Synapse-associated astrocyte mitochondria stabilize motor circuits to prevent excitotoxicity

Neurons have an outsized metabolic demand, requiring continuous metabolic support from non-neuronal cells called glia. When this support fails, toxic metabolic byproducts accumulate, ultimately leading to excitotoxicity and neurodegeneration. Astrocytes, the primary synapse-associated glial cell type, are known to provide essential metabolites (e.g. lactate) to sustain neuronal function. Here, we leverage the well-characterized Drosophila motor circuit to investigate another means of astrocyte-to-neuron metabolic support: activity-dependent trafficking of astrocyte mitochondria. Following optogenetic activation, motor neuron mitochondria migrate away from synapses. By contrast, astrocytic mitochondria accumulated peri-synaptically, and at times, were transferred into neighboring neurons. A genetic screen identified the mitochondrial adaptor protein Milton as a key regulator of this process. Astrocyte-specific milton knockdown disrupted regular mitochondrial trafficking, resulting in locomotor deficits, dysfunctional motor activity, and altered synapse number at the neuromuscular junction. These findings suggest that astrocytes dynamically redistribute mitochondria to buffer metabolic demand at synapses, highlighting a potential mechanism by which glia protect neural circuits from metabolic failure and neurodegeneration.