Induction of Lipocalin-2 in Colonic Epithelial Cells in Inflammatory Bowel Disease

Abstract

In our gene expression analysis on colonic biopsies from an IBD cohort we found Lipocalin-2 (LCN2) to be among the most upregulated genes in inflamed mucosa compared to un-inflamed mucosa of both ulcerative colitis (UC) and Crohn’s Disease (CD). The protein LCN2 acts as an acute phase protein and has antimicrobial properties, making it a part of the innate immune system. We sought to identify localization and regulation of LCN2 in the colonic mucosa and also quantify LCN2 in serum. Microarray of colonic biopsies from an IBD population (n = 133) was done using Illumina Bead Chip technology. Immunohistochemical staining and in situ hybridization of colonic biopsies was done on a subset of biopsies to identify cellular sources of LCN2. We studied release of LCN2 from colonic epithelial cell lines HT-29 and SW620, upon pattern recognition receptor stimulation (PRR). LCN2 was quantified in serum using ELISA and hsCRP quantified using immunoturbidometric method. LCN2 mRNA was among the 10 most upregulated gene in inflamed vs uninflamed mucosa of UC and CD. LCN2 is located to the epithelial cells and infiltrating neutrophils in inflamed mucosa. The LCN2 mRNA synthesis is found solely in epithelial cells indicating the de novo synthesis to take place in the epithelium. LCN2 is abundantly and constitutively released from the colonic epithelial cell line HT-29 and its release is enhanced by both IL1b and the TLR3 ligand polyinosinic: polycytidylic acid (poly(I:C)). Serum LCN2 correlates with hsCRP. LCN2 is among the most upregulated genes in active IBD. The epithelial cells of colonic mucosa are an important source of LCN2. LCN2 seems to be released into the intestinal lumen and has a potential role in shaping the intestinal bacterial flora. The synthetic dsRNA analog poly(I:C) increased synthesis and release of LCN2 for colonic epithelial cell line HT-29 and the TLR3 mediates this release, supporting a role of TLR3 in intestinal homeostasis and mucosal inflammation.