Age-associated antigen-presenting cell alterations promote dry-eye inducing Th1 cells

Effects of age on lacrimal gland bioactive lipids

PURPOSE

Polyunsaturated fatty acids (PUFA) are a source of bioactive lipids regulating inflammation and its resolution.

METHODS

Changes in PUFA metabolism were compared between lacrimal glands (LGs) from young and aged C57BL/6 J mice using a targeted lipidomics assay, as was the gene expression of enzymes involved in the metabolism of these lipids.

RESULTS

Global reduction in PUFAs and their metabolites was observed in aged LGs compared to young controls, averaging between 25 and 66 % across all analytes. ꞷ-6 arachidonic acid (AA) metabolites were all reduced in aged LGs, where the changes in prostaglandin E2 (PGE2) and lipoxin A4 (LXA4) were statistically significant. Several other 5-lipoxygenase (5-LOX) mediated metabolites were significantly reduced in the aged LGs, including D-series resolvins (e.g., RvD4, RvD5, and RvD6). Along with the RvDs, several ꞷ-3 docosahexaenoic acid (DHA) metabolites such as 14-HDHA, neuroprotectin D1 (NPD1), Maresin 2 (MaR2), and MaR 1 metabolite (22-COOH-MaR1) were significantly reduced in aged LGs. Similarly, ꞷ-3 eicosapentaenoic acid (EPA) and its metabolites were significantly reduced in aged LGs, where the most significantly reduced was 18-HEPE. Using metabolite ratios (product:precursor) for specific metabolic conversions as surrogate enzymatic measures, reduced 12-LOX activity was identified in aged LGs.

CONCLUSION

In this study, global reduction of PUFAs and their metabolites was found in the LGs of aged female C57BL/6 J compared to young controls. A consistent reduction was observed across all detected lipid analytes except for ꞷ-3 docosapentaenoic acid (DPA) and its special pro-resolving mediator (SPM) metabolites in aged mice, suggesting an increased risk for LG inflammation.

Age-Related Differences in the Mouse Corneal Epithelial Transcriptome and Their Impact on Corneal Wound Healing

Purpose

Aging is a risk factor for dry eye. We sought to identify changes in the aged mouse corneal epithelial transcriptome and determine how age affects corneal sensitivity, re-epithelialization, and barrier reformation after corneal debridement.

Methods

Corneal epithelium of female C57BL/6J (B6) mice of different ages (2, 12, 18, and 24 months) was collected, RNA extracted, and bulk RNA sequencing performed. Cornea sensitivity was measured with an esthesiometer in 2- to 3-month-old, 12- to 13-month-old, 18- to 19-month-old, and 22- to 25-month-old female and male mice. The 2-month-old and 18-month-old female and male mice underwent unilateral corneal debridement using a blunt blade. Wound size and fluorescein staining were visualized and photographed at different time points, and a re-epithelialization rate curve was calculated.

Results

There were 157 differentially expressed genes in aged mice compared with young mice. Several pathways downregulated with age control cell migration, proteoglycan synthesis, and collagen trimerization, assembly, biosynthesis, and degradation. Male mice had decreased corneal sensitivity compared with female mice at 12 and 24 months of age. Aged mice, irrespective of sex, had delayed corneal re-epithelialization in the first 48 hours and worse corneal fluorescein staining intensity at day 14 than young mice.

Conclusions

Aged corneal epithelium has an altered transcriptome. Aged mice regardless of sex heal more slowly and displayed more signs of corneal epithelial defects after wounding than young mice. These results indicate that aging significantly alters the corneal epithelium and its ability to coordinate healing.

The existence of senescent cells in conjunctival epithelium from elderly individuals

PURPOSE

The ocular surface microenvironment changes with aging. However, it remains unclear if cellular senescence influences the ocular surface. We investigated the presence of p16INK4a-expressing senescent cells in healthy human conjunctiva.

STUDY DESIGN

Clinical and experimental.

METHODS

Healthy conjunctival tissue samples were obtained from middle-aged and elderly subjects. RT-qPCR was performed to assess the expression of senescence markers CDKN2A (p16INK4a) and CDKN1A (p21CIP1/WAF1) and immunostaining was performed to examine the expression of the senescence marker p16INK4a, stem cell markers Ki67 and p63, tight-junction marker ZO-1.

RESULTS

Our study involved 19 conjunctival tissue samples (10 elderly and 9 middle-aged), mean age [elderly: 75.8 ± 3.7 years (72-81), middle-aged: 52.7 ± 7 years (38-59)], sex (elderly: 3 men, 7 women; middle-aged: 3 men, 6 women). The expression of p16INK4a was significantly increased at the RNA level in the elderly compared to middle-aged (p < 0.05). Positivity rate of p16INK4a was significantly elevated in the elderly (15.0 ± 7.8%) compared to middle-aged (0.2 ± 0.6%) (p < 0.05). Positivity rate of Ki67and p63 was significantly reduced in the elderly (1.7 ± 1.7% and 16.5 ± 9.5%) compared to middle-aged (3.9 ± 1.8% and 24.7 ± 5.7%) (p < 0.05). ZO-1 expression was reduced in tissue samples showing p16INK4a-positivity but retained in tissue samples in which p16INK4a was undetectable.

CONCLUSIONS

Senescent cells accumulate with age in the conjunctival epithelium, accompanied by a decrease in Ki67, p63 and ZO-1 expressing cells.

