Inflammatory cytokines stimulate vascular smooth muscle cells locomotion and growth by enhancing α5β1 integrin expression and function

doi:10.1016/S0021-9150(00)00506-2

Atherosclerosis

Volume 154, Issue 2, 1 February 2001, Pages 377-385

https://doi.org/10.1016/S0021-9150(00)00506-2 Get rights and content

Abstract

The formation of atherosclerotic lesions requires the migration of vascular smooth muscle cells from the media into the intima of the artery and their proliferation. These events, which are preceded and accompanied by inflammation, are modulated by integrin receptors linking vascular smooth muscle cells to extracellular matrix molecules. Among them, fibronectin induces vascular smooth muscle cells to acquire the phenotype they show in the atherosclerotic plaque. Here we show that amounts of interleukin-1 β, tumor necrosis factor α and interferon-γ as possibly released by activated immune cells infiltrating atherosclerotic lesions, upregulate vascular smooth muscle cell expression of the α5β1 integrin, a fibronectin receptor. This improves vascular smooth muscle cell capability of migrating toward soluble or anchored fibronectin and of adhering to immobilized fibronectin. The latter effect, in turn, augments vascular smooth muscle cell proliferative response to mitogens, as suggested by the increase of intracellular pH. Finally, the effects that inflammatory cytokines have on vascular smooth muscle cell locomotion and growth, are specifically blocked by anti-α5β1 antibodies. As fibronectin and α5β1 levels are augmented in vivo in the atherosclerotic plaques, these findings support the use of integrin antagonists as potential adjuvants in atherosclerosis treatment.

Introduction

Migration of vascular smooth muscle cells (VSMC) from the media to the intima and proliferation of intimal VSMC are key early events in atherosclerotic lesion development [1].

Although triggered by soluble chemotactic and growth factors, cellular migration and growth are modulated by the interactions occurring between cells and extracellular matrix molecules [2].

It is of interest that one of the characteristics that accompanies atherosclerotic lesion development is a dramatic change in the composition of the extracellular matrix of the vascular wall. This is expressed by a marked increase in fibronectin, a blood vessel wall component that is necessary for the integrity of the vasculature [3]. The fibronectin increase occurring in atherogenesis is due both to the augmented fibronectin synthesis by vascular cells and to the deposition of soluble, plasmatic fibronectin on damaged endothelial membrane [3], [4].

Fibronectin has profounds effects on VSMC physiology. In particular, when normal VSMC are plated on fibronectin they switch from the ‘contractile’, non-proliferative phenotype to the ‘synthetic’, highly proliferative phenotype, which is the same as shown by VSMC in atherosclerotic plaques [3]. In fact, VSMC seeded on fibronectin quickly reach confluence, which is in agreement with the fact that in vivo VSMC proliferate both in the media and in the intima, where immobilized fibronectin is found [3], [4]. These findings are consistent with VSMC proliferation occurring in malignant hypertension, where high amounts of plasma fibronectin are deposited in the wall of small arteries [5]. Interestingly, matrixes rich in fibronectin also promote VSMC calcification, a key feature in atherosclerotic lesion development [6].

As for other extracellular matrix molecules, the interactions between fibronectin and the cells are mediated by membrane receptors belonging to the integrin family [2]. Among them, the α5β1 integrin, which is expressed by VSMC both in vitro [7] and in vivo [8], is considered to be the main fibronectin receptor, since it mediates most of fibronectin biological activities. In particular, α5β1 triggering by soluble or anchored fibronectin promotes cellular locomotion [9], while α5β1 binding to immobilized fibronectin induces cellular adhesion and spreading, supporting cell survival and modulating cellular response to growth factors [10], [11].

During atherogenesis, VSMC locomotion and growth are preceded and followed by an inflammatory response [1], [12], [13]. Since integrin expression and function are deeply influenced by inflammatory cytokines [14], [15], in this study we examined α5β1 expression and function in VSMC exposed to concentrations of inflammatory cytokines as released by activated immune cells.

Section snippets

Reagents

Human recombinant interleukin (IL)-1 α and β, IL-2, IL-6, tumor necrosis factor (TNF)α and β, interferon (IFN)-γ, granulocyte monocyte-colony stimulating factor (GM-CSF), basic fibroblast growth factor (bFGF) and fibronectin (from human plasma) were purchased from Boehringer–Mannheim (Mannheim, Germany). Laminin (from human placenta) and bovine serum albumine (BSA, fraction V) were from Sigma (St. Louis, MO). The monoclonal antibodies directed against the whole α5β1 integrin or the β1 chain

Inflammatory cytokines increase α5β1 expression in VSMC

To assess the effect that concentrations of inflammatory cytokines as released by activated immune cells have on α5β1 expression by VSMC, these were cultured with conditioned media of PHA-activated peripheral blood mononuclear cells for different periods of time. Exposure to conditioned media of activated peripheral blood mononuclear cells increased in VSMC, as compared to the same cells cultured in the absence of conditioned media, α5β1 expression at both the RNA and the protein level. The

Discussion

Endothelial denudation, a fundamental step of atherogenesis, is followed by an inflammatory reaction which lasts throughout the development of the atherosclerotic plaques [1]. These, in fact, are infiltrated by activated monocytes-macrophages and T cells, which are virtually absent in the wall of normal arteries [1], [12], [13]. Consequently, the expression of inflammatory cytokines is high in atherosclerotic lesions, whereas it is absent in normal arteries [1], [12], [13].

Previous studies

Acknowledgements

This work was supported by grants from Istituto Superiore di Sanità and the Ministry of Research, Rome, Italy. We thank Mr Lionello Ruggeri for technical assistance.

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Inflammatory cytokines stimulate vascular smooth muscle cells locomotion and growth by enhancing α5β1 integrin expression and function

Abstract

Introduction

Section snippets

Reagents

Inflammatory cytokines increase α5β1 expression in VSMC

Discussion

Acknowledgements

Cell

Curr. Op. Cell Biol.

J. Biol. Chem.

FEBS Lett.

Curr. Op. Cell Biol.

The pathogenesis of atherosclerosis: a perspective for the 1990s

Nature

Phenotypic modulation of smooth muscle cells after arterial injury is associated with changes in the distribution of laminin and fibronectin

J. Histochem. Cytochem.

Fibronectin and the basement membrane components laminin and collagen type III influence the phenotypic properties of subcultured rat aortic smooth muscle cells differently

Cell Tissue Res.

Angiotensin and hypertensive vascular damage: a review

Am. J. Med.

Fibronectin and collagen I matrixes promote calcification of vascular cells in vitro, whereas collagen IV matrix is inhibitory

Arterioscl. Thromb. Vasc. Biol.