Abstract
Proliferation of endogenous neural stem/progenitor cells (NSPCs) has been identified in both normal and injured adult mammalian spinal cord. Yet the signaling mechanisms underlying the regulation of adult spinal cord NSPCs proliferation and commitment toward a neuronal lineage remain undefined. In this study, the role of three growth factor-mediated signaling pathways in proliferation and neuronal differentiation was examined. Adult spinal cord NSPCs were enriched in the presence of fibroblast growth factor 2 (FGF2). We observed an increase in the number of cells expressing the microtubule-associated protein 2 (MAP2) over time, indicating neuronal differentiation in the culture. Inhibition of the mitogen-activated protein kinase or extracellular signal-regulated kinase (ERK) kinase 1 and 2/ERK 1 and 2 (MEK/ERK1/2) or the phosphoinositide 3-kinase (PI3K)/Akt pathways suppressed active proliferation in adult spinal cord NSPC cultures; whereas neuronal differentiation was negatively affected only when the ERK1/2 pathway was inhibited. Inhibition of the phospholipase Cγ (PLCγ) pathway did not affect proliferation or neuronal differentiation. Finally, we demonstrated that the blockade of either the ERK1/2 or PLCγ signaling pathways reduced neurite branching of MAP2+ cells derived from the NSPC cultures. Many of the MAP2+ cells expressed synaptophysin and had a glutamatergic phenotype, indicating that over time adult spinal cord NSPCs had differentiated into mostly glutamatergic neurons. Our work provides new information regarding the contribution of these pathways to the proliferation and neuronal differentiation of NSPCs derived from adult spinal cord cultures, and emphasizes that the contribution of these pathways is dependent on the origin of the NSPCs.
Highlights
Studies of the adult mammalian central nervous system identified the presence of neural stem/progenitor cells (NSPCs) in the adult spinal cord (Weiss et al, 1996; Shihabuddin et al, 1997)
The enriched adult spinal cord NSPCs were obtained by using a cell isolation protocol that yielded about 1% of the total number of cells in the spinal cord (Figure 1A); these cells could proliferate as neurospheres or in adherent cultures in medium containing fibroblast growth factor 2 (FGF2) (Figure 1B)
Since the role of the MEK/ERK1/2, phosphoinositide 3-kinase (PI3K)/Akt, and phospholipase Cγ (PLCγ) signaling pathways in adult spinal cord NSPCs has not been established, we assessed the contribution of these pathways to the proliferation and neuronal differentiation of NSPCs derived from adult rat spinal cord cultures
Summary
Studies of the adult mammalian central nervous system identified the presence of neural stem/progenitor cells (NSPCs) in the adult spinal cord (Weiss et al, 1996; Shihabuddin et al, 1997). Subsequent research showed that proliferation of the adult NSPCs are stimulated in animal models of spinal cord injury (Johansson et al, 1999; Horner et al, 2000; Yamamoto et al, 2001; Danilov et al, 2006). Some studies reported that the fate of the proliferating NSPCs is restricted to glial cell types in vivo due to the inhibitory microenvironment of the adult spinal cord (Johansson et al, 1999; Shihabuddin et al, 2000; Horky et al, 2006; Yang et al, 2006; Barnabe-Heider et al, 2010). A better understanding of the basic biology of these NSPCs will facilitate future attempts to manipulate these cells under pathological conditions
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