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Hypercholesterolemia in Rats Induces Podocyte Stress and Decreases Renal Cortical Nitric Oxide Synthesis via an Angiotensin II Type 1 Receptor–Sensitive Mechanism

Diana M. Attia^*, Olivier Feron, Roel Goldschmeding, Louk H. Radermakers, Nosratola D. Vaziri, Peter Boer^*, Jean-Luc Balligand, Hein A. Koomans^* and Jaap A. Joles^*

*Department of Nephrology and Hypertension, University Medical Center, Utrecht, the Netherlands; Department of Internal Medicine, Louvain University, Brussels, Belgium; Department of Pathology, University Medical Center, Utrecht, the Netherlands; and Division of Nephrology, Departments of Medicine, Physiology, and Biophysics, University of California Irvine, Irvine, California

Correspondence to Dr. Jaap A. Joles, Department of Nephrology and Hypertension (Room F03.226), University Medical Center, Heidelberglaan 100, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. Phone: 31-30-2507329; Fax: 31-30-2543492; E-mail: J.A.Joles{at}med.uu.nl

ABSTRACT. Podocyte stress precedes proteinuria in hypercholesterolemic rats. Molsidomine, a nitric oxide (NO) donor, prevented podocyte stress and proteinuria in long-term hypercholesterolemia, suggesting that podocyte stress was due to NO deficiency. Podocytes express the angiotensin II type 1 receptor, which influences their function. Because NO counteracts angiotensin II, it was hypothesized that in a setting of impaired renal NO availability, angiotensin II receptor inhibition could prevent podocyte stress. For determining the effect of NO deficiency on podocyte stress, one group of female rats were fed 2% cholesterol and another group the arginine analogue N--nitro-L-arginine (L-NNA; 40 mg/kg food) for 2 wk. Another group of rats that were fed 2% cholesterol also received the NO donor molsidomine (120 mg/L water) for 2 wk before and during cholesterol feeding. For determining the influence of angiotensin II in the setting of decreased renal NO availability, rats that were treated with cholesterol or L-NNA received the angiotensin II type 1 antagonist losartan (200 mg/L water) for 2 wk before and during cholesterol or L-NNA administration. Desmin staining and electron microscopy were used to monitor podocyte activation. Glomerular caveolin was quantified by immunohistochemistry. Renal cortical NO synthesis, NO synthase isoforms, and caveolin-1 protein mass were also measured. Both short-term cholesterol and L-NNA induced podocyte stress as evidenced by enhanced desmin staining and electron-dense fused foot processes. Podocyte stress was prevented by molsidomine in short-term hypercholesterolemia. Furthermore, losartan prevented podocyte stress in rats that were treated with cholesterol or with L-NNA. Finally, hypercholesterolemia decreased renal cortical NO synthase activity and increased caveolin-1 protein mass and glomerular caveolin staining, and these changes were also prevented by losartan. It is suggested that podocyte stress in these models of early injury results from angiotensin II, unopposed by the action of endogenous NO. This underscores the strategic role of angiotensin II blockers in early kidney disease.

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Copyright © 2008 by the American Society of Nephrology. Online ISSN: 1533-3450 Print ISSN: 1046-6673