N-myc downstream-regulated gene 1 expression in injured sciatic nerves

N-myc downstream-regulated gene 1 (NDRG1)/RTP/Drg1/Cap43/rit42/TDD5/Ndr1 is expressed ubiquitously and has been proposed to play a role in growth arrest and cell differentiation. A recent study showed that mutation of this gene is responsible for hereditary motor and sensory neuropathy-Lom. However, the role of this gene in the peripheral nervous system is not fully understood. In our study, rabbit polyclonal antibodies were raised against this gene product and were used to examine changes in its expression over the time course of Wallerian degeneration and ensuing regeneration after crush injury of mouse sciatic nerves. Fluorescent immunohistochemistry showed that NDRG1 was expressed over the intact nerve fibers. Double labeling with a Schwann cell (SC) marker, S-100 protein (S-100), revealed that NDRG1 was localized in the cytoplasm of S-100-positive Schwann cells (SCs). NDRG1 expression was maintained in the early stage of myelin degradation but was then markedly depleted at the end stage of myelin degradation when frequent occurrence of BrdU-labeled SCs was observed (at 7-9 days). The depletion of NDRG1 at this time point was also confirmed by Western blotting analysis. NDRG1 expression finally recovered at the stage of remyelination, with immunoreactivity stronger than that in intact nerves. These findings suggest that NDRG1 may play an important role in the terminal differentiation of SCs during nerve regeneration.