| 1. |
- Schober, Florian A., et al.
(author)
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The one-carbon pool controls mitochondrial energy metabolism via complex I and iron-sulfur clusters
- 2021
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:8
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Journal article (peer-reviewed)abstract
- Induction of the one-carbon cycle is an early hallmark of mitochondrial dysfunction and cancer metabolism. Vital intermediary steps are localized to mitochondria, but it remains unclear how one-carbon availability connects to mitochondrial function. Here, we show that the one-carbon metabolite and methyl group donor S-adenosylmethionine (SAM) is pivotal for energy metabolism. A gradual decline in mitochondrial SAM (mitoSAM) causes hierarchical defects in fly and mouse, comprising loss of mitoSAM-dependent metabolites and impaired assembly of the oxidative phosphorylation system. Complex I stability and iron-sulfur cluster biosynthesis are directly controlled by mitoSAM levels, while other protein targets are predominantly methylated outside of the organelle before import. The mitoSAM pool follows its cytosolic production, establishing mitochondria as responsive receivers of one-carbon units. Thus, we demonstrate that cellular methylation potential is required for energy metabolism, with direct relevance for pathophysiology, aging, and cancer.
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| 2. |
- Filograna, Roberta, et al.
(author)
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PARKIN is not required to sustain OXPHOS function in adult mammalian tissues
- 2024
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In: npj Parkinson's Disease. - 2373-8057. ; 10
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Journal article (peer-reviewed)abstract
- Loss-of-function variants in the PRKN gene encoding the ubiquitin E3 ligase PARKIN cause autosomal recessive early-onset Parkinson's disease (PD). Extensive in vitro and in vivo studies have reported that PARKIN is involved in multiple pathways of mitochondrial quality control, including mitochondrial degradation and biogenesis. However, these findings are surrounded by substantial controversy due to conflicting experimental data. In addition, the existing PARKIN-deficient mouse models have failed to faithfully recapitulate PD phenotypes. Therefore, we have investigated the mitochondrial role of PARKIN during ageing and in response to stress by employing a series of conditional Parkin knockout mice. We report that PARKIN loss does not affect oxidative phosphorylation (OXPHOS) capacity and mitochondrial DNA (mtDNA) levels in the brain, heart, and skeletal muscle of aged mice. We also demonstrate that PARKIN deficiency does not exacerbate the brain defects and the pro-inflammatory phenotype observed in mice carrying high levels of mtDNA mutations. To rule out compensatory mechanisms activated during embryonic development of Parkin-deficient mice, we generated a mouse model where loss of PARKIN was induced in adult dopaminergic (DA) neurons. Surprisingly, also these mice did not show motor impairment or neurodegeneration, and no major transcriptional changes were found in isolated midbrain DA neurons. Finally, we report a patient with compound heterozygous PRKN pathogenic variants that lacks PARKIN and has developed PD. The PARKIN deficiency did not impair OXPHOS activities or induce mitochondrial pathology in skeletal muscle from the patient. Altogether, our results argue that PARKIN is dispensable for OXPHOS function in adult mammalian tissues.
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| 3. |
- Katsu-Jimenez, Yurika, et al.
(author)
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Absence of TXNIP in Humans Leads to Lactic Acidosis and Low Serum Methionine Linked to Deficient Respiration on Pyruvate
- 2019
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In: Diabetes. - : AMER DIABETES ASSOC. - 0012-1797 .- 1939-327X. ; 68:4, s. 709-723
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Journal article (peer-reviewed)abstract
- Thioredoxin-interacting protein (TXNIP) is an -arrestin that can bind to and inhibit the antioxidant protein thioredoxin (TXN). TXNIP expression is induced by glucose and promotes -cell apoptosis in the pancreas, and deletion of its gene in mouse models protects against diabetes. TXNIP is currently studied as a potential new target for antidiabetic drug therapy. In this study, we describe a family with a mutation in the TXNIP gene leading to nondetectable expression of TXNIP protein. Symptoms of affected family members include lactic acidosis and low serum methionine levels. Using patient-derived TXNIP-deficient fibroblasts and myoblasts, we show that oxidative phosphorylation is impaired in these cells when given glucose and pyruvate but normalized with malate. Isolated mitochondria from these cells appear to have normal respiratory function. The cells also display a transcriptional pattern suggestive of a high basal activation of the Nrf2 transcription factor. We conclude that a complete lack of TXNIP in human is nonlethal and leads to specific metabolic distortions that are, at least in part, linked to a deficient respiration on pyruvate. The results give important insights into the impact of TXNIP in humans and thus help to further advance the development of antidiabetic drugs targeting this protein.
