Resident Innate Immune Cells in the Cornea

Immune-Mediated Ocular Surface Disease in Diabetes Mellitus-Clinical Perspectives and Treatment: A Narrative Review

Diabetes mellitus (DM) is a chronic metabolic disorder marked by hyperglycemia due to defects in insulin secretion, action, or both, with a global prevalence that has tripled in recent decades. This condition poses significant public health challenges, affecting individuals, healthcare systems, and economies worldwide. Among its numerous complications, ocular surface disease (OSD) is a significant concern, yet understanding its pathophysiology, diagnosis, and management remains challenging. This review aims to explore the epidemiology, pathophysiology, clinical manifestations, diagnostic approaches, and management strategies of diabetes-related OSD. The ocular surface, including the cornea, conjunctiva, and associated structures, is vital for maintaining eye health, with the lacrimal functional unit (LFU) playing a crucial role in tear film regulation. In DM, changes in glycosaminoglycan metabolism, collagen synthesis, oxygen consumption, and LFU dysfunction contribute to ocular complications. Persistent hyperglycemia leads to the expression of cytokines, chemokines, and cell adhesion molecules, resulting in neuropathy, tear film abnormalities, and epithelial lesions. Recent advances in molecular research and therapeutic modalities, such as gene and stem cell therapies, show promise for managing diabetic ocular complications. Future research should focus on pathogenetically oriented therapies for diabetic neuropathy and keratopathy, transitioning from animal models to clinical trials to improve patient outcomes.

Immune Mechanisms of Filamentous Fungal Keratitis

Filamentous fungal keratitis is a particularly serious eye infection that often results in ulceration, corneal perforation, and blindness. The cornea acts as a natural barrier against harmful agents due to the close connection of its epithelial cells. In addition, on its surface, there is a large number of substances with anti-inflammatory and bactericidal properties, such as secretory IgA and mucin glycoproteins, and antimicrobial peptides (AMPs), such as human β-defensin 2 (HBD-2) and LL-37, which are especially increased in filamentous fungal keratitis. The interaction between pathogenic fungi and the host's immune mechanisms is a complex process: pathogen-associated molecular pattern (PAMP) molecules (chitin, β-glucan, and mannan) found in the fungal cell wall are recognized by pattern recognition receptors (PRRs) (toll-like receptors {TLRs}, C-type lectin receptors {CLRs}, nucleotide-binding oligomerization domain-like receptors {NLRs}, and scavenger receptors {SR}) found in host defense cells, triggering the secretion of various types of cytokines, such as interleukins (IL), tumor necrosis factors (TNFs), and chemokines, which recruit macrophages and neutrophils to migrate to the site of infection and activate inflammatory responses. In addition, the interaction of hyphae and corneal epithelial cells can activate cluster of differentiation (CD) 4+ T cells, CD8+ T cells, and B cells and induce secretion of T-helper (Th)-type cytokines 2 (IL-4 and IL-13) and IgG.

Objective Analysis of Corneal Nerves and Dendritic Cells

Corneal nerves and dendritic cells are increasingly being visualised to serve as clinical parameters in the diagnosis of ocular surface diseases using intravital confocal microscopy. In this review, different methods of image analysis are presented. The use of deep learning algorithms, which enable automated pattern recognition, is explained in detail using our own developments and compared with other established methods.

Collagen-Based Artificial Cornea for Lamellar Keratoplasty: An Early Case Report

PURPOSE

The aim of this study was to evaluate Viscoll collagen membrane (VCM) for lamellar keratoplasty.

METHODS

A 54-year-old man with grade 4 recurrent pterygium underwent lamellar keratoplasty using VCM as the graft material. Standard keratoplasty postoperative treatments, including topical antibiotic-corticosteroid and artificial tears, were administered.

RESULTS

Complete graft epithelialization was achieved after 4 days of the surgery. Follow-up at 9 months showed no pterygium recurrence as well as good integration of the VCM graft into the surrounding tissues with preserved transparency.

CONCLUSIONS

This case demonstrated that VCM possesses great potential as an alternative to the human donor cornea for lamellar keratoplasty; however, the application of VCM for lamellar keratoplasty still needs additional evaluation.

Conditional deletion of Zeb1 in Csf1r+ cells reduces inflammatory response of the cornea to alkali burn

ZEB1 is an essential factor in embryonic development. In adults, it is often highly expressed in malignant tumors with low expression in normal tissues. The major biological function of ZEB1 in developing embryos and progressing cancers is to transdifferentiate cells from an epithelial to mesenchymal phenotype; but what roles ZEB1 plays in normal adult tissues are largely unknown. We previously reported that the reduction of Zeb1 in monoallelic global knockout (Zeb1+/-) mice reduced corneal inflammation-associated neovascularization following alkali burn. To uncover the cellular mechanism underlying the Zeb1 regulation of corneal inflammation, we functionally deleted Zeb1 alleles in Csf1r+ myeloid cells using a conditional knockout (cKO) strategy and found that Zeb1 cKO reduced leukocytes in the cornea after alkali burn. The reduction of immune cells was due to their increased apoptotic rate and linked to a Zeb1-downregulated apoptotic pathway. We conclude that Zeb1 facilitates corneal inflammatory response by maintaining Csf1r+ cell viability.

Corneal Nerve Assessment by Aesthesiometry: History, Advancements, and Future Directions

The measurement of corneal sensation allows clinicians to assess the status of corneal innervation and serves as a crucial indicator of corneal disease and eye health. Many devices are available to assess corneal sensation, including the Cochet-Bonnet aesthesiometer, the Belmonte Aesthesiometer, the Swiss Liquid Jet Aesthesiometer, and the newly introduced Corneal Esthesiometer Brill. Increasing the clinical use of in vivo confocal microscopy and optical coherence tomography will allow for greater insight into the diagnosis, classification, and monitoring of ocular surface diseases such as neurotrophic keratopathy; however, formal esthesiometric measurement remains necessary to assess the functional status of corneal nerves. These aesthesiometers vary widely in their mode of corneal stimulus generation and their relative accessibility, precision, and ease of clinical use. The development of future devices to optimize these characteristics, as well as further comparative studies between device types should enable more accurate and precise diagnosis and treatment of corneal innervation deficits. The purpose of this narrative review is to describe the advancements in the use of aesthesiometers since their introduction to clinical practice, compare currently available devices for assessing corneal innervation and their relative limitations, and discuss how the assessment of corneal innervation is crucial to understanding and treating pathologies of the ocular surface.

