Human corneal endothelial cell expansion for corneal endothelium transplantation: an overview. Transplantation. 2011;91:811-819. [PMID: 21358368 DOI: 10.1097/tp.0b013e3182111f01]

Revisiting Existing Evidence of Corneal Endothelial Progenitors and Their Potential Therapeutic Applications in Corneal Endothelial Dysfunction

PURPOSE

A recent successful clinical trial demonstrated that a less invasive cell-injection procedure is a viable medical modality for treating corneal endothelial dystrophy. This medical advance still relies on human corneal endothelial cell (HCEC) sources derived from rare cornea donations. The progenitor of the corneal endothelium, which has the characteristics of active proliferation and lineage restriction, will be an ideal cell source for expansion ex vivo. However, the distribution of progenitor-like cells in the corneal endothelial sheet has been under debate for more than a decade.

METHODS

This paper re-examines the scientific evidence of the existence of human corneal endothelial progenitors (HCEPs) from the aspects of (1) the origin of cornea formation during ocular development, (2) manifestations from clinical studies, and (3) the distinctive properties of ex vivo-cultured subpopulations.

RESULTS

The discrepancies regarding different types of progenitor-like cells in various locations of the cornea are based on the fact that the corneal endothelium is derived from different cell types with multiple origins during corneal formation.

CONCLUSIONS

Resolving this long-standing issue in corneal biology will enable various types of progenitors to be isolated and their potencies regarding the formation of functional endothelial cells to be examined. Additionally, an effective niche system for quantitatively producing therapeutic cells can be formulated to satisfy the burning need associated with corneal endothelial dystrophy in the future.

Optimisation of Storage and Transportation Conditions of Cultured Corneal Endothelial Cells for Cell Replacement Therapy

As the cornea is one of the most transplanted tissues in the body it has placed a burden on the provision of corneas from cadaveric donors. Corneal endothelial dysfunction is the leading indication for cornea transplant. Therefore, tissue engineering is emerging as an alternative approach to overcome the global shortage of transplant-grade corneas. The propagation and expansion of corneal endothelial cells has been widely reported. However, one obstacle to overcome is the transport and storage of corneal endothelial cells. In this study we investigated whether tissue engineered corneal endothelial cells can be preserved in hypothermic conditions. Human corneal endothelial cells (HCEnCs) were exposed to various temperatures (4 °C, 23 °C, and 37 °C) in both adherent and suspension storage models. Optimal storage media and storage duration was tested along with post-storage viability. Following storage and subsequent recovery at 37 °C, cell phenotype was assessed by immunofluorescence, gene and protein expression, and proliferative capacity analysis. Functionality was also assessed within a rabbit model of bullous keratopathy. Our data support our hypothesis that functional HCEnCs can be preserved in hypothermic conditions.

Peroxiredoxin-1 regulates lipid peroxidation in corneal endothelial cells

Corneal transparency is maintained by a monolayer of corneal endothelial cells. Defects in corneal endothelial cells (CEnCs) can be rectified surgically through transplantation. Fuchs’ endothelial corneal dystrophy (FECD) is the foremost cause of endothelial dysfunction and the leading indication for transplantation. Increased sensitivity of CEnCs to oxidative stress is thought to contribute to the pathogenesis of FECD through increased apoptosis. In part, this is thought to be due to loss of NRF2 expression: a global regulator of oxidative stress. We demonstrate that expression of the redox sensor, peroxiredoxin 1 (PRDX1) is selectively lost from CEnCs in FECD patient samples. We reveal that expression of PRDX1 is necessary to control the response of CEnCs to agents that cause lipid peroxidation. Iron-dependent lipid peroxidation drives non-apoptotic cell death termed ferroptosis. We establish that the inhibitor of ferroptosis, ferrostatin-1 rescues lipid peroxidation and cell death in CEnCs. Furthermore, we provide evidence that the transcription factor NRF2 similarly regulates lipid peroxidation in CEnCs.

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PRDX1 is a key regulator of lipid peroxidation.

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Expression of PRDX1 is lost in Fuchs' endothelial corneal dystrophy.

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Oxidative stress reduces PRDX1 expression in cultures of CEnCs.

Characterization of Human Transition Zone Reveals a Putative Progenitor-Enriched Niche of Corneal Endothelium

: The corneal endothelium regulates corneal hydration to maintain the transparency of cornea. Lacking regenerative capacity, corneal endothelial cell loss due to aging and diseases can lead to corneal edema and vision loss. There is limited information on the existence of corneal endothelial progenitors. We conducted ultrastructural examinations and expression analyses on the human transition zone (TZ) at the posterior limbus of corneal periphery, to elucidate if the TZ harbored progenitor-like cells, and to reveal their niche characteristics. Within the narrow TZ (~190 μm width), the inner TZ-adjacent to the peripheral endothelium (PE)-contained cells expressing stem/progenitor markers (Sox2, Lgr5, CD34, Pitx2, telomerase). They were located on the inner TZ surface and in its underlying stroma. Lgr5 positive cells projected as multicellular clusters into the PE. Under transmission electron microscopy and serial block face-scanning electron microscopy and three-dimensional (3D) reconstruction, the terminal margin of Descemet's membrane was inserted beneath the TZ surface, with the distance akin to the inner TZ breadth. Porcine TZ cells were isolated and proliferated into a confluent monolayer and differentiated to cells expressing corneal endothelial markers (ZO1, Na⁺K⁺ATPase) on cell surface. In conclusion, we have identified a novel inner TZ containing progenitor-like cells, which could serve the regenerative potential for corneal endothelium.

Ex vivo construction of rabbit corneal endothelial cell sheets on a porcine descemet membrane graft

The aim of the present study was to investigate the feasibility of a new graft construction method using rabbit corneal endothelial cells (RCECs) and a porcine descemet membrane (DM) carrier. RCECs were isolated and the experimental group was treated with Y-27632, whereas the control group were cultured in medium without Y-27632. RCEC morphology was observed using an inverted microscope, and cell proliferation and apoptosis were detected by flow cytometry. To confirm the presence of RCECs, reverse transcription-quantitative PCR was used to detect gene expression levels of Na+-K+-ATPase, aquaporin 1, collagen α₂ (IV), collagen α₁ (VIII) and keratin-12. Histocompatibility testing was used to detect porcine DM antigenicity. A DM-RCEC graft was constructed, and morphology was observed using alizarin red-trypan blue and haematoxylin and eosin staining. Cell membrane potential was measured to evaluate the physical function of the DM-RCEC graft. Complex graft tension was measured using a modified tension detector and compared with fresh porcine DM-endothelium complex. In vitro-cultured RCECs formed a monolayer with a polygon morphology and cobblestone-like arrangement. In vitro-cultured RCECs exhibited typical RCEC characteristics before and after transplantation. The proliferation rates of the experimental and control groups were 62.68 and 34.50%, respectively (P<0.05); the apoptosis rates of the experimental and control groups were 8.99 and 35.68%, respectively (P<0.05). There was no antigenicity observed with the porcine DM. The action potential amplitude of the experimental and control groups was over −80 mV, reflecting normal RCEC physiological function. The tension measurements of the experimental and control groups were 20.0248±1.048 and 20.5013±0.657 g, respectively (P>0.05). Taken together, the results of the present study demonstrated that Y-27632 enhanced RCEC proliferation. In addition, the findings revealed the successful ex vivo construction of a RCEC sheet on a porcine DM graft.

