The collagens of the developing bovine cornea

Human corneal endothelial cells from older donors can be cultured and passaged on cell-derived extracellular matrix

PURPOSE

To investigate the effect of culturing human corneal endothelial cells (HCEnCs) from older donors on extracellular matrix (ECM) derived from human corneal endothelial cell line (HCEC-12).

METHODS

HCEC-12 cells were cultured on lab-tek chamber slides for 9 days. Upon confluence, the cells were ruptured using ammonium hydroxide leaving the released ECM on the slide surface which was visualized using scanning electron microscope (SEM). HCEnCs from old aged donor tissues (n = 40) were isolated and cultured on either fibronectin-collagen (FNC) or HCEC-12 ECM at passage (P) 0. At subsequent passages (P1 and P2), cells were sub-cultured on FNC and ECM separately. Live/dead analysis and tight junction using ZO-1 staining were used to record percentage viability and morphological changes. The protein composition of HCEC-12 ECM was then analysed using liquid chromatography-mass spectrometry.

RESULTS

SEM images showed long fibrillar-like structures and a fully laid ECM upon confluence. HCEnCs cultured from older donor tissues on this ECM showed significantly better proliferation and morphometric characteristics at subsequent passages. Out of 1307 proteins found from the HCEC-12 derived ECM, 93 proteins were evaluated to be matrix oriented out of which 20 proteins were exclusively found to be corneal endothelial specific.

CONCLUSIONS

ECM derived from HCEC-12 retains protein and growth factors that stimulate the growth of HCEnCs. As the current clinical trials are from younger donors that are not available routinely for cell culture, HCEnCs from older donors can be cultured on whole ECM and passaged successfully.

Engineering a Corneal Stromal Equivalent Using a Novel Multilayered Fabrication Assembly Technique

To overcome the serious shortage of donor corneas for transplantation, alternatives based on tissue engineering need to be developed. Decellularized corneas are one potential alternative, but their densely packed collagen architecture inhibits recellularization in vitro. Therefore, a new rapid method of recellularizing these constructs to ensure high cellularity throughout the collagen scaffold is needed. In this study, we developed a novel method for fabricating corneal constructs by using decellularized porcine corneal sheets assembled using a bottom-up approach by layering multiple sheets between cell-laden collagen I hydrogel.

Corneal lenticules were cut from porcine corneas by cryosectioning, then decellularized with detergents and air-dried for storage as sheets. Human corneal stromal cells were encapsulated in collagen I hydrogel and cast between the dried sheets. Constructs were cultured in serum-free medium supplemented with ascorbic acid and insulin for 2 weeks. Epithelial cells were then seeded on the surface and cultured for an additional week. Transparency, cell viability, and phenotype were analyzed by qPCR, histology, and immunofluorescence. Constructs without epithelial cells were sutured onto an ex vivo porcine cornea and cultured for 1 week.

Lenticules were successfully decellularized, achieving dsDNA values of 13 ± 1.2 ng/mg dry tissue, and were more resistant to degradation than the collagen I hydrogels. Constructs maintained high cell viability with a keratocyte-like phenotype with upregulation of keratocan, decorin, lumican, collagen I, ALDH3A1, and CD34 and the corneal epithelial cells stratified with a cobblestone morphology. The construct was amenable to surgical handling and no tearing occurred during suturing. After 7 days ex vivo, constructs were covered by a neoepithelium from the host porcine cells and integration into the host stroma was observed.

This study describes a novel approach toward fabricating anterior corneal substitutes in a simple and rapid manner, obtaining mature and suturable constructs using only tissue-derived materials.

Decellularization and recellularization of cornea: Progress towards a donor alternative

The global shortage of donor corneas for transplantation has led to corneal bioengineering being investigated as a method to generate transplantable tissues. Decellularized corneas are among the most promising materials for engineering corneal tissue since they replicate the complex structure and composition of real corneas. Decellularization is a process that aims to remove cells from organs or tissues resulting in a cell-free scaffold consisting of the tissues extracellular matrix. Here different decellularization techniques are described, including physical, chemical and biological methods. Analytical techniques to confirm decellularization efficiency are also discussed. Different cell sources for the recellularization of the three layers of the cornea, recellularization methods used in the literature and techniques used to assess the outcome of the implantation of such scaffolds are examined. Studies involving the application of decellularized corneas in animal models and human clinical studies are discussed. Finally, challenges for this technology are explored involving scalability, automatization and regulatory affairs.

