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Fasting promotes the expression of SIRT1, an NAD+-dependent protein deacetylase, via activation of PPARα in mice

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Calorie restriction (CR) extends lifespans in a wide variety of species. CR induces an increase in the NAD(+)/NADH ratio in cells and results in activation of SIRT1, an NAD(+)-dependent protein deacetylase that is thought to be a metabolic master switch linked to the modulation of lifespans. CR also affects the expression of peroxisome proliferator-activated receptors (PPARs). The three subtypes, PPARalpha, PPARgamma, and PPARbeta/delta, are expressed in multiple organs. They regulate different physiological functions such as energy metabolism, insulin action and inflammation, and apparently act as important regulators of longevity and aging. SIRT1 has been reported to repress the PPARgamma by docking with its co-factors and to promote fat mobilization. However, the correlation between SIRT1 and other PPARs is not fully understood. CR initially induces a fasting-like response. In this study, we investigated how SIRT1 and PPARalpha correlate in the fasting-induced anti-aging pathways. A 24-h fasting in mice increased mRNA and protein expression of both SIRT1 and PPARalpha in the livers, where the NAD(+) levels increased with increasing nicotinamide phosphoribosyltransferase (NAMPT) activity in the NAD(+) salvage pathway. Treatment of Hepa1-6 cells in a low glucose medium conditions with NAD(+) or NADH showed that the mRNA expression of both SIRT1 and PPARalpha can be enhanced by addition of NAD(+), and decreased by increasing NADH levels. The cell experiments using SIRT1 antagonists and a PPARalpha agonist suggested that PPARalpha is a key molecule located upstream from SIRT1, and has a role in regulating SIRT1 gene expression in fasting-induced anti-aging pathways.
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Fasting promotes the expression of SIRT1, an NAD
+
-dependent
protein deacetylase, via activation of PPARain mice
Satoru Hayashida Akie Arimoto Yukako Kuramoto
Tomohiro Kozako Shin-ichiro Honda
Hiroshi Shimeno Shinji Soeda
Received: 16 September 2009 / Accepted: 25 January 2010
ÓSpringer Science+Business Media, LLC. 2010
Abstract Calorie restriction (CR) extends lifespans in a
wide variety of species. CR induces an increase in the
NAD
?
/NADH ratio in cells and results in activation of
SIRT1, an NAD
?
-dependent protein deacetylase that is
thought to be a metabolic master switch linked to the
modulation of lifespans. CR also affects the expression of
peroxisome proliferator-activated receptors (PPARs). The
three subtypes, PPARa, PPARc, and PPARb/d, are
expressed in multiple organs. They regulate different
physiological functions such as energy metabolism, insulin
action and inflammation, and apparently act as important
regulators of longevity and aging. SIRT1 has been reported
to repress the PPARcby docking with its co-factors and to
promote fat mobilization. However, the correlation between
SIRT1 and other PPARs is not fully understood. CR ini-
tially induces a fasting-like response. In this study, we
investigated how SIRT1 and PPARacorrelate in the fast-
ing-induced anti-aging pathways. A 24-h fasting in mice
increased mRNA and protein expression of both SIRT1 and
PPARain the livers, where the NAD
?
levels increased
with increasing nicotinamide phosphoribosyltransferase
(NAMPT) activity in the NAD
?
salvage pathway. Treat-
ment of Hepa1-6 cells in a low glucose medium conditions
with NAD
?
or NADH showed that the mRNA expression of
both SIRT1 and PPARacan be enhanced by addition of
NAD
?
, and decreased by increasing NADH levels. The cell
experiments using SIRT1 antagonists and a PPARaagonist
suggested that PPARais a key molecule located upstream
from SIRT1, and has a role in regulating SIRT1 gene
expression in fasting-induced anti-aging pathways.
Keywords SIRT1 PPARaCalorie restriction
NAD
?
/NADH
Introduction
The prevalence of metabolic disorders has been increasing
over the past decades with the adoption of a secondary
lifestyle combined with excessive calorie intake. The liver
is the central metabolic organ that regulates several key
aspects of lipid metabolism including fatty acid b-oxidation
and lipogenesis. The capacity of the liver to regulate
metabolism is governed by highly dynamic transcriptional
regulatory network. SIRT1 is one of the seven mammalian
orthologs (SIRT1 to 7) of the yeast protein silent infor-
mation regulator 2 (Sir2), a NAD
?
-dependent histone
deacetylase (HDAC) that was discovered through its role in
chromatin remodeling associated with gene silencing and
the prolongation of lifespan in yeast [1,2]. SIRT1 as well
as other SIRTs catalyze deacetylation of many non-histone
proteins and play an important role in the regulation of
transcriptional networks in various critical metabolic pro-
cesses. The main targets of deacetylation by SIRT1 are
currently thought to be peroxisome proliferator-activated
receptor c(PPARc)-coactivator-1a(PGC-1a), forkhead
box-type O transcription factors (FOXOs), and nuclear
factor-jB (NF-jB) [1]. The deacetylase activity of SIRT1
is controlled by the cellular [NAD
?
]/[NADH] ratio, i.e.,
NAD
?
works as an activator, whereas nicotinamide and
NADH inhibit its activities [35]. SIRT1-mediated
deacetylation of PGC-1aincreases its ability to co-activate
HNF-4a, a transcription factor that promotes the expression
S. Hayashida A. Arimoto Y. Kuramoto T. Kozako
S. Honda H. Shimeno S. Soeda (&)
Department of Biochemistry, Faculty of Pharmaceutical
Sciences, Fukuoka University, 8-19-1 Nanakuma,
Jonan-ku, Fukuoka 814-0180, Japan
e-mail: ssoeda@fukuoka-u.ac.jp
123
Mol Cell Biochem
DOI 10.1007/s11010-010-0391-z
of gluconeogenetic genes and therefore increases glucose
production [6]. Thus, SIRT1 functions as a nutrient sensor
by decoding fluctuations in cellular NAD
?
levels.
In adipose tissue, SIRT1 inhibits fat storage and
increases lipolysis via repression of PPARc[7]. PPARcis a
key regulator in adipogenesis and fat storage, controlling
the expression of many adipocyte-specific genes [8].
PPARs are members of the nuclear receptor superfamily
that are ligand-dependent transcription factors, involving
PPARa, PPARb/d, and PPARc. It has been suggested
either that PPARs mediate the effects of calorie restriction
(CR) or that PPARs and CR activate the same signaling
pathways to prolong lifespan [9]. PPARacontrols the
expression of genes related to lipid metabolism in the liver,
including genes involved in mitochondrial b-oxidation,
fatty acid uptake and binding, and lipoprotein transport [9].
