FASEB J.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Sun, X.
Right arrow Articles by Song, W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Sun, X.
Right arrow Articles by Song, W.
(The FASEB Journal. 2006;20:1361-1368.)
© 2006 FASEB

Increased BACE1 maturation contributes to the pathogenesis of Alzheimer’s disease in Down syndrome

Xiulian Sun*,{dagger}, Yigang Tong*, Hong Qing*, Chia-Hsiung Chen*,{dagger} and Weihong Song*,{dagger},1

* Department of Psychiatry, Brain Research Center,

{dagger} Graduate Program in Neuroscience, The University of British Columbia, Vancouver, Canada

1 Correspondence: Department of Psychiatry, The University of British Columbia, 2255 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada. E-mail: weihong{at}interchange.ubc.ca


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Almost all Down syndrome (DS) patients develop characteristic Alzheimer’s disease (AD) neuropathology, including neuritic plaques and neurofibrillary tangles, after middle age. The mechanism underlying AD neuropathology in DS has been unknown. Aß is the central component of neuritic plaques and is generated from APP by cleavage by the ß- and {gamma}-secretases. Here we show that ß-secretase activity is markedly elevated in DS. The ratio of mature to immature forms of BACE1 is altered in DS. DS has significantly higher levels of mature BACE1 proteins in Golgi than normal controls. Time-lapse live image analysis showed that BACE1 proteins were predominantly immobile in Golgi in DS cells, while they underwent normal trafficking in controls. Thus, overproduction of Aß in DS is caused by abnormal BACE1 protein trafficking and maturation. Our results provide a novel molecular mechanism by which AD develops in DS and support the therapeutic potential of inhibiting BACE1 in AD and DS.—Sun, X., Tong, Y., Qing, H., Chen, C-H., Song, W. Increased BACE1 maturation contributes to Alzheimer’s disease pathogenesis in Down syndrome.


Key Words: amyloid ß • Alzheimer’s disease pathogenesis


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
DS IS THE MOST COMMON genetic cause of mental retardation, affecting ~1 in 700 to 1000 live births (1 2 3) . The majority of DS cases are caused by an extra copy of chromosome 21, known as Trisomy 21. AD is the most common neurodegenerative disease leading to dementia. Deposition of Aß in the brain is the hallmark of AD pathology (4) . Aß, the major component of neuritic plaques, is derived from ß-amyloid precursor protein (APP) after sequential cleavage by ß-secretase and {gamma}-secretase (5) . Beta site APP cleaving enzyme 1 (BACE1) has been identified as the major ß-secretase in vivo (6 7 8 9 10 11 12) . BACE1 cleaves APP at the major Asp + 1 site and a minor Glu + 11 of Aß. BACE1 is the ß-secretase for processing APP (6 , 8 , 9 , 13) and ß-secretase activity is dependent on the protein levels of BACE1 (14) . BACE2 is a homologue of BACE1 (12 , 15 16 17 18) . However, we recently reported that despite being homologous in an amino acid sequence, BACE2 and BACE1 have distinct functions and transcriptional regulation, and BACE2 is not a ß-secretase (13) . BACE2 processes APP at a novel {theta}-secretase site within the Aß domain that precludes Aß production.

BACE1 undergoes a complex set of post-translational modifications during its maturation. Pro-BACE1is cleaved by Furin and other members of the Furin family of convertases to remove the 24-amino acid N-terminal region of the pro-peptide within the trans-Golgi network (TGN) (19 20 21 22) . The 24-amino acid prodomain is required for the efficient exit of pro-BACE1 from the endoplasmic reticulum (19) . The majority of BACE1 is located in Golgi and endosomal compartments. Mature BACE1 has four N-glycosylation sites at Asn153, 172, 223, and 354, and the ß-secretase activity is dependent on the extent of N-glycosylation (22 23 24 25) . The cytoplasmic domain of BACE1 and its phosphorylation are required for efficient maturation and its intracellular trafficking through the TGN and endosomal system (12 , 22 , 26 , 27) . BACE1 is also processed between Leu (228) and Ala (229) to generate stable N- and C-terminal fragments that remain covalently associated via a disulfide bond (26) . BACE1 forms a dimer prior to its full maturation, and pro-peptide cleavage and dimerization of BACE may help APP binding and cleavage (28 , 29) . BACE1 also interacts with reticulon family member proteins, and reticulon proteins block access of BACE1 to APP and reduce the APP cleavage (30) . The degradation of BACE1 is mediated by the ubiquitin proteasome pathway and the proteasomal degradation of BACE1 regulates APP processing and Aß generation (31) . BACE1 gene expression is tightly regulated at the transcription level (13 , 14 , 32) and translational level (33 34 35 36) . Although genetic analysis has failed to uncover any BACE1 coding sequence mutation in the patients with familial AD (FAD) (37 , 38) , increased ß-secretase activity was reported in some FAD brains (39) and greater expression level of BACE1 in the cortex of sporadic AD patients vs. age-matched controls (40 41 42 43) . BACE1-KO mice, without developmental deficits, have abolished Aß generation (6 , 8 , 9) . Disruption of BACE1 gene rescues memory deficits and cholinergic dysfunction in the Swedish APP mutant mice (44) . Suppression of BACE1 with siRNA also reduced Aß production in APP mutant transgenic neurons (45) . In addition to APP, BACE1 substrates also include the LDL receptor-related protein (LRP) (46) , ß amyloid precursor-like protein-1 (APLP1) (47) , -2 (APLP2) (48) , a Golgi resident sialyltransferase ST6Gal I (49) , and the cell adhesion protein P-selectin glycoprotein ligand-1 (PSGL-1) (50) .

After middle age, people with DS inevitably develop characteristic AD neuropathology including neuritic plaques and neurofibrillary tangles (51 52 53) . The levels of APP C-terminal fragment C99, the major ß-secretase product, and Aß are increased in DS (54) . While the additional copy of the APP gene is seen in 99% of DS, the onset age of AD in DS varies significantly (55) , and the gene dosage effect cannot fully account for the occurrence of AD in DS (56) . The mechanism underlying the pathogenesis of AD in DS remains unknown.

