bims-mitmed 2023-05-14 papers

bims-mitmed

Biomed News

on Mitochondrial medicine

Issue of 2023–05–14
27 papers selected by
Dario Brunetti, Fondazione IRCCS Istituto Neurologico

FBXL4 suppresses mitophagy by restricting the accumulation of NIX and BNIP3 mitophagy receptors.
C. elegans as a model to study mitochondrial biology and disease.
Mitochondrial Dysfunction as a Signaling Target for Therapeutic Intervention in Major Neurodegenerative Disease.
Depletion of WFS1 compromises mitochondrial function in hiPSC-derived neuronal models of Wolfram syndrome.
Protein transport along the presequence pathway.
Fuel oxidation under the control of mitochondrial shape and dynamics.
A two-step mitochondrial import pathway couples the disulfide relay with matrix complex I biogenesis.
The ARG8m Reporter for the Study of Yeast Mitochondrial Translation.
From mitochondria to sarcopenia: role of 17β-estradiol and testosterone.
Assembly of the Mitochondrial Translation Initiation Complex.
APOE expression and secretion are modulated by mitochondrial dysfunction.
Severe neonatal onset neuroregression with paroxysmal dystonia and apnoea: Expanding the phenotypic and genotypic spectrum of CARS2-related mitochondrial disease.
Mitochondrial citrate metabolism and efflux regulate BeWo differentiation.
Mitochondrial Ion Channels.
Newly imported proteins in mitochondria are particularly sensitive to aggregation.
TIM23 facilitates PINK1 activation by safeguarding against OMA1-mediated degradation in damaged mitochondria.
Inflammatory, mitochondrial, and senescence-related markers: Underlying biological pathways of muscle aging and new therapeutic targets.
Biallelic variants in COQ7 cause distal hereditary motor neuropathy with upper motor neuron signs.
Omaveloxolone: First Approval.
Reduced mitophagy is an early feature of NAFLD and liver-specific PARKIN knockout hastens the onset of steatosis, inflammation and fibrosis.
Adult-onset leukodystrophy with vanishing white matter: a case series of 19 patients.
Immune Responses to Muscle-Directed AAV Gene Transfer in Clinical Studies.
Human embryo science: can the world's regulators keep pace?
Imaging Subcellular AMPK Activity Using an Excitation-Ratiometric AMPK Activity Reporter.
Selection of iPSCs without mtDNA deletion for autologous cell therapy in a patient with Pearson syndrome.
Anatomical and functional maturation of the mid-gestation human enteric nervous system.
Exercise improves homeostasis of the intestinal epithelium by activation of APJ-AMPK signaling.

EMBO J. 2023 May 10. e112767

FBXL4 suppresses mitophagy by restricting the accumulation of NIX and BNIP3 mitophagy receptors.

Giang Thanh Nguyen-Dien, Keri-Lyn Kozul, Yi Cui, Brendan Townsend, Prajakta Gosavi Kulkarni, Soo Siang Ooi, Antonio Marzio, Nissa Carrodus, Steven Zuryn, Michele Pagano, Robert G Parton, Michael Lazarou, S Sean Millard, Robert W Taylor, Brett M Collins, Mathew Jk Jones, Julia K Pagan.

  To maintain both mitochondrial quality and quantity, cells selectively remove damaged or excessive mitochondria through mitophagy, which is a specialised form of autophagy. Mitophagy is induced in response to diverse conditions, including hypoxia, cellular differentiation and mitochondrial damage. However, the mechanisms that govern the removal of specific dysfunctional mitochondria under steady-state conditions to fine-tune mitochondrial content are not well understood. Here, we report that SCFFBXL4 , an SKP1/CUL1/F-box protein ubiquitin ligase complex, localises to the mitochondrial outer membrane in unstressed cells and mediates the constitutive ubiquitylation and degradation of the mitophagy receptors NIX and BNIP3 to suppress basal levels of mitophagy. We demonstrate that the pathogenic variants of FBXL4 that cause encephalopathic mtDNA depletion syndrome (MTDPS13) do not efficiently interact with the core SCF ubiquitin ligase machinery or mediate the degradation of NIX and BNIP3. Thus, we reveal a molecular mechanism whereby FBXL4 actively suppresses mitophagy by preventing NIX and BNIP3 accumulation. We propose that the dysregulation of NIX and BNIP3 turnover causes excessive basal mitophagy in FBXL4-associated mtDNA depletion syndrome.

Keywords:  BNIP3; FBXL4; NIX/BNIP3L; mitochondria; mitophagy

DOI:  https://doi.org/10.15252/embj.2022112767
Semin Cell Dev Biol. 2023 May 04. pii: S1084-9521(23)00101-5. [Epub ahead of print]

C. elegans as a model to study mitochondrial biology and disease.

Tessa Onraet, Steven Zuryn.

  Mitochondria perform a myriad of essential functions that ensure organismal homeostasis, including maintaining bioenergetic capacity, sensing and signalling the presence of pathogenic threats, and determining cell fate. Their function is highly dependent on mitochondrial quality control and the appropriate regulation of mitochondrial size, shape, and distribution during an entire lifetime, as well as their inheritance across generations. The roundworm Caenorhabditis elegans has emerged as an ideal model organism through which to study mitochondria. The remarkable conservation of mitochondrial biology has allowed C. elegans researchers to investigate complex processes that are challenging to study in higher organisms. In this review, we explore the key recent contributions of C. elegans to mitochondrial biology through the lens of mitochondrial dynamics, organellar removal, and mitochondrial inheritance, as well as their involvement in immune responses, various types of stress, and transgenerational signalling.

