Pathology Associated with AAV Mediated Expression of
Beta Amyloid or C100 in Adult Mouse Hippocampus and
Eleanor S. Drummond1,2*, Jill Muhling1, Ralph N. Martins2,3, Linda K. Wijaya3, Erich M. Ehlert4,
Alan R. Harvey1
1School of Anatomy, Physiology and Human Biology, The University of Western Australia, Western Australia, Australia, 2School of Psychiatry and Clinical Neurosciences,
The University of Western Australia, Western Australia, Australia, 3Centre of Excellence for Alzheimer’s Disease Research and Care, School of Exercise, Biomedical and
Health Sciences, Edith Cowan University, Western Australia, Australia, 4Laboratory for Neuroregeneration, Netherlands Institute for Neuroscience, Royal Academy of Arts
and Sciences, Amsterdam, The Netherlands
Accumulation of beta amyloid (Ab) in the brain is a primary feature of Alzheimer’s disease (AD) but the exact molecular
mechanisms by which Ab exerts its toxic actions are not yet entirely clear. We documented pathological changes 3 and 6
months after localised injection of recombinant, bi-cistronic adeno-associated viral vectors (rAAV2) expressing human Ab40-
GFP, Ab42-GFP, C100-GFP or C100V717F-GFP into the hippocampus and cerebellum of 8 week old male mice. Injection of all
rAAV2 vectors resulted in wide-spread transduction within the hippocampus and cerebellum, as shown by expression of
transgene mRNA and GFP protein. Despite the lack of accumulation of Ab protein after injection with AAV vectors, injection
of rAAV2-Ab42-GFP and rAAV2- C100V717F-GFP into the hippocampus resulted in significantly increased microgliosis and
altered permeability of the blood brain barrier, the latter revealed by high levels of immunoglobulin G (IgG) around the
injection site and the presence of IgG positive cells. In comparison, injection of rAAV2-Ab40-GFP and rAAV2-C100-GFP into
the hippocampus resulted in substantially less neuropathology. Injection of rAAV2 vectors into the cerebellum resulted in
similar types of pathological changes, but to a lesser degree. The use of viral vectors to express different types of Ab and
C100 is a powerful technique with which to examine the direct in vivo consequences of Ab expression in different regions of
the mature nervous system and will allow experimentation and analysis of pathological AD-like changes in a broader range
of species other than mouse.
Citation: Drummond ES, Muhling J, Martins RN, Wijaya LK, Ehlert EM, et al. (2013) Pathology Associated with AAV Mediated Expression of Beta Amyloid or C100
in Adult Mouse Hippocampus and Cerebellum. PLoS ONE 8(3): e59166. doi:10.1371/journal.pone.0059166
Editor: Gemma Casadesus, Case Western Reserve University, United States of America
Received April 29, 2012; Accepted February 13, 2013; Published March 13, 2013
Copyright: ? 2013 Drummond et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by funding from the School of Anatomy, Physiology and Human Biology, The University of Western Australia. ESD was
supported by an Australian Postgraduate Award and Jean Rogerson Postgraduate Scholarship. The funders had no role in study design, data collection and
analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: E.Drummond@murdoch.edu.au
There is a large body of evidence suggesting that beta amyloid
(Ab) accumulation in the brain may be a primary cause of
Alzheimer’s disease (AD). However, exactly how Ab contributes to
AD pathology and the mechanisms involved are still not yet fully
understood. The two main isoforms of Ab are Ab40 and Ab42.
While it is widely accepted that Ab42 is more neurotoxic than
Ab40, surprisingly few studies have attempted to determine the
individual physiological and pathological effects directly attributed
to Ab40 and Ab42 in vivo and even fewer studies have directly
compared the effects of Ab40 and Ab42 expression [1,2]. It is
important to understand the physiological and pathological
functions of each Ab isoform as many proposed therapies for
AD act by modulating Ab levels [3,4,5,6].
It is difficult to determine the exact role of Ab in AD using the
current available animal models, which are predominantly trans-
genic mice. Therefore it was the aim of this study to develop an
alternative animal model for AD research using viral vectors to
initiate localised expression of human Ab. There are many benefits
associated with using viral vectors to develop animal models of
disease. For example, viral vectors can rapidly express transgene
proteins localised to desired brain regions, or even specific cell
types. Viral vectors can also induce transgene expression in many
species and at specific ages, hence preventing developmental or
other unwanted compensatory variables in response to life-long
transgene expression. Viral vectors also allow for the expression of
multiple genes with much greater ease than in transgenic mice,
a feature that is particularly important when studying a multi-
factorial disease such as AD.
To date, two studies have used viral vectors to directly express
Ab. The first study developed viral vectors that produced Ab40-
BRI or Ab42-BRI fusion proteins . The BRI protein is involved
in amyloid deposition in Familial British Dementia and Familial
Danish Dementia, and fusion of BRI to Ab results in enhanced
secretion of Ab-BRI fusion proteins. Expression of Ab42-BRI
resulted in development of amyloid plaques at 3 months post-
injection and injection of a combination of BRI-Ab42 and BRI-
Ab40 vectors resulted in cognitive impairment. The second study
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developed a LV-Ab42 vector, which was injected into the primary
motor cortex of rats . While resulting brain pathology was only
examined at the early post-injection time point of 4 weeks, Ab42
expression resulted in astrogliosis, increased TNF-a expression
and increased tau phosphorylation.
In the present study, recombinant bi-cistronic adeno-associated
viral vectors (rAAV2) were constructed, expressing either human
Ab40, Ab42, C100 or C100V717F. Direct expression of human
Ab40 and Ab42 was performed in an attempt to determine the
individual functions of each of these forms of Ab, while bypassing
the possible confounding functional effects of other APP fragments
such as sAPPa, N-APP, C100 and AICD, which are also produced
during APP processing [8,9,10,11,12]. Viral vectors expressing
C100, the immediate precursor to Ab, with and without the
Indiana mutation (V717F) were also developed in case Ab
expression and/or functional effects were influenced by pro-
duction from a precursor protein. The Indiana mutation results in
preferential production of Ab42 rather than Ab40 [13,14], so this
strategy allowed for the indirect comparison of Ab40 and Ab42 by
comparing the downstream effects of C100 and C100V717F
expression. Each of these rAAV2 vectors was injected into the
adult mouse hippocampus and cerebellum, brain regions that are
vulnerable or relatively spared in AD respectively. rAAV2-GFP
and PBS injections served as controls. A targeted number of
changes associated with increased Ab were examined, including
glial reactivity (both astrogliosis and microgliosis), neuronal
degeneration, blood brain barrier disruption and expression of
apolipoprotein E (apoE), clusterin, synaptophysin and presenilin 1
Materials and Methods
All animal experimentation was approved by the UWA Animal
Ethics Committee and conformed to published NHMRC guide-
Plasmid and rAAV2 Construction
rAAV2 vectors were generated from the pTRUF12 plasmid,
which contains two inverted terminal repeat sequences from AAV
serotype 2, the inserted transgene under the control of the
cytomegalovirus early enhancer-chicken beta actin (CMV-CAG)
promoter and an additional intron sequence with an enhancer
element. Four novel plasmids were generated containing transgene
sequences for Ab40, Ab42, C100 and C100V717F. The pTRUF12
plasmid without an inserted transgene was used as the GFP control
plasmid. An internal ribosome entry site (IRES) allowed the bi-
cistronic expression of the inserted transgene with enhanced GFP
(eGFP), resulting in transgene and GFP production as individual
proteins within each transduced cell. All plasmids were sequenced
to ensure that the transgene sequences were in the correct
orientation and that no unwanted mutations were present.
