Astrocyte glypican 5 regulates synapse maturation and stabilization.

The maturation and stabilization of appropriate synaptic connections is a vital step in neural circuit development; however, the molecular signals underlying these processes are not fully understood. We show that astrocytes, through production of glypican 5 (GPC5), are required for maturation and refinement of synapses in the mouse cortex during the critical period. In the absence of astrocyte GPC5, thalamocortical synapses show structural immaturity, including smaller presynaptic terminals, decreased postsynaptic density area, and presence of more postsynaptic partners at multisynaptic connections. This structural immaturity is accompanied by a delay in developmental incorporation of GLUA2-containing AMPARs at intracortical synapses. The functional impact of this is that mice lacking astrocyte GPC5 exhibit increased levels of ocular dominance plasticity in adulthood. This demonstrates that astrocyte GPC5 is necessary for maturation and stabilization of synaptic connections, which has implications for disorders with altered synaptic function where GPC5 levels are altered, including Alzheimer's disease and frontotemporal dementia.