Interaction of retinal pericytes, capillary endothelial cells and pigment epithelial cells in vasoproliferative retinopathies

Degeneration of intramural pericytes is the first histopathological lesion seen in diabetic retinopathy. Since pericytes from the optic nerve and brain are spared, such degeneration appears to be specific to the retinal circulation. Recent studies have shown that when retinal pericytes and microvascular endothelial cells are co‐cultured in vitro , direct contact between the two types of cells leads to the inhibition of proliferation of endothelial cells. Previously it was shown that when pericytes are cultured in the absence of microvascular endothelial cells, the cultured medium conditioned by the pericytes is actively mitogenic for retinal capillary endothelial cells. Furthermore, conditioned medium from human retinal pigment epithelial cells is also mitogenic for retinal capillary endothelial cells and pericytes. On the basis of these results, a new working hypothesis is proposed for the mechanism of action of photocoagulation used in vasoproliferative retinopathies.