Persistent proteinuria up-regulates angiotensin II type 2 receptor and induces apoptosis in proximal tubular cells

Am J Pathol. 2004 May;164(5):1817-26. doi: 10.1016/S0002-9440(10)63740-6.


Apoptosis is implicated in the progressive cell loss and fibrosis both at glomerular and tubulointerstitial level. In this study, we examined the potential mechanisms by which persistent proteinuria (protein-overload model) could induce apoptosis. After uninephrectomy (UNX), Wistar rats received daily injections of 0.5 g of bovine serum albumin (BSA)/100 g body weight or saline. Both at day 8 and day 28, rats receiving BSA had proteinuria and renal lesions characterized by tubular atrophy and/or dilation and mononuclear cell infiltration. In relation to control-UNX rats, renal cortex of nephritic rats showed an increment in AT2 mRNA (reverse transcriptase-polymerase chain reaction) and protein (Western blot) expression. In both groups, AT2 receptor immunostaining was mainly localized in proximal tubular cells. Rats with persistent proteinuria showed a significantly increased number of terminal dUTP nick-end labeling positive apoptotic cells compared with UNX-controls, both in glomeruli and tubulointerstitium. Double staining for apoptosis and AT2 receptor showed that most terminal dUTP nick-end labeling positive cells were found in tubules expressing AT2 receptor. Using an antibody that recognizes the active form caspase-3, we observed an increment in caspase-3 activation in rats receiving BSA with respect to those receiving saline. Rats with persistent proteinuria showed a diminution in the phosphorylation of Bcl-2 with respect to UNX-controls both at day 8 and day 28. By contrast, no changes were observed either in the Bax or in the Bcl-2 protein levels. The administration of BSA to UNX rats induced a diminution in the phosphorylation of ERK with respect to UNX-control at all times studied. The changes observed in ERK activities took place without alterations of ERK1/2 protein levels. In summary, our data suggest that persistent proteinuria causes apoptosis in tubular cells through the activation of AT2 receptor, which can, in turn, inhibit MAP kinase (ERK1/2) activation and Bcl-2 phosphorylation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Blotting, Western
  • Caspase 3
  • Caspases / biosynthesis
  • Caspases / metabolism
  • Enzyme Activation
  • Female
  • Immunohistochemistry
  • In Situ Nick-End Labeling
  • Kidney / pathology
  • Kidney Glomerulus / metabolism
  • Kidney Tubules / metabolism
  • Kidney Tubules / pathology*
  • MAP Kinase Signaling System
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases / metabolism
  • Phosphorylation
  • Precipitin Tests
  • Proteinuria / pathology*
  • Rats
  • Rats, Wistar
  • Receptor, Angiotensin, Type 2 / biosynthesis*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sodium Chloride / metabolism
  • Time Factors
  • Up-Regulation*


  • Receptor, Angiotensin, Type 2
  • Sodium Chloride
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases
  • Casp3 protein, rat
  • Caspase 3
  • Caspases