Neuro-immune interactions in the GI tract: Defining the role of endogenous opioid-producing regulatory T cells

Principle Investigator

Scientific interest within the context of the graduate college:

Chronically stimulated surfaces of the body, in particular the gastrointestinal (GI) tract, are major sites where immune cells traffic and reside. Since the intestinal surface is constantly challenged by fluctuating environmental perturbations (microbiota, diet, pathogens), immune cells at this site display a remarkable capacity to adapt their functionality in order to safeguard organ homeostasis and health.

The Neumann lab is specifically interested in the molecular basis of immune cell adaption to the GI tract. The goal of our research is to understand the molecular mechanisms that determine the gut-specific functions of distinct immune cell populations. Furthermore, we aim to identify the specific (micro)environmental cues that trigger adaptation of immune cells in the gut. In addition, a major focus of our research lies on the crosstalk between gut immune cells and distinct intestinal tissue cells, such as epithelial or neuronal cell populations, to better understand the cellular networks that are in place to establish and maintain intestinal health.

Project description:

Introduction: The GI tract is equipped with the largest collection of neurons outside the brain, known as the enteric nervous system. Consequently, neuroactive substances, such as endogenous opioid peptides that are synthesized by the human body, can activate opioid receptors on the enteric circuitry to control crucial physiological functions such as gastric emptying and intestinal motility. Clinically, the importance of opioids in the gut is illustrated by the side effects associated with pharmacological opioid intervention during pain therapy, such as Opioid-induced bowel dysfunction (OIBD) or constipation. Vice versa, therapeutic administration of exogenous opioids is widely used to manage severe diarrhea as well as irritable bowel syndrome (IBS). Thus, the amount of bioavailable opioid peptides in the GI tract is strictly determining gut function and health. In addition, endogenous opioids have immunomodulatory functions and can counteract inflammation-associated pain, making them prime therapeutic targets during (intestinal) inflammatory diseases. Intestinal Foxp3+ regulatory T cells (Treg cells) are key for intestinal tolerance induction and host defense by actively controlling immune responses towards dietary and microbial antigens as well as invading pathogens. In addition to these cardinal immune-related roles, intestinal Treg cells also exert important non-immune functions in the gut, such as promoting local tissue repair and preserving the integrity of the epithelial barrier. Importantly, recent data obtained from mouse models in our lab have generated the hypothesis that intestinal Treg cells are also prominent producers of endogenous opioids in the gut. Thus, this project aims to better characterize and functionally understand these opioid-producing Treg cells.

Aim 1: Phenotypic, functional and spatial characterization of opioid-producing intestinal Treg cells. Intestinal Foxp3+ Treg cells are a heterogenous cell population, comprising of distinct subsets with different developmental origins, functions and phenotypes. Therefore, in Aim 1, we plan to thoroughly characterize murine opioid-producing gut-resident Treg cells in depth by multi-parameter flow cytometry and fluorescence-activated cell sorting (FACS). In addition, with the help of immunofluorescence microscopy, we aim to determine the precise location of opioid-producing Treg cells within the gut tissue, especially in close vicinity to e.g. enteric neurons. Thus, Aim 1 will be instrumental to obtain a detailed phenotypic, functional and spatial mapping of opioid-producing Treg cells and their potential interaction partners in the mouse gut.

Aim 2: Identification of signals regulating opioid-producing intestinal Treg cells. To identify the regulatory circuits that control the expression of opioids by intestinal Treg cells, we will systematically test potential signals (e.g. immune signals, dietary signals, microbial signals) during in vitro cultures or with the help of transgenic knock-out mice. Thus, Aim 2, will define the unique signals that induce and control the expression of endogenous opioids by gut-resident Treg cells.

Aim 3: Analysis of the functional role of opioid-producing intestinal Treg cells. To ultimately test the functional role of opioid-producing Treg cells, we have generated conditional Treg cell-specific opioid knock-out mice. In Aim 3, we will use these mice to perform functional analyses testing neuro-dependent gut functions, such as gut motility, peristalsis or secretion. Furthermore, we also aim to characterize the impact of opioid-deficiency on the phenotype and function of the enteric nervous system.

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