bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
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Choline supplementation in early life improves and low levels of choline
can impair outcomes in a mouse model of Alzheimer’s disease.
Elissavet Chartampila1,2, Karim S. Elayouby1,3, Paige Leary1,4, John J.
LaFrancois1,5, David Alcantara-Gonzalez1,5, Swati Jain1, Kasey Gerencer1,6,
Justin J. Botterill1,7, Stephen D. Ginsberg1,4,8,9, and Helen E. Scharfman1,4,5,8,9
1Center
for Dementia Research
The Nathan Kline Institute for Psychiatric Research
Orangeburg, NY 10962
2 Current
address:
Department of Cell Biology and Physiology
University of North Carolina
Chapel Hill, NC 27510
3Current
address:
Department of Neurology
Mount Sinai School of Medicine
New York, NY 10029
4Department
of Neuroscience and Physiology
New York University Grossman School of Medicine
New York, NY 100016
5Departments
of Child and Adolescent Psychiatry
New York University Grossman School of Medicine
New York, NY 10016
6Current
address:
Department of Psychology
University of Maine
Orono, ME 04469
7Current
address:
Department of Anatomy, Physiology, & Pharmacology
College of Medicine
Saskatoon, SK S7N 5E5
8Department
of Psychiatry
New York University Grossman School of Medicine
New York, NY 10016
9NYU
Neuroscience Institute
New York University Grossman School of Medicine
New York, NY 10016
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Address for correspondence:
Helen E. Scharfman
Center for Dementia Research
The Nathan Kline Institute for Psychiatric Research
Orangeburg, NY 10962
Key words: dementia, maternal choline supplementation, hippocampus, dentate
gyrus, hilus, interictal spike, novel object location, novel object recognition
Word count:
Abstract: 250
Introduction: 726
Discussion: 1705
Number of figures: 7
Number of supplemental figures: 4
Acknowledgements:
Supported by NIH R01 AG055328 (HES, SDG), MH109305 (HES) and
AG077103 (SDG) and the New York State Office of Mental Health (HES, JJL).
We thank Dr. Christos Lisgaras for comments on the manuscript and Dr. Korey
Kam for contributions at an early stage of this project.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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ABSTRACT
Maternal choline supplementation (MCS) improves cognition in Alzheimer’s
disease (AD) models. However, effects of MCS on neuronal hyperexcitability in
AD are unknown. We investigated effects of MCS in a well-established mouse
model of AD with hyperexcitability, the Tg2576 mouse. The most common type of
hyperexcitability in Tg2576 mice, and many other mouse models and AD
patients, are generalized EEG spikes (interictal spikes; IIS). Hyperexcitability is
also reflected by elevated expression of the transcription factor ∆FosB in the
principal cells of the dentate gyrus (DG), granule cells (GCs). We also studied
the hilus of the DG because hilar neurons regulate GC excitability. We found
reduced expression of the neuronal marker NeuN within hilar neurons in Tg2576
mice, which other studies have shown is a sign of oxidative stress or other
pathology.
Tg2576 breeding pairs received a diet with a relatively low, intermediate or
high concentration of choline. After weaning, all mice received the intermediate
diet. In offspring of mice fed the high choline diet, IIS frequency declined, GC
∆FosB expression was reduced, and NeuN expression restored. Spatial memory
improved. In contrast, offspring exposed to the relatively low choline diet had
several adverse effects, such as increased mortality. The results provide new
evidence that a diet high in choline in early life can improve outcomes in a mouse
model of AD, and relatively low choline can have negative consequences. This is
the first study showing that dietary choline can regulate hyperexcitability, hilar
neurons, and spatial memory in an animal model of AD.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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I. INTRODUCTION
Diet has been suggested to influence several aspects of brain health. One
dietary intervention that has been studied extensively in rodents and humans is
supplementation of the maternal diet with the nutrient choline, (maternal choline
supplementation; MCS). MCS improves many aspects of brain health in humans
(Zeisel & da Costa 2009, Jiang et al. 2014). In normal rats, MCS also is
beneficial, with numerous studies showing improved behavior in the adult
offspring (for review, see (for review see Meck & Williams 2003)).
In Alzheimer’s disease (AD), changes to the diet have been recommended
(Bourre 2006, Power et al. 2019, Mao et al. 2021, Lobo et al. 2022), including
MCS (Strupp et al. 2016, Velazquez et al. 2020). The recommendation to use
MCS is based primarily on data from the Ts65Dn mouse model of Down
syndrome (DS) and AD, where MCS led to improved memory and attention in
Ts65Dn offspring (Strupp et al. 2016, Powers et al. 2017, Powers et al. 2021). In
addition, degeneration of basal forebrain cholinergic neurons (BFCNs) in Ts65Dn
mice, a hallmark of DS and AD, was reduced (Kelley et al. 2016, Powers et al.
2017).
Based on the studies of Ts65Dn mice, we asked if MCS would improve
another impairment that has been found in AD patients and mouse models of
AD, hyperexcitability. We chose to study Tg2576 mice because hyperexcitability
is robust, and BFCNs are likely to play a role (Kam et al. 2016, Lisgaras &
Scharfman 2023). In our past work, the primary type of hyperexcitability was
interictal spikes (IIS), which are named because they occur in between seizures
(ictal events) in epilepsy. They are studied by EEG. We also studied
hyperexcitability using ΔFosB expression, a transcription factor that is increased
when neurons have been highly active over the prior 10-14 days (McClung et al.
2004). We studied ΔFosB in granule cells (GCs) of the dentate gyrus (DG),
because numerous ΔFosB-expressing GCs occur when there are IIS (You et al.
2017, You et al. 2018).
We also asked if behavior would improve if MCS reduced IIS frequency in
Tg2576 mice. The basis for this question is in studies of epilepsy, where IIS
disrupt cognition (Rausch et al. 1978, Aarts et al. 1984, Holmes & Lenck-Santini
2006, Kleen et al. 2010, Kleen et al. 2013, Gelinas et al. 2016) . Also, IIS in the
Tg2576 mouse start early in life (by 1 month of age), before memory impairment,
which occurs at 3-4 months of age (Duffy et al. 2015). Therefore, IIS might
disrupt activity sufficiently to promote behavioral impairments. We previously
found that the novel object location (NOL) task is impaired at 3-4 months of age
in Tg2576 mice (Duffy et al. 2015), so we evaluated NOL, and a related task,
novel object recognition (NOR; Vogel-Ciernia & Wood 2014). We also studied
expression of NeuN, a neuronal marker that is reduced in numerous disease
conditions (Buckingham et al. 2008, Kadriu et al. 2009, Matsuda et al. 2009,
Duffy et al. 2011, Duffy et al. 2015). Here we report loss of NeuN-ir in the DG
hilus of Tg2576 mice, which is important because impaired hilar neurons could
cause GC hyperexcitability (Sperk et al. 2007, Scharfman & Myers 2012).
We fed dams one of three diets, which were relatively low, intermediate or
high in choline. The high choline diet provided levels of choline similar to other
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
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studies of MCS in rodents (Meck et al. 1988, Loy et al. 1991, Holler et al. 1996,
Meck & Williams 1999, Sandstrom et al. 2002, Mellott et al. 2004, Glenn et al.
2012, Kelley et al. 2019). After weaning the intermediate diet was used. Offspring
were implanted with electrodes for EEG at 1 month of age, and 24 hr-long
recordings began 1/month starting at 1 week after surgery. NOL and NOR were
tested at 3 months and again at 6 months, and then we perfusion-fixed mice,
sectioned the brains, and evaluated ΔFosB and NeuN protein expression (Figure
1A).
