Effects of hepatocyte growth factor, transforming growth factor-beta1 and epidermal growth factor on bovine corneal epithelial cells under epithelial-keratocyte interaction in reconstruction culture

Topical Losartan Inhibition of Myofibroblast Generation in Rabbit Corneas With Acute Incisions

PURPOSE

The purpose of this study was to study whether deep central corneal incisions close during topical losartan treatment and the effect of topical losartan on myofibroblast generation after incisions in rabbit corneas.

METHODS

Rabbits (12) had a 0.35-mm deep radial incision from the center of the cornea into the limbus in 1 eye that was approximated with a single 10-0 nylon suture 1 mm inside the limbus. The incision was treated with 50 μL of topical 0.8 mg/mL losartan or 50 μL of balanced salt solution vehicle 6 times per day for 1 month. Standardized slitlamp photographs of the central incisions were analyzed for opacity with ImageJ before euthanasia. Triplex IHC was performed on cryofixed corneas for myofibroblast marker alpha-smooth muscle actin, mesenchymal cell marker vimentin, and basement membrane marker laminin alpha-5. Stromal α-SMA-positive myofibroblasts surrounding the incisions were quantitated with ImageJ.

RESULTS

Topical losartan compared with vehicle did not affect closure of the radial incisions or the opacity that developed surrounding the incisions at 1 month after injury. Topical losartan compared with vehicle did significantly decrease the average density of stromal myofibroblasts surrounding the incisions.

CONCLUSIONS

Topical losartan, a known inhibitor of transforming growth factor beta signaling, did not affect closure of deep corneal incisions. Losartan decreased myofibroblast generation surrounding nearly full-thickness radial corneal incisions compared with vehicle. The opacity at the incisions was not significantly affected by losartan-likely because corneal fibroblasts that develop in the stroma adjacent to the incisions were not changed by the losartan compared with the vehicle.

Bio-orthogonally crosslinked hyaluronate-collagen hydrogel for suture-free corneal defect repair

Biomaterials that mimic corneal stroma could decrease the need for donor corneal tissue and could decrease the prevalence of complications associated with corneal transplantation, including infection and rejection. We developed a bio-orthogonally crosslinked hyaluronate-collagen hydrogel which can fill corneal defects in situ without the need for any sutures, initiators, or catalysts. We studied the effects of biorthogonal crosslinking on the light transmittance of the hydrogel, which was greater than 97% water. The transmittance of the optimized hydrogel in the visible light range was over 94%. We also investigated the mechanical properties, refractive index, morphology, biocompatibility, and corneal re-epithelialization capacity of the hyaluronate-collagen hydrogel. Our in vitro, in vivo, and ex vivo results demonstrated that this bio-orthogonally crosslinked hyaluronate-collagen hydrogel has excellent potential as a biomaterial for cornea repair and regeneration.

Characterizing the impact of 2D and 3D culture conditions on the therapeutic effects of human mesenchymal stem cell secretome on corneal wound healing in vitro and ex vivo

The therapeutic effects of secreted factors (secretome) produced by bone marrow-derived human mesenchymal stem cells (MSCs) were evaluated as a function of their growth in 2D culture conditions and on 3D electrospun fiber scaffolds. Electrospun fiber scaffolds composed of polycaprolactone and gelatin were fabricated to provide a 3D microenvironment for MSCs, and their mechanical properties were optimized to be similar to corneal tissue. The secretome produced by the MSCs cultured on 3D fiber matrices versus 2D culture dishes were analyzed using a Luminex immunoassay, and the secretome of MSCs cultured on the 3D versus 2D substrates showed substantial compositional differences. Concentrations of factors such as HGF and ICAM-1 were increased over 5 times in 3D cultures compared to 2D cultures. In vitro proliferation and scratch-based wound healing assays were performed to compare the effects of the secretome on corneal fibroblast cells (CFCs) when delivered synchronously from co-cultured MSCs through a trans-well co-culture system versus asynchronously after harvesting the factors separately and adding them to the media. Cell viability of CFCs was sustained for 6 days when co-cultured with MSCs seeded on the fibers but decreased with time under other conditions. Scratch assays showed 95% closure at 48 h when CFCs were co-cultured with MSCs seeded on fibers, while the control group only exhibited 50% closure at 48 h. Electrospun fibers seeded with MSCs were then applied to a rabbit corneal organ culture system, and MSCs seeded on fibers promoted faster epithelialization and less scarring. Corneas were fixed and stained for alpha smooth muscle actin (α-SMA), and then analyzed by confocal microscopy. Immunostaining showed that expression of α-SMA was lower in corneas treated with MSCs seeded on fibers, suggesting suppression of myofibroblastic transformation. MSCs cultured on electrospun fibers facilitate wound healing in CFCs and on explanted corneas through differential secretome profiles compared to MSCs cultured on 2D substrates. Future work is merited to further understand the nature and basis of these differences and their effects in animal models. STATEMENT OF SIGNIFICANCE: Previous studies have shown that the secretome of bone marrow-derived mesenchymal stem cells (MSC) is promotes corneal wound healing by facilitating improved wound closure rates and reduction of scarring and neovascularization. The present research is significant because it provides evidence for the modulation of the secretome as a function of the MSC culture environment. This leads to differential expression of therapeutic factors secreted, which can impact corneal epithelial and stromal healing after severe injury. In addition, this article shows that co-continuous delivery of the MSC secretome improves cell migration and proliferation over aliquoted delivery, and that MSCs grown on three-dimensional electrospun fiber constructs may provide a favorable microenvironment for cultured MSCs and as a carrier to deliver their secreted factors to the ocular surface.

