Hyperosmolarity-induced cornification of human corneal epithelial cells is regulated by JNK MAPK

Tear Film Hyperosmolarity is Associated with Increased Variation of Light Scatter Following Cataract Surgery

Purpose

To study the association between tear film hyperosmolarity and ocular light scatter in a cataract surgery population.

Patients and Methods

Contiguous, 20-second objective scatter index (OSI) scans were recorded in hyperosmolar (≥320 mOsm/L) and normal subjects (<308 mOsm/L) with cataract nuclear opacity ≥3. OSI was measured at screening, baseline and 90 days following surgery. Along with symptoms of ocular surface disease, slit-lamp examination included corneal staining (0-3), tear film breakup time (TBUT) and evaluation of meibomian gland disease (MGD). An additional cohort of hyperosmolar subjects were measured for OSI at screening, baseline, and 5, 10, 15 and 30 minutes following instillation of 0.18% sodium hyaluronate (HA).

Results

Thirty-one eyes of 31 patients were included. There was a significant difference in post-operative OSI variation when comparing hyperosmolar (0.65±0.30, N=11) to normal subjects (0.33±0.11, N=10, p=0.005). Of note, there were no significant differences in OSI variation when subjects were sorted by staining (p=0.9), TBUT (p=0.7), symptoms (p=0.7), or MGD status (p=0.9). Instillation of 0.18% HA (N=10) did not alter OSI at 5 minutes, but significant reductions in OSI of 28.8%, 38.5% and 36.7% (all p < 0.001) were observed at 10, 15 and 30 minutes.

Conclusion

Hyperosmolar patients exhibited significantly increased variation in light scatter following cataract surgery that was undifferentiated by staining or TBUT. Elevated osmolarity may be indicative of light scatter equivalent to that of a grade 2-3 cataract.

Impact of Clinician Subjectivity on the Assessment of Dry Eye Disease Prevalence in a UK Public Health Care Patient Population

Purpose

To understand the impact of subjectivity on diagnosis rates of dry eye disease (DED) in an unbiased population.

Patients and Methods

A multicenter study enrolled 818 subjects with complete report forms (465 females, 67.1 ± 16.7 years, 353 males, 65.0 ± 15.9 years). Subjects were evaluated for staining, TBUT, tear osmolarity, meibomian gland disease, and OSDI.

Results

Physicians diagnosed 48.7% of subjects as having DED, ranging from 42.9% to 62.3% between sites. Positivity rates for staining (≥ grade 1) ranged from 41.3% to 84.1% (mean = 0.8 ± 0.9 grade), TBUT (<10s) ranged from 39.1% to 61.6% (mean = 10.4 ± 6.6 seconds), osmolarity (>308 mOsm/L) ranged from 63.7% to 72.4% (mean = 319.7 ± 20.8), MGD grading ranged from 28.9% to 51.3% (mean = 0.5 ± 0.7), and symptoms measured by OSDI ranged from 57.6% to 71.0% (mean = 23.5 ± 20.5) between sites. Tear osmolarity was the most consistent between sites (max/min positivity = 114%), followed by OSDI (123%), TBUT (158%), MGD (178%), and staining (204%). DED markers were uncorrelated (average r2 = 0.05 ± 0.07). A substantial number of subjects (N = 110) exhibited positive symptoms (OSDI = 32.4 ± 15.7) and hyperosmolarity (338.1 ± 20.1 mOsm/L) but no other obvious signs of DED (MGD grade = 0.2 ± 0.4, TBUT = 13.5 ± 7.0 seconds, staining grade = 0.4 ± 0.5).

Conclusion

Subjective signs of DED varied considerably, whereas objective measurements of OSDI and osmolarity were the most consistent between sites. A large proportion of subjects exhibited high symptoms and hyperosmolarity but no other obvious signs of dry eye disease, most of whom were undiagnosed by clinical assessment without access to the osmolarity measurement.

Effects of climate factors and Demodex infestation on meibomian gland dysfunction-associated dry eye diseases

We examined the effects of climatic factors and Demodex infestations on meibomian gland dysfunction (MGD)-associated dry eye disease (DED) in a cross-sectional study. This study included 123 patients from Tianjin and Chengdu regions, and climate factors and the Air Quality Index (AQI) were recorded for one year. Ocular surface parameters and Demodex infestations were evaluated using various tests. Significant differences in all climatic factors and AQI were observed between Tianjin and Chengdu (P < 0.01), and ocular surface parameters also differed significantly between the two regions (P < 0.05). Temperature, relative humidity, and precipitation positively correlated with tear break-up time (BUT), meibum gland expressibility, and lid margin irregularity but negatively correlated with lissamine green staining scores (P < 0.05). Wind speed and atmospheric pressure positively correlated with corneal fluorescein staining and lissamine green staining but negatively correlated with BUT and lid margin irregularity (P < 0.05). AQI positively correlated with DED symptoms and corneal findings but negatively correlated with tear film stability and meibomian gland characteristics (P < 0.05). Demodex infestation was only positively correlated with meibum quality scores (P < 0.05). Our findings suggest that geographic climates influence ocular surface characteristics in MGD-associated DED, with daily precipitation potentially playing a significant role, and Demodex infestation contributes to meibum gland degeneration.

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

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

Profiling tear film enzymes reveals major metabolic pathways involved in the homeostasis of the ocular surface

The ocular surface (OS) enzymes are of great interest due to their potential for novel ocular drug development. We aimed first to profile and classify the enzymes of the OS to describe major biological processes and pathways that are involved in the maintenance of homeostasis. Second, we aimed to compare the enzymatic profiles between the two most common tear collection methods, capillary tubes (CT) and Schirmer strips (ScS). A comprehensive tear proteomic dataset was generated by pooling all enzymes identified from nine tear proteomic analyses of healthy subjects using mass spectrometry. In these studies, tear fluid was collected using CT (n = 4), ScS (n = 4) or both collection methods (n = 1). Classification and functional analysis of the enzymes was performed using a combination of bioinformatic tools. The dataset generated identified 1010 enzymes. The most representative classes were hydrolases (EC 3) and transferases (EC 2). Phosphotransferases, esterases and peptidases were the most represented subclasses. A large portion of the identified enzymes was common to both collection methods (n = 499). More enzymes were specifically detected in the ScS-extracted proteome. The major pathways in which the identified enzymes participate are related to the immune system and protein, carbohydrate and lipid metabolism. Metabolic processes for nucleosides, cellular amides, sugars and sulfur compounds constituted the most enriched biological processes. Knowledge of these molecules highly susceptible to pharmacological manipulation might help to predict the metabolism of ophthalmic medications and develop novel prodrug strategies as well as new drug delivery systems. Combining such extensive knowledge of the OS enzymes with new analytical approaches and techniques might create new prospects for understanding, predicting and manipulating the metabolism of ocular pharmaceuticals. Our study reports new, essential data on OS enzymes while also comparing the enzyme profiles obtained via the two most popular methods of tear collection, capillary tubes and Schirmer strips.

