High-fat diet induces dry eye-like ocular surface damages in murine

Pioglitazone alleviates lacrimal gland impairments induced by high-fat diet through suppressing M1 polarization

A high-fat diet (HFD) contributes to the pathogenesis of various inflammatory and metabolic diseases. Previous research confirms that under HFD conditions, the extraorbital lacrimal glands (ELGs) can be impaired, with significant infiltration of pro-inflammatory macrophages (Mps). However, the relationship between HFD and Mps polarization in the ELGs remains unexplored. We first identified and validated the differential expression of PPAR-γ in murine ELGs fed ND and HFD through RNA sequencing. Tear secretion was measured using the Schirmer test. Lipid droplet deposition within the ELGs was observed through Oil Red O staining and transmission electron microscopy. Mps phenotypes were determined through quantitative RT-PCR, immunofluorescence, and flow cytometric analysis. An in vitro high-fat culture system for Mps was established using palmitic acid (PA), with supernatants collected for co-culture with lacrimal gland acinar cells. Gene expression was determined through ELISA, immunofluorescence, immunohistochemistry, quantitative RT-PCR, and Western blot analysis. Pioglitazone reduced M1-predominant infiltration induced by HFD by increasing PPAR-γ levels in ELGs, thereby alleviating lipid deposition and enhancing tear secretion. In vitro tests indicated that PPAR-γ agonist shifted Mps from M1-predominant to M2-predominant phenotype in PA-induced Mps, reducing lipid synthesis in LGACs and promoting lipid catabolism, thus alleviating lipid metabolic disorders within ELGs. Conversely, the PPAR-γ antagonist induced opposite effects. In summary, the lacrimal gland is highly sensitive to high-fat and lipid metabolic disorders. Downregulation of PPAR-γ expression in ELGs induces Mps polarization toward predominantly M1 phenotype, leading to lipid metabolic disorder and inflammatory responses via the NF-κb/ERK/JNK/P38 pathway.

Diesel exhaust exposure induced squamous metaplasia of corneal epithelium via yes-associated protein activation

Atmospheric pollution has been demonstrated to be associated with ocular surface diseases characterized by corneal epithelial damage, including impaired barrier function and squamous metaplasia. However, the specific mechanisms underlying the impact of atmospheric pollution on corneal damage are still unknow. To address this gap in knowledge, we conducted a study using a whole-body exposure system to investigate the detrimental effects of traffic-related air pollution, specifically diesel exhaust (DE), on corneal epithelium in C57BL/6 mice over a 28-day period. Following DE exposure, the pathological alterations in corneal epithelium, including significant increase in corneal thickness and epithelial stratification, were observed in mice. Additionally, exposure to DE was also shown to disrupt the barrier functions of corneal epithelium, leading to excessive proliferation of basal cells and even causing squamous metaplasia in corneal epithelium. Further studies have found that the activation of yes-associated protein (YAP), characterized by nuclear translocation, may play a significant role in DE-induced corneal squamous metaplasia. In vitro assays confirmed that DE exposure triggered the YAP/β-catenin pathway, resulting in squamous metaplasia and destruction of barrier functions. These findings provide the preliminary evidence that YAP activation is one of the mechanisms of the damage to corneal epithelium caused by traffic-related air pollution. These findings contribute to the knowledge base for promoting eye health in the context of atmospheric pollution.

Recommendations for nutritional supplements for dry eye disease: current advances

Dry eye disease (DED) represents a prevalent ocular surface disease. The development of effective nutritional management strategies for DED is crucial due to its association with various factors such as inflammation, oxidative stress, deficiencies in polyunsaturated fatty acids (PUFAs), imbalanced PUFA ratios, and vitamin insufficiencies. Extensive research has explored the impact of oral nutritional supplements, varying in composition and dosage, on the symptoms of DED. The main components of these supplements include fish oils (Omega-3 fatty acids), vitamins, trace elements, and phytochemical extracts. Beyond these well-known nutrients, it is necessary to explore whether novel nutrients might contribute to more effective DED management. This review provides a comprehensive update on the therapeutic potential of nutrients and presents new perspectives for combination supplements in DED treatment.

