Logo cin2003

Discussion Board

Paneles de Discussión

Paneais de Discussio

Free Papers

Comunicaciones libres

Comunicaçoes livres

Home cin2003

Volver al Inicio cin2003

Voltar ao inicio cin2003

Recent insights into the renin-angiotensin aldosterone system and progression of renal disease

Prof. Gunter Wolf MD.
Department of Medicine, Division of Nephrology and Osteology, University of Hamburg, Hamburg, Germany


The number of patients with end-stage renal failure is steadily, if not exponentially, increasing1. The majority of patients have a chronic decline of kidney function and dialysis is required months or even years after initial diagnosis2. Such a continuous decline of renal function is called progression of renal disease and is characterized by the common pathomorphological endpoint of tubulointerstitial fibrosis and tubular atrophy, irrespectively of the primary etiology of the renal disease. Clinical and experimental evidence accumulating over the last decade convincingly suggests that the renin-angiotensin aldosterone system (RAAS) is a key player in this complex events of progression of chronic renal failure.

Angiotensin II and renal hemodynamic

The classical function of ANG II is the maintenance of extracellular volume and blood pressure during volume depletion3. Activation of the RAAS causes an ANG II-dependent increase in renal vascular resistance leading consequently to a decrease in renal plasma flow (RPF). However, micropuncture studies have shown that ANG II preferentially raises efferent glomerular resistance4. The consequence is an increase in the glomerular capillary filtration pressure that results in a protected glomerular filtration rate (GFR) despite an ANG II-induced decrease in RPF4. Micropuncture investigations in the rat demonstrated that infusion of exogenous ANG II reduces the capillary ultrafiltration coefficient (Kf;5).

It has been traditionally argued that ANG II-mediated contraction of mesangial cells is responsible for the reduction in Kf by decreasing available glomerular capillary surface area6. This somewhat mechanistic explanation has been more recently questioned because electron microscopy failed to detect changes of ANG II on the area of the capillary surface7, and the geometrical arrangement of the mesangial contractile fibers compresses the capillary interface in case of mesangial cell contraction, but leaves the peripheral filtration area unchanged7.

Alternative explanations how ANG II reduces Kf may be a decline in the hydraulic permeability of the capillary for water or constriction of only defined subset of glomerular capillaries resulting in a reduction in effective filtration surface7. Hostetter and colleagues found an increase in glomerular capillary pressure in many animals models of progressive nephron loss8. This increase was seen as an adaptive response how the kidney tries to maintain GFR after irreversible destruction of renal tissue by increasing the single-nephron GFR of surviving nephrons9.

Although these adaptive mechanisms may maintain indeed renal function in the early phase of chronic renal injury, glomerular hypertension and hyperfunction are ultimately detrimental to renal function and structure9. An increase in capillary pressure may directly stimulate in glomerular cells through mechanical forces injury, proliferation, and production of extracellular matrix10. ANG II is an important mediator of glomerular hemodynamic changes and the increase in tubular transport in chronic renal injury. The RAAS is activated in chronic renal disease. The landmark study by Anderson and co-workers demonstrated that an ACE inhibitor limited glomerular injury in rats with experimentally induced reduction in renal mass11. This protective effects of ACE inhibitor treatment were independent of systemic blood pressure and were then solely attributed to a reduction of the increased glomerular capillary pressure11. Subsequently, it became clear that ANG II exhibit many other non-hemodynamic effects (see following paragraph) that may partly explain the protective effect of ACE inhibitor treatment on renal injury12.

More than 15 years ago, Bertani and Remuzzi proposed that an increased amount of proteins filtered through the glomerular capillary could have intrinsic renal toxicity and contributes to the progression of renal disease13. The pathophysiological mechanisms have been fairly well worked out and include induction of a variety of proinflammatory and vasoactive substances in proximal tubular cells exposed to an increased concentration of proteins14. Tubular cells exposed to protein synthesize more ANG II that may in turn influence tubular transport or exhibit profibrogenic effects. However, in regards of hemodynamic mechanisms of ANG II, the peptide plays an important role in increasing proteinuria because high intraglomerular capillary pressure impairs the barrier´s size-selective function15. In addition, ANG II directly modulates glomerular permeability and increases proteinuria by a variety of mechanisms including loss and suppressed synthesis of negative charged proteoglycans, increase in glomerular basement membrane-associated extracellular matrix components, and decrease of nephrin, an important component of the podocyte slit diaphragm16.

