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

Acacetin alleviates neuroinflammation and oxidative stress injury via the Nrf2/HO-1 pathway in a mouse model of spinal cord injury

Spinal cord injury (SCI) is a severe central nervous system disease, which may cause serious locomotor deficit. Acacetin is a flavone that possesses antioxidant and anti-inflammatory effects in different human diseases. The main purpose of this study was to explore whether acacetin ameliorates SCI in mice. A model of SCI was established in C57BL/6 mice. The Basso Mouse Scale (BMS) score, BMS subscore, mechanical hypersensitivity, and thermal hypersensitivity of mice were tested for determining the motor function. Immunofluorescence staining was utilized to detect NeuN, GFAP, and Iba-1 levels in spinal cord tissues. ELISA was utilized to assess the contents of proinflammatory factors such as interleukin (IL)-1β, IL-18, and tumor necrosis factor-alpha (TNF-α) in spinal cord tissues. The levels of oxidative stress markers, reactive oxygen species, thiobarbituric acid-reactive substances, superoxide dismutase, catalase, glutathione peroxidase, and glutathione were detected using their corresponding kits. Western blot was employed for estimating the levels of heme oxygenase 1 (HO-1), nuclear factor E2-related factor 2 (Nrf2), and Kelch-like ECH-associated protein 1 (Keap-1). In this study, acacetin treatment recovered the motor function in SCI mice. Acacetin improved neuron integrity and repressed glial cell activation in the spinal cord tissues of SCI mice. Furthermore, acacetin administration reduced the SCI-induced high concentrations of IL-1β, IL-18, and TNF-α, as well as inhibited oxidative stress in SCI mice. Moreover, acacetin activated HO-1/Nrf2 pathway in SCI mice. The neuroprotective effects of acacetin against SCI were reversed by Nrf2 inhibitor. Overall, acacetin alleviated neuroinflammation and oxidative stress injury by activating the Nrf2/HO-1 signaling pathway in the mouse models of SCI.

Neurological recovery and antioxidant effect of erythropoietin for spinal cord injury: A systematic review and meta-analysis

Background

To critically evaluate the neurological recovery effects and antioxidant effects of erythropoietin (EPO) in rat models of spinal cord injury (SCI).

Methods

The PubMed, EMBASE, MEDLINE, ScienceDirect, and Web of Science were searched for animal experiments applying EPO to treat SCI to January 2022. We included studies which examined neurological function by the Basso, Beattie, and Bresnahan (BBB) scale, as well as cavity area and spared area, and determining the molecular-biological analysis of antioxidative effects by malondialdehyde (MDA) levels in spinal cord tissues. Meta-analysis were performed with Review Manager 5.4 software.

Results

A total of 33 studies were included in this review. The results of the meta-analysis showed that SCI rats receiving EPO therapy showed a significant locomotor function recovery after 14 days compared with control, then the superiority of EPO therapy maintained to 28 days from BBB scale. Compared with the control group, the cavity area was reduced [4 studies, weighted mean difference (WMD) = −16.65, 95% CI (−30.74 to −2.55), P = 0.02] and spared area was increased [3 studies, WMD =11.53, 95% CI (1.34 to 21.72), P = 0.03] by EPO. Meanwhile, MDA levels [2 studies, WMD = −0.63 (−1.09 to −0.18), P = 0.007] were improved in the EPO treatment group compared with control, which indicated its antioxidant effect. The subgroup analysis recommended 5,000 UI/kg is the most effective dose [WMD = 4.05 (2.23, 5.88), P < 0.0001], although its effect was not statistically different from that of 1,000 UI/kg. Meanwhile, the different rat strains (Sprague-Dawley vs. Wistar), and models of animals, as well as administration method (single or multiple administration) of EPO did not affect the neuroprotective effect of EPO for SCI.

Conclusions

This systematic review indicated that EPO can promote the recovery of the locomotor function of SCI rats. The mechanism exploration of EPO needs to be verified by experiments, and then carefully designed randomized controlled trials are needed to explore its neural recovery effects.

Hypoxia signaling in human health and diseases: implications and prospects for therapeutics

Molecular oxygen (O₂) is essential for most biological reactions in mammalian cells. When the intracellular oxygen content decreases, it is called hypoxia. The process of hypoxia is linked to several biological processes, including pathogenic microbe infection, metabolic adaptation, cancer, acute and chronic diseases, and other stress responses. The mechanism underlying cells respond to oxygen changes to mediate subsequent signal response is the central question during hypoxia. Hypoxia-inducible factors (HIFs) sense hypoxia to regulate the expressions of a series of downstream genes expression, which participate in multiple processes including cell metabolism, cell growth/death, cell proliferation, glycolysis, immune response, microbe infection, tumorigenesis, and metastasis. Importantly, hypoxia signaling also interacts with other cellular pathways, such as phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-B (NF-κB) pathway, extracellular signal-regulated kinases (ERK) signaling, and endoplasmic reticulum (ER) stress. This paper systematically reviews the mechanisms of hypoxia signaling activation, the control of HIF signaling, and the function of HIF signaling in human health and diseases. In addition, the therapeutic targets involved in HIF signaling to balance health and diseases are summarized and highlighted, which would provide novel strategies for the design and development of therapeutic drugs.

