bims-mitdis Biomed News
on Mitochondrial Disorders
Issue of 2021‒01‒31
thirty-five papers selected by
Catalina Vasilescu
University of Helsinki

  1. iScience. 2021 Jan 22. 24(1): 102022
      Chaperonins play an important role in folding newly synthesized or translocated proteins in all organisms. The bacterial chaperonin GroEL has served as a model system for the understanding of these proteins. In comparison, its human homolog, known as mitochondrial heat shock protein family member D1 (HSPD1) is poorly understood. Here, we present the structure of HSPD1 in the apo state determined by cryo-electron microscopy (cryo-EM). Unlike GroEL, HSPD1 forms mostly single ring assemblies in the absence of co-chaperonin (HSPE1). Comparison with GroEL shows a rotation and increased flexibility of the apical domain. Together with published structures of the HSPD1/HSPE1 co-chaperonin complex, this work gives insight into the structural changes that occur during the catalytic cycle. This new understanding of HSPD1 structure and its rearrangements upon complex formation may provide new insights for the development of HSPD1-targeting treatments against a diverse range of diseases including glioblastoma.
    Keywords:  Molecular Biology; Molecular Structure
  2. Nat Commun. 2021 Jan 29. 12(1): 707
      Mitochondrial complex I is central to the pathological reactive oxygen species (ROS) production that underlies cardiac ischemia-reperfusion (IR) injury. ND6-P25L mice are homoplasmic for a disease-causing mtDNA point mutation encoding the P25L substitution in the ND6 subunit of complex I. The cryo-EM structure of ND6-P25L complex I revealed subtle structural changes that facilitate rapid conversion to the "deactive" state, usually formed only after prolonged inactivity. Despite its tendency to adopt the "deactive" state, the mutant complex is fully active for NADH oxidation, but cannot generate ROS by reverse electron transfer (RET). ND6-P25L mitochondria function normally, except for their lack of RET ROS production, and ND6-P25L mice are protected against cardiac IR injury in vivo. Thus, this single point mutation in complex I, which does not affect oxidative phosphorylation but renders the complex unable to catalyse RET, demonstrates the pathological role of ROS production by RET during IR injury.
  3. Mov Disord. 2021 Jan 29.
      Over the past four decades, mitochondrial dysfunction has been a recurring theme in Parkinson's disease (PD) and is hypothesized to play a central role in its disease pathogenesis. Given the instrumental role of mitochondria in cellular energy production, their dysfunction can be detrimental to highly energy-dependent dopaminergic neurons, known to degenerate in PD. Mitochondria harbor multiple copies of their own genomes (mtDNA), encoding critical respiratory chain complexes required for energy production. Consequently, mtDNA has been investigated as a source of mitochondrial dysfunction in PD. As seen in multiple mitochondrial diseases, deleterious mtDNA variation and mtDNA copy number depletion can impede mtDNA protein synthesis, leading to inadequate energy production in affected cells and the onset of a disease phenotype. As such, high burdens of mtDNA defects but also mtDNA depletion, previously identified in the substantia nigra of PD patients, have been suggested to play a role in PD. Genetic variation in nuclear DNA encoding factors required for replicating, transcribing, and translating mtDNA, could underlie these observed mtDNA changes. Herein we examine this possibility and provide an overview of studies that have investigated whether nuclear-encoded genes associated with mtDNA processes may influence PD risk. Overall, pathway-based analysis studies, mice models, and case reports of mitochondrial disease patients manifesting with parkinsonism all implicate genes encoding factors related to mtDNA processes in neurodegeneration and PD. Most notably, cumulative genetic variation in these genes likely contributes to neurodegeneration and PD risk by acting together in common pathways to disrupt mtDNA processes or impair their regulation. © 2021 International Parkinson and Movement Disorder Society © 2021 International Parkinson and Movement Disorder Society.
    Keywords:  Parkinson's disease; mitochondrial DNA; mtDNA maintenance; mtDNA transcription and translation; parkinsonism
  4. Reprod Med Biol. 2021 Jan;20(1): 53-61
      Background: Pathogenic mitochondrial (mt)DNA mutations, which often cause life-threatening disorders, are maternally inherited via the cytoplasm of oocytes. Mitochondrial replacement therapy (MRT) is expected to prevent second-generation transmission of mtDNA mutations. However, MRT may affect the function of respiratory chain complexes comprised of both nuclear and mitochondrial proteins.Methods: Based on the literature and current regulatory guidelines (especially in Japan), we analyzed and reviewed the recent developments in human models of MRT.
    Main findings: MRT does not compromise pre-implantation development or stem cell isolation. Mitochondrial function in stem cells after MRT is also normal. Although mtDNA carryover is usually less than 0.5%, even low levels of heteroplasmy can affect the stability of the mtDNA genotype, and directional or stochastic mtDNA drift occurs in a subset of stem cell lines (mtDNA genetic drift). MRT could prevent serious genetic disorders from being passed on to the offspring. However, it should be noted that this technique currently poses significant risks for use in embryos designed for implantation.
    Conclusion: The maternal genome is fundamentally compatible with different mitochondrial genotypes, and vertical inheritance is not required for normal mitochondrial function. Unresolved questions regarding mtDNA genetic drift can be addressed by basic research using MRT.
    Keywords:  mitochondrial DNA; mitochondrial DNA carryover; mitochondrial disease; mitochondrial replacement; mtDNA genetic drift
  5. Front Genet. 2020 ;11 610764
      Mitochondrial diseases are a heterogeneous group of rare genetic disorders that can be caused by mutations in nuclear (nDNA) or mitochondrial DNA (mtDNA). Mutations in mtDNA are associated with several maternally inherited genetic diseases, with mitochondrial dysfunction as a main pathological feature. These diseases, although frequently multisystemic, mainly affect organs that require large amounts of energy such as the brain and the skeletal muscle. In contrast to the difficulty of obtaining neuronal and muscle cell models, the development of induced pluripotent stem cells (iPSCs) has shed light on the study of mitochondrial diseases. However, it is still a challenge to obtain an appropriate cellular model in order to find new therapeutic options for people suffering from these diseases. In this review, we deepen the knowledge in the current models for the most studied mt-tRNA mutation-caused mitochondrial diseases, MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) and MERRF (myoclonic epilepsy with ragged red fibers) syndromes, and their therapeutic management. In particular, we will discuss the development of a novel model for mitochondrial disease research that consists of induced neurons (iNs) generated by direct reprogramming of fibroblasts derived from patients suffering from MERRF syndrome. We hypothesize that iNs will be helpful for mitochondrial disease modeling, since they could mimic patient's neuron pathophysiology and give us the opportunity to correct the alterations in one of the most affected cellular types in these disorders.