Mesenchymal cells and fluid flow stimulation synergistically regulate the kinetics of corneal epithelial cells at the air-liquid interface

PURPOSE

In vivo microenvironments are critical to tissue homeostasis and wound healing, and the cornea is regulated by a specific microenvironment complex that consists of cell-cell interactions, air-liquid interfaces, and fluid flow stimulation. In this study, we aimed to clarify the effects of and the correlations among these three component factors on the cell kinetics of corneal epithelial cells.

METHODS

Human corneal epithelial-transformed (HCE-T) cells were cocultured with either primary rat corneal fibroblasts or NIH 3T3 fibroblasts. We employed a double-dish culture method to create an air-liquid interface and a gyratory shaker to create fluid flow stimulation. Morphometric and protein expression analyses were performed for the HCE-T cells.

RESULTS

Both the primary rat fibroblasts and the NIH 3T3 cells promoted HCE-T cell proliferation, and the presence of fluid flow synergistically enhanced this effect and inhibited the apoptosis of HCE-T cells. Moreover, fluid flow enhanced the emergence of myofibroblasts when cocultured with primary rat fibroblasts or NIH 3T3 cells. Extracellular signal-regulated kinase and p38 signaling were regulated either synergistically or independently by both fluid flow and cellular interaction between the HCE-T and NIH 3T3 cells.

CONCLUSION

The cell-cell interaction and fluid flow stimulation in the air-liquid interface synergistically or independently regulated the behavior of HCE-T cells. Fluid flow accelerated the phenotypic change from corneal fibroblasts and NIH 3T3 cells to myofibroblasts. Elucidation of the multicomponent interplay in this microenvironment will be critical to the homeostasis and regeneration of the cornea and other ocular tissues.

Thrombospondin-1 in ocular surface health and disease

Thrombospondin 1 (TSP-1) is an extracellular matrix protein that interacts with a wide array of ligands including cell receptors, growth factors, cytokines and proteases to regulate various physiological and pathological processes. Constitutively expressed by certain ocular surface tissues (e.g. corneal and conjunctival epithelium), TSP-1 expression is modulated during ocular surface inflammation. TSP-1 is an important activator of latent TGF-β, serving to promote the immunomodulatory and wound healing functions of TGF-β. Mounting research has deepened our understanding of how TSP-1 expression (and lack thereof) contributes to ocular surface homeostasis and disease. Here, we review current knowledge of the function of TSP-1 in dry eye disease, ocular allergy, angiogenesis/lymphangiogenesis, corneal transplantation, corneal wound healing and infectious keratitis.

Construction of a full-thickness human corneal substitute from anterior acellular porcine corneal matrix and human corneal cells

AIM

To construct functional human full-thickness corneal replacements.

METHODS

Acellular porcine corneal matrix (APCM) was developed from porcine cornea by decellulariztion. The biomechanical properties of anterior-APCM (AAPCM) and posterior-APCM (PAPCM) were checked using uniaxial tensile testing. Human corneal cells were obtained by cell culture. Suspending ring was designed by deformation of an acupuncture needle. MTT cytotoxicity assay was used to check the cytotoxicity of suspending ring soaking solutions. A new three-dimensional organ culture system was established by combination of suspending ring, 48-well plate and medium together. A human full-thickness corneal substitute was constructed from human corneal cells with AAPCM in an organ coculture system. Biochemical marker expression of the construct was measured by immunofluorescent staining and morphological structures were observed using scanning electron microscopy. Pump function and biophysical properties were examined by penetrating keratoplasty and follow-up clinical observations.

RESULTS

There were no cells in the AAPCM or PAPCM, whereas collagen fibers, Bowman's membrane, and Descemet's membrane were retained. The biomechanical property of AAPCM was better than PAPCM. Human corneal cells grew better on the AAPCM than on the PAPCM. There was no cytotoxicity for the suspending ring soaking solutions. For the constructed full-depth human corneal replacements keratocytes scattered uniformly throughout the AAPCM and expressed vimentin. The epithelial layer was located on the surface of Bowman's membrane and composed of three or four layers of epithelial cells expressing cytokeratin 3. One layer of endothelial cells covered the stromal surface of AAPCM, expressed Na⁺/K⁺ATPase and formed the endothelial layer. The construct was similar to normal human corneas, with many microvilli on the epithelial cell surface, stromal cells with a long shuttle shape, and zonula occludens on the interface of endothelial cells. The construct withstood surgical procedures during penetrating keratoplasty. The corneal transparency increased gradually and was almost completely restored 7d after surgery.

CONCLUSION

AAPCM is an ideal scaffold for constructing full-thickness corneal replacement, and functional human full-thickness corneal replacements are successfully constructed using AAPCM and human corneal cells.

Regulating temporospatial dynamics of morphogen for structure formation of the lacrimal gland by chitosan biomaterials

The lacrimal gland is an important organ responsible for regulating tear synthesis and secretion. The major work of lacrimal gland (LG) is to lubricate the ocular surface and maintain the health of eyes. Functional deterioration of the lacrimal gland happens because of aging, diseases, or therapeutic complications, but without effective treatments till now. The LG originates from the epithelium of ocular surface and develops by branching morphogenesis. To regenerate functional LGs, it is required to explore the way of recapitulating and facilitating the organ to establish the intricate and ramified structure. In this study, we proposed an approach using chitosan biomaterials to create a biomimetic environment beneficial to the branching structure formation of developing LG. The morphogenetic effect of chitosan was specific and optimized to promote LG branching. With chitosan, increase in temporal expression and local concentration of endogenous HGF-related molecules creates an environment around the emerging tip of LG epithelia. By efficiently enhancing downstream signaling of HGF pathways, the cellular activities and behaviors were activated to contribute to LG branching morphogenesis. The morphogenetic effect of chitosan was abolished by either ligand or receptor deprivation, or inhibition of downstream signaling transduction. Our results elucidated the underlying mechanism accounting for chitosan morphogenetic effects on LG, and also proposed promising approaches with chitosan to assist tissue structure formation of the LG.

