Decreased PPAR-γ expression in the conjunctiva and increased expression of TNF-α and IL-1β in the conjunctiva and tear fluid of dry eye mice

Effect of low dose honey on the apoptosis and inflammation gene expression in corneal limbal stem cells and keratocytes and its efficacy as an ophthalmic formulation in the treatment of dry eye: in-vitro and clinical study

Background

The use of honey as an eye treatment encounters challenges due to its high osmolarity, low pH, and difficulties in sterilization. This study addresses these issues by employing a low concentration of honey, focusing on both in-vitro experiments and clinical trials for treating dry eye disease in corneal cells.

Methods

In the in-vitro experiment, we investigated the impact of a 1% honey-supplemented medium (HSM) on limbal stem cells (LSCs) and keratocytes using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and real-time polymerase chain reaction (PCR) for BCL-2, BAX, and IL-1β gene expression. Simultaneously, in the clinical trial, 80 participants were divided into two groups, receiving either a 1% w/v honey ophthalmic formulation or a placebo for 3 months. Study outcomes included subjective improvement in dry eye symptoms, tear break-up time (TBUT), and Schirmer's test results.

Results

MTT results indicated that 1% HSM did not compromise the survival of corneal cells and significantly reduced the expression of the IL-1β gene. Additionally, participants in the honey group demonstrated a higher rate of improvement in dry eye symptoms and a significant enhancement in TBUT values at the three-month follow-up. However, there was no significant difference between the study groups in terms of Schirmer's test values. No adverse events were observed or reported.

Conclusion

In conclusion, 1% honey exhibits anti-inflammatory and anti-infective properties, proving effective in ameliorating dry eye symptoms and enhancing tear film stability in patients with dry eye disease.Clinical Trial Registration: https://irct.behdasht.gov.ir/trial/63800.

IL-1β induced down-regulation of miR-146a-5p promoted pyroptosis and apoptosis of corneal epithelial cell in dry eye disease through targeting STAT3

AIM

To elaborate the underlying mechanisms by which IL-1β promote progression of Dry eye disease(DED) through effect on pyroptosis and apoptosis of corneal epithelial cells(CECs).

METHODS

400 mOsM solutions were used to establish the DED model (hCECs- DED). RT-qPCR was performed to measure IL-1β mRNA and miR-146a-5p in CECs. Western blotting was performed to measure STAT3, GSDMD, NLRP3, and Caspase-1 levels. Cell counting kit-8 assay was adopted to check cell viability. Apoptosis was detected by flow cytometry. ELISAs were performed to determine IL-18, IL-33 and LDH. The luciferase test detects targeting relationships.

RESULTS

After treatment with 400 mOsM solution, cell viability decreased and apoptosis increased. Compared with hCECs, IL-1β was increased and miR-146a-5p was decreased in hCECs-DED. At the same time, GSDMD, NLRP3, Caspase-1, IL-18, IL-33 and LDH were significantly higher in hCECs-DED than in hCECs, while IL-1β silencing reversed this effect. In addition, IL-1β negatively regulated miR-146a-5p. MiR-146a-5p mimics eliminated the inhibition of hCECs-DED pyroptosis and apoptosis caused by IL-1β silencing. At the same time, miR-146a-5p reduced STAT3 levels in hCECs.

CONCLUSION

Highly expressed IL-1β promoted pyroptosis and apoptosis of hCECs- DED through downregulated miR-146a-5p and inhibited STAT3.

