Idebenone increases mitochondrial complex I activity in fibroblasts from LHON patients while producing contradictory effects on respiration.

Background: Leber's hereditary optic neuropathy (LHON) is caused by mutations in the complex I subunits of the respiratory chain. Although patients have been treated with idebenone since 1992, the efficacy of the drug is still a matter of debate.

Methods: We evaluated the effect of idebenone in fibroblasts from LHON patients using enzymatic and polarographic measurements.

OPA1 links human mitochondrial genome maintenance to mtDNA replication and distribution.

Eukaryotic cells harbor a small multiploid mitochondrial genome, organized in nucleoids spread within the mitochondrial network. Maintenance and distribution of mitochondrial DNA (mtDNA) are essential for energy metabolism, mitochondrial lineage in primordial germ cells, and to prevent mtDNA instability, which leads to many debilitating human diseases. Mounting evidence suggests that the actors of the mitochondrial network dynamics, among which is the intramitochondrial dynamin OPA1, might be involved in these processes.

Adenine nucleotide translocase 2 is a key mitochondrial protein in cancer metabolism.

Adenine nucleotide translocase (ANT), a mitochondrial protein that facilitates the exchange of ADP and ATP across the mitochondrial inner membrane, plays an essential role in cellular energy metabolism. Human ANT presents four isoforms (ANT1-4), each with a specific expression depending on the nature of the tissue, cell type, developmental stage and status of cell proliferation. Thus, ANT1 is specific to muscle and brain tissues; ANT2 occurs mainly in proliferative, undifferentiated cells; ANT3 is ubiquitous; and ANT4 is found in germ cells.

Quantitative two-dimensional HRMAS 1H-NMR spectroscopy-based metabolite profiling of human cancer cell lines and response to chemotherapy.

NMR spectroscopy-based metabolomics still needs development in quantification procedures. A method was designed for quantitative two-dimensional high resolution magic angle spinning (HRMAS) proton-NMR spectroscopy-based metabolite profiling of intact cells. It uses referencing of metabolite-related NMR signals to protein-related NMR signals and yields straightforward and automatable metabolite profiling.

Adenine nucleotide translocase is involved in a mitochondrial coupling defect in MFN2-related Charcot-Marie-Tooth type 2A disease.

Charcot-Marie-Tooth type 2A disease (CMT2A), a dominantly inherited peripheral neuropathy, is caused by mutations in MFN2, a mitochondrial fusion protein. Having previously demonstrated a mitochondrial coupling defect in CMT2A patients' fibroblasts, we here investigate mitochondrial oxygen consumption and the expression of adenine nucleotide translocase (ANT) and uncoupling proteins from eight other patients with the disease. The mitochondrial uncoupling was associated with a higher respiratory rate, essentially involving complex II proteins.

OPA1-associated disorders: phenotypes and pathophysiology.

The OPA1 gene, encoding a dynamin-like mitochondrial GTPase, is involved in autosomal dominant optic atrophy (ADOA, OMIM #165500). ADOA, also known as Kjer's optic atrophy, affects retinal ganglion cells and the axons forming the optic nerve, leading to progressive visual loss. OPA1 gene sequencing in patients with hereditary optic neuropathies indicates that the clinical spectrum of ADOA is larger than previously thought.

Mitochondrial bioenergetic background confers a survival advantage to HepG2 cells in response to chemotherapy.

Cancer cells mainly rely on glycolysis for energetic needs, and mitochondrial ATP production is almost inactive. However, cancer cells require the integrity of mitochondrial functions for their survival, such as the maintenance of the internal membrane potential gradient (DeltaPsim). It thus may be predicted that DeltaPsim regeneration should depend on cellular capability to produce sufficient ATP by upregulating glycolysis or recruiting oxidative phosphorylation (OXPHOS).

Hereditary optic neuropathies share a common mitochondrial coupling defect.

Hereditary optic neuropathies are heterogeneous diseases characterized by the degeneration of retinal ganglion cells leading to optic nerve atrophy and impairment of central vision. We found a common coupling defect of oxidative phosphorylation in fibroblasts of patients affected by autosomal dominant optic atrophy (mutations of OPA1), autosomal dominant optic atrophy associated with cataract (mutations of OPA3), and Leber's hereditary optic neuropathy, a disorder associated with point mutations of mitochondrial DNA complex I genes. Interestingly, the energetic defect was significantly more pronounced in Leber's hereditary optic neuropathy and autosomal dominant optic atrophy patients with a more complex phenotype, the so-called plus phenotype.

