AIMS/HYPOTHESIS: The 309G SNP in the second promoter of the gene encoding mouse double minute 2 (MDM2) has been implicated in multiple human diseases. The aims of this study were to determine whether MDM2 SNP309G is associated with proliferative diabetic retinopathy (PDR), and whether it contributes to pathological angiogenesis.
METHODS: Sanger DNA sequencing was used to determine the MDM2 SNP309 status in peripheral blood and fibrovascular membranes (FVMs) from individuals with PDR, as well as in epiretinal membranes from individuals with proliferative vitreoretinopathy (PVR). An ELISA was used to quantify the levels of the oxidative DNA damage biomarker 8-oxo-2'-deoxyguanosine in vitreous humour samples from individuals with PDR or PVR. Prime editing was employed to introduce MDM2 SNP309G into primary human retinal microvascular endothelial cells (HRECs), which were then assessed for in vitro angiogenic activities, including proliferation, migration and tube formation. A mouse model of oxygen-induced retinopathy (OIR) was used to evaluate pathological retinal neovascularisation in humanised mice carrying MDM2 SNP309T or SNP309G. Quantitative RT-PCR and western blot analyses were performed to assess gene and protein expression related to MDM2-mediated signalling pathways.
RESULTS: An association between MDM2 SNP309G and PDR was identified. Among 110 individuals with PDR, 60.1% harboured MDM2 SNP309G in their FVMs, and 20.9% exhibited a T→G substitution at position 309 in FVMs compared with matched blood samples. The vitreous humour from individuals with PDR contained significantly higher levels of 8-oxo-2'-deoxyguanosine (7.8±1.2-fold) compared with PVR control participants. Chronic exposure of primary HRECs to vitreous humour containing a high concentration of D-glucose suppressed expression of 8-oxoguanine DNA glycosylase, promoted conversion of MDM2 SNP309T to G (36.1%), and increased MDM2 protein levels. Prime editing-mediated conversion of MDM2 SNP309T to G in HRECs (51.6%) further enhanced high-glucose-induced MDM2 expression and angiogenic responses in vitro. In vivo, humanised C57BL/6J mice carrying MDM2 SNP309G exhibited increased retinal levels of MDM2, hypoxia-inducible factor-1α (HIF-1α), phosphorylated vascular endothelial growth factor receptor 2 (VEGFR2), phosphorylated Erk1/2 and phosphorylated specificity protein 1 (Sp1), together with elevated vascular endothelial growth factor (VEGF) in the vitreous humour, and exacerbated pathological retinal angiogenesis in the OIR model, compared with mice harbouring MDM2 SNP309T.
CONCLUSIONS/INTERPRETATION: These findings suggest that MDM2 SNP309G drives a positive feedback loop involving MDM2 and VEGF signalling in vascular endothelial cells, thereby promoting pathological angiogenesis. Targeting the second promoter of MDM2 may represent a novel therapeutic strategy for preventing aberrant angiogenesis in PDR.