Keywords:  Aging; Biogenesis; Fission; Fusion; Mitochondrial disease; Mitophagy; MtDNA; Neurodegeneration; Proteotoxicity; UPRmt

DOI:  https://doi.org/10.1016/j.semcdb.2023.04.006
Neurotox Res. 2023 May 10.

Mitochondrial Dysfunction as a Signaling Target for Therapeutic Intervention in Major Neurodegenerative Disease.

Shubhada V Mangrulkar, Nitu L Wankhede, Mayur B Kale, Aman B Upaganlawar, Brijesh G Taksande, Milind J Umekar, Md Khalid Anwer, Hamad Ghaleb Dailah, Syam Mohan, Tapan Behl.

  Neurodegenerative diseases (NDD) are incurable and the most prevalent cognitive and motor disorders of elderly. Mitochondria are essential for a wide range of cellular processes playing a pivotal role in a number of cellular functions like metabolism, intracellular signaling, apoptosis, and immunity. A plethora of evidence indicates the central role of mitochondrial functions in pathogenesis of many aging related NDD. Considering how mitochondria function in neurodegenerative diseases, oxidative stress, and mutations in mtDNA both contribute to aging. Many substantial reports suggested the involvement of numerous contributing factors including, mitochondrial dysfunction, oxidative stress, mitophagy, accumulation of somatic mtDNA mutations, compromised mitochondrial dynamics, and transport within axons in neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic Lateral Sclerosis. Therapies therefore target fundamental mitochondrial processes such as energy metabolism, free-radical generation, mitochondrial biogenesis, mitochondrial redox state, mitochondrial dynamics, mitochondrial protein synthesis, mitochondrial quality control, and metabolism hold great promise to develop pharmacological based therapies in NDD. By emphasizing the most efficient pharmacological strategies to target dysfunction of mitochondria in the treatment of neurodegenerative diseases, this review serves the scientific community engaged in translational medical science by focusing on the establishment of novel, mitochondria-targeted treatment strategies.

Keywords:  Fission; Fusion; Mitochondrial dysfunction; Mitochondrial medicine; Mitochondrial quality control; Oxidative stress

DOI:  https://doi.org/10.1007/s12640-023-00647-2
Stem Cell Reports. 2023 May 09. pii: S2213-6711(23)00136-4. [Epub ahead of print]18(5): 1090-1106

Depletion of WFS1 compromises mitochondrial function in hiPSC-derived neuronal models of Wolfram syndrome.

Malgorzata Zatyka, Tatiana R Rosenstock, Congxin Sun, Adina M Palhegyi, Georgina W Hughes, Samuel Lara-Reyna, Dewi Astuti, Alessandro di Maio, Axel Sciauvaud, Miriam E Korsgen, Vesna Stanulovic, Gamze Kocak, Malgorzata Rak, Sandra Pourtoy-Brasselet, Katherine Winter, Thiago Varga, Margot Jarrige, Hélène Polvèche, Joao Correia, Eva-Maria Frickel, Maarten Hoogenkamp, Douglas G Ward, Laetitia Aubry, Timothy Barrett, Sovan Sarkar.

  Mitochondrial dysfunction involving mitochondria-associated ER membrane (MAM) dysregulation is implicated in the pathogenesis of late-onset neurodegenerative diseases, but understanding is limited for rare early-onset conditions. Loss of the MAM-resident protein WFS1 causes Wolfram syndrome (WS), a rare early-onset neurodegenerative disease that has been linked to mitochondrial abnormalities. Here we demonstrate mitochondrial dysfunction in human induced pluripotent stem cell-derived neuronal cells of WS patients. VDAC1 is identified to interact with WFS1, whereas loss of this interaction in WS cells could compromise mitochondrial function. Restoring WFS1 levels in WS cells reinstates WFS1-VDAC1 interaction, which correlates with an increase in MAMs and mitochondrial network that could positively affect mitochondrial function. Genetic rescue by WFS1 overexpression or pharmacological agents modulating mitochondrial function improves the viability and bioenergetics of WS neurons. Our data implicate a role of WFS1 in regulating mitochondrial functionality and highlight a therapeutic intervention for WS and related rare diseases with mitochondrial defects.

Keywords:  Cyclosporin A; Human induced pluripotent stem cell-derived neurons; Mitochondria-associated ER membrane; Mitochondrial dysfunction; Mitochondrial membrane potential; MnTBAP; Neurodegeneration; VDAC1; WFS1; Wolfram syndrome

DOI:  https://doi.org/10.1016/j.stemcr.2023.04.002
Biol Chem. 2023 May 09.

Protein transport along the presequence pathway.

Abhijith Makki, Peter Rehling.

  Most mitochondrial proteins are nuclear-encoded and imported by the protein import machinery based on specific targeting signals. The proteins that carry an amino-terminal targeting signal (presequence) are imported via the presequence import pathway that involves the translocases of the outer and inner membranes - TOM and TIM23 complexes. In this article, we discuss how mitochondrial matrix and inner membrane precursor proteins are imported along the presequence pathway in Saccharomyces cerevisiae with a focus on the dynamics of the TIM23 complex, and further update with some of the key findings that advanced the field in the last few years.

Keywords:  PAM; TIM23 complex; TOM complex; mitochondria; presequence translocase; protein translocation

DOI:  https://doi.org/10.1515/hsz-2023-0133
EMBO J. 2023 May 08. e114129

Fuel oxidation under the control of mitochondrial shape and dynamics.

Erin L Seifert, György Hajnóczky.

How mitochondrial shape and substrate-specific metabolism are related has been a difficult question to address. Here, new work by Ngo et al (2023) reports that mitochondrial shape-long versus fragmented-determines the activity of β-oxidation of long-chain fatty acids, supporting a novel role for mitochondrial fission products as β-oxidation hubs.