A multi-ancestry GWAS of Fuchs corneal dystrophy highlights the contributions of laminins, collagen, and endothelial cell regulation

Fuchs endothelial corneal dystrophy (FECD) is a leading indication for corneal transplantation, but its molecular etiology remains poorly understood. We performed genome-wide association studies (GWAS) of FECD in the Million Veteran Program followed by multi-ancestry meta-analysis with the previous largest FECD GWAS, for a total of 3970 cases and 333,794 controls. We confirm the previous four loci, and identify eight novel loci: SSBP3, THSD7A, LAMB1, PIDD1, RORA, HS3ST3B1, LAMA5, and COL18A1. We further confirm the TCF4 locus in GWAS for admixed African and Hispanic/Latino ancestries and show an enrichment of European-ancestry haplotypes at TCF4 in FECD cases. Among the novel associations are low frequency missense variants in laminin genes LAMA5 and LAMB1 which, together with previously reported LAMC1, form laminin-511 (LM511). AlphaFold 2 protein modeling, validated through homology, suggests that mutations at LAMA5 and LAMB1 may destabilize LM511 by altering inter-domain interactions or extracellular matrix binding. Finally, phenome-wide association scans and colocalization analyses suggest that the TCF4 CTG18.1 trinucleotide repeat expansion leads to dysregulation of ion transport in the corneal endothelium and has pleiotropic effects on renal function.

Nerve-myeloid cell interactions in persistent human pain: a reappraisal using updated cell subset classifications

ABSTRACT

The past 20 years have seen a dramatic shift in our understanding of the role of the immune system in initiating and maintaining pain. Myeloid cells, including macrophages, dendritic cells, Langerhans cells, and mast cells, are increasingly implicated in bidirectional interactions with nerve fibres in rodent pain models. However, our understanding of the human setting is still poor. High-dimensional functional analyses have substantially changed myeloid cell classifications, with recently described subsets such as epidermal dendritic cells and DC3s unveiling new insight into how myeloid cells interact with nerve fibres. However, it is unclear whether this new understanding has informed the study of human chronic pain. In this article, we perform a scoping review investigating neuroimmune interactions between myeloid cells and peripheral nerve fibres in human chronic pain conditions. We found 37 papers from multiple pain states addressing this aim in skin, cornea, peripheral nerve, endometrium, and tumour, with macrophages, Langerhans cells, and mast cells the most investigated. The directionality of results between studies was inconsistent, although the clearest pattern was an increase in macrophage frequency across conditions, phases, and tissues. Myeloid cell definitions were often outdated and lacked correspondence with the stated cell types of interest; overreliance on morphology and traditional structural markers gave limited insight into the functional characteristics of investigated cells. We therefore critically reappraise the existing literature considering contemporary myeloid cell biology and advocate for the application of established and emerging high-dimensional proteomic and transcriptomic single-cell technologies to clarify the role of specific neuroimmune interactions in chronic pain.

Single cell analysis of short-term dry eye induced changes in cornea immune cell populations

Background

Dry eye causes corneal inflammation, epitheliopathy and sensorineural changes. This study evaluates the hypothesis that dry eye alters the percentages and transcriptional profiles of immune cell populations in the cornea.

Methods

Desiccating stress (DS) induced dry eye was created by pharmacologic suppression of tear secretion and exposure to drafty low humidity environment. Expression profiling of corneal immune cells was performed by single-cell RNA sequencing (scRNA-seq). Cell differentiation trajectories and cell fate were modeled through RNA velocity analysis. Confocal microscopy was used to immunodetect corneal immune cells. Irritation response to topical neurostimulants was assessed.

Results

Twelve corneal immune cell populations based on their transcriptional profiles were identified at baseline and consist of monocytes, resident (rMP) and MMP12/13 high macrophages, dendritic cells (cDC2), neutrophils, mast cells, pre T/B cells, and innate (γDT, ILC2, NK) and conventional T and B lymphocytes. T cells and resident macrophages (rMP) were the largest populations in the normal cornea comprising 18.6 and 18.2 percent, respectively. rMP increased to 55.2% of cells after 5 days of DS. Significant changes in expression of 1,365 genes (adj p < 0.0001) were noted in rMP with increases in cytokines and chemokines (Tnf, Cxcl1, Ccl12, Il1rn), inflammatory markers (Vcam, Adam17, Junb), the TAM receptor (Mertk), and decreases in complement and MHCII genes. A differentiation trajectory from monocytes to terminal state rMP was found. Phagocytosis, C-type lectin receptor signaling, NF-kappa B signaling and Toll-like receptor signaling were among the pathways with enhanced activity in these cells. The percentage of MRC1+ rMPs increased in the cornea and they were observed in the basal epithelium adjacent to epithelial nerve plexus. Concentration of the chemokine CXCL1 increased in the cornea and it heightened irritation/pain responses to topically applied hypertonic saline.

Conclusion

These findings indicate that DS recruits monocytes that differentiate to macrophages with increased expression of inflammation associated genes. The proximity of these macrophages to cornea nerves and their expression of neurosensitizers suggests they contribute to the corneal sensorineural changes in dry eye.

In vivo confocal microscopy evaluation of infiltrated immune cells in corneal stroma treated with cell therapy in advanced keratoconus

PURPOSE

This study investigates immune cell (ICs) infiltration in advanced keratoconus patients undergoing autologous adipose-derived adult stem cell (ADASC) therapy with recellularized human donor corneal laminas (CL).

METHODS

A prospective clinical trial included fourteen patients divided into three groups: G-1, ADASCs; G-2, decellularized CL (dCL); and G-3, dCL recellularized with ADASCs (ADASCs-rCL). Infiltrated ICs were assessed using in vivo confocal microscopy (IVCM) at 1,3,6, and12 months post-transplant.