Corneal wound healing after laser vision correction

Any trauma can trigger a cascade of responses in tissues, with the purpose of safeguarding the integrity of the organ affected by the trauma and of preventing possible damage to nearby organs. Subsequently, the body tries to restore the function of the organ affected. The introduction of the excimer laser for keratorefractive surgery has changed the treatment landscape for correcting refractive errors, such as myopia, hyperopia, and astigmatism. In recent years, with the increased understanding of the basic science of refractive errors, higher-order aberrations, biomechanics, and the biology of corneal wound healing, a reduction in the surgical complications of keratorefractive surgery has been achieved. The understanding of the cascade of events involved in the corneal wound healing process and the examination of how corneal wound healing influences corneal biomechanics and optics are crucial to improving the efficacy and safety of laser vision correction.

Effect of Structural Differences in Collagen Sponge Scaffolds on Tracheal Epithelium Regeneration

OBJECTIVE

We developed an in situ regeneration-inducible artificial trachea composed of a porcine collagen sponge and polypropylene framework and used it for tracheal reconstruction. In the present study, collagen sponges with different structures were prepared from various concentrations of collagen solutions, and their effect on the regeneration of tracheal epithelium was examined.

METHODS

Collagen sponges were prepared from type I and III collagen solutions. The structures of the sponges were analyzed using scanning electron microscopy (SEM). Artificial tracheae, which were formed using the collagen sponges with different structures, were implanted into rabbits, and regeneration of the tracheal epithelium on the artificial tracheae was evaluated by SEM analysis and histological examination.

RESULTS

The SEM analysis showed that collagen sponges prepared from 0.5% and 1.0% collagen solutions had a porous structure. However, the sponges prepared from a 1.5% collagen solution had a nonporous structure. After implantation of artificial tracheae prepared from 0.5% and 1.0% collagen solutions, their luminal surfaces were mostly covered with epithelium within 14 days. However, epithelial reorganization occurred later on artificial tracheae prepared from the 1.5% collagen solution.

CONCLUSION

Collagen sponges with a porous structure are suitable for regeneration of the tracheal epithelium in our artificial trachea.

Stromal-epithelial interaction study: The effect of corneal epithelial cells on growth factor expression in stromal cells using organotypic culture model

Interactions between stromal and epithelial cells play important roles in the development, homeostasis, and pathological conditions of the cornea. Soluble cytokines are critical factors in stromal-epithelial interactions, and growth factors secreted from corneal stromal cells contribute to the regulation of proliferation and differentiation of corneal epithelial cells (CECs). However, the manner in which the expression of growth factors is regulated in stromal cells has not been completely determined. To study stromal-epithelial cell interactions, we used an organotypic culture model. Human or rabbit CECs (HCECs or RCECs) were cultured on amniotic membranes placed on human corneal fibroblasts (HCFs) embedded in a collagen gel. The properties of the organotypic culture were examined by hematoxylin-eosin staining and immunofluorescence. In the organotypic culture, HCECs or RCECs were stratified into two-three layers after five days and five-seven layers after nine days. However, stratification was not observed when the HCECs were seeded on a collagen gel without fibroblasts. K3/K12 were expressed on day 9. The HCF-embedded collagen gels were collected on days 3, 5, or 9 after seeding the RCECs, and mRNA expression of growth factors FGF7, HGF, NGF, EGF, TGF-α, SCF, TGF-β1, TGF-β2, and TGF-β3 were quantified by real-time PCR. mRNA expression of the growth factors in HCFs cultured with RCECs were compared with those cultured without RCECs, as well as in monolayer cultures. mRNA expression of TGF-α was markedly increased in HCFs cultured with RCECs. However, mRNA expression of the TGF-β family was suppressed in HCFs cultured with RCECs. Principal component analysis revealed that mRNA expression of the growth factors in HCFs were generally similar when they were cultured with RCECs. In organotypic cultures, the morphological changes in the CECs and the expression patterns of the growth factors in the stromal cells clearly demonstrated stromal-epithelial cell interactions, and the results suggest that stromal cells and epithelial cells may act in concert in the cornea.

Limbal epithelial stem-microenvironmental alteration leads to pterygium development

Maintenance of tissue homeostasis relies on the accurate regulation of tissue specific stem cell activity which is governed by the dynamic interaction between the positive and negative feedback modulating mechanism of stem cell microenvironmental niche. Alteration or deregulation of the "stem-microenvironmental networking" provokes disease development. Limbal epithelial stem cells (LESC) are the initiator hierarchy that maintains corneal integrity. Compartmentalization of LESC within the limbal vicinity provides an opportunity to understand the stem-microenvironmental relationship. The purpose of this study was to determine the microenvironmental alteration associated with LESCs fate in pterygium condition in comparison with healthy state. Clinical observations evaluated the ocular surface disorder with respect to corneal vascularization, tear film abnormality, and thickening of limbal area in pterygium patients. Structural alteration of limbal stem/progenitor cells and its neighboring niche components were observed using histology and scanning electron microscopy. Receptor overexpression of TGFβ-R1, EGF-R1, and IL6-Rα and alteration of IL2-Rα expression pointed toward aberration of "stem-microenvironmental networking" in the limbal vicinity during disease development. Increased cell proliferation index along with TERT, Cyclin-D1, and PCNA over-expression in limbal part of pterygium epithelial cells indicated increased cellular proliferation and disturbed homeostatic equilibrium. We postulate that pterygium is associated with limbal microenvironmental anomaly where the resident epithelial cells became hyperproliferative.

