Reduced Growth Factor Responses in Vascular Smooth
Muscle Cells Derived from
12/15-Lipoxygenase–Deficient Mice
Marpadga A. Reddy, Young-Sook Kim, Linda Lanting, Rama Natarajan
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Abstract—Biochemical and genetic evidence support the involvement of leukocyte-type 12/15-lipoxygenase enzyme and
its products in the atherogenic process. We recently showed that products of the 12/15-lipoxygenase pathway play an
important role in mediating hypertrophy, matrix protein production, and inflammatory gene expression in vascular
smooth muscle cells (VSMC) through activation of mitogen activated protein kinases and key transcription factors. The
current study is aimed at establishing the in vivo role of 12/15-lipoxygenase in VSMC by comparing growth
factor–induced responses in VSMC derived from 12/15-lipoxygenase knockout mice versus genetic control wild-type
mice. In the lipoxygenase knockout cells, 12/15-lipoxygenase protein was not expressed, and levels of its product,
12(S)-hydroxyeicosatetraenoic acid, were reduced (51% of wild type). Knockout cells exhibited significantly lower rates
of growth factor–induced migration, fibronectin production, and incorporation of 3H-thymidine and 3H-leucine (54%,
55%, 61%, and 57% of wild type, respectively). Growth factor–induced superoxide production and p38 mitogen–activated protein kinase activation were also reduced in knockout cells. Serum-stimulated AP-1 transcription factor
activation was markedly reduced (50% of wild type), whereas cAMP response element binding protein activation was
abrogated in knockout cells. Furthermore, growth factor–induced mRNA expression of immediate early genes and
fibronectin were also greatly reduced. These results suggest that the modulation of specific signaling pathways and
growth-responsive genes may be responsible for the altered growth factor responses in the lipoxygenase knockout cells.
They also demonstrate the important in vivo role of vascular 12/15-lipoxygenase in VSMC growth, migration, and
matrix responses associated with hypertension, atherosclerosis, and restenosis. (Hypertension. 2003;41:1294-1300.)
Key Words: lipoxygenase 䡲 muscle, smooth, vascular 䡲 signal transduction 䡲 angiotensin II
䡲 platelet-derived growth factor 䡲 gene regulation
T
he lipoxygenase (LO) pathway has been implicated in the
pathogenesis of atherogenesis and hypertension.1,2 LOs
metabolize arachidonic acid to oxidized lipids and are classified as 5-, 8-, 12-, and 15-LOs, based on the ability to insert
molecular oxygen at the corresponding carbon atom of
arachidonic acid. Three major functionally distinct isoforms
of 12-LO, namely, platelet-type, leukocyte-type, and
epidermal-type 12-LO, have been cloned.3–5 Human and
rabbit 15-LOs as well as the leukocyte-type 12-LO have high
homology and are classified as 12/15-LOs because they can
form both 12(S)-hydroxyeicosatetraenoic acid [12(S)HETE)] and 15(S)-HETE from arachidonic acid via their
peroxy precursors, and mainly 13(S)-hydroperoxyoctadecadienoic acid from linoleic acid.3–5 Leukocyte-type
12-LO has a wide tissue distribution, including vascular
smooth muscle cells (VSMC).6,7 In mice, both leukocyte
12/15-LO and platelet 12-LO are expressed.8
Studies indicate that LO inhibition reduced blood pressure
in renovascular hypertensive rats.9 Furthermore, 12(S)-HETE
levels were elevated in spontaneously hypertensive rats compared with age-matched Wistar-Kyoto rats, and 12(S)-HETE
directly regulated calcium signals in VSMC.10,11 Several lines
of evidence implicate 12/15-LO in the development of
atherosclerosis. 12/15-LO can mediate the oxidation of
LDL,12 and the enzyme and its products have been detected in
atherosclerotic lesions.13,14 Convincing evidence comes from
recent data showing that disruption of 12/15-LO in apoE⫺/⫺ or
LDL-R⫺/⫺ mice significantly reduced atherosclerosis in these
mice models.15,16
Additionally, growth factors (GFs) such as angiotensin II
(Ang II) and platelet-derived growth factor (PDGF) and
cytokines such as IL-1, IL-4, and IL-8 could induce 12/15-LO
activity and expression in VSMC.7,17–19 Furthermore, the
12-LO product 12(S)-HETE could induce VSMC migration
and extracellular matrix production.20,21 Ang II–induced hypertrophy as well as PDGF-induced chemotactic effects were
significantly blocked by pharmacological LO inhibitors and a
molecular inhibitor, 12-LO ribozyme.17,21–23 Expression of
Received January 30, 2003; first decision February 28, 2003; revision accepted March 1, 2003.
