IKK mediates ischemia-induced neuronal death

NF-kappaB in the nervous system

The transcription factor NF-kappaB has diverse functions in the nervous system, depending on the cellular context. NF-kappaB is constitutively activated in glutamatergic neurons. Knockout of p65 or inhibition of neuronal NF-kappaB by super-repressor IkappaB resulted in the loss of neuroprotection and defects in learning and memory. Similarly, p50-/- mice have a lower learning ability and are sensitive to neurotoxins. Activated NF-kappaB can be transported retrogradely from activated synapses to the nucleus to translate short-term processes to long-term changes such as axon growth, which is important for long-term memory. In glia, NF-kappaB is inducible and regulates inflammatory processes that exacerbate diseases such as autoimmune encephalomyelitis, ischemia, and Alzheimer's disease. In summary, inhibition of NF-kappaB in glia might ameliorate disease, whereas activation in neurons might enhance memory. This review focuses on results produced by the analysis of genetic models.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Functional testing in a mouse stroke model induced by occlusion of the distal middle cerebral artery

Reducing post-stroke disability is the major goal of stroke therapy. Consequently, functional testing is essential in experimental stroke studies to increase the predictive value of animal models. We used several sensory and motor tests to assess functional disability in a mouse model of permanent distal middle cerebral artery occlusion (pdMCAO) that induced mainly cortical infarcts. Gait dynamics were transiently disturbed after pdMCAO as measured by different analysis techniques. Stance and brake duration were shorter after pdMCAO. Consistent with sensory and motor deficits the latency to move was prolonged up to 14 days after pdMCAO and the performance in the corner test and handedness were affected on day 1 or 2 after pdMCAO. Heart rate was decreased and heart rate variability were increased after pdMCAO indicating sympathetic-parasympathetic imbalance. In summary, pdMCAO-induced cortical infarcts lead to clinically relevant sensory, motor and cardiac autonomic dysfunction in mice. The present study provides a basis to explore the potential of functional testing for neuroprotection and neuroregeneration after stroke.

TNFalpha promotes osteogenic differentiation of human mesenchymal stem cells by triggering the NF-kappaB signaling pathway

Mesenchymal stem cells are multipotent cells able to differentiate into different mesenchymal lineages. Studies in the past had suggested that two of these mesenchymal differentiation directions, the chondrogenic and the myogenic differentiation, are negatively regulated by the transcription factor NF-kappaB. Although osteogenic differentiation has been extensively studied, the influence of NF-kappaB on this differentiation lineage was not subject of detailed analyses in the past. We have analyzed the consequences of TNF-alpha treatment and genetic manipulation of the NF-kappaB pathway for osteogenic differentiation of hMSCs. Treatment of hMSCs during differentiation with TNF-alpha activates NF-kappaB and this results in enhanced expression of osteogenetic proteins like bone morphogenetic protein2 (BMP-2) and alkaline phosphatase (ALP). In addition, enhanced matrix mineralization was observed. The direct contribution of the NF-kappaB pathway was confirmed in cells that express a constitutively active version of the NF-kappaB-inducing kinase IKK2 (CA-IKK2). The IKK2/NF-kappaB-induced BMP-2 up-regulation results in the enhancement of RUNX2 and Osterix expression, two critical regulators of the osteogenic differentiation program. Interestingly, a genetic block of the NF-kappaB pathway did not interfere with osteogenic differentiation. We conclude that TNFalpha mediated NF-kappaB activation, although not absolutely required for BMP-2 expression and matrix mineralization nevertheless supports osteogenic differentiation and matrix mineralization by increasing BMP-2 expression. Our results therefore suggest that NF-kappaB activation may function in lineage selection during differentiation of hMSCs by fostering osteogenic differentiation at the expense of other differentiation lineages.

Inactivation of astroglial NF-kappa B promotes survival of retinal neurons following ischemic injury

Reactive astrocytes have been implicated in neuronal loss following ischemic stroke. However, the molecular mechanisms associated with this process are yet to be fully elucidated. In this work, we tested the hypothesis that astroglial NF-kappaB, a key regulator of inflammatory responses, is a contributor to neuronal death following ischemic injury. We compared neuronal survival in the ganglion cell layer (GCL) after retinal ischemia-reperfusion in wild-type (WT) and in GFAP-IkappaBalpha-dn transgenic mice, where the NF-kappaB classical pathway is suppressed specifically in astrocytes. The GFAP-IkappaBalpha-dn mice showed significantly increased survival of neurons in the GCL following ischemic injury as compared with WT littermates. Neuroprotection was associated with significantly reduced expression of pro-inflammatory genes, encoding Tnf-alpha, Ccl2 (Mcp1), Cxcl10 (IP10), Icam1, Vcam1, several subunits of NADPH oxidase and NO-synthase in the retinas of GFAP-IkappaBalpha-dn mice. These data suggest that certain NF-kappaB-regulated pro-inflammatory and redox-active pathways are central to glial neurotoxicity induced by ischemic injury. The inhibition of these pathways in astrocytes may represent a feasible neuroprotective strategy for retinal ischemia and stroke.

IKKalpha and IKKbeta regulation of DNA damage-induced cleavage of huntingtin

Background

Proteolysis of huntingtin (Htt) plays a key role in the pathogenesis of Huntington's disease (HD). However, the environmental cues and signaling pathways that regulate Htt proteolysis are poorly understood. One stimulus may be the DNA damage that accumulates in neurons over time, and the subsequent activation of signaling pathways such as those regulated by IκB kinase (IKK), which can influence neurodegeneration in HD.

Methodology/Principal Findings

We asked whether DNA damage induces the proteolysis of Htt and if activation of IKK plays a role. We report that treatment of neurons with the DNA damaging agent etoposide or γ-irradiation promotes cleavage of wild type (WT) and mutant Htt, generating N-terminal fragments of 80–90 kDa. This event requires IKKβ and is suppressed by IKKα. Elevated levels of IKKα, or inhibition of IKKβ expression by a specific small hairpin RNA (shRNA) or its activity by sodium salicylate, prevents Htt proteolysis and increases neuronal resistance to DNA damage. Moreover, IKKβ phosphorylates the anti-apoptotic protein Bcl-xL, a modification known to reduce Bcl-xL levels, and activates caspases that can cleave Htt. When IKKβ expression is blocked, etoposide treatment does not decrease Bcl-xL and activation of caspases is diminished. Similar to silencing of IKKβ, increasing the level of Bcl-xL in neurons prevents etoposide-induced caspase activation and Htt proteolysis.

Conclusions/Significance

These results indicate that DNA damage triggers cleavage of Htt and identify IKKβ as a prominent regulator. Moreover, IKKβ-dependent reduction of Bcl-xL is important in this process. Thus, inhibition of IKKβ may promote neuronal survival in HD as well as other DNA damage-induced neurodegenerative disorders.