    Keywords:  direct reprogramming; disease modeling; induced neurons; mitochondrial diseases; mtDNA
  6. Mol Genet Metab. 2021 Jan 14. pii: S1096-7192(21)00006-8. [Epub ahead of print]
      TRMU is a nuclear gene crucial for mitochondrial DNA translation by encoding tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase, which thiolates mitochondrial tRNA. Biallelic pathogenic variants in TRMU are associated with transient infantile liver failure. Other less common presentations such as Leigh syndrome, myopathy, and cardiomyopathy have been reported. Recent studies suggested that provision of exogenous L-cysteine or N-acetylcysteine may ameliorate the effects of disease-causing variants and improve the natural history of the disease. Here, we report six infants with biallelic TRMU variants, including four previously unpublished patients, all treated with exogenous cysteine. We highlight the first report of an affected patient undergoing orthotopic liver transplantation, the long-term effects of cysteine supplementation, and the ability of the initial presentation to mimic multiple inborn errors of metabolism. We propose that TRMU deficiency should be suspected in all children presenting with persistent lactic acidosis and hypoglycemia, and that combined N-acetylcysteine and L-cysteine supplementation should be considered prior to molecular diagnosis, as this is a low-risk approach that may increase survival and mitigate the severity of the disease course.
    Keywords:  Cysteine; Liver failure; Mitochondrial disorder; Orthotopic liver transplant; TRMU
  7. Nat Immunol. 2021 Jan 28.
      Mitochondrial abnormalities have been noted in lupus, but the causes and consequences remain obscure. Autophagy-related genes ATG5, ATG7 and IRGM have been previously implicated in autoimmune disease. We reasoned that failure to clear defective mitochondria via mitophagy might be a foundational driver in autoimmunity by licensing mitochondrial DNA-dependent induction of type I interferon. Here, we show that mice lacking the GTPase IRGM1 (IRGM homolog) exhibited a type I interferonopathy with autoimmune features. Irgm1 deletion impaired the execution of mitophagy with cell-specific consequences. In fibroblasts, mitochondrial DNA soiling of the cytosol induced cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)-dependent type I interferon, whereas in macrophages, lysosomal Toll-like receptor 7 was activated. In vivo, Irgm1-/- tissues exhibited mosaic dependency upon nucleic acid receptors. Whereas salivary and lacrimal gland autoimmune pathology was abolished and lung pathology was attenuated by cGAS and STING deletion, pancreatic pathology remained unchanged. These findings reveal fundamental connections between mitochondrial quality control and tissue-selective autoimmune disease.
  8. BMC Biol. 2021 Jan 25. 19(1): 14
      BACKGROUND: Lipoylation of 2-ketoacid dehydrogenases is essential for mitochondrial function in eukaryotes. While the basic principles of the lipoylation processes have been worked out, we still lack a thorough understanding of the details of this important post-translational modification pathway. Here we used yeast as a model organism to characterize substrate usage by the highly conserved eukaryotic octanoyl/lipoyl transferases in vivo and queried how amenable the lipoylation system is to supplementation with exogenous substrate.RESULTS: We show that the requirement for mitochondrial fatty acid synthesis to provide substrates for lipoylation of the 2-ketoacid dehydrogenases can be bypassed by supplying the cells with free lipoic acid (LA) or octanoic acid (C8) and a mitochondrially targeted fatty acyl/lipoyl activating enzyme. We also provide evidence that the S. cerevisiae lipoyl transferase Lip3, in addition to transferring LA from the glycine cleavage system H protein to the pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KGD) E2 subunits, can transfer this cofactor from the PDH complex to the KGD complex. In support of yeast as a model system for human metabolism, we demonstrate that the human octanoyl/lipoyl transferases can substitute for their counterparts in yeast to support respiratory growth and protein lipoylation. Like the wild-type yeast enzyme, the human lipoyl transferase LIPT1 responds to LA supplementation in the presence of the activating enzyme LplA.
    CONCLUSIONS: In the yeast model system, the eukaryotic lipoylation pathway can use free LA and C8 as substrates when fatty/lipoic acid activating enzymes are targeted to mitochondria. Lip3 LA transferase has a wider substrate specificity than previously recognized. We show that these features of the lipoylation mechanism in yeast are conserved in mammalian mitochondria. Our findings have important implications for the development of effective therapies for the treatment of LA or mtFAS deficiency-related disorders.
    Keywords:  Lip2/LIPT2; Lip3 substrate; Lip3/LIPT1; Lipoylation; Lipoylation disorders; Mitochondrial fatty acid synthesis (mtFAS); Octanoyl/lipoyl transferases; S. cerevisiae model; Supplementation studies
  9. FEBS Lett. 2021 Jan 29.
      Mitochondrial diseases are clinically and genetically heterogeneous disorders, caused by pathogenic variants in either the nuclear or mitochondrial genome. This heterogeneity is particularly striking for disease caused by variants in mitochondrial DNA-encoded tRNA (mt-tRNA) genes, posing challenges for both the treatment of patients and for understanding the molecular pathology. In this review, we consider disease caused by the two most common pathogenic mt-tRNA variants: m.3243A>G (within MT-TL1, encoding mt-tRNALeu(UUR) ) and m.8344A>G (within MT-TK, encoding mt-tRNALys ), which together account for the vast majority of all mt-tRNA-related disease. We compare and contrast the clinical disease they are associated with, as well as their molecular pathologies and consider what is known about the likely molecular mechanisms of disease. Finally, we discuss the role of mitochondrial-nuclear cross-talk in the manifestation of mt-tRNA-associated disease and how research in this area has not only the potential to uncover molecular mechanisms responsible for the vast clinical heterogeneity associated with these variants but also pave the way to develop treatment options for these devastating diseases.
