Ilenia Sarnico

Bim and Noxa Are Candidates to Mediate the Deleterious Effect of the NF-κB Subunit RelA in Cerebral Ischemia

The transcription factor nuclear factor κB (NF-κB) is well known for its antiapoptotic action. However, in some disorders, such as cerebral ischemia, a proapoptotic function of NF-κB has been demonstrated. To analyze which subunit of NF-κB is functional in cerebral ischemia, we induced focal cerebral ischemia in mice with a germline deletion of the p52 or c-Rel gene or with a conditional deletion of RelA in the brain. Only RelA deficiency reduced infarct size. Interestingly, expression of the proapoptotic BH3 (Bcl-2 homology domain 3)-only genes Bim and Noxa in cerebral ischemia depended on RelA and the upstream kinase IKK (IκB kinase). RelA stimulated Bim and Noxa gene transcription in primary cortical neurons and bound to the promoter of both genes. Thus, the deleterious function in cerebral ischemia is specific for the NF-κB subunit RelA and may be mediated through Bim and Noxa.

NF-κB factor c-Rel mediates neuroprotection elicited by mGlu5 receptor agonists against amyloid β -peptide toxicity

Opposite effects of nuclear factor-κB (NF-κB) on neuron survival rely on activation of diverse NF-κB factors. While p65 is necessary for glutamate-induced cell death, c-Rel mediates prosurvival effects of interleukin-1β. However, it is unknown whether activation of c-Rel-dependent pathways reduces neuron vulnerability to amyloid-β (Aβ), a peptide implicated in Alzheimers disease pathogenesis. We show that neuroprotection elicited by activation of metabotropic glutamate receptors type 5 (mGlu5) against Aβ toxicity depends on c-Rel activation. Aβ peptide induced NF-κB factors p50 and p65. The mGlu5 agonists activated c-Rel, besides p50 and p65, and the expression of manganese superoxide dismutase (MnSOD) and Bcl-XL. Targeting c-Rel expression by RNA interference suppressed the induction of both antiapoptotic genes. Targeting c-Rel or Bcl-XL prevented the prosurvival effect of mGlu5 agonists. Conversely, c-Rel overexpression or TAT-Bcl-XL addition rescued neurons from Aβ toxicity. These data demonstrate that mGlu5 receptor activation promotes a c-Rel-dependent antiapoptotic pathway responsible for neuroprotection against Aβ peptide.

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

Diverse nuclear factor‐κB 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.

Prevention of neuron and oligodendrocyte degeneration by interleukin-6 (IL-6) and IL-6 receptor/IL-6 fusion protein in organotypic hippocampal slices

We investigated the effects of IL-6 and a chimeric derivative of IL-6 and soluble IL-6 receptor (IL6RIL6 chimera) on excitotoxic injury in rat organotypic hippocampal slices. Brief application of N-methyl-d-aspartate (NMDA) induced astrocyte reactivity, neuron cell death, and oligodendrocyte degeneration, the latter caused by secondary activation of AMPA/kainate receptors. Both these cytokines rescued neurons and oligodendrocytes, albeit the chimeric compound was much more potent and efficient than IL-6. No change was produced on reactive astrocytosis. The cytokines preserved myelin basic protein (MBP) production in slices exposed to excitotoxic insult, and when applied singularly for a week, they also enhanced both MBP and proteolipid protein expression. These effects occurred through activating the signal transducer gp130 and were associated with stimulation of transcription factors STAT1 and STAT3. Our results suggest that IL-6 and IL6RIL6 may prove to be valuable in treating neurodegenerative and demyelinating diseases.

