Reduced β‑2‑glycoprotein І inhibits hypoxia‑induced retinal angiogenesis in neonatal mice through the vascular endothelial growth factor pathway

Aqueous Humor Apolipoprotein Concentration and Severity of Diabetic Retinopathy in Type 2 Diabetes

An imbalance of plasma apolipoproteins has been linked to diabetic retinopathy (DR); however, there is scarce information regarding their presence in the aqueous humor (AH) and their role in DR. Here, we aimed at analysing the relationship between apolipoprotein concentrations in human AH and the severity of DR. Concentrations of apolipoproteins were measured retrospectively in patients with type 2 diabetes mellitus (T2DM) without DR (n = 23), with mild to moderate nonproliferative DR (NPDR) (n = 13), and advanced NPDR/proliferative DR (PDR) (n = 14) using a multiplex immunoassay. Compared to the non-apparent DR group, the concentrations of seven apolipoproteins were elevated in advanced NPDR/PDR (Apo AI 5.8-fold, Apo AII 4.5-fold, Apo CI 3.3-fold, Apo CIII 6.8-fold, Apo D 3.3-fold, Apo E 2.4-fold, and Apo H 6.6-fold). No significant differences were observed in apolipoprotein concentrations between patients with non-apparent DR and healthy controls (n = 17). In conclusion, the AH concentrations of apolipoproteins AI, AII, CI, CIII, D, E, and H increased in advancing stages of DR, suggesting their role in the pathogenesis of DR, which deserves further examination.

Reduced β2GPI Inhibiting Glomerular Mesangial Cells VEGF-NO Axis Uncoupling Induced by High Glucose

VEGF-NO axis uncoupling is an important pathogenesis for DN. Reduced β2GPI could play a part in VEGF signaling pathway and has a protective effect on diabetic vascular disease. This study investigates the effect of reduced β2GPI on glomerular mesangial cells VEGF-NO axis uncoupling induced by high glucose. Compared to control group, glomerular mesangial cell line HBZY-1 cells treated with high glucose expressed higher levels of VEGF mRNA and protein and produced more ROS but less NO. The related proteins related to VEGF-NO axis were assayed. High glucose could significantly increase the expression of the level of VEGFR2 and obviously increase phosphorylation of Akt and eNOS but significantly decrease the expression of GTP cyclohydrolase 1 (GCH-1), reducing the production of eNOS dimer. Both β2GPI and reduced β2GPI partly reverse these effects caused by high glucose. Reduced β2GPI had stronger effect than β2GPI. GCH-1 is the speed limit of tetrahydrobiopterin (BH4) synthesis enzyme. As the key part of eNOS cofactors, BH4 could partly restore eNOS dimer induced by high glucose. Our results indicated that high glucose could interfere with eNOS dimer formation. β2GPI and reduced β2GPI can partly reverse the VEGF-NO axis uncoupling by restoring the GCH-1 expression level and then promote eNOS dimer formation.

The purification of reduced β2-glycoprotein I showed its native activity in vitro

Background

New evidence has shown that reduced β2-glycoprotein I (β2GPI) has anti-oxidative stress and anti-inflammatory activity. However, the details are still poorly understood. This study aims to prepare stable reduced β2GPI with its native bioactivity in vitro.

Methods

Human β2GPI was purified from plasma first with perchloric acid precipitation and then purified with a series of chromatography methods including Sephadex G-25 desalting, SP HP, AF-heparin HC-650 M, and Sephacryl S-200. The purified human β2GPI was reduced with thioredoxin-1 (TRX-1) activated by DL-dithiothreitol (DTT). Glutathione (GSH) was selected to block the free thiols in reduced β2GPI. LC/MS was used to verify the location of free thiols. Western blot analysis was used to detect β2GPI immunoreactivity. MTS and flow cytometry were conducted to investigate its biological effect on oxidative-stress-induced death of human umbilical vein endothelial cells (HUVECs). The levels of tumour necrosis factor-alpha (TNF-α),interleukin-6 (IL-6) interleukin-10 (IL-10),interleukin-12P70 (IL-12P70),interferon-gamma (IFN-γ) and monocyte chemoattractant protein −1(MCP-1) in mouse serum were quantified to assess its anti-inflammatory activity in lipopolysaccharide (LPS)-mediated systemic inflammation.

Results

We obtained approximately 10 mg β2GPI (purity 98.7%) from 200 ml plasma. The protein yield was 0.05 mg/ml plasma. β2GPI was then reduced by TRX-1/DTT in vitro; the free thiols were detected on Cys288 and Cys326 in domain V of β2GPI. The GSH blockage stabilized the reduced β2GPI in vitro. This reduced β2GPI can be recognized by the anti-β2GPI antibody, can significantly reduce the death of HUVECs after H₂O₂ treatment and can significantly decrease the levels of TNF-α, IL-6,IFN-γ and MCP-1 in mice upon LPS stimulation.

Conclusion

Stable reduced β2GPI can be obtained in vitro by TRX-1 deoxidation followed by the blockage of thiols with GSH. This reduced β2GPI maintains the same immunological activity as oxidized β2GPI and has the ability to counter the oxidative stress induced by H₂O₂ in HUVECs and inflammation in LPS-mediated inflammation in mice.

Salubrinal attenuated retinal neovascularization by inhibiting CHOP-HIF1α-VEGF pathways

Retinal neovascularization (RNV) related disease is the leading cause of irreversible blindness in the world. The aim of this study is to identify whether salubrinal could attenuate RNV by inhibiting CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP)- hypoxia inducible factors 1α (HIF1α) -vascular endothelial growth factor (VEGF) pathways in both mouse retinal microvascular endothelial cells (mRMECs) and oxygen-induced retinopathy (OIR) mouse model. After being treated with salubrinal (20μmol/L) or CHOP-siRNA, mRMECs were exposed to a hypoxia environment. OIR mice were intraperitoneally injected with salubrinal (0.5 mg/kg/day) from P12 to P17. With salubrinal or CHOP-siRNA treatment, the elevated CHOP protein and mRNA levels in hypoxia-induced mRMECs were significantly decreased. HIF1α-VEGF pathways were activated under hypoxia condition, then HIF1α protein was degraded and VEGF secretion was down-regulated after salubrinal or CHOP-siRNA treatment. In OIR mice, the areas of RNV were markedly decreased with salubrinal treatment. Moreover, elevated expressions of CHOP, HIF1α and VEGF in retinas of OIR mice were all reduced after salubrinal treatment. It suggested that salubrinal attenuated RNV in mRMECs and OIR mice by inhibiting CHOP-HIF1α-VEGF pathways and could be a potential therapeutic target for hypoxia-induced retinal microangiopathy.