D-Mannose reduces cellular senescence and NLRP3/GasderminD/IL-1β-driven pyroptotic uroepithelial cell shedding in the murine bladder

Aging is a risk factor for disease via increased susceptibility to infection, decreased ability to maintain homeostasis, inefficiency in combating stress, and decreased regenerative capacity. Multiple diseases, including urinary tract infection (UTI), are more prevalent with age; however, the mechanisms underlying the impact of aging on the urinary tract mucosa and the correlation between aging and disease remain poorly understood. Here, we show that, relative to young (8-12 weeks) mice, the urothelium of aged (18-24 months) female mice accumulates large lysosomes with reduced acid phosphatase activity and decreased overall autophagic flux in the aged urothelium, indicative of compromised cellular homeostasis. Aged bladders also exhibit basal accumulation of reactive oxygen species (ROS) and a dampened redox response, implying heightened oxidative stress. Furthermore, we identify a canonical senescence-associated secretory phenotype (SASP) in the aged urothelium, along with continuous NLRP3-inflammasome- and Gasdermin-D-dependent pyroptotic cell death. Consequently, aged mice chronically exfoliate urothelial cells, further exacerbating age-related urothelial dysfunction. Upon infection with uropathogenic E. coli, aged mice harbor increased bacterial reservoirs and are more prone to spontaneous recurrent UTI. Finally, we discover that treatment with D-mannose, a natural bioactive monosaccharide, rescues autophagy flux, reverses the SASP, and mitigates ROS and NLRP3/Gasdermin/interleukin (IL)-1β-driven pyroptotic epithelial cell shedding in aged mice. Collectively, our results demonstrate that normal aging affects bladder physiology, with aging alone increasing baseline cellular stress and susceptibility to infection, and suggest that mannose supplementation could serve as a senotherapeutic to counter age-associated urothelial dysfunction.

Transmembrane Protein CMTM6 Alleviates Ocular Inflammatory Response and Improves Corneal Epithelial Barrier Function in Experimental Dry Eye

Purpose

To investigate the impact of transmembrane protein CMTM6 on the pathogenesis of dry eye disease (DED) and elucidate its potential mechanisms.

Methods

CMTM6 expression was confirmed by database analysis, real-time polymerase chain reaction (RT-PCR), western blot, and immunohistochemistry. Tear secretion was measured using the phenol red thread test. Immune cell infiltration was assessed through flow cytometry. Barrier function was evaluated by fluorescein sodium staining, immunofluorescence staining of zonula occludens 1 (ZO-1), and electric cell-substrate impedance sensing (ECIS) assessment. For silencing CMTM6 expression, siRNA and shRNA were employed, along with lentiviral vector-mediated overexpression of CMTM6. Proinflammatory cytokine levels were analyzed by RT-PCR and cytometric bead array (CBA) analysis.

Results

CMTM6 showed high expression in healthy human and mouse corneal and conjunctival epithelium but was notably reduced in DED. Notably, this downregulation was correlated with disease severity. Cmtm6-/- dry eye (DE) mice displayed reduced tear secretion, severe corneal epithelial defects, decreased conjunctival goblet cell density, and upregulated inflammatory response. Additionally, Cmtm6-/- DE mice and CMTM6 knockdown human corneal epithelial cell-transformed (HCE-T) cells showed more severe barrier disruption and reduced expression of ZO-1. Knockdown of CMTM6 in HCE-T cells increased inflammatory responses induced by hyperosmotic stress, which was significantly mitigated by CMTM6 overexpression. Moreover, the level of phospho-p65 in hyperosmolarity-stimulated HCE-T cells increased after silencing CMTM6. Nuclear factor kappa B (NF-κB) p65 inhibition (JSH-23) reversed the excessive inflammatory responses caused by hyperosmolarity in CMTM6 knockdown HCE-T cells.

Conclusions

The reduction in CMTM6 expression on the ocular surface contributes to the pathogenesis of DED. The CMTM6-NF-κB p65 signaling pathway may serve as a promising therapeutic target for DED.

Immunosenescence and immunotherapy in older NSCLC patients

Nonsmall cell lung cancer (NSCLC) predominantly affects the elderly since its incidence and mortality rates skyrocket beyond the age of 65. The landscape of NSCLC treatment has been revolutionized by immune checkpoint inhibitors (ICIs), which have emerged after a long and mostly inactive period of conventional treatment protocols. However, there is limited data on the exact effects of these chemicals on older patients, whose care can be complicated by a variety of conditions. This highlights the need to understand the efficacy of emerging cancer medicines in older patients. In this study, we will review the data of ICIs from clinical trials that were relevant to older people with NSCLC and poor performance status. We will also discuss the role of immunosenescence in immunotherapy and biomarkers in predicting the efficacy of ICIs in patients with advanced NSCLC.

Aquaporins in lacrimal glands and their role in dry eye disease

Aging is the most important known risk factor for dry eye is aging, which is associated with changes in the structure and function of the lacrimal gland (LG) and characterized by atrophy, duct blocking lymphocyte infiltration, and reduced protein secretion. Aquaporins (AQP) have been proposed as a potential producer of exocrine gland fluids since exocrine secretion depends on the mobility of water. Therefore, the main topics of this review will be the expression, localization, and function of AQPs in LG. In addition, we review the mechanisms of fluid transport in exocrine gland fluid secretion and discuss the potential role of AQPs in dry eye.

