Remnant-Like Lipoproteins May Accelerate Endothelial Progenitor Cells Senescence Through Inhibiting Telomerase Activity via the Reactive Oxygen Species-Dependent Pathway

Abstract

Background We previously found that remnant-like lipoproteins (RLPs), lipolytic products of triglyceride-rich lipoproteins including very low-density lipoprotein and chylomicron, can accelerate endothelial progenitor cell (EPC) senescence, which involves telomerase activity. The aim of this study was to investigate the effects of RLPs on telomerase activity and the catalytic subunit telomerase reverse transcriptase (TERT) in EPCs and the associated signal pathway. Methods RLPs were prepared from plasma samples by the immunoaffinity method. EPCs at day 8 were incubated with RLPs at 10-, 50-, 100-, and 200-μg/mL for 24 hours. Telomerase activity was measured with telomeric repeat amplification protocol assay, and optimum concentration of RLPs was determined. Human TERT (hTERT) and phosphorylated Akt protein kinase were detected by Western blot analysis in RLP-incubated EPCs with or without pretreatment of either superoxide dismutase or atorvastatin for 3 hours. Phosphorylated hTERT was measured by immunoprecipitation and Western blot assay. Nitrotyrosine was evaluated by immunofluorescence assay, and senescent EPCs were determined by senescence-associated β-galactosidase staining. Results Dose dependently, RLPs resulted in a decrease in telomerase activity, with a maximal effect at 200 μg protein/mL. The optimum concentration of RLPs was determined as 100 μg protein/mL. This dosage resulted in significant increases in senescence-associated β-galactosidase–positive cell and nitrotyrosine staining. In addition, RLPs decreased the expression of hTERT and repressed the phosphorylation of Akt and hTERT. Pretreatment of either superoxide dismutase or atorvastatin remarkably reversed these effects. Conclusions RLPs may suppress telomerase activity and accelerate EPC senescence through downregulating hTERT expression via the reactive oxygen species–dependent pathway.