How gut microbiota may impact ocular surface homeostasis and related disorders

Changes in the bacterial flora in the gut, also described as gut microbiota, are readily acknowledged to be associated with several systemic diseases, especially those with an inflammatory, neuronal, psychological or hormonal factor involved in the pathogenesis and/or the perception of the disease. Maintaining ocular surface homeostasis is also based on all these four factors, and there is accumulating evidence in the literature on the relationship between gut microbiota and ocular surface diseases. The mechanisms involved are mostly interconnected due to the interaction of central and peripheral neuronal networks, inflammatory effectors and the hormonal system. A better understanding of the influence of the gut microbiota on the maintenance of ocular surface homeostasis, and on the onset or persistence of ocular surface disorders could bring new insights and help elucidate the epidemiology and pathology of ocular surface dynamics in health and disease. Revealing the exact nature of these associations could be of paramount importance for developing a holistic approach using highly promising new therapeutic strategies targeting ocular surface diseases.

Potential New Target for Dry Eye Disease-Oxidative Stress

Dry eye disease (DED) is a multifactorial condition affecting the ocular surface. It is characterized by loss of tear film homeostasis and accompanied by ocular symptoms that may potentially result in damage to the ocular surface and even vision loss. Unmodifiable risk factors for DED mainly include aging, hormonal changes, and lifestyle issues such as reduced sleep duration, increased screen exposure, smoking, and ethanol consumption. As its prevalence continues to rise, DED has garnered considerable attention, prompting the exploration of potential new therapeutic targets. Recent studies have found that when the production of ROS exceeds the capacity of the antioxidant defense system on the ocular surface, oxidative stress ensues, leading to cellular apoptosis and further oxidative damage. These events can exacerbate inflammation and cellular stress responses, further increasing ROS levels and promoting a vicious cycle of oxidative stress in DED. Therefore, given the central role of reactive oxygen species in the vicious cycle of inflammation in DED, strategies involving antioxidants have emerged as a novel approach for its treatment. This review aims to enhance our understanding of the intricate relationship between oxidative stress and DED, thereby providing directions to explore innovative therapeutic approaches for this complex ocular disorder.

Ozone exposure affects corneal epithelial fate by promoting mtDNA leakage and cGAS/STING activation

Ozone is a common air pollutant associated with various human diseases. The human ocular surface is frequently exposed to ozone in the troposphere, but the mechanisms by which ozone affects the ocular surface health remain unclear. This study aimed to establish a mouse model to investigate the effects of ozone exposure on the ocular surface and the corneal epithelium. The findings revealed that ozone exposure disrupted corneal epithelial homeostasis and differentiation, resulting in corneal squamous metaplasia. Further, ozone exposure induced oxidative damage and cytoplasmic leakage of mitochondrial DNA (mtDNA), thereby activating the cGAS/STING signaling pathway. The activation of the cGAS/STING signaling pathway triggered the activation of downstream NF-κB and TRAF6 signaling pathways, causing corneal inflammation, thereby promoting corneal inflammation and squamous metaplasia. Finally, C-176, a selective STING inhibitor, effectively prevented and treated corneal inflammation and squamous metaplasia caused by ozone exposure. This study revealed the role of mtDNA leakage-mediated cGAS/STING activation in corneal squamous epithelial metaplasia caused by ozone exposure. It also depicted the abnormal expression pattern of corneal epithelial keratin using three-dimensional images, providing new targets and strategies for preventing and treating corneal squamous metaplasia and other ocular surface diseases.

Robust and Objective Evaluation of Superficial Punctate Keratopathy in a Murine Dry Eye Model

Purpose

To establish a robust and objective method to evaluate (SPK) superficial punctate keratopathy in a murine dry eye model by developing a reliable photographic system.

Design

Experimental study.

Subjects

A murine dry eye model was generated by exorbital lacrimal gland excision. Sham-operated mice were used as healthy controls. For the sham operation, an incision was made without touching the gland.

Methods

A photographic system was constructed, consisting of an LED lamp and a digital camera fitted with a zoom lens and sharp cut filter. SPK was detected by applying fluorescein solution. To validate the system, SPK was compared between dry eye mice and healthy control mice, and diquafosol (DIQUAS ophthalmic solution 3%; Santen Pharmaceutical Co., Ltd.) or cyclosporine (PAPILOCK Mini ophthalmic solution 0.1%; Santen Pharmaceutical Co., Ltd.) was used to dry eye mice.

