Phosphoprotein network analysis of corneal epithelium of Keratoconus patients

Keratoconus (KC) is non-inflammatory, bilateral progressive corneal ectasia, and a disease of established biomechanical instability. The etiology of KC is believed to be multifactorial. Although previous studies gained insight into the understanding of the disease, little is known thus far on global protein phosphorylation changes in Keratoconus. We performed phosphoproteome analysis of corneal epithelium from control (n = 5) and KC patients. Tandem mass tag (TMT) multiplexing technology along with immobilized metal affinity chromatography (IMAC) were used for the phosphopeptides enrichment and quantitation. Enriched peptides were analyzed on Orbitrap Fusion Tribrid mass spectrometer. This leads to the identification of 2939 unique phosphopeptides derived from 1270 proteins. We observed significant differential phosphorylation of 591 phosphopeptides corresponding to 375 proteins. Our results provide first phosphoproteomic signature of the Keratoconus disease and identified dysregulated signalling pathways that can be targeted for therapy in future studies. This article is protected by copyright. All rights reserved.

Graphitic Carbon Nitride Causes Widespread Global Molecular Changes in Epithelial and Fibroblast Cells

For scaffold and imaging applications, nanomaterials such as graphene and its derivatives have been widely used. Graphitic carbon nitride (g-C₃N₄) is among one such derivative of graphenes, which draws strong consideration due to its physicochemical properties and photocatalytic activity. To use g-C₃N₄ for biological applications, such as molecular imaging or drug delivery, it must interact with the epithelium, cross the epithelial barrier, and then come in contact with the extracellular matrix of the fibroblast cells. Thus, it becomes essential to understand its molecular mechanism of action. Hence, in this study, to understand the molecular reprogramming associated with g-C₃N₄, global gene expression using DNA microarrays and proteomics using tandem mass tag (TMT) labeling and mass spectrometry were performed in epithelial and fibroblast cells, respectively. Our results showed that g-C₃N₄ can cross the epithelial barrier by regulating the adherens junction proteins. Further, using g-C₃N₄-PDMS scaffolds as a mimic of the extracellular matrix for fibroblast cells, the common signaling pathways were identified between the epithelium and fibroblast cells. These pathways include Wnt signaling, integrin signaling, TGF-β signaling, cadherin signaling, oxidative stress response, ubiquitin proteasome pathway, and EGF receptor signaling pathways. These altered signature pathways identified could play a prominent role in g-C₃N₄-mediated cellular interactions in both epithelial and fibroblast cells. Additionally, β catenin, EGFR, and MAP2K2 protein-protein interaction networks could play a prominent role in fibroblast cell proliferation. The findings could further our knowledge on g-C₃N₄-mediated alterations in cellular molecular signatures, enabling the potential use of these materials for biological applications such as molecular imaging and drug delivery.

Deciphering the mechanoresponsive role of β-catenin in keratoconus epithelium

Keratoconus (KC) is a corneal dystrophy characterized by progressive ectasia that leads to severe visual impairment and remains one of the leading indications for corneal transplantation. The etiology is believed to be multifactorial and alterations have been documented in the biomechanical, biochemical and ultrastructural characteristics of the cornea. While the exact site of disease origin is still debated, changes in the corneal epithelium are believed to occur even before the disease is clinically manifested. In this study we investigate the possible role of β-catenin as mechanotransducer in KC corneal epithelium. The sheets of corneal epithelium removed from keratoconic eyes when they underwent collagen crosslinking as a therapeutic procedure were used for this study. The healthy corneal epithelium of patients undergoing Laser Refractive Surgery for the correction of their refractive error, served as controls. Immunoblotting and tissue immunofluorescence studies were performed on KC epithelium to analyse the expression and localization of β-catenin, E-cadherin, ZO1, α-catenin, Cyclin D1, α-actinin, RhoA, and Rac123. Co-immunoprecipitation of β-catenin followed by mass spectrometry of KC epithelium was performed to identify its interacting partners. This was further validated by using epithelial tissues grown on scaffolds of different stiffness. Histology data reported breaks in the Bowman’s layer in KC patients. We hypothesize that these breaks expose the epithelium to the keratoconic corneal stroma, which, is known to have a decreased elastic modulus and that β-catenin acts as a mechanotransducer that induces structural changes such as loss of polarity (Syntaxin3) and barrier function (ZO1) through membrane delocalization. The results of our study strongly suggest that β-catenin could be a putative mechanotransducer in KC epithelium, thus supporting our hypothesis.

Probing the effect of matrix stiffness in endocytic signalling pathway of corneal epithelium

Matrix stiffness regulates the physiology of the cells and plays an important role in maintaining its homeostasis. It has been reported to regulate cell division, proliferation, migration, extracellular uptake and various other physiological processes. The alteration in matrix stiffness has also been well reported in various disease pathologies. However, in ocular system, Keratoconus (KC) is an ideal model to study the effect of matrix stiffness on endocytosis since the progression of the disease is controlled by increasing the stromal elasticity. Our study using corneal epithelial and retinal pigment epithelial cell lines showed that ocular cells do respond to matrix stiffness by altering their morphology and endocytic uptake of FITC-Dextran 20 kDa. Further, by using KC epithelium as a clinical model, we hypothesize that change in stromal elasticity may also affect the endocytosis of KC epithelium. Our results clearly showed alteration in the expression of actin binding proteins such as Phosphorylated Cofilin, Profilin, Focal adhesion kinase, and Vinculin. Apart from cytoskeletal rearrangement proteins, we also observed endocytic proteins such as Clathrin, Caveolin1 and Rab 11 to be affected by matrix stiffness. Our study thus establishes connecting role between endocytosis and matrix stiffness which could be used to understand the pathophysiology of keratoconus that it is influenced by both mechanical and biochemical factors.

Designing and enhancing the antifungal activity of corneal specific cell penetrating peptide using gelatin hydrogel delivery system

Background

Fungal keratitis is a major cause of corneal blindness accounting for more than one-third of microbiologically proven cases. The management of fungal keratitis is through topical or systemic antifungal medications alone or in combination with surgical treatment. Topical medications such as natamycin and voriconazole pose major challenges due to poor penetration across the corneal epithelium. To address the issue various carrier molecules like nanoparticles, lipid vesicles, and cell penetrating peptides were explored. But the major drawback such as non-specificity and lack of bioavailability remains.

Purpose

In this study, we have attempted to design corneal specific cell penetrating peptide using subtractive proteomic approach from the published literature and tried to improve its bioavailability through gelatin hydrogel delivery system.

Material and Methods

Using subtractive proteomic approach two peptides VRF005 and VRF007 were identified on the basis of solubility, cell permeability and amphipathicity. The peptides were modeled for three-dimensional structure and simulated for membrane penetration. The peptides were characterized using circular dichroism spectroscopy, dynamic light scattering and native polyacrylamide gel electrophoresis. Further uptake studies were performed on primary corneal epithelial cells and the stability was analyzed in corneal epithelial tissue lysates. Insilico prediction of peptides showed it to have antifungal activity which was further validated using colony forming assay and time killing kinetics. The duration of antifungal activity of peptide was improved using gelatin hydrogel through sustained delivery.

Results

VRF005 and VRF007 showed α-helical structure and was within the allowed region of Ramachandran plot. The simulation study showed their membrane penetration. The peptide uptake was found to be specific to corneal epithelial cells and also showed intracellular localization in Candida albicans and Fusarium solani. Peptides were found to be stable up to 2 hours when incubated with corneal epithelial tissue lysate. Dynamic light scattering, and native polyacrylamide gel electrophoresis revealed aggregation of peptides. VRF007 showed antifungal activity up to 24 hour whereas VRF005 showed activity up to 4 hours. Hence gelatin hydrogel-based delivery system was used to improve the activity. Actin staining of corneal epithelial cells showed that the cells were attached on gelatin hydrogel.

Conclusion

We have designed corneal specific cell penetrating peptides using subtractive proteomic approach. Bioavailability and delivery of peptide was enhanced using gelatin hydrogel system.