Intermittent fasting and caloric restriction ameliorate age-related
behavioral deficits in the triple-transgenic mouse model of
Veerendra Kumar Madala Halagappa,aZhihong Guo,aMichelle Pearson,aYasuji Matsuoka,b
Roy G. Cutler,aFrank M. LaFerla,cand Mark P. Mattsona,⁎
aLaboratory of Neurosciences, National Institute on Aging, Intramural Research Program, Baltimore, MD 21224, USA
bDepartment of Neurology, Georgetown University Medical Center, Washington, DC 20057, USA
cDepartment of Neurobiology and Behavior, University of California, Irvine, CA 92697, USA
Received 24 June 2006; revised 1 December 2006; accepted 20 December 2006
Available online 13 January 2007
Alzheimer's disease (AD) is a neurodegenerative disorder character-
ized by progressive decline in cognitive function associated with the
neuropathological hallmarks amyloid β-peptide (Aβ) plaques and
neurofibrillary tangles. Because aging is the major risk factor for AD,
and dietary energy restriction can retard aging processes in the brain,
we tested the hypothesis that two different energy restriction regimens,
40% calorie restriction (CR) and intermittent fasting (IF) can protect
against cognitive decline in the triple-transgenic mouse model of AD
(3xTgAD mice). Groups of 3xTgAD mice were maintained on an ad
libitum control diet, or CR or IF diets, beginning at 3 months of age.
Half of the mice in each diet group were subjected to behavioral testing
(Morris swim task and open field apparatus) at 10 months of age and
the other half at 17 months of age. At 10 months 3xTgAD mice on the
control diet exhibited reduced exploratory activity compared to non-
transgenic mice and to 3xTgAD mice on CR and IF diets. Overall,
there were no major differences in performance in the water maze
among genotypes or diets in 10-month-old mice. In 17-month-old
3xTgAD mice the CR and IF groups exhibited higher levels of
exploratory behavior, and performed better in both the goal latency
and probe trials of the swim task, compared to 3xTgAD mice on the
control diet. 3xTgAD mice in the CR group showed lower levels of
Aβ1–40, Aβ1–42 and phospho-tau in the hippocampus compared to
the control diet group, whereas Aβ and phospho-tau levels were not
decreased in 3xTgAD mice in the IF group. IF may therefore protect
neurons against adverse effects of Aβ and tau pathologies on synaptic
function. We conclude that CR and IF dietary regimens can ameliorate
age-related deficits in cognitive function by mechanisms that may or
may not be related to Aβ and tau pathologies.
© 2007 Elsevier Inc. All rights reserved.
Keywords: Amyloid; Caloric restriction; Hippocampus; Learning and
memory; Synaptic plasticity
Alzheimer's disease (AD) is characterized by progressive
impairment of memory accompanied by psychiatric disturbances
(Lyketsos et al., 2002; Mattson, 2004; Steffens et al., 2006). The
behavioral abnormalities in AD result from dysfunction and death
of neurons in brain regions involved in cognition and mood such as
the hippocampus, entorhinal cortex, basal forebrain, and frontal
and parietal lobes. These brain regions suffer degeneration of
synapses and neurons associated with abnormal accumulation of
extracellular deposits of amyloid β-peptide (Aβ), a 40–42 amino
acid proteolytic cleavage product of the amyloid precursor protein
(APP). Aβ may cause synaptic dysfunction and degeneration of
neurons by inducing membrane-associated oxidative stress, result-
ing in disruption of cellular ion homeostasis (Mattson, 2004).