Characterization of neural stem cells modified with hypoxia/neuron-specific VEGF expression system for spinal cord injury

Spinal cord injury (SCI) is an incurable disease causing an ischemic environment and functional defect, thus a new therapeutic approach is needed for SCI treatment. Vascular endothelial growth factor (VEGF) is a potent therapeutic gene to treat SCI via angiogenesis and neuroprotection, and both tissue-specific gene expression and high gene delivery efficiency are important for successful gene therapy. Here we design the hypoxia/neuron dual-specific gene expression system (pEpo-NSE) and efficient gene delivery platform can be achieved by the combination ex vivo gene therapy with erythropoietin (Epo) enhancer, neuron-specific enolase (NSE) promoter and neural stem cells (NSCs). An in vitro model, NSCs transfected with pEpo-NSE were consistently and selectively overexpressing therapeutic genes in response to neural differentiation and hypoxic conditions. Also, in SCI model, ex vivo gene therapy using pEpo-NSE system with NSCs significantly enhanced gene delivery efficiency compared with pEpo-NSE system gene therapy alone. However, microarray analysis reveals that introducing exogenous pEpo-NSE and VEGF triggers biological pathways in NSCs such as glycolysis and signaling pathways such as Ras and mitogen-activated protein kinase, leading to cell proliferation, differentiation and apoptosis. Collectively, it indicates that the pEpo-NSE gene expression system works stably in NSCs and ex vivo gene therapy using pEpo-NSE system with NSCs improves gene expression efficiency. However, exogenously introduced pEpo-NSE system has an influence on gene expression profiles in NSCs. Therefore, when we consider ex vivo gene therapy for SCI, the effects of changes in gene expression profiles in NSCs on safety should be investigated.

Hypoxia-inducible tumour-specific promoters as a dual-targeting transcriptional regulation system for cancer gene therapy

Transcriptional targeting is the best approach for specific gene therapy. Hypoxia is a common feature of the tumour microenvironment. Therefore, targeting gene expression in hypoxic cells by placing transgene under the control of a hypoxia-responsive promoter can be a good strategy for cancer-specific gene therapy. The hypoxia-inducible gene expression system has been investigated more in suicide gene therapy and it can also be of great help in knocking down cancer gene therapy with siRNAs. However, this system needs to be optimised to have maximum efficacy with minimum side effects in normal tissues. The combination of tissue-/tumour-specific promoters with HRE core sequences has been found to enhance the specificity and efficacy of this system. In this review, hypoxia-inducible gene expression system as well as gene therapy strategies targeting tumour hypoxia will be discussed. This review will also focus on hypoxia-inducible tumour-specific promoters as a dual-targeting transcriptional regulation systems developed for cancer-specific gene therapy.

IL-17 induces reactive astrocytes and up-regulation of vascular endothelial growth factor (VEGF) through JAK/STAT signaling

Spinal cord injury is a grave neurological disability resulting in neuron degeneration and permanent paralysis. The inflammation triggered by the injury would promote the spinal cord lesion in turn. Activated astrocytes during inflammatory response could promote glial scar formation and contribute to the progression of the spinal cord injury. Interleukin 17 (IL-17) was upregulated in inflammatory responses to contusion or compression of the spinal cord. in this study, IL-17 could induce reactive astrocytes which was indicated by a well-known hallmark glial fibrillary acidic protein (GFAP) in vitro and in vivo. Moreover, we demonstrated that the upregulation of VEGF was induced by IL-17 human astrocytoma cells. In our further investigation, IL-17 induced the expression of VEGF in spinal cord injury by activating JAK/STAT signaling pathway both in vitro and in vivo. In addition, we also found that IL-17 significantly changed tissue preservation and residual urine volumes and blood-spinal cord-barrier integrity in vivo. This newly found IL-17-JAK/STAT-VEGF axis improves our understanding of the molecular mechanism of spinal cord injury during inflammatory response and provides another potential target of spinal cord injury.

