Atherosclerotic plaque rupture in the apolipoprotein E knockout mouse

The rupture of an atherosclerotic plaque is the main underlying cause of coronary artery thrombotic occlusion and subsequent myocardial infarction, but research into the causes and treatment of plaque rupture is hampered by the lack of a suitable animal model. Although complex atherosclerotic plaques can be induced in a number of experimental animal systems, in none of these is plaque rupture an established feature. We have surveyed branch points in the carotid arteries and aortas of apolipoprotein E knockout mice fed a diet supplemented with 21% lard and 0.15% cholesterol for up to 14 months. Six male and five female mice were used. Four of the male mice and four of the female mice died, after 46+/-3 weeks of feeding (range 37-59 weeks). Lumenal thrombus associated with atherosclerotic plaque rupture was observed in three male and all four female mice. In six of these seven mice, an atherosclerotic plaque rupture was found where the brachiocephalic artery branches into the right common carotid and right subclavian arteries. The ruptures were characterised by fragmentation and loss of elastin in the fibrous caps of relatively small and lipid-rich plaques overlying large complex lesions, with intraplaque haemorrhage. Immunocytochemical analysis revealed loss of smooth muscle cells from ruptured caps. These data suggest that long-term fat-feeding of apolipoprotein E knockout mice is a useful and reproducible model of atherosclerotic plaque rupture, and that these ruptures occur predominantly in the brachiocephalic artery.     

Characteristics of intact and ruptured atherosclerotic plaques in brachiocephalic arteries of apolipoprotein E knockout mice

The brachiocephalic arteries of fat-fed apolipoprotein E knockout mice develop plaques that frequently rupture and form luminal thromboses. The morphological characteristics of plaques without evidence of instability or with healed previous ruptures (intact) and vessels with acutely ruptured plaques (ruptured) have now been defined, to understand the process of plaque destabilization in more detail. Ninety-eight apolipoprotein E knockout mice were fed a diet supplemented with 21% lard and 0.15% cholesterol, for 5 to 59 weeks. Of these 98 mice, 51 had an acutely ruptured plaque in the brachiocephalic artery. Ruptured and intact plaques differed in terms of plaque cross-sectional area (intact, 0.109+/-0.016 mm2; ruptured, 0.192+/-0.009 mm2; P=0.0005), luminal occlusion (intact, 35.3+/-3.3%; ruptured, 57.7+/-1.9%; P<0.0001), the number of buried caps within the lesion (intact, 1.06+/-0.12; ruptured, 2.66+/-0.16; P<0.0001), fibrous cap thickness (intact, 4.7+/-0.6 microm; ruptured, 2.0+/-0.3 microm; P=0.0004), and lipid fractional volume (intact, 35.9+/-3.0%; ruptured, 50.7+/-2.2%; P=0.0019). This study confirms that plaque rupture is a frequent occurrence in the brachiocephalic arteries of apolipoprotein E knockout mice on a high-fat diet. The data also show that ruptured plaques in these mice show many of the characteristics of vulnerable plaques in humans. This supports the use of this model in studies of the mechanisms and therapy of plaque rupture.     

Diabetic macroangiopathy

Summary A morphometric study was performed on histological sections of the extramural coronary arteries from 10 Type 2 (non-insulin-dependent) diabetic patients and 10 nondiabetic subjects, matched for age and sex. Standardised samples were taken from the two coronary arteries and the fractional contents of Periodic Acid-Schiff-positive material, acid mucopolysaccharides and connective tissue was determined in the arterial tunica media from the two groups using a point-counting technique. The thickness of tunica intima and tunica media was obtained by micrometric measurements. There was no difference in the thickness of tunica intima with and without atherosclerotic plaque between the vessels from diabetic and nondiabetic hearts. However, the thickness of tunica media was significantly reduced in arteries from the diabetic patients (2p<0.01). In tunica media of the diabetic patients there was a significant increase (50%) in the amount of Periodic Acid-Schiff-positive material (2p<0.01), whereas the content of acid mucopolysaccharides (alcian-blue positive) was significantly reduced (2p<0.02). These changes in tunica media were similar in areas below and outside the intimai atherosclerotic plaques. The content of connective tissue was found to be significantly increased in the arteries from the diabetic patients, but only in areas outside atherosclerotic plaques (2p<0.025). There was no correlation between the observed changes in tunica media and the known duration of diabetes. The results obtained in the present study may be ascribed to the presence of a non-atherosclerotic diabetic macroangiopathy.     

