Corneal endothelial cells are protected from apoptosis by gene therapy

Fusogenic liposome-coated nanoparticles for rapid internalization into donor corneal endothelial tissue to enable prophylaxis before transplantation

Cold stress (hypothermia) during storage and cytokine stress due to acute allograft rejection adversely affect the donor corneal endothelium in the short term. Pharmacological pre-treatment (before transplantation) of the donor corneal endothelium or cells (propagated in vitro for cell injection therapy) with microtubule stabilizers, cold stress protectants, and other molecules is an attractive strategy to tackle damage caused by hypothermia and cytokine stress. These molecules can be delivered intracellularly to the donor corneal endothelium or cells at controlled rates for desired periods and with one-time administration using nanoparticles. However, the death-to-preservation time of donor corneas of more than 4 to 6 h significantly decreases endothelial cell density and increases the risk of microbial contamination. Therefore, we have developed fusogenic liposome-coated nanoparticles for rapid internalization of nanoparticles into cultured corneal endothelial cells and ex vivo corneal endothelial tissue. Here, we have shown that the fusogenic liposome-coated nanoparticles have the intrinsic ability to efficiently and rapidly internalize into cultured corneal endothelial cells and ex vivo corneal tissue within 3 h by possibly fusing with the cell membrane and bypassing the endocytic pathway. Lactate dehydrogenase assay showed that the internalized fusogenic liposome-coated nanoparticles did not cause cytotoxicity in endothelial cells associated with the ex vivo cornea for at least up to 2 days. Thus, fusogenic liposome-coated nanoparticles have great potential as a platform for engineering cells and endothelial tissue of donor corneas to facilitate prophylactic drug delivery during storage and after transplantation.

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.

Role of Oxidative Stress in the Disruption of the Endothelial Apical Junctional Complex During Corneal Cold Storage

Purpose: To characterize the impact of corneal cold storage (CS) on the endothelial apical junctional complex (AJC). Methods: Porcine corneas were held in CS (4°C; 1-7 days) with Cornisol™ preservation medium supplemented with epothilone B (EpoB; microtubule stabilizer; 100 nM), SB-203580 (p38 mitogen-activated protein [MAP] kinase inhibitor; 20 μM), or antioxidants (quercetin, 100 μM; vitamin E, 1 mM; deferoxamine, an iron chelator, 10 mM). After CS termination, the damage to endothelial AJC was characterized by imaging perijunctional actomyosin ring (PAMR) and zonula occludens (ZO-1). The effects of EpoB and SB-203580 were characterized by imaging microtubules. The loss in the barrier function was assessed in cultured cells grown on biotin-coated gelatin by permeability to fluorescein isothiocyanate (FITC)-avidin. The accumulation of reactive oxygen species (ROS), altered mitochondrial membrane potential (MMP), lipid peroxidation, and lactate dehydrogenase (LDH) release were also determined in response to CS. Results: CS led to the loss of microtubules, destruction of PAMR, and breakdown of ZO-1 in the endothelium. The severity of damage increased when CS was prolonged. Although rewarming of the tissue increased the damage, the effect was marginal. CS also induced accumulation of ROS, alteration in MMP, lipid peroxidation, enhanced LDH release, and increased permeability to FITC-avidin. These changes were opposed by EpoB, SB-203580, and antioxidants. Conclusion: Corneal CS destroys AJC of the endothelium, leading to loss of its barrier function. The effects were surmounted by microtubule stabilization, p38 MAP kinase inhibition, and antioxidants. Thus, there is potential for reformulation of the preservation medium to maintain the health of the donor corneal endothelium before transplantation.

Lentiviral Vectors for Ocular Gene Therapy

This review offers the basics of lentiviral vector technologies, their advantages and pitfalls, and an overview of their use in the field of ophthalmology. First, the description of the global challenges encountered to develop safe and efficient lentiviral recombinant vectors for clinical application is provided. The risks and the measures taken to minimize secondary effects as well as new strategies using these vectors are also discussed. This review then focuses on lentiviral vectors specifically designed for ocular therapy and goes over preclinical and clinical studies describing their safety and efficacy. A therapeutic approach using lentiviral vector-mediated gene therapy is currently being developed for many ocular diseases, e.g., aged-related macular degeneration, retinopathy of prematurity, inherited retinal dystrophies (Leber congenital amaurosis type 2, Stargardt disease, Usher syndrome), glaucoma, and corneal fibrosis or engraftment rejection. In summary, this review shows how lentiviral vectors offer an interesting alternative for gene therapy in all ocular compartments.