Hypoxia-specific, VEGF-expressing neural stem cell therapy for safe and effective treatment of neuropathic pain

Vascular endothelial growth factor (VEGF) is an angiogenic cytokine that stimulates the differentiation and function of vascular endothelial cells. VEGF has been implicated in improving nervous system function after injury. However, uncontrolled overexpression of VEGF increases the risk of tumor formation at the site of gene delivery. For this reason, VEGF expression needs to be strictly controlled. The goal of the present study was to understand the effects of hypoxia-induced gene expression system to control VEGF gene expression in neural stem cells (NSCs) on the regeneration of neural tissue after sciatic nerve injury. In this study, we used the erythropoietin (Epo) enhancer-SV40 promoter system (EpoSV-VEGF-NSCs) for hypoxia-specific VEGF expression. We used three types of NSCs: DsRed-NSCs as controls, SV-VEGF-NSCs as uncontrolled VEGF overexpressing NSCs, and EpoSV-VEGF-NSCs. For comparison of VEGF expression at normoxia and hypoxia, we measured the amount of VEGF secreted. VEGF expression decreased at normoxia and increased at hypoxia for EpoSV-VEGF-NSCs; thus, EpoSV-VEGF-NSCs controlled VEGF expression, dependent upon oxygenation condition. To demonstrate the therapeutic effect of EpoSV-VEGF-NSCs, we transplanted each cell line in a neuropathic pain sciatic nerve injury rat model. The transplanted EpoSV-VEGF-NSCs improved sciatic nerve functional index (SFI), mechanical allodynia, and re-myelination similar to the SV-VEGF-NSCs. Additionally, the number of blood vessels increased to a level similar to that of the SV-VEGF-NSCs. However, we did not observe tumor generation in the EpoSV-VEGF-NSC animals that were unlikely to have tumor formation in the SV-VEGF-NSCs. From our results, we determined that EpoSV-VEGF-NSCs safely regulate VEGF gene expression which is dependent upon oxygenation status. In addition, we found that they are therapeutically appropriate for treating sciatic nerve injury.

Peptide micelle-mediated delivery of tissue-specific suicide gene and combined therapy with avastin in a glioblastoma model

Bevacizumab (Avastin) is an angiogenesis inhibitor used as a treatment for various cancers. In this study, the combination therapy of Avastin and glioblastoma-specific thymidine kinase gene [pEpo-NI2-SV-herpes simplex virus thymidine kinase(HSVtk)] was evaluated in a glioblastoma animal model. The R7L10 peptide was used as a gene carrier of pEpo-NI2-SV-HSVtk. Gel retardation assays confirmed that R7L10 formed stable complexes with pEpo-NI2-SV-HSVtk. R7L10 protected DNA from nuclease digestion. R7L10 had lower transfection efficiency than polyethylenimine (PEI; 25 kDa). However, the in vitro and in vivo toxicity assays showed that R7L10 had lower cytotoxicity than PEI, suggesting that R7L10 is safer than PEI. For the combination therapy, Avastin was injected intravenously and the pEpo-NI2-SV-HSVtk/R7L10 complexes were injected intratumorally in the glioblastoma animal model. Tumor growth was most effectively inhibited by the combination therapy of Avastin and the gene. The immunostaining results confirmed that the HSVtk genes were expressed in the groups with the pEpo-NI2-SV-HSVtk/R7L10 complex. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed a higher level of apoptotic cells in the combination group than the pEpo-NI2-SV-HSVtk/R7L10 complex or Avastin group. In conclusion, the combination of Avastin and the glioblastoma-specific HSVtk gene has a higher antitumor effect than single therapy of Avastin or HSVtk after intratumoral administration in glioblastoma animal model.

VEGF transfer based on gene-modified fibroblasts using a hypoxia-induced vector to modulate neoangiogenesis in ischaemic regions of myocutaneous transplants

The effect of a hypoxia-inducible VEGF-expressing on wound healing in an ischaemic hind leg rat model was evaluated in this study. 180 Wistar rats were assigned randomly to three groups. After ligation of the femoral artery, group 1 received pRTP801-VEGF165, group 2 untransfected fibroblasts, group 3 saline; injection was into the subcutaneous tissue, proximal and distal to the artery ligation. Biopsy specimens were obtained on days 3, 5, 7, 14 after implementation. VEGF transgene expression, vessel architecture, the amount and total area of vessel formation were investigated. Results showed a significantly higher level of VEGF protein expression in group 1 compared to group 2 (P≤0.001) throughout the investigational period. Group 1 exhibited a significant growth of CD31-positive blood vessels in the subcutaneous tissue on day 14 compared to groups 2 and 3 (P≤0.001) (group 1, 62.20±1.92; group 2, 20.60±1.67; group 3, 12.40±1.14). Alpha-SMA-positive staining also showed significant vessel growth in group 1 on day 5 (group 1, 27.00±1.87; group 2, 7.20±1.48; group 3, 10.00±1.73). These results were confirmed in the distal muscle tissue. No significant results were obtained for the proximal muscle tissue. The subcutaneous application of pRTP801-VEGF165 showed a long-lasting effect, with an increased expression of VEGF over the entire observation period. It appears that the use of fibroblasts transfected with VEGF is a promising way to increase early angiogenesis in ischaemic tissue.

