Cholesterol-induced changes of type VIII collagen expression and distribution in carotid arteries of rabbit

Type VIII collagen mediates vessel wall remodeling after arterial injury and fibrous cap formation in atherosclerosis

Collagens in the atherosclerotic plaque signal regulation of cell behavior and provide tensile strength to the fibrous cap. Type VIII collagen, a short-chain collagen, is up-regulated in atherosclerosis; however, little is known about its functions in vivo. We studied the response to arterial injury and the development of atherosclerosis in type VIII collagen knockout mice (Col8(-/-) mice). After wire injury of the femoral artery, Col8(-/-) mice had decreased vessel wall thickening and outward remodeling when compared with Col8(+/+) mice. We discovered that apolipoprotein E (ApoE) is an endogenous repressor of the Col8a1 chain, and, therefore, in ApoE knockout mice, type VIII collagen was up-regulated. Deficiency of type VIII collagen in ApoE(-/-) mice (Col8(-/-);ApoE(-/-)) resulted in development of plaques with thin fibrous caps because of decreased smooth muscle cell migration and proliferation and reduced accumulation of fibrillar type I collagen. In contrast, macrophage accumulation was not affected, and the plaques had large lipid-rich necrotic cores. We conclude that in atherosclerosis, type VIII collagen is up-regulated in the absence of ApoE and functions to increase smooth muscle cell proliferation and migration. This is an important mechanism for formation of a thick fibrous cap to protect the atherosclerotic plaque from rupture.

Type VIII collagen signals via β1 integrin and RhoA to regulate MMP-2 expression and smooth muscle cell migration

The extracellular matrix signals and regulates the behavior of vascular cells during the pathogenesis of atherosclerosis. Type VIII collagen, a short chain collagen, is scarcely present in normal arteries, but is dramatically upregulated in atherosclerosis and after other types of vascular injury. Cell culture studies have revealed that this protein supports smooth muscle cell (SMC) adhesion and stimulates migration, however little is known about the signaling or the mechanisms by which this occurs. SMCs isolated from wild-type C57BL/6 and type VIII collagen deficient mice were studied using assays to measure chemotactic and haptotactic migration, and remodeling and contraction of 3-dimensional type I collagen gels. Col8(-/-) SMCs exhibited impairments in migration, and a strongly adhesive phenotype with prominent stress fibers, stable microtubules and pronounced central basal focal adhesions. The addition of exogenous type VIII collagen to the Col8(-/-) SMCs rescued the impairments in migration, and restored cytoskeletal architecture so that it was similar to Col8(+/+) cells. We measured elevated levels of active GTP-RhoA in the Col8(-/-) cells, and this too was reversed by treatment with exogenous type VIII collagen. We showed that type VIII collagen normally suppresses RhoA activation through a beta-1 integrin dependent mechanism. MMP-2 levels were reduced in the Col8(-/-) SMCs, and knockdown of MMP-2 in Col8(+/+) SMCs partially recapitulated the decreases in migration and 3D gel contraction seen in Col8(-/-) cells, showing that type VIII collagen-stimulated migration was dependent on MMP-2. Inhibition of Rho restored MMP-2 activity in the Col8(-/-) cells, and partially rescued migration, demonstrating that the elevations in RhoA activity were responsible for the suppression of migration of these cells. In conclusion, we have shown that type VIII collagen signals through beta-1 integrin receptors to suppress RhoA, allowing optimal configuration of the cytoskeleton, and the stimulation of MMP-2-dependent cell migration.

Proteomics of acute coronary syndromes

Acute coronary syndromes (ACS), such as unstable angina, acute myocardial infarction, and sudden cardiac death, are commonly associated with the presence of vulnerable plaques in coronary arteries. Rupture or erosion of vulnerable plaques results in the formation of luminal thrombi due to the physical contact between platelets and thrombogenic elements within the atherosclerotic lesions. Considering the socioeconomic burden of ACS, it is imperative that the scientific community achieves a clear understanding of the multifaceted pathophysiology of vulnerable atheroma to identify accurate prognostic biomarkers and therapeutic targets. The analytical power of modern proteomic technologies could facilitate our understanding of vulnerable plaques and lead to the discovery of novel therapeutic targets and diagnostic biomarkers.

Oxidized phospholipids induce type VIII collagen expression and vascular smooth muscle cell migration

Phenotypic switching of vascular smooth muscle cells (VSMCs) is known to play a critical role in the development of atherosclerosis. However, the factors present within lesions that mediate VSMC phenotypic switching are unclear. Oxidized phospholipids (OxPLs), including 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC), are active components of minimally modified low density lipoprotein and have been previously shown to induce multiple proatherogenic events in endothelial cells and macrophages, but their effects on VSMCs have been largely unexplored until recently. We previously showed that OxPLs induced phenotypic switching of VSMCs, including suppression of SMC differentiation marker genes. The goal of the present studies was to test the hypothesis that OxPLs alter extracellular matrix production and VSMC migration. Results showed that POVPC activated expression of several extracellular matrix proteins in VSMC. POVPC increased expression of type VIII collagen alpha1 chain (Col8a1) mRNA in cultured VSMCs and in vivo in rat carotid arteries by 9-fold and 4-fold, respectively. POVPC-induced activation of Col8a1 gene expression was reduced by small interfering RNA-mediated suppression of Krüppel-like factor 4 (Klf4) and Sp1, and was abolished in Klf4-knockout VSMCs. POVPC increased Klf4 binding to the Col8a1 gene promoter both in vivo in rat carotid arteries and in cultured VSMCs based on chromatin immunoprecipitation assays. Moreover, POVPC-induced VSMC migration was markedly reduced in Klf4- or type VIII collagen-knockout VSMCs. Given evidence that OxPLs are present within atherosclerotic lesions, it is interesting to suggest that OxPL-induced changes in VSMC phenotype may contribute to the pathogenesis of atherosclerosis at least in part through changes in extracellular matrix composition.

Decellularized Xenogenic Heart Valves Reveal Remodeling and Growth Potentialin Vivo

We have developed an advanced tissue processing technique on porcine pulmonary heart valves for pulmonary valve replacement and its initial clinical application during the autograft operation according to Ross. The novel concept consists of a cell-free matrix achieved by deoxycholic acid treatment that is repopulated by host cells in vivo. Molecular biology, radioligand binding, and electron microscopy consistently showed that these valves are almost free of cellular components. Animal experiments and clinical investigations revealed excellent hemodynamic properties of the valves, no need for antithrombotic therapy, and repopulation by host cells without any signs of calcification. In juvenile sheep the internal diameter of the implanted valves significantly increased in growing animals by approximately 10 mm. The repopulation of the decellularized heart valves was found not only in sheep but also in humans, which indicates that the underlying mechanisms, presumably repair mechanisms, might be common in mammals. If these findings can be confirmed by others, they will lead to new concepts in the field of cardiovascular tissue engineering that will eliminate the need for in vitro construction of autologous heart valves.

Vascular collagens: spotlight on the role of type VIII collagen in atherogenesis

Collagens play a central role in maintaining the integrity and stability of the undiseased as well as of the atherosclerotic vessel wall. An imbalanced metabolism may lead to uncontrolled collagen accumulation reducing vessel wall velocity, frequently resulting in arterial occlusion or thrombosis. A reduced production of collagen and its uncontrolled degradation may affect the stability of the vessel wall and especially of the atherosclerotic plaques by making them prone to rupture and aneurysm. This review presents an overview on the four groups of vascular collagens and on their role in atherogenesis. The major focus was to highlight the extraordinary role and importance of the short chain network forming type VIII collagen in the extracellular matrix of undiseased arteries and of atherosclerotic plaques. The molecular structure of type VIII collagen, its cellular origin, its implication in atherogenesis, its temporal and spatial expression patterns in human and experimental models of atherogenesis, the factors modulating its expression, and--not at least--its potential function is discussed.

Smooth muscle-specific expression of SV40 large TAg induces SMC proliferation causing adaptive arterial remodeling

To study the effects of enhanced smooth muscle cell (SMC) proliferation on arterial vessel geometry in the absence of vessel trauma, we developed a transgenic mouse model expressing SV40 large T antigen under control of the 2.3-kb smooth muscle-myosin heavy chain promoter. Transgenic mice studied at ages from 3 to 13 wk showed a 3.2-fold increase in arterial wall SMC density, with 28% of SMC exhibiting proliferative cell nuclear antigen staining, confirming enhanced SMC proliferation, which was accompanied by two- to threefold increases in arterial wall areas (P < 0.05). Remarkably, despite increased vessel wall mass, the lumen area was not compromised, but rather was increased. A tightly conserved linear relationship was found between arterial circumference and wall thickness with slopes of 0.036 for both transgenics (r = 0.93, P < 0.01) and controls (r = 0.77, P < 0.01), suggesting the hypothesis that the conservation of wall stress functions as a primary determinant of adaptive arterial remodeling. This establishes a new model of adaptive vessel remodeling occurring in response to a proliferative input in the absence of mechanical injury or primary flow perturbation.

The interleukin-6/interleukin-6-receptor system is activated in donor hearts

OBJECTIVES

To assess the potential of the donor heart to respond to interleukin-6 (IL6), the present study investigated the expression of IL6 receptor components in the myocardium of donor hearts before transplantation.

BACKGROUND

Donor heart dysfunction early after transplantation has been associated with the cytokine storm after donor brain death. Proinflammatory cytokines are thought to play a central role in this process. Interleukin-6 is of specific interest because it has been associated with cardiac allograft dysfunction and is related to an impaired prognosis. Its action requires expression of the specific IL6 receptor (IL6R), and the common signal transducer of the IL6 family glycoprotein 130 (gp130) in the donor heart.

METHODS

The activation of IL6, IL6R and gp130 messenger ribonucleic acid (mRNA) and protein was studied via reverse transcription-polymerase chain reaction (RT-PCR) and immunohistology in donor hearts (n = 6) and compared with patients undergoing evaluation of ventricular arrhythmias (control, n = 9) or with advanced heart failure (n = 20).

RESULTS

Messenger RNA of IL6, IL6R and gp130 was strongly expressed in all chambers of donor hearts, whereas right ventricles of control patients did not show any expression (donor vs. control: p < 0.005). Right ventricles of failing hearts showed IL6, IL6R and gp130 mRNA levels comparable with those found in donor hearts. Immunohistochemistry paralleled the RT-PCR data on the protein level. While IL6 was mainly expressed by myocytes, both receptor components were preferentially found mainly on interstitial cells.

CONCLUSIONS

The expression of the IL6 receptor components in the donor heart before transplantation establishes the condition sine qua non for the response of the donor heart to circulating IL6. This mechanism may explain the close association of elevated IL6 serum levels to acute cardiac allograft dysfunction in the early perioperative period.

The extracellular matrix can regulate vascular cell migration, proliferation, and survival: relationships to vascular disease

The extracellular matrix (ECM) of the normal artery wall is a collection of fibrous proteins and associated glycoproteins embedded in a hydrated ground substance of glycosaminoglycans and proteoglycans. These distinct molecules are organized into a highly ordered network that are closely associated with the vascular cells that produce them. In addition to providing the architectural framework for the artery wall that imparts mechanical support and viscoelasticity, the ECM can regulate the behaviour of vascular cells, including their ability to migrate, proliferate and survive injury. The composition of the ECM is different within intimal lesions of atherosclerosis, which are composed of monocytes and lymphocytes from the circulation and smooth muscle cells (SMC) that migrate from the media to the intima (Ross 1993, 1999), and these differences may contribute to the altered phenotype of vascular cells within lesions. This review will briefly outline the ECM changes observed in atherosclerosis and restenosis and the potential relationship of these changes to altered vascular cell functions.