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1 Department of Medicine, Division of Nephrology and General Medicine, University Hospital Freiburg, Freiburg, Germany
2 Department of Medicine D, Division of General Internal Medicine and Nephrology, University Hospital Munster, Muenster, Germany
3 Department of Pathology, University of Freiburg, Freiburg, Germany
4 Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
5 Children's Renal Unit and Academic Renal Unit, Southmead Hospital, University of Bristol, Bristol, United Kingdom
* To whom correspondence should be addressed. E-mail: karl-georg.fischer{at}uniklinik-freiburg.de.
Experimental and clinical studies impressively demonstrate that angiotensin converting enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARB) significantly reduce proteinuria and retard progression of glomerular disease. The underlying intraglomerular mechanisms are not yet fully elucidated. As podocyte injury constitutes a critical step in the pathogenesis of glomerular proteinuria, beneficial effects of ACEI and ARB may partially result from interference with a local renin angiotensin system (RAS) in podocytes. The knowledge of expression and function of a local RAS in podocytes is limited. In this study, we demonstrate functional expression of key components of the RAS in differentiated human podocytes: Podocytes express mRNA for angiotensinogen, renin, ACE type 1, and the AT1 and AT2 angiotensin receptor subtypes. In Western blot experiments and immunostainings expression of the AT1 and AT2 receptor was demonstrated both in differentiated human podocytes and in human kidney cortex. Angiotensin II (Ang II) induced a concentration-dependent increase of the cytosolic Ca2+ concentration via AT1 receptors in differentiated human podocytes, whereas it did not increase cAMP. Further, Ang II secretion was detected, which was neither blocked by the ACEI captopril, nor the renin inhibitor remikiren, nor the chymase inhibitor chymostatin. Ang II secretion of podocytes was not increased by mechanical stress. Finally, Ang II was found to increase staurosporine-induced apoptosis in podocytes. We speculate that ACEI and ARB exert their beneficial effects in part by interfering with a local RAS in podocytes. Further experiments are required to identify the underlying molecular mechanism(s) of podocyte protection.
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