Pathophysiology of the endothelin system - lessons from genetically manipulated animal models.

Shortly after discovery of ET-1 in 1988, the entire endothelin system was characterized. The endothelin system consists of the three peptides ET-1, ET-2 and ET-3, their G-protein-coupled receptors endothelin receptor A and B (ETRA and ETRB) and the two endothelin-converting enzymes (ECE-1 and ECE-2). Genetically modified animal models are an important tool in biomedical research. Here we describe the key findings obtained from genetically modified animal models either over-expressing compounds of the ET system or lacking these compounds (knockout mice). Results from the different transgenic and knockout models disclose that the ET system plays a major role in embryonic development. Two ET system-dependent neural crest-driven developmental pathways become obvious: one of them being an ET-1/ETAR axis, responsible for cardio-renal function and development as well as cranial development; the other seems to be an ET-3/ETBR mediated signalling pathway. Mutations within this axis are associated with disruptions in epidermal melanocytes and enteric neurons. These findings led to the discovery of similar findings in humans with Hirschsprung disease. In adult life the ET system is most important in the cardiovascular system and plays a role in fibrotic remodelling of the heart, lung and kidney as well as in the regulation of water and salt excretion.