Tumor necrosis factor-alpha triggers cell death of sensitized potassium chloride-stimulated cholinergic neurons

Microcontact Printing of Cholinergic Neurons in Organotypic Brain Slices

Alzheimer's disease is a severe neurodegenerative disorder of the brain, characterized by beta-amyloid plaques, tau pathology, and cell death of cholinergic neurons, resulting in loss of memory. The reasons for the damage of the cholinergic neurons are not clear, but the nerve growth factor (NGF) is the most potent trophic factor to support the survival of these neurons. In the present study we aim to microprint NGF onto semipermeable 0.4 μm pore membranes and couple them with organotypic brain slices of the basal nucleus of Meynert and to characterize neuronal survival and axonal growth. The brain slices were prepared from postnatal day 10 wildtype mice (C57BL6), cultured on membranes for 2–6 weeks, stained, and characterized for choline acetyltransferase (ChAT). The NGF was microcontact printed in 28 lines, each with 35 μm width, 35 μm space between them, and with a length of 8 mm. As NGF alone could not be printed on the membranes, NGF was embedded into collagen hydrogels and the brain slices were placed at the center of the microprints and the cholinergic neurons that survived. The ChAT+ processes were found to grow along with the NGF microcontact prints, but cells also migrated. Within the brain slices, some form of re-organization along the NGF microcontact prints occurred, especially the glial fibrillary acidic protein (GFAP)+ astrocytes. In conclusion, we provided a novel innovative microcontact printing technique on semipermeable membranes which can be coupled with brain slices. Collagen was used as a loading substance and allowed the microcontact printing of nearly any protein of interest.

Tumor Necrosis Factor α Influences Phenotypic Plasticity and Promotes Epigenetic Changes in Human Basal Forebrain Cholinergic Neuroblasts

TNFα is the main proinflammatory cytokine implicated in the pathogenesis of neurodegenerative disorders, but it also modulates physiological functions in both the developing and adult brain. In this study, we investigated a potential direct role of TNFα in determining phenotypic changes of a recently established cellular model of human basal forebrain cholinergic neuroblasts isolated from the nucleus basalis of Meynert (hfNBMs). Exposing hfNBMs to TNFα reduced the expression of immature markers, such as nestin and β-tubulin III, and inhibited primary cilium formation. On the contrary, TNFα increased the expression of TNFα receptor TNFR2 and the mature neuron marker MAP2, also promoting neurite elongation. Moreover, TNFα affected nerve growth factor receptor expression. We also found that TNFα induced the expression