An enhanced model for environmental dry eye: Exploring pathological features and underlying factors

This study aimed to develop an enhanced environmental dry eye (EDE) model that accurately reproduces the etiology of prolonged visual fatigue and investigates the underlying pathological features. A total of 40 adult SPF-grade Wistar rats were randomly assigned to control (n = 20) and model (n = 20) groups. Rats in the control group were maintained under normal conditions, while rats in the model group were exposed to a controlled frontal airflow of 2-4 m/s from a fan for 7.5 h daily while placed on a suspended cylindrical wire mesh frame. Various assessments were performed at different time points during the 14-day experiment, including blink frequency, tear secretion (phenol red thread test), tear film breakup time (BUT), fluorescein staining (FL), corneal epithelial status (light microscopy), ultrastructure of corneal epithelial cells (electron microscopy), and expression levels of inflammatory cytokines (IL-1β, TNF-α) in tears (enzyme-linked immunosorbent assay). Additionally, mRNA and protein expression levels of MMP-9, IL1β, IL6, TNF-α, IFN-γ, and caspase-3 in corneal tissues were quantified (real-time quantitative PCR and Western blotting). Compared to the control group, the model group rats exhibited significant decreases in blink frequency (P < 0.001), tear secretion (Schirmer I test) values (P < 0.001), and tear film breakup time levels (P < 0.001). There was also a significant increase in fluorescein staining scores (P < 0.001) in the model group. Histological examination revealed distinct differences of the corneal epithelium between groups. The corneal epithelium of the model group appeared thicker, with disorganized cell arrangement in the superficial and basal layers, partial defects or detachment of superficial epithelial cells, and a rough, uneven surface. Scanning electron microscopy observations showed a rough corneal epithelial surface with numerous cracks and scattered vesicular-like structures in the model group. Furthermore, the model group rats exhibited a significant increase in expression of IL-1β and TNF-α in tears (P < 0.001), and upregulated expression levels of MMP-9, TNF-α, IL-1β, caspase-3, IL-6, and IFN-γ at both the mRNA and protein levels in corneal tissues (P < 0.001). In conclusion, the modified "wire-meshing cylindrical board" model effectively overcomes the limitations of the traditional "jogging board " dry eye model and successfully simulates the etiology of prolonged visual fatigue. This innovative EDE model demonstrates a high degree of relevance to dry eye conditions resulting from prolonged visual tasks, with a high success rate of model induction. Moreover, it proves to be a simple, practical, and easily replicable model, making it highly suitable for further studies on prolonged visual fatigue and facilitating its widespread adoption in research and clinical applications.

KCNK5 Regulating Potassium Efflux and Inducing Pyroptosis in Corneal Epithelial Cells Through TNFSF10-Mediated Autophagy in Dry Eye

Purpose

The purpose of this study was to elucidate the involvement of potassium two pore domain channel subfamily K member 5 (KCNK5)-mediated potassium efflux in the pathogenesis of dry eye and to unravel the underlying molecular mechanisms.

Methods

To induce experimental dry eye in adult wild-type C57BL/6 mice, scopolamine was administered via subcutaneous injection, and the mice were subjected to desiccating stress. To create an in vitro model of dry eye, desiccation stress was applied to the human corneal epithelial cell line (HCE-T). Intracellular potassium concentration was quantified using inductively coupled plasma mass spectrometry. Cellular death was assessed through lactate dehydrogenase assays. Gene expression profiling was conducted through both RNA sequencing and quantitative real-time PCR. Protein analysis was carried out through Western blotting and immunofluorescence staining. Assessment of the corneal epithelial defect area was conducted through fluorescein sodium staining. Tear secretion was quantified using the phenol red cotton thread method.

Results

Potassium efflux was observed to further facilitate corneal epithelial pyroptosis. KCNK5 exhibited upregulation in both in vivo and in vitro models of dry eye. The overexpression of KCNK5 was observed to induce potassium efflux and activate the NLR family pyrin domain containing 3 (NLRP3) inflammasome-mediated pyroptosis in vitro. Silencing KCNK5 effectively mitigated pyroptosis in dry eye. Additionally, the overexpression of KCNK5 results in the downregulation of TNF superfamily member 10 (TNFSF10) and subsequent impairment of autophagy. TNFSF10 supplementation could promote autophagy and mitigate pyroptosis in dry eye.

Conclusions

The upregulation of KCNK5 mediates TNFSF10 to impair autophagy and induce pyroptosis in dry eye. Consequently, targeting KCNK5 may represent a novel and promising approach to therapeutic intervention in the management of dry eye.