The results showed a remarkable effect of the high choline diet. IIS and
spatial memory were improved, as was ΔFosB and NeuN expression.
Interestingly, the relatively low choline diet had mixed effects, reducing IIS
frequency, but making memory, ΔFosB, and NeuN worse. The mice also died
prematurely. In summary, we make a strong argument for choline
supplementation in early life to improve outcomes in an AD model, and
potentially AD.
II. METHODS
A. Animals
All experimental procedures followed the guidelines set by the National
Institute of Health (NIH) and were approved by the Institutional Animal Care and
Use Committee (IACUC) of the Nathan Kline Institute for Psychiatric Research.
Mice were housed in standard mouse cages with corn cob bedding and a 12-hr
light-dark cycle. Food and water were provided ad libitum.
Tg2576 mice express a mutant form of human APP (isoform 695) with a
mutation found in a Swedish cohort (Lys670Arg, Met671Leu). The expression is
driven by the hamster prion protein promoter. Mice were bred in-house from
heterozygous Tg2576 males and non-transgenic female mice (C57BL6/SJL F1
hybrid). Wildtype (WT) mice were obtained from Jackson Laboratories (Stock#
100012). At weaning, genotypes were determined using a protocol to detect
APP695.
Breeding pairs were randomly assigned to receive one of three diets with
different concentrations of choline chloride: 1.1 g/kg (AIN-76A, Dyets), 2.0 g/kg
(Purina 5008, W.F. Fisher and Son Inc.) and 5.0 g/kg (AIN-76A, Dyets;
Supplemental Table 1). These diets (relatively “low choline” diet, “intermediate
choline” diet and “high choline” diet, respectively) were used until weaning (25-30
days of age). After weaning, all mice were fed the intermediate diet. Mice were
housed with others of the same sex (1-4 per cage).
B. Behavior
1. General information.
Mice were housed in the room where they would be tested behaviorally
starting at least 24 hr prior to all experiments. Both NOL and NOR included three
acclimations (5 min each) followed by a training and a testing session (5 min
each; Figure 1B-D). The interval between training and testing was 60 minutes
and therefore tested short-term memory (Vogel-Ciernia & Wood 2014). NOL and
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NOR tests were separated by 7 days to ensure effects of one task did not affect
the next. Prior studies have failed to find an effect on one task on the next when
a 7 day-long interval is used (Botterill et al. 2021). The order of testing (NOL
before NOR or NOR before NOL) was randomized.
Video recordings of all training and testing sessions were captured using a
USB camera (Logitech HD Pro C920, Logitech). Acclimations were conducted
between 10:00 a.m. and 12:00 p.m., while training and testing was conducted
between 1:00 p.m. and 4:00 p.m. All equipment was cleaned using 70% ethanol
before each use. In pilot studies, we chose objects that would be explored
equally by animals. Indeed, animals showed no preference for either of the
objects (i.e., LEGO object and pineapple, Supplemental Figure 1) during training,
as reported in the Results.
2. NOL
NOL was conducted in a standard rat cage (26 cm wide x 40 cm long x 20
cm high) with different pictures on 3 sides of the cage to provide a consistent
context and therefore foster acclimation. Pictures included several shapes and
colors. The dimensions of the pictures were 1) 10 cm x 21 cm, 2) 16 cm x 18 cm,
and 3) 17 cm x 20 cm. During the acclimations, animals were allowed to freely
explore the cage. During the training session, mice were placed in the cage
where they had been acclimated, with two identical objects, 1 in a corner of the
cage (e.g., left top) and the second in the adjacent corner (e.g., left bottom,
Supplemental Figure 1). The mice were then removed and placed in their home
cage for 1 hr. During the test session, one of the objects was moved to the
opposite end of the cage (left top to right top; Supplemental Figure 1). The two
objects were identical pineapple-like objects made of metal that were painted and
approximately 3 cm x 3 cm x 5 cm (Supplemental Figure 1; Botterill et al. 2021).
3. NOR
NOR was conducted in a standard rat cage as described above. During the
acclimations, animals were allowed to freely explore the cage. During the training
session, mice were placed in the cage used for acclimation with two identical
objects centered along the shortest cage wall (Supplemental Figure 1). The
mouse was then removed and placed in their home cage for 1 hr. During the
testing session, one of the objects was replaced with a different one. The objects
that were identical were 2 pineapple-like objects, and the new object was made
of 2 green LEGO pieces approximately 5 cm x 7 cm x 7 cm (Supplemental Fig. 1;
Botterill et al. 2021).
4. Quantification
The experimenter who conducted the analysis was blind to the genotype of
the offspring and which object was novel or familiar. Videos of the training and
testing sessions were analyzed offline. Exploration was quantified based on the
guidelines of Vogel-Ciernia & Wood (2014), but in addition to time spent
exploring, the number of approaches to an object was also quantified. Time
spent exploring each object was defined as the duration of time the nose was
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pointed at the object and the nose was located within 2 cm of the object. In
addition, exploration time included the time animals spent on top of the object if
they were looking down and sniffing it. An approach was defined by a movement
toward the object and ending at least 2 cm from the edge of the object.
Animals that remembered the objects explored during the training phase
were expected to demonstrate an increased preference for novelty in the test
phase (Ennaceur & Delacour 1988). In other words, exploration of the novel
object during testing was expected to be higher than 50% of the total time of
object exploration.
C. Anatomy
1. Perfusion-fixation and sectioning.
Mice were initially anesthetized by isoflurane inhalation (NDC# 07-893-1389,
Patterson Veterinary), followed by urethane (2.5 g/kg; i.p.; Cat# U2500, SigmaAldrich). Under deep anesthesia, the abdominal and heart cavities were opened
and the animal was transcardially-perfused using 10 mL of room temperature
(RT) saline (0.9% sodium chloride in double distilled (dd) H2O) using a peristaltic
pump (Minipuls1; Gilson), followed by 30 mL of 4oC 4% paraformaldehyde (PFA,
Cat# 19210, Electron Microscopy Sciences) in 0.1 M phosphate buffer (PB; pH
7.4). The brains were immediately extracted, hemisected, and post-fixed for at
least 24 hr in 4% PFA (at 4oC).
Following post-fixation, the left hemisphere was sectioned in the coronal
plane and the right hemisphere was sectioned in the horizontal plane (50 µmthick sections) using a vibratome (VT 1000P, Leica Biosystems). Sections were
collected serially and stored at 4oC in 24-well tissue culture plates containing
cryoprotectant solution (30% glycerol, 30% ethylene glycol, 40% 0.1 M
phosphate buffer, pH 6.7). Throughout the hippocampus, every 6th section was
processed with an antibody to NeuN or ΔFosB.
2. NeuN and ∆FosB immunohistochemistry
Free floating sections were washed in 0.1 M Tris Buffer (TB; 3 x 5 min),
followed by a 3 min wash in 1% H2O2. Sections were then washed in 0.1 M TB (3
x 5 min) and incubated for 60 min in 5% horse serum for NeuN (Cat# S-2000,
Vector) or 5% goat serum for ∆FosB (Cat# S-1000, Vector), diluted in a solution
of 0.25% (volume/volume or v/v) Triton-X 100, and 1% (weight/volume or w/v)
bovine serum albumin in 0.1 M TB. Sections were then incubated overnight at
4oC in primary antibody to NeuN (mouse monoclonal, 1:5000; Cat# MAB377,
Chemicon International) or anti-ΔFosB (rabbit monoclonal, 1:1000; Cat# D3S8R,
Cell Signaling), diluted in a solution of 0.25% (v/v) Triton-X 100, and 1% (w/v)
bovine serum albumin in 0.1M TB. Both NeuN and ΔFosB have been wellcharacterized as antigens (Mullen et al. 1992, Wolf et al. 1996, Chen et al. 1997,
Sarnat et al. 1998) and the antibodies we used have been commonly employed
in the past (Chen et al. 1997, Duffy et al. 2013, Corbett et al. 2017).