rAAV2 vectors were produced using a previously described
method . An infection assay of HEK 293T cells was performed
to ensure infectivity and titres were determined by quantitative
PCR (qPCR) for viral genomic copies (GC) extracted from DNase-
ranged from 1.461012
In vitro Transfection
HEK 293T, PC12 (A.T.C.C. CRL-1721) and HeLa cells were
grown to approximately 90% confluency. HEK 293T and HeLa
cells were maintained in DMEM media (Sigma) containing 10%
fetal calf serum, 2 mM L-glutamine (Invitrogen), 100 Units/ml
penicillin (Invitrogen) and 100 mg/ml streptomycin (Invitrogen).
PC12 cells were maintained in DMEM media containing 5% fetal
calf serum, 10% horse serum, 2 mM L-glutamine, 100 Units/ml
penicillin, 100 mg/ml streptomycin and 0.1 mM non-essential
amino acids (Invitrogen). All cell types were transfected using 4 mg
of plasmid DNA and 10 ml of Lipofectamine 2000 (Invitrogen)
according to the manufacturer’s instructions. Cells were examined
for GFP expression 24 and 48 hrs after transfection. Transfection
experiments were performed a minimum of three times for each
Media and cell lysates were collected for Western blot 48 hours
post-transfection. Cells were lysed with RIPA buffer (150 mM
NaCl, 50 mM Tris-HCl, 1% Triton-X100, 0.5% sodium deox-
ycholate, 0.1% SDS, 0.1 mM PMSF). Cell media was immuno-
precipitated for Ab using 6 E10 antibody (Signet) and Gamma-
Bind Plus Sepharose beads (Amersham/GE Healthcare). Western
blot was used to assay GFP, C100 and Ab levels in cell
homogenates and immunoprecipitated media. Briefly, between
25–200 mg of cell homogenate and immunoprecipitated media
was added to SDS loading buffer (166 mM Tris-HCl, 8% sodium
dodecylsulfate, 4% glycine, 2.5% 2-mercaptoethanol, pinch of
phenol red, pH 6.8), boiled at 95uC for 10 min and loaded onto
tris-trycine polyacrylamide gels. Proteins were separated using
electrophoresis and transferred to nitrocellulose membranes at
250 mA overnight at 4uC. Membranes were blocked with 5%
skim milk in TBS for 1 hr at room temperature and immuno-
blotted for GFP (1:3,000; Sigma) and C100/Ab (WO2; 1:2,500;
kindly provided by Professor Colin Masters at University of
Melbourne, Vic, Australia). Membranes were also blotted for b-
actin (1:20,000; Abcam) to ensure consistent protein loading.
Protein bands were detected using enhanced chemiluminescence
(ECL; Amersham Biosciences) and developed onto film. 50 mg of
brain protein homogenate from APPSWEtransgenic mouse brain
was used as a positive control for Ab detection.
Surgery and Tissue Processing
Eight week old male C57Bl6/J mice were anesthetised by an
intraperitoneal (i.p.) injection (10 ml/g) of a 1:1 mixture of
ketamine (100 mg/ml) and xylazine (20 mg/ml) that was diluted
1:10 in sterile saline. Mice were secured in a stereotaxic frame and
a small section of the skull was removed using a dental drill at the
co-ordinates of 1.9 mm rostral and 1.3 mm lateral relative to
lambda. For cerebellar injections a burr hole was drilled at
approximately 1 mm caudal to lambda and 2 mm lateral to the
midline. 1 ml of rAAV2 vector (1012GC/ml) or vehicle (phosphate
buffered saline; PBS, pH 7.4) was directly injected into the
hippocampus (1.5 mm ventral from the dura) and cerebellum
using a pulled glass capillary at a rate of 0.2 ml/min. After each
injection, the glass capillary was left in place for an additional 2
minutes before withdrawal. The skull fragment was then replaced
and the skin closed using 4.0 sutures (Ethilon; Johnson & Johnson,
Australia). After each experimental procedure mice received
a subcutaneous injection of buprenorphine (0.02 mg/kg; Temge-
sic; Reckitt & Colman, Hull, UK) and an intramuscular injection
of Benacillin (25 ml, Troy Laboratories Pty. Ltd. Australia).
The number of animals included in each group and the type of
molecular analysis carried out at 3 months post-injection is shown
in Table 1. Analysis of cerebellar rAAV2-C100-GFP injections
was not possible due to problems with injection and thus consistent
transduction of neurons in the cerebellar cortex. rAAV2-GFP,
rAAV2-C100V717F-GFP and rAAV2-Ab42-GFP were used as
representative groups for further analysis at 6 months post-
AAV Mediated Expression of Beta Amyloid or C100
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For cryosectioning, mice received an overdose of sodium
pentobarbitone (i.p.; Lethabarb, Virbac) and were transcardially
perfused with PBS (pH 7.4) containing 0.1% heparin followed by
4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4). Brains
were post-fixed in 4% paraformaldehyde for 2 hours, cryopro-
tected by sinking in 30% sucrose and incubated in increasing
concentrations of Jung freezing medium, all at 4uC. Brains were
frozen in 100% Jung Freezing medium by immersion into
isopentane on a bed of dry ice and stored at -80uC until
sectioning. Serial coronal cryosections were cut at a thickness of
25 mm for slides 1–13 of each series (for immunohistochemistry)
and a thickness of 14 mm for slides 14–15 of each series (for PCR),
resulting in each slide containing between 5–6 serial sections,
which were approximately 350 mm apart. Every section through
the hippocampus and cerebellum was collected.
For Western blot and ELISA, mice received an overdose of
sodium pentobarbitone (i.p.). The injected hippocampus, contra-
lateral hippocampus, cerebellum and rest of the brain were
collected individually, snap frozen in liquid nitrogen and stored at
280uC until homogenisation. Brain samples were homogenised in
a volume of ice-cold PBS containing protease inhibitor (Roche)
three times the weight of the tissue sample. Total protein was
quantified using the Micro BCA protein assay kit (Pierce) and
samples were stored at 280uC.