Role of VEGF and VEGFR2 Receptor in Reversal of ALS-CSF Induced Degeneration of NSC-34 Motor Neuron Cell Line

Vascular endothelial growth factor (VEGF), the well-known angiogenic factor is both neurotrophic and neuroprotective. Altered VEGF signalling is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), a fatal degenerative disease of motor neurons. We have shown earlier that VEGF protects NSC-34 motor neuronal cell line, when exposed to cerebrospinal fluid (CSF) from sporadic ALS patients (ALS-CSF). Here, we have investigated the consequences of ALS-CSF and VEGF supplementation on the VEGFR2 receptor and endogenous VEGF expression. ALS-CSF caused significant down-regulation of VEGFR2 as well as the Calbindin-D28K levels, but not endogenous VEGF. Exogenous supplementation restored the depletion of VEGFR2 and Calbindin-D28K with a concomitant up-regulation of endogenous VEGF. The up-regulated caspase 3 in the ALS-CSF group was reinstated to basal levels along with a significant reduction in the number of TUNEL-positive cells. Electron photomicrographs of ALS-CSF-exposed cells divulged presence of cytoplasmic vacuoles alongside severe damage to organelles like mitochondria, endoplasmic reticulum, etc. Substantial recovery of most of the damaged organelles was noted in response to VEGF supplementation. While the enhancement in endogenous VEGF levels highlights the autocrine functions, the up-regulation of VEGFR2 receptor emphasizes the paracrine functions of VEGF in modulating its neuroprotective effect against ALS-CSF. The revival of cellular organellar structure, increased calbindin expression and enhanced survival in response to VEGF supplementation consolidates the opinion that VEGF indeed has a therapeutic potential in sporadic ALS.

Delayed administration of a bio-engineered zinc-finger VEGF-A gene therapy is neuroprotective and attenuates allodynia following traumatic spinal cord injury

Following spinal cord injury (SCI) there are drastic changes that occur in the spinal microvasculature, including ischemia, hemorrhage, endothelial cell death and blood-spinal cord barrier disruption. Vascular endothelial growth factor-A (VEGF-A) is a pleiotropic factor recognized for its pro-angiogenic properties; however, VEGF has recently been shown to provide neuroprotection. We hypothesized that delivery of AdV-ZFP-VEGF--an adenovirally delivered bio-engineered zinc-finger transcription factor that promotes endogenous VEGF-A expression--would result in angiogenesis, neuroprotection and functional recovery following SCI. This novel VEGF gene therapy induces the endogenous production of multiple VEGF-A isoforms; a critical factor for proper vascular development and repair. Briefly, female Wistar rats--under cyclosporin immunosuppression--received a 35 g clip-compression injury and were administered AdV-ZFP-VEGF or AdV-eGFP at 24 hours post-SCI. qRT-PCR and Western Blot analysis of VEGF-A mRNA and protein, showed significant increases in VEGF-A expression in AdV-ZFP-VEGF treated animals (p<0.001 and p<0.05, respectively). Analysis of NF200, TUNEL, and RECA-1 indicated that AdV-ZFP-VEGF increased axonal preservation (p<0.05), reduced cell death (p<0.01), and increased blood vessels (p<0.01), respectively. Moreover, AdV-ZFP-VEGF resulted in a 10% increase in blood vessel proliferation (p<0.001). Catwalk™ analysis showed AdV-ZFP-VEGF treatment dramatically improves hindlimb weight support (p<0.05) and increases hindlimb swing speed (p<0.02) when compared to control animals. Finally, AdV-ZFP-VEGF administration provided a significant reduction in allodynia (p<0.01). Overall, the results of this study indicate that AdV-ZFP-VEGF administration can be delivered in a clinically relevant time-window following SCI (24 hours) and provide significant molecular and functional benefits.

Increased progression to kidney fibrosis after erythropoietin is used as a treatment for acute kidney injury

Treatment of renal ischemia-reperfusion (IR) injury with recombinant human erythropoietin (rhEPO) reduces acute kidney injury and improves function. We aimed to investigate whether progression to chronic kidney disease associated with acute injury was also reduced by rhEPO treatment, using in vivo and in vitro models. Rats were subjected to bilateral 40-min renal ischemia, and kidneys were studied at 4, 7, and 28 days postreperfusion for renal function, tubular injury and repair, inflammation, and fibrosis. Acute injury was modulated using rhEPO (1,000 or 5,000 IU/kg, intraperitoneally) at the time of reperfusion. Renal tubular epithelial cells or fibroblasts in culture were subjected to hypoxia or oxidative stress, with or without rhEPO (200 IU/ml), and fibrogenesis was studied. The results of the in vivo model confirmed functional and structural improvement with rhEPO at 4 days post-IR (P < 0.05). At 7 days post-IR, fibrosis and myofibroblast stimulation were increased with IR with and without rhEPO (P < 0.01). However, at 28 days post-IR, renal fibrosis and myofibroblast numbers were significantly greater with IR plus rhEPO (P < 0.01) compared with IR only. Mechanistically, rhEPO stimulated profibrotic transforming growth factor-β, oxidative stress (marker 8-hydroxy-deoxyguanosine), and phosphorylation of the signal transduction protein extracellular signal-regulated kinase. In vitro, rhEPO protected tubular epithelium from apoptosis but stimulated epithelial-to-mesenchymal transition and also protected and activated fibroblasts, particularly with oxidative stress. In summary, although rhEPO was protective of renal function and structure in acute kidney injury, the supraphysiological dose needed for renoprotection contributed to fibrogenesis and stimulated chronic kidney disease in the long term.

Post-translational regulation of gene expression using the ATF4 oxygen-dependent degradation domain for hypoxia-specific gene therapy

Solid tumors have hypoxic regions in their cores, due to low blood supply levels. Therefore, hypoxia-specific gene regulation systems have been developed for tumor-specific gene therapy. In this study, the oxygen-dependent degradation (ODD) domain on activating transcription factor-4 (ATF4) was evaluated for post-translational regulation of proteins. The ATF4 ODD cDNA was amplified by RT-PCR, and a luciferase plasmid containing the ATF4 ODD domain, pSV-Luc-ATF4-ODD, was constructed. Luciferase expression was induced under hypoxia by the ATF4 ODD domain in transfection assays into N2A neuroblastoma cells, C6 glioblastoma cells, and U87 glioblastoma cells. In the transfection assay with pSV-Luc-ATF4-ODD, RT-PCR results showed that the mRNA level did not change under hypoxia. This suggests that the induction of luciferase under hypoxia was mediated by post-translational regulation. A plasmid expressing thymidine kinase from herpes simplex virus (HSV-tk), pSV-HSVtk-ATF4-ODD, was constructed with the ATF4 ODD cDNA. The transfection assay with pSV-TK-ATF4-ODD showed that the ATF4 ODD domain induced HSV-tk expression under hypoxia and facilitated the death of C6 cells in the presence of ganciclovir (GCV). Furthermore, pSV-HSVtk-ATF4-ODD induced caspase-3 activity in the hypoxic cells. In conclusion, the ATF4 ODD may be useful for hypoxia-specific gene therapy by post-translational regulation of gene expression.

Contribution of intracellular calcium and pH in ischemic uncoupling of cardiac gap junction channels formed of connexins 43, 40, and 45: a critical function of C-terminal domain

Ischemia is known to inhibit gap junction (GJ) mediated intercellular communication. However the detail mechanisms of this inhibition are largely unknown. In the present study, we determined the vulnerability of different cardiac GJ channels formed of connexins (Cxs) 43, 40, and 45 to simulated ischemia, by creating oxygen glucose deprived (OGD) condition. 5 minutes of OGD decreased the junctional conductance (Gj) of Cx43, Cx40 and Cx45 by 53±3%, 64±1% and 85±2% respectively. Reduction of Gj was prevented completely by restricting the change of both intracellular calcium ([Ca(2+)]i) and pH (pHi) with potassium phosphate buffer. Clamping of either [Ca(2+)]i or pHi, through BAPTA (2 mM) or HEPES (80 mM) respectively, offered partial resistance to ischemic uncoupling. Anti-calmodulin antibody attenuated the uncoupling of Cx43 and Cx45 significantly but not of Cx40. Furthermore, OGD could reduce only 26±2% of Gj in C-terminus (CT) truncated Cx43 (Cx43-Δ257). Tethering CT of Cx43 to the CT-truncated Cx40 (Cx40-Δ249), and Cx45 (Cx45-Δ272) helped to resist OGD mediated uncoupling. Moreover, CT domain played a significant role in determining the junction current density and plaque diameter. Our results suggest; OGD mediated uncoupling of GJ channels is primarily due to elevated [Ca(2+)]i and acidic pHi, though the latter contributes more. Among Cx43, Cx40 and Cx45, Cx43 is the most resistant to OGD while Cx45 is the most sensitive one. CT of Cx43 has major necessary elements for OGD induced uncoupling and it can complement CT of Cx40 and Cx45.

