Abstract
Abstract: :
Purpose:Hypertension is well known to exacerbate diabetic retinopathy. Previously we reported that hypertension exacerbates diabetic retinopathy through augmenting VEGF-mediated neovascular system (Diabetes 50:444-454,2001). Pericyte loss has been well established as the earliest stage of diabetic retinopathy. ROS has been implicated to contribute to the pathogenesis of diabetic complications. In this study, we investigated the contribution of cyclic stretch mimicking hypertensive state to the early stage or onset of diabetic retinopathy. Methods:PRPCs were exposed to cardiac-profile uniform radial cyclic stretch using a Flexcell apparatus. Phosphorylation of SAPK/JNK was assessed by Western blot analysis using phospho-specific antibodies. Caspasep-3 activity was measured by the colorimetric assay using the spectrophotometer. Production of ROS was measured with DCFH-DA. Apoptosis was evaluated by DNA fragmentation and TUNEL methods. The role of JNK was confirmed by overexpressing wild type (WT-) or dominant negative (DN-) mutants using adenovirus-mediated gene transfer. Results:Cyclic stretch (10%/60cpm) increased ROS generation (260%, p<0.01). Stretch activated JNK phosphorylation in a time-and magnitude-dependent manner (15.4-fold increase after 15mins, p<0.01), which was reduced by inhibitors for ROS, NAC or DPI (82%, p=0.026, 83%, p=0.011, respectively). Stretch induced caspase cleavage and activated Caspase-3 (290%, p<0.01). Stretch induced DNA fragmentation and increased TUNEL positive cells (17.8% vs 39.8%, p<0.01). JNK inhibition normalized Caspase-3 activity by 83% (p=0.0089) and rescued stretch-induced TUNEL positive cells (90%, p=0.0045). Conclusions:These data indicate that cyclic stretch induces apoptotic changes in PRPCs by activation of ROS-JNK-caspase cascades, suggesting a novel molecular mechanism to account for the exacerbation of early diabetic retinopathy by concomitant hypertension.
Keywords: diabetic retinopathy • signal transduction • vascular cells