Figure 6 A, B. ATMWT U2OS cells were treated with 10 μM CCCP for 8 h. After treatment, cells were incubated with 5 μM 2',7'-H2DCF-DA (A) or MitoSox (B) to evaluate the production of H2O2 or mitochondrial superoxide, respectively. Values are shown as units of DCF or MitoSox fluorescence relative to untreated cells (arbitrarily set as 1) and represent the means ± SD of n = 3 independent experiments. ***p< 0.001.  C. In the same experimental settings, basal and phospho-active forms of ATM, and GSNOR were assessed by Western blot. Vinculin and GAPDH were used as loading controls.  U2OS cells were depleted of endogenous ATM by repeated transfections with shRNA and induced, by doxycycline incubation, to express ATMWT, ATM2RA, or ATMCL mutant. Where indicated, cells were further transfected with a GSNOR-coding vector and then treated for 2 h with 10 μM CCCP. Mitophagy was evaluated by: (D) RT-qPCR relative quantitation of D-loop normalized to genomic actin (gActin). Results shown are the means ± SD of n = 4 experiments. *p<0.05; **p<0.01; ***p<0.001.  U2OS cells were depleted of endogenous ATM by repeated transfections with shRNA and induced, by doxycycline incubation, to express ATMWT, ATM2RA, or ATMCL mutant. Where indicated, cells were further transfected with a GSNOR-coding vector and then treated for 2 h with 10 μM CCCP. (E fluorescence microscopy analyses upon incubation with chloroquine (CLQ) to enhance differences in mitophagy. Anti-TOM20 (red) was used to visualize mitochondria; anti-LC3 (green) was used to identify autophagosomes.  U2OS cells were depleted of endogenous ATM by repeated transfections with shRNA and induced, by doxycycline incubation, to express ATMWT, ATM2RA, or ATMCL mutant. Where indicated, cells were further transfected with a GSNOR-coding vector and then treated for 2 h with 10 μM CCCP. F) fluorescence microscopy analyses upon incubation with chloroquine (CLQ) to enhance differences in mitophagy. Percentage of mitochondria merging with LC3-positive puncta calculated by Fiji analysis software using the open-source plugin ComDet v. 0.3.7. Values are expressed as % of mitochondria (TOM20+ particles) co-localizing with LC3/cell and graphed as boxes (25th-75th interquartile range) and whiskers (minimum to maximum showing all points), with central bands representing the median of n ≥ 9 different cells. **p<0.01; ***p<0.001; n.s., not significant.  U2OS cells were depleted of endogenous ATM by repeated transfections with shRNA and induced, by doxycycline incubation, to express ATMWT, ATM2RA, or ATMCL mutant. Where indicated, cells were further transfected with a GSNOR-coding vector and then treated for 2 h with 10 μM CCCP. (G Western blot of different subunits of mitochondrial proteins, i.e., NDUFB8 (complex I), SDHA and SDHB (complex II), MTCO2 (complex IV) and voltage-dependent anion channel (VDAC). Tubulin, LDH and Vinculin were used as loading controls.  U2OS cells were depleted of endogenous ATM by repeated transfections with shRNA and induced, by doxycycline incubation, to express ATMWT, ATM2RA, or ATMCL mutant. Where indicated, cells were further transfected with a GSNOR-coding vector and then treated for 2 h with 10 μM CCCP. H) Densitometry of mitochondrial protein immunoreactive bands and expressed as arbitrary units. Values shown represent the means ± SD of n = 3 independent experiments. *, p<0.05; **, p<0.01; ***, p<0.001; n.s., not significant.