Action potential-coupled Rho GTPase signaling drives presynaptic plasticity

In contrast to their postsynaptic counterparts, the contributions of activity-dependent cytoskeletal signaling to presynaptic plasticity remain controversial and poorly understood. To identify and evaluate these signaling pathways, we conducted a proteomic analysis of the presynaptic cytomatrix using in vivo biotin identification (iBioID). The resultant proteome was heavily enriched for actin cytoskeleton regulators, including Rac1, a Rho GTPase that activates the Arp2/3 complex to nucleate branched actin filaments. Strikingly, we find Rac1 and Arp2/3 are closely associated with presynaptic vesicle membranes and negatively regulate synaptic vesicle replenishment at both excitatory and inhibitory synapses. Using optogenetics and fluorescence lifetime imaging, we show this pathway bidirectionally sculpts short-term synaptic depression and that its presynaptic activation is coupled to action potentials by voltage-gated calcium influx. Thus, this study provides a new proteomic framework for understanding presynaptic physiology and uncovers a previously unrecognized mechanism of actin-regulated short-term presynaptic plasticity that is conserved across cell types.