bims-mecosi Biomed News
on Membrane contact sites
Issue of 2024–07–21
ten papers selected by
Verena Kohler, Umeå University
  1. Imaging Interorganelle Phospholipid Transport by Extended Synaptotagmins Using Bioorthogonally Tagged Lipids.
  2. ER-associated VAP27-1 and VAP27-3 proteins functionally link the lipid-binding ORP2A at the ER-chloroplast contact sites.
  3. Exploring the pathological mechanisms underlying Cohen syndrome.
  4. Nup358 restricts ER-mitochondria connectivity by modulating mTORC2/Akt/GSK3β signalling.
  5. INF2-mediated actin polymerization at ER-organelle contacts regulates organelle size and movement.
  6. SYNAPTOTAGMIN 4 is expressed mainly in the phloem and participates in abiotic stress tolerance in Arabidopsis.
  7. The reciprocal relationship between amyloid precursor protein and mitochondrial function.
  8. Dysregulation of FLVCR1a-dependent mitochondrial calcium handling in neural progenitors causes congenital hydrocephalus.
  9. MAMs and Mitochondrial Quality Control: Overview and Their Role in Alzheimer's Disease.
  10. Dysferlin Enables Tubular Membrane Proliferation in Cardiac Hypertrophy.
  1. ACS Chem Biol. 2024 Jul 18.
    Imaging Interorganelle Phospholipid Transport by Extended Synaptotagmins Using Bioorthogonally Tagged Lipids.
    Lin Luan, Dongjun Liang, Din-Chi Chiu, Reika Tei, Jeremy M Baskin.
      The proper distribution of lipids within organelle membranes requires rapid interorganelle lipid transport, much of which occurs at membrane contact sites and is mediated by lipid transfer proteins (LTPs). Our current understanding of LTP mechanism and function is based largely on structural studies and in vitro reconstitution. Existing cellular assays for LTP function use indirect readouts, and it remains an open question as to whether substrate specificity and transport kinetics established in vitro are similar in cellular settings. Here, we harness bioorthogonal chemistry to develop tools for direct visualization of interorganelle transport of phospholipids between the plasma membrane (PM) and the endoplasmic reticulum (ER). Unnatural fluorescent phospholipid analogs generated by the transphosphatidylation activity of phospholipase D (PLD) at the PM are rapidly transported to the ER dependent in part upon extended synaptotagmins (E-Syts), a family of LTPs at ER-PM contact sites. Ectopic expression of an artificial E-Syt-based tether at ER-mitochondria contact sites results in fluorescent phospholipid accumulation in mitochondria. Finally, in vitro reconstitution assays demonstrate that the fluorescent lipids are bona fide E-Syt substrates. Thus, fluorescent lipids generated in situ via PLD activity and bioorthogonal chemical tagging can enable direct visualization of the activity of LTPs that mediate bulk phospholipid transport at ER-PM contact sites.
    DOI:  https://doi.org/10.1021/acschembio.4c00345
  2. Nat Commun. 2024 Jul 17. 15(1): 6008
    ER-associated VAP27-1 and VAP27-3 proteins functionally link the lipid-binding ORP2A at the ER-chloroplast contact sites.
    Luciana Renna, Giovanni Stefano, Maria Paola Puggioni, Sang-Jin Kim, Anastasiya Lavell, John E Froehlich, Graham Burkart, Stefano Mancuso, Christoph Benning, Federica Brandizzi.