Transgenic mouse models that express a familial AD (FAD) APP
mutation alone or in combination with an FAD presenilin-1
mutation exhibit progressive Aβ deposition and variable levels of
synaptic dysfunction and cognitive impairment depending upon the
particular model (Morgan et al., 2000; Ashe, 2001; Jankowsky et
al., 2005; Kobayashi and Chen, 2005; Jacobsen et al., 2006). We
recently generated a novel triple mutant mouse model of AD
(3xTgAD mice) in which the mice express FAD APP and
presenilin-1 mutations together with a tau mutation (Oddo et al.,
2003a). The 3xTgAD mice exhibit age-dependent Aβ deposition
and tau pathology in the hippocampus and cerebral cortex which
are associated with impaired synaptic plasticity (Oddo et al.,
2003a,b) and deficits in spatial learning tasks (Billings et al.,
Previous studies have shown that caloric restriction (CR) and
intermittent fasting (IF) diets are neuroprotective and improve
functional outcome in animal models of stroke, Parkinson's and
Huntington's diseases (reviewed in Mattson, 2005). The animal
studies suggest that CR and IF may benefit the brain by reducing
levels of oxidative stress and by enhancing cellular stress resistance
Neurobiology of Disease 26 (2007) 212–220
⁎Corresponding author. Fax: +1 410 558 8465.
E-mail address: email@example.com (M.P. Mattson).
Available online on ScienceDirect (www.sciencedirect.com).
0969-9961/$ - see front matter © 2007 Elsevier Inc. All rights reserved.
mechanisms. Data from studies of human populations and animal
models suggest that reduced food intake may also protect against
AD. For example, a prospective epidemiological study of a large
cohort in New York City provided evidence that individuals with a
low calorie intake have a reduced risk of developing AD
(Luchsinger et al., 2002). Another study showed that obesity at
midlife increases the risk of AD (Kivipelto et al., 2005). Moreover,
diseases caused by excessive calorie intake (diabetes and
cardiovascular disease) are associated with increased risk of AD
(Launer, 2005). CR was recently reported to reduce the develop-
ment of amyloid pathology in the hippocampus and cerebral cortex
of transgenic mice overexpressing FAD APP mutations (Patel et
al., 2005; Wang et al., 2005), suggesting that CR can suppress a
key pathogenic process in AD. However, the effects of CR and IF
diets on the development of cognitive dysfunction in AD are
unknown. In the present study we determined if long-term CR and/
or IF could ameliorate age-related behavioral impairments in
Materials and methods
Animals and experimental design
Male and female non-transgenic C57BL/6 mice and 3xTgAD
mice (Oddo et al., 2003a) were housed in cages (4–5 five per
cage) and maintained under a 12 h light and dark cycle. These
mice were in a colony that had been exposed to mouse hepatitis
virus, but the mice were not shedding virus at the time of analysis.
At 3 months of age mice were divided into 4 groups of 20 males
and 20 females per group assigned to the following dietary
regimens: non-transgenic ad libitum (nonTg,AL), 3xTgAD ad
libitum (3xTgAD,AL), 3xTgAD 40% calorie restriction (3xTgAD,
CR), 3xTgAD intermittent fasting (3xTgAD,IF). All mice ate
standard mouse food pellets (AIN-93G; catalog #101845 from
Dyets, Inc., Bethlehem, PA). Mice on the CR diet were provided
an amount of food equal to 60% of that consumed by mice in the
3xTgAD,AL group (40% caloric restriction). Mice on the IF diet
were deprived of food for 24 h every other day. Half of the mice
in each diet group were subjected to behavioral testing after 7
months on the diets, and the other half were tested after 14 months
on the diets. One week after behavioral testing the mice were
euthanized and the hippocampus was dissected and frozen for
analyses of Aβ1–40 and Aβ1–42. During the different dietary
regimens body weights were measured weekly; the mice in the
3xTgAD,AL group gained less weight than the nonTg,AL mice
such that the 3xTgAD mice weighed 5–10 g less than the non-
transgenic mice at the end of the study. Similar to a previous study
of C57BL/6 mice (Anson et al., 2003), the 3xTgAD mice (both
males and females) in the CR group maintained significantly
lower body weights (approximately 3–7 g lower) than 3xTgAD
mice on either AL or IF diets. Over the course of the 14-month
diet interventions, some mice in each group died prior to
behavioral analyses resulting in numbers that were different
among the groups.
Open field activity
Spontaneous locomotor activity in the open field was assessed
using an apparatus equipped with infrared light sensitive photo-
cells. The apparatus was placed in a darkened, ventilated and quiet
testing room with other behavioral testing apparatus. Each animal
was placed in the apparatus and ambulatory counts and total
distance traveled were recorded over a period of 10 min.
