Histopathology and selective biomarker expression in human meibomian glands

The effects of age and dysfunction on meibomian gland population dynamics

PURPOSE

While meibomian gland dysfunction (MGD) is widely recognized as a major cause of evaporative dry eye disease, little is known about normal gland differentiation and lipid synthesis or the mechanism underlying gland atrophy and abnormal lipid secretion. The purpose of this study was to use single-cell and spatial transcriptomics to probe changes in cell composition, differentiation, and gene expression associated with two murine models of MGD: age-related gland atrophy in wild-type mice and altered meibum quality in acyl-CoA wax alcohol acyltransferase 2 (Awat2) knockout (KO) mice.

METHODS

Young (6 month) and old (22 month) wild type, C57Bl/6 mice and young (3 month) and old (13 month) Awat2 KO mice were used in these studies. For single-cell analysis, the tarsal plate was dissected from the upper and lower eyelids, and single cells isolated and submitted to the UCI Genomic Core, while for the spatial analysis frozen tissue sections were shipped to Resolve Biosciences on dry ice and sections probed in duplicate using a meibomian gland specific, 100 gene Molecular Chartography panel.

RESULTS

Analysis of gene expression patterns identified the stratified expression of lipogenic genes during meibocyte differentiation, which may control the progressive synthesis of meibum lipids; an age-related decrease in meibocytes; and increased immune cell infiltration. Additionally, we detected unique immune cell populations in the Awat2 KO mouse suggesting activation of psoriasis-like, inflammatory pathways perhaps caused by ductal dilation and hyperplasia.

CONCLUSION

Together these findings support novel mechanism controlling gland function and dysfunction.

Meibography signal intensity as a novel image biomarker for meibomian gland function: evidence from cross-sectional and longitudinal analyses

Background

Meibomian gland dysfunction (MGD), one of the most common ocular surface diseases, can induce dry eye and reduce patients' quality of life. Methodological limitations have resulted in contradictory interpretations of gland function. This study sought to investigate the correlation between meibography signal intensity (SI) and meibomian gland (MG) function and to validate an MGD classification strategy based on different levels of SI.

Methods

A multicenter, cross-sectional analysis was conducted on 817 eyes from 361 patients with MGD and 52 healthy controls. Additionally, 78 eyes from 39 patients with MGD who had undergone LipiFlow treatment were recruited for longitudinal analyses. The SI value was obtained via meibography using an automated analyzer, and all participants underwent ocular surface examinations. A cross-sectional analysis was performed to determine SI distribution and its relationship to clinical characteristics via a generalized estimating equation model. Longitudinal analyses were conducted on the treatment cohort using a mixed-effects model to explore the outcome in different SI levels.

Results

Regression analysis revealed significant correlations between SI and lipid layer thickness (β=0.016), meibum expressibility (β=-0.676), meibum quality (β=-0.251), and fluorescein-stained tear-film break-up time (FBUT) (β=0.064) (all P values <0.001 for the above associations). Low-level SI MGD cases exhibited the most severe clinical signs, including the worst meibum expressibility (16% for level 3) and quality scores (19% for level 3), the shortest FBUT (3.82±0.13 s), and the thinnest lipid layer (65.68±2.58 nm), (all P values <0.05, respectively). Patients with medium SI showed the lowest ocular surface disease index (OSDI) value (26.64±1.06), the longest FBUT (4.56±0.08 s), and the thickest lipid layer (80.20±2.90 nm). After treatment, the high SI values reduced significantly at each follow-up point compared to baseline (all P values <0.05). The medium SI group demonstrated the greatest improvement in symptoms and signs, followed by the high SI group, and the low SI group.

Conclusions

Automated measurements of SI can effectively reflect MG secretory activity. The proposed low, medium, and high SI classifications represent different functional subtypes of MGD.

The biomechanical proteins different between low myopic corneas and moderate to high myopic corneas in human

PURPOSE

To explore the biomechanical proteins different between low myopic corneas and moderate to high myopic corneas.

