Human corneal limbal organoids maintaining limbal stem cell niche function.

Corneal epithelial stem cells reside in the limbal area between the cornea and conjunctiva. We examined the potential use of limbal organoids as a source of transplantable limbal stem cells. After treating tissue with collagenase, limbal cells were seeded onto Matrigel and cultivated using limbal phenotype maintenance medium. After 1-month, approximately 500 organoids were formed from one donor cornea. Organoids derived from vertical sites (superior and inferior limbus) showed large colony forming efficiency, a higher ratio of slow cycling cells and N-cadherin-expressing epithelial cells compared to horizontal sites. The progenitor markers Keratin (K) 15 and p63 were expressed in epithelial sheets engineered form a single organoid. Organoids transplanted in the limbus of a rabbit limbal deficiency model confirmed the presence of organoid-derived cells extending on to host corneas by immunohistochemistry. Our data show that limbal organoids with a limbal phenotype can be maintained for up to 1 month in vitro which can each give rise to a fully stratified corneal epithelium complete with basal progenitor cells. Limbal organoids were successfully engrafted in vivo to provide epithelial cells in a rabbit limbal deficiency model, suggesting that organoids may be an efficient cell source for clinical use.

Corneal Endothelial Regeneration Using Mesenchymal Stem Cells Derived from Human Umbilical Cord.

Corneal blindness is the third leading cause of blindness in the world, and one of the main etiologies is dysfunction of the corneal endothelium. Current treatment of corneal endothelial disease is allogenic corneal transplantation, which is limited by the global shortage of donor corneas and immunological rejection. The corneal endothelium consists of a monolayer of cells derived from the neural crest and mesoderm. Its main function is to prevent corneal edema by tight junctions formed by zonular occludens-1 (ZO-1) and Na, K-ATPase pump function. The human umbilical cord (UC) is a rich source of mesenchymal stem cells (MSCs). UC-MSCs that have multi-lineage potential may be an accessible allogenic source. After inducing differentiation with medium containing glycogen synthase kinase (GSK) 3-ß inhibitor, UC-MSCs formed polygonal corneal endothelial-like cells that functioned as tissue-engineered corneal endothelium (UTECE). Expressions of major corneal endothelial markers were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and quantitative RT-PCR (qRT-PCR). Western blotting confirmed the expression of Na,K-ATPase and PITX2, the functional and developmental markers of corneal endothelial cells. Immunohistochemistry revealed the localization of Na,K-ATPase and ZO-1 in cell-cell junctions, suggesting the presence of tight junctions. In vitro functional analysis revealed that UTECE had significantly high pump function compared with UC-MSCs. Moreover, UTECE transplanted into a rabbit model of bullous keratopathy successfully maintained corneal thickness and transparency. Our findings suggest that UTECE may be used as a source of allogenic cells for the treatment of corneal endothelial disease.

Long-term homeostasis and wound healing in an in vitro epithelial stem cell niche model.

Cultures of epithelial cells are limited by the proliferative capacity of primary cells and cell senescence. Herein we show that primary human epithelial cell sheets cultured without dermal equivalents maintained homeostasis in vitro for at least 1 year. Transparency of these sheets enabled live observation of pigmented melanocytes and Fluorescent Ubiquitination-based Cell Cycle Indicator (FUCCI) labeled epithelial cells during wound healing. Cell turn over and KRT15 expression pattern stabilized within 3 months, when KRT15 bright clusters often associated with niche-like melanocytes became apparent. EdU labels were retained in a subset of epithelial cells and melanocytes after 6 months chasing, suggesting their slow cell cycling property. FUCCI-labeling demonstrated robust cell migration and proliferation following wounding. Transparency and long-term (1 year) homeostasis of this model will be a powerful tool for the study of wound healing and cell linage tracing.

Expression and distribution of claudin subtypes in human corneal endothelium.

