The cytoplasmic nuclear shuttling of Beclin 1 in neurons with Alzheimer's disease-like injury.

The abnormal expression of the autophagy-related protein Beclin 1 has been implicated in Alzheimer's disease (AD) brains, whereas the precise involvement of Caspase-mediated Beclin 1 cleavage in AD neurons has not yet been fully clarified. In this study, we investigated the distribution of Beclin 1 fragments in neurons with AD-like injury. Our results demonstrated that Beclin 1 was expressed in neurons but not in astrocytes in both neuron-glia co-cultures and in cortical tissue slices. The full length and C-terminal fragments of human Beclin 1 was mainly expressed in cytoplasm, while the N-terminal fragment of Beclin 1 was predominantly localized in nucleus. Compared to amyloid-ß (Aß)42-1 treatment control, exposure of PC12 cells or cortical neurons to Aß1-42 resulted in cell injury, with the appearance of neuritic shortening, reduced nuclear diameter in PC12 cells, beading formation and fragmentation in cortical neurons. A partial nuclear translocation of Beclin 1 was detected in cells incubated with Aß1-42, which could be inhibited by the administration of pan-Caspase inhibitor or Caspase 3 specific inhibitor. Moreover, Beclin 1 mutation at 146/149 sites was resistant to Aß1-42-induced nuclear translocation. The nuclear translocation of Beclin 1 could also been detected in the brains of 12-month-old APPSwe/PS1dE9 transgenic mice. Our findings suggest that after Caspase 3-mediated Beclin 1 cleavage at 146/149 sites, the N-terminal fragments of Beclin 1 may partially translocate into nuclei in neurons subjected to AD-like injury.

Involvement of cysteinyl leukotriene signaling in microglial morphological changes and CASP1 expression in vitro / 中国药理学与毒理学杂志

OBJECTIVE We have recently reported that cysteinyl leukotriene (CysLT) signaling plays an important role in microglial interleukin (IL)-1β secretion and subsequent neurotoxicity. The present study aimed to examine microglial morphological changes and the upstream molecular underlying IL-1βproduction in CysLT receptor agonist leukotriene D4 (LTD4)-treated BV2 microglia in vitro. METHODS Twenty-four hours after murine microglial BV2 cells were stimulated with LTD4 (1-100 nmol·L- 1), the cell proliferation and morphology were observed. The expression level of cysteinyl aspartate-specific protease 1 (CASP1) protein was measured by Western blotin BV2 cells. In addition, BV2 cells were pretreated with or without CysLT1 receptor antagonist montelukast for 1 h and the effects of monte-lukaston LTD4-stimulated microglial activation and CASP1 expression were evaluated. RESULTS The number of BV2 cells had an increasing tendency after 24 h treatment with LTD4, but no significant differences were observed between the control and LTD4-treated cells (P>0.05). Under basal and resting conditions, BV2 microglial cells displayed a ramified morphology. However, LTD4 at 100 nmool · L- 1 drove microglial morphological changes from a ramified towards an amoeboid shape. The expression of CASP1 protein was significantly upregulated in 100 nmool·L-1 LTD4-treated BV2 microglia (P<0.01). Furthermore, pretreatment with CysLT1 receptor antagonist montelukast prevented cell morphological changes and suppressed the increased CASP1 expression in LTD4-treated BV2 cells (P<0.05). CONCLUSION CysLT receptor agonist LTD4 induces morphological changes and CASP1 expressionin BV2 microglia, which can be inhibited by CysLT1 antagonist. These results suggest the involvement of CysLT signaling in microglial morphological changes and CASP1 expression.

[Zileuton, a 5-lipoxygenase inhibitor, attenuates mouse microglial cell-mediated rotenone toxicity in PC12 cells].

OBJECTIVE: To examine the effect of a selective inhibitor of 5-lipoxygenase (5-LOX) zileuton on microglia-mediated rotenone neurotoxicity. METHODS: The supernatant from different concentrations of rotenone-stimulated mouse microglia BV2 cells was used as the conditioned media (CM) for PC12 cells. The viability of PC12 cells was determined by MTT assay and lactate dehydrogenase (LDH) release. Cell death was observed by LDH release and double fluorescence staining with Hoechst/propidiumiodide (PI). The effect of zileuton on microglia-mediated rotenone toxicity was evaluated by the above methods. RESULTS: Rotenone at 1-10 nmol/L was nontoxic to PC12 cells directly. However, the CM from BV2 cells that were treated with rotenone (1-10 nmol/L) resulted in toxicity of PC12 cells. The BV2 CM which stimulated with rotenone (1-10 nmol/L) induced morphological changes, reduced cell viability, and increased LDH release and cell necrosis in PC12 cells. Pretreatment of BV2 cells with the 5-LOX inhibitor zileuton (0.01-1 µmol/L) protected PC12 cells from the microglia-mediated rotenone toxicity. CONCLUSION: The 5-LOX inhibitor zileuton effectively attenuates microglia-mediated rotenone toxicity in PC12 cells. These results suggest that 5-LOX pathway may be involved in neuronal death induced by microglial inflammation.

[5-lipoxygenase is involved in rotenone-induced injury in PC12 cells].

OBJECTIVE: To determine whether 5-lipoxygenase (5-LOX) is involved in rotenone-induced injury in PC12 cells, which is a cell model of Parkinson disease. METHODS: After rotenone treatment for various durations, cell viability was determined by colorimetric MTT reduction assay, and 5-LOX translocation was detected by immunocytochemistry. The effect of 5-LOX inhibitor zileuton was also investigated. RESULT: Rotenone (0.3-30 µmol/L) induced PC12 cell injury, and zileuton (3-100 µmol/L) attenuated this injury. Rotenone also time-and concentration-dependently induced 5-LOX translocation into the nuclear envelope, and zileuton (1-30 µmo/L) significantly inhibited rotenone-induced 5-LOX translocation. CONCLUSION: 5-LOX is involved in rotenone-induced injury in PC12 cells, and 5-LOX inhibitor zileuton can reduce rotenone-induced 5-LOX activation and cell injury.

Baicalin attenuates oxygen-glucose deprivation-induced injury by inhibiting oxidative stress-mediated 5-lipoxygenase activation in PC12 cells.

AIM: To determine whether the flavonoid baicalin attenuates oxygen-glucose deprivation (OGD)-induced injury by inhibiting oxidative stress-mediated 5-lipoxygenase (5-LOX) activation in PC12 cells. METHODS: The effects of baicalin and the 5-LOX inhibitor zileuton on the changes induced by OGD/recovery or H(2)O(2) (an exogenous reactive oxygen species [ROS]) in green fluorescent protein-5-LOX-transfected PC12 cells were compared. RESULTS: Both baicalin and zileuton attenuated OGD/recovery- and H(2)O(2)-induced injury and inhibited OGD/recovery-induced production of 5-LOX metabolites (cysteinyl leukotrienes) in a concentration-dependent manner. However, baicalin did not reduce baseline cysteinyl leukotriene levels. Baicalin also reduced OGD/recovery-induced ROS production and inhibited 5-LOX translocation to the nuclear envelope and p38 phosphorylation induced by OGD/recovery and H(2)O(2). In contrast, zileuton did not show these effects. CONCLUSION: Baicalin can inhibit 5-LOX activation after ischemic injury, which may partly result from inhibition of the ROS/p38 mitogen-activated protein kinase pathway.

Pranlukast attenuates ischemia-like injury in endothelial cells via inhibiting reactive oxygen species production and nuclear factor-kappaB activation.

The anti-inflammatory effects of pranlukast, an antagonist of cysteinyl leukotriene receptor 1, may be rendered not only by antileukotriene activity but also by other pharmacological activities. Previous studies indicate that pranlukast reduces ischemic tissue injury partially through decreasing vascular permeability, but its effect on ischemic injury in endothelial cells is not known. Thus, in this study, we investigated the effect of pranlukast on ischemia-like injury induced by oxygen-glucose deprivation (OGD) in EA.hy926 cells, a human endothelial cell line, and the possible mechanisms. We found that cell viability was reduced, lactate dehydrogenase release was increased 4-8 hours after OGD, and necrosis was induced 8 hours after OGD. Production of reactive oxygen species (ROS) increased by 211%, 176%, and 128%, respectively, 0.5, 1, and 2 hours after OGD. Nuclear factor-kappaB (NF-kappaB) was translocated to the nuclei 4-8 hours after OGD. Pranlukast ameliorated the reduced viability, the increased lactate dehydrogenase release, and necrosis after OGD. It also reduced ROS production and inhibited NF-kappaB nuclear translocation after OGD. The ROS scavenger, edaravone, inhibited OGD-induced nuclear translocation of NF-kappaB as well. Edaravone and pyrrolidine dithiocarbamate (a specific NF-kappaB inhibitor) protected endothelial cells from the OGD-induced injury. However, zileuton, a 5-lipoxygenase inhibitor, did not affect the cell injury, ROS production, and NF-kappaB nuclear translocation after OGD. The exogenous leukotriene D4 did not induce cell injury, ROS production, and NF-kappaB translocation. Thus, we conclude that pranlukast protects endothelial cells from ischemia-like injury via decreasing ROS production and inhibiting NF-kappaB activation, which is leukotriene independent.

Oxygen-glucose deprivation activates 5-lipoxygenase mediated by oxidative stress through the p38 mitogen-activated protein kinase pathway in PC12 cells.

5-Lipoxygenase (5-LOX) is a key enzyme catalyzing arachidonic acid to form leukotrienes. We have reported that ischemic-like injury activates 5-LOX in PC12 cells; however, the mechanisms are unknown. To determine whether ischemic-like injury activates 5-LOX mediated by oxidative stress through the p38 MAPK pathway, we transfected GFP-5-LOX into PC12 cells and induced ischemic-like injury by oxygen-glucose deprivation (OGD). We found that the transfected GFP-5-LOX was localized primarily in the nuclei and translocated to the nuclear envelope after OGD/recovery reaching a maximum 2 hr after a 2-hr exposure to OGD. The nonselective 5-LOX inhibitor caffeic acid, 5-LOX-activating protein inhibitor MK886, and selective 5-LOX inhibitor zileuton attenuated the cell injury and reduced the production of 5-LOX products, cysteinyl leukotrienes, after OGD/recovery. However, only caffeic acid inhibited OGD/recovery-induced 5-LOX translocation. OGD/recovery also increased reactive oxygen species (ROS), which was inhibited by caffeic acid only. Hydrogen peroxide, an exogenous ROS, evoked similar cell injury and 5-LOX translocation, and the inhibitors had effects on the changes after H(2)O(2) similar to those after OGD/recovery. Both OGD/recovery and H(2)O(2) increased the phosphorylated p38 MAPK level, which was inhibited by caffeic acid and the ROS scavenger edaravone, but not by MK886 or zileuton. Moreover, SB203580 (a p38 MAPK inhibitor) and edaravone inhibited the cell injury and 5-LOX translocation induced by OGD/recovery and H(2)O(2). Thus, we conclude that OGD/recovery-induced ischemic-like injury induces 5-LOX activation, which is mediated by oxidative stress through activating the p38 MAPK pathway.

Dihydroartemisinin potentiates the cytotoxic effect of temozolomide in rat C6 glioma cells.

Gliomas are the most common primary brain tumor in adults, but the efficacy of chemotherapy is limited. Artemisinin and its analogs, such as dihydroartemisinin (DHA), can kill cancer cells via generating free radicals. In the present study, we determined whether DHA at low concentrations potentiates the cytotoxic effect of temozolomide in rat glioma C6 cells. We found that the IC50 values of DHA and temozolomide for cell viability were 23.4 and 560 micromol/l, respectively. The cytotoxic effect of temozolomide was enhanced by 177% at a nontoxic DHA concentration (1 micromol/l), and by 321% at a low-toxic DHA concentration (5 micromol/l). DHA substantially increased temozolomide-induced apoptosis and necrosis. The generation of intracellular reactive oxygen species (ROS) was increased by temozolomide combined with DHA at noneffective concentrations of both agents. Edaravone (20 micromol/l), a ROS scavenger, reversed the effects of temozolomide/DHA on both ROS generation and cell viability reduction. These results indicate that DHA at low concentrations potentiates the cytotoxic effects of temozolomide in C6 cells partly via generating ROS, suggesting a beneficial combination for the chemotherapy of gliomas.

Activation of CysLT receptors induces astrocyte proliferation and death after oxygen-glucose deprivation.

We recently found that 5-lipoxygenase (5-LOX) is activated to produce cysteinyl leukotrienes (CysLTs), and CysLTs may cause neuronal injury and astrocytosis through activation of CysLT(1) and CysLT(2) receptors in the brain after focal cerebral ischemia. However, the property of astrocyte responses to in vitro ischemic injury is not clear; whether 5-LOX, CysLTs, and their receptors are also involved in the responses of ischemic astrocytes remains unknown. In the present study, we performed oxygen-glucose deprivation (OGD) followed by recovery to induce ischemic-like injury in the cultured rat astrocytes. We found that 1-h OGD did not injure astrocytes (sub-lethal OGD) but induced astrocyte proliferation 48 and 72 h after recovery; whereas 4-h OGD moderately injured the cells (moderate OGD) and led to death 24-72 h after recovery. Inhibition of phospholipase A(2) and 5-LOX attenuated both the proliferation and death. Sub-lethal and moderate OGD enhanced the production of CysLTs that was inhibited by 5-LOX inhibitors. Sub-lethal OGD increased the expressions of CysLT(1) receptor mRNA and protein, while moderate OGD induced the expression of CysLT(2) receptor mRNA. Exogenously applied leukotriene D(4) (LTD(4)) induced astrocyte proliferation at 1-10 nM and astrocyte death at 100-1,000 nM. The CysLT(1) receptor antagonist montelukast attenuated astrocyte proliferation, the CysLT(2) receptor antagonist BAY cysLT2 reversed astrocyte death, and the dual CysLT receptor antagonist BAY u9773 exhibited both effects. In addition, LTD(4) (100 nM) increased the expression of CysLT(2) receptor mRNA. Thus, in vitro ischemia activates astrocyte 5-LOX to produce CysLTs, and CysLTs result in CysLT(1) receptor-mediated proliferation and CysLT(2) receptor-mediated death.

[Transfection with 5-lipoxygenase/green fluorescence protein for evaluating injury-induced 5-lipoxygenase translocation to the nuclear membrane in PC12 cells].

OBJECTIVE: To evaluate the translocation of 5-lipoxygenase (5-LOX)) after injuries by transfection with green fluorescence protein (GFP)/5-LOX in PC12 cells. METHODS: PC12 cells were stably transfected with pEGFP-C2/5-LOX (GFP/5-LOX) or pEGFP-C2 vectors (control). After treatment with oxygen-glucose deprivation (OGD), H(2)O(2) or NMDA, GFP/5-LOX localization in the cells was observed under a fluorescence microscope. Wild-type 5-LOX was determined by immunostaining after the treatment. RESULT: In the GFP/5-LOX-transfected cells, GFP/5-LOX was primarily localized in the nucleus; while in the GFP-transfected cells, GFP was localized in both the cytoplasm and nucleus. After OGD and H(2)O(2) treatments, GFP/5-LOX was translocated to the nuclear membrane in 50.6 % and 57.7% cells respectively. However, after NMDA treatment or in GFP-transfected cells, no translocation was observed. Wild-type 5-LOX was distributed in the nuclei and cytoplasm, and all the 3 treatments induced 5-LOX translocation to the nuclear membrane. CONCLUSION: In the PC12 cells stably transfected with GFP/5-LOX, GFP/5-LOX is primarily distributed in the nuclei; the OGD-, H(2)O(2)- and NMDA-induced 5-LOX translocation exhibits different properties.

Distinct roles of CysLT1 and CysLT2 receptors in oxygen glucose deprivation-induced PC12 cell death.

Cysteinyl leukotrienes are involved in ischemic brain injury, and their receptors (CysLT(1) and CysLT(2)) have been cloned. To clarify which subtype mediates the ischemic neuronal injury, we performed permanent transfection to increase CysLT(1) and CysLT(2) receptor expressions in PC12 cells. Oxygen glucose deprivation (OGD)-induced cell death was detected by Hoechst 33258 and propidium iodide fluorescent staining as well as by flow cytometry. OGD induced late phase apoptosis mainly and necrosis minimally. Over-expression of CysLT(1) receptor decreased and over-expression of CysLT(2) receptor increased OGD-induced cell death. An agonist LTD(4) (10(-7)M) also induced apoptosis, especially in CysLT(2) receptor over-expressing cells. A selective CysLT(1) receptor antagonist montelukast did not affect OGD-induced apoptosis; while non-selective CysLT receptor antagonist Bay u9773 inhibited OGD-induced apoptosis, especially in CysLT(2) receptor over-expressing cells. Thus, CysLT(1) and CysLT(2) receptors play distinct roles in OGD-induced PC12 cell death; CysLT(1) attenuates while CysLT(2) facilitates the cell death.