Localization of Vascular Adhesion Protein-1 in Human Ocular Tissues

Abstract

Purpose: : Recently we showed a critical role for Vascular Adhesion Protein-1 (VAP-1) in a model of uveitis. VAP-1 inhibition ameliorated signs of acute inflammation, including retinal leukostasis and cytokine production in EIU animals. However, until now the expression of VAP-1 in the human eye was not known.

Methods: : Paraffin blocks of human ocular tissues were obtained from MEEI’s tissue sample archives. VAP-1 tissue localization was assessed in 5 µm thick sections using immunohistochemistry. Sections were incubated with primary mAbs against VAP-1 (5 µg/ml), smooth muscle actin (1 µg/ml), or isotype matched IgG at 4 °C overnight. Subsequently, a secondary antibody (mouse envision system) was used for 30 min at room temperature followed by Dako Envision + HRP (AEC) System for signal detection. The stained sections were examined using light microscopy and the signal intensity was quantified by two masked evaluators and graded into 4 different categories, non-detectable (0) to higher intensities (1, 2 and 3).

Results: : Within various ocular tissues, VAP-1 staining was confined to the vasculature. VAP-1 labeling showed the highest intensity in both arteries and veins of neuronal tissues, retina and optic nerve, and the lowest intensity in the iris vasculature. Scleral and choroidal vessels showed moderate staining for VAP-1. VAP-1 intensity was significantly higher in the arteries compared to veins. Furthermore, VAP-1 staining in arteries co-localized with SM-actin staining, suggesting expression of VAP-1 in smooth muscle cells or potentially pericytes.

Conclusions: : Immunohistochemistry reveals a constitutive expression of VAP-1 in human ocular tissues. VAP-1 expression is exclusive to the vasculature with arteries showing higher expression than veins. Furthermore, the vessels of the optic nerve and the retina show the highest level of expression. These and our previous results suggest VAP-1 to be a key molecule in ocular vascular and inflammatory diseases.

Keywords: age-related macular degeneration • uveitis-clinical/animal model • diabetic retinopathy