Expansion of conjunctival epithelial progenitor cells on amniotic membrane

Subretinal Amniotic Membrane Transplantation in a Porcine Model of Retinal Hole

Purpose

To investigate the histopathological changes following subretinal amniotic membrane transplantation in an in vivo porcine model of retinal holes.

Methods

Left eyes of 12 Danish Landrace pigs were vitrectomized under full anesthesia. A subretinal bleb was created before excising a retinal hole (1154-2934 µm) using a 23-gauge vitrector. The pigs underwent transplantation of human freeze-dried amniotic membrane into the subretinal space, with no tamponade applied. Optical coherence tomography and color fundus photography were performed just after surgery and at 2 and 4 weeks post-surgery. At the end of follow-up, the eyes were enucleated for hematoxylin and eosin staining and fluorescence immunohistochemistry, using antibodies against retinal glial cells and inner retinal neurons.

Results

The amniotic membrane sheets facilitated hole closure by gliosis and centripetal migration of the edges of the hole. Immunohistochemical examination showed that the cells within the closed hole expressed anti-glial fibrillary acidic protein (GFAP) and anti-S100B, but not anti-glutamine synthetase (GS), suggesting that astrocytes were the predominant glial cells involved in hole closure. Gliosis was observed between the amniotic membrane sheet and the overlying photoreceptors of the surrounding retina. Morphological restoration of the retinal layers within the closed retinal hole was not observed.

Conclusions

The amniotic membrane acted as a stimulator for retinal hole closure by inducing glial cell proliferation and providing a scaffold for the centripetal migration of the edges of the hole. No morphological restoration was observed.

Establishment of a bi-layered tissue engineered conjunctiva using a 3D-printed melt electrowritten poly-(ε-caprolactone) scaffold

PURPOSE

To utilize melt electrowriting (MEW) technology using poly-(ε-caprolactone) (PCL) coupled with a 2-step co-culturing strategy for the development of a conjunctival bi-layer synthetic construct.

METHODS

Melt electrowritten scaffolds using PCL were fabricated using an in-house-built MEW printer. Human conjunctival stromal cells (CjSCs) and epithelial cells (CjECs) were isolated from donor tissue. A 2-step co-culture method was done by first seeding the CjSCs and culturing for 4 weeks to establish a stromal layer, followed by CjECs and co-culturing for 2 more weeks. Cultured cells were each characterized by morphology and marker expression on immunofluorescence and qPCR. The produced construct was assessed for cellular proliferation using viability assays. The bi-layer morphology was assessed using scanning electron microscopy (SEM), confocal microscopy, and immunofluorescence imaging. The expression of extracellular matrix components and TGF-b was evaluated using qPCR.

RESULTS

CjSCs were spindle-shaped and vimentin + while CjECs were polygonal and CK13 + . CjSCs showed consistent proliferation and optimal adherence with the scaffold at the 4-week culture mark. A 2-layered construct consisting of a CjSC-composed stromal layer and a CjEC-composed epithelial layer was appreciated on confocal microscopy, SEM, and immunofluorescence. CjSCs secreted collagens (types I, V, VI) but at differing amounts from natural tissue while TGF-b production was comparable.

CONCLUSION

The 3D-printed melt electrowritten PCL scaffold paired with the 2-step co-culturing conditions of the scaffold allowed for the first approximation of a bi-layered stromal and epithelial reconstruction of the conjunctiva that can potentially improve the therapeutic arsenal in ocular surface reconstruction.

[Methods of surgical reconstruction of the conjunctiva]

Reconstruction of the conjunctiva is required for restoration of damaged ocular surface and is an essential part of that process. Traumas, chemical and thermal burns, multiple surgical intervention can seriously damage the integrity of conjunctival tissue and promote the growth of fibrous tissue, scarring of contractures and their shortening, as well as other complications such as trichiasis, erosion and ulcers on the cornea. When a larger area is affected, there may not be enough donor tissue to replace the defect, in which case the tissue grafts are required to be large enough. Modern modifications of surgical techniques and the continued development of tissue engineering, as well as advancements in stem cell research offer promising novel alternatives for solution of those problems. This article reviews the existing surgical methods of conjunctival reconstruction.

Rapid 3D bioprinting of a multicellular model recapitulating pterygium microenvironment

Pterygium is an ocular surface disorder with high prevalence that can lead to vision impairment. As a pathological outgrowth of conjunctiva, pterygium involves neovascularization and chronic inflammation. Here, we developed a 3D multicellular in vitro pterygium model using a digital light processing (DLP)-based 3D bioprinting platform with human conjunctival stem cells (hCjSCs). A novel feeder-free culture system was adopted and efficiently expanded the primary hCjSCs with homogeneity, stemness and differentiation potency. The DLP-based 3D bioprinting method was able to fabricate hydrogel scaffolds that support the viability and biological integrity of the encapsulated hCjSCs. The bioprinted 3D pterygium model consisted of hCjSCs, immune cells, and vascular cells to recapitulate the disease microenvironment. Transcriptomic analysis using RNA sequencing (RNA-seq) identified a distinct profile correlated to inflammation response, angiogenesis, and epithelial mesenchymal transition in the bioprinted 3D pterygium model. In addition, the pterygium signatures and disease relevance of the bioprinted model were validated with the public RNA-seq data from patient-derived pterygium tissues. By integrating the stem cell technology with 3D bioprinting, this is the first reported 3D in vitro disease model for pterygium that can be utilized for future studies towards personalized medicine and drug screening.

Fabrication of Decellularized Amnion and Chorion Scaffolds to Develop Bioengineered Cell-Laden Constructs

INTRODUCTION

Human mesenchymal stem cells (hMSCs) holds great promise for managing several clinical conditions. However, the low engraftment efficiency and obscurity to harvest these cells without compromising the cellular viability, structural and functional properties from the culture niche still remain major obstacles for preparing intact regenerative constructs. Although few studies have demonstrate different methods for generating cell-liberated amniotic scaffolds, a common method for producing completely cell-liberated amnion (D-HAM) and chorion (D-HCM) scaffolds and their cytocompatibility with hMSCs yet to be demonstrated.

METHODS

A common process was developed for preparing D-HAM and D-HCM scaffolds for assessing hMSCs engraftment efficiency, proliferation and molecular shifts to generate cell-laden biological discs. The structural and functional integrity of D-HAM and D-HCM was evaluated using different parameters. The compatibility and proliferation efficiency of hMSCs with D-HAM and D-HCM was evaluated.

RESULTS

Histological analysis revealed completely nucleic acid-free D-HAM and D-HCM scaffolds with intact extracellular matrix, mechanical and biological properties almost similar to the native membranes. Human MSCs were able to adhere and engraft on D-HCM better than D-HAM and expanded faster. Ultrastructural observations, crystal violet staining and expression studies showed better structural and functional integrity of hMSCs on D-HCM than D-HAM and control conditions.

