bims-mitdis 2024-04-21 papers

bims-mitdis

Biomed News

on Mitochondrial disorders

Issue of 2024‒04‒21
forty papers selected by
Catalina Vasilescu, Helmholz Munich

OMA1 clears traffic jam in TOM tunnel in mammals.
Uncovering the impact of UV radiation on mitochondria in dermal cells: a STED nanoscopy study.
Cross-link assisted spatial proteomics to map sub-organelle proteomes and membrane protein topologies.
The role of lipoylation in mitochondrial adaptation to methionine restriction.
Optineurin-facilitated axonal mitochondria delivery promotes neuroprotection and axon regeneration.
A challenging differential diagnosis - Leber's Hereditary Optic Neuropathy.
Mitochondrial energy state controls AMPK-mediated foraging behavior in C. elegans.
A systematic review on the biochemical threshold of mitochondrial genetic variants.
Focusing on mitochondria in the brain: from biology to therapeutics.
High-resolution In-situ Structures of Mammalian Mitochondrial Respiratory Supercomplexes in Reaction within Native Mitochondria.
A very rare presentation of mitochondrial elongation factor Tu deficiency-TUFM mutation and literature review.
Delineating the contribution of ageing and physical activity to changes in mitochondrial characteristics across the lifespan.
Attenuating mitochondrial dysfunction and morphological disruption with PT320 delays dopamine degeneration in MitoPark mice.
Cdk8/CDK19 promotes mitochondrial fission through Drp1 phosphorylation and can phenotypically suppress pink1 deficiency in Drosophila.
PGC-1a mediated mitochondrial biogenesis promotes recovery and survival of neuronal cells from cellular degeneration.
NDUFV1-Related Mitochondrial Complex-1 Disorders: A Retrospective Case Series and Literature Review.
Carnitine-acylcarnitine translocase deficiency: a case report with autopsy.
Altered lipid homeostasis is associated with cerebellar neurodegeneration in SNX14 deficiency.
Safari with an Electron Gun: Visualization of Protein and Membrane Interactions in Mitochondria in Natural Environment.
AI's keen diagnostic eye.
Mitochondria function in cytoplasmic FeS protein biogenesis.
Early heart and skeletal muscle mitochondrial response to a moderate hypobaric hypoxia environment.
Improving access to gene therapy for rare diseases.
AAV-mediated upregulation of VDAC1 rescues the mitochondrial respiration and sirtuins expression in a SOD1 mouse model of inherited ALS.
Cross-Sectional Analysis of Exome Sequencing Diagnosis in Patients With Neurologic Phenotypes Facing Barriers to Clinical Testing.
Mitochondrial tRNA pseudouridylation governs erythropoiesis.
Variant Effect Prediction in the Age of Machine Learning.
Effect of 2-aminoethoxydiphenyl borate on the functions of mouse skeletal muscle mitochondria.
RANKL signaling drives skeletal muscle into the oxidative profile.
The Structure of the Drp1 Lattice on Membrane.
Hydroxymethylglutaryl-CoA reductase activity is essential for mitochondrial β-oxidation of fatty acids to prevent lethal accumulation of long-chain acylcarnitines in the mouse liver.
Enhanced ROS Production in Mitochondria from Prematurely Aging mtDNA Mutator Mice.
Patient-Centric Approaches: Revolutionizing Rare Disease Drug Research.
New insights into the structure and dynamics of the TOM complex in mitochondria.
A step along the path towards AlphaFold - 50 years ago.
Bioinformatics pipeline for the systematic mining genomic and proteomic variation linked to rare diseases: The example of monogenic diabetes.
Implementing polygenic risk scores in the clinic.
Inhibition of the mPTP and Lipid Peroxidation Is Additively Protective Against I/R Injury.
Minimum information and guidelines for reporting a multiplexed assay of variant effect.
Lethal phenotypes in Mendelian disorders.

J Cell Biol. 2024 May 06. pii: e202403190. [Epub ahead of print]223(5):

OMA1 clears traffic jam in TOM tunnel in mammals.

Shiori Sekine, Yusuke Sekine.

Using an engineered mitochondrial clogger, Krakowczyk et al. (https://doi.org/10.1083/jcb.202306051) identified the OMA1 protease as a critical component that eliminates import failure at the TOM translocase in mammalian cells, providing a novel quality control mechanism that is distinct from those described in yeast.

DOI: https://doi.org/10.1083/jcb.202403190
Sci Rep. 2024 04 15. 14(1): 8675

Uncovering the impact of UV radiation on mitochondria in dermal cells: a STED nanoscopy study.

Hyung Jun Kim, Seon-Pil Jin, Jooyoun Kang, So Hyeon Bae, Jung Bae Son, Jang-Hee Oh, Hyewon Youn, Seong Keun Kim, Keon Wook Kang, Jin Ho Chung.

Mitochondria are essential organelles in cellular energy metabolism and other cellular functions. Mitochondrial dysfunction is closely linked to cellular damage and can potentially contribute to the aging process. The purpose of this study was to investigate the subcellular structure of mitochondria and their activities in various cellular environments using super-resolution stimulated emission depletion (STED) nanoscopy. We examined the morphological dispersion of mitochondria below the diffraction limit in sub-cultured human primary skin fibroblasts and mouse skin tissues. Confocal microscopy provides only the overall morphology of the mitochondrial membrane and an indiscerptible location of nucleoids within the diffraction limit. Conversely, super-resolution STED nanoscopy allowed us to resolve the nanoscale distribution of translocase clusters on the mitochondrial outer membrane and accurately quantify the number of nucleoids per cell in each sample. Comparable results were obtained by analyzing the translocase distribution in the mouse tissues. Furthermore, we precisely and quantitatively analyzed biomolecular distribution in nucleoids, such as the mitochondrial transcription factor A (TFAM), using STED nanoscopy. Our findings highlight the efficacy of super-resolution fluorescence imaging in quantifying aging-related changes on the mitochondrial sub-structure in cells and tissues.

DOI: https://doi.org/10.1038/s41598-024-55778-z
Nat Commun. 2024 Apr 17. 15(1): 3290

Cross-link assisted spatial proteomics to map sub-organelle proteomes and membrane protein topologies.

Ying Zhu, Kerem Can Akkaya, Julia Ruta, Nanako Yokoyama, Cong Wang, Max Ruwolt, Diogo Borges Lima, Martin Lehmann, Fan Liu.

The functions of cellular organelles and sub-compartments depend on their protein content, which can be characterized by spatial proteomics approaches. However, many spatial proteomics methods are limited in their ability to resolve organellar sub-compartments, profile multiple sub-compartments in parallel, and/or characterize membrane-associated proteomes. Here, we develop a cross-link assisted spatial proteomics (CLASP) strategy that addresses these shortcomings. Using human mitochondria as a model system, we show that CLASP can elucidate spatial proteomes of all mitochondrial sub-compartments and provide topological insight into the mitochondrial membrane proteome. Biochemical and imaging-based follow-up studies confirm that CLASP allows discovering mitochondria-associated proteins and revising previous protein sub-compartment localization and membrane topology data. We also validate the CLASP concept in synaptic vesicles, demonstrating its applicability to different sub-cellular compartments. This study extends the scope of cross-linking mass spectrometry beyond protein structure and interaction analysis towards spatial proteomics, and establishes a method for concomitant profiling of sub-organelle and membrane proteomes.

DOI: https://doi.org/10.1038/s41467-024-47569-x
Bioessays. 2024 Apr 14. e2300218

The role of lipoylation in mitochondrial adaptation to methionine restriction.

Jingyuan Xue, Cunqi Ye.

  Dietary methionine restriction (MR) is associated with a spectrum of health-promoting benefits. Being conducive to prevention of chronic diseases and extension of life span, MR can activate integrated responses at metabolic, transcriptional, and physiological levels. However, how the mitochondria of MR influence metabolic phenotypes remains elusive. Here, we provide a summary of cellular functions of methionine metabolism and an overview of the current understanding of effector mechanisms of MR, with a focus on the aspect of mitochondria-mediated responses. We propose that mitochondria can sense and respond to MR through a modulatory role of lipoylation, a mitochondrial protein modification sensitized by MR.

Keywords:  cellular metabolism; lipidomics; metabolomics; methioinine metabolism; phospholipid

DOI:  https://doi.org/10.1002/bies.202300218
bioRxiv. 2024 Apr 03. pii: 2024.04.02.587832. [Epub ahead of print]

Optineurin-facilitated axonal mitochondria delivery promotes neuroprotection and axon regeneration.

