Expression of vascular endothelial growth factor C and vascular endothelial growth factor receptor 3 in corneal lymphangiogenesis

Lymphangiogenesis has been reported in vascularized corneas. However, the molecular mechanisms of lymphangiogenesis in the cornea are still unclear. Since lymphatic vessels may contribute to a decreased success rate of keratoplasty in vascularized cornea by accelerating antigen recognition and graft rejection, elucidation of the mechanisms of corneal lymphangiogenesis will facilitate the inhibition of lymphatic vessels and may improve the outcome of keratoplasty. This study aimed to examine the expression of vascular endothelial growth factor-C (VEGF-C), which is the only endogenous lymphangiogenic factor reported so far, and one of its receptors, vascular endothelial growth factor receptor-3 (VEGFR-3), in corneal lymphangiogenesis. A rat model was used in which silver nitrate application resulted in corneal circumferential neovascularization. The presence of lymphatic vessels in the rat injured cornea was examined with electron microscope. Corneal VEGF-C and VEGFR-3 mRNA levels were quantified with competitive reverse transcription polymerase chain reaction (RT-PCR), and VEGF-C and VEGFR-3 proteins were studied in situ using immunohistochemical analysis. Electron microscopy revealed lymphatic vessels in the vascularized rat corneas. Competitive RT-PCR demonstrated that the expression of VEGF-C mRNA in the rat cornea was normally absent, and was dramatically up-regulated 3 days after the injury, which gradually decreased. The VEGFR-3 expression in the rat cornea was minimally detected before the injury and was up-regulated 3 and 7 days after the injury. It was also minimally detected 2 and 4 weeks after the injury. In immunohistochemical analysis of the pat cornea 3 days after the injury, VEGF-C was mainly detected in inflammatory cells, and VEGFR-3 was demonstrated in several new vessels in the corneal stroma. These data suggest that VEGF-C and VEGFR-3 are pathophysiologically relevant endogenous factors in corneal lymphangiogenesis. (C) 2000 Academic Press.