The Corneal Basement Membranes and Stromal Fibrosis

In Vitro and Ex Vivo Models of Microbial Keratitis: Present and Future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Restoration of corneal epithelial barrier function: A possible target for corneal neovascularization

Corneal neovascularization (CoNV) is the second leading common cause of vision impairment worldwide and is a blinding pathological alteration brought on by ocular trauma, infection, and other factors. There are some limitations in the treatment of CoNV, hence it's critical to look into novel therapeutic targets. The corneal epithelial barrier, which is the initial barrier of the ocular surface, is an important structure that shields the eye from changes in the internal environment or invasion by the external environment. This study sought to collate evidence on the regulation of corneal epithelial barrier injury on the activation of vascular endothelial cells (VECs), basement membrane (BM) degradation, differentiation, migration, and proliferation of VECs, vascular maturation and stability, and other key processes in CoNV, so as to provide a novel concept for CoNV therapy targeting corneal epithelial barrier repair.

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

Association of Changes in Thickness of Limbal Epithelial and Stroma with Corneal Scars Detected by High-Resolution Anterior Segment Optic Coherence Tomography

AIM

To investigate the corneal central and limbal thickness in cornea scar patients using high-resolution anterior segment optical coherence tomography (AS-OCT) and to determine the changes in the limbal region due to the corneal scar. Also, to evaluate tear film parameters in scar patients.

METHODS

Thirty patients with central corneal scar and 30 control subjects. The control subjects were healthy individuals who came to our clinic for routine ophthalmological examination. They were enrolled in this matched case-control study. Central epithelial thickness (ET), stromal thickness (ST), limbal epithelial thickness (LET), and limbal stromal thickness (LST) were analyzed using high-resolution AS-OCT. For evaluation of the ocular surface, the following techniques were used: tear break-up time (BUT) employing standard sterile strips of fluorescein sodium, Schirmer test-I (SCH), and the Ocular Surface Disease Index (OSDI) Questionnaire.

RESULTS

The mean central ET of the patient group was 51.5 ± 12.4 µm, while the mean central ET of the control group was 59.2 ± 9.0 µm. There was a statistically significant difference between patients and controls (p = 0.008). The mean LST of the patients was 747.9 ± 115.7 µm, and the mean LST of the controls was 726.3 ± 79.7 µm. There was a statistically significant difference between patients and controls according to BUT (p = 0.009) and SCH (p = 0.04). However, there was no significant difference between OSDI results of patients and controls (p = 0.08).

CONCLUSION

Corneal monitoring with high-resolution AS-OCT is a simple, noninvasive, useful technique for corneal scar patients. Cornea scars cause decreased ET. This result could be associated with lower tear film parameters in scar patients. The scar length is associated with higher intraocular pressure (IOP) values. Decreased LET and increased LST were detected in scar patients.

Dimensionality Matters: Exploiting UV-Photopatterned 2D and Two-Photon-Printed 2.5D Contact Guidance Cues to Control Corneal Fibroblast Behavior and Collagen Deposition

In the event of disease or injury, restoration of the native organization of cells and extracellular matrix is crucial for regaining tissue functionality. In the cornea, a highly organized collagenous tissue, keratocytes can align along the anisotropy of the physical microenvironment, providing a blueprint for guiding the organization of the collagenous matrix. Inspired by this physiological process, anisotropic contact guidance cues have been employed to steer the alignment of keratocytes as a first step to engineer in vitro cornea-like tissues. Despite promising results, two major hurdles must still be overcome to advance the field. First, there is an enormous design space to be explored in optimizing cellular contact guidance in three dimensions. Second, the role of contact guidance cues in directing the long-term deposition and organization of extracellular matrix proteins remains unknown. To address these challenges, here we combined two microengineering strategies-UV-based protein patterning (2D) and two-photon polymerization of topographies (2.5D)-to create a library of anisotropic contact guidance cues with systematically varying height (H, 0 µm ≤ H ≤ 20 µm) and width (W, 5 µm ≤ W ≤ 100 µm). With this unique approach, we found that, in the short term (24 h), the orientation and morphology of primary human fibroblastic keratocytes were critically determined not only by the pattern width, but also by the height of the contact guidance cues. Upon extended 7-day cultures, keratocytes were shown to produce a dense, fibrous collagen network along the direction of the contact guidance cues. Moreover, increasing the heights also increased the aligned fraction of deposited collagen and the contact guidance response of cells, all whilst the cells maintained the fibroblastic keratocyte phenotype. Our study thus reveals the importance of dimensionality of the physical microenvironment in steering both cellular organization and the formation of aligned, collagenous tissues.

Topical application of calcitonin gene-related peptide as a regenerative, antifibrotic, and immunomodulatory therapy for corneal injury

Calcitonin gene-related peptide (CGRP) is a multifunctional neuropeptide abundantly expressed by corneal nerves. Using a murine model of corneal mechanical injury, we found CGRP levels in the cornea significantly reduced after injury. Topical application of CGRP as an eye drop accelerates corneal epithelial wound closure, reduces corneal opacification, and prevents corneal edema after injury in vivo. CGRP promotes corneal epithelial cell migration, proliferation, and the secretion of laminin. It reduces TGF-β1 signaling and prevents TGF-β1-mediated stromal fibroblast activation and tissue fibrosis. CGRP preserves corneal endothelial cell density, morphology, and pump function, thus reducing corneal edema. Lastly, CGRP reduces neutrophil infiltration, macrophage maturation, and the production of inflammatory cytokines in the cornea. Taken together, our results show that corneal nerve-derived CGRP plays a cytoprotective, pro-regenerative, anti-fibrotic, and anti-inflammatory role in corneal wound healing. In addition, our results highlight the critical role of sensory nerves in ocular surface homeostasis and injury repair.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Pirfenidone: A Promising Drug in Ocular Therapeutics

Pirfenidone, initially indicated for lung fibrosis, has gone beyond its original purpose, and shown promise in eye care. This detailed review tracks its evolution from lung treatment to aiding eye healing as evidenced by published literature. Pirfenidone's multifaceted attributes extend to mitigating corneal fibrosis, inflammation, and trauma. Through rigorous investigations, its efficacy emerges in diabetic retinopathy, macular degeneration, and postoperative glaucoma interventions. As an unheralded protagonist, pirfenidone reshapes ocular care paradigms, inviting renewed research opportunities.

Topical Losartan Inhibition of Myofibroblast Generation in Rabbit Corneas With Acute Incisions

PURPOSE

The purpose of this study was to study whether deep central corneal incisions close during topical losartan treatment and the effect of topical losartan on myofibroblast generation after incisions in rabbit corneas.

METHODS

Rabbits (12) had a 0.35-mm deep radial incision from the center of the cornea into the limbus in 1 eye that was approximated with a single 10-0 nylon suture 1 mm inside the limbus. The incision was treated with 50 μL of topical 0.8 mg/mL losartan or 50 μL of balanced salt solution vehicle 6 times per day for 1 month. Standardized slitlamp photographs of the central incisions were analyzed for opacity with ImageJ before euthanasia. Triplex IHC was performed on cryofixed corneas for myofibroblast marker alpha-smooth muscle actin, mesenchymal cell marker vimentin, and basement membrane marker laminin alpha-5. Stromal α-SMA-positive myofibroblasts surrounding the incisions were quantitated with ImageJ.

RESULTS

Topical losartan compared with vehicle did not affect closure of the radial incisions or the opacity that developed surrounding the incisions at 1 month after injury. Topical losartan compared with vehicle did significantly decrease the average density of stromal myofibroblasts surrounding the incisions.

CONCLUSIONS

Topical losartan, a known inhibitor of transforming growth factor beta signaling, did not affect closure of deep corneal incisions. Losartan decreased myofibroblast generation surrounding nearly full-thickness radial corneal incisions compared with vehicle. The opacity at the incisions was not significantly affected by losartan-likely because corneal fibroblasts that develop in the stroma adjacent to the incisions were not changed by the losartan compared with the vehicle.

