Stromal fibroblasts are associated with collagen IV in scar tissues of alkali-burned and lacerated corneas

Long-term alterations of collagen reconstruction and basement membrane regeneration after corneal full-thickness penetrating injury in rabbits

PURPOSE

To investigate the long-term alterations of collagen reconstruction and basement membrane (BM) regeneration after corneal full-thickness penetrating injury in rabbits.

METHODS

The corneal full-thickness penetrating injury model was established in the left eye of New Zealand White rabbits using a 2.0 mm trephine. All corneas were evaluated using slit-lamp photography, hematoxylin and eosin staining, immunofluorescent staining for collagen types I and III (Col I, III), and transmission electron microscopy for collagen fibers and basement membrane.

RESULTS

Between 3 days and 3 weeks, Col I and III expression were documented, exhibiting a largely disorganized distribution throughout the stromal thickness. At 3 weeks, the epithelial basement membrane (EBM) partially regenerated. From 3 weeks to 2 months, Col III was undetectable in the anterior stroma but present in the posterior stroma; Col I was disorganized in the posterior stroma. At 2 months, Descemet's membrane (DM) exhibited incomplete regeneration. From 3 to 4 months, Col I was disorganized in only a small part of the posterior stroma; Col III persisted in the posterior stroma; the EBM fully regenerated while DM exhibited incomplete regeneration.

CONCLUSIONS

Following full-thickness corneal injury, persistent fibrosis within the posterior stroma appears to be primarily responsible for the persistence of corneal scarring. Notably, regeneration of the EBM coincides with remodeling of the anterior stroma, whereas incomplete regeneration of DM is associated with posterior stromal fibrosis.

The corneal fibroblast: The Dr. Jekyll underappreciated overseer of the responses to stromal injury

PURPOSE

To review the functions of corneal fibroblasts in wound healing.

METHODS

Literature review.

RESULTS

Corneal fibroblasts arise in the corneal stroma after anterior, posterior or limbal injuries and are derived from keratocytes. Transforming growth factor (TGF) β1 and TGFβ2, along with platelet-derived growth factor (PDGF), are the major modulators of the keratocyte to corneal fibroblast transition, while fibroblast growth factor (FGF)-2, TGFβ3, and retinoic acid are thought to regulate the transition of corneal fibroblasts back to keratocytes. Adequate and sustained levels of TGFβ1 and/or TGFβ2, primarily from epithelium, tears, aqueous humor, and corneal endothelium, drive the development of corneal fibroblasts into myofibroblasts. Myofibroblasts have been shown in vitro to transition back to corneal fibroblasts, although apoptosis of myofibroblasts has been documented as a major contributor to the resolution of fibrosis in several in situ corneal injury models. Corneal fibroblasts, aside from their role as a major progenitor to myofibroblasts, also perform many critical functions in the injured cornea, including the production of critical basement membrane (BM) components during regeneration of the epithelial BM and Descemet's membrane, production of non-basement membrane-associated stromal collagen type IV to control and downregulate TGFβ effects on stromal cells, release of chemotactic chemokines that attract bone marrow-derived cells to the injured stroma, production of growth factors that modulate regeneration and maturation of the overlying epithelium, and production of collagens and other ECM components that contribute to stromal integrity after injury.

CONCLUSIONS

Corneal fibroblasts are major contributors to and overseers of the corneal response to injuries.

Collagen as a Biomaterial for Skin and Corneal Wound Healing

The cornea and the skin are two organs that form the outer barrier of the human body. When either is injured (e.g., from surgery, physical trauma, or chemical burns), wound healing is initiated to restore integrity. Many cells are activated during wound healing. In particular, fibroblasts that are stimulated often transition into repair fibroblasts or myofibroblasts that synthesize extracellular matrix (ECM) components into the wound area. Control of wound ECM deposition is critical, as a disorganized ECM can block restoration of function. One of the most abundant structural proteins in the mammalian ECM is collagen. Collagen type I is the main component in connective tissues. It can be readily obtained and purified, and short analogs have also been developed for tissue engineering applications, including modulating the wound healing response. This review discusses the effect of several current collagen implants on the stimulation of corneal and skin wound healing. These range from collagen sponges and hydrogels to films and membranes.

