Absence of tyrosinase leads to altered distribution of corneal immune cells, corneal thinning and reduced corneal graft survival

Abstract

Purpose : Different eye diseases and injuries to the eye lead to ingrowth of lymphatic and blood vessels into the otherwise avascular cornea. Tyrosinase was recently described as a regulator of developmental and inflammation-induced lymphangiogenesis. Until now, the exact mechanism behind this remains unknown. Here we analyze the influence of tyrosinase on corneal thickness, distribution of immune cells in the cornea as well as the expression of vascular endothelial growth factors (VEGF) in central cornea.

Methods : Wild-type C57BL/6 and the corresponding albino C57BL/6 (B6N-Tyr^cBrd) were used. Immunohistochemical analysis of the corneas was done for several immune cell markers. The number of cell layers in central corneal epithelium was counted from histological staining of paraffin sections. Corneal thickness was determined by utilizing in vivo optical coherence tomography (OCT). From naïve central corneas RNA was extracted and expression levels of VEGF family members were detected by qPCR. Furthermore, BALB/c mice underwent corneal transplantations and received a 2 mm graft from C57BL/6 mice or B6N-Tyr^cBrd mice where graft survival was evaluated.

Results : Absence of tyrosinase results in a thinner cornea and fewer cell layers in the central corneal epithelium compared to the wild-type. Besides, in the B6N-Tyr^cBrd corneas an altered distribution of immune cells was detected, where CD45⁺ and F4/80⁺ cells were more present in the central region. In the wild-type the distribution of CD45⁺ and F4/80⁺ cells was equal between central and limbal region. Moreover, a higher expression of the VEGF family members was detected in the central cornea of the albino animals. Interestingly, grafts from B6N-Tyr^cBrd corneas showed only 25% of graft survival under normal-risk conditions, whereas for the C57BL/6 there was a 50% graft survival over 8 weeks.

Conclusions : In the present study, we reveal the novel effect of tyrosinase on the distribution of immune cells in the cornea. Furthermore, we noticed that loss-of-function in tyrosinase leads to reduced corneal thickness in mice. It was shown that tyrosinase also plays a role in the regulation of the expression of VEGF family members in central cornea and corneal graft survival. Thus, we believe that tyrosinase could be a potential therapeutic target for treatment of pathological corneal lymphangiogenesis and to improve graft survival.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.