Synapse elimination processes have also been observed during synaptic plasticity in the adult brain, such as when sensory experience induces the formation of new spines and eliminates pre-existing spines during learning and memory formation. Thus, synapse elimination is likely a central feature of nervous system remodeling and reorganization throughout the lifespan. Moreover, certain neurodegenerative diseases, such as Alzheimer’s disease, are associated with profound synapse loss early in the disease state, underscoring the importance of under- standing the molecular mechanisms underlying this synapse loss. Recently, we found that astrocytes in the mouse visual system and hippocampus mediate synapse remodeling by actively engulfing weak but live synapses through phagocytosis and that this process is regulated by neuronal activity. Furthermore, we have found evi- dence that defective astrocyte-mediated synapse elimination can be a critical link to the initiation and progression of neurodegener- ative diseases, such as Alzheimer’s disease. This data suggests that astrocytes can participate in the constant remodeling of synaptic structures through our life in the healthy and diseased brain.
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