Chemotactic Response Of Neural Stem Cells To SDF-1α Correlates Closely With Their Differentiation Status

Precise migration of neural stem cells (NSCs) is a prerequisite during developmentfor the formation of the nervous system and plays a pivotal role in avariety ofpathological events. Increasing numbers of studies have demonstrated that NSCs, eitherendogenous or transplanted NSCs, would be guided to migrate over considerabledistance to sites of injury in the brain, where they contribute to recorve the impairedbrain zone by differentiating into the special cell to replace the injury ones in theimpaired zone or secreting tropic factors to improve the microenvironment. Thediscovery of the ability of chemotaxis of NSCs under physiological and pathologicalconditions has raised hopes for the brain repair after injury, but the chemotaxis of NSCsin vivo is a complex process, both the changing microenvironment and thedifferentiation status of NSCs or other factors during migration will affect the migratoryability. While much effort has focused on the delineation of factors that involved in themigration of NSCs, the relationship between the chemotactic response and differentstatus of these cells, however, remains elusive. In the present study, we used neural stemcell line C17.2cells to analyze the chemotactic response of NSCs to concentrationgradients of SDF-1α in relation to their differentiation states.Many factors, including stromal cell-derived factor (SDF-1α), which is wildlyexpressed in rostral migratory stream, olfactory bulb and inflammatory sites in the brain,is involved in the navigation of NSCs to their final destination. SDF-1α, viadownstream signaling molecules, such as extracellular signal-regulated kinase-1/2(ERK1/2), stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK),p38MAPK, and phosphatidylinositol3-kinase/Akt (PI3K/Akt), is involved in cellsurvival, differentiation and migration. In response to external stimuli, activation ofthese mitogen-activated protein kinases (MAPKs) and PI3K/Akt cascade, in turn,activates intracellular signaling molecules and/or induces crucial alterations in severalcytoskeleton-related proteins that are essential for cell migration. So we used SDF-1α as a chemottractant to analyze the effect of differentiation status of NSCs onSDF-1α-induced chemotaxis.In oreder to analysze the chemotactic responses of NSCs to concentration gradientsof SDF-1α in relation to their differentiation, using the well-characterized murine neuralstem cell line C17.2, which was derived from the external germinal layer of thepostnatal cerebellum, to analyze the molecular mechanism that parcipate in regulatingchemotaxis upon differentiation. Firstly, the number of chemotaxing cells as well as theoptimum concentrations of SDF-1α that induced the peak transfilter migration variesgreatly in a microchemotaxis Boyden chamber, cells of0.5-d and1-d differentiationdisplayed a stronger chemotaxis toward SDF-1α than cells of0-d and3-d differentiation.Secondly, time-lapse video analysis in conjunction with the direct viewing Dunnchamber shows that cells at certain differentiation states (cells of0.5-d and1-ddifferentiation) migrate more efficiently towards SDF-1α. However, the migrationefficiency of cells showed a significant increase in cells of1-d differentiation, whilehigher migration speed was detected in0.5-d and1-d cells. Thirdly, the phosphorylationstatus of Akt, ERK1/2, SAPK/JNK and p38MAPK is closely related to thedifferentiation levels of cells subject to SDF-1α stimulation, being sustained orincreased transiently at different times, and finally, inhibition of ERK1/2significantlyattenuate SDF-1α-stimulated transfilter migration of cells of0-d,0.5-d and1-ddifferentiation, but not NSCs of3-d differentiation. Meanwhile, interference ofPI3K/Akt, p38MAPK or SAPK/JNK only significantly attenuated SDF-1α-inducedmigration in cells of0-d,0.5-d and1-d differentiation respectively. Moreover, blockingof PI3K/Akt or MAPKs signaling led to a deficit chemotaxis of NSCs with decreasedmigration efficiency and/or migration speed of cells at certain differentiation stage(s),the extent of which depends on the cell differentiation status. Collectively, these resultsdemonstrate that differentiation of NSCs influences their chemotactic responses toSDF-1α: NSCs in varying differentiation states have different migratory capacities,thereby shedding light on optimization of the therapeutic potential of NSCs to beemployed for neural regeneration after injury.