TNF is a critical cytokine in age-related dry eye disease

Aging is a complex biological process that is characterized by low-grade inflammation, called inflammaging. Aging affects multiple organs including eye and lacrimal gland. Tumor necrosis factor (TNF) is a pleiotropic cytokine that participates in inflammation, activation of proteases such as cathepsin S, and formation of ectopic lymphoid organs. Using genetic and pharmacological approaches, we investigated the role of TNF in age-related dry eye disease, emphasizing the ocular surface and lacrimal gland inflammation. Our results show the increased protein and mRNA levels of TNF in aged lacrimal glands, accompanied by increased TNF, IL1β, IL-18, CCL5, CXCL1, IL-2, IL-2 receptor alpha (CD25), IFN-γ, IL-12p40, IL-17, and IL-10 proteins in tears of aged mice. Moreover, genetic loss of the Tnf-/- in mice decreased goblet cell loss and the development of ectopic lymphoid structures in the lacrimal gland compared to wild-type mice. This was accompanied by a decrease in cytokine production. Treatment of mice at an early stage of aging (12-14-month-old) with TNF inhibitor tanfanercept eye drops for eight consecutive weeks decreased cytokine levels in tears, improved goblet cell density, and decreased the marginal zone B cell frequency in the lacrimal gland compared to vehicle-treated animals. Our studies indicate that modulation of TNF during aging could be a novel strategy for age-related dry eye disease.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Effects of Cathepsin S Inhibition in the Age-Related Dry Eye Phenotype

Purpose

Aged C57BL/6J (B6) mice have increased levels of cathepsin S, and aged cathepsin S (Ctss-/-) knockout mice are resistant to age-related dry eye. This study investigated the effects of cathepsin S inhibition on age-related dry eye disease.

Methods

Female B6 mice aged 15.5 to 17 months were randomized to receive a medicated diet formulated by mixing the RO5461111 cathepsin S inhibitor or a standard diet for at least 12 weeks. Cornea mechanosensitivity was measured with a Cochet-Bonnet esthesiometer. Ocular draining lymph nodes and lacrimal glands (LGs) were excised and prepared for histology or assayed by flow cytometry to quantify infiltrating immune cells. The inflammatory foci (>50 cells) were counted under a 10× microscope lens and quantified using the focus score. Goblet cell density was investigated in periodic acid-Schiff stained sections. Ctss-/- mice were compared to age-matched wild-type mice.

Results

Aged mice subjected to cathepsin S inhibition or Ctss-/- mice showed improved conjunctival goblet cell density and cornea mechanosensitivity. There was no change in total LG focus score in the diet or Ctss-/- mice, but there was a lower frequency of CD4+IFN-γ+ cell infiltration in the LGs. Furthermore, aged Ctss-/- LGs had an increase in T central memory, higher numbers of CD19+B220-, and fewer CD19+B220+ cells than wild-type LGs.

Conclusions

Our results indicate that therapies aimed at decreasing cathepsin S can ameliorate age-related dry eye disease with a highly beneficial impact on the ocular surface. Further studies are needed to investigate the role of cathepsin S during aging.

Heterochronic Parabiosis Causes Dacryoadenitis in Young Lacrimal Glands

Aging is associated with inflammation and oxidative stress in the lacrimal gland (LG). We investigated if heterochronic parabiosis of mice could modulate age-related LG alterations. In both males and females, there were significant increases in total immune infiltration in isochronic aged LGs compared to that in isochronic young LGs. Male heterochronic young LGs were significantly more infiltrated compared to male isochronic young LGs. While both females and males had significant increases in inflammatory and B-cell-related transcripts in isochronic and heterochronic aged LGs compared to levels isochronic and heterochronic young LGs, females had a greater fold expression of some of these transcripts than males. Through flow cytometry, specific subsets of B cells were increased in the male heterochronic aged LGs compared to those in male isochronic aged LGs. Our results indicate that serum soluble factors from young mice were not enough to reverse inflammation and infiltrating immune cells in aged tissues and that there were specific sex-related differences in parabiosis treatment. This suggests that age-related changes in the LG microenvironment/architecture participate in perpetuating inflammation, which is not reversible by exposure to youthful systemic factors. In contrast, male young heterochronic LGs were significantly worse than their isochronic counterparts, suggesting that aged soluble factors can enhance inflammation in the young host. Therapies that aim at improving cellular health may have a stronger impact on improving inflammation and cellular inflammation in LGs than parabiosis.

T-Cell Repertoire Analysis in the Conjunctiva of Murine Dry Eye Model

Purpose

Dry eye is closely related to the activation and proliferation of immune cells, especially T cells. However, the determination of the preferential T-cell clonotypes is technically challenging. This study aimed to investigate the characterization of T-cell receptor (TCR) repertoire in the conjunctiva during dry eye.

Methods

A desiccating stress animal model was established using C57/BL6 mice (8-10 weeks, female). After 7 days of stress stimulation, the slit-lamp image and Oregon-green-dextran staining were used to evaluate the ocular surface injury. Periodic acid-Schiff staining was used to measure the number of goblet cells. Flow cytometry was used to detect the activation and proliferation of T cells in the conjunctiva and cervical lymph nodes. Next-generation sequencing was used to detect the αβ TCR repertoire of the conjunctiva.

Results

The αβ TCR diversity increased significantly in the dry eye group, including the higher CDR3 amino acid length, marked gene usage on TCR V and J gene segments, extensive V(D)J recombination, and distinct CDR3 aa motifs. More important, several T-cell clonotypes were uniquely identified in dry eye. Furthermore, these perturbed rearrangements were reversed after glucocorticoid administration.

Conclusions

A comprehensive analysis of the αβ TCR repertoire in the conjunctiva of the dry eye mouse model was performed. Data in this study contributed significantly to the research on dry eye pathogenesis by demonstrating the TCR gene distribution and disease-specific TCR signatures. This study further provided some potential predictive T-cell biomarkers for future studies.

