NF-kappa B transcription factor subunits in rat brain: colocalization of p65 and alpha-MSH

Synaptic NF-kappa B pathway in neuronal plasticity and memory

Several transcription factors are present at the synapse, and among these are the Rel-NF-kappa B pathway components. NF-kappa B is a constitutive transcription factor, with a strong presence in the brain of which a considerable part is located in the neuropiles. This localization of the transcription factor, plus evidence pointing to different functions, is what gave place to two general hypotheses for synaptic NF-kappa B: (a) The transcription factor plays a role in the synapse to nucleus communication, and it is retrogradely transported from polarized localizations to regulate gene expression; (b) The transcription factor modulates the synaptic function locally. Evidence indicates that both mechanisms can operate simultaneously; here we will present different possibilities of these hypotheses that are supported by an increasing amount of data. We pay special attention to the local role of the transcription factor at the synapse, and based in the described evidence from different animal models, we propose several processes in which the transcription factor may change the synaptic strength.

Glucocorticoid receptor signaling contributes to constitutive activation of the noncanonical NF-κB pathway in term human placenta

Our recent study demonstrated that constitutively activated RelB/NF-κB2 positively regulates the CRH in the human placenta. In the current study, we explored the role of the glucocorticoid receptor (GR) signaling in constitutive activation of the noncanonical NF-κB pathway. A glucocorticoid response element (GRE) motif search suggests that both NF-κB inducing kinase (NIK) and RelB genes, which are key regulators of the noncanonical NF-κB pathway, have a putative GRE within their promoter, approximately 1 kb upstream from the transcription start site. By using chromatin immunoprecipitation assay we identified that the GR and phosphorylated GR at Ser211 were associated with the GREs of both NIK and RelB. Dexamethasone stimulated expression of NIK, RelB, NF-κB2 as well as CRH and cyclooxygenase-2 (COX-2). Repression of GR by short interfering RNA resulted in inhibition of NIK, RelB, NF-κB2, CRH, and COX-2. In addition, depletion of GR attenuated glucocorticoid-mediated up-regulation of NIK, RelB, NF-κB2, CRH, and COX-2. Furthermore, siRNA specifically targeting NIK down-regulated CRH and COX-2. Taken together, these results suggest that constitutive activation of the noncanonical NF-κB pathway in term human placenta is driven by the GR signaling, which in turn up-regulates placental CRH and other NF-κB-responsive genes.

Role of alpha-melanocyte stimulating hormone and melanocortin 4 receptor in brain inflammation

Inflammatory processes contribute widely to the development of neurodegenerative diseases. The expression of many inflammatory mediators was found to be increased in central nervous system (CNS) disorders suggesting that these molecules are major contributors to neuronal damage. Melanocortins are neuropeptides that have been implicated in a wide range of physiological processes. The melanocortin alpha-melanocyte stimulating hormone (alpha-MSH) has pleiotropic functions and exerts potent anti-inflammatory actions by antagonizing the effects of pro-inflammatory cytokines and by decreasing important inflammatory mediators. Five subtypes of melanocortin receptors (MC1R-MC5R) have been identified. Of these, the MC4 receptor is expressed predominantly throughout the CNS. Evidence of effectiveness of selective MC4R agonists in modulating inflammatory processes and their low toxicity suggest that these molecules may be useful in the treatment of CNS disorders with an inflammatory component. This review describes the involvement of the MC4R in central anti-inflammatory effects of melanocortins and discusses the potential value of MC4R agonists for the treatment of inflammatory-related disorders.

Adenosine and sleep deprivation promote NF-kappaB nuclear translocation in cholinergic basal forebrain

In our investigations related to the homeostatic sleep factor adenosine (AD), we previously demonstrated that the DNA-binding activity of the transcription factor NF-kappaB in rat cholinergic basal forebrain increased following 3 h of sleep deprivation (SD). However, the neurotransmitter nature of the cells and the SD-induced stimuli responsible for NF-kappaB activation were not defined. In this report, we demonstrate, using double labeling immunohistochemistry, that nuclear translocation of NF-kappaB occurs almost exclusively in the cholinergic neurons of the basal forebrain following 3 h of SD. Furthermore, cholinergic basal forebrain microinjection of AD (25 nmol/L) or the A(1) receptor agonist N(6)-cyclo-hexyladenosine (100 nmol/L) induced nuclear translocation of NF-kappaB, thus suggesting that SD-induced increased extracellular concentrations of AD, acting via the A(1) AD receptor, may be responsible for the nuclear translocation of NF-kappaB in cholinergic neurons. Moreover, blocking the nuclear translocation of NF-kappaB by injection of inhibitor peptide, SN50, immediately prior to 6 h SD significantly reduced delta activity (1-4 Hz) during the first two hours of recovery sleep. Together, these data suggest a role in sleep homeostasis for the SD-induced activation of NF-kappaB in cholinergic basal forebrain, and that transcription factor NF-kappaB may code for factor(s) that play a role in sleep homeostasis.

