bims-nenemi Biomed News
on Neuroinflammation, neurodegeneration and mitochondria
Issue of 2024–06–30
eight papers selected by
Marco Tigano, Thomas Jefferson University
  1. Sequence-specific dynamic DNA bending explains mitochondrial TFAM's dual role in DNA packaging and transcription initiation.
  2. Coordinated DNA polymerization by Polγ and the region of LonP1 regulated proteolysis.
  3. The extracellular matrix integrates mitochondrial homeostasis.
  4. Implications of mitochondrial membrane potential gradients on signaling and ATP production analyzed by correlative multi-parameter microscopy.
  5. Single-Mitochondrion Sequencing Uncovers Distinct Mutational Patterns and Heteroplasmy Landscape in Mouse Astrocytes and Neurons.
  6. ANT2: the first mammalian mitochondrial RNA transport translocon.
  7. Mitochondrial Reactive Oxygen Species in Infection and Immunity.
  8. IFNγ causes mitochondrial dysfunction and oxidative stress in myositis.
  1. Nat Commun. 2024 Jun 27. 15(1): 5446
    Sequence-specific dynamic DNA bending explains mitochondrial TFAM's dual role in DNA packaging and transcription initiation.
    Hyun Huh, Jiayu Shen, Yogeeshwar Ajjugal, Aparna Ramachandran, Smita S Patel, Sang-Hyuk Lee.
      Mitochondrial transcription factor A (TFAM) employs DNA bending to package mitochondrial DNA (mtDNA) into nucleoids and recruit mitochondrial RNA polymerase (POLRMT) at specific promoter sites, light strand promoter (LSP) and heavy strand promoter (HSP). Herein, we characterize the conformational dynamics of TFAM on promoter and non-promoter sequences using single-molecule fluorescence resonance energy transfer (smFRET) and single-molecule protein-induced fluorescence enhancement (smPIFE) methods. The DNA-TFAM complexes dynamically transition between partially and fully bent DNA conformational states. The bending/unbending transition rates and bending stability are DNA sequence-dependent-LSP forms the most stable fully bent complex and the non-specific sequence the least, which correlates with the lifetimes and affinities of TFAM with these DNA sequences. By quantifying the dynamic nature of the DNA-TFAM complexes, our study provides insights into how TFAM acts as a multifunctional protein through the DNA bending states to achieve sequence specificity and fidelity in mitochondrial transcription while performing mtDNA packaging.
    DOI:  https://doi.org/10.1038/s41467-024-49728-6
  2. Nucleic Acids Res. 2024 Jun 27. pii: gkae539. [Epub ahead of print]
    Coordinated DNA polymerization by Polγ and the region of LonP1 regulated proteolysis.
    Amanda A Riccio, Asia J Brannon, Juno M Krahn, Jonathan Bouvette, Jason G Williams, Mario J Borgnia, William C Copeland.
      The replicative mitochondrial DNA polymerase, Polγ, and its protein regulation are essential for the integrity of the mitochondrial genome. The intricacies of Polγ regulation and its interactions with regulatory proteins, which are essential for fine-tuning polymerase function, remain poorly understood. Misregulation of the Polγ heterotrimer, consisting of (i) PolG, the polymerase catalytic subunit and (ii) PolG2, the accessory subunit, ultimately results in mitochondrial diseases. Here, we used single particle cryo-electron microscopy to resolve the structure of PolG in its apoprotein state and we captured Polγ at three intermediates within the catalytic cycle: DNA bound, engaged, and an active polymerization state. Chemical crosslinking mass spectrometry, and site-directed mutagenesis uncovered the region of LonP1 engagement of PolG, which promoted proteolysis and regulation of PolG protein levels. PolG2 clinical variants, which disrupted a stable Polγ complex, led to enhanced LonP1-mediated PolG degradation. Overall, this insight into Polγ aids in an understanding of mitochondrial DNA replication and characterizes how machinery of the replication fork may be targeted for proteolytic degradation when improperly functioning.
    DOI:  https://doi.org/10.1093/nar/gkae539
  3. Cell. 2024 Jun 24. pii: S0092-8674(24)00638-X. [Epub ahead of print]
    The extracellular matrix integrates mitochondrial homeostasis.
    Hanlin Zhang, C Kimberly Tsui, Gilberto Garcia, Larry K Joe, Haolun Wu, Ayane Maruichi, Wudi Fan, Sentibel Pandovski, Peter H Yoon, Brant M Webster, Jenni Durieux, Phillip A Frankino, Ryo Higuchi-Sanabria, Andrew Dillin.
      Cellular homeostasis is intricately influenced by stimuli from the microenvironment, including signaling molecules, metabolites, and pathogens. Functioning as a signaling hub within the cell, mitochondria integrate information from various intracellular compartments to regulate cellular signaling and metabolism. Multiple studies have shown that mitochondria may respond to various extracellular signaling events. However, it is less clear how changes in the extracellular matrix (ECM) can impact mitochondrial homeostasis to regulate animal physiology. We find that ECM remodeling alters mitochondrial homeostasis in an evolutionarily conserved manner. Mechanistically, ECM remodeling triggers a TGF-β response to induce mitochondrial fission and the unfolded protein response of the mitochondria (UPRMT). At the organismal level, ECM remodeling promotes defense of animals against pathogens through enhanced mitochondrial stress responses. We postulate that this ECM-mitochondria crosstalk represents an ancient immune pathway, which detects infection- or mechanical-stress-induced ECM damage, thereby initiating adaptive mitochondria-based immune and metabolic responses.
    Keywords:  TGF-β; TMEM2; extracellular matrix; hyaluronan; immunity; mitochondria
    DOI:  https://doi.org/10.1016/j.cell.2024.05.057
  4. Sci Rep. 2024 06 26. 14(1): 14784
    Implications of mitochondrial membrane potential gradients on signaling and ATP production analyzed by correlative multi-parameter microscopy.
    Benjamin Gottschalk, Zhanat Koshenov, Roland Malli, Wolfgang F Graier.
      The complex architecture and biochemistry of the inner mitochondrial membrane generate ultra-structures with different phospholipid and protein compositions, shapes, characteristics, and functions. The crista junction (CJ) serves as an important barrier separating the cristae (CM) and inner boundary membranes (IBM). Thereby CJ regulates the movement of ions and ensures distinct electrical potentials across the cristae (ΔΨC) and inner boundary (ΔΨIBM) membranes. We have developed a robust and flexible approach to visualize the CJ permeability with super-resolution microscopy as a readout of local mitochondrial membrane potential (ΔΨmito) fluctuations. This method involves analyzing the distribution of TMRM fluorescence intensity in a model that is restricted to the mitochondrial geometry. We show that mitochondrial Ca2+ elevation hyperpolarizes the CM most likely caused by Ca2+ sensitive increase of mitochondrial tricarboxylic acid cycle (TCA) and subsequent oxidative phosphorylation (OXPHOS) activity in the cristae. Dynamic multi-parameter correlation measurements of spatial mitochondrial membrane potential gradients, ATP levels, and mitochondrial morphometrics revealed a CJ-based membrane potential overflow valve mechanism protecting the mitochondrial integrity during excessive cristae hyperpolarization.
    Keywords:  Correlative microscopy; Cristae junctions; Membrane potential gradient; Mitochondria; Mitochondrial membranes
    DOI:  https://doi.org/10.1038/s41598-024-65595-z
  5. bioRxiv. 2024 Jun 19. pii: 2024.06.13.598906. [Epub ahead of print]
    Single-Mitochondrion Sequencing Uncovers Distinct Mutational Patterns and Heteroplasmy Landscape in Mouse Astrocytes and Neurons.
    Parnika S Kadam, Zijian Yang, Youtao Lu, Hua Zhu, Yasemin Atiyas, Nishal Shah, Stephen Fisher, Erik Nordgren, Junhyong Kim, David Issadore, James Eberwine.
       Background: Mitochondrial (mt) heteroplasmy can cause adverse biological consequences when deleterious mtDNA mutations accumulate disrupting 'normal' mt-driven processes and cellular functions. To investigate the heteroplasmy of such mtDNA changes we developed a moderate throughput mt isolation procedure to quantify the mt single-nucleotide variant (SNV) landscape in individual mouse neurons and astrocytes In this study we amplified mt-genomes from 1,645 single mitochondria (mts) isolated from mouse single astrocytes and neurons to 1. determine the distribution and proportion of mt-SNVs as well as mutation pattern in specific target regions across the mt-genome, 2. assess differences in mtDNA SNVs between neurons and astrocytes, and 3. Study cosegregation of variants in the mouse mtDNA.
    Results: 1. The data show that specific sites of the mt-genome are permissive to SNV presentation while others appear to be under stringent purifying selection. Nested hierarchical analysis at the levels of mitochondrion, cell, and mouse reveals distinct patterns of inter- and intra-cellular variation for mt-SNVs at different sites. 2. Further, differences in the SNV incidence were observed between mouse neurons and astrocytes for two mt-SNV 9027:G>A and 9419:C>T showing variation in the mutational propensity between these cell types. Purifying selection was observed in neurons as shown by the Ka/Ks statistic, suggesting that neurons are under stronger evolutionary constraint as compared to astrocytes. 3. Intriguingly, these data show strong linkage between the SNV sites at nucleotide positions 9027 and 9461. f.
    Conclusion: This study suggests that segregation as well as clonal expansion of mt-SNVs is specific to individual genomic loci, which is important foundational data in understanding of heteroplasmy and disease thresholds for mutation of pathogenic variants.
    DOI:  https://doi.org/10.1101/2024.06.13.598906
  6. Cell Res. 2024 Jun 24.
    ANT2: the first mammalian mitochondrial RNA transport translocon.
    Huanhuan Zhu, Weiqiang Lin, Aifu Lin.
      
    DOI:  https://doi.org/10.1038/s41422-024-00994-5
  7. Biomolecules. 2024 Jun 08. pii: 670. [Epub ahead of print]14(6):
    Mitochondrial Reactive Oxygen Species in Infection and Immunity.
    Arunima Mukherjee, Krishna Kanta Ghosh, Sabyasachi Chakrabortty, Balázs Gulyás, Parasuraman Padmanabhan, Writoban Basu Ball.
      Reactive oxygen species (ROS) contain at least one oxygen atom and one or more unpaired electrons and include singlet oxygen, superoxide anion radical, hydroxyl radical, hydroperoxyl radical, and free nitrogen radicals. Intracellular ROS can be formed as a consequence of several factors, including ultra-violet (UV) radiation, electron leakage during aerobic respiration, inflammatory responses mediated by macrophages, and other external stimuli or stress. The enhanced production of ROS is termed oxidative stress and this leads to cellular damage, such as protein carbonylation, lipid peroxidation, deoxyribonucleic acid (DNA) damage, and base modifications. This damage may manifest in various pathological states, including ageing, cancer, neurological diseases, and metabolic disorders like diabetes. On the other hand, the optimum levels of ROS have been implicated in the regulation of many important physiological processes. For example, the ROS generated in the mitochondria (mitochondrial ROS or mt-ROS), as a byproduct of the electron transport chain (ETC), participate in a plethora of physiological functions, which include ageing, cell growth, cell proliferation, and immune response and regulation. In this current review, we will focus on the mechanisms by which mt-ROS regulate different pathways of host immune responses in the context of infection by bacteria, protozoan parasites, viruses, and fungi. We will also discuss how these pathogens, in turn, modulate mt-ROS to evade host immunity. We will conclude by briefly giving an overview of the potential therapeutic approaches involving mt-ROS in infectious diseases.
    Keywords:  bacteria; electron transport chain; fungi; inflammasome; mitochondrial reactive oxygen species; protozoa; virus
    DOI:  https://doi.org/10.3390/biom14060670
  8. Nat Commun. 2024 Jun 26. 15(1): 5403
    IFNγ causes mitochondrial dysfunction and oxidative stress in myositis.
    Catalina Abad, Iago Pinal-Fernandez, Clement Guillou, Gwladys Bourdenet, Laurent Drouot, Pascal Cosette, Margherita Giannini, Lea Debrut, Laetitia Jean, Sophie Bernard, Damien Genty, Rachid Zoubairi, Isabelle Remy-Jouet, Bernard Geny, Christian Boitard, Andrew Mammen, Alain Meyer, Olivier Boyer.
      Idiopathic inflammatory myopathies (IIMs) are severe autoimmune diseases with poorly understood pathogenesis and unmet medical needs. Here, we examine the role of interferon γ (IFNγ) using NOD female mice deficient in the inducible T cell co-stimulator (Icos), which have previously been shown to develop spontaneous IFNγ-driven myositis mimicking human disease. Using muscle proteomic and spatial transcriptomic analyses we reveal profound myofiber metabolic dysregulation in these mice. In addition, we report muscle mitochondrial abnormalities and oxidative stress in diseased mice. Supporting a pathogenic role for oxidative stress, treatment with a reactive oxygen species (ROS) buffer compound alleviated myositis, preserved muscle mitochondrial ultrastructure and respiration, and reduced inflammation. Mitochondrial anomalies and oxidative stress were diminished following anti-IFNγ treatment. Further transcriptomic analysis in IIMs patients and human myoblast in vitro studies supported the link between IFNγ and mitochondrial dysfunction observed in mice. These results suggest that mitochondrial dysfunction, ROS and inflammation are interconnected in a self-maintenance loop, opening perspectives for mitochondria therapy and/or ROS targeting drugs in myositis.
    DOI:  https://doi.org/10.1038/s41467-024-49460-1
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