Tonicity-responsive enhancer binding protein regulates the expression of aldose reductase and protein kinase C δ in a mouse model of diabetic retinopathy

Recent studies revealed that Tonicity-responsive enhancer binding protein (TonEBP) directly regulates the transcription of aldose reductase (AR), which catalyzes the first step of the polyol pathway of glucose metabolism. Activation of protein kinase C delta (PKC delta) is dependent on AR and it has been linked to diabetic complications. However, whether TonEBP affects expressions of AR and PKC delta in diabetic retinopathy was not clearly shown. In this study, we used TonEBP heterozygote mice to study the role of TonEBP in streptozotocin (STZ)-induced diabetic retinopathy. We performed immunofluorescence staining and found that retinal expressions of AR and PKC delta were significantly reduced in the heterozygotes compared to wild type littermates, particularly in ganglion cell layer. To examine further the effect of TonEBP reduction in retinal tissues, we performed intravitreal injection of TonEBP siRNA and confirmed the decrease in AR and PKC delta levels. In addition, we found that a proapoptotic factor, Bax level was reduced and a survival factor, BcI2 level was increased after injection of TonEBP siRNA, indicating that TonEBP mediates apoptotic cell death. In parallel, TonEBP siRNA was applied to the in vitro human retinal pigment epithelial (ARPE-19) cells cultured in high glucose media. We have consistently found the decrease in AR and PKC delta levels and changes in apoptotic factors for survival. Together, these results clearly demonstrated that hyperglycemia-induced TonEBP plays a crucial role in increasing AR and PKC delta levels and leading to apoptotic death. Our findings suggest that TonEBP reduction is an effective therapeutic strategy for diabetic retinopathy. (C) 2014 Elsevier Ltd. All rights reserved.