CONCLUSION

A common, simple and reliable process of decellularization can generate large number of cell-liberated amniotic scaffolds in lesser time. D-HCM has better efficiency for hMSCs engraftment and proliferation and can be utilized for preparing suitable cell-laden constructs for tissue engineering applications.

Molecular mechanisms and treatments for ocular symblephara

There are currently no effective methods to prevent or durably treat ocular symblephara, the adhesions between the palpebral and bulbar conjunctiva. How symblephara form at the molecular level is largely unknown. We present here an overview of current clinical symblephara treatments and describe potential molecular mechanisms behind conjunctival adhesion formation that may inform future symblephara treatment and prevention options. Understanding how symblephara form at the molecular level will facilitate treatment development. Preventative therapies may be possible by targeting symblephara progenitor cells immediately after injuries, while novel therapeutics should be aimed at modulating TGF-β pathways and effector cells in conjunctival scarring to treat symblephara formation more effectively.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Rapid bioprinting of conjunctival stem cell micro-constructs for subconjunctival ocular injection

Ocular surface diseases including conjunctival disorders are multifactorial progressive conditions that can severely affect vision and quality of life. In recent years, stem cell therapies based on conjunctival stem cells (CjSCs) have become a potential solution for treating ocular surface diseases. However, neither an efficient culture of CjSCs nor the development of a minimally invasive ocular surface CjSC transplantation therapy has been reported. Here, we developed a robust in vitro expansion method for primary rabbit-derived CjSCs and applied digital light processing (DLP)-based bioprinting to produce CjSC-loaded hydrogel micro-constructs for injectable delivery. Expansion medium containing small molecule cocktail generated fast dividing and highly homogenous CjSCs for more than 10 passages in feeder-free culture. Bioprinted hydrogel micro-constructs with tunable mechanical properties enabled the 3D culture of CjSCs while supporting viability, stem cell phenotype, and differentiation potency into conjunctival goblet cells. These hydrogel micro-constructs were well-suited for scalable dynamic suspension culture of CjSCs and were successfully delivered to the bulbar conjunctival epithelium via minimally invasive subconjunctival injection. This work integrates novel cell culture strategies with bioprinting to develop a clinically relevant injectable-delivery approach for CjSCs towards the stem cell therapies for the treatment of ocular surface diseases.

Novel Method of Plugging the Hole: Anatomical and Functional Outcomes of Human Amniotic Membrane-Assisted Macular Hole Surgery

Purpose:

To describe the surgical outcomes of macular holes (MHs) by inserting a human amniotic membrane (hAM) plug.

Methods:

In this retrospective, interventional, comparative case series, 10 patients who had undergone hAM plugging for a MH were included in the study. Seven patients had idiopathic full-thickness MHs, 1 patient had traumatic MH, and 1 patient each had a MH-induced retinal detachment and combined retinal detachment. The control group included 10 cases with similar configuration and duration of MHs treated with the inverted peeling of the internal limiting membrane technique. All patients underwent a standard 3-port, 25-gauge transconjunctival pars plana vitrectomy and hAM plug transplantation in the subretinal space under the MH. The anatomic and functional outcomes were assessed at 4 weeks postsurgery.

Results:

At the 4-week follow-up visit, all the MHs in the hAM plug group achieved hole closure, whereas 80% of the eyes in the control group were able to achieve hole closure. Improvement of 0.1 logMAR vision was noted in 8 of the 10 patients. At the 4-week follow-up visit, the external limiting membrane and ellipsoid zone layer continuity over the hAM was defined only in one case. No significant difference was found between the hAM plug group and controls in visual and anatomical responses. No complications following hAM transplantation such as rejection, endophthalmitis, or hypotony were noted following surgery.

Conclusion:

Subretinal hAM graft transplantation can be a useful option in the repair of primary or refractory MHs not only for achieving anatomic closure but also for the accompanying visual improvement.

Decellularized porcine conjunctiva as an alternative substrate for tissue-engineered epithelialized conjunctiva

PURPOSE

The long-term success of visual rehabilitation in patients with severe conjunctival scarring is reliant on the reconstruction of the conjunctiva with a suitable substitute. The purpose of this study is the development and investigation of a re-epithelialized conjunctival substitute based on porcine decellularized conjunctiva (PDC).

METHODS

PDC was re-epithelialized either with pre-expanded human conjunctival epithelial cells (PDC + HCEC) or with a human conjunctival explant placed directly on PDC (PDC + HCEx). Histology and immunohistochemistry were performed to evaluate epithelial thickness, proliferation (Ki67), apoptosis (Caspase 3), goblet cells (MUC5AC), and progenitor cells (CK15, ΔNp63, ABCG2). The superior construct (PDC + HCEx) was transplanted into a conjunctival defect of a rabbit (n = 6). Lissamine green staining verified the epithelialization in vivo. Orbital tissue was exenterated on day 10 and processed for histological and immunohistochemical analysis to examine the engrafted PDC + HCEx. A human-specific antibody was used to detect the transplanted cells.

RESULTS

From day-14 in vitro onward, a significantly thicker epithelium and greater number of cells expressing Ki67, CK15, ΔNp63, and ABCG2 were noted for PDC + HCEx versus PDC + HCEC. MUC5AC-positive cells were found only in PDC + HCEx. The PDC + HCEx-grafted rabbit conjunctivas were lissamine-negative during the evaluation period, indicating epithelial integrity. Engrafted PDC + HCEx showed preserved progenitor cell properties and an increased number of goblet cells comparable to those of native conjunctiva.

CONCLUSION

Placing and culturing a human conjunctival explant directly on PDC (PDC + HCEx) enables the generation of a stable, stratified, goblet cell-rich construct that could provide a promising alternative conjunctival substitute for patients with extensive conjunctival stem and goblet cell loss.

Expansion of Human Limbal Epithelial Stem/Progenitor Cells Using Different Human Sera: A Multivariate Statistical Analysis

Transplantation of human cultured limbal epithelial stem/progenitor cells (LESCs) has demonstrated to restore the integrity and functionality of the corneal surface in about 76% of patients with limbal stem cell deficiency. However, there are different protocols for the expansion of LESCs, and many of them use xenogeneic products, being a risk for the patients’ health. We compared the culture of limbal explants on the denuded amniotic membrane in the culture medium—supplemental hormone epithelial medium (SHEM)—supplemented with FBS or two differently produced human sera. Cell morphology, cell size, cell growth rate, and the expression level of differentiation and putative stem cell markers were examined. Several bioactive molecules were quantified in the human sera. In a novel approach, we performed a multivariate statistical analysis of data to investigate the culture factors, such as differently expressed molecules of human sera that specifically influence the cell phenotype. Our results showed that limbal cells cultured with human sera grew faster and contained similar amounts of small-sized cells, higher expression of the protein p63α, and lower of cytokeratin K12 than FBS cultures, thus, maintaining the stem/progenitor phenotype of LESCs. Furthermore, the multivariate analysis provided much data to better understand the obtaining of different cell phenotypes as a consequence of the use of different culture methodologies or different culture components.