Ectopic lymphoid structures in the aged lacrimal glands

Aging is a complex biological process in which many organs are pathologically affected. We previously reported that aged C57BL/6J had increased lacrimal gland (LG) lymphoid infiltrates that suggest ectopic lymphoid structures. However, these ectopic lymphoid structures have not been fully investigated. Using C57BL/6J mice of different ages, we analyzed the transcriptome of aged murine LGs and characterized the B and T cell populations. Age-related changes in the LG include increased differentially expressed genes associated with B and T cell activation, germinal center formation, and infiltration by marginal zone-like B cells. We also identified an age-related increase in B1+ cells and CD19+B220+ cells. B220+CD19+ cells were GL7+ (germinal center-like) and marginal zone-like and progressively increased with age. There was an upregulation of transcripts related to T follicular helper cells, and the number of these cells also increased as mice aged. Compared to a mouse model of Sjögren syndrome, aged LGs have similar transcriptome responses but also unique ones. And lastly, the ectopic lymphoid structures in aged LGs are not exclusive to a specific mouse background as aged diverse outbred mice also have immune infiltration. Altogether, this study identifies a profound change in the immune landscape of aged LGs where B cells become predominant. Further studies are necessary to investigate the specific function of these B cells during the aged LGs.

Innate immunity dysregulation in aging eye and therapeutic interventions

The prevalence of eye diseases increases considerably with age, resulting in significant vision impairment. Although the pathobiology of age-related eye diseases has been studied extensively, the contribution of immune-related changes due to aging remains elusive. In the eye, tissue-resident cells and infiltrating immune cells regulate innate responses during injury or infection. But due to aging, these cells lose their protective functions and acquire pathological phenotypes. Thus, dysregulated ocular innate immunity in the elderly increases the susceptibility and severity of eye diseases. Herein, we emphasize the impact of aging on the ocular innate immune system in the pathogenesis of infectious and non-infectious eye diseases. We discuss the role of age-related alterations in cellular metabolism, epigenetics, and cellular senescence as mechanisms underlying altered innate immune functions. Finally, we describe approaches to restore protective innate immune functions in the aging eye. Overall, the review summarizes our current understanding of innate immune functions in eye diseases and their dysregulation during aging.

Topographical Distribution and Phenotype of Resident Meibomian Gland Orifice Immune Cells (MOICs) in Mice and the Effects of Topical Benzalkonium Chloride (BAK)

Meibomian gland orifices (MGOs) are located along the eyelid margin and secrete meibum into the tear film. The profile of resident innate immune cells (ICs) at this site is not well understood. The distribution and phenotype of resident ICs around MGOs in mice was investigated and herein defined as MGO-associated immune cells (MOICs). The effect of topical 0.1% benzalkonium chloride (BAK) on MOICs was also assessed. Eyelids from healthy CD11ceYFP and Cx3cr1gfp/gfp mice aged three or seven months were compared. ICs were identified as CD11c+, Cx3cr1+, and MHC-II+ using four-colour immunostaining and confocal microscopy. MOIC density was variable but clustered around MGOs. There were more CD11c+ MOICs in three-month-old compared with seven-month-old mice (three-month-old: 893 ± 449 cells/mm2 vs. seven-month-old: 593 ± 493 cells/mm2, p = 0.004). Along the eyelid margin, there was a decreasing gradient of CD11c+ MOIC density in three-month-old mice (nasal: 1003 ± 369 cells/mm2, vs. central: 946 ± 574 cells/mm2, vs. temporal: 731 ± 353 cells/mm2, p = 0.044). Cx3cr1-deficient mice had two-fold fewer MHC-II+ MOICs, suggesting a role for Cx3cr1 receptor signaling in meibomian gland surveillance. CD11c+ MOIC density was lower in BAK-exposed eyes compared to saline-treated controls, suggesting a change in homeostasis. This study provides novel insight into resident ICs located at MGOs, and their contribution to MG homeostasis.

Impact of aging on the pathophysiology of dry eye disease: A systematic review and meta-analysis

PURPOSE

Dry eye disease (DED) is a common age-related ocular surface disease. However, it is unknown how aging influences the ocular surface microenvironment. This systematic review aims to investigate how the aging process changes the ocular surface microenvironment and impacts the development of DED.

METHODS

An article search was performed in PubMed, EMBASE, and Web of Science. 44 studies reporting on age-related ocular changes and 14 large epidemiological studies involving the prevalence of DED were identified. 8 out of 14 epidemiological studies were further analyzed with meta-analysis. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines were followed. Study-specific estimates (impact of aging on the prevalence of DED) were combined using one-group meta-analysis in a random-effects model.

RESULTS

Meta-analysis revealed the prevalence of DED in the elderly aged 60 years old or older was 5519 of 60107 (9.2%) and the odds ratio of aging compared to younger age was 1.313 (95% confidence interval [CI]; 1.107, 1.557). With increasing age, the integrity of the ocular surface and tear film stability decreased. Various inflammatory cells, including senescent-associated T-cells, infiltrated the ocular surface epithelium, lacrimal gland, and meibomian gland, accompanied by senescence-related changes, including accumulation of 8-OHdG and lipofuscin-like inclusions, increased expression of p53 and apoptosis-related genes, and decreased Ki67 positive cells.

CONCLUSIONS

The aging process greatly impacts the ocular surface microenvironment, consequently leading to DED.