CR does not alter the mRNA and protein levels of PPARc,
but increases those of PPARaand SIRT1 [9]. In this con-
text, it is true that CR enhances the expressions of PPARa
and SIRT1. However, it is not known whether or how an
increase in NAD
?
in the salvage pathway under CR, can
directly enhance the expression of PPARaand SIRT1.
Also, there have been no reports elucidating whether
PPARaor SIRT1 is the key molecule located upstream to
regulate the CR-induced anti-aging pathways.
This study was conducted to elucidate whether and how
the NAD
?
metabolic system is involved in controlling the
expression of SIRT1 and PPARaunder CR, by using 24-h
fasting mice and hepatic cells cultured in a low glucose
medium.
Materials and methods
Reagents
The following reagents were obtained commercially:
b-NAD
?
from MP Biomedicals, LLC, Solon, OH; b-NADH
from Oriental Yeast Co., LTD, Tokyo, Japan; GW7647 from
Sigma-Aldrich, Tokyo, Japan; sirtinol and trichostatin A
(TSA) from Calbiochem, La Jolla, CA, USA; low glucose
Dulbecco’s modified Eagle’s medium (DMEM) and fetal
bovine serum from GIBCO BRL Life Technologies, Inc.
Animal and cell experiments
Male C57BL/6 mice (4 weeks of age) were purchased from
CREA Japan Inc., Shizuoka, Japan. They were housed in a
light-controlled room (light on 07:00 to 19:00 h) at a room
temperature of 24 ±1°C and a humidity of 60 ±10% with
food and water ad lib for 2 months. Animal treatment fol-
lowed the animal care guidelines in Japanese Government
Law No. 105 and Notification No. 6. CR in mice was carried
out by giving the animals only water for 24 h, prior to
experiments. The Hepa1-6 cell line was obtained from the
Dai-Nippon Seiyaku Co., Osaka, Japan. Stock cultures of the
cells were maintained in low glucose DMEM supplemented
with 10% fetalbovine serum, 50 U/ml penicillin and 50 mg/ml
streptomycin at 37°Cinahumidied5%CO
2
atmosphere.
For experiments, the cells were seeded in six-well culture
plates (1 910
5
cells/well) and cultured in the above growth
medium. After a 48-h incubation, the cells were extensively
washed with low glucose DMEM alone. Incubation fol-
lowed either for *2 h in growth media containing NAD
?
or NADH or for 6 or 12 h in media containing GW7647,
GW9662, sirtinol, or TSA.
Quantitative RT-PCR analysis
Total RNA was extracted from Hepa1-6 cells or mouse liver
using TRIzol reagent (Invitrogen, Carlsbad, CA, USA). The
cDNAs of SIRT1 and PPARawere synthesized and ampli-
fied with a superscript one-step RT-PCR system (Invitro-
gen). The RT-PCR reaction was performed using 100 pmol
each of forward and reverse primers. The sequences for the
primer pairs are as follows: SIRT1, 50-CCTGACTTC
AGATCAAGAGA-30and 50-TGTCTCCACGAACAGC
TTCA-30(GenBank accession No.BC016892); PPARa,
50-CTGAACATCGACTGTCGAAT-30and 50-GCTCTCC
ATGTCATGTATGA-30(GenBank accession No.AY377984);
b-actin, 50-GAGGGAAATCGTGCGTGACAT-30and 50-A
CATCTGCTGGAAGGTGGACA-30(GenBank accession
No.X03672). To evaluate the quantitative reliability of RT-
PCR, we performed a kinetic analysis of amplified products
to ensure that signals were derived only from the exponential
phase of amplifications. The ratios of the amplified target to
the amplified internal control (calculated by dividing the
value of each gene by that of b-actin) were compared among
groups. Quantitative densitometry analysis was performed
using Quantity One software (Bio-Rad).
Western blot analysis
Twenty-four hours after mice were either fed ad lib or
given only water, the livers were removed. A piece of the
tissue (50 mg wet weight) was lysed at 4°C in 500 ml of
ice-cold RIPA buffer [50 mM Tris–HCl (pH 8.0), 150 mM
NaCl, 1% NP40, 0.5% deoxycholate, and 0.1% SDS]
containing protease inhibitor cocktail (SIGMA). After
40-min incubation on ice, the lysate was centrifuged at
10,000gfor 10 min at 4°C. The protein content in the
lysate was determined using BCA protein assay kit
(PIERCE). Aliquots containing 10 lg of proteins were
separated on 6% SDS-polyacrylamide gels and transferred
Mol Cell Biochem
123
to polyvinylidene difluoride membranes. The membrane
was reacted with antibodies against SIRT1 (cat# sc-15404),
PPARa(cat# sc-9000), NAMPT (cat# sc-67020), CD38
(cat# sc-15362), and Actin (cat# sc-1616) from Santa Cruz
Biotechnology, Inc., CA, USA. Specific antigen/antibody
complexes were visualized by using horseradish peroxi-
dase-conjugated secondary antibodies and Chemi-Lumi
One (Nacalai Tesque, Kyoto, Japan). Quantitative densi-
tometry analysis was performed using Quantity One soft-
ware (Bio-Rad).
Measurement of NAD
?
and NADH
NAD
?
and NADH in mouse liver were measured by using
Amplite Fluorimetric NAD
?
/NADH Assay Kit (ABD
Bioquest, Inc.), according the manufacturer’s instructions.
The liver lysate was prepared per the protocol for ‘‘Western
blot analysis’’ and the total amount of intracellular NAD
?
and NADH was determined. To detect NADH only, NAD
?
in the liver lysate was removed in advance by using the
strong acid–base method. The lysate supernatant contain-
ing both NAD
?
and NADH was treated with an 0.5 ml
volume of 0.5 M NaOH, and thereafter heated at 95°C for
5 min. The suspension was rapidly cooled on ice, then
neutralized and buffered at pH 8.0. The treated suspension
was centrifuged at 17,700gfor 5 min at 4°C) to obtain the
sample for NADH assay.
Statistical analysis
All values are expressed as the mean ±SEM, and signif-
icant levels between groups were assessed by ANOVA and
Bonferroni’s test. Pvalues of less than 0.05 were consid-
ered to be statistically significant.
Results
Twenty-four hours fasting-induced SIRT1 and PPARa
mRNA and protein expression in mice
The mRNA and protein expression of both SIRT1 and
PPARawere induced by a short-term CR. When mice were
made to fast for 24 h, the SIRT1 mRNA and protein levels
in their livers increased significantly in comparison to those
in mice with ad lib access to food and water (Fig. 1a and
b). Fasting also increased the PPARamRNA and protein
levels (Fig. 1a and b).