Cooperation between molecular targets of costimulation in promoting T cell persistence and tumor regression

Costimulation regulates multiple cellular processes of T cells inducing proliferation, expansion, and survival. The molecular targets of costimulation might then be useful to augment T cell activities. Two defined targets of costimulatory signals in primary T cells are the anti-apoptotic bcl-2 family molecule Bcl-x(L), and survivin, an inhibitor of apoptosis family member that might regulate both cell division and survival. However, the relative importance of, and relationship between, these molecules in primary T cells is not clear. To understand whether they have overlapping or cooperative functions, we used retrovirus-mediated transduction to introduce Bcl-x(L) and survivin separately, or together linked by a 2A picornavirus self-cleaving peptide, into Ag-responding CD8(+) T cells. We found that CD8(+) effector T cells expressing both Bcl-x(L) and survivin strongly expanded at an early stage and had a long-term survival advantage over cells transduced with either molecule alone. In vivo, with response to tumor-expressed Ag following adoptive T cell transfer, Ag-reactive CD8(+) T cells expressing both Bcl-x(L) and survivin displayed greatly enhanced tumor protective activity compared with CD8(+) T cells expressing either molecule introduced separately. These results indicate that Bcl-x(L) and survivin can critically contribute in a cooperative, nonredundant manner to augment the accumulation and persistence of CD8(+) T cells following encounter with Ag. The data provide new insights into why costimulatory signals might need to be sustained over time and suggest a potential novel approach to augment cellular immunotherapy for cancer.

The I{kappa}B kinase {beta}/nuclear factor {kappa}B signaling pathway protects the heart from hemodynamic stress mediated by the regulation of manganese superoxide dismutase expression

Cardiomyocyte death plays an important role in the pathogenesis of heart failure. The nuclear factor (NF)-kappaB signaling pathway regulates cell death, however, the effect of NF-kappaB pathway on cell death can vary in different cells or stimuli. The purpose of the present study was to clarify the in vivo role of the NF-kappaB pathway in response to pressure overload. First, we subjected C57Bl6/J mice to pressure overload by means of transverse aortic constriction (TAC) and examined the activity of the NF-kappaB pathway in response to pressure overload. IkappaB kinase (IKK) and NF-kappaB were activated after TAC. Then, we investigated the role of the activation using cardiac-specific IKKbeta-deficient mice (CKO). CKO displayed normal global cardiac structure and function compared with control littermates. We subjected CKO and control mice to pressure overload. One week after TAC, CKO showed cardiac dilation, dysfunction, and lung congestion, which are characteristics of heart failure. The number of apoptotic cells in the hearts of CKO mice increased significantly after TAC. The levels of manganese superoxide dismutase mRNA and protein expression in CKO after TAC were significantly attenuated compared with control mice. The levels of oxidative stress and c-Jun N-terminal kinase (JNK) activation in CKO after TAC were significantly greater than those in control mice. Isoproterenol-induced cell death of isolated adult CKO cardiomyocytes was inhibited by treatment with either a manganese superoxide dismutase mimetic or a JNK inhibitor. Thus, the IKKbeta/NF-kappaB signaling pathway plays a protective role in cardiomyocytes because of the attenuation of oxidative stress and JNK activation in a setting of acute pressure overload.

Panax notoginseng Attenuates the Infarct Volume in Rat Ischemic Brain and the Inflammatory Response of Microglia

The roots of Panax notoginseng (PN) are commonly used as a therapeutic agent to stop hemorrhage and as a tonic to promote health in traditional Korean medicine. Stroke triggers an inflammatory response that not only plays a central role in the pathogenesis of cerebral ischemia, but also induces secondary damage. This study was designed to investigate the neuroprotective effects of the methanol extract of PN on the infarct volume induced by middle cerebral artery occlusion (MCAO) (90-min occlusion and 24-h reperfusion) in rat brains. The PN extract (50 mg/kg, i.p.) was administered 2 h after the onset of MCAO. The PN-treated groups had a reduction in infarct volume by 23.82 +/- 8.9%. In the PN extract-treated groups, the microglial density was significantly decreased in the peri-infarct region; the underlying mechanism was inhibition of inflammatory mediators, such as inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, via blocking of the NF-kappaB pathway. Furthermore, in vitro studies showed that the PN extract significantly reduced the production of iNOS-derived NO and COX-2-derived prostaglandin E(2) through the regulation of gene transcription levels in primary microglia and BV-2 cells. These results suggest that anti-inflammatory and microglial activation inhibitory effects of the PN extract may contribute to its neuroprotective effects in brain ischemia.

Network analysis of human glaucomatous optic nerve head astrocytes

Background

Astrocyte activation is a characteristic response to injury in the central nervous system, and can be either neurotoxic or neuroprotective, while the regulation of both roles remains elusive.

Methods

To decipher the regulatory elements controlling astrocyte-mediated neurotoxicity in glaucoma, we conducted a systems-level functional analysis of gene expression, proteomic and genetic data associated with reactive optic nerve head astrocytes (ONHAs).

Results

Our reconstruction of the molecular interactions affected by glaucoma revealed multi-domain biological networks controlling activation of ONHAs at the level of intercellular stimuli, intracellular signaling and core effectors. The analysis revealed that synergistic action of the transcription factors AP-1, vitamin D receptor and Nuclear Factor-kappaB in cross-activation of multiple pathways, including inflammatory cytokines, complement, clusterin, ephrins, and multiple metabolic pathways. We found that the products of over two thirds of genes linked to glaucoma by genetic analysis can be functionally interconnected into one epistatic network via experimentally-validated interactions. Finally, we built and analyzed an integrative disease pathology network from a combined set of genes revealed in genetic studies, genes differentially expressed in glaucoma and closely connected genes/proteins in the interactome.

Conclusion

Our results suggest several key biological network modules that are involved in regulating neurotoxicity of reactive astrocytes in glaucoma, and comprise potential targets for cell-based therapy.

NF-kappaB induces PGE2-synthesizing enzymes in neurons

The transcription factor NF-kappaB is activated in neurons and promotes neuronal death in cerebral ischemia. Its target genes include cytosolic phospholipase A-2 (cPLA-2), cyclooxygenase-2 (COX-2), and microsomal prostaglandin E(2) synthase-1 (mPGES-1), three genes that are involved in the synthesis of prostaglandin E(2) (PGE(2)). In our study, oxygen glucose deprivation (OGD), an in vitro model of cerebral ischemia, activated NF-kappaB activity in primary cortical neurons. Furthermore, OGD and the NF-kappaB activator tumor necrosis factor stimulated the expression of cPLA-2, cyclooxygenase-2 (COX-2), and mPGES-1 and increased the release of PGE(2) from neurons. Expression of a constitutively active IkappaB kinase (IKK) or the NF-kappaB subunit p65 in neurons stimulated the transcription of cPLA-2, COX-2, and mPGES-1. Finally, inhibition of IKK in neurons blocked the induction of the three genes involved in PGE(2) synthesis in vivo. In summary, NF-kappaB controls the neuronal expression of three genes involved in PGE(2) synthesis in cerebral ischemia.

