Injury‐induced NF‐κB activation in the hippocampus: implications for neuronal survival

Inhibitors of Lipoxygenase and Cyclooxygenase-2 Attenuate Trimethyltin-Induced Neurotoxicity through Regulating Oxidative Stress and Pro-Inflammatory Cytokines in Human Neuroblastoma SH-SY5Y Cells

Trimethyltin (TMT) is an environmental neurotoxin that mediates dopaminergic neuronal injury in the brain. In this study, we characterized the toxic mechanism and possible protective compounds against TMT-induced neurotoxicity in human dopaminergic neuroblastoma SH-SY5Y cells. Antioxidants such as melatonin, N-acetylcysteine (NAC), α-tocopherol, and allopurinol alleviated TMT toxicity. Apoptosis induced by TMT was identified by altered expression of cleaved caspase-3, Bax, Bcl-2, and Bcl-xL through Western blot analysis. The iron chelator deferoxamine ameliorated the alteration of apoptosis-related proteins through TMT exposure. TMT also induced delayed ultrastructural necrotic features such as mitochondrial swelling and cytoplasmic membrane rupture; NAC reduced these necrotic injuries. Esculetin, meloxicam, celecoxib, and phenidone decreased TMT toxicity. Elevation of the pro-inflammatory cytokines IL-1β, TNF-α, and NF-ĸB and reduction of the antioxidant enzymes catalase and glutathione peroxidase-1 (GPx-1) were induced by TMT and ameliorated by inhibitors of LOX and COX-2 enzymes. Both NMDA and non-NMDA antagonists attenuated TMT toxicity. The free calcium ion modulators nimodipine and BAPTA/AM contributed to neuronal survival against TMT toxicity. Inhibitors of the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin pathway, an autophagy regulator, decreased TMT toxicity. These results imply that TMT neurotoxicity is the chief participant in LOX- and COX-2-mediated apoptosis, partly via necrosis and autophagy in SH-SY5Y cells.

Nuclear factor kappa B inhibitor suppresses experimental autoimmune neuritis in mice via declining macrophages polarization to M1 type

Guillain-Barré syndrome (GBS) is an acute inflammatory and immune-mediated demyelinating disease of the peripheral nervous system (PNS). Macrophages play a central role in its animal model, experimental autoimmune neuritis (EAN), which has been well accepted. Additionally, nuclear factor (NF)-κB inhibitors have been used to treat cancers and have shown beneficial effects. Here, we investigated the therapeutic effect of M2 macrophage and the NF-κB pathway's correlation with macrophage activation in EAN in C57BL/6 mice. We demonstrate that M2 macrophage transfusion could alleviate the clinical symptoms of EAN by reducing the proportion of M1 macrophage in the peak period, inhibiting the phosphorylation of NF-κB p65. The NF-κB inhibitor (BAY-11-7082) could alleviate the clinical symptoms of EAN and shorten the duration of symptoms by reducing the proportion of M1 macrophages and the expression of proinflammatory cytokines. Consequently, BAY-11-7082 exhibits strong potential as a therapeutic strategy for ameliorating EAN by influencing the balance of M1/M2 macrophages and inflammatory cytokines.

NF-κB as a Key Mediator of Brain Inflammation in Alzheimer's Disease

Alzheimer's disease is the most common form of dementia. It is characterized by betaamyloid peptide fibrils which are extracellular deposition of a specific protein, accompanied by extensive neuroinflammation. Various studies show the presence of a number of inflammation markers in the AD brain: elevated inflammatory cytokines and chemokines, and an accumulation of activated microglia in the damaged regions. NF-κB is a family of redox sensitive transcriptional factors, and it is known that NF-κB has binding sites in the promoter region of the genes involved in amyloidogenesis and inflammation. Long-term use of non-steroidal anti-inflammatory drugs prevents progression of AD and delays its onset, suggesting that there is a close correlation between NF-κB and AD pathogenesis. This study aims to (1) assess the association between NF-κB activity and AD through discussion of a variety of experimental and clinical studies on AD and (2) review treatment strategies designed to treat or prevent AD with NF-κB inhibitors.

Nuclear factor-kappa β as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD) is a typical progressive, chronic neurodegenerative disorder with worldwide prevalence. Its clinical manifestation involves the presence of extracellular plaques and intracellular neurofibrillary tangles (NFTs). NFTs occur in brain tissues as a result of both Aβ agglomeration and Tau phosphorylation. Although there is no known cure for AD, research into possible cures and treatment options continues using cell-cultures and model animals/organisms. The nuclear factor-kappa β (NF-κβ) plays an active role in the progression of AD. Impairment to this signaling module triggers undesirable phenotypic changes such as neuroinflammation, activation of microglia, oxidative stress related complications, and apoptotic cell death. These imbalances further lead to homeostatic abnormalities in the brain or in initial stages of AD essentially pushing normal neurons toward the degeneration process. Interestingly, the role of NF-κβ signaling associated receptor-interacting protein kinase is currently observed in apoptotic and necrotic cell death, and has been reported in brains. Conversely, the NF-κβ signaling pathway has also been reported to be involved in normal brain functioning. This pathway plays a crucial role in maintaining synaptic plasticity and balancing between learning and memory. Since any impairment in the pathways associated with NF-κβ signaling causes altered neuronal dynamics, neurotherapeutics using compounds including, antioxidants, bioflavonoids, and non-steroidal anti-inflammatory drugs against such abnormalities offer possibilities to rectify aberrant excitatory neuronal activity in AD. In this review, we have provided an extensive overview of the crucial role of NF-κβ signaling in normal brain homeostasis. We have also thoroughly outlined several established pathomechanisms associated with NF-κβ pathways in AD, along with their respective therapeutic approaches.

Role of GABAB receptors and p38MAPK/NF-κB pathway in paclitaxel-induced apoptosis of hippocampal neurons

CONTEXT

The effects of the anticancer drug paclitaxel on learning and memory are rarely studied.

OBJECTIVE

This study investigated changes in GABAB receptor expression during paclitaxel-induced apoptosis of hippocampal neurons and the role of the p38MAPK/NF-κB pathway in this process.

MATERIALS AND METHODS

Hippocampal neurons isolated from neonatal Sprague-Dawley rats were divided into six groups: Control (C), SB (10 µL of 10-µmol/L SB203580), SN (53 µg/mL SN50), N (1 µmol/L paclitaxel), SB + N (10 µmol/L SB203580 + 1 µmol/L paclitaxel) and SN + N (53 µg/mL SN50 + 1 µmol/L paclitaxel). Cells in different groups were treated with corresponding agents for 24 h at 37 °C. The apoptosis rate and protein levels of GABAB1 receptors and NF-κB p65 were evaluated. Rat models of neuropathic pain was induced by paclitaxel and were divided into four groups such as N, B + N, SN + N and SN + B + N groups. Rats in the N group received intrathecal injections of normal saline solution. Rats in the B + N group received intrathecal injections of 10 μL baclofen (0.05 μg/μL). Rats in the SN + N and SN + B + N groups received intrathecal injections of SN50 and SN50 plus baclofen, respectively. Spatial learning and memory were evaluated in rat models based on the escape latency and the number of crossings over the platform and protein levels of GABAB1 receptors, NF-κB, IL-1β and TNFα were measured by immunohistochemistry assay and western blot.