Water maze test
A circular tank (diameter 100 cm, height 50 cm, painted white)
was filled with water (22±1 °C) to a depth of 30 cm; the water was
rendered opaque by the addition of non-toxic water paint (Palmer
Paints Products Inc, Michigan, USA). Spatial visual clues were
provided in the form of different shaped objects on the walls of
each quadrant. A circular, white escape platform (diameter 10 cm)
was submerged approximately 1 cm below the surface of the water,
10 cm off the edge of the tank at a position designated as quadrant
3 (target quadrant). A video camera was mounted on the ceiling in
the center of the pool. The swimming path length was monitored
with a Videomex tracking system and data were collected using
Videomex Water Maze Software (Columbus Instruments, Ohio,
USA) and stored on disk for future analysis.
Acquisition trials (4 trials per day for 8 days) were started by
placing the mouse in the pool facing the wall of the tank from
different randomly chosen start positions, and the time required to
find the invisible platform was recorded. A trial lasted until the
mouse found the platform or until 60 s had elapsed. If the mouse
did not find the platform within 60 s, it was guided to the platform
and placed on it for 60 s. After the completion of the fourth trial on
each day, the mouse was dried and returned to its home cage.
Twenty four hours after the final acquisition trial, the platform was
removed from the pool and a probe trial lasting 60 s was
performed; the time spent and path length in the target quadrant
were recorded. In the probe trial the mouse was started facing the
wall of the tank from the position opposite to the removed
platform. Twenty four hours after the probe trial, mice were trained
for visible platform test (4 trials per day for 2 days) to confirm that
each mouse had no visual deficits.
Quantification of Aβ1–40 and Aβ1–42 levels
Hippocampal tissue was homogenized in a buffer containing
100 mM PIPES, 500 mM NaCl, 0.2% Triton X-100, 0.1% NaN3,
2% BSA, 0.5 mM sodium vanadate, 2 mM EDTA, 200 μM PMSF
and a cocktail of protease inhibitors (10.4 mM AEBSF, 8 μM
aprotinin, 0.2 mM leupeptin, 0.4 mM bestatin, 0.15 mM pepstatin
A and 0.14 mM E-64). Samples were homogenized on ice at a
power level of 4 and pulses at 1 s intervals for 30 s. Samples were
allowed to sit on ice for 1 h, centrifuged at 12,000×g for 15 min
(4 °C) and supernatants were collected and used for ELISA.
Protein concentrations were determined using a BCA kit (Pierce).
The concentrations of Aβ1–40 and Aβ1–42 in the samples were
measured using ELISA with antibodies that specifically recognize
full-length Aβ1–40 or Aβ1–42 using methods described pre-
viously (Horikoshi et al., 2004).
The protein concentration in hippocampal tissue samples was
determined by the BCA protein assay kit (Pierce, USA). Fifty
micrograms of protein was separated by SDS–PAGE (8–12%) and
transferred to nitrocellulose membranes. The membranes were
blocked in 5% nonfat milk for 1 h at room temperature, followed
by an overnight incubation at 4 °C with antibodies against total tau
(HT7; Innogenetics), phospho-tau (AT8; Innogenetics) or β-actin
213V.K.M. Halagappa et al. / Neurobiology of Disease 26 (2007) 212–220
(Sigma). Membranes were then washed and incubated with
secondary antibodies for 1 h at room temperature. Protein bands
were visualized using a chemiluminescence detection kit (Amer-
sham Biosciences). Band intensities were quantified by densito-
metric analysis, and values for total tau and phospho-tau were
normalized to levels of actin and total tau, respectively.
In the acquisition trials of the Morris water maze the following
parameters were recorded: the escape latency (time required to
reach the platform from the releasing point in seconds), the path
length (distance traveled by the mouse from the release point to
reach platform in centimeters) and the swim speed (cm/s). Analysis
of variance (ANOVA) was conducted on these data (using
SYSTAT 8.0), with group as the between-subject factor and with
repeated measures such as trial and day as within subject factors.
