Neurotrophin-3 Regulates Synapse Development by Modulating TrkC-PTPσ Synaptic Adhesion and Intracellular Signaling Pathways.
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 σ (PTPσ) to govern excitatory synapse development. However, whether and how NT-3 cooperates with the TrkC-PTPσ 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 PTPσ. 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 μW) activated only extracellular signal-regulated kinase (ERK) and Akt, whereas 100 ng/ml NT-3 (light intensity, 25 μW) further triggered the activation of phospholipase C-γ1 and CREB independently of PTPσ. 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/PTPσ complex and activate distinct intracellular signaling cascades in a concentration-dependent manner to promote competition-based synapse development processes.



In this study, we present several lines of experimental evidences to support the conclusion that neurotrophin-3 (NT-3) modulates the synaptic adhesion pathway involving neurotrophin receptor tyrosine kinase C (TrkC) and presynaptic protein tyrosine phosphatase σ (PTPσ) in a bidirectional manner at excitatory synapses. NT-3 acts in concentration-independent manner to facilitate TrkC-mediated presynaptic differentiation, whereas it acts in a concentration-dependent manner to exert differential effects on TrkC-mediated organization of postsynaptic development. We further investigated TrkC extracellular ligand binding, intracellular signaling pathways, and kinase activity in NT-3-induced synapse development. Last, we found that interneuronal differences in TrkC levels regulate the synapse number. Overall, these results suggest that NT-3 functions as a positive modulator of synaptogenesis involving TrkC and PTPσ.
Department of Physiology and BK21 PLUS Project to Medical Sciences Yonsei University College of Medicine, Seoul 120-752, Korea.
Kyung Ah
KA
Han
Department of Biological Sciences, Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon 305-701, Korea.
Doyeon
0000-0002-9527-2089
D
Woo
Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
Seungjoon
S
Kim
Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
Gayoung
G
Choii
Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
Sangmin
S
Jeon
Department of Chemistry, and.
Seoung Youn
SY
Won
Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea, and.
Ho Min
HM
Kim
Department of Biological Sciences, Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon 305-701, Korea.
Won Do
WD
Heo
Department of Physiology and BK21 PLUS Project to Medical Sciences Yonsei University College of Medicine, Seoul 120-752, Korea, jiwonum@yuhs.ac jaewonko@yonsei.ac.kr.
Ji Won
JW
Um
Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea, jiwonum@yuhs.ac jaewonko@yonsei.ac.kr.
Jaewon
0000-0001-9184-1574
J
Ko
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006624:Hippocampus; D009474:Neurons / Q000502:physiology; D020933:Neurotrophin 3 / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D020812:Receptor, trkC / Q000378:metabolism*; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013569:Synapses / Q000378:metabolism* / Q000502:physiology
D020933:Neurotrophin 3; D020812:Receptor, trkC; D048049:Extracellular Signal-Regulated MAP Kinases; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2
PTPσ; TrkC; excitatory synapse; neurotrophin-3; synaptic cell adhesion