bims-midtic Biomed News
on Mitochondrial dynamics and trafficking in cells
Issue of 2024–04–28
fourteen papers selected by
Omkar Joshi, Turku Bioscience
  1. OMA1-Mediated Mitochondrial Dynamics Balance Organellar Homeostasis Upstream of Cellular Stress Responses.
  2. Driving mitochondrial fission improves cognitive, but not motor deficits in a mouse model of Ataxia of Charlevoix-Saguenay.
  3. Lineage-specific changes in mitochondrial properties during neural stem cell differentiation.
  4. Mitochondrial sites of contact with the nucleus.
  5. Mitofusin-mediated contacts between mitochondria and peroxisomes regulate mitochondrial fusion.
  6. Organelle-targeted Laurdans measure heterogeneity in subcellular membranes and their responses to saturated lipid stress.
  7. Inflammation and mitophagy are mitochondrial checkpoints to aging.
  8. Combining sophisticated fast FLIM, confocal microscopy, and STED nanoscopy for live-cell imaging of tunneling nanotubes.
  9. The role of mitochondrial dynamics and mitophagy in skeletal muscle atrophy: from molecular mechanisms to therapeutic insights.
  10. Geranylgeranylated-SCF FBXO10 Regulates Selective Outer Mitochondrial Membrane Proteostasis and Function.
  11. Mitochondrial fractions located in the cytoplasmic and peridroplet areas of white adipocytes have distinct roles.
  12. Cryo-EM structures of membrane-bound dynamin in a post-hydrolysis state primed for membrane fission.
  13. Mitochondria inside acute myeloid leukemia cells hydrolyze ATP to resist chemotherapy.
  14. Vimentin regulates mitochondrial ROS production and inflammatory responses of neutrophils.
  1. Int J Mol Sci. 2024 Apr 22. pii: 4566. [Epub ahead of print]25(8):
    OMA1-Mediated Mitochondrial Dynamics Balance Organellar Homeostasis Upstream of Cellular Stress Responses.
    Robert Gilkerson, Harpreet Kaur, Omar Carrillo, Isaiah Ramos.
      In response to cellular metabolic and signaling cues, the mitochondrial network employs distinct sets of membrane-shaping factors to dynamically modulate organellar structures through a balance of fission and fusion. While these organellar dynamics mediate mitochondrial structure/function homeostasis, they also directly impact critical cell-wide signaling pathways such as apoptosis, autophagy, and the integrated stress response (ISR). Mitochondrial fission is driven by the recruitment of the cytosolic dynamin-related protein-1 (DRP1), while fusion is carried out by mitofusins 1 and 2 (in the outer membrane) and optic atrophy-1 (OPA1) in the inner membrane. This dynamic balance is highly sensitive to cellular stress; when the transmembrane potential across the inner membrane (Δψm) is lost, fusion-active OPA1 is cleaved by the overlapping activity with m-AAA protease-1 (OMA1 metalloprotease, disrupting mitochondrial fusion and leaving dynamin-related protein-1 (DRP1)-mediated fission unopposed, thus causing the collapse of the mitochondrial network to a fragmented state. OMA1 is a unique regulator of stress-sensitive homeostatic mitochondrial balance, acting as a key upstream sensor capable of priming the cell for apoptosis, autophagy, or ISR signaling cascades. Recent evidence indicates that higher-order macromolecular associations within the mitochondrial inner membrane allow these specialized domains to mediate crucial organellar functionalities.
    Keywords:  DRP1; OMA1; OPA1; apoptosis; autophagy; bioenergetics; cristae; fission; fusion; integrated stress response; mitochondria; transmembrane potential
    DOI:  https://doi.org/10.3390/ijms25084566
  2. Res Sq. 2024 Apr 10. pii: rs.3.rs-4178088. [Epub ahead of print]
    Driving mitochondrial fission improves cognitive, but not motor deficits in a mouse model of Ataxia of Charlevoix-Saguenay.
    Chunling Chen, Ronald A Merrill, Chian Ju Jong, Stefan Strack.
