Introduction: Vasa vasorum (VV) neovasculogenic potential is now widely accepted, and possibly related to the presence of progenitor cells. We studied the morphology of VV in healthy arteries and their immunohistochemical (IHC) expression of Nestin and WT1, two markers of endothelial progenitor cells.
Materials and methods: Twenty arteries from 16 multiorgan donors were analyzed; IHC was performed manually (CD34, CD31, Nestin) or automatically (WT1). Microvessel positivity "density" for each antibody was calculated dividing vascular adventitia in 1-mm2 fields with an ocular micrometer. Double immunofluorescence was used to investigate Nestin and WT1 co-localization in VV.
Results: The mean positivity "densities" for CD31, CD34, Nestin and WT1 were 13.63, 12.20, 8.90 and 7.98/mm² respectively. Mean Nestin/CD31 and WT1/CD31 ratios were 0.69 and 0.63 respectively. VV <50 µm in diameter showed a higher percentage of Nestin/WT1-positive cells than larger ones, especially in "hot spots", characterized by several small-sized arteriolar VV, often together with nerva vasorum. Immunofluorescence indentified Nestin and WT1 in the same endothelial cells. WT1 nuclear expression was mainly seen in <50 µm VV.
Discussion: We describe Nestin and WT1 in adult VV, especially <50 µm and gathered in "hot spots". The nuclear localization of WT1 could express an increasing transcriptional activity in progenitor-committed Nestin-positive cells. The "hot spot" could therefore represent a valid model for the vasculogenic niche in normal arteries and could potentially represent the main source for neovasculogenesis during atherosclerosis.