A Tissue Renewal-Based Mechanism Drives Colon Tumorigenesis

Our Goal is to identify how colorectal cancer (CRC) arises in the single-layered-cell epithelium (simple columnar epithelium) that lines the luminal surface of the large intestine. We recently reported that the dynamic organization of cells in colonic epithelium is encoded by five biological rules and conjectured that colon tumorigenesis involves an autocatalytic tissue renewal reaction. Our objective was to define how altered crypt turnover explains tissue disorganization that leads to adenoma morphogenesis and CRC. Hypothesis: Changes in rate of tissue renewal-based cell polymerization leads to epithelial expansion and tissue disorganization during adenoma histogenesis. Accordingly, we created a computational model that considers the structure of colonic epithelium to be a polymer of cells and that tissue renewal is autocatalytic. Indeed, self-renewal of stem cells in colonic crypts continuously produces cells that act like monomers to form a polymer of cells (an interconnected, continuous cell sheet) in a polymerization-based process. Our model is a system of nonlinear differential equations that simulates changes in human crypt cell population dynamics. We investigated how changes occur in the proportion of different cell types during adenoma development in FAP patients. The results show premalignant colonic crypts have a decreased rate of tissue renewal due to APC-mutation. This slower rate of cell polymerization causes a rate-limiting step in the crypt renewal process that expands the proliferative cell population size. Our findings provide a mechanism that explains how a prolonged rate of crypt renewal leads to tissue disorganization with local epithelial expansion, infolding, and contortion during adenoma morphogenesis.