METHODS

A total of 27 myopic corneas were used for the Tandem Mass Tag (TMT) proteomics analysis. Differentially expressed proteins (DEPs) were clustered with fold changes > 1.20 or < 0.83 and p < 0.05. Proteins and Proteins Interactions (PPIs) were conducted to find hub proteins; Uniprot database was to screen proteins with biomechanical functions, and Parallel Reaction Monitoring (PRM) was performed to verify the TMT results. Pearson analysis was used to reveal the correlations between myopic degrees and biomechanical proteins. The Immunofluorescence (IF) staining was used to observe the protein distributions.

RESULTS

In total, 34 DEPs were observed between moderate myopic corneas and low myopic corneas; 103 DEPs were observed between high myopic corneas and low myopic corneas, 20 proteins overlapped. The PPIs analysis showed keratin 2, keratins 10 and PRSS1 were hub proteins. The Uniprot function analysis suggested keratin 2 and keratin 10 exhibited biomechanical functions. The PRM demonstrated keratin 2 and keratin 10 levels were significantly lower in moderate and high myopic corneas, which was consistent with the TMT proteomics results. IF staining also demonstrated keratin 2 and keratin 10 were less distributed in moderate and high myopic corneas than in low myopic corneas.

CONCLUSIONS

The levels of biomechanical proteins keratin 2 and keratin 10 are significantly lower in moderate and high myopic corneas than in low myopic corneas.

Elucidating the mechanism of corneal epithelial cell repair: unraveling the impact of growth factors

The repair mechanism for corneal epithelial cell injuries encompasses migration, proliferation, and differentiation of corneal epithelial cells, and extracellular matrix remodeling of the stromal structural integrity. Furthermore, it involves the consequential impact of corneal limbal stem cells (LSCs). In recent years, as our comprehension of the mediating mechanisms underlying corneal epithelial injury repair has advanced, it has become increasingly apparent that growth factors play a pivotal role in this intricate process. These growth factors actively contribute to the restoration of corneal epithelial injuries by orchestrating responses and facilitating specific interactions at targeted sites. This article systematically summarizes the role of growth factors in corneal epithelial cell injury repair by searching relevant literature in recent years, and explores the limitations of current literature search, providing a certain scientific basis for subsequent basic research and clinical applications.

The Yin and Yang of non-immune and immune responses in meibomian gland dysfunction

Meibomian gland dysfunction (MGD) is a leading cause of dry eye disease and one of the most common ophthalmic conditions encountered in eye clinics worldwide. These holocrine glands are situated in the eyelid, where they produce specialized lipids, or meibum, needed to lubricate the eye surface and slow tear film evaporation - functions which are critical to preserving high-resolution vision. MGD results in tear instability, rapid tear evaporation, changes in local microflora, and dry eye disease, amongst other pathological entities. While studies identifying the mechanisms of MGD have generally focused on gland obstruction, we now know that age is a major risk factor for MGD that is associated with abnormal cell differentiation and renewal. It is also now appreciated that immune-inflammatory disorders, such as certain autoimmune diseases and atopy, may trigger MGD, as demonstrated through a T cell-driven neutrophil response. Here, we independently discuss the underlying roles of gland and immune related factors in MGD, as well as the integration of these two distinct mechanisms into a unified perspective that may aid future studies. From this unique standpoint, we propose a revised model in which glandular dysfunction and immunopathogenic pathways are not primary versus secondary contributors in MGD, but are fluid, interactive, and dynamic, which we likened to the Yin and Yang of MGD.

Cellular senescence promotes meibomian gland dysfunction in a chronic graft-versus-host disease mouse model

PURPOSE

Aging is a well-established risk factor for meibomian gland dysfunction (MGD). We previously reported an accelerated cellular senescence phenomenon in the lacrimal glands of a murine model of chronic graft-versus-host disease (cGVHD). Herein, we aimed to elucidate the relationship between cellular senescence and MGD in cGVHD mice, utilizing the senolytic agent ABT-263.