DOI: https://doi.org/10.15252/embj.2023114129
J Cell Biol. 2023 Jul 03. pii: e202210019. [Epub ahead of print]222(7):

A two-step mitochondrial import pathway couples the disulfide relay with matrix complex I biogenesis.

Esra Peker, Konstantin Weiss, Jiyao Song, Christine Zarges, Sarah Gerlich, Volker Boehm, Aleksandra Trifunovic, Thomas Langer, Niels H Gehring, Thomas Becker, Jan Riemer.

Mitochondria critically rely on protein import and its tight regulation. Here, we found that the complex I assembly factor NDUFAF8 follows a two-step import pathway linking IMS and matrix import systems. A weak targeting sequence drives TIM23-dependent NDUFAF8 matrix import, and en route, allows exposure to the IMS disulfide relay, which oxidizes NDUFAF8. Import is closely surveyed by proteases: YME1L prevents accumulation of excess NDUFAF8 in the IMS, while CLPP degrades reduced NDUFAF8 in the matrix. Therefore, NDUFAF8 can only fulfil its function in complex I biogenesis if both oxidation in the IMS and subsequent matrix import work efficiently. We propose that the two-step import pathway for NDUFAF8 allows integration of the activity of matrix complex I biogenesis pathways with the activity of the mitochondrial disulfide relay system in the IMS. Such coordination might not be limited to NDUFAF8 as we identified further proteins that can follow such a two-step import pathway.

DOI: https://doi.org/10.1083/jcb.202210019
Methods Mol Biol. 2023 ;2661 281-301

The ARG8m Reporter for the Study of Yeast Mitochondrial Translation.

Daniel Flores-Mireles, Yolanda Camacho-Villasana, Xochitl Pérez-Martínez.

  Mitochondrial translation is an intricate process involving both general and mRNA-specific factors. In addition, in the yeast Saccharomyces cerevisiae, translation of mitochondrial mRNAs is coupled to assembly of nascent polypeptides into the membrane. ARG8m is a reporter gene widely used to study the mechanisms of yeast mitochondrial translation. This reporter is a recodified gene that uses the mitochondrial genetic code and is inserted at the desired locus in the mitochondrial genome. After deletion of the endogenous nuclear gene, this reporter produces Arg8, an enzyme necessary for arginine biosynthesis. Since Arg8 is a soluble protein with no relation to oxidative phosphorylation, it is a reliable reporter to study mitochondrial mRNAs translation and dissect translation form assembly processes. In this chapter, we explain how to insert the ARG8m reporter in the desired spot in the mitochondrial DNA, how to analyze Arg8 synthesis inside mitochondria, and how to follow steady-state levels of the protein. We also explain how to use it to find spontaneous suppressors of translation defects.

Keywords:  ARG8m; ATP synthase; Cytochrome c oxidase; Mitochondria; Mitochondrial DNA; Respiratory complexes; Suppressor; Translation; Yeast; bc1 complex

DOI:  https://doi.org/10.1007/978-1-0716-3171-3_16
Front Endocrinol (Lausanne). 2023 ;14 1156583

From mitochondria to sarcopenia: role of 17β-estradiol and testosterone.

Xu Tian, Shujie Lou, Rengfei Shi.

  Sarcopenia, characterized by a loss of muscle mass and strength with aging, is prevalent in older adults. Although the exact mechanisms underlying sarcopenia are not fully understood, evidence suggests that the loss of mitochondrial integrity in skeletal myocytes has emerged as a pivotal contributor to the complex etiology of sarcopenia. Mitochondria are the primary source of ATP production and are also involved in generating reactive oxygen species (ROS), regulating ion signals, and initiating apoptosis signals in muscle cells. The accumulation of damaged mitochondria due to age-related impairments in any of the mitochondrial quality control (MQC) processes, such as proteostasis, biogenesis, dynamics, and mitophagy, can contribute to the decline in muscle mass and strength associated with aging. Interestingly, a decrease in sex hormones (e.g., 17β-estradiol and testosterone), which occurs with aging, has also been linked to sarcopenia. Indeed, 17β-estradiol and testosterone targeted mitochondria and exhibited activities in regulating mitochondrial functions. Here, we overview the current literature on the key mechanisms by which mitochondrial dysfunction contribute to the development and progression of sarcopenia and the potential modulatory effects of 17β-estradiol and testosterone on mitochondrial function in this context. The advance in its understanding will facilitate the development of potential therapeutic agents to mitigate and manage sarcopenia.

Keywords:  17β-estradiol; aging; mitochondria; sarcopenia; skeletal muscle; testosterone

DOI:  https://doi.org/10.3389/fendo.2023.1156583
Methods Mol Biol. 2023 ;2661 217-232

Assembly of the Mitochondrial Translation Initiation Complex.

Cristina Remes, Minh Duc Nguyen, Henrik Spahr, Martin Ng, Clark Fritsch, Arpan Bhattacharya, Hong Li, Barry Cooperman, Joanna Rorbach.

  Mitochondria maintain their own translational machinery that is responsible for the synthesis of essential components of the oxidative phosphorylation system. The mammalian mitochondrial translation system differs significantly from its cytosolic and bacterial counterparts. Here, we describe detailed protocols for efficient in vitro reconstitution of the mammalian mitochondrial translation initiation complex, which can be further used for mechanistic analyses of different aspects of mitochondrial translation.

Keywords:  Mitoribosome; Translation; Translation factors; Translation initiation; tRNA purification

DOI:  https://doi.org/10.1007/978-1-0716-3171-3_13
Elife. 2023 May 12. pii: e85779. [Epub ahead of print]12

APOE expression and secretion are modulated by mitochondrial dysfunction.