Immunohistochemistry and Density Quantification
Primary antibodies used for immunohistochemistry were rabbit
anti-GFP (Millipore; 1:400), rabbit anti-GFAP (Sigma; 1:500),
mouse anti-NeuN (Chemicon; 1:500), rabbit anti-IBA-1 (Wako;
1:1000), rabbit anti-MAP2 (Millipore; 1:500) and rabbit CT20
(Calbiochem; 1:16,000). Secondary antibodies used were anti-
rabbit Alexa 488 (Invitrogen; 1:400), anti-mouse Cy3 (Jackson;
1:300) and anti-rabbit Cy3 (Jackson; 1:300).
For immunohistochemistry, cryosections were washed with
PBS, blocked for 1 hr in blocking buffer (PBS; 10% normal goat
serum; 0.2% Triton-X100) and incubated overnight (4uC) with
primary antibodies diluted in blocking buffer. Sections were
washed with PBS, incubated with secondary antibodies diluted in
blocking buffer for 2 hrs at room temperature, counterstained with
Hoechst 33342 (Sigma; 4 ml/ml in PBS) and coverslipped with
Dako fluorescent mounting media. Images were collected using
a multiphoton laser scanning confocal microscope.
Immunoreactivity for GFAP, IBA-1 and MAP2 was semi-
quantified as staining density in the injected hippocampus and
cerebellum. Low magnification confocal images were collected of
the injected and contralateral hippocampi and cerebellar hemi-
spheres. Three serial sections per brain in each brain region were
analysed, the central section containing the injection site to
maintain consistency between animals. Images were collected
using the lowest magnification that allowed for adequate
visualisation of immuno-positive staining. Thus, GFAP images
were collected at 56magnification, IBA-1 images were collected at
106magnification and MAP2 images were collected at 206mag-
nification. Because of the higher magnification necessary to image
MAP2 staining, images of the hippocampus were collected from
both the dentate gyrus and CA3 to ensure that the entire
transduced region was imaged. Every image for each immuno-
histochemistry stain was collected using the same imaging
GFAP, IBA-1 and MAP2 staining density was quantified using
ImageJ analysis software (NIH). The area for quantification of
hippocampal staining was defined by the hippocampal anatomical
boundaries and density was measured in the injected and
contralateral hippocampi. In the cerebellum the analysis region
was defined by a rectangular area containing the GFP positive
transduced region in the injected hemisphere and the correspond-
ing region of the same area in the contralateral hemisphere. The
staining density of the injected hippocampus and cerebellar
hemisphere was calculated as a percentage of the corresponding
contralateral hippocampus or cerebellar hemisphere and averaged
across three sections per brain region. While it is acknowledged
that injection of rAAV2 vectors could cause distal changes in
contralateral brain regions, which would not be accounted for
using this quantification method, the staining density was
calculated this way in an attempt to standardise staining intensity
across multiple immunohistochemistry runs. Furthermore, general
observation of immunoreactivity in the contralateral hemisphere
showed minimal distal effects and no individual differences
between rAAV2 vectors and vehicle control, suggesting that
contralateral differences would not bias results.
Multiple antibodies against Ab were trialled including; anti-
mouse 6E10 (Signet), anti-rabbit pan Ab (Zymed), anti-mouse 4G8
(Signet) and biotinylated Ab40 and Ab42 antibodies (gifts from Dr.
Pankaj Mehta, NYS Institute for Basic Research, New York,
USA). Extensive optimisation of the immunohistochemistry pro-
tocol was also performed, trialling heat and formic acid antigen
retrieval methods either alone or in combination, multiple
blocking reagents including 10% goat serum, 20% fetal bovine
serum, 0.2% bovine serum albumin and mouse-on-mouse
blocking reagent (M.O.M; Vector Laboratories) and both fluores-
cent and peroxidase immunohistochemistry. Positive control tissue
sections from 18 month old APPSWEtransgenic mice were used in
every Ab immunohistochemistry trial.
IgG Staining and Quantification
Mouse IgG was stained by incubation with anti-mouse
secondary antibodies. Briefly, sections were washed with PBS,
blocked for 1 hr in blocking buffer (PBS; 10% normal goat serum;
0.2% Triton-X100) and incubated with anti-mouse secondary
antibodies diluted in blocking buffer for 2 hrs at room temperature
(anti-mouse Cy3; 1:300; Jackson or anti-mouse FITC; 1:100; MP
Biochem). Sections were counterstained with Hoechst 33342
Table 1. Animal experimental groups used for different
Vector injectedn Post-injection time Analysis techniques
AAV2-C100-GFP4 3 monthsImmunohistochemistry/PCR
AAV2-C100V717F-GFP8 3 months Immunohistochemistry/PCR
AAV2- Ab40-GFP4 3 months Immunohistochemistry/PCR
AAV2- Ab42-GFP4 3 months Immunohistochemistry/PCR
AAV2-GFP73 months Immunohistochemistry/PCR
PBS4 3 monthsImmunohistochemistry/PCR
AAV2-C100V717F-GFP4 3 months Western blot
AAV2- Ab42-GFP43 months Western blot
AAV2-GFP4 3 months Western blot
AAV2-C100V717F-GFP4 6 months Immunohistochemistry/PCR
AAV2- Ab42-GFP4 6 months Immunohistochemistry/PCR
AAV2-GFP46 months Immunohistochemistry/PCR
AAV Mediated Expression of Beta Amyloid or C100
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(Sigma; 4 ml/ml in PBS) and coverslipped with Dako fluorescent
mounting media. Mouse IgG positive cells were identified by their
distinctive morphology of intense circular IgG staining closely
surrounding a nucleus. All mouse IgG positive cells were counted
in three serial sections per brain in the hippocampus and the
cerebellum, with the injection site as the central section for each
For semi-quantitative analysis of IgG staining, we used sections
immunostained for NeuN followed by a Cy3 anti-mouse
secondary antibody. This allowed for consistent intensity grading
of NeuN immunoreactivity versus non-specific IgG staining by
comparing label in the injected hemisphere with the contralateral
hemisphere. IgG staining intensity was graded in all serial sections
through the hippocampus and cerebellum on a scale of 0–3, based
on the relative intensity of extracellular IgG staining to positive
staining in the surrounding densely packed neuronal layers
(including the dentate gyrus, the pyramidal cell layer of CA
regions and the granule cell layer in the cerebellum). Grading
definitions: 0; no excess IgG staining, 1; stronger IgG staining
intensity in neuronal layers than in the surrounding extracellular
space, 2; same IgG staining intensity in the neuronal layers and
extracellular space, 3; stronger IgG staining intensity in the
extracellular space than in neuronal layers.