METHODS

A cGVHD mouse model was established through allogeneic bone marrow transplantation (BMT) from B10.D2 to BALB/c mice. Subsequently, cGVHD mice were treated with either ABT-263 or vehicle. The eyelids of recipients were analyzed at 4-week intervals post-BMT in both groups.

RESULTS

Meibomian gland (MG) area was significantly smaller in cGVHD mice than in syngeneic control mice. ABT-263-treated mice retained a significantly larger MG area than their vehicle-treated counterparts. Pathological and immunohistochemical examinations revealed significant reductions in eyelid tissue inflammation and pathological fibrosis in the ABT-263 group compared to that in the vehicle-treated group. Additionally, expression of DNA damage markers, senescent cell markers, and senescence-associated secretory phenotype (SASP) factors was elevated in the eyelids of cGVHD mice compared with that in syngeneic mice. The expression of these cellular senescence-associated molecules was considerably suppressed in ABT-263-treated eyelids compared to that in vehicle-treated ones.

CONCLUSIONS

Cellular senescence, along with expression of SASP factors, exhibited increased activity in the eyelids, particularly in the MGs of cGVHD mice. ABT-263 mitigated the severity of MGD. These findings highlight the potential of targeting cellular senescence as an effective approach for MGD treatment in cGVHD.

Factors affecting long-term changes of meibomian gland in MGD patients

PURPOSE

To explore the long-term course of patients with meibomian gland dysfunction (MGD), and to analyse potential factors affecting the recovery of meibomian gland (MG) dropout.

METHODS

Seventy-nine MGD patients (79 eyes) aged 36.03±15.78 years old who underwent more than one year of follow-up were enrolled in this retrospective study. Corneal fluorescein staining (CFS), tear meniscus height (TMH), noninvasive breakup time (NIBUT), and noncontact meibography at baseline and last visit were collected and analysed. Then an automatic MG analyzer was used to measure the morphological and functional parameters of MGs, including their area ratio (AR), tortuosity index (TI), and signal index (SI). The patients whose AR increased by more than 5% were defined as MG improvement, and AR decreased by more than 5% was MG worsening.

RESULTS

A total of 79 patients (79 eyes) were assessed with at least 1-year of follow-up. More than 1/3 of MGD patients (27 eyes, 34.2%) underwent MG improvement, and 30.4% of MGs became worsened. Age (P=0.002), gender (P<0.001), IPL treatment (P=0.013), the change of CFS (P=0.0015), and the recovery of SI (P=0.035) showed significant differences among different recovery groups. Age(P<0.001), female sex (P=0.003), ΔCFS (P<0.001), AR at baseline (P<0.001) were negative correlation with AR recovery, and the change of SI (P=0.003) and IPL treatment (P=0.003) had a positive correlation with it. Among them, age (P=0.038), the change of CFS (P=0.004), and AR at baseline (P=0.007) were confirmed as negatively correlated factors predicting the long-term change of the MG.

CONCLUSION

Although the MGD treatment has continued for more than 1 year, only 34.2% of MGD patients were observed to undergo MG improvement. Younger patients and patients with better CFS recovery seem to have more opportunities to improve their MGs.

Modeling meibum secretion: Alternatives for obstructive Meibomian Gland Dysfunction (MGD)

PURPOSE

While changes in meibum quality are correlated with severity of meibomian gland dysfunction (MGD) and dry eye disease, little is known regarding the mechanics of meibum secretion. The purpose of this study was to develop a finite element model of meibum secretion and evaluate the effect of various factors that might impact meibum delivery to the ocular surface.

METHODS

A finite element analysis in COMSOL 6.0 was used to simulate the flow of meibum within the gland's terminal excretory duct. Historical normal human meibum rheology data taken over the meibum melting range from fluid (35-40 °C) to solid (25-30 °C) were then used to calculate the minimum yield stress and plastic viscosity of meibum. The effects of meibum melting state, eyelid pressure and terminal duct diameter on meibum flow rates were then systematically investigated.