Fumonisin B1 Induces Immunotoxicity and Apoptosis of Chicken Splenic Lymphocytes

Fumonisin B₁ (FB₁), produced by Fusarium, is among the most abundant and toxic mycotoxin contaminations in feed, causing damages to the health of livestock. However, the mechanisms of FB₁ toxicity in chickens are less understood. As splenic lymphocytes play important roles in the immune system, the aim of this study was to investigate the immunotoxic effects and mechanisms of FB₁ on chicken splenic lymphocytes. In the present study, the chicken primary splenic lymphocytes were harvested and treated with 0, 2.5, 5, 10, 20 and 40 μg/mL FB₁. Then, the cell proliferation, damage, ultrastructure, inflammation and apoptosis were evaluated. Results showed that the proliferation rate of splenic lymphocytes was decreased by FB₁ treatments. The activity of lactate dehydrogenase (LDH) was increased by FB₁ treatments in a dose-dependent manner, implying the induction of cell damage. Consistently, the ultrastructure of splenic lymphocytes showed that FB₁ at all the tested concentrations caused cell structure alterations, including nuclear vacuolation, mitochondrial swelling and mitochondrial crest fracture. Besides, immunosuppressive effects of FB₁ were observed by the decreased concentrations of interleukin-2 (IL-2), IL-4, IL-12 and interferon-γ (IFN-γ) in the cell culture supernatant. Furthermore, apoptosis was observed in FB₁-treated cells by flow cytometry. The mRNA expressions of apoptosis-related genes showed that the expression of Bcl-2 was decreased, while the expressions of the P53, Bax, Bak-1, and Caspase-3 were increased with FB₁ treatment. Similar results were found in the concentrations of apoptosis-related proteins in the cell supernatant by ELISA assay. Moreover, regression analysis indicated that increasing FB₁ concentration increased LDH activity, concentrations of Bax, Bak-1 and mRNA expression of Bak-1 linearly, increased M1 area percentage quadratically, decreased concentration of IFN-γ, mRNA expression of Bcl-2 linearly, and decreased concentrations of IL-2 and IL-4 quadratically. Besides, regression analysis also showed reciprocal relationships between IL-12 concentration, Caspase-3 mRNA expression and increasing FB₁ concentration. The increasing FB₁ concentration could decrease IL-12 concentration and increase Caspase-3 mRNA expression. Altogether, this study reported that FB₁ induced the immunotoxicity of chicken splenic lymphocytes and caused splenic lymphocytes apoptosis by the Bcl-2 family-mediated mitochondrial pathway of caspase activation.

Tissue Engineering Meets Nanotechnology: Molecular Mechanism Modulations in Cornea Regeneration

Nowadays, tissue engineering is one of the most promising approaches for the regeneration of various tissues and organs, including the cornea. However, the inability of biomaterial scaffolds to successfully integrate into the environment of surrounding tissues is one of the main challenges that sufficiently limits the restoration of damaged corneal tissues. Thus, the modulation of molecular and cellular mechanisms is important and necessary for successful graft integration and long-term survival. The dynamics of molecular interactions affecting the site of injury will determine the corneal transplantation efficacy and the post-surgery clinical outcome. The interactions between biomaterial surfaces, cells and their microenvironment can regulate cell behavior and alter their physiology and signaling pathways. Nanotechnology is an advantageous tool for the current understanding, coordination, and directed regulation of molecular cell-transplant interactions on behalf of the healing of corneal wounds. Therefore, the use of various nanotechnological strategies will provide new solutions to the problem of corneal allograft rejection, by modulating and regulating host-graft interaction dynamics towards proper integration and long-term functionality of the transplant.

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.

Effect of Rho-associated kinase inhibitor on human corneal endothelial cell apoptosis

PURPOSE

To evaluate whether exposure to Rho-associated protein kinase (ROCK) inhibitor will promote human-cultured corneal endothelial cells (CECs) survival in a commercial storage medium.

