Meibomian Gland Absence Related Dry Eye in Ectodysplasin A Mutant Mice

Strip and boundary detection multi-task learning network for segmentation of meibomian glands

BACKGROUND

Automatic segmentation of meibomian glands in near-infrared meibography images is basis of morphological parameter analysis, which plays a crucial role in facilitating the diagnosis of meibomian gland dysfunction (MGD). The special strip shape and the adhesion between glands make the automatic segmentation of meibomian glands very challenging.

PURPOSE

A strip and boundary detection multi-task learning network (SBD-MTLNet) based on encoder-decoder structure is proposed to realize the automatic segmentation of meibomian glands.

METHODS

A strip mixed attention module (SMAM) is proposed to enhance the network's ability to recognize the strip shape of glands. To alleviate the problem of adhesion between glands, a boundary detection auxiliary network (BDA-Net) is proposed, which introduces boundary features to assist gland segmentation. A self-adaptive interactive information fusion module (SIIFM) based on reverse attention mechanism is proposed to realize information complementation between meibomian gland segmentation and boundary detection tasks. The proposed SBD-MTLNet has been evaluated on an in-house dataset (453 images) and a public dataset MGD-1K (1000 images). Due to the limited number of images, a five-fold cross validation strategy is adopted.

RESULTS

Average dice coefficient of the proposed SBD-MTLNet reaches 81.08% and 84.32% on the in-house dataset and the public one, respectively. Comprehensive experimental results demonstrate the effectiveness the proposed SBD-MTLNet, outperforming other state-of-the-art methods.

CONCLUSIONS

The proposed SBD-MTLNet can focus more on the shape characteristics of the meibomian glands and the boundary contour information between the adjacent glands via multi-task learning strategy. The segmentation results of the proposed method can be used for the quantitative morphological characteristics analysis of meibomian glands, which has potential for the auxiliary diagnosis of MGD in clinic.

Atrophic meibomian gland dysfunction induced by eyelid margin cryotherapy with liquid nitrogen

To develop an atrophic Meibomian Gland Dysfunction (MGD) animal model via liquid nitrogen cryotherapy, the eyelid edges of C57 mice exposure to liquid nitrogen for 30 s. Morphology of MG and ocular surface were assessed using stereomicroscopy and a slit lamp microscope at multiple time points post-injury. Acinar loss and atrophy were observed from day 7, with increased inflammation and apoptosis, and decreased proliferation in acinar cells. Corneal epithelial defects appeared after day 14. Liquid nitrogen induced selective damage to meibomian acinar cells, simulating MGD pathology effectively, with peak effects at day 21, providing a relevant model for atrophic MGD research.

Inflammation in Dry Eye Disease-Pathogenesis, Preclinical Animal Models, and Treatments

Dry eye disease (DED) is a rapidly growing ocular surface disease with a significant socioeconomic impact that affects the patients' visual function and, thus, their quality of life. It is distinguished by a loss of tear film homeostasis, leading to tear film instability, hyperosmolarity, ocular surface inflammation, and neurosensory abnormalities, with all of these playing etiological roles in the propagation of the vicious DED circle. While current treatments primarily focus on reducing tear film instability and hyperosmolarity, increasingly more attention is being placed on tackling the underlying inflammation that propagates and potentiates these factors. As such, preclinical models are crucial to further elucidate the DED pathophysiology and develop novel therapeutic strategies. This review outlines the role of inflammation in DED, highlighting related signs and diagnostic tools before focusing on relevant preclinical animal models and potential therapeutic strategies to tackle DED-associated inflammation.

Models for Meibomian gland dysfunction: In vivo and in vitro

Meibomian gland dysfunction (MGD) is a chronic abnormality of the Meibomian glands (MGs) that is recognized as the leading cause of evaporative dry eye worldwide. Despite its prevalence, however, the pathophysiology of MGD remains elusive, and effective disease management continues to be a challenge. In the past 50 years, different models have been developed to illustrate the pathophysiological nature of MGD and the underlying disease mechanisms. An understanding of these models is crucial if researchers are to select an appropriate model to address specific questions related to MGD and to develop new treatments. Here, we summarize the various models of MGD, discuss their applications and limitations, and provide perspectives for future studies in the field.

Absent meibomian glands and cone dystrophy in ADULT syndrome: identification by whole exome sequencing of pathogenic variants in two causal genes TP63 and CNGB3

BACKGROUND

Ectrodactyly is a rare congenital limb malformation characterized by a deep median cleft of the hand and/or foot due to the absence of central rays. It could be isolated or depicts a part of diverse syndromic forms. Heterozygous pathogenic variants in the TP63 gene are responsible for at least four rare syndromic human disorders associated with ectrodactyly. Among them, ADULT (Acro-Dermato-Ungual-Lacrimal-Tooth) syndrome is characterized by ectodermal dysplasia, excessive freckling, nail dysplasia, and lacrimal duct obstruction, in addition to ectrodactyly and/or syndactyly. Ophthalmic findings are very common in TP63-related disorders, consisting mainly of lacrimal duct hypoplasia. Absent meibomian glands have also been well documented in EEC3 (Ectrodactyly Ectodermal dysplasia Cleft lip/palate) syndrome but not in ADULT syndrome.