Preclinical characterization of water-free cyclosporine eye drops - factors impacting ocular penetration ex vivo and in vivo

Although the efficacy of Cyclosporine A (CsA) in the management of ocular inflammation is well-demonstrated, ocular delivery remains challenging due to its hydrophobic nature. The semifluorinated alkane, perfluorobutylpentane (F4H5) has previously been suggested as an efficient vehicle for preparation of CsA eyedrops. Here we evaluated the influence of drop volume and the formulation aid, ethanol (EtOH), on ocular penetration of CsA and compared it to that of the commercial eyedrop, Ikervis, ex vivo and in vivo. Moreover, conjunctival and corneal tolerability after EtOH addition were evaluated ex vivo. The F4H5/EtOH vehicle was well tolerated and resulted in better corneal CsA penetration (AUC_{(0 - 4h)}: 63,008 ± 3,946 ng.h.g^-1) than Ikervis (AUC_{(0 - 4h)}: 10,328 ± 1,462 ng.h.g^-1) or F4H5 alone (AUC_{(0 - 4h)}: 50,734 ± 3,472 ng.h.g^-1) ex vivo. Interestingly, in vivo the CsA concentration in cornea, conjunctiva and lacrimal glands observed after administration of the F4H5 formulation (AUC_{(0.133-24 h)}: 7,741 ± 1,334 ng.h.g^-1, 1,313 ± 291 ng.h.g^-1, 48.2 ± 26.3 ng.h.g^-1) and F4H5/EtOH both at a reduced dose of 11 µl (AUC_{(0.133-24 h)}: 9,552 ± 1,738 ng.h.g^-1, 1,679 ± 285 ng.h.g^-1, 50.3 ± 21.1 ng.h.g^-1) was similar or even greater than what was observed on administration of 50 µl Ikervis (AUC_{(0.133-24 h)}: 9,943 ± 1,413 ng.h.g^-1, 2,069 ± 263 ng.h.g^-1, 30.6 ± 18.4 ng.h.g^-1). Thus, F4H5-based eyedrops were shown to deliver CsA more efficiently to anterior ocular tissues at a reduced dose in comparison to Ikervis, reducing dose wastage and minimizing any potential systemic side effects.

Interleukin-20 is involved in dry eye disease and is a potential therapeutic target

Background

Dry eye disease (DED) is a common disease in ophthalmology, affecting millions of people worldwide. Recent studies have shown that inflammation is the core mechanism of DED. IL-20 is a proinflammatory cytokine involved in various inflammatory diseases. Therefore, we aimed to explore the role of this cytokine in the pathogenesis of DED and evaluate the therapeutic potential of the anti-IL-20 monoclonal antibody (mAb) 7E for DED treatment.

Methods

Clinical tear samples from patients with DED and non-DED controls were collected and their IL-20 protein levels were determined. We established three DED animal models to explore the role of IL-20 and the efficacy of IL-20 antibody in DED. Benzalkonium chloride (BAC)-induced over-evaporative DED, extra-orbital lacrimal gland excision (LGE)-induced aqueous tear-deficient DED, and desiccating stress (DS)-induced combined over-evaporative and aqueous tear-deficient DED animal models were established to investigate the role of IL-20. The anti-IL-20 antibody 7E was established to neutralize IL-20 activity. The effects of IL-20 or 7E on human corneal epithelial cells and macrophages under hyperosmotic stress were analyzed. 7E was topically applied to eyes to evaluate the therapeutic effects in the DED animal models.

Results

IL-20 was significantly upregulated in the tears of patients with DED and in the tears and corneas of DED animal models. Under hyperosmotic stress, IL-20 expression was induced via NFAT5 activation in corneal epithelial cells. 7E suppressed hyperosmotic stress-induced activation of macrophages. IL-20 induced cell death in corneal epithelial cells and 7E protected cells from hyperosmotic stress-induced cell death. Blocking IL-20 signaling with 7E protected mice from BAC-induced, LGE-induced, and DS-induced DED by reducing DED symptoms and inhibiting inflammatory responses, macrophage infiltration, apoptosis, and Th17 populations in the conjunctiva and draining lymph nodes.

Conclusions

Our results demonstrated the functions of IL-20 in DED and presented a potential therapeutic option for this condition.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00821-2.

Conjunctivochalasis and Tear Osmolarity Are Associated With Reduced Conjunctival Epithelial Thickness in Dry Eye

PURPOSE

To investigate the hypothesis that ocular surface epithelial thickness is correlated with tear osmolarity, conjunctivochalasis (CCh), and dry eye clinical tests.

DESIGN

A case-control study.

METHODS

A total of 50 patients with different types of dry eye disease (DED) and 15 age- and sex-matched control subjects were enrolled in this study. We performed a detailed diagnostic assessment of tear film and ocular surface parameters, including Ocular Surface Disease Index questionnaire, visual analog scale questionnaire, topographic surface regularity and surface asymmetry indices, tear film break-up time, corneal and conjunctival dye staining, Schirmer I test, and tear osmolarity. The corneal and bulbar conjunctival epithelial thickness (CET) were obtained using the latest version of spectral domain optical coherence tomography (SDOCT).

RESULTS

Patients with aqueous-deficient DED (ADDED) had lower bulbar CET values, particularly in the temporal region, than those of normal subjects and patients with evaporative-type DED (EDED); however, the difference did not quite reach a statistically significant level. Patients with DED and CCh had lower bulbar CET values in temporal (38.52 ± 9.58 µm) and inferior regions (50.79 ± 9.10 µm) compared to those with DED without CCh (47.39 ± 11.71 µm, 60.38 ± 14.36 µm, respectively, P < .02). In the DED group, tear osmolarity was found to be negatively correlated with CET values in temporal bulbar region (P = .006 and r = -0.403) and central corneal epithelial thickness values (P = .029 and r = -0.325).

CONCLUSIONS

CCh and tear osmolarity are associated with reduced conjunctival epithelial thickness in DED.

Modern approach to the treatment of dry eye, a complex multifactorial disease: a P.I.C.A.S.S.O. board review

Dry eye disease (DED) is a growing public health concern affecting quality of life and visual function, with a significant socio-economic impact. It is characterised by the loss of homoeostasis, resulting in tear film instability, hyperosmolarity and inflammation of the ocular surface. If the innate immune response is unable to cope with internal bodily or environmental adverse conditions, the persistent, self-maintaining vicious circle of inflammation leads to the chronic form of the disease. Treatment of DED should be aimed at the restoration of the homoeostasis of the ocular surface system. A proper diagnostic approach is fundamental to define the relevance and importance of each of the DED main pathogenic factors, namely tear film instability, epithelial damage and inflammation. Consideration also needs to be given concerning two other pathogenic elements: lid margin changes and nerve damage. All the factors that maintain the vicious circle of DED in the patient's clinical presentation have to be considered and possibly treated simultaneously. The treatment should be long-lasting and personalised since it has to be adapted to the different clinical conditions observed along the course of the disease. Since DED treatment is frequently unable to provide fast and complete relief from symptoms, empathy with patients and willingness to explain to them the natural history of the disease are mandatory to improve patients' compliance. Furthermore, patients should be instructed about the possible need to increase the frequency and/or change the type of treatment according to the fluctuation of symptoms, following a preplanned rescue regimen.

Trehalose Induces Autophagy Against Inflammation by Activating TFEB Signaling Pathway in Human Corneal Epithelial Cells Exposed to Hyperosmotic Stress

Purpose

Autophagy plays an important role in balancing the inflammatory response to restore homeostasis. The aim of this study was to explore the mechanism by which trehalose suppresses inflammatory cytokines via autophagy activation in primary human corneal epithelial cells (HCECs) exposed to hyperosmotic stress.

Methods

An in vitro dry eye model was used in which HCECs were cultured in hyperosmolar medium with the addition of sodium chloride (NaCl). Trehalose was applied in different concentrations. The levels of TNF-α, IL-1β, IL-6, and IL-8 were detected using RT-qPCR and ELISA. Cell viability assays, immunofluorescent staining of LC3B, and western blots of Beclin1, Atg5, Atg7, LC3B, and P62 were conducted. The key factors in upstream signaling pathways of autophagy activation were measured: P-Akt, Akt, and transcription factor EB (TFEB).

Results

Trehalose reduced the proinflammatory mediators TNF-α, IL-1β, IL-6, and IL-8 in primary HCECs at 450 mOsM. This effect was osmolarity dependent, and a level of 1.0% trehalose showed the most suppression. Trehalose promoted autophagosome formation and autophagic flux, as evidenced by increased production of Beclin1, Atg5, and Atg7, as well as higher LC3B I protein turnover to LC3B II, with decreased protein levels of P62/SQSTM1. The addition of 3-methyladenine blocked autophagy activation and increased the release of proinflammatory cytokines. Trehalose further activated TFEB, with translocation from cytoplasm to the nucleus, but diminished Akt activity.

