IKK mediates ischemia-induced neuronal death.

The IkappaB kinase complex IKK is a central component of the signaling cascade that controls NF-kappaB-dependent gene transcription. So far, its function in the brain is largely unknown. Here, we show that IKK is activated in a mouse model of stroke. To investigate the function of IKK in brain ischemia we generated mice that contain a targeted deletion of Ikbkb (which encodes IKK2) in mouse neurons and mice that express a dominant inhibitor of IKK in neurons. In both lines, inhibition of IKK activity markedly reduced infarct size. In contrast, constitutive activation of IKK2 enlarged the infarct size. A selective small-molecule inhibitor of IKK mimicked the effect of genetic IKK inhibition in neurons, reducing the infarct volume and cell death in a therapeutic time window of 4.5 h. These data indicate a key function of IKK in ischemic brain damage and suggest a potential role for IKK inhibitors in stroke therapy.

Neuronal activation of NF-kappaB contributes to cell death in cerebral ischemia.

The transcription factor NF-kappaB is a key regulator of inflammation and cell survival. NF-kappaB is activated by cerebral ischemia in neurons and glia, but its function is controversial. To inhibit NF-kappaB selectively in neurons and glial cells, we have generated transgenic mice that express the IkappaBalpha superrepressor (IkappaBalpha mutated at serine-32 and serine-36, IkappaBalpha-SR) under transcriptional control of the neuron-specific enolase (NSE) and the glial fibrillary acidic protein (GFAP) promoter, respectively. In primary cortical neurons of NSE-IkappaBalpha-SR mice, NF-kappaB activity was partially inhibited. To assess NF-kappaB activity in vivo after permanent middle cerebral artery occlusion (MCAO), we measured the expression of NF-kappaB target genes by real-time polymerase chain reaction (PCR). The induction of c-myc and transforming growth factor-beta2 by cerebral ischemia was inhibited by neuronal expression of IkappaBalpha-SR, whereas induction of GFAP by MCAO was reduced by astrocytic expression of IkappaBalpha-SR. Neuronal, but not astrocytic, expression of the NF-kappaB inhibitor reduced both infarct size and cell death 48 hours after permanent MCAO. In summary, the data show that NF-kappaB is activated in neurons and astrocytes during cerebral ischemia and that NF-kappaB activation in neurons contributes to the ischemic damage.

Tumor necrosis factor-like weak inducer of apoptosis-induced neurodegeneration.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) family of cytokines. It has proangiogenic and proinflammatory properties in vivo and induces cell death in tumor cell lines. TWEAK effects are mediated by the membrane receptor Fn14. In a systematic search for genes regulated in a murine stroke model with the tag-sequencing technique massively parallel signature sequencing, we have identified TWEAK as an induced gene. After 24 hr of focal cerebral ischemia in vivo or oxygen glucose deprivation in primary cortical neurons, both TWEAK and its receptor Fn14 were significantly upregulated. TWEAK induced cell death in primary neurons. Transfection of a nuclear factor (NF)-kappaB-luciferase fusion gene demonstrated that TWEAK stimulated transcriptional activity of NF-kappaB through Fn14 and the IkappaB kinase. Inhibition of NF-kappaB reduced TWEAK-stimulated neuronal cell death, suggesting that NF-kappaB mediates TWEAK-induced neurodegeneration at least in part. Intraperitoneal injection of a neutralizing anti-TWEAK antibody significantly reduced the infarct size after 48 hr of permanent cerebral ischemia. In summary, our data show that TWEAK induces neuronal cell death and is involved in neurodegeneration in vivo.

The cannabinoid dexanabinol is an inhibitor of the nuclear factor-kappa B (NF-kappa B).

Exogenous and endogenous cannabinoids have been shown to have neuroprotective effects in vitro and in vivo. Although many of the pharmacological effects of cannabinoids have been identified, the mechanism of neuroprotection still represents a controversy. Here we demonstrate for the first time protective effects of the synthetic cannabinoid dexanabinol by inhibiting apoptosis in a neuron-like cell line using nuclear staining and FACS analysis and in primary neurons. We provide further evidence of inhibition of nuclear factor-kappakappa B (NF-kappaB) by dexanabinol: Dexanabinol inhibits (1) phosphorylation and degradation of the inhibitor of NF-kappaB IkappaBalpha and translocation of NF-kappaB to the nucleus; dexanabinol reduces (2) the transcriptional activity of NF-kappaB and (3) mRNA accumulation of the NF-kappaB target genes tumor necrosis factor-alpha and interleukin-6 (TNF-alpha and IL-6). Dexanabinol does not bind to cannabinoid (CB) receptors 1 and 2. To investigate the mechanism of action, we employed the non-antioxidant CB1 receptor agonist WIN 55,212-2 and the antioxidant cannabinol, which binds to CB1 receptors only weakly. Both cannabinoids mimicked the effect of dexanabinol on NF-kappaB and apoptosis. This suggests that neither the antioxidant properties of cannabinoids nor binding to CB1 or CB2 receptors are responsible for the inhibition of NF-kappaB activity and apoptosis. Our results clearly demonstrate that dexanabinol inhibits NF-kappaB. NF-kappaB has been shown to be involved in brain damage and to promote neuronal cell death in vitro and in in vivo models of ischemic and neurodegenerative neurological diseases.

Glutamate activates NF-kappaB through calpain in neurons.

Glutamate induces gene transcription in numerous physiological and pathological conditions. Among the glutamate-responsive transcription factors, NF-kappaB has been mainly implicated in neuronal survival and death. Recent data also suggest a role of NF-kappaB in neural development and memory formation. In non-neuronal cells, degradation of the inhibitor IkappaBalpha represents a key step in NF-kappaB activation. However, little is known of how glutamate activates NF-kappaB in neurons. To investigate the signalling cascade involved we used primary murine cerebellar granule cells. Glutamate induced a rapid reduction of IkappaBalpha levels and nuclear translocation of the NF-kappaB subunit p65. The glutamate-induced reduction of IkappaBalpha levels was blocked by the N-methyl-d-aspartate inhibitor MK801. Specific inhibitors of the proteasome, caspase 3, and the phosphoinositide 3-kinase had no effect on glutamate-induced IkappaBalpha degradation. However, inhibition of the glutamate-activated Ca2+-dependent protease calpain by calpeptin completely blocked IkappaBalpha degradation and reduced the nuclear translocation of p65. Calpeptin also partially blocked glutamate-induced cell death. Our data indicate that the Ca2+-dependent protease calpain is involved in the NF-kappaB activation in neurons in response to N-methyl-d-aspartate receptor occupancy by glutamate. NF-kappaB activation by calpain may mediate the long-term effects of glutamate on neuron survival or memory formation.