Divergent roles for tumor necrosis factor-alpha in the brain

Proinflammatory cytokines and chemokines have been implicated in the pathogenesis of several neurological and neurodegenerative disorders. Prominent among such factors is the pleiotropic cytokine, tumor necrosis factor (TNF)-alpha. Under normal physiological conditions, TNF-alpha orchestrates a diverse array of functions involved in immune surveillance and defense, cellular homeostasis, and protection against certain neurological insults. However, paradoxical effects of this cytokine have been observed. TNF-alpha is elicited in the brain following injury (ischemia, trauma), infection (HIV, meningitis), neurodegeneration (Alzheimer's, Parkinson's), and chemically induced neurotoxicity. The multifarious identity for this cytokine appears to be influenced by several mechanisms. Among the most prominent are the regulation of TNFalpha-induced NF-kappaB activation by adapter proteins such as TRADD and TRAF, and second, the heterogeneity of microglia and their distribution pattern across brain regions. Here, we review the differential role of TNF-alpha in response to brain injury, with emphasis on neurodegeneration, and discuss the possible mechanisms for such diverse and region-specific effects.

Deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP-induced neurotoxicity: role of TNF-alpha

Enhanced expression of tumor necrosis factor (TNF) -alpha, is associated with the neuropathological effects underlying disease-, trauma- and chemically induced neurodegeneration. Previously, we have shown that deficiency of TNF receptors protects against MPTP-induced striatal dopaminergic neurotoxicity, findings suggestive of a role for TNF-alpha in neurodegeneration. Here, we demonstrate that deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP. MPTP-induced expression of microglia-derived factors, TNF-alpha, MCP-1, and IL-1alpha, preceded the degeneration of striatal dopaminergic nerve terminals and astrogliosis, as assessed by loss of striatal dopamine and TH, and an increase in striatal GFAP. Pharmacological neuroprotection with the dopamine reuptake inhibitor, nomifensine, abolished striatal dopaminergic neurotoxicity and associated microglial activation. Similarly, in mice lacking TNF receptors, microglial activation was suppressed, findings consistent with a role for TNF-alpha in striatal MPTP neurotoxicity. In the hippocampus, however, TNF receptor-deficient mice showed exacerbated neuronal damage after MPTP, as evidenced by Fluoro Jade-B staining (to identify degenerating neurons) and decreased microtubule-associated protein-2 (MAP-2) immunoreactivity. These effects were not accompanied by microglial activation, but were associated with increased oxidative stress (nitrosylation of tyrosine residues). These findings suggest that TNF-alpha exerts a neurotrophic/neuroprotective effect in hippocampus. The marked differences we observed in the regional density, distribution and/or activity of microglia and microglia-derived factors may influence the region-specific role for this cell type. Taken together, our results are indicative of a region-specific and dual role for TNF-alpha in the brain: a promoter of neurodegeneration in striatum and a protector against neurodegeneration in hippocampus.

Sleep deprivation increases the activation of nuclear factor kappa B in lateral hypothalamic cells

Sleep deprivation increases sleep propensity in rats and mice as well as the production of several sleep-regulatory substances. Nuclear factor kappa B (NF-kappa B) is a transcription factor implicated in the activation of many of these sleep-promoting substances. A unique population of neurons immunoreactive for the p65 subunit of NF-kappa B was previously localized within the caudal dorsolateral hypothalamus of rats. Therefore, we evaluated the effect of sleep deprivation on NF-kappa Bp65-immunoreactivity (IR) in cells of this region in rats as well as its nuclear translocation in a kappa B-lacZ transgenic mouse line. In rats after 6 h of sleep deprivation beginning at light onset, the number of neurons with NF-kappa Bp65-IR increased significantly in the caudal lateral hypothalamus, specifically the magnocellular lateral hypothalamus adjacent to the subthalamus. Sleep deprivation also significantly increased the number of cells expressing NF-kappa B-dependent beta-galactosidase in the magnocellular lateral hypothalamus, zona incerta dorsal, as well as the adjacent subthalamus in the transgenic mice. These results suggest that NF-kappa B expressing cells within the lateral hypothalamus may be important in the maintenance of the sleep-wake cycle.

Tumor necrosis factor(alpha) and insulin-like growth factor-I in the brain: is the whole greater than the sum of its parts?

The cytokine tumor necrosis factor(alpha) (TNFalpha) and the hormone insulin-like growth factor-I (IGF-I) have both been shown to regulate inflammatory events in the central nervous system (CNS). This review summarizes the seemingly independent roles of TNFalpha and IGF-I in promoting and inhibiting neurodegenerative diseases. We then offer evidence that the combined effects of IGF-I and TNFalpha on neuronal survival can be vastly different when both receptors are stimulated simultaneously, as is likely to occur in vivo. We propose the framework of a molecular model of hormone-cytokine receptor cross talk in which disparate cell surface receptors share intracellular substrates that regulate neuronal survival.