To investigate the molecular mechanism by which AD neuropathology develops in DS patients, we examined the role of BACE1 gene in APP processing and Aß generation in DS using cerebral cortical tissues. In this report, the level of total BACE1 proteins, and particularly the mature form of BACE1, are significantly increased in DS. Time-lapse live image analysis revealed that BACE1 proteins were predominantly immobile and accumulated in Golgi in DS cells, whereas trafficking in controls was normal. Our study demonstrates that the abnormal BACE1 protein trafficking and accumulation contribute to the increased ß-secretase activity, and subsequent Aß generation in DS. Our results provide a novel molecular mechanism by which AD develops in DS.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Plasmids, transfection, cell culture, and stable cell lines
Human Trisomy-21 (47, XX, +21) and control (46, XX) fibroblast cells were derived from 18 wk of gestation fetal abortuses. The identities of the cell lines were further confirmed by karyotyping. APP C99 and C83 cDNA were amplified by polymerase chain reaction (PCR), then cloned into pcDNA3 vector (Invitrogen, San Diego, CA, USA) to generate mammalian expression plasmid pAPP-C99 and pAPP-C83. pAPP-C99 and pAPP-C83 were transfected into cells and the expressed fragments were used as the APP CTF protein markers. HEK293 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM) containing 10% FBS, 1 mM sodium pyruvate, 2 mM L-glutamine, 50 U/ml penicillin G sodium, and 50 µg/ml streptomycin sulfate (Invitrogen). All cells were maintained at 37°C in an incubator containing 5% CO2. For transient transfection, cells were grown to ~ 70% confluency and transfected with plasmids using Lipofectamine plus (Invitrogen) according to the manufacturer’s instructions. The cells were harvested 48–72 h after transfection.

Immunoblotting
The frozen brain tissues were homogenized in radio-immuno-precipitation assay (RIPA) lysis buffer (1% Triton X-100, 1% sodium deoxycholate, 0.1% SDS, 0.15M NaCl, 0.05M Tris-HCl, pH 7.2) supplemented with protease inhibitors cocktail Complete (Roche, Nutley, NJ, USA) and sonicated. Tissue lysates were resolved by 12% Tris-glycine or 16% Tris-tricine gels. Immunoblotting was performed as described previously. BACE1 was detected by 208 antibody (Ab) against C terminus of BACE1 (RCLRCLRQQHDDFADD). APP was detected by the C20 Ab against the last 20 amino acids of its C terminus. Internal control ß-actin expression was analyzed using monoclonal anti-ß-actin Ab AC-15 (Sigma, St. Louis, MO, USA).

Aß40/42 sandwich ELISA assay
ELISA assay was performed as described (31) . In brief, protein inhibitors and AEBSF (Sigma) were added to tissue lysates to prevent degradation of Aß. The concentration of Aß40/42 was measured using the ß-amyloid 1–40 or 1–42 Colorimetric ELISA kit (Biosource International, Inc., Camarillo, CA, USA) according to the manufacturer’s protocol.

Quantitative RT-polymerase chain reaction and real-time PCR
Total RNA was isolated from frozen brain tissue using TRI-Reagent (Sigma). PowerScriptTM reverse transcriptase (Invitrogen) was used to synthesize the first-strand cDNA from equal amount of the RNA sample following the manufacturer’s instruction. The newly synthesized cDNA templates were further amplified by Platinum TaqDNA polymerase (Invitrogen) in a 50 µl reaction. 25 to 35 cycles of PCR reaction were used to cover the linear range of the PCR amplification. The BACE1 gene-specific primers 5'-cggaattcgccaccatgaccgacgaagagcccgag-3' and 5'-cgggatcccacaatgctcttgtcatag-3' were used to amplify a 725 bp fragment of the BACE1 coding region. The APP gene-specific primers 5'-cggaattcccttggtgttctttgcagaag-3' and 5'-cggaattccgttctgcatctgctcaaag-3' were used to amplify a 248 bp fragment of the APP coding region. ß-Actin was used as an internal control. A pair of gene-specific primers 5'-ggacttcgagcaagagatgg-3' and 5'-gaagcatttgcggtggag-3' was used to amplify a 462 bp fragment of ß-actin. The samples were further analyzed on 1% agarose gel. Kodak Image Station 1000 software (Perkin Elmer, Norwalk, CT, USA) was used to analyze the data.

Real-time PCR was performed with the TaqMan® Universal PCR Master Mix (Applied Biosystems, Foster City, CA, USA) using the Smart Cycler II (Cephoid) according to the manufacturer’s instructions. The sequence of BACE1 primers are 5'-gcccaagaaagtgtttgaagct-3' and 5'-gccagaaaccatcagggaact-3'. The Taqman probe for BACE1 is FAMTM–5'-aatccatcaaggcagcctcctccac-3'-TAMRATM. The sequence for actin primers are 5'-aggccaaccgcgagaag-3' and 5'-acagcctggatagcaacgtacat-3'. The probe for actin is TETTM-5'-tgacccagatcatgtttgagacctt-3'TAMRATM.

Karyotyping of DS cell lines
Colchicine was added to cell culture at a concentration of 5 µg/ml 3 h before harvest. Cells were swollen in 0.075% KCI for 30 min, then fixed in freshly made fixative (methanol: glacial acetic acid, 3: 1). Cell suspension was dropped onto the slides. The slides were trypsinized with 0.025% trypsin (Sigma) for 1 min. The slides were stained with Giemsa solution (Sigma) for 10 min. Karyotype of the cells was analyzed under microscope.

Live cell image analysis
Plasmid pBACE1-EGFP with enhanced GFP (EGFP) fused with BACE1 at its C terminus was transfected into Trisomy-21 and control cells using Lipofectamine Plus (from Invitrogen). Live cell image analysis was performed 48 h after transfection. Time-lapse images were recorded with the Axiovert 200M microscope using a AxioCam HRm Rev.2 camera. The objective lens of the microscope was Plan Apochromat 63x/1.40 Oil (DIC III). The images were acquired every 500 ms.

Fractionation
The brain tissues were homogenized in HB Buffer (0.25M sucrose, 5 mM HEPES pH7.4, 1 mM EDTA, 3 mM imidazole with protease/phosphotase inhibitors) on ice using a 23G1 needle. A discontinuous 4 step sucrose gradient was made by loading 1 ml 2M, 1.5 ml 1.3M, 1.5 ml 1.0M, and 1 ml 0.6M sucrose into an ultracentrifuge tube. The homogenate was loaded onto the sucrose cushion and centrifuged at 45,000 rpm for 2 h using a SW50.1 Beckman rotor. Golgi fraction located at the 1.0M/0.6M sucrose interface was collected and lysed with the 6x SDS loading buffer. The fractions were separated on a 15% SDS-glysine gel and blotted with 208 Ab to detect BACE1.

