Mechanisms and modulation of neuro-immune interactions: Cross-talk between mast cells and enteric neurons

• Applicant: Professor Dr. Martin Diener
• Subject Area: Veterinary Medical Science
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 299037655

The enteric nervous system (ENS) is able to regulate nearly all functions of the gastrointestinal tract independent from the brain or the spinal cord. There is a strong interaction of this part of the autonomous nervous system with other cells in the gastrointestinal wall such as e.g. mast cells, which are located in high densitiy within the lamina propria and the submucosa in close vicinitiy to nerve cells. A degranulation of mast cells induces the release of mediators like histamine, proteases, eicosanoids and others stimulating secretomotor submucosal neurons. The consequence is the induction of epithelial anion secretion, clinically leading to secretory diarrhea. From previous experiments performed at isolated submucosal neurons it is known that these neurons express several types of histamine receptors. Activation of these receptors leads to depolarization of the membrane and an increase in the cytosolic Ca2+ concentration. Coculture experiments with mast cells show that histamine receptors are centrally involved in the response of the ENS to mast cell degranulation.The aim of the project is to elucidate the mechanisms and the potential modulation of this neuro-immune-interaction. It shall be clarified by which signaling mechanisms histamine H1 and H2, receptors, i.e. the functionally predominant histamine receptor subtypes of rat submucosal neurons, excite neurons in this part of the enteric nervous system. Whole-cell patch-clamp recordings shall elucidate the ionic mechanisms and the signal transduction pathways underlying the membrane depolarization evoked by histamine observed during microelectrode impalements. As mast cells are assumed not only to be involved in food allergy, but are also thought to play a significant role e.g. for inflammatory bowel disease, the cross-talk of mast cells with submucosal neurons will be studied in coculture experiments with RBL-2H3 cells (a permanent mast cell-equivalent cell line) as well as in submucosa-lamina propria-preparations (to study neuronal interaction with mucosal mast cells) after pretreatment with proinflammatory cytokins. Changes in the cytosolic Ca2+ concentration within the neurons induced by mast cell degranulation serves as functional read-out for these experiments. At preparations from animals which have been sensitized against ovalbumin it will be tested whether changes in ion transport or paracellular permeability induced ex vivo by antigen exposure in Ussing chambers is altered, when the animals have been pretreaded with TNBS (trinitrobenzenesulfonic acid), i.e. whether a colitis aggravates allergic responses in the gut. Furthermore, it shall be investigated whether the cross-talk between mast cells and enteric neurons is modulated by cholinergic receptors as suggested by data from the literature.

• DFG Programme: Research Grants