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1.
eNeuro ; 11(6)2024 Jun.
Article in English | MEDLINE | ID: mdl-38744490

ABSTRACT

Oligodendrocytes, the myelin-producing glial cells of the central nervous system (CNS), crucially contribute to myelination and circuit function. An increasing amount of evidence suggests that intracellular calcium (Ca2+) dynamics in oligodendrocytes mediates activity-dependent and activity-independent myelination. Unraveling how myelinating oligodendrocytes orchestrate and integrate Ca2+ signals, particularly in relation to axonal firing, is crucial for gaining insights into their role in the CNS development and function, both in health and disease. In this framework, we used the recombinant adeno-associated virus/Olig001 capsid variant to express the genetically encoded Ca2+ indicator jGCaMP8s, under the control of the myelin basic protein promoter. In our study, this tool exhibits excellent tropism and selectivity for myelinating and mature oligodendrocytes, and it allows monitoring Ca2+ activity in myelin-forming cells, both in isolated primary cultures and organotypic spinal cord explants. By live imaging of myelin Ca2+ events in oligodendrocytes within organ cultures, we observed a rapid decline in the amplitude and duration of Ca2+ events across different in vitro developmental stages. Active myelin sheath remodeling and growth are modulated at the level of myelin-axon interface through Ca2+ signaling, and, during early myelination in organ cultures, this phase is finely tuned by the firing of axon action potentials. In the later stages of myelination, Ca2+ events in mature oligodendrocytes no longer display such a modulation, underscoring the involvement of complex Ca2+ signaling in CNS myelination.


Subject(s)
Calcium , Dependovirus , Myelin Sheath , Oligodendroglia , Organ Culture Techniques , Spinal Cord , Animals , Oligodendroglia/metabolism , Spinal Cord/metabolism , Spinal Cord/cytology , Calcium/metabolism , Dependovirus/genetics , Myelin Sheath/metabolism , Calcium Signaling/physiology , Mice, Inbred C57BL , Mice , Cells, Cultured , Female , Rats
2.
Cell Commun Signal ; 22(1): 87, 2024 01 31.
Article in English | MEDLINE | ID: mdl-38297346

ABSTRACT

BACKGROUND: Arginyltransferase (Ate1) orchestrates posttranslational protein arginylation, a pivotal regulator of cellular proteolytic processes. In eukaryotic cells, two interconnected systems-the ubiquitin proteasome system (UPS) and macroautophagy-mediate proteolysis and cooperate to maintain quality protein control and cellular homeostasis. Previous studies have shown that N-terminal arginylation facilitates protein degradation through the UPS. Dysregulation of this machinery triggers p62-mediated autophagy to ensure proper substrate processing. Nevertheless, how Ate1 operates through this intricate mechanism remains elusive. METHODS: We investigated Ate1 subcellular distribution through confocal microscopy and biochemical assays using cells transiently or stably expressing either endogenous Ate1 or a GFP-tagged Ate1 isoform transfected in CHO-K1 or MEFs, respectively. To assess Ate1 and p62-cargo clustering, we analyzed their colocalization and multimerization status by immunofluorescence and nonreducing immunoblotting, respectively. Additionally, we employed Ate1 KO cells to examine the role of Ate1 in autophagy. Ate1 KO MEFs cells stably expressing GFP-tagged Ate1-1 isoform were used as a model for phenotype rescue. Autophagy dynamics were evaluated by analyzing LC3B turnover and p62/SQSTM1 levels under both steady-state and serum-starvation conditions, through immunoblotting and immunofluorescence. We determined mTORC1/AMPk activation by assessing mTOR and AMPk phosphorylation through immunoblotting, while mTORC1 lysosomal localization was monitored by confocal microscopy. RESULTS: Here, we report a multifaceted role for Ate1 in the autophagic process, wherein it clusters with p62, facilitates autophagic clearance, and modulates its signaling. Mechanistically, we found that cell-specific inactivation of Ate1 elicits overactivation of the mTORC1/AMPk signaling hub that underlies a failure in autophagic flux and subsequent substrate accumulation, which is partially rescued by ectopic expression of Ate1. Statistical significance was assessed using a two-sided unpaired t test with a significance threshold set at P<0.05. CONCLUSIONS: Our findings uncover a critical housekeeping role of Ate1 in mTORC1/AMPk-regulated autophagy, as a potential therapeutic target related to this pathway, that is dysregulated in many neurodegenerative and cancer diseases.


Subject(s)
Aminoacyltransferases , Aminoacyltransferases/genetics , Aminoacyltransferases/metabolism , Ubiquitin/metabolism , Autophagy , Proteasome Endopeptidase Complex/metabolism , Mechanistic Target of Rapamycin Complex 1 , Protein Isoforms
3.
FEBS Lett ; 596(9): 1165-1177, 2022 05.
Article in English | MEDLINE | ID: mdl-35114005

ABSTRACT

The ubiquitin-proteasome system (UPS) degrades intracellular proteins through the 26S proteasome. We analysed how cold stress affects the UPS in glial cells. Together with a reduction in the 20S proteolytic activity and increased levels of polyubiquitinated proteins, exposure of glial cell cultures to cold induces a partial disassembly of the 26S proteasome. In particular, we found that Rpt5, a subunit of the 19S proteasome, relocates to cold-stable microtubules, although no apparent cytoskeletal redistribution was detected for other analysed subunits of the 19S or 20S complexes. Furthermore, we demonstrate that both the expression of the microtubule-associated protein MAP6 and the post-translational acetylation of α-tubulin modulate the association of Rpt5 with microtubules. This reversible association could be related to functional preservation of the proteolytic complex during cold stress.


Subject(s)
Proteasome Endopeptidase Complex , Ubiquitin , Microtubules/metabolism , Neuroglia/metabolism , Proteasome Endopeptidase Complex/metabolism , Proteins , Temperature
4.
Glia ; 70(2): 303-320, 2022 02.
Article in English | MEDLINE | ID: mdl-34669233

ABSTRACT

Addition of arginine (Arg) from tRNA can cause major alterations of structure and function of protein substrates. This post-translational modification, termed protein arginylation, is mediated by the enzyme arginyl-tRNA-protein transferase 1 (Ate1). Arginylation plays essential roles in a variety of cellular processes, including cell migration, apoptosis, and cytoskeletal organization. Ate1 is associated with neuronal functions such as neurogenesis and neurite growth. However, the role of Ate1 in glial development, including oligodendrocyte (OL) differentiation and myelination processes in the central nervous system, is poorly understood. The present study revealed a peak in Ate1 protein expression during myelination process in primary cultured OLs. Post-transcriptional downregulation of Ate1 reduced the number of OL processes, and branching complexity, in vitro. We conditionally ablated Ate1 from OLs in mice using 2',3'-cyclic nucleotide 3'-phosphodiesterase-Cre promoter ("Ate1-KO" mice), to assess the role of Ate1 in OL function and axonal myelination in vivo. Immunostaining for OL differentiation markers revealed a notable reduction of mature OLs in corpus callosum of 14-day-old Ate1-KO, but no changes in spinal cord, in comparison with wild-type controls. Local proliferation of OL precursor cells was elevated in corpus callosum of 21-day-old Ate1-KO, but was unchanged in spinal cord. Five-month-old Ate1-KO displayed reductions of mature OL number and myelin thickness, with alterations of motor behaviors. Our findings, taken together, demonstrate that Ate1 helps maintain proper OL differentiation and myelination in corpus callosum in vivo, and that protein arginylation plays an essential role in developmental myelination.


Subject(s)
Neurogenesis , Oligodendroglia , Animals , Arginine/metabolism , Central Nervous System/metabolism , Mice , Myelin Sheath/metabolism , Oligodendroglia/metabolism , Protein Processing, Post-Translational
5.
Biochim Biophys Acta Mol Basis Dis ; 1868(4): 166324, 2022 04 01.
Article in English | MEDLINE | ID: mdl-34954343

ABSTRACT

BACKGROUND: Myelin-associated glycoprotein (MAG) is a key molecule involved in the nurturing effect of myelin on ensheathed axons. MAG also inhibits axon outgrowth after injury. In preclinical stroke models, administration of a function-blocking anti-MAG monoclonal antibody (mAb) aimed to improve axon regeneration demonstrated reduced lesion volumes and a rapid clinical improvement, suggesting a mechanism of immediate neuroprotection rather than enhanced axon regeneration. In addition, it has been reported that antibody-mediated crosslinking of MAG can protect oligodendrocytes (OLs) against glutamate (Glu) overload by unknown mechanisms. PURPOSE: To unravel the molecular mechanisms underlying the protective effect of anti-MAG therapy with a focus on neuroprotection against Glu toxicity. RESULTS: MAG activation (via antibody crosslinking) triggered the clearance of extracellular Glu by its uptake into OLs via high affinity excitatory amino acid transporters. This resulted not only in protection of OLs but also nearby neurons. MAG activation led to a PKC-dependent activation of factor Nrf2 (nuclear-erythroid related factor-2) leading to antioxidant responses including increased mRNA expression of metabolic enzymes from the glutathione biosynthetic pathway and the regulatory chain of cystine/Glu antiporter system xc- increasing reduced glutathione (GSH), the main antioxidant in cells. The efficacy of early anti-MAG mAb administration was demonstrated in a preclinical model of excitotoxicity induced by intrastriatal Glu administration and extended to a model of Experimental Autoimmune Encephalitis showing axonal damage secondary to demyelination. CONCLUSIONS: MAG activation triggers Glu uptake into OLs under conditions of Glu overload and induces a robust protective antioxidant response.


