(Hypertension. 2001;37:1184.)
© 2001 American Heart Association, Inc.
Scientific Contribution |
8-iso-Prostaglandin F2
Increases Expression of LOX-1 in JAR Cells
From the Institute for Nutrition Research (B.H., A.C.S., T.H., T.R.), Faculty of Medicine, University of Oslo; Departments of Obstetrics and Gynecology (A.C.S.), Aker University Hospital; and Departments of Obstetrics and Gynecology (T.H.), National Hospital, University of Oslo, Norway; and Department of Bioscience (T.S.), National Cardiovascular Center Research Institute, Suita, Osaka, Japan. Dr Halvorsen is currently with the Research Institute for Internal Medicine, National Hospital, University of Oslo, Norway.
Correspondence to Bente Halvorsen, PhD, Research Institute for Internal Medicine, National Hospital, University of Oslo, 0027 Oslo, Norway. E-mail bente.halvorsen{at}klinmed.uio.no
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Abstract |
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Abstract—Lectinlike oxidized LDL receptor-1 (LOX-1), a cell-surface receptor for oxidized LDL (ox-LDL), is proposed to be involved in endothelial dysfunction and in the pathogenesis of atherosclerosis. Preeclampsia is a pregnancy complication diagnosed by hypertension and proteinuria, characterized by endothelial dysfunction, and supposedly caused by compounds from hypoxic uteroplacental tissues. A feature of preeclampsia is formation of foam cells in maternal arterial walls of gestational tissue ("acute atherosis"). Oxidative stress is believed to play a role in the pathophysiology of preeclampsia. 8-iso-prostaglandin F2
(8-iso-PGF2) is
a marker of oxidative stress in vivo, is biologically active in vitro,
and is elevated in preeclamptic plasma and gestational tissue. In the
present article, we hypothesized that
8-iso-PGF2 could induce the expression of
LOX-1 in trophoblastic cells (JAR). We demonstrated augmented cellular
uptake of 125I-tyraminylcellobiose ox-LDL in
JAR cells incubated with 8-iso-PGF2 (10
µmol/L) versus control cells. Ligand blots revealed an increased
binding of ox-LDL to LOX-1 in JAR cells incubated with
8-iso-PGF2 (10 µmol/L). Incubation with
8-iso-PGF2 (10 µmol/L) also resulted in
augmented LOX-1 protein levels (Western blots) and mRNA levels
(Northern blots). JAR cells transfected with 3 copies of a nuclear
factor-
B binding site demonstrated dose-dependent activation of the
reporter gene luciferase after incubation with
8-iso-PGF2 (0 to 10 µmol/L). We also
demonstrated increased accumulation of neutral fats in JAR cells
incubated with 8-iso-PGF2 (10 µmol/L) and
ox-LDL compared with controls by oil red O staining. We speculate a
potential role of isoprostanes and LOX-1 in preeclampsia in the
development of "acute atherosis" of gestational spiral
arteries.