SETTING

Edith Wolfson Medical Center, Holon, and Sheba Medical Center, Tel Hashomer, Israel.

DESIGN

Experimental study.

METHODS

Fragments of human donor corneolimbal rings were stored in commercial storage media for 1 week, half with the addition of 10 μM ROCK inhibitor (Y-27632). Evaluation of CECs for early and late apoptosis\necrosis rates was performed using anti-human CD166 antibody and flow cytometric double staining analysis of propidium iodide and Annexin V.

RESULTS

CECs of 6 corneolimbal rings demonstrated a reduced early apoptosis rate (4.35% ± 1.07% vs 12.18% ± 5.5%, P = .026) and a reduced late apoptosis\necrosis rate (5.5% ± 2.39% vs 9.43% ± 2.61%, P = .004) compared with control. Subsequently, the rate of apoptotic CECs expressing ROCK was significantly lower in cells exposed to ROCK inhibitor compared with cells that were not (19.01% ± 4.17 vs 30.42% ± 4.27, P < .001).

CONCLUSIONS

ROCK inhibitor reduced endothelial cell loss in vitro and might be used to limit or slow CEC loss in donor corneal tissue during eye banking. This might be a promising new method for promoting future graft survival.

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.

Foot-and-Mouth Disease Virus Antagonizes NOD2-Mediated Antiviral Effects by Inhibiting NOD2 Protein Expression

The role of nucleotide-binding oligomerization domain 2 (NOD2) in foot-and-mouth disease virus (FMDV)-infected cells remains unknown. Here, we showed that FMDV infection activated NOD2-mediated beta interferon (IFN-β) and nuclear factor-κB (NF-ĸB) signaling pathways. NOD2 inhibited FMDV replication in the infected cells. FMDV infection triggered NOD2 transcription, while it reduced the abundance of NOD2 protein. Our results revealed that FMDV 2B, 2C, and 3C proteinase (3C^pro) were responsible for the decrease in NOD2 protein levels. 3C^pro is a viral proteinase that can cleave multiple host proteins and limit protein synthesis. Our previous studies determined that FMDV 2B suppressed protein expression of RIG-I and LGP2. Here, we found that 3C^pro and 2B also decreased NOD2 expression. However, this is the first report that 2C induced the reduction of NOD2 protein levels. We determined that both 2B- and 2C-induced decreases in NOD2 were independent of the cleavage of host eukaryotic translation initiation factor 4 gamma (eIF4G), induction of cellular apoptosis, or proteasome, lysosome, and caspase pathways. The interactions between NOD2 and 2B or 2C were observed in the context of viral infection. The carboxyl-terminal amino acids 105 to 114 and 135 to 144 of 2B were essential for the reduction of NOD2, while the residues 105 to 114 were required for the interaction. Amino acids 116 to 260 of the carboxyl terminus of 2C were essential for the interaction, while truncated 2C mutants did not reduce NOD2. These data suggested novel antagonistic mechanisms of FMDV that were mediated by 2B, 2C, and 3C^pro proteins.IMPORTANCE NOD2 was identified as a cytoplasmic viral pattern recognition receptor in 2009. Subsequently, many viruses were reported to activate NOD2-mediated signaling pathways. This study demonstrated that FMDV infection activated NOD2-mediated IFN-β and NF-ĸB signaling pathways. Host cells have developed multiple strategies against viral infection; however, viruses have evolved many strategies to escape host defenses. FMDV has evolved multiple mechanisms to inhibit host type I IFN production. Here, we showed that NOD2 suppressed FMDV replication during viral infection. FMDV 2B, 2C, and 3C^pro decreased NOD2 protein expression by different mechanisms to promote viral replication. This study provided new insight into the immune evasion mechanisms mediated by FMDV and identified 2B, 2C, and 3C^pro as antagonistic factors for FMDV to evade host antiviral responses.

[Novel concepts for treatment of the corneal endothelium with nanoparticles]

BACKGROUND

The number of corneal transplantations has increased in Germany in recent years. One reason is an earlier time point of surgery due to less invasive posterior lamellar grafting techniques. To date, penetrating and lamellar corneal transplantations are the only established therapeutic options to treat corneal diseases resulting from endothelial cell pathologies.