Corneal Regeneration After Photorefractive Keratectomy: A Review

Photorefractive keratectomy (PRK) remodels corneal stroma to compensate refractive errors. The removal of epithelium and the ablation of stroma provoke the disruption of corneal nerves and a release of several peptides from tears, epithelium, stroma and nerves. A myriad of cytokines, growth factors, and matrix metalloproteases participate in the process of corneal wound healing. Their balance will determine if reepithelization and stromal remodeling are appropriate. The final aim is to achieve corneal transparency for restoring corneal function, and a proper visual quality. Therefore, wound-healing response is critical for a successful refractive surgery. Our goal is to provide an overview into how corneal wounding develops following PRK. We will also review the influence of intraoperative application of mitomycin C, bandage contact lenses, anti-inflammatory and other drugs in preventing corneal haze and post-PRK pain.

Importance of the stem cell microenvironment for ophthalmological cell-based therapy

Cell therapy is a promising treatment for diseases that are caused by cell degeneration or death. The cells for clinical transplantation are usually obtained by culturing healthy allogeneic or exogenous tissue in vitro. However, for diseases of the eye, obtaining the adequate number of cells for clinical transplantation is difficult due to the small size of tissue donors and the frequent needs of long-term amplification of cells in vitro, which results in low cell viability after transplantation. In addition, the transplanted cells often develop fibrosis or degrade and have very low survival. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPS) are also promising candidates for cell therapy. Unfortunately, the differentiation of ESCs can bring immune rejection, tumorigenicity and undesired differentiated cells, limiting its clinical application. Although iPS cells can avoid the risk of immune rejection caused by ES cell differentiation post-transplantation, the low conversion rate, the risk of tumor formation and the potentially unpredictable biological changes that could occur through genetic manipulation hinder its clinical application. Thus, the desired clinical effect of cell therapy is impaired by these factors. Recent research findings recognize that the reason for low survival of the implanted cells not only depends on the seeded cells, but also on the cell microenvironment, which determines the cell survival, proliferation and even reverse differentiation. When used for cell therapy, the transplanted cells need a specific three-dimensional structure to anchor and specific extra cellular matrix components in addition to relevant cytokine signaling to transfer the required information to support their growth. These structures present in the matrix in which the stem cells reside are known as the stem cell microenvironment. The microenvironment interaction with the stem cells provides the necessary homeostasis for cell maintenance and growth. A large number of studies suggest that to explore how to reconstruct the stem cell microenvironment and strengthen its combination with the transplanted cells are key steps to successful cell therapy. In this review, we will describe the interactions of the stem cell microenvironment with the stem cells, discuss the importance of the stem cell microenvironment for cell-based therapy in ocular diseases, and introduce the progress of stem cell-based therapy for ocular diseases.

Effect of Surgical Technique on Corneal Implant Performance

PURPOSE

Our aim was to determine the effect of a surgical technique on biomaterial implant performance, specifically graft retention.

METHODS

Twelve mini pigs were implanted with cell-free, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) cross-linked recombinant human collagen type III (RHCIII) hydrogels as substitutes for donor corneal allografts using overlying sutures with or without human amniotic membrane (HAM) versus interrupted sutures with HAM. The effects of the retention method were compared as well as the effects of collagen concentration (13.7% to 15% RHCIII).

RESULTS

All implanted corneas showed initial haze that cleared with time, resulting in corneas with optical clarity matching those of untreated controls. Biochemical analysis showed that by 12 months post operation, the initial RHCIII implants had been completely remodeled, as type I collagen, was the major collagenous protein detected, whereas no RHCIII could be detected. Histological analysis showed all implanted corneas exhibited regeneration of epithelial and stromal layers as well as nerves, along with touch sensitivity and tear production. Most neovascularization was seen in corneas stabilized by interrupted sutures.

CONCLUSIONS

This showed that the surgical technique used does have a significant effect on the overall performance of corneal implants, overlying sutures caused less vascularization than interrupted sutures.

TRANSLATIONAL RELEVANCE

Understanding the significance of the suturing technique can aid the selection of the most appropriate procedure when implanting artificial corneal substitutes. The same degree of regeneration, despite a higher collagen content indicates that future material development can progress toward stronger, more resistant implants.

Hydration dependent viscoelastic tensile behavior of cornea

The cornea is a protective transparent connective tissue covering the front of the eye. The standard uniaxial tensile experiments are among the most popular techniques for investigating biomechanical properties of the cornea. This experimental method characterizes the stress-strain response of corneal strips immersed in a bathing solution. In the present study, the important roles of corneal hydration on tensile viscoelastic properties were investigated. The thickness was used as a surrogate for hydration and uniaxial tensile experiments were performed on bovine corneal samples with four different average thickness (hydration), i.e., 1100 μm (4.87 mg water/mg dry tissue), 900 μm (4.13 mg water/mg dry tissue), 700 μm (3.20 mg water/mg dry tissue), and 500 μm (1.95 mg water/mg dry tissue). The samples were immersed in mineral oil in order to prevent their swelling during the experiments. A quasilinear viscoelastic (QLV) model was used to analyze the experimental measurements and determine viscoelastic material constants. It was observed that both maximum and equilibrium (relaxed) stresses were exponentially increased with decreasing tissue thickness (hydration). Furthermore, the QLV model successfully captured the corneal viscoelastic response with an average R (2) value greater than 0.99. Additional experiments were conducted in OBSS in order to confirm that these significant changes in viscoelastic properties were because of corneal hydration and not the bathing solution. The findings of this study suggest that extra care must be taken in interpreting the results of earlier uniaxial tensile testings and their correspondence to the corneal biomechanical properties.