Novel Correlation between TGF-β1/-β3 and Hormone Receptors in the Human Corneal Stroma

This study investigated the interplay between transforming growth factor beta (TGF-β1/T1 and TGF-β3/T3), and sex hormone receptors using our 3D in vitro cornea stroma model. Primary human corneal fibroblasts (HCFs) from healthy donors were plated in transwells at 106 cells/well and cultured for four weeks. HCFs were supplemented with stable vitamin C (VitC) and stimulated with T1 or T3. 3D construct proteins were analyzed for the androgen receptor (AR), progesterone receptor (PR), estrogen receptor alpha (ERα) and beta (ERβ), luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), gonadotropin-releasing hormone receptor (GnRHR), KiSS1-derived peptide receptor (KiSS1R/GPR54), and follicle-stimulating hormone subunit beta (FSH-B). In female constructs, T1 significantly upregulated AR, PR, ERα, FSHR, GnRHR, and KiSS1R. In male constructs, T1 significantly downregulated FSHR and FSH-B and significantly upregulated ERα, ERβ, and GnRHR. T3 caused significant upregulation in expressions PR, ERα, ERβ, LHR, FSHR, and GNRHR in female constructs, and significant downregulation of AR, ERα, and FSHR in male constructs. Semi-quantitative Western blot findings present the interplay between sex hormone receptors and TGF-β isoforms in the corneal stroma, which is influenced by sex as a biological variable (SABV). Additional studies are warranted to fully delineate their interactions and signaling mechanisms.

Posterior corneoscleral limbus: Architecture, stem cells, and clinical implications

The limbus is a transition from the cornea to conjunctiva and sclera. In human eyes, this thin strip has a rich variation of tissue structures and composition, typifying a change from scleral irregularity and opacity to corneal regularity and transparency; a variation from richly vascularized conjunctiva and sclera to avascular cornea; the neural passage and drainage of aqueous humor. The limbal stroma is enriched with circular fibres running parallel to the corneal circumference, giving its unique role in absorbing small pressure changes to maintain corneal curvature and refractivity. It contains specific niches housing different types of stem cells for the corneal epithelium, stromal keratocytes, corneal endothelium, and trabecular meshwork. This truly reflects the important roles of the limbus in ocular physiology, and the limbal functionality is crucial for corneal health and the entire visual system. Since the anterior limbus containing epithelial structures and limbal epithelial stem cells has been extensively reviewed, this article is focused on the posterior limbus. We have discussed the structural organization and cellular components of the region beneath the limbal epithelium, the characteristics of stem cell types: namely corneal stromal stem cells, endothelial progenitors and trabecular meshwork stem cells, and recent advances leading to the emergence of potential cell therapy options to replenish their respective mature cell types and to correct defects causing corneal abnormalities. We have reviewed different clinical disorders associated with defects of the posterior limbus and summarized the available preclinical and clinical evidence about the developing topic of cell-based therapy for corneal disorders.

Topical application of calcitonin gene-related peptide as a regenerative, antifibrotic, and immunomodulatory therapy for corneal injury

Calcitonin gene-related peptide (CGRP) is a multifunctional neuropeptide abundantly expressed by corneal nerves. Using a murine model of corneal mechanical injury, we found CGRP levels in the cornea to be significantly reduced after injury. Topical application of CGRP as an eye drop three times daily accelerates corneal epithelial wound closure, reduces corneal opacification, and prevents corneal edema after injury in vivo. We then used a series of in vitro and in vivo techniques to investigate the mechanisms underlying CGRP's functions. CGRP promotes corneal epithelial cell migration, proliferation, and the secretion of laminin. It reduces TGF-β1 signaling and prevents TGF-β1-mediated stromal fibroblast activation and tissue fibrosis. CGRP reduces corneal endothelial cell apoptosis and death, preserves cell density and morphology, and promotes their pump function, thus reducing edema. Lastly, CGRP reduces neutrophil infiltration, macrophage maturation, and the production of inflammatory cytokines in the cornea. Taken together, our results show that corneal nerve-derived CGRP plays a cyto-protective, pro-regenerative, anti-fibrotic, and anti-inflammatory role in corneal wound healing. Given that current treatment options for corneal injury and opacity are scarce, CGRP has significant therapeutic potential in this area of unmet medical needs. In addition, our results highlight the critical role of sensory nerves in ocular surface homeostasis and injury repair.

Corneal gene therapy: Structural and mechanistic understanding

Cornea, a dome-shaped and transparent front part of the eye, affords 2/3rd refraction and barrier functions. Globally, corneal diseases are the leading cause of vision impairment. Loss of corneal function including opacification involve the complex crosstalk and perturbation between a variety of cytokines, chemokines and growth factors generated by corneal keratocytes, epithelial cells, lacrimal tissues, nerves, and immune cells. Conventional small-molecule drugs can treat mild-to-moderate traumatic corneal pathology but requires frequent application and often fails to treat severe pathologies. The corneal transplant surgery is a standard of care to restore vision in patients. However, declining availability and rising demand of donor corneas are major concerns to maintain ophthalmic care. Thus, the development of efficient and safe nonsurgical methods to cure corneal disorders and restore vision in vivo is highly desired. Gene-based therapy has huge potential to cure corneal blindness. To achieve a nonimmunogenic, safe and sustained therapeutic response, the selection of a relevant genes, gene editing methods and suitable delivery vectors are vital. This article describes corneal structural and functional features, mechanistic understanding of gene therapy vectors, gene editing methods, gene delivery tools, and status of gene therapy for treating corneal disorders, diseases, and genetic dystrophies.

The corneal fibroblast: The Dr. Jekyll underappreciated overseer of the responses to stromal injury

PURPOSE

To review the functions of corneal fibroblasts in wound healing.

METHODS

Literature review.

RESULTS

Corneal fibroblasts arise in the corneal stroma after anterior, posterior or limbal injuries and are derived from keratocytes. Transforming growth factor (TGF) β1 and TGFβ2, along with platelet-derived growth factor (PDGF), are the major modulators of the keratocyte to corneal fibroblast transition, while fibroblast growth factor (FGF)-2, TGFβ3, and retinoic acid are thought to regulate the transition of corneal fibroblasts back to keratocytes. Adequate and sustained levels of TGFβ1 and/or TGFβ2, primarily from epithelium, tears, aqueous humor, and corneal endothelium, drive the development of corneal fibroblasts into myofibroblasts. Myofibroblasts have been shown in vitro to transition back to corneal fibroblasts, although apoptosis of myofibroblasts has been documented as a major contributor to the resolution of fibrosis in several in situ corneal injury models. Corneal fibroblasts, aside from their role as a major progenitor to myofibroblasts, also perform many critical functions in the injured cornea, including the production of critical basement membrane (BM) components during regeneration of the epithelial BM and Descemet's membrane, production of non-basement membrane-associated stromal collagen type IV to control and downregulate TGFβ effects on stromal cells, release of chemotactic chemokines that attract bone marrow-derived cells to the injured stroma, production of growth factors that modulate regeneration and maturation of the overlying epithelium, and production of collagens and other ECM components that contribute to stromal integrity after injury.

CONCLUSIONS

Corneal fibroblasts are major contributors to and overseers of the corneal response to injuries.

A Biomimetic Peptide-drug Supramolecular Hydrogel as Eyedrops Enables Controlled Release of Ophthalmic Drugs

The rapid clearance of instilled drugs from the ocular surface due to tear flushing and excretion results in low drug bioavailability, necessitating the development of new drug delivery routes. Here, we generated an antibiotic hydrogel eye drop that can extend the pre-corneal retention of a drug after topical instillation to address the risk of side effects (e.g., irritation and inhibition of enzymes), resulting from frequent and high-dosage administrations of antibiotics used to obtain the desired therapeutic drug concentration. The covalent conjugation of small peptides to antibiotics (e.g., chloramphenicol) first endows the self-assembly ability of peptide-drug conjugate to generate supramolecular hydrogels. Moreover, the further addition of calcium ions, which are also widely present in endogenous tears, tunes the elasticity of supramolecular hydrogels, making them ideal for ocular drug delivery. The in vitro assay revealed that the supramolecular hydrogels exhibited potent inhibitory activities against both gram-negative (e.g., Escherichia coli) and gram-positive (e.g., Staphylococcus aureus) bacteria, whereas they were innocuous toward human corneal epithelial cells. Moreover, the in vivo experiment showed that the supramolecular hydrogels remarkably increased pre-corneal retention without ocular irritation, thereby showing appreciable therapeutic efficacy for treating bacterial keratitis. This work, as a biomimetic design of antibiotic eye drops in the ocular microenvironment, addresses the current issues of ocular drug delivery in the clinic and further provides approaches to improve the bioavailability of drugs, which may eventually open new directions to resolve the difficulty of ocular drug delivery. STATEMENT OF SIGNIFICANCE: Herein, we present a biomimetic design for antibiotic hydrogel eye drops mediated by calcium ions (Ca²⁺) in the ocular microenvironment, which can extend the pre-corneal retention of antibiotics after topical instillation. The mediation of Ca²⁺ which is widely present in endogenous tears, tunes the elasticity of hydrogels, making them ideal for ocular drug delivery. Since increasing the ocular retention of antibiotic eye drops enhances its action and reduces its adverse effects, this work may lead to an approach of peptide-drug-based supramolecular hydrogel for ocular drug delivery in clinics to combat ocular bacterial infections.

