Selective injury to dopaminergic neurons up-regulates GDNF in substantia nigra postnatal cell cultures: Role of neuron–glia crosstalk

The effect of selective injury to dopaminergic neurons on the expression of glial cell line-derived neurotrophic factor (GDNF) was examined in substantia nigra cell cultures. H 2O 2, mimicking increased oxidative stress, or l-DOPA, the main symptomatic treatment for Parkinson's disease, increased GDNF mRNA and protein levels in a time-dependent mode in neuron–glia mixed cultures. The concentration dependence indicated that mild, but not extensive, injury induced GDNF up-regulation. GDNF neutralization with an antibody decreased dopaminergic cell viability in H 2O 2-treated cultures, showing that up-regulation of GDNF was protecting dopaminergic neurons. Neither H 2O 2 nor l-DOPA directly affected GDNF expression in astrocyte cultures, but conditioned media from challenged mixed cultures increased GDNF mRNA and protein levels in astrocyte cultures, indicating that GDNF up-regulation was mediated by neuronal factors. Since pretreatment with 6-OHDA completely abolished H 2O 2-induced GDNF up-regulation, we propose that GDNF up-regulation is triggered by failing dopaminergic neurons that signal astrocytes to increase GDNF expression.