Alterations in corneal innervation result in impaired corneal sensation, severe dry eye and damage to the epithelium that may in turn lead to corneal ulcers, melting and perforation. These alterations frequently occur after refractive surgery, corneal transplant, herpetic infection, chemical burns, keratoconus, multiple sclerosis, Sjogren's syndrome and diabetes mellitus. Although there are treatments to alleviate severe dry eye, there are no therapies to compensate for the loss of innervation. This research project builds upon our finding that pigment epithelium-derived factor (PEDF) plus docosahexaenoic acid (DHA) or the docosanoid derivative neuroprotectin D1 (NPD1) induces nerve regeneration after corneal surgery that damages stromal nerves. We now focus on defining the molecular mechanism by which PEDF plus DHA or NPD1 regenerates corneal nerves after experimental refractive surgery. We additionally investigate the bioactivity of these mediators in an animal model of herpes simplex virus type-1 (HSV-1), focusing on compromised sensitivity, nerve regeneration and inflammation. Our central hypothesis is that PEDF acts through a mediated mechanism that activates cytosolic phospholipase A2/extracellular-regulated kinase (cPLA2/ERK1/2) signaling to release DHA for the synthesis of NPD1, which stimulates nerve growth factor (NGF) expression that, in turn, modulates corneal nerve regeneration. In addition to corneal surgery, HSV-1 infections cause lost sensitivity, dry eye and corneal lesions that could lead to stromal and epithelial damage. We propose to test the hypothesis that NPD1 induces recovery of sensitivity and regenerates corneal nerves after herpes viral infection. We will employ: 1) in vivo models of refractive surgery and HSV-1 infection relevant to the clinical setting;2) primary and cell line cultures and co-cultures of trigeminal ganglion neurons with corneal epithelial cells and stromal fibroblasts to uncover the molecular mechanisms of neurite outgrowth;3) LC-tandem mass- spectrometry lipidomic analysis to characterize and quantify DHA and its derivative, NPD1;4) gas esthesiometry to assess corneal sensitivity to different modalities of stimulus after nerve regeneration;and 5) molecular biology techniques and our immunostaining method to quantify the epithelial, sub-basal and stromal corneal nerves. The proposed studies target new mechanisms to understand and treat complications due to corneal nerve damage. Our innovative approach will define potential agents for neurotrophic keratitis and dry eye after refractive surgery and HSV-1 infection.
The research proposed in this project focuses on understanding the molecular mechanisms of enhancing the regeneration of nerves damaged after corneal surgery procedures and after herpes simplex virus (HSV)-1 infection, and decreasing the incidence of complications by providing innovative understanding of the role played by the novel omega-3-derived lipid mediator, neuroprotectin D1. Our innovative approach will define potential therapeutic agents for neurotrophic keratitis and dry eye, yielding new insights into how nerve injury stemming from surgical procedures and HSV-1 infection can be ameliorated or prevented.
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