Understanding disruption of the gut barrier during inflammation: Should we abandon traditional epithelial cell lines and switch to intestinal organoids?

Abstract

Disruption of the intestinal epithelial barrier is a hallmark of mucosal inflammation. It increases exposure of the immune system to luminal microbes, triggering a perpetuating inflammatory response. For several decades, the inflammatory stimuli-induced breakdown of the human gut barrier was studied in vitro by using colon cancer derived epithelial cell lines. While providing a wealth of important data, these cell lines do not completely mimic the morphology and function of normal human intestinal epithelial cells (IEC) due to cancer-related chromosomal abnormalities and oncogenic mutations. The development of human intestinal organoids provided a physiologically-relevant experimental platform to study homeostatic regulation and disease-dependent dysfunctions of the intestinal epithelial barrier. There is need to align and integrate the emerging data obtained with intestinal organoids and classical studies that utilized colon cancer cell lines. This review discusses the utilization of human intestinal organoids to dissect the roles and mechanisms of gut barrier disruption during mucosal inflammation. We summarize available data generated with two major types of organoids derived from either intestinal crypts or induced pluripotent stem cells and compare them to the results of earlier studies with conventional cell lines. We identify research areas where the complementary use of colon cancer-derived cell lines and organoids advance our understanding of epithelial barrier dysfunctions in the inflamed gut and identify unique questions that could be addressed only by using the intestinal organoid platforms.

Keywords: actin cytoskeleton; adherens junctions; colonoids; cytokines; enteroids; epithelial barrier; inflammatory bowel diseases; tight junctions.

Figure 1

Apical junctions in normal and inflamed intestinal epithelium. (A) Normal intestinal epithelial barrier is established by assembly of tight junctions and adherens junctions. Both junctional complexes are physically associated with the circumferential cytoskeletal belt containing actin bundles and myosin II filaments. (B) Signaling by different cytokines accumulating in the inflamed intestinal mucosa triggers disruption of the epithelial barrier that is driven by removal of junctional proteins from the intercellular contacts and remodeling of the perijunctional actomyosin cytoskeleton. Figure 1 by Gwendolyn Fuller, MFA. Reprinted with the permission of the Cleveland Clinic Center for Medical Art & Photography ^© 2023. All Rights Reserved.

Figure 2

Measurements of epithelial barrier permeability in human intestinal organoids. Intestinal organoids that are derived from either induced pluripotent stem cells or isolated intestinal crypts (A) form cyst-like structure after embedding into 3-D extracellular matrix (B). Epithelial permeability could be evaluated in a 3-D spherical organoids by monitoring the passage of fluorescent markers into organoid lumen (C). Alternatively, organoids could be cultured as 2-D epithelial monolayers in Transwell chambers (D). Permeability of organoid-derived monolayers could be examined by measuring either transepithelial electrical resistance, or transmonolayer flux of fluorescent markers. Figure 2 by Gwendolyn Fuller, MFA. Reprinted with the permission of the Cleveland Clinic Center for Medical Art & Photography ^© 2022. All Rights Reserved.