Sustained release of decorin to the surface of the eye enables scarless corneal regeneration

Regenerative Therapy for Corneal Scarring Disorders

The cornea is a transparent and vitally multifaceted component of the eye, playing a pivotal role in vision and ocular health. It has primary refractive and protective functions. Typical corneal dysfunctions include opacities and deformities that result from injuries, infections, or other medical conditions. These can significantly impair vision. The conventional challenges in managing corneal ailments include the limited regenerative capacity (except corneal epithelium), immune response after donor tissue transplantation, a risk of long-term graft rejection, and the global shortage of transplantable donor materials. This review delves into the intricate composition of the cornea, the landscape of corneal regeneration, and the multifaceted repercussions of scar-related pathologies. It will elucidate the etiology and types of dysfunctions, assess current treatments and their limitations, and explore the potential of regenerative therapy that has emerged in both in vivo and clinical trials. This review will shed light on existing gaps in corneal disorder management and discuss the feasibility and challenges of advancing regenerative therapies for corneal stromal scarring.

Local decorin delivery via hyaluronic acid microrods improves cardiac performance, ventricular remodeling after myocardial infarction

Heart failure (HF) remains a global public health burden and often results following myocardial infarction (MI). Following injury, cardiac fibrosis forms in the myocardium which greatly hinders cellular function, survival, and recruitment, thus severely limits tissue regeneration. Here, we leverage biophysical microstructural cues made of hyaluronic acid (HA) loaded with the anti-fibrotic proteoglycan decorin to more robustly attenuate cardiac fibrosis after acute myocardial injury. Microrods showed decorin incorporation throughout the entirety of the hydrogel structures and exhibited first-order release kinetics in vitro. Intramyocardial injections of saline (n = 5), microrods (n = 7), decorin microrods (n = 10), and free decorin (n = 4) were performed in male rat models of ischemia-reperfusion MI to evaluate therapeutic effects on cardiac remodeling and function. Echocardiographic analysis demonstrated that rats treated with decorin microrods (5.21% ± 4.29%) exhibited significantly increased change in ejection fraction (EF) at 8 weeks post-MI compared to rats treated with saline (-4.18% ± 2.78%, p < 0.001) and free decorin (-3.42% ± 1.86%, p < 0.01). Trends in reduced end diastolic volume were also identified in decorin microrod-treated groups compared to those treated with saline, microrods, and free decorin, indicating favorable ventricular remodeling. Quantitative analysis of histology and immunofluorescence staining showed that treatment with decorin microrods reduced cardiac fibrosis (p < 0.05) and cardiomyocyte hypertrophy (p < 0.05) at 8 weeks post-MI compared to saline control. Together, this work aims to contribute important knowledge to guide rationally designed biomaterial development that may be used to successfully treat cardiovascular diseases.

Small leucine rich proteoglycans: Biology, function and their therapeutic potential in the ocular surface

Small leucine rich proteoglycans (SLRPs) are the largest family of proteoglycans, with 18 members that are subdivided into five classes. SLRPs are small in size and can be present in tissues as glycosylated and non-glycosylated proteins, and the most studied SLRPs include decorin, biglycan, lumican, keratocan and fibromodulin. SLRPs specifically bind to collagen fibrils, regulating collagen fibrillogenesis and the biomechanical properties of tissues, and are expressed at particularly high levels in fibrous tissues, such as the cornea. However, SLRPs are also very active components of the ECM, interacting with numerous growth factors, cytokines and cell surface receptors. Therefore, SLRPs regulate major cellular processes and have a central role in major fundamental biological processes, such as maintaining corneal homeostasis and transparency and regulating corneal wound healing. Over the years, mutations and/or altered expression of SLRPs have been associated with various corneal diseases, such as congenital stromal corneal dystrophy and cornea plana. Recently, there has been great interest in harnessing the various functions of SLRPs for therapeutic purposes. In this comprehensive review, we describe the structural features and the related functions of SLRPs, and how these affect the therapeutic potential of SLRPs, with special emphasis on the use of SLRPs for treating ocular surface pathologies.

An X-ray inactivated vaccine against Pseudomonas aeruginosa Keratitis in mice

Pseudomonas aeruginosa (P. aeruginosa) is one of the most prevalent pathogens of bacterial keratitis. Bacterial keratitis is a major cause of blindness worldwide. The rising incidence of multidrug resistance of P. aeruginosa precludes treatment with conventional antibiotics. Herein, we evaluated the protective efficiency and explored the possible underlying mechanism of an X-ray inactivated vaccine (XPa) using a murine P. aeruginosa keratitis model. Mice immunized with XPa exhibit reduced corneal bacterial loads and pathology scores. XPa vaccination induced corneal macrophage polarization toward M2, averting an excessive inflammatory reaction. Furthermore, histological observations indicated that XPa vaccination suppressed corneal fibroblast activation and prevented irreversible visual impairment. The potency of XPa against keratitis highlights its potential utility as an effective and promising vaccine candidate for P. aeruginosa.

Urgent unmet needs in the care of bacterial keratitis: An evidence-based synthesis

Bacterial corneal infections, or bacterial keratitis (BK), are ophthalmic emergencies that frequently lead to irreversible visual impairment. Though increasingly recognized as a major cause of global blindness, modern paradigms of evidence-based care in BK have remained at a diagnostic and therapeutic impasse for over half a century. Current standards of management - based on the collection of corneal cultures and the application of broad-spectrum topical antibiotics - are beset by important yet widely underrecognized limitations, including approximately 30% of all patients who will develop moderate to severe vision loss in the affected eye. Though recent advances have involved a more clearly defined role for adjunctive topical corticosteroids, and novel therapies such as corneal crosslinking, overall progress to improve patient and population-based outcomes remains incommensurate to the chronic morbidity caused by this disease. Recognizing that the care of BK is guided by the clinical axiom, "time equals vision", this chapter offers an evidence-based synthesis for the clinical management of these infections, underscoring critical unmet needs in disease prevention, diagnosis, and treatment.

