Culture, immortalization, and characterization of human meibomian gland epithelial cells

The effect of airborne particulate matter 2.5 (PM2.5) on meibomian gland

Exposure to particulate matters in air pollution of 2.5 μm or less (PM2.5) was associated with loss of meibomian glands. The aim of this study was to verify that PM2.5 could directly impact meibomian gland epithelial cells and damage their function. To investigate the impact of PM2.5 on meibomian gland, immortalized human meibomian gland epithelial cells were treated with various concentrations of PM2.5in vitro. Meibomian gland cell microstructure, cell viability, expression of proliferating cell nuclear antigen and IL-1β, and intracellular accumulation of acidic vesicles were measured by transmission electron microscopy, cell counting, Western blot and LysoTracker staining, respectively. To further study the effect of PM2.5in vivo, male C57BL/6J mice were treated with 5 mg/ml PM2.5 or vehicle for 3 months. Corneal fluorescein staining and ocular examinations were done before and after the treatment. Eyelids tissues were processed for morphological studies, immunostaining and Oil Red O staining. Our data suggest that exposure to PM2.5 caused significant meibomian gland dropout, clogged gland orifice and increased corneal fluorescein staining that were consistent with the clinical presentations of meibomian gland dysfunction. Prominent changes in the morphology and ultrastructure of meibomian glands was observed with PM2.5 treatment. PM2.5 promoted ductal keratinization, inhibited cell proliferation, induced cell apoptosis and increased Interleukin-1β production in meibomian gland epithelial cells. This study may explain the association between PM2.5 exposure and meibomian gland dropout observed in clinic. PM2.5 resuspension instillation could be used to induce a meibomian gland dysfunction animal model.

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.

Oleic acid induces lipogenesis and NLRP3 inflammasome activation in organotypic mouse meibomian gland and human meibomian gland epithelial cells

The accumulation of oleic acid (OA) in the meibum from patients with meibomian gland dysfunction (MGD) suggests that it may contribute to meibomian gland (MG) functional disorder, as it is a potent stimulator of acne-related lipogenesis and inflammation in sebaceous gland. Therefore, we investigate whether OA induces lipogenesis and inflammasome activation in organotypic cultured mouse MG and human meibomian gland epithelial cells (HMGECs). Organotypic cultured mouse MG and HMGECs were exposed to OA or combinations with specific AMPK agonists 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). Lipogenic status, ductal keratinization, squamous metaplasia, NLRP3/ASC/Caspase-1 inflammasome activation, proinflammatory cytokine IL-1β production, and AMPK pathway phosphorylation in MG were subsequently examined by lipid staining, immunofluorescence staining, immunohistochemical staining, ELISA assay, and Western blot analyses. We found that OA significantly induced lipid accumulation, ductal keratinization, and squamous metaplasia in organotypic cultured MG, as evidenced by increased lipids deposition within acini and duct, upregulated expression of lipogenic proteins (SREBP-1 and HMGCR), and elevation of K10/Sprr1b. Additionally, OA induced NLRP3/ASC/Caspase-1 inflammasome activation, cleavage of Caspase-1, and production of downstream proinflammatory cytokine IL-1β. The findings of lipogenesis and NLRP3-related proinflammatory response in OA-stimulated HMGECs were consistent with those in organotypic cultured MG. OA exposure downregulated phospho-AMPK in two models, while AICAR treatment alleviated lipogenesis by improving AMPK/ACC phosphorylation and SREBP-1/HMGCR expression. Furthermore, AMPK amelioration inhibited activation of the NLRP3/ASC/Caspase-1 axis and secretion of IL-1β, thereby relieving the OA-induced proinflammatory response. These results demonstrated that OA induced lipogenic disorder and NLRP3 inflammasome activation in organotypic cultured mouse MG and HMGECs by suppressing the AMPK signaling pathway, indicating OA may play an etiological role in MGD.

Expression of ATP-Binding Cassette Transporter A1 (ABCA1) in Eyelid Tissues and Meibomian Gland Epithelial Cells

Purpose

To validate the adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1) expression and distribution in human eyelid tissues and meibomian gland epithelial cells.

Methods

Meibomian gland tissues from human eyelids were isolated by collagenase A digestion and cultured in defined keratinocyte serum-free medium (DKSFM). Infrared imaging was used to analyze the general morphology of meibomian glands. Hematoxylin and eosin (H&E) staining and Oil Red O staining were used to observe the morphological structure and lipid secretion in the human meibomian gland tissues. Quantitative real-time polymerase chain reaction, western blotting, and immunostaining were used to detect the mRNA and protein expression and cytolocalization of ABCA1 in the meibomian gland tissues and cultured cells.

Results

The degree of loss of human meibomian gland tissue was related to age. Meibomian gland lipid metabolism was also associated with age. Additionally, human meibomian gland tissues express ABCA1 mRNA and protein; glandular epithelial cells express more ABCA1 mRNA and protein than acinar cells, and their expression in acinar cells decreases with differentiation. Furthermore, the expression of ABCA1 was downregulated in abnormal meibomian gland tissues. ABCA1 was mainly localized on the cell membrane in primary human meibomian gland epithelial cells (pHMGECs), whereas it was localized in the cytoplasm of immortalized human meibomian gland epithelial cells (iHMGECs). The mRNA and protein levels of ABCA1 in pHMGECs were higher than those in iHMGECs.

Conclusions

Meibomian gland tissues of the human eyelid degenerate with age. ABCA1 expression in acinar cells decreases after differentiation and plays an important role in meibomian gland metabolism.

Isolation and Culture of Human Meibomian Gland Ductal Cells

Purpose

Hyperkeratinization of meibomian gland (MG) ducts is currently recognized as the primary pathologic mechanism of meibomian gland dysfunction (MGD). This research figured out a method to isolate the MG ducts and established a novel system to culture the human meibomian gland ductal cells (HMGDCs) for investigating the process of MGD.

Methods

The MG ducts were obtained from the eyelids of recently deceased donors and subjected to enzymatic digestion. The acini were then removed to isolate independent ducts. These MG ducts were subsequently cultivated on Matrigel-coated wells and covered with a glass plate to obtain HMGDCs. The HMGDCs were further cultivated until passage 2, and when they reached 60% confluence, they were treated with IL-1β and rosiglitazone for a duration of 48 hours. Immunofluorescence staining and Western blot techniques were employed to identify ductal cells and analyze the effects of IL-1β on HMGDCs in an in vitro setting.

Results

Ophthalmic micro-forceps and insulin needles can be employed for the purpose of isolating ducts. Within this particular culture system, the rapid expansion of HMGDCs occurred in close proximity to the duct tissue. MG ducts specifically expressed keratin 6 (Krt6) and hardly synthesized lipids. Furthermore, the expression of Krt6 was significantly higher (P < 0.0001) in HMGDCs compared to human meibomian gland cells. Upon treatment with IL-1β, HMGDCs exhibited an overexpression of keratin 1, which was effectively blocked by the administration of rosiglitazone.

Conclusions

The present study successfully isolated human MG ducts and cultured HMGDCs, providing a valuable in vitro model for investigating the mechanism of MGD. Additionally, the potential therapeutic efficacy of rosiglitazone in treating hyperkeratinization of ducts in patients with MGD was identified.

Standardized In Vitro Models of Human Adipose Tissue Reveal Metabolic Flexibility in Brown Adipocyte Thermogenesis

Functional human brown and white adipose tissue (BAT and WAT) are vital for thermoregulation and nutritional homeostasis, while obesity and other stressors lead, respectively, to cold intolerance and metabolic disease. Understanding BAT and WAT physiology and dysfunction necessitates clinical trials complemented by mechanistic experiments at the cellular level. These require standardized in vitro models, currently lacking, that establish references for gene expression and function. We generated and characterized a pair of immortalized, clonal human brown (hBA) and white (hWA) preadipocytes derived from the perirenal and subcutaneous depots, respectively, of a 40-year-old male individual. Cells were immortalized with hTERT and confirmed to be of a mesenchymal, nonhematopoietic lineage based on fluorescence-activated cell sorting and DNA barcoding. Functional assessments showed that the hWA and hBA phenocopied primary adipocytes in terms of adrenergic signaling, lipolysis, and thermogenesis. Compared to hWA, hBA were metabolically distinct, with higher rates of glucose uptake and lactate metabolism, and greater basal, maximal, and nonmitochondrial respiration, providing a mechanistic explanation for the association between obesity and BAT dysfunction. The hBA also responded to the stress of maximal respiration by using both endogenous and exogenous fatty acids. In contrast to certain mouse models, hBA adrenergic thermogenesis was mediated by several mechanisms, not principally via uncoupling protein 1 (UCP1). Transcriptomics via RNA-seq were consistent with the functional studies and established a molecular signature for each cell type before and after differentiation. These standardized cells are anticipated to become a common resource for future physiological, pharmacological, and genetic studies of human adipocytes.

