Activity dependent neuroprotective protein mediates the protective effects against VEGF-induced corneal barrier disruption in diabetes.

Diabetic keratopathy (DK) is a severe complication of diabetes mellitus characterized by corneal epithelial barrier dysfunction. Although the vascular endothelial growth factor (VEGF) is known to compromise barrier integrity in the retina, its specific role in DK pathogenesis remains to be fully elucidated. In the present study, we investigated the protective role of activity-dependent neuroprotective protein (ADNP), to counteract hyperglycemia-induced corneal damage. Initially, ADNP and VEGF expression were analyzed in the corneas of streptozotocin-injected diabetic rats. Results showed a downregulation of ADNP immunoreactivity with a concomitant upregulation of VEGF signal in STZ-injected cornea as compared to controls. Subsequently, rabbit corneal epithelial cells (SIRC) were cultured under high-glucose (HG) conditions in an Air-Liquid Interface (ALI) system to mimic the stratified corneal epithelium. Our results demonstrated that HG conditions induced corneal epithelial impairment, characterized by decreased TEER values and the downregulation of the tight junction (TJ) proteins, such as occludin and ZO-1. The exogenous administration of NAP (the smallest active fragment of ADNP) rescued barrier function by increasing TJ expression and restoring TEER values. Furthermore, NAP counteracted the HG-induced loss of EB1 and Tau, two microtubule-associated proteins, suggesting a key role in stabilizing the microtubule network. NAP antagonizes the effects of VEGF, which otherwise triggers the internalization of EB1 and Tau, leading to microtubule disruption. Moreover, we demonstrated that NAP significantly enhanced the wound-healing capacity of SIRC cells, which was severely impaired by hyperglycemic conditions. Overall, our findings demonstrate that ADNP preserves corneal epithelial integrity and promotes wound repair by stabilizing the cytoskeletal-junctional complex.