Intracellular nicotinamide phosphoribosyltransferase
(NAMPT) up-regulates the NAD
?
/NADH ratio in mouse
liver under fasting conditions, but CD38 does not
CR enhances the mRNA and protein levels of PPARaand
SIRT1 [9]. Therefore, we next examined whether and how
(A)
(B)
Fig. 1 Effect of fasting on
mRNA (a) and protein (b)
expression of SIRT1 and
PPARain mouse liver. Mice
either had ad lib access to food
and water or were given only
water for 24 h. aTotal RNA
was extracted from mouse liver
using TRIzol reagent
(Invitrogen). SIRT1 and PPARa
mRNA levels were evaluated by
RT-PCR as described in
‘‘Materials and methods’’
section. The bands were
quantified using Quantity One
software (Bio-Rad). bLiver
lysates (10 lg protein) were
subjected to SDS-
polyacrylamide gel
electrophoresis. SIRT1 and
PPARaproteins were made
visible by Western blotting as
described in Materials and
methods. The bands were
quantified using Quantity One
software (Bio-Rad). Each value
represents the mean ±SE of six
mice. *** P\0. 005 compared
to the group fed ad lib
Mol Cell Biochem
123
the levels of NAD
?
and NADH are changed in the fasting
mouse liver. As shown in Fig. 2a, restriction of calorie
intake increased the hepatic NAD
?
levels, while NADH
levels were decreased. These alterations resulted in an
increase in the NAD
?
/NADH ratio and suggest that NAD
?
biosynthesis pathways in the liver fluctuated because of
fasting.
In mammals, NAD
?
is synthesized via two major
pathways: the de novo and salvage pathways. These two
pathways converge at nicotinic acid mononucleotide. In the
de novo pathway, the nicotinic acid moiety of NAD
?
is
synthesized from tryptophan via the kynurenine pathway.
In the NAD
?
salvage pathway, NAD
?
is generated through
the recycling of its degradation products such as nicotin-
amide (NAM). NAM is directly transformed to nicotin-
amide mononucleotide (NMN) by NAMPT [10], which
then yields NAD
?
through the action of nicotinamide
mononucleotide adenyltransferase (NMNAT). Intracellular
NAMPT is an essential and rate-limiting enzyme in the
NAD
?
biosynthetic pathway. Intracellular NAMPT protein
levels in mouse liver were significantly increased by 24-h
fasting (Fig. 2b). However, CD38, the major NADase that
converts NAD
?
to NMN, was not affected by fasting
(Fig. 2b). These data suggest that the NAD
?
levels in CR
mouse liver are controlled by NAPMT activity in the
NAD
?
salvage pathway.
NAD
?
and NADH regulate mRNA expression
of SIRT1 and PPARain Hepa1-6 cells cultured
in a low glucose medium
To better understand the role of the NAD
?
/NADH ratio in
the expression of SIRT1 and PPARa, we next examined
whether the mRNA levels of SIRT1 and PPARain cultured
Hepa1-6 cells were altered by adding NAD
?
and NADH
directly. As shown in Fig. 3a, addition of 10 mM NAD
?
to
the medium promoted mRNA expression in a time-
dependent manner: for SIRT1, 2.3 times and for PPARa,
(A)
(B)
Fig. 2 Alterations in NAD
?
and NADH levels (a) and in the
activities of NAD
?
-biosynthetic
enzymes, NAMPT and CD38
(b), in the livers of fasting mice.
Mice either had ad lib access to
food and water or were given
only water for 24 h. (a) The
levels of NAD
?
and NADH in
the liver lysates were measured
as described in Materials and
methods. (b) The protein levels
of intracellular NAMPT and
CD38 in the liver lysates were
evaluated by Western blotting.
Aliquots (10 lg protein) were
subjected to SDS-
polyacrylamide gel
electrophoresis. NAMPT and
CD38 proteins were made
visible as described in
‘‘Materials and methods’’
section. Quantitative
densitometry analyses were
performed using Quantity One
software (Bio-Rad). Each value
represents the mean ±SE of six
mice. *** P\0.005, compared
to the group fed ad lib
Mol Cell Biochem
123
1.7 times after 120 min, respectively. In contrast, SIRT1
and PPARamRNA levels were significantly decreased by
treating the cells with 10 mM NADH for 30 min (Fig. 3b).
These data suggest that the mRNA expression of both
SIRT1 and PPARawas directly up-regulated by intracel-
lular NAD
?
increasing during fasting, but reduced by an
increase in NADH levels.
Inhibition of SIRT1deacetylase activity does
not influence the mRNA expression of PPARa
To assess the correlation between SIRT1 activity and
PPARaexpression, we treated cultured Hepa1-6 cells with
sirtinol, an HDAC inhibitor, which preferentially inhibits
Sir2 and SIRT1. Figure 4a demonstrates that sirtinol
treatment of the cells has little or no effect on the mRNA
levels of PPARa. A transcription factor, p53, is a substrate
of SIRT1, and the deacetylated p53 reduces its
DNA-binding [1113]. As shown in Fig. 4b, the sirtinol
treatment increased acetylated-p53 protein in a concentra-
tion-dependent manner, suggesting that the compound
effectively inhibited SIRT1 in the experimental systems.
HDACs present in the nuclei have an important role in
chromatin remodeling associated with gene silencing. The
addition of TSA, an HDAC inhibitor whose specificity is
broader than sirtinol’s, significantly enhanced the mRNA
expression of PPARain a dose-dependent manner
(Fig. 4c). These results suggest that the inhibition of
HDAC activities by TSA up-regulates many nuclear gene
expressions including that of the PPARagene. Sirtinol
treatment did not influence on PPARaexpression in the
cells. This result suggests a possible role for PPARaas an
upstream regulator of SIRT1 expression.
mRNA expression of SIRT1 is induced
by the activation of PPARa
To clarify whether PPARaprotein can up-regulate SIRT1
gene expression, we next treated Hepa1-6 cells with
GW7647, a PPARaagonist. As shown in Fig. 5, the ago-
nist significantly enhanced the mRNA expression of SIRT1
at a concentration of 100 nM. Concomitant treatment of the
cells with GW7647 and GW9662, a PPARaantagonist
resulted in no enhancement of SIRT1 mRNA expression.
Our present data suggest that fasting induces an increase in
hepatic PPARamRNA and protein, which can successively
activate SIRT1 gene expression in mice.
Discussion
In this study, we have investigated whether and how the
NAD
?
metabolic system controls the expression of SIRT1
and PPARaduring CR, by using 24-h fasted mice and
hepatic cells cultured under a low glucose medium condi-
tion. A previous study of Revollo et al. [5] demonstrated
that NAMPT, but not NMNAT, was the rate-limiting
component in the NAD
?
biosynthesis in mouse fibroblasts.
