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Axonal regeneration after sciatic nerve lesion is delayed but complete in GFAP- and vimentin-deficient mice.

Berg A, Zelano J, Pekna M, Wilhelmsson U, Pekny M, Cullheim S - PLoS ONE (2013)

Bottom Line: The mechanisms of synaptic stripping remain elusive, but reactive astrocytes and microglia appear to be important in this process.After sciatic nerve crush in GFAP(-/-)Vim(-/-) mice, the fraction of reinnervated motor endplates on muscle fibers of the gastrocnemius muscle was reduced 13 days after the injury, and axonal regeneration and functional recovery were delayed but complete.Thus, the absence of GFAP and vimentin in glial cells does not seem to affect the outcome after peripheral motoneuron injury but may have an important effect on the response dynamics.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.

ABSTRACT
Peripheral axotomy of motoneurons triggers Wallerian degeneration of injured axons distal to the lesion, followed by axon regeneration. Centrally, axotomy induces loss of synapses (synaptic stripping) from the surface of lesioned motoneurons in the spinal cord. At the lesion site, reactive Schwann cells provide trophic support and guidance for outgrowing axons. The mechanisms of synaptic stripping remain elusive, but reactive astrocytes and microglia appear to be important in this process. We studied axonal regeneration and synaptic stripping of motoneurons after a sciatic nerve lesion in mice lacking the intermediate filament (nanofilament) proteins glial fibrillary acidic protein (GFAP) and vimentin, which are upregulated in reactive astrocytes and Schwann cells. Seven days after sciatic nerve transection, ultrastructural analysis of synaptic density on the somata of injured motoneurons revealed more remaining boutons covering injured somata in GFAP(-/-)Vim(-/-) mice. After sciatic nerve crush in GFAP(-/-)Vim(-/-) mice, the fraction of reinnervated motor endplates on muscle fibers of the gastrocnemius muscle was reduced 13 days after the injury, and axonal regeneration and functional recovery were delayed but complete. Thus, the absence of GFAP and vimentin in glial cells does not seem to affect the outcome after peripheral motoneuron injury but may have an important effect on the response dynamics.

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Synaptic stripping in the spinal cord 7 and 35 days after SNT.Synaptophysin IR in the ventral horn harbouring the sciatic motor pool (A-F) displayed a similar pattern in uninjured WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice (A, B). At 7 days after SNT there was a clear decrease in synaptophysin IR in both WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice on the ipsilateral side (C, D) compared to the contralateral side (not shown). At 35 days after SNT, synaptophysin IR had increased compared to 7 days after SNT (E, F), but no significant difference between the strains were seen at any of the two time points (H). A representative electron microscopic picture shows a motoneuron (mn) and two apposing synaptic terminals (x), (G). Seven days after SNT, electron microscopy revealed fewer boutons/100 µm of soma membrane length on the injured motoneurons in WT (n = 3) compared to GFAP–/–Vim–/– (n = 3) mice (I). Error bars indicate SEM. * p<0.05, ns =  non-significant. Scale bar, 200 µm.
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pone-0079395-g003: Synaptic stripping in the spinal cord 7 and 35 days after SNT.Synaptophysin IR in the ventral horn harbouring the sciatic motor pool (A-F) displayed a similar pattern in uninjured WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice (A, B). At 7 days after SNT there was a clear decrease in synaptophysin IR in both WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice on the ipsilateral side (C, D) compared to the contralateral side (not shown). At 35 days after SNT, synaptophysin IR had increased compared to 7 days after SNT (E, F), but no significant difference between the strains were seen at any of the two time points (H). A representative electron microscopic picture shows a motoneuron (mn) and two apposing synaptic terminals (x), (G). Seven days after SNT, electron microscopy revealed fewer boutons/100 µm of soma membrane length on the injured motoneurons in WT (n = 3) compared to GFAP–/–Vim–/– (n = 3) mice (I). Error bars indicate SEM. * p<0.05, ns =  non-significant. Scale bar, 200 µm.

Mentions: Since axon transection has been the preferred lesion model for studying synaptic stripping of motoneurons [6]-[9], [24], we used SNT for semiquantative assessment of synaptophysin IR in lesioned motor nuclei and a quantitative ultrastructural analysis of the synaptic inputs to the cell soma of lesioned motoneurons. We first investigated the extent of synaptic stripping by assessing synaptophysin IR, in uninjured spinal cords, 1 week after SNT, when synapses are removed, and at 35 days, when synapses are being re-established. At neither time point did we observe any difference between GFAP–/–Vim–/– and WT mice, although there was a trend toward higher synaptophysin levels in GFAP–/–Vim–/– mice (Fig. 3 A-D). Seven days after SNT, GFAP–/–Vim–/– and WT mice had lost synapses on the somata of injured motoneurons, as shown by ultrastructural analysis; however, GFAP–/–Vim–/– mice had approximately 35% more boutons covering the injured somata (p<0.05 vs. WT). No difference was seen between uninjured GFAP–/–Vim–/– and WT mice (Fig. 3E).


Axonal regeneration after sciatic nerve lesion is delayed but complete in GFAP- and vimentin-deficient mice.

