Significant amounts of oxygen free radicals (oxidants) are generated during cerebral ischemia=reperfusion, and oxidative stress plays an important role in brain damage after stroke. In addition to oxidizing macromolecules, leading to cell injury, oxidants are also involved in cell death=survival signal pathways and cause mitochondrial dysfunction. Experimental data from laboratory animals that either overexpress (transgenic) or are deficient in (knock-out) antioxidant proteins, mainly superoxide dismutase, have provided strong evidence of the role of oxidative stress in ischemic brain damage. In addition to mitochondria, recent reports demonstrate that NADPH oxidase (NOX), an important pro-oxidant enzyme, is also involved in the generation of oxidants in the brain after stroke. Inhibition of NOX is neuroprotective against cerebral ischemia. We propose that superoxide dismutase and NOX activity in the brain is a major determinant for ischemic damage=repair and that these major anti-and pro-oxidant enzymes are potential endogenous molecular targets for stroke therapy. Antioxid. Redox Signal. 14, 1505-1517.

Aberrantly enhanced vascular endothelial growth factor (VEGF) gene expression is associated with increased tumor growth and metastatic spread of solid malignancies, including human renal carcinomas. Persistent activation of STAT3 is linked to tumor-associated angiogenesis, but underlying mechanisms remain unclear. Therefore, we examined whether STAT3 modulates the stability and activity of hypoxia-inducible factor-1alpha (HIF-1alpha), and in turn enhances VEGF expression. We found that STAT3 was activated in ischemic rat kidneys and hypoxic human renal carcinoma cells. We also found that hypoxia-induced activation of STAT3 transactivated the VEGF promoter and increased the expression of VEGF transcripts. Consistent with these findings, STAT3 inhibition attenuated the hypoxic induction of VEGF. Interestingly, activated STAT3 increased HIF-1alpha protein levels due to the HIF-1alpha stability by blocking HIF-1alpha degradation and accelerated its de novo synthesis. The novel interaction of STAT3 with HIF-1alpha was identified in hypoxic renal carcinoma cells. Furthermore, hypoxia recruited STAT3, HIF-1alpha, and p300 to the VEGF promoter and induced histone H3 acetylation. Therefore, these findings provide compelling evidence that a causal relationship exists between STAT3 activation and HIF-1-dependent angiogenesis and suggest that therapeutic modalities designed to disrupt STAT3 signaling hold considerable promise for the blocking tumor growth and enhancing apoptosis of cancer cells and tissues.

Mitochondria play important roles as the powerhouse of the cell. After cerebral ischemia, mitochondria overproduce reactive oxygen species (ROS), which have been thoroughly studied with the use of superoxide dismutase transgenic or knockout animals. ROS directly damage lipids, proteins, and nucleic acids in the cell. Moreover, ROS activate various molecular signaling pathways. Apoptosis-related signals return to mitochondria, then mitochondria induce cell death through the release of pro-apoptotic proteins such as cytochrome c or apoptosis-inducing factor. Although the mechanisms of cell death after cerebral ischemia remain unclear, mitochondria obviously play a role by activating signaling pathways through ROS production and by regulating mitochondria-dependent apoptosis pathways.

Effective stroke therapies require recanalization of occluded cerebral blood vessels. However, reperfusion can cause neurovascular injury, leading to cerebral edema, brain hemorrhage, and neuronal death by apoptosis/necrosis. These complications, which result from excess production of reactive oxygen species in mitochondria, significantly limit the benefits of stroke therapies. We have developed a focal stroke model using mice deficient in mitochondrial manganese-superoxide dismutase (SOD2−/+) to investigate neurovascular endothelial damage that occurs during reperfusion. Following focal stroke and reperfusion, SOD2−/+ mice had delayed blood-brain barrier breakdown, associated with activation of matrix metalloproteinase and high brain hemorrhage rates, whereas a decrease in apoptosis and hemorrhage was observed in SOD2 overexpressors. Thus, induction and activation of SOD2 is a novel strategy for neurovascular protection after ischemia/reperfusion. Our recent study identified the signal transducer and activator of transcription 3 (STAT3) as a transcription factor of the mouse SOD2 gene. During reperfusion, activation of STAT3 and its recruitment into the SOD2 gene were blocked, resulting in increased oxidative stress and neuronal apoptosis. In contrast, pharmacological activation of STAT3 induced SOD2 expression, which limits ischemic neuronal death. Our studies point to antioxidant-based neurovascular protective strategies as potential treatments to expand the therapeutic window of currently approved therapies.

