Need for Animal Models of Meibomian Gland Dysfunction

Recent advances in age-related meibomian gland dysfunction (ARMGD)

Meibomian glands (MGs), located within the tarsal plate of the eyelid, secrete meibum which is the lipid-rich secretion necessary for stabilizing the tear film and preventing tear evaporation. Changes in the quality and quantity of meibum produced causes MG dysfunction (MGD), the leading cause of evaporative dry eye disease (EDED). MGD is an underdiagnosed disease and it is estimated that, in the US, approximately 70 % of the population over 60 have MGD. Three forms of MGD occur based on their meibum secretion: hyposecretory, obstructive, and hypersecretory MGD. The pathophysiology of MGD remains poorly understood, however aging is the primary risk factor. With age, MGs undergo various age-related changes, including decreased acinar basal cell proliferation, hyperkeratinization, MG atrophy, and eventual MG drop-out, leading to age-related MGD (ARMGD). Additionally, studies have suggested that MGs can suffer inflammatory cell infiltration and changes innervation patterns with aging, which could also contribute towards ARMGD. This review focuses on how the aging process affects the MG, and more importantly, how age-related changes to the MG can lead to MG atrophy and MG drop-out, ultimately leading to ARMGD. This review also highlights the most recent developments in potential therapeutic interventions for ARMGD.

Cyclosporin A improves the hyperosmotic response in an experimental dry eye model by inhibiting the HMGB1/TLR4/NF-κB signaling pathway

Hyperosmolarity is closely related to dry eye disease (DED), which induces corneal epithelial cell structure and dysfunction leading to ocular surface inflammation. Cyclosporine A (CSA) is a cyclopeptide consisting of 11 deduced amino acids. It has an immunosuppressive effect and shows a vital function in inhibiting the inflammatory response. The mechanism of CSA in DED is still not entirely clear. This experiment aimed to investigate the possible mechanism of CSA in the hyperosmotic DED model. This study found that CSA can inhibit the transcript levels of DED high mobility group protein 1 (HMGB1), Toll-like receptor 4 (TLR4) and nuclear transcription factor κB (NF-κB) in signaling pathways. In addition, the study also found that 550 mOsm/L can induce the formation of DED models in vivo or in vitro. Furthermore, different concentrations of CSA have different effects on the expression of HMGB1 in human corneal epithelial cells under hyperosmotic stimulation, and high concentrations of CSA may increase the expression of HMGB1. In addition, CSA effectively reduced the corneal fluorescence staining score of the DE group and increased the tear volume of mice. Therefore, this experimental investigation might supply new evidence for the mechanism of CSA in DED, provide a potential new therapy for treating DED, and provide a theoretical basis for CSA treatment of DED.

A New Organotypic 3D Slice Culture of Mouse Meibomian Glands Reveals Impact of Melanocortins

The meibomian glands (MGs) within the eyelids produce a lipid-rich secretion that forms the superficial layer of the tear film. Meibomian gland dysfunction (MGD) results in excessive evaporation of the tear film, which is the leading cause of dry eye disease (DED). To develop a research model similar to the physiological situation of MGs, we established a new 3D organotypic slice culture (OSC) of mouse MGs (mMGs) and investigated the effects of melanocortins on exocrine secretion. Tissue viability, lipid production and morphological changes were analyzed during a 21-day cultivation period. Subsequently, the effects on lipid production and gene expression were examined after stimulation with a melanocortin receptor (MCR) agonist, α-melanocyte-stimulating hormone (α-MSH), and/or an MCR antagonist, JNJ-10229570. The cultivation of mMGs OSCs was possible without impairment for at least seven days. Stimulation with the MCR agonists induced lipid production in a dose-dependent manner, whereas this effect was tapered with the simultaneous incubation of the MCR antagonist. The new 3D OSC model is a promising approach to study the (patho-) physiological properties of MG/MGD while reducing animal studies. Therefore, it may accelerate the search for new treatments for MGD/DED and lead to new insights, such as that melanocortins likely stimulate meibum production.

The effects of systemic aromatase inhibitors on meibomian glands and corneal structure

OBJECTIVES

To evaluate the ocular surface, meibomian glands and corneal structural changes using in vivo confocal microscopy (IVCM) in patients receiving aromatase inhibitor (AI) therapy due to the breast cancer.

METHODS

This prospective observational study included 13 patients undergoing AI therapy. The patients were evaluated before the treatment, at 3- and 6-month timepoints of AI therapy. To examine the ocular surface and tear film, corneal sensitivity (CS) measurement with Cochet-Bonnet Aesthesiometer, tear film break-up time (TBUT), lissamine green (LG) staining, Schirmer I test with anaesthesia (ST) and the ocular-surface disease index (OSDI) questionnaire were performed consecutively. Corneal cell densities and sub-basal nerve plexus were evaluated with IVCM (ConfoScan 4, Nidek, Japan). Finally, quantitative MG drop-out assessment was made using infrared meibography. Shapiro Wilk, Friedman's and Post-hoc Dunn tests were used for the statistical analysis.

