Characterization of extracellular matrix components in the limbal epithelial stem cell compartment

A specialized microenvironment or niche, which regulates maintenance, self-renewal, activation, and proliferation of stem cells by external signals, is one of the key prerequisites for stem cell function. However, the parameters determining the limbal stem cell niche are not yet defined. In order to characterize the role of basement membrane (BM) and extracellular matrix components in the generation of a microenvironmental niche for limbal stem and progenitor cells, we extensively analyzed the topographical variations of the BM zone of human ocular surface epithelia using immunohistochemistry and a large panel of antibodies to most of the presently described intrinsic and associated BM components. Apart from BM components uniformly expressed throughout all ocular surface epithelia (e.g. type IV collagen alpha5 and alpha6 chains, collagen types VII, XV, XVII, and XVIII, laminin-111, laminin-332, laminin chains alpha3, beta3,and gamma2, fibronectin, matrilin-2 and -4, and perlecan), the BM of the limbal epithelium shared many similarities with that of the conjunctival epithelium, including positive labelling for type IV collagen alpha1 and alpha2 chains, laminin alpha5, beta2, and gamma1 chains, nidogen-1 and -2, and thrombospondin-4, whereas type IV collagen alpha3, type V collagen, fibrillin-1 and -2, thrombospondin-1, and endostatin were present in the corneal BM, but lacking or more weakly expressed in the limbal and conjunctival BMs. As compared to both the corneal and conjunctival BMs, the limbal BM showed a markedly increased immunoreactivity for laminin alpha1, alpha2, beta1 chains, and agrin, and a specific but patchy immunoreactivity for laminin gamma3 chain, BM40/SPARC, and tenascin-C, which co-localized with ABCG2/p63/K19-positive and K3/Cx43/desmoglein/integrin-alpha2-negative cell clusters comprising putative stem and early progenitor cells in the basal epithelium of the limbal palisades. Components that were particularly expressed in the corneal-limbal transition zone included type XVI collagen, fibulin-2, tenascin-C/R, vitronectin, bamacan, chondroitin sulfate, and versican, all of which co-localized with vimentin-positive cell clusters comprising putative late progenitor cells in the basal epithelium. This pronounced heterogeneity of the BM in the limbal area, both in the region of limbal palisades and the corneal-limbal transition zone, appears to be involved in providing unique microenvironments for corneal epithelial stem and late progenitor cells. Identification of specific niche parameters might not only help to understand limbal stem cell regulation, but also to improve their selective enrichment and in vitro expansion for therapeutic strategies.     

Characterization of extracellular matrix components in the limbal epithelial stem cell compartment

A specialized microenvironment or niche, which regulates maintenance, self-renewal, activation, and proliferation of stem cells by external signals, is one of the key prerequisites for stem cell function. However, the parameters determining the limbal stem cell niche are not yet defined. In order to characterize the role of basement membrane (BM) and extracellular matrix components in the generation of a microenvironmental niche for limbal stem and progenitor cells, we extensively analyzed the topographical variations of the BM zone of human ocular surface epithelia using immunohistochemistry and a large panel of antibodies to most of the presently described intrinsic and associated BM components. Apart from BM components uniformly expressed throughout all ocular surface epithelia (e.g. type IV collagen α5 and α6 chains, collagen types VII, XV, XVII, and XVIII, laminin-111, laminin-332, laminin chains α3, β3,and γ2, fibronectin, matrilin-2 and -4, and perlecan), the BM of the limbal epithelium shared many similarities with that of the conjunctival epithelium, including positive labelling for type IV collagen α1 and α2 chains, laminin α5, β2, and γ1 chains, nidogen-1 and -2, and thrombospondin-4, whereas type IV collagen α3, type V collagen, fibrillin-1 and -2, thrombospondin-1, and endostatin were present in the corneal BM, but lacking or more weakly expressed in the limbal and conjunctival BMs. As compared to both the corneal and conjunctival BMs, the limbal BM showed a markedly increased immunoreactivity for laminin α1, α2, β1 chains, and agrin, and a specific but patchy immunoreactivity for laminin γ3 chain, BM40/SPARC, and tenascin-C, which co-localized with ABCG2/p63/K19-positive and K3/Cx43/desmoglein/integrin-α2-negative cell clusters comprising putative stem and early progenitor cells in the basal epithelium of the limbal palisades. Components that were particularly expressed in the corneal–limbal transition zone included type XVI collagen, fibulin-2, tenascin-C/R, vitronectin, bamacan, chondroitin sulfate, and versican, all of which co-localized with vimentin-positive cell clusters comprising putative late progenitor cells in the basal epithelium. This pronounced heterogeneity of the BM in the limbal area, both in the region of limbal palisades and the corneal–limbal transition zone, appears to be involved in providing unique microenvironments for corneal epithelial stem and late progenitor cells. Identification of specific niche parameters might not only help to understand limbal stem cell regulation, but also to improve their selective enrichment and in vitro expansion for therapeutic strategies.     