Dendrimers in Corneal Drug Delivery: Recent Developments and Translational Opportunities

Dendrimers are biocompatible organic nanomaterials with unique physicochemical properties, making them the focus of recent research in drug delivery. The cornea of the human eye presents a challenge for drug transit due to its inherently impenetrable nature, requiring nanocarrier-mediated targeted drug delivery. This review intends to examine recent advancements in the use of dendrimers for corneal drug delivery, including their properties and their potential for treating various ocular diseases. The review will also highlight the benefit of the novel technologies that have been developed and applied in the field, such as corneal targeting, drug release kinetics, treatments for dry eye disease, antibacterial drug delivery, corneal inflammation, and corneal tissue engineering. The review seeks to provide a comprehensive overview of the current state of research in this field, along with the translational developments in the field of dendrimer-based therapeutics and imaging agents and inspire the potential for future developments and translational opportunities in dendrimers based corneal drug delivery.

Basement membrane regeneration and TGF-β1 expression in rabbits with corneal perforating injury

Purpose

To evaluate the relationship between basement membrane (BM) regeneration and the spatiotemporal expression of TGF-β1 during wound healing in rabbits with corneal perforating injury.

Methods

Forty-two rabbits were randomly allocated into 7 experimental groups, with 6 rabbits per group at each time point. The central cornea of the left eye was injured with 2.0 mm trephine to establish the perforating injury model. Six rabbits that received no treatment were used as controls. The cornea was evaluated at 3 days, 1-3 weeks, and 1-3 months after injury with a slit lamp for haze levels. Real-time quantitative polymerase chain reaction (qRT-PCR) was performed to quantify the relative expression of TGF-β1 and α-SMA mRNA. Immunofluorescence (IF) was used to assess TGF-β1 and alpha-smooth actin (α-SMA) expression and localization. BM regeneration was assessed using transmission electron microscopy (TEM).

Results

After injury, dense haze appeared at 1 month and then gradually faded. The relative expression of TGF-β1 mRNA peaked at 1 week and then decreased until 2 months. The relative α-SMA mRNA expression reached its peak at 1 week, then reached a small peak again at 1 month. IF results showed that TGF-β1 was initially detected in the fibrin clot at 3 days and then in the entire repairing stroma at 1 week. TGF-β1 localization gradually diminished from the anterior region to the posterior region at 2 weeks to 1 month, and it was nearly absent at 2 months. The myofibroblast marker α-SMA was observed in the entire healing stroma at 2 weeks. Localization of α-SMA gradually disappeared from the anterior region at 3 weeks to 1 month, remaining only in the posterior region at 2 months and disappearing at 3 months. Defective epithelial basement membrane (EBM) was first detected at 3 weeks after injury, then gradually repaired, and was nearly regenerated at 3 months. A thin and uneven Descemet's membrane (DM) was initially detected at 2 months after injury, then gradually regenerated to some extent, but remained abnormal at 3 months.

Conclusions

In the rabbit corneal perforating injury model, EBM regeneration was observed earlier than DM. At 3 months, complete EBM regeneration was observed, while the regenerated DM was still defective. TGF-β1 was distributed throughout the entire wound area in the early stages and then decreased from the anterior to the posterior region. α-SMA exhibited a similar temporospatial expression to TGF-β1. EBM regeneration may play a key role in low expression of TGF-β1 and α-SMA in the anterior stroma. Meanwhile, incomplete DM regeneration may contribute to the sustained expression of TGF-β1 and α-SMA in the posterior stroma.

Case Report: Corneal Inlay Removal after Myofibroblast Detection under in Vivo Confocal Microscopy

SIGNIFICANCE

Corneal inlays, one of the treatment options for presbyopia, are effective and safe, and various such devices have been developed. However, there have been cases of inlay removal due to complications or patient dissatisfaction.

PURPOSE

The purpose of this study was to report a case of inlay removal due to corneal opacity after inlay implantation and the results of 5 years of follow-up.

CASE REPORT

A 63-year-old man was referred to our hospital with visual disturbance and double vision in his left eye. Two years before presentation at our hospital, he had undergone bilateral laser in situ keratomileusis with corneal inlay implantation in the left eye at another clinic. Slit-lamp examinations showed paracentral corneal opacity. The patient was treated with tranilast eye drops for 18 months, with no progression of symptoms. However, 6 months after stopping the eye drop treatment, the opacity recurred, and vision acuity decreased, along with the formation of myofibroblasts around the inlay, as revealed by in vivo confocal microscopy. Consequently, the inlay was removed at the previous clinic. During the subsequent 5-year follow-up period, ophthalmic examination revealed reduced corneal opacity, although visual acuity did not change; moreover, no myofibroblast was found.

CONCLUSIONS

Corneal inlays can sometimes cause complications. In this case, the patient experienced corneal fibrosis and associated vision loss. In vivo confocal microscopy detected myofibroblasts that cause corneal stromal fibrosis; thus, the removal was decided to avoid fibrosis progression.

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.

Unravelling the Impact of Cyclic Mechanical Stretch in Keratoconus-A Transcriptomic Profiling Study

Biomechanical and molecular stresses may contribute to the pathogenesis of keratoconus (KC). We aimed to profile the transcriptomic changes in healthy primary human corneal (HCF) and KC-derived cells (HKC) combined with TGFβ1 treatment and cyclic mechanical stretch (CMS), mimicking the pathophysiological condition in KC. HCFs (n = 4) and HKCs (n = 4) were cultured in flexible-bottom collagen-coated 6-well plates treated with 0, 5, and 10 ng/mL of TGFβ1 with or without 15% CMS (1 cycle/s, 24 h) using a computer-controlled Flexcell FX-6000T Tension system. We used stranded total RNA-Seq to profile expression changes in 48 HCF/HKC samples (100 bp PE, 70-90 million reads per sample), followed by bioinformatics analysis using an established pipeline with Partek Flow software. A multi-factor ANOVA model, including KC, TGFβ1 treatment, and CMS, was used to identify differentially expressed genes (DEGs, |fold change| ≥ 1.5, FDR ≤ 0.1, CPM ≥ 10 in ≥1 sample) in HKCs (n = 24) vs. HCFs (n = 24) and those responsive to TGFβ1 and/or CMS. PANTHER classification system and the DAVID bioinformatics resources were used to identify significantly enriched pathways (FDR ≤ 0.05). Using multi-factorial ANOVA analyses, 479 DEGs were identified in HKCs vs. HCFs including TGFβ1 treatment and CMS as cofactors. Among these DEGs, 199 KC-altered genes were responsive to TGFβ1, thirteen were responsive to CMS, and six were responsive to TGFβ1 and CMS. Pathway analyses using PANTHER and DAVID indicated the enrichment of genes involved in numerous KC-relevant functions, including but not limited to degradation of extracellular matrix, inflammatory response, apoptotic processes, WNT signaling, collagen fibril organization, and cytoskeletal structure organization. TGFβ1-responsive KC DEGs were also enriched in these. CMS-responsive KC-altered genes such as OBSCN, CLU, HDAC5, AK4, ITGA10, and F2RL1 were identified. Some KC-altered genes, such as CLU and F2RL1, were identified to be responsive to both TGFβ1 and CMS. For the first time, our multi-factorial RNA-Seq study has identified many KC-relevant genes and pathways in HKCs with TGFβ1 treatment under CMS, suggesting a potential role of TGFβ1 and biomechanical stretch in KC development.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

