Chronically stimulated surfaces of the body, in particular the gastrointestinal (GI) tract, are major sites where immune cells traffic and reside. Because mucosal surfaces are constantly challenged by fluctuating environmental perturbations, immune cells at these sites display a remarkable adaptive capacity in order to fend off microbial challenges and safeguard organ homeostasis and health.
The Neumann lab is specifically interested in the molecular basis of lymphocyte adaption to mucosal organs. The goal of our research is to understand the genetic, epigenetic and transcriptional mechanisms that determine the tissue-specific functions of distinct lymphocyte populations. Furthermore, we aim to identity the specific (micro)environmental cues that trigger tissue adaptation. In addition, a major focus of our research lies on the crosstalk between gut lymphocytes and distinct intestinal tissue cells, such as epithelial or neuronal populations, to better understand the cellular networks that are in place to establish and maintain intestinal health.
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, can activate opioid receptors on the enteric circuitry to control crucial physiological functions such as gut motility and secretion. The importance of opioids in regulating gut homeostasis is illustrated by the adverse effects associated with pharmacological opioid intervention during pain therapy, such as Opioid-induced bowel dysfunction (OIBD) that is commonly described as constipation. Vice versa, therapeutic administration of exogenous opioids is widely used to manage severe diarrhea as well as irritable bowel syndrome. Thus, the amount of bioavailable opioid peptides in the GI tract is strictly determining gut function and health.
Throughout the last years, gut-resident Foxp3+ Treg cells have been associated with a growing number of tissue-specific functions in the intestine, comprising various aspects of gut immunity and physiology. Treg cells have pivotal roles in intestinal tolerance induction and host defense by actively controlling immune responses towards dietary antigens and commensal microorganisms as well as towards invading pathogens. In addition to these cardinal immune-related roles, it has become increasingly clear that 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 a specific cellular source of endogenous opioid peptides in the gut. Since intestinal Treg cells are known to incorporate diverse external signals in the GI tract, such as signals derived from the diet or microbiota, their potential involvement in the opioid-mediated control of gut function may represent a key mechanism of tissue adaptation to constantly changing environmental cues.
Aim 1: Phenotypic, functional and spatial characterization of opioid-releasing Treg cells in the intestine. Intestinal Foxp3+ Treg cells are a heterogenous cell population, comprising of distinct subsets with different developmental origins, functions and phenotypes, tailored to the diverse challenges of the intestinal tissue microenvironment. Therefore, in Aim 1, we plan to thoroughly characterize murine opioid-releasing 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-releasing 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-releasing Treg cells and their potential interaction partners in the murine gut.
Aim 2: Identification of signals regulating opioid-releasing 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. cytokines, dietary signals, and microbiota) 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-releasing Treg cells for gut physiology and homeostasis. To ultimately test the role of Treg cell-derived opioids for gut homeostasis and function, we have generated conditional T cell and Treg cell-specific opioid knockout mice. Hence, in Aim 3, we will use these mice to perform functional analysis 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.