On the following day, sections were washed in 0.1 M TB (3 x 5 min) and
then incubated for 60 min in biotinylated horse anti-mouse secondary antibody
for NeuN (1:500, Cat# BA-2000, Vector) or biotinylated goat anti-rabbit
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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secondary antibody for ∆FosB (1:500, Cat# BA-1000), diluted in a solution of
0.25% (v/v) Triton-X 100, and 1% (w/v) bovine serum albumin in 0.1 M TB. The
sections were then washed in 0.1 M TB (3 x 5 min) and incubated in avidin-biotin
complex for 2 hrs (1:1000; Cat# PK-6100, Vector). They were washed in 0.1 M
TB (3 x 5 min) and then reacted in a solution containing 0.5 mg/mL 3, 3’diaminobenzidine (DAB; Cat# D5905, Sigma-Aldrich), 40 µg/mL ammonium
chloride (Cat# A4514, Sigma-Aldrich), 25 mg/mL D(+)-glucose (Cat# G5767,
Sigma-Aldrich), and 3 g/mL glucose oxidase (Cat# G2133, Sigma-Aldrich) in 0.1
M TB. This method slowed the reaction time so that the reaction could be
temporally controlled, meaning that the reaction could be stopped when the
immunoreactivity was robust but background was still low. The sections were
then washed in 0.1 M TB (3 x 5 min), mounted on gelatin-coated slides (1%
bovine gelatin, Cat# G9391, Sigma-Aldrich) and dried at RT overnight. The
following day they were dehydrated in increasing concentrations of ethanol (90%,
10 min; 95% 10 min; 100%, 10 min; 100% again, 10 min), washed in Xylene (10
min; Cat# 534056, Sigma-Aldrich) and cover-slipped with Permount (Cat# 1798601, Electron Microscopy Sciences).
2. Analysis
Photomicrographs were acquired using ImagePro Plus V7.0 (Media
Cybernetics) and a digital camera (Model RET 2000R-F-CLR-12, Q-Imaging).
NeuN and ∆FosB staining were quantified from micrographs using ImageJ
(V1.44, National Institutes of Health). All images were first converted to grayscale
and in each section, the hilus was traced, defined by zone 4 of Amaral (1978). A
threshold was then calculated to identify the NeuN-stained cell bodies but not
background. Then NeuN-stained cell bodies in the hilus were quantified
manually. Note that the threshold was defined in ImageJ using the distribution of
intensities in the micrograph. A threshold was then set to identify the dark cells
but not the background slide using A slider was pushed from the low level of
staining corresponding to background to the location where staining intensity
makes a sharp rise, reflecting strongly stained cells. Below that was considered
background and above that was defined as above threshold.
To count ∆FosB-stained cells, images were converted to grayscale and in
each section, the dentate gyrus GCL was outlined and defined as a region of
interest (ROI). A threshold was then set to identify the dark cells but not the
background, analogous to the method to define threshold in the preceding
paragraph. Two thresholds were used. The first threshold was most inclusive of
immunoreactive cells. Presumably this group reflected cells with less neuronal
activity. Then counts were made a second time with a higher threshold. This
group probably corresponded to cells with the highest activity. ImageJ was used
to calculate the area (in pixels) within the ROI that was above threshold.
D. Video-electroencephalographic (video-EEG) recordings
1. Stereotaxic surgery
EEG electrodes (stainless steel jeweler’s screws) were implanted in Tg2576
animals at 4 weeks of age. WT littermates were not implanted because previous
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work from our laboratory has shown that WT mice have no IIS (Kam et al. 2016).
The animals were anesthetized by isoflurane inhalation (3% isoflurane. 2%
oxygen for induction). For maintenance during surgery, isoflurane was < 1.75%
and flow rate was 1.2 L/min. Mice were placed in a stereotaxic apparatus (David
Kopf Instruments). Prior to the implantation of the electrodes, animals were
injected with the analgesic Buprenex (0.2 mg/kg, s.c.; buprenorphine hydroxide,
NDC# 12496-0757-5, Reckitt Benckiser), which was diluted in saline (0.03
mg/mL in sterile 0.9% sodium chloride solution, Vedco Inc.). The skull was
exposed with a midline incision and six holes were drilled for the placement of
subdural screw electrodes (Cat# 8209, 0.10” stainless steel screws, Pinnacle
Technology).
The coordinates for the electrode placement were: right occipital cortex (AP 3.5 mm, ML 2.0 mm), left frontal cortex (AP -0.5 mm, ML -1.5 mm), left
hippocampus (AP -2.5 mm, ML -2.0 mm), and right hippocampus (AP -2.5 mm,
ML 2.0 mm (Kam et al. 2016). Two additional screws were placed, one over the
right olfactory bulb as ground (AP 2.3 mm, ML 1.8 mm) and another at the
midline over the cerebellum as a reference (relative to Lambda: AP -1.5 mm, ML
-0.5 mm). Screws were attached to an eight-pin connector (Cat# ED85100-ND,
Digi-Key Corporation), which was placed over the skull and secured with dental
cement (Cat# 4734FIB, Lang Dental Mfg. Co., Inc.).
After surgery, animals were placed on a heating blanket overnight and
injected with lactated Ringer’s solution (50 mL/kg at 31oC; NDC# 099355000476,
Aspen Veterinary Resources Ltd). They were then transferred to the room where
the video-EEG is recorded. Implanted animals were allowed to recover for one
week following the surgery.
2. Video-EEG recording
Video-EEG was recorded stating at 1.25 months (5 weeks) of age. The
animals were then recorded at 2, 3, 4, 5 and 6 months of age. Each recording
session lasted 24 hr so that a long period of sleep could be acquired, since IIS
occur primarily in sleep (Kam et al. 2016).
Mice were placed into 21 cm x 19 cm transparent cages with food and water
provided ad libitum and corncob bedding. A pre-amplifier was inserted into the
eight-pin connector on the skull, which was connected to a multichannel
commutator (Cat# 8408, Pinnacle Technology). This arrangement allowed for
free range of movement throughout the recording. EEG signals were acquired at
2000 Hz and bandpass filtered at 0.5 – 200 Hz using Sirenia Acquisition )V2.0.4,
Pinnacle Technology). Simultaneous video recordings were captured using an
infrared camera (Cat# AP-DCS100W, Apex CCTV).
3. Analysis
EEG recordings were analyzed offline with Neuroscore V3.2.1 (Data Science
International). IIS were defined as large amplitude, 10-75 msec deflections
occurring synchronously in all four leads (Kam et al. 2016). They were quantified
by first setting an amplitude threshold (calculated separately for each recording)
and a duration criterion (10-75 msec). To determine the amplitude threshold, we
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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calculated the root mean square (RMS) amplitude for noise in each recording
during a 60 sec segment of baseline activity that did not include any artifacts.
The threshold for IIS was set at 9 standard deviations above the RMS amplitude.
This threshold was selected because it identified IIS extremely well and excluded
movement or other artifacts. The IIS in one of the hippocampal channels was
used because of data suggesting IIS begin in the hippocampus (Kam et al.
2016). Following the automatic analysis of the IIS, the software’s detection
accuracy was verified manually for each recording to ensure that all spikes
appeared in all four channels and that no artifacts were included in the final IIS
count.
