Fig. 6: Evidence that cryptic mtDNA mutations have heteroplasmy levels that might be controlled for therapeutic benefit and associations with neurodegeneration-linked genes.
a, b We find the cSFS for rats in three groups, young ad libitum (Y-AL), old ad libitum (O-AL), and old calorically restricted (O-CR), for variants called at a 5% heteroplasmy. This is displayed for liver in (a) and for brown adipose tissue in (b). Pairwise RBC-difference (see ‘Methods’ section) between each group’s cSFS indicates that caloric restriction slows the accumulation of cryptic mutation. This comparison was done between all pairings of the three groups and is displayed in the inset in (a) for liver and for brown adipose tissue in (b). Mutations in the O-CR are marginally more likely to be at a higher heteroplasmy than the Y-AL in both the liver and the brown adipose tissue (p > 0.05). Compared to this, mutations in the O-AL are far more likely to be at a higher heteroplasmy than Y-AL mice (two-sided Mann–Whitney U test p < 0.0001 & p < 0.001 Bonferroni corrected in liver and brown adipose tissue, respectively). Critically, mutations in O-AL rats are statistically significantly more likely to be at a higher heteroplasmy than mutations found in O-CR (two-sided Mann–Whitney U test p < 0.01 & p < 0.05 Bonferroni corrected in liver and brown adipose tissue, respectively). Mean heteroplasmies of observed liver mutations in Y-AL, O-CR, and O-AL, respectively, are 0.0846 ± 0.0025, 0.115 ± 0.0013, 0.228 ± 0.0035. In BAT the means are 0.0796 ± 0.00068, 0.0909 ± 0.00072, 0.144 ± 0.0035. c High-heteroplasmy mutational load μ95% in single brain cells coincides with differential expression of neurodegeneration-linked genes. Differential expression analysis was done using the Wilcoxon rank-sum test.