Meghan E Wynne, Oluwaseun Ogunbona, Alicia R Lane, Avanti Gokhale, Stephanie A Zlatic, Chongchong Xu, Zhexing Wen, Duc M Duong, Sruti Rayaprolu, Anna Ivanova, Eric A Ortlund, Eric B Dammer, Nicholas T Seyfried, Blaine R Roberts, Amanda Crocker, Vinit Shanbhag, Michael Petris, Nanami Senoo, Selvaraju Kandasamy, Steven Michael Claypool, Antoni Barrientos, Aliza Wingo, Thomas S Wingo, Srikant Rangaraju, Allan I Levey, Erica Werner, Victor Faundez.

  Mitochondria influence cellular function through both cell-autonomous and non-cell autonomous mechanisms, such as production of paracrine and endocrine factors. Here, we demonstrate that mitochondrial regulation of the secretome is more extensive than previously appreciated, as both genetic and pharmacological disruption of the electron transport chain caused upregulation of the Alzheimer's disease risk factor apolipoprotein E (APOE) and other secretome components. Indirect disruption of the electron transport chain by gene editing of SLC25A mitochondrial membrane transporters as well as direct genetic and pharmacological disruption of either complexes I, III, or the copper-containing complex IV of the electron transport chain, elicited upregulation of APOE transcript, protein, and secretion, up to 49-fold. These APOE phenotypes were robustly expressed in diverse cell types and iPSC-derived human astrocytes as part of an inflammatory gene expression program. Moreover, age- and genotype-dependent decline in brain levels of respiratory complex I preceded an increase in APOE in the 5xFAD mouse model. We propose that mitochondria act as novel upstream regulators of APOE-dependent cellular processes in health and disease.

Keywords:  cell biology; human; neuroscience

DOI:  https://doi.org/10.7554/eLife.85779
JIMD Rep. 2023 May;64(3): 223-232

Severe neonatal onset neuroregression with paroxysmal dystonia and apnoea: Expanding the phenotypic and genotypic spectrum of CARS2-related mitochondrial disease.

Jessie Poquérusse, Melinda Nolan, David R Thorburn, Johan L K Van Hove, Marisa W Friederich, Donald R Love, Juliet Taylor, Christopher A Powell, Michal Minczuk, Russell G Snell, Klaus Lehnert, Emma Glamuzina, Jessie C Jacobsen.

  Disorders of mitochondrial function are a collectively common group of genetic diseases in which deficits in core mitochondrial translation machinery, including aminoacyl tRNA synthetases, are key players. Biallelic variants in the CARS2 gene (NM_024537.4), which encodes the mitochondrial aminoacyl-tRNA synthetase for cysteine (CARS2, mt-aaRScys; MIM*612800), result in childhood onset epileptic encephalopathy and complex movement disorder with combined oxidative phosphorylation deficiency (MIM#616672). Prior to this report, eight unique pathogenic variants in the CARS2 gene had been reported in seven individuals. Here, we describe a male who presented in the third week of life with apnoea. He rapidly deteriorated with paroxysmal dystonic crises and apnoea resulting in death at 16 weeks. He had no evidence of seizure activity or multisystem disease and had normal brain imaging. Skeletal muscle biopsy revealed a combined disorder of oxidative phosphorylation. Whole-exome sequencing identified biallelic variants in the CARS2 gene: one novel (c.1478T>C, p.Phe493Ser), and one previously reported (c.655G>A, p.Ala219Thr; rs727505361). Northern blot analysis of RNA isolated from the patient's fibroblasts confirmed a clear defect in aminoacylation of the mitochondrial tRNA for cysteine (mt-tRNACys). To our knowledge, this is the earliest reported case of CARS2 deficiency with severe, early onset dystonia and apnoea, without epilepsy.

Keywords:  CARS2; mitochondrial disorders; neurodevelopmental disorder; tRNA synthetases; whole‐exome sequencing

DOI:  https://doi.org/10.1002/jmd2.12360
Sci Rep. 2023 05 06. 13(1): 7387

Mitochondrial citrate metabolism and efflux regulate BeWo differentiation.

Renee M Mahr, Snehalata Jena, Sereen K Nashif, Alisa B Nelson, Adam J Rauckhorst, Ferrol I Rome, Ryan D Sheldon, Curtis C Hughey, Patrycja Puchalska, Micah D Gearhart, Eric B Taylor, Peter A Crawford, Sarah A Wernimont.

Cytotrophoblasts fuse to form and renew syncytiotrophoblasts necessary to maintain placental health throughout gestation. During cytotrophoblast to syncytiotrophoblast differentiation, cells undergo regulated metabolic and transcriptional reprogramming. Mitochondria play a critical role in differentiation events in cellular systems, thus we hypothesized that mitochondrial metabolism played a central role in trophoblast differentiation. In this work, we employed static and stable isotope tracing untargeted metabolomics methods along with gene expression and histone acetylation studies in an established BeWo cell culture model of trophoblast differentiation. Differentiation was associated with increased abundance of the TCA cycle intermediates citrate and α-ketoglutarate. Citrate was preferentially exported from mitochondria in the undifferentiated state but was retained to a larger extent within mitochondria upon differentiation. Correspondingly, differentiation was associated with decreased expression of the mitochondrial citrate transporter (CIC). CRISPR/Cas9 disruption of the mitochondrial citrate carrier showed that CIC is required for biochemical differentiation of trophoblasts. Loss of CIC resulted in broad alterations in gene expression and histone acetylation. These gene expression changes were partially rescued through acetate supplementation. Taken together, these results highlight a central role for mitochondrial citrate metabolism in orchestrating histone acetylation and gene expression during trophoblast differentiation.