RESULTS

The neuronal apoptosis rate was significantly increased in N (49.16 ± 3.12)%, SB + N (31.18 ± 3.02)% and SN + N (28.47 ± 3.75)% groups, accompanied by increased levels of GABAB1 receptors and NF-κB p65 (p < 0.05). The paclitaxel-treated rats demonstrated significantly increased latency (24.32 ± 2.94)s and decreased the crossings number (3.14 ± 0.63) after 15 d in the Morris water maze (p < 0.05). Immunohistochemistry assay showed that compared with the N group (GABAB1:9.0 ± 1.6, NF-κB p65:29.6 ± 2.4, IL-1β: 30.4 ± 3.4, TNFα: 31.0 ± 3.4), B + N, SN + N and SN + B + N groups evidently increased levels of GABAB1 receptor (B + N:SN + N:SN + B + N = 19.4 ± 2.1:20.8 ± 1.9:28.0 ± 1.9) but significantly decreased levels of NF-κB p65 (B + N:SN + N:SN + B + N = 21.2 ± 1.5:18.6 ± 2.1:12.6 ± 1.5), IL-1β (B + N:SN + N:SN + B + N = 22.0 ± 1.0:19.6 ± 1.8:14.6 ± 1.5) and TNF α (B + N:SN + N:SN + B + N = 23.0 ± 1.6:22.2 ± 0.8:16.6 ± 1.7). Similar findings were found in western blot analysis.

DISCUSSIONS AND CONCLUSIONS

Paclitaxel may reduce cognitive function in rats through the p38MAPK/NF-κB pathway and GABAB1 receptors.

The Ying and Yang of Adenosine A1 and A2A Receptors on ERK1/2 Activation in a Rat Model of Global Cerebral Ischemia Reperfusion Injury

Adenosine impacts cerebral ischemia reperfusion (IR) through the inhibitory A₁ and the excitatory A₂ receptors. The present study aimed at investigating the contrasting role of pERK1/2 in mediating adenosine A₁R (protective) versus A_2AR (deleterious) effects in IR. Male Wistar rats subjected to bilateral carotid occlusion (45 min) followed by reperfusion (24 h) exhibited increased pERK1/2 activity, downstream from DAG pathway, along with increases in hippocampal glutamate, c-Fos, NF-κB, TNF-α, iNOS, TBARS, cytochrome c, caspase-3, BDNF, Nrf2, and IL-10 contents. Further, hippocampal microglial reactivity, glial TNF-α, and BDNF expression were observed. Although unilateral intrahippocampal injection of either the A₁R agonist CHA or the A_2AR agonist CGS21680 increased pERK1/2, only CHA mitigated histopathological and behavioral deficits along with reducing glutamate, microglial activation, c-Fos, TNF-α, iNOS, TBARS, cytochrome c and caspase-3 and elevating Nrf2 and IL-10 levels in IR rats. These results yield insight into the double-faceted nature of pERK1/2 in mediating protective and deleterious effects of A₁R and A_2AR signaling, respectively, against IR injury.

Neuronal Gene Targets of NF-κB and Their Dysregulation in Alzheimer's Disease

Although, better known for its role in inflammation, the transcription factor nuclear factor kappa B (NF-κB) has more recently been implicated in synaptic plasticity, learning, and memory. This has been, in part, to the discovery of its localization not just in glia, cells that are integral to mediating the inflammatory process in the brain, but also neurons. Several effectors of neuronal NF-κB have been identified, including calcium, inflammatory cytokines (i.e., tumor necrosis factor alpha), and the induction of experimental paradigms thought to reflect learning and memory at the cellular level (i.e., long-term potentiation). NF-κB is also activated after learning and memory formation in vivo. In turn, activation of NF-κB can elicit either suppression or activation of other genes. Studies are only beginning to elucidate the multitude of neuronal gene targets of NF-κB in the normal brain, but research to date has confirmed targets involved in a wide array of cellular processes, including cell signaling and growth, neurotransmission, redox signaling, and gene regulation. Further, several lines of research confirm dysregulation of NF-κB in Alzheimer's disease (AD), a disorder characterized clinically by a profound deficit in the ability to form new memories. AD-related neuropathology includes the characteristic amyloid beta plaque formation and neurofibrillary tangles. Although, such neuropathological findings have been hypothesized to contribute to memory deficits in AD, research has identified perturbations at the cellular and synaptic level that occur even prior to more gross pathologies, including transcriptional dysregulation. Indeed, synaptic disturbances appear to be a significant correlate of cognitive deficits in AD. Given the more recently identified role for NF-κB in memory and synaptic transmission in the normal brain, the expansive network of gene targets of NF-κB, and its dysregulation in AD, a thorough understanding of NF-κB-related signaling in AD is warranted and may have important implications for uncovering treatments for the disease. This review aims to provide a comprehensive view of our current understanding of the gene targets of this transcription factor in neurons in the intact brain and provide an overview of studies investigating NF-κB signaling, including its downstream targets, in the AD brain as a means of uncovering the basic physiological mechanisms by which memory becomes fragile in the disease.

Coenzyme Q10 Ameliorates Trimethyltin Chloride Neurotoxicity in Experimental Model of Injury in Dentate Gyrus of Hippocampus: A Histopathological and Behavioral Study

Background

Coenzyme Q10 has antioxidative and free radical scavenging effects. CoQ10 supplementation is known to have neuroprotective effects in some neurodegenerative diseases, such as Parkinson’s disease and Huntington’s disease.

Objectives

The aim of this study was to evaluate both histopathologic and behavioral whether Coenzyme Q10 is protective against trimethyltin chloride (TMT) induced hippocampal damage.

Materials and Methods

This was an experimental study. Thirty-six Balb/c mice were divided into four groups, as follows: 1) control group; 2) sham group of mice that received a 100 µL intraperitoneal injection (IP) of sesame oil; 3) TMT group of mice that received a single 2.5 mg/kg/day IP injection of TMT; and 4) TMT + CoQ10 group of mice that received a 10 mg/kg IP injection of CoQ10. Body weight and Morris water maze (MWM) responses were investigated. In addition, the dentate gyrus neurons of the hippocampus were evaluated histopathologically by light and electron microscopes.

