The Ultrastructures and Mechanical Properties of the Descement's Membrane in Fuchs Endothelial Corneal Dystrophy

Differences in Guttae Ultramorphology in Relation to Visual Function in Fuchs Endothelial Corneal Dystrophy

PURPOSE

The purpose of this study was to investigate the differences in guttae ultramorphology and their relation to visual function in eyes with Fuchs endothelial corneal dystrophy (FECD).

METHODS

Thirty FECD eyes without ocular comorbidities were included. Visual functional parameters (best-corrected visual acuity with high-contrast and low-contrast letters and contrast sensitivity/LogCS) and corneal morphology measured with Scheimpflug tomography (Pentacam) were assessed. The surgically removed Descemet membranes were examined by light and transmission electron microscopy.

RESULTS

Preoperative mean best-corrected visual acuity (logarithm of the minimum angle of resolution) was 0.52 ± 0.18, LogCS 0.96 ± 0.21 and central corneal thickness 640 ± 55 μm. All eyes had signs of subclinical corneal edema in Scheimpflug tomography; clinically visible corneal edema was present in 40% of eyes. Histological findings included a posterior fibrillar zone (PFZ) in 10 specimens (33%) and abnormal collagen depositions in Descemet membranes in 14 specimens (47%). Guttae buried within the PFZ were present only in eyes with clinically visible edema (n = 4, 13%). There was no difference in visual function results and tomography parameters between eyes with and without PFZ or between protruding guttae and guttae embedded in a PFZ, respectively.

CONCLUSIONS

Guttae morphology and density were not correlated with visual functional parameters. Guttae buried in a PFZ occurred only in eyes with clinically manifest edema, and thereby, they are an ultramorphological sign for advanced FECD. Subclinical edema was present in all eyes and might be more relevant for quality of vision than guttae ultramorphology.

Nanotopography by chromatic confocal microscopy of the endothelium in Fuchs endothelial corneal dystrophy, pseudophakic bullous keratopathy and healthy corneas

AIM

To investigate the interest of chromatic confocal microscopy (CCM) to characterise guttae in Fuchs endothelial corneal dystrophy (FECD).

METHODS

Descemet's membranes (DM) were obtained during endothelial keratoplasty in patients with FECD and pseudophakic bullous keratopathy (PBK). They were compared with healthy samples obtained from body donation to science. Samples were fixed in 0.5% paraformaldehyde and flat mounted. Surface roughness of DMs was quantified using CCM and the AltiMap software that provided the maximum peak (Sp) and valley (Sv) heights, the mean square roughness (Rq) and the asymmetry coefficient (Ssk).

RESULTS

The physiological roughness of healthy samples was characterised by an Rq of 0.12±0.05 µm, which was two times rougher than in PBK (Rq=0.06±0.03 µm), but both were still flat with a symmetrical distribution between peaks and valleys (Ssk close to 0, npeaks=nvalleys), smaller than 1 µm. In FECD, the maximum peak height was 5.10±2.40 µm, up to 5.8 and 8.3 times higher than the control and PBK, respectively. The maximum valley depth was half than the peak (2.28±0.89 µm). The surface with guttae was very rough (Rq=0.45±0.14 µm) and the Ssk=1.84± 0.43 µm, greater than 0, confirms an asymmetric surface with high peaks and low valleys (npeaks>nvalleys). Moreover, the CCM provided quantitative parameters allowing to distinguish different types of guttae from different patients.

CONCLUSIONS

CCM is an innovative approach to describe and quantify different morphologies of guttae. It could be useful to analyse the different stages of FECD and define subgroups of patients.

Expression of Hormones' Receptors in Human Corneal Endothelium from Fuchs' Dystrophy: A Possible Gender' Association

Background: Age and sex are the most significant risk of factors for advanced Fuchs dystrophy. Nevertheless, few data are available on the hormone's receptor pattern expressed in adult and advanced fuchs endothelial corneal dystrophy (FECD). We investigated the impact of gender, growth factors and extracellular matrix (ECM) regulatory proteins expressed by the dystrophic endothelia. Methods: Ten dystrophic endothelial tissues and 10 normal endothelial sheets (corneoscleral specimens; Eye Bank) were used for this characterization study. Hormones' receptors (ERα, AR, PR, SHBG), few growth factors (VEGFA, βNGF, TGFβ1), some ECM regulators (MMP1, MMP7) and few inflammatory cytokines (IFNγ, IL10) were analyzed by real-time RT-PCR. Results: ERα transcripts were significantly increased, AR and SHBG transcripts were decreased in Fuchs endothelia from female patients, and no changes were detected for PR transcripts. VEGFA, βNGF and TGFβ1 transcripts were upregulated in Fuchs' endothelia, but not significantly linked to gender. High MMP1 and low MMP7 transcripts' expression were detected in Fuchs' specimens, mainly in males than females. An increased IFNγ (Th1) transcript expression was observed in females than males, and a trend to increase for IL10 (Th2) transcripts was detected in males than females. Conclusions: Our findings clearly indicate that hormone receptors, growth factors and matrix mediators as well as a Th1 pathway are predominant in Fuchs' dystrophy, displaying a pattern of expression specific for the female phenotype. The differential expression of hormones' receptors and the Th1/Th2 ratio might prompt to new theories to be tested in vitro and in vivo models, such as the use of hormonal substitute for counteracting this endothelial cell lost.

