DNA repair, mitochondria, and neurodegeneration.

Accumulation of nuclear and mitochondrial DNA damage is thought to be particularly deleterious in post-mitotic cells, which cannot be replaced through cell division. Recent experimental evidence demonstrates the importance of DNA damage responses for neuronal survival. Here, we summarize current literature on DNA damage responses in the mammalian CNS in aging and neurodegeneration. Base excision repair (BER) is the main pathway for the removal of small DNA base modifications, such as alkylation, deamination and oxidation, which are generated as by-products of normal metabolism and accumulate with age in various experimental models. Using neuronal cell cultures, human brain tissue and animal models, we and others have shown an active BER pathway functioning in the brain, both in the mitochondrial and nuclear compartments. Mitochondrial DNA repair may play a more essential role in neuronal cells because these cells depend largely on intact mitochondrial function for energy metabolism. We have characterized several BER enzymes in mammalian mitochondria and have shown that BER activities change with age in mitochondria from different brain regions. Together, the results reviewed here advocate that mitochondrial DNA damage response plays an important role in aging and in the pathogenesis of neurodegenerative diseases.