Effect of TRPM8 Functional Loss on Corneal Epithelial Wound Healing in Mice

PURPOSE: To reveal the role of cold-sensing transient receptor potential melastatin 8 (TRPM8) channels in corneal epithelial wound healing. METHODS: Cold sensitivity, tear production, corneal thickness, and corneal opacity assessments were used to evaluate the effect of Trpm8 knockout on the ocular surface. A corneal epithelial wounding model was generated by scraping the corneal epithelium once or multiple times using C57BL/6J (wild-type [WT]) and Trpm8(−/−) mice. The processes of corneal epithelial repair and corneal epitheliopathy were observed and recorded. Corneas were collected for sequencing, immunofluorescence staining, hematoxylin and eosin staining, and quantitative PCR. RESULTS: The perception of coldness, basal tear secretion, and corneal thickness were decreased in young Trpm8(−/−) mice compared with those in WT mice, except for the corneal sensitivity. Corneal opacity and increased corneal thickness were observed in aged Trpm8(−/−) mice. TRPM8 deficiency promoted corneal epithelial wound closure, consistent with the observed increase in Ki67-positive epithelial cells, and the pharmacological activation of TRPM8 in WT mice delayed corneal re-epithelization. After subjecting mice to multiple injuries, squamous metaplasia emerged in Trpm8(−/−) corneas, as verified by cytokeratin-1 and small proline-rich protein 1B–positive staining. The IFN-β and IFN-γ signaling pathways were significantly activated in Trpm8(−/−) mice, which was confirmed based on the up-regulated expression of the key mediators, signal transducer and activator of transcription-1 and phosphor–signal transducer and activator of transcription-1, as well as the induction of IFN-stimulated genes, compared with levels in WT mice. CONCLUSIONS: In corneal wound healing, the loss of TRPM8 function could promote epithelial repair, but predispose the cornea to epithelial lesions.