Reduced intraepithelial corneal nerve density and sensitivity accompany desiccating stress and aging in C57BL/6 mice

Mary Ann Stepp,Sonali Pal-Ghosh,Gauri Tadvalkar,Alexa Williams,Stephen C Pflugfelder,Cintia S De Paiva

doi:10.1016/j.exer.2018.01.024

Mary Ann Stepp, Sonali Pal-Ghosh + Show 4 more

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https://doi.org/10.1016/j.exer.2018.01.024

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Abstract

Dry Eye disease causes discomfort and pain in millions of patients. Using a mouse acute desiccating stress (DS) model we show that DS induces a reduction in intraepithelial corneal nerve (ICN) density, corneal sensitivity, and apical extension of the intraepithelial nerve terminals (INTs) that branch from the subbasal nerves (SBNs). Topical application of 0.02% Mitomycin C (MMC) or vehicle alone has no impact on the overall loss of axon density due to acute DS. Chronic dry eye, which develops progressively as C57BL/6 mice age, is accompanied by significant loss of the ICNs and corneal sensitivity between 2 and 24 months of age. QPCR studies show that mRNAs for several proteins that regulate axon growth and extension are reduced in corneal epithelial cells by 24 months of age but those that regulate phagocytosis and autophagy are not altered. Taken together, these data demonstrate that dry eye disease is accompanied by alterations in intraepithelial sensory nerve morphology and function and by reduced expression in corneal epithelial cells of mRNAs encoding genes mediating axon extension.Précis: Acute and chronic mouse models of dry eye disease are used to evaluate the pathologic effects of dry eye on the intraepithelial corneal nerves (ICNs) and corneal epithelial cells. Data show reduced numbers of sensory nerves and alterations in nerve morphology, sensitivity, corneal epithelial cell proliferation, and expression of mRNAs for proteins mediating axon extension accompany the pathology induced by dry eye.

Highlights

The cornea is innervated by a dense collection of sensory axons termed intraepithelial corneal nerves (ICNs) that consist of two components: subbasal nerves (SBNs) ensheathed by corneal epithelial basal cells and intraepithelial nerve terminals (INTs) which branch
Given the millions of patients who have dry eye disease and the numerous ophthalmic uses of topically applied Mitomycin C (MMC), here we evaluate the impact of MMC on axon density in C57BL/6 mice subjected to acute desiccating stress (DS)
We previously reported that the corneas of 15 to 24-month-old female C57BL/6 mice show evidence of dry eye disease with increased Oregon Green dextran (OGD) corneal staining, reduced conjunctival goblet cell density and corneal surface irregularity noted in reflected rings (McClellan et al, 2014; Volpe et al, 2016)

Summary

Introduction

The cornea is innervated by a dense collection of sensory axons termed intraepithelial corneal nerves (ICNs) that consist of two components: subbasal nerves (SBNs) ensheathed by corneal epithelial basal cells and intraepithelial nerve terminals (INTs) which branch from the SBNs and extend perpendicularly towards the apical squames. The nerve cell bodies for the ICNs are located in the trigeminal ganglion (Lopez de Armentia et al, 2000). When damage to the trigeminal ganglion occurs or majority of the ICNs are severed, corneal sensitivity is lost, the corneal epithelium erodes, stroma becomes cloudy, and epithelial cells cease proliferating (Ferrari et al, 2011, 2013; Yamaguchi et al, 2013); ICNs are vital for maintaining a healthy ocular surface. Altered morphology and numbers of the corneal sensory nerves have been reported by clinicians studying small fiber neuropathy and in diseases affecting the central nervous system including Multiple Sclerosis, Parkinson's Disease, and Fibromyalgia (Cruzat et al, 2017). In vivo corneal confocal imaging has been proposed as a method to diagnose the early stages of these conditions and follow the responses of patients to treatment

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