1 Institut National de la Santé et de la Recherche Médicale (INSERM) U380, 2 INSERM U445, and 3 INSERM U363, Institut Cochin de Génétique Moléculaire, Université René Descartes, 75014 Paris, France
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ABSTRACT |
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Stimulation of the
cAMP-signaling pathway modulates apoptosis in several cell types and
inhibits Jo2-mediated apoptosis in cultured rat hepatocytes. No
information is yet available as to whether the hepatic
2-adrenergic receptor (AR)
expression level, including
2-AR-dependent adenylyl cyclase
activation, modulates hepatocyte sensitivity to apoptosis in vivo or
whether this sensitivity can be modified by
2-AR ligands. We have examined
this using C57BL/6 mice, in which hepatic
2-AR densities are low, and
transgenic F28 mice, which overexpress
2-ARs and have elevated basal
liver adenylyl cyclase activity. The F28 mice were resistant to
Jo2-induced liver apoptosis and death. The
-AR antagonist
propranolol sensitized the F28 livers to Jo2. In normal mice
clenbuterol, a
2-AR-specific agonist, considerably reduced Jo2-induced liver apoptosis and death;
salbutamol, another
2-AR-selective agonist, also
reduced Jo2-induced apoptosis and retarded death but with less efficacy than clenbuterol; and propranolol blocked the protective effect of
clenbuterol. This indicates that the expression level of functional
2-ARs modulates Fas-regulated
liver apoptosis and that this apoptosis can be inhibited in vivo by
giving
2-AR agonists. This may
well form the basis for a new therapeutic approach to diseases
involving abnormal apoptosis.
-adrenoceptor antagonist; C57BL/6 mouse; transgenic F28 mouse; anti-Fas monoclonal antibody
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INTRODUCTION |
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APOPTOSIS or programmed cell death is of great importance in normal development, homeostasis, and pathogenic processes. Diseases such as acquired immunodeficiency syndrome (AIDS), neurodegenerative diseases, ischemia, and hepatitis are characterized by excessive apoptosis, whereas carcinogenesis, autoimmune diseases, and viral infection are associated with insufficient apoptosis.
Apoptosis is mainly triggered by the interaction of Fas-L and tumor
necrosis factor (TNF)- (6, 13, 19, 25) with their receptors at the
cell surface. Fas-L-mediated apoptosis seems to play a key role in the
development of hepatitis (19). Hence, mice given the anti-Fas
monoclonal antibody (MAb) Jo2 develop a phenotype of fulminant
hepatitis and die (33). Several factors are potent in vivo inhibitors
of Fas-mediated apoptosis in the liver. For instance, the destruction
of the livers by Jo2 MAb is inhibited in transgenic mice that
overexpress human Bcl-2 (22, 35), SV40 T antigen (39), or a
nontransforming SV40 T-antigen mutant (38) in the liver or mice given
interleukin 1
-converting enzyme-like protease inhibitors (36, 40),
hepatocyte growth factor (20), or the immunomodulator linomide (34). In
all animals but one (35), the lethal effect of anti-Fas MAb was also
either retarded (39) or inhibited (20, 22, 34, 36, 38, 40).
cAMP is a modulator of apoptosis in many cells in culture. Hence,
increases of the intracellular cAMP concentration and/or stimulation of the cAMP-signaling pathway with cAMP analogs can inhibit
apoptosis in bone marrow-derived cells (3), T-cell hybridomas (14, 24),
neutrophils (37), and macrophages (29) and can induce apoptosis in
myeloid leukemia cells (41), malignant glioma cells (7), T cells (18,
28), B lymphocytes (26), and ovarian granulosa cells (1). cAMP also
protects rat hepatocytes in culture against bile acid-induced and
Fas-mediated apoptosis (11, 44). Adenylyl cyclase activity, and thus
intracellular cAMP production, can be stimulated by activating several
membrane-bound receptors via interaction with heterotrimeric
GTP-binding proteins. One of these receptors, the
2-adrenergic receptor (AR),
mediates glycogenolysis and gluconeogenesis in the liver (16).
There is no information as to whether the hepatic
2-AR expression level,
including
2-AR-dependent
adenylyl cyclase activity and cAMP production, modulates the
sensitivity of the hepatocytes to apoptosis in vivo or whether this
sensitivity can be modified by giving
2-AR ligands. The present study
examines this question using C57BL/6 mice, in which the hepatic density
of
2-ARs is low, and recently
described transgenic F28 mice, whose hepatic
2-AR densities are much higher
and mimic those reported for humans (2).
