Protease dependent signalling at the glomerular filtration barrier

• Applicant: Professor Dr. Berend Isermann
• Subject Area: Nephrology ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: from 2016 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 281777554

Diabetic nephropathy (dNP) is gaining pandemic dimensions, putting an enormous burden on affected individuals, health care providers, and insurances. Established therapies, such as blood glucose and blood pressure control delay, but do not avert dNP. In recent years we established an important function of coagulation proteases in regulating glomerular function. In particular, we demonstrated that the serine protease activated protein C (aPC) protects against dNP. This finding has been confirmed by others and clinical studies support such a role of aPC. However, how coagulation protease dependent signalling is regulated locally at the glomerular filtration barrier remains largely enigmatic. Of note, not only receptors for coagulation factors (e.g. protease activated receptors, PARs), but also their regulators, such as thrombomodulin (TM) and tissue factor (TF), and even the proteases themselves (e.g. protein C ,PC), are locally expressed by glomerular cells such as podocytes and endothelial cells. Yet, it remains unknown whether and how locally expressed coagulation factors and regulators contribute to signalling via coagulation proteases. Furthermore, it is not known whether and how endothelial cells and podocytes interact via coagulation proteases. In preliminary work we identified that podocyte specific expression of TM protects against dNP - at least in part independent of PC-activation. Furthermore, we detected an interaction between aPC and alphavbeta3-integrin, which is relevant for podocyte signalling. Likewise, TF modulates glomerular function in dNP. Potential mechanism through which TM and TF may coordinately modulate glomerular function will be evaluated within the current proposal. We wish to determine whether TM provides a functional signaling switch between PAR-1 and integrin dependent signalling and whether TM modulates signalling either by functionally interacting with TF or with intracellular proteins via its cytoplasmic domain. Specifically, we wish to 1) characterize the expression and activity of locally expressed coagulation regulators, 2) evaluate whether TM provides a functional switch between PAR-1 and PAR-3 - avb3 signalling, 3) identify the role of TMs cytoplasmic domain for glomerular cell function and dNP, 4) characterize the functional relevance of TM-dependent complement regulation for TF-activity, 5) delineate the mechanism through which TF modulates glomerular cell function, 6) characterize TM- and TF-mediated receptorsome formation, including the interaction with integrins, 7) analyze the relevance of isomerase switches for protease dependent signalling in podocytes. These comprehensive studies will provide novel insight into coagulation protease dependent signalling in glomerular disease. We expect that these findings will provide new impetus for translational efforts and will have implications for studies addressing coagulation protease signalling in other tissues.

• DFG Programme: Research Grants