Altered expression of type XIII collagen in keratoconus and scarred human cornea: Increased expression in scarred cornea is associated with myofibroblast transformation

Is Keratoconus More Than Just a Corneal Disease?

PURPOSE

The aims of this study were to compare the scleral thickness (ST), lamina cribrosa thickness (LCT), and lamina cribrosa curvature index between patients with keratoconus and healthy controls and to evaluate the relationship between these values and corneal parameters.

METHODS

This cross-sectional study included 41 eyes of 41 patients with keratoconus and 30 eyes of 30 age-matched, sex-matched, and axial length-matched controls. Nasal and temporal STs were measured vertically, 4 mm posterior to the scleral spur, using anterior segment optical coherence tomography. The LCT was measured on the radial scans of the optic nerve head. The lamina cribrosa curvature index (lamina cribrosa curvature depth/curvature width × 100) was calculated to determine the degree of posterior bowing of the lamina cribrosa.

RESULTS

The nasal ST and temporal ST were significantly lower in the keratoconus group than in the control group ( P = 0.016 and P = 0.023, respectively). The LCT was significantly lower in the keratoconus group compared with the control group ( P < 0.001). There was no significant difference between the groups for the lamina cribrosa curvature index ( P = 0.375). Correlation analysis revealed a significant correlation between the nasal and temporal STs and the central corneal thickness (r = 0.376, P < 0.001 and r = 0.387, P < 0.001, respectively). There was also a significant correlation between the temporal ST and the minimum corneal thickness in the keratoconus group (r = 0.332, P = 0.015). The LCT was significantly correlated with the central corneal thickness (r = 0.445, P < 0.001).

CONCLUSIONS

Structural features of the cornea, sclera, and lamina cribrosa with similar collagen content may be similarly affected in patients with keratoconus. Further histologic studies are needed to confirm our results.

Pathogenesis of Common Ocular Diseases: Emerging Trends in Extracellular Matrix Remodeling

The prevalence of visual impairments in human societies is worrying due to retinopathy complications of several chronic diseases such as diabetes, cardiovascular diseases, and many more that are on the rise worldwide. Since the proper function of this organ plays a pivotal role in people's quality of life, identifying factors affecting the development/exacerbation of ocular diseases is of particular interest among ophthalmology researchers. The extracellular matrix (ECM) is a reticular, three-dimensional (3D) structure that determines the shape and dimensions of tissues in the body. The ECM remodeling/hemostasis is a critical process in both physiological and pathological conditions. It consists of ECM deposition, degradation, and decrease/increase in the ECM components. However, disregulation of this process and an imbalance between the synthesis and degradation of ECM components are associated with many pathological situations, including ocular disorders. Despite the impact of ECM alterations on the development of ocular diseases, there is not much research conducted in this regard. Therefore, a better understanding in this regard, can pave the way toward discovering plausible strategies to either prevent or treat eye disorders. In this review, we will discuss the importance of ECM changes as a sentimental factor in various ocular diseases based on the research done up to now.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

Features of morphological and ultrastructural organization of the cornea (literature review)

The human cornea – the anterior fibrous membrane of the eye, is a unique ordered optical-biological system that is avascular, saturated with nerve endings, includes tissue-specific cells, consists mainly of various types of collagen. An exceptional feature of the collagen layers of the cornea, including the collagen plates of the stroma, is transparency, which provides physiological refraction and light transmission due to the stable supporting properties of the cornea. The data on the morphological structure of the cornea, which is an important element of the optical system of the eye, are of considerable interest not only from theoretical, but also from practical positions. This is due to the fact that the identification of the first signs of deviation from normal physiological morphological and ultrastructural criteria in the cornea allows us to establish the nature of its pathological changes, which can be caused by both hereditary predisposition and local and general disorders. It has been shown that the thinning of the layers of the cornea, a decrease in the density of endotheliocytes or keratocytes signal the development of dystrophic processes in it. In addition to evaluating quantitative morphometric data, changes in qualitative ultrastructural indicators play an important role. In particular it was found that a decrease in the density of endothelial cells is accompanied by an increase in their size and a decrease in the cell nucleus. In addition, a number of degenerative pathological conditions are characterized by a decrease in the diameter of collagen fibrils and a change in the density of fibrillary packaging.This literature review presents basic information, features of morphology, ultrastructural organization and functional purpose of layers and cells of the human cornea.

Presence of Protease Inhibitor 9 and Granzyme B in Healthy and Pathological Human Corneas

Simple Summary

Detailed knowledge of the structure and properties of the human cornea is a prerequisite not only for the treatment of various corneal diseases but also for successful corneal transplantation and its long-term survival after grafting. Using various cell and molecular biology approaches, we found in cornea the protease inhibitor 9. This protein, known to be present in other human tissues but not yet reported in cornea, is directly involved in the immune response after transplantation. Together with its inhibitor (granzyme B), we localized this protein, especially in the superficial and inner cornea layers. This localization indicates that protease inhibitor 9 protein may be involved in protecting the cornea from external damage, but also in protection against immune cells inducing corneal graft rejection. Furthermore, we have shown on pathological corneal samples from corneal melting and herpes virus keratitis that the increased expression of both proteins is linked to these diseases. These experiments and their results represent an important contribution to the basic research of cornea biological properties with direct overlap into clinical practice.

