Boyle, Joseph J; Johns, Michael; Kampfer, Theresa; Nguyen, Aivi T; Game, Laurence; Schaer, Dominik J; Mason, Justin C; Haskard, Dorian O (2012). Activating transcription factor 1 directs Mhem atheroprotective macrophages through coordinated iron handling and foam cell protection. Circulation Research, 110(1):20-33.
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Intraplaque hemorrhage (IPH) drives atherosclerosis through the dual metabolic stresses of cholesterol-enriched erythrocyte membranes and pro-oxidant heme/iron. When clearing tissue hemorrhage, macrophages are typically seen storing either iron or lipid. We have recently defined hemorrhage-associated macrophages (HA-mac) as a plaque macrophage population that responds adaptively to IPH.
This study aimed to define the key transcription factor(s) involved in HO-1 induction by heme.
METHODS AND RESULTS:
To address this question, we used microarray analysis and transfection with siRNA and plasmids. To maintain physiological relevance, we focused on human blood-derived monocytes. We found that heme stimulates monocytes through induction of activating transcription factor 1 (ATF-1). ATF-1 coinduces heme oxygenase-1 (HO-1) and Liver X receptor beta (LXR-β). Heme-induced HO-1 and LXR-β were suppressed by knockdown of ATF-1, and HO-1 and LXR-β were induced by ATF-1 transfection. ATF-1 required phosphorylation for full functional activity. Expression of LXR-β in turn led to induction of other genes central to cholesterol efflux, such as LXR-α and ABCA1. This heme-directed state was distinct from known macrophage states (M1, M2, Mox) and, following the same format, we have designated them Mhem.
These results show that ATF-1 mediates HO-1 induction by heme and drives macrophage adaptation to intraplaque hemorrhage. Our definition of an ATF-1-mediated pathway for linked protection from foam cell formation and oxidant stress may have therapeutic potential.
|Item Type:||Journal Article, refereed, original work|
|Communities & Collections:||04 Faculty of Medicine > University Hospital Zurich > Clinic and Policlinic for Internal Medicine|
|DDC:||610 Medicine & health|
|Deposited On:||03 Apr 2012 09:34|
|Last Modified:||23 Nov 2012 15:42|
|Publisher:||Lippincott Wiliams & Wilkins|
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