Type II Diabetes Mellitus Causes Extracellular Matrix Alterations in the Posterior Cornea That Increase Graft Thickness and Rigidity

Purpose

There is a pressing need to investigate the impact of type II diabetes mellitus on the posterior cornea in donor tissues given its increasing prevalence and potential impact on endothelial keratoplasty surgical outcomes.

Methods

Immortalized human cultured corneal endothelial cells (CECs; HCEC-B4G12) were grown in hyperglycemic media for 2 weeks. Extracellular matrix (ECM) adhesive glycoprotein expression and advanced glycation end products (AGEs) in cultured cells and corneoscleral donor tissues, as well as the elastic modulus for the Descemet membrane (DMs) and CECs of diabetic and nondiabetic donor corneas, were measured.

Results

In CEC cultures, increasing hyperglycemia resulted in increased transforming growth factor beta-induced (TGFBI) protein expression and colocalization with AGEs in the ECM. In donor corneas, the thicknesses of the DM and the interfacial matrix (IFM) between the DM and stroma both increased from 8.42 ± 1.35 µm and 0.504 ± 0.13 µm in normal corneas, respectively, to 11.13 ± 2.91 µm (DM) and 0.681 ± 0.24 µm (IFM) in non-advanced diabetes (P = 0.013 and P = 0.075, respectively) and 11.31 ± 1.76 µm (DM) and 0.744 ± 0.18 µm (IFM) in advanced diabetes (AD; P = 0.0002 and P = 0.003, respectively). Immunofluorescence in AD tissues versus controls showed increased AGEs (P < 0.001) and markedly increased labeling intensity for adhesive glycoproteins, including TGFBI, that colocalized with AGEs. The elastic modulus significantly increased between AD and control tissues for the DMs (P < 0.0001) and CECs (P < 0.0001).

Conclusions

Diabetes and hyperglycemia alter human CEC ECM structure and composition, likely contributing to previously documented complications of endothelial keratoplasty using diabetic donor tissue, including tearing during graft preparation and reduced graft survival. AGE accumulation in the DM and IFM may be a useful biomarker for determining diabetic impact on posterior corneal tissue.

In Vitro Profiling of the Extracellular Matrix and Integrins Expressed by Human Corneal Endothelial Cells Cultured on Silk Fibroin-Based Matrices

Developing a scaffold for culturing human corneal endothelial (HCE) cells is crucial as an alternative cell therapeutic approach to bridge the growing gap between the demand and availability of healthy donor corneas for transplantation. Silk films are promising substrates for the culture of these cells; however, their tensile strength is several-fold greater than the native basement membrane which can possibly influence the dynamics of cell-matrix interaction and the extracellular matrix (ECM) secreted by the cells in long-term culture. In our current study, we assessed the secretion of ECM and the expression of integrins by the HCE cells on Philosamia ricini (PR) and Antheraea assamensis (AA) silk films and fibronectin-collagen (FNC)-coated plastic dishes to understand the cell-ECM interaction in long-term culture. The expression of ECM proteins (collagens 1, 4, 8, and 12, laminin, and fibronectin) on silk was comparable to that on the native tissue. The thicknesses of collagen 8 and laminin at 30 days on both PR (4.78 ± 0.55 and 5.53 ± 0.51 μm, respectively) and AA (4.66 ± 0.72 and 5.71 ± 0.61 μm, respectively) were comparable with those of the native tissue (4.4 ± 0.63 and 5.28 ± 0.72 μm, respectively). The integrin expression by the cells on the silk films was also comparable to that on the native tissue, except for α3 whose fluorescence intensity was significantly higher on PR (p ≤ 0.01) and AA (p ≤ 0.001), compared to that on the native tissue. This study shows that the higher tensile strength of the silk films does not alter the ECM secretion or cell phenotype in long-term culture, confirming the suitability of using this material for engineering the HCE cells for transplantation.

DNA methylation changes and increased mRNA expression of coagulation proteins, factor V and thrombomodulin in Fuchs endothelial corneal dystrophy

Late-onset Fuchs endothelial corneal dystrophy (FECD) is a disease affecting the corneal endothelium (CE), associated with a cytosine-thymine-guanine repeat expansion at the CTG18.1 locus in the transcription factor 4 (TCF4) gene. It is unknown whether CTG18.1 expansions affect global methylation including TCF4 gene in CE or whether global CE methylation changes at advanced age. Using genome-wide DNA methylation array, we investigated methylation in CE from FECD patients with CTG18.1 expansions and studied the methylation in healthy CE at different ages. The most revealing DNA methylation findings were analyzed by gene expression and protein analysis. 3488 CpGs had significantly altered methylation pattern in FECD though no substantial changes were found in TCF4. The most hypermethylated site was in a predicted promoter of aquaporin 1 (AQP1) gene, and the most hypomethylated site was in a predicted promoter of coagulation factor V (F5 for gene, FV for protein). In FECD, AQP1 mRNA expression was variable, while F5 gene expression showed a ~ 23-fold increase. FV protein was present in both healthy and affected CE. Further gene expression analysis of coagulation factors interacting with FV revealed a ~ 34-fold increase of thrombomodulin (THBD). THBD protein was detected only in CE from FECD patients. Additionally, we observed an age-dependent hypomethylation in elderly healthy CE.Thus, tissue-specific genome-wide and gene-specific methylation changes associated with altered gene expression were discovered in FECD. TCF4 pathological methylation in FECD because of CTG18.1 expansion was ruled out.

