Targeted AAV5-Smad7 gene therapy inhibits corneal scarring in vivo

PI3K signaling and lysyl oxidase is critical to corneal stroma fibrosis following mustard gas injury

Sulfur mustard gas (SM), an alkylating and vesicating agent, has been used frequently in many wars and conflicts. SM exposure to the eye results in several corneal abnormalities including scar/fibrosis formation. However, molecular mechanism for SM induced corneal fibrosis development is poorly understood. After SM insult to the eye, excessive synthesis/secretion of extracellular matrix components (ECM) including collagen (COL) I, COL III, and lysyl oxidase (LOX) by corneal myofibroblasts causes corneal fibrosis, however, precise mechanism remains elusive. This study tested the hypothesis that Phosphoinositide 3-kinase (PI3K) signaling alterations post SM in cornea enhances stromal ECM synthesis and corneal fibrosis. New Zealand White Rabbits were used. The right eyes were exposed to SM (200 mg-min/m3) and left eye to the air for 8min at MRI Global. Rabbit corneas were collected on day-3, day-7, and day-14 for molecular analysis. SM exposure caused a significant increase in mRNA expression of PI3K, AKT, COL I, COL III, and LOX and protein levels of LOX in a time-dependent manner in rabbit corneas. The in vitro studies were performed with human corneal stromal fibroblasts (hCSFs) by growing cultures in -/+ nitrogen mustard (NM) and LY294002, a PI3K specific inhibitor, for 30min, 8h, 24h, 48h, and 72h. NM significantly increased mRNA and protein levels of PI3K, AKT, COL I, COL III, and LOX. On the contrary, LY294002 in NM hCSFs significantly reduced PI3K, AKT, COL I, COL III, and LOX protein expression. We concluded that PI3K signaling mediates stromal collagen synthesis and LOX production following SM injury.

Analysis of Smad3 in the modulation of stromal extracellular matrix proteins in corneal scarring after alkali injury

Purpose

During ocular trauma, excessive proliferation and transdifferentiation of corneal stromal fibroblasts cause haze/fibrosis in the cornea. Transforming growth factor β (TGFβ) plays a key role in corneal fibrosis through the Smad signaling pathway. The aberrant activity of TGFβ signaling during ocular trauma (viz. mechanical, infectious, chemical, or surgically altered TGFβ/Smad signaling) leads to regulating the predominant expression of myogenic proteins and the extracellular matrix (ECM). We sought to investigate the functional role of Smad3 in corneal wound repair and stromal ECM assembly using Smad3+/+ wild-type and Smad3-/- deficient mice.

Methods

Corneal injury was introduced with the topical application of an alkali-soaked 2-mm filter disc on the central cornea in the Smad3+/+ (C57BL/6J) and Smad3-/- (129-Smad3tm1Par/J) mouse strains. Slit-lamp and stereo microscopy were used for clinical assessment and corneal haze grading in live animals. Hematoxylin and eosin and Masson's trichrome staining were used to study comparative morphology and collagen level alterations between the groups. Real-time qRT-PCR, western blot, and immunohistochemistry were used to measure changes in profibrotic genes at the mRNA and protein levels.

Results

Slit-lamp clinical exams and stereo microscopy detected notably less opaque cornea in the eyes of Smad3-/- compared with Smad3+/+ mice at 3 weeks (p<0.01) in live animals. Corneal tissue sections of Smad3-/- mice showed significantly fewer α-smooth muscle actin-positive cells compared with those of the Smad3+/+ animals (p<0.05). The corneas of the Smad3-/- mice showed significantly lower mRNA levels of pro-fibrotic genes, α-smooth muscle actin, fibronectin, and collagen I (p<0.05, p<0.01, and p<0.001). In addition, the matrix metalloproteinase and tissue inhibitors of metalloproteinase levels were significantly increased (p<0.001) in the corneal tissue during alkali injury in both Smad3+/+ wild-type and Smad3-/- deficient mice.

Conclusions

The significant changes in profibrotic genes and stromal ECM proteins revealed a direct role of Smad3 in stromal ECM proteins and TGFβ/Smad-driven wound healing. Smad3 appears to be an attractive molecular target for limiting abnormal stroma wound healing to treat corneal fibrosis in vivo.

Anti-fibrotic effects of lisinopril (ACE inhibitor) and fasudil (ROCK inhibitor) in combination for canine corneal fibrosis in vitro

BACKGROUND

Corneal fibrosis is a leading cause of blindness in mammalian species and may result in compromised performance in sports and daily functions. This study evaluated the safety and anti-fibrotic effects of the FDA-approved drugs, angiotensin-converting enzyme inhibitor (ACE-I) lisinopril and rho-kinase inhibitor (ROCK-I) fasudil, alone and in combination, on the canine cornea using an established in vitro model.

METHODS

To test the safety and efficacy of lisinopril and fasudil, primary canine corneal fibroblasts (CCFs) generated from donor corneas of healthy dogs (n = 20) were used. A series of dose-dependent and time-dependent assays with lisinopril (1-50 μM) and fasudil (1-10 nM) were performed. qRT-PCR, immunofluorescence (IF) staining, cell viability assay, cell proliferation assay, LIVE/DEAD viability/cytotoxicity assay, TUNEL assay, and total cell count were performed.

RESULTS

A 25-μM lisinopril and 3-nM fasudil dose were safe, nontoxic, and optimal for therapeutic evaluations in vitro. Treatments of lisinopril or fasudil, alone or in-combination, to CCFs grown in the presence of TGF-β1 (5 ng/mL) showed inhibition of myofibroblast formation based on phase-contrast microscopy. The qRT-PCR and IF studies showed a significant decrease in expression of profibrotic markers, including α-smooth muscle actin (α-SMA; p < .0001), fibronectin (FN; p = .0002), tenascin C (TNC; p < .0001), Collagen I (Col-I; p < .0001), Collagen IIIA1 (Co-IIIA1; p < .0001), and Collagen IV (Co-lV; p < .0001).

CONCLUSION

An ophthalmic formulation consisting of lisinopril and fasudil may offer a safe and effective method to treat canine corneal fibrosis. Additional studies evaluating safety and efficacy of this formulation in vivo are warranted.

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.

Tissue-targeted and localized AAV5-DCN and AAV5-PEDF combination gene therapy abrogates corneal fibrosis and concurrent neovascularization in rabbit eyes in vivo

PURPOSE

Corneal fibrosis and neovascularization (CNV) after ocular trauma impairs vision. This study tested therapeutic potential of tissue-targeted adeno-associated virus5 (AAV5) mediated decorin (DCN) and pigment epithelium-derived factor (PEDF) combination genes in vivo.

METHODS

Corneal fibrosis and CNV were induced in New Zealand White rabbits via chemical trauma. Gene therapy in stroma was delivered 30-min after chemical-trauma via topical AAV5-DCN and AAV5-PEDF application using a cloning cylinder. Clinical eye examinations and multimodal imaging in live rabbits were performed periodically and corneal tissues were collected 9-day and 15-day post euthanasia. Histological, cellular, and molecular and apoptosis assays were used for efficacy, tolerability, and mechanistic studies.

RESULTS

The AAV5-DCN and AAV5-PEDF combination gene therapy significantly reduced corneal fibrosis (p < 0.01 or p < 0.001) and CNV (p < 0.001) in therapy-given (chemical-trauma and AAV5-DCN + AAV5-PEDF) rabbit eyes compared to the no-therapy given eyes (chemical-trauma and AAV5-naked vector). Histopathological analyses demonstrated significantly reduced fibrotic α-smooth muscle actin and endothelial lectin expression in therapy-given corneas compared to no-therapy corneas on day-9 (p < 0.001) and day-15 (p < 0.001). Further, therapy-given corneas showed significantly increased Fas-ligand mRNA levels (p < 0.001) and apoptotic cell death in neovessels (p < 0.001) compared to no-therapy corneas. AAV5 delivered 2.69 × 107 copies of DCN and 2.31 × 107 copies of PEDF genes per μg of DNA. AAV5 vector and delivered DCN and PEDF genes found tolerable to the rabbit eyes and caused no significant toxicity to the cornea.