NF‐κB pathway: a target for preventing β‐amyloid (Aβ)‐induced neuronal damage and Aβ42 production

Beta‐amyloid (Aβ) peptides are key proteins in the pathophysiology of Alzheimers disease (AD). While Aβ42 aggregates very rapidly to form early diffuse plaques, supplemental Aβ40 deposition is required to form mature neuritic plaques. We here investigated the role of nuclear factor‐κB (NF‐κB) pathway in Aβ40‐mediated neuronal damage and amyloid pathology. In rat primary neurons and human postmitotic neuronal cells, the Aβ peptide induced a dose‐dependent neuronal death, reduced the levels of the anti‐apoptotic protein Bcl‐XL, enhanced the cytosolic release of cytochrome c, and elicited the intracellular accumulation and secretion of Aβ42 oligomers. Moreover, Aβ40 activated the NF‐κB pathway by selectively inducing the nuclear translocation of p65 and p50 subunits, and promoted an apoptotic profile of gene expression. As inhibitors of the NF‐κB pathway, we tested the capability of a double‐stranded κB decoy oligonucleotide, the anti‐inflammatory drug aspirin and the selective IκB kinase 2 inhibitor, AS602868, to modify the Aβ40‐mediated effects. These treatments, transiently applied before Aβ exposure, completely inhibited p50/p65 nuclear translocation and neuronal damage. The κB decoy also inhibited the Aβ‐induced release of cytochrome c, restored the levels of Bcl‐XL, and prevented intraneuronal accumulation and secretion of Aβ42. These results open up interesting perspectives on the development of novel strategies targeting out NF‐κB p50/p65 dimers for pharmacological intervention in AD.

Leptin Is Induced in the Ischemic Cerebral Cortex and Exerts Neuroprotection Through NF-κB/c-Rel–Dependent Transcription

Background and Purpose— Leptin is an adipose hormone endowed with angiopoietic, neurotrophic, and neuroprotective properties. We tested the hypothesis that leptin might act as an endogenous mediator of recovery after ischemic stroke and investigated whether nuclear transcription factors &kgr;B activation is involved in leptin-mediated neuroprotection. Methods— The antiapoptotic effects of leptin were evaluated in cultured mouse cortical neurons from wild-type or NF-&kgr;B/c-Rel−/− mice exposed to oxygen–glucose deprivation. Wild-type, c-Rel−/− and leptin-deficient ob/ob mice were subjected to permanent middle cerebral artery occlusion. Leptin production was measured in brains from wild-type mice with quantitative reverse transcriptase–polymerase chain reaction and immunostaining. Mice received a leptin bolus (20 μg/g) intraperitoneally at the onset of ischemia. Results— Leptin treatment activated the nuclear translocation of nuclear transcription factors &kgr;B dimers containing the c-Rel subunit, induced the expression of the antiapoptotic c-Rel target gene Bcl-xL in both control and oxygen–glucose deprivation conditions, and counteracted the oxygen–glucose deprivation-mediated apoptotic death of cultured cortical neurons. Leptin-mediated Bcl-xL induction and neuroprotection against oxygen–glucose deprivation were hampered in cortical neurons from c-Rel−/− mice. Leptin mRNA was induced and the protein was detectable in microglia/macrophage cells from the ischemic penumbra of wild-type mice subjected to permanent middle cerebral artery occlusion. Ob/ob mice were more susceptible than wild-type mice to the permanent middle cerebral artery occlusion injury. Leptin injection significantly reduced the permanent middle cerebral artery occlusion-mediated cortical damage in wild-type and ob/ob mice, but not in c-Rel−/− mice. Conclusions— Leptin acts as an endogenous mediator of neuroprotection during cerebral ischemia. Exogenous leptin administration protects against ischemic neuronal injury in vitro and in vivo in a c-Rel-dependent manner.

Chapter 24 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.

NF-kappaB pathway: a target for preventing beta-amyloid (Abeta)-induced neuronal damage and Abeta42 production

