bims-mitdis Biomed News
on Mitochondrial disorders
Issue of 2021‒09‒05
twenty-five papers selected by
Catalina Vasilescu
University of Helsinki

  1. J Cell Biol. 2021 Nov 01. pii: e202104073. [Epub ahead of print]220(11):
      Defects in autophagy cause problems in metabolism, development, and disease. The autophagic clearance of mitochondria, mitophagy, is impaired by the loss of Vps13D. Here, we discover that Vps13D regulates mitophagy in a pathway that depends on the core autophagy machinery by regulating Atg8a and ubiquitin localization. This process is Pink1 dependent, with loss of pink1 having similar autophagy and mitochondrial defects as loss of vps13d. The role of Pink1 has largely been studied in tandem with Park/Parkin, an E3 ubiquitin ligase that is widely considered to be crucial in Pink1-dependent mitophagy. Surprisingly, we find that loss of park does not exhibit the same autophagy and mitochondrial deficiencies as vps13d and pink1 mutant cells and contributes to mitochondrial clearance through a pathway that is parallel to vps13d. These findings provide a Park-independent pathway for Pink1-regulated mitophagy and help to explain how Vps13D regulates autophagy and mitochondrial morphology and contributes to neurodegenerative diseases.
  2. Life Sci Alliance. 2021 Nov;pii: e202101034. [Epub ahead of print]4(11):
      Mitochondrial transcription factor A (TFAM) is compacting mitochondrial DNA (dmtDNA) into nucleoids and directly controls mtDNA copy number. Here, we show that the TFAM-to-mtDNA ratio is critical for maintaining normal mtDNA expression in different mouse tissues. Moderately increased TFAM protein levels increase mtDNA copy number but a normal TFAM-to-mtDNA ratio is maintained resulting in unaltered mtDNA expression and normal whole animal metabolism. Mice ubiquitously expressing very high TFAM levels develop pathology leading to deficient oxidative phosphorylation (OXPHOS) and early postnatal lethality. The TFAM-to-mtDNA ratio varies widely between tissues in these mice and is very high in skeletal muscle leading to strong repression of mtDNA expression and OXPHOS deficiency. In the heart, increased mtDNA copy number results in a near normal TFAM-to-mtDNA ratio and maintained OXPHOS capacity. In liver, induction of LONP1 protease and mitochondrial RNA polymerase expression counteracts the silencing effect of high TFAM levels. TFAM thus acts as a general repressor of mtDNA expression and this effect can be counterbalanced by tissue-specific expression of regulatory factors.
  3. Biol Cell. 2021 Aug 31.
      Mitochondria are dynamic organelles playing essential metabolic and signaling functions in cells. Their ultrastructure has been largely investigated with electron microscopy (EM) techniques. Super-resolution microscopy approaches such as direct stochastic optical reconstruction microscopy (dSTORM) provide a fluorescent-based, quantitative alternative to EM. However, dSTORM is mainly used to image integral mitochondrial proteins, and there is little or no information on proteins transiently present at this compartment. Here, we first benchmark the power of dSTORM to resolve protein proximities on individual mitochondrial subcompartments, coupled to Geo-coPositioning System (GcoPS) to quantify the degree of protein colocalization. With our dSTORM/GcoPS method, we then analyze the submitochondrial distribution of the cancer-related Aurora kinase A/AURKA, a protein localized at various subcellular locations including mitochondria. We show that dSTORM provides sufficient spatial resolution to detect a large pool of endogenous AURKA within the matrix, and we also uncover a second pool of the kinase at the Outer Mitochondrial Membrane (OMM). We conclude by demonstrating that an aldehyde-based fixation allows for a more specific detection of the OMM pool of AURKA. Our results indicate that dSTORM coupled to GcoPS colocalization analysis is a suitable approach to explore the compartmentalization of non-integral mitochondrial proteins as AURKA, in a qualitative and quantitative manner. This method also opens up the possibility of analyzing the proximity between AURKA and its multiple mitochondrial partners with exquisite spatial resolution, thereby allowing novel insights into the mitochondrial functions controlled by AURKA. This article is protected by copyright. All rights reserved.
