Mitochondrial DNA damage in iron overload
Xueshan Gao1, Jian Li Campian, Mingwei Qian
1Department of Oncology, University of Linköping, Linköping 58185, Sweden.
Abstract:
Chronic iron overload has slow and insidious effects on heart, liver, and other organs. Because iron-driven oxidation of most biologic materials (such as lipids and proteins) is readily repaired, this slow progression of organ damage implies some kind of biological "memory." We hypothesized that cumulative iron-catalyzed oxidant damage to mtDNA might occur in iron overload, perhaps explaining the often lethal cardiac dysfunction. Real time PCR was used to examine the "intactness" of mttDNA in cultured H9c2 rat cardiac myocytes. After 3-5 days exposure to high iron, these cells exhibited damage to mtDNA reflected by diminished amounts of near full-length 15.9-kb PCR product with no change in the amounts of a 16.1-kb product from a nuclear gene. With the loss of intact mtDNA, cellular respiration declined and mRNAs for three electron transport chain subunits and 16 S rRNA encoded by mtDNA decreased, whereas no decrements were found in four subunits encoded by nuclear DNA. To examine the importance of the interactions of iron with metabolically generated reactive oxygen species, we compared the toxic effects of iron in wild-type and rho(o) cells. In wild-type cells, elevated iron caused increased production of reactive oxygen species, cytostasis, and cell death, whereas the rho(o) cells were unaffected. We conclude that long-term damage to cells and organs in iron-overload disorders involves interactions between iron and mitochondrial reactive oxygen species resulting in cumulative damage to mtDNA, impaired synthesis of respiratory chain subunits, and respiratory dysfunction.
Insights
Chronic iron overload causes cumulative damage to mitochondrial DNA (mtDNA) through iron-catalyzed oxidation. This damage impairs cellular respiration and contributes to organ dysfunction in iron overload disorders.
Area of Science:
- Biochemistry
- Cell Biology
- Pathophysiology
Background:
- Chronic iron overload insidiously damages organs like the heart and liver.
- Organ damage progression suggests a biological memory, possibly linked to cumulative oxidative stress.
- Iron-catalyzed oxidation of biomolecules is usually repaired, but mtDNA damage may persist.
Purpose of the Study:
- To investigate the hypothesis that cumulative iron-catalyzed oxidant damage to mitochondrial DNA (mtDNA) occurs in iron overload.
- To explore the role of mtDNA damage in the cardiac dysfunction associated with iron overload.
- To elucidate the mechanism of iron-induced cellular damage in cardiac myocytes.
Main Methods:
- Cultured H9c2 rat cardiac myocytes were exposed to high iron concentrations for 3-5 days.
- Real-time PCR was used to assess the integrity of mtDNA by examining PCR product lengths.
- Mitochondrial function was evaluated by measuring cellular respiration and mRNA levels for electron transport chain subunits.
- Wild-type and rho(0) cells (lacking mtDNA) were compared to assess the role of mitochondria in iron toxicity.
Main Results:
- High iron exposure led to diminished amounts of near full-length mtDNA (15.9-kb PCR product) in cardiac myocytes.
- Cellular respiration declined with mtDNA damage, and mtDNA-encoded mRNAs decreased.
- Elevated iron increased reactive oxygen species production, cytostasis, and cell death in wild-type cells but not in rho(0) cells.
- Nuclear DNA integrity (16.1-kb PCR product) remained unchanged, indicating specific mtDNA damage.
Conclusions:
- Long-term organ damage in iron overload involves iron-mitochondrial reactive oxygen species interactions.
- Cumulative damage to mtDNA impairs the synthesis of respiratory chain subunits, leading to respiratory dysfunction.
- Mitochondrial dysfunction driven by mtDNA damage is a key mechanism in the pathogenesis of iron overload disorders.
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