Rescue of a deficiency in ATP synthesis by transfer of MTATP6, a mitochondrial DNA-encoded gene, to the nucleus

@article{Manfredi2002RescueOA,
  title={Rescue of a deficiency in ATP synthesis by transfer of MTATP6, a mitochondrial DNA-encoded gene, to the nucleus},
  author={Giovanni Manfredi and Jin Fu and Joseline Ojaimi and James E. Sadlock and Jennifer Q Kwong and John R Guy and Eric A. Schon},
  journal={Nature Genetics},
  year={2002},
  volume={30},
  pages={394-399}
}
A T→G transversion at nt 8993 in mitochondrial DNA of MTATP6 (encoding ATPase 6 of complex V of the respiratory chain) causes impaired mitochondrial ATP synthesis in two related mitochondrial disorders: neuropathy, ataxia and retinitis pigmentosa and maternally inherited Leigh syndrome. To overcome the biochemical defect, we expressed wildtype ATPase 6 protein allotopically from nucleus-transfected constructs encoding an amino-terminal mitochondrial targeting signal appended to a recoded ATPase… 
Allotopic mRNA localization to the mitochondrial surface rescues respiratory chain defects in fibroblasts harboring mitochondrial DNA mutations affecting complex I or v subunits.
TLDR
This study shows that allotopic expression of a recoded ATP6 gene leads to a long-lasting and complete rescue of mitochondrial dysfunction of fibroblasts harboring the neurogenic muscle weakness, ataxia and retinitis Pigmentosa T8993G ATP6 mutation or the Leber hereditary optic neuropathy G11778A ND4 mutation.
Stable nuclear expression of ATP8 and ATP6 genes rescues a mtDNA Complex V null mutant
TLDR
Tests for ATP hydrolysis / synthesis, oxygen consumption, glycolytic metabolism and viability all indicate a significant functional rescue of the mutant phenotype (including re-assembly of Complex V) following stable co-expression of ATP8 and ATP6.
Limitations of allotopic expression of mitochondrial genes in mammalian cells.
TLDR
Allotopic expression of apocytochrome b and ND4 induced a loss of mitochondrial membrane potential in transfected cells, which can lead to cell death, andalyses of the hydrophobic patterns of different polypeptides suggest that hydrophobicity of the N-terminal segment is the main determinant for the importability of peptides into mammalian mitochondria.
An algal nucleus-encoded subunit of mitochondrial ATP synthase rescues a defect in the analogous human mitochondrial-encoded subunit.
TLDR
In spite of the evolutionary distance between algae and mammals, C. reinhardtii ATPase 6 functioned in human cells, because deficiencies in both cell viability and ATP synthesis in transmitochondrial cell lines harboring a pathogenic mutation in the human mtDNA-encoded ATP6 gene were overcome by expression of CrATP6.
Expression of algal nuclear ATP synthase subunit 6 in human cells results in protein targeting to mitochondria but no assembly into ATP synthase.
TLDR
Nuclear compatible versions of human subunit a (A6) of ATP synthase, linked to a mitochondrial targeting signal are created, finding obstacles remain to functional expression of mitochondrial genes transferred to the nucleus.
Rescue of a mitochondrial deficiency causing Leber hereditary optic neuropathy
TLDR
Restoration of respiration by allotopic expression opens the door for gene therapy of Leber Hereditary Optic Neuropathy by correcting a defect in the mitochondrial genome linked to a human disease.
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TLDR
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