Results

This study revealed that the body weight scale was found to be significantly higher in the CoQ10 group (21.39 ± 2.70), compared to the TMT group (19.39 ± 2.74) (P < 0.05). In the TMT group, the animals showed body a weight loss that was significantly lower than that of the control group (22.33 ± 3.06) (P < 0.05). Our results showed that CoQ10 provided protection against MWM deficits. Furthermore, TMT impaired the ability of mice to locate the hidden platform, compared to the control group (P < 0.05). Microscopic studies showed that TMT caused histopathological changes in the dentate gyrus and increased the number of necrotic neurons (476 ± 78.51), compared to the control group (208 ± 40.84) (P < 0.001). But, CoQ10 significantly attenuated (31 9 ± 60.08) the density of necrotic neurons compared to TMT (P < 0.05).

Conclusions

The results of the present study indicate that Coenzyme Q10 diminished neuronal necrosis and improved learning memory. Part of its beneficial effect is due to its potential to discount oxidative stress.

Trimethyltin-Induced Microglial Activation via NADPH Oxidase and MAPKs Pathway in BV-2 Microglial Cells

Trimethyltin (TMT) is known as a potent neurotoxicant that causes neuronal cell death and neuroinflammation, particularly in the hippocampus. Microglial activation is one of the prominent pathological features of TMT neurotoxicity. Nevertheless, it remains unclear how microglial activation occurs in TMT intoxication. In this study, we aimed to investigate the signaling pathways in TMT-induced microglial activation using BV-2 murine microglial cells. Our results revealed that TMT generates reactive oxygen species (ROS) and increases the expression of CD11b and nuclear factor-κB- (NF-κB-) mediated nitric oxide (NO) and tumor necrosis factor- (TNF-) α in BV-2 cells. We also observed that NF-κB activation was controlled by p38 and JNK phosphorylation. Moreover, TMT-induced ROS generation occurred via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in BV-2 cells. Interestingly, treatment with the NADPH oxidase inhibitor apocynin significantly suppressed p38 and JNK phosphorylation and NF-κB activation and ultimately the production of proinflammatory mediators upon TMT exposure. These findings indicate that NADPH oxidase-dependent ROS generation activated p38 and JNK mitogen-activated protein kinases (MAPKs), which then stimulated NF-κB to release proinflammatory mediators in the TMT-treated BV-2 cells.

Gene expression profiling as a tool to investigate the molecular machinery activated during hippocampal neurodegeneration induced by trimethyltin (TMT) administration

Trimethyltin (TMT) is an organotin compound exhibiting neurotoxicant effects selectively localized in the limbic system and especially marked in the hippocampus, in both experimental animal models and accidentally exposed humans. TMT administration causes selective neuronal death involving either the granular neurons of the dentate gyrus or the pyramidal cells of the Cornu Ammonis, with a different pattern of localization depending on the different species studied or the dosage schedule. TMT is broadly used to realize experimental models of hippocampal neurodegeneration associated with cognitive impairment and temporal lobe epilepsy, though the molecular mechanisms underlying the associated selective neuronal death are still not conclusively clarified. Experimental evidence indicates that TMT-induced neurodegeneration is a complex event involving different pathogenetic mechanisms, probably acting differently in animal and cell models, which include neuroinflammation, intracellular calcium overload, and oxidative stress. Microarray-based, genome-wide expression analysis has been used to investigate the molecular scenario occurring in the TMT-injured brain in different in vivo and in vitro models, producing an overwhelming amount of data. The aim of this review is to discuss and rationalize the state-of-the-art on TMT-associated genome wide expression profiles in order to identify comparable and reproducible data that may allow focusing on significantly involved pathways.

Minimal NF-κB activity in neurons

Nuclear factor-kappa B (NF-κB) is a ubiquitous transcription factor that regulates immune and cell-survival signaling pathways. NF-κB has been reported to be present in neurons wherein it reportedly responds to immune and toxic stimuli, glutamate, and synaptic activity. However, because the brain contains many cell types, assays specifically measuring neuronal NF-κB activity are difficult to perform and interpret. To address this, we compared NF-κB activity in cultures of primary neocortical neurons, mixed brain cells, and liver cells, employing Western blot of NF-κB subunits, electrophoretic mobility shift assay (EMSA) of nuclear κB DNA binding, reporter assay of κB DNA binding, immunofluorescence of the NF-κB subunit protein p65, quantitative real-time polymerase chain reaction (PCR) of NF-κB-regulated gene expression, and enzyme-linked immunosorbent assay (ELISA) of produced proteins. Assay of p65 showed its constitutive presence in cytoplasm and nucleus of neurons at levels significantly lower than in mixed brain or liver cells. EMSA and reporter assays showed that constitutive NF-κB activity was nearly absent in neurons. Induced activity was minimal--many fold lower than in other cell types, as measured by phosphorylation and degradation of the inhibitor IκBα, nuclear accumulation of p65, binding to κB DNA consensus sites, NF-κB reporting, or induction of NF-κB-responsive genes. The most efficacious activating stimuli for neurons were the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin-beta (IL-β). Neuronal NF-κB was not responsive to glutamate in most assays, and it was also unresponsive to hydrogen peroxide, lipopolysaccharide, norepinephrine, ATP, phorbol ester, and nerve growth factor. The chemokine gene transcripts CCL2, CXCL1, and CXCL10 were strongly induced via NF-κB activation by TNFα in neurons, but many candidate responsive genes were not, including the neuroprotective genes SOD2 and Bcl-xL. Importantly, the level of induced neuronal NF-κB activity in response to TNFα or any other stimulus was lower than the level of constitutive activity in non-neuronal cells, calling into question the functional significance of neuronal NF-κB activity.

Apoptosis induced by trimethyltin chloride in human neuroblastoma cells SY5Y is regulated by a balance and cross-talk between NF-κB and MAPKs signaling pathways

Trimethyltin chloride (TMT) has been known as a classic neurotoxicant which can cause serious neuronal degeneration diseases. Nuclear factor κB (NF-κB) and mitogen-activated protein kinases (MAPKs) signaling pathways play pivotal role in the central nerves system. In the present study, the intracellular pathways involved in TMT-induced apoptosis on human neuroblastoma cells SY5Y (SH-SY5Y) were investigated. We observed high level of nuclear NF-κB p65 submit, activated JNK, ERK, and p38 by TMT exposure. In contrast, low level of Bcl-2 and XIAP (two known NF-κB-regulated endogenous anti-apoptotic molecules) was present. To further investigate the role of these pathways and the relationship between them, specific inhibitors were used and the alteration of each pathway was evaluated. Pretreatment with MG132, an inhibitor of proteasome activity, and BAY11-7082, an inhibitor of IκBα phosphorylation, both inhibited NF-κB p65 translocation and significantly promoted apoptosis. NF-κB inhibition also induced down-expression of Bcl-2 and XIAP, exaggerated JNK phosphorylation, and ERK inhibition. SP600125 and U0126, by blocking the phosphorylation of c-Jun and MEK1/2, inhibited JNK and ERK phosphorylation, respectively, and attenuated apoptosis significantly. JNK and ERK inhibition also induced IκBα degradation and NF-κB p65 translocation, leading to expression of Bcl-2 and XIAP. The detrimental role of MG132 and BAY11-7082 appears related to the exaggerated JNK phosphorylation. The SP600125 and U0126 neuroprotection appears related to NF-κB-regulated transcriptional control of Bcl-2 and XIAP. These results suggest that the cross-talk and a balance between NF-κB and MAPKs may be involved in TMT-induced apoptosis on SH-SY5Y cells.