Abstract

The aim of this study was to find out whether protease inhibitor 9 (PI-9) and granzyme B (GrB) molecules that contribute to immune response and the immunological privilege of various tissues are expressed in healthy and pathological human corneas. Using cryosections, cell imprints of control corneoscleral discs, we showed that PI-9 was expressed particularly in the endothelium, the superficial and suprabasal epithelium of healthy corneas, limbus, and conjunctiva. GrB was localized in healthy corneal and conjunctival epithelium, while the endothelium showed weak immunostaining. The expression of PI-6 and GrB was confirmed by qRT-PCR. Increased expression levels of the PI-9 and GrB genes were determined when the corneas were cultured with proinflammatory cytokines. Fluorescent and enzymatic immunohistochemistry of pathological corneal explants (corneal melting and herpes virus keratitis) showed pronounced PI-9, GrB, human leucocyte antigen (HLA)-DR, and leukocyte-common antigen (CD45) signals localized in multicellular stromal infiltrates and inflammatory cells scattered in the corneal stroma. We conclude that increased expression of the PI-9 and GrB proteins under pathological conditions and their upregulation in an inflammatory environment indicate their participation in immune response of the cornea during the inflammatory process.

Systematically Displaying the Pathogenesis of Keratoconus via Multi-Level Related Gene Enrichment-Based Review

Keratoconus (KC) is an etiologically heterogeneous corneal ectatic disorder. To systematically display the pathogenesis of keratoconus (KC), this study reviewed all the reported genes involved in KC, and performed an enrichment analysis of genes identified at the genome, transcription, and protein levels respectively. Combined analysis of multi-level results revealed their shared genes, gene ontology (GO), and pathway terms, to explore the possible pathogenesis of KC. After an initial search, 80 candidate genes, 2,933 transcriptional differential genes, and 947 differential proteins were collected. The candidate genes were significantly enriched in extracellular matrix (ECM) related terms, Wnt signaling pathway and cytokine activities. The enriched GO/pathway terms of transcription and protein levels highlight the importance of ECM, cell adhesion, and inflammatory once again. Combined analysis of multi-levels identified 13 genes, 43 GOs, and 12 pathways. The pathogenic relationships among these overlapping factors maybe as follows. The gene mutations/variants caused insufficient protein dosage or abnormal function, together with environmental stimulation, leading to the related functions and pathways changes in the corneal cells. These included response to the glucocorticoid and reactive oxygen species; regulation of various signaling (P13K-AKT, MAPK and NF-kappaB), apoptosis and aging; upregulation of cytokines and collagen-related enzymes; and downregulation of collagen and other ECM-related proteins. These undoubtedly lead to a reduction of extracellular components and induction of cell apoptosis, resulting in the loosening and thinning of corneal tissue structure. This study, in addition to providing information about the genes involved, also provides an integrated insight into the gene-based etiology and pathogenesis of KC.

Transmembrane collagens-Unexplored mediators of epidermal-dermal communication and tissue homeostasis

Tissue homeostasis is maintained through constant, dynamic and heterogeneous communication between cells and their microenvironment. Proteins that are at the same time active at the intracellular, cell periphery and deeper extracellular levels possess the ability to, on the individual molecular level, influence the cells and their microenvironment in a bidirectional manner. The transmembrane collagens are a family of such proteins, which are of notable interest for tissue development and homeostasis. In skin, expression of all transmembrane collagens has been reported and deficiency of transmembrane collagen XVII manifests with distinct skin phenotypes. Nevertheless, transmembrane collagens in skin remain understudied despite the association of them with epidermal wound healing and dermal fibrotic processes. Here, we present an overview of transmembrane collagens and put a spotlight on them as regulators of epidermal-dermal communication and as potential players in fibrinogenesis.

Mesenchymal stem cell-derived extracellular vesicles as a new therapeutic strategy for ocular diseases

Mesenchymal stem cells (MSCs) have attracted considerable attention for their activity in the treatment of refractory visual disorders. Since MSCs were found to possess the beneficial effects by secreting paracrine factors rather than direct differentiation, MSC-derived extracellular vesicles (EVs) were widely studied in various disease models. MSCs generate abundant EVs, which act as important mediators by exchanging protein and genetic information between MSCs and target cells. It has been confirmed that MSC-derived EVs possess unique anti-inflammatory, anti-apoptotic, tissue repairing, neuroprotective, and immunomodulatory properties, similar to their parent cells. Upon intravitreal injection, MSC-derived EVs rapidly diffuse through the retina to alleviate retinal injury or inflammation. Due to possible risks associated with MSC transplantation, such as vitreous opacity and pathological proliferation, EVs appear to be a better choice for intravitreal injection. Small size EVs can pass through biological barriers easily and their contents can be modified genetically for optimal therapeutic effect. Hence, currently, they are also explored for the possibility of serving as drug delivery vehicles. In the current review, we describe the characteristics of MSC-derived EVs briefly, comprehensively summarize their biological functions in ocular diseases, and discuss their potential applications in clinical settings.

The Proteins of Keratoconus: a Literature Review Exploring Their Contribution to the Pathophysiology of the Disease

INTRODUCTION

Keratoconus (KC) is a complex, genetically heterogeneous multifactorial degenerative disorder characterized by corneal ectasia and thinning. Its incidence is approximately 1/2000-1/50,000 in the general population. KC is associated with moderate to high myopia and irregular astigmatism, resulting in severe visual impairment. KC structural abnormalities primarily relate to the weakening of the corneal collagen. Their understanding is crucial and could contribute to effective management of the disease, such as with the aid of corneal cross-linking (CXL). The present article critically reviews the proteins involved in the pathophysiology of KC, with particular emphasis on the characteristics of collagen that pertain to CXL.