E. Statistical comparisons
Data are expressed as mean ± standard error of the mean (SEM). P-value
was set to <0.05 prior to all experiments. Parametric data comparing two groups
used unpaired two-tailed t-tests. For >2 groups, one-way ANOVA was used
followed by Tukey-Kramer post-hoc tests that corrected for multiple comparisons.
For data with two main factors, two-way ANOVA was followed by Tukey-Kramer
post-hoc tests. Interactions are not reported unless they were significant.
For the analysis of IIS frequency, a repeated measures ANOVA was not
possible because animal numbers were not the same at all ages. This was due
to mortality in low choline-treated mice or other unidentified reasons. Therefore, a
mixed effects analysis was conducted.
For non-parametric data, Mann-Whitney U tests were used to compare two
groups and Kruskal-Wallis for >2 groups. The post-hoc tests were Dunn’s test for
multiple comparisons. Tests were conducted using Prism (V 9.4.1, Graphpad
Software).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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III. RESULTS
A. Behavior
NOL and the NOR, unlike other tasks previously used to evaluate cognitive
deficits in >9 months-old Tg2576 mouse model (i.e., Morris Water Maze, Radial
Arm Water Maze, Y-Maze; Yassine et al. 2013, Wolf et al. 2016), provided an
opportunity to capture cognitive deficits in animals as young as three months-old
(Duffy et al. 2015). Figure 1B-D shows a schematic of the specific experimental
procedures for NOL and NOR.
1. NOL
The results of the NOL task are presented in Figure 2. Exploration of the
novel object is expressed as a percentage of the total exploration of both objects.
During the training session, animals did not show preference for one object over
the other and this result was independent of genotype. Thus, a two-way ANOVA
revealed no main effects of genotype on novel object exploration during training
at three (F(1,97) = 0.40, p = 0.53) or six months of age (F(1,70) = 1.94, p = 0.17).
There also was no effect of maternal diet on training at three (F(2,97) = 0.06, p =
0.94) or six months of age (F(2,70) = 2.94, p = 0.06).
Next, we asked whether Tg2576 mice were deficient in the test phase of
NOL. First we studied the 3 months-old mice. We used a two-way ANOVA with
genotype and task phase (training versus testing) as main factors. In animals that
received the intermediate diet, a two-way ANOVA revealed a significant main
effect of the phase of the task (training or testing; F(1,24) = 7.48, p = 0.01).
Consistent with previous studies (Duffy et al. 2015), post-hoc analyses revealed
a significant increase in the exploration of the novel object during testing in WT (p
= 0.02) but not Tg2576 mice (p = 0.50; Figure 2A2). Thus, Tg2576 mice were
impaired in NOL when fed the intermediate diet.
In animals that received the high choline diet, a two-way ANOVA revealed a
main effect of the task phase (F(1,36) = 48.23, p < 0.001). Post-hoc analyses
revealed a significant increase in the exploration of the novel object during
testing in both WT (p < 0.001) and Tg2576 mice (p < 0.001; Figure 2A3).
Therefore, high choline supplementation improved memory in Tg2576 mice.
In animals treated with the low choline diet, there was no effect of phase of
the task (F(1,37) = 1.39, p = 0.25). These data suggesting that relatively low
levels of choline during early life impaired spatial memory in both WT and
Tg2576 mice (Figure 2A). Thus, low choline had a significant adverse effect.
Adverse effects are further supported by survival plots showing that there was
more mortality at earlier ages in offspring exposed to the low choline diet
(Supplemental Figure 1).
Figure 2B shows the results in 6 months-old WT and Tg2576 mice. In
animals that received the intermediate diet, a two-way ANOVA showed no main
effect of genotype (F(1,18) = 0.01, p = 0.92) or task phase (F(1,18) = 3.40, p =
0.08), revealing age-related memory deficits even in WT mice at six months of
age (Figure 2B). In contrast, the high choline group showed a main effect of task
phase (F(1,29) = 28.32, p < 0.001). Post-hoc analyses showed a significant
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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increase in the exploration of the novel object during testing in both WT (p <
0.001) and Tg2576 (p = 0.02; Figure 2B). In animals that received the relatively
low choline diet, there was no effect of task phase (F(1,25) = 3.00, p = 0.10;
Figure 2B). Thus, low choline had adverse effects on NOL in both WT and
Tg2576 mice.
Taken together, these results demonstrate the lasting beneficial effects of the
high choline diet and adverse effects of low choline on offspring in a spatial
memory task in Tg2576 as well as WT littermates.
2. NOR
We first confirmed that animals did not show preference for one object over
the other in training. A two-way ANOVA revealed no main effects of genotype at
three months (F(1,71) = 2.59, p = 0.54) and no effect of diet (F(2,71) = 0.22, p =
0.81). The same result was obtained at six months of age (genotype: (F(1,66) =
0.11, p = 0.75); diet: (F(2,66) = 0.98, p = 0.38). Thus, novel object exploration
during training approached 50% in all treatment groups, independent of genotype
and maternal diet, and at both ages.
Figure 3A shows the results of the testing phase of the NOR task in 3
months-old WT and Tg2576 mice. In animals that received the intermediate
choline diet, a two-way ANOVA revealed a significant main effect of task phase
(F(1,19) = 40.53, p < 0.01) and no effect of genotype (F(1,19) = 0.78, p = 0.39).
Post-hoc analyses revealed a significant increase in the exploration of the novel
object during testing compared to training for both WT (p < 0.01) and Tg2576 (p
< 0.01; Figure 3A). These results suggest that Tg2576 did not have a deficit in
NOR at 3 months of age.
Mice fed the high choline diet also showed no deficit in NOR at 3 months of
age. Thus, a two-way ANOVA revealed a main effect of task phase (F(1,26) =
17.51, p < 0.01) but not genotype (F(1,26) = 3.53, p = 0.07). Post-hoc analyses
revealed a significant increase in the exploration of the novel object during
testing in both WT (p < 0.01) and Tg2576 (p = 0.03; Figure 3A).
In animals treated with the low choline diet in early life, there was no
impairment in NOR at 3 months of age (task phase (F(1,26) = 22.61, p < 0.01;
genotype (F(1,26) = 0.02, p = 0.89). There was a significant increase in the
exploration of the novel object in testing both in WT (p = 0.03) and Tg2576 (p <
0.01).
Figure 3B shows that there were no impairments at 6 months of age. In
animals that received the intermediate diet, a two-way ANOVA revealed a
significant main effect of task phase (F(1,19) = 13.65, p < 0.01) but no main
effect of genotype (F(1,19) = 0.28, p = 0.60). Animals explored the novel object
significantly more during testing in WT (p = 0.03) and Tg2576 mice (p = 0.04;
Figure 3B). In animals that received the other diets, results were the same. For
the high choline group, there was an effect of task phase (F(1,27) = 16.26, p <
0.01) but not genotype (F(1,27) = 0.24, p = 0.63) and a significant increase in the
exploration of the novel object during testing in both WT (p = 0.04) and Tg2576
(p < 0.01; Figure 3B). Similarly, in animals treated with the low choline diet, there
was a main effect of task phase (F(1,26) = 32.66, p < 0.01), no effect of genotype
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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(F(1, 6) = 0.05, p = 0.82), and more exploration of the novel object during the test
phase (WT, p < 0.01; Tg2576, p < 0.01).