Feasibility of a cryopreservation of cultured human corneal endothelial cells

Transparency of the cornea is essential for vision and is maintained by the corneal endothelium. Consequently, corneal endothelial decompensation arising from irreversible damage to the corneal endothelium causes severe vision impairment. Until recently, transplantation of donor corneas was the only therapeutic choice for treatment of endothelial decompensation. In 2013, we initiated clinical research into cell-based therapy involving injection of a suspension of cultured human corneal endothelial cells (HCECs), in combination with Rho kinase inhibitor, into the anterior chamber. The aim of the present study was to establish a protocol for cryopreservation of HCECs to allow large-scale commercial manufacturing of these cells. This study focused on the effects of various cryopreservation reagents on HCEC viability. Screening of several commercially available cryopreservation reagents identified Bambanker hRM as an effective agent that maintained a cell viability of 89.4% after 14 days of cryopreservation, equivalent to the cell viability of 89.2% for non-cryopreserved control cells. The use of Bambanker hRM and HCECs at a similar grade to that used clinically for cell based therapy (passage 3–5 and a cell density higher than 2000 cells/mm²) gave a similar cell density for cryopreserved HCECs to that of non-preserved control HCECs after 28 days of cultivation (2099 cells/mm² and 2111 cells/mm², respectively). HCECs preserved using Bambanker hRM grew in a similar fashion to non-preserved control HCECs and formed a monolayer sheet-like structure. Cryopreservation of HCECs has multiple advantages including the ability to accumulate stocks of master cells, to transport HCEC stocks, and to manufacture HCECs on demand for use in cell-based treatment of endothelial decompensation.

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.

Functional Evaluation of Two Corneal Endothelial Cell-Based Therapies: Tissue-Engineered Construct and Cell Injection

Restoration of vision due to corneal blindness from corneal endothelial dysfunction can be achieved via a corneal transplantation. However, global shortage of donor tissues has driven the development cell-based therapeutics. With the capacity to propagate regulatory compliant human corneal endothelial cells (CEnCs), this study evaluated the functionality of propagated CEnCs delivered via tissue-engineered endothelial keratoplasty (TE-EK) or corneal endothelial cell injection (CE-CI) within a rabbit model of bullous keratopathy. For animals with TE-EK grafts, central corneal thickness (CCT) increased to >1000 μm post-operatively. Gradual thinning with improvements in corneal clarity was observed from week 1. CCT at week 3 was 484.3 ± 73.7 μm. In rabbits with CE-CI, corneal clarity was maintained throughout, and CCT at week 3 was 582.5 ± 171.5 μm. Control corneas remained significantly edematous throughout the study period compared to their respective experimental groups (p < 0.05). Characterization of excised corneas showed a monolayer with heterogeneously shaped CEnCs in both TE-EK and CE-CI groups. Immunohistochemistry demonstrated reactivity to anti-human specific nuclei antibody attributing corneal recovery to the functional human CEnCs. This study showed that regulatory compliant cell-based therapy for corneal endothelial dysfunction can be delivered by both TE-EK and CE-CI, and holds great promise as an alternative to traditional corneal transplantation.

Effect of a p38 Mitogen-Activated Protein Kinase Inhibitor on Corneal Endothelial Cell Proliferation

Purpose

We have performed clinical research on cell-based therapy for corneal endothelial decompensation since 2013. The purpose of this study was to investigate the usefulness of a p38 MAPK inhibitor for promoting proliferation of human corneal endothelial cells (HCECs).

Methods

HCECs were cultured in media supplemented with various low-molecular-weight compounds to screen for the effect of those compounds on cell proliferation. Activation of substrates of p38 MAPK and cell cycle regulatory proteins were evaluated by western blotting. Corneal endothelial wounds were created in a rabbit model, and p38 MAPK was applied in eye drop form, followed by evaluation of cell proliferation in the corneal endothelium by Ki67-immunostaining.

Results

HCECs cultured with SB203580 exhibited hexagonal morphology and similar size and morphology, whereas control HCECs cultured without inhibitor exhibited monolayer morphology and varied in size and morphology. Flow cytometry demonstrated that cell proliferation was significantly increased by SB203580. Western blotting showed activation of ATF2 and HSP27 (substrates of p38 MAPK), and upregulation of cyclin D and downregulation of p27 were induced by inhibiting p38 MAPK. In the rabbit model, promotion of wound healing of the corneal endothelium was associated with significant upregulation of Ki67-positive proliferating cells following topical administration of SB203580 when compared with untreated endothelium (50.9% and 36.1%, respectively).

Conclusions

Activation of p38 MAPK signaling due to culture stress might suppress the proliferation of HCECs, whereas a p38 MAPK inhibitor can counteract this activation and enable efficient in vitro HCEC expansion.

Electrospun gelatin/PCL and collagen/PCL scaffolds for modulating responses of bone marrow endothelial progenitor cells

The determination of potential transplantable substrates and substitution cells for corneal endothelium transplantation may compensate for the shortage of cornea donors. Appropriate biodegradable and biocompatible tissue-engineered substratum with seed cells for endothelial keratoplasty has been increasingly studied. In the present study, electrospun gelatin/polycaprolactone (PCL) and collagen/PCL scaffolds were successfully established. Bone marrow endothelial progenitor cells (BEPCs) were cultured on these scaffolds to determine whether the scaffolds may promote the proliferation of BEPCs as well as maintain stem cell characteristics. Two variations of hybrid scaffolds, collagen/PCL (70% collagen and 30% PCL) and gelatin/PCL (70% gelatin and 30% PCL), were established via electrospinning. Microscopic structure, hydrophilicity and wettability of the two scaffolds were subsequently investigated. BEPCs were separately cultured on the scaffolds and were also seeded on glass slides to establish the control group. Furthermore, cell morphology; adherence, as determined by investigation of F-actin expression levels; proliferation, as determined via Cell Counting Kit-8 assays, Ki-67 staining and bromodeoxyuridine (BrdU) staining; and stem cell markers, as determined by cluster of differentiation (CD)-34 and CD-133 protein expression levels; were investigated. In addition, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to determine gene expression. The two nanofiber scaffolds were established using electrospun techniques with expected hydrophilicity, wettability and biocompatibility. BEPCs were revealed to spread well on and strongly adhere to the collagen/PCL (70:30) and gelatin/PCL (70:30) scaffolds. Furthermore, Ki-67 and BrdU staining results revealed greater levels of positive dots on the two hybrid scaffolds compared with the control group. CD-34 and CD-133 protein staining demonstrated increased levels of fluorescence intensity on scaffolds compared with the control group. Furthermore, increased expression levels of differentiation markers, such as ATP binding cassette subfamily G member 2, leucine rich repeat containing G protein-coupled receptor 5 and CD166, were detected on both scaffolds. RT-qPCR results demonstrated that the expression of caspase-3, which is associated with apoptosis, was decreased on the two scaffolds compared with in the control group. The expression of inflammatory factors, including interleukin (IL)-1, exhibited a significant decrease on the gelatin/PCL scaffold compared with in the control group; whereas the difference between the expression level of IL-1 exhibited by the collagen/PCL group and the control group were not markedly different. Electrospun collagen/PCL and gelatin/PCL scaffolds exhibited the potential to enhance the adherence and proliferation of BEPCs. BEPCs cultured on the two scaffolds demonstrated increased stem cell characteristics and differentiation potential. Electrospun gelatin/PCL and collagen/PCL scaffolds may represent a promising substratum in tissue-engineered corneal endothelium.

