It has been theorized for decades that mitochondria act as the biological clock of ageing1, but the evidence is incomplete. Here we show a strong coupling between mitochondrial function and ageing by in vivo visualization of the mitochondrial flash (mitoflash), a frequency-coded optical readout reflecting free-radical production and energy metabolism at the single-mitochondrion level2, 3. Mitoflash activity in Caenorhabditis elegans pharyngeal muscles peaked on adult day 3 during active reproduction and on day 9 when animals started to die off. A plethora of genetic mutations and environmental factors inversely modified the lifespan and the day-3 mitoflash frequency. Even within an isogenic population, the day-3 mitoflash frequency was negatively correlated with the lifespan of individual animals. Furthermore, enhanced activity of the glyoxylate cycle contributed to the decreased day-3 mitoflash frequency and the longevity of daf-2 mutant animals. These results demonstrate that the day-3 mitoflash frequency is a powerful predictor of C. elegans lifespan across genetic, environmental and stochastic factors. They also support the notion that the rate of ageing, although adjustable in later life, has been set to a considerable degree before reproduction ceases.
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Extended data figures and tables
Extended Data Figures
- Extended Data Figure 1: Targeted expression of cpYFP in the mitochondrial matrix of C. elegans. (221 KB)
a, SDHB-1 is the iron–sulphur subunit of complex II. The promoter and mitochondrial localization sequence of SDHB-1 was used for targeted expression of cpYFP in the mitochondrial matrix. SDHA, B, C and D, succinate dehydrogenase subunit A, B, C and D; Q, coenzyme Q. b, Low-magnification images of a C. elegans worm with an integrated Psdhb-1::mtLS::cpYFP transgene at a long (left) or short (right) exposure time. The pharynx has the highest expression level of mt-cpYFP. c, High-magnification images showing that mt-cpYFP co-localized with mito-tracker red in the pharynx, body-wall muscles, intestine and germ cells. The mitoflash activity in the pharynx (about one to four mitoflash events per anterior pharynx per 200 s; see Fig. 1e and the WT traces in Fig. 2) is at least tenfold that in the body-wall muscles (the average mitoflash events per cell per 200 s on adult days 1, 3, 5 and 9 were 0.1, 0.1, 0.1 and 0.2, respectively; n = 16, 16, 12 and 12) or the intestine (less than 0.1 mitoflash event per cell per 200 s on adult day 3; n = 40).
- Extended Data Figure 2: Characteristics of the C. elegans mitoflash. (70 KB)
a, Averaged time courses of mitoflash events in adult worms under the basal condition (black, n = 19), after 6 h of starvation (orange, n = 15) or in the presence of 20 mg l−1 glucose (maroon, n = 25). b, Averaged time courses of mitoflash events in untreated adult worms (black, n = 19), or those treated with 100 mM H2O2 (blue, n = 21) or paraquat (magenta, n = 16), or subjected to mitochondrial ROS generated by the photoactivation of KillerRed (brown, n = 15). An average mitoflash event starts with a 19 ± 2% increase in the cpYFP fluorescence intensity (ΔFmax/F0) in 1.8 ± 0.2 s, followed by a fluorescence decay with a half-time of 5.4 ± 0.3 s, and ends with a fluorescence intensity slightly below the baseline level.
- Extended Data Figure 3: The first mitoflash peak on adult days 2–3 can be suppressed by eliminating the germline. (197 KB)
a, Germline elimination by treating WT C. elegans with 5-fluoro-2′-deoxyuridine (FUDR) or by using the gon-2(q362ts) allele at the restrictive temperature. Differential interference contrast images of day-3 adults are shown. b, Mitoflash frequencies (means ± s.e.m.) of WT, FUDR-treated WT, and gon-2(q362ts) mutant worms on adult days 1–5 (n = 15 worms). All animals were cultured at 27 °C until the late larval stage 2 or early larval stage 3 before being moved to 25 °C, at which point half of the WT animals were cultured on plates containing 100 μg ml−1 FUDR. The worms were checked for the presence or absence of a germline before imaging for mt-cpYFP.
- Extended Data Figure 4: Relationship between day-3 mitoflash frequency and lifespan variation due to stochastic factors. (265 KB)
a, Linear regression of day-3 mitoflash frequency and the lifespan of individual animals in a population of mt-cpYFP-expressing WT, long-lived age-1(hx546), or short-lived elo-5(RNAi) worms (n = 78, 65 and 58, respectively). Superimposed data are offset by a value of 0.1 along the x axis. b, Survival curves of the high, medium and low mitoflash frequency (MF) groups in a. P < 0.001 between high and low MF groups in each population; P < 0.05 between any two groups within a population except for the age-1 low and medium MF groups (log-rank). The mean lifespans of the high, medium and low MF groups were, respectively: for WT, 13.7, 20.1 and 24.8 days; for age-1(hx546), 17.9, 23.7 and 27.2 days; and for elo-5(RNAi) 15.3, 17.9 and 20.7 days.
- Extended Data Figure 5: No correlation between day-9 mitoflash activity and the lifespan of individual WT worms. (95 KB)
Scatter plot of lifespans of individual C. elegans animals as a function of the number of mitoflash events per 200 s on adult day 9. The linear regression line (solid black) and the 95% prediction interval (dashed lines) are drawn. There is no statistically significant correlation between the values on the x and y axes (n = 132, R2 < 0.01, P = 0.46).
- Video 2: 4D (XYZ-T) imaging of mitoflash activity in a day-3 WT worm. (6.63 MB, Download)
- Stacks of 3 optical sections at 0.5 μm Z intervals were obtained every 1 s. Mitoflash events are colour-coded in the time-lapse projections generated from the stacks with varying angles of view.
- Supplementary Information (361 KB)
This file contains Supplementary Tables 1-3 and additional references.