Possible Role of Pigment-epithelium-derived Factor in Corneal Angiogenesis

Abstract

The detection of pigment-epithelium-derived factor (PEDF) in corneal tissue has allowed greater understanding of the avascularity of corneal tissue. The ability of the cornea to maintain the avascular nature of this tissue, also referred to as the angiogenic privilege of the cornea, could be partly attributed to the presence of this factor. This privilege is severely impaired by various diseases of the ocular surface associated with inflammation and infection that are often followed by neovascularisation, which compromises the transparency of the cornea and results in visual impairment. The rapidly increasing insights into the basic mechanisms controlling neovascularisation, i.e. balance of growth factor activation and enzymatic activity, has most recently led to the development of large-scale use of specific antiangiogenic agents in the treatment of neovascular age-related macular degeneration (AMD). Focusing on the effects of vascular endothelial growth factor (VEGF), the use of such agents, including bevacizumab (Avastin®), a humanised anti-VEGF monoclonal antibody originally used in the treatment of metastatic colorectal cancer, has been investigated in corneal angiogenesis. PEDF is only one of the many factors involved in ocular angiogenesis. However, although it is only a small protein, it has strong antiangiogenic actions that are expressed in the retinal pigment epithelial (RPE) layer, as well as in other parts of the eye. There are specific characteristics that could designate a special role for PEDF in the regulation of avascularity in the eye. In this article, we focus on corneal angiogenesis and highlight the special features of this somewhat unexplored cytokine, outlining the current knowledge and possible role of PEDF in corneal neovascularisation.