CONCLUSION

The combination AAV5-DCN and AAV5-PEDF topical gene therapy effectively reduces corneal fibrosis and CNV with high tolerability in vivo in rabbits. Additional studies are warranted.

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.

Lack of Elevated Expression of TGFβ3 Contributes to the Delay of Epithelial Wound Healing in Diabetic Corneas

Purpose

To investigate the mechanisms underlying the differential roles of TGFβ1 and TGFβ3 in accelerating corneal epithelial wound healing (CEWH) in diabetic (DM) corneas, with normoglycemia (NL) corneas as the control.

Methods

Two types of diabetic mice, human corneal organ cultures, mouse corneal epithelial progenitor cell lines, and bone marrow-derived macrophages (BMDMs) were employed to assess the effects of TGFβ1 and TGFβ3 on CEWH, utilizing quantitative PCR, western blotting, ELISA, and whole-mount confocal microscopy.

Results

Epithelial debridement led to an increased expression of TGFβ1 and TGFβ3 in cultured human NL corneas, but only TGFβ1 in DM corneas. TGFβ1 and TGFβ3 inhibition was significantly impeded, but exogenous TGFβ1 and, more potently, TGFβ3 promoted CEWH in cultured TKE2 cells and in NL and DM C57BL6 mouse corneas. Wounding induced similar levels of p-SMAD2/SMAD3 in NL and DM corneas but weaker ERK1/2, Akt, and EGFR phosphorylation in DM corneas compared to NL corneas. Whereas TGFβ1 augmented SMAD2/SMAD3 phosphorylation, TGFβ3 preferentially activated ERK, PI3K, and EGFR in healing DM corneas. Furthermore, TGFβ1 and TGFβ3 differentially regulated the expression of S100a9, PAI-1, uPA/tPA, and CCL3 in healing NL and DM corneas. Finally, TGFβ1 induced the expression of M1 macrophage markers iNOS, CD86, and CTGF, whereas TGFβ3 promoted the expression of M2 markers CD206 and NGF in BMDMs from db/db or db/+ mice.

Conclusions

Hyperglycemia disrupts the balanced expression of TGFβ3/TGFβ1, resulting in delayed CEWH, including impaired sensory nerve regeneration in the cornea. Supplementing TGFβ3 in DM wounds may hold therapeutic potential for accelerating delayed wound healing in diabetic patients.

Chemical (Alkali) Burn-Induced Neurotrophic Keratitis Model in New Zealand Rabbit Investigated Using Medical Clinical Readouts and In Vivo Confocal Microscopy (IVCM)

PURPOSE

Chemical eye injury is an acute emergency that can result in vision loss. Neurotrophic keratitis (NK) is the most common long-term manifestation of chemical injury. NK due to alkali burn affects ocular surface health and is one of its most common causes. Here, we established a rabbit model of corneal alkali burns to evaluate the severity of NK-associated changes.

MATERIAL METHODS

Alkali burns were induced in NZ rabbits by treating the cornea with (i) a 5 mm circular filter paper soaked in 0.75 N NaOH for 10 s (Mild NK) and (ii) trephination using a guarded trephine (5 mm diameter and 150-micron depth), followed by alkali burn, with a 5 mm circular filter paper soaked in 0.75 N NaOH for 10 s (a severe form of NK). Immediately after, the cornea was rinsed with 10 mL of normal saline to remove traces of NaOH. Clinical features were evaluated on Day 0, Day 1, Day 7, Day 15, and Day 21 post-alkali burn using a slit lamp, Pentacam, and anterior segment optical coherence tomography (AS-OCT). NK-like changes in epithelium, sub-basal nerve plexus, and stroma were observed using in vivo confocal microscopy (IVCM), and corneal sensation were measured using an aesthesiometer post alkali injury. After 21 days, pro-inflammatory cytokines were evaluated for inflammation through ELISA.

RESULTS

Trephination followed by alkali burn resulted in the loss of epithelial layers (manifested using fluorescein stain), extensive edema, and increased corneal thickness (550 µm compared to 380 µm thickness of control) evaluated through AS-OCT and increased opacity score in alkali-treated rabbit (80 compared to 16 controls). IVCM images showed complete loss of nerve fibers, which failed to regenerate over 30 days, and loss of corneal sensation-conditions associated with NK. Cytokines evaluation of IL6, VEGF, and MMP9 indicated an increased angiogenic and pro-inflammatory milieu compared to the milder form of NK and the control.

DISCUSSION

Using clinical parameters, we demonstrated that the alkali-treated rabbit model depicts features of NK. Using IVCM in the NaOH burn animal model, we demonstrated a complete loss of nerve fibers with poor self-healing capability associated with sub-basal nerve degeneration and compromised corneal sensation. This pre-clinical rabbit model has implications for future pre-clinical research in neurotrophic keratitis.

AAV for Gene Therapy in Ocular Diseases: Progress and Prospects

Owing to the promising therapeutic effect and one-time treatment advantage, gene therapy may completely change the management of eye diseases, especially retinal diseases. Adeno-associated virus (AAV) is considered one of the most promising viral gene delivery tools because it can infect various types of tissues and is considered as a relatively safe gene delivery vector. The eye is one of the most popular organs for gene therapy, since its limited volume is suitable for small doses of AAV stably transduction. Recently, an increasing number of clinical trials of AAV-mediated gene therapy are underway. This review summarizes the biological functions of AAV and its application in the treatment of various ocular diseases, as well as the characteristics of different AAV delivery routes in clinical applications. Here, the latest research progresses in AAV-mediated gene editing and silencing strategies to modify that the genetic ocular diseases are systematically outlined, especially by base editing and prime editing. We discuss the progress of AAV in ocular optogenetic therapy. We also summarize the application of AAV-mediated gene therapy in animal models and the difficulties in its clinical transformation.

Management of Corneal Haze After Photorefractive Keratectomy

Photorefractive keratectomy (PRK) is a safe and popular corneal surgery performed worldwide. Nevertheless, there is potential risk of corneal haze development after surgery. Proper management of post PRK haze is important for good visual outcome. We performed a comprehensive review of the literature on the various risk factors and treatments for PRK haze, searching the PubMed, Google Scholar, SCOPUS, ScienceDirect, and Embase databases using relevant search terms. All articles in English from August 1989 through April 2023 were reviewed for this study, among which 102 articles were chosen to be included in the study. Depending on the characteristics of and examination findings on post PRK haze, different management options may be preferred. In the proposed framework, management of PRK haze should include a full workup that includes patient's subjective complaints and loss of vision as well as visual acuity, biomicroscopy, anterior segment optical coherence tomography, epithelial mapping, and Scheimpflug densitometry. Topical steroid treatment for haze should be stratified based on early- or late-onset haze. Mechanical debridement or superficial phototherapeutic keratectomy (PTK) may be used to treat superficial corneal haze. Deep PTK and/or PRK can be used to treat deep corneal haze. Mitomycin-C and topical steroids are prophylactic post-surgery agents to prevent recurrence of haze.