Conclusions

Our findings demonstrate that trehalose, functioning as an autophagy enhancer, suppresses the inflammatory response by promoting autophagic flux via TFEB activation in primary HCECs exposed to hyperosmotic stress, a process that is beneficial to dry eye.

Autophagy Activation Protects Ocular Surface from Inflammation in a Dry Eye Model In Vitro

Inflammation is the main pathophysiology of dry eye, characterized by tear film instability and hyperosmolarity. The aim of this study was to investigate the association of inflammation and cellular autophagy using an in vitro dry eye model with primary cultured human corneal epithelial cells (HCECs). Primary HCECs cultured with fresh limbal explants from donors were switched to a hyperosmotic medium (450 mOsM) by adding sodium chloride into the culture medium. We observed the stimulated inflammatory mediators, TNF-α, IL-1β, IL-6 and IL-8, as well as the increased expression of autophagy related genes, Ulk1, Beclin1, Atg5 and LC3B, as evaluated by RT-qPCR and ELISA. The immunofluorescent staining of LC3B and Western blotting revealed the activated autophagosome formation and autophagic flux, as evidenced by the increased LC3B autophagic cells with activated Beclin1, Atg5, Atg7 and LC3B proteins, and the decreased levels of P62 protein in HCECs. Interestingly, the autophagy activation was later at 24 h than inflammation induced at 4 h in HCECs exposed to 450 mOsM. Furthermore, application of rapamycin enhanced autophagy activation also reduced the inflammatory mediators and restored cell viability in HCECs exposed to the hyperosmotic medium. Our findings for the first time demonstrate that the autophagy activation is a late phase response to hyperosmotic stress, and is enhanced by rapamycin, which protects HCECs by suppressing inflammation and promoting cells survival, suggesting a new therapeutic potential to treat dry eye diseases.

The cornea in keratoconjunctivitis sicca

The lacrimal functional unit (LFU) regulates tear production, composition, distribution and clearance to maintain a stable protective tear layer that is essential for maintaining corneal epithelial health. Dysfunction of the LFU, commonly referred to as dry eye, leads to increased tear osmolarity and levels of inflammatory mediators in tears that cause ocular surface epithelial disease, termed keratoconjunctivitis sicca (KCS). Corneal changes in KCS include glycocalyx loss, barrier disruption, surface irregularity inflammatory cytokine/chemokine production, cornification and apoptosis. These can reduce visual function and the increased shear force on the corneal epithelium can stimulate nociceptors sensitized by inflammation causing irritation and pain that may precede frank clinical signs. Therapy of keratoconjunctivitis sicca should be tailored to improve tear stability, normalize tear composition, improve barrier function and minimize shear forces and damaging inflammation to improve corneal epithelial health.

Oxidative stress in corneal injuries of different origin: Utilization of 3D human corneal epithelial tissue model

The purpose of the current work was to utilize a three dimensional (3D) corneal epithelial tissue model to study dry eye disease and oxidative stress-related corneal epithelial injuries for the advancement of ocular therapeutics. Air-liquid interface cultures of normal human corneal epithelial cells were used to produce 3D corneal epithelial tissues appropriate for physiologically relevant exposure to environmental factors. Oxidative stress was generated by exposing the tissues to non-toxic doses of ultraviolet radiation (UV), hydrogen peroxide, vesicating agent nitrogen mustard, or desiccating conditions that stimulated morphological, cellular, and molecular changes relevant to dry eye disease. Corneal specific responses, including barrier function, tissue viability, reactive oxygen species (ROS) accumulation, lipid peroxidation, cytokine release, histology, and gene expression were evaluated. 3D corneal epithelial tissue model structurally and functionally reproduced key features of molecular responses of various types of oxidative stress-induced ocular damage. The most pronounced effects for different treatments were: UV irradiation - intracellular ROS accumulation; hydrogen peroxide exposure - barrier impairment and IL-8 release; nitrogen mustard exposure - lipid peroxidation and IL-8 release; desiccating conditions - tissue thinning, a decline in mucin expression, increased lipid peroxidation and IL-8 release. Utilizing a PCR gene array, we compared the effects of corneal epithelial damage on the expression of 84 oxidative stress-responsive genes and found specific molecular responses for each type of damage. The topical application of lubricant eye drops improved tissue morphology while decreasing lipid peroxidation and IL-8 release from tissues incubated at desiccating conditions. This model is anticipated to be a valuable tool to study molecular mechanisms of corneal epithelial damage and aid in the development of therapies against dry eye disease, oxidative stress- and vesicant-induced ocular injuries.

Tear Film Proteomics Reveal Important Differences Between Patients With and Without Ocular GvHD After Allogeneic Hematopoietic Cell Transplantation

Purpose

To date, no biomarkers for ocular graft versus host disease (GvHD), a frequent complication following allogeneic hematopoietic cell transplantation (HCT), exist. In this prospective study, we evaluated the potential of human tear proteins as biomarkers for ocular GvHD.

Methods

Tears from 10 patients with moderate-to-severe ocular GvHD were compared to 10 patients without ocular GvHD. After a full ocular surface clinical examination, tears were collected onto Schirmer strips and protein composition was analyzed by liquid chromatography tandem mass spectrometry. Statistical evaluation was performed using the Mann-Whitney U test to compare means and the false discovery rate method to adjust for multiple comparisons. Functional annotation of differentially expressed proteins was done with the PANTHER classification system.

Results

We identified 282 proteins in tryptic digests of Schirmer strips; 79 proteins were significantly differentially expressed between the two groups, from which 54 were up- and 25 downregulated. The most upregulated proteins were classified as nucleic acid binding and cytoskeletal proteins, while the most extensively downregulated proteins belong to an array of classes including transfer and receptor proteins, enzyme modulators, and hydrolases. In addition to proteins already confirmed as differentially expressed in dry eye disease, we report changes in 36 novel proteins.

Conclusions

This study reports the proteomic profile of tears in ocular GvHD for the first time and identifies a number of unique differentially expressed proteins. Further studies with a higher number of participants are necessary to confirm these results and to evaluate the reliability of these expression patterns in longitudinal studies.

Anti-Inflammatory and Anti-Apoptotic Effects of Acer Palmatum Thumb. Extract, KIOM-2015EW, in a Hyperosmolar-Stress-Induced In Vitro Dry Eye Model

The aim of this study was to assess the anti-inflammatory and anti-apoptotic effects of KIOM-2015EW, the hot-water extract of maple leaves in hyperosmolar stress (HOS)-induced human corneal epithelial cells (HCECs). HCECs were exposed to hyperosmolar medium and exposed to KIOM-2015EW with or without the hyperosmolar media. Tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 production and apoptosis were observed, and the activation of mitogen-activated protein kinases (MAPKs) including extracellular signal regulated kinase (ERK), p38 and c-JUN N-terminal kinase (JNK) signaling and nuclear factor (NF)-κB was confirmed. Compared to isomolar medium, the induction of cell cytotoxicity significantly increased in HCECs exposed to hyperosmolar medium in a time-dependent manner. KIOM-2015EW-treatment significantly reduced the mRNA and protein expression of pro-inflammatory mediators and apoptosis. KIOM-2015EW-treatment inhibited HOS-induced MAPK signaling activation. Additionally, the HOS-induced increase in NF-κB phosphorylation was attenuated by KIOM-2015EW. The results demonstrated that KIOM-2015EW protects the ocular surface by suppressing inflammation in dry eye disease, and suggest that KIOM-2015EW may be used to treat several ocular surface diseases where inflammation plays a key role.

