Anterograde and retrograde transport of active extracellular signal-related kinase 1 (ERK1) in the ligated rat sciatic nerve

Neurons are one of the most polarized cells and often the nerve terminals may be located long distances from the cell body, thus signal transduction in neurons unlike other cells may need to be conducted over large distances. The mitogen-activated protein/extracellular signal-regulated kinases (MAP kinases or ERKs) regulate a diverse array of functions and in neurons, the ERK signalling pathways appear to have an important role in activity-dependent regulation of neuronal function. Using the ligated rat sciatic nerve as an experimental model we previously showed that the ERK1/2, MAP/ERK kinase (MEK1/2) and the p110 catalytic subunit of PI3-kinase are transported in the rat sciatic nerve. We have extended these findings to determine if these proteins are transported in the active state using antibodies that specifically detect the active form of ERK1/2, MEK1/2 and AKT which is activated downstream of PI3-kinase. We show significant accumulation of active ERK1 on the proximal and distal sides of a nerve ligation after 16 h. Active ERK2 also appeared to be accumulating at the ligature, however this did not reach statistical significance. In contrast there was not any significant accumulation of active MEK1/2 or active AKT. A component of both active ERK1 and active ERK2 is present in between the two ligations suggesting they are also present in the surrounding Schwann cells and are activated in response to nerve injury. Taken together our results suggest that a component of the accumulation of active ERK1 on the distal and proximal side of the nerve ligations results from transport in the anterograde and retrograde direction in the rat sciatic nerve.