Antiatherogenic effect of pioglitazone on uremic apolipoprotein E knockout mice by modulation of the balance of regulatory and effector T cells

Objective

Uremia markedly accelerates atherogenesis, but the pathogenesis remains to be elucidated and effective anti-atherogenic treatments are needed. The aim of this study was to investigate the relationship between accelerated atherosclerosis (AS) and the balance of regulatory/effector T cells (Treg/Teff) in uremic apolipoprotein E knockout (apoE−/−) mice, and the effect of pioglitazone on uremic AS and possible mechanisms.

Methods and results

Uremia was induced surgically in 8-week-old male apoE−/− mice. Two weeks after induction of uremia, the mice were randomized to receive pioglitazone (daily oral gavage with 20 mg/kg) or vehicle. Control apoE−/− mice were sham-operated and received vehicle. After 8 weeks’ treatment, all mice were sacrificed. The cross-sectional area of atherosclerotic lesions at the aortic root was significantly larger and plaques were unstable in uremic mice, which was associated with a Treg/Teff imbalance (Treg down-regulated/Teff up-regulated) compared with controls. Renal function and the percentage of Treg cells in splenocytes were negatively correlated in control and uremic mice that received vehicle. Treatment with pioglitazone dramatically inhibited AS progression, stabilized plaque and modulated the Treg/Teff imbalance (up-regulated Treg/down-regulated Teff) in uremic mice, without influencing serum lipid profiles and blood glucose. In vitro, oxidized low density lipoprotein induced a Treg/Teff imbalance in splenocytes from uremic mice. Pioglitazone modulated the imbalance by upregulating Treg cells and downregulating Teff cells. The former was not abolished by the peroxisome proliferator-activated receptor (PPAR)γ antagonist GW9662, whereas the latter was completely abolished by GW9662.

Conclusion

Pioglitazone ameliorates accelerated AS in uremic apoE−/− mice, probably through PPARγ-independent and -dependent mechanisms to modulate the Treg/Teff imbalance.     

人股动脉粥样硬化斑块内尿激酶型纤溶酶原激活物受体的表达

目的选用正常乳内动脉作为对照,分析人股动脉粥样硬化斑块中尿激酶型纤溶酶原激活物受体（uPAR）在不同部位的表达差异。方法从2005年9月至2006年2月,收集我院血管外科行股动脉粥样硬化斑块剥脱术中获取的血管内膜或内-中膜标本20例,以及心脏外科行冠状动脉搭桥术中的正常乳内动脉标本16例。通过免疫组织化学染色等方法,观察uPAR在斑块中的表达情况;明确uPAR与内膜巨噬细胞、平滑肌细胞的关系;同时半定量检测斑块不同部位uPAR表达量的差异。结果uPAR在正常乳内动脉的内膜和中膜未见表达,但在粥样硬化斑块内膜uPAR的平均光密度值（A）为92±37,明显高于中膜（46±28,P〈0．05）;内膜uPAR的积分光密度值（IA）较中膜升高约7倍（P〈0．01）。内膜uPAR表达定位于巨噬细胞、泡沫细胞和平滑肌细胞处,以平滑肌细胞与uPAR分布最为一致。斑块肩部、脂质池、破裂及血栓形成部位的uPAR IA值分别为42131±31671、45747±19963和55344±23069,均明显高于相对正常部位（5072±2588,P〈0．05）,其中在斑块破裂处表达量最高。结论人股动脉粥样硬化斑块的肩部、脂质池和破裂处,uPAR表达明显升高,提示uPAR可能在斑块破裂中起着重要作用。     

Atherosclerotic plaque-like lesions in synthetic arteriovenous grafts: implications for atherogenesis.