Immune phenotype of the CD4+ T cells in the aged lymphoid organs and lacrimal glands

Aging is associated with a massive infiltration of T lymphocytes in the lacrimal gland. Here, we aimed to characterize the immune phenotype of aged CD4⁺ T cells in this tissue as compared with lymphoid organs. To perform this, we sorted regulatory T cells (Tregs, CD4⁺CD25⁺GITR⁺) and non-Tregs (CD4⁺CD25^negGITR^neg) in lymphoid organs from female C57BL/6J mice and subjected these cells to an immunology NanoString® panel. These results were confirmed by flow cytometry, live imaging, and tissue immunostaining in the lacrimal gland. Importantly, effector T helper 1 (Th1) genes were highly upregulated on aged Tregs, including the master regulator Tbx21. Among the non-Tregs, we also found a significant increase in the levels of EOMES^med/high, Tbet^negIFN-γ⁺, and CD62L⁺CD44^negCD4⁺ T cells with aging, which are associated with cell exhaustion, immunopathology, and the generation of tertiary lymphoid tissue. At the functional level, aged Tregs from lymphoid organs are less able to decrease proliferation and IFN-γ production of T responders at any age. More importantly, human lacrimal glands (age range 55-81 years) also showed the presence of CD4⁺Foxp3⁺ cells. Further studies are needed to propose potential molecular targets to avoid immune-mediated lacrimal gland dysfunction with aging.

Neutrophils and neutrophil extracellular trap components: Emerging biomarkers and therapeutic targets for age-related eye diseases

Age-related eye diseases, including dry eye, glaucoma, age-related macular degeneration, and diabetic retinopathy, represent a major global health issue based on their increasing prevalence and disabling action. Unraveling the molecular mechanisms underlying these diseases will provide novel opportunities to reduce the burden of age-related eye diseases and improve eye health, contributing to sustainable development goals achievement. The impairment of neutrophil extracellular traps formation/degradation processes seems to be one of these mechanisms. These traps formed by a meshwork of DNA and neutrophil cytosolic granule proteins may exacerbate the inflammatory response promoting chronic inflammation, a pivotal cause of age-related diseases. In this review, we describe current findings that suggest the role of neutrophils and their traps in the pathogenesis of the above-mentioned age-related eye diseases. Furthermore, we discuss why these cells and their constituents could be biomarkers and therapeutic targets for dry eye, glaucoma, age-related macular degeneration, and diabetic retinopathy. We also examine the therapeutic potential of some neutrophil function modulators and provide several recommendations for future research in age-related eye diseases.

Cathepsin S is a novel target for age-related dry eye

Cathepsin S (Ctss) is a protease that is proinflammatory on epithelial cells. The purpose of this study was to investigate the role of Ctss in age-related dry eye disease. Ctss^-/- mice [in a C57BL/6 (B6) background] of different ages were compared to B6 mice. Ctss activity in tears and lacrimal gland (LG) lysates was measured. The corneal barrier function was investigated in naïve mice or after topical administration of Ctss eye drops 5X/day for two days. Eyes were collected, and conjunctival goblet cell density was measured in PAS-stained sections. Immunoreactivity of the tight junction proteins, ZO-1 and occludin, was investigated in primary human cultured corneal epithelial cells (HCEC) without or with Ctss, with or without a Ctss inhibitor. A significant increase in Ctss activity was observed in the tears and LG lysates in aged B6 compared to young mice. This was accompanied by higher Ctss transcripts and protein expression in LG and spleen. Compared to B6, 12 and 24-month-old Ctss^-/- mice did not display age-related corneal barrier disruption and goblet cell loss. Treatment of HCEC with Ctss for 48 h disrupted occludin and ZO-1 immunoreactivity compared to control cells. This was prevented by the Ctss inhibitor LY3000328 or Ctss-heat inactivation. Topical reconstitution of Ctss in Ctss^-/- mice for two days disrupted corneal barrier function. Aging on the ocular surface is accompanied by increased expression and activity of the protease Ctss. Our results suggest that cathepsin S modulation might be a novel target for age-related dry eye disease.

Close Association between Altered Urine-Urothelium Barrier and Tertiary Lymphoid Structure Formation in the Renal Pelvis during Nephritis

BACKGROUND

Kidneys with chronic inflammation develop tertiary lymphoid structures (TLSs). Infectious pyelonephritis is characterized by renal pelvis (RP) inflammation. However, the pathologic features of TLSs, including their formation and association with non-infectious nephritis, are unclear.

METHODS

RPs from humans and mice that were healthy or had non-infectious chronic nephritis were analyzed for TLS development, and the mechanism of TLS formation investigated using urothelium or lymphoid structure cultures.

RESULTS

Regardless of infection, TLSs in the RP, termed urinary tract-associated lymphoid structures (UTALSs), formed in humans and mice with chronic nephritis. Moreover, urine played a unique role in UTALS formation. Specifically, we identified urinary IFN-γ as a candidate factor affecting urothelial barrier integrity because it alters occludin expression. In a nephritis mouse model, urine leaked from the lumen of the RP into the parenchyma. In addition, urine immunologically stimulated UTALS-forming cells via cytokine (IFN-γ, TNF-α) and chemokine (CXCL9, CXCL13) production. CXCL9 and CXCL13 were expressed in UTALS stromal cells and urine stimulation specifically induced CXCL13 in cultured fibroblasts. Characteristically, type XVII collagen (BP180), a candidate autoantigen of bullous pemphigoid, was ectopically localized in the urothelium covering UTALSs and associated with UTALS development by stimulating CXCL9 or IL-22 induction via the TNF-α/FOS/JUN pathway. Notably, UTALS development indices were positively correlated with chronic nephritis development.

CONCLUSIONS

TLS formation in the RP is possible and altered urine-urothelium barrier-based UTALS formation may represent a novel mechanism underlying the pathogenesis of chronic nephritis, regardless of urinary tract infection.

