GM-CSF inhibits glial scar formation and shows long-term protective effect after spinal cord injury

doi:10.1016/j.jns.2008.10.022

Journal of the Neurological Sciences

Volume 277, Issues 1–2, 15 February 2009, Pages 87-97

https://doi.org/10.1016/j.jns.2008.10.022 Get rights and content

Abstract

Object

This study investigated the effects of granulocyte macrophage-colony stimulating factor (GM-CSF) on the scar formation and repair of spinal cord tissues in rat spinal cord injury (SCI) model.

Methods

Sprague–Dawley male rats (8 weeks old) were randomly divided into the sham-operated group, spinal cord injury group, and injury with GM-CSF treated group. A spinal cord injury was induced at T9/10 levels of rat spinal cord using a vascular clip. GM-CSF was administrated via intraperitoneal (IP) injection or on the dural surface using Gelfoam at the time of SCI. The morphological changes, tissue integrity, and scar formation were evaluated until 4 weeks after SCI using histological and immunohistochemical analyses.

Results

The administration of GM-CSF either via IP injection or local treatment significantly reduced the cavity size and glial scar formation at 3–4 weeks after SCI. GM-CSF also reduced the expression of core proteins of chondroitin sulfate proteoglycans (CSPGs) such as neurocan and NG2 but not phosphacan. In particular, an intensive expression of glial fibriallary acidic protein (GFAP) and neurocan found around the cavity at 4 weeks was obviously suppressed by GM-CSF. Immunostaining for neurofilament (NF) and Luxol fast blue (LFB) showed that GM-CSF preserved well the axonal arrangement and myelin structure after SCI. The expression of GAP-43, a marker of regenerating axons, also apparently increased in the rostral grey matter by GM-CSF.

Conclusion

These results suggest that GM-CSF could enhance long-term recovery from SCI by suppressing the glial scar formation and enhancing the integrity of axonal structure.

Introduction

The adult central nervous system (CNS) has limited regenerative capacity and is unable to achieve full functional recovery after traumatic injury. Many complicated factors including immune mediators and inhibitory factors are known to interfere with regeneration of damaged neurons in the CNS lesion area, which eventually leads to cavitation and glial scar formation [1]. Astrocytes expressing glial fibrillary acidic protein (GFAP) become hypertrophic and highly proliferative to form eventually a dense network of glial scars around the cavity. Chondroitin sulfate proteoglycans (CSPGs) such as NG2, neurocan and phosphacan are also up-regulated and constitute the glial scars [2], [3]. CSPGs also play a role in preventing unwanted synaptic plasticity in the uninjured perineuronal nets (PNNs) [4]. Suppression of glial scar formation and CSPGs production are believed to provide a favorable environment for axonal regeneration. Many studies have investigated to prevent or remove them, for example, by administration of chondroitinase ABC (ChABC), an enzyme that selectively cleaves glycosaminoglycan (GAG) chains from the protein core [5]. In addition to CSPGs, degenerating myelin debris is another source of inhibitory cause to endogenous cellular and axonal repairs after CNS injury [6]. Thus, the glial scar formation and inhibitory myelin debris will be a potential target to be regulated for the regeneration of injured CNS axons.

GM-CSF is a hematopoietic cytokine but also involved in diverse neural functions in normal or many pathologic conditions [7], [8]. GM-CSF can function as a neurotrophic factor [9] and induce proliferation of neural progenitor cells (NPCs) [10] in vitro. Therapeutic effect of GM-CSF is already well known in the peripheral nervous system (PNS) injury by activating macrophages and Schwann cells to remove myelin debris [11], [12], [13]. Similarly, activation of microglia by GM-CSF is suggested to induce axonal regeneration and functional recovery after CNS injury either via phagocytosis of myelin debris or release of brain-derived neurotrophic factor (BDNF) [14], [15], [16]. Recently, we also reported that intraperitoneal (IP) injection of GM-CSF induced long-term functional recovery in rat SCI model [17] and in clinical trials combined with autologous bone marrow transplantation [18], [19]. The therapeutic effect of GM-CSF was also observed when it was treated directly on the dural surface of spinal cord using Gelfoam as a carrier immediately after SCI. In addition, the early administration of GM-CSF by either method showed a neuroprotective and anti-apoptotic activity within 3 days after SCI as well as a long term behavioral recovery after 2–3 weeks [20]. In this study, we hypothesized that the early GM-CSF administration immediately after SCI could also exert neuroprotective effects and influence scar formation that occurs in the weeks after injury. GM-CSF was treated IP or directly on the spinal cord immediately after SCI in rats as described previously [20]. The long-term therapeutic effect of GM-CSF was evaluated by the structural and axonal integrity of spinal cord tissues, cavitation and CSPGs production in the 4 weeks after injury.

