Abstract
Purpose: :
To characterise age-related mitochondrial dysfunction in the retina of the xenomitochondrial mouse and determine how this renders retinal ganglion cells (RGCs) more vulnerable to injury induced by acute eye pressure elevation.
Methods: :
Mice harbouring an interspecific mtDNA (Xeno-mito mice) on a C57BL6 background and strain-matched controls were subjected to full-field (ganzfeld) scotopic electroretinogram (ERG) to assess retinal function at baseline and during IOP stress (50mm Hg for 30 minutes, n>8 mice). Retinal and brain mitochondrial respiration (n=6) was measured by high resolution respirometer. Retinas (n=6) were examined by western blotting for oxidative phosphorylation (OXPHOS) complex protein levels. RT-PCR was used to measure mtDNA encoded transcripts, and Blue Native PAGE to examine OXPHOS complex assembly.
Results: :
The Xeno-mito mice showed no baseline impairment on ERG. In response to IOP stress, Xeno-mito mice showed a 91% loss of ganglion cell function one week post injury compared with a 46% reduction in controls (p<0.05). Complex I driven mitochondrial respiration in the retina was decreased by 18% in 12 month Xeno mice (p=0.019) and by 16% in 18+ month Xeno mice (p=0.020). We found an age related decrease in complex I expression in xeno retinas, with a 46% decrease by 18 months (P<0.05), and 58% by 24 months (P<0.001). In both the retina and the brain we found significant increases in complex IV expression, activity and assembly in younger xeno animals which may be a compensation for the impaired complex I. The levels of complex IV decreased more than in WT mice with age, suggesting loss of this compensation with aging. RT-PCR showed 3-fold increased cytochrome oxidase subunit II transcript levels in 3 month old animals (p<0.001) that decreased to WT levels by 12 months of age.
Conclusions: :
Xeno-mito mice provide insight into the in vivo effects mtDNA-linked OXPHOS defects on neural retinal function. The Xeno-mito mice have defective complex I in the retina and brain. This defect manifests when the neural retina is exposed to aging and IOP stress. Upregulation of complex IV may compensate age-related decline of complex I.
Keywords: ganglion cells • mitochondria • metabolism