Oxidation of hemoglobin to ferryl hemoglobin contributes to remodeling of the artery wall in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) with potentially fatal outcomes affects cardiovascular health via inflammation-related abnormalities. We revealed the presence of the oxidized hemoglobin (Hb), ferrylHb in the circulation in patients diagnosed with ruptured AAA. The aim of our study was to identify the source of oxidation of Hb in human hemorrhaged AAA and in an angiotensin II provoked AAA model in mice leading to generation of ferrylHb and to describe its fate in the pathophysiology. We demonstrate that two electron oxidations of Hb leading to the formation of ferrylHb with the characteristics of oxidation of βCys93, αCys104, and βCys112 residues is the terminal product of the interaction of neutrophils and macrophages with Hb in the hemorrhaged AAA. This oxidized Hb, ferrylHb is taken up by neutrophils and macrophages via CD163 mediated endocytosis with subsequent activations including peptidylarginine deiminase 4 (PAD4) driven NETosis, liberation of elastase, myeloperoxidase and subsequent degradation of extracellular matrix. AAA exhibits increased expression of CD163 in macrophages and neutrophils revealed to be inducible by ferrylHb involving PAD4 signaling. RNA-seq analysis demonstrated that human ruptured AAA has a unique transcriptomic profile, different from healthy aorta, with a 43 % overlap in the differential gene expressions of human macrophages exposed to ferrylHb. Among these 884 genes, we found inflammatory-, angiogenesis-, and tissue remodeling gene clusters. These data suggest that oxidation of Hb to ferryl state and the interactions of neutrophils and macrophages with ferrylHb within aortic wall contribute to AAA progression.