From bench to clinic: Emerging therapies for corneal scarring

Corneal diseases are one of the leading causes of moderate-to-severe visual impairment and blindness worldwide, after glaucoma, cataract, and retinal disease in overall importance. Given its tendency to affect people at a younger age than other blinding conditions such as cataract and glaucoma, corneal scarring poses a huge burden both on the individuals and society. Furthermore, corneal scarring and fibrosis disproportionately affects people in poorer and remote areas, making it a significant ophthalmic public health problem. Traditional medical strategies, such as topical corticosteroids, are not effective in preventing fibrosis or scars. Corneal transplantation, the only effective sight-restoring treatment for corneal scars, is curbed by challenges including a severe shortage of tissue, graft rejection, secondary conditions, cultural barriers, the lack of well-trained surgeons, operating rooms, and well-equipped infrastructures. Thanks to tremendous research efforts, emerging therapeutic options including gene therapy, protein therapy, cell therapy and novel molecules are in development to prevent the progression of corneal scarring and compliment the surgical options currently available for treating established corneal scars in clinics. In this article, we summarise the most relevant preclinical and clinical studies on emerging therapies for corneal scarring in recent years, showing how these approaches may prevent scarring in its early development.

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.

Injectable Decorin/Gellan Gum Hydrogel Encapsulating Adipose-Derived Stem Cells Enhances Anti-Inflammatory Effect in Cartilage Injury via Autophagy Signaling

Adipose-derived stem cells (ADSCs) are employed as a promising alternative in treating cartilage injury. Regulating the inflammatory "fingerprint" of ADSCs to improve their anti-inflammatory properties could enhance therapy efficiency. Herein, a novel injectable decorin/gellan gum hydrogel combined with ADSCs encapsulation for arthritis cartilage treatment is proposed. Decorin/gellan gum hydrogel was prepared according to the previous manufacturing protocol. The liquid-solid form transition of gellan gum hydrogel is perfectly suitable for intra-articular injection. Decorin-enriched matrix showing an immunomodulatory ability to enhance ADSCs anti-inflammatory phenotype under inflammation microenvironment by regulating autophagy signaling. This decorin/gellan gum/ADSCs hydrogel efficiently reverses interleukin-1β-induced cellular injury in chondrocytes. Through a mono-iodoacetate-induced arthritis mice model, the synergistic therapeutic effect of this ADSCs-loaded hydrogel, including inflammation attenuation and cartilage protection, is demonstrated. These results make the decorin/gellan gum hydrogel laden with ADSCs an ideal candidate for treating inflammatory joint disorders.

Role of Decorin in the Lens and Ocular Diseases

Decorin is an archetypal member of the small leucine-rich proteoglycan gene family and is involved in various biological functions and many signaling networks, interacting with extra-cellular matrix (ECM) components, growth factors, and receptor tyrosine kinases. Decorin also modulates the growth factors, cell proliferation, migration, and angiogenesis. It has been reported to be involved in many ischemic and fibrotic eye diseases, such as congenital stromal dystrophy of the cornea, anterior subcapsular fibrosis of the lens, proliferative vitreoretinopathy, et al. Furthermore, recent evidence supports its role in secondary posterior capsule opacification (PCO) after cataract surgery. The expression of decorin mRNA in lens epithelial cells in vitro was found to decrease upon transforming growth factor (TGF)-β-2 addition and increase upon fibroblast growth factor (FGF)-2 addition. Wound healing of the injured lens in mice transgenic for lens-specific human decorin was promoted by inhibiting myofibroblastic changes. Decorin may be associated with epithelial-mesenchymal transition and PCO development in the lens. Gene therapy and decorin administration have the potential to serve as excellent therapeutic approaches for modifying impaired wound healing, PCO, and other eye diseases related to fibrosis and angiogenesis. In this review, we present findings regarding the roles of decorin in the lens and ocular diseases.

Decorin Promotes Osteoblastic Differentiation of Human Periodontal Ligament Stem Cells

The aim of this study is to clarify the biological functions of decorin (DCN) in the healing and regeneration of wounded periodontal tissue. We investigated the expression pattern of DCN during the healing of wounded periodontal tissue in rats by immunohistochemistry and the effects of DCN on the osteoblastic differentiation of human periodontal ligament (PDL) stem cells (HPDLSCs) and preosteoblasts by Alizarin red S staining, quantitative reverse transcription-polymerase chain reactions, and western blotting. The expression of DCN was increased around the wounded PDL tissue on day 5 after surgery compared with the nonwounded PDL tissue, whereas its expression was not changed in the osteoblastic layer around the wounded alveolar bone. Furthermore, DCN promoted the osteoblastic differentiation of HPDLSCs, but it did not affect the osteoblastic differentiation of preosteoblasts. ERK1/2 phosphorylation was upregulated during the DCN-induced osteoblastic differentiation of HPDLSCs. DCN did not affect proliferation, migration, or the PDL-related gene expression of HPDLSCs. In conclusion, this study demonstrates that DCN has a role in the healing of wounded periodontal tissue. Furthermore, DCN secreted from PDL cells may contribute to bone healing by upregulating osteoblastic differentiation through ERK1/2 signaling in HPDLSCs, indicating a therapeutic effect of DCN in periodontal tissue regeneration.

