Nerve growth factor and proprotein convertases furin and PC7 in transectedsciatic nerves and in nerve segments cultured in conditioned media: Their presence in Schwann cells, macrophages, and smooth muscle cells

Synthesis of proteins such as nerve growth factor (NGF) is induced after ne rve lesion. The NGF precursor (pro-NGF) requires a posttranslational proces sing by proprotein convertases to become active. In this report, we re-exam ine the localization of NGF protein and mRNA in injured nerve and show that the candidate pro-NGF convertases furin and PC7 colocalize with NGF in non -neuronal cells in nerve. By Northern blot analysis, 1.5-kb and 1.3-kb NGF mRNAs were shown to be increased in distal and immediately proximal nerve s egments on days 1, 4, and 14 after lesion; by Western blot analysis, NGF pr oteins of high molecular weight were detected after injury. In vivo, two ph ases of NGF immunopositivity were observed, in macrophages and perivascular cells shortly after lesion and in endoneurial cells on day 1 and 4. To ide ntify the cells containing NGF, nerve segments were incubated in serum-cont aining medium with or without conditioning by white blood cells isolated fr om the circulation. Both hybridization and immunoreactivity signals for NGF were elevated after incubation of nerve segments for 4 hours in conditione d media, so that cells with NGF immunoreactivity could be identified by ant ibodies to specific cell markers. In these nerve fragments, Schwann cells, perivascular smooth muscle cells, and macrophages contained NGF immunoreact ivity. The concentration of furin and PC7 mRNA also increased in lesioned n erves. By immunocytochemical investigation of nerve explants, furin and PC7 were detected in endoneurial cells, macrophages and perivascular cells and were colocalized with NGF. These in vitro and in vivo findings suggest tha t bath furin and PC7 are associated with NGF in several cell types of the s ciatic nerve and, hence, may be implicated in intracellular processing of p ro-NGF. (C) 1999 Wiley-Liss, Inc.