  4. Development. 2021 Sep 02. pii: dev.199477. [Epub ahead of print]
      The STAT3 transcription factor, acting both in the nucleus and mitochondria, maintains embryonic stem cell pluripotency and promotes their proliferation. In this work, using zebrafish, we determined in vivo that mitochondrial STAT3 regulates mtDNA transcription in embryonic and larval stem cell niches and that this activity affects their proliferation rates. As a result, we demonstrated that STAT3 import inside mitochondria requires Y705 phosphorylation by Jak, while its mitochondrial transcriptional activity, as well as its effect on proliferation, depends on the MAPK target S727. These data were confirmed using mouse embryonic stem cells: while the Y705 mutated STAT3 cannot enter mitochondria, the S727 mutation does not affect the import in the organelle and is responsible for STAT3-dependent mitochondrial transcription. Surprisingly, STAT3-dependent increase of mitochondrial transcription seems independent from STAT3 binding to STAT3 responsive elements. Finally, loss of function experiments, with chemical inhibition of the JAK/STAT3 pathway or genetic ablation of stat3 gene, demonstrated that STAT3 is also required for cell proliferation in the intestine of zebrafish.
    Keywords:  ESC; STAT3; mitochondria; transcription; zebrafish
  5. Nat Commun. 2021 Sep 02. 12(1): 5241
      Individual induced pluripotent stem cells (iPSCs) show considerable phenotypic heterogeneity, but the reasons for this are not fully understood. Comprehensively analysing the mitochondrial genome (mtDNA) in 146 iPSC and fibroblast lines from 151 donors, we show that most age-related fibroblast mtDNA mutations are lost during reprogramming. However, iPSC-specific mutations are seen in 76.6% (108/141) of iPSC lines at a mutation rate of 8.62 × 10-5/base pair. The mutations observed in iPSC lines affect a higher proportion of mtDNA molecules, favouring non-synonymous protein-coding and tRNA variants, including known disease-causing mutations. Analysing 11,538 single cells shows stable heteroplasmy in sub-clones derived from the original donor during differentiation, with mtDNA variants influencing the expression of key genes involved in mitochondrial metabolism and epidermal cell differentiation. Thus, the dynamic mtDNA landscape contributes to the heterogeneity of human iPSCs and should be considered when using reprogrammed cells experimentally or as a therapy.
  6. Elife. 2021 Sep 01. pii: e68610. [Epub ahead of print]10
      Most age-related human diseases are accompanied by a decline in cellular organelle integrity, including impaired lysosomal proteostasis and defective mitochondrial oxidative phosphorylation. An open question, however, is the degree to which inherited variation in or near genes encoding each organelle contributes to age-related disease pathogenesis. Here, we evaluate if genetic loci encoding organelle proteomes confer greater-than-expected age-related disease risk. As mitochondrial dysfunction is a 'hallmark' of aging, we begin by assessing nuclear and mitochondrial DNA loci near genes encoding the mitochondrial proteome and surprisingly observe a lack of enrichment across 24 age-related traits. Within nine other organelles, we find no enrichment with one exception: the nucleus, where enrichment emanates from nuclear transcription factors. In agreement, we find that genes encoding several organelles tend to be 'haplosufficient', while we observe strong purifying selection against heterozygous protein-truncating variants impacting the nucleus. Our work identifies common variation near transcription factors as having outsize influence on age-related trait risk, motivating future efforts to determine if and how this inherited variation then contributes to observed age-related organelle deterioration.
    Keywords:  genetics; genomics; human
  7. Bio Protoc. 2021 Aug 05. 11(15): e4110
      Mitochondrial ribosomes (mitoribosomes) perform protein synthesis inside mitochondria, the organelles responsible for energy conversion and adenosine triphosphate (ATP) production in eukaryotic cells. To investigate their functions and structures, large-scale purification of intact mitoribosomes from mitochondria-rich animal tissues or HEK cells have been developed. However, the fast purification of mitoribosomes anchored to the mitochondrial inner membrane in complex with the Oxa1L translocase remains particularly challenging. Herein, we present a protocol recently developed and modified in our lab that provides details for the efficient isolation of intact mitoribosomes with its translocase Oxa1L. We combined the cell culture of PDE12-/- or wild-type HEK293 cell lines with the isolation of mitochondria and the purification steps used for the biochemical and structural studies of mitoribosomes and Oxa1L. Graphic abstract: Schematic procedure for the purification of mitoribosomes from HEK cells. The protocol described herein includes two main sections: 1) isolation of mitochondria from HEK cells; and 2) purification of mitoribosome-Oxa1L from mitochondria. RB: Resuspension Buffer (see Recipes) (Created with
    Keywords:  Biochemistry; Cryo-EM; Mitochondria; Mitoribosome; Oxa1L; Ribosome purification
