Assessment of mucin-related gene alterations following treatment with rebamipide ophthalmic suspension in Sjögren's syndrome-associated dry eyes

Beneficial Effect of Rebamipide Eye Drops on Blue Light-Induced Oxidative Damage in the Ocular Surface

Purpose: We evaluated the capacity of rebamipide (REB) to alleviate corneal epithelial damage induced via blue light (BL) exposure. Methods: Eight-week-old C57BL/6 mice were exposed to BL (410 nm, 100 J) twice daily for 10 days. The mice were randomly divided into 5 groups: 1 untreated and 4 groups receiving BL exposure ± different topical treatments: BL exposure alone, carboxymethylcellulose, 5% N-acetylcysteine, and REB. Reactive oxygen species (ROS) levels were assessed, and Bcl-2-associated X protein (BAX) protein was analyzed. Apoptotic cells were detected, inflammatory cytokine levels [tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6)] were measured using enzyme-linked immunosorbent assay (ELISA), and histopathological changes in the cornea were evaluated using hematoxylin and eosin (H&E) staining. Results: The REB group demonstrated significantly lower BL exposure-induced ROS levels (P < 0.01) and BAX expression (P < 0.01) than the BL group. The number of Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive cells were lower in the REB group than in the BL group (P < 0.01). Furthermore, ELISA analysis revealed significantly reduced TNF-α and IL-6 levels in the REB group relative to BL group levels (P < 0.01). Hematoxylin and eosin staining showed preservation of corneal epithelial thickness. Conclusions: Rebamipide alleviated BL-induced oxidative damage to ocular surfaces by reducing ROS levels, inhibiting apoptosis, and suppressing inflammatory cytokine expression.

Ectoine Enhances Mucin Production Via Restoring IL-13/IFN-γ Balance in a Murine Dry Eye Model

Purpose

This study aimed to explore protective effects and potential mechanism of ectoine, a natural osmoprotectant, on ocular surface mucin production in dry eye disease.

Methods

A dry eye model was established in C57BL/6 mice exposed to desiccating stress (DS) with untreated (UT) mice as controls. DS mice were topically treated with 2.0% ectoine or PBS vehicle. Corneal epithelial defects were assessed by Oregon Green Dextran (OGD) fluorescent staining. Conjunctival goblet cells, ocular mucins, and T help (Th) cytokines were evaluated by immunofluorescent staining or ELISA, and RT-qPCR.

Results

Compared with UT mice, corneal epithelial defects were detected as strong punctate OGD fluorescent staining in DS mice with vehicle, whereas ectoine treatment largely reduced OGD staining to near-normal levels. Conjunctival goblet cell density and cell size decreased markedly in DS mice, but was significantly recovered by ectoine treatment. The protein production and mRNA expression of two gel-forming secreted MUC5AC and MUC2, and 4 transmembrane mucins, MUC1, MUC4, MUC16, and MUC15, largely decreased in DS mice, but was restored by ectoine. Furthermore, Th2 cytokine IL-13 was inhibited, whereas Th1 cytokine IFN-γ was stimulated at protein and mRNA levels in conjunctiva and draining cervical lymph nodes (CLNs) of DS mice, leading to decreased IL-13/IFN-γ ratio. Interestingly, 2.0% ectoine reversed their alternations and restored IL-13/IFN-γ balance.

Conclusions

Our findings demonstrate that topical ectoine significantly reduces corneal damage, and enhances goblet cell density and mucin production through restoring imbalanced IL-13/IFN-γ signaling in murine dry eye model. This suggests therapeutic potential of natural osmoprotectant ectoine for dry eye disease.

Assessment of Mucin-Associated Gene Expression Levels on the Ocular Surface

The ocular surface is covered with a mucus layer. The mucin-associated genes expressed in the ocular surface cells include MUC1, MUC4, MUC5AC, and MUC16. Impression cytology is useful for collecting specimens from the ocular surface, their histological examination, and measuring mucin-associated gene expression levels. The expression of mucin-associated gene levels was assessed by quantitative polymerase chain reaction. The expression levels of these mucin-associated genes are potential biomarkers for ocular surface diseases, including dry eye disease.

Involvement of aquaporin 5 in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease with the pathological hallmark of lymphoplasmacytic infiltration of exocrine glands - more specifically salivary and lacrimal glands - resulting in a diminished production of tears and saliva (sicca syndrome). The pathophysiology underscoring the mechanisms of the sicca symptoms in SS has still yet to be unraveled but recent advances have identified a cardinal role of aquaporin-5 (AQP5) as a key player in saliva secretion as well as salivary gland epithelial cell dysregulation. AQP5 expression and localization are significantly altered in salivary glands from patients and mice models of the disease, shedding light on a putative mechanism accounting for diminished salivary flow. Furthermore, aberrant expression and localization of AQP5 protein partners, such as prolactin-inducible protein and ezrin, may account for altered AQP5 localization in salivary glands from patients suffering from SS and are considered as new players in SS development. This review provides an overview of the role of AQP5 in SS salivary gland epithelial cell dysregulation, focusing on its trafficking and protein-protein interactions.

Transmembrane Mucin 1 Blocks Fluorescein Ingress to Corneal Epithelium

Purpose

To determine the role of transmembrane mucins in blocking fluorescein ingress to the corneal epithelium and its deficiency in contributing to corneal fluorescein punctate staining.

Methods

A dry eye model was established by extirpating lacrimal and Harderian glands in rabbits to correlate the expression of mucins with fluorescein-stained areas on the corneal button using immunofluorescence. Expression of transmembrane mucins was promoted in human corneal epithelial cells (HCECs) by culturing with the mucin-promoting medium (MPM) or diquafosol treatment. Conversely, the expression of mucins was downregulated by knockdown with short hairpin RNA. The role of mucin1 extracellular domain in fluorescein ingress was further verified by overexpression of N-terminally truncated mucin1 in HCECs.

Results

In the rabbit dry eye model, the expression level of mucin1 was significantly decreased in superficial corneal epithelial cells where fluorescein punctate staining was observed. Upregulation of mucin1 and mucin16 in HCECs promoted by MPM or by diquafosol treatment impeded intracellular fluorescein ingress. Downregulation of mucin1 and mucin16 enhanced fluorescence ingress in HCECs after fluorescein staining. Overexpression of truncated mucin1 did not alter the fluorescein intensity of fluorescein-stained HCECs, supporting the notion that the ability of mucin1 to block fluorescein ingress was primarily mediated by its extracellular domain. Minimal inherent expression of mucin16 in the rabbit cornea limited the validation of its role in blocking fluorescein ingress in vivo.

Conclusion

Transmembrane mucin1 blocks fluorescein ingress in the corneal epithelium, explaining how fluorescein staining is positive when the level of transmembrane mucins is disturbed in dry eyes.

Alterations in Mucin-Associated Gene Expression on the Ocular Surface in Active and Stable Stages of Atopic and Vernal Keratoconjunctivitis

Purpose

To evaluate the presence of ocular surface mucin in patients with atopic and vernal keratoconjunctivitis (AKC/VKC), we investigated the mRNA expression levels of SAM-pointed domain-containing ETS-like factor (SPDEF) and mucin-related genes on the ocular surface.

Methods

Nineteen patients with AKC or VKC were divided into two groups based on the severity of the disease as determined by their clinical scores for AKC/VKC: the stable group and the active group. Impression cytology was performed in all patients using filter paper, and the expression levels of SPDEF, MUC1, MUC4, MUC5AC, MUC16, and eotaxin-2 mRNA were determined by real-time reverse-transcription polymerase chain reaction.

Results

The results showed that the expression levels of SPDEF and MUC5AC mRNA in the active group were significantly decreased compared with those in the stable group. Furthermore, clinical scores were significantly negatively correlated with the expression levels of SPDEF mRNA and significantly positively correlated with the expression levels of eotaxin-2, which is a biomarker for eosinophilic inflammation on the ocular surface. Cluster analysis classified the patients with AKC/VKC into three clusters, and the stable group was divided into two clusters according to the condition of ocular surface mucin.

Conclusions

Ocular surface mucin in patients with AKC/VKC is altered in accordance with the clinical severity of the disease.