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Alteration of synaptic connectivity of oligodendrocyte precursor cells following demyelination.

Sahel A, Ortiz FC, Kerninon C, Maldonado PP, Angulo MC, Nait-Oumesmar B - Front Cell Neurosci (2015)

Bottom Line: A reduction in synaptic connectivity was confirmed by the lack of VGluT1+ axon-OPC contacts in virtually all rapidly proliferating OPCs stained with EdU (50-ethynyl-20-deoxyuridine).At the end of the massive proliferation phase in lesions, the proportion of innervated OPCs rapidly recovers, although the frequency of spontaneous synaptic currents did not reach control levels.In conclusion, our results demonstrate that newly-generated OPCs do not receive synaptic inputs during their active proliferation after demyelination, but gain synapses during the remyelination process.

View Article: PubMed Central - PubMed

Affiliation: INSERM U1127, Institut du Cerveau et de la Moelle Epinière Paris, France ; Université Paris 6, Sorbonne Paris Cité, UMR-S1127 Paris, France ; Centre National de la Recherche Scientifique UMR 7225 Paris, France.

ABSTRACT
Oligodendrocyte precursor cells (OPCs) are a major source of remyelinating oligodendrocytes in demyelinating diseases such as Multiple Sclerosis (MS). While OPCs are innervated by unmyelinated axons in the normal brain, the fate of such synaptic contacts after demyelination is still unclear. By combining electrophysiology and immunostainings in different transgenic mice expressing fluorescent reporters, we studied the synaptic innervation of OPCs in the model of lysolecithin (LPC)-induced demyelination of corpus callosum. Synaptic innervation of reactivated OPCs in the lesion was revealed by the presence of AMPA receptor-mediated synaptic currents, VGluT1+ axon-OPC contacts in 3D confocal reconstructions and synaptic junctions observed by electron microscopy. Moreover, 3D confocal reconstructions of VGluT1 and NG2 immunolabeling showed the existence of glutamatergic axon-OPC contacts in post-mortem MS lesions. Interestingly, patch-clamp recordings in LPC-induced lesions demonstrated a drastic decrease in spontaneous synaptic activity of OPCs early after demyelination that was not caused by an impaired conduction of compound action potentials. A reduction in synaptic connectivity was confirmed by the lack of VGluT1+ axon-OPC contacts in virtually all rapidly proliferating OPCs stained with EdU (50-ethynyl-20-deoxyuridine). At the end of the massive proliferation phase in lesions, the proportion of innervated OPCs rapidly recovers, although the frequency of spontaneous synaptic currents did not reach control levels. In conclusion, our results demonstrate that newly-generated OPCs do not receive synaptic inputs during their active proliferation after demyelination, but gain synapses during the remyelination process. Hence, glutamatergic synaptic inputs may contribute to inhibit OPC proliferation and might have a physiopathological relevance in demyelinating disorders.

No MeSH data available.


Related in: MedlinePlus

VGluT1+ a xon-OPC contacts in LPC-demyelinated and MS lesions. (A) Immunohistochemistry showing NG2 (red) and VGluT1 (green) labeling in a LPC-induced lesion at 7 dpi. Arrow indicates a VGluT1 puncta. (B,C) 3D reconstruction of NG2 (red) and VGluT1 (green) labeling in control (B) and LPC-induced lesions at 7 dpi (C). Contacts are indicated by arrows. (D) MS brain section stained with Luxol fast blue/MHCII (black), illustrating a typical chronic active lesion in the subcortical white matter. The different areas of the lesion were classified as active, chronic silent and normal appearing white matter (NAWM). Active borders of chronic active lesions were filled with MHCII+ macrophages/microglia, while chronic silent cores were devoid of labeling. (E) Immunohistochemistry showing NG2 (red) and VGluT1 (green) staining in the active border of a chronic active lesion. (F) 3D reconstruction of a NG2 cell (red) with VGluT1 puncta (green, arrows) in the active border of a lesion. Nuclei were stained with Dapi (blue).
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Figure 5: VGluT1+ a xon-OPC contacts in LPC-demyelinated and MS lesions. (A) Immunohistochemistry showing NG2 (red) and VGluT1 (green) labeling in a LPC-induced lesion at 7 dpi. Arrow indicates a VGluT1 puncta. (B,C) 3D reconstruction of NG2 (red) and VGluT1 (green) labeling in control (B) and LPC-induced lesions at 7 dpi (C). Contacts are indicated by arrows. (D) MS brain section stained with Luxol fast blue/MHCII (black), illustrating a typical chronic active lesion in the subcortical white matter. The different areas of the lesion were classified as active, chronic silent and normal appearing white matter (NAWM). Active borders of chronic active lesions were filled with MHCII+ macrophages/microglia, while chronic silent cores were devoid of labeling. (E) Immunohistochemistry showing NG2 (red) and VGluT1 (green) staining in the active border of a chronic active lesion. (F) 3D reconstruction of a NG2 cell (red) with VGluT1 puncta (green, arrows) in the active border of a lesion. Nuclei were stained with Dapi (blue).

