Post-injury born oligodendrocytes incorporate into the glial scar and contribute to the inhibition of axon regeneration
Ontology highlight
ABSTRACT: Pathologies of the central nervous system (CNS) white matter often result in permanent functional deficits because mature mammalian projection neurons fail to regenerate long-distance axons after injury. A major barrier to axonal regenerative research is that the CNS axons that regenerate in response to experimental treatments stall growth before reaching their post-synaptic targets. Here, we test the hypothesis that interaction of regenerating axons with live oligodendrocytes, which were absent during developmental axon growth, stalls axonal growth. To test this hypothesis, first, we used single cell RNA-seq (scRNA-seq) and immunohistological analysis to investigate whether post-injury born oligodendrocytes incorporate into the glial scar after optic nerve injury. Then, we administered demyelination-inducing cuprizone (used in studies of multiple sclerosis), concurrently with the stimulation of axon regeneration by Pten knockdown (KD) in projection neurons after optic nerve injury. We found that post-injury born oligodendrocyte lineage cells incorporate into the glial scar, where they are susceptible to the demyelination diet treatment, which reduced their presence in the glial scar. We further found that the demyelination diet enhanced Pten KD-stimulated axon regeneration, and localized injection of cuprizone promoted axon regeneration. We also present a website for comparing the gene expression of scRNA-seq-profiled optic nerve oligodendrocyte lineage cells under physiological and pathophysiological conditions. Annotation of oligodendrocyte lineage cell subtypes, and normal or injured condition, are indicated in the last two rows of the cell matrix CSV file.
Project description:Complement component C3 mediates pathology in several CNS neurodegenerative diseases, but the cellular and molecular mechanisms leading to neuronal injury remain unclear. We examined how C3 deletion affects glial profiles and anterior visual pathway pathology in an animal model of neuroinflammation, EAE. scRNA-seq from mouse brain and optic nerve revealed that C3 expression defined disease-associated glial subtypes characterized by increased expression of genes associated with mTOR activation, cell metabolism, and translation. This was confirmed with proteomic analysis of the optic nerves of C3KO and WT EAE mice. Deletion of C3 restored glia towards homeostatic profiles. Myeloid-derived C3 mediated injury in optic nerve axons and retinal ganglion cells (RGCs) at disease peak. Our study supports a direct role for C3 in activating the mTOR-ribosomal biogenesis axis in glia which subsequently mediate early neuro-axonal stress and synapse loss.
Project description:In an attempt to repair injured central nervous system (CNS) nerves/tracts, immune cells are recruited into the injury site, but endogenous response in adult mammals is insufficient for promoting regeneration of severed axons. Here, we found that a portion of retinal ganglion cell (RGC) CNS projection neurons that survive after optic nerve crush (ONC) injury are enriched for and upregulate fibronectin (Fn)-interacting integrins Itga5 and ItgaV, and that Fn promotes long-term survival and long-distance axon regeneration of a portion of axotomized adult RGCs in culture. We then show that, Fn is developmentally downregulated in the axonal tracts of optic nerve and spinal cord, but injury-activated macrophages/microglia upregulate Fn while axon regeneration-promoting zymosan augments their recruitment (and thereby increases Fn levels) in the injured optic nerve. Finally, we found that Fn’s RGD motif, established to interact with Itga5 and ItgaV, promotes long-term survival and long-distance axon regeneration of adult RGCs after ONC in vivo, with some axons reaching the optic chiasm when co-treated with Rpl7a gene therapy. Thus, experimentally augmenting Fn levels in the injured CNS is a promising approach for therapeutic neuroprotection and axon regeneration of at least a portion of neurons.