Total levels of C100, Ab and GFP protein were measured using
the Western blot described above. 200 mg of total protein
homogenate from each brain region was loaded and proteins
were detected using the following primary antibodies; GFP
(1:3,000; Sigma), C100/Ab (6E10; 1:1,000; Signet) and b-actin
Ab40 and Ab42 levels were measured in the injected
hippocampus and cerebellum after injection of rAAV2-GFP,
rAAV2-C100V717F-GFP or rAAV2-Ab42-GFP. Protein was ex-
tracted from tissue samples using a previously published method
designed to maximise the amount of Ab detection using ELISA
. Ab40 and Ab42 levels were quantified using the INNO-BIA
plasma Ab forms test (Innogenetics) according to manufacturer’s
instructions. This kit combines ELISA and multiplex technology to
assay Ab40 and Ab42 levels in the same sample, allowing high
sensitivity detection of Ab using a small volume of sample. All
samples were assayed in triplicate. A small amount of non-specific
background protein detection was observed in the Ab42 assay
results. Therefore, we conservatively deemed that any values that
were greater than two standard deviations outside this background
level to contain significant levels of Ab42.
RNA from the injected hippocampus, contralateral hippocam-
pus and transduced cerebellar hemisphere was extracted from
cryosections adjacent to those used for immunohistochemistry.
Tissue was collected from five serial sections in the hippocampus
and three serial sections in the cerebellum, with the injection site as
the central section in each brain region. Injected and contralateral
hippocampi and the transduced cerebellar hemisphere were
carefully removed from whole brain sections using a scalpel blade
and were collected individually. RNA was extracted from tissue
samples using the FFPE RNeasy miniprep kit (Qiagen) according
to the manufacturer’s instructions and nucleic acid quality was
assessed using a Nanodrop spectrophotometer. Between 300 ng
and 400 ng of RNA was used in reverse transcription reactions
performed using the Quantitect RT kit, which included a genomic
DNA removal step (Qiagen).
Each qPCR reaction was performed using IQ PCR mix
(BioRad) with 2 ml cDNA template, 5 mM of each primer and 1 ml
of sterile water to a final volume of 10 ml, using a RotorGene RG
6000 PCR machine. Primer sequences and specific qPCR
conditions are shown in Table 2. All runs were repeated, and
values for each sample averaged. All PCRs were initially validated
by agarose gel electrophoresis to check product specificity and size,
with correct single bands excised from gels and purified using a Gel
Purification kit (Qiagen) and sequenced using Big Dye Terminator
v3.1 mix (Applied Biosystems) to confirm product identity. L19
and PPIA housekeeping genes were used for qPCR analysis and it
was ensured that normalisation to each of these housekeeping
genes resulted in similar expression patterns.
Table 2. Primers and PCR conditions.
PrimerSequence (5`-3`)Annealing temp (oC)GenBank ID
L19 F *CTGAAGGTCAAAGGGAATGTG 51NM_031103
L19 R * GGACAGAGTCTTGATGATCTC
PPIA F * AGCATACAGGTCCTGGCATC62 BC059141
PPIA R * TTCACCTTCCCAAAGACCAC
Transgene FTTGCAGAAGATGTGGGTTCA59 N/A
Transgene R GGTACCGCAATACCGGAGTA
Synaptophysin F CTGGCCACCTACATCTTCCT58 NM_009305
Synaptophysin R CCACATGAAAGCGAACACTG
Clusterin F TATGCACGTGTCTGCAGGAG58 NM_013492
Clusterin R CGCCGTTCATCCAGAAGTAG
ApoE FAACCGCTTCTGGGATTACCT 58 NM_009696.3
ApoE R AGCTGTTCCTCCAGCTCCTT
PS-1 F CACCCCATTCACAGAAGACA58 NM_008943
*denotes reference gene.
AAV Mediated Expression of Beta Amyloid or C100
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All statistics were performed using SPSS (Version 17). Two-
tailed independent t-tests were initially used to determine if there
was a significant difference between PBS and AAV2-GFP control
groups in each brain region for all measures. The Levene’s test for
equality of variances was also performed to ensure normality of the
distribution and to test the equality of variances assumption. As
there was no difference observed between brain regions injected
with PBS and rAAV2-GFP for any measure, rAAV2-GFP was
used as the only control group for all further analysis, as this was
the most appropriate control for comparison with experimental
rAAV2 vectors. Univariate, one-way ANOVA was used when
comparing more than two groups and the Bonferroni post-hoc test
was used to determine individual significant differences between
groups. The non-parametric Kruskal-Wallis Test was used to
perform statistics on the intensity grading results from IgG
staining. In all cases p,0.05 was deemed significant.
In vitro Production of C100 and Ab
To confirm that rAAV2 transgenes were translated into protein,
HEK 293T, PC12 and HeLa cells were transfected with C100-
GFP, C100V717F-GFP, Ab40-GFP and Ab42-GFP plasmids.
Strong GFP protein expression was observed using microscopy
and Western blot (Figure 1A), indicating that transfection with all
plasmids was successful in each cell type. Transfection with C100-
GFP and C100V717F-GFP plasmids resulted in abundant in-
tracellular C100 protein expression (Figure 1A). Immunohisto-
chemistry using the 6E10 antibody confirmed that C100 protein
was only present in GFP-positive transfected cells, with immuno-
positive staining observed throughout the cytoplasm in a punctate
pattern (data not shown).
No intracellular Ab protein could be detected using Western
blot (Figure 1A) or immunohistochemistry after transfection with
all plasmids, in any cell type. Immunoprecipitation of Ab from the
media of transfected cells showed that Ab was secreted from cells
transfected with C100-GFP and C100V717F-GFP plasmids, but we
did not detect any secreted Ab from cells transfected with Ab40-
GFP and Ab42-GFP plasmids (Figure 1B).
In vivo Transduction of Hippocampus and Cerebellum
GFP and rAAV2-Ab42-GFP vectors were injected into the
hippocampus and cerebellum of 8 week old wild-type male mice.
Transduction and resulting pathology was examined at 3 and 6
months post-injection. Injection of all AAV2 vectors resulted in
wide-spread transduction in both brain regions, as shown by
strong GFP expression (Figure 2A–C). Transduction efficiency
appeared similar at 3 and 6 months post-injection.
Hippocampal injection resulted in transduction of all major
hippocampal sub-regions including the dentate gyrus (Figure 2G–
I), CA regions of Amon’s horn (Figure 2D–F) and the subiculum.
