FROM:
Nature 2006 (Nov 16); 444 (7117): 337–342
Joseph A. Baur, Kevin J. Pearson, Nathan L. Price, Hamish A. Jamieson,
Carles Lerin, Avash Kalra, Vinayakumar V. Prabhu, Joanne S. Allard,
Guillermo Lopez-Lluch, Kaitlyn Lewis, Paul J. Pistell
Department of Pathology,
Paul F. Glenn Laboratories for the Biological Mechanisms of Aging,
Harvard Medical School,
77 Avenue Louis Pasteur,
Boston, Massachusetts 02115, USA
Resveratrol (3,5,4'-trihydroxystilbene) extends the lifespan of diverse species including Saccharomyces cerevisiae, Caenorhabditis elegans and Drosophila melanogaster. In these organisms, lifespan extension is dependent on Sir2, a conserved deacetylase proposed to underlie the beneficial effects of caloric restriction. Here we show that resveratrol shifts the physiology of middle-aged mice on a high-calorie diet towards that of mice on a standard diet and significantly increases their survival. Resveratrol produces changes associated with longer lifespan, including increased insulin sensitivity, reduced insulin-like growth factor-1 (IGF-I) levels, increased AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) activity, increased mitochondrial number, and improved motor function. Parametric analysis of gene set enrichment revealed that resveratrol opposed the effects of the high-calorie diet in 144 out of 153 significantly altered pathways. These data show that improving general health in mammals using small molecules is an attainable goal, and point to new approaches for treating obesity-related disorders and diseases of ageing.
From the FULL TEXT Article:
Background
The number of overweight individuals worldwide has reached 2.1
billion, leading to an explosion of obesity-related health problems
associated with increased morbidity and mortality. [1, 2] Although the
association of obesity with increased risk of cardiovascular disease
and diabetes is well known, it is often under-appreciated that the risks
of other age-related diseases, such as cancer and inflammatory disorders,
are also increased. At the other end of the spectrum, reducing
caloric intake by,40% below that of ad libitum-fed animals (caloric
restriction) is the most robust and reproducible way to delay agerelated
diseases and extend lifespan in mammals. [3, 4]
Experiments with Saccharomyces cerevisiae and Drosophila melanogaster
have implicated the sirtuin/Sir2 family of NAD1-dependent
deacetylases and mono-ADP-ribosyltransferases as mediators of the
physiological effects of caloric restriction5. In mammals, seven sirtuin
genes have been identified (SIRT1–7). SIRT1 regulates such processes
as glucose and insulin production, fat metabolism, and cell survival,
leading to speculation that sirtuins might mediate effects of caloric
restriction in mammals. [5] We previously screened over 20,000
molecules to identify, 25 that enhance SIRT1 activity in vitro. [6]
Resveratrol, a molecule produced by a variety of plants in response
to stress, emerged as the most potent.
Resveratrol has since been shown to extend the lifespan of evolutionarily
distant species including S. cerevisiae, C. elegans and D. melanogaster
in a Sir2-dependent manner.6–9] A recent study found that
resveratrol improves health and extends maximum lifespan by
59% in a vertebrate fish. [10] In mammalian cells, resveratrol produces
SIRT1-dependent effects that are consistent with improved cellular
function and organismal health. [11–15] Whether resveratrol acts directly
or indirectly through Sir2 in vivo is currently a subject of debate. [16]
On the basis of the unprecedented ability of resveratrol to improve
health and extend lifespan in simple organisms, we have asked
whether it has similar effects in mice. We hypothesized that resveratrol
might shift the physiology of mice on a high-calorie diet towards
that of mice on a standard diet and provide the associated health
benefits without the mice having to reduce calorie intake. Cohorts of
middle-aged (one-year-old) male C57BL/6NIA mice were provided
with either a standard diet (SD) or an otherwise equivalent highcalorie
diet (60% of calories from fat, HC) for the remainder of their
lives. To each of the diets, we added resveratrol at two concentrations
that provided an average of 5.2 ± 0.1 and 22.4 ± 0.4 mg kg–1 day–1,
which are feasible daily doses for humans. After 6 months of treatment,
there was a clear trend towards increased survival and insulin
sensitivity. Because the effects were more prominent in the higher
dose (22.4 ± 0.4 mg kg–1 day–1, HCR), we initially focused our
resources on this group and present the results of those analyses
herein. Analyses of the other groups will be presented at a later date.