PURPOSE: To investigate the expression pattern of claudins in human corneal endothelium, and to evaluate the functional role of the claudin-10b subtype. METHODS: Corneal endothelium with Descemet's membrane and the corneal epithelium were stripped from donor human corneal stroma. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate the claudin subtypes expressed in corneal endothelium, stroma, and epithelium. Immunohistochemistry was performed to confirm the expression of claudin subtypes in corneal endothelium, and the expression pattern was compared to that of corneal epithelium. Finally, transendothelial resistance (TER), short-circuit current (SCC), and potential difference (PD) were measured in human corneal endothelial cell line B4G12 cells with or without claudin-10 small interfering RNA (siRNA) transfection by Ussing chamber system. RESULTS: Transcripts for claudin-1, -2, -3, -4, -7, -10b, -11, -15, -22, -23, and -24 were identified in corneal endothelium sample by RT-PCR. Immunohistochemistry confirmed the expression of claudin-1, -2, -4, -7, -10, -11 -15, -22, and -23 in corneal endothelium. In corneal stroma, claudin-1, -2, -3, -4, -5, -6, -7, -8, -10b, -11, -12, -14, -15, -22, -23, and -24 were identified by RT-PCR. In corneal epithelium, claudin-1, -3, -4, -7, -11, -14, and -23 were identified by immunohistochemistry and RT-PCR. Downregulation of claudin-10b by siRNA resulted in the decrease of SCC and PD, but not TER, in B4G12 cells. CONCLUSIONS: The expression pattern of claudin-10b(+)/claudin-14(-) was specific in corneal endothelium among the three corneal layers. Claudin-10b may play an important role in the tight junction of corneal endothelium.

Long-term maintenance of limbal epithelial progenitor cells using rho kinase inhibitor and keratinocyte growth factor.

Corneal epithelial stem cells are located in the limbus, the junction between the cornea and the conjunctiva. A limbal epithelium model in vitro would be useful for the study of epithelial stem cells, as well as improving the quality of cultivated epithelial sheets for the treatment of limbal stem cell deficiency. In this study, we succeeded in constructing a limbal epithelium-like structure that could be maintained for at least 5 months in vitro. We modified conventional medium by replacing epidermal growth factor with keratinocyte growth factor (KGF) and adding Y-27632, a rho kinase inhibitor. Using this medium, epithelial cells freshly isolated from human limbus were cocultured with human mesenchymal stem cell-derived feeder cells. Cells formed a stratified layer without air exposure, and both basal and suprabasal layers maintained their unique morphologies for up to 5 months. Basal layers expressed the progenitor marker p63 uniformly and K15 heterogeneously. Expressions of PAX6, K3, and K12 indicated that cell sheets underwent normal differentiation in the corneal epithelium lineage. Although medium was changed daily after day 7, cell debris was observed every day, suggesting that cell sheets underwent turnover. Furthermore, secondary colonies were observed from cells dissociated from 1-month and 3-month cultured sheets. In conclusion, human limbal epithelial cell sheet cultures with KGF and Y-27632 maintained stratification, high expression of both stem/progenitor markers and differentiation markers, and colony-forming cells long-term. This protocol may be useful as an in vitro limbal epithelial model for basic studies.

Angiotensin II type 1 receptor antagonist attenuates lacrimal gland, lung, and liver fibrosis in a murine model of chronic graft-versus-host disease.

