A novel method of isolation, preservation, and expansion of human corneal endothelial cells

Biomaterial-based strategies for primary human corneal endothelial cells for therapeutic applications: from cell expansion to transplantable carrier

The treatment of corneal blindness due to corneal diseases and injuries often requires the transplantation of healthy cadaveric corneal endothelial graft tissue to restore corneal clarity and visual function. However, the limited availability of donor corneas poses a significant challenge in meeting the demand for corneal transplantation. As a result, there is a growing interest in developing strategies alleviate this unmet need, and one of the postulated approaches is to isolate and expand primary human corneal endothelial cells (HCECs) in vitro for use in cell therapy. This review summarizes the recent advancements in the expansion of HCECs using biomaterials. Two principal biomaterial-based approaches, including extracellular matrix (ECM) coating and functionalized synthetic polymers, have been investigated to create an optimal microenvironment for the expansion and maintenance of corneal endothelial cells (CECs). This review highlights the challenges and opportunities in expanding primary HCECs using biomaterials. It emphasizes the importance of optimizing biomaterial properties, cell culture conditions, and the roles of biophysical cues to achieve efficient expansion and functional maintenance of CECs. Biomaterial-based strategies hold significant promise for expanding primary HCECs and improving the outcomes of CEC transplantation. The integration of biomaterials as cell culture substrates and transplantable carriers offers a comprehensive approach to address the limitations associated with current corneal tissue engineering techniques.

Controlled Release of Molecules to Enhance Cell Survival and Regeneration

Controlled release or controlled drug delivery comprises the set of techniques and approaches to improve bioavailability through improved safety and/or efficacy using a carrier material for the molecule of interest. The predictability and tunability of these carriers make them ideal for protection, localization, and sustained presentation of a wide range of therapeutics, including growth factors implicated in cell survival and regeneration. Here we provide a method for encapsulating epidermal growth factor in a degradable polymer matrix for delivery to the cornea. Additional notes are included to demonstrate the wide-ranging capabilities of such methods for other materials, therapeutic agents, and sites of action within the eye.

Biomaterials used for tissue engineering of barrier-forming cell monolayers in the eye

Cell monolayers that form a barrier between two structures play an important role for the maintenance of tissue functionality. In the anterior portion of the eye, the corneal endothelium forms a barrier that controls fluid exchange between the aqueous humor of the anterior chamber and the corneal stroma. This monolayer is central in the pathogenesis of Fuchs endothelial corneal dystrophy (FECD). FECD is a common corneal disease, in which corneal endothelial cells deposit extracellular matrix that increases the thickness of its basal membrane (Descemet's membrane), and forms excrescences (guttae). With time, there is a decrease in endothelial cell density that generates vision loss. Transplantation of a monolayer of healthy corneal endothelial cells on a Descemet membrane substitute could become an interesting alternative for the treatment of this pathology. In the back of the eye, the retinal pigment epithelium (RPE) forms the blood-retinal barrier, controlling fluid exchange between the choriocapillaris and the photoreceptors of the outer retina. In the retinal disease dry age-related macular degeneration (dry AMD), deposits (drusen) form between the RPE and its basal membrane (Bruch's membrane). These deposits hinder fluid exchange, resulting in progressive RPE cell death, which in turn generates photoreceptor cell death, and vision loss. Transplantation of a RPE monolayer on a Bruch's membrane/choroidal stromal substitute to replace the RPE before photoreceptor cell death could become a treatment alternative for this eye disease. This review will present the different biomaterials that are proposed for the engineering of a monolayer of corneal endothelium for the treatment of FECD, and a RPE monolayer for the treatment of dry AMD.

Manufacturing of human corneal endothelial grafts

PURPOSE

Human corneal endothelial cells (HCECs) play a significant role in maintaining visual function. However, these cells are notorious for their limited proliferative capacity in vivo. Current treatment of corneal endothelial dysfunction resorts to corneal transplantation. Herein we describe an ex vivo engineering method to manufacture HCEC grafts suitable for transplantation through reprogramming into neural crest progenitors.

METHODS

HCECs were isolated by collagenase A from stripped Descemet membrane of cadaveric corneoscleral rims, and induced reprogramming via knockdown with p120 and Kaiso siRNAs on collagen IV-coated atelocollagen. Engineered HCEC grafts were released after assessing their identity, potency, viability, purity and sterility. Phase contrast was used for monitoring cell shape, graft size, and cell density. Immunostaining was used to determine the normal HCEC phenotype with expression of N-cadherin, ZO-1, ATPase, acetyl-α-tubulin, γ-tubulin, p75NTR, α-catenin, β-catenin, and F-actin. Stability of manufactured HCEC graft was evaluated after transit and storage for up to 3 weeks. The pump function of HCEC grafts was measured by lactate efflux.

RESULTS

One HCEC graft suitable for corneal transplantation was generated from 1/8th of the donor corneoscleral rim with normal hexagonal cell shape, density, and phenotype. The manufactured grafts were stable for up to 3 weeks at 37 °C or up to 1 week at 22 °C in MESCM medium and after transcontinental shipping at room temperature by retaining normal morphology (hexagonal, >2000 cells/mm2, >8 mm diameter), phenotype, and pump function.

CONCLUSIONS

This regenerative strategy through knockdown with p120 and Kaiso siRNAs can be used to manufacture HCEC grafts with normal phenotype, morphology and pump function following prolonged storage and shipping.

GSK-3 inhibition reverts mesenchymal transition in primary human corneal endothelial cells

Human corneal endothelial cells are organized in a tight mosaic of hexagonal cells and serve a critical function in maintaining corneal hydration and clear vision. Regeneration of the corneal endothelial tissue is hampered by its poor proliferative capacity, which is partially retrieved in vitro, albeit only for a limited number of passages before the cells undergo mesenchymal transition (EnMT). Although different culture conditions have been proposed in order to delay this process and prolong the number of cell passages, EnMT has still not been fully understood and successfully counteracted. In this perspective, we identified herein a single GSK-3 inhibitor, CHIR99021, able to revert and avoid EnMT in primary human corneal endothelial cells (HCEnCs) from old donors until late passages in vitro (P8), as shown from cell morphology analysis (circularity). In accordance, CHIR99021 reduced expression of α-SMA, an EnMT marker, while restored endothelial markers such as ZO-1, Na⁺/K⁺ ATPase and N-cadherin, without increasing cell proliferation. A further analysis on RNA expression confirmed that CHIR99021 induced downregulation of EnMT markers (α-SMA and CD44), upregulation of the proliferation repressor p21 and revealed novel insights into the β-catenin and TGFβ pathways intersections in HCEnCs. The use of CHIR99021 sheds light on the mechanisms involved in EnMT, providing a substantial advantage in maintaining primary HCEnCs in culture until late passages, while preserving the correct morphology and phenotype. Altogether, these results bring crucial advancements towards the improvement of the corneal endothelial cells based therapy.

A Framework for Human Corneal Endothelial Cell Culture and Preliminary Wound Model Experiments with a New Cell Tracking Approach

Cell injection therapy is emerging as an alternative to treat corneal endothelial dysfunction (CED) and to avoid corneal scarring due to bullous keratopathy. However, establishing a standardized culture procedure that provides appropriate cell yield while retaining functional features remains a challenge. Here, we describe a detailed framework obtained from in vitro culture of human corneal endothelial cells (HCECs) and comparative in vivo experimental models for CED treatment with a new cell tracking approach. Two digestion methods were compared regarding HCEC morphology and adhesion. The effect of Y-27632 (ROCKi) supplementation on final cell yield was also assessed. Cell adhesion efficacy with two cell delivery systems (superparamagnetic embedding and cell suspension) was evaluated in an ex vivo human cornea model and in an in vivo rabbit CED model. The injection of supplemented culture medium or balanced salt solution (BSS) was used for the positive and negative controls, respectively. HCEC isolation with collagenase resulted in better morphology and adhesion of cultured HCEC when compared to EDTA. Y-27632 supplementation resulted in a 2.6-fold increase in final cell yield compared to the control. Ex vivo and in vivo adhesion with both cell delivery systems was confirmed by cell tracker fluorescence detection. Corneal edema and opacity improved in both animal groups treated with cultured HCEC. The corneas in the control groups remained opaque. Both HCEC delivery systems seemed comparable as treatments for CED and for the prevention of corneal scarring.