Main Outcome Measures

SPK was evaluated using the parameters of fluorescence score and fluorescein-stained area.

Results

The photographs clearly indicated SPK in dry eye mice. A fluorescence score of 0 to 9 could be easily assessed, and the fluorescein-stained area was quantifiable. The fluorescein-stained area correlated with fluorescence score (correlation coefficient: 0.98), with good interobserver reliability (intraclass correlation coefficient: 0.999). The fluorescein-stained area increased significantly in dry eye mice compared with that of healthy controls (P < 0.0001). Both types of therapeutic eye drops decreased the fluorescein-stained area relative to saline-treated mice (P < 0.05 in diquafosol vs. saline; P < 0.01 in cyclosporine vs. saline).

Conclusions

This newly developed system is a robust alternative for quantitative evaluation of SPK in a murine dry eye model.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

ER-1 deficiency induces inflammation and lipid deposition in meibomian gland and lacrimal gland

PURPOSE

To investigated the role of estrogen receptor-1 (ER-1) in maintaining homeostasis in ocular surface.

METHODS

ER-1-knockout (ER-1KO) mice were studied at 4 months of age. The ocular surface was examined using a slit lamp. Histological alterations in the meibomian gland (MG) and lacrimal gland (LG) were observed with H&E staining. Protein levels of P-ERK, peroxisome proliferator-activated receptor gamma (PPAR-γ), p-NFκB-P65, IL-1β, aquaporin 5 (AQP-5), fatty acid-binding protein 5 (Fabp5) and K10 were determined by immunofluorescence and Western blotting. Gene expressions of APO-F, APO-E, K10, ELOVL4, PPAR-γ, SCD-1, and SREBP1 were quantified by qPCR. Conjunctival (CJ) goblet cell alterations were detected by PAS staining. Lipid metabolism in MG and LG was assessed using LipidTox. Apoptosis in MG and LG was analyzed through the TUNEL assay.

RESULTS

Both male and female ER-1KO mice demonstrated increased corneal fluorescence staining scores. MG showed abnormal lipid metabolism and ductal dilation. LG displayed lipid deposition and reduced AQP-5 expression. CJ experienced goblet cell loss. MG, LG exhibited signs of inflammation and apoptosis.

CONCLUSION

ER1 is pivotal for ocular surface homeostasis in both genders of mice. ER1 deficiency induces inflammation and lipid deposition to MG and LG, culminating in dry eye-like manifestations on the ocular surface.

Leger AJ, Galor A. Living with your biome: how the bacterial microbiome impacts ocular surface health and disease

Introduction

Microbiome research has grown exponentially but the ocular surface microbiome (OSM) remains an area in need of further study. This review aims to explore its complexity, disease-related microbial changes, and immune interactions, and highlights the potential for its manipulation as a therapeutic for ocular surface diseases.

Areas Covered

We introduce the OSM by location and describe what constitutes a normal OSM. Second, we highlight aspects of the ocular immune system and discuss potential immune microbiome interactions in health and disease. Finally, we highlight how microbiome manipulation may have therapeutic potential for ocular surface diseases.

Expert Opinion

The ocular surface microbiome varies across its different regions, with a core phyla identified, but with genus variability. A few studies have linked microbiome composition to diseases like dry eye but more research is needed, including examining microbiome interactions with the host. Studies have noted that manipulating the microbiome may impact disease presentation. As such, microbiome manipulation via diet, oral and topical pre and probiotics, and hygienic measures may provide new therapeutic algorithms in ocular surface diseases.

Chronic Sleep Deprivation Impairs Visual Functions via Oxidative Damage in Mice

Sleep deprivation (SD) is a global public health burden, and has a detrimental role in the nervous system. Retina is an important part of the central nervous system; however, whether SD affects retinal structures and functions remains largely unknown. Herein, chronic SD mouse model indicated that loss of sleep for 4 months could result in reductions in the visual functions, but without obvious morphologic changes of the retina. Ultrastructural analysis by transmission electron microscope revealed the deterioration of mitochondria, which was accompanied with the decrease of multiple mitochondrial proteins in the retina. Mechanistically, oxidative stress was provoked by chronic SD, which could be ameliorated after rest, and thus restore retinal homeostasis. Moreover, the supplementation of two antioxidants, α-lipoic acid and N-acetyl-l-cysteine, could reduce retinal reactive oxygen species, repair damaged mitochondria, and, as a result, improve the retinal functions. Overall, this work demonstrated the essential roles of sleep in maintaining the integrity and health of the retina. More importantly, it points towards supplementation of antioxidants as an effective intervention strategy for people experiencing sleep shortages.

