Interleukin-10 prevents glutamate-mediated cerebellar granule cell death by blocking caspase-3-like activity

Interleukin-10 (IL-10) has been shown to reduce neuronal degeneration after CNS injury. However, the molecular mechanisms underlying the neuroprotecti ve properties of this cytokine are still under investigation. Glutamate exa cerbates secondary injury caused by trauma. Thus, we examined whether IL-10 prevents glutamate-mediated cell death. We used rat cerebellar granule cel ls in culture because these neurons undergo apoptosis upon exposure to toxi c concentrations of glutamate (100-500 muM) or NMDA (300 muM). Pretreatment of cerebellar granule cells with IL-10 (1-50 ng/ml) elicited a dose- and t ime-dependent reduction of glutamate-induced excitotoxicity. Most important ly, IL-10 reduced the number of apoptotic cells when added to the cultures together or 1 hr after glutamate. Using patch-clamping and fluorescence Ca2 + imaging techniques, we examined whether IL-10 prevents glutamate toxicity by blocking the function of NMDA channel. IL-10 failed to affect NMDA chan nel properties and to reduce NMDA-mediated rise in intracellular Ca2+. Thus , this cytokine appears to prevent glutamate toxicity by a mechanism unrela ted to a blockade of NMDA receptor function. Various proteases, such as cas pase-3, and transcription factors, such as nuclear factor kappaB (NF-kappaB ), have been proposed to participate in glutamate-mediated apoptosis. Thus, we examined whether IL-10 modulates the activity of these apoptotic marker s. IL-10 blocked both the glutamate-mediated induction of caspase-3 as well as NF-kappaB DNA binding activity, suggesting that the neuroprotective pro perties of IL-10 may rely on its ability to block the activity of proapopto tic proteins.