Comparison of different lipid staining methods in human meibomian gland epithelial cells

This study aimed to compare the utility of four different dyes for intracellular lipid detection in immortalized human meibomian gland epithelial cells (IHMGECs). IHMGECs were cultured in a serum-containing medium for 10 days in the presence or absence of Roxadustat (Roxa), a known inducer of IHMGEC differentiation. Cells were then fixed and stained with Oil Red O (ORO), Sudan III (SIII), LipidTOX green (LT), or Nile Red (NR). IHMGECs were evaluated for the number, size, and area of stained intracellular lipid vesicles or the intensity of staining using bright field (ORO, SIII) or fluorescence (LT, NR) microscopy. Data were captured with ImageJ and analyzed with Student's two-tailed t-test. Our findings demonstrate that different staining methods can yield significantly different patterns of intracellular lipid quantity and/or distribution in IHMGECs. ORO and SIII significantly increased the size and area of lipid-containing vesicles in Roxa-treated cells. Neither stain showed a change in the number of vesicles during IHMGEC differentiation. Vesicle size was significantly greater in cells stained with ORO, as compared to SIII. In addtion, LT, but not NR, showed a significant increase in intracellular lipid intensity in IHMGECs following Roxa -induced differentiation. Our results demonstrate significant differences in the distribution patterns and intensities of lipid-containing vesicles in IHMGECs after staining with ORO, SIII, LT, and NR. ORO, SIII, and LT, but not NR staining, are helpful methods to help identify and quantitate the extent of intracellular lipid accumulation during IHMGEC differentiation.

Organotypic culture model of mouse meibomian gland as a screening platform for risk factors related to meibomian gland dysfunction

PURPOSE

Meibomian glands (MGs) are crucial for maintaining tear film stability and ocular surface health. Here, we aim to establish a novel organotypic culture model of MGs and explore the risk factors of MG dysfunction (MGD).

METHODS

We developed a novel organotypic culture model for MGs at the air-liquid interface. The viability and cell proliferation of MGs were assessed using CCK-8, immunofluorescence, and qPCR. Lipid accumulation was evaluated by Nile red staining and microscopic examination. Protein expression levels were evaluated by immunofluorescence and Western blot assay. EdU assay was employed to track the proliferation of acinar cells. The validity of the model was confirmed through culturing MGs from mice of different ages and incorporating certain drugs (Dex) into the culture system.

RESULTS

Utilizing the novel culture model, the MG tissue exhibited sustained viability, cellular division, and continuous production of lipids for a duration of 7 days. Lipid droplets formed were directly visualized using light field microscopy. Through the cultivation of aged mice's MGs, it was discovered that aging resulted in diminished proliferation and lipid synthesis, along with an aberrant increase in Krt10 expression. Further application of this model showed that Dex treatment diminished MG's proliferation and lipid synthesis. Finally, an in vivo study was conducted to provide additional confirmation of the phenomenon of Dex-induced abnormalities.

CONCLUSIONS

In this study, a stable organotypic culture model of the MGs was established. The organotypic culture model offers a valuable tool to investigate the pathophysiological mechanisms and facilitate drug screening for MG-related diseases.

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.

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.

Azithromycin-carrying and microtubule-orientated biomimetic poly (lactic-co-glycolic acid) scaffolds for eyelid reconstruction

Introduction

Tarsal plate repair is the major challenge of eyelid reconstruction for the oculoplastic surgeon. The ideal synthetic tarsal plate substitute should imitate the microstructure and mechanical strength of the natural eyelid. The aim of this work was to develop a novel bionic substitute for eyelid reconstruction.

Methods

Three types of poly(lactic-co-glycolic acid) (PLGA) scaffolds (random, oriented, and azithromycin-loaded oriented scaffolds) were prepared using an improved thermal-induced phase separation technique. The microstructure of the scaffolds was examined by scanning electron microscopy. In vitro cytotoxicity was assessed using scaffold extracts. Fibroblast and primary rat meibomian gland epithelial cells (rMGCs) were cultured within the scaffolds, and their behavior was observed using fluorescence staining. Three types of PLGA scaffolds were implanted into rabbit eyelid defect in vivo to evaluate their inductive tissue repair function.

Results

We successfully fabricated three types of PLGA scaffolds with varying pore architectures, and the axially aligned scaffold demonstrated interconnected and vertically parallel channels. In vitro cytotoxicity tests using scaffold extracts revealed no apparent cytotoxicity. Fluorescence staining showed that both Fibroblast and rMGCs could adhere well onto the pore walls, with fibroblast elongating along the axially aligned porous structure. At 8 weeks post-implantation, all scaffolds were well integrated by fibrovascular tissue. The axially aligned scaffold groups exhibited faster degradation compared to the random scaffold group, with smaller fragments surrounded by mature collagen fibers.

Conclusion

The study found that the axially aligned scaffolds could well support and guide cellular activities in vitro and in vivo. Moreover, the axially aligned scaffold group showed a faster degradation rate with a matched integration rate compared to the random scaffold group. The findings suggest that the oriented scaffold is a promising alternative for eyelid tarsal plate substitutes.

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.

Induction of meibocyte differentiation by three-dimensional, matrigel culture of immortalized human meibomian gland epithelial cells to form acinar organoids

PURPOSE

Recent studies have shown that two-dimensional (2D) culture of primary rabbit and immortalized human meibomian gland epithelial cells (iHMGEC) do not recapitulate normal meibocyte differentiation and fail to express critical enzymes necessary for synthesis of meibum lipids. The purpose of this study was to test the hypothesis that 3D-spheroid culture of iHMGEC can facilitate meibocyte differentiation and induce the expression of acyl-CoA wax-alcohol acyltransferase 2 (AWAT2), shown to be required for synthesis of meibum wax esters.

METHODS

iHMGEC were suspended in matrigel/basement membrane matrix and grown in proliferation media to form distinct cell clusters or spheroids. Cells were then treated with serum-free, differentiation media (advanced DMEM/F12) with and without FGF10 and synthetic agonists for the nuclear lipid receptor, peroxisome proliferator activator receptor gamma (PPARγ). Cells were then evaluated for differentiation markers using western blotting, immunocytochemistry (ICC) and real-time PCR. Control cells were grown in standard 2D culture systems.

RESULTS

Under proliferative conditions, 3D culture induced the formation of KRT5+ spheroids that contained a Ki67+/P63+ undifferentiated, basal cell population. When spheroids were switched to differentiation media containing PPARγ agonists, two different organoid populations were detected, a KRT6low population that was AWAT2+/PPARγ+ and a KRT6high population that was AWAT2-/PPARγ-, suggesting that iHMGEC exhibit a dual differentiation potential toward either a ductal or meibocyte organoid phenotype.

CONCLUSION

The 3D culturing of iHMGEC can induce the formation of both meibocyte and ductal organoids and may thus serve as a better in vitro model system for studying the regulatory mechanisms controlling meibomian gland function.

Effects of PPAR-γ and RXR-α on mouse meibomian gland epithelial cells during inflammation induced by latanoprost

The purpose of this study is to investigate the effects of latanoprost on the secretion of cytokines and chemokines from meibomian gland epithelial cells, and to evaluate the modulation of peroxisome proliferator-activated receptor γ (PPAR-γ) and retinoid X receptor α (RXR-α) during latanoprost-induced inflammation. Mouse meibomian gland epithelial cells were cultured in proliferation and differentiation medium, respectively. Cells were exposed to latanoprost, rosiglitazone (PPAR-γ agonist), or LG100268 (RXR-α agonist), respectively. The expression of IL-6, IL-1β, TNF-α, MMP-9, MCP-1, and CCL-5 were detected by real-time PCR and ELISA. The effect of latanoprost, rosiglitazone, LG100268, and inflammatory cytokines on the differentiation of meibocyte were evaluated by related gene expression and lipid staining. The expression of Keratin-1, 6, 17 protein was detected by western immunoblotting. The results showed that the above cytokines could be induced by latanoprost in meibomian gland epithelial cells. LG100268 and rosiglitazone could inhibit the production of IL-6 and TNF-α induced by latanoprost, respectively. Latanoprost suppressed the expression of differentiation-related mRNA through a positive feedback loop by enhancement of COX-2 expression via FP receptor-activated ERK signaling. The expression of Keratin-17 was upregulated by rosiglitazone and suppressed by LG100268. The application of IL-6 and TNF-α showed negative effects on lipid accumulation in meibomian gland epithelial cells. These results demonstrated that latanoprost could induce inflammation and suppress differentiation of mouse meibomian gland epithelial cells. The activation of PPAR-γ and RXR-α showed an anti-inflammatory effect, showing a potential role to antagonize the effect of latanoprost eyedrops on meibomian gland epithelial cells.