Immunohistochemical evaluation of two corneal buttons with post-LASIK keratectasia

PURPOSE: To examine immunohistochemically 2 human corneal buttons after corneal transplantation for post-laser in situ keratomileusis (LASIK) keratectasia. METHODS: Two ectatic corneas after penetrating keratoplasty and 2 postmortem control corneas from a patient after uncomplicated LASIK were used. Cryostat sections were stained by immunofluorescence for >30 extracellular matrix (ECM) components and proteinases. RESULTS: The ratios of distance between LASIK flap interface and the upper epithelial layer to total corneal thickness were 0.27-0.34 in all cases. The whole flap interface was positive only for total and cellular fibronectin. Stromal types VI and XIV collagen, fibrillin-1, tenascin-C, and vitronectin were unchanged with no evidence of fibrosis. In ectasia cases, keratocytes adjacent to the flap did not express nidogens. Staining for type IV collagen alpha5 chain, nidogen-2, chains of laminin-8, and laminin-10 was weak and discontinuous in the epithelial basement membrane (EBM). Type IV collagen alpha1/alpha2 chains were found in the EBM of ectasia cases only. Matrix metalloproteinase (MMP)-10 showed increase in the epithelium, and MMP-3, in some keratocytes near the flap interface of ectatic corneas. Also, cathepsin F was seen at the flap margin only. Staining for limbal basal epithelial marker, alpha-enolase, was mostly absent in the ectatic cases, suggesting largely normal epithelial differentiation. CONCLUSIONS: Abnormal EBM structure similar to that previously observed in keratoconus and bullous keratopathy and an increase in certain proteinases suggest ongoing EBM lysis and remodeling. Immunohistochemical staining for fibronectin may be used to reveal the position of flap interface.     

Human diabetic corneas preserve wound healing,basement membrane,integrin and MMP-10 differences from normal corneas in organ culture

The authors have previously documented decreased epithelial basement membrane (BM) components and alpha3beta1 epithelial integrin, and increased expression of matrix metalloproteinase (MMP)-10 in corneas of patients with diabetic retinopathy (DR) compared to normal corneas. The purpose of this study was to examine if organ-cultured DR corneas exhibited the same alterations in wound healing and diabetic marker distribution as the autopsy DR corneas. Twenty normal and 17 DR corneas were organ-cultured in serum-free medium over agar-collagen gel at the air-liquid interface for up to 45 days. Circular 5 mm central epithelial wounds were made with n-heptanol, the procedure that will preserve fragile diabetic corneal BM. Wound healing was monitored microscopically every 12 hr. Distribution of diabetic corneal epithelial markers including laminin-10 alpha5 chain, nidogen-1/entactin, integrin alpha3beta1, and MMP-10, was examined by immunofluorescence. Normal corneas healed the central epithelial defect within 3 days (mean=2.3 days), whereas DR corneas on average healed about two times slower (mean=4.5 days). In wounded and completely healed organ-cultured corneas, the patterns of studied markers were the same as in the unwounded organ-cultured corneas. This concerned both normal and DR corneas. As in vivo, normal organ-cultured corneas had continuous staining for laminin-10 and nidogen-1/entactin in the epithelial BM, strong and homogeneous staining for both chains of alpha3beta1 integrin in epithelial cells, and little if any staining for MMP-10. Organ-cultured DR corneas also had marker patterns specific for in vivo DR corneas: interrupted to no staining for laminin-10 and nidogen-1/entactin in the epithelial BM, areas of weak or disorganized alpha3beta1 integrin in epithelial cells, and significant MMP-10 staining in the epithelium and keratocytes. Fibrotic extracellular matrix and myofibroblast markers were largely absent. Thus, epithelial wound healing was much slower in organ-cultured DR corneas than in normal corneas, in complete accordance with clinical data in diabetic patients. DR corneas in organ culture preserved the same marker abnormalities as in vivo. The marker distribution was unchanged in wounded and healed organ-cultured corneas, compared to unwounded corneas. The established corneal organ culture provides an adequate system for elucidating mechanisms of epithelial alterations in human DR corneas.     

