Abstract
Purpose :
The intraepithelial sub-basal nerve plexus of the cornea is characterized by a tell-tale central swirl pattern and terminal ramification in and between the apical cells of the epithelium. This plexus is a critical component of maintaining homeostatic function of the ocular surface, which contains a high concentration of collagen that is damaged in ocular surface disease, including neuropathic pain, neurotrophic keratitis, and dry eye. Here we tested whether topical application of a collagen mimetic peptide (CMP) was efficacious in repairing the corneal nerve bed in a mouse model of dry eye disease.
Methods :
We induced corneal tear film reduction, epithelial damage, and nerve bed degradation through a combination of environmental and pharmaceutical (atropine) desiccation. Mice (C57) were subjected to desiccating air turbulence and bilateral topical application of 1% atropine solution (4x daily) for two weeks. During the latter half of this desiccation regimen, mice received topical vehicle (PBS) or CMP (200 µm (Pro-Pro-Gly)7, 10 µl) once daily two hours prior to the first atropine treatment for that day. After sacrifice, we labeled corneal wholemounts with antibodies against βIII tubulin to visualize and quantify changes to the nerve bed.
Results :
In the vehicle cohort, the desiccation regimen reduced neuronal coverage of the central sub-basal plexus by 60 ± 5% and epithelial terminals by 58 ± 5% compared to naïve cornea (p<0.001), with some corneas demonstrating completely degenerated nerve beds. Accordingly, fragmentation of both sub-basal and epithelial βIII tubulin-labeled neuronal processes increased 3-fold, indicative of degenerative disassembly (p<0.001). Topical treatment with CMP significantly expanded both sub-basal (+73%) and epithelial (+43%) nerve coverage compared to vehicle (p=0.001), while reducing fragmentation by about 40% in both zones (p≤0.02). We found that CMP also improved the integrity of the corneal epithelium, stromal keratocyte survival, tear film production, and corneal sensitivity compared to vehicle.
Conclusions :
Together, these results indicate that topical CMP reduces neurodegeneration characteristics of corneal surface desiccation. The preservation of the nerve plexus in our mouse model could explain the significant improvement in Schirmer’s test score (% of patients with a ≥10 mm increase) for dry eye patients receiving CMP in a recent double-masked, placebo-controlled Phase 2 clinical trial.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.