Activation of ADRB2/PKA Signaling Pathway Facilitates Lipid Synthesis in Meibocytes, and Beta-Blocker Glaucoma Drug Impedes PKA-Induced Lipid Synthesis by Inhibiting ADRB2

Meibomian gland dysfunction is one of the main causes of dry eye disease and has limited therapeutic options. In this study, we investigated the biological function of the beta 2-adrenergic receptor (ADRB2)/protein kinase A (PKA) pathway in lipid synthesis and its underlying mechanisms in human meibomian gland epithelial cells (HMGECs). HMGECs were cultured in differentiation media with or without forskolin (an activator of adenylate cyclase), salbutamol (an ADRB2 agonist), or timolol (an ADRB2 antagonist) for up to 4 days. The phosphorylation of the cAMP-response element-binding protein (CREB) and the expression of peroxisome proliferator activator receptor (PPAR)γ and sterol regulatory element-binding protein (SREBP)-1 were measured by immunoblotting and quantitative PCR. Lipid synthesis was examined by LipidTOX immunostaining, AdipoRed assay, and Oil Red O staining. PKA pathway activation enhanced PPARγ expression and lipid synthesis in differentiated HMGECs. When treated with agonists of ADBR2 (upstream of the PKA signaling system), PPARγ expression and lipid synthesis were enhanced in HMGECs. The ADRB2 antagonist timolol showed the opposite effect. The activation of the ADRB2/PKA signaling pathway enhances lipid synthesis in HMGECs. These results provide a potential mechanism and therapeutic target for meibomian gland dysfunction, particularly in cases induced by beta-blocker glaucoma drugs.

Association of Serum Lipid Level with Meibum Biosynthesis and Meibomian Gland Dysfunction: A Review

The primary role of meibomian glands (MGs) is to actively synthesize and secret lipids and proteins spread onto the tear film, and the glandular lipids promote tear stability, prevent evaporation, and reduce friction. Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease and one of the most common ophthalmic problems worldwide. MGs are densely innervated and regulated by hormones and growth factors. However, since the polar and nonpolar lipids are produced through processes in MGs that are not completely understood, a relevant question has been raised: Would the altered systemic lipids metabolism affect the physiology and structure of MGs? This review introduces the recent update regarding the relationships between serum lipid and MGD in clinical and basic research while providing answers to this question. A causal relationship remains to be established; however, serum lipid level or dyslipidemia may be related to MGD directly or indirectly, or both. Further studies are warranted to establish the role of serum lipid level and meibocyte differentiation/maturation and lipid synthesis.

Melatonin Attenuates LPS-Induced Proinflammatory Cytokine Response and Lipogenesis in Human Meibomian Gland Epithelial Cells via MAPK/NF-κB Pathway

Purpose

Inflammation contributes to the development of meibomian gland dysfunction (MGD) under specific disease conditions, but the underlying mechanisms remain elusive. We examined whether lipopolysaccharide (LPS) induced a proinflammatory cytokine response and lipogenesis in human meibomian gland epithelial cells (HMGECs) and whether melatonin (MLT), a powerful anti-inflammatory regent in the eyes, could protect against LPS-induced disorders.

Methods

Human meibomian gland (MG) tissues and immortalized HMGECs were stained to identify Toll-like receptor (TLR) 4 and MLT receptors (MT₁ and MT₂). HMGECs were pretreated with or without MLT and then stimulated with LPS. Then, TLR4 activation, cytokine levels, lipid synthesis, apoptosis, autophagy, and MAPK/NF-κB factor phosphorylation in HMGECs were analyzed.

Results

TLR4, MT₁, and MT₂ were expressed in human MG acini and HMGECs. Pretreatment with MLT inhibited the TLR4/MyD88 signaling and attenuated proinflammatory cytokine response and lipogenesis in LPS-stimulated HMGECs, which manifested as decreased production of cytokines (IL-1β, IL-6, IL-8, and TNF-α), reduced lipid droplet formation, and downregulated expression of meibum lipogenic proteins (ADFP, ELOVL4, and SREBP-1). Phospho-histone H2A.X foci, lysosome accumulation, and cytoplasmic cleaved caspase 3/LC3B-II staining were increased in LPS-stimulated HMGECs, indicating enhanced cell death mediated by apoptosis and autophagy during LPS-induced lipogenesis. MLT downregulated cleaved caspase 3 levels and the Bax/Bcl-2 ratio to alleviate apoptosis and ameliorated the expression of Beclin 1 and LC3B-II to inhibit autophagy. The protective mechanisms of MLT include the inhibition of MAPK and NF-κB phosphorylation.

Conclusions

MLT attenuated lipogenesis, apoptosis, and autophagy in HMGECs induced by proinflammatory stimuli, indicating the protective potential of MLT in MGD.

Prostaglandin E2 and F2α Alter Expression of Select Cholesteryl Esters and Triacylglycerols Produced by Human Meibomian Gland Epithelial Cells

PURPOSE

PGF2α analogs are commonly used to treat glaucoma and are associated with higher rates of meibomian gland dysfunction (MGD). The purpose of this study was to evaluate the physiological effects of PGF2α and PGE2 on immortalized human meibomian gland epithelial cells (HMGECs).

METHODS

HMGECs were immunostained for the 4 PGE2 receptors (EP1, EP2, EP3, and EP4) and 1 PGF2α receptor (FP) and imaged. Rosiglitazone-differentiated HMGECs were exposed to PGF2α and PGE2 (10-9 to 10-6 M) for 3 hours. Cell viability was assessed by an adenosine triphosphate-based luminescent assay, and lipid extracts were analyzed for cholesteryl esters (CEs), wax esters (WEs), and triacylglycerols (TAGs) by ESI-MSMSALL in positive ion mode by a Triple TOF 5600 Mass Spectrometer using SCIEX LipidView 1.3.

RESULTS

HMGECs expressed 3 PGE2 receptors (EP1, EP2, and EP4) and the 1 PGF2α receptor (FP). Neither PGE2 nor PGF2α showed signs of cytotoxicity at any of the concentrations tested. WEs were not detected from any of the samples, but both CEs and TAGs exhibited a diverse and dynamic profile. PGE2 suppressed select CEs (CE 22:1, CE 26:0, CE 28:1, and CE 30:1). PGF2α dose dependently increased several CEs (CE 20:2, CE 20:1, CE 22:1, and CE 24:0) yet decreased others. Both prostaglandins led to nonspecific TAG remodeling.

CONCLUSIONS

PGE2 and PGF2α showed minimal effect on HMGEC viability. PGF2α influences lipid expression greater than PGE2 and may do so by interfering with meibocyte differentiation. This work may provide insight into the mechanism of MGD development in patients with glaucoma treated with PGF2α analogs.

Human meibomian gland epithelial cell culture models: Current progress, challenges, and future directions

The widely used immortalised human meibomian gland epithelia cell (iHMGEC) line has made possible extensive studies of the biology and pathophysiology of meibomian glands (MG). Tissue culture protocols for iHMGEC have been revised and modified to optimise the growth conditions for cell differentiation and lipid accumulation. iHMGEC proliferate in serum-free medium but require serum or other appropriate exogenous factors to differentiate. Several supplements can enhance differentiation and neutral lipid accumulation in iHMGEC grown in serum-containing medium. In serum-free medium, rosiglitazone, a peroxisome proliferator activator receptor-γ (PPARγ) agonist, is reported to induce iHMGEC differentiation, neutral lipid accumulation and expression of key biomarkers of differentiation. iHMGEC cultured in serum-containing medium under hypoxia or with azithromycin increases DNAse 2 activity, a biomarker of terminal differentiation in sebocytes. The production of lipids with composition similar to meibum has not been observed in vitro and this remains a major challenge for iHMGEC culture. Innovative methodologies such as 3D ex vivo culture of MG and generation of MG organoids from stem cells are important for further developing a model that more closely mimics the in vivo biology of human MG and to facilitate the next generation of studies of MG disease and dry eye.

Expression of Acyl-CoA wax-alcohol acyltransferase 2 (AWAT2) by human and rabbit meibomian glands and meibocytes

PURPOSE

Previously, we showed that Acyl-CoA wax-alcohol acyltransferase 2 (AWAT2), an essential enzyme required for meibum wax ester synthesis, was not expressed by immortalized human meibomian gland epithelial cells (hMGEC) in culture. To begin to understand the mechanisms controlling AWAT2 expression, we have analyzed its expression in human and rabbit meibomian glands and cultured meibocytes.

METHODS

Rabbit meibocyte progenitor cells (rMPC) were first grown in Cnt-BM.1 basal medium (Cellntec) supplemented with rhEGF, FGF10, and ROCK inhibitor (Y-27632 dihydrochloride), and then passed at 70-80% confluency with Accutase. Differentiation of rMPC to meibocytes (rMC) was induced by removal of Y-27632 and addition of 1 mM calcium with and without PPARγ agonists. RNA from the tissue, primary, passaged rMPC and differentiated rMC were obtained for AWAT2 qPCR analysis. Proteins and cells were evaluated for western blotting and neutral lipid synthesis, respectively. For comparison, human meibomian glands were separated for RNA and protein analysis. hMGEC was cultured to collect RNA and protein.

