Figure 2

Higher levels of 12 A heteroplasmy at 5172 in the origin of light strand replication reduces mtDNA/nDNA copy number ratio, while the expression levels of the mtDNA-encoded gene are increased. (a) The ratio of mtDNA (mt-Co1)- to nDNA (Vdac1) copy number was determined using liver genomic DNA obtained from B6 and B6-mt^AKR (AKR) mice (females, young: 3 months of age, aged: 18–22 months of age). The copy number ratio (mt-Co1/Vdac1) negatively correlates to levels of 12 A heteroplasmy in OriL. N = 48, ρ = −0.4264, *P = 0.0025, Spearman test. (b) The values presented in a. were compared between strains, for which no difference is observed between B6 and AKR in each age group. (c) MtDNA gene copy number ratio based on mt-Nd5/Vdac1 shows the same trend found by mt-Co1/Vdac1. (d) Higher 12 A heteroplasmy levels in OriL also correlate with the copy number ratio of mt-Nd5/Vdac1. (e) The expression levels of mt-Co1 in liver mitochondrial RNA were quantified using droplet digital PCR. The mt-Co1 expression normalized to the mt-Co1 copy number ratio reveals a significant correlation with the levels of 12 A heteroplasmy. ρ = 0.5646, **P = 0.0033, Spearman test. (f) The values presented in e. display no significant difference when compared between the strains in each age group. (g) Quantified values of Western blotting of liver samples reveal unaltered protein levels of mitochondrial OXPHOS subunits. Females, three months of age, n = 10 (B6), n = 8 (AKR). (h) The same samples tested in g. were quantified for beta-actin.