Pulse-chase experiment
Cells were transfected with BACE1-mychis cDNA in a 10 cm plate with Lipofectamine Plus. 48 h after transfection, the cells were starved in methionine-free DMEM for 30 min, then radiolabeled in a medium containing 125 µCi/ml of 35S-methionine and 35S-cysteine for 2 h. Subsequently the cells were chased for 0, 4, and 9 h with nonradioactive media with 10 x excess of methionine and cysteine. The cell lysates were immunoprecipitated with the anti-BACE1 208 Ab. The radiolabeled proteins were separated on a 12% SDS-glysine gel and quantitated by INSTANT-IMAGER (Packard Bioscience Company, Meriden, CT, USA).

Tunicamycin treatment
2EB2 cells (13) were treated with 10 µg/ml tunicamycin (Sigma) for 0, 3, and 6 h. The cells were harvested in RIPA buffer and the lysates were separated using a 16% Tris-tricine gel. APP C99 and C89 fragments were detected by the C20 Ab. ß-Actin was used as the control.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Markedly elevated ß-secretase activity in the DS brains
Abnormal APP processing has been implicated in DS. To investigate the role of ß-secretase in APP processing and Aß generation in DS, we first measured the APP, C99, and Aß levels in DS and control samples. The fetal cortical tissues from Trisomy-21 and gestation age-matched control brains were homogenized for protein extraction. The Aß concentration in the DS and control tissues was measured by a colorimetric ELISA method. ELISA results showed that the Aß40 levels were significantly elevated from 107.0 ± 9.11 in the normal controls to 183.9 ± 9.49 pg/mg lysates in the DS patients (P<0.0001), and Aß42 levels were increased from 54.87 ± 3.51 to 83.81 ± 5.54 pg/mg lysates (P<0.0001) (Fig. 1 A, B). To assay the levels of APP and APP C-terminal fragments (CTFs), the tissue lysates were separated in SDS-PAGE gels and immunoblotted with an anti-APP C terminus C20 Ab (31) . The level of APP protein was slightly elevated in DS by 121.2 ± 18.47% relative to control (P>0.05) (Fig. 1C, E ). Compared to control samples, the level of C99 in DS was markedly increased by 490.0 ± 96.29% (P<0.0001) (Fig. 1D, F ). These results are consistent with previous report that C99 and Aß are increased in DS (54) . The increased APP levels in DS can be attributed to the extra copy of the APP gene in Trisomy-21. However, the drastic increase in the level of C99, the major ß-secretase product, suggests a significant increase in ß-secretase activity. The increased APP substrate level only partially contributes to the overgeneration of Aß in DS.


Figure 1
View larger version (24K):
[in this window]
[in a new window]
  		Figure 1. Marked elevation of Aß and C99, the major ß-secretase product in the DS brains. The cerebral cortical tissues from 16 to 20 wk gestational fetal abortuses of 7 DS and 7 age-matched controls were lysed in RIPA buffer (1% Triton X-100, 1% sodium deoxycholate, 0.1% SDS, 0.15M NaCl, 0.05M Tris-HCl, pH 7.2) supplemented with protease inhibitors cocktail Complete (Roche) and AEBSF (Sigma). The concentrations of Aß40 (A) and Aß42 (B) were measured by ß-amyloid 1–40 or 1–42 colorimetric ELISA kit (Biosource International). The values represent mean ± SE, n = 7. C) 150 µg of total protein from control and DS brain tissue lysates was separated by 12% SDS-PAGE with C20 Ab to detect APP proteins. ß-Actin was detected by the monoclonal anti ß-actin Ab AC-15 (Sigma). C represents control samples. D) Brain samples were separated in 16% Tris-tricine gel and immunoblotted with C20 to detect the APP C-terminal fragments. Plasmid pAPP-C99 and pAPP-C83 were transfected into HEK293 cells and the cell lysates were used as the protein size markers for C99 and C83 fragments. Quantitative analysis of full-length APP (E) and APP C99 (F). Western blots were quantified using Kodak image analysis. Values are means ± SE and n = 7. The protein levels are expressed as a % of the levels in control. *P < 0.01 relative to the controls by the Student’s t test.

Increased BACE1 total and glycosylated protein levels in the DS brains
APP C99 is produced by ß-secretase cleavage of APP at the ß site. Since the marked increase in C99 in DS indicated increased ß-secretase activity, we then examined whether BACE1 is up-regulated and responsible for the abnormal APP processing in DS. The brain tissue lysates from DS and control were analyzed by SDS-PAGE gel and immunoblotted with BACE1 Ab 208 (Fig. 2 A). The results showed that the BACE1 protein level was markedly elevated in DS (215.31±39.40%) compared to control (P<0.01) (Fig. 2B ). More important, there was a change in the ratio of the mature and immature forms of BACE1 protein in DS. The mature form of BACE1 was predominant in DS, while the immature form of BACE1 was predominant in the control tissues. The ratio of mature to immature forms of BACE1 was significantly higher in DS (389.30±27.56%) than in control (Fig. 2C ) (P<0.0001). The results clearly demonstrate that abnormal BACE1 protein level causes up-regulated ß-secretase activity, resulting in more Aß generation leading to the AD neuropathology in DS.


Figure 2
View larger version (27K):
[in this window]
[in a new window]
  		Figure 2. Significant increase in total and mature BACE1 protein levels in the DS brains. A) The brain tissue lysates were separated on a 15% Tris-glycine gel and immunoblotted with the 208 Ab to detect BACE1. B) Quantitative analysis of total BACE1 protein levels by Kodak image analysis. C) Quantitative analysis of the ratio of mature BACE1 vs. immature BACE1 levels. Values are means ± SE and n = 7. The total protein levels are expressed as a % of the levels in control. *P < 0.05 by the Student’s t test.

