P4-167: Investigation of mitochondrial DNA damage in late-onset Alzheimer's disease

Abstract

Age is the major risk factor for Late Onset Alzheimer's disease (LOAD). Multiple reports indicate an association between mitochondrial dysfunction and age, consequently investigation of mitochondrial dysfunction is an excellent and valid area of research for this disease. Mitochondrial DNA (mtDNA) is particularly vulnerable to damage and mutation from reactive oxygen species, given its location within the metabolic centre of the cell and relatively unprotected structure. It has been demonstrated that mtDNA damage can be measured using quantitative PCR, where molecular lesions such as deletions, base modifications and strand breaks can block the PCR polymerase resulting in reduced efficiency of the PCR reaction. The pathological changes that occur in LOAD are more severe in the temporal cortex than in the cerebellum. Using quantitative PCR we evaluated the level of mtDNA damage at the 16s locus in these two brain regions from 10 LOAD subjects and 10 age-matched controls. DNA was prepared using techniques that enrich the sample for mtDNA and reduce in vitro DNA damage. The proportion of nuclear DNA was quantified for each sample to determine the [mtDNA] since variation in mtDNA copy number has been reported. Initial results suggest increased mtDNA damage in the temporal cortex, as compared to the cerebellum, for both AD and control subjects (p<0.004). In the temporal cortex we observed a significant difference in mtDNA damage between AD and control subjects (p=0.0011) but not in the cerebellum (p=0.2799), We also found a significant reduction in the proportion of nuclear to mitochondrial DNA in AD as compared to control samples from the temporal cortex (p=0.001). These data indicate that mtDNA damage may be more severe in tissue affected by LOAD pathology and suggest an increase in mtDNA copy number in the temporal cortex. Investigation of additional subjects and mitochondrial loci is underway to confirm these findings.