RESULTS

Infiltrated ICs, encompassing granulocytes and agranulocytes, were observed across all groups, categorized by luminosity, structure, and area. Stromal ICs infiltration ranged from 1.19% to 6.62%, with a consistent increase in group-related cell density (F = 10.68, P < .0001), independent of post-op time (F = 0.77, P = 0.511); the most substantial variations were observed in G-3 at 6 and 12 months (2.0 and 1.87-fold, respectively). Similarly, significant size increases were more group-dependent (F = 5.76, P < .005) rather than time-dependent (F = 2.84, P < .05); G-3 exhibited significant increases at 6 and 12 months (3.70-fold and 2.52-fold, respectively). A lamina-induced shift in IC size occurred (F = 110.23, P < .0001), primarily with 50-100 μm2 sizes and up to larger cells > 300μm2, presumably macrophages, notably in G-3, indicating a potential role in tissue repair and remodeling, explaining reductions in cells remnants < 50μm2.

CONCLUSIONS

ADASCs-rCL therapy may lead to increased IC infiltration compared to ADASCs alone, impacting cell distribution and size due to the presence of the lamina. The findings reveal intricate immune patterns shaped by the corneal microenvironment and highlight the importance of understanding immune responses for the development of future therapeutic strategies.

Ocular mucosal homeostasis of teleost fish provides insight into the coevolution between microbiome and mucosal immunity

BACKGROUND

The visual organ plays a crucial role in sensing environmental information. However, its mucosal surfaces are constantly exposed to selective pressures from aquatic or airborne pathogens and microbial communities. Although few studies have characterized the conjunctival-associated lymphoid tissue (CALT) in the ocular mucosa (OM) of birds and mammals, little is known regarding the evolutionary origins and functions of immune defense and microbiota homeostasis of the OM in the early vertebrates.

RESULTS

Our study characterized the structure of the OM microbial ecosystem in rainbow trout (Oncorhynchus mykiss) and confirmed for the first time the presence of a diffuse mucosal-associated lymphoid tissue (MALT) in fish OM. Moreover, the microbial communities residing on the ocular mucosal surface contribute to shaping its immune environment. Interestingly, following IHNV infection, we observed robust immune responses, significant tissue damage, and microbial dysbiosis in the trout OM, particularly in the fornix conjunctiva (FC), which is characterized by the increase of pathobionts and a reduction of beneficial taxa in the relative abundance in OM. Critically, we identified a significant correlation between viral-induced immune responses and microbiome homeostasis in the OM, underscoring its key role in mucosal immunity and microbiota homeostasis.

CONCLUSIONS

Our findings suggest that immune defense and microbiota homeostasis in OM occurred concurrently in early vertebrate species, shedding light on the coevolution between microbiota and mucosal immunity. Video Abstract.

Effects of 1,25-Vitamin D3 and 24,25-Vitamin D3 on Corneal Nerve Regeneration in Diabetic Mice

Corneal nerve homeostasis is essential for the functional integrity of the ocular surface. Vitamin D deficiency (VDD) and vitamin D receptor knockout (VDR KO) have been found to reduce corneal nerve density in diabetic mice. This is the first study to comprehensively examine the influence of vitamin D on nerve regeneration following corneal epithelial injury in diabetic mice. Corneal nerve regeneration was significantly retarded by diabetes, VDR KO, and VDD, and it was accelerated following topical 1,25 Vit D and 24,25 Vit D administration. Furthermore, topical 1,25 Vit D and 24,25 Vit D increased nerve growth factor, glial cell line-derived neurotropic factor, and neurotropin-3 protein expression, and it increased secretion of GDNF protein from human corneal epithelial cells. CD45+ cells and macrophage numbers were significantly decreased, and vitamin D increased CD45+ cell and macrophage recruitment in these wounded diabetic mouse corneas. The accelerated nerve regeneration observed in these corneas following topical 1,25 Vit D and 24,25 Vit D administration may be related to the vitamin D-stimulated expression, secretion of neurotrophic factors, and recruitment of immune cells.

Neurotrophic keratitis: inflammatory pathogenesis and novel therapies

PURPOSE OF REVIEW

Neurotrophic keratitis is a rare degenerative disease characterized by decrease or absence of corneal sensation. Neurotrophic keratitis varies from mild forms with mild epitheliopathy to severe manifestations such as corneal ulceration, melting and perforation that can lead to irreversible visual loss. The cause of neurotrophic keratitis comprises a long list of diseases, medications, congenital or genetic conditions as well as trauma. The mechanism of neurotrophic keratitis is complex and multifactorial and its understanding is crucial to better address the treatment strategies. We aimed to review neurotrophic keratitis pathology, mechanisms and management.

RECENT FINDINGS

Corneal nerves are critical for the homeostasis of a healthy ocular surface. The lack of nerve-derived neuromediators and corneal-released neuropeptides, neuro-trophins and neurotrophic factors in neurotrophic keratitis leads to a decrease in trophic supply to corneal cells in addition to a decrease in afferent signaling to the brain. This results in pathological tear secretion, decreased blinking rate, corneal healing along with ocular surface and corneal inflammation. Lately, nerve growth factor in special gained emphasis as a treatment strategy targeting the disease mechanism rather than its manifestations. Other therapies, including surgical interventions, are in the pipeline of neurotrophic keratitis management. However, there are still no proper therapeutic guidelines and neurotrophic keratitis treatment remains challenging.

SUMMARY

Neurotrophic keratitis may have a devastating outcome and treatment is still challenging. Understanding the disease pathology may assist in the development of new treatment strategies. Prompt disease recognition and immediate intervention are key factors to promote corneal healing and avoid further deterioration.

Interleukin-11 Suppresses Ocular Surface Inflammation and Accelerates Wound Healing

Purpose

Regulation of inflammation is critical for achieving favorable outcomes in wound healing. In this study, we determine the functional role and mechanism of action of IL-11, an immunomodulatory cytokine, in regulating inflammatory response at the ocular surface.