Chronic graft-versus-host disease (cGVHD), a serious complication following allogeneic HSCT (hematopoietic stem cell transplantation), is characterized by systemic fibrosis. The tissue renin-angiotensin system (RAS) is involved in the fibrotic pathogenesis, and an angiotensin II type 1 receptor (AT1R) antagonist can attenuate fibrosis. Tissue RAS is present in the lacrimal gland, lung, and liver, and is known to be involved in the fibrotic pathogenesis of the lung and liver. This study aimed to determine whether RAS is involved in fibrotic pathogenesis in the lacrimal gland and to assess the effect of an AT1R antagonist on preventing lacrimal gland, lung, and liver fibrosis in cGVHD model mice. We used the B10.D2→BALB/c (H-2(d)) MHC-compatible, multiple minor histocompatibility antigen-mismatched model, which reflects clinical and pathological symptoms of human cGVHD. First, we examined the localization and expression of RAS components in the lacrimal glands using immunohistochemistry and quantitative real-time polymerase chain reaction (PCR). Next, we administered an AT1R antagonist (valsartan; 10 mg/kg) or angiotensin II type 2 receptor (AT2R) antagonist (PD123319; 10 mg/kg) intraperitoneally into cGVHD model mice and assessed the fibrotic change in the lacrimal gland, lung, and liver. We demonstrated that fibroblasts expressed angiotensin II, AT1R, and AT2R, and that the mRNA expression of angiotensinogen was greater in the lacrimal glands of cGVHD model mice than in controls generated by syngeneic-HSCT. The inhibition experiment revealed that fibrosis of the lacrimal gland, lung, and liver was suppressed in mice treated with the AT1R antagonist, but not the AT2R antagonist. We conclude that RAS is involved in fibrotic pathogenesis in the lacrimal gland and that AT1R antagonist has a therapeutic effect on lacrimal gland, lung, and liver fibrosis in cGVHD model mice. Our findings point to AT1R antagonist as a possible target for therapeutic intervention in cGVHD.

Functional corneal endothelium derived from corneal stroma stem cells of neural crest origin by retinoic acid and Wnt/ß-catenin signaling.

Corneal endothelial dysfunction remains a major indication for corneal transplantation. Both corneal endothelial cells and stromal cells originate from the neural crest, but have distinct phenotypes and function in the adult cornea. We previously reported that stem cells isolated from the adult corneal stroma [cornea-derived precursors (COPs)] show characteristics of multipotent neural crest-derived stem cells. In this study, we report the induction of functional tissue-engineered corneal endothelium (TECE) from mouse and human COPs. TECE was engineered from Wnt1-Cre/Floxed EGFP mouse COPs in a medium containing retinoic acid and glycogen synthase kinase (GSK) 3ß inhibitor (activator of Wnt/ß-catenin signaling). The expression levels of major markers characterizing corneal endothelial function (Atp1a1, Slc4a4, Car2, Col4a2, Col8a2, and Cdh2) were significantly upregulated. Both retinoic acid and GSK 3ß inhibitor upregulated the expression of Pitx2, a homeobox gene involved in the development of the anterior segment of the eye. GSK 3ß inhibitor increased Atp1a1 expression and Na,K-ATPase pump activity of TECE, which was significantly higher than COPs or control 3T3 cells, and 2.6-fold higher than cultured mouse corneal endothelial cells. Mouse TECE transplanted into rabbit corneas maintained transparency and corneal thickness, whereas control corneas without TECE showed marked edema and increased corneal thickness. Furthermore, we successfully induced TECE from human COPs, and human TECE transplanted into rabbit corneas also maintained corneal transparency and thickness. This protocol enables efficient production of corneal endothelium from corneal stromal stem cells by direct induction, which may lead to a novel stem cell therapy for corneal endothelial dysfunction.

The semaphorin 3A inhibitor SM-345431 accelerates peripheral nerve regeneration and sensitivity in a murine corneal transplantation model.

BACKGROUND: Peripheral nerve damage of the cornea is a complication following surgery or infection which may lead to decreased visual function. We examined the efficacy of the semaphorin 3A inhibitor, SM-345431, in promoting regeneration of peripheral nerves in a mouse corneal transplantation model. METHODOLOGY/PRINCIPAL FINDINGS: P0-Cre/Floxed-EGFP mice which express EGFP in peripheral nerves cells were used as recipients of corneal transplantation with syngeneic wild-type mouse cornea donors. SM-345431 was administered subconjunctivally every 2 days while control mice received vehicle only. Mice were followed for 3 weeks and the length of regenerating nerves was measured by EGFP fluorescence and immunohistochemistry against ßIII tubulin. Cornea sensitivity was also measured by the Cochet-Bonnet esthesiometer. CD31 staining was used to determine corneal neovascularization as a possible side effect of SM-345431. Regeneration of ßIII tubulin positive peripheral nerves was significantly higher in SM-345431 treated mice compared to control. Furthermore, corneal sensitivity significantly improved in the SM-345431 group by 3 weeks after transplantation. Neovascularization was limited to the peripheral cornea with no difference between SM-345431 group and control. CONCLUSIONS/SIGNIFICANCE: Subconjunctival injections of SM-345431 promoted a robust network of regenerating nerves as well as functional recovery of corneal sensation in a mouse keratoplasty model, suggesting a novel therapeutic strategy for treating neurotrophic corneal disease.