Human Amniotic Membrane Plug for Macular Holes Coexisting with Rhegmatogenous Retinal Detachment

Purpose

To evaluate the efficacy of human amniotic membrane in promoting closure of macular holes coexisting with rhegmatogenous retinal detachment.

Methods

This is a retrospective case series of 14 eyes (14 patients) with macula off retinal detachment. These patients had a macular hole coexistent with peripheral retinal breaks. A human amniotic membrane plug was used to close the macular hole during vitrectomy without ILM peeling.

Results

The mean preoperative BCVA (logMAR value) was 1.87 ± 0.31. At the 6-month follow-up visit, the mean LogMAR best-corrected visual acuity was 0.67 ± 0.17. At the 6-month follow-up, all patients showed complete retinal reattachment with macular hole closure.

Conclusion

The use of human amniotic membrane is a valid option in surgery for macular holes coexisting with rhegmatogenous retinal detachment.

Conjunctival goblet cells: Ocular surface functions, disorders that affect them, and the potential for their regeneration

Conjunctival goblet cells (CGCs) are specialized cells that produce and secrete soluble mucins to the tear film that bathes the ocular surface. CGC numbers and functions are affected in various ocular surface diseases including dry eye disease with diverse etiologies. In this review we will (i) summarize the important functions of CGCs in ocular surface health, (ii) describe the ocular surface diseases that affect CGC numbers and function, (iii) provide an update on recent research outcomes that elucidate CGC differentiation, gene expression and functions, and (iv) present evidence in support of the prediction that restoring CGC numbers and/or functions is a viable strategy for alleviating ocular surface disorders that impact the CGCs.

Basic science review of birth tissue uses in ophthalmology

The birth tissue is predominantly comprised of amniotic membrane (AM) and umbilical cord (UC), which share the same cell origin as the fetus. These versatile biological tissues have been used to treat a wide range of conjunctival and corneal conditions since 1940. The therapeutic benefits of the birth tissue stem from its anti-inflammatory and anti-scarring properties that orchestrate regenerative healing. Although the birth tissue also contains many cytokines, growth factors, and proteins, the heavy chain 1-hyaluronic acid/pentraxin 3 (HC-HA/PTX3) matrix has been identified to be a major active tissue component responsible for AM/UC's multifactorial therapeutic actions. HC-HA/PTX3 complex is abundantly present in fresh and cryopreserved AM/UC, but not in dehydrated tissue. In this review, we discuss the tissue anatomy, the molecular mechanism of action based on HC-HA/ PTX3 to explain their therapeutic potentials, and the various forms available in ophthalmology.

Resorbable and running suture for stable fixation of amniotic membrane multilayers: A useful modification in deep or perforating sterile corneal ulcers

Purpose

To present a modified technique for secure tightening and fixing of multilayer amniotic membranes in deep or perforating corneal ulcers.

Observations

The modified procedure for application and fixation of multilayer amniotic membranes is retrospectively described step by step, and the results of three patients treated with this technique were retrospectively analysed and presented.

The modification consists basically in fixing the inlays with one mini-overlay that is sutured intracorneally with resorbable and running Vicryl 10.0, before a corneoscleral overlay is fixed on top conjunctivally with a running nylon 10.0 suture. The resorbable Vicryl suture is left in place permanently.

Conclusions and Importance

The method described avoids any risk of destroying or displacing the inlays by removing sutures later. In each of the three patients demonstrated as case reports the cornea remained stable throughout the 3- to 5-month follow-up period. This modified technique represents a very useful auxiliary means of treating deep or perforating non-infectious corneal ulcers.

Amniotic Membrane Transplantation in Surgical Treatment of Conjunctival Melanoma: Long-term Results

Objectives

To investigate the long-term efficacy and results of surgical management of conjunctival melanoma reconstructed with amniotic membrane transplantation.

Materials and Methods

Conjunctival melanoma in 10 patients (5 female, 5 male) was totally excised with adjunctive cryotherapy to the surgical margins, corneal epitheliectomy with absolute alcohol in cases of corneal involvement, lamellar sclerectomy in cases with episcleral involvement, and ocular surface grafting with cryopreserved amniotic membrane. Complications and tumor control rates were evaluated.

Results

The mean age of the patients was 57.4±15.2 (range, 37-84) years. The mean diameter of the tumors was 15.5±4.9 (range, 10-25) mm and histopathologically confirmed complete excision was performed in all cases. Mild limbal stem cell deficiency (2 eyes) and subclinical symblepharon (3 eyes) were observed as long-term complications. In a mean follow-up of 56.7±40.4 (range, 30-132) months, only one local tumor recurrence was detected. Despite retreatment, exenteration was performed in this patient due to re-recurrence. One patient died due to disseminated metastasis despite the absence of local recurrence.

Conclusion

In large conjunctival melanomas, reconstruction of the ocular surface is usually very challenging. The use of cryopreserved amniotic membrane for conjunctival defect repair is safe and effective with mild complications, and allows the excision of wider margins around the tumor.

Decellularised conjunctiva for ocular surface reconstruction

Conjunctival reconstruction is an integral component of ocular surface restoration. Decellularised tissues are frequently used clinically for tissue engineering. This study identifies porcine decellularised conjunctiva (PDC) and human decellularised conjunctiva (HDC) as promising substitutes for conjunctival reconstruction. PDC and HDC were nearly DNA-free, structurally intact and showed no cytotoxic effects in vitro, which was confirmed by DNA quantification, histology, transmission electron microscopy, collagen quantification and cytotoxicity assay. Comparing the biomechanical properties to amniotic membrane (AM), the most frequently applied matrix for ocular surface reconstruction today, the decellularised conjunctiva was more extensible and elastic but exhibited less tensile strength. The in vivo application in a rabbit model proofed significantly enhanced transplant stability and less suture losses comparing PDC and HDC to AM while none of the matrices induced considerable inflammation. Ten days after implantation, all PDC, 4 of 6 HDC but none of the AM transplants were completely integrated into the recipient conjunctiva with a partially multi-layered epithelium. Altogether, decellularised conjunctivas of porcine and human origin were superior to AM for conjunctival reconstruction after xenogeneic application in vivo.

STATEMENT OF SIGNIFICANCE

Conjunctival integrity is essential for a healthy ocular surface and clear vision. Its reconstruction is required in case of immunological diseases, after trauma, chemical or thermal burns or surgery involving the conjunctiva. Due to limitations of currently used substitute tissues such as amniotic membrane, there is a need for the development of new matrices for conjunctival reconstruction. Decellularised tissues are frequently applied clinically for tissue engineering. The present study identifies porcine and human decellularised conjunctiva as biocompatible and well tolerated scaffolds with superior integration into the recipient conjunctiva compared to amniotic membrane. Decellularised conjunctiva depicts a promising substitute for conjunctival reconstruction in ophthalmology.