Trophic and inflammatory effects of ANG II in the kidney

One of the first hints that ANG II may be involved in renal growth and tissue remodeling stems from studies investigating the effects of ACE inhibitors17. Direct infusion of ANG II into naive rats leads to a tubulointerstitial injury with proliferation of distal tubules, collecting ducts, and interstitial cells, but not of proximal tubules18. We showed in the early 90s that ANG II causes a small but significant proliferation of murine mesangial cells in the absence of other factors19.ANG II also stimulates proliferation of rat glomerular endothelial cells20. This mitogenesis is transduced by AT1 receptors. However, ANG II stimulates cellular hypertrophy of a murine proximal tubular cell line (MCT cells;21) and in porcine LLC-PK1 cells22. ANG II-induced hypertrophy is mediated through AT1 receptors and requires G1-phase arrest. ANG II treatment in vitro and in vivo enhances p27Kip1 protein but not mRNA expression23, 24. p27Kip1 is an inhibitor of cyclin-dependent kinases and overexpression of this protein clamps cells in the G1-phase of the cell cycle.

Oxygen radicals and activation of mitogen-activated kinases (Erk 1, 2) play an important role in the ANG II-mediated induction of p27Kip125, 26. ANG II upregulates the membrane-bound NAD(P)H oxidase resulting in an increased formation of oxygen radicals. ANG II induces also in vitro apoptosis27. It has been suggested that activation of AT2 receptors is responsible for this effect, but this issue is controversial because AT1 receptor antagonists also attenuated apoptosis in certain models28, 29. The decision whether cells undergo hypertrophy or rather apoptosis may depend on the presence of additional growth factors and cytokines30.

Indirect evidence that ANG II may be involved in tubulointerstitial fibrosis comes from comprehensive studies in rats with unilateral ureteral ligation31. Tubular TGF-β expression precedes the development of tubulointerstitial scarring and is partly reduced when animals were treated with enalapril32, 33. Administration of an ACE-inhibitor or an AT1 receptor blocker blunts the increase in TGF-β mRNA and decreases the structural manifestations of injury, indicating an in vivo relationship between ANG II, TGF-β and renal fibrosis34. TGF-β expression is also elevated in the contralateral kidney of rats with 2 kidney-1 clip hypertension35, 36. Probably the most direct evidence that the RAAS is involved in renal scarring stems from targeted overexpression of renin and angiotensinogen in rat glomeruli37. Seven days after transfection, extracellular matrix was expanded in rats with glomerular renin and angiotensinogen overexpression without systemic hypertension37.

Some of the therapeutic effects of ACE-inhibitor treatment in the prevention of renal fibrosis may be due to the inhibition of the endothelin system 38. ANG II induces mRNA encoding the extracellular matrix proteins type I procollagen and fibronectin in cultured mesangial cells39. ANG II also stimulates the transcription and synthesis of collagen type α1(IV), but not type I, in cultured proximal tubular cells. We have recently demonstrated that the vasopeptide additionally induces mRNA and protein expression of α3(IV) collagen which is more restricted to the kidney than the common α1 and α2 chains 40. ANG II stimulates in cultured proximal tubular and mesangial cells the induction of TGF-β, an important profibrogenic mediator41, 42. The stimulatory effects of ANG II on collagen expression in cultured proximal tubular cells depends on TGF-β expression. Interesting recent studies suggest that ANG II stimulates proliferation of cultured renal fibroblasts43. Stimulation of fibroblasts with ANG II also increases mRNA expression of TGF-β, fibronectin and type I collagen (43). Moreover, recent findings indicate that ANG II also modulates the plasmin protease system and inhibits the degradation and turnover of extracellular matrix44.

