5'-AMP-activated protein kinase-activating transcription factor 1 cascade modulates human monocyte-derived macrophages to atheroprotective functions in response to heme or metformin.
OBJECTIVE
Intraplaque hemorrhage (IPH) is an important driver of the progression of atherosclerotic plaques. Recently, we characterized Mhem as a novel macrophage phenotype that limits the atherogenicity of IPH. Mhem are directed by activating transcription factor 1 (ATF1), which is activated by phosphorylation. A better understanding of the counteratherogenic ATF1-Mhem pathway may facilitate antiatherosclerotic therapies.


RESULTS
We tested the hypothesis that heme in pathologically relevant concentrations activates the ATF1-Mhem pathway via 5'-AMP-activated protein kinase (AMPK) in primary human monocyte-derived macrophages and mouse bone marrow macrophages. We found that heme (10 μmol/L) activates AMPK, and downstream ATF1-mediated coinduction of heme oxygenase and liver X receptor that characterize Mhem. Heme increased macrophage phospho-AMPK, phospho-ATF1, and its target genes, and these effects were inhibited by the AMPK antagonist dorsomorphin, or by AMPK-knockdown with small inhibitory ribonucleic acid. The AMPK-activating oral hypoglycemic agent metformin also induced and phosphorylated ATF1 at a clinically relevant concentration (10 μmol/L). Functional effects of heme and metformin were inhibited by AMPK-knockdown and included suppression of macrophage oxidative stress; increased cholesterol export; protection from foam-cell formation; and suppression of macrophage inflammatory activation (human leukocyte antigen type DR expression).


CONCLUSIONS
Our data indicate that heme activates the ATF1 pathway in human macrophages via AMPK, and that a similar response occurs after treatment of cells with metformin. Our results suggest an in vitro mechanism that may explain the clinical evidence that metformin has vascular protective effects beyond its role in treating hyperglycemia.
From the Section of Vascular Sciences, National Heart & Lung Institute (X.W., Y.H., M.J., E.P., J.C.M., D.O.H., J.J.B.) and MRC Clinical Sciences Centre (D.C.), Imperial College, London, UK.
Xinyi
X
Wan
Yilin
Y
Huo
Michael
M
Johns
Emma
E
Piper
Justin C
JC
Mason
David
D
Carling
Dorian O
DO
Haskard
Joseph J
JJ
Boyle
D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D051697:Activating Transcription Factor 1 / Q000235:genetics / Q000378:metabolism*; D050197:Atherosclerosis / Q000378:metabolism*; D006418:Heme / Q000494:pharmacology*; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D000071518:Liver X Receptors; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008687:Metformin / Q000494:pharmacology*; D057093:Orphan Nuclear Receptors / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D061251:Primary Cell Culture; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
C531110:ATF1 protein, human; D051697:Activating Transcription Factor 1; D007004:Hypoglycemic Agents; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D034741:RNA, Small Interfering; D006418:Heme; D008687:Metformin; D051547:Heme Oxygenase-1; D055372:AMP-Activated Protein Kinases
AMPK; HO-1; atherosclerosis; cholesterol; heme; liver X receptor; macrophages; metformin; redox