Julie Bruyère’s research while affiliated with Grenoble Alpes University and other places

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Publications (17)


Huntingtin recruits KIF1A to transport synaptic vesicle precursors along the mouse axon to support synaptic transmission and motor skill learning
  • Article
  • Full-text available

July 2023

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67 Reads

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6 Citations

eLife

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Julie Bruyère

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Hao Xu

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[...]

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Neurotransmitters are released at synapses by synaptic vesicles (SVs), which originate from SV precursors (SVPs) that have traveled along the axon. Because each synapse maintains a pool of SVs, only a small fraction of which are released, it has been thought that axonal transport of SVPs does not affect synaptic function. Here, studying the corticostriatal network both in microfluidic devices and in mice, we find that phosphorylation of the Huntingtin protein (HTT) increases axonal transport of SVPs and synaptic glutamate release by recruiting the kinesin motor KIF1A. In mice, constitutive HTT phosphorylation causes SV over-accumulation at synapses, increases the probability of SV release, and impairs motor skill learning on the rotating rod. Silencing KIF1A in these mice restored SV transport and motor skill learning to wild-type levels. Axonal SVP transport within the corticostriatal network thus influences synaptic plasticity and motor skill learning.

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Huntingtin recruits KIF1A to transport synaptic vesicle precursors along the mouse axon to support synaptic transmission and motor skill learning

July 2023

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12 Reads

Neurotransmitters are released at synapses by synaptic vesicles (SVs), which originate from SV precursors (SVPs) that have traveled along the axon. Because each synapse maintains a pool of SVs, only a small fraction of which are released, it has been thought that axonal transport of SVPs does not affect synaptic function. Here, studying the corticostriatal network both in microfluidic devices and in mice, we find that phosphorylation of the Huntingtin protein (HTT) increases axonal transport of SVPs and synaptic glutamate release by recruiting the kinesin motor KIF1A. In mice, constitutive HTT phosphorylation causes SV over-accumulation at synapses, increases the probability of SV release, and impairs motor skill learning on the rotating rod. Silencing KIF1A in these mice restored SV transport and motor skill learning to wild-type levels. Axonal SVP transport within the corticostriatal network thus influences synaptic plasticity and motor skill learning.


Huntingtin recruits KIF1A to transport synaptic vesicle precursors along the mouse axon to support synaptic transmission and motor skill learning

July 2023

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14 Reads

Neurotransmitters are released at synapses by synaptic vesicles (SVs), which originate from SV precursors (SVPs) that have traveled along the axon. Because each synapse maintains a pool of SVs, only a small fraction of which are released, it has been thought that axonal transport of SVPs does not affect synaptic function. Here, studying the corticostriatal network both in microfluidic devices and in mice, we find that phosphorylation of the Huntingtin protein (HTT) increases axonal transport of SVPs and synaptic glutamate release by recruiting the kinesin motor KIF1A. In mice, constitutive HTT phosphorylation causes SV over-accumulation at synapses, increases the probability of SV release, and impairs motor skill learning on the rotating rod. Silencing KIF1A in these mice restored SV transport and motor skill learning to wild-type levels. Axonal SVP transport within the corticostriatal network thus influences synaptic plasticity and motor skill learning.


Huntingtin recruits KIF1A to transport synaptic vesicle precursors along the mouse axon to support synaptic transmission and motor skill learning

July 2023

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16 Reads

Neurotransmitters are released at synapses by synaptic vesicles (SVs), which originate from SV precursors (SVPs) that have traveled along the axon. Because each synapse maintains a pool of SVs, only a small fraction of which are released, it has been thought that axonal transport of SVPs does not affect synaptic function. Here, studying the corticostriatal network both in microfluidic devices and in mice, we find that phosphorylation of the Huntingtin protein (HTT) increases axonal transport of SVPs and synaptic glutamate release by recruiting the kinesin motor KIF1A. In mice, constitutive HTT phosphorylation causes SV over-accumulation at synapses, increases the probability of SV release, and impairs motor skill learning on the rotating rod. Silencing KIF1A in these mice restored SV transport and motor skill learning to wild-type levels. Axonal SVP transport within the corticostriatal network thus influences synaptic plasticity and motor skill learning.