BACE1 transcription was unchanged in DS
To investigate whether the abnormal BACE1 protein increase results from up-regulation of BACE1 gene transcription in DS, quantitative reverse transcription-polymerase chain reaction was used to measure its mRNA levels in DS and normal controls (Fig. 3 A). The APP level was increased in DS brain tissues by 142.2 ± 17.61% relative to controls (P<0.05) (Fig. 3B ). Such increases might be due to the extra copies of the APP gene on chromosome 21 in DS. The BACE1 mRNA levels were unchanged (92.32±2.154%) (P>0.05) (Fig. 3B ). A similar result was obtained by real-time PCR. In Fig. 2 we show that the protein level of BACE1 was significantly increased, resulting in up-regulated ß-secretase activity. Since the BACE1 mRNA levels were not changed in DS, this suggests that the elevation of BACE1 in DS is not due to abnormal BACE1 transcription.


Figure 3
View larger version (28K):
[in this window]
[in a new window]
  		Figure 3. BACE1 transcription was unchanged in DS patients whereas APP mRNA was increased by ~1.5-fold. A) RNA was isolated from DS and control brain tissues. Quantitative RT-polymerase chain reaction was performed to measure the endogenous levels of the APP, BACE1 mRNA. Specific APP, BACE1, and ß-actin coding sequence primers were used to amplify the cDNA. Different cycles and amounts of PCR products were analyzed and the DNA gel represents 25 cycles of RT-polymerase chain reaction products separated on 1% agarose gel. DNA Marker VIII (Roche) was used as the size marker on gel. B) The ratio of APP, BACE1 to ß-actin mRNA in DS and age-matched controls were quantitated by Kodak image analysis. Endogenous APP mRNA level was increased in DS relative to controls. *P < 0.05 relative to controls by Student’s t test. Endogenous BACE1 mRNA level is similar between DS and controls (P>0.05 by the Student’s t test). Shown are the mean ± SE.

Time-lapse analysis of BACE1 trafficking in DS cell lines
To define the mechanism by which the mature BACE1 protein is abnormally increased in DS, we examined the trafficking and post-translational modification of BACE1. To examine the trafficking of BACE1 protein, the Trisomy-21 and control fibroblast cells derived from 18 wk of gestation fetal abortuses were transfected with EGFP-tagged BACE1 cDNA and time-lapse images were recorded on the live cells to monitor the BACE1-enhanced GFP protein trafficking (Fig. 4 , QuickTime movie files attached: Control.mov and DS.mov). In the control cells we observed normal patterns of BACE1 protein trafficking; BACE1 fluorescent particles moved smoothly and rapidly through subcellular compartments, mostly inside ER and Golgi complex (Fig. 4 , top panel). However, in the Trisomy-21 cells, BACE1 fluorescent proteins were predominantly immobile in Golgi-like complexes (Fig. 4 , lower panel), suggesting abnormal protein trafficking. Transient fluorescent signals were observed in the ER and Golgi complexes of control cells, while abnormally prolonged signals were observed in Trisomy-21 cells (Fig. 4) .


Figure 4
View larger version (12K):
[in this window]
[in a new window]
  		Figure 4. Time-lapse analysis of BACE1 trafficking in DS cell lines. Live image analysis of the cells transfected with pBACE1-enhanced GFP. Time-lapse images were recorded with Axiovert 200M microscope using the Plan Apochromat 63x/1.40 Oil (DIC III) objective lens. The images were acquired every 500 milliseconds. Arrows indicate the trafficking of BACE1-enhanced GFP particles. Top panel: Representative images of the live control cells at the 1st, 10th, 20th, and 30th frames (C-1 to C30) illustrating quick BACE1 movement; Lower panel: images of the live Trisomy-21 cells at the 1st, 10th, 20th, and 30th frames (DS-1 to DS-30) illustrating immobile EGFP-BACE1 particles. The movie files of the BACE1-enhanced GFP trafficking (QuickTime format) are attached.

Abnormal BACE1 protein trafficking and accumulation in the Golgi of DS cells
To examine the abnormal accumulation of BACE1 in DS, the Golgi samples were extracted from brain tissues. A subcellular fractionation experiment revealed that while there were similar levels in mature and immature BACE1 protein in the Golgi fraction of controls, mature form of BACE1 proteins were markedly increased in the Golgi fraction of DS samples (Fig. 5 A). Furthermore, pulse-chase experiments showed that both mature and immature BACE1 proteins were detected and the half-life of the newly synthesized proteins was ~9 h in the control fibroblast cells. However, the predominant BACE1 proteins in the DS cell samples were mature and there was a slightly longer half-life of the protein (Fig. 5B ). These data indicated that BACE1 proteins underwent abnormal trafficking and accumulated in the DS cells. BACE1 undergoes a complex set of post-translational modification, including phosphorylation, glycosylation, and ubiquitination, during its maturation and degradation (22 , 25 , 27 , 31) . BACE1 has 4 N-glycosylation sites at Asn-153, -172, -223, and -354 (22 , 23 , 25) . Our data indicate there are more glycosylated mature BACE1 proteins in DS than controls. To determine whether glycosylation affects the BACE1 protease activity, BACE1 stable cells were treated with tunicamycin, an inhibitor of N-acetylglucosamine transferases. Tunicamycin treatment significantly reduced the generation of the ß-secretase cleavage product, C99 and C89 fragments in 2EB2 cells (Fig. 5C ). This result suggests that inhibition of the BACE1 glycosylation reduces APP processing at the ß-secretase site. This is consistent with previous reports that the BACE1 activity depends on the extent of N-glycosylation (22 , 23) .


Figure 5
View larger version (21K):
[in this window]
[in a new window]
  		Figure 5. Abnormal trafficking and accumulation of mature BACE1 protein in DS. A) Fractionation of brain tissue lysates from Trisomy-21 and control. Golgi fractions were collected and separated by 15% SDS-glysine gel. 208 Ab was used to detect BACE1. Monoclonal anti ß-actin Ab AC-15 was used to detect ß-actin. Mature BACE1 is significantly increased in the Golgi compartment of DS samples. B) BACE1 Pulse-Chase experiment. Trisomy-21 and control cells transfected with pBACE1-mychis were incubated with 35S-methione and 35S-cystine labeling media for 2 h, then replaced with nonradioactive chasing media. The cell lysates were immunoprecipitated with the 208 Ab and separated with 15% SDS-glysine gel. While control cells show the newly synthesized mature and immature 35S-BACE proteins, Trisomy-21 cells predominantly show a mature form. C) Tunicamycin inhibits ß-secretase activity. BACE1 stable 2EB2 cells were treated with tunicamycin at 10 µg/ml for 0, 3 and 6 h. The cell lysates were analyzed by 16% Tris-tricine gel with C20 Ab to detect APP C99 and C89. Tunicamycin treatment markedly reduced ß-secretase activity, resulting in lower levels of C99 and C89 generation, without affecting ß-actin.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
AD is the most common neurodegenerative disease leading to dementia. Almost all DS patients inevitably develop characteristic AD neuropathology. The mechanism by which AD neuropathogenesis develops in DS was previously unknown. It was reported that altered APP metabolism was associated with mitochondrial dysfunction in Down syndrome (54) . Since the APP and BACE2 genes are on chromosome 21 and there are extra copies of these two genes in DS, it was speculated that the extra copy of the genes might therefore play a role in the abnormal processing of APP in DS. While the additional copy of the APP gene is seen in 99% of DS, the gene dosage effect cannot fully account for the occurrence of AD in DS (56) . In this report, our data show that the transcription of the APP was indeed increased in DS, however the APP protein level was not significantly changed in DS. The slightly increased APP protein level cannot fully explain AD pathogenesis in DS patients.