  8. Hum Mutat. 2021 Sep 01.
      Preterm birth (PTB), or birth that occurs earlier than 37 weeks of gestational age, is a major contributor to infant mortality and neonatal hospitalization. Mutations in the mitochondrial genome (mtDNA) have been linked to various rare mitochondrial disorders, and may be a contributing factor in PTB given that maternal genetic factors have been strongly linked to PTB. However, to date, no study has found a conclusive connection between a particular mtDNA variant and PTB. Given the high mtDNA copy number per cell, an automated pipeline was developed for detecting mtDNA variants using low-pass whole genome sequencing (lcWGS) data. The pipeline was first validated against samples of known heteroplasmy, and then applied to 929 samples from a PTB cohort from diverse ethnic backgrounds with an average gestational age of 27.18 weeks (range: 21-30). Our new pipeline successfully identified haplogroups and a large number of mtDNA variants in this large PTB cohort, including 8 samples carrying known pathogenic variants and 47 samples carrying rare mtDNA variants. These results confirm that lcWGS can be utilized to reliably identify mtDNA variants. These mtDNA variants may make a contribution toward preterm birth in a small proportion of live births. This article is protected by copyright. All rights reserved.
    Keywords:  Preterm birth; human genetics; low coverage whole genome sequencing; mitochondrial disease; mitochondrial genome
  9. J Biol Chem. 2021 Aug 27. pii: S0021-9258(21)00935-2. [Epub ahead of print] 101134
      The mitochondrial matrix protease LONP1 is an essential part of the organellar protein quality control system. LONP1 has been shown to be involved in respiration control and apoptosis. Furthermore, a reduction in LONP1 level correlates with ageing. Up to now, the effects of a LONP1 defect were mostly studied by utilizing transient, siRNA-mediated knockdown approaches. We generated a new cellular model system for studying the impact of LONP1 on mitochondrial protein homeostasis by a CRISPR/Cas-mediated genetic knockdown (gKD). These cells show a stable reduction of LONP1 along with a mild phenotype characterized by absent morphological differences and only small negative effects on mitochondrial functions under normal culture conditions. To assess the consequences of a permanent LONP1 depletion on the mitochondrial proteome, we analyzed the alterations of protein levels by quantitative mass spectrometry, demonstrating small adaptive changes, in particular with respect to mitochondrial protein biogenesis. In an additional proteomic analysis, we determined the temperature-dependent aggregation behavior of mitochondrial proteins and its dependence on a reduction of LONP1 activity, demonstrating the important role of the protease for mitochondrial protein homeostasis in mammalian cells. We identified a significant number of mitochondrial proteins that are affected by LONP1 activity especially with respect to their stress-induced solubility. Taken together, our results suggest a very good applicability of the LONP1 gKD cell line as a model system for human ageing processes.
    Keywords:  Human; LONP1 protease; cell biology; mitochondria; protein aggregation; proteostasis
  10. Neuromuscul Disord. 2021 Jul 18. pii: S0960-8966(21)00188-7. [Epub ahead of print]
      Multiple acyl-CoA dehydrogenase deficiency (MADD) is a heterogeneous group of inborn error of metabolic disease affecting the oxidation of fatty acids and amino acids, and choline metabolism. Genes involved in electrons transfer to the mitochondrial respiratory chain typically induce MADD. Recently, FLAD1, which encodes flavin adenine dinucleotide synthase, has also been reported as a cause of MADD. Here, we present a case of a 28-month girl with progressive weakness in facial and bulbar muscle. She has been suffering from feeding difficulty and recurrent respiratory distress. Lipid storage myopathy was evident from muscle biopsy. Furthermore, whole exome sequencing identified homozygous variant of c.745C > T (p.Arg249*) in FLAD1, confirming the diagnosis of FLAD1-related MADD. The patient showed improvements in her symptoms and exhibited catch-up growth following the supplementation of riboflavin. Lipid storage myopathy with FLAD1-related MADD is potentially treatable. Therefore, we should have high clinical suspicion, even though the diagnosis is challenging.