Recent Advancements in Molecular Therapeutics for Corneal Scar Treatment

The process of corneal wound healing is complex and induces scar formation. Corneal scarring is a leading cause of blindness worldwide. The fibrotic healing of a major ocular wound disrupts the highly organized fibrillar collagen arrangement of the corneal stroma, rendering it opaque. The process of regaining this organized extracellular matrix (ECM) arrangement of the stromal layer to restore corneal transparency is complicated. The surface retention capacity of ocular drugs is poor, and there is a large gap between suitable corneal donors and clinical requirements. Therefore, a more efficient way of treating corneal scarring is needed. The eight major classes of interventions targeted as therapeutic tools for healing scarred corneas include those based on exosomes, targeted gene therapy, microRNAs, recombinant viral vectors, histone deacetylase inhibitors, bioactive molecules, growth factors, and nanotechnology. This review highlights the recent advancements in molecular therapeutics to restore a cornea without scarring. It also provides a scope to overcome the limitations of present studies and perform robust clinical research using these strategies.

Decorin mediated biomimetic PCL-gelatin nano-framework to impede scarring

Scars occur as a result of fibrosis after tissue damage or surgery and reports suggest that excessive Transforming growth factor-β (TGF-β) activity during the process of wound healing leads to progressive fibrosis. Decorin is an extracellular matrix (ECM) protein which regulates collagen fibrillogenesis. However, targeted delivery and effective protein therapy remains a challenge owing to degradation byproteases. Hence, we aimed to deliver Decorin in a sustainable mode for the reduction of TGF-β levels and subsequent scar formation. Herein, we have fabricated PCL-Gelatin bio-mimetic scaffolds to optimize the bio-activity and provide localized delivery of recombinant Decorin. The degradation and drug release patterns reveals that this biomaterial is biodegradable and offers sustained release of the recombinant Decorin. Decorin loaded nanofiber displayed lower adhesion and proliferation rates in in-vitro conditions. Moreover, Decorin loaded scaffolds demonstrated morphological changes in cells, specifically targeting the myofibroblast. The expression of TGF-β was also scrutinized to understand the effect of Decorin loaded nanofibers. Besides, in the in-vitro fibrotic model, Decorin loaded nanofibers efficiently reduced the expression of ECM related proteins. Therefore, we report the sustained delivery of the recombinant Decorin from nanofiber dressing to potentially obstruct scar formation during the process of wound healing.

The Biology of Extracellular Matrix Proteins in Hypertrophic Scarring

Significance: Hypertrophic scars (HTS) are a fibroproliferative disorder that occur following deep dermal injury and affect up to 72% of burn patients. These scars result in discomfort, impaired mobility, disruption of normal function and cosmesis, and significant psychological distress. Currently, there are no satisfactory methods to treat or prevent HTS, as the cellular and molecular mechanisms are complex and incompletely understood. This review summarizes the biology of proteins in the dermal extracellular matrix (ECM), which are involved in wound healing and hypertrophic scarring. Recent Advances: New basic research continues toward understanding the diversity of cellular and molecular mechanisms of normal wound healing and hypertrophic scarring. Broadening the understanding of these mechanisms creates insight into novel methods for preventing and treating HTS. Critical Issues: Although there is an abundance of research conducted on collagen in the ECM and its relationship to HTS, there is a significant gap in understanding the role of proteoglycans and their specific isoforms in dermal fibrosis. Future Directions: Exploring the biological roles of ECM proteins and their unique isoforms in HTS, mature scars, and normal skin will further the understanding of abnormal wound healing and create a more robust understanding of what constitutes dermal fibrosis. Research into the biological roles of ECM protein isoforms and their regulation during wound healing warrants a more extensive investigation to identify their distinct biological functions in cellular processes and outcomes.

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Therapeutic effects of equine amniotic membrane suspension on corneal re-epithelialization and haze in a modified lagomorph ex vivo wound healing model

OBJECTIVE

To investigate the therapeutic effects of topical equine amniotic membrane (eAM) suspension following corneal wounding in a controlled experimental setting.

PROCEDURES

Equine amniotic membrane was collected, gamma irradiated, homogenized for topical suspension preparation, and cryopreserved. Corneoscleral rims harvested from fresh rabbit globes were wounded via keratectomy and were maintained in an air-liquid interface ex vivo corneal culture model. Treatment groups included topical gamma irradiated eAM suspension (n = 20) and a control group (n = 20). Re-epithelialization of the wound was assessed with daily photographic evaluation of area of fluorescein uptake (mm² ). Corneal wound haze after a 21-day period was assessed by photographic analysis of haze area (mm² ) and pixel intensity (0-255). Histologic processing of corneal tissue was performed, and protein identification of eAM suspension using Liquid chromatography-mass spectrometry (LC-MS).

RESULTS

The average day of complete corneal re-epithelialization in controls (5.5 ± 1.1) and topically treated (5.5 ± 0.6) corneas, and rates of reduction in area of fluorescein uptake over time did not significantly differ (p = .44). The corneal wound haze was significantly reduced in mean area by approximately 52% and intensity by 57% in corneas treated with topical eAM suspension (p < .05), compared to controls 21 days following wounding. Protein analysis identified numerous proteins, specifically decorin, dermatopontin, and lumican, which have previously been documented in eAM.

CONCLUSIONS

Area and intensity of corneal wound haze were significantly reduced in corneas treated with gamma irradiated eAM suspension, which may be due to previously identified therapeutic proteins which promote corneal clarity.

Six-Month In Vivo Safety Profiling of Topical Ocular AVV5-Decorin Gene Transfer

Purpose

A significant remission of corneal fibrosis and neovascularization in rabbit eye in vivo was observed from a tissue-selective localized adeno-associated virus (AAV)5–Decorin (Dcn) gene therapy. This study sought to investigate 6-month toxicity profiling of this gene therapy for the eye in vivo using a rabbit model.

Methods

A small epithelial scrape followed by corneal drying was performed unilaterally in 12 rabbit eyes and either AAV5–Dcn (n = 6) or naked vector (n = 6) was delivered topically using a cloning cylinder technique. Contralateral eyes served as naïve control (n = 6). Safety and tolerability measurements in live rabbits were performed periodically until month 6 using multimodel clinical ophthalmic imaging tools—a slit lamp, stereomicroscope, and HRT3-RCM in vivo confocal microscope. Thereafter, corneas were excised and subjected to hematoxylin and eosin staining, Mason trichome staining, propidium iodide nuclear staining, and quantitative real-time polymerase chain reaction analyses.