Dong Liu, Hannah C Webber, Fuyun Bian, Yangfan Xu, Manjari Prakash, Xue Feng, Ming Yang, Hang Yang, In-Jee You, Liang Li, Liping Liu, Pingting Liu, Haoliang Huang, Chien-Yi Chang, Liang Liu, Sahil H Shah, Anna La Torre, Derek S Welsbie, Yang Sun, Xin Duan, Jeffrey Louis Goldberg, Marcus Braun, Zdenek Lansky, Yang Hu.

Optineurin (OPTN) mutations are linked to amyotrophic lateral sclerosis (ALS) and normal tension glaucoma (NTG), but a relevant animal model is lacking, and the molecular mechanisms underlying neurodegeneration are unknown. We found that OPTN C-terminus truncation (OPTNΔC) causes late-onset neurodegeneration of retinal ganglion cells (RGCs), optic nerve (ON), and spinal cord motor neurons, preceded by a striking decrease of axonal mitochondria. Surprisingly, we discover that OPTN directly interacts with both microtubules and the mitochondrial transport complex TRAK1/KIF5B, stabilizing them for proper anterograde axonal mitochondrial transport, in a C- terminus dependent manner. Encouragingly, overexpressing OPTN/TRAK1/KIF5B reverses not only OPTN truncation-induced, but also ocular hypertension-induced neurodegeneration, and promotes striking ON regeneration. Therefore, in addition to generating new animal models for NTG and ALS, our results establish OPTN as a novel facilitator of the microtubule-dependent mitochondrial transport necessary for adequate axonal mitochondria delivery, and its loss as the likely molecular mechanism of neurodegeneration.

DOI: https://doi.org/10.1101/2024.04.02.587832
Rom J Ophthalmol. 2024 Jan-Mar;68(1):68(1): 65-71

A challenging differential diagnosis - Leber's Hereditary Optic Neuropathy.

Raluca Eugenia Iorga, Răzvana Sorina Munteanu-Dănulescu, Ciprian Danielescu.

  Leber's hereditary optic neuropathy (LHON) is the most common maternally inherited disease linked to mitochondrial DNA (mtDNA). The patients present with subacute asymmetric bilateral vision loss. Approximately 95% of the LHON cases are caused by m.3460G>A (MTND1), m.11778G>A (MTND4), and m.14484T>C (MTND6) mutations. The hallmark of hereditary optic neuropathies determined by mitochondrial dysfunction is the vulnerability and degeneration of retinal ganglion cells (RGC). We present the case of a 28-year-old man who came to our clinic complaining of a subacute decrease in visual acuity of his left eye. From his medical history, we found out that one month before he had the same symptoms in the right eye. From the family history, we noted that an uncle has had vision problems since childhood. We carried out complete blood tests, including specific antibodies for autoimmune and infectious diseases. Laboratory tests and MRI were within normal limits. A blood test of the mtDNA showed the presence of 11778 G>A mutation on the mtND6 gene. The medical history, the fundus appearance, the OCT, and the paraclinical investigations, made us diagnose our patient with Leber's hereditary optic neuropathy. As soon as possible, we began the treatment with systemic idebenone, 900 mg/day. We examined the patient 2, 6, and 10 weeks after initiating the treatment. Abbreviations: LHON = Leber's Hereditary Optic Neuropathy, mtDNA = mitochondrial DNA, VA = visual acuity, RE = right eye, LE = left eye, OCT = Optical coherence tomography, pRNFL = peripapillary retinal nerve fiber layer, GCL = retinal ganglion cells layer, MRI = magnetic resonance imaging, VEP = visual evoked potentials, VEP IT = VEP implicit time, VEP A = VEP amplitude.

Keywords:  Leber’s hereditary optic neuropathy; idebenone; optic atrophy; optic coherence tomography; retinal ganglion cell layer

DOI:  https://doi.org/10.22336/rjo.2024.13
Sci Adv. 2024 Apr 19. 10(16): eadm8815

Mitochondrial energy state controls AMPK-mediated foraging behavior in C. elegans.

Anežka Vodičková, Annika Müller-Eigner, Chidozie N Okoye, Andrew P Bischer, Jacob Horn, Shon A Koren, Nada Ahmed Selim, Andrew P Wojtovich.

Organisms surveil and respond to their environment using behaviors entrained by metabolic cues that reflect food availability. Mitochondria act as metabolic hubs and at the center of mitochondrial energy production is the protonmotive force (PMF), an electrochemical gradient generated by metabolite consumption. The PMF serves as a central integrator of mitochondrial status, but its role in governing metabolic signaling is poorly understood. We used optogenetics to dissipate the PMF in Caenorhabditis elegans tissues to test its role in food-related behaviors. Our data demonstrate that PMF reduction in the intestine is sufficient to initiate locomotor responses to acute food deprivation. This behavioral adaptation requires the cellular energy regulator AMP-activated protein kinase (AMPK) in neurons, not in the intestine, and relies on mitochondrial dynamics and axonal trafficking. Our results highlight a role for intestinal PMF as an internal metabolic cue, and we identify a bottom-up signaling axis through which changes in the PMF trigger AMPK activity in neurons to promote foraging behavior.

DOI: https://doi.org/10.1126/sciadv.adm8815
Genome Res. 2024 Apr 16.

A systematic review on the biochemical threshold of mitochondrial genetic variants.

Karan K Smith, Jesse D Moreira, Callum R Wilson, June O Padera, Ashlee N Lamason, Liying Xue, Deepa M Gopal, David B Flynn, Jessica L Fetterman.

Mitochondrial DNA (mtDNA) variants cause a range of diseases from severe pediatric syndromes to aging-related conditions. The percentage of mtDNA copies carrying a pathogenic variant, variant allele frequency (VAF), must reach a threshold before a biochemical defect occurs, termed the biochemical threshold. Whether the often-cited biochemical threshold of >60% VAF is similar across mtDNA variants and cell types is unclear. In our systematic review, we sought to identify the biochemical threshold of mtDNA variants in relation to VAF by human tissue/cell type. We used controlled vocabulary terms to identify articles measuring oxidative phosphorylation (OXPHOS) complex activities in relation to VAF. We identified 76 eligible publications, describing 69, 12, 16, and 49 cases for complexes I, III, IV, and V, respectively. Few studies evaluated OXPHOS activities in diverse tissue types, likely reflective of clinical access. A number of cases with similar VAFs for the same pathogenic variant had varying degrees of residual activity of the affected complex, alluding to the presence of modifying variants. Tissues and cells with VAFs <60% associated with low complex activities were described, suggesting the possibility of a biochemical threshold of <60%. Using Kendall rank correlation tests, the VAF of the m.8993T > G variant correlated with complex V activity in skeletal muscle (τ = -0.58, P = 0.01, n = 13); however, no correlation was observed in fibroblasts (P = 0.7, n = 9). Our systematic review highlights the need to investigate the biochemical threshold over a wider range of VAFs in disease-relevant cell types to better define the biochemical threshold for specific mtDNA variants.

DOI: https://doi.org/10.1101/gr.278200.123
Transl Neurodegener. 2024 Apr 17. 13(1): 23

Focusing on mitochondria in the brain: from biology to therapeutics.

Nanshan Song, Shuyuan Mei, Xiangxu Wang, Gang Hu, Ming Lu.

  Mitochondria have multiple functions such as supplying energy, regulating the redox status, and producing proteins encoded by an independent genome. They are closely related to the physiology and pathology of many organs and tissues, among which the brain is particularly prominent. The brain demands 20% of the resting metabolic rate and holds highly active mitochondrial activities. Considerable research shows that mitochondria are closely related to brain function, while mitochondrial defects induce or exacerbate pathology in the brain. In this review, we provide comprehensive research advances of mitochondrial biology involved in brain functions, as well as the mitochondria-dependent cellular events in brain physiology and pathology. Furthermore, various perspectives are explored to better identify the mitochondrial roles in neurological diseases and the neurophenotypes of mitochondrial diseases. Finally, mitochondrial therapies are discussed. Mitochondrial-targeting therapeutics are showing great potentials in the treatment of brain diseases.

Keywords:  Brain; Mitochondria; Mitochondrial transfer; Neurological disorders

DOI:  https://doi.org/10.1186/s40035-024-00409-w
bioRxiv. 2024 Apr 03. pii: 2024.04.02.587796. [Epub ahead of print]

High-resolution In-situ Structures of Mammalian Mitochondrial Respiratory Supercomplexes in Reaction within Native Mitochondria.

