Aa21127: A Novel Endogenous Inhibitor of Corneal Lymphangiogenesis and Allograft Rejection

Abstract

Purpose: : The absence of lymphatic vessels in the cornea partially underlies its immune privilege and contributes to the high success rate of corneal transplants. However, the molecular basis of an alymphatic cornea remains unclear. Here, we establish the existence of a secreted corneal protein, which we named AA21127; and to investigate its role in preserving an alymphatic cornea, in suture induced corneal lymphangiogenesis, and in allograft survival.

Methods: : Balb/C and C57Bl/6 mice were studied. PCR was used to clone the AA21127 mRNA. pcDNA vector was constructed for over-expression of AA21127. Corneal AA21127 mRNA was detected by PCR and visualized by in-situ hybridization. Western blotting and immunohistochemistry were used to study AA21127 expression in the cornea. Corneal intra-stromal (11-0) sutures were placed in the peripheral cornea. In vivo enforced expression of AA21127 was achieved by naked plasmid intra-corneal injection. Conditional ablation of AA21127 in the cornea was achieved by interbreeding LeCre (Pax6 P0) and aa21127-floxed mice. Recombinant AA21127 administration was studied in the mouse model of corneal transplantation.

Results: : AA21127 mRNA and protein were cloned from a mouse cornea cDNA library. Its mRNA and protein were upregulated by suture injury. Enforced expression of AA21127 reduced suture-induced corneal lymphangiogenesis by 70%, while AA21127 genetic ablation resulted in spontaneous invasion of lymphatic vessels in neonatal mouse corneas. There was no difference in hemangiogenesis in the aforementioned studies. AA21127 administration significantly increased allograft survival in the mouse model of corneal transplantation.

Conclusions: : AA21127 is required to maintain an avascular cornea in uninjured mice, inhibits injury-induced lymphangiogenesis, and prolongs allograft survival. These data provide a rationale for investigating its role in other diseases driven primarily by lymphatic disturbances such as lymphedema and tumor metastasis. The identification of AA21127 as the first known anti-lymphangiogenic cytokine should also prompt a search for additional endogenous lymphatic inhibitors.

Keywords: neovascularization • transplantation • cornea: epithelium