METHODS

PubMed, MEDLINE, Google Scholar and GeneCards databases were screened for relevant articles published in English between January 2006 and June 2018. Keyword combinations of the words "keratoconus," "risk factor(s)," "genetics," "genes," "genetic association(s)," "proteins", "collagen" and "cornea'' were used. In total, 272 articles were retrieved, reviewed and selected, with greater weight placed on more recently published evidence. Based on the reviewed literature, an attempt was made to tabulate the up- and down-regulation of genes involved in KC and their protein products and to delineate the mechanisms involved in CXL.

RESULTS

A total of 117 proteins and protein classes have been implicated in the pathogenesis and pathophysiology of KC. These have been tabulated in seven distinct tables according to their gene coding, their biochemistry and their metabolic control.

CONCLUSION

The pathogenesis and pathophysiology of KC remain enigmatic. Emerging evidence has improved our understanding of the molecular characteristics of KC and could further improve the success rate of CXL therapies.

Familial association of keratoconus and granular corneal dystrophy: The familial case series

OBJECTIVE:

The aim of the present study was to evaluate the coexistence of bilateral keratoconus and granular corneal dystrophy (GCD) in the members of a family.

METHODS:

A total of 22 patients were examined in four generations of the family tree in this family screening study. Visual acuity test, biomicroscopic examination, and fundus examination were performed in all patients. The diagnosis of granular dystrophy was based on biomicroscopic examination findings. Corneal topography was performed on the patients diagnosed with granular dystrophy and other family members aged >5 years with normal examination findings. Corneal photographs were obtained from all patients with granular dystrophy except one case.

RESULTS:

Keratoconus or subclinical keratoconus was detected in seven cases. In addition, GCD type 1 was found in six of the seven cases. All patients diagnosed with keratoconus and granular dystrophy were females. On the other hand, there was no ophthalmologic problem in the men of the family tree. Although an autosomal dominant inheritance was found, the onset of the disease only in women suggests that there may be a variant expression.

CONCLUSION:

The present study showed an association of GCD and keratoconus in four generations of a family. More research is required to further explain this association.

Membrane associated collagen XIII promotes cancer metastasis and enhances anoikis resistance

BACKGROUND

Increased collagen expression and deposition are associated with cancer progression and poor prognosis in breast cancer patients. However, function and regulation of membrane-associated collagen in breast cancer have not been determined. Collagen XIII is a type II transmembrane protein within the collagen superfamily. Experiments in tissue culture and knockout mouse models show that collagen XIII is involved in cell adhesion and differentiation of certain cell types. In the present study, we determined roles of collagen XIII in breast cancer progression and metastasis.

METHODS

We analyzed the association of collagen XIII expression with breast cancer development and metastasis using published gene expression profiles generated from human breast cancer tissues. Utilizing gain- and loss- of function approaches and 3D culture assays, we investigated roles of collagen XIII in regulating invasive tumor growth. Using the tumorsphere/mammosphere formation assay and the detachment cell culture assay, we determined whether collagen XIII enhances cancer cell stemness and induces anoikis resistance. We also inhibited collagen XIII signaling with β1 integrin function-blocking antibody. Finally, using the lung colonization assay and the orthotopic mammary tumor model, we investigated roles of collagen XIII in regulating breast cancer colonization and metastasis. Cox proportional hazard (log-rank) test, two-sided Student's t-test (two groups) and one-way ANOVA (three or more groups) analyses were used in this study.

RESULTS

Collagen XIII expression is significantly higher in human breast cancer tissue compared with normal mammary gland. Increased collagen XIII mRNA levels in breast cancer tissue correlated with short distant recurrence free survival. We showed that collagen XIII expression promoted invasive tumor growth in 3D culture, enhanced cancer cell stemness, and induced anoikis resistance. Collagen XIII expression induced β1 integrin activation. Blocking β1 integrin activation significantly reduced collagen XIII-induced invasion and mammosphere formation. Importantly, silencing collagen XIII in MDA-MB-231 cells reduced lung colonization and metastasis.

CONCLUSIONS

Our results demonstrate a novel function of collagen XIII in promoting cancer metastasis, cell invasion, and anoikis resistance.

Effects of Adipose-derived Mesenchymal Stem Cell Exosomes on Corneal Stromal Fibroblast Viability and Extracellular Matrix Synthesis

Background

Corneal stromal cells (CSCs) are components of the corneal endothelial microenvironment that can be induced to form a functional tissue-engineered corneal endothelium. Adipose-derived mesenchymal stem cells (ADSCs) have been reported as an important component of regenerative medicine and cell therapy for corneal stromal damage. We have demonstrated that the treatment with ADSCs leads to phenotypic changes in CSCs in vitro. However, the underlying mechanisms of such ADSC-induced changes in CSCs remain unclear.

