Age–dependent Spontaneous Induction of Corneal Neovascularization in CD36 Knock–out Mice

Abstract

Abstract: : Purpose: Corneal neovascularization is a potentially sight–threatening condition characterized by the sprouting of new blood vessels into the normally avascular tissue. Corneal avascularity is tightly regulated by a balance between angiogenic factors and anti–angiogenic factors such as thrombospondin (TSP). Thrombospondins are naturally occurring potent inhibitors of angiogenesis, and their action is mediated by the CD36 scavenger receptor. CD36 is expressed by a variety of cells including microvascular endothelial cells. Consequently, we hypothesize that CD36 is protective against the development of corneal neovascularization by mediating anti–angiogenic activities. Methods: Corneas of CD36 knock–out (KO) and wildtype (WT) C57BL6/J mice aged 1, 4, 12, and 18 months were first assessed for corneal haze immediately following eye excision. The corneas were then examined for changes in histology using Periodic Acid Schiff staining. Neovascularization was quantified by counting the number of vessels observed microscopically per corneal section, in a blind manner. RT–PCR and Western blot analysis were used to determine expression of CD36 and TSP–1 in the cornea. Results: Corneal haze and neovascularization were absent in WT corneas at all ages. Conversely, in CD36 KO mice, corneal haze and NV were evident at 12 and 18 months. At 12 months, 1 out 3 corneas exhibited haze, and this was especially profound at 18 months when all the corneas (5 out of 5) were hazy. The results also indicate a significant difference in the vessel density of WT vs. CD36 null mice at 12 months (0 vs. 45 ± 17 vessels/corneal section; p < 0.05) and 18 months (0 vs. 78 ± 21 vessels/corneal section; p < 0.05). We have also demonstrated CD36 and TSP–1 expression in the cornea. Conclusions: The current findings strongly suggest that CD36 may have a protective role against corneal neovascularization, given that mice null for CD36 developed neovascularization in an age–dependent manner.

Keywords: neovascularization • cornea: basic science • aging