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Centre National de la Recherche Scientifique 6543, Centre de Biochimie (F.M., P.S.-M., R.N., G.A., M.T.), Nice 06108, France; University Medical Center, Department of Physiology, Faculty of Medicine (J.S.), Genève, 1211, Switzerland; INSERM, U-352, Institut National des Sciences Appliquées (A.G.), Villeurbanne 69100, France; INSERM, U-465 (A.Q.-B., S.T.), Paris 75270, France; and University of Tsukuba (A.F.), Tsukuba, Ibaraki 305, Japan
Address all correspondence and requests for reprints to: Dr. Gérard Ailhaud, Centre de Biochimie, UMR 6543, Centre National de la Recherche Scientifique, Université de Nice-Sophia Antipolis, Faculté des Sciences, Parc Valrose, 06108 Nice Cedex 2, France.
| Abstract |
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| Introduction |
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| Materials and Methods |
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Only male agt-/- mice were used in the experiments herein, and ICR-CD1 control WT mice were purchased from Harlan (Gammat, France). Animals were housed five per cage and had free access to food and water in a controlled environment with a 12-h light, 12-h dark cycle and constant temperature (22 C). At weaning, the mice were fed either a standard laboratory chow diet or a high fat diet containing 1% cholesterol, 30% corn oil (representing 65% of calories as fat), 27% carbohydrates, 11.5% proteins, and 1.9% minerals (UAR, Villemoisson, France). Body weight was assessed weekly for up to 46 wk. At the indicated times mice were killed by cervical dislocation according to French Centre National de la Recherche Scientifique ethical guidelines. Epididymal WAT, BAT, and hind limb skeletal muscle were rapidly removed and immediately used for RNA preparation.
Food consumption and feces analysis
Mice were housed individually in metabolic cages (Marty
Technology, Marcilly-sur-Eure, France) for 1 wk, fed ad
libitum with a standard or high fat diet, and given free access to
water in a controlled environment at 22 C with a 12-h light, 12-h dark
cycle. Food consumption was measured during the last 4 d as the
difference between the amount of food given and that removed from the
cage after the amount of any food spilled was taken into account.
Similarly, feces were collected during the last 4 d of feeding,
and the weight of pooled feces was determined after drying at 70 C to a
constant weight. The fat content of the feces was determined by the
Soxhlet extraction method using petroleum benzine.
Body weight and body composition
Body weight was measured at the same time each day. For body
composition, mice were killed by cervical dislocation, and the whole
carcasses were incised, dried to a constant weight at 70 C, then
subsequently homogenized. Total body fat content was determined by the
Soxhlet extraction method as described above. The results are presented
as absolute weight (grams) and as percentage of total body weight. The
fat-free mass, which includes mineral content (which accounts for
2% of fat-free mass in mice) was obtained by subtraction of body
fat content from dry weight.
Adipose tissue cellularity
The size and number of adipocytes were determined as previously
described (16). Briefly, fat cell size was determined by a
procedure derived from a microphotometric method; micrographs of
isolated cells were taken with a light microscope, and measurement of
cell diameters was performed using a computer equipped with an image
analyzer. Fat cell number was estimated from a portion of adipose
tissue by dividing the lipid content by the average fat cell
weight.
Fatty acid synthase (FAS) activities
FAS activities were assayed spectrophotometrically in crude
cytosolic extracts of epididymal fat pads by measuring the oxidation of
NAPDH in the presence of acetyl coenzyme A and malonyl coenzyme A
(17). Data are expressed as nanomoles of NAPDH oxidized
per min/mg, i.e. milliunits per mg cytosolic proteins, which
were assayed by the method of Bradford (17).
Isolation and analysis of RNA
RNA was extracted using the RNeasy Midi kit according to the
manufacturers protocol (QIAGEN, Cortaboeuf,
France). Northern blot analysis was performed as described
previously (18). Autoradiographs were quantified using a
Fujix PhosphorImager (Tokyo, Japan). All results were normalized to
ß-actin signals.