Atherosclerotic plaque-like lesions are prevalent in synthetic arteriovenous shunts created to provide vascular access for hemodialysis. Similarities to atherosclerotic plaques in native arteries include eccentric location, immunoreactivity for smooth muscle actin, dystrophic calcifications, superimposed thrombi, and foam cells. Fatty streaks were not grossly identified on Sudan IV staining. Because of the similarities to atherosclerosis in native vessels, these findings may have several implications for atherogenesis. The development of raised, fibrous lesions does not require decades. The presence of smooth muscle in atherosclerotic plaque-like lesions does not require a source from tunica media. A precursor fatty streak may not be required for the development of raised, fibrous lesions. Finally, development of atherosclerotic plaque-like lesions does not require putative inflammatory effects from cholesterol or LDL accumulation, or even a native vessel that can respond to injury. The atherosclerotic plaque-like lesions in this study probably developed from organization of mural thrombi.     

Intravascular Polarimetry in Patients With Coronary Artery Disease

ObjectivesThe aims of this first-in-human pilot study of intravascular polarimetry were to investigate polarization properties of coronary plaques in patients and to examine the relationship of these features with established structural characteristics available to conventional optical frequency domain imaging (OFDI) and with clinical presentation.BackgroundPolarization-sensitive OFDI measures birefringence and depolarization of tissue together with conventional cross-sectional optical frequency domain images of subsurface microstructure.MethodsThirty patients undergoing polarization-sensitive OFDI (acute coronary syndrome, n = 12; stable angina pectoris, n = 18) participated in this study. Three hundred forty-two cross-sectional images evenly distributed along all imaged coronary arteries were classified into 1 of 7 plaque categories according to conventional OFDI. Polarization features averaged over the entire intimal area of each cross section were compared among plaque types and with structural parameters. Furthermore, the polarization properties in cross sections (n = 244) of the fibrous caps of acute coronary syndrome and stable angina pectoris culprit lesions were assessed and compared with structural features using a generalized linear model.ResultsThe median birefringence and depolarization showed statistically significant differences among plaque types (p < 0.001 for both, one-way analysis of variance). Depolarization differed significantly among individual plaque types (p < 0.05), except between normal arteries and fibrous plaques and between fibrofatty and fibrocalcified plaques. Caps of acute coronary syndrome lesions and ruptured caps exhibited lower birefringence than caps of stable angina pectoris lesions (p < 0.01). In addition to clinical presentation, cap birefringence was also associated with macrophage accumulation as assessed using normalized SD.ConclusionsIntravascular polarimetry provides quantitative metrics that help characterize coronary arterial tissues and may offer refined insight into coronary arterial atherosclerotic lesions in patients.     

Structure-dependent dynamic mechanical behavior of fibrous caps from human atherosclerotic plaques

BACKGROUND. Although thrombosis associated with a fissured atherosclerotic plaque is believed to be the most common cause of acute coronary syndromes, the underlying factors that trigger plaque rupture are currently unknown. However, the mechanical behavior of the plaque is probably of critical importance. METHODS AND RESULTS. To test the hypothesis that the mechanical properties of a plaque are dependent on its composition and, in particular, that the stiffness of fibrous caps changes within the range of frequencies carried by a physiological pressure wave, the stress-strain relation was studied in 27 fibrous caps and related to the underlying histological structure of the fibrous cap. Fibrous caps were obtained during 14 autopsies from the abdominal aorta and were classified by histological examination as cellular (n = 7), hypocellular (n = 9), or calcified (n = 11). Hypocellular fibrous caps were 1-2 times stiffer than cellular caps (p less than 0.005), and calcified caps were 4-5 times stiffer than cellular caps (p less than 0.005). All 27 fibrous caps demonstrated an increase in stiffness with increasing frequencies of stress ranging from 0.05 to 10 Hz; the increase in stiffness was similar in all three histological classes. CONCLUSIONS. We conclude that the stiffness of fibrous caps from human atherosclerotic plaques is related to the underlying histological structure and that the stiffness increases with frequency in the range of physiological heart rates. The protective benefit of beta-adrenergic receptor blocking agents in coronary artery disease may, in part, be related to the frequency dependence of atherosclerotic plaque stiffness.     