Results

Clinical eye examinations based on the modified Hackett–McDonald ocular scoring system, and in vivo confocal imaging of the cornea showed no signs of ocular toxicity in rabbit eyes given AAV5–Dcn gene transfer vs control eyes (P > 0.05) through 6 months after treatment. The histologic and molecular analyses showed no significant differences in AAV5–Dcn vs AAV naked or naïve control groups (P > 0.05) and were in accordance with the masked clinical ophthalmic observations showing no abnormalities.

Conclusions

Topical tissue-targeted localized AAV5–Dcn gene therapy seems to be safe and nontoxic to the rabbit eye in vivo.

Translational Relevance

AAV5–Dcn gene therapy has the potential to treat corneal fibrosis and neovascularization in vivo safely without significant ocular toxicity.

Foundational concepts in the biology of bacterial keratitis

Bacterial infections of the cornea, or bacterial keratitis (BK), are notorious for causing rapidly fulminant disease and permanent vision loss, even among treated patients. In the last sixty years, dramatic upward trajectories in the frequency of BK have been observed internationally, driven in large part by the commercialization of hydrogel contact lenses in the late 1960s. Despite this worsening burden of disease, current evidence-based therapies for BK - including broad-spectrum topical antibiotics and, if indicated, topical corticosteroids - fail to salvage vision in a substantial proportion of affected patients. Amid growing concerns of rapidly diminishing antibiotic utility, there has been renewed interest in urgently needed novel treatments that may improve clinical outcomes on an individual and public health level. Bridging the translational gap in the care of BK requires the identification of new therapeutic targets and rational treatment design, but neither of these aims can be achieved without understanding the complex biological processes that determine how bacterial corneal infections arise, progress, and resolve. In this chapter, we synthesize the current wealth of human and animal experimental data that now inform our understanding of basic BK pathophysiology, in context with modern concepts in ocular immunology and microbiology. By identifying the key molecular determinants of clinical disease, we explore how novel treatments can be developed and translated into routine patient care.

Tailoring Therapeutic Responses via Engineering Microenvironments with a Novel Synthetic Fluid Gel

This study reports the first fully synthetic fluid gel (SyMGels) using a simple poly(ethylene glycol) polymer. Fluid gels are an interesting class of materials: structured during gelation via shear-confinement to form microparticulate suspensions, through a bottom-up approach. Structuring in this way, when compared to first forming a gel and subsequently breaking it down, results in the formation of a particulate dispersion with particles "grown" in the shear flow. Resultantly, systems form a complex microstructure, where gelled particles concentrate remaining non-gelled polymer within the continuous phase, creating an amorphous-like interstitial phase. As such, these materials demonstrate mechanical characteristics typical of colloidal glasses, presenting solid-like behaviors at rest with defined yielding; likely through intrinsic particle-particle and particle-polymer interactions. To date, fluid gels have been fabricated using polysaccharides with relatively complex chemistries, making further modifications challenging. SyMGels are easily functionalised, using simple click-chemistry. This chemical flexibility, allows the creation of microenvironments with discrete biological decoration. Cellular control is demonstrated using MSC (mesenchymal stem cells)/chondrocytes and enables the regulation of key biomarkers such as aggrecan and SOX9. These potential therapeutic platforms demonstrate an important advancement in the biomaterial field, underpinning the mechanisms which drive their mechanical properties, and providing a versatile delivery system for advanced therapeutics.

Cell-Free Biological Approach for Corneal Stromal Wound Healing

Corneal opacification is the fourth most common cause of blindness globally behind cataracts, glaucoma, and age-related macular degeneration. The standard treatment of serious corneal scarring is corneal transplantation. Though it is effective for restoring vision, the treatment outcome is not optimal, due to limitations such as long-term graft survival, lifelong use of immunosuppressants, and a loss of corneal strength. Regulation of corneal stromal wound healing, along with inhibition or downregulation of corneal scarring is a promising approach to prevent corneal opacification. Pharmacological approaches have been suggested, however these are fraught with side effects. Tissue healing is an intricate process that involves cell death, proliferation, differentiation, and remodeling of the extracellular matrix. Current research on stromal wound healing is focused on corneal characteristics such as the immune response, angiogenesis, and cell signaling. Indeed, promising new technologies with the potential to modulate wound healing are under development. In this review, we provide an overview of cell-free strategies and some approaches under development that have the potential to control stromal fibrosis and scarring, especially in the context of early intervention.

Decorin as a possible strategy for the amelioration of COVID-19

Coronavirus pandemic has emerged as an extraordinary healthcare crisis in modern times. The SARS-CoV-2 novel coronavirus has high transmission rate, is more aggressive and virulent in comparison to previously known coronaviruses. It primarily attacks the respiratory system by inducing cytokine storm that causes systemic inflammation and pulmonary fibrosis. Decorin is a pluripotent molecule belonging to a leucine rich proteoglycan group that exerts critical role in extracellular matrix (ECM) assembly and regulates cell growth, adhesion, proliferation, inflammation, and fibrogenesis. Interestingly, decorin has potent anti-inflammatory, cytokine inhibitory, and anti-fibrillogenesis effects which make it a potential drug candidate against the COVID-19 related complications especially in the context of lung fibrosis. Herein, we postulate that owing to its distinctive pharmacological actions and immunomodulatory effect, decorin can be a promising preclinical therapeutic agent for the therapy of COVID-19.