Potential role of extracellular granzyme B in wet age-related macular degeneration and fuchs endothelial corneal dystrophy

Age-related ocular diseases are the leading cause of blindness in developed countries and constitute a sizable socioeconomic burden worldwide. Age-related macular degeneration (AMD) and Fuchs endothelial corneal dystrophy (FECD) are some of the most common age-related diseases of the retina and cornea, respectively. AMD is characterized by a breakdown of the retinal pigment epithelial monolayer, which maintains retinal homeostasis, leading to retinal degeneration, while FECD is characterized by degeneration of the corneal endothelial monolayer, which maintains corneal hydration status, leading to corneal edema. Both AMD and FECD pathogenesis are characterized by disorganized local extracellular matrix (ECM) and toxic protein deposits, with both processes linked to aberrant protease activity. Granzyme B (GrB) is a serine protease traditionally known for immune-mediated initiation of apoptosis; however, it is now recognized that GrB is expressed by a variety of immune and non-immune cells and aberrant extracellular localization of GrB substantially contributes to various age-related pathologies through dysregulated cleavage of ECM, tight junction, and adherens junction proteins. Despite growing recognition of GrB involvement in multiple age-related pathologies, its role in AMD and FECD remains poorly understood. This review summarizes the pathophysiology of, and similarities between AMD and FECD, outlines the current knowledge of the role of GrB in AMD and FECD, as well as hypothesizes putative contributions of GrB to AMD and FECD pathogenesis and highlights the therapeutic potential of pharmacologically inhibiting GrB as an adjunctive treatment for AMD and FECD.

Eye bank versus surgeon prepared Descemet stripping automated endothelial keratoplasty tissues: Influence on adhesion force in a pilot study

PURPOSE

To evaluate and compare the biomechanical properties of the eye bank-prepared and surgeon prepared Descemet stripping automated endothelial keratoplasty (DSAEK) tissues.

METHODS

In this laboratory study, corneal tissues for research were randomly allocated in the following groups: a) surgeon-cut DSAEK and b) eye bank-prepared (pre-cut and pre-loaded) DSAEK. Endothelial cell loss (ECL), immunostaining for tight junction protein ZO-1, elastic modulus, and adhesion force were investigated.

RESULTS

ECL was not found to be significantly different between surgeon-cut DSAEK (7.8% ±6.5%), pre-cut DSAEK (8.6% ±2.3%), and pre-loaded DSAEK (11.1% ±4.8%) (P = 0.5910). ZO-1 was expressed equally across all groups. Surgeon-cut DSAEK grafts showed a significantly higher elastic modulus compared to pre-cut and pre-loaded DSAEK groups (P = 0.0047 and P < 0.0001, respectively). Adhesion force was significantly greater in the surgeon-cut DSAEK compared to pre-cut (P < 0.0001) or pre-loaded DSAEK groups (P = 0.0101).

CONCLUSION

The laboratory data on the biomechanics of DSAEK grafts suggests that surgeon-cut DSAEK grafts present higher elastic modulus and adhesion force compared to eye bank-prepared DSAEK grafts.

Use of biomaterials in corneal endothelial repair

Human corneal endothelium (HCE) is a single layer of hexagonal cells that lines the posterior surface of the cornea. It forms the barrier that separates the aqueous humor from the rest of the corneal layers (stroma and epithelium layer). This layer plays a fundamental role in maintaining the hydration and transparency of the cornea, which in turn ensures a clear vision. In vivo, human corneal endothelial cells (HCECs) are generally believed to be nonproliferating. In many cases, due to their nonproliferative nature, any damage to these cells can lead to further issues with Descemet’s membrane (DM), stroma and epithelium which may ultimately lead to hazy vision and blindness. Endothelial keratoplasties such as Descemet’s stripping automated endothelial keratoplasty (DSAEK) and Descemet’s membrane endothelial keratoplasty (DEK) are the standard surgeries routinely used to restore vision following endothelial failure. Basically, these two similar surgical techniques involve the replacement of the diseased endothelial layer in the center of the cornea by a healthy layer taken from a donor cornea. Globally, eye banks are facing an increased demand to provide corneas that have suitable features for transplantation. Consequently, it can be stated that there is a significant shortage of corneal grafting tissue; for every 70 corneas required, only 1 is available. Nowadays, eye banks face long waiting lists due to shortage of donors, seriously aggravated when compared with previous years, due to the global COVID-19 pandemic. Thus, there is an urgent need to find alternative and more sustainable sources for treating endothelial diseases, such as utilizing bioengineering to use of biomaterials as a remedy. The current review focuses on the use of biomaterials to repair the corneal endothelium. A range of biomaterials have been considered based on their promising results and outstanding features, including previous studies and their key findings in the context of each biomaterial.

