from the Department of Surgery at the University of Chicago for allowing us to use the images of ileal tissue seen in Figure 2A. Funding Statement This work was supported, in part, by the National Institutes of Health, Grants NIGMS P50GM53789 and NIDDK P30DK42086. of the pouch epithelial tissue C. While not a true conversion to colonic tissue, the metaplastic epithelial architecture exhibits defined changes that more closely resemble colonic tissue: a change in the crypt-villus relationship where the crypts deepen and the villi become shortened and an increase in the relative population of goblet cells (mucous producing cells) C. Chronic, low-level inflammation has been associated with colonic metaplasia, and has been implicated as a mechanism driving the alterations seen in the mucosal architecture . However, previously identified connections between inflammatory signaling and the morphogenesis Adrenalone HCl pathway C did not produce the appropriate tissue architecture alterations, i.e. increasing crypt depth and shortened villi, consistent with the metaplasia phenotype. To address this issue we identified the key role of apoptosis (programmed cell death) in the generation of the metaplasia architecture: apoptosis plays a crucial role in morphogenesis by regulating life span of the GECs, subsequently affecting the height of the villus. However, existing knowledge links inflammation primarily to either anti-apoptotic (i.e., NFB) or necrotic behavior (i.e. Receptor Interacting Protein Kinase, or RIP), neither of which would generate or is associated with a colonic metaplasia phenotype in the ileal pouch. Therefore, there existed a gap between the recognized role of inflammation and the actual processes needed to generate the target phenotype. A search of the literature identified that one proposed link between inflammation and the induction of apoptosis is through the Phosphotase and tensin homolog/phosphoinositide 3-kinase (PTEN/PI3K) pathway . Based on this report, we hypothesized a putative link between gut epithelial inflammation and its effect on enteric mucosal tissue patterning: GEC apoptosis induced via the PTEN/PI3K pathway (Figure S1). The incorporation of this hypothetical mechanism not only increases the rate of GEC apoptosis, thus shortening the villus, but also inhibits Hh production. Inhibition of Hh production leads to reduced inhibition on the Wnt pathway and increases the size of the proliferative compartment in the crypt, thereby generating the essential crypt-villus architectural features characteristic of colonic metaplasia. Simulations were performed with SEGMEnT to demonstrate the plausibility of a hypothesis previously published in the literature that prolonged low-level inflammation, acting as a persistent perturbation to the signaling network, would lead to a change in the morphology of the epithelial layer . The simulation experiments involved implementing a continuous low-grade stimulation of TLR4s on SEGMEnT’s GECs to represent a chronic low-level inflammatory milieu, mimicking the effects of luminal stasis and bacterial overgrowth in an ileal pouch. The effect of this condition on the crypt/villus architecture was evaluated in terms STMY of alterations of the crypt/villus ratio as well as absolute changes Adrenalone HCl Adrenalone HCl in both crypt and villus dimensions. Figure 9A displays crypt and villus GEC populations when the system is exposed to chronic low-level TLR4 signaling (an abstraction of fecal stasis). This up-regulation leads to an increased rate of apoptosis, shortening the villus, as well as an inhibition of the Hh pathway, which leads to an increase in the size of the proliferative compartment. Figure 9B displays output from SEGMEnT when simulating conditions leading to colonic metaplasia. Crypt hyperplasia and villus atrophy are clearly evident (compare with normal homeostatic condition in Figure 9C, and as seen in Figure 5C), along with a villus to crypt height ratio that matches the alterations seen in colonic metaplasia , suggesting the plausibility of this mechanism as the driver for colonic metaplasia. Open in a separate window Figure 9 Colonic metaplasia in the ileal pouch.Panel A displays standard crypt and villus gut epithelial cell (GEC) populations after contact with sustained low-level Adrenalone HCl toll-like receptor (TLR4) arousal and signaling (an abstraction of fecal stasis). This low-level up-regulation of irritation communicates via our hypothesized Phosphotase and tensin homolog (PTEN) systems, leading to elevated apoptosis, shortening the villus, aswell as an inhibition from the Sonic Hedgehog homolog (Hh) pathway, which escalates the size from the proliferative area (i.e. crypt). -panel B shows a screenshot from Portion when simulating circumstances resulting in colonic metaplasia. Crypt hyperplasia and villus atrophy are obviously evident (equate to regular homeostatic condition in -panel C, so that as seen in Amount 4C), plus a change in the villus to crypt elevation proportion that fits the alterations observed in colonic metaplasia as reported in Ref . Debate Portion dynamically represents and integrates existing understanding concerning irritation and homeostasis in the ileum and.