title: Angiotensin II accelerates endothelial progenitor cell senescence through induction of oxidative stress.
abstract: OBJECTIVE
  Recent studies have revealed an association between coronary risk factors and both the number and function of bone marrow-derived endothelial progenitor cell (EPC). We investigated the effect of angiotensin II (Ang II) on EPC senescence, leading to the impairment of proliferative activity.
  
  
  RESULTS
  EPCs were isolated from peripheral blood and characterized. Both reverse transcription (RT)-polymerase chain reaction (PCR) and Western blotting were used to assess gp91phox expression. Immunofluorescence of nitrotyrosine provided evidence of peroxynitrite formation. Our data indicate that Ang II increased the expression of gp91phox mRNA in a dose-dependent manner, which was attenuated by Ang II type 1 (AT1) receptor antagonist valsartan. Similarly, Western blotting revealed that Ang II stimulated an increase in gp91phox, whereas pre-treatment with Valsartan reduced the Ang II-induced expression of gp91phox protein. Valsartan as well as superoxide dismutase (SOD) also inhibited Ang II-induced peroxynitrite formation. The exposure of cultured EPC to Ang II (100 nmol/l) significantly accelerated the rate of senescence compared to a control during 14 days in culture as determined by acidic beta-galactosidase staining. Ang II-induced EPC senescence was significantly inhibited by pre-treatment of either valsartan or SOD (P < 0.01). Because cellular senescence is critically influenced by telomerase, which elongates telomeres, we measured telomerase activity by using PCR-enzyme-linked immunosorbent-based assay. Ang II significantly diminished telomerase activity, although the effect was significantly reduced by pre-treatment with either valsartan or SOD (P < 0.01). We examined whether Ang II-induced EPC senescence translates into an impairment of EPC proliferation. MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetrazolium] assay disclosed an inhibitory effect of Ang II on EPC proliferation.
  
  
  CONCLUSIONS
  Ang II increases gp91phox expression in EPC, which may contribute to oxidative stress, as evidenced by peroxynitrite formation. Ang II accelerates the onset of EPC senescence via increased oxidative stress, which may be related to telomerase inactivation. In addition, Ang II-induced EPC senescence leads to the impairment of proliferative activity.
authors.affiliation: Department of Cardiovascular Medicine, Wakayama Medical University, Wakayama, Japan. t-imani@wakayama-med.ac.jp
authors.forename: Toshio
authors.initials: T
authors.lastname: Imanishi
authors.forename: Takuzo
authors.initials: T
authors.lastname: Hano
authors.forename: Ichiro
authors.initials: I
authors.lastname: Nishio
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects*; D042783:Endothelial Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000378:metabolism; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D030421:Peroxynitrous Acid / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D019098:Telomerase / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D008562:Membrane Glycoproteins; D044140:Receptor, Angiotensin, Type 1; D042461:Vascular Endothelial Growth Factor A; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D030421:Peroxynitrous Acid; C056558:CYBB protein, human; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D019098:Telomerase