Hypertension and kidney disease: is renalase a new player or an innocent bystander?

Most patients on dialysis are hypertensive and their blood pressure (BP) control is often poor. Renalase is preferentially expressed in proximal tubules, but it is also present in glomeruli and distant tubules, as well as in cardiomyocytes, liver, and skeletal muscle. It had been proposed that renalase had a flavin adenine dinucleotide (FAD)-binding domain and that FAD was an essential cofactor for its stability and monoamine oxidase activity. It was reported that renalase, secreted by the kidney and circulating in the blood, degraded catecholamines and might play a role in the regulation of sympathetic tone and BP. It has been also proposed that renalase-coding gene is a novel susceptibility gene for essential hypertension and its variations may influence BP. In addition, polymorphisms of the renalase gene in hemodialysed patients were associated with hypertension. However, several unresolved and controversial issues still remain such as how to measure renalase and its physiological activity. Furthermore, there are few data on possible activators and/or inhibitors of renalase. We are at the very beginning of solving the problem of whether renalase is a causative factor of hypertension in kidney disease or just an innocent bystander. Therefore, more research is needed to establish whether renalase can become a useful therapeutic target.