Thus, at both 3 and 6 months of age, WT and Tg2576 mice performed well in
the NOR task. These results suggest that young Tg2576 mice are less sensitive
to NOR than NOL. The greater sensitivity to NOL is consistent with past
demonstrations that the dentate gyrus contributes to NOL (Sahay et al. 2011,
Kesner et al. 2015, Spyrka & Hess 2018, Vandrey et al. 2020, Gulmez Karaca et
al. 2021, GoodSmith et al. 2022), and early signs of adverse effects in the
dentate gyrus in mouse models of AD (impaired LTP; Jacobsen et al. 2006,
altered gene expression; Palop et al. 2011). Our implementation of NOL may
have increased the dentate gyrus-dependence of the task by making the object
locations relatively close together, because the dentate gyrus is critical to
distinguishing small differences in locations. In studies by Pofahl and colleagues,
it was shown that distances between objects like those we used made NOL
dentate gyrus-dependent (Pofahl et al. 2021).
3. Exploration time
Total object exploration (TOE) was measured to address any effects of
genotype or diet on the total duration of exploration of objects (Figure 4).
a. 3 months of age
For NOL at 3 months of age, there were effects of genotype (F(1,67) = 6.891,
p = 0.01) but not maternal diet (F(2,87) = 0.67, p = 0.63; Figure 4A). TukeyKramer post-hoc tests showed that Tg2576 mice fed the low choline diet showed
more exploration than WT mice fed the same diet but the effect was on the
border of significance (p = 0.049; data not shown). Three months-old mice tested
with NOR showed no significant effect of genotype (F(1,76) = 1.35, p = 0.25) or
diet (F(2,76) = 0.30, p = 0.61; Figure 4C).
b. 6 months of age
1) Exploration
NOL and NOR showed significant effects of diet on exploration at 6 months
of age (Figure 4B,D). For NOL, there was no effect of genotype (F(1,66) = 0.33; p
= 0.57) but there was an effect of maternal diet (F(2,66) = 8.82; p = 0.0004). For
NOR, the same was true (genotype: F(1,72) = 0.96, p = 0.33; diet: F(2,72) =
8.50, p = 0.0005). We then pooled genotypes to determine which diets differed.
For NOL, mice treated with the relatively low choline diet had less exploration
than mice fed the high choline diet (one-way ANOVA, F(2,77) = 6.90; p = 0.002;
Tukey post-hoc test, p = 0.005; Figure 4B) and the mice that were fed the
intermediate diet also had less exploration than mice fed the high choline diet
(Tukey post-hoc test, p = 0.008; Figure 4B). Results for NOR were the same:
mice treated with the low choline diet had less exploration than mice fed the high
choline diet (one-way ANOVA, F(2,74) =4.81; p = 0.02; Tukey post-hoc test, p =
0.02; Figure 4D) and the mice that were fed the intermediate diet also had less
exploration than mice fed the high choline diet (Tukey post-hoc test, p = 0.03;
Figure 4D).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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2) Approaches
To gain insight into the potential reason for differences in exploration, we
measured total object approaches (TOA; Figure 4A-D). TOA was defined as the
number of approaches to the familiar object + number of approaches to the novel
object. There were no differences by genotype (two-way ANOVA, F(1,73) =
2.930, p = 0.09) or maternal diet (F(2,73) = 2.36, p = 0.10; Figure 4A-D).
Taken together, the results indicate that, in 6 months-old mice, animals that
received the high choline diet spent more time with objects at each approach.
This may underlie increased object location memory in high choline-treated mice
by increasing time for information processing during an approach. It may also
help in the NOR task with object recognition memory, although it did not seem
impaired in mice fed other diets. Another possibility is that as Tg2576 mice age
they show compensatory changes that enhance memory. This has been
suggested for procedural learning (Middei et al. 2004) but not for memory of
objects. A third possibility is that the high choline diet reduces anxiety (Glenn et
al. 2012, Langley et al. 2015, McCall et al. 2015). Reduced anxiety may lessen
fear of exploring objects, and as a result, animals may spend more time with
objects.
For 3 months-old mice there were no effects of maternal diet on exploration,
suggesting that increased time with objects for a given approach is a change that
develops with age. To our knowledge, this age-related change has not been
previously reported. It could be a strategy to cope with impairments that are
developing as AD pathology manifests.
B Anatomy
1. NeuN
To further analyze the effects of dietary choline early in life, we used an
antibody against a neuronal nuclear antigen, NeuN. Previous studies have found
that reduced expression of NeuN often occurs in neurons after insults or injury
(e.g., ischemia, toxicity and even aging; Lind et al. 2005, Portiansky et al. 2006,
Buckingham et al. 2008, Kadriu et al. 2009, Matsuda et al. 2009, Won et al.
2009, Duffy et al. 2011). For example, when NeuN is reduced after a reduction in
ankyrin-rich membrane spanning kinase D-interacting substrate of 220K,
ARMS/Kidins, a protein critical to neurotrophin signaling, neurons in the
entorhinal cortex demonstrate signs of toxicity such as pkynosis (Duffy et al.
2011, Duffy et al. 2015). Since NeuN is reduced when A levels are elevated
(Wu et al. 2016) and NeuN is reduced in AD patients (Camporez et al. 2021), we
used NeuN expression to ask if the high choline diet could rescue the loss of
NeuN-ir.
As shown in Figure 5, relatively weak NeuN-ir was observed in Tg2576
animals in the hilus, an area known to be highly vulnerable to insult and injury
(Scharfman 1999). The most NeuN loss appeared to be in mice that received the
low choline diet and the intermediate diet compared to the high choline diet
(Figure 5B). Therefore, we conducted a two-way ANOVA with diet and
septotemporal levels as main factors. To examine the septotemporal axis,
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was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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quantification from 2-3 dorsal coronal sections were averaged to provide a value
for dorsal DG and 2-3 ventral horizontal sections were averaged for a ventral
value. There was no effect of diet (F(2,30) = 2.11, p = 0.14) nor septotemporal
level (F(1,30) = 0.02, p = 0.88) but there was a significant interaction of diet and
septotemporal level (F(2,30) = 3.88, p = 0.04). A one-way ANOVA using dorsal
values showed a significant effect of diet (F(2,21)= 7.58, p = 0.003) but this was
not the case for ventral values (F(2,23) = 0.13; p = 0.88; Figure 5D). In the dorsal
DG, there was less NeuN-ir in mice fed the low choline diet versus the high
choline diet (Tukey-Kramer post hoc test, p = 0.03) and less NeuN in mice fed
the intermediate vs high choline diet (p = 0.003; Figure 5D). The results suggest
that choline enrichment protected hilar neurons from NeuN loss in Tg2576 mice.
2. ∆FosB
To complement the information from the video-EEG recordings we used a
marker of elevated neuronal activity, ∆FosB (Figure 6). ∆FosB is a truncated
variant of the transcription factor FosB, which is increased by enhanced neuronal
activity; ∆FosB has a half-life of approximately 8 days (Ulery-Reynolds et al.,
2009), so when ∆FosB is elevated, it reflects increased neuronal activity over the
last 10-14 days (McClung et al. 2004). Previous studies have shown that when
the J20 mouse model of AD is examined with an antibody to ∆FosB, the GC layer
shows extremely high levels of ∆FosB expression (Corbett et al. 2017), similar to
a mouse with chronic spontaneous seizures (epilepsy; Morris et al. 2000). This is
not surprising since the J20 mice have recurrent seizures (Palop et al. 2007).
Therefore, we asked if Tg2576 mice would have robust ∆FosB in the GC layer,
and choline supplementation would reduce it.
There was strong expression of ∆FosB in Tg2576 GCs especially in mice fed
the low choline diet (Figure 6). Two-way ANOVA showed a main effect of
maternal diet (F(2,18) = 3.76, p = 0.04) but there was not a main effect of
septotemporal level (F(1,18) = 1.3, p = 0.26).
