(Circulation. 2000;101:2935.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department of Pediatrics (A.S.), Tokyo Teishin Hospital; the Department of Pediatric Cardiology (S.M.-T., M.N.), the Cardiovascular Research Division (K.K.), the Department of Pathology (T.N.), and the Department of Cardiology (Y.S.), Tokyo Womens Medical University; and the Department of Cardiology (T.H.), Obara Cardiovascular Center, Tokyo, Japan.
Correspondence to Atsuko Suzuki, MD, Department of Pediatrics, Tokyo Teishin Hospital, 2-14-23 Fujimi, Chiyoda-ku, Tokyo, 102-8796, Japan. E-mail asuzuki{at}tpth.go.jp
| Abstract |
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Methods and ResultsWe examined formalin-fixed specimens of the coronary arteries immunohistochemically by using antibodies against vascular growth factors (GFs) and their receptors in 7 children with Kawasaki disease, 9 children with no coronary disease, and 3 adults with atherosclerosis. In the thickened intima at stenotic sites and at recanalized vessels with Kawasaki disease, extensive expression of vascular GFs, such as transforming GF-ß1, platelet-derived GF-A, and basic fibroblast GF, was observed both within and surrounding smooth muscle cells. Vascular endothelial GF was observed within smooth muscle cells. Furthermore, all of these GFs were strongly expressed in the newly formed microvessels within the intima. In the thinned media, these GFs were focally and weakly expressed. In contrast, these GFs were expressed only in the media in the control children. In cases of adult atherosclerosis, GFs were expressed diffusely in the media but focally and weakly if at all in the intima.
ConclusionsActive remodeling of the coronary artery lesions in Kawasaki disease continues in the form of luxuriant intimal proliferation and neoangiogenesis for several years after the onset of the disease. This process is distinct from adult-onset atherosclerosis.
Key Words: growth substances vasculature stenosis aneurysm thrombosis
| Introduction |
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| Methods |
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Tissue Specimens
The specimens of Kawasaki disease had been preserved in formalin
solution for 11 months to 18 years. The specimens include 5 segments of
localized stenosis, 11 aneurysms, and 5 segments of old
thrombotic occlusion with subsequent recanalization
(Table 1
).
We also studied specimens for a normal control from 9 children who had
had no coronary artery disease (Table 2
). Specimens from 3 of them had been
preserved in formalin for 11 to 20 years, and those from another 4 were
fixed in formalin for 1 night. The remaining 2 were fresh-frozen
specimens. We used them not only for the normal control study but also
to compare the patterns of staining between fresh samples and old
formalin-preserved samples. To compare the remodeling pathology, we
studied 3 adult patients who had died suddenly of acute myocardial
infarction.
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All coronary arteries were dehydrated and embedded in paraffin. Serial sections (6 µm) were stained with hematoxylin-eosin, Victoria bluevan Gieson, and Masson-trichrome stains. Immunohistochemical staining was performed >3 times for each region for all antibodies, and 2 to 3 serial sections were used each time for each factor to confirm the specific pattern of staining.
To determine interobserver variability, 3 of us (A.S., S.T., Y.S.) examined each staining. Only the findings reached by consensus were adopted as positive or negative data. As to the evaluation of the degree of expression, "strong" expression was defined as deeply stained cells in high-power magnification or densely concentrated positive cells in lower-power magnification. "Weak" expression was defined as a faintly stained positive cell or sparsely distributed positive cells among the same cell group. Further, we classified the expression as diffuse and focal.
Antibodies Tested
The antibodies used were against transforming
GF-ß1 (TGF-ß1), TGF-ß
type I receptor (TßR-I), platelet-derived GF-A (PDGF-A), basic
fibroblast GF (bFGF), vascular endothelial GF (VEGF)
(Santa Cruz Biotech), TGF-ß type II receptor (TßR-II) (Upstate
Biotech), and
-actin for identification of smooth muscle cells and
macrophages (Dako).
Immunohistochemistry
Except for
-actin and TGF-ß1
antigens, antigen retrieval was performed with trypsin, pepsin (Zymed),
or hyaluronidase (Sigma) or by boiling in citric acid
monohydrate.
Tissues for frozen sections were fixed in 4% paraformaldehyde for 20 minutes. They were transferred to 5% to 30% sucrose in PBS before embedding in OCT compound and frozen. Frozen sections (10 µm) did not require antigen retrieval.
The sections were treated with 5 mmol/L periodic acid for 10
minutes. They were then preincubated with PBS containing 0.5% skim
milk, 3% goat serum, and 0.1% sodium azide (blocking solution) for 15
minutes at 37°C. The following primary antibodies were subsequently
diluted in the blocking solution or PBS containing 1% BSA and 0.1%
sodium azide: TGF-ß1 (1:25), TßR-I (1:800),
TßR-II (1:20), PDGF-A (1:40), VEGF (1:100), bFGF (1:100),
-actin
(1A4, 1:50), and macrophages (CD68, 1:20; HAM56, 1:20). After
incubation with the primary antibodies for 2 to 3 days at 4°C, the
sections were washed in PBS containing 0.5% skim milk.