Generation of stratified squamous epithelial progenitor cells from mouse induced pluripotent stem cells.

BACKGROUND: Application of induced pluripotent stem (iPS) cells in regenerative medicine will bypass ethical issues associated with use of embryonic stem cells. In addition, patient-specific IPS cells can be useful to elucidate the pathophysiology of genetic disorders, drug screening, and tailor-made medicine. However, in order to apply iPS cells to mitotic tissue, induction of tissue stem cells that give rise to progeny of the target organ is required. METHODOLOGY/PRINCIPAL FINDINGS: We induced stratified epithelial cells from mouse iPS cells by co-culture with PA6 feeder cells (SDIA-method) with use of BMP4. Clusters of cells positive for the differentiation markers KRT1 or KRT12 were observed in KRT14-positive colonies. We successfully cloned KRT14 and p63 double-positive stratified epithelial progenitor cells from iPS-derived epithelial cells, which formed stratified epithelial sheets consisting of five- to six-polarized epithelial cells in vitro. When these clonal cells were cultured on denuded mouse corneas, a robust stratified epithelial layer was observed with physiological cell polarity including high levels of E-cadherin, p63 and K15 expression in the basal layer and ZO-1 in the superficial layer, recapitulating the apico-basal polarity of the epithelium in vivo. CONCLUSIONS/SIGNIFICANCE: These results suggest that KRT14 and p63 double-positive epithelial progenitor cells can be cloned from iPS cells in order to produce polarized multilayer epithelial cell sheets.

Clusterin promotes corneal epithelial cell growth through upregulation of hepatocyte growth factor by mesenchymal cells in vitro.

PURPOSE: Although the cornea expresses high levels of clusterin (CLU), the role of CLU in the cornea is poorly understood. This study was performed to investigate the possible role of CLU in corneal epithelial homeostasis. METHODS: CLU was overexpressed in 3T3 cells by transfection of a vector encoding full-length CLU (Clu-3T3). Colony-forming efficacy (CFE) was compared in mouse corneal cell line (TKE2) and human primary corneal/limbal epithelial cells that were cocultured with Clu-3T3 and mock-3T3. To determine whether feeder cells have a contact effect, cocultures without feeder-epithelium contact were also performed. Neutralizing antibody against CLU was used to assess the effects of secretory CLU in TKE2 cells cocultured with Clu-3T3 cells. The expression of growth factors associated with limbal stem/progenitor cell maintenance and growth were analyzed by RT-PCR and Western blot analysis. RESULTS: TKE2 cells cocultured with Clu-3T3 feeders showed higher CFE and were larger in colony size than TKE2 cells cocultured with mock-3T3 feeders. Increased CFE of TKE2 was observed without direct contact with Clu-3T3 cells, which was significantly blocked by treatment with CLU neutralizing antibody. Clu-3T3 cells expressed higher levels of HGF than mock-3T3 cells, which were significantly suppressed with anti-HGF neutralizing antibodies. Collectively, the promotion of colony-forming and cell proliferation by Clu-3T3 cells was partially mediated by the induction of HGF. CONCLUSIONS: Clusterin indirectly enhances the CFE of corneal/limbal epithelial cells by inducing the production of HGF by feeder cells, suggesting a role in epithelial-mesenchymal interaction.

Hydrogen and N-acetyl-L-cysteine rescue oxidative stress-induced angiogenesis in a mouse corneal alkali-burn model.