To clarify the effect of maternal diet, a one-way ANOVA was conducted.
There was an effect of diet (F(2,9) = 10.74, p = 0.004) with post-hoc tests
showing significantly less GC ΔFosB expression in high choline-treated mice
compared to low choline (p = 0.003). Low choline-treated mice were not
significantly different from mice that were fed the intermediate diet (p = 0.08).
These data used dorsal sections so we repeated the analysis for the ventral DG,
and there also was no significant effect of diet (F2,9) = 0.79, p = 0.52; Figure 6).
∆FosB quantification was repeated with a lower threshold to define ∆FosB-ir
GCs (see Methods) and results were the same (Figure 6). One-way ANOVA
showed a significant effect of diet (F(2,41) = 14.66, p < 0.0001), and low choline
mice had greater ΔFosB-ir than high choline mice (p =0.003). Mice fed the
intermediate diet had higher expression than mice fed the high choline diet (p =
0.0001). These data suggest that high choline in the diet early in life can reduce
hyperexcitability of GCs in offspring later in life. In addition, low choline has an
opposite effect, again suggesting this maternal diet has adverse effects.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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C. IIS
Previous research has shown that Tg2576 mice exhibit IIS (Figure 7A)
starting at very young ages: 4 weeks (Kam et al. 2016) or 6 weeks (Bezzina et al.
2015). Therefore, we performed video-EEG using cortical (left frontal cortex, right
occipital cortex) and hippocampal (left and right) electrodes in WT and Tg2576
mice (Figure 7B-C). Animals were recorded for 24 hr each session so that there
was sufficient time to capture major behavioral states (exploration, awake rest,
and sleep). Consistent with previous studies (Bezzina et al. 2015, Kam et al.
2016) we observed IIS in Tg2576 mice but not WT littermates.
As shown in Figure 7, animals that received the intermediate diet had a
significantly higher number of IIS in the 24 hr recording periods compared to
animals that received the high choline and the low choline diets. A mixed model
analysis showed that there was a significant effect of age (F(2,37) = 3.38; p =
0.04) and maternal diet (F(2,36) = 8.12; p = 0.01). At the 1.25-month recording,
Tukey post-hoc analyses showed that IIS frequency in animals treated with the
intermediate diet was higher compared to animals treated with the low (p = 0.03)
or high choline diets (p = 0.04). This also was true for 2 months and 3 months
(low choline, high choline, p <0.05). At 4 months, the low choline groups had
significantly reduced IIS frequency compared to the intermediate diet (p = 0.009)
but not the high choline group (p = 0.98). At 5-6 months, IIS frequencies were not
significantly different in the mice fed the maternal diets (all p > 0.05).
As shown previously (Kam et al. 2016), and in Figure 7, at 4-6 months of age
there was high variability in IIS frequency between animals. It is possible that IIS
frequency becomes more variable because we found that seizures occur in the
Tg2576 mice after 2 months of age (Kam et al. 2016), and there was a sharp
increase in IIS during the day before and after a seizure (Supplemental Figure 3).
D. Seizures and premature mortality in mice fed the low choline diet
We found mice fed the low choline diet had greater ΔFosB-ir in GCs and
the hilus showed very low NeuN-ir. Therefore we asked whether low cholinetreated mice had more seizures than mice fed the other diets. We recorded 8
mice by video-EEG for 5 days each (at 6 months of age) to examine seizures
and found 2 mice from the low choline group had seizures (11 seizures over 2 of
the 5 days in one mouse, 1 seizure in the other mouse) whereas none of the
other mice had seizures (n=0/4, 2 intermediate and 2 high choline, data not
shown).
These values are probably an underestimate for the low choline group
because many mice in this group appeared to die in a severe seizure prior to 6
months of age (Supplemental Figure 2). Therefore, the survivors at 6 months
probably were the subset with few seizures.
The reason that low choline-treated mice appeared to die in a seizure was
that they were found in a specific posture in their cage which occurs when a
severe seizure leads to death (Supplemental Figure 2). They were found in a
prone posture with extended, rigid limbs (Supplemental Figure 2). Regardless of
how the mice died, there was greater mortality in the low choline group compared
to mice that had been fed the high choline diet (Supplemental Figure 2).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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E. Sex differences
As shown in Figures 2-3, there appeared to be no sex differences in NOL or
NOR. For confirmation, we studied NOL further, since that was the task that
showed effects of diet. A three-way ANOVA with sex, genotype and task phase
as factors showed no significant effect of sex at three months of age (low choline
diet, F(1,35) = 0.0001; p = 0.99). Results were the same for the three months-old
mice fed the intermediate diet (F(1,22) = 0.062; p = 0.81) and three months-old
mice that were fed the high choline diet (F(1,34) = 0.43; p = 0.52). At six months
of age there also were no significant effects of sex (low choline diet, F(1,23) =
0.34; p = 0.57; intermediate diet, F(1,16) = 2.49; p = 0.13; high choline diet,
F(1,27) = 0.29; p = 0.87).
Regarding IIS, we did not find sex differences (Supplemental Figure 4). A
two-way ANOVA with sex and diet as factors showed no effect of sex (F(1,20)
=2.48; p = 0.13) or diet (F(1,20) = 3.56; p = 0.07). Note that for this comparison
we used the low choline and high choline groups only because sex information
was only available for these mice. The results for months 2-3 also showed no
effect of sex (2 months: F(1,17) = 0.64; p = 0.43; 3 months: F(1,15) = 0.19; p =
0.67).
IV. DISCUSSION
Summary
This study showed that early life choline supplementation had several
beneficial effects in Tg2576 mice. The high choline diet led to reduced IIS
frequency, improved behavior in the NOL task, and improved expression of
ΔFosB.
We showed for the first time that Tg2576 mice have pathology in the hilus at
six months of age in that hilar neurons are deficient in immunostaining with an
anti-NeuN antibody. Tg2576 offspring on the high choline diet showed a
restoration of hilar NeuN staining. Because hilar neurons play a role in NOL (Bui
et al. 2018), it is possible that rescue of hilar neurons by the high choline diet led
to improved spatial memory. Hilar neurons have been suggested to contribute to
excitability of GCs (Sloviter 1994, Scharfman 1999, Scharfman & Myers 2012,
Jinde et al. 2013, Bui et al. 2018, Botterill et al. 2019), so phenotypic rescue of
hilar neurons may also have contributed to the ability of the high choline diet to
reduce hyperexcitability.
We also found surprising effects of treating mice with relatively low choline in
the maternal diet. On the one hand, IIS frequency was reduced. However, these
mice showed premature mortality. Furthermore, in WT mice where no
impairments in NOL normally occur, WT mice fed the low choline diet were
impaired. In Tg2576 mice, the group that had the low maternal choline diet had
the highest ΔFosB expression and the lowest NeuN expression of any
experimental group. Potential reasons for these surprising effects are discussed
below.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Benefits of high choline
The results of this study are consistent with previous reports that prenatal or
postnatal choline supplementation improves object memory. One study of iron
deficiency showed that choline supplementation improved NOR (Kennedy et al.
2014). Wistar rats treated with a diet high in choline had improved NOR relative
to rats that had been fed a diet low in choline (Moreno et al. 2013). In rats that
were aged to 24 months, animals that had been fed a high choline diet showed
improved NOR, but only in females (Glenn et al. 2008).
