BACKGROUNDThe Ras/Raf/ERK1/2 signaling pathway controls many cellular responses such as cell proliferation, migration, differentiation, and death. In the nervous system, emerging evidence also points to a death-promoting role for ERK1/2 in both in vitro and in vivo models of neuronal death. To further investigate how Ras/Raf/ERK1/2 up-regulation may lead to the development of spinal cord injury, we developed a cellular model of Raf/ERK up-regulation by overexpressing c-Raf in cultured spinal cord neurons (SCNs) and dorsal root ganglions (DRGs).

METHODSDRGs and SCNs were prepared from C57BL/6J mouse pups. DRGs or SCNs were infected with Ad-Raf-1 or Ad-Null adenovirus alone. Cell adhesion assay and cell migration assay were investigated, DiI labeling was employed to examine the effect of the up-regulation of Ras/Raf/ERK1/2 signaling on the dendritic formation of spinal neurons. We used the TO-PRO-3 staining to examine the apoptotic effect of c-Raf on DRGs or SCNs. The effect on the synapse formation of neurons was measured by using immunofluorescence.

RESULTSWe found that Raf/ERK up-regulation stimulates the migration of both SCNs and DRGs, and impairs the formation of excitatory synapses in SCNs. In addition, we found that Raf/ERK up-regulation inhibits the development of mature dendritic spines in SCNs. Investigating the possible mechanisms through which Raf/ERK up-regulation affects the excitatory synapse formation and dendritic spine development, we discovered that Raf/ERK up-regulation suppresses the development and maturation of SCNs.

CONCLUSIONThe up-regulation of the Raf/ERK signaling pathway may contribute to the pathogenesis of spinal cord injury through both its impairment of the SCN development and causing neural circuit imbalances.