Articles |
-Actin in Early Atherosclerotic Lesions
From the Institute of Pathology, Heinrich-Heine-University Düsseldorf, Germany, and the Department of Cardiology, University of Ulm, Germany (J.T., J.W., V.H.), and the Department of Pathology, University of Cambridge, Cambridge, UK (D.E.B., C.F.)
Correspondence to Dr David Bowyer, University of Cambridge, Department of Pathology, Division of Cellular Pathology, Tennis Court Road, Cambridge CB2 1QP, England. E-mail david.bowyer{at}mole.bio.cam.ac.uk.
| Abstract |
|---|
|
|
|---|
-actin, but not with
intact macrophages, thus supporting the hypothesis that
interaction of complement with smooth muscle cells may indeed be
important in atherogenesis.
Key Words: atherogenesis C5b-9 early lesions complement
| Introduction |
|---|
|
|
|---|
Previously, it was suggested that SMCs might be a major target for C5b-9 attack in the developing atherosclerotic plaque.12 In contrast to other cells in the lesion, SMCs do not express the C5b-9(m)-protecting surface molecule CD59 constitutively, although under some circumstances it may be induced. Recently it was demonstrated, in an in vitro system, that formation of MAC on human SMCs leads to release of MCP-1.6 Such an attack on SMCs with release of MCP-1 may possibly represent an initiating event in atherosclerotic lesion formation, because it might cause the initial monocyte recruitment into the arterial wall.
Early studies demonstrated C3 in atherosclerotic lesions,1315 and C5b-9 has been demonstrated.1620 Previous evidence suggested that C5b-9 colocalizes with macrophages and cell debris, but the lesions studied were intermediate and advanced and thus contained much necrotic material.
In light of the evidence for a potential role of complement attack on
SMCs, the present studies were performed on early atherosclerotic
lesions. Paraffin-embedded tissue sections of coronary arteries
were costained with affinity-purified immunoglobulins against the
neoantigens of C5b-9 and against smooth muscle
-actin. Sections were
also costained with antibodies against the neoantigens of C5b-9 and the
macrophage marker CD68. We report here that C5b-9 and
-actin
widely colocalize in early lesions. Our observations support the
hypothesis that interactions of C5b-9 and SMCs might contribute to the
promotion of atherosclerotic plaque formation in the
arterial wall.
| Methods |
|---|
|
|
|---|
Antibodies
The murine monoclonal antibody (clone 978/394 [IgG1] used at a
1:200 dilution) was kindly provided by Professor S. Bhakdi, University
of Mainz, Germany. It is directed against epitopes of the terminal
C5b-9 complement complex that are not exposed on native C9 and are,
therefore, termed "neoantigens." Thus, this antibody is specific
for epitopes of C9 exposed on generation of
MAC.22 The murine monoclonal antibody (clone 1A4
[IgG2a], used at a 1:100 dilution) directed against the smooth muscle
-actin and the murine monoclonal antibodies (clone PG-M1 [IgG3]
and clone KP1 [IgG1], both used at a 1:100 dilution) directed against
the macrophage marker CD68 were purchased from DAKO. Primary
antibodies were detected using biotinylated anti-mouse polyclonal
secondary antibodies (Vector Laboratories).
Immunohistochemical Staining With Individual Antibodies
For immunohistochemical analysis, 4 to 5 µm thick
serial slices were deparaffinized in xylene. All slides were treated
with 3% H2O2 to block
endogenous peroxidase activity. Sections chosen to be
assayed for the macrophage marker CD68 were predigested with
0.1% Pronase E solution for 20 minutes at room temperature. Slides
were then incubated with 5% normal horse serum to block nonspecific
conjugation and then with primary antibody for 1 hour at room
temperature. The slides were then incubated with biotin-conjugated
anti-mouse antibody for 30 minutes at room temperature and then with
avidin-biotin-peroxidase reagent for 45 minutes at room
temperature.23 The reaction products were
revealed by immersing the slides in diaminobenzidine-tetrachloride to
give a brown-colored reaction product. Finally, the slides were
counterstained with hematoxylin and mounted.
Negative controls included replacement of the primary antibody by phosphate-buffered saline or irrelevant immunoglobulins.
Double Staining for C5b-9 and Either Smooth Muscle
-Actin
or CD68
Estimations of colocalization of C5b-9 with
-actin, on the
one hand, and C5b-9 with CD68, on the other hand, were performed as
follows. The slides were incubated with the first antibody against the
neoantigens of the terminal C5b-9 complement complex, visualized by
immersion in diaminobenzidine-tetrachloride as described above, giving
a brown reaction product and then rinsed in Tris-buffered saline.