Association between dyslipidaemia and dry eye disease: a systematic review and meta-analysis

PURPOSE

To report a systematic review and meta-analysis of the association between dry eye disease (DED) and dyslipidaemia.

METHODS

PubMed, Embase, Web of Science and Cochrane Library were systematically searched from January 2000 to December 2021. We included observational studies to assess the correlation of DED with meibomian gland dysfunction and dyslipidaemia without any language restrictions. The pooled OR with 95% CI was calculated in Stata V.15.

RESULTS

Of 6727 identified studies, 18 studies (21 databases) with a total of 2 663 126 patients were analysed in our meta-analysis. The results showed that DED risk was associated with dyslipidaemia (OR=1.53, 95% CI: 1.41 to 1.66, p=0.001), especially elevated total cholesterol levels (OR=1.57, 95% CI: 1.25 to 1.99, p<0.001), elevated low-density lipoprotein cholesterol levels (OR=1.13, 95% CI: 1.06 to 1.20, p<0.001) and high-density lipoprotein cholesterol levels (OR=1.06, 95% CI: 1.01 to 1.11, p<0.001), but not with serum triglyceride levels. Moreover, having a history of lipid-lowering drug use (OR=1.41, 95% CI: 1.19 to 1.67, p<0.001) was also found to be positively associated with DED risk.

CONCLUSIONS

The findings suggested that dyslipidaemia and lipid-lowering drug use might be associated with an increased risk of DED. More evidence is needed to confirm the findings by prospective studies.

PROSPERO REGISTRATION NUMBER

CRD42022296664.

Genetic evidence implicating circulating lipids and lipid drug targets in pterygium

There is limited knowledge about the impact of circulating lipids and lipid-modifying drugs on pterygium development, with conflicting results reported. Our study aimed to address these questions by applying the Mendelian randomization (MR) approach. A two-step MR model was developed. In the first step, bidirectional two-sample MR was employed to establish the causal relationship between circulating lipids and pterygium risk. In the second step, drug-target MR analysis was conducted to assess the causal effect of proprotein convertase subtilisin/kexin type 9 (PCSK9) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) inhibitors on pterygium outcomes. Genetically predicted low-density lipoprotein cholesterol (LDL-c) levels were found to be significantly associated with an increased risk of pterygium (Inverse variance weighted [IVW] odds ratio [OR] = 2.227; P = 1.53 × 10-4). Similarly, higher total cholesterol (TC) levels exhibited a suggestive association with greater susceptibility to pterygium (IVW OR = 1.806; P = 1.70 × 10-3). Through drug-target MR, a positive causal association was noted between HMGCR-mediated LDL-c levels and pterygium (IVW OR = 6.999; P = 0.016), suggesting that statins may be effective in reducing pterygium risk. The present findings suggest that circulating TC and LDL-c are risk factors for pterygium. Additionally, the results indicate that HMGCR inhibitors, which lower LDL-c levels, have a potential protective effect on pterygium outcomes. Further research is warranted to elucidate the underlying mechanisms involved in pterygium pathogenesis, with a particular focus on cholesterol metabolism.

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.

Isolation and Identification of a Novel Anti-Dry Eye Peptide from Tilapia Skin Peptides Based on In Silico, In Vitro, and In Vivo Approaches

Tilapia skin is a great source of collagen. Here, we aimed to isolate and identify the peptides responsible for combating dry eye disease (DED) in tilapia skin peptides (TSP). In vitro cell DED model was used to screen anti-DED peptides from TSP via Sephadex G-25 chromatography, LC/MS/MS, and in silico methods. The anti-DED activity of the screened peptide was further verified in the mice DED model. TSP was divided into five fractions (TSP-I, TSP-II, TSP-III, TSP-IV, and TSP-V), and TSP-II exerted an effective effect for anti-DED. A total of 131 peptides were identified using LC/MS/MS in TSP-II, and NGGPSGPR (NGG) was screened as a potential anti-DED fragment in TSP-II via in silico methods. In vitro, NGG restored cell viability and inhibited the expression level of Cyclooxygenase-2 (COX-2) protein in Human corneal epithelial cells (HCECs) induced by NaCl. In vivo, NGG increased tear production, decreased tear ferning score, prevented corneal epithelial thinning, alleviated conjunctival goblet cell loss, and inhibited the apoptosis of corneal epithelial cells in DED mice. Overall, NGG, as an anti-DED peptide, was successfully identified from TSP, and it may be devoted to functional food ingredients or medicine for DED.