Toxicological effects of ocular acrolein exposure to eyelids in rabbits in vivo

Acrolein is a highly reactive volatile toxic chemical that injures the eyes and many organs. It has been used in wars and terrorism for wounding masses on multiple occasions and is readily accessible commercially. Our earlier studies revealed acrolein's toxicity to the cornea and witnessed damage to other ocular tissues. Eyelids play a vital role in keeping eyes mobile, moist, lubricated, and functional utilizing a range of diverse lipids produced by the Meibomian glands located in the upper and lower eyelids. This study sought to investigate acrolein's toxicity to eyelid tissues by studying the expression of inflammatory and lipid markers in rabbit eyes in vivo utilizing our reported vapor-cap model. The study was approved by the institutional animal care and use committees and followed ARVO guidelines. Twelve New Zealand White Rabbits were divided into 3 groups: Naïve (group 1), 1-min acrolein exposure (group 2), or 3-min acrolein exposure (group 3). The toxicological effects of acrolein on ocular health in live animals were monitored with regular clinical eye exams and intraocular pressure measurements and eyelid tissues post-euthanasia were subjected to H&E and Masson's trichrome histology and qRT-PCR analysis. Clinical eye examinations witnessed severely swollen eyelids, abnormal ocular discharge, chemosis, and elevated intraocular pressure (p < 0.001) in acrolein-exposed eyes. Histological studies supported clinical findings and exhibited noticeable changes in eyelid tissue morphology. Gene expression studies exhibited significantly increased expression of inflammatory and lipid mediators (LOX, PAF, Cox-2, and LTB4; p < 0.001) in acrolein-exposed eyelid tissues compared to naïve eyelid tissues. The results suggest that acrolein exposure to the eyes causes acute damage to eyelids by altering inflammatory and lipid mediators in vivo.

[Gene therapy in ophthalmology]

In 2017 the gene therapy medication voretigene neparvovec-rzyl was approved by the U.S. Food and Drug Administration (FDA) for retinal gene therapy of hereditary retinal dystrophies caused by mutations in the RPE65 gene. Voretigene neparvovec-rzyl is a gene augmentation therapy using an  adeno-associated virus-based vector to express a healthy copy of the human RPE65 gene in the patient's retinal pigment epithelial (RPE) cells. The success of gene augmentation therapy in RPE65-linked retinal dystrophy encouraged research activities on the concept of gene supplementation to be extended to nongenetic diseases, such as age-related macular degeneration; however, it also showed that the principle of success cannot be easily extended to other retinal dystrophies. This review article presents the most commonly used principles and technologies of gene therapy and provides an overview of the current challenges and limitations. Furthermore, practice-relevant aspects of the indications and the treatment procedure are discussed. Particular attention is paid to the consideration of disease stages, especially with respect to patient's expectations and the evaluation of treatment success.

Fibrosis-the tale of H3K27 histone methyltransferases and demethylases

Fibrosis, or excessive scarring, is characterized by the emergence of alpha-smooth muscle actin (αSMA)-expressing myofibroblasts and the excessive accumulation of fibrotic extracellular matrix (ECM). Currently, there is a lack of effective treatment options for fibrosis, highlighting an unmet need to identify new therapeutic targets. The acquisition of a fibrotic phenotype is associated with changes in chromatin structure, a key determinant of gene transcription activation and repression. The major repressive histone mark, H3K27me3, has been linked to dynamic changes in gene expression in fibrosis through alterations in chromatin structure. H3K27-specific homologous histone methylase (HMT) enzymes, Enhancer of zeste 1 and 2 (EZH1, EZH2), which are the alternative subunits of the Polycomb Repressive Complex 2 (PRC2) and demethylase (KDM) enzymes, Ubiquitously transcribed tetratricopeptide repeat, X chromosome (UTX), and Lysine demethylase 6B (KDM6B), are responsible for regulating methylation status of H3K27me3. In this review, we explore how these key enzymes regulate chromatin structure to alter gene expression in fibrosis, highlighting them as attractive targets for the treatment of fibrosis.

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.

Ocular-Surface Regeneration Therapies for Eye Disorders: The State of the Art

The ocular surface is a complex structure that includes cornea, conjunctiva, limbus, and tear film, and is critical for maintaining visual function. When the ocular-surface integrity is altered by a disease, conventional therapies usually rely on topical drops or tissue replacement with more invasive procedures, such as corneal transplants. However, in the last years, regeneration therapies have emerged as a promising approach to repair the damaged ocular surface by stimulating cell proliferation and restoring the eye homeostasis and function. This article reviews the different strategies employed in ocular-surface regeneration, including cell-based therapies, growth-factor-based therapies, and tissue-engineering approaches. Dry eye and neurotrophic keratopathy diseases can be treated with nerve-growth factors to stimulate the limbal stem-cell proliferation and the corneal nerve regeneration, whereas conjunctival autograft or amniotic membrane are used in subjects with corneal limbus dysfunction, such as limbal stem-cell deficiency or pterygium. Further, new therapies are available for patients with corneal endothelium diseases to promote the expansion and migration of cells without the need of corneal keratoplasty. Finally, gene therapy is a promising new frontier of regeneration medicine that can modify the gene expression and, potentially, restore the corneal transparency by reducing fibrosis and neovascularization, as well as by stimulating stem-cell proliferation and tissue regeneration.

Mustard Gas Exposure Actuates SMAD2/3 Signaling to Promote Myofibroblast Generation in the Cornea

Sulfur mustard gas (SM) is a vesicating and alkylating agent used as a chemical weapon in many mass-casualty incidents since World War I. Ocular injuries were reported in >90% of exposed victims. The mechanisms underlying SM-induced blindness remain elusive. This study tested the hypothesis that SM-induced corneal fibrosis occurs due to the generation of myofibroblasts from resident fibroblasts via the SMAD2/3 signaling pathway in rabbit eyes in vivo and primary human corneal fibroblasts (hCSFs) isolated from donor corneas in vitro. Fifty-four New Zealand White Rabbits were divided into three groups (Naïve, Vehicle, SM-Vapor treated). The SM-Vapor group was exposed to SM at 200 mg-min/m3 for 8 min at the MRI Global facility. Rabbit corneas were collected on day 3, day 7, and day 14 for immunohistochemistry, RNA, and protein lysates. SM caused a significant increase in SMAD2/3, pSMAD, and ɑSMA expression on day 3, day 7, and day 14 in rabbit corneas. For mechanistic studies, hCSFs were treated with nitrogen mustard (NM) or NM + SIS3 (SMAD3-specific inhibitor) and collected at 30 m, 8 h, 24 h, 48 h, and 72 h. NM significantly increased TGFβ, pSMAD3, and SMAD2/3 levels. On the contrary, inhibition of SMAD2/3 signaling by SIS3 treatment significantly reduced SMAD2/3, pSMAD3, and ɑSMA expression in hCSFs. We conclude that SMAD2/3 signaling appears to play a vital role in myofibroblast formation in the cornea following mustard gas exposure.

Corneal Regeneration Using Gene Therapy Approaches

One of the most remarkable advancements in medical treatments of corneal diseases in recent decades has been corneal transplantation. However, corneal transplants, including lamellar strategies, have their own set of challenges, such as graft rejection, delayed graft failure, shortage of donor corneas, repeated treatments, and post-surgical complications. Corneal defects and diseases are one of the leading causes of blindness globally; therefore, there is a need for gene-based interventions that may mitigate some of these challenges and help reduce the burden of blindness. Corneas being immune-advantaged, uniquely avascular, and transparent is ideal for gene therapy approaches. Well-established corneal surgical techniques as well as their ease of accessibility for examination and manipulation makes corneas suitable for in vivo and ex vivo gene therapy. In this review, we focus on the most recent advances in the area of corneal regeneration using gene therapy and on the strategies involved in the development of such therapies. We also discuss the challenges and potential of gene therapy for the treatment of corneal diseases. Additionally, we discuss the translational aspects of gene therapy, including different types of vectors, particularly focusing on recombinant AAV that may help advance targeted therapeutics for corneal defects and diseases.

