A Novel, Powerful Tool to Unveil the Communication Between Gut Microbes and the Brain

Summary: Researchers develop a new tool that allows the study of microbial communication in the gastrointestinal tract and brain.

Source: Baylor College of Medicine

In the past decade, researchers have begun to appreciate the importance of a two-way communication that occurs between microbes in the gastrointestinal tract and the brain, known as the gut-brain axis.

These “conversations” can modify the way these organs function and involve a complex network of chemical signals emanating from microbes and the brain that are challenging for scientists to disentangle in order to understand.

“Currently, it is difficult to determine which microbial species induce specific brain changes in a living organism,” said first author Dr. Thomas D. Horvath, instructor of pathology and immunology at Baylor College of Medicine and Texas Children’s Hospital.

“Here we present a valuable tool that enables investigations into the connections between gut microbes and the brain. Our laboratory protocol allows for the comprehensive identification and evaluation of metabolites – the compounds that microbes produce – at the cellular and whole-animal level.”

The gastrointestinal tract harbors a rich and diverse community of beneficial microorganisms known collectively as the gut microbiota. In addition to their role in maintaining the gut environment, gut microbes are increasingly recognized for their influence on other distant organs, including the brain.

“Gut microbes can communicate with the brain through several pathways, for example by producing metabolites, such as short-chain fatty acids and peptidoglycans, neurotransmitters, such as gamma-aminobutyric acid and histamine, and compounds that modulate the immune system, among others. ,” said co-first author Dr. Melinda A. Engevik, assistant professor of regenerative and cellular medicine at the Medical University of South Carolina.

The role of microbes in central nervous system health is highlighted by links between the gut microbiome and anxiety, obesity, autism, schizophrenia, Parkinson’s disease and Alzheimer’s disease.

“Animal models have been important in linking microbes to these fundamental neural processes,” said co-author Dr. Jennifer K. Spinler, assistant professor of pathology and immunology at Baylor and Texas Children’s Hospital Microbiome Center.

“The protocol in the current study enables researchers to take steps toward uncovering the specific involvement of the gut-brain axis in these conditions, as well as its role in health.”

A road map to understanding the complex traffic system in the gut-brain axis

One strategy the researchers used to gain insight into how a single type of microbe might affect the gut and brain consisted of growing the microbes in the lab first, collecting the metabolites they produced and analyzing them using mass spectrometry and metabolomics.

Mass spectrometry is a laboratory technique that can be used to identify unknown compounds by determining their molecular weight and to quantify known compounds. Metabolomics is a technique for the large-scale study of metabolites.

This protocol gives researchers a road map to understand the complex trafficking system between the gut and the brain and its effects on health and disease. Credit: Baylor College of Medicine

“The effect of the metabolites was then studied in the mini-gut, a laboratory model of human intestinal cells that retains the properties of the small intestine and is physiologically active,” said Engevik. “In addition, the microbe’s metabolites can be studied in living animals.”

“We can extend our study to a microbial community,” Spinler said.

“In this way we investigate how microbial communities work together, synergize and influence the host. This protocol gives researchers a road map to understand the complex traffic system between the gut and the brain and its effects.”

“We were able to create this protocol thanks to extensive interdisciplinary collaborations involving clinicians, behavioral scientists, microbiologists, molecular biologists and metabolomics experts,” said Horvath.

“We hope that our approach will help create engineered communities of beneficial microbes that can contribute to maintaining a healthy body. Our protocol also provides a way to identify potential solutions when miscommunication between the gut and the brain leads to disease.”

Read full details of this work in Nature Protocols.

Other contributors to this work included Sigmund J. Haidacher, Berkley Luck, Wenly Ruan, Faith Ihekweazu, Meghna Bajaj, Kathleen M. Hoch, Numan Oezguen, James Versalovic, and Anthony M. Haag. The authors are affiliated with one or more of the following institutions: Baylor College of Medicine, Texas Children’s Hospital, and Alcorn State University.

Funding: This study was supported by an NIH grant K01 K12319501 and Global Probiotics Council 2019-19319, grants from the National Institute of Diabetes and Digestive and Kidney Diseases (Grant P30-DK-56338 to the Texas Medical Center Digestive Diseases Experiment, Gastroeriin Systems), NIH grant U01CA170930, and unrestricted research support from BioGaia AB (Stockholm, Sweden).

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About this gut-brain axis research news

Author: Homa Shalchi
Source: Baylor College of Medicine
Contact: Homa Shalchi – Baylor College of Medicine
Image: Image credited to Baylor College of Medicine

Original Research: Closed Access.
“Interrogating the mammalian gut-brain axis using LC-MS/MS-based targeted metabolomics with in vitro bacterial and organoid cultures and in vivo gnotobiotic mouse models” by Thomas D. Horvath et al. Nature Protocols

abstract

Interrogating the mammalian gut-brain axis using LC-MS/MS-based targeted metabolomics with bacterial and organoid cultures in vitro and gnotobiotic mouse models in vivo

Interest in the communication between the gastrointestinal tract and the central nervous system, known as the gut-brain axis, has driven the development of quantitative analytical platforms to analyze signals emanating from microbes and hosts.

This protocol enables investigations into the connections between microbial colonization and gut and brain neurotransmitters and contains strategies for comprehensive metabolite assessment in in vitro (organoid) and in vivo mouse model systems.

Here we present an optimized workflow that includes procedures for the preparation of these gut-brain axis model systems: (step 1) growth of microbes in defined media; (phase 2) microinjection of intestinal organoids; and (phase 3) generation of animal models including germ-free (germ-free), specific pathogen-free (complete gut microbiota), and pathogen-specific re-conventionalized (germ-free mice paired with a complete gut microbiota from a mouse no specific pathogen), and Bifidobacterium dentium and Bacteroides ovatus mono-companion (germ-free mice colonized with a single gut microbe).

We describe targeted liquid chromatography-tandem mass spectrometry-based metabolomic methods for analyzing microbially derived short-chain fatty acids and neurotransmitters from these samples.

Unlike other protocols that usually only examine stool samples, this protocol includes bacterial cultures, organoid cultures, and in vivo samples, in addition to monitoring the metabolite content of stool samples. The inclusion of three experimental models (microbial, organoid and animal) increases the impact of this protocol.

The protocol requires 3 weeks of microbial colonization of the moss and ~1–2 weeks for instrumental and quantitative mass spectrometry-based analyzes along with liquid chromatography and sample processing and normalization.