(Circulation. 2000;101:2030.)
© 2000 American Heart Association, Inc.
Brief Rapid Communications |
From the Departments of Medicine and Clinical Science (N.S., H.I., J.Y., K.D., T.-H.C., M.I., K.M., T.S., Y.F., S.S., H.A., K.N.) and Cardiovascular Surgery (K.U., N.O., M.K.), Kyoto University Graduate School of Medicine, Kyoto, Japan.
Correspondence to Hiroshi Itoh, Department of Medicine and Clinical Science, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507 Japan. E-mail hiito{at}kuhp.kyoto-u.ac.jp
| Abstract |
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Methods and ResultsY-27632, a specific ROCK inhibitor, and the overexpression of dominant-negative ROCK suppressed the mitogen-induced DNA synthesis of cultured vascular smooth muscle cells (VSMCs), which indicates the essential role of ROCK in the control of VSMC proliferation in vitro. Y-27632 also suppressed the chemotaxis of VSMCs. Male Wistar rats were systemically given Y-27632 (35 to 70 mg · kg-1 · day-1) through an intraperitoneal infusion. The neointimal formation of balloon-injured carotid arteries was significantly suppressed in Y-27632treated rats (intima/media ratio, 0.22±0.02) compared with vehicle-treated rats (intima/media ratio, 0.92±0.21) or hydralazine-treated rats with a similar blood pressure decrease (intima/media ratio, 1.03±0.15). The phosphorylation of myosin phosphatase and myosin light chain was elevated in injured arteries in a Y-27632sensitive manner, indicating the augmentation of ROCK activity in neointimal formation. The downregulation of the cyclin-dependent kinase inhibitor p27kip1 in injured vessels was reversed by Y-27632 treatment, reflecting the antiproliferative effect of ROCK inhibition in vivo.
ConclusionsWe conclude that ROCK plays a key role in the process of neointimal formation after balloon injury. Thus, the inhibition of ROCK may be a potential therapeutic strategy for treating vascular proliferative disorders and hypertension.
Key Words: atherosclerosis muscle, smooth remodeling signal transduction hypertension
| Introduction |
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We and others have reported that regulators of vascular tone, such as angiotensin II or natriuretic peptides, are also involved in vascular growth.4 Thus, we postulated that intracellular mechanism(s) should exist that govern both vascular contraction and growth. Using Y-27632 and dominant-negative ROCK, the present study demonstrates that ROCK, the key regulator of vascular contraction, also controls vascular growth in vitro and in vivo.
| Methods |
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DNA Synthesis and Cell Migration Assay
3H-thymidine uptake and modified Boyden
chamber analyses for human aortic smooth muscle cells (AOSMCs;
Clonetics) were performed as described previously.4 6
Then, 24 hours after transfection using lipofectamine PLUS (Gibco-BRL),
cells were stimulated with 5% FCS, 50 ng/mL platelet-derived growth
factor-BB (PDGF-BB), or 50 µmol/L lysophosphatidic acid
(LPA) for 16 hours. They were then pulsed with 30 µmol/L
5-bromodeoxyuridine (BrdU). Immunostaining for BrdU and
myc-tag epitope were superimposed using a confocal laser
scanning microscope.
Animal Experiments
Animals were cared for according to the Guide for the Care
and Use of Laboratory Animals by the National Academy of Sciences
(NIH Publication No. 8523; revised 1985). Male Wistar rats (14 to 16
weeks old) were used in the study. ALZET osmotic pumps (2 ML4, Alza)
were filled with vehicle (phosphate-buffer, n=6), hydralazine
(2 mg · kg-1 ·
day-1, n=5) or Y-27632 (35 mg ·
kg-1 · day-1, n=4;
70 mg · kg-1 ·
day-1, n=4) and implanted
intraperitoneally. Three days later, a balloon
injury to the right carotid artery was made.7 On days
7 and 14 after the injury, rats were killed for
morphometric7 and
immunoblotting5 analyses,
respectively.
Statistical Analysis
The data were expressed as means±SEM. Statistical differences
were determined by ANOVA. P<0.05 was considered
significant.
| Results |
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Suppression of Neointimal Formation by Y-27632
Continuous systemic delivery of Y-27632 at doses of 35 and 70
mg · kg-1 ·
day-1 resulted in a decrease of SBP by 20 to
30 mm Hg compared with control rats throughout the observation
period. A comparable SBP decrease was also achieved by
hydralazine treatment. The steady-state level of Y-27632 in
carotid arteries was 5 to 6 times higher than the plasma level (for 35
mg · kg-1 ·
day-1, plasma: 1.25±0.21 µmol/L, tissue:
7.15±1.40 µmol/kg; for 70 mg ·
kg-1 · day-1,
plasma: 3.65±0.29 µmol/L, tissue: 20.18±2.68 µmol/kg).
Thus, the vascular Y-27632 level achieved in the present study
seems optimal for effective and specific ROCK inhibition, as inferred
from the in vitro data above and previous reports.3 6 8
Y-27632 administration resulted in neither abnormal laboratory data nor
systemic adverse effects, such as body weight loss or diarrhea.
Y-27632 treatment dramatically reduced neointima
formation 14 days after balloon injury in a dose-dependent manner
(Figure 2
and
Table
). With the higher dose, the
blockade was profound (76% decrease in intima/media ratio).
Hydralazine treatment did not prevent neointima
formation, which suggests that the effect of Y-27632 was not exerted
via the lowering of SBP. Considering the optimal tissue level achieved
in this study, Y-27632 is thought to have effects locally. However, the
involvement of other systemic effects remains to be determined.
A significantly smaller number of VSMCs were found in Y-27632treated
vessel sections than in sections treated with vehicle (740±21 versus
1337±54 nuclei/section for 70 mg ·
kg-1 · day-1
Y-27632 versus vehicle), indicating that the inhibition of VSMC
proliferation should contribute, at least in part, to the effect of
Y-27632. Fasudil, another inhibitor of protein kinases
including ROCK,9 suppresses VSMC migration in
vivo.10 Considering its in vitro suppression of VSMC
migration and proliferation, Y-27632 likely suppressed
neointima formation through the inhibition of both the
migration and proliferation of VSMCs in vivo.
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The luminal narrowing of the injured vessels was also prevented by the
administration of Y-27632. The areas surrounded by internal and
external elastic laminae were enlarged by Y-27632 treatment when
compared with vehicle (Table
).
Activation of ROCK in Balloon-Injured Arteries and its Reversal
by Y-27632
ROCK inactivates myosin phosphatase through the
specific phosphorylation of myosin phosphatase target
subunit 1 (MYPT1) at Thr695,2
which results in an increase in the
phosphorylated content of the 20-kDa myosin light chain
(MLC20).5 As shown in Figure 2f
, balloon injury
increased the phosphorylation of both MYPT1 (at
Thr695) and MLC20; this increase was almost
reversed by Y-27632 treatment. MLC20 is also
phosphorylated by MLCK.2 Y-27632 has
a much higher inhibition constant (>250 µmol/L) for MLCK
than for ROCK (0.14 µmol/L).3 This, together with
the specific phosphorylation of MYPT1 at
Thr695 by ROCK,2 leads us to
conclude that ROCK is activated in neointimal
hyperplasia after balloon injury. Thus, it seems quite plausible that
Y-27632 suppressed neointima formation by specifically
inhibiting the augmented ROCK activity of VSMCs.
Reversal of Injury-Induced Decrease of p27kip1 by
Y-27632
Cyclin-dependent kinase inhibitors have been
implicated in cell cycle regulation. Rho promotes cell proliferation
through the titration of p27kip1.11
In addition, the downregulation of p27kip1
correlates well with VSMC proliferation in balloon-injured arteries;
however, the involvement of p21cip1, another
cyclin-dependent kinase inhibitor, is
controversial.7 As shown in Figure 2f
, balloon
injury decreased the level of p27kip1 after 7
days, reflecting VSMC proliferation. p21cip1 was
only faintly detectable in both noninjured and injured arteries.
Y-27632 treatment almost reversed this decrease in levels of
p27kip1, which suggests that the compound exerted
its suppressive effect on neointimal formation via its
antiproliferative action. Similar results were also obtained with
cultured AOSMCs (data not shown).
| Discussion |
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| Acknowledgments |
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Received January 7, 2000; revision received March 8, 2000; accepted March 8, 2000.
| References |
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