The role of sphingolipids in meibomian gland dysfunction and ocular surface inflammation

Inflammation occurs in response to tissue injury and invasion of microorganisms and is carried out by the innate and adaptive immune systems, which are regulated by numerous chemokines, cytokines, and lipid mediators. There are four major families of bioactive lipid mediators that play an integral role in inflammation - eicosanoids, sphingolipids (SPL), specialized pro-resolving mediators (SPM), and endocannabinoids. SPL have been historically recognized as important structural components of cellular membranes; their roles as bioactive lipids and inflammatory mediators are recent additions. Major SPL metabolites, including sphingomyelin, ceramide, ceramide 1-phosphate (C1P), sphingosine, sphingosine 1-phosphate (S1P), and their respective enzymes have been studied extensively, primarily in cell-culture and animal models, for their roles in cellular signaling and regulating inflammation and apoptosis. Less focus has been given to the involvement of SPL in eye diseases. As such, the aim of this review was to examine relationships between the SPL family and ocular surface diseases, focusing on their role in disease pathophysiology and discussing the potential of therapeutics that disrupt SPL pathways.

The Extracts of Dendrobium Alleviate Dry Eye Disease in Rat Model by Regulating Aquaporin Expression and MAPKs/NF-κB Signalling

Dry eye is one of the most common ocular surface diseases caused by tear film instability and ocular surface damage due to an abnormal quality or quantity of tears. Inflammatory factors can initiate relevant transduction signalling pathways and trigger the inflammatory cascade response, resulting in ocular surface inflammation. It has been shown that the active ingredients in Dendrobium, such as polysaccharides, alkaloids and phenols, have anti-inflammatory, anti-tumour and immunity-boosting effects, and Dendrobium officinale extract can improve glandular secretion function, increase salivary secretion and increase the expression level of water channel protein in salivary glands in patients with dry eye syndromes. We investigated the in vitro cytoprotective effect of Dendrobium extracts in sodium chloride induced hyperosmotic conditions in human cornea keratocytes (HKs). Results showed that Dendrobium officinale Kimura et Migo water extract (DOW) and Dendrobium loddigesii Rolfe water extract (DLW) could upregulate the expression of aquaporins (AQP)5 protein, thus exerting a repairing effect by promoting cell migration. Furthermore, oral administration of DOW and DLW enhanced tear production in rats and exerted a protective effect on ocular surface damage. DOW and DLW could upregulate the expression of AQP5 and mucin (muc)5ac proteins in the lacrimal gland and reduce the inflammatory response. DOW and DLW inhibited the activation of the corresponding mitogen-activated protein kinases (MAPK) and NF-KB pathway, thereby playing a role in improving dry eye symptoms. This study provides a new perspective on dry eye treatment, and DOW and DLW may be potential therapeutic agents for dry eye.

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.

Animal models of dry eye disease: Useful, varied and evolving (Review)

Dry eye disease (DED), which is a prevalent disease that still lacks successful treatment options, remains a major challenge in ophthalmology. Multiple animal models of DED have been used to decipher its pathophysiology and to develop novel treatments. These models use mice, rats, rabbits, cats, dogs and non-human primates. Each model assesses aspects of DED by focusing on elements of the lacrimal functional unit, which controls the homeostasis of the tear film. The present review outlines representative DED animal models and assesses their contribution to the study of DED. Murine models are the most extensively used, followed by rabbit models; the latter offer the advantage of larger eyes, a favorable biochemical profile for drug studies, experimental ease and relatively low cost, contrasting with non-human primates, which, although closer to humans, are not as accessible and are expensive. No comprehensive ‘ideal’ animal model encompassing all aspects of human DED exists nor is it feasible. Investigators often choose an animal model based on their experimental needs and the following four features of a given model: The size of the eye, its biochemical composition, the available research reagents and cost. As research efforts in DED expand, more refined animal models are needed to supplement the enormous contribution made to date by existing models.