There was also evidence of anterograde and retrograde transport
of rAAV2 and/or GFP as a result of hippocampal injection, as
shown by GFP expression in brain regions distant from the
injection site including the entorhinal cortex, contralateral
hippocampus (Figure 2J–L) and the anterior cingulate area of
the cerebral cortex. Hippocampal rAAV2 injection resulted in
transduction across a distance of up to 2.5 mm in the rostro-caudal
Injection into the cerebellar cortex predominantly resulted in
transduction of Purkinje cells (Figure 2M–O), while transduction
was also observed in the granule cell layer to a lesser extent. There
was also evidence of anterograde and retrograde transport of
rAAV2 and/or GFP with GFP expression observed in the deep
cerebellar nuclei, the granule cell layer of the contralateral
cerebellar cortex and in the external cuneate nucleus in the
medulla. Cerebellar AAV2 injection resulted in transduction
across a distance of up to 1.75 mm in the rostral-caudal plane.
All AAV2 vectors specifically transduced neurons in both the
hippocampus and cerebellum, which was determined by mor-
phology and by co-localisation with neuronal markers NeuN (for
examples see Figure 2F, I, L, O) and MAP2 (data not shown).
Furthermore, there was no co-localisation of GFP with GFAP or
IBA-1, markers of astrocytes and microglia respectively, indicating
that glia were not transduced by rAAV2 vectors (data not shown),
a finding supported by previous studies .
To ensure that transduced brain regions also expressed the
transgenes for the desired APP fragments in addition to GFP,
qPCR was used to quantify C100-GFP, C100V717F-GFP, Ab40-
GFP and Ab42-GFP transgene mRNA levels in the injected
Figure 1. C100 and Ab protein production in vitro after plasmid
transfection. Analysis of C100 and Ab protein production in vitro after
transfection with plasmids expressing Ab40-GFP, Ab42-GFP, C100-GFP
or C100V717F-GFP in cell homogenates (A) and media (B). C100 protein
was only detected in cell homogenates after transfection with C100-
GFP and C100V717F-GFP plasmids. No Ab was detected in cell
homogenates after transfection with any plasmid. APPSWEbrain
homogenate was used as a positive control for Ab detection. Strong
GFP protein expression indicated successful transfection using all
plasmids and b-actin was used as a loading control. Immunoprecipi-
tation of Ab from the cell culture media revealed Ab in the media from
cells transfected with C100-GFP and C100V717F-GFP plasmids. Control
refers to non-transfected cells.
AAV Mediated Expression of Beta Amyloid or C100
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Figure 2. Transduction in the hippocampus and cerebellum as indicated by GFP expression. Low magnification images show widespread
GFP protein throughout the hippocampus (A) and cerebellar cortex (C). GFP protein was also observed in the contralateral hippocampus (B). Double
AAV Mediated Expression of Beta Amyloid or C100
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hippocampus, contralateral hippocampus and the injected cere-
bellar hemisphere. RNA was extracted from fixed cryosections
adjacent to those used for immunohistochemistry and GFP
localisation. Strong mRNA expression of the human APP
fragments was observed in transduced regions of the hippocampus
and cerebellum at 3 and 6 months post-injection in all mice
injected with C100 and Ab transgenes (Figure 3A). There was also
lower, but detectable expression of C100 and Ab mRNA in the
contralateral hippocampus, providing evidence for retrograde
transport of rAAV2 vectors and not just GFP protein. This finding
supports previous studies that have shown neurons can transport
AAV particles by retrograde axonal transport and that AAV then
has the capability to express transgenes in distal brain regions
[18,19]. There was qualitatively similar transgene mRNA
expression in the hippocampus and cerebellum, indicating a similar
level of transduction in both brain regions. Importantly, no human
Ab or C100 mRNA expression was observed in any brain region
of mice injected with rAAV2-GFP or PBS.
Human C100 and Ab protein expression was also examined
using Western blot and immunohistochemistry. C100 immuno-
positive staining was observed throughout the cytoplasm and in
primary processes of transduced neurons in the hippocampus and
cerebellum (Figure 3B–G). C100 protein was also detected using
Western blot in hippocampal and cerebellar tissue injected with
rAAV2-C100V717F-GFP (Figure 3H). In contrast, Ab could not be
detected in either transduced brain region using immunohisto-
chemistry trialling multiple antibodies against Ab or Western blot
after injection with any rAAV2 vector (data not shown). These
results led to the hypothesis that Ab may be present at very low
levels and hence undetectable using Western blot or immunohis-
tochemistry. Therefore, the high sensitivity INNO-BIA plasma Ab
forms test was used to measure Ab40 and Ab42 levels in the
injected hippocampus and cerebellum. Ab42 was detected in
cerebellar tissue from every animal injected with rAAV2-
C100V717F-GFP, with Ab42 levels on average 5.964.3 (6
standard deviation) fold higher than baseline levels. Ab42 protein
was also present in the cerebellum of one of the four animals
injected with rAAV2-Ab42-GFP, this animal having Ab42 levels
that were 3.3 fold higher than baseline levels. Ab42 protein was
also detected in the hippocampus from animals injected with
either rAAV2-C100V717F-GFP or rAAV2-Ab42-GFP but Ab42
protein levels did not reach the two standard deviation criterion
relative to baseline. It is important to note that, because the same
viral vectors were injected into each brain region, the lack of
definitive detection of Ab42 in the hippocampus suggests that
Ab42 may be processed differently in each brain region.
Significant levels of Ab40 were not found in the cerebellum or
hippocampus after injection of either rAAV2-C100V717F-GFP or
rAAV2-Ab42-GFP, although a relatively high level of Ab40
protein expression was seen in hippocampal tissue from one
rAAV2-C100V717F-GFP injected animal. The inter-animal varia-
tion in the amount of Ab detected, and the differences in Ab levels
between the cerebellum and hippocampus, leads to speculation
that Ab was produced but was then degraded or cleared after
production, resulting in overall low levels available for detection in
the murine brain samples.
Immuno-positive staining density of the microglial marker IBA-
1 was analysed to determine the extent of microgliosis following
injection of rAAV2 vectors. This analysis technique was designed
to examine wide-spread microgliosis across the whole transduced
region. IBA-1 positive microglia in areas of gliosis showed
morphological signs of activation including enlarged cell bodies,
ramified processes and increased IBA-1 staining within individual
microglia (Figure 4G, K).
In the hippocampus, injection of rAAV2-C100V717F-GFP and
rAAV2-Ab42-GFP resulted in significantly higher IBA-1 staining
density at 3 months post-injection than that observed after
rAAV2-GFP injection (Bonferroni; p,0.001 and p,0.01 re-
spectively), while there was no significant difference in IBA-1
staining density between hippocampi injected with rAAV2-C100-
GFP or rAAV2-Ab40-GFP and rAAV2-GFP (Figure 4A, E, I, M).