Inhibitor kappa B kinase beta dependent cytokine upregulation in nociceptive neurons contributes to nociceptive hypersensitivity after sciatic nerve injury

Inhibitor kappa B kinase (IKK)-mediated nuclear factor-kappa B (NF-κB) activation is a major pathway for transcriptional control of various pro-inflammatory factors. We here assessed whether activation of this pathway specifically in primary nociceptive neurons of the dorsal root ganglia (DRG) contributes to the development of nociceptive hypersensitivity. Mice carrying a cre-loxP-mediated deletion of inhibitor kappa B kinase beta (IKKβ) in DRG neurons were protected from nerve injury-evoked allodynia and hyperalgesia. This effect was mimicked by systemic treatment with an IKKβ inhibitor but was not observed upon specific inhibition of IKKβ in the spinal cord, suggesting a specific role of IKKβ in the peripheral neurons. The deletion of IKKβ in DRG neurons did not affect constitutive neuronal NF-κB activity, but reduced nerve injury-evoked NF-κB stimulation in the DRG and was associated with reduced upregulation of interleukin-16, monocyte chemoattractant protein-1/chemokine (CC motif) ligand 2 (MCP-1/CCL2), and tumor necrosis factor alpha (TNFα) in the DRG. These cytokines evoked a rapid rise of intracellular calcium in subsets of primary DRG neurons. The results suggest that IKKβ-mediated NF-κB stimulation in injured primary sensory neurons promotes cytokine and chemokine production and contributes thereby to the development of chronic pain.

PERSPECTIVE

Inhibitors of IKK that do not pass the blood-brain barrier and act only in the periphery might be useful for reduction of the pro-inflammatory response in peripheral DRG neurons and reduce thereby nerve injury-evoked pain without affecting neuroprotective effects of NF-κB in the central nervous system.

Endoplasmic reticulum stress responses differ in meninges and associated vasculature, striatum, and parietal cortex after a neurotoxic amphetamine exposure

Amphetamine (AMPH) is used to treat attention deficit and hyperactivity disorders, but it can produce neurotoxicity and adverse vascular effects at high doses. The endoplasmic reticulum (ER) stress response (ERSR) entails the unfolded protein response, which helps to avoid or minimize ER dysfunction. ERSR is often associated with toxicities resulting from the accumulation of unfolded or misfolded proteins and has been associated with methamphetamine toxicity in the striatum. The present study evaluates the effect of AMPH on several ERSR elements in meninges and associated vasculature (MAV), parietal cortex, and striatum. Adult, male Sprague-Dawley rats were exposed to saline, environmentally induced hyperthermia (EIH) or four consecutive doses of AMPH that produce hyperthermia. Expression changes (mRNA and protein levels) of key ERSR-related genes in MAV, striatum, and parietal cortex at 3 h or 1 day postdosing were monitored. AMPH increased the expression of some ERSR-related genes in all tissues. Atf4 (activating transcription factor 4, an indicator of Perk pathway activation), Hspa5/Grp78 (Glucose regulated protein 78, master regulator of ERSR), Pdia4 (protein disulfide isomerase, protein-folding enzyme), and Nfkb1 (nuclear factor of kappa b, ERSR sensor) mRNA increased significantly in MAV and parietal cortex 3 h after AMPH. In striatum, Atf4 and Hspa5/Grp78 mRNA significantly increased 3 h after AMPH, but Pdia4 and Nfkb11 did not. Thus, AMPH caused a robust activation of the Perk pathway in all tissues, but significant Ire1 pathway activation occurred only after AMPH treatment in the parietal cortex and striatum. Ddit3/Chop, a downstream effector of the ERSR pathway related to the neurotoxicity, was only increased in striatum and parietal cortex. Conversely, Pdia4, an enzyme protective in the ERSR, was only increased in MAV. The overall ERSR manifestation varied significantly between MAV, striatum, and parietal cortex after a neurotoxic exposure to AMPH.

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.

NF-kappaB-driven STAT2 and CCL2 expression in astrocytes in response to brain injury

Tissue response to injury includes expression of genes encoding cytokines and chemokines. These regulate entry of immune cells to the injured tissue. The synthesis of many cytokines and chemokines involves NF-kappaB and signal transducers and activators of transcription (STAT). Injury to the CNS induces glial response. Astrocytes are the major glial population in the CNS. We examined expression of STATs and the chemokine CCL2 and their relationship to astroglial NF-kappaB signaling in the CNS following axonal transection. Double labeling with Mac-1/CD11b and glial fibrillary acidic protein revealed that STAT2 up-regulation and phosphorylation colocalized exclusively to astrocytes, suggesting the involvement of STAT2 activating signals selectively in astroglial response to injury. STAT1 was also up-regulated and phosphorylated but not exclusively in astrocytes. Both STAT2 up-regulation and phosphorylation were NF-kappaB -dependent since they did not occur in the lesion-reactive hippocampus of transgenic mice with specific inhibition of NF-kappaB activation in astrocytes. We further showed that lack of NF-kappaB signaling significantly reduced injury-induced CCL2 expression as well as leukocyte infiltration. Our results suggest that NF-kappaB signaling in astrocytes controls expression of both STAT2 and CCL2, and thus regulates infiltration of leukocytes into lesion-reactive hippocampus after axonal injury. Taken together, these findings indicate a central role for astrocytes in directing immune-glial interaction in the CNS injury response.