    Keywords:  FLAD1; Multiple acyl-CoA dehydrogenase deficiency; Riboflavin: Vacuolar myopathy
  11. Am J Physiol Cell Physiol. 2021 09 01.
      Mitochondria are dynamic organelles that differ significantly in their morphologies across cell types, reflecting specific cellular needs and stages in development. Despite the wide biological significance in disease and health, delineating mitochondrial morphologies in complex systems remains challenging. Here, we present the Mitochondrial Cellular Phenotype (MitoCellPhe) tool developed for quantifying mitochondrial morphologies and demonstrate its utility in delineating differences in mitochondrial morphologies in a human fibroblast and human induced pluripotent stem cell (hiPSC) line. MitoCellPhe generates 24 parameters, allowing for a comprehensive analysis of mitochondrial structures and importantly allows for quantification to be performed on mitochondria in images containing single cells or clusters of cells. With this tool, we were able to validate previous findings that show networks of mitochondria in healthy fibroblast cell lines and a more fragmented morphology in hiPSCs. Using images generated from control and diseased fibroblasts and hiPSCs, we also demonstrate the efficacy of the toolset in delineating differences in morphologies between healthy and the diseased state in both stem cell (hiPSC) and differentiated fibroblast cells. Our results demonstrate that MitoCellPhe enables high-throughput, sensitive, detailed and quantitative mitochondrial morphological assessment and thus enables better biological insights into mitochondrial dynamics in health and disease.
    Keywords:  mitochondria; morphology; networks; stem cells; structure
  12. Elife. 2021 Aug 31. pii: e69312. [Epub ahead of print]10
      Ca2+ entry into mitochondria is through the mitochondrial calcium uniporter complex (MCUcx), a Ca2+-selective channel composed of five subunit types. Two MCUcx subunits (MCU and EMRE) span the inner mitochondrial membrane, while three Ca2+-regulatory subunits (MICU1, MICU2 and MICU3) reside in the intermembrane space. Here we provide rigorous analysis of Ca2+ and Na+ fluxes via MCUcx in intact isolated mitochondria to understand the function of MICU subunits. We also perform direct patch clamp recordings of macroscopic and single MCUcx currents to gain further mechanistic insight. This comprehensive analysis shows that the MCUcx pore, composed of the EMRE and MCU subunits, is not occluded nor plugged by MICUs during the absence or presence of extramitochondrial Ca2+ as has been widely reported. Instead, MICUs potentiate activity of MCUcx as extramitochondrial Ca2+ is elevated. MICUs achieve this by modifying the gating properties of MCUcx allowing it to spend more time in the open state.
    Keywords:  molecular biophysics; mouse; structural biology
  13. Neurol Sci. 2021 Sep 03.
      Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder that affects 1% of the population worldwide. Etiology of PD is likely to be multi-factorial such as protein misfolding, mitochondrial dysfunction, oxidative stress, and neuroinflammation that contributes to the pathology of Parkinson's disease (PD), numerous studies have shown that mitochondrial dysfunction may play a key role in the dopaminergic neuronal loss. In multiple ways, the two most important are the activation of neuroinflammation and mitochondrial dysfunction, while mitochondrial dysfunction could cause neuroinflammation and vice versa. Thus, the mitochondrial proteins are the highly promising target for the development of PD. However, the limited amount of dopaminergic neurons prevented the detailed investigation of Parkinson's disease with regard to mitochondrial dysfunction. Both genetic and environmental factors are also associated with mitochondrial dysfunction and PD pathogenesis. The induction of PD by neurotoxins that inhibit mitochondrial complex I provide direct evidence linking mitochondrial dysfunction to PD. A decrease of mitochondrial complex I activity is observed in PD brain and in neurotoxin- or genetic factor-induced in vitro and in vivo models. Moreover, PINK1, Parkin, DJ-1 and LRRK2 mitochondrial PD gene products have important roles in mitophagy, a cellular process that clear damaged mitochondria. This review paper would discuss the evidence for the mitochondrial dysfunction and neuroinflammation in PD.