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MATERIALS AND METHODS |
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Animals. F28 transgenic mice were produced using the untransformed complete 3458-bp genomic fragment isolated from the human epidermoid cell line A-431 (10) as previously described (2). Control C57BL/6 mice were from Iffa Credo (Lyon, France). The studies were done on 6- to 10-wk-old (16-21 g) males. The animals were killed by cervical disruption. All animal procedures were conducted in accordance with French government regulations (Services Vétérinaires de la Santé et de la Production Animale, Ministère de l'Agriculture).
Particulate fraction preparation.
Livers were homogenized for 10-20 s in a Polytron mixer and then
in a Potter homogenizer (5 strokes, 2,000 rpm) in 50 mmol/l Tris · HCl, pH 7.6, 5 mmol/l EDTA, 250 mmol/l
sucrose, 10 µg/ml benzamidine, 5 µg/ml trypsin inhibitor, 5 µg/ml
leupeptin, and 10 mmol/l phenylmethylsulfonyl fluoride (PMSF) at
4°C. The homogenate was centrifuged for 20 min at 50,000 g, and the resulting particulate fraction was dispersed in 75 mmol/l Tris · HCl, pH
7.6, 5 mmol/l EDTA, 12.5 mmol/l
MgCl2, 10 µg/ml benzamidine, 5 µg/ml trypsin inhibitor, 5 µg/ml leupeptin, and 10 mmol/l PMSF
supplemented with 10% glycerol and stored at 80°C. Protein
concentrations were determined with the bicinchoninic acid (BCA)
protein assay kit (Pierce, Rockford, IL).
Determination of -AR binding characteristics and
functionality on liver particulate fractions.
Total
-AR-binding,
2-AR-binding, and adenylyl
cyclase activities were determined as described earlier (2).
Incubations for adenylyl cyclase assays were done in the presence of 10 µmol/l of l-isoproterenol, 100 µmol/l 5'-guanylylimidodiphosphate (Gpp[NH]p), or 1 mmol/l forskolin to determine maximal
-AR agonist-induced, maximal G
protein-induced, or maximal non-receptor-mediated stimulation of
adenylyl cyclase, respectively. Isoproterenol, Gpp[NH]p,
and forskolin were from Sigma Chemical (St. Louis, MO).
Quantification of cAMP in perfused and nonperfused livers.
The liver lobes were carefully removed from newly killed mice. Lobes
used for experiments on nonperfused livers were immediately frozen in
liquid nitrogen and kept at 80°C until the extraction of cAMP.
Western blotting. Western blot analysis of Fas in liver particulate fractions of young adult control and F28 mice was essentially done as described previously (35). Briefly, samples containing 100-150 µg of protein in Laemmli sampling buffer were heated for 5 min at 94°C and run on 12.5% SDS-polyacrylamide gels. Proteins were transferred to nitrocellulose membranes, which were then blocked with 5% nonfat milk in PBS containing 0.25% Tween (PBS-T) for 1 h. The membranes were incubated overnight at 4°C with 0.5 µg/ml hamster anti-mouse Fas antigen MAb (Jo2; PharMingen, San Diego, CA) in 2.5% nonfat milk in PBS-T, washed in PBS, and incubated with peroxidase-conjugated goat anti-hamster IgG (Jackson ImmunoResearch Labs, West Grove, PA) (0.8 µg/ml in PBS-T) for 1 h at room temperature. Finally, the membranes were washed with PBS, incubated in enhanced chemiluminescence (ECL) detection reagents (Amersham) for 1 min at room temperature, and exposed to Hyperfilm ECL (Amersham). Full-range molecular weight markers (Amersham) were used to determine apparent molecular weights.
Treatment of mice and Jo2 MAb injection.
The mice were given -adrenergic agonists or antagonists in drinking
water. Clenbuterol (1.3 or 2.6 mg/l; Sigma Chemical) or salbutamol (1.4 or 2.1 mg/l; Salbumol, Glaxo Wellcome) was given for ~17 h,
and propranolol (14 or 21 mg/l; Avlocardyl, Zeneca-Pharma) was given
for 48 h. The inhibition of the clenbuterol effects by propranolol was
examined in mice first given propranolol (14 mg/l) for 48 h and then
propranolol (14 mg/l) plus clenbuterol (2.6 mg/l) for 17 h. All
treatments were started at 4:00-6:00 PM. The monoclonal antibody
Jo2 was given by intravenous injection (15 µg/200 µl in 0.9 g/l NaCl).