PACAP through EGFR transactivation preserves human corneal endothelial integrity

The corneal endothelium is composed of a single hexagonal-shaped cells layer adherent to the Descemet's membrane. The primary function of these cells is maintaining of tissue clarity by regulating its hydration. Trauma, aging or other pathologies cause their loss, counterbalanced by enlargement of survived cells unable to guarantee an efficient fluid pumping to and from the stroma. Regenerative medicine using human corneal endothelial cells (HCECs) isolated from peripheral corneal-scleral tissue of a donor could be an attractive solution, overcoming transplantation problems. In a previous study, we have demonstrated that HCECs treatment with pituitary adenylate cyclase-activating polypeptide (PACAP) following growth factors deprivation prevents their degeneration. However, the molecular mechanism mediating this effect has not been clarified, yet. Here, we have shown for the first time the expression of PACAP and its receptor (PAC1R) in human corneal endothelium and demonstrated that this peptide, selectively binding to PAC1R, induces epidermal growth factor receptor (EGFR) phosphorylation and the MAPK/ERK1/2 signaling pathway activation. In conclusion, our data have suggested that PACAP could represent an important trophic factor in maintaining human corneal endothelial integrity through EGFR transactivation. Therefore, PACAP, as well as epidermal growth factor and fibroblast growth factor, could co-operate to guarantee tissue physiological functioning by supporting corneal endothelial barrier integrity.

Corneal endothelial cell dysfunction: etiologies and management

A transparent cornea is essential for the formation of a clear image on the retina. The human cornea is arranged into well-organized layers, and each layer plays a significant role in maintaining the transparency and viability of the tissue. The endothelium has both barrier and pump functions, which are important for the maintenance of corneal clarity. Many etiologies, including Fuchs’ endothelial corneal dystrophy, surgical trauma, and congenital hereditary endothelial dystrophy, lead to endothelial cell dysfunction. The main treatment for corneal decompensation is replacement of the abnormal corneal layers with normal donor tissue. Nowadays, the trend is to perform selective endothelial keratoplasty, including Descemet stripping automated endothelial keratoplasty and Descemet’s membrane endothelial keratoplasty, to manage corneal endothelial dysfunction. This selective approach has several advantages over penetrating keratoplasty, including rapid recovery of visual acuity, less likelihood of graft rejection, and better patient satisfaction. However, the global limitation in the supply of donor corneas is becoming an increasing challenge, necessitating alternatives to reduce this demand. Consequently, in vitro expansion of human corneal endothelial cells is evolving as a sustainable choice. This method is intended to prepare corneal endothelial cells in vitro that can be transferred to the eye. Herein, we describe the etiologies and manifestations of human corneal endothelial cell dysfunction. We also summarize the available options for as well as recent developments in the management of corneal endothelial dysfunction.

Regulation of Oxidative Stress in Corneal Endothelial Cells by Prdx6

The inner layer of the cornea, the corneal endothelium, is post-mitotic and unable to regenerate if damaged. The corneal endothelium is one of the most transplanted tissues in the body. Fuchs’ endothelial corneal dystrophy (FECD) is the leading indication for corneal endothelial transplantation. FECD is thought to be an age-dependent disorder, with a major component related to oxidative stress. Prdx6 is an antioxidant with particular affinity for repairing peroxidised cell membranes. To address the role of Prdx6 in corneal endothelial cells, we used a combination of biochemical and functional studies. Our data reveal that Prdx6 is expressed at unusually high levels at the plasma membrane of corneal endothelial cells. RNAi-mediated knockdown of Prdx6 revealed a role for Prdx6 in lipid peroxidation. Furthermore, following induction of oxidative stress with menadione, Prdx6-deficient cells had defective mitochondrial membrane potential and were more sensitive to cell death. These data reveal that Prdx6 is compartmentalised in corneal endothelial cells and has multiple functions to preserve cellular integrity.

Functional role of peroxiredoxin 6 in the eye

Peroxiredoxin 6 (Prdx6) is the only mammalian 1-Cys member of the Prdx family, a group of enzymes which share the ability to reduce peroxides. In addition to its peroxidase function, Prdx6 also demonstrates phospholipase A₂ and lysophosphatidylcholine acyl transferase (LPCAT) activities. These enzymatic activities play an important role in regenerating oxidized membrane phospholipids and maintaining an appropriate balance of intracellular reactive oxygen species. Development of clinical pathologies, including those within the eye, have been linked to dysregulation of Prdx6 function. Interplay between external stressors like exposure to UV light, transforming growth factor β (TGF-β), and hyperglycemia in conjunction with diminished Prdx6 levels and loss of redox balance is associated with cellular changes in a variety of ophthalmic pathologies including cataracts, glaucoma, and retinal degeneration. Many of these cellular abnormalities can be rescued through supplementation with exogenous Prdx6. Additionally, corneal endothelial cells have been found to express high levels of Prdx6 in the plasma membrane. These findings highlight the importance of Prdx6 as an essential regulator of oxidative stress in the eye.

A Cell Culture Approach to Optimized Human Corneal Endothelial Cell Function

Purpose

Cell-based therapies to replace corneal endothelium depend on culture methods to optimize human corneal endothelial cell (HCEC) function and minimize endothelial-mesenchymal transition (EnMT). Here we explore contribution of low-mitogenic media on stabilization of phenotypes in vitro that mimic those of HCECs in vivo.

Methods

HCECs were isolated from cadaveric donor corneas and expanded in vitro, comparing continuous presence of exogenous growth factors (“proliferative media”) to media without those factors (“stabilizing media”). Identity based on canonical morphology and expression of surface marker CD56, and function based on formation of tight junction barriers measured by trans-endothelial electrical resistance assays (TEER) were assessed.

Results

Primary HCECs cultured in proliferative media underwent EnMT after three to four passages, becoming increasingly fibroblastic. Stabilizing the cells before each passage by switching them to a media low in mitogenic growth factors and serum preserved canonical morphology and yielded a higher number of cells. HCECs cultured in stabilizing media increased both expression of the identity marker CD56 and also tight junction monolayer integrity compared to cells cultured without stabilization.

Conclusions

HCECs isolated from donor corneas and expanded in vitro with a low-mitogenic media stabilizing step before each passage demonstrate more canonical structural and functional features and defer EnMT, increasing the number of passages and total canonical cell yield. This approach may facilitate development of HCEC-based cell therapies.