Drug delivery systems for the treatment of ischemic stroke

Stroke is the third leading cause of death in the United States. Reduced cerebral blood flow causes acute damage to the brain due to excitotoxicity, reactive oxygen species (ROS), and ischemia. Currently, the main treatment for stroke is to revive the blood flow by using thrombolytic agents. Reviving blood flow also causes ischemia-reperfusion (I/R) damage. I/R damage results from inflammation and apoptosis and can persist for days to weeks, increasing the infarct size. Drugs can be applied to stroke to intervene in the sub-acute and chronic phases. Chemical, peptide, and genetic therapies have been evaluated to reduce delayed damage to the brain. These drugs have different characteristics, requiring that delivery carriers be developed based on these characteristics. The delivery route is another important factor affecting the efficiency of drug delivery. Various delivery routes have been developed, such as intravenous injection, intranasal administration, and local direct injection to overcome the blood-brain-barrier (BBB). In this review, the delivery carriers and delivery routes for peptide and gene therapies are discussed and examples are provided. Combined with new drugs, drug delivery systems will eventually provide useful treatments for ischemic stroke.

Gene regulation systems for gene therapy applications in the central nervous system

Substantial progress has been made in the development of novel gene therapy strategies for central nervous system (CNS) disorders in recent years. However, unregulated transgene expression is a significant issue limiting human applications due to the potential side effects from excessive levels of transgenic protein that indiscriminately affect both diseased and nondiseased cells. Gene regulation systems are a tool by which tight tissue-specific and temporal regulation of transgene expression may be achieved. This review covers the features of ideal regulatory systems and summarises the mechanics of current exogenous and endogenous gene regulation systems and their utility in the CNS.

Neural stem cells modified by a hypoxia-inducible VEGF gene expression system improve cell viability under hypoxic conditions and spinal cord injury

STUDY DESIGN

An in vitro neural hypoxia model and rat spinal cord injury (SCI) model were used to assess the regulation of therapeutic vascular endothelial growth factor (VEGF) gene expression in mouse neural stem cells (mNSCs) by the EPO (erythropoietin) enhancer or RTP801 promoter.

OBJECTIVE

To increase VEGF gene expression in mNSCs under hypoxic conditions in SCI lesions but avoid unwanted overexpression of VEGF in normal sites, we developed a hypoxia-inducible gene expression system consisting of the EPO enhancer and RTP801 promoter fused to VEGF or the luciferase gene, then transfected into mNSCs.

SUMMARY OF BACKGROUND DATA

On the basis of the ischemic response in the injured area, poor cell survival at the transplantation site is a consistent problem with NSC transplantation after SCI. Although VEGF directly protects neurons and enhances neurite outgrowth, uncontrolled overexpression of VEGF in uninjured tissue may cause serious adverse effects. To effectively improve NSC survival in ischemic sites after transplantation, we evaluated mNSCs modified by a hypoxia-inducible VEGF gene expression system in an SCI model.

METHODS

Hypoxia-inducible luciferase or VEGF plasmids were constructed using the EPO enhancer or RTP801 promoter. The effect of these systems on targeted gene expression and cell viability was evaluated in mNSCs in both hypoxic in vitro injury and a rat SCI model in vivo.

RESULTS

The gene expression system containing the EPO enhancer or RTP801 promoter significantly increased the expression of the luciferase reporter gene and therapeutic VEGF gene under hypoxic conditions. The Epo-SV-VEGF plasmid transfection group had significantly fewer apoptotic cells in vitro. This system also augmented cell viability in the in vivo SCI model.

CONCLUSION

These results strongly suggest the potential utility of mNSCs modified by a hypoxia-inducible VEGF gene expression system in the development of effective stem cell transplantation protocols in SCI.

Effect of VEGF treatment on the blood-spinal cord barrier permeability in experimental spinal cord injury: dynamic contrast-enhanced magnetic resonance imaging

Compromised blood-spinal cord barrier (BSCB) is a factor in the outcome following traumatic spinal cord injury (SCI). Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis and vascular permeability. The role of VEGF in SCI is controversial. Relatively little is known about the spatial and temporal changes in the BSCB permeability following administration of VEGF in experimental SCI. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) studies were performed to noninvasively follow spatial and temporal changes in the BSCB permeability following acute administration of VEGF in experimental SCI over a post-injury period of 56 days. The DCE-MRI data was analyzed using a two-compartment pharmacokinetic model. Animals were assessed for open field locomotion using the Basso-Beattie-Bresnahan score. These studies demonstrate that the BSCB permeability was greater at all time points in the VEGF-treated animals compared to saline controls, most significantly in the epicenter region of injury. Although a significant temporal reduction in the BSCB permeability was observed in the VEGF-treated animals, BSCB permeability remained elevated even during the chronic phase. VEGF treatment resulted in earlier improvement in locomotor ability during the chronic phase of SCI. This study suggests a beneficial role of acutely administered VEGF in hastening neurobehavioral recovery after SCI.