AIM

This review article provides an insight into nanoparticle-related translational strategies to improve or to avoid corneal transplantation.

RESULTS

Nanoparticle-based strategies for optimization of the corneal endothelium have different fields of application: 1. during donor cornea cultivation in culture medium, 2. for single cell injection therapies and 3. to treat the patients' own endothelium in an effort to avoid transplantation.

CONCLUSION

Several translational concepts exist to improve or to avoid grafting of a donor cornea. The coming decade will provide established alternatives to conventional corneal transplantation.

Gene Therapy for Modulation of T-Cell-Mediated Immune Response Provoked by Corneal Transplantation

Corneal transplantation (keratoplasty) is the most common type of tissue replacement in the world. The increased rate of graft rejection after keratoplasty is a central problem for repeated transplantations and in inflamed host corneas. It has been shown that apoptosis of grafted epithelium has a role in corneal allograft rejection. This study focused on the T-cell response triggered in BALB/c mice after allogeneic corneal transplantation with and without anti-apoptotic p35-transduced epithelium. To restrict p35 expression to the epithelial cells, modified allogeneic composite grafts were created. As a result, it was found that the proportion of alloreactive CD4⁺ T cells in postoperatively removed cervical lymph nodes was reduced in the p35-transduced group compared to the allogeneic control group. Diminished priming of the CD4⁺ T cells was supported by significantly decreased proliferation and lower interferon gamma secretion when compared to allogeneic engraftments. The reduced priming of CD4⁺ lymphocytes is the first confirmation of the functionality of p35 in the epithelium of corneal grafts to alter the development of the recipient's immune response. Thus, modification of allosensibilization seems to be a promising tool for reducing graft-mediated immune response following corneal transplantation.

[Critical endothelial procedures during posterior lamellar graft preparation and transplantation]

BACKGROUND

In view of the very low proliferation rate and functional importance of the corneal endothelium in maintaining corneal transparency, safeguarding the integrity of this monolayer plays a central role in posterior lamellar corneal transplantation. Several critical endothelial procedural stages are necessary to carry out such a transplantation.

OBJECTIVE

This article presents various preparatory and operative approaches for carrying out the necessary and critical stages within the framework of posterior lamellar corneal transplantation and concentrates on the question of optimization.

METHODS

A review of our own studies and studies of other groups is presented.

RESULTS

For the performance of critical endothelial procedural steps, a variety of approaches are available. These range from preparation and insertion of the transplant, through the manipulation during centralization up to the effects of postoperative air or gas bubble tamponade.

CONCLUSION

Because endothelial damage can permanently impair the integrity of lamellar transplants, a minimal handling and no touch policy should be strived for in all critical procedures. Long-term data on the follow-up course will show which of the procedures favored by various authors lead to the best postoperative results.

Foot-and-Mouth Disease Virus Viroporin 2B Antagonizes RIG-I-Mediated Antiviral Effects by Inhibition of Its Protein Expression

The role of retinoic acid-inducible gene I (RIG-I) in foot-and-mouth disease virus (FMDV)-infected cells remains unknown. Here, we showed that RIG-I inhibits FMDV replication in host cells. FMDV infection increased the transcription of RIG-I, while it decreased RIG-I protein expression. A detailed analysis revealed that FMDV leader proteinase (Lpro), as well as 3C proteinase (3Cpro) and 2B protein, decreased RIG-I protein expression. Lpro and 3Cpro are viral proteinases that can cleave various host proteins and are responsible for several of the viral polyprotein cleavages. However, for the first time, we observed 2B-induced reduction of host protein. Further studies showed that 2B-mediated reduction of RIG-I is specific to FMDV, but not other picornaviruses, including encephalomyocarditis virus, enterovirus 71, and coxsackievirus A16. Moreover, we found the decreased protein level of RIG-I is independent of the cleavage of eukaryotic translation initiation factor 4 gamma, the induction of cellular apoptosis, or the association of proteasome, lysosome, and caspase pathways. A direct interaction was observed between RIG-I and 2B. The carboxyl-terminal amino acids 105 to 114 and amino acids 135 to 144 of 2B were essential for the reduction of RIG-I, while residues 105 to 114 were required for the interaction. These data suggest the antiviral role of RIG-I against FMDV and a novel antagonistic mechanism of FMDV that is mediated by 2B protein.