BACE1 levels were found to be higher in some of sporadic AD patients than controls (40 41 42 43) . However, the molecular mechanism of increased BACE1 in sporadic AD is not clear. Our recent study indicates that weak BACE1 gene promoter activity contributes to relatively low BACE1 gene expression and a slight increase in BACE1 will lead to drastic increase in C99 production and subsequently Aß generation (14) . Our data show that ß-secretase activity is up-regulated in DS. Increased BACE1 protein levels, and particularly the higher levels of N-glycosylated mature BACE1 proteins in DS, result in the up-regulated ß-secretase activity, leading to higher C99 production and Aß generation. The cause of the BACE1 elevation and increased glycosylation in DS is unknown. The BACE1 elevation is not due to increased transcription, and may therefore be explained by its post-translational modification, and particularly the reduction of BACE1 degradation. Our studies using time-lapse analysis on the live cells and subcellular fractionation experiments show that abnormal trafficking resulted in BACE1 proteins accumulated in Golgi complexes in DS. We have shown that BACE1 is degraded by the ubiquitin-proteasome pathway (31) . The longer half-life shown by the pulse-chase experiment indicates that BACE1 degradation might be affected in DS. The trafficking abnormality in DS might prevent the BACE1 proteins from undergoing their normal degradation process, resulting in increased ß-secretase activity. Further study of the proteasomal degradation of BACE1 in DS is needed. The abnormal trafficking and drastic elevation of BACE1 and subsequent increase in Aß deposition in DS would explain the development of AD pathogenesis in DS (Fig. 6 ). Furthermore, we have another report showing that BACE2, as a novel {theta}-secretase, is not responsible for AD pathogenesis in DS patients (57) . Thus, our results provide a novel mechanism by which AD develops in DS and suggest the therapeutic potential of inhibiting BACE1 or potentiating BACE2 in AD and DS.


Figure 6
View larger version (18K):
[in this window]
[in a new window]
  		Figure 6. Increased BACE1 maturation contributes to AD pathogenesis in DS. Overproduction of Aß in DS is caused by abnormal BACE1 protein trafficking and maturation. Increased BACE1 protein levels, and particularly the higher levels of N-glycosylated mature BACE1 proteins in DS, result in the up-regulated ß-secretase activity, leading to higher Aß generation.


   ACKNOWLEDGMENTS
 
We thank University of Maryland Brain and Tissue Bank for Developmental Disorders for Trisomy-21 and control brain tissues. We thank Alaa El-Husseini, Weihui Zhou, and Jane Wang for their technical assistance. We also thank Steven R. Vincent and Anthony G. Phillips for helpful discussion. This work was supported by Canadian Institutes of Health Research (CIHR), Jack Brown and Family Alzheimer’s Research Foundation, and the Michael Smith Foundation for Health Research (to W.S.). W.S. is the Holder of Canada Research Chair in Alzheimer’s disease. Y.T. was the recipient of the Michael Smith Foundation for Health Research Post Doctoral Fellowship.