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| 4. |
- Stranneheim, Henrik, et al.
(author)
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Rapid pulsed whole genome sequencing for comprehensive acute diagnostics of inborn errors of metabolism
- 2014
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In: BMC Genomics. - : Springer Science and Business Media LLC. - 1471-2164. ; 15, s. 1090-
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Journal article (peer-reviewed)abstract
- Background: Massively parallel DNA sequencing (MPS) has the potential to revolutionize diagnostics, in particular for monogenic disorders. Inborn errors of metabolism (IEM) constitute a large group of monogenic disorders with highly variable clinical presentation, often with acute, nonspecific initial symptoms. In many cases irreversible damage can be reduced by initiation of specific treatment, provided that a correct molecular diagnosis can be rapidly obtained. MPS thus has the potential to significantly improve both diagnostics and outcome for affected patients in this highly specialized area of medicine. Results: We have developed a conceptually novel approach for acute MPS, by analysing pulsed whole genome sequence data in real time, using automated analysis combined with data reduction and parallelization. We applied this novel methodology to an in-house developed customized work flow enabling clinical-grade analysis of all IEM with a known genetic basis, represented by a database containing 474 disease genes which is continuously updated. As proof-of-concept, two patients were retrospectively analysed in whom diagnostics had previously been performed by conventional methods. The correct disease-causing mutations were identified and presented to the clinical team after 15 and 18 hours from start of sequencing, respectively. With this information available, correct treatment would have been possible significantly sooner, likely improving outcome. Conclusions: We have adapted MPS to fit into the dynamic, multidisciplinary work-flow of acute metabolic medicine. As the extent of irreversible damage in patients with IEM often correlates with timing and accuracy of management in early, critical disease stages, our novel methodology is predicted to improve patient outcome. All procedures have been designed such that they can be implemented in any technical setting and to any genetic disease area. The strategy conforms to international guidelines for clinical MPS, as only validated disease genes are investigated and as clinical specialists take responsibility for translation of results. As follow-up in patients without any known IEM, filters can be lifted and the full genome investigated, after genetic counselling and informed consent.
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| 5. |
- Tegelberg, Saara, et al.
(author)
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Respiratory chain complex III deficiency due to mutated BCS1L : A novel phenotype with encephalomyopathy, partially phenocopied in a Bcs1l mutant mouse model
- 2017
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In: Orphanet Journal of Rare Diseases. - : Springer Science and Business Media LLC. - 1750-1172. ; 12:1
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Journal article (peer-reviewed)abstract
- Background: Mitochondrial diseases due to defective respiratory chain complex III (CIII) are relatively uncommon. The assembly of the eleven-subunit CIII is completed by the insertion of the Rieske iron-sulfur protein, a process for which BCS1L protein is indispensable. Mutations in the BCS1L gene constitute the most common diagnosed cause of CIII deficiency, and the phenotypic spectrum arising from mutations in this gene is wide. Results: A case of CIII deficiency was investigated in depth to assess respiratory chain function and assembly, and brain, skeletal muscle and liver histology. Exome sequencing was performed to search for the causative mutation(s). The patient's platelets and muscle mitochondria showed respiration defects and defective assembly of CIII was detected in fibroblast mitochondria. The patient was compound heterozygous for two novel mutations in BCS1L, c.306A > T and c.399delA. In the cerebral cortex a specific pattern of astrogliosis and widespread loss of microglia was observed. Further analysis showed loss of Kupffer cells in the liver. These changes were not found in infants suffering from GRACILE syndrome, the most severe BCS1L-related disorder causing early postnatal mortality, but were partially corroborated in a knock-in mouse model of BCS1L deficiency. Conclusions: We describe two novel compound heterozygous mutations in BCS1L causing CIII deficiency. The pathogenicity of one of the mutations was unexpected and points to the importance of combining next generation sequencing with a biochemical approach when investigating these patients. We further show novel manifestations in brain, skeletal muscle and liver, including abnormality in specialized resident macrophages (microglia and Kupffer cells). These novel phenotypes forward our understanding of CIII deficiencies caused by BCS1L mutations.