The Pathophysiology of Dry Eye Disease: What We Know and Future Directions for Research

Clinical and laboratory studies performed over the past few decades have discovered that dry eye is a chronic inflammatory disease that can be initiated by numerous extrinsic or intrinsic factors that promote an unstable and hyperosmolar tear film. These changes in tear composition, in some cases combined with systemic factors, lead to an inflammatory cycle that causes ocular surface epithelial disease and neural stimulation. Acute desiccation activates stress signaling pathways in the ocular surface epithelium and resident immune cells. This triggers production of innate inflammatory mediators that stimulate the production of matrix metalloprotease, inflammatory cell recruitment, and dendritic cell maturation. These mediators, combined with exposure of autoantigens, can lead to an adaptive T cell-mediated response. Cornea barrier disruption develops by protease-mediated lysis of epithelial tight junctions, leading to accelerated cell death; desquamation; an irregular, poorly lubricated cornea surface; and exposure and sensitization of epithelial nociceptors. Conjunctival goblet cell dysfunction and death are promoted by the T helper 1 cytokine interferon gamma. These epithelial changes further destabilize the tear film, amplify inflammation, and create a vicious cycle. Cyclosporine and lifitegrast, the 2 US Food and Drug Administration-approved therapies, inhibit T-cell activation and cytokine production. Although these therapies represent a major advance in dry eye therapy, they are not effective in improving discomfort and corneal epithelial disease in all patients. Preclinical studies have identified other potential therapeutic targets, biomarkers, and strategies to bolster endogenous immunoregulatory pathways. These discoveries will, it is hoped, lead to further advances in diagnostic classification and treatment.

TFOS DEWS II Sex, Gender, and Hormones Report

One of the most compelling features of dry eye disease (DED) is that it occurs more frequently in women than men. In fact, the female sex is a significant risk factor for the development of DED. This sex-related difference in DED prevalence is attributed in large part to the effects of sex steroids (e.g. androgens, estrogens), hypothalamic-pituitary hormones, glucocorticoids, insulin, insulin-like growth factor 1 and thyroid hormones, as well as to the sex chromosome complement, sex-specific autosomal factors and epigenetics (e.g. microRNAs). In addition to sex, gender also appears to be a risk factor for DED. "Gender" and "sex" are words that are often used interchangeably, but they have distinct meanings. "Gender" refers to a person's self-representation as a man or woman, whereas "sex" distinguishes males and females based on their biological characteristics. Both gender and sex affect DED risk, presentation of the disease, immune responses, pain, care-seeking behaviors, service utilization, and myriad other facets of eye health. Overall, sex, gender and hormones play a major role in the regulation of ocular surface and adnexal tissues, and in the difference in DED prevalence between women and men. The purpose of this Subcommittee report is to review and critique the nature of this role, as well as to recommend areas for future research to advance our understanding of the interrelationships between sex, gender, hormones and DED.

Hyperosmolarity-induced AQP5 upregulation promotes inflammation and cell death via JNK1/2 Activation in human corneal epithelial cells

Tear film hyperosmolarity and anterior ocular inflammation are two clinical signs that may be indicative of dry eye disease (DED). This condition can cause pathological and functional changes to the anterior ocular surface tissues. A contributing factor may be dysfunctional aquaporin 5 (AQP5) water channels as they are the AQP subtype that expressed in the corneal epithelium and contribute to fluid efflux needed for corneal function. We determined if described hyperosmolarity-induced increases in proinflammatory cytokine expression and cell death are mediated through AQP5 upregulation and JNK1/2 MAPK signaling activation in both primary human corneal epithelial cells (HCECs), and in a HCEC line. Real time RT-PCR identified rises in IL-1β, IL-6, IL-8, TNF-α, caspase-1, and AQP5 mRNA levels upon step increases in osmolarity up to 550 mOsm. Western blot analysis and the TUNEL assay identified corresponding rises in AQP5 and p-JNK1/2 protein expression and cell death respectively. JNK1/2 inhibition with SP600125, or siRNA AQP5 gene silencing reduced hypertonic-induced rises in proinflammatory cytokine expression and cell death. Taken together, hypertonicity-induced AQP5 upregulation leads to increases in proinflammatory cytokine expression and cell death through JNK1/2 MAPK activation. These results suggest that drug targeting AQP5 upregulation may be a therapeutic option in DED management.

Assessment of meibomian glands and tear film in post-refractive surgery patients

IMPORTANCE

Corneal refractive surgery may impact meibomian gland and tear film in post-refractive surgery patients.

BACKGROUND

To compare ocular surface parameters between post-refractive surgery patients and normal controls.

DESIGN

Cross-sectional single centre study.

PARTICIPANTS

A total of 120 eyes of 120 subjects were divided into three groups: (i) 60 controls and 60 patients underwent corneal refractive surgery at least 12 months ago; (ii) 30 post-laser in-situ keratomileusis (LASIK) patients and (iii) 30 post-laser epithelial keratomileusis (LASEK)/photo-refractive keratectomy (PRK) patients.

METHODS

Tear meniscus height, non-invasive keratographic tear film break-up time and meibography were measured using the Keratograph^® 5M. Fluorescein break-up time, ocular surface staining, examination of lid margins and meibomian glands, Schirmer's test and Ocular Surface Disease Index questionnaire were performed.

MAIN OUTCOME MEASURES

Ordinary logistic regression was performed to evaluate the impact of clinical variables including refractive surgery on the meiboscores.

RESULTS

In post-LASIK patients, ocular surface parameters including Ocular Surface Disease Index scores, fluorescein break-up time and staining scores, except Schirmer's scores, were significantly worse than those in controls (P < 0.050). Ocular surface staining scores in post-LASEK/PRK patients was higher than that in the controls (P = 0.001). In post-refractive surgery patients, grade of meibomian gland parameters and meiboscores were worse than those of controls (all P < 0.050). Histories of refractive surgery were associated with high meiboscore (β = 1.100, P = 0.043 for LASIK and β = 1.039, P = 0.042 for LASEK/PRK).

CONCLUSIONS AND RELEVANCE

Corneal refractive surgery may adversely affect the ocular surface, and a reduction of functional meibomian glands can contribute to chronic tear film dysfunction after corneal refractive surgery.

An Antifungal Mechanism of Protolichesterinic Acid from the Lichen Usnea albopunctata Lies in the Accumulation of Intracellular ROS and Mitochondria-Mediated Cell Death Due to Apoptosis in Candida tropicalis

Candida species causes superficial and life-threatening systemic infections and are difficult to treat due to the resistance of these organism to various clinically used drugs. Protolichesterinic acid is a well-known lichen compound. Although the antibacterial activity of protolichesterinic acid has been reported earlier, the antifungal property and its mechanism of action are still largely unidentified. The goal of the present investigation is to explore the anticandidal activity and mechanism of action of protolichesterinic acid, especially against Candida tropicalis. The Minimum Inhibitory Concentration (MIC) value was established through microdilution techniques against four Candida species and out of four species tested, C. tropicalis showed a significant effect (MIC: 2 μg/ml). In the morphological interference assay, we observed the enhanced inhibition of hyphae when the cells were treated with protolichesterinic acid. Time-kill assay demonstrated that the maximum rate of killing was recorded between 2 and 6 h. C. tropicalis exposed to protolichesterinic acid exhibited an increased ROS production, which is one of the key factors of fungal death. The rise in ROS was due to the dysfunction of mitochondria caused by protolichesterinic acid. We confirmed that protolichesterinic acid-induced dysfunction of mitochondria in C. tropicalis. The damage of cell membrane due to protolichesterinic acid treatment was confirmed by the influx of propidium iodide and was further confirmed by the release of potassium ions. The treatment of protolichesterinic acid also triggered calcium ion signaling. Moreover, it commenced apoptosis which is clearly evidenced by Annexin V and propidium iodide staining. Interestingly protolichesterinic acid recorded excellent immunomodulatory property when tested against lymphocytes. Finally protolichesterinic acid showed low toxicity toward a normal human cell line Foreskin (FS) normal fibroblast. In in vivo test, protolichesterinic acid significantly enhanced the survival of C. tropicalis infected Caenorhabditis elegans. This investigation proposes that the protolichesterinic acid induces apoptosis in C. tropicalis via the enhanced accumulation of intracellular ROS and mitochondrial damage, which leads fungal cell death via apoptosis. Our work revealed a new key aspect of mechanisms of action of protolichesterinic acid in Candida species. This article is the first study on the antifungal and mechanism of action of protolichesterinic acid in Candida species.

