PROTEIN FROM CHROMAFFIN GRANULES PROMOTES SURVIVAL OF MESENCEPHALIC DOPAMINERGIC-NEURONS BY AN EGF-RECEPTOR LIGAND-MEDIATED MECHANISM

Chromaffin cells grafted to the brain of animals with experimental par kinsonism and patients with Parkinson's disease can restore nigrostria tal functions. Mechanisms underlying these beneficial effects are unkn own, but may include growth factors rather than the minute amounts of dopamine (DA) liberated from chromaffin cells. We now report that prot ein from chromaffin granules, which release their contents by exocytos is, promotes survival and uptake of H-3-DA of mesencephalic DAergic ne urons in vitro and protect against N-methylpyridinium ion toxicity. Th is neurotrophic effect is accompanied by cell proliferation and mediat ed by astroglial cells induced in these cultures. Inhibition of cell p roliferation and concomitant astrogliosis by 5-fluorodeoxyuridine and alpha-aminoadipic acid abolishes the trophic effect. Two highly specif ic inhibitors of the epidermal growth factor receptor (EGFR) signal tr ansduction pathway, 4,5-dianilinophthalimide (10 mu M) and tyrphostin B56 (10 mu M), selectively block the neurotrophic capacity of chromaff in granule protein. As expected, they also block the mitogenic effects of EGF and TGF-alpha. However, these two mitogens do not mimic the pr onounced mitogenic and trophic actions of chromaffin granule protein, Culture medium conditioned by mesencephalic cells pretreated with chro maffin granule protein promotes survival of DAergic neurons without in creasing numbers of astroglial cells. The effective molecule is unlike ly to be glial cell line-derived neurotrophic factor, whose mRNA is no t detectable in cultures treated with chromaffin granule protein. We c onclude that chromaffin granules contain a putatively novel growth fac tor, which signals through the EGFR and may be responsible for the kno wn protective and restorative actions of chromaffin cell grafts to the lesioned nigrostriatal system. (C) 1997 Wiley-Liss, Inc.