Novel Therapies for the Prevention of Fibrosis in Glaucoma Filtration Surgery

Conjunctival fibrosis remains the major impediment to the success of glaucoma filtration surgery. Anti-metabolites remain the gold standard for mitigating post-surgical fibrosis, but they are associated with high complication rates and surgical failure rates. Establishing a more targeted approach to attenuate conjunctival fibrosis may revolutionize the surgical approach to glaucoma. A new strategy is needed to prevent progressive tissue remodeling and formation of a fibrotic scar, subsequently increasing surgical success and reducing the prevalence of glaucoma-related vision loss. Advancements in our understanding of molecular signaling and biomechanical cues in the conjunctival tissue architecture are broadening the horizon for new therapies and biomaterials for the mitigation of fibrosis. This review aims to highlight the strategies and current state of promising future approaches for targeting fibrosis in glaucoma filtration surgery.

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.

Corneal stromal repair and regeneration

The cornea is a specialized, transparent, avascular, immune-privileged, and heavily innervated tissue that affords 2/3rd of refraction to the eye. Ocular injuries, infections, and genetic factors affect corneal function and cause vision impairment. Presently, a variety of laser/non-laser surgeries, immunosuppressants, and/or corneal transplants are predominantly used to revive sight in human patients. The development of novel, precision-guided, and tissue-targeted non-surgical therapies promoting corneal repair and regeneration based on mechanistic understanding is of paramount importance to reduce the impact of global blindness. Research over the past decade revealed that modulation of pathological signaling pathways and factors by a variety of therapeutic delivery methods effectively treats corneal disorders including corneal scar/haze, inflammation, and angiogenesis in various pre-clinical animal models and are primed for human translation. This review discusses recent advances in the areas of corneal repair, restoration, and regeneration. Herein, we provide an overview of evolving approaches and therapeutic modalities that have shown great promise in reviving corneal transparency and function through the use of small drug molecules, gene therapy, nanomedicine, stem cells, trophic factors, exosomes, stromal equivalents, bioengineered stromal scaffolds, tissue adhesives, and 3D bioprinting.

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.

Corneal fibrosis abrogation by a localized AAV-mediated inhibitor of differentiation 3 (Id3) gene therapy in rabbit eyes in vivo

Previously we found that inhibitor of differentiation 3 (Id3) gene, a transcriptional repressor, efficiently inhibits corneal keratocyte differentiation to myofibroblasts in vitro. This study evaluated the potential of adeno-associated virus 5 (AAV5)-mediated Id3 gene therapy to treat corneal scarring using an established rabbit in vivo disease model. Corneal scarring/fibrosis in rabbit eyes was induced by alkali trauma, and 24 h thereafter corneas were administered with either balanced salt solution AAV5-naked vector, or AAV5-Id3 vector (n = 6/group) via an optimized reported method. Therapeutic effects of AAV5-Id3 gene therapy on corneal pathology and ocular health were evaluated with clinical, histological, and molecular techniques. Localized AAV5-Id3 gene therapy significantly inhibited corneal fibrosis/haze clinically from 2.7 to 0.7 on the Fantes scale in live animals (AAV5-naked versus AAV5-Id3; p < 0.001). Furthermore, AAV5-Id3 treatment significantly reduced profibrotic gene mRNA levels: α-smooth muscle actin (α-SMA) (2.8-fold; p < 0.001), fibronectin (3.2-fold; p < 0.001), collagen I (0.8-fold; p < 0.001), and collagen III (1.4-fold; p < 0.001), as well as protein levels of α-SMA (23.8%; p < 0.001) and collagens (1.8-fold; p < 0.001). The anti-fibrotic activity of AAV5-Id3 is attributed to reduced myofibroblast formation by disrupting the binding of E-box proteins to the promoter of α-SMA, a transforming growth factor-β signaling downstream target gene. In conclusion, these results indicate that localized AAV5-Id3 delivery in stroma caused no clinically relevant ocular symptoms or corneal cellular toxicity in the rabbit eyes.

Ocular Drug Delivery: Advancements and Innovations

Ocular drug delivery has been significantly advanced for not only pharmaceutical compounds, such as steroids, nonsteroidal anti-inflammatory drugs, immune modulators, antibiotics, and so forth, but also for the rapidly progressed gene therapy products. For conventional non-gene therapy drugs, appropriate surgical approaches and releasing systems are the main deliberation to achieve adequate treatment outcomes, whereas the scope of “drug delivery” for gene therapy drugs further expands to transgene construct optimization, vector selection, and vector engineering. The eye is the particularly well-suited organ as the gene therapy target, owing to multiple advantages. In this review, we will delve into three main aspects of ocular drug delivery for both conventional drugs and adeno-associated virus (AAV)-based gene therapy products: (1) the development of AAV vector systems for ocular gene therapy, (2) the innovative carriers of medication, and (3) administration routes progression.

BMP3 inhibits TGFβ2-mediated myofibroblast differentiation during wound healing of the embryonic cornea

Often acute damage to the cornea initiates drastic tissue remodeling, resulting in fibrotic scarring that disrupts light transmission and precedes vision impairment. Very little is known about the factors that can mitigate fibrosis and promote scar-free cornea wound healing. We previously described transient myofibroblast differentiation during non-fibrotic repair in an embryonic cornea injury model. Here, we sought to elucidate the mechanistic regulation of myofibroblast differentiation during embryonic cornea wound healing. We found that alpha-smooth muscle actin (αSMA)-positive myofibroblasts are superficial and their presence inversely correlates with wound closure. Expression of TGFβ2 and nuclear localization of pSMAD2 were elevated during myofibroblast induction. BMP3 and BMP7 were localized in the corneal epithelium and corresponded with pSMAD1/5/8 activation and absence of myofibroblasts in the healing stroma. In vitro analyses with corneal fibroblasts revealed that BMP3 inhibits the persistence of TGFβ2-induced myofibroblasts by promoting disassembly of focal adhesions and αSMA fibers. This was confirmed by the expression of vinculin and pFAK. Together, these data highlight a mechanism to inhibit myofibroblast persistence during cornea wound repair.

Quercetin Decreases Corneal Haze In Vivo and Influences Gene Expression of TGF-Beta Mediators In Vitro

We have previously reported the flavonoid, quercetin, as a metabolic regulator and inhibitor of myofibroblast differentiation in vitro. Our current study evaluated the effects of topical application of quercetin on corneal scar development using two different animal models followed by RNA analysis in vitro. Wild-type C57BL/6J mice were anesthetized and the corneal epithelium and stroma were manually debrided, followed by quercetin (0.5, 1, 5, or 50 mM) or vehicle application. Corneal scarring was assessed for 3 weeks by slit lamp imaging and clinically scored. In a separate animal study, six New Zealand White rabbits underwent lamellar keratectomy surgery, followed by treatment with 5 mM quercetin or vehicle twice daily for three days. Stromal backscattering was assessed at week 3 by in vivo confocal microscopy. In mice, a single dose of 5 mM quercetin reduced corneal scar formation. In rabbits, stromal backscattering was substantially lower in two out of three animals in the quercetin-treated group. In vitro studies of human corneal fibroblasts showed that quercetin modulated select factors of the transforming growth factor-β (TGF-β) signaling pathway. These results provide evidence that quercetin may inhibit corneal scarring. Further studies in a larger cohort are required to validate the efficacy and safety of quercetin for clinical applications.

