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Meningeal cells and glia establish a permissive environment for axon regeneration after spinal cord injury in newts.

Zukor KA, Kent DT, Odelberg SJ - Neural Dev (2011)

Bottom Line: Meningeal and endothelial cells regenerate into the lesion first and are associated with a loose extracellular matrix that allows axon growth cone migration.Axons grow into the injury site next and are closely associated with meningeal cells and glial processes extending from cell bodies surrounding the central canal.After crossing the injury site, axons travel through white matter to reach synaptic targets, and though ascending axons regenerate, sensory axons do not appear to be among them.

View Article: PubMed Central - HTML - PubMed

Affiliation: Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, UT 84132, USA.

ABSTRACT

Background: Newts have the remarkable ability to regenerate their spinal cords as adults. Their spinal cords regenerate with the regenerating tail after tail amputation, as well as after a gap-inducing spinal cord injury (SCI), such as a complete transection. While most studies on newt spinal cord regeneration have focused on events occurring after tail amputation, less attention has been given to events occurring after an SCI, a context that is more relevant to human SCI. Our goal was to use modern labeling and imaging techniques to observe axons regenerating across a complete transection injury and determine how cells and the extracellular matrix in the injury site might contribute to the regenerative process.

Results: We identify stages of axon regeneration following a spinal cord transection and find that axon regrowth across the lesion appears to be enabled, in part, because meningeal cells and glia form a permissive environment for axon regeneration. Meningeal and endothelial cells regenerate into the lesion first and are associated with a loose extracellular matrix that allows axon growth cone migration. This matrix, paradoxically, consists of both permissive and inhibitory proteins. Axons grow into the injury site next and are closely associated with meningeal cells and glial processes extending from cell bodies surrounding the central canal. Later, ependymal tubes lined with glia extend into the lesion as well. Finally, the meningeal cells, axons, and glia move as a unit to close the gap in the spinal cord. After crossing the injury site, axons travel through white matter to reach synaptic targets, and though ascending axons regenerate, sensory axons do not appear to be among them. This entire regenerative process occurs even in the presence of an inflammatory response.

Conclusions: These data reveal, in detail, the cellular and extracellular events that occur during newt spinal cord regeneration after a transection injury and uncover an important role for meningeal and glial cells in facilitating axon regeneration. Given that these cell types interact to form inhibitory barriers in mammals, identifying the mechanisms underlying their permissive behaviors in the newt will provide new insights for improving spinal cord regeneration in mammals.

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Meningeal and endothelial cells are associated with wisping axons. (A-D) Axons were labeled with the axon tracer (B, C) or 3A10 (D) and are shown in magenta, von Willeband factor (vWF) is green (A-C) and nuclei are blue. (A) Cross-section through intact spinal cord. (B) Longitudinal section through the SCI of a wisping stage regenerate labeled with anti-FN (white, shown separately in (B')) and anti-vWF (green, shown separately in (B")). Arrowheads, cells double-labeled with FN and vWF. (C) Cross-section through axons wisping into the injury site of a wisping stage regenerate. Schematic longitudinal section of the spinal cord in the upper right corner shows where the section is in relationship to the injury site. (D) Single confocal plane of a longitudinal thick section of a wisping/spiking stage regenerate. Arrowhead, meninges (m). (E-I) Longitudinal section through a wisping stage regenerate imaged with electron microscopy. (E) Region containing axons wisping ahead of the TV. Asterisks, phagocytic cells. (F) Enlargement of meningeal cells in box F of (E). (G) Enlargement of meningeal-like cell in box G of (E) that is associated with dura mater ECM (ecm). Arrowhead, closed loop formed by meningeal-like cell processes; arrow, process resembling dura mater cell process. (H) Enlargement of meningeal-like cell in box H of (E), rotated 90°. This cell's processes (arrowheads) wrap around a bundle of axons (ax) cut in cross-section. (I) Enlargement of box I in (H) showing that this cell's processes (arrowheads) are also associated with ECM (ecm). D, dorsal; V, ventral; R, rostral; C, caudal. Scale bars: 200 μm (A-D); 50 μm (E); 10 μm (F-H); 1 μm (I).
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Figure 5: Meningeal and endothelial cells are associated with wisping axons. (A-D) Axons were labeled with the axon tracer (B, C) or 3A10 (D) and are shown in magenta, von Willeband factor (vWF) is green (A-C) and nuclei are blue. (A) Cross-section through intact spinal cord. (B) Longitudinal section through the SCI of a wisping stage regenerate labeled with anti-FN (white, shown separately in (B')) and anti-vWF (green, shown separately in (B")). Arrowheads, cells double-labeled with FN and vWF. (C) Cross-section through axons wisping into the injury site of a wisping stage regenerate. Schematic longitudinal section of the spinal cord in the upper right corner shows where the section is in relationship to the injury site. (D) Single confocal plane of a longitudinal thick section of a wisping/spiking stage regenerate. Arrowhead, meninges (m). (E-I) Longitudinal section through a wisping stage regenerate imaged with electron microscopy. (E) Region containing axons wisping ahead of the TV. Asterisks, phagocytic cells. (F) Enlargement of meningeal cells in box F of (E). (G) Enlargement of meningeal-like cell in box G of (E) that is associated with dura mater ECM (ecm). Arrowhead, closed loop formed by meningeal-like cell processes; arrow, process resembling dura mater cell process. (H) Enlargement of meningeal-like cell in box H of (E), rotated 90°. This cell's processes (arrowheads) wrap around a bundle of axons (ax) cut in cross-section. (I) Enlargement of box I in (H) showing that this cell's processes (arrowheads) are also associated with ECM (ecm). D, dorsal; V, ventral; R, rostral; C, caudal. Scale bars: 200 μm (A-D); 50 μm (E); 10 μm (F-H); 1 μm (I).