Adeno-associated virus serotypes 7 and 8 outperform serotype 9 in expressing atheroprotective human apoE3 from mouse skeletal muscle

Intramuscular injection of adeno-associated viral (AAV) vectors is potentially a safe, minimally invasive procedure for the long-term gene expression of circulating antiatherogenic proteins. Here, we compare secretion and atheroprotective effects of human apoE3 after injection of 3 pseudotyped AAV vectors (AAV2/7, AAV2/8, or AAV2/9), driven by the CMV enhancer/chicken β-actin (CAG) promoter, into skeletal muscle of hyperlipidemic apolipoprotein E-deficient (apoE^−/−) mice. Vector viabilities were verified by transducing cultured C2C12 mouse myotubes and assessing secretion of human apoE3 protein. Both hind limb tibialis anterior muscles of female C57BL/6 apoE^−/− mice, 2 months old and fed a high-fat diet, were each injected with 1 × 10¹⁰ vector genomes of AAV vector. Identical noninjected mice served as controls; and blood was collected at weeks 0, 1, 2, 4, and 13. At termination (13 weeks), the brachiocephalic artery was excised; and after staining sections, plaque morphometry and fractional lipid content were quantified by computerized image analysis. Intramuscular injection of AAV2/7 and AAV2/8 vectors produced up to 2 μg human apoE3 per milliliter plasma, just below the threshold to reverse dyslipoproteinemia. AAV2/9 was notably less effective, mice having a 3-fold lower level of plasma apoE3 at 13 weeks and a 50% greater burden of atherosclerotic plaque lipid in their brachiocephalic arteries. We conclude that although vector refinement is needed to exploit fully apoE3 atheroprotective functions, AAV2/7 and AAV2/8 are promising gene transfer vectors for muscle-based expression of antiatherogenic circulating proteins.     

Atherosclerosis—Relationship to coronary blood flow

Human atherosclerotic plaques in coronary arteries consist of a variable mixture of lipids, cells and fiber proteins synthesized by the cells. The 2 major space-occupying components of the advanced lesions, which together obstruct the lumen, are the fibrous cap and the necrotic core from which the lesions derive their name. The smooth muscle cells, which make up most cells of the plaque, including the fibrous caps, are produced by migration from the media as well as by proliferation of these cells in the intima. The lipids, mostly supplied by circulating lipoproteins, are present not only in the atheromatous acellular core, but also in the cytoplasm of the cells of the lesion and extracellularly, often attached to 1 or more constituents of the fibrous matrix of the plaque (collagen, elastin and proteoglycans).In both human and rhesus monkey coronary arteries, the lumen becomes more stenotic as the plaque becomes larger and enlarges as the plaque becomes smaller in response to lipid-lowering therapy. Recent studies in other nonhuman primate models of advanced atherosclerosis have questioned the influence of the plaque lesion on coronary blood flow. For example, in the cynomolgus species of macaque (M. fascicularis), depending on how the plaques are induced, the artery lumens may dilate as the plaques become larger because the outside diameters of the arteries increase. Furthermore, some diseased arteries are found to stenose further when the animals with advanced coronary plaques are treated by measures that substantially reduce the lipids in the plaques.Questions now being studied in several animal models and in human arteries include the relative influence of the degree of medial involvement, of lesion cell types, and of lesion circumferential localization (concentric versus eccentric) on these paradoxical phenomena.     