Berg A, Zelano J, Pekna M, Wilhelmsson U, Pekny M, Cullheim S - PLoS ONE (2013)

Synaptic stripping in the spinal cord 7 and 35 days after SNT.Synaptophysin IR in the ventral horn harbouring the sciatic motor pool (A-F) displayed a similar pattern in uninjured WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice (A, B). At 7 days after SNT there was a clear decrease in synaptophysin IR in both WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice on the ipsilateral side (C, D) compared to the contralateral side (not shown). At 35 days after SNT, synaptophysin IR had increased compared to 7 days after SNT (E, F), but no significant difference between the strains were seen at any of the two time points (H). A representative electron microscopic picture shows a motoneuron (mn) and two apposing synaptic terminals (x), (G). Seven days after SNT, electron microscopy revealed fewer boutons/100 µm of soma membrane length on the injured motoneurons in WT (n = 3) compared to GFAP–/–Vim–/– (n = 3) mice (I). Error bars indicate SEM. * p<0.05, ns =  non-significant. Scale bar, 200 µm.
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Related In: Results  -  Collection

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pone-0079395-g003: Synaptic stripping in the spinal cord 7 and 35 days after SNT.Synaptophysin IR in the ventral horn harbouring the sciatic motor pool (A-F) displayed a similar pattern in uninjured WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice (A, B). At 7 days after SNT there was a clear decrease in synaptophysin IR in both WT (n = 6) and GFAP–/–Vim–/– (n = 6) mice on the ipsilateral side (C, D) compared to the contralateral side (not shown). At 35 days after SNT, synaptophysin IR had increased compared to 7 days after SNT (E, F), but no significant difference between the strains were seen at any of the two time points (H). A representative electron microscopic picture shows a motoneuron (mn) and two apposing synaptic terminals (x), (G). Seven days after SNT, electron microscopy revealed fewer boutons/100 µm of soma membrane length on the injured motoneurons in WT (n = 3) compared to GFAP–/–Vim–/– (n = 3) mice (I). Error bars indicate SEM. * p<0.05, ns =  non-significant. Scale bar, 200 µm.
Mentions: Since axon transection has been the preferred lesion model for studying synaptic stripping of motoneurons [6]-[9], [24], we used SNT for semiquantative assessment of synaptophysin IR in lesioned motor nuclei and a quantitative ultrastructural analysis of the synaptic inputs to the cell soma of lesioned motoneurons. We first investigated the extent of synaptic stripping by assessing synaptophysin IR, in uninjured spinal cords, 1 week after SNT, when synapses are removed, and at 35 days, when synapses are being re-established. At neither time point did we observe any difference between GFAP–/–Vim–/– and WT mice, although there was a trend toward higher synaptophysin levels in GFAP–/–Vim–/– mice (Fig. 3 A-D). Seven days after SNT, GFAP–/–Vim–/– and WT mice had lost synapses on the somata of injured motoneurons, as shown by ultrastructural analysis; however, GFAP–/–Vim–/– mice had approximately 35% more boutons covering the injured somata (p<0.05 vs. WT). No difference was seen between uninjured GFAP–/–Vim–/– and WT mice (Fig. 3E).

Bottom Line: The mechanisms of synaptic stripping remain elusive, but reactive astrocytes and microglia appear to be important in this process.After sciatic nerve crush in GFAP(-/-)Vim(-/-) mice, the fraction of reinnervated motor endplates on muscle fibers of the gastrocnemius muscle was reduced 13 days after the injury, and axonal regeneration and functional recovery were delayed but complete.Thus, the absence of GFAP and vimentin in glial cells does not seem to affect the outcome after peripheral motoneuron injury but may have an important effect on the response dynamics.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.

ABSTRACT
Peripheral axotomy of motoneurons triggers Wallerian degeneration of injured axons distal to the lesion, followed by axon regeneration. Centrally, axotomy induces loss of synapses (synaptic stripping) from the surface of lesioned motoneurons in the spinal cord. At the lesion site, reactive Schwann cells provide trophic support and guidance for outgrowing axons. The mechanisms of synaptic stripping remain elusive, but reactive astrocytes and microglia appear to be important in this process. We studied axonal regeneration and synaptic stripping of motoneurons after a sciatic nerve lesion in mice lacking the intermediate filament (nanofilament) proteins glial fibrillary acidic protein (GFAP) and vimentin, which are upregulated in reactive astrocytes and Schwann cells. Seven days after sciatic nerve transection, ultrastructural analysis of synaptic density on the somata of injured motoneurons revealed more remaining boutons covering injured somata in GFAP(-/-)Vim(-/-) mice. After sciatic nerve crush in GFAP(-/-)Vim(-/-) mice, the fraction of reinnervated motor endplates on muscle fibers of the gastrocnemius muscle was reduced 13 days after the injury, and axonal regeneration and functional recovery were delayed but complete. Thus, the absence of GFAP and vimentin in glial cells does not seem to affect the outcome after peripheral motoneuron injury but may have an important effect on the response dynamics.

Show MeSH
Related in: MedlinePlus