(A)
(B)
Fig. 3 Effect of exogenously
added NAD
?
(a) or NADH (b)
on mRNA expressions of SIRT1
and PPARain Hepal-6 cells.
Cells were incubated at 37°C for
set periods ranging from 0 to
120 min in media containing
10 mM NAD
?
(a) or from 0 to
60 min in media containing
10 mM NADH (b). Total RNA
was extracted from the cells
using TRIzol reagent
(Invitrogen). SIRT1 and PPARa
mRNA levels were evaluated by
RT-PCR as described in
‘‘Materials and methods’’
section. The bands were
quantified using Quantity One
software (Bio-Rad). Each value
represents the mean ±SE of
three independent experiments.
*P\0.05; ** P\0.01;
*** P\0.005, compared to the
control (0 min)
Mol Cell Biochem
123
Increased NAMPT activity increased the total cellular
NAD
?
levels and enhanced the transcriptional regulatory
activity of SIRT1 [5]. Our present in vivo data also show
that 24-h fasting of mice can increase the ratio of NAD
?
/
NADH in the livers by increasing the protein levels of
NAMPT, but not of CD38. These findings suggest that
NAD
?
biosynthesis mediated by NAMPT induced under
CR or fasting can regulate the functions of SIRT1 and
thereby plays important roles in controlling various bio-
logical events in mammals.
PPARs play an important role in metabolic disturbances
seen in the metabolic syndrome, such as abnormal lipid and
carbohydrate metabolism and a low-grade inflammatory
state [14]. Synthetic PPAR agonists, such as fibrates and
thiazolidinediones are already used to treat hyperlipidemia
and diabetes mellitus, respectively. PPARais the first gene,
cloned from this family and mainly expressed in the liver,
skeletal muscle, heart, and kidney [9]. PPARaalters the
expression of genes encoding enzymes involved in the fatty
acid metabolic pathway, which activate the regulation of
fatty acid b- and w-oxidation [1517]. Corton et al. [18]
have indicated that 19% of hepatic genes involved in lipid
metabolism, inflammation, and cell growth which were
altered by CR were dependent on PPARa. The results
(A) (B)
(C)
Fig. 4 Effect of sirtinol on the mRNA expression of PPARa(a), the
deacetylation of p53 protein (b) and effect of TSA on the mRNA
expression of PPARa(c) in Hepal-6 cells. Cells were incubated at
37°C for 6 h in media alone or containing 50 and 100 lM sirtinol or
50, 500, and 1000 nM TSA. Total RNA was extracted from the cells
using TRIzol reagent (Invitrogen), and PPARamRNA levels (aand
c) were evaluated by RT-PCR as described in ‘‘Materials and
methods’ section. The bands were quantified using Quantity One
software (Bio-Rad). bCell lysates (10 lg protein) were subjected to
SDS-polyacrylamide gel electrophoresis, and acetylated and non-
acetylated p53 were made visible by Western blotting as described in
Materials and methods. The bands were quantified using Quantity
One software (Bio-Rad). Each value represents the mean ±S.E of
three independent experiments. *** P\0.005, compared to the
untreated group
Fig. 5 Effects of GW7647, a PPARaagonist, and GW9662, a
PPARaantagonist, on the mRNA expression of SIRT1. Cells were
incubated at 37°C for 12 h in media alone or containing 100 nM
GW7647, 100 nM GW9662 or both. Total RNA was extracted from
the cells using TRIzol reagent (Invitrogen). SIRT1 mRNA levels were
evaluated by RT-PCR as described in ‘‘Materials and methods’’
section. The bands were quantified using Quantity One software (Bio-
Rad). Each value represents the mean ±SE of three independent
experiments. *** P\0.005, compared to the untreated group
Mol Cell Biochem
123
obtained in mice treated with a PPARaagonist indicated
overlap of genes influenced by CR and by a compound
activating PPARa[18]. Thus, PPARahas been shown to
play an important role in mediating the action of CR;
however, it is unclear how NAD
?
, SIRT1, and PPARalink
to and work together in the anti-aging signaling pathways
evoked by CR.
In this study, we demonstrated that the addition of
NAD
?
in the media of cultured Hepa1-6 cells promotes the
mRNA expression of both SIRT1 and PPARa, while the
addition of NADH suppressed mRNA expression. The
findings indicate that NAD
?
evoked by CR can directly
enhance not only the enzyme activity of SIRT1, but also
the mRNA expressions of both SIRT1 and PPARagenes.
In our regulation experiments on SIRT1 activity in Hepa1-
6 cells using an HDAC inhibitor, TSA, the inhibition of
HDAC activities by the broad HDAC inhibitor up-regu-
lated the PPARamRNA expression. This result suggests
that the increased PPARamRNA expression resulted from
being opened from gene silencing. There was no influence
of sirtinol treatment on the PPARaexpression in the cells,
suggesting a possible role of PPARaas an upstream reg-
ulator of SIRT1 expression.
We investigated whether PPARaprotein can up-regulate
SIRT1 gene expression. Treatment of Hepa1-6 cells with
GW7647, a PPARaagonist, significantly enhanced the
mRNA expression of SIRT1. However, simultaneous
addition of GW7647 and GW9662, a PPARaantagonist
reduced the mRNA expression of SIRT1 to the control
level. In addition to the enhancement of the SIRT1 mRNA
expression with PPARaagonist, sequence analysis of
human SIRT1 promoter region revealed the presence of a
putative PPAR-responsive element (PPRE) (data not
shown). Therefore, it is possible that PPARaregulates the
SIRT1 gene expression via putative PPRE in the promoter.
Though many reports have shown the functional charac-
terization of SIRT1, the regulatory mechanisms of SIRT1
gene expression are not understood. The result suggests
that PPARaprotein can promote SIRT1 mRNA expression
as the transcriptional factor in the livers of fasting mice.
Our data show that a switch to oxidative metabolism
during fasting in mice increases the NAD
?
/NADH ratio by
increasing the protein levels of NAMPT. The precise
mechanisms of CR action on aging and longevity are still
not well established, but the present results could connect
NAD
?
, PPARa, and SIRT1 with the line of CR-induced
longevity signalings: NAD
?
significantly promoted the
mRNA levels of both PPARaand SIRT1 in vitro. Next,
PPARawas capable of enhancing the SIRT1 mRNA
expression, suggesting a new regulator of SIRT1 functions.
