Correlation between the presence of an immature smooth muscle cell population in tunica media and the development of atherosclerotic lesion. A study on different-sized rabbit arteries from cholesterol-fed and Watanabe heritable hyperlipemic rabbits

A CMV-actin-globin hybrid promoter improves adeno-associated viral vector gene expression in the arterial wallin vivo

BACKGROUND

Adeno-associated virus (AAV) vectors are attractive tools for direct intralumenal arterial gene transfer in interventional cardiology or cardiovascular surgery, but clinical application has been constrained by poor gene expression in this setting.

METHODS

To improve arterial wall gene expression, a hybrid promoter consisting of a cytomegalovirus (CMV) immediate-early enhancer, a chicken beta-actin transcription start site, and a rabbit beta-globin intron (CAG promoter) was substituted for the Rous sarcoma virus (RSV) promoter in an AAV type 2 vector with an alkaline phosphatase (AP) reporter gene.

RESULTS

Intralumenal transduction of rabbit carotid arteries by an AAV2 vector containing a CAG promoter resulted in gene expression in a mean of > or = 80% of the lumenal area at 14 days following exposure, compared to < or = 25% gene-expressing area with the RSV promoter-based control vector. The high prevalence of gene expression was maintained at 3, 7, 14, and 28 days. Importantly, in carotid arteries transduced with the CAG promoter, gene product expression was readily visible by the third day following transduction whereas gene expression was rarely seen before day 10 using the RSV promoter in the same animal model. On histology, AP gene expression was predominantly in vascular smooth muscle cells although some endothelial cell expression was also present.

CONCLUSIONS

Substituting the CAG for the RSV promoter results in widespread gene expression, demonstrating efficient arterial wall transduction by AAV2 vectors. This finding plus the early time to gene expression hold promise for AAV vectors as agents for direct intralumenal arterial wall gene delivery during cardiovascular interventions.

Application of stereological methods for the quantification of VCAM-1 and ICAM-1 expression in early stages of rabbit atherogenesis

Early stages of atherogenesis are characterized by the overexpression of cell adhesion molecules with the subsequent accumulation of macrophages, smooth muscle cells and proliferation of extracellular matrix in arterial intima. The quantification of atherogenic changes is necessary for the objective evaluation of the atherogenic process. The purpose of this study was to introduce stereological methods that may be used for the quantification of immunohistochemical staining, namely intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Twenty-four New Zealand White rabbits were subdivided into the three groups. Eighteen rabbits received a 0.4% cholesterol diet for 1, 2 and 3 months, respectively. Stereological principles of the systematic uniform random sampling and the point-counting method were applied for the quantification. Stereological analysis showed that VCAM-1 and ICAM-1 were upregulated during the consumption of high cholesterol diet and that VCAM-1, but not ICAM-1, has a considerable role in the formation of early atherosclerotic lesions. Stereological methods proved to be useful for the quantification of immunohistochemistry and can be used for an objective characterization of atherogenic changes in atherosclerosis.

Phenotypic diversity of smooth muscle cells isolated from human intracranial basilar artery

The present work examined heterogeneity of vascular smooth muscle cells cultured from human cerebral arteries that has not been previously reported. Primary smooth muscle cell cultures were isolated from human intracranial basilar arteries. Using a ring isolation method, multiple clones were generated from the cell cultures. These clones had two distinctly different morphologies: (1) fusiform; and (2) stellate. At confluence the fusiform-shaped clones grew in compact clusters with overlapping cells while the stellate-shaped clones were contact-inhibited growing in a monolayered pattern. The smooth muscle differentiation markers, alpha-smooth muscle-actin, calponin and smooth muscle-myosin heavy chains were expressed in all these clones. In response to serum stimulation, the stellate-shaped clones had a higher growth rate than the fusiform clones. This study reports that smooth muscle cells derived from human basilar arteries are heterogeneous.

Vascular smooth muscle cells derived from atherosclerotic human arteries exhibit greater adhesion, migration, and proliferation than venous cells

BACKGROUND

Phenotypic variation of vascular smooth muscle cells (VSMC) may result in altered biological behavior and responses. Within the vessel wall, arterial VSMC have a greater propensity to form atherosclerotic lesions as compared to venous VSMC. In this study the rates of proliferation, adhesion, and migration were compared between VSMC of atherosclerotic arterial and venous origin.

MATERIALS AND METHODS

Human VSMC cultures were isolated from 18 infragenicular arteries at the time of below knee amputation and from 20 saphenous veins during lower extremity revascularization surgery. Cell cultures were isolated from the media of each specimen and maintained in distinct cell lines for all assays. Cells from passages 2 and 3 were assayed for their proliferative capacity using total DNA fluorescence photometry and for adhesion and migration using a modified Boyden chamber.

RESULTS

Patient age and the incidence of atherosclerotic risk factors did not vary significantly between the arterial and the venous patient groups. VSMC of atherosclerotic arterial origin demonstrated greater proliferation (arterial, 162 +/- 59 absorption units, vs. venous, 106 +/- 56 absorption units, P < 0.001), adhesion (arterial, 74.1 +/- 22.6 cells/microscopic field, vs. venous, 41.3 +/- 12.8 cells/microscopic field, P < 0.001) and migration (arterial, 427 +/- 185 cells/microscopic field, vs venous, 119 +/- 101 cells/microscopic field, P < 0.001) than VSMC of venous origin.

CONCLUSION

Human atherosclerotic arterial VSMC exhibit significantly increased rates of proliferation, adhesion, and migration as compared to human venous VSMC. These observations of VSMC in culture are consistent with the clinical predilection for the hyperplasic responses that result in the development of atherosclerosis in the arterial wall. Possible intrinsic differences in VSMC phenotype should be considered in designing methods to limit atherosclerosis.

Adeno-associated virus vector transduction of vascular smooth muscle cells in vivo

Adeno-associated virus (AAV) vectors might offer solutions for restenosis and angiogenesis by transducing nondividing cells and providing long-term gene expression. We investigated the feasibility of vascular cell transduction by AAV vectors in an in vivo rabbit carotid artery model. Time course of gene expression, inflammatory reaction to the vector, and effects of varying viral titer, exposure time, and intraluminal pressures on gene expression were examined. Recombinant AAV vectors with an Rous sarcoma virus promoter and alkaline phosphatase reporter gene were injected intraluminally into transiently isolated carotid segments. Following transduction, gene expression increased significantly over 14 days and then remained stable to 28 days, the last time point examined. Medial vascular smooth muscle cells were the main cell type transduced even with an intact endothelial layer. Increasing the viral titer and intraluminal pressure both enhanced transduction efficiency to achieve a mean of 34 +/- 7% of the subintimal layer of smooth muscle cells expressing gene product. A mild inflammatory reaction, composed of T cells with only rare macrophages, with minimal intimal thickening was demonstrated in 40% of transduced vessels; inflammatory cells were not detected in sham-operated control arteries. These findings demonstrate that AAV is a promising vector for intravascular applications in coronary and peripheral vascular diseases.

Fish oil supplementation prevents neointima formation in nonhypercholesterolemic balloon-injured rabbit carotid artery by reducing medial and adventitial cell activation

We asked whether balloon-injured neointima formation in the presence of high/low serum cholesterol (CT) levels might be affected by dietary supplementation with fish oil (FO). To test this hypothesis, we examined the differentiation, proliferation, or apoptosis profile of smooth muscle cell (SMC) and adventitial cell response to a mild injury induced via a Fogarty catheter in the carotid artery of adult rabbits that had been fed a standard chow or 0.5% CT-enriched diet starting 4 weeks before the lesion. One week before surgery, animals received FO supplementation. This regimen was continued for the following 3 weeks. The effect of FO on the early proliferative/migratory response of carotid SMCs was also examined in 2- and 7-day-injured normocholesterolemic rabbits. As controls, animals subjected to 3-week endothelial injury and animals kept on a 7-week CT diet were used. Carotid cryosections from the various animal groups were evaluated for morphometry (image analysis), differentiation (immunofluorescence with monoclonal antibodies specific for smooth muscle markers, ie, myosin isoforms, SM22, and fibronectin), proliferation (bromodeoxyuridine incorporation), and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling). FO treatment significantly reduced the development of intimal thickening in normocholesterolemic rabbits but had no efficacy in the presence of relatively higher serum CT levels. At day 2 (adventitia) and day 7 (neointima, media, and adventitia), the proliferation index of SMCs in FO-treated injured rabbits was markedly lower than in untreated injured controls. Concomitantly with the antiproliferative effect, FO was able to decrease the size of 2 cell types involved in the cell growth response to endothelial injury, namely, the "fetal-type" medial SMC subpopulation and the fibroblast-derived adventitial myofibroblasts. Thus, in our experimental conditions, a low CT level is a permissive condition for FO to prevent neointima formation to a considerable extent. This event is attributable to the early postinjury effect of FO on SMC/adventitial cell proliferation/differentiation patterns.

