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Amyloid- β Oligomers Interact with Neurexin and Diminish Neurexin-mediated Excitatory Presynaptic Organization

View Article: PubMed Central - PubMed

ABSTRACT

Alzheimer’s disease (AD) is characterized by excessive production and deposition of amyloid-beta (Aβ) proteins as well as synapse dysfunction and loss. While soluble Aβ oligomers (AβOs) have deleterious effects on synapse function and reduce synapse number, the underlying molecular mechanisms are not well understood. Here we screened synaptic organizer proteins for cell-surface interaction with AβOs and identified a novel interaction between neurexins (NRXs) and AβOs. AβOs bind to NRXs via the N-terminal histidine-rich domain (HRD) of β-NRX1/2/3 and alternatively-spliced inserts at splicing site 4 of NRX1/2. In artificial synapse-formation assays, AβOs diminish excitatory presynaptic differentiation induced by NRX-interacting proteins including neuroligin1/2 (NLG1/2) and the leucine-rich repeat transmembrane protein LRRTM2. Although AβOs do not interfere with the binding of NRX1β to NLG1 or LRRTM2, time-lapse imaging revealed that AβO treatment reduces surface expression of NRX1β on axons and that this reduction depends on the NRX1β HRD. In transgenic mice expressing mutated human amyloid precursor protein, synaptic expression of β-NRXs, but not α-NRXs, decreases. Thus our data indicate that AβOs interact with NRXs and that this interaction inhibits NRX-mediated presynaptic differentiation by reducing surface expression of axonal β-NRXs, providing molecular and mechanistic insights into how AβOs lead to synaptic pathology in AD.

No MeSH data available.


Synaptic expression of endogenous β-neurexins is decreased in J20 APP mice.(a) Representative immunoblots of neurexins (NRXs) in synaptosomes from the hippocampus and from the cerebral cortex of J20 APP mice and wild-type (WT) littermates at 6 months of age. The labels 1, 2, and 3 indicate samples from different mice. Full gel blots for the cropped blots (a) are shown in the Supplementary Fig. 4. (b) Quantification of synaptic expression of β-NRXs (bands indicated by a lower right square bracket in (a) and α-NRXs (bands indicated by upper right square bracket in (a) normalized to β-actin protein expression in synaptosomes from the hippocampus and the cortex, expressed relative to WT. n = 5 samples per genotype for hippocampus, with each n representing pooled hippocampi from two mice. n = 6 samples per genotype for cortex, with each n representing a cortex from one mouse. Unpaired t tests, #P < 0.05 for β-NRXs and P = 0.15 for α-NRXs in hippocampus, and **P < 0.001 for β-NRXs and P = 0.31 for α-NRXs in cortex. n.s., not significant. Data are presented as mean ± SEM.
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f7: Synaptic expression of endogenous β-neurexins is decreased in J20 APP mice.(a) Representative immunoblots of neurexins (NRXs) in synaptosomes from the hippocampus and from the cerebral cortex of J20 APP mice and wild-type (WT) littermates at 6 months of age. The labels 1, 2, and 3 indicate samples from different mice. Full gel blots for the cropped blots (a) are shown in the Supplementary Fig. 4. (b) Quantification of synaptic expression of β-NRXs (bands indicated by a lower right square bracket in (a) and α-NRXs (bands indicated by upper right square bracket in (a) normalized to β-actin protein expression in synaptosomes from the hippocampus and the cortex, expressed relative to WT. n = 5 samples per genotype for hippocampus, with each n representing pooled hippocampi from two mice. n = 6 samples per genotype for cortex, with each n representing a cortex from one mouse. Unpaired t tests, #P < 0.05 for β-NRXs and P = 0.15 for α-NRXs in hippocampus, and **P < 0.001 for β-NRXs and P = 0.31 for α-NRXs in cortex. n.s., not significant. Data are presented as mean ± SEM.

Mentions: Finally, we tested whether AβOs affect synaptic expression of endogenous NRXs in vivo (Fig. 7). We prepared synaptosomal fractions from the hippocampus and the cortex of J20 APP mice, transgenic mice expressing a mutant form of human amyloid precursor protein (APP) that have progressively increasing AβO expression and amyloid deposition51. When compared to those of wild-type littermates, the hippocampal and cortical synaptosomes from J20 APP mice both had significantly reduced levels of β-NRX proteins, but not α-NRX proteins (Fig. 7a,b). These data indicate that there is selective reduction of endogenous β-NRXs in synapses in the J20 transgenic AD mouse model.