Highly stable fibronectin-mimetic-peptide-based supramolecular hydrogel to accelerate corneal wound healing

Without timely treatment, poor wound healing in corneal injuries can seriously impair vision and lead to blindness. Thus, it is vital to develop a therapeutic strategy to accelerate corneal re-epithelialization. The conjugation of self-assembled motifs with a fibronectin-mimetic peptide sequence (PHSRN) drastically improves the chemical stability of PHSRN against protease hydrolysis and minimally affects its biological activity to promote the migration of corneal epithelial cells. The optimized Nap-FFPHSRN self-assembled into bioactive supramolecular hydrogels increases cell motility by remolding F-actin and boosts the tight junction of the corneal epithelium by increasing the expression of zonula occludens-1 (ZO-1). An in vivo experiment showed that a Nap-FFPHSRN hydrogel provided extended precorneal retention with good ocular tolerance after topical instillation. An animal model of corneal scrape showed that a single daily dose of Nap-FFPHSRN hydrogel had a superior therapeutic effect in facilitating corneal re-epithelialization with complete morphological and architectural recovery. With a rational approach to mimic bioactive proteins, this study presents a new strategy to demonstrate the potential of peptide-based supramolecular hydrogels for use in clinical treatment of corneal injury. STATEMENT OF SIGNIFICANCE: Here we systematically investigate the self-assembly behavior and chemical stability of designed peptide amphiphiles (Nap-FPHRSN, Nap-FFPHSRN and Nap-FFFPHSRN). The introduction of self-assembled motifs (Nap-F, Nap-FF and Nap-FFF) drastically enhances the chemical stability of fibronectin-mimetic peptide (PHSRN). Moreover, topical instillation of Nap-FFPHSRN hydrogel once daily, exhibits a better in vivo effect than PHSRN and the same in vivo effect as fibronectin, both of which are instilled three times daily, for promoting full morphological and architectural recovery after corneal re-epithelialization. As a rational design of conjugating bioactive peptides with self-assembled motifs to mimic bioactive proteins, this work may lead to a new approach that improves the in vivo therapeutic effect for treating corneal injury in clinic settings.

Pre-Clinical Evaluation of Efficacy and Safety of Human Limbus-Derived Stromal/Mesenchymal Stem Cells with and without Alginate Encapsulation for Future Clinical Applications

Corneal opacification or scarring is one of the leading causes of blindness worldwide. Human limbus-derived stromal/mesenchymal stem cells (hLMSCs) have the potential of clearing corneal scarring. In the current preclinical studies, we aimed to determine their ability to heal the scarred corneas, in a murine model of corneal scar, and examined their ocular and systemic toxicity after topical administration to rabbit eyes. The hLMSCs were derived from human donor corneas and were cultivated in a clean room facility in compliance with the current good manufacturing practices (cGMP). Before the administration, the hLMSCs were analyzed for their characteristic properties including immunostaining, and were further subjected to sterility and stability analysis. The corneas (right eye) of C57BL/6 mice (n = 56) were stripped of their central epithelium and superficial anterior stroma using a rotary burr (Alger Brush® II). Few mice were left untreated (n = 8), while few (n = 24) were treated immediately with hLMSCs after debridement (prophylaxis group). The rest (n = 24, scar group) were allowed to develop corneal scarring for 2 weeks and then treated with hLMSCs. In both groups, the treatment modalities included encapsulated (En+) and non-encapsulated (En−) hLMSCs and sham (vehicle) treatment. The follow-up (4 weeks) after the treatment or debridement included clinical photography, fluorescein staining, and optical coherence tomography at regular intervals. All the images and scans were analyzed using ImageJ software to assess the changes in corneal haze, scar area, and the reflectivity ratio of the epithelium to the stroma. The scar area and the scar intensity were found to be decreased in the groups that received hLMSCs. The reflectivity of the stroma was found to be normalized to the baseline levels before the debridement in the eyes that were treated with hLMSCs, relative to the untreated. In the safety study, the central corneas of the left eye of 18 New Zealand rabbits were scraped with a needle and then treated with En+ hLMSCs, En− hLMSCs, and the sham (n = 6 each). Rabbits were then followed up for 4 weeks, during which blood and tear samples were collected at regular intervals. These rabbits were then assessed for changes in the quantities of inflammatory markers (TNF-α, IL-6, and IgE) in the sera and tears, changes in the ocular surface observations such as intraocular pressure (IOP), and the hematological and clinical chemistry parameters. Four weeks later, the rabbits were euthanized and examined histopathologically. No significant changes in conjunctival congestion, corneal clarity, or IOP were noticed during the ophthalmic examination. The level of inflammatory molecules (TNF-α and IL-6 TNF-α) and the hematological parameters were similar in all groups without any significant changes. Histological examination of the internal organs and ocular tissues did not reveal any abnormalities. The results of these studies summarize that the En+ and En− hLMSCs are not harmful to the recipient and potentially restore the transparency of debrided or scarred corneas, indicating that hLMSCs can be assessed for clinical use in humans.

Relationship of Density, Depth, and Surface Irregularity of Superficial Corneal Opacification with Visual Acuity

PURPOSE

To explore the relationship between the density, depth, and surface irregularity of superficial corneal opacities and vision.

METHODS

This prospective imaging study included 19 patients with unilateral superficial corneal opacification due to scarring post-microbial keratitis. Each eye underwent an assessment of uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), contact lens corrected visual acuity (CLCVA), and Scheimpflug and anterior segment optical tomography imaging. Regression analysis was performed to detect the association between density, depth of scarring, and the surface irregularity in terms of higher order aberrations (HOA), and keratometry and UCVA, CLCVA, and the difference between BSCVA and CLCVA.

RESULTS

The mean logMAR UCVA, BSCVA, and CLCVA were 0.76, 0.35, and 0.28, respectively. The corneal scars had a mean thickness of 158.7 ± 61 µ and density of 65.73 ± 24.46 GSU. Bivariate analysis model for UCVA showed an association with Z₄² secondary astigmatism (p = 0.02), Z₄⁴ quadrafoil (p = 0.01), combined coma Z₃ ^± 1(p = 0.03), and combined HOA Z₃-Z₆ (p = 0.045), out of which Z₄⁴ Quadrafoil (p = 0.04) was most significant with multivariate analysis. Bivariate analysis for BCVA-CLVA showed association with Z₃¹ coma horizontal (p = 0.04), Z₃³ oblique trefoil (p = 0.02), Z₄⁰ primary spherical aberration (p = 0.008), and Z₅ ^- 5 (p = 0.007), out of which Z₃¹ horizontal coma (p = 0.04) and Z₄⁰ spherical aberration (p = 0.009) were significant on multivariate analysis. Change in densitometry, corneal thickness, epithelial:stromal reflectivity ratio, scar depth, and keratometry did not show any significant association with UCVA, BSCVA-CLCVA, or CLCVA.

CONCLUSION

In superficial corneal stromal scarring, deranged surface irregularity parameters like higher-order aberrations affect the final visual acuity more than the depth or density of the opacity.

Molecular mechanisms regulating wound repair: Evidence for paracrine signaling from corneal epithelial cells to fibroblasts and immune cells following transient epithelial cell treatment with Mitomycin C

In this paper, we use RNAseq to identify senescence and phagocytosis as key factors to understanding how mitomyin C (MMC) stimulates regenerative wound repair. We use conditioned media (CM) from untreated (CMC) and MMC treated (CMM) human and mouse corneal epithelial cells to show that corneal epithelial cells indirectly exposed to MMC secrete elevated levels of immunomodulatory proteins including IL-1α and TGFβ1 compared to cells exposed to CMC. These factors increase epithelial and macrophage phagocytosis and promote ECM turnover. IL-1α supplementation can increase phagocytosis in control epithelial cells and attenuate TGFβ1 induced αSMA expression by corneal fibroblasts. Yet, we show that epithelial cell CM contains factors besides IL-1α that regulate phagocytosis and αSMA expression by fibroblasts. Exposure to CMM also impacts the activation of bone marrow derived dendritic cells and their ability to present antigen. These in vitro studies show how a brief exposure to MMC induces corneal epithelial cells to release proteins and other factors that function in a paracrine way to enhance debris removal and enlist resident epithelial and immune cells as well as stromal fibroblasts to support regenerative and not fibrotic wound healing.