Perillaldehyde, a Promising Antifungal Agent Used in Food Preservation, Triggers Apoptosis through a Metacaspase-Dependent Pathway in Aspergillus flavus

In the present study, we provide detailed insights into perillaldehyde (PAE)'s mechanisms of action on Aspergillus flavus and offer evidence in favor of the induction of an apoptosis-like phenotype. Specifically, PAE's antifungal mode of action was investigated through the detection of mitochondrial membrane potential (MtΔψ) and phosphatidylserine (PS) exposure, as well as intracellular Ca²⁺ level, reactive oxygen species accumulation, and metacaspase activation. This was done by way of fluorometry, measuring DNA fragmentation, and condensation by fluorescent microscopy. Furthermore, we searched for phenotypic changes characteristic of apoptosis by transmission electron microscopy and flow cytometry, determining the amount of cytochrome c released using Western blotting. Results indicated that cultivation of A. flavus in the presence of PAE caused depolarization of MtΔψ, rapid DNA condensation, large-scale DNA fragmentation, and an elevation of intracellular Ca²⁺ level. The percentage of early apoptotic cells with exposure of PS were 27.4% and 48.7%, respectively, after 9 h incubations with 0.25 and 0.5 μL/mL of PAE. The percentage of stained cells with activated intracellular metacaspases exposed to PAE at concentrations of 0.25 and 0.5 μL/mL compared with control subjects were increased by 28.4 ± 3.25% and 37.9 ± 4.24%, respectively. The above results has revealed that PAE induces fungal apoptosis through a caspase-dependent mitochondrial pathway. In all, our findings provide a novel mechanism for exploring a possible antifungal agent used in food preservation.

In Vitro Inhibition of NFAT5-Mediated Induction of CCL2 in Hyperosmotic Conditions by Cyclosporine and Dexamethasone on Human HeLa-Modified Conjunctiva-Derived Cells

Purpose

To investigate the pro-inflammatory intracellular mechanisms induced by an in vitro model of dry eye disease (DED) on a Hela-modified conjunctiva-derived cells in hyperosmolarity (HO) stress conditions. This study focused on CCL2 induction and explored the implications of the nuclear factor of activated T-cells 5 (NFAT5) as well as mitogen-activated protein kinases (MAPK) and nuclear factor kappa B (NFĸB). This work was completed by an analysis of the effects of cyclosporine A (CsA), dexamethasone (Dex) and doxycycline (Dox) on HO-induced CCL2 and NFAT5 induction.

Methods

A human HeLa-modified conjunctiva-derived cell line was cultured in NaCl-hyperosmolar medium for various exposure times. Cellular viability, CCL2 secretion, NFAT5 and CCL2 gene expression, and intracytoplasmic NFAT5 were assessed using the Cell Titer Blue^® assay, enzyme-linked immunosorbent assay (ELISA), RT-qPCR and immunostaining, respectively. In selected experiments, inhibitors of MAPKs or NFκB, therapeutic agents or NFAT5 siRNAs were added before the hyperosmolar stimulations.

Results

HO induced CCL2 secretion and expression as well as NFAT5 gene expression and translocation. Adding NFAT5-siRNA before hyperosmolar stimulation led to a complete inhibition of CCL2 induction and to a decrease in cellular viability. p38 MAPK (p38), c-Jun NH₂-terminal kinase (JNK) and NFĸB inhibitors, CsA and Dex induced a partial inhibition of HO-induced CCL2, while Dox and extracellular signal-regulated kinase (ERK) inhibitor did not. Dex also induced a partial inhibition of HO-induced NFAT5 gene expression but not CsA or Dox.

Conclusions

These in vitro results suggest a potential role of CCL2 in DED and highlight the crucial role of NFAT5 in the pro-inflammatory effect of HO on HeLa-modified conjunctiva-derived cells, a rarely studied cellular type. This inflammatory pathway involving NFAT5 and CCL2 could offer a promising target for developing new therapies to treat DED, warranting further investigations to fully grasp the complete intracellular mechanisms.

Hyperosmolar Tears Induce Functional and Structural Alterations of Corneal Nerves: Electrophysiological and Anatomical Evidence Toward Neurotoxicity

PURPOSE

In an effort to elucidate possible neural mechanisms underlying diminished tearing in dry eye disease, this study sought to determine if hyperosmolar tears, a ubiquitous sign of dry eye disease, produce functional changes in corneal nerve responses to drying of the cornea and if these changes correlate with alterations in corneal nerve morphology.

METHODS

In vivo extracellular electrophysiological recordings were performed in rat trigeminal ganglion neurons that innervated the cornea before, and up to 3 hours after, the ocular application of continuous hyperosmolar tears or artificial tears. In corollary experiments, immunohistochemical staining was performed to compare corneal nerve morphology in control and in eyes treated with hyperosmolar solutions.

RESULTS

Our previous studies identified a population of corneal afferents, dry-sensitive neurons that are strongly excited by corneal dessication ("dry response"), a response thought to trigger the lacrimation reflex. In the present study, we found that the dry responses of corneal dry-sensitive neurons were depressed or even completely abolished by hyperosmolar tears in a time- (30 minutes to 3 hours) and dose (450- to 1000-mOsm solutions)-dependent manner. Furthermore, eyes treated with hyperosmolar tears for 3 hours contained large numbers of morphologically abnormal (granular, fragmented, or prominently beaded) subbasal nerves that appeared to be undergoing degeneration.

CONCLUSIONS

These results demonstrate that tear hyperosmolarity, considered to be a "core" mechanism of dry eye disease, significantly decreases physiological sensitivity and morphologic integrity of the corneal nerves important in tear production. These alterations might contribute to the diminished tearing seen clinically in dry eye patients.

Revisiting the vicious circle of dry eye disease: a focus on the pathophysiology of meibomian gland dysfunction

Meibomian gland dysfunction (MGD) is the most frequent cause of dry eye disease (DED). Eyelid inflammation, microbial growth, associated skin disorders as well as potentially severe corneal complications culminate to make MGD a complex multifactorial disorder. It is probable that MGD is a heterogeneous condition arising from any combination of the following five separate pathophysiological mechanisms: eyelid inflammation, conjunctival inflammation, corneal damage, microbiological changes and DED resulting from tear film instability. The pathogenesis of both MGD and DED can be described in terms of a 'vicious circle': the underlying pathophysiological mechanisms of DED and MGD interact, resulting in a double vicious circle. The MGD vicious circle is self-stimulated by microbiological changes, which results in increased melting temperature of meibum and subsequent meibomian gland blockage, reinforcing the vicious circle of MGD. Meibomian gland blockage, dropout and inflammation directly link the two vicious circles. MGD-associated tear film instability provides an entry point into the vicious circle of DED and leads to hyperosmolarity and inflammation, which are both a cause and consequence of DED. Here we propose a new pathophysiological scheme for MGD in order to better identify the pathological mechanisms involved and to allow more efficient targeting of therapeutics. Through better understanding of this scheme, MGD may gain true disease status rather than being viewed as a mere dysfunction.

Lacritin and other autophagy associated proteins in ocular surface health

Advantage may be taken of macroautophagy ('autophagy') to promote ocular health. Autophagy continually captures aged or damaged cellular material for lysosomal degradation and recyling. When autophagic flux is chronically elevated, or alternatively deficient, health suffers. Chronic elevation of flux and stress are the consequence of inflammatory cytokines or of dry eye tears but not normal tears invitro. Exogenous tear protein lacritin transiently accelerates flux to restore homeostasis invitro and corneal health invivo, and yet the monomeric active form of lacritin appears to be selectively deficient in dry eye. Tissue transglutaminase-dependent cross-linking of monomer decreases monomer quantity and monomer affinity for coreceptor syndecan-1 thereby abrogating activity. Tissue transglutaminase is elevated in dry eye. Mutation of arylsulfatase A, arylsulfatase B, ceroid-lipofuscinosis neuronal 3, mucolipin, or Niemann-Pick disease type C1 respectively underlie several diseases of apparently insufficient autophagic flux that affect the eye, including: metachromatic leukodystrophy, mucopolysaccharidosis type VI, juvenile-onset Batten disease, mucolipidosis IV, and Niemann-Pick type C associated with myelin sheath destruction of corneal sensory and ciliary nerves and of the optic nerve; corneal clouding, ocular hypertension, glaucoma and optic nerve atrophy; accumulation of 'ceroid-lipofuscin' in surface conjunctival cells, and in ganglion and neuronal cells; decreased visual acuity and retinal dystrophy; and neurodegeneration. For some, enzyme or gene replacement, or substrate reduction, therapy is proving to be successful. Here we discuss examples of restoring ocular surface homeostasis through alteration of autophagy, with particular attention to lacritin.

