Signaling by hepatocyte growth factor in neurons is induced by pharmacological stimulation of synaptic activity

Activity-dependent signaling by growth factors is hypothesized to link synaptic activity to structural and functional modifications of neurons. The receptor tyrosine kinase Met and its ligand, hepatocyte growth factor (HGF), are clustered at excitatory synapses and may regulate aspects of excitatory synaptic function, as HGF increases expression of excitatory synaptic proteins, enhances their clustering at sites along dendrites, and increases current through the NMDA receptor. In this article, we test for secretion or activation of HGF and for activation of Met in response to pharmacological stimulation of synaptic activity. Stimulation of dissociated hippocampal neuron cultures with glutamate caused increased immunocytochemical staining against HGF on nonpermeabilized cells. Glutamate treatment also decreased the amount of pro HGF and increased the amount of the proteolytically-activated HGF in immunoblots of neuron culture lysates, and increased the levels of activated HGF in culture media. Stimulation of neuron cultures with glutamate or bicuculline induced autophosphorylation of Met on dendrites and the soma of neurons. Pretreatment of neurons with glutamate receptor inhibitors prior to glutamate treatment blocked autophosphorylation of Met. These results suggest that HGF can participate in activity dependent signaling in neurons.