Corneal Opacity: Cell Biological Determinants of the Transition From Transparency to Transient Haze to Scarring Fibrosis, and Resolution, After Injury

Purpose

To highlight the cellular, matrix, and hydration changes associated with opacity that occurs in the corneal stroma after injury.

Methods

Review of the literature.

Results

The regulated transition of keratocytes to corneal fibroblasts and myofibroblasts, and of bone marrow-derived fibrocytes to myofibroblasts, is in large part modulated by transforming growth factor beta (TGFβ) entry into the stroma after injury to the epithelial basement membrane (EBM) and/or Descemet's membrane. The composition, stoichiometry, and organization of the stromal extracellular matrix components and water is altered by corneal fibroblast and myofibroblast production of large amounts of collagen type I and other extracellular matrix components-resulting in varying levels of stromal opacity, depending on the intensity of the healing response. Regeneration of EBM and/or Descemet's membrane, and stromal cell production of non-EBM collagen type IV, reestablishes control of TGFβ entry and activity, and triggers TGFβ-dependent myofibroblast apoptosis. Eventually, corneal fibroblasts also disappear, and repopulating keratocytes reorganize the disordered extracellular matrix to reestablish transparency.

Conclusions

Injuries to the cornea produce varying amounts of corneal opacity depending on the magnitude of cellular and molecular responses to injury. The EBM and Descemet's membrane are key regulators of stromal cellularity through their modulation of TGFβ. After injury to the cornea, depending on the severity of the insult, and possibly genetic factors, trace opacity to severe scarring fibrosis develops. Stromal cellularity, and the functions of different cell types, are the major determinants of the level of the stromal opacity.

Creation and grading of experimental corneal scars in mice models

PURPOSE

To develop a stromal wound healing model and a reliable scar classification score system that correlates photographic evaluation with changes in the structure and organization of the extracellular matrix.

MATERIALS AND METHODS

We tested three stromal injury techniques in adult C57BL/6 mice. Technique 1, a lineal partial thickness keratotomy in the horizontal axis. Technique 2, corneal epithelial and stromal debridement using a diamond burr in the horizontal axis, and technique 3, a combination of techniques 1 and 2. To assess intra-observer and inter-observer agreement between two examiners evaluating formed stromal scars, stereo microscopic photographs of anterior segment were scored by two masked examiners at around 1-month. Depending on the severity of opacification and the area of involvement, scars were classified on a scale from 0 to 3 based on a modified Fantes haze scale. Extracellular matrix composition as well as matrix organization, macrophage infiltration and neovascularization were evaluated with immunofluorescence and second harmonic generation (SHG) microscopy.

RESULTS

Technique 1 created mild scars, with a score of 0.5 ± 0.43, while techniques 2 (score 2.1 ± 0.45) and 3 (score 2 ± 0.66), created dense scars with a higher score. A significant difference in scar severity score was noted between the 3 techniques (one way ANOVA, p < 0.0001). Masked graders demonstrated excellent agreement (intraclass correlation = 0.927 [95% confidence interval: 0.87-0.96]). The severity of scars noted at stereo microscopy correlated with the severity of changes in extracellular matrix in the stroma as demonstrated by the expression of collagens I, IV and fibronectin and evaluation of matrix hierarchical organization. In contrast to mild scarring, moderate and severe scars had increased expression of CD31 and CD68, markers of vascular endothelial cells and macrophages, respectively.

CONCLUSION

Mouse models of stromal scarring using simple surgical techniques are described. Corneal scars can be consistently classified by two observers. Grading of scar severity positively correlates with changes in extracellular matrix composition, disorganization and cell infiltration.