Before reaction with the antibody for
-actin or CD68, slides were
again blocked with 5% normal horse serum and then incubated with the
primary antibody against the smooth muscle cell marker
-actin or one
of the two antibodies against the macrophage marker CD68,
respectively, for 40 minutes at 37°C (in the case of antibodies
against CD68, PG-M1 or KP-1, the slides were previously predigested in
0.1% Pronase E solution for 20 minutes). Slides were then incubated
with biotin-conjugated anti-mouse antibody for 20 minutes at 37°C,
this time followed by streptavidin-conjugated alkaline phosphatase for
20 minutes at 37°C. The reaction products were visualized by
immersing the slides in New Fuchsin to give a red reaction product.
Finally, the slides were counterstained with hematoxylin and
mounted.
| Results |
|---|
|
|
|---|
|
General Morphological Findings
All of the lesions studied were within diffuse adaptive intimal
thickenings (Fig 1
). This consisted of
two distinguishable layers, a fibromuscular layer at the base of the
intima adjacent to the internal elastic lamella, which was rich in SMCs
and a fibroelastic layer bordering the lumen, which was much less
cellular. The atherosclerotic lesions within the diffuse intimal
thickening were all early lesions characterized by isolated
macrophage foam cells (Fig 1
, arrowheads) or groups of foam
cells forming small fatty dots and streaks. Larger lesions had a
necrotic core containing extracellular lipid.
|
Distribution of SMCs
SMCs were present in the intima in all of the 10 early
atherosclerotic lesions examined. They were abundant in the basal layer
of the intima adjacent to the media (Fig 2
, arrowheads). In other segments, SMCs
were scattered over the whole intima, sometimes present in the area
occupied by foam cells and mingling with them. As a rule, SMCs were
arranged irregularly within the intima, whereas in the media, they
appeared in close layers. On the whole, there was no evident difference
in the number of SMCs in a segment of the intima with an early lesion
compared with the number in a segment with only diffuse adaptive
intimal thickening. The controls processed with phosphate-buffered
saline or irrelevant immunoglobulins instead of the specific antibody
did not show any immunostaining in the blood
vessels.
|
C5b-9 Deposits
C5b-9 deposits were present in all 10 early atherosclerotic
lesions examined. The predominant manifestation of C5b-9 was a
deposition of small granules in the deeper part of the intima adjacent
to the media (Fig 3
, arrowheads).
Occasionally, a more diffuse deposition extending over the whole width
of the intima was observed. Usually, the C5b-9 deposits were limited by
the internal elastic lamina, but in two cases, a deposition of long,
clearly defined granules within the media was evident (Fig 4
). C5b-9 deposits were never associated
with intact foam cells. There was no obvious difference in the quantity
of C5b-9 detected between cases.
|
|
No C5b-9 deposits could be seen in the atherosclerosis-free intima or the media beneath it. The controls processed with phosphate-buffered saline or irrelevant immunoglobulins instead of the specific antibody were completely negative.
Distribution of Macrophages
In the samples examined, macrophages appeared either as
isolated groups of round or spindle shaped cells within the intima, or
formed one or more layers next to the luminal surface (Fig 5
). In more advanced lesions they were
obvious throughout most of the intima. In the
atherosclerosis-free regions, macrophages were
absent or diffusely distributed in the intima in small numbers (not
shown). In general, there was no macrophage staining within the
media of the artery wall. All controls of the immunoperoxidase reaction
were negative.
|
Colocalization of Terminal Complement Complex, Intimal SMCs,
and Macrophages
Using the double-staining immunoperoxidase method, various
manifestations of a strong association between C5b-9 deposits and SMCs
in the early atherosclerotic lesion could be observed (Fig 6
). In a large majority of cases, small
granules of C5b-9 (brown color, large arrowheads) were found in the
close proximity to SMCs (red color, small arrowheads) within the
fibromuscular layer at the base of the intima. Frequently, there was an
overlapping of the antigens unequivocally identifying the SMC (red
staining, small arrowheads) as the one cell type colocalizing with
C5b-9 (brown deposits, large arrowheads) (Fig 6
). The large majority of
the SMCs showed colocalization with C5b-9. Sometimes C5b-9 deposits and
SMCs were also localized in different areas, but this was rather an
exception to the rule and was due to small necrotic areas, in which
only the neoantigens of C5b-9 were detectable. In the media, C5b-9
deposits also colocalized with SMCs.