Figure 5
Huntingtin-KIF1A-mediated axonal transport of synaptic vesicle precursors influences synaptic transmission and motor skill learning in mice

August 2022

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90 Reads

Neurotransmitters are released at synapses by synaptic vesicles (SVs), which originate from SV precursors (SVPs) that have traveled along the axon. Because each synapse maintains a pool of SVs, only a small fraction of which are released, it is unclear whether axonal transport of SVPs modifies synaptic function. Here, studying the corticostriatal network both in microfluidic devices and in mice, we find that phosphorylation of the Huntingtin protein (HTT) causes it to recruit the kinesin motor KIF1A, which in turn increases axonal transport of SVPs and synaptic glutamate release. In mice, constitutive HTT phosphorylation leads to SV over-accumulation at synapses, increases the probability of SV release, and impairs motor skill learning on the rotating rod. Silencing KIF1A in these mice restored SV transport and motor skill learning to wild-type levels. Axonal SVP transport within the corticostriatal network thus influences synaptic plasticity and motor skill learning.


The prefrontal cortex and dorsomedial striatum in sensorimotor gating
a Startle (120 dB) and prepulse (78 dB) stimuli used for testing PPI (top). Two-second trace of single neuron spikes and LFP (local field potential) activity recorded in a mouse during the PPI test (bottom). b Perievent time histograms (PETH) showing examples of the prefrontal cortex (PFC, left) and the dorsomedial striatum (DMS, right) unit responses during startle and PPI trials (n = 30 per trial, data are shown in 20 ms bins). Dashed lines correspond to the presentation of the 78 dB stimulus (−120 ms) and the 120 dB stimulus (0 ms). Horizontal bars represent the 95% confidence interval for mean firing rate during baseline. The percentage of neurons that responded to the startle stimulus during the startle and PPI trials are shown below. c PFC LFPs recorded during prepulse and startle trials. Zero millisecond (ms) corresponds to the time of presentation of the 120 dB pulse for both trial types. Data are shown as means ± SEM (n = 30 trials for each stimulus). d Amplitude-frequency components of the PFC (left) and DMS (right) LFP normalized to the mean LFP amplitudes observed during the −5 s to −1 s window prior to the presentation of the 120 dB pulse. e The prepulse significantly reduced the mean cortical (left), but not the DMS (right) beta response to the startle pulse (data were averaged within animals across 8–16 LFP channels per brain area). *P < 0.05 using mixed-model ANOVA followed by Bonferroni-corrected Wilcoxon signed-rank test.
Sensorimotor gating in Disc1 LI mice
aDisc1 LI (−/−) mice show reduced PPI. WT ( +/+ ), n = 7; Disc1 LI ( −/− ), n = 8. Data are shown as means ± SEM. *P < 0.05, **P < 0.01 (Student’s t test). b Startle and prepulse stimuli used for testing PPI (top). A similar portion of PFC neurons modulated their firing rates in response to the 78 dB low amplitude stimulus in Disc1 LI mice and their WT littermates (P > 0.05 using Z-test). A significantly lower proportion of DMS neurons modulated their response to this stimulus in Disc1 LI mice compared to their WT littermates (*P < 0.05 using Z-test). c Raster plot of DMS neuron response during startle and prepulse trials (top). Area under the ROC curve (AUC) demonstrating unit detection of gating across the stimulus interval (bottom). d Population AUC magnitude functions in WT and Disc1 LI mice (top). Differences between genotypes were identified by comparing AUC functions averaged within 20 ms bins using a Wilcoxon rank-sum test (bottom). The gray line corresponds with P = 0.05. The black line corresponds with the significance threshold following Bonferroni correction for multiple comparisons (n = 102 PFC neurons and 80 DMS neurons in WT mice; n = 108 PFC neurons and 102 DMS neurons in Disc1 LI mice). e The prepulse stimulus showed no effect on the mean PFC (top) or DMS (bottom) response to the startle stimulus across any frequency band examined (data were averaged within animal across 8–16 LFP channels per brain area, n = 10). f Schematic of concurrent optogenetic stimulation and neurophysiological recordings in Disc1 LI and WT mice infected with AAV-CaMKII-Chr2 in PFC. g Sixty light pulses (10 ms pulse width) were delivered with a pseudorandomized inter-pulse-interval ranging between 8 s and 23 s. Left: Raster plot (top) and firing rate perievent time histogram (PETH) of a representative striatal neuron (bottom). Right: A similar proportion of PFC neurons modulated their firing rates in response to cortical stimulation (P > 0.05 using Z-test) in Disc1 LI mice and WT littermates. A significantly lower proportion of DMS neurons modulated their firing rates in response to cortical stimulation (right; *P < 0.05 using Z-test) in Disc1 LI mice compared to WT littermates.
