Role of atrial endothelial cells in the development of atrial fibrosis and fibrillation in response to pressure overload

doi:10.1016/j.carpath.2016.12.001

Cardiovascular Pathology

Volume 27, March–April 2017, Pages 18-25

https://doi.org/10.1016/j.carpath.2016.12.001 Get rights and content

Highlights

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The left atrial (LA) endothelium was morphologically changed shortly after pressure overload.
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Pressure overload increased macrophage infiltration into LA tissue through endothelial gaps.
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Pressure overload enhanced the expression of adhesion molecules in the LA endothelium.
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Pressure overload facilitated LA fibrosis and increased the inducibility of atrial fibrillation.

Abstract

Background

Monocyte chemoattractant protein-1 (MCP-1)-mediated inflammatory mechanisms have been shown to play a crucial role in atrial fibrosis induced by pressure overload. In the present study, we investigated whether left atrial endothelial cells would quickly respond structurally and functionally to pressure overload to trigger atrial fibrosis and fibrillation.

Methods and results

Six-week-old male Sprague–Dawley rats underwent suprarenal abdominal aortic constriction (AAC) or a sham operation. By day 3 after surgery, macrophages were observed to infiltrate into the endocardium. The expression of MCP-1 and E-selectin in atrial endothelium and the expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and ED1 in left atrial tissue were enhanced. Atrial endothelial cells were irregularly hypertrophied with the disarrangement of lines of cells by scanning electron microscopy. Various-sized gap formations appeared along the border in atrial endothelial cells, and several macrophages were located just in the endothelial gap. Along with the development of heterogeneous interstitial fibrosis, interatrial conduction time was prolonged and the inducibility of atrial fibrillation by programmed extrastimuli was increased in the AAC rats compared to the sham-operated rats.

Conclusions

Atrial endothelium responds rapidly to pressure overload by expressing adhesion molecules and MCP-1, which induce macrophage infiltration into the atrial tissues. These processes could be an initial step in the development of atrial remodeling for atrial fibrillation.

Introduction

Leukocyte adhesion to the endothelium is a first step in atherosclerosis progression. Leukocyte migration into the intima is mediated via monocyte chemoattractant protein-1 (MCP-1), a key chemokine that recruits monocytes to atherosclerotic lesions [1], [2]. Endothelial function is impaired by oxidized low-density lipoprotein and the turbulent blood flow in arterial branching areas, which increases endothelial cell expression of adhesion molecules, such as E-selectin, intercellular adhesion molecule (ICAM-1), and vascular cell adhesion molecule (VCAM-1) [3]. Hence, endothelium works as a key moderator in the progression of atherosclerosis.

Increasing evidence indicates that left atrial (LA) inflammation and interstitial fibrosis contribute to the pathogenesis of atrial fibrillation (AF) [4], [5]. We previously reported that LA fibrosis and AF vulnerability were increased 28 days after suprarenal abdominal aortic constriction (AAC) in rats [6]. Similar to the progression of atherosclerosis, MCP-1, ICAM-1, VCAM-1, and E-selectin expressions were significantly increased and macrophages were recruited across the atrial endocardium in AF patients [7], [8], [9]. These results may indicate the possible pathologic similarity between AF and atherosclerosis, and dysfunction of the endothelium may be a critical facilitator in both pathogenesis. Chronic exposure to pressure overload overwhelms the defense mechanisms of endothelial cells and compromises its functional integrity. Endothelial dysfunction exhibits proinflammatory, pro-oxidant, proliferative, and proadhesion features, which will facilitate AF substrate formation [10]. Several studies have suggested that inflammation exerts its remodeling effects through reactive oxygen species (ROS) [11]. ROS can activate matrix metalloproteinases, resulting in an imbalance between accumulation and breakdown of extracellular matrix, enhancing LA fibrosis [12]. In fact, inflammatory cells have been demonstrated to infiltrate atrial tissue [13]. In the present study, we investigated the early morphological changes in the atrial endothelium in response to pressure overload and whether the changes in endothelium may induce inflammation and fibrosis in the LA which may lead to AF.

