Age-dependent guanine oxidation in DNA of different brain regions of Wistar rats and prematurely aging OXYS rats

BACKGROUND

Oxidative damage to the cell, including the formation of 8-oxoG, has been regarded as a significant factor in carcinogenesis and aging. An inbred prematurely aging rat strain (OXYS) is characterized by high sensitivity to oxidative stress, lipid peroxidation, protein oxidation, DNA rearrangements, and pathological conditions paralleling several human degenerative diseases including learning and memory deterioration.

METHODS

We have used monoclonal antibodies against a common pre-mutagenic base lesion 8-oxoguanine (8-oxoG) and 8-oxoguanine DNA glycosylase (OGG1) in combination with indirect immunofluorescence microscopy and image analysis to follow the relative amounts and distribution of 8-oxoG and OGG1 in various cells of different brain regions from OXYS and control Wistar rats.

RESULTS

It was shown that 8-oxoG increased with age in mature neurons, nestin- and glial fibrillary acidic protein (GFAP)-positive cells of hippocampus and frontal cortex in both strains of rats, with OXYS rats always displaying statistically significantly higher levels of oxidative DNA damage than Wistar rats. The relative content of 8-oxoG and OGG1 in nestin- and GFAP-positive cells was higher than in mature neurons in both Wistar and OXYS rats. However, there was no significant interstrain difference in the content of OGG1 for all types of cells and brain regions analyzed, and no difference in the relative content of 8-oxoG between different brain regions.

CONCLUSIONS

Oxidation of guanine may play an important role in the development of age-associated decrease in memory and learning capability of OXYS rats.

GENERAL SIGNIFICANCE

The findings are important for validation of the OXYS rat strain as a model of mammalian aging.

Site-directed photoproteolysis of 8-oxoguanine DNA glycosylase 1 (OGG1) by specific porphyrin-protein probe conjugates: a strategy to improve the effectiveness of photodynamic therapy for cancer

The specific light-induced, non-enzymatic photolysis of mOGG1 by porphyrin-conjugated or rose bengal-conjugated streptavidin and porphyrin-conjugated or rose bengal-conjugated first specific or secondary anti-IgG antibodies is reported. The porphyrin chlorin e6 and rose bengal were conjugated to either streptavidin, rabbit anti-mOGG1 primary specific antibody fractions or goat anti-rabbit IgG secondary antibody fractions. Under our experimental conditions, visible light of wavelengths greater than 600 nm induced the non-enzymatic degradation of mOGG1 when this DNA repair enzyme either directly formed a complex with chlorin e6-conjugated anti-mOGG1 primary specific antibodies or indirectly formed complexes with either streptavidin-chlorin e6 conjugates and biotinylated first specific anti-mOGG1 antibodies or first specific anti-mOGG1 antibodies and chlorin e6-conjugated anti-rabbit IgG secondary antibodies. Similar results were obtained when rose bengal was used as photosensitizer instead of chlorin e6. The rate of the photochemical reaction of mOGG1 site-directed by all three chlorin e6 antibody complexes was not affected by the presence of the singlet oxygen scavenger sodium azide. Site-directed photoactivatable probes having the capacity to generate reactive oxygen species (ROS) while destroying the DNA repair system in malignant cells and tumors may represent a powerful strategy to boost selectivity, penetration and efficacy of current photodynamic (PDT) therapy methodologies.

Immunofluorescent detection of 8-oxoguanine DNA lesions in liver cells from aging OXYS rats, a strain prone to overproduction of free radicals

Production of free radicals in animals is accompanied with a number of pathologic conditions, some of which may be manifested through DNA damage. Studies of mechanisms of oxidative DNA damage by free radicals in vivo are hindered by the lack of good animal models with significant overgeneration of or increased sensitivity to free radicals. An inbred rat strain (OXYS) is characterized by inherited overgeneration of free radicals, lipid peroxidation, protein oxidation, DNA rearrangements, and pathological conditions paralleling several human degenerative diseases. We have used monoclonal antibodies against a common pre-mutagenic base lesion 8-oxoguanine (8-oxoG) in combination with indirect immunofluorescence microscopy and image analysis to follow the relative age-dependent amounts and distribution of 8-oxoG in liver cells from OXYS and Wistar rats. 8-OxoG increased with age in both strains of rats, with OXYS rats always displaying statistically significantly higher levels of oxidative DNA damage than Wistar rats. Statistical analysis indicates that 8-oxoG does not uniformly accumulate in all cells with advancing age or increasing free radical load, but rather concentrates in a minor fraction of cells with a high damage level.

