Published Online
on August 20, 2007

A more recent version of this article appeared on September 11, 2007

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Submitted on December 10, 2006
Accepted on July 6, 2007

Increased Endoplasmic Reticulum Stress in Atherosclerotic Plaques Associated With Acute Coronary Syndrome

Masafumi Myoishi MD, Hiroyuki Hao MD, PhD, Tetsuo Minamino MD, PhD, Kouki Watanabe MD, PhD, Kensaku Nishihira MD, PhD, Kinta Hatakeyama MD, PhD, Yujiro Asada MD, PhD, Ken-ichiro Okada MD, PhD, Hatsue Ishibashi-Ueda MD, PhD, Giulio Gabbiani MD, PhD, Marie-Luce Bochaton-Piallat PhD, Naoki Mochizuki MD, PhD, and Masafumi Kitakaze MD, PhD^*

From the Departments of Cardiovascular Medicine (M.M., M.K.), Structural Analysis (M.M., N.M.), and Pathology (H.H., H.I.-U.), National Cardiovascular Center, Suita, Osaka, Japan; Department of Surgical Pathology (H.H.), Hyogo College of Medicine, Nishinomiya, Hyogo, Japan; Departments of Bioregulatory Medicine (M.M.) and Cardiovascular Medicine (T.M., K.-i.O.), Osaka University Graduate School of Medicine, Suita, Osaka, Japan; Division of Cardiology (K.W.), Uwajima City Hospital, Uwajima, Ehime, Japan; Department of Pathology (K.N., K.H., Y.A.), Faculty of Medicine, University of Miyazaki, Miyazaki, Japan; and Department of Pathology and Immunology (G.G., M.-L.B.-P.), University of Geneva–CMU, Geneva, Switzerland.

^* To whom correspondence should be addressed. E-mail: kitakaze{at}zf6.so-net.ne.jp.

Background—The endoplasmic reticulum (ER) responds to various stresses by upregulation of ER chaperones, but prolonged ER stress eventually causes apoptosis. Although apoptosis is considered to be essential for the progression and rupture of atherosclerotic plaques, the influence of ER stress and apoptosis on rupture of unstable coronary plaques remains unclear.

Methods and Results—Coronary artery segments were obtained at autopsy from 71 patients, and atherectomy specimens were obtained from 40 patients. Smooth muscle cells and macrophages in the fibrous caps of thin-cap atheroma and ruptured plaques, but not in the fibrous caps of thick-cap atheroma and fibrous plaques, showed a marked increase of ER chaperone expression and apoptotic cells. ER chaperones also showed higher expression in atherectomy specimens from patients with unstable angina pectoris than in specimens from those with stable angina. Expression of 7-ketocholesterol was increased in the fibrous caps of thin-cap atheroma compared with thick-cap atheroma. Treatment of cultured coronary artery smooth muscle cells or THP-1 cells with 7-ketocholesterol induced upregulation of ER chaperones and apoptosis, whereas these changes were prevented by antioxidants. We also investigated possible signaling pathways for ER-initiated apoptosis and found that the CHOP (a transcription factor induced by ER stress)-dependent pathway was activated in unstable plaques. In addition, knockdown of CHOP expression by small interfering RNA decreased ER stress-dependent death of cultured coronary artery smooth muscle cells and THP-1 cells.

Conclusions—Increased ER stress occurs in unstable plaques. Our findings suggest that ER stress-induced apoptosis of smooth muscle cells and macrophages may contribute to plaque vulnerability.

Key words: apoptosis • plaque • myocardial infarction • endoplasmic reticulum

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