Aiping Yu

Intracellular redox imbalance and extracellular amino acid metabolic abnormality contribute to arsenic-induced developmental retardation in mouse preimplantation embryos†

Inorganic arsenic, an environmental contaminant, is known to cause cancer, developmental retardation, and many other serious diseases. Previous researches have shown that arsenic exerts its toxicity partially through generating reactive oxygen species (ROS). However, it is still not well understood how ROS links arsenic exposure to developmental retardation of preimplantation embryo. Here we demonstrate that high‐level arsenite induces severe redox imbalance by decreasing the levels of glutathione and increasing the levels of ROS through the oxidative stress adaptor p66Shc, which induces apoptosis by activating the cytochrome c‐caspase. In addition, low‐level arsenite seriously perturbs the metabolism of extracellular amino acid, especially that of the cytotoxic and antioxidative amino acids in preimplantation embryos, may also be the reason for developmental delay. Furthermore, An antioxidant, N‐acetyl‐L‐cysteine, improves the development of arsenite‐exposed embryos by reducing intracellular ROS and adjusting amino acid metabolism, suggesting that increasing the intracellular antioxidant level may have preventive or therapeutic effects on arsenic‐induced embryonic toxicity. In conclusion, we suggest that p66Shc‐linked redox imbalance and abnormal extracellular amino acid metabolism mediate arsenite‐induced embryonic retardation. J. Cell. Physiol. 222: 444–455, 2010.

Role of spastin and protrudin in neurite outgrowth.

Hereditary spastic paraplegia (HSP) is a neurodegenerative disorder characterized by retrograde axonal degeneration that primarily affects long spinal neurons. The gene encoding spastin has a well‐established association with HSP, and protrudin is a known binding partner of spastin. Here, we demonstrate that the N‐terminal domain of protrudin mediates the interaction with spastin, which is responsible for neurite outgrowth. We show that spastin promotes protrudin‐dependent neurite outgrowth in PC12 cells. To further confirm these physiological functions in vivo, we microinjected zebrafish embryos with various protrudin/spastin mRNA and morpholinos. The results suggest that the spinal cord motor neuron axon outgrowth of zebrafish is regulated by the interaction between spastin and protrudin. In addition, the putative HSP‐associated protrudinG191V mutation was shown to alter the subcellular distribution and impair the yolk sac extension of zebrafish, but without significant defects in neurite outgrowth both in PC12 cells and zebrafish. Taken together, our findings indicate that protrudin interacts with spastin and induces axon formation through its N‐terminal domain. Moreover, protrudin and spastin may work together to play an indispensable role in motor axon outgrowth. J. Cell. Biochem. 113: 2296–2307, 2012.

Construction and functional evaluation of hirudin derivatives with low bleeding risk.

The purpose of this study was to design and evaluate hirudin (HIR) derivatives with low bleeding risk. In these derivatives, the factor (F) XIa, FXa, and thrombin recognition peptides (EPR, GVYAR, and LGPR, respectively) were linked to the N-terminus of HIR. The intact derivatives have no anticoagulant activity because of the extension of the N-terminus of HIR. After cleavage by the corresponding coagulation factor that occurs on the activation of the coagulation system and in the presence of the thrombus, its activity is released. This limited the anticoagulant activity of these derivatives to the vicinity of the thrombus, and as a result, systemic bleeding complications were avoided. The definite antithrombotic effect and low bleeding parameters of these derivatives were investigated in rat carotid artery and inferior vena cava thrombosis models. In both models, the three derivatives showed significant antithrombotic effects, indicating that anticoagulant activity could be successfully released in vivo. Moreover, the bleeding parameters of these derivatives were lower than that of HIR as indicated by the values of activated partial thromboplastin time (APTT) and thrombin time (TT). To further assess the safety of these derivatives, bleeding time was measured in a mouse tail-cut model. Although the derivatives had obvious effects on bleeding at a dose of 6 mg/kg, the effect of these derivatives on bleeding was significantly weaker than that of HIR at a dose of 1.5 mg/kg. Thus, the benefit-to-risk profiles of the derivatives were superior to that of HIR.

