Heme induces heme oxygenase 1 via Nrf2: role in the homeostatic macrophage response to intraplaque hemorrhage

JJ Boyle, M Johns, J Lo, A Chiodini… - … , and vascular biology, 2011 - Am Heart Assoc
JJ Boyle, M Johns, J Lo, A Chiodini, N Ambrose, PC Evans, JC Mason, DO Haskard
Arteriosclerosis, thrombosis, and vascular biology, 2011Am Heart Assoc
Objective—Intraplaque hemorrhage (IPH) is an important progression event in advanced
atherosclerosis, in large part because of the delivery of prooxidant hemoglobin in
erythrocytes. We have previously defined a novel macrophage phenotype (hemorrhage-
associated-mac) in human advanced plaques with IPH. These may be atheroprotective in
view of raised heme oxygenase 1 (HO-1), CD163, and interleukin-10 expression and
suppressed oxidative stress. Methods and Results—We have used a combination of small …
Objective
Intraplaque hemorrhage (IPH) is an important progression event in advanced atherosclerosis, in large part because of the delivery of prooxidant hemoglobin in erythrocytes. We have previously defined a novel macrophage phenotype (hemorrhage-associated-mac) in human advanced plaques with IPH. These may be atheroprotective in view of raised heme oxygenase 1 (HO-1), CD163, and interleukin-10 expression and suppressed oxidative stress.
Methods and Results
We have used a combination of small interfering RNA and pharmacological reagents, protein analysis, and oxidative stress measurements to dissect the pathway leading to the development of this phenotype. We found that erythrocytes, hemoglobin, or purified heme similarly induced CD163 and suppressed human leukocyte antigen and reactive oxygen species. HO-1 was required for the development of each of these features. Challenge of macrophages with purified heme provoked nuclear translocation of Nrf2, and Nrf2 small interfering RNA resulted in significant inhibition of the ability of heme to induce HO-1 protein. Furthermore, tert-butyl-hydroquinone, which activates Nrf2, upregulated CD163, suppressed human leukocyte antigen, and induced interleukin-10, further supporting a role for Nrf2-mediated signaling. However, an inducible protein transactivator is also probably necessary, as heme-induced HO-1 mRNA expression was fully inhibited by the protein synthesis inhibitor cycloheximide.
Conclusion
Our experiments define an Nrf2-mediated pathway by which heme induces a homeostatic macrophage response following IPH.
Am Heart Assoc