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Levels of DNA damage are unaltered in mice overexpressing human catalase in nuclei
S E Schriner1, C E Ogburn, A C Smith
1Department of Genetics, University of Washington, Seattle, WA 98195-7470, USA.
Abstract:
Two types of transgenic mice were generated to evaluate the role of hydrogen peroxide in the formation of nuclear DNA damage. One set of lines overexpresses wild-type human catalase cDNA, which is localized to peroxisomes. The other set overexpresses a human catalase construct that is targeted to the nucleus. Expression of the wild-type human catalase transgene was found in liver, kidney, skeletal muscle, heart, spleen, and brain with muscle and heart exhibiting the highest levels. Animals containing the nuclear-targeted construct had a similar pattern of expression with the highest levels in muscle and heart, but with lower levels in liver and spleen. In these animals, immunofluorescence detected catalase present in the nuclei of kidney, muscle, heart, and brain. Both types of transgenic animals had significant increases of catalase activities compared to littermate controls in most tissues examined. Despite enhanced activities of catalase, and its presence in the nucleus, there were no changes in levels of 8OHdG, a marker of oxidative damage to DNA. Nor were there differences in mutant frequencies at a Lac Z reporter transgene. This result suggests that in vivo levels of H(2)O(2) may not generate 8OHdG or other types of DNA damage. Alternatively, antioxidant defenses may be optimized such that additional catalase is unable to further protect nuclear DNA against oxidative damage.
Insights
This study investigated hydrogen peroxide's role in nuclear DNA damage using transgenic mice with enhanced catalase. Results showed increased catalase activity did not alter DNA damage markers, suggesting endogenous antioxidant defenses may be sufficient.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Hydrogen peroxide (H₂O₂) is a reactive oxygen species implicated in DNA damage.
- Catalase is a key enzyme that neutralizes H₂O₂.
- Understanding H₂O₂'s role in nuclear DNA damage is crucial for cellular health.
Purpose of the Study:
- To evaluate the role of hydrogen peroxide in nuclear DNA damage formation.
- To assess the impact of enhanced catalase activity, both peroxisomal and nuclear, on DNA damage markers.
Main Methods:
- Generation of two transgenic mouse lines: one overexpressing wild-type human catalase (peroxisomal) and another with nuclear-targeted catalase.
- Measurement of catalase activity in various tissues.
- Quantification of 8-hydroxy-2'-deoxyguanosine (8OHdG) levels and Lac Z reporter transgene mutant frequencies.
Main Results:
- Transgenic mice exhibited significantly increased catalase activity in multiple tissues.
- Nuclear catalase was detected in kidney, muscle, heart, and brain tissues.
- No significant changes in 8OHdG levels or Lac Z mutant frequencies were observed in either transgenic line compared to controls.
Conclusions:
- In vivo hydrogen peroxide levels may not directly cause 8OHdG formation or other nuclear DNA damage.
- Existing cellular antioxidant defenses might be optimized, preventing further protection by enhanced catalase.
- Further research is needed to fully elucidate the relationship between H₂O₂ and nuclear DNA integrity.