Elsevier

Atherosclerosis

Volume 205, Issue 2, August 2009, Pages 376-384
Atherosclerosis

Telmisartan induces proliferation of human endothelial progenitor cells via PPARγ-dependent PI3K/Akt pathway

https://doi.org/10.1016/j.atherosclerosis.2008.12.036Get rights and content

Abstract

Objective

Although recent clinical trials have suggested that angiotensin II type 1 receptor blockers (ARBs) reduced cardiovascular events, the precise mechanisms involved are still unknown. Telmisartan, an ARB, has recently been identified as a ligand of peroxisome proliferator-activated receptor-gamma (PPARγ). On the other hand, since endothelial progenitor cells (EPCs) are thought to play a critical role in ischemic diseases, we investigated effects of telmisartan on proliferation of EPCs.

Methods and results

Human peripheral blood mononuclear cells were isolated from healthy volunteers, and cultured on fibronectin-coated dishes in the presence or absence of telmisartan. Four days after starting culture, adherent cells were collected, and equal numbers of cells were reseeded into methylcellulose medium with or without telmisartan. In the presence of telmisartan, numbers of colonies increased in a dose-dependent manner. DiI-AcLDL uptake and lectin and CD31, CD34 staining revealed that these colonies were EPCs. Increase in colony number by treatment with telmisartan was absolutely inhibited when cultured with a specific inhibitor of PPARγ. In addition, we observed that specific inhibitors of phosphoinositide-3 kinase (PI3K) abolished telmisartan-stimulated increase of monocytic EPC-like cells and telmisartan induced phosphorylation of Akt. Furthermore, mRNA expression of p21 was downregulated in a dose dependent manner, suggesting that growth inductive effects of telmisartan might be regulated by the PI3K/Akt and p21 signaling pathway.

Conclusions

These findings suggest that telmisartan might contribute to endothelial integrity and vasculogenesis in ischemic regions by increasing numbers of EPCs.

Introduction

Promotion of neovascularization aims to rescue ischemic tissues. Although angiogenesis, a process involving proliferation and migration of preexisting endothelial cells was thought to be the main mechanism of postnatal neovascularization, recent evidence shows that bone marrow-derived circulating endothelial progenitor cells (EPCs) partly contribute to this mechanism [1]. Injections of bone marrow-derived EPCs to ischemic tissues have been reported to result in new blood vessel formation, and to protect tissues from ischemic damages [2], [3]. In addition to animal model experiments, clinical trials demonstrate that intracoronary injection of EPCs improves left ventricular ejection fraction and end systolic volumes [4]. Numbers of atherosclerotic risk factors have been reported to correlate with reduced numbers of circulating EPCs [5]. Furthermore, increases in numbers and colonies of EPCs have been reported to predict beneficial occurrence of cardiovascular events and death from cardiovascular causes [6], [7]. Therefore, stimulation of proliferation of circulating EPCs might be a useful novel preventive and therapeutic strategy for the treatment of ischemic cardiovascular diseases.

Angiotensin II receptor blockers (ARBs) are widely used for the treatment of hypertension, ischemic heart disease and heart failure. ARBs have been reported to have protective effects on the cardiovascular system beyond blood pressure lowering effect in many clinical trials [8]. Telmisartan, one of the ARBs, has recently been identified as a ligand of peroxisome proliferator-activated receptor-gamma (PPARγ) [9], [10]. PPARs are transcription factors belonging to the nuclear receptor superfamily that heterodimerizing with the retinoid X receptor and bind to PPAR responsive elements in target gene promoters [11]. Thiazolidinediones (TZDs) have been proposed to ameliorate insulin resistance by binding to and activating PPARγ in adipose tissue, thereby promoting adipose differentiation and increasing the number of small adipocytes that are more sensitive to insulin. Besides the effects on insulin resistance, TZDs are known to be capable of reducing vascular inflammation [12], [13]. TZDs have recently been shown to promote new blood vessel formation in a cerebral ischemic model [14]. Furthermore, recent reports showed that pioglitazone and rosiglitazone, included in TZDs, increased the number of EPCs with unknown mechanisms [15], [16]. Telmisartan induces adiponectin expression via PPARγ activation [17], and adiponectin has been reported to induce angiogenesis [18]. But the direct evidences of telmisartan on angiogenesis have not been reported. To elucidate the mechanisms involved in neovascularization by telmisartan, we investigated effects of telmisartan on EPCs, and the underlying signaling pathway.

In this study, we showed that telmisartan induced proliferation of human peripheral blood-derived EPCs in vitro via the phosphoinositide-3 kinase/Akt (PI3K/Akt) pathway, and telmisartan affected cellular senescence of EPCs.

