skip to main content


Title: The Composition and Cellular Sources of CSPGs in the Glial Scar After Spinal Cord Injury in the Lamprey
Axon regrowth after spinal cord injury (SCI) is inhibited by several types of inhibitory extracellular molecules in the central nervous system (CNS), including chondroitin sulfate proteoglycans (CSPGs), which also are components of perineuronal nets (PNNs). The axons of lampreys regenerate following SCI, even though their spinal cords contain CSPGs, and their neurons are enwrapped by PNNs. Previously, we showed that by 2 weeks after spinal cord transection in the lamprey, expression of CSPGs increased in the lesion site, and thereafter, decreased to pre-injury levels by 10 weeks. Enzymatic digestion of CSPGs in the lesion site with chondroitinase ABC (ChABC) enhanced axonal regeneration after SCI and reduced retrograde neuronal death. Lecticans (aggrecan, versican, neurocan, and brevican) are the major CSPG family in the CNS. Previously, we cloned a cDNA fragment that lies in the most conserved link-domain of the lamprey lecticans and found that lectican mRNAs are expressed widely in lamprey glia and neurons. Because of the lack of strict one-to-one orthology with the jawed vertebrate lecticans, the four lamprey lecticans were named simply A, B, C, and D. Using probes that distinguish these four lecticans, we now show that they all are expressed in glia and neurons but at different levels. Expression levels are relatively high in embryonic and early larval stages, gradually decrease, and are upregulated again in adults. Reductions of lecticans B and D are greater than those of A and C. Levels of mRNAs for lecticans B and D increased dramatically after SCI. Lectican D remained upregulated for at least 10 weeks. Multiple cells, including glia, neurons, ependymal cells and microglia/macrophages, expressed lectican mRNAs in the peripheral zone and lesion center after SCI. Thus, as in mammals, lamprey lecticans may be involved in axon guidance and neuroplasticity early in development. Moreover, neurons, glia, ependymal cells, and microglia/macrophages, are responsible for the increase in CSPGs during the formation of the glial scar after SCI.  more » « less
Award ID(s):
1656843
NSF-PAR ID:
10379175
Author(s) / Creator(s):
; ; ; ; ; ;
Date Published:
Journal Name:
Frontiers in Molecular Neuroscience
Volume:
15
ISSN:
1662-5099
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Rapid activation of resident glia occurs after spinal cord injury. Somewhat later, innate and adaptive immune responses occur with the invasion of peripheral immune cells into the wound site. The activation of resident and peripheral immune cells has been postulated to play harmful as well as beneficial roles in the regenerative process. Mauthner cells, large identifiable neurons located in the hindbrain of most fish and amphibians, provided the opportunity to study the morphological relationship between reactive cells and Mauthner axons (M‐axons) severed by spinal cord crush or by selective axotomy. After crossing in the hindbrain, the M‐axons of adult goldfish,Carassius auratus, extend the length of the spinal cord. Following injury, the M‐axon undergoes retrograde degeneration within its myelin sheath creating an axon‐free zone (proximal dieback zone). Reactive cells invade the wound site, enter the axon‐free dieback zone and are observed in the vicinity of the retracted M‐axon tip as early as 3 hr postinjury. Transmission electron microscopy allowed the detection of microglia/macrophages and granulocytes, some of which appear to be neutrophil‐like, at each of these locations. We believe that this is the first report of the invasion of such cells within the myelin sheath of an identifiable axon in the vertebrate central nervous system (CNS). We speculate that microglia/macrophages and granulocytes that are attracted within a few hours to the damaged M‐axon are part of an inflammatory response that allows phagocytosis of debris and plays a role in the regenerative process. Our results provide the baseline from which to utilize immunohistochemical and genetic approaches to elucidate the role of non‐neuronal cells in the regenerative process of a single axon in the vertebrate CNS.

     
    more » « less
  2. Abstract

    Neural activity and learning lead to myelin sheath plasticity in the intact central nervous system (CNS), but this plasticity has not been well‐studied after CNS injury. In the context of spinal cord injury (SCI), demyelination occurs at the lesion site and natural remyelination of surviving axons can take months. To determine if neural activity modulates myelin and axon plasticity in the injured, adult CNS, we electrically stimulated the contralesional motor cortex at 10 Hz to drive neural activity in the corticospinal tract of rats with sub‐chronic spinal contusion injuries. We quantified myelin and axonal characteristics by tracing corticospinal axons rostral to and at the lesion epicenter and identifying nodes of Ranvier by immunohistochemistry. Three weeks of daily stimulation induced very short myelin sheaths, axon branching, and thinner axons outside of the lesion zone, where remodeling has not previously been reported. Surprisingly, remodeling was particularly robust rostral to the injury which suggests that electrical stimulation can promote white matter plasticity even in areas not directly demyelinated by the contusion. Stimulation did not alter myelin or axons at the lesion site, which suggests that neuronal activity does not contribute to myelin remodeling near the injury in the sub‐chronic period. These data are the first to demonstrate wide‐scale remodeling of nodal and myelin structures of a mature, long‐tract motor pathway in response to electrical stimulation. This finding suggests that neuromodulation promotes white matter plasticity in intact regions of pathways after injury and raises intriguing questions regarding the interplay between axonal and myelin plasticity.