Evaluation of CRISPR/Cas9 mediated TGIF gene editing to inhibit corneal fibrosis in vitro

Corneal wound healing is influenced by many factors including transcriptional co-repressors and co-activators. Interactions of co-activators and co-repressors with Smads influence mechanistic loop facilitating transcription of alpha-smooth muscle actin (α-SMA), a key profibrotic gene, in corneal repair. The role of a transcriptional repressor, 5'TG3'-interacting factor (TGIF), in the regulation of α-SMA and myofibroblast formation in the cornea was shown previously by our group. This study tested a hypothesis if TGIF1 gene editing via CRISPR/Cas9 can ease myofibroblast formation in the cornea using an in vitro model. Primary human corneal stromal fibroblasts (hCSFs) generated from donor corneas received gene-editing plasmid facilitating loss (CRISPR/Cas9 knockout) or gain (CRISPR activation) of TGIF function by UltraCruz transfection reagent. Phase-contrast microscopy, immunoblotting, immunocytochemistry and quantitative polymerase chain reaction (qPCR) were used to measure levels of myofibroblast profibrotic genes (α-SMA, fibronectin, Collagen-I, and Collagen-IV) in hCSFs lacking or overexpressing TGIF1 after growing them in± transforming growth factor beta1 (TGF-β1) under serum-free conditions. The CRISPR-assisted TGIF1 activation (gain of function) in hCSFs demonstrated significantly decreased myofibroblast formation and messenger ribonucleic acid (mRNA) and protein levels of profibrotic genes. Conversely, CRISPR/Cas9-assisted TGIF knockdown (loss of function) in hCSFs demonstrated no significant change in the levels of myofibroblast formation or profibrotic genes under similar conditions. These results suggest that TGIF gene-editing approach can be employed to modulate the transcriptional activity of α-SMA in controlling pathological and promoting physiological wound healing in an injured cornea.

New Frontier in the Management of Corneal Dystrophies: Basics, Development, and Challenges in Corneal Gene Therapy and Gene Editing

ABSTRACT

Corneal dystrophies represent a group of heterogeneous hereditary disorders causing progressive corneal opacification and blindness. Current corneal transplant management for corneal dystrophies faces the challenges of repeated treatments, complex surgical procedures, shortage of appropriate donor cornea, and, more importantly, graft rejection. Genetic medicine could be an alternative treatment regime to overcome such challenges. Cornea carries promising scope for a gene-based therapy involving gene supplementation, gene silencing, and gene editing in both ex vivo and in vivo platforms. In the cornea, ex vivo gene therapeutic strategies were attempted for corneal graft survival, and in vivo gene augmentation therapies aimed to prevent herpes stromal keratitis, neovascularization, corneal clouding, and wound healing. However, none of these studies followed a clinical trial-based successful outcome. CRISPR/Cas system offers a broad scope of gene editing and engineering to correct underlying genetic causes in corneal dystrophies. Corneal tissue--specific gene correction in vitro with minimal off-target effects and optimal gene correction efficiency followed by their successful surgical implantation, or in vivo CRISPR administration targeting pathogenic genes finds a way to explore therapeutic intervention for corneal dystrophies. However, there are many limitations associated with such CRISPR-based corneal treatment management. This review will look into the development of corneal gene therapy and CRISPR-based study in corneal dystrophies, associated challenges, potential approaches, and future directions.

Decorin regulates collagen fibrillogenesis during corneal wound healing in mouse in vivo

A characteristic rigid spatial arrangement of collagen fibrils in the stroma is critical for corneal transparency. This unique organization of collagen fibrils in corneal stroma can be impacted by the presence and interactions of proteoglycans and extracellular matrix (ECM) proteins in a corneal microenvironment. Earlier studies revealed that decorin, a leucine-rich proteoglycan in stroma, regulates keratocyte-collagen matrix assembly and wound healing in the cornea. This study investigated the role of decorin in the regulation of stromal fibrillogenesis and corneal transparency in vivo employing a loss-of-function genetic approach using decorin null (dcn^-/-) and wild type (dcn^+/+) mice and a standard alkali-injury model. A time-dependent ocular examinations with Slit lamp microscope in live animals assessed corneal clarity, haze, and neovascularization levels in normal and injured eyes. Morphometric changes in normal and injured dcn^+/+ and dcn^-/- corneas, post-euthanasia, were analyzed with Masson's Trichrome and Periodic Acid-Schiff (PAS) histology evaluations. The ultrastructure changes in all corneas were investigated with transmission electron microscopy (TEM). Injury to eye produced clinically relevant corneal haze and neovascularization in dcn^-/- and dcn^+/+ mice while corneas of uninjured eyes remained clear and avascular. A clinically significant haze and neovascularization appeared in injured dcn^-/- corneas compared to the dcn^+/+ corneas at day 21 post-injury and not at early tested times. Histological examinations revealed noticeably abnormal morphology and compromised collagen levels in injured dcn^-/- corneas compared to the injured/normal dcn^+/+ and uninjured dcn^-/- corneas. TEM analysis exhibited remarkably uneven collagen fibrils size and distribution in the stroma with asymmetrical organization and loose packing in injured dcn^-/- corneas than injured/normal dcn^+/+ and uninjured dcn^-/- corneas. The minimum and maximum inter-fibril distances were markedly irregular in injured dcn^-/- corneas compared to all other corneas. Together, results of clinical, histological, and ultrastructural investigations in a genetic knockout model suggested that decorin influenced stromal fibrillogenesis and transparency in healing cornea.

Evaluation of a novel combination of TRAM-34 and ascorbic acid for the treatment of corneal fibrosis in vivo

Corneal injury and aberrant wound healing commonly result in corneal fibrosis and subsequent vision loss. Intermediate-conductance calmodulin/calcium-activated K+ channels (KCa3.1) have been shown to promote fibrosis in non-ocular and ocular tissues via upregulation of transforming growth factor beta (TGFβ). TRAM-34 is a selective inhibitor of KCa3.1 and reduces fibrosis by downregulation of TGFβ-induced transdifferentiation of stromal fibroblasts to myofibroblasts. Ascorbic acid has been demonstrated to be effective in promoting corneal re-epithelialization and reduction of neovascularization via anti-VEGF and anti-MMP mechanisms. This study evaluates tolerability and efficacy of a novel combination of TRAM-34 (25μM) and ascorbic acid (10%) topical treatment for corneal fibrosis using an established in vivo rabbit model and conducting clinical eye examinations. Markers of corneal fibrosis were evaluated in all corneas at study endpoint via histopathology, immunofluorescence, and quantitative real-time PCR. The eyedrop treated eyes showed significantly improved clinical outcomes based on modified McDonald Shadduck scores, reduction of clinical haze on Fantes scores, and reduction of central corneal thickness (CCT). At cellular and molecular levels, eyedrop treatment also significantly reduced expression of alpha smooth muscle actin (α-SMA) mRNA and protein, collagen III mRNA, and fibronectin mRNA compared to non-treated eyes. Our study suggests that a tested new bimodal eyedrop is well tolerated and effectively reduces corneal fibrosis/haze in rabbits in vivo.

Long-Term Safety and Tolerability of BMP7 and HGF Gene Overexpression in Rabbit Cornea

Purpose

Tissue-targeted localized BMP7+HGF genes delivered into the stroma via nanoparticle effectively treats corneal fibrosis and rehabilitates transparency in vivo without acute toxicity. This study evaluated the long-term safety and tolerability of BMP7+HGF nanomedicine for the eye in vivo.

Methods

One eye each of 36 rabbits received balanced salt solution (group 1, naïve; n = 12), naked vector with polyethylenimine-conjugated gold nanoparticles (PEI2-GNP; group 2, naked-vector; n = 12), or BMP7+HGF genes with PEI2-GNP (group 3, BMP7+HGF; n = 12) via a topical delivery technique. Safety and tolerability measurements were performed by clinical biomicroscopy in live rabbits at predetermined time intervals up to 7 months. Corneal tissues were collected at 2 months and 7 months after treatment and subjected to histology, immunofluorescence, and quantitative real-time PCR analyses.

