Redox Status of β2GPI in Different Stages of Diabetic Angiopathy

Domain 5 of Beta 2 glycoprotein I: Friend or foe in health? Context matters

Beta 2 glycoprotein I (β2GPI) is the major autoantigen in the antiphospholipid syndrome, an autoimmune disorder characterized by thrombotic and obstetric complications. The autoantibodies that target beta 2 glycoprotein I are pathogenic and contribute to disease pathogenesis. The β2GPI molecule is composed of 5 domains that are numbered 1 through to 5. Autoantibodies bind mainly to domain 1 whereas the majority of the biological functions of the β2GPI molecule in diverse processes such as apoptotic cell clearance, complement regulation, lipopolysaccharide clearance and anticoagulation have been localised to domain 5 and its unique biochemistry, reviewed in this article. The role of purified domain 5 peptide as a potential therapeutic agent in APS and ischemia reperfusion injury is discussed.

Basolateral amygdala calpain is required for extinction of contextual fear-memory

Extinction of fear-memory is essential for emotional and mental changes. However, the mechanisms underlying extinction of fear-memory are largely unknown. Calpain is a type of calcium-dependent protease that plays a critical role in memory consolidation and reconsolidation. Whether calpain functions in extinction of fear-memory is unknown, as are the molecular mechanisms. In this study, we investigated the pivotal role of calpain in extinction of fear-memory in mice, and assessed its mechanism. Conditioned stimulation/unconditioned stimulation-conditioned stimulation paradigms combined with pharmacological methods were employed to evaluate the action of calpain in memory extinction. Our data demonstrated that intraperitoneal or intra-basolateral amygdala (BLA) injection of calpain inhibitors could eliminate extinction of fear-memory in mice. Moreover, extinction of fear-memory paradigm-activated BLA calpain activity, which degraded suprachiasmatic nucleus circadian oscillatory protein (SCOP) and phosphatase and tensin homolog (PTEN), subsequently contributing to activation of a protein kinase B (AKT)-mammalian target of the rapamycin (mTor) signaling pathway. Additionally, cAMP-response element binding protein (CREB) phosphorylation was also augmented following extinction of fear-memory. Calpain inhibitor blocked the signaling pathway activation induced by extinction of fear-memory. Additionally, intra-BLA injection of rapamycin or cycloheximide also blocked the extinction of fear-memory. Conversely, intra-BLA injection of PTEN inhibitor, bpV, reversed the effect of calpeptin on extinction of fear-memory. Together, our data confirmed the function of BLA calpain in extinction of fear-memory, likely via degrading PTEN and activating AKT-mTor-dependent protein synthesis.

Reduced beta 2 glycoprotein I prevents high glucose-induced cell death in HUVECs through miR-21/PTEN

High serum beta 2 glycoprotein I (β2GPI) is associated with complications of type 2 diabetes mellitus (DM), and especially microvascular disorders. In contrast, reduced β2GPI (Rβ2GPI) can prevent diabetic vascular injury. This study aimed to investigate the protective function of Rβ2GPI in DM vascular disorders, and to assess the under lying mechanisms. High glucose-induced injury in human umbilical vein endothelial cells (HUVECs) was used to model hyperglycemia. Alow concentration of Rβ2GPI (0.5 μM), but not β2GPI, mitigated high glucose-induced cell injury. High glucose decreased miR-21 expression and Akt phosphorylation at 6 h, but facilitated their expression at 48 h. Moreover, high glucose decreased phosphatase and tensin homolog deleted on chromosome ten(PTEN) expression at 6 h, but facilitatedits expression at 48 h. Importantly, by promoting miR-21 expression, Rβ2GPI mitigated high glucose-induced PTEN expression, reduced Akt phosphorylation and nitric oxide synthase activity, and increased cyclooxygenase-2 activity and cell loss. Similar to Rβ2GPI, an miR-21 mimic (1 pM) and PTEN inhibition (1 μM bpV, or PTEN silencing) exerted protective action, while an Akt signaling pathway inhibitor (LY294002, 1 μM) aborted the effect of Rβ2GPI on high glucose-induced cell injury. Finally, Rβ2GPI inhibited high glucose-induced apoptosis via a mitochondria-dependent pathway. These data reveal that Rβ2GPI exerts protective action in high glucose-induced HUVEC injury. The mechanism is related to the miR-21-PTEN-Akt pathway and mitochondria-dependent apoptosis. This study provides in vitro data supporting the therapeutic effect of Rβ2GPI in diabetic vascular injury.

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.