Fig. 4. TERT overexpression protects mitochondrial DNA integrity and mitochondrial function under oxidative stress. Frequency of lesions in mtDNA as measured by the relative amplification efficiency of an 11 kb mtDNA fragment in MRC5 (black circles) and MRC5-TERT (white circles) following treatment with hydrogen peroxide in the indicated concentrations (A) and under long-term hyperoxia (B). Data are mean±s.e.m. from quadruplicate measurements. (C) Mitochondrial superoxide generation as measured by MitoSOX fluorescence intensity per cell. (D) Cellular peroxide levels as measured by DHR123 fluorescence. (E) MMP as measured by JC1 fluorescence ratio. (F) UCP2 expression as measured by duplex RT-PCR with Gapdh as control. All data in C to F were measured in MRC5 (black bars) and MRC5-TERT (white bars) under normoxia (left) and after 1 week of hyperoxia (right), and are mean±s.e.m. from three experiments. Differences between parental and TERT-overexpressing cells marked by an asterisk are significant with P<0.05 (ANOVA). (G) Expression of endogeneous TERT was measured by semi-quantitative TERT RT-PCR 2 days after transfection with the indicated siRNAs. GAPDH was measured as control. (H) MitoSOX and DHR fluorescence intensity in HUVECs at 2 days after transfection with the indicated siRNAs. Data are mean±s.e.m. from quadruplicate measurements. Asterisks indicate significant differences to cells treated with control siRNA with P<0.05 (ANOVA).