Results

Clinical ophthalmic examinations and modified MacDonald-Shadduck scores showed no significant changes in corneal thickness (P = 0.3389), tear flow (P = 0.2121), intraocular pressure (P = 0.9958), epithelial abrasion, or ocular abnormality. Slit-lamp, stereo, confocal, and specular biomicroscopy showed no signs of blepharospasm chemosis, erythema, epiphora, abnormal ocular discharge, or changes in epithelium, stroma, and endothelium after BMP7+HGF therapy for up to 7 months, as compared with control groups. Throughout the 7-month period, no significant changes were recorded in endothelial density (P = 0.9581). Histological and molecular data were well corroborated with the subjective clinical analyses and showed no differences in the naïve, naked-vector, and BMP7+HGF groups.

Conclusions

Localized BMP7+HGF therapy is a safe, tolerable, and innovative modality for the treatment of corneal fibrosis.

Translational Relevance

Nanoparticle-mediated BMP7+HGF combination gene therapy has the potential to treat corneal fibrosis in vivo without short- or long-term toxicity.

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.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

Challenges and strategies for the delivery of biologics to the cornea

Biologics, like peptides, proteins and nucleic acids, have proven to be promising drugs for the treatment of numerous diseases. However, besides the off label use of the monoclonal antibody bevacizumab for the treatment of corneal neovascularization, to date no other biologics for corneal diseases have reached the market. Indeed, delivering biologics in the eye remains a challenge, especially at the level of the cornea. While it appears to be a rather accessible tissue for the administration of drugs, the cornea in fact presents several anatomical barriers to delivery. In addition, also intracellular delivery barriers need to be overcome to achieve a promising therapeutic outcome with biologics. This review outlines efforts that have been reported to successfully deliver biologics into the cornea. Biochemical and physical methods for achieving delivery of biologics in the cornea are discussed, with a critical view on their efficacy in overcoming corneal barriers.

Interleukin-1 and Transforming Growth Factor Beta: Commonly Opposing, but Sometimes Supporting, Master Regulators of the Corneal Wound Healing Response to Injury

Purpose

Interleukin (IL)-1α/IL-1β and transforming growth factor (TGF)β1/TGFβ2 have both been promoted as “master regulators” of the corneal wound healing response due to the large number of processes each regulates after injury or infection. The purpose of this review is to highlight the interactions between these systems in regulating corneal wound healing.

Methods

We conducted a systematic review of the literature.

Results

Both regulator pairs bind to receptors expressed on keratocytes, corneal fibroblasts, and myofibroblasts, as well as bone marrow-derived cells that include fibrocytes. IL-1α and IL-1β modulate healing functions, such as keratocyte apoptosis, chemokine production by corneal fibroblasts, hepatocyte growth factor (HGF), and keratinocyte growth factor (KGF) production by keratocytes and corneal fibroblasts, expression of metalloproteinases and collagenases by corneal fibroblasts, and myofibroblast apoptosis. TGFβ1 and TGFβ2 stimulate the development of myofibroblasts from keratocyte and fibrocyte progenitor cells, and adequate stromal levels are requisite for the persistence of myofibroblasts. Conversely, TGFβ3, although it functions via the same TGF beta I and II receptors, may, at least in some circumstances, play a more antifibrotic role—although it also upregulates the expression of many profibrotic genes.

Conclusions

The overall effects of these two growth factor-cytokine-receptor systems in controlling the corneal wound healing response must be coordinated during the wound healing response to injury or infection. The activities of both systems must be downregulated in coordinated fashion to terminate the response to injury and eliminate fibrosis.

Translational Relevance

A better standing of the IL-1 and TGFβ systems will likely lead to better approaches to control the excessive healing response to infections and injuries leading to scarring corneal fibrosis.

Glutathione is a potential therapeutic target for acrolein toxicity in the cornea

Toxic and volatile chemicals are widely used in household products and previously used as warfare agents, causing a public health threat worldwide. This study aimed to evaluate the extent of injury and mechanisms of acrolein toxicity in the cornea. Primary human corneal stromal fibroblasts cultures (hCSFs) from human donor cornea were cultured and exposed to acrolein toxicity with -/+ N-acetylcysteine (NAC) to study the mode of action in the presence of Buthionine sulphoximine (BSO). PrestoBlue and MTT assays were used to optimize acrolein, NAC, and BSO doses for hCSFs. Cell-based assays and qRT-PCR analyses were performed to understand the acrolein toxicity and mechanisms. Acrolein exposure leads to an increased reactive oxygen species (ROS), compromised glutathione (GSH) levels, and mitochondrial dysfunction. The TUNEL and caspase assays showed that acrolein caused cell death in hCSFs. These deleterious effects can be mitigated using NAC in hCSFs, suggesting that GSH can be a potential target for acrolein toxicity in the cornea.

Double viral vector technology for selective manipulation of neural pathways with higher level of efficiency and safety

Pathway-selective gene delivery would be critical for future gene therapy against neuropsychiatric disorders, traumatic neuronal injuries, or neurodegenerative diseases, because the impaired functions depend on neural circuits affected by the insults. Pathway-selective gene delivery can be achieved by double viral vector techniques, which combine an injection of a retrograde transport viral vector into the projection area of the target neurons and that of an anterograde viral vector into their somas. In this study, we tested the efficiency of gene delivery with different combinations of viral vectors to the pathway extending from the ventral tegmental area (VTA) to the cortical motor regions in rats, considered to be critical in the promotion of motor recovery from neural injuries. It was found that retrograde recombinant adeno-associated virus 2-retro (rAAV2reto) combined with anterograde AAVDJ (type2/type4/type5/type8/type9/avian/bovine/caprine chimera) exhibited the highest transduction efficiency in the short term (3-6 weeks) but high toxicity in the long term (3 months). In contrast, the same rAAV2reto combined with anterograde AAV5 displayed moderate transduction efficiency in the short term but low toxicity in the long term. These data suggest that the combination of anterograde AAV5 and retrograde rAAV2retro is suitable for safe and efficient gene delivery to the VTA-cortical pathway.

Novel insights into gene therapy in the cornea

Corneal disease remains a leading cause of impaired vision world-wide, and advancements in gene therapy continue to develop with promising success to prevent, treat and cure blindness. Ideally, gene therapy requires a vector and gene delivery method that targets treatment of specific cells or tissues and results in a safe and non-immunogenic response. The cornea is a model tissue for gene therapy due to its ease of clinician access and immune-privileged state. Improvements in the past 5-10 years have begun to revolutionize the approach to gene therapy in the cornea with a focus on adeno-associated virus and nanoparticle delivery of single and combination gene therapies. In addition, the potential applications of gene editing (zinc finger nucleases [ZNFs], transcription activator-like effector nucleases [TALENs], Clustered Regularly Interspaced Short Palindromic Repeats/Associated Systems [CRISPR/Cas9]) are rapidly expanding. This review focuses on recent developments in gene therapy for corneal diseases, including promising multiple gene therapy, while outlining a practical approach to the development of such therapies and potential impediments to successful delivery of genes to the cornea.

Development of a Corneal Bioluminescence Mouse for Real-Time In Vivo Evaluation of Gene Therapies

Purpose

The purpose of this study was to develop and characterize a novel bioluminescence transgenic mouse model that facilitates rapid evaluation of genetic medicine delivery methods for inherited and acquired corneal diseases.

Methods

Corneal expression of the firefly luciferase transgene (luc2) was achieved via insertion into the Krt12 locus, a type I intermediate filament keratin that is exclusively expressed in the cornea, to generate the Krt12luc2 mouse. The transgene includes a multiple target cassette with human pathogenic mutations in K3 and K12.

Results

The Krt12luc2 mouse exclusively expresses luc2 in the corneal epithelium under control of the keratin K12 promoter. The luc2 protein is enzymatically active, can be readily visualized, and exhibits a symmetrically consistent readout. Moreover, structural integrity of the corneal epithelium is preserved in mice that are heterozygous for the luc2 transgene (Krt12+/luc2).