Histology. Livers were removed 5-6 h after Jo2 MAb injection or immediately after death, whichever occurred first. Fragments of tissue were fixed in 4% formaldehyde and embedded in paraffin. Sections (5 µm) were cut and stained with hematoxylin-eosin.
Incidence of apoptosis. The incidence of apoptosis in the mice in each study group shown in Figs. 2, 4, 5, and 7 was summarized as described earlier (23): hematoxylin-eosin-stained liver sections were prepared for all animals used, and the cells undergoing apoptosis (chromatin condensation, nuclear fragmentation, extensive surface blebbing) were scored. The number of apoptotic bodies was counted in four fields, each of ~100 cells.
In situ detection of apoptosis. The transferase UTP nick-end labeling procedure was used. Sections were incubated in 0.1 mol/l HCl containing 50 U/ml pepsin for 5 min, washed (3 × 5 min) in distilled water, and incubated in CC buffer (140 mmol/l sodium cacodylate, pH 7.2, 1 mmol/l CoCl) for 10 min. The sections were then incubated in CC buffer containing 0.25 U/µl terminal deoxynucleotidyl transferase and 10 µmol/l bio-11-dUTP (Amersham) for 60 min in a water-saturated atmosphere and washed at room temperature once with 2× SSC (1× SSC is 0.15 mol/l NaCl and 0.015 mol/l sodium citrate, pH 7.0) for 10 min and twice with 100 mmol/l Tris · HCl, pH 7.6 for 3 min. Endogenous alkaline phosphatases were eliminated by incubation in 2% levamisol in PBS (Sigma) for 10 min, and the sections were washed with 100 mmol/l Tris · HCl, pH 7.6. They were then incubated with alkaline phosphatase-streptavidin in 100 mmol/l Tris · HCl, pH 7.6 (1:1,000; Vector Laboratories, Burlingame, CA) for 30 min, washed twice in 100 mmol/l Tris · HCl, pH 7.6, for 3 min and twice in 100 mmol/l Tris · HCl, pH 9.4, for 5 min, and incubated in the dark with NBT-BCIP, as indicated by the manufacturer (GIBCO BRL, Gaithersburg, MD) for 10 min. Finally, they were washed with distilled water and counterstained with methyl green. All manipulations were done at room temperature except the incubation with 10 µmol/l bio-11-dUTP, which was at 37°C.
Serum analysis. Biochemical parameters of the serum [alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT)] were quantified using a standard clinical automatic analyzer (type 917, Hitachi).
Statistical analysis. Results are presented as means ± SE. The significance of differences between means of two groups was assessed by using the Student's t-tests for unpaired variates and that between more than two groups by using ANOVA, which was followed, when significant, by the Bonferroni test.
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RESULTS |
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-AR expression and functionality in livers of F28
and control mice.
We monitored the total
-AR and
2-AR binding capacities as well
as the basal, maximal isoproterenol-induced, maximal G protein-induced, and maximal non-receptor-mediated adenylyl cyclase activity in particulate fractions that were prepared from livers of 8-wk-old mice.
The F28 mice had a 17-fold greater
2-AR density, an 11-fold greater maximum agonist-induced adenylyl cyclase response, and a
slightly higher basal and maximum G protein-induced adenylyl cyclase
activity than the control mice. The maximal activity of the adenylyl
cyclase enzyme was similar for both groups (Table 1). We subsequently evaluated the extent to
which
-AR agonists can modulate
-AR-dependent adenylyl cyclase
activity and cAMP accumulation in the livers of F28 and C57BL/6 mice in
vivo.
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F28 mice are spontaneously protected against Jo2-mediated liver
apoptosis and lethality.
Control and F28 mice were injected intravenously with 15 µg of
anti-Fas MAb. All the F28 mice survived, whereas ~75% of the control
mice died within 5 h and only 1 of 20 survived for >24 h (Fig.
2B). The
livers taken from the control mice showed extensive hepatocyte
apoptosis (Fig.
3A),
with chromatin condensation, nuclear fragmentation, extensive surface
blebbing, acidophilic Councilman bodies (Fig.
4C,
inset), and DNA fragmentation (Fig.
4D) and had severe
intraparenchymatous hemorrhages (Fig.
4C). This is consistent with
previous work (33). In contrast, the livers from F28 mice were largely
unaltered 5 h after injection, with very few apoptotic foci (Figs.
