Lipid Mediators in Corneal Nerve Regeneration

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Abstract 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, cornea transplant, herpetic infection, chemical burns, keratoconus, multiple sclerosis, Sjogren’s syndrome, aging 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 the w-3 fatty acid docosahexaenoic acid (DHA) or the docosanoid derivative neuroprotectin D1 (NPD1) stimulate nerve regeneration after corneal surgery that damages the stromal nerves. We have recently found that: 1) corneas stimulated with PEDF+DHA also synthesize other docosanoids, one of them identified as resolvin D6 (RvD6); 2) treatment with PEDF results in activation of a calcium independent phospholipase A2ζ (iPLA2ζ); and 3) treatment also stimulates the gene expression in the cornea of neurotrophins and Semaphorin 7A (SEMA7A), which are secreted into tears, and neuropeptides in the trigeminal ganglia (TG) of a mouse model. Our objective will be to define the cascade of molecular events that conduct the corneal nerve regeneration stimulated by PEDF+DHA. Our central hypothesis is that PEDF+DHA, through specific docosanoids, activates selective gene programs and modulates the inflammatory response that in turn, induces the nerve regeneration that leads to preservation of corneal integrity. We will employ: 1) PEDF-receptor (PEDF-R) knockout (KO) mice and in vivo models of corneal injury relevant to the clinical setting; 2) microfluidic chambers for co-culture of TG neurons and corneal epithelial cells to define the molecular mechanism of neurite outgrowth; 3) LC-tandem mass spectrometry lipidomic analysis to identify and quantify the incorporation of DHA in membrane phosphatidylcholine molecular species and DHA-derivatives NPD1, RvD6 and other docosanoids; 4) flow cytometry and our immunostaining assays to determine content of lymphocytes, dendritic cells, macrophages and neutrophils; 5) immunostaining to quantify corneal nerves; 6) behavioral measurements of ocular sensation to assess the functionality of the regenerated nerves; and 7) molecular biology techniques, including gene editing to study the role of the different genes involved in the signaling of nerve regeneration activated by PEDF+DHA and docosanoids. The proposed studies target new molecular mechanisms to understand and treat complications due to corneal nerve damage. Our innovative approach will define agents for neurotrophic keratitis and dry eye after refractive surgery.