Atypical antipsychotics alter microglial functions via astrocyte-derived extracellular vesicles

A limited understanding of the underlying molecular mechanisms of atypical antipsychotics has hindered efforts to develop the next generation of treatments for schizophrenia. In particular, there has been little investigation of how medications like clozapine and olanzapine modulate human non-neuronal cells, including astrocytes and microglia. Recent postmortem and serum-based studies suggest that schizophrenia etiology involves dysregulated cellular communication through extracellular vesicles (EVs). Astrocytes are a major source of these EVs and are strongly implicated in the etiology of schizophrenia by convergent data from human postmortem, brain imaging, RNA-sequencing, and genome-wide association studies. We hypothesized that clozapine and olanzapine can affect microglia biology indirectly via astrocytic secretion of EVs. We used in vitro cellular models with human astrocytes and PBMC-derived microglial-like cells to investigate the downstream impact of isolated astrocyte-derived EVs (ADEVs) on microglial phenotypes relevant to schizophrenia, including microglial phagocytosis, motility, and morphology. To model microglia-mediated synaptic pruning in vitro, we utilized image-based quantification of microglia engulfment of isolated human synaptosomes. We found that treatment with ADEVs reduced microglial synaptosome phagocytosis in a dose-dependent manner. This reduction was reversed upon addition of ADEVs isolated from astrocytes treated with norclozapine or olanzapine. ADEVs isolated from clozapine-treated astrocytes increased microglial motility, indicating that clozapine alters microglial surveillance activity without affecting phagocytosis through these ADEVs. Together, these results suggest that atypical antipsychotics have distinct and indirect impact on microglia biology mediated by ADEVs. These results highlight a potentially critical role for ADEVs in regulating glial cell communication, and suggest they may be promising therapeutic targets for next-generation antipsychotic development.