Extracellular matrix-based sticky sealants for scar-free corneal tissue reconstruction

Regenerative medicine requires both tissue restoration and ease of compliance for clinical application. Considering this, sticky tissue sealants have been shown to have great potentials over surgical suturing and wound treatment. However, tissue sealants currently used pose challenges such as uncontrollable adhesion formation, mechanical mismatch, and lack of tissue restoration. A new sticky sealant based on gelatinized cornea-derived extracellular matrix (GelCodE) with a visible light-activating system is firstly being introduced in this study. De novo tissue regeneration relies on the matrisome in charge of tissue-organization and development within GelCodE while visible light-based photopolymerization with ruthenium/sodium persulfate rapidly induces covalent bonds with the adjacent tissues. The ease of not only in vivo application, biocompatibility, and biointegration, but also exceptional de novo tissue formation is demonstrated in this study. Interestingly, newly regenerated tissues were shown to have normal tissue-like matrices with little scar formation. Hence, this work presents a promising strategy to meet clinical demands for scar-free tissue recovery with superior ease of clinical application.

The Yin and Yang of Mesenchymal Cells in the Corneal Stromal Fibrosis Response to Injury: The Cornea as a Model of Fibrosis in Other Organs

Mesenchymal cells (keratocytes, corneal fibroblasts, and myofibroblasts), as well as mesenchymal progenitor bone marrow-derived fibrocytes, are the major cellular contributors to stromal fibrosis after injury to the cornea. Corneal fibroblasts, in addition to being major progenitors to myofibroblasts, also have anti-fibrotic functions in (1) the production of non-basement membrane collagen type IV that binds activated transforming growth factor (TGF) beta-1 and TGF beta-2 to downregulate TGF beta effects on cells in the injured stroma, (2) the production of chemokines that modulate the entry of bone marrow-derived cells into the stroma, (3) the production of hepatocyte growth factor and keratinocyte growth factor to regulate corneal epithelial healing, (4) the cooperation with the epithelium or corneal endothelium in the regeneration of the epithelial basement membrane and Descemet's membrane, and other functions. Fibrocytes also serve as major progenitors to myofibroblasts in the corneal stroma. Thus, mesenchymal cells and mesenchymal cell progenitors serve Yin and Yang functions to inhibit and promote tissue fibrosis depending on the overall regulatory milieu within the injured stroma.

The Soluble Guanylate Cyclase Stimulator BAY 41-2272 Attenuates Transforming Growth Factor β1-Induced Myofibroblast Differentiation of Human Corneal Keratocytes

Corneal transparency, necessary for vision and depending on the high organization of stromal extracellular matrix, is maintained by keratocytes. Severe or continuous corneal injuries determine exaggerated healing responses resulting in the formation of irreversible fibrotic scars and vision impairment. Soluble guanylate cyclase (sGC) stimulation demonstrated antifibrotic effects in both experimental fibrosis and human lung and skin fibroblasts. Here, we assessed whether sGC stimulation with BAY 41-2272 could attenuate transforming growth factor β1 (TGFβ1)-induced myofibroblast differentiation of human corneal keratocytes. Cells were challenged with TGFβ1, with/without BAY 41-2272 preincubation, and subsequently assessed for viability, proliferation, migration, chemoinvasion, as well for the expression of myofibroblast/fibroblast activation markers and contractile abilities. Treatment with BAY 41-2272 did not affect keratocyte viability, while preincubation of cells with the sGC stimulator was able to inhibit TGFβ1-induced proliferation, wound healing capacity, and invasiveness. BAY 41-2272 was also able to attenuate TGFβ1-induced myofibroblast-like profibrotic phenotype of keratocytes, as demonstrated by the significant decrease in ACTA2, COL1A1, COL1A2, FN1 and PDPN gene expression, as well as in α-smooth muscle actin, α-1 chain of type I collagen, podoplanin, vimentin and N-cadherin protein expression. Finally, BAY 41-2272 significantly counteracted the TGFβ1-induced myofibroblast-like ability of keratocytes to contract collagen gels, reduced phosphorylated Smad3 protein levels, and attenuated gene expression of proinflammatory cytokines. Collectively, our data show for the first time that BAY 41-2272 is effective in counteracting keratocyte-to-myofibroblast transition, thus providing the rationale for the development of sGC stimulators as novel promising modulators of corneal scarring and fibrosis.

Prolactin-Induced Protein facilitates corneal wound healing

The purpose of the study was to investigate the role of Prolactin-Induced Protein (PIP) in corneal wound healing, in vivo and in vitro. In C57BL/6J mice, corneal epithelia was removed using an ocular burr. Phosphate buffered saline (PBS) or PIP (0.5 and 1.0 μg/mL) was applied topically or subconjunctivally injected. PIP accelerated wound closure as early as 24 h. PIP treatment promoted corneal wound healing and epithelial integrity and thickness. Integrin α6, integrin β4, Thrombospondin-1, and TGF-β1 expressions were all downregulated by PIP after wound closure. In vitro, scratch assays were performed using primary human epithelial cells (HCECs) and human corneal fibroblasts (HCFs), stimulated with PIP at various dosages. PIP treatment promoted both HCECs and HCFs migration. PIP upregulated expression of integrin α6, integrin β4, and Thrombospondin-1 in HCECs. Expression of TGF-β1 in HCECs and expression of smooth muscle actin (SMA) and Type III Collagen (Col III) in HCFs were significantly downregulated at 150 ng/mL PIP. PIP exhibits noteworthy anti-fibrotic potentiality. While the mechanism of how PIP is impactful on the corneal wound healing cascade is unknown, our findings are novel and further studies are warranted in order to unravel any therapeutic potential.

Sulfur mustard corneal injury is associated with alterations in the epithelial basement membrane and stromal extracellular matrix

Sulfur mustard (SM; bis(2-chloroethyl) sulfide) is a highly reactive bifunctional alkylating agent synthesized for chemical warfare. The eyes are particularly sensitive to SM where it causes irritation, pain, photophobia, and blepharitis, depending on the dose and duration of exposure. In these studies, we examined the effects of SM vapor on the corneas of New Zealand white male rabbits. Edema and hazing of the cornea, signs of acute injury, were observed within one day of exposure to SM, followed by neovascularization, a sign of chronic or late phase pathology, which persisted for at least 28 days. Significant epithelial-stromal separation ranging from ~8-17% of the epithelial surface was observed. In the stroma, there was a marked increase in CD45+ leukocytes and a decrease of keratocytes, along with areas of disorganization of collagen fibers. SM also disrupted the corneal basement membrane and altered the expression of perlecan, a heparan sulfate proteoglycan, and cellular fibronectin, an extracellular matrix glycoprotein. This was associated with an increase in basement membrane matrix metalloproteinases including ADAM17, which is important in remodeling of the basement membrane during wound healing. Tenascin-C, an extracellular matrix glycoprotein, was also upregulated in the stroma 14-28 d post SM, a finding consistent with its role in organizing structural components of the stroma necessary for corneal transparency. These data demonstrate that SM vapor causes persistent alterations in structural components of the cornea. Further characterization of SM-induced injury in rabbit cornea will be useful for the identification of targets for the development of ocular countermeasures.

Rare giant corneal keloid presenting 26 years after trauma: A case report

BACKGROUND

Corneal keloid is a rare clinical disease with an unknown etiology, which is easily misdiagnosed. Surgery is the most effective treatment but is rarely reported in the literature. Herein, we report the clinical features, histopathology, and surgical outcome of a giant corneal keloid with trophoblastic vessels and discuss the genesis of the mass.

CASE SUMMARY

A 36-year-old young man was admitted to the hospital because of a large mass on the surface of the left cornea. The patient had suffered an injury to his left eye at the age of 6-years-old; however, as the injury did not cause cornea perforation, he did not undergo treatment. Slit lamp exam showed a large, elevated, opaque lesion that covered the entire cornea and protruded from the surface of the eyeball. Anterior segment optical coherence tomography (AS-OCT) revealed a lesion of irregular density involving the anterior stroma. We suspected a secondary corneal fibroproliferative mass based on the clinical history, and slit lamp and AS-OCT findings. The patient subsequently underwent a superficial keratectomy and keratoplasty, and the final diagnosis of corneal keloid was confirmed by intraoperative histopathological examination.