Received for publication December 14, 2005. Accepted for publication March 3, 2006.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Down, J. L. H. (1866) Observations on an ethnic classification of idiots. London Hospital Reports 3,259-262
  2. Jacobs, P. A., Baikie, A. G., Court Brown, W. M., Strong, J. A. (1959) The somatic chromosomes in mongolism. Lancet 1,710[Medline]
  3. Lejeune, J., Turpin, R., Gautier, M. (1959) [Mongolism; a chromosomal disease (trisomy).]. Bull. Acad. Natl. Med. 143,256-265[Medline]
  4. Mattson, M. P. (2004) Pathways towards and away from Alzheimer’s disease. Nature 430,631-639[CrossRef][Medline]
  5. Selkoe, D. J. (2001) Alzheimer’s disease: genes, proteins, and therapy. Physiol. Rev. 81,741-766[Abstract/Free Full Text]
  6. Cai, H., Wang, Y., McCarthy, D., Wen, H., Borchelt, D. R., Price, D. L., Wong, P. C. (2001) BACE1 is the major beta-secretase for generation of Abeta peptides by neurons. Nat. Neurosci. 4,233-234[CrossRef][Medline]
  7. Hussain, I., Powell, D., Howlett, D. R., Tew, D. G., Meek, T. D., Chapman, C., Gloger, I. S., Murphy, K. E., Southan, C. D., Ryan, D. M., Smith, T. S., Simmons, D. L., Walsh, F. S., Dingwall, C., Christie, G. (1999) Identification of a novel aspartic protease (Asp 2) as beta-secretase. Mol. Cell Neurosci. 14,419-427[CrossRef][Medline]
  8. Luo, Y., Bolon, B., Kahn, S., Bennett, B. D., Babu-Khan, S., Denis, P., Fan, W., Kha, H., Zhang, J., Gong, Y., Martin, L., Louis, J. C., Yan, Q., Richards, W. G., Citron, M., Vassar, R. (2001) Mice deficient in BACE1, the Alzheimer’s beta-secretase, have normal phenotype and abolished beta-amyloid generation. Nat. Neurosci. 4,231-232[CrossRef][Medline]
  9. Roberds, S. L., Anderson, J., Basi, G., Bienkowski, M. J., Branstetter, D. G., Chen, K. S., Freedman, S. B., Frigon, N. L., Games, D., Hu, K., Johnson-Wood, K., Kappenman, K. E., Kawabe, T. T., Kola, I., Kuehn, R., Lee, M., Liu, W., Motter, R., Nichols, N. F., Power, M., Robertson, D. W., Schenk, D., Schoor, M., Shopp, G. M., Shuck, M. E., Sinha, S., Svensson, K. A., Tatsuno, G., Tintrup, H., Wijsman, J., Wright, S., McConlogue, L. (2001) BACE knockout mice are healthy despite lacking the primary beta-secretase activity in brain: implications for Alzheimer’s disease therapeutics. Hum. Mol. Genet. 10,1317-1324[Abstract/Free Full Text]
  10. Sinha, S., Anderson, J. P., Barbour, R., Basi, G. S., Caccavello, R., Davis, D., Doan, M., Dovey, H. F., Frigon, N., Hong, J., Jacobson-Croak, K., Jewett, N., Keim, P., Knops, J., Lieberburg, I., Power, M., Tan, H., Tatsuno, G., Tung, J., Schenk, D., Seubert, P., Suomensaari, S. M., Wang, S., Walker, D., John, V., et al (1999) Purification and cloning of amyloid precursor protein beta-secretase from human brain. Nature 402,537-540[CrossRef][Medline]
  11. Vassar, R., Bennett, B. D., Babu-Khan, S., Kahn, S., Mendiaz, E. A., Denis, P., Teplow, D. B., Ross, S., Amarante, P., Loeloff, R., Luo, Y., Fisher, S., Fuller, J., Edenson, S., Lile, J., Jarosinski, M. A., Biere, A. L., Curran, E., Burgess, T., Louis, J. C., Collins, F., Treanor, J., Rogers, G., Citron, M. (1999) Beta-secretase cleavage of Alzheimer’s amyloid precursor protein by the transmembrane aspartic protease BACE. Science 286,735-741[Abstract/Free Full Text]
  12. Yan, R., Bienkowski, M. J., Shuck, M. E., Miao, H., Tory, M. C., Pauley, A. M., Brashier, J. R., Stratman, N. C., Mathews, W. R., Buhl, A. E., Carter, D. B., Tomasselli, A. G., Parodi, L. A., Heinrikson, R. L., Gurney, M. E. (1999) Membrane-anchored aspartyl protease with Alzheimer’s disease beta-secretase activity. Nature 402,533-537[CrossRef][Medline]
  13. Sun, X., Wang, Y., Qing, H., Christensen, M. A., Liu, Y., Zhou, W., Tong, Y., Xiao, C., Huang, Y., Zhang, S., Liu, X., Song, W. (2005) Distinct transcriptional regulation and function of the human BACE2 and BACE1 genes. FASEB J. 19,739-749[Abstract/Free Full Text]
  14. Li, Y., Zhou, W., Tong, Y., He, G., Song, W. (2006) Control of APP processing and Abeta generation level by BACE1 enzymatic activity and transcription. FASEB J. 20,285-292[Abstract/Free Full Text]
  15. Acquati, F., Accarino, M., Nucci, C., Fumagalli, P., Jovine, L., Ottolenghi, S., Taramelli, R. (2000) The gene encoding DRAP (BACE2), a glycosylated transmembrane protein of the aspartic protease family, maps to the down critical region. FEBS Lett. 468,59-64[CrossRef][Medline]
  16. Bennett, B. D., Babu-Khan, S., Loeloff, R., Louis, J. C., Curran, E., Citron, M., Vassar, R. (2000) Expression analysis of BACE2 in brain and peripheral tissues. J. Biol. Chem. 275,20647-20651[Abstract/Free Full Text]
  17. Lin, X., Koelsch, G., Wu, S., Downs, D., Dashti, A., Tang, J. (2000) Human aspartic protease memapsin 2 cleaves the beta-secretase site of beta-amyloid precursor protein. Proc. Natl. Acad. Sci. USA 97,1456-1460[Abstract/Free Full Text]
  18. Solans, A., Estivill, X., de La Luna, S. (2000) A new aspartyl protease on 21q22.3, BACE2, is highly similar to Alzheimer’s amyloid precursor protein beta-secretase. Cytogenet. Cell Genet. 89,177-184[CrossRef][Medline]
  19. Benjannet, S., Elagoz, A., Wickham, L., Mamarbachi, M., Munzer, J. S., Basak, A., Lazure, C., Cromlish, J. A., Sisodia, S., Checler, F., Chretien, M., Seidah, N. G. (2001) Post-translational processing of beta-secretase (beta-amyloid-converting enzyme) and its ectodomain shedding. The pro- and transmembrane/cytosolic domains affect its cellular activity and amyloid-beta production. J. Biol. Chem. 276,10879-10887[Abstract/Free Full Text]
  20. Bennett, B. D., Denis, P., Haniu, M., Teplow, D. B., Kahn, S., Louis, J. C., Citron, M., Vassar, R. (2000) A furin-like convertase mediates propeptide cleavage of BACE, the Alzheimer’s beta-secretase. J. Biol. Chem. 275,37712-37717[Abstract/Free Full Text]
  21. Creemers, J. W. M., Ines Dominguez, D., Plets, E., Serneels, L., Taylor, N. A., Multhaup, G., Craessaerts, K., Annaert, W., De Strooper, B. (2001) Processing of beta-secretase by Furin and other members of the proprotein convertase family. J. Biol. Chem. 276,4211-4217[Abstract/Free Full Text]
  22. Capell, A., Steiner, H., Willem, M., Kaiser, H., Meyer, C., Walter, J., Lammich, S., Multhaup, G., Haass, C. (2000) Maturation and pro-peptide cleavage of beta-secretase. J. Biol. Chem. 275,30849-30854[Abstract/Free Full Text]
  23. Charlwood, J., Dingwall, C., Matico, R., Hussain, I., Johanson, K., Moore, S., Powell, D. J., Skehel, J. M., Ratcliffe, S., Clarke, B., Trill, J., Sweitzer, S., Camilleri, P. (2001) Characterization of the glycosylation profiles of Alzheimer’s beta-secretase protein Asp-2 expressed in a variety of cell lines. J. Biol. Chem. 276,16739-16748[Abstract/Free Full Text]
  24. Haniu, M., Denis, P., Young, Y., Mendiaz, E. A., Fuller, J., Hui, J. O., Bennett, B. D., Kahn, S., Ross, S., Burgess, T., Katta, V., Rogers, G., Vassar, R., Citron, M. (2000) Characterization of Alzheimer’s beta-secretase protein BACE. A pepsin family member with unusual properties. J. Biol. Chem. 275,21099-21106[Abstract/Free Full Text]
  25. Huse, J. T., Pijak, D. S., Leslie, G. J., Lee, V. M., Doms, R. W. (2000) Maturation and endosomal targeting of beta-site amyloid precursor protein-cleaving enzyme. The Alzheimer’s disease beta-secretase. J. Biol. Chem. 275,33729-33737[Abstract/Free Full Text]
  26. Huse, J. T., Byant, D., Yang, Y., Pijak, D. S., D’Souza, I., Lah, J. J., Lee, V. M., Doms, R. W., Cook, D. G. (2003) Endoproteolysis of beta-secretase (beta-site amyloid precursor protein-cleaving enzyme) within its catalytic domain. A potential mechanism for regulation. J. Biol. Chem. 278,17141-17149[Abstract/Free Full Text]
