title: Persistent proteinuria up-regulates angiotensin II type 2 receptor and induces apoptosis in proximal tubular cells.
abstract: 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.
authors.affiliation: Renal and Vascular Laboratory, Fundación Jiménez Díaz-Universidad Autónoma, Madrid, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: Tejera
authors.forename: Dulcenombre
authors.initials: D
authors.lastname: Gómez-Garre
authors.forename: Alberto
authors.initials: A
authors.lastname: Lázaro
authors.forename: Julio
authors.initials: J
authors.lastname: Gallego-Delgado
authors.forename: Covadonga
authors.initials: C
authors.lastname: Alonso
authors.forename: Julia
authors.initials: J
authors.lastname: Blanco
authors.forename: Alberto
authors.initials: A
authors.lastname: Ortiz
authors.forename: Jesús
authors.initials: J
authors.lastname: Egido
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000096:biosynthesis / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007668:Kidney / Q000473:pathology; D007678:Kidney Glomerulus / Q000378:metabolism; D007684:Kidney Tubules / Q000378:metabolism / Q000473:pathology*; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011507:Proteinuria / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar; D044139:Receptor, Angiotensin, Type 2 / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000378:metabolism; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D044139:Receptor, Angiotensin, Type 2; D012965:Sodium Chloride; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases