A chronic imbalance in
DNA precursors, caused by one-
carbon metabolism impairment, can result in a deficiency of DNA repair and increased DNA damage. Although indirect evidence suggests that DNA damage plays a role in neuronal apoptosis and in the pathogenesis of
neurodegenerative disorders, the underlying mechanisms are poorly understood. In particular, very little is known about the role of base excision repair of misincorporated
uracil in neuronal survival. To test the hypothesis that repair of DNA damage associated with
uracil misincorporation is critical for neuronal survival, we employed an antisense (AS)
oligonucleotide directed against
uracil-DNA glycosylase encoded by the UNG gene to deplete UNG in cultured rat hippocampal neurons. AS, but not a scrambled control
oligonucleotide, induced apoptosis, which was associated with DNA damage analyzed by comet assay and up-regulation of p53. UNG
mRNA and
protein levels were decreased within 30 min and were undetectable within 6-9 h of exposure to the UNG AS
oligonucleotide. Whereas UNG expression is significantly higher in proliferating as compared with nonproliferating cells, such as neurons, the levels of UNG
mRNA were increased in brains of
cystathionine beta-synthase knockout mice, a model for
hyperhomocysteinemia, suggesting that one-
carbon metabolism impairment and
uracil misincorporation can induce the up-regulation of UNG expression.