Mentions: To complement our electrophysiological data on OPC synaptic connectivity, we visualized glutamatergic contacts of OPCs, using 3D confocal reconstructions of VGluT1 and NG2 immunolabeling in control corpus callosum and within demyelinated lesions at 7 dpi (Figures 5A–C). NG2+ OPCs were distinguished from activated microglia/macrophages based on their typical amoeboid morphology (data not shown). Our data revealed numerous VGluT1+ puncta on OPC in both the control tissue and within the lesion at 7 dpi (Figures 5A–C). We also examined VGluT1 and NG2 expression in MS post-mortem brain samples. MS lesions were first classed as active, chronic active, chronic silent, shadow plaques and normal appearing white matter (NAWM) according to Luxol-fast blue/MHCII staining. Figure 5D illustrates a typical chronic active lesion in the subcortical white matter with a typical silent core and an active border filled with MHCII+ microglia/macrophages. Interestingly, 3D reconstruction of VGluT1 and NG2 immunostaining in MS brain sections (Figures 5E,F) revealed also glutamatergic VGluT1+ puncta on NG2+ OPCs in active lesions as well as in active borders of chronic lesions (Figure 5F). It is noteworthy that NG2+ cells in these human brain samples also expressed the specific oligodendroglial marker Olig1, which never co-localized with Iba1 (Supplementary Figure 2). Therefore, our data demonstrate the presence of glutamatergic axon-OPC contacts both in mouse LPC-induced demyelinated lesions and in active MS lesions.


Alteration of synaptic connectivity of oligodendrocyte precursor cells following demyelination.

Sahel A, Ortiz FC, Kerninon C, Maldonado PP, Angulo MC, Nait-Oumesmar B - Front Cell Neurosci (2015)

VGluT1+ a xon-OPC contacts in LPC-demyelinated and MS lesions. (A) Immunohistochemistry showing NG2 (red) and VGluT1 (green) labeling in a LPC-induced lesion at 7 dpi. Arrow indicates a VGluT1 puncta. (B,C) 3D reconstruction of NG2 (red) and VGluT1 (green) labeling in control (B) and LPC-induced lesions at 7 dpi (C). Contacts are indicated by arrows. (D) MS brain section stained with Luxol fast blue/MHCII (black), illustrating a typical chronic active lesion in the subcortical white matter. The different areas of the lesion were classified as active, chronic silent and normal appearing white matter (NAWM). Active borders of chronic active lesions were filled with MHCII+ macrophages/microglia, while chronic silent cores were devoid of labeling. (E) Immunohistochemistry showing NG2 (red) and VGluT1 (green) staining in the active border of a chronic active lesion. (F) 3D reconstruction of a NG2 cell (red) with VGluT1 puncta (green, arrows) in the active border of a lesion. Nuclei were stained with Dapi (blue).
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Related In: Results  -  Collection