CONCLUSION

Non-penetrating corneal trauma damages corneal epithelium basement membrane, initiating stromal fibrosis and causing corneal keloids. AS-OCT and biopsy confirm diagnosis.

Transcriptomic Profiling of Human Limbus-Derived Stromal/Mesenchymal Stem Cells-Novel Mechanistic Insights into the Pathways Involved in Corneal Wound Healing

Limbus-derived stromal/mesenchymal stem cells (LMSCs) are vital for corneal homeostasis and wound healing. However, despite multiple pre-clinical and clinical studies reporting the potency of LMSCs in avoiding inflammation and scarring during corneal wound healing, the molecular basis for the ability of LMSCs remains unknown. This study aimed to uncover the factors and pathways involved in LMSC-mediated corneal wound healing by employing RNA-Sequencing (RNA-Seq) in human LMSCs for the first time. We characterized the cultured LMSCs at the stages of initiation (LMSC−P0) and pure population (LMSC−P3) and subjected them to RNA-Seq to identify the differentially expressed genes (DEGs) in comparison to native limbus and cornea, and scleral tissues. Of the 28,000 genes detected, 7800 DEGs were subjected to pathway-specific enrichment Gene Ontology (GO) analysis. These DEGs were involved in Wnt, TGF-β signaling pathways, and 16 other biological processes, including apoptosis, cell motility, tissue remodeling, and stem cell maintenance, etc. Two hundred fifty-four genes were related to wound healing pathways. COL5A1 (11.81 ± 0.48) and TIMP1 (20.44 ± 0.94) genes were exclusively up-regulated in LMSC−P3. Our findings provide new insights involved in LMSC-mediated corneal wound healing.

Myofibroblast transdifferentiation of keratocytes results in slower migration and lower sensitivity to mesoscale curvatures

Functional tissue repair after injury or disease is governed by the regenerative or fibrotic response by cells within the tissue. In the case of corneal damage, keratocytes are a key cell type that determine the outcome of the remodeling response by either adapting to a fibroblast or myofibroblast phenotype. Although a growing body of literature indicates that geometrical cues in the environment can influence Myo(fibroblast) phenotype, there is a lack of knowledge on whether and how differentiated keratocyte phenotype is affected by the curved tissue geometry in the cornea. To address this gap, in this study we characterized the phenotype of fibroblastic and transforming growth factor β (TGFβ)-induced myofibroblastic keratocytes and studied their migration behavior on curved culture substrates with varying curvatures. Immunofluorescence staining and quantification of cell morphological parameters showed that, generally, fibroblastic keratocytes were more likely to elongate, whereas myofibroblastic keratocytes expressed more pronounced α smooth muscle actin (α-SMA) and actin stress fibers as well as more mature focal adhesions. Interestingly, keratocyte adhesion on convex structures was weak and unstable, whereas they adhered normally on flat and concave structures. On concave cylinders, fibroblastic keratocytes migrated faster and with higher persistence along the longitudinal direction compared to myofibroblastic keratocytes. Moreover, this behavior became more pronounced on smaller cylinders (i.e., higher curvatures). Taken together, both keratocyte phenotypes can sense and respond to the sign and magnitude of substrate curvatures, however, myofibroblastic keratocytes exhibit weaker curvature sensing and slower migration on curved substrates compared to fibroblastic keratocytes. These findings provide fundamental insights into keratocyte phenotype after injury, but also exemplify the potential of tuning the physical cell environments in tissue engineering settings to steer towards a favorable regeneration response.

Mimicking the Natural Basement Membrane for Advanced Tissue Engineering

Advancements in the field of tissue engineering have led to the elucidation of physical and chemical characteristics of physiological basement membranes (BM) as specialized forms of the extracellular matrix. Efforts to recapitulate the intricate structure and biological composition of the BM have encountered various advancements due to its impact on cell fate, function, and regulation. More attention has been paid to synthesizing biocompatible and biofunctional fibrillar scaffolds that closely mimic the natural BM. Specific modifications in biomimetic BM have paved the way for the development of in vitro models like alveolar-capillary barrier, airway models, skin, blood-brain barrier, kidney barrier, and metastatic models, which can be used for personalized drug screening, understanding physiological and pathological pathways, and tissue implants. In this Review, we focus on the structure, composition, and functions of in vivo BM and the ongoing efforts to mimic it synthetically. Light has been shed on the advantages and limitations of various forms of biomimetic BM scaffolds including porous polymeric membranes, hydrogels, and electrospun membranes This Review further elaborates and justifies the significance of BM mimics in tissue engineering, in particular in the development of in vitro organ model systems.

Topical Losartan and Corticosteroid Additively Inhibit Corneal Stromal Myofibroblast Generation and Scarring Fibrosis After Alkali Burn Injury

Purpose

To evaluate the efficacy of losartan and prednisolone acetate in inhibiting corneal scarring fibrosis after alkali burn injury in rabbits.

Methods

Sixteen New Zealand White rabbits were included. Alkali injuries were produced using 1N sodium hydroxide on a 5-mm diameter Whatman #1 filter paper for 1 minute. Four corneas in each group were treated six times per day for 1 month with 50 µL of (1) 0.8 mg/mL losartan in balanced salt solution (BSS), (2) 1% prednisolone acetate, (3) combined 0.8 mg/mL losartan and 1% prednisolone acetate, or (4) BSS. Area of opacity and total opacity were analyzed in standardized slit-lamp photos with ImageJ. Corneas in both groups were cryofixed in Optimal cutting temperature (OCT) compound at 1 month after surgery, and immunohistochemistry was performed for alpha-smooth muscle actin (α-SMA) and keratocan or transforming growth factor β1 and collagen type IV with ImageJ quantitation.

Results

Combined topical losartan and prednisolone acetate significantly decreased slit-lamp opacity area and intensity, as well as decreased stromal myofibroblast α-SMA area and intensity of staining per section and confined myofibroblasts to only the posterior stroma with repopulation of the anterior and mid-stroma with keratocan-positive keratocytes after 1 month of treatment. Corneal fibroblasts produced collagen type IV not associated with basement membranes, and this production was decreased by topical losartan.

Conclusions

Combined topical losartan and prednisolone acetate decreased myofibroblast-associated fibrosis after corneal alkali burns that produced full-thickness injury, including corneal endothelial damage. Increased dosages and duration of treatment may further decrease scarring fibrosis.

Translational Relevance

Topical losartan and prednisolone acetate decrease myofibroblast-mediated scarring fibrosis after corneal injury.

Combined Therapy Using Human Corneal Stromal Stem Cells and Quiescent Keratocytes to Prevent Corneal Scarring after Injury

Corneal blindness due to scarring is conventionally treated by corneal transplantation, but the shortage of donor materials has been a major issue affecting the global success of treatment. Pre-clinical and clinical studies have shown that cell-based therapies using either corneal stromal stem cells (CSSC) or corneal stromal keratocytes (CSK) suppress corneal scarring at lower levels. Further treatments or strategies are required to improve the treatment efficacy. This study examined a combined cell-based treatment using CSSC and CSK in a mouse model of anterior stromal injury. We hypothesize that the immuno-regulatory nature of CSSC is effective to control tissue inflammation and delay the onset of fibrosis, and a subsequent intrastromal CSK treatment deposited collagens and stromal specific proteoglycans to recover a native stromal matrix. Using optimized cell doses, our results showed that the effect of CSSC treatment for suppressing corneal opacities was augmented by an additional intrastromal CSK injection, resulting in better corneal clarity. These in vivo effects were substantiated by a further downregulated expression of stromal fibrosis genes and the restoration of stromal fibrillar organization and regularity. Hence, a combined treatment of CSSC and CSK could achieve a higher clinical efficacy and restore corneal transparency, when compared to a single CSSC treatment.

