Vasa vasorum in normal and diseased arteries.

Abstract

The vasa vasorum are a specialized microvasculature that play a major role in normal vessel wall biology and pathology. Under physiological conditions, the adventitial vasa vasorum take up molecules that are transmitted from the blood to the adventitia by mass transport through the arterial wall. The adventitia is the primary early site for vessel wall response to arterial injury that occurs on the luminal side. The vasa vasorum expand in response to the injury, which alters vessel homeostasis. This review focuses on the impact the vasa vasorum expansion has on development of vascular pathology, particularly neointima development and growth of atherosclerotic plaque. The adventitia, the outermost layer of the vessel wall, has received considerable attention in recent years. It contains a heterogeneous population of cells, including macrophages,1,2 T cells,3 B cells,1,2 dendritic cells,1,2 progenitor cells,4,5 and fibroblasts that can differentiate into myofibroblasts.6 It also contains an adrenergic nervous system,7 a lymphatic network,8 and vasa vasorum, a specialized microvasculature that plays a major role in normal vessel wall biology and pathology that is the subject of the present review. Under physiological conditions, the adventitial vasa vasorum and lymphatic vessels take up molecules that are transmitted from the blood to the adventitia by mass transport through the arterial wall.9–11 Vascular injury at the luminal side of the vessel wall significantly impacts the adventitia by convection of soluble factors, microparticles and macroparticles, mediators such as products of oxidation, tissue cytolysis, and proteolysis from the intima to the adventitia by hydraulic conductance.12 As a result, the adventitia becomes the primary early site for the vessel wall response to arterial injury, which includes myofibroblast migration into the vessel wall,13,14 inflammatory cell accumulation, …