Deficits in corticostriatal Bdnf transport in Disc1 LI mice
a Age-dependent reduction in striatal, but not cortical, Bdnf in Disc1 LI (−/−) mice as measured by ELISA. WT (+/+), n = 9−10; Disc1 LI (−/−), n = 9−10. *P < 0.05 using Student’s t test. b No difference in Bdnf mRNA in the cortex and striatum between WT and Disc1 LI mice at 3 months of age (WT striatum, 1.00 ± 0.05; Disc1 LI striatum 0.97 ± 0.05; WT cortex, 59.15 ± 3.01; and Disc1 LI cortex 58.72 ± 2.90). Bdnf mRNA in WT striatum was assigned as “1” to which the other results were normalized. WT, n = 6; Disc1 LI, n = 6. c Impaired antero-/retro-grade transport velocity in Disc1 LI primary cortical neurons was rescued by overexpression of full-length Disc1 (−/−, Disc1-HA). *P < 0.05 (Kruskal–Wallis test with Dunn’s multiple comparisons). dDisc1 LI mice injected with control AAV-mCherry showed significantly low PPI, as compared with WT mice injected with either AAV-mCherry or AAV-Bdnf (#P < 0.05). Injection of AAV-Bdnf significantly improved PPI in Disc1 LI mice (*P < 0.05, as compared with control AAV-mCherry injection in Disc1 LI; repeated measures two-way ANOVA followed by Bonferroni post-hoc tests). There were no statistically significant differences between “+/+, AAV-mCherry” and “−/−, AAV-Bdnf”, nor between “+/+, AAV-Bdnf” and “−/−, AAV-Bdnf” (n.s.: not significant). WT + AAV-mCherry, n = 10; WT + AAV-Bdnf, n = 10; Disc1 LI + AAV-mCherry, n = 8; Disc1 LI + AAV-Bdnf, n = 8. Data are shown as means ± SEM.
Lithium-mediated augmentation of Bdnf transport can rescue PPI deficits in Disc1 LI mice
a Lithium (Li, 100 mg/kg body weight, i.p., daily, 14 days) rescued the PPI deficits in Disc1 LI (−/−) mice. n = 8 per cohort. Veh, vehicle. **P < 0.01, ***P < 0.001 as compared with Disc1 LI cohort treated with Veh (repeated measures two-way ANOVA followed by Bonferroni post-hoc tests). b Li-mediated rescue of PPI was abolished by Bdnf knockdown. n = 8 per cohort. Veh, vehicle. *P < 0.05 as compared with WT (+/+) cohort injected with AAV-scramble and treated with Veh, #P < 0.05 as compared with Disc1 LI (−/−) cohort injected with AAV-scramble and treated with Li (repeated measures two-way ANOVA followed by Bonferroni post-hoc tests). c Li (2 mM in the culture media 30 min before imaging) rescued the antero-/retro-grade Bdnf transport speed in cultured primary cortical neurons prepared from Disc1 LI (−/−) mice. *P < 0.05 (Kruskal–Wallis test with Dunn’s multiple comparisons). d Li (100 mg/kg body weight, i.p., daily, 14 days) increased the levels of Bdnf in the striatum of Disc1 LI (−/−) mice to levels equivalent to WT mice. n = 8 per cohort. The injections also increased Bdnf in WT, but the effects were more prominent in Disc1 LI mice. **P < 0.01, ***P < 0.001 (Kruskal–Wallis test with Dunn’s multiple comparisons).
Lithium upregulates Htt Ser-421 phosphorylation and enhances assembly of the Bdnf transport machinery in Disc1 LI mice
a Levels of phospho-Htt Ser-421 normalized by total Htt levels in prefrontal cortex of Disc1 LI (−/−) mice at 3 months of age, compared to WT (+/+) mice. *P < 0.05 (Student’s t test). b Levels of phospho-Htt Ser-421 normalized by total Htt levels in prefrontal cortex of Disc1 LI (−/−) mice at 3 months of age after administration of Li (100 mg/kg body weight, i.p., daily, 14 days) (+) or vehicle (−). *P < 0.05 (Student’s t test). c Prefrontal cortical homogenates from WT (+/+) and Disc1 LI (−/−) mice, chronically treated with Li (100 mg/kg body weight, i.p., daily, 14 days) (+) or with vehicle (−), were immunoprecipitated (IP) with anti-Htt antibody and analyzed by Western blots using the antibodies indicated. Equal amounts of protein extracts (100 μg/mouse) were used for each immunoprecipitation and lesser amounts (5–10%) of protein extracts were used as input (5 μg for Htt and α-Tubulin, 10 μg for the rest of the proteins) in order to allow quantitative evaluation of the signals. Graph: Relative binding capacity between Htt and each component of the Bdnf transport machinery. The ratio of the densitometry of a given protein band divided by the densitometry of Htt in IP blots for each condition was normalized to that for control condition (WT without Li). The experiments were done in triplicate. Data are shown as means ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001 (Student’s t test). d Schematic model for Htt-mediated BDNF transport facilitated by DISC1, Akt1 and Li. BDNF-containing cargo is linked to the motor machinery (kinesin and dynactin) via Htt adaptor protein and thereby transported along the cortico-striatal tract. DISC1 supports BDNF transport by facilitating the complex formation among Htt, cargo (BDNF) and motors, in part through augmentation of Ser-421 phosphorylation of Htt. Lithium (Li) could also enhance this complex formation via Ser-421 phosphorylation of Htt, possibly through upregulation of Akt1 activity or Akt1 recruitment.
Regulation of sensorimotor gating via Disc1/Huntingtin-mediated Bdnf transport in the cortico-striatal circuit