Corneal stromal wound healing: Major regulators and therapeutic targets

Corneal stromal wound healing is a complex event that occurs to restore the transparency of an injured cornea. It involves immediate apoptosis of keratocytes followed by their activation, proliferation, migration, and trans-differentiation to myofibroblasts. Myofibroblasts contract to close the wound and secrete extracellular matrix and proteinases to remodel it. Released proteinases may degenerate the basement membrane allowing an influx of cytokines from overlying epithelium. Immune cells infiltrate the wound to clear cellular debris and prevent infections. Gradually basement membrane regenerates, myofibroblasts and immune cells disappear, abnormal matrix is resorbed, and transparency of the cornea is restored. Often this cascade deregulates and corneal opacity results. Factors that prevent corneal opacity after an injury have always intrigued the researchers. They hold clinical relevance as they can guide the outcomes of corneal surgeries. Studies in the past have shed light on the role of various factors in stromal healing. TGFβ (transforming growth factor-beta) signaling is the central player guiding stromal responses. Other major regulators include myofibroblasts, basement membrane, collagen fibrils, small leucine-rich proteoglycans, biophysical cues, proteins derived from extracellular matrix, and membrane channels. The knowledge about their roles helped to develop novel therapies to prevent corneal opacity. This article reviews the role of major regulators that determine the outcome of stromal healing. It also discusses emerging therapies that modulate the role of these regulators to prevent stromal opacity.

Role of Endogenous Regulators of Hem- And Lymphangiogenesis in Corneal Transplantation

Under normal conditions, the cornea, being the transparent “windscreen” of the eye, is free of both blood and lymphatic vessels. However, various diseases of the eye, like infections, can interfere with the balance between promoting and inhibiting factors, which leads to ingrowth of blood and lymphatic vessels. The newly formed lymphatic vessels increase the risk of graft rejection after subsequent corneal transplantation. Corneal transplantation is one of the most commonly performed transplantations worldwide, with more than 40,000 surgeries per year in Europe. To date, various anti-hem- and anti-lymphangiogenic treatment strategies have been developed specifically for the corneal vascular endothelial growth factor (VEGF) pathway. Currently, however, no treatment strategies are clinically available to specifically modulate lymphangiogenesis. In this review, we will give an overview about endogenous regulators of hem- and lymphangiogenesis and discuss potential new strategies for targeting pathological lymphangiogenesis. Furthermore, we will review recently identified modulators and demonstrate that the cornea is a suitable model for the identification of novel endogenous modulators of lymphangiogenesis. The identification of novel modulators of lymphangiogenesis and a better understanding of the signaling pathways involved will contribute to the development of new therapeutic targets for the treatment of pathological lymphangiogenesis. This, in turn, will improve graft rejection, not only for the cornea.

Cell Therapy of Corneal Diseases

Mesenchymal stem cells isolated from connective tissues are pluripotent and differentiate into phenotypes of connective tissue cell lineages (osteoblasts, chondrocytes, and adipocytes) in vitro and in vivo. They have been used to treat mouse models of connective tissue disease such as lumican-null (Lum) and mucopolysaccharidosis (Gusb) mice. Mesenchymal stem cells have unique immunosuppressive properties allowing evasion of host rejection; thus, they are valuable tools for cell therapy of congenital and acquired diseases involving immune dysfunction of multiple tissues including ocular surface tissues (cornea). We previously showed that human umbilical mesenchymal stem cells (UMSCs) modulated host immune responses, enabling them to survive xenograft transplantation. In vitro, UMSCs modulated inflammatory cells by inhibiting adhesion and invasion, and inducing cell death. UMSCs also regulated M1/M2 macrophage polarization and induced T-regulatory cell maturation from naive intraperitoneal cavity lavage cells. UMSCs exposed to inflammatory cells synthesized a rich extracellular glycocalyx composed of hyaluronan (HA) bound to the heavy chains (HCs) of inter-alpha-trypsin inhibitor (HC-HA), which contains tumor necrosis factor-α-stimulated gene 6 (TSG6) that catalyzes the transfer of HCs to HA, versican, and pentraxin-3. Our in vivo and in vitro results showed that the glycocalyx regulated inflammatory cells, allowing UMSCs to survive host immune rejection. Administration of antibodies against glycocalyx constituents or digestion with hyaluronidase and chondroitinase ABC abolished the UMSCs' ability to modulate immune responses. Treatment with anti-CD44 antibodies also diminished modulation of M2 macrophages by UMSCs, indicating that cell surface CD44 is required for correct UMSC glycocalyx assembly to modulate inflammatory cells.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Limbal Fibroblasts Maintain Normal Phenotype in 3D RAFT Tissue Equivalents Suggesting Potential for Safe Clinical Use in Treatment of Ocular Surface Failure