Methods

Corneal injury was induced by mechanical removal of the epithelium and anterior stroma using an AlgerBrush II. Transcript and protein levels of IL-11 in injured cornea were quantified using real-time PCR and ELISA analysis. Corneal inflammation was assessed by measuring frequencies of total CD45+ inflammatory cells, CD11b+Ly6G+ polymorphonuclear cells (neutrophils), and CD11b+Ly6G- mononuclear cells (macrophages, monocytes) at the ocular surface using flow cytometry. To assess the effect of IL-11 on innate immune cell function, cell activation marker and inflammatory cytokines including major histocompatibility complex (MHC) class II, myeloperoxidase (MPO), TNFα, and inducible nitric oxide synthase (iNOS) were measured following recombinant IL-11 treatment (1 µg/mL). Injured corneas were topically treated with IL-11 (1 µg/mL), and wound healing was evaluated using corneal fluorescein staining.

Results

Corneal injury resulted in increased levels of IL-11 in the cornea, particularly in the stroma. Neutrophils and CD11b+ mononuclear cells (macrophages, monocytes) substantially expressed IL-11 receptor. Interestingly, IL-11 significantly downregulated the activation of immune cells, as evidenced by the lower expression of MHC II and TNFα by CD11b+ mononuclear cells and lower levels of MPO by neutrophils. Topical administration of IL-11 to injured corneas led to faster wound healing and better retention of tissue architecture.

Conclusions

Our findings demonstrate IL-11 is a key modulator of ocular surface inflammation and provide novel evidence of IL-11 as a potential therapeutic to control inflammatory damage and accelerate wound repair following injury.

Single-Cell Transcriptomics Reveals Cellular Heterogeneity and Complex Cell-Cell Communication Networks in the Mouse Cornea

Purpose

To generate a single-cell RNA-sequencing (scRNA-seq) map and construct cell-cell communication networks of mouse corneas.

Methods

C57BL/6 mouse corneas were dissociated to single cells and subjected to scRNA-seq. Cell populations were clustered and annotated for bioinformatic analysis using the R package "Seurat." Differential expression patterns were validated and spatially mapped with whole-mount immunofluorescence staining. Global intercellular signaling networks were constructed using CellChat.

Results

Unbiased clustering of scRNA-seq transcriptomes of 14,732 cells from 40 corneas revealed 17 cell clusters of six major cell types: nine epithelial cell, three keratocyte, two corneal endothelial cell, and one each of immune cell, vascular endothelial cell, and fibroblast clusters. The nine epithelial cell subtypes included quiescent limbal stem cells, transit-amplifying cells, and differentiated cells from corneas and two minor conjunctival epithelial clusters. CellChat analysis provided an atlas of the complex intercellular signaling communications among all cell types.

Conclusions

We constructed a complete single-cell transcriptomic map and the complex signaling cross-talk among all cell types of the cornea, which can be used as a foundation atlas for further research on the cornea. This study also deepens the understanding of the cellular heterogeneity and heterotypic cell-cell interaction within corneas.

Ocular Surface Allostasis-When Homeostasis Is Lost: Challenging Coping Potential, Stress Tolerance, and Resilience

The loss of ocular surface (OS) homeostasis characterizes the onset of dry eye disease. Resilience defines the ability to withstand this threat, reflecting the ability of the ocular surface to cope with and bounce back after challenging events. The coping capacity of the OS defines the ability to successfully manage cellular stress. Cellular stress, which is central to the outcome of the pathophysiology of dry eye disease, is characterized by intensity, continuity, and receptivity, which lead to the loss of homeostasis, resulting in a phase of autocatalytic dysregulation, an event that is not well-defined. To better define this event, here, we present a model providing a potential approach when homeostasis is challenged and the coping capacities have reached their limits, resulting in the stage of heterostasis, in which the dysregulated cellular stress mechanisms take over, leading to dry eye disease. The main feature of the proposed model is the concept that, prior to the initiation of the events leading to cellular stress, there is a period of intense activation of all available coping mechanisms preventing the imminent dysregulation of ocular surface homeostasis. When the remaining coping mechanisms and resilience potential have been maximally exploited and have, finally, been exceeded, there will be a transition to manifest disease with all the well-known signs and symptoms, with a shift to allostasis, reflecting the establishment of another state of balance. The intention of this review was to show that it is possibly the phase of heterostasis preceding the establishment of allostasis that offers a better chance for therapeutic intervention and optimized recovery. Once allostasis has been established, as a new steady-state of balance at a higher level of constant cell stress and inflammation, treatment may be far more difficult, and the potential for reversal is drastically decreased. Homeostasis, once lost, can possibly not be fully recovered. The processes established during heterostasis and allostasis require different approaches and treatments for their control, indicating that the current treatment options for homeostasis need to be adapted to a more-demanding situation. The loss of homeostasis necessarily implies the establishment of a new balance; here, we refer to such a state as allostasis.

Redefining the human corneal immune compartment using dynamic intravital imaging

The healthy human cornea is a uniquely transparent sensory tissue where immune responses are tightly controlled to preserve vision. The cornea contains immune cells that are widely presumed to be intraepithelial dendritic cells (DCs). Corneal immune cells have diverse cellular morphologies and morphological alterations are used as a marker of inflammation and injury. Based on our imaging of corneal T cells in mice, we hypothesized that many human corneal immune cells commonly defined as DCs are intraepithelial lymphocytes (IELs). To investigate this, we developed functional in vivo confocal microscopy (Fun-IVCM) to investigate cell dynamics in the human corneal epithelium and stroma. We show that many immune cells resident in the healthy human cornea are T cells. These corneal IELs are characterized by rapid, persistent motility and interact with corneal DCs and sensory nerves. Imaging deeper into the corneal stroma, we show that crawling macrophages and rare motile T cells patrol the tissue. Furthermore, we identify altered immune cell behaviors in response to short-term contact lens wear (acute inflammatory stimulus), as well as in individuals with allergy (chronic inflammatory stimulus) that was modulated by therapeutic intervention. These findings redefine current understanding of immune cell subsets in the human cornea and reveal how resident corneal immune cells respond and adapt to chronic and acute stimuli.

