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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

LPC-induced demyelination model. (A) Lysolecithin (LPC) was injected in the corpus callosum (CC) under anesthesia in a stereotaxic apparatus (coordinates respect to bregma: 1 mm lateral, 1.5 mm rostral; 1.8 mm depth to brain surface); Cx, cortex; Hip, hippocampus; St, striatum; OB, olfactory bulb. (B,C) Sagittal slices of a healthy control corpus callosum(B) and an LPC-induced lesion at 7 days post injection (dpi) (C) stained with MBP (green) and Dapi (blue). (D) Sagittal slice of an LPC-induced lesion in the mouse corpus callosum at 7 dpi stained with MBP (green), CD45 (red) and DAPI (blue). (E) DIC video microscopy of the LPC lesion (dashed lines) at 7 dpi in a coronal acute corpus callosum slice. Note the trace of the injection pipette (arrowhead).
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Figure 1: LPC-induced demyelination model. (A) Lysolecithin (LPC) was injected in the corpus callosum (CC) under anesthesia in a stereotaxic apparatus (coordinates respect to bregma: 1 mm lateral, 1.5 mm rostral; 1.8 mm depth to brain surface); Cx, cortex; Hip, hippocampus; St, striatum; OB, olfactory bulb. (B,C) Sagittal slices of a healthy control corpus callosum(B) and an LPC-induced lesion at 7 days post injection (dpi) (C) stained with MBP (green) and Dapi (blue). (D) Sagittal slice of an LPC-induced lesion in the mouse corpus callosum at 7 dpi stained with MBP (green), CD45 (red) and DAPI (blue). (E) DIC video microscopy of the LPC lesion (dashed lines) at 7 dpi in a coronal acute corpus callosum slice. Note the trace of the injection pipette (arrowhead).

Mentions: All experiments followed European Union and institutional guidelines for the care and use of laboratory animals. Histochemical and electrophysiological experiments were performed with transgenic mice used at adult heterozygous stages: NG2-DsRed (Ziskin et al., 2007), PDGFRα-GFP (Hamilton et al., 2003), CNPase-GFP (Yuan et al., 2002) and Cx3CR1-GFP (Jung et al., 2000). Wild-type (Wt) C57BL/6 adult mice were also used for histological analysis of VGluT1 on NG2+ cells. Focal demyelinating lesions were induced by a stereotaxic injection of 2 μl lysolecithin solution (LPC, Sigma, 1% LPC in 0.9% NaCl) in the corpus callosum in single or double adult (PN40-PN70) transgenic mice anesthetized with Ketamine (0.1 mg/g) and Xylazine (0.01 mg/g) as previously described (coordinates: 1 mm lateral, 1.5 mm rostral to Bregma, and 1.8 mm depth to brain surface; Figure 1A, (see also Tepavcevic et al., 2011). Control mice were injected with saline solution only.


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)

LPC-induced demyelination model. (A) Lysolecithin (LPC) was injected in the corpus callosum (CC) under anesthesia in a stereotaxic apparatus (coordinates respect to bregma: 1 mm lateral, 1.5 mm rostral; 1.8 mm depth to brain surface); Cx, cortex; Hip, hippocampus; St, striatum; OB, olfactory bulb. (B,C) Sagittal slices of a healthy control corpus callosum(B) and an LPC-induced lesion at 7 days post injection (dpi) (C) stained with MBP (green) and Dapi (blue). (D) Sagittal slice of an LPC-induced lesion in the mouse corpus callosum at 7 dpi stained with MBP (green), CD45 (red) and DAPI (blue). (E) DIC video microscopy of the LPC lesion (dashed lines) at 7 dpi in a coronal acute corpus callosum slice. Note the trace of the injection pipette (arrowhead).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4362325&req=5

Figure 1: LPC-induced demyelination model. (A) Lysolecithin (LPC) was injected in the corpus callosum (CC) under anesthesia in a stereotaxic apparatus (coordinates respect to bregma: 1 mm lateral, 1.5 mm rostral; 1.8 mm depth to brain surface); Cx, cortex; Hip, hippocampus; St, striatum; OB, olfactory bulb. (B,C) Sagittal slices of a healthy control corpus callosum(B) and an LPC-induced lesion at 7 days post injection (dpi) (C) stained with MBP (green) and Dapi (blue). (D) Sagittal slice of an LPC-induced lesion in the mouse corpus callosum at 7 dpi stained with MBP (green), CD45 (red) and DAPI (blue). (E) DIC video microscopy of the LPC lesion (dashed lines) at 7 dpi in a coronal acute corpus callosum slice. Note the trace of the injection pipette (arrowhead).
Mentions: All experiments followed European Union and institutional guidelines for the care and use of laboratory animals. Histochemical and electrophysiological experiments were performed with transgenic mice used at adult heterozygous stages: NG2-DsRed (Ziskin et al., 2007), PDGFRα-GFP (Hamilton et al., 2003), CNPase-GFP (Yuan et al., 2002) and Cx3CR1-GFP (Jung et al., 2000). Wild-type (Wt) C57BL/6 adult mice were also used for histological analysis of VGluT1 on NG2+ cells. Focal demyelinating lesions were induced by a stereotaxic injection of 2 μl lysolecithin solution (LPC, Sigma, 1% LPC in 0.9% NaCl) in the corpus callosum in single or double adult (PN40-PN70) transgenic mice anesthetized with Ketamine (0.1 mg/g) and Xylazine (0.01 mg/g) as previously described (coordinates: 1 mm lateral, 1.5 mm rostral to Bregma, and 1.8 mm depth to brain surface; Figure 1A, (see also Tepavcevic et al., 2011). Control mice were injected with saline solution only.

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