Immunoreactivities were detected with an ABC kit (Vector Labs). Peroxidase activity was visualized by 0.02% 3-3' diaminobenzidine (Sigma) and 0.05% hydrogen peroxide. The sections were counterstained with hematoxylin. Two different controls were used. Negative controls were incubated with normal nonimmune sera instead of the primary antibodies. Second, each antibody was preincubated with the appropriate antigen (Santa Cruz Biotech) before the immunohistochemical staining was performed. No immunoreactivity was seen in either of these controls.
| Results |
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-actin (data not shown).
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When we compared the expression pattern of these GFs and receptors between the freshly fixed specimens and those fixed for a lengthy period, we noticed that the expression pattern was identical, except that the staining tended to be a little weaker against the background in the formalin-preserved specimens.
Coronary Artery Lesions of Kawasaki Disease
Localized Stenosis
At the localized stenosis, there were multiple
layers within markedly thickened intima, consisting of linearly
arranged microvessels, layers rich in smooth muscle cells, and fibrous
layers. The lamina interna was disrupted at many points, with a large
number of medial smooth muscle cells migrating into the intima (Figure 3A
). Abundant stellate-shaped smooth
muscle cells were observed at the cell-rich layer in the middle intima,
indicating their active proliferation (Figure 3B
). The media
layer was very thin, whereas the adventitia was thick, interspersed
with numerous vasa vasorum. There was no accumulation of lipid or
macrophages in the intima.
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TßR-I and TßR-II were expressed diffusely in the thick
intima, but they were expressed only focally in the media. The intimal
TßR-IIpositive cells (Figure 1
, B-II) were apparently fewer
compared with the intimal TßR-Ipositive cells (Figure 1
, B-I). The positive cells were identified as smooth muscle cells by the
presence of actin, which was observed in serial sections.
The expression of bFGF (Figure 2B
and Figure 3I
),
TGF-ß1 (Figure 3C
), and PDGF-A (Figure 3D
) were basically similar in distribution to that of TßRs,
and they were expressed principally within the smooth muscle cells but
also expressed extracellularly. TGF-ß1 (Figure 3E
), PDGF-A, VEGF (Figure 3F
), and bFGF (Figure 2B
and Figure 3I
) were also expressed strongly in microvascular
smooth muscle cells. VEGF (Figure 4E
) and
bFGF (Figure 2B
) were expressed especially strongly in the
adventitial vasa vasorum.
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VEGF was expressed in the intimal smooth muscle cells and more
strongly expressed in the endothelial cells of the
neomicrovessels in the intima (Figure 3F
). In the layer of deep
intima adjacent to the media, the VEGF-positive cell groups were
connected to adventitial vasa vasorum by tiny tubes through the media
(Figure 3G
). Some macrophages, which were stained by
antimacrophage antibody, were observed around these angiogenic
sites (Figure 3H
).
Aneurysm
None of the aneurysms observed in this study with
the exception of one contained either endothelial cells
or cell-rich layers, and advanced scar tissue and calcifications filled
the aneurysmal wall; thus, no staining of GFs could be clearly
observed. In one aneurysm there was a cell-rich layer in the
innermost part of the intima expressing GFs focally and sparsely.
Occlusion
Organized thrombotic occlusion contained well-developed
recanalized vessels, which were surrounded by a thick smooth muscle
cell layer where
-actin was strongly expressed (Figure 4B
).
The thick smooth muscle cell layer was further surrounded by a line of
numerous microvessels (Figure 4A
). The intima of the occluded
native aneurysm was not thick but was often difficult to
distinguish from the adjacent thick smooth muscle cell layer of
recanalized vessels. The media of occluded aneurysm was thin
and severely degenerated where
-actin was sparsely expressed (Figure 4B
). The adventitia had abundant vasa vasorum, and some of them
were observed to be connected with new recanalized vessels (Figure 4E
).
TGF-ß1, PDGF-A, and bFGF were diffusely
and strongly expressed in the thick smooth muscle cell layers of the
newly recanalized vessels (Figure 4
, C, D, and F). These GFs
were only focally expressed in severely degenerated media of occluded
aneurysms and not at all expressed in the organized thrombus.
VEGF was expressed strongly in the endothelial cells
and in the perivascular smooth muscle cells of neomicrovessels in the
thrombus and vasa vasorum (Figure 4E
). bFGF was also expressed
strongly in the vasa vasorum and smooth muscle cells of neomicrovessels
(Figure 4F
).