Lycium barbarum polysaccharide promotes corneal Re-epithelialization after alkaline injury

Chemical injury of the cornea results in epithelial defect and subsequent stromal scarring and infection. Our study aims to evaluate the effectiveness of pre-treatment of Lycium barbarum polysaccharide (LBP) in promoting corneal re-epithelialization after alkaline burn. The corneas of C57BL/6J mice were pre-treated with topical phosphate-buffered saline or LBP (0.2/2/20 mg/mL) for 7 days, following by 0.1M sodium hydroxide injury for 30 s and washing with distilled water for another 30 s. Area of epithelial defect and thickness of cornea were evaluated. Inflammatory cytokines and water channel expression levels were assessed using immunohistochemistry and Western blot. Compared to the injury group, mice with 2 mg/mL LBP pre-treatment revealed a significant decrease in fluorescein stained area after injury (p = 0.025), with increased epithelial layer thickness (p = 0.004). The corneal opacity was significantly reduced in the group with 2 mg/mL LBP pre-treatment followed by injury (p = 0.02). The expression of matrix metalloproteinase 12 (p = 0.033), platelet derived growth factor-BB (p = 0.031), and aquaporin 5 (p = 0.022) resulted in a decrease in expression level in group with 2 mg/mL LBP pre-treatment. Our results showed that 2 mg/mL LBP, with no apoptotic effect on corneal cells, promoted corneal epithelial growth and minimized disruption of the collagen architecture after injury in vivo. We suggest that LBP, as a natural Traditional Chinese Medicine, may potentially be a novel topical pre-treatment option for patients highly susceptible to ocular injury.

Notch1 signaling in keratocytes maintains corneal transparency by suppressing VEGF expression

The cornea fends off chemicals, dirt, and infectious particles and provides most of the eye's focusing power. Corneal transparency is of paramount importance to normal vision, yet how it is established and maintained remains unclear. Here, we ablated Notch1 in keratocytes using Twist2-Cre mice and found that Twist2-Cre; Notch1^f/f mice developed stroma expansion and neovascularization, followed by hyperproliferation and metaplasia of corneal epithelial progenitor cells and plaque formation at central cornea, leading to loss of transparency. Development of these phenotypes does not involve bacteria-caused inflammation; instead, Notch1 deletion upregulates Vegfa and Vegfc via Hif1α in keratocytes. Vascular endothelial growth factor (VEGF) receptor inhibitor axitinib prevented development of these anomalies in Twist2-Cre; Notch1^f/f mice, suggesting that VEGFs secreted by keratocytes promote not only neovascularization but also proliferation and metaplasia of epithelial progenitor cells at central cornea. This study uncovers a Notch1-Hif1α-VEGF pathway in keratocytes that maintains corneal transparency and represents a potential target for treatment of related corneal disorders.

Shhedding New Light on the Role of Hedgehog Signaling in Corneal Wound Healing

The cornea, an anterior ocular tissue that notably serves to protect the eye from external insults and refract light, requires constant epithelium renewal and efficient healing following injury to maintain ocular homeostasis. Although several key cell populations and molecular pathways implicated in corneal wound healing have already been thoroughly investigated, insufficient/impaired or excessive corneal wound healing remains a major clinical issue in ophthalmology, and new avenues of research are still needed to further improve corneal wound healing. Because of its implication in numerous cellular/tissular homeostatic processes and oxidative stress, there is growing evidence of the role of Hedgehog signaling pathway in physiological and pathological corneal wound healing. Reviewing current scientific evidence, Hedgehog signaling and its effectors participate in corneal wound healing mainly at the level of the corneal and limbal epithelium, where Sonic Hedgehog-mediated signaling promotes limbal stem cell proliferation and corneal epithelial cell proliferation and migration following corneal injury. Hedgehog signaling could also participate in corneal epithelial barrier homeostasis and in pathological corneal healing such as corneal injury-related neovascularization. By gaining a better understanding of the role of this double-edged sword in physiological and pathological corneal wound healing, fascinating new research avenues and therapeutic strategies will undoubtedly emerge.

Comparison of transepithelial and conventional photorefractive keratectomy in myopic and myopic astigmatism patients: a randomized contralateral trial

Background

To assess transepithelial photorefractive keratectomy (tPRK) in terms of corneal epithelial healing rate, postoperative pain, postoperative discomfort, and visual and refraction outcomes compared to mechanical epithelial debridement PRK (mPRK) and alcohol-assisted PRK (aaPRK).

Methods

In this double-masked, randomized clinical trial, thirty-nine patients underwent tPRK in one eye and mPRK in the fellow eye (arm A), and 33 patients underwent tPRK in one eye and aaPRK in the contralateral eye (arm B). All surgical procedures were done using the Schwind Amaris excimer laser. The area of corneal epithelial defect in all eyes was captured and analyzed using ImageJ software.

Results

Mean epithelial healing time was respectively 3.74 ± 0.82 and 3.59 ± 0.79 days in tPRK versus mPRK (P = 0.21) in arm A, and 3.67 ± 0.92 and 3.67 ± 0.74 days in tPRK versus aaPRK (P = 1.00) in arm B. Accounting for the initial corneal epithelial defect area, the epithelial healing rate was faster in conventional PRK groups compared to tPRK (both P<0.001) in both arms. However, there was no significant difference in safety, efficacy, spherical equivalent refractive accuracy, or corneal haze development between tPRK and conventional PRK groups (all P > 0.05).

Conclusions

All three methods are effective in terms of visual and refractive outcomes. However, although time to complete re-epithelialization was similar with the three methods, the epithelial healing rate was faster in conventional PRK considering the initial corneal epithelial defect area, and the patients experienced less pain and discomfort in the first postoperative day.

Trial registration

IRCT, IRCT20200317046804N1. Retrospectively registered 5 May 2020.

Molecular mechanisms and treatments for ocular symblephara

There are currently no effective methods to prevent or durably treat ocular symblephara, the adhesions between the palpebral and bulbar conjunctiva. How symblephara form at the molecular level is largely unknown. We present here an overview of current clinical symblephara treatments and describe potential molecular mechanisms behind conjunctival adhesion formation that may inform future symblephara treatment and prevention options. Understanding how symblephara form at the molecular level will facilitate treatment development. Preventative therapies may be possible by targeting symblephara progenitor cells immediately after injuries, while novel therapeutics should be aimed at modulating TGF-β pathways and effector cells in conjunctival scarring to treat symblephara formation more effectively.

Descemet's membrane injury and regeneration, and posterior corneal fibrosis, in rabbits

The purpose of this investigation was to study Descemet's membrane and corneal endothelial regeneration, myofibroblast generation and disappearance, and TGF beta-1 localization after Descemet's membrane-endothelial excision (Descemetorhexis) in rabbits. Thirty-six rabbits had 8 mm Descemetorhexis and standardized slit lamp photos at 1, 2 and 4 days, 1, 2 and 4 weeks, and 2, 4 and 6 months, as well as multiplex IHC for stromal cell markers keratocan, vimentin, and alpha-smooth muscle actin (SMA); basement membrane (BM) components perlecan, nidogen-1, laminin alpha-5, and collagen type IV; and corneal endothelial marker Na,K-ATPase β1, and TGF beta-1, with ImageJ quantitation. Stromal transparency increased from the periphery beginning at two months after injury and progressed into the central cornea by six months. At six months, central transparency was primarily limited by persistent mid-stromal neovascularization. Stromal myofibroblast zone thickness in the posterior stroma peaked at one month after injury, and then progressively decreased until to six months when few myofibroblasts remained. The regeneration of a laminin alpha-5 and nidogen-1 Descemet's membrane "railroad track" structure was accompanied by corneal endothelial closure and stromal cell production of BM components in corneas from four to six months after injury. TGF beta-1 deposition at the posterior corneal surface from the aqueous humor peaked at one day after Descemetorhexis and diminished even before regeneration of the endothelium and Descemet's membrane. This decrease was associated with collagen type IV protein production by corneal fibroblasts, and possibly myofibroblasts, in the posterior stroma. Descemet's membrane and the corneal endothelium regenerated in the rabbit cornea by six months after eight mm Descemetorhexis. Real-time quantitative RT-PCR experiments in vitro with marker-verified rabbit corneal cells found that 5 ng/ml or 10 ng/ml TGF beta-1 upregulated col4a1 or col4a2 mRNA expression after 6 h or 12 h of exposure in corneal fibroblasts, but not in myofibroblasts. Stromal cells produced large amounts of collagen type IV that likely decreased TGF beta-1 penetration into the stroma and facilitated the resolution of myofibroblast-generated fibrosis.