PURPOSE: To investigate the role of reactive oxygen species (ROS) as the prime initiators of the angiogenic response after alkali injury of the cornea and observe the effects of antioxidants in preventing angiogenesis. METHODS: The corneal epithelia of SOD-1-deficient mice or wild-type (WT) mice were removed after application of 0.15 N NaOH to establish the animal model of alkali burn. ROS production was semiquantitatively measured by dihydroethidium (DHE) fluorescence. Angiogenesis was visualized by CD31 immunohistochemistry. The effects of the specific NF-κB inhibitor DHMEQ, the antioxidant N-acetyl-L-cysteine (NAC), and hydrogen (H2) solution were observed. RESULTS: ROS production in the cornea was enhanced immediately after alkali injury, as shown by increased DHE fluorescence (P<0.01). NF-κB activation and the upregulation of vascular endothelial growth factor (VEGF) and monocyte chemoattractant protein-1 (MCP-1) were significantly enhanced (P<0.01), leading to a significantly larger area of angiogenesis. Angiogenesis in SOD-1-/- mice corneas were significantly higher in WT mice (P<0.01), confirming the role of ROS. Pretreatment with the specific NF-κB inhibitor DHMEQ or the antioxidant NAC significantly reduced corneal angiogenesis by downregulating the NF-κB pathway (P<0.01) in both WT and SOD-1-/- mice. Furthermore, we showed that irrigation of the cornea with hydrogen (H2) solution significantly reduced angiogenesis after alkali-burn injury (P<0.01). CONCLUSIONS: Immediate antioxidant therapy with H2-enriched irrigation solution is a new potent treatment of angiogenesis in cornea to prevent blindness caused by alkali burn.

The anti-oxidative role of ABCG2 in corneal epithelial cells.

PURPOSE: ABCG2 is a putative marker of progenitor cells, including the corneal epithelium. The authors investigated whether ABCG2 functions in the homeostasis of corneal epithelial cells using abcg2 knockout (KO) mice and corneal epithelial cell lines. METHODS: abcg2 KO mice and a spontaneously immortalized murine corneal epithelial cell line (TKE2) were used for experiments. Flow cytometry was used to determine the presence of side population (SP) cells based on the ability of ABCG2 to efflux Hoechst 33342 dye. Expression of ABCG2 was also examined by RT-PCR. Cytotoxicity assay (IC(50)) and propidium iodide staining were performed in semiconfluent cells treated with hypoxia (1% O(2)) or with the pro-oxidant mitoxantrone. RESULTS: abcg2 KO mice had a normal corneal epithelial phenotype; however, cultured abcg2 KO epithelial cells were prone to oxidative damage by mitoxantrone. TKE2 cells were resistant to mitoxantrone at low doses, but higher concentrations were toxic in a dose-dependent manner. Coculture with the ABCG2 inhibitors reserpine and Ko143 inhibited resistance to mitoxantrone, with a statistically higher cell death ratio. abcg2 KO cells were also significantly more sensitive to hypoxia than were wild-type control cells. CONCLUSIONS: ABCG2 may protect corneal epithelial progenitor SP cells against oxidative stress induced by toxins and hypoxia.

N-cadherin in the maintenance of human corneal limbal epithelial progenitor cells in vitro.

PURPOSE: To demonstrate the role of N-cadherin (N-cad) in maintaining the progenitor status of primary human limbal epithelial cells in vitro. METHODS: Immunohistochemistry and immunoelectron microscopy against N-cad was performed in human limbal tissue. The expression of N-cad, cytokeratin (K) 12, and K14 was also observed in primary cultured limbal epithelial cell colonies in 3T3 feeder cells, which also express N-cad. Laser microdissection of individual colonies was performed to separate central cells from peripheral cells to compare secondary colony formation. Finally, an artificial small interfering RNA (siRNA) expression vector was used to downregulate N-cad in 3T3 cells (N-cad(low) 3T3) to observe changes in colony formation and cultivated epithelial sheet phenotype. RESULTS: N-cad was expressed in clusters of basal limbal epithelial cells. Limbal epithelial cell colonies cocultured with N-cad(+) 3T3 feeder cells showed N-cad expression along the edge of each colony. When individual colonies were divided into peripheral and central sections by laser microdissection, peripheral cells had a significantly higher secondary colony-forming efficiency than did central cells. Furthermore, colonies using N-cad(low) 3T3 cells were significantly smaller than mock-transfected cells. Then a duplex-feeder model with two layers of either 3T3 or N-cad(low) 3T3 cells was used to produce stratified epithelial sheets. Only N-cad(+) 3T3 cells produced epithelial sheets with basal K15/ suprabasal K12 expression observed in limbal tissue. CONCLUSIONS: N-cad plays a pivotal role in the maintenance of the progenitor phenotype in cultured limbal epithelial cells.

