Dr. Nathaniel Winsor, first as a PhD candidate and now a Postdoctoral Fellow worked with the team when they encountered an unexpected issue in mice used to study the gut microbiome and colon cancer. Faced with the choice of abandoning two years of research or investigating further they chose curiosity leading to insights that could reshape our understanding of parasites in gut inflammation. Their decade-long study was recently published in Cell Host & Microbe.

The Girardin lab focuses on immune regulation in mucosal barriers particularly in the gut. They explore how innate sensors in gut epithelial cells detect microbiome changes and trigger inflammation which plays a role in cancer development. The team studied NLRP6 a protein abundant in these cells whose function remained unclear.

Research suggested that NLRP6 responded to microbiome imbalances and was linked to colorectal cancer. To test this the team developed a mouse model where cancer was driven by microbiome changes. They found that mice lacking NLRP6 developed more cancer revealing a connection between the microbiota inflammation and colorectal cancer explains Dr. Nathaniel Winsor.

Initially they believed NLRP6 was detecting microbiota changes but no differences were found between the two groups of mice. The breakthrough came when an Immunology colleague examined the data and discovered that the mice were filled with single-celled organisms protozoans later identified as the parasite Tritrichomonas.

This was a major setback we discovered that all the mice in our facility were unknowingly infected with this parasite says Dr. Girardin. It introduced an unexpected variable into our experiments forcing us to make a tough choice: abandon the project or start over with parasite-free mice repeating two years of work.

When they repeated the experiment with parasite-free mice there was no difference in cancer levels with or without NLRP6 revealing that the protozoans were the key factor. This completely shifted our focus. Instead of cancer we became more interested in the interaction between the protozoan the microbiome and NLRP6 they explain. In our controlled lab environments we usually study bacteria or viruses parasites were rarely considered. This unexpected discovery opened up a unique and overlooked niche in our field.

Parasites trigger a goblet cell response in the intestine stimulating mucus production to form a protective barrier. To explore this Girardin and Winsor developed an experimental model and assay to measure goblet cell activity uncovering a clear connection. Mice with NLRP6 produced more mucus while those lacking it had reduced mucus levels leading to increased inflammation and a higher cancer risk.

To understand how NLRP6 was activated and why the parasite induced this response they conducted experiments at U of T’s Germ-Free Animal Facility. They also collaborated with Dr. George Birchenough from the University of Gothenburg an expert in ex vivo imaging to further investigate the mechanism.

The team discovered that NLRP6 wasn’t reacting to the parasite itself but rather to microbiome changes caused by the parasite. The detection mechanism was completely unexpected says Dr. Girardin. We don’t respond directly to the parasite we respond to the changes it triggers. This could represent a new paradigm in our field.

What could have derailed their research instead led to a groundbreaking discovery about how parasites interact with the gut microbiome and influence overall health. This accidental finding has shifted our perspective revealing a previously overlooked group of organisms and a new set of immunostimulatory molecules that could have significant health implications adds Dr. Winsor.

Source: https://lmp.utoronto.ca/news/scientists-discover-new-connection-between-gut-microbiome-and-inflammation-through-happy