From the Department of Diabetes, Beckman Research Institute of the City of Hope, Duarte, Calif.
Correspondence to Rama Natarajan, PhD, Department of Diabetes, Beckman Research Institute of the City of Hope, 1500 East Duarte Road, Duarte,
CA 91010. E-mail [email protected]
© 2003 American Heart Association, Inc.
Hypertension is available at http://www.hypertensionaha.org
DOI: 10.1161/01.HYP.0000069011.18333.08
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12/15-LO was also increased in balloon-injured arteries,
whereas 12-LO ribozymes and pharmacological inhibitors
reduced the extent of neointimal thickening in these injured
rat carotid arteries.22,24 Recently, we showed that 12-LO
products directly stimulated VSMC hypertrophy, activation
of p38 mitogen–activated protein kinase (p38 MAPK), transcription factors NF-kappa B (NF-␬B), and cAMP response
element binding protein (CREB) and induced transcription
from the fibronectin and VCAM-1 promoters.25,26 Furthermore, stable 12/15-LO overexpression in VSMC increased
MAPK activity and induced hypertrophy.25 Thus, 12/15-LO
activation in VSMC may play a key role in vascular growth
and injury responses. The aim of the current study was to
determine the in vivo pathologic role of 12/15-LO in VSMC
by comparing basal and GF-mediated responses of VSMC
derived from 12/15-LO knockout mice (LOKO)27 with those
isolated from genetic control (WT) mice. Our new results
indicate that cellular growth, matrix production, and migration are greatly attenuated in VSMC from the LOKO mice
relative to WT mice.
Methods
All animal experiments were conducted in accordance with National
Institutes of Health guidelines with an approved protocol from the
Research Animal Care Committee of the City of Hope.
VSMC From 12/15-Lipoxygenase Knockout Mice
1295
Figure 1. MVSMC from LOKO mice have reduced 12/15-LO
and 12(S)-HETE levels. A, Immunoblotting of whole-cell lysates
from WT- and LOKO-derived MVSMC and porcine VSMC (PV)
with 12/15-LO–specific antibody. B, Basal 12(S)-HETE levels in
MVSMC culture supernatants by RIA. Data represent
mean⫾SEM of 3 independent experiments (*P⬍0.001).
detected by a confocal microscope. Cells were also stained with
Hoechst dye (Molecular Probes) to detect nuclei.
Immunoblotting and Gel Shift Assays
These were performed as described previously.25
Isolation and Culture of MVSMC
RNA Isolation and RT-PCR
Control (WT, C57BL/6) and leukocyte 12/15-LO knockout mice
(LOKO) on a C57BL/6 background (strain name: B6.129S2Alox15tm1Fun; stock No: 002778) were obtained from Jackson
Laboratories. VSMC from aortas of 7- to 9-week-old mice were
isolated by enzymatic digestion as described earlier.28 These primary
cultures of mouse VSMC (MVSMC) were cultured in Dulbecco’s
modified Eagle’s medium containing 10% FCS, glutamine (2 mmol/
L), streptomycin (100 ␮g/mL), penicillin (100 U/mL), and amphotericin B (25 ␮g/mL) as fungizone. The SMC identity of the cells
was confirmed by staining with SMC-specific ␣-actin monoclonal
antibody (clone 1A4, Sigma Chemicals Inc). In all experiments,
MVSMC (passages 4 to 8) were serum-depleted for 48 hours in
medium containing 0.2% BSA and treated with GFs for the indicated
time intervals.