高分辨磁共振成像评价颈动脉粥样硬化斑块成分

目的探讨高分辨MRI不同序列检查评价缺血性脑血管病患者颈动脉粥样硬化斑块成分的临床意义。方法选择64例缺血性脑血管病患者,其中短暂性脑缺血发作(TIA)患者18例,脑梗死患者46例。采用头颈联合线圈,行高分辨MRI检查,先后选用三维时间飞跃法、T_1WI、T_2WI和质子加权成像4种不同序列,分析斑块成分。结果 64例患者中,有完整厚纤维帽25例(39.1%)、完整薄纤维帽20例(31.2%)、破损纤维帽19例(29.7%),脂质池和坏死核心53例(82.8%),斑块内钙化44例(68.8%),斑块内出血31例(48.4%),斑块内纤维化33例(51.6%),脑梗死患者与TIA患者各类斑块成分所占比例比较,差异均无统计学意义(P>0.05)。结论高分辨MRI不同序列检查对颈动脉斑块的检测有助于分析斑块的成分特征,确定斑决的稳定性。     

Increased vulnerability of pre-existing atherosclerosis in ApoE-deficient mice following adenovirus-mediated Fas ligand gene transfer

OBJECTIVE: The death receptor Fas and Fas ligand (FasL) are present in human advanced atherosclerotic plaques. The activation of the Fas/FasL pathway of apoptosis has been implicated in plaque vulnerability. In the present study, we investigated whether overexpression of FasL in pre-existing atherosclerotic lesions can induce lesion remodelling and rupture-related events. METHODS AND RESULTS: Carotid atherogenesis was initiated in apolipoprotein E-deficient mice by placement of a perivascular silastic collar. The resulting plaques were incubated transluminally with recombinant adenovirus carrying FasL (Ad-FasL, lateral) or control beta-galactosidase (Ad-LacZ, contralateral). Transfection was restricted to the smooth muscle cell-rich cap of the plaque, and FasL expression led to a three-fold increase in apoptosis in the cap one day after gene transfer. Three days after gene transfer, FasL expression led to a 38% reduction in the number of cap cells. Two weeks after Ad-FasL transfer, non-thrombotic rupture, intra-plaque haemorrhage, buried caps and iron deposits were observed in 6 out of 17 Ad-FasL-treated carotid arteries versus 0 out of 17 controls (P=0.009), indicative of enhanced plaque vulnerability. CONCLUSIONS: These data demonstrate that advanced murine plaques are sensitive to Fas/FasL-induced apoptosis, which may indicate that stimulation of this pathway could result in plaque remodelling towards a more vulnerable phenotype.     

AT1 blockade attenuates atherosclerotic plaque destabilization accompanied by the suppression of cathepsin S activity in apoE-deficient mice

Although it has been suggested that the renin–angiotensin (RA) system and cathepsins contribute to the development and vulnerability of atherosclerotic plaque, the interaction of the RA system and cathepsins is unclear. Thus, we investigated the effects of an angiotensin II type 1 receptor (AT1) antagonist, olmesartan, on the levels of cathepsins in brachiocephalic atherosclerotic plaque and plaque stabilization in apolipoprotein E (apoE)-deficient mice receiving a high-fat diet.Under a high fat diet, treatment with olmesartan (3 mg/kg per day) maintained collagen and elastin at high levels and attenuated the plaque development and cathepsin S (Cat S) level in the atherosclerotic plaque of apoE-deficient mice. The administration of olmesartan suppressed the accumulation of macrophages in plaque. Immunoreactivities of Cat S and AT1 were observed in macrophages. The amount of Cat S mRNA and the macrophage-mediated collagenolytic and elastolytic activities in cultured macrophages were increased by exposure to angiotensin II (Ang II), and these effects were diminished by olmesartan and the NADPH-oxidase inhibitor apocynin. These results suggested that Cat S derived from macrophages is involved in the mechanisms of atherosclerotic plaque vulnerability, and AT1 blocker maintained the plaque stabilization alongside the suppression of Cat S and macrophage activities.     

