Chronic innate immune activation of TBK1 suppresses mTORC1 activity and dysregulates cellular metabolism.

Three-prime repair exonuclease 1 knockout (Trex1) mice suffer from systemic inflammation caused largely by chronic activation of the cyclic GMP-AMP synthase-stimulator of interferon genes-TANK-binding kinase-interferon regulatory factor 3 (cGAS-STING-TBK1-IRF3) signaling pathway. We showed previously that Trex1-deficient cells have reduced mammalian target of rapamycin complex 1 (mTORC1) activity, although the underlying mechanism is unclear. Here, we performed detailed metabolic analysis in Trex1 mice and cells that revealed both cellular and systemic metabolic defects, including reduced mitochondrial respiration and increased glycolysis, energy expenditure, and fat metabolism.

A unique combination of rare mitochondrial ribosomal RNA variants affects the kinetics of complex I assembly.

Mitochondrial DNA (mtDNA) mutations in respiratory complexes subunits contribute to a large spectrum of human diseases. Nonetheless, ribosomal RNA variants remain largely under-investigated from a functional point of view. We here report a unique combination of two rare mitochondrial rRNA variants detected by serendipity in a subject with chronic granulomatous disease and never reported to co-occur within the same mitochondrial haplotype.

Metabolic plasticity maintains proliferation in pyruvate dehydrogenase deficient cells.

Background: Pyruvate dehydrogenase (PDH) occupies a central node of intermediary metabolism, converting pyruvate to acetyl-CoA, thus committing carbon derived from glucose to an aerobic fate rather than an anaerobic one. Rapidly proliferating tissues, including human tumors, use PDH to generate energy and macromolecular precursors. However, evidence supports the benefits of constraining maximal PDH activity under certain contexts, including hypoxia and oncogene-induced cell growth.

Glutamine oxidation maintains the TCA cycle and cell survival during impaired mitochondrial pyruvate transport.

Alternative modes of metabolism enable cells to resist metabolic stress. Inhibiting these compensatory pathways may produce synthetic lethality. We previously demonstrated that glucose deprivation stimulated a pathway in which acetyl-CoA was formed from glutamine downstream of glutamate dehydrogenase (GDH).

Analysis of the mitochondrial proteome of cybrid cells harbouring a truncative mitochondrial DNA mutation in respiratory complex I.

Transmitochondrial cytoplasmic hybrids (cybrids) are well established model systems to reveal the effects of mitochondrial DNA (mtDNA) mutations on cell metabolism excluding the interferences of a different nuclear background. The m.3571insC mutation in the MTND1 gene of respiratory complex I (CI) is commonly detected in oncocytic tumors, in which it causes a severe CI dysfunction leading to an energetic impairment when present above 83% mutant load.

Respiratory complex I is essential to induce a Warburg profile in mitochondria-defective tumor cells.

Background: Aerobic glycolysis, namely the Warburg effect, is the main hallmark of cancer cells. Mitochondrial respiratory dysfunction has been proposed to be one of the major causes for such glycolytic shift. This hypothesis has been revisited as tumors appear to undergo waves of gene regulation during progression, some of which rely on functional mitochondria.

Different mtDNA mutations modify tumor progression in dependence of the degree of respiratory complex I impairment.

Mitochondrial DNA mutations are currently investigated as modifying factors impinging on tumor growth and aggressiveness, having been found in virtually all cancer types and most commonly affecting genes encoding mitochondrial complex I (CI) subunits. However, it is still unclear whether they exert a pro- or anti-tumorigenic effect. We here analyzed the impact of three homoplasmic mtDNA mutations (m.

Genome-wide expression profiling and functional characterization of SCA28 lymphoblastoid cell lines reveal impairment in cell growth and activation of apoptotic pathways.

Background: SCA28 is an autosomal dominant ataxia associated with AFG3L2 gene mutations. We performed a whole genome expression profiling using lymphoblastoid cell lines (LCLs) from four SCA28 patients and six unrelated healthy controls matched for sex and age.

