Neural mechanism underlying corneal injuries by ammonia

Washington University, Saint Louis MO

Investigators

Abstract

Project Summary Chemical injury of the eye is devastating and frequently leads to permanent eye damage or even blindness. Among those chemical agents that cause ocular injuries, ammonia is known to cause most severe corneal burns and related pain. Prevailing researches have suggested that ammonia impairs the corneal epithelial wound healing via inflammation and damaging corneal basal epithelia cells or limbal stem cells. However, the impacts of ammonia on corneal sensory fibers have not been characterized. We recently discovered that ammonia can massively activate corneal sensory fibers upon exposure. We hence hypothesize that over-activation of corneal sensory fibers by ammonia leads to nerve degeneration and contributes to impairment of corneal wound healing. To test this hypothesis, we will first use histochemical and transcriptomic studies to correlate the delayed corneal wound regeneration with the extent of corneal nerve degradation in mouse models. The ocular pain associated with ammonia exposure will be quantified by behavioral studies in mice (Aim 1). Results from these studies will help define corneal damage caused by ammonia exposure and provide knowledge regarding ammonia-induced corneal denervation in corneal wound healing. Second, to delineate the activating mechanism of corneal sensory fibers by ammonia, we will conduct ex vivo calcium imaging to characterize the sensitivity and response profiles of corneal sensory fibers to ammonia. As over-activation of sensory fibers often leads to nerve degeneration, we will conduct genetic axonal tracing to elucidate the changes of corneal sensory fibers over time after ammonia exposure and the role of various ion channels of sensory fibers in responding to ammonia (Aim 2). Results from these experiments will provide the critical link between the ammonia sensitivity and degeneration of corneal sensory fibers, shedding light on the neural mechanism underlying ocular pain and corneal denervation by ammonia. Third, we will investigate the effects of activity-dependent neuronal silencing in preventing over-activation of corneal sensory nerves by ammonia, thereby attenuating ammonia-induced ocular pain and promoting corneal wound healing (Aim 3). These studies will lead to a new and dual therapeutic strategy of using neural silencing for ocular chemical burn. In summary, the discovery that corneal sensory fibers are activated and then degraded by ammonia opens a new research arena for corneal chemical burns. The proposed studies will not only reveal a previously unrecognized neural mechanism behind corneal injuries by ammonia, but may also help develop novel therapeutic strategies to alleviate ocular pain and corneal injuries by ammonia for the first time.