[New approaches to ocular surface reconstruction beyond the cornea]

BACKGROUND

Reconstruction of the conjunctiva is an essential part of ocular surface reconstruction. Clinically applied and experimentally tested tissue- and stem-cell-based approaches are presented and evaluated.

MATERIALS AND METHODS

Current literature and our own results will be presented.

RESULTS

Autologous conjunctiva, mucous membrane of the mouth or nose, and amniotic membrane are routinely used for conjunctival reconstruction. Limitations are limited availability, involvement in autoimmune diseases, donor heterogeneity, and degradation in an inflamed environment. Experimentally tested matrices as tissues made from extracellular matrix proteins, synthetic polymers, temperature-sensitive culture dishes, and decellularized conjunctiva have been tested in vitro and partly in vivo. To replace conjunctival cells, cells of conjunctiva and mucous membrane of mouth and nose have been evaluated and show progenitor cell properties as well as secretory capacity (goblet cell differentiation).

CONCLUSIONS

Although different matrices are available for conjunctival reconstruction there is-due to specific limitations of existing tissues-a need for the development of new therapies for conjunctival replacement. Matrices produced in the laboratory have already been partly investigated in vivo and may thus be clinically applicable in the near future. Adult mucous membrane cells show many properties of conjunctival epithelium after expansion in vitro and thus are a promising cell source for conjunctival tissue engineering. Other stem cells sources require further evaluation.

Seeding of Corneal Wounds by Epithelial Cell Transfer from Micropatterned PDMS Contact Lenses

Persistent corneal wounds result from numerous eye disorders, and to date, available treatments often fail to accelerate reepithelialization, the key initial step in wound healing. To speed reepithelialization, we explored a cell-transfer transplant method utilizing polydimethylsiloxane (PDMS) contact lenses to deliver epithelial cells derived from limbal explants directly within a corneal wound. Human primary epithelial cells and an immortalized corneal epithelial cell line (HCE-SV40) grew well on PDMS contact lenses and their morphology and growth rates where similar to cells grown on tissue culture polystyrene. To initially study cell transfer from PDMS, HCE-SV40 cells were seeded onto PDMS with or without micropatterned posts. After a day in culture, HCE-SV40 cells attached to the unpatterned PDMS uniformly, whereas on micropatterned PDMS they appeared to attach primarily between posts. The cell-covered PDMS contacts were then placed cell-side down onto tissue culture plastic and, after 1, 2, or 3 days, the PDMS contact was removed and the transferred cells were trypsinized and counted. Micropatterned PDMS contact lenses with 100-μm-diameter posts and a post height of 40 μm transferred three times as many cells as unpatterned PDMS. Cell transfer to a wounded cornea was tested in a pig cornea organ culture model deepithelialized by alkali treatment. Post micropatterned PDMS contact lenses were seeded with labeled HCE-SV40 cells at a density 50,000 cells/cm2 and applied to the wounded pig corneas. After 24, 48, or 96 h of application, PDMS contact lenses were removed, corneas fixed with formaldehyde, and sectioned. After 48 h, epithelial cells transferred from post micropatterned contact lenses to provide 35% epithelial coverage of denuded pig corneas; after 96 h coverage was 65%. We conclude that cell transfer from epithelial-coated PDMS contact lenses micropatterned with posts provides a promising approach to reepithelialize corneal surfaces.

Minor ipsilateral simple limbal epithelial transplantation (mini-SLET) for pterygium treatment

We describe a novel surgical technique for pterygium removal taking advantage of the properties of amniotic membrane and limbal epithelial stem cells. A total of 10 eyes underwent pterygium excision with amniotic membrane coverage of the bare sclera and placement of pieces of limbal epithelium in a linear fashion in the affected limbal area covered by a second amniotic membrane using fibrin glue. After up to 8 months of follow-up, there were no signs of early recurrence or sight-threatening complications. The minor ipsilateral simple limbal epithelial transplantation technique for the treatment of pterygium requires less tissue than the conventional conjunctival autograft, leaving healthy conjunctiva if needed for another procedure in the future and offers the advantages of epithelial stem cells, which in the long term may reduce the rate of recurrence significantly.

Amniotic membrane transplantation in surgical management of ocular surface squamous neoplasias: long-term results

OBJECTIVE

To evaluate the long-term efficacy of amniotic membrane transplantation for ocular surface reconstruction in the surgical management of ocular surface squamous neoplasia (OSSN).

METHODS

OSSN in 21 patients (7 female, 14 male patients) was managed with excisional biopsy, cryotherapy, corneal epitheliectomy with absolute alcohol application when the cornea is involved, lamellar sclerectomy and adjunctional absolute alcohol application to the base when episclera is involved, and ocular surface reconstruction with cryopreserved amniotic membrane transplantation. Tumor control and complications were evaluated.

RESULTS

The mean age of the patients was 62.42 ± 20.9 (range, 16-84). The average diameter of the base of the tumors was 13.1 ± 4.8 (range, 9-21) mm and complete removal was achieved in all cases as revealed histopathologically. Ocular surface healing was achieved in all cases. At the postoperative period, limbal stem cell deficiency in three eyes and mild symblepharon in one eye were detected. In a mean follow-up of 30.95 ± 18.8 (range, 13-75) months, no recurrence was detected.

CONCLUSION

For large or multifocal conjunctival tumors, the reconstruction of ocular surface and fornix is challenging. The amniotic-membrane use to repair conjunctival defects larger than 10 mm is a safe and effective technique with minimal complications allowing surgeons to make large enough excisions.

Vitrified collagen-based conjunctival equivalent for ocular surface reconstruction

The main functions of the conjunctiva, an essential part of the ocular surface, are to maintain the equilibrium of the tear film and to protect the eye. Upon injuries, the prerequisite to successful ocular surface repair is conjunctival reconstruction. Tissue engineering techniques, including transplantation of autografts, amniotic membranes and numerous synthetic/natural materials, have been developed. However, none of these strategies is completely satisfactory due to lack of goblet cell repopulation, poor mechanical properties or non-standardized preparation procedure. Here, we cultured conjunctival epithelial cells on vitrified collagen membranes and developed a tissue equivalent for repairing damaged conjunctiva. Optimized vitrified collagen has superior mechanical and optical properties to previous biomaterials for ocular surface application, and its unique fibrillar structure significantly benefited conjunctival epithelial cell growth and the phenotypic development in vitro. In a rabbit model, vitrified collagen greatly promoted conjunctival regeneration with rapid re-epithelization, sufficient repopulation of goblet cells and minimized fibrosis and wound contracture, proved by gene expression analyses and histological staining. In conclusion, we have demonstrated the potential suitability of utilizing vitrified collagen-based tissue equivalent in ocular surface reconstruction.

