Gut microbiota shape the inflammatory response in mice with an epithelial defect

Area of Science:

• Gastroenterology and Immunology
• Molecular Biology
• Microbiology

Background:

• Endoplasmic reticulum (ER) stress in intestinal epithelial cells is linked to intestinal inflammation, but its role as an initiator or response is unclear.
• Winnie mice, with a Muc2 gene mutation, exhibit goblet cell ER stress, leading to spontaneous colitis, mucus barrier depletion, and bacterial translocation.
• The contribution of microbiota to Winnie colitis development and the direct inflammatory potential of protein misfolding without microbiota require investigation.

Purpose of the Study:

• To determine if microbiota is essential for Winnie colitis development.
• To investigate whether protein misfolding can directly initiate inflammation in the absence of microbiota.
• To compare the colitis phenotype of Winnie mice in germ-free versus specific pathogen-free conditions.

Main Methods:

• Germ-free (GF) rederivation of Wild-Type (WT) and Winnie mice.
• Housing mice in isolators and comparing colitis phenotypes to specific pathogen-free (SPF) housed mice.
• Assessing inflammatory gene expression, ER stress, mucin misfolding, and RNA-sequencing of colon organoids.

Main Results:

• Winnie colitis was significantly reduced but not eliminated in GF conditions, indicating a partial role for microbiota.
• Inflammatory cytokine gene expression decreased in GF Winnie mice, though some chemokines remained elevated, and ER stress diminished despite persistent mucin misfolding.
• RNA-Seq showed reduced expression of negative inflammatory regulators and increased Mip2a chemokine in Winnie organoids, suggesting heightened epithelial responsiveness.
• Intestinal epithelial protein misfolding can prime inflammation without initiating the unfolded protein response in the absence of microbiota.

Conclusions:

• While genetic predisposition to mucin misfolding initiates mild inflammatory signals, the microbiota is necessary for the amplification and progression of colitis in Winnie mice.
• Epithelial cells in Winnie mice exhibit increased responsiveness to inflammatory stimuli.
• Protein misfolding in intestinal epithelial cells can initiate inflammation, but microbiota drives its amplification.