Abstract
Purpose :
There is increasing evidence that corneal innervation contributes to the angiogenic privilege of the cornea. The underlying mechanisms, however, are not fully understood. Herein, we investigate the role of sensory nerve-derived α-MSH in modulating corneal angiogenesis.
Methods :
Adult Balb/c mice were used. Expression of α-MSH and its receptors was analyzed using RT-PCR and immunohistochemistry (IHC). Sensory neurons and nerves were stained with β-Tubulin III. Corneal neovascularization (CNV) was induced by intrastromal placement of a figure-8 suture. Mice were treated with α-MSH (10-4 M three times a day) topically after suture placement for 2 weeks, and CNV was photographed and analyzed using ImageJ. IHC was performed using CD31 and LYVE1 antibodies. mRNA expression of inflammatory cytokines and vascular endothelial growth factor A (VEGF-A) and VEGF receptor 2 (VEGFR2) were analyzed using RT-PCR.
Results :
Using IHC, we found 86.2±3.2% of TG neurons, 83.5%±1.8% of corneal stromal nerves, and 93.8%±2.9% of corneal subbasal nerve plexus express α-MSH. In the cornea, minimal POMC (α-MSH precursor) mRNA was detected and α-MSH immunohistochemical staining was exclusively co-localized with β-Tubulin III, suggesting sensory nerves are likely the source of α-MSH in the cornea. Among the melanocortin receptors (MCR), we found MC1R to be highly expressed in the cornea and vascular endothelial cells. Using a transgenic mouse model lacking MC1R signaling, we found a 3.2-fold increase (P=0.0001) in CNV by slit lamp photography, compared to wild-type mice. Topical application of α-MSH after suture placement led to a 27.8 % reduction (P=0.044) in CNV, and 72.7% and 46.7% decrease in heme-angiogenesis (P=0.0003) and lymph-angiogenesis (P=0.0017), compared to PBS-treated controls. α-MSH treatment reduced the infiltration of CD45+ leukocytes into the cornea, and decreased the expression of proinflammatory cytokines TNF-α, IL-6, IL-1β, and increased the expression of IL-10 in the trigeminal ganglion and cornea. α-MSH treatment also reduced the expression of VEGF-A and VEGFR2 in the cornea in vivo.
Conclusions :
Sensory nerves contribute to corneal angiogenic privilege via α-MSH/MC1R signaling. Topical application of α-MSH reduces corneal angiogenesis by dampening tissue inflammation and VEGF signaling, suggesting that it may have therapeutic potential in treating corneal neovascularization.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.