RESULTS

Rabbit rMPCs were successfully grown, passaged, and differentiated, showing a significant increase in lipid droplet accumulation. AWAT2 RNA was highly expressed in tissue but showed a -16.9 log2 fold decrease in primary and passaged rMPCs and was not induced by differentiation to rMC. By comparison, human meibomian glands showed high expression of AWAT2, and hMGEC expressed non-detectable levels of AWAT2 transcripts or protein.

CONCLUSIONS

AWAT2 expression is lost in cultured rMPC and rMC suggesting that cells in culture do not undergo complete meibocyte differentiation and require yet to be identified culture conditions.

Hyperkeratinization and Proinflammatory Cytokine Expression in Meibomian Glands Induced by Staphylococcus aureus

Purpose

This exploratory study aimed to investigate the morphological and pathological alterations of the meibomian gland (MG) with the Staphylococcus aureus crude extracts (SACEs) treatment.

Methods

Mouse MG explants were cultured and differentiated with or without SACEs for 48 hours. Explant's viability and cell death were determined by thiazolyl blue tetrazolium bromide (MTT) assay and TUNEL assay. MG morphology was observed by Hematoxylin and Eosin staining. Lipid droplet production was detected by Nile Red staining and LipidTox immunostaining. The pro-inflammatory cytokines were detected by ELISA. The relative gene and protein expression in MG explants was determined via quantitative RT-PCR, immunostaining, and immunoblotting. The components of the SACEs were analyzed by immunoblotting and silver staining.

Results

Our findings demonstrated that the SACEs treatment induced overexpression of keratin 1 (Krt1) in the ducts and acini of MG explants, accompanied by a decrease in viability and an increase in cell death in explants. Furthermore, the SACEs treatment dose-dependently increased the levels of TNF-α, IL-1β, and IL-6 in MG explants. The SACEs treatment induced activation of the nuclear factor kappa B (NF-κB) and AIM2 (absent in melanoma 2)/ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) inflammasome signaling pathway in explants. Further investigation showed expression of the key adipogenesis-related molecule peroxisome proliferator-activated receptor γ was decreased after SACEs treatment. However, no change was found in the lipid synthesis of MG explants after treatment with the SACEs. Staphylococcal enterotoxins B (SEB) was detected in the SACEs. SEB induced the overexpression of Krt1 and IL-1β in ducts and acini of MG explants.

Conclusions

Our findings confirm that Staphylococcus aureus induced hyperkeratinization and pro-inflammatory cytokines expression in MG explants ducts and acini. These effects might be mediated by SEB. Activation of the NF-κB and AIM2/ASC signaling pathway is involved in this process.

Semi-quantification of lipids in human meibomian gland epithelial cells using dual staining microplate assays

Two spectrophotometric microplate assays with dual staining for either fluorescent Nile red (NR) plus 4,6-diamidino-2-phenylindole (DAPI) or non-fluorescent Oil red O (ORO) plus Crystal violet (CV) were applied and optimised to evaluate the lipid producing capacity of immortalised human meibomian gland epithelial cells (iHMGEC). Cells were treated with rosiglitazone (Rosi, 10-50 μM), a known lipid producing inducer for iHMGEC, and were analysed for lipids using the NR-DAPI and ORO-CV microplate assays. The lipid producing capacity of iHMGEC after each treatment was determined by normalising lipid quantity (measured with NR or ORO) to cell number (measured with DAPI or CV). The dye concentrations of NR 1 μg/mL, DAPI 5 μg/mL, ORO 0.3% (v/v) and CV 0.5% (v/v), provided optimal linearity and coverage of signals over a range of cell densities (corresponding to 10-100% cell confluence). Both NR-DAPI and ORO-CV showed a dose-dependent effect of Rosi on lipid production in iHMGEC, consistent with the results reported previously using traditional microscopic imaging methods. The microplate assays offer a rapid, high throughput and objective measurement of the amount of lipids in iHMGEC (and potentially other lipid-producing cells) and can be used for screening the effects of biological agents or incubation changes on lipid production in cells in future studies.

Effects of Terpinen-4-ol on Meibomian Gland Epithelial Cells In Vitro

PURPOSE

Infestation with demodex mites has been linked to the development of chalazion, meibomian gland dysfunction, and blepharitis. An effective treatment is the eyelid application of terpinen-4-ol (T4O), a tea tree oil component. However, T4O is also known to be toxic to nonocular epithelial cells. We hypothesize that T4O toxicity also extends to human meibomian gland epithelial cells (HMGECs).

METHODS

Immortalized (I) HMGECs were cultured with varying concentrations (1.0%-0.001%) of T4O under proliferating or differentiating conditions up to 5 days. Experimental procedures included analyses of cell appearance, survival, P-Akt signaling, lysosome accumulation, and neutral lipid content.

RESULTS

Our findings show that T4O causes a dose- and time-dependent decrease in the cell survival of IHMGECs. After 15 minutes of exposure to 1% T4O, IHMGECs exhibited rounding, atrophy, and poor adherence. Within 90 minutes of such treatment, almost all cells died. Reducing the T4O concentration to 0.1% also led to a marked decrease in P-Akt signaling and cell survival of IHMGECs. Decreasing the T4O amount to 0.01% caused a slight, but significant, reduction in the IHMGEC number after 5 days of culture and did not influence the ability of these cells to differentiate.

CONCLUSIONS

T4O, even at levels 10-fold to 100-fold lower than demodicidal concentrations, is toxic to HMGECs in vitro.

Hedgehog Signaling Pathway Regulates the Proliferation and Differentiation of Rat Meibomian Gland Epithelial Cells

Purpose

Meibomian glands play a vital role in maintaining ocular surface stability. This study aimed to investigate whether Hedgehog signaling is involved in the regulation of meibomian gland epithelial cells.

Methods

Rat meibomian glands epithelial cells (RMGECs) were isolated from ducts and ductules, and then were cultivated to passage two on Matrigel coated wells in meibomian gland epithelial cells medium (MGECM). Cells were switched from MGECM to differentiation medium (DM) or DM added 10 µg/mL azithromycin (DM + AZM) when reached 50% to 60% confluence. The effects of the Smoothened (Smo) agonist (Smo agonist [SAG]) and antagonist (by cyclopamine) on RMGECs were analyzed using quantitative RT-PCR, cell proliferation analysis, immunofluorescence staining, and Nile red staining.

Results

The Hedgehog receptor, Smo, and its downstream molecules, Glis, were expressed both in vivo and in vitro. Smo and Gli1 both decreased with the increase of differentiation in vitro. Smo antagonist, cyclopamine, reduced cell numbers, and the expression of Ki67 in MGECM, and promoted the expression of SREBP1 and lipid production in DM + AZM. Smo agonist, SAG, inhibited the expression of SREBP1 and lipid accumulation in DM + AZM but showed no significant effects on raising cell numbers and the expression of Ki67 in MGECM.

Conclusions

The Hedgehog signaling pathway appears to play important roles in RMGECs proliferation and differentiation. This may provide a potential therapeutic way to treat meibomian gland dysfunction (MGD).

Establishment and Characterization of a Novel Human Ocular Adnexal Sebaceous Carcinoma Cell Line

Purpose

Sebaceous carcinoma (SC) is a malignant eyelid tumor of the ocular adnexa that is primarily treated via surgical excision. Few therapies exist in advanced cases, and medical therapy is limited because of our incomplete understanding of SC biology. Herein, we describe a technique to culture human ocular adnexal SC for use as an in vitro model.

Methods

Human ocular adnexal SC tumor cells were isolated from a patient undergoing orbital exenteration surgery and named Bascom Palmer 50 (BP50). They were cultured in Dulbecco's modified Eagle medium/nutrient mixture F-12 supplemented with 10% fetal bovine serum and antibiotics and were maintained at 37°C in humidified 5% CO₂. The cells were characterized by immunohistochemistry, exome sequencing, and short tandem repeats analysis. In vitro drug screening against mitomycin-C (MMC) was performed using a cell viability assay.

Results

BP50 grew past 40 passages with a doubling time of 52.3 hours. Immunocytochemical staining revealed expression of SC-associated markers adipophilin, epithelial membrane antigen, p53, and androgen receptor. Whole exome sequencing showed a significant carryover in somatic mutations between the tumor tissue and corresponding cell line, revealing genetic markers consistent with SC. MMC affected cell viability in a dose-dependent manner.

Conclusions

BP50 displays characteristics of ocular adnexal SC and therefore may facilitate improved understanding of SC biology and the high throughput assessment of novel therapeutic compounds and new drug combinatorial approaches targeted for this disease.

Translational Relevance

Drug screening with MMC against these cells shows in vitro evidence to support its continued clinical use in SC.