The rheology of direct and suspended extrusion bioprinting

Bioprinting is a tool increasingly used in tissue engineering laboratories around the world. As an extension to classic tissue engineering, it enables high levels of control over the spatial deposition of cells, materials, and other factors. It is a field with huge promise for the production of implantable tissues and even organs, but the availability of functional bioinks is a barrier to success. Extrusion bioprinting is the most commonly used technique, where high-viscosity solutions of materials and cells are required to ensure good shape fidelity of the printed tissue construct. This is contradictory to hydrogels used in tissue engineering, which are generally of low viscosity prior to cross-linking to ensure cell viability, making them not directly translatable to bioprinting. This review provides an overview of the important rheological parameters for bioinks and methods to assess printability, as well as the effect of bioink rheology on cell viability. Developments over the last five years in bioink formulations and the use of suspended printing to overcome rheological limitations are then discussed.

Prevention of Corneal Myofibroblastic Differentiation In Vitro Using a Biomimetic ECM Hydrogel for Corneal Tissue Regeneration

Corneal scarring is one of the major causes of blindness, affecting millions worldwide. Despite recent advancements in surgical strategies, there is an unmet need for a clinically feasible material and methods to prevent scarring following corneal injury. In this study, we report the potential utility of a hydrogel derived from cadaveric animal corneas, using a decellularized corneal matrix hydrogel (abbreviated as dCMH), which is prepared by a simple method. This hydrogel is easily injectable, biocompatible, and has the ability to maintain good shape-retention properties at 37 °C, which make it suitable for in vivo applications. Furthermore, our gene expression studies and immunofluorescence studies indicate that dCMH maintains the morphology and function of keratocytes in vitro and prevents their transdifferentiation to myofibroblasts. From the above results, it is evident that dCMH maintains the keratocytes with the ability to regenerate the corneal defect without scar. We thus suggest a simple yet effective approach for corneal tissue decellularization and that dCMH can be a promising material for prophylaxis against blinding scar formation in an injured cornea.

ILB® resolves inflammatory scarring and promotes functional tissue repair

Fibrotic disease is a major cause of mortality worldwide, with fibrosis arising from prolonged inflammation and aberrant extracellular matrix dynamics. Compromised cellular and tissue repair processes following injury, infection, metabolic dysfunction, autoimmune conditions and vascular diseases leave tissues susceptible to unresolved inflammation, fibrogenesis, loss of function and scarring. There has been limited clinical success with therapies for inflammatory and fibrotic diseases such that there remains a large unmet therapeutic need to restore normal tissue homoeostasis without detrimental side effects. We investigated the effects of a newly formulated low molecular weight dextran sulfate (LMW-DS), termed ILB^®, to resolve inflammation and activate matrix remodelling in rodent and human disease models. We demonstrated modulation of the expression of multiple pro-inflammatory cytokines and chemokines in vitro together with scar resolution and improved matrix remodelling in vivo. Of particular relevance, we demonstrated that ILB^® acts, in part, by downregulating transforming growth factor (TGF)β signalling genes and by altering gene expression relating to extracellular matrix dynamics, leading to tissue remodelling, reduced fibrosis and functional tissue regeneration. These observations indicate the potential of ILB^® to alleviate fibrotic diseases.

Shear sensitive injectable hydrogels of cross-linked tragacanthic acid for ocular drug delivery: Rheological and biological evaluation

Drug delivery to posterior segment of eye has always been challenging. The aim of the present study was to provide a novel injectable, shear sensitive hydrogel based on tragacanthic acid (TA) with three kinds of acetate salts as cross-linker. Rheological properties by strain and shear stress sweep measurements and also dynamic rheological experiments including frequency and time sweep measurements were studied. Biological studies comprising, cell culture, Draize test on rabbit eyes and histopathological tests were done. The results showed the optimized hydrogel was biocompatible, injectable and owning acceptable firmness in rest state after injection. Healing time of the hydrogel was 46 s and was shear-sensitive. It showed no cytotoxicity on HUVEC cells. No allergic reaction was seen in Draize test and histological examination showed integrity of the retinal layers with no evidence of pathological changes, such as deformations, degeneration, or inflammation. TA hydrogel is promising in ocular drug delivery.

Corneal stromal wound healing: Major regulators and therapeutic targets

Corneal stromal wound healing is a complex event that occurs to restore the transparency of an injured cornea. It involves immediate apoptosis of keratocytes followed by their activation, proliferation, migration, and trans-differentiation to myofibroblasts. Myofibroblasts contract to close the wound and secrete extracellular matrix and proteinases to remodel it. Released proteinases may degenerate the basement membrane allowing an influx of cytokines from overlying epithelium. Immune cells infiltrate the wound to clear cellular debris and prevent infections. Gradually basement membrane regenerates, myofibroblasts and immune cells disappear, abnormal matrix is resorbed, and transparency of the cornea is restored. Often this cascade deregulates and corneal opacity results. Factors that prevent corneal opacity after an injury have always intrigued the researchers. They hold clinical relevance as they can guide the outcomes of corneal surgeries. Studies in the past have shed light on the role of various factors in stromal healing. TGFβ (transforming growth factor-beta) signaling is the central player guiding stromal responses. Other major regulators include myofibroblasts, basement membrane, collagen fibrils, small leucine-rich proteoglycans, biophysical cues, proteins derived from extracellular matrix, and membrane channels. The knowledge about their roles helped to develop novel therapies to prevent corneal opacity. This article reviews the role of major regulators that determine the outcome of stromal healing. It also discusses emerging therapies that modulate the role of these regulators to prevent stromal opacity.

