Pericytes are branched cells located in the wall of capillary blood vessels that are found throughout the body, embedded within the microvascular basement membrane and wrapping endothelial cells, with which they establish a strong physical contact. Pericytes regulate angiogenesis, vessel stabilization, and contribute to the formation of both the blood-brain and blood-retina barriers by
Angiopoietin-1/Tie-2,
platelet derived growth factor (PDGF) and
transforming growth factor (TGF) signaling pathways, regulating pericyte-endothelial cell communication. Human pericytes that have been cultured for a long period give rise to multilineage progenitor cells and exhibit mesenchymal stem cell (MSC) features. We focused our attention on the roles of pericytes in brain and ocular diseases. In particular, pericyte involvement in
brain ischemia,
brain tumors,
diabetic retinopathy, and
uveal melanoma is described. Several molecules, such as
adenosine and
nitric oxide, are responsible for pericyte shrinkage during
ischemia-reperfusion. Anti-inflammatory molecules, such as
IL-10, TGFβ, and MHC-II, which are increased in
glioblastoma-activated pericytes, are responsible for
tumor growth. As regards the eye, pericytes play a role not only in ocular vessel stabilization, but also as a stem cell niche that contributes to regenerative processes in
diabetic retinopathy. Moreover, pericytes participate in
melanoma cell extravasation and the genetic ablation of the
PDGF receptor reduces the number of pericytes and aberrant
tumor microvessel formation with important implications for
therapy efficacy. Thanks to their MSC features, pericytes could be considered excellent candidates to promote nervous tissue repair and for regenerative medicine.