Angiotensin II Increases Macrophage-mediated Modification of Low Density Lipoprotein via a Lipoxygenase-dependent Pathway

doi:10.1074/jbc.272.34.21609

Angiotensin II Increases Macrophage-mediated Modification of Low Density Lipoprotein via a Lipoxygenase-dependent Pathway*

From the Department of Medicine, University of California, San Diego, La Jolla, California 92093-0682

Abstract

The molecular and cellular mechanisms by which hypertension enhances atherosclerosis are poorly understood. Angiotensin II (Ang II) has been implicated in the regulation of cellular lipoxygenases (LO), which are thought to play a role in atherogenesis by inducing oxidative modification of low density lipoprotein (LDL). We sought to test the hypothesis that Ang II would stimulate murine macrophage LO activity (which has both 12- and 15-LO activity). Competitive binding studies revealed the presence of Ang II AT₁ receptors on mouse peritoneal macrophages (MPM) and J-774 cells, but not on the RAW cell line. Valsartan, a specific AT₁ receptor antagonist inhibited Ang II binding, whereas PD 123319, an AT₂ receptor antagonist did not. Incubation of MPM or J-774 cells with Ang II (10 pm to 1 μm) for 24 h led to a 2.5–3.5-fold increase in LO activity, measured as generated 13-HODE or 12(S)-HETE. This stimulation was inhibited by valsartan, but not by PD 123319. In contrast, Ang II did not stimulate LO activity in RAW macrophages. Semiquantitative reverse transcriptase-polymerase chain reaction showed a 2–3-fold increase in LO mRNA in MPM, but not in RAW cells after treatment with Ang II. Ang II also induced an increase in 12-LO protein. In addition, pretreatment of J-774 cells with Ang II increased in a dose-dependent manner the ability of the cells to modify LDL, resulting in greater chemotactic activity for monocytes, typical of minimally modified LDL. This stimulation was inhibited by AT₁ receptor blockade.

In summary, these data suggest that Ang II increases macrophage LO activity via AT₁ receptor-mediated mechanisms and this further increases the ability of the cells to generate minimally oxidized LDL. These studies provide a link between hypertension and the associated increased atherosclerosis observed in hypertensive patients.

Footnotes

↵* This work was supported in part by National Institutes of Health, National Heart, Lung, and Blood Institute Grant 14197 (SCOR, La Jolla, CA).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ Supported by the Swiss National Science Foundation, Roche Research Foundation, Theodor Engelmann-Stiftung, and the Schweizerische Stiftung für medizinisch-biologische Stipendien.
↵§ To whom correspondence should be addressed: Dept. of Medicine, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0682. Tel.: 619-534-4347; Fax: 619-534-2005; E-mail:jwitztum{at}ucsd.edu.
↵1 The abbreviations used are: LDL, low density lipoprotein; MPM, mouse peritoneal macrophage(s); Ang II, angiotensin II; RAS, renin angiotensin system; BSA, bovine serum albumin; FMLP,N-formyl-l-methionyl-l-leucyl-l-phenylalanine; ETYA, eicosatetraynoic acid; 12-LO, 12-lipoxygenase; 15-LO, 15-lipoxygenase; 13-HODE, 13(S)-hydroxyoctadecadienoic acid; 12(S)-HETE, 12-hydroxyeicosatretraenoic acid; TBARS, thiobarbituric acid-reactive substances; RT-PCR, reverse transcriptase-polymerase chain reaction; PAGE, polyacrylamide gel electrophoresis; HPLC, high performance liquid chromatography; GAPDH, glyceraldehyde-3-phosphate dehydrogenase.
- Received January 16, 1997.
- Revision received June 5, 1997.