Abstract
Purpose: :
Vascular endothelial growth factor (VEGF) can mediate nerve growth in addition to its well-described effects on angiogenesis. We evaluated the effects of VEGF on existing and regenerating corneal nerves in thy1-YFP mice using a corneal micropocket assay.
Methods: :
Sucralfate/hydron pellets were impregnated with VEGF or vehicle (negative control). A partial thickness corneal stromal micropocket was made in the cornea of an anesthetized thy-1-YFP mouse, and the pellets implanted midway between the central corneal and limbus. For the analysis of VEGF effects on corneal nerve regeneration, mice received a superficial injury via debridement of the epithelium and underlying corneal nerve plexus one day after pellet implantation. Mice were sacrificed 4 days after surgery and nerves imaged via fluorescence microscopy at the site of pellet implantation and at a site 180 degrees away from the pellet. Images were analyzed using neuron analysis software (Neurolucida) to quantify axonal density and morphology. Stimulation of angiogenesis was monitored via slit lamp examination.
Results: :
In the absence of concomitant nerve injury, Mice receiving VEGF pellets demonstrated minimal neurogenesis at the site of pellet implantation and no changes in nerve density at sites away from the pellet. However, when a concomitant superficial nerve injury was applied with the pellets, a significant increase in nerve regeneration was measured at the site of the pellet as well as at sites distant from the pellet in mice receiving VEGF. No angiogenesis was observed with the doses of VEGF used in these experiments.
Conclusions: :
Sub-angiogenic concentrations of VEGF appeared to have minimal effects on pre-existing innervation of the cornea, but did significantly stimulate corneal nerve regeneration following injury to the corneal sub-basal neuronal plexus. These data suggest a specific role for VEGF in corneal neurobiology and in possible use of VEGF in treating corneal nerve injury.
Keywords: cornea: basic science • innervation: sensation • vascular endothelial growth factor