Tumor necrosis factor p55 and p75 receptors are involved in chemical-induced apoptosis of dentate granule neurons

Localized tumor necrosis factor-alpha (TNFalpha) elevation has diverse effects in brain injury often attributed to signaling via TNFp55 or TNFp75 receptors. Both dentate granule cells and CA pyramidal cells express TNF receptors (TNFR) at low levels in a punctate pattern. Using a model to induce selective death of dentate granule cells (trimethyltin; 2 mg/kg, i.p.), neuronal apoptosis [terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ end labeling, active caspase 3 (AC3)] was accompanied by amoeboid microglia and elevated TNFalpha mRNA levels. TNFp55R (55 kDa type-1 TNFR) and TNFp75R (75 kDa type-2 TNFR) immunoreactivity in AC3(+) neurons displayed a pattern suggestive of receptor internalization and a temporal sequence of expression of TNFp55R followed by TNFp75R associated with the progression of apoptosis. A distinct ramified microglia response occurred around CA1 neurons and healthy dentate neurons that displayed an increase in the normal punctate pattern of TNFRs. Neuronal damage was decreased with i.c.v. injection of TNFalpha antibody and in TNFp55R-/-p75R-/- mice that showed higher constitutive mRNA levels for interleukin (IL-1alpha), macrophage inflammatory protein 1-alpha (MIP-1alpha), TNFalpha, transforming growth factor beta1, Fas, and TNFRSF6-assoicated via death domain (FADD). TNFp75R-/- mice showed exacerbated injury and elevated mRNA levels for IL-1alpha, MIP-1alpha, and TNFalpha. In TNFp55R-/- mice, constitutive mRNA levels for TNFalpha, IL-6, caspase 8, FADD, and Fas-associated phosphatase were higher; IL-1alpha, MIP-1alpha, and transforming growth factor beta1 lower. The mice displayed exacerbated neuronal death, delayed microglia response, increased FADD and TNFp75R mRNA levels, and co-expression of TNFp75R in AC3(+) neurons. The data demonstrate TNFR-mediated apoptotic death of dentate granule neurons utilizing both TNFRs and suggest a TNFp75R-mediated apoptosis in the absence of normal TNFp55R activity.

Cerebral ischemia/stroke and small ubiquitin-like modifier (SUMO) conjugation--a new target for therapeutic intervention?

Transient cerebral ischemia/stroke activates various post-translational protein modifications such as phosphorylation and ubiquitin conjugation that are believed to play a major role in the pathological process triggered by an interruption of blood supply and culminating in cell death. A new system of post-translational protein modification has been identified, termed as small ubiquitin-like modifier (SUMO) conjugation. Like ubiquitin, SUMO is conjugated to the lysine residue of target proteins in a complex process. This review summarizes observations from recent experiments focusing on the effect of cerebral ischemia on SUMO conjugation. Transient global and focal cerebral ischemia both induced a rapid, dramatic and long-lasting rise in levels of SUMO2/3 conjugation. After transient focal cerebral ischemia, SUMO conjugation was particularly prominent in neurons located at the border of the ischemic territory where SUMO-conjugated proteins translocated to the nucleus. Many SUMO conjugation target proteins are transcription factors and sumoylation has been shown to have a major impact on the activity, stability, and cellular localization of target proteins. The rise in levels of SUMO-conjugated proteins is therefore likely to have a major effect on the fate of post-ischemic neurons. The sumoylation process could provide an exciting new target for therapeutic intervention.

Development of spontaneous optic neuropathy in NF-kappaBetap50-deficient mice: requirement for NF-kappaBetap50 in ganglion cell survival

Although the transcription factor NF-kappaBeta is known to regulate cell death and survival, its precise role in cell death within the central nervous system remains unknown. The purpose of this study was to investigate the role of NF-kappaBetap50 in the age-related survival of retinal ganglion cells (RGCs). Eyes of mice with a deleted NF-kappaBetap50 gene and its wild-type mice at each of age were studied by histopathological studies. The number of RGCs was counted using retrograde labelling methods. Mice were subjected to intravitreous injection of N-methyl-D aspartate (NMDA) to induce RGC death. In p50-deficient mice, the number of RGCs significantly decreased with age in total independence of intraocular pressure measurement. Optic nerves of p50-deficient mice showed hypertrophy astrocytes and enlargement of the axons, together with a decreased number of axons. Immunohistochemistry showed a strong expression of glial fibrillary acidic protein. The histological results show obvious excavation of the optic nerve head in p50-deficient mice at 10 months of age. Intravitreal injection of NMDA in young p50-deficient mice damaged RGCs more intensively than in control animals. We further noticed that autoantibodies against RGCs were produced in p50-deficient mice. Our results show that p50 deficiency induced age-related RGC death, indicating a new insight into the role of p50 in the pathophysiology of neuropathy, and further experiments with p50-deficient mice may provide new targets for therapeutic intervention for human glaucoma.

Transcriptional regulation of polysialylated neural cell adhesion molecule expression by NMDA receptor activation in retinoic acid-differentiated SH-SY5Y neuroblastoma cultures

NMDA receptors exhibit a dichotomy of signaling with excessive stimulation leading to neuronal damage that occurs during neurodegenerative disorders, whereas the normal burst of activity results in plastic responses with the expression of molecular substrates of long-term plasticity, growth and survival. Control of polysialylated neural cell adhesion molecule (PSA-NCAM) expression by NMDA receptor activation has been described in several systems, suggesting a functional link between these two proteins. The coordinated induction of several different transcription factors initiated by NMDA receptor stimulation may be a key mechanism in the orchestration of specific target gene expression that underlies various aspects of CNS function, including plastic responses. We report here the transcriptional regulation of PSA-NCAM expression by subtoxic dose of NMDA in retinoic acid-differentiated SH-SY5Y cell cultures. SH-SY5Y cell cultures differentiated with retinoic acid (10 microM) were exposed to NMDA (100 microM) or to antagonist MK-801 (200 nM) prior to treatment with NMDA and cells were harvested after 24 h of treatment to study the expression of PSA-NCAM, nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) by Western blotting and dual immunocytofluorescence and expression of polysialyltransferase (PST) mRNA by fluorescent in situ hybridization (FISH). We observed the induction of transcription factors NF-kappaB and AP-1 along with PSA-NCAM expression in response to NMDA receptor activation. Also, PSA-NCAM regulation in response to NMDA receptor activity was shown to be transcriptionally controlled, as seen by temporal and spatial changes observed in the expression of PST mRNA in NMDA-treated SH-SY5Y cell cultures. This raises the interesting possibility that NF-kappaB and AP-1 expression is involved in propagating the signals of NMDA receptor activity that leads to downstream strengthening of long-term plasticity changes in differentiated SH-SY5Y neuroblastoma cell cultures. Thus understanding the regulation of PSA-NCAM expression by NMDA receptor-mediated activity may represent a fundamental prerequisite for the development of therapies in order to maintain neuronal plasticity throughout life and functional recovery after brain damage.

Nuclear factor kappa-B p50 and p65 subunits expression in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia after Alzheimer's disease (AD). Parkinsonism in DLB is mainly caused by neuronal loss with Lewy bodies (LBs) in the substantia nigra, thereby inducing degeneration of the nigrostriatal dopaminergic pathway similar to that in Parkinson's disease (PD). To clarify the pathogenesis of DLB, it is important to investigate the mechanisms involved in the degenerative process of LB-bearing neurones. Several reports suggest a role for nuclear factor kappa-B (NFkappaB) in the manifestation of neurodegenerative conditions such as AD and PD. The aim of the present study was to investigate whether NFkappaB subunits are involved in the pathogenesis of neurodegeneration in DLB by measuring tyrosine hydroxylase (TH), NFkappaB p65 and p50 protein expression in frontal cortex and substantia nigra pars compacta of DLB and control human brains. An increase, although not statistically significant, in nigral TH expression in DLB cases was observed. There were no differences in the cortical and nigral expression levels of NFkappaB p65 subunit between control and DLB cases. Western blots of the frontal cortex showed no differences in the expression levels of NFkappaB p50 subunit. However, NFkappaB p50 levels were significantly decreased (P < 0.05) in the pars compacta of the substantia nigra in the DLB cases in comparison with controls. The decrease in the expression of the p50 subunit in the substantia nigra of DLB cases achieved in the present study may increase the vulnerability of the dopaminergic neurones to a possible neurotoxic effect of p65 subunit. Thus, normal levels of NFkappaB p65 might be toxic in neurones with a low expression of the NFkappaB p50 subunit.