DOI: https://doi.org/10.1038/s41598-023-34435-x
Annu Rev Biophys. 2023 05 09. 52 229-254

Mitochondrial Ion Channels.

Ildiko Szabo, Adam Szewczyk.

  Mitochondria are involved in multiple cellular tasks, such as ATP synthesis, metabolism, metabolite and ion transport, regulation of apoptosis, inflammation, signaling, and inheritance of mitochondrial DNA. The majority of the correct functioning of mitochondria is based on the large electrochemical proton gradient, whose component, the inner mitochondrial membrane potential, is strictly controlled by ion transport through mitochondrial membranes. Consequently, mitochondrial function is critically dependent on ion homeostasis, the disturbance of which leads to abnormal cell functions. Therefore, the discovery of mitochondrial ion channels influencing ion permeability through the membrane has defined a new dimension of the function of ion channels in different cell types, mainly linked to the important tasks that mitochondrial ion channels perform in cell life and death. This review summarizes studies on animal mitochondrial ion channels with special focus on their biophysical properties, molecular identity, and regulation. Additionally, the potential of mitochondrial ion channels as therapeutic targets for several diseases is briefly discussed.

Keywords:  calcium channels; chloride channels; mitochondria; mitochondrial megachannel; porin; potassium channels

DOI:  https://doi.org/10.1146/annurev-biophys-092622-094853
Acta Physiol (Oxf). 2023 May 12. e13985

Newly imported proteins in mitochondria are particularly sensitive to aggregation.

Carmela Vazquez-Calvo, Verena Kohler, Johanna L Höög, Sabrina Büttner, Martin Ott.

   AIM: A functional proteome is essential for life and maintained by protein quality control (PQC) systems in the cytosol and organelles. Protein aggregation is an indicator of a decline of PQC linked to aging and disease. Mitochondrial PQC is critical to maintain mitochondrial function and thus cellular fitness. How mitochondria handle aggregated proteins is not well understood. Here we tested how the metabolic status impacts on formation and clearance of aggregates within yeast mitochondria and assessed which proteins are particularly sensitive to denaturation.
METHODS: Confocal microscopy, electron microscopy, immunoblotting and genetics were applied to assess mitochondrial aggregate handling in response to heat shock and ethanol, using the mitochondrial disaggregase Hsp78 as a marker for protein aggregates.
RESULTS: We show that aggregates formed upon heat or ethanol stress with different dynamics depending on the metabolic state. While fermenting cells displayed numerous small aggregates that coalesced into one large foci that was resistant to clearance, respiring cells showed less aggregates and cleared these aggregates more efficiently. Acute inhibition of mitochondrial translation had no effect, while preventing protein import into mitochondria by inhibition of cytosolic translation prevented aggregate formation.
CONCLUSION: Collectively, our data show that the metabolic state of the cells impacts the dynamics of aggregate formation and clearance, and that mainly newly imported and not yet assembled proteins are prone to form aggregates. Because mitochondrial functionality is crucial for cellular metabolism, these results highlight the importance of efficient protein biogenesis to maintain the mitochondrial proteome operational during metabolic adaptations and cellular stress.

Keywords:  Ageing; Aggregates; Cellular stress; Hsp78; Metabolism; Mitochondria; Protein quality control; Proteostasis

DOI:  https://doi.org/10.1111/apha.13985
Cell Rep. 2023 Apr 30. pii: S2211-1247(23)00465-5. [Epub ahead of print] 112454

TIM23 facilitates PINK1 activation by safeguarding against OMA1-mediated degradation in damaged mitochondria.

Shiori Akabane, Kiyona Watanabe, Hidetaka Kosako, Shun-Ichi Yamashita, Kohei Nishino, Masahiro Kato, Shiori Sekine, Tomotake Kanki, Noriyuki Matsuda, Toshiya Endo, Toshihiko Oka.

  PINK1 is activated by autophosphorylation and forms a high-molecular-weight complex, thereby initiating the selective removal of damaged mitochondria by autophagy. Other than translocase of the outer mitochondrial membrane complexes, members of PINK1-containing protein complexes remain obscure. By mass spectrometric analysis of PINK1 co-immunoprecipitates, we identify the inner membrane protein TIM23 as a component of the PINK1 complex. TIM23 downregulation decreases PINK1 levels and significantly delays autophosphorylation, indicating that TIM23 promotes PINK1 accumulation in response to depolarization. Moreover, inactivation of the mitochondrial protease OMA1 not only enhances PINK1 accumulation but also represses the reduction in PINK1 levels induced by TIM23 downregulation, suggesting that TIM23 facilitates PINK1 activation by safeguarding against degradation by OMA1. Indeed, deficiencies of pathogenic PINK1 mutants that fail to interact with TIM23 are partially restored by OMA1 inactivation. These findings indicate that TIM23 plays a distinct role in activating mitochondrial autophagy by protecting PINK1.

Keywords:  CP: Cell biology; OMA1; PINK1; TIM23; mitochondrial quality control

DOI:  https://doi.org/10.1016/j.celrep.2023.112454
Exp Gerontol. 2023 May 09. pii: S0531-5565(23)00125-0. [Epub ahead of print] 112204

Inflammatory, mitochondrial, and senescence-related markers: Underlying biological pathways of muscle aging and new therapeutic targets.

Anna Picca, Biliana Lozanoska-Ochser, Riccardo Calvani, Hélio José Coelho-Júnior, Christiaan Leewenburgh, Emanuele Marzetti.