After stimulation with agonists, total RNA was extracted, and
gene-specific relative multiplex RT-PCRs, with 18S RNA used as
internal control, were performed as described earlier.31 After normalization to 18S RNA, results were expressed as fold expression
over unstimulated cells. Mouse fibronectin mRNA was amplified
using primers 5⬘-GCACAACAGACCACCAAACTCG-3⬘ (forward)
and 5⬘-CTGAAGTCACTTCTCGGGGTGC-3⬘ (reverse). Primers
for c-fos, c-jun, and 18S RNA were from Ambion Inc.
12(S)-HETE Assay
Migration Assay
VSMC migration assay was performed with the use of a modified
48-well Boyden’s microchemotaxis chamber as described earlier.17
Briefly, VSMC were placed in the upper chamber and PDGF (0.1
nmol/L) in the lower chamber. The number of cells migrated to the
lower side of filter were counted after 4-hour incubation.
MVSMC were serum-depleted for 48 hours and basal 12(S)-HETE
levels (without any added arachidonic acid) in the cell supernatants
were quantified with the use of a specific radioimmunoassay (RIA)
as described earlier.7,29 This RIA is specific for 12(S)-HETE and
does not cross-react with 12(R)-HETE.
[3H]-Leucine and [3H]-thymidine incorporation were determined
as described earlier.18,21
Data Analyses
Fibronectin Assay
Characterization of MVSMC From WT and
LOKO Mice
Cells were serum-starved for 48 hours, replaced with fresh serumfree medium, and incubated for another 24 hours. The supernatant
conditioned medium was then assayed for fibronectin by a specific
sandwich ELISA as described earlier.21
Intracellular Superoxide Production
Intracellular superoxide production was evaluated with the use of a
superoxide probe dihydroethidium (Molecular Probes Inc) as described.30 MVSMC cultured on chamber slides were treated with
PBS or the indicated GFs for 30 minutes, washed, and incubated with
dihydroethidium (10 ␮mol/L) for 15 minutes. Cells were then
washed to remove extracellular dye, and the red fluorescence in cells,
which is an indicator of intracellular superoxide production, was
Data are expressed as mean⫾SEM of multiple experiments. Paired
Student t tests were used to compare 2 groups, or ANOVA with the
Dunnett posttest for multiple groups using Prism software (Graph
Pad). Statistical significance was detected at the 0.05 level.
Results
To examine the in vivo role of 12/15-LO signaling in VSMC
and in GF responses, MVSMC were isolated from WT or
LOKO mice. Both WT and LOKO cells stained positive with
SMC-specific ␣-actin and did not show significant differences in morphology. Immunoblotting of whole-cell lysates
with 12/15-LO–specific antibody17 showed that in contrast to
WT cells, LOKO cells did not have a 72-kDa protein (Figure
1A). Lysates from porcine VSMC, which we have shown to
express leukocyte-type 12-LO,7 was included for comparison
(lane PV). Furthermore, basal levels of 12(S)-HETE (Figure
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were stimulated with FBS (10%) or Ang II (0.1 ␮mol/L) or
PDGF-BB (0.1 nmol/L) for 30 minutes. Intracellular superoxide production was then monitored by red fluorescence
resulting from oxidation of intracellular probe DHE. As seen
in Figure 3, on stimulation with GFs (FBS, Ang II, or PDGF),
WT cells produced markedly greater amounts of superoxide
compared with LOKO cells. Thus, reduced superoxide production may be one of the mechanisms by which GF-induced
responses are inhibited in 12-LOKO cells.
Reduced Activation of p38 MAPK in
LOKO MVSMC
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Figure 2. Protein and DNA syntheses are reduced in LOKO
cells. MVSMC were incubated with either 3H-Leucine (A) or
3
H-Thymidine (B) for 4 hours. Data represent mean⫾SEM of at
least 3 experiments (*P⬍0.001).
1B), an arachidonic acid metabolite of 12/15-LO, were
significantly lower in MVSMC from LOKO mice (65⫾7
pg/106 cells in WT versus 33.5⫾4 pg/106 cells in LOKO
cells).
Protein and DNA Syntheses Are Decreased in
MVSMC From LOKO Mice
Next, we examined the effect of 12/15-LO deficiency on
cellular growth–promoting effects by incubating MVSMC in
the presence of 3H-Leucine or 3H-thymidine to determine the
rates of protein and DNA syntheses, respectively. As shown
in Figure 2, rates of both 3H-Leucine (A) or 3H–thymidine (B)
incorporation were significantly reduced in LOKO cells
compared with WT cells (61% and 57% of WT, respectively,
P⬍0.01). These results suggest that LO activation plays an
important role in MVSMC hypertrophy and growth.
GF-Stimulated Superoxide Production Is Reduced
in MVSMC Derived From LOKO Mice
Since oxidant stress is essential for GF signaling and LO
activation has been associated with increased oxidant
stress,32,33 we next compared superoxide production in WT
versus LOKO cells. Quiescent MVSMC from WT and LOKO
Earlier studies from our laboratory demonstrated that p38
MAPK plays a key role in hypertrophy as well as inflammatory gene induction by 12-LO products.25,26 Furthermore, p38
MAPK activity was augmented in rat VSMC and cardiac
fibroblasts overexpressing 12-LO cells.25,34 Hence, we hypothesized that p38 MAPK activation may be reciprocally
attenuated in LOKO VSMC. MVSMC were stimulated with
serum (10% FBS) and cell lysates immunoblotted with
phosphospecific-p38 MAPK antibody. Results showed that
serum-activated p-p38 MAPK was attenuated in LOKO cells
compared with WT cells (Figure 4A, top panel, and Figure
4B). Levels of total p38 MAPK were unchanged (Figure 4A,
middle panel). In contrast, serum-stimulated p44/42 MAPK
activation was similar in the 2 cell types (Figure 4A, lower
panel). Reduced p38 MAPK activation associated with 12/
15-LO deficiency is consistent with our previous in vitro
observations.
Comparison of AP1 and CREB DNA
Binding Activities
Since serum-induced MAPK activation was reduced in
MVSMC, we evaluated whether the activation of key downstream MAPK target transcription factors such as AP1 and
CREB are altered. AP1 and CREB are induced by GFs
and induce expression of genes required for cell growth and
matrix protein production.35,36 Nuclear extracts prepared from
FBS-stimulated (10%) MVSMC were analyzed by gel shift
assays, using 32P-labeled oligonucleotides containing consensus DNA-binding sequences for AP1, CREB, and a constitutively active transcription factor SP1. Results in Figure 5A
show that both basal (3851 versus 11 960 cpm phosphorim-
Figure 3. Growth factor–stimulated
superoxide production is reduced in
LOKO MVSMC. MVSMC were either left
untreated (control) or stimulated with
indicated GFs for 30 minutes and superoxide levels were determined by using
dihydroethidium. Ang II, 0.1 ␮mol/L;
FBS, 10%; and PDGF, 0.1 nmol/L.
Reddy et al
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Figure 4. Serum-induced p38 MAPK activation is decreased in
MVSMC. A, MVSMC were stimulated with FBS (10%) for 5 to
30 minutes and whole-cell lysates immunoblotted with indicated
antibodies. B, Density of p38 MAPK bands was determined with
Quantity One software; results are shown as fold stimulation
over respective control cells. Data represent mean⫾SEM of 3 to
7 experiments (*P⬍0.02, **P⬍0.0033).
ager counts) as well as serum-induced (6933 versus 45 020
cpm) AP1 DNA-binding activities were greatly reduced in
LOKO relative to WT cells. Basal CREB DNA binding
(30 506 versus 42 247 cpm) was also reduced, and serum
failed to increase CREB DNA-binding activity in LOKO
cells (31 556 cpm compared with 92 123 in WT cells).
However, SP-1 DNA-binding activity (50 000 to 60 000
cpm/lane) was similar in these nuclear extracts, indicating
equal loading of nuclear proteins and specificity of effects for
AP1 and CREB.
Expression of Immediate Early Response Genes
Activation of MAPK cascade by GF stimulation leads to the
expression of immediate early response (IE) genes such as
c-fos and c-jun, which are involved in cellular growth,
migration, and differentiation. We therefore compared their
expression in the 2 cell types. MVSMC were stimulated with
FBS (10%) for 15 minutes to 4 hours, and c-fos and c-jun
mRNA expression was determined by relative RT-PCR.
Results showed that the expression of c-fos (Figure 5B) and
c-jun (Figure 5C) mRNAs were stimulated by serum in both
WT and LOKO cells with similar time course, that is, peak at
30 minutes and returning to basal after 2 hours. However, the
fold induction of both genes was greatly reduced in LOKO
compared with WT. Thus, reduced expression of IE genes
may be one of the mechanisms by which LO-deficient cells
exhibit reduced rates of migration and hypertrophy.
Reduced Fibronectin Expression in LOKO Cells
GFs induce the transcription of the key extracellular matrix
(ECM) protein fibronectin through activation of CREB. Hence,
we compared fibronectin mRNA expression by relative RT-PCR
Figure 5. Serum-stimulated transcription factor activation and
immediate early response gene expression are lower in LOKOderived VSMC. A, Gel shift assays of nuclear extracts from serumstimulated (10% FBS for 2 hours) MVSMC with 32P-labeled oligonucleotides containing consensus DNA-binding sequences for
AP1, CREB, or SP1 transcription factors. P indicates probe alone;
C, control. Similar data were obtained with cells from at least 3
separate experiments. B and C, IE gene expression. Serum stimulated c-fos (B) and c-jun (C) expression were determined by
RT-PCR with mouse gene–specific primers and 18S RNA primers.
Ratios of specific gene/18S RNA were expressed as fold stimulation over control at each time period (*P⬍0.03, **P⬍0.01, n⫽3).
Data in C are representative of 2 similar experiments.
after stimulation with Ang II (0.1 ␮mol/L) for 4 hours. Basal
levels were attenuated and Ang II–induced fibronectin mRNA
levels were greatly reduced in LOKO cells relative to WT
(Figures 6A and 6B). In addition, Figure 6C shows that basal
fibronectin protein levels (measured by ELISA in culture supernates) were significantly lower in LOKO compared with WT
cells (55% of WT, P⬍0.001). Thus, 12-LO may play an
important role in GF-induced matrix production in VSMC.
GF-Induced Migration Is Reduced in
LO-Deficient MVSMC
Using pharmacological inhibitors and 12-LO–specific ribozymes, we previously demonstrated that LO plays an
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Figure 6. Fibronectin expression is reduced in LOKO cells. A,
RT-PCR reaction was performed with primers for mouse
fibronectin and 18S RNA using RNA extracted from control (C)
MVSMC or from MVSMC stimulated with Ang II (0.1 ␮mol/L) for
4 hours. B, FN to 18S RNA ratios expressed as fold stimulation
by Ang II over corresponding controls (*P⬍0.05, n ⫽3). C,
Fibronectin levels in supernatants of WT or LOKO cultures (16
to 24 hours serum-depleted) were determined by ELISA
(*P⬍0.001, n⫽3).
important role in GF-induced migration in VSMC. To further
determine the in vivo functional significance of 12/15-LO in
VSMC migration, we compared rates of PDGF-induced
migration in MVSMC from LOKO mice versus WT mice.
Figure 7 shows that PDGF-induced migration was significantly attenuated in LOKO compared with WT cells (54% of
WT, P⬍0.001). These results clearly demonstrate an important role for the 12/15-LO pathway in GF-induced migration.
Discussion
In this study, we examined the functional role of mouse
12/15-LO expression in VSMC by evaluating basal and
GF-stimulated oxidant stress, growth, migration, MAPK
activation, and IE gene and fibronectin expression in
MVSMC derived from WT versus LOKO mice. The rationale
partly stems from earlier observations that 12-LO activity and
expression were increased in porcine VSMC in response to
Figure 7. PDGF-stimulated migration is attenuated in VSMC
from LOKO mice. PDGF-stimulated (0.1 nmol/L) migration. Data
represent mean⫾SEM of 5 experiments (*P⬍0.0001 vs PDGFinduced migration in WT cells).
GFs and cytokines.7,17–19 Furthermore, the 12-LO pathway
was demonstrated to mediate Ang II–induced hypertrophic
responses and PDGF-induced chemotactic responses in
PVSMC.17,21 Additionally, 12-LO products such as 12(S)HETE could directly induce VSMC hypertrophy and fibronectin expression in VSMC through activation of p38
MAPK and CREB activation.25
MVSMC from LOKO mice showed absence of the
leukocyte-type 12/15-LO protein and reduced levels of 12(S)HETE. Funk and coworkers8 showed that mice express both
platelet 12-LO and leukocyte-type 12/15-LO. Since LOKO
mice in which leukocyte 12/15-LO was disrupted still express
platelet 12-LO,27 this could be responsible for the residual
12(S)-HETE seen in the LOKO VSMC. There is no specific
report of a platelet-type 12-LO in murine VSMC. However,
since mice express both types of 12-LO8,27 and there is one
report of a novel platelet 12-LO in human VSMC,37 it is
possible that murine VSMC express both isoforms or another
novel as yet unidentified 12-LO isoform. Both platelet and
vascular 12(S)-HETE have been implicated in hypertension,9 –11,38 – 40 whereas macrophage and VSMC 12/15-LO
have been implicated in atherosclerosis.7,13–16,41 Activation of
LO is associated with oxidant stress and superoxide production.12,32,33 Our present observations of decreased GF-induced
superoxide production in the LOKO cells are consistent with
the pro-oxidative role of LO. We also observed reduced rates
of 3H-thymidine and 3H-leucine incorporation in the MVSMC
from LOKO mice relative to WT.
12/15-LO products such as 12(S)-HETE and 13(S)HPODE have been shown to induce cellular effects through
activation of MAPKs such as ERK1/2 and p38 in
VSMC.25,26,42 We observed that serum-induced p38 MAPK is
attenuated in the LOKO cells relative to WT. Furthermore,
DNA binding activities of key MAPK target transcription
factors AP-1 and CREB were attenuated in the LOKO
MVSMC. These effects were functionally relevant, since
serum-induced expression of the target immediate early genes
c-fos and c-jun (components of AP-1) were greatly reduced in
LOKO cells. Furthermore, the expression of the key ECM
protein, fibronectin, which is regulated by CREB, was also
significantly reduced in the LOKO cells. Our present observations in vivo are supportive of the recent in vitro data that
12(S)-HETE leads to the transcription of fibronectin via
CREB DNA binding and transactivation of the fibronectin
promoter in PVSMC.25 They are also in agreement with
observations that overexpression of mouse 12/15-LO in
VSMC or fibroblasts leads to increased hypertrophy and p38
MAPK activity.25,34
Evidence suggests that 12(S)-HETE can directly induce
VSMC migration20 and 12-LO can mediate PDGF-induced
chemotactic effects in VSMC.17,22,23 In the current study, we
observed that PDGF-induced migration was significantly
attenuated in the LOKO cells relative to WT, thus providing
in vivo relevance to the in vitro observations.
Animal models have now demonstrated the key role of the
LO pathway in the development of hypertension, restenosis,
and atherosclerosis.1,9,15,16,22,24 Pharmacological 12/15-LO inhibitors as well as a rat 12/15-LO ribozyme could significantly reduce neointimal thickening in injured rat arteries.22,24
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A 15-LO inhibitor could block diet-induced atherosclerosis in
rabbits.43 Increased 12/15-LO expression has been reported in a
swine model of atherosclerosis.41 Recent observations that crossbreeding LOKO mice with the apoE⫺/⫺ or LDL-R⫺/⫺ mice could
greatly reduce atherosclerosis development in the latter 2 mice
models provide the first clear demonstration of the significant
role played by leukocyte 12/15-LO in atherosclerosis.15,16 In
these in vivo models, the decrease in atherosclerosis was
attributed to reduced LDL oxidation caused by the absence of
macrophage 12/15-LO.15,16 Very recently, a novel observation
was made that the macrophages from 12/15-LO– deficient mice
had a selective defect in LPS-induced interleukin-12 synthesis.44
Our present observations of reduced growth and matrix responses in VSMC from LOKO mice suggest that these could be
additional mechanisms for the atheroprotective role conferred by
ablation of 12/15-LO. Since LO activation can lead to the
consumption of nitric oxide,45 this could be another key route by
which vascular LO mediates the pathogenesis of atherosclerosis
and hypertension. Patricia et al46 showed that 12(S)-HETE
treatment of endothelial cells could lead to increased monocyte
binding and that the 12/15-LO ribozyme blocked high glucoseinduced binding of monocytes to endothelial cells.23 Thus, lack
of 12/15-LO in endothelial cells of the LOKO mice may also
contribute to the atheroprotective effects of these mice. A recent
genetic study suggesting that 5-LO may be an important
proatherogenic gene is interesting,47 and it is not yet clear how it
relates to the data on 12/15-LO. Furthermore, the relevance of
LO to human hypertension and atherosclerosis needs to be
established. Taken together, our studies show for the first time
that vascular 12/15-LO may play an important role in VSMC
growth, migration, oxidant stress, and ECM production under
pathological conditions such as hypertension, restenosis, and
atherosclerosis.
Perspectives
LO enzymes in vascular, inflammatory, renal, and other cells
can form products that have several physiological and pathological effects. These include potent growth-promoting, chemotactic, adhesive, and inflammatory effects, which therefore
implicate them in the pathogenesis of diseases such as
atherosclerosis, hypertension, and diabetic complications.
The in vivo role of LO in these diseases is further supported
by recent data with mouse models of 12/15-LO deficiency,
including our present studies. These data therefore make
12/15-LO an attractive target for drug design. There are
currently no clinically available safe and selective pharmacological inhibitors of the LO enzymes. One approach would
be to use genetic approaches to block the enzyme. The
ribozyme targeted to 12/15-LO has been effective in vitro in
VSMC and endothelial cells and in vivo in animal models of
restenosis. Hence, therapeutic approaches to block this pathway may provide new ways to combat cardiovascular
diseases.
Acknowledgments
These studies were supported by grants from the National Institutes
of Health (PO1-HL55798 and RO1-58191).
VSMC From 12/15-Lipoxygenase Knockout Mice
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Reduced Growth Factor Responses in Vascular Smooth Muscle Cells Derived from
12/15-Lipoxygenase−Deficient Mice
Marpadga A. Reddy, Young-Sook Kim, Linda Lanting and Rama Natarajan
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Hypertension. 2003;41:1294-1300; originally published online April 21, 2003;
doi: 10.1161/01.HYP.0000069011.18333.08
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