The current state of stem cell therapy for ocular disease

Herein, we review the safety, efficacy, regulatory standards and ethical implications of the use of stem cells in ocular disease. A literature review was conducted, registered clinical trials reviewed, and expert opinions sought. Guidelines and codes of conduct from international societies and professional bodies were also reviewed. Collated data is presented on current progress in the field of ocular regenerative medicine, future challenges, the clinical trial process and ethical considerations in stem cell therapy. A greater understanding of the function and location of ocular stem cells has led to rapid advances in possible therapeutic applications. However, in the context of significant technical challenges and potential long-term complications, it is imperative that stem cell practices operate within formal clinical trial frameworks. While there remains broad scope for innovation, ongoing evidence-based review of potential interventions and the development of standardized protocols are necessary to ensure patient safety and best practice in ophthalmic care.

Cultivation of corneal endothelial cells from sheep

Research is currently under way to produce tissue engineered corneal endothelium transplants for therapeutic use in humans. This work requires the use of model animals, both for the supply of corneal endothelial cells (CECs) for experimentation, and to serve as recipients for test transplants. A variety of species can be used, however, a number of important advantages can be gained by using sheep as transplant recipients. The purpose of the present study was therefore to develop a method for culturing sheep CECs that would be suitable for the eventual construction of corneal endothelium grafts destined for sheep subjects. A method was established for culturing sheep CECs and these were compared to cultured human CECs. Results showed that cultured sheep and human CECs had similar growth characteristics when expanded from corneal endothelium explants on gelatin-coated plates, and achieved similar cell densities after several weeks. Furthermore, the markers zonula occludens-1, N-cadherin and sodium potassium ATPase could be immunodetected in similar staining patterns at cell boundaries of cultured CECs from both species. This work represents the first detailed study of sheep CEC cultures, and is the first demonstration of their similarities to human CEC cultures. Our results indicate that sheep CECs would be an appropriate substitute for human CECs when developing methods to produce tissue engineered corneal endothelium transplants.

Characterizing human decellularized crystalline lens capsules as a scaffold for corneal endothelial tissue engineering

The idea of transplanting a sheet of laboratory-grown corneal endothelium dates back to 1978; however, the ideal scaffold is still lacking. We hypothesized that human crystalline lens capsules (LCs) could qualify as a scaffold and aimed to characterize the properties of this material for endothelial tissue engineering. LCs were isolated from donor eyes, stored at -80 °C, and decellularized with water and trypsin-EDTA. The decellularization was investigated by nuclear staining and counting and the capsule thickness was determined by optical coherence tomography and compared with Descemet's membrane (DM). Transparency was examined by spectrometry, and collagenase degradation was performed to evaluate its resistance to degradation. Cell-scaffold interaction was assessed by measuring focal adhesions surface area on LC and plastic. Finally, primary corneal endothelial cells were grown on LCs to validate the phenotype. Trypsin-EDTA decellularized most effectively, removing 99% of cells. The mean LC thickness was 35.76 ± 0.43 μm, whereas DM measured 25.93 ± 0.26 μm (p < .0001). Light transmission was 90% for both LC and DM. On a collagenase challenge, LC and amniotic membrane were digested after 13 hr, whereas DM was digested after 17 hr. The surface area of focal adhesions for cells grown on coated LCs was at least double that compared with other conditions, whereas tight junctions, ion pumps, and hexagonal morphology were well maintained when endothelial cells were cultured on LCs. In conclusion, LCs demonstrate excellent scaffolding properties for tissue engineering and sustain the cell phenotype and can be considered a suitable substrate for ocular tissue engineering or as a template for future scaffolds.

TGF-β1 promotes cell barrier function upon maturation of corneal endothelial cells

Human corneal endothelial cells (HCECs) easily become fibroblastic-like when cultured, rendering them unsuitable for tissue engineering of the cornea. Transforming growth factor β (TGF-β) could be a key factor in this phenomenon; however, TGF-β is also known to maintain the endothelium in a quiescent state in vivo. This work aimed to compare the effects of TGF-β1 on the phenotype of HCECs during the proliferation and maturation phases. Our results show that addition of TGF-β1 during the active proliferation phase produced fibroblastic HCECs and loss of the cell junction markers ZO-1 and n-cadherin, independent from the presence of epidermal growth factor (EGF). By contrast, addition of TGF-β1 in maturation media containing few mitogens led to an endothelial phenotype and functional cell junctions as HCECs developed a high trans-endothelial resistance. Furthermore, addition of AG-1478, an epithelial growth factor receptor inhibitor, enhanced the gain of the endothelial phenotype and cell barrier function. Overall, these results show that TGF-β1 can be used to promote the formation of a typical leaky endothelial barrier during the maturation phase of cultured HCECs. A two-phase culture of HCECs using distinct proliferation and maturation media could also be key for developing ideal HCEC culture conditions.

Trophic effect of PACAP on human corneal endothelium

Cornea's posterior surface includes endothelium maintaining stromal hydration and clarity. Due to their limited proliferative capability, the loss of endothelial cells can outcome in permanent opacity. In the last years, different studies have demonstrated the protective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) in different ocular diseases. However, its role on human corneal endothelial cells (HCECs) has not been investigated, yet. Here, we have developed a culture protocol to differentiate HCECs from donor's cornea. PACAP treatment prevented damage induced by growth factors deprivation of cells grown on transwell supports as revealed by TERR measurements. Moreover, this peptide significantly increased tight junction proteins expression by conferring resistance to endothelial barrier. This effect is also related to promotion of cell viability as demonstrated by MTT assay. Furthermore, PACAP stimulated repairing of corneal endothelium lesion as shown by wound healing analysis. In conclusion, our data suggest that this peptide could represent an important trophic factor in maintaining functionality of human corneal endothelium.

Promoting the expansion and function of human corneal endothelial cells with an orbital adipose-derived stem cell-conditioned medium

BACKGROUND

Corneal endothelial dysfunction causes severe impairment of vision. The only solution is corneal transplantation. However, this treatment is hampered by a worldwide shortage of donor corneas. New therapies may replace the conventional donor corneal transplantation alongside the developments in regenerative medicine and tissue engineering, but sufficient functional corneal endothelial cells (CECs) are essential. The aim of this study was to promote the expansion and function of human corneal endothelial cells (HCECs) in vitro and in vivo.

METHODS

The phenotypes of human orbital adipose-derived stem cells (OASCs) were detected by flow cytometry and immunofluorescence. HCECs were isolated and cultured using a conditioned medium obtained from OASCs (OASC-CM) in vitro. Related cell markers of HCECs were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR), Western blot, and immunofluorescence. The cell counting kit-8 (CCK-8) assay and the wound healing assay were performed to evaluate the proliferation ability of the cells. The cultured HCECs were then transplanted into rabbit and monkey corneal endothelial dysfunction models by cell injection.

RESULTS

CD29, CD105, CD49e, CD166, and vimentin were highly expressed in cultured human OASCs. The CEC-relative markers zonula occludens-1 (ZO-1), Na⁺/K⁺ ATPase, N-cadherin, Col8a2, and SLC4A4 were expressed in HCECs cultured by OASC-CM. The HCECs were able to maintain polygonal cell morphology and good proliferative capacity. In animal experiments, corneal transparency was achieved after the injection of HCECs, which demonstrated the good repair capacity of the cells.