Measurements of metabolic rate and locomotor activity
For locomotor activity and metabolic rate measurements, mice
were randomly and alternatively placed into the respective experimental
chambers; at least 1 wk separated successive testing. Metabolic rate
was measured by indirect calorimetry during 24 h. An open circuit
calorimeter, as described in detail previously (19),
equipped with a sensitive mass flow meter (model 5875, Brooks
Instrument, Veenendaal, The Netherlands) was used. Food and
water were available during testing. The ambient temperature was set at
22 C. The data were recorded every 5 sec by an on-line computerized
data acquisition system (SICMU, CMU, Geneva, Switzerland). The
metabolic rate was calculated using Weirs equation and expressed in
terms of watts per kg BW to the 0.75 power. For each mouse, the mean
metabolic rate was calculated for the last 23 h.
For locomotor activity, the system used has been previously described (19). The home-cage traveled distance was measured during either the lights on or lights off cycle. When placed in this experimental set-up, mice did not have access to food or water. Quantitative analyses of the distance traveled during the entire period were made off-line. The fraction of time spent in activity was calculated by measuring the time during which the animal showed a displacement of its center of mass of at least 1 cm. All calculations were made using 386-Matlab (Mathworks, Sherborn, MA).
Blood parameters
Mice were anesthetized 2 h after lights on with 60 µl
xylene/ketamine (1:4, vol/vol). Blood was collected by eye puncture
into tubes containing citrate at a final concentration of 0.01
M. After 10 min in ice, plasma was separated by
centrifugation at 10,000 x g for 10 min and stored at
-20 C. A volume of 100 µl of a 1:2 dilution was used for mouse
leptin assays using a commercial kit (R & D Systems, Inc.,
London, UK). Glucose, triglycerides, total cholesterol, and free
T3 were determined using standard laboratory
procedures. Insulin was determined by RIA using a commercial kit with a
rat insulin standard (CIS Biointernational, Gif-sur-Yvette,
France).
Statistical analysis
All data are expressed as the mean ± SEM. The
values were examined by the one-way ANOVA or t test with the
computer software STATISTIX, version 4.0 (Analytical Software,
Tallahassee, FL).
| Results |
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To gain some insights on the metabolic pathways leading to triglyceride
accumulation in adipocytes, measurement of endogenous fatty acid
synthesis was performed by determining FAS activities of cytosolic
extracts of epididymal fat pads of WT and
agt-/- mice. Data from Table 2
show that FAS
activity was 2.2-fold higher in extracts from WT mice than in those
from agt-/- mice, consistent with the 2.6-fold
increase observed in adipocyte weight. This observation is also in
accordance with a report showing that AngII regulates lipogenesis by
increasing FAS activity (10). Upon high fat feeding, it is
known that the exogenous supply of fatty acids from chylomicrons
increases dramatically, leading to a down-regulation of FAS activity.
As shown in Table 2
, this down-regulation was taking place in WT mice,
but not in agt-/- mice, suggesting that this
modulation was AngII related.
AGT deficiency and thermogenesis-related parameters
Comparative analysis of the main metabolic blood parameters is
shown in Table 3
. Compared with WT mice,
agt-/- mice exhibited a moderate decrease in
circulating levels of cholesterol and triglycerides. Although
statistically significant, the increase observed in glucose levels in
agt-/- mice was slight and could not be
considered physiologically important. In addition, insulin levels were
similar. Upon high fat feeding, some interesting features emerged.
First, glucose levels of agt-/- mice remained
unchanged, thus abolishing the slight difference observed between the
two genotypes. Second, triglyceride levels were significantly
decreased, whereas cholesterol levels were increased, in agreement with
the responsiveness to dietary fat and cholesterol reported in various
strains of inbred mice (20). Free T3
was also determined, as this hormone has been long known to be involved
in thermogenesis (21). Table 3
shows similar levels of
free T3 in chow-fed WT and
agt-/- mice. However, upon high fat feeding,
the levels were significantly increased in both genotypes.
