Myeloid HIF1α has only a minor impact on atherosclerosis development

Atherosclerosis is a progressive inflammatory disease, of which initiation and progression are potentially mediated by myeloid cells. An imbalance of oxygen supply and, therefore, hypoxic situations in the arterial wall have been hypothesized to be a major driver of development and progression of atherosclerosis. Herein, we analyze the significance of hypoxia-inducible factor (HIF) in myeloid cells in atherosclerosis. Myeloid-specific Hif1α and Hif2α knockout mice were crossed into the ApoE-/- background, and angiotensin II (AngII) infusion was performed to induce accelerated plaque formation. Myeloid Hif1α, but not Hif2α, limited the increase in heart weight after 7 days of AngII infusion, indicating a transient protective effect restricted to early phases of AngII-induced remodeling. With prolonged treatment (4 weeks), these differences were lost, suggesting a protective role for myeloid HIF-1α only in early hypertension-induced cardiac hypertrophy. Macrophages of aged mice (12 months old) showed decreased expression of Hif1α and Hif2α, which did not yield overt differences in classical/alternative polarization markers. Nevertheless, aged ApoE-/- mice with macrophage-specific Hif1α knockout had a higher body weight and developed more aortic plaques compared to wild-type littermates. These observations suggest that activation of Hif1α in macrophages may be protective for plaque formation under chronic hyperlipidemic conditions. Supporting this, a reanalysis of single-cell RNA-sequencing data from human atherosclerotic and normal vessel wall specimens shows that HIF target gene expression is elevated in anti-inflammatory macrophage subsets along pseudotime trajectories. This association suggests that macrophage HIF1α activity may contribute to reparative or stabilizing responses during plaque progression.