Wan Zheng, Pengxin Chai, Jiapeng Zhu, Kai Zhang.

Mitochondria play a pivotal role in ATP energy production through oxidative phosphorylation, which occurs within the inner membrane via a series of respiratory complexes. Despite extensive in-vitro structural studies, revealing the atomic details of their molecular mechanisms in physiological states remains a major challenge, primarily because of the loss of the native environment during purification. Here, we directly image porcine mitochondria using an in-situ cryo-electron microscopy approach. This enables us to determine the structures of various high-order assemblies of respiratory supercomplexes in their native states, achieving up to 1.8-Å local resolution. We identify four major supercomplex organizations: I1III2IV1, I1III2IV2, I2III2IV2, and I2III4IV2, which can potentially expand into higher-order arrays on the inner membranes. The formation of these diverse supercomplexes is largely contributed by 'protein-lipids-protein' interactions, which in turn dramatically impact the local geometry of the surrounding membranes. Our in-situ structures also capture numerous reactive intermediates within these respiratory supercomplexes, shedding light on the dynamic processes of the ubiquinone/ubiquinol exchange mechanism in complex I and the Q-cycle in complex III. By comparing supercomplex structures from mitochondria treated under distinct conditions, we elucidate how conformational changes and ligand binding states interplay between complexes I and III in response to environmental redox alterations. Our approach, by preserving the native membrane environment, enables structural studies of mitochondrial respiratory supercomplexes in reaction at high resolution across multiple scales, spanning from atomic-level details to the broader subcellular context.

DOI: https://doi.org/10.1101/2024.04.02.587796
J Pediatr Endocrinol Metab. 2024 Apr 18.

A very rare presentation of mitochondrial elongation factor Tu deficiency-TUFM mutation and literature review.

Sabire Gokalp, Asli Inci, Ayse Kilic, Ekin Ozsaydi, Ayse Nur Altun, Fevzi Demir, Filiz Basak Ergin, Mehmet Nuri Ozbek, Ilyas Okur, Fatih Ezgu, Leyla Tumer.

  OBJECTIVES: The mitochondrial elongation factor Tu (EF-Tu), encoded by the TUFM gene, is a GTPase, which is part of the mitochondrial protein translation mechanism. If it is activated, it delivers the aminoacyl-tRNAs to the mitochondrial ribosome. Here, a patient was described with a homozygous missense variant in the TUFM [c.1016G>A (p.Arg339Gln)] gene. To date, only six patients have been reported with bi-allelic pathogenic variants in TUFM, leading to combined oxidative phosphorylation deficiency 4 (COXPD4) characterized by severe early-onset lactic acidosis, encephalopathy, and cardiomyopathy.CASE PRESENTATION: The patient presented here had the phenotypic features of TUFM-related disease, lactic acidosis, hypotonia, liver dysfunction, optic atrophy, and mild encephalopathy.
CONCLUSIONS: We aimed to expand the clinical spectrum of pathogenic variants of TUFM.

Keywords:  TUFM mutation; combined oxidative phosphorylation deficiency 4; mitochondiral diseases

DOI:  https://doi.org/10.1515/jpem-2023-0569
Mol Aspects Med. 2024 Apr 15. pii: S0098-2997(24)00031-1. [Epub ahead of print]97 101272

Delineating the contribution of ageing and physical activity to changes in mitochondrial characteristics across the lifespan.

Matthew J-C Lee, Nicholas J Saner, Alessandra Ferri, Esther García-Domínguez, James R Broatch, David J Bishop.

Ageing is associated with widespread physiological changes prominent within all tissues, including skeletal muscle and the brain, which lead to a decline in physical function. To tackle the growing health and economic burdens associated with an ageing population, the concept of healthy ageing has become a major research priority. Changes in skeletal muscle mitochondrial characteristics have been suggested to make an important contribution to the reductions in skeletal muscle function with age, and age-related changes in mitochondrial content, respiratory function, morphology, and mitochondrial DNA have previously been reported. However, not all studies report changes in mitochondrial characteristics with ageing, and there is increasing evidence to suggest that physical activity (or inactivity) throughout life is a confounding factor when interpreting age-associated changes. Given that physical activity is a potent stimulus for inducing beneficial adaptations to mitochondrial characteristics, delineating the influence of physical activity on the changes in skeletal muscle that occur with age is complicated. This review aims to summarise our current understanding and knowledge gaps regarding age-related changes to mitochondrial characteristics within skeletal muscle, as well as to provide some novel insights into brain mitochondria, and to propose avenues of future research and targeted interventions. Furthermore, where possible, we incorporate discussions of the modifying effects of physical activity, exercise, and training status, to purported age-related changes in mitochondrial characteristics.

DOI: https://doi.org/10.1016/j.mam.2024.101272
J Biomed Sci. 2024 Apr 17. 31(1): 38

Attenuating mitochondrial dysfunction and morphological disruption with PT320 delays dopamine degeneration in MitoPark mice.

Vicki Wang, Kuan-Yin Tseng, Tung-Tai Kuo, Eagle Yi-Kung Huang, Kuo-Lun Lan, Zi-Rong Chen, Kuo-Hsing Ma, Nigel H Greig, Jin Jung, Ho-Ii Choi, Lars Olson, Barry J Hoffer, Yuan-Hao Chen.

  BACKGROUND: Mitochondria are essential organelles involved in cellular energy production. Changes in mitochondrial function can lead to dysfunction and cell death in aging and age-related disorders. Recent research suggests that mitochondrial dysfunction is closely linked to neurodegenerative diseases. Glucagon-like peptide-1 receptor (GLP-1R) agonist has gained interest as a potential treatment for Parkinson's disease (PD). However, the exact mechanisms responsible for the therapeutic effects of GLP-1R-related agonists are not yet fully understood.METHODS: In this study, we explores the effects of early treatment with PT320, a sustained release formulation of the GLP-1R agonist Exenatide, on mitochondrial functions and morphology in a progressive PD mouse model, the MitoPark (MP) mouse.
RESULTS: Our findings demonstrate that administration of a clinically translatable dose of PT320 ameliorates the reduction in tyrosine hydroxylase expression, lowers reactive oxygen species (ROS) levels, and inhibits mitochondrial cytochrome c release during nigrostriatal dopaminergic denervation in MP mice. PT320 treatment significantly preserved mitochondrial function and morphology but did not influence the reduction in mitochondria numbers during PD progression in MP mice. Genetic analysis indicated that the cytoprotective effect of PT320 is attributed to a reduction in the expression of mitochondrial fission protein 1 (Fis1) and an increase in the expression of optic atrophy type 1 (Opa1), which is known to play a role in maintaining mitochondrial homeostasis and decreasing cytochrome c release through remodeling of the cristae.
CONCLUSION: Our findings suggest that the early administration of PT320 shows potential as a neuroprotective treatment for PD, as it can preserve mitochondrial function. Through enhancing mitochondrial health by regulating Opa1 and Fis1, PT320 presents a new neuroprotective therapy in PD.

Keywords:  Exenatide; Glucagon-like peptide-1 receptor agonist; MitoPark mouse; Mitochondria; PT320; Parkinson’s disease

DOI:  https://doi.org/10.1186/s12929-024-01025-6
Nat Commun. 2024 Apr 18. 15(1): 3326

Cdk8/CDK19 promotes mitochondrial fission through Drp1 phosphorylation and can phenotypically suppress pink1 deficiency in Drosophila.

Jenny Zhe Liao, Hyung-Lok Chung, Claire Shih, Kenneth Kin Lam Wong, Debdeep Dutta, Zelha Nil, Catherine Grace Burns, Oguz Kanca, Ye-Jin Park, Zhongyuan Zuo, Paul C Marcogliese, Katherine Sew, Hugo J Bellen, Esther M Verheyen.

Cdk8 in Drosophila is the orthologue of vertebrate CDK8 and CDK19. These proteins have been shown to modulate transcriptional control by RNA polymerase II. We found that neuronal loss of Cdk8 severely reduces fly lifespan and causes bang sensitivity. Remarkably, these defects can be rescued by expression of human CDK19, found in the cytoplasm of neurons, suggesting a non-nuclear function of CDK19/Cdk8. Here we show that Cdk8 plays a critical role in the cytoplasm, with its loss causing elongated mitochondria in both muscles and neurons. We find that endogenous GFP-tagged Cdk8 can be found in both the cytoplasm and nucleus. We show that Cdk8 promotes the phosphorylation of Drp1 at S616, a protein required for mitochondrial fission. Interestingly, Pink1, a mitochondrial kinase implicated in Parkinson's disease, also phosphorylates Drp1 at the same residue. Indeed, overexpression of Cdk8 significantly suppresses the phenotypes observed in flies with low levels of Pink1, including elevated levels of ROS, mitochondrial dysmorphology, and behavioral defects. In summary, we propose that Pink1 and Cdk8 perform similar functions to promote Drp1-mediated fission.

