Protease activated receptor mediated actions in the human intestine
Protease activated receptors (PARs) belong to a family of seven transmembrane domain G-protein-coupled receptors that are activated by the cleavage of their N-terminal domain by a protease. This cleavage frees a new N-terminus that acts as a tethered ligand which binds intramolecularly to initiate cellular signals. Four different PARs, PAR-1, PAR-2, PAR-3 and PAR-4 have been identified so far. Short synthetic peptides based on the tethered ligand sequences of the different PARs, so called PAR-activating peptides (PAR-APs) – mimic the effects of proteases, activating selectively the different members of the PAR familiy.
PARs are expressed throughout the gastrointestinal tract on several cell types, as enterocytes, mast cells, smooth muscle cells, enteric neurons as well as peripheral terminals of sensory nerves of the gut brain axis.
Based on the fact, that IBD and IBS patients exhibit increased luminal protease activity and are characterised by high-grade and low grade inflammation respectively, bacterial proteases (commensal or pathogenic origin) as well as host-derived endogenous proteases (e.g. mast cell trypatse) are in focus as key pathogenic factors in these intestinal diseases.
The role of PAR has been studied in small laboratory animals revealing that enteric neurons are stimulated by PAR-AP as well as proteases. Reed et al. (J Physiol 2003, 547:531-542) showed that activation of PAR-2 on guinea pig submucosal neurons by mast cell tryptase caused neuronal hyperexcitability. Furthermore it has been shown that PAR-2 activation induced increased paracellular permeability, neurogenic inflammation and visceral hypersensitivity. As a result, PAR-2 has received most of the attention. The aim of our study is to identify the so far unknown effects of PAR-APs on human submucous neurons and to study their effects on ion secretion. To study nerve modulating effects of the PAR-1 AP TFLLR-NH2, the PAR-2 AP SLIGKV-NH2 and PAR-4 AP GYPGQV- NH2 we use neuroimaging techniques in combination with voltage or calcium sensitive dyes. Using the Ussing Chamber technique we study their prosecretory potential.
Funded by: Deutsche Forschungsgemeinschaft ( DFG, Graduiertenkolleg GRK 1482), European Union (IPODD - Intestinal Proteases: Opportunity for drug discovery).