RESULTS

The melting state of meibum from liquid to solid was associated with an increase in the minimum yield stress and plastic viscosity that caused an exponential decrease in meibum flow. Modeling also established that there was a linear correlation between meibum flow rate and eyelid pressure needed to express meibum and the 4th power of the terminal duct radius.

CONCLUSIONS

Our results suggest that changes in the melting state of meibum from fluid to solid, as well as changes in the radius of the terminal excretory duct and the force exerted by the eyelid can lead to dramatic decreases in the flow of meibum. Together these findings suggest alternative mechanisms for meibomian gland obstruction.

Anatomical and Histological Study of the Upper Tarsus in Asian

OBJECTIVE

The aim of this study was to observe and analyze the anatomical and histological characteristics of the upper tarsus in Asian.

METHODS

A total of 15 Asians (14 adults, 1 child) were used. The sagittal sections with thickness of 3 μm in the middle of the upper eyelid were prepared and stained with hematoxylin-eosin, Masson trichrome and anti-smooth muscle actin antibody staining, and then were observed and photographed under light microscopy.

RESULTS

On the sagittal section, the upper end of the tarsus was connected with the Müller muscle and the part of the posterior layer of the levator aponeurosis; the lower end was the inflated part of the palpebral margin; the superficial surface was connected with the pretarsal fascia; and the deep surface was connected with Müller muscle aponeurosis and palpebral conjunctiva. Histologically, the tarsus was similar to the structure between dense fibrous connective tissue and cartilage, and its main structures include meibomian glands and its ducts, accessory lacrimal glands, glands of Moll, glands of Zeis, eyelash hair follicles, Riolan muscle, blood vessels, and collagen fibers. Through the observation of the tarsus of a child, compared with the adult specimen, the meibomian gland tissue was more abundant; the collagen fibers density was significantly lower and arranged orderly; the blood vessel density was significantly higher; α-SMA positive smooth muscle cells could be seen in the upper end of the tarsus and its superficial and deep surfaces.

CONCLUSIONS

In this study, the internal and adjacent anatomical structures of the upper tarsus in Asians were observed under a microscope, and according to the histological characteristics, the tarsus was divided into 3 parts and 3 types. Through the preliminary analysis, the tarsus was likely to show different histological characteristics in different individuals and age groups of Asians. There was a certain correlation between the degree of meibomian gland atrophy, the degree of collagen fibrosis and the density of blood vessel in the tarsus.

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.

Culture of primary human meibomian gland cells from surgically excised eyelid tissue

Meibomian gland dysfunction is one of the most common ocular diseases, with therapeutic treatment being primarily palliative due to our incomplete understanding of meibomian gland (MG) pathophysiology. To progress in vitro studies of human MG, this study describes a comprehensive protocol, with detailed troubleshooting, for the successful isolation, cultivation and cryopreservation of primary MG cells using biopsy-size segments of human eyelid tissue that would otherwise be discarded during surgery. MG acini were isolated and used to establish and propagate lipid-producing primary human MG cells. The primary cell viability during culture procedure was maintained through the application of Rho-associated coiled-coil containing protein kinase inhibitor (Y-27632, 10 μM) and collagen I from rat tails. Transcriptomic analysis of differentiated primary human MG cells confirmed cell origin and revealed high-level expression of many lipogenesis-related genes such as stearoyl-CoA desaturase (SCD), ELOVL Fatty Acid Elongase 1 (ELOVL1) and fatty acid synthase (FASN). Primary tarsal plate fibroblasts were also successfully isolated, cultured and cryopreserved. Established primary human MG cells and tarsal plate fibroblasts presented in this study have potential for applications in 3D models and bioengineered tissue that facilitate research in understanding of MG biology and pathophysiology.