Conclusions

This novel Krt12luc2 mouse model represents a potentially ideal in vivo system for evaluating the efficacies of cornea-targeting gene therapies and for establishing and/or validating new delivery modalities. Importantly, the multiple targeting cassette that is included in the Luc2 transgene will greatly reduce mouse numbers required for in vivo therapy evaluation.

Role of inhibitor of differentiation 3 gene in cellular differentiation of human corneal stromal fibroblasts

Purpose

Inhibitor of differentiation (Id) proteins are helix-loop-helix (HLH) transcriptional repressors that modulate a range of developmental and cellular processes, including cell differentiation and cell cycle mobilization. The inhibitor of differentiation 3 (Id3) gene, a member of the Id gene family, governs the expression and progression of transforming growth factor beta (TGFβ)-mediated cell differentiation. In the face of mechanical, chemical, or surgical corneal insults, corneal keratocytes differentiate into myofibroblasts for wound repair. Excessive development or persistence or both of myofibroblasts after wound repair results in corneal haze that compromises corneal clarity and visual function. The objective of this study was to investigate whether Id3 overexpression in human corneal stromal fibroblasts governs TGFβ-driven cellular differentiation and inhibits keratocyte to myofibroblast transformation.

Methods

Primary human corneal stromal fibroblast (h-CSF) cultures were generated from donor human corneas. Human corneal myofibroblasts (h-CMFs) were produced by growing h-CSF in the presence of TGFβ1 under serum-free conditions. The Id3 gene was cloned into a mammalian expression vector (pcDNA3 mCherry LIC cloning vector), and the nucleotide sequence of the vector constructs was confirmed with sequencing as well as through restriction enzyme analysis. The Id3 mammalian overexpression vector was introduced into h-CSFs using a lipofectamine transfection kit. The expression of Id3 in selected clones was characterized with quantitative real-time PCR (qRT-PCR), immunocytochemistry, and western blotting. Phase contrast microscopy and trypan blue exclusion assays were used to evaluate the effects of the transfer of the Id3 gene on the hCSF phenotype and viability, respectively. To analyze the inhibitory effects of the Id3 gene transfer on TGFβ-induced formation of h-CMFs, expression of the mRNA and protein of the myofibroblast marker alpha smooth muscle actin (α-SMA) was examined with qRT-PCR, western blotting, and immunocytochemistry. Student t test, analysis of variance (ANOVA), and Bonferroni adjustment for repeated measures were used for statistical analysis.

Results

The results indicate that Id3 overexpression does not alter the cellular phenotype or viability of h-CSFs. Overexpression of the Id3 gene in h-CSF cells grown in the presence of TGFβ1 under serum-free conditions showed a statistically significant decrease (76.3±4.3%) in α-SMA expression (p<0.01) compared to the naked-vector transfected or non-transfected h-CSF cells. Id3-transfected, naked-vector transfected, and non-transfected h-CSF cells grown in the absence of TGFβ1 showed the expected low expression of α-SMA (0-5%). Furthermore, Id3 overexpression statistically significantly decreased TGFβ-induced mRNA levels of profibrogenic genes such as fibronectin, collagen type I, and collagen type IV (1.80±0.26-, 1.70±0.35- and 1.70±0.36-fold, respectively; p<0.05) that a play role in stromal matrix modulation and corneal wound healing. Results of the protein analysis with western blotting indicated that Id3 overexpression in h-CSF cells effectively slows TGFβ-driven differentiation and formation of h-CMFs. Results for subsequent overexpression studies showed that this process occurs through the regulation of E2A, a TATA box protein.

Conclusions

Id3 regulates TGFβ-driven differentiation of h-CSFs and formation of h-CMFs in vitro. Targeted Id3 gene delivery has potential to treat corneal fibrosis and reestablish corneal clarity in vivo.

Lycium barbarum Polysaccharide Suppresses Expression of Fibrotic Proteins in Primary Human Corneal Fibroblasts

(1) Objective: To study the anti-fibrotic effects of Lycium barbarum polysaccharides (LBP) on corneal stromal fibroblasts and assess LBP’s effect on cell viability. (2) Methods: Primary human corneal keratocytes of passage 3 to 6 were used for all experiments. Cells are pretreated with LBP solution for 24 h and then transforming growth factor beta 1 (TGFβ1) for 48 h and collected for experiments. Fibrotic protein analysis was performed using immunofluorescence and Western blot. The effect of LBP on cell viability was assessed using the MTS assay. (3) Results: LBP significantly reduced the expression of fibrotic proteins, including α-SMA and extracellular matrix proteins (collagen type I and III). LBP significantly decreased the viability of myofibroblasts but not the fibroblasts. Conclusions: In this study, LBP was effective in the prevention of fibrosis gene expression. Further studies to assess the underlying mechanism and pharmacological properties will facilitate the formation of a topical LBP solution for in vivo studies.

Therapeutic Potential of Extracellular Vesicles for the Treatment of Corneal Injuries and Scars

Infection, trauma, and chemical exposure of the ocular surface can severely damage the cornea, resulting in visually significant stromal scars. Current medical treatments are ineffective in mitigating corneal scarring, and corneal transplantation is the only therapy able to restore vision in these eyes. However, because of a severe shortage of corneal tissues, risks of blinding complications associated with corneal transplants, and a higher rate of graft failure in these eyes, an effective and deliverable alternative therapy for the prevention and treatment of corneal scarring remains a significant unmet medical need globally. In recent years, the therapeutic potential of extracellular vesicles (EVs) secreted by cells to mediate cell-cell communication has been a topic of increasing interest. EVs derived from mesenchymal stem cells, in particular human corneal stromal stem cells, have antifibrotic, anti-inflammatory, and regenerative effects in injured corneas. The exact mechanism of action of these functional EVs are largely unknown. Therapeutic development of EVs is at an early stage and warrants further preclinical studies.

A rabbit model for evaluating ocular damage from acrolein toxicity in vivo

Acrolein is a highly reactive and volatile unsaturated aldehyde commonly used for producing scores of commercial products. It has been recognized as a chemical weapon since its use during World War I, and more recently, in Syria. Acrolein exposure causes severe eye, skin, and lung damage in addition to many casualties. In the eye, it causes severe pain, eyelid swelling, corneal burns, and vision impairment. Very little information is available about how acrolein damages the cornea and causes vision loss. At present, the lack of clinically relevant animal models limits evaluation of acrolein toxicity and mechanisms specific to the eye. We aim to standardize the mode of delivery and exposure duration of acrolein, damaging the rabbit eye in vivo as an ocular injury model for studying the toxicity of acrolein and developing medical countermeasures. Rabbit eyes were exposed to two modes of delivery (topical and vapor) for different durations (1-5 minutes). Clinical ophthalmic examinations with a slit lamp, stereomicroscope, fluorescein dye, pachymeter, tonometer, and tearing examinations in live rabbits were performed at various times up to 4 weeks. Corneas were histologically diagnosed for transparency, fibrosis, collagens, and neovascularization. Our study successfully established an in vivo rabbit model for evaluating acrolein toxicity to the eye, accounting for different modes and durations of exposure.

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.

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.

Adeno-Associated Virus Mediated Gene Therapy for Corneal Diseases

According to the World Health Organization, corneal diseases are the fourth leading cause of blindness worldwide accounting for 5.1% of all ocular deficiencies. Current therapies for corneal diseases, which include eye drops, oral medications, corrective surgeries, and corneal transplantation are largely inadequate, have undesirable side effects including blindness, and can require life-long applications. Adeno-associated virus (AAV) mediated gene therapy is an optimistic strategy that involves the delivery of genetic material to target human diseases through gene augmentation, gene deletion, and/or gene editing. With two therapies already approved by the United States Food and Drug Administration and 200 ongoing clinical trials, recombinant AAV (rAAV) has emerged as the in vivo viral vector-of-choice to deliver genetic material to target human diseases. Likewise, the relative ease of applications through targeted delivery and its compartmental nature makes the cornea an enticing tissue for AAV mediated gene therapy applications. This current review seeks to summarize the development of AAV gene therapy, highlight preclinical efficacy studies, and discuss potential applications and challenges of this technology for targeting corneal diseases.