Increased survival
Mice on the HC diet steadily gained weight until ~75 weeks of age,
after which average weight slowly declined (Fig. 1a). Although mice
on the HCR diet were slightly lighter than the HC mice during the
initial months, there was no significant weight difference between the
groups from 18–24months, when most of our analyses were performed.
There was also no difference in body temperature (Table 1),
food consumption (Supplementary Fig. 1a, b), total faecal output or
lipid content (Supplementary Fig. 1c, d), or post-mortem body fat
distribution (Supplementary Fig. 2).
Table 1.
Effects of a high-fat diet and resveratrol on various biomarkers in plasma
Figure 1
Resveratrol increases survival and improves rotarod performance.
a, Body weights of mice fed a standard diet (SD), high-calorie
diet (HC), or high-calorie diet plus resveratrol (HCR).
b, Kaplan–Meier
survival curves. Hazard ratio for HCR is 0.69 (x255.39, P50.020) versus
HC, and 1.03 (x250.022, P50.88) versus SD. The hazard ratio for HC
versus SD is 1.43 (x255.75, P50.016).
c, Time to fall from an accelerating
rotarod was measured every 3 months for all survivors from a pre-designated
subset of each group; n515 (SD), 6 (HC) and 9 (HCR). Asterisk, P,0.05
versus HC; hash, P,0.05 versus SD. Error bars indicate s.e.m.
|
Figure 1 A.
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Figure 1B.
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Figure 1C.
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At 60 weeks of age, the survival curves of the HC and HCR groups
began to diverge and have remained separated by a 3–4-month interval
(Fig. 1b). A similar effect on survival was observed in a previous
study of one-year-old C57BL/6 mice on caloric restriction, ultimately
resulting in a 20% extension of mean lifespan. [17] With the present age
of the colony at 114 weeks, 58% of the HC control animals have died
(median lifespan 108 weeks), as compared to 42% of the HCR group
and 42% of the SD controls. Although we cannot yet confidently
predict the ultimate mean lifespan extension, Cox proportional
hazards regression shows that resveratrol reduced the risk of death
from the HC diet by 31% (hazard ratio = 0.69, P = 0.020), to a point
where it was not significantly different from the SD group (hazard ratio = 1.03, P = 0.88).
Although resveratrol increased survival, it was important to ascertain
whether quality of life was maintained. One way to assess this was
to measure balance and motor coordination, which we did by examining
the ability to perform on a rotarod. Surprisingly, the resveratrol-
fed HC mice steadily improved their motor skills as they aged, to
the point where they were indistinguishable from the SD group
(Fig. 1c). It is possible that the improved rotarod performance might
have been due to minor differences in body weight but we view this as
unlikely because we found no correlation between body weight and
performance within groups and rotarod performance was also
improved for resveratrol-treated SD mice (R.deC. and K.P., unpublished data). These data are reminiscent of the resveratrol-mediated
increase in motor activity in older individuals of the vertebrate fish
species Nothobranchius furzeri. [10]
Increased insulin sensitivity
In humans, high-calorie diets cause numerous pathological conditions
including increased glucose and insulin levels leading to diabetes,
cardiovascular disease and non-alcoholic fatty liver disease, a
condition for which there is no effective treatment. [18] The HC-fed
mice had alterations in plasma levels of markers that predict the onset
of diabetes and a shorter lifespan, including increased levels of insulin,
glucose and IGF-1 (Table 1). The HCR group had significantly
lower levels of these markers, paralleling the SD group. An oral glucose
tolerance test indicated that the insulin sensitivity of the resveratrol-
treated mice was considerably higher than controls (Fig. 2a–d).