Reduced vascular endothelial growth factor expression in contusive spinal cord injury

Vascular endothelial growth factor (VEGF) is being investigated as a potential interventional therapy for spinal cord injury (SCI). In the current study, we examined SCI-induced changes in VEGF protein levels using Western blot analysis around the epicenter of injury. Our results indicate a significant decrease in the levels of VEGF(165) and other VEGF isoforms at the lesion epicenter 1 day after injury, which was maintained up to 1 month after injury. We also examined if robust VEGF(165) decrease in injured spinal cords affects neuronal survival, given that a number of reported studies show neuroprotective effect of this VEGF isoform. However, exogenously administered VEGF(165) at the time of injury did not affect the number of sparred neurons. In contrast, exogenous administration of VEGF antibody that inhibits actions of not only VEGF(165) but also of several other VEGF isoforms, significantly decreased number of sparred neurons after SCI. Together these results indicate a general reduction of VEGF isoforms following SCI and that isoforms other than VEGF(165) (e.g., VEGF(121) and/or VEGF(189)) provide neuroprotection, suggesting that VEGF(165) isoform is likely involved in other pathophysiological process after SCI.

Neuroprotective effect of combined hypoxia-induced VEGF and bone marrow-derived mesenchymal stem cell treatment

PURPOSES

To avoid unwanted adverse effects of higher doses of single treatment of stem cells and gene therapy and increase the therapeutic efficacies, we hypothesized the combined therapy with stem cells and gene therapy. This study assessed the neuroprotective effects of combined gene therapy and stem cell treatment under ischemic hypoxia conditions using hypoxia-inducible vascular endothelial growth factor (VEGF) and bone marrow-derived mesenchymal stem cells (BMSC).

METHODS

Experimental groups included the control which was N2A cells transfected with empty vectors, the transfection only group which was N2A cells treated with pEpo-SV-VEGF alone, the BMSC only group which was N2A cells transfected with empty vectors and cocultured with BMSCs, and the combined treatment group which was N2A cells treated with pEpo-SV-VEGF and cocultured with BMSCs. Each group was transfected for 4 h and cultured at 37 degrees C and 5% CO2 for 24 h. Each group was then cultivated under hypoxic conditions (1% O2) for 12 h. Neuroprotective effects were assessed by reverse transcription polymerase chain reaction, annexin V, and cytotoxicity assay.

RESULTS

Neurons exposed to hypoxic conditions exhibited neuronal apoptosis. Compared to single treatments, the combined hypoxia-inducible VEGF and BMSC treatment demonstrated a significant increase in VEGF expression and decreased neuronal apoptosis.

CONCLUSIONS

These results suggest that combined pEpo-SV-VEGF and BMSC treatment is effective in protecting neurons against hypoxic ischemic injury.

Role of the oxygen-dependent degradation domain in a hypoxia-inducible gene expression system in vascular endothelial growth factor gene therapy

STUDY DESIGN.: An in vitro neural hypoxia model and rat spinal cord injury (SCI) model were used to assess the regulation effect of a reporter or therapeutic gene expression by an oxygen-dependent degradation (ODD) domain in a hypoxia-inducible gene expression system with or without the erythropoietin (EPO) enhancer. OBJECTIVE.: To increase vascular endothelial growth factor (VEGF) gene expression in SCI lesions but avoid unwanted overexpression of VEGF in normal sites, we developed a hypoxia-inducible gene expression system consisting of the EPO enhancer upstream of the SV promoter and an ODD domain C-terminally fused to VEGF. SUMMARY OF BACKGROUND DATA.: ODD domain plays a major role in the degradation of hypoxia-inducible factor 1alpha and has been used in a hypoxia-specific gene expression system as a post-translational regulatory factor. METHODS.: The hypoxia-inducible luciferase or VEGF plasmid was constructed using the EPO enhancer combined with or without the ODD domain. The constructed plasmid was transfected into mouse Neuro 2a (N2a) neuroblastoma cells by Lipofectamine 2000, followed by a 24-hour incubation in hypoxia or normoxia. For in vivo analysis, the naked plasmid DNA was directly injected into the injured rat spinal cord. The gene expression was evaluated by luciferase activity assay, enzyme-linked immunosorbent assay, reverse transcriptase-polymerase chain reaction, and immunofluorescence staining. RESULTS.: The EPO enhancer/ODD domain-combined hypoxia-inducible gene expression system clearly increased the expression of the reporter luciferase gene and therapeutic VEGF gene specifically under hypoxic conditions and SCI, and quickly downregulated protein expression to a very low level after reoxygenation. CONCLUSION.: These results strongly suggest the potential applicability of this EPO enhancer/ODD domain-based hypoxia-inducible gene expression system in the development of a safer and more effective VEGF gene therapy for SCI.

