Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 5 (6), 1552-63

A Function for EHD Family Proteins in Unidirectional Retrograde Dendritic Transport of BACE1 and Alzheimer's Disease Aβ Production

Affiliations

A Function for EHD Family Proteins in Unidirectional Retrograde Dendritic Transport of BACE1 and Alzheimer's Disease Aβ Production

Virginie Buggia-Prévot et al. Cell Rep.

Abstract

Abnormal accumulation of β-secretase (BACE1) in dystrophic neurites and presynaptic β-amyloid (Aβ) production contribute to Alzheimer's disease pathogenesis. Little, however, is known about BACE1 sorting and dynamic transport in neurons. We investigated BACE1 trafficking in hippocampal neurons using live-cell imaging and selective labeling. We report that transport vesicles containing internalized BACE1 in dendrites undergo exclusive retrograde transport toward the soma, whereas they undergo bidirectional transport in axons. Unidirectional dendritic transport requires Eps15-homology-domain-containing (EHD) 1 and 3 protein function. Furthermore, loss of EHD function compromises dynamic axonal transport and overall BACE1 levels in axons. EHD1/3 colocalize with BACE1 and APP β-C-terminal fragments in hippocampal mossy fiber terminals, and their depletion in neurons significantly attenuates Aβ levels. These results demonstrate unidirectional endocytic transport of a dendritic cargo and reveal a role for EHD proteins in neuronal BACE1 transcytosis and Aβ production, processes that are highly relevant for Alzheimer's disease.