Isolation efficiency of collagenase and EDTA for the culture of corneal endothelial cells

PURPOSE

Tissue engineering of the corneal endothelium, as well as cell therapy, has been proposed as an alternative approach for the treatment of corneal endotheliopathies. These approaches require in vitro amplification of functional corneal endothelial cells (CECs). The goal of this study was to compare two common isolation methods, collagenase A and EDTA (EDTA), and determine whether they influence cell viability, morphology, and barrier function.

METHODS

Human eye bank research-grade corneas were used to isolate and cultivate CECs. All donors were more than 40 years old. Two Descemet membranes from the same donor were used separately to compare the collagenase A and EDTA cell isolation methods. The number of isolated cells, cell viability, morphology, and barrier functionality were compared.

RESULTS

A higher isolation efficiency of viable CECs and a higher circularity index (endothelial morphology) were obtained using collagenase A. Passage 3 cells presented similar barrier functionalities regardless of the isolation method.

CONCLUSIONS

This study showed that isolation of CECs using collagenase A yields higher isolation efficiency than EDTA, delaying the loss of endothelial morphology for early passage cells.

In Vitro Expansion of Corneal Endothelial Cells for Clinical Application: Current Update

ABSTRACT

Endothelial dysfunction is one of the leading causes of corneal blindness and one of the common indications for keratoplasty. At present, the standard of treatment involves the replacement of the dysfunctional endothelium with healthy tissue taken from a donor. Because there is a paucity of healthy donor tissues, research on the corneal endothelium has focused primarily on expanding these cells in the laboratory for transplantation in an attempt to reduce the gap between the demand and supply of donor tissues for transplantation. To expand these cells, which are nonmitotic in vivo, various mitogens, substrates, culture systems, and alternate strategies have been tested with varying success. The biggest challenge has been the limited proliferative capacity of these cells compounded with endothelial to mesenchymal transition that alters the functioning of these cells and renders them unsuitable for human transplantation. This review aims to give a comprehensive overview of the most common and successful techniques used in the culture of the cells, the current available evidence in support of epithelial to mesenchymal transition (EMT), alternate sources for deriving the corneal endothelial cells, and advances made in transplantation of these cells.

Effect of Collagenase A on Descemet Membrane Endothelial Keratoplasty Scroll Tightness

PURPOSE

The scrolling properties of the Descemet membrane endothelial keratoplasty (DMEK) graft are essential for surgical success. Currently, there is limited knowledge on what dictates the tightness of the DMEK scroll. The purpose of this study was to determine the impact of temperature and protein digestion on DMEK graft scroll tightness.

METHODS

For the temperature experiment, a total of 28 eyes were used for this study. Scrolls in the cold group were kept at 4°C while scrolls in the hot group were kept at 37°C. Scroll width was recorded at the 5-, 15-, and 30-minute mark. For the protein digestion experiment, a total of 18 eyes were exposed to collagenase A (10 CDU/mL) in Optisol solution. Scroll width was recorded at the time points of 1, 3, 5, 10, and 20 minutes.

RESULTS

The results of the temperature experiment did not yield any statistically significant changes in the mean scroll width of the DMEK scrolls across both temperature ranges and observation times. For the protein digestion experiment, the mean scroll width grew from 1.85 mm to 2.13 mm from the beginning of the experiment until the final observation at 20 minutes. This is a 14.7% change over 20 minutes with a P value (<0.001), exemplifying a statistically significant change in scroll width.

CONCLUSIONS

Temperature did not have any significant effect over scroll tightness, but scroll tightness decreased with collagenase exposure.

Design of functional biomaterials as substrates for corneal endothelium tissue engineering

Corneal endothelium defects are one of the leading causes of blindness worldwide. The actual treatment is transplantation, which requires the use of human cadaveric donors, but it faces several problems, such as global shortage of donors. Therefore, new alternatives are being developed and, among them, cell therapy has gained interest in the last years due to its promising results in tissue regeneration. Nevertheless, the direct administration of cells may sometimes have limited success due to the immune response, hence requiring the combination with extracellular mimicking materials. In this review, we present different methods to obtain corneal endothelial cells from diverse cell sources such as pluripotent or multipotent stem cells. Moreover, we discuss different substrates in order to allow a correct implantation as a cell sheet and to promote an enhanced cell behavior. For this reason, natural or synthetic matrixes that mimic the native environment have been developed. These matrixes have been optimized in terms of their physicochemical properties, such as stiffness, topography, composition and transparency. To further enhance the matrixes properties, these can be tuned by incorporating certain molecules that can be delivered in a sustained manner in order to enhance biological behavior. Finally, we elucidate future directions for corneal endothelial regeneration, such as 3D printing, in order to obtain patient-specific substrates.

In vivo engraftment into the cornea endothelium using extracellular matrix shrink-wrapped cells

Cell injection is a common clinical approach for therapeutic delivery into diseased and damaged tissues in order to achieve regeneration. However, cell retention, viability, and engraftment at the injection site have generally been poor, driving the need for improved approaches. Here, we developed a technique to shrink-wrap micropatterned islands of corneal endothelial cells in a basement membrane-like layer of extracellular matrix that enables the cells to maintain their cell-cell junctions and cytoskeletal structure while in suspension. These μMonolayers exhibited the ability to rapidly engraft into intact, high-density corneal endothelial monolayers in both in vitro and in vivo model systems. Importantly, the engrafted μMonolayers increased local cell density, something that the clinical-standard single cells in suspension failed to do. These results show that shrink-wrapping cells in extracellular matrix dramatically improves engraftment and provides a potential alternative to cornea transplant when low endothelial cell density is the cause of corneal blindness.

Low Colorectal Tumor Removal by E-Cadherin Destruction-Enabled Tumor Cell Dissociation

Treatments for low colorectal cancer (CRC) remain a great challenge due to the heavy physical and psychological burdens of colostomy, strong drug toxicity in chemotherapy, and myelosuppression-/chemoradiation-related gastrointestinal symptoms. In this study, a highly biosafe and effective tumor cell dissociation-based low CRC treatment modality has been verified on both PDOs in vitro and colorectal tumor models in vivo. Notably, controllable EDTA release at the tumor sites was achieved by the LDH degradation in response to a slightly acidic microenvironment of low CRC tumors. Resultantly, the intratumoral E-cadherin for intercellular junctions of low CRC tumors was effectively destroyed via Ca²⁺ depletion by released EDTA from the interlayers, initiating remarkable tumor cell dissociation and resultant tumor disaggregation/removal via defecation. Dissociated tumor cells were prevailingly enveloped by LDH/EDTA, which prevented them from readhering to adjacent tissues, providing an unprecedented, efficient and safe therapeutic modality for low CRC, which will benefit patients suffering low CRC.

Heterogeneity of human corneal endothelium implicates lncRNA NEAT1 in Fuchs endothelial corneal dystrophy

The corneal endothelium is critical for maintaining corneal clarity by mediating hydration through barrier and pump functions. Progressive loss of corneal endothelial cells during aging has been associated with the development of Fuchs endothelial corneal dystrophy (FECD), one of the main causes of cornea-related vision loss. The mechanisms underlying FECD development remain elusive. Single-cell RNA sequencing of isolated healthy human corneas discovered 4 subpopulations of corneal endothelial cells with distinctive signatures. Unsupervised clustering analysis uncovered nuclear enriched abundant transcript 1 (NEAT1), a long non-coding RNA (lncRNA), as the top expressed gene in the C0-endothelial subpopulation, but markedly downregulated in FECD. Consistent with human corneas, a UVA-induced mouse FECD model validated the loss of NEAT1 expression. Loss of NEAT1 function by an in vivo genetic approach reproduced the exacerbated phenotype of FECD by ablating corneal endothelial cells. Conversely, gain of function by a CRISPR-activated adenoviral delivery system protected corneas from UVA-induced FECD. Our findings provide novel mechanistic insights into the development of FECD, and targeting NEAT1 offers an attractive approach for treating FECD.

Use of biomaterials in corneal endothelial repair

Human corneal endothelium (HCE) is a single layer of hexagonal cells that lines the posterior surface of the cornea. It forms the barrier that separates the aqueous humor from the rest of the corneal layers (stroma and epithelium layer). This layer plays a fundamental role in maintaining the hydration and transparency of the cornea, which in turn ensures a clear vision. In vivo, human corneal endothelial cells (HCECs) are generally believed to be nonproliferating. In many cases, due to their nonproliferative nature, any damage to these cells can lead to further issues with Descemet’s membrane (DM), stroma and epithelium which may ultimately lead to hazy vision and blindness. Endothelial keratoplasties such as Descemet’s stripping automated endothelial keratoplasty (DSAEK) and Descemet’s membrane endothelial keratoplasty (DEK) are the standard surgeries routinely used to restore vision following endothelial failure. Basically, these two similar surgical techniques involve the replacement of the diseased endothelial layer in the center of the cornea by a healthy layer taken from a donor cornea. Globally, eye banks are facing an increased demand to provide corneas that have suitable features for transplantation. Consequently, it can be stated that there is a significant shortage of corneal grafting tissue; for every 70 corneas required, only 1 is available. Nowadays, eye banks face long waiting lists due to shortage of donors, seriously aggravated when compared with previous years, due to the global COVID-19 pandemic. Thus, there is an urgent need to find alternative and more sustainable sources for treating endothelial diseases, such as utilizing bioengineering to use of biomaterials as a remedy. The current review focuses on the use of biomaterials to repair the corneal endothelium. A range of biomaterials have been considered based on their promising results and outstanding features, including previous studies and their key findings in the context of each biomaterial.

New developments in corneal endothelial cell replacement

Corneal transplantation is currently the most effective treatment to restore corneal clarity in patients with endothelial disorders. Endothelial transplantation, either by Descemet membrane endothelial keratoplasty (DMEK) or by Descemet stripping (automated) endothelial keratoplasty (DS(A)EK), is a surgical approach that replaces diseased Descemet membrane and endothelium with tissue from a healthy donor eye. Its application, however, is limited by the availability of healthy donor tissue. To increase the pool of endothelial grafts, research has focused on developing new treatment options as alternatives to conventional corneal transplantation. These treatment options can be considered as either 'surgery-based', that is tissue-efficient modifications of the current techniques (e.g. Descemet stripping only (DSO)/Descemetorhexis without endothelial keratoplasty (DWEK) and Quarter-DMEK), or 'cell-based' approaches, which rely on in vitro expansion of human corneal endothelial cells (hCEC) (i.e. cultured corneal endothelial cell sheet transplantation and cell injection). In this review, we will focus on the most recent developments in the field of the 'cell-based' approaches. Starting with the description of aspects involved in the isolation of hCEC from donor tissue, we then describe the different natural and bioengineered carriers currently used in endothelial cell sheet transplantation, and finally, we discuss the current 'state of the art' in novel therapeutic approaches such as endothelial cell injection.

Ex vivo expansion and characterization of human corneal endothelium for transplantation: a review

The corneal endothelium plays a key role in maintaining corneal transparency. Its dysfunction is currently treated with penetrating or lamellar keratoplasty. Advanced cell therapy methods seek to address the persistent global deficiency of donor corneas by enabling the renewal of the endothelial monolayer with tissue-engineered grafts. This review provides an overview of recently published literature on the preparation of endothelial grafts for transplantation derived from cadaveric corneas that have developed over the last decade (2010–2021). Factors such as the most suitable donor parameters, culture substrates and media, endothelial graft storage conditions, and transplantation methods are discussed. Despite efforts to utilize alternative cellular sources, such as induced pluripotent cells, cadaveric corneas appear to be the best source of cells for graft preparation to date. However, native endothelial cells have a limited natural proliferative capacity, and they often undergo rapid phenotype changes in ex vivo culture. This is the main reason why no culture protocol for a clinical-grade endothelial graft prepared from cadaveric corneas has been standardized so far. Currently, the most established ex vivo culture protocol involves the peel-and-digest method of cell isolation and cell culture by the dual media method, including the repeated alternation of high and low mitogenic conditions. Culture media are enriched by additional substances, such as signaling pathway (Rho-associated protein kinase, TGF-β, etc.) inhibitors, to stimulate proliferation and inhibit unwanted morphological changes, particularly the endothelial-to-mesenchymal transition. To date, this promising approach has led to the development of endothelial grafts for the first in-human clinical trial in Japan. In addition to the lack of a standard culture protocol, endothelial-specific markers are still missing to confirm the endothelial phenotype in a graft ready for clinical use. Because the corneal endothelium appears to comprise phenotypically heterogeneous populations of cells, the genomic and proteomic expression of recently proposed endothelial-specific markers, such as Cadherin-2, CD166, or SLC4A11, must be confirmed by additional studies. The preparation of endothelial grafts is still challenging today, but advances in tissue engineering and surgery over the past decade hold promise for the successful treatment of endothelial dysfunctions in more patients worldwide.

Methods for Investigating Corneal Cell Interactions and Extracellular Vesicles In Vitro

Science and medicine have become increasingly "human-centric" over the years. A growing shift away from the use of animals in basic research has led to the development of sophisticated in vitro models of various tissues utilizing human-derived cells to study physiology and disease. The human cornea has likewise been modeled in vitro using primary cells derived from corneas obtained from cadavers or post-transplantation. By utilizing a cell's intrinsic ability to maintain its tissue phenotype in a pre-designed microenvironment containing the required growth factors, physiological temperature, and humidity, tissue-engineered corneas can be grown and maintained in culture for relatively long periods of time on the scale of weeks to months. Due to its transparency and avascularity, the cornea is an optimal tissue for studies of extracellular matrix and cell-cell interactions, toxicology and permeability of drugs, and underlying mechanisms of scarring and tissue regeneration. This paper describes methods for the cultivation of corneal keratocytes, fibroblasts, epithelial, and endothelial cells for in vitro applications. We also provide detailed, step-by-step protocols for assembling and culturing 3D constructs of the corneal stroma, epithelial- and endothelial-stromal co-cultures and isolation of extracellular vesicles. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Isolating and culturing human corneal keratocytes and fibroblasts Basic Protocol 2: Isolating and culturing human corneal epithelial cells Basic Protocol 3: Isolating and culturing human corneal endothelial cells Basic Protocol 4: 3D corneal stromal construct assembly Basic Protocol 5: 3D corneal epithelial-stromal construct assembly Basic Protocol 6: 3D corneal endothelial-stromal construct assembly Basic Protocol 7: Isolating extracellular vesicles from corneal cell conditioned medium Support Protocol: Cryopreserving human corneal fibroblasts, corneal epithelial cells, and corneal endothelial cells.

