Loss of dopaminergic neurons by the induction of inducible nitric oxide synthase and cyclooxygenase-2 via CD40: Relevance to Parkinson's disease

A glial reaction associated with up-regulation of inflammatory molecules has been suggested to play an important role in dopaminergic neuron loss in Parkinson's disease (PD). Among inflammatory molecules, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) have been focused upon as key factors in the pathogenesis. However, the mechanism of how these molecules are induced in PD brains is not clearly understood. We focused on CD40, which is expressed on neural cells and could be implicated in the neuroinflammation by inducing inflammatory molecules. We showed that both iNOS and COX-2 were up-regulated in microglia and astrocytes by CD40 stimulation in association with a low dose of interferon-γ (IFN-γ) in vitro. Selective loss of dopaminergic neurons was induced by costimulation with CD40 and IFN-γ in mesencephalic cultures, which was protected by selective inhibitors of iNOS and/or COX-2. We also found in CD40-stimulated astrocytes an increase of a low-affinity IgE receptor CD23, which is known to induce iNOS expression. Together these data suggest that up-regulated iNOS and COX-2 via the CD40 pathway may lead to dopaminergic neuron loss and may participate in the neuroinflammaory pathway of PD.