The role of peroxisome proliferator-activated receptors in healthy and diseased eyes

Peroxisome Proliferator-Activated Receptors (PPARs) are a family of nuclear receptors that play essential roles in modulating cell differentiation, inflammation, and metabolism. Three subtypes of PPARs are known: PPAR-alpha (PPARα), PPAR-gamma (PPARγ), and PPAR-beta/delta (PPARβ/δ). PPARα activation reduces lipid levels and regulates energy homeostasis, activation of PPARγ results in regulation of adipogenesis, and PPARβ/δ activation increases fatty acid metabolism and lipolysis. PPARs are linked to various diseases, including but not limited to diabetes, non-alcoholic fatty liver disease, glaucoma and atherosclerosis. In the past decade, numerous studies have assessed the functional properties of PPARs in the eye and key PPAR mechanisms have been discovered, particularly regarding the retina and cornea. PPARγ and PPARα are well established in their functions in ocular homeostasis regarding neuroprotection, neovascularization, and inflammation, whereas PPARβ/δ isoform function remains understudied. Naturally, studies on PPAR agonists and antagonists, associated with ocular pathology, have also gained traction with the development of PPAR synthetic ligands. Studies on PPARs has significantly influenced novel therapeutics for diabetic eye disease, ocular neuropathy, dry eye, and age-related macular degeneration (AMD). In this review, therapeutic potentials and implications will be highlighted, as well as reported adverse effects. Further investigations are necessary before any of the PPARs ligands can be utilized, in the clinics, to treat eye diseases. Future research on the prominent role of PPARs will help unravel the complex mechanisms involved in order to prevent and treat ocular diseases.

Dexamethasone-Loaded Nanostructured Lipid Carriers for the Treatment of Dry Eye Disease

Dry eye disease (DED) or keratoconjunctivitis sicca is a chronic multifactorial disorder of the ocular surface caused by tear film dysfunction. Symptoms include dryness, irritation, discomfort and visual disturbance, and standard treatment includes the use of lubricants and topical steroids. Secondary inflammation plays a prominent role in the development and propagation of this debilitating condition. To address this we have investigated the pilot scale development of an innovative drug delivery system using a dexamethasone-encapsulated cholesterol-Labrafac™ lipophile nanostructured lipid carrier (NLC)-based ophthalmic formulation, which could be developed as an eye drop to treat DED and any associated acute exacerbations. After rapid screening of a range of laboratory scale pre-formulations, the chosen formulation was prepared at pilot scale with a particle size of 19.51 ± 0.5 nm, an encapsulation efficiency of 99.6 ± 0.5%, a PDI of 0.08, and an extended stability of 6 months at 4 °C. This potential ophthalmic formulation was observed to have high tolerability and internalization capacity for human corneal epithelial cells, with similar behavior demonstrated on ex vivo porcine cornea studies, suggesting suitable distribution on the ocular surface. Further, ELISA was used to study the impact of the pilot scale formulation on a range of inflammatory biomarkers. The most successful dexamethasone-loaded NLC showed a 5-fold reduction of TNF-α production over dexamethasone solution alone, with comparable results for MMP-9 and IL-6. The ease of formulation, scalability, performance and biomarker assays suggest that this NLC formulation could be a viable option for the topical treatment of DED.

Chemokines Up-Regulated in Epithelial Cells Control Senescence-Associated T Cell Accumulation in Salivary Glands of Aged and Sjögren's Syndrome Model Mice

Immunosenescence is characterized by age-associated changes in immunological functions. Although age- and autoimmune-related sialadenitis cause dry mouth (xerostomia), the roles of immunosenescence and cellular senescence in the pathogenesis of sialadenitis remain unknown. We demonstrated that acquired immune cells rather than innate immune cells infiltrated the salivary glands (SG) of aged mice. An analysis of isolated epithelial cells from SG revealed that the expression levels of the chemokine CXCL13 were elevated in aged mice. Senescence-associated T cells (SA-Ts), which secrete large amounts of atypical pro-inflammatory cytokines, are involved in the pathogenesis of metabolic disorders and autoimmune diseases. The present results showed that SA-Ts and B cells, which express the CXCL13 receptor CXCR5, accumulated in the SG of aged mice, particularly females. CD4⁺ T cells derived from aged mice exhibited stronger in vitro migratory activity toward CXCL13 than those from young mice. In a mouse model of Sjögren’s syndrome (SS), SA-Ts also accumulated in SG, presumably via CXCL12-CXCR4 signaling. Collectively, the present results indicate that SA-Ts accumulate in SG, contribute to the pathogenesis of age- and SS-related sialadenitis by up-regulating chemokines in epithelial cells, and have potential as therapeutic targets for the treatment of xerostomia caused by these types of sialadenitis.