Effects of L-carnitine, erythritol and betaine on pro-inflammatory markers in primary human corneal epithelial cells exposed to hyperosmotic stress

PURPOSE

To explore the effects of osmoprotectants on pro-inflammatory mediator production in primary human corneal epithelial cells (HCECs) exposed to hyperosmotic stress.

METHODS

HCECs cultured in iso-osmolar medium (312 mOsM) were switched to hyperosmotic media with or without prior incubation with 2-20 mM of l-carnitine, erythritol or betaine for different time periods. The mRNA expression and protein production of pro-inflammatory markers in HCECs were evaluated by RT-qPCR and ELISA.

RESULTS

Hyperosmolar media significantly stimulated the mRNA and protein expression of pro-inflammatory cytokines, TNF-α, IL-1β and IL-6, and chemokines, IL-8, CCL2 and CCL20 in HCECs in an osmolarity dependent manner. The stimulated expression of these pro-inflammatory mediators was significantly but differentially suppressed by l-carnitine, erythritol or betaine. l-Carnitine displayed the greatest inhibitory effects and down-regulated 54-77% of the stimulated mRNA levels of TNF-α (down from 12.3-5.7 fold), IL-1β (2.2-0.9 fold), IL-6 (7.3-2.9 fold), IL-8 (4.6-2.0 fold), CCL2 (15.3-3.5 fold) and CCL20 (4.1-1.5 fold) in HCECs exposed to 450 mOsM. The stimulated protein production of TNF-α, IL-1β, IL-6 and IL-8 was also significantly suppressed by l-carnitine, erythritol and betaine. l-carnitine suppressed 49-79% of the stimulated protein levels of TNF-α (down from 81.3 to 17.4 pg/ml), IL-1β (56.9-29.2 pg/ml), IL-6 (12.8-4.6 ng/ml) and IL-8 (21.2-10.9 ng/ml) by HCECs exposed to 450 mOsM. Interestingly, hyperosmolarity stimulated increase in mRNA and protein levels of TNF-α, IL-1β and IL-6 were significantly suppressed by a transient receptor potential vanilloid channel type 1 (TRPV1) activation inhibitor capsazepine.

CONCLUSIONS

l-carnitine, erythritol and betaine function as osmoprotectants to suppress inflammatory responses via TRPV1 pathway in HCECs exposed to hyperosmotic stress. Osmoprotectants may have efficacy in reducing innate inflammation in dry eye disease.

Extraorbital lacrimal gland excision: a reproducible model of severe aqueous tear-deficient dry eye disease

PURPOSE

The aim of this study was to establish and characterize extraorbital lacrimal gland excision (LGE) as a model of aqueous tear-deficient dry eye disease in mice.

METHODS

Female C57BL/6 mice at 6 to 8 weeks of age were randomized to extraorbital LGE, sham surgery, or scopolamine groups. Mice that underwent extraorbital LGE or sham surgery were housed in the standard vivarium. Scopolamine-treated mice were housed in a controlled environment chamber that allowed for the continuous regulation of airflow (15 L/min), relative humidity (30%), and temperature (21-23°C). Clinical disease severity was assessed over the course of 14 days using the phenol red thread test and corneal fluorescein staining. Real-time polymerase chain reaction was performed to assess corneal mRNA expression of interleukin 1β, tumor necrosis factor α, and matrix metalloproteinase 9. Flow cytometry was used to assess T helper cell frequencies in the conjunctivae and draining lymph nodes.

RESULTS

Extraorbital LGE markedly reduced aqueous tear secretion as compared with the sham procedure and induced a more consistent decrease in aqueous tear secretion than was observed in mice that received scopolamine while housed in the controlled environment chamber. Extraorbital LGE significantly increased corneal fluorescein staining scores as compared with those of both the sham surgery and scopolamine-treated groups. Extraorbital LGE significantly increased the corneal expression of interleukin 1β, tumor necrosis factor α, and matrix metalloproteinase 9. Further, extraorbital LGE increased T helper 17-cell frequencies in the conjunctivae and draining lymph nodes.

CONCLUSIONS

Extraorbital LGE induces aqueous tear-deficient dry eye disease in mice as evidenced by decreased aqueous tear secretion, increased corneal epitheliopathy, and induced ocular surface inflammation and immunity.

Dynamics and function of the tear film in relation to the blink cycle

Great strides have recently been made in quantitative measurements of tear film thickness and thinning, mathematical modeling thereof and linking these to sensory perception. This paper summarizes recent progress in these areas and reports on new results. The complete blink cycle is used as a framework that attempts to unify the results that are currently available. Understanding of tear film dynamics is aided by combining information from different imaging methods, including fluorescence, retroillumination and a new high-speed stroboscopic imaging system developed for studying the tear film during the blink cycle. During the downstroke of the blink, lipid is compressed as a thick layer just under the upper lid which is often released as a narrow thick band of lipid at the beginning of the upstroke. "Rippling" of the tear film/air interface due to motion of the tear film over the corneal surface, somewhat like the flow of water in a shallow stream over a rocky streambed, was observed during lid motion and treated theoretically here. New mathematical predictions of tear film osmolarity over the exposed ocular surface and in tear breakup are presented; the latter is closely linked to new in vivo observations. Models include the effects of evaporation, osmotic flow through the cornea and conjunctiva, quenching of fluorescence, tangential flow of aqueous tears and diffusion of tear solutes and fluorescein. These and other combinations of experiment and theory increase our understanding of the fluid dynamics of the tear film and its potential impact on the ocular surface.

Matrix metalloproteinase 9 and transglutaminase 2 expression at the ocular surface in patients with different forms of dry eye disease

OBJECTIVE

To evaluate the expression of matrix metalloproteinase 9 (MMP9) and transglutaminase 2 (TG2) in different forms of dry eye.

DESIGN

Case control study.

PARTICIPANTS

Seventy-five female subjects divided into 3 groups: group 1, 15 healthy controls; group 2, 30 subjects with Sjögren syndrome (SS); and group 3, 30 subjects with Meibomian gland dysfunction (MGD).

METHODS

A clinical assessment was carried out and impression cytologic specimens were processed for immunoperoxidase staining for MMP9 and TG2 and real-time polymerase chain reaction analyses were carried out for MMP9, TG2, interleukin-6, interferon-γ, B-cell lymphoma 2, and caspase 3. To study MMP9 and TG2 expression after anti-inflammatory treatment, patients were divided into 2 subgroups, one treated with saline and the other treated with saline plus topical corticosteroid eye drops (0.5% loteprednol etabonate) 4 times daily for 15 days. For statistical analysis, Student t test, Mann-Whitney U test, and Spearman's correlation coefficient were used as appropriate.

MAIN OUTCOME MEASURES

Conjunctival expression of MMP9 and TG2.

RESULTS

MMP9 and TG2 expression were higher in both patient groups than in controls (P < 0.0001). Group 2 patients showed higher expression than group 3 (P < 0.0001). The Spearman's correlation coefficient showed in group 2 a positive correlation between MMP9 and TG2 expression (ρ = 0.437; P = 0.01), but no correlation in group 3 (ρ = 0.143; P = 0.45). Corticosteroid treatment significantly reduced MMP9 and TG2 expression in both groups, ameliorating symptoms and signs. A much higher percentage reduction was observed in SS.

