Switching from astrocytic neuroprotection to neurodegeneration by cytokine stimulation

Abstract

Background: Astrocytes are the largest cell population in the human brain, and they react to injury and cytokines with activation. Only few experimental studies have examined the interaction of activated astrocytes with human neurons and the pharmacology thereof.<br />Experimental approach: Immortalized murine astrocytes (IMA) were combined with human LUHMES neurons, and stimulated with an inflammatory (TNF, IL-1) cytokine mix (CM). Neuronal survival was studied both in co-cultures and in monocultures after transfer of conditioned medium from activated IMA. Interventions with >20 pharmaceutical compounds were used to profile the model system.<br />Key results: Control IMA supported neurons, and protected them from neurotoxicants. Inflammatory activation reduced this protection, and prolonged exposure of co-cultures to CM triggered neurotoxicity. This neither involved direct effects of cytokines on neurons, nor secretion of nitric oxide from astrocytes, but it was prevented by the corticosteroid dexamethasone. The neurotoxicity-mediating effect of IMA was faithfully reproduced by human astrocytes. Moreover, glia-dependent toxicity was also observed, when IMA cultures were stimulated with CM, and the culture medium was transferred to neurons. Such neurotoxicity was prevented when astrocytes were treated by p38 kinase inhibitors or dexamethasone, whereas such compounds had no effect, when added to neurons. Conversely, treatment of neurons with five different drugs, including resveratrol and CEP1347, prevented toxicity of astrocyte supernatants.<br />Conclusion: The sequential IMA-LUHMES neuroinflammation model is suitable for separate profiling of both glial-directed and directly neuroprotective strategies. Moreover, direct evaluation in co-cultures of the same cells allows for testing of therapeutic effectiveness in more complex settings, in which astrocytes affect pharmacological properties of neurons.