Key Words: receptors, lipoprotein • isoprostanes • nuclear factor • trophoblast • preeclampsia
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Lectinlike oxidized LDL receptor-1 (LOX-1)1 has recently been identified as a cell-surface receptor for oxidized LDL (ox-LDL), a major atherogenic substance.2 Ox-LDL is believed to get trapped in the macrophage through uptake by scavenger receptors on the surface, resulting in foam cell formation and development of atherosclerotic lesions.3 Modified LDL is also internalized and degraded in the endothelium4 and impairs endothelium-dependent vasorelaxation.5 Besides the novel LOX-1, multiple molecules, including class A and B scavenger receptors, MARCO, CD36, and CD68 have also been identified to be ox-LDL receptors.3 LOX-1 is expressed abundantly on vascular endothelial cells,1 but is also expressed on macrophages in humans and mice.6 Other cell types present in the atherosclerotic lesions, such as vascular smooth muscle cells and monocytes-macrophages, have also been demonstrated to express LOX-1.7 8 This newly described receptor is proposed to be involved in endothelial dysfunction and foam cell formation in the pathogenesis of atherosclerosis.9
Preeclampsia complicates 3% to 7% of all human pregnancies, and is diagnosed by hypertension and proteinuria in the latter half of the pregnancy. Preeclampsia is a major cause of maternal and perinatal mortality and morbidity worldwide. The cause of the disease is still unknown, but dysfunction of maternal systemic endothelial cells is a key feature of the syndrome.10 Altered placentation with a reduced invasion of cytotrophoblast cells from the outer cell mass of the blastocyst into the inner part of maternal uterine wall is another feature of preeclampsia.11 This condition is probably the cause of incomplete transformation of maternal spiral arteries in the gestational endometrium (decidua),12 which causes inadequate uteroplacental circulation and local ischemia. Among uteroplacental compounds that are proposed to mediate disturbance of the maternal endothelium are lipid products, in particular, lipid peroxides.13
In preeclampsia, areas of lipid deposition in the maternal spiral arterial walls resemble early stages of atherosclerotic lesions, named "acute atherosis."14 Maternal risk factors for the syndrome include risk factors for atherosclerosis in later life, such as obesity, lipid abnormalities, insulin resistance, black race, hypertension, and elevated serum homocysteine concentrations.15 In particular, a predominance exists in preeclampsia of smaller, denser LDL particles that are more prone to oxidative modification than larger particles.16 In addition, elevated levels of autoantibodies against ox-LDL occur in established preeclampsia.17 Finally, hyperlipidemia of preeclampsia is present long before onset of the disease, and levels of triglycerides and free fatty acids are higher than in uncomplicated pregnancies.18
Isoprostanes are prostaglandin isomers formed by
free radical peroxidation of arachidonic acid
present in phospholipids. Isoprostanes are released to free forms
by the action of phospholipase
A2.19
Among the isoprostanes, 8-iso-prostaglandin
F2 (8-iso-PGF2) is
of special interest; it is a marker of oxidative stress in vivo and
also has potent biological activity in vitro.
8-iso-PGF2 is a potent vasoconstrictor,
mediates smooth muscle cell growth, activates
platelets,20 and induces
derangement of endothelial cell barrier
function.21 Oxidative stress
has been proposed to be involved in the pathophysiology of
preeclampsia. Elevated formation of
8-iso-PGF2 is associated with
cardiovascular risk factors such as
hypercholesterolemia and diabetes
mellitus.20 In women with
preeclampsia, plasma level of free 8-iso-PGF2
is elevated compared with in control
pregnancies.22 In previous
studies, we have demonstrated elevated levels of lipid
peroxides23 and free
8-iso-PGF224
in gestational endometrium (decidua) at delivery in preeclamptic
pregnancies compared with controls.
In the present article, we investigated whether the
receptor for ox-LDL, LOX-1, was expressed by trophoblastic cells, and
we hypothesized that the expression as well as the functional activity
of the receptor was induced by 8-iso-PGF2. We
further questioned whether the oxidative stress marker
8-iso-PGF2 could influence the red-ox
level in JAR cells, by examining the effect of
8-iso-PGF2 on nuclear factor (NF)–B
activity in JAR cells transfected with NF-B binding sites coupled to
a reporter gene. Finally, we studied whether trophoblastic cells could
accumulate neutral lipids after incubation with
8-iso-PGF2 and
ox-LDL.
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Methods |
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Materials
Tissue-culture dishes and flasks were supplied by Costar. Reagents, when not otherwise specified, were purchased from Sigma Chemical Co. Polyvinyldifluoride (PVDF) filters were from NEN, and Hybond-N filters were from Amersham. Sodium dodecyl sulfate–polyacrylamide gel electrophoretic (SDS-PAGE) gels (5%) were obtained from Bio-Rad.