5, C and
D, and
3B). Accordingly, the serum
aminotransferase (ALAT and ASAT) activity 3 h after the injection of
Jo2 increased markedly in the C57BL/6 mice but remained very low in the
F28 mice (Fig. 6).
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Antagonist propranolol decreased resistance of F28 mice to Jo2 MAb.
Because F28 mice with overexpressed hepatic
2-ARs are naturally protected
against Jo2 MAb, we examined the response of these mice to Jo2 MAb when
the
-ARs were blocked with the
-AR antagonist propranolol. F28
mice were given 21 mg/l propranolol for 48 h and then injected with 15 µg of Jo2 MAb. None of the pretreated F28 mice died, but they all had
significantly more apoptotic cell bodies than did untreated F28 mice
given Jo2 MAb (Figs. 5, G and H vs.
C and
D, Fig.
3B). The percentage of
apoptotic cells for the propranolol-treated F28 mice nevertheless
remained much lower than that for untreated or even clenbuterol-treated
C57BL/6 mice (Fig. 3, B vs.
A), and serum levels of
aminotransferase 3 h after the injection of Jo2 remained as low in
propranolol-treated as in untreated F28 mice (Fig. 6).
2-AR-selective agonist
clenbuterol inhibited Jo2-induced lethality and liver apoptosis in
C57BL/6 mice.
We attempted to protect control mice against Fas-induced hepatic
apoptosis by giving
2-AR
agonists to activate the hepatic
2-ARs. C57BL/6 mice were given
1.3 mg/l of the
2-AR-selective agonist clenbuterol in drinking water for 17 h and then injected with
15 µg Jo2 MAb. The clenbuterol-treated C57BL/6 mice had considerably less liver apoptosis than the untreated animals (Fig. 4,
E and F vs.
C and
D; Fig.
3A). About 63% of the
agonist-treated control mice were protected from the lethal effect of
the Jo2 MAb (Fig. 2B).
Clenbuterol-treated F28 mice also had greater natural resistance to
Jo2-induced hepatocyte apoptosis than did untreated F28 mice and often
had no more apoptotic cells (Fig. 5, E
and F vs.
C and D; Fig.
3B). Despite less severe liver
injury in the C57BL/6 mice treated with 1.3 mg/l clenbuterol, the
biochemical sequels were still large and only the serum ASAT activity
was significantly different from that of the untreated mice. Serum
aminotransferase activity was very low in clenbuterol-treated F28 mice
(Fig. 6).
Effect of clenbuterol in C57BL/6 mice was dose and
2-AR dependent.
The dose dependence of the clenbuterol effect was assessed by giving
control mice drinking water with 1.3 or 2.6 mg/l clenbuterol before
injection of Jo2 MAb. One-half of the mice given the low dose died
within 6 h, but all the mice given the high dose survived (Fig.
7A). The
high-dose mice had fewer apoptotic hepatocytes (Fig.
3A) and significantly lower serum
aminotransferase activity than the low-dose mice (Fig. 6).
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DISCUSSION |
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Changes in cAMP concentration or activation of the cAMP-signaling pathway modulate the sensitivity of many cell types to apoptosis (1, 3, 7, 14, 18, 24, 26, 28, 29, 37, 41) including the sensitivity of rat hepatocytes in culture to bile acid-induced and Fas-mediated apoptosis (11, 44). The liver of normal mice in vivo is particularly sensitive to the anti-Fas antibodies Jo2: they cause massive liver apoptosis in these animals that is followed by death in only a few hours, a phenotype that resembles fulminant hepatitis (33).
We have described a line of transgenic mice, F28, that carries the
human 2-AR gene under the
control of its own promoter and expresses the transgene in several
organs. These mice overexpress functional
2-ARs in the liver (Table 1)
and have a slightly increased number of
2-ARs in lung, heart, brain,
and muscle (26). This study provides data suggesting that there is a
higher production of cAMP in the liver of F28 mice compared with
controls under normal physiological conditions, although the hepatic
cAMP levels in the two strains were similar under these conditions
(Fig. 1A). Indeed, the livers of
F28 mice accumulated about two times more cAMP than did those of
control mice when they were treated ex vivo with the phosphodiesterase
blocker IBMX to inhibit the metabolism of cAMP (Fig.