CONCLUSIONS

The proliferation abilities of the cells were significantly enhanced, and related functional markers were strongly positive, while HCEC morphology was maintained using OASC-CM. HCECs obtained some stem cell-like properties. This preclinical study confirmed the therapeutic ability of the HCECs in vivo. Our findings demonstrated that cultured HCECs with OASC-CM might be a promising source for research and clinical treatment.

Optimized human platelet lysate as novel basis for a serum-, xeno-, and additive-free corneal endothelial cell and tissue culture

The expansion of donor-derived corneal endothelial cells (ECs) is a promising approach for regenerative therapies in corneal diseases. To achieve the best Good Manufacturing Practice standard the entire cultivation process should be devoid of nonhuman components. However, so far, there is no suitable xeno-free protocol for clinical applications. We therefore introduce a processed variant of a platelet lysate for the use in corneal cell and tissue culture based on a Good Manufacturing Practice-grade thrombocyte concentrate. This processed human platelet lysate (phPL), free of any animal components and of anticoagulants such as heparin with a physiological ionic composition, was used to cultivate corneal ECs in vitro and ex vivo in comparison to standard cultivation with fetal calf serum (FCS). Human donor corneas were cut in quarters while 2 quarters of each cornea were incubated with the respective medium supplement. Three fields of view per quarter were taken into account for the analysis. Evaluation of phPL as a medium supplement in cell culture of immortalized EC showed a superior viability compared with FCS control with reduced cell proliferation. Furthermore, the viability during the expansion of primary cells is significantly (3-fold ±0.5) increased with phPL compared with FCS standard medium. Quartering donor corneas was traumatic for the endothelium and therefore resulted in increased EC loss. Interestingly, however, cultivation of the quartered pieces for 2 weeks in 0.1-mg/ml pHPL in Biochrome I showed a 21 (±10) % EC loss compared with 67 (±12) % EC loss when cultivated in 2% FCS in Biochrome I. The cell culture protocol with pHPL as FCS replacement seems to be superior to the standard FCS protocols with respect to EC survival. It offers a xeno-free and physiological environment for corneal endothelial cells. This alternative cultivation protocol could facilitate the use of EC for human corneal cell therapy.

The role of lipids in corneal diseases and dystrophies: a systematic review

Corneal diseases are an extensive cause of blindness worldwide and continue to persist as a challenging public health concern. Recently, various lipid-based therapies have been advocated for the modulation of corneal diseases; however, the number of studies is still very limited. Here we focus on developments and challenges on lipid-based therapies for dry eye disease, diabetic neuropathy, and Fuchs' endothelial corneal dystrophy. All three diseases are highly prevalent conditions and involve corneal stress and inflammation. Lipid-based therapeutics discussed includes cyclooxygenase inhibitors, essential fatty acids, and resolvin analogs. Lipids also show increasing promise as biomarkers of disease and are explored in this review.

Restricted Presence of POU6F2 in Human Corneal Endothelial Cells Uncovered by Extension of the Promoter-level Expression Atlas

Corneal endothelial cells (CECs) are essential for maintaining the clarity of the cornea. Because CECs have limited proliferative ability, interest is growing in their potentially therapeutic regeneration from pluripotent stem cells. However, the molecular mechanisms of human CEC differentiation remain largely unknown. To determine the key regulators of CEC characteristics, here we generated a comprehensive promoter-level expression profile of human CECs, using cap analysis of gene expression (CAGE) with a single molecule sequencer. Integration with the FANTOM5 promoter-level expression atlas, which includes transcriptome profiles of various human tissues and cells, enabled us to identify 45 promoters at 28 gene loci that are specifically expressed in CECs. We further discovered that the expression of transcription factor POU class 6 homeobox 2 (POU6F2) is restricted to CECs, and upregulated during human CEC differentiation, suggesting that POU6F2 is pivotal to terminal differentiation of CECs. These CEC-specific promoters would be useful for the assessment of fully differentiated CECs derived from pluripotent stem cells. These findings promote the development of corneal regenerative medicine.

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We comprehensively profiled promoter-level expression of human corneal endothelial cells.

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Integrative transcriptome analysis identified 28 corneal endothelial cell-specific marker genes.

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POU6F2 expression is restricted to corneal endothelial cells, and upregulated during differentiation.

Corneal endothelial cells (CECs) are essential for maintaining corneal transparency. Owing to the high prevalence of corneal endothelial disorders, CECs are important targets in regenerative medicine. However, it has been difficult to evaluate the final CEC products owing to the lack of appropriate CEC-specific markers. In this study, we identified 28 CEC-specific marker genes by integrative transcriptome analysis. One gene of particular interest, POU6F2, is expressed almost exclusively in CECs, and upregulated during differentiation. These markers would be useful for the assessment of CECs derived from pluripotent stem cells, and this study will facilitate the translation of corneal regenerative medicine.

Regulatory Compliant Tissue-Engineered Human Corneal Endothelial Grafts Restore Corneal Function of Rabbits with Bullous Keratopathy

Corneal transplantation is the only treatment available to restore vision for individuals with blindness due to corneal endothelial dysfunction. However, severe shortage of available donor corneas remains a global challenge. Functional regulatory compliant tissue-engineered corneal endothelial graft substitute can alleviate this reliance on cadaveric corneal graft material. Here, isolated primary human corneal endothelial cells (CEnCs) propagated using a dual media approach refined towards regulatory compliance showed expression of markers indicative of the human corneal endothelium, and can be tissue-engineered onto thin corneal stromal carriers. Both cellular function and clinical adaptability was demonstrated in a pre-clinical rabbit model of bullous keratopathy using a tissue-engineered endothelial keratoplasty (TE-EK) approach, adapted from routine endothelial keratoplasty procedure for corneal transplantation in human patients. Cornea thickness of rabbits receiving TE-EK graft gradually reduced over the first two weeks, and completely recovered to a thickness of approximately 400 µm by the third week of transplantation, whereas corneas of control rabbits remained significantly thicker over 1,000 µm (p < 0.05) throughout the course of the study. This study showed convincing evidence of the adaptability of the propagated CEnCs and their functionality via a TE-EK approach, which holds great promises in translating the use of cultured CEnCs into the clinic.

Human corneal cell culture models for drug toxicity studies

In vivo toxicity and absorption studies of topical ocular drugs are problematic, because these studies involve invasive tissue sampling and toxic effects in animal models. Therefore, different human corneal models ranging from simple monolayer cultures to three-dimensional models have been developed for toxicological prediction with in vitro models. Each system has its own set of advantages and disadvantages. Use of non-corneal cells, inadequate characterization of gene-expression profiles, and accumulation of genomic aberrations in human corneal models are typical drawbacks that decrease their reliability and predictive power. In the future, further improvements are needed for verifying comparable expression profiles and cellular properties of human corneal models with their in vivo counterparts. A rapidly expanding stem cell technology combined with tissue engineering may give future opportunities to develop new tools in drug toxicity studies. One approach may be the production of artificial miniature corneas. In addition, there is also a need to use large-scale profiling approaches such as genomics, transcriptomics, proteomics, and metabolomics for understanding of the ocular toxicity.