Figures

Figure 1
Figure 1. BTX-Labeling Strategy to Selectively Visualize Internalized BACE1
(A) The schematics of the assay used to label internalized BACE1 using fluorescently-tagged BTX. (B and C) Development of the BTX-labeling assay. HeLa cells grown on coverslips were transiently transfected with BBS-BACE1-YFP and incubated with AF555-BTX at 37°C for 1 h. The coverslips were washed with ice cold HBSS and subjected to an acid wash to remove surface-bound BTX before fixing. YFP and BTX fluorescence intensities were quantified from individual cells and plotted (n=50 cells). (D) HEK293 cells stably expressing BBS-BACE1-YFP were cultured in 96-well dishes and incubated with AF647-BTX for different periods of time. The cells were subjected to an acid wash before fixing. AF647-BTX fluorescence intensity was quantified using a Tecan Safire 2 microplate reader and converted to fold differences using an intensity standard generated by different cell-plating densities. n=3 independent experiments, each performed in triplicates. (E) BTX-labeling of internalized BACE1 in hippocampal neurons. DIV12 neurons transfected or not with BBS-BACE1-YFP were incubated with AF647-BTX for 4 h at 37°C. The coverslips were subjected to acid wash before fixing. Z-stacks were acquired and projected onto a single plane to visualize YFP and BTX fluorescence. Identical conditions were used for image acquisition and processing for untransfected and BBS-BACE-YFP transfected cells. See also Figure S1.
Figure 2
Figure 2. Dynamic Characteristics of Internalized BACE1
(A) Localization of internalized BACE1 in dendrites and axons. DIV12 neurons were transfected with BBS-BACE1-YFP and internalized BACE1 was labeled by incubation with AF647-BTX for 4 h at 37°C followed by acid wash to remove surface-bound BTX. Deconvolved images of a transfected neuron depict the distribution of total and internalized pool of BACE1 in cell body and dendrites (top) and the corresponding axonal network (bottom). (B) Unidirectional transport of internalized BACE1 in dendrites. Time-lapse images of total (YFP fluorescence) and internalized BACE1 (BTX fluorescence) were sequentially acquired following AF647-BTX uptake, at the rate of 1 frame/sec for 3 min. Images of a dendritic segment with the cell body on the left, and the corresponding kymographs of total and internalized BACE1, are shown. (C) Quantification of total and internalized BACE1 motility in dendrites (n=760 total and 699 internalized carriers from 18 neurons). Unlike the bidirectional transport of total BACE1 in dendrites, internalized BACE1 undergoes transport exclusively in the retrograde direction. (D) A still image from the first frame of Movie S2 depicting internalized BACE1 dynamic transport in a distal dendrite. The retrograde transport tracks of representative transport vesicles in different branches of the same dendrites are indicated. (E) Dynamic axonal transport of internalized BACE1. Time-lapse images of total and internalized BACE1 were sequentially acquired from neurons following AF555-BTX uptake, at the rate of 1 frame/sec for 3 min. Bidirectional axonal transport of total and internalized BACE1 were visualized by generating kymographs. See also Figure S2.
Figure 3
Figure 3. Subcellular Localization of Internalized BACE1
(A and B) Neurons transfected with BBS-BACE1-YFP were labeled by AF647-BTX uptake, subjected to acid wash, and immunolabeled for EEA1, NEEP21, and TfR. Manders’ coefficient of colocalization with endosome markers was quantified by confocal microscopy for total BACE1 [YFP] (A; n=11-16 neurons) and internalized BACE1 [BTX fluorescence] (B; n=7-13 neurons). Representative confocal images are depicted in Figure S3. (C) Representative confocal images of a dendrite segment depicting colocalization of internalized BACE1 dendrites and spines with endogenous TfR. Scale bar=10 μm. (D) Neurons co-transfected with BACE1-YFP and mCherry-Rab11b were labeled by AF647-BTX uptake, subjected to acid wash, and immunostained for MAP2. The extent of colocalization of Rab11b and internalized BACE1 in dendrites and axons were quantified (n=8 neurons). See also Figure S3.
Figure 4
Figure 4. Colocalization of Internalized BACE1 with EHD1 and EHD3 and neuronal Aβ production following EHD knockdown
(A) Neurons co-transfected with BBS-BACE1-YFP and DsRed-tagged EHD1 or EHD3 were labeled by AF647-BTX uptake, subjected to acid wash, and analyzed by confocal microscopy. Insets show magnified segments of dendrites. (B) Images of representative axon segments show colocalization of internalized BACE1 with EHD1 and EHD3 in tubulo-vesicular carriers. (C) Manders’ coefficient of colocalization of total or internalized BACE1 with EHD1 (n=16 neurons) or EHD3 (n=12 neurons) were quantified. (D) Primary neurons were transfected with siRNA against EHD1 or EHD3. A scrambled siRNA was used as the negative control. The levels of Aβ38, Aβ40, and Aβ42 in the conditioned media were quantified by ELISA and normalized to control siRNA (n=4 technical replicates).
Figure 5
Figure 5. Colocalization of Endogenous EHD1 and EHD3 with BACE1 and APP β-CTFs in Mouse Brain
(A) Sagittal sections of P19 mouse brain were immunostained with antibodies against BACE1 and EHD1 or EHD3 and confocal images were acquired using 10X (top) and 100X objectives (bottom). Insets show higher magnification of the boxed area within the terminal field of mossy fibers (MF). (B) Sagittal sections of 2-month old APP/PS1 transgenic mouse brain were stained with antibodies against APP β-CTF (mAb 3D6) and EHD1 or EHD3 and analyzed by confocal microscopy. Lack of strong mAb 3D6 staining in mossy fibers of non-transgenic mice (NTg, inset) indicates the selectively of this antibody for APP β-CTFs and/or Aβ. See also Figure S4.
Figure 6
Figure 6. EHD1 and EHD3 are Required for Retrograde Transport of Internalized BACE1 in Dendrites
(A) Neurons co-transfected with BBS-BACE1-YFP and the indicated DsRed-tagged EHD WT or EHD-ΔEH construct were labeled by AF647-BTX uptake. Representative kymographs of internalized BACE1 transport in dendrites are shown. (B) Quantification of total and internalized BACE1 motility in dendrites. EHD1 WT n=679 total (T) and 312 internalized (I) vesicles from 13 neurons; EHD1-ΔEH n=427 T- and 227 I-vesicles from 8 neurons; EHD3 WT n=546 T and 291 I-vesicles from 12 neurons; EHD3-ΔEH n= 462 T-and 182 I-vesicles from 9 neurons.
Figure 7
Figure 7. EHD1 and EHD3 are Required for Axonal Localization and Dynamic Axonal Transport of BACE1
(A) Neurons were co-transfected with BBS-BACE1-YFP and the indicated DsRed-tagged EHD WT or EHD-ΔEH construct were labeled by AF647-BTX uptake, subjected to acid wash, and immunostained for MAP2. Pseudocolor images of total (YFP) and internalized BACE1 (BTX fluorescence) in representative neurons among the set of neurons used for quantitative analysis is shown. Insets show magnified segments of axons. (B) Mean axon and dendrite fluorescence intensities for total (YFP) and internalized BACE1 (BTX fluorescence) were quantified from individual neurons (n=11-15 neurons each) and used to calculate axon:dendrite ratios. Note the significant decrease of axonal BACE1 localization in neurons expressing EHD-ΔEH. (C) Representative kymograph analysis of BACE1-YFP transport in axons of transfected neurons is shown along with the quantification of BACE1-YFP vesicle motility. Vector n=773, EHD1 WT n=412, EHD1-ΔEH n=385, EHD3 WT n=952, EHD3-ΔEH n=281 vesicles were analyzed from 7-14 neurons. (D) Neurons were co-transfected with NPY-mCherry and empty vector or the indicated GFP-tagged EHD-ΔEH constructs. Representative kymographs of NPY-mCherry axonal transport are shown. See also Figure S5.

Similar articles

See all similar articles

Cited by 33 PubMed Central articles

See all "Cited by" articles

Publication types

MeSH terms

Feedback