The murine DNA glycosylase NEIL2 (mNEIL2) and human DNA polymerase beta bind microtubules in situ and in vitro

8-oxoguanine DNA glycosylase (OGG1), a major DNA repair enzyme in mammalian cells and a component of the base excision repair (BER) pathway, was recently shown to be associated with the microtubule network and the centriole at interphase and the spindle assembly at mitosis. In this study, we determined whether other participants in the BER pathway also bind microtubules in situ and in vitro. Purified recombinant human DNA polymerase beta (DNA Pol beta) and purified recombinant mNEIL2 were chemically conjugated to fluorochromes and photosensitive dyes and used in in situ localization and binding experiments. Results from in situ localization, microtubule co-precipitation and site-directed photochemical experiments showed that recombinant human DNA Pol beta and recombinant mNEIL2 associated with microtubules in situ and in vitro in a manner similar to that shown earlier for another BER pathway component, OGG1. Observations reported in this study suggest that these BER pathway components are microtubule-associated proteins (MAPs) themselves or utilize yet to be identified MAPs to bind microtubules in order to regulate their intracellular trafficking and activities during the cell cycle.

Cell cycle regulation of the murine 8-oxoguanine DNA glycosylase (mOGG1): mOGG1 associates with microtubules during interphase and mitosis

8-Oxoguanine DNA glycosylase (OGG1) is a major DNA repair enzyme in mammalian cells. OGG1 participates in the repair of 8-oxoG, the most abundant known DNA lesion induced by endogenous reactive oxygen species in aerobic organisms. In this study, antibodies directed against purified recombinant human OGG1 (hOGG1) or murine (mOGG1) protein were chemically conjugated to either the photosensitizer Rose Bengal or the fluorescent dye Texas red. These dye-protein conjugates, in combination with binding assays, were used to identify associations between mOGG1 and the cytoskeleton of NIH3T3 fibroblasts. Results from these binding studies showed that mOGG1 associates with the cytoskeleton by specifically binding to the centriole and microtubules radiating from the centrosome at interphase and the spindle assembly at mitosis. Similar results were obtained with hOGG1. Together results reported in this study suggest that OGG1 is a microtubule-associated protein itself or that OGG1 utilizes yet to be identified motor proteins to ride on microtubules as tracks facilitating the movement and redistribution of cytoplasmic OGG1 pools during interphase and mitosis and in response to oxidative DNA damage.

‘Knock down’ of DNA polymerase β by RNA interference: recapitulation of null phenotype

DNA polymerase beta (pol beta) is the major DNA polymerase involved in the base excision repair (BER) pathway in mammalian cells and, as a consequence, BER is severely compromised in cells lacking pol beta. Pol beta null (-/-) mouse embryos are not viable and pol beta null cells are hypersensitive to alkylating agents. Using RNA interference (RNAi) technology in mouse cells, we have reduced the pol beta protein and mRNA to undetectable levels. Pol beta knockdown cell lines display a pattern of hypersensitivity to DNA damaging agents similar to that observed in pol beta null cells. Generation of pol beta knock down cells makes it possible to combine the pol beta null phenotype with deficiencies in other DNA repair proteins, thereby helping to elucidate the role of pol beta and its interactions with other proteins in mammalian cells.

Immunofluorescent localization of the murine 8-oxoguanine DNA glycosylase (mOGG1) in cells growing under normal and nutrient deprivation conditions

OGG1 is a major DNA glycosylase in mammalian cells, participating in the repair of 7,8-dihydro-8-oxoguanine (8-oxoguanine, 8-oxoG), the most abundant known DNA lesion induced by endogenous reactive oxygen species in aerobic organisms. 8-oxoG is therefore often used as a marker for oxidative DNA damage. In this study, polyclonal and monoclonal antibodies were raised against the purified wild-type recombinant murine 8-oxoG DNA glycosylase (mOGG1) protein and their specificity against the native enzyme and the SDS-denatured mOGG1 polypeptide were characterized. Specific antibodies directed against the purified wild-type recombinant mOGG1 were used to localize in situ this DNA repair enzyme in established cell lines (HeLa cells, NIH3T3 fibroblasts) as well as in primary culture mouse embryo fibroblasts growing under either normal or oxidative stress conditions. Results from these studies showed that mOGG1 is localized to the nucleus and the cytoplasm of mammalian cells in culture. However, mOGG1 levels increase and primarily redistribute to the nucleus and its peripheral cytoplasm in cells exposed to oxidative stress conditions. Immunofluorescent localization results reported in this study suggest that susceptibility to oxidative DNA damage varies among mammalian tissue culture cells and that mOGG1 appears to redistribute once mOGG1 cell copy number increases in response to oxidative DNA damage.

Site-directed photochemical disruption of the actin cytoskeleton by actin-binding Rose Bengal-conjugates

The in situ light-induced, non-enzymatic digestion of cytoskeletal actin by a xanthene dye conjugated to heavy meromyosin, anti-actin antibodies and/or anti-myosin antibodies is reported. The dye Rose Bengal was conjugated to either anti-actin antibodies, anti-myosin antibodies or heavy meromyosin. Under our experimental conditions, visible light induced the non-enzymatic breakdown of cytoskeletal actin when mammalian tissue culture cells were probed either with Rose Bengal-conjugated anti-actin and/or anti-myosin antibodies. Similar results were obtained when tissue culture cells were probed with Rose Bengal-conjugated heavy meromyosin before irradiation with visible light. The in situ photochemical reaction depended on the presence of actin-binding Rose Bengal-conjugates.