      Autosomal-recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is caused by loss-of-function mutation in the SACS gene, which encodes sacsin, a putative HSP70-HSP90 co-chaperone. Previous studies with Sacs knock-out (KO) mice and patient-derived fibroblasts suggested that SACSIN mutations inhibit the function of the mitochondrial fission enzyme dynamin-related protein 1 (Drp1). This in turn resulted in mitochondrial hyperfusion and dysfunction. We experimentally tested this hypothesis by genetically manipulating the mitochondrial fission/fusion equilibrium, creating double KO (DKO) mice that also lack positive (PP2A/Bβ2) and negative (PKA/AKAP1) regulators of Drp1. Neither promoting mitochondrial fusion ( B β 2 KO) nor fission ( Akap1 KO) influenced progression of motor symptoms in Sacs KO mice. However, our studies identified profound learning and memory deficits in aged Sacs KO mice. Moreover, this cognitive impairment was rescued in a gene dose-dependent manner by deletion of the Drp1 inhibitor PKA/Akap1. Our results are inconsistent with mitochondrial dysfunction as a primary pathogenic mechanism in ARSACS. Instead, they imply that promoting mitochondrial fission may be beneficial at later stages of the disease when pathology extends to brain regions subserving learning and memory.
    DOI:  https://doi.org/10.21203/rs.3.rs-4178088/v1
  3. Life Sci Alliance. 2024 Jul;pii: e202302473. [Epub ahead of print]7(7):
    Lineage-specific changes in mitochondrial properties during neural stem cell differentiation.
    Rita Soares, Diogo M Lourenço, Isa F Mota, Ana M Sebastião, Sara Xapelli, Vanessa A Morais.
      Neural stem cells (NSCs) reside in discrete regions of the adult mammalian brain where they can differentiate into neurons, astrocytes, and oligodendrocytes. Several studies suggest that mitochondria have a major role in regulating NSC fate. Here, we evaluated mitochondrial properties throughout NSC differentiation and in lineage-specific cells. For this, we used the neurosphere assay model to isolate, expand, and differentiate mouse subventricular zone postnatal NSCs. We found that the levels of proteins involved in mitochondrial fusion (Mitofusin [Mfn] 1 and Mfn 2) increased, whereas proteins involved in fission (dynamin-related protein 1 [DRP1]) decreased along differentiation. Importantly, changes in mitochondrial dynamics correlated with distinct patterns of mitochondrial morphology in each lineage. Particularly, we found that the number of branched and unbranched mitochondria increased during astroglial and neuronal differentiation, whereas the area occupied by mitochondrial structures significantly reduced with oligodendrocyte maturation. In addition, comparing the three lineages, neurons revealed to be the most energetically flexible, whereas astrocytes presented the highest ATP content. Our work identified putative mitochondrial targets to enhance lineage-directed differentiation of mouse subventricular zone-derived NSCs.
    DOI:  https://doi.org/10.26508/lsa.202302473
  4. J Cell Biol. 2024 Jun 03. pii: e202305010. [Epub ahead of print]223(6):
    Mitochondrial sites of contact with the nucleus.
    Michelangelo Campanella, Brindha Kannan.
      Membrane contact sites (MCS) between mitochondria and the nucleus have been recently described. Termed nucleus associated mitochondria (NAM), they prime the expression of genes required for cellular resistance to stressors, thus offering a tethering mechanism for homeostatic communication. Here, we discuss the composition of NAM and their physiological and pathological significance.
    DOI:  https://doi.org/10.1083/jcb.202305010
  5. PLoS Biol. 2024 Apr 26. 22(4): e3002602
    Mitofusin-mediated contacts between mitochondria and peroxisomes regulate mitochondrial fusion.
    Cynthia Alsayyah, Manish K Singh, Maria Angeles Morcillo-Parra, Laetitia Cavellini, Nadav Shai, Christine Schmitt, Maya Schuldiner, Einat Zalckvar, Adeline Mallet, Naïma Belgareh-Touzé, Christophe Zimmer, Mickaël M Cohen.
      Mitofusins are large GTPases that trigger fusion of mitochondrial outer membranes. Similarly to the human mitofusin Mfn2, which also tethers mitochondria to the endoplasmic reticulum (ER), the yeast mitofusin Fzo1 stimulates contacts between Peroxisomes and Mitochondria when overexpressed. Yet, the physiological significance and function of these "PerMit" contacts remain unknown. Here, we demonstrate that Fzo1 naturally localizes to peroxisomes and promotes PerMit contacts in physiological conditions. These contacts are regulated through co-modulation of Fzo1 levels by the ubiquitin-proteasome system (UPS) and by the desaturation status of fatty acids (FAs). Contacts decrease under low FA desaturation but reach a maximum during high FA desaturation. High-throughput genetic screening combined with high-resolution cellular imaging reveal that Fzo1-mediated PerMit contacts favor the transit of peroxisomal citrate into mitochondria. In turn, citrate enters the TCA cycle to stimulate the mitochondrial membrane potential and maintain efficient mitochondrial fusion upon high FA desaturation. These findings thus unravel a mechanism by which inter-organelle contacts safeguard mitochondrial fusion.
    DOI:  https://doi.org/10.1371/journal.pbio.3002602
  6. bioRxiv. 2024 Apr 20. pii: 2024.04.16.589828. [Epub ahead of print]
    Organelle-targeted Laurdans measure heterogeneity in subcellular membranes and their responses to saturated lipid stress.
    Adrian M Wong, Itay Budin.
      Cell organelles feature characteristic lipid compositions that lead to differences in membrane properties. In living cells, membrane ordering and fluidity are commonly measured using the solvatochromic dye Laurdan, whose fluorescence is sensitive to membrane packing. As a general lipophilic dye, Laurdan stains all hydrophobic environments in cells, so it is challenging to characterize membrane properties in specific organelles or assess their responses to pharmacological treatments in intact cells. Here, we describe the synthesis and application of Laurdan-derived probes that read out membrane packing of individual cellular organelles. The set of Organelle-targeted Laurdans (OTL) localizes to the ER, mitochondria, lysosomes and Golgi compartments with high specificity, while retaining the spectral resolution needed to detect biological changes in membrane packing. We show that ratiometric imaging with OTL can resolve membrane heterogeneity within organelles, as well as changes in membrane packing resulting from inhibition of lipid trafficking or bioenergetic processes. We apply these probes to characterize organelle-specific responses to saturated lipid stress. While ER and lysosomal membrane fluidity is sensitive to exogenous saturated fatty acids, that of mitochondrial membranes is protected. We then use differences in ER membrane fluidity to sort populations of cells based on their fatty acid diet, highlighting the ability of organelle-localized solvatochromic probes to distinguish between cells based on their metabolic state. These results expand the repertoire of targeted membrane probes and demonstrate their application to interrogating lipid dysregulation.
    DOI:  https://doi.org/10.1101/2024.04.16.589828
  7. Nat Commun. 2024 Apr 20. 15(1): 3375
    Inflammation and mitophagy are mitochondrial checkpoints to aging.
    Emma Guilbaud, Kristopher A Sarosiek, Lorenzo Galluzzi.
      
    DOI:  https://doi.org/10.1038/s41467-024-47840-1
  8. Life Sci Alliance. 2024 Jul;pii: e202302398. [Epub ahead of print]7(7):
    Combining sophisticated fast FLIM, confocal microscopy, and STED nanoscopy for live-cell imaging of tunneling nanotubes.
    Magalie Bénard, Christophe Chamot, Damien Schapman, Aurélien Debonne, Alexis Lebon, Fatéméh Dubois, Guénaëlle Levallet, Hitoshi Komuro, Ludovic Galas.
      Cell-to-cell communication via tunneling nanotubes (TNTs) is a challenging topic with a growing interest. In this work, we proposed several innovative tools that use red/near-infrared dye labeling and employ lifetime-based imaging strategies to investigate the dynamics of TNTs in a living mesothelial H28 cell line that exhibits spontaneously TNT1 and TNT2 subtypes. Thanks to a fluorescence lifetime imaging microscopy module being integrated into confocal microscopy and stimulated emission depletion nanoscopy, we applied lifetime imaging, lifetime dye unmixing, and lifetime denoising techniques to perform multiplexing experiments and time-lapses of tens of minutes, revealing therefore structural and functional characteristics of living TNTs that were preserved from light exposure. In these conditions, vesicle-like structures, and tubular- and round-shaped mitochondria were identified within living TNT1. In addition, mitochondrial dynamic studies revealed linear and stepwise mitochondrial migrations, bidirectional movements, transient backtracking, and fission events in TNT1. Transfer of Nile Red-positive puncta via both TNT1 and TNT2 was also detected between living H28 cells.
    DOI:  https://doi.org/10.26508/lsa.202302398
  9. Cell Mol Biol Lett. 2024 Apr 23. 29(1): 59
    The role of mitochondrial dynamics and mitophagy in skeletal muscle atrophy: from molecular mechanisms to therapeutic insights.
    Yuhang Lei, Mailin Gan, Yanhao Qiu, Qiuyang Chen, Xingyu Wang, Tianci Liao, Mengying Zhao, Lei Chen, Shunhua Zhang, Ye Zhao, Lili Niu, Yan Wang, Li Zhu, Linyuan Shen.
      Skeletal muscle is the largest metabolic organ of the human body. Maintaining the best quality control and functional integrity of mitochondria is essential for the health of skeletal muscle. However, mitochondrial dysfunction characterized by mitochondrial dynamic imbalance and mitophagy disruption can lead to varying degrees of muscle atrophy, but the underlying mechanism of action is still unclear. Although mitochondrial dynamics and mitophagy are two different mitochondrial quality control mechanisms, a large amount of evidence has indicated that they are interrelated and mutually regulated. The former maintains the balance of the mitochondrial network, eliminates damaged or aged mitochondria, and enables cells to survive normally. The latter degrades damaged or aged mitochondria through the lysosomal pathway, ensuring cellular functional health and metabolic homeostasis. Skeletal muscle atrophy is considered an urgent global health issue. Understanding and gaining knowledge about muscle atrophy caused by mitochondrial dysfunction, particularly focusing on mitochondrial dynamics and mitochondrial autophagy, can greatly contribute to the prevention and treatment of muscle atrophy. In this review, we critically summarize the recent research progress on mitochondrial dynamics and mitophagy in skeletal muscle atrophy, and expound on the intrinsic molecular mechanism of skeletal muscle atrophy caused by mitochondrial dynamics and mitophagy. Importantly, we emphasize the potential of targeting mitochondrial dynamics and mitophagy as therapeutic strategies for the prevention and treatment of muscle atrophy, including pharmacological treatment and exercise therapy, and summarize effective methods for the treatment of skeletal muscle atrophy.
    Keywords:  Intermodulation; Mitochondrial dynamics; Mitophagy; Molecular mechanism; Prevention and treatment; Skeletal muscle atrophy
    DOI:  https://doi.org/10.1186/s11658-024-00572-y
  10. bioRxiv. 2024 Apr 16. pii: 2024.04.16.589745. [Epub ahead of print]
    Geranylgeranylated-SCF FBXO10 Regulates Selective Outer Mitochondrial Membrane Proteostasis and Function.
    Sameer Ahmed Bhat, Zahra Vasi, Liping Jiang, Shruthi Selvaraj, Rachel Ferguson, Anish Gudur, Hagar Ismail, Ritika Adhikari, Avantika Dhabaria, Beatrix Ueberheide, Shafi Kuchay.
      E3-ubiquitin ligases (E3s) are main components of the ubiquitin-proteasome system (UPS), as they determine substrate specificity in response to internal and external cues to regulate protein homeostasis. However, the regulation of membrane protein ubiquitination by E3s within distinct cell membrane compartments or organelles is not well understood. We show that FBXO10, the interchangeable component of the SKP1/CUL1/F-box ubiquitin ligase complex (SCF-E3), undergoes lipid-modification with geranylgeranyl isoprenoid at Cysteine953 (C953), facilitating its dynamic trafficking to the outer mitochondrial membrane (OMM). FBXO10 polypeptide does not contain a canonical mitochondrial targeting sequence (MTS); instead, its geranylgeranylation at C953 and the interaction with two cytosolic factors, PDE6δ (a prenyl group-binding protein), and HSP90 (a mitochondrial chaperone) orchestrate specific OMM targeting of prenyl-FBXO10 across diverse membrane compartments. The geranylgeranylation-deficient FBXO10(C953S) mutant redistributes away from the OMM, leading to impaired mitochondrial ATP production, decreased mitochondrial membrane potential, and increased mitochondrial fragmentation. Phosphoglycerate mutase 5 (PGAM5) was identified as a potential substrate of FBXO10 at the OMM using comparative quantitative mass spectrometry analyses of enriched mitochondria (LFQ-MS/MS), leveraging the redistribution of FBXO10(C953S). FBXO10, but not FBXO10(C953S), promoted polyubiquitylation and degradation of PGAM5. Examination of the role of this pathway in a physiological context revealed that the loss of FBXO10 or expression of prenylation-deficient-FBXO10(C953S) inhibited PGAM5 degradation, disrupted mitochondrial homeostasis, and impaired myogenic differentiation of human iPSCs and murine myoblasts. Our studies identify a mechanism for selective E3-ligase mediated regulation of mitochondrial membrane proteostasis and metabolic health, potentially amenable to therapeutic intervention.
    DOI:  https://doi.org/10.1101/2024.04.16.589745
  11. FEBS Lett. 2024 Apr 24.
    Mitochondrial fractions located in the cytoplasmic and peridroplet areas of white adipocytes have distinct roles.
    Masayuki Fuwa, Kazuo Kajita, Ichiro Mori, Motochika Asano, Toshiko Kajita, Takao Senda, Takeshi Inagaki, Hiroyuki Morita.
      The role of mitochondria in white adipocytes (WAs) has not been fully explored. A recent study revealed that brown adipocytes contain functionally distinct mitochondrial fractions, cytoplasmic mitochondria, and peridroplet mitochondria. However, it is not known whether such a functional division of mitochondria exists in WA. Herein, we observed that mitochondria could be imaged and mitochondrial DNA and protein detected in pellets obtained from the cytoplasmic layer and oil layer of WAs after centrifugation. The mitochondria in each fraction were designated as cytoplasmic mitochondria (CMw) and peridroplet mitochondria (PDMw) in WAs, respectively. CMw had higher β-oxidation activity than PDMw, and PDMw was associated with diacylglycerol acyltransferase 2. Therefore, CMw may be involved in β-oxidation and PDMw in droplet expansion in WAs.
    Keywords:  lipid droplet; mitochondria; triglyceride; white adipocyte
    DOI:  https://doi.org/10.1002/1873-3468.14877
  12. Dev Cell. 2024 Apr 23. pii: S1534-5807(24)00233-8. [Epub ahead of print]
    Cryo-EM structures of membrane-bound dynamin in a post-hydrolysis state primed for membrane fission.
    John R Jimah, Nidhi Kundu, Abigail E Stanton, Kem A Sochacki, Bertram Canagarajah, Lieza Chan, Marie-Paule Strub, Huaibin Wang, Justin W Taraska, Jenny E Hinshaw.
      Dynamin assembles as a helical polymer at the neck of budding endocytic vesicles, constricting the underlying membrane as it progresses through the GTPase cycle to sever vesicles from the plasma membrane. Although atomic models of the dynamin helical polymer bound to guanosine triphosphate (GTP) analogs define earlier stages of membrane constriction, there are no atomic models of the assembled state post-GTP hydrolysis. Here, we used cryo-EM methods to determine atomic structures of the dynamin helical polymer assembled on lipid tubules, akin to necks of budding endocytic vesicles, in a guanosine diphosphate (GDP)-bound, super-constricted state. In this state, dynamin is assembled as a 2-start helix with an inner lumen of 3.4 nm, primed for spontaneous fission. Additionally, by cryo-electron tomography, we trapped dynamin helical assemblies within HeLa cells using the GTPase-defective dynamin K44A mutant and observed diverse dynamin helices, demonstrating that dynamin can accommodate a range of assembled complexes in cells that likely precede membrane fission.
    Keywords:  clathrin-mediated endocytosis; cryo-EM; cryo-ET; dynamin; endocytosis; membrane fission; membrane remodeling; structural biology
    DOI:  https://doi.org/10.1016/j.devcel.2024.04.008
  13. bioRxiv. 2024 Apr 15. pii: 2024.04.12.589110. [Epub ahead of print]
    Mitochondria inside acute myeloid leukemia cells hydrolyze ATP to resist chemotherapy.
    James T Hagen, Mclane M Montgomery, Raphael T Aruleba, Brett R Chrest, Thomas D Green, Miki Kassai, Tonya N Zeczycki, Cameron A Schmidt, Debajit Bhowmick, Su-Fern Tan, David J Feith, Charles E Chalfant, Thomas P Loughran, Darla Liles, Mark D Minden, Aaron D Schimmer, Myles C Cabot, Joseph M Mclung, Kelsey H Fisher-Wellman.
      Despite early optimism, therapeutics targeting oxidative phosphorylation (OxPhos) have faced clinical setbacks, stemming from their inability to distinguish healthy from cancerous mitochondria. Herein, we describe an actionable bioenergetic mechanism unique to cancerous mitochondria inside acute myeloid leukemia (AML) cells. Unlike healthy cells which couple respiration to the synthesis of ATP, AML mitochondria were discovered to support inner membrane polarization by consuming ATP. Because matrix ATP consumption allows cells to survive bioenergetic stress, we hypothesized that AML cells may resist cell death induced by OxPhos damaging chemotherapy by reversing the ATP synthase reaction. In support of this, targeted inhibition of BCL-2 with venetoclax abolished OxPhos flux without impacting mitochondrial membrane potential. In surviving AML cells, sustained polarization of the mitochondrial inner membrane was dependent on matrix ATP consumption. Mitochondrial ATP consumption was further enhanced in AML cells made refractory to venetoclax, consequential to downregulations in both the proton-pumping respiratory complexes, as well as the endogenous F 1 -ATPase inhibitor ATP5IF1 . In treatment-naive AML, ATP5IF1 knockdown was sufficient to drive venetoclax resistance, while ATP5IF1 overexpression impaired F 1 -ATPase activity and heightened sensitivity to venetoclax. Collectively, our data identify matrix ATP consumption as a cancer-cell intrinsic bioenergetic vulnerability actionable in the context of mitochondrial damaging chemotherapy.
    DOI:  https://doi.org/10.1101/2024.04.12.589110
  14. bioRxiv. 2024 Apr 15. pii: 2024.04.11.589146. [Epub ahead of print]
    Vimentin regulates mitochondrial ROS production and inflammatory responses of neutrophils.
    Thao Ngoc Huynh, Jody Toperzer, Allison Scherer, Anne Gumina, Tonya Brunetti, Michael K Mansour, David M Markovitz, Brian C Russo.
      The intermediate filament vimentin is present in immune cells and is implicated in proinflammatory immune responses. Whether and how it supports antimicrobial activities of neutrophils is not well established. Here, we developed an immortalized neutrophil model to examine the requirement of vimentin. We demonstrate that vimentin restricts the production of proinflammatory cytokines and reactive oxygen species (ROS), but enhances phagocytosis and swarming. We observe that vimentin is dispensable for neutrophil extracellular trap (NET) formation, degranulation, and inflammasome activation. Moreover, gene expression analysis demonstrated that the presence of vimentin was associated with changes in expression of multiple genes required for mitochondrial function and ROS overproduction. Treatment of wild-type cells with rotenone, an inhibitor for complex I of the electron transport chain, increases the ROS levels. Likewise, treatment with mitoTEMPO, a SOD mimetic, rescues the ROS production in cells lacking vimentin. Together, these data show vimentin regulates neutrophil antimicrobial functions and alters ROS levels through regulation of mitochondrial activity.
    DOI:  https://doi.org/10.1101/2024.04.11.589146
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