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| 6. |
- Edgar, Daniel, et al.
(author)
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Random point mutations with major effects on protein-coding genes are the driving force behind premature aging in mtDNA mutator mice.
- 2009
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In: Cell metabolism. - : Elsevier BV. - 1932-7420 .- 1550-4131. ; 10:2, s. 131-8
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Journal article (peer-reviewed)abstract
- 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. These findings refute recent claims that circular mtDNA molecules with large deletions are driving the premature aging phenotype. We further show that the stability of several respiratory chain complexes is severely impaired despite normal synthesis of the corresponding mtDNA-encoded subunits. Our findings reveal a mechanism for induction of aging phenotypes by demonstrating a causative role for amino acid substitutions in mtDNA-encoded respiratory chain subunits, which, in turn, leads to decreased stability of the respiratory chain complexes and respiratory chain deficiency.
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| 7. |
- Rosenhahn, Erik, et al.
(author)
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Bi-allelic loss-of-function variants in PPFIBP1 cause a neurodevelopmental disorder with microcephaly, epilepsy, and periventricular calcifications
- 2022
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In: American Journal of Human Genetics. - : Cell Press. - 0002-9297 .- 1537-6605. ; 109:8, s. 1421-1435
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Journal article (peer-reviewed)abstract
- PPFIBP1 encodes for the liprin-β1 protein, which has been shown to play a role in neuronal outgrowth and synapse formation in Drosophila melanogaster. By exome and genome sequencing, we detected nine ultra-rare homozygous loss-of-function variants in 16 individuals from 12 unrelated families. The individuals presented with moderate to profound developmental delay, often refractory early-onset epilepsy, and progressive microcephaly. Further common clinical findings included muscular hyper- and hypotonia, spasticity, failure to thrive and short stature, feeding difficulties, impaired vision, and congenital heart defects. Neuroimaging revealed abnormalities of brain morphology with leukoencephalopathy, ventriculomegaly, cortical abnormalities, and intracranial periventricular calcifications as major features. In a fetus with intracranial calcifications, we identified a rare homozygous missense variant that by structural analysis was predicted to disturb the topology of the SAM domain region that is essential for protein-protein interaction. For further insight into the effects of PPFIBP1 loss of function, we performed automated behavioral phenotyping of a Caenorhabditis elegans PPFIBP1/hlb-1 knockout model, which revealed defects in spontaneous and light-induced behavior and confirmed resistance to the acetylcholinesterase inhibitor aldicarb, suggesting a defect in the neuronal presynaptic zone. In conclusion, we establish bi-allelic loss-of-function variants in PPFIBP1 as a cause of an autosomal recessive severe neurodevelopmental disorder with early-onset epilepsy, microcephaly, and periventricular calcifications.
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| 8. |
- Ruzzenente, Benedetta, et al.
(author)
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LRPPRC is necessary for polyadenylation and coordination of translation of mitochondrial mRNAs.
