Abstract
Purpose: :
Large variation in the degree of vision loss is observed among Autosomal Dominant Optic Atrophy (ADOA) siblings who harbour identical mutations in OPA1. The cause for this variation in phenotype is not known. We performed detailed analysis of mitochondrial oxidative phosphorylation in ADOA patients with good vision compared to patients with significant visual loss.
Methods: :
EBV transformed lymphoblasts of ADOA patients with poor (<6/36, n=10) or good (>6/9, n=10) visual acuities or non mutation carrier controls (n=20) were established. Mitochondrial OXPHOS enzyme activity was measured spectrophotometrically from sonicated mitochondria. To determine mtDNA content southern blots were probed with primers overlapping the entire human mtDNA genome. Changes in protein expression level of OPA1, nuclear and mitochondrial subunits of Complex IV and actin were measured by western blot. Statistical analysis was measured by single factor ANOVA.
Results: :
Measuring OXPHOS in all ADOA patients compared to controls we found a significant decrease in complex I activity (p=0.05) and significant increase in II+III linked activity (p<0.01) whilst no changes in activity of complexes II, III or IV. Southern blotting of mtDNA content revealed no significant difference in mtDNA copy number across patient samples. Total OPA1 content detected by western blot was significantly decreased by 74% in both poor (p<0.01) and good (p<0.01) vision ADOA compared to controls, but no difference between good and poor vision.Interestingly in good vision ADOA compared to poor vision ADOA there was a significant increase in the II+III linked (P=0.05) and complex IV activity (p=0.026). Furthermore there was upregulation of both nuclear (p=0.063) and mitochondrial encoded (p=0.025) complex IV subunits in patients with good vision compared to poor vision.
Conclusions: :
We describe impaired complex I activity in lymphoblast mitochondria of ADOA patients, and in good vision ADOA show an increase in activity of complexes II+III as well as IV, which correlated with the increased protein levels of complex IV. Identifying specific defects in mitochondrial function that are associated with vision loss in ADOA may provide a method for predicting which individuals are most at risk of losing vision.
Keywords: mitochondria • genetics • optic nerve