CannabinEYEds: The Endocannabinoid System as a Regulator of the Ocular Surface Nociception, Inflammatory Response, Neovascularization and Wound Healing

The endocannabinoid system (ECS) is a complex regulatory system, highly conserved among vertebrates. It has been widely described in nearly all human tissues. In the conjunctiva and cornea, the ECS is believed to play a pivotal role in the modulation of the local inflammatory state as well as in the regulation of tissue repair and fibrosis, neo-angiogenesis and pain perception. This review aims to summarize all the available data on ECS expression and its function in ocular surface structures to provide a specific insight concerning its modulation in dry eye disease, and to propose directions for future research.

In Vivo Anti-Inflammation Potential of Aster koraiensis Extract for Dry Eye Syndrome by the Protection of Ocular Surface

Dry eye syndrome (DES) is a corneal disease often characterized by an irritating, itching feeling in the eyes and light sensitivity. Inflammation and endoplasmic reticulum (ER) stress may play a crucial role in the pathogenesis of DES, although the underlying mechanism remains elusive. Aster koraiensis has been used traditionally as an edible herb in Korea. It has been reported to have wound-healing and inhibitory effects against insulin resistance and inflammation. Here, we examined the inhibitory effects of inflammation and ER stress by A. koraiensis extract (AKE) in animal model and human retinal pigmented epithelial (ARPE-19) cells. Oral administration of AKE mitigated DE symptoms, including reduced corneal epithelial thickness, increased the gap between lacrimal gland tissues in experimental animals and decreased tear production. It also inhibited inflammatory responses in the corneal epithelium and lacrimal gland. Consequently, the activation of NF-κB was attenuated by the suppression of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Moreover, AKE treatment ameliorated TNF-α-inducible ocular inflammation and thapsigargin (Tg)-inducible ER stress in animal model and human retinal pigmented epithelial (ARPE-19) cells. These results prove that AKE prevents detrimental functional and histological remodeling on the ocular surface and in the lacrimal gland through inhibition of inflammation and ER stress, suggesting its potential as functional food material for improvement of DES.

Cluster Analysis of Dry Eye Disease Models Based on Immune Cell Parameters - New Insight Into Therapeutic Perspective

Dry eye disease (DED) can be represented as a display of disease in the mucosal part of the eye. It is quite distinct from the retinal side of the eye which connects with the neurons and thus represents the neuroimmunological disease. DED can occur either by the internal damage of the T cells inside the body or by microbial infections. Here we summarize the most common animal model systems used for DED relating to immune factors. We aimed to identify the most important immune cell/cytokine among the animal models of the disease. We also show the essential immune factors which are being tested for DED treatment. In our results, both the mechanism and the treatment of its animal models indicate the involvement of Th1 cells and the pro-inflammatory cytokine (IL-1β and TNF-α) related to the Th1-cells. The study is intended to increase the knowledge of the animal models in the field of the ocular surface along with the opening of a dimension of thoughts while designing a new animal model or treatment paradigm for ocular surface inflammatory disorders.

PPAR-α Agonist Fenofibrate Suppressed the Formation of Ocular Surface Squamous Metaplasia Induced by Topical Benzalkonium Chloride

Purpose

To investigate the effects and mechanisms of the peroxisome proliferator-activated receptor alpha (PPAR-α) agonist fenofibrate on the formation of ocular surface squamous metaplasia induced by topical benzalkonium chloride (BAC) in a mouse model.