It is well known that CR protects neurons from degen-
eration in mouse models of Alzheimer’s disease (AD) and
Parkinson’s disease (PD). SIRT1 might also facilitate
neuronal survival [1921]. Accumulation of the aggregated
Abis hypothesized to initiate a pathological cascade
resulting in the onset and progression of AD [22]. Ab
induces NF-jB activity in microglia. Administration of
SIRT1 activator markedly reduced the NF-jB signaling
[23]. This strongly suggests that SIRT1 can attenuate Ab-
induced neurotoxicity via inhibition of microglial NF-jB
signaling. Further studies are needed to define the exact
roles of SIRT1, in relation to PPARa, in the pathophysi-
ology of human diseases. It is predicted that SIRT1 and
PPARamay show promise in future therapies against age-
related diseases, such as cancer, diabetes mellitus, and
cardiovascular diseases.
Acknowledgments This work was supported in part by fund from
the Central Research Institute of Fukuoka University. Our thanks go
to Mr. Steven Sabotta for reading the manuscript.
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... For instance, nicotinate and nicotinamide, two precursors of nicotinamide adenine dinucleotide (NAD) essential for multiple metabolic pathways, including TCA cycle and oxidative phosphorylation (Zapata-Perez et al., 2021), were augmented in intestinal lumens of VB12gavaged mice. NAD, acting as a signaling molecule, may support the activation of NAD-consuming enzymes, particularly PPARs (Hayashida et al., 2010), to regulate epithelial lipid metabolism in response to STm infection. Additionally, it has been reported that Turicibacter controls host lipid metabolic process in the ileum and increases the cellular levels of LCFAs, including arachidonate (Fung et al., 2019). ...
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Deprivation of vitamin B12 (VB12) is linked to various diseases, but the underlying mechanisms in disease progression are poorly understood. Using multiomic approaches, we elucidated the responses of ileal epithelial cells (iECs) and gut microbiome to VB12 dietary restriction. Here, VB12 deficiency impaired the transcriptional and metabolic programming of iECs and reduced epithelial mitochondrial respiration and carnitine shuttling during intestinal Salmonella Typhimurium (STm) infection. Fecal microbial and untargeted metabolomic profiling identified marked changes related to VB12 deficiency, including reductions of metabolites potentially activating mitochondrial β-oxidation in iECs and short-chain fatty acids (SCFAs). Depletion of SCFA-producing microbes by streptomycin treatment decreased the VB12-dependent STm protection. Moreover, compromised mitochondrial function of iECs correlated with declined cell capability to utilize oxygen, leading to uncontrolled oxygen-dependent STm expansion in VB12-deficient mice. Our findings uncovered previously unrecognized mechanisms through which VB12 coordinates ileal epithelial mitochondrial homeostasis and gut microbiota to regulate epithelial oxygenation, resulting in the control of aerobic STm infection.
... AMPK activates FOXOs through phosphorylation or co-action with SIRT1, triggering the expression of antioxidant enzymes to restore cardiac function [55]. Resveratrol can indirectly enhance the activity of PPARα by activating AMPK, SIRT1, and PGC-1α, thereby inhibiting NF-κB and attenuating oxidative stress and inflammation [131][132][133][134]. Collectively, resveratrol can activate multiple pathways fostering the cooperation between AMPK and SIRT1, which plays a beneficial role in improving diabetic cardiovascular disease. ...
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Diabetes mellitus (DM) is one of the most prevalent chronic diseases worldwide. High morbidity and mortality caused by DM are closely linked to its complications in multiple organs/tissues, including cardiovascular complications, diabetic nephropathy, and diabetic neuropathy. Resveratrol is a plant-derived polyphenolic compound with pleiotropic protective effects, ranging from antioxidant and anti-inflammatory to hypoglycemic effects. Recent studies strongly suggest that the consumption of resveratrol offers protection against diabetes and its cardiovascular complications. The protective effects of resveratrol involve the regulation of multiple signaling pathways, including inhibition of oxidative stress and inflammation, enhancement of insulin sensitivity, induction of autophagy, regulation of lipid metabolism, promotion of GLUT4 expression, and translocation, and activation of SIRT1/AMPK signaling axis. The cardiovascular protective effects of resveratrol have been recently reviewed in the literature, but the role of resveratrol in preventing diabetes mellitus and its cardiovascular complications has not been systematically reviewed. Therefore, in this review, we summarize the pharmacological effects and mechanisms of action of resveratrol based on in vitro and in vivo studies, highlighting the therapeutic potential of resveratrol in the prevention and treatment of diabetes and its cardiovascular complications.
... Sirtuin 1 (SIRT1), memeli hücrelerinde yüksek oranda eksprese edilir ve birçok dokuda (karaciğer, iskelet kası, yağ dokusu, pankreas βhücreleri) çalışılmıştır [8][9][10] . SIRT1, NAD bağımlı protein deasetilazdır ve hücresel enerji durumuna yanıt olarak önemli bir metabolik sensördür 11 . SIRT1, yağ dokusundan lipid oksidasyonunu ve inflamasyonu düzenlemek için yağ mobilizasyonunu destekler 12 ...
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Giriş: Yağ doku, obezite ve insülin direnci üzerindeki sistemik etkilere aracılık eden sitokinleri salgılamaktadır. Kullanılan antidiyabetik ilaçlar, 3T3-L1 adiposit hücrelerinde metabolik farklılıklar ve gen anlatım profillerinde farklılıklar oluşmaktadır. Çalışmamızda 3T3-L1 adipositlerde Vitamin D reseptörü (VDR), Sirtuin (SIRT1), Apelin ve Forkhead box protein O1 (FOXO1) gen anlatım seviyelerinin farklı oral antidiyabetik kullanımlarına cevaben değişimleri değerlendirildi. Yöntemler: 3T3-L1 hücreleri ATCC den temin edildi. Sitotoksisite testleri iCELLigence sistemi ile gerçek zamanlı olarak yapıldı. Çalışılan genler, gerçek zamanlı polimeraz zincir reaksiyonu (qPCR) ile belirlendi. Bulgular: Farklı oral antidiyabetik (akarboz, metformin ve glipizid) etken maddeleri uygulanan adiposit hücreleri kontrol adiposit hücreleri ile karşılaştırıldığında, VDR gen anlatım seviyeleri daha yüksek bulundu. SIRT1 ekspresyonu 6 saat 17 mg/ml akarboz, 6 saat 192 mM metformin ve 24 saat 180 µM glipizid uygulamasında kontrol adiposit hücrelerine kıyasla daha yüksek bulunurken, 6 saat 10 mg/ml akarboz ve 24 saat 175 mM metformin uygulamasında kontrol hücrelere göre daha düşük bulunmuştur (p=0.005). Apelin gen anlatım seviyelerini farklı oral antidiyabetik kullanımı ile kontrol hücrelere kıyasla azaldığı bulunmuştur (p=0.005). FOXO1 gen anlatım seviyesi 24 saat metfomin uygulaması dışında Adiposit hücrelerinde kontrole göre yüksek bulunmuştur (p=0.005). Sonuç: Sonuçlarımız, glipizid, akarboz ve metforminin obezitede yağ metabolizmasının düzenlenmesi üzerindeki faydalı etkilerine dair yeni fikirler vermesinin yanı sıra, terapötik yolakları hedefleyen çalışmalar için yeni stratejiler sağlayabilir düşüncesindeyiz.