Beta‐amyloid (Aβ) peptides are key proteins in the pathophysiology of Alzheimers disease (AD). While Aβ42 aggregates very rapidly to form early diffuse plaques, supplemental Aβ40 deposition is required to form mature neuritic plaques. We here investigated the role of nuclear factor‐κB (NF‐κB) pathway in Aβ40‐mediated neuronal damage and amyloid pathology. In rat primary neurons and human postmitotic neuronal cells, the Aβ peptide induced a dose‐dependent neuronal death, reduced the levels of the anti‐apoptotic protein Bcl‐XL, enhanced the cytosolic release of cytochrome c, and elicited the intracellular accumulation and secretion of Aβ42 oligomers. Moreover, Aβ40 activated the NF‐κB pathway by selectively inducing the nuclear translocation of p65 and p50 subunits, and promoted an apoptotic profile of gene expression. As inhibitors of the NF‐κB pathway, we tested the capability of a double‐stranded κB decoy oligonucleotide, the anti‐inflammatory drug aspirin and the selective IκB kinase 2 inhibitor, AS602868, to modify the Aβ40‐mediated effects. These treatments, transiently applied before Aβ exposure, completely inhibited p50/p65 nuclear translocation and neuronal damage. The κB decoy also inhibited the Aβ‐induced release of cytochrome c, restored the levels of Bcl‐XL, and prevented intraneuronal accumulation and secretion of Aβ42. These results open up interesting perspectives on the development of novel strategies targeting out NF‐κB p50/p65 dimers for pharmacological intervention in AD.

Expression of functional NR1/NR2B‐type NMDA receptors in neuronally differentiated SK‐N‐SH human cell line

The present study demonstrates that human SK‐N‐SH neuroblastoma cells, differentiated by retinoic acid (RA), express functional NMDA receptors and become vulnerable to glutamate toxicity. During exposure to RA, SK‐N‐SH cells switched from non‐neuronal to neuronal phenotype by showing antigenic changes typical of postmitotic neurons together with markers specific for cholinergic cells. Neuronally differentiated cells displayed positive immunoreactivity to the vesicular acetylcholine transporter and active acetylcholine release in response to depolarizing stimuli. The differentiation correlated with the expression of NMDA receptors. RT‐PCR and immunoblotting analysis identified NMDA receptor subunits NR1 and NR2B, in RA‐differentiated cultures. The NR1 protein immunolocalized to the neuronal cell population and assembled with the NR2B subunit to form functional N‐methyl‐d‐aspartate (NMDA) receptors. Glutamate or NMDA application, concentration‐dependently increased the intracellular Ca2+ levels and acetylcholine release in differentiated cultures, but not in undifferentiated SK‐N‐SH cells. Moreover, differentiated cultures became vulnerable to NMDA receptor‐mediated excitotoxicity. The glutamate effects were enhanced by glycine application and were prevented by the NMDA receptor blocker MK 801, as well as by the NR2B selective antagonist ifenprodil. These data suggest that SK‐N‐SH cells differentiated by brief treatment with RA may represent an unlimited source of neuron‐like cells suitable for studying molecular events associated with activation of human NR1/NR2B receptors.

The γ-secretase modulator CHF5074 restores memory and hippocampal synaptic plasticity in plaque-free Tg2576 mice.

Abnormal amyloid-β (Aβ) production and deposition is believed to represent one of the main causes of Alzheimers disease (AD). γ-Secretase is the enzymatic complex responsible for Aβ generation from its precursor protein. Inhibition or modulation of γ-secretase represents an attractive therapeutic approach. CHF5074 is a new γ-secretase modulator that has been shown to inhibit brain plaque deposition and to attenuate memory deficit in adult AD transgenic mice after chronic treatment. To date, it is not known whether the positive behavioral effects of this compound also occur in young transgenic mice without plaque deposition. Here, we evaluated the effects of acute and subchronic treatment with CHF5074 on contextual and recognition memory and on hippocampal synaptic plasticity in plaque-free Tg2576 mice. We found that at 5 months of age, contextual memory impairment was significantly attenuated after acute subcutaneous administration of 30 mg/kg CHF5074. At 6 months of age, recognition memory impairment was fully reversed after a 4-week oral treatment in the diet (≈60 mg/kg/day). These cognitive effects were associated with a reversal of long-term potentiation (LTP) impairment in the hippocampus. A significant reduction in brain intraneuronal AβPP/Aβ levels and hyperphosphorylated tau, but no change in soluble or oligomeric Aβ levels was detected in Tg2576 mice showing functional recovery following CHF5074 treatment. We conclude that the beneficial effects of CHF5074 treatment in young transgenic mice occurred at a stage that precedes plaque formation and were associated with a reduction in intraneuronal AβPP/Aβ and hyperphosphorylated tau.