Homeostatic model assessment, which is used to quantify insulin
resistance, gave scores of 2.5 for SD, 8.8 for HC and 3.5 for HCR,
confirming improved sensitivity (HCR versus HC, P50.01).
Although the persistence of high glucose levels for more than
60 min following an oral dose is unusual for young mice, it is typical
for older animals. [19] Compared to the HC controls, the areas under
the curves for both glucose and insulin levels were significantly
decreased in the resveratrol-fed HC group and were not significantly
different from mice in the SD group (Fig. 2b, d).
Figure 2 & Supplementary Figure 3
Resveratrol improves insulin sensitivity and activates AMPK.
a–d, Plasma levels of glucose (a, b) and insulin (c, d) were measured after a 2 g kg21 oral glucose dose. Areas under the curves (AUC) were significantly reduced by resveratrol treatment. e, Activation of AMPK by resveratrol in CHO cells. In the presence of resveratrol or 5-aminoimidazole-4-carboxamide-1-b-D-ribofuranoside (AICAR) as a positive control, phosphorylation of AMPK and its downstream target, acetyl-coA
carboxylase (ACC), are increased. f,AMPKactivity in liver. Phosphorylation of AMPK (f), acetyl-coA carboxylase
(Supplementary Fig. 3e) and decreased expression of fatty acid synthase
(Supplementary Fig. 3f) are indicative of enhanced AMPK activity. Asterisk, P,0.05 versus HC; hash, P,0.05 versus SD. n55 for all groups. Error bars indicate s.e.m.
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Figure 2 A, B.
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Figure 2 C, D.
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Figure 3 E, F.
|
Next, we investigated possible mechanisms behind these metabolic
effects. AMPK is a metabolic regulator that promotes insulin
sensitivity and fatty acid oxidation. Its activity correlates tightly
with phosphorylation at Thr 172 (p-AMPK). Chronic activation of
AMPK occurs on a calorically restriction diet and has been proposed
as a longevity strategy for mammals. [20] Consistent with this idea,
additional copies of the AMPK gene are sufficient to extend lifespan
in C. elegans. [21] Because we and others [22] have observed that resveratrol
can activate AMPK in cultured cells through an indirect mechanism
(Fig. 2e; see also Supplementary 3a–d), we examined whether AMPK
activation occurred in the livers of the resveratrol-fed group. Resveratrol
showed a strong tendency towards inducing phosphorylation
of AMPK (Fig. 2f), as well as two downstream indicators of
activity, namely phosphorylation of acetyl-coA carboxylase at Ser 79
and decreased expression of fatty acid synthase (Supplementary
Fig. 3e, f).
Decreased organ pathology
At 18 months of age it was apparent that the high-calorie diet greatly
increased the size and weight of livers and that resveratrol prevented
these changes (Fig. 3a–c; see also Supplementary Fig. 4a, b) without
altering plasma lipid levels (Table 1). Histological examination of
liver sections by staining with haematoxylin and eosin or oil red O
revealed a loss of cellular integrity and the accumulation of large lipid
droplets in the livers of the HC but not the HCR group. Blinded
scoring of the liver sections for overall pathology on a scale of 0–4
(with 4 being the most severe) gave mean values of 1.3 for the SD
group, 2.8 for the HC group and 0.8 for the HCR group (Fig. 3b).
Plasma amylase, which can indicate pancreatic damage, was elevated
in the HC group and was significantly reduced by resveratrol
(Table 1). The reasons for the elevation of plasma amylase levels in
the HC group are unclear given that pancreatic sections of all animals
revealed no damage to the pancreas or decrease in islet area (data not
shown). Differences in the weights of other organs did not reach
statistical significance.
Figure 3.