Genomics of corneal wound healing: a review of the literature

Corneal wound healing is a complex process: its mechanisms and the underlying genetic control are not fully understood. It involves the integrated actions of multiple growth factors, cytokines and proteases produced by epithelial cells, stromal keratocytes, inflammatory cells and lacrimal gland cells. Following an epithelial insult, multiple cytokines are released triggering a cascade of events that leads to repair the epithelial defect and remodelling of the stroma to minimize the loss of transparency and function. In this review, we examine the literature surrounding the genomics of corneal wound healing with respect to the following topics: epithelial and stromal wound healing (including inhibition); corneal neovascularisation; the role of corneal nerves in wound healing; the endothelium; the role of aquaporins and aptamers. We also examine the effect of ectasia on corneal wound healing with regard to keratoconus and following corneal surgery. A better understanding of the cellular and molecular changes that occur during repair of corneal wounds will provide the opportunity to design treatments that selectively modulate key phases of the healing process resulting in scars that more closely resemble normal corneal architecture.

Corneal stromal cell plasticity: in vitro regulation of cell phenotype through cell-cell interactions in a three-dimensional model

In vivo, epithelial cells are connected both anatomically and functionally with stromal keratocytes. Co-culturing aims at recapturing this cellular anatomy and functionality by bringing together two or more cell types within the same culture environment. Corneal stromal cells were activated to their injury phenotype (fibroblasts) and expanded before being encapsulated in type I collagen hydrogels constructs. Three different epithelial-stromal co-culture methods were then examined: epithelial explant; transwell; and the use of conditioned media. The aim was to determine whether the native, inactivated keratocyte cell phenotype could be restored in vitro. Media supplementation with transforming growth factor beta-1 (TGF-β1) was then used to determine whether the inactivated stromal cells retained their plasticity in vitro and could be re-activated to the fibroblast phenotype. Finally, media supplementation with wortmannin was used to inhibit epithelial-stromal cell interactions. Two different nondestructive techniques, spherical indentation and optical coherence tomography, were used to reveal how epithelial-stromal co-culturing with TGF-β1, and wortmannin media supplementation, respectively, affect stromal cell behavior and differentiation in terms of construct contraction and elastic modulus measurement. Cell viability, phenotype, morphology, and protein expression were investigated to corroborate our mechanical findings. It was shown that activated stromal cells could be inactivated to a keratocyte phenotype via co-culturing and that they retained their plasticity in vitro. Activated corneal stromal cells that were fibroblastic in phenotype were successfully reverted to a nonactivated keratocyte cell lineage in terms of behavior and biological properties; and then back again via TGF-β1 media supplementation. It was then revealed that epithelial-stromal interactions can be blocked via the use of wortmannin inhibition. A greater understanding of stromal-epithelial interactions and what mediates them offers great pharmacological potential in the regulation of corneal wound healing, with the potential to treat corneal diseases and injury by which such interactions are vital.

Control of scar tissue formation in the cornea: strategies in clinical and corneal tissue engineering

Corneal structure is highly organized and unified in architecture with structural and functional integration which mediates transparency and vision. Disease and injury are the second most common cause of blindness affecting over 10 million people worldwide. Ninety percent of blindness is permanent due to scarring and vascularization. Scarring caused via fibrotic cellular responses, heals the tissue, but fails to restore transparency. Controlling keratocyte activation and differentiation are key for the inhibition and prevention of fibrosis. Ophthalmic surgery techniques are continually developing to preserve and restore vision but corneal regression and scarring are often detrimental side effects and long term continuous follow up studies are lacking or discouraging. Appropriate corneal models may lead to a reduced need for corneal transplantation as presently there are insufficient numbers or suitable tissue to meet demand. Synthetic optical materials are under development for keratoprothesis although clinical use is limited due to implantation complications and high rejection rates. Tissue engineered corneas offer an alternative which more closely mimic the morphological, physiological and biomechanical properties of native corneas. However, replication of the native collagen fiber organization and retaining the phenotype of stromal cells which prevent scar-like tissue formation remains a challenge. Careful manipulation of culture environments are under investigation to determine a suitable environment that simulates native ECM organization and stimulates keratocyte migration and generation.

Polymeric implant materials for the reconstruction of tracheal and pharyngeal mucosal defects in head and neck surgery

The existing therapeutical options for the tracheal and pharyngeal reconstruction by use of implant materials are described. Inspite of a multitude of options and the availability of very different materials none of these methods applied for tracheal reconstruction were successfully introduced into the clinical routine. Essential problems are insufficiencies of anastomoses, stenoses, lack of mucociliary clearance and vascularisation. The advances in Tissue Engineering (TE) offer new therapeutical options also in the field of the reconstructive surgery of the trachea. In pharyngeal reconstruction far reaching developments cannot be recognized at the moment which would allow to give a prognosis of their success in clinical application. A new polymeric implant material consisting of multiblock copolymers was applied in our own work which was regarded as a promising material for the reconstruction of the upper aerodigestive tract (ADT) due to its physicochemical characteristics. In order to test this material for applications in the ADT under extreme chemical, enzymatical, bacterial and mechanical conditions we applied it for the reconstruction of a complete defect of the gastric wall in an animal model. In none of the animals tested either gastrointestinal complications or negative systemic events occurred, however, there was a multilayered regeneration of the gastric wall implying a regular structured mucosa.

In future the advanced stem cell technology will allow further progress in the reconstruction of different kind of tissues also in the field of head and neck surgery following the principles of Tissue Engineering.

Corneal Epithelial Cultures Generated from Organ-Cultured Limbal Tissue: Factors Influencing Epithelial Cell Growth

PURPOSE

To explore the in vitro proliferative potential of human limbal epithelial cells after 31 degrees C organ-culture storage and to investigate putative factors influencing it.

METHODS

185 cultures of limbal explants were carried-out either from full-thickness explants (n = 102) or from enzymatically dissociated cells (n = 83) seeded on a feeder layer of human keratocytes. Epithelial outgrowth was assessed by phase contrast microscopy using a computerized image analysis software. Cell phenotype was evaluated by transmission electron microscopy and immunocytology. Univariate and multivariate analysis were performed to determine factors influencing epithelial growth in culture.