Subject(s)
Antibodies, Monoclonal/immunology , Glutamic Acid/metabolism , Myelin-Associated Glycoprotein/metabolism , Amino Acid Transport Systems, Acidic/genetics , Amino Acid Transport Systems, Acidic/metabolism , Animals , Antibodies, Monoclonal/pharmacology , Antibodies, Monoclonal/therapeutic use , Axons/metabolism , Cells, Cultured , Disease Models, Animal , Encephalomyelitis, Autoimmune, Experimental/drug therapy , Encephalomyelitis, Autoimmune, Experimental/pathology , Glutamic Acid/administration & dosage , Glutamic Acid/pharmacology , Glutathione/metabolism , Mice , Mice, Inbred C57BL , Myelin-Associated Glycoprotein/immunology , NF-E2-Related Factor 2/genetics , NF-E2-Related Factor 2/metabolism , Neurons/metabolism , Oligodendroglia/cytology , Oligodendroglia/metabolism , Oxidative Stress/drug effects , Protein Kinase C/metabolism , Rats , Receptors, Glutamate/metabolism , Signal Transduction/drug effects
6.
Exp Neurol ; 278: 42-53, 2016 Apr.
Article in English | MEDLINE | ID: mdl-26804001

ABSTRACT

Several reports have linked the presence of high titers of anti-Gg Abs with delayed recovery/poor prognosis in GBS. In most cases, failure to recover is associated with halted/deficient axon regeneration. Previous work identified that monoclonal and patient-derived anti-Gg Abs can act as inhibitory factors in an animal model of axon regeneration. Further studies using primary dorsal root ganglion neuron (DRGn) cultures demonstrated that anti-Gg Abs can inhibit neurite outgrowth by targeting gangliosides via activation of the small GTPase RhoA and its associated kinase (ROCK), a signaling pathway common to other established inhibitors of axon regeneration. We aimed to study the molecular basis of the inhibitory effect of anti-Gg abs on neurite outgrowth by dissecting the molecular dynamics of growth cones (GC) cytoskeleton in relation to the spatial-temporal analysis of RhoA activity. We now report that axon growth inhibition in DRGn induced by a well characterized mAb targeting gangliosides GD1a/GT1b involves: i) an early RhoA/ROCK-independent collapse of lamellipodia; ii) a RhoA/ROCK-dependent shrinking of filopodia; and iii) alteration of GC microtubule organization/and presumably dynamics via RhoA/ROCK-dependent phosphorylation of CRMP-2 at threonine 555. Our results also show that mAb 1B7 inhibits peripheral axon regeneration in an animal model via phosphorylation/inactivation of CRMP-2 at threonine 555. Overall, our data may help to explain the molecular mechanisms underlying impaired nerve repair in GBS. Future work should define RhoA-independent pathway/s and effectors regulating actin cytoskeleton, thus providing an opportunity for the design of a successful therapy to guarantee an efficient target reinnervation.


Subject(s)
Antibodies/pharmacology , Microtubules/pathology , Nerve Regeneration/drug effects , Nerve Tissue Proteins/metabolism , Neurons/cytology , Polysaccharides/immunology , rhoA GTP-Binding Protein/metabolism , Animals , Animals, Newborn , Cells, Cultured , Disease Models, Animal , Enzyme Inhibitors/pharmacology , Ganglia, Spinal/cytology , Gene Expression Regulation/drug effects , Intercellular Signaling Peptides and Proteins , Microtubules/drug effects , Nerve Regeneration/physiology , Neurites/drug effects , Neurites/metabolism , Neurons/drug effects , Neurons/metabolism , Rats , Rats, Wistar , Sciatic Neuropathy/metabolism , Sciatic Neuropathy/pathology , Signal Transduction
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