|
As described above, macrophage foam cells were localized predominantly to the parts of the intima near the luminal surface, whereas depositions of C5b-9 were found in the deeper layers of the intima adjacent to the media, so the C5b-9 was not associated with intact foam cells. Control experiments of the double-staining immunoperoxidase reaction were completely negative.
| Discussion |
|---|
|
|
|---|
-actin was investigated by
immunohistochemical analysis in 10 early atherosclerotic
lesions of coronary arteries collected from autopsies. C5b-9
was generally found at the base of the intima near the
intimal/medial junction in the zone of fibrocellular thickening,
which contains abundant SMCs. Furthermore, this staining for C5b-9 in
the deep intima showed extensive colocalization with SMC
-actin in
various morphologic forms, including close apposition and overlap. The
overlying fibroelastic zone, which is relatively acellular, rarely
showed any C5b-9. This lack of staining for C5b-9 in the fibroelastic
layer of the intima argues against deposition of preformed complexes
from the blood. A previous attempt to detect colocalization of C5b-9 and SMCs, albeit by the use of parallel sections rather than double immunostaining, revealed C5b-9 staining mainly in necrotic tissue.18 In that study, however, only advanced plaques were investigated and, as the main feature of the advanced plaque is the necrotic core,21 these results are not too surprising. It has also been reported that C5b-9 is associated with macrophages and cell debris.19,20 The present results show that in early lesions C5b-9 is colocalized with SMCs; there was never any colocalization with macrophages as identified by CD68.
This study was performed in light of increasing evidence for a role of complement activation in atherosclerotic lesion formation. In this context, the role of C5b-9 has recently become a subject matter of debate. C5b-9 complexes have been demonstrated to be present in atherosclerotic lesions.5,1618 As it is not possible to distinguish between sC5b-9 and C5b-9(m) by specific antibodies,5 it is as yet not really known whether the molecules provide sC5b-9 complexes or C5b-9(m) complexes and, thus, whether they are biologically active or presumably inactive. Two arguments, however, suggest the occurrence of C5b-9(m) in the arterial wall. First, C5b-9 complexes have been isolated from atherosclerotic lesions and their identity as MACs has been demonstrated by electron microscopy.5 Second, there is obviously different localization of C5b-9 and S-protein (a protein that associates with sC5b-9)24 and, thus, at least some of the C5b-9 complexes seem to be membrane-bound.
It is not known whether the C5b-9 found on SMCs is formed in situ by activation of complement directly on the target cell or whether activation nearby gives rise to a so-called bystander attack.4 In any event, SMCs are a likely target, not only because they are the predominant cell type in the intima of diffuse and adaptive intimal thickenings and early lesions,21 but also because SMCs, in contrast to other cells in the lesion, do not express the MAC-protecting surface molecule CD59 constitutively.12 Some protection of the cells from attack may occur, because of the presence of decay-accelerating factor, which has been detected within lesions.25 The association between C5b-9 deposition and the expression of decay-accelerating factor or other complement regulatory molecules such as complement receptors4 was not assessed in the present study.
In addition to these observations in human plaque material, it has recently been demonstrated in an in vitro system that MAC-formation on human SMCs leads to the release of MCP-1, a specific chemoattractant for human blood monocytes.6 Monocyte infiltration is one of the outstanding cellular features in atherosclerotic lesion formation and, thus, these in vitro data suggest a novel pathway by which complement activation may trigger chronic inflammation in the arterial wall.
In conclusion, the results of our study, ie, the demonstration of C5b-9 in the early atherosclerotic lesion and its colocalization with SMCs, provide further evidence for a possible role of complement activation in the early stages of atherogenesis.
| Selected Abbreviations and Acronyms |
|---|
|
| Acknowledgments |
|---|
Received April 10, 1997; accepted July 2, 1997.