Post hoc analysis (Scheffe test) was used to determine significance
between the groups. For probe trial data time spent and distance
traveled in quadrant 3 were recorded and analyzed by one way
ANOVA and post hoc analysis by Scheffe test. Values for Aβ1–40
and Aβ1–42 levels were expressed as fmol/mg of hippocampal
tissue and were analyzed by ANOVA followed by post hoc using
LSD (Fischer's Least-Significant-Difference test).
An age-related decrease in open-field activity in 3xTgAD mice is
attenuated by CR and IF
3xTgAD mice that had been maintained on the AL diet for 7 or
14 months exhibited significantly less ambulatory activity
compared to nonTg,AL control mice (Fig. 1a). There was no
effect of diet on ambulatory counts in 3xTgAD mice maintained
for 7 months on the diets. However, 3xTgAD mice maintained on
CR or IF diets for 14 months exhibited significantly greater
ambulation compared to 3xTgAD mice maintained on the AL diet
for 14 months. Consistent with the ambulatory count data,
3xTgAD mice that had been maintained on the AL diet for 7 or
14 months exhibited significantly greater distance traveled in the
open field compared to nonTg,AL control mice (Fig. 1b). There
was no effect of diet on distance traveled in 3xTgAD mice
maintained for 7 months on the diets. However, the distance
traveled by 3xTgAD mice maintained on CR or IF diets for
14 months was significantly greater than that of 3xTgAD mice
maintained on the AL diet for 14 months. These findings indicate
that 3xTgAD mice exhibit reduced locomotion and exploratory
behavior compared to non-transgenic control mice and that CR and
IF diets enhance locomotion and exploratory behavior in the
Caloric restriction and intermittent fasting ameliorate age-related
deficits in the Morris swim task
After 7 months on the diets, non-transgenic control mice, and
3xTgAD mice in all three diet groups, improved their performance
in the hidden platform test as indicated by progressive decreases in
goal latency times with increasing trials (Figs. 2a, b). Because there
were no sex differences for any of the four groups at this age, data
for males and females were combined. Two way ANOVA with
repeated measures revealed a significant main effect of days
(p<0.001). There were no significant differences in goal latency
times among the four groups of mice. The distance traveled by the
mice to reach the platform (path length) decreased across days
(F(6,511)=18.553, p<0.0001), and there was also a significant
day×group interaction (F(21,511)=2.152, p<0.002) indicating
differences among groups within each trial day. There was a
significant difference between groups (F(3,73)=13.983, p<0.01);
post hoc analysis showed that the mice in the 3xTgAD,AL group
swam longer path lengths as compared to the nonTg,AL group
(p<0.01). 3xTgAD mice in the CR (p<0.05) and IF (p<0.04)
groups swam significantly shorter path lengths as compared to the
3xTgAD,AL group indicating beneficial effects of the CR and IF
diets in the 3xTgAD mice. Analysis of swim speed data in 10-
month-old mice showed that there was a progressive increase in
swim speed across days during the first 7 days of testing in all
groups, and no significant differences in swim speeds among
groups (Supplementary Fig. 1a).
On the platform removal in the probe test, there was a general
tendency of the mice to swim preferentially in the target quadrant as
opposed to the other quadrants (Table 1). ANOVA showed
significant differences between the groups (group effect, F(3,73)=
Fig. 1. Age-related decrease in open field activity is attenuated by CR and IF
in 3xTgAD mice. Male and female mice of the indicated genotypes (non-
transgenic and 3xTgAD) were maintained on the indicated diets (ad libitum,
caloric restriction or intermittent fasting) for either 7 or 14 months. The open
field activities (ambulatory counts and distance traveled) were quantified.
Values are the mean and SEM (n=17–20 mice per group).
compared to the corresponding non-transgenic AL value. *p<0.02
compared to the corresponding 3xTgAD AL value.
214V.K.M. Halagappa et al. / Neurobiology of Disease 26 (2007) 212–220
3.532, p<0.02); post hoc analysis showed that 3xTgAD,CR mice
spent significantly more time in target quadrant as compared to
3xTgAD,AL. Analysis of path lengthin the target quadrant revealed
significant differences between the groups (group effect, F(3,73)=
3.423, p<0.03); post hoc analysis showed that 3xTgAD,CR mice
group traversed more distance in quadrant 3 compared to 3xTgAD,
After 14 months on the diets, 3xTgAD male and female mice in
all three diet groups improved their performance in the hidden
platform test as indicated by a decrease in escape latencies across
successive days (day effect, F(7,413)=34.674, p<0.0001) with no
day×group interaction (F(21,413)=1.080, p>0.37) (Figs. 3 and 4).
p<0.0001). Post hoc analysis showed that the nonTg,AL group had
significantly faster escape latencies as compared to the 3xTgAD,AL
group (p<0.0001). There was also a significant effect of sex in the
3xTgAD mice with female 3xTgAD,AL mice performing more
poorly (longer escape latencies and path lengths) compared to male
3xTgAD,AL mice. Also, there were significant differences between
the 3xTgAD,AL and the 3xTgAD,CR (p<0.02) and 3xTgAD,IF
(p<0.002) groups (both males and females). The path length
analysis showed that there was an overall decrease in the distance
traveled to reach the platform from the start positions (F(7,413)=
42.324, p<0.0001), but there was no significant interaction between
days and group (day×group effect (F(21,413)=1.086, p<0.360)).
There was a significant group effect (F(4,59)=19.602, p<0.0001).
Post hoc analyses showed that the CR (p<0.001) and IF (p<0.001)
groups (both males and females) had significantly shorter path
lengths as compared to 3xTgAD,AL group. The swim speed data
showed that there was a progressive increase in swim speed across
trial days (day effect, F(7,413)=5.338, p<0.0001), but there was no
significant interaction between days and groups (F(21,413)=1.011,
p>0.45). However, there were significant differences between the
groups (group effect, F(3,59)=2.705, p<0.05); post hoc analysis
the 3xTgAD,AL male mice (p<0.02).
The removal of the platform from the target quadrant resulted
in a general tendency to swim preferentially in the target quadrant
as opposed to the other quadrants (groups effect, F(3,59)=5.881,
p<0.001). Further post hoc analysis revealed a significant
difference in the time spent in the target quadrant between the
Fig. 2. Middle-age 3xTgAD mice exhibit modest deficits in performance in
the water maze that is significantly ameliorated by caloric restriction. Male
and female mice of the indicated genotypes (non-transgenic and 3xTgAD)
were maintained on the indicated diets (AL, CR or IF) for 7 months. The
goal latency and path length were measured in the hidden platform test.
Values are the mean and SEM (n=17–20 mice per group). 1DayP and
2DayP, first and second days of the visible platform test.
Caloric restriction and intermittent fasting improve the performance of 3xTgAD mice in the water maze probe trial task
GroupsPercent of time spent in quadrantPercent distance traveled in quadrant
Quad 1Quad 2 Quad 3
Quad 4Quad 1Quad 2 Quad 3
10 month-old mice
7 month-old mice
Non-transgenic and 3xTgAD mice were maintained on the indicated diets (AL, ad-libitum; CR, caloric restriction; IF, intermittent fasting) beginning at 3 months
of age. One cohort of mice was tested in the water maze at 10 months of age (upper) and the other at 17 months of age (lower). The percent time spent in each
quadrant, and the percent distance traveled in each quadrant, were measured in the probe trial. Values are the mean and SEM (n = 16-20 mice per group; values
for males and females were combined). *p<0.01 compared to NonTg AL,τp<0.01 compared to NonTg AL,+p<0.001 compared to the corresponding 3xTgAD
AL,#p<0.05 compared to the corresponding 3xTgAD AL value,##p<0.001 compared to the corresponding 3xTgAD AL value.
215V.K.M. Halagappa et al. / Neurobiology of Disease 26 (2007) 212–220
groups. CR and IF 3xTgAD groups spent significantly more time
in target quadrant as compared to 3xTgAD,AL group (Table 1).
