Activity-dependent astrocytic cholesterol release fine-tunes modes of synaptic exo- and endocytosis

Cholesterol is essential for the organization of neurotransmitter release machinery, yet how it regulates the balance among different forms of synaptic exo- and endocytosis remains poorly understood. Moreover, which pre-synaptic processes rely on neuronal vs. astrocyte-derived cholesterol is unknown. Using nanoscale-precision imaging of single-vesicle release in hippocampal synapses, we demonstrate that astrocytic cholesterol is a critical determinant of both temporal and spatial aspects of presynaptic dynamics by differentially modulating the two main forms of synchronous release, univesicular (UVR) and multivesicular (MVR), effectively fine-tuning their balance. Moreover, astrocytic cholesterol determines the spatial distribution of vesicle release across the active zone and the balance of the two main forms of single-vesicle endocytosis, fast and ultrafast. Imaging of a cholesterol biosensor revealed that astrocyte-neuron cholesterol signaling is activity dependent. These findings suggest that astrocytic cholesterol release modulates synaptic strength in an activity-dependent manner to fine-tune the balance of different forms of synaptic vesicle exo- and endocytosis.