Pericytes and periendothelial cells of brain parenchyma vessels co‐express aminopeptidase N, aminopeptidase A, and nestin

Within the parenchyma of the CNS, the endothelium of all vessels is surrounded by a layer of cells, pericytes in capillaries and periendothelial or intima smooth muscle cells in other vessels. The origin of these cell types, their relationship, and their role are unclear. However, it has been recently shown that genetically engineered mice that lack pericytes develop microaneurysms at late gestation and die before birth (Lindahl et al. [1997] Science 277:242–245). The goal of this study was to identify in situ molecular markers that would be common to pericytes and periendothelial cells of adult mouse brain. Immunocytochemistry experiments were carried out at the optical and electron‐microscopic levels on mouse brain sections with antibodies specific for aminopeptidase N, aminopeptidase A, and the intermediate filament nestin. The results of our experiments show that in all brain parenchyma vessels of all sizes, pericytes and periendothelial cells are immunoreactive for aminopeptidase N, essentially at the plasma membrane level, and are also labeled by nestin specific antibodies, which decorate typical intermediate filaments. In addition, brain pericytes and periendothelial cells are also immunoreactive to monoclonal antibodies to aminopeptidase A. In contrast, pericytes and periendothelial cells do not express microglial markers. Taken together these data show that pericytes and periendothelial intima smooth muscle cells share common markers, suggesting a common origin or function, and are distinct from microglia. J. Neurosci. Res. 58:367–378, 1999. © 1999 Wiley‐Liss, Inc.