RESULTS

An epithelial outgrowth of 100 square mm or more was observed in 52% of cultures, (average growth area: 440 +/- 256 mm at three weeks). Corneal epithelial phenotype was confirmed by transmission electron microscopy, and cytokeratin pattern. Cytokeratine 19, deltaNp63, nestin and vimentin positive staining revealed undifferentiated epithelial cells in both explant and cell suspension cultures at three weeks. Short death to cornea retrieval time (p < 0.03) and female donors (p < 0.01) were associated with higher cell growth. Enzymatic treatment of explants by trypsin, but not dispase, decreased cell proliferation at two (p < 0.03) and three weeks (p < 0.04). Donor age, duration of corneal storage, and source of the explant did not influence the cell growth.

CONCLUSION

Organ-culture conditions can preserve limbal cell mitotic potential if limbal tissue is excised early after circulatory arrest. Human keratocytes can be used as a feeder layer allowing epithelial cells to maintain poorly differentiated phenotype in culture. Further investigations are needed to explain the influence of the donor sex on epithelial cell growth in culture.

Corneal epithelial stem cells: characterization, culture and transplantation

The epithelium covering the cornea at the front of the eye is maintained by stem cells located at its periphery, in a region known as the limbus. A lack or dysfunction of these so-called limbal stem cells (LSCs) results in the painful and blinding disease of LSC deficiency. In this review, current knowledge regarding the biology of these particular stem cells will be outlined, including recent advances that are enabling the gene expression analysis of these cells. The use of LSCs in therapeutic interventions for LSC deficiency will also be discussed, including the role for ex vivo expansion. In particular, the translation of basic science advances in LSC biology into therapeutic strategies will be highlighted.

Effect of Fibroblasts on Tracheal Epithelial Regenerationin vitro

Several artificial grafts for covering deficient trachea have been produced through tissue engineering. Recently, our group clinically used an artificial trachea made from collagen sponge for patients with noncircumferential tracheal resection. However, the slowness of epithelial regeneration on the surface of the artificial trachea was confirmed as one particular problem. In this study, we co-cultured tracheal epithelial cells with fibroblasts and examined effects of fibroblasts on epithelial regeneration in vitro. Fibroblasts activated epithelial cell proliferation and migration. In co-culture with fibroblasts, epithelial cells reconstructed pseudostratified epithelium, which was composed of ciliated, goblet, and basal cells. Furthermore, a basement membrane was reconstructed between epithelial cells and fibroblasts, and integrin beta4 was also observed there. Fibroblasts rapidly increased mucin secretion by epithelial cells. These results indicate that stimulatory effects of fibroblasts on epithelial cell migration, proliferation, and differentiation would reduce the time required for covering of epithelial cells on the defect of luminal surface and hasten regeneration of morphologically and functionally normalized epithelium involving the reconstruction of basement membrane.

Met-Independent Hepatocyte Growth Factor-mediated regulation of cell adhesion in human prostate cancer cells

BACKGROUND

Prostate cancer cells communicate reciprocally with the stromal cells surrounding them, inside the prostate, and after metastasis, within the bone. Each tissue secretes factors for interpretation by the other. One stromally-derived factor, Hepatocyte Growth Factor (HGF), was found twenty years ago to regulate invasion and growth of carcinoma cells. Working with the LNCaP prostate cancer progression model, we found that these cells could respond to HGF stimulation, even in the absence of Met, the only known HGF receptor. The new HGF binding partner we find on the cell surface may help to clarify conflicts in the past literature about Met expression and HGF response in cancer cells.

METHODS

We searched for Met or any HGF binding partner on the cells of the PC3 and LNCaP prostate cancer cell models, using HGF immobilized on agarose beads. By using mass spectrometry analyses and sequencing we have identified nucleolin protein as a novel HGF binding partner. Antibodies against nucleolin (or HGF) were able to ameliorate the stimulatory effects of HGF on met-negative prostate cancer cells. Western blots, RT-PCR, and immunohistochemistry were used to assess nucleolin levels during prostate cancer progression in both LNCaP and PC3 models.

RESULTS

We have identified HGF as a major signaling component of prostate stromal-conditioned media (SCM) and have implicated the protein nucleolin in HGF signal reception by the LNCaP model prostate cancer cells. Antibodies that silence either HGF (in SCM) or nucleolin (on the cell surfaces) eliminate the adhesion-stimulatory effects of the SCM. Likewise, addition of purified HGF to control media mimics the action of SCM. C4-2, an LNCaP lineage-derived, androgen-independent human prostate cancer cell line, responds to HGF in a concentration-dependent manner by increasing its adhesion and reducing its migration on laminin substratum. These HGF effects are not due to shifts in the expression levels of laminin-binding integrins, nor can they be linked to expression of the known HGF receptor Met, as neither LNCaP nor clonally-derived C4-2 sub-line contain any detectable Met protein. Even in the absence of Met, small GTPases are activated, linking HGF stimulation to membrane protrusion and integrin activation. Membrane-localized nucelolin levels increase during cancer progression, as modeled by both the PC3 and LNCaP prostate cancer progression cell lines.

CONCLUSION

We propose that cell surface localized nucleolin protein may function in these cells as a novel HGF receptor. Membrane localized nucleolin binds heparin-bound growth factors (including HGF) and appears upregulated during prostate cancer progression. Antibodies against nucleolin are able to ameliorate the stimulatory effects of HGF on met-negative prostate cancer cells. HGF-nucleolin interactions could be partially responsible for the complexity of HGF responses and met expression reported in the literature.