Analysis of distance traveled in the target quadrant showed a
significant difference between the groups (group effect, F(3,59)=
4.398, p<0.008). The IF and CR 3xTgAD groups had signifi-
cantly longer path lengths in the target quadrant as compared to the
3xTgAD,AL group (Table 1). The results of the probe trial tests
suggest that old 3xTgAD mice exhibit impaired memory retention
compared to non-transgenic control mice and that both the CR and
IF diets ameliorate this age-related memory deficit.
Caloric restriction, but not intermittent fasting, decreases Aβ and
phospho-tau levels in the hippocampus of 3xTgAD mice
Previous studies of mouse models of AD have established
associations between the amount of Aβ present in the hippocam-
pus and deficits in spatial learning (Chapman et al., 1999; Chen et
al., 2000; Hock et al., 2003). It was also reported that CR can
reduce the accumulation of Aβ in the brains of APP mutant mice
(Patel et al., 2005; Wang et al., 2005). We therefore employed a
highly sensitive ELISA method to quantify levels of Aβ1–40 and
Aβ1–42 in hippocampal tissues from 3xTgAD mice that had been
maintained for 14 months on AL, CR or IF diets. The
concentrations of Aβ1–40 and Aβ1–42 were significantly lower
in the hippocampus of mice in the CR group compared to the AL
and IF groups (Fig. 5). One way ANOVA showed that there was a
significant difference between the groups (group effect, F(2,32)=
3.161, p<0.05); post hoc analysis showed that the CR group had
significantly lower Aβ1–40 and Aβ1–42 levels as compared to the
AL group (Aβ1–40, p<0.05; Aβ1–42, p<0.03). In contrast Aβ
levels in the hippocampus of 3xTgAD,IF mice were not
significantly different than Aβ levels in the hippocampus of
Fig. 5. Caloric restriction, but not intermittent fasting, reduces levels of
Aβ1–40 and Aβ1–42 in the hippocampus of older 3xTgAD mice. Levels of
Aβ1–40 and Aβ1–42 in hippocampal tissues from the indicated groups of
mice were quantified by ELISA methods. Values are the mean and SEM
(n=13–19). *p<0.05 compared to the AL and IF values.
Fig. 4. Old female 3xTgAD mice exhibit a deficit in performance in the
hidden platform test in the water maze that is ameliorated by caloric
restriction and intermittent fasting. Seventeen-month-old female mice of the
indicated genotypes (non-transgenic and 3xTgAD) were maintained on the
indicated diets (ad libitum, caloric restriction or intermittent fasting) for 14
months. The goal latency (a) and path length (b) were measured in the
1DayP and 2DayP, first and second days of the visible platform test.
Fig. 3. Old male 3xTgAD mice exhibit a deficit in performance in the hidden
platform test in the water maze that is ameliorated by caloric restriction and
intermittent fasting. Male mice of the indicated genotypes (non-transgenic
and 3xTgAD) were maintained on the indicated diets (ad libitum, caloric
restriction or intermittent fasting) for 14 months. The goal latency (a) and
path length (b) were measured in the hidden platform test. Values are the
mean and SEM (n=7–10 mice per group). 1DayP and 2DayP, first and
second days of the visible platform test.
216 V.K.M. Halagappa et al. / Neurobiology of Disease 26 (2007) 212–220
Levels of phosphorylated tau increase in an age-dependent
To determine the effects of dietary energy restriction on the
development of tau pathology, we measured levels of total tau and
phospho-tau by immunoblot analysis in hippocampal tissue
samples from 3xTgAD mice that had been maintained on AL, CR
or IF diets for 14 months. Levels of total tau, measured using
antibody HT7, were not different in samples from 3xTgAD mice on
AL, CR and IF diets (Fig. 6). However, levels of phosphorylated
tau, measured using antibody AT8, were significantly lower in
samples from mice in group CR, compared to mice in either the AL
or IF groups (Fig. 6).
