Rolle von Serinproteasen bei der Ödementstehung

19/04/2017 to 01/07/2020

Serine proteases belong to the class of endopeptidases with known members such as digestive enzymes or coagulation factors. Within the kidney, serine proteases are involved in the regulation of the epithelial sodium channel ENaC and play an important role in the regulation of sodium balance. In 2009 it was proposed that the non-physiological formation of plasmin during proteinuria might lead to activation of ENaC through proteolysis of its y-subunit and hereby induce edema. In this context, plasminogen is filtered into the tubular space from diseased glomeruli and converted to plasmin by the locally abundant urokinase. The proteolytical activation of ENaC is a new mechanism that might explain the high coincidence of edema and hypertension with proteinuric kidney disease and the association with high morbidity and mortality of these patients. Preliminary work of the applicant identified the serine protease plasma kallikrein in the urine of proteinuric patients. Both urokinase and plasma kallikrein are capable of converting plasminogen to plasmin. Own data indicate that treatment with the broad spectrum serine protease inhibitor aprotinin completely blocks edema formation in mice with experimental nephrotic syndrome. These data suggest strongly that a cascade of different serine proteases are active during proteinuria which remains to be identified. In this application we aim to investigate the role of serine proteases during proteinuria and to elucidate its involvement in sodium retention which in turn lays the foundation to new therapeutic strategies. To this end, we want to identify all serine proteases that are involved in edema formation by a proteomic approach and that could be targeted for treatment. Using knockout mice, we want to clarify the role of the serine proteases urokinase, plasmin and plasma kallikrein that are hitherto known to be excreted during proteinuria. Finally we want to develop a diagnostic ELISA test that allows the detection of a y-ENaC fragment in the urine after proteolysis by plasmin indicating patients with proteolytic ENaC activation.