METHODS

We report a case of syndromic ectrodactyly consistent with ADULT syndrome, with an additional ophthalmic manifestation of agenesis of meibomian glands. The proband, as well as her elder sister, presented with congenital cone dystrophy.The molecular investigation was performed in the proband using Whole Exome Sequencing. Family segregation of the identified variants was confirmed by Sanger sequencing.

RESULTS

Two clinically relevant variants were found in the proband: the novel de novo heterozygous missense c.931A > G (p.Ser311Gly) in the TP63 gene classified as pathogenic, and the homozygous nonsense pathogenic c.1810C > T (p.Arg604Ter) in the CNGB3 gene. The same homozygous CNGB3 variation was also found in the sister, explaining the cone dystrophy in both cases.

CONCLUSIONS

Whole Exome Sequencing allowed dual molecular diagnoses: de novo TP63-related syndromic ectrodactyly and familial CNGB3-related congenital cone dystrophy.

Comparative evaluation of corneal and limbal epithelial thickness in brachycephalic dogs with and without corneal diseases using spectral domain optical coherence tomography

OBJECTIVE

To evaluate alterations in epithelial thickness during corneal degeneration, corneal pigmentation, and additional features observed through spectral-domain optical coherence tomography (SD-OCT) in brachycephalic dogs.

ANIMALS AND PROCEDURES

The study used 55 eyes from 49 brachycephalic dogs that underwent OCT-containing ophthalmic examinations. The examined eyes were classified into corneal degeneration, corneal pigmentation, and normal groups according to corneal lesions. For each eye, corneal epithelial thickness (CET) in the central cornea and maximum limbal epithelial thickness (maxLET) in 4 quadrants of limbus (superior, inferior, nasal, and temporal) were measured from OCT images. Additional abnormal findings on OCT images, including irregular epithelium, subepithelial hyperreflectivity, and conjunctivochalasis, were also recorded.

RESULTS

The corneal degeneration group had significantly thinner nasal and temporal maxLETs than that of the normal group (p < .001). In the central corneal OCT image of the corneal degeneration group, an irregular epithelium was observed in 70.6% and subepithelial hyperreflectivity in 82.4%, both of which were significantly higher than the normal group (p < .001). In a comparative analysis, the nasal, temporal, and inferior maxLETs were significantly thinner in the corneal pigmentation group than those in the normal group (p < .001, p < .001, and p = .01, respectively).

CONCLUSIONS

Morphological changes in the limbal epithelium were observed in dogs with corneal degeneration and corneal pigmentation. LET reduction could be associated with their pathogenesis and would be valuable as an additional parameter for corneal diseases.

Limbal Stem Cell Dysfunction Induced by Severe Dry Eye via Activation of the p38 MAPK Signaling Pathway

Severe dry eye (SDE) can cause grievous damage to the ocular surface and result in vision impairment and even blindness. To investigate the fate of limbal stem cells in SDE and the underlying mechanism, the current study established an SDE rat model by removing the extraorbital and infraorbital lacrimal glands and maintaining them in a low-humidity environment. One month after the surgery, aqueous tear secretion was reduced dramatically, blood vessels invaded into the central cornea, and inflammatory cells infiltrated into the limbal stroma. The expressions of keratin 12 and paired box gene 6 were down-regulated dramatically, while those of keratin 10, small proline-rich protein 1b, and mucin 5AC were up-regulated in the corneal epithelium of the SDE rats. Cell proliferation in the limbal epithelium was up-regulated, while the stem/progenitor marker adenosine 5'-triphosphate-binding cassette member 2 and the limbal epithelial colony-forming efficiency were decreased in the SDE condition. Furthermore, the p38 mitogen-activated protein kinase signaling pathway was activated in the limbal corneal epithelium of SDE rats. The abnormal differentiation and stemness loss in the corneal epithelium could be reversed upon treatment with a p38 inhibitor in a SDE in vivo model and in vitro hyperosmolar corneal epithelial culture conditions. These data suggest that SDE can lead to limbal stem cell dysfunction, and p38 mitogen-activated protein kinase signaling pathway activation plays an essential role in this process.

Meibomian gland development: Where, when and how?

The Meibomian gland (MG) is an indispensable adnexal structure of eye that produces meibum, an important defensive component for maintaining ocular homeostasis. Normal development and maintenance of the MGs is required for ocular health since atrophic MGs and disturbances in composition and/or secretion of meibum result in major ocular pathologies, collectively termed as Meibomian gland dysfunction (MGD). Currently available therapies for MGD merely provide symptomatic relief and do not treat the underlying deficiency of the MGs. Hence, a thorough understanding of the timeline of MG development, maturation and aging is required for regenerative purposes along with signaling molecules & pathways controlling proper differentiation of MG lineage in mammalian eye. Understanding the factors that contribute to the development of MGs, developmental abnormalities of MGs, and changes in the quality & quantity of meibum with developing phases of MGs are essential for developing potential treatments for MGD. In this review, we compiled a timeline of events and the factors involved in the structural and functional development of MGs and the associated developmental defects of MGs during development, maturation and aging.