Inductive differentiation of conjunctival goblet cells by γ-secretase inhibitor and construction of recombinant conjunctival epithelium

γ-secretase inhibitor has been shown to promote intestinal goblet cell differentiation. We now demonstrated that the in vitro addition of γ-secretase inhibitor in the culture of human conjunctival epithelial cells significantly promoted the differentiation of conjunctival goblet cells with typical droplet-like phenotype, positive periodic acid-Schiff and goblet cell-specific Muc5Ac, cytokeratin 7 and Helix pomatia agglutinin lectin staining. Moreover, topical application of γ-secretase inhibitor promoted the differentiation of mouse conjunctival goblet cells in vivo. Furthermore, the expression of Notch target gene HES-1 was down-regulated during the differentiation of conjunctival goblet cells. In addition, we found that the recombinant conjunctival epithelium on amniotic membrane showed less goblet cell density and abnormal location when compared with normal conjunctival epithelium, which were improved by the addition of γ-secretase inhibitor in the final induction.

Coculture of autologous limbal and conjunctival epithelial cells to treat severe ocular surface disorders: long-term survival analysis

BACKGROUND

Cultivated limbal epithelium for reconstruction of corneal surface is a well-established procedure; however, it is not adequate for damage which also extensively involves the conjunctiva. In severe cases of ocular surface damage that warrant additional conjunctival transplantation apart from cultivated limbal stem cell transplantation, we describe the long-term survival of a novel method of cocultivating autologous limbal and conjunctival epithelium on a single substrate.

MATERIALS AND METHODS

Forty eyes of 39 patients with severe limbal stem cell deficiency and conjunctival scarring or symblepharon underwent transplantation of autologous cocultivated epithelium on human amniotic membrane. A ring barrier was used to segregate the central limbal and peripheral conjunctival epithelia in vitro. Patients were followed up at regular intervals to assess stability of the ocular surface, defined by absence of conjunctivalization into the central 4 mm of the cornea and absence of diffuse fluorescein staining. Penetrating keratoplasty (PKP) was subsequently performed, where indicated, in patients with surface stability.

RESULTS

The cumulative survival probability was 60% at 1 year and 45% at 4 years by Kaplan-Meier analysis (mean follow-up duration: 33 ± 29 months, range: 1-87 months). Best-corrected visual acuity improved to greater than 20/200 in 38% eyes at the last follow-up, compared with 5% eyes before surgery. Immunohistochemistry in five of the corneal buttons excised for PKP showed an epithelial phenotype similar to cornea in all five.

CONCLUSIONS

Synchronous use of cultured limbal and conjunctival epithelium offers a feasible alternative and a simpler one-step surgical approach to treat severe ocular surface disorders involving limbus and conjunctiva.

Amniotic membrane properties and current practice of amniotic membrane use in ophthalmology in Slovenia

Amniotic membrane (AM) is the innermost, multilayered part of the placenta. When harvested, processed and stored properly, its properties, stemming from AM biological composition, make it a useful tissue for ophthalmic surgery. AM was shown to have several beneficial effects: it promotes epithelization, has antimicrobial effects, decreases inflammation, fibrosis and neovascularization. Many case reports and case series as well as practical experience (e.g. reconstruction of conjunctival and corneal defects, treatment of corneal ulcers) demonstrated the beneficial effect of AM for different ophthalmological indications. The combination of the above mentioned beneficial effects and reasonable mechanical properties are also the reason why AM is used as a substrate for ex vivo expansion of epithelial progenitor cells. Recently, amnion-derived cells, which also have stem cell characteristics, have been proposed as potential contributors to cell-based treatment of ocular surface disease. However, the use of AM remains one of the least standardized methods in ophthalmic surgery. In this review, the various properties of AM and its current clinical use in ophthalmology in Slovenia are discussed.

[Characterization of epithelial primary culture from human conjunctiva]

OBJECTIVE

To evaluate primary cultures from human conjunctiva supplemented with fetal bovine serum, autologous serum, and platelet-rich autologous serum, over human amniotic membrane and lens anterior capsules.

METHODS

One-hundred and forty-eight human conjunctiva explants were cultured in CnT50(®) supplemented with 1, 2.5, 5 and 10% fetal bovine serum, autologous serum and platelet-rich autologous serum. Conjunctival samples were incubated at 37°C, 5% CO2 and 95% HR, for 3 weeks.

RESULTS

The typical phenotype corresponding to conjunctival epithelial cells was present in all primary cultures. Conjunctival cultures had MUC5AC-positive secretory cells, K19-positive conjunctival cells, and MUC4-positive non-secretory conjunctival cells, but were not corneal phenotype (cytokeratin K3-negative) and fibroblasts (CD90-negative).

CONCLUSIONS

Conjunctiva epithelial progenitor cells were preserved in all cultures; thus, a cell culture in CnT50(®) supplemented with 1 to 5% autologous serum over human amniotic membrane can provide better information of epithelial cell differentiation for the conjunctival surface reconstruction.

Transplantation of conjunctival epithelial cells cultivated ex vivo in patients with total limbal stem cell deficiency

PURPOSE

To report the outcomes of transplantation of autologous conjunctival epithelial cells cultivated ex vivo (EVCAU) in patients with total limbal stem cell deficiency (LSCD).

METHODS

EVCAU were cultivated on denuded human amniotic membrane and transplanted in 12 eyes of 10 patients with total LSCD. We evaluated the improvement in the defined clinical parameters of LSCD (loss of corneal epithelial transparency, superficial corneal neovascularization and epithelial irregularity/recurrent epithelial breakdown), vision acuity, impression cytology, immunocytochemical analysis (CK3/CK19), and the appearance of a regular hexagonal basal layer of cells on corneal confocal microscopy. Histologic and immunohistochemical features were studied in 3 corneal buttons of patients submitted to penetrating keratoplasty after EVCAU.

RESULTS

Cultivated conjunctival epithelium formed 4 to 5 layers with the formation of basement membrane-like structures. Immunocytochemical analysis showed positivity for CK3, CK19, MUC5AC, Ki-67, P63, and ABCG2. The improvement of the clinical parameters for this treatment in our cohort was 10 of 12 (83.3%) in a mean follow-up time of 18.5 months (range, 15-26 months), and these eyes showed an improvement in impression cytology, immunocytochemistry, and in vivo confocal analysis. Corneal buttons showed a well-formed epithelium with 5 to 6 layers, with rare cells periodic acid-Schiff+, and positivity for CK3, CK19, P63, connexin 43, and MUC5AC.

CONCLUSION

We demonstrated the preliminary results of transplantation of EVCAU for corneal surface reconstruction in cases with total LSCD. Future studies are needed to further assess the long-term efficacy of this procedure.

Ex-vivo ocular surface stem cell therapies: current techniques, applications, hurdles and future directions

Engineered tissue derived from ocular surface stem cells (SCs) are a cutting edge biotechnology for repair and restoration of severely damaged eyes as a result of ocular surface dysfunction because of SC failure. Ex-vivo SC expansion techniques have advanced significantly since the first patients were treated in the late 1990s. The techniques and clinical reports reviewed here highlight the evolution and successes of these techniques, while also revealing gaps in our understanding of ocular surface and SC biology that drives further research and development in this field. Although hurdles still remain before stem-cell-based therapies are more widely available for patients with devastating ocular surface disease, recent discoveries in the field of mesenchymal SCs and the potential of induced pluripotent SCs heralds a promising future for clinicians and our patients.