Effects of Topical 1,25 and 24,25 Vitamin D on Diabetic, Vitamin D Deficient and Vitamin D Receptor Knockout Mouse Corneal Wound Healing

Delayed or prolonged corneal wound healing and non-healing corneas put patients at risk for ocular surface infections and subsequent stromal opacification, resulting in discomfort or visual loss. It is important to enhance corneal wound healing efficiency and quality. Vitamin D (Vit D) is both a hormone and a vitamin, and its insufficiency has been linked to immune disorders and diabetes. For this study, wound healing and recruitment of CD45+ cells into the wound area of normoglycemic and diabetic mice were examined following corneal epithelial debridement and treatment with 1,25-dihyroxyvitamin D (1,25 Vit D) or 24,25-dihydroxyvitamin D (24,25 Vit D). Treatment with topical 1,25-dihyroxyvitamin D (1,25 Vit D) resulted in significantly increased corneal wound healing rates of normoglycemic, diabetic and diabetic Vit D deficient mice. Furthermore, 24,25-dihydroxyvitamin D (24,25 Vit D) significantly increased corneal wound healing of diabetic Vit D deficient and Vit D receptor knockout (VDR KO) mice. In addition, CD45+ cell numbers were reduced in diabetic and VDR KO mouse corneas compared to normoglycemic mice, and 24,25 Vit D increased the recruitment of CD45+ cells to diabetic mouse corneas after epithelial debridement. CD45+ cells were found to infiltrate into the corneal basal epithelial layer after corneal epithelial debridement. Our data indicate that topical Vit D promotes corneal wound healing and further supports previous work that the Vit D corneal wound healing effect is not totally VDR-dependent.

Multi-ancestry GWAS of Fuchs corneal dystrophy highlights roles of laminins, collagen, and endothelial cell regulation

Fuchs endothelial corneal dystrophy (FECD) is a leading indication for corneal transplantation, but its molecular pathophysiology remains poorly understood. We performed genome-wide association studies (GWAS) of FECD in the Million Veteran Program (MVP) and meta-analyzed with the previous largest FECD GWAS, finding twelve significant loci (eight novel). We further confirmed the TCF4 locus in admixed African and Hispanic/Latino ancestries, and found an enrichment of European-ancestry haplotypes at TCF4 in FECD cases. Among the novel associations are low frequency missense variants in laminin genes LAMA5 and LAMB1 which, together with previously reported LAMC1, form laminin-511 (LM511). AlphaFold 2 protein modeling suggests that mutations at LAMA5 and LAMB1 may destabilize LM511 by altering inter-domain interactions or extracellular matrix binding. Finally, phenome-wide association scans and co-localization analyses suggest that the TCF4 CTG18.1 trinucleotide repeat expansion leads to dysregulation of ion transport in the corneal endothelium and has pleiotropic effects on renal function.

Novel ocular immunotherapy induces tumor regression in an equine model of ocular surface squamous neoplasia

Ocular surface squamous neoplasia (OSSN) is the major cause of corneal cancer in man and horses worldwide, and the prevalence of OSSN is increasing due to greater UVB exposure globally. Currently, there are no approved treatments for OSSN in either species, and most patients are managed with surgical excision or off-label treatment with locally injected interferon alpha, or topically applied cytotoxic drugs such as mitomycin C. A more broadly effective and readily applied immunotherapy could exert a significant impact on management of OSSN worldwide. We therefore evaluated the effectiveness of a liposomal TLR complex (LTC) immunotherapy, which previously demonstrated strong antiviral activity in multiple animal models following mucosal application, for ocular antitumor activity in a horse spontaneous OSSN model. In vitro studies demonstrated strong activation of interferon responses in horse leukocytes by LTC and suppression of OSSN cell growth and migration. In a trial of 8 horses (9 eyes), treatment with topical or perilesional LTC resulted in an overall tumor response rate of 67%, including durable regression of large OSSN tumors. Repeated treatment with LTC ocular immunotherapy was also very well tolerated clinically. We conclude therefore that ocular immunotherapy with LTC warrants further investigation as a novel approach to management of OSSN in humans.

Mesenchymal Stem Cell Exosomes as Immunomodulatory Therapy for Corneal Scarring

Corneal scarring is a leading cause of worldwide blindness. Human mesenchymal stem cells (MSC) have been reported to promote corneal wound healing through secreted exosomes. This study investigated the wound healing and immunomodulatory effects of MSC-derived exosomes (MSC-exo) in corneal injury through an established rat model of corneal scarring. After induction of corneal scarring by irregular phototherapeutic keratectomy (irrPTK), MSC exosome preparations (MSC-exo) or PBS vehicle as controls were applied to the injured rat corneas for five days. The animals were assessed for corneal clarity using a validated slit-lamp haze grading score. Stromal haze intensity was quantified using in-vivo confocal microscopy imaging. Corneal vascularization, fibrosis, variations in macrophage phenotypes, and inflammatory cytokines were evaluated using immunohistochemistry techniques and enzyme-linked immunosorbent assays (ELISA) of the excised corneas. Compared to the PBS control group, MSC-exo treatment group had faster epithelial wound closure (0.041), lower corneal haze score (p = 0.002), and reduced haze intensity (p = 0.004) throughout the follow-up period. Attenuation of corneal vascularisation based on CD31 and LYVE-1 staining and reduced fibrosis as measured by fibronectin and collagen 3A1 staining was also observed in the MSC-exo group. MSC-exo treated corneas also displayed a regenerative immune phenotype characterized by a higher infiltration of CD163+, CD206+ M2 macrophages over CD80+, CD86+ M1 macrophages (p = 0.023), reduced levels of pro-inflammatory IL-1β, IL-8, and TNF-α, and increased levels of anti-inflammatory IL-10. In conclusion, topical MSC-exo could alleviate corneal insults by promoting wound closure and reducing scar development, possibly through anti-angiogenesis and immunomodulation towards a regenerative and anti-inflammatory phenotype.