Section snippets

Rat spinal cord injury (SCI) model

Animal experiments were performed in the authorized animal care facility and approved by the ‘Committee for the Care and Use of Laboratory Animals’ in Inha University College of Medicine. The male Sprague–Dawley (SD) rats (280–300 g; Sang Jung Co., Seoul, Korea) were anesthetized by intraperitoneal (IP) injection of ketamine and the laminectomy was performed at T8–10 levels. A spinal cord injury was made by applying a vascular clip (Biemer-Clip, Aesculap, Tuttlingen, Germany) on the T9 level of

GM-CSF reduced lesion volume and enhanced structural integrity after SCI

Our previous studies showed that GM-CSF improved functional recovery and inhibited apoptosis of cells at early times after SCI [17], [18], [20], [23]. In this study, we investigated whether early treatment of GM-CSF could protect spinal cord tissues from progressive degenerative changes and reduce lesion volume at several weeks after injury. GM-CSF was administrated immediately after injury either IP or locally using Gelfoam in rat SCI model as reported previously [20]. When examined at 1, 2

Discussion

This study investigated the effects of GM-CSF on the long-term histological changes and glial scar formation after SCI in rats. Our results demonstrated that early treatment of GM-CSF protected neural tissues and axonal alignments from severe degenerative changes at 3–4 weeks after SCI. GM-CSF also reduced the lesion volume and suppressed glial scar formation (GFAP expression) and CSPGs production such as neurocan and NG2 in the lesion area. There was no significant difference in the GM-CSF

Acknowledgement

This study was supported by the grant of the Korea Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (A050082).

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GM-CSF inhibits glial scar formation and shows long-term protective effect after spinal cord injury

Abstract

Object

Methods

Results

Conclusion

Introduction

Section snippets

Rat spinal cord injury (SCI) model

GM-CSF reduced lesion volume and enhanced structural integrity after SCI

Discussion

Acknowledgement

Exp Neurol

Blood

Neurosci Lett

Neurosci Lett

Neurosci Res

Neurosci Lett

Neuron

Neurobiol Dis

Exp Neurol

Exp Neurol

Mol Cell Neurosci

Myelin-, reactive glia-, and scar-derived CNS axon growth inhibitors: expression, receptor signaling, and correlation with axon regeneration

Glia

Cellular and molecular mechanisms of glial scarring and progressive cavitation: in vivo and in vitro analysis of inflammation-induced secondary injury after CNS trauma

J Neurosci

Aggrecan glycoforms contribute to the molecular heterogeneity of perineuronal nets

J Neurosci

Regeneration beyond the glial scar

Nat Rev Neurosci

Myelin inhibitors: does NO mean GO?

Nat Rev Neurosci

Neurotrophic action of interleukin 3 and granulocyte-macrophage colony stimulating factor on murine sympathetic neurons

Neuroimmunomodulation

Effects of GM-CSF on the neural progenitor cells

NeuroReport

Granulocyte macrophage colony stimulating factor produced in lesioned peripheral nerves induces the up-regulation of cell surface expression of MAC-2 by macrophages and Schwann cells

J Cell Biol

MIP-1a, MCP-1, GM-CSF, and TNF-a control the immune cell response that mediate rapid phagocytosis of myelin from the adult mouse spinal cord

J Neurosci

The role of macrophages in degeneration and regeneration in the peripheral nervous system

Recruiting the immune response to promote axon regeneration in the injured spinal cord

Neuroscientist

Delayed GM-CSF treatment stimulates axonal regeneration and functional recovery in paraplegic rats via an increased BDNF expression by endogenous macrophages

FASEB J

Role of granulocyte macrophage colony stimulating factor in preventing apoptosis and improving functional outcome in experimental spinal cord contusion injury

J Neurosurg Spine