A new potential pharmacological target in diabetic retinopathy: the HuR pathway

Abstract

Abstract Purpose A key player within diabetic retinopathy is the Vascular Endothelial Growth Factor (VEGF) whose expression seems under Protein Kinase C (PKC) control, although no data are available on the molecular pathway underlying this process. Our previous in vitro work in retinal bovine pericytes (Amadio et al., Pharmacol Res. 57: 60, 2008) described a new molecular cascade involving PKCβ, the mRNA‐stabilizing protein HuR and VEGF. We investigated whether this pathway is operant also in vivo and altered by diabetes. Methods After 10 days treatment, retinal tissues from streptozotocin (STZ)‐induced diabetic rats were processed to detect PKCβI and βII, HuR and VEGF content. HuR activation/phosphorylation was also investigated. Immunoprecipitation coupled to real‐time quantitative PCR was employed to evaluate HuR binding to VEGF mRNA in ribonucleoproteic complexes (mRNP). The specificity of the PKCβ involvement was tested by experiments performed with a selective PKCβ inhibitor. Results In retinal tissues from STZ‐induced diabetic rats, PKCβI (+160%, p<0.01) and PKCβII (+113%, p<0.05) levels were increased versus sham. In the same STZ tissues a PKC‐mediated phosphorylation of HuR (+209%, p<0.01) occurred. A specific binding between HuR protein and VEGF mRNA was also detected in retinal mRNP. As well, the PKCβ/HuR activation was accompanied by enhanced VEGF protein expression (+256%, p<0.05). All these effects were blunted by a selective PKCβ inhibitor. Conclusion These findings first demonstrate the existence of the PKCβ/HuR/VEGF pathway in experimental diabetic retinopathy, suggesting that this cascade may represent a potential pharmacological target to counteract diabetic retinopathy, and more generally pathologies implicating VEGF deregulation.