A temporal single cell transcriptome atlas of zebrafish anterior segment development

Anterior segment dysgenesis (ASD), resulting in vision impairment, stems from maldevelopment of anterior segment (AS) tissues. Incidence of ASD has been linked to malfunction of periocular mesenchyme cells (POM). POM cells specify into anterior segment mesenchyme (ASM) cells which colonize and produce AS tissues. In this study we uncover ASM developmental trajectories associated with formation of the AS. Using a transgenic line of zebrafish that fluorescently labels the ASM throughout development, Tg[foxc1b:GFP], we isolated GFP+ ASM cells at several developmental timepoints (48-144 hpf) and performed single cell RNA sequencing. Clustering analysis indicates subdifferentiation of ASM as early as 48 hpf and subsequent diversification into corneal epithelium/endothelium/stroma, or annular ligament (AL) lineages. Tracking individual clusters reveals common developmental pathways, up to 72 hpf, for the AL and corneal endothelium/stroma and distinct pathways for corneal epithelium starting at 48 hpf. Spatiotemporal validation of over 80 genes found associated with AS development demonstrates a high degree of conservation with mammalian trabecular meshwork and corneal tissues. In addition, we characterize thirteen novel genes associated with annular ligament and seven with corneal development. Overall, the data provide a molecular verification of the long-standing hypothesis that POM derived ASM give rise to AS tissues and highlight the high degree of conservation between zebrafish and mammals.

Glabridin Inhibits Aspergillus fumigatus Growth and Alleviate Inflammation Mediated by Dectin-2 and NLRP3 Inflammasome

PURPOSE

The research was used to uncover the mechanism of glabridin in Aspergillus fumigatus keratitis in anti-fungus and anti-inflammation.

METHODS

In vitro, RAW 264.7 cells were infected with A. fumigatus with incubation of glabridin in different concentrations. Real-time quantitative polymerase chain reaction (RT‑qPCR), Western blot, and enzyme-linked immunosorbent assay (ELISA) were used to assess the inflammatory severe and alternation with the intervention of Dectin-2 siRNA and glabridin. In vivo, A. fumigatus keratitis mouse models were established by spore intra-stromal injection and treated with glabridin or PBS. And disease scores, inflammatory mediators, and periodic acid-schiff (PAS) staining were exhibited to demonstrate the therapeutic efficiency of glabridin in vivo. Morphological interference assay monitored fungal germination. Scanning and transmission electron microscopy were used to observe the growth of fungi.

RESULTS

In RAW 264.7 cells and mouse keratitis models, noncytotoxic 16 μg/mL glabridin showed significant inhibition in the expression of Dectin-2, NLRP3, Caspase-1, IL-1β, and TNF-α after A. fumigatus infection, almost similar to the intervention of Dectin-2 siRNA. PAS staining illustrated the reduced hyphal distribution in cornea stroma with glabridin treatment. Glabridin remarkably inhibited A. fumigatus growth through delaying germination and disrupting the integrity of the hyphae membrane.

CONCLUSION

Glabridin plays an anti-inflammatory role in A. fumigatus challenge via suppression of the Dectin-2 and NLRP3 inflammasome, and plays an anti-fungal role through delaying germination and changing the hyphal integrity.KEY MESSAGESGlabridin plays an anti-inflammatory role in A. fumigatus infection of RAW264.7 cells in a concentration-dependent manner and through Dectin-2 mediation.Glabridin decreases fungal distribution and inflammation in mouse A. fumigatus keratitis.Glabridin inhibits A. fumigatus growth by delaying germination and disrupting cellular structure in vitro.

Laser-induced microinjury of the corneal basal epithelium and imaging of resident macrophage responses in a live, whole-eye preparation

The corneal epithelium is continuously subjected to external stimuli that results in varying degrees of cellular damage. The use of live-cell imaging approaches has facilitated understanding of the cellular and molecular mechanisms underlying the corneal epithelial wound healing process. Here, we describe a live, ex vivo, whole-eye approach using laser scanning confocal microscopy to simultaneously induce and visualize short-term cellular responses following microdamage to the corneal epithelium. Live-cell imaging of corneal cell layers was enabled using the lipophilic fluorescent dyes, SGC5 or FM4-64, which, when injected into the anterior chamber of enucleated eyes, readily penetrated and labelled cell membranes. Necrotic microdamage to a defined region (30 μm x 30 μm) through the central plane of the corneal basal epithelium was induced by continuously scanning for at least one minute using high laser power and was dependent on the presence of lipophilic fluorescent dye. This whole-mount live-cell imaging and microdamage approach was used to examine the behavior of Cx3cr1:GFP-expressing resident corneal stromal macrophages (RCSMs). In undamaged corneas, RCSMs remained stationary, but exhibited a constant extension and retraction of short (~5 μm) semicircular, pseudopodia-like processes reminiscent of what has previously been reported in corneal dendritic cells. Within minutes of microdamage, nearby anterior RCSMs became highly polarized and extended projections towards the damaged region. The extension of the processes plateaued after about 30 minutes and remained stable over the course of 2-3 hours of imaging. Retrospective immunolabeling showed that these responding RCSMs were MHC class II+. This study adds to existing knowledge of immune cell behavior in response to corneal damage and introduces a simple corneal epithelial microdamage and wound healing paradigm.

A synthetic tear protein resolves dry eye through promoting corneal nerve regeneration

Corneal architecture is essential for vision and is greatly perturbed by the absence of tears due to the highly prevalent disorder dry eye. With no regenerative therapies available, pathological alterations of the ocular surface in response to dryness, including persistent epithelial defects and poor wound healing, result in life-long morbidity. Here, using a mouse model of aqueous-deficient dry eye, we reveal that topical application of the synthetic tear protein Lacripep reverses the pathological outcomes of dry eye through restoring the extensive network of corneal nerves that are essential for tear secretion, barrier function, epithelial homeostasis, and wound healing. Intriguingly, the restorative effects of Lacripep occur despite extensive immune cell infiltration, suggesting tissue reinnervation and regeneration can be achieved under chronic inflammatory conditions. In summary, our data highlight Lacripep as a first-in-class regenerative therapy for returning the cornea to a near homeostatic state in individuals who suffer from dry eye.