Methods

Ocular surface squamous metaplasia was induced in 16 days by topical BAC application in mice. During the period of induction, mice were divided into four groups: no additional treatment (BAC+UT), topical vehicle (BAC+Vehicle), topical fenofibrate (BAC+Feno), or topical fenofibrate plus intraperitoneal injection of MK886 (BAC+Feno+MK886). The parameters of tear film were evaluated on day 16, and eye specimens were collected. Histologic investigation; PAS assays; immunostaining for cytokeratin 10 (K10), Ki67, and F4/80; and PCR assays for TNF-α and IL-6 were performed. Cell Counting Kit 8 (CCK-8) assays were performed to evaluate the inhibitory effects of fenofibrate on RAW264.7 cells.

Results

Fenofibrate suppressed the formation of BAC-induced instable tear film. In the BAC+Feno group, the expression of K10 and Ki67 was lower than in the other three groups. The number of goblet cells was reduced in eyes of the BAC+UT and BAC+Vehicle groups but was maintained in eyes of the BAC+Feno group. The number of F4/80-positive cells and the levels of TNF-α and IL-6 mRNA were significantly reduced in the cornea of the BAC+Feno group. These effects of fenofibrate could be attenuated by MK886. The cell viability of RAW264.7 cells could be significantly inhibited by fenofibrate in a dose-dependent pattern.

Conclusions

Topical application of fenofibrate suppressed the formation of ocular surface squamous metaplasia, which might be mediated through the PPAR-α signaling pathway.

PPARγ: the dominant regulator among PPARs in dry eye lacrimal gland and diabetic lacrimal gland

AIM

To investigate the regulatory roles of the members of the peroxisome proliferator-activated receptor (PPAR) family in lacrimal gland dysfunction under conditions of desiccating stress or diabetes.

METHODS

Quantitative polymerase chain reaction (qPCR) was used to examine the expression of PPARs in the cornea, conjunctiva, meibomian gland, and lacrimal gland in adult rats. The rats were divided into 3 groups: a control group, dry eye group, and diabetic group. The phenol red threads test, tear film break-up time (BUT) test and fluorescein staining were carried out to evaluate the development of dry eye. Based on bioinformatics research, qPCR was used to examine the expression level of PPARγ, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), sirtuin 1 (Sirt1), myeloid differentiation factor 88 (MyD88) and transforming growth factor-β (TGF-β) in the lacrimal glands.

RESULTS

PPARα and PPARβ/δ were mainly expressed in the conjunctiva and the lacrimal gland, respectively. However, PPARγ was expressed in both the conjunctiva and lacrimal gland, at much higher levels than those measured for PPARα and PPARβ/δ. Dry eye rats and diabetic rats both showed decreased tear secretion, shortened BUT, and increased corneal staining. Significant changes in gene expression were observed compared with the control group. In the lacrimal glands of dry eye rats and diabetic rats, expression of PPARγ decreased (P<0.05), expression of Sirt1 also decreased (P<0.01), whereas expression of TNF-α, IL-1β, IL-6, MyD88, and TGF-β increased (P<0.05).

CONCLUSION

Among PPARs, PPARγ might play a dominant role in the regulation of metabolic- and inflammatory-signaling pathways on the ocular surfaces and in lacrimal glands. Down-regulation of PPARγ is highly relevant to lacrimal gland dysfunction under desiccating-stress and diabetic conditions. PPARγ, thus, is a potential therapeutic target in the treatment of environment- or diabetes-induced dry eye diseases.