Animal models of corneal endothelial dysfunction to facilitate development of novel therapies

Progressive corneal endothelial disease eventually leads to corneal edema and vision loss due to the limited regenerative capacity of the corneal endothelium in vivo and is a major indication for corneal transplantation. Despite the relatively high success rate of corneal transplantation, there remains a pressing global clinical need to identify improved therapeutic strategies to address this debilitating condition. To evaluate the safety and efficacy of novel therapeutics, there is a growing demand for pre-clinical animal models of corneal endothelial dysfunction. In this review, experimentally induced, spontaneously occurring and genetically modified animal models of corneal endothelial dysfunction are described to assist researchers in making informed decisions regarding the selection of the most appropriate animal models to meet their research goals.

The impact of biomechanics on corneal endothelium tissue engineering

The integrity of innermost layer of the cornea, the corneal endothelium, is key to sustaining corneal transparency. Therefore, disease or injury causing loss or damage to the corneal endothelial cell population may threaten vision. Transplantation of corneal tissue is the standard treatment used to replace malfunctioning corneal endothelial cells. However, this surgery is dependent upon donor tissue, which is limited in supply. Hence, tissue engineers have attempted to construct alternative transplantable tissues or cell therapies to alleviate this problem. Nevertheless, the intrinsic non-dividing nature of corneal endothelial cells continues to foil scientists in their attempts to yield large numbers of cells in the laboratory for use in such novel therapies. Interestingly, the contribution of the biomechanical properties of the underlying extracellular matrix (ECM) on cell division, tissue development and maintenance has been extensively investigated in other many cell types. However, the impact of biomechanics on corneal endothelial cell behaviour is relatively unexplored. Here, we describe contemporary tissue engineering solutions aimed at circumventing donor tissue scarcity. We review the ECM structure and biomechanical features of corneal endothelial cells. We discuss the alterations of ECM in endothelial disease development and progression and point out the role of ECM in developing a tissue-engineered corneal endothelium. We highlight the main biomechanical cues, including topographical and mechanical features, that impact cellular behaviors. Finally, we discuss the influence of biomechanical cues on cell and tissue development, and how corneal endothelial cells response to individual biomechanical stimuli in tissue engineering, which have implications for designing an engineered endothelium and maintaining cell function.

Collagen Remodeling Plays a Pivotal Role in Endothelial Corneal Dystrophies

Purpose

To elucidate the collagen structure in the Descemet membrane (DM) of the human cornea and to characterize its rearrangement in patients with endothelial corneal dystrophies.

Methods

Corneas from nine human donors and dystrophic DMs removed from 16 affected eyes of 13 patients by endothelial keratoplasty (DMEK) were investigated using a correlative RT-qPCR and label-free two-channel multiphoton microscopy (MPM) setup. Although collagen formation was visualized by second harmonic generation, the cellular structure was determined by autofluorescence.

Results

The DM of the human donor cornea was characterized by a consistent pattern of fine hexagonal collagen structures that form a supportive scaffold for the endothelial cells. Accordingly, network-forming collagens (8A1 and 8A2) but less fibrillar collagens (only 1A2) were expressed. DMEK resulted in significant (P < 0.0001) improvement of best-corrected visual acuity. In the removed dystrophic DMs, MPM analyses revealed collagen rearrangement in addition to loss of endothelial cells and the development of guttae. MPM analyses of the whole patient's DM demonstrated this collagen remodeling in its entirety and facilitated correlation to Scheimpflug corneal tomography. In most DMs a unique honeycomb collagen network was identified, with distinct bundles surrounding the guttae and correlating with expression of fibrillar collagens (1A1). Conversely, some DMs showed either reduced collagen on MPM and RT-qPCR analysis or diffuse thickening and storage of extracellular matrix.

Conclusions

The collagen structure of the DM and its adaptive remodeling in endothelial corneal dystrophies has been characterized for the first time here and will facilitate individual therapeutic approaches.

Diseases of the corneal endothelium

The corneal endothelial monolayer and associated Descemet's membrane (DM) complex is a unique structure that plays an essential role in corneal function. Endothelial cells are neural crest derived cells that rest on a special extracellular matrix and play a major role in maintaining stromal hydration within a narrow physiologic range necessary for clear vision. A number of diseases affect the endothelial cells and DM complex and can impair corneal function and vision. This review addresses different human corneal endothelial diseases characterized by loss of endothelial function including: Fuchs endothelial corneal dystrophy (FECD), posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), bullous keratopathy, iridocorneal endothelial (ICE) syndrome, post-traumatic fibrous downgrowth, glaucoma and diabetes mellitus.

