Society: AGA

This session will feature speakers who will examine the mechanisms of inflammation and epithelial tissue repair during mucosal inflammation. Signaling pathways active in epithelial cells to modulate repair as well as epithelial cell mitochondrial dysfunction and its contribution to epithelial injury during chronic inflammation will be discussed.The contribution of stromal fibroblasts to matrix remodeling and would healing will be addressed.

Background: We previously identified post-translational prenylation as a key regulator of intestinal barrier function. Although reduced GGTase-1 expression in Intestinal Epithelial Cells (IECs) was observed in IBD patients, the mechanisms underlying the association between inflammation and prenylation in IECs remained undefined. The mevalonate pathway (MVP), the metabolic route dictating cellular availability of isoprenoids, has been highlighted as an immunomodulation target. Strikingly, patients carrying alterations on MVP genes suffer from autoinflammatory disorders manifested, among others, by gastro-intestinal symptoms similar to IBD. Thus, we hypothesized the MVP contributes to gut epithelial homeostasis, and might be exploited in epithelial restoration.
Methods: We utilized mouse colitis models, gut tissue from IBD patients and intestinal organoid cultures to analyze the interplay between MVP within IECs and intestinal inflammation. Therefore, histological analysis, mouse endoscopy, RNA-Sequencing, immunohistochemistry-CLSM and gene/protein assays were performed.
Results: RNA Seq. data from IBD patients showed altered transcription of most enzymes within the MVP in the colon of UC patients. The interplay between MVP and inflammation was confirmed in mice. IECs from colitic mice (DSS and T-cell transfer colitis) depicted elevated cholesterol levels, downregulated MVK and increased expression of farnesylation related proteins. Strikingly, IECs from the inflamed gut of IBD patients also showed decreased MVK and increased FNTB/FDPS protein expression. Mechanistically, T-cell derived IFNγ induced FNTB expression in IECs in vitro and in vivo; while MVK downregulation was attributed to the isoprenoid accumulation in in vitro assays. Functionally, blockade of the MVP within IECs in vitro (simvastatin, organoids) or in vivo (Hmgcr^iΔIEC mice) lead to IBD-like epithelial alterations; and resulting transcriptomic changes suggested that lipid metabolism adaptations went along with impaired IEC survival due to cell cycle/division alterations. Importantly, signs of mitochondria dysfunction occurred in simvastatin treated intestinal organoids, intestinal epithelium from statin treated IBD patients and mice carrying GGTase- or HMGCR-deficient epithelium. Hence, epithelial damage in GGTase-deficient intestinal organoids was partially rescued upon impaired mitochondrial fission (P110 treatment). Last, inflammatory alterations in cytokine-stimulated intestinal organoids can also be reverted upon modulation of the MVP with zaragozic acid (FDFT1 inhibitor) or GGPP (prenylation substrate).
Conclusion: Taken together, our data strongly demonstrate the link between modulation of the MVP/prenylation within IECs and intestinal inflammation in IBD, suggesting MVP as a new target in the diagnosis/therapy of epithelial injury and mucosal inflammation in IBD patients.

James West

Appearances