Limbal epithelial stem cell deficiency can cause blindness, but transplantation of these cells on a carrier such as human amniotic membrane can restore vision. Unfortunately, clinical graft manufacture using amnion can be inconsistent. Therefore, we have developed an alternative substrate, Real Architecture for 3D Tissue (RAFT), which supports human limbal epithelial cells (hLE) expansion. Epithelial organization is improved when human limbal fibroblasts (hLF) are incorporated into RAFT tissue equivalent (TE). However, hLF have the potential to transdifferentiate into a pro-scarring cell type, which would be incompatible with therapeutic transplantation. The aim of this work was to assess the scarring phenotype of hLF in RAFT TEs in hLE+ and hLE- RAFT TEs and in nonairlifted and airlifted RAFT TEs. Diseased fibroblasts (dFib) isolated from the fibrotic conjunctivae of ocular mucous membrane pemphigoid (Oc-MMP) patients were used as a pro-scarring positive control against which hLF were compared using surrogate scarring parameters: matrix metalloproteinase (MMP) activity, de novo collagen synthesis, α-smooth muscle actin (α-SMA) expression, and transforming growth factor-β (TGF-β) secretion. Normal hLF and dFib maintained different phenotypes in RAFT TE. MMP-2 and -9 activity, de novo collagen synthesis, and α-SMA expression were all increased in dFib cf. normal hLF RAFT TEs, although TGF-β1 secretion did not differ between normal hLF and dFib RAFT TEs. Normal hLF do not progress toward a scarring-like phenotype during culture in RAFT TEs and, therefore, may be safe to include in therapeutic RAFT TE, where they can support hLE, although in vivo work is required to confirm this. dFib RAFT TEs (used in this study as a positive control) may be useful toward the development of an ex vivo disease model of Oc-MMP.

Lipoxin A₄ inhibits platelet-activating factor inflammatory response and stimulates corneal wound healing of injuries that compromise the stroma

Platelet-activating factor (PAF) is a bioactive lipid mediator with strong inflammatory properties. PAF induces the expression and activation of metalloproteinase-9 (MMP-9) in corneal epithelial cells and myofibroblasts, and delays epithelial wound healing in an organ culture system. Lipoxin A(4) (LXA(4)) is a lipid mediator involved in resolution of inflammation and cornea epithelial wound healing. We developed an in vivo mouse model of injury to the anterior stroma that is sustained by PAF and evaluated the action of LXA(4). In this model mice were treated with vehicle, PAF alone and in combination with PAF receptor antagonist LAU-0901 or LXA(4). Mice were euthanized 1, 2 and 7 days after injury and corneas were processed for histology (H&E staining) and immunofluorescence with antibodies for MMP-9, α-smooth muscle actin (α-SMA), fibronectin (FN) and neutrophil. Interleukin 1-α (IL-1α) and keratinocyte-derived chemokine (KC/CXCL1) were assayed by ELISA. Myeloperoxidase (MPO) activity was performed in corneal homogenates. In this in vivo model PAF inhibited epithelial wound healing that was blocked by the PAF receptor antagonist LAU-0901. Treatment with LXA(4) significantly reduced the injured area compared to PAF at 1 and 2 days of treatment. The strong stromal cell infiltration and MPO activity stimulated by PAF was also decreased with LXA(4) treatment. PAF increased MMP-9 and decreased FN expression compared to vehicle treatment and less α-SMA positive cells migrated to the wounded area. The PAF actions were reverted by LXA(4) treatment. The results demonstrated a powerful action of LXA(4) in protecting corneas with injuries that compromise the stroma by decreasing inflammation and increasing wound healing.