Fibrillar Layer as a Marker for Areas of Pronounced Corneal Endothelial Cell Loss in Advanced Fuchs Endothelial Corneal Dystrophy

PURPOSE

We sought to assess the correlation of corneal endothelial cell (CEC) density to alterations of collagen composition of Descemet membrane (DM) in advanced Fuchs endothelial corneal dystrophy (FECD) and to image such changes by slit-lamp biomicroscopy in vivo.

DESIGN

Prospective, observational consecutive case series.

METHODS

Fifty eyes (50 subjects) with advanced FECD were enrolled. After slit-lamp biomicroscopy and corneal Scheimpflug imaging, the Descemet endothelium complex (DEC) was retrieved during DM endothelial keratoplasty (DMEK) surgery. The expression of collagens I, III, and IV (COL I, COL III, and COL IV) and corresponding CEC density were analyzed by immunofluorescence flat mount-staining. Presence, diameter and surface area of collagen expression, and CEC density served as the main outcome measures.

RESULTS

Immunofluorescence staining revealed central coherent collagen positive areas (mean surface area = 10 mm² ± 6 mm²) corresponding to a fibrillar layer burying the guttae of DM in 84% (42/50) of DECs. CEC density overlying the fibrillar layer compared with the periphery was significantly reduced (-54.8%, P < .0001) with a steep decline of CEC density at its borders. Subgroup analysis revealed that the fibrillar layer may be imaged by slit-lamp biomicroscopy in vivo with significant positive correlation of mean maximum diameter detected by slit-lamp biomicroscopy (d_{SL max} = 4.1 mm ± 0.9 mm) and by immunofluorescence staining (d_{IF max} = 4.7 mm ± 1.1 mm; r = 0.76; P = .001).

CONCLUSION

A fibrillar layer with a clear geographic pattern marks areas of pronounced loss of CEC density in advanced FECD eyes and may be imaged by slit-lamp biomicroscopy in vivo.

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

[Molecular genetic aspects of Fuchs' endothelial corneal dystrophy pathogenesis]

Fuchs' corneal dystrophy (FCD) is a common bilateral non-inflammatory endothelial pathology. It is a multigenic disorder with various expressivity, penetrance and population prevalence. This review discusses corneal endothelium pump function, FCD pathogenesis and its known genetic factors.

Ex vivo excimer laser ablation of cornea guttata and ROCK inhibitor-aided endothelial recolonization of ablated central cornea

PURPOSE

To determine whether excimer laser ablation of guttae is a viable strategy for removal of diseased tissue in Fuchs' endothelial corneal dystrophy (FECD) on excised human Descemet membranes and whether an excimer laser-created wound on healthy human corneas ex vivo is recolonized with corneal endothelial cells.

METHODS

Descemet membranes of FECD patients and corneal endothelium of normal human corneas were ablated ex vivo using an excimer laser licensed for glaucoma surgery. Specimens were kept in cell culture medium supplemented with 10 μm of rho-kinase inhibitor ripasudil. Corneal endothelial cell regeneration was observed using light and electron scanning microscopy. Furthermore, the whole corneal samples were evaluated by haematoxylin/eosin staining and immunohistochemical analysis using antibodies against Na⁺ /K⁺ -ATPase.

RESULTS

Guttae and corneal endothelium could be ablated with an excimer laser without total ultrastructural damage to the Descemet membrane or stroma. Nearly complete endothelial wound closure was accomplished after 26-38 days in treated corneas. Light and electron scanning microscopy suggested the establishment of a layer of flat endothelial cells. Additionally, Na⁺ /K⁺ -ATPase expression could only be observed on the inner side of the Descemet membrane.

CONCLUSION

Our proof of concept study demonstrated that excimer lasers can be used to ablate diseased tissue from excised FECD Descemet membranes ex vivo. Additionally, corneal endothelial cells recolonize a previously ablated endothelial area in healthy human corneas ex vivo under treatment with ripasudil. Thus, our results are the first experimental basis to further investigate the feasibility of an excimer laser ablation as a graftless FECD treatment option.

Integrin: Basement membrane adhesion by corneal epithelial and endothelial cells

Integrins mediate adhesion of cells to substrates and maintain tissue integrity by facilitating mechanotransduction between cells, the extracellular matrix, and gene expression in the nucleus. Changes in integrin expression in corneal epithelial cells and corneal endothelial cells impacts their adhesion to the epithelial basement membrane (EpBM) and Descemet's membrane, respectively. Integrins also play roles in assembly of basement membranes by both activating TGFβ1 and other growth factors. Over the past two decades, this knowledge has been translated into methods to grow corneal epithelial and endothelial cells in vitro for transplantation in the clinic thereby transforming clinical practice and quality of life for patients. Current knowledge on the expression and function of the integrins that mediate adhesion to the basement membrane expressed by corneal epithelial and endothelial cells in health and disease is summarized. This is the first review to discuss similarities and differences in the integrins expressed by both cell types.