Sorting of murine vascular smooth muscle cells during wound healing in the chicken chorioallantoic membrane

The vascular wall is built up of a heterogeneous population of smooth muscle cells, which exhibit not only morphological distinctions but also important differences in the composition of their structural and contractile proteins. "Epithelioid" smooth muscle cells correspond to an intimal-like type and display features associated with immaturity, whereas "spindle-shaped" cells closely resemble the more typical medial smooth muscle population. We have investigated the integration of these two cell types into the vascular architecture of an in vivo wound-healing model. Stably transfected with the beta-galactosidase gene, intima- and media-like cells were injected intravenously into the chicken chorioallantoic membrane, within which superficial foci of granulation tissue had been created by thermal or chemical injury. At 24 to 72 h after injection, cells had honed in on the lesion sites and were observed in juxtaposition to the endothelial lining of the capillaries. They began to deposit laminin, thereby indicating an impending role in the formation of the vascular wall. Intima- and media-like smooth muscle cells did not differ in their capacity to associate with capillaries, and, in so doing, their biochemical lineage characteristics became indistinguishable from one another. However, intima-like cells also penetrated the adventitial and medial layers of arteries. These findings reveal vascular smooth muscle cells to possess an extraordinary degree of plasticity, being able to adapt flexibly to changes in functional demands.

Myosin gene expression and cell phenotypes in vascular smooth muscle during development, in experimental models, and in vascular disease

In the aortic wall of mammalian species, the maturation phase of smooth muscle cell (SMC) lineage is characterized by two temporally correlated but opposite regulatory processes of gene expression: upregulation of SM type SM2 myosin isoform and downregulation of brain (myosin heavy chain B)- and platelet (myosin heavy chain A(pla))-type nonmuscle myosins. Using the myosin isoform approach to study vascular SMC biology, we have shown (1) a marked SMC heterogeneity in adult arterial vessels, ie, coexistence of an "immature" and a fully differentiated SMC population; and (2) the propensity of the immature type SMC population to be activated in experimental models and human vascular diseases that are characterized by proliferation and migration of medial SMCs into the subendothelial space.

Prolonged inhibition of nitric oxide synthesis in Yoshida hyperlipidemic rat: aorta functional and structural properties

To test whether inhibition of nitric oxide synthesis, associated with high levels of plasmatic lipids, can induce atherosclerotic lesions and phenotypic changes in smooth muscle cell composition in the aortic wall of an atherosclerotic-resistant species such as the rat, an inbred strain of hyperlipidemic Pittsburgh Yoshida rat was subjected to prolonged treatment (2 months) with the nitric oxide-synthase inhibitor L omega-nitro-arginine-methyl ester or with L-arginine. The two types of in vivo treatments were not able to modify in vitro aortic endothelium-mediated relaxation induced by acetylcholine or calcium-ionophore A-23187, the endothelium-independent sodium nitrite relaxation and the contractile response to serotonin. Histology and lipid infiltration of vascular specimens showed that L omega-nitro-arginine-methyl ester in vivo treatment did not induce any significant change in the aortic wall. Monoclonal antibodies to myosin isoforms and immunofluorescence procedures revealed the presence of an immature smooth muscle cell subpopulation in aortic specimens from saline-treated Pittsburgh Yoshida rats, whose expansion has been related in other species to atherogenesis. This peculiar cell phenotype disappeared in our animal model after prolonged L omega-nitro-arginine-methyl ester treatment. These data indicate that, despite interference with endothelium-mediated nitric oxide synthesis, atherosclerosis does not develop in this animal model and furnish for the first time a biological justification for atherogenesis resistance of rat, i.e., the lack of activation of an immature aortic smooth muscle cell population which in atherosclerosis-prone species is involved in lesion formation.