Methods

ADSCs and CSCs were isolated from New Zealand white rabbits and cultured in vitro. An Exosome Isolation Kit, Western blotting, and nanoparticle tracking analysis (NTA) were used to isolate and confirm the exosomes from ADSC culture medium. Meanwhile, the optimal exosome concentration and treatment time were selected. Cell Counting Kit-8 and annexin V-fluorescein isothiocyanate/propidium iodide assays were used to assess the effect of ADSC- derived exosomes on the proliferation and apoptosis of CSCs. To evaluate the effects of ADSC- derived exosomes on CSC invasion activity, Western blotting was used to detect the expression of matrix metalloproteinases (MMPs) and collagens.

Results:

ADSCs and CSCs were successfully isolated from New Zealand rabbits. The optimal concentration and treatment time of exosomes for the following study were 100 μg/ml and 96 h, respectively. NTA revealed that the ADSC-derived exosomes appeared as nanoparticles (40-200 nm), and Western blotting confirmed positive expression of CD9, CD81, flotillin-1, and HSP70 versus ADSC cytoplasmic proteins (all P < 0.01). ADSC-derived exosomes (50 μg/ml and 100 μg/ml) significantly promoted proliferation and inhibited apoptosis (mainly early apoptosis) of CSCs versus non-exosome-treated CSCs (all P < 0.05). Interestingly, MMPs were downregulated and extracellular matrix (ECM)-related proteins including collagens and fibronectin were upregulated in the exosome-treated CSCs versus non-exosome-treated CSCs (MMP1: t = 80.103, P < 0.01; MMP2: t = 114.778, P < 0.01; MMP3: t = 56.208, P < 0.01; and MMP9: t = 60.617, P < 0.01; collagen I: t = -82.742, P < 0.01; collagen II: t = -72.818, P < 0.01; collagen III: t = -104.452, P < 0.01; collagen IV: t = -133.426, P < 0.01, and collagen V: t = -294.019, P < 0.01; and fibronectin: t = -92.491, P < 0.01, respectively).

Conclusion:

The findings indicate that ADSCs might play an important role in CSC viability regulation and ECM remodeling, partially through the secretion of exosomes.

Myofibroblast transdifferentiation: The dark force in ocular wound healing and fibrosis

Wound healing is one of the most complex biological processes to occur in life. Repair of tissue following injury involves dynamic interactions between multiple cell types, growth factors, inflammatory mediators and components of the extracellular matrix (ECM). Aberrant and uncontrolled wound healing leads to a non-functional mass of fibrotic tissue. In the eye, fibrotic disease disrupts the normally transparent ocular tissues resulting in irreversible loss of vision. A common feature in fibrotic eye disease is the transdifferentiation of cells into myofibroblasts that can occur through a process known as epithelial-mesenchymal transition (EMT). Myofibroblasts rapidly produce excessive amounts of ECM and exert tractional forces across the ECM, resulting in the distortion of tissue architecture. Transforming growth factor-beta (TGFβ) plays a major role in myofibroblast transdifferentiation and has been implicated in numerous fibrotic eye diseases including corneal opacification, pterygium, anterior subcapsular cataract, posterior capsular opacification, proliferative vitreoretinopathy, fibrovascular membrane formation associated with proliferative diabetic retinopathy, submacular fibrosis, glaucoma and orbital fibrosis. This review serves to introduce the pathological functions of the myofibroblast in fibrotic eye disease. We also highlight recent developments in elucidating the multiple signaling pathways involved in fibrogenesis that may be exploited in the development of novel anti-fibrotic therapies to reduce ocular morbidity due to scarring.

Cell viability and extracellular matrix synthesis in a co-culture system of corneal stromal cells and adipose-derived mesenchymal stem cells

AIM

To investigate the impact of adipose-derived mesenchymal stem cells (ADSCs) on cell viability and extracellular matrix (ECM) synthesis of corneal stromal cells (CSCs).

METHODS

ADSCs and CSCs were obtained from the corneas of New Zealand white rabbits and indirectly co-cultured in vitro. The proliferative capacity of CSCs in the different groups was assessed by CCK-8 assays. Annexin V-fluorescein isothiocyanate (FITC)/proliferation indices (PI) assays were used to detect the apoptosis of CSCs. The expression levels of matrix metalloproteinase (MMP), such as MMP1, MMP2, MMP9, and collagens were also evaluated by Western blot.

RESULTS

ADSCs significantly promoted proliferation and invasion of CSCs in the indirect co-culture assays. The co-cultural group displayed much higher ability of proliferation, especially under the co-culture conditions of ADSCs for 3d, compared with that CSCs cultured alone. The PI of CSCs in the co-culture system were increased approximately 3-8-fold compared with the control group. A significant change was observed in the proportions of cells at apoptosis (early and late) between the negative control group (6.34% and 2.06%) and the ADCSs-treated group (4.69% and 1.59%). The expression levels of MMPs were down regulated in the co-culture models. Compared with the control group, the decrease intensities of MMP-1, MMP-2 and MMP-9 in CSCs/ADSCs group were observed, 3.90-fold, 1.09-fold and 3.03-fold, respectively. However, the increase intensities of collagen type (I, II, III, IV, and V) in CSCs were observed in CSCs/ADSCs group, 3.47-fold, 4.30-fold, 2.35-fold, 2.55-fold and 2.43-fold, respectively, compared to that in the control group. The expressions of aldehyde dehydrogenase and fibronectin in CSCs were upregulated in the co-culture models.