Cell Cultures
The human choriocarcinoma cell line JAR from American
Type Tissue Collection (ATTC), was grown in RPMI-1640 supplemented with
10% heat-inactivated FBS,
L-glutamine 2 mmol/L,
penicillin 50 IU/mL, and streptomycin 50 µg/mL (Bio Whittaker). The
murine macrophage cell line J774 A1 (J774) from ATTC was grown
in DMEM with the same supplements as above except that gentamycin (60
µg/mL) was used as the only
antibiotic.25 The J774 cells
were used as positive controls in the various experiments for
expression of the macrophage type of LOX-1, which has
previously been
described.8
Isolation, Labeling, and Oxidation of
LDL
LDL was isolated, labeled with
125I-tyraminylcellobiose
(125I-TC), and oxidized with
CuSO4 as described
previously.25
Cellular Uptake of
125I-TC Ox-LDL
We measured cellular uptake of
125I-TC ox-LDL in JAR cells seeded in
24-well plate (1x105 cells/well) and grown
overnight (o/n) in growth medium. Fresh growth medium was then
added with either vehicle (0.09% ethanol) or 10 µmol/L
8-iso-PGF2 and incubated for 6 hours at
37°C. Thereafter, RPMI-1640 was added to
125I-TC ox-LDL (10 µg/mL; 100 cpm/ng), 2%
BSA, 2 mmol/L CaCl2, and either vehicle or
10 µmol/L 8-iso-PGF2 and incubated for 
24
hours at 37°C. Thereafter, the cells were chilled on ice and
harvested, and cell-associated radioactivity was determined and results
calculated as described
elsewhere.25 The
125I-TC ox-LDL cannot escape the
endosomal-lysosomal compartments, and the cell-associated radioactivity
represents both bound and internalized as well as degraded
forms of 125I-TC ox-LDL. "Cell-associated
radioactivity" is used synonymously with "cellular uptake" of
125I-TC ox-LDL in the present
article.
Isolation and Preparation of Membrane Proteins
From JAR Cells
JAR cells were incubated in growth medium
supplemented with either 0.09% ethanol (vehicle and control cells),
100 nmol/L 8-iso-PGF2, or 10 µmol/L
8-iso-PGF2 for 6 or 24 hours. After they were
incubated, cells were washed in ice-cold buffer A (150 mmol/L
NaCl, 50 mmol/L Tris-HCl, and 2.5 mmol/L
CaCl2; pH 7.5) that contained a protease
inhibitor cocktail (Boehringer Mannheim). JAR cell
membranes were isolated and solubilized, and the protein concentration
was determined as described
previously.26
Visualization of Ox-LDL Binding Proteins by
Immunolabeling on Blot
Solubilized membrane proteins (50 µg per lane) from
the JAR and J774 cells were separated by nonreducing SDS-PAGE (5%) and
blotted onto PVDF membranes, as described
elsewhere.26 The membranes
were blocked for 2 hours at room temperature with 5% skimmed milk in
TBS that contained 0.2% Tween (vol:vol) (TBST) after incubation with
ox-LDL (10 µg/mL) o/n at 4°C. After several washes in TBST with
0.5% skimmed milk, blots were incubated at room temperature for 1 hour
with anti–human apolipoprotein B-100 antibody (ICN Biomedicals) in
TBST with 0.5% milk. After blots washed, proteins were detected by
enhanced chemiluminescence with horseradish peroxidase–labeled
anti-mouse IgG (Vector Laboratories).
Western Blot Analysis
JAR cells were incubated in growth medium
supplemented with either 0.09% ethanol (control cells) or
8-iso-PGF2 (10 µmol/L) for 6 and 24 hours.
Western blotting was performed as described
previously,27 which separated
20 µg of cell protein from each experiment by SDS-PAGE (10%) and
transferred it to PVDF membranes. Filters were incubated with
anti–bovine LOX-1 antibody28
from mouse ascites, which cross reacts with human LOX-1. Proteins were
detected by enhanced chemiluminescence with horseradish
peroxidase–labeled anti-mouse IgG.