CONCLUSIONS

The pathogenic mechanisms of the 2 forms of dry eye give an account for the different MMP9 and TG2 expressions in the 2 groups of patients. The higher expression in SS is determined by the direct autoimmune insult to the ocular surface epithelia, whereas in MGD patients, with an epithelial damage due to an unbalanced tear secretion, the molecules expression is significantly lower, although higher than in controls. The corticosteroid treatment induced a reduction of both molecules, although higher in SS than in MGD, because of its direct inhibitory effect on inflammation.

Topical administration of lacritin is a novel therapy for aqueous-deficient dry eye disease

PURPOSE

Lacritin is a tear glycoprotein with prosecretory, prosurvival, and mitogenic properties. We examined lacritin levels in the tears of Sjögren's syndrome (SS) patients and explored the therapeutic potential of topical lacritin for the treatment of keratoconjunctivitis sicca.

METHODS

Tears from healthy controls (n = 14) and SS patients (n = 15) were assayed for lacritin using a C-terminal antibody. In a paired-eye study, autoimmune regulator (Aire) knockout (KO) mice (n = 7) were treated three times daily for 21 days with 10 μL of 4 μM lacritin (left eye) or vehicle (PBS) control (right eye). Tear secretion and ocular surface integrity were assessed at baseline and after treatment. Immunohistochemical staining of CD4+ T cells, cytokeratin-10 (K10), and cytokeratin-12 (K12) expression in the cornea and CD4+ T cell infiltration in the lacrimal glands were assessed.

RESULTS

Lacritin monomer (421.8 ± 65.3 ng [SS] vs. 655.8 ± 118.9 ng [controls]; P = 0.05) and C-terminal fragment protein (125 ± 34.1 ng [SS] vs. 399.5 ± 84.3 ng [controls]; P = 0.008) per 100 μL of tear eluate were significantly lower in SS patients. In Aire KO mice treated with lacritin, tear secretion increased by 46% (13.0 ± 3.5 mm vs. 8.9 ± 2.9 mm; P = 0.01) and lissamine green staining score significantly decreased relative to baseline (-0.417 ± 0.06 vs. 0.125 ± 0.07; P = 0.02). Expression of K10 but not K12 in the cornea was significantly decreased in lacritin-treated eyes. Focal CD4+ T cell infiltration of the lacrimal glands was significantly reduced on the lacritin-treated side versus the untreated side.

CONCLUSIONS

Lacritin is significantly reduced in the tears of SS patients. Topically administered lacritin has therapeutic potential for the treatment of aqueous-deficient dry eye disease.

Differential effects of hepatocyte growth factor and keratinocyte growth factor on corneal epithelial cell cycle protein expression, cell survival, and growth

PURPOSE

Hepatocyte growth factor (HGF) and keratinocyte growth factor (KGF) are secreted in the cornea in response to injury. In this study, we investigated the HGF- and KGF-mediated effect on the expression of cell cycle and apoptosis controlling proteins, cell survival, and growth in the corneal epithelium to better understand the possible role of their signaling mechanisms in repairing epithelial injuries.

METHODS

The cell survival capability of HGF and KGF in epithelial primary cultures was evaluated by using a staurosporine-induced apoptosis model. Apoptosis was quantified with image analysis following nuclear staining with Hoechst fluorescent dye and DNA laddering. Western immunoblotting was used to study the effect of growth factors on the expression of cell cycle- and apoptosis-regulating proteins.

RESULTS

HGF and KGF protected cells from apoptosis for a short duration (10 h), but only KGF exhibited cell survival capability and maintained cell growth for a longer period (24 h). The onset of apoptosis was accompanied by a significant increase in cell cycle inhibitor p27(kip). HGF and KGF suppressed p27(kip) levels in the apoptosis environment; however, KGF- but not HGF-dependent downregulation in p27(kip) expression was sustained for a longer duration. Inhibition of phosphatidylinositol 3-kinase/Akt activation blocked HGF- and KGF-mediated control of p27(kip) expression. Further, when compared to HGF, the presence of KGF produced significant downregulation of p53 and poly(adenosine diphosphate-ribose) polymerase, the key proteins involved in apoptosis and blocked the degradation of G1/S cell cycle progression checkpoint protein retinoblastoma. HGF and KGF upregulated the levels of p21(cip), cyclins A, D, and E and cyclin-dependent kinases (CDK2 and CDK4) as well, but the KGF-mediated effect on the expression of these molecules lasted longer.

CONCLUSIONS

Sustained effect of KGF on cell survival and proliferation could be attributed to its ability to inhibit p53, retinoblastoma, caspases, and p27(kip) functions in apoptosis and cell cycle arrest and promote the expression of cell cycle progressing molecules for longer duration. Designing therapeutic strategies targeting cell cycle control through KGF may be beneficial for repairing difficult-to-heal corneal epithelial injuries that require sustained growth and cell survival promoting signals.

Lacritin and the tear proteome as natural replacement therapy for dry eye

Tear proteins are potential biomarkers, drug targets, and even biotherapeutics. As a biotherapeutic, a recombinant tear protein might physiologically rescue the ocular surface when a deficiency is detected. Such a strategy pays more attention to the natural prosecretory and protective properties of the tear film and seeks to alleviate symptoms by addressing cause, rather than the current palliative, non-specific and temporary approaches. Only a handful of tear proteins appear to be selectively downregulated in dry eye, the most common eye disease. Lacritin and lipocalin-1 are two tear proteins selectively deficient in dry eye. Both proteins influence ocular surface health. Lacritin is a prosecretory mitogen that promotes basal tearing when applied topically. Levels of active monomeric lacritin are negatively regulated by tear tissue transglutaminase, whose expression is elevated in dry eye with ocular surface inflammation. Lipocalin-1 is the master lipid sponge of the ocular surface, without which residual lipids could interfere with epithelial wetting. It also is a carrier for vitamins and steroid hormones, and is a key endonuclease. Accumulation of DNA in tears is thought to be proinflammatory. Functions of these and other tear proteins may be influenced by protein-protein interactions. Here we discuss new advances in lacritin biology and provide an overview on lipocalin-1, and newly identified members of the tear proteome.

Topical biological agents targeting cytokines for the treatment of dry eye disease

Because inflammation plays a key role in the pathogenesis of dry eye disease and Sjögren’s syndrome, topical anti-inflammatory agents such as corticosteroids and cyclosporine A have been used to treat inflammation of the ocular surface and lacrimal gland. Systemic biological agents that target specific immune molecules or cells such as tumor necrosis factor (TNF)-α, interferone-α, interleukin (IL)-1, IL-6, or B cells have been used in an attempt to treat Sjögren’s syndrome. However, the efficacy of systemic biological agents, other than B-cell targeting agents, has not yet been confirmed in Sjögren’s syndrome. Several studies have recently evaluated the efficacy of topical administration of biological agents targeting cytokines in the treatment of dry eye disease. Topical blockade of IL-1 by using IL-1 receptor antagonist could ameliorate clinical signs and inflammation of experimental dry eye. Using a mouse model of desiccating stress-induced dry eye, we have demonstrated that topical application of a TNF-α blocking agent, infliximab, could improve tear production and ocular surface irregularity, decrease inflammatory cytokines and Th-1 CD4+ cells on the ocular surface, and increase goblet cell density in the conjunctiva. Although controversy still remains, the use of topical biological agents targeting inflammatory cytokines may be a promising therapy for human dry eye disease.