IMPORTANCE

This study demonstrated that RIG-I could suppress FMDV replication during virus infection. FMDV infection increased the transcriptional expression of RIG-I, while it decreased RIG-I protein expression. FMDV 2B protein interacted with RIG-I and induced reduction of RIG-I. 2B-induced reduction of RIG-I was independent of the induction of the cleavage of eukaryotic translation initiation factor 4 gamma or cellular apoptosis. In addition, proteasome, lysosome, and caspase pathways were not involved in this process. This study provides new insight into the immune evasion mediated by FMDV and identifies 2B as an antagonistic factor for FMDV to evade the antiviral response.

Efficient and safe gene delivery to human corneal endothelium using magnetic nanoparticles

Aim: To develop a safe and efficient method for targeted, anti-apoptotic gene therapy of corneal endothelial cells (CECs). Materials & methods: Magnetofection (MF), a combination of lipofection with magnetic nanoparticles (MNPs; PEI-Mag2, SO-Mag5, PalD1-Mag1), was tested in human CECs and in explanted human corneas. Effects on cell viability and function were investigated. Immunocompatibility was assessed in human peripheral blood mononuclear cells. Results: Silica iron-oxide MNPs (SO-Mag5) combined with X-tremeGENE-HP achieved high transfection efficiency in human CECs and explanted human corneas, without altering cell viability or function. Magnetofection caused no immunomodulatory effects in human peripheral blood mononuclear cells. Magnetofection with anti-apoptotic P35 gene effectively blocked apoptosis in CECs. Conclusion: Magnetofection is a promising tool for gene therapy of corneal endothelial cells with potential for targeted on-site delivery.

[Protection of corneal endothelium from apoptosis by gene and cell therapy]

Protection of corneal endothelium from apoptosis using gene and cell therapy is in a translational phase. This approach offers advantages for eye banking and after transplantation. Safe vehicles for gene or cell therapeutic transduction of corneal endothelium with nucleic acids are available. This strategy will be further developed in consultation with the Paul Ehrlich Institute and European regulatory authorities.

Self-Complementary Adeno-Associated Virus Vectors Improve Transduction Efficiency of Corneal Endothelial Cells

Transplantation of a donor cornea to restore vision is the most frequently performed transplantation in the world. Corneal endothelial cells (CEC) are crucial for the outcome of a graft as they maintain corneal transparency and avoid graft failure due to corneal opaqueness. Given the characteristic of being a monolayer and in direct contact with culture medium during cultivation in eye banks, CEC are specifically suitable for gene therapeutic approaches prior to transplantation. Recombinant adeno-associated virus 2 (rAAV2) vectors represent a promising tool for gene therapy of CEC. However, high vector titers are needed to achieve sufficient gene expression. One of the rate-limiting steps for transgene expression is the conversion of single-stranded (ss-) DNA vector genome into double-stranded (ds-) DNA. This step can be bypassed by using self-complementary (sc-) AAV2 vectors. Aim of this study was to compare for the first time transduction efficiencies of ss- and scAAV2 vectors in CEC. For this purpose AAV2 vectors containing enhanced green fluorescent protein (GFP) as transgene were used. Both in CEC and in donor corneas, transduction with scAAV2 resulted in significantly higher transgene expression compared to ssAAV2. The difference in transduction efficiency decreased with increasing vector titer. In most cases, only half the vector titer of scAAV2 was required for equal or higher gene expression rates than those of ssAAV2. In human donor corneas, GFP expression was 64.7±11.3% (scAAV) and 38.0±8.6% (ssAAV) (p<0.001), respectively. Furthermore, transduced cells maintained their viability and showed regular morphology. Working together with regulatory authorities, a translation of AAV2 vector-mediated gene therapy to achieve a temporary protection of corneal allografts during cultivation and transplantation could therefore become more realistic.