    Keywords:  MELAS; MERRF; Mitochondrial disease; heteroplasmy; m.3243A>G; m.8344A>G; mitochondrial DNA; mitochondrial tRNA
  10. Hum Mutat. 2021 Jan 27.
      Mutations in structural subunits and assembly factors of complex I of the oxidative phosphorylation system constitute the most common cause of mitochondrial respiratory chain defects. Such mutations can present a wide range of clinical manifestations, varying from mild deficiencies to severe, lethal disorders. We describe a patient presenting intrauterine growth restriction and anaemia, which displayed postpartum hypertrophic cardiomyopathy, lactic acidosis, encephalopathy, and a severe complex I defect with fatal outcome. Whole genome sequencing revealed an intronic biallelic mutation in the NDUFB7 gene (c.113-10C>G) and splicing pattern alterations in NDUFB7 mRNA were confirmed by RNA Sequencing. The detected variant resulted in a significant reduction of the NDUFB7 protein and reduced complex I activity. Complementation studies with expression of wild-type NDUFB7 in patient fibroblasts normalised complex I function. Here we report a case with a primary complex I defect due to a homozygous mutation in an intron region of the NDUFB7 gene. This article is protected by copyright. All rights reserved.
    Keywords:  Intrauterine clinical manifestations; NDUFB7; cryptic splice site mutation; isolated complex I deficiency; mitochondrial disease
  11. PLoS Comput Biol. 2021 Jan 25. 17(1): e1008624
      Mitochondria are vital organelles inside the cell and contribute to intracellular calcium (Ca2+) dynamics directly and indirectly via calcium exchange, ATP generation, and production of reactive oxygen species (ROS). Arrhythmogenic Ca2+ alternans in cardiac myocytes has been observed in experiments under abnormal mitochondrial depolarization. However, complex signaling pathways and Ca2+ cycling between mitochondria and cytosol make it difficult in experiments to reveal the underlying mechanisms of Ca2+ alternans under abnormal mitochondrial depolarization. In this study, we use a newly developed spatiotemporal ventricular myocyte computer model that integrates mitochondrial Ca2+ cycling and complex signaling pathways to investigate the mechanisms of Ca2+ alternans during mitochondrial depolarization. We find that elevation of ROS in response to mitochondrial depolarization plays a critical role in promoting Ca2+ alternans. Further examination reveals that the redox effect of ROS on ryanodine receptors and sarco/endoplasmic reticulum Ca2+-ATPase synergistically promote alternans. Upregulation of mitochondrial Ca2+ uniporter promotes Ca2+ alternans via Ca2+-dependent mitochondrial permeability transition pore opening. Due to their relatively slow kinetics, oxidized Ca2+/calmodulin-dependent protein kinase II activation and ATP do not play significant roles acutely in the genesis of Ca2+ alternans after mitochondrial depolarization, but their roles can be significant in the long term, mainly through their effects on sarco/endoplasmic reticulum Ca2+-ATPase activity. In conclusion, mitochondrial depolarization promotes Ca2+ alternans acutely via the redox effect of ROS and chronically by ATP reduction. It suppresses Ca2+ alternans chronically through oxidized Ca2+/calmodulin-dependent protein kinase II activation.
  12. Mitochondrion. 2021 Jan 26. pii: S1567-7249(21)00006-4. [Epub ahead of print]
      Mitochondrial dysfunction has emerged to be associated with a broad spectrum of diseases, and there is an increasing demand for accurate detection of mitochondrial DNA (mtDNA) variants. Whole genome sequencing (WGS) has been the dominant sequencing approach to identify genetic variants in recent decades, but most studies focus on variants on the nuclear genome. Whole genome sequencing is also costly and time consuming. Sequencing specifically targeted for mtDNA is commonly used in the diagnostic settings and has lower costs. However, there is a lack of pairwise comparisons between these two sequencing approaches for calling mtDNA variants on a population basis. In this study, we compared WGS and mtDNA-targeted sequencing (targeted-seq) in analyzing mitochondrial DNA from 1499 participants recruited into the Severe Asthma Research Program (SARP). Our study reveals that targeted-sequencing and WGS have comparable capacity to determine genotypes and to call haplogroups and homoplasmies on mtDNA. However, there exists a large variability in calling heteroplasmies, especially for low-frequency heteroplasmies, which indicates that investigators should be cautious about heteroplasmies acquired from different sequencing methods. Further research is highly desired to improve variant detection methods for mitochondrial DNA.
    Keywords:  Asthma; Mitochondrial DNA; Targeted sequencing; Whole genome sequencing
  13. J Med Genet. 2021 Jan 25. pii: jmedgenet-2020-107447. [Epub ahead of print]
      BACKGROUND: Singleton-Merten syndrome (SGMRT) is a rare immunogenetic disorder that variably features juvenile open-angle glaucoma (JOAG), psoriasiform skin rash, aortic calcifications and skeletal and dental dysplasia. Few families have been described and the genotypic and phenotypic spectrum is poorly defined, with variants in DDX58 (DExD/H-box helicase 58) being one of two identified causes, classified as SGMRT2.METHODS: Families underwent deep systemic phenotyping and exome sequencing. Functional characterisation with in vitro luciferase assays and in vivo interferon signature using bulk and single cell RNA sequencing was performed.
    RESULTS: We have identified a novel DDX58 variant c.1529A>T p.(Glu510Val) that segregates with disease in two families with SGMRT2. Patients in these families have widely variable phenotypic features and different ethnic background, with some being severely affected by systemic features and others solely with glaucoma. JOAG was present in all individuals affected with the syndrome. Furthermore, detailed evaluation of skin rash in one patient revealed sparse inflammatory infiltrates in a unique distribution. Functional analysis showed that the DDX58 variant is a dominant gain-of-function activator of interferon pathways in the absence of exogenous RNA ligands. Single cell RNA sequencing of patient lesional skin revealed a cellular activation of interferon-stimulated gene expression in keratinocytes and fibroblasts but not in neighbouring healthy skin.
    CONCLUSIONS: These results expand the genotypic spectrum of DDX58-associated disease, provide the first detailed description of ocular and dermatological phenotypes, expand our understanding of the molecular pathogenesis of this condition and provide a platform for testing response to therapy.