Biopsy harvesting site and distance from the explant affect conjunctival epithelial phenotype ex vivo

The purpose of the study was to investigate if the number of goblet cells expanded ex vivo from a conjunctival explant is affected by the biopsy harvesting site on the conjunctiva and the distance from the explant. Conjunctival explants from six regions: superior and inferior bulbus, fornix, and tarsus of male Sprague-Dawley rats were grown in RPMI 1640 with 10% fetal bovine serum on coverslips for eight days. Histochemical and immunofluorescent staining of goblet (CK-7/UEA-1/MUC5AC), stratified squamous, non-goblet (CK-4), proliferating (PCNA) and progenitor (ABCG2) cells were analyzed by epifluorescence and laser confocal microscopy. Outgrowth was measured with NIH ImageJ. For statistical analysis the Mann-Whitney test and Spearman's rank-order correlation test were used. Cultures from superior and inferior fornix contained the most goblet cells as indicated by the presence of CK-7+, UEA-1+ and MUC5AC+ cells. Superior and inferior forniceal cultures displayed 60.8% ± 9.2% and 64.7% ± 6.7% CK-7+ cells, respectively, compared to the superior tarsal (26.6% ± 8.4%; P < 0.05), superior bulbar (31.0% ± 4.0%; P < 0.05), inferior bulbar (38.5% ± 9.3%; P < 0.05) and inferior tarsal cultures (27.7% ± 8.3%; P < 0.05). While 28.4% ± 6.3% of CK-7+ goblet cells co-labeled with PCNA, only 7.4% ± 1.6% of UEA-1+ goblet cells did (P < 0.01). CK-7+ goblet cells were located at a lower concentration close to the explant (39.8% ± 3.1%) compared to near the leading edge (58.2% ± 4.5%; P < 0.05). Both markers for goblet cell secretory product (UEA-1 and MUC5AC), however, displayed the opposite pattern with a higher percentage of positive cells close to the explant than near the leading edge (P < 0.05). The percentage of CK-4+ cells was higher near the explant compared to near the leading edge (P < 0.01). The percentage of CK-7+ goblet cells in the cultures did not correlate with the outgrowth size (r(s) = -0.086; P = 0.435). The percentage of UEA-1+ goblet cells correlated negatively with outgrowth size (r(s) = -0.347; P < 0.01), whereas the percentage of CK-4+ cells correlated positively with the outgrowth size (r(s) = 0.473; P < 0.05). We conclude that forniceal explants yield the highest number of goblet cells ex vivo and thereby seem to be optimal for goblet cell transplantation. We also suggest that CK-7+/UEA-1- cells represent highly proliferative immature goblet cells. These cells could be important during conjunctival migration as they are mostly located close to the leading edge and their density does not decrease with increasing outgrowth size.

Effects of serum-free storage on morphology, phenotype, and viability of ex vivo cultured human conjunctival epithelium

The use of amniotic membrane (AM) represents one of the major developments in ocular surface reconstruction. However, in a study on patients with primary pterygium, transplantation of AM with ex vivo expanded human conjunctival epithelial cells (HCjE) promoted earlier epithelialization than AM alone. We previously showed that cultured human limbal epithelial cells maintain their morphology, phenotype, and viability for one week when stored at 23°C. The current study investigates the feasibility of storing HCjE in HEPES-MEM and Optisol-GS at 23°C for 4 and 7 days, respectively. The five experimental groups were analyzed by light microscopy, immunohistochemistry, transmission electron microscopy, and a viability assay. The ultrastructural integrity of cultured HCjE was well preserved following 4 days of storage, however, 7 days of storage resulted in some loss of cell-cell contacts and epithelial detachment from the amniotic membrane. The number of microvilli in cultured HCjE not subjected to storage was 2.03±0.38 microvilli/μm. In comparison, after 4 and 7 days of HEPES-MEM storage this number was 1.69±0.54 microvilli/μm; P=0.98 and 0.89±1.0 microvilli/μm; P=0.28, respectively. After Optisol-GS storage for 4 and 7 days, the mean number of microvilli was 1.07±1.0 microvilli/μm; P=0.47 and 0.07±0.07 microvilli/μm; P=0.03, respectively. The number of cell layers in cultured HCjE not subjected to storage was 4.4±0.3 cell layers, as opposed to 4.0±0.9 cell layers; P=0.89 after 4 days of HEPES-MEM storage and 2.8±0.6 cell layers; P=0.01 after 7 days of storage in HEPES-MEM. The number of cell layers after 4 and 7 days of storage in Optisol-GS was 3.7±0.2 cell layers; P=0.46 and 3.4±0.4 cell layers; P=0.18, respectively. The expression of markers for undifferentiated cells (ΔNp63α, ABCG2 and p63), proliferating cells (Ki67 and PCNA), goblet cells (Ck7 and MUC5AC), stratified squamous epithelial cells (Ck4), and apoptotic cells (caspase-3) in cultured HCjE appeared to be unchanged after 4 and 7 days of HEPES-MEM and Optisol-GS storage. The percentage of viable cells in cultured HCjE not subjected to storage (91.4%±3.2%) was sustained after 4 and 7 days of storage in HEPES-MEM (94.1%±4.5%; P=0.99 and 85.1%±13.7%; P=0.87, respectively) as well as after 4 and 7 days of storage in Optisol-GS (87.7%±15.2%; P=0.97 and 79.8%±15.7%; P=0.48, respectively). We conclude that cultured HCjE may be stored for at least 4 days in serum-free conditions at 23°C while maintaining the phenotype and viability. HEPES-MEM appears to be comparable to Optisol-GS for serum-free storage with preservation of the ultrastructure for at least 4 days.

Ocular epithelial transplantation: current uses and future potential

Visual loss may be caused by a variety of ocular diseases and places a significant burden on society. Replacing or regenerating epithelial structures in the eye has been demonstrated to recover visual loss in a number of such diseases. Several types of cells (e.g., embryonic stem cells, adult stem/progenitor/differentiated epithelial cells and induced pluripotent cells) have generated much interest and research into their potential in restoring vision in a variety of conditions: from ocular surface disease to age-related macular degeneration. While there has been some success in clinical transplantation of conjunctival and particularly corneal epithelium utilizing ocular stem cells, in particular, from the limbus, the replacement of the retinal pigment epithelium by utilizing stem cell sources has yet to reach the clinic. Advances in our understanding of all of these cell types, their differentiation and subsequent optimization of culture conditions and development of suitable substrates for their transplantation will enable us to overcome current clinical obstacles. This article addresses the current status of knowledge concerning the biology of stem cells, their progeny and the use of differentiated epithelial cells to replace ocular epithelial cells. It will highlight the clinical outcomes to date and their potential for future clinical use.

