INSENSITIVITY OF CULTURED RAT CORTICAL-NEURONS TO MITOCHONDRIAL-DNA SYNTHESIS INHIBITORS - EVIDENCE FOR A SLOW TURNOVER OF MITOCHONDRIAL-DNA

Mitochondrial dysfunction is a major contributor to aging and neurodeg eneration. Defects in mitochondrial DNA (mtDNA) have been identified i n several neuromuscular diseases. Even though there is a high rate of phenotypic expression of mtDNA mutations in the central nervous system and replication of DNA introduces errors, little is known about the r eplicative activity of mtDNA in the brain. In this study, we investiga ted the sensitivity of cultured rat cortical neurons to mtDNA synthesi s inhibitors as a means to assess the turnover rate of mtDNA. Four-day treatment with dideoxycytidine (ddC) (0.2 mu M) or ethidium bromide ( EtB) (0.25 mu g/mL) reduced the mtDNA content approximately 80% in the human lymphoblastoid cell line, GEM. Concentrations of ddC ranging fr om 0.2 to 10 mu M did not reduce mtDNA content in primary cultures of rat cortical neurons. Similarly, treatment with EtB (0.1, 0.25, and 0. 5 mu g/mL) did not affect significantly neuronal mtDNA. EtB (0.25 mu g /mL) was effective in reducing mtDNA content in the undifferentiated e mbryonic carcinoma cell line, P 19. However, once P 19 cells were diff erentiated into a neuronal phenotype, they became insensitive to inhib ition of mtDNA synthesis by EtB. Thus, cultured rat cortical neurons w ere less sensitive to mtDNA synthesis inhibitors than cell lines, sugg esting that the turnover of mtDNA in central neurons is very slow. Thi s may protect central neurons from accumulating mutations during the r eplication of mtDNA. (C) 1991 Elsevier Science Inc.