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BDNF-induced recruitment of TrkB receptor into neuronal lipid rafts: roles in synaptic modulation.

Suzuki S, Numakawa T, Shimazu K, Koshimizu H, Hara T, Hatanaka H, Mei L, Lu B, Kojima M - J. Cell Biol. (2004)

Bottom Line: Moreover, disruption of lipid rafts prevented potentiating effects of BDNF on transmitter release in cultured neurons and synaptic response to tetanus in hippocampal slices.In contrast, lipid rafts are not required for BDNF regulation of neuronal survival.Thus, ligand-induced TrkB translocation into lipid rafts may represent a signaling mechanism selective for synaptic modulation by BDNF in the central nervous system.

View Article: PubMed Central - PubMed

Affiliation: Research Institute for Cell Engineering, National Institute for Advanced Industrial Science and Technology, Ikeda, Osaka, Japan.

ABSTRACT
Brain-derived neurotrophic factor (BDNF) plays an important role in synaptic plasticity but the underlying signaling mechanisms remain unknown. Here, we show that BDNF rapidly recruits full-length TrkB (TrkB-FL) receptor into cholesterol-rich lipid rafts from nonraft regions of neuronal plasma membranes. Translocation of TrkB-FL was blocked by Trk inhibitors, suggesting a role of TrkB tyrosine kinase in the translocation. Disruption of lipid rafts by depleting cholesterol from cell surface blocked the ligand-induced translocation. Moreover, disruption of lipid rafts prevented potentiating effects of BDNF on transmitter release in cultured neurons and synaptic response to tetanus in hippocampal slices. In contrast, lipid rafts are not required for BDNF regulation of neuronal survival. Thus, ligand-induced TrkB translocation into lipid rafts may represent a signaling mechanism selective for synaptic modulation by BDNF in the central nervous system.

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BDNF-induced translocation of TrkB-FL into lipid rafts in cultured cortical neurons. (A) Effect of BDNF on the distribution of membrane proteins in lipid raft and nonraft fractions. Cultured neurons were treated with or without 200 ng/ml BDNF for 30 min. An example is shown on the left. Note that TrkB-FL, but not EGFR or TfR, was recruited into fraction 2 after BDNF stimulation. The quantification of TrkB-FL and total proteins in fractions 2 and 6 is shown on the right. The value of densitometry unit was determined for each TrkB-FL band, and normalized to that of “−BDNF” in fraction 2. (B) Time course of BDNF-induced recruitment of TrkB-FL into rafts. Neurons were treated with 200 ng/ml BDNF for the indicated times. (C) Dose-dependent translocation of TrkB-FL into rafts. Neurons were treated with the indicated concentration of BDNF for 30 min. *Indicates significantly different from “−BDNF” in fraction 2; t test; P < 0.05. n = 6 preparations from five independent experiments (A), 4 preparations from three independent experiments (B), and 3 preparations from two independent experiments (C). Error bars in this and all other figures represent SEM.
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fig1: BDNF-induced translocation of TrkB-FL into lipid rafts in cultured cortical neurons. (A) Effect of BDNF on the distribution of membrane proteins in lipid raft and nonraft fractions. Cultured neurons were treated with or without 200 ng/ml BDNF for 30 min. An example is shown on the left. Note that TrkB-FL, but not EGFR or TfR, was recruited into fraction 2 after BDNF stimulation. The quantification of TrkB-FL and total proteins in fractions 2 and 6 is shown on the right. The value of densitometry unit was determined for each TrkB-FL band, and normalized to that of “−BDNF” in fraction 2. (B) Time course of BDNF-induced recruitment of TrkB-FL into rafts. Neurons were treated with 200 ng/ml BDNF for the indicated times. (C) Dose-dependent translocation of TrkB-FL into rafts. Neurons were treated with the indicated concentration of BDNF for 30 min. *Indicates significantly different from “−BDNF” in fraction 2; t test; P < 0.05. n = 6 preparations from five independent experiments (A), 4 preparations from three independent experiments (B), and 3 preparations from two independent experiments (C). Error bars in this and all other figures represent SEM.

Mentions: To directly test whether BDNF recruits TrkB into lipid rafts, we prepared the rafts in cultured cortical neurons treated with BDNF. In the cortical cultures used here, 93.3 ± 2.4% and 3.8 ± 0.7% are NSE-positive neurons and GFAP-positive astrocytes, respectively (n = 6 independent experiments). As shown in Fig. 1 A, application of BDNF induced an increase in TrkB-FL in the raft fraction. There was a low amount of TrkB-FL in lipid rafts in naïve neurons, suggesting that in naive cells TrkB-FL may be associated with rafts with a low affinity. In cultures stimulated with 200 ng/ml BDNF for 30 min, the amount of TrkB-FL was markedly increased in rafts (TrkB-FLBDNF-treated/TrkB-FLcontrol: 3.4 ± 0.8-fold, P < 0.03) but decreased slightly in nonrafts (23.1 ± 6.4%). Total proteins in both regions were not changed by the BDNF treatment (Fig. 1 A). When expressed as TrkB-FL/total protein, BDNF increased TrkB-FL in rafts by 3.63 ± 0.73-fold, indicating that BDNF selectively increases the amount of TrkB-FL, but not protein concentration, in rafts.