In vitro evaluation of the interactions between human corneal endothelial cells and extracellular matrix proteins

The corneal endothelium is the innermost cell layer of the cornea and rests on Descemet's membrane consisting of various extracellular matrix (ECM) proteins which can directly affect the cellular behaviors such as cell adhesion, proliferation, polarity, morphogenesis and function. The objective of this study was to investigate the interactions between the ECM environment and human corneal endothelial cells (HCECs), with the ultimate goal to improve cell proliferation and function in vitro. To evaluate the interaction of HCECs with ECM proteins, cells were seeded on ECM-coated tissue culture dishes, including collagen type I (COL I), collagen type IV (COL IV), fibronectin (FN), FNC coating mix (FNC) and laminin (LM). Cell adhesion and proliferation of HCECs on each substratum and expression of CEC markers were studied. The results showed that HCECs plated on the COL I, COL IV, FN and FNC-coated plates had enhanced cell adhesion initially; the number for COL I, COL IV, FN and FNC was significantly higher than the control (P < 0.05). In addition, cells grown on ECM protein-coated dishes showed more compact cellular morphology and CEC marker expression compared to cells seeded on uncoated dishes. Collectively, our results suggest that an adequate ECM protein combination can provide a long-term culture environment for HCECs for corneal endothelium transplantation.

Ultrastructure alteration in the corneal stroma of hydrated camel corneoscleral button and corneal button

PURPOSE

To investigate the changes in the ultrastructural architecture of hydrated corneoscleral button (HCSB) and hydrated corneal button (HCB).

METHOD

Corneoscleral buttons (n = 4) and corneal buttons (n = 4) were hydrated in deionized water for 24 and 48 h and were fixed in 2.5% glutaraldehyde containing cuprolinic blue in sodium acetate buffer and processed for electron microscopy. The tissue was dehydrated and embedded in TAAB 031 resin. Normal CSB and CB were also processed using the same method. Ultrathin sections were stained with uranyl acetate and lead citrate. The sections were observed under JEOL 1400 transmission electron microscope.

RESULTS

In both HCSB and HCB, the lamellae were disorganized and proteoglycans (PGs) were degenerated and detached from the collagen fibrils (CFs). In the HCSB samples, interfibrillar spacing increased but the diameter of the CF had not changed compared with those in the normal tissue. Within the HCSB, the interfibrillar spacing in the posterior stroma was significantly higher compared with those in the anterior and middle stroma. In the HCB, both the interfibrillar spacing and CF diameter had significantly increased compared to those observed in both the HCSB and normal tissue. The CFs were severely damaged exhibiting very thin microfilaments within CFs. Remnants of the CFs were present in the stromal matrix.

CONCLUSION

Hydration of the cornea in both the HCSB and HCB increases the interfibrillar spacing in the anterior, middle, and posterior stroma. The CF in the HCB was enlarged and had degenerated. This could be due to penetration of water into the intermolecular spacing within the CF.

Effect of processing methods for transmission electron microscopy on corneal collagen fibrils diameter and spacing

INTRODUCTION

The corneal tissue was processed in fixatives and embedded in resin for transmission electron microscopy to observe the ultrastructure of the collagen fibrils (CFs). The effect of these processing methods on the CF diameter and the interfibrillar spacing was studied.

METHODS

Four normal human corneal buttons were used for this study. A part of each cornea was fixed in 2.5% glutaraldehyde containing cuprolinic blue in sodium acetate buffer and embedded in spurr's resin (SpurrCB). A second part of each cornea was fixed in 2.5% glutaraldehyde + osmium tetroxide and embedded spurr's resin (SpurrOsm). The third part of each cornea was fixed in paraformaldehyde (4%) and embedded in LR White at 4°C (LRWhite). Ultrathin sections were stained with uranyl acetate and lead citrate.

RESULTS

In the tissue, fixed in SpurrCB, the diameter was 38.4 ± 5.9 nm and spacing between CF was 52.5 ± 5.3 nm. In the tissue fixed in SpurrOsm, the diameter was 28.37 ± 5.84 nm and spacing between CF was 45 ± 4.57 nm. In the tissue fixed in LR White, the CF diameter was 24 ± 2.3 nm and spacing between CF was 39.0 ± 4.2 nm. The diameters and interfibrillar spacing of the tissue processed by SpurrCB, SpurrOsm, and LRWhite were significantly different (P < 0.001) from one another.

CONCLUSION

Our study shows that there is a variation in the CF diameter and spacing depending on the method of fixation and embedding resins used. This needs to be considered when comparative studies using different methods are done.

Effect of Latanoprost on Cultured Porcine Corneal Stromal Cells

PURPOSE

Latanoprost reduces intraocular pressure mainly by enhancing uveoscleral outflow that may be involved in the decreased of extracellular matrixes such as collagens. However, the effect of latanoprost on corneal stromal cells is not well understood. In the current study, we investigated the changes of cultured porcine corneal stromal cells upon exposure to latanoprost.

METHODS

Porcine corneal stromal cells were acquired from primary culture and maintained in fetal bovine serum-containing medium. Cells were estimated on 3H-thymidine, 3H-leucine, 3H-uridine, 3H-proline uptakes and migration. Dead and living cells were estimated with MTT assay. The changes of type 1 collagen and fibronectin proteins were detected by means of immunofluorescent staining and Western blot assay. Intracellular free Ca2+ ([Ca2+]i) mobility was studied by spectrofluorophotometer after loading with fura-2-AM.

RESULTS

Latanoprost has remarkable effects inhibiting cultured corneal stromal cells on 3H-thymidine, 3H-leucine, 3H-uridine, 3H-proline uptakes and cellular migration. The inhibitory effects are in a dose-dependent manner at concentrations ranging from 10(- 5), 10(- 6), 10(- 7) to 10(- 8) M. The 50% inhibitory dosages (ID50) for latanoprost to corneal stromal cells, as measured by 3H-thymidine uptake, 3H-uridine uptake, 3H-leucine uptake, 3H-proline uptakes and cellular migration were 5.01 x 10(- 6) M, 2.81 x 10(- 6) M, 2.09 x 10(- 6) M, 3.89 x 10(- 7) M and 2.2 x 10(- 6) M, respectively. In the presence of latanoprost, the cellular MTT values were also decreased significantly. Immunofluorescent staining displayed that latanoprost changed type 1 collagen distribution in cultured corneal stromal cells. Western blot assay revealed that latanoprost caused cells to decrease in fibronectin protein. In Ca2+-containing buffer, latanoprost induced a significant rise in [Ca2+]i at 10(- 5) and 10(- 6) M.

CONCLUSIONS

These results indicate that latanoprost may induce the morphological and biochemical changes in cultured corneal stromal cells. Long-term use of latanoprost needs to be carefully monitored for change in corneal stroma.

A comparative analysis of the collagen type and distribution in the trabecular meshwork, sclera, lamina cribrosa and the optic nerve in the human eye

A theory has been advanced (Tengroth et al 1984) that one common factor might be involved in the pathogenesis of chronic open angle glaucoma. The mechanical properties of the collagen could be one such factor. To characterize the collagen composition of the critical structures in cases with chronic open angle glaucoma i.e. the trabecular meshwork and the lamina cribrosa in the human eye, the following investigations were performed. Using immunoperoxidase technique and type specific antibodies to the genetically distinct collagen types I, III, IV and procollagen I along with the major non collagen proteins in the extracellular matrix laminin and fibronectin a light microscopic study was undertaken on the trabecular meshwork, cornea, sclera, lamina cribrosa and the optic nerve of the human eye. Furthermore biochemical analysis was performed on the collagen associated aminoacids hydroxyproline (Hyp), hydroxylysine (Hyl) and prolin (Pro) from microdissected samples of trabecular meshwork, sclera, lamina cribrosa and optic nerve. Both the immunohistological and the biochemical findings suggested similarities in the collagen composition between the trabecular meshwork and the lamina cribrosa. The immunohistochemical findings showed stronger staining of type III and IV in the trabecular meshwork and lamina cribrosa as compared to sclera or cornea while the opposite was true for type I and procollagen I. Fibronectin and laminin were present in both the trabecular meshwork and lamina cribrosa. These findings were in agreement with the amino acid analysis when the Hyp/Hyl ratio was calculated for each sample.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagens and proteoglycans of the corneal extracellular matrix

The cornea is a curved and transparent structure that provides the initial focusing of a light image into the eye. It consists of a central stroma that constitutes 90% of the corneal depth, covered anteriorly with epithelium and posteriorly with endothelium. Its transparency is the result of the regular spacing of collagen fibers with remarkably uniform diameter and interfibrillar space. Corneal collagen is composed of heterotypic fibrils consisting of type I and type V collagen molecules. The cornea also contains unusually high amounts of type VI collagen, which form microfibrillar structures, FACIT collagens (XII and XIV), and other nonfibrillar collagens (XIII and XVIII). FACIT collagens and other molecules, such as leucine-rich repeat proteoglycans, play important roles in modifying the structure and function of collagen fibrils.Proteoglycans are macromolecules composed of a protein core with covalently linked glycosaminoglycan side chains. Four leucine-rich repeat proteoglycans are present in the extracellular matrix of corneal stroma: decorin, lumican, mimecan and keratocan. The first is a dermatan sulfate proteoglycan, and the other three are keratan sulfate proteoglycans. Experimental evidence indicates that the keratan sulfate proteoglycans are involved in the regulation of collagen fibril diameter, and dermatan sulfate proteoglycan participates in the control of interfibrillar spacing and in the lamellar adhesion properties of corneal collagens. Heparan sulfate proteoglycans are minor components of the cornea, and are synthesized mainly by epithelial cells. The effect of injuries on proteoglycan synthesis is discussed.

Collagen-binding domain of a Clostridium histolyticum collagenase exhibits a broad substrate spectrum both in vitro and in vivo

The substrate spectrum of the tandem collagen-binding domain (CBD) of Clostridium histolyticumclass I collagenase (ColG) was examined both in vitro and in vivo. CBD bound to insoluble type I, II, III and IV collagens in vitro, and to skin, aorta, tendon, kidney, trachea and corneal tissues containing various types of collagen fibrils or sheets. CBD bound to all kinds of collagen fibrils regardless of their diameters and also bound to sheet-forming collagen in the glomerular basal lamina or Descemet's membrane of the cornea. This wide substrate spectrum expands possible applications of the drug delivery system we proposed previously (PNAS 95:7018-7023, 1998). Therapeutic agents fused with CBD will bind not only to subcutaneous tissues, but also to other tissues containing non-type I collagen.

Organization of fibrillar collagen in the human and bovine cornea: collagen types V and III

The localization and fibrillar organization of collagen types V and III in the human and bovine corneal stromas were studied. In the chicken cornea, type V co-assembles with type I collagen as heterotypic fibrils and this interaction is involved in the regulation of fibril diameter necessary for corneal transparency. To determine whether this is a regulatory mechanism common to the corneas of different species the human and bovine corneal stroma were studied. Collagen type V was found in the epithelium and Bowman's membrane in the untreated adult human and bovine cornea using immunofluorescence microscopy. In the absence of any treatment, there was no type V reactivity within the stroma. However, type V collagen was detected homogeneously throughout the corneal stroma after treatments that partially disrupt fibril structure. The reactivity was strongest in the cornea, weaker in the limbus and weakest in the sclera. Fetal corneas showed similar reactivity for type V collagen, but unlike the adult, the stroma was slightly reactive. Immunoelectron microscopy demonstrated that type V collagen was associated with disrupted, but not with intact, fibrils in both human and bovine corneal stroma. Type III collagen reactivity was not detected in the cornea, but was present subepithelially in the limbus and in the scleral stroma. These data indicate that type V collagen is a component of striated collagen fibrils throughout the human and bovine corneal stromas. The interaction of type I and V collagen as heterotypic fibrils masks the helical epitope recognized by the monoclonal antibody against type V collagen. The heterotypic interactions of collagen type V indicate a role in the regulation of fibril diameter analogous to that described in the avian cornea.

Production of neocollagen by cells invading hydrogel sponges implanted in the rabbit cornea

BACKGROUND

Poly(2-hydroxyethyl methacrylate) sponges are artificial tissue-equivalent matrices with potential value as materials for the peripheral zone of artificial corneas. A keratoprosthetic device was developed incorporating a poly(HEMA) spongy skirt which allowed cellular invasion. The present in vivo study investigated the biosynthetic activity of stromal fibroblasts growing within a poly(HEMA) sponge implanted into the rabbit cornea.

METHODS

A porous poly(HEMA) hydrogel was synthesized by polymerization in a large excess of water. Specimens with a pore size larger than 10 microns were impregnated with collagen type I and then implanted into the limbal region of cornea in four rabbits. The animals were followed clinically for 28 days, when they were anaesthetized and new sponge specimens were implanted in their second eye. After 2 h, both eyes were enucleated. The 28-day and 2-h explants were subjected to autoradiographic analysis following labelling with tritiated proline and to an immunostaining technique using antibodies to collagen types I-VI.

RESULTS

The autoradiographic analysis showed that the fibroblasts within the 28-day explants continued to be synthetically active and deposited proteins. Using the immunostaining technique, the deposition was most clearly demonstrated by the localization of collagen type III in the tissue invading the sponge. Both techniques failed to indicate any cellular activity in the short-time implants.

CONCLUSIONS

The presence of collagen type III is consistent with a normal healing response of the stromal fibroblasts and indicates that poly(-HEMA) sponges are able to function as tissue-equivalent matrices.