Approaches for corneal endothelium regenerative medicine

The state of the art therapy for treating corneal endothelial disease is transplantation. Advances in the reproducibility and accessibility of surgical techniques are increasing the number of corneal transplants, thereby causing a global deficit of donor corneas and leaving 12.7 million patients with addressable visual impairment. Approaches to regenerate the corneal endothelium offer a solution to the current tissue scarcity and a treatment to those in need. Methods for generating corneal endothelial cells into numbers that could address the current tissue shortage and the possible strategies used to deliver them have now become a therapeutic reality with clinical trials taking place in Japan, Singapore and Mexico. Nevertheless, there is still a long way before such therapies are approved by regulatory bodies and become clinical practice. Moreover, acellular corneal endothelial graft equivalents and certain drugs could provide a treatment option for specific disease conditions without the need of donor tissue or cells. Finally, with the emergence of gene modulation therapies to treat corneal endothelial disease, it would be possible to treat presymptomatic patients or those presenting early symptoms, drastically reducing the need for donor tissue. It is necessary to understand the most recent developments in this rapidly evolving field to know which conditions could be treated with which approach. This article provides an overview of the current and developing regenerative medicine therapies to treat corneal endothelial disease and provides the necessary guidance and understanding towards the treatment of corneal endothelial disease.

Effects of human platelet lysate on the growth of cultured human corneal endothelial cells

Human platelet lysate (hPL) as a replacement for foetal bovine serum (FBS) in culturing human corneal endothelium is an emerging area of interest, although there are limited studies evaluating the quality of the hPL being used. Our study aimed to evaluate variations between sources of hPL and to explore the efficacy of hPL (with and without heparin) as a replacement for FBS in culturing human corneal endothelial cells in vitro. Immortalized human corneal endothelial cells (B4G12) and primary human corneal endothelial cells (PHCEnCs, n = 11 donors, age from 36 to 85 years old) were cultured with 5% hPL or FBS. A full characterisation of the effects of hPL and FBS on cell growth was conducted using IncuCyte Zoom (percentage cell confluence and population doubling time, PDT) to analyse cell proliferation. AlamarBlue assays were used to measure cell viability. The concentration of fibrinogen, PDGF, hEGF, VEGF and bFGF in two sources of hPL were analyzed by Enzyme-linked immunosorbent assay. Expression and localization of Na+/K+-ATPase, ZO-1 and CD166 on PHCEnCs and B4G12 cells were assessed with immunofluorescence and immunoblotting. Our results showed that a significant difference in fibrinogen, hEGF and VEGF concentrations was found between two sources of hPL. Heparin impaired the positive effect of hPL on cell growth. PDT and alamarBlue showed that hPL significantly increased proliferation and viability of PHCEnCs in two of three donors, and immunostaining indicated that hPL increased ZO-1 and CD166 expression but not Na+/K+-ATPase on PHCEnCs. In addition, heterogeneities on immunopositivity of Na+/K+-ATPase and ZO-1 and morphology were found on PHCEnCs derived from an individual donor cultured with hPL medium. In conclusion, hPL showed positive effect on primary corneal endothelial cell growth, and maintenance of their cellular characteristics compared to FBS. hPL can be considered as a supplement to replace FBS in PHCEnC culture. However, the variation observed between different hPL sources suggests that a standard quality control monitoring system such as storage time and a minimal concentration of growth factors may need to be established.

Translational and Regulatory Challenges of Corneal Endothelial Cell Therapy: A Global Perspective

Cell therapies are emerging as a unique class of clinical therapeutics in medicine. In 2015, Holoclar (ex vivo expanded autologous human corneal epithelial cells containing stem cells) gained the regulatory approval for treating limbal stem cell deficiency after chemical eye burn. This has set a precedent in ophthalmology and in medicine, reinforcing the therapeutic promise of cell therapy. However, to generalize and commercialize cell therapies on a global scale, stringent translational and regulatory requirements need to be fulfilled at both local and international levels. Over the past decade, the Singapore group has taken significant steps in developing human corneal endothelial cell (HCEnC) therapy for treating corneal endothelial diseases, which are currently the leading indication for corneal transplantation in many countries. Successful development of HCEnC therapy may serve as a novel solution to the current global shortage of donor corneas. Based on the experience in Singapore, this review aims to provide a global perspective on the translational and regulatory challenges for bench-to-bedside translation of cell therapy. Specifically, we discussed about the characterization of the critical quality attributes (CQA), the challenges that can affect the CQA, and the variations in the regulatory framework embedded within different regions, including Singapore, Europe, and the United States. Impact statement Functional corneal endothelium is critical to normal vision. Corneal endothelial disease-secondary to trauma, surgery, or pathology-represents an important cause of visual impairment and blindness in both developed and developing countries. Currently, corneal transplantation serves as the current gold standard for treating visually significant corneal endothelial diseases, although limited by the shortage of donor corneas. Over the past decade, human corneal endothelial cell therapy has emerged as a promising treatment option for treating corneal endothelial diseases. To allow widespread application of this therapy, significant regulatory challenges will need to be systematically overcome.

A Method for Developing Novel 3D Cornea-on-a-Chip Using Primary Murine Corneal Epithelial and Endothelial Cells

Microfluidic-based organ-on-a-chip assays with simultaneous coculture of multi-cell types have been widely utilized for basic research and drug development. Here we describe a novel method for a primary cell-based corneal microphysiological system which aims to recapitulate the basic functions of the in vivo cornea and to study topically applied ocular drug permeation. In this study, the protocols for isolating and cultivating primary corneal epithelial cells and endothelial cells from mouse inbred strain C57BL/6J were optimized, to allow for the development of a primary-cell based microfluidic 3D micro-engineered cornea. This tissue unit, by overcoming the limitations of 2D conventional cell culture, supports new investigations on cornea function and facilitates drug delivery testing.

Lysophosphatidic acid improves corneal endothelial density in tissue culture by stimulating stromal secretion of interleukin-1β

The short supply of donor corneas is exacerbated by the unsuitability of donors with insufficient endothelial cell density. Few studies have investigated promoting corneal endothelial cell proliferation to increase the endothelial cell density. We hypothesize that pre‐transplantation treatment of proliferative tissue‐cultivated corneas may increase corneal endothelial cell density. We observed that the airlift cultures were superior to immersion cultures with respect to both transparency and thickness. In this tissue culture system, we observed that lysophosphatidic acid increased the rabbit corneal endothelial cell density, number of BrdU‐positive cells and improve wound healing. We also observed an indirect effect of lysophosphatidic acid on corneal endothelial cell proliferation mediated by the stimulation of interleukin‐1β secretion from stromal cells. Human corneal tissues treated with lysophosphatidic acid or interleukin‐1β contained significantly more Ki‐67‐positive cells than untreated group. The lysophosphatidic acid‐ or interleukin‐1β‐treated cultured tissue remained hexagon‐shaped, with ZO‐1 expression and no evidence of the endothelial‐mesenchymal transition. Our novel protocol of tissue culture may be applicable for eye banks to optimize corneal grafting.

In Vitro Expansion of Corneal Endothelial Cells for Transplantation

The corneal endothelium forms a leaky barrier between the corneal stroma and the aqueous humor of the anterior chamber. This cell monolayer maintains the corneal stroma in a state of relative dehydration, a process called deturgescence, which is required in order to obtain corneal stromal transparency. Endothelial dysfunctions lead to visual impairment that ultimately can only be treated surgically via the corneal transplantation of a functional endothelium. Shortages of corneas suitable for transplantation has motivated research toward new alternatives involving in vitro corneal endothelial cell (CEC) expansion.This chapter describes current methods that allow isolate and culture CECs. In brief, Descemet membrane is peeled out of the cornea and digested in order to obtain CECs. Cells are then seeded and cultured.

Extracellular Matrix Protein Coating of Processed Fish Scales Improves Human Corneal Endothelial Cell Adhesion and Proliferation

Purpose

Corneal transplantation can treat corneal endothelial diseases. Implanting cultivated human corneal endothelial cells (HCECs) via a cell carrier has clinical value as an alternative therapeutic strategy. This study was performed to compare the feasibility of fish scales and other biomaterials (gelatin and chitosan) as cell carriers and to investigate the effects of an extracellular matrix (ECM) protein coating to improve the cytocompatibility of fish scales.

Methods

The physical properties of gelatin, chitosan, and fish scales were compared. Immortalized HCECs (B4G12) were cultured on processed fish scales, which were coated with fibronectin, laminin, collagen IV, or FNC Coating Mix. Cell attachment and proliferation were evaluated by immunofluorescence, cell counting, and bromodeoxyuridine (BrdU) labeling assays. Immunoblots were used to examine the expression levels of integrin-linked kinase (ILK), phosphate-ILK, β-catenin, p63, and cell cycle mediators (cyclin D1 and p27^Kip1).

Results

The transparency of processed fish scales was better than that of chitosan, while the strength was higher than that of gelatin. The laminin, collagen IV, and FNC coatings facilitated B4G12 cell adhesion and proliferation, while fibronectin only facilitated cell adhesion. The laminin, collagen IV, and FNC coatings also upregulated phosphate-ILK and p63 expression. In addition, the FNC coating activated cell cycle mediators.

Conclusion

ECM protein-coated processed fish scales can serve as a novel cell carrier to facilitate the development of HCEC transplantation.

Translational Relevance

Improving the physical properties and cytocompatibility of fish scales as a cell carrier will facilitate the transplantation of HCECs into corneas for the purpose of cell therapy.

Investigating the effect of chitosan/ polycaprolactone blends in differentiation of corneal endothelial cells and extracellular matrix compositions

This study aimed to investigate the underlying mechanisms of corneal endothelial cells (CECs) differentiation and identify the extracellular matrix (ECM) compositions using chitosan/polycaprolactone (PCL) blended membrane, hence exploring the potential use of chitosan/PCL blends in tissue engineering of CECs. We utilized the chitosan/PCL blends named as PCL25 consisting of PCL at 25% by weight. The surface characteristics of PCL25 were confirmed by using Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscope (AFM). Bovine CECs were cultured on the blends, compared with TCPS and pure chitosan membrane. Cell behaviors in terms of cell attachment, proliferation, differentiation phenotype and expression of differentiation proteins were examined. Furthermore, ECM protein productions were also analyzed. From the experiments, we found the topography (roughness) of PCL25 membrane examined by AFM was greater than pure chitosan membrane. FTIR results confirmed the functional groups of C=O bond of PCL. The CECs displayed hexagonal morphology and similar proliferation rate on both PCL25 membrane and TCPS. In addition, the immunofluorescence evidence showed well-localized ZO-1 and Na⁺/K⁺ ATPase expression of membrane proteins. ECM protein productions of CECs on PCL were no inferior to TCPS. Moreover, western blot results verified the higher amount of collagen type IV, and reduced TGF-β2 expression on PCL25 membrane compared to TCPS substrate. In conclusions, chitosan/PCL blends membrane provided a favorable environment for CECs in terms of ECM compositions, therefore enhancing the growth and differentiation. Accordingly, for CEC tissue engineering applications, PCL 25 might be a suitable alternative for cadaveric cornea transplantation in the near future.

Advances in culture, expansion and mechanistic studies of corneal endothelial cells: a systematic review

Human corneal endothelial cells are notorious for their restricted proliferative ability in vivo and in vitro. Hence, injury or dysfunction of these cells may easily result in blindness. Currently, the only treatment is to transplant a donor cornea that contains a healthy corneal endothelium. However there is a severe global shortage of donor corneas and there remains an unmet clinical need to engineer human corneal grafts with healthy corneal endothelium. In this review, we present current advances in the culture, expansion, and molecular understandings of corneal endothelial cells in vitro in order to help establish methods of engineering human corneal endothelial grafts.

Engineering of Human Corneal Endothelial Cells In Vitro

Human corneal endothelial cells are responsible for controlling corneal transparency, however they are notorious for their limited proliferative capability. Thus, damage to these cells may cause irreversible blindness. Currently, the only way to cure blindness caused by corneal endothelial dysfunction is via corneal transplantation of a cadaver donor cornea with healthy corneal endothelium. Due to severe shortage of donor corneas worldwide, it has become paramount to develop human corneal endothelial grafts in vitro that can subsequently be transplanted in humans. Recently, we have reported effective expansion of human corneal endothelial cells by reprogramming the cells into progenitor status through use of p120-Kaiso siRNA knockdown. This new reprogramming approach circumvents the need of using induced pluripotent stem cells or embryonic stem cells. Successful promotion of this technology will encourage scientists to re-think how "contact inhibition" can safely be perturbed to our benefit, i.e., effective engineering of an in vivo-like tissue while successful maintaining the normal phenotype. In this review, we present current advances in reprogramming corneal endothelial cells in vitro, detail the methods to successful engineer human corneal endothelial grafts, and discuss their future clinical applications to cure corneal blindness.

Isolation and Expansion of Multipotent Progenitors from Human Trabecular Meshwork

To expand multi-potent progenitors from human trabecular meshwork (TM), we have created a new optimized method on two-dimensional (2D) followed by three-dimensional (3D) Matrigel in modified embryonic stem cell medium supplemented with 5% fetal bovine serum (MESCM + 5% FBS). The expanded TM cells were small cuboidal cells expressing TM markers such as AQP1, MGP, CHI3L1, and AnkG, embryonic stem cell (ESC) markers such as Oct4, Sox2, Nanog, and ABCG2, and neural crest (NC) markers such as p75NTR, FOXD3, Sox9, Sox10, and MSX1. Although expanded cells lost expression of these markers after passage, the cells regained the markers when Passage 2 cells were seeded on 3D Matrigel through activation of canonical BMP signaling. Such restored progenitors could differentiate into corneal endothelial cells, adipocytes, and chondrocytes but not keratocytes or osteocytes. Therefore, we have concluded that human TM harbors multipotent progenitors that can be effectively isolated and expanded using 2D Matrigel in MESCM + 5% FBS. This unique in vitro model system can be used to understand how TM is altered in glaucoma and whether such TM progenitor cells might one day be used for treating glaucoma or corneal endothelial dysfunction.

The role of hepatocyte growth factor in corneal wound healing

Hepatocyte growth factor (HGF) is a glycoprotein produced by mesenchymal cells and operates as a key molecule for tissue generation and renewal. During corneal injury, HGF is primarily secreted by stromal fibroblasts and promotes epithelial wound healing in a paracrine manner. While this mesenchymal-epithelial interaction is well characterized in various organs and the cornea, the role of HGF in corneal stromal and endothelial wound healing is understudied. In addition, HGF has been shown to play an anti-fibrotic role by inhibiting myofibroblast generation and subsequent production of a disorganized extracellular matrix and tissue fibrosis. Therefore, HGF represents a potential therapeutic tool in numerous organs in which myofibroblasts are responsible for tissue scarring. Corneal fibrosis can be a devastating sequela of injury and can result in corneal opacification and retrocorneal membrane formation leading to severe vision loss. In this article, we concisely review the available literature regarding the role of HGF in corneal wound healing. We highlight the influence of HGF on cellular behaviors in each corneal layer. Additionally, we suggest the possibility that HGF may represent a therapeutic tool for interrupting dysregulated corneal repair processes to improve patient outcomes.

Comparison of three human platelet lysates used as supplements for in vitro expansion of corneal endothelium cells

BACKGROUND

Human platelet lysates (HPLs) are emerging as the new gold standard supplement of growth media for ex vivo expansion of cells for transplant. However, variations do exist in the way how HPLs are prepared. In particular, uncertainties still exist regarding the type of HPL most suitable for corneal endothelium cells (CEC) expansion, especially as these cells have limited proliferative capacity.

MATERIAL AND METHODS

Three distinct HPL preparations were produced, with or without calcium chloride/glass beads activation, and with or without heat treatment at 56°C for 30min. These HPLs were used to supplement basal D-MEM growth medium, each at a protein concentration equivalent to that of 10% fetal bovine serum (FBS; control). Impact on CEC (BCE C/D-1b cells) in vitro morphology, viability and capacity to express Zonula occludens-1 (ZO-1) tight junction marker was assessed by Western blotting.

RESULTS

BCE C/D-1b cells grown in all HPL supplements exhibited four of essential characteristic properties: adhesion capacity, microscopic morphology and viability similar to that observed when using 10% FBS. In addition, Western blots analysis revealed an expression of the ZO-1 marker by BCE C/D-1b cells in all conditions of culture.

CONCLUSION

CECs can expand ex vivo in a basal medium supplemented with the three HPLs without noticeable difference compared to FBS supplement. These data support further studies to evaluate the potential to use HPLs as a clinical-grade xeno-free supplement of CEC for corneal transplant.

Human Corneal Endothelial Cells Expanded In Vitro Are a Powerful Resource for Tissue Engineering

Human corneal endothelial cells have two major functions: barrier function mediated by proteins such as ZO-1 and pump function mediated by Na-K-ATPase which help to maintain visual function. However, human corneal endothelial cells are notorious for their limited proliferative capability in vivo and are therefore prone to corneal endothelial dysfunction that eventually may lead to blindness. At present, the only method to cure corneal endothelial dysfunction is by transplantation of a cadaver donor cornea with normal corneal endothelial cells. Due to the global shortage of donor corneas, it is vital to engineer corneal tissue in vitro that could potentially be transplanted clinically. In this review, we summarize the advances in understanding the behavior of human corneal endothelial cells, their current engineering strategy in vitro and their potential applications.

Characterization and Prospective of Human Corneal Endothelial Progenitors

Corneal endothelial cells play a critical role in maintaining corneal transparency and dysfunction of these cells caused by aging, diseases (such as Fuch's dystrophy), injury or surgical trauma, which can lead to corneal edema and blindness. Due to their limited proliferative capacity in vivo, the only treatment method is via transplantation of a cadaver donor cornea. However, there is a severe global shortage of donor corneas. To circumvent such issues, tissue engineering of corneal tissue is a viable option thanks to the recent discoveries in this field. In this review, we summarize the recent advances in reprogramming adult human corneal endothelial cells into their progenitor status, the expansion methods and characteristics of human corneal endothelial progenitors, and their potential clinical applications as corneal endothelial cell grafts.

Preservation of epithelial progenitor cells from collagenase-digested oral mucosa during ex vivo cultivation

To avoid xenogeneic infection, we report a novel protocol for producing animal-derived component-free oral mucosal epithelial cells (OMECs) sheet for transplantation, in which collagenase was used to replace dispase II/trypsin-EDTA for digesting oral mucosal tissue, and human platelet-derived PLTMax to replace fetal bovine serum. The resulting epithelial aggregates were expanded on de-epithelialized amniotic membranes without 3T3 feeder cells, and serum-free EpiLife was used to reduce contamination by submucosal mesenchymal cells. The OMEC sheets thus generated showed similar positive keratin 3/76-positive and keratin 8-negative staining patterns compared with those generated by the original protocol. Colony formation efficiency assay, BrdU label retention assay, and p63 and p75^NTR immunostaining results indicated that higher proliferative potentials and more progenitor cells were preserved by the modified protocol. TaqMan array analysis revealed that the transcription of integrin-linked kinase (ILK) was up-regulated along with an increase in β-catenin signaling and its downstream cell cycle modulators, cyclin D1 and p27^KIP1. Furthermore, ILK silencing led to the inhibition of nuclear β-catenin accumulation, suppressed p63 expression, and reduced the expression of cyclin D1 and p27^KIP1; these observations suggest that ILK/β-catenin pathway may be involved in cell proliferation regulation during the ex vivo expansion of OMECs for transplantation purposes.

Senescence Mediated by p16INK4a Impedes Reprogramming of Human Corneal Endothelial Cells into Neural Crest Progenitors

Human corneal endothelial cells (HCECs) have limited proliferative capacity due to “contact-inhibition” at G1 phase. Such contact-inhibition can be delayed from Day 21 to Day 42 by switching EGF-containing SHEM to LIF/bFGF-containing MESCM through transient activation of LIF-JAK1-STAT3 signaling that delays eventual nuclear translocation of p16^INK4a. Using the latter system, we have reported a novel tissue engineering technique by implementing 5 weekly knockdowns with p120 catenin (p120) and Kaiso siRNAs since Day 7 to achieve effective expansion of HCEC monolayers to a transplantable size with a normal HCEC density, through reprogramming of HCECs into neural crest progenitors by activating p120-Kaiso-RhoA-ROCK-canonical BMP signaling. Herein, we noted that a single knockdown with p120-Kaiso siRNAs at Day 42 failed to achieve such reprogramming when contact inhibition transitioned to senescence with nuclear translocation of p16^INK4a. In contrast, 5 weekly knockdowns with p120-Kaiso siRNAs since Day 7 precluded senescence mediated by p16^INK4a by inducing nuclear translocation of Bmi1 because of sustained activation of JAK2-STAT3 signaling downstream of p120-Kaiso-RhoA-ROCK signaling. STAT3 or Bmi1 siRNA impeded nuclear exclusion of p16^INK4a and suppressed the reprogramming induced by p120-Kaiso siRNAs, suggesting that another important engineering strategy of HCEC lies in prevention of senescence mediated by nuclear translocation of p16^INK4a.

Generation and Feasibility Assessment of a New Vehicle for Cell-Based Therapy for Treating Corneal Endothelial Dysfunction

The corneal endothelium maintains corneal transparency by its pump and barrier functions; consequently, its decompensation due to any pathological reason causes severe vision loss due to corneal haziness. Corneal transplantation is the only therapeutic choice for treating corneal endothelial dysfunction, but associated problems, such as a shortages of donor corneas, the difficulty of the surgical procedure, and graft failure, still need to be resolved. Regenerative medicine is attractive to researchers as a means of providing innovative therapies for corneal endothelial dysfunction, as it now does for other diseases. We previously demonstrated the successful regeneration of corneal endothelium in animal models by injecting cultured corneal endothelial cells (CECs) in combination with a Rho kinase (ROCK) inhibitor. The purpose of the present study was to optimize the vehicle for clinical use in cell-based therapy. Our screening of cell culture media revealed that RELAR medium promoted CEC adhesion. We then modified RELAR medium by removing hormones, growth factors, and potentially toxic materials to generate a cell therapy vehicle (CTV) composed of amino acid, salts, glucose, and vitamins. Injection of CECs in CTV enabled efficient engraftment and regeneration of the corneal endothelium in the rabbit corneal endothelial dysfunction model, with restoration of a transparent cornea. The CECs retained >85% viability after a 24 hour preservation as a cell suspension in CTV at 4°C and maintained their potency to regenerate the corneal endothelium in vivo. The vehicle developed here is clinically applicable for cell-based therapy aimed at treating the corneal endothelium. Our strategy involves the generation of vehicle from a culture medium appropriate for a given cell type by removing materials that are not favorable for clinical use.

