Pioglitazone activates aortic telomerase and prevents stress-induced endothelial apoptosis

Telomeres and associated proteins are regulators of cellular survival, regeneration and aging. PPAR-γ agonists may mediate vascular effects in addition to insulin sensitizing. We therefore examined whether pioglitazone regulates vascular telomere biology.

C57/Bl6 mice were randomized to treatment with pioglitazone (20mg/kg i.p. daily) or vehicle for 4 weeks (n = 6-8 per group). Telomere repeat amplification protocols showed a 2-fold increase of aortic telomerase activity in the pioglitazone group. Telomere repeat-binding factor 2 protein and mRNA levels (236%+172% of vehicle) as well as phosphorylation of protein kinase Akt (479% of vehicle) were up-regulated. Western blots demonstrated reduced aortic expression of senescence markers p16, cell-cycle checkpoint kinase 2 and p53. These regulatory mechanisms were independent of acute changes of telomere length. Similar observations were made in mononuclear cells (MNC) from these mice and in cultivated bovine aortic endothelial cells, human MNC and endothelial progenitor cells (EPC). Telomerase activation by pioglitazone in cultivated cells was prevented by Akt inhibitors. To test the functional relevance of the findings, isolated mononuclear cells (MNC) were exposed to H(2)O(2). MNC from pioglitazone-treated mice exhibited reduced apoptosis (AnnexinV-FACS). In vivo, lipopolysaccharide-induced aortic endothelial apoptosis was potently prevented in pioglitazone-treated animals (hairpin oligonucleotide assay). Both, up-regulation of telomere-regulating proteins and prevention of oxidative stress-induced aortic apoptosis, were absent in telomerase reverse transcriptase (TERT)-deficient mice.

Pioglitazone treatment up-regulates telomerase activity, telomere-stabilizing proteins and reduces senescence markers in vascular cells. These effects and the reduction of LPS-induced endothelial apoptosis by thiazolidinediones depend on TERT. The findings underscore the important role of telomere-regulating proteins for vascular cell function and survival.