Microgliosis remained significantly higher in the hippocampus at 6
months post-injection with rAAV2-Ab42-GFP than after injection
of rAAV2-GFP (Bonferroni; p,0.01, Figure 4M).
In the cerebellum, injection of rAAV2-Ab42-GFP also resulted
in a significantly greater level of microgliosis at 3 months post-
injection than after injection of rAAV2-GFP (Bonferroni; p,0.05;
Figure 4N). Microgliosis was no longer elevated at 6 months post-
injection. Therefore, combined results from the hippocampus and
cerebellum suggest that microgliosis was strongly associated with
Ab42 rather than Ab40 expression, as it was most extensive after
injection with rAAV2-Ab42-GFP and rAAV2-C100V717F-GFP.
Astrogliosis and Neuronal Density
Ab expression has been associated with astrogliosis and
neuronal death, therefore the extent of astrogliosis and neuronal
density were examined using immunohistochemistry for GFAP
and MAP2 respectively. Quantification of GFAP staining density
showed that while there was some evidence of increased astrocyte
activation surrounding the injection site in both brain regions
following injection of rAAV2-C100-GFP, rAAV2-C100V717F-
GFP, rAAV2-Ab40-GFP and rAAV2-Ab42-GFP in comparison
to after injection of rAAV2-GFP or PBS, this increase was not
extensive enough to be significantly different at either 3 or 6
months post-injection (data not shown). Quantification of MAP2
staining density showed that neuronal density was not altered in
the hippocampus or cerebellum as a result of injection of any
rAAV2 vector at either 3 or 6 months post-injection (data not
Permeability of the Blood Brain Barrier
An unexpected consequence of injection with rAAV2 vectors
was the presence of increased mouse IgG staining around the
injection site, first detected after immunohistochemistry using anti-
mouse secondary antibodies. Further testing showed that the
increased IgG staining was observed when sections were incubated
only with anti-mouse secondary antibodies, was localised to
transduced brain regions, and was not observed after injection
with PBS, therefore showing that it was not a technical artefact of
the immunohistochemistry procedure.
Increased IgG staining was observed in the hippocampus and
cerebellum after injection of rAAV2 vectors expressing APP
fragments, but not after injection of rAAV2-GFP or PBS (Figure 5).
The relative extracellular IgG staining intensity was graded in the
immunostaining for GFP (green) and NeuN (red) revealed that neurons were specifically transduced (D–O). Merged images (F, I, L, O) also show
Hoechst counterstaining. Neurons in many hippocampal sub-regions were transduced including Amon’s horn (D–F) and dentate gyrus (G–I). GFP
was observed in Purkinje cells and other neurons in the cerebellum (M–O). Scale bar =500 mm (A–C) and 50 mm (D–O).
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hippocampus and cerebellum after immunohistochemistry for
NeuN, using the IgG staining intensity of the surrounding densely
packed neuronal layers as the staining intensity comparison. IgG
staining intensity in the hippocampus at 3 months post-injection
was significantly higher after injection of rAAV2-C100-GFP
(Kruskal-Wallis; p=0.009), rAAV2-C100V717F-GFP (Kruskal-
p=0.016) than after injection of AAV2-GFP. There was also
a non-significant trend for increased IgG staining in the
hippocampus after injection of rAAV2-Ab40-GFP than after
injection of AAV2-GFP at 3 months post-injection (Kruskal-
Wallis; p=0.056). Similarly, IgG staining intensity in the
cerebellum was significantly higher at 3 months post-injection
with rAAV2-C100V717F-GFP (Kruskal-Wallis; p=0.014), rAAV2-
Ab40-GFP (Kruskal-Wallis; p=0.014) and rAAV2-Ab42-GFP
(Kruskal-Wallis; p=0.013) than after injection with rAAV2-GFP.
In contrast, IgG staining intensity was no longer significantly
elevated at 6 months post-injection with any rAAV2 vector in
either the hippocampus or cerebellum, indicating that the
increased IgG in the brain decreased with time.
Staining for mouse IgG also strongly labelled small, round cells
that were predominantly observed in transduced regions of the
hippocampus and cerebellum (Figure 6-A–C). Immunohistochem-
istry revealed that these IgG positive cells were also immunopo-
sitive for IBA-1 (Figure 6D–G), a calcium binding peptide
produced specifically by monocytes and activated microglia .
The number of IgG positive cells was counted and averaged across
three serial sections in the hippocampus and cerebellum. The vast
majority of IgG positive cells were observed throughout the
injected hippocampus and cerebellum and in the lateral ventricles
adjacent to the injected hippocampus, with a small number of cells
also observed in the contralateral hemispheres in both brain
regions. Almost no IgG positive cells were seen after control PBS
injections. 3 months post-injection, there were significantly more
IgG positive cells in the hippocampus after injection with rAAV2-
C100-GFP, rAAV2-C100V717F-GFP and rAAV2-Ab42-GFP than
p,0.001). In comparison, while the number of IgG positive cells
in hippocampi at 3 months post-injection with rAAV2-Ab40-GFP
was higher than after rAAV2-GFP injection, this difference was
not statistically significant. There was no longer a significant
difference between groups in the number of IgG positive cells in
the hippocampus at 6 months post-injection (Figure 6H).
The number of IgG positive cells was also increased in the
cerebellum after injection with rAAV2 vectors containing APP
fragments, but high inter-animal variation meant that these
increases were not statistically significant at 3 months post-
injection (Bonferroni; Figure 6I). However, analysis using the less
stringent LSD post-hoc test found that injection with rAAV2-
C100V717F-GFP resulted in significantly more infiltrating cells than
injection with rAAV2-GFP (LSD; p=0.049). This effect was still
observed at 6 months post-injection (Bonferroni; p,0.05).
PS1, apoE, clusterin and synaptophysin gene expression was
examined in the injected hippocampus, contralateral hippocampus
and injected cerebellar hemisphere at 3 and 6 months post-
injection. ApoE and clusterin expression was also examined to
determine if expression of genes involved in Ab clearance was
altered . Synaptophysin is a synaptic protein marker and was
therefore examined as an additional marker of neurodegeneration
and PS1 expression was examined to determine if C100 mediated
endogenous PS1 expression, hence altering production of Ab.
Altered levels of each of these genes and the resulting proteins have
also been previously associated with AD [22,23,24,25]. Differences
in gene expression between groups were only deemed significant if
the statistical difference was consistently observed after normal-
isation to two housekeeping genes; L19 and PPIA. It was found
that there was not a significant difference in expression of any gene
examined as a result of injection of any vector at 3 or 6 months
post-injection in either the hippocampus or cerebellum.
Injection of rAAV2 vectors expressing transgenes for human
Ab40, Ab42, C100 and C100V717Finto the mouse hippocampus
and cerebellum resulted in wide-spread transduction in both brain
regions and the development of some pathological changes
characteristic of AD, most notably increased microgliosis and
increased permeability of the blood brain barrier.
