Macrophage-specific expression of group IIA sPLA2 results in accelerated atherogenesis by increasing oxidative stress

Uwe J.F Tietge,Domenico Pratico,Tao Ding,Colin D Funk,Reeni B Hildebrand,Theo Van Berkel,Miranda Van Eck

doi:10.1194/jlr.m400469-jlr200

Abstract

Group IIA secretory phospholipase A2 (sPLA2) is an acute-phase protein mediating decreased plasma HDL cholesterol and increased atherosclerosis. This study investigated the impact of macrophage-specific sPLA2 overexpression on lipoprotein metabolism and atherogenesis. Macrophages from sPLA2 transgenic mice have 2.5 times increased rates of LDL oxidation (thiobarbituric acid-reactive substances formation) in vitro (59 +/- 5 vs. 24 +/- 4 nmol malondialdehyde/mg protein; P < 0.001) dependent on functional 12/15-lipoxygenase (12/15-LO). Low density lipoprotein receptor-deficient (LDLR-/-) mice were transplanted with bone marrow from either sPLA2 transgenic mice (sPLA2--> LDLR-/-; n = 19) or wild-type C57BL/6 littermates (C57 BL/6-->LDLR-/-; n = 19) and maintained for 8 weeks on chow and then for 9 weeks on a Western-type diet. Plasma sPLA2 activity and plasma lipoprotein profiles were not significantly different between sPLA2-->LDLR-/- and C57BL/6-->LDLR-/- mice. Aortic root atherosclerosis was increased by 57% in sPLA2-->LDLR-/- mice compared with C57BL/6-->LDLR-/- controls (P < 0.05). Foam cell formation in vitro and in vivo was increased significantly. Urinary, plasma, and aortic levels of the isoprostane 8,12-iso-iPF2alpha-VI and aortic levels of 12/15-LO reaction products were each significantly higher (P < 0.001) in sPLA2-->LDLR-/- compared with C57BL/6-->LDLR-/- mice, indicating significantly increased in vivo oxidative stress in sPLA2--> LDLR-/-. These data demonstrate that macrophage-specific overexpression of human sPLA2 increases atherogenesis by directly modulating foam cell formation and in vivo oxidative stress without any effect on systemic sPLA2 activity and lipoprotein metabolism.

Highlights

Consistent with our previous observation that the human secretory phospholipase A2 (sPLA2) transgene is regulatable by inflammatory stimuli in these mice [18, 26], a strong signal was detected for the sPLA2 mRNA by RT-PCR in elicited peritoneal macrophages from sPLA2 transgenic mice, whereas human sPLA2 mRNA was absent in control C57BL/6 mice (Fig. 1A)
Relative data are given as means Ϯ SEM, with the value observed in control macrophages without PD146176 set to 1. * Significantly different from control values (P Ͻ 0.05). # Significantly different from the values observed in the respective experimental groups without the use of PD146176 (P Ͻ 0.05)
The results of this study demonstrate that macrophagespecific overexpression of human sPLA2 accelerates early atherogenesis in LDLRϪ/Ϫ mice by increasing foam cell formation as well as vascular oxidative stress but without affecting plasma cholesterol levels and plasma sPLA2 activity

Summary

Introduction

As determined by Western blot analysis, macrophages from sPLA2 transgenic mice had increased 12/15-LO protein levels compared with wild-type controls (Fig. 3A). SPLA2-overexpressing macrophages displayed a significantly higher cholesteryl ester accumulation compared with controls (9.2 Ϯ 0.9 vs 6.6 Ϯ 0.8 ␮g/mg cell protein, respectively; P Ͻ 0.05) (Fig. 4), indicating increased foam cell formation independent of the effects on the oxidation status of LDL.

Results

Conclusion