DOI: https://doi.org/10.1038/s41467-024-47623-8
Cell Death Discov. 2024 Apr 17. 10(1): 180

PGC-1a mediated mitochondrial biogenesis promotes recovery and survival of neuronal cells from cellular degeneration.

Wenting You, Kèvin Knoops, Tos T J M Berendschot, Birke J Benedikter, Carroll A B Webers, Chris P M Reutelingsperger, Theo G M F Gorgels.

Neurodegenerative disorders are characterized by the progressive loss of structure and function of neurons, often including the death of the neuron. Previously, we reported that, by removing the cell death stimulus, dying/injured neurons could survive and recover from the process of regulated cell death, even if the cells already displayed various signs of cellular damage. Now we investigated the role of mitochondrial dynamics (fission/fusion, biogenesis, mitophagy) in both degeneration and in recovery of neuronal cells. In neuronal PC12 cells, exposure to ethanol (EtOH) induced massive neurite loss along with widespread mitochondrial fragmentation, mitochondrial membrane potential loss, reduced ATP production, and decreased total mitochondrial volume. By removing EtOH timely all these mitochondrial parameters recovered to normal levels. Meanwhile, cells regrew neurites and survived. Study of the mitochondrial dynamics showed that autophagy was activated only during the cellular degeneration phase (EtOH treatment) but not in the recovery phase (EtOH removed), and it was not dependent on the Parkin/PINK1 mediated mitophagy pathway. Protein expression of key regulators of mitochondrial fission, phospho-Drp1Ser616 and S-OPA1, increased during EtOH treatment and recovered to normal levels after removing EtOH. In addition, the critical role of PGC-1α mediated mitochondrial biogenesis in cellular recovery was revealed: inhibition of PGC-1α using SR-18292 after EtOH removal significantly impeded recovery of mitochondrial damage, regeneration of neurites, and cell survival in a concentration-dependent manner. Taken together, our study showed reversibility of mitochondrial morphological and functional damage in stressed neuronal cells and revealed that PGC-1α mediated mitochondrial biogenesis played a critical role in the cellular recovery. This molecular mechanism could be a target for neuroprotection and neurorescue in neurodegenerative diseases.

DOI: https://doi.org/10.1038/s41420-024-01953-0
Pediatr Neurol. 2024 Mar 06. pii: S0887-8994(24)00075-4. [Epub ahead of print]155 91-103

NDUFV1-Related Mitochondrial Complex-1 Disorders: A Retrospective Case Series and Literature Review.

Aakash Mahesan, Puneet Kumar Choudhary, Gautam Kamila, Aradhana Rohil, Ankit Kumar Meena, Atin Kumar, Prashant Jauhari, Biswaroop Chakrabarty, Sheffali Gulati.

  BACKGROUND: Pathogenic variants in the NDUFV1 gene disrupt mitochondrial complex I, leading to neuroregression with leukoencephalopathy and basal ganglia involvement on neuroimaging. This study aims to provide a concise review on NDUFV1-related disorders while adding the largest cohort from a single center to the existing literature.METHODS: We retrospectively collected genetically proven cases of NDUFV1 pathogenic variants from our center over the last decade and explored reported instances in existing literature. Magnetic resonance imaging (MRI) patterns observed in these patients were split into three types-Leigh (putamen, basal ganglia, thalamus, and brainstem involvement), mitochondrial leukodystrophy (ML) (cerebral white matter involvement with cystic cavitations), and mixed (both).
RESULTS: Analysis included 44 children (seven from our center and 37 from literature). The most prevalent comorbidities were hypertonia, ocular abnormalities, feeding issues, and hypotonia at onset. Children with the Leigh-type MRI pattern exhibited significantly higher rates of breathing difficulties, whereas those with a mixed phenotype had a higher prevalence of dystonia. The c.1156C>T variant in exon 8 of the NDUFV1 gene was the most common variant among individuals of Asian ethnicity and is predominantly associated with irritability and dystonia. Seizures and Leigh pattern of MRI of the brain was found to be less commonly associated with this variant. Higher rate of mortality was observed in children with Leigh-type pattern on brain MRI and those who did not receive mitochondrial cocktail.
CONCLUSIONS: MRI phenotyping might help predict outcome. Appropriate and timely treatment with mitochondrial cocktail may reduce the probability of death and may positively impact the long-term outcomes, regardless of the genetic variant or age of onset.

Keywords:  Leigh syndrome; Mitochondrial cocktail; Mitochondrial complex-I disorder; NDUFV1

DOI:  https://doi.org/10.1016/j.pediatrneurol.2024.02.012
Autops Case Rep. 2024 ;14 e2024483

Carnitine-acylcarnitine translocase deficiency: a case report with autopsy.

Chennakeshava Thunga, Suvradeep Mitra, Devi Dayal, Sadhna Lal.

  Fatty acid oxidation defects are a heterogeneous group of disorders related to the mitochondrial fatty acid oxidation pathway. Carnitine acylcarnitine translocase (CACT) is an enzyme responsible for the unidirectional transport of acylcarnitine across the inner mitochondrial membrane. This enzyme plays a crucial role in the oxidation of fatty acids. The autopsy pathology of the CACT deficiency is described in only a few cases. We describe the autopsy pathology of a child with CACT deficiency dominantly in the form of microvesicular steatosis of the hepatocytes, renal proximal tubular epithelia, cardiac myocytes, and rhabdomyocytes. The diagnosis was further confirmed on whole exome sequencing with compound heterozygous variants in the exon 1 (c.82G>T, p.Gly28Cys; likely pathogenic) and exon 5 (c.535G>A, p.Asp179Asn; uncertain significance) of the SLC25A20 gene. This case elucidates the histopathology of the liver and the detailed autopsy of a case of CACT deficiency from India.

Keywords:  Autopsy; Fatty liver; Pathology

DOI:  https://doi.org/10.4322/acr.2024.483
JCI Insight. 2024 Apr 16. pii: e168594. [Epub ahead of print]

Altered lipid homeostasis is associated with cerebellar neurodegeneration in SNX14 deficiency.

Yijing Zhou, Vanessa B Sanchez, Peining Xu, Thomas Roule, Marco Flores-Mendez, Brianna Ciesielski, Donna Yoo, Hiab Teshome, Teresa Jimenez, Shibo Liu, Mike Henne, Tim O'Brien, Ye He, Clementina Mesaros, Naiara Akizu.

  Dysregulated lipid homeostasis is emerging as a potential cause of neurodegenerative disorders. However, evidence of errors in lipid homeostasis as a pathogenic mechanism of neurodegeneration remains limited. Here, we show that cerebellar neurodegeneration caused by Sorting Nexin 14 (SNX14) deficiency is associated with lipid homeostasis defects. Recent studies indicate that SNX14 is an inter-organelle lipid transfer protein that regulates lipid transport, lipid droplet (LD) biogenesis, and fatty acid desaturation, suggesting that human SNX14 deficiency belongs to an expanding class of cerebellar neurodegenerative disorders caused by altered cellular lipid homeostasis. To test this hypothesis, we generated a mouse model that recapitulates human SNX14 deficiency at a genetic and phenotypic level. We demonstrate that cerebellar Purkinje cells (PCs) are selectively vulnerable to SNX14 deficiency while forebrain regions preserve their neuronal content. Ultrastructure and lipidomic studies reveal widespread lipid storage and metabolism defects in SNX14 deficient mice. However, pre-degenerating SNX14 deficient cerebella show a unique accumulation of acylcarnitines and depletion of triglycerides. Furthermore, defects in LD content and telolysosome enlargement in pre-degenerating PCs, suggest lipotoxicity as a pathogenic mechanism of SNX14 deficiency. Our work shows a selective cerebellar vulnerability to altered lipid homeostasis and provides a mouse model for future therapeutic studies.

Keywords:  Lysosomes; Monogenic diseases; Neurodegeneration; Neuroscience

DOI:  https://doi.org/10.1172/jci.insight.168594
Biochemistry (Mosc). 2024 Feb;89(2): 257-268

Safari with an Electron Gun: Visualization of Protein and Membrane Interactions in Mitochondria in Natural Environment.