Correlation of proliferative and anti-apoptotic effects of HGF, insulin, IGF-1, IGF-2, and EGF in SV40-transformed human corneal epithelial cells

The effects of various growth factors on the proliferation and apoptosis of human corneal epithelial cells were investigated. Simian virus 40-transformed human corneal epithelial cells were thus incubated separately with eight different growth factors, after which cell proliferation was evaluated by measurement of [(3)H]thymidine incorporation or with the MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay and apoptosis was quantified by the terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick-end labeling assay. Phosphorylation of the protein kinase Akt, which plays an important role in anti-apoptotic signaling, was also assessed by immunoblot analysis. The growth factors examined could be classified into three groups on the basis of their effects on the proliferation and apoptosis of human corneal epithelial cells: hepatocyte growth factor (HGF), insulin, insulin-like growth factor (IGF)-1, IGF-2, and epidermal growth factor (EGF) each increased cell proliferation, inhibited the induction of apoptosis by sodium nitroprusside, and elicited the activation of Akt; transforming growth factor-beta1 and -beta2 inhibited [3H]thymidine incorporation but had no effect on sodium nitroprusside-induced apoptosis or on Akt activity; and platelet-derived growth factor-BB had no effects on the measured parameters. HGF, insulin, IGF-1, IGF-2, and EGF may thus contribute to maintenance of the corneal epithelium and coordinate the proliferative and apoptotic responses of this tissue.

Transplantation of Reconstructed Corneal Layer Composed of Corneal Epithelium and Fibroblasts on a Lyophilized Amniotic Membrane to Severely Alkali-burned Cornea

The purpose of this article was to evaluate the graft efficacy of reconstructed corneal layer, composed of autologous corneal epithelium and fibroblasts on a lyophilized amniotic membrane (LAM), in a severely alkali-burned corneal model. After biopsy specimens were obtained from the left eyes of 24 rabbits, the corneal epithelial cells and fibroblasts were expanded in vitro and the corneal layer was reconstructed on LAM. Thirty-six eyes of rabbits underwent alkali burn (1 N NaOH, 30 s) to create a limbal deficiency and a deeply damaged corneal stroma. Four weeks later, group 1 underwent a graft of the reconstructed corneal layer composed of autologous corneal epithelium and fibroblasts on LAM. Group 2 was transplanted with a graft of the reconstructed autologous corneal epithelium, and group 3 served as a control without surgery. Wound healing and stabilization of the ocular surfaces occurred much faster in group 1 than in groups 2 and 3. The eyes in group 3 revealed typical limbal deficiencies with conjuctivalization and persistent corneal epithelial defects. However, the corneas in group 1 developed only mild peripheral neovascularization. Immunohistochemical staining in group 1 demonstrated that p63, cytokeratin 3, E-cadherin, transforming growth factor (TGF)-beta1, and collagen IV were expressed strongly in the corneal epithelium and basement membrane. On the basis of these results, transplantation of the reconstructed corneal layer, composed of autologous corneal epithelium and fibroblasts on LAM, partially accelerated the recovery of the alkali-injured rabbit ocular surface, and might be useful therapeutically for the treatment of patients with severely damaged cornea.

Hepatocyte growth factor and keratinocyte growth factor regulation of epithelial and stromal corneal wound healing

PURPOSE

To investigate the effects of hepatocyte growth factor (HGF) and keratinocyte growth factor (KGF) on early wound healing in the corneal epithelium and stroma.

SETTING

Cell and Molecular Biology Unit, Department of Optometry and Vision Sciences, Cardiff University, and the Cardiff Institute of Tissue Engineering and Repair, Cardiff, United Kingdom.

METHODS

Corneal keratocyte cell cultures and wounded corneal organ cultures (both maintained in serum-free conditions) were treated with 0.1 to 100 ng/mL of HGF or KGF for up to 5 days. Cell cultures were assessed for proliferation, migration, and differentiation into myofibroblasts. Organ cultures were used to evaluate the effect of HGF and KGF on reepithelialization following a wound, epithelial morphology and stratification, keratocyte numbers directly beneath the wounded area, and differentiation into myofibroblasts.

RESULTS

The 2 growth factors had opposite effects on the rate of reepithelialization, with HGF delaying and KGF accelerating epithelial coverage of the wound. Morphologic assessment showed that both growth factors affected the stratification and differentiation of the epithelium. Both factors stimulated proliferation of keratocytes in serum-free cell culture, although neither induced the appearance of myofibroblasts. This was in contrast to wounded organ cultures treated with 100 ng/mL HGF, in which large numbers of myofibroblasts were observed under the wound. Control corneas and those receiving KGF contained very few myofibroblasts. Keratocyte repopulation of the denuded area under the wound was enhanced in the presence of HGF but decreased in response to KGF.

CONCLUSIONS

Hepatocyte growth factor and KGF appeared to have potent and often opposite effects on epithelial and stromal cells following a wound. Hepatocyte growth factor was more detrimental than KGF, resulting in an aberrant epithelium and mass differentiation of keratocytes into myofibroblasts. Inhibition of HGF may be an appropriate therapeutic intervention in the case of persistent epithelial defects and to prevent fibrosis following a corneal stromal wound such as can occur after refractive surgery.

TGF-beta1 stimulates production of gelatinase (MMP-9), collagenases (MMP-1, -13) and stromelysins (MMP-3, -10, -11) by human corneal epithelial cells

Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of ocular surface diseases. This study investigated the regulated expression of gelatinases (MMP-2 and -9), collagenases (MMP-1 and -13) and stromelysins (MMP-3, -10, and -11) by TGF-beta1 in cultured human corneal epithelial cells. Primary human corneal epithelial cell cultures were grown to confluence and treated with different concentrations (0.1, 1.0, 10 ng ml(-1)) of TGF-beta1 in serum-free medium for 6-24 hr. Total RNA was isolated from cultured cells with or without TGF-beta1 treatment for 6 hr and subjected to semi-quantitative RT-PCR and Northern hybridization. Conditioned media were collected from cultures with or without TGF-beta1 treatment for 24 hr to evaluate the MMP production by ELISA and activity assays. Semi-quantitative RT-PCR revealed that the expressions of MMP-9, -1, -13, -3, -10 and -11 mRNA were up-regulated by TGF-beta1 in a concentration-dependent fashion, while MMP-2 and MMP-14 production did not change. Northern hybridization confirmed these findings. Gelatin zymography, MMP ELISA and activity assays showed concentration-dependent stimulated production and activity of MMP-9, -1, -13, -3 and -10 protein in the conditioned media of cultures treated for 24 hr with TGF-beta1. In conclusion, our results demonstrate that TGF-beta1 stimulates the expression and production of gelatinase (MMP-9), collagenases (MMP-1, -13) and stromelysins (MMP-3, -10, -11) in human corneal epithelial cells. These findings suggest that TGF-beta1 may play a role in the pathogenesis of MMP mediated ocular surface diseases, such as sterile corneal ulceration.

