Corneal Anatomy

Characterization of Cell Surface Glycan Profiles in Human and Mouse Corneas Using Lectin Microarrays

The advent of high-throughput sequencing technologies has facilitated the profiling of glycosylation genes at a single-cell level in complex biological systems, but the significance of these gene signatures to the composition of the glycocalyx remains ambiguous. Here, we used lectin microarrays to characterize the composition of cell surface glycans in human and mouse corneas and determine its relationship to single-cell transcriptomic data. Our results identify a series of cell surface glycan signatures that are unique to the different cell types of the human cornea and that correlate, to a certain extent, with the transcriptional expression of glycosylation genes. These include pathways involved in the biosynthesis of O-glycans in epithelial cells and core fucose on stromal and endothelial cell surfaces. Moreover, we show that human and mouse corneas display some structural differences in terms of cell surface glycan composition. These results could provide insights into the specialized function of individual cell types in the cornea and foster the identification of novel cornea-specific biomarkers.

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.

Nanoscaled Morphology and Mechanical Properties of a Biomimetic Polymer Surface on a Silicone Hydrogel Contact Lens

Materials taking advantage of the characteristics of biological tissues are strongly sought after in medical science and bioscience. On the natural corneal tissue surface, the highly soft and lubricated surface is maintained by composite structures composed of hydrophilic biomolecules and substrates. To mimic this structure, the surface of a silicone hydrogel contact lens was modified with a biomimetic phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and the nanoscaled morphology and mechanical properties of the surface were confirmed with advanced surface characterization and imaging techniques under an aqueous medium. Concavities and convexities on the nanometer order were recognized on the surface. The surface was completely covered with a PMPC layer and remained intact even after 30 days of clinical use in a human ocular environment. The mechanical properties of the natural corneal tissue and the PMPC-modified surface were similar in the living environment, that is, low modulus and frictional properties comparable to natural tissues. These results show the validity of material preparation by biomimetic methods. The methodologies developed in this study may contribute to future development of human-friendly medical devices.

A guide to the composition and functions of the extracellular matrix

Extracellular matrix (ECM) is a dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues. Accumulated knowledge clearly demonstrated over the last decade that ECM plays key regulatory roles since it orchestrates cell signaling, functions, properties and morphology. Extracellularly secreted as well as cell-bound factors are among the major members of the ECM family. Proteins/glycoproteins, such as collagens, elastin, laminins and tenascins, proteoglycans and glycosaminoglycans, hyaluronan, and their cell receptors such as CD44 and integrins, responsible for cell adhesion, comprise a well-organized functional network with significant roles in health and disease. On the other hand, enzymes such as matrix metalloproteinases and specific glycosidases including heparanase and hyaluronidases contribute to matrix remodeling and affect human health. Several cell processes and functions, among them cell proliferation and survival, migration, differentiation, autophagy, angiogenesis, and immunity regulation are affected by certain matrix components. Structural alterations have been also well associated with disease progression. This guide on the composition and functions of the ECM gives a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface, summarizes their main structural features and their roles in tissue organization and cell functions, and emphasizes the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.