  The maintenance of functional health is pivotal for achieving independent life in older age. The aged muscle is characterized by ultrastructural changes, including loss of type I and type II myofibers and a greater proportion of cytochrome c oxidase deficient and succinate dehydrogenase positive fibers. Both intrinsic (e.g., altered proteostasis, DNA damage, and mitochondrial dysfunction) and extrinsic factors (e.g., denervation, altered metabolic regulation, declines in satellite cells, and inflammation) contribute to muscle aging. Being a hub for several cellular activities, mitochondria are key to myocyte viability and mitochondrial dysfunction has been implicated in age-associated physical decline. The maintenance of functional organelles via mitochondrial quality control (MQC) processes is, therefore, crucial to skeletal myofiber viability. The autophagy-lysosome pathway has emerged as a critical step of MQC in muscle by disposing organelles and proteins via their tagging for autophagosome incorporation and delivery to the lysosome for clearance. This pathway has been reported to be altered in muscle of physically inactive older people. A relationship between this pathway and muscle tissue composition of the lower extremities as well as physical performance has been identified. Therefore, integrating muscle structure and myocyte quality control measures in the evaluation of muscle health may be a promising strategy for devising interventions fostering muscle health.

Keywords:  Cytokine; Extracellular matrix; Mitochondrial quality; Physical performance; Sarcopenia; Satellite cells

DOI:  https://doi.org/10.1016/j.exger.2023.112204
Brain. 2023 May 12. pii: awad158. [Epub ahead of print]

Biallelic variants in COQ7 cause distal hereditary motor neuropathy with upper motor neuron signs.

Adriana P Rebelo, Pedro J Tomaselli, Jessica Medina, Ying Wang, Maike Dohrn, Eva Nyvltova, Matt Denzi, Mark Garrett, Sean Smith, Alan Pestronk, ChengCheng Li, Ariel Ruiz, Elizabeth Jacobs, Shawna M E Feely, Marcondes C França, Marcus V Gomes, Diogo Santos, Surinder Kumar, David B Lombard, Mario Saporta, Siegfried Hekimi, Antonio Barrientos, Conrad Weihl, Michael Shy, Wilson Marques, Stephan Zuchner.

  COQ7 encodes a hydroxylase responsible for the penultimate step of coenzyme Q10 (CoQ10) biosynthesis in mitochondria. CoQ10 is essential for multiple cellular functions, including mitochondrial oxidative phosphorylation, lipid metabolism, and reactive oxygen species homeostasis. Mutations in COQ7 have been previously associated with primary coenzyme Q10 deficiency, a clinically heterogeneous multisystemic mitochondrial disorder. We identified COQ7 biallelic variants in nine families diagnosed with distal hereditary motor neuropathy (dHMN) with upper neuron involvement, expending the clinical phenotype associated with defects in this gene. A recurrent p.Met1? change was identified in five families from Brazil with evidence of a founder effect. Fibroblasts isolated from patients revealed a substantial depletion of COQ7 protein levels, indicating protein instability leading to loss of enzyme function. HPLC assay showed that fibroblasts from patients had reduced levels of CoQ10, and abnormal accumulation of the biosynthetic precursor DMQ10. Accordingly, fibroblasts from patients displayed significantly decreased oxygen consumption rates in patients, suggesting mitochondrial respiration deficiency. iPSC-derived motor neurons from patient fibroblasts showed significantly increased levels of extracellular neurofilament light protein, indicating axonal degeneration. Our findings indicate a molecular pathway involving CoQ10 biosynthesis deficiency and mitochondrial dysfunction in patients with dHMN. Further studies will be important to evaluate the potential benefits of CoQ10 supplementation in the clinical outcome of the disease.

Keywords:  Charcot-Marie-Tooth disease; CoQ10; hereditary motor neuropathy; mitochondria; motor neuron

DOI:  https://doi.org/10.1093/brain/awad158
Drugs. 2023 May 08.

Omaveloxolone: First Approval.

Arnold Lee.

Omaveloxolone (SKYCLARYS™) is an orally active, small molecule semi-synthetic triterpenoid drug that increases antioxidant activity, which is being developed by Reata Pharmaceuticals, Inc. for the treatment of Friedreich's ataxia. In patients with Friedreich's ataxia, the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway is suppressed, which is associated with oxidative stress, mitochondrial dysfunction and damage to cells, including central and peripheral neurones. The Nrf2 pathway may be activated by omaveloxolone as it blocks the ubiquitination and degradation of Nrf2. Omaveloxolone was approved in February 2023 in the USA for the treatment of Friedreich's ataxia. This article summarizes the milestones in the development of omaveloxolone leading to this first approval for the treatment of Friedreich's ataxia in adults and adolescents aged 16 years and older.

DOI: https://doi.org/10.1007/s40265-023-01874-9
Sci Rep. 2023 May 10. 13(1): 7575

Reduced mitophagy is an early feature of NAFLD and liver-specific PARKIN knockout hastens the onset of steatosis, inflammation and fibrosis.

R Undamatla, O G Fagunloye, J Chen, L R Edmunds, A Murali, A Mills, B Xie, M M Pangburn, I Sipula, G Gibson, C St Croix, M J Jurczak.

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of pathologies that includes steatosis, steatohepatitis (NASH) and fibrosis and is strongly associated with insulin resistance and type 2 diabetes. Changes in mitochondrial function are implicated in the pathogenesis of NAFLD, particularly in the transition from steatosis to NASH. Mitophagy is a mitochondrial quality control mechanism that allows for the selective removal of damaged mitochondria from the cell via the autophagy pathway. While past work demonstrated a negative association between liver fat content and rates of mitophagy, when changes in mitophagy occur during the pathogenesis of NAFLD and whether such changes contribute to the primary endpoints associated with the disease are currently poorly defined. We therefore undertook the studies described here to establish when alterations in mitophagy occur during the pathogenesis of NAFLD, as well as to determine the effects of genetic inhibition of mitophagy via conditional deletion of a key mitophagy regulator, PARKIN, on the development of steatosis, insulin resistance, inflammation and fibrosis. We find that loss of mitophagy occurs early in the pathogenesis of NAFLD and that loss of PARKIN accelerates the onset of key NAFLD disease features. These observations suggest that loss of mitochondrial quality control in response to nutritional stress may contribute to mitochondrial dysfunction and the pathogenesis of NAFLD.