Effects of the signal modulation on the response of human fibroblasts to in vitro stimulation with subthermal RF currents

Capacitive-Resistive Electric Transfer (CRET) thermotherapies aim at tissue repair and regeneration through non-invasive application of RF currents. We have reported that the cellular response to subthermal CRET currents is non-linearly dependent on the signal frequency, and that in vitro exposure to a 448-kHz CRET signal promotes ADSC proliferation, as well as collagen and glycosaminoglycan synthesis in prechondrocytic cells. The present work investigates the response of neonatal fibroblasts to subthermal exposure (100 µA/mm²) to two CRET signals: a 448-kHz, non-modulated sinusoidal wave vs. a 20-kHz amplitude-modulation of the 448-kHz carrier. To that end, cell proliferation and expression of the biomarkers Hsp47, Hsp27 and decorin were assessed by cell count, PCNA and Western blotting. The results revealed that while both signals significantly and equivalently increased early (4 h) expression of Hsp47, the modulated signal was more efficient in inducing Hsp27 and decorin overexpression and promoting cell proliferation. These data indicate that the cellular response is dependent on the RF signal modulation and suggest that the therapeutic effects of CRET could be mediated by promotion of fibroblastic proliferation and overexpression of biomarkers that are essential in skin regeneration.

Steroid-eluting contact lenses for corneal and intraocular inflammation

Ocular inflammation is one of the leading causes of blindness worldwide, and steroids in topical ophthalmic solutions (e.g. dexamethasone eye drops) are the mainstay of therapy for ocular inflammation. For many non-infectious ocular inflammatory diseases, such as uveitis, eye drops are administered as often as once every hour. The high frequency of administration coupled with the side effects of eye drops leads to poor adherence for patients. Drug-eluting contact lenses have long been sought as a potentially superior alternative for sustained ocular drug delivery; but loading sufficient drug into contact lenses and control the release of the drug is still a challenge. A dexamethasone releasing contact lens (Dex-Lens) was previously developed by encapsulating a dexamethasone-polymer film within the periphery of a hydrogel-based contact lens. Here, we demonstrate safety and efficacy of the Dex-Lens in rabbit models in the treatment of anterior ocular inflammation. The Dex-Lens delivered drug for 7 days in vivo (rabbit model). In an ocular irritation study (Draize test) with Dex-Lens extracts, no adverse events were observed in normal rabbit eyes. Dex-Lenses effectively inhibited suture-induced corneal neovascularization and inflammation for 7 days and lipopolysaccharide-induced anterior uveitis for 5 days. The efficacy of Dex-Lenses was similar to that of hourly-administered dexamethasone eye drops. In the corneal neovascularization study, substantial corneal edema was observed in rabbit eyes that received no treatment and those that wore a vehicle lens as compared to rabbit eyes that wore the Dex-Lens. Throughout these studies, Dex-Lenses were well tolerated and did not exhibit signs of toxicity. Dexamethasone-eluting contact lenses may be an option for the treatment of ocular inflammation and a platform for ocular drug delivery. STATEMENT OF SIGNIFICANCE: Inflammation of the eye can happen either on the ocular surface (i.e. the cornea) or inside the eye, both of which can result in loss of vision or even blindness. Ocular inflammation is normally treated by steroid eye drops. Depending on the type and severity of inflammation, patients may have to take drops every hour for days at a time. Such severe dosing regimen can lead to patients missing doses. Also, more than 95% drug in an eye drop never goes inside the eye. Here we present a contact lens that release a steroid (dexamethasone) for seven days at a time. It is much more efficient than eye drops and a significant improvement since once worn, the patient will avoid missing doses.

USP10 Targeted Self-Deliverable siRNA to Prevent Scarring in the Cornea

Ocular scarring after surgery, trauma, or infection leads to vision loss. The transparent cornea is an excellent model system to test anti-scarring therapies. Cholesterol-conjugated fully modified asymmetric small interfering RNAs (siRNAs) (self-deliverable siRNAs [sdRNAs]) are a novel modality for in vivo gene knockdown, transfecting cells and tissues without any additional formulations. Myofibroblasts are a main contributor to scarring and fibrosis. α_v integrins play a central role in myofibroblast pathological adhesion, overcontraction, and transforming growth factor β (TGF-β) activation. Previously, we demonstrated that α_v integrins are protected from intracellular degradation after wounding by upregulation of the deubiquitinase (DUB) ubiquitin-specific protease 10 (USP10), leading to integrin cell surface accumulation. In this study, we tested whether knockdown of USP10 with a USP10-targeting sdRNA (termed US09) will reduce scarring after wounding a rabbit cornea in vivo. The wounded corneal stroma was treated once with US09 or non-targeting control (NTC) sdRNA. At 6 weeks US09 treatment resulted in faster wound closure, limited scarring, and suppression of fibrotic markers and immune response. Specifically, fibronectin-extra domain A (EDA), collagen III, and a-smooth muscle actin (p < 0.05), CD45⁺ cell infiltration (p < 0.01), and apoptosis at 24 (p < 0.01) and 48 h (p < 0.05) were reduced post-wounding. Corneal thickness and cell proliferation were restored to unwounded parameters. Targeting the DUB, USP10 is a novel strategy to reduce scarring. This study indicates that ubiquitin-mediated pathways should be considered in the pathogenesis of fibrotic healing.

Sustained Release of TPCA-1 from Silk Fibroin Hydrogels Preserves Keratocyte Phenotype and Promotes Corneal Regeneration by Inhibiting Interleukin-1β Signaling

Corneal injury due to ocular trauma or infection is one of the most challenging vision impairing pathologies that exists. Many studies focus on the pro-inflammatory and pro-angiogenic effects of interleukin-1β (IL-1β) on corneal wound healing. However, the effect of IL-1β on keratocyte phenotype and corneal repair, as well as the underlying mechanisms, is not clear. This study reports, for the first time, that IL-1β induces phenotype changes of keratocytes in vitro, by significantly down-regulating the gene and protein expression levels of keratocyte markers (Keratocan, Lumican, Aldh3a1 and CD34). Furthermore, it is found that the NF-κB pathway is involved in the IL-1β-induced changes of keratocyte phenotype, and that the selective IKKβ inhibitor TPCA-1, which inhibits NF-κB, can preserve keratocyte phenotype under IL-1β simulated pathological conditions in vitro. By using a murine model of corneal injury, it is shown that sustained release of TPCA-1 from degradable silk fibroin hydrogels accelerates corneal wound healing, improves corneal transparency, enhances the expression of keratocyte markers, and supports the regeneration of well-organized epithelium and stroma. These findings provide insights not only into the pathophysiological mechanisms of corneal wound healing, but also into the potential development of new treatments for patients with corneal injuries.

