Essential roles of sensory nerve in maintenance of cornea-phenotype in mice

To the best of our knowledge, no reports have been published on the long-term changes in corneal tissue during the course of neuroparalytic keratopathy caused by destruction of the ophthalmic nerve in experimental animals. To bridge this research gap, we investigated the histopathology of the cornea in mice 3, 12, and 24 months after coagulation of the ophthalmic nerve.

Nerves were severely coagulated by inserting an 18-gauge bipolar needle into the skull of C57Bl/6 mice, as previously reported. Mice were sacrificed 3, 12, and 24 months later. Eyes were processed for histological and immunohistochemical analyses to identify the phenotypes of corneal epithelium and stroma.

At 3 months after denervation, the affected eyes showed severe inflammation and epithelial damage. In 3-, 14- and 24-month-old corneas, the stroma was found to be hypercellular with stromal neovascularization and keratinized epithelial hyperplasia. Such epithelium no longer expressed keratin 12, but markedly featured keratinization markers. The affected stroma had no keratocan expression, indicating loss of keratocyte cell-type differentiation. Neutrophils, macrophages, and Sox10-positive putative Schwann cells were found distributed in the affected stroma in association with the accumulation of Sonic hedgehog and galectin-3.

Ophthalmic denervation causes prolonged inflammation lasting up to 2 years, the appearance of repair-type Schwann cells in the stroma, loss of cornea-type differentiation of the epithelium with keratinization, and loss of stroma-specific gene expression. Sonic hedgehog and galectin-3 are upregulated in tissues and thought to be involved in pathology.