Mechanisms of Extraorbital Lacrimal Gland Aging in Mice: An Integrative Analysis of the Temporal Transcriptome

Purpose

This study used high-throughput RNA sequencing (RNA-Seq) and bioinformatics analysis to investigate the altered transcriptome profile of aging lacrimal glands in mice that occurs over the course of a 24-hour cycle.

Methods

Male C57BL/6J mice aged 12 weeks (young) and 20 months (aging) were housed in a pathogen-free setting with a 12-hour light/12-hour dark cycle. Throughout a 24-hour cycle, mouse extraorbital lacrimal glands (ELGs) were collected at eight time points at three-hour intervals. To prepare for the high-throughput RNA-Seq, whole mRNA was extracted. Differentially expressed genes (DEGs) in the young and aging groups were subjected to bioinformatic analysis based on diurnal patterns. Furthermore, the cell populations in which significant DEGs express and signaling pathways occur were validated at the single-cell RNA sequencing (scRNA-seq) level.

Results

The total transcriptome composition was significantly altered in aging ELGs compared with that in young mouse ELGs at eight time points during the 24-hour cycle, with 864 upregulated and 228 downregulated DEGs, which were primarily enriched in inflammatory pathways. Further comparative analysis of the point-to-point transcriptome revealed that aging ELGs underwent alterations in the temporal transcriptome profile in several pathways, including the inflammation-related, metabolism-related, mitochondrial bioenergetic function-associated, synaptome neural activity-associated, cell processes-associated, DNA processing-associated and fibrosis-associated pathways. Most of these pathways occurred separately in distinct cell populations.

Conclusions

Transcriptome profiles of aging lacrimal glands undergo considerable diurnal time-dependent changes; this finding offers a comprehensive source of information to better understand the pathophysiology of lacrimal gland aging and its underlying mechanisms.

Study of pathological processes of meibomian gland dysfunction by in vitro culture airlifting conditions

Meibomian gland dysfunction (MGD) is a group of disorders linked by functional abnormalities of the meibomian glands. Current studies on MGD pathogenesis focus on meibomian gland cells, providing information on a single cell's response to experimental manipulation, and do not maintain the architecture of an intact meibomian gland acinus and the acinar epithelial cells' secretion state in vivo. In this study, rat meibomian gland explants were cultured by a Transwell chamber-assisted method under an air-liquid interface (airlift) in vitro for 96 h. Analyses for tissue viability, histology, biomarker expression, and lipid accumulation were performed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and TUNEL assays, hematoxylin and eosin (H&E) staining, immunofluorescence, Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR), transmission electron microscopy (TEM), and western blotting (WB). MTT, TUNEL, and H&E staining indicated better tissue viability and morphology than the submerged conditions used in previous studies. Levels of MGD biomarkers, including keratin 1 (KRT1) and 14 (KRT14) and peroxisome proliferator-activated receptor-gamma (PPAR-γ), along with oxidative stress markers, including reactive oxygen species, malondialdehyde, and 4-hydroxy-2-nonenal, gradually increased over culture time. The MGD pathophysiological changes and biomarker expression of meibomian gland explants cultured under airlift conditions were similar to those reported by previous studies, indicating that abnormal acinar cell differentiation and glandular epithelial cell hyperkeratosis may contribute to obstructive MGD occurrence.