Distribution of laminins in the developing human eye

PURPOSE: To examine the distribution of laminin (Ln) chains in basement membranes (BMs) of the human cornea, lens, and retina in fetal development. METHODS: Ten fetal eyes (9-20 weeks of gestation [wg]) were serially sectioned and treated with specific antibodies against the Ln-alpha1, -alpha2, -alpha3, -alpha4, -alpha5, -beta1, -beta2, -beta3, and -gamma1 chains. RESULTS: The BM of the corneal epithelium was reactive for Ln-alpha3, -alpha5, -beta1, and beta3 chains through all ages, whereas the Ln-alpha1 chain was present at 9 to 12 wg and the Ln-alpha4 chain from 10 wg. The Descemet's membrane (DM) was labeled with the Ln-alpha1 and -alpha4 chains at 10 to 17 wg, the Ln-alpha5 chain from 10 wg, the Ln-beta1 chain at 11 to 17 wg, and the Ln-beta3 chain from 17 wg. The Ln-alpha1, alpha5, -beta1, and -beta2 chains were present in the lens capsule and the internal limiting membrane (ILM) through all ages. The Bruch's membrane (BrM) was immunoreactive for the Ln-alpha3, alpha4, -alpha5, -beta1, and -beta2 chains through all ages, whereas the Ln-alpha1 chain was absent from 20 wg onward. The Ln-alpha2 chain was not detected in the eye, but it was present in the extraocular muscles. CONCLUSIONS: BMs play an important role during morphogenesis, in that they influence cell proliferation, migration, and tissue differentiation. Lns are the major noncollagenous component of BMs. The presence of four different alpha chains, three beta chains, and one gamma chain of Ln in the eye reveals a high degree of complexity from the early stages of development and suggests an important role for the different Ln chains in human ocular differentiation.     

Immunohistochemical characterization of extracellular matrix in the developing human cornea

Collagen, fibronectin and laminin are important components of the extracellular matrix of the human cornea. We used the immunofluorescence technique with polyclonal antibodies directed against these proteins and to bullous pemphigoid antigen (BPA), in order to study their distribution in human corneas from 8 weeks of gestation to term and in adult corneas. Immunoreactivity was observed with antibodies to type I collagen in the limbus and the corneal stroma at 8 weeks of gestation. At 11 weeks of gestation it was found in epithelial basement membrane (EBM) and Descemet's membrane (DM) and continued thus throughout fetal and adult life. Type II collagen was not detected in fetal or adult cornea. Type III collagen was detected during 8-20th weeks of gestation in the EBM, DM and stroma. After 27th weeks of gestation, type III collagen could no longer be detected in the central cornea. Type IV collagen was detected in the EBM as early as 8 weeks of gestation and remained positive throughout fetal and adult life. Descemet's membrane was negative for type IV collagen at 8 weeks of gestation and became positive thereafter. Immunostaining for fibronectin in DM was negative at 8 weeks of gestation, followed by patchy staining of corneal stroma and EBM up to the age of 37 weeks of gestation. Staining in the EBM was negative or variable up to 70 years of age, and then became positive again in a 77 year old individual. Staining for LN was positive in the EBM after 8 weeks of gestation. Staining was negative in DM at that age, but became positive after 9 weeks of gestation. Staining for BPA was negative at 8-9 weeks of gestation, then gradually became positive.     

Changes in the localization of collagens IV and VIII in corneas obtained from patients with posterior polymorphous corneal dystrophy

Posterior polymorphous corneal dystrophy (PPCD) is a hereditary bilateral disorder affecting primarily the endothelium and Descemet's membrane (DM). The aim of this study was to determine the changes in the presence and localization of the α1-α6 collagen IV chains and α1, α2 collagen VIII chains in Czech patients with PPCD. Twelve corneal buttons from ten PPCD patients who underwent corneal grafting, as well as eight unaffected corneas, were used. Enzymatic indirect immunohistochemistry was performed on cryosections using antibodies against the α1-α6 collagen IV chains and α1, α2 collagen VIII chains. The intensity of the signal was examined separately in the basal membrane of the epithelium (BME), stroma and DM. More than 50% of PPCD specimens exhibited positivity for α1 and α2 collagen IV chains in the BME and in the posterior stroma, while no staining was detected in these areas in control specimens. The signal for the α1 and α2 collagen IV chains was more intense in DM of PPCD corneas compared to controls and it was shifted from the stromal side (in control tissue) to the endothelial side of DM (in the patients). A less intensive signal in PPCD corneas for the α3 and α5 chains in DM and an accumulation of α3-α5 in the posterior stroma in diseased corneas were the only differences in staining for the α3-α6 collagen IV chains. The α1 collagen VIII chain was detected on both the endothelial and the stromal sides of DM in 90% of patients with PPCD, compared with the prevailing localization on the stromal side of DM in control corneas. A change in the localization of the α2 collagen VIII chain in DM from vertically striated features in control specimens to double line positivity in the DM of PPCD corneas and positive staining in the posterior collagenous layer of four patients were also detected. In three PPCD patients a fibrous pannus located under the BME, positive for α1-α3, α5 collagen IV chains and α1 collagen VIII chain, was observed. The increased expression of the α1, α2 collagen IV and α1 collagen VIII chains and the change in their localization in DM may contribute to the increased endothelial proliferative capacity observed in PPCD patients.     

Extracellular matrix and matrix metalloproteinase changes in human corneas after complicated laser-assisted in situ keratomileusis (LASIK).

PURPOSE: To characterize extracellular matrix (ECM) and nine matrix metalloproteinase (MMP) changes in two corneas that underwent a complicated laser-assisted in situ keratomileusis (LASIK) procedure. METHODS: The first patient underwent bilateral LASIK. The flap on the left eye was transected in several locations and placed back. This cornea later developed edema, and the removed flap was analyzed after lamellar keratoplasty. The second patient had a LASIK flap lifted, replaced twice, and then completely removed. The epithelium grew over the stroma, but haze and severe ectasia occurred. After penetrating keratoplasty, the recipient cornea was analyzed. An autopsy cornea from a person who underwent uneventful LASIK and ten normal autopsy corneas served as controls. Corneas were analyzed by immunohistochemistry. RESULTS: Both flap regions in the treated corneas had marked alterations of ECM components and MMPs. Stromal deposits of various ECM proteins, including those normally absent in the central cornea (tenascin-C, fibrillin-1, type XIV collagen), were found. Rare myofibroblasts and inflammatory cells were present. The epithelial basement membrane (BM) was altered in both cases. The most dramatic change was poor or no staining for alpha3-alpha6 type IV collagen chains and thrombospondin. The limbal alpha1-alpha2 type IV collagen and laminin-2 (alpha2beta1gamma1) appeared in the central epithelial BM. Other components were altered to a lesser extent. The anterior stroma was positive for MMP-1 and MMP-2, and some MMP-7 was seen in the epithelium. These ECM and MMP patterns were not seen in uneventful LASIK or normal corneas. CONCLUSIONS: In the flaps of LASIK-treated corneas, fibrosed areas of anterior stroma had increased levels of MMP-1 and MMP-2 that may have caused loss of specific type IV collagen isoforms in the epithelial BM. These changes may reflect an ongoing wound healing process and contribute to the development of ectasia.     

Distribution of very late activation integrins in the human cornea. An immunohistochemical study using monoclonal antibodies

There is growing evidence that cellular adhesion mechanisms characterized by cell-cell and cell-matrix interactions are a fundamental process in the immunobiology of the cornea. Interactions with various extracellular matrix components are mediated by the very late activation (VLA) subgroup of the integrin superfamily of adhesion molecules. The six different VLA dimers known thus far consist of a common beta 1 subunit and a variable alpha (1 to 6) subunit. They serve as receptors for laminin (alpha 3 and alpha 6), collagen (alpha 2 and alpha 3), and fibronectin (alpha 4 and alpha 5). Using in situ immunohistochemistry and monoclonal antibodies, the distribution of the common beta 1 and the variable alpha-chains of VLA molecules was studied in normal human cornea and in cases with scarring or subepithelial/retrocorneal fibrous tissue. Epithelial cells were VLA-beta 1 and VLA-alpha 2, -alpha 3, -alpha 4, -alpha 5, and -alpha 6 positive. This is consistent with their intercellular adhesion and may aid in their attachment to the basement membrane which is composed of collagen, laminin, and fibronectin. Keratocytes in normal stroma expressed only the common beta 1-chain and no detectable alpha-chains. In regions of scar or fibrous tissue, however, an upregulated expression of the alpha-chains was detected. The VLA- alpha 1, -alpha 3, -alpha 4, and -alpha 5 were expressed in young fibrous tissue; in older lesions, VLA- alpha 1, -alpha 2, -alpha 3, -alpha 4, and -alpha 5 could be detected. The corneal endothelium showed a strikingly strong positivity for all VLA integrins.(ABSTRACT TRUNCATED AT 250 WORDS)     

Basement membrane dissolution and reassembly by limbal corneal epithelial cells expanded on amniotic membrane

PURPOSE: To investigate basement membrane (BM) formation during ex vivo expansion of limbal corneal epithelial cells on intact amniotic membrane (iAM) and epithelially denuded (d)AM. METHODS: Human limbal explants were cultured on iAM and dAM. Expression of BM components, including laminin-5, type IV collagen, type VII collagen, perlecan, integrin alpha6, and epithelial cell differentiation markers such as p63, cytokeratin 3 (K3), and cytokeratin 12 (K12), were investigated by immunostaining. Levels of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 in the conditioned media were determined by ELISA and gelatin zymography. RESULTS: All four BM components were preserved in both iAM and dAM before culturing, but dissolved 1 week afterward when MMP-2 was increased. Epithelial outgrowth correlated with increased expression of MMP-2 and -9 for both cultures. Resynthesis of BM began with laminin-5 followed by other components. This process took place at 1 week on iAM but at 2 weeks on dAM after culturing. At 4 weeks, BM was more maturely deposited as a linear band from the explant toward the leading edge on iAM and temporally correlated with a sharp decline of MMP-9 levels. In contrast, such BM deposition began at the leading edge on dAM only when TIMP-1 levels were increased. Epithelial cell outgrowth on iAM expressed more p63 but less K3 and K12 than did that on dAM. CONCLUSIONS: After dissolution of original amniotic BM, new BM formed by ex vivo expanded human limbal corneal epithelial cells on iAM deposits much faster and is more mature, resulting in regeneration of a limbal epithelial phenotype. In contrast, BM deposition is delayed and remains immature on dAM, resembling wound healing by a corneal epithelial phenotype. Thus, BM resynthesis may be used as another objective readout for assessing the success of ex vivo expansion of limbal epithelial progenitor cells on AM.     

Alterations of epithelial adhesion molecules and basement membrane components in lattice corneal dystrophy (LCD)

Background

The aim of the study was to investigate the histopathological and ultrastructural correlate of delayed epithelial healing in eyes with lattice corneal dystrophy (LCD).

Materials and Methods

Corneal buttons from 4 patients with LCD (two with subepithelial, two with stromal amyloid deposits) and 2 control corneas were examined. Cell-matrix adhesion molecules and basement membrane components of the corneal epithelium were analyzed by immunohistochemistry and hemidesmosomes between epithelium and stroma were quantified by transmission electron microscopy (TEM).

Results

By TEM well-developed hemidesmosomes anchored the basal epithelial cells to the underlying basement membrane in all normal and LCD corneas. Hemidesmosome density was not significantly different in subepithelial (224.7?±?34.1/100 µm) and stromal (234.3?±?36.3/100 µm) LCD compared to controls (241.3?±?26.8/100 µm). The basement membrane was interrupted in subepithelial, but continous in stromal LCD. Integrin α6 and ß4 staining formed a continous line along the basal surface of the corneal epithelium in control corneas, whereas it appeared discontinous and patchy both in subepithelial and stromal forms of LCD. Staining for αV integrin showed irregular staining patterns, i.e. enhanced labelling intensity in subepithelial and interrupted pattern in stromal LCD, respectively. Integrins α3, ß1, ß2, and ß5, dystroglycan, and plectin were not markedly different in dystrophic corneas. Type VII collagen showed a discontinuous staining in subepithelial forms of LCD. In stromal forms of LCD, type VII collagen staining occurred in additional patches underneath the epithelial basement membrane zone. Type XVII collagen staining was reduced in subepithelial LCD. Laminin-1, laminin-5 and laminin γ2 showed variable irregular staining patterns in dystrophic corneas with focal interruptions, focal thickenings, and reduplications of basement membrane. Some irregularities in corneas with subepithelial amyloid were observed for collagen types IV, V, and XVIII, laminin α1, α3, and γ1, nidogen-1 and -2, perlecan, fibrillin-1.

Conclusions

Immunohistochemical and electron microscopic evidence of structural alterations was found in LCD compared to normal corneas concerning cell-matrix adhesion molecules and basement membrane components. These alterations were more pronounced in dystrophic corneas with subepithelial amyloid deposits than in those with stromal deposits. Histopathological findings may correspond to reduced cell-matrix interactions and partly explain delayed epithelial healing in patients with lattice corneal dystrophy.     

Biochemical and morphological analysis of basement membrane component expression in corneoscleral and cribriform human trabecular meshwork cells

PURPOSE: To determine whether cells of the cribriform trabecular meshwork (TM) express basement membrane (BM) components similar to corneoscleral TM cells and to determine whether cribriform cells are connected to the elastic tendon net of the TM. METHODS: TM cells of the corneoscleral and the cribriform regions were cultured from 10 eyes of 10 donors, aged 20 to 87 years. Cell types were classified by alpha-smooth muscle actin (smA), desmin, and alphaB-crystallin staining. Expression of collagen type IV (ColIV) chains alpha1 to 6; collagen type VIII (ColVIII) alpha1; laminin subunits alpha1 to 5, beta1 to 3, and gamma1 to 3; and nidogen 1 and 2 was tested in both cell types by semiquantitative RT-PCR (sqPCR). Expression of ColIValpha2, ColVIIIalpha1, laminin beta2, and nidogen 1 was quantified by Northern blot analysis. The response to transforming growth factor (TGF)-beta2 treatment was investigated. Serial tangential and sagittal TM sections of 16 eyes from 10 donors (aged 12-90 years) were used for electron- and immunoelectron microscopy. RESULTS: Both TM cell types expressed ColIV chains alpha1, alpha2, alpha4, alpha5, and alpha6; ColVIII alpha1; laminin subunits alpha3, alpha4, beta1, beta2, beta3, gamma1, and gamma2; and nidogen 1, as determined by Northern blot analysis and sqPCR. ColIV alpha3; laminin subunits alpha1, alpha2, and gamma3; and nidogen 2 were not detectable by PCR. Responses to TGF-beta2 treatment did not differ between cell types. In vivo, all cribriform cells were in contact with ColIV containing BM material and were found to connect to the cribriform elastic network. CONCLUSIONS: Cribriform and corneoscleral TM cells show no differences in expression of BM components and response to TGF-beta2. The direct connection of cribriform cells to the elastic tendon network suggests that they are under mechanical tension. This could explain previous findings of alphaB-crystallin expression in the cribriform region.     

Immunohistochemical and ultrastructural analysis of dysplastic epithelium of human ocular surface: basement membrane and intermediate filament.

PURPOSE: The dysplastic corneal epithelium is characterized by the abnormal proliferation of epithelial cells. The phenotypes of these cells have not been elucidated. We investigated whether such epithelium expresses the phenotypes of corneal or conjunctival epithelial cells. METHODS: The corneas and conjunctivae from four normal subjects and from one patient with epithelial dysplasia of the central cornea were immunostained for IV and VII collagens and for cytokeratins. Monoclonal antibodies against collagen IV reacted to the [alpha1(IV)]2alpha2(IV) or alpha5(IV) molecule. Anti-cytokeratin antibodies were used to define epithelial cell types. The ultrastructure of the basement membrane (BM) of each specimen also was examined. RESULTS: Type VII collagen immunoreactivity was detected in all the specimens of epithelial BM. The anti-collagen IV [alpha1(IV)]2alpha2(IV) antibody labeled the conjunctival BMs, not the BMs of the corneal epithelia, of each subject. The normal corneal epithelial BM, not the BM of the conjunctival or dysplastic corneal epithelium, was immunolabeled with anti-alpha5(IV) antibody. The pattern of cytokeratin expression in the corneal epithelial dysplasia resembled that seen in the normal conjunctivae. Small breaks in the BM of dysplastic corneal epithelium were ultrastructurally revealed. The number of hemidesmosomes in the dysplastic corneal epithelium was decreased as compared with that in the normal BM. CONCLUSION: The composition of collagen types within the BM and the cellular phenotype of the dysplastic epithelium in the cornea resembled those of conjunctival epithelium, not of the cornea.     