... In addition, as nuclear receptors, peroxisome proliferator-activated receptor (PPAR) also can increase the expression of SIRT1. Fasting for 24 h can increase the expression level of SIRT1 in mice, which may be due to the binding of PPARα to the PPAR-responsive element (PPRE) on the SIRT1 promoter (Hayashida et al., 2010). PPARβ/δ is another transcription factor, which can increase the expression of SIRT1 by binding to the Sp1 binding site in a state of starvation (Okazaki et al., 2010). ...
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The intracellular energy state will alter under the influence of physiological or pathological stimuli. In response to this change, cells usually mobilize various molecules and their mechanisms to promote the stability of the intracellular energy status. Mitochondria are the main source of ATP. Previous studies have found that the function of mitochondria is impaired in aging, neurodegenerative diseases, and metabolic diseases, and the damaged mitochondria bring lower ATP production, which further worsens the progression of the disease. Silent information regulator-1 (SIRT1) is a multipotent molecule that participates in the regulation of important biological processes in cells, including cellular metabolism, cell senescence, and inflammation. In this review, we mainly discuss that promoting the expression and activity of SIRT1 contributes to alleviating the energy stress produced by physiological and pathological conditions. The review also discusses the mechanism of precise regulation of SIRT1 expression and activity in various dimensions. Finally, according to the characteristics of this mechanism in promoting the recovery of mitochondrial function, the relationship between current pharmacological preparations and aging, neurodegenerative diseases, metabolic diseases, and other diseases was analyzed.
... Moreover, NAD + plays a crucial role in activating SIRT1 activity. Under caloric restriction or fasting, the level of NAD + rises and SIRT1 function is induced (Cantó et al., 2009;Canto et al.,2010;Hayashida et al., 2010). Increased levels of NAD + due to elevated NAD + salvage pathway synthesis, external NAD + precursor addition or the inhibition of NAD + utilizing enzymes such as PARP all have been shown to promote SIRT1 activity (Zhang et al., 2009;Bai et al., 2011;Li et al., 2016). ...
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Silent information regulator 2-related enzyme 1 (SIRT1) is an NAD+-dependent class III deacetylase and a key component of the cellular metabolic sensing pathway. The requirement of NAD+ for SIRT1 activity led us to assume that NQO1, an NADH oxidoreductase producing NAD+, regulates SIRT1 activity. We show here that SIRT1 is capable of increasing NQO1 (NAD(P)H Dehydrogenase Quinone 1) transcription and protein levels. NQO1 physically interacts with SIRT1 but not with an enzymatically dead SIRT1 H363Y mutant. The interaction of NQO1 with SIRT1 is markedly increased under mitochondrial inhibition. Interestingly, under this condition the nuclear pool of NQO1 is elevated. Depletion of NQO1 compromises the role of SIRT1 in inducing transcription of several target genes and eliminates the protective role of SIRT1 following mitochondrial inhibition. Our results suggest that SIRT1 and NQO1 form a regulatory loop where SIRT1 regulates NQO1 expression and NQO1 binds and mediates the protective role of SIRT1 during mitochondrial stress. The interplay between an NADH oxidoreductase enzyme and an NAD+ dependent deacetylase may act as a rheostat in sensing mitochondrial stress.
... NAMPT protein in human skeletal muscle is positively correlated with whole-body insulin sensitivity and negatively correlated with body fat [87]. NAMPT and NAD + levels were decreased by HFD feeding in the liver and white adipose tissue (WAT) [33], whereas fasting and calorie restriction (CR) increased NAMPT expression in the liver and skeletal muscle [47,[88][89][90][91]. NAMPT and NMN have been shown to increase insulin secretion in human islets [92], and NAD + levels that are mediated by NAMPT were decreased in T2DM mice, whereas administration of NMN, which is converted into NAD + by NMNATs, improved glucose tolerance [33]. ...
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Mitochondria play vital roles, including ATP generation, regulation of cellular metabolism, and cell survival. Mitochondria contain the majority of cellular nicotinamide adenine dinucleotide (NAD+), which an essential cofactor that regulates metabolic function. A decrease in both mitochondria biogenesis and NAD+ is a characteristic of metabolic diseases, and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) orchestrates mitochondrial biogenesis and is involved in mitochondrial NAD+ pool. Here we discuss how PGC-1α is involved in the NAD+ synthesis pathway and metabolism, as well as the strategy for increasing the NAD+ pool in the metabolic disease state.
... Fasting regimens and SIRT1 activation have been shown to increase longevity and delay onset of disease in yeast, fruit flies, mice and more recently, non-human primate animal models [26]. Fastinginduced SIRT1 activation has been linked to increased NAD + levels, increased mitochondrial biogenesis and delayed senescence [27,28]. The current study addresses the use of fasting and fasting-mimicking treatments to activate SIRT1 signalling. ...