1B). We also showed that mice
treated with the
2-AR agonist
clenbuterol have a higher hepatic cyclase activity; this effect was
considerably more marked in F28 mice than in C57BL/6 mice. The in vivo
hepatic cAMP level in clenbuterol-treated F28 mice is significantly
higher than in untreated F28 mice, despite the natural presence of
phosphodiesterase activity (Fig.
1A). Also, ex vivo experiments
done with IBMX not only confirmed that clenbuterol strongly increases
cAMP production in the liver of F28 mice but also showed that the
agonist stimulates hepatic adenylyl cyclase activity in C57BL/6 mice,
although to a lesser extent (Fig.
1B). Interestingly, ex vivo
experiments strongly suggest that the hepatic cAMP level in F28 mice
under normal physiological conditions is at least as high as the
clenbuterol-induced hepatic cAMP level in C57BL/6 mice. The difference
in the adenylyl cyclase activities observed in the liver tissues of the
F28 and the control mice under nonstimulating conditions might simply
be caused by stimulation of the
-AR systems by circulating
catecholamines. However, liver particulate fractions from F28 mice also
had higher basal adenylyl cyclase activities than did those from
control mice (Table 1). This suggests that an increase of spontaneously active receptors might contribute to the difference between the strains. Indeed, it was shown earlier that the overexpression of
2-ARs in mouse heart results in
a higher basal adenylyl cyclase activity caused by more spontaneously
active receptors (30). The higher maximum G protein-inducible adenylyl
cyclase activity in F28 mouse liver particulate fractions (Table 1)
suggests that a change in the amounts of the G proteins might also be involved.
Because the above findings indicate that a change in the abundance of
functional hepatic 2-ARs
and/or the administration of
-AR ligands may lead to a
change in the adenylyl cyclase activity and consequently the production
of intracellular cAMP, the major concern of the studies described here
is to determine whether these also modulate the sensitivity of the
mouse to Jo2 MAb in vivo.
It is shown that F28 mice are naturally protected against Jo2. There is
no great difference in the amounts of Fas in F28 and C57BL/6 mice, but
the F28 mice survive an intravenous injection of Jo2 and have only few
apoptotic foci in their livers (Figs. 2 and 5). The protection of F28
mice against liver apoptosis is also partially inhibited by the potent
-AR antagonist propranolol (Figs. 3 and 5). This indicates that the
overexpression of
2-ARs in the
liver probably plays an important part in the natural resistance of F28 mice.
We have also demonstrated that the Jo2-induced hepatic apoptosis and
lethality can be inhibited in vivo by giving
2-adrenergic agonists. F28 mice
treated with the
2-AR-specific
agonist clenbuterol have greater natural resistance to anti-Fas MAb
than do untreated F28 mice (Fig. 5). Remarkably, although there are
fewer hepatic
2-ARs in control
mice (Table 1), clenbuterol also protects them from the lethal effect
of the anti-Fas MAb (Fig. 2) and considerably reduces liver apoptosis
(Figs. 3 and 4) and the biochemical sequels of liver destruction (Fig.
6) in a dose-dependent fashion (Fig. 7A). Several experiments confirmed
that the protective effect of clenbuterol in control mice is caused by
activation of
2-ARs: the
-AR
antagonist propranolol blocks the action of the
2-AR agonist clenbuterol (Figs.
3, 4, and 7A), whereas another
2-AR agonist, salbutamol,
causes a dose-dependent delay in the lethal effect of the Jo2 MAb (Fig.
7B) and slightly reduces liver cell apoptosis (Fig. 3).
We do not yet know the mechanisms underlying the natural protection of
F28 mice and the resistance conferred by the -AR agonists. Activation of the cAMP-dependent protein kinase with cAMP or cAMP analogs inhibits the apoptosis of rat hepatocytes induced by polyclonal rabbit anti-murine Fas antibodies (M-20) (11). Data provided here
strongly support the idea that activation of the cAMP-signaling pathways, modulation of hepatic adenylyl cyclase activity, and cAMP
production are probably involved in altering the sensitivity of the
liver to Jo2-mediated apoptosis in untreated F28 mice and in
clenbuterol-treated mice. We have obtained evidence that clenbuterol activates the hepatic
2-AR
system and that this activation can lead to increased hepatic cAMP
production, which is twofold in normal mice and fivefold in F28 mice.