Human corneal fibrosis: an in vitro model

PURPOSE

Corneal injury may ultimately lead to a scar by way of corneal fibrosis, which is characterized by the presence of myofibroblasts and improper deposition of extracellular matrix (ECM) components. TGF-beta1 is known to stimulate overproduction and deposition of ECM components. Previously, an in vitro three-dimensional (3-D) model of a corneal stroma was developed by using primary human corneal fibroblasts (HCFs) stimulated with stable vitamin C (VitC). This model mimics corneal development. The authors postulate that with the addition of TGF-beta1, a 3-D corneal scar model can be generated.

METHODS

HCFs were grown in four media conditions for 4 or 8 weeks: VitC only; VitC+TGF-beta1 for the entire time; VitC+TGF-beta1 for 1 week, then VitC only for 3 or 7 weeks; and VitC for 4 weeks, then VitC+TGF-beta1 for 4 weeks. Cultures were analyzed with TEM and indirect immunofluorescence.

RESULTS

Compared with the control, addition of TGF-beta1 increased construct thickness significantly, with maximum increase in constructs with TGF-beta1 present for the entire time-2.1- to 3.2-fold at 4 and 8 weeks, respectively. In all TGF-beta-treated cultures, cells became long and flat, numerous filamentous cells were seen, collagen levels increased, and long collagen fibrils were visible. Smooth muscle actin, cellular fibronectin, and type III collagen expression all appeared to increase. Cultures between weeks 4 and 8 showed minimal differences.

CONCLUSIONS

Human corneal fibroblasts stimulated by VitC and TGF-beta1 appear to generate a model that resembles processes observed in human corneal fibrosis. This model should be useful in examining matrix deposition and assembly in a wound-healing situation.

Expression of matrix metalloproteinases (MMP)-12 by myofibroblasts during alkali-burned corneal wound healing

PURPOSE

The purpose of this study was to determine the expression of MMP-12 by myofibroblasts during the healing of alkali-burned rabbit corneas (ARC), thus implicating its role in ECM remodeling.

METHODS

Rabbit corneas during alkali burn were examined for MMP-12 mRNA expression by RT-PCR. Immunohistochemistry was used to determine the presence of alpha-SMA, MMP-12 protein, and macrophages. In situ hybridization was performed to identify MMP-12 mRNA expressing cells.

RESULTS

RT-PCR showed that MMP-12 mRNA was expressed in the alkali-burned corneas from one week after the injury. Immunohistochemistry showed myofibroblasts positive for MMP-12 expression. In situ hybridization revealed that MMP-12 mRNA was expressed by myofibroblasts.

CONCLUSION

Our results indicate that, in alkali-burned corneas, myofibroblasts express both MMP-12 mRNA and protein. We suggest that MMP-12 may disintegrate some components of the ECM released after severe alkali burn, which may be involved in the ECM remodeling.

Corneal stromal changes following reconstruction by ex vivo expanded limbal epithelial cells in rabbits with total limbal stem cell deficiency

AIM

To study corneal stromal changes and the presence of myofibroblasts after transplantation of ex vivo expanded limbal epithelium.

METHODS

A state of limbal deficiency was induced in 16 rabbits. After transplantation with autologous ex vivo expanded limbal epithelium on amniotic membrane (AM), their clinical outcomes were classified as success, partial success or failure according to surface smoothness, stromal clarity, and vascularisation. Clinical outcomes were correlated with phenotypic outcomes of corneal, conjunctival, or mixed epithelium, defined by expression of K3 keratin or MUC5AC. Immunostaining was performed with antibodies against collagen IV, fibronectin, and alpha-smooth muscle actin (alpha-SMA) to assess stromal wound remodelling.

RESULTS

Rabbits were sacrificed after a mean follow up of 10 (SD 3.3) months. Collagen IV, expressed in the basement membrane of all three groups, was found in the stroma of the partial success, but not in that of the success or the failure. Fibronectin was absent in the success and the failure, but expressed in the stroma of the partial success. Alpha-SMA was expressed in superficial stroma of the partial success, but suppressed in areas with AM remnants.

