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

Citation: Ozaki K, Terayama Y, Matsuura T. Hyperglycemia suppresses age-related increases in corneal peripheral sensory nerves in Wistar Bon Kobori (WBN/Kob) rats. Invest Ophthalmol Vis Sci. 2019;60:4151-4158. https://doi.org/10.1167/iovs.19-28060 PURPOSE. Nerve fiber density in the cornea is an alternative marker for diabetic peripheral neuropathy combined with intraepidermal nerve fiber density (IENFD). Recent studies investigated corneal nerves using rodent models of diabetes. Male Wistar Bon Kobori (WBN/ Kob) rats spontaneously develop long-lasting diabetes and human-like diabetic peripheral neuropathy with vascular lesions. This study investigated corneal nerve fiber density and IENFD in diabetic male WBN/Kob rats as morphological markers of diabetic peripheral neuropathy.METHODS. Male WBN/Kob rats exhibit abnormal glucose tolerance and diabetes at approximately 30 weeks of age, which progresses until approximately 90 weeks of age. Male WBN/Kob rats aged 36 and 90 weeks were therefore used for histological investigations and compared with age-matched nondiabetic female rats. RESULTS.Terminal epithelial nerve density and subbasal nerve plexus density in the central cornea were significantly greater in nondiabetic female rats aged 90 weeks when compared with nondiabetic female rats aged 36 weeks. However, terminal epithelial nerve density and subbasal nerve plexus density did not increase with age in diabetic male WBN/Kob rats, instead lowering by up to 40%, relative to measurements in nondiabetic female rats aged 90 weeks. However, this difference was not statistically significant. IENFD was significantly lower in diabetic male rats aged 90 weeks than in male rats aged 36 weeks, but did not differ between diabetic male rats and nondiabetic female rats aged 90 weeks. CONCLUSIONS.In WBN/Kob rats, hyperglycemia suppresses an age-related increase in peripheral sensory corneal nerve density; therefore, corneal sensory nerves may be important morphological markers of diabetic peripheral sensory neuropathy.

Section: Discussionmentioning

confidence: 99%

Hyperglycemia Suppresses Age-Related Increases in Corneal Peripheral Sensory Nerves in Wistar Bon Kobori (WBN/Kob) Rats

Ozaki

Terayama

Matsuura

2019

“…8,9 By contrast, several rodent studies have demonstrated agerelated changes to corneal structure, including an increase in the thickness of Descemet's membrane and a decrease in endothelial cell density. 10,11 The neural architecture has also shown significant changes including a reduction in density in both the SBNP [12][13][14] and SNTs. 14 Functionally, Stepp et al 13 demonstrated that mechanical corneal sensitivity in mice decreased with age, which paralleled a reduced density of sub-basal nerve axons, despite no change to SNTs.…”

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confidence: 99%

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

Silva

Hill

Downie

et al. 2019

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.

“…1 The density of sensory nerves is influenced by many factors, including sex, age, surgery, and the use of contact lenses. [3][4][5][6] Through the release of neuropeptides, this dense network of corneal nerves exerts different functions in both healthy and pathological conditions, including nerve/ epithelial layer homeostasis and production of tears. 3 A significant part of the corneal sensory nerves contain the neuropeptide Substance P (SP), 7,8 which exerts its activities by binding to the members of the G protein-coupled neurokinin receptors, expressed by a multitude of cell populations.…”

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confidence: 99%

“…[3][4][5][6] Through the release of neuropeptides, this dense network of corneal nerves exerts different functions in both healthy and pathological conditions, including nerve/ epithelial layer homeostasis and production of tears. 3 A significant part of the corneal sensory nerves contain the neuropeptide Substance P (SP), 7,8 which exerts its activities by binding to the members of the G protein-coupled neurokinin receptors, expressed by a multitude of cell populations. 9,10 Among neurokinin receptors, Neurokinin 1 receptor is expressed mainly on neuronal and immune cells, [11][12][13][14] and it has the highest affinity for SP.…”

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confidence: 99%

“…31 Dry eye disease is associated with a reduction of corneal SP expression levels, 32 nerve density, and sensitivity. 3 The aim of this study is to assess the influence of physiological aging on ocular surface sensitivity and tear and corneal SP levels in mouse and in human subjects. Moreover, Copyright 2018 The Authors iovs.arvojournals.org j ISSN: 1552-5783 we investigate the consequence of SP ablation on nerve morphology and nociception in a substance P-knockout mouse.…”

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confidence: 99%

See 1 more Smart Citation

The Effect of Aging on Nerve Morphology and Substance P Expression in Mouse and Human Corneas

Barbariga

Rabiolo

Fonteyne

et al. 2018

PURPOSE. Aging impairs corneal nerve density and sensitivity. Substance P (SP), a neuropeptide secreted by sensory nerves, regulates nerve morphology and nociception. Here, we investigate the relationship between aging, nerve morphology, and SP expression in mouse and human corneas. METHODS. SP levels in mouse corneas (wild type and substance P-knockout) and human corneas and tears were quantified with an ELISA assay. Corneal total nerve length (TNL) was measured with whole-mount b3-tubulin immunofluorescence in mouse and in vivo laser corneal confocal microscopy in humans. SP and b3-tubulin stained cross-sections were used to assess the colocalization of SP and nerves in human and mouse corneas. Ocular surface nociception was assessed with a wiping test in mice. RESULTS. SP colocalizes with sub-basal neurons in mice and humans. In WT mice, SP levels decrease with age (P ¼ 0.0045, 8 vs. 52 weeks; P ¼ 0.004, 26 vs. 52 weeks) as well as TNL (P ¼ 0.018, 8 vs. 26 weeks; P ¼ 0.0001, 8 vs. 52 weeks). Knockout mice show a greater TNL reduction (8 vs. 26 weeks, P ¼ 0.0016) than WT mice. In the oldest WT and age-matched KO mice, nociception is impaired (P ¼ 0.007 and P < 0.0001, respectively), and KO mice sensitivity is restored by topical SP treatment. In humans, SP levels are reduced in old subject corneas and correlate, in tears, with age (P ¼ 0.0368); TNL also decreases in older patients (P ¼ 0.0002). CONCLUSIONS. Age-associated corneal nerve loss is paralleled by reduction of SP expression in mice and humans. SP promotes the maintenance of normal nerve morphology in the long term and modulates nociception in the cornea.