Finally, cAMP production in untreated F28 mice is at least as high as
in clenbuterol-treated normal mice. This might explain why even
untreated F28 mice are that well protected against Jo2. This does not
exclude the possibility that other regulatory mechanisms might be
involved in the protection against Jo2 and even that there are
differences between the regulatory mechanisms modulated by the hepatic
2-AR overexpression in the F28
mice and those that are triggered by clenbuterol. Stimulation of
protein kinase A and regulation of protein phosphorylation are perhaps
involved in the protective action of cAMP in hepatocytes (11, 44). The
phosphorylation and dephosphorylation mechanisms regulating the
Fas/Fas-L pathway are, however, very complex (17), and it is not known
yet precisely which proteins are involved.
The regression of Jo2-induced mortality parallels the decrease in liver
apoptosis mediated by 2-AR
overexpression and
2-AR agonists (Figs. 2B and
7A vs. Fig. 3). The
2-AR agonist salbutamol has a
smaller protective effect than does clenbuterol; it inhibits liver
apoptosis less well and only delays the death of the mouse. The lower
efficacy of this agonist is probably caused by differences in agonist
potency and/or systemic bioavailability. This strongly suggests
that the mouse is rescued from Jo2-induced death by reduction of liver
apoptosis. A line of transgenic mice overexpressing Bcl-2 is protected
against Jo2 MAb-induced liver apoptosis but not lethality, indicating
that the stimulation of Fas on other target organs or cells could
contribute to the lethal effect of Jo2 (35). Changing the
2-AR activity in other tissues
might thus also be involved in the inhibition of the lethal effects of
Jo2 MAb.
The expression of 2-ARs
increases during liver regeneration after partial hepatectomy and in
hepatocarcinoma (4, 15), whereas desensitization (which
involves functional uncoupling, sequestration, and
downregulation of the
-ARs, with a less active cAMP-signaling
pathway and lower cAMP-dependent protein kinase activation of hepatic
2-ARs) is induced by chronic
ethanol consumption (8), which can ultimately lead to cirrhosis. As we
have shown that increased hepatic
2-AR activity diminishes the
sensitivity of liver toward anti-Fas MAb-induced apoptosis and that a
decreased hepatic
-AR activity makes hepatic cells more sensitive to
anti-Fas MAb-induced apoptosis, it is possible that the regulation of
the hepatic
2-AR/adenylyl
cyclase system might also be implicated in the abnormal inhibition or
stimulation of hepatocyte apoptosis.
2- and
1-ARs are present in most
tissues and on the cells of the immune system, and cAMP seems to be
involved in regulating apoptosis in several types of cells (1, 3, 7,
11, 14, 18, 24, 26, 28, 29, 37, 41, 44). Hence, the regulation of
-AR expression might be important for regulating apoptosis in other
tissues, and dysregulation of
-AR expression might be implicated in
the dysregulation of apoptosis that occurs in several major disorders.
Several findings seem to support this. Desensitization of the cardiac
-AR system and apoptosis both occur in cardiac ischemia (5,
32), and
-AR ligands can modulate myocyte apoptosis (45, 46). The
activity of the pulmonary
-AR system and the production of cytokines
such as TNF-
are closely linked in chronic airway inflammation (see,
e.g., Refs. 9, 12, 42). The abundance of the subsets of cells from the
immune system changes considerably in immunologic responses,
inflammation, and stress (see, e.g., Ref. 31), and this reorganization
also involves changes in the expression of
-ARs on cells (21, 27) as
well as the apoptotic regulation of cell survival (e.g., Ref. 43),
which can be modulated by activation of the cAMP-dependent signaling
pathway (see, e.g., Refs. 1, 18, 26).
We have shown here that mice can be protected in vivo from Jo2-induced
massive liver apoptosis and death by increasing the hepatic
2-AR activity, either by
increasing the number of
2-ARs or by stimulating the hepatic
2-AR-mediated signaling with
synthetic agonists. This suggests new approaches to the treatment of
diseases involving abnormal apoptosis in liver and perhaps, more
generally, in other tissues or cells.
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ACKNOWLEDGEMENTS |
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The authors thank Prof. A. D. Strosberg and Prof. A. Kahn for helpful discussions, Dr. B. Cheriot for serum analysis, and Dr. O. Parkes for editing the English text.
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FOOTNOTES |
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This work was supported by grants from the Association de Recherche contre le Cancer (ARC) and the Ligue Nationale contre le Cancer (LNC).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: C. André, INSERM U380, Institut Cochin de Génétique Moléculaire, Université René Descartes, 22 rue Méchain, 75014 Paris, France (E-mail: claudine.andre{at}cochin.inserm.fr).
Received 13 March 1998; accepted in final form 9 November 1998.
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