Inflammatory bowel disease (IBD) is a recurrent inflammatory disorder of the intestine which causes mucosal destruction. IBD intestinal epithelial cells (IEC) display altered expression of various cell surface antigens, indicative of an intrinsic defect in the processing of cell surface molecules and antigen presentation. Furthermore, increased expression and secretion of a number of cytokines by IBD IECs may contribute to the uncontrolled immune response in IBD. The pathogenic mechanisms responsible for the phenotype alterations in IBD IECs are not yet understood. Keratinocyte growth factor (KGF) is an epithelial cell- specific growth factor which is widely expressed by mesenchymal cells derived from epithelial tissues. We present new data which indicate that in IBD, but not normal or uninvolved intestinal tissue, KGF is expressed at high levels by a subpopulation of lamina propria mononuclear cells (LPMC). The topographical distribution of the KGF signal was consistent with its production by T cells. The KGF receptor (KGFR) signal was localized to intestinal epithelial cells (IEC) in both normal and IBD tissue. The localizations of these transcripts would indicate a role for KGF in mediating the altered immunoregulatory functions of IECs (antigen presentation, cytokine synthesis, etc) in IBD. The long term objective of this proposal is to test this hypothesis using purified populations of IEC and LPMC, isolated from normal, histologically uninvolved and inflamed IBD surgical specimens, for both descriptive and functional studies.
In Specific Aim 1, the cellular sites of KGF and KGFR synthesis will be determined in the purified cell populations. These results will be confirmed using methods that allow simultaneous detection of KGF and KGFR gene expression or immunoreactivity with cell type- specific antigens within the same tissue section. Quantitative analysis of KGF protein expression will be performed using an enzyme-linked immunosorbent assay and immunoblotting.
In Specific Aim 2, functional differences between normal and IBD IECs in the response to KGF stimulation will be determined. KGF binding, and subsequent KGFR mediated tyrosine phosphorylation of cellular proteins will be examined. Studies of KGF effects on IEC surface antigen expression as well as IEC cytokine secretion will determine whether chronic KGF stimulation of IEVs contributes to the continued inflammatory process in IBD. The mixed lymphocyte reaction will be used to determine the role KGF plays in mediating the interactions between normal and IBD IECs and T cells.
In Specific Aim 3, we will determine which factors are involved in up- regulating KGF expression in IBD. The mechanisms underlying this process will be elucidated using the cloned KGF promoter region. Potential regulatory elements within this region will be characterized using an electrophoretic mobility shift assay, DNase 1 footprinting analysis, and in vitro mutagenesis. A greater understanding of the cellular and molecular mechanisms of KGF induction in IBD, and the effects this factor has on normal and IBD IECs will serve to identify how antagonists to KGF action would be of therapeutic benefit in this disease.