Resveratrol improves liver histology, increases mitochondrial number
and decreases acetylation of PGC-1a.
a–c, Resveratrol prevents the development of fatty liver, as assessed by organ size (a), overall pathology
(b) and decreased fat accumulation asmeasured by oil red O staining (c). AU, arbitrary units. d, Pathology of heart sections. Additional histology of liver, heart and aorta is shown in Supplementary Fig. 4. e, f, Transmission electron microscopy of liver sections (e) and mitochondrial counts (f). g, h,Mitochondrial number in HeLa cells treated with serumfromad libitumfed (AL) or calorically restricted (CR) rats, or resveratrol, and stained with Mitotracker green FM. i, j, Resveratrol reduces the acetylation of PGC-1a, a known SIRT1 target and regulator ofmitochondrial biogenesis, in vivo. PGC-1a was immunoprecipitated from liver extracts then blotted for acetyl lysine (i) and quantified (j). Asterisk, P,0.05 versus HC; hash, P,0.05 versus SD.
n55 for b and d; n53 for f and j. Error bars indicate s.e.m.
|
|
The ability of resveratrol to improve motor function and increase
insulin sensitivity indicated that its effects were not confined to the
liver. To test directly whether other organs also benefited, we examined
heart tissue of the SD, HC and HCR mice. Blinded scoring of
overall pathology—taking into account subtle changes in the abundance
of fatty lesions, cardiac muscle vacuolization, degeneration and
inflammation—on a relative scale of 0–4 (with 4 being the most
severe) gave mean values of 1.6 for the SD group, 3.2 for the HC
group and 1.2 for HCR group (Fig. 3d; see also Supplementary Fig.
4c). Improvements in the morphology of the aortic elastic lamina
were also apparent (Supplementary Fig. 4d).
Increased mitochondria
Exercise and reduced caloric intake increase hepatic mitochondrial
number [23, 24] and we wondered whether resveratrol might produce the
same effect. The livers of the resveratrol-treated mice had considerably
more mitochondria than those of HC controls and were not
significantly different compared to those of the SD group (Fig. 3e, f).
There was also a trend towards higher citrate synthase activity in the
resveratrol-fed mice (an indicator of increased mitochondrial content)
although the effect was not significant (Table 1). Culturing FaO
hepatoma or HeLa cells in the presence of resveratrol increased mitochondrial
number (Fig. 3g, h), similar to the previously reported
effect of culturing cells in serum from calorically restricted rats24.
Mitochondrial biogenesis in liver and muscle is controlled, in large
part, by the transcriptional coactivator PGC-1a [25, 26], the activity of
which, in turn, is positively regulated by SIRT1-mediated deacetylation
27,28. Hence, the acetylation status of PGC-1a is considered a
marker of SIRT1 activity in vivo. [27] Because this assay required more
tissue than was available, we examined a separate cohort of one-yearold
mice on the HC diet that had been treated with resveratrol for
6 weeks at 186 mg kg
–1 d–1. The acetylation status of PGC-1a in
the resveratrol-fed mice was threefold lower than the diet-matched
controls (Fig. 3i, j). There was no detectable increase in SIRT1 protein
levels in resveratrol-treated mice (data not shown), suggesting that
SIRT1 enzymatic activity was enhanced by resveratrol.
Microarrays and pathway analysis
These data demonstrate that resveratrol can alleviate the negative
impact of a high-calorie diet on overall health and lifespan. To determine
to what extent resveratrol had shifted the physiology of the
high-calorie group towards the lower calorie group, we performed
whole-genome microarrays and pathway analysis on liver samples.
Z ratios were calculated as described previously [29] and a subset of
expression changes was verified by polymerase chain reaction with
reverse transcription (RT–PCR) (Supplementary Fig. 5). In the HCR
group, expression patterns for 782 out of 41,534 (,2%) individual
genes changed significantly relative to the diet-matched controls
(Fig. 4a, b). Notably, within the top 12 most highly elevated transcripts
were serum amyloid proteins (Saa1–3), major urinary
proteins (Mup1 and Mup3), and both forms of hydroxysteroid dehydrogenase
that degrade testosterone (Hsd3b4, Hsd3b5). The list of
12 most highly downregulated transcripts included three cytochrome
p450 enzymes (Cyp2a4, Cyp2a5 and Cyp2b9) that are known to activate
pro-carcinogens. [30]
The complete data set is available at
http://www.grc.nia.nih.gov/branches/rrb/dna/index/dnapubs.htm#2.