Atherosclerosis
Advanced atherosclerosis showed fibrous
layers, a mass of cholesterol crystals, and accumulation of
a large number of macrophages at the plaque shoulder lesions in
the intima, but the media and adventitia were apparently normal (Figure 1
, C-I and C-II). TßR-I and TßR-II were expressed
approximately in the same degree in the media but in the intima
TßR-IIpositive smooth muscle cells (Fig 1
, C-II) appeared somewhat
less than TßR-Ipositive cells (Figure 1
, C-I). The
expression of TGF-ß1 and PDGF-A were focal and
weak in the smooth muscle cells of media and intima, and their
distributions were similar to that of TßRs. bFGF (Figure 2C
)
and VEGF were expressed diffusely in the medial smooth muscle cells but
not in the intima, unlike the intima of Kawasaki disease. All the data
are summarized in Table 3
.
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| Discussion |
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These results are compatible with the notion that TGF-ß1 stimulates proliferation of smooth muscle cells by PDGF-A and bFGF as well as synthesis of extracellular matrix by smooth muscle cells.7 Recently, McCaffrey et al6 have reported that the migration and proliferation of smooth muscle cells in response to TGF-ß1 occurs in the injured vessels. Injured smooth muscle cells are induced to proliferate markedly and to excrete large quantities of extracellular matrix. They have also shown that this process is associated with a decreased ratio of type II/type I TGF-ß receptors.5 6 It was intriguing that the ratio of type II/type I receptorpositive cells in the intima were very likely decreased in Kawasaki disease.
TGF-ß1 is known to be preserved in its inactive form and is converted to a biologically active form8 in several situations, such as the stimulation of endothelial cells by platelet aggregation,9 exposure to steady sheer stress,10 or the presence of mild pH change and/or plasmin.11 In Kawasaki disease, it is highly possible that the platelets aggregate in the aneurysm as the result of turbulent flow, thus activating latent TGF-ß1.12 Furthermore, sheer stress is increased at the inlet and outlet of the aneurysm, where almost all progressing localized stenosis with intimal thickening appeared.1 3 Exposure of the endothelium to increased sheer stress induces the expression of tissue plasminogen activator, which then converts the latent TGF-ß1 to the activated form13 and provides a mechanism for the release of biologically active bFGF from the extracellular matrix.14 bFGF has been reported to be a strong inducer of smooth muscle cell synthesis together with PDGF AA homodimer.15 In our study, bFGF was expressed together with PDGF-A in the thick intima of Kawasaki disease. PDGF-A may be possibly expressed as PDGF-AA homodimer or as PDGF-AB heterodimer. PDGF-AA together with bFGF may stimulate active synthesis of smooth muscle cells in the intima.
Another possibility of cause of intimal proliferation is an increased local angiotensinogen production, which induces the PDGF-A.16 However, we have no information about the in situ activation of angiotensin II in the context of late-phase Kawasaki disease, and up to now we have not been able to quantify angiotensinogen mRNA expression in our formalin-fixed specimens.
Aneurysm regression occurs usually within several months after the disease. Thereafter, the size of aneurysm either does not change or decreases slowly only in some cases.1 This clinical observation can be explained by the result of the present study. In most of our aneurysm specimens, the aneurysm wall was totally replaced by thick fibrous scar tissue and had no remaining endothelial cells or a cell-rich layer that would normally express GFs, indicating that no active remodeling was taking place within the aneurysm proper. Tissue expressing GFs was observed only in 1 of 11 aneurysm specimens and may have been progressive intimal thickening.
As to neoangiogenesis, which is another important feature of vascular remodeling in Kawasaki disease,2 it is reported that VEGF is expressed in the medial smooth muscle cells of normal coronary artery at a low level and that the strong expression of VEGF at the vascular wall is an evidence of active angiogenesis.17 In our study, overexpression of VEGF was observed at well-developed recanalized vessels in the occluded aneurysms, microvessels in the thick intima, and numerous vasa vasorum in the adventitia. Additionally, strong expression of TGF-ß1, PDGF-A, and bFGF in the neovascular smooth muscle cells and the appearance of macrophages around new vessels indicate active angiogenesis even in the late phase.
Finally, the present study has obvious limitations because immunohistochemistry was done with specimens preserved in formalin for long periods. We first carried out a careful absorption test for each GF and receptor and examined fresh specimens to compare the pattern of staining with that of the old specimens. On the basis of these studies, we found that the methodology we used was acceptable. However, we were not able to carry out accurate quantitative analysis by these immunohistochemical methods. To elucidate the precise role of the GFs in the time sequence of coronary artery remodeling in Kawasaki disease, one must quantify mRNA expression at various stages of the disease. Such studies were impossible with our formalin-preserved specimens.
In conclusion, in Kawasaki disease, the arterial lesions continue to undergo active remodeling processes several years after the onset of the disease. These processes are different from that of adult-type atherosclerosis. Better understanding of the basic mechanisms of long-term coronary arterial remodeling may lead us to more effective and innovative treatments for patients with Kawasaki disease.
| Acknowledgments |
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Received September 9, 1999; accepted February 1, 2000.
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