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Oxidative damage plays a pathogenic role in various chronic degenerative diseases. Oxidative damage targeting trabecular meshwork (TM) cells as a consequence of mitochondrial damage is a pathogenic mechanism for glaucoma, the most common cause of irreversible blindness worldwide. Consequences of oxidative damage are attenuated by endocellular activities involved in scavenging reactive oxidative species and DNA repair. Selected bacterial genes are highly efficient at protecting cells from oxidative DNA damage. This situation occurs for Escherichia coli formamidopyrimidine DNA glycosylase (FPG), a major DNA glycosylase that repairs oxidatively damaged DNA. Accordingly, this study was aimed at transfecting human TM cells (HTMC) with Fpg in order to increase their resistance to oxidative damage. This study demonstrates that it is feasible to increase resistance of HTMC to endogenous oxidative damage by gene transfection. These findings bear relevance for primary and secondary prevention of degenerative glaucomas and other degenerative diseases where oxidative damage plays a pathogenic role.

Repair of the oxidized purine 8-oxo-7,8-dihydro-2'-deoxyguanosine is inefficient in cells belonging to both complementation groups A and B of Cockayne syndrome (CS), a developmental and neurological disorder characterized by defective transcription-coupled repair. We show here that both CS-A and CS-B cells are also defective in the repair of 5-hydroxy-2'-deoxycytidine (5-OHdC), an oxidized pyrimidine with cytotoxic and mutagenic properties. The defect in the repair of oxidatively damaged DNA in CS cells thus extends to oxidized pyrimidines, indicating a general flaw in the repair of oxidized lesions in this syndrome. The defect could not be reproduced in in vitro repair experiments on oligonucleotide substrates, suggesting a role for both CS-A and CS-B proteins in chromatin remodeling during 5-OHdC repair. Expression of Escherichia coli formamidopyrimidine DNA glycosylase (FPG) or endonuclease III complemented the 5-OHdC repair deficiency. Hence, the expression of a single enzyme, FPG from E. coli, stably corrects the delayed removal of both oxidized purines and oxidized pyrimidines in CS cells.

We have previously shown that DNA repair of oxidized bases (either purines or pyrimidines) is inefficient in cells from patients with Cockayne syndrome (cs), a rare developmental and neurological genetic disorder. Here, we show for the first time that resolution of ionizing radiation (IR)-induced pH2AX foci, an indicator of DNA double-strand breaks, is significantly delayed in IR-treated cells belonging to the B complementation group of cs (csb). Using alkaline single-cell gel electrophoresis, which predominantly detects single-strand breaks, we further demonstrate elevated DNA breakage in csb cells early after irradiation. Both the delayed resolution of pH2AX foci and the early DNA breakage of csb cells were partially complemented by expression of wild-type CSB protein. Hence, the csb mutation impairs resolution of pH2AX foci and causes DNA fragility, broadening the spectrum of lesions whose processing is altered in this syndrome. © 2011 IUBMB IUBMB Life, 63(4): 272–276, 2011

Cigarette smoke (CS) is associated to a number of pathologies including lung cancer. Its mutagenic and carcinogenic effects are partially linked to the presence of reactive oxygen species and polycyclic aromatic hydrocarbons (PAH) inducing DNA damage. The bacterial DNA repair enzyme formamidopyrimidine DNA glycosylase (FPG) repairs both oxidized bases and different types of bulky DNA adducts. We investigated in vitro whether FPG expression may enhance DNA repair of CS-damaged DNA and counteract the mutagenic effects of CS in human lung cells. NCI-H727 non small cell lung carcinoma cells were transfected with a plasmid vector expressing FPG fused to the Enhanced Green Fluorescent Protein (EGFP). Cells expressing the fusion protein EGFP-FPG displayed accelerated repair of adducts and DNA breaks induced by CS condensate. The mutant frequencies induced by low concentrations of CS condensate to the Na(+)K(+)-ATPase locus (oua(r)) were significantly reduced in cells expressing EGFP-FPG. Hence, expression of the bacterial DNA repair protein FPG stably protects human lung cells from the mutagenic effects of CS by improving cells' capacity to repair damaged DNA.