March 2022

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146 Reads

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2 Citations

Molecular Psychiatry

Sensorimotor information processing underlies normal cognitive and behavioral traits and has classically been evaluated through prepulse inhibition (PPI) of a startle reflex. PPI is a behavioral dimension deregulated in several neurological and psychiatric disorders, yet the mechanisms underlying the cross-diagnostic nature of PPI deficits across these conditions remain to be understood. To identify circuitry mechanisms for PPI, we performed circuitry recording over the prefrontal cortex and striatum, two brain regions previously implicated in PPI, using wild-type (WT) mice compared to Disc1-locus-impairment (LI) mice, a model representing neuropsychiatric conditions. We demonstrated that the corticostriatal projection regulates neurophysiological responses during the PPI testing in WT, whereas these circuitry responses were disrupted in Disc1-LI mice. Because our biochemical analyses revealed attenuated brain-derived neurotrophic factor (Bdnf) transport along the corticostriatal circuit in Disc1-LI mice, we investigated the potential role of Bdnf in this circuitry for regulation of PPI. Virus-mediated delivery of Bdnf into the striatum rescued PPI deficits in Disc1-LI mice. Pharmacologically augmenting Bdnf transport by chronic lithium administration, partly via phosphorylation of Huntingtin (Htt) serine-421 and its integration into the motor machinery, restored striatal Bdnf levels and rescued PPI deficits in Disc1-LI mice. Furthermore, reducing the cortical Bdnf expression negated this rescuing effect of lithium, confirming the key role of Bdnf in lithium-mediated PPI rescuing. Collectively, the data suggest that striatal Bdnf supply, collaboratively regulated by Htt and Disc1 along the corticostriatal circuit, is involved in sensorimotor gating, highlighting the utility of dimensional approach in investigating pathophysiological mechanisms across neuropsychiatric disorders.


