Open AccessOsteoprotegerin Causes Apoptosis of Endothelial Progenitor Cells by Induction of Oxidative Stress
Author(s) -
Kim JiYoung,
Park YuneJung,
Kim KiJo,
Choi JinJung,
Kim WanUk,
Cho ChulSoo
Publication year - 2013
Publication title -
arthritis & rheumatism
Language(s) - English
Resource type - Journals
eISSN - 1529-0131
pISSN - 0004-3591
DOI - 10.1002/art.37997
Subject(s) - p38 mitogen activated protein kinases , mapk/erk pathway , apoptosis , reactive oxygen species , progenitor cell , oxidative stress , osteoprotegerin , flow cytometry , chemistry , kinase , microbiology and biotechnology , medicine , biology , stem cell , biochemistry , receptor , activator (genetics)
Objective Elevated serum osteoprotegerin (OPG) levels represent an independent risk factor for atherosclerotic disease, although the underlying mechanism is not clear. The aim of this study was to investigate the association of serum OPG levels and circulating endothelial progenitor cell (EPC) numbers, and to explore the effect of OPG on EPC apoptosis and its underlying mechanisms. Methods Flow cytometry was used to enumerate EPCs in the peripheral blood of 91 patients with systemic lupus erythematosus (SLE). Cultured EPCs, isolated from peripheral blood, were challenged with OPG, and apoptosis was evaluated by TUNEL staining. Expression of apoptosis‐related proteins was measured by real‐time quantitative polymerase chain reaction (qPCR) and Western blotting. Reactive oxygen species (ROS) were detected by flow cytometry, and the expression of NADPH oxidase (NOX) and MAP kinases (MAPK) was measured by qPCR and Western blotting. Results The serum OPG level was independently associated with reduced numbers of EPCs in patients with SLE. In vitro treatment with OPG significantly induced apoptosis of EPCs; this effect was mediated by syndecan 4. OPG‐induced apoptosis was abolished by the ROS scavenger N ‐acetylcysteine and the NOX inhibitor diphenyleniodonium. OPG increased ROS production through activation of NOX‐2 and NOX‐4 and triggered phosphorylation of ERK‐1/2 and p38 MAPK. Quenching of ROS by knockdown of NOX‐2 or NOX‐4 transcripts inhibited phosphorylation of ERK‐1/2 and p38 MAPK. Moreover, inhibitors of ERK‐1/2 and p38 MAPK decreased ROS production and subsequent EPC apoptosis, indicating a feed‐forward loop between NOX and MAPK to amplify ROS production related to apoptosis. Conclusion Elevated OPG levels increase apoptosis of EPCs by induction of oxidative stress.