Immune - Goblet cell interaction in the conjunctiva

The conjunctiva is a goblet cell rich mucosal tissue. Goblet cells are supported by tear growth factors and IL-13 produced by resident immune cells. Goblet cell secretions are essential for maintaining tear stability and ocular surface homeostasis. In addition to producing tear stabilizing mucins, they also produce cytokines and retinoic acid that condition monocyte-derived phagocytic cells in the conjunctiva. Aqueous tear deficiency from lacrimal gland disease and systemic inflammatory conditions results in goblet cell loss that amplifies dry eye severity. Reduced goblet cell density is correlated with more severe conjunctival disease, increased IFN-γ expression and antigen presenting cell maturation. Sterile Alpha Motif (SAM) pointed domain epithelial specific transcription factor (Spdef) gene deficient mice that lack goblet cells have increased infiltration of monocytes and dendritic cells with greater IL-12 expression in the conjunctiva. Similar findings were observed in the conjunctiva of aged mice. Reduced retinoic acid receptor (RXRα) signaling also increases conjunctival monocyte infiltration, IFN-γ expression and goblet cell loss. Evidence suggests that dry eye therapies that suppress IFN-γ expression preserve conjunctival goblet cell number and function and should be considered in aqueous deficiency.

Involvement of adiponectin in age-related increases in tear production in mice

Common age-related changes in the human eye contribute to the development of dry eye, including decreases in aqueous tear production. Although the infiltration of lymphocytes into the lacrimal glands occurs with age, age-related increases in tear production have also been observed in mice; however, the mechanisms underlying this increase remain unclear. We herein demonstrated that increases in tear production were not dependent on body weight gain or systemic conditions, such as insulin resistance, using aged mice and high-fat diet-fed mice. The results obtained also showed that senescence-associated T (SA-T) cells accumulated in the lacrimal glands of aged mice, particularly females. Expression levels of the nuclear transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) in whole lacrimal glands and epithelial cells isolated from lacrimal glands were significantly higher in aged mice than in young mice. The expression levels of adiponectin and one of its receptors, AdipoR2, also increased in the lacrimal glands of aged mice, but not in those of high-fat diet-fed mice. Collectively, the present results indicate that PPARγ and adiponectin-mediated signaling contribute to age-related increases in tear production in mice and have potential as therapeutic targets for the treatment of dry eye in humans.

High-Mobility Group Box 1 in Dry Eye Inflammation

Purpose

To determine high-mobility group box 1 (HMGB1) expression during experimental dry eye (EDE) and dry eye-like culture conditions and elucidate its role in corneal dry eye-related inflammation.

Methods

EDE was induced in 8- to 12-week-old C57BL/6 mice. Corneal tissue sections and lysates from EDE and untreated mice were evaluated for HMGB1 expression by immunostaining and quantitative real-time PCR (qPCR). For in vitro studies, human corneal epithelial cells (HCEC) were treated with hyperosmolar media, toll-like receptor (TLR) agonists, or proinflammatory cytokines to determine HMGB1 expression. HCEC were also treated with human recombinant HMGB1 (hrHMGB1) alone or in combination with inflammatory stimuli, and TNFα, IL-6, and IL-8 expression evaluated by qPCR and ELISA. Nuclear factor-κB (NF-κB) p65 nuclear translocation was determined by immunostaining.

Results

EDE mice had higher corneal HMGB1 RNA and protein expression compared to untreated animals. In HCEC, hyperosmolar stress and TNFα treatment stimulated HMGB1 production and secretion into culture supernatants. However, in vitro stimulation with hrHMGB1 did not induce secretion of TNFα, IL-6, or IL-8 or NF-κB p65 nuclear translocation. In addition, the inflammatory response elicited by TLR agonists fibroblast-stimulating lipopeptide-1 and lipopolysaccharide was not enhanced by hrHMGB1 treatment.

Conclusions

HMGB1 expression was enhanced by dry eye conditions in vivo as well as in vitro, during hyperosmolar stress and cytokine exposure, suggesting an important role for HMGB1 in dry eye disease. However, no direct inflammatory effect was observed with HMGB1 treatment. Therefore, under these conditions, HMGB1 does not contribute directly to dry eye-induced inflammation and its function at the ocular surface needs to be explored further.