Figure 5. HTT S421 phosphorylation affects presynaptic APP targeting. (A) Effect of HTT S421 phosphorylation on exocytosis rate of APP was analyzed in COS cells co-transfected with APP-SEP (Super Ecliptic pHluorin) and with pARIS HTT or pARIS HTT SA visualized by TIRF microscopy. Magnification represents a time lapse of events showing 2 events of APP vesicle exocytosis (green arrows). Histograms represent means +/-SEM of exocytosis event number per minute in 39 HTT and 40 HTT SA cells from four independent experiments. Significance was determined using an unpaired t-test; *p<0.05. Scale bar = 20 mm. (see also Video 5). (B) Effect of HTT S421 phosphorylation on APP targeting at the synapse was assessed by anti-APP western blotting (22C11) analysis of extracts from synaptic chambers of a WT or HTT SA corticocortical network. SNAP25 was used as a control for protein content in the synaptic compartment and nuclear marker Lamin B1 for the somatic compartment. Histograms represent means +/-SEM of APP signal per synaptophysin signal on five independent experiments. Significance was determined using a Mann-Whitney test; *p<0.05, ns = not significant. (C) Western blotting analysis of pre-and postsynaptic fractions obtained from synaptosome preparations. Fractionation gives the first pellet, P1, the first supernatant, S1, and the second supernatant, S2. Lamin B1, a nuclear marker is enriched in P1 fraction. The pre-(non-PSD) and the post-synaptic (PSD) fractions are respectively enriched in synaptophysin and PSD95. (D) APP from WT or HTT SA cortices fractions was quantified by western blotting analyses. APP signal was quantified as the ratio of synaptophysin signal for non-PSD fraction and as the ratio of PSD95 signal for PSD fraction. One line represents one experiment. Significance was determined using Mann-Whitney test; *p<0.05, ns = not significant. The online version of this article includes the following source data for figure 5: Source data 1. Statistical analysis of APP exocytosis rate. Source data 2. Statistical analysis of APP levels in microfluidics device. Source data 3. Statistical analysis of APP levels in synaptosome from brains.
Figure 7. HTT phosphorylation regulates synaptic contacts by reducing presynaptic APP levels. (A) Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT and HTT SA network. Right microphotographs for each genotype show magnification of representative neurites. Scale bars = 20 mm (low magnification) or 2 mm (high magnification). Histograms represent means +/-SEM of 3 independent experiments and 85 WT and 91 HTT SA neurites. Significance was determined using an unpaired t-test; ****p<0.0001. (B) Representative image of APP-mCherry transduced presynaptic neurons. APP-mCherry is present in axon terminals positive for synaptophysin (white arrows). Scale bar = 2 mm. Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT and HTT SA network transduced at presynaptic site with APP-mCherry or mCherry as a control. Histograms represent means +/-SEM of 3 independent experiments and 75 WT + mCherry; 59 WT + APP-mCherry and 71 HTT SA APP-mCherry neurites. (C) Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT mature network transduced at presynaptic site with a lentivirus encoding an HTT construct containing the first 480 amino acids without (HTT-480-WT) or with the S421A mutation (HTT-480-SA). Histograms represent means +/-SEM of at least three independent experiments and 132 HTT-480-WT and 130 HTT-480-SA neurites. Significance was determined using Mann and Whitney test; ****p<0.0001. (D) Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT mature network transduced at presynaptic site with APP-mCherry or mCherry as a control and with a lentivirus encoding a HTT-480-WT or HTT-480-SA. Histograms represent means +/-SEM of 3 independent experiments and 132 HTT-480-WT + mCherry, 134 HTT-480-WT + APP mCherry and 136 HTT-480-SA + APP mCherry neurites. Significance was determined using one-way Kruskal-Wallis test followed by Dunn's post-hoc analysis for multiple comparisons; **p<0.01, ***p<0.001, ****p<0.0001, ns = not significant. The online version of this article includes the following source data for figure 7:
Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of huntingtin

May 2020

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51 Reads

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2 Citations

Studies have suggested that amyloid precursor protein (APP) regulates synaptic homeostasis, but the evidence has not been consistent. In particular, signaling pathways controlling APP transport to the synapse in axons and dendrites remain to be identified. Having previously shown that Huntingtin (HTT), the scaffolding protein involved in Huntington’s disease, regulates neuritic transport of APP, we used a microfluidic corticocortical neuronal network-on-a-chip to examine APP transport and localization to the pre- and post-synaptic compartments. We found that HTT, upon phosphorylation by the Ser/Thr kinase Akt, regulates APP transport in axons but not dendrites. Expression of an unphosphorylatable HTT decreased axonal anterograde transport of APP, reduced presynaptic APP levels, and increased synaptic density. Ablating in vivo HTT phosphorylation in APPPS1 mice, which overexpress APP, reduced presynaptic APP levels, restored synapse number and improved learning and memory. The Akt-HTT pathway and axonal transport of APP thus regulate APP presynaptic levels and synapse homeostasis.


Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of Huntingtin

May 2020

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78 Reads

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29 Citations

eLife

Studies have suggested that amyloid precursor protein (APP) regulates synaptic homeostasis, but the evidence has not been consistent. In particular, signaling pathways controlling APP transport to the synapse in axons and dendrites remain to be identified. Having previously shown that Huntingtin (HTT), the scaffolding protein involved in Huntington's disease, regulates neuritic transport of APP, we used a microfluidic corticocortical neuronal network-on-a-chip to examine APP transport and localization to the pre- and post-synaptic compartments. We found that HTT, upon phosphorylation by the Ser/Thr kinase Akt, regulates APP transport in axons but not dendrites. Expression of an unphosphorylatable HTT decreased axonal anterograde transport of APP, reduced presynaptic APP levels, and increased synaptic density. Ablating in vivo HTT phosphorylation in APPPS1 mice, which overexpress APP, reduced presynaptic APP levels, restored synapse number and improved learning and memory. The Akt-HTT pathway and axonal transport of APP thus regulate APP presynaptic levels and synapse homeostasis.


Figure 5. HTT S421 phosphorylation affects presynaptic APP targeting. (A) Effect of HTT S421 phosphorylation on exocytosis rate of APP was analyzed in COS cells co-transfected with APP-SEP (Super Ecliptic pHluorin) and with pARIS HTT or pARIS HTT SA visualized by TIRF microscopy. Magnification represents a time lapse of events showing 2 events of APP vesicle exocytosis (green arrows). Histograms represent means +/-SEM of exocytosis event number per minute in 39 HTT and 40 HTT SA cells from four independent experiments. Significance was determined using an unpaired t-test; *p<0.05. Scale bar = 20 mm. (see also Video 5). (B) Effect of HTT S421 phosphorylation on APP targeting at the synapse was assessed by anti-APP western blotting (22C11) analysis of extracts from synaptic chambers of a WT or HTT SA corticocortical network. SNAP25 was used as a control for protein content in the synaptic compartment and nuclear marker Lamin B1 for the somatic compartment. Histograms represent means +/-SEM of APP signal per synaptophysin signal on five independent experiments. Significance was determined using a Mann-Whitney test; *p<0.05, ns = not significant. (C) Western blotting analysis of pre-and postsynaptic fractions obtained from synaptosome preparations. Fractionation gives the first pellet, P1, the first supernatant, S1, and the second supernatant, S2. Lamin B1, a nuclear marker is enriched in P1 fraction. The pre-(non-PSD) and the post-synaptic (PSD) fractions are respectively enriched in synaptophysin and PSD95. (D) APP from WT or HTT SA cortices fractions was quantified by western blotting analyses. APP signal was quantified as the ratio of synaptophysin signal for non-PSD fraction and as the ratio of PSD95 signal for PSD fraction. One line represents one experiment. Significance was determined using Mann-Whitney test; *p<0.05, ns = not significant. The online version of this article includes the following source data for figure 5: Source data 1. Statistical analysis of APP exocytosis rate. Source data 2. Statistical analysis of APP levels in microfluidics device. Source data 3. Statistical analysis of APP levels in synaptosome from brains.
Figure 7. HTT phosphorylation regulates synaptic contacts by reducing presynaptic APP levels. (A) Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT and HTT SA network. Right microphotographs for each genotype show magnification of representative neurites. Scale bars = 20 mm (low magnification) or 2 mm (high magnification). Histograms represent means +/-SEM of 3 independent experiments and 85 WT and 91 HTT SA neurites. Significance was determined using an unpaired t-test; ****p<0.0001. (B) Representative image of APP-mCherry transduced presynaptic neurons. APP-mCherry is present in axon terminals positive for synaptophysin (white arrows). Scale bar = 2 mm. Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT and HTT SA network transduced at presynaptic site with APP-mCherry or mCherry as a control. Histograms represent means +/-SEM of 3 independent experiments and 75 WT + mCherry; 59 WT + APP-mCherry and 71 HTT SA APP-mCherry neurites. (C) Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT mature network transduced at presynaptic site with a lentivirus encoding an HTT construct containing the first 480 amino acids without (HTT-480-WT) or with the S421A mutation (HTT-480-SA). Histograms represent means +/-SEM of at least three independent experiments and 132 HTT-480-WT and 130 HTT-480-SA neurites. Significance was determined using Mann and Whitney test; ****p<0.0001. (D) Number of PSD95/Synaptophysin contacts in the synaptic chamber of WT mature network transduced at presynaptic site with APP-mCherry or mCherry as a control and with a lentivirus encoding a HTT-480-WT or HTT-480-SA. Histograms represent means +/-SEM of 3 independent experiments and 132 HTT-480-WT + mCherry, 134 HTT-480-WT + APP mCherry and 136 HTT-480-SA + APP mCherry neurites. Significance was determined using one-way Kruskal-Wallis test followed by Dunn's post-hoc analysis for multiple comparisons; **p<0.01, ***p<0.001, ****p<0.0001, ns = not significant. The online version of this article includes the following source data for figure 7:
Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of huntingtin