Reversible optic neuropathy with OPA1 exon 5b mutation.

A new c.740G>A (R247H) mutation in OPA1 alternate spliced exon 5b was found in a patient presenting with bilateral optic neuropathy followed by partial, spontaneous visual recovery. R247H fibroblasts from the patient and his unaffected father presented unusual highly tubular mitochondrial network, significant increased susceptibility to apoptosis, oxidative phosphorylation uncoupling, and altered OPA1 protein profile, supporting the pathogenicity of this mutation.

mtDNA controls expression of the Death Associated Protein 3.

The Death Associated Protein 3 (DAP3), a GTP-binding constituent of the small subunit of the mitochondrial ribosome, is implicated in the TNFalpha and IFNgamma apoptotic pathways of the cell and is involved in the maintenance of the mitochondrial network. We have investigated the mitochondrial role of DAP3 by analyzing its mRNA and protein expression in transformed and non-transformed cell lines presenting various levels of mtDNA. The 3 mtDNA-less (rho degrees ) cell lines showed a complete absence of DAP3, whereas the mRNA expression was conserved.

Dinitrophenol-induced mitochondrial uncoupling in vivo triggers respiratory adaptation in HepG2 cells.

Here, we show that 3 days of mitochondrial uncoupling, induced by low concentrations of dinitrophenol (10 and 50 microM) in cultured human HepG2 cells, triggers cellular metabolic adaptation towards oxidative metabolism. Chronic respiratory uncoupling of HepG2 cells induced an increase in cellular oxygen consumption, oxidative capacity and cytochrome c oxidase activity. This was associated with an upregulation of COXIV and ANT3 gene expression, two nuclear genes that encode mitochondrial proteins involved in oxidative phosphorylation.

ANT2 isoform required for cancer cell glycolysis.

The three adenine nucleotide translocator (ANT1 to ANT3) isoforms, differentially expressed in human cells, play a crucial role in cell bioenergetics by catalyzing ADP and ATP exchange across the mitochondrial inner membrane. In contrast to differentiated tissue cells, transformed cells, and their rho(0) derivatives, i.e.

[What is the specific role of ANT2 in cancer cells?].

In the mitochondrial internal membrane, the adenine nucleotide translocator (ANT) carries out the ATP/ADP exchange between cytoplasm and mitochondrial matrix. Three isoforms with different kinetic properties are encoded from three different genes in Human: the muscle specific ANT1 and the ubiquitary ANT3 isoforms export ATP produced by mitochondrial oxidative phosphorylation (OXPHOS). The ANT2 isoform is specifically expressed in proliferative cells with a predominant glycolytic metabolism and is associated with cellular undifferentiation which is a major characteristic in carcinogenesis.

ANT2 expression under hypoxic conditions produces opposite cell-cycle behavior in 143B and HepG2 cancer cells.

Under hypoxic conditions, mitochondrial ATP production ceases, leaving cells entirely dependent on their glycolytic metabolism. The cytoplasmic and intramitochondrial ATP/ADP ratios, partly controlled by the adenine nucleotide translocator (ANT), are drastically modified. In dividing and growing cells that have a predominantly glycolytic metabolism, the ANT isoform 2, which has kinetic properties allowing ATP import into mitochondria, is over-expressed in comparison to control cells.

Oxygen consumption and expression of the adenine nucleotide translocator in cells lacking mitochondrial DNA.

It has been shown previously that human rho degrees cells, deprived of mitochondrial DNA and consequently of functional oxidative phosphorylation, maintain a mitochondrial membrane potential, which is necessary for their growth. The goal of our study was to determine the precise origin of this membrane potential in three rho degrees cell lines originating from the human HepG2, 143B, and HeLa S3 cell lines. Residual cyanide-sensitive oxygen consumption suggests the persistence of residual mitochondrial respiratory chain activity, about 8% of that of the corresponding parental cells.