Fuchs Endothelial Corneal Dystrophy: Clinical, Genetic, Pathophysiologic, and Therapeutic Aspects

Fuchs endothelial corneal dystrophy (FECD) is a bilateral corneal endothelial disorder and the most common cause of corneal transplantation worldwide. Professor Ernst Fuchs described the first 13 cases of FECD more than 100 years ago. Since then, we have seen far-reaching progress in its diagnosis and treatment. In the field of diagnostics, new technologies enable the development of more accurate classification systems and the more detailed breakdown of the genetic basis of FECD. Laboratory studies help in deciphering the molecular pathomechanisms. The development of minimally invasive surgical techniques leads to a continuous improvement of the postoperative result. This review highlights and discusses clinical, genetic, pathophysiologic, and therapeutic aspects of this common and important corneal disorder.

Histological study of the effect of granulocyte colony-stimulating factor on experimentally induced corneal burn in adult male albino rats

Chemical injuries to the eye represent one of the true ophthalmic emergencies that require immediate and intensive intervention to minimize severe complications and visual loss. Granulocyte colony-stimulating factor (G-CSF) is a potent hematopoietic cytokine that influences the proliferation, survival, maturation, and the functional activation of granulocytes. The present work was performed to evaluate the histological effect of G-CSF in treating rat corneal alkali burn model. Thirty adult male albino rats were divided equally into three main groups: Group I was served as a control group, and in Group II and III, their corneas of the right eyes were injured by applying a piece of filter paper soaked in 1M NaOH. Group II (alkali burn-induced group) was left without any treatment, while Group III (G-CSF-treated group) was injected subcutaneously by 100 µg/kg of G-CSF for 5 consecutive days. All animals were sacrificed after 3 weeks. Cornea specimens were processed for histological and immunohistochemical staining for P63 followed by morphometry. Microscopic examination of Group II revealed marked alterations in the corneal epithelium, inflammatory cellular infiltration, and neovascularization. Treatment with G-CSF showed great improvement of the corneal structure, disappearance of the neovascularization and the inflammatory cells, and decreased p63 reaction of the basal layers.

Molecular Mechanisms of Fuchs and Congenital Hereditary Endothelial Corneal Dystrophies

The cornea, the eye's outermost layer, protects the eye from the environment. The cornea's innermost layer is an endothelium separating the stromal layer from the aqueous humor. A central role of the endothelium is to maintain stromal hydration state. Defects in maintaining this hydration can impair corneal clarity and thus visual acuity. Two endothelial corneal dystrophies, Fuchs Endothelial Corneal Dystrophy (FECD) and Congenital Hereditary Endothelial Dystrophy (CHED), are blinding corneal diseases with varied clinical presentation in patients across different age demographics. Recessive CHED with an early onset (typically age: 0-3 years) and dominantly inherited FECD with a late onset (age: 40-50 years) have similar phenotypes, although caused by defects in several different genes. A range of molecular mechanisms have been proposed to explain FECD and CHED pathology given the involvement of multiple causative genes. This critical review provides insight into the proposed molecular mechanisms underlying FECD and CHED pathology along with common pathways that may explain the link between the defective gene products and provide a new perspective to view these genetic blinding diseases.

Association of the Gutta-Induced Microenvironment With Corneal Endothelial Cell Behavior and Demise in Fuchs Endothelial Corneal Dystrophy

Importance

The number and size of guttae increase over time in Fuchs endothelial corneal dystrophy (FECD); however, the association between these physical parameters and disease pathogenesis is unclear.

Objective

To determine the role of guttae in corneal endothelial cell function.

Design, Settings, and Participants

In an in vitro model, cells from a human corneal endothelial cell line, HCENC-21T, were seeded on decellularized normal (n = 30) and FECD (n = 70) endothelial basement (Descemet) membranes (DMs). Normal human corneas were sent to our laboratory from 3 sources. The study took place at the Schepens Eye Research Institute, Massachusetts Eye and Ear, Boston, and was performed from September 2015 to July 2017. Normal DMs were obtained from 3 different tissue banks and FECD-DMs were obtained from patients undergoing endothelial keratoplasty in 2 departments.

Main Outcomes and Measures

Endothelial cell shape, growth, and migration were assessed by live-cell imaging, and gene expression analysis as a function of guttae diameter was assessed by laser capture microscopy.

Results

Mean (SD) age of normal-DMs donors was 65.6 (4.4) years (16 women [53%]), and mean (SD) age of FECD-DMs donors was 68.9 (10.6) years (43 women [61%]). Cells covered a greater area (mean [SD], 97.7% [8.5%]) with a greater mean (SD) number of cells (2083 [153] cells/mm2) on the normal DMs compared with the FECD DMs (72.8% [11%]; P = .02 and 1541 [221] cells/mm2 221/mm2; P = .01, respectively). Differences in endothelial cell growth over guttae were observed on FECD DMs depending on the guttae diameter. Guttae with a mean (SD) diameter of 10.5 (2.9) μm did not impede cell growth, whereas those with a diameter of 21.1 (4.9) μm were covered only by the cell cytoplasm. Guttae with the largest mean (SD) diameter, 31.8 (3.8) μm, were not covered by cells, which instead surrounded them in a rosette pattern. Moreover, cells adjacent to large guttae upregulated αSMA, N-cadherin, Snail1, and NOX4 genes compared with ones grown on normal DMs or small guttae. Furthermore, large guttae induced TUNEL-positive apoptosis in a rosette pattern, similar to ex vivo FECD specimens.