Implication of bone regulatory factors in human coronary artery calcification

Background

Although emerging evidence suggests that vascular calcification constitutes an active process sharing common features with bone formation, several aspects of this process in human coronary artery calcification are still poorly understood. We therefore investigated the expression of key bone regulatory factors in human atherosclerotic coronary arteries.

Methods – Results

Formalin, fixed-paraffin embedded tissue samples of human atherosclerotic coronary arteries (n = 41) and normal arteries as controls (n = 9) were studied immunohistochemically for the expression of osteoprotegerin (OPG), RANKL, RANK, Runx2, Sox9, NFATc1 and Osterix (Osx). All factors where expressed in atherosclerotic lesions while absent in normal arteries, with the exception of OPG. While expression of NFATc1 and Osx was confined to tunica intima of diseased arteries, the others factors were expressed in both tunica intima and tunica media. Most factors were expressed in smooth muscle-like cells of tunica intima while NFATc1 and the OPG/RANKL/RANK system were also expressed in inflammatory cells. Wheareas expression of OPG and RANKL was invariable, expression of RANK, Runx2, Sox9, Osx and NFATc1 was significantly higher in advanced calcified lesions. Significant correlations were also observed among the bone regulatory factors in atherosclerotic arteries.

Conclusions

Our results confirm the hypothesis that highly regulated osteogenic processes are involved in the mineralization of human coronary arteries and implicate the bone regulatory factors Osx and NFATc1 in coronary artery calcification.     

SIRT6 protects against endothelial dysfunction and atherosclerosis in mice

SIRT6 is an important member of sirtuin family that represses inflammation, aging and DNA damage, three of which are causing factors for endothelial dysfunction. SIRT6 expression is decreased in atherosclerotic lesions from ApoE^−/− mice and human patients. However, the role of SIRT6 in regulating vascular endothelial function and atherosclerosis is not well understood. Here we show that SIRT6 protects against endothelial dysfunction and atherosclerosis. Global and endothelium-specific SIRT6 knockout mice exhibited impaired endothelium-dependent vasorelaxation. Moreover, SIRT6^+/− haploinsufficient mice fed a high-fat diet (HFD) also displayed impaired endothelium-dependent vasorelaxation. Importantly, SIRT6^+/−;ApoE^−/− mice after HFD feeding exhibited exacerbated atherosclerotic lesion development, concurrent with increased expression of the proinflammatory cytokine VCAM-1. Loss- and gain-of-SIRT6 function studies in cultured human endothelial cells (ECs) showed that SIRT6 attenuated monocyte adhesion to ECs. RNA-sequencing profiling revealed that SIRT6 overexpression decreased the expression of multiple atherosclerosis-related genes, including proatherogenic gene TNFSF4 (tumor necrosis factor superfamily member 4). Chromatin immunoprecipitation assays showed that SIRT6 decreased TNFSF4 gene expression by binding to and deacetylating H3K9 at TNFSF4 gene promoter. Collectively, these findings demonstrate that SIRT6 play a pivotal role in maintaining endothelial function and increased SIRT6 activity could be a new therapeutic strategy to combat atherosclerotic disease.     