Recent Studies on the Trimethyltin Actions in Central Nervous Systems

Trimethyltin (TMT) is a toxic organotin compound that produces injury to the central nervous systems of mammals. Recently, high-dose TMT (2.8 mg/kg) has been shown to produce neurodegeneration and subsequent neurogenesis specifically in the hippocampal dentate gyrus of mice, indicating that mice injected with TMT serve as a useful in vivo model to study neurogenesis as well as neurodegeneration in this brain region. In addition, gene-engineered mice have allowed research to focuse on the mechanisms of TMT toxicity. These studies have revealed the involvement of stannin, nuclear factor kappa B (NF-kappaB), presenilin-1, apolipoprotein E, and pituitary adenylyl cyclase-activating polypeptide (PACAP) in TMT toxicity and suggested the relationship between genetic mutations and neuronal susceptibility to degeneration. In this review, we briefly summarize the previous studies and discuss the current status of research on TMT.

Ion transport in alveolar type I cells

This highlight article summarizes the current published literature of ion channels and ion transport in type I cells. Twenty years ago, the general theory of ion and fluid transport in the lung was that the alveolar type II cells, known to contain ion channels, governed ion transport and that the type I cells, believed to be incapable of ion transport, only allowed passive movement of water. Unable to reconcile the extraordinarily large surface area covered by type I cells (95% of the internal surface area of the lung) with such minimal biological activity, investigators set out to demonstrate that type I cells were capable of ion transport and played a role in regulating lung fluid balance. Various methods were employed to show that type I cells contained ENaC (HSC and NSC channels), CNG and K(+) channels, and CFTR, further necessitating a revision of the current theories of ion and fluid transport in the lung.

Multiplicity of expression of FXYD proteins in mammalian cells: dynamic exchange of phospholemman and gamma-subunit in response to stress

Functional properties of Na-K-ATPase can be modified by association with FXYD proteins, expressed in a tissue-specific manner. Here we show that expression of FXYDs in cell lines does not necessarily parallel the expression pattern of FXYDs in the tissue(s) from which the cells originate. While being expressed only in lacis cells in the juxtaglomerular apparatus and in blood vessels in kidney, FXYD1 was abundant in renal cell lines of proximal tubule origin (NRK-52E, LLC-PK1, and OK cells). Authenticity of FXYD1 as a part of Na-K-ATPase in NRK-52E cells was demonstrated by co-purification, co-immunoprecipitation, and co-localization. Induction of FXYD2 by hypertonicity (500 mosmol/kgH(2)O with NaCl for 48 h or adaptation to 700 mosmol/kgH(2)O) correlated with downregulation of FXYD1 at mRNA and protein levels. The response to hypertonicity was influenced by serum factors and entailed, first, dephosphorylation of FXYD1 at Ser(68) (1-5 h) and, second, induction of FXYD2a and a decrease in FXYD1 with longer exposure. FXYD1 was completely replaced with FXYD2a in cells adapted to 700 mosmol/kgH(2)O and showed a significantly decreased sodium affinity. Thus dephosphorylation of FXYD1 followed by exchange of regulatory subunits is utilized to make a smooth transition of properties of Na-K-ATPase. We also observed expression of mRNA for multiple FXYDs in various cell lines. The expression was dynamic and responsive to physiological stimuli. Moreover, we demonstrated expression of FXYD5 protein in HEK-293 and HeLa cells. The data imply that FXYDs are obligatory rather than auxiliary components of Na-K-ATPase, and their interchangeability underlies responses of Na-K-ATPase to cellular stress.

NF-kappaB functions in the nervous system: from development to disease

The transcription factor nuclear factor-kappaB (NF-kappaB) is an ubiquitously expressed dimeric molecule with post-translationally regulated activity. Its role in the immune system and host defense has been well characterized over the last two decades. In contrast, our understanding of the function of this transcription factor in the nervous system (NS) is only emerging. Given their cytoplasmic retention and nuclear translocation upon stimulus, NF-kappaB members are likely to exert an important role in transduction of signals from synaptic terminals to nucleus, to initiate transcriptional responses. This report describes recent findings deciphering the diverse functions of NF-kappaB in NS development and activity, which range from the control of cell growth, survival and inflammatory response to synaptic plasticity, behavior and cognition. Particular attention is given to the specific roles of NF-kappaB in the various cells of the NS, e.g. neurons and glia. Current knowledge of the contribution of NF-kappaB to several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases is also summarized.

Reduced Nuclear Factor kappa B activation in dentate gyrus after active avoidance training

Nuclear Factor kappa B (NF-kappaB) is a transcription factor associated with neuroplasticity and neuronal survival during injury. Although NF-kappaB has been proven to be involved in various processes of repair, there is also evidence that NF-kappaB is associated with learning and memory formation. Our laboratory has previously observed that mice lacking the NF-kappaB p50 subunit are not proficient in learning tasks associated with active avoidance training, an effective learning paradigm. The purpose of this study is to identify changes in NF-kappaB levels after active avoidance training using kappaB-dependent lacZ transgenic mice. Levels of NF-kappaB activity were detected immunohistochemically after active avoidance training in brain regions associated with learning and memory. NF-kappaB activity in trained mice was significantly decreased in the dentate gyrus, but no significant changes were found in other brain regions of trained mice compared to untrained mice. The number of p50-containing neurons was counted in the dentate gyrus and a significant increase was discovered in the trained mice relative to untrained mice. The decrease of NF-kappaB-containing neurons in the dentate gyrus coincides with elevated levels of activated p50 neurons and may be caused by the ability of p50 homodimers to inhibit NF-kappaB transactivation. These results indicate that increased p50 expression down-regulates NF-kappaB activity in the dentate gyrus after exposure to unconditioned stimulus. Therefore, a reduction of NF-kappaB activation and its target genes appears to be a necessary event for early stages of learning and memory consolidation associated with active avoidance training.

