Pericytes of Newly Formed Vessels in Experimental Subretinal Neovascularization

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Abstract
Objective: To examine the role of pericytes in the progression of subretinal neovascularization in a primate model. Methods: Subretinal neovascularization was induced by intense laser photocoagulation in four monkey eyes. Single eyes were enucleated at 3, 7, 14, and 21 days after photocoagulation and were studied with light and electron microscopy. Results: Three days after photocoagulation, newly formed vessels were observed in the choroid and subretinal space. Although most of these vessels had an immature appearance and consisted only of endothelial cells that formed narrow lumens, mitotic figures of pericytes were occasionally found near the endothelial cells. Seven days after photocoagulation, all of the newly formed vessels possessed pericytes. Fourteen days after photocoagulation, many vessels appeared to be mature. Many sites of pericyte-endothelial cell contact were observed. These contacts were composed of cytoplasmic interdigitation and membrane apposition. By 21 days after photocoagulation, the mature vessels had increased in number, and the endothelial cells had many fenestrations with diaphragms. The pericyte coverage of the endothelial cells was less at this stage than at 14 days after photocoagulation, and sites of pericyte-endothelial cell contacts were observed only rarely. Conclusion: Pericytes are involved in maturation of the endothelial cells that form subretinal new vessels.