The Effects of Aging on Corneal and Ocular Surface Homeostasis in Mice

Abstract

PURPOSE. Aging is a risk factor for dry eye disease. The aim of this study was to investigate if aging is associated with a range of signs of dry eye disease, including tear hyperosmolarity, reduced nerve density, and increased dendritic cell number, in mice. METHOD. Healthy C57BL/6 female mice, aged 2 months (young, n ¼ 10) and 22 months (aged, n ¼ 11) were used. Clinical assessments included corneal sensitivity (Cochet-Bonnet esthesiometry), tear secretion (Phenol red thread test), tear film osmolarity (TearLab osmometer), and corneal thickness (optical coherence tomography). The sum length of the corneal superficial terminals and sub-basal nerves, density of vertical nerve projections, and density and tree area of resident epithelial dendritic cells, were assessed using immunofluorescence and confocal microscopy. RESULTS. Aged mice had significantly higher tear secretion, lower corneal sensitivity, and a thicker corneal stroma but thinner epithelium. There was no significant intergroup difference for tear osmolarity. Aged mice showed a significantly lower sum length of nerves in the superficial terminals and sub-basal plexus, relative to young mice. Dendritic cell density and morphology were similar in both groups. CONCLUSIONS. In mice, aging is associated with higher tear secretion and corneal epithelial thinning, together with lower corneal nerve density and sensitivity. However, aging was not significantly associated with changes to tear osmolarity or dendritic cell density or size, despite a significant reduction in total nerve length. These findings demonstrate that aged mice exhibit some changes to ocular surface parameters that parallel the anomalies evident in dry eye disease.

Transient tear hyperosmolarity disrupts the neuroimmune homeostasis of the ocular surface and facilitates dry eye onset

“…Then, the field area (dendrite tip to tip) of up to 10 DCs per image was determined using the Polygons Selections tool in Image J. Cells were randomly selected starting from the top left corner, as described by De Silva et al 33 For dendrite quantification, up to 10 DCs per image were similarly selected from the same images, and the dendrites were counted manually.…”

“…We followed the methods validated previously by others. 32,33 For sub-basal nerve quantification in the central corneal, Sholl analysis was applied using the corresponding ImageJ plugin. A maximal intensity Zprojection of the 3-5 slices spanning the basal corneal epithelial cells was created, then 50-pixel rolling ball background correction was applied and, finally, 12 concentric circles with a 10-µm radius step size were traced onto it; the results are expressed as the mean number of intersections of TUBB3 + nerves in each concentric circle.…”

“…30 In a DED model, desiccating stress rapidly induces a break in the apical corneal epithelial barrier, 31 along with structural and functional alterations in corneal intraepithelial nerves. 32,33 Given these observations, increased exposure of the corneal intraepithelial nerves to the abnormal tear film might be responsible for the aforementioned changes, which in turn also play a role in DED pathophysiology.…”

The neuroregenerative effects of topical decorin on the injured mouse cornea

“…Three non-overlapping z-series (z-step size 1 μm, image size 290 × 290 μm) were captured from the central (within central 1.5 mm of the cornea) and peripheral cornea (between 2 mm and 2.5 mm from the centre of the cornea) respectively. Separate z-stacks of the SNTs and SBNP were created by generating z-projections of the superficial and basal epithelial layers [9,47]. To compare the innate inflammatory response between groups, z-stack images of the anterior corneal stroma (5 μm directly below the basal epithelium) were created for analysing neutrophils (CD45 + Iba1 − with a distinct polymorphonuclear appearance) and macrophages (CD45 + Iba1 + ).…”

Combining In Vivo Corneal Confocal Microscopy with Deep Learning-based Analysis Reveals Sensory Nerve Fiber Loss in Acute SIV Infection

“…Of note, reduced corneal nerve fiber density has been reported with aging in both mice and humans of advanced age. (21,22) Only tortuosity was higher in the oldest group, but not significantly. Our previous studies of HIV-induced damage to the peripheral nervous system based in the SIV/pigtailed macaque model have revealed significant loss of small sensory nerve fibers in the epidermis of the skin in the SIV/pigtailed macaque model at 14 days post-SIV infection (25); similar early loss of epidermal nerve fibers was found in a rhesus macaque SIV model 21 days post-SIV infection.…”