Improving the success rate of human corneal endothelial cell cultures from single donor corneas with stabilization medium

Main objective of this study was to improve the success rate of human corneal endothelial cell (hCEC) cultures from single donor corneas. We could show that the use of stabilization medium prior to cell isolation may have a positive effect on the success rate of hCEC cultures from single research-grade donor corneas by allowing growth of otherwise possibly not successful cultures and by improving their proliferative rate. hCEC were obtained from corneo-scleral rims of 7 discarded human research-grade cornea pairs. The Descemet membrane-endothelium (DM-EC) sheets of each pair were assigned to 2 experimental conditions: (1) immediate cell isolation after peeling, and (2) storage of the DM-EC sheet in a growth factor-depleted culture medium (i.e. stabilization medium) for up to 6 days prior to cell isolation. hCEC isolated by enzymatic digestion were then induced to proliferate on pre-coated culture plates. The success rate of primary cultures established from single donor corneas were higher for DM-EC sheets kept in stabilization medium before cell isolation. All cultures (7/7) initiated from stabilized DM-EC sheets were able to proliferate up to the third passage, while only 4 out of 7 cultures initiated from freshly peeled DM-EC sheets reached the third passage. In addition, for the 4 successful paired cultures we observed a faster growth rate if the DM-EC sheet was pre-stabilized prior to cell isolation (13.8 ± 1.8 vs 18.5 ± 1.5 days, P < 0.05). Expression of the phenotypical markers Na⁺/K⁺-ATPase and ZO-1 could be shown for the stabilized cultures that successfully proliferated up to the third passage.

Preoperative photocoagulation reduces corneal endothelial cell damage after vitrectomy in patients with proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) is a severe complication of diabetes and is a leading cause of visual decline and irreversible blindness. So we designed this study to investigate retrospectively the effect of preoperative photocoagulation on corneal endothelial cells after vitrectomy in patients with PDR.The study included 52 eyes of 46 patients with PDR complicated with vitreous hemorrhage, who underwent vitrectomy. Patients were apportioned to a photocoagulation group (26 eyes/23 patients) or nonphotocoagulation group (26/23 patients), according to their history of preoperative photocoagulation. A specular microscope was used to assess the corneal endothelial cell density and percentage of hexagonal cells (PHC) before surgery, and at 1 week, 1 month, and 3 months after surgery.The cell density was lower 3 months after surgery in the photocoagulation group, but at 1 month in the nonphotocoagulation group, all cases were significantly different from the preoperative value (P < .05 or P < .01). One week after surgery, the mean cell densities between the photocoagulation and nonphotocoagulation groups were not statistically different (P > .05). However, the mean cell densities at 1 and 3 months after surgery in the photocoagulation group were significantly higher than those in the nonphotocoagulation group (P < .05). The PHC values in the photocoagulation group at 1 week and in the nonphotocoagulation group at 1 week, 1 month, and 3 months were much lower than their respective preoperative values (P < .05 or P < .01). More importantly, at 1 and 3 months, the PHC had recovered to preoperative values in the photocoagulation group, but not in the nonphotocoagulation group. As for cell density and PHC, they were both significantly higher 1 and 3 months after surgery in the photocoagulation group than in the nonphotocoagulation group (P < .05).Photocoagulation before vitrectomy reduces subsequent corneal endothelial cell damage in PDR patients.

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.

Transplanting embryonic stem cells onto damaged human corneal endothelium

AIM

To investigate whether human embryonic stem cells (hESCs) could be made to attach, grow and differentiate on a human Descemet’s membrane (DM).

METHODS

Spontaneously differentiated hESCs were transferred onto a human corneal button with the endothelial layer removed using ocular sticks. The cells were cultured on a DM for up to 15 d. The genetically engineered hESC line expressed green fluorescent protein, which facilitated identification during the culture experiments, tissue preparation, and analysis. To detect any differentiation into human corneal endothelial-like cells, we analysed the transplanted cells by immunohistochemistry using specific antibodies.

RESULTS

We found transplanted cells form a single layer of cells with a hexagonal shape in the periphery of the DM. The majority of the cells were negative for octamer-binding transcription factor 4 but positive for paired box 6 protein, sodium potassium adenosine triphosphatase (NaKATPase), and Zona Occludens protein 1. In four of the 18 trials, the transplanted cells were found to express CK3, which indicates that the stem cells differentiated into corneal epithelial cells in these cases.

CONCLUSION

It is possible to get cells originating from hESCs to become established on a human DM, where they grow and differentiate into corneal endothelial-like cells in vitro.

Conditionally Immortal Slc4a11-/- Mouse Corneal Endothelial Cell Line Recapitulates Disrupted Glutaminolysis Seen in Slc4a11-/- Mouse Model

Purpose

To establish conditionally immortal mouse corneal endothelial cell lines with genetically matched Slc4a11+/+ and Slc4a11-/- mice as a model for investigating pathology and therapies for SLC4A11 associated congenital hereditary endothelial dystrophy (CHED) and Fuchs' endothelial corneal dystrophy.

Methods

We intercrossed H-2Kb-tsA58 mice (Immortomouse) expressing an IFN-γ dependent and temperature-sensitive mutant of the SV40 large T antigen (tsTAg) with Slc4a11+/+ and Slc4a11-/- C57BL/6 mice. The growth characteristics of the cell lines was assessed by doubling time. Ion transport activities (Na+/H+ exchange, bicarbonate, lactate, and Slc4a11 ammonia transport) were analyzed by intracellular pH measurement. The metabolic status of the cell lines was assessed by analyzing TCA cycle intermediates via gas chromatography mass spectrometry (GC-MS).

Results

The immortalized Slc4a11+/+ and Slc4a11-/- mouse corneal endothelial cells (MCECs) remained proliferative through passage 49 and maintained similar active ion transport activity. As expected, proliferation was temperature sensitive and IFN-γ dependent. Slc4a11-/- MCECs exhibited decreased proliferative capacity, reduced NH3:H+ transport, altered expression of glutaminolysis enzymes similar to the Slc4a11-/- mouse, and reduced proportion of TCA cycle intermediates derived from glutamine with compensatory increases in glucose flux compared with Slc4a11+/+ MCECs.

Conclusions

This is the first report of the immortalization of MCECs. Ion transport of the immortalized endothelial cells remains active, except for NH3:H+ transporter activity in Slc4a11-/- MCECs. Furthermore, Slc4a11-/- MCECs recapitulate the glutaminolysis defects observed in Slc4a11-/- mouse corneal endothelium, providing an excellent tool to study the pathogenesis of SLC4A11 mutations associated with corneal endothelial dystrophies and to screen potential therapeutic agents.

Novel Identity and Functional Markers for Human Corneal Endothelial Cells

Purpose

Human corneal endothelial cell (HCEC) density decreases with age, surgical complications, or disease, leading to vision impairment. Such endothelial dysfunction is an indication for corneal transplantation, although there is a worldwide shortage of transplant-grade tissue. To overcome the current poor donor availability, here we isolate, expand, and characterize HCECs in vitro as a step toward cell therapy.

