Isolation of a cytochrome oxidase gene overexpressed in Alzheimer's disease brain

Several lines of evidence suggest that many cases of Alzheimer's disease (AD) may be due to genetic factors. We used subtraction hybridization to isolate genes that were differentially expressed in AD compared to control brains. Directionally cloned cDNA libraries from AD and control patients' cerebral temporal cortices were used for the production of sense and antisense cDNA using the polymerase chain reaction (PCR). A 30- to 40-fold excess of sense cDNA from Alzheimer's disease brain was photobiotinylated and hybridized to ³²P-labeled antisense cDNA from control brain. The hybridized and unhybridized "driver" DNA was removed by streptavidin binding and phenol extraction. The subtracted antisense cDNA sequences were PCR amplified and cloned into λ-GEM-4 producing a subtracted cDNA library. This subtracted cDNA library was rescreened using duplicate differential colony hybridization to select specific subtracted clones. An 850-bp cDNA that was overexpressed in the AD compared to the control library was isolated and sequenced. It had >95% homology to cytochrome oxidase subunit 3. Overexpression of this gene in AD brains was confirmed using Northern blots. Since cytochrome oxidase is important for neuronal function, these findings suggest a possible role for this gene in the pathogenesis of AD.