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1.
Proc Natl Acad Sci U S A ; 121(31): e2407472121, 2024 Jul 30.
Article in English | MEDLINE | ID: mdl-39047038

ABSTRACT

The integrated stress response (ISR), a pivotal protein homeostasis network, plays a critical role in the formation of long-term memory (LTM). The precise mechanism by which the ISR controls LTM is not well understood. Here, we report insights into how the ISR modulates the mnemonic process by using targeted deletion of the activating transcription factor 4 (ATF4), a key downstream effector of the ISR, in various neuronal and non-neuronal cell types. We found that the removal of ATF4 from forebrain excitatory neurons (but not from inhibitory neurons, cholinergic neurons, or astrocytes) enhances LTM formation. Furthermore, the deletion of ATF4 in excitatory neurons lowers the threshold for the induction of long-term potentiation, a cellular model for LTM. Transcriptomic and proteomic analyses revealed that ATF4 deletion in excitatory neurons leads to upregulation of components of oxidative phosphorylation pathways, which are critical for ATP production. Thus, we conclude that ATF4 functions as a memory repressor selectively within excitatory neurons.


Subject(s)
Activating Transcription Factor 4 , Memory, Long-Term , Neurons , Animals , Mice , Activating Transcription Factor 4/metabolism , Activating Transcription Factor 4/genetics , Astrocytes/metabolism , Long-Term Potentiation , Memory, Long-Term/physiology , Mice, Knockout , Neurons/metabolism , Prosencephalon/metabolism , Male
2.
Cell ; 138(1): 172-85, 2009 Jul 10.
Article in English | MEDLINE | ID: mdl-19596243

ABSTRACT

The transcriptional control of CNS myelin gene expression is poorly understood. Here we identify gene model 98, which we have named myelin gene regulatory factor (MRF), as a transcriptional regulator required for CNS myelination. Within the CNS, MRF is specifically expressed by postmitotic oligodendrocytes. MRF is a nuclear protein containing an evolutionarily conserved DNA binding domain homologous to a yeast transcription factor. Knockdown of MRF in oligodendrocytes by RNA interference prevents expression of most CNS myelin genes; conversely, overexpression of MRF within cultured oligodendrocyte progenitors or the chick spinal cord promotes expression of myelin genes. In mice lacking MRF within the oligodendrocyte lineage, premyelinating oligodendrocytes are generated but display severe deficits in myelin gene expression and fail to myelinate. These mice display severe neurological abnormalities and die because of seizures during the third postnatal week. These findings establish MRF as a critical transcriptional regulator essential for oligodendrocyte maturation and CNS myelination.


Subject(s)
Brain/cytology , Gene Expression Regulation , Myelin Sheath/metabolism , Oligodendroglia/metabolism , Transcription Factors/metabolism , Animals , Brain/metabolism , Cell Differentiation , Cells, Cultured , Mice , Neurons/cytology , Neurons/metabolism , Oligodendroglia/cytology
3.
Curr Opin Neurol ; 31(6): 693-701, 2018 12.
Article in English | MEDLINE | ID: mdl-30320612

ABSTRACT

PURPOSE OF REVIEW: The current review analyzes recent findings that suggest that axon degeneration is a druggable process in the treatment of neurodegenerative disorders and a subset of traumas. RECENT FINDINGS: Emerging evidence reveals that axon degeneration is an active and regulated process in the early progression of some neurodegenerative diseases and acute traumas, which is orchestrated through a combination of axon-intrinsic and somatically derived signaling events. The identification of these pathways has presented appealing drug targets whose specificity for the nervous system and phenotypes in mouse models offers significant clinical opportunity. SUMMARY: As the biology of axon degeneration becomes clear, so too has the realization that the pathways driving axon degeneration overlap in part with those that drive neuronal apoptosis and, importantly, axon regeneration. Axon-specific disorders like those seen in CIPN, where injury signaling to the nucleus is not a prominent feature, have been shown to benefit from disruption of Sarm1. In injury and disease contexts, where involvement of somatic events is prominent, inhibition of the MAP Kinase DLK exhibits promise for neuroprotection. Here, however, interfering with somatic signaling may preclude the ability of an axon or a circuit to regenerate or functionally adapt following acute injuries.