    Keywords:  Mitochondrial dysfunction; Mitochondrial proteins; Neuroinflammation; Parkinson’s disease
  14. DNA Repair (Amst). 2021 Aug 17. pii: S1568-7864(21)00168-3. [Epub ahead of print]107 103212
      Several mutations in the gene for the mitochondrial single stranded DNA binding protein (SSBP1) have recently been implicated in human disease, but initial reports are insufficient to explain the molecular mechanism of disease, including the possible role of SSBP1 heterotetramers in heterozygous patients. Here we employed molecular simulations to model the dynamics of wild type and 31 variant SSBP1 tetramer systems, including 7 variant homotetramer and 24 representative heterotetramer systems. Our simulations indicate that all variants are stable and most have stronger intermonomer interactions, reduced solvent accessible surface areas, and a net loss of positive surface charge. We then used structural alignments and phosphate binding simulations to predict DNA binding surfaces on SSBP1. Our models suggest that nearly the entire surface of SSBP1, excluding flexible loops and protruding helices, is available for DNA binding, and we observed several potential DNA binding hotspots. Changes to the protein surface in variant SSBP1 tetramers potentially alter anchor points or wrapping paths, rather than abolishing binding altogether. Overall, our findings disqualify tetramer destabilization or gross disruption of DNA binding as mechanisms of disease. Instead, they are consistent with subtle changes to DNA binding, wrapping, or release that cause rare but consequential failures of mtDNA maintenance, which, in turn, are consistent with the late onset of disease in most of the reported SSBP1 cases.
    Keywords:  Human disease variants; Mitochondrial DNA replication; Molecular modeling; Single stranded DNA binding protein; mtSSB
  15. J Biol Chem. 2021 Aug 27. pii: S0021-9258(21)00936-4. [Epub ahead of print] 101135
      Yeast is a facultative anaerobe and uses diverse electron acceptors to maintain redox-regulated import of cysteine-rich precursors via the mitochondrial intermembrane space assembly (MIA) pathway. With the growing diversity of substrates utilizing the MIA pathway, understanding the capacity of the intermembrane space (IMS) to handle different types of stress is crucial. We used mass spectrometry to identify additional proteins that interacted with the sulfhydryl oxidase Erv1 of the MIA pathway. Aim32, a thioredoxin-like [2Fe-2S] ferredoxin protein, was identified as an Erv1 binding protein. Detailed localization studies showed that Aim32 resided in both the mitochondrial matrix and IMS. Aim32 interacted with additional proteins including redox protein Osm1 and protein import components Tim17, Tim23, and Tim22. Deletion of Aim32 or mutation of conserved cysteine residues that coordinate the Fe-S center in Aim32 resulted in an increased accumulation of proteins with aberrant disulfide linkages. In addition, the steady-state level of assembled TIM22, TIM23, and Oxa1 protein import complexes was decreased. Aim32 also bound to several mitochondrial proteins under nonreducing conditions, suggesting a function in maintaining the redox status of proteins by potentially targeting cysteine residues that may be sensitive to oxidation. Finally, Aim32 was essential for growth in conditions of stress such as elevated temperature and hydroxyurea (HU), and under anaerobic conditions. These studies suggest that the Fe-S protein Aim32 has a potential role in general redox homeostasis in the matrix and IMS. Thus, Aim32 may be poised as a sensor or regulator in quality control for a broad range of mitochondrial proteins.
