The metalloprotease ADAMTS13 prevents spontaneous thrombosis in the microvasculature by cleaving hyperactive ultra large von Willebrand factor (ULVWF) multimers into smaller and less active forms. Recently, we and others have demonstrated that ADAMTS13-deficiency aggravates vascular inflammation and early atherosclerosis in apolipoprotein E-deficient (ApoE−/−) mice fed a high-fat Western diet. Although VWF is the only known substrate for ADAMTS13, it is not known if the effects of ADAMTS13 on vascular inflammation and atherosclerosis are mediated through its proteolytic effects on VWF or possibly another ADAMTS13 substrate. In this study, we determined whether the exacerbated atherosclerosis observed in the Adamts13−/−/ApoE−/− mice is dependent or independent of VWF.
ApoE−/−, Adamts13−/−/ApoE−/−, Adamts13−/−/Vwf−/−/ApoE−/− and Vwf−/−/ApoE−/− male mice were fed a high-fat Western diet (20% fat, 0.2% cholesterol) beginning at 6 weeks of age until they were sacrificed at 4 months. We compared the extent of atherosclerosis in the cross section area of the aortic sinus using the VerHoeffs/Van Gieson stain. Inflammatory cells (neutrophils and macrophages) in the aortic lesions were quantitated by immunohistochemistry.
Similar to previous published reports by us and others, we found that the mean lesion area in the aortic sinus of the Adamts13−/−/ApoE−/− mice were significantly larger (mean ± SEM: 26.6 % ± 1.9 %, P<0.01) compared with ApoE−/− mice (mean ± SEM: 20.4 % ± 1.5 %). Next, we quantitated macrophage and neutrophil infiltration into lesions in the aortic sinus by immunohistochemistry. We observed significantly increased macrophages (mac-3 positive) and neutrophils (Ly6 B.2 positive) recruitment in the aortic sinus of Adamts13−/−/ApoE−/− mice compared with ApoE−/− mice. The mean lesion area in the aortic sinus of Adamts13−/−/Vwf−/−/ApoE−/− mice (mean ± SEM: 15.2 % ± 1.5 %) were similar to Vwf−/−/ApoE−/− mice (mean ± SEM: 15.6 % ± 0.9 %), suggesting that the accelerated atherosclerosis observed in ADAMTS13-deficient mice is VWF-dependent. Finally, macrophages and neutrophils recruitment in the aortic sinus of Adamts13−/−/Vwf−/−/ApoE−/− mice were similar to Vwf−/−/ApoE−/− mice, suggesting that increased vascular inflammation observed in ADAMTS13-deficient mice is also VWF-dependent. Total cholesterol and triglyceride levels were similar among groups fed a high-fat Western diet.
These findings reveal that VWF-deficiency abrogates accelerated early atherosclerosis in ADAMTS13-deficient mice, suggesting that VWF the only relevant substrate for ADAMTS13 in murine atherosclerosis.
Lentz:Novo Nordisk A/S: Consultancy, Investigator Other.
Asterisk with author names denotes non-ASH members.