ANG II stimulates mRNA and protein expression of the chemokine RANTES, a member of the C-C chemokine subfamily with chemoattractant properties for monocytes/macrophages (M/M), in cultured glomerular endothelial cells45. The ANG II-stimulated RANTES expression is transduced by AT2 receptors45. ANG II-infused rats exhibitean increase in glomerular M/M compared with controls. Treatment with an AT2 receptor antagonist attenuates the glomerular M/M influx without normalizing the slightly elevated systolic blood pressure caused by ANG II infusion, suggesting that the effects on blood pressure and RANTES induction can be separated45. These data were recently confirmed by Ruiz-Ortega and associates who demonstrated that ANG II infusion for 72 hours increased glomerular and interstitial inflammatory cells46. In agreement with our findings, an AT2 receptor antagonist but not losartan significantly reduced this inflammation46.

The group of Jesus Egido were among the first demonstrating that ANG II activates nuclear factor κB (NF-κB;47). NF-κB is a key proinflammatory factor involved in the transcriptional regulation of many genes including MCP-1 and RANTES. Using specific ANG II-receptor antagonists, they showed that ANG II activates NF-κB in vascular smooth muscle cells (VSMC) through AT1 and AT2 receptors 47. NF-κB is strongly activated in double-transgenic rats harboring both human renin and angiotensinogen genes 48. We used an alternative approach to study a potential role of AT2 receptors in NF-κB activation and selectively overexpressed AT1 and AT2 receptors in COS7 cells that do not normally bear ANG II-receptors 49. COS7 cells transfected with an AT2 receptor expression construct demonstrated NF-κB activation after treatment with ANG II49.

Aldosterone as a direct mediator of renal injury

In the traditional concept of the RAAS and renal injury, aldosterone mediates volume-dependent hypertension and contributes through this mechanism indirectly to chronic renal injury50. However, aldosterone exerts, similar as ANG II, directs effects on renal cells that may contribute to progression of renal disease50. Greene and co-workers defined the role of aldosterone in the remnant kidney model51. Combined treatment with ACE-inhibitor and AT1 antagonist totally attenuated renal pathology51. However, infusion of exogenous aldosterone reestablished kidney injury despite ACE-inhibitor and AT1 antagonist treatment51. This strongly indicates that secondary hyperaldosteronism contributes to proteinuria and glomerulosclerosis in this model. Aldosterone also inhibits matrix turover. Interestingly, glomerular osteopontin expression is also upregulated in the deoxycorticosterone acetate (DOCA)-salt model52. Its is currently unclear, however, whether this induction of a chemoattractant is directly mediated by aldosterone or may be rather an effect of systemic hypertension. Observation from animals with cardiac fibrosis clearly revealed that aldosterone increased collagen expression in the heart53, 54. Aldosterone also stimulates collagen type I and III expression in cultured cardiac fibroblasts55, 56. A recent study suggest an important role of aldosterone in the pathogenesis of thrombotic microangiopathy in stroke-prone spontaneously hypertensive rats57.


There is now ample evidence that the RAAS plays a central role in the progression of chronic renal disease. Although hemodynamic effects of ANG II certainly contribute to renal damage, research from the last decade clearly suggest that this vasopeptide is a multifarious cytokine engaged in may non-hemodynamic processes such as growth stimulation, apoptosis, induction of profibrogenic actions, and inflammation. In addition, animal experiments suggest that aldosterone could mediate direct renal injury independent of ANG II. Therefore, it is strongly recommended that ACE-inhibitors therapy should be used in every normotensive and hypertensive patient with clinically evident nephropathy and proteinuria who is at risk for progression.


