Macrophages polarize into heterogeneous proinflammatory M1 and antiinflammatory M2 subtypes. Heme oxygenase 1 (HO-1) protects against inflammatory processes such as ischemia-reperfusion injury (IRI), organ transplantation, and atherosclerosis. To test our hypothesis that HO-1 regulates macrophage polarization and protects against IRI, we generated myeloid-specific HO-1–knockout (mHO-1–KO) and –transgenic (mHO-1–Tg) mice, with deletion or overexpression of HO-1, in various macrophage populations. Bone marrow–derived macrophages (BMDMs) from mHO-1–KO mice, treated with M1-inducing LPS or M2-inducing IL-4, exhibited increased mRNA expression of M1 (CXCL10, IL-1β, MCP1) and decreased expression of M2 (Arg1 and CD163) markers as compared with controls, while BMDMs from mHO-1–Tg mice displayed the opposite. A similar pattern was observed in the hepatic M1/M2 expression profile in a mouse model of liver IRI. mHO-1–KO mice displayed increased hepatocellular damage, serum AST/ALT levels, Suzuki’s histological score of liver IRI, and neutrophil and macrophage infiltration, while mHO-1–Tg mice exhibited the opposite. In human liver transplant biopsies, subjects with higher HO-1 levels showed lower expression of M1 markers together with decreased hepatocellular damage and improved outcomes. In conclusion, myeloid HO-1 expression modulates macrophage polarization, and protects against liver IRI, at least in part by favoring an M2 phenotype.
Min Zhang, Kojiro Nakamura, Shoichi Kageyama, Akeem O. Lawal, Ke Wei Gong, May Bhetraratana, Takehiro Fujii, Dawoud Sulaiman, Hirofumi Hirao, Subhashini Bolisetty, Jerzy W. Kupiec-Weglinski, Jesus A. Araujo