CONCLUSION

Restoration of a clear and transparent cornea is associated with a normal corneal epithelium and complete wound remodelling. In contrast, wound healing remains active and incomplete in conjunctivalised corneas, which remain opaque with myofibroblasts.

Wound healing in rabbit corneas after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE

To compare the wound-healing process in the rabbit cornea after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with the same refractive correction.

SETTING

Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan.

METHODS

Adult albino rabbits (N = 24) were used. One eye of each animal had PRK or LASIK with the same refractive correction. Each animal was killed after an interval of up to 6 months. The expression pattern of corneal stromal injury-related molecules with the 2 treatments were compared. Paraffin sections of the cornea were processed immunohistochemically for alpha-smooth muscle actin (alpha-SMA), collagen type IV [alpha1(IV)](2),alpha2(IV), and heat shock protein (HSP) 47 as well as other HSPs. Sections were also examined after hematoxylin and eosin or periodic acid-Schiff staining.

RESULTS

Hematoxylin and eosin staining showed the central epithelium to be thick in PRK-treated corneas. The thick epithelium was restricted to the area around the corneal flap edge adhesion in LASIK-treated corneas at 3 months. Periodic acid-Schiff staining showed an absence of or interruption in the epithelial basement membrane in PRK-treated corneas for up to 6 months. Heat shock protein 47 was detected in keratocytes on day 3 but not after that in PRK-treated corneas. There was no difference in the expression of other HSPs. Alpha-smooth muscle actin was expressed in keratocytes repopulated in the central anterior cornea of PRK-treated corneas at 28 days. Keratocytes with immunoreactivity for these 2 proteins were not seen in LASIK-treated corneas. Collagen IV [alpha1(IV)](2),alpha2(IV) was not detected in either group of corneas. The central epithelium became transiently thicker in PRK-treated corneas.

CONCLUSION

Keratocyte responses to laser stromal ablation were more marked in corneas treated with PRK than in those treated with LASIK.

Epithelial repair: roles of extracellular matrix

PURPOSE

To review studies of the roles of extracellular matrix (ECM) metabolism in corneal epithelium during wound repair. Methods. 1) Alterations in the structure and composition of epithelial basement membrane during corneal epithelial healing were examined histologically and immunohistochemically. 2) The effects of procollagen and hyaluronan synthesis inhibitors on the spread of rabbit corneal epithelium were determined in organ culture. 3) Expression of keratan sulfate proteoglycan (KSPG) proteins in corneal epithelium was examined during repair after injury in wild-type and lumican-null mice.

RESULTS

1) Corneal epithelial basement membrane was transiently degraded and reassembled during tissue repair. Patterns of type IV collagen immunoreactivity were also transiently altered. The system of matrix metalloproteinase-tissue inhibitors of metalloproteinases may play an important role in the disassembly and reorganization of epithelial basement membrane. 2) Inhibitors of procollagen secretion and hyaluronan biosynthesis disrupted the spread of a corneal epithelial sheet in situ. 3) Among the corneal KSPG proteins examined, lumican was transiently expressed in migrating murine corneal epithelial cells. Anti-lumican antibody inhibited corneal epithelial resurfacing in organ culture. The absence of lumican was found to delay corneal epithelial wound healing in mice.

CONCLUSION

Extracellular matrix metabolism by the injured corneal epithelium is important in the repair process.

Critical role of type IV collagens in the growth of bile duct carcinoma. In vivo and in vitro studies

Most extrahepatic bile duct carcinomas (EBDC) are characterized by a striking stromal response (desmoplasia). Our previous studies showed deposition of type IV collagen in the desmoplastic stroma beyond the basement membrane. Although type IV collagen is expressed in EBDC, little is known about the pattern of deposition in tumor stroma and how this matrix component influences the behavior of tumor cells. With the progression of desmoplasia in EBDC, different changes occurred in the quantity and localization of type IV collagen from that of type I collagen. Type I collagen was diffusely distributed in the stroma and appeared to be concentrated in the center of the tumors. In contrast, type IV collagen was deposited in the interstitium alongside carcinoma cells at the tumors' periphery. Weak or no type IV collagen deposition was detected in the more central portion of the tumors containing sclerotic collagens. To investigate the role of stromal type IV collagen in tumor cell proliferation, EBDC cell lines were cultured in a three-dimensional matrix containing varying compositions of type I collagen and type IV collagen. They were also assayed for cell adhesion and migration using in vitro models. Type IV collagen more extensively stimulated tumor cell proliferation, adhesion and migration in a dose-dependent manner than did type I collagen. All of these results suggest that modified tumor stroma with the presence of type IV collagen in EBDC provides a better environment for tumor growth and invasion.

