(a) Fluorescence microscopy of DHE→Eth conversion and annexin V (green)/PI (red) co-staining of wild-type cells at day 18 of the chronological ageing experiment shown in Fig. 1b. Scale bars, 10 μm. (b, c) Quantification of DHE→Eth conversion (b) and annexin V/PI co-staining (c) using FACS analysis performed at indicated time-points of the chronological ageing experiment shown in Fig. 1b. Data represent means ± s.e.m. (n = 3; *P 0.001). 