Genetic ablation of myeloid integrin α9 attenuates early atherosclerosis.

Integrin α9β1 is known to stabilize leukocyte adhesion to the activated endothelium. We determined the role of myeloid cell α9β1 in early atherosclerosis in two models: α9MyeKOApoe-/- or the Ldlr-/- mice transplanted with bone marrow (BM) from α9Mye-KO mice fed a high-fat "Western" diet for four weeks. α9Mye-KOApoe-/- mice exhibited reduced early lesions in the aortae and aortic sinuses (p<0.05 vs. α9WT Apoe-/- mice). Similar results were obtained in α9Mye-KO BM→Ldlr-/- mice (p<0.05 vs α9WT BM→Ldlr-/- mice). Reduced early atherosclerosis in α9Mye-KOApoe-/- mice was associated with decreased neutrophil and neutrophil extracellular traps (NETs) content in the aortic lesions (p<0.05 vs. α9WTApoe-/-). VCAM-1-stimulated neutrophils from α9Mye-KO mice exhibited reduced adhesion, transmigration, and NETs formation (NETosis) (p<0.05 vs. α9WT neutrophils). Reduced NETosis was associated with decreased ERK phosphorylation, PAD4, and H3Cit expression. In summary, genetic ablation of myeloid cell-specific α9 reduces early atherosclerosis, most likely by reducing neutrophil adhesion, transmigration, and NETosis.