TGFbeta2 in corneal morphogenesis during mouse embryonic development

To examine the roles of TGFbeta isoforms on corneal morphogenesis, the eyes of mice that lack TGFbetas were analyzed at different developmental stages for cell proliferation, migration and apoptosis, and for expression patterns of keratin 12, lumican, keratocan and collagen I. Among the three Tgfb(-/-) mice, only Tgfb2(-/-) mice have abnormal ocular morphogenesis characterized by thin corneal stroma, absence of corneal endothelium, fusion of cornea to lens (a Peters'-like anomaly phenotype), and accumulation of hyaline cells in vitreous. In Tgfb2(-/-) mice, fewer keratocytes were found in stroma that has a decreased accumulation of ECM; for example, lumican, keratocan and collagen I were greatly diminished. The absence of TGFbeta2 did not compromise cell proliferation, nor enhance apoptosis. The thinner stroma resulting from decreased ECM synthesis may account for the decreased cell number in the stroma of Tgfb2 null mice. Keratin 12 expression was not altered in Tgfb2(-/-) mice, implicating normal corneal type epithelial differentiation. Delayed appearance of macrophages in ocular tissues was observed in Tgfb2(-/-) mice. Malfunctioning macrophages may account for accumulation of cell mass in vitreous of Tgfb2 null mice.

Extracellular matrix components in a case of retrocorneal membrane associated with syphilitic interstitial keratitis

PURPOSE

A web-like retrocorneal membrane (RCM) is an uncommon complication of chronic syphilitic interstitial keratitis. Extracellular matrix components have not yet been defined in this structure, although previous histologic examinations have suggested the presence of collagen. We examined the presence and distribution of extracellular matrix components in a patient with an RCM.

METHODS

A specimen of the opaque cornea affected by syphilitic interstitial keratitis with RCM formation was obtained during penetrating keratoplasty in a 62-year-old woman and was evaluated by histology, immunohistochemistry, and scanning electron microscopy (SEM). Antibodies against collagen types I, III, and IV; fibronectin; vimentin; alpha-smooth muscle actin (alpha-SMA); heat shock protein 47 (Hsp 47); proliferating cell nuclear antigen (PCNA); and Ki67 were used.

RESULTS

Histologic analysis detected multiple concentric, acellular layers positive for collagen types I, III, and IV. The corneal endothelial cells (CECs) were positive for vimentin, collagen I, fibronectin, and Hsp 47 but not for alpha-SMA. Furthermore, the CECs were negative for PCNA and Ki67, indicating that they were not proliferating. SEM revealed the RCM was covered by CECs with a fibroblastic appearance.

CONCLUSION

RCM associated with syphilitic interstitial keratitis contained collagen types I, III, and IV and fibroblast-like CECs. These CECs may secrete the extracellular matrix components found in the RCM. Hsp 47 up-regulation in the CECs may play an important role in RCM formation. These findings provide further insights into the phenotypic modulation of CECs.