    Keywords:  and neonatal diseases and abnormalities; autoimmune diseases; congenital; dermatology; eye diseases; gain of function mutation; hereditary
  14. Int J Mol Sci. 2021 Jan 20. pii: E1006. [Epub ahead of print]22(3):
      Several genetic variants in the mitochondrial genome (mtDNA), including ancient polymorphisms, are associated with chronic inflammatory conditions, but investigating the functional consequences of such mtDNA polymorphisms in humans is challenging due to the influence of many other polymorphisms in both mtDNA and the nuclear genome (nDNA). Here, using the conplastic mouse strain B6-mtFVB, we show that in mice, a maternally inherited natural mutation (m.7778G > T) in the mitochondrially encoded gene ATP synthase 8 (mt-Atp8) of complex V impacts on the cellular metabolic profile and effector functions of CD4+ T cells and induces mild changes in oxidative phosphorylation (OXPHOS) complex activities. These changes culminated in significantly lower disease susceptibility in two models of inflammatory skin disease. Our findings provide experimental evidence that a natural variation in mtDNA influences chronic inflammatory conditions through alterations in cellular metabolism and the systemic metabolic profile without causing major dysfunction in the OXPHOS system.
    Keywords:  ATP8; autoimmune disease; complex V; conplastic mice; immunometabolism; metabolomics; mitochondria; mt-Atp8; mtDNA polymorphisms; propionate; short chain fatty acids; skin inflammation
  15. Arch Toxicol. 2021 Jan 29.
      Inhibition of complex I of the mitochondrial respiratory chain (cI) by rotenone and methyl-phenylpyridinium (MPP +) leads to the degeneration of dopaminergic neurons in man and rodents. To formally describe this mechanism of toxicity, an adverse outcome pathway (AOP:3) has been developed that implies that any inhibitor of cI, or possibly of other parts of the respiratory chain, would have the potential to trigger parkinsonian motor deficits. We used here 21 pesticides, all of which are described in the literature as mitochondrial inhibitors, to study the general applicability of AOP:3 or of in vitro assays that are assessing its activation. Five cI, three complex II (cII), and five complex III (cIII) inhibitors were characterized in detail in human dopaminergic neuronal cell cultures. The NeuriTox assay, examining neurite damage in LUHMES cells, was used as in vitro proxy of the adverse outcome (AO), i.e., of dopaminergic neurodegeneration. This test provided data on whether test compounds were unspecific cytotoxicants or specifically neurotoxic, and it yielded potency data with respect to neurite degeneration. The pesticide panel was also examined in assays for the sequential key events (KE) leading to the AO, i.e., mitochondrial respiratory chain inhibition, mitochondrial dysfunction, and disturbed proteostasis. Data from KE assays were compared to the NeuriTox data (AO). The cII-inhibitory pesticides tested here did not appear to trigger the AOP:3 at all. Some of the cI/cIII inhibitors showed a consistent AOP activation response in all assays, while others did not. In general, there was a clear hierarchy of assay sensitivity: changes of gene expression (biomarker of neuronal stress) correlated well with NeuriTox data; mitochondrial failure (measured both by a mitochondrial membrane potential-sensitive dye and a respirometric assay) was about 10-260 times more sensitive than neurite damage (AO); cI/cIII activity was sometimes affected at > 1000 times lower concentrations than the neurites. These data suggest that the use of AOP:3 for hazard assessment has a number of caveats: (i) specific parkinsonian neurodegeneration cannot be easily predicted from assays of mitochondrial dysfunction; (ii) deriving a point-of-departure for risk assessment from early KE assays may overestimate toxicant potency.
    Keywords:  AOP:3; High-content imaging; In vitro neurotoxicity; Mechanistic safety assessment; Mitotoxicity; TempO-Seq
  16. Front Neurosci. 2020 ;14 612757
      Aging is the time-dependent process that all living organisms go through characterized by declining physiological function due to alterations in metabolic and molecular pathways. Many decades of research have been devoted to uncovering the cellular changes and progression of aging and have revealed that not all organisms with the same chronological age exhibit the same age-related declines in physiological function. In assessing biological age, factors such as epigenetic changes, telomere length, oxidative damage, and mitochondrial dysfunction in rescue mechanisms such as autophagy all play major roles. Recent studies have focused on autophagy dysfunction in aging, particularly on mitophagy due to its major role in energy generation and reactive oxidative species generation of mitochondria. Mitophagy has been implicated in playing a role in the pathogenesis of many age-related diseases, including Alzheimer's disease (AD), Parkinson's, Huntington's, and amyotrophic lateral sclerosis. The purpose of our article is to highlight the mechanisms of autophagy and mitophagy and how defects in these pathways contribute to the physiological markers of aging and AD. This article also discusses how mitochondrial dysfunction, abnormal mitochondrial dynamics, impaired biogenesis, and defective mitophagy are related to aging and AD progression. This article highlights recent studies of amyloid beta and phosphorylated tau in relation to autophagy and mitophagy in AD.
    Keywords:  Alzheimer’s disease; aging; autophagy; mitochondria reactive oxygen species; mitophagy
  17. Cells. 2021 Jan 21. pii: 204. [Epub ahead of print]10(2):
      Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder in which learning, memory and cognitive functions decline progressively. Familial forms of AD (FAD) are caused by mutations in amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes. Presenilin 1 (PS1) and its homologue, presenilin 2 (PS2), represent, alternatively, the catalytic core of the γ-secretase complex that, by cleaving APP, produces neurotoxic amyloid beta (Aβ) peptides responsible for one of the histopathological hallmarks in AD brains, the amyloid plaques. Recently, PSEN1 FAD mutations have been associated with a loss-of-function phenotype. To investigate whether this finding can also be extended to PSEN2 FAD mutations, we studied two processes known to be modulated by PS2 and altered by FAD mutations: Ca2+ signaling and mitochondrial function. By exploiting neurons derived from a PSEN2 knock-out (PS2-/-) mouse model, we found that, upon IP3-generating stimulation, cytosolic Ca2+ handling is not altered, compared to wild-type cells, while mitochondrial Ca2+ uptake is strongly compromised. Accordingly, PS2-/- neurons show a marked reduction in endoplasmic reticulum-mitochondria apposition and a slight alteration in mitochondrial respiration, whereas mitochondrial membrane potential, and organelle morphology and number appear unchanged. Thus, although some alterations in mitochondrial function appear to be shared between PS2-/- and FAD-PS2-expressing neurons, the mechanisms leading to these defects are quite distinct between the two models. Taken together, our data appear to be difficult to reconcile with the proposal that FAD-PS2 mutants are loss-of-function, whereas the concept that PS2 plays a key role in sustaining mitochondrial function is here confirmed.