May 2020

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75 Reads

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3 Citations

Studies have suggested that amyloid precursor protein (APP) regulates synaptic homeostasis, but the evidence has not been consistent. In particular, signaling pathways controlling APP transport to the synapse in axons and dendrites remain to be identified. Having previously shown that Huntingtin (HTT), the scaffolding protein involved in Huntington’s disease, regulates neuritic transport of APP, we used a microfluidic corticocortical neuronal network-on-a-chip to examine APP transport and localization to the pre- and post-synaptic compartments. We found that HTT, upon phosphorylation by the Ser/Thr kinase Akt, regulates APP transport in axons but not dendrites. Expression of an unphosphorylatable HTT decreased axonal anterograde transport of APP, reduced presynaptic APP levels, and increased synaptic density. Ablating in vivo HTT phosphorylation in APPPS1 mice, which overexpress APP, reduced presynaptic APP levels, restored synapse number and improved learning and memory. The Akt-HTT pathway and axonal transport of APP thus regulate APP presynaptic levels and synapse homeostasis.


Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of Huntingtin

April 2020

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84 Reads

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1 Citation

Studies have suggested that amyloid precursor protein (APP) regulates synaptic homeostasis, but the evidence has not been consistent. In particular, signaling pathways controlling APP transport to the synapse in axons and dendrites remain to be identified. Having previously shown that Huntingtin (HTT), the scaffolding protein involved in Huntington's disease, regulates neuritic transport of APP, we used a microfluidic corticocortical neuronal network-on-a-chip to examine APP transport and localization to the pre- and post-synaptic compartments. We found that HTT, upon phosphorylation by the Ser/Thr kinase Akt, regulates APP transport in axons but not dendrites. Expression of an unphosphorylatable HTT decreased axonal anterograde transport of APP, reduced presynaptic APP levels, and increased synaptic density. Ablating in vivo HTT phosphorylation in APPPS1 mice, which overexpress APP, reduced presynaptic APP levels, restored synapse number and improved learning and memory. The Akt-HTT pathway and axonal transport of APP thus regulate APP presynaptic levels and synapse homeostasis.


Citations (10)


... Efforts to improve neurotransmitter availability by enhancing synaptic vesicle dynamics are also underway [359]. Targeting proteins like synapsin, crucial for vesicle mobilization, could improve neurotransmitter release and recycling, addressing transmission deficits seen in HD [360]. These interventions aim to restore efficient signal transmission, preserving connectivity and overall neural network health. ...

Reference:

Decoding Neurodegeneration: A Review of Molecular Mechanisms and Therapeutic Advances in Alzheimer’s, Parkinson’s, and ALS
Huntingtin recruits KIF1A to transport synaptic vesicle precursors along the mouse axon to support synaptic transmission and motor skill learning

eLife

... The expression of genes Htt and Disc1 was also low, and their downregulation correlates with the development of various neurodegenerative and neuropsychiatric diseases [58,59]. Protein products of these genes participate in the regulation of synaptic function, axon and dendritic transport (trafficking), and interactions of Disc1/Huntingtin-mediated BDNF transport in the cortico-striatal circuit [60]. Both disturbances of the BDNF-TrkB pathway and abnormalities in cortico-striatal circuits are characteristic of depression [61]. ...