Project description:In an attempt to repair injured central nervous system (CNS) nerves/tracts, immune cells are recruited into the injury site, but endogenous response in adult mammals is insufficient for promoting regeneration of severed axons. Here, we found that a portion of retinal ganglion cell (RGC) CNS projection neurons that survive after optic nerve crush (ONC) injury are enriched for and upregulate fibronectin (Fn)-interacting integrins Itga5 and ItgaV, and that Fn promotes long-term survival and long-distance axon regeneration of a portion of axotomized adult RGCs in culture. We then show that, Fn is developmentally downregulated in the axonal tracts of optic nerve and spinal cord, but injury-activated macrophages/microglia upregulate Fn while axon regeneration-promoting zymosan augments their recruitment (and thereby increases Fn levels) in the injured optic nerve. Finally, we found that Fn’s RGD motif, established to interact with Itga5 and ItgaV, promotes long-term survival and long-distance axon regeneration of adult RGCs after ONC in vivo, with some axons reaching the optic chiasm when co-treated with Rpl7a gene therapy. Thus, experimentally augmenting Fn levels in the injured CNS is a promising approach for therapeutic neuroprotection and axon regeneration of at least a portion of neurons.
Project description:Irreversible blindness from glaucoma and optic neuropathies is attributed to retinal ganglion cells (RGCs) losing the ability to regenerate axons. While several transcription factors and proteins have demonstrated enhancement of axon regeneration after optic nerve injury, mechanisms contributing to the age-related decline in axon regenerative capacity remains elusive. Here, we show that microRNAs are differentially expressed during RGC development, and identify microRNA-19a (miR-19a) as a heterochronic marker; developmental decline of miR-19a relieves suppression of PTEN, a key regulator of axon regeneration, and serves as a temporal indicator of decreasing axon regenerative capacity. Intravitreal injection of miR-19a promotes axon regeneration after optic nerve crush in adult mice, and increases axon extension in RGCs isolated from aged human donors. This uncovers a previously unrecognized involvement of the miR-19a-PTEN axis in RGC axon regeneration, and demonstrates therapeutic potential of microRNA-mediated restoration of axon regenerative capacity via intravitreal injection in patients with optic neuropathies.
Project description:CNS neurons lose their ability to grow and regenerate axons during development. This is the case for Retinal Ganglion Cells (RGCs) in the retina, which transmit visual information to the brain via axons projecting into the optic nerve. RGCs are unable to regenerate their axon after injury, and start a degeneration process that leads to cell death and loss of vision. To identifying molecular mechanisms that increase regeneration of RGC and may offer new treatment strategies for patients with glaucoma or other types of optic neuropathies, we focused on the identification of transcription factors and chromatin accessible sites that are enriched in RGC during developmental stages, in which axon growth capacity is robust. We find that stage-specific gene expression changes are correlated with temporal changes in promoter chromatin accessibility. We also find that Creb binding motifs are enriched in the differentially opened regions of the chromatin at embryonic developmental stage. Overexpression of active Creb promotes axon regeneration after optic nerve injury. Our results provide a map of the chromatin accessibility during RGC development and highlights that manipulating TF associated with developmental stages can stimulate axon growth in adulthood.
Project description:CNS neurons lose their ability to grow and regenerate axons during development. This is the case for Retinal Ganglion Cells (RGCs) in the retina, which transmit visual information to the brain via axons projecting into the optic nerve. RGCs are unable to regenerate their axon after injury, and start a degeneration process that leads to cell death and loss of vision. To identifying molecular mechanisms that increase regeneration of RGC and may offer new treatment strategies for patients with glaucoma or other types of optic neuropathies, we focused on the identification of transcription factors and chromatin accessible sites that are enriched in RGC during developmental stages, in which axon growth capacity is robust. We find that stage-specific gene expression changes are correlated with temporal changes in promoter chromatin accessibility. We also find that Creb binding motifs are enriched in the differentially opened regions of the chromatin at embryonic developmental stage. Overexpression of active Creb promotes axon regeneration after optic nerve injury. Our results provide a map of the chromatin accessibility during RGC development and highlights that manipulating TF associated with developmental stages can stimulate axon growth in adulthood.