Although few studies have examined the effects of MCS on hyperexcitability,
our results showing the benefits of high choline are consistent with reports that a
methyl-enriched diet (including choline but also betaine, folic acid, vitamin B12,
L-methionine and zinc) reduced spike wave discharges in the offspring
(Sarkisova et al. 2023) and audiogenic seizure severity (Poletaeva et al. 2014).
Perinatal ethanol treatment that increased excitability was mitigated by choline
chloride injection from postnatal day 10-30 (Grafe et al. 2022).
To our knowledge our study is the first to show that MCS can exert effects on
IIS and ΔFosB. However, prior studies have shown that MCS in rats improved
memory after severe seizures. Using a convulsant to induce several hours of
severe seizures (status epilepticus, SE), there is usually extensive hippocampal
neuronal loss and when tested in the subsequent days and weeks, memory
impairment. MCS reduced this impairment following SE in the Morris water maze
(Yang et al. 2000, Holmes et al. 2002, Wong-Goodrich et al. 2011).
Our results are consistent with previous studies of mouse models of AD. In
the APP/PS1 mouse model, it was shown that life-long choline supplementation,
to the level we used (5.0 g/kg) improved memory in aged mice compared to the
1.1 g/kg diet (Velazquez et al. 2019). Postnatal choline supplementation also
improved memory in APP/PS1 mice (Wang et al. 2019). Other improvements
were also shown in the APP/PS1 mice, such as improved cholinergic expression
via upregulation of choline acetyltransferase (Mellott et al. 2017, Velazquez et al.
2019).
Adverse effects of low choline
The effects of the relatively low choline diet were surprising because several
adverse effects were found. This is unexpected because 1.1 g/kg choline is not
considered very low in several studies of the past, and some publications
consider it normal (e.g., Lamoureux et al. 2008). The majority of past studies
used rats (Meck et al. 1988, Meck & Williams 1999, 2003, Meck et al. 2007,
Lamoureux et al. 2008), however, so there could be a species difference. Also,
some of the past studies used the diet for a shorter timespan than we did (e.g.,
Lamoureux et al. 2008) because of evidence that perinatal choline
supplementation exerts its maximal effects during critical periods (Meck &
Williams 2003, Meck et al. 2007).
It was also surprising to find high mortality in mice exposed to the low choline
diet in early life. Also, the offspring of mothers fed the low choline diet had very
high ΔFosB expression in the GCs, suggesting they had chronic seizures. The
observation that mice died from seizures is consistent with the ΔFosB data.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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There also was weak NeuN in the hilus. When WT mice were tested, NOL was
impaired in the low choline group. These data suggest that the offspring of
mothers fed the low choline diet were unhealthy, possibly leading to or because
of seizures.
On the other hand, IIS were reduced in frequency in the same mice. There
are several possible explanations for this apparent paradox. The most
parsimonious explanation is the mice were unhealthy. If there was disruption of
sleep, IIS might be reduced since IIS occur in sleep primarily. However, there is
no evidence that MCS influences sleep in humans or laboratory animals. The
one study that looked at the sleep/wake cycle in rats did not find effects (Cheng
et al. 2008).
A more radical explanation is that the intermediate diet promoted IIS rather
than low choline reducing IIS. The idea here is that choline is not critical to IIS
because both low and high choline groups had low IIS frequency compared to
the intermediate group, at least for 3 months of life. Instead of choline, a
constituent of the intermediate diet may have promoted IIS. The reason why the
effect of diet waned over time could have been due to the fact that after weaning
all animals had the intermediate diet.
More seizures could explain premature mortality in the low choline group.
However, why it would decrease IIS is not clear. One reason seizures could
cause IIS to be reduced is that seizures in the Tg2576 mice typically started
during sleep and woke mice from sleep. The arousal from sleep would interrupt
the behavioral state when IIS usually occur as mentioned above. Also, seizures
in the Tg2576 mice were followed by a depression of the EEG that would reduce
IIS (postictal depression; Supplemental Figure 3).
NeuN
As mentioned above, NeuN is a neuronal nuclear antigen that can be
phosphorylated, and when that occurs the antibody to NeuN no longer binds to
NeuN. NeuN is phosphorylated in response to oxidative damage, brain injury,
and toxicity (Lind et al. 2005). Therefore, it was of interest when we saw that hilar
neurons of the dentate gyrus showed reduced NeuN in Tg2576 mice. Hilar
neurons are mainly glutamatergic mossy cells and somatostatin
(SOM)/neuropeptide Y (NPY)-expressing GABAergic neurons (HIPP cells;
(Houser 2007, Scharfman & Myers 2012, Scharfman 2016), and both neuronal
types are implicated in spatial memory functions of the GCs, as well as their
excitability (Myers & Scharfman 2009, 2011, Scharfman & Myers 2012, Jinde et
al. 2013, Scharfman 2016, Raza et al. 2017, Bui et al. 2018, GoodSmith et al.
2019, Li et al. 2021). If damaged by the high intracellular APP/A levels in young
Tg2576 mice, the hilar neurons would be expected to show NeuN loss. This idea
is consistent with deficits in SOM and NPY-stained cells (Chan-Palay 1987),
indicating a vulnerability.
The reason for rescue of dorsal hilar but not ventral hilar NeuN with the high
choline diet is unclear. However, there was a trend for the high choline mice to
have greater NeuN in ventral tissue sections. The greater sensitivity of dorsal
neurons may be related to differences in dorsal and ventral dentate gyrus gene
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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expression patterns, since some of the genes that are differentially expressed
could affect vulnerability to insult or injury (Cembrowski et al. 2016, Zhang et al.
2018). Resilience of vulnerable neuronal populations, especially in the
hippocampus, is a topic of high interest in AD research.
∆FosB
Given that seizures are associated with elevated GC expression of ∆FosB
(Chen et al. 1997, McClung et al. 2004, Corbett et al. 2017, You et al. 2017), the
differences in ∆FosB expression levels observed here could be the result of
increased seizures in animals that received the low choline diet. Therefore, we
suggest that the high ΔFosB in Tg2576 mice fed the low choline diet reflects
more seizures than in the other two diets.
∆FosB is a transcription factor that is linked to cognition. In the J20 mouse
model of AD, elevated ∆FosB in GCs led to reduced cognition, and when ∆FosB
was selectively reduced the cognition improved (Corbett et al. 2017). Therefore,
the reduction in ∆FosB by the high choline diet was important to show
hyperexcitability was reduced and also important because it showed how high
choline may benefit cognition.
Additional considerations
Although the low and high choline diets only had differences in choline, the
intermediate diet had different amounts of choline as well as other constituents
(Supplementary Table 1). Therefore, the only diet comparison with a difference
restricted to choline is the low versus high choline diets (Supplemental Table 1).
The intermediate diet was useful however, because numerous studies in AD
mouse models employ this standard diet. Moreover, it may have promoted IIS as
discussed above.
Although we failed to detect sex differences, there may actually have been
differences if females had been analyzed according to their stage of the estrous
cycle at death. This possibility is raised by prior data showing that rats and mice
during diestrus have low excitability in hippocampal slices; at other cycle stages
hyperexcitability occurs (Scharfman et al. 2003).
The Tg2576 mouse model is one of many murine models of AD, and as with
all models there are inherent limitations. The Tg2576 model of cerebral amyloid
overexpression lacks tau pathology and recapitulates familial AD, whereas the
majority of AD is sporadic. However, MCS has now demonstrated
structural/functional benefits in several AD-relevant models, namely Tg2576 (this
report), APP-PS1 (Mellott et al. 2017), and Ts65Dn (Powers et al. 2016, Strupp
et al. 2016, Powers et al. 2017, Alldred et al. 2021, Alldred et al. 2023).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 1. Schematic of the behavioral procedures for the NOL and NOR
tasks.