TFOS Lifestyle: Impact of nutrition on the ocular surface

Nutrients, required by human bodies to perform life-sustaining functions, are obtained from the diet. They are broadly classified into macronutrients (carbohydrates, lipids, and proteins), micronutrients (vitamins and minerals) and water. All nutrients serve as a source of energy, provide structural support to the body and/or regulate the chemical processes of the body. Food and drinks also consist of non-nutrients that may be beneficial (e.g., antioxidants) or harmful (e.g., dyes or preservatives added to processed foods) to the body and the ocular surface. There is also a complex interplay between systemic disorders and an individual's nutritional status. Changes in the gut microbiome may lead to alterations at the ocular surface. Poor nutrition may exacerbate select systemic conditions. Similarly, certain systemic conditions may affect the uptake, processing and distribution of nutrients by the body. These disorders may lead to deficiencies in micro- and macro-nutrients that are important in maintaining ocular surface health. Medications used to treat these conditions may also cause ocular surface changes. The prevalence of nutrition-related chronic diseases is climbing worldwide. This report sought to review the evidence supporting the impact of nutrition on the ocular surface, either directly or as a consequence of the chronic diseases that result. To address a key question, a systematic review investigated the effects of intentional food restriction on ocular surface health; of the 25 included studies, most investigated Ramadan fasting (56%), followed by bariatric surgery (16%), anorexia nervosa (16%), but none were judged to be of high quality, with no randomized-controlled trials.

Purple Sweet Potato Powder Containing Anthocyanin Mitigates High-Fat-Diet-Induced Dry Eye Disease

Purple sweet potato (PSP) powder with anthocyanins possesses the ability to reduce oxidative stress and inflammation. Studies have presumed a positive correlation between body fat and dry eye disease (DED) in adults. The regulation of oxidative stress and inflammation has been proposed as the mechanism underlying DED. This study developed an animal model of high fat diet (HFD)-induced DED. We added 5% PSP powder to the HFD to evaluate the effects and underlying mechanisms in mitigating HFD-induced DED. A statin drug, atorvastatin, was also added to the diet separately to assess its effect. The HFD altered the structure of lacrimal gland (LG) tissue, reduced LG secretory function, and eliminated the expression of proteins related to DED development, including α-smooth muscle actin and aquaporin-5. Although PSP treatment could not significantly reduce body weight or body fat, it ameliorated the effects of DED by preserving LG secretory function, preventing ocular surface erosion, and preserving LG structure. PSP treatment increased superoxide dismutase levels but reduced hypoxia-inducible factor 1-α levels, indicating that PSP treatment reduced oxidative stress. PSP treatment increased ATP-binding cassette transporter 1 and acetyl-CoA carboxylase 1 levels in LG tissue, signifying that PSP treatment regulated lipid homeostasis maintenance to reduce the effects of DED. In conclusion, PSP treatment ameliorated the effects of HFD-induced DED through the regulation of oxidative stress and lipid homeostasis in the LG.

High-fat diet-induced intestinal dysbiosis is associated with the exacerbation of Sjogren’s syndrome

Environmental factors are believed to influence the evolution of primary Sjögren’s syndrome (pSS). The aims of this study were to investigate the association of pSS with a high-fat diet (HFD) and to relate HFD-induced gut dysbiosis to pSS exacerbation. Male Wild Type (WT) and IL-14α transgenic mice (IL-14α TG) were fed a standard diet (SD) and HFD for 11 months. We found an increase in the autoantibody level, more severe dry eye, severe dry mouth symptoms, and an earlier presence of systemic features in the IL-14α TG mice treated with HFD. These data suggest that HFD can promote the process of pSS in the IL-14α TG mice. In addition, an HFD leads to a decrease in the richness of gut microbiota of IL-14α TG mice treated with HFD. The abundance of Deferribacterota was significantly enriched in the IL-14α TG mice treated with HFD compared with other groups. Through the mental test between gut microbiota and clinical parameters, we found that HFD-induced dysbiosis gut microbiota were associated with pSS clinical parameters. In conclusion, HFD results in the aggravation of pSS progression, likely due to the increase of potentially pathogenic microorganisms.