Meibomian gland stem/progenitor cells: The hunt for gland renewal

Meibomian glands (MGs) secrete lipid (meibum) onto the ocular surface to form the outermost layer of the tear film. Proper meibum secretion is essential for stabilizing the tear film, reducing aqueous tear evaporation, and maintaining the homeostasis of the ocular surface. Atrophy of MG as occurs with aging, leads to reduction of meibum secretion, loss of ocular surface homeostasis and evaporative dry eye disease (EDED). Since MGs are holocrine glands, secretion of meibum requires continuous self-renewal of lipid-secreting acinar meibocytes by stem/progenitor cells, whose proliferative potential is dramatically reduced with age leading to MG atrophy and an age-related meibomian gland dysfunction (ARMGD). Understanding the cellular and molecular mechanisms regulating meibocyte stem/progenitor cell maintenance and renewal may provide novel approaches to regenerating MG and treating EDED. Towards that end, recent label retaining cell and lineage-tracing experiments as well as knock-out transgenic mouse studies have begun to identify the location and identities of meibocyte progenitor cells and potential growth and transcription factors that may regulate meibocyte renewal. In addition, recent reports have shown that ARMGD may be reversed by novel therapeutics in mice. Herein, we discuss our current understanding of meibocyte stem/progenitor cells and the hunt for gland renewal.

Morphological variants of meibomian glands: correlation of meibography features with histopathology findings

PURPOSE

This study describes the histopathological features of different morphological variants of human meibomian glands (MGs) seen on infrared imaging.

METHODS

Tarsal plates dissected from seven cadaveric upper eyelids were imaged using infrared meibography, and then studied histopathologically using H&E, peroxisome proliferator-activated receptor gamma (PPARγ, meibocyte differentiation marker) and Ki-67 (cellular proliferation marker) antibody staining. The different morphological characteristics (varying size and shape) of MGs on meibography were correlated with histopathology findings using image analysis software.

RESULTS

Of the total 127 glands, the morphological variants observed on meibography based on size were: normal (n=62), short (n=18), severely short (n=6) and dropout (n=12) glands, and on shape were: hooked (n=2), tortuous (n=5), overlapping (n=1), thick (n=15) and fluffy (n=6) glands. Short, hooked, tortuous and overlapping glands had similar acinar and ductal histology as seen in normal glands whereas thick, and fluffy glands had increased acinar diameter. All glands except the severely short type demonstrated normal signs of holocrine secretory activity and normal nuclear and cytoplasmic PPARγ expression. Severely short glands had nil while short glands had reduced Ki-67 proliferation index (3%±1%) as compared with normal and other variants (8%±5.2%). Gland dropout areas showed no evidence of any glandular tissue on histology.

CONCLUSION

Hooked, tortuous and overlapping glands had completely normal glandular histology, whereas severely short glands showed atrophic changes with loss of meibocyte differentiation and cellular proliferation. Dropout areas showed total loss of glandular elements. Further studies are needed to validate and to explore the clinical implications of these findings.

Role of FGF10/FGFR2b Signaling in Homeostasis and Regeneration of Adult Lacrimal Gland and Corneal Epithelium Proliferation

Purpose

Fibroblast growth factor 10 (FGF10) is involved in eye, meibomian, and lacrimal gland (LG) development, but its function in adult eye structures remains unknown. This study aimed to characterize the role of FGF10 in homeostasis and regeneration of adult LG and corneal epithelium proliferation.

Methods

Quantitative reverse transcription PCR was used for analysis of FGF10 expression in both early postnatal and adult mouse LG, and RNA sequencing was used to analyze gene expression during LG inflammation. FGF10 was injected into the LG of two mouse models of Sjögren's syndrome and healthy controls. Flow cytometry, BrdU cell proliferation assay, immunostaining, and hematoxylin and eosin staining were used to evaluate the effects of FGF10 injection on inflammation and cell proliferation in vivo. Mouse and human epithelial cell cultures were treated with FGF10 in vitro, and cell viability was assessed using WST-8 and adenosine triphosphate (ATP) quantification assays.

Results

The level of Fgf10 mRNA expression was lower in adult LG compared to early postnatal LG and was downregulated in chronic inflammation. FGF10 injection into diseased LGs significantly increased cell proliferation and decreased the number of B cells. Mouse and human corneal epithelial cell cultures treated with FGF10 showed significantly higher cell viability and greater cell proliferation.

Conclusions

FGF10 appears to promote regeneration in damaged adult LGs. These findings have therapeutic potential for developing new treatments for dry eye disease targeting the ability of the cornea and LG to regenerate.