Transitory alkali exposure on meibomian gland orifices induces meibomian gland dysfunction

PURPOSE

To determine pathological changes of meibomian glands (MGs) after transient exposure of the rat eyelid margin to alkali solution.

METHODS

Filter paper infiltrated with 1 N sodium hydroxide solution was applied to the eyelid margin of Sprague-Dawley rats for 30 s under general anesthesia, without touching the conjunctiva, after which the ocular surface and eyelid margin were examined by slit-lamp microscopy. In vivo confocal microscopy and stereomicroscopy were subsequently applied to observe MG morphology on day 5, day 10 and day 30 post alkali injury. Eyelid cross-sections were processed for H&E staining, Oil red O staining and immunofluorescent staining.

RESULTS

After alkali injury, there was marked plugging of MG orifices, telangiectasia and hypertrophy of the eyelid margin, while corneal epithelium was intact at post-injury days 5 and 10. However, 30 days after alkali injury, mild corneal epithelial damage was observed. Degeneration of MG acini was observed at days 5 and became aggravated at days 10 and 30, along with MG duct dilation and acini loss. Oil red O staining showed lipid accumulation in the dilated duct. Inflammatory cell infiltration and the presence of apoptotic cells was seen in the MG loci 5 days post injury, but diminished at days 10 and 30. Cytokeratin 10 expression was increased in dilated duct, while cytokeratin 14, PPAR-γ, Ki67 and LRIG1 expression were decreased in the acini of injured loci.

CONCLUSIONS

Transitory alkali exposure of the rat eyelid margin obstructs the MG orifice and induces pathological changes of MG dysfunction.

The Role of Ectodysplasin A on the Ocular Surface Homeostasis

Ectodysplasin A (EDA), a ligand of the TNF family, plays an important role in maintaining the homeostasis of the ocular surface. EDA is necessary for the development of the meibomian gland, the lacrimal gland, as well as the proliferation and barrier function of the corneal epithelium. The mutation of EDA can induce the destruction of the ocular surface resulting in keratopathy, abnormality of the meibomian gland and maturation of the lacrimal gland. Experimental animal studies showed that a prenatal ultrasound-guided intra-amniotic injection or postnatal intravenous administration of soluble recombinant EDA protein can efficiently prevent the development of ocular surface abnormalities in EDA mutant animals. Furthermore, local application of EDA could restore the damaged ocular surface to some extent. Hence, a recombinant EDA-based therapy may serve as a novel paradigm to treat ocular surface disorders, such as meibomian gland dysfunction and corneal epithelium abnormalities.

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.

Extended Overview of Ocular Phenotype with Recent Advances in Hypohidrotic Ectodermal Dysplasia

The term ectodermal dysplasias (EDs) describes a heterogeneous group of inherited developmental disorders that affect several tissues of ectodermal origin. The most common form of EDs is hypohidrotic ectodermal dysplasia (HED), which is characterized by hypodontia, hypotrichosis, and partial or total eccrine sweat gland deficiency. HED is estimated to affect at least 1 in 17,000 people worldwide. Patients with HED have characteristic facies with periorbital hyperpigmentation, depressed nasal bridge, malar hypoplasia, and absent or sparse eyebrows and eyelashes. The common ocular features of HED include madarosis, trichiasis, and ocular chronic surface disease due to dry eye syndrome, which manifests clinically with discomfort, photophobia, and redness. Dry eye is common in HED and results from a combination of ocular surface defects: mucus abnormalities (abnormal conjunctival mucinous glands), aqueous tear deficiency (abnormalities in the lacrimal gland) and lipid deficiency (due to the partial or total absence of the meibomian glands; modified sebaceous glands with the tarsal plate). Sight-threatening complications result from ocular surface disease, including corneal ulceration and perforation with subsequent corneal scarring and neovascularization. Rare ocular features have been reported and include bilateral or unilateral congenital cataracts, bilateral glaucoma, chorioretinal atrophy and atresia of the nasolacrimal duct. Recognition of the ocular manifestations of HED is required to perform clinical surveillance, instigate supportive and preventative treatment, and manage ocular complications.

Lacrimal Gland Microenvironment Changes After Obstruction of Lacrimal Gland Ducts

Purpose

To investigate microenvironment changes of the lacrimal gland after obstruction of lacrimal gland ducts.

Methods

The ducts of rat exorbital lacrimal gland were ligated by sutures for different durations. After that, the sutures in some animals were released, and they were observed for 21 days to evaluate the recovery of the lacrimal gland. Slit lamp and tear secretion test was performed to evaluate ocular surface and lacrimal gland function. The lacrimal gland and cornea were harvested and processed for hematoxylin and eosin staining, oil red O staining, LipidTOX staining, Masson staining, quantitative real time polymerase chain reaction, and immunofluorescence staining.

