Fig. 4. Impaired mtDNA replication and altered mitochondrial morphology in MERKO muscle.

(A) Muscle mtDNA content, expressed as a ratio of mtDNA/nuclear (nuc) DNA (n = 8 per group). (B) Muscle polymerase γ1 (Polγ1), Polγ2, and Polrmt expression. (C) mtDNA replication as measured by ²H₂O incorporation into newly synthesized mtDNA (deoxynucleosides, dG and dC) from Control f/f and MERKO mice (n = 6 per genotype). (D) Representative electron micrographs of soleus muscle from female Control f/f and MERKO mice, low- and high-magnification inset (IM, intramyofibrillar; SS, subsarcolemmal; scale bar, 1 µm). (E) Skeletal muscle intermyofibrillar mitochondrial area (n = 3 mice per genotype). (F) mtDNA mutation load was detected by random mutation capture (RMC) at basal (no treatment), after H₂O₂ treatment, and during recovery from H₂O₂ treatment. (G) mtDNA copy number at basal, after H₂O₂ treatment [in the presence of chloramphenicol (Chl) plus cycloheximide (Chx), and during recovery (in the presence of bafilomycin A₁ (BafA₁)]. All values are expressed as means ± SEM. Mean differences detected by Student’s t test and ANOVA where appropriate; *P < 0.05, between-genotype difference; ^#P < 0.05, within-genotype between treatment difference.