Association between NDRG2/IL-6/STAT3 signaling pathway and diabetic retinopathy in rats

The aim of this study was to observe the association between N-myc downstream regulated gene 2 (NDRG2)/interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) signaling pathway and diabetic retinopathy (DR) in rats.

The model of diabetes was successfully established in Sprague-Dawley rats. All rats were divided into diabetes model group (model group, n=10), pathway inhibitor group (CLT-005 group, n=10), and normal control group (control group, n=10). After successful modeling, blood and retinal tissues of rats were collected. The levels of blood glucose and serum IL-6 were detected. Meanwhile, oxidative and antioxidant indexes reactive oxygen species (ROS), superoxide dismutase (SOD), and malondialdehyde (MDA) were detected via enzyme-linked immunosorbent assay (ELISA). Morphological changes in retinal tissues were observed using hematoxylin-eosin (HE) staining, and the number of corneal nerve fibers was observed under a microscope. The expressions of vascular endothelial growth factor (VEGF) and NDRG2/IL-6/STAT3 pathway genes in tissues were determined via quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR). Furthermore, the expressions of NDRG2/IL-6/STAT3 pathway proteins were determined via Western blotting.

The level of blood glucose in model group was significantly higher than that of control group (p<0.05), suggesting successful modeling. The levels of tumor necrosis factor-α (TNF-α), IL-6, and IL-1 in model group were significantly higher than those of control group (p<0.05). The content of ROS and MDA in tissues was significantly higher in model group than the other two groups (p<0.05). However, SOD increased markedly in CLT-005 group and was close to that of control group. Besides, the number of corneal nerve fibers decreased remarkably in model group. However, it increased significantly in CLT-005 group, but was still smaller than that in control group. According to HE staining, there were significant retinal edema and telangiectasia in model group. Mild retinal edema and more ganglion cells and inner nuclear layers were observed in CLT-005 group than model group. QRT-PCR demonstrated that the mRNA expressions of VEGF, NDRG2, IL-6, and STAT3 were remarkably higher in model group than those in control group (p<0.05). However, they decreased significantly in CLT-005 group (p<0.05). Model group exhibited remarkably higher protein expressions of NDRG2, IL-6, and STAT3 than control group (p<0.05). However, CLT-005 group had decreased protein expressions of these molecules (p<0.05), which were close to those in control group.

The activation of NDRG2/IL-6/STAT3 signaling pathway is positively correlated with the occurrence and development of DR in rats. Therefore, inhibiting the activation of NDRG2/IL-6/STAT3 signaling pathway can affect oxidation and antioxidation, thereby exerting a protective effect against retinal injury in diabetes rats.