Subject(s)
Axons/pathology , Neurodegenerative Diseases/pathology , Neurodegenerative Diseases/therapy , Animals , Brain Injuries, Traumatic/pathology , Brain Injuries, Traumatic/therapy , Disease Models, Animal , Humans , Nerve Regeneration , Signal Transduction
4.
Proc Natl Acad Sci U S A ; 110(10): 4039-44, 2013 Mar 05.
Article in English | MEDLINE | ID: mdl-23431164

ABSTRACT

The cell intrinsic factors that determine whether a neuron regenerates or undergoes apoptosis in response to axonal injury are not well defined. Here we show that the mixed-lineage dual leucine zipper kinase (DLK) is an essential upstream mediator of both of these divergent outcomes in the same cell type. Optic nerve crush injury leads to rapid elevation of DLK protein, first in the axons of retinal ganglion cells (RGCs) and then in their cell bodies. DLK is required for the majority of gene expression changes in RGCs initiated by injury, including induction of both proapoptotic and regeneration-associated genes. Deletion of DLK in retina results in robust and sustained protection of RGCs from degeneration after optic nerve injury. Despite this improved survival, the number of axons that regrow beyond the injury site is substantially reduced, even when the tumor suppressor phosphatase and tensin homolog (PTEN) is deleted to enhance intrinsic growth potential. These findings demonstrate that these seemingly contradictory responses to injury are mechanistically coupled through a DLK-based damage detection mechanism.


Subject(s)
Apoptosis/physiology , Axons/physiology , MAP Kinase Kinase Kinases/physiology , Nerve Regeneration/physiology , Animals , Apoptosis/genetics , Axons/pathology , MAP Kinase Kinase Kinases/deficiency , MAP Kinase Kinase Kinases/genetics , Mice , Mice, Inbred C57BL , Mice, Transgenic , Nerve Degeneration/genetics , Nerve Degeneration/pathology , Nerve Degeneration/physiopathology , Nerve Regeneration/genetics , Optic Nerve Injuries/genetics , Optic Nerve Injuries/pathology , Optic Nerve Injuries/physiopathology , PTEN Phosphohydrolase/deficiency , PTEN Phosphohydrolase/genetics , PTEN Phosphohydrolase/physiology , Retinal Ganglion Cells/pathology , Retinal Ganglion Cells/physiology , Transcription, Genetic
5.
bioRxiv ; 2023 Feb 01.
Article in English | MEDLINE | ID: mdl-36778383

ABSTRACT

Currently there are no effective treatments for an array of neurodegenerative disorders to a large part because cell-based models fail to recapitulate disease. Here we developed a robust human iPSCbased model where laser axotomy causes retrograde axon degeneration leading to neuronal cell death. Time-lapse confocal imaging revealed that damage triggers a wave of mitochondrial fission proceeding from the site of injury to the soma. We demonstrated that mitochondrial fission and resultant cell death is entirely dependent on phosphorylation of dynamin related protein 1 (DRP1) by dual leucine zipper kinase (DLK). Importantly, we show that CRISPR mediated Drp1 depletion protected mouse retinal ganglion neurons from mitochondrial fission and degeneration after optic nerve crush. Our results provide a powerful platform for studying degeneration of human neurons, pinpoint key early events in damage related neural death and new focus for therapeutic intervention.

6.
bioRxiv ; 2023 Mar 31.
Article in English | MEDLINE | ID: mdl-37034690

ABSTRACT

Previously we showed that neurodegeneration initiated by axonal insults depends in part on the stress-responsive kinase Perk (Larhammar et al., 2017). Here we show that Perk acts primarily through Activating Transcription Factor-4 (Atf4) to stimulate not only pro-apoptotic but also pro-regenerative responses following optic nerve injury. Using conditional knockout mice, we find an extensive Perk/Atf4-dependent transcriptional response that includes canonical Atf4 target genes and modest contributions by C/ebp homologous protein (Chop). Overlap with c-Jun-dependent transcription suggests interplay with a parallel stress pathway that couples regenerative and apoptotic responses. Accordingly, neuronal knockout of Atf4 recapitulates the neuroprotection afforded by Perk deficiency, and Perk or Atf4 knockout impairs optic axon regeneration enabled by disrupting the tumor suppressor Pten. These findings contrast with the transcriptional and functional consequences reported for CRISPR targeting of Atf4 or Chop and reveal an integral role for Perk/Atf4 in coordinating neurodegenerative and regenerative responses to CNS axon injury.

7.
bioRxiv ; 2023 Oct 12.
Article in English | MEDLINE | ID: mdl-37873342

ABSTRACT

Chronic demyelination is theorized to contribute to neurodegeneration and drive progressive disability in demyelinating diseases like multiple sclerosis. Here, we describe two genetic mouse models of inducible demyelination, one distinguished by effective remyelination, and the other by remyelination failure and persistent demyelination. By comparing these two models, we find that remyelination protects neurons from apoptosis, improves conduction, and promotes functional recovery. Chronic demyelination of neurons leads to activation of the mitogen-associated protein kinase (MAPK) stress pathway downstream of dual leucine zipper kinase (DLK), which ultimately induces the phosphorylation of c-Jun in the nucleus. Both pharmacological inhibition and CRISPR/Cas9-mediated disruption of DLK block c-Jun phosphorylation and the apoptosis of demyelinated neurons. These findings provide direct experimental evidence that remyelination is neuroprotective and identify DLK inhibition as a potential therapeutic strategy to protect chronically demyelinated neurons.

8.
Neuron ; 43(2): 183-91, 2004 Jul 22.
Article in English | MEDLINE | ID: mdl-15260955

ABSTRACT

Axons dictate whether or not they will become myelinated in both the central and peripheral nervous systems by providing signals that direct the development of myelinating glia. Here we identify the neurotrophin nerve growth factor (NGF) as a potent regulator of the axonal signals that control myelination of TrkA-expressing dorsal root ganglion neurons (DRGs). Unexpectedly, these NGF-regulated axonal signals have opposite effects on peripheral and central myelination, promoting myelination by Schwann cells but reducing myelination by oligodendrocytes. These findings indicate a novel role for growth factors in regulating the receptivity of axons to myelination and reveal that different axonal signals control central and peripheral myelination.


Subject(s)
Axons/physiology , Myelin Sheath/physiology , Nerve Growth Factor/physiology , Oligodendroglia/physiology , Receptor, trkA , Schwann Cells/physiology , Animals , Carrier Proteins/metabolism , Carrier Proteins/physiology , Coculture Techniques , Ganglia, Spinal/metabolism , Ganglia, Spinal/physiology , Ganglia, Spinal/ultrastructure , Membrane Proteins/metabolism , Membrane Proteins/physiology , Mice , Mice, Knockout , Rats , Rats, Sprague-Dawley , Receptor, Nerve Growth Factor/physiology
9.
Annu Rev Pathol ; 13: 93-116, 2018 01 24.
Article in English | MEDLINE | ID: mdl-29414247

ABSTRACT

From injury to disease to aging, neurons, like all cells, may face various insults that can impact their function and survival. Although the consequences are substantially dictated by the type, context, and severity of insult, distressed neurons are far from passive. Activation of cellular stress responses aids in the preservation or restoration of nervous system function. However, stress responses themselves can further advance neuropathology and contribute significantly to neuronal dysfunction and neurodegeneration. Here we explore the recent advances in defining the cellular stress responses within neurodegenerative diseases and neuronal injury, and we emphasize axonal injury as a well-characterized model of neuronal insult. We highlight key findings and unanswered questions about neuronal stress response pathways, from the initial detection of cellular insults through the underlying mechanisms of the responses to their ultimate impact on the fates of distressed neurons.


Subject(s)
Nerve Degeneration/pathology , Neurodegenerative Diseases/pathology , Neurons/pathology , Stress, Physiological , Animals , Humans , Nerve Degeneration/physiopathology , Neurodegenerative Diseases/physiopathology
10.
Curr Biol ; 12(19): R654-6, 2002 Oct 01.
Article in English | MEDLINE | ID: mdl-12361584

ABSTRACT

Three different myelin proteins, Nogo, MAG, and OMgp, inhibit regenerating axons after CNS injury. New work reveals that they all share a common receptor and that blockade of this receptor promotes CNS repair and functional recovery.


Subject(s)
Nerve Regeneration/physiology , Receptors, Cell Surface/metabolism , Animals , Axons/metabolism , Myelin Proteins/metabolism , Myelin Sheath/metabolism , Myelin-Associated Glycoprotein/metabolism , Myelin-Oligodendrocyte Glycoprotein , Nogo Proteins , Receptors, Cell Surface/antagonists & inhibitors
11.
Elife ; 62017 04 25.
Article in English | MEDLINE | ID: mdl-28440222

ABSTRACT

The PKR-like endoplasmic reticulum kinase (PERK) arm of the Integrated Stress Response (ISR) is implicated in neurodegenerative disease, although the regulators and consequences of PERK activation following neuronal injury are poorly understood. Here we show that PERK signaling is a component of the mouse MAP kinase neuronal stress response controlled by the Dual Leucine Zipper Kinase (DLK) and contributes to DLK-mediated neurodegeneration. We find that DLK-activating insults ranging from nerve injury to neurotrophin deprivation result in both c-Jun N-terminal Kinase (JNK) signaling and the PERK- and ISR-dependent upregulation of the Activating Transcription Factor 4 (ATF4). Disruption of PERK signaling delays neurodegeneration without reducing JNK signaling. Furthermore, DLK is both sufficient for PERK activation and necessary for engaging the ISR subsequent to JNK-mediated retrograde injury signaling. These findings identify DLK as a central regulator of not only JNK but also PERK stress signaling in neurons, with both pathways contributing to neurodegeneration.