Methods: Gene expression was evaluated with the Affymetrix GeneChip Human Genome U133A 2.

The cytochrome b p.278Y>C mutation causative of a multisystem disorder enhances superoxide production and alters supramolecular interactions of respiratory chain complexes.

Cytochrome b is the only mtDNA-encoded subunit of the mitochondrial complex III (CIII), the functional bottleneck of the respiratory chain. Previously, the human cytochrome b missense mutation m.15579A>G, which substitutes the Tyr 278 with Cys (p.

Cybrid studies establish the causal link between the mtDNA m.3890G>A/MT-ND1 mutation and optic atrophy with bilateral brainstem lesions.

Complex I (CI) deficiency is a frequent cause of mitochondrial disorders and, in most cases, is due to mutations in CI subunit genes encoded by mitochondrial DNA (mtDNA). In this study, we establish the pathogenic role of the heteroplasmic mtDNA m.3890G>A/MT-ND1 (p.

Complex I impairment in mitochondrial diseases and cancer: parallel roads leading to different outcomes.

Respiratory chain complex I (CI) dysfunctions have been recognized as one of the most frequent causes of mitochondrial neuro-muscular disorders. Moreover, latest reports reveal that CI impairment is a major contributing factor in many other pathological processes, including cancer. In fact, energy depletion, oxidative stress and metabolites unbalance are frequently associated with CI functional and structural alterations.

Metabolic consequences of NDUFS4 gene deletion in immortalized mouse embryonic fibroblasts.

Human mitochondrial complex I (CI) deficiency is associated with progressive neurological disorders. To better understand the CI pathomechanism, we here studied how deletion of the CI gene NDUFS4 affects cell metabolism. To this end we compared immortalized mouse embryonic fibroblasts (MEFs) derived from wildtype (wt) and whole-body NDUFS4 knockout (KO) mice.

Mitochondrial complex III stabilizes complex I in the absence of NDUFS4 to provide partial activity.

Mitochondrial complex I (CI) is a multi-subunit enzyme that forms the major entry point of nicotinamide adenine dinucleotide (NADH) electrons into the respiratory chain. Mutations in the NDUFS4 gene, encoding an accessory subunit of this complex, cause a Leigh-like phenotype in humans. To study the nature and penetrance of the CI defect in different tissues, we investigated the role of NDUFS4 in mice with fatal mitochondrial encephalomyopathy, caused by a systemic inactivation of the Ndufs4 gene.

New mitochondrial tRNA HIS mutation in a family with lactic acidosis and stroke-like episodes (MELAS).

We report a new mutation in m.12146 A>G in the mt-tRNA(His) in a family with a remarkable clinical history having different degrees of lactic acidosis and stroke-like episodes. Biochemical measurements of a muscle biopsy established an isolated complex IV deficiency, while similar analysis of fibroblasts showed a combined complex I,III and IV deficiency.

Random point mutations with major effects on protein-coding genes are the driving force behind premature aging in mtDNA mutator mice.

The mtDNA mutator mice have high levels of point mutations and linear deletions of mtDNA causing a progressive respiratory chain dysfunction and a premature aging phenotype. We have now performed molecular analyses to determine the mechanism whereby these mtDNA mutations impair respiratory chain function. We report that mitochondrial protein synthesis is unimpaired in mtDNA mutator mice consistent with the observed minor alterations of steady-state levels of mitochondrial transcripts.

Electrophoresis techniques to investigate defects in oxidative phosphorylation.

Defects in mitochondrial oxidative phosphorylation (OXPHOS) are a frequent cause of severe inherited metabolic disorders and also contribute to aging. The OXPHOS system constitutes five multi-subunit complexes embedded in the mitochondrial inner membrane. Correct function of this system requires proper assembly of the approximately 80 proteins in the complexes, as well as numerous assembly factors.