Methods

Human corneal endothelial cells were isolated from cadaveric corneas and expanded in vitro. Cell identity was evaluated based on morphology and immunocytochemistry, and gene expression analysis and flow cytometry were used to identify novel HCEC-specific markers. The functional ability of HCEC to form barriers was assessed by transendothelial electrical resistance (TEER) assays.

Results

Cultured HCECs demonstrated canonical morphology for up to four passages and later underwent endothelial-to-mesenchymal transition (EnMT). Quality of donor tissue influenced cell measures in culture including proliferation rate. Cultured HCECs expressed identity markers, and microarray analysis revealed novel endothelial-specific markers that were validated by flow cytometry. Finally, canonical HCECs expressed higher levels of CD56, which correlated with higher TEER than fibroblastic HCECs.

Conclusions

In vitro expansion of HCECs from cadaveric donor corneas yields functional cells identifiable by morphology and a panel of novel markers. Markers described correlated with function in culture, suggesting a basis for cell therapy for corneal endothelial dysfunction.

Expansion and cryopreservation of porcine and human corneal endothelial cells

Impairment of the corneal endothelium causes blindness that afflicts millions worldwide and constitutes the most often cited indication for corneal transplants. The scarcity of donor corneas has prompted the alternative use of tissue-engineered grafts which requires the ex vivo expansion and cryopreservation of corneal endothelial cells. The aims of this study are to culture and identify the conditions that will yield viable and functional corneal endothelial cells after cryopreservation. Previously, using human umbilical vein endothelial cells (HUVECs), we employed a systematic approach to optimize the post-thaw recovery of cells with high membrane integrity and functionality. Here, we investigated whether improved protocols for HUVECs translate to the cryopreservation of corneal endothelial cells, despite the differences in function and embryonic origin of these cell types. First, we isolated endothelial cells from pig corneas and then applied an interrupted slow cooling protocol in the presence of dimethyl sulfoxide (Me₂SO), with or without hydroxyethyl starch (HES). Next, we isolated and expanded endothelial cells from human corneas and applied the best protocol verified using porcine cells. We found that slow cooling at 1 °C/min in the presence of 5% Me₂SO and 6% HES, followed by rapid thawing after liquid nitrogen storage, yields membrane-intact cells that could form monolayers expressing the tight junction marker ZO-1 and cytoskeleton F-actin, and could form tubes in reconstituted basement membrane matrix. Thus, we show that a cryopreservation protocol optimized for HUVECs can be applied successfully to corneal endothelial cells, and this could provide a means to address the need for off-the-shelf cryopreserved cells for corneal tissue engineering and regenerative medicine.

In vitro biomimetic platforms featuring a perfusion system and 3D spheroid culture promote the construction of tissue-engineered corneal endothelial layers

Corneal endothelial cells (CECs) are very important for the maintenance of corneal transparency. However, in vitro, CECs display limited proliferation and loss of phenotype via endothelial to mesenchymal transformation (EMT) and cellular senescence. In this study, we demonstrate that continuous supplementary nutrition using a perfusion culture bioreactor and three-dimensional (3D) spheroid culture can be used to improve CEC expansion in culture and to construct a tissue-engineered CEC layer. Compared with static culture, perfusion-derived CECs exhibited an increased proliferative ability as well as formed close cell-cell contact junctions and numerous surface microvilli. We also demonstrated that the CEC spheroid culture significantly down-regulated gene expression of the proliferation marker Ki67 and EMT-related markers Vimentin and α-SMA, whereas the gene expression level of the CEC marker ATP1A1 was significantly up-regulated. Furthermore, use of the perfusion system in conjunction with a spheroid culture on decellularized corneal scaffolds and collagen sheets promoted the generation of CEC monolayers as well as neo-synthesized ECM formation. This study also confirmed that a CEC spheroid culture on a curved collagen sheet with controlled physiological intraocular pressure could generate a CEC monolayer. Thus, our results show that the use of a perfusion system and 3D spheroid culture can promote CEC expansion and the construction of tissue-engineered corneal endothelial layers in vitro.

Human Corneal Endothelial Cell Cultivation From Old Donor Corneas With Forced Attachment

Human corneal endothelial cells (HCEnCs) are responsible for maintaining the transparency of the cornea. Damaged or diseased HCEnCs may cause blindness. Replacement of the diseased cells with a healthy donor endothelium is the only currently available treatment. Tissue-engineering can serve as an alternative to conventional donor corneal transplantation. Due to the global shortage of donor corneas, a wide interest in the development of cultured graft substitutes and artificial corneas has increased. Availability of the old donor corneas is higher especially for research. Although it can be proposed as a valuable source for cell culture, its less proliferative capability emerges a challenge for the researchers. This article describes the use of hyaluronic acid (HA) in combination with Rho-kinase inhibitor (ROCK) Y-27632 for the cultivation of HCEnCs from older donor corneas (age > 60 years). Four conditions including and excluding HA + ROCK and its effect on early attachment rates and proliferation was studied on forty-eight corneas. It was observed that HCEnCs reach confluence within 10–15 days when cultured with HA + ROCK. This approach improves the efficiency of cell adhesion due to force attachment. HCEnCs from old donor corneas can be cultured using this method which may further lead to cell-based therapy for treating corneal endothelial dysfunction.

Skin-Derived Precursors as a Source of Progenitors for Corneal Endothelial Regeneration

Corneal blindness is the fourth leading cause of blindness in the world. Current treatment is allogenic corneal transplantation, which is limited by shortage of donors and immunological rejection. Skin-derived precursors (SKPs) are postnatal stem cells, which are self-renewing, multipotent precursors that can be isolated and expanded from the dermis. Facial skin may therefore be an accessible autologous source of neural crest derived cells. SKPs were isolated from facial skin of Wnt1-Cre/Floxed EGFP mouse. After inducing differentiation with medium containing retinoic acid and GSK 3-β inhibitor, SKPs formed polygonal corneal endothelial-like cells (sTECE). Expression of major corneal endothelial markers were confirmed by Reverse transcription polymerase chain reaction (RT-PCR) and quantitative Real time polymerase chain reaction (qRT-PCR). Western blots confirmed the expression of Na, K-ATPase protein, the major functional marker of corneal endothelial cells. Immunohistochemistry revealed the expression of zonular occludens-1 and Na, K-ATPase in cell-cell junctions. In vitro functional analysis of Na, K-ATPase pump activity revealed that sTECE had significantly high pump function compared to SKPs or control 3T3 cells. Moreover, sTECE transplanted into a rabbit model of bullous keratopathy successfully maintained corneal thickness and transparency. Furthermore, we successfully induced corneal endothelial-like cells from human SKPs, and showed that transplanted corneas also maintained corneal transparency and thickness. Our findings suggest that SKPs may be used as a source of autologous cells for the treatment of corneal endothelial disease. Stem Cells Translational Medicine 2017;6:788-798.

