Abstract 16261: PPAR-Gamma Agonist-Induced Telomerase Activation in Endothelial Cells and Endothelial Progenitor Cells is Mediated by the Survival Kinase Akt
Introduction: In addition to their action as insulin sensitizers PPAR-γ agonists (thiazolidinediones, TZDs) such as pioglitazone mediate glucose-independent vascular effects. Telomerase and telomere-associated proteins regulate cellular senescence and survival. Endothelial cell and endothelial progenitor cell (EPC) senescence may lead to vascular disease. Pioglitazone prevents stress-induced endothelial apoptosis in mice in-vivo.
Hypothesis: The aim of the study was to determine the effect of pioglitazone on telomerase and Akt in cultured endothelial cells and EPC.
Methods and results: Bovine aortic endothelial cells (BAEC) and human EPC from healthy donors were treated with 10µM/l pioglitazone for 24h. Western blots indicated that Akt phosphorylation was increased in both BAEC (178 ± 27% vs. vehicle-treated cells, p<0.05) and EPC (282 ± 56% vs. control, p<0.01) by TZD treatment. The PPAR-γ agonist induced telomerase activation in BAEC (175 ± 13% vs. control, p<0.001, TRAP assay) and EPC (195 ± 15% vs. control, p<0.01). Furthermore, protein expression of telomere repeat-binding factor (TRF) 2 was increased to 235 ± 41% vs. controls (p<0.01) in BAEC and to 281 ± 41% vs. control in EPC (p<0.01). Pioglitazone down-regulated protein expression of the senescence marker p16 (23 ± 16% vs. control, p<0.05) and the cell cycle inhibitor p53 (31 ± 16% vs. control, p<0.01) in EPC. Pinpointing downstream mechanisms, bcl2/bax ratio was increased in TZD-treated BAEC (284 ± 92%, p<0.001), implicating that pioglitazone may inhibit the endothelial mitochondrial death pathway. TZD effects in BAEC and EPC required Akt, because pioglitazone-induced telomerase activation and TRF2 up-regulation were abolished in both cell types by co-incubation with an upstream Akt inhibitor or a direct Akt inhibitor.
Conclusion: In adult endothelial cells and endothelial progenitor cells, stimulation with the PPAR-γ agonist pioglitazone activates telomerase, elevates TRF2 expression and reduces senescence marker expression. The survival kinase Akt is a major upstream regulator of these effects and the mitochondrial death pathway is part of the signaling cascade. Thus, PPAR-γ agonists may improve endothelial stress resistance and susceptibility to senescence stimuli.
- © 2011 by American Heart Association, Inc.