Amyloid- β Oligomers Interact with Neurexin and Diminish Neurexin-mediated Excitatory Presynaptic Organization
Synaptic expression of endogenous β-neurexins is decreased in J20 APP mice.(a) Representative immunoblots of neurexins (NRXs) in synaptosomes from the hippocampus and from the cerebral cortex of J20 APP mice and wild-type (WT) littermates at 6 months of age. The labels 1, 2, and 3 indicate samples from different mice. Full gel blots for the cropped blots (a) are shown in the Supplementary Fig. 4. (b) Quantification of synaptic expression of β-NRXs (bands indicated by a lower right square bracket in (a) and α-NRXs (bands indicated by upper right square bracket in (a) normalized to β-actin protein expression in synaptosomes from the hippocampus and the cortex, expressed relative to WT. n = 5 samples per genotype for hippocampus, with each n representing pooled hippocampi from two mice. n = 6 samples per genotype for cortex, with each n representing a cortex from one mouse. Unpaired t tests, #P < 0.05 for β-NRXs and P = 0.15 for α-NRXs in hippocampus, and **P < 0.001 for β-NRXs and P = 0.31 for α-NRXs in cortex. n.s., not significant. Data are presented as mean ± SEM.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5304201&req=5

f7: Synaptic expression of endogenous β-neurexins is decreased in J20 APP mice.(a) Representative immunoblots of neurexins (NRXs) in synaptosomes from the hippocampus and from the cerebral cortex of J20 APP mice and wild-type (WT) littermates at 6 months of age. The labels 1, 2, and 3 indicate samples from different mice. Full gel blots for the cropped blots (a) are shown in the Supplementary Fig. 4. (b) Quantification of synaptic expression of β-NRXs (bands indicated by a lower right square bracket in (a) and α-NRXs (bands indicated by upper right square bracket in (a) normalized to β-actin protein expression in synaptosomes from the hippocampus and the cortex, expressed relative to WT. n = 5 samples per genotype for hippocampus, with each n representing pooled hippocampi from two mice. n = 6 samples per genotype for cortex, with each n representing a cortex from one mouse. Unpaired t tests, #P < 0.05 for β-NRXs and P = 0.15 for α-NRXs in hippocampus, and **P < 0.001 for β-NRXs and P = 0.31 for α-NRXs in cortex. n.s., not significant. Data are presented as mean ± SEM.
Mentions: Finally, we tested whether AβOs affect synaptic expression of endogenous NRXs in vivo (Fig. 7). We prepared synaptosomal fractions from the hippocampus and the cortex of J20 APP mice, transgenic mice expressing a mutant form of human amyloid precursor protein (APP) that have progressively increasing AβO expression and amyloid deposition51. When compared to those of wild-type littermates, the hippocampal and cortical synaptosomes from J20 APP mice both had significantly reduced levels of β-NRX proteins, but not α-NRX proteins (Fig. 7a,b). These data indicate that there is selective reduction of endogenous β-NRXs in synapses in the J20 transgenic AD mouse model.

View Article: PubMed Central - PubMed

ABSTRACT

Alzheimer&rsquo;s disease (AD) is characterized by excessive production and deposition of amyloid-beta (A&beta;) proteins as well as synapse dysfunction and loss. While soluble A&beta; oligomers (A&beta;Os) have deleterious effects on synapse function and reduce synapse number, the underlying molecular mechanisms are not well understood. Here we screened synaptic organizer proteins for cell-surface interaction with A&beta;Os and identified a novel interaction between neurexins (NRXs) and A&beta;Os. A&beta;Os bind to NRXs via the N-terminal histidine-rich domain (HRD) of &beta;-NRX1/2/3 and alternatively-spliced inserts at splicing site 4 of NRX1/2. In artificial synapse-formation assays, A&beta;Os diminish excitatory presynaptic differentiation induced by NRX-interacting proteins including neuroligin1/2 (NLG1/2) and the leucine-rich repeat transmembrane protein LRRTM2. Although A&beta;Os do not interfere with the binding of NRX1&beta; to NLG1 or LRRTM2, time-lapse imaging revealed that A&beta;O treatment reduces surface expression of NRX1&beta; on axons and that this reduction depends on the NRX1&beta; HRD. In transgenic mice expressing mutated human amyloid precursor protein, synaptic expression of &beta;-NRXs, but not &alpha;-NRXs, decreases. Thus our data indicate that A&beta;Os interact with NRXs and that this interaction inhibits NRX-mediated presynaptic differentiation by reducing surface expression of axonal &beta;-NRXs, providing molecular and mechanistic insights into how A&beta;Os lead to synaptic pathology in AD.

No MeSH data available.