Results

After the lacrimal gland ducts were blocked, tear secretion and the weight of the lacrimal gland were reduced. Incidence of corneal neovascularization increased after seven days. Intraglandular ducts dilated and acini destroyed. Long-term ligation induced fibrosis and lipid accumulation of the lacrimal glands. Inflammatory cell infiltrated and inflammatory factors upregulated. Proliferative and apoptotic cells increased. Structure of myoepithelial cells and basement membrane was destroyed. The p63 expression increased whereas Pax6 expression decreased. After suture release, tear secretion and structure of acini could recover in less than seven days after ligation, with a decrease in inflammatory cell infiltration and fibrosis relief. Apoptotic cells and proliferative cells increased at five days thereafter. The structure of the myoepithelial cells and basement membrane could not recover three days after ligation, and the number of mesenchymal cells increased in ligation after five to 14 days.

Conclusions

Blockage of the lacrimal gland ducts results in dystrophy of lacrimal gland acini cells, inflammation, and lipid accumulation of the lacrimal gland microenvironment. Long-term duct blockage will cause irreversible lacrimal gland failure.

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

The EDA deficient mouse has Zymbal's gland hypoplasia and acute otitis externa

In mice, rats, dogs and humans, the growth and function of sebaceous glands and eyelid Meibomian glands depend on the ectodysplasin signalling pathway. Mutation of genes encoding the ligand EDA, its transmembrane receptor EDAR and the intracellular signal transducer EDARADD leads to hypohidrotic ectodermal dysplasia, characterised by impaired development of teeth and hair, as well as cutaneous glands. The rodent ear canal has a large auditory sebaceous gland, the Zymbal’s gland, the function of which in the health of the ear canal has not been determined. We report that EDA-deficient mice, EDAR-deficient mice and EDARADD-deficient rats have Zymbal’s gland hypoplasia. Eda^Ta mice have 25% prevalence of otitis externa at postnatal day 21 and treatment with agonist anti-EDAR antibodies rescues Zymbal’s glands. The aetiopathogenesis of otitis externa involves infection with Gram-positive cocci, and dosing pregnant and lactating Eda^Ta females and pups with enrofloxacin reduces the prevalence of otitis externa. We infer that the deficit of sebum is the principal factor in predisposition to bacterial infection, and the Eda^Ta mouse is a potentially useful microbial challenge model for human acute otitis externa.

Summary: Ectodysplasin-deficient mice have growth retardation of the auditory sebaceous Zymbal's gland and are predisposed to spontaneous bacterial infection of the outer ear canal by opportunistic pathogens.

Exocrine gland structure-function relationships

Fluid secretion by exocrine glandular organs is essential to the survival of mammals. Each glandular unit within the body is uniquely organized to carry out its own specific functions, with failure to establish these specialized structures resulting in impaired organ function. Here, we review glandular organs in terms of shared and divergent architecture. We first describe the structural organization of the diverse glandular secretory units (the end-pieces) and their fluid transporting systems (the ducts) within the mammalian system, focusing on how tissue architecture corresponds to functional output. We then highlight how defects in development of end-piece and ductal architecture impacts secretory function. Finally, we discuss how knowledge of exocrine gland structure-function relationships can be applied to the development of new diagnostics, regenerative approaches and tissue regeneration.

Artificial Intelligence to Detect Meibomian Gland Dysfunction From in-vivo Laser Confocal Microscopy

Background: In recent years, deep learning has been widely used in a variety of ophthalmic diseases. As a common ophthalmic disease, meibomian gland dysfunction (MGD) has a unique phenotype in in-vivo laser confocal microscope imaging (VLCMI). The purpose of our study was to investigate a deep learning algorithm to differentiate and classify obstructive MGD (OMGD), atrophic MGD (AMGD) and normal groups. Methods: In this study, a multi-layer deep convolution neural network (CNN) was trained using VLCMI from OMGD, AMGD and healthy subjects as verified by medical experts. The automatic differential diagnosis of OMGD, AMGD and healthy people was tested by comparing its image-based identification of each group with the medical expert diagnosis. The CNN was trained and validated with 4,985 and 1,663 VLCMI images, respectively. By using established enhancement techniques, 1,663 untrained VLCMI images were tested. Results: In this study, we included 2,766 healthy control VLCMIs, 2,744 from OMGD and 2,801 from AMGD. Of the three models, differential diagnostic accuracy of the DenseNet169 CNN was highest at over 97%. The sensitivity and specificity of the DenseNet169 model for OMGD were 88.8 and 95.4%, respectively; and for AMGD 89.4 and 98.4%, respectively. Conclusion: This study described a deep learning algorithm to automatically check and classify VLCMI images of MGD. By optimizing the algorithm, the classifier model displayed excellent accuracy. With further development, this model may become an effective tool for the differential diagnosis of MGD.

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.

IL-22 promotes the formation of a MUC17 glycocalyx barrier in the postnatal small intestine during weaning

The intestine is under constant exposure to chemicals, antigens, and microorganisms from the external environment. Apical aspects of transporting epithelial cells (enterocytes) form a brush-border membrane (BBM), shaped by packed microvilli coated with a dense glycocalyx. We present evidence showing that the glycocalyx forms an epithelial barrier that prevents exogenous molecules and live bacteria from gaining access to BBM. We use a multi-omics approach to investigate the function and regulation of membrane mucins exposed on the BBM during postnatal development of the mouse small intestine. Muc17 is identified as a major membrane mucin in the glycocalyx that is specifically upregulated by IL-22 as part of an epithelial defense repertoire during weaning. High levels of IL-22 at time of weaning reprogram neonatal postmitotic progenitor enterocytes to differentiate into Muc17-expressing enterocytes, as found in the adult intestine during homeostasis. Our findings propose a role for Muc17 in epithelial barrier function in the small intestine.

Meibomian gland dysfunction model induced with complete Freund's adjuvant in C57BL/6 mice

AIM

To establish a new inflammatory animal model of meibomian gland dysfunction (MGD) in C57BL/6 mice.

METHODS

C57BL/6 mice were randomly divided into complete Freund's adjuvant (CFA) group (14 animals, 14 eyes), naphthazolin hydrochloride (NH) group (14 animals, 14 eyes) and control group (14 animals, 14 eyes). In CFA group, CFA was used in eyelid conjunctiva injection; in NH group, NH eye drops were used twice a day; control group was injected with equal dose of saline at the same time point and same site with animals in CFA group. The meibomian gland orifices score (MGOS) was evaluated on a scale of 0 to 3 in the middle five meibomian gland orifices of the upper and lower eyelid using slit lamp. After the successful induction of each animal model, intense pulsed light (IPL) was introduced on each mouse in CFA and NH group. Oil red O (ORO), hematoxylin and eosin (H&E) staining were performed before and after successful induction of CFA, NH and control group.

RESULTS

At 12wk after CFA injection, inflammatory cell infiltration and fiber necrosis was observed, with acinar density and duct dilatation significantly lower compared with control group. In NH group, the meibomian gland acini were relatively smaller and deformed compared with control group, the number of meibomian gland acini was also slightly lower. No inflammatory cell or fiber necrosis was observed in NH group. After three times of IPL treatment (5/10 mice in each group, and the other 5 mice served as non-IPL control), MGOS was significantly lower in IPL-treated mice in NH group (P<0.01). After three times of IPL treatment, the MGOS of NH group was significantly lower than that in the CFA group (P<0.01).

CONCLUSION

We develop a novel animal model that studies the role of inflammation in the development of MGD and IPL treatment. This model indicates that persistent inflammatory state may be the cause of MGD and weaken the therapeutic effect of IPL.

Meibomian Gland Dysfunction: What Have Animal Models Taught Us?

Studies have estimated that currently 344 million people worldwide and 16.4 million adults in the US have some form of dry eye disease (DED). It is believed that approximately 70% of DED cases are due to some form of evaporative dry eye, for which Meibomian gland dysfunction (MGD) is the major cause. Unfortunately, currently there is no effective treatment for MGD, and solely palliative care is available. Given the importance of MGD in DED, there has been a growing interest in studying Meibomian gland development, homeostasis and pathology, and, also, in developing therapies for treating and/or preventing MGD. For such, animal models have shown to be a vital tool. Much of what is known today about the Meibomian gland and MGD was learnt from these important animal models. In particular, canine and rabbit models have been essential for studying the physiopathology and progression of DED, and the mouse model, which includes different knockout strains, has enabled the identification of specific pathways potentially involved in MGD. Herein, we provide a bibliographic review on the various animal models that have been used to study Meibomian gland development, Meibomian gland homeostasis and MGD, primarily focusing on publications between 2000 and 2020.

Fetal gene therapy and pharmacotherapy to treat congenital hearing loss and vestibular dysfunction

Disabling hearing loss is expected to affect over 900 million people worldwide by 2050. The World Health Organization estimates that the annual economic impact of hearing loss globally is US$ 750 billion. The inability to hear may complicate effective interpersonal communication and negatively impact personal and professional relationships. Recent advances in the genetic diagnosis of inner ear disease have keenly focused attention on strategies to restore hearing and balance in individuals with defined gene mutations. Mouse models of human hearing loss serve as the primary approach to test gene therapies and pharmacotherapies. The goal of this review is to articulate the rationale for fetal gene therapy and pharmacotherapy to treat congenital hearing loss and vestibular dysfunction. The differential onset of hearing in mice and humans suggests that a prenatal window of therapeutic efficacy in humans may be optimal to restore sensory function. Mouse studies demonstrating the utility of early fetal intervention in the inner ear show promise. We focus on the modulation of gene expression through two strategies that have successfully treated deafness in animal models and have had clinical success for other conditions in humans: gene replacement and antisense oligonucleotide-mediated modulation of gene expression. The recent establishment of effective therapies targeting the juvenile and adult mouse provide informative counterexamples where intervention in the maturing and fully functional mouse inner ear may be effective. Distillation of the current literature leads to the conclusion that novel therapeutic strategies to treat genetic deafness and imbalance will soon translate to clinical trials.