IL-20 is regulated by hypoxia-inducible factor and up-regulated after experimental ischemic stroke

IL-20, an IL-10 family member, is involved in various inflammatory diseases, such as psoriasis, rheumatoid arthritis, and atherosclerosis. We investigated whether hypoxia in vitro and an in vivo model of ischemic stroke would up-regulate IL-20 expression. In vitro, IL-20 expression increased in hypoxic HaCaT, HEK293 cells, chondrocytes, monocytes, and glioblastoma cells. Inhibition of hypoxia-inducible factor 1alpha inhibited CoCl(2)-induced IL-20 expression. We identified two putative hypoxia response elements in the human il20 gene promoter. Promoter activity assays showed that CoCl(2) mimicked hypoxia-activated luciferase reporter gene expression. In vivo, experimental ischemic stroke up-regulated IL-20 in the sera and brain tissue of rats. IL-20 stained positively in glia-like cells in peri-infarcted lesions, but not in contralateral tissue. Administration of IL-20 mAb ameliorated ischemia-induced brain infarction of rats after experimental ischemic stroke. In vitro, RT-PCR analysis showed that glioblastoma cells, GBM8901, expressed IL-20 and its receptor subunits IL-20R1, IL-20R2, and IL-22R1. IL-20 induced cell proliferation in GBM8901 cells by activating the JAK2/STAT3 and ERK1/2 pathways. IL-20 also induced production of IL-1beta, IL-8, and MCP-1 in GBM8901 cells. We conclude that IL-20 was responsive to hypoxia in vitro and in the ischemic stroke model and that up-regulation of IL-20 in the ischemic brain may contribute to brain injury.

NF-kappaB p50/RelA and c-Rel-containing dimers: opposite regulators of neuron vulnerability to ischaemia

Diverse nuclear factor-kappaB subunits mediate opposite effects of extracellular signals on neuron survival. While RelA is activated by neurotoxic agents, c-Rel drives neuroprotective effects. In brain ischaemia RelA and p50 factors rapidly activate, but how they associate with c-Rel to form active dimers and contribute to the changes in diverse dimer activation for neuron susceptibility is unknown. We show that in both cortical neurons exposed to oxygen glucose deprivation (OGD) and mice subjected to brain ischaemia, activation of p50/RelA was associated with inhibition of c-Rel/RelA dimer and no change p50/c-Rel. Targeting c-Rel and RelA expression revealed that c-Rel dimers reduced while p50/RelA enhanced neuronal susceptibility to anoxia. Activation of p50/RelA complex is known to induce the pro-apoptotic Bim and Noxa genes. We now show that c-Rel-containing dimers, p50/c-Rel and RelA/c-Rel, but not p50/RelA, promoted Bcl-xL transcription. Accordingly, the OGD exposure induced Bim, but reduced Bcl-xL promoter activity and decreased the content of endogenous Bcl-xL protein. These findings demonstrate that within the same neuronal cell, the balance between activation of p50/RelA and c-Rel-containing complexes fine tunes the threshold of neuron vulnerability to the ischaemic insult. Selective targeting of different dimers will unravel new approaches to limit ischaemia-associated apoptosis.

p65 activity and ZAP-70 status predict the sensitivity of chronic lymphocytic leukemia cells to the selective IkappaB kinase inhibitor BMS-345541

PURPOSE

Constitutive nuclear factor-kappaB (NF-kappaB) activation has been implicated in the pathogenesis of chronic lymphocytic leukemia (CLL). Our purpose was to characterize the molecular mechanisms underlying for the selective IkappaB kinase inhibitor BMS-345541 in CLL cells together with the analysis of its combination with several antineoplasic drugs.

EXPERIMENTAL DESIGN

Primary cells from 34 CLL patients were incubated with different doses of BMS-345541. NF-kappaB DNA-binding activity was analyzed by ELISA-based kits and the characterization of the apoptotic pathway was done by flow cytometry, immunoblotting, quantitative reverse transcription-PCR, and immunofluorescence techniques.

RESULTS

BMS-345541 selectively induced apoptosis in CLL cells in the low micromolar range irrespective of p53 status. Noteworthy, the high ZAP-70 group was significantly more sensitive to BMS-345541 than the low ZAP-70 group, in correlation with high levels of p65 phosphorylation and DNA-binding activity. Following NF-kappaB inhibition, BMS-345541 led to induction of the mitochondrial apoptotic pathway and activation of both caspase-dependent and caspase-independent factors. Moreover, BMS-345541-induced apoptosis was accompanied by down-regulation of several antiapoptotic NF-kappaB-target genes, including both BCL2 family members and apoptotic endogenous inhibitors. In addition, we showed a strong synergism between BMS-345541 and conventional chemotherapeutics such as mitoxantrone and dexamethasone as well as with new promising drugs such as the BH3-mimetic GX15-070/Obatoclax or the anti-TRAIL-R1 monoclonal antibody mapatumumab.

CONCLUSIONS

These data confirm that NF-kappaB is a relevant target in CLL and indicate that inhibitors of IkappaB kinase, alone or in combination, represent a novel therapeutic strategy for the treatment of CLL patients, especially for the group with high ZAP-70.

Borna disease virus: a unique pathogen and its interaction with intracellular signalling pathways

Borna disease virus (BDV) is a neurotropic RNA virus that establishes non-cytolytic persistent infection in the central nervous system of warm-blooded animals. Depending on the host species and the route of infection, BDV persistence can modulate neuronal plasticity and animal behaviour and/or may provoke a T cell-mediated immunopathological reaction with high mortality. Therefore, BDV functions as a model pathogen to study persistent virus infection in the central nervous system. Here, we review recent evidence showing that BDV interferes with a spectrum of intracellular signalling pathways, which may be involved in viral spread, maintenance of persistence and modulation of neurotransmitter pathways.

Post-ischemic brain damage: NF-kappaB dimer heterogeneity as a molecular determinant of neuron vulnerability

Nuclear factor-kappaB (NF-kappaB) has been proposed to serve a dual function as a regulator of neuron survival in pathological conditions associated with neurodegeneration. NF-kappaB is a transcription family of factors comprising five different proteins, namely p50, RelA/p65, c-Rel, RelB and p52, which can combine differently to form active dimers in response to external stimuli. Recent research shows that diverse NF-kappaB dimers lead to cell death or cell survival in neurons exposed to ischemic injury. While the p50/p65 dimer participates in the pathogenesis of post-ischemic injury by inducing pro-apoptotic gene expression, c-Rel-containing dimers increase neuron resistance to ischemia by inducing anti-apoptotic gene transcription. We present, in this report, the latest findings and consider the therapeutic potential of targeting different NF-kappaB dimers to limit ischemia-associated neurodegeneration.

The HMGB1 receptor RAGE mediates ischemic brain damage

In ischemic stroke, the necrotic core is surrounded by a zone of inflammation, in which delayed cell death aggravates the initial insult. Here, we provide evidence that the receptor for advanced glycation end products (RAGE) functions as a sensor of necrotic cell death and contributes to inflammation and ischemic brain damage. The RAGE ligand high mobility group box 1 (HMGB1) was elevated in serum of stroke patients and was released from ischemic brain tissue in a mouse model of cerebral ischemia. A neutralizing anti-HMGB1 antibody and HMGB1 box A, an antagonist of HMGB1 at the receptor RAGE, ameliorated ischemic brain damage. Interestingly, genetic RAGE deficiency and the decoy receptor soluble RAGE reduced the infarct size. In vitro, expression of RAGE in (micro)glial cells mediated the toxic effect of HMGB1. Addition of macrophages to neural cultures further enhanced the toxic effect of HMGB1. To test whether immigrant macrophages in the ischemic brain mediate the RAGE effect, we generated chimeric mice by transplanting RAGE(-/-) bone marrow to wild-type mice. RAGE deficiency in bone marrow-derived cells significantly reduced the infarct size. Thus, HMGB1-RAGE signaling links necrosis with macrophage activation and may provide a target for anti-inflammatory therapy in stroke.