Injection of rAAV2-Ab42-GFP and rAAV2-C100V717F-GFP in
the hippocampus resulted in significantly increased IBA-1 density
at 3 months post-injection, while injection of rAAV2-Ab40-GFP
and rAAV2-C100-GFP did not, suggesting that Ab42 may be
a more potent mediator of microgliosis than Ab40. It is known that
Ab attracts and causes activation of microglia [26,27], but it has
been previously suggested that this may only occur in response to
fibrillar Ab [1,28,29,30]. The association between fibrillar Ab and
microgliosis is further supported by the fact that the onset of gliosis
in AD transgenic mice is closely linked to the onset of plaque
deposition [31,32], and manipulating the amount of plaque
deposition results in similar changes in the extent of microgliosis
[33,34,35]. However, the results from this study suggest that
microgliosis can also occur in response to soluble forms of Ab, as
no plaques were observed after injection of any rAAV2 vector.
The rAAV2 vectors used in this study also resulted in pathology
indicative of increased permeability of the blood brain barrier,
which was most extensive in the hippocampus at 3 months post-
injection. Injection of rAAV2 vectors into the hippocampus
resulted in increased brain IgG and increased numbers of IgG/
IBA-1 positive cells. IgG cannot cross the blood brain barrier and
is only found in the brain under pathological conditions . As
a result, IgG is a well established marker of blood brain barrier
permeabilisation and has been shown to be a good alternative to
other markers of blood brain barrier disruption such as Evans blue
dye staining [37,38,39,40,41]. Cells with similar morphology to
the IgG positive cells observed in this study have been
characterised previously and a large number of these cells is also
a common marker of blood brain barrier disruption . Previous
studies have suggested that these cells are leukocytes and as the
cells observed in this study were also immuno-positive for IBA-1,
this suggests that they were leukocytes of monocyte-macrophage
lineage , in agreement with previous studies [37,44].
In the hippocampus at 3 months post-injection, blood brain
barrier disruption was more extensive after exposure to Ab42, via
Figure 3. Ab and C100 mRNA and protein expression in the hippocampus and cerebellum. mRNA for Ab and C100 transgenes was
detected using PCR (A). Immunostaining for C100 using CT20 antibody revealed C100 protein in GFP positive neurons (B–G). C100 protein was also
detected using western blot (H). HIP (INJ): injected hippocampus, HIP (CONTRA) contralateral hippocampus, CB: cerebellum, ROB: rest of the brain.
Lanes 1, 4, 7, 10; representative brain injected with AAV2-C100V717F-GFP, lanes 2, 5, 8, 11; representative brain injected with AAV2-Ab42-GFP, lanes 3,
6, 9, 12; representative brain injected with AAV2-GFP.
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expression of Ab42 directly or the C100 and C100V717F
precursors. In comparison, while IgG staining intensity and
numbers of infiltrating cells after injection with rAAV2-Ab40-
GFP were elevated, these changes were not significantly different
from that observed after injection with rAAV2-GFP. Blood brain
barrier disruption is a pathological feature of AD [45,46] and
previous studies have hypothesised that it may be directly caused
by Ab [42,47,48]. The results from this study not only support the
hypothesis that Ab expression may directly cause blood brain
barrier disruption, but also suggest that Ab42 may be a more
potent mediator of blood brain barrier disruption than Ab40.
Injection of rAAV2 vectors did not induce widespread
astrogliosis or altered neuronal density in either the hippocampus
or cerebellum. Activation of astrocytes in response to Ab
expression was observed to some extent, however it was primarily
localised to the injection site, in contrast to the more extensive
microgliosis. Previous studies have found Ab to cause activation
and migration of astrocytes [49,50,51]. However, it has also been
shown that the activation of astrocytes in AD is dependent upon
the conformation and aggregation state of Ab; astrocytes
surrounding dense core plaques become activated, while astrocytes
surrounding diffuse plaques or those not associated with aggre-
gated Ab do not show signs of activation and can often show signs
of atrophy [52,53]. Therefore, it is possible that the lack of
extensive astrogliosis observed in this study was due to the lack of
aggregated, fibrillar Ab following injection of viral vectors. The
lack of widespread neurodegeneration observed in this study is
consistent with previous studies that have shown that Ab is not
a potent mediator of neurodegeneration in vivo . It is now
becoming more accepted that tau hyperphosphorylation and the
development of neurofibrillary tangles is more likely to be
a mediator of neurodegeneration in AD than Ab [55,56,57]. It
is interesting that synaptophysin mRNA levels were unaffected as
Ab, particularly soluble oligomers of Ab, has been shown to
decrease expression of synaptic markers, including synaptophysin
[32,58,59,60,61]. However, this finding is not consistent across all
studies [62,63], indicating that decreased synaptophysin expres-
sion may not be a direct consequence of Ab expression and that
other additional factors may be necessary. It is important to note
that only gross neurodegeneration would have been observed by
the quantification measures used in this study and that the use
other neuronal and cell death markers may have provided a more
specific indication of neurodegeneration.
Western blot and immunohistochemical processing failed to
detect significant Ab40 and Ab42 protein expression in transduced
brain regions. We do not believe that this was due to the use of
inefficient viral vectors because Ab42 was detected in tissues
injected with rAAV2-C100V717F-GFP or rAAV2-Ab42-GFP using
the more sensitive ELISA technique, thus proving that these
vectors were capable of producing Ab. Furthermore, there was
strong transduction of all bi-cistronic rAAV2 vectors in the
hippocampus and cerebellum, as shown by high expression levels
Figure 4. Immunostaining of microglia using IBA-1 antibody. Representative figures show microglial staining at low (A–B, E–F, I–J) and high
magnification (C–D, G–H, K–L) in injected (INJ) and contralateral (CONTRA) hippocampi at 3 months post-injection with AAV2-GFP (A–D), AAV2-
C100V717F-GFP (E–H) and AAV2-Ab42-GFP (I–L). IBA-1 staining density was quantified in the hippocampus (M) and cerebellum (N) at 3 and 6 months
post-injection. Data shown as density of injected region as a percentage of the corresponding contralateral region and is presented as mean 6
standard deviation. ***p,0.001, **p,0.01, *p,0.05. Scale bar =300 mm (A–B, E–F, I–J) and 20 mm (C–D, G–H, K–L).
Figure 5. Increased mouse IgG staining in the hippocampus and cerebellum. Example images show normal IgG staining following
immunohistochemistry for NeuN after AAV2-GFP injection (A–D) and intense IgG staining after injection of AAV2-Ab42-GFP (E, G). Increased IgG
staining was only observed surrounding the injection site and not in the contralateral hemisphere (F, H). INJ; injected region, CONTRA; contralateral
region. Scale bar =500 mm.