    Keywords:  Alzheimer′s disease; Ca2+ signaling; PS2–/–; bioenergetics; mitochondria; mitochondrial membrane potential; neuronal hyperexcitability; oxygen consumption rate; presenilin 2
  18. Mov Disord. 2021 Jan 26.
      BACKGROUND: Parkinson's disease (PD) is a genetically complex neurodegenerative disease with ~20 genes known to contain mutations that cause PD or atypical parkinsonism. Large-scale next-generation sequencing projects have revolutionized genomics research. Applying these data to PD, many genes have been reported to contain putative disease-causing mutations. In most instances, however, the results remain quite limited and rather preliminary. Our aim was to assist researchers on their search for PD-risk genes and variant candidates with an easily accessible and open summary-level genomic data browser for the PD research community.METHODS: Sequencing and imputed genotype data were obtained from multiple sources and harmonized and aggregated.
    RESULTS: In total we included a total of 102,127 participants, including 28,453 PD cases, 1650 proxy cases, and 72,024 controls.
    CONCLUSIONS: We present here the Parkinson's Disease Sequencing Browser: a Shiny-based web application that presents comprehensive summary-level frequency data from multiple large-scale genotyping and sequencing projects Published © 2021 This article is a U.S. Government work and is in the public domain in the USA. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.
    Keywords:  Parkinson's disease; data browser; genetics; sequencing
  19. PLoS One. 2021 ;16(1): e0246114
      PURPOSE: Mitochondrial (mt) DNA damage is associated with age-related macular degeneration (AMD) and other human aging diseases. This study was designed to quantify and characterize mtDNA low-frequency heteroplasmy single nucleotide polymorphisms (SNPs) of three different tissues isolated from AMD subjects using Next Generation Sequencing (NGS) technology.METHODS: DNA was extracted from neural retina, [RPE+choroid] and blood from three deceased age-related macular degeneration (AMD) subjects. Entire mitochondrial genomes were analyzed for low-frequency heteroplasmy SNPs using NGS technology that independently sequenced both mtDNA strands. This deep sequencing method (average sequencing depth of 30,000; range 1,000-100,000) can accurately differentiate low-frequency heteroplasmy SNPs from DNA modification artifacts. Twenty-three 'hot-spot' heteroplasmy mtDNA SNPs were analyzed in 222 additional blood samples.
    RESULTS: Germline homoplasmy SNPs that defined mtDNA haplogroups were consistent in the three tissues of each subject. Analyses of SNPs with <40% heteroplasmy revealed the blood had significantly greater numbers of heteroplasmy SNPs than retina alone (p≤0.05) or retina+choroid combined (p = 0.008). Twenty-three 'hot-spot' mtDNA heteroplasmy SNPs were present, with three being non-synonymous (amino acid change). Four 'hot-spot' heteroplasmy SNPs (m.1120C>T, m.1284T>C, m.1556C>T, m.7256C>T) were found in additional samples (n = 222). Five heteroplasmy SNPs (m.4104A>G, m.5320C>T, m.5471G>A, m.5474A>G, m.5498A>G) declined with age. Two heteroplasmy SNPs (m.13095T>C, m.13105A>G) increased in AMD compared to Normal samples. In the heteroplasmy SNPs, very few transversion mutations (purine to pyrimidine or vice versa, associated with oxidative damage) were found and the majority were transition changes (purine to purine or pyrimidine to pyrimidine, associated with replication errors).
    CONCLUSION: Within an individual, the blood, retina and [RPE+choroid] contained identical homoplasmy SNPs representing inherited germline mtDNA haplogroup. NGS methodology showed significantly more mtDNA heteroplasmy SNPs in blood compared to retina and [RPE+choroid], suggesting the latter tissues have substantial protection. Significantly higher heteroplasmy levels of m.13095T>C and m.13105A>G may represent potential AMD biomarkers. Finally, high levels of transition mutations suggest that accumulation of heteroplasmic SNPs may occur through replication errors rather than oxidative damage.
  20. Brain Commun. 2021 ;3(1): fcaa222
      The aim of this study was to explore the utility of the serum biomarkers neurofilament light chain, fibroblast growth factor 21 and growth and differentiation factor 15 in diagnosing primary mitochondrial disorders. We measured serum neurofilament light chain, fibroblast growth factor 21 and growth and differentiation factor 15 in 26 patients with a genetically proven mitochondrial disease. Fibroblast growth factor 21 and growth and differentiation factor 15 were measured by enzyme-linked immunosorbent assay and neurofilament light chain with the Simoa assay. Neurofilament light chain was highest in patients with multi-systemic involvement that included the central nervous system such as those with the m.3242A>G mutation. Mean neurofilament light chain was also highest in patients with epilepsy versus those without [49.74 pg/ml versus 19.7 pg/ml (P = 0.015)], whereas fibroblast growth factor 21 and growth and differentiation factor 15 levels were highest in patients with prominent myopathy, such as those with single-mitochondrial DNA deletion. Our results suggest that the combination of neurofilament light chain, fibroblast growth factor 21 and growth and differentiation factor 15 is useful in the diagnostic evaluation of mitochondrial disease. Growth and differentiation factor 15 and fibroblast growth factor 21 identify those with muscle involvement, whereas neurofilament light chain is a clear marker for central nervous system involvement independent of underlying mitochondrial pathology. Levels of neurofilament light chain appear to correlate with the degree of ongoing damage suggesting, therefore, that monitoring neurofilament light chain levels may provide prognostic information and a way of monitoring disease activity.
    Keywords:  FGF-21; GDF-15; mitochondrial disease; neurofilaments
  21. Nat Genet. 2021 Jan 28.
      Genome-wide association studies (GWAS) have identified many risk loci for Alzheimer's disease (AD)1,2, but how these loci confer AD risk is unclear. Here, we aimed to identify loci that confer AD risk through their effects on brain protein abundance to provide new insights into AD pathogenesis. To that end, we integrated AD GWAS results with human brain proteomes to perform a proteome-wide association study (PWAS) of AD, followed by Mendelian randomization and colocalization analysis. We identified 11 genes that are consistent with being causal in AD, acting via their cis-regulated brain protein abundance. Nine replicated in a confirmation PWAS and eight represent new AD risk genes not identified before by AD GWAS. Furthermore, we demonstrated that our results were independent of APOE e4. Together, our findings provide new insights into AD pathogenesis and promising targets for further mechanistic and therapeutic studies.