Effects of insulin sensitizers on plaque vulnerability associated with elevated lipid content in atheroma in ApoE-knockout mice

Abstract. Acute coronary syndromes are generally precipitated by rupture of lipid-laden, relatively acellular, vulnerable atherosclerotic plaques with thin fibrous caps. We investigated whether a high-fat diet alters insulin sensitivity and whether insulin sensitizers (troglitazone and rosiglitazone) alter the composition of otherwise lipidladen atherosclerotic plaques in mice deficient in apolipoprotein E (ApoE). ApoE-knockout mice were fed a high-fat (n=30) or standard chow (n=10) diet for two weeks. Thereafter, those fed the high-fat diet were treated with troglitazone (n=10), rosiglitazone (n=10) or no drug (n=10) for 16 weeks beginning at 8 weeks of age. Carbohydrate metabolism was assessed with intraperitoneal glucose tolerance tests and insulin tolerance tests. Plaque composition was characterised with confocal laser scanning microscopy. The high-fat diet induced insulin resistance in the absence of weight gain. Compared with control animals on the high-fat diet, animals given troglitazone (400 mg/kg/day) or rosiglitazone (4 mg/kg/day) had significantly less area under the curve (AUC) for insulin (p<0.05) and glucose disposal (p<0.05). Despite significant increases in insulin sensitivity with drug treatment, no change in HDL-cholesterol and triglyceride levels, nor reduction in atheroma size or lipid content was noted. Thus, improvement in insulin resistance induced by a high-fat diet in this animal model of vasculopathy did not alter plaque composition.     

Divergent effects of matrix metalloproteinases 3, 7, 9, and 12 on atherosclerotic plaque stability in mouse brachiocephalic arteries

Matrix metalloproteinases (MMPs) are thought to be involved in the growth, destabilization, and eventual rupture of atherosclerotic lesions. Using the mouse brachiocephalic artery model of plaque instability, we compared apolipoprotein E (apoE)/MMP-3, apoE/MMP-7, apoE/MMP-9, and apoE/MMP-12 double knockouts with their age-, strain-, and sex-matched apoE single knockout controls. Brachiocephalic artery plaques were significantly larger in apoE/MMP-3 and apoE/MMP-9 double knockouts than in controls. The number of buried fibrous layers was also significantly higher in the double knockouts, and both knockouts exhibited cellular compositional changes indicative of an unstable plaque phenotype. Conversely, lesion size and buried fibrous layers were reduced in apoE/MMP-12 double knockouts compared with controls, and double knockouts had increased smooth muscle cell and reduced macrophage content in the plaque, indicative of a stable plaque phenotype. ApoE/MMP-7 double knockout plaques contained significantly more smooth muscle cells than controls, but neither lesion size nor features of stability were altered in these animals. Hence, MMP-3 and MMP-9 appear normally to play protective roles, limiting plaque growth and promoting a stable plaque phenotype. MMP-12 supports lesion expansion and destabilization. MMP-7 has no effect on plaque growth or stability, although it is associated with reduced smooth muscle cell content in plaques. These data demonstrate that MMPs are directly involved in atherosclerotic plaque destabilization and clearly show that members of the MMP family have widely differing effects on atherogenesis.     

Invasion of atheromatous plaques into tunica media causes coronary outward remodeling in WHHLMI rabbits

To clarify the mechanism of coronary outward remodeling, we examined atherosclerotic coronary arteries morphologically using WHHLMI rabbits that develop coronary atherosclerosis spontaneously. Perfusion-fixed coronary segments of WHHLMI rabbits were prepared at 500microm intervals. After immunohistochemical staining and histopathological staining, the areas and lengths of the arterial wall and the lesions were measured. Obvious outward remodeling was observed in coronary sections with greater than 40% cross-sectional narrowing. In coronary sections with greater than 40% cross-sectional narrowing, the tunica media was thick at the shoulder of atheromatous plaque and was thin beneath the atheromatous plaques. Macrophages infiltrated those attenuated tunica media expressed matrix metalloproteinases and oxidized LDL was accumulated in those areas. In those areas, collagen fibers and the internal elastic lamina had disappeared partly and apoptotic smooth muscle cells were observed. Proliferation of smooth muscle cells was observed at the attenuated tunica media and adjacent adventitia. The present results suggest that invasion of atheromatous plaques into the tunica media causes coronary outward remodeling.