Influence of different types of pulp treatment during isolation in the obtention of human dental pulp stem cells

Background

Different methods have been used in order to isolate dental pulp stem cells. The aim of this study was to study the effect of different types of pulp treatment during isolation, under 3% O2 conditions, in the time needed and the efficacy for obtaining dental pulp stem cells.

Material and Methods

One hundred and twenty dental pulps were used to isolate dental pulp stem cells treating the pulp tissue during isolation using 9 different methods, using digestive, disgregation, or mechanical agents, or combining them. The cells were positive for CD133, Oct4, Nestin, Stro-1, CD34 markers, and negative for the hematopoietic cell marker CD-45, thus confirming the presence of mesenchymal stem cells. The efficacy of dental pulp stem cells obtention and the minimum time needed to obtain such cells comparing the 9 different methods was analyzed.

Results

Dental pulp stem cells were obtained from 97 of the 120 pulps used in the study, i.e. 80.8% of the cases. They were obtained with all the methods used except with mechanical fragmentation of the pulp, where no enzymatic digestion was performed. The minimum time needed to isolate dental pulp stem cells was 8 hours, digesting with 2mg/ml EDTA for 10 minutes, 4mg/ml of type I collagenase, 4mg/ml of type II dispase for 40 minutes, 13ng/ml of thermolysine for 40 minutes and sonicating the culture for one minute.

Conclusions

Dental pulp stem cells were obtained in 97 cases from a series of 120 pulps. The time for obtaining dental pulp stem cells was reduced maximally, without compromising the obtention of the cells, by combining digestive, disgregation, and mechanical agents.

Key words:Dental pulp stem cells, mesenchymal stem cells, isolation method.

LIF-JAK1-STAT3 signaling delays contact inhibition of human corneal endothelial cells

Human corneal endothelial cells (HCECs) responsible for corneal transparency have limited proliferative capacity in vivo because of "contact-inhibition." This feature has hampered the ability to engineer HCECs for transplantation. Previously we have reported an in vitro model of HCECs in which contact inhibition was re-established at Day 21, even though cell junction and cell matrix interaction were not perturbed during isolation. Herein, we observe that such HCEC monolayers continue to expand and retain a normal phenotype for 2 more weeks if cultured in a leukemia inhibitory factor (LIF)-containing serum-free medium. Such expansion is accompanied initially by upregulation of Cyclin E2 colocalized with nuclear translocation of phosphorylated retinoblastoma tumor suppressor (p-Rb) at Day 21 followed by a delay in contact inhibition through activation of LIF-Janus kinase1 (JAK1)-signal transducer and activator of transcription 3 (STAT3) signaling at Day 35. The LIF-JAK1-STAT3 signaling is coupled with upregulation of E2F2 colocalized with nuclear p-Rb and with concomitant downregulation of p16(INK4a), of which upregulation is linked to senescence. Hence, activation of LIF-JAK1-STAT3 signaling to delay contact inhibition can be used as another strategy to facilitate engineering of HCEC grafts to solve the unmet global shortage of corneal grafts.

Stemness characteristics of human corneal endothelial cells cultured in various media

PURPOSE

To investigate stemness characteristics of human corneal endothelial cells (HCECs) cultured in various media.

METHODS

Human corneal endothelial cells were isolated using a sphere-forming assay. Cells were allowed to attach to the bottom of culture plates and were cultured in different media designated as medium A (Opti-MEM I with 8% fetal bovine serum), medium B (DMEM/F12 with B27 supplement), medium E (DMEM/F12 with epidermal growth factor [EGF]), and medium BE (DMEM/F12 with B27 supplement and EGF), respectively. Cell morphology was evaluated with an phase-contrast inverted microscope. Immunofluorescence staining and western blotting of nestin, octamer-binding transcription factor (OCT3/4), glial fibrillary acidic protein (GFAP), zonula occludens-1 (ZO-1), collagen VIII alpha2, and Na-K ATPase was performed. Cell proliferation was assessed with a cell counting kit-8 assay.

RESULTS

A few cultured cells stained with nestin. The cells cultured in medium A expressed high levels of GFAP, OCT3/4, and nestin, and higher levels of ZO-1 were expressed in the cells cultured in medium A and medium B compared with cells cultured in the other media. The cells cultured in medium A assumed a fibroblast-like shape, whereas the cells cultured in medium B and medium BE appeared as mosaics. Cell proliferation was highest in medium A compared with those cultured in the other media.

CONCLUSIONS

Cultured HCECs expressed stem cell markers, including nestin, OCT3/4, and GFAP. The expression of stem cell markers differed according to the culture media and associated proliferation rate.

WNT10B enhances proliferation through β-catenin and RAC1 GTPase in human corneal endothelial cells

The cornea is the anterior, transparent tissue of the human eye that serves as its main refractive element. Corneal endothelial cells are arranged as a monolayer on the posterior surface of the cornea and function as a pump to counteract the leakiness of its basement membrane. Maintaining the cornea in a slightly dehydrated state is critical for the maintenance of corneal transparency. Adult human corneal endothelial cells are G1-arrested, even in response to injury, leading to an age-dependent decline in endothelial cell density. Corneal edema and subsequent vision loss ensues when endothelial cell density decreases below a critical threshold. Vision loss secondary to corneal endothelial dysfunction is a common indication for transplantation in developed nations. An impending increase in demand for and a current global shortage of donor corneas will necessitate the development of treatments for vision loss because of endothelial dysfunction that do not rely on donor corneas. Wnt ligands regulate many critical cellular functions, such as proliferation, making them attractive candidates for modulation in corneal endothelial dysfunction. We show that WNT10B causes nuclear transport and binding of RAC1 and β-catenin in human corneal endothelial cells, leading to the activation of Cyclin D1 expression and proliferation. Our findings indicate that WNT10B promotes proliferation in human corneal endothelial cells by simultaneously utilizing both β-catenin-dependent and -independent pathways and suggest that its modulation could be used to treat vision loss secondary to corneal endothelial dysfunction.

Substrates for Expansion of Corneal Endothelial Cells towards Bioengineering of Human Corneal Endothelium

Corneal endothelium is a single layer of specialized cells that lines the posterior surface of cornea and maintains corneal hydration and corneal transparency essential for vision. Currently, transplantation is the only therapeutic option for diseases affecting the corneal endothelium. Transplantation of corneal endothelium, called endothelial keratoplasty, is widely used for corneal endothelial diseases. However, corneal transplantation is limited by global donor shortage. Therefore, there is a need to overcome the deficiency of sufficient donor corneal tissue. New approaches are being explored to engineer corneal tissues such that sufficient amount of corneal endothelium becomes available to offset the present shortage of functional cornea. Although human corneal endothelial cells have limited proliferative capacity in vivo, several laboratories have been successful in in vitro expansion of human corneal endothelial cells. Here we provide a comprehensive analysis of different substrates employed for in vitro cultivation of human corneal endothelial cells. Advances and emerging challenges with ex vivo cultured corneal endothelial layer for the ultimate goal of therapeutic replacement of dysfunctional corneal endothelium in humans with functional corneal endothelium are also presented.

Engineering of Human Corneal Endothelial Grafts

Human corneal endothelial cells (HCEC) play a pivotal role in maintaining corneal transparency. Unlike in other species, HCEC are notorious for their limited proliferative capacity in vivo after diseases, injury, aging, and surgery. Persistent HCEC dysfunction leads to sight-threatening bullous keratopathy with either an insufficient cell density or retrocorneal membrane due to endothelial-mesenchymal transition (EMT). Presently, the only solution to restore vision in eyes inflicted with bullous keratopathy or retrocorneal membrane relies upon transplantation of a cadaver human donor cornea containing a healthy corneal endothelium. Due to a severe global shortage of donor corneas, in conjunction with an increasing trend toward endothelial keratoplasty, it is opportune to develop a tissue engineering strategy to produce HCEC grafts. Prior attempts of producing these grafts by unlocking the contact inhibition-mediated mitotic block using trypsin-EDTA and culturing of single HCEC in a bFGF-containing medium run the risk of losing the normal phenotype to EMT by activating canonical Wnt signaling and TGF-β signaling. Herein, we summarize our novel approach in engineering HCEC grafts based on selective activation of p120-Kaiso signaling that is coordinated with activation of Rho-ROCK-canonical BMP signaling to reprogram HCEC into neural crest progenitors. Successful commercialization of this engineering technology will not only fulfill the global unmet need but also encourage the scientific community to re-think how cell-cell junctions can be safely perturbed to uncover novel therapeutic potentials in other model systems.