Thrombospondin-1 accelerates wound healing of corneal epithelia

To investigate a role of thrombospondin-1 (TSP-1), a multifunctional extracellular matrix protein, in corneal epithelial wound healing, we analyzed the expression of TSP-1 in the normal and wounded mouse corneal epithelia and the effect of exogenous TSP-1 on the wound healing. In immunohistochemical analyses of unwounded corneas, TSP-1 was only detectable in endothelial cells. In contrast, TSP-1 appeared on the wounded corneal surface and on the corneal stroma, at 30 min and 8-16 h, respectively, after making an abrasion on the corneal epithelium. This expression of TSP-1 disappeared after 36-48 h, when re-epithelialization was completed. The TSP-1 mRNA level in the wounded corneas increased as much as three fold compared with that in the unwounded corneas. In organ culture, exogenous TSP-1 stimulated the re-epithelialization of corneal epithelial wounds whereas anti-TSP-1 antibody significantly inhibited the re-epithelialization. These findings suggest the possibility that epithelial defects in the corneas stimulate the expression of TSP-1 in the wound area, resulting in the accelerated re-epithelialization of the cornea.

Effects of irradiation on biological behavior of carcinoma cells under carcinoma-stromal cell interaction and air-liquid interface: a possible model for testing radiosensitivity of carcinoma of the upper aerodigestive tract using a collagen gel culture system

Carcinoma-stromal cell interaction and air-liquid interface (ALI) constitute a specific microenvironment that modulates the biological behavior of carcinoma cells of the upper aerodigestive tract. Although radiotherapy is a useful tool for treating carcinomas of this organ, effects of irradiation on carcinoma cells under carcinoma-stromal cell interaction and ALI are unclear. To address this issue, we examined the effects of irradiation on the proliferation and apoptosis of squamous cell carcinoma cell lines (KB and HEp-2), using three-dimensional collagen gel culture with both carcinoma-stromal cell interaction and ALI. During the second week after irradiation with or without the two factors mentioned above, bromodeoxyuridin (BrdU) uptake and apoptosis of KB, and HEp-2 cell types decreased and increased, respectively. After this stage, the carcinoma cells with these two factors actively re-proliferated together with increased BrdU uptake and decreased apoptosis, whereas the magnitude of these parameters was considerably lower in culture without these factors. We applied our method to carcinoma tissues obtained from several clinical cases. At the same stage, the irradiated carcinoma cells replicated the phenomena observed in cell lines. The data indicate that carcinoma-stromal cell interaction and ALI together promote the re-proliferation of irradiated carcinoma cells and their decreased apoptosis, suggesting that our method is a possible model for testing radiosensitivity of carcinomas in a more physiological condition.

A new organotypic culture of thyroid tissue maintains three-dimensional follicles with C cells for a long term

Thyroid follicles embedded in extracellular matrix (ECM) seem to be supplied enough oxygen by a dense network of capillaries in vivo. Air exposure (AE) causes cells to increase oxygen availability in vitro. We speculated that three-dimensional (3D) environment of ECM together with AE may be applied to a thyroid tissue-organotypic culture, simply simulating such a microenvironment of follicles. To address the issue, we performed 3D collagen gel culture of minced thyroid tissues with or without AE. Most follicles in the tissues without AE died within 7 days. In culture with AE, most of the follicles with calcitonin-positive C cells were kept for over one month. Immunohistochemistry showed that thyrocytes displayed thyroglobulin, thyrotropin receptor, thyroid transcription factor-1 (TTF-1), and pendrin, which are all crucial for thyroid function. C cells expressed calcitonin gene-related peptide and TTF-1. Our study is the first demonstration that 3D collagen gel culture with AE retains 3D thyroid follicles with C cells for a long term. This suggests that ECM and oxygen supply together may be crucial for maintenance of 3D follicle structure and function. Our method will possibly open a new path to the study of thyrocyte-C cell interaction and thyroid biology.

Growth factors in corneal wound healing following refractive surgery: A review

The first part of this review article aims to provide important basic definitions of growth factor terminology, and to put forward a model for understanding the role of growth factors in a wound healing context. In the second part of the paper, we review the literature on growth factors in the cornea, including that on changes associated with wound healing following refractive surgery in the epithelial, stromal, and endothelial layers. The role of growth factors in stromal removal, corneal neovascularization, corneal innervation and wound healing is considered. The importance of the epithelial-stromal interaction is discussed, including the role of growth factors in keratocyte apoptosis. In the final section, we review the current literature on endogenous and exogenous modulation of growth factors in corneal wound healing. This includes important in vitro work but aims to emphasize clinically relevant results. Photorefractive keratectomy (PRK) may have short-term complications such as pain and haze, whereas laser in situ keratomilieusis (LASIK) may have longer-term adverse effects on corneal biomechanics. The emerging technique of laser epithelial keratomilieusis (LASEK) provides an interesting alternative wound which may be less susceptible to the inherent complications of PRK and LASIK. At present, the phenomenon of iatrogenic keratectasia following LASIK is not fully understood, but these features of wound healing following PRK may be amenable to growth factor modulation.