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

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

Gut Microbiome and Its Influence On Ocular Surface and Ocular Surface Diseases

ABSTRACT

The gut microbiome plays a substantial immunologic and pathophysiologic role in maintaining the health of the host, and dysregulation of this dynamic ecosystem has been associated with several inflammatory conditions. Many studies have explored the influence of gut microbiota on the ocular surface and whether gut microbiota impact the pathophysiology of ophthalmic conditions. These findings have highlighted the advantages of enhancing gut microbes through probiotics, prebiotics, diet, vitamin supplementations, and fecal microbial transplant in clinical practice. The purpose of this review article was to provide an up-to-date overview of the knowledge on this topic. Further exploration of this area of research is important to help guide new therapeutic targets to develop treatment and prevention of certain ocular surface diseases.

High-Fat Nutritional Challenge Reshapes Circadian Signatures in Murine Extraorbital Lacrimal Glands

Purpose

A high-fat diet (HFD) increases the risk of developing many systemic diseases; however, the effects of high fat intake on lacrimal gland functions and the molecular mechanisms underlying these effects are unknown. We explored the effects of an HFD on the circadian rhythms of the extraorbital lacrimal glands (ELGs).

Methods

Male C57BL/6J mice maintained on a 12/12-hour light/dark cycle were fed an ad libitum HFD or normal chow (NC) for 2 weeks. The ELGs were collected from euthanized animals every 3 hours throughout the circadian cycle (24 hours). Using high-throughput RNA-sequencing (RNA-Seq), we studied the circadian transcriptomic profile of the ELGs. Circadian oscillations in cell size, secretion response, lipid deposition, and immune cell trafficking of the ELGs were also analyzed.

Results

An HFD modulated the circadian transcriptomic profile of the ELGs, including the composition, phase, and amplitude of cyclical transcript oscillations, and affected the associated signaling pathways at spatiotemporal levels. HFD feeding significantly altered the normal rhythmic oscillations of ELG cell size, immune cell trafficking, secretion response, and lipid deposition. After dietary reversal in HFD-fed animals, the activity, core temperature, and lipid accumulation in lacrimal glands recovered partially to the level of NC-fed animals. However, the average cell size of the ELGs, the recruitment of immune cells, and the rhythm of lacrimal secretion did not return to the levels of the NC-fed group.

Conclusions

HFD perturbation interferes with the cyclical transcriptomic profile, cell size, immune cell trafficking, and secretion function of the ELGs with a strikingly high sensitivity.

Nicotinamide mononucleotide increases cell viability and restores tight junctions in high-glucose-treated human corneal epithelial cells via the SIRT1/Nrf2/HO-1 pathway

BACKGROUND

Diabetes mellitus (DM)-related corneal epithelial dysfunction is a severe ocular disorder; however, the effects of nicotinamide mononucleotide (NMN) on high-glucose (HG)-treated human corneal epithelial cells (HCECs) remain unclear.

METHODS

We conducted an in-vitro study to examine the effects of NMN treatment on HG-treated HCECs. Cell viability was measured using trypan blue stain, mitochondrial membrane potential was measured using JC-1 stain, and intracellular reactive oxygen species and apoptosis assays were conducted using flow cytometry. Transepithelial electrical resistance (TEER) and zonula occludens-1 (ZO-1) immunofluorescence for tight junction examinations were conducted. Immunoblot analyses were conducted to analyze the expression of silent information regulator-1 (SIRT1), nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) of the SIRT1/Nrf2/HO-1 pathway.

RESULTS

NMN increased cell viability by reducing cell damage, reducing apoptosis, increasing cell migration, and restoring tight junctions in HG-treated HCECs. By analyzing the expressions of SIRT1, Nrf2, HO-1, NMN demonstrated protective effects via the SIRT1/Nrf2/HO-1 pathway.

