Several cytokines and chemokines possess important chemo

Several cytokines and chemokines possess important chemo-attractant functions during fetal CNS development (Stumm and Hollt, 2007; Li and Ransohoff, 2008). This suggests that neural stem and precursor ptc124 may respond to cues by these mediators of inflammation in immune-mediated pathological conditions. In vitro migration assays showed that stromal cell-derived factor 1α (SDF-1α, CXCL12) enhanced NPC migration in a dose-dependent manner (Robin et al., 2006). Monocyte chemo-attractant protein-1 (MCP-1, CCL2) induces migration of adult neural stem cells in-vitro (Widera et al., 2004) and in an inflammation induced model in hippocampal slices (Belmadani et al., 2006). In vitro studies showed that hepatocyte growth factor (HGF) is secreted by microglia upon TGF-β treatment, attracts oligodendrocyte precursor cells (Lalive et al., 2005) and is also a powerful chemo-attractant molecule for neural stem cells (Heese et al., 2005). Several pathological conditions lead to the release of chemokines which trigger the migration of neural stem cells in vivo. In a stroke model, SDF-1α plays a critical role in recruiting endogenous stem cells to the lesion site (Imitola et al., 2004). Brain hypoxia leads to the up-regulation of vascular-endothelial growth factor (VEGF), stem cell factor (SCF), SDF-1α, MCP-1, HGF and urokinase-type plasminogen activator and triggers migration of NPCs (Xu et al., 2007; Zhao et al., 2008). Brain tumors attract NPCs through SDF-1α/CXCR4 signaling (van der Meulen et al., 2009), MCP-1/CCR2 signaling (Magge et al., 2009), or HGF/c-Met signaling pathways (Heese et al., 2005). In view of these studies, we examined the role of these factors in mediating EAE-induced NPC migration.
Methods
Results
Discussion and conclusion First, cytokines and chemokines are mediators of inflammation and strong chemo-attractant proteins. Specifically, SDF-1α, MCP-1 and HGF play important roles in the pathogenesis of EAE. MCP-1 is involved in mediating the infiltration of macrophages and T-cells into the CNS during EAE. MCP-1 deficient mice are resistant to EAE induction (Huang et al., 2001) and the MCP-1/CCR2 signaling pathway has become a potential target for MS therapy (Giraud et al., 2010; Karpus et al., 2008). SDF-1α regulates the severity of EAE (Meiron et al., 2008). It is thought to maintain the integrity of the blood–brain barrier in normal condition and its effect is disrupted in EAE (McCandless et al., 2006). Furthermore, a recent study suggested that SDF-1α is involved in the migration of oligodendrocyte progenitors during EAE (Banisadr et al., 2011). The role of HGF in EAE is controversial with reports on the promotion of macrophage proliferation and a pro-inflammatory role (Moransard et al., 2010) versus an immunomodulatory and neuroprotective effect (Benkhoucha et al., 2010). Since inflammation-induced NPC migration was dependent on the three chemokine receptors\' signaling, we examined the expression of their major ligands. There was an increase in tissue immuno-reactivity of SDF-1α, MCP-1 and HGF in the corpus callosum during EAE. Specifically, induction of EAE was associated with chemokine staining in activated tissue microglia and astrocytes. Our findings are in agreement with previous reports on increased tissue immuno-reactivity of SDF-1α in EAE and MS brain tissue derived astrocytes and microglia (Banisadr et al., 2011; Moll et al., 2009), and with the correlation between the Iba-1+ microglia density and NPC migration in EAE brain (Ben-Hur et al., 2007). A motile phenotype is required for enabling cellular migratory response to these chemokine signaling. Epidermal growth factor (EGF) is a powerful mitogen for NPCs and was shown to increase motility of several cell populations(Ayuso-Sacido et al., 2010; Boockvar et al., 2003; Fricker-Gates et al., 2000). We show here that without EGF supplementation, transplanted NPCs fail to respond to inflammatory cues in almost 90% of EAE mice. The motile phenotype induced by EGF was not due to the induction of chemokine receptors (Fig. 7A and Supplementary Fig. 2) and not dependent on any additional external signal as observed in vitro (Fig. 7B). However, a motile phenotype is essential for cell migration in response to inflammatory cues. In addition, EGF supplementation influences NPC fate commitment towards glial differentiation (Gonzalez-Perez et al., 2009; Sanalkumar et al., 2010). Thus, glial committed NPCs acquire superior migratory properties over multi-potential NPCs in response to inflammation. This may be an important property since regenerative therapy in MS is mostly aimed at promoting remyelination. Therefore the final differentiation of NPCs into mature myelinating oligodendrocytes is highly sought (Ben-Hur, 2011; Gonzalez-Perez and Alvarez-Buylla, 2011). Indeed, NPCs grown in the presence of EGF and FGF2 achieved a stronger clinical effect when transplanted to EAE mice than NPCs grown with FGF2 alone. Multiple studies have shown that the main therapeutic effect of transplanted NPCs in EAE is via their immunomodulatory and neurotrophic properties, rather than participating directly in regeneration (Ben-Hur et al., 2007; Einstein et al., 2006; Pluchino et al., 2005). The improved therapeutic properties of FGF2-EGF NPCs may be partly related to their increased motility and glial preference, bringing them in close proximity to the site of inflammation and injury.