Anatomy and morphology of the cornea of bovine eyes from a slaughterhouse

Over a 1-year period, isolated bovine eyes were obtained from a slaughterhouse and assessed within 3 h post mortem. The gross disposition (including damage or disease) and corneal surface characteristics (overall appearance and wettability) were assessed by visual inspection and light and scanning electron microscopy. The results from 315 eyes (assessed to be free of gross abnormalities or damage) showed that the corneal thickness was 1015 ± 104 μm (mean ± SD; n = 315). Measures on 100 of these eyes revealed corneal dimensions averaging 29.8 ± 1.3 mm horizontally and 23.9 ± 1.5 mm vertically. The horizontal corneal diameter was greater in eyes with thicker corneas (r = 0.917). Regardless of thickness, corneas evaluated within 3 h post mortem had a uniform thickness within ± 3% from center to edge. Histology and scanning electron microscopy revealed that even corneas subjectively assessed to be in good condition had relatively large numbers of exfoliating cells at the epithelial surface, indicating that the corneal surface of bovine eyes from the slaughterhouse is likely to be slightly compromised. Scanning electron microscopy showed the endothelium to be a mosaic of uniformly sized polygons of which 67.1 ± 2.7% were six-sided cells (hexagons).

Expression of collagens I, III, IV and V mRNA in excimer wounded rat cornea: analysis by semi-quantitative PCR

A semi-quantitative polymerase chain reaction (PCR) methodology was used to evaluate the kinetic changes occurring in collagens I, III, IV and V mRNA in rat cornea following excimer laser keratectomy. cDNA was synthesized from RNA extracted from rat cornea at various times following excimer laser photoablative keratectomy. Collagen cDNA sequences were subsequently amplified using specific sets of oligonucleotide primers. Competitive PCR amplification was carried out using an internal standard so that a semi-quantitative analysis of message for synthesis of collagen types I, III, IV and V could be performed and time course dynamics of message for these collagens studied. There was a biphasic increase in the levels of collagens III, IV and V mRNA following excimer laser keratectomy. Collagen I mRNA levels demonstrated a more sustained increase and were still elevated at 6 weeks following wounding. Collagens IV and V mRNA showed the largest increase with an approximate three fold increase over controls between 4 days and 1 week. Our results demonstrate that upregulation of stromal collagens I, III, and V mRNA and basement membrane collagen IV mRNA occurs in rat cornea following excimer laser keratectomy.

Immunohistochemical analysis of unsutured and sutured corneal wound healing

In the unsutured partial thickness penetrating wounds of the cornea, the epithelium migrates over the wounded stromal surface prior to the onset of stromal regeneration. To determine the possible affects of the epithelial ingrowth on the organization of the stromal scar tissues, the healing of unsutured and sutured wounds was compared immunohistochemically. Immunostaining patterns for fibronectin, types III, VI and VII collagen, keratan sulfate proteoglycan (KSPG), and intermediate filament-associated protein (IFAP 130) in fibroblasts, were analyzed in unsutured and adjacent sutured keratotomy wounds in monkeys, at 2-9 weeks after surgery. At 2-4 weeks, fibronectin, type III and type VI collagen showed a lamellar interweaving pattern across unsutured wounds that was absent in sutured wounds. Type VII collagen was detected along the entire depth of regenerated stroma in unsutured wounds, but not in sutured wounds indicating that the epithelium had formerly been present in the regenerated stroma in unsutured wounds. Fibroblasts in both types of wounds expressed IFAP 130, but staining was more pronounced in sutured wounds. At 5-9 weeks, cellular re-activation, as judged from the expression for IFAP 130, was concomitant with a loss of lamellar interweaving with fibronectin, type III and type VI collagen across unsutured wounds, and proceeded in a posterior to anterior direction. In contrast, in sutured wounds, lamellar interweaving was established in anterior to posterior direction. At all postoperative times, unsutured and sutured wounds showed minimal staining for KSPG in the anterior scar.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen arrangements in ureter

The collagen fibres of rabbit and human ureter were exposed by digestion with trypsin and hyaluronidase. The fibre structure was examined using an SEM and examples of the inner and outer fibre structures are shown together with the effects of different types of mechanical strain. An interesting difference between the arrangements of the inner fibres of human and rabbit was seen where the human ureter had a cross-ply structure while in the rabbit it was helical.

The role of nonenzymatic glycosylation, transition metals, and free radicals in the formation of collagen aggregates

Incubation of corneal collagen type I with glucose in the presence of transition metal ions (copper, iron) results in the formation of collagen aggregates insoluble in 6 M urea, and in 2% sodium dodecyl sulfate + 5% beta-mercaptoethanol. The reaction is mediated by hydrogen peroxide and transition metals since it is inhibited by catalase and by the chelating agent diethylenetriaminepentaacetic acid. Comparative studies showed that copper is more efficient than iron and that the reaction proceeds more rapidly with ribose than with glucose. The data support a mechanism involving transition metal ion catalyzed autoxidation of glucose (and possibly of Amadori products) with generation of superoxide radical. Superoxide dismutation produces hydrogen peroxide, which then generates hydroxyl radicals in the presence of transition metal ions (Fenton reaction). Hydroxyl radical attack is known to lead to cross-linking, which is enhanced in glycated proteins. The experimental data presented are consistent with in vivo alteration of collagen properties during normal aging and with the acceleration of similar changes in diabetes mellitus.

Immunogold fine structural localization of extracellular matrix components in aged human cornea. II. Collagen types V and VI

Using immunogold immunocytochemical techniques we studied the distribution of collagen types V and VI in corneal tissue from seven enucleated human eyes (age range, 63-78 years). Results obtained by cryoultramicrotomy were marginally more intense than those obtained using London Resin white (LR white) embedding. Type V collagen was present in the striated collagen fibrils in Bowman's layer, in the stroma and in a thin, non-banded anterior zone of Descemet's membrane. Our results suggest that types I, III and V collagen co-distribute in striated collagen fibrils. By contrast, type VI collagen was located in fine filaments in the interfibrillar matrix of the stroma, in Bowman's layer and in the anchoring plaques of the sub-epithelial basement-membrane complex. This implies an importance in epithelial adhesion which was previously unsuspected. Keratocyte bodies were electron-dense, amorphous extracellular deposits of matrix-like material, and these were labelled with types III, V and VI collagen antibodies. Long-spacing collagen was observed in the corneal stroma, and this deposit did not contain any of the collagen types studied.

Collagen metabolism during healing of lacerated rabbit corneas

We previously demonstrated that there are two waves of increased collagen synthesis following corneal laceration in rabbits. In the present study, we have examined whether increases in collagen synthesis and degradation result from increased amounts of mRNAs for collagen and collagenase, respectively. Rabbits were anesthetized by combined administration of ketamine (intramuscular) and pentobarbital (intravenous). A penetrating 8-mm incision was made at the center of each cornea. The lacerated corneas were allowed to heal for 0-49 days. The rabbits were then killed and the corneas excised. The total RNA was extracted from the tissue and subjected to slot-blot hybridization using 32P-labeled alpha 1(I) cDNA. The results indicate that there is a two-phase increase in the amount of alpha 1(I) mRNA in injured corneas and that the collagenase mRNA is elevated at most times throughout the healing period. However, the increase is collagenase mRNA may not fully account for the accelerated collagen degradation during corneal wound-healing. Thus, we propose that cells in the wound area may be directly involved in collagen degradation by phagocytosis. To examine our hypothesis, we cultured injured rabbit corneas in the presence or absence of leupeptin, a proteinase inhibitor. The tissues were then examined by electron microscopy. In the presence of leupeptin, lysosomes within fibroblasts or fibroblast-like cells in the wound area of the lacerated corneas healed for 2 and 3 weeks, contain collagen fibrils. In the absence of leupeptin no identifiable collagen was seen in the lysosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunogold fine structural localization of extracellular matrix components in aged human cornea. I. Types I-IV collagen and laminin

Using the immunogold technique combined with cryoultramicrotomy and London Resin white (LR white) embedding, we studied the fine structural distribution of types I-IV collagen and laminin in corneal tissue from seven enucleated human eyes (age range, 63-78 years). Type II collagen was not identified in any corneal layer. Type I and type III collagen were distributed in a similar fashion in striated collagen fibrils in Bowman's layer and in the stroma. Type IV collagen was located only in the posterior non-banded region of Descemet's membrane. Laminin was identified in subepithelial anchoring plaques and the sub-endothelial region of Descemet's membrane in accordance with its recognized adhesive function.

Immunocytochemical localisation of collagens (I-V) in the human iris

In this study we investigated the distribution of collagen types I-V in the human iris at the fine-structural level using cryoultramicrotomy and London Resin White plastic embedding. Collagen type I was shown to be present in the basement membrane of iris vessels, in contrast to type III, which was absent; both types I and III were present in the iris stroma. Collagen type IV was a major component of basement membranes of vascular cells, myoepithelial cells, fibroblasts and epithelial cells. Types II and V were absent. Both cryo and plastic embedding techniques produced closely comparable results.