Triacylglycerol lipidome from human meibomian gland epithelial cells: Description, response to culture conditions, and perspective on function

Preliminary work has shown that select triacylglycerols (TAGs) are upregulated in a preclinical model of MGD, suggesting that TAGs may be an important outcome variable in research involving human meibomian gland epithelial cells (HMGECs). The purpose of this study was to explore the HMGEC TAG lipidome in culture conditions known to influence differentiation. HMGECs were differentiated in DMEM/F12 with 10 ng/ml EGF, FBS (2% or 10%), and rosiglitazone (0, 20, or 50 μM) for two or five days. Following culture, lipids were extracted, processed, and directly infused into a Triple TOF 5600 mass spectrometer (SCIEX, Framingham, MA) with electrospray ionization. MS and MS/MS^ALL spectra were acquired in the positive ion mode and performed with the SWATH technology. Only the TAGs that were present in all 48 samples were included in the analysis. Multiple regression techniques were utilized to assess the effects of each factor (FBS, rosiglitazone, and culture duration) on each expressed TAG. The HMGEC TAG lipidome consisted of 115 TAGs with 42-62 carbons and zero to 10 double bonds. Fatty acyl chains had 14 to 26 carbons and zero to five double bonds. C18:1 (oleic acid, 25/115, 21.7%) and C16:0 (palmitic acid, 16/115, 13.9%) were the most common fatty acids. FBS, rosiglitazone, and culture duration were significant predictors for 93 TAGs (80.9%) with R² values ranging from 0.20 to 0.77 (p < 0.05). FBS and rosiglitazone achieved significance (p < 0.05) for 80 (69.6%) and 67 TAGs (58.3%), respectively. Rosiglitazone demonstrated a selective upregulation of TAGs containing 16 or 18 carbons. Culture duration reached significance (p < 0.05) for only 36 TAGs (31.3%). When comparing the 10 most abundant C18:1-containing TAGs in meibum, FBS was a negative predictor for five TAGs (mean standardized coefficient [SC] = -0.58, p < 0.001), rosiglitazone was a positive predictor for six TAGs (mean SC = 0.41, p ≤ 0.03), and culture duration weakly influenced one TAG (SC = 0.27, p = 0.008). FBS and rosiglitazone, unlike culture duration, are powerful modulators of the TAG profile. Rosiglitazone induces changes that could be consistent with fatty acid synthesis, suggesting that quantifying the TAG lipidome could be an indirect measure of lipogenesis. Though both have been described as differentiating agents, FBS and rosiglitazone induce opposing effects on meibum-relevant TAGs. Culturing with rosiglitazone is associated with a TAG profile that is more consistent with the expected outcome of lipogenesis and with the profile observed in normal human meibum.

Imaging host-pathogen interactions using epithelial and bacterial cell infection models

The age-old saying, seeing is believing, could not be truer when we think about the value of imaging interactions between epithelial cells and bacterial pathogens. Imaging and culturing techniques have vastly improved over the years, and the breadth and depth of these methods is ever increasing. These technical advances have benefited researchers greatly; however, due to the large number of potential model systems and microscopy techniques to choose from, it can be overwhelming to select the most appropriate tools for your research question. This Review discusses a variety of available epithelial culturing methods and quality control experiments that can be performed, and outlines various options commonly used to fluorescently label bacterial and mammalian cell components. Both light- and electron-microscopy techniques are reviewed, with descriptions of both technical aspects and common applications. Several examples of imaging bacterial pathogens and their interactions with epithelial cells are discussed to provide researchers with an idea of the types of biological questions that can be successfully answered by using microscopy.

Comparative influence of differentiation and proliferation on gene expression in human meibomian gland epithelial cells

We recently discovered that by changing environmental signals, differentiated immortalized human meibomian gland epithelial cells (IHMGECs) de-differentiate into proliferating cells. We also discovered that following exposure to appropriate stimuli, these proliferative cells re-differentiate into differentiated IHMGECs. We hypothesize that this plasticity of differentiated and proliferative IHMGECs is paralleled by very significant alterations in cellular gene expression. To begin to test this hypothesis, we compared the gene expression patterns of IHMGECs during differentiation and proliferation. IHMGECs were cultured for four days in either differentiating or proliferating media. After four days of culture, cells were processed for the analysis of gene expression by using Illumina BeadChips and bioinformatic software. Our study identified significant differences in the expression of more than 9200 genes in differentiated and proliferative IHMGECs. Differentiation was associated with significant increases in the expression of specific genes (e.g. S100 calcium binding protein P; 7,194,386-fold upregulation) and numerous ontologies (e.g. 83 biological process [bp] ontologies with ≥100 genes were upregulated), such as those related to development, transport and lysosomes. Proliferation also led to a significant rise in specific gene expressions (e.g. cathelicidin antimicrobial peptide; 859,100-fold upregulation) and many ontologies (115 biological process [bp] ontologies with ≥100 genes were upregulated), with most of the highly significant ontologies related to cell cycle (z scores > 13.9). Our findings demonstrate that gene expression in differentiated and proliferative IHMGECs is extremely different. These results may have significant implications for the regeneration of HMGECs and the reversal of MG dropout in MG dysfunction.

Three-Dimensional Human Cell Culture Models to Study the Pathophysiology of the Anterior Eye

In recent decades, the establishment of complex three-dimensional (3D) models of tissues has allowed researchers to perform high-quality studies and to not only advance knowledge of the physiology of these tissues but also mimic pathological conditions to test novel therapeutic strategies. The main advantage of 3D models is that they recapitulate the spatial architecture of tissues and thereby provide more physiologically relevant information. The eye is an extremely complex organ that comprises a large variety of highly heterogeneous tissues that are divided into two asymmetrical portions: the anterior and posterior segments. The anterior segment consists of the cornea, conjunctiva, iris, ciliary body, sclera, aqueous humor, and the lens. Different diseases in these tissues can have devastating effects. To study these pathologies and develop new treatments, the use of cell culture models is instrumental, and the better the model, the more relevant the results. Thus, the development of sophisticated 3D models of ocular tissues is a significant challenge with enormous potential. In this review, we present a comprehensive overview of the latest advances in the development of 3D in vitro models of the anterior segment of the eye, with a special focus on those that use human primary cells.

Saturation of cholesteryl esters produced by human meibomian gland epithelial cells after treatment with rosiglitazone

PURPOSE

The purpose of this study was to compare the cholesteryl ester (CE) profiles expressed from human meibomian gland epithelial cells (HMGECs) in response to rosiglitazone-induced differentiation to that of normal human meibum.

METHODS

HMGECs were cultured with rosiglitazone (vehicle control, 20 μM, or 50 μM) and fetal bovine serum (FBS, 2% or 10%) for 2 days or 5 days. Following culture, lipid extracts were processed and analyzed by ESI-MSMS^ALL in positive ion mode. CEs were identified using both LipidView 1.2 and PeakView 2.2 (SCIEX, Framingham, MA) and compared to literature reports of CEs in normal human meibum.

RESULTS

There were 34 CEs with carbon number ranging from 14 to 34 detected from HMGECs. Across all conditions, HMGECs provided a CE profile that was 14.0% saturated, 60.6% monounsaturated, and 25.4% polyunsaturated. Culturing with 50 μM rosiglitazone and 2% FBS for 2 days resulted in the greatest number of upregulated saturated and monounsaturated CEs and downregulated polyunsaturated CEs. Five CEs were identified as being the most responsive to 50 μM rosiglitazone: CE 24:1, CE 28:1, CE 26:1, CE 18:1, and CE 22:1.

CONCLUSION

Although differences in the CE profile exist between meibum and HMGECs, rosiglitazone promotes upregulation of highly expressed meibum-relevant CEs and shifts the saturation level toward a more meibum-like profile. The use of rosiglitazone as a differentiating agent is recommended in HMGEC research, and analysis by ESI-MSMS^ALL is encouraged to differentiate meibum-relevant CEs from other nonpolar distractors detected by vital stains.

Establishment and characterization of a canine sebaceous epithelial cell line derived from an eyelid mass

Little is known about the pathological roles of sebaceous glands in canine skin diseases, as most examinations have been conducted with cultured human sebaceous epithelial cell lines. To our knowledge, there is no available canine sebaceous epithelial cell line. The purpose of this study was to establish a canine sebaceous epithelial cell line and characterize it. An eyelid mass in a dog was surgically resected for treatment, and it was histologically diagnosed as sebaceous epithelioma. Collected tissue was conducted for culture, and the growing epithelial-like cells were passaged. The cells showed continuous proliferation for over 6 months. After 40 passages, the cells were named CMG-1. Lipid droplets in the cytoplasm of CMG-1 cells were confirmed by Oil Red O staining. As reported in studies with human sebaceous epithelial cell lines, lipogenesis in CMG-1 cells was promoted by linoleic acid, whereas transforming growth factor-β (TGF-β) suppressed it. Additionally, real-time PCR revealed that the expression levels of chemokines and cytokines, including CC chemokine ligand (CCL)-2, CCL-20, CXCL-10, Tumor necrosis factor-α (TNF-α), Interleukin (IL)-1α, IL-1β, and IL-8, were significantly increased in CMG-1 cells following treatment with lipopolysaccharide. In conclusion, we successfully established a new canine sebaceous epithelial cell line. Our data indicated that lipogenesis and inflammatory responses were quantitatively evaluable in this cell line. CMG-1 cells could be useful for the pathological analysis of sebaceous gland diseases in dogs.