3-MA Inhibits Autophagy and Favors Long-Term Integration of Grafted Gad67–GFP GABAergic Precursors in the Developing Neocortex by Preventing Apoptosis

In human neonates, immature GABAergic interneurons are markedly affected by an excitotoxic insult. While in adults the interest of cell transplantation has been demonstrated in several neurological disorders, few data are available regarding the immature brain. The low survival rate constitutes a strong limitation in the capacity of transplanted neurons to integrate the host tissue. Because i) autophagy is an adaptive process to energetic/nutrient deprivation essential for cell survival and ii) literature describes cross-talks between autophagy and apoptosis, we hypothesized that regulation of autophagy would represent an original strategy to favor long-term survival of GABAergic precursors grafted in the immature neocortex. Morphological, neurochemical, and functional data showed that in control conditions, few grafted Gad67-GFP precursors survived. The first hours following transplantation were a critical period with intense apoptosis. Experiments performed on E15.5 ganglionic eminences revealed that Gad67-GFP precursors were highly sensitive to autophagy. Rapamycin and 3-MA impacted on LC3 cleavage, LC3II translocation, and autophagosome formation. Quantification of Bax, mitochondrial integrity, caspase-3 cleavage, and caspase-3 immunolocalization and activity showed that 3-MA induced a significant decrease of Gad67-GFP precursor apoptosis. In vivo, 3-MA induced, within the first 24 h, a diffuse LC3 pattern of grafted Gad67-GFP precursors, an increase of precursors with neurites, a reduction of the density of caspase-3 immunoreactive cells. A twofold increase in the survival rate occurred 15 days after the graft. Surviving neurons were localized in the cortical layers II–IV, which were still immature when the transplantation was done. Altogether, these data indicate that inhibition of autophagy represents an original strategy to allow GABAergic interneurons to overpass the first critical hours following transplantation and to increase their long-term survival in mice neonates.

Gene therapy in corneal transplantation

Corneal transplantation is the most commonly performed organ transplantation. Immune privilege of the cornea is widely recognized, partly because of the relatively favorable outcome of corneal grafts. The first-time recipient of corneal allografts in an avascular, low-risk setting can expect a 90% success rate without systemic immunosuppressive agents and histocompatibility matching. However, immunologic rejection remains the major cause of graft failure, particularly in patients with a high risk for rejection. Corticosteroids remain the first-line therapy for the prevention and treatment of immune rejection. However, current pharmacological measures are limited in their side-effect profiles, repeated application, lack of targeted response, and short duration of action. Experimental ocular gene therapy may thus present new horizons in immunomodulation. From efficient viral vectors to sustainable alternative splicing, we discuss the progress of gene therapy in promoting graft survival and postulate further avenues for gene-mediated prevention of allogeneic graft rejection.

Gene therapy for corneal dystrophies and disease, where are we?

PURPOSE OF REVIEW

We assess the studies on vector systems for delivery of transgenes to the cornea that have been published over the last year and summarize new work on the identification of specific transgenes for corneal diseases.

RECENT FINDINGS

Adeno-associated viral vectors are increasingly being successfully applied to the cornea, although transgene expression requires corneal epithelial debridement or intrastromal injection of the vector. Gene delivery platforms based on nanoparticles of chitosan or gold also show promise. Overexpression of vasoinhibin-1 or decorin, or siRNA-mediated blockade of the cannabinoid receptor CB1, can all reduce corneal neovascularization. Overexpression of decorin or matrix metalloproteinase 14 can reduce corneal fibrosis and haze, whereas overexpression of c-Met accelerates the epithelial wound healing. Induction of corneal endothelial cell replication by overexpression of E2F2, p16 or p21 can maintain or even increase corneal endothelial cell density in eye bank corneas. Overexpression of the antiapoptotic transgenes Bcl-xL or p35 significantly enhances corneal endothelial cell survival and reduces apoptosis in stored human corneas.

SUMMARY

Despite a wealth of information on the methods for the delivery of nucleic acids to the human cornea and ever-increasing information on the transgenes with substantial therapeutic potential, gene therapy for corneal disorders has yet to reach the clinic.