Construction of tissue-engineered full-thickness cornea substitute using limbal epithelial cell-like and corneal endothelial cell-like cells derived from human embryonic stem cells

The aim of this study was to construct a full-thickness artificial cornea substitute in vitro by coculturing limbal epithelial cell-like (LEC-like) cells and corneal endothelial cell-like (CEC-like) cells derived from human embryonic stem cells (hESCs) on APCM scaffold. A 400 μm thickness, 11 mm diameter APCM lamella containing Bowman's membrane was prepared as the scaffold using trephine and a special apparatus made by ourselves. LEC-like cells and CEC-like cells, derived from hESCs as our previously described, were cocultured on the scaffold using a special insert of 24-well plates that enabled seeding both sides of the scaffold. Three or four layers of epithelium-like cells and a uniform monolayer of CEC-like cells could be observed by H&E staining. The thickness, endothelial cell density, and mechanical properties of the construct were similar to that of native rabbit corneas. Immunofluorescence analysis showed expression of ABCG2 and CK3 in the epithelium-like cell layers and expression of N-cadherin, ZO-1 and Na+/K + ATPase in the CEC-like cells. The corneal substitutes were well integrated within the host corneas, and the transparency increased gradually in 8-week follow-up after transplantation in the rabbits. These results suggest that the strategy we developed is feasible and effective for construction of tissue-engineered full-thickness cornea substitute with critical properties of native cornea.

The use of in vivo, ex vivo, in vitro, computational models and volunteer studies in vision research and therapy, and their contribution to the Three Rs

Much is known about mammalian vision, and considerable progress has been achieved in treating many vision disorders, especially those due to changes in the eye, by using various therapeutic methods, including stem cell and gene therapy. While cells and tissues from the main parts of the eye and the visual cortex (VC) can be maintained in culture, and many computer models exist, the current non-animal approaches are severely limiting in the study of visual perception and retinotopic imaging. Some of the early studies with cats and non-human primates (NHPs) are controversial for animal welfare reasons and are of questionable clinical relevance, particularly with respect to the treatment of amblyopia. More recently, the UK Home Office records have shown that attention is now more focused on rodents, especially the mouse. This is likely to be due to the perceived need for genetically-altered animals, rather than to knowledge of the similarities and differences of vision in cats, NHPs and rodents, and the fact that the same techniques can be used for all of the species. We discuss the advantages and limitations of animal and non-animal methods for vision research, and assess their relative contributions to basic knowledge and clinical practice, as well as outlining the opportunities they offer for implementing the principles of the Three Rs (Replacement, Reduction and Refinement).

Prospect of Human Pluripotent Stem Cell-Derived Neural Crest Stem Cells in Clinical Application

Neural crest stem cells (NCSCs) represent a transient and multipotent cell population that contributes to numerous anatomical structures such as peripheral nervous system, teeth, and cornea. NCSC maldevelopment is related to various human diseases including pigmentation abnormalities, disorders affecting autonomic nervous system, and malformations of teeth, eyes, and hearts. As human pluripotent stem cells including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) can serve as an unlimited cell source to generate NCSCs, hESC/hiPSC-derived NCSCs can be a valuable tool to study the underlying mechanisms of NCSC-associated diseases, which paves the way for future therapies for these abnormalities. In addition, hESC/hiPSC-derived NCSCs with the capability of differentiating to various cell types are highly promising for clinical organ repair and regeneration. In this review, we first discuss NCSC generation methods from human pluripotent stem cells and differentiation mechanism of NCSCs. Then we focus on the clinical application potential of hESC/hiPSC-derived NCSCs on peripheral nerve injuries, corneal blindness, tooth regeneration, pathological melanogenesis, Hirschsprung disease, and cardiac repair and regeneration.

In Vitro and In Vivo Models to Study Corneal Endothelial-mesenchymal Transition

Corneal endothelial cells (CECs) play a crucial role in maintaining corneal clarity through active pumping. A reduced CEC count may lead to corneal edema and diminished visual acuity. However, human CECs are prone to compromised proliferative potential. Furthermore, stimulation of cell growth is often complicated by gradual endothelial-mesenchymal transition (EnMT). Therefore, understanding the mechanism of EnMT is necessary for facilitating the regeneration of CECs with competent function. In this study, we prepared a primary culture of bovine CECs by peeling the CECs with Descemet's membrane from the corneal button and demonstrated that bovine CECs exhibited the EnMT process, including phenotypic change, nuclear translocation of β-catenin, and EMT regulators snail and slug, in the in vitro culture. Furthermore, we used a rat corneal endothelium cryoinjury model to demonstrate the EnMT process in vivo. Collectively, the in vitro primary culture of bovine CECs and in vivo rat corneal endothelium cryoinjury models offers useful platforms for investigating the mechanism of EnMT.

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.

Nature-Derived Aloe Vera Gel Blended Silk Fibroin Film Scaffolds for Cornea Endothelial Cell Regeneration and Transplantation

The goal of this study was to fabricate an appropriate replacement for cadaveric corneas to overcome a shortage of cadaveric corneas for transplantation. In this study, we fabricated transparent ultrathin film scaffolds with nature-derived aloe vera (AV) gel and silk fibroin (SF) for corneal endothelial cells (CECs). The scaffolds were subjected to analysis of transparency and contact angle using field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy to determine their physical and chemical properties. FESEM images revealed that the critical morphology of CECs was formed on the AV gel in the blend with SF rather than in the scaffold with SF alone. The cell proliferation, phenotype, and specific gene marker expressions for CECs were determined by MTT assays, immunofluorescence, and reverse transcription polymerase chain reactions. Incorporation of a small amount of AV gel increased the cell viability and maintained its functions well. The scaffolds were easily handled for transplantation into rabbit eyes with small incisions and examined by their transparency after transplantation and histological staining. The scaffolds attached to the surface of the corneal stroma and integrated with surrounding corneal tissue without a significant inflammatory reaction. These results indicate that AV blended SF film scaffolds might be a suitable substitute for alternative corneal grafts for transplantation.

Rho kinase inhibitor enables cell-based therapy for corneal endothelial dysfunction

The corneal endothelium maintains corneal transparency; consequently, its dysfunction causes severe vision loss. Tissue engineering-based therapy, as an alternative to conventional donor corneal transplantation, is anticipated to provide a less invasive and more effective therapeutic modality. We conducted a preclinical study for cell-based therapy in a primate model and demonstrated regeneration of the corneal endothelium following injection of cultured monkey corneal endothelial cells (MCECs) or human CECs (HCECs), in combination with a Rho kinase (ROCK) inhibitor, Y-27632, into the anterior chamber. We also evaluated the safety and efficacy of Good Manufacturing Practice (GMP)-grade HCECs, similar to those planned for use as transplant material for human patients in a clinical trial, and we showed that the corneal endothelium was regenerated without adverse effect. We also showed that CEC engraftment is impaired by limited substrate adhesion, which is due to actomyosin contraction induced by dissociation-induced activation of ROCK/MLC signaling. Inclusion of a ROCK inhibitor improves efficiency of engraftment of CECs and enables cell-based therapy for treating corneal endothelial dysfunction as a clinically relevant therapy.