Synaptosome-associated protein of 25 kD (SNAP25) promotes corneal epithelial repair via maintaining trigeminal nerve autophagy homeostasis and function in diabetes-related dry eye.

Diabetic keratopathy affects more than 70% of patients, and there are limited effective intervention options for diabetes-related dry eye. Physically, the trigeminal nerve nourishes the corneal epithelial cells via neurotransmitter vesicles to support their integrity and function. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of small, evolutionarily conserved proteins found in eukaryotic cells that mediate neurotransmission through membrane fusion. Within SNARE complexes, the synaptosome-associated protein of 25 kDa (SNAP25) is the functional protein in neurotransmission. In this study, we investigated whether and how SNAP25 regulates the trigeminal nerve to promote corneal repair in diabetes. Using high-throughput protein mass spectrometry, we found that SNAP25 expression was significantly reduced in the corneas of diabetic rats with dry eye compared with healthy controls. Western blot analysis confirmed reduced SNAP25 expression in the trigeminal nerves of diabetic rats with dry eye. This was accompanied by an increased LC3B-II/I ratio and decreased p62 expression. Exogenous overexpression of SNAP25 via lentivirus-mediated gene transfer into the subconjunctival space improved corneal and trigeminal nerve repair. In cultured trigeminal neuronal primary cells isolated from postnatal rats, treatment with the oxidative trigger 4-hydroxynonenal (4-HNE) induced autophagosome accumulation, which was reversed by SNAP25 overexpression through enhanced autophagosome fusion. Nevertheless, knockdown of SNAP25 exacerbated autophagosome accumulation in 4-HNE-exposed trigeminal neurons. Furthermore, SNAP25 expression was down-regulated in the trigeminal nerve partially due to 4-HNE-induced ERK phosphorylation. In conclusion, SNAP25 could be used to maintain nerve function and support corneal repair in cases of dry eye related to diabetes.