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Figure 5: VGluT1+ a xon-OPC contacts in LPC-demyelinated and MS lesions. (A) Immunohistochemistry showing NG2 (red) and VGluT1 (green) labeling in a LPC-induced lesion at 7 dpi. Arrow indicates a VGluT1 puncta. (B,C) 3D reconstruction of NG2 (red) and VGluT1 (green) labeling in control (B) and LPC-induced lesions at 7 dpi (C). Contacts are indicated by arrows. (D) MS brain section stained with Luxol fast blue/MHCII (black), illustrating a typical chronic active lesion in the subcortical white matter. The different areas of the lesion were classified as active, chronic silent and normal appearing white matter (NAWM). Active borders of chronic active lesions were filled with MHCII+ macrophages/microglia, while chronic silent cores were devoid of labeling. (E) Immunohistochemistry showing NG2 (red) and VGluT1 (green) staining in the active border of a chronic active lesion. (F) 3D reconstruction of a NG2 cell (red) with VGluT1 puncta (green, arrows) in the active border of a lesion. Nuclei were stained with Dapi (blue).
Mentions: To complement our electrophysiological data on OPC synaptic connectivity, we visualized glutamatergic contacts of OPCs, using 3D confocal reconstructions of VGluT1 and NG2 immunolabeling in control corpus callosum and within demyelinated lesions at 7 dpi (Figures 5A–C). NG2+ OPCs were distinguished from activated microglia/macrophages based on their typical amoeboid morphology (data not shown). Our data revealed numerous VGluT1+ puncta on OPC in both the control tissue and within the lesion at 7 dpi (Figures 5A–C). We also examined VGluT1 and NG2 expression in MS post-mortem brain samples. MS lesions were first classed as active, chronic active, chronic silent, shadow plaques and normal appearing white matter (NAWM) according to Luxol-fast blue/MHCII staining. Figure 5D illustrates a typical chronic active lesion in the subcortical white matter with a typical silent core and an active border filled with MHCII+ microglia/macrophages. Interestingly, 3D reconstruction of VGluT1 and NG2 immunostaining in MS brain sections (Figures 5E,F) revealed also glutamatergic VGluT1+ puncta on NG2+ OPCs in active lesions as well as in active borders of chronic lesions (Figure 5F). It is noteworthy that NG2+ cells in these human brain samples also expressed the specific oligodendroglial marker Olig1, which never co-localized with Iba1 (Supplementary Figure 2). Therefore, our data demonstrate the presence of glutamatergic axon-OPC contacts both in mouse LPC-induced demyelinated lesions and in active MS lesions.

Bottom Line: A reduction in synaptic connectivity was confirmed by the lack of VGluT1+ axon-OPC contacts in virtually all rapidly proliferating OPCs stained with EdU (50-ethynyl-20-deoxyuridine).At the end of the massive proliferation phase in lesions, the proportion of innervated OPCs rapidly recovers, although the frequency of spontaneous synaptic currents did not reach control levels.In conclusion, our results demonstrate that newly-generated OPCs do not receive synaptic inputs during their active proliferation after demyelination, but gain synapses during the remyelination process.

View Article: PubMed Central - PubMed

Affiliation: INSERM U1127, Institut du Cerveau et de la Moelle Epinière Paris, France ; Université Paris 6, Sorbonne Paris Cité, UMR-S1127 Paris, France ; Centre National de la Recherche Scientifique UMR 7225 Paris, France.

ABSTRACT
Oligodendrocyte precursor cells (OPCs) are a major source of remyelinating oligodendrocytes in demyelinating diseases such as Multiple Sclerosis (MS). While OPCs are innervated by unmyelinated axons in the normal brain, the fate of such synaptic contacts after demyelination is still unclear. By combining electrophysiology and immunostainings in different transgenic mice expressing fluorescent reporters, we studied the synaptic innervation of OPCs in the model of lysolecithin (LPC)-induced demyelination of corpus callosum. Synaptic innervation of reactivated OPCs in the lesion was revealed by the presence of AMPA receptor-mediated synaptic currents, VGluT1+ axon-OPC contacts in 3D confocal reconstructions and synaptic junctions observed by electron microscopy. Moreover, 3D confocal reconstructions of VGluT1 and NG2 immunolabeling showed the existence of glutamatergic axon-OPC contacts in post-mortem MS lesions. Interestingly, patch-clamp recordings in LPC-induced lesions demonstrated a drastic decrease in spontaneous synaptic activity of OPCs early after demyelination that was not caused by an impaired conduction of compound action potentials. A reduction in synaptic connectivity was confirmed by the lack of VGluT1+ axon-OPC contacts in virtually all rapidly proliferating OPCs stained with EdU (50-ethynyl-20-deoxyuridine). At the end of the massive proliferation phase in lesions, the proportion of innervated OPCs rapidly recovers, although the frequency of spontaneous synaptic currents did not reach control levels. In conclusion, our results demonstrate that newly-generated OPCs do not receive synaptic inputs during their active proliferation after demyelination, but gain synapses during the remyelination process. Hence, glutamatergic synaptic inputs may contribute to inhibit OPC proliferation and might have a physiopathological relevance in demyelinating disorders.

No MeSH data available.


Related in: MedlinePlus