    Keywords:  disulfide; mitochondria; mitochondrial transport; protein import; redox regulation; thiol; thioredoxin
  16. Free Radic Biol Med. 2021 Aug 26. pii: S0891-5849(21)00692-4. [Epub ahead of print]175 18-27
      Iron is an essential nutrient that forms cofactors required for the activity of hundreds of cellular proteins. However, iron can be toxic and must be precisely managed. Poly r(C) binding protein 1 (PCBP1) is an essential, multifunctional protein that binds both iron and nucleic acids, regulating the fate of both. As an iron chaperone, PCBP1 binds cytosolic iron and delivers it to iron enzymes for activation and to ferritin for storage. Mice deleted for PCBP1 in the liver exhibit dysregulated iron balance, with lower levels of liver iron stores and iron enzymes, but higher levels of chemically-reactive iron. Unchaperoned iron triggers the formation of reactive oxygen species, leading to lipid peroxidation and ferroptotic cell death. Hepatic PCBP1 deletion produces chronic liver disease in mice, with steatosis, triglyceride accumulation, and elevated plasma ALT levels. Human and mouse models of fatty liver disease are associated with mitochondrial dysfunction. Here we show that, although deletion of PCBP1 does not affect mitochondrial iron balance, it does affect mitochondrial function. PCBP1 deletion affected mitochondrial morphology and reduced levels of respiratory complexes II and IV, oxygen consumption, and ATP production. Depletion of mitochondrial lipids cardiolipin and coenzyme Q, along with reduction of mitochondrial oxygen consumption, were the first manifestations of mitochondrial dysfunction. Although dietary supplementation with vitamin E ameliorated the liver disease in mice with hepatic PCBP1 deletion, supplementation with coenzyme Q was required to fully restore mitochondrial lipids and function. In conclusion, our studies indicate that mitochondrial function can be restored in livers subjected to ongoing oxidative damage from unchaperoned iron by supplementation with coenzyme Q, a mitochondrial lipid essential for respiration that also functions as a lipophilic radical-trapping agent.
    Keywords:  Cardiolipin; Coenzyme Q; Ferroptosis; NAFLD; NASH; Oxidative stress; PCBP1; Steatosis
  17. BMC Bioinformatics. 2021 Sep 01. 22(1): 417
      BACKGROUND: Variation in mitochondrial DNA (mtDNA) identified by genotyping microarrays or by sequencing only the hypervariable regions of the genome may be insufficient to reliably assign mitochondrial genomes to phylogenetic lineages or haplogroups. This lack of resolution can limit functional and clinical interpretation of a substantial body of existing mtDNA data. To address this limitation, we developed and evaluated a large, curated reference alignment of complete mtDNA sequences as part of a pipeline for imputing missing mtDNA single nucleotide variants (mtSNVs). We call our reference alignment and pipeline MitoImpute.RESULTS: We aligned the sequences of 36,960 complete human mitochondrial genomes downloaded from GenBank, filtered and controlled for quality. These sequences were reformatted for use in imputation software, IMPUTE2. We assessed the imputation accuracy of MitoImpute by measuring haplogroup and genotype concordance in data from the 1000 Genomes Project and the Alzheimer's Disease Neuroimaging Initiative (ADNI). The mean improvement of haplogroup assignment in the 1000 Genomes samples was 42.7% (Matthew's correlation coefficient = 0.64). In the ADNI cohort, we imputed missing single nucleotide variants.
    CONCLUSION: These results show that our reference alignment and panel can be used to impute missing mtSNVs in existing data obtained from using microarrays, thereby broadening the scope of functional and clinical investigation of mtDNA. This improvement may be particularly useful in studies where participants have been recruited over time and mtDNA data obtained using different methods, enabling better integration of early data collected using less accurate methods with more recent sequence data.
    Keywords:  Imputation; Mitochondrial DNA; Reference panel
  18. Elife. 2021 09 01. pii: e63453. [Epub ahead of print]10
      Mitochondrial activity determines aging rate and the onset of chronic diseases. The mitochondrial permeability transition pore (mPTP) is a pathological pore in the inner mitochondrial membrane thought to be composed of the F-ATP synthase (complex V). OSCP, a subunit of F-ATP synthase, helps protect against mPTP formation. How the destabilization of OSCP may contribute to aging, however, is unclear. We have found that loss OSCP in the nematode Caenorhabditis elegans initiates the mPTP and shortens lifespan specifically during adulthood, in part via initiation of the mitochondrial unfolded protein response (UPRmt). Pharmacological or genetic inhibition of the mPTP inhibits the UPRmt and restores normal lifespan. Loss of the putative pore-forming component of F-ATP synthase extends adult lifespan, suggesting that the mPTP normally promotes aging. Our findings reveal how an mPTP/UPRmt nexus may contribute to aging and age-related diseases and how inhibition of the UPRmt may be protective under certain conditions.
