GLIAL CELL-SPECIFIC DIFFERENCES IN REPAIR OF O-6-METHYLGUANINE

Normal and malignant cells of the oligodendrocyte lineage show increas ed sensitivity to alkylating agents compared to astrocytes. One of the most mutagenic DNA lesions formed following exposure to alkylating ag ents is O-6-alkylguanine. To determine whether the increased sensitivi ty to nitrosoureas seen in oligodendrocytes is due to decreased repair capacity for O-6-alkylguanine, removal of this lesion from DNA was as sessed in primary cultures of rat oligodendrocytes, astrocytes, and mi croglia, Glial cells were exposed to 1 nM N-methyl-N-nitrosourea for 1 h and allowed 8 or 24 h for repair. Repair was evaluated using an imm unoslot blot technique and a monoclonal antibody which recognizes O-6- methylguanine (O(6)MeGua). Astrocytes removed O(6)MeGua more efficient ly (approximate to 80% in 24 h) than either oligodendrocytes (approxim ate to 20%) or microglia (approximate to 4%). Determination of O-6-alk ylguanine-DNA-alkyltransferase (AT) activity revealed that astrocytes contain 0.4 pmol/mg protein, which is average by comparison to other c ell types. Both oligodendrocytes and microglia exhibited very low leve ls of AT (oligodendrocytes, 0.08; microglia, 0.01 pmol/mg protein). Th ese data are the first to show that within different populations of gl ial cells, O(6)MeGua adduct removal is substantially reduced in both o ligodendrocytes and microglia, Rapid removal of O(6)MeGua in astrocyte s coupled with persistence of this mutagenic lesion in oligodendrocyte s following exposure of the developing central nervous system to nitro soureas could contribute to the observed formation of oligodendrogliom as. Inefficient removal of O(6)MeGua in oligodendrogliomas might also account for their response to chemotherapeutic regimens involving alky lating agents such as procarbazine, lomustine, and carmustine, The lac k of repair of O(6)MeGua in microglia suggests that primary lymphomas of the central nervous system might be sensitive to treatment with alk ylating drugs whose toxicity depends on repair of this adduct.