Activation of a local tissue angiotensin system in podocytes by mechanical strain.

Activation of a local tissue angiotensin system in podocytes by mechanical strain. Background Glomerular capillary hypertension, a common denominator in various forms of progressive glomerular disease, results in mechanical distention of the capillary tuft, and subsequent injury of the overlying podocyte layer. The mechanisms by which elevated intraglomerular pressure is translated into a maladaptive podocyte response remain poorly understood. Angiotensin II plays a central role in the pathogenesis of chronic renal injury, largely through its actions on the subtype 1 receptor. Accordingly, we have tested the hypothesis that mechanical strain up-regulates local angiotensin II in podocytes, thereby resulting in a progressive reduction in podocyte number. Methods Conditionally immortalized mouse podocytes were subjected to cyclical stretch of 10% amplitude. Nonstretched podocytes served as controls. Angiotensin II levels were measured in whole cell lysate by competitive enzyme-linked immunosorbent assay (ELISA). Expression of angiotensin II receptors (AT 1 R, AT 2 R) was measured by quantitative polymerase chain reaction (PCR) and Western blot analysis. Apoptosis was measured by Hoechst staining. Immunostaining for AT 1 R was performed in tissue sections from rats with 5/6 remnant kidney disease, a model of glomerular hypertension. Results Mechanical strain increased angiotensin II production in podocytes at 24, 48, and 72hours ( P 1 R mRNA expression at 24hours and a twofold increase in protein levels vs. controls ( P 1 R staining was increased in a podocyte distribution in the 5/6 remnant kidney, consistent with our in vitro findings. Mechanical strain resulted in a 2.5-fold increase in apoptosis ( P Conclusion Mechanical strain leads to up-regulation of the AT 1 R and increased angiotensin II production in conditionally immortalized podocytes. The resulting activation of a local tissue angiotensin system leads to an increase in podocyte apoptosis, mainly in an AT 1 R-mediated fashion.