Semen V Nesterov, Konstantin S Plokhikh, Yuriy M Chesnokov, Denis A Mustafin, Tatyana N Goleva, Anton G Rogov, Raif G Vasilov, Lev S Yaguzhinsky.

  This paper presents new structural data about mitochondria using correlative light and electron microscopy (CLEM) and cryo-electron tomography. These state-of-the-art structural biology methods allow studying biological objects at nanometer scales under natural conditions. Non-invasiveness of these methods makes them comparable to observing animals in their natural environment on a safari. The paper highlights two areas of research that can only be accomplished using these methods. The study visualized location of the Aβ42 amyloid aggregates in relation to mitochondria to test a hypothesis of development of mitochondrial dysfunction in Alzheimer's disease. The results showed that the Aβ42 aggregates do not interact with mitochondria, although some of them are closely located. Therefore, the study demonstrated that mitochondrial dysfunction is not directly associated with the effects of aggregates on mitochondrial structure. Other processes should be considered as sources of mitochondrial dysfunction. Second unique area presented in this work is high-resolution visualization of the mitochondrial membranes and proteins in them. Analysis of the cryo-ET data reveals toroidal holes in the lamellar structures of cardiac mitochondrial cristae, where ATP synthases are located. The study proposes a new mechanism for sorting and clustering protein complexes in the membrane based on topology. According to this suggestion, position of the OXPHOS system proteins in the membrane is determined by its curvature. High-resolution tomography expands and complements existing ideas about the structural and functional organization of mitochondria. This makes it possible to study the previously inaccessible structural interactions of proteins with each other and with membranes in vivo.

Keywords:  ATP synthase; Aβ42; amyloid aggregates; cryo-electron microscopy; membrane; mitochondria; oxidative phosphorylation; respirasome; supercomplex

DOI:  https://doi.org/10.1134/S0006297924020068
Nature. 2024 Apr 18.

AI's keen diagnostic eye.

Neil Savage.



Keywords:  Imaging; Machine learning; Medical research; Software

DOI:  https://doi.org/10.1038/d41586-024-01132-2
Biochim Biophys Acta Mol Cell Res. 2024 Apr 17. pii: S0167-4889(24)00076-4. [Epub ahead of print] 119733

Mitochondria function in cytoplasmic FeS protein biogenesis.

Andrew Dancis, Ashutosh K Pandey, Debkumar Pain.

  Iron‑sulfur (FeS) clusters are cofactors of numerous proteins involved in various essential functions including cellular respiration, protein translation, DNA synthesis and repair, ribosome maturation, anti-viral responses, and isopropylmalate isomerase activity. Novel FeS cluster proteins are still being discovered due to the widespread use of cryogenic electron microscopy (cryo-EM) and elegant genetic screens targeted at protein discovery. A complex sequence of biochemical reactions mediated by a conserved machinery controls biosynthesis of FeS clusters. In eukaryotes, a remarkable epistasis has been observed: the mitochondrial machinery, termed ISC (Iron-Sulfur Cluster), lies upstream of the cytoplasmic machinery, termed CIA (Cytoplasmic Iron‑sulfur protein Assembly). The basis for this arrangement is the production of a hitherto uncharacterized intermediate, termed X-S or (FeS)int, produced in mitochondria by the ISC machinery, exported by the mitochondrial ABC transporter Atm1 (ABC7 in humans), and then utilized by the CIA machinery for the cytoplasmic/nuclear FeS cluster assembly. Genetic and biochemical findings supporting this sequence of events are herein presented. New structural views of the Atm1 transport phases are reviewed. The key compartmental roles of glutathione in cellular FeS cluster biogenesis are highlighted. Finally, data are presented showing that every one of the ten core components of the mitochondrial ISC machinery and Atm1, when mutated or depleted, displays similar phenotypes: mitochondrial and cytoplasmic FeS clusters are both rendered deficient, consistent with the epistasis noted above.

Keywords:  (FeS)(int); Atm1; Cytoplasm; FeS cluster trafficking; FeS proteins; Glutaredoxin; Glutathione; Mitochondria; X-S

DOI:  https://doi.org/10.1016/j.bbamcr.2024.119733
J Physiol. 2024 Apr 17.

Early heart and skeletal muscle mitochondrial response to a moderate hypobaric hypoxia environment.

Jerónimo Aragón-Vela, Rafael A Casuso, Ana Sagrera Aparisi, Julio Plaza-Díaz, Ascensión Rueda-Robles, Agustín Hidalgo-Gutiérrez, Luis Carlos López, Andrea Rodríguez-Carrillo, José Antonio Enriquez, Sara Cogliati, Jesús R Huertas.

  In eukaryotic cells, aerobic energy is produced by mitochondria through oxygen uptake. However, little is known about the early mitochondrial responses to moderate hypobaric hypoxia (MHH) in highly metabolic active tissues. Here, we describe the mitochondrial responses to acute MHH in the heart and skeletal muscle. Rats were randomly allocated into a normoxia control group (n = 10) and a hypoxia group (n = 30), divided into three groups (0, 6, and 24 h post-MHH). The normoxia situation was recapitulated at the University of Granada, at 662 m above sea level. The MHH situation was performed at the High-Performance Altitude Training Centre of Sierra Nevada located in Granada at 2320 m above sea level. We found a significant increase in mitochondrial supercomplex assembly in the heart as soon as the animals reached 2320 m above sea level and their levels are maintained 24 h post-exposure, but not in skeletal muscle. Furthermore, in skeletal muscle, at 0 and 6 h, there was increased dynamin-related protein 1 (Drp1) expression and a significant reduction in Mitofusin 2. In conclusion, mitochondria from the muscle and heart respond differently to MHH: mitochondrial supercomplexes increase in the heart, whereas, in skeletal muscle, the mitochondrial pro-fission response is trigged. Considering that skeletal muscle was not actively involved in the ascent when the heart was beating faster to compensate for the hypobaric, hypoxic conditions, we speculate that the different responses to MHH are a result of the different energetic requirements of the tissues upon MHH. KEY POINTS: The heart and the skeletal muscle showed different mitochondrial responses to moderate hypobaric hypoxia. Moderate hypobaric hypoxia increases the assembly of the electron transport chain complexes into supercomplexes in the heart. Skeletal muscle shows an early mitochondrial pro-fission response following exposure to moderate hypobaric hypoxia.

Keywords:  heart; mitochondria; moderate hypobaric hypoxia; skeletal muscle; supercomplexes

DOI:  https://doi.org/10.1113/JP285516
Dis Model Mech. 2024 Jun 01. pii: dmm050623. [Epub ahead of print]17(6):

Improving access to gene therapy for rare diseases.

Thomas A Fox, Claire Booth.

  Effective gene therapy approaches have been developed for many rare diseases, including inborn errors of immunity and metabolism, haemoglobinopathies and inherited blindness. Despite successful pre-clinical and clinical results, these gene therapies are not widely available, primarily for non-medical reasons. Lack of commercial interest in therapies for ultra-rare diseases, costs of development and complex manufacturing processes required for advanced therapy medicinal products (ATMPs) are some of the main problems that are restricting access. The complexities and costs of navigating the regulatory environments in different jurisdictions for treatments that affect small numbers of patients is a problem unique to ATMPS for rare and ultra-rare diseases. In this Perspective, we outline some of the challenges and potential solutions that, we hope, will improve access to gene therapy for rare diseases.

Keywords:  Gene therapy; Inborn errors of immunity; Inborn errors of metabolism; Rare disease

DOI:  https://doi.org/10.1242/dmm.050623
Cell Death Discov. 2024 Apr 16. 10(1): 178

AAV-mediated upregulation of VDAC1 rescues the mitochondrial respiration and sirtuins expression in a SOD1 mouse model of inherited ALS.

Andrea Magrì, Cristiana Lucia Rita Lipari, Antonella Caccamo, Giuseppe Battiato, Stefano Conti Nibali, Vito De Pinto, Francesca Guarino, Angela Messina.

Mitochondrial dysfunction represents one of the most common molecular hallmarks of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder caused by the selective degeneration and death of motor neurons. The accumulation of misfolded proteins on and within mitochondria, as observed for SOD1 G93A mutant, correlates with a drastic reduction of mitochondrial respiration and the inhibition of metabolites exchanges, including ADP/ATP and NAD+/NADH, across the Voltage-Dependent Anion-selective Channel 1 (VDAC1), the most abundant channel protein of the outer mitochondrial membrane. Here, we show that the AAV-mediated upregulation of VDAC1 in the spinal cord of transgenic mice expressing SOD1 G93A completely rescues the mitochondrial respiratory profile. This correlates with the increased activity and levels of key regulators of mitochondrial functions and maintenance, namely the respiratory chain Complex I and the sirtuins (Sirt), especially Sirt3. Furthermore, the selective increase of these mitochondrial proteins is associated with an increase in Tom20 levels, the receptor subunit of the TOM complex. Overall, our results indicate that the overexpression of VDAC1 has beneficial effects on ALS-affected tissue by stabilizing the Complex I-Sirt3 axis.

DOI: https://doi.org/10.1038/s41420-024-01949-w
Neurol Genet. 2024 Jun;10(3): e200133

Cross-Sectional Analysis of Exome Sequencing Diagnosis in Patients With Neurologic Phenotypes Facing Barriers to Clinical Testing.

Sonya Watson, Kathie J Ngo, Hannah A Stevens, Darice Y Wong, Jihye Kim, Yongjun Song, Beomman Han, Seong-In Hyun, Rin Khang, Seung Woo Ryu, Eugene Lee, Gohun Seo, Hane Lee, Clara Lajonchere, Brent L Fogel.

Background and Objectives: Exome sequencing (ES) demonstrates a 20-50 percent diagnostic yield for patients with a suspected monogenic neurologic disease. Despite the proven efficacy in achieving a diagnosis for such patients, multiple barriers for obtaining exome sequencing remain. This study set out to assess the efficacy of ES in patients with primary neurologic phenotypes who were appropriate candidates for testing but had been unable to pursue clinical testing.Methods: A total of 297 patients were identified from the UCLA Clinical Neurogenomics Research Center Biobank, and ES was performed, including bioinformatic assessment of copy number variation and repeat expansions. Information regarding demographics, clinical indication for ES, and reason for not pursuing ES clinically were recorded. To assess diagnostic efficacy, variants were interpreted by a multidisciplinary team of clinicians, bioinformaticians, and genetic counselors in accordance with the American College of Medical Genetics and Genomics variant classification guidelines. We next examined the specific barriers to testing for these patients, including how frequently insurance-related barriers such as coverage denials and inadequate coverage of cost were obstacles to pursuing exome sequencing.
Results: The cohort primarily consisted of patients with sporadic conditions (n = 126, 42.4%) of adult-onset (n = 239, 80.5%). Cerebellar ataxia (n = 225, 75.8%) was the most common presenting neurologic phenotype. Our study found that in this population of mostly adult patients with primary neurologic phenotypes that were unable to pursue exome sequencing clinically, 47 (15.8%) had diagnostic results while an additional 24 patients (8.1%) had uncertain results. Of the 297 patients, 206 were initially recommended for clinical exome but 88 (42.7%) could not pursue ES because of insurance barriers, of whom 14 (15.9%) had diagnostic findings, representing 29.8% of all patients with diagnostic findings. In addition, the incorporation of bioinformatic repeat expansion testing was valuable, identifying a total of 8 pathogenic repeat expansions (17.0% of all diagnostic findings) including 3 of the common spinocerebellar ataxias and 2 patients with Huntington disease.
Discussion: These findings underscore the importance and value of clinical ES as a diagnostic tool for neurogenetic disease and highlight key barriers that prevent patients from receiving important clinical information with potential treatment and psychosocial implications for patients and family members.

DOI: https://doi.org/10.1212/NXG.0000000000200133
Blood. 2024 Apr 18. pii: blood.2023022004. [Epub ahead of print]

Mitochondrial tRNA pseudouridylation governs erythropoiesis.

Bichen Wang, Deyang Shi, Shuang Yang, Yu Lian, Haoyuan Li, Mutian Cao, Yifei He, Lele Zhang, Chen Qiu, Tong Liu, Wei Wen, Yuanwu Ma, Lei Shi, Tao Cheng, Lihong Shi, Weiping Yuan, Yajing Chu, Jun Shi.

Pseudouridine is the most prevalent RNA modification, and its aberrant function is implicated in various human diseases. However, the specific impact of pseudouridylation on hematopoiesis remains poorly understood. In this study, we investigated the role of tRNA pseudouridylation in erythropoiesis and its association with mitochondrial myopathy, lactic acidosis, and sideroblastic anemia syndrome (MLASA) pathogenesis. By utilizing patient-specific induced pluripotent stem cells (iPSCs) carrying a genetic PUS1 mutation and a corresponding mutant mouse model, we demonstrated impaired erythropoiesis in MLASA iPSCs and anemia in the MLASA mouse model. Both MLASA iPSCs and mouse erythroblasts exhibited compromised mitochondrial function and impaired protein synthesis. Mechanistically, we revealed that PUS1 deficiency resulted in reduced mitochondrial tRNA levels due to pseudouridylation loss, leading to aberrant mitochondrial translation. Screening of mitochondrial supplements aimed at enhancing respiration or heme synthesis showed limited effect in promoting erythroid differentiation. Interestingly, the mTOR inhibitor rapamycin facilitated erythroid differentiation in MLASA-iPSCs by suppressing mTOR signaling and protein synthesis, and consistent results were observed in the MLASA mouse model. Importantly, rapamycin treatment effectively ameliorated anemia phenotypes in the MLASA patient. Our findings provide novel insights into the crucial role of mitochondrial tRNA pseudouridylation in governing erythropoiesis and present potential therapeutic strategies for anemia patients facing challenges related to protein translation.

DOI: https://doi.org/10.1182/blood.2023022004
Cold Spring Harb Perspect Biol. 2024 Apr 15. pii: a041467. [Epub ahead of print]

Variant Effect Prediction in the Age of Machine Learning.

Yana Bromberg, R Prabakaran, Anowarul Kabir, Amarda Shehu.

Over the years, many computational methods have been created for the analysis of the impact of single amino acid substitutions resulting from single-nucleotide variants in genome coding regions. Historically, all methods have been supervised and thus limited by the inadequate sizes of experimentally curated data sets and by the lack of a standardized definition of variant effect. The emergence of unsupervised, deep learning (DL)-based methods raised an important question: Can machines learn the language of life from the unannotated protein sequence data well enough to identify significant errors in the protein "sentences"? Our analysis suggests that some unsupervised methods perform as well or better than existing supervised methods. Unsupervised methods are also faster and can, thus, be useful in large-scale variant evaluations. For all other methods, however, their performance varies by both evaluation metrics and by the type of variant effect being predicted. We also note that the evaluation of method performance is still lacking on less-studied, nonhuman proteins where unsupervised methods hold the most promise.

DOI: https://doi.org/10.1101/cshperspect.a041467
Biochem Biophys Res Commun. 2024 Apr 16. pii: S0006-291X(24)00480-7. [Epub ahead of print]712-713 149944

Effect of 2-aminoethoxydiphenyl borate on the functions of mouse skeletal muscle mitochondria.

Mikhail V Dubinin, Alexander V Chulkov, Anastasia D Igoshkina, Alena A Cherepanova, Natalia V Mikina.

  This work examined the effect of 2-aminoethoxydiphenyl borate (2-APB) on the functioning of isolated mouse skeletal muscle mitochondria and modeled its putative interaction with mitochondrial proteins. We have shown that 2-APB is able to dose-dependently suppress mitochondrial respiration in state 3 and 3UDNP driven by substrates of complex I and II. This effect of 2-APB was accompanied by a slight dose-dependent decrease in mitochondrial membrane potential and appears to be due to inhibition of complex I and complex III of the electron transport chain (ETC) with IC50 values of 200 and 120 μM, respectively. The results of molecular docking identified putative 2-APB interaction sites in these ETC complexes. 2-APB was shown to dose-dependently inhibit both mitochondrial Ca2+ uptake and Ca2+ efflux, which seems to be caused by a decrease in the membrane potential of the organelles. We have found that 2-APB has no significant effect on mitochondrial calcium retention capacity. On the other hand, 2-APB exhibited antioxidant effect by reducing mitochondrial hydrogen peroxide production but without affecting superoxide generation. It is concluded that the effect of 2-APB on mitochondrial targets should be taken into account when interpreting the results of cell and in vivo experiments.

Keywords:  2-Aminoethoxydiphenyl borate; Calcium; Electron transport chain; MPT-Pore; Skeletal muscle mitochondria

DOI:  https://doi.org/10.1016/j.bbrc.2024.149944
J Bone Miner Res. 2024 Apr 15. pii: zjae058. [Epub ahead of print]

RANKL signaling drives skeletal muscle into the oxidative profile.

Paulo Henrique Cavalcanti de Araújo, Maria Eduarda Ramos Cezine, Anderson Vulczak, Luiz Carlos Vieira, Flávia Sayuri Matsuo, Júlia Maranghetti Remoto, Audrei Dos Reis Santos, Elen Haruka Miyabara, Luciane Carla Alberici, Mariana Kiomy Osako.

  The bone-muscle unit refers to the reciprocal regulation between bone and muscle by mechanical interaction and tissue communication via soluble factors. The receptor activator of NF-κB ligand (RANKL) stimulation induces mitochondrial biogenesis and increases the oxidative capacity in osteoclasts and adipocytes. RANKL may bind to the membrane bound receptor activator of NF-κB (RANK) or to osteoprotegerin (OPG), a decoy receptor that inhibits RANK-RANKL activation. RANK is highly expressed in skeletal muscle, but the contribution of RANKL to healthy skeletal muscle fiber remains elusive. Here we show that RANKL stimulation in C2C12-derived myotubes induced activation of mitochondrial biogenesis pathways as detected by RNA-seq and western blot. RANKL expanded the mitochondrial reticulum, as shown by mitochondrial DNA quantification and MitoTracker staining, and boosted the spare respiratory capacity. Using MEK and MAPK inhibitors, we found that RANKL signals via ERK and p38 to induce mitochondrial biogenesis. The soleus from OPG-/- and OPG+/- mice showed higher respiratory rates compared to C57BL6/J wild-type (WT) mice, which correlates with high serum RANKL levels. RANKL infusion using a mini-osmotic pump in WT mice increased the number of mitochondria, boosted the respiratory rate, increased succinate dehydrogenase (SDH) activity in skeletal muscle, and improved the fatigue resistance of gastrocnemius. Therefore, our findings reveal a new role of RANKL as an osteokine-like protein that impacts muscle fiber metabolism.

Keywords:  OPG; RANKL; fiber type switch; mitochondrial biogenesis; skeletal muscle

DOI:  https://doi.org/10.1093/jbmr/zjae058
bioRxiv. 2024 Apr 04. pii: 2024.04.04.588123. [Epub ahead of print]

The Structure of the Drp1 Lattice on Membrane.

Ruizhi Peng, Kristy Rochon, Scott M Stagg, Jason A Mears.

Mitochondrial health relies on the membrane fission mediated by dynamin-related protein 1 (Drp1). Previous structural studies of Drp1 on remodeled membranes were hampered by heterogeneity, leaving a critical gap in the understanding of the mitochondrial fission mechanism. Here we present a cryo-electron microscopy structure of full-length human Drp1 decorated on membrane tubules. Using the reconstruction of average subtracted tubular regions (RASTR) technique, we report that Drp1 forms a locally ordered lattice along the tubule without global helical symmetry. The filaments in the lattice are similar to dynamin rungs with conserved stalk interactions. Adjacent filaments are connected by GTPase domain interactions in a novel stacked conformation. Additionally, we observed contact between Drp1 and membrane that can be assigned to variable domain sequence. We identified two states of the Drp1 lattice representing conformational changes related to membrane curvature differences. Together these structures revealed a putative mechanism by which Drp1 constricts mitochondria membranes in a stepwise, "ratchet" manner.SUMMARY: This study provides new insights into the structure of Drp1 on lipid membranes. A locally ordered Drp1 lattice structure is solved and reveals intermolecular contacts and conformational rearrangements that suggest a mechanism for constriction of mitochondrial membranes.

DOI: https://doi.org/10.1101/2024.04.04.588123
Br J Pharmacol. 2024 Apr 19.

Hydroxymethylglutaryl-CoA reductase activity is essential for mitochondrial β-oxidation of fatty acids to prevent lethal accumulation of long-chain acylcarnitines in the mouse liver.

Edgars Liepinsh, Liga Zvejniece, Laura Clemensson, Melita Ozola, Edijs Vavers, Helena Cirule, Stanislava Korzh, Sandra Skuja, Valerija Groma, Monta Briviba, Solveiga Grinberga, Wen Liu, Paweł Olszewski, Mélissa Gentreau, Robert Fredriksson, Maija Dambrova, Helgi B Schiöth.

  BACKGROUND AND PURPOSE: Statins are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR), and exert adverse effects on mitochondrial function, although the mechanisms underlying these effects remain unclear. We used a tamoxifen-induced Hmgcr-knockout (KO) mouse model, a multi-omics approach and mitochondrial function assessments to investigate whether decreased HMGCR activity impacts key liver energy metabolism pathways.EXPERIMENTAL APPROACH: We established a new mouse strain using the Cre/loxP system, which enabled whole-body deletion of Hmgcr expression. These mice were crossed with Rosa26Cre mice and treated with tamoxifen to delete Hmgcr in all cells. We performed transcriptomic and metabolomic analyses and thus evaluated time-dependent changes in metabolic functions to identify the pathways leading to cell death in Hmgcr-KO mice.
KEY RESULTS: Lack of Hmgcr expression resulted in lethality, due to acute liver damage caused by rapid disruption of mitochondrial fatty acid β-oxidation and very high accumulation of long-chain (LC) acylcarnitines in both male and female mice. Gene expression and KO-related phenotype changes were not observed in other tissues. The progression to liver failure was driven by diminished peroxisome formation, which resulted in impaired mitochondrial and peroxisomal fatty acid metabolism, enhanced glucose utilization and whole-body hypoglycaemia.
CONCLUSION AND IMPLICATIONS: Our findings suggest that HMGCR is crucial for maintaining energy metabolism balance, and its activity is necessary for functional mitochondrial β-oxidation. Moreover, statin-induced adverse reactions might be rescued by the prevention of LC acylcarnitine accumulation.

Keywords:  HMG‐CoA reductase; Rosa26Cre mice; mitochondria; statins; tamoxifen‐induced knockout mouse model

DOI:  https://doi.org/10.1111/bph.16363
Biochemistry (Mosc). 2024 Feb;89(2): 279-298

Enhanced ROS Production in Mitochondria from Prematurely Aging mtDNA Mutator Mice.

Irina G Shabalina, Daniel Edgar, Natalia Gibanova, Anastasia V Kalinovich, Natasa Petrovic, Mikhail Yu Vyssokikh, Barbara Cannon, Jan Nedergaard.

  An increase in mitochondrial DNA (mtDNA) mutations and an ensuing increase in mitochondrial reactive oxygen species (ROS) production have been suggested to be a cause of the aging process ("the mitochondrial hypothesis of aging"). In agreement with this, mtDNA-mutator mice accumulate a large amount of mtDNA mutations, giving rise to defective mitochondria and an accelerated aging phenotype. However, incongruously, the rates of ROS production in mtDNA mutator mitochondria have generally earlier been reported to be lower - not higher - than in wildtype, thus apparently invalidating the "mitochondrial hypothesis of aging". We have here re-examined ROS production rates in mtDNA-mutator mice mitochondria. Using traditional conditions for measuring ROS (succinate in the absence of rotenone), we indeed found lower ROS in the mtDNA-mutator mitochondria compared to wildtype. This ROS mainly results from reverse electron flow driven by the membrane potential, but the membrane potential reached in the isolated mtDNA-mutator mitochondria was 33 mV lower than that in wildtype mitochondria, due to the feedback inhibition of succinate oxidation by oxaloacetate, and to a lower oxidative capacity in the mtDNA-mutator mice, explaining the lower ROS production. In contrast, in normal forward electron flow systems (pyruvate (or glutamate) + malate or palmitoyl-CoA + carnitine), mitochondrial ROS production was higher in the mtDNA-mutator mitochondria. Particularly, even during active oxidative phosphorylation (as would be ongoing physiologically), higher ROS rates were seen in the mtDNA-mutator mitochondria than in wildtype. Thus, when examined under physiological conditions, mitochondrial ROS production rates are indeed increased in mtDNA-mutator mitochondria. While this does not prove the validity of the mitochondrial hypothesis of aging, it may no longer be said to be negated in this respect. This paper is dedicated to the memory of Professor Vladimir P. Skulachev.

Keywords:  ROS production; aging; membrane potential; mtDNA mutator mice; oxidative phosphorylation; succinate

DOI:  https://doi.org/10.1134/S0006297924020081
Infect Disord Drug Targets. 2024 Apr 16.

Patient-Centric Approaches: Revolutionizing Rare Disease Drug Research.

Abhishek Verma, Ankit Awasthi.