| References |
|---|
|
|
|---|
1-antitrypsin
and
2-macroglobulin. Atherosclerosis. 1979;34:391405.[Medline]
[Order article via Infotrieve]
This article has been cited by other articles:
![]() |
A. R. Kinderlerer, F. Ali, M. Johns, E. A. Lidington, V. Leung, J. J. Boyle, S. S. Hamdulay, P. C. Evans, D. O. Haskard, and J. C. Mason KLF2-dependent, Shear Stress-induced Expression of CD59: A NOVEL CYTOPROTECTIVE MECHANISM AGAINST COMPLEMENT-MEDIATED INJURY IN THE VASCULATURE J. Biol. Chem., May 23, 2008; 283(21): 14636 - 14644. [Abstract] [Full Text] [PDF] |
||||
![]() |
V. K. Bhatia, S. Yun, V. Leung, D. C. Grimsditch, G. M. Benson, M. B. Botto, J. J. Boyle, and D. O. Haskard Complement C1q Reduces Early Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient Mice Am. J. Pathol., January 1, 2007; 170(1): 416 - 426. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. A. Lidington, R. Steinberg, A. R. Kinderlerer, R. C. Landis, M. Ohba, A. Samarel, D. O. Haskard, and J. C. Mason A role for proteinase-activated receptor 2 and PKC-{epsilon} in thrombin-mediated induction of decay-accelerating factor on human endothelial cells Am J Physiol Cell Physiol, December 1, 2005; 289(6): C1437 - C1447. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Matsunaga and M.-a. Muramatsu Knowledge-based computational search for genes associated with the metabolic syndrome Bioinformatics, July 15, 2005; 21(14): 3146 - 3154. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Rus and F. Niculescu Association of Complement Inhibitors With Connective Tissue Matrix in Atherosclerotic Lesions Arterioscler. Thromb. Vasc. Biol., August 1, 2003; 23(8): 1478 - 1478. [Full Text] [PDF] |
||||
![]() |
R. Oksjoki, H. Jarva, P. T. Kovanen, P. Laine, S. Meri, and M. O. Pentikainen Association Between Complement Factor H and Proteoglycans in Early Human Coronary Atherosclerotic Lesions: Implications for Local Regulation of Complement Activation Arterioscler. Thromb. Vasc. Biol., April 1, 2003; 23(4): 630 - 636. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Dimayuga, B. Cercek, S. Oguchi, G. N. Fredrikson, J. Yano, P. K. Shah, S. Jovinge, and J. Nilsson Inhibitory Effect on Arterial Injury-Induced Neointimal Formation by Adoptive B-Cell Transfer in Rag-1 Knockout Mice Arterioscler. Thromb. Vasc. Biol., April 1, 2002; 22(4): 644 - 649. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. A. Lidington, D. O. Haskard, and J. C. Mason Induction of decay-accelerating factor by thrombin through a protease-activated receptor 1 and protein kinase C-dependent pathway protects vascular endothelial cells from complement-mediated injury Blood, October 15, 2000; 96(8): 2784 - 2792. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Orlandi, M. Marcellini, and L. G. Spagnoli Aging Influences Development and Progression of Early Aortic Atherosclerotic Lesions in Cholesterol-Fed Rabbits Arterioscler. Thromb. Vasc. Biol., April 1, 2000; 20(4): 1123 - 1136. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. D. Collard, A. Agah, W. Reenstra, J. Buras, and G. L. Stahl Endothelial Nuclear Factor-{kappa}B Translocation and Vascular Cell Adhesion Molecule-1 Induction by Complement : Inhibition With Anti-Human C5 Therapy or cGMP Analogues Arterioscler. Thromb. Vasc. Biol., November 1, 1999; 19(11): 2623 - 2629. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. C. Mason, H. Yarwood, K. Sugars, B. P. Morgan, K. A. Davies, and D. O. Haskard Induction of Decay-Accelerating Factor by Cytokines or the Membrane-Attack Complex Protects Vascular Endothelial Cells Against Complement Deposition Blood, September 1, 1999; 94(5): 1673 - 1682. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Torzewski, M. Torzewski, D. E. Bowyer, M. Frohlich, W. Koenig, J. Waltenberger, C. Fitzsimmons, and V. Hombach C-Reactive Protein Frequently Colocalizes With the Terminal Complement Complex in the Intima of Early Atherosclerotic Lesions of Human Coronary Arteries Arterioscler. Thromb. Vasc. Biol., September 1, 1998; 18(9): 1386 - 1392. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Torzewski, M. Klouche, J. Hock, M. Meßner, B. Dorweiler, J. Torzewski, H. E. Gabbert, and S. Bhakdi Immunohistochemical Demonstration of Enzymatically Modified Human LDL and Its Colocalization With the Terminal Complement Complex in the Early Atherosclerotic Lesion Arterioscler. Thromb. Vasc. Biol., March 1, 1998; 18(3): 369 - 378. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Dimayuga, B. Cercek, S. Oguchi, G. N. Fredrikson, J. Yano, P. K. Shah, S. Jovinge, and J. Nilsson Inhibitory Effect on Arterial Injury-Induced Neointimal Formation by Adoptive B-Cell Transfer in Rag-1 Knockout Mice Arterioscler. Thromb. Vasc. Biol., April 1, 2002; 22(4): 644 - 649. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
ATVB Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 1997 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |