Introduction
Diabetic retinopathy (DR) is one of the complications caused by diabetes, and is the leading cause of blindness of the working-age population.1 DR can be divided into two stages: non-proliferative diabetic retinopathy and proliferative diabetic retinopathy (PDR). Neovascularization is a pathological feature of PDR.2 In recent days, a meta-analysis study that included 22 896 patients with diabetes revealed that for patients with diabetes, the prevalence of patients with DR was 34.6%. Furthermore, among these patients, the prevalence of PDR was 6.96%, while the prevalence of diabetic macular edema was 6.81%.3 The pathological changes of DR is retinal capillary endothelial damage, which includes selective loss of retinal capillary pericytes, a thickened basement membrane, occluded capillaries and vascular leakage, and these are due to the blood-retinal barrier damage. These changes lead to a wide range of retinal ischemia and retinal hypoxia, which eventually lead to the formation of new blood vessels. DR is a chronic disease. On the basis of hyperglycemia, multiple factors can lead to the occurrence and development of DR,4 5 such as the increased polyol pathway activity, the activation of the protein kinase C and hexosamine biosynthesis pathway (HBP), oxidative damage to the retina, and increased formation of advanced glycated end-products. However, the specific molecular mechanism remains not completely clear.
O-linked N-acetylglucosamine (O-GlcNAc) modification is a unique form of post-translational protein modification (PTM). Its uniqueness is embodied in its highly dynamic and revisible form of PTM. This can be regulated by two enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Furthermore, this uses UDP-GlcNAc as a donor, under the catalysis of OGT, it connects the O-glycosidic bond to protein serine/threonine residues, and under the catalysis of OGA, it hydrolyzes O-GlcNAc from serine/threonine residues.6 The changes in blood glucose levels can influence the UDP-GlcNAc level through the HBP pathway, and affect the O-GlcNAc modification of proteins. The most important feature of diabetes is sustained hyperglycemia. Elevated blood glucose can lead to increased UDP-GlcNAc donor, and subsequently lead to increased O-GlcNAc modification of proteins. Previous studies have revealed that O-GlcNAc modification plays an important role in diabetic cardiomyopathy and diabetic nephropathy.7 8 Recent studies have revealed that O-GlcNAc modification has similar effects in the process of DR.9 In high glucose (HG)-cultured retina endothelial cells, glycosyl transferases participate in the glycosylation process, and these glycosylation products change.10 In diabetic rat retina tissues, the O-GlcNAc modification of proteins increase.11
Neovascularization is a sign of PDR. Retinal neovascularization rupture leads to vitreous hemorrhage, and causes retinal vasoconstriction and traction retinal detachment, which are the main causes of visual impairment in patients with DR.12 13 Neovascularization is a dynamic and balanced process, which is regulated by angiogenic factors, such as vascular endothelial growth factor (VEGF) and antiangiogenic factors, such as pigment epithelium-derived factors (PEDFs).14 Under the action of angiogenic factors, vascular endothelial cells proliferate, migrate and form the lumen, and subsequently form new blood vessels. At present, the treatment for DR is neovascularization with the intraocular injection of anti-VEGF drugs, such as lucentis, ziv-aflibercept and conbercept, which have achieved good therapeutic effects. However, there are some side effects with the intraocular injection of anti-VEGF drugs, such as intraocular hemorrhage, endophthalmitis, neuroretinal injury, and ischemia-reperfusion injury.15–18 Therefore, ophthalmologists are still searching for new targets and the mechanism of DR neovascularization. Previous studies have found that in high-glucose cultured retinal cells, the O-GlcNAc modification of transcription factor specificity protein 1 (Sp1) can promote the expression of VEGF.19 The upregulation of VEGF expression is the direct cause of the neovascularization of DR.20 These above findings suggest that there are some relationships between O-GlcNAc modification and the formation of retinal neovascularization.
Runt-related transcription factor 1 (RUNX1) is a member of the Runx transcription factor family, and plays an important role in the determination of cell lineage differentiation direction, the formation of normal hematopoietic cells, and stem cell proliferation.21 RUNX1 was first obtained by the Miyoshi research group in 1991 in the leukemia cell clone of patients with acute myeloid leukemia. Hence, this was named AML1.22 Previous studies have revealed that the inhibition of RUNX1 can significantly inhibit the formation of retinal neovascularization in hypoxia-induced retinal neovascularization model mice. The knockdown of RUNX1 in human retinal microvascular endothelial cells (HRMECs) can reduce the ability of cells to form tubes,23 indicating that RUNX1 has a clear role in promoting angiogenesis. However, its mechanism remains unknown.
This present study investigates whether high glucose conditions and increased O-GlcNAc modification can promote the proliferation and migration of HRMECs and whether RUNX1 takes part in this process.