Spdef null mice lack conjunctival goblet cells and provide a model of dry eye

Goblet cell numbers decrease within the conjunctival epithelium in drying and cicatrizing ocular surface diseases. Factors regulating goblet cell differentiation in conjunctival epithelium are unknown. Recent data indicate that the transcription factor SAM-pointed domain epithelial-specific transcription factor (Spdef) is essential for goblet cell differentiation in tracheobronchial and gastrointestinal epithelium of mice. Using Spdef(-/-) mice, we determined that Spdef is required for conjunctival goblet cell differentiation and that Spdef(-/-) mice, which lack conjunctival goblet cells, have significantly increased corneal surface fluorescein staining and tear volume, a phenotype consistent with dry eye. Microarray analysis of conjunctival epithelium in Spdef(-/-) mice revealed down-regulation of goblet cell-specific genes (Muc5ac, Tff1, Gcnt3). Up-regulated genes included epithelial cell differentiation/keratinization genes (Sprr2h, Tgm1) and proinflammatory genes (Il1-α, Il-1β, Tnf-α), all of which are up-regulated in dry eye. Interestingly, four Wnt pathway genes were down-regulated. SPDEF expression was significantly decreased in the conjunctival epithelium of Sjögren syndrome patients with dry eye and decreased goblet cell mucin expression. These data demonstrate that Spdef is required for conjunctival goblet cell differentiation and down-regulation of SPDEF may play a role in human dry eye with goblet cell loss. Spdef(-/-) mice have an ocular surface phenotype similar to that in moderate dry eye, providing a new, more convenient model for the disease.

Quantitative analysis of tear film fluorescence and discomfort during tear film instability and thinning

PURPOSE

The purpose of this study was to test the association between tear film fluorescence changes during tear break-up (TBU) or thinning and the concurrent ocular sensory response.

METHODS

Sixteen subjects kept one eye open as long as possible (MBI), indicated their discomfort level continuously, and rated ocular sensations of irritation, stinging, burning, pricking, and cooling using visual analog scales (VAS). Fluorescence of the tear film was quantified by a pixel-based analysis of the median pixel intensity (PI), TBU, and percentage of dark pixels (DarkPix) over time. A cutoff of 5% TBU was used to divide subjects into either break-up (BU) or minimal break-up (BUmin) groups.

RESULTS

Tear film fluorescence decreased (median PI) and the percentage of TBU and DarkPix increased in all trials, with the rate significantly greater in the BU than the BUmin group (Mann-Whitney U test, P < 0.05). The rate of increasing discomfort during trials was highly correlated with the rate of decrease in median PI and developing TBU (Spearman's, r ≥ 0.70). Significant correlations were found between corneal fluorescence, MBI, and sensory measures.

CONCLUSIONS

Concentration quenching of fluorescein dye with tear film thinning best explains decreasing tear film fluorescence during trials. This was highly correlated with increasing ocular discomfort, suggesting that both tear film thinning and TBU stimulate underlying corneal nerves, although TBU produced more rapid stimulation. Slow increases in tear film hyperosmolarity may cause the gradual increase in discomfort during slow tear film thinning, whereas the sharp increases in discomfort during TBU suggest a more complex stimulus.

Tissue transglutaminase is a negative regulator of monomeric lacritin bioactivity

PURPOSE

Molar accounting of bioactive fluids can expose new regulatory mechanisms in the growing proteomic focus on epithelial biology. Essential for the viability of the surface epithelium of the eye and for normal vision is the thin, but protein-rich, tear film in which the small tear glycoprotein lacritin appears to play a prominent prosecretory, cytoprotective, and mitogenic role. Although optimal bioactive levels in cell culture are 1 to 10 nM over a biphasic dose optimum, ELISA suggests a sustained tear lacritin concentration in the midmicromolar range in healthy adults. Here we identify a reconciling mechanism.

METHODS

Monoclonal anti-lacritin 1F5 antibody was generated, and applied together with a new anti-C-terminal polyclonal antibody to tear and tissue Western blotting. In vitro tissue transglutaminase (Tgm2) cross-linking was monitored and characterized by mass spectrometry.

RESULTS

Blotting for lacritin in human tears or saliva surprisingly detected immunoreactive material with a higher molecular weight and prominence equal or exceeding the ∼23 to 25 kDa band of monomeric glycosylated lacritin. Exogenous Tgm2 initiated lacritin cross-linking within 1 minute and was complete by 90 minutes-even with as little as 0.1 nM lacritin, and involved the donors lysine 82 and 85 and the acceptor glutamine 106 in the syndecan-1 binding domain. Lacritin spiked into lacritin-depleted tears formed multimers, in keeping with ∼0.6 μM TGM2 in tears. Cross-linking was absent when Tgm2 was inactive, and cross-linked lacritin, unlike recombinant monomer, bound syndecan-1 poorly.

CONCLUSIONS

Since syndecan-1 binding is necessary for lacritin mitogenic and cytoprotective activities, TGM2 cross-linking negatively regulates lacritin bioactivity.

Tear proteome and protein network analyses reveal a novel pentamarker panel for tear film characterization in dry eye and meibomian gland dysfunction

Dry eye and meibomian gland dysfunction are common ocular surface disorders. Discrimination of both conditions often may be difficult given the overlapping of signs and symptoms, and the lack of correlation with clinical parameters. A total of 144 individuals were included in this study. To search for proteome differences, tear proteins were collected by Merocel sponge and analyzed using 2D-PAGE. Comparative tear protein profile analysis indicated changes in the expression levels of fifteen proteins. Subsequent to MALDI-TOF/TOF protein identification, network analysis revealed expression/interaction connections with other proteins, thereby identifying additional putative markers. A screening validation assay demonstrated the discriminative power of six candidate biomarkers. A further validation study using multiplexed-like ELISA assays in tear samples collected with both sponge and capillary confirmed the high discriminatory power of five biomarkers: S100A6, annexin A1 (ANXA1), annexin A11 (ANXA11), cystatin-S (CST4), and phospholipase A2-activating protein (PLAA) with an area under ROC curve (AUC)≥ 97.9% (sensitivity ≥ 94.3%; specificity ≥ 97.6%) when comparing dry eye and control individuals. This panel also discriminated between dry eye, meibomian gland dysfunction and control individuals, with a global correct assignment (CA) of 73.2% between all groups. Correct assignment was not found to be significantly dependent on the tear collection method.

17-β-estradiol inhibits hyperosmolarity-induced proinflammatory cytokine elevation via the p38 MAPK pathway in human corneal epithelial cells

PURPOSE

To evaluate the effects of 17-β-estradiol on hyperosmolar stress-induced proinflammatory cytokine production of interleukin (IL)-6, IL-1, and tumor necrosis factor-alpha (TNF-α) in SV40-immortalized human corneal epithelial cells (hCECs) and the regulatory effects of the mitogen-activated protein kinase (MAPK) signaling pathways in this process.

METHODS

SV40 hCECs cultured in normal osmolar media were switched to a higher osmolarity (450 mOsM) by adding NaCl with or without pretreatment with 17-β-estradiol. Real-time polymerase chain reaction and ELISA were applied to characterize IL-6, IL-1, and TNF-α gene and protein expression. Cells were treated for 15-60 min, lysed in radioimmunoprecipitation assay (RIPA) buffer and subjected to a western blot with phospho (p)-specific antibodies against extracellular signal-regulated protein kinase 1/2 (ERK1/2), P38 kinase, and c-Jun N-terminal kinase 1/2 (JNK1/2).

RESULTS

The expression and production of IL-6, IL-1, and TNF-α in SV40 hCECs increased when the media osmolarity was switched to 450 mOsM. Pretreatment with 10(-10) M 17-β-estradiol greatly inhibited the increased expression and production of IL-6, IL-1, and TNF-α induced by hyperosmolarity, whereas with the administration of SB203580 (10 μM), an inhibitor of the p38 pathway, the inhibiting effect of 17-β-estradiol disappeared. The western blot results showed that the increased phosphorylation level of p38 caused by hyperosmolarity was greatly inhibited by 17-β-estradiol.

CONCLUSIONS

17-β-estradiol greatly inhibited the expression and production of proinflammatory cytokines IL-6, IL-1, and TNF-α, which were stimulated by hyperosmolarity in SV40-immortalized hCECs. The results also suggested that the p38 MAPK signaling pathway was involved in the regulatory effects of estrogen on hCECs. These findings may contribute to an understanding of the etiologic roles and therapeutic implications of the hormone estrogen in dry eye disease.