Phenotypes of trypsin- and collagenase-prepared bovine corneal endothelial cells in the presence of a selective Rho kinase inhibitor, Y-27632

PURPOSE

To optimize isolation of viable bovine corneal endothelial cells (BCECs), we evaluated the effectiveness of various preparation protocols. This entailed comparing the effects of collagenase A and trypsin in the presence and absence of a Rho kinase inhibitor, Y-27632, on proliferation and tight junctional and cytoskeletal integrity during their expansion.

METHODS

5-bromo-2'-deoxyuridine (BrdU) incorporation evaluated cell proliferation. Western blot analysis evaluated F-actin, zonule occludin, and ZO-1 associated nucleic acid binding protein (ZONAB) and RhoA expression. Rho A pulldown assay evaluated Rho A activity.

RESULTS

In the trypsin (TrypLE)-prepared BCECs, BrdU incorporation decreased whereas nuclear ZONAB expression increased and became stable from day 3 to 7. In contrast, in the collagenase-A-prepared BCECs, we observed preserved ZO-1 integrity, invariant nuclear ZONAB expression, and dense cortical F-actin expression, and BrdU incorporation was invariant from days 1 to 7. Y-27632 did not increase BrdU incorporation and nuclear ZONAB expression in the TrypLE-prepared and the collagenase-A-prepared BCECs. Moreover, Y-27632 increased irregular cellular morphology and downregulated the expression of ZO-1 in the collagenase-A-prepared BCECs from days 1 to 7. Y-27632 inhibited RhoA activation irrespective of whether the cells were isolated with trypsin or collagenase A.

CONCLUSIONS

It is preferable to isolate BCECs with collagenase A and expand them without Y-27632. With this protocol, proliferative activity and tight junctional and cytoskeletal integrity are better preserved than if trypsin is used in the presence or absence of Y-27632.

Micro- and nano-topography to enhance proliferation and sustain functional markers of donor-derived primary human corneal endothelial cells

One of the most common indications for corneal transplantation is corneal endothelium dysfunction, which can lead to corneal blindness. Due to a worldwide donor cornea shortage, alternative treatments are needed, but the development of new treatment strategies relies on the successful in vitro culture of primary human corneal endothelial cells (HCECs) because transformed cell lines and animal-derived corneal endothelial cells are not desirable for therapeutic applications. Primary HCECs are non-proliferative in vivo and challenging to expand in vitro while maintaining their characteristic cell morphology and critical markers. Biochemical cues such as growth factors and small molecules have been investigated to enhance the expansion of HCECs with a limited increase in proliferation. In this study, patterned tissue culture polystyrene (TCPS) was shown to significantly enhance the expansion of HCECs. The proliferation of HCECs increased up to 2.9-fold, and the expression amount and localization of cell-cell tight junction protein Zona Occludens-1 (ZO-1) was significantly enhanced when grown on 1 μm TCPS pillars. 250 nm pillars induced an optimal hexagonal morphology of HCEC cells. Furthermore, we demonstrated that the topographical effect on tight-junction expression and cell morphology could be maintained throughout each passage, and was effectively 'remembered' by the cells. Higher amount of tight-junction protein expression was maintained at cell junctions when topographic cues were removed in the successive seeding. This topographic memory suggested topography-exposed/induced cells would maintain the enhanced functional markers, which would be useful in cell-therapy based approaches to enable the in situ endothelial cell monolayer formation upon delivery. The development of patterned TCPS culture platforms could significantly benefit those researching human corneal endothelial cell cultivation for cell therapy, and tissue engineering applications.

Lysophosphatidic acid induces YAP-promoted proliferation of human corneal endothelial cells via PI3K and ROCK pathways

The first two authors contributed equally to this work.Silence of p120-catenin has shown promise in inducing proliferation in human corneal endothelial cells (HCECs), but there is concern regarding off-target effects in potential clinical applications. We aimed to develop ex vivo expansion of HCECs using natural compounds, and we hypothesized that lysophosphatidic acid (LPA) can unlock the mitotic block in contact-inhibited HCECs via enhancing nuclear translocation of yes-associated protein (YAP). Firstly, we verified that exogenous YAP could induce cell proliferation in contact-inhibited HCEC monolayers and postconfluent B4G12 cells. In B4G12 cells, enhanced cyclin D1 expression, reduced p27^KIP1/p21^CIP1 levels, and the G₁/S transition were detected upon transfection with YAP. Secondly, we confirmed that LPA induced nuclear expression of YAP and promoted cell proliferation. Moreover, PI3K and ROCK, but not ERK or p38, were required for LPA-induced YAP nuclear translocation. Finally, cells treated with LPA or transfected with YAP remained hexagonal in shape, in addition to unchanged expression of ZO-1, Na/K-ATPase, and smooth muscle actin (SMA), suggestive of a preserved phenotype, without endothelial–mesenchymal transition. Collectively, our findings indicate an innovative strategy for ex vivo cultivation of HCECs for transplantation and cell therapy.

Rho-associated protein kinase inhibitor, Y-27632, significantly enhances cell adhesion and induces a delay in G1 to S phase transition in rabbit corneal endothelial cells

Human corneal endothelial cells are a non-proliferative cell type. As a result of the increase in corneal endothelium disease, increasing numbers of studies have been conducted in order to promote corneal endothelial cell proliferation. The aim of the present study was to investigate the proliferative effects of Rho-associated protein kinase inhibitor, Y-27632, on rabbit corneal endothelial cells (rCECs). Y-27632 (1, 10 or 30 μM) was added at two different time points to two groups of rCECs. The first group received Y-27632 when rCECs were initially plated, and the second following 72 h of cell growth. Cell morphology and cell adhesion ratios were subsequently observed using light microscopy. A cell counting kit was used to measure the number of viable cells that adhered to culture plates. Cell cycle transitions and levels of Annexin V-positive apoptotic cells were detected using flow cytometry. Cells treated with 1 μM Y-27632 and 10 μM Y-27632 retained their cell shape. At a concentration of 30 μM Y-27632, the cell shape became irregular. Cell adhesion ratios, in 1 μM Y-27632 (36.84%), 10 μM Y-27632 (84.21%) and 30 μM Y-27632 (84.21%) were higher than the adhesion ratio in the control group (P<0.01). The optical densities of rCECs treated with 10 μM or 30 μM Y-27632 following 72 h of cell growth was less than that of the control cells (P<0.01), but higher than that of cells which received Y-27632 at the time of plating (P<0.01). Flow cytometry results also demonstrated that there was a delay in G1 to S phase cell cycle progression in rCECs following administration of 10 μM Y-27632 (P<0.01). Cell apoptosis was inhibited when 10 μM Y-27632 was added, at the time of cell plating, as well as when added following 72 h of cell growth (P<0.01). At a concentration of 10 μM Y-27632, there was an improvement in cell adhesion and an inhibition of the cell cycle in rabbit corneal endothelial cells. In conclusion, Y-27632 has different effects on rCECs when administered at varying concentrations and at particular stages of cell growth.