Figure 4.
Resveratrol shifts expression patterns of mice on a high-calorie
diet towards those on a standard diet.
a, b, The most highly significant upregulated (a) and downregulated (b) genes in livers of HC and HCR
groups are shown. c, Parametric analysis of gene-set enrichment (PAGE) comparing every pathway significantly upregulated (red) or downregulated (blue) by either the HC diet or resveratrol (153 in total, with 144 showing
opposing effects). d, Principal component analysis of PAGE data. The first principal component (PC1) is dominant, with 88.4% variability, and shows HCR to be more similar to SD than HC. e, Comparison of pathways
significantly altered by resveratrol treatment and caloric restriction using data from the AGEMAP caloric restriction study. Pathways with significant differences between HC and HCR are indicated by an asterisk. Complete pathway listings are in Supplementary Fig. 7. Asterisk, P,0.05 versus HC. n55 for SD and HC; n54 for HCR.
We next performed parametric analysis of gene set enrichment
(PAGE), a computational method that determines differences
between pathways using a priori defined gene sets. [31, 32] PAGE analysis
indicated that resveratrol caused a significant alteration in 127 pathways,
including the TCA cycle, glycolysis, the classic and alternative
complement pathways, butanoate and propanoate metabolism,
sterol biosynthesis and Stat3 signalling (Supplementary Fig. 6; for a
complete list see Supplementary Fig. 7). Some of the most highly
downregulated pathways in the resveratrol-fed group are known to
extend lifespan in model organisms when attenuated, including insulin
signalling, IGF-1 and mTOR signalling, oxidative phosphorylation
and electron transport. [33–36] Downregulation of glycolysis is a
well known marker of caloric restriction37 and has been proposed
as a mechanism by which caloric restriction works. [38] The increase
in Stat3, a transcription factor involved in cell survival and liver
regeneration [39], is of note because its activity is known to be suppressed
in the liver by high caloric diets and shows an age-related
decline in activity that is attenuated by caloric restriction. [40, 41]
A few of the pathway changes were unanticipated. Although we
had observed an increase in mitochondrial number in the HCR
group, there was a decrease in the transcription of numerous mitochondrial
genes, suggesting that the turnover of mitochondrial proteins
was reduced. This result was unexpected, but is consistent with a
previous report showing that SIRT1-dependent activation of PGC-
1a does not enhance transcription of mitochondrial genes. [27]
Upregulation of complement, which occurs in obese and aged mice,
was also observed in the HCR group for reasons that are currently
unclear.
It is notable that resveratrol opposed the effects of high caloric
intake in 144 out of 153 significantly altered pathways (Fig. 4c). In
fact, the PAGE signature of the HCR group was considerably more
similar to that of the SD group than the HC controls. Principal
component analysis yielded values of 21.82 (SD), 21.41 (HCR)
and 3.22 (HC), with 88.4% of the variability assigned to the first
principal component, making the HC group the clear outlier
(Fig. 4d).
We next compared our PAGE results to a pre-existing caloric
restriction data set for C57BL/6 mice known as AGEMAP, hypothesizing
that the comparison of changes induced by these two paradigms
might reveal pathways common to the enhancement of health and
longevity. Of the 36 different pathways identified by AGEMAP as
being significantly altered by caloric restriction, there was sufficient
overlap to compare 19 of them to our data (Fig. 4e). Pathways altered
in the same direction by caloric restriction and resveratrol included
the downregulation of IGF-1 and mTOR signalling, downregulation
of glycolysis, and upregulation of Stat3 signalling. One interesting
difference was that cell cycle checkpoint and apoptotic pathways were
elevated in the caloric restriction group but downregulated by resveratrol.
We do not favour the interpretation that the resveratrol-treated
livers were undergoing less apoptosis because levels of AST and ALT,
two indicators of hepatic apoptosis, were unchanged (see Table 1).
Perhaps the downregulation of cell cycle checkpoints is linked to the
recent discovery that inhibition of checkpoint function in C. elegans
increases stress resistance and lifespan. [42] Although the statistical
power of this analysis is limited by the overlap in data sets, the results
suggest that more comprehensive comparisons of the effects of
resveratrol and caloric restriction are warranted.