Currently, there are no regenerative treatments for ocular pathologies due to dry eye. Efraim et al. demonstrate the synthetic tear peptide Lacripep as a regenerative therapy capable of restoring the damaged, dysfunctional ocular surface to a near homeostatic state through promoting nerve regeneration in the presence of chronic inflammation.

Molecular Characteristics and Distribution of Adult Human Corneal Immune Cell Types

Background

The limbus is located at a 2-mm-wide area between the bulbar conjunctiva and the cornea and has been suggested to be the niche of corneal epithelial stem cells and immune cells. Like the skin and intestines, the cornea is also an important mucosal surface, and immune cells on the cornea play critical roles in immune surveillance to ensure barrier surface homeostasis and protection from various environmental damage and infections. Single-cell RNA sequencing (scRNA-seq) analysis of protein tyrosine phosphatase receptor type C positive (PTPRC⁺) hematopoietic cells from the corneal limbus could provide a single cell atlas of all the immune cell subsets.

Methods

We performed single-cell RNA sequencing to generate transcriptomic profile for 804 sort-purified hematopoietic cells from the corneal limbus of three healthy donors.

Results

Our analysis identified a primary transcriptomic pattern for multiple immune cell subtypes, including naive T cells, antiviral effector CD8⁺ T cells, and innate immune cells such as IDO1⁺ mature regulatory dendritic cells (mregDCs), macrophages, monocytes, and basophils in the human corneal limbus.

Conclusion

Overall, single-cell transcriptomic analysis of limbal immune cells suggested the possible contribution of these cells on the adaptive and innate immune response of the human cornea.

TRPV1+ sensory nerves modulate corneal inflammation after epithelial abrasion via RAMP1 and SSTR5 signaling

Timely initiation and termination of inflammatory response after corneal epithelial abrasion is critical for the recovery of vision. The cornea is innervated with rich sensory nerves with highly dense TRPV1 nociceptors. However, the roles of TRPV1⁺ sensory neurons in corneal inflammation after epithelial abrasion are not completely understood. Here, we found that depletion of TRPV1⁺ sensory nerves using resiniferatoxin (RTX) and blockade of TRPV1 using AMG-517 delayed corneal wound closure and enhanced the infiltration of neutrophils and γδ T cells to the wounded cornea after epithelial abrasion. Furthermore, depletion of TRPV1⁺ sensory nerves increased the number and TNF-α production of corneal CCR2⁺ macrophages and decreased the number of corneal CCR2^- macrophages and IL-10 production. In addition, the TRPV1⁺ sensory nerves inhibited the recruitment of neutrophils and γδ T cells to the cornea via RAMP1 and SSTR5 signaling, decreased the responses of CCR2⁺ macrophages via RAMP1 signaling, and increased the responses of CCR2^- macrophages via SSTR5 signaling. Collectively, our results suggest that the TRPV1⁺ sensory nerves suppress inflammation to support corneal wound healing via RAMP1 and SSTR5 signaling, revealing potential approaches for improving defective corneal wound healing in patients with sensory neuropathy.

The effect of topical decorin on temporal changes to corneal immune cells after epithelial abrasion

BACKGROUND

Corneal immune cells interact with corneal sensory nerves during both homeostasis and inflammation. This study sought to evaluate temporal changes to corneal immune cell density in a mouse model of epithelial abrasion and nerve injury, and to investigate the immunomodulatory effects of topical decorin, which we have shown previously to promote corneal nerve regeneration.

METHODS

Bilateral corneal epithelial abrasions (2 mm) were performed on C57BL/6J mice. Topical decorin or saline eye drops were applied three times daily for 12 h, 24 h, 3 days or 5 days. Optical coherence tomography imaging was performed to measure the abrasion area. The densities of corneal sensory nerves (β-tubulin III) and immune cells, including dendritic cells (DCs; CD11c⁺), macrophages (Iba-1⁺) and neutrophils (NIMP-R14⁺) were measured. Cx3cr1^gfp/gfp mice that spontaneously lack resident corneal intraepithelial DCs were used to investigate the specific contribution of epithelial DCs. Neuropeptide and cytokine gene expression was evaluated using qRT-PCR at 12 h post-injury.

RESULTS

In decorin-treated corneas, higher intraepithelial DC densities and lower neutrophil densities were observed at 24 h after injury, compared to saline controls. At 12 h post-injury, topical decorin application was associated with greater re-epithelialisation. At 5 days post-injury, corneal stromal macrophage density in the decorin-treated and contralateral eyes was lower, and nerve density was higher, compared to eyes treated with saline only. Lower expression of transforming growth factor beta (TGF-β) and higher expression of CSPG4 mRNA was detected in corneas treated with topical decorin. There was no difference in corneal neutrophil density in Cx3cr1^gfp/gfp mice treated with or without decorin at 12 h.

CONCLUSIONS

Topical decorin regulates immune cell dynamics after corneal injury, by inhibiting neutrophils and recruiting intraepithelial DCs during the acute phase (< 24 h), and inhibiting macrophage density at the study endpoint (5 days). These immunomodulatory effects were associated with faster re-epithelialisation and likely contribute to promoting sensory nerve regeneration. The findings suggest a potential interaction between DCs and neutrophils with topical decorin treatment, as the decorin-induced neutrophil inhibition was absent in Cx3cr1^gfp/gfp mice that lack corneal epithelial DCs. TGF-β and CSPG4 proteoglycan likely regulate decorin-mediated innate immune cell responses and nerve regeneration after injury.

Immunohistochemical staining of immunoglobulin G in healthy equine, canine, and feline corneas

Objective

Establishing an immunohistochemical approach for semi‐quantitative assessment of the presence of immunoglobulin G (IgG) in equine, canine, and feline corneas.