Therapeutic Effects of STAT3 Inhibition on Experimental Murine Dry Eye

Purpose

To investigate the therapeutic effects of targeting signal transducer and activator of transcription-3 (STAT3) activation on the ocular surface damage of dry eye in mice.

Methods

Adult Balb/C and C57BL/6 mice with benzalkonium chloride (BAC) treatment, lacrimal gland excision, and meibomian gland dysfunction were used as dry eye models. The levels of phosphorylated STAT3 (p-STAT3) were detected with immunofluorescence staining and Western blotting. STAT3 inhibition was performed by topical application of STAT3 inhibitor S3I-201. Corneal epithelial barrier function, tear production, and conjunctival goblet cell density were quantified with fluorescein sodium staining, phenol red cotton test, and histochemical staining. The expressions of matrix metalloproteinase (MMP)-3/9, TUNEL, and inflammation cytokines were assessed with immunofluorescence staining, qPCR, and ELISA assays. The therapeutic effect of S3I-201 was further compared with the Janus kinase inhibitor tofacitinib and ruxolitinib.

Results

Elevated levels of nuclear p-STAT3 were detected in the corneal and conjunctival epithelium of three dry eye models. Topical application of S3I-201 improved corneal epithelial barrier function, increased tear production and conjunctival goblet cell density in BAC-induced dry eye mice. Moreover, S3I-201 decreased the expression of MMP-3/9, suppressed the apoptosis of corneal and conjunctival epithelial cells, and reduced the levels of IL-1β, IL-6, IL-17A, and IFN-γ. Compared with tofacitinib and ruxolitinib, the STAT3 inhibitor S3I-201 showed superior improvement of tear production and inflammatory cytokine expression in lacrimal gland.

Conclusions

Elevated STAT3 activation is involved in the pathogenesis of dry eye, while targeting STAT3 effectively alleviates BAC-induced ocular surface damage.

Ocular mucins in dry eye disease

Dry eye disease is a common and multifactorial disease with a high prevalence worldwide. Water loss, reduced expression of glycocalyx mucins, and loss of goblet cells secreting gel-forming mucins are hallmarks of dry eye disease. Mucins are large and complex heavily glycosylated proteins. Their organization in the tear film remains unclear, but they play a key role to protect and maintain integrity of the ocular surface. Mice have been extremely valuable mammalian models with which to study ocular physiology and disease, and to evaluate eye therapies. Genetically modified mice and spontaneously occurring mutants with eye defects have proven to be powerful tools for the pharmaceutical industry, clinicians, and basic researchers investigating dry eye disease. However, ocular mucins remain relatively under-studied and inadequately characterized. This review aims to summarize current knowledge about mucin production at the ocular surface in healthy individuals and in dry eye disease, and to compile an overview of mouse models available for the study of mucins in dry eye disease.

Ectodysplasin-A signaling is a key integrator in the lacrimal gland-cornea feedback loop

A lack of ectodysplasin-A (Eda) signaling leads to dry eye symptoms, which have so far only been associated with altered Meibomian glands. Here, we used loss-of-function (Eda ^-/-) mutant mice to unravel the impact of Eda signaling on lacrimal gland formation, maturation and subsequent physiological function. Our study demonstrates that Eda activity is dispensable during lacrimal gland embryonic development. However, using a transcriptomic approach, we show that the Eda pathway is necessary for proper cell terminal differentiation in lacrimal gland epithelium and correlated with modified expression of secreted factors commonly found in the tear film. Finally, we discovered that lacrimal glands present a bilateral reduction of Eda signaling activity in response to unilateral corneal injury. This observation hints towards a role for the Eda pathway in controlling the switch from basal to reflex tears, to support corneal wound healing. Collectively, our data suggest a crucial implication of Eda signaling in the cornea-lacrimal gland feedback loop, both in physiological and pathophysiological conditions. Our findings demonstrate that Eda downstream targets could help alleviate dry eye symptoms.

Hyperlipidemia induces meibomian gland dysfunction

PURPOSE

To investigate the pathological changes of the meibomian gland (MG) and ocular surface in Apolipoprotein E knockout (ApoE^-/-) mice and to investigate the association of meibomian gland dysfunction (MGD) with hyperlipidemia.

METHODS

Total plasma cholesterol was measured in different ages of ApoE^-/- and wild type (WT) mice, whilst the ocular surfaces were observed by slit-lamp biomicroscopy. MG sections were subjected to H&E staining, Oil Red O staining, TUNEL assay and immunostaining. Quantitate RT-PCR and Western blot analyses were performed to detect the relative gene expression in MGs. The 5-month-old ApoE^-/- mice were administered with rosiglitazone or GW9662 + rosiglitazone via oral gavage for 2 months to determine their effect on MG pathological change.

