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Schwann cell-derived Apolipoprotein D controls the dynamics of post-injury myelin recognition and degradation.

García-Mateo N, Ganfornina MD, Montero O, Gijón MA, Murphy RC, Sanchez D - Front Cell Neurosci (2014)

Bottom Line: Our previous study shows that axon regeneration is delayed without ApoD, and suggests its participation in early events during Wallerian degeneration.Here we demonstrate that ApoD is expressed by myelinating and non-myelinating Schwann cells and is induced early upon nerve injury.We show that ApoD, known to bind arachidonic acid (AA), also interacts with lysophosphatidylcholine (LPC) in vitro.

View Article: PubMed Central - PubMed

Affiliation: Lazarillo Lab, Departamento de Bioquímica y Biología Molecular y Fisiología, Instituto de Biología y Genética Molecular, Universidad de Valladolid-CSIC Valladolid, Spain.

ABSTRACT
Management of lipids, particularly signaling lipids that control neuroinflammation, is crucial for the regeneration capability of a damaged nervous system. Knowledge of pro- and anti-inflammatory signals after nervous system injury is extensive, most of them being proteins acting through well-known receptors and intracellular cascades. However, the role of lipid binding extracellular proteins able to modify the fate of lipids released after injury is not well understood. Apolipoprotein D (ApoD) is an extracellular lipid binding protein of the Lipocalin family induced upon nervous system injury. Our previous study shows that axon regeneration is delayed without ApoD, and suggests its participation in early events during Wallerian degeneration. Here we demonstrate that ApoD is expressed by myelinating and non-myelinating Schwann cells and is induced early upon nerve injury. We show that ApoD, known to bind arachidonic acid (AA), also interacts with lysophosphatidylcholine (LPC) in vitro. We use an in vivo model of nerve crush injury, a nerve explant injury model, and cultured macrophages exposed to purified myelin, to uncover that: (i) ApoD regulates denervated Schwann cell-macrophage signaling, dampening MCP1- and Tnf-dependent macrophage recruitment and activation upon injury; (ii) ApoD controls the over-expression of the phagocytosis activator Galectin-3 by infiltrated macrophages; (iii) ApoD controls the basal and injury-triggered levels of LPC and AA; (iv) ApoD modifies the dynamics of myelin-macrophage interaction, favoring the initiation of phagocytosis and promoting myelin degradation. Regulation of macrophage behavior by Schwann-derived ApoD is therefore a key mechanism conditioning nerve injury resolution. These results place ApoD as a lipid binding protein controlling the signals exchanged between glia, neurons and blood-borne cells during nerve recovery after injury, and open the possibility for a therapeutic use of ApoD as a regeneration-promoting agent.

No MeSH data available.