BDNF-induced recruitment of TrkB receptor into neuronal lipid rafts: roles in synaptic modulation.

Suzuki S, Numakawa T, Shimazu K, Koshimizu H, Hara T, Hatanaka H, Mei L, Lu B, Kojima M - J. Cell Biol. (2004)

BDNF-induced translocation of TrkB-FL into lipid rafts in cultured cortical neurons. (A) Effect of BDNF on the distribution of membrane proteins in lipid raft and nonraft fractions. Cultured neurons were treated with or without 200 ng/ml BDNF for 30 min. An example is shown on the left. Note that TrkB-FL, but not EGFR or TfR, was recruited into fraction 2 after BDNF stimulation. The quantification of TrkB-FL and total proteins in fractions 2 and 6 is shown on the right. The value of densitometry unit was determined for each TrkB-FL band, and normalized to that of “−BDNF” in fraction 2. (B) Time course of BDNF-induced recruitment of TrkB-FL into rafts. Neurons were treated with 200 ng/ml BDNF for the indicated times. (C) Dose-dependent translocation of TrkB-FL into rafts. Neurons were treated with the indicated concentration of BDNF for 30 min. *Indicates significantly different from “−BDNF” in fraction 2; t test; P < 0.05. n = 6 preparations from five independent experiments (A), 4 preparations from three independent experiments (B), and 3 preparations from two independent experiments (C). Error bars in this and all other figures represent SEM.
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Related In: Results  -  Collection

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fig1: BDNF-induced translocation of TrkB-FL into lipid rafts in cultured cortical neurons. (A) Effect of BDNF on the distribution of membrane proteins in lipid raft and nonraft fractions. Cultured neurons were treated with or without 200 ng/ml BDNF for 30 min. An example is shown on the left. Note that TrkB-FL, but not EGFR or TfR, was recruited into fraction 2 after BDNF stimulation. The quantification of TrkB-FL and total proteins in fractions 2 and 6 is shown on the right. The value of densitometry unit was determined for each TrkB-FL band, and normalized to that of “−BDNF” in fraction 2. (B) Time course of BDNF-induced recruitment of TrkB-FL into rafts. Neurons were treated with 200 ng/ml BDNF for the indicated times. (C) Dose-dependent translocation of TrkB-FL into rafts. Neurons were treated with the indicated concentration of BDNF for 30 min. *Indicates significantly different from “−BDNF” in fraction 2; t test; P < 0.05. n = 6 preparations from five independent experiments (A), 4 preparations from three independent experiments (B), and 3 preparations from two independent experiments (C). Error bars in this and all other figures represent SEM.
Mentions: To directly test whether BDNF recruits TrkB into lipid rafts, we prepared the rafts in cultured cortical neurons treated with BDNF. In the cortical cultures used here, 93.3 ± 2.4% and 3.8 ± 0.7% are NSE-positive neurons and GFAP-positive astrocytes, respectively (n = 6 independent experiments). As shown in Fig. 1 A, application of BDNF induced an increase in TrkB-FL in the raft fraction. There was a low amount of TrkB-FL in lipid rafts in naïve neurons, suggesting that in naive cells TrkB-FL may be associated with rafts with a low affinity. In cultures stimulated with 200 ng/ml BDNF for 30 min, the amount of TrkB-FL was markedly increased in rafts (TrkB-FLBDNF-treated/TrkB-FLcontrol: 3.4 ± 0.8-fold, P < 0.03) but decreased slightly in nonrafts (23.1 ± 6.4%). Total proteins in both regions were not changed by the BDNF treatment (Fig. 1 A). When expressed as TrkB-FL/total protein, BDNF increased TrkB-FL in rafts by 3.63 ± 0.73-fold, indicating that BDNF selectively increases the amount of TrkB-FL, but not protein concentration, in rafts.

Bottom Line: Moreover, disruption of lipid rafts prevented potentiating effects of BDNF on transmitter release in cultured neurons and synaptic response to tetanus in hippocampal slices.In contrast, lipid rafts are not required for BDNF regulation of neuronal survival.Thus, ligand-induced TrkB translocation into lipid rafts may represent a signaling mechanism selective for synaptic modulation by BDNF in the central nervous system.

View Article: PubMed Central - PubMed

Affiliation: Research Institute for Cell Engineering, National Institute for Advanced Industrial Science and Technology, Ikeda, Osaka, Japan.

ABSTRACT
Brain-derived neurotrophic factor (BDNF) plays an important role in synaptic plasticity but the underlying signaling mechanisms remain unknown. Here, we show that BDNF rapidly recruits full-length TrkB (TrkB-FL) receptor into cholesterol-rich lipid rafts from nonraft regions of neuronal plasma membranes. Translocation of TrkB-FL was blocked by Trk inhibitors, suggesting a role of TrkB tyrosine kinase in the translocation. Disruption of lipid rafts by depleting cholesterol from cell surface blocked the ligand-induced translocation. Moreover, disruption of lipid rafts prevented potentiating effects of BDNF on transmitter release in cultured neurons and synaptic response to tetanus in hippocampal slices. In contrast, lipid rafts are not required for BDNF regulation of neuronal survival. Thus, ligand-induced TrkB translocation into lipid rafts may represent a signaling mechanism selective for synaptic modulation by BDNF in the central nervous system.

Show MeSH
Related in: MedlinePlus