Pilot-scale production and purification of a staphylokinase-based fusion protein over-expressed in Escherichia coli

SFH, a recombinant staphylokinase-based fusion protein linked by the factor Xa recognition peptide at the N-terminus of hirudin, is a promising therapeutic candidate for thromboembolic diseases. To develop SFH into a new thrombolytic agent, scaled-up production was carried out to provide sufficient preparation for animal safety and clinical studies. Here, we describe a pilot-scale cultivation and purification process for the production of SFH. A high-cell-density fed-batch cultivation for the production of SFH in E. coli was developed in a 40-L bioreactor, which produced about 1.1 g/L of recombinant protein. SFH was purified to homogeneity from the E. coli lysate by expanded bed adsorption chromatography and anion-exchange chromatography, with over 99% purity and 54% recovery. Moreover, the residual endotoxin content was less than 0.5 EU/mL. The molecular weight and in vitro bioactivity of SFH were also determined by electrospray ionization-mass spectrometry (ESI-MS) and fibrinolytic activity assay, respectively.

A fusion protein with improved thrombolytic effect and low bleeding risk

To resolve the therapeutic dilemma between efficacy of thrombolysis and bleeding risk associated with the use of a combination of thrombolytic and anticoagulant treatments, we created a fusion protein. Staphylokinase was fused to the N-terminus of hirudin using thrombin recognition sequence as linker peptide, resulting in a fusion protein STH. We hypothesised that STH would be cleaved by thrombin at the thrombus site, releasing staphylokinase and hirudin to perform bifunctionally, and attenuating bleeding risk. SDS-PAGE and Western blot analyses indicated that the linker peptide could be specially recognised and cleaved by thrombin. Amidolytic and thromboelastogram assays showed that the N-terminus of hirudin in STH was blocked by staphylokinase and linker peptide, impeding hirudins anticoagulant activity. Once cleaved, STH displayed 35.7% of the anticoagulant activity of equimolar hirudin and exhibited anticoagulant effects in the fibrin clot lysis assay. Thrombin-binding and fibrin clot lysis assays showed that the C-terminus of hirudin retained its high affinity for thrombin. Moreover, STH showed improved thrombolytic effects and a lower bleeding risk in animals. Thus, STH may have the capacity to perform bifunctionally and release anticoagulant activity in a thrombus-targeted manner in vivo, which may reduce the bleeding risk that often accompanies high thrombolytic efficacy in the treatment of thromboembolic diseases.

Two Characteristics of a Recombinant Fusion Protein Composed of Staphylokinase and Hirudin: High Thrombus Affinity and Thrombus-targeting Release of Anticoagulant Activity

To improve thrombolytic effect, a fusion protein SFH composed of staphylokinase (SAK) and hirudin (HV) with blood coagulation factor Xa (FXa) recognition peptide as a linker, was designed. SFH showed improved thrombolytic effect and low bleeding in vivo. Two thrombus-targeting mechanisms might account for the above features of SFH. This study was designed to study the two thrombus-targeting mechanisms of SFH. ELISA and immunohistochemistry assay were used to study the improved thrombus selectivity of SFH and the results showed that SFH, compared with SAK, displayed higher affinity for thrombin and thrombin-rich thrombus. To verify the thrombus-targeting release of anticoagulant activity of SFH, FH-a derivative of HV with only FXa recognition sequence at N terminus of HV was designed and used in animal tests. In inferior vena cava thrombosis model, FH showed equal antithrombotic effect as HV, indicating that HV could be successfully released from FH by FXa cleavage in vivo. More importantly, no prolongation of plasma TT, APTT and PT were found in FH group, but significant prolongations were discovered in HV group. This revealed that the anticoagulant activity of FH was released in thrombus-targeting way and limited in the vicinity of the thrombus, and this could be extrapolated to SFH. In conclusion, the high thrombus affinity and thrombus-targeting release of anticoagulant activity of SFH assigned low bleeding risk to SFH.