Related Experiment Videos
Introduction of disease-related mitochondrial DNA deletions into HeLa cells lacking mitochondrial DNA results in
1Department of Biochemistry, Saitama Cancer Center Research Institute, Japan.
Abstract:
Mutant mitochondrial DNA with large-scale deletions (delta-mtDNA) has been frequently observed in patients with chronic progressive external ophthalmoplegia (CPEO), a subgroup of the mitochondrial encephalomyopathies. To exclude involvement of the nuclear genome in expression of the mitochondrial dysfunction characteristic of CPEO, we introduced the mtDNA of a CPEO patient into clonal mtDNA-less HeLa cells and isolated cybrid clones. Quantitation of delta-mtDNA in the cybrids revealed that delta-mtDNA was selectively propagated with higher levels of delta-mtDNA correlating with slower cellular growth rate. In these cybrid clones, translational complementation of the missing tRNAs occurred only when delta-mtDNA was less than 60% of the total mtDNA, whereas accumulation of delta-mtDNA to greater than 60% resulted in progressive inhibition of overall mitochondrial translation as well as reduction of cytochrome c oxidase activity throughout the organelle population. Because these cybrids shared the same nuclear background as HeLa cells, these results suggest that large-scale deletion mutations of mtDNA alone are sufficient for the mitochondrial dysfunction characteristic of CPEO.
Insights
Large-scale deletions in mitochondrial DNA (mtDNA) cause cellular dysfunction in chronic progressive external ophthalmoplegia (CPEO). These mtDNA deletions alone are sufficient to induce mitochondrial disease, independent of nuclear genome involvement.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Chronic progressive external ophthalmoplegia (CPEO) is linked to mitochondrial DNA (mtDNA) deletions.
- The role of the nuclear genome versus mtDNA in CPEO pathogenesis remains unclear.
Purpose of the Study:
- To determine if large-scale mtDNA deletions alone cause mitochondrial dysfunction in CPEO.
- To investigate the impact of mtDNA deletions on cellular growth and mitochondrial function.
Main Methods:
- Introduced CPEO patient mtDNA with large-scale deletions (delta-mtDNA) into mtDNA-less HeLa cells to create cybrids.
- Quantified delta-mtDNA levels and assessed cellular growth rates.
- Evaluated mitochondrial translation and cytochrome c oxidase activity in cybrid clones.
Main Results:
- Delta-mtDNA was selectively propagated in cybrids, with higher levels correlating to slower growth.
- Mitochondrial translation and tRNA complementation were impaired when delta-mtDNA exceeded 60% of total mtDNA.
- Accumulation of delta-mtDNA led to reduced cytochrome c oxidase activity.
Conclusions:
- Large-scale mtDNA deletions are sufficient to cause the mitochondrial dysfunction observed in CPEO.
- Nuclear genome is not required for the development of CPEO-associated mitochondrial dysfunction.
- Threshold of delta-mtDNA accumulation significantly impacts mitochondrial function and cellular viability.