      The plant endoplasmic reticulum (ER) contacts heterotypic membranes at membrane contact sites (MCSs) through largely undefined mechanisms. For instance, despite the well-established and essential role of the plant ER-chloroplast interactions for lipid biosynthesis, and the reported existence of physical contacts between these organelles, almost nothing is known about the ER-chloroplast MCS identity. Here we show that the Arabidopsis ER membrane-associated VAP27 proteins and the lipid-binding protein ORP2A define a functional complex at the ER-chloroplast MCSs. Specifically, through in vivo and in vitro association assays, we found that VAP27 proteins interact with the outer envelope membrane (OEM) of chloroplasts, where they bind to ORP2A. Through lipidomic analyses, we established that VAP27 proteins and ORP2A directly interact with the chloroplast OEM monogalactosyldiacylglycerol (MGDG), and we demonstrated that the loss of the VAP27-ORP2A complex is accompanied by subtle changes in the acyl composition of MGDG and PG. We also found that ORP2A interacts with phytosterols and established that the loss of the VAP27-ORP2A complex alters sterol levels in chloroplasts. We propose that, by interacting directly with OEM lipids, the VAP27-ORP2A complex defines plant-unique MCSs that bridge ER and chloroplasts and are involved in chloroplast lipid homeostasis.
    DOI:  https://doi.org/10.1038/s41467-024-50425-7
  3. Front Neurosci. 2024 ;18 1431400
    Exploring the pathological mechanisms underlying Cohen syndrome.
    Fabrizio Vacca, Binnaz Yalcin, Muhammad Ansar.
      Cohen Syndrome (CS) is a rare autosomal recessive disorder caused by biallelic mutations in the VPS13B gene. It is characterized by multiple clinical features, including acquired microcephaly, developmental delay, intellectual disability, neutropenia, and retinal degeneration. VPS13B is part of the bridge-like lipid transport (BLTP) protein family, which in mammals also includes VPS13A, -C, and -D. The proteins of this family are peripheral membrane proteins with different sub-cellular localization, but all share similar structural features and have been proposed to act as lipid transport proteins at organellar membrane contact sites. VPS13B is localized at the Golgi apparatus and is essential for the maintenance of organelle architecture. Here we present a review of the experimental data on the function of the protein at the cellular level, discussing the potential link with disease phenotype and review the studies on animal models recapitulating features of the human disease.
    Keywords:  BLTP; COH1; Golgi; VPS13B; lipid transfer protein; membrane contact sites; neurodevelopment
    DOI:  https://doi.org/10.3389/fnins.2024.1431400
  4. EMBO Rep. 2024 Jul 18.
    Nup358 restricts ER-mitochondria connectivity by modulating mTORC2/Akt/GSK3β signalling.
    Misha Kalarikkal, Rimpi Saikia, Lizanne Oliveira, Yashashree Bhorkar, Akshay Lonare, Pallavi Varshney, Prathamesh Dhamale, Amitabha Majumdar, Jomon Joseph.
      ER-mitochondria contact sites (ERMCSs) regulate processes, including calcium homoeostasis, energy metabolism and autophagy. Previously, it was shown that during growth factor signalling, mTORC2/Akt gets recruited to and stabilizes ERMCSs. Independent studies showed that GSK3β, a well-known Akt substrate, reduces ER-mitochondria connectivity by disrupting the VAPB-PTPIP51 tethering complex. However, the mechanisms that regulate ERMCSs are incompletely understood. Here we find that annulate lamellae (AL), relatively unexplored subdomains of ER enriched with a subset of nucleoporins, are present at ERMCSs. Depletion of Nup358, an AL-resident nucleoporin, results in enhanced mTORC2/Akt activation, GSK3β inhibition and increased ERMCSs. Depletion of Rictor, a mTORC2-specific subunit, or exogenous expression of GSK3β, was sufficient to reverse the ERMCS-phenotype in Nup358-deficient cells. We show that growth factor-mediated activation of mTORC2 requires the VAPB-PTPIP51 complex, whereas, Nup358's association with this tether restricts mTORC2/Akt signalling and ER-mitochondria connectivity. Expression of a Nup358 fragment that is sufficient for interaction with the VAPB-PTPIP51 complex suppresses mTORC2/Akt activation and disrupts ERMCSs. Collectively, our study uncovers a novel role for Nup358 in controlling ERMCSs by modulating the mTORC2/Akt/GSK3β axis.
    Keywords:  Annulate Lamellae; ER-mitochondria Contact Sites; GSK3β; Nucleoporins; mTORC2
    DOI:  https://doi.org/10.1038/s44319-024-00204-8
  5. bioRxiv. 2024 Jul 07. pii: 2024.07.06.602365. [Epub ahead of print]
    INF2-mediated actin polymerization at ER-organelle contacts regulates organelle size and movement.
    Cara R Schiavon, Yuning Wang, Jasmine W Feng, Stephanie Garrett, Tsung-Chang Sung, Yelena Dayn, Chunxin Wang, Richard J Youle, Omar A Quintero-Carmona, Gerald S Shadel, Uri Manor.
      Proper regulation of organelle dynamics and inter-organelle contacts is critical for cellular health and function. Both the endoplasmic reticulum (ER) and actin cytoskeleton are known to regulate organelle dynamics, but how, when, and where these two subcellular components are coordinated to control organelle dynamics remains unclear. Here, we show that ER-associated actin consistently marks mitochondrial, endosomal, and lysosomal fission sites. We also show that actin polymerization by the ER-anchored isoform of the formin protein INF2 is a key regulator of the morphology and mobility of these organelles. Together, our findings establish a mechanism by which INF2-mediated polymerization of ER-associated actin at ER-organelle contacts regulates organelle dynamics.
    DOI:  https://doi.org/10.1101/2024.07.06.602365
  6. Front Plant Sci. 2024 ;15 1363555
    SYNAPTOTAGMIN 4 is expressed mainly in the phloem and participates in abiotic stress tolerance in Arabidopsis.
    Ajay Kumar, Miroslav Krausko, Ján Jásik.
      Plant synaptotagmins structurally resemble animal synaptotagmins and extended-synaptotagmins. Animal synaptotagmins are well-characterized calcium sensors in membrane trafficking, and extended-synaptotagmins mediate lipid transfer at the endoplasmic reticulum-plasma membrane contact sites. Here, we characterize SYNAPTOTAGMIN 4 (SYT4), which belongs to the six-member family in Arabidopsis. Fluorometric GUS assay showed that the SYT4 promoter was strongest in roots and the least active in rosettes and cauline leaves, which was confirmed by qPCR. In seedlings, promoter activity was influenced by several factors, such as plant growth regulators, mannitol, sucrose, polyethylene glycol and cold. GUS histochemistry revealed SYT4 promoter activity in the phloem of all organs and even almost exclusively in sieve element precursors and differentiating sieve elements. Accordingly, the SYT-GFP fusion protein also accumulated in these cells with maximal abundance in sieve element precursors. The protein formed a network in the cytoplasm, but during sieve tube differentiation, it deposited at the cell periphery and disappeared from mature tubes. Using photoconvertible fluorescence technology, we showed that a high abundance of SYT4 protein in meristematic protophloem cells was due to its extensive synthesis. SYT4 protein synthesis was interrupted in differentiating sieve elements, but protein degradation was also reduced. In addition to phloem, the fusion protein was detected in shoot and root stem cell niche as early as the late heart stage of the embryo. We isolated and molecularly and biologically characterized five syt4 T-DNA insertion alleles and subjected them to phenotype analysis. The allele with the C2B domain interrupted by an T-DNA insertion exhibits increased sensitivity to factors such as auxins, osmotics, salicylic acid, sodium chloride, and the absence of sucrose in the root growth test.
    Keywords:  Arabidopsis SYT4; gene expression; insertion mutants; phloem; root cap; stress response
    DOI:  https://doi.org/10.3389/fpls.2024.1363555
  7. J Neurochem. 2024 Jul 18.
    The reciprocal relationship between amyloid precursor protein and mitochondrial function.
    Taylor A Strope, Heather M Wilkins.
      Amyloid precursor protein (APP), secretase enzymes, and amyloid beta (Aβ) have been extensively studied in the context of Alzheimer's disease (AD). Despite this, the function of these proteins and their metabolism is not understood. APP, secretase enzymes, and APP processing products (Aβ and C-terminal fragments) localize to endosomes, mitochondria, endoplasmic reticulum (ER), and mitochondrial/ER contact sites. Studies implicate significant relationships between APP, secretase enzyme function, APP metabolism, and mitochondrial function. Mitochondrial dysfunction is a key pathological hallmark of AD and is intricately linked to proteostasis. Here, we review studies examining potential functions of APP, secretase enzymes, and APP metabolites in the context of mitochondrial function and bioenergetics. We discuss implications and limitations of studies and highlight knowledge gaps that remain in the field.
    Keywords:  Alzheimer's disease; amyloid beta; amyloid precursor protein; mitochondria; γ‐Secretase
    DOI:  https://doi.org/10.1111/jnc.16183
  8. Cell Rep Med. 2024 Jul 16. pii: S2666-3791(24)00361-6. [Epub ahead of print]5(7): 101647
    Dysregulation of FLVCR1a-dependent mitochondrial calcium handling in neural progenitors causes congenital hydrocephalus.
    Francesca Bertino, Dibyanti Mukherjee, Massimo Bonora, Christoph Bagowski, Jeannette Nardelli, Livia Metani, Diletta Isabella Zanin Venturini, Diego Chianese, Nicolas Santander, Iris Chiara Salaroglio, Andreas Hentschel, Elisa Quarta, Tullio Genova, Arpana Arjun McKinney, Anna Lucia Allocco, Veronica Fiorito, Sara Petrillo, Giorgia Ammirata, Francesco De Giorgio, Evan Dennis, Garrett Allington, Felicitas Maier, Moneef Shoukier, Karl-Philipp Gloning, Luca Munaron, Federico Mussano, Ettore Salsano, Davide Pareyson, Maja di Rocco, Fiorella Altruda, Georgia Panagiotakos, Kristopher T Kahle, Pierre Gressens, Chiara Riganti, Paolo P Pinton, Andreas Roos, Thomas Arnold, Emanuela Tolosano, Deborah Chiabrando.
      Congenital hydrocephalus (CH), occurring in approximately 1/1,000 live births, represents an important clinical challenge due to the limited knowledge of underlying molecular mechanisms. The discovery of novel CH genes is thus essential to shed light on the intricate processes responsible for ventricular dilatation in CH. Here, we identify FLVCR1 (feline leukemia virus subgroup C receptor 1) as a gene responsible for a severe form of CH in humans and mice. Mechanistically, our data reveal that the full-length isoform encoded by the FLVCR1 gene, FLVCR1a, interacts with the IP3R3-VDAC complex located on mitochondria-associated membranes (MAMs) that controls mitochondrial calcium handling. Loss of Flvcr1a in mouse neural progenitor cells (NPCs) affects mitochondrial calcium levels and energy metabolism, leading to defective cortical neurogenesis and brain ventricle enlargement. These data point to defective NPCs calcium handling and metabolic activity as one of the pathogenetic mechanisms driving CH.
    DOI:  https://doi.org/10.1016/j.xcrm.2024.101647
  9. Neurochem Res. 2024 Jul 13.
    MAMs and Mitochondrial Quality Control: Overview and Their Role in Alzheimer's Disease.
    Jian-Sheng Luo, Wen-Hu Zhai, Ling-Ling Ding, Xian-Jie Zhang, Jia Han, Jia-Qi Ning, Xue-Meng Chen, Wen-Cai Jiang, Ru-Yu Yan, Meng-Jie Chen.
      Alzheimer's disease (AD) represents the most widespread neurodegenerative disorder, distinguished by a gradual onset and slow progression, presenting a substantial challenge to global public health. The mitochondrial-associated membrane (MAMs) functions as a crucial center for signal transduction and material transport between mitochondria and the endoplasmic reticulum, playing a pivotal role in various pathological mechanisms of AD. The dysregulation of mitochondrial quality control systems is considered a fundamental factor in the development of AD, leading to mitochondrial dysfunction and subsequent neurodegenerative events. Recent studies have emphasized the role of MAMs in regulating mitochondrial quality control. This review will delve into the molecular mechanisms underlying the imbalance in mitochondrial quality control in AD and provide a comprehensive overview of the role of MAMs in regulating mitochondrial quality control.
    Keywords:  Alzheimer’s disease; MAMs; Mitochondrial quality control
    DOI:  https://doi.org/10.1007/s11064-024-04205-w
  10. Circ Res. 2024 Jul 16.
    Dysferlin Enables Tubular Membrane Proliferation in Cardiac Hypertrophy.
    Nora Josefine Paulke, Carolin Fleischhacker, Justus B Wegener, Gabriel C Riedemann, Constantin Cretu, Mufassra Mushtaq, Nina Zaremba, Wiebke Möbius, Yannik Zühlke, Jasper Wedemeyer, Lorenz Liebmann, Anastasiia A Gorshkova, Daniel Kownatzki-Danger, Eva Wagner, Tobias Kohl, Carolin Wichmann, Olaf Jahn, Henning Urlaub, Karl Toischer, Gerd Hasenfuß, Tobias Moser, Julia Preobraschenski, Christof Lenz, Eva A Rog-Zielinska, Stephan E Lehnart, Sören Brandenburg.
       BACKGROUND: Cardiac hypertrophy compensates for increased biomechanical stress of the heart induced by prevalent cardiovascular pathologies but can result in cardiac failure if left untreated. We hypothesized that the tail-anchored protein dysferlin with multiple Ca2+-binding C2-domains is critical for the integrity of the transverse-axial tubule (TAT) network inside cardiomyocytes and contributes to the proliferation of TAT endomembranes during pressure overload-induced cardiac hypertrophy.
    OBJECTIVE: To reveal the impact of the membrane fusion and repair protein dysferlin on TAT network stabilization and proliferation necessary for the hypertrophic growth of cardiomyocytes.
    METHODS AND RESULTS: Super-resolution light and electron microscopy of mouse cardiomyocytes identified a specific localization of dysferlin in a vesicular compartment in nanometric proximity to contact sites of the TAT network with the sarcoplasmic reticulum, a.k.a. junctional complexes for Ca2+-induced Ca2+ release. Mass spectrometry was used to characterize the cardiac dysferlin interactome, thereby identifying a novel protein interaction with the membrane-tethering sarcoplasmic reticulum protein juncophilin-2, a putative interactor of L-type Ca2+ channels and ryanodine receptor Ca2+ release channels in junctional complexes. While the dysferlin knockout caused a mild progressive phenotype of dilated cardiomyopathy in the mouse heart, global proteome analysis revealed changes preceding systolic failure. Following transverse aortic constriction, dysferlin protein expression was significantly increased in hypertrophied wild-type myocardium, while dysferlin knockout animals presented markedly reduced left-ventricular hypertrophy. Live-cell membrane imaging demonstrated a profound reorganization of the TAT network in wild-type left-ventricular myocytes post-transverse aortic constriction with robust proliferation of axial tubules, which critically depended on the increased expression of dysferlin within newly emerging tubule components.
    CONCLUSIONS: Dysferlin represents a new molecular target in cardiac disease that protects the integrity of tubule-sarcoplasmic reticulum junctional complexes for regulated excitation-contraction coupling and controls TAT network reorganization and tubular membrane proliferation in cardiomyocyte hypertrophy induced by pressure overload.
    Keywords:  cell membrane; constriction; dysferin; mice; phenotype
    DOI:  https://doi.org/10.1161/CIRCRESAHA.124.324588
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