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Aims/hypothesis Homo sapiens evolved under conditions of intermittent food availability and prolonged fasting between meals. Periods of fasting are important for recovery from meal-induced oxidative and metabolic stress, and tissue repair. Constant high energy-density food availability in present-day society contributes to the pathogenesis of chronic diseases, including diabetes and its complications, with intermittent fasting (IF) and energy restriction shown to improve metabolic health. We have previously demonstrated that IF prevents the development of diabetic retinopathy in a mouse model of type 2 diabetes (db/db); however the mechanisms of fasting-induced health benefits and fasting-induced risks for individuals with diabetes remain largely unknown. Sirtuin 1 (SIRT1), a nutrient-sensing deacetylase, is downregulated in diabetes. In this study, the effect of SIRT1 stimulation by IF, fasting-mimicking cell culture conditions (FMC) or pharmacological treatment using SRT1720 was evaluated on systemic and retinal metabolism, systemic and retinal inflammation and vascular and bone marrow damage. Methods The effects of IF were modelled in vivo using db/db mice and in vitro using bovine retinal endothelial cells or rat retinal neuroglial/precursor R28 cell line serum starved for 24 h. mRNA expression was analysed by quantitative PCR (qPCR). SIRT1 activity was measured via histone deacetylase activity assay. NR1H3 (also known as liver X receptor alpha [LXRα]) acetylation was measured via western blot analysis. Results IF increased Sirt1 mRNA expression in mouse liver and retina when compared with non-fasted animals. IF also increased SIRT1 activity eightfold in mouse retina while FMC increased SIRT1 activity and expression in retinal endothelial cells when compared with control. Sirt1 expression was also increased twofold in neuronal retina progenitor cells (R28) after FMC treatment. Moreover, FMC led to SIRT1-mediated LXRα deacetylation and subsequent 2.4-fold increase in activity, as measured by increased mRNA expression of the genes encoding ATP-binding cassette transporter (Abca1 and Abcg1). These changes were reduced when retinal endothelial cells expressing a constitutively acetylated LXRα mutant were tested. Increased SIRT1/LXR/ABC-mediated cholesterol export resulted in decreased retinal endothelial cell cholesterol levels. Direct activation of SIRT1 by SRT1720 in db/db mice led to a twofold reduction of diabetes-induced inflammation in the retina and improved diabetes-induced visual function impairment, as measured by electroretinogram and optokinetic response. In the bone marrow, there was prevention of diabetes-induced myeloidosis and decreased inflammatory cytokine expression. Conclusions/interpretation Taken together, activation of SIRT1 signalling by IF or through pharmacological activation represents an effective therapeutic strategy that provides a mechanistic link between the advantageous effects associated with fasting regimens and prevention of microvascular and bone marrow dysfunction in diabetes. Graphical abstract
... to alleviate oxidative stress and endothelial dysfunction in type 2 diabetic nephropathy (58). However, unlike FOXOs, PPARa is not a directly target deacetylated by SIRT1, but its activity can be enhanced by SIRT1 indirectly through the coactivators, such as AMPK and PGC-1a (75,76). Moreover, various PPAR agonists have been proved to prevent diabetes in the non-obese diabetic mouse model, suggesting the therapeutic function of SIRT1-PPARa axis in DM. ...
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Diabetic mellitus (DM) is a significant public health concern worldwide with an increased incidence of morbidity and mortality, which is particularly due to the diabetic vascular complications. Several pivotal underlying mechanisms are associated with vascular complications, including hyperglycemia, mitochondrial dysfunction, inflammation, and most importantly, oxidative stress. Oxidative stress triggers defective angiogenesis, activates pro-inflammatory pathways and causes long-lasting epigenetic changes to facilitate the development of vascular complications. Therefore, therapeutic interventions targeting oxidative stress are promising to manage diabetic vascular complications. Sirtuin1 (SIRT1), a class III histone deacetylase belonging to the sirtuin family, plays critical roles in regulating metabolism and ageing-related pathological conditions, such as vascular diseases. Growing evidence has indicated that SIRT1 acts as a sensing regulator in response to oxidative stress and attenuates vascular dysfunction via cooperating with adenosine-monophosphate-activated protein kinase (AMPK) to activate antioxidant signals through various downstream effectors, including peroxisome proliferator-activated receptor-gamma co-activator 1 (PGC-1α), forkhead transcription factors (FOXOs), and peroxisome proliferative-activated receptor α (PPARα). In addition, SIRT1 interacts with hydrogen sulfide (H2S), regulates NADPH oxidase, endothelial NO synthase, and mechanistic target of rapamycin (mTOR) to suppress oxidative stress. Furthermore, mRNA expression of sirt1 is affected by microRNAs in DM. In the current review, we summarize recent advances illustrating the importance of SIRT1 in antagonizing oxidative stress. We also discuss whether modulation of SIRT1 can serve as a therapeutic strategy to treat diabetic vascular complications.
Chapter
Nicotinamide adenine dinucleotide (NAD⁺) is an essential coenzyme involved in several redox reactions. NAD⁺ also serves as an important substrate for several enzymes associated with DNA repair, secondary messenger signaling, and transcriptional regulation. These NAD⁺-consuming enzymes include poly-ADP-ribose polymerases (PARPs), CD38/157 ectoenzymes, and histone deacetylases known as sirtuins. NAD⁺ levels have been shown to decline during the aging process in several murine models and human clinical studies. NAD⁺ depletion has been associated with deficits in nuclear and mitochondrial function leading to many age-associated pathologies. Maintaining cellular NAD⁺ anabolism by supplementing with NAD⁺ and its related precursors has been reported to attenuate age-related functional defects and improve overall quality of life. Sirtuins are thought to be partly responsible for the beneficial effects of NAD⁺ on the aging phenotype. Thus supplementation with NAD⁺ intermediates may be an efficacious therapeutic intervention to manipulate sirtuin function, improve health span and promote “healthy” aging, bringing hope to our growing aging societies both nationally and abroad.
Article
Aims The aim of this study is to provide new insights on the association of lipid metabolites, circadian genes and lipid metabolism associated genes in spontaneously hypertensive rats. Materials and methods An untargeted lipidomics using ultrahigh performance liquid chromatography-mass spectrometry metabolomics was used to identify the differentially expressed lipid metabolites over 24 h in Spontaneously hypertensive rats (SHR) with reference to Wistar-Kyoto rats (WKY). The expression of circadian clock genes (Bmal1, Clock, Per1, Per2, Cry1, Cry2) and lipid metabolism related genes (Rev-erbα, Pparα and Sirt1) was analysed RT-qPCR. Key findings Ten lipid metabolites with significant differences in their levels in SHR compared to WKY were identified. The levels of MG (25:0), PA (36:3) and PE (38:2) were lower and the levels of LysoPC (20:0 and 20:3) and TGs (54:5, 59:12, 28:0, 60:10 and 60:13) were found to be higher in SHR. SHR showed obvious disorders in the expression of circadian genes and lipid metabolism associated genes. A strong association between the levels of lipid metabolites and circadian genes and lipid metabolism associated genes was found. Significance Rhythm genes may further affect the 24-hour lipid metabolism level of spontaneously hypertensive rats by mediating lipid metabolism associated genes. This research provides new insights on the association of lipid metabolites, circadian genes and lipid metabolism associated genes in SHR.