"Inflammatory" cytokines: neuromodulators in normal brain?

If cytokines are constitutively expressed by and act on neurons in normal adult brain, then we may have to modify our current view that they are predominantly inflammatory mediators. We critically reviewed the literature to determine whether we could find experimental basis for such a modification. We focused on two "proinflammatory" cytokines, interleukin (IL)-1 and tumor necrosis factor-alpha (TNFalpha) because they have been most thoroughly investigated in shaping our current thinking. Evidence, although equivocal, indicates that the genes coding for these cytokines and their accessory proteins are expressed by neurons, in addition to glial cells, in normal brain. Their expression is region- and cell type-specific. Furthermore, bioactive cytokines have been extracted from various regions of normal brain. The cytokines' receptors selectively are present on all neural cell types, rendering them responsive to cytokine signaling. Blocking their action modifies multiple neural "housekeeping" functions. For example, blocking IL-1 or TNFalpha by several independent means alters regulation of sleep. This indicates that these cytokines likely modulate in the brain behavior of a normal organism. In addition, these cytokines are likely involved in synaptic plasticity, neural transmission, and Ca2+ signaling. Thus, the evidence strongly suggests that these cytokines perform neural functions in normal brain. We therefore propose that they should be thought of as neuromodulators in addition to inflammatory mediators.

Mechanisms of the antiinflammatory effects of alpha-MSH. Role of transcription factor NF-kappa B and adhesion molecule expression

The recruitment of leukocytes from the circulation to inflamed tissue is regulated by the expression of adhesion molecules on both leukocytes and endothelial cells. The proopiomelanocortin-derived peptide alpha-melanocyte stimulating hormone (alpha-MSH) is known to modulate inflammation. Thus, we investigated the influence of alpha-MSH on the LPS-induced expression of the adhesion molecules E-selectin and VCAM-1 on endothelial cells. Human microvascular endothelial cells (HMEC-1) were treated with LPS (100 ng/ml) alone or in the presence of alpha-MSH (10(-8) to 10(-16) M). RT-PCR analysis showed that alpha-MSH significantly reduced LPS-induced expression of VCAM-1 and E-selectin. Since many adhesion molecules contain regulatory NF-kappa B sites in their promoter region, the role of alpha-MSH in the activation of the transcription factor NF-alpha B was also investigated. alpha-MSH significantly downregulated the LPS-mediated activation of NF-kappa B, in a dose-dependent manner. These findings indicate that modulation of the transcription factor NF-kappa B is a crucial molecular event, one that seems to be responsible for the antiinflammatory effects of alpha-MSH.

α-Melanocyte-Stimulating Hormone Inhibits the Nuclear Transcription Factor NF-κB Activation Induced by Various Inflammatory Agents

α-Melanocyte-stimulating hormone (α-MSH) is a tridecapeptide found mainly in the brain, pituitary, and circulation. It inhibits most forms of inflammation by a mechanism that is not known. As most types of inflammation require activation of NF-κB, we investigated the effect of α-MSH on the activation of this transcription factor by a wide variety of inflammatory stimuli. Electrophoretic mobility shift assay showed that α-MSH completely abolished TNF-mediated NF-κB activation in a dose- and time-dependent manner. It also suppressed NF-κB activation induced by LPS, okadaic acid, and ceramide. The effect was specific, as the activation of the transcription factor activating protein-1 by TNF was unaffected. Western blot analysis revealed that TNF-dependent degradation of the inhibitory subunit of NF-κB, IκBα, and nuclear translocation of the p65 subunit of NF-κB were also inhibited. This correlated with suppression of NF-κB-dependent reporter gene expression induced by TNF. The inhibitory effect of α-MSH appeared to be mediated through generation of cAMP, as inhibitors of adenylate cyclase and of protein kinase A reversed its inhibitory effect. Similarly, addition of membrane-permeable dibutyryl cAMP, like α-MSH, suppressed TNF-induced NF-κB activation. Overall, our results suggest that α-MSH suppresses NF-κB activated by various inflammatory agents and that this mechanism probably contributes to its anti-inflammatory effects.

Age-associated alterations in hippocampal and basal forebrain nuclear factor kappa B activity

Age-related cognitive deficits are often associated with loss of cholinergic activity within the neurotrophin-dependent cholinergic neurons that project from the basal forebrain to the hippocampus. The cause of reduced cholinergic function is unknown, but alterations in transcription factor-signaling pathways causing altered gene expression may cause decreased specific tissue function, resulting in loss of cholinergic activity. We measured transcription factor Nuclear Factor kappa B by electrophoretic mobility shift assay and Western analysis in young and aged rat brain tissues and report that basal levels of Nuclear Factor kappa B DNA-binding activity increase in the hippocampus and basal forebrain with age to significantly higher levels at 30 months of age. This age-associated increase in binding activity is associated with increased translocation of p65 to the nucleus. These data show an age-associated alteration in Nuclear Factor kappa B signal transduction pathways that may contribute to age-associated decreases in specific tissue function.