Effects Of Hyperglycemia On The Expression Of Corneal Epithelial Tight Junction Protein Claudin-1 In Diabetic Rats

Purpose To assess the expression of the corneal epithelial tight junction protein claudin-1 in a high-fat diet combined with streptozocin(STZ)-induced rat model of type 2 diabetes mellitus(DM) at different time points.Materials and Methods 80 eight-week-old male SD rats were randomly divided into the normal control(NC) and DM groups(n = 40 each). A high-fat diet combined with STZ injection was used to induce type 2 DM. Normal and diabetic rats were sacrificed at 4, 8, 16 weeks respectively(after STZ injection) before debridement. Hematoxylin and eosin was used to study the morphological differences between normal and diabetic cornea. Immunofluorescene and Western blot were used to determine the expression of corneal epithelial TJ protein claudin-1.Results 1. The average NC rats body weight(381 g) was 7.5% lower than DM rats(412 g) at 8 weeks(before STZ injection; p < 0.01). While NC rats obtained a steady weight gain, the DM rats only maintained a slow increase of body weight. The DM rats(418 g) weighed 6.4% less than NC rats(447 g) at 4 weeks(after STZ injection)(p< 0.01). At 8 weeks, the DM rats(422 g) weighed 17.1% less than NC rats(509 g)(p< 0.01). At 16 weeks, the DM rats(428 g) weighed 24.4% less than NC rats(566 g)(p< 0.01). 2. The fasting blood-glucose(FGB) levels were approximately 5 mmol/L in NC rats and 6 mmol/L in DM rats at 8 weeks(before STZ injection; p < 0.01). After STZ injection, the FGB levels were approximately 21 mmol/L in DM rats while they were still 5 mmol/L in the NC rats(p< 0.01). 3. Compared with NC rats, the corneal epithelial cells reduction and stroma edema were evident in DM rats at 8 and 16 weeks after STZ injection by HE. 4. Measurement of corneal epithelium permeability.No Sulfo-NHS-LC-Biotin penetrated beyond the superficial cells in the two groups at different time point. 5. The expression of claudin-1 was observed with the immunofluorescence staining. Claudin-1 was localized at the surface cell and wing cell layers of the corneal epithelium. There was no significant difference in claudin-1 expression between the NC and DM groups at 4 weeks and 8 weeks(after STZ injection).At 16 weeks, the pattern of claudin-1 in the DM corneas showed lower and fainter expression compared to the NC group. 6. The expression of claudin-1 was detected with Western blot analysis. The claudin-1 expression in the corneal epithelium of the DM group was lower compared to the NC group at 16 weeks(after STZ injection)(p < 0.05), which were similar to the normal group at 4 and 8 weeks(p> 0.05).Conclusions Continual hyperglycemia has a negative effect on ocular surface tissues and the expression of corneal epithelial tight junction protein claudin-1 with progressing of type 2 diabetic mellitus.