PEROXYNITRITE AND NITRIC-OXIDE DONORS INDUCE NEURONAL APOPTOSIS BY ELICITING AUTOCRINE EXCITOTOXICITY

Endogenous generation of nitric oxide and its congeners, including per oxynitrite (ONOO-), has been implicated in the mechanism of neuron los s in neurodegenerative diseases. Accordingly, nitric oxide donors and ONOO- can elicit both apoptosis and necrosis in neuron cultures. Here we show that nitric oxide donors and ONOO- are each able to trigger ap optosis of mouse cerebellar granule cells by an excitotoxic mechanism requiring exocytosis and NMDA receptor-mediated intracellular Ca2+ ove rload. This conclusion is supported by the following findings. Apoptos is was induced by various nitric oxide donors or by direct addition of ONOO- to differentiated cerebellar granule cell cultures that were se nsitive to NMDA toxicity, but not in cerebellar granule cells that did not display NMDA-induced cell death (i.e. early days in culture) or i n various glial cell populations. Donors of ONOO- or nitric oxide stim ulated a sustained increase in intracellular Ca2+, which was prevented by inhibitors of NMDA receptors, such as MK-801 and 5-phospho-aminova leric acid, or by dampening neuronal electrical activity with high con centrations of extracellular Mg2+. Moreover, these treatments and the exposure of cerebellar granule cells in nominally Ca2+-free media prev ented apoptotic cell death. Both the intracellular Ca2+ increase and a poptosis elicited by ONOO- or the nitric oxide donors were prevented b y blocking exocytosis with tetanus toxin or botulinum neurotoxin C.