TFOS DEWS II pathophysiology report

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

The Effect of TNF-α Blocker HL036337 and Its Best Concentration to Inhibit Dry Eye Inflammation

Purpose

Dry eye syndrome is commonly thought of as an inflammatory disease, and we have previously presented data showing the effectiveness of topical TNF-α blocker agents for the treatment of this condition. The purpose of this study was to investigate the effectiveness of the TNF-α blocking agent HL036337 compared to cyclosporine A for the treatment of dry eye induced inflammation in order to establish whether HL036337 represents a more effective method for suppressing inflammation. The efficacy of HL036337 and cyclosporine A was determined using an experimental murine dry eye model.

Methods

The TNF-α blocker HL036337 is a modified form of TNF receptor I. Using dry eye induced C57BL/6 mice (n = 45), corneal erosion was measured at day 4 and 7 after topical treatment with cyclosporine A or HL036337. To determine the effective treatment dose, 0.25, 0.5, 1, 2.5, and 5 mg/mL of HL036337 were topically administered twice per day to dry eye induced murine corneas for 1 week.

Results

The optimal concentration of the TNF-α blocker HL036337 for treatment of dry eye induced corneal erosion was determined to be 1 mg/mL. Dry eye induced corneal erosion was improved after 1 week with topically applied cyclosporine A and HL036337 at 1 mg/mL.

Conclusions

HL036337 administered topically at 1 mg/mL effectively improved corneal erosion induced by dry eye. This finding may also suggest that inhibition of TNF-α can improve dry eye syndrome.

Effects of carvedilol reduce conjunctivitis through changes in inflammation, NGF and VEGF levels in a rat model

Carvedilol is a novel third generation β-blocker that acts as an antagonist of β and α adrenergic receptors, and is able to regulate various cell factors. In addition, it possesses antioxidant activity, is capable of reversing cardiac remodeling effects and has anti-arrhythmic effects. The present study aimed to investigate whether the effects of carvedilol were able to reduce conjunctivitis clinical scores. Initially, 24 Sprague Dawley (SD) rats were randomly divided into three equal groups as follows: Control group, model group and carvedilol group. The model and carvedilol group adult SD rats were injected with lipopolysaccharide (LPS) to induce conjunctivitis. In the carvedilol group, the eight SD rats with LPS-induced conjunctivitis also received 50 mg/kg/day of carvedilol for 4 weeks. Next, the effects carvedilol were assessed utilizing a system of clinical sign scores, and an enzyme-linked immunosorbent assay was used to determine the expression levels of interleukin-1β (IL-1β), IL-6, IL-8 and tumor necrosis factor-α (TNF-α). Finally, nuclear factor-κB (NF-κB), nerve growth factor (NGF) and vascular endothelial growth factor (VEGF) were analyzed by western blotting. Carvedilol was observed to significantly reduce clinical sign scores in a dose-dependent manner (P<0.01), and reduce IL-1β, IL-6, IL-8 and TNF-α expression levels (P<0.01) in the LPS-induced rat model of conjunctivitis. Carvedilol was also able to significantly reduce the protein expression levels of NF-κB, and induce the protein expression levels of NGF and VEGF in the LPS-induced rat model of conjunctivitis (P<0.01). In conclusion, the effects of carvedilol may reduce conjunctivitis clinical scores through inflammation, NGF and VEGF in LPS-induced rat models.

Role of Peroxisome Proliferator-Activated Receptor γ in Ocular Diseases

Peroxisome proliferator-activated receptor γ (PPAR γ), a member of the nuclear receptor superfamily, is a ligand-activated transcription factor that plays an important role in the control of a variety of physiological processes. The last decade has witnessed an increasing interest for the role played by the agonists of PPAR γ in antiangiogenesis, antifibrosis, anti-inflammation effects and in controlling oxidative stress response in various organs. As the pathologic mechanisms of major blinding diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), keratitis, and optic neuropathy, often involve neoangiogenesis and inflammation- and oxidative stress-mediated cell death, evidences are accumulating on the potential benefits of PPAR γ to improve or prevent these vision threatening eye diseases. In this paper we describe what is known about the role of PPAR γ in the ocular pathophysiological processes and PPAR γ agonists as novel adjuvants in the treatment of eye diseases.