Astrocytic extracellular vesicles modulate neuronal calcium homeostasis via transglutaminase-2

We have uncovered a novel role for astrocytes-derived extracellular vesicles (EVs) in controlling intraneuronal Ca 2+ concentration ([Ca 2+ ] i ) and identified transglutaminase-2 (TG2) as a surface-cargo of astrocytes-derived EVs. Incubation of hippocampal neurons with primed astrocyte-derived EVs have led to an increase in [Ca 2+ ] i , unlike EVs from TG2-knockout astrocytes. Exposure of neurons or brain slices to extracellular TG2 promoted a [Ca 2+ ] i rise, which was reversible upon TG2 removal and was dependent on Ca 2+ influx through the plasma membrane. Patch-clamp and calcium imaging recordings revealed TG2-dependent neuronal membrane depolarisation and activation of inward currents, due to the opening of L-type-VOCCs and to Na + /Ca 2+ -exchanger (NCX) operation in the reverse mode, as indicated by VOCCs/NCX pharmacological inhibitors. A subunit of Na + /K + -ATPase was selected by comparative proteomics and identified as being functionally inhibited by extracellular TG2, implicating Na + /K + -ATPase inhibition in NCX reverse mode-switching leading to Ca 2+ influx and higher basal [Ca 2+ ] i . These data suggest that reactive astrocytes control intraneuronal [Ca 2+ ] i through release of EVs with TG2 as responsible cargo, which could have a significant impact on synaptic activity in brain inflammation.