Extracellular Matrix in Inflammatory Bowel Disease

Case Western Reserve University, Cleveland OH

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Abstract

Tissue damage in Ulcerative colitis (UC) is predominantly ulceration of the epithelium and its underlying basement membrane. In contrast, Crohn's disease (CD) is characterized by excessive deposition of fibrillar collagen in the lamina propria, muscularis mucosa, submucosa, muscularis propria, and serosa. Thus, in both forms of inflammatory bowel disease (IBD) tissue remodeling and the destruction and restitution of the interstitium are continual and dynamic processes that contribute to anatomical destruction and major clinical consequences. In that mucosal T lymphocytes are enmeshed in the complex and highly organized network of proteins, glycoproteins, and proteoglycans known as the extracellular matrix (ECM), we propose that the chronicity, exacerbation, and recurrence of IBD are multifactorial, involving a process by which the intermingled pathogenic T cells adversely affects tissue injury and fibrosis, and vice versa. Our published and preliminary results show that integrin-mediated adhesion to the ECM is a central event in the generation of an immune response. Therefore, we postulate that ECM adhesion and accessory function is also a pivotal mechanism that modulates IBD. We report that the signal transduction pathway initiated by collagen in an effector/memory T cell is different from that initiated by fibronectin. In addition, the Rho family member of small GTPases, which regulate cytoskeletal reorganization, activated in a T cell adherent to fibronectin differs from that activated when the T cell is bound to collagen, and that the pattern of serine phosphorylation on the head domain of vimentin (the key component of the intermediate filament in T cells) is similarly distinct. We also demonstrate that a three dimensional, native ECM synthesized by human intestinal fibroblasts (HIF) from a control patient initiates a signal transduction cascade in T cells different from that initiated by a native matrix secreted by HIF from patients with Crohn's disease. When we couple the observation that (i) CD-derived native ECM mimics the transduction cascade initiated by purified collagen to (ii) the excessive deposition of collagen in the chronically inflamed CD mucosa and lamina propria, we propose the following central hypothesis: During the continuous remodeling of the ECM in IBD, a repair process quite distinct between UC and CD, engagement of select integrins on mucosal T cells modulates and potentially disrupts their signaling and function, thus contributing to chronicity and recurrence of the inflammatory process. This hypothesis will be tested by two specific aims: Aim 1. Molecular: Define the signaling pathways engaged by alternate ECM receptors that regulate LPT cytoskeletal rearrangement with a particular focus on the Rho family of small GTPases. Aim 2. Biochemical: Evaluate the specific protein serine kinases and target proteins modulated by the ligation of distinct integrin molecules in the migratory LPT, with a particular focus on vimentin.