     
    more » « less
  3. Abstract

    Neural tissue damaged after central nervous system (CNS) injury does not naturally regenerate but is instead replaced by non‐neural fibrotic scar tissue that serves no neurological function. Scar‐free repair to create a more permissive environment for regeneration requires altering the natural injury responses of glial cells. In this work, glycopolymer‐based supramolecular hydrogels are synthesized to direct adaptive glia repair after CNS injury. Combining poly(trehalose‐co‐guanosine) (pTreGuo) glycopolymers with free guanosine (fGuo) generates shear‐thinning hydrogels through stabilized formation of long‐range G‐quadruplex secondary structures. Hydrogels with smooth or granular microstructures and mechanical properties spanning three orders of magnitude are produced through facile control of pTreGuo hydrogel composition. Injection of pTreGuo hydrogels into healthy mouse brains elicits minimal stromal cell infiltration and peripherally derived inflammation that is comparable to a bioinert methyl cellulose benchmarking material. pTreGuo hydrogels alter astrocyte borders and recruit microglia to infiltrate and resorb the hydrogel bulk over 7 d. Injections of pTreGuo hydrogels into ischemic stroke alter the natural responses of glial cells after injury to reduce the size of lesions and increase axon regrowth into lesion core environments. These results support the use of pTreGuo hydrogels as part of neural regeneration strategies to activate endogenous glia repair mechanisms.

     
    more » « less
  4. Abstract

    This study investigates the response to spinal cord injury in the gray short‐tailed opossum (Monodelphis domestica). In opossums spinal injury early in development results in spontaneous axon growth through the injury, but this regenerative potential diminishes with maturity until it is lost entirely. The mechanisms underlying this regeneration remain unknown. RNA sequencing was used to identify differential gene expression in regenerating (SCI at postnatal Day 7, P7SCI) and nonregenerating (SCI at Day 28, P28SCI) cords +1d, +3d, and +7d after complete spinal transection, compared to age‐matched controls. Genes showing significant differential expression (log2FC ≥ 1,Padj≤ 0.05) were used for downstream analysis. Across all time‐points 233 genes altered expression after P7SCI, and 472 genes altered expression after P28SCI. One hundred and forty‐seven genes altered expression in both injury ages (63% of P7SCI data set). The majority of changes were gene upregulations. Gene ontology overrepresentation analysis in P7SCI gene‐sets showed significant overrepresentations only in immune‐associated categories, while P28SCI gene‐sets showed overrepresentations in these same immune categories, along with other categories such as “cell proliferation,” “cell adhesion,” and “apoptosis.” Cell‐type–association analysis suggested that, regardless of injury age, injury‐associated gene transcripts were most strongly associated with microglia and endothelial cells, with strikingly fewer astrocyte, oligodendrocyte and neuron‐related genes, the notable exception being a cluster of mostly downregulated oligodendrocyte‐associated genes in the P7SCI + 7d gene‐set. Our findings demonstrate a more complex transcriptomic response in nonregenerating cords, suggesting a strong influence of non‐neuronal cells in the outcome after injury and providing the largest survey yet of the transcriptomic changes occurring after SCI in this model.

     
    more » « less
  5. Abstract

    The spinal cord of the teleost fishApteronotus leptorhynchuscontinues to grow during adulthood, in concert with the overall body growth. Immunohistological studies, combined with mathematical modeling, suggest that this growth is driven by proliferative activity of Sox2‐expressing stem/progenitor cells (SPCs) and by cell drift due to population pressure. The SPCs exhibit high volumetric density in the caudal filament and the ependymal layer. Nevertheless, the majority of these cells are found in the parenchyma throughout the rostro‐caudal axis of the spinal cord, albeit at much lower volumetric densities than in the ependymal layer. The SPCs give rise, via transit‐amplifying cells, to neurons and glia. The relative number of neurons and glia is primarily regulated through apoptosis of supernumerary neurons. Quantitative analysis has demonstrated that the continued cell proliferation results in additive neurogenesis. This addition includes adult‐born spinal electromotoneurons, thereby resulting in a continuous increase in the amplitude of the fish’s electric organ discharge during adult life. Amputation of the caudal part of the spinal cord induces initially a degenerative response, dominated by massive apoptotic cell death in spinal cord tissue immediately rostral to the injury site, and distinguished by a partial loss of the electric organ discharge amplitude. This phase is followed by a regenerative response, characterized by absence of gliosis and by rapid stem‐cell‐driven tissue regrowth. Although the quality of the regenerated tissue is variable among individuals, the structural repair has led in every fish examined thus far to full recovery of the electric organ discharge amplitude.

     
    more » « less