Procedures

Healthy corneas of horses, dogs, and cats, euthanized because of a fatal disease or an unrecoverable trauma unrelated to and without a history of ophthalmic disease were formalin‐fixed, paraffin‐embedded, and determined to be pathomorphologically healthy by light microscopy. Automated immunohistochemistry was performed using primary antibodies against IgG, biotin‐conjugated secondary antibodies, and streptavidin‐peroxidase, as well as diaminobenzidine for visualization. After counterstaining with hematoxylin, epithelium, stroma, Descemet´s membrane (DM), and endothelium were semi‐quantitatively scored for the presence of IgG on a 4‐grade scale (0 = no, 1 = faint, 2 = medium, 3 = strong staining) by light microscopy.

Results

Corneal specimens of 20 horses (40 eyes) with a median age of 15.5 years (range 2–31 years), 12 dogs (21 eyes) with a median age of 10.0 years (range 4–16), and 13 cats (24 eyes) with a median age of 10.0 years (range 2–18) were included in the study. Different sexes and breeds were represented. In all corneas (100%), significant medium signal intensity in the stroma was observed. Variable immunosignal was obtained in epithelium, DM, and endothelium.

Conclusion

This method reproducibly allows for the detection of IgG in healthy equine, canine, and feline corneas, particularly stroma. Semi‐quantitative results evidence medium presence of IgG in the corneal stroma. Further research is needed to evaluate IgG presence in diseased corneas.

Autophagy in Extracellular Matrix and Wound Healing Modulation in the Cornea

Autophagy is a robust cellular mechanism for disposing of harmful molecules or recycling them to cells, which also regulates physiopathological processes in cornea. Dysregulated autophagy causes inefficient clearance of unwanted proteins and cellular debris, mitochondrial disorganization, defective inflammation, organ dysfunctions, cell death, and diseases. The cornea accounts for two-thirds of the refraction of light that occurs in the eyes, but is prone to trauma/injury and infection. The extracellular matrix (ECM) is a noncellular dynamic macromolecular network in corneal tissues comprised of collagens, proteoglycans, elastin, fibronectin, laminins, hyaluronan, and glycoproteins. The ECM undergoes remodeling by matrix-degrading enzymes and maintains corneal transparency. Autophagy plays an important role in the ECM and wound healing maintenance. Delayed/dysregulated autophagy impacts the ECM and wound healing, and can lead to corneal dysfunction. Stromal wound healing involves responses from the corneal epithelium, basement membrane, keratocytes, the ECM, and many cytokines and chemokines, including transforming growth factor beta-1 and platelet-derived growth factor. Mild corneal injuries self-repair, but greater injuries lead to corneal haze/scars/fibrosis and vision loss due to disruptions in the ECM, autophagy, and normal wound healing processes. Presently, the precise role of autophagy and ECM remodeling in corneal wound healing is elusive. This review discusses recent trends in autophagy and ECM modulation in the context of corneal wound healing and homeostasis.

Regulation of Limbal Epithelial Stem Cells: Importance of the Niche

Limbal epithelial stem/progenitor cells (LSCs) reside in a niche that contains finely tuned balances of various signaling pathways including Wnt, Notch, BMP, Shh, YAP, and TGFβ. The activation or inhibition of these pathways is frequently dependent on the interactions of LSCs with various niche cell types and extracellular substrates. In addition to receiving molecular signals from growth factors, cytokines, and other soluble molecules, LSCs also respond to their surrounding physical structure via mechanotransduction, interaction with the ECM, and interactions with other cell types. Damage to LSCs or their niche leads to limbal stem cell deficiency (LSCD). The field of LSCD treatment would greatly benefit from an understanding of the molecular regulation of LSCs in vitro and in vivo. This review synthesizes current literature around the niche factors and signaling pathways that influence LSC function. Future development of LSCD therapies should consider all these niche factors to achieve improved long-term restoration of the LSC population.

Wound healing of the corneal epithelium: a review

The corneal epithelium (CE) forms the outermost layer of the cornea. Despite its thickness of only 50 μm, the CE plays a key role as an initial barrier against any insults to the eye and contributes to the light refraction onto the retina required for clear vision. In the event of an injury, the cornea is equipped with many strategies contributing to competent wound healing, including angiogenic and immune privileges, and mechanotransduction. Various factors, including growth factors, keratin, cytokines, integrins, crystallins, basement membrane, and gap junction proteins are involved in CE wound healing and serve as markers in the healing process. Studies of CE wound healing are advancing rapidly in tandem with the rise of corneal bioengineering, which employs limbal epithelial stem cells as the primary source of cells utilizing various types of biomaterials as substrates.

Short-Term High Fructose Intake Impairs Diurnal Oscillations in the Murine Cornea

Purpose

Endogenous and exogenous stressors, including nutritional challenges, may alter circadian rhythms in the cornea. This study aimed to determine the effects of high fructose intake (HFI) on circadian homeostasis in murine cornea.

Methods

Corneas of male C57BL/6J mice subjected to 10 days of HFI (15% fructose in drinking water) were collected at 3-hour intervals over a 24-hour circadian cycle. Total extracted RNA was subjected to high-throughput RNA sequencing. Rhythmic transcriptional data were analyzed to determine the phase, rhythmicity, unique signature, metabolic pathways, and cell signaling pathways of transcripts with temporally coordinated expression. Corneas of HFI mice were collected for whole-mounted techniques after immunofluorescent staining to quantify mitotic cell number in the epithelium and trafficking of neutrophils and γδ-T cells to the limbal region over a circadian cycle.

Results

HFI significantly reprogrammed the circadian transcriptomic profiles of the normal cornea and reorganized unique temporal and clustering enrichment pathways, but did not affect core-clock machinery. HFI altered the distribution pattern and number of corneal epithelial mitotic cells and enhanced recruitment of neutrophils and γδ-T cell immune cells to the limbus across a circadian cycle. Cell cycle, immune function, metabolic processes, and neuronal-related transcription and associated pathways were altered in the corneas of HFI mice.

Conclusions

HFI significantly reprograms diurnal oscillations in the cornea based on temporal and spatial distributions of epithelial mitosis, immune cell trafficking, and cell signaling pathways. Our findings reveal novel molecular targets for treating pathologic alterations in the cornea after HFI.