Immunolocalization and activation of nuclear factor-κB in the sciatic nerves of rats with experimental autoimmune neuritis

Recent data support an important role played by nuclear factor kappa B (NF-kappaB) in peripheral neuropathies. We investigated expression and activation of NF-kappaB in experimental autoimmune neuritis (EAN) in rat sciatic nerves removed after 7, 14 and 21 days after immunization. Immunoreactivity for the activated form of NF-kappaB was found in the nuclei of T cells and macrophages at days 14 and 21, and also in the nuclei of few Schwann cells and of vascular endothelial cells at all time points, especially during the peak stage. Western blot showed a single band corresponding to 65 kDa in all EAN animals. NF-kappaB DNA-binding activity was revealed by electrophoretic mobility shift assay. Our results support NF-kappaB activation in EAN during the induction stage as well as in the disease remission.

NF-kappaB protects neurons from ischemic injury after middle cerebral artery occlusion in mice

Knowledge about the molecular mechanisms of neuronal survival following ischemia is crucial to the development of therapeutic interventions for victims of stroke. Previous research in our laboratory has implicated nuclear factor-kappaB (NF-kappaB) as contributing to neuronal survival in response to toxic or ischemic brain insult, with in vivo models having focused on the rat. To take advantage of genetic alterations available in the mouse, we utilized a murine transient endovascular middle cerebral artery occlusion (MCAO) model to examine the influence of NF-kappaB on neuronal survival. When brains were immunostained for the nuclear localization sequence (NLS) of the p50 subunit of NF-kappaB, a unilateral increase in immunoreactivity was seen, especially in pyramidal cell layers of the ipsilateral (stroked) hippocampus. When transgenic mice lacking p50 were compared with non-transgenic counterparts using Fluoro-Jade, a marker for neurodegeneration, both the hippocampus and striatum showed enhanced neurodegeneration at various survival times after 1 h of MCAO. In the hippocampus specifically, there was an eightfold increase in Fluoro-jade staining in the p50 knockout group vs. the non-transgenic group. Sections double stained for Fluoro-Jade and NF-kappaB activity (using a mouse engineered with a NF-kappaB responsive promoter driving a LacZ gene to produce beta galactosidase) demonstrated neuronal degeneration only in regions sparsely showing NF-kappaB activity, and those demonstrating NF-kappaB activity failed to degenerate. These data provide evidence that NF-kappaB participates in survival signaling following temporary focal ischemia, and thus may represent an attractive target for pharmacologic activation in the treatment of stroke.

FXYD proteins: new regulators of Na-K-ATPase

FXYD proteins belong to a family of small-membrane proteins. Recent experimental evidence suggests that at least five of the seven members of this family, FXYD1 (phospholemman), FXYD2 (gamma-subunit of Na-K-ATPase), FXYD3 (Mat-8), FXYD4 (CHIF), and FXYD7, are auxiliary subunits of Na-K-ATPase and regulate Na-K-ATPase activity in a tissue- and isoform-specific way. These results highlight the complexity of the regulation of Na+ and K+ handling by Na-K-ATPase, which is necessary to ensure appropriate tissue functions such as renal Na+ reabsorption, muscle contractility, and neuronal excitability. Moreover, a mutation in FXYD2 has been linked to cases of human hypomagnesemia, indicating that perturbations in the regulation of Na-K-ATPase by FXYD proteins may be critically involved in pathophysiological states. A better understanding of this novel regulatory mechanism of Na-K-ATPase should help in learning more about its role in pathophysiological states. This review summarizes the present knowledge of the role of FXYD proteins in the modulation of Na-K-ATPase as well as of other proteins, their regulation, and their structure-function relationship.

Splice Variants of the Gamma Subunit (FXYD2) and Their Significance in Regulation of the Na, K-ATPase in Kidney

The recent discovery of a family of single-span membrane proteins (the FXYD proteins) introduced a new direction to the rather complicated area of regulation of Na, K-ATPase. At least six members of the family have been shown to associate with the Na, K-ATPase in a cell- and tissue-specific manner, while four of them, namely the gamma subunit (FXYD2), CHIF (FXYD4), phospholemman (FXYD1), and dysadherin (FXYD5) have been identified in kidney. All four exhibited different effects on the properties of the pump in heterologous expression systems. Taken along with their non-overlapping expression patterns in the nephron, this provides a potential structural basis for the segment-specific properties of the Na, K-ATPase that had been reported in a number of papers on kidney physiology. This brief review summarizes our own contributions on structure/functional characterization of one of the family members, the gamma subunit (FXYD2). The focus is on splice variants of gamma, their structural similarity and yet distinct effects conferred to Na, K-ATPase.

Distinct nuclear factor-kappaB/Rel proteins have opposing modulatory effects in glutamate-induced cell death in HT22 cells

Members of the nuclear factor-kappaB (NF-kappaB)/Rel family (p50, p52, p65 (RelA), RelB and c-Rel) is sequestered in the cytoplasm through its tight association with the inhibitor of NF-kappaB (IkappaB). NF-kappaB has been shown to function as key regulators of either cell death or survival in neurons after activation of the cells by various extracellular signals. In the study presented here, we investigated whether the selective activation of diverse NF-kappaB/Rel family members in HT22 cells might lead to distinct effects on glutamate-induced cell death. Exposing HT22 cells to glutamate, which blocks cystine uptake into the cells via inhibition of the glutamate-cystine antiporter, resulted in a transient activation of IkappaB and NF-kappaB/Rel and caused delayed cell death. Aspirin, which has been shown to block phosphorylation of the IkappaB component of the cytoplasmic NF-kappaB complex, significantly suppressed glutamate-induced cell death, whereas the NF-kappaB decoy oligonucleotide potentiated it. The inhibition of NF-kappaB/Rel protein expression by antisense oligonucleotides showed that p65 is involved in glutamate-mediated cell death, whereas p50 is involved in inhibitory pathways of the cell death. These findings suggest that in HT22 cells, the balance between promoting and presenting cell death to glutamate-induced oxidative stress relies on the activation of distinct NF-kappaB proteins.

Signaling via NF-κB in the nervous system

Nuclear factor kappa B (NF-kappaB) is an inducible transcription factor present in neurons and glia. Recent genetic models identified a role for NF-kappaB in neuroprotection against various neurotoxins. Furthermore, genetic evidence for a role in learning and memory is now emerging. This review highlights our current understanding of neuronal NF-kappaB in response to synaptic transmission and summarizes potential physiological functions of NF-kappaB in the nervous system. This article contains a listing of NF-kappaB activators and inhibitors in the nervous system, furthermore specific target genes are discussed. Synaptic NF-kappaB activated by glutamate and Ca2+ will be presented in the context of retrograde signaling. A controversial role of NF-kappaB in neurodegenerative diseases will be discussed. A model is proposed explaining this paradox as deregulated physiological NF-kappaB activity, where novel results are integrated, showing that p65 could be turned from an activator to a repressor of anti-apoptotic genes.