Erxian Decoction modulates Th17/Treg cells differentiation through LFA-1/ICAM-1/STAT3 pathway in menopausal dry eye disease

With the development of modern societies and the ageing of the population, the treatment of menopausal dry eye disease (MDED) has become a thorny issue for the medical profession. Erxian Decoction (EXD) is a traditional Chinese medicine prescription, which has performed good clinical effect on dry eye disease. In this research, we purposed to investigate the molecular mechanisms of EXD for the treatment of MDED. A MDED rat model was established, the results indicated that high concentration of EXD could significantly improve the tear secretion and tear film stability of the animal model. Next, we found that EXD worked through the LFA-1/ICAM-1/STAT3 pathway in the body, and EXD could regulate IL-17, IL-10, CTLA-4 and TGF-β1 to get Th17/Treg balance. In vitro experiments, the results indicated that EXD affected the differentiation of CD4⁺ T cells into Th17/Treg cells by inhibiting the expression and activation of LFA-1 on CD4⁺ T cells, thus exerting immunotherapy effect. Our research provided the experimental basis and associated mechanisms for the clinical application of EXD in dry eye disease.

Protective effects of low-molecular-weight components of adipose stem cell-derived conditioned medium on dry eye syndrome in mice

The present study demonstrated the protective effects of low-molecular-weight adipose-derived stem cell-conditioned medium (LADSC-CM) in a mouse model of dry eye syndrome. Mice subjected to desiccating stress and benzalkonium chloride had decreased tear secretion, impaired corneal epithelial tight junction with microvilli, and decreased conjunctival goblet cells. Topical application of adipose-derived stem cell-conditioned medium (ADSC-CM) stimulated lacrimal tear secretion, preserved tight junction and microvilli of the corneal epithelium, and increased the density of goblet cells and MUC16 expression in the conjunctiva. The low-molecular-weight fractions (< 10 kDa and < 3 kDa) of ADSC-CM (LADSC-CM) provided better protections than the > 10 kDa or > 3 kDa fractions of ADSC-CM. In the in vitro study, desiccation for 10 min or hyperosmolarity (490 osmols) for 24 h caused decreased viability of human corneal epithelial cells, which were reversed by LADSC-CM. The active ingredients in the LADSC-CM were lipophobic and stable after heating and lyophilization. Our study demonstrated that LADSC-CM had beneficial effects on experimental dry eye. It is worthy of further exploration for the active ingredient(s) and the mechanism.

Autoimmunity in dry eye disease - An updated review of evidence on effector and memory Th17 cells in disease pathogenicity

The classic Th1/Th2 dogma has been significantly reshaped since the subsequent introduction of several new T helper cell subsets, among which the most intensively investigated during the last decade is the Th17 lineage that demonstrates critical pathogenic roles in autoimmunity and chronic inflammation - including the highly prevalent dry eye disease. In this review, we summarize current concepts of Th17-mediated disruption of ocular surface immune homeostasis that leads to autoimmune inflammatory dry eye disease, by discussing the induction, activation, differentiation, migration, and function of effector Th17 cells in disease development, highlighting the phenotypic and functional plasticity of Th17 lineage throughout the disease initiation, perpetuation and sustention. Furthermore, we emphasize the most recent advance in Th17 memory formation and function in the chronic course of dry eye disease, a major area to be better understood for facilitating the development of effective treatments in a broader field of autoimmune diseases that usually present a chronic course with recurrent episodes of flare in the target tissues or organs.

Age-related changes in ocular mucosal tolerance: Lessons learned from gut and respiratory tract immunity

The ocular surface is the part of the visual system directly exposed to the environment, and it comprises the cornea, the first refractive tissue layer and its surrounding structures. The ocular surface has evolved to keep the cornea smooth and wet, a prerequisite for proper sight, and also protected. To this aim, the ocular surface is a bona fide mucosal niche with an immune system capable of fighting against dangerous pathogens. However, due to the potential harmful effects of uncontrolled inflammation, the ocular surface has several mechanisms to keep the immune response in check. Specifically, the ocular surface is maintained inflammation-free and functional by a particular form of peripheral tolerance known as mucosal tolerance, markedly different from the immune privilege of intraocular structures. Remarkably, conjunctival tolerance is akin to the oral and respiratory tolerance mechanisms found in the gut and airways, respectively. And also similarly, this form of immunoregulation in the eye is affected by ageing just as it is in the digestive and respiratory tracts. With ageing comes an increased prevalence of immune-based ocular surface disorders, which could be related to an age-related impairment of conjunctival tolerance. The purpose of this review was to summarize the present knowledge of ocular mucosal tolerance and how it is affected by the ageing process in the light of the current literature on mucosal immunoregulation of the gut and airways.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

Retinoid Regulation of Ocular Surface Innate Inflammation

Corneal and conjunctival inflammation and dry eye develop in systemic vitamin A deficiency (VAD). The objective of this study was to investigate the lacrimal ocular surface retinoid axis, particularly immunomodulatory effects of retinoic acid (RA) and change in conjunctival myeloid cell number and phenotype in VAD. We discovered that ocular surface epithelial and myeloid cells express retinoid receptors. Both all trans- and 9-cis-RA suppressed production of dry eye relevant inflammatory mediators [interleukin(IL)-1β, IL-12, regulated upon activation, normal T cell expressed and secreted (RANTES)] by myeloid cells. Systemic VAD was associated with significant goblet cell loss and an increased number of CD45+ immune cells in the conjunctiva. MHCII^-CD11b⁺ classical monocytes were significantly increased in the conjunctiva of VAD C57BL/6 and RXR-α mutated Pinkie strains. RNA seq revealed significantly increased expression of innate immune/inflammatory genes in the Pinkie conjunctiva. These findings indicate that retinoids are essential for maintaining a healthy, well-lubricated ocular surface and have immunomodulatory effects in the conjunctiva that are mediated in part via RXR-α signaling. Perturbation of the homeostatic retinoid axis could potentiate inflammation on the ocular surface.