  27. Walter, J., Fluhrer, R., Hartung, B., Willem, M., Kaether, C., Capell, A., Lammich, S., Multhaup, G., Haass, C. (2001) Phosphorylation regulates intracellular trafficking of beta-secretase. J. Biol. Chem. 276,14634-14641[Abstract/Free Full Text]
  28. Schmechel, A., Strauss, M., Schlicksupp, A., Pipkorn, R., Haass, C., Bayer, T. A., Multhaup, G. (2004) Human BACE forms dimers and colocalizes with APP. J. Biol. Chem. 279,39710-39717[Abstract/Free Full Text]
  29. Westmeyer, G. G., Willem, M., Lichtenthaler, S. F., Lurman, G., Multhaup, G., Assfalg-Machleidt, I., Reiss, K., Saftig, P., Haass, C. (2004) Dimerization of beta-site beta-amyloid precursor protein-cleaving enzyme. J. Biol. Chem. 279,53205-53212[Abstract/Free Full Text]
  30. He, W., Lu, Y., Qahwash, I., Hu, X. Y., Chang, A., Yan, R. (2004) Reticulon family members modulate BACE1 activity and amyloid-beta peptide generation. Nat. Med. 10,959-965[CrossRef][Medline]
  31. Qing, H., Zhou, W., Christensen, M. A., Sun, X., Tong, Y., Song, W. (2004) Degradation of BACE by the ubiquitin-proteasome pathway. FASEB J. 18,1571-1573[Abstract/Free Full Text]
  32. Christensen, M. A., Zhou, W., Qing, H., Lehman, A., Philipsen, S., Song, W. (2004) Transcriptional regulation of BACE1, the beta-amyloid precursor protein beta-secretase, by Sp1. Mol. Cell. Biol. 24,865-874[Abstract/Free Full Text]
  33. De Pietri Tonelli, D., Mihailovich, M., Di Cesare, A., Codazzi, F., Grohovaz, F., Zacchetti, D. (2004) Translational regulation of BACE-1 expression in neuronal and non-neuronal cells. Nucleic Acids Res. 32,1808-1817[Abstract/Free Full Text]
  34. Lammich, S., Schobel, S., Zimmer, A. K., Lichtenthaler, S. F., Haass, C. (2004) Expression of the Alzheimer protease BACE1 is suppressed via its 5'-untranslated region. EMBO Rep. 5,620-625[CrossRef][Medline]
  35. Rogers, G. W., Jr, Edelman, G. M., Mauro, V. P. (2004) Differential utilization of upstream AUGs in the beta-secretase mRNA suggests that a shunting mechanism regulates translation. Proc. Natl. Acad. Sci. USA 101,2794-2799[Abstract/Free Full Text]
  36. Zhou, W., Song, W. (2006) Leaky scanning and reinitiation regulate BACE1 gene expression. Mol. Cell. Biol. 26In press
  37. Cruts, M., Dermaut, B., Rademakers, R., Roks, G., Van den Broeck, M., Munteanu, G., van Duijn, C. M., Van Broeckhoven, C. (2001) Amyloid beta secretase gene (BACE) is neither mutated in nor associated with early-onset Alzheimer’s disease. Neurosci. Lett. 313,105-107[CrossRef][Medline]
  38. Nicolaou, M., Song, Y. Q., Sato, C. A., Orlacchio, A., Kawarai, T., Medeiros, H., Liang, Y., Sorbi, S., Richard, E., Rogaev, E. I., Moliaka, Y., Bruni, A. C., Jorge, R., Percy, M., Duara, R., Farrer, L. A., St Georg-Hyslop, P., Rogaeva, E. A. (2001) Mutations in the open reading frame of the beta-site APP cleaving enzyme (BACE) locus are not a common cause of Alzheimer’s disease. Neurogenetics 3,203-206[Medline]
  39. Russo, C., Schettini, G., Saido, T. C., Hulette, C., Lippa, C., Lannfelt, L., Ghetti, B., Gambetti, P., Tabaton, M., Teller, J. K. (2000) Presenilin-1 mutations in Alzheimer’s disease. Nature 405,531-532[CrossRef][Medline]
  40. Fukumoto, H., Cheung, B. S., Hyman, B. T., Irizarry, M. C. (2002) Beta-secretase protein and activity are increased in the neocortex in Alzheimer disease. Arch. Neurol. 59,1381-1389[Abstract/Free Full Text]
  41. Fukumoto, H., Rosene, D. L., Moss, M. B., Raju, S., Hyman, B. T., Irizarry, M. C. (2004) Beta-secretase activity increases with aging in human, monkey, and mouse brain. Am. J. Pathol. 164,719-725[Abstract/Free Full Text]
  42. Holsinger, R. M., McLean, C. A., Beyreuther, K., Masters, C. L., Evin, G. (2002) Increased expression of the amyloid precursor beta-secretase in Alzheimer’s disease. Ann. Neurol. 51,783-786[CrossRef][Medline]
  43. Yang, L. B., Lindholm, K., Yan, R., Citron, M., Xia, W., Yang, X. L., Beach, T., Sue, L., Wong, P., Price, D., Li, R., Shen, Y. (2003) Elevated beta-secretase expression and enzymatic activity detected in sporadic Alzheimer disease. Nat. Med. 9,3-4[CrossRef][Medline]
  44. Ohno, M., Sametsky, E. A., Younkin, L. H., Oakley, H., Younkin, S. G., Citron, M., Vassar, R., Disterhoft, J. F. (2004) BACE1 Deficiency rescues memory deficits and cholinergic dysfunction in a mouse model of Alzheimer’s disease. Neuron 41,27-33[CrossRef][Medline]
  45. Kao, S. C., Krichevsky, A. M., Kosik, K. S., Tsai, L. H. (2004) BACE1 suppression by RNA interference in primary cortical neurons. J. Biol. Chem. 279,1942-1949[Abstract/Free Full Text]
  46. von Arnim, C. A. F., Kinoshita, A., Peltan, I. D., Tangredi, M. M., Herl, L., Lee, B. M., Spoelgen, R., Hshieh, T. T., Ranganathan, S., Battey, F. D., Liu, C.-X., Bacskai, B. J., Sever, S., Irizarry, M. C., Strickland, D. K., Hyman, B. T. (2005) The low density lipoprotein receptor-related protein (LRP) is a novel {beta}-secretase (BACE1) substrate. J. Biol. Chem. 280,17777-17785[Abstract/Free Full Text]
  47. Li, Q., Sudhof, T. C. (2004) Cleavage of amyloid-beta precursor protein and amyloid-beta precursor-like protein by BACE 1. J. Biol. Chem. 279,10542-10550[Abstract/Free Full Text]
  48. Pastorino, L., Ikin, A. F., Lamprianou, S., Vacaresse, N., Revelli, J. P., Platt, K., Paganetti, P., Mathews, P. M., Harroch, S., Buxbaum, J. D. (2004) BACE (beta-secretase) modulates the processing of APLP2 in vivo. Mol. Cell Neurosci. 25,642-649[CrossRef][Medline]
  49. Kitazume, S., Saido, T. C., Hashimoto, Y. (2004) Alzheimer’s beta-secretase cleaves a glycosyltransferase as a physiological substrate. glycoconj. J. 20,59-62[Medline]
  50. Lichtenthaler, S. F., Dominguez, D. I., Westmeyer, G. G., Reiss, K., Haass, C., Saftig, P., De Strooper, B., Seed, B. (2003) The cell adhesion protein P-selectin glycoprotein ligand-1 is a substrate for the aspartyl protease BACE1. J. Biol. Chem. 278,48713-48719[Abstract/Free Full Text]
  51. Glenner, G. G., Wong, C. W. (1984) Alzheimer’s disease and Down’s syndrome: sharing of a unique cerebrovascular amyloid fibril protein. Biochem. Biophys. Res. Commun. 122,1131-1135[CrossRef][Medline]
  52. Glenner, G. G., Wong, C. W. (1984) Alzheimer’s disease: initial report of the purification and characterization of a novel cerebrovascular amyloid protein. Biochem. Biophys. Res. Commun. 120,885-890[CrossRef][Medline]
  53. Hardy, J., Selkoe, D. J. (2002) The amyloid hypothesis of Alzheimer’s disease: progress and problems on the road to therapeutics. Science 297,353-356[Abstract/Free Full Text]
  54. Busciglio, J., Pelsman, A., Wong, C., Pigino, G., Yuan, M., Mori, H., Yankner, B. A. (2002) Altered metabolism of the amyloid beta precursor protein is associated with mitochondrial dysfunction in Down’s syndrome. Neuron 33,677-688[CrossRef][Medline]
  55. Mutton, D., Alberman, E., Hook, E. B. (1996) Cytogenetic and epidemiological findings in Down syndrome, England and Wales 1989 to 1993. National Down syndrome Cytogenetic Register and the Association of Clinical Cytogeneticists. J Med Genet 33,387-394[Abstract/Free Full Text]
  56. Podlisny, M. B., Lee, G., Selkoe, D. J. (1987) Gene dosage of the amyloid beta precursor protein in Alzheimer’s disease. Science 238,669-671[Abstract/Free Full Text]
  57. Sun, X., He, G., Song, W. (2006) BACE, as a novel APP {theta}-secretase, is not responsible for the pathogenesis of Alzheimer’s disease in Down syndrome. FASEB J. 20,1369-1376[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 Arch Gen PsychiatryHome page
Z. Zhong, M. Ewers, S. Teipel, K. Burger, A. Wallin, K. Blennow, P. He, C. McAllister, H. Hampel, and Y. Shen
Levels of beta-Secretase (BACE1) in Cerebrospinal Fluid as a Predictor of Risk in Mild Cognitive Impairment
Arch Gen Psychiatry, June 1, 2007; 64(6): 718 - 726.
[Abstract] [Full Text] [PDF]