RESULTS

We found eyelid abnormality, MG dropout, abnormal MG acinar morphology, dilated MG duct and plugging of the MG orifice in ApoE^-/- mice. MG acini in ApoE^-/- mice showed exaggerated lipid accumulation. Abnormal keratinization increased in MG duct, accompanied with decreased proliferation and increased apoptosis in ApoE^-/- mice. Inflammatory cells infiltrated into the surrounding microenvironment of MG acini, and the NF-κB signaling pathway was activated in MG acinar cells. Oxidative stress was evident in MG acinar cells of ApoE^-/- mice. Further investigation showed downregulation of PPAR-γ in MG acinar cells of ApoE^-/- mice. PPAR-γ agonist rosiglitazone treatment reduced the morbidity of eyelid, as well as corneal pathological changes and MG inflammation in ApoE^-/- mice.

CONCLUSION

MGD and hyperlipidemia are closely associated in ApoE^-/- mice, which represent a new model to study the pathophysiology of MGD related to dyslipidemia.

Morphology of the Meibomian gland evaluated using meibography in patients with hypohidrotic ectodermal dysplasia

INTRODUCTION

Hypohidrotic ectodermal dysplasia (HED) is a rare disease that results from the abnormal development of the ectodermal germ layer in early embryogenesis. In these patients, hypoplasia of Meibomian glands is one of the most frequent ophthalmological manifestations. The main aim of this study is to evaluate the usefulness of meibography for the morphology of Meibomian glands in a group of patients with HED, and to compare it with a control group.

METHODS

A total of 14 eyes of 7 patients diagnosed with HED were included, and 32 eyes of 16 patients were included as a control group. The meibographic study was carried out using CA-800 Corneal Analyser (Topcon®). Grading of images was assessed by a meibomian gland atrophy score: grade 0, no alterations; grade 1, ≤25% gland atrophy; grade 2, 25% to 50% gland atrophy; grade 3, 51% to 75% gland atrophy; and grade 4 >75% gland atrophy. Both groups were compared using the Mann-Whitney U non-parametric test.

RESULTS

All patients with HED showed some degree of gland atrophy, with 57% showing severe atrophy (>75% of gland atrophy), 35.8% with a grade 3, and 7.2% grade 2. The mean grade of glandular atrophy in HED was 3 (1-4). In the control group, 62.5% had no involvement (grade 0), with 28.1% showing grade 1 and 9.4% grade 2 gland atrophy. The mean glandular atrophy grade within the control group was 0 (0-2). There were statistically significant differences between both groups.

CONCLUSIONS

Meibography is a simple diagnostic tool that allows to differentiate between patients without disease and those with HED.

Sleep deprivation disrupts the lacrimal system and induces dry eye disease

Sleep deficiency is a common public health problem associated with many diseases, such as obesity and cardiovascular disease. In this study, we established a sleep deprivation (SD) mouse model using a 'stick over water' method and observed the effect of sleep deficiency on ocular surface health. We found that SD decreased aqueous tear secretion; increased corneal epithelial cell defects, corneal sensitivity, and apoptosis; and induced squamous metaplasia of the corneal epithelium. These pathological changes mimic the typical features of dry eye. However, there was no obvious corneal inflammation and conjunctival goblet cell change after SD for 10 days. Meanwhile, lacrimal gland hypertrophy along with abnormal lipid metabolites, secretory proteins and free amino-acid profiles became apparent as the SD duration increased. Furthermore, the ocular surface changes induced by SD for 10 days were largely reversed after 14 days of rest. We conclude that SD compromises lacrimal system function and induces dry eye. These findings will benefit the clinical diagnosis and treatment of sleep-disorder-related ocular surface diseases.

Loss of β Epithelial Sodium Channel Function in Meibomian Glands Produces Pseudohypoaldosteronism 1-Like Ocular Disease in Mice

Human subjects with pseudohypoaldosteronism-1 because of loss-of-function mutations in epithelial sodium channel (ENaC) subunits exhibit meibomian gland (MG) dysfunction. A conditional βENaC MG knockout (KO) mouse model was generated to elucidate the pathogenesis of absent ENaC function in the MG and associated ocular surface disease. βENaC MG KO mice exhibited a striking age-dependent, female-predominant MG dysfunction phenotype, with white toothpaste-like secretions observed obstructing MG orifices at 7 weeks of age. There were compensatory increases in tear production but higher tear sodium and indexes of mucin concentration in βENaC MG KO mice. Histologically, MG acinar atrophy was observed with ductal enlargement and ductal epithelial hyperstratification. Inflammatory cell infiltration was observed in both MG and conjunctiva of βENaC MG KO mice. In older βENaC MG KO mice (5 to 11 months), significant ocular surface pathologies were noted, including corneal opacification, ulceration, neovascularization, and ectasia. Inflammation in MG and conjunctiva was confirmed by increased cytokine gene and protein expression and positive Ly-6B.2 immunostaining. Cell proliferation assays revealed lower proliferation rates of MG cells derived from βENaC MG KO than control mice, suggesting that βENaC plays a role in cell renewal of mouse MG. Loss of βENaC function resulted in MG disease and severe ocular surface damage that phenocopied aspects of human pseudohypoaldosteronism-1 MG disease and was sex dependent.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.