Hypoxia-specific gene expression for ischemic disease gene therapy

Gene therapy for ischemic diseases has been developed with various growth factors and anti-apoptotic genes. However, non-specific expression of therapeutic genes may induce deleterious side effects such as tumor formation. Hypoxia-specific regulatory systems can be used to regulate transgene expression in hypoxic tissues, in which gene expression is induced in ischemic tissues, but reduced in normal tissues by transcriptional, translational or post-translational regulation. Since hypoxia-inducible factor 1 (HIF-1) activates transcription of genes in hypoxic tissues, it can play an important role in the prevention of myocardial and cerebral ischemia. Hypoxia-specific promoters including HIF-1 binding sites have been used for transcriptional regulation of therapeutic genes. Also, hypoxia-specific untranslated regions (UTRs) and oxygen dependent degradation (ODD) domains have been investigated for translational and post-translational regulations, respectively. Hypoxia-specific gene expression systems have been applied to various ischemic disease models, including ischemic myocardium, stroke, and injured spinal cord. This review examines the current status and future challenges of hypoxia-specific systems for safe and effective gene therapy of ischemic diseases.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

Gene therapy of neural cell injuries in vitro using the hypoxia-inducible GM-CSF expression plasmids and water-soluble lipopolymer (WSLP)

Non-viral polymeric gene carriers have been widely investigated but no promising biocompatible polymer was developed for the gene therapy of neural system injuries yet. This study evaluated the potential usage of water-soluble lipopolymer (WSLP) as a gene delivery vehicle in neural lineage cells of SK-N-BE(2)C, a neuroblastoma cell line and primary culture of mouse neural progenitor cells (mNPCs). When tested with the luciferase reporter (pSV-Luc), WSLP showed higher gene transfection efficiency by more than 8-10 folds yet with lower cytotoxicity than polyethylenimine of 1800 Da (PEI1800), a parental polymer, and Lipofectamine 2000. The optimum N/P ratios were 40:1 for WSLP and 10:1 for PEI1800, respectively. The transfection efficiency for both of WSLP and PEI1800 was higher overall in SK-N-BE(2)C cells than in mNPCs. WSLP was also used successfully for the delivery and hypoxia-inducible expression of luciferase reporter plasmid containing the erythropoietin (Epo) enhancer (pEpo-SV-Luc) or RTP801 promoter (pRTP801-Luc). The hypoxia-inducible system and WSLP were then successfully applied to the delivery of granulocyte macrophage colony-stimulating factor (GM-CSF) gene that was previously shown to have neuroprotective effect on neural cell death in vitro and in rat SCI model. The hypoxia-inducible GM-CSF plasmids (pEpo-SV-GM-CSF and pRTP801-GM-CSF) showed induced expression of GM-CSF under hypoxia and decrease in the hypoxia-induced cell death in SK-N-BE(2)C cells. In conclusion, this study demonstrated that WSLP could be an efficient gene delivery carrier for neural cells and gene therapy of GM-CSF using the hypoxia-inducible system could be a potential therapeutic intervention for neural injuries. Further studies are necessary to confirm the current findings in animal models of CNS injuries.

Integrated transcriptomic response to cardiac chronic hypoxia: translation regulators and response to stress in cell survival

Complementary deoxyribonucleic acid microarray data from 36 mice subjected for 1, 2, or 4 weeks of their early life to normal atmospheric conditions (normoxia) or chronic intermittent (CIH) or constant (CCH) hypoxia were analyzed to extract organizational principles of the developing heart transcriptome and determine the integrated response to oxygen deprivation. Although both CCH and CIH regulated numerous genes involved in a wide diversity of processes, the changes in maturational profile, expression stability, and coordination were vastly different between the two treatments, indicating the activation of distinct regulatory mechanisms of gene transcription. The analysis focused on the main regulators of translation and response to stress because of their role in the cardiac hypertrophy and cell survival in hypoxia. On average, the expression of each heart gene was tied to the expression of about 20% of other genes in normoxia but to only 8% in CCH and 9% in CIH, indicating a strong decoupling effect of hypoxia. In contrast to the general tendency, the interlinkages among components of the translational machinery and response to stress increased significantly in CIH and much more in CCH, suggesting a coordinated response to the hypoxic stress. Moreover, the transcriptomic networks were profoundly and differently remodeled by CCH and CIH.