Purpose: The avascular cornea is in direct contact with aqueous humor (AqH). Here we investigate whether AqH exerts anti(lymph)angiogenic effects and thereby may contribute to corneal (lymph)angiogenic privilege.
Methods: Using the murine model of suture-induced inflammatory corneal hem- and lymphangiogenesis, the potential anti(lymph)angiogenic effect of AqH was analyzed by applying murine AqH as eyedrops. Anti(lymph)angiogenic effects were measured using morphometric analysis of flat mounts stained with CD31 as panendothelial and LYVE-1 as specific lymphatic endothelial marker. The potential antilymphangiogenic effect of immunomodulatory factors contained in AqH such as vasoactive intestinal peptide (VIP) and α-melanocyte stimulating hormone (α-MSH) was analyzed in lymphatic and blood vascular endothelial cell proliferation assays in vitro.
Results: Topically applied AqH significantly inhibited corneal hemangiogenesis and even more so lymphangiogenesis in vivo and directly in vitro. The immunoregulatory factors VIP and α-MSH significantly inhibited lymphatic endothelial cell proliferation in vitro. Depletion of VIP or α-MSH from AqH diminished its anti-hem- and lymphangiogenic potential.
Conclusions: Aqueous humor exerts significant antilymphangiogenic effects in vivo. This is at least partially mediated by the known immunomodulatory factors VIP and α-MSH present in the AqH. Therefore, AqH not only contributes to corneal lymphangiogenic privilege and is a new tool to identify novel endogenous regulators of lymphangiogenesis but also may have therapeutic applications.