CONCLUSIONS

NMN increases cell viability by reversing cell damage, reducing apoptosis, increasing cell migration, and restoring tight junctions in HG-treated HCECs, and these effects may be mediated by the SIRT1/Nrf2/HO-1 pathway.

Prevalence and associated factors for climatic droplet keratopathy in Kazakhs adults: a cross-sectional study in Tacheng, Xinjiang, China

Background

Investigation of the prevalence of climatic droplet keratopathy (CDK) in Tacheng, Xinjiang, China.

Methods

A total of 1030 participants, in their 40s or older, from the Kazakh ethnic group in Tacheng, were randomly sampled by stratification method. Ophthalmic examinations and surveys were carried out on these participants. Factors associated with CDK were analyzed with logistic regression models.

Results

CDK was found in 66 (6.4%; 95% confidence interval [CI]: 4.9–7.9%) Kazakh individuals.

After multiple regression model analysis, it demonstrated that age (< 0.001), exposure time (< 0.001), exposure protection (< 0.001), and vegetable intake (< 0.001) were of correlation with CDK, of which age (OR = 1.21[CI]: 1.16–1.27) and long-term outdoor exposure (OR = 2.42[CI]: 1.26–4.67) were the risk factors, and that vegetable intake (OR = 0.29[CI]: 0.14–0.59) and wearing a hat (OR = 0.24[CI]: 0.10–0.56) were protective factors.

Conclusions

This study has revealed the risk and protective factors of CDK, providing a new insight on related research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02065-4.

High-Fat Diet Induces Inflammation of Meibomian Gland

Purpose

To determine if a high-fat diet (HFD) induces meibomian gland (MG) inflammation in mice.

Methods

Male C57BL/6J mice were fed a standard diet (SD), HFD, or HFD supplemented with the peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist rosiglitazone for various durations. Body weight, blood lipid levels, and eyelid changes were monitored at regular intervals. MG sections were subjected to hematoxylin and eosin staining, LipidTox staining, TUNEL assay, and immunostaining. Quantitative RT-PCR and western blot analyses were performed to detect relative gene expression and signaling pathway activation in MGs.

Results

MG acinus accumulated more lipids in the mice fed the HFD. Periglandular CD45-positive and F4/80-positive cell infiltration were more evident in the HFD mice, and they were accompanied by upregulation of inflammation-related cytokines. PPAR-γ downregulation accompanied activation of the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways in the HFD mice. There was increased acini cell apoptosis and mitochondria damage in mice fed the HFD. MG inflammation was ameliorated following a shift to the standard diet and rosiglitazone treatment in the mice fed the HFD.

Conclusions

HFD-induced declines in PPAR-γ expression and MAPK and NF-κB signaling pathway activation resulted in MG inflammation and dysfunction in mice.

Dry eye disease: an (in)convenient truth

The salient rise of chronic disease from the mid-twentieth century threatens to overwhelm public health systems in an increasing number of countries and is now considered an epidemic. Dry eye disease is an underappreciated disorder that bears all the hallmarks of chronic disease. Preventative health care seeks improved and sustainable patient engagement in the self-management of health to limit the progress and extent of chronic disease. Anthropogenic environments engendering lifestyles and behaviours that can be detrimental to human health, can be considered as direct or indirect threats to successful preventative health strategies. Chronic disease can be viewed as the result of physiological responses of the human body to the modern environment. The quest for an increasingly convenient, global, and disease-free lifestyle is ironically threatening to undo the gains in health and quality of life made over the last one hundred years. Considering dry eye disease as an anthropogenic chronic disease, contributions of diet (food and beverages consumed) and nutrition (extending to relationships with self, community, and nature) to development of dry eye disease are explored in this review. Evidence of environmental and behavioural instigators of chronic disease with an emphasis on production, disbursement, and preservation of food, is presented. Furthermore, evidence of traditional food practices that offer resistance to the development of chronic systemic inflammatory disorders are reviewed as an exemplar of potential strategies that can be put into practice by individuals and communities to reinstate a balanced life, community and planet.