CONCLUSION

ADSCs play a promotive role in CSCs' growth and invasion, which may be partially associated with MMPs decrease and collagens increase, resulting in a positive participation in the plasticity and ECM synthesis of CSCs. This provided a new insight into the extensive role of ADSCs in CSCs and a potential molecular target for corneal therapy.

Effect of bone marrow and adipose tissue-derived mesenchymal stem cells on the natural course of corneal scarring after penetrating injury

In the present study, we investigate and compare the efficacy of bone marrow- and adipose tissue-derived mesenchymal stem cell (MSCs) in corneal wound healing. A penetrating injury was created in the right corneas of Wistar rats (n = 40). Ten microliters of phosphate-buffered solution (PBS) containing 2 × 10(5) green fluorescent protein (GFP) labeled bone-marrow-derived MSCs to group 1 (n = 15), 10 μl of PBS containing 2 × 10(5) GFP-labeled adipose-tissue-derived MSCs to group 2 (n = 15), 10 μl PBS was injected into anterior chamber in group 3 (n = 10, control). Corneal opacity scoring, in vivo confocal microscopy, and histopathological evaluation were done at the end of 8 weeks. Immunofluorescence sections were evaluated to detect transplanted cells. Immune staining was performed to measure the expression levels of keratocan, aldehyde dehydrogenase (ALDH) and CD34. The gene expression levels of tumor necrosis factor (TNF-α), the interleukin 6 receptor (IL-6R), interleukin 12b (IL-12b), and transforming growth factor beta (TGF-β1) was measured on corneas. The establishment of stem cells in the corneas of the transplanted groups was confirmed by immunofluorescence staining. The expression of keratocan, ALDH, and CD34 increased in the transplanted groups (p < 0.05). The density of keratocytes increased significantly in both transplanted groups according to the in vivo confocal microscopy data (p < 0.05). The expression of TNF-α, IL-6R, and IL-12b decreased significantly in the transplanted groups (p < 0.05). Based on our findings, we consider that allogeneic stem cells facilitate the regeneration of corneal stroma and can be a cell source for stromal repopulation in diseased cornea.

Keratoconus: an inflammatory disorder?

Keratoconus has been classically defined as a progressive, non-inflammatory condition, which produces a thinning and steepening of the cornea. Its pathophysiological mechanisms have been investigated for a long time. Both genetic and environmental factors have been associated with the disease. Recent studies have shown a significant role of proteolytic enzymes, cytokines, and free radicals; therefore, although keratoconus does not meet all the classic criteria for an inflammatory disease, the lack of inflammation has been questioned. The majority of studies in the tears of patients with keratoconus have found increased levels of interleukin-6 (IL-6), tumor necrosis factor-α(TNF-α), and matrix metalloproteinase (MMP)-9. Eye rubbing, a proven risk factor for keratoconus, has been also shown recently to increase the tear levels of MMP-13, IL-6, and TNF-α. In the tear fluid of patients with ocular rosacea, IL-1α and MMP-9 have been reported to be significantly elevated, and cases of inferior corneal thinning, resembling keratoconus, have been reported. We performed a literature review of published biochemical changes in keratoconus that would support that this could be, at least in part, an inflammatory condition.

Evaluation of scleral and corneal thickness in keratoconus patients

PURPOSE

To determine whether the scleral stroma is affected as much as the corneal stroma in keratoconus.

SETTING

University Eye Clinic, Bern, Switzerland.

DESIGN

Comparative case-control study.

METHODS

Eyes with keratoconus (keratoconus group) and eyes of age-, sex-, and axial length-matched controls (control group) were analyzed. Corneal videokeratometry and pachymetry were performed using a Scheimpflug tomographer (Pentacam). For measurements of the peripheral cornea and the anterior sclera, a spectral-domain anterior segment optical coherence tomography device (Spectralis) was used.

RESULTS

The study group comprised 51 eyes and the control group, 50 eyes. The mean central corneal thickness in the keratoconus group was statistically significantly lower than in the control group (447.8 μm ± 57.8 [SD] versus 550.5 ± 35.5 μm) (P < .0001). No significant difference in the mean anterior scleral thickness was found between the keratoconus group and the control group (479.1 ± 43.7 μm versus 474.2 ± 43.0 μm) (P =.57).

CONCLUSION

Although corneal thinning was observed in keratoconus patients, the anterior scleral stroma thickness in these patients seemed to be similar to that in healthy control eyes.

Viability, apoptosis, proliferation, activation, and cytokine secretion of human keratoconus keratocytes after cross-linking

Purpose. The purpose of this study was to determine the impact of cross-linking (CXL) on viability, apoptosis, proliferation, activation, and cytokine secretion of human keratoconus (KC) keratocytes, in vitro. Methods. Primary KC keratocytes were cultured in DMEM/Ham's F12 medium supplemented with 10% FCS and underwent UVA illumination (370 nm, 2 J/cm²) during exposure to 0.1% riboflavin and 20% Dextran in PBS. Twenty-four hours after CXL, viability was assessed using Alamar blue assay; apoptosis using APO-DIRECT Kit; proliferation using ELISA-BrdU kit; and CD34 and alpha-smooth muscle actin (α-SMA) expression using flow cytometry. Five and 24 hours after CXL, FGFb, HGF, TGFβ1, VEGF, KGF, IL-1β, IL-6, and IL-8 secretion was measured using enzyme-linked-immunoabsorbent assay (ELISA). Results. Following CXL, cell viability and proliferation decreased (P < 0.05; P = 0.009), the percentage of apoptotic keratocytes increased (P < 0.05) significantly, and CD34 and α-SMA expression remained unchanged (P > 0.06). Five hours after CXL, FGFb secretion increased significantly (P = 0.037); however no other cytokine secretion differed significantly from controls after 5 or 24 hours (P > 0.12). Conclusions. Cross-linking decreases viability, triggers apoptosis, and inhibits proliferation, without an impact on multipotent hematopoietic stem cell transformation and myofibroblastic transformation of KC keratocytes. CXL triggers FGFb secretion of KC keratocytes transiently (5 hours), normalizing after 24 hours.