Long-term culture and growth kinetics of murine corneal epithelial cells expanded from single corneas.

PURPOSE: To develop a reproducible procedure for the long-term culture of corneal epithelial cells from a single mouse cornea. METHODS: Corneal limbal explants of C57BL6/J mice were cultured in serum-free, low-Ca(2+) medium supplemented with EGF and cholera toxin. Epithelial cells were subcultured at a 1:3 split until passage (P)4 and at lower densities after P4. Colony-forming efficiency, population-doubling times, and population doublings were determined. The expression of p63, keratin (K)19, K12, and involucrin was analyzed by RT-PCR, immunocytochemistry, and Western blotting. Differentiation potential was examined by switching the medium to serum or high Ca(2+)-containing medium. Stratification ability was analyzed by air-lift culture. RESULTS: Thirty of 32 (93.8%) corneal explants were successfully subcultured to P1. Cultures without cholera toxin did not proliferate past P2 (n = 12), but 55% of cultures supplemented with cholera toxin achieved P4 (n = 20). After P4, cells were stably subcultured over 25 passages. Colony-forming efficiency increased from 9.7% +/- 2.6% at P5 to 29.0% +/- 3.3% at P20. The cells showed cobblestone appearance and expressed p63, K19, and involucrin but were negative for K12. Serum and high Ca(2+) induced differentiation, and cells cultured in DMEM/F12 with serum showed K12 mRNA expression. Stratified epithelium was formed by air-lifting. CONCLUSIONS: With this procedure, corneal epithelial cells from a single cornea can be cultured long term and can retain the potential to differentiate and stratify. This procedure can be a powerful tool for studies that require comparison of corneal epithelial cells from normal and transgenic mice in vitro.

The use of human mesenchymal stem cell-derived feeder cells for the cultivation of transplantable epithelial sheets.

PURPOSE: To report the efficacy of human bone marrow-derived mesenchymal stem cells as a source of feeder cells for the cultivation of transplantable corneal epithelial cell sheets. METHODS: Human mesenchymal stem cells (marrow adherent stem cells; MASCs) were cultured in alpha-modified Eagle's medium with 10% serum and were treated with mitomycin C. Expression of cytokines in MASCs was confirmed by reverse transcription-polymerase chain reaction. Human limbal epithelial cells were cocultured with MASCs or 3T3 feeder cells to compare colony-forming efficiency (CFE). Limbal epithelial cells were cultured on MASCs or 3T3 feeder cells at the air-liquid interface to allow stratification, and stratified epithelial sheets were analyzed by immunohistochemistry against cytokeratin 3 (K3), K15, p63alpha, and ABCG2. Rabbit limbal epithelial cell sheets were cultivated with MASC feeder cells and transplanted to the ocular surface of the limbal-deficient rabbits. Epithelial grafts were observed by slit lamp microscopy for 4 weeks and then evaluated by histology and immunohistochemistry against K3 and K4. RESULTS: MASC feeder cells expressed keratinocyte growth factor, hepatocyte growth factor, and N-cadherin. The CFE of human limbal epithelial cells was similar in MASC and 3T3 feeder groups. Stratified cell sheets were successfully cultivated with MASC feeder cells expressing K3, K15, p63alpha, and ABCG2. Transplanted epithelial sheets regenerated the corneal phenotype in limbal-deficient rabbits. CONCLUSIONS: MASC-derived feeder cells are suitable for the engineering of epithelial sheets, avoiding the use of potentially hazardous xenologic feeder cells.