Interestingly, a significant increase (1.3-fold) was observed in the
level of free T3 in
agt-/- mice compared with that in WT mice. The
levels of insulin and leptin were similar in both genotypes when fed a
standard chow or a high fat diet. Moreover, these data are in agreement
with the fact that at 6 wk of age, no statistically significant
difference between the two genotypes was observed with respect to
interscapular BAT weight (59.4 ± 2.9 mg for WT mice
vs. 61.9 ± 2.2 mg for agt-/-
mice; n = 12) and uncoupling protein-1 (UCP-1) mRNA levels (Fig. 2
). Northern blot analysis was also
performed for UCP-2 from epididymal fat pads and for UCP-3 from
skeletal muscle. Using ß-actin mRNA levels as an internal standard
and taking an arbitrary unit of 1 for WT mice, the values for
agt-/- mice were, respectively, 1.09 for UCP-1
(n = 9; P = NS), 1.13 for UCP-2 (n = 6;
P = NS), and 1.24 for UCP-3 (n = 3;
P = NS).
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| Discussion |
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In contrast to WT mice, which gained weight between 12 and 46 wk of age on high fat feeding, the body weight of agt-/- mice remained stable. Under the conditions of augmented exogenous fatty acid supply, the weight of epididymal fat pads remained 1.8-fold higher in WT mice than in agt-/- mice at 6 wk of age, and this increase became more evident at 16 wk of age. As anticipated, during high fat feeding, hypertrophy of adipocytes occurred in agt-/- mice, but a large difference persisted, as the weights of adipocytes of WT mice remained much higher than those of agt-/- mice. The stable body weight of agt-/- mice appears at odds with the increase in adipocyte size observed in the epididymal depot. However, it cannot be ruled out that the growth of this depot may not be identical to that of the other adipose depots, in a way similar to the differential growth of different adipose depots in response to nutritional or environmental stimuli (22).
In search of additional factors that could explain the lower body weight of agt-/- mice compared with WT mice in response to a chow or a high fat diet, deficient mice show a decrease in food efficiency, as estimated by the ratio of the mean 23-h metabolic rate divided by the energy content of the food eaten by the same animal. This ratio is significantly (P < 0.001) lower in agt-/- mice than in WT mice. This finding suggests the occurrence of activation of futile cycles in the metabolic pathways of agt-/- mice. In looking for possible mechanisms to explain the increased energy dissipation of these mice, our data probably exclude a difference in intestinal absorption, as both the amount and the fat content of feces were similar. In addition, leptin, which is known to increase sympathetic activity (23) and energy expenditure in ob/ob mice (24), is also excluded, as circulating leptin levels were similar in the two genotypes fed either a standard or a high fat diet. In agreement with this assumption, the sympathetic pathway did not seem to be altered, as shown indirectly by UCP-1 expression levels in BAT. Free T3 levels were similar in agt-/- mice and WT mice fed a chow diet. Upon high fat feeding, although both genotypes increased their levels of free T3 compared with those in chow-fed animals, a significant hyperthyroidism was seen in agt-/- mice compared with WT mice. This additional component may contribute to lower the metabolic efficiency of AGT-deficient mice.
Locomotor activity, as expressed by the distance covered, was clearly and significantly increased in agt-/- mice compared with WT mice and may participate to some extent in the higher energy dissipation (19). Therefore, it is assumed that the more frequent and longer activity periods of AGT-deficient mice, in addition to decreased lipogenesis, are responsible for the decreased fat deposition. It has been reported in rats that brain AGT participates in a central regulation of blood pressure (25), and it can be hypothesized that AngII affects similarly the central pathway(s) leading to increased locomotor activity. In summary, our results show that, compared with WT mice, agt-/- mice do not gain weight in response to a high fat diet and exhibit alterations in WAT development and locomotor activity, supporting the involvement of AngII in the regulation of body fat mass.
| Acknowledgments |
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| Footnotes |
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Abbreviations: AGT, Angiotensinogen; AngII, angiotensin II; BAT, brown adipose tissue; FAS, fatty acid synthase; UCP-1, uncoupling protein-1; WAT, white adipose tissue; WT, wild-type.
Received May 7, 2001.
Accepted for publication August 20, 2001.
| References |
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in preadipose cells. Mol Cell
Endocrinol 160:149156
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