Discussion
The ability of resveratrol to prevent the deleterious effects of excess
caloric intake and modulate known longevity pathways suggests that
resveratrol and molecules with similar properties might be valuable
tools in the search for key regulators of energy balance, health and
longevity. As a case in point, the most highly upregulated gene in the
HC group and second most highly downregulated gene in the HCR
group was Cidea, which regulates energy balance in brown fat and
provides resistance to obesity and diabetes when knocked out. [43]
Taken together, the findings in this study show that resveratrol
shifts the physiology of mice consuming excess calories towards that
of mice on a standard diet, modulates known longevity pathways,
and improves health, as indicated by a variety of measures including
survival, motor function, insulin sensitivity, organ pathology, PGC-
1a activity, and mitochondrial number. Notably, all these changes
occurred without a significant reduction in body weight. Whether
these effects are due to resveratrol working primarily through SIRT1,
which is the case for simpler metazoans, or through a combination
of interactions, as predicted by the xenohormesis hypothesis [6, 44],
remains to be determined. In either case, this study shows that an
orally available small molecule at doses achievable in humans can
safely reduce many of the negative consequences of excess caloric
intake, with an overall improvement in health and survival.
METHODS
Animals and diets.
Animal housing and diets are described in Supplementary
Information. Briefly, one-year-old male C57BL/6NIA mice were maintained on
AIN-93G standard diet (SD), AIN-93G modified to provide 60% of calories from
fat (HC), or HC diet with the addition of 0.04% resveratrol (HCR).
Electron microscopy.
Tissues were processed as previously reported, imaged at
31,500 on a Jeol 1210 transmission microscope, and photographed using a
Gatan US 4000 MP Digital camera. Mitochondria per cell and hepatocyte size
were quantified using grid counting by three blinded raters.
PAGE analysis.
RNA extracted from the livers of five 18-month-old mice per
group was hybridized to Agilent 44k whole-genome microarrays following protocols
listed on the Gene Expression and Genomics Unit website at the National
Institute on Aging (http://www.grc.nia.nih.gov/branches/rrb/dna/index/protocols.
htm). One array from the HCR group was discarded owing to RNA degradation.
Raw data were subjected to Z normalization and tested for significant
changes as previously described. [29] For parametric analysis of gene set enrichment
(PAGE), a complete set of 522 pathways in the cell was obtained from http://
www.broad.mit.edu/gsea/msigdb/msigdb_index.html. Details of the method are
described in Supplementary Information and elsewhere. [31] Principal component
analysis was performed on the replicate average for the three groups. These tools
are part of DIANE 1.0, a program developed by V.V.P and available at http://
www.grc.nia.nih.gov/branches/rrb/dna/diane_software.pdf. Caloric restriction
data were extracted from the AGEMAP project.
Cell-based mitochondrial assays.
Mitochondrial mass was determined using
the mitochondria-specific fluorescent dye Mitotracker greenFMafter fixation of
cells, with minor modifications. Staining after fixation permits determination of
the incorporation of the dye due to mitochondrial mass independently of the
mitochondrial membrane potential (Dym).
Serum markers and hormones.
Details of biochemical assays are described in
Supplementary Information.
AMPK and PGC-1a analysis.
Extraction of tissues and cells for western blotting
were performed using standard techniques. Details and antibodies are outlined
in Supplementary Information.
Histology.
Eighteen-month-old mice were fasted overnight and fixed using
Streck fixative (Streck). Organs were sectioned and stained with haematoxylin
and eosin or frozen and stained with oil red O lipid stain, then scored blindly for
overall pathology.
Rotarod.
Results shown are the average of three trials per mouse, measuring time
to fall from an accelerating rotarod (4–40 r.p.m. over 5 min). Data from animals
that survived to 24 months are shown.
Statistical analyses.
Single factor analysis of variance followed by Fisher’s posthoc
tests were used for all comparisons, except where noted. Details are provided
in Supplementary Information.
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