Objective o observe the expression of Notch1 and Delta-like ligand 4 (Dll4) on the fibrovascular membranes in proliferative diabetic retinopathy (PDR), and investigate its relationship with vascular endothelial growth factor receptor 2 (VEGFR2). Methods Fifty-seven PDR patients (60 eyes) who underwent vitrectomy were enrolled in this study. The PDR patients were divided into non-injection group (30 patients, 32 eyes) and injection group (27 patients, 28 eyes). The eyes in injection group received intravitreal injection with ranibizumab at 2 to 7 days before surgery. The preretinal fibrovascular membranes were obtained from the PDR patients during vitrectomy. Eighteen epiretinal membranes were obtained from the non-diabetic patients was served as controls. The real-time polymerase chain reaction (RT-PCR) and immunohistochemical methods were used to detecting the expression of Notch1, Dll4 and VEGFR2. In the meantime, the numbers of the nucleus of vascular endothelial cells in the membranes stained with hematoxylin were counted. Results The immunohistochemical staining revealed that there were positive expression of Notch1, Dll4 and VEGFR2 in all PDR membranes, regardless of the injection of the ranibizumab. The levels of Notch1, Dll4 and VEGFR2 protein in non-injection group were higher than those of injection group (t=3.45, 6.01, 4.08;P=0.030, 0.008, 0.023). In injection group, the number of endothelial cells in the membranes reduced (17.17±2.48) compared with that of the non-injection group (41.50±5.57). There was significant difference in the number of endothelial cells in the membranes between the two groups (t=9.58,P＜0.05). RT-PCR showed that the differences of the mRNA expression of Notch1, Dll4 and VEGFR2 were all statistically significant among the PDR group and control group (H=12.50, 12.50, 12.02;P＜0.05).The expression of Notch1, Dll4 and VEGFR2 in the PDR membranes was higher than that of epiretinal membranes from non-diabetic patients. In the PDR group, the expression of Notch1, Dll4 and VEGFR2 of non-injection group was higher than that of injection group. Spearman correlation analysis showed that the expression of mRNA between VEGFR2 and Dll4 (r=0.83), VEGFR2 and Notch1 (r=0.81), Notch1 and Dll4 (r=0.87) were all significantly correlated (P＜0.05). Conclusions The expression of Notch1 and Dll4 in the PDR membranes are higher than that of the control group, and it is positively correlated with the expression of the VEGFR2. Notch1 and Dll4 play a regulatory rule in the neovascularization in PDR, the acting way may be correlated with VEGFR2.
The neuroretinal injuries of diabetic retinopathy (DR) include retinal neuronal damage and reactive gliosis, both of which are induced by hyperglycemia and presented as early features of DR. They promote to develop mutually and accelerate the progression of DR. The molecular mechanisms study of neuronal damage mainly focuses on the alterations of extracellular environment and related signaling pathways, include inflammation, oxidative stress, endoplasmic reticulum stress, the formation of advanced glycation end products, glutamate toxicity and so on. These alterations mainly result in neuronal apoptosis and autophagy. The damaged neurons activate the glial cells with apparent changes in morphology, cell counts and the level of intracellular protein expression. In non-proliferative DR, glial cells are moderately hypertrophic and slightly increased in numbers. In proliferative DR, there is a significant rise in glial cell number with enhanced level of inflammatory factors and vascular active substances which lead a further neuronal damage. Signaling pathways of extracellular signal-regulated kinase 1/2, c-Fos and p38 mitogen-activated protein kinase are associated with their activation. Researches on the molecular mechanisms and signaling pathways of the DR will promote controlling the DR progression at the cellular level.