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Cerebral ischemia and reperfusion increase superoxide anions (O 2⅐ Ϫ ) in brain mitochondria. Manganese superoxide dismutase (Mn-SOD; SOD2), a primary mitochondrial antioxidant enzyme, scavenges superoxide radicals and its overexpression provides neuroprotection. However, the regulatory mechanism of Mn-SOD expression during cerebral ischemia and reperfusion is still unclear. In this study, we identified the signal transducer and activator of transcription 3 (STAT3) as a transcription factor of the mouse Mn-SOD gene, and elucidated the mechanism of O 2 ⅐ Ϫ overproduction after transient focal cerebral ischemia (tFCI). We found that Mn-SOD expression is significantly reduced by reperfusion in the cerebral ischemic brain. We also found that activated STAT3 is usually recruited into the mouse Mn-SOD promoter and upregulates transcription of the mouse Mn-SOD gene in the normal brain. However, at early postreperfusion periods after tFCI, STAT3 was rapidly downregulated, and its recruitment into the Mn-SOD promoter was completely blocked. In addition, transcriptional activity of the mouse Mn-SOD gene was significantly reduced by STAT3 inhibition in primary cortical neurons. Moreover, we found that STAT3 deactivated by reperfusion induces accumulation of O 2 ⅐ Ϫ in mitochondria. The loss of STAT3 activity induced neuronal cell death by reducing Mn-SOD expression. Using SOD2Ϫ/ϩ heterozygous knock-out mice, we found that Mn-SOD is a direct target of STAT3 in reperfusion-induced neuronal cell death. Our study demonstrates that STAT3 is a novel transcription factor of the mouse Mn-SOD gene and plays a crucial role as a neuroprotectant in regulating levels of reactive oxygen species in the mouse brain.

Transplantation of neural stem cells (NSCs) offers a novel therapeutic strategy for stroke; however, massive grafted-cell death following transplantation, possibly due to a hostile host-brain environment, lessens the effectiveness of this approach. Here, we have investigated whether reprogramming NSCs with minocycline, a broadly-used antibiotic also known to possess cytoprotective properties, enhances survival of grafted cells and promotes neuroprotection in ischemic stroke. NSCs harvested from the subventricular zone of fetal rats were preconditioned with minocycline in vitro and transplanted into rat brains 6 h after transient middle cerebral artery occlusion. Histological and behavioral tests were examined from days 0–28 after stroke. For in vitro experiments, NSCs were subjected to oxygen-glucose deprivation and reoxygenation. Cell viability and antioxidant gene expression were analyzed. Minocycline preconditioning protected the grafted NSCs from ischemic reperfusion injury via up-regulation of Nrf2 and Nrf2-regulated antioxidant genes. Additionally, preconditioning with minocycline induced the NSCs to release paracrine factors, including brain-derived neurotrophic factor, nerve growth factor, glial cell-derived neurotrophic factor, and vascular endothelial growth factor. Moreover, transplantation of the minocycline-preconditioned NSCs significantly attenuated infarct size and improved neurological performance, compared with non-preconditioned NSCs. Minocycline-induced neuroprotection was abolished by transfecting the NSCs with Nrf2-small interfering RNA before transplantation. Thus, preconditioning with minocycline, which reprograms NSCs to tolerate oxidative stress after ischemic reperfusion injury and to express higher levels of paracrine factors through Nrf2 up-regulation, is a simple and safe approach to enhance the effectiveness of transplantation therapy in ischemic stroke.

Tumor angiogenesis is required for tumor development and is stimulated by angiogenic inducers like VEGF (vascular endothelial growth factor). Our previous study demonstrated that STAT3 (signal transducer and activator of transcription 3) up-regulates HIF-1alpha (hypoxia inducible factor-1alpha) protein stability and enhances HIF-1-mediated VEGF expression in hypoxic solid tumor cells, thus suggesting that the inhibition of STAT3 signaling may have clinical applications. In this study, we examined in vitro and in vivo, whether caffeic acid (CA) or its derivative CADPE [3-(3,4-dihydroxy-phenyl)-acrylic acid 2-(3,4-dihydroxy-phenyl)-ethyl ester] exert anticancer activity by targeting STAT3. It was found that CA or CADPE significantly inhibit STAT3 activity, and that this in turn down-regulates HIF-1alpha activity. Consequently, sequential blockade of STAT3 and HIF-1alpha resulted in the down-regulation of VEGF by inhibiting their recruitment to the VEGF promoter. In mice bearing a Caki-I carcinoma, both CA and CADPE retarded tumor growth and suppressed STAT3 phosphorylation, HIF-1alpha expression, vascularization and STAT3-inducible VEGF gene expression in tumors. Taken together, our results demonstrate that CA and CADPE are potential inhibitors of STAT3 and that they suppress tumor angiogenesis by inhibiting the activity of STAT3, the expression of HIF-1alpha and VEGF.