- 2012
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In: The EMBO journal. - : Wiley. - 1460-2075 .- 0261-4189. ; 31:2, s. 443-56
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Journal article (peer-reviewed)abstract
- Regulation of mtDNA expression is critical for maintaining cellular energy homeostasis and may, in principle, occur at many different levels. The leucine-rich pentatricopeptide repeat containing (LRPPRC) protein regulates mitochondrial mRNA stability and an amino-acid substitution of this protein causes the French-Canadian type of Leigh syndrome (LSFC), a neurodegenerative disorder characterized by complex IV deficiency. We have generated conditional Lrpprc knockout mice and show here that the gene is essential for embryonic development. Tissue-specific disruption of Lrpprc in heart causes mitochondrial cardiomyopathy with drastic reduction in steady-state levels of most mitochondrial mRNAs. LRPPRC forms an RNA-dependent protein complex that is necessary for maintaining a pool of non-translated mRNAs in mammalian mitochondria. Loss of LRPPRC does not only decrease mRNA stability, but also leads to loss of mRNA polyadenylation and the appearance of aberrant mitochondrial translation. The translation pattern without the presence of LRPPRC is misregulated with excessive translation of some transcripts and no translation of others. Our findings point to the existence of an elaborate machinery that regulates mammalian mtDNA expression at the post-transcriptional level.
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| 9. |
- Wredenberg, Anna
(author)
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Mitochondrial dysfunction in ageing and degenerative disease
- 2007
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Doctoral thesis (other academic/artistic)abstract
- The cytoplasm of eukaryotic cells contains a dynamic network of double-membraned organelles, called mitochondria, which perform the process of oxidative phosphorylation (OXPHOS) that provides cellular energy in the form of ATP. The respiratory chain creates an electrochemical gradient across the inner mitochondrial membrane, which drives ATP synthesis by the ATP synthase. Mitochondria are indispensable for normal cell function and survival, and dysfunction of the OXPHOS system can lead to a variety of disease syndromes, collectively termed mitochondrial encephalomyopathies. Mitochondrial dysfunction has also been proposed to be involved in age-associated diseases such as diabetes mellitus, heart disease and neurodegeneration, as well as in the ageing process itself. Tissues with high metabolism seem to be particularly vulnerable to mitochondrial dysfunction and myopathy is one of the common phenotypes in mitochondrial disorders. However, the pathophysiological mechanisms linking respiratory chain deficiency to the various phenotypic manifestations are poorly understood. We therefore generated a mouse model for mitochondrial myopathy by tissue-specific disruption of the nuclear gene encoding mitochondrial transcription factor A (TFAM). These myopathy mice develop a progressive respiratory chain dysfunction in skeletal muscle with typical morphological changes consistent with mitochondrial myopathy. Surprisingly the overall mitochondrial ATP production rate was close to normal in the knockout muscles, likely due to the compensatory increase of mitochondrial mass in the affected muscles. Thus, other factors besides ATP deficiency are likely of importance in mitochondrial myopathy. There is a large number of correlative studies suggesting that mitochondrial dysfunction in skeletal muscle is causing the peripheral insulin resistance observed in patients with diabetes mellitus type 2 (DM2). Unexpectedly, the myopathy mice exhibited normal insulin sensitivity and increased glucose uptake in skeletal muscle, suggesting that reduced respiratory chain function in peripheral tissues may be protective against DM2. The mitochondrial theory of aging proposes that oxidative damage to mitochondrial DNA (mtDNA) leads to mutations and impaired respiratory chain function, which in turn, increases reactive oxygen species (ROS) production. ROS have been suggested to induce oxidative damage to various molecules of the cell and thereby cause the progressive decline seen in ageing. We generated mice expressing a proof-reading-deficient version of the mtDNA polymerase gamma. These mtDNA mutator mice accumulated mtDNA mutations at an increased rate and developed a progressive respiratory chain deficiency. They also developed premature ageing phenotypes and exhibited a reduced lifespan, supporting the suggestion of a causative link between mitochondrial dysfunction and ageing. However, we found no differences in ROS production, no increased expression of ROS scavenging enzymes, and no or minor changes in levels of oxidative damage in cell lines and tissues from the mtDNA mutator mice. We instead propose that the accumulation of mtDNA mutations beyond a critical threshold leads to bioenergetic failure and loss of vital cells. This cell loss caused by respiratory chain dysfunction may lead to reduced organ function and eventually organ failure, giving rise to age-associated disease and important ageing phenotypes.
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