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Figure 6. IgG positive cells in the hippocampus and cerebellum. Mouse IgG positive cells (red) were frequently observed in the hippocampus
(B) and cerebellum (C) after injection with AAV2-Ab40-GFP, AAV2-Ab42-GFP, AAV2-C100-GFP and AAV2-C100V717F-GFP in comparison to after AAV2-
GFP injection (A). Sections were counterstained with Hoechst (blue). Inserts show distinctive morphology of IgG positive cells. High magnification
images of mouse IgG positive cells co-labelled with IBA-1 are shown in D–G (D: IgG staining, E: IBA-1 staining, F: Hoechst, G: merged image). The
total number of IgG positive cells was counted in 3 sections per brain in both the hippocampus (H) and cerebellum (I) in the injected hemisphere at 3
and 6 months post-injection. Scale bar =200 mm (A–C) and 10 mm (D–G). INJ: injected hemisphere, CONTRA: contralateral hemisphere, ***p,0.001,
AAV Mediated Expression of Beta Amyloid or C100
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of transgene mRNA and post-IRES GFP protein, the latter
produced only after C100 or Ab protein translation. Finally,
injection of rAAV2-Ab40-GFP and rAAV2-Ab42-GFP resulted in
the development of obvious brain pathology that was unique to
each Ab isoform and was not present after injection of vehicle or
rAAV2-GFP controls, strongly suggesting that the Ab produced as
a result of rAAV2 vector injection was responsible for the observed
pathologies. We hypothesise that the inability to detect Ab using
the less sensitive immunohistochemistry and western blotting
methods, and the observation of variance between animals in the
amount of Ab detected using ELISA, was due to rapid clearance
and/or degradation of Ab. Ab levels are highly regulated in vivo by
rapid clearance across the blood brain barrier, phagocytosis by glia
and degradation by multiple enzymes. Enhancement of any of
these mechanisms could result in low Ab levels. Indeed, some of
the pathology observed in vivo including microgliosis and in-
filtration of cells from the periphery indicate that Ab degradation
may have been increased in response to expression of Ab as both
microglia and infiltrating monocytes are capable of Ab phagocy-
tosis and enhance degradation [44,64,65,66,67,68]. Increased Ab
clearance may also explain the lack of Ab40 detected using the
ELISA-mutiplex assay, as this isoform is more readily cleared and
degraded than Ab42 [69,70]. Furthermore, the Indiana mutation
promotes the preferential production of Ab42 rather than Ab40,
therefore the presence of this mutation and the hypothesised
increased clearance of Ab could account for the very low levels of
Ab40 observed after injection of rAAV2-C100V717F-GFP. Lack of
available tissue prevented ELISA-based quantification of Ab40
levels after injection of rAAV2-Ab40-GFP.
An intriguing finding was that, while significant levels of Ab42
protein were detected in the cerebellum but not in the
hippocampus, injection of rAAV2 vectors into the hippocampus
resulted in greater pathological changes than those seen in the
cerebellum. Why there was this apparent paradox of increased
Ab42 but reduced pathology in the cerebellum is not clear, but
these observations do suggest that there are differences in the way
different brain regions process and respond to C100 and/or Ab.
Previous studies have tried to determine why the cerebellum is less
vulnerable to AD pathology. It has been shown that the
cerebellum contains all of the necessary proteins to produce Ab
[71,72], and that plaques do eventually appear in the cerebellum
as AD pathology advances , indicating that the cerebellum is
capable of producing amyloid pathology. Nonetheless, the
cerebellum consistently has fewer plaques and lower levels of
insoluble Ab and intracellular Ab42 [73,74,75] than other brain
regions that are primarily affected in AD such as the hippocampus
and cortex. It seems that the cerebellum is better equipped to
prevent AD pathology from progressing. A recent study reported
that secreted metabolites produced from cerebellar neurons
reversed AD brain pathology in AD transgenic mice, while
metabolites from hippocampal neurons exacerbated pathology
. The exact proteins or pathways involved in the protection of
the cerebellum in AD are not yet known, but it has been suggested
that this may be specifically due to enhanced clearance or
degradation of Ab [77,78]. The present data suggest an alternative
hypothesis, that cerebellar cells may be intrinsically less responsive
to the presence of Ab and/or C100. Future research is needed to
further examine why AD brain pathology develops differently in
different brain regions as this could help determine what initiates
the development of AD brain pathology.
Vectors expressing the C100 transgene were more effective at
consistently producing higher amounts of Ab than vectors directly
expressing Ab transgenes, both in vitro and in vivo. This most likely
resulted from the more physiological method of production of Ab
from C100, in comparison to the non-physiological production by
direct expression of either Ab40 or Ab42. Direct expression of Ab
may not be optimal for Ab accumulation, possibly due to Ab
production occurring in the incorrect sub-cellular location.
Previous in vitro studies have shown that fusing Ab and C100 to
a signal protein that directs expression in the secretory pathway
greatly increases the amount of Ab detected after plasmid
transfection [79,80], hence suggesting that sub-cellular location
of Ab may be important for expression.
A further aim of this study was to determine if the effects of
transduction with rAAV2 vectors expressing APP fragments were
exacerbated at 6 months post-injection in comparison to 3 months
post-injection. This was not found to be the case in either brain
region as less extensive pathological changes were observed at 6
months post-injection. The level of transduction was similar at 3
and 6 months post-injection, therefore the less extensive pathology
observed at 6 months post-injection is unlikely to be a result of any
technical issues associated with long-term transduction. Instead, it
is possible that brain regions may have adapted to the long-term
expression of C100 and/or Ab and as a result became better
equipped to deal with the consequent pathology, such as by
increasing levels of Ab degrading enzymes or increasing anti-
inflammatory proteins. However, further studies are necessary to
confirm this hypothesis.
In conclusion, the use of viral vectors to over-express Ab and
C100 is a promising technique with which to examine the
consequences of Ab expression in mature CNS tissues in vivo.
Results from this study provide evidence that Ab42 causes greater
pathology than Ab40, particularly by promoting microgliosis and
inducing abnormal permeability changes in the blood brain
The authors thank Karl De Ruyck for his assistance performing ELISA.
The authors acknowledge the facilities, scientific and technical assistance of
the Australian Microscopy & Microanalysis Research Facility at the Centre
for Microscopy, Characterisation & Analysis, The University of Western
Australia, a facility funded by the University, State and Commonwealth
Conceived and designed the experiments: ESD RNM ARH. Performed
the experiments: ESD JM EME LKW. Analyzed the data: ESD.
Contributed reagents/materials/analysis tools: ARH RNM. Wrote the
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