Effect of High Glucose on Ocular Surface Epithelial Cell Barrier and Tight Junction Proteins

PURPOSE. Patients with diabetes mellitus are reported to have ocular surface defects, impaired ocular surface barrier function, and a higher incidence of corneal and conjunctival infections. Tight junctions are critical for ocular surface barrier function. The present study was designed to investigate the effect of high glucose exposure on human corneal and conjunctival epithelial cell barrier function and tight junction proteins. METHODS. Human corneal and conjunctival epithelial cells were exposed to 15 mM and 30 mM glucose for 24 and 72 hours. The barrier function was measured using transepithelial electrical resistance (TEER). The cell migration was quantified using scratch assay. The cells were harvested for protein extraction and mRNA isolation. Gene and protein expression of claudins, zonula occludens (ZOs), and occludin was quantified using realtime PCR and Western blot. RESULTS. Glucose caused a significant decrease in TEER after 72 hours of exposure in both corneal and conjunctival epithelial cells. Glucose did not cause any notable change in migration of either corneal or conjunctival epithelial cells. Glucose exposure did not cause any notable change in protein expression of claudin-1, ZO-1, ZO-2, ZO-3, or occludin. On the other hand, 15 mM glucose caused an increase in gene expression of claudin-1, claudin-3, ZO-2, ZO-3, and occludin, a likely response to osmotic stress since 15 mM mannitol also caused consistently similar increase in gene expression of these proteins. CONCLUSIONS. High glucose exposure causes impairment of corneal and conjunctival epithelial cell barrier function, but this detrimental effect is not caused by a decrease in expression of tight junction proteins: claudin-1, ZO-1, ZO-2, ZO-3, and occludin

Effect of Diabetes Mellitus on Ocular Surface Tight Junctions and Glycocalyx

Introduction: Diabetes mellitus is the disease of the century that affects many body organs. In the eye, diabetes mellitus causes retinopathy, cataract, glaucoma, papillopathy, and ocular surface disease. Ocular surface abnormalities in patients of diabetes mullites include impairment of corneal epithelial barrier function, conjunctival defects, increased incidence of corneal and conjunctival infections and higher prevalence of dry eye disease. Impairment of tight junctions and glycocalyx, which are critical for ocular surface barrier function, may underlie these diabetes-associated ocular surface defects. Therefore, the present study was designed to investigate the effect of high glucose exposure and type I diabetes mellitus on the conjunctival tight junction proteins, tear secretion and corneal glycocalyx. Methods: Cultured human conjunctival epithelial cells were exposed to high glucose (15 mM and 30mM) concentrations for 24 and 72 hours. Trans-epithelial electrical resistance and scratch assay were performed to quantify barrier functions and cell migration. Gene and protein expression of tight junction proteins: claudin-1, claudin-2, claudin-3, ZO-1, ZO-2, ZO-3, and occludin was quantified using real time PCR and western blotting. Type I diabetes was induced in mice by streptozotocin injection. Phenol red thread test, fluorescein staining and wheat-germ agglutinin corneal staining and confocal microscopy of whole mount corneas were performed to quantify tears, keratopathy and corneal glycocalyx area. Results: Our data demonstrates that high glucose causes a significant decrease in transepithelial electrical resistance of cultured human conjunctival epithelial cells. However, high glucose did not modulate the cellular migration or protein expression of claudin-1, ZO-1,-2,-3 or occludin. Interestingly, an increase in gene expression of all the tight junction proteins was observed at 72-hour exposure with 15 mM glucose. This effect on gene expression is likely due to the cellular osmotic stress caused by glucose since mannitol also caused the similar increase after 72 hours exposure. Type I diabetes caused a significant decreased in the tear film volume which was accompanied by corneal keratopathy and a decrease in the area of corneal glycocalyx. In summary, our data demonstrates that high glucose impairs the conjunctival epithelial cell barrier functions, but the alterations in cellular migration and tight junction proteins are not the likely cause of conjunctival epithelial barrier dysfunction. Type I diabetes mellitus causes tear film abnormalities and corneal keratopathy which is accompanied by a concurrent decrease in corneal glycocalyx