Immune responses to injury and their links to eye disease

The eye is regarded as an immune privileged site. Since the presence of a vasculature would impair vision, the vasculature of the eye is located outside of the central light path. As a result, many regions of the eye evolved mechanisms to deliver immune cells to sites of dysgenesis, injury, or in response to the many age-related pathologies. While the purpose of these immune responses is reparative or protective, cytokines released by immune cells compromise visual acuity by inducing inflammation and fibrosis. The response to traumatic or pathological injury is distinct in different regions of the eye. Age-related diseases impact both the anterior and posterior segment and lead to reduced quality of life and blindness. Here we focus attention on the role that inflammation and fibrosis play in the progression of age-related pathologies of the cornea and the lens as well as in glaucoma, the formation of epiretinal membranes, and in proliferative vitreoretinopathy.

The anti-scarring role of Lycium barbarum polysaccharide on cornea epithelial-stromal injury

PURPOSE

Cornea epithelial-stromal scarring is related to the differentiation of fibroblasts into opaque myofibroblasts. Our study aims to assess the effectiveness of Lycium barbarum polysaccharide (LBP) solution as a pre-treatment in minimizing corneal scarring.

METHODS

Human corneal fibroblasts were cultured in a three-dimensional collagen type I-based hydrogel in an eye-on-a-chip model. Fibroblasts were pre-treated with 2 mg/mL LBP for 24 h, followed by another 24-h incubation with 10 ng/mL transforming growth factor-beta 1 (TGF-β1) to induce relevant physiological events after stromal injury. Intracellular pro-fibrotic proteins, extracellular matrix proteins, and pro-inflammatory cytokines that involved in fibrosis, were assessed using immunocytochemistry and enzyme-linked immunosorbent assays.

RESULTS

Compared to the positive control TGF-β1 group, LBP pre-treated cells had a significantly lower expression of alpha-smooth muscle actin, marker of myofibroblasts, vimentin (p < 0.05), and also extracellular matrix proteins both collagen type II and type III (p < 0.05) that can be found in scar tissues. Moreover, LBP pre-treated cells had a significantly lower secretion of pro-inflammatory cytokines interleukin-6 and interleukin-8 (p < 0.05). The cell-laden hydrogel contraction and stiffness showed no significant difference between LBP pre-treatment and control groups. Fibroblasts pretreated with LBP as well had reduced angiogenic factors expression and suppression of undesired proliferation (p < 0.05).

CONCLUSION

Our results showed that LBP reduced both pro-fibrotic proteins and pro-inflammatory cytokines on corneal injury in vitro. We suggest that LBP, as a natural Traditional Chinese Medicine, may potentially be a novel topical pre-treatment option prior to corneal refractive surgeries with an improved prognosis.

Extracellular Vesicles in the Cornea: Insights from Other Tissues

Extracellular vesicles (EVs) are phospholipid bilayer-bound particles secreted by cells that have been found to be important in mediating cell-cell communication, signal transduction, and extracellular matrix remodeling. Their role in both physiological and pathological processes has been established in different tissues throughout the human body. The human cornea functions as a transparent and refractive barrier that protects the intraocular elements from the external environment. Injury, infection, or disease may cause the loss of corneal clarity by altering extracellular matrix organization within the stroma that may lead to detrimental effects on visual acuity. Over the years, numerous studies have identified many of the growth factors (e.g., transforming growth factor-β1, thrombospondin-1, and platelet-derived growth factor) important in corneal wound healing and scarring. However, the functional role of bound factors encapsulated in EVs in the context of corneal biology is less defined. In this review, we describe the discovery and characterization of EVs in the cornea. We focus on EV-matrix interactions, potential functions during corneal wound healing, and the bioactivity of mesenchymal stem cell-derived EVs. We also discuss the development of EVs as stable, drug-loaded therapeutics for ocular applications.

Cord blood and amniotic membrane extract eye drop preparations display immune-suppressive and regenerative properties

Diseases and injuries that compromise the ocular surface cause considerable patient distress and have long term consequences for their quality of life. Treatment modalities that can address the delicate balance of tissue regeneration, inflammation and maintenance of corneal transparency are therefore needed. We have recently formulated two novel eye drops from placental tissues: cord blood platelet lysate (CBED) and amniotic membrane extract eye drops (AMED), which can be used to treat severe ocular disorders. Here we characterise these two preparations by measuring: (a) growth factors (GF) and cytokines composition, (b) promotion of human corneal epithelial cell (HCEC) growth and (c) effects on immune cells in a lymphocyte culture assay. Finally, their bioavailability was assayed in an ex vivo porcine corneal model. We show that both preparations contain GF and cytokines that were able to promote the in vitro growth of HCEC and support repair in an in vitro scratch test. When assessed in a lymphocyte culture, both favoured immune suppression reducing the cellular expression of NKG2D and CD107a as well as the production of interferon gamma (IFN-γ) in natural killer, NKT and T cells. Regarding bioavailability, CBED active molecules were found mainly in the pre-corneal fraction with some penetration into the corneal fraction, in an ex vivo model. In summary, both placental-derived allogeneic preparations, CBED and AMED, display regenerative and immunomodulatory capabilities. These results will help define mechanisms of action and the best indications and doses of each product for use in a particular patient and support the development of off-the-shelf therapies for ocular surface pathologies in which wound healing defects and inflammatory events are contributing factors.

[Corneal wound healing-Pathophysiology and principles]

The cornea forms the anterior border of the eye and significantly contributes to a sharp optical image quality on the retina through its transparency, avascular nature and curvature. Because of its anatomical structure and as a barrier to the environment, the cornea is particularly exposed to various external factors, such as injuries and pathogens. A correct wound healing without the formation of light diverging scarring is therefore essential to preserve the integrity and function of the cornea. Misguided wound healing is of outstanding clinical relevance and can lead to corneal fibrogenesis. Corneal fibrosis results in scarring with a loss of optical transparency, which significantly reduces eyesight and can lead to blindness. Understanding the pathophysiological mechanisms of wound healing and fibrogenesis is of great importance for the diagnostics, treatment and evaluation of the subsequent healing process in order to prevent permanent damage as far as possible.

Canonical NF-κB signaling maintains corneal epithelial integrity and prevents corneal aging via retinoic acid

Disorders of the transparent cornea affect millions of people worldwide. However, how to maintain and/or regenerate this organ remains unclear. Here, we show that Rela (encoding a canonical NF-κB subunit) ablation in K14+ corneal epithelial stem cells not only disrupts corneal regeneration but also results in age-dependent epithelial deterioration, which triggers aberrant wound-healing processes including stromal remodeling, neovascularization, epithelial metaplasia, and plaque formation at the central cornea. These anomalies are largely recapitulated in normal mice that age naturally. Mechanistically, Rela deletion suppresses expression of Aldh1a1, an enzyme required for retinoic acid synthesis from vitamin A. Retinoic acid administration blocks development of ocular anomalies in Krt14-Cre; Relaf/f mice and naturally aged mice. Moreover, epithelial metaplasia and plaque formation are preventable by inhibition of angiogenesis. This study thus uncovers the major mechanisms governing corneal maintenance, regeneration, and aging and identifies the NF-κB-retinoic acid pathway as a therapeutic target for corneal disorders.

Serp-1 Promotes Corneal Wound Healing by Facilitating Re-epithelialization and Inhibiting Fibrosis and Angiogenesis

Purpose: Chemical corneal injuries carry a high morbidity and commonly lead to visual impairment. Here, we investigate the role of Serp-1, a serine protease inhibitor, in corneal wound healing.

Methods: An alkaline-induced corneal injury was induced in 14 mice. Following injury, five mice received daily topical saline application while nine mice received Serp-1 100 μL topically combined with a daily subcutaneous injection of 100 ng/gram body weight of Serp-1. Corneal damage was monitored daily through fluorescein staining and imaging. Cross sectional corneal H&E staining were obtained. CD31 was used as marker for neovascularization.

Results: Serp-1 facilitates corneal wound healing by reducing fibrosis and neovascularization while mitigating inflammatory cell infiltration with no noticeable harm related to its application.

Conclusions: Serp-1 effectively mitigates inflammation, decreases fibrosis, and reduce neovascularization in a murine model of corneal injury without affecting other organs.

Translational Relavence: Our study provides preclinical data for topical application of Serp-1 to treat corneal wounds.