Distribution and Function of Glycosaminoglycans and Proteoglycans in the Development, Homeostasis and Pathology of the Ocular Surface

The ocular surface, which forms the interface between the eye and the external environment, includes the cornea, corneoscleral limbus, the conjunctiva and the accessory glands that produce the tear film. Glycosaminoglycans (GAGs) and proteoglycans (PGs) have been shown to play important roles in the development, hemostasis and pathology of the ocular surface. Herein we review the current literature related to the distribution and function of GAGs and PGs within the ocular surface, with focus on the cornea. The unique organization of ECM components within the cornea is essential for the maintenance of corneal transparency and function. Many studies have described the importance of GAGs within the epithelial and stromal compartment, while very few studies have analyzed the ECM of the endothelial layer. Importantly, GAGs have been shown to be essential for maintaining corneal homeostasis, epithelial cell differentiation and wound healing, and, more recently, a role has been suggested for the ECM in regulating limbal stem cells, corneal innervation, corneal inflammation, corneal angiogenesis and lymphangiogenesis. Reports have also associated genetic defects of the ECM to corneal pathologies. Thus, we also highlight the role of different GAGs and PGs in ocular surface homeostasis, as well as in pathology.

The neuroregenerative effects of topical decorin on the injured mouse cornea

Background

The cornea is innervated with a rich supply of sensory nerves that play important roles in ocular surface health. Any injury or pathology of the corneal nerves increases the risk of dry eye disease and infection. This study aims to evaluate the therapeutic potential of topical decorin to improve corneal nerve regeneration in a mouse model of sterile epithelial abrasion injury.

Methods

Bilateral central corneal epithelial abrasions (2-mm, Alger Brush) were performed on young C57BL/6 J mice to remove the corneal sensory nerves. Decorin, or vehicle, was applied topically, three times per day for 1 week or every 2 h for 6 h. Spectral-domain optical coherence tomography was performed to measure the abrasion area and corneal thickness. Wholemount immunofluorescence staining was used to assess sensory nerve regeneration (β-tubulin III) and immune cell density (CD45, Iba1, CD11c). To investigate the specific role of dendritic cells (DCs), Cx3cr1^gfp/gfp mice, which spontaneously lack resident corneal epithelial DCs, were also investigated. The effect of prophylactic topical administration of recombinant human decorin (applied prior to the abrasion) was also investigated. Nerve tracing (NeuronJ software) was performed to compare recovery of basal nerve axons and superficial nerve terminals in the central and peripheral cornea.

Results

At 6 h after injury, topical decorin application was associated with greater intraepithelial DC recruitment but no change in re-epithelialisation or corneal thickness, compared to the vehicle control. One week after injury, sub-basal nerve plexus and superficial nerve terminal density were significantly higher in the central cornea in the decorin-treated eyes. The density of corneal stromal macrophages in the decorin-treated eyes and their contralateral eyes was significantly lower compared to saline-treated corneas. No significant improvement in corneal nerve regeneration was observed in Cx3cr1^gfp/gfp mice treated with decorin.

Conclusions

Decorin promotes corneal epithelial nerve regeneration after injury. The neuroregenerative effect of topical decorin was associated with a higher corneal DC density during the acute phase, and fewer macrophages at the study endpoint. The corneal neuroregenerative effects of decorin were absent in mice lacking intraepithelial DCs. Together, these findings support a role for decorin in DC-mediated neuroregeneration following corneal abrasion injury.

A Novel CD147 Inhibitor, SP-8356, Attenuates Pathological Fibrosis in Alkali-Burned Rat Cornea

The corneal fibrotic responses to corneal damage often lead to severe corneal opacification thereby resulting in severe visual impairment or even blindness. The persistence of corneal opacity depends heavily on the activity of corneal myofibroblast. Myofibroblasts are opaque and synthesize a disorganized extracellular matrix (ECM) and thus promoting opacification. Cluster of differentiation 147 (CD147), a member of the immunoglobulin superfamily, is known to play important roles in the differentiation process from fibroblast to myofibroblast in damaged cornea and may therefore be an effective target for treatment of corneal opacity. Here, we examined the therapeutic efficacy of novel CD147 inhibiting verbenone derivative SP-8356 ((1S,5R)-4-(3,4-dihydroxy-5-methoxystyryl)-6,6-dimethylbicyclo[3.1.1]hept-3-en-2-one) on corneal fibrosis. Topical SP-8356 significantly reduced corneal haze and fibrosis in the alkali-burned cornea. In detail, SP-8356 inhibited both alpha-smooth muscle actin (α-SMA) expressing myofibroblast and its ECM-related products, such as matrix-metalloproteinase-9 and collagen type III and IV. Similar to SP-8356, topical corticosteroid (prednisolone acetate, PA) also reduced the ECM-related products and opacification. However, prednisolone acetate failed to decrease the population of α-SMA-positive corneal myofibroblast. In conclusion, SP-8356 is capable enough to prevent corneal haze by preventing pathological fibrosis after severe corneal damage. Therefore, SP-8356 could be a potentially promising therapeutic drug for corneal fibrosis.