Update on amniotic membrane transplantation

Cryopreserved amniotic membrane modulates adult wound healing by promoting epithelialization while suppressing stromal inflammation, angiogenesis and scarring. Such clinical efficacies of amniotic membrane transplantation have been reported in several hundred publications for a wide spectrum of ophthalmic indications. The success of the aforementioned therapeutic actions prompts investigators to use amniotic membrane as a surrogate niche to achieve ex vivo expansion of ocular surface epithelial progenitor cells. Further investigation into the molecular mechanism whereby amniotic membrane exerts its actions will undoubtedly reveal additional applications in the burgeoning field of regenerative medicine. This article will focus on recent advances in amniotic membrane transplantation and expand to cover its clinical uses beyond the ocular surface.

Tissue engineering for conjunctival reconstruction: established methods and future outlooks

Reconstruction of the conjunctiva is an essential part of ocular surface regeneration, especially if an extensive area or the whole ocular surface is affected, such as in patients with ocular cicatricial pemphigoid, Stevens-Johnson syndrome, toxic epidermal necrolysis, or chemical/thermal burns. In these situations, corneal reconstruction almost inevitably fails unless the conjunctival surface is first repaired and a deep fornix is restored. The growing field of tissue engineering and advances in stem cell research offer promising new alternatives for these challenges. This article reviews the present approaches for reconstruction of the conjunctival surface, considering the established strategies and new potential methodologies.

Epithelial stem cells of the eye surface

OBJECTIVES

Epithelial stem cells of the eye surface, of the cornea and of the conjunctiva, have the ability to give rise to self renewal and progeny production of differentiated cells with no apparent limit. The two epithelia are separated from each other by the transition zone of the limbus. The mechanisms adopted by stem cells of the two epithelia to accomplish their different characteristics, and how their survival, replacement and unequal division that generates differentiated progeny formation are controlled, are complex and still poorly understood. They can be learned only by understanding how stem cells/progenitors are regulated by their neighbouring cells, that may themselves be differently unspecialised, forming particular microenvironments, known as 'niches'. Stem cells operate by signals and a variety of intercellular interactions and extracellular substrates with adjacent cells in the niche. Technical advances are now making it possible to identify zones in the corneal limbus and conjunctiva that can house stem cells, to isolate and expand them ex vivo and to control their behaviour creating optimal niche conditions. With improvements in biotechnology, regenerative cornea and conjunctiva transplantation using adult epithelial stem cells becomes now a reality.

RESULTS AND CONCLUSIONS

Here we review our current understanding of stem cell niches and illustrate recent significant progress for identification and characterization of adult epithelial stem cells/progenitors at cellular, molecular and mechanistic levels, improvement in cell culture techniques for their selective expansion ex vivo and prospects for a variety of therapeutic applications.

Current prospects for adult stem cell-based therapies in ocular repair and regeneration

Recent advances in stem cell biology have led to the exploration of stem cell-based therapies to treat a wide range of human diseases. In the ophthalmic field, much hope has been placed on the potential use of these cells to restore sight, particularly in those conditions in which other established treatments have failed and in which visual function has been irreversibly damaged by disease or injury. At present, there are many limitations for the immediate use of embryonic stem cells to treat ocular disease, and as more evidence emerges that adult stem cells are present in the adult human eye, it is clear that these cells may have advantages to develop into feasible therapeutic treatments without the problems associated with embryonic research and immune rejection. Here we discuss the current prospects for the application of various adult ocular stem cells to human therapies for restoration of vision.

Enhancement of the Mechanical and Biological Properties of a Biomembrane for Tissue Engineering the Ocular Surface

Introduction: In this study, we have developed and optimised a novel gelatin-chitosan (GC) substrate for use as a cellular carrier for tissue-engineered conjunctival epithelium. Materials and Methods: The substrate was fabricated by casting and the mechanical properties of the substrate, including tensile strength and elongation, were measured. Using the MTT, cell proliferation assay with rabbit conjunctival fibroblasts, we optimised the G:C ratio to enhance cytocompatibility. Rabbit conjunctival epithelial cells were immunostained using monoclonal antibodies for keratin 4 and pancytokeratin to investigate the biological effects of the GC substrate on the proliferation and differentiation of epithelial cells. Results: We found that increasing the amount of gelatin resulted in an increase in elasticity (from 1:9 to 1:1 ratio), reaching a maximum (101.89% ± 7.13%) at a ratio of 1:1. The MTT assay showed that the proliferation of conjunctival fibroblasts significantly increased from 0.068 ± 0.017 to 0.177 ± 0.011 (P = 0.014) as the gelatin was increased from 20% (1:4) to 50% (1:1). Additional studies using tissue-cultured conjunctiva explants showed that these explants grew well on the substrate, forming a multilayered epithelium. Cell morphology on this substrate was similar to that of cells grown on culture dishes alone. Positive staining of keratin 4 and pancytokeratin indicated that the substrate supported normal differentiation of conjunctival epithelial cells. Conclusion: By enhancing the proportion of gelatin, both the mechanical and biological properties of the chitosan substrate were improved. The results also suggest that this GC biomembrane may be a useful candidate for reconstructive tissue engineering of the conjunctiva.

Cell markers and the side population phenotype in ocular surface epithelial stem cell characterization and isolation

The ocular surface is covered by tworapidly renewing and embryologically-related linings, the corneal and conjunctival epithelia. The long-term survival of thesetissues is ultimately dependent on their respective resident stem cells. In the corneal epithelium, the stem cells and their early precursors are exclusively circumscribed to the narrow vasscularize limbal rim that provides epithelial precursor cells to the critically transparent central cornea. Limbal damage causes an interruption of this essential cell supply and allows the invasion of the corneal surface by the conjunctival epithelium, an event that ultimately leads to corneal scarring. The limited supply of immunocompatible tissue is a major hindrance to efforts to develop effective procedures for ocular surface reconstruction. This review describes some of the current work and strategies being developed to achieve the isolation of the limbal stem cell and define its genetic, biochemical, and functional make-up. The study of isolated ocular surface stem cells will foster basic understanding of the environmentalrequisites for their survival and proliferation in a self-replicative mode, leading eventually to advances in therapeutic approaches.

Amniotic Membrane Transplantation for Ocular Surface Reconstruction

The amniotic membrane, composed of 3 layers, the epithelium, basement membrane, and the stroma, was first used along with the chorion as a biologic membrane to promote healing of skin burns in 1910. In ophthalmology, it was used in 1940 in the management of conjunctival defects. Its revival in the 1990s was due to its ability to reduce ocular surface inflammation and scarring, promote rapid epithelialization due to the presence of growth factors, and antimicrobial properties. This has resulted in its application in several ocular disorders. A review of the literature shows that amniotic membrane is definitely beneficial in some but not all pathology. The future of amniotic membrane transplantation is very exciting, especially in the field of limbal stem cell research. However, further work is needed to elucidate whether it functions merely as a biologic contact lens or whether it has additional benefits.

