Targeted depletion of monocyte/macrophage suppresses aortic dissection with the spatial regulation of MMP-9 in the aorta

Aortic dissection (AD) is a devastating disease with rapid progression and high mortality, while the initiation mechanism of AD is far from clear. AD was established by feeding mice with β-aminopropionitrile in the diet and usage of angiotensin II (AngII) to trigger the rupture of aorta. LysMiDTR mice were constructed by crossing of LysM-Cre mice with ROSA26iDTR mice and characterized by diphtheria toxin receptor (DTR) expression in monocytes/macrophages specifically. Then, monocyte/macrophage depletion in LysMiDTR mice was conducted to evaluate the function of monocyte/macrophage in AD. Finally, the underlying mechanism was elucidated by proteomics, Western blot analysis, immunofluorescence staining and bioinformatics analysis. First, we detected T lymphocytes, macrophages and neutrophils infiltrated into the aorta simultaneously when AD occurred, and macrophages were the most abundant cell type. Then, targeted depletion of monocyte/macrophage in LysMiDTR mice considerably inhibited the occurrence of AD and infiltration of T lymphocytes and neutrophils. Furthermore, monocyte transfusion into LysMiDTR mice augmented the rupture of aorta, jointly supporting the key roles of monocytes/macrophages in AD development. Mechanistically, a total of 347 proteins exhibited significant differences in intensity after monocyte/macrophage depletion according to quantitative mass spectrometry. Specifically, increased matrix metalloprotein-9 (MMP-9) level in AD may be of concern due to its functions in vascular remodeling. The infiltration of macrophages considerably up-regulated MMP-9, and MMP-9 co-localized with macrophages at the tearing area of aorta. Macrophages infiltrated into the tear sites of the aortic wall, regulated extracellular remodeling pathway, functioned as initiators to switch on the occurrence of AD.