Mentions: Given that cells closely associated with axons growing across the injury site and cells that create the permissive ECM are likely to be playing an important role in enabling axon regeneration, we sought to identify these cells. We hypothesized that they may be meningeal and/or endothelial cells because, in the intact and regenerating spinal cord, ECM appears to be expressed by cells of the meninges and blood vessels, not by cells in the grey or white matter (Figure 4). Thus, astrocytes and EG in the spinal cord do not appear to express ECM, at least not around their cell bodies. Our hypothesis is also supported by the fact that in the intact spinal cord, pigmented cells are only found in the meninges and blood vessels (Figure 4U), and pigmented cells are associated with wisping axons (Figure 4V). Additionally, many cells associated with wisping axons appear to be meningeal cells because they are continuous with the meninges (Figure 2). The meninges appear to regenerate ahead of regrowing axons, and some regrowing axons even appear to follow the regenerating meninges (Figure 5D; Additional file 5).


Meningeal cells and glia establish a permissive environment for axon regeneration after spinal cord injury in newts.

Zukor KA, Kent DT, Odelberg SJ - Neural Dev (2011)

Meningeal and endothelial cells are associated with wisping axons. (A-D) Axons were labeled with the axon tracer (B, C) or 3A10 (D) and are shown in magenta, von Willeband factor (vWF) is green (A-C) and nuclei are blue. (A) Cross-section through intact spinal cord. (B) Longitudinal section through the SCI of a wisping stage regenerate labeled with anti-FN (white, shown separately in (B')) and anti-vWF (green, shown separately in (B")). Arrowheads, cells double-labeled with FN and vWF. (C) Cross-section through axons wisping into the injury site of a wisping stage regenerate. Schematic longitudinal section of the spinal cord in the upper right corner shows where the section is in relationship to the injury site. (D) Single confocal plane of a longitudinal thick section of a wisping/spiking stage regenerate. Arrowhead, meninges (m). (E-I) Longitudinal section through a wisping stage regenerate imaged with electron microscopy. (E) Region containing axons wisping ahead of the TV. Asterisks, phagocytic cells. (F) Enlargement of meningeal cells in box F of (E). (G) Enlargement of meningeal-like cell in box G of (E) that is associated with dura mater ECM (ecm). Arrowhead, closed loop formed by meningeal-like cell processes; arrow, process resembling dura mater cell process. (H) Enlargement of meningeal-like cell in box H of (E), rotated 90°. This cell's processes (arrowheads) wrap around a bundle of axons (ax) cut in cross-section. (I) Enlargement of box I in (H) showing that this cell's processes (arrowheads) are also associated with ECM (ecm). D, dorsal; V, ventral; R, rostral; C, caudal. Scale bars: 200 μm (A-D); 50 μm (E); 10 μm (F-H); 1 μm (I).
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Related In: Results  -  Collection

