The vascular stem cell niches and their significance in the brain.

Aim. This cytohistopathological study was performed for a better knowledge of phenotypes derived from pluripotent stem cells, as well as for precise location of stem cells within the vascular niche in the brain. Methods. We used light and transmission electron microscopy to demonstrate the presence of stem cells in the vascular wall of microvessels in the cerebral and cerebellar cortex, pia mater (considered by us a cordocytic-vascular tissue), adventitia of larger cortical arteries and veins, and around vessels. We investigated multiple vascular segments and brain tissue in a variety of clinical cases, such as cerebral tumors, cerebrovascular malformations, thromboses in the carotid system, and direct laceration. Results. Our morphological and ultrastructural observations pointed out many changing phenotypes, as well as cell interrelationships within the vascular niche, both for repair processes when cordocytes cooperate with mesenchymal stem cells, and pathological processes such as atherogenesis, tumorigenesis, and neurotrauma. Our results underlie the important roles of cordocytes in their interrelations with precursor/stem cells in the arterial adventitia. Conclusion. The cells derived from pluripotent stem cells along different lineages have had different phenotypes as they derived from hematopoietic stem cells or mesenchymal stem cells, with or without epigenetic disregulations or depending on different microenviromnents. Cell interactions, phenotypes, and underlying mechanisms, as well as biological responses to different small molecules or compounds, remain to be determined by future molecular insights within the vascular niche.