Protease activated receptors in cardiovascular function and disease.

Recent studies have shown that a novel class of protease activated receptors (PARs), which are composed of seven transmembrane G protein-coupled domains, are activated by serine proteases such as thrombin, trypsin and tryptase. Although four types (PAR 1, PAR 2, PAR 3 and PAR 4) of this class of receptors have been identified, their discrete physiological and pathological roles are still being unraveled. Extracellular proteolytic activation of PARs results in the cleavage of specific sites in the extracellular domain and formation of a new N-terminus which functions as a tethered ligand. The newly formed tethered ligand binds intramolecularly to an exposed site in the second transmembrane loop and triggers G-protein binding and intracellular signaling. Recent studies have shown that PAR-1, PAR-2 and PAR-4 have been involved in vascular development and a variety of other biological processes including apoptosis and remodeling. The use of animal model systems, mainly transgenic mice and synthetic tethered ligand domains, have contributed enormously to our knowledge of molecular signaling and the regulatory properties of various PARs in cardiomyocytes. This review focuses on the role of PARs in cardiovascular function and disease.