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

Aim: Aortic dissection (AD) is a devastating disease with rapid progression and high mortality, while the initiation mechanism of AD is far from clear.

Main Methods: AD was established by feeding mice with β-aminopropionitrile in the diet and usage of angiotensin II (AngII) to trigger the rupture of aorta. LysM mice were constructed by crossing of LysM-Cre mice with ROSA26 mice and characterized by diphtheria toxin receptor (DTR) expression in monocytes/macrophages specifically. Then, monocyte/macrophage depletion in LysM 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.

Key Findings: 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 LysM mice considerably inhibited the occurrence of AD and infiltration of T lymphocytes and neutrophils. Furthermore, monocyte transfusion into LysM 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.

Significance: Macrophages infiltrated into the tear sites of the aortic wall, regulated extracellular remodeling pathway, functioned as initiators to switch on the occurrence of AD.