Regulation of sensorimotor gating via Disc1/Huntingtin-mediated Bdnf transport in the cortico-striatal circuit

Molecular Psychiatry

... We had previously shown that depletion of HTT in mouse pyramidal layer II/III neurons leads to signifi-cantly shorter dendrites and simplification of the dendritic arbor (Barnat et al., 2017), but did not pursue the mechanisms by which HTT affects postnatal dendritic maturation. Nonetheless, several of HTT's many functions could be expected to affect synaptogenesis or synaptic function : HTT governs microtubule-based axonal transport of cargos such as the brain's dominant neurotrophic factor (BDNF) to presynaptic compartments (Gauthier et al., 2004;Bruyè re et al., 2020), and HTT downregulation affects presynaptic vesicle endocytosis (McAdam et al., 2020). At the postsynaptic level, HTT interaction with HAP1/KIF5 enables the delivery of GABA A (Twelvetrees et al., 2010). ...

Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of huntingtin

... The relative abundance of Bifidobacteriaceae at family and genus levels were increased in mice with heroin dependence (p < 0.001, Figures 4C,D) compared with control mice. However, it is generally agreed that Bifidobacteriaceae is considered to be beneficial in humans and animals (39). A recent study showed that the Bifidobacterium were significantly elevated in early days while returned to Example images. ...

Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of huntingtin

... The HTT gene contains 67 exons and encodes a large protein with a molecular weight of about 350 KD. HTT is a scaffold protein with roles in many cellular functions, including cellular transport, endocytosis, and gene transcription, as well as stress response [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The pathological mechanisms of HD are believed to involve predominantly a gain of toxic function of mHTT at RNA and/or protein levels, resulting in abnormal transcription, mitochondrial dysfunction, oxidative stress, abnormal metabolism, abnormal axonal transportation, protein dislocation, and impaired protein clearance [16,[24][25][26]. ...

Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of Huntingtin

eLife

... For example, wtHTT loss interferes with the delivery of large dense core vesicles (DCV), which carry neurotrophins and neuropeptides, to release sites (Weiss and Littleton, 2016;Bulgari et al., 2017). Growing evidence supports a key role of APP in regulating synaptic structure and function (Priller et al., 2006;Tyan et al., 2012;Müller et al., 2017), and wtHTT also facilitates the transport of APP to the presynapse (Colin et al., 2008;Her and Goldstein, 2008;Bruyère et al., 2020). Either silencing wtHTT (Her and Goldstein, 2008) or preventing wtHTT phosphorylation at S421 (Bruyère et al., 2020) impairs APP axonal transport. ...

Presynaptic APP levels and synaptic homeostasis are regulated by Akt phosphorylation of Huntingtin

... MeCp2 knockout mice have lower levels of BDNF, and conditional deletion of BDNF in MeCp2 knockout mice expedites the onset of Rett syndromelike symptoms [21]. On the contrary, BDNF overexpression in the brain of MeCp2 knockout mice leads to ameliorating epileptiform potentials [21,22]. ...

Huntingtin phosphorylation governs BDNF homeostasis and improves the phenotype of Mecp2 knockout mice

EMBO Molecular Medicine

... The microfluidic device was developed by the Institut de Neurophysiophatologie (Timone, Marseille, France). It was fabricated using soft lithography as previously described [25,26]. First, a master mold of the chamber and microchannel was fabricated in polymerized resin (type R123, Soloplast, Vosschemie, France). ...

Reconstituting Corticostriatal Network on-a-Chip Reveals the Contribution of the Presynaptic Compartment to Huntington’s Disease

Cell Reports

... Among them, PDMS-based microfluidic circuits have emerged as highly versatile tools providing many suitable properties for positioning, culturing and interfacing large populations of neurons 12,13 . Since the first demonstrations, PDMS-based microfluidics has been used for modeling brain circuits on a chip [14][15][16][17] , as well as for single-neuron analysis [18][19][20][21][22] . This approach combines neuron-adhesive coating and physical barriers for efficient cell adhesion and time-stable architectures 13,23-26 while maintaining high optical transparency for high-resolution imaging 27,28 . ...

B41 HD on chip : reconstituting the cortico-striatal network on microfluidics to study intracellular trafficking and synaptic transmission
  • Citing Article
  • September 2016

Journal of Neurology, Neurosurgery, and Psychiatry

... In mammals, the N-terminal region of HTT, akin to Atg23, interacts with the C-terminal region, akin to Atg11 [26,37]. Interestingly, it has been shown that interactions between the N-and C-terminal regions are disrupted upon mHTT proteolysis at multiple sites, and promoting the interaction between these two regions can have protective effects [38]. ...

Huntingtin proteolysis releases non‐polyQ fragments that cause toxicity through dynamin 1 dysregulation

The EMBO Journal