Home page
 J. Lipid Res.Home page
G. H. Tansley, B. L. Burgess, M. T. Bryan, Y. Su, V. Hirsch-Reinshagen, J. Pearce, J. Y. Chan, A. Wilkinson, J. Evans, K. E. Naus, et al.
The cholesterol transporter ABCG1 modulates the subcellular distribution and proteolytic processing of {beta}-amyloid precursor protein
J. Lipid Res., May 1, 2007; 48(5): 1022 - 1034.
[Abstract] [Full Text] [PDF]

Home page
 J. Biol. Chem.Home page
X. Zhang, K. Zhou, R. Wang, J. Cui, S. A. Lipton, F.-F. Liao, H. Xu, and Y.-w. Zhang
Hypoxia-inducible Factor 1{alpha} (HIF-1{alpha})-mediated Hypoxia Increases BACE1 Expression and beta-Amyloid Generation
J. Biol. Chem., April 13, 2007; 282(15): 10873 - 10880.
[Abstract] [Full Text] [PDF]

Home page
 Proc. Natl. Acad. Sci. USAHome page
X. Sun, G. He, H. Qing, W. Zhou, F. Dobie, F. Cai, M. Staufenbiel, L. E. Huang, and W. Song
Hypoxia facilitates Alzheimer's disease pathogenesis by up-regulating BACE1 gene expression
PNAS, December 5, 2006; 103(49): 18727 - 18732.
[Abstract] [Full Text] [PDF]

Home page
 FASEB J.Home page
X. Sun, G. He, and W. Song
BACE2, as a novel APP {theta}-secretase, is not responsible for the pathogenesis of Alzheimer's disease in Down syndrome
FASEB J, July 1, 2006; 20(9): 1369 - 1376.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Sun, X.
Right arrow Articles by Song, W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Sun, X.
Right arrow Articles by Song, W.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS