Involvement of phosphoinositide 3-kinase gamma in the neuro-inflammatory response and cognitive impairments induced by beta-amyloid 1-40 peptide in mice

determine if the effectiveness of minocycline in reducing b-amyloid-induced abnormal tau processing and neuronal death is mediated by glia. Secondly to investigate the role of glia in Ab-mediated degenerative pathways. Methods: We have investigated the effect of minocycline treatment on Ab-induced tau processing and neuronal death in primary neuronal, mixed and glial cultures. Mixed cortical cultures were prepared from E18 rat embryos, and neuronal cultures were derived following the suppression of glial proliferation with cytosine arabinoside. Analysis of mixed cultures by immunocytochemistry determined that these cultures contain 4.3 6 0.4% astrocytes and negligible numbers of microglia (<0.0001%). Glial cultures, containing astrocytes, microglia and small numbers of oligodendrocytes were prepared from P2 rat pups. Cultures were pre-treated with 20mM minocycline for 24h prior to treatment with 10mM soluble oligomeric Ab. Neuronal cell death, caspase activation, pathological changes in tau proteins and the secretion of inflammatory mediators were assessed by a variety of methods. Results: We show that the presence of astrocytes accelerates the onset of neuronal death in response to Ab, and that the neuroprotective influence of minocycline is only observed when astrocytes are present. Furthermore, we observe that astrocytes are required for Ab-induced tau phosphorylation, and that astrocytes mediate caspase-3-mediated cleavage of tau in response to Ab. In glial cultures, we find increased secretion of several inflammatory factors upon Ab treatment, including IL-1a, IL6 and IL10. Pre-treatment of glial cultures with minocycline suppresses the secretion of these pro-inflammatory mediators. The influence of specific inflammatory factors on Ab-induced neurotoxicity is currently under investigation. Conclusions: These results suggest that glia, and more specifically astrocytes, play a major role in Ab-induced abnormal tau processing and neuronal death. These findings also confirm that glia are a primary target of minocycline. It is possible that suppression of specific neuroinflammatory responses, either alone or in combination with other treatments, may represent an effective therapeutic strategy for the treatment of Alzheimer’s disease.