Nerve Growth Factor Treatment and the Corneal Epithelium: Extracellular Vesicle-Mediated Signaling.

Recombinant human nerve growth factor (NGF) is used to treat patients with impaired corneal wound healing. NGF exerts its effects through complex signaling processes initiated by the binding of one of two cell membrane receptors-TrkA and p75NTR. While the intracellular signaling pathways have been studied extensively, how NGF mediates intercellular signaling to coordinate wound healing is less understood. Here, we demonstrate that extracellular vesicles (EVs) produced by the corneal epithelium in response to exogenous NGF negatively affect the viability, proliferation, and migration of corneal epithelial cells. We found that EVs produced in response to NGF include an over-enrichment in miR-34a-3p, while the same miRNA is under-expressed in the cell lysate after NGF treatment. Conversely, treatment with a miR-34a-3p antagonist, miR34a-i, induces a significant upregulation of endogenous NGF, suggesting a potential feedback pathway between miR-34a-3p and NGF. Furthermore, media conditioned with EVs produced in response to miR34a-i treatment significantly enhances the proliferative response in the corneal epithelium. We identified bex3-encoding NGF receptor associated protein 1-as a potential target of miR-34a-3p in the NGF signaling pathway. These data highlight a potential intercellular negative feedback pathway induced by NGF treatment in the corneal epithelium.