Conclusions and Relevance

These findings highlight the important role of guttae in endothelial cell growth, migration, and survival. These data suggest that cell therapy procedures in FECD might be guided by the diameter of the host guttae if subsequent clinical studies confirm these laboratory findings.

Poly-ε-lysine based hydrogels as synthetic substrates for the expansion of corneal endothelial cells for transplantation

Dysfunction of the corneal endothelium (CE) resulting from progressive cell loss leads to corneal oedema and significant visual impairment. Current treatments rely upon donor allogeneic tissue to replace the damaged CE. A donor cornea shortage necessitates the development of biomaterials, enabling in vitro expansion of corneal endothelial cells (CECs). This study investigated the use of a synthetic peptide hydrogel using poly-ε-lysine (pεK), cross-linked with octanedioic-acid as a potential substrate for CECs expansion and CE grafts. PεK hydrogel properties were optimised to produce a substrate which was thin, transparent, porous and robust. A human corneal endothelial cell line (HCEC-12) attached and grew on pεK hydrogels as confluent monolayers after 7 days, whereas primary porcine CECs (pCECs) detached from the pεK hydrogel. Pre-adsorption of collagen I, collagen IV and fibronectin to the pεK hydrogel increased pCEC adhesion at 24 h and confluent monolayers formed at 7 days. Minimal cell adhesion was observed with pre-adsorbed laminin, chondroitin sulphate or commercial FNC coating mix (fibronectin, collagen and albumin). Functionalisation of the pεK hydrogel with synthetic cell binding peptide H-Gly-Gly-Arg-Gly-Asp-Gly-Gly-OH (RGD) or α2β1 integrin recognition sequence H-Asp-Gly-Glu-Ala-OH (DGEA) resulted in enhanced pCEC adhesion with the RGD peptide only. pCECs grown in culture at 5 weeks on RGD pεK hydrogels showed zonula occludins 1 staining for tight junctions and expression of sodium-potassium adenosine triphosphase, suggesting a functional CE. These results demonstrate the pεK hydrogel can be tailored through covalent binding of RGD to provide a surface for CEC attachment and growth. Thus, providing a synthetic substrate with a therapeutic application for the expansion of allogenic CECs and replacement of damaged CE.

REVIEW: Current understanding of the pathogenesis of Fuchs' endothelial corneal dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is the most prominent reason for corneal-endothelial transplantations across the globe. The disease pathophysiology manifests through a combination of various genetic and non-heritable factors. This review provides a comprehensive list of known genetic players that cause FECD, and discusses the prominent pathological features that participate in disease progression, such as channel dysfunction, abnormal extracellular matrix deposition, RNA toxicity, oxidative stress, and apoptosis. Although current practices to correct visual acuity involve surgical intervention, this review also discusses the scope of various non-surgical therapeutics to remedy FECD.

Quantified forces between HepG2 hepatocarcinoma and WA07 pluripotent stem cells with natural biomaterials correlate with in vitro cell behavior

In vitro cell culture or tissue models that mimic in vivo cellular response have potential in tissue engineering and regenerative medicine, and are a more economical and accurate option for drug toxicity tests than animal experimentation. The design of in vivo-like cell culture models should take into account how the cells interact with the surrounding materials and how these interactions affect the cell behavior. Cell-material interactions are furthermore important in cancer metastasis and tumor progression, so deeper understanding of them can support the development of new cancer treatments. Herein, the colloidal probe microscopy technique was used to quantify the interactions of two cell lines (human pluripotent stem cell line WA07 and human hepatocellular carcinoma cell line HepG2) with natural, xeno-free biomaterials of different chemistry, morphology, and origin. Key components of extracellular matrices -human collagens I and IV, and human recombinant laminin-521-, as well as wood-derived, cellulose nanofibrils -with evidenced potential for 3D cell culture and tissue engineering- were analysed. Both strength of adhesion and force curve profiles depended on biomaterial nature and cell characteristics. The successful growth of the cells on a particular biomaterial required cell-biomaterial adhesion energies above 0.23 nJ/m. The information obtained in this work supports the development of new materials or hybrid scaffolds with tuned cell adhesion properties for tissue engineering, and provides a better understanding of the interactions of normal and cancerous cells with biomaterials in the human body.