A novel NIH/3T3 duplex feeder system to engineer corneal epithelial sheets with enhanced cytokeratin 15-positive progenitor populations.

Corneal epithelial cell sheets co-cultivated with feeder cells are used to reconstruct the ocular surface in stem cell-depleted eyes. The present study was conducted to investigate the optimal method of using feeder cells in the interest of preserving progenitor cells in cultivated sheets. We compared the phenotype and secondary colony forming efficiency (CFE) of cell sheets that were engineered using 3T3 feeder cells as a separate layer or as a contact layer. We also devised a novel "duplex feeder" system that consists of two separate layers of feeder cells. After cells reached confluence, cells were cultured at the air-liquid interface to allow full stratification. Stratified sheets were then analyzed using immunohistochemistry and secondary colony formation. Contact feeder cultures and duplex feeder cultures yielded epithelial sheets with small, cuboid basal cells with strong expression of keratin (K)3, K12, and K 15. Furthermore, only duplex feeder layers reproduced the basal K 15, suprabasal K12 limbal phenotype where epithelial stem cells reside. A similar effect was observed when cornea stroma-derived progenitor cells were used as feeder cells. Duplex feeder sheets also produced significantly more secondary colonies than cells dissociated from single layer sheets, suggesting that the duplex feeder system produces transplantable sheets with a higher yield of progenitor cells.

Hypoxia enhances the expansion of human limbal epithelial progenitor cells in vitro.

PURPOSE: To demonstrate the effects of hypoxia on proliferation and differentiation of human limbal epithelial cells in vitro. METHODS: Primary human limbal epithelial cells were harvested from the rim of donor corneas. Colony-forming efficiency (CFE) and cell proliferation were observed in standard (20% O(2)) or hypoxic (2% O(2)) culture conditions. Cell cycle, forward scatter (FSC) and side scatter (SCC) of cells were analyzed by flow cytometry. Proliferating cells were also observed by pulse labeling (2 hours) with BrdU and Ki67 staining. Apoptosis was detected by TUNEL assay. Isolated colonies were examined by immunohistochemistry against K15, p63, involucrin, and K3. Involucrin expression was also analyzed by Western blot analysis. RESULTS: Both CFE and proliferation of limbal epithelial cells was significantly enhanced in hypoxia. Flow cytometry revealed a higher fraction of hypoxic cells in the G(0)/G(1)-phase and fewer cells in the S-phase, compared with normoxia. However, there was no difference in the uptake of BrdU during a 2-hour pulse, suggesting that hypoxic colonies contained rapidly cycling cells. Apoptotic cells were sparse in both groups, and hypoxic cells showed lower FSC compared with normoxic cells. Although there was no difference in the staining pattern of K15, p63, and Ki67, cells cultivated in normoxia expressed higher levels of the differentiation markers involucrin and K3. Significantly higher involucrin expression was also observed by Western blot. CONCLUSIONS: Hypoxic culture (2%) enhances proliferation while inhibiting differentiation of limbal epithelial cells in vitro.

Beta-catenin activation and epithelial-mesenchymal transition in the pathogenesis of pterygium.

PURPOSE: To investigate whether beta-catenin activation and epithelial-mesenchymal transition (EMT) is involved in the pathogenesis of pterygium. METHODS: beta-Catenin and E-cadherin expression were examined in surgically excised tissue and eye bank corneas with intact pterygium. Snail and Slug, the transcriptional repressors of E-cadherin, and matrix metalloproteinase (MMP)-7, a down-stream gene regulated by beta-catenin were also investigated. Epithelial cells undergoing EMT-like changes were identified by double immunostaining for alpha-smooth muscle actin (SMA)/vimentin and cytokeratin 14. Transmission electron microscopy was used to examine the ultrastructure of the pterygial head. RESULTS: Histopathology showed aberrant fibrotic proliferation beneath the pterygium epithelium, with epithelial processes extending into the stroma. Transmission electron microscopy revealed the dissociation of epithelial cells, which were surrounded by activated fibroblast-like cells. Characteristic downregulation of E-cadherin and intranuclear accumulation of beta-catenin and lymphoid-enhancer-factor-1 in pterygial epithelium were also observed by immunohistochemistry. Of note, epithelial cells extending into the stroma were positive for both alpha-SMA/vimentin and cytokeratin 14. Snail and Slug were immunopositive in the nuclei of pterygial epithelial cells, but not in normal corneal epithelial cells. CONCLUSIONS: EMT of basal epithelial cells may play a key role in the pathogenesis of pterygium.

