Effects of urotensin II on functional activity of late endothelial progenitor cells

Abstract

Urotensin II (UII) is a potent vasoactive cyclic peptide which has multiple effects on the cardiovascular system. However, the effects of UII on late endothelial progenitor cells (EPCs) are still unclear. The aim of the present study is to investigate whether UII influences the functional activity of late EPCs. Late EPCs were isolated from human umbilical cord blood by Ficoll density gradient centrifugation and treated with UII (10⁻¹⁰, 10⁻⁹, 10⁻⁸, 10⁻⁷ and 10⁻⁶ M), or vehicle control. Expression of urotensin II receptor (UT) in late EPCs was confirmed by indirect immunofluorescence staining. Late EPCs proliferation, migration and in vitro vasculogenesis activity were assayed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, transwell chamber assay, and matrigel tube formation assay. Late EPCs adhesive assay was performed by replating cells on fibronectin-coated dishes, and then adherent cells were counted. Incubation with UII increased the migratory, adhesive and in vitro vasculogenesis capacity and inhibited the proliferative activity of late EPCs. Furthermore, these UII-mediated effects on late EPCs were attenuated by pretreatment with the UT antagonist urantide. These findings indicate that UII may exert multiple effects on functional activity of late EPCs through UT.

Introduction

Urotensin II (UII) is a somatostatin-like cyclic peptide with vasoactive potential [1]. In human, UII binds with high affinity to the orphan G-protein-coupled receptor 14 (GPR14) [18], recently referred to as UII receptor (UT) [4]. UII and its receptor are widely expressed in the cardiovascular tissues [20], [21], and UII has multiple effects on the cardiovascular system, including modulation of vascular tone, myocardial contraction and heart rate [16], [24]. More recently, a potential role of the UII system in the development of atherosclerosis is emerging [19]. Increased expression of UII and its receptor were found in both atherosclerotic carotid arteries and aortae with a large degree of inflammatory cells involvement [3], and UT antagonist alleviated the atherosclerosis lesions [22]. The plasma level of UII was positively correlated with carotid atherosclerosis in hypertensive patients [28] and was associated with a higher risk of carotid plaque formation as compared with the traditional risk factors [31]. Although these data suggested that UII may be involved in the progression of atherosclerosis, the exact role of UII in the pathogenesis of atherosclerosis remains to be determined.

Emerging evidence suggested that endothelial progenitor cells (EPCs) play a crucial role in neovascularization of ischemic tissue and contribute to re-endothelialization of injured blood vessels [12], [14], [15]. These beneficial properties make EPCs protective against the development of atherosclerosis and cardiovascular disease. However, various risk factors for coronary artery disease, such as smoking, hypertension, hyperlipidemia and diabetes, reduce the number of EPCs and impair their functional activity [11], [30]. Reduced levels of circulating EPCs are independently associated with atherosclerosis disease progression and predict the occurrence of a higher incidence of cardiovascular events and death [25], [32].

Circulating EPCs consist of two different types: early EPCs and late EPCs [13]. The early EPCs have low proliferative capacity and fail to form vessels. In contrast, late EPCs have high proliferative potential and play a crucial role in neoangiogenesis [26]. Recently, Xu et al. [33] reported that UT was expressed on early EPCs, and UII was able to induce their migration. However, it is still unknown whether UII has influence on late EPCs. In the present study, we investigated the effects of UII on the proliferation, adhesion, migration, and in vitro vasculogenesis capacity of late EPCs. Furthermore, we investigated whether these effects would be prevented by urantide, an antagonist of UT.