Keywords:  Patient-Reported Outcome Measures (PROMs); Rare diseases; drug development; patient-centric approaches; precision medicine.

DOI:  https://doi.org/10.2174/0118715265296986240329060452
Biochem Soc Trans. 2024 Apr 17. pii: BST20231236. [Epub ahead of print]

New insights into the structure and dynamics of the TOM complex in mitochondria.

Stephan Nussberger, Robin Ghosh, Shuo Wang.

  To date, there is no general physical model of the mechanism by which unfolded polypeptide chains with different properties are imported into the mitochondria. At the molecular level, it is still unclear how transit polypeptides approach, are captured by the protein translocation machinery in the outer mitochondrial membrane, and how they subsequently cross the entropic barrier of a protein translocation pore to enter the intermembrane space. This deficiency has been due to the lack of detailed structural and dynamic information about the membrane pores. In this review, we focus on the recently determined sub-nanometer cryo-EM structures and our current knowledge of the dynamics of the mitochondrial two-pore outer membrane protein translocation machinery (TOM core complex), which provide a starting point for addressing the above questions. Of particular interest are recent discoveries showing that the TOM core complex can act as a mechanosensor, where the pores close as a result of interaction with membrane-proximal structures. We highlight unusual and new correlations between the structural elements of the TOM complexes and their dynamic behavior in the membrane environment.

Keywords:  Tom complex; electron cryo-microscopy; mechanosensitivity; mitochondria; protein translocation; single-molecule microscopy

DOI:  https://doi.org/10.1042/BST20231236
Nature. 2024 Apr;628(8008): 509

A step along the path towards AlphaFold - 50 years ago.



Keywords:  History; Physics; Structural biology

DOI:  https://doi.org/10.1038/d41586-024-01094-5
PLoS One. 2024 ;19(4): e0300350

Bioinformatics pipeline for the systematic mining genomic and proteomic variation linked to rare diseases: The example of monogenic diabetes.

Ksenia G Kuznetsova, Jakub Vašíček, Dafni Skiadopoulou, Janne Molnes, Miriam Udler, Stefan Johansson, Pål Rasmus Njølstad, Alisa Manning, Marc Vaudel.

Monogenic diabetes is characterized as a group of diseases caused by rare variants in single genes. Like for other rare diseases, multiple genes have been linked to monogenic diabetes with different measures of pathogenicity, but the information on the genes and variants is not unified among different resources, making it challenging to process them informatically. We have developed an automated pipeline for collecting and harmonizing data on genetic variants linked to monogenic diabetes. Furthermore, we have translated variant genetic sequences into protein sequences accounting for all protein isoforms and their variants. This allows researchers to consolidate information on variant genes and proteins linked to monogenic diabetes and facilitates their study using proteomics or structural biology. Our open and flexible implementation using Jupyter notebooks enables tailoring and modifying the pipeline and its application to other rare diseases.

DOI: https://doi.org/10.1371/journal.pone.0300350
Nat Genet. 2024 Apr;56(4): 557

Implementing polygenic risk scores in the clinic.

Kyle Vogan.

DOI: https://doi.org/10.1038/s41588-024-01730-w
Circ Res. 2024 Apr 15.

Inhibition of the mPTP and Lipid Peroxidation Is Additively Protective Against I/R Injury.

Arielys Mendoza, Pooja Patel, Dexter Robichaux, Daniel Ramirez, Jason Karch.

  BACKGROUND: During myocardial ischemia/reperfusion (I/R) injury, high levels of matrix Ca2+ and reactive oxygen species (ROS) induce the opening of the mitochondrial permeability transition pore (mPTP), which causes mitochondrial dysfunction and ultimately necrotic death. However, the mechanisms of how these triggers individually or cooperatively open the pore have yet to be determined.METHODS: Here, we use a combination of isolated mitochondrial assays and in vivo I/R surgery in mice. We challenged isolated liver and heart mitochondria with Ca2+, ROS, and Fe2+ to induce mitochondrial swelling. Using inhibitors of the mPTP (cyclosporine A or ADP) lipid peroxidation (Fer-1 [ferrostatin-1], mitoquinone), we determined how the triggers elicit mitochondrial damage. Additionally, we used the combination of inhibitors during I/R injury in mice to determine if dual inhibition of these pathways is additivity protective.
RESULTS: In the absence of Ca2+, we determined that ROS fails to trigger mPTP opening. Instead, high levels of ROS induce mitochondrial dysfunction and rupture independently of the mPTP through lipid peroxidation. As expected, Ca2+ in the absence of ROS induces mPTP-dependent mitochondrial swelling. Subtoxic levels of ROS and Ca2+ synergize to induce mPTP opening. Furthermore, this synergistic form of Ca2+- and ROS-induced mPTP opening persists in the absence of CypD (cyclophilin D), suggesting the existence of a CypD-independent mechanism for ROS sensitization of the mPTP. These ex vivo findings suggest that mitochondrial dysfunction may be achieved by multiple means during I/R injury. We determined that dual inhibition of the mPTP and lipid peroxidation is significantly more protective against I/R injury than individually targeting either pathway alone.
CONCLUSIONS: In the present study, we have investigated the relationship between Ca2+ and ROS, and how they individually or synergistically induce mitochondrial swelling. Our findings suggest that Ca2+ mediates mitochondrial damage through the opening of the mPTP, although ROS mediates its damaging effects through lipid peroxidation. However, subtoxic levels both Ca2+ and ROS can induce mPTP-mediated mitochondrial damage. Targeting both of these triggers to preserve mitochondria viability unveils a highly effective therapeutic approach for mitigating I/R injury.

Keywords:  apoptosis; cell death; heart attack; mice; mitochondria

DOI:  https://doi.org/10.1161/CIRCRESAHA.123.323882
Genome Biol. 2024 Apr 19. 25(1): 100

Minimum information and guidelines for reporting a multiplexed assay of variant effect.

Melina Claussnitzer, Victoria N Parikh, Alex H Wagner, Jeremy A Arbesfeld, Carol J Bult, Helen V Firth, Lara A Muffley, Alex N Nguyen Ba, Kevin Riehle, Frederick P Roth, Daniel Tabet, Benedetta Bolognesi, Andrew M Glazer, Alan F Rubin.

  Multiplexed assays of variant effect (MAVEs) have emerged as a powerful approach for interrogating thousands of genetic variants in a single experiment. The flexibility and widespread adoption of these techniques across diverse disciplines have led to a heterogeneous mix of data formats and descriptions, which complicates the downstream use of the resulting datasets. To address these issues and promote reproducibility and reuse of MAVE data, we define a set of minimum information standards for MAVE data and metadata and outline a controlled vocabulary aligned with established biomedical ontologies for describing these experimental designs.

Keywords:  DMS; Deep mutational scanning; Genetic variants; Genomics; MAVE; Multiplexed assays of variant effect; Standards

DOI:  https://doi.org/10.1186/s13059-024-03223-9
Genet Med. 2024 Apr 13. pii: S1098-3600(24)00074-1. [Epub ahead of print] 101141

Lethal phenotypes in Mendelian disorders.

Pilar Cacheiro, Samantha Lawson, Ignatia B Van den Veyver, Gabriel Marengo, David Zocche, Stephen A Murray, Michael Duyzend, Peter N Robinson, Damian Smedley.

  PURPOSE: Existing resources that characterise the essentiality status of genes are based on either proliferation assessment in human cell lines, viability evaluation in mouse knockouts, or constraint metrics derived from human population sequencing studies. Several repositories document phenotypic annotations for rare disorders, however there is a lack of comprehensive reporting on lethal phenotypes.METHODS: We queried Online Mendelian Inheritance in Man for terms related to lethality and classified all Mendelian genes according to the earliest age of death recorded for the associated disorders, from prenatal death to no reports of premature death. We characterised the genes across these lethality categories, examined the evidence on viability from mouse models and explored how this information could be used for novel gene discovery.
RESULTS: We developed the Lethal Phenotypes Portal to showcase this curated catalogue of human essential genes. Differences in the mode of inheritance, physiological systems affected and disease class were found for genes in different lethality categories as well as discrepancies between the lethal phenotypes observed in mouse and human.
CONCLUSION: We anticipate that this resource will aid clinicians in the diagnosis of early lethal conditions and assist researchers in investigating the properties that make these genes essential for human development.

Keywords:  Essential genes; Lethal mouse knockouts; Lethal phenotypes; Mendelian disorders; Novel gene discovery

DOI:  https://doi.org/10.1016/j.gim.2024.101141