    Keywords:  C. elegans; F-ATP synthase; aging; c-subunit; cell biology; mitochondrial permeability transition pore; mitochondrial unfolded protein response; oscp/atp-3
  19. Front Physiol. 2021 ;12 693734
      Leigh syndrome is a rare, complex, and incurable early onset (typically infant or early childhood) mitochondrial disorder with both phenotypic and genetic heterogeneity. The heterogeneous nature of this disorder, based in part on the complexity of mitochondrial genetics, and the significant interactions between the nuclear and mitochondrial genomes has made it particularly challenging to research and develop therapies. This review article discusses some of the advances that have been made in the field to date. While the prognosis is poor with no current substantial treatment options, multiple studies are underway to understand the etiology, pathogenesis, and pathophysiology of Leigh syndrome. With advances in available research tools leading to a better understanding of the mitochondria in health and disease, there is hope for novel treatment options in the future.
    Keywords:  Leigh syndrome; mitochondria; mitochondrial DNA; mitochondrial genetics; respiratory chain complex
  20. Cell Discov. 2020 Sep 01. 6(1): 59
      Mitochondrial morphology and function are crucial for tissue homeostasis, such as for skeletal development, but the cellular and molecular mechanisms remain unclear. Here, we provide evidence that regulator of G-protein signaling 12 (RGS12) is present in the mitochondria of primary chondrocytes and cartilage tissues. Deletion of RGS12 in type II collagen-positive cells led to a significant decrease in mitochondrial number, membrane potential, and oxidative phosphorylation function. Mechanistically, RGS12 promoted the function of ATP5A as an enhancer of tyrosine phosphorylation. Mice with RGS12 deficiency in the chondrocyte lineage showed serious body retardation, decreased bone mass, and chondrocyte apoptosis due to the defective activity of ATP synthase. To our knowledge, this is the first report that RGS12 is required for maintaining the function of mitochondria, which may allow it to orchestrate responses to cellular homeostasis.
  21. Cell Rep Med. 2021 Aug 17. 2(8): 100370
      LPIN1 mutations are responsible for inherited recurrent rhabdomyolysis, a life-threatening condition with no efficient therapeutic intervention. Here, we conduct a bedside-to-bench-and-back investigation to study the pathophysiology of lipin1 deficiency. We find that lipin1-deficient myoblasts exhibit a reduction in phosphatidylinositol-3-phosphate close to autophagosomes and late endosomes that prevents the recruitment of the GTPase Armus, locks Rab7 in the active state, inhibits vesicle clearance by fusion with lysosomes, and alters their positioning and function. Oxidized mitochondrial DNA accumulates in late endosomes, where it activates Toll-like receptor 9 (TLR9) and triggers inflammatory signaling and caspase-dependent myolysis. Hydroxychloroquine blocks TLR9 activation by mitochondrial DNA in vitro and may attenuate flares of rhabdomyolysis in 6 patients treated. We suggest a critical role for defective clearance of oxidized mitochondrial DNA that activates TLR9-restricted inflammation in lipin1-related rhabdomyolysis. Interventions blocking TLR9 activation or inflammation can improve patient care in vivo.
    Keywords:  Toll-like receptor 9; autophagosome; hydroxychloroquine; inflammation; late endosome; lipin1; mitochondrial quality control; rhabdomyolysis
  22. Elife. 2021 Sep 02. pii: e69438. [Epub ahead of print]10
      Concussion is associated with a myriad of deleterious immediate and long-term consequences. Yet the molecular mechanisms and genetic targets promoting the selective vulnerability of different neural subtypes to dysfunction and degeneration remain unclear. Translating experimental models of blunt force trauma in C. elegans to concussion in mice, we identify a conserved neuroprotective mechanism in which reduction of mitochondrial electron flux through complex IV suppresses trauma-induced degeneration of the highly vulnerable dopaminergic neurons. Reducing cytochrome C oxidase function elevates mitochondrial-derived reactive oxygen species, which signal through the cytosolic hypoxia inducing transcription factor, Hif1a, to promote hyperphosphorylation and inactivation of the pyruvate dehydrogenase, PDHE1α. This critical enzyme initiates the Warburg shunt, which drives energetic reallocation from mitochondrial respiration to astrocyte-mediated glycolysis in a neuroprotective manner. These studies demonstrate a conserved process in which glycolytic preconditioning suppresses Parkinson-like hypersensitivity of dopaminergic neurons to trauma-induced degeneration via redox signaling and the Warburg effect.
