Neuroligins mediate presynaptic maturation through brain-derived neurotrophic factor signaling

Maturation is a process that allows synapses to acquire full functionality; failures in synaptic maturation may contribute to neurodevelopmental disorders. Neuroligins are postsynaptic cell-adhesion molecules essential for synapse maturation, but the underlying pathways are incompletely understood. Here, we show that maturational increases in active zone stability and synaptic vesicle recycling rely on the joint action of Neuroligins and brain-derived neurotrophic factor (BDNF). Applying BDNF to neuronal cultures mimicked the maturation-promoting effects of overexpressing the Neuroligin isoforms NL1 or NL2. Inhibiting BDNF signaling reduced the effects of NL1 and NL2 on presynaptic maturation and of NL2 on synapse formation. Applying BDNF to NL1-knockout mouse cultures rescued defective presynaptic maturation, indicating that BDNF acts downstream of NL1 and can restore presynaptic maturation at late stages of network development. Our data introduce BDNF as a novel and essential component in a transsynaptic pathway linking Neuroligin-mediated cell adhesion, neurotrophin action and presynaptic maturation.