Creating a more accurate model of inflammatory bowel disease

A research team led by Junior Associate Professor Kazuo Takayama, from the Department of Cell Growth and Differentiation, recently constructed a new model of inflammatory bowel disease using iPS cells that enables more accurate modeling of the condition for studying the underlying disease mechanisms and identifying new therapies.

Nearly 5 million people worldwide are affected by inflammatory bowel disease (IBD), a condition characterized by chronic inflammation in the intestines that causes gastrointestinal symptoms, such as diarrhea and abdominal pain. While some medications are available for IBD treatment, disease remission remains suboptimal because they do not cure the underlying disease.

A critical factor hindering the identification of new drugs for treating and curing IBD is that we currently lack accurate models of the disease that can accurately recapitulate the conditions inside patients when they experience IBD.

To tackle this problem, the Takayama-led team hypothesized that they could create a better IBD model by constructing colon organoids that include the different cell types comprising the intestines because current models typically employ intestinal cell lines or contain only colonic epithelial cells.

By leveraging the power of iPS cells to turn into nearly all cells comprising the human body, the researchers induced iPS cells to differentiate into colonic epithelial and stromal cells through a five-step process to colonic organoids. The work is published in the journal iScience.

By examining various cell type-specific markers and performing single-cell RNA sequencing (scRNA-seq) analysis, both colonic epithelial and stromal cells were identified in these organoids, thus demonstrating the team’s successful attempt to build organoids consisting of different fundamental cell types of the intestines for better IBD modeling.

Equipped with these advanced organoids, the research team next aimed to identify ways to recreate the disease conditions of IBD. Because levels of various inflammatory cytokines rise during the onset and progression of IBD, the researchers treated colonic organoids with different combinations of several cytokines (TNF-α, IFN-γ, and IL-1β) detectable in IBD patients during the disease.

This combined cytokine treatment led to inflammatory tissue damage and increased levels of IL-8, another cytokine known to elevate in IBD patients, thus indicating to the researchers that they had succeeded in mimicking disease conditions.

The research team next characterized this newly constructed colonic organoid-based IBD model by histological, immunofluorescence, and gene expression analyses, observing numerous morphological and cellular changes that parallel biopsied intestinal tissues from IBD patients.

Additional analyses further showed disruptions in intestinal barrier functions. Notably, scRNA-seq identified stromal and endothelial cells to highly express genes encoding inflammatory cytokines upon the combined treatment of TNF-α, IFN-γ, and IL-1β, suggesting these cells to be the primary source of inflammatory cytokines and illustrating the importance of including such cell types to portray IDB pathophysiology accurately.

Using the three cytokines to trigger IBD-like conditions, the researchers examined whether a similar treatment of a commonly used cell line used to model IBD could produce a comparable response.

While gene expression analysis revealed the initiation of an inflammatory response, they observed that a similar cytokine treatment could not reproduce the epithelial damage or as much of a spike in inflammatory cytokine production observed in their new IBD colonic organoid model.

Because IBD is classified into ulcerative colitis (UC) and Crohn’s disease (CD), the research team compared gene expression profiles of IBD-like colonic organoids and colon tissues collected from active sites of UC and CD patients to determine whether their model simulates UC or CD conditions more closely.

This analysis revealed that the model more closely resembles UC biopsied tissues. Thus, focusing on the ability of this model to portray UC pathophysiology, the research team next tested the effects of a commonly used drug for treating UC, tofacitinib, in IBD-like colonic organoids.

As expected, through various experiments, they observed the clear therapeutic effects of tofacitinib in reversing tissue damage and inflammatory cytokine production, demonstrating the potential of using this model system to evaluate new drugs against UC.

Altogether, the research team led by Takayama showed the critical involvement of stromal cells and other cell types when replicating IBD pathophysiology in in vitro model systems. They hope their new and more accurate model enables the identification of novel drug candidates for IBD so that the millions affected by this disease worldwide can one day enjoy a better life.