Hypoxia-inducible expression of vascular endothelial growth factor for the treament of spinal cord injury in rat model

Abstract

Background Vascular endothelial growth factor (VEGF) has been investigated for the therapy of many disorders and injuries with ischemia. However, unregulated VEGF mediated angiogenesis has the potential to promote tumor growth, accelerate diabetic proliferative retinopathy and promote rupture of atherosclerotic plaque. To limit the risk of pathological angiogenesis, hypoxia-inducible VEGF expression systems were constructed and evaluated as a treatment for spinal cord injury. Method The hypoxia-inducible luciferase or VEGF plasmids were constructed with the erythropoietin (Epo) enhancer with the SV40 promoter (pEpo-SV-Luc and pEpo-SV-VEGF) or the RTP801 promoter (pRTP801-Luc and pRTP801-VEGF). The in vitro VEGF expression was evaluated after the transfection into N2A cells. The plasmids were then injected into the rat spinal cord with a contusion injury. The in vivo VEGF expression was measured by RT-PCR and ELISA. The locomotor recovery was evaluated by Basso, Beattie and Bresnahan (BBB) locomotor analysis. Results pEpo-SV-Luc and pRTP801-Luc showed over three times higher luciferase expression in N2A cells under hypoxia than normoxia. pEpo-SV-VEGF or pRTP801-VEGF also induced the VEGF expression under hypoxia in in vitro transfection assay, while pSV-VEGF did not. The VEGF level was higher in the pEpo-SV-VEGF and pRTP801-VEGF groups than the control groups. The VEGF expression was detected in neurons and astrocytes of the spinal cord. The locomotor recovery was improved in the pEpo-SV-VEGF and pRTP801-VEGF groups, showing higher BBB scores when compared with the control groups. Conclusion These results suggest that the hypoxia-inducible gene expression system with the Epo enhancer-SV40 promoter and the RTP801 promoter may be useful to eventually treat spinal cord injury by gene therapy.