Proliferation and differentiation of transplantable rabbit epithelial sheets engineered with or without an amniotic membrane carrier.

PURPOSE: To report a novel method of engineering transplantable, carrier-free corneal epithelial sheets by using a biodegradable fibrin sealant and to compare its characteristics with epithelial sheets cultivated on denuded amniotic membrane carriers. METHODS: Stratified corneal epithelial sheets were prepared in culture dishes coated with biodegradable fibrin glue. Amniotic membrane (AM) carriers served as the control. The quality of cultivated sheets was compared by immunohistochemistry for cytokeratin (K)3, K12, K14, p63, occludin, and integrin beta1; electron microscopy; and colony-forming assays. K3 protein expression was compared by Western blot analysis. In a limbal-deficient rabbit transplantation model, postoperative adaptation and proliferation of BrdU-labeled cell sheets were examined by histology and anti-Ki67 staining. RESULTS: Epithelial sheets were successfully engineered by using a biodegradable fibrin sealant. Cell sheets in both groups were multilayered, expressed K3, K12, and K14, and had functioning occludin(+) apical tight junctions as well as p63 and integrin beta1 staining in basal cells. The carrier-free sheets appeared to be more differentiated than the AM sheets, which was also demonstrated by the higher levels of K3 in the Western blots. The colony-forming efficiency of dissociated cells was similar in both groups, although larger colonies were observed on the AM sheets. AM sheets retained higher levels of BrdU-labeled cells and fewer Ki67(+) cells compared with carrier-free sheets after transplantation. CONCLUSIONS: Tissue engineering with a commercially available fibrin sealant was an effective means of creating a carrier-free, transplantable corneal epithelial sheet. Carrier-free sheets were more differentiated compared with AM sheets, while retaining similar levels of colony-forming progenitor cells.

Amniotic membrane immobilized poly(vinyl alcohol) hybrid polymer as an artificial cornea scaffold that supports a stratified and differentiated corneal epithelium.

Poly(vinyl alcohol) (PVA) is a biocompatible, transparent hydrogel with physical strength that makes it promising as a material for an artificial cornea. In our previous study, type I collagen was immobilized onto PVA (PVA-COL) as a possible artificial cornea scaffold that can sustain a functional corneal epithelium. The cellular adhesiveness of PVA in vitro was improved by collagen immobilization; however, stable epithelialization was not achieved in vivo. To improve epithelialization in vivo, we created an amniotic membrane (AM)-immobilized polyvinyl alcohol hydrogel (PVA-AM) for use as an artificial cornea material. AM was attached to PVA-COL using a tissue adhesive consisting of collagen and citric acid derivative (CAD) as a crosslinker. Rabbit corneal epithelial cells were air-lift cultured with 3T3 feeder fibroblasts to form a stratified epithelial layer on PVA-AM. The rabbit corneal epithelial cells formed 3-5 layers of keratin-3-positive epithelium on PVA-AM. Occludin-positive cells were observed lining the superficial epithelium, the gap-junctional protein connexin43-positive cells was localized to the cell membrane of the basal epithelium, while both collagen IV were observed in the basement membrane. Epithelialization over implanted PVA-AM was complete within 2 weeks, with little inflammation or opacification of the hydrogel. Corneal epithelialization on PVA-AM in rabbit corneas improved over PVA-COL, suggesting the possibility of using PVA-AM as a biocompatible hybrid material for keratoprosthesis.