Corneal surface injuries are painful and expose the eye to infections that can destroy vision. During our previous funding period, we characterized a model for the study of recurrent corneal erosions in mice and showed that subbasal nerves (SBNs) fail to reinnervate the cornea prior to erosion formation. In addition, we showed that we could induce SBN reinnervation by treating debridement wounded corneas with mitomycin C (MMC). The long-term goal of our research is to identify the factors that prevent the corneal epithelium from reforming an intact stable barrier after trauma. One factor is failed reinnervation of the SBNs. Our data lead us to propose two hypotheses.
The first (Aim A) is that corneal epithelial basal cells adhere to, protect, organize, and maintain the subbasal nerves (SBNs) that originate from the trigeminal ganglion. The corneal epithelial cells protect individual SBNs by secreting a laminin-rich ECM to insulate them from one another, organize SBNs by enclosing clusters of several SBNs within infoldings of their basal and basolateral cell membranes forming epithelial cell:axon adhesions, and maintain optimal SBN function by removing damaged SBN stubs during homeostasis and after injury by phagocytosis. We will test this hypothesis by conducting experiments to answer the following questions: 1. Do corneal epithelial cells adhere to and provide support to SBNs using adhesion complexes and proteins similar to those used by non-myelinating Schwann cells? 2. Do corneal epithelial cells phagocytose axonal debris during homeostasis and in response to SBN damage? 3. Do corneal epithelial cells respond to SBN denervation by altering expression of genes that regulate axon regeneration in Schwann cells? A second hypothesis (Aim B) proposed is to resolve corneal pathology after trauma or disease, adhesion between corneal epithelial cells, SBNs, and the basement membrane must be restored to levels present prior to development of pathology. This hypothesis is supported by preliminary data showing that MMC reduces corneal epithelial cell migration in vitro and MMP9 expression in vivo. We will test this hypothesis by conducting experiments to answer the following questions: 1. Do corneal epithelial cells at the center of the wounded mouse cornea undergo senescence? 2. Can reinnervation be accelerated by treating crush (trephine only) wounded corneas with MMC? 3. Can erosions be eliminated after they form by treating mouse corneas with MMC? 4. Can MMC improve reinnervation of corneas in mice with dry eye disease? 5. Does a prior injury (conditioning lesion) improve reinnervation after crush or debridement wounds? Comparing reinnervation after different wound types allows us to differentiate between mechanisms that permit reinnervation after crush wounds from those that prevent reinnervation after debridement wounds and will give us insight into how MMC enhances reinnervation.
Statement: Reduced innervation of the cornea by sensory nerves occurs after surgery, with aging, and in patients with recurrent erosions. The proposed experiments use mice to characterize adhesion between corneal epithelial cells, sensory nerves, and the stroma after different types of corneal wounds treated with or without the drug Mitomycin C. These studies will give us a better understanding of how corneal sensory nerves are maintained and how they regenerate after injury.
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