  1. Manns BJ, Taub K, Donaldson C: Economic evaluation and end-stage renal disease: from basics to bedside. Am J Kidney Dis 2000;36:12-28.
  2. Klahr S, Scheiner G, Ichikawa I: The progression of renal disease. N Engl J Med 1988;318:1657-1666.
  3. Toke A, Meyer TW: Hemodynamic effects of angiotensin II in the kidney. Contrib Nephrol 2001;135:34-46.
  4. Arima S, Kohagura K, Abe M, Ito S: Mechanisms that control glomerular hemodynamics. Clin Exp Nephrol 2001;5:55-61.
  5. Blantz RC, Konnen KS, Tucker BJ: Angiotensin II effects upon the glomerular microcirculation and ultrafiltration coefficient of the rat. J Clin Invest 1976;57:419-434.
  6. Pagtalunan ME, Rasch R, Rennke HG, Meyer TW: Morphometric analysis of effects of angiotensin II on glomerular structure in rats. Am J Physiol 1995;268:F82-F88.
  7. Kriz W, Elger M, Mundel P, Lemley KV: Structure-stabilizing forces in the glomerular tuft. J Am Soc Nphrol 1995;5:1731-1739.
  8. Hostetter TH, Olson JL, Rennke HG, Venkatachalam MA, Brenner BM: Hyperfiltration in remnant nephrons: a potentially adverse response to renal ablation. Am J Physiol 1981;241:F85-F93.
  9. Brenner BM: Nephron adaptation to renal injury or ablation. Am J Physiol 1985;249:F324-F337.
  10. Matsuka T, Hymes J, Ichikawa I: Angiotensin in progressive renal disease: theory and practice. J Am Soc Nephrol 1996;7:2025-2043.
  11. Anderson S, Rennke HG, Brenner BW: Therapeutic advantage of converting enzyme inhibitors in arresting progressive renal disease associated with systemic hypertension in the rat. J Clin Invest 1986;77:1993-2000.
  12. Franco M, Paniagua R, Herrera-Acosta J: Renal effects of renin-angiotensin system blockade. Curr Opin Nephrol Hypertens 1998;7:153-158.
  13. Bertanin T, Cutillo F, Zoja C, Broggini M, Remuzzi G: Tubulointerstitial lesions mediate renal damage in adriamycin glomerulopathy. Kidney Int 1986;30:488-496.
  14. Remuzzi G, Bertanin T: Pathophysiology of progressive nephropathies. N Engl J Med 1998;339:1448-1456.
  15. Yoshioka T, Rennke HG, Salant DJ, Deen WM, Ichikawa I: Role of abnormally high transmural pressure in the permselectivity defect of glomerular capillary wall: a study in early passive Heymann nephritis. Circ Res 1987;61:531-538.
  16. Benigni A, Tomasoni S, Gagliardini E, Zoja C, Grunkemeyer JA, Kalluri R, Remuzzi G: Blocking angiotensin II synthesis/activity preserves glomerular nephrin in rats with severe nephrosis. J Am Soc Nephrol 2001;12:941-948.
  17. Kaneto H, Morrissey JJ, McCreaken R, Reyers A, Klahr S: Enalapril reduces collagen type IV synthesis and expansion of the interstitium in the obstructed rat kidney. Kidney Int 1994; 45:1637-1647.
  18. Johnson RJ, Alpers CE, Yoshimura A, Lombardi D, Pritzl P, Floege J, Schwartz SM: Renal injury from angiotensin II-mediated hypertension. Hypertension 1992;19:464-474.
  19. Wolf G, Haberstroh U, Neilson EG: Angiotensin II stimulates the proliferation and biosynthesis of type I collagen in cultured murine mesangial cells. Am J Pathol 1992;140:95-107.
  20. Wolf G, Ziyadeh FN, Zahner G, Stahl RAK: Angiotensin II is mitogenic for cultured rat glomerular endothelial cells. Hypertension 1996;27:897-905.
  21. Wolf G, Neilson EG: Angiotensin II induces cellular hypertrophy in cultured murine proximal tubular cells. Am J Physiol 1990;259:F768-F777.
  22. Wolf G, Zahner G, Mondorf U, Schoeppe W, Stahl RAK: Angiotensin II stimulates cellular hypertrophy of LLC-PK1 cells through the AT1 receptor. Nephrol Dial Transplant 1993;8:128-133.