A. Experimental timeline. Dams were fed one of three diets for mating, gestation,
and offspring consumed the diet until weaning at 25-30 days of age. At 1 monthold, offspring were implanted with electrodes for EEG and recorded for a 24 hr
period at 1.2, 2, 3, 4, 5, and 6 months of age. At 3 and 6 months of age behavior
was tested. At 6 months of age, after behavioral testing, mice were perfused,
brains were sectioned, and sections were processed with antibodies against
NeuN and ∆FosB.
B. Prior to NOL or NOR, animals were acclimated to the testing arena. There
were three acclimation sessions separated by 24hrs during which animals were
allowed to freely explore for 5 min.
C. In the NOL task, animals were placed in a cage with two identical objects and
allowed to freely explore for 5 min (Training). After one hour they were brought
back to the cage, where one object was displaced, and allowed to freely explore
for 5 min (Testing).
D. In the NOR task. animals were placed in a cage with two identical objects and
allowed to freely explore for 5 min (Training). After one hour they were brought
back to the cage, where one object was replaced, and allowed to freely explore
for 5 min (Testing).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 2. Choline enrichment reduced spatial memory deficits.
A. Three months-old mice.
1. WT and Tg2576 mice exposed to the low choline diet showed spatial memory
deficits.
2. Tg2576 exposed to the intermediate diet showed spatial memory deficits but
not WT.
3. Spatial memory was improved in animals exposed to the high choline diet.
B. Six months-old mice.
1. WT and Tg2576 mice exposed to the low choline diet showed spatial memory
deficits.
2. WT and Tg2576 mice exposed to the intermediate diet showed spatial
memory deficits.
3. WT and Tg2576 mice exposed to the high choline diet had improved spatial
memory.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 3. WT and Tg2576 mice showed recognition memory regardless of
diet.
A. Three months-old mice.
1-3. WT and Tg2576 mice treated performed the NOR task.
B. Six months-old mice.
1-3. WT and Tg2576 mice performed the NOR task.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 4. Tg2576 mice treated with the choline supplemented diet spent
more time with the objects at each approach.
A-B. NOL.
There was no effect of diet on time exploring or approaches to the novel object in
the NOL task at 3 months of age (A) but there were significant differences at 6
months of age (B). Mice exposed to the high choline diet spent more time
exploring than mice that had been fed the low choline or the intermediate diet.
C-D. NOR.
There was no effect of diet on time exploring or approaches to the novel object in
the NOR task at 3 months of age (C) but there were significant differences at 6
months of age (D). Mice that had been fed the high choline diet spent more time
exploring than mice that had been fed the low choline or the intermediate diet.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 5. Choline supplementation improves NeuN immunoreactivity (ir) in
hilar cells in Tg2576 animals
A. A sagittal view of the brain illustrating the coronal sectioning plane.
B. Representative images of NeuN-ir staining in the dorsal dentate gyrus of
Tg2576 animals from each treatment group.
C. Quantification methods. Representative images demonstrating the
thresholding criteria established to quantify NeuN-ir.
1. A NeuN-stained section shows an inset (arrow) expanded at the top left to
show 3 hilar cells. NeuN-ir cells are marked by blue arrows. NeuN-ir that was too
close to background staining to be considered positive is marked by a green
arrow.
2. After converting the image to grayscale, a threshold was set so that all cells
stained well with NeuN antibody were red. The inset shows that the two cells that
were darkest met the threshold while the weakly stained cell did not.
D. Six months-old Tg2576 mice treated with the high choline diet had significantly
more NeuN-ir cells in the hilus in the dorsal dentate gyrus (1) compared to other
treatment groups but not ventral dentate gyrus (2).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 6. Choline supplementation reduced ∆FosB expression in dorsal
GCs of Tg2576 mice.
A. A sagittal view of the brain illustrating the coronal sectioning plane.
B. Representative images of ∆FosB staining in the anterior dentate gyrus of
Tg2576 animals from each treatment group.
C. Quantification methods. Representative images demonstrating the
thresholding criteria established to quantify ∆FosB.
1. A ∆FosB -stained section shows strongly-stained cells (white arrows).
2. A strict thresholding criteria was used to make only the darkest stained cells
red.
D. Six months-old Tg2576 mice treated with the choline supplemented diet had
significantly more ∆FosB -ir pixels above threshold in the dorsal dentate gyrus (1)
compared to other treatment groups but not ventral dentate gyrus (2).
E. Methods are shown using a threshold that was less strict.
1. Some of the stained cells that were included are not as dark as those used for
the strict threshold (white arrows).
2. All cells above the less conservative threshold are shown in red.
F. With the less conservative threshold, the results were the same as D. Mice
that were fed the high choline diet had less ΔFosB-ir pixels than the mice that
were fed the other diets. However, this was true for dorsal (1) but not ventral (2)
sections.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Figure 7. The high choline diet reduced IIS frequency in Tg2576 animals.
A. 1. Representative example of an IIS (red arrow). IIS were defined as occurring
in all four channels (generalized) to distinguish them from focal spikes that can
often be artifact.
2-3. The IIS shown in A1 is expanded.
B. 1. Scatter plot of IIS frequency at each age of recording.
2. Means and sem are plotted. The high choline diet group had fewer IIS than the
intermediate diet group at ages 1-3 months ($, p<0.05) and the low choline group
had less IIS than the intermediate diet at ages 1-4 months (@, p<0.05). The high
and low choline diet groups were significantly different at ages 3 and 4 months (*,
p<0.05).
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Supplemental Table 1. Comparison of the three diets used in this study.
Choline
Low
choline
1.1g/kg
Intermediate
choline
2.0g/kg
High
choline
5.0g/kg
Carbohydrate
Protein
Fat
Thiamin
Riboflavin
Pyridoxine
Niacin
Folic Acid
Biotin
690
177
120
0.020
0.600
0.700
3.000
0.200
0.020
570
236
170
0.015
0.005
0.006
0.780
0.003
0.002
690
177
120
0.020
0.600
0.700
3.000
0.200
0.020
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Supplemental Figure 1. Details of behavioral tasks.
A standard mouse cage is diagrammed with the locations of objects inside it. For
NOL, there were two pineapple-like objects and one was moved across the cage
for the test session. For the NOR test session, one pineapple-like object was
removed and an object made of LEGO was placed in the location where the
original pineapple-like object had been.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Supplemental Figure 2. Mortality was high in mice treated with the low
choline diet.
A. Survival curves are shown for mice fed the low choline diet and mice fed the
high choline diet.
B. A photo of a mouse after sudden unexplained death. The mouse was found in
a posture consistent with death during a convulsive seizure.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Supplemental Figure 3. IIS frequency before and after seizures.
A. Representative EEG trace of a seizure in a 5 months-old Tg2576 mouse.
B. IIS frequency was quantified from continuous video-EEG for 4 days. During
the first 24 hrs, IIS frequency was low. The next day a seizure occurred (arrow),
and IIS frequency increased approximately 5 fold, and for the next 24 hr period.
On day 4, IIS frequency returned to lower levels.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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Supplemental Figure 4. IIS frequency was similar for each sex.
A. At 1.2 months-old, female and male Tg2576 mice were not significantly
different in IIS frequency for the low and high choline diets.
B-C. There were no significant sex differences at 2 (B) and 3 (C) months of age.
bioRxiv preprint doi: https://doi.org/10.1101/2023.05.12.540428; this version posted May 24, 2023. The copyright holder for this preprint (which
was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
available under aCC-BY-ND 4.0 International license.
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