Phenotypic study of a case receiving a keratolimbal allograft and amniotic membrane for total limbal stem cell deficiency

PURPOSE: To report the expression pattern of key molecules by the reconstructed corneal epithelium after a keratolimbal allograft (KLAL) and amniotic membrane transplantation (AMT) for total limbal stem cell deficiency. DESIGN: Interventional case report. METHOD: A 50-year-old woman with severe chemical burns in both eyes received an AMT as a temporary patch at the acute stage, and a KLAL with AMT as a graft at the chronic stage for total limbal stem cell deficiency. The corneal button removed during subsequent corneal transplantation was submitted for immunofluorescence staining with monoclonal antibodies against keratin K3, MUC5AC, connexin 43, integrins alpha3beta1 and alpha6beta4, and laminin 5 for comparison with a normal cornea. RESULTS: Histologically, a normal stratified corneal epithelium has five to six cell layers that lay on the thick amniotic membrane basement membrane. The phenotype was of a corneal origin, based on expression of positive keratin K3, negative MUC5AC, and positive connexin 43. Furthermore, intact basement membrane complexes were present, evidenced by positive staining to integrins alpha3beta1 and alpha6beta4 and to laminin 5. CONCLUSIONS: A normal corneal epithelial phenotype with normal basement membrane complexes was restored after a KLAL and AMT in a case with total limbal stem cell deficiency.     

The phenotype of limbal epithelial stem cells

PURPOSE: The purpose of this study was to identify phenotypic markers of human limbal stem cells in fetal and adult corneas. METHODS: RNA from microscopically dissected superficial limbal and central fetal (18 weeks) corneas was amplified and used to generate P(32)-labeled, reverse-transcribed antisense RNA that was linearly amplified and hybridized to a focused stem cell cDNA microarray. Differential gene expression of fetal limbus was compared with the expression of central cornea. Microarray differential expression experiments were performed on P63-expressing primary cultured limbal epithelial cells (passage 1; Pa1) and primary cells passaged 5 times (Pa5). Semiquantitative RT-PCR assay and immunohistochemistry were performed on fetal and adult corneas and cultured primary limbal epithelial cells, to confirm the results of the microarray experiments. Slow-cycling (pulsed bromodeoxyuridine label-retaining) limbal epithelium in corneal organ culture was studied for the expression of four selected upregulated limbal genes. RESULTS: Of the 266 genes tested, 33 were differentially overexpressed (more than twofold) in the fetal limbus (compared with central cornea) and primary cultured limbal epithelium compared with primary cells after 5 passages. Cytokeratin 15 (CK15) and cytokeratin 14 (CK14) are expressed in limbal basal epithelium and P-cadherin (CDH3) and Wnt-4 expression was restricted to basal and immediate parabasal limbal epithelium of both the adult and fetal corneas). Bromodeoxyuridine label retaining epithelium in corneal organ culture (slow-cycling cells) expressed the four selected limbal upregulated genes. CONCLUSIONS: For the first time, a focused stem cell pathway microarray analysis has been performed on fetal cornea and cultured limbal explant epithelium. CK15, CK14, CDH3, and Wnt-4 are expressed in the basal limbal epithelial cells.     

