Neurotrophin-3 Regulates Synapse Development by Modulating TrkC-PTPσ Synaptic Adhesion and Intracellular Signaling Pathways

Abstract

Neurotrophin-3 (NT-3) is a secreted neurotrophic factor that binds neurotrophin receptor tyrosine kinase C (TrkC), which in turn binds to presynaptic protein tyrosine phosphatase (PTP) to govern excitatory synapse development. However, whether and how NT-3 cooperates with the TrkC-PTP synaptic adhesion pathway and TrkC-mediated intracellular signaling pathways in rat cultured neurons has remained unclear. Here, we report that NT-3 enhances TrkC binding affinity for PTP. Strikingly, NT-3 treatment bidirectionally regulates the synaptogenic activity of TrkC: at concentrations of 10 -25 ng/ml, NT-3 further enhanced the increase in synapse density induced by TrkC overexpression, whereas at higher concentrations, NT-3 abrogated TrkC-induced increases in synapse density. Semiquantitative immunoblotting and optogenetics-based imaging showed that 25 ng/ml NT-3 or light stimulation at a power that produced a comparable level of NT-3 (6.25 W) activated only extracellular signal-regulated kinase (ERK) and Akt, whereas 100 ng/ml NT-3 (light intensity, 25 W) further triggered the activation of phospholipase C-␥1 and CREB independently of PTP. Notably, disruption of TrkC intracellular signaling pathways, extracellular ligand binding, or kinase activity by point mutations compromised TrkC-induced increases in synapse density. Furthermore, only sparse, but not global, TrkC knock-down in cultured rat neurons significantly decreased synapse density, suggesting that intercellular differences in TrkC expression level are critical for its synapse-promoting action. Together, our data demonstrate that NT-3 is a key factor in excitatory synapse development that may direct higher-order assembly of the TrkC/ PTP complex and activate distinct intracellular signaling cascades in a concentration-dependent manner to promote competitionbased synapse development processes.

Activation of EphB2 Forward Signaling Enhances Memory Consolidation

“…This technique allows us to activate EphB2 at the highest required spatiotemporal resolution in vivo. Similar approach was used to activate TrkC in neurons (OptoTrkC; Han et al, 2016). …”

Structural basis of SALM3 dimerization and synaptic adhesion complex formation with PTPσ

“…HEK293T cells were transfected with the indicated mutants and the WT SALM3 cloned in pDisplay vector (Clontech; listed in Table S4). After 48 hours, transfected HEK293T cells were trypsinized, seeded onto cultured hippocampal neurons at DIV9, and then coimmunostained with antibodies against synapsin 46 at DIV11. Images were acquired by confocal microscopy (LSM700, Carl Zeiss).…”

Infralimbic Neurotrophin-3 Infusion Rescues Fear Extinction Impairment in a Mouse Model of Pathological Fear

“…Moreover, exogenous application of NT3 can enhance glutamatergic synaptic transmission via activation of TrkC receptor, by increasing the efficacy of glutamate release (Lessmann, 1998). More recently, evidence showed that NT3 modulates the TrkC-mediated differentiation of excitatory presynaptic terminals (Ammendrup-Johnsen et al, 2015;Han et al, 2016). Therefore, the rescue of the impaired LTP in TgNTRK3 mice by exogenous application of NT3 might be contributed by a restored glutamatergic transmission.…”

“…In the adult brain, neurotrophic tyrosine kinase receptor, type 3 (NTRK3, aka TrkC) promotes synaptogenesis by inducing differentiation of functional excitatory presynaptic terminals (Takahashi et al, 2011). Recently, it was shown that this effect is modulated by its cognate ligand-NT3 (AmmendrupJohnsen et al, 2015;Han et al, 2016). In another study, establishment of dendritic arborization of Purkinje cells of the cerebellum depends on a correct balance between NT3 and TrkC levels (Joo et al, 2014).…”