Gab Seok Kim

Stanford University, Stanford, CA, United States

Are you Gab Seok Kim?

Claim your profile

Publications (16)93.56 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Rosiglitazone, a synthetic peroxisome proliferator-activated receptor-γ (PPARγ) agonist, prevents cell death after cerebral ischemia in animal models, but the underlying mechanism has not been clarified. In this study, we examined how rosiglitazone protects neurons against ischemia. Mice treated with rosiglitazone were subjected to 60 minutes of focal ischemia followed by reperfusion. Rosiglitazone reduced infarct volume after ischemia and reperfusion. We show that this neuroprotective effect was reversed with a PPARγ antagonist. Western blot analysis showed a significant increase in expression of phosphorylated stress-activated protein kinases (c-Jun N-terminal kinase (JNK) and p38) in ischemic brain tissue. Rosiglitazone blocked this increase. Furthermore, we observed that rosiglitazone increased expression of the dual-specificity phosphatase 8 (DUSP8) protein and messenger RNA in ischemic brain tissue. Dual-specificity phosphatase 8 is a mitogen-activated protein kinase phosphatase that can dephosphorylate JNK and p38. Another key finding of the present study was that knockdown of DUSP8 in primary cultured cortical neurons that were subjected to oxygen-glucose deprivation diminished rosiglitazone's effect on downregulation of JNK phosphorylation. Thus, rosiglitazone's neuroprotective effect after ischemia is mediated by blocking JNK phosphorylation induced by ischemia via DUSP8 upregulation.Journal of Cerebral Blood Flow & Metabolism advance online publication, 3 October 2012; doi:10.1038/jcbfm.2012.138.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 10/2012; · 5.46 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 upregulation 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 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.
    Journal of Neuroscience 03/2012; 32(10):3462-73. · 6.91 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Oxidative stress and glucose affect the expression of various genes that contribute to both reactive oxygen species generation and antioxidant systems. However, systemic alteration of oxidative stress-related gene expression in normal brains and in brains with a high-glucose status after ischemic-reperfusion has not been explored. Using a polymerase chain reaction array system, we demonstrate that thioredoxin-interacting protein (Txnip) is induced by both oxidative stress and glucose. We found that Txnip mRNA is induced by ischemic-reperfusion injury and that Txnip is located in the cytoplasm of neurons. Moreover, in vitro oxygen-glucose deprivation (OGD) and subsequent reoxygenation without glucose and in vivo administration of 3-nitropropionic acid also promoted an increase in Txnip in a time-dependent manner, indicating that oxidative stress without glucose can induce Txnip expression in the brain. However, calcium channel blockers inhibit induction of Txnip after OGD and reoxygenation. Using the polymerase chain reaction array with ischemic and hyperglycemic-ischemic samples, we confirmed that enhanced expression of Txnip was observed in hyperglycemic-ischemic brains after middle cerebral artery occlusion. Finally, transfection of Txnip small interfering RNA into primary neurons reduced lactate dehydrogenase release after OGD and reoxygenation. This is the first report showing that Txnip expression is induced in neurons after oxidative or glucose stress under either ischemic or hyperglycemic-ischemic conditions, and that Txnip is proapoptotic under these conditions.
    Neurobiology of Disease 02/2012; 46(2):440-9. · 5.62 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Activation of the NADPH oxidase subunit, NOX2, and increased oxidative stress are associated with neuronal death after cerebral ischemia and reperfusion. Inhibition of NOX2 by casein kinase 2 (CK2) leads to neuronal survival, but the mechanism is unknown. In this study, we show that in copper/zinc-superoxide dismutase transgenic (SOD1 Tg) mice, degradation of CK2α and CK2α' and dephosphorylation of CK2β against oxidative stress were markedly reduced compared with wild-type (WT) mice that underwent middle cerebral artery occlusion. Inhibition of CK2 pharmacologically or by ischemic reperfusion facilitated accumulation of poly(ADP-ribose) polymers, the translocation of apoptosis-inducing factor (AIF), and cytochrome c release from mitochondria after ischemic injury. The eventual enhancement of CK2 inhibition under ischemic injury strongly increased 8-hydroxy-2'-deoxyguanosine and phosphorylation of H2A.X. Furthermore, CK2 inhibition by tetrabromocinnamic acid (TBCA) in SOD1 Tg and gp91 knockout (KO) mice after ischemia reperfusion induced less release of AIF and cytochrome c than in TBCA-treated WT mice. Inhibition of CK2 in gp91 KO mice subjected to ischemia reperfusion did not increase brain infarction compared with TBCA-treated WT mice. These results strongly suggest that NOX2 activation releases reactive oxygen species after CK2 inhibition, triggering release of apoptogenic factors from mitochondria and inducing DNA damage after ischemic brain injury.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 12/2011; 32(4):720-30. · 5.46 Impact Factor
  • Source
    Joo Eun Jung, Gab Seok Kim, Pak H Chan
    [Show abstract] [Hide abstract]
    ABSTRACT: Interleukin-6 (IL-6) has been shown to have a neuroprotective effect in brain ischemic injury. However, its molecular mechanisms are still poorly understood. In this study, we investigated the neuroprotective role of the IL-6 receptor (IL-6R) by IL-6 in the reactive oxygen species defense system after transient focal cerebral ischemia (tFCI). IL-6 was injected in mice before and after middle cerebral artery occlusion. Coimmunoprecipitation assays were performed for analysis of an IL-6R association after tFCI. Primary mouse cerebral cortical neurons were transfected with small interfering RNA probes targeted to IL-6Rα or gp130 and were used for chromatin-immunoprecipitation assay, luciferase promoter assay, and cell viability assay. Reduction in infarct volumes by IL-6 was measured after tFCI. IL-6R was disrupted through a disassembly between IL-6Rα and gp130 associated by protein oxidation after reperfusion after tFCI. This suppressed phosphorylation of signal transducer and activator of transcription 3 (STAT3) and finally induced neuronal cell death through a decrease in manganese-superoxide dismutase. However, IL-6 injections prevented disruption of IL-6R against reperfusion after tFCI, consequently restoring activity of STAT3 through recovery of the binding of STAT3 to gp130. Moreover, IL-6 injections restored the transcriptional activity of the manganese-superoxide dismutase promoter through recovery of the recruitment of STAT3 to the manganese-superoxide dismutase promoter and reduced infarct volume after tFCI. This study demonstrates that IL-6 has a neuroprotective effect against cerebral ischemic injury through IL-6R-mediated STAT3 activation and manganese-superoxide dismutase expression.
    Stroke 09/2011; 42(12):3574-9. · 6.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Antioxidants & Redox Signaling 04/2011; 14(8):1505-17. · 8.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Medium spiny neurons (MSNs) constitute most of the striatal neurons and are known to be vulnerable to ischemia; however, the mechanisms of the vulnerability remain unclear. Activated forms of nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase (NOX), which require interaction between cytosolic and membrane-bound subunits, are among the major sources of superoxide in the central nervous system. Although increasing evidence suggests that NOX has important roles in neurodegenerative diseases, its roles in MSN injury after transient global cerebral ischemia (tGCI) have not been elucidated. To clarify this issue, C57BL/6 mice were subjected to tGCI by bilateral common carotid artery occlusion for 22 minutes. Western blot analysis revealed upregulation of NOX subunits and recruitment of cytosolic subunits to the cell membrane at early (3 to 6 hours) and late (72 hours) phases after tGCI. Taken together with immunofluorescent studies, this activation arose in MSNs and endothelial cells at the early phase, and in reactive microglia at the late phase. Pharmacological and genetic inhibition of NOX attenuated oxidative injury, microglial activation, and MSN death after tGCI. These findings suggest that NOX has pivotal roles in MSN injury after tGCI and could be a therapeutic target for brain ischemia.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 03/2011; 31(3):868-80. · 5.46 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is widely expressed in brain tissue including neurons, glia, and endothelia in neurovascular units. It is a major source of oxidants in the post-ischemic brain and significantly contributes to ischemic brain damage. Inflammation occurs after brain ischemia and is known to be associated with post-ischemic oxidative stress. Post-ischemic inflammation also causes progressive brain injury. In this study we investigated the role of NOX2 in post-ischemic cerebral inflammation using a transient middle cerebral artery occlusion model in mice. We demonstrate that mice with NOX2 subunit gp91(phox) knockout (gp91 KO) showed 35-44% less brain infarction at 1 and 3 days of reperfusion compared with wild-type (WT) mice. Minocycline further reduced brain damage in the gp91 KO mice at 3 days of reperfusion. The gp91 KO mice exhibited less severe post-ischemic inflammation in the brain, as evidenced by reduced microglial activation and decreased upregulation of inflammation mediators, including interleukin-1β (IL-1β), tumor necrosis factor-α, inducible nitric oxide synthases, CC-chemokine ligand 2, and CC-chemokine ligand 3. Finally, we demonstrated that an intraventricular injection of IL-1β enhanced ischemia- and reperfusion-mediated brain damage in the WT mice (double the infarction volume), whereas, it failed to aggravate brain infarction in the gp91 KO mice. Taken together, these results demonstrate the involvement of NOX2 in post-ischemic neuroinflammation and that NOX2 inhibition provides neuroprotection against inflammatory cytokine-mediated brain damage.
    Neurobiology of Disease 02/2011; 42(3):341-8. · 5.62 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The IkappaB kinase (IKK) complex is a central component in the classic activation of the nuclear factor-kappaB (NF-kappaB) pathway. It has been reported to function in physiologic responses, including cell death and inflammation. We have shown that IKK is regulated by oxidative status after transient focal cerebral ischemia (tFCI) in mice. However, the mechanism by which oxidative stress influences IKKs after tFCI is largely unknown. Nuclear accumulation and phosphorylation of IKKalpha (pIKKalpha) were observed 1 h after 30 mins of tFCI in mice. In copper/zinc-superoxide dismutase knockout mice, levels of NF-kappaB-inducing kinase (NIK) (an upstream kinase of IKKalpha), pIKKalpha, and phosphorylation of histone H3 (pH3) on Ser10 were increased after tFCI and were higher than in wild-type mice. Immunohistochemistry showed nuclear accumulation and pIKKalpha in mouse brain endothelial cells after tFCI. Nuclear factor-kappaB-inducing kinase was increased, and it enhanced pH3 by inducing pIKKalpha after oxygen-glucose deprivation (OGD) in mouse brain endothelial cells. Both NIK and pH3 interactions with IKKalpha were confirmed by coimmunoprecipitation. Treatment with IKKalpha small interfering RNA significantly reduced cell death after OGD. These results suggest that augmentation of NIK, IKKalpha, and pH3 in response to oxidative stress is involved in cell death after cerebral ischemia (or stroke).
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 07/2010; 30(7):1265-74. · 5.46 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Molecular Neurobiology 02/2010; 41(2-3):172-9. · 5.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: NADPH oxidase is a major complex that produces reactive oxygen species (ROSs) during the ischemic period and aggravates brain damage and cell death after ischemic injury. Although many approaches have been tested for preventing production of ROSs by NADPH oxidase in ischemic brain injury, the regulatory mechanisms of NADPH oxidase activity after cerebral ischemia are still unclear. In this study, we identified casein kinase 2 (CK2) as a critical modulator of NADPH oxidase and elucidated the role of CK2 as a neuroprotectant after oxidative insults to the brain. We found that the protein levels of the catalytic subunits CK2alpha and CK2alpha', as well as the total activity of CK2, are significantly reduced after transient focal cerebral ischemia (tFCI). We also found this deactivation of CK2 caused by ischemia/reperfusion increases expression of Nox2 and translocation of p67(phox) and Rac1 to the membrane after tFCI. Interestingly, we found that the inactive status of Rac1 was captured by the catalytic subunit CK2alpha under normal conditions. However, binding between CK2alpha and Rac1 was immediately diminished after tFCI, and Rac1 activity was markedly increased after CK2 inhibition. Moreover, we found that deactivation of CK2 in the mouse brain enhances production of ROSs and neuronal cell death via increased NADPH oxidase activity. The increased brain infarct volume caused by CK2 inhibition was restored by apocynin, a NADPH oxidase inhibitor. This study suggests that CK2 can be a direct molecular target for modulation of NADPH oxidase activity after ischemic brain injury.
    Journal of Neuroscience 11/2009; 29(47):14779-89. · 6.91 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Biochimica et Biophysica Acta 09/2009; 1802(1):92-9. · 4.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cerebral ischemia and reperfusion increase superoxide anions (O(2)(*-)) 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)(*-) 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)(*-) in mitochondria. The loss of STAT3 activity induced neuronal cell death by reducing Mn-SOD expression. Using SOD2-/+ 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.
    Journal of Neuroscience 06/2009; 29(21):7003-14. · 6.91 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The transient global ischemia model is used to analyze selective neuronal death in vulnerable regions including the CA1 subregion of the hippocampus and in certain cortical neurons. In this mouse global ischemia model, bilateral common carotid arteries are reversibly occluded, and the individual anatomical backgrounds are normalized by evaluating the patency of the posterior communicating artery. Using this evaluation, this model might be used for mouse strains with various genetic backgrounds.
    12/2008: pages 115-125;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Reactive oxygen species, derived from hypoxia and reoxygenation during transient focal cerebral ischemia (tFCI), are associated with the signaling pathway that leads to neuronal survival or death, depending on the severity and duration of the ischemic insult. The Akt survival signaling pathway is regulated by oxidative stress and is implicated in activation of nuclear factor-kappaB (NF-kappaB). Mild cerebral ischemia in mice was used to induce increased levels of Akt phosphorylation in the cortex and striatum. To clarify the role of Akt activation by NF-kappaB after tFCI, we injected the specific Akt inhibitor IV that inhibits Akt phosphorylation/activation. Inhibition of Akt phosphorylation induced decreases in sequential NF-kappaB signaling after 30 mins of tFCI at 1 h. Furthermore, the downstream survival signals of the Akt pathway were also decreased. Akt inhibitor IV increased ischemic infarct volume and apoptotic-related DNA fragmentation. Superoxide production in the ischemic brains of mice pretreated with the Akt inhibitor was higher than in vehicle-treated mice. In addition, those pretreated mice showed a reduction of approximately 33% in copper/zinc-superoxide dismutase expression. We propose that Akt signaling exerts its neuroprotective role by NF-kappaB activation in oxidative cerebral ischemia in mice.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 12/2008; 28(12):1917-26. · 5.46 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A brief period of global brain ischemia, such as that induced by cardiac arrest or cardiopulmonary bypass surgery, causes cell death in vulnerable hippocampal CA1 pyramidal neurons days after reperfusion. Although numerous factors have been suggested to account for this phenomenon, the mechanisms underlying it are poorly understood. We describe a cell death signal called the PIDDosome, a protein complex of p53-induced protein with a death domain (PIDD), receptor-interacting protein-associated ICH-1/CED-3 homologous protein with a death domain (RAIDD), and procaspase-2. We induced 5 min of transient global cerebral ischemia (tGCI) using bilateral common carotid artery occlusion with hypotension. Western blot analysis showed that expression of twice-cleaved fragment of PIDD (PIDD-CC) increased in the cytosolic fraction of the hippocampal CA1 subregion and preceded procaspase-2 activation after tGCI. Caspase-2 cleaved Bid in brain homogenates. Co-immunoprecipitation and immunofluorescent studies demonstrated that PIDD-CC, RAIDD, and procaspase-2 were co-localized and bound directly, which indicates the formation of the PIDD death domain complex. Furthermore, we tested inhibition of PIDD expression by using small interfering RNA (siRNA) treatment that was initiated 48 h before tGCI. Administration of siRNA against PIDD decreased not only expression of PIDD-CC, but also activation of procaspase-2 and Bid, resulting in a decrease in histological neuronal damage and DNA fragmentation in the hippocampal CA1 subregion after tGCI. These results imply that PIDD plays an important role in procaspase-2 activation and delayed CA1 neuronal death after tGCI. We propose that PIDD is a hypothetical molecular target for therapy against neuronal death after tGCI.
    Proceedings of the National Academy of Sciences 11/2008; 105(42):16368-73. · 9.81 Impact Factor

Publication Stats

453 Citations
93.56 Total Impact Points

Institutions

  • 2008–2012
    • Stanford University
      • • Department of Neurology and Neurological Sciences
      • • Department of Neurosurgery
      Stanford, CA, United States
    • Stanford Medicine
      • Department of Neurosurgery
      Stanford, California, United States