Northern Blot Analysis
Triazol (Gibco) was used according to manufacturer
directions for total RNA isolation from JAR cells incubated either 6 or
24 hours in growth medium that contained either 0.09% ethanol
(control) or 8-iso-PGF2 (10 µmol/L).
Northern blotting was performed as previously described with the use of
Hybond-N membranes.25 A human
LOX-1 cDNA probe was used1 and
calibrated against the signals from yeast 18S ribosomal
RNA.
DNA Transfection
JAR cells were plated at
1x105 cells per well in 6-well plates and
transfected 2 days after plating. Transfections were performed in the
absence of serum with 3 µg of DNA by use of 9 µL of TransFast
reagent (Promega Corp). The 3x-B-luciferase (3x-B-luc) plasmid
was kindly provided by Dr T.
Wirth.29 This promoter
construct contains 3 copies of a binding site for NF-B. All
transfections were overlaid with growth medium after 1 hour. Cells were
incubated 1 day after transfection in growth medium supplemented with
8-iso-PGF2 (100 nmol/L, 1 µmol/L, or 10
µmol/L) for 24 hours. Control cells were incubated in growth medium
supplemented with 0.09% ethanol. After incubation, the cells were
harvested for luciferase assays (Promega Corporation), and the
luminescence was measured by a luminometer (Turner Designs,
TD-20/20).
Oil Red O Staining
JAR cells were seeded on Chamber slides
(Laboratory-Tek) (5x105 cells per slide)
and grown o/n in 3 mL of growth medium. Cells were then added either to
fresh growth medium alone, growth medium with 0.9% ethanol and ox-LDL
(20 µg/mL), or growth medium with 10 µmol/L
8-iso-PGF2 and ox-LDL (20 µg/mL). Additives
were freshly renewed after 24 hours. After a total of 48 hours of
incubation, the slides were washed, fixed, and stained with oil red O
as described previously30 and
examined by light microscopy.
Statistical Analyses
Results are presented as means±SEM, and the
differences between control and treatment groups were tested using the
Mann-Whitney U test.
P<0.05 was considered
statistically significant.
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Results |
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Cellular Uptake of 125I-TC Ox-LDL
Figure 1 demonstrates increased cell-associated 125I-TC ox-LDL in JAR cells incubated with 8-iso-PGF2
(10 µmol/L) for 6 and 24 hours
(35% elevation, P=0.02, and
27% elevation, P=0.04,
respectively) compared with control cells. The time course shows a high
uptake of radiolabeled ligand (8 to 10 µg
125I-TC ox-LDL per milligram cell protein)
early in the time course that reached a plateau after 6 hours of
incubation, which suggests saturated kinetics of the uptake of
125I-TC ox-LDL in JAR cells.
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To rule out the possibility that
8-iso-PGF2 could affect the binding of ox-LDL
to LOX-1, we performed a binding assay similar to the uptake assay but
omitted the preincubation step. JAR cells were kept for 2 hours at
4°C in 125I-TC ox-LDL to which RPMI was
added, 2% BSA, 2 mmol/L CaCl2, and either
vehicle (0.09% ethanol) or 10 µmol/L
8-iso-PGF2. No statistical significant
difference was seen in cell-associated
125I-TC ox-LDL between control and
8-iso-PGF2-treated cells
(P=0.5; n=4), which showed that
8-iso-PGF2 does not interfere with the
ligand-binding activity of LOX-1.
Immunolabeling of Ligand Blot
Figure 2, top, demonstrates a major immunoreactive band at
50 kDa, which indirectly shows LOX-1. The figure shows 1.7-fold
elevated expression of binding protein for ox-LDL at 50 kDa in JAR
cells after 6 hours of incubation with
8-iso-PGF2 (10 µmol/L) versus control cells
(P=0.01; SEM, 0.5). A 2.3-fold
elevated expression occurred after 24 hours’ incubation with the same
test compound (P=0.01; SEM,
0.7). On the other hand, incubation for 6 or 24 hours with 100 nmol/L
8-iso-PGF2 did not result in significantly
altered expression of immunoreactive protein (1.0-fold and 1.1-fold
elevated compared with control, respectively; data not shown). The
immunoblots also demonstrated a distinct band at a lower
molecular size of 40 kDa from the membrane proteins of JAR cells (not
shown), which was comparable to the major band of the untreated J774
cells. J774 cells were used as positive controls for
macrophage-type LOX-1 at 40
kDa.8 In addition, a
immunoreactive band occurred at 50 kDa from the membrane proteins of
J774 cells, which was comparable to endothelial-type
LOX-1
(Figure 2, top).