Pinpointing the sites of hydroxylysine glycosides in peptide alpha 1-CB7 of bovine corneal collagen, and their possible role in determining fibril diameter and thus transparency

Two cyanogen bromide fragments (alpha 1-CB7 and alpha 1-CB8) of bovine corneal stromal collagen have been isolated and characterized. These added to those characterized in our previous work account for 95% of the amino acid sequence of the alpha 1(1)-chain. The hydroxylysine glycoside content of each fragment was determined and in this way the general distribution of glycoside over the entire molecule was deduced accounting for all the galactosylhydroxylysine and most of the glucosylgalactosylhydroxylysine of this heavily glycosylated type I collagen. The characterization of fragments alpha 1-CB7 and alpha 1-CB8 has enabled us to resolve the controversy over the relative mobilities of these fragments on SDS gels. Fragment alpha 1-CB7 of bovine corneal collagen was digested by trypsin and by staphylococcal proteinase V8. The resultant peptides were isolated by gel and ion-exchange chromatography and identified in relation to the known amino acid sequence of type I collagen. The hydroxylysine glycosides were determined in the relevant peptides providing a complete account of their distribution along this part of the collagen molecule. Most of the glycoside was found in the gap region of collagen especially near the edges of the axial holes where it could act as a peg to facilitate fibre formation. In addition, some glycoside was found in the overlap region where, being unable to fit into axial holes, it might impede the growth of the fibre and, with other glycoside of the overlap region, might be responsible for the narrow fibres of corneal collagen that are essential for corneal transparency. This glycoside, with that previously found in the peptide alpha 1-CB3 is the only hydroxylysine glycoside identified in the overlap region of a type I collagen.

Use of the collagen I-deficient Mov13 mouse mutant to analyse epithelial-mesenchymal tissue interaction

The collagen I-deficient mouse mutant (Mov13 - an embryonic recessive lethal) was used to investigate the function of this major constituent of the extracellular matrix (ECM) in organ development. All epithelial-mesenchymal organs tested as explants (lung, kidney, pancreas, salivary glands, skin) developed normally and, in particular, showed typical branching morphogenesis in the absence of collagen I. It is concluded that the ECM of these organs can organize for proper developmental function in the absence of the major interstitial collagen, but a possible morphogenetic function of other fibrillar collagens (types III and V) cannot be excluded. The only insufficiencies in the mutant were seen in the cornea where deposition and organization of the collagenous stroma was highly inadequate; but even there, development and migration of cells proceeded normally. In summary, the results indicate that 'cellular' development in epithelial-mesenchymal organs (including growth, morphogenesis, and differentiation) does not depend on collagen I.

Collagen type I and type V are present in the same fibril in the avian corneal stroma

The distribution, supramolecular form, and arrangement of collagen types I and V in the chicken embryo corneal stroma were studied using electron microscopy, collagen type-specific monoclonal antibodies, and a preembedding immunogold method. Double-label immunoelectron microscopy with colloidal gold-tagged monoclonal antibodies was used to simultaneously localize collagen type I and type V within the chick corneal stroma. The results definitively demonstrate, for the first time, that both collagens are codistributed within the same fibril. Type I collagen was localized to striated fibrils throughout the corneal stroma homogeneously. Type V collagen could be localized only after pretreatment of the tissue to partially disrupt collagen fibril structure. After such pretreatments the type V collagen was found in regions where fibrils were partially dissociated and not in regions where fibril structure was intact. When pretreated tissues were double labeled with antibodies against types I and V collagen coupled to different size gold particles, the two collagens colocalized in areas where fibril structure was partially disrupted. Antibodies against type IV collagen were used as a control and were nonreactive with fibrils. These results indicate that collagen types I and V are assembled together within single fibrils in the corneal stroma such that the interaction of these collagen types within heterotypic fibrils masks the epitopes on the type V collagen molecule. One consequence of the formation of such heterotypic fibrils may be the regulation of corneal fibril diameter, a condition essential for corneal transparency.

Collagen degradation and synthesis in experimental corneal grafts

Thirty-two weanling New Zealand white rabbits were labelled repeatedly with [2,3-3-H]-proline for 4 weeks. Four weeks after the end of labelling, 32 rabbits underwent bilateral 6 mm trephinations for donor purposes. One control cornea of each pair was frozen at -70 degrees C. The contralateral corneas were used for autografts, allografts, and xenografts. Grafts were observed from 7-200 days, then retrephined out for determination of loss in total radioactivity in hydroxyproline (specific for collagen), increase in newly synthesized collagen, and net change in collagen mass, by comparing with the matched, ungrafted control corneas. For all three transplant groups there was a small, but significant, decrease early in total radioactivity (loss of original collagen) and a significant increase in new collagen. These data also indicated that the loss of original collagen was replaced by an equivalent or greater increase in new collagen in all transplant groups. Significant relationships between graft clarity and collagen turnover were noted in both the auto- and allograft groups. The degradation of old collagen was significantly greater in the cloudy vs. the clear grafts; however, there was no significant difference in the increase in new collagen between these groups. A progressive loss of original collagen over time was noted in the cloudy autografts, but not the allografts. A trend toward a progressive increase in new collagen was noted over time in both the cloudy auto- and allografts. No relation for these variables to time, however, was noted in the clear grafts.