  23. Wolf G, Stahl RAK: Angiotensin II-stimulated hypertrophy of LLC-PK1 cells depends on the induction of the cyclin-dependent kinase inhibitor p27Kip1. Kidney Int 1996;50:2112-2119.
  24. Wolf G, Wenzel U, Hannken T, Stahl RAK: Angiotensin II induces p27Kip1 expression in renal tubules in vivo: role of reactive oxygen species. J Mol Med 2001;79:382-389.
  25. Hannken T, Schroeder R, Stahl RAK, Wolf G: Angiotensin II-mediated expression of p27Kip1 and induction of cellular hypertrophy in renal tubular cells depends on the generation of oxygen radicals. Kidney int 1998;54:1923-1933.
  26. Hannken T, Schroeder R, Zahner G, Stahl RAK, Wolf G: Reactive oxygen species stimulate p44/42 mitogen-activated protein kinase and induce p27Kip1: role in angiotensin II-mediated hypertrophy of proximal tubular cells. J Am Soc Nephrol 2000;11:1387-1397.
  27. Yamada T, Horiuchi M, Dzau VJ: Angiotensin II type 2 receptor mediates programmed cell death. Proc Natl Acad Sci USA 1996;93:156-160.
  28. Dimmeler S, Rippmann V, Weialnd U, Haendeler J, Zeiher AM: Angiotensin II induces apoptosis of human endothelial cells. Protective effects of nitric oxide. Circ Res 1997,81:970-976.
  29. Maric C, Alfred GP, Harris PJ, Alcorn D: Angiotensin II inhibits growth of cultured embryonic renomedullary interstitial cells through the AT2 receptor. Kidney Int 1998;53:92-99.
  30. Shankland SJ, Wolf G: Cell cycle regulatory proteins in renal disease: role in hypertrophy, proliferation, and apoptosis. Am J Physiol 2000;278:F515-F529.
  31. Ishidoya S, Morrissey J, McCracken R, Klahr S: Delayed treatment with enalapril halts tubulointerstitial fibrosis in rats with obstructive nephropathy. Kidney Int 1996;49:1110-1119.
  32. Wolf G: Link between angiotensin II and TGF-β in the kidney. Miner Electrolyte Metab 1998;24:174-180.
  33. Gaedeke J, Peters H, Noble NA, Border WA: Angiotensin II, TGF-β and renal fibrosis. Contrib Nephrol 2001;135:153-160.
  34. Wu LL, Cox A, Roe CJ, Dziadek M, Cooper ME, Gilbert RE: Transforming growth factor β1 and renal injury following subtotal nephrectomy in the rat: role of the renin-angiotensin system. Kidney Int 1997;51:1553-1567.
  35. Wolf G, Schneider A, Wenzel U, Helmchen U, Stahl RAK: Regulation of glomerular TGF-beta expression in the contralateral kidney of two-kidney, one-clip hypertensive rats. J Am Soc Nephrol 1998; 9:763-772.
  36. Wenzel UO, Wolf G, Thaiss F, Helmchen U, Stahl RAK: Renovascular hypertension does not influence repair of glomerular lesions induced by anti-thymocyte glomerulonephritis. Kidney Int 2000; 58:1135-1147.
  37. Arai M, Isaka Y, Akagi Y, Sugiura T, Miyazaki M, Moriyama T, Kaneda Y, Naruse K, Naruse M, Orita Y, Ando A, Kamada T, Ueda N, Imai E: In vivo transfection of genes for renin and angiotensinogen into the glomerular cells induced phentypic changes of the mesangial cells and glomerular sclerosis. Biochem Biophys Res Commun 1995; 206:525-532.
  38. Amann K, Simonaviciene A, Medwedewa T, Koch A, Orth S, Gross ML, Haas C, Kuhlmann A, Linz W, Schölkens B, Ritz E: Blood pressure-independent additive effects of pharmacologic blockade of the renin-angiotensin and endothelin systems on progression in a low-renin model of renal damage. J Am Soc Nephrol 2001;12:2572-2584.
  39. Wolf G, Killen PD, Neilson EG: Intracellular signaling of transcription and secretion of type IV collagen after angiotensin II-induced cellular hypertrophy in cultured proximal tubular cells. Cell Reg 1991;2:219-227.
