The Role Of Ubiquitin-proteasome Pathway In Diabetic Retinopathy

Diabetic retinopathy(DR)is one of the main causes of blindness for the middle aged and elders,nearly 50%of diabetic would suffer from DR and the pathogenesis of which is complicated.The leading theory of diabetes indicates that high glucose in blood would lead to accumulation of reactive oxygen species(ROS),promoting DNA double strain break,activating poly adenosine diphosphate ribose polymerase(PARP)which is a DNA repairing enzyme,inducing a signaling cascade in retinal endothelial cells,results in activation of polyhydric pathway and NF-κB,and increase of advanced glycation end products(AGEs)and protein kinase C(PKC).The key point of prevention and treatment for DR would be to suppress ROS production.Our early research shows that over-expression of uncoupling protein 2(UCP-2)in bovine retinal endothelial cell(BRECs)can inhibit the production of ROS,while high glucose in blood would activate the ubiquitin-proteasome pathway(UPP)which will lead to degradation of UCP-2 in late stage.We suppose the upregulation of UPP could degrade UCP-2,which may increase of ROS and over-expression of PARP,and result in apoptosis of BRECs on the one hand,and lead to degradation of IκB which function as the inhibitor of NF-κB,the dissociation of activated NF-κB increase of inflammatory cytokines such as ICAM-1、IL-6、iNOS、TNF-α,and result in the damage of vessel on the other hand.Serum,vitreous body,proliferative epiretinal membranes and aqueous humor were harvested from proliferative diabetic retinopathy(PDR)patients and idiopathic epiretinal membrane(ERM)patients respectively.The expression of ubiquitin(Ub),26S proteasome(26S),E3 ubiquitin ligase(E3)were detected by ELISA and the results showed that there were higher expression of Ub,26S,E3 in PDR patients than in ERM.BRECs were cultured and stimulated by high glucose,higher ROS production,lower mitochondrial membrane potential,up-regulation of Ub,E3,26S,NF-κB,inflammatory cytokines,and more apoptosis rate of BRECs were detected,these effects were counterbalanced by shRNA of Ub or the inhibitor of UPP.Diabetes rat model were achieved through STZ intraperitoneal injection,then rats were treated with MG132,decreased expression of UPP,ROS and NF-κB,and lower apoptosis rate of retina cells were detected.In conclusion,our research indicates the mechanism of DR is that high glucose activate ROS production,lower mitochondrial membrane potential and more apoptosis rate of retina cells;In addition,up-regulation of UPP by high glucose lead to up-regulation of NF-κB pathway,result in over-expression of inflammatory cytokines.Our study proves that MG132 could inhibit the up-regulation of UPP stimulated by high glucose and which show the potential to prevent and cure DR.UPP plays a pivotal role in the progression of DR,thus UPP could be an ideal drug target.