Matrix metalloproteinase-9 and TIMP-1 in peripheral nerve: Implications for myelin formation

Remyelination is a key step in functional nerve regeneration performed by Schwann cells (SC). We have demonstrated that matrix metalloproteinase (MMP)-9 is a major regulator of signal transduction and phenotypic switching in SCs. Herein, genome-wide transcriptional profiling, followed by Ingenuity Pathway Analysis revealed the MMP-9 signaling network and its endogenous inhibitor, TIMP-1, among the top induced genes of the injured sciatic nerve, that co-distributed with MMP-9 in myelinating SCs and the paranodal/nodal areas of myelinated fibers. Homo- and heterodimers of the active and proMMP-9 were purified from injured nerves using gelatin-sepharose. MMP-9 gene deletion increased the number of immature, GFAP+ mSC and post-mitotic cell counts that correlate with shorter myelin internodes in remyelinated fibers lacking MMP-9. MMP-9 is essential to nodal clustering of voltage-gated Na+ (Nav) channels. MMP inhibitor therapy diminished the expression of Nav 1.7 and 1.8. These data established the essential role of MMP-9 in guiding SC differentiation toward myelin production and in molecular assembly of the myelin domains. Modification of Nav channels in myelinated fibers may thus provide an important therapeutic approach for a number of facilitates regeneration and attenuated neuropathic pain. Gene expression profiling of total RNAs extracted from murine sciatic nerves, dorsal root ganglion and spinal cords at day 1 and day 5 post injury.