    Keywords:  C. elegans; cell biology; mouse; neuroscience
  23. Mol Brain. 2021 Sep 03. 14(1): 132
      The medium-chain fatty acids octanoic acid (C8) and decanoic acid (C10) are gaining attention as beneficial brain fuels in several neurological disorders. The protective effects of C8 and C10 have been proposed to be driven by hepatic production of ketone bodies. However, plasma ketone levels correlates poorly with the cerebral effects of C8 and C10, suggesting that additional mechanism are in place. Here we investigated cellular C8 and C10 metabolism in the brain and explored how the protective effects of C8 and C10 may be linked to cellular metabolism. Using dynamic isotope labeling, with [U-13C]C8 and [U-13C]C10 as metabolic substrates, we show that both C8 and C10 are oxidatively metabolized in mouse brain slices. The 13C enrichment from metabolism of [U-13C]C8 and [U-13C]C10 was particularly prominent in glutamine, suggesting that C8 and C10 metabolism primarily occurs in astrocytes. This finding was corroborated in cultured astrocytes in which C8 increased the respiration linked to ATP production, whereas C10 elevated the mitochondrial proton leak. When C8 and C10 were provided together as metabolic substrates in brain slices, metabolism of C10 was predominant over that of C8. Furthermore, metabolism of both [U-13C]C8 and [U-13C]C10 was unaffected by etomoxir indicating that it is independent of carnitine palmitoyltransferase I (CPT-1). Finally, we show that inhibition of glutamine synthesis selectively reduced 13C accumulation in GABA from [U-13C]C8 and [U-13C]C10 metabolism in brain slices, demonstrating that the glutamine generated from astrocyte C8 and C10 metabolism is utilized for neuronal GABA synthesis. Collectively, the results show that cerebral C8 and C10 metabolism is linked to the metabolic coupling of neurons and astrocytes, which may serve as a protective metabolic mechanism of C8 and C10 supplementation in neurological disorders.
    Keywords:  Capric acid (C10); Caprylic acid (C8); MCFA; MCT; Mitochondria; Neurotransmitter recycling; β-hydroxybutyrate
  24. Mol Psychiatry. 2021 Sep 01.
      To characterize neuronal mitochondrial abnormalities in major depressive disorder (MDD), functional mitochondrial proteins (MPs) extracted from enriched plasma neuron-derived extracellular vesicles (NDEVs) of MDD participants (n = 20) were quantified before and after eight weeks of treatment with a selective serotonin reuptake inhibitor (SSRI). Pretreatment baseline NDEV levels of the transcriptional type 2 nuclear respiratory factor (NRF2) which controls mitochondrial biogenesis and many anti-oxidant gene responses, regulators of diverse neuronal mitochondrial functions cyclophilin D (CYPD) and mitofusin-2 (MFN2), leucine zipper EF-hand containing transmembrane 1 protein (LETM1) component of a calcium channel/calcium channel enhancer, mitochondrial tethering proteins syntaphilin (SNPH) and myosin VI (MY06), inner membrane electron transport complexes I (subunit 6) and III (subunit 10), the penultimate enzyme of nicotinamide adenine dinucleotide (NAD) generation nicotinamide mononucleotide adenylytransferase 2 (NMNAT2), and neuronal mitochondrial metabolic regulatory and protective factors humanin and mitochondrial open-reading frame of the 12S rRNA-c (MOTS-c) all were significantly lower than those of NDEVs from matched controls (n = 10), whereas those of pro-neurodegenerative NADase Sterile Alpha and TIR motif-containing protein 1 (SARM1) were higher. The baseline NDEV levels of transcription factor A mitochondrial (TFAM) and the transcriptional master-regulator of mitochondrial biogenesis PPAR γ coactivator-1α (PGC-1α) showed no differences between MDD participants and controls. Several of these potential biomarker proteins showed substantially different changes in untreated MDD than those we reported in untreated first-episode psychosis. NDEV levels of MPs of all functional classes, except complex I-6, NRF2 and PGC-1α were normalized in MDD participants who responded to SSRI therapy (n = 10) but not in those who failed to respond (n = 10) by psychiatric evaluation. If larger studies validate NDEV MP abnormalities, they may become useful biomarkers and identify new drug targets.
  25. EMBO J. 2021 Aug 30. e108863
      Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.
    Keywords:  aging; cancer; inflammation; metabolic syndromes; neurodegeneration