Corneal gene therapy: basic science and translational perspective

Corneal blindness is the third leading cause of blindness worldwide. Gene therapy is an emerging technology for corneal blindness due to the accessibility and immune-privileged nature of the cornea, ease of vector administration and visual monitoring, and ability to perform frequent noninvasive corneal assessment. Vision restoration by gene therapy is contingent upon vector and mode of therapeutic gene introduction into targeted cells/tissues. Numerous efficacious vectors, delivery techniques, and approaches have evolved in the last decade for developing gene-based interventions for corneal diseases. Maximizing the potential benefits of gene therapy requires efficient and sustained therapeutic gene expression in target cells, low toxicity, and a high safety profile. This review describes the basic science associated with many gene therapy vectors and the present progress of gene therapy carried out for various ocular surface disorders and diseases.

Regenerative approaches as alternatives to donor allografting for restoration of corneal function

A range of alternatives to human donor tissue for corneal transplantation are being developed to address the shortfall of good quality tissues as well as the clinical conditions for which allografting is contraindicated. Classical keratoprostheses, commonly referred to as artificial corneas, are being used clinically to replace minimal corneal function. However, they are used only as last resorts, as they are associated with significant complications, such as extrusion/rejection, glaucoma, and retinal detachment. The past few years have seen significant developments in technologies designed to replace part or the full thickness of damaged or diseased corneas with materials that encourage regeneration to different extents. This review describes selected examples of these corneal substitutes, which range from cell-based regenerative strategies to keratoprostheses with regenerative capabilities via tissue-engineered scaffolds pre-seeded with stem cells. It is unlikely that one corneal substitute will be best for all indications, but taken together, the various approaches may soon be able to supplement the supply of human donor corneas for transplantation or allow restoration of diseased or damaged corneas that cannot be treated by currently available techniques.

A new tool for the transfection of corneal endothelial cells: calcium phosphate nanoparticles

Calcium phosphate nanoparticles (CaP-NP) are ideal tools for transfection due to their high biocompatibility and easy biodegradability. After transfection these particles dissociate into calcium and phosphate ions, i.e. physiological components found in every cell, and it has been shown that the small increase in intracellular calcium level does not affect cell viability. CaP-NP functionalized with pcDNA3-EGFP (CaP/DNA/CaP/DNA) and stabilized using different amounts of poly(ethylenimine) (PEI) were prepared. Polyfect®-pcDNA3-EGFP polyplexes served as a positive control. The transfection of human and murine corneal endothelial cells (suspensions and donor tissue) was optimized by varying the concentration of CaP-NP and the duration of transfection. The transfection efficiency was determined as EGFP expression detected by flow cytometry and fluorescence microscopy. To evaluate the toxicity of the system the cell viability was detected by TUNEL staining. Coating with PEI significantly increased the transfection efficiency of CaP-NP but decreased cell viability, due to the cytotoxic nature of PEI. The aim of this study was to develop CaP-NP with the highest possible transfection efficiency accompanied by the least apoptosis in corneal endothelial cells. EGFP expression in the tissues remained stable as corneal endothelial cells exhibit minimal proliferative capacity and very low apoptosis after transfection with CaP-NP. In summary, CaP-NP are suitable tools for the transfection of corneal endothelial cells. As CaP-NP induce little apoptosis these nanoparticles offer a safe alternative to viral transfection agents.

Gene therapy in the cornea: 2005--present

Successful restoration of vision in human patients with gene therapy affirmed its promise to cure ocular diseases and disorders. The efficacy of gene therapy is contingent upon vector and mode of therapeutic DNA introduction into targeted cells/tissues. The cornea is an ideal tissue for gene therapy due to its ease of access and relative immune-privilege. Considerable progress has been made in the field of corneal gene therapy in last 5 years. Several new gene transfer vectors, techniques and approaches have evolved. Although corneal gene therapy is still in its early stages of development, the potential of gene-based interventions to treat corneal abnormalities has begun to surface. Identification of next generation viral and nanoparticle vectors, characterization of delivered gene levels, localization, and duration in the cornea, and significant success in controlling corneal disorders, particularly fibrosis and angiogenesis, in experimental animal disease models, with no major side effects have propelled gene therapy a step closer toward establishing gene-based therapies for corneal blindness. Recently, researchers have assessed the delivery of therapeutic genes for corneal diseases and disorders due to trauma, infections, chemical, mechanical, and surgical injury, and/or abnormal wound healing. This review provides an update on the developments in gene therapy for corneal diseases and discusses the barriers that hinder its utilization for delivering genes in the cornea.