Rapamycin Eyedrops Increased CD4+Foxp3+ Cells and Prevented Goblet Cell Loss in the Aged Ocular Surface

Dry eye disease (DED), one of the most prevalent conditions among the elderly, is a chronic inflammatory disorder that disrupts tear film stability and causes ocular surface damage. Aged C57BL/6J mice spontaneously develop DED. Rapamycin is a potent immunosuppressant that prolongs the lifespan of several species. Here, we compared the effects of daily instillation of eyedrops containing rapamycin or empty micelles for three months on the aged mice. Tear cytokine/chemokine profile showed a pronounced increase in vascular endothelial cell growth factor-A (VEGF-A) and a trend towards decreased concentration of Interferon gamma (IFN)-γ in rapamycin-treated groups. A significant decrease in inflammatory markers in the lacrimal gland was also evident (IFN-γ, IL-12, CIITA and Ctss); this was accompanied by slightly diminished Unc-51 Like Autophagy Activating Kinase 1 (ULK1) transcripts. In the lacrimal gland and draining lymph nodes, we also observed a significant increase in the CD45⁺CD4⁺Foxp3⁺ cells in the rapamycin-treated mice. More importantly, rapamycin eyedrops increased conjunctival goblet cell density and area compared to the empty micelles. Taken together, evidence from these studies indicates that topical rapamycin has therapeutic efficacy for age-associated ocular surface inflammation and goblet cell loss and opens the venue for new investigations on its role in the aging process of the eye.

Modulation of Oxidative Stress and Inflammation in the Aged Lacrimal Gland

Inflammation and oxidative stress accompany aging. This study investigated the interplay between oxidative stress and inflammation in the lacrimal gland. C57BL/6 mice were used at 2 to 3, 12, and 24 months of age. Nuclear factor erythroid derived-2-related factor 2 (Nrf2)^-/- and corresponding wild-type mice were used at 2 to 3 and 12 to 13 months of age. A separate group of 15.5 to 17 months of age C57BL/6 mice received a diet containing an Nrf2 inducer (Oltipraz) for 8 weeks. Aged C57BL/6 lacrimal glands showed significantly greater lymphocytic infiltration, higher levels of MHC II, IFN-γ, IL-1β, TNF-α, and cathepsin S (Ctss) mRNA transcripts, and greater nitrotyrosine and 4-hydroxynonenal protein. Young Nrf2^-/- mice showed an increase in IL-1β, IFN-γ, MHC II, and Ctss mRNA transcripts compared with young wild-type mice and greater age-related changes at 12 to 13 months of age. Oltipraz diet significantly decreased nitrotyrosine and 4-hydroxynonenal and decreased the expression of IL-1β and TNF-α mRNA transcripts, while decreasing the frequency of CD45⁺CD4⁺ cells in lacrimal glands and significantly increasing conjunctival goblet cell density compared with a standard diet. The findings provide novel insight into the development of chronic, low-grade inflammation and oxidative stress in age-related dry eye. New therapies targeting oxidative stress pathways will be valuable in treating age-related dry eye.

Disease-Specific Expression of Conjunctiva Associated Lymphoid Tissue (CALT) in Mouse Models of Dry Eye Disease and Ocular Allergy

Conjunctiva-associated tissue (CALT) is assumed to play a crucial role in the immune system of the ocular surface. Its function in several ocular surface diseases (OSD) is still not fully understood. This study investigates the function of CALT in mouse models of dry-eye disease and ocular allergy. Since antigen-presentation is the central similarity in the pathologies, this study focuses on antigen-presentation in CALT Morphology and the expression of CALT, which was investigated in mice after induction of dry-eye, ocular allergy, topical antigen-stimulation, and after local depletion of phagocytic cells. Antigen uptake was investigated after the application of fluorescent ovalbumin (OVA). OSD influences the appearance and morphology of CALT in a disease-dependent manner. Ocular allergy leads to an increase and dry-eye disease to a decrease in number and size of CALT. The development of CALT is dependent on the presence of APCs. Professional APCs are present in CALT, and soluble antigen is transported into the follicle. CALT appearance is disease-specific and indicative of differing functions. Although the specific involvement of CALT in OSD needs further study, the existence of functional APCS and antigen-uptake supports the hypothesis that CALT is an immunological key player at the ocular surface.

Age-Dependent Decrease in the Induction of Regulatory T Cells Is Associated With Decreased Expression of RALDH2 in Mesenteric Lymph Node Dendritic Cells

A decline in immune function with aging has been reported. Regulatory T cell (Treg) induction is known to decrease with age, and elucidating the underlying mechanism is important for preventing age-related diseases due to age-related chronic inflammation. In the intestine, dendritic cells (DCs) play an important role in inducing Tregs specific to oral antigens, and they efficiently induce Tregs via production of retinoic acid (RA), a vitamin A metabolite, catalyzed by the enzyme retinaldehyde dehydrogenase 2 (RALDH2). We have previously reported that in the mesenteric lymph node (MLN), a secondary lymphoid tissue in which immune responses to oral antigens are induced, four DC subsets express different levels of CD11b, CD103, and PD-L1, and we have reported that the CD11b^–CD103⁺PD-L1^high subset expresses the highest levels of the RALDH2 gene and induces Tregs in vitro. We examined Treg induction in young and aged mice using a Treg induction model by administering a food antigen, and we found that antigen-specific Treg induction was decreased in aged mice. We further investigated the MLN DCs, and a significant decrease in RALDH2 gene expression was observed in MLN DCs from aged mice. As factors, we found that the proportion of the CD11b^–CD103⁺PD-L1^high subset was decreased in aged mice compared with that in young mice and that RALDH enzyme activity was decreased in the CD11b^–CD103⁺PD-L1^high and CD11b⁺CD103⁺PD-L1^high subsets. Furthermore, analysis of the methylation of the RALDH2 gene promoter region revealed that CpG motifs were more methylated in the MLN DCs of aged mice, suggesting that RALDH2 expression was suppressed by epigenetic changes. Finally, we found that RA treatment tended to increase Treg induction. These results suggest that the regulation of RA production may be involved in the age-related decrease in antigen-specific Treg induction.