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Figure 5: Meningeal and endothelial cells are associated with wisping axons. (A-D) Axons were labeled with the axon tracer (B, C) or 3A10 (D) and are shown in magenta, von Willeband factor (vWF) is green (A-C) and nuclei are blue. (A) Cross-section through intact spinal cord. (B) Longitudinal section through the SCI of a wisping stage regenerate labeled with anti-FN (white, shown separately in (B')) and anti-vWF (green, shown separately in (B")). Arrowheads, cells double-labeled with FN and vWF. (C) Cross-section through axons wisping into the injury site of a wisping stage regenerate. Schematic longitudinal section of the spinal cord in the upper right corner shows where the section is in relationship to the injury site. (D) Single confocal plane of a longitudinal thick section of a wisping/spiking stage regenerate. Arrowhead, meninges (m). (E-I) Longitudinal section through a wisping stage regenerate imaged with electron microscopy. (E) Region containing axons wisping ahead of the TV. Asterisks, phagocytic cells. (F) Enlargement of meningeal cells in box F of (E). (G) Enlargement of meningeal-like cell in box G of (E) that is associated with dura mater ECM (ecm). Arrowhead, closed loop formed by meningeal-like cell processes; arrow, process resembling dura mater cell process. (H) Enlargement of meningeal-like cell in box H of (E), rotated 90°. This cell's processes (arrowheads) wrap around a bundle of axons (ax) cut in cross-section. (I) Enlargement of box I in (H) showing that this cell's processes (arrowheads) are also associated with ECM (ecm). D, dorsal; V, ventral; R, rostral; C, caudal. Scale bars: 200 μm (A-D); 50 μm (E); 10 μm (F-H); 1 μm (I).
Mentions: Given that cells closely associated with axons growing across the injury site and cells that create the permissive ECM are likely to be playing an important role in enabling axon regeneration, we sought to identify these cells. We hypothesized that they may be meningeal and/or endothelial cells because, in the intact and regenerating spinal cord, ECM appears to be expressed by cells of the meninges and blood vessels, not by cells in the grey or white matter (Figure 4). Thus, astrocytes and EG in the spinal cord do not appear to express ECM, at least not around their cell bodies. Our hypothesis is also supported by the fact that in the intact spinal cord, pigmented cells are only found in the meninges and blood vessels (Figure 4U), and pigmented cells are associated with wisping axons (Figure 4V). Additionally, many cells associated with wisping axons appear to be meningeal cells because they are continuous with the meninges (Figure 2). The meninges appear to regenerate ahead of regrowing axons, and some regrowing axons even appear to follow the regenerating meninges (Figure 5D; Additional file 5).

Bottom Line: Meningeal and endothelial cells regenerate into the lesion first and are associated with a loose extracellular matrix that allows axon growth cone migration.Axons grow into the injury site next and are closely associated with meningeal cells and glial processes extending from cell bodies surrounding the central canal.After crossing the injury site, axons travel through white matter to reach synaptic targets, and though ascending axons regenerate, sensory axons do not appear to be among them.

View Article: PubMed Central - HTML - PubMed

Affiliation: Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, UT 84132, USA.

ABSTRACT

Background: Newts have the remarkable ability to regenerate their spinal cords as adults. Their spinal cords regenerate with the regenerating tail after tail amputation, as well as after a gap-inducing spinal cord injury (SCI), such as a complete transection. While most studies on newt spinal cord regeneration have focused on events occurring after tail amputation, less attention has been given to events occurring after an SCI, a context that is more relevant to human SCI. Our goal was to use modern labeling and imaging techniques to observe axons regenerating across a complete transection injury and determine how cells and the extracellular matrix in the injury site might contribute to the regenerative process.

Results: We identify stages of axon regeneration following a spinal cord transection and find that axon regrowth across the lesion appears to be enabled, in part, because meningeal cells and glia form a permissive environment for axon regeneration. Meningeal and endothelial cells regenerate into the lesion first and are associated with a loose extracellular matrix that allows axon growth cone migration. This matrix, paradoxically, consists of both permissive and inhibitory proteins. Axons grow into the injury site next and are closely associated with meningeal cells and glial processes extending from cell bodies surrounding the central canal. Later, ependymal tubes lined with glia extend into the lesion as well. Finally, the meningeal cells, axons, and glia move as a unit to close the gap in the spinal cord. After crossing the injury site, axons travel through white matter to reach synaptic targets, and though ascending axons regenerate, sensory axons do not appear to be among them. This entire regenerative process occurs even in the presence of an inflammatory response.

Conclusions: These data reveal, in detail, the cellular and extracellular events that occur during newt spinal cord regeneration after a transection injury and uncover an important role for meningeal and glial cells in facilitating axon regeneration. Given that these cell types interact to form inhibitory barriers in mammals, identifying the mechanisms underlying their permissive behaviors in the newt will provide new insights for improving spinal cord regeneration in mammals.

Show MeSH
Related in: MedlinePlus