Section snippets

Materials and methods

All experimental procedures were conducted in accordance with the guidelines of the Physiological Society of Oita University for the care and use of laboratory animals, which follow the guidelines established by the US National Institutes of Health.

Physiological changes induced by AAC

The physiological and hemodynamic characteristics are summarized in Table 2. The LV systolic blood pressure, heart weight, and heart-to-body weight ratio measured on the third day after the procedure were significantly increased in the AAC rats (n=20) compared with those in the sham-operated rats (n=20). The echocardiographic findings are summarized in Table 3 (n=10 for each group). Pressure overload resulted in a significant increase in interventricular septum wall thickness and LV posterior

Discussion

The core findings of the present study are as follows: (a) the LA endothelium exhibited morphological changes shortly after the AAC procedure: LA was significantly dilated, and LA endothelial cells were hypertrophied with small gaps along the cell border; (b) AAC increased macrophage infiltration into LA tissue through endothelial gaps; (c) AAC enhanced the expression of MCP-1, E-selectin, ICAM-1, and VCAM-1 in the LA, and MCP-1 and E-selectin were expressed in the LA endothelium; and (d) AAC

Conclusion

In conclusion, the results presented here suggest that LA endothelial cells respond quickly to pressure overload structurally and functionally to express MCP-1 and adhesion molecules. These molecules may be associated with the recruitment of macrophages to endothelial surface and their possible transmigration into the LA subendothelial tissue layer via the endothelial gap. Hence, initial profibrotic process of atrium in response to pressure overload appears quite similar to that of

Acknowledgments

The authors acknowledge the help of the following in carrying out the electron microscopic studies: Hiroaki Kawazato and Aiko Yasuda, Division of Biomolecular Medicine and Medical Imaging, Institute of Scientific Research, Faculty of Medicine, Oita University, Oita, Japan.

References (27)

T.T. Issac et al.
Role of inflammation in initiation and perpetuation of atrial fibrillation
J Am Coll Cardiol
(2007)
O. Kume et al.
Pioglitazone attenuates inflammatory atrial fibrosis and vulnerability to atrial fibrillation induced by pressure overload in rats
Heart Rhythm
(2011)
B. Freestone et al.
Soluble E-selectin, von Willebrand factor, soluble thrombomodulin, and total body nitrate/nitrite product as indices of endothelial damage/dysfunction in paroxysmal, persistent, and permanent atrial fibrillation
Chest
(2007)
J. Li et al.
Role of inflammation and oxidative stress in atrial fibrillation
Heart Rhythm
(2010)
G. Casaclang-Verzosa et al.
Structural and functional remodeling of the left atrium: clinical and therapeutic implications for atrial fibrillation
J Am Coll Cardiol
(2008)
J. Kotur-Stevuljevic et al.
Correlation of oxidative stress parameters and inflammatory markers in coronary artery disease patients
Clin Biochem
(2007)
C.A. Souders et al.
Pressure overload induces early morphological changes in the heart
Am J Pathol
(2012)
I. Nagata et al.
Experimentally induced cerebral aneurysms in rats: VII. Scanning electron microscope study
Surg Neurol
(1981)
N.S. Greenhill et al.
Scanning electron-microscopic study of the inner surface of experimental aneurysms in rabbits
Atherosclerosis
(1982)
O.E. Zaikina et al.
Analysis of injury to the endothelium of rabbit aorta and carotid artery during experimental atherosclerosis
Atherosclerosis
(1982)

I.F. Charo et al.

Chemokines in the pathogenesis of vascular disease

Circ Res

(2004)

S. Inoue et al.

Anti-monocyte chemoattractant protein-1 gene therapy limits progression and destabilization of established atherosclerosis in apolipoprotein E-knockout mice

Circulation

(2002)

G.K. Hansson et al.

The immune system in atherosclerosis

Nat Immunol

(2011)

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: Conflict of interest: none.

: This study was supported by Grants-in-Aid for Scientific Research (C) 26462758 (Y. Teshima) and 15K01720 (N. Takahashi) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

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Original ArticleRole of atrial endothelial cells in the development of atrial fibrosis and fibrillation in response to pressure overload