NF-kappaB dimers in the regulation of neuronal survival

Nuclear factor-kappaB (NF-kappaB) is a dimeric transcription factor composed of five members, p50, RelA/p65, c-Rel, RelB, and p52 that can diversely combine to form the active transcriptional dimer. NF-kappaB controls the expression of genes that regulate a broad range of biological processes in the central nervous system such as synaptic plasticity, neurogenesis, and differentiation. Although NF-kappaB is essential for neuron survival and its activation may protect neurons against oxidative-stresses or ischemia-induced neurodegeneration, NF-kappaB activation can contribute to inflammatory reactions and apoptotic cell death after brain injury and stroke. It was proposed that the death or survival of neurons might depend on the cell type and the timing of NF-kappaB activation. We here discuss recent evidence suggesting that within the same neuronal cell, activation of diverse NF-kappaB dimers drives opposite effects on neuronal survival. Unbalanced activation of NF-kappaB p50/RelA dimer over c-Rel-containing complexes contributes to cell death secondary to the ischemic insult. While p50/RelA acts as transcriptional inducer of Bcl-2 family proapoptotic Bim and Noxa genes, c-Rel dimers specifically promote transcription of antiapototic Bcl-xL gene. Changes in the nuclear content of c-Rel dimers strongly affect the threshold of neuron vulnerability to ischemic insult and agents, likewise leptin, activating a NF-kappaB/c-Rel-dependent transcription elicit neuroprotection in animal models of brain ischemia.

Observations on the function of nuclear factor kappa B (NF-kappaB) in the survival of adult primary sensory neurons after nerve injury

Peripheral nerve transections cause much more neuronal death in embryonic and neonatal dorsal root ganglia (DRG) than in adult DRG. Here we used transgenic approaches to examine the hypothesis that NF-kappaB is an important intrinsic factor of adult DRG neurons for their in vivo capacity to survive after nerve injury. We generated transgenic mice expressing the NF-kappaB super-inhibitor (IkappaBalpha-SI), a multi-mutant form of IkappaBalpha, specifically in adult neurons. Adult DRG neurons in these transgenic animals are not abnormally susceptible to apoptosis after peripheral nerve injury, although there is a significant inhibition in the ability of NF-kappaB to translocate into their nucleus. We investigated the observed lack of NF-kappaB neuroprotective function at the level of NF-kappaB transcriptional activity using transgenic NF-kappaB/LacZ reporter mice. We show that the expression of the NF-kappaB reporter transgene is restricted in naïve and injured DRG neurons. However, NF-kappaB transcriptional activity in adult DRG neurons is evident upon exposure to Trichostatin A (TSA) which is a specific inhibitor of histone deacetylases. Taken together our results illustrate that the functions of NF-kappaB are limited in adult primary sensory neurons due to a transcriptional repression mechanism mediated by histone deacetylases, and that intrinsic neuroprotective factors other than NF-kappaB are responsible for the resistance of adult DRG neurons to apoptosis in response to nerve injury.

Protective effect of Ginkgolids (A+B) is associated with inhibition of NIK/IKK/IkappaB/NF-kappaB signaling pathway in a rat model of permanent focal cerebral ischemia

BACKGROUND AND PURPOSE

We have previously reported that Ginkgolids which contain Ginkgolids A and B (Ginkgolids (A+B), GKAB) reduce infarct size in a rat model of focal ischemia. NF-kappaB-inducing kinase (NIK)-IkappaBalpha kinase (IKK) pathway plays an important role in activation of nuclear factor kappaB (NF-kappaB). A previous study demonstrated that Ginkgolid B inhibited lipopolysaccharide (LPS)- and platelet activating factor (PAF)-induced NF-kappaB activation in rat pleural polymorphonuclear granulocytes. However, little is known about the inhibitory mechanisms of Ginkgolids on the activation of NF-kappaB. The present study evaluated the effects of GKAB on NIK/IKK/IkappaB/NF-kappaB signaling pathway in a rat model of permanent focal cerebral ischemia.

METHODS

Rats were subjected to permanent middle cerebral artery occlusion (pMCAO) by intraluminal suture blockade. GKAB was injected intravenously (iv) immediately after ischemic onset. Western blot analysis was employed to determine alterations in IkappaBalpha, phosphorylated NIK (p-NIK) and phosphorylated IKKalpha (p-IKKalpha). Immunohistochemistry was used to confirm the nuclear translocation of NF-kappaB p65. RT-PCR was used to detect induction of NF-kappaB target gene c-Myc mRNA.

RESULTS

The results showed a brief increase in p-NIK levels after ischemia. GKAB blocked ischemia-induced increases in p-NIK and p-IKKalpha levels, and reversed the decline in IkappaBalpha levels. Ischemia-induced nuclear translocation of NF-kappaB p65 was attenuated by GKAB(.) GKAB also repressed the ischemia-induced increase in expression of NF-kappaB target gene c-Myc mRNA.

CONCLUSIONS

These findings suggest that GKAB-mediated neuroprotective effect against ischemia appears to be associated with blocking NF-kappaB activation by suppressing the NIK-IKK pathway.

Activation of NF-kappaB1 by OX40 contributes to antigen-driven T cell expansion and survival

The costimulatory molecule OX40 (CD134) is required in many instances for effective T cell-mediated immunity, controlling proliferation, and survival of T cells after encountering specific Ag. We previously found that the functional targets of OX40 are survivin and aurora B that regulate proliferation and Bcl-2 antiapoptotic family members that regulate survival. However, the intracellular pathways from OX40 that mediate these effects are unclear. In this study, we show that OX40 signaling can target the canonical NF-kappaB (NF-kappaB1) pathway in peripheral Ag-responding CD4 T cells. Phosphorylation of IkappaBalpha, nuclear translocation of NF-kappaB1/p50 and RelA, and NF-kappaB1 activity, are impaired in OX40-deficient T cells. Retroviral transduction of active IkappaB kinase that constitutively activates NF-kappaB1 rescues the poor expansion and survival of OX40-deficient T cells, directly correlating with increased expression and activity of survivin, aurora B, and Bcl-2 family members. Moreover, active IkappaB kinase expression alone is sufficient to restore the defective expansion and survival of OX40-deficient T cells in vivo when responding to Ag. Thus, OX40 signals regulate T cell number and viability through the NF-kappaB1 pathway that controls expression and activity of intracellular targets for proliferation and survival.

A dual role of the NF-kappaB pathway in neonatal hypoxic-ischemic brain damage

BACKGROUND AND PURPOSE

NF-kappaB is a transcription factor that regulates inflammatory and apoptotic pathways. We described previously that intraperitoneal administration of the NF-kappaB inhibitor TAT-NBD at 0 and 3 hours after neonatal hypoxia-ischemia (HI) markedly reduced brain damage. We hypothesize that timing and duration of NF-kappaB inhibition will be a major factor in determining outcome.

METHODS

HI was induced in P7 rats by unilateral carotid artery occlusion and hypoxia. In vivo TAT-NBD effects were determined on cerebral damage, NF-kappaB activity, cytokine expression, and pro- and antiapoptotic molecules. In vitro effects of TAT-NBD were determined using primary neurons and cell lines.

RESULTS

HI induced 2 peaks of cerebral NF-kappaB activity at 3 to 6 and 24 hours after HI. Neuroprotective 0/3-hour TAT-NBD treatment only inhibited early NF-kappaB activity. However, inhibition of both early and late NF-kappaB-activity by 0/6/12-hour TAT-NBD or only late NF-kappaB activity by 18/21-hour TAT-NBD aggravated damage. 0/6/12-hour TAT-NBD did not prevent HI-induced upregulation of cytokines at 24 hours after HI. Protective 0/3-hour TAT-NBD treatment prevented nuclear accumulation of p53 at 24 hours after HI. Nuclear p53 was not reduced after 0/6/12-hour TAT-NBD. Prolonged TAT-NBD increased the proapoptotic factor PUMA and reduced the antiapoptotic factors Bcl-2 and Bcl-xL. Also in neuronal cultures prolonged TAT-NBD exposure overruled protective short-term TAT-NBD treatment.

CONCLUSIONS

Early NF-kappaB activation contributes to neonatal HI brain damage. Late NF-kappaB provides endogenous neuroprotection and upregulates antiapoptotic molecules. Inhibition of early NF-kappaB activity is neuroprotective only when late NF-kappaB activity is maintained. Moreover, cerebral cytokine production can occur independently of NF-kappaB.

Strong neuroprotection by inhibition of NF-kappaB after neonatal hypoxia-ischemia involves apoptotic mechanisms but is independent of cytokines

BACKGROUND AND PURPOSE

Interactions between excitotoxic, inflammatory, and apoptotic pathways determine outcome in hypoxic-ischemic brain damage. The transcription factor NF-kappaB has been suggested to enhance brain damage via stimulation of cytokine production. There is also evidence that NF-kappaB activity is required for neuronal survival. We used the NF-kappaB inhibitor NBD, coupled to TAT to facilitate cerebral uptake, to determine the neuroprotective capacity of NF-kappaB inhibition in neonatal hypoxia-ischemia (HI) and to identify its contribution to cerebral inflammation and damage.

METHODS

Brain damage was induced in neonatal rats by unilateral carotid artery occlusion and hypoxia and analyzed immunohistochemically; NF-kappaB activity was analyzed by EMSA. We analyzed cytokine mRNA levels and activation of apoptotic pathways by Western blotting. In vitro effects of TAT-NBD were determined in a neuronal cell line.

RESULTS

Inhibition of cerebral NF-kappaB activity by TAT-NBD had a significant neuroprotective effect; brain damage was reduced by more than 80% with a therapeutic window of at least 6 hours. In contrast to earlier suggestions, the protective effect of TAT-NBD did not involve suppression of early cytokine upregulation after HI. Moreover, NF-kappaB inhibition prevented HI-induced upregulation and nuclear as well as mitochondrial accumulation of p53, prevented mitochondrial cytochrome-c release and activation of caspase-3. Finally, TAT-NBD could directly increase neuronal survival because TAT-NBD was sufficient to inhibit death in a neuronal cell line. A nonactive mutant peptide did not have any effect.

CONCLUSIONS

Inhibition of NF-kappaB has strong neuroprotective effects that involve downregulation of apoptotic molecules but are independent of inhibition of cytokine production.

IkappaB kinase beta (IKKbeta/IKK2/IKBKB)--a key molecule in signaling to the transcription factor NF-kappaB

IKKbeta/IKBKB (IkappaB kinase beta), also designated as IKK2, was named after its function of phosphorylating IkappaB molecules, the inhibitors of NF-kappaB transcription factors. The kinase activity of IKKbeta targets two adjacent serine residues of IkappaB leading to ubiquitination and proteasomal degradation of the inhibitor, followed by release and activation of NF-kappaB. Many signaling pathways that activate NF-kappaB converge at the level of IKKbeta. Examples of stimuli leading to IKKbeta and subsequent NF-kappaB activation include inflammatory cytokines (IL-1, TNFalpha), endotoxins (lipopolysaccharide), viral infection and double strand RNA as well as physical signals such as UV-irradiation. Transcription factors of the NF-kappaB protein family have a great variety of functions in regulating the immune system, cellular differentiation, survival and proliferation. NF-kappaB is an essential factor in acute as well as chronic inflammation, a pathological state which is either cause or co-factor in a great variety of diseases. Moreover, recent data suggest that many variants of cancer are characterized by elevated constitutive activity of NF-kappaB, which can act as a survival factor for malignant cells by its predominantly anti-apoptotic function. Given the tight regulation of NF-kappaB by IkappaB molecules and the central role of IKKbeta in phosphorylation and degradation of the inhibitor, IKKbeta is a very promising target for pharmaceutical substances aiming at interfering with NF-kappaB activation.

Improving outcome after stroke: overcoming the translational roadblock

Stroke poses a massive burden of disease, yet we have few effective therapies. The paucity of therapeutic options stands contrary to intensive research efforts. The failure of these past investments demands a thorough re-examination of the pathophysiology of ischaemic brain injury. Several critical areas hold the key to overcoming the translational roadblock: (1) vascular occlusion: current recanalization strategies have limited effectiveness and may have serious side effects; (2) complexity of stroke pathobiology: therapy must acknowledge the 'Janus-faced' nature of many stroke targets and must identify endogenous neuroprotective and repair mechanisms; (3) inflammation and brain-immune-system interaction: inflammation contributes to lesion expansion, but is also instrumental in lesion containment and repair; stroke outcome is modulated by the interaction of the injured brain with the immune system; (4) regeneration: the potential of the brain for reorganization, plasticity and repair after injury is much greater than previously thought; (5) confounding factors, long-term outcome and predictive modelling. These 5 areas are linked on all levels and therefore need to be tackled by an integrative approach and innovative therapeutic strategies.

Nuclear factor-kappaB activation and postischemic inflammation are suppressed in CD36-null mice after middle cerebral artery occlusion

CD36, a class-B scavenger receptor involved in multiple functions, including inflammatory signaling, may also contribute to ischemic brain injury through yet unidentified mechanisms. We investigated whether CD36 participates in the molecular events underlying the inflammatory reaction that accompanies cerebral ischemia and may contribute to the tissue damage. We found that activation of nuclear factor-kappaB, a transcription factor that coordinates postischemic gene expression, is attenuated in CD36-null mice subjected to middle cerebral artery occlusion. The infiltration of neutrophils and the glial reaction induced by cerebral ischemia were suppressed. Treatment with an inhibitor of inducible nitric oxide synthase, an enzyme that contributes to the tissue damage, reduced ischemic brain injury in wild-type mice, but not in CD36 nulls. In contrast to cerebral ischemia, the molecular and cellular inflammatory changes induced by intracerebroventricular injection of interleukin-1beta were not attenuated in CD36-null mice. The findings unveil a novel role of CD36 in early molecular events leading to nuclear factor-kappaB activation and postischemic inflammation. Inhibition of CD36 signaling may be a valuable therapeutic approach to counteract the deleterious effects of postischemic inflammation.

Targeting IKK2 by pharmacological inhibitor AS602868 prevents excitotoxic injury to neurons and oligodendrocytes

Among the diverse mechanisms involved in the pathophysiology of post-ischemic and post-traumatic injuries, excitotoxicity and nuclear factor-kappaB (NF-kappaB) activation through induction of IkappaB kinase (IKK) complex have a primary role. We investigated the effects of the selective inhibitor of the IKK2 subunit, the anilinopyrimidine derivative AS602868, on excitotoxic injury produced in rat organotypic hippocampal slices and cerebellar primary neurons. Brief exposure to N-methyl-D-aspartate (NMDA) induces astrocyte reactivity, neuron cell death and oligodendrocyte degeneration in hippocampal slices. Application of AS602868 elicited a long-lasting protection of both neurons and oligodendrocytes. Maximal effect was observed with prolonged application of the compound after NMDA exposure. Neuroprotection was also evident in primary cultures of cerebellar granule cells starting from 20 nM concentration. AS602868-elicited neuroprotection correlated with inhibition of NF-kappaB activity. Our results suggest that AS602868 may prove to be a valuable approach in treating neurodegeneration and demyelination associated with cerebral trauma and ischemia.

Dual roles of NF-kappaB in cell survival and implications of NF-kappaB inhibitors in neuroprotective therapy

NF-kappaB is a well-characterized transcription factor with multiple physiological and pathological functions. NF-kappaB plays important roles in the development and maturation of lymphoids, regulation of immune and inflammatory response, and cell death and survival. The influence of NF-kappaB on cell survival could be protective or destructive, depending on types, developmental stages of cells, and pathological conditions. The complexity of NF-kappaB in cell death and survival derives from its multiple roles in regulating the expression of a broad array of genes involved in promoting cell death and survival. The activation of NF-kappaB has been found in many neurological disorders, but its actual roles in pathogenesis are still being debated. Many compounds with neuroprotective actions are strongly associated with the inhibition of NF-kappaB, leading to speculation that blocking the pathological activation of NF-kappaB could offer neuroprotective effects in certain neurodegenerative conditions. This paper reviews the recent developments in understanding the dual roles of NF-kappaB in cell death and survival and explores its possible usefulness in treating neurological diseases. This paper will summarize the genes regulated by NF-kappaB that are involved in cell death and survival to elucidate why NF-kappaB promotes cell survival in some conditions while facilitating cell death in other conditions. This paper will also focus on the effects of various NF-kappaB inhibitors on neuroprotection in certain pathological conditions to speculate if NF-kappaB is a potential target for neuroprotective therapy.

Notch and NFkappaB signaling pathways: Do they collaborate in normal vertebrate brain development and function?

Both Notch and NFkappaB signaling pathways are well-known for regulating proliferation, differentiation and apoptosis. Recent studies have presented several lines of evidence supporting an integration of the Notch and NFkappaB signaling pathways in differentiation/maturation of a diverse range of cell types. It is notable that Notch and NFkappaB signaling pathways share many common features: (i) both are activated by common stimuli such as TNF-alpha and hypoxia, (ii) activated Notch (NICD) and NFkappaB mediate transcription by regulating corepressors such as SMRT/N-COR, and (iii) both regulate similar target genes such as Hes-1 and IkappaBalpha. This review expands on how the collaboration between these pathways may play an important role in the CNS. We will speculate on the mechanisms by which Notch and NFkappaB signaling may collaborate to regulate stem cell renewal and differentiation during brain development and function.

Oestrogen and progesterone reduce lipopolysaccharide-induced expression of tumour necrosis factor-alpha and interleukin-18 in midbrain astrocytes

Besides microglia, astrocytes exert an important regulatory function in the initiation and control of neuro-inflammatory processes in the central nervous system. Clinical and experimental data suggest that sex steroids are neuroprotective and that neurological/neurodegenerative disorders display sex-specific characteristics. Astroglia is known to respond to toxic stimuli by secretion of distinct pro-inflammatory/apoptotic cytokines. In the present study, we investigated the influence of oestrogen and progesterone on the expression of the cytokines tumour necrosis factor (TNF)-alpha and interleukin (IL)-18 in primary astrocytes obtained from neonatal mouse midbrain and cerebral cortex after the stimulation with lipopolysaccharides (LPS). LPS strongly induced the expression of TNF-alpha in astrocytes from both brain regions and IL-18 in those from midbrain. Oestrogen significantly attenuated LPS-induced TNF-alpha expression in the midbrain glia but not in the cortex glia. Combined treatment with oestrogen and progesterone together diminished LPS-induced IL-18 expression in the midbrain completely. Both steroid effects could be specifically antagonised by the steroid hormone receptor antagonists ICI 182 780 and mifepristone. We conclude that neuroprotective oestrogen and progesterone effects in the midbrain might be in part the consequence of a reduced pro-inflammatory response of astroglia.

Vascular endothelial cell-specific NF-kappaB suppression attenuates hypertension-induced renal damage

Nuclear factor kappa B (NF-kappaB) participates in hypertension-induced vascular and target-organ damage. We tested whether or not endothelial cell-specific NF-kappaB suppression would be ameliorative. We generated Cre/lox transgenic mice with endothelial cell-restricted NF-kappaB super-repressor IkappaBalphaDeltaN (Tie-1-DeltaN mice) overexpression. We confirmed cell-specific IkappaBalphaDeltaN expression and reduced NF-kappaB activity after TNF-alpha stimulation in primary endothelial cell culture. To induce hypertension with target-organ damage, we fed mice a high-salt diet and N(omega)-nitro-l-arginine-methyl-ester (L-NAME) and infused angiotensin (Ang) II. This treatment caused a 40-mm Hg blood pressure increase in both Tie-1-DeltaN and control mice. In contrast to control mice, Tie-1-DeltaN mice developed a milder renal injury, reduced inflammation, and less albuminuria. RT-PCR showed significantly reduced expression of the NF-kappaB targets VCAM-1 and ICAM-1, compared with control mice. Thus, the data demonstrate a causal link between endothelial NF-kappaB activation and hypertension-induced renal damage. We conclude that in vivo NF-kappaB suppression in endothelial cells stops a signaling cascade leading to reduced hypertension-induced renal damage despite high blood pressure.

Alteration of NF-kappaB activity leads to mitochondrial apoptosis after infection with pathological prion protein

Nuclear factor kappa B (NF-kappaB) is a key regulator of the immune response, but in almost the same manner it is involved in induction of inflammation, proliferation and regulation of apoptosis. In the central nervous system activated NF-kappaB plays a neuroprotective role. While in some neurodegenerative disorders the role of NF-kappaB is well characterized, there is poor knowledge on the role of NF-kappaB in prion disease. We found binding but no transcriptional activity of the transcription factor in vitro. Characterizing the mechanism of cell death after infection with pathological prion protein increased caspase-9 and caspase-3 activity was detected and the lack of NF-kappaB activity resulted in the inability to activate target genes that usually play an important role in neuroprotection. Additionally, we investigated the role of NF-kappaB after prion infection of Nfkb1(-/-), Nfkb2(-/-) and Bcl3(-/-) mice and central nervous system-specific p65-deleted mice revealing an accelerated prion disease in NF-kappaB2- and Bcl-3-deficient mice, which is in line with a reduced neuroprotective activity in prion infection. Based on our findings, we propose a model whereby the alteration of NF-kappaB activity at the early stages of infection with pathological prion protein leads to neuronal cell death mediated by mitochondrial apoptosis.

Hepatocyte-specific IKK gamma/NEMO expression determines the degree of liver injury

BACKGROUND & AIMS

NEMO is the regulatory subunit of the I kappa B kinase (IKK) complex and is involved in controlling nuclear factor kappaB (NF-kappaB) activation. NEMO knockout mice die during embryogenesis due to massive hepatocyte apoptosis. Here we investigated the role of NEMO-dependent signaling in hepatocytes during acute liver injury.

METHODS

We generated conditional hepatocyte-specific NEMO knockout mice using the loxP system with the Cre recombinase under the control of the albumin promoter (NEMODeltaLPC). In these mice, we studied mechanisms of tumor necrosis factor (TNF)- and ischemia/reperfusion-dependent liver cell damage.

RESULTS

In adult NEMODeltaLPC animals, NEMO is specifically deleted in hepatocytes and no differences in survival, growth, and fertility were found when compared with wild-type (NEMO(f/f)) mice. TNF stimulation of NEMODeltaLPC mice resulted in high serum transaminase levels and massive hepatocyte apoptosis, which were associated with lack of I kappa B alpha degradation, inhibition of NF-kappaB activation, and target gene transcription. Additionally, ischemia/reperfusion resulted in higher nonparenchymal cell-dependent induction of oxidative stress and stronger inflammation in NEMODeltaLPC mice. This led to massive hepatocyte apoptosis and death of the animals, while NEMO(f/f) mice survived with significantly lesser liver damage, showing mainly necrotic cell death. Thus, complete inhibition of NF-kappaB activation in hepatocytes, in contrast to attenuation in hepatocyte-specific IKK2(-/-) mice, determines the type of liver cell damage during ischemia/reperfusion injury and is associated with a poor prognosis.

CONCLUSIONS

Our results show that understanding of the fine tuning of NF-kappaB modulation during liver injury is essential to develop new therapeutic strategies.

Conditional mutant mice using tetracycline-controlled gene expression system in the brain

Generation of knockout mice with targeted mutations in desired genes is one of the most important technologies available for determining the functions of gene products in the brain. However, conventional knockout technology has limitations, such as when conventional knockout results in a lethal phenotype or when gene function at a certain developmental stage must be elucidated. To circumvent these limitations, a tetracycline-controlled gene expression system has been exploited to generate conditional mutant mice in which expression of desired genes can be switched on or off by oral administration of tetracycline derivatives. This up-date article introduces conditional mutant mice obtained using the tetracycline-controlled gene expression system, and presents several examples including our versatile mouse line, the mGluR1 conditional knockout mouse.

Activin is a neuronal survival factor that is rapidly increased after transient cerebral ischemia and hypoxia in mice

One approach for developing targeted stroke therapies is to identify the neuronal protective and destructive signaling pathways and gene expression that follow ischemic insult. In some neural injury models, the transforming growth factor-beta family member activin can provide neuroprotective effects in vivo and promote neuronal survival. This study tests if activin supports cortical neurons after ischemic challenge in vitro and if signals after cerebral ischemia involve activin in vivo. In a defined cell culture model that uses hydrogen peroxide (H(2)O(2))-free radical stress, activin addition maintained neuronal survival. H(2)O(2) treatment increased activin mRNA twofold in surviving cortical neurons, and inhibition of activin with neutralizing antibodies caused neuronal death. These data identify activin gene changes as a rapid response to oxidative stress, and indicate that endogenous activin acts as a protective factor for cortical neurons in vitro. Similarly, after transient focal cerebral ischemia in adult mice, activin mRNA increased at 1 and 4 h ipsilateral to the infarct but returned to control values at 24 h after reperfusion. Intracellular activated smad signals were detected in neurons adjacent to the infarct. Activin was also increased after 2 h of 11% hypoxia. Activin mRNA increased at 1 h but not 4 or 24 h after hypoxia, similar to the time course of erythropoietin and vascular endothelial growth factor induction. These findings identify activin as an early-regulated gene response to transient ischemia and hypoxia, and its function in cortical neuron survival during oxidative challenge provides a basis to test activin as a potential therapeutic in stroke injury.

Constitutive IKK2 activation in acinar cells is sufficient to induce pancreatitis in vivo

Activation of the inhibitor of NF-kappaB kinase/NF-kappaB (IKK/NF-kappaB) system and expression of proinflammatory mediators are major events in acute pancreatitis. However, the in vivo consequences of IKK activation on the onset and progression of acute pancreatitis remain unclear. Therefore, we modulated IKK activity conditionally in pancreatic acinar cells. Transgenic mice expressing the reverse tetracycline-responsive transactivator (rtTA) gene under the control of the rat elastase promoter were generated to mediate acinar cell-specific expression of IKK2 alleles. Expression of dominant-negative IKK2 ameliorated cerulein-induced pancreatitis but did not affect activation of trypsin, an initial event in experimental pancreatitis. Notably, expression of constitutively active IKK2 was sufficient to induce acute pancreatitis. This acinar cell-specific phenotype included edema, cellular infiltrates, necrosis, and elevation of serum lipase levels as well as pancreatic fibrosis. IKK2 activation caused increased expression of known NF-kappaB target genes, including mediators of the inflammatory response such as TNF-alpha and ICAM-1. Indeed, inhibition of TNF-alpha activity identified this cytokine as an important effector of IKK2-induced pancreatitis. Our data identify the IKK/NF-kappaB pathway in acinar cells as being key to the development of experimental pancreatitis and the major factor in the inflammatory response typical of this disease.

Identification of prothymosin-alpha1, the necrosis-apoptosis switch molecule in cortical neuronal cultures

We initially identified a nuclear protein, prothymosin-α1 (ProTα), as a key protein inhibiting necrosis by subjecting conditioned media from serum-free cultures of cortical neurons to a few chromatography steps. ProTα inhibited necrosis of cultured neurons by preventing rapid loss of cellular adenosine triphosphate levels by reversing the decreased membrane localization of glucose transporters but caused apoptosis through up-regulation of proapoptotic Bcl₂-family proteins. The apoptosis caused by ProTα was further inhibited by growth factors, including brain-derived neurotrophic factor. The ProTα-induced cell death mode switch from necrosis to apoptosis was also reproduced in experimental ischemia-reperfusion culture experiments, although the apoptosis level was markedly reduced, possibly because of the presence of growth factors in the reperfused serum. Knock down of PKCβ_II expression prevented this cell death mode switch. Collectively, these results suggest that ProTα is an extracellular signal protein that acts as a cell death mode switch and could be a promising candidate for preventing brain strokes with the help of known apoptosis inhibitors.

Transcriptional regulation of neurogenesis: potential mechanisms in cerebral ischemia

Recent data provides evidence that new neurons are born in cerebral ischemia. Although ultimate evidence for their functional importance is lacking, correlational data suggest that they contribute to recovery. Therefore, the underlying mechanisms of neurogenesis are interesting as a basis for pharmacological enhancement of the phenomenon. Neurogenesis is a multistep process that includes proliferation of precursor cells, migration of the newborn cells to the site of lesion, differentiation, integration into neuronal circuits, and survival. All these steps rely on gene transcription. However, only preliminary data about the specific transcriptional control of neurogenesis in cerebral ischemia have been obtained so far. To promote this investigation, we review currently available information on six pathways (Notch, Wnt/beta-catenin, NF-kappaB, signal transducers and activators of transcription (STA) 3, HIF-1, and cyclic AMP response element-binding protein [CREB]) that have been shown to regulate transcription in neurogenesis and that have been implicated in cerebral ischemia. With the exception of CREB, direct involvement in postischemic neurogenesis is quite conjectural and much more must be learned to draw practical conclusions.

Platelet-derived growth factor-mediated gliomagenesis and brain tumor recruitment

Platelet-derived growth factor (PDGF) is a growth factor family of ligands and receptors known to activate phosphatidylinositol 3-kinase, mitogen-activated protein kinase, Jak family kinase, Src family kinase, and phospholipase Cgamma signal transduction pathways, some of which have been causally linked to glioma formation. Extensive involvement of PDGF in development and its implication in a variety of pathologic conditions, including gliomagenesis, are mediated not only by autocrine effects but by paracrine effects. Many researchers view brain tumors as clonal entities derived from the cancer stem cell; however, recent documentation of the importance of the tumor microenvironment for glioma initiation and progression as well as the ability of neural stem or progenitor cells to migrate toward the sites of injury or tumor formation reveals additional complexities in brain tumorigenesis. Paracrine effects of PDGF in animal models of gliomagenesis, continued adult neurogenesis capable of increasing in response to brain injury, and the growth factor-rich environment of brain tumors suggest that recruitment may play a role in gliomagenesis. In this view, glioma formation involves recruitment of cells from the adjacent brain and possibly other sites.

Killer proteases and little strokes--how the things that do not kill you make you stronger

The phenomenon of ischemic preconditioning was initially observed over 20 years ago. The basic tenant is that if stimuli are applied at a subtoxic level, cells upregulate endogenous protective mechanisms to block injury induced by subsequent stress. Since this discovery, many conserved signaling mechanisms that contribute to activation of this potent protective program have been identified in the brain. A clinical correlate of this basic research finding can be found in patients with a history of transient ischemic attack (TIA), who have a decreased morbidity after stroke. In spite of multidisciplinary efforts to design safer, more effective stroke therapies, we have thus far failed to translate our understanding of endogenous protective pathways to treatments for neurodegeneration. This review is designed to provide clinicians and basic scientists with an overview of stress biology after TIA and preconditioning, discuss new therapeutic strategies to target the protein dysfunction that follows ischemic injury, and propose enhanced biochemical profiling to identify individuals at risk of stroke after TIA. We pay particular attention to the unanticipated consequences of overly aggressive intervention after TIA in which we have found that traditional cytotoxic agents such as free radicals and apoptosis associated proteases is essential for neuroprotection and communication in the stressed brain. These data emphasize the importance of understanding the complex interplay between chaperones, apoptotic proteases including caspases, and the proteolytic degradation machinery in adaptation to neurological injury.

NF-kappa B as a therapeutic target in neurodegenerative diseases

NF-kappaB is a transcription factor that regulates numerous physiological functions, and that is involved in the pathogenesis of various diseases. In the nervous system there is evidence supporting a dual role of NF-kappaB in neurodegenerative diseases; activation of NF-kappaB in neurons promotes their survival, whereas activation in glial and immune cells mediates pathological inflammatory processes. The reason for such a dichotomy lies in the complexity of the NF-kappaB system. Emerging research has begun to dissect the pathways leading to the activation of the different NF-kappaB proteins, and the gene targets of NF-kappaB, in cells of the nervous system. In this article the authors discuss recent findings concerning the roles of NF-kappaB in the pathogenesis of several neurodegenerative disorders, and its potential as a pharmaceutical target for these disorders.

Increase in PGE2 biosynthesis induces a Bax dependent apoptosis correlated to patients’ survival in glioblastoma multiforme

Prostaglandin E(2) plays multiple roles both in the physiology and the physiopathology of human brain, which are not completely understood. We have identified in a subset of human glioblastoma multiforme (GBM) tumors, the most common form of adult brain cancer, an increased expression of mPGES-1, the enzyme which catalyses the isomerization of PGH(2) into PGE(2) downstream of cyclooxygenase 2 (COX-2). The sensitivity of primary cultures of GBM to apoptosis was augmented by the overexpression of mPGES-1, whereas the knockdown of its expression by shRNA decreased the apoptotic threshold in vitro and stimulated tumor growth in vivo. Adding extracellular PGE(2) in the culture medium failed to reproduce mPGES-1 effect on the cell viability in vitro. However, the intracellular injection of PGE(2) induced a dose-dependent apoptosis in GBM cultures, which was dependent on the presence of Bax, a pro-apoptotic protein. We show that PGE(2) physically associates with Bax, triggering its apoptotic-like change in conformation and its subsequent association with mitochondria. Our results raise questions about the role of PGE(2) in the control of apoptosis and in its potential impact in central nervous system pathologies.

Brain oedema in focal ischaemia: molecular pathophysiology and theoretical implications

Focal cerebral ischaemia and post-ischaemic reperfusion cause cerebral capillary dysfunction, resulting in oedema formation and haemorrhagic conversion. There are substantial gaps in understanding the pathophysiology, especially regarding early molecular participants. Here, we review physiological and molecular mechanisms involved. We reaffirm the central role of Starling's principle, which states that oedema formation is determined by the driving force and the capillary "permeability pore". We emphasise that the movement of fluids is largely driven without new expenditure of energy by the ischaemic brain. We organise the progressive changes in osmotic and hydrostatic conductivity of abnormal capillaries into three phases: formation of ionic oedema, formation of vasogenic oedema, and catastrophic failure with haemorrhagic conversion. We suggest a new theory suggesting that ischaemia-induced capillary dysfunction can be attributed to de novo synthesis of a specific ensemble of proteins that determine osmotic and hydraulic conductivity in Starling's equation, and whose expression is driven by a distinct transcriptional program.

The inflammatory response in stroke

Recent works in the area of stroke and brain ischemia has demonstrated the significance of the inflammatory response accompanying necrotic brain injury. Acutely, this response appears to contribute to ischemic pathology, and anti-inflammatory strategies have become popular. This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in experimental stroke. It will review the role of specific cell types including leukocytes, endothelium, glia, microglia, the extracellular matrix and neurons. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Integrating cell-signalling pathways with NF-kappaB and IKK function

Nuclear factor (NF)-kappaB and inhibitor of NF-kappaB kinase (IKK) proteins regulate many physiological processes, including the innate- and adaptive-immune responses, cell death and inflammation. Disruption of NF-kappaB or IKK function contributes to many human diseases, including cancer. However, the NF-kappaB and IKK pathways do not exist in isolation and there are many mechanisms that integrate their activity with other cell-signalling networks. This crosstalk constitutes a decision-making process that determines the consequences of NF-kappaB and IKK activation and, ultimately, cell fate.