Peripheral hypertrophic subepithelial corneal degeneration - clinical and histopathological features

PURPOSE

To refine the diagnostic criteria for peripheral hypertrophic subepithelial corneal degeneration (PHSD) and characterize its clinical phenotype, histopathology and immunohistochemical features.

METHODS

Diagnostic criteria were refined on the basis of literature data. Fourteen patients (13 women and one man; median age 52 years, range 33-66) were identified based on these criteria. Keratectomy specimens were evaluated via routine and immunohistochemical stainings. The main outcome measures were symptoms, clinical phenotype, immunological status and histopathologic results.

RESULTS

We defined the diagnostic criteria of typical PHSD as elevated circumferential and perilimbal subepithelial fibrosis with focal superficial corneal neovascularization, which were supported by female sex (93%), bilaterality (86%), the centre being in the upper quadrants (81%) and irregular astigmatism of two dioptres or more. The typical symptoms were reduced vision (86%) and the symptoms of ocular surface disease (64%). Light microscopy showed fibrosis with abundant collagen deposition but no inflammation in all patients. An immunohistochemical analysis of nine patients showed uniform staining for vimentin in three distinct types of fibroblasts in variable proportions: keratocyte-like cells that were positive for CD34, myofibroblasts that were positive for smooth muscle actin (SMA) and fibroblasts that were negative for CD34 and SMA. Small numbers of CD68-positive macrophages were also found.

CONCLUSIONS

Peripheral hypertrophic subepithelial degeneration is characteristic of middle-aged women, in whom it is typically a bilateral idiopathic degeneration of the cornea associated with ocular surface disease and reduced vision. The fibrotic lesions probably undergo remodelling, inducing changes in corneal contour. A smouldering low-grade inflammation favouring low TGF-β1 concentrations is postulated as the primary pathological process leading to PHSD.

Segregation analysis suggests that keratoconus is a complex non-mendelian disease

PURPOSE

Complex segregation analysis of 60 unrelated sporadic keratoconus (KC) families was performed to reveal the presumed mode of inheritance in our dataset.

METHODS

Sixty probands, 212 family members and 212 age and gender matched healthy controls underwent clinical and videokeratographic examination. Family aggregation and distribution of videokeratography parameters were examined. Segregation of KSI, KISA and 6mm Fourier asymmetry alone or in covariate analysis with gender or the presence of Fleischer ring, exploring mendelian and non-mendelian models of inheritance was tested using complex segregation analysis with the S.A.G.E. program package.

RESULTS

In 145 relatives of probands, the estimated prevalence of manifest KC was 7.6% (95% CI: 3.3-11.9) based on KISA index, indicating strong familial aggregation. All examined videokeratography indices were able to differentiate between KC and non-KC family members as well as normal controls (anova p < 0.001). Hypotheses accepted as most parsimonius models of inheritance (p > 0.1) for all indices indicated the presence of a non-mendelian major gene effect (MG). Inclusion of Fleischer ring as covariate improved the fit of MG models. Mendelian, Sporadic and polygenic models were consistently rejected.

CONCLUSIONS

Complex segregation analysis indicates a strong genetic contribution to the transmission of keratoconus. Inheritance is most probably due to a non-mendelian major gene effect. Low genotype-phenotype correlation in sporadic KC families can make linkage studies difficult, thus genome wide association studies, epigenetic and pathway analyses may provide more information on disease pathogenesis in non-familial keratoconus.

The integrin needle in the stromal haystack: emerging role in corneal physiology and pathology

Several studies have established the role of activated corneal keratocytes in the fibrosis of the cornea. However, the role of keratocytes in maintaining the structural integrity of a normal cornea is less appreciated. We focus on the probable functions of integrins in the eye and of the importance of integrin-mediated keratocyte interactions with stromal matrix in the maintenance of corneal integrity. We point out that further understanding of how keratocytes interact with their matrix could establish a novel direction in preventing corneal pathology including loss of structural integrity as in keratoconus or as in fibrosis of the corneal stroma.

Deficient repair regulatory response to injury in keratoconic stromal cells

BACKGROUND

Keratoconus manifests as a conical protrusion of the cornea and is characterised by stromal thinning. This causes debilitating visual impairment, which may necessitate corneal transplantation. Hypothetically, many of the pathological features in keratoconus may be manifestations of defects in wound healing; however, as the pathobiology remains unclear, therapeutic targets related to disease mechanisms are currently lacking. This study investigated the protein expression of cytokines which may control stromal wound healing and the effect of an induced secondary injury (SI) on stromal cells from ex vivo human keratoconus and control corneas.