  40. Wolf G, Kalluri R, Ziyadeh FN, Neilson E, Stahl RAK: Angiotensin II induces alpha3 (IV) collagen expression in cultured murine proximal tubular cells. Proc Assoc Am Physicians 1999;11:357-364.
  41. Wolf G, Mueller E, Stahl RAK, Ziyadeh FN: Angiotensin II-induced hypertrophy of cultured murine proximal tubular cells is mediated by endogenous transforming growth factor-β. J Clin Invest 1993; 92:1366-1372.
  42. Kagami S, Border WA, Miller DE, Noble NA: Angiotensin II stimulates extracellular matrix protein synthesis through induction of transforming growth fcator.beta expression in rat glomerular mesangial cells. J Clin Invest 1994;93:2431-2437.
  43. Ruiz-Ortega M, Egido J: Angiotensin II modulates cell growth-related events and synthesis of matrix proteins in renal interstitial fibroblasts. Kidney int 52:1497-1510, 1997.
  44. Fogo AB: The role of angiotensin II and plasminogen activator-inhibitor-1 in progressive glomerulosclerosis. Am J Kidney Dis 2000;35:179-188.
  45. Wolf G, Ziyadeh FN, Thaiss F, Tomaszewski J, Caron RJ, Wenzel U, Zahner G, Helmchen U, Stahl RAK: Angiotensin II stimulates expression of the chemokine RANTES in rat glomerular endothelial cells. Role of the angiotensin type 2 receptor. J Clin Invest 1997;100:1047-1058.
  46. Ruiz-Ortega M, Lorenzo O, Rupérez M, Blanco J, Egido J: Systemic infusion of angiotensin II into normal rats activates nuclear factor-κB and AP-1 in the kidney. Role of AT1 and AT2 receptors. Am J Pathol 2001, 158:1743-1756
  47. Ruiz-Ortega M, Lorenzo O, Rupérez M, König S, Wittig B, Egido J: Angiotensin II activates nuclear transcription factor κB through AT1 and AT2 in vascular smooth muscle cells. Molecular mechanisms. Cir Res 2000; 86: 1266-1272.
  48. Muller DN, Dechend R, Mervaala EMA, Park JK, Schmidt F, Fiebeler A, Theuer J, Breu V, Ganten D, Haller H, Luft FC: NF-κB inhibition ameliorates angiotensin II-induced inflammatory damage in rats. Hypertension 2000;35:193-201.
  49. Wolf G, Wenzel U, Burns KD, Harris RC, Stahl RAK, Thaiss T: Angiotensin II activates nuclear transcription factor κB through AT1 and AT2 receptors. Kidney Int (2002); 61: 1986-1995.
  50. Epstein M: Aldosterone as a mediator of progressive renal disease: pathogenetic and clinical implications. Am J Kidney Dis 2001; 37:677-688.
  51. Greene EL, Kren S, Hostetter TH: Role of aldosterone in the remnant kidney model in the rat. J Clin Invest 1996;98:1063-1068.
  52. Hartner A, Porst M, Gauer S, Pröls F, Veelken R, Hilgers KF: Glomerular osteopontin expression and macrophage infiltration in glomerulosclerosis of DOCA-salt rats. Am J Kidney Dis 2001;38:153-164.
  53. Weber KT: Aldosterone in congestive heart failure. N Engl J Med 2001;345:1689-1697.
  54. Brilla CG: Aldosterone and myocardial fibrosis in heart failure. Herz 2000;25:299-306.
  55. Young M, Fullerton M, Dilley R, Funder J: Mineralcorticoids, hypertension, and cardiac fibrosis. J Clin Invest 1994;93:2578-2583.
  56. Robert V, Silvestre JS, Charlemagne D, Sabri AA, Trouvé P, Wassef M, Swynghedauw B, Delcayre C: Biological determinants of aldosterone-induced cardiac fibrosis in rats. Hypertension 1995;26:971-978.
  57. Chnader PN, Rocha R, Ranaudo J, Singh G, Zuckerman A, Stier CT: Aldosterone plays a pivotal role in the pathogenesis of thrombotic microangiopathy in SHRSP. J Am Soc Nephrol 2003; 14:1990-1997.