Figure 4.

Total and wild-type mtDNA copies in muscle fibres containing low-level mtDNA deletions.

(a) and (b): Total mtDNA copies (deleted and wild-type mtDNA copies) were analysed in muscle fibres containing low level (<60%) mtDNA deletions using real-time PCR (a) to determine whether there was mtDNA depletion within these fibres in MS cases. Overall, a significant increase in total mtDNA copies was found in these respiratory enzyme-deficient muscle fibres (in blue) compared to fibres with intact complex IV activity (stained brown) (p<0.001), consistent with clonal expansion of mtDNA deletions. The wild-type mtDNA copies were significantly decreased in fibres harbouring high-level mtDNA deletions, as previously recognised, in MS and controls. The extent of wild-type mtDNA depletion in fibres harbouring high-level mtDNA deletions was significantly less (p=0.02) in MS compared with controls, despite the difference in ambulation. There was no evidence of a significant decrease in either total or wild-type mtDNA copies within respiratory enzyme-deficient fibres from MS cases compared with controls (b).

mtDNA: mitochondrial DNA; PCR: polymerase chain reaction; MS: multiple sclerosis; CON: control; COX: cytochrome c oxidase; Neg: negative or deficiency of complex IV with intact complex II (stained blue); Pos: intact respiratory enzyme activity (stained brown). ‘+’ indicates the mean value. Box plots indicate 25th and 75th centiles with median value by the horizontal line and fifth to 95th centiles by the whiskers.