METHODS

Total protein was extracted from stromal cells from human keratoconic and non-keratoconic central corneas (n = 12) with (+SI) and without (-SI) an ex vivo corneal incision wound. The levels of interleukin 1 alpha (IL-1α), fibroblast growth factor 2 (FGF-2), nerve growth factor beta (β-NGF), insulin-like growth factor 1 (IGF-1), tumour necrosis factor alpha (TNF-α), epidermal growth factor (EGF), transforming growth factor beta 1 (TGF-β1), platelet-derived growth factor (PDGF) and hepatocyte growth factor (HGF) were quantified using chemiluminescence-based immunoarrays.

RESULTS

In stromal cells from -SI keratoconic corneas (compared with -SI normal corneas), the levels of IL-1α, IGF-1, TNF-α and TGF-β1 were increased and the levels of HGF and β-NGF were reduced. These alterations were also observed in +SI non-keratoconic corneas (compared with -SI non-keratoconic corneas). In stromal cells from +SI keratoconic corneas (compared with -SI keratoconic corneas), the quantities of IL-1α, FGF-2, TNF-a, EGF, TGF-a1 and PDGF were decreased.

CONCLUSION

The repair-modulating milieu in keratoconic corneas appears comparable to that in wounded normal corneas. Moreover, wounded keratoconic corneas may be less capable of orchestrating a normal reparative response. These novel findings may improve our understanding of the pathobiology and may facilitate the identification of potential biological targets and therapeutic agents to advance the clinical management of this disorder.

Collagen XIII: a type II transmembrane protein with relevance to musculoskeletal tissues, microvessels and inflammation

Collagen XIII and the homologous collagens XXIII and XXV form a subgroup of type II transmembrane proteins within the collagen superfamily. Collagen XIII consists of a short cytosolic domain, a transmembrane domain and a large extracellular ectodomain, which may be shed into the pericellular matrix. It has been proposed that collagen XIII may function as an adhesion molecule, due to its cellular localization at focal contacts, numerous interactions with basement membrane (BM) and other extracellular matrix (ECM) proteins and expression at various cell-cell and cell-matrix junctions. Recent in vivo studies highlight its involvement in the development, differentiation and maturation of musculoskeletal tissues and vessels and in maintaining tissue integrity.

Transforming growth factor-β signaling pathway activation in Keratoconus

PURPOSE

To assess the presence of transforming growth factor-β (TGFβ) pathway markers in the epithelium of keratoconus patient corneas.

DESIGN

Retrospective, comparative case series of laboratory specimens.

METHODS

Immunohistochemistry results for TGFβ2, total TGFβ, mothers against decacentaplegic homolog (Smad) 2, and phosphorylated Smad2 was performed on formalin-fixed, paraffin-embedded sections of keratoconus patient corneas and normal corneas from human autopsy eyes. Keratoconus patient corneas were divided in two groups, depending on their severity based on keratometer readings and pachymetry. Autopsy controls were age-matched with the keratoconus cases. Immunohistochemistry signal quantification was performed using automated software. Real-time reverse-transcriptase polymerase chain reaction was performed on total ribonucleic acid of epithelium of keratoconus patient corneas and autopsy control corneas.

RESULTS

Immunohistochemistry quantification showed a significant increase in mean signal in the group of severe keratoconus cases compared with normal corneas for TGFβ2 and phosphorylated Smad2 (P < .05). Immunohistochemistry analysis using antibodies against total TGFβ and Smad2 did not show any significant increase in the keratoconus cases versus the autopsy controls. Reverse-transcriptase polymerase chain reaction exhibited elevated messenger ribonucleic acid levels of Smad2 and TGFβ2 in severe keratoconus corneal epithelium.

CONCLUSIONS

This work shows increased TGFβ pathway markers in severe keratoconus cases and provides the rationale for investigating TGFβ signaling further in the pathophysiology of keratoconus.

Keratoconus: a review

Keratoconus is the most common primary ectasia. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 54 per 100,000. Ocular signs and symptoms vary depending on disease severity. Early forms normally go unnoticed unless corneal topography is performed. Disease progression is manifested with a loss of visual acuity which cannot be compensated for with spectacles. Corneal thinning frequently precedes ectasia. In moderate and advance cases, a hemosiderin arc or circle line, known as Fleischer's ring, is frequently seen around the cone base. Vogt's striaes, which are fine vertical lines produced by Descemet's membrane compression, is another characteristic sign. Most patients eventually develop corneal scarring. Munson's sign, a V-shape deformation of the lower eyelid in downward position; Rizzuti's sign, a bright reflection from the nasal area of the limbus when light is directed to the limbus temporal area; and breakages in Descemet's membrane causing acute stromal oedema, known as hydrops, are observed in advanced stages. Classifications based on morphology, disease evolution, ocular signs and index-based systems of keratoconus have been proposed. Theories into the genetic, biomechanical and biochemical causes of keratoconus have been suggested. Management varies depending on disease severity. Incipient cases are managed with spectacles, mild to moderate cases with contact lenses and severe cases can be treated with keratoplasty. This article provides a review on the definition, epidemiology, clinical features, classification, histopathology, aetiology and pathogenesis, and management and treatment strategies for keratoconus.