Our findings provide evidence that dietary energy restriction
regimens can ameliorate learning and memory deficits in an animal
model of AD. 3xTgAD mice fed ad libitum exhibited age-
dependent impairment in performance in both acquisition (goal
latency) and retention (probe trial) tasks in the Morris water maze
compared to non-transgenic control mice. In contrast, 3xTgAD
mice maintained on CR or IF diets for 14 months exhibited no
deficits in water maze tasks, performing as well as non-transgenic
mice. We found that levels of Aβ1–40 and Aβ1–42 were
significantly lower in 3xTgAD mice on the CR diet compared to
those on the ad libitum diet. The ability of CR to reduce Aβ levels
in the 3xTgAD mice is consistent with two previous studies in
which APP mutant mice on CR diets exhibited lower levels of Aβ
in their brains (Patel et al., 2005; Wang et al., 2005). The
mechanism whereby CR reduces Aβ levels is not known, but may
involve reduced levels of oxidative stress because oxidative stress
enhances Aβ production and aggregation in mouse models (Pratico
et al., 2001; McLellan et al., 2003), whereas CR reduces levels of
oxidative stress in brain cells during normal aging (Sohal et al.,
1994; Ugochukwu et al., 2006). Consistent with the latter
mechanism, treatment of APP mutant mice with antioxidants
reduces Aβ levels and ameliorates memory deficits (Lim et al.,
2001; Quinn et al., 2006). On the other hand, diet-induced diabetes
(which is known to increase oxidative stress) enhanced Aβ
accumulation in a mouse model of AD (Ho et al., 2004).
Interestingly, we found that IF ameliorated behavioral deficits
in the 3xTgAD mice, but did not affect levels of Aβ1–40 or Aβ1–
42 in the hippocampus. Recent studies have documented beneficial
effects of IF in animal models of Parkinson's disease (Duan and
Mattson, 1999; Maswood et al., 2004), Huntington's disease (Duan
et al., 2003) and stroke (Yu and Mattson, 1999). IF protects
neurons against oxidative and excitotoxic and metabolic insults
(Bruce-Keller et al., 1999). The neuroprotective mechanism of IF
involves induction of a mild adaptive cellular stress response in
which neurons upregulate the expression of neurotrophic factors
and protein chaperones such as heat-shock protein 70 (Yu and
Mattson, 1999; Lee et al., 2002). Aβ has been shown to impair
synaptic function (Keller et al., 1997), and synapses from rats
maintained on IF exhibit increased resistance to being damaged by
Aβ (Guo and Mattson, 2000). It is therefore likely that IF preserves
synaptic function in 3xTgAD mice even in the presence of levels of
Aβ that impair synaptic function in mice fed ad libitum. One
specific mechanism whereby IF may protect neurons and promote
synaptic plasticity is by enhancing brain-derived neurotrophic
factor (BDNF) signaling. Consistent with the latter possibility,
mice maintained on IF exhibit increased levels of BDNF in
multiple brain regions including the hippocampus (Duan et al.,
2001; Lee et al., 2002), BDNF plays an important role in
Fig. 6. Caloric restriction, but not intermittent fasting, suppresses tau pathology in the hippocampus of older 3xTgAD mice. Levels of total tau and phospho-tau
were measured by immunoblot analysis using HT7 and AT8 antibodies, respectively, in hippocampal tissues from the indicated groups of mice. (a) Immunoblot
probed with the indicated antibodies. (b) Results of densitometric analysis (values are the mean and SEM; n=3–5). *p<0.05 compared to the AL and IF values.
217V.K.M. Halagappa et al. / Neurobiology of Disease 26 (2007) 212–220
hippocampal synaptic plasticity and learning and memory (Tyler et
al., 2002; Lu, 2003) and BDNF can protect neurons from being
damaged by various oxidative and metabolic insults (Spina et al.,
1992; Duan et al., 2001).
Several dietary and behavioral factors have been suggested to
modify the risk of AD. In addition to positive associations of high
calorie intakes and diabetes with AD risk (Luchsinger et al., 2002;
Launer, 2005), low levels of exercise (Laurin et al., 2001; Larson et
al., 2006) and low levels of cognitive stimulation (Wilson et al.,
2002) may increase the risk of AD. Studies in transgenic mouse
models of AD have demonstrated ameliorative effects of exercise
and environmental enrichment on amyloid pathology and cognitive
function (Adlard et al., 2005; Jankowsky et al., 2005; Lazarov et
al., 2005). Our findings provide direct evidence that long-term
dietary energy restriction, either CR or IF, can ameliorate age-
related impairments in learning and memory tasks. The differential
effects of CR and IF on Aβ accumulation in the hippocampus
suggest that dietary factors can suppress the disease process either
upstream or downstream of Aβ pathology. The dissociation
between Aβ and performance in the water maze task, evident in
3xTgAD,IF mice, also provides a possible explanation for the fact
that some humans can tolerate a high Aβ load in their brains
without cognitive impairment (Mufson et al., 1999; Giannakopou-
los et al., 2003).