Phenotypic study of a case with successful transplantation of ex vivo expanded human limbal epithelium for unilateral total limbal stem cell deficiency

OBJECTIVE: To minimize the risk to the donor eye when a conjunctival limbal autograft is performed for unilateral total limbal stem cell deficiency (LSCD), a new approach has been reported of expanding limbal epithelial progenitor cells from a small limbal biopsy cultured on amniotic membrane (AM). Herein, we present for the first time the morphologic and phenotypic outcome of one such patient. DESIGN: Interventional case report. METHODS: A 31-year-old male with a severe acid burn to his left eye received AM transplantation at the acute stage and a keratolimbal allograft (KLAL) at the chronic stage for total LSCD. As an alternative to combat the failed KLAL, the above-mentioned new surgical procedure was performed. The corneal button, obtained after a penetrating keratoplasty performed 5.5 months later, and a normal corneal button as a control were submitted to hematoxylin-eosin and immunofluorescence staining for keratin K3, connexin 43, goblet-cell mucin MUC 5AC, laminin 5, and integrins alpha3beta1 and alpha6beta4. MAIN OUTCOME MEASURES: Clinical and immunohistologic features. RESULTS: The resultant epithelium was stratified with five to six cell layers and anchored to laminin 5 of the amniotic basement membrane via integrins alpha3beta1 and alpha6beta4 in a manner similar to the normal corneal epithelium. Intriguingly, the epithelial phenotype was limbal and not corneal, based on the negative expression of keratin K3 and connexin 43 of the basal epithelium. CONCLUSIONS: The technique described ensures the preservation of amniotic basement membrane, which allows formation of adhesion complexes and maintains normal corneal architecture. The preservation of a limbal epithelial phenotype on the reconstructed corneal surface indicates that AM provides a unique stromal environment conducive to the preservation and expansion of limbal epithelial progenitor cells.     

Localization of corneal epithelial stem cells in the developing rat.

A monoclonal antibody, 4G10.3, was developed that preferentially binds limbal basal cells in adult rat, rabbit, and human corneas. These cells were hypothesized to be the stem cells for the corneal epithelium. The antibody 4G10.3 was localized by immunofluorescence microscopy in rats 1 d and 1, 1.5, 2, 3, 4, and 6 wk of age. Until 1.5 wk, 4G10.3 bound intensely to all basal cells in the cornea and the limbus. At 2 wks, the basal cells at the central cornea abruptly changed their shape from flattened or ovoid to large and cuboidal and bound 4G10.3 with greatly reduced intensity. Increased stratification of epithelium also was seen. Cells binding 4G10.3 gradually became sequestered to the limbal area after 2 wk, concomitant with increased stratification. At 4 and 6 wk, 4G10.3 binding was identical to that in adult corneas with only limbal basal cells showing positive binding. Basal cells in the limbal epithelium did not decrease their intense binding of 4G10.3 or change their ovoid cellular shape from 1 d through adult life. These results suggest that, during development, stem or stem-like cells are localized throughout the basal layer of the corneal and limbal epithelium. As the cornea matures, these cells are sequestered in the limbus at the same time that stratification of the epithelium and shape changes occur in the basal cells.     

Laminin isoforms in human extraocular muscles

PURPOSE: To determine the laminin isoform composition of the basement membranes (BMs) in the human extraocular muscles (EOMs) and relate it to the fact that EOMs are spared in laminin alpha2-chain-deficient congenital muscular dystrophy. METHODS: Samples from adult human EOMs and limb muscle were processed for immunocytochemistry, with monoclonal antibodies against laminin chains (Ln) alpha1 to -5, beta1 and -2, and gamma1. Neuromuscular junctions (NMJs) were identified with acetylcholinesterase reaction. The capillary density was measured in sections stained with anti-Lnalpha5. RESULTS: The extrasynaptic BM of the EOM muscle fibers contained Lnalpha2, -beta1, -beta2, and -gamma1, and, in contrast to limb muscle, it also contained Lnalpha4 and -alpha5, to some extent. The distinct laminin composition of the EOMs was confirmed by the presence of Lutheran protein, an alpha5-chain-specific receptor not found in limb muscle. At the NMJs, there was increased expression of Lnalpha4 and expression of Lnalpha2, -alpha5, -beta1, -beta2, and -gamma1 was also maintained. The capillary density was very high (1050 +/- 190 capillaries/mm(2)) in the EOMs and significantly (P < 0.05) higher in the orbital (1170 +/- 180 capillaries/mm(2)) than in the global (930 +/- 110 capillaries/mm(2)) layer. CONCLUSIONS: The human EOMs showed important differences in laminin isoform composition and capillary density when compared with human limb muscle and muscles of other species. The presence of additional laminin isoforms other than laminin-2 in the BM of the extrasynaptic sarcolemma could partly explain the sparing of the EOMs in Lnalpha2-deficient congenital muscular dystrophy.