The use of human serum in supporting the in vitro and in vivo proliferation of human conjunctival epithelial cells

AIM

To evaluate the use of human serum (HS) in supporting the in vitro and in vivo proliferation of human conjunctival epithelial cells, and compare it with fetal bovine serum (FBS) and bovine pituitary extract (BPE).

METHODS

Conjunctival epithelial cells were cultivated in media supplemented with HS (5%, 10%), FBS (5%, 10%), and BPE (70 microg/ml, 140 microg/ml). The colony forming efficiency (CFE), bromodeoxyuridine (BrdU) ELISA proliferation assay, and cell generations were analysed. Cells were evaluated for keratin (K4, K19, and K3) and MUC5AC expression by immunostaining and RT-PCR. Conjunctival equivalents constructed on amniotic membranes were transplanted onto severe combined immune deficient (SCID) mice for 10 days and analysed histologically.

RESULTS

The proliferation assays of HS supplemented cultures (CFE, 6.7% (SD 1.8%); BrdU absorbance, 0.86 (0.16)) were comparable to FBS supplemented (CFE, 9.3% (1.8%); BrdU absorbance, 1.11 (0.18)) and BPE supplemented cultures (CFE, 5.9 (1.5); BrdU absorbance, 0.65 (0.12)). Goblet cell densities for HS, FBS, and BPE supplemented media were 52 cells/cm(2), 60 cells/cm(2), and 50 cells/cm(2), respectively. HS supplemented cultures formed stratified epithelial sheets in vivo following transplantation.

CONCLUSIONS

The proliferative capacity of conjunctival epithelial cells cultivated in HS supplemented cultures was comparable to FBS and BPE supplemented cultures. The elimination of animal material from the culture system is advantageous when cultivating cells for clinical transplantation.

Stem cells in the eye

In the adult organism, all tissue renewal and regeneration depends ultimately on somatic stem cells, and the eye is no exception. The importance of limbal stem cells in the maintenance of the corneal epithelium has long been recognised, and such cells are now used clinically for repair of a severely damaged cornea. The slow cycling nature of lens epithelial cells and their ability to terminally differentiate into fiber cells are suggestive of a stem cell lineage. Furthermore, recent studies have identified progenitor cells in the retina and ocular vasculature which may have important implications in health and disease. Although the recent literature has become flooded with articles discussing aspects of stem cells in a variety of tissues our understanding of stem cell biology, especially in the eye, remains limited. For instance, there is no definitive marker for ocular stem cells despite a number of claims in the literature, the patterns of stem cell growth and amplification are poorly understood and the microenvironments important for stem cell regulation and differentiation pathways are only now being elucidated. A greater understanding of ocular stem cell biology is essential if the clinical potential for stem cells is to be realised. For instance; How do we treat stem cell deficiencies? How do we use stem cells to regenerate damaged retinal tissue? How do we prevent stem cell lineages contributing to retinal vascular disease? This review will briefly consider the principal stem cells in the mature eye but will focus in depth on limbal stem cells and corneal epithelium. It will further discuss their role in pathology and their potential for therapeutic intervention.

Amniotic membrane as support for human retinal pigment epithelium (RPE) cell growth

PURPOSE

The aim of this work was to culture human retinal pigment epithelium (hRPE) cells over human amniotic membrane (hAM). Human AM was studied for its viability as an adequate support for transplantation of an hRPE cell monolayer with preserved cell polarity to the subretinal space.

METHODS

Human AM was obtained from pregnant women during caesarean section. The hAM was sectioned and the pieces were fixed to culture dishes. Human RPE cells were cultured from adult corneal donors and were seeded over hAM. Phase-contrast photographs were obtained. Selected specimens were processed by transmission electronic microscopy (TEM).

RESULTS

The attachment and growth of hRPE cells over hAM was observed. Human RPE cells constituted tight colonies that maintained epithelial phenotype. Using TEM, we identified a monolayer of hRPE cells, with cuboidal to spheroidal morphology. These cells showed integration with the substrate and cell-cell contacts were detected.

CONCLUSION

Amniotic membrane may be a suitable substrate for hRPE growth. Further studies are required in order to determine the viability of hRPE on hAM in the subretinal space.

Gap junctional communication in microinjected human limbal and peripheral corneal epithelial cells cultured on intact amniotic membrane

The aim of the study was to determine if human limbal epithelial cells (HLEC) do not form gap junctions (GJ) during ex vivo expansion on preserved and intact human amniotic membrane (AM). Thereby, we attempt to evaluate if characteristic features of the limbal epithelial progenitor cells are preserved on AM. Primary human limbal (HLEC) and peripheral corneal (HPCEC) epithelial cells from limbal and peripheral corneal explants were cultured with SHEM either on intact AM or plastic. After 3-4 weeks, cell cultures were terminated and processed for immunofluorescence. In all cell cultures, formations of GJs were analyzed with a mouse monoclonal antibody to connexin 43 (Cx43) and a rabbit affinity purified antibody against connexin 26 (Cx26). Sections of human limbus and cornea served as positive control. Lucifer yellow (LY) known to be a GJ permeant dye was used to analyse functionality of GJ. Microinjection of LY into single cells was performed with a pressure microinjection device under visual control and with the aid of phase contrast optics. Dye spread of LY into adjacent cells indicating intercellular communication was compared between HLEC and HPCEC cultured either on AM or plastic. In vivo, a punctate pattern of Cx43 was typically found in basal and suprabasal corneal epithelial cells and labeling for Cx26 was observed in all cell layers of the human corneal epithelium, however, subpopulations of limbal basal epithelial cells lacked detectable fluorescence signals for both connexins. In HLEC cultured on AM, a scanty immunolabeling for Cx43 (12.6%) was noted, but HPCEC cultured on AM as well as HLEC cultured on plastic showed a higher labeling index (LI) for Cx43 (42.7 and 52.3%, respectively). A significant lower immunostaining for Cx26 was observed in HLEC cultured on AM (LI: 35.16%) in comparison to HLEC cultured on plastic (68.4%), as well as, HPCEC cultured either on AM or plastic (61% and 79.3%, respectively; p<0.001). Gap junctional communication was evidenced more frequently in HLEC cultured on plastic (51%, p<0.05) in contrast to HLEC cultures on AM, which exhibited a limited dye spread in 29.7% of injected cells. A significant difference in dye coupling was also evidenced between HPCEC on AM (52.9%; p<0.05) and HLEC on AM. Subpopulations of HLEC cultured on AM remain Cx43 and Cx26 negative and without functional GPs indicating that characteristic features of limbal epithelial progenitor cells might be preserved during ex-vivo expansion on AM. These data provide support to the use of the ex-vivo expansion of HLEC as an alternative therapeutic strategy for corneal surface reconstruction in distinct ocular surface diseases.