Angiotensin II type 1 receptor-associated protein regulates carotid intimal hyperplasia through controlling apoptosis of vascular smooth muscle cells

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Highlights

  • ATRAP as a negative regulator of AT1 receptor plays an inhibitory role in VSMCs proliferation both in vitro and in vivo.

  • ATRAP triggers the marked apoptosis of VSMCs in balloon-injuried carotid arteries and depresses neointimal formation.

  • ATRAP induces VSMCs apoptosis through the influence of the PI3K/Akt signaling pathway.

Abstract

Intimal hyperplasia is the main cause of restenosis after carotid artery injury, and the underlying mechanism involves the proliferation and migration of vascular smooth muscle cells (VSMCs). Angiotensin II Type 1 Receptor-Associated Protein (ATRAP) has been reported to withstand intimal hyperplasia by inhibiting VSMCs proliferation and migration; however, whether the beneficial effect of ATRAP associates with VSMCs apoptosis remains unclarified. We demonstrated that the adenoviral-mediated overexpression of ATRAP induced VSMC apoptosis, alleviating the balloon injury-induced neointima formation in rats. Under the condition of Angiotensin-II stimulation, ATRAP overexpression induced the apoptosis of rat VSMCs by depressing the PI3K-Akt signaling; whereas up-regulation of Akt by PTEN inhibitor abolished the apoptotic death. Thus, ATRAP regulates carotid intimal hyperplasia through controlling the PI3K-Akt signal-mediated VSMCs apoptosis.

Introduction

Atherosclerotic carotid artery stenosis accounts for 7–10% of transient ischemic attack and stroke [1]. Current clinical treatment of carotid stenosis includes percutaneous transluminal balloon angioplasty or carotid artery stenting (CAS) and carotid endarterectomy (CEA), supplemented by multifaceted medical therapy. However, severe restenosis or occlusion of the carotid artery was often observed after the revascularization with CAS and CEA, which might restrict the long-term efficacy of endovascular treatment and endarterectomy for preventing stenosis. Postoperative restenosis is an important problem looming over clinicians [[2], [3], [4]].

Primary pathological change of post-angioplasty restenosis is neointimal formation, which involves the proliferation, the migration toward the intima and the matrix accumulation of vascular smooth muscle cells (VSMCs) induced by the increased growth factors and the loss of growth-inhibitory factors [5,6]. The increase of Angiotensin II (Ang-II) in the injuried arteries contributes to endothelial dysfunction via vascular NADPH oxidase activation, production of reactive oxygen species and nitric oxide (NO) reduction. Moreover, Ang-II promotes VSMCs proliferation and migration by activating platelet-derived growth factors (PDGF), basic fibroblast growth factors (bFGF), transforming growth factor-β (TGF-β), and matrix metalloproteinases (MMPs) [7].

Angiotensin II Type 1 Receptor-Associated Protein(ATRAP) interacts specifically with the carboxyl-terminal cytoplasmic domain of Ang-II type 1 receptor(AT1R) but not with those of Ang-II type 2(AT2), M3 muscarinergic acetylcholine, B2 bradykinin, endothelin B, and β2 adrenergic receptors [8,9]. In vitro, overexpression of ATRAP induces the desensitization and/or internalization of AT1 receptor and markedly inhibits the phosphorylation of signal transducers and activators of transcription 3 (STAT3), Akt and extracellular signal–regulated kinase (ERK) [10,11]. ATRAP also attenuates the Ang-II-mediated increases in c-fos gene expression and TGF-β production, decreasing the proliferative response in vascular smooth muscle cells [12]. In vivo, the transgenesis of ATRAP inhibits neointimal formation after cuff-mediated vascular injury in mice, which is attributable to the reductions in cell proliferation, NADPH oxidase activity and p22phox [13]. These reports suggest that ATRAP as a negative regulator of AT1 receptor plays an inhibitory role in VSMCs proliferation both in vitro and in vivo, and thus in neointimal formation.

The dynamic balance of cell proliferation and cell death of VSMCs is important for vessel homeostasis in response to various external stress stimuli. A fundamental strategy for the treatment of neointimal formation is to inhibit VSMC proliferation and/or to promote VSMCs apoptosis [14]. Emerging evidence demonstrates that captopril inhibits neointimal formation by triggering the apoptotic death of neointimal VSMCs in the rat carotid artery balloon injury model [15]. However, the effect of ATRAP on VSMC apoptosis and the underlying mechanism remain largely elusive. Here we demonstrated that overexpression of ATRAP promotes VSMC apoptosis by inhibiting the phosphoinositide 3-kinase (PI3K)-Akt (PI3K-Akt) signaling pathway to prevent intimal dysplasia disorders. This finding suggests that ATRAP as a negative regulator of the PI3K-Akt axis, tilts the balance toward apoptosis of VSMCs.

Section snippets

Agents

Angiotensin-II and PTEN inhibitor potassium bisperoxo (bipyridine) oxovanadate (bpv, phen) were purchased from Med Chem Express (USA). Rabbit monoclonal antibodies against FLAG (DYKDDDDK), caspase-8, caspase-3, cleaved-caspase-3, bax, Akt and phospho-Akt (Ser473) and total Akt (?) were purchased from Cell Signaling Technology, Inc (Germany). Mouse monoclonal antibodies against bcl-2 and GAPDH were purchased from Santa Cruz Biotechnology (USA) and Invitrogen (USA), respectively. Alexa Fluor®

Adenovirus-mediated gene transfer of ATRAP alleviates balloon injury-induced neointimal formation

A previous study indicates that the protein and mRNA levels of ATRAP were transiently decreased in the media at 7 days after cuff placement, and the decreases were recovered at 14 days after injury. Neointimal formation in the injured femoral artery was attenuated in ATRAP-transgenic mice [13]. To clarify the roles of ATRAP in vascular remodeling, we adopted Adv.ATRAP or Adv.GFP to incubate the injuried artery and examined the morphometric changes of the injured arteries at 3, 7, and 14 days

Discuss

Angiotensin II has been recognized as a regulator of cell growth and apoptosis contributing to the pathophysiological processes of cardiovascular and renal disease. Previous study showed that the up-regulated AT1 receptor in the rat balloon-injured carotid artery contributed to neointimal formation and resultant restenosis [20].Similarly, the PI3K-Akt signaling activated by Angiotensin II or arterial injury also contributes to VSMC hyperplasia and neointimal formation [19,21,22]. It is accepted

Conflicts of interest

The authors have declared that no competing interest exists.

Acknowledgments

This work was supported by grants from the National Natural Science Foundation of China(No.81270393). We thank Dr.Li Jun and Shi Dan(Dongfang Hospital of Tongji University) for their invaluable suggestions on technical issues concerning experimental improvement.

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