What Makes Cornea Immunologically Unique and Privileged? Mechanistic Clues from a High-Resolution Proteomic Landscape of the Human Cornea

Success rates of corneal transplantation are particularly high owing to its unique, innate immune privilege derived from a phenomenon known as Anterior Chamber-Associated Immune Deviation (ACAID). Of note, cornea is a transparent, avascular structure that acts as a barrier along with sclera to protect the eye and contributes to optical power. Molecular and systems biology mechanisms underlying ACAID and the immunologically unique and privileged status of cornea are not well known. We report here a global unbiased proteomic profiling of the human cornea and the identification of 4824 proteins, the largest catalog of human corneal proteins identified to date. Moreover, signaling pathway analysis revealed enrichment of spliceosome, phagosome, lysosome, and focal adhesion pathways, thereby demonstrating the protective functions of corneal proteins. We observed an enrichment of neutrophil-mediated immune response processes in the cornea as well as proteins belonging to the complement and ER-Phagosome pathways that are suggestive of active immune and inflammatory surveillance response. This study provides a key expression map of the corneal proteome repertoire that should enable future translational medicine studies on the pathological conditions of the cornea and the mechanisms by which cornea immunology are governed. Molecular mechanisms of corneal immune privilege have broad relevance to understand and anticipate graft rejection in the field of organ transplantation.

Lowered Decorin With Aberrant Extracellular Matrix Remodeling in Aqueous Humor and Tenon's Tissue From Primary Glaucoma Patients

Purpose

To evaluate the inflammatory cytokine, growth factors, extracellular matrix (ECM) remodeling genes, profibrotic and antifibrotic molecules in patients undergoing glaucoma filtration surgery (GFS). Additionally, the effect of preoperative antiglaucoma medications (AGMs) and postoperative bleb status were related to these parameters.

Methods

Tenon's tissue and aqueous humour (AH) were collected from 207 patients undergoing GFS with primary open-angle glaucoma (POAG) (n = 77), primary angle-closure glaucoma (PACG) (n = 62), and cataract controls (n = 68). Monocyte chemoattractant protein-1 (MCP-1), connective tissue growth factor (CTGF), transforming growth factor β1/2 (TGF-β1/2), lysyl oxidase (LOX), lysyl oxidase L2 (LOXL2), elastin (ELN), collagen type 1 α 1 (COL1A1), secreted protein acidic and rich in cysteine (SPARC), α-smooth muscle actin (α-SMA), and decorin (DCN) were determined in tenon's tissue by real-time PCR and in AH using ELISA.

Results

A significant increase was observed in the transcripts of MCP-1, TGF-β2, and SPARC in POAG and PACG (P < 0.05); CTGF, TGF-β1, LOX, LOXL2, ELN, COL1A1, and α-SMA in PACG (P < 0.05) compared with control. DCN transcript was significantly decreased in POAG and PACG (P < 0.05) compared with control. The protein levels of CTGF, TGF-β1/β2, ELN, SPARC, and LOXL2 was significantly elevated in POAG and PACG (P < 0.05); DCN was decreased (P < 0.05) compared with control. These parameters showed significant association with duration of preoperative AGMs and postoperative bleb status.

Conclusions

This study demonstrates increased expression of growth factors and ECM molecules, both at protein and transcript levels in GFS patients. A decreased DCN in AH seems striking, and if restored might have a therapeutic role in minimizing postoperative scarring to improve GFS outcome.

Proteoglycans in Biomedicine: Resurgence of an Underexploited Class of ECM Molecules

Proteoglycans have emerged as biomacromolecules with important roles in matrix remodeling, homeostasis, and signaling in the past two decades. Due to their negatively charged glycosaminoglycan chains as well as distinct core protein structures, they interact with a variety of molecules, including matrix proteins, growth factors, cytokines and chemokines, pathogens, and enzymes. This led to the dawn of glycan therapies in the 20^th century, but this research was quickly overshadowed by readily available DNA and protein-based therapies. The recent development of recombinant technology and advances in our understanding of proteoglycan function have led to a resurgence of these molecules as potential therapeutics. This review focuses on the recent preclinical efforts that are bringing proteoglycan research and therapies back to the forefront. Examples of studies using proteoglycan cores and mimetics have also been included to give the readers a perspective on the wide-ranging and extensive applications of these versatile molecules. Collectively, these advances are opening new avenues for targeting diseases at a molecular level, and providing avenues for the development of new and exciting treatments in regenerative medicine.

Encapsulating curcumin in ethylene diamine-β-cyclodextrin nanoparticle improves topical cornea delivery

Curcumin is a powerful scavenger of reactive oxygen species and could prevent the corneal cells from oxidative damage. However, the clinical efficacy of curcumin is limited by its low aqueous solubility and stability, leading to poor bioavailability. β-cyclodextrin, with a hydrophilic surface and a hydrophobic cavity and self-assembling properties, can form inclusion complexes with lipophilic drugs such as curcumin for ocular delivery. We synthesized ethylene diamine (EDA)-modified β-cyclodextrin and prepared the curcumin complexation using the solvent evaporation method. The EDA-β-cyclodextrin provided a better thermodynamic stability and higher complex yield for curcumin complexes, compared to β-cyclodextrin, which were demonstrated on the analysis of their van't Hoff plots and phase solubility diagrams. We characterized EDA-β-cyclodextrin curcumin nanoparticles and determined that the EDA modified β-cyclodextrin is a more suitable carrier than parental β-cyclodextrin, using FT-IR, XRD, TEM, and analyses of solubility and storage stability. In addition, the curcumin-EDA-β-cyclodextrin nanoparticles had better in vitro corneal penetration and 3 -h cumulative flux in a porcine cornea experiment, and displayed an improved biocompatibility, confirmed by the histological examination of porcine corneas and cell viability of bovine corneal epithelial cells. These results together revealed a role of EDA modification in the β-cyclodextrin carrier, including the improvement of curcumin complex formation, thermodynamic properties, cytotoxicity, and the in vitro corneal penetration. The EDA-β-cyclodextrin inclusion can provide curcumin a higher degree of aqueous solubility and corneal permeability.