Ectodysplasin A protein promotes corneal epithelial cell proliferation

The EDA gene encodes ectodysplasin A (Eda), which if mutated causes X-linked hypohidrotic ectodermal dysplasia (XLHED) disease in humans. Ocular surface changes occur in XLHED patients whereas its underlying mechanism remains elusive. In this study, we found Eda was highly expressed in meibomian glands, and it was detected in human tears but not serum. Corneal epithelial integrity was defective and the thickness was reduced in the early postnatal stage of Eda mutant Tabby mice. Corneal epithelial cell proliferation decreased and the epithelial wound healing was delayed in Tabby mice, whereas it was restored by exogenous Eda. Eda exposure promoted mouse corneal epithelial wound healing during organ culture, whereas scratch wound assay showed that it did not affect human corneal epithelial cell line migration. Epidermal growth factor receptor (EGFR), phosphorylated EGFR (p-EGFR), and phosphorylated ERK1/2 (p-ERK) were down-regulated in Tabby mice corneal epithelium. Eda treatment up-regulated the expression of Ki67, EGFR, p-EGFR, and p-ERK in human corneal epithelial cells in a dose-dependent manner. In conclusion, Eda protein can be secreted from meibomian glands and promotes corneal epithelial cell proliferation through regulation of the EGFR signaling pathway. Eda release into the tears plays an essential role in the maintenance of corneal epithelial homeostasis.

A Novel Model of Meibomian Gland Dysfunction Induced with Complete Freund's Adjuvant in Rabbits

A novel meibomian gland dysfunction (MGD) model induced by the injection of complete Freund’s adjuvant (CFA) in rabbits was developed to facilitate the understanding of the pathophysiology of MGD with meibomitis. In addition, we sought to evaluate treatment with steroid eye drops in this model. Male Japanese white rabbits were subcutaneously injected with CFA into the upper eyelid margin. The eyelid margins of the rabbits were chronologically observed through slit lamp examination. The development of meibomitis was assessed through histopathology. We evaluated the effects of topically applied tobramycin/dexamethasone (Tob/Dex) eye drops on the plugged orifices and telangiectasia. After the injection of CFA, slit lamp examination revealed markedly plugged orifices, telangiectasia around the orifices and a toothpaste-like meibum, as compared with the normal eyelids. Histopathology revealed granulation tissue with infiltration of inflammatory cells, hyperkeratinization of the ductal epithelium, and cystic dilatation of ducts in the meibomian gland. The orifices were plugged with a proteinaceous substance. Tob/Dex eye drops significantly suppressed the plugging and telangiectasia around the orifices. Through the injection of CFA, we successfully established a novel rabbit MGD that mimics the symptoms observed in humans meibomitis. This model should be useful in the evaluation of the efficacy of drug candidates.

Genetically modified laboratory mice with sebaceous glands abnormalities

Sebaceous glands (SG) are exocrine glands that release their product by holocrine secretion, meaning that the whole cell becomes a secretion following disruption of the membrane. SG may be found in association with a hair follicle, forming the pilosebaceous unit, or as modified SG at different body sites such as the eyelids (Meibomian glands) or the preputial glands. Depending on their location, SG fulfill a number of functions, including protection of the skin and fur, thermoregulation, formation of the tear lipid film, and pheromone-based communication. Accordingly, SG abnormalities are associated with several diseases such as acne, cicatricial alopecia, and dry eye disease. An increasing number of genetically modified laboratory mouse lines develop SG abnormalities, and their study may provide important clues regarding the molecular pathways regulating SG development, physiology, and pathology. Here, we summarize in tabulated form the available mouse lines with SG abnormalities and, focusing on selected examples, discuss the insights they provide into SG biology and pathology. We hope this survey will become a helpful information source for researchers with a primary interest in SG but also as for researchers from unrelated fields that are unexpectedly confronted with a SG phenotype in newly generated mouse lines.

Need for Animal Models of Meibomian Gland Dysfunction

Evaporative dry eye has gained increasing interest in recent years in academia, pharmaceutical, and medical device industries. The main cause of this type of dry eye is attributed to meibomian gland dysfunction (MGD). MGD is a diffuse abnormality of the meibomian glands characterised by terminal duct obstruction and eventually leading to signs and symptoms of dry eye. There have been only a few reported animal models of MGD, but recent advances are likely to lead to new models and better ways to assess the pathology in these animals. Recent models reported include one based on cautery of the meibomian glands in mice and another based on aggravated allergy in mice. These developments will enable better pre-clinical assessment of novel therapies in the future.