Discoidin domain receptor (DDR) 1 and 2: collagen-activated tyrosine kinase receptors in the cornea

Discoidin domain receptor (DDR) 1 and 2 have recently been found to serve as receptors for several collagen types. These receptors have been found to modulate cell proliferation and metalloprotease expression in response to collagen stimulation. The purpose of this study was to examine expression of DDR1 and DDR2 in the cornea and to determine the effect of several collagen types on proliferation and response to pro-apoptotic cytokines by corneal fibroblasts. DDR1 and DDR2 mRNAs were detected by RT-PCR. Proteins were detected by immunocytochemistry and immunoprecipitation with Western blotting. Cell proliferation in response to acetic acid-solubilized collagen type I, II, IV, IX or X was determined by cell counting. The effect of these collagen types on Fas-stimulating antibody-induced cell death was determined by trypan blue assay. DDR1 and DDR2 mRNAs were detected in each major human cell type of the cornea. Both were also detected in ex vivo human corneal epithelium. DDR1 and DDR2 proteins were detected in all three major cell types in culture and in human corneal tissue. Collagen types I, II, IV, IX and X stimulated proliferation, but had no effect on Fas-mediated apoptosis, of corneal fibroblasts. DDR1 and DDR2 tyrosine kinase receptors are expressed in the cornea. Collagen-stimulated mitosis of corneal fibroblasts in culture is likely mediated by the DDR receptors. Collagen had no effect on Fas-mediated apoptosis of corneal fibroblasts.

Abnormal distribution of collagen type IV in extrahepatic bile duct carcinoma

The present study investigated the pathogenesis of desmoplastic stroma formation, which is characteristic of most bile duct carcinomas and other scirrhous carcinomas. Using immunohistochemical analysis, the expression of collagen types I and IV, laminin and TGF-beta1 was examined in human extrahepatic bile duct carcinoma and compared with gastric and colon carcinoma. In addition to delineating the basement membranes of carcinoma nests and blood vessels, collagen type IV was present along the thick bundles of collagenous fibers in the stroma of extrahepatic bile duct carcinoma and scirrhous gastric carcinoma. The immunoreactivity of collagen type IV was strong in the adjacent or surrounding interstitium of tumor cell nests, but was absent or weak in older, more central portions of the tumor that contained sclerotic collagen. In situ hybridization demonstrated active expression of collagen alpha1(IV) mRNA in extrahepatic bile duct carcinoma and scirrhous gastric carcinoma cells. These results suggest that, although collagen type IV is typically a component of the basement membrane, it is expressed in the interstitial stroma of extrahepatic bile duct carcinoma and scirrhous gastric carcinoma where it may play a role in desmoplastic stroma formation.

The management of corneal trauma: advances in the past twenty-five years

Over the past quarter century, advances in our understanding of corneal anatomy, physiology, and wound healing have all played an integral role in the management of corneal trauma. As the etiologies of corneal trauma have changed, so has our understanding of the impact of injury on corneal function as it relates to visual rehabilitation. Numerous new classes of antibiotics, antiinflammatory agents, and tissue adhesives have emerged. Occlusive therapy has advanced from simple pressure patching bandage soft contact lenses and collagen shields. Surgical instrumentation, operating microscopes, viscoelastic substances, and suture materials have all improved the outcomes of corneal trauma repair. Improved understanding of the refractive properties of the cornea through topography and alternative suture techniques has helped us restore the natural corneal curvature and visual outcomes. Consequently, in the last quarter of this century our therapeutic approaches to cornea trauma, both medical and surgical, have improved.

An aggressive desmoid tumor in a patient with familial adenomatous polyposis: immunohistochemical findings

A case of an aggressive desmoid tumor in a patient with familial adenomatous polyposis is described. The lesion rapidlyenlarged with compression of adjacent structures including the ureter and small bowel, and the patient died because of small bowel perforation and hydronephrosis 3 years after detection of small desmoid tumors at the time of a prophylactic coloproctectomy for a colon carcinoma. Immunohistochemically, proliferating cell nuclear antigen (PCNA), p21WAF1/CIP1 and cathepsin D indices, but not the bcl-2 index, which were defined as the numbers of immunoreactive tumor cells per 1000 tumor cells, increased in line with tumor progression. The tumor did not show staining for collagen IV, but was characterized by intense staining for basic fibroblast growth factor (bFGF). Accordingly, tumor aggression was related to increases in both cell proliferation and protease activity, as well as an enhanced expression of bFGF. In addition, the desmoid tumor showed deregulation between PCNA and p21WAF1/CIP1 because the normal inverse relation between these two was not apparent.