Corneal epithelial wound healing

One of the important functions of the cornea is to maintain normal vision by refracting light onto the lens and retina. This property is dependent in part on the ability of the corneal epithelium to undergo continuous renewal. Epithelial renewal is essential because it enables this tissue to act as a barrier that protects the corneal interior from becoming infected by noxious environmental agents. Furthermore, the smooth optical properties of the corneal epithelial surface are sustained through this renewal process. The rate of renewal is dependent on a highly integrated balance between the processes of corneal epithelial proliferation, differentiation, and cell death. One experimental approach to characterize these three aspects of the renewal process has been to study the kinetics and dynamics of corneal re-epithelialization in a wound-healing model. This effort has employed in vivo and in vitro studies. From such studies it is evident that the appropriate integration and coordination of corneal epithelial proliferation, adhesion, migration, and cell demise is dependent on the actions of a myriad of cytokines. Our goal here is to provide an overview into how these mediators and environmental factors elicit control of cellular proliferation, adhesion, migration, and apoptosis. To this end we review the pertinent literature dealing with the receptor and the cell signaling events that are responsible for mediating cytokine control of corneal epithelial renewal. It is our hope that a better appreciation can be obtained about the complexity of the control processes that are responsible for assuring continuous corneal epithelial renewal in health and disease.

Thyrocyte integration, and thyroid folliculogenesis and tissue regeneration: perspective for thyroid tissue engineering

The thyroid gland is composed of many ball-like structures called thyroid follicles, which are supported by the interfollicular extracellular matrix (ECM) and a capillary network. The component thyrocytes are highly integrated in their specific structural and functional polarization. In conventional monolayer and floating culture systems, thyrocytes cannot organize themselves into follicles with normal polarity. In contrast, in 3-D collagen gel culture, thyrocytes easily form stable follicles with physiological polarity. Integration of thyrocyte growth and differentiation results ultimately in thyroid folliculogenesis. This culture method and subacute thyroiditis are two promising models for addressing mechanisms of folliculogenesis, because thyroid-follicle formation actively occurs both in the culture system and at the regenerative phase of the disorder. The understanding of the mechanistic basis of folliculogenesis is prerequisite for generation of artificial thyroid tissue, which would enable a more physiological strategy to the treatment of hypothyroidism caused by various diseases and surgical processes than conventional hormone replacement therapy. We review here thyrocyte integration, and thyroid folliculogenesis and tissue regeneration. We also briefly discuss a perspective for thyroid tissue regeneration and engineering.

Ets family transcription factor ESE-1 is expressed in corneal epithelial cells and is involved in their differentiation

Involvement of an epithelium-specific transcription factor ESE-1/ESX/ELF3/jen (ESE-1) in corneal epithelial cell differentiation was investigated. ESE-1 was reported to be induced during terminal differentiation of the epidermis and primary keratinocytes and to transactivate target genes through ets binding sites. However, its expression and function in corneal epithelium have not been examined. We report here that ESE-1 is upregulated upon differentiation in mouse corneal epithelium and in immortalized human corneal epithelial cells (HCE). ESE-1 transactivates through the regulatory element of cornea-specific K12 keratin. Moreover, introduction of ESE-1 antisense RNA in HCE cells affect their differentiation. These data suggest the involvement of ESE-1 in differentiation of corneal epithelial cells.

An air-liquid interface promotes the differentiation of gastric surface mucous cells (GSM06) in culture

The gastric surface epithelium is situated at an air-liquid interface because the luminal surface of the alimentary tract is in continuity with the air phase. However, the effects of this microenvironment on the gastric epithelium remain unclear. The aim of this study was to clarify the effects of an air-liquid interface on gastric epithelial cell biology. Gastric surface mucous cells (GSM06) were cultured at an air-liquid interface. Cultured cells were examined by histology, histochemistry, and transmission electron microscopy. When the cells were cultured at an air-liquid interface, the surface cells on the collagen gel became tall columnar and secreted periodic acid-Shiff-positive substances at the apical surface. These cells indicated many mucous granules in the apical cytoplasm and organized the basal lamina at the contact side with the gel. In contrast, under immersed condition, the surface cells showed immature features. This is the first report of an air-liquid interface promoting the differentiation of gastric surface mucous cells in a reconstruction culture of the gastric surface epithelial layer, suggesting that an air-liquid interface may function as a crucial luminal factor to maintain the homeostasis of gastric mucosa.

Air exposure promotes fibroblast growth with increased expression of mitogen-activated protein kinase cascade

Subepithelial tissue cell types in vivo are separated from air by the surface-covering epithelial layer of various organs, e.g., the skin, cornea, and respiratory and upper alimentary tracts. The epithelial defect caused by inflammatory, traumatic or surgical injury would be expected to expose the subepithelial tissue-localized fibroblasts to influx air. However, it is unclear what effects air stimulation elicits in fibroblast growth, which is critical for wound healing. To address this question, we examined the proliferation of 3T3 fibroblasts with bromodeoxyuridine (BrdU) uptake, using fibroblast-embedded collagen gel culture with or without air exposure. The BrdU intake of air-exposed fibroblasts was about 6 times that of air-nonexposed cells. To further characterize this fibroblast growth, we examined the expression of mitogen-activated protein kinase (MAPK) cascade, which plays a key role in the growth-signaling pathway of various cell types. Immunohistochemistry and Western blotting showed that air exposure increased MAPK cascade expression of the cells more strongly than air nonexposure. The data indicate that air exposure promotes MAPK cascade-associated fibroblast growth, suggesting in turn that in wound repair air stimulation itself may be involved in the basic mechanisms of subepithelial fibroblast proliferation and that it may be related to the pathogenesis of excessive fibroplasia through fibroblast overgrowth.