DOI: https://doi.org/10.1038/s41598-023-34710-x
J Neurol. 2023 May 12.

Adult-onset leukodystrophy with vanishing white matter: a case series of 19 patients.

Chiara Benzoni, Marco Moscatelli, Laura Farina, Stefania Magri, Claudia Ciano, Vidmer Scaioli, Sara Alverà, Gabriella Cammarata, Stefania Bianchi-Marzoli, Massimo Castellani, Felicia Margherita Zito, Giorgio Marotta, Sylvie Piacentini, Alberto Villacara, Renato Mantegazza, Cinzia Gellera, João Durães, Ana Gouveia, Anabela Matos, Maria do Carmo Macário, Davide Pareyson, Franco Taroni, Daniela Di Bella, Ettore Salsano.

   BACKGROUND: Leukodystrophy with vanishing white matter (LVWM) is an autosomal recessive disease with typical pediatric-onset caused by mutations in one of the five EIF2B genes. Adult-onset (AO) cases are rare.
METHODS: In this observational study, we reviewed clinical and laboratory information of the patients with AO-LVWM assessed at two referral centers in Italy and Portugal from Jan-2007 to Dec-2019.
RESULTS: We identified 18 patients (13 females) with AO-LVWM caused by EIF2B5 or EIF2B3 mutations. Age of neurological onset ranged from 16 to 60 years, with follow-ups occurring from 2 to 37 years. Crucial symptoms were cognitive and motor decline. In three patients, stroke-like events were the first manifestation; in another, bladder dysfunction remained the main complaint across decades. Brain MRI showed white matter (WM) rarefaction in all cases, except two. Diffusion-weighted imaging documented focal hyperintensity in the acute stage of stroke-like events. 1H-spectroscopy primarily showed N-acetyl-aspartate reduction; 18fluorodeoxyglucose-PET revealed predominant frontoparietal hypometabolism; evoked potential studies demonstrated normal-to-reduced amplitudes; neuro-ophthalmological assessment showed neuroretinal thinning, and b-wave reduction on full-field electroretinogram. Interestingly, we found an additional patient with LVWM-compatible phenotype and monoallelic variants in two distinct eIF2B genes, EIF2B1 and EIF2B2.
CONCLUSIONS: AO-LVWM presents varying clinical manifestations at onset, including stroke-like events. WM rarefaction is the most consistent diagnostic clue even in the latest onset cases. Spectroscopy and electrophysiological features are compatible with axon, rather than myelin, damage. Cerebral glucose metabolic abnormalities and retinal alterations can be present. LVWM might also be caused by a digenic inheritance affecting the eIF2B complex.

Keywords:  Genetic leukoencephalopathies; Leukodystrophies; MRI; PET; Stroke

DOI:  https://doi.org/10.1007/s00415-023-11762-7
Hum Gene Ther. 2023 May 08.

Immune Responses to Muscle-Directed AAV Gene Transfer in Clinical Studies.

Sandeep R P Kumar, Dongsheng Duan, Roland Herzog.

Muscle-directed gene therapy with adeno-associated viral (AAV) vectors is undergoing clinical development for treating neuromuscular disorders and for systemic delivery of therapeutic proteins. While these approaches show considerable therapeutic benefits, they are also prone to induce potent immune responses against vector or transgene products owing to the immunogenic nature of the intramuscular delivery route, or the high doses required for systemic delivery to muscle. Major immunological concerns include antibody formation against viral capsid, complement activation, and cytotoxic T-cell responses against capsid or transgene products. They can negate therapy and even lead to life-threatening immunotoxicities. Herein we review clinical observations and provide an outlook for how the field addresses these problems through a combination of vector engineering and immune modulation.

DOI: https://doi.org/10.1089/hum.2023.056
Nature. 2023 May;617(7960): 242-243

Human embryo science: can the world's regulators keep pace?

Philip Ball.



Keywords:  Developmental biology; Genetics; Policy

DOI:  https://doi.org/10.1038/d41586-023-01550-8
Curr Protoc. 2023 May;3(5): e771

Imaging Subcellular AMPK Activity Using an Excitation-Ratiometric AMPK Activity Reporter.

Danielle L Schmitt.

  Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a master regulator of cellular metabolism, phosphorylating a variety of downstream targets throughout the cell. Subcellular AMPK activity results in regulation of glycolysis, lipid and protein biosynthesis, mitochondrial function, and gene expression. But how AMPK senses and responds to stimuli in a compartment-specific manner is not well understood, leaving an incomplete picture of compartmentalized AMPK activity. Key tools for studying subcellular AMPK activity are genetically encoded AMPK activity reporters (AMPKARs), which allow for the quantitative visualization of subcelluar AMPK activity. However, many AMPKARs suffer from poor dynamic range and sensitivity, limiting their application. I recently reported the development of a new excitation-ratiometric (ExRai) AMPKAR, a single-fluorophore AMPKAR with enhanced dynamic range for detection of subtle, subcellular AMPK activity. I used ExRai AMPKAR to study subcellular AMPK activity at several locations, including the lysosome and mitochondria, identifying new mechanisms for the regulation of AMPK activity. Here, I describe the use of ExRai AMPKAR to image subcellular AMPK activity in mouse embryonic fibroblasts using both widefield and confocal microscopy. I also describe the culture of mouse embryonic fibroblasts. Through the use of ExRai AMPKAR, subcellular AMPK activity can be illuminated to better understand how this central kinase regulates cellular metabolism. © 2023 The Author. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Imaging subcellular AMPK activity using ExRai AMPKAR Support Protocol 1: Culturing of mouse embryonic fibroblasts for live-cell imaging Support Protocol 2: Live-cell imaging of ExRai AMPKAR using confocal microscopy.

Keywords:  AMPK; biosensor; compartmentalized signaling; fluorescence; live-cell imaging

DOI:  https://doi.org/10.1002/cpz1.771
BMB Rep. 2023 May 09. pii: 5823. [Epub ahead of print]

Selection of iPSCs without mtDNA deletion for autologous cell therapy in a patient with Pearson syndrome.

Yeonmi Lee, Jongsuk Han, Sae-Byeok Hwang, Soon-Suk Kang, Hyeoung-Bin Son, Chaeyeon Jin, Jae Eun Kim, Beom Hee Lee, Eunju Kang.

Screening for genetic defects in the cells should be examined for clinical application. The Pearson syndrome (PS) patient harbored nuclear mutations in the POLG and SSBP1 genes, which could induce systemic large-scale mitochondrial genome (mtDNA) deletion. We investigated iPSCs with mtDNA deletions in PS patient and whether deletion levels could be maintained during differentiation. The iPSC clones derived from skin fibroblasts (9% deletion) and blood mononuclear cells (24% deletion) were measured for mtDNA deletion levels. Of the 13 skin-derived iPSC clones, only 3 were found to be free of mtDNA deletions, whereas all blood-derived iPSC clones were found to be free of deletions. The iPSC clones with (27%) and without mtDNA deletion (0%) were selected and performed in vitro and in vivo differentiation, such as embryonic body (EB) and teratoma formation. After differentiation, the level of deletion was retained or increased in EBs (24%) or teratoma (45%) from deletion iPSC clone, while, the absence of deletions showed in all EBs and teratomas from deletion-free iPSC clones. These results demonstrated that non-deletion in iPSCs was maintained during in vitro and in vivo differentiation, even in the presence of nuclear mutations, suggesting that deletion-free iPSC clones could be candidates for autologous cell therapy in patients.
Nat Commun. 2023 May 09. 14(1): 2680

Anatomical and functional maturation of the mid-gestation human enteric nervous system.

Lori B Dershowitz, Li Li, Anca M Pasca, Julia A Kaltschmidt.

Immature gastrointestinal motility impedes preterm infant survival. The enteric nervous system controls gastrointestinal motility, yet it is unknown when the human enteric nervous system matures enough to carry out vital functions. Here we demonstrate that the second trimester human fetal enteric nervous system takes on a striped organization akin to the embryonic mouse. Further, we perform ex vivo functional assays of human fetal tissue and find that human fetal gastrointestinal motility matures in a similar progression to embryonic mouse gastrointestinal motility. Together, this provides critical knowledge, which facilitates comparisons with common animal models to advance translational disease investigations and testing of pharmacological agents to enhance gastrointestinal motility in prematurity.

DOI: https://doi.org/10.1038/s41467-023-38293-z
J Physiol. 2023 May 08.

Exercise improves homeostasis of the intestinal epithelium by activation of APJ-AMPK signaling.

Song Ah Chae, Min Du, Jun Seok Son, Mei-Jun Zhu.

  Intestinal remodeling is dynamically regulated by energy metabolism. Exercise is beneficial for gut health, but the specific mechanisms remain poorly understood. Both intestine-specific apelin receptor (APJ) knockdown (KD) and wild-type male mice were randomly divided into two subgroups with/without exercise to obtain four groups: WT, WT with exercise, APJ KD, and APJ KD with exercise. Animals in exercise groups were subjected to daily treadmill exercise for 3 weeks. Duodenum was collected at 48h after the last bout of exercise. AMP-activated protein kinase (AMPK) α1 KD and wild-type mice were also utilized for investigating the mediatory role of AMPK on exercise-induced duodenal epithelial development. AMPK and peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1 α) were upregulated by exercise via APJ activation in the intestinal duodenum. Correspondingly, exercise induced permissive histone modifications in the PR domain containing 16 (PRDM16) promoter to activate its expression, which was dependent on APJ activation. In agreement, exercise elevated the expression of mitochondrial oxidative markers. The expression of intestinal epithelial markers was downregulated due to AMPK deficiency, and AMPK signaling facilitated epithelial renewal. These data demonstrate that exercise-induced activation of APJ-AMPK axis facilitates the homeostasis of the intestinal duodenal epithelium. ONE-SENTENCE SUMMARY: Exercise-induced APJ-AMPK axis upregulated the expression of PGC-1α and PRDM16 to improve homeostasis of intestinal epithelium. KEY POINTS: APJ signaling is required for improved epithelial homeostasis of the small intestine in response to exercise. Exercise intervention activates PRDM16 through inducing histone modifications, improving mitochondrial biogenesis and fatty acid metabolism in duodenum. Structure of intestinal epithelium is improved by muscle-derived exerkine apelin through APJ-AMPK axis. Abstract figure legend. Exercise training increases expression of apelin in muscle and the circulating apelin level. Exercise-induced apelin-APJ signaling enhances villus and crypt structure of the small intestine (duodenum) through the activation of AMPK and stimulation of mitochondrial biogenesis. Of note, exercise program induces histone modifications for PRDM16 expression, which enhances mitochondrial oxidative metabolism, thereby improving intestinal epithelial homeostasis. This article is protected by copyright. All rights reserved.

Keywords:  AMPK, APJ, duodenum, exercise; mitochondrial oxidation, PRDM16

DOI:  https://doi.org/10.1113/JP284552