Abstract 252: Potently Proteolytic Microvesicles Derived from Neutrophils Are Present Within the Intraluminal Thrombus of Human Abdominal Aortic Aneurysms
BACKGROUND— Extracellular matrix degradation and the formation of a non-occlusive intraluminal thrombus (ILT) are important clinical features of human abdominal aortic aneurysms (AAAs). The aortic wall under the ILT is thinner with less elastin than the wall without ILT. Leukocytes are trapped within the ILT, mainly in its luminal layer, and proteolytic activity derived from these cells could contribute to degradation of the underlying wall. In prior work, however, we detected only scant enzymatic activity of soluble, secreted matrix metalloproteinases (MMPs) in the abluminal layer of the ILT, i.e., the layer closest to the vessel wall. AIM- To examine two major insoluble, transmembrane MMPs - namely, ADAM17 (TACE) and ADAM10, in the abluminal layer of the ILT as a source of proteolytic activity.
METHODS/RESULTS— Aortic segments and ILTs were collected from 9 male and 3 female patients, all present or former smokers, during elective AAA surgery. Immunoblots showed abundant ADAM17 and ADAM10 in all three layers (luminal, middle, and abluminal) of their ILTs. ADAM 17 exhibited high levels of proteolytic activity in all layers of the ILT. By immunohistochemical staining, ADAM10 co-localized with the neutrophil marker CD66acd, but not with the macrophage marker CD163. Importantly, ADAM10 and CD66acd co-localized within the abluminal ILT in structures < 2 μm, without intact cells or nuclei. FACS analysis confirmed the presence of a significant number of microvesicles (MVs) in the abluminal layer of ILT. Moreover, exposure of cultured human HL-60 neutrophils to tobacco smoke stimulated large, time-dependent increases in the cellular content of both ADAM17 and ADAM10, cleavage of these proteases into their active forms, and release of enzymatically active ADAM17- and 10-positive MVs.
CONCLUSIONS— These results for the first time implicate persistent, enzymatically active transmembrane ADAM proteases within cell-free structures in the abluminal ILT, adjacent to the aortic wall of human AAA, as novel participants in mural weakening. Moreover, the production of proteolytically active MVs from smoke-exposed neutrophils provides a novel molecular mechanism for the vastly accelerated risk of AAA in smokers.
- © 2012 by American Heart Association, Inc.