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ApoD is over-expressed by Schwann cells at 7 days after sciatic nerve crush injury. (A) Immunoblot analysis of ApoD in the region distal to the nerve lesion of WT and ApoD-KO mice. High levels of ApoD protein are observed 7d-PCI. (B) HRP-immunohistochemistry of ApoD in sagittal sections of intact sciatic nerves. Scattered ApoD-positive cells are seen in the endoneurium (arrows), while no labeling is seen in the perineurium (white arrow). (C–F) Fluorescence-immunohistochemical detection of ApoD in sagittal sections of intact sciatic nerves. Co-localization of ApoD and S100 (arrows in C) confirms Schwann cells (SCs) as a source of ApoD in sciatic nerves. A subset of non-myelinating SCs also expresses ApoD as evidenced by co-localization with the GFAP marker (arrows in D) compared to GFAP-only signal (open arrow in D). Confocal image (E) and a 3-D reconstruction of a Z-stack of confocal images (F) of fluorescence immunohistochemistry show ApoD labeling in secretion vesicles (arrowhead in E) and the SCs outer sheath (arrows in E,F). (G–I) Co-localization of ApoD and the SC marker S100 in sagittal sections of a crushed WT sciatic nerve 7d-PCI at different positions with respect to the injury site. Arrows point to ApoD labeling in intact and denervated SCs. Arrowheads in (I) (region distal to the crush) show ApoD adjacent to S100-positive myelin debris. Calibration bars: 50 μm.
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Figure 1: ApoD is over-expressed by Schwann cells at 7 days after sciatic nerve crush injury. (A) Immunoblot analysis of ApoD in the region distal to the nerve lesion of WT and ApoD-KO mice. High levels of ApoD protein are observed 7d-PCI. (B) HRP-immunohistochemistry of ApoD in sagittal sections of intact sciatic nerves. Scattered ApoD-positive cells are seen in the endoneurium (arrows), while no labeling is seen in the perineurium (white arrow). (C–F) Fluorescence-immunohistochemical detection of ApoD in sagittal sections of intact sciatic nerves. Co-localization of ApoD and S100 (arrows in C) confirms Schwann cells (SCs) as a source of ApoD in sciatic nerves. A subset of non-myelinating SCs also expresses ApoD as evidenced by co-localization with the GFAP marker (arrows in D) compared to GFAP-only signal (open arrow in D). Confocal image (E) and a 3-D reconstruction of a Z-stack of confocal images (F) of fluorescence immunohistochemistry show ApoD labeling in secretion vesicles (arrowhead in E) and the SCs outer sheath (arrows in E,F). (G–I) Co-localization of ApoD and the SC marker S100 in sagittal sections of a crushed WT sciatic nerve 7d-PCI at different positions with respect to the injury site. Arrows point to ApoD labeling in intact and denervated SCs. Arrowheads in (I) (region distal to the crush) show ApoD adjacent to S100-positive myelin debris. Calibration bars: 50 μm.

Mentions: Before assaying the role of ApoD in the early myelin clearance and macrophage recruitment stage of nerve injury, we first confirmed the induction of ApoD expression in the distal region of crushed nerves at 7d-PCI by immunoblot (Figure 1A). ApoD protein over-expression had been described in the rat at 21 days after denervation (Boyles et al., 1990), but no data was available from mice.


Schwann cell-derived Apolipoprotein D controls the dynamics of post-injury myelin recognition and degradation.

García-Mateo N, Ganfornina MD, Montero O, Gijón MA, Murphy RC, Sanchez D - Front Cell Neurosci (2014)

ApoD is over-expressed by Schwann cells at 7 days after sciatic nerve crush injury. (A) Immunoblot analysis of ApoD in the region distal to the nerve lesion of WT and ApoD-KO mice. High levels of ApoD protein are observed 7d-PCI. (B) HRP-immunohistochemistry of ApoD in sagittal sections of intact sciatic nerves. Scattered ApoD-positive cells are seen in the endoneurium (arrows), while no labeling is seen in the perineurium (white arrow). (C–F) Fluorescence-immunohistochemical detection of ApoD in sagittal sections of intact sciatic nerves. Co-localization of ApoD and S100 (arrows in C) confirms Schwann cells (SCs) as a source of ApoD in sciatic nerves. A subset of non-myelinating SCs also expresses ApoD as evidenced by co-localization with the GFAP marker (arrows in D) compared to GFAP-only signal (open arrow in D). Confocal image (E) and a 3-D reconstruction of a Z-stack of confocal images (F) of fluorescence immunohistochemistry show ApoD labeling in secretion vesicles (arrowhead in E) and the SCs outer sheath (arrows in E,F). (G–I) Co-localization of ApoD and the SC marker S100 in sagittal sections of a crushed WT sciatic nerve 7d-PCI at different positions with respect to the injury site. Arrows point to ApoD labeling in intact and denervated SCs. Arrowheads in (I) (region distal to the crush) show ApoD adjacent to S100-positive myelin debris. Calibration bars: 50 μm.
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Figure 1: ApoD is over-expressed by Schwann cells at 7 days after sciatic nerve crush injury. (A) Immunoblot analysis of ApoD in the region distal to the nerve lesion of WT and ApoD-KO mice. High levels of ApoD protein are observed 7d-PCI. (B) HRP-immunohistochemistry of ApoD in sagittal sections of intact sciatic nerves. Scattered ApoD-positive cells are seen in the endoneurium (arrows), while no labeling is seen in the perineurium (white arrow). (C–F) Fluorescence-immunohistochemical detection of ApoD in sagittal sections of intact sciatic nerves. Co-localization of ApoD and S100 (arrows in C) confirms Schwann cells (SCs) as a source of ApoD in sciatic nerves. A subset of non-myelinating SCs also expresses ApoD as evidenced by co-localization with the GFAP marker (arrows in D) compared to GFAP-only signal (open arrow in D). Confocal image (E) and a 3-D reconstruction of a Z-stack of confocal images (F) of fluorescence immunohistochemistry show ApoD labeling in secretion vesicles (arrowhead in E) and the SCs outer sheath (arrows in E,F). (G–I) Co-localization of ApoD and the SC marker S100 in sagittal sections of a crushed WT sciatic nerve 7d-PCI at different positions with respect to the injury site. Arrows point to ApoD labeling in intact and denervated SCs. Arrowheads in (I) (region distal to the crush) show ApoD adjacent to S100-positive myelin debris. Calibration bars: 50 μm.
Mentions: Before assaying the role of ApoD in the early myelin clearance and macrophage recruitment stage of nerve injury, we first confirmed the induction of ApoD expression in the distal region of crushed nerves at 7d-PCI by immunoblot (Figure 1A). ApoD protein over-expression had been described in the rat at 21 days after denervation (Boyles et al., 1990), but no data was available from mice.

Bottom Line: Our previous study shows that axon regeneration is delayed without ApoD, and suggests its participation in early events during Wallerian degeneration.Here we demonstrate that ApoD is expressed by myelinating and non-myelinating Schwann cells and is induced early upon nerve injury.We show that ApoD, known to bind arachidonic acid (AA), also interacts with lysophosphatidylcholine (LPC) in vitro.

View Article: PubMed Central - PubMed

Affiliation: Lazarillo Lab, Departamento de Bioquímica y Biología Molecular y Fisiología, Instituto de Biología y Genética Molecular, Universidad de Valladolid-CSIC Valladolid, Spain.

ABSTRACT
Management of lipids, particularly signaling lipids that control neuroinflammation, is crucial for the regeneration capability of a damaged nervous system. Knowledge of pro- and anti-inflammatory signals after nervous system injury is extensive, most of them being proteins acting through well-known receptors and intracellular cascades. However, the role of lipid binding extracellular proteins able to modify the fate of lipids released after injury is not well understood. Apolipoprotein D (ApoD) is an extracellular lipid binding protein of the Lipocalin family induced upon nervous system injury. Our previous study shows that axon regeneration is delayed without ApoD, and suggests its participation in early events during Wallerian degeneration. Here we demonstrate that ApoD is expressed by myelinating and non-myelinating Schwann cells and is induced early upon nerve injury. We show that ApoD, known to bind arachidonic acid (AA), also interacts with lysophosphatidylcholine (LPC) in vitro. We use an in vivo model of nerve crush injury, a nerve explant injury model, and cultured macrophages exposed to purified myelin, to uncover that: (i) ApoD regulates denervated Schwann cell-macrophage signaling, dampening MCP1- and Tnf-dependent macrophage recruitment and activation upon injury; (ii) ApoD controls the over-expression of the phagocytosis activator Galectin-3 by infiltrated macrophages; (iii) ApoD controls the basal and injury-triggered levels of LPC and AA; (iv) ApoD modifies the dynamics of myelin-macrophage interaction, favoring the initiation of phagocytosis and promoting myelin degradation. Regulation of macrophage behavior by Schwann-derived ApoD is therefore a key mechanism conditioning nerve injury resolution. These results place ApoD as a lipid binding protein controlling the signals exchanged between glia, neurons and blood-borne cells during nerve recovery after injury, and open the possibility for a therapeutic use of ApoD as a regeneration-promoting agent.

No MeSH data available.


Related in: MedlinePlus