Activity-dependent protein synthesis in neurons requires microglial-metabolic coupling

De novo protein synthesis is required for long-lasting synaptic plasticity and memory, but it comes with a great metabolic cost. In the mammalian brain, it remains unclear which cell types and biological mechanisms are critical for sensing and responding to increased metabolic demand. Here, we demonstrate that microglia, the resident macrophages of the brain, are required for metabolic coupling between endothelial cells, astrocytes, and neurons, which fuels protein synthesis in active neurons. Increasing metabolic demand via a motor task stimulates microglia to secrete the hypoxia-responsive protein CYR61, which increases glucose transporter expression in brain vasculature. Depleting microglia reduces training-induced metabolic fluxes and neuronal protein synthesis, which can be reproduced by blocking CYR61 signaling. Thus, we define a neuroimmune metabolic circuit that is required for on-demand protein synthesis in mouse motor cortex.