RESULTS

TBUT, ST scores, basal epithelium, anterior and posterior keratocytes and endothelial cell densities, long and total sub-basal nerve densities were found to be decreased (p < 0.001, p = 0.023, p < 0.001, p = 0.01, p = 0.002, p = 0.004, p < 0.001, p < 0.001), and meiboscore, CS, OSDI scores and sub-basal nerve tortuosity values were increased (p < 0.001, p = 0.015, p = 0.001, p = 0.004) during the treatment. Endothelial pleomorphism rates were lower at the 3- and 6-month timepoints compared to before the treatment (p = 0.04).

CONCLUSION

This study showed that aromatase inhibitor therapy causes deteriorations in many of the ocular-surface parameters and corneal structural changes in relation with the duration of treatment. These patients should be observed during the therapy in terms of the ocular-surface side effects.

Experimental Models, Induction Protocols, and Measured Parameters in Dry Eye Disease: Focusing on Practical Implications for Experimental Research

Dry eye disease (DED) is one of the major ophthalmological healthcare challenges worldwide. DED is a multifactorial disease characterized by a loss of homeostasis of the tear film, and its main pathogenesis is chronic ocular surface inflammation related with various cellular and molecular signaling cascades. The animal model is a reliable and effective tool for understanding the various pathological mechanisms and molecular cascades in DED. Considerable experimental research has focused on developing new strategies for the prevention and treatment of DED. Several experimental models of DED have been developed, and different animal species such as rats, mice, rabbits, dogs, and primates have been used for these models. Although the basic mechanisms of DED in animals are nearly identical to those in humans, proper knowledge about the induction of animal models is necessary to obtain better and more reliable results. Various experimental models (in vitro and in vivo DED models) were briefly discussed in this review, along with pathologic features, analytical approaches, and common measurements, which will help investigators to use the appropriate cell lines, animal, methods, and evaluation parameters depending on their study design.

Epithelial stem cell homeostasis in Meibomian gland development, dysfunction, and dry eye disease

Dry eye disease affects over 16 million adults in the US, and the majority of cases are due to Meibomian gland dysfunction. Unfortunately, the identity of the stem cells involved in Meibomian gland development and homeostasis is not well elucidated. Here, we report that loss of Krox20, a zinc finger transcription factor involved in the development of ectoderm-derived tissues, or deletion of KROX20-expressing epithelial cells disrupted Meibomian gland formation and homeostasis, leading to dry eye disease secondary to Meibomian gland dysfunction. Ablation of Krox20-lineage cells in adult mice also resulted in dry eye disease, implicating Krox20 in homeostasis of the mature Meibomian gland. Lineage-tracing and expression analyses revealed a restricted KROX20 expression pattern in the ductal areas of the Meibomian gland, although Krox20-lineage cells generate the full, mature Meibomian gland. This suggests that KROX20 marks a stem/progenitor cell population that differentiates to generate the entire Meibomian gland. Our Krox20 mouse models provide a powerful system that delineated the identity of stem cells required for Meibomian gland development and homeostasis and can be used to investigate the factors underlying these processes. They are also robust models of Meibomian gland dysfunction-related dry eye disease, with a potential for use in preclinical therapeutic screening.

A novel transillumination meibography device for in vivo imaging of mouse meibomian glands

PURPOSE

While mouse models of dry eye disease (DED) have been developed, studies evaluating the role of the meibomian glands limited by the inability to temporally document changes. In this report we describe the development of a novel mouse transillumination meibography device and assess the ability of this device to detect age-related changes in the meibomian glands of young and old mice.

METHODS

The mouse meibography device was comprised of a 3 mm wide right angle prism attached to broad spectrum light source by an optical fiber. Eyelids were then pulled over the prism using double tooth forceps and imaged using a stereomicroscope and low light level camera. Meibomian glands from four young and four old male, BALB/c mice were then imaged and analyzed using ImageJ.

RESULTS

In young mice, meibography documented the presence of 7-8 meibomian glands appearing as black and distinct eyelid structures with the length shorter in the lower eyelid compared to the upper eyelids. Eyelids of old mice showed apparent dropout of meibomian glands along with smaller and more irregularly shaped acini. The mean acini area of one meibomian gland was 0.088 ± 0.025 mm² in young mice and 0.080 ± 0.020 mm² in old mice (p = 0.564), but the Meibomian gland density was significantly lower in older mice (41.7 ± 6.4%, 27.3 ± 4.2%) (p = 0.021).

CONCLUSION

We have developed an in vivo meibography device that may prove useful in sequentially documenting changes during development of meibomian gland dysfunction and following treatment.

Neutrophils cause obstruction of eyelid sebaceous glands in inflammatory eye disease in mice

Meibomian glands (MGs) are sebaceous glands of the eyelid margin that secrete lipids needed to avert tear evaporation and to help maintain ocular surface homeostasis. Obstruction of MGs or other forms of MG dysfunction can promote chronic diseases of the ocular surface. Although chronic eyelid inflammation, such as allergic eye disease, is an associated risk factor for obstructive MG dysfunction, it is not clear whether inflammatory processes contribute to the pathophysiology of MG obstruction. We show that polymorphonuclear neutrophils (PMNs) promoted MG obstruction in a chronic inflammatory model of allergic eye disease in mice. Analysis of leukocytes in tears of patients with MG dysfunction showed an increase in PMN numbers compared to healthy subjects. Moreover, PMN numbers in tears positively correlated with clinical severity of MG dysfunction. Our findings point to a role for PMNs in the pathogenesis and progression of MG dysfunction.