Protease-activated receptor-2 (PAR-2) is present in the rat hippocampus and is associated with neurodegeneration

Protease-activated receptor-2 (PAR-2) is a seven-transmembrane G protein-coupled receptor that possesses a structure and activation mechanism similar to those of the thrombin receptor. It is activated by low concentrations of trypsin (300 pM) and a synthetic hexapeptide [sequence of serine, leucine, isoleucine, glycine, arginine, leucine (SLIGRL), the rodent PAR-2 ''tethered ligand''] representing the first six amino acids following the putative PAR-2 cleavage site. Previous studies have indicated that alpha-thrombin and SFLLRN (synthetic hexapeptide sequence of serine, phenylalanine, leucine, leucine, arginine, asparagine; the human thrombin receptor ''tethered ligand'') induce neurite retraction and neurotoxicity. Because of the strong similarities between thrombin receptor and PAR-2, we have proposed that PAR-2 may also participate in neurodegeneration. In the present study, we used reverse transcriptase polymerase chain reaction and immunocytochemistry to provide the first evidence that PAR-2 is present in the rat hippocampus. Moreover, we found SLIGRL to be toxic to hippocampal neurons in a concentration-dependent manner (greater than or equal to 100 mu M). Calcium signaling studies were performed to aid in determining the mechanism by which PAR-2 activation is neurotoxic.