The Anti-Thrombotic Enzyme ADAMTS13 Reduces Inflammation and the Development of Atherosclerosis In Mice

ADAMTS13 (A Disintegrin-like And Metalloprotease with Thrombospondin type I repeats-13) plays a pivotal role in preventing spontaneous thrombosis in the microvasculature by cleaving hyperactive ultra large von Willebrand factor (ULVWF) multimers into smaller, less active multimers. Severe deficiency of ADAMTS13 in humans causes thrombotic thrombocytopenic purpura (TTP) and numerous epidemiological studies have demonstrated associations between decreased ADAMTS13 activity and adverse disease outcome in patients with systemic inflammation. It remains unknown, however, whether reduced ADAMTS13 activity plays a direct pathogenic role in inflammatory diseases or rather simply serves as an inflammation-associated marker. We hypothesized that deficiency of ADAMTS13 enhances inflammation and accelerates the development of early atherosclerotic plaques.

Using intravital fluorescence microscopy, we show that the number of adherent leukocytes (adherent for > 60 s) was increased approximately four-fold at the carotid sinus, a lesion prone site, of Adamts13−/−/ApoE−/− mice (Mean ± SEM = 37 ± 6) as compared to ApoE−/− mice (Mean ± SEM = 9 ± 4, P <0.01) fed a high-fat Western diet. Interestingly, intravital microscopy showed that 100% (10/10) of the Adamts13−/−/ApoE−/− mice had plaque that occluded the carotid sinus by approximately 70–80%, whereas only 20% (2/10) of the ApoE−/− mice had plaque at the carotid sinus, and the plaques were smaller in size than those in Adamts13−/−/ApoE−/− mice (P=0.0003). Next, we determined the effects of ADAMTS13 deficiency on atherosclerotic plaque formation in the aorta and aortic sinus. We compared the extent of atherosclerosis in whole aortae stained with Oil Red O and en face lesion area measured by morphometry. Both Adamts13−/−/ApoE−/− male and female mice demonstrated significantly larger lesions in the descending aorta (P<0.01), arch of the aorta (P<0.001), and total aorta (P<0.0001) compared to ApoE−/− mice fed a high-fat Western diet. Next, we quantified the corss-sectional area of lesions in the aortic sinus using the VerHoeffs/Van Gieson method. We observed a two-fold increase in the mean lesion area in the aortic sinus of both male and female Adamts13−/−/ApoE−/− mice (P<0.01) compared to ApoE−/− mice. Macrophage content (% of total lesion area), as quantitated by immunohistochemistry, was significantly elevated in the aortic root lesions of Adamts13−/−/ApoE−/− mice compared to ApoE−/− mice, suggesting that exacerbated atherosclerosis was due to increased inflammation. Adamts13−/−/ApoE−/− mice fed a normal chow diet also demonstrated accelerated atherosclerotic plaque formation compared to ApoE−/− mice. Total cholesterol and triglyceride levels were similar in Adamts13−/−/ApoE−/− and ApoE−/− mice fed a high-fat Western diet or normal chow diet.

These findings unravel a new functional role for the anti-thrombotic enzyme ADAMTS13 in reducing excessive inflammation and plaque formation during atherosclerosis.

Lentz:Celgene: Ownership interest; Novo Nordisk: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.