Increased multimeric mitochondrial DNA in the brain of scrapie-infected hamsters.

We observed a marked increase in multimeric mitochondrial DNA (mtDNA) in brains of scrapie-infected hamsters compared with those of uninfected hamsters. Homogenized brain tissue was subjected to subcellular fractionation to isolate scrapie-associated fibrils and tubulofilamentous structures. Nucleic acids were extracted from the scrapie-associated fibril/tubulofilament fraction which also contained mitochondria. Agarose gel electrophoresis revealed a band corresponding to the size of circular hamster mtDNA in both infected and uninfected samples, but slower migrating bands were observed only in samples from scrapie-infected brain. We showed by molecular cloning, nucleotide sequencing, and Southern blotting that the slower migrating bands are mtDNA. These findings confirm the recent demonstration by differential hybridization that multimeric mtDNA occurs in hamster scrapie brain. Elevated levels of multimeric circular mtDNA have been reported previously in various tumors and cultured cell lines.