  22. Trends Mol Med. 2021 Jan 21. pii: S1471-4914(20)30329-4. [Epub ahead of print]
      Genome editing holds great promise for treating a range of human genetic diseases. While emerging clustered regularly interspaced short-palindromic repeats (CRISPR) technologies allow editing of the nuclear genome, it is still not possible to precisely manipulate mitochondrial DNA (mtDNA). Here, we summarize past developments and recent advances in nuclear and mitochondrial genome editing.
    Keywords:  gene therapy; genome editing; mitochondria; translational medicine
  23. Int J Mol Sci. 2021 Jan 21. pii: 1045. [Epub ahead of print]22(3):
      Missense mutations in the LRRK2 gene were first identified as a pathogenic cause of Parkinson's disease (PD) in 2004. Soon thereafter, a founder mutation in LRRK2, p.G2019S (rs34637584), was described, and it is now estimated that there are approximately 100,000 people worldwide carrying this risk variant. While the clinical presentation of LRRK2 parkinsonism has been largely indistinguishable from sporadic PD, disease penetrance and age at onset can be quite variable. In addition, its neuropathological features span a wide range from nigrostriatal loss with Lewy body pathology, lack thereof, or atypical neuropathology, including a large proportion of cases with concomitant Alzheimer's pathology, hailing LRRK2 parkinsonism as the "Rosetta stone" of parkinsonian disorders, which provides clues to an understanding of the different neuropathological trajectories. These differences may result from interactions between the LRRK2 mutant protein and other proteins or environmental factors that modify LRRK2 function and, thereby, influence pathobiology. This review explores how potential genetic and biochemical modifiers of LRRK2 function may contribute to the onset and clinical presentation of LRRK2 parkinsonism. We review which genetic modifiers of LRRK2 influence clinical symptoms, age at onset, and penetrance, what LRRK2 mutations are associated with pleomorphic LRRK2 neuropathology, and which environmental modifiers can augment LRRK2 mutant pathophysiology. Understanding how LRRK2 function is influenced and modulated by other interactors and environmental factors-either increasing toxicity or providing resilience-will inform targeted therapeutic development in the years to come. This will allow the development of disease-modifying therapies for PD- and LRRK2-related neurodegeneration.
    Keywords:  GWAS; LRRK2; Parkinson’s disease; environmental risk factors; genetics; modifier; neuropathology; parkinsonism; polygenic risk score
  24. Cells. 2021 Jan 20. pii: E203. [Epub ahead of print]10(2):
      Mutations in LRRK2 play a critical role in both familial and sporadic Parkinson's disease (PD). Up to date, the role of LRRK2 in PD onset and progression remains largely unknown. However, experimental evidence highlights a critical role of LRRK2 in the control of vesicle trafficking, likely by Rab phosphorylation, that in turn may regulate different aspects of neuronal physiology. Here we show that LRRK2 interacts with Sec8, one of eight subunits of the exocyst complex. The exocyst complex is an evolutionarily conserved multisubunit protein complex mainly involved in tethering secretory vesicles to the plasma membrane and implicated in the regulation of multiple biological processes modulated by vesicle trafficking. Interestingly, Rabs and exocyst complex belong to the same protein network. Our experimental evidence indicates that LRRK2 kinase activity or the presence of the LRRK2 kinase domain regulate the assembly of exocyst subunits and that the over-expression of Sec8 significantly rescues the LRRK2 G2019S mutant pathological effect. Our findings strongly suggest an interesting molecular mechanism by which LRRK2 could modulate vesicle trafficking and may have important implications to decode the complex role that LRRK2 plays in neuronal physiology.
    Keywords:  LRRK2; Parkinson’s disease; Sec8; exocyst complex
  25. Genome Biol. 2021 Jan 26. 22(1): 49
      The resources generated by the GTEx consortium offer unprecedented opportunities to advance our understanding of the biology of human diseases. Here, we present an in-depth examination of the phenotypic consequences of transcriptome regulation and a blueprint for the functional interpretation of genome-wide association study-discovered loci. Across a broad set of complex traits and diseases, we demonstrate widespread dose-dependent effects of RNA expression and splicing. We develop a data-driven framework to benchmark methods that prioritize causal genes and find no single approach outperforms the combination of multiple approaches. Using colocalization and association approaches that take into account the observed allelic heterogeneity of gene expression, we propose potential target genes for 47% (2519 out of 5385) of the GWAS loci examined.
  26. Aging Cell. 2021 Jan 29. e13290
      Using samples from the New England Centenarian Study (NECS), we sought to characterize the serum proteome of 77 centenarians, 82 centenarians' offspring, and 65 age-matched controls of the offspring (mean ages: 105, 80, and 79 years). We identified 1312 proteins that significantly differ between centenarians and their offspring and controls (FDR < 1%), and two different protein signatures that predict longer survival in centenarians and in younger people. By comparing the centenarian signature with 2 independent proteomic studies of aging, we replicated the association of 484 proteins of aging and we identified two serum protein signatures that are specific of extreme old age. The data suggest that centenarians acquire similar aging signatures as seen in younger cohorts that have short survival periods, suggesting that they do not escape normal aging markers, but rather acquire them much later than usual. For example, centenarian signatures are significantly enriched for senescence-associated secretory phenotypes, consistent with those seen with younger aged individuals, and from this finding, we provide a new list of serum proteins that can be used to measure cellular senescence. Protein co-expression network analysis suggests that a small number of biological drivers may regulate aging and extreme longevity, and that changes in gene regulation may be important to reach extreme old age. This centenarian study thus provides additional signatures that can be used to measure aging and provides specific circulating biomarkers of healthy aging and longevity, suggesting potential mechanisms that could help prolong health and support longevity.
    Keywords:  SomaLogic; aging; longevity; protein; senescence
  27. NPJ Syst Biol Appl. 2021 01 27. 7(1): 6
      Lipid mediators are major factors in multiple biological functions and are strongly associated with disease. Recent lipidomics approaches have made it possible to analyze multiple metabolites and the associations of individual lipid mediators. Such systematic approaches have enabled us to identify key changes of biological relevance. Against this background, a knowledge-based pathway map of lipid mediators would be useful to visualize and understand the overall interactions of these factors. Here, we have built a precise map of lipid mediator metabolic pathways (LimeMap) to visualize the comprehensive profiles of lipid mediators that change dynamically in various disorders. We constructed the map by focusing on ω-3 and ω-6 fatty acid metabolites and their respective metabolic pathways, with manual curation of referenced information from public databases and relevant studies. Ultimately, LimeMap comprises 282 factors (222 mediators, and 60 enzymes, receptors, and ion channels) and 279 reactions derived from 102 related studies. Users will be able to modify the map and visualize measured data specific to their purposes using CellDesigner and VANTED software. We expect that LimeMap will contribute to elucidating the comprehensive functional relationships and pathways of lipid mediators.
  28. Mitochondrion. 2021 Jan 21. pii: S1567-7249(21)00004-0. [Epub ahead of print]
      Currently, pathogenic variants in more than 25 nuclear genes, involved in mtDNA maintenance, are associated with human disorders. mtDNA maintenance disorders manifest with a wide range of phenotypes, from severe infantile-onset forms of myocerebrohepatopathy to late-onset forms of myopathies, chronic progressive external ophthalmoplegia, and parkinsonism. This study represents the results of molecular genetic analysis and phenotypes of 102 probands with mtDNA maintenance disorders. So far, this is the largest Russian cohort for this group of diseases. Mutations were identified in 10 mtDNA maintenance genes: POLG (n=57), DGUOK (n=14), TWNK (n=14), TK2 (n=8), MPV17 (n=2), OPA3 (n=1), FBXL4 (n=1), RRM2B (n=1), SUCLG1 (n=1) and TYMP (n=1). We review a mutation spectrum for the DGUOK and TWNK genes, that can be specific for the Russian population. In 34 patients we measured the blood mtDNA copy number and showed its significant reduction. Novel variants were found in 41 cases, which significantly expands the mutational landscape of mtDNA maintenance disorders.
    Keywords:  Mitochondrial replication; mitochondrial DNA copy number; mitochondrial depletion syndrome; mutations; nuclear genes; qPCR
  29. Life (Basel). 2021 Jan 23. pii: 82. [Epub ahead of print]11(2):
      The major role of mitochondria is to provide cells with energy, but no less important are their roles in responding to various stress factors and the metabolic changes and pathological processes that might occur inside and outside the cells. The post-translational modification of proteins is a fast and efficient way for cells to adapt to ever changing conditions. Phosphorylation is a post-translational modification that signals these changes and propagates these signals throughout the whole cell, but it also changes the structure, function and interaction of individual proteins. In this review, we summarize the influence of kinases, the proteins responsible for phosphorylation, on mitochondrial biogenesis under various cellular conditions. We focus on their role in keeping mitochondria fully functional in healthy cells and also on the changes in mitochondrial structure and function that occur in pathological processes arising from the phosphorylation of mitochondrial proteins.
    Keywords:  disease; kinases; mitochondria; phosphorylation
  30. Genes (Basel). 2021 Jan 22. pii: 147. [Epub ahead of print]12(2):
      Inherited optic neuropathies, including Leber Hereditary Optic Neuropathy (LHON) and Dominant Optic Atrophy (DOA), are monogenetic diseases with a final common pathway of mitochondrial dysfunction leading to retinal ganglion cell (RGC) death and ultimately loss of vision. They are, therefore, excellent models with which to investigate this ubiquitous disease process-implicated in both common polygenetic ocular diseases (e.g., Glaucoma) and late-onset central nervous system neurodegenerative diseases (e.g., Parkinson disease). In recent years, cellular and animal models of LHON and DOA have matured in parallel with techniques (such as RNA-seq) to determine and analyze the transcriptomes of affected cells. This confluence leaves us at a particularly exciting time with the potential for the identification of novel pathogenic players and therapeutic targets. Here, we present a discussion of the importance of inherited optic neuropathies and how transcriptomic techniques can be exploited in the development of novel mutation-independent, neuroprotective therapies.
    Keywords:  DOA; LHON; OPA1; RNA-seq; gene-therapy; mitochondrial; neuroprotection; optic neuropathies; transcriptomics
  31. Epigenetics. 2021 Jan 25. 1-17
      Obesity is a major risk factor for cardiovascular disease. Blood-detected epigenetic profiles may serve as non-invasive clinically relevant biomarkers. Therefore, we investigated DNA methylation of genes involved in inflammation in peripheral blood of obese subjects and lean controls and their correlation with cardiometabolic measurements. We obtained blood and adipose tissue (AT) samples from bariatric patients (n = 24) and control adults (n = 24). AT-isolated arterioles were tested for flow-induced dilation (FID) and production of nitric oxide (NO) and reactive oxygen species (ROS). Brachial artery flow-mediated dilation (FMD) was measured via doppler ultrasound. Promoter methylation of 94 genes involved in inflammation and autoimmunity were analysed in whole-blood DNA in relation to vascular function and cardiometabolic risk factors. 77 genes had ahigher methylated fraction in the controls compare obese subjects and 28 proinflammatory genes were significantly hypomethylated in the obese individuals; on top of these genes are CXCL1, CXCL12, CXCL6, IGF2BP2, HDAC4, IL12A, and IL17RA. Fifteen of these genes had significantly higher mRNA in obese subjects compared to controls; on top of these genes are CXCL6, TLR5, IL6ST, EGR1, IL15RA, and HDAC4. Methylation % inversely correlated with BMI, total fat %, visceral fat%, blood pressure, fasting plasma insulin, serum IL6 and C-reactive protein, arteriolar ROS, and alcohol consumption and positive correlations with lean %, HDL, plasma folate and vitamin B12, arteriolar FID and NO production, and brachial FMD. Our results suggest that vascular dysfunction in obese adults may be attributed to asystemic hypomethylation and over expression of the immune-related genes.
    Keywords:  DNA methylation; cardiometabolic risk; flow-induced dilation; inflammation; obesity; vascular Function
  32. Brief Bioinform. 2021 Jan 30. pii: bbaa429. [Epub ahead of print]
      MOTIVATION: Over the past decade, the field of next-generation sequencing (NGS) has seen dramatic advances in methods and a decrease in costs. Consequently, a large expansion of data has been generated by NGS, most of which have originated from RNA-sequencing (RNA-seq) experiments. Because mitochondrial genes are expressed in most eukaryotic cells, mitochondrial mRNA sequences are usually co-sequenced within the target transcriptome, generating data that are commonly underused or discarded. Here, we present MITGARD, an automated pipeline that reliably recovers the mitochondrial genome from RNA-seq data from various sources. The pipeline identifies mitochondrial sequence reads based on a phylogenetically related reference, assembles them into contigs, and extracts a complete mtDNA for the target species.RESULTS: We demonstrate that MITGARD can reconstruct the mitochondrial genomes of several species throughout the tree of life. We noticed that MITGARD can recover the mitogenomes in different sequencing schemes and even in a scenario of low-sequencing depth. Moreover, we showed that the use of references from congeneric species diverging up to 30 million years ago (MYA) from the target species is sufficient to recover the entire mitogenome, whereas the use of species diverging between 30 and 60 MYA allows the recovery of most mitochondrial genes. Additionally, we provide a case study with original data in which we estimate a phylogenetic tree of snakes from the genus Bothrops, further demonstrating that MITGARD is suitable for use on biodiversity projects. MITGARD is then a valuable tool to obtain high-quality information for studies focusing on the phylogenetic and evolutionary aspects of eukaryotes and provides data for easily identifying a sample using barcoding, and to check for cross-contamination using third-party tools.
  33. Biology (Basel). 2021 Jan 21. pii: 77. [Epub ahead of print]10(2):
      Skeletal muscle is a plastic and complex tissue, rich in proteins that are subject to continuous rearrangements. Skeletal muscle homeostasis can be affected by different types of stresses, including physical activity, a physiological stressor able to stimulate a robust increase in different heat shock proteins (HSPs). The modulation of these proteins appears to be fundamental in facilitating the cellular remodeling processes related to the phenomenon of training adaptations such as hypertrophy, increased oxidative capacity, and mitochondrial activity. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin (CRYAB), proteins constitutively expressed in the skeletal muscle, where their specific features could be highly relevant in understanding the impact of different volumes of training regimes on myofiber types and in explaining the complex picture of exercise-induced mechanical strain and damaging conditions on fiber population. This knowledge could lead to a better personalization of training protocols with an optimal non-harmful workload in populations of individuals with different needs and healthy status. Here, we introduce for the first time to the reader these peculiar HSPs from the perspective of exercise response, highlighting the control of their expression, biological function, and specific distribution within skeletal muscle fiber-types.
    Keywords:  CRYAB; heat shock protein 60; myosin heavy chain; physical exercise; skeletal muscle
  34. Proc Natl Acad Sci U S A. 2021 Feb 02. pii: e2019768118. [Epub ahead of print]118(5):
      5-Methylcytosine (5mC) is an important type of epigenetic modification. Bisulfite sequencing (BS-seq) has limitations, such as severe DNA degradation. Using single molecule real-time sequencing, we developed a methodology to directly examine 5mC. This approach holistically examined kinetic signals of a DNA polymerase (including interpulse duration and pulse width) and sequence context for every nucleotide within a measurement window, termed the holistic kinetic (HK) model. The measurement window of each analyzed double-stranded DNA molecule comprised 21 nucleotides with a cytosine in a CpG site in the center. We used amplified DNA (unmethylated) and M.SssI-treated DNA (methylated) (M.SssI being a CpG methyltransferase) to train a convolutional neural network. The area under the curve for differentiating methylation states using such samples was up to 0.97. The sensitivity and specificity for genome-wide 5mC detection at single-base resolution reached 90% and 94%, respectively. The HK model was then tested on human-mouse hybrid fragments in which each member of the hybrid had a different methylation status. The model was also tested on human genomic DNA molecules extracted from various biological samples, such as buffy coat, placental, and tumoral tissues. The overall methylation levels deduced by the HK model were well correlated with those by BS-seq (r = 0.99; P < 0.0001) and allowed the measurement of allele-specific methylation patterns in imprinted genes. Taken together, this methodology has provided a system for simultaneous genome-wide genetic and epigenetic analyses.
    Keywords:  base modifications; epigenetics; epigenomics; third-generation sequencing
  35. Brief Bioinform. 2021 Jan 26. pii: bbaa438. [Epub ahead of print]
      Exon skipping (ES), the most common alternative splicing event, has been reported to contribute to diverse human diseases due to the loss of functional domains/sites or frameshifting of the open reading frame (ORF) and noticed as therapeutic targets. Accumulating transcriptomic studies of aging brains show the splicing disruption is a widespread hallmark of neurodegenerative diseases such as Alzheimer's disease (AD). Here, we built ExonSkipAD, the ES annotation database aiming to provide a resource/reference for functional annotation of ES events in AD and identify therapeutic targets in exon units. We identified 16 414 genes that have ~156 K, ~ 69 K, ~ 231 K ES events from the three representative AD cohorts of ROSMAP, MSBB and Mayo, respectively. For these ES events, we performed multiple functional annotations relating to ES mechanisms or downstream. Specifically, through the functional feature retention studies followed by the open reading frames (ORFs), we identified 275 important cellular regulators that might lose their cellular regulator roles due to exon skipping in AD. ExonSkipAD provides twelve categories of annotations: gene summary, gene structures and expression levels, exon skipping events with PSIs, ORF annotation, exon skipping events in the canonical protein sequence, 3'-UTR located exon skipping events lost miRNA-binding sites, SNversus in the skipped exons with a depth of coverage, AD stage-associated exon skipping events, splicing quantitative trait loci (sQTLs) in the skipped exons, correlation with RNA-binding proteins, and related drugs & diseases. ExonSkipAD will be a unique resource of transcriptomic diversity research for understanding the mechanisms of neurodegenerative disease development and identifying potential therapeutic targets in AD. Significance AS the first comprehensive resource of the functional genomics of the alternative splicing events in AD, ExonSkipAD will be useful for many researchers in the fields of pathology, AD genomics and precision medicine, and pharmaceutical and therapeutic researches.
    Keywords:  Alzheimer’s disease; RNA-binding protein; alternative splicing; exon skipping; mutation; protein domain retention; resource; transcriptome