Corneal wound-associated glycoconjugates analyzed by lectin histochemistry

Reducing Sialylation Enhances Electrotaxis of Corneal Epithelial Cells

Corneal wound healing is a complex biological process that integrates a host of different signals to coordinate cell behavior. Upon wounding, there is the generation of an endogenous wound electric field that serves as a powerful cue to guide cell migration. Concurrently, the corneal epithelium reduces sialylated glycoforms, suggesting that sialylation plays an important role during electrotaxis. Here, we show that pretreating human telomerase-immortalized corneal epithelial (hTCEpi) cells with a sialyltransferase inhibitor, P-3FAX-Neu5Ac (3F-Neu5Ac), improves electrotaxis by enhancing directionality, but not speed. This was recapitulated using Kifunensine, which inhibits cleavage of mannoses and therefore precludes sialylation on N-glycans. We also identified that 3F-Neu5Ac enhanced the responsiveness of the hTCEpi cell population to the electric field and that pretreated hTCEpi cells showed increased directionality even at low voltages. Furthermore, when we increased sialylation using N-azidoacetylmannosamine-tetraacylated (Ac4ManNAz), hTCEpi cells showed a decrease in both speed and directionality. Importantly, pretreating enucleated eyes with 3F-Neu5Ac significantly improved re-epithelialization in an ex vivo model of a corneal injury. Finally, we show that in hTCEpi cells, sialylation is increased by growth factor deprivation and reduced by PDGF-BB. Taken together, our results suggest that during corneal wound healing, reduced sialylated glycoforms enhance electrotaxis and re-epithelialization, potentially opening new avenues to promote corneal wound healing.

Cultivation and characterisation of the surface markers and carbohydrate profile of human corneal endothelial cells

BACKGROUND

The study aims to characterise human corneal endothelial cell (HCEnC) cultures generated by the peel-and-digest method based on their surface protein/carbohydrate expression pattern.

METHODS

Quantitative polymerase chain reaction was used to compare expression of vimentin, CD90, Cytokeratin-19, ZO-1 and Claudin 14 in cultured HCEnC and cell line B4G12 versus stromal cells. Fluorescence-activated cell sorting was used to assess surface protein distribution of cultured and uncultured HCEnC. Distribution of surface proteins/carbohydrates was visualised by immunofluorescent and lectin staining.

RESULTS

Human corneal endothelial cell and B4G12 showed lower expression level for vimentin, CD90, Cytokeratin-19 compared with stromal cells; while ZO-1 was expressed in endothelial cells, Claudin 14 was detected in B4G12 only. Fluorescence-activated cell sorting analyses revealed CD166, CD47, CD44, CD54, CD73, CD90, CD105, CD106, CD112, CD146 and CD325 to be present, with CD34 to be absent from cultured HCEnC. Freshly isolated, non-cultivated HCEnCs were CD90, CD73, CD146 and CD325 positive. Carbohydrates were detected by lectins LCA, PHA E, PHA L, PSA, sWGA, Con A, RCA 120 and WGA, but cultured HCEnC showed negative for GSL I, SBA, DBA, PNA and UEA I.

CONCLUSION

Cultures established by the peel-and-digest method are probably not prone to stromal contamination, but the cells are likely to undergo endothelial-to mesenchymal transition as suggested by apparent morphological changes.

Adhesion/growth-regulatory galectins in the human eye: localization profiles and tissue reactivities as a standard to detect disease-associated alterations

OBJECTIVES

To characterize the localization profiles of seven adhesion/growth-regulatory galectins in the normal human eye using immunodetection of endogenous galectins and binding of labeled galectins to sections, useful as a basis to detect disease-associated alterations.

METHODS

Non-cross-reactive anti-galectin antibodies and biotinylated galectins were tested on acetone-fixed cryosections of normal human donor eyes. Controls included omission of first-step reagent, testing of an antibody against a galectin specific for rat (galectin-5), and blocking of galectin binding with lactose.

RESULTS

Galectin presence was not restricted to one or few members of this family. Signal occurrence can even include all tested or most proteins (conjunctival or corneal epithelium), whereas choroid positivity is fully accounted for by galectin-9. Regional specificity and characteristic profiles for each protein, immuno- and galectin histochemically, were determined. Differences in tissue reactivity among the galectins were detected.

CONCLUSIONS

That the galectins have characteristic localization/reactivity profiles supports the concept of a network with potential for non-overlapping functions. The reported data thus prompt to proceed to the respective analysis of specimens from ocular diseases.

Role of carbohydrates in repair of human respiratory epithelium using an in vitro model

BACKGROUND

The epithelial layer in the conducting airway provides a primary protective barrier. Repair of this barrier normally occurs rapidly after damage, but is compromised in diseases such as asthma.

OBJECTIVE

We have developed a human in vitro model system to test our hypothesis that cell surface glycoconjugate-based interactions are required for the normal repair of damaged epithelium.

METHODS

Lectins having narrow carbohydrate specificities were used to identify and block specific carbohydrate moieties on human airway-derived epithelial cells in culture.

RESULTS

The lectin wheat germ agglutinin bound to N-acetyl glucosamine and inhibited the repair of epithelial damage while having little effect on cell viability. In contrast, other N-acetyl glucosamine binding lectins had no effect even when bound to the cell surface. The involvement of glycoconjugates was confirmed by pre-incubating the lectin with its specific sugar, preventing the inhibition of repair.

CONCLUSION

These results indicate that lectin-binding sites are involved in epithelial repair and may be important in the repetitive cycles of injury and repair seen in asthma. This model system provides an insight into the role of glycoconjugates and will help to determine the function of specific carbohydrate groups in epithelial repair. These may present a target for therapeutic intervention in respiratory and other diseases.