Plasmacytoid dendritic cells in the eye

Plasmacytoid dendritic cells (pDCs) are a unique subpopulation of immune cells, distinct from classical dendritic cells. pDCs are generated in the bone marrow and following development, they typically home to secondary lymphoid tissues. While peripheral tissues are generally devoid of pDCs during steady state, few tissues, including the lung, kidney, vagina, and in particular ocular tissues harbor resident pDCs. pDCs were originally appreciated for their potential to produce large quantities of type I interferons in viral immunity. Subsequent studies have now unraveled their pivotal role in mediating immune responses, in particular in the induction of tolerance. In this review, we summarize our current knowledge on pDCs in ocular tissues in both mice and humans, in particular in the cornea, limbus, conjunctiva, choroid, retina, and lacrimal gland. Further, we will review our current understanding on the significance of pDCs in ameliorating inflammatory responses during herpes simplex virus keratitis, sterile inflammation, and corneal transplantation. Moreover, we describe their novel and pivotal neuroprotective role, their key function in preserving corneal angiogenic privilege, as well as their potential application as a cell-based therapy for ocular diseases.

Parity Attenuates Intraepithelial Corneal Sensory Nerve Loss in Female Mice

Aging impacts the ocular surface and reduces intraepithelial corneal nerve (ICN) density in male and female mice. Many researchers use retired breeders to study naturally aged female mice. Yet, the impact of parity and the length of time since breeders were retired on age-related changes in the intraepithelial corneal nerves is not known. Here we study 2 month (M) nulliparous (NP) females as well as 9M, 10M, and 11M NP and multiparous (MP) female mice to determine whether parity impacts the age-related decline seen in corneal axon density; 9M male mice are also included in these assessments. After showing that parity attenuates age-related loss in axon density, we also assess the impact of parity on corneal epithelial cell proliferation and find that it impacts cell proliferation and axon density normalized by cell proliferation. Stromal nerve arborization is also impacted by aging with parity enhancing stromal nerves in older mice. qPCR was performed on 20 genes implicated in ICN density using corneal epithelial RNA isolated from 10M NP and MP mice and showed that NGF expression was significantly elevated in MP corneal epithelium. Corneal sensitivity was significantly higher in 9M MP mice compared to NP mice and increased sensitivity in MP mice was accompanied by increased nerve terminals in the apical and middle cell layers. Together, these data show that parity in mice attenuates several aspects of the age-related decline seen on the ocular surface by retaining sensory axons and corneal sensitivity as mice age.

Comparative Analysis of Age-Related Changes in Lacrimal Glands and Meibomian Glands of a C57BL/6 Male Mouse Model

It is not known how biological changes in the lacrimal (LGs) and meibomian (MGs) glands contribute to dry eye disease (DED) in a time-dependent manner. In this study, we investigated time-sequenced changes in the inflammation, oxidative stress, and senescence of stem cells in both glands of an aging-related DED mouse model. Eight-week (8W)-, one-year (1Y)-, and two-year (2Y)-old C57BL/6 male mice were used. MG areas of the upper and lower eyelids were analyzed by transillumination meibography imaging. The number of CD45⁺, 8-OHdG⁺, Ki-67⁺, and BrdU⁺ cells was compared in both glands. Increased corneal staining and decreased tear secretion were observed in aged mice. The MG dropout area increased with aging, and the age-adjusted MG area in lower lids was negatively correlated with the National Eye Institute (NEI) score. Increased CD4⁺ interferon (IFN)-γ⁺ cells in LGs were found in both aged mice. An increase in 8-OHdG⁺ cells in both glands was evident in 2Y-old mice. Reduced Ki-67⁺ cells, but no change in CD45⁺ cells, was observed in the MGs of 1Y-old mice. Increased BrdU⁺ cells were observed in the LGs of aged mice. This suggests that age-dependent DED in C57BL/6 mice is related to inflammation of the LGs, the development of MG atrophy, and oxidative stress in both glands.

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.

Age-related Autoimmune Changes in Lacrimal Glands

Aging is a complex process associated with dysregulation of the immune system and low levels of inflammation, often associated with the onset of many pathologies. The lacrimal gland (LG) plays a vital role in the maintenance of ocular physiology and changes related to aging directly affect eye diseases. The dysregulation of the immune system in aging leads to quantitative and qualitative changes in antibodies and cytokines. While there is a gradual decline of the immune system, there is an increase in autoimmunity, with a reciprocal pathway between low levels of inflammation and aging mechanisms. Elderly C57BL/6J mice spontaneously show LGs infiltration that is characterized by Th1 but not Th17 cells. The aging of the LG is related to functional alterations, reduced innervation and decreased secretory activities. Lymphocytic infiltration, destruction, and atrophy of glandular parenchyma, ductal dilatation, and secretion of inflammatory mediators modify the volume and composition of tears. Oxidative stress, the capacity to metabolize and eliminate toxic substances decreased in aging, is also associated with the reduction of LG functionality and the pathogenesis of autoimmune diseases. Although further studies are required for a better understanding of autoimmunity and aging of the LG, we described anatomic and immunology aspects that have been described so far.