Astrocytic synapse elimination controls ocular dominance plasticity

Ocular dominance plasticity (ODP) is a representative form of experience-dependent synaptic plasticity observed in the primary visual cortex (V1). However, the cellular mechanisms and physiological roles of synapse elimination in ODP are largely unknown. Here, we show that astrocytic phagocytosis of thalamo-cortical synapses in V1 is a critical mediator of ODP. We found that astrocytes, but not microglia, start to engulf thalamo-cortical synapses within 24 hours after monocular deprivation and that astrocytic synapse elimination is highly selective for synapses from the deprived eye, as revealed by AAV1-mediated trans-synaptic anterograde tracing of synapse phagocytosis reporters. Importantly, mice without the Megf10 phagocytic receptor in astrocytes exhibit deficits in eliminating the synapses from the deprived eye, leading to the failure to reduce the number of thalamo-cortical synapses after monocular deprivation. Remarkably, Megf10-deficient animals show severe defects in monocular deprivation-induced cortical synapse remodeling and subsequent expansion of the thalamo-cortical circuitry from the nondeprived eye. Taken together, our data show that astrocytic synapse elimination through MEGF10 is one of the key components in ODP, revealing the physiological importance of astrocytic phagocytosis in experience-dependent synaptic plasticity.