Neuroprotection by stem cell factor in rat cortical neurons involves AKT and NFκB

Stem cell factor (SCF) is a highly expressed cytokine in the central nervous system. In the present study, we demonstrate a neuroprotective role for SCF and its tyrosine kinase receptor, c-kit, against camptothecin-induced apoptosis and glutamate excitotoxicity in rat cortical neurons. This protection was blocked by pharmacological or molecular inhibition of either the MEK/ERK or PI3K/Akt signaling pathways. The importance of these pathways was further confirmed by the activation of both ERK, in a MEK-dependent manner, and Akt, via PI3K. Activation of Akt increased the binding of the p50 and p65 subunits of NFkappaB, which was also important for neuroprotection. Akt inhibition prevented NFkappaB binding, suggesting a role for Akt in SCF-induced NFkappaB. Pharmacological inhibition of NFkappaB or dominant negative IkappaB also prevented neuroprotection by SCF. SCF up-regulated the anti-apoptotic genes, bcl-2 and bcl-xL in an NFkappaB-dependent manner. Together, these findings demonstrate a neuroprotective role for SCF in cortical neurons, an effect that was mediated by Akt and ERK, as well as NFkappaB-mediated gene transcription. SCF represents a novel therapeutic target in the treatment of neurodegenerative disease.

p53 in neuronal apoptosis

The tumor suppressor and transcription factor p53 is a key modulator of cellular stress responses, and activation of p53 can trigger apoptosis in many cell types including neurons. Apoptosis is a form of programmed cell death that occurs in neurons during development of the nervous system and may also be responsible for neuronal deaths that occur in neurological disorders such as stroke, and Alzheimer's and Parkinson's diseases. p53 production is rapidly increased in neurons in response to a range of insults including DNA damage, oxidative stress, metabolic compromise, and cellular calcium overload. Target genes induced by p53 in neurons include those encoding the pro-apoptotic proteins Bax and the BH3-only proteins PUMA and Noxa. In addition to such transcriptional control of the cell death machinery, p53 may more directly trigger apoptosis by acting at the level of mitochondria, a process that can occur in synapses (synaptic apoptosis). Preclinical data suggest that agents that inhibit p53 may be effective therapeutics for several neurodegenerative conditions.

Activation of NF-κB in the mouse spinal cord following sciatic nerve transection

NF-kappaB is a ubiquitous nuclear transcription factor that regulates a number of physiological processes. NF-kappaB activity has been implicated in enhancing neuronal survival following CNS injury. The present study was conducted to test the hypothesis that NF-kappaB activity is up-regulated in neurons of the spinal cord in response to peripheral nerve transection. In this series of experiments, we used NF-kappaB reporter mice in which activation of NF-kappaB drives the expression of the lac-z gene. The response to injury of cells in the spinal cord was assessed by evaluating the number and distribution of beta-galalactosidase (beta-gal)-positive cells following sciatic nerve transection. The animals were randomly assigned to four groups, which were allowed to survive for one, three, five and ten days. Four mice that did not undergo sciatic nerve transection were assigned to each group to serve as controls. The total number of beta-gal-positive cells in the right and left dorsal and ventral horns were compared. The numbers of beta-gal-positive cells between the right and left sides were significantly different three and five days post axotomy (p<0.05). Double immunofluorescent labeling was utilized to characterize which cells showed NF-kappaB activity, and it revealed that all beta-gal-positive cells were colocalized with MAP-2-positive neurons. The results of this study demonstrated that complete sciatic nerve transection leads to an up-regulation of NF-kappaB transactivation in spinal neurons ipsilateral to the side of transection. The increase in activity in the ipsilateral dorsal horn is consistent with this transcription factor acting as neuronal survival signal during this time frame in response to the peripheral nerve insult.

Physiological functions for brain NF-kappaB

Members of the nuclear factor kappaB (NF-kappaB) family of transcription factors are activated within the CNS in pathological settings of apoptosis and neurological disease. Recent work using several model systems provides accumulating evidence that these transcription factors also participate in the regulation of neuronal activity-dependent transcription and behavior under physiological conditions. This review highlights advances in our understanding of the mechanisms of Ca(2+)-responsive activation and synaptic signaling to the nucleus by NF-kappaB transcription factors within the CNS, and the relevance of this transcription factor family for learning and memory.

Spectrum of ion channels in alveolar epithelial cells: implications for alveolar fluid balance

The efficient transition from placental to atmospheric delivery of oxygen at birth is critically dependent on rapid reabsorption of fetal lung fluid. In the perinatal period, this process is driven by active transepithelial sodium transport and is almost exclusively dependent on expression and modulation of the amiloride-sensitive epithelial sodium channel (ENaC). However, later in development, the amiloride sensitivity of the reabsorptive response, which must be sustained to keep the lungs effectively dry, wanes as a function of postnatal age. This Featured Topic (Experimental Biology Meeting, Washington, DC, April, 2004) presented exciting new evidence to demonstrate that, in addition to ENaC, the adult alveolar epithelium expresses a plethora of amiloride-insensitive ion channels, including cystic fibrosis transmembrane conductance regulator, proton channels, voltage-dependent potassium channels, and cyclic nucleotide-gated cation channels. Furthermore, important evidence for selective modulation of ENaC subunits in the lung in response to cardiovascular disease was demonstrated. Finally, it is clear that newly emerging models of human alveolar epithelium in combination with the novel lung slice electrophysiological preparation will ensure that the ascription of function to specific ion channels in the in situ human lung will soon be a real possibility.

Stress-induced expression of the gamma subunit (FXYD2) modulates Na,K-ATPase activity and cell growth

In kidney, the Na,K-ATPase is associated with a single span protein, the gamma subunit (FXYD2). Two splice variants are differentially expressed along the nephron and have a differential influence on Na,K-ATPase when stably expressed in mammalian cells in culture. Here we used a combination of gene induction and gene silencing techniques to test the functional impact of gamma by means other than transfection. NRK-52E cells (of proximal tubule origin) do not express gamma as a protein under regular tissue culture conditions. However, when they were exposed to hyperosmotic medium, induction of only the gammaa splice variant was observed, which was accompanied by a reduction in the rate of cell division. Kinetic analysis of stable enzyme properties from control (alpha1beta1) and hypertonicity-treated cultures (alpha1beta1gammaa) revealed a significant reduction (up to 60%) of Na,K-ATPase activity measured under V(max) conditions with little or no change in the amounts of alpha1beta1. This effect as well as the reduction in cell growth rate was practically abolished when gamma expression was knocked down using specific small interfering RNA duplexes. Surprisingly, a similar induction of endogenous gammaa because of hypertonicity was seen in rat cell lines of other than renal origin: C6 (glioma), PC12 (pheochromocytoma), and L6 (myoblasts). Furthermore, exposure of NRK-52E cells to other stress inducers such as heat shock, exogenous oxidation, and chemical stress also resulted in a selective induction of gammaa. Taken together, the data imply that induction of gammaa may have adaptive value by being a part of a general cellular response to genotoxic stress.