Mediators of neovascularization and the hypoxic cornea

The maintenance of corneal avascularity is essential to vision. The mechanisms by which the cornea becomes vascularized in response to inflammation or hypoxic stress are beginning to be elucidated. A detailed understanding of the molecular responses of the cornea to hypoxia is critical for prevention and development of novel treatments for neovascularization in a range of disease states. Here, we have examined the current literature on the major mediators of angiogenesis, which have previously been reported during hypoxia in the cornea in order to better understand the mechanisms by which corneal angiogenesis occurs in circumstances where the available oxygen is reduced. The normal cornea produces angiogenic factors that are regulated by the production of anti-angiogenic molecules. The various cell types of the cornea respond differentially to inflammatory and hypoxic stimuli. An understanding of the factors that may predispose patients to development of corneal blood vessels may provide an opportunity to develop novel prophylactic strategies. The difficulties with extrapolating data from other cell types and animal models to the cornea are also examined.

Collagen ultrastructural changes during stromal wound healing in organ cultured bovine corneas

Corneal collagen ultrastructural changes occur during the healing process. The present study was designed to compare collagen ultrastructural changes after trephine wounding or flap creation. Bovine corneas were injured and maintained in organ culture for up to 4 weeks. Samples were removed from culture at 0, 1, 2, 3 and 4 weeks and snap frozen in liquid N(2). X-ray scattering was used to measure changes in collagen interfibrillar spacing, intermolecular spacing and fibrillar diameter. Some samples were fixed in 10% Neutral Buffered Formalin solution and wax embedded for immunohistochemistry to monitor myofibroblast differentiation in corneal flaps. Swelling effects (i.e. changes in interfibrillar spacing) were more severe in trephined corneas than in those with stromal flaps. Collagen fibrillar diameter remained normal in the periphery of injured corneas, but increased significantly in areas within and around the wound in trephined samples and in the epithelial incision site in corneal flaps. Intermolecular spacing was unchanged in all samples. In the flaps, alphaSMA expression was only detected in an area adjacent to the epithelial plug, and cell numbers gradually increased during the culture. We conclude that stromal swelling is more rapid for trephine-wounded corneas than in stromal flaps, indicating that the intensity of the corneal healing response depends on the type of injury.

Alterations of extracellular matrix components and proteinases in human corneal buttons with INTACS for post-laser in situ keratomileusis keratectasia and keratoconus

PURPOSE

To perform an immunohistochemical evaluation of corneas with INTACS for post-laser in situ keratomileusis (LASIK) keratectasia and keratoconus, obtained after corneal transplantation.

METHODS

Corneas from 1 patient with INTACS for post-LASIK keratectasia and 2 patients with INTACS for keratoconus were obtained within 3 hours after penetrating keratoplasty, and cryostat sections were analyzed by immunostaining for 35 extracellular matrix (ECM) components and proteinases.

RESULTS

In the stroma of all corneas next to an INTACS implant, ECM components typically associated with fibrosis were observed. These included tenascin-C, fibrillin-1, and types III, IV (alpha1/alpha2 chains), and XIV collagen. Also, significant deposition of perlecan, nidogen-2, and cellular fibronectin was revealed in the same locations. The keratoconus cases displayed typical Bowman layer breaks and subepithelial fibrosis with deposition of various ECM components. In all cases, some keratocytes around INTACS were positive for specific proteinases associated with stromal remodeling, including cathepsins F and H, matrix metalloproteinase (MMP)-1, MMP-3, and MMP-10. Staining for MMP-7 was variable; MMP-2 and MMP-9 were mostly negative. Patterns of type IV collagen alpha 3, alpha 4, and alpha 6 chains; types VI and VIII collagen; laminin-332, alpha 4, alpha 5, beta1, beta2, and gamma 1 laminin chains; vitronectin; thrombospondin-1; urokinase; EMMPRIN; and cathepsins B and L were unchanged around INTACS in all 3 cases compared with normal.

CONCLUSIONS

Abnormal accumulation of fibrotic ECM components and proteinases near INTACS suggests ongoing lysis and remodeling of corneal stroma. Specific changes observed in each case may be related to underlying pathology.

Adipose-derived stem cells are a source for cell therapy of the corneal stroma

Most corneal diseases affect corneal stroma and include immune or infectious diseases, ecstatic disorders, traumatic scars, and corneal dystrophies. Cell-based therapy is a promising therapeutic approach to overcome the current disadvantages of corneal transplantation. We intended to search for a cell source to repopulate and regenerate corneal stroma. We investigated the ability of human processed lipoaspirate derived (PLA) cells to regenerate corneal stroma in experimental animals. In the first set of experiments, we tested the biosafety and immunogenicity of human PLA stem cells transplanted into the corneal stroma of rabbits. No immune response was elicited even though we used immune-competent animals. PLA cells survived up to 10 weeks post-transplant, maintained their shape, and remained intermingled in the stroma without disrupting its histological pattern. Interestingly, transparency was preserved even 10 weeks after the transplant, when PLA cells formed a discontinuous layer in the stroma. In the second set of experiments, regeneration of the corneal stroma by PLA cells was assessed, creating a niche by partial ablation of the stroma. After 12 weeks, human cells were disposed following a multilayered pattern and differentiated into functional keratocytes, as assessed by the expression of aldehyde-3-dehydrogenase and cornea-specific proteoglycan keratocan. Based on our results, we believe that adipose-derived adult stem cells can be a cell source for stromal regeneration and repopulation in diseased corneas. The low health impact of the surgical procedure performed to obtain the PLA cells provides this cell source with an additional beneficial feature for its possible future autologous use in human patients.