The ocular microbiome and microbiota and their effects on ocular surface pathophysiology and disorders

The ocular surface flora perform an important role in the defense mechanisms of the ocular surface system. Its regulation of the immunological activity and the barrier effect against pathogen invasion are remarkable. Composition of the flora differs according to the methods of investigation, because the microbiome, composed of the genetic material of bacteria, fungi, viruses, protozoa, and eukaryotes on the ocular surface, differs from the microbiota, which are the community of microorganisms that colonize the ocular surface. The observed composition of the ocular surface flora depends on harvesting and examining methods, whether with traditional culture or with more refined genetic analysis based on rRNA and DNA sequencing. Environment, diet, sex, and age influence the microbial flora composition, thus complicating the analysis of the baseline status. Moreover, potentially pathogenic organisms can affect its composition, as do various disorders, including chronic inflammation, and therapies applied to the ocular surface. A better understanding of the composition and function of microbial communities at the ocular surface could bring new insights and clarify the epidemiology and pathology of ocular surface dynamics in health and disease. The purpose of this review is to provide an up-to-date overview of knowledge about this topic.

Impacts of high fat diet on ocular outcomes in rodent models of visual disease

High fat diets (HFD) have been utilized in rodent models of visual disease for over 50 years to model the effects of lipids, metabolic dysfunction, and diet-induced obesity on vision and ocular health. HFD treatment can recapitulate the pathologies of some of the leading causes of blindness, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) in rodent models of visual disease. However, there are many important factors to consider when using and interpreting these models. To synthesize our current understanding of the importance of lipid signaling, metabolism, and inflammation in HFD-driven visual disease processes, we systematically review the use of HFD in mouse and rat models of visual disease. The resulting literature is grouped into three clusters: models that solely focus on HFD treatment, models of diabetes that utilize both HFD and streptozotocin (STZ), and models of AMD that utilize both HFD and genetic models and/or other exposures. Our findings show that HFD profoundly affects vision, retinal function, many different ocular tissues, and multiple cell types through a variety of mechanisms. We delineate how HFD affects the cornea, lens, uvea, vitreous humor, retina, retinal pigmented epithelium (RPE), and Bruch's membrane (BM). Furthermore, we highlight how HFD impairs several retinal cell types, including glia (microglia), retinal ganglion cells, bipolar cells, photoreceptors, and vascular support cells (endothelial cells and pericytes). However, there are a number of gaps, limitations, and biases in the current literature. We highlight these gaps and discuss experimental design to help guide future studies. Very little is known about how HFD impacts the lens, ciliary bodies, and specific neuronal populations, such as rods, cones, bipolar cells, amacrine cells, and retinal ganglion cells. Additionally, sex bias is an important limitation in the current literature, with few HFD studies utilizing female rodents. Future studies should use ingredient-matched control diets (IMCD), include both sexes in experiments to evaluate sex-specific outcomes, conduct longitudinal metabolic and visual measurements, and capture acute outcomes. In conclusion, HFD is a systemic exposure with profound systemic effects, and rodent models are invaluable in understanding the impacts on visual and ocular disease.

Meibomian Gland Dysfunction: What Have Animal Models Taught Us?

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

Can Gut Microbiota Affect Dry Eye Syndrome?

Using metagenomics, continuing evidence has elicited how intestinal microbiota trigger distant autoimmunity. Sjögren's syndrome (SS) is an autoimmune disease that affects the ocular surface, with frequently unmet therapeutic needs requiring new interventions for dry eye management. Current studies also suggest the possible relation of autoimmune dry eye with gut microbiota. Herein, we review the current knowledge of how the gut microbiota interact with the immune system in homeostasis as well as its influence on rheumatic and ocular autoimmune diseases, and compare their characteristics with SS. Both rodent and human studies regarding gut microbiota in SS and environmental dry eye are explored, and the effects of prebiotics and probiotics on dry eye are discussed. Recent clinical studies have commonly observed a correlation between gut dysbiosis and clinical manifestations of SS, while environmental dry eye portrays characteristics in between normal and autoimmune. Moreover, a decrease in both the Firmicutes/Bacteroidetes ratio and genus Faecalibacterium have most commonly been observed in SS subjects. The presumable pathways forming the "gut dysbiosis-ocular surface-lacrimal gland axis" are introduced. This review may provide perspectives into the link between the gut microbiome and dry eye, enhance our understanding of the pathogenesis in autoimmune dry eye, and be useful in the development of future interventions.