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Western Blot
Figure 2, bottom, demonstrates immunoreaction to the LOX-1
protein at 50 kDa in JAR cells, which corresponds to the
endothelial size of the receptor. JAR cells subjected
to 8-iso-PGF2 (10 µmol/L) for 6 hours
demonstrate a 1.4-fold elevated protein level of LOX-1 of 50 kDa versus
controls (P=0.04; SEM, 0.07).
The 24-hour incubation of JAR cells with
8-iso-PGF2 (10 µmol/L) resulted in
unaltered 50-kDa protein expression of LOX-1 (1.0 relative to control
cells, P=0.5; SEM, 0.06).
Weaker immunoreactivity existed at a lower molecular size of 40 kDa,
which probably corresponded to the macrophage type of the
receptor (not shown).
Expression of mRNA
Northern blots demonstrated that JAR trophoblasts
exhibit the 2.8-kb LOX-1 transcript. A statistically significant
1.4-fold elevated mRNA–level signal density of LOX-1 exists relative
to 18S ribosomal RNA in JAR cells subjected to 10 µmol/L
8-iso-PGF2 for 6 hours compared with control
cells
(Table).
The 1.1-fold elevated mRNA–level relative signal density for LOX-1 in
JAR cells subjected to 10 µmol/L 8-iso-PGF2
for 24 hours compared with control cells was not statistically
significant.
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NF-B–Transfected JAR Cells
Figure 3 demonstrates dose-dependent induction of luciferase
activity in the transfected JAR cells incubated with
8-iso-PGF2 relative to control cells, which
ranged from 1.6-fold (0.1 µmol/L
8-iso-PGF2) to 12.8-fold (10 µmol/L
8-iso-PGF2) induction (all
P<0.03).
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Oil Red O Staining
Staining of neutral lipids on the Chamber slides with
oil red O revealed that JAR cells incubated with ox-LDL accumulate
significant amounts of oil red O–positive material compared with
control cells without ox-LDL added
(Figure 4B and A, respectively). In addition, cells grown
with both 8-iso-PGF2 (10 µmol/L) and ox-LDL
show a more intensive red staining versus cells exposed to only ox-LDL
and vehicle
(Figure 4C and B,
respectively).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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In the present study, we report the expression and 8-iso-PGF2
-induced upregulation of the
endothelial scavenger receptor LOX-1 in the
trophoblastic cell-line JAR, by ligand, Western, and Northern blots. In
addition, we report dose-dependent activation of the reporter gene
luciferase after incubation with 8-iso-PGF2
(0 to 10 µmol/L) in JAR cells transfected with 3 copies of an NF-B
binding site. We also show that incubation with
8-iso-PGF2 (10 µmol/L) augments cellular
uptake of 125I-TC ox-LDL in addition to
enhancing the lipid staining of JAR cells incubated with
ox-LDL.
The plasma level of 8-iso-PGF2 is
elevated in pregnant compared with nonpregnant
women,31 but even the
elevated plasma level found in preeclampsia is usually much lower than
used in our study.22 On the
other hand, the local level in gestational decidual tissue is likely to
be much higher than plasma levels as a result of areas of oxidative
stress and successively atherosclerosis-like foam cell
lesions in preeclampsia. Analogously, very high tissue levels of
8-iso-PGF2 in atherosclerotic arteries
compared with control vessels and plasma levels have been demonstrated
previously.32 Therefore, the
high concentrations of 8-iso-PGF2 used in our
study could be considered physiological for
purposes of studying the local effects on trophoblastic cells in
preeclamptic decidua. In a manner analogous to
8-iso-PGF2, lysophosphatidylcholine (lysoPC)
is accumulated at high concentrations in atherosclerotic plaques,
whereas the concentration in plasma is
low.33 LysoPC constitutes
40% of the total lipids of
ox-LDL,34 whereas the
measured amount of ox-LDL is negligible in
plasma.35
8-iso-PGF2 is associated with the LDL
particle in plasma. In addition, 8-iso-PGF2
is generated during oxidation of
LDL.36 The high amounts of
8-iso-PGF2 and lysoPC in atherosclerotic
plaques could stem from local oxidation of LDL.
To further study the specific involvement of LOX-1 in the
uptake of 125I-TC ox-LDL in JAR cells, we
used an antibody against the ligand-binding domain of LOX-1 receptor
(JTX-92).28 After 6 hours of
preincubation in the presence or absence of 10 µmol/L
8-iso-PGF2, we performed an uptake study as
described in "Methods" above. After 6 hours of incubation at 37°C
with or without 8 µg/mL of the blocking antibody, JAR cells were
harvested and the degraded radiolabeled material was determined after
TCA precipitation as reported
elsewhere.37 We showed that
the level of degraded 125I-TC ox-LDL was
25% higher in JAR cells grown with 10 µmol/L
8-iso-PGF2 versus control cells
(P=0.02). These results are
comparable to the augmented uptake demonstrated in
Figure 1. When 8 µg/mL of the blocking antibody was added
to the JAR cells incubated with 10 µmol/L
8-iso-PGF2, a 46% reduction occurred in the
level of degraded 125I-TC ox-LDL compared
with JAR cells grown in 10 µmol/L
8-iso-PGF2 without antibody
(P=0.034; n=3). These data
suggest that 40% to 50% of the cellular uptake of ox-LDL in the JAR
cells could be LOX-1–mediated. This is in line with results of other
groups that have reported that LOX-1 contributes to 50% to 70% of
ox-LDL uptake in endothelial
cells.34
NF-B is a red-ox sensitive transcription
factor,38 and
8-iso-PGF2 represents a marker of
oxidative stress. We showed that 8-iso-PGF2
produced dose-dependent activation of the reporter gene luciferase in
the NF-B–transfected JAR cells
(Figure 3). We thereby demonstrated in the JAR cells a link
between the oxidative stress marker
8-iso-PGF2 and the red-ox–regulated system
of NF-B. The presence of an NF-B site on the LOX-1
promoter39 may suggest that
8-iso-PGF2 could regulate the LOX-1 gene
through this site in JAR cells and explains the upregulation of LOX-1
mRNA
(Table)
and protein (50 kDa)
(Figure 2, bottom) in trophoblastic JAR cells and augmented
ligand binding
(Figure 2, top) and elevated uptake of modified LDL
(Figure 1) demonstrated in the present article.
Interestingly, recent research has demonstrated that ox-LDL binding to
LOX-1 in endothelial cells induces activation of
NF-B through increased production of intracellular reactive
oxygen species.40 Also, Li
and Mehta41 show upregulation
of LOX-1 by its ligand ox-LDL and indicate that NF-B activation
plays an important role in this process.
In plasma, 8-iso-PGF2 is
associated with the LDL particle, and
8-iso-PGF2 is found to be generated during
oxidation of LDL.36
Interestingly, increased levels of autoantibodies against ox-LDL
epitopes are found in preeclamptic women versus those in normal
pregnancies, which suggests an increased oxidative
condition.17 Moreover, in
preeclampsia, the level of plasma lipid peroxides is elevated and
antioxidant capacity is reduced versus in uneventful
pregnancies.42 In addition to
the lipid peroxide species generated by ox-LDL,
8-iso-PGF2 may be involved in the
transcription activation of NF-B described in
endothelial cells and
macrophages.43 44
Recently, ox-LDL was found to increase LOX-1 expression both in bovine
aortic
endothelial28
and in human coronary artery
endothelial41
cells. Li et al45
demonstrated that angiotensin (Ang) II upregulates LOX-1
receptor and ox-LDL uptake in human coronary artery
endothelial cells (HCAECs) and that Ang II enhances
ox-LDL–mediated injury to these cells, which suggests a plausible link
between atherogenesis and
hypertension.9 Interestingly,
a study recently has found a connection between free
8-iso-PGF2 plasma levels and low-dose Ang II
infusion.46 In preeclampsia,
heightened pressor sensitivity to infused Ang II occurs, although
plasma Ang II concentrations are reduced; the mechanisms for this are
unknown.47
LOX-1 mRNA has been demonstrated in highly vascularized organs such as the placenta, lung, kidney, and vasculatures.1 48 Expression is low in the brain, heart, adrenals, and other organs, and LOX-1 has been suggested to be expressed specifically in endothelial cells and macrophages and to play an important role in atherosclerotic lesion formation.39 The present study demonstrates that LOX-1 is also expressed in trophoblastic cells; as far as we know, the present article represents the first demonstration of accumulation of neutral lipids (such as cholesterol and cholesteryl esters) in trophoblastic cells (Figure 4). Recent research has demonstrated that smooth muscle cells in vitro can gain a macrophage-like phenotype by expressing the scavenger receptor CD36, and thus possibly could present an origin of foam cells other than monocytes.49 Our findings supports the notion that cells other than macrophages can be converted to foam cells. We speculate that this augmented LOX-1 expression could contribute to the formation of foam cells in the spiral arterial wall in preeclampsia (acute atherosis).
The biological function of upregulation of LOX-1
receptor in JAR trophoblastic cells and possibly trophoblasts in
gestational tissues in response to 8-iso-PGF2
remains to be seen. LOX-1 has been proposed to be involved in
atherosclerosis through the actions of ox-LDL on the
endothelium,39
such as induction of adhesion
molecules50 and growth
factors.51 Moreover, LOX-1
recently has been demonstrated to work as an adhesion molecule for
platelets, and could therefore initiate and promote
atherosclerosis by binding both ox-LDL and
platelets.52 One
hypothesis is that more-adhesive trophoblasts could be less prone to
invade the maternal spiral arteries, which could result in less
remodeling of the spiral arteries, with the more narrow, tortuous, and
thick-walled arteries that are seen in preeclampsia. This would fit
with our previously published data that showed that
8-iso-PGF2 reduces invasion of JAR cells,
possibly by reducing the activity of matrix metalloproteinase-2 and
matrix
metalloproteinase-9.53
We chose the choriocarcinoma cell line JAR for the present study because it provides a large number of uniform cells and shares many of the characteristics of early placental trophoblasts.53 On the other hand, this malignant cell line also differs from normal trophoblast cells in the regulation of, for example, cell invasion. In vivo, interaction with, for example, maternal host cells, is complicated; therefore, one cannot directly extrapolate from the present in vitro study.
In conclusion, 8-iso-PGF2 induces
expression of LOX-1 at the mRNA and protein levels in addition to
functional capacity of the receptor in JAR cells. This establishes a
link between a marker of oxidative stress and a receptor for ox-LDL. We
speculate a potential role of LOX-1 in preeclampsia, both in formation
of the foam cells in the spiral arterial walls (acute
atherosis) and in reduced trophoblast
invasion.
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Acknowledgments |
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The Throne-Holst Foundation, The Norwegian Cancer Society, and the Norwegian Research Council supported this work. The technical assistance of Vivi Volden, Institute for Nutrition Research, Faculty of Medicine, University of Oslo, Norway, is greatly appreciated.
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Footnotes |
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Drs Halvorsen and Staff contributed equally to this article.
Received June 15, 2000; first decision August 2, 2000; accepted September 29, 2000.
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References |
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