Indirect Application of Intense Pulsed Light Induces Therapeutic Effects on Experimental Murine Meibomian Gland Dysfunction

Purpose

To investigate the indirect effects of intense pulsed light (IPL) on morphological and pathological changes of the meibomian glands (MGs) in apolipoprotein E knockout (ApoE^–/–) mice and explore the underlying mechanisms.

Methods

ApoE^–/– mice were treated with or without IPL three times below the lower eyelids and MGs were not directly exposed to irradiation. The eyelids and ocular surface were observed under a stereoscope. The morphology of MGs was examined by photographing and hematoxylin and eosin staining. Lipid droplets in MGs were examined by Oil Red O staining. The ultrastructure of meibocytes and mitochondria was observed under transmission electron microscopy. The relative gene and protein expression in MGs of upper eyelids was determined by immunostaining, Western blot, and qRT–PCR.

Results

Three IPL treatments decreased the toothpaste-like plugging of orifices and thickening and irregularity of the upper and lower eyelid margins in ApoE^–/– mice. The morphology of some MGs improved after IPL treatments, accompanied by increased proliferation of acinar basal cells and decreased ductal keratinization. Furthermore, the accumulation of hyperchromatic lipid droplets in the acini increased, and the lipid droplets distributed in the cells around the acini were round and small. Compared with untreated ApoE^–/– mice, oxidative stress and apoptosis were downregulated by IPL treatment, accompanied by the improvements in mitochondrial structure. Further research showed that IPL treatments reduced the levels of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-17A, IL-6 in MGs and inactivated nuclear factor kappa B (NF-κ B).

Conclusion

Collectively, the results demonstrate that indirect effects of IPL can improve the structure and function of MGs and mitigate the progression of MGD, which may be related to the indirect effects of photobiomodulation.

Candidate Molecular Compounds as Potential Indicators for Meibomian Gland Dysfunction

Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease throughout the world. Studies have shown that several molecules in meibum, including but not limited to interleukins, amino acids, cadherins, eicosanoids, carbohydrates, and proteins, are altered in meibomian gland dysfunction compared with healthy normal controls. Some of these molecules such as antileukoproteinase, phospholipase A2, and lactoperoxidase also show differences in concentrations in tears between meibomian gland dysfunction and dry eye disease, further boosting hopes as candidate biomarkers. MGD is a complex condition, making it difficult to distinguish patients using single biomarkers. Therefore, multiple biomarkers forming a multiplex panel may be required. This review aims to describe molecules comprising lipids, proteins, and carbohydrates with the potential of serving various capacities as monitoring, predictive, diagnostic, and risk biomarkers for meibomian gland dysfunction.

Physiological effects of inactivation and the roles of Elovl3/ELOVL3 in maintaining ocular homeostasis

Recently, elongase of very long chain fatty acids-3 (ELOVL3) was demonstrated to play a pivotal role in physiology and biochemistry of the ocular surface by maintaining a proper balance in the lipid composition of meibum. The goal of this study was to further investigate the effects of ELOVL3 ablation in homozygous Elovl3-knockout mice (E3hom) in comparison with age and sex matched wild-type controls (E3wt). Slit lamp examination of the ocular surface of mice, and histological examination of their ocular tissues, highlighted a severe negative impact of Elovl3 inactivating mutation on the Meibomian glands (MG) and conjunctiva of mice. MG transcriptomes of the E3hom and E3wt mice were assessed and revealed a range of up- and downregulated genes related to lipid biosynthesis, inflammation, and stress response, compared with E3wt mice. Heat stage polarized light microscopy was used to assess melting characteristics of normal and abnormal meibum. The loss of Elovl3 led to a 8°C drop in the melting temperature of meibum in E3hom mice, and increased its fluidity. Also noted were the excessive accumulation of lipid material and tears around the eye and severe ocular inflammation, among other abnormalities.

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.