (abs) and QRT-PCR. Morphology of the GI mucosa was examined in sections stained with H&E. Phosphorylation of the BMP-signal transducers Smad1-5-8 was determined by IHC with anti-p-Smad1-5-8 abs. Identification of myofibroblasts, B and T lymphocytes, neutrophils and macrophages was achieved by IHC with antiα smooth muscle actin (SMA), -CD19, -CD3, -MPO, and -F4/80 abs, respectively. Biopsies were obtained from the colonic mucosa of normal (16 samples from 4 patients) and Inflammatory Bowel Disease (IBD) individuals (12 samples from 4 patients) with severe inflammation. RESULTS: BMP-4 is expressed in the mesenchymal layers of the GI mucosa while BMP signaling targets cells of the GI epithelium. BMP-4 staining was seen in α-SMA-positive cells of both the gastric and the colonic mucosa. HF-induced inflammation led to decreased BMP4 expression and signaling. No BMP-4 staining was seen in CD19-, CD3-, F4/80and MPOpositive cells of the gastric mucosa. Similarly, no p-Smad1-5-8 signals were seen in cells of the inflammatory infiltrates. 3% DSS caused inflammatory infiltrates, stromal expansion and loss of glands. The inflamed areas exhibited decreased BMP-4 expression and signaling and reduced BMPR1A mRNA expression. BMP-4 and BMPR1A mRNAs were also decreased in biopsies from patients with severe colonic IBD. CONCLUSIONS: BMP-4 is expressed in αSMA-positive cells of the GI mucosa but not in immune cells. BMP signals target epithelial cells but not cells of the inflammatory infiltrates. Inflammation reduces both the expression of BMP-4 and the intensity of BMP signaling in mouse models of gastric and colonic inflammation and in biopsies from IBD patients. Thus, BMP signaling, a pathway that exerts anti-inflammatory effects, is reduced during severe GI inflammation. Induction and reactivation of this mechanism might therefore represent a possible, novel modality for the treatment of inflammatory diseases of the gut.