Project description:Xenopus is uniquely suited for identifying core features of successful CNS axon regeneration, because parts of its CNS (e.g., eye), regenerate axons throughout life, whereas others (e.g., hindbrain) do so only as tadpoles. To aid in the interpretation of bisulfite whole genome methylation sequencing (WGBS) on juvenile frog eye after optic nerve injury, and on hindbrain samples from tadpole and juvenile frog after spinal cord injury during the peak phase of axon regeneration, we performed ChIP-seq for histone modifications associated with active gene expression (H3K4me3 & H3K27ac) and repressed gene expression (H3K27me3 & H3K9me3) on these same tissues, as well as DNA-immunoprecipitation sequencing (DIP seq) for 5-hydroxymethyl cytosine (5hmC) on eye samples during optic nerve regeneration.
Project description:Xenopus is uniquely suited for identifying core features of successful CNS axon regeneration, because parts of its CNS (e.g., eye), regenerate axons throughout life, whereas others (e.g., hindbrain) do so only as tadpoles. We performed bisulfite whole genome bisulfite methylation sequencing (WGBS) on juvenile frog eye after optic nerve injury, and on hindbrain samples from tadpole and juvenile frog after spinal cord injury during the peak phase of axon regeneration, to compare tissue-related and injury-induced differences in DNA methylation among them.
Project description:Collapsin response mediator proteins (Crmps) play roles in neuronal development and axon growth. However, neuronal-specific roles of Crmp1, Crmp4, and Crmp5 in regeneration of injured central nervous system (CNS) axons in vivo are unclear. Here, we analyzed developmental and subtype-specific expression of Crmp genes in retinal ganglion cells (RGCs), tested whether overexpressing Crmp1, Crmp4, or Crmp5 in RGCs through localized intralocular AAV2 delivery promotes axon regeneration after optic nerve injury in vivo, and characterized developmental co-regulation of gene-concept networks associated with Crmps. We found that all Crmp genes are developmentally downregulated in RGCs during maturation. However, while Crmp1, Crmp2, and Crmp4 were expressed to a varying degree in most RGC subtypes, Crmp3 and Crmp5 were expressed only in a small subset of RGC subtypes. We then found that after optic nerve injury, Crmp1, Crmp4, and Crmp5 promote RGC axon regeneration to varying extents, with Crmp4 promoting the most axon regeneration and also localizing to axons. We also found that Crmp1 and Crmp4, but not Crmp5, promote RGC survival. Finally, we found that Crmp1, Crmp2, Crmp4, and Crmp5's ability to promote axon regeneration is associated with neurodevelopmental mechanisms, which control RGC’s intrinsic axon growth capacity.
Project description:Collapsin response mediator proteins (Crmps) play roles in neuronal development and axon growth. However, neuronal-specific roles of Crmp1, Crmp4, and Crmp5 in regeneration of injured central nervous system (CNS) axons in vivo are unclear. Here, we analyzed developmental and subtype-specific expression of Crmp genes in retinal ganglion cells (RGCs), tested whether overexpressing Crmp1, Crmp4, or Crmp5 in RGCs through localized intralocular AAV2 delivery promotes axon regeneration after optic nerve injury in vivo, and characterized developmental co-regulation of gene-concept networks associated with Crmps. We found that all Crmp genes are developmentally downregulated in RGCs during maturation. However, while Crmp1, Crmp2, and Crmp4 were expressed to a varying degree in most RGC subtypes, Crmp3 and Crmp5 were expressed only in a small subset of RGC subtypes. We then found that after optic nerve injury, Crmp1, Crmp4, and Crmp5 promote RGC axon regeneration to varying extents, with Crmp4 promoting the most axon regeneration and also localizing to axons. We also found that Crmp1 and Crmp4, but not Crmp5, promote RGC survival. Finally, we found that Crmp1, Crmp2, Crmp4, and Crmp5's ability to promote axon regeneration is associated with neurodevelopmental mechanisms, which control RGC’s intrinsic axon growth capacity.