INSULIN-LIKE GROWTH-FACTOR FINDING PROTEIN-1 IS PRESYNAPTIC AT MOUSE NEUROMUSCULAR SYNAPSES AND IS TRANSPORTED IN NERVE

In a previous study, we localized insulin-like growth factor binding p rotein 1 (IGFBP-1) to mouse neuromuscular junctions, and intramuscular nerves. To determine if pre-synaptic accumulation of IGFBP-1 occurred , we used double ligation of sciatic nerve in adult mice at different time points. IGFBPs were detected by Western ligand blot (WLB) with I- 125-IGF-I. WLB and Western immunoblot (WIB) analysis of extracts from double-ligated nerves showed a delayed (6 days) increase of IGFBP-1 in the soluble fraction between the ligatures and distal to the distal l igature. For comparison we evaluated transport of neurofilament compon ents, using WIB and confirmed the primarily anterograde transport of t hese intraaxonal proteins. These data suggest that expression of IGFBP -1 is both by activated Schwann cells as well as retrograde axonal tra nsport with likely entry into the axon at the synapse.