Organotypic Culture of Mouse Meibomian Gland: A Novel Model to Study Meibomian Gland Dysfunction In Vitro

Purpose

Meibomian glands are essential in maintaining the integrity and health of the ocular surface. Meibomian gland dysfunction (MGD), mainly induced by ductal occlusion, is considered as the major cause of dry eye disease. In this study, a novel in vitro model was established for investigating the role of inflammation in the process of MGD.

Methods

Mouse tarsal plates were removed from eyelids after dissection and explants were cultured during various time ranging from 24 to 120 hours. Meibomian gland epithelial cells were further enzymatically digested and dissociated from tarsal plates before culturing. Both explants and cells were incubated in different media with or without serum or azithromycin (AZM). Furthermore, explants were treated with IL-1β or vehicle for 48 hours. Analyses for tissue viability, histology, biomarker expression, and lipid accumulation were performed with hematoxylin and eosin (H&E) staining, immunofluorescence staining, and Western blot.

Results

Higher viability was preserved when explants were cultured on Matrigel with immediate addition of culture medium. The viability, morphology, biomarker expression, and function of meibomian glands were preserved in explants cultured for up to 72 hours. Lipid accumulation and peroxisome proliferator-activated receptor γ (PPARγ) expression increased in both explants and cells cultured in media containing serum or AZM. Treatment with IL-1β induced overexpression of Keratin (Krt) 1 in meibomian gland ducts.

Conclusions

Intervention with pro-inflammatory cytokine IL-1β induces hyperkeratinization in meibomian gland ducts in vitro. This novel organotypic culture model can be used for investigating the mechanism of MGD.

The Role of Hypoxia-Inducible Factor 1α in the Regulation of Human Meibomian Gland Epithelial Cells

Purpose

We recently discovered that a hypoxic environment is beneficial for meibomian gland (MG) function. The mechanisms underlying this effect are unknown, but we hypothesize that it is due to an increase in the levels of hypoxia-inducible factor 1α (HIF1α). In other tissues, HIF1α is the primary regulator of cellular responses to hypoxia, and HIF1α expression can be induced by multiple stimuli, including hypoxia and hypoxia-mimetic agents. The objective of this study was to test our hypothesis.

Methods

Human eyelid tissues were stained for HIF1α. Immortalized human MG epithelial cells (IHMGECs) were cultured for varying time periods under normoxic (21% O2) or hypoxic (1% O2) conditions, in the presence or absence of the hypoxia-mimetic agent roxadustat (Roxa). IHMGECs were then processed for the analysis of cell number, HIF1α expression, lipid-containing vesicles, neutral and polar lipid content, DNase II activity, and intracellular pH.

Results

Our results show that HIF1α protein is present in human MG acinar epithelial cells in vivo. Our findings also demonstrate that exposure to 1% O2 or to Roxa increases the expression of HIF1α, the number of lipid-containing vesicles, the content of neutral lipids, and the activity of DNase II and decreases the pH in IHMGECs in vitro.

Conclusions

Our data support our hypothesis that the beneficial effect of hypoxia on the MG is mediated through an increased expression of HIF1α.

The Carbonic Anhydrase Inhibitor Dorzolamide Stimulates the Differentiation of Human Meibomian Gland Epithelial Cells

PURPOSE

Clinical studies have indicated that the long-term use of topical antiglaucoma drugs, such as carbonic anhydrase inhibitors (CAIs), may lead to meibomian gland dysfunction (MGD). We hypothesize that these adverse effects involve a direct influence on human MG epithelial cells (HMGECs). The purpose our present investigation was to test our hypothesis and determine whether exposure to dorzolamide, a CAI, impacts the proliferation, intracellular signaling and differentiation of HMGECs.

MATERIALS AND METHODS

We cultured immortalized (i) HMGECs with vehicle or various concentrations of dorzolamide for 6 days. Cells were enumerated with a hemocytometer, and examined for their morphology, Akt signaling activity, accumulation of neutral lipids, phospholipids and lysosomes, and the expression of protein biomarkers for lipogenesis regulation, lysosomes and autophagosomes.

RESULTS

Our results show that a high, 500 µg/ml concentration of dorzolamide causes a significant decrease in Akt signaling and the proliferation of iHMGECs. However, the high dose of dorzolamide also promotes the differentiation of iHMGECs. This response features increases in the number of lysosomes, the accumulation of phospholipids, and the expression of the light chain 3A biomarker for autophagosomes. In contrast, the therapeutic amount (50 µg/ml) of dorzolamide has no impact on the proliferative or differentiative abilities of iHMGECs.

CONCLUSIONS

Our results support our hypothesis and demonstrate that the CAI dorzolamide does exert a direct influence on the proliferation and differentiation of iHMGECs. However, this effect is elicited only by a high, and not a therapeutic, amount of dorzolamide. Abbreviations: AKT: phosphoinositide 3-kinase-protein kinase B; BPE: bovine pituitary extract; CAD: cationic amphiphilic drug; DED: dry eye disease; DMEM/F12: 1:1 mixture of Dulbecco's modified Eagle's medium and Ham's F-12; EGF: epidermal growth factor; FBS: fetal bovine serum; iHMGECs: immortalized human meibomian gland epithelial cells; KSFM: keratinocyte serum-free medium; LAMP-1: lysosomal-associated membrane protein 1; LC3A: light chain 3A; MGD: meibomian gland dysfunction; SREBP-1: sterol regulatory element-binding protein 1.

Evaluation of Cell Harvesting Techniques to Optimize Lipidomic Analysis from Human Meibomian Gland Epithelial Cells in Culture

The lipidomic analysis of immortalized human meibomian gland epithelial cells (HMGECs) has been proposed as a preclinical model to study meibomian gland dysfunction. An in vitro study was conducted to evaluate neutral lipid recovery following three harvesting techniques and to identify candidate lipid biomarkers of HMGECs. HMGECs were cultured in serum-containing media for two days to promote lipid production. Cells were either harvested by 0.25% trypsin–ethylenediaminetetraacetic acid (EDTA), harvested by 10 mM EDTA, or simultaneously harvested and extracted by 2:1 chloroform–methanol (CM). After extraction by a modified Folch technique, the nonpolar phase was processed and infused into a TripleTOF 5600 mass spectrometer (Sciex, Framingham, MA, USA) with electrospray ionization. MS and MS/MS^all spectra were acquired. Nonpolar cholesteryl esters (CEs) were consistently detected in all samples, while wax esters were not. Only small differences in two out of twenty CEs were detected between harvesting methods. CM yielded less CE18:1 than the other methods but greater CE20:4 than the trypsin–EDTA method (p < 0.05 for all). Similar to human meibum, very long-chain CEs with carbon number (n_c) ≥ 24 were detected in all samples and may serve as HMGEC lipid biomarkers. Further work is needed to address the absence of wax esters. Overall, the three harvesting methods are reasonably equivalent, though CM promotes much better efficiency and is recommended for higher throughput.

Eicosapentaenoic acid (EPA) activates PPARγ signaling leading to cell cycle exit, lipid accumulation, and autophagy in human meibomian gland epithelial cells (hMGEC)

PURPOSE

The purpose of this study was to access the ability of the natural PPAR agonist, eicosapentaenoic acid (EPA), to activate PPAR gamma (γ) signaling leading to meibocyte differentiation in human meibomian gland epithelial cell (hMGEC).

METHODS

HMGEC were exposed to EPA, alone and in combination with the specific PPARγ antagonist, T0070907, to selectively block PPARγ signaling. Expression of PPARγ response genes were evaluated by qPCR. Effect on cell cycle was evaluated using Ki-67 labelling and western blots. During differentiation, autophagy was monitored using the Autophagy Tandem Sensor (ATS) and LysoTracker. Lipid accumulation was characterized by Stimulated Raman Scattering microscopy (SRS) and neutral lipid staining in combination with ER-Tracker, LysoTracker, and ATS. Autophagy was also investigated using western blotting. Seahorse XF analysis was performed to monitor mitochondrial function.

RESULTS

EPA specifically upregulated expression of genes related to lipid synthesis and induced cell cycle exit through reduced cyclin D1 expression and increased p21 and p27 expression. EPA also induced accumulation of lipid droplets in a time and dose dependent manner (P < 0.05) by specific PPARγ signaling. Lipid analysis identified both de novo synthesis and extracellular transport of lipid to form lipid droplets that were localized to the ER. PPARγ signaling also induced activation of AMPK-ULK1 signaling and autophagy, while inhibition of autophagy induced mitochondrial crisis with no effect on lipid accumulation.