Section snippets

Reagents

The following reagents and antibodies were used: valsartan (The United States Pharmacopeia, Rockville, MD), GW9662 (Sigma Aldrich, St. Louis. MO), Ly294002 (CALBIOCHEM, San Diego, CA), human VEGF (R&D systems, Minneapolis, MN), mouse monoclonal antibodies against human vascular endothelium (VE)-cadherin (Beckman coulter, France), mouse monoclonal anti-human CD14 antibody (CHEMICON, Australia), mouse monoclonal anti-human CD31 (PECAM-1) antibody (R&D systems, Minneapolis, MN), mouse monoclonal

Telmisartan induces the proliferation of monocytic EPC-like cells and EPCs

First, we isolated the peripheral blood mononuclear cells from healthy human volunteers and cultured these cells on the fibronectin-coated dishes in endothelial growth medium. Four days after starting culture, adherent and spindle-shaped cells were recognized. Almost all of these adherent cells were positive for DiI-AcLDL uptake, FITC-conjugated UEA-1 lectin binding (Fig. 1a). To further characterize these adherent cells, we compared the expression of CD14 and CD45 between adherent cells and

Discussion

In this paper, we demonstrated, for the first time, that telmisartan induced proliferation of human EPCs via PPARγ-dependent PI3K/Akt signaling pathway in vitro.

Recently, telmisartan has been identified as a partial agonist of PPARγ. The other clinically approved ARBs appear to have relatively little or no effect on PPARγ activity, with the exception of irbesartan and a metabolite of losartan, both of which are much less potent activators of PPARγ than telmisartan [9], [26]. So far, it has been

Conflict of interest

The authors declare that they have no competing financial interests.

Acknowledgements

This study was supported in part by a Grant-in-Aid for Scientific Research, Developmental Scientific Research, and Scientific Research from the Ministry of Education, Science, Sports, and Culture (to K.M.).

References (56)

  • N. Gao et al.

    Role of PI3K/AKT/mTOR signaling in the cell cycle progression of human prostate cancer

    Biochem Biophys Res Commun

    (2003)
  • A. Rosso et al.

    p53 Mediates the accelerated onset of senescence of endothelial progenitor cells in diabetes

    J Biol Chem

    (2006)
  • D.A. Ingram et al.

    Unresolved questions, changing definitions, and novel paradigms for defining endothelial progenitor cells

    Blood

    (2005)
  • J. Case et al.

    Human CD34+ AC133+ VEGFR-2+ cells are not endothelial progenitor cells but distinct, primitive hematopoietic progenitors

    Exp Hematol

    (2007)
  • T. Asahara et al.

    Isolation of putative progenitor endothelial cells for angiogenesis

    Science

    (1997)
  • A. Kawamoto et al.

    Therapeutic potential of ex vivo expanded endothelial progenitor cells for myocardial ischemia

    Circulation

    (2001)
  • C. Kalka et al.

    Transplantation of ex vivo expanded endothelial progenitor cells for therapeutic neovascularization

    Proc Natl Acad Sci USA

    (2000)
  • M. Vasa et al.

    Number and migratory activity of circulating endothelial progenitor cells inversely correlate with risk factors for coronary artery disease

    Circ Res

    (2001)
  • J.M. Hill et al.

    Circulating endothelial progenitor cells, vascular function, and cardiovascular risk

    N Engl J Med

    (2003)
  • N. Werner et al.

    Circulating endothelial progenitor cells and cardiovascular outcomes

    N Engl J Med

    (2005)
  • S.C. Benson et al.

    Identification of telmisartan as a unique angiotensin II receptor antagonist with selective PPARgamma-modulating activity

    Hypertension

    (2004)
  • T.W. Kurtz

    Treating the metabolic syndrome: telmisartan as a peroxisome proliferator-activated receptor-gamma activator

    Acta Diabetol

    (2005)
  • M. Li et al.

    Peroxisome proliferator-activated receptor gamma-dependent repression of the inducible nitric oxide synthase gene

    Mol Cell Biol

    (2000)
  • C. Jiang et al.

    PPAR-gamma agonists inhibit production of monocyte inflammatory cytokines

    Nature

    (1998)
  • R. Clasen et al.

    PPARgamma-activating angiotensin type-1 receptor blockers induce adiponectin

    Hypertension

    (2005)
  • K. Matsuura et al.

    Cardiomyocytes fuse with surrounding noncardiomyocytes and reenter the cell cycle

    J Cell Biol

    (2004)
  • B. Assmus et al.

    HMG-CoA reductase inhibitors reduce senescence and increase proliferation of endothelial progenitor cells via regulation of cell cycle regulatory genes

    Circ Res

    (2003)
  • T. Minamino et al.

    Endothelial cell senescence in human atherosclerosis: role of telomere in endothelial dysfunction

    Circulation

    (2002)
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