There are strong associations between tau pathology (tangles
and levels of phosphorylated tau) and cognitive function in human
subjects with AD or mild cognitive impairment (Nagy et al., 1995;
Fellgiebel et al., 2004). However, there are human subjects with a
relatively high amounts of tau pathology that perform well on
cognitive tests. Strong evidence that tau pathology is not sufficient
to cause cognitive decline comes from a study of transgenic mice
expressing a repressible human tau variant; after suppression of the
transgenic tau, memory function recovered (Santacruz et al., 2005).
Studies of another mouse model of tauopathy have shown that
some neurons degenerate before neurofibrillary lesions develop,
whereas other neurons exhibit neurofibrillary pathology, but do not
degenerate (Spires et al., 2006). Moreover, studies of transgenic
mouse model with conditional overexpression of glycogen
synthase kinase-3 (a kinase believed to contribute to hyperpho-
sphorylation of tau in AD) have shown that tau hyperpho-
sphorylation can be reversed (Engel et al., 2006). In the present
study we found that 3xTgAD mice maintained on the IF diet
exhibited levels of phosphorylated tau similar to 3xTgAD mice on
the AL diet, and yet the IF diet improved performance of the mice
in the behavioral tasks. Although we did not establish the
mechanism by which hippocampal neurons in 3xTgAD mice on
the IF diet are able to function well despite considerable tau
pathology, we do know that the IF diet increases the resistance of
neurons to a range of adverse conditions including oxidative and
metabolic stress and excitotoxicity (Bruce-Keller et al., 1999; Yu
and Mattson, 1999; Duan et al., 2001). Our findings in the
3xTgAD mice are consistent with the possibility that IF results in
changes in neurons that increase their resistance to adverse effects
of Aβ and tau.
Increasing evidence from studies of human populations
suggests that overeating and diabetes increase the risk of AD
(Ott et al., 1999; Janson et al., 2004; Luchsinger et al., 2004; Xu et
al., 2004; Launer, 2005), whereas low calorie diets may reduce
disease risk (Luchsinger et al., 2002; Gustafson et al., 2003). This
influence of dietary energy intake appears to be exerted on
fundamental aspects of the disease process, either accelerating or
retarding Aβ production and oxidative stress. A diabetogenic diet
resulted in increased γ-secretase activity, production of Aβ1–40
and Aβ1–42 and amyloid plaque burden in APP mutant mice (Ho
et al., 2004). IF and CR diets exert anti-diabetic effects in mice
resulting in reduced levels of insulin and increased insulin
sensitivity (Anson et al., 2003). It was reported that hyperinsuli-
nemia results in increased levels of Aβ and inflammatory cytokines
which have deleterious effects on memory (Craft, 2005). We found
that a diabetogenic diet worsens performance of 3xTgAD mice in
water maze tasks (V. Halagappa and M. P. Mattson, unpublished
data) suggesting an adverse effect of high energy diets on synaptic
plasticity and cognitive function. Collectively, the available data
suggest that long-term reductions in energy intake during adult life
may protect the brain against diseases of aging and should be
considered, together with exercise and cognitive enrichment, as an
approach for reducing the risk of AD.
This research was supported by the National Institute on Aging
Intramural Research Program; and by NIA grant AG022455 (YM).
The authors thank Ms Chiho Hirata-Fukae (Department of
Neurology, Georgetown University Medical Center) for technical
assistance. Antibodies used for Abeta ELISAs were generously
provided by Dr Noriaki Kinoshita (Immuno-Biological Labora-
tories Co., Ltd., Takasaki, Gunma, Japan).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
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