Function and regulation of the CD163-HO-1 pathway in hemin-differentiated macrophages from patients with abdominal...

In abdominal aortic aneurysms (AAA), immature and leaky neovessels facilitate the extravasation of erythrocytes. The breakdown of hemoglobin releases heme, which promotes the formation of reactive oxygen species. Macrophages can scavenge free hemoglobin via CD163 and degrade heme through heme oxygenase-1 (HO-1), thereby contributing to its detoxification.

The specific function and regulatory mechanisms of hemoglobin-derived hemin on macrophages in late-stage AAA remain poorly understood.

In AAA tissues, CD163-positive cells were found in areas with a high erythrocyte content and showed an inverse correlation with erythrocyte abundance. In vitro, hemin-differentiated macrophages from AAA patients exhibited increased HO-1 and CD163 mRNA expression but tended to display reduced CD163 protein expression, while these cells show no evidence of oxidative stress or intracellular iron dysregulation. Interestingly, soluble CD163 concentrations were higher in the supernatant of hemin-differentiated macrophages. Hemin stimulation did not alter the release of IL-10, TNF-α, or IL-6 by macrophages derived from AAA patients. To further elucidate the regulation of CD163 and HO-1, HO-1 activity was pharmacologically inhibited using zinc protoporphyrin (ZnPP). ZnPP decreased the GSH/GSSG ratio and increased HO-1 protein levels but decreased CD163 protein, suggesting a potential interaction or feedback mechanism between the two proteins. CRISPR-Cas9-mediated knockout led to a complete loss of HO-1 protein while leaving CD163 protein expression unaffected, suggesting that HO-1 is required for the reduction of CD163. Interestingly, the truncated form of HO-1 protein (t-HO-1) appeared upon HO-1 inhibition with ZnPP and was found to regulate the mRNA expression of CD163 and NQO1. This suggests a novel role of t-HO-1 in the regulation of CD163 responses during HO-1 inhibition in patients with late-stage AAA.

Hemin-differentiated macrophages likely exert a protective role in late-stage AAA.