Abstract
Purpose :
Corneal innervations derived from trigeminal ganglion maintains the homeostasis and turnover of corneal epithelium. The dysfunction of corneal innervations, named corneal denervation, may cause the epithelial defects, stromal thinning and even perforation as neurotrophic keratopathy. However, the regulatory mechanism of corneal innervation on epithelium remains unclear. Here we used a mouse corneal denervation model and explored the mechanistic relationship between corneal innervation and epithelial homeostasis.
Methods :
Corneal denervation of C57BL/6 mice was conducted according to the previous description of trigeminal axotomy. The apoptosis of corneal epithelium was examined by microarray analysis and TUNEL assay. Neurotransmitter (TRP, KYN, 3-HK and 3-HAA), intracellular NAD content and NAD biosynthesis-related enzymes were analyzed by real-time PCR, immunofluorescence staining and Western blot. The inhibitor of nicotinamide phosphoribosyltransferase (NAMPT) FK866, or the exogenous nicotinamide mononucleotide (NMN) or NAD was used to evaluate the effect of inhibiting or replenishing NAD in the apoptosis of cultured corneal epithelial cells and epithelial erosion in corneal denervated mice. The related signaling pathways were further analyzed by Western blot.
Results :
The mice after corneal denervation showed apparent epithelial cell apoptosis and erosion, accompanied with increased TRP, KYN and 3-HK levels, reduced intracellular NAD contents and NAMPT expression in denervated corneal epithelium. In mice and cultured cells, the NAMPT inhibitor FK866 recapitulated the apoptotic induction of corneal epithelial cells. Moreover, the replenishment of NMN or NAD improved the epithelial erosion in denervated mice, and the proliferation inhibition and apoptosis induction in cultured cells. Mechanistically, NMN or NAD restored the phosphorylation levels of EGFR, ERK1/2, AKT and CREB signaling pathways.
Conclusions :
Corneal denervation impaired the intracellular NAD level, caused cell apoptosis and epithelial defect. The data suggests corneal innervation controls epithelial homeostasis through regulating NAD biosynthesis.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.