A reliable animal model of corneal stromal opacity: Development and validation using in vivo imaging

PURPOSE

To validate an animal model of corneal stromal opacity by using objective vision-independent in vivo imaging metrics.

METHODS

This was a prospective study, with two arms: (i) observational human arm which included 14 patients with healed unilateral ulcerative keratitis; and (ii) experimental rabbit arm, which included 6 New Zealand white rabbits. A 3-mm central wound was created in the left eye of the rabbits by manually removing 200-250 μm of the superficial stroma, followed by rotating-burr application. Both groups underwent photography, high-resolution anterior segment optical coherence tomography, and Scheimpflug imaging using similar diagnostic platforms and standardized image capturing protocols. Parameters studied were relative change in (i) corneal thickness; (ii) corneal epithelial: stromal (E:S) reflectivity ratio; (iii) corneal stromal light scattering using densitometry; and (iv) central corneal keratometry.

RESULTS

In the experimental arm, there was a significant decrease in corneal thickness (273 ± 51.3 vs. 407.3 ± 10.3 μm, p = 0.0038), E:S reflectivity ratio (0.71 ± 0.09 vs. 0.99 ± 0.06, p = 0.0018), and keratometry (40.4 ± 2.3 vs. 45.8 ± 0.9D, p = 0.0033) and increase in densitometry (54.2 ± 11.65 vs.18.7 ± 3.8 GSU, p = 0.0001) from baseline, which stabilized at 4 to 8-weeks post-wounding (p > 0.3632). At 8-weeks, the relative change from baseline in corneal thickness (28.4 ± 13.5% vs.22.4 ± 13%, p = 0.368), E:S reflectivity ratio (28.1 ± 11.5% vs. 30.6 ± 8.9%, p = 0.603), corneal densitometry (204.17 ± 97.3% vs. 304.9 ± 113.6%, p = 0.1113), and central corneal keratometry (13.6 ± 6.9% vs. 18.9 ± 7.4%, p = 0.1738) in rabbits was similar to human corneal scars.

CONCLUSION

The animal model of corneal opacification was objectively comparable to human post-keratitis scars and can be valuable for in vivo evaluation of emerging therapies for corneal opacities.

Gene-based Therapeutic Tools in the Treatment of Cornea Disease

BACKGROUND

As one of the main blinding ocular diseases, corneal blindness resulted from neovascularization that disrupts the angiogenic privilege of corneal avascularity. Following neovascularization, inflammatory cells are infiltrating into cornea to strengthen corneal injury. How to maintain corneal angiogenic privilege to treat corneal disease has been investigated for decades.

METHODOLOGY

Local administration of viral and non-viral-mediated anti-angiogenic factors reduces angiogenic protein expression in situ with limited or free of off-target effects upon gene delivery. Recently, Mesenchymal Stem Cells (MSCs) have been studied to treat corneal diseases. Once MSCs are manipulated to express certain genes of interest, they could achieve superior therapeutic efficacy after transplantation.

DISCUSSION

In the text, we first introduce the pathological development of corneal disease in the aspects of neovascularization and inflammation. We summarize how MSCs become an ideal candidate in cell therapy for treating injured cornea, focusing on cell biology, property and features. We provide an updated review of gene-based therapies in animals and preclinical studies in the aspects of controlling target gene expression, safety and efficacy. Gene transfer vectors are potent to induce candidate protein expression. Delivered by vectors, MSCs are equipped with certain characters by expressing a protein of interest, which facilitates better for MSC-mediated therapeutic intervention for the treatment of corneal disease.

CONCLUSION

As the core of this review, we discuss how MSCs could be engineered to be vector system to achieve enhanced therapeutic efficiency after injection.

Systematic Review on Therapeutic Strategies to Minimize Corneal Stromal Scarring After Injury

OBJECTIVES

To evaluate recent studies on available and experimental therapies in preventing or minimizing corneal stromal scarring after injury.

METHODS

We performed an Entrez PubMed literature search using keywords "cornea," "scarring," "haze," "opacity," "ulcer," "treatments," "therapies," "treatment complications," and "pathophysiology" resulting in 390 articles of which 12 were analyzed after filtering, based on English language and publication within 8 years, and curation for relevance by the authors.

RESULTS

The 12 articles selected included four randomized control trials (RCTs) (two were double-blinded placebo-controlled RCTs, one was a prospective partially masked RCT, and one was an open-label RCT), two retrospective observational studies, and six laboratory-based studies including two studies having in vivo and in vitro experiments, one was in vivo study, one was ex vivo study, and the last two were in vitro studies. The current mainstay for preventing or minimizing corneal scarring involves the use of topical corticosteroids and local application of mitomycin C. However, supportive evidence for their use in clinical practice from well-designed RCTs is lacking. Laboratory studies on topical rosiglitazone therapy, vitamin C prophylaxis, gene therapy, and stem cell therapy have shown promising results but have yet to be translated to clinical research.

CONCLUSION

There is a need for more robust randomized controlled trials to support treatments using topical corticosteroids and mitomycin C. Furthermore, their clinical efficacy and safety profile should be compared with new treatments that have shown promising results in the laboratory setting. Ultimately, the goal should be to personalize cornea scarring treatment according to the most effective treatment for the specific underlying pathology.

Biology of corneal fibrosis: soluble mediators, integrins, and extracellular vesicles

Corneal fibrosis develops in response to injury, infection, postsurgical complications, or underlying systemic disease that disrupts the homeostasis of the tissue leading to irregular extracellular matrix deposition within the stroma. The mechanisms that regulate corneal scarring are focused heavily on the canonical transforming growth factor-β pathway and relevant activators, and their role in promoting myofibroblast differentiation. In this paper, we discuss the biochemical pathways involved in corneal fibrosis in the context of different injury models-epithelial debridement, superficial keratectomy, and penetrating incision. We elaborate on the interplay of the major pro-fibrotic factors involved in corneal scar development (e.g., transforming growth factor-β1, thrombospondin-1, and ανβ6), and explore a novel role for extracellular vesicles secreted by the wounded epithelium and the importance of the basement membrane.

The myofibroblast, biological activities and roles in eye repair and fibrosis. A focus on healing mechanisms in avascular cornea

Tissue healing is one of the mysteries of modern medicine. Healing involves complex processes and many cellular types, amongst which the myofibroblast plays a major role. In the eye, when needed, myofibroblasts can be found from the cornea to the retina, derived from a wide variety of different cells, and aimed at effectively repairing tissue damage. Myofibroblast differentiation requires transforming growth factor (TGF)-β1, the presence of specific extracellular matrix components such as the ED-A domain of fibronectin, and mechanical tension. Control of this process may, in some cases, be abnormal leading to development of fibrotic tissue, which alters and compromises the integrity of the original tissue. The eye is no exception to this rule with normal visual function, a highly demanding process, only possible in a fully integrated organ. The cornea, a transparent protective tissue and first dioptre of the eye, has the particularity of being entirely avascular and very richly innervated under normal physiological conditions. However, these anatomical features do not prevent it from developing myofibroblasts in the event of a deep corneal lesion. Activated by growth factors such as TGF-β1 and platelet-derived growth factor from the aqueous humour, tears or corneal epithelial cells, myofibroblasts can cause corneal scarring, sometimes with devastating consequences. Understanding the factors involved in healing and its signalling pathways, will potentially enable us to control corneal healing in the future, and thus avoid fibrotic ocular surface disease and the blindness that this may induce. Currently, this issue is the subject of very active research and development with the aim of discovering new antifibrotic therapies.