Abstract WP165: Prevention of JNK Phosphorylation and Activation of Dual Specificity Phosphatase as a Mechanism for Rosiglitazone in Neuroprotection after Transient Cerebral Ischemia

Rosiglitazone, a synthetic peroxisome proliferator-activated receptor-γ (PPAR γ) agonist, prevents cell death after cerebral ischemia in animal models, but the underlying mechanism has not been clarified. 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 found that this neuroprotective effect was reversed with a PPAR γ 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, especially in the cortex area after early reperfusion (3 hr). Rosiglitazone blocked this increase of phosphorylation which caused cell death signaling activation. Furthermore, we observed that rosiglitazone increased expression of the dual-specificity phosphatase 8 (DUSP8) protein and mRNA in ischemic brain tissue. DUSP8 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.

Release of mitochondrial apoptogenic factors and cell death are mediated by CK2 and NADPH oxidase

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.

Oxidative stress in ischemic brain damage: mechanisms of cell death and potential molecular targets for neuroprotection

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.

Consistent injury to medium spiny neurons and white matter in the mouse striatum after prolonged transient global cerebral ischemia

A reproducible transient global cerebral ischemia (tGCI) mouse model has not been fully established. Although striatal neurons and white matter are recognized to be vulnerable to ischemia, their injury after tGCI in mice has not been elucidated. The purpose of this study was to evaluate injuries to striatal neurons and white matter after tGCI in C57BL/6 mice, and to develop a reproducible tGCI model. Male C57BL/6 mice were subjected to tGCI by bilateral common carotid artery occlusion (BCCAO). Mice whose cortical cerebral blood flow after BCCAO decreased to less than 13% of the pre-ischemic value were used. Histological analysis showed that at 3 days after 22 min of BCCAO, striatal neurons were injured more consistently than those in other brain regions. Quantitative analysis of cytochrome c release into the cytosol and DNA fragmentation in the striatum showed consistent injury to the striatum. Immunohistochemistry and Western blot analysis revealed that DARPP-32-positive medium spiny neurons, the majority of striatal neurons, were the most vulnerable among the striatal neuronal subpopulations. The striatum (especially medium spiny neurons) was susceptible to oxidative stress after tGCI, which is probably one of the mechanisms of vulnerability. SMI-32 immunostaining showed that white matter in the striatum was also consistently injured 3 days after 22 min of BCCAO. We thus suggest that this is a tGCI model using C57BL/6 mice that consistently produces neuronal and white matter injury in the striatum by a simple technique. This model can be highly applicable for elucidating molecular mechanisms in the brain after global ischemia.

NADPH oxidase mediates striatal neuronal injury after transient global cerebral ischemia

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.

NADPH oxidase is involved in post-ischemic brain inflammation

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.

Hemoglobin-induced oxidative stress contributes to matrix metalloproteinase activation and blood-brain barrier dysfunction in vivo

Hemoglobin (Hb) released from extravasated erythrocytes is implicated in brain edema after intracerebral hemorrhage (ICH). Hemoglobin is a major component of blood and a potent mediator of oxidative stress after ICH. Oxidative stress and matrix metalloproteinases (MMPs) are associated with blood-brain barrier (BBB) dysfunction. This study was designed to elucidate whether Hb-induced oxidative stress contributes to MMP-9 activation and BBB dysfunction in vivo. An intracerebral injection of Hb into rat striata induced increased hydroethidine (HEt) signals in parallel with MMP-9 levels. In situ gelatinolytic activity colocalized with oxidized HEt signals in vessel walls, accompanied by immunoglobulin G leakage and a decrease in immunoactivity of endothelial barrier antigen, a marker of endothelial integrity. Administration of a nonselective MMP inhibitor prevented MMP-9 levels and albumin leakage in injured striata. Moreover, reduction in oxidative stress by copper/zinc-superoxide dismutase (SOD1) overexpression reduced oxidative stress, MMP-9 levels, albumin leakage, and subsequent apoptosis compared with wild-type littermates. We speculate that Hb-induced oxidative stress may contribute to early BBB dysfunction and subsequent apoptosis, partly through MMP activation, and that SOD1 overexpression may reduce Hb-induced oxidative stress, BBB dysfunction, and apoptotic cell death.

Reperfusion and neurovascular dysfunction in stroke: from basic mechanisms to potential strategies for neuroprotection

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.

Mitochondrial and apoptotic neuronal death signaling pathways in cerebral ischemia

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.

Infantile gliosarcoma: a case and a review of the literature

INTRODUCTION

Gliosarcoma in infant is a very rare entity.

CASE REPORT

The authors present a case of gliosarcoma in a 23-month-old boy. The patient was admitted to our hospital with persistent headache and frequent vomiting. MR imaging demonstrated a large frontal well-circumscribed lesion with a heterogeneous gadolinium enhancement. Although macroscopically the tumor was totally extirpated, the boy died of rapid tumor regrowth 2 months after surgery. The surgical specimens obtained from the tumor showed an admixture of two distinctive neoplastic tissues. One was a malignant mesenchymal feature. Its fibrosarcomatous nature was characterized by spindle-shaped cells with fine fibers that were deeply stained in silver preparations for reticulin. The other was gliomatous tissue forming islands surrounded by the sarcomatous tissues. Its glioblastomatous nature was obvious, as it was characterized by endothelial proliferation and perinecrotic pseudopalisading. Both tissues were histologically malignant, as evidenced by mitotic figure, high cellularity, atypical features, and variability.

DISCUSSION

The literature concerning gliosarcomatous tumors is reviewed, and pathological and clinical features of the tumor are briefly discussed.

Surgical treatment of falcotentorial meningioma

Meningiomas arising from the falcotentorial junction are rare. Among our surgical experience of 375 meningiomas, only 4 cases of so-called falcotentorial meningiomas were encountered. We present these four surgical cases. An occipital transtentorial approach was used in three cases, and a combined midline occipital and suboccipital approach in one case. Total tumour excision was impossible in two cases because of engulfing deep venous structures including the great vein of Galen. Postoperative Gamma knife radiosurgery was performed in these two cases. On the other hand, a posteriorly located tumour was relatively easy to remove, and macroscopic total removal was accomplished. In conclusion, precise microvascular anatomical knowledge is indispensable to satisfactorily excise meningiomas in the falcotentorial area without significant morbidity.

[Primary central nervous system malignant lymphoma originating from the cerebellum and extending along the lower cranial nerves]

We report a case of primary central nervous system (CNS) malignant lymphoma of the central nervous system originating from the cerebellum and growing along the lower cranial nerves. A 67-year-old woman presented with hoarseness, vertigo, nausea, and vomiting. Gd-DTPA enhanced MRI showed a homogeneous enhanced mass lesion extending from the cerebellum to the medulla oblongata around the jugular foramen on the right side. Although pre- and intra-operative diagnosis had been schwannoma, histopathological examination revealed a B-cell, diffuse malignant lymphoma. The growth pattern of malignant lymphoma in the present case, which extended extra-axially, is considered to be rare. We discuss here the growth patterns and difficulties of diagnosis of primary CNS malignant lymphoma in this area.

[Brain abscess following thalamic hemorrhage: a case report]

Brain abscess following stroke is rare. We present a case of brain abscess which developed after hypertensive thalamic hemorrhage. A 51-year-old man had a left thalamic hemorrhage. Three months later, the patient was admitted to our hospital due to deterioration of right hemiparesis and motor aphasia. On admission, CT scan showed a ring-like high density area with peripheral edema in the left thalamus. T1-weighted magnetic resonance (MR) images revealed a large ring-enhanced lesion with surrounding edema in the same region. Laboratory examination demonstrated no signs of infectious disease. The patient's neurological state rapidly deteriorated 10 days after admission. Yellowish pus was aspirated during the emergent surgery. Bacteriological study of the pus revealed Staphylococcus Aureus. His symptoms improved after surgery followed by antibiotics therapy. The correct diagnosis prior to surgery was difficult in the present case because of lack of any signs of infection. Our case indicates that possibility of brain abscess should be taken into consideration as a rare differential diagnosis following intracerebral hemorrhage.

[Selective peripheral denervation for spasmodic torticollis involving the levator scapulae muscle]

Patients with laterocollis or rotatory type torticollis tend to show abnormal contraction of the levator scapulae muscle and the scalene muscles. These muscles are innervated from the anterior branches of the cervical spinal nerves. Because of this, the traditional Bertrand operation dealing with posterior branches does not adequately affect the symptoms of laterocollis. The authors report selective denervation of the levator scapulae muscle in three patients and discuss its rationale. All the three patients underwent denervation of both the C1-C6 posterior spinal rami and the branches from the C3 and C4 anterior rami to the levator scapulae muscle. We added myotomy of the scalene muscle in one patient, and denervation of the omohyoid muscle which is innervated from the ansa cervicalis and the descending branch of the hypoglossal nerve. The pre/post-operative Tsui scores were 12/4, 15/1, and 14/3 respectively. There were no complications. We conclude that selective peripheral denervation of the levator scapulae muscle is safe and effective in the treatment of laterocollic type torticollis.