CONCLUSIONS

EPA induces meibocyte differentiation through PPARγ activation that is characterized by cell cycle exit, de novo and transported lipid accumulation in the ER, and autophagy.

Dihydrotestosterone suppression of proinflammatory gene expression in human meibomian gland epithelial cells

PURPOSE

We discovered that dihydrotestosterone (DHT) decreases the ability of lipopolysaccharide, a bacterial toxin, to stimulate the secretion of leukotriene B4, a potent proinflammatory mediator, by immortalized human meibomian gland epithelial cells (IHMGECs). We hypothesize that this hormone action reflects an androgen suppression of proinflammatory gene activity in these cells. Our goal was to test this hypothesis. For comparison, we also examined whether DHT treatment elicits the same effect in immortalized human corneal (IHC) and conjunctival (IHConj) ECs.

METHODS

Differentiated cells were cultured in media containing vehicle or 10 nM DHT. Cells (n = 3 wells/treatment group) were then processed for RNA isolation and the analysis of gene expression by using Illumina BeadChips, background subtraction, cubic spline normalization and Geospiza software.

RESULTS

Our results demonstrate that DHT significantly suppressed the expression of numerous immune-related genes in HMGECs, such as those associated with antigen processing and presentation, innate and adaptive immune responses, chemotaxis, and cytokine production. DHT also enhanced the expression of genes for defensin β1, IL-1 receptor antagonist, and the anti-inflammatory serine peptidase inhibitor, Kazal type 5. In contrast, DHT had no effect on proinflammatory gene expression in HCECs, and significantly increased 33 gene ontologies linked to the immune system in HConjECs.

CONCLUSIONS

Our findings support our hypothesis that androgens suppress proinflammatory gene expression in IHMGECs. This hormone effect may contribute to the typical absence of inflammation within the human meibomian gland.

The Effect of Androgens on Proinflammatory Cytokine Secretion from Human Ocular Surface Epithelial Cells

Purpose: The purpose of this study is to explore the effects of dihydrotestosterone (DHT) on lipopolysaccharide (LPS)-induced proinflammatory cytokine release in human ocular surface epithelial cells exposed to LPS and LPS-binding protein (LBP).Methods: Immortalized human corneal, conjunctival, and meibomian gland epithelial cells were cultured in keratinocyte-free medium. After confluency, they were exposed to a stratification medium Dulbecco's modified Eagle medium (DMEM)/F12 in the presence of fetal bovine serum and were exposed to vehicle, LPS + LBP, or DHT. Culture media were processed for multiplex-bead analysis of specific proinflammatory cytokines including interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-2, IL-4, IL-8, IL-6, IL-10, IL-1β, vascular endothelial growth factor (VEGF)-A. Cytokine concentrations were compared by analysis of variance with Tukey post hoc testing. p < 0.05 was considered statistically significant.Results: The results are LPS + LBP-induced the secretion of IFN-γ, IL-6, IL-10, IL-1β, VEGF-A cytokines in corneal epithelial cells; TNF-α, IL-2, IL-8, IL-6, IL-1β, VEGF-A cytokines in conjunctival epithelial cells; and IL-8, IL-6, IL-1β, VEGF-A cytokines in meibomian gland epithelial cells. When these LPS + LBP-stimulated cells were exposed to DHT for 2 days, it was found that DHT suppressed the secretion of IL-6, IL-10, IL-1β, VEGF-A cytokines in corneal epithelial cells; TNF-α, IL-6, IL-1β, VEGF-A cytokines in conjunctival epithelial cells; and IL-6, IL-1β, VEGF-A cytokines in meibomian gland epithelial cells.Conclusion: LPS + LBP is shown to induce the secretion of certain proinflammatory cytokines from ocular surface and adnexal epithelial cells. DHT showed anti-inflammatory activity by suppressing some of those cytokines in these cell lines.

Neutrophil extracellular traps (NETs) contribute to pathological changes of ocular graft-vs.-host disease (oGVHD) dry eye: Implications for novel biomarkers and therapeutic strategies

PURPOSE

To investigate the role of neutrophil extracellular traps (NETs) and NET-associated proteins in the pathogenesis of oGVHD and whether dismantling of NETs with heparin reduces those changes.

METHODS

Ocular surface washings from oGVHD patients and healthy subjects were analyzed. Isolated peripheral blood human neutrophils were stimulated to generate NETs and heparinized NETs. We performed in vitro experiments using cell lines (corneal epithelial, conjunctival fibroblast, meibomian gland (MG) epithelial and T cells), and in vivo experiments using murine models, and compared the effects of NETs, heparinized NETs, NET-associated proteins and neutralizing antibodies to NET-associated proteins.

RESULTS

Neutrophils, exfoliated epithelial cells, NETs and NET-associated proteins (extracellular DNA, Neutrophil Elastase, Myeloperoxidase, Oncostatin M (OSM), Neutrophil gelatinase-associated lipocalin (NGAL) and LIGHT/TNFSF14) are present in ocular surface washings (OSW) and mucocellular aggregates (MCA). Eyes with high number of neutrophils in OSW have more severe signs and symptoms of oGVHD. NETs (and OSM) cause epitheliopathy in murine corneas. NETs (and LIGHT/TNFSF14) increase proliferation of T cells. NETs (and NGAL) inhibit proliferation and differentiation of MG epithelial cells. NETs enhance proliferation and myofibroblast transformation of conjunctival fibroblasts. Sub-anticoagulant dose Heparin (100 IU/mL) dismantles NETs and reduces epithelial, fibroblast, T cell and MG cell changes induced by NETs.

CONCLUSION

NETs and NET-associated proteins contribute to the pathological changes of oGVHD (corneal epitheliopathy, conjunctival cicatrization, ocular surface inflammation and meibomian gland disease). Our data points to the potential of NET-associated proteins (OSM or LIGHT/TNFSF14) to serve as biomarkers and NET-dismantling biologics (heparin eye drops) as treatment for oGVHD.

Transcriptome analysis after PPARγ activation in human meibomian gland epithelial cells (hMGEC)

PURPOSE

PPARγ plays a critical role in the maturation of immortalized human meibomian gland epithelial cells (hMGEC). To further understand the molecular changes associated with meibocyte differentiation, we analyzed transcriptome profiles from hMGEC after PPARγ activation.

METHODS

Three sets of cultivated hMGEC with or without exposure to PPARγ agonist, rosiglitazone were used for RNA-seq analysis. RNA was isolated and processed to generate 6 libraries. The libraries were then sequenced and mapped to the human reference genome, and the expression results were gathered as reads per length of transcript in kilobases per million mapped reads (RPKM) values. Differential gene expression analyses were performed using DESeq2 and NOISeq. Gene ontology enrichment analysis (GOEA) was performed on gene sets that were upregulated or downregulated after rosiglitazone treatment. Five genes were selected for validation and differential expression was confirmed using quantitative PCR. The Differential expression of CK5 was evaluated using Western blotting.

RESULTS

Expression data indicated that about 58,000 genes are expressed in hMGEC. DESeq2 and NOISeq indicated that 296 and 3436 genes were upregulated and 258 and 3592 genes were down regulated after rosiglitazone treatment, respectively. Of genes showing significant differences > 2 fold, GOEA indicated that cellular and metabolic processes were highly represented. Expression of ANGPTL4, PLIN2, SQSTM1, and DDIT3 were significantly upregulated and HHIP was downregulated by rosiglitazone. CK5 was downregulated by rosiglitazone.

CONCLUSIONS

The RNA-seq data suggested that PPARγ activation induced alterations in cell differentiation and metabolic process and affected multiple signaling pathways such as PPAR, autophagy, WNT, and Hedgehog.

In vitro effects of benzalkonium chloride and prostaglandins on human meibomian gland epithelial cells

PURPOSE

Benzalkonium chloride is the most widely used preservative in ophthalmic topical solutions. The aim of this study was to investigate the influence of BAC as a single substance or as a component of several commercially available ophthalmic solutions on meibomian gland epithelial cells in vitro.

MATERIALS AND METHODS

An immortalized human meibomian gland epithelial cell line (HMGEC) was used and cells were cultured in the absence or presence of fetal bovine serum to assess cell morphology, cell proliferation, cell viability (MTS assay) and impedance sensing (ECIS) after stimulation with BAC. Further, the viability of HMGECs stimulated with BAC-containing and BAC-free bimatoprost, travoprost and latanoprost was evaluated using the MTS assay. Real-time PCR analysis for hyperkeratinization associated genes (cornulin, involucrin) was performed.