Biomechanical changes to Descemet's membrane precede endothelial cell loss in an early-onset murine model of Fuchs endothelial corneal dystrophy

Early-onset Fuchs endothelial corneal dystrophy (FECD) has been associated with nonsynonymous mutations in collagen VIII α2 (COL8A2), a key extracellular matrix (ECM) protein in Descemet's membrane (DM). Two knock-in strains of mice have been generated to each express a mutant COL8A2 protein (Col8a2^L450W/L450W and Col8a2^Q455K/Q455K) that recapitulate the clinical phenotype of early-onset FECD including endothelial cell loss, cellular polymegathism and pleomorphism, and guttae. Due to abnormalities in ECM protein composition and structure in FECD, the stiffness of DM in Col8a2 knock-in mice and wildtype (WT) controls was measured using atomic force microscopy at 5 and 10 months of age, coinciding with the onset of FECD phenotypic abnormalities. At 5 months, only sporadic guttae were identified via in vivo confocal microscopy (IVCM) in Col8a2^Q455K/Q455K mice, otherwise both strains of Col8a2 transgenic mice were indistinguishable from WT controls in terms of endothelial cell density and size. By 10 months of age, Col8a2^L450W/L450W and Col8a2^Q455K/Q455K mice developed reduced corneal endothelial density, increased endothelial cell area and guttae, with the Col8a2^Q455K/Q455K strain exhibiting a more severe phenotype. However, at 5 months of age, prior to the development endothelial cell abnormalities, Col8a2^L450W/L450W and Col8a2^Q455K/Q455K mice knock-in mice had reduced tissue stiffness of DM that was statistically significant in the Col8a2^Q455K/Q455K mice when compared with wildtype controls. These data indicate that alterations in the tissue compliance of DM precede phenotypic changes in endothelial cell count and morphology, and may play a role in onset and progression of FECD.

Scanning Acoustic Microscopy Comparison of Descemet's Membrane Normal Tissue and Tissue With Fuchs' Endothelial Dystrophy

Purpose

To describe the application of scanning acoustic microscopy in the GHz-range (GHz-SAM) for qualitative imaging and quantitative characterization of the micromechanical properties of the Descemet's membrane and endothelial cells of cornea tissue.

Methods

Investigated were samples of a normal tissue and a tissue with Fuchs' endothelial dystrophy (FECD, cornea Guttata). Descemet's membranes were fixed on glass substrates and imaged utilizing a focused acoustic lens operating at a center frequency of 1 GHz.

Results

GHz-SAM data, based on the well-established V(z) technique, revealed discrepancies in the velocity of the propagation of Rayleigh surface acoustic waves (RSAW). RSAW were found to be slower in glass substrates with FECD samples than in the same glass substrates (soda-lime) with normal Descemet membrane, which indicates lower shear and bulk moduli of elasticity in tissues affected by FECD.

Conclusions

Noninvasive/nondestructive GHz-SAM, is utilized in this study for the imaging and characterization of Descemet membranes, fixated on glass substrates. V(z) signatures containing sufficient oscillations were obtained for the system of Descemet membranes on glass substrates. The observed variation in the microelastic properties indicates potential for further investigations with GHz-SAM based on the V(z) technique.

Scanning electron microscopy assessment of the Descemet membrane interface during DMEK graft preparation

We set out to determine microscopic characteristics of the Descemet membrane interface during Descemet membrane endothelial keratoplasty (DMEK) graft preparation. Ten corneas were partially prepared, preserving half of the Descemet membrane attached to the stroma to enable visualisation of the Descemet-stroma interface. This tissue was prepared for viewing with a scanning electron microscope. The Descemet-stroma interface was categorised into three regions: centre, mid-periphery and periphery. We classified adhesions in these regions as either minor thread-like adhesions or major bridge-like adhesions with stromal detachments. We found a region-specific differentiation of the Descemet-stroma morphology. The presence of minor (P = 0,0001) and major (P = 0,0001) adhesions at the explored regions of the Descemet-stroma interface were found to be statistically significant. Fibrotic linear adhesions were predominant in the centre and mid-periphery, whereas the larger bridge-like adhesions were found mainly in the periphery. In addition, we observed a positive correlation between the size of the adhesions and the presence of ruptures in the underlying stromal bed. Viewing of the Descemet-stroma interface with electron microscopy reveals morphological differences between the centre of a graft and its periphery. These findings are of potential clinical relevance in terms of developing a better understanding of tissue behaviour during graft preparation.

Biomechanical relationships between the corneal endothelium and Descemet's membrane

The posterior face of the cornea consists of the corneal endothelium, a monolayer of cuboidal cells that secrete and attach to Descemet's membrane, an exaggerated basement membrane. Dysfunction of the endothelium compromises the barrier and pump functions of this layer that maintain corneal deturgesence. A large number of corneal endothelial dystrophies feature irregularities in Descemet's membrane, suggesting that cells create and respond to the biophysical signals offered by their underlying matrix. This review provides an overview of the bidirectional relationship between Descemet's membrane and the corneal endothelium. Several experimental methods have characterized a richly topographic and compliant biophysical microenvironment presented by the posterior surface of Descemet's membrane, as well as the ultrastructure and composition of the membrane as it builds during a lifetime. We highlight the signaling pathways involved in the mechanotransduction of biophysical cues that influence cell behavior. We present the specific example of Fuchs' corneal endothelial dystrophy as a condition in which a dysregulated Descemet's membrane may influence the progression of disease. Finally, we discuss some disease models and regenerative strategies that may facilitate improved treatments for corneal dystrophies.