Subject(s)
MAP Kinase Kinase Kinases/metabolism , Nerve Degeneration , Neurons/enzymology , eIF-2 Kinase/metabolism , Animals , Gene Expression Regulation , MAP Kinase Signaling System , Mice , Neurons/metabolism
13.
Cold Spring Harb Protoc ; 2014(10): pdb.prot074971, 2014 Oct 01.
Article in English | MEDLINE | ID: mdl-25275100

ABSTRACT

This protocol describes the generation of a rapidly myelinating central nervous system coculture for the study of complex neuronal-glial interactions in vitro. Postnatal rat retinal ganglion cells (RGCs) purified by immunopanning are promoted to cluster into reaggregates and then allowed to extend dense beds of radial axons for 10-14 d. Subsequently, rodent oligodendrocyte precursor cells are purified by immunopanning, transfected if desired, and seeded on top of the RGC reaggregates. Under the conditions described here, compact myelin can be observed within 6 d.


Subject(s)
Coculture Techniques , Myelin Sheath/physiology , Oligodendroglia/physiology , Optic Nerve/cytology , Retina/cytology , Retinal Ganglion Cells/physiology , Animals , Antigens/metabolism , Axons/physiology , Cell Differentiation/drug effects , Cells, Cultured , Dendrites/physiology , Glial Fibrillary Acidic Protein/metabolism , Microtubule-Associated Proteins/metabolism , Myelin Basic Protein/metabolism , Proteoglycans/metabolism , Rats , Retinal Ganglion Cells/cytology , tau Proteins/metabolism
14.
Cold Spring Harb Protoc ; 2014(10): pdb.top070839, 2014 Oct 01.
Article in English | MEDLINE | ID: mdl-25275113

ABSTRACT

In this article, we introduce methods for generating rapidly myelinating cocultures with reaggregates of purified retinal ganglion cells and optic nerve oligodendrocyte precursor cells. This coculture system facilitates the study of complex central nervous system neuronal-glial interactions and myelination. It enables control of the extracellular environment and allows the use of transfected, virally infected, mutant, or knockout neurons and/or glial cell types. It is therefore possible to assess the role of various signaling pathways and genes in myelination and node of Ranvier formation.


Subject(s)
Myelin Basic Protein/metabolism , Myelin Sheath/physiology , Oligodendroglia/physiology , Retina/cytology , Retinal Ganglion Cells/physiology , Animals , Antigens/metabolism , Axons/physiology , Cell Differentiation , Cells, Cultured , Coculture Techniques , Enzyme Inhibitors/pharmacology , Glial Fibrillary Acidic Protein/metabolism , Microtubule-Associated Proteins/metabolism , Oligodendroglia/cytology , Proteoglycans/metabolism , Stem Cells/cytology , tau Proteins/metabolism
15.
Neuron ; 60(4): 555-69, 2008 Nov 26.
Article in English | MEDLINE | ID: mdl-19038214

ABSTRACT

Mechanistic studies of CNS myelination have been hindered by the lack of a rapidly myelinating culture system. Here, we describe a versatile CNS coculture method that allows time-lapse microscopy and molecular analysis of distinct stages of myelination. Employing a culture architecture of reaggregated neurons fosters extension of dense beds of axons from purified retinal ganglion cells. Seeding of oligodendrocyte precursor cells on these axons results in differentiation and ensheathment in as few as 3 days, with generation of compact myelin within 6 days. This technique enabled (1) the demonstration that oligodendrocytes initiate new myelin segments only during a brief window early in their differentiation, (2) identification of a contribution of astrocytes to the rate of myelin wrapping, and (3) molecular dissection of the role of oligodendrocyte gamma-secretase activity in controlling the ensheathment of axons. These insights illustrate the value of this defined system for investigating multiple aspects of CNS myelination.


Subject(s)
Amyloid Precursor Protein Secretases/metabolism , Astrocytes/metabolism , Central Nervous System/metabolism , Nerve Fibers, Myelinated/metabolism , Neurogenesis/physiology , Oligodendroglia/metabolism , Animals , Cell Communication/physiology , Cell Culture Techniques , Cells, Cultured , Central Nervous System/cytology , Coculture Techniques/methods , Growth Cones/metabolism , Growth Cones/ultrastructure , Mice , Mice, Knockout , Myelin Sheath/metabolism , Oligodendroglia/cytology , Rats , Retinal Ganglion Cells/cytology , Retinal Ganglion Cells/metabolism , Stem Cells/cytology , Stem Cells/metabolism , Time Factors
16.
Neural Regen Res ; 20(2): 469-470, 2025 Feb 01.
Article in English | MEDLINE | ID: mdl-38819051
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