RESULTS

In the absence of serum, the proliferation rate of HMGECs decreased starting with 0.1μg/ml BAC. At concentrations of 50μg/ml BAC and higher, cell viability was reduced after 10min exposure with a corresponding change in cell morphology. Toxicity of BAC-containing ophthalmic solutions was greater than that of BAC alone, whereas BAC-free alternative products did not significantly influence cell viability. Confluence, cell-cell contacts and serum-containing medium appeared to facilitate HMGECs survival. Expression rate of involucrin and cornulin declined after exposure to preserved bimatoprost and BAC.

CONCLUSIONS

BAC showed cytotoxic effects on HMGECs starting with a concentration of 0.1μg/ml. The combination of BAC and prostaglandin-analogs might have a synergistic effect which results in higher toxicity than BAC alone. Unpreserved eye drops and eye drops preserved with Polyquaternium-1 are less damaging to HMGECs.

Hypoxia: A breath of fresh air for the meibomian gland

PURPOSE

Optimal meibomian gland (MG) function is critically important for the health and wellbeing of the ocular surface. We hypothesize that low oxygen (O₂) conditions promote the function of human MG epithelial cells (HMGECs) and that human MGs exist in a relatively hypoxic environment. The purpose of this study was to test our hypotheses.

METHODS

We used human and mouse eyelid segments, and immortalized human MG epithelial cells (IHMGECs) in our studies. To evaluate oxygen (O₂) levels in the mouse MG and vicinity, we injected pimonidazole (pimo), a hypoxia marker, before sacrifice. Human eyelid samples were stained with the hypoxia marker glucose transporter 1 (Glut-1). To determine the effect of low O₂ levels on IHMGECs, we cultured cells under proliferating and differentiating conditions in both normoxic (21% O₂) and hypoxic (3% O₂) conditions for 5-15 days. IHMGECs were evaluated for cell number, neutral lipid content, lysosome accumulation, expression of biomarker proteins and DNase II activity.

RESULTS

Our results demonstrate that human and mouse MGs, but not the surrounding connective tissue, exist in a relatively hypoxic environment in vivo. In addition, our findings show that hypoxia does not influence IHMGEC numbers in basal or proliferating culture conditions, but does stimulate the expression of SREBP-1 in differentiating IHMGECs. Hypoxia also significantly increased DNase II activity, and apparently IHMGEC terminal differentiation.

CONCLUSIONS

Our Results support our hypotheses, and indicate that relative hypoxia promotes MG function.

Biomarkers for Progenitor and Differentiated Epithelial Cells in the Human Meibomian Gland

The meibomian gland (MG) is a sebaceous gland that secretes through a holocrine process. Because such secretion requires the destruction of MG acinar epithelial cells, they need constant renewal and differentiation. The processes that promote these regenerative events in the human MG are unknown, nor is it known how to distinguish MG progenitor and differentiated cells. We discovered that Lrig1 and DNase2 serve as biomarkers for human MG progenitor and differentiated cells, respectively. Lrig1 is expressed in MG basal epithelial cells in the acinar periphery, a location where progenitor cells originate in sebaceous glands. DNase2 is expressed in the differentiated epithelial cells of the MG central acinus. Furthermore, proliferation stimulates, and differentiation suppresses, Lrig1 expression in human MG epithelial cells. The opposite is true for DNase2 expression. Our biomarker identification may have significant value in clinical efforts to restore MG function and to regenerate MGs after disease‐induced dropout. Stem Cells Translational Medicine2018;7:887–892

Establishment and characterization of a telomerase-immortalized porcine bronchial epithelial cell line

Primary porcine bronchial epithelial cells (PBECs) are an ideal model to study the molecular and pathogenic mechanisms of various porcine respiratory pathogens. However, the short lifespan of primary PBECs greatly limit their application. Here, we isolated and cultured primary PBECs and established immortalized PBECs by transfecting primary PBECs with the pEGFP-hTERT recombinant plasmid containing human telomerase reverse transcriptase (hTERT). Immortalized PBECs (hTERT-PBECs) retained the morphological and functional features of primary PBECs as indicated by cytokeratin 18 expression, telomerase activity assay, proliferation assays, karyotype analysis, and quantitative reverse-transcriptase polymerase chain reaction. Compared to primary PBECs, hTERT-PBECs had higher telomerase activity, extended replicative lifespan, and displayed enhanced proliferative activity. Moreover, this cell line is not transformed in vitro and does not exhibit a malignant phenotype in vivo, suggesting that it can be safely used in further studies. Besides, hTERT-PBECs were susceptible to swine influenza virus of H3N2 subtype and porcine circovirus type 2. In conclusion, the immortalized hTERT-PBECs represent a valuable in vitro model, which can be widely used in the study of porcine respiratory pathogenic infections.

Generation of Immortalised But Unstable Cells after hTERT Introduction in Telomere-Compromised and p53-Deficient vHMECs

Telomeres, the natural ends of chromosomes, hide the linear telomeric DNA from constitutive exposure to the DNA damage response with a lariat structure or t-loop. Progressive telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in t-loop collapse and unmasked telomeres. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptosis, but they can also promote tumour initiation when cell cycle checkpoints are disabled. In this setting, telomere dysfunction promotes increasing chromosome instability (CIN) through breakage-fusion-bridge cycles. Excessive instability may hamper cell proliferation but might allow for the appearance of some rare advantageous mutations that could be selected and ultimately favour neoplastic progression. With the aim of generating pre-malignant immortalised cells, we ectopically expressed telomerase in telomere-compromised variant human mammary epithelial cells (vHMECs), proficient and deficient for p53, and analysed structural and numerical chromosomal aberrations as well as abnormal nuclear morphologies. Importantly, this study provides evidence that while immortalisation of vHMECs at early stages results in an almost stable karyotype, a transient telomere-dependent CIN period—aggravated by p53 deficiency—and followed by hTERT overexpression serves as a mechanism for the generation of immortal unstable cells which, due to their evolving karyotype, could attain additional promoting properties permissive to malignancy.

PPARγ regulates meibocyte differentiation and lipid synthesis of cultured human meibomian gland epithelial cells (hMGEC)

PURPOSE

To evaluate the role of PPARγ in regulating meibocyte differentiation and lipid synthesis in a human meibomian gland epithelial cell line (hMGEC).

METHODS

HMGEC were exposed to the PPARγ agonist, Rosiglitazone, from 10-50 μM. Cultures were also exposed to specific PPARγ antagonist, T0070907, to block PPARγ receptor signaling. Cells were then stained with Ki-67 and LipidTox to determine the effects on cell cycling and lipid synthesis, respectively. Expression of meibocyte differentiation related proteins, ADFP, PPARγ, ELOVL4, and FABP4, were evaluated by quantitative PCR and western blotting. A human corneal epithelial cell line (hTCEpi) was used as a control.

RESULT

Rosiglitazone significantly decreased Ki-67 staining within 2 days in a dose-dependent manner (P = 0.003) and increased lipid accumulation in hMGEC in a dose dependent manner. T0070907 suppressed both lipid droplet synthesis and cell cycle exit. Rosiglitazone significantly upregulated expression of ADFP, PPARγ, ELOVL4, and FABP4 by 9.6, 2.7, 2.6, and 3.3 fold on average (all P < 0.05 except for FABP4, P = 0.057) in hMGEC. T0070907 significantly abrogated rosiglitazone-induced upregulation of these genes when treated prior to rosiglitazone treatment (all P < 0.05). The observed lipogenic differentiation response was not duplicated in hTCEpi after exposure to rosiglitazone.

CONCLUSION

Rosiglitazone induced cell cycle exit and upregulation of lipogenic gene expression leading to lipid accumulation in hMGEC. These effects were suppressed by PPARγ antagonist indicating that PPARγ signaling specifically directs lipogenesis in hMGEC. These findings suggest that PPARγ plays a critical role in meibocyte differentiation.

Short Tandem Repeat (STR) Profiles of Commonly Used Human Ocular Surface Cell Lines

PURPOSE

The purpose of this study is to establish the short tandem repeat (STR) profiles of several human cell lines commonly used in ocular surface research.

MATERIALS AND METHODS

Independently DNA was extracted from multiple passages of three human corneal epithelial cell lines, two human conjunctival epithelial cell lines and one meibomian gland cell line, from different laboratories actively involved in ocular surface research. The samples were then subjected to STR analysis on a fee-for-service basis in an academic setting and the data compared against that in available databases.

RESULTS

The STR profiles for the human corneal epithelial cells were different among the three cell lines studied and for each line the profiles were identical across the samples provided by three laboratories. Profiles for the human conjunctival epithelial cells were different among the two cell lines studied. Profiles for the meibomian gland cell line were identical across the samples provided by three laboratories. No samples were contaminated by elements of other cell lines such as HeLa.

CONCLUSIONS

This comprehensive study provides verification of STR profiles for commonly used human ocular surface cell lines that can now be used as a reference by others in the field to authenticate the cell lines in use in their own laboratories.