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Prolonged deprivation of food induces dramatic changes in mammalian metabolism, including the release of large amounts of fatty acids from the adipose tissue, followed by their oxidation in the liver. The nuclear receptor known as peroxisome proliferator-activated receptor α (PPARα) was found to play a role in regulating mitochondrial and peroxisomal fatty acid oxidation, suggesting that PPARα may be involved in the transcriptional response to fasting. To investigate this possibility, PPARα-null mice were subjected to a high fat diet or to fasting, and their responses were compared with those of wild- type mice. PPARα-null mice chronically fed a high fat diet showed a massive accumulation of lipid in their livers. A similar phenotype was noted in PPARα-null mice fasted for 24 hours, who also displayed severe hypoglycemia, hypoketonemia, hypothermia, and elevated plasma free fatty acid levels, indicat- ing a dramatic inhibition of fatty acid uptake and oxidation. It is shown that to accommodate the increased requirement for hepatic fatty acid oxidation, PPARα mRNA is induced during fasting in wild- type mice. The data indicate that PPARα plays a pivotal role in the management of energy stores during fasting. By modulating gene expression, PPARα stimulates hepatic fatty acid oxidation to supply sub- strates that can be metabolized by other tissues.
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Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptors superfamily. The three subtypes, PPARα, PPARγ, and PPARβ/δ, are expressed in multiple organs. These transcription factors regulate different physiological functions such as energy metabolism (including lipid and carbohydrate metabolism), insulin action, and immunity and inflammation, and apparently also act as important mediators of longevity and aging. Calorie restriction (CR) is the most effective intervention known to delay aging and increase lifespan. Calorie restriction affects the same physiological functions as PPARs. This review summarizes recent findings on the effects of CR and aging on the expression of PPARγ, α, and β/δ in mice and discusses possible involvement of PPARs in mediating the effects of murine longevity genes. The levels of PPARs change with age and CR appears to prevent these alterations which make “PPARs-CR-AGING” dependence of considerable interest.
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Peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the steroid/nuclear receptor superfamily and mediates the biological and toxicological effects of peroxisome proliferators. To determine the physiological role of PPARalpha in fatty acid metabolism, levels of peroxisomal and mitochondrial fatty acid metabolizing enzymes were determined in the PPARalpha null mouse. Constitutive liver beta-oxidation of the long chain fatty acid, palmitic acid, was lower in the PPARalpha null mice as compared with wild type mice, indicating defective mitochondrial fatty acid catabolism. In contrast, constitutive oxidation of the very long chain fatty acid, lignoceric acid, was not different between wild type and PPARalpha null mice, suggesting that constitutive expression of enzymes involved in peroxisomal beta-oxidation is independent of PPARalpha. Indeed, the PPARalpha null mice had normal levels of the peroxisomal acyl-CoA oxidase, bifunctional protein (hydratase + 3-hydroxyacyl-CoA dehydrogenase), and thiolase but lower constitutive expression of the D-type bifunctional protein (hydratase + 3-hydroxyacyl-CoA dehydrogenase). Several mitochondrial fatty acid metabolizing enzymes including very long chain acyl-CoA dehydrogenase, long chain acyl-CoA dehydrogenase, short chain-specific 3-ketoacyl-CoA thiolase, and long chain acyl-CoA synthetase are also expressed at lower levels in the untreated PPARalpha null mice, whereas other fatty acid metabolizing enzymes were not different between the untreated null mice and wild type mice. A lower constitutive expression of mRNAs encoding these enzymes was also found, suggesting that the effect was due to altered gene expression. In wild type mice, both peroxisomal and mitochondrial enzymes were induced by the peroxisome proliferator Wy-14,643; induction was not observed in the PPARalpha null animals. These data indicate that PPARalpha modulates constitutive expression of genes encoding several mitochondrial fatty acid-catabolizing enzymes in addition to mediating inducible mitochondrial and peroxisomal fatty acid beta-oxidation, thus establishing a role for the receptor in fatty acid homeostasis.
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Regulation of gene expression of three putative long-chain fatty acid transport proteins, fatty acid translocase (FAT), mitochondrial aspartate aminotransferase (mAspAT), and fatty acid transport protein (FATP), by drugs that activate peroxisome proliferator-activated receptor (PPAR) alpha and gamma were studied using normal and obese mice and rat hepatoma cells. FAT mRNA was induced in liver and intestine of normal mice and in hepatoma cells to various extents only by PPARalpha-activating drugs. FATP mRNA was similarly induced in liver, but to a lesser extent in intestine. The induction time course in the liver was slower for FAT and FATP mRNA than that of an mRNA encoding a peroxisomal enzyme. An obligatory role of PPARalpha in hepatic FAT and FATP induction was demonstrated, since an increase in these mRNAs was not observed in PPARalpha-null mice. Levels of mAspAT mRNA were higher in liver and intestine of mice treated with peroxisome proliferators, while levels in hepatoma cells were similar regardless of treatment. In white adipose tissue of KKAy obese mice, thiazolidinedione PPARgamma activators (pioglitazone and troglitazone) induced FAT and FATP more efficiently than the PPARalpha activator, clofibrate. This effect was absent in brown adipose tissue. Under the same conditions, levels of mAspAT mRNA did not change significantly in these tissues. In conclusion, tissue-specific expression of FAT and FATP genes involves both PPARalpha and -gamma. Our data suggest that among the three putative long-chain fatty acid transporters, FAT and FATP appear to have physiological roles. Thus, peroxisome proliferators not only influence the metabolism of intracellular fatty acids but also cellular uptake, which is likely to be an important regulatory step in lipid homeostasis.
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DNA damage-induced acetylation of p53 protein leads to its activation and either growth arrest or apoptosis. We show here that the protein product of the gene hSIR2(SIRT1), the human homolog of the S. cerevisiae Sir2 protein known to be involved in cell aging and in the response to DNA damage, binds and deacetylates the p53 protein with a specificity for its C-terminal Lys382 residue, modification of which has been implicated in the activation of p53 as a transcription factor. Expression of wild-type hSir2 in human cells reduces the transcriptional activity of p53. In contrast, expression of a catalytically inactive hSir2 protein potentiates p53-dependent apoptosis and radiosensitivity. We propose that hSir2 is involved in the regulation of p53 function via deacetylation.
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Dietary influences on Alzheimer disease (AD) are gaining recognition. Because many aging processes are attenuated in laboratory mammals by caloric restriction (CR), we examined the effects of short-term CR in two AD-transgenic mice, APPswe/ind (J20) and APPswe+PS1M146L (APP+PS1). CR substantially decreased the accumulation of Aβ-plaques in both lines: by 40% in APPswe/ind (CR, 6 weeks), and by 55% in APP+PS1 (CR, 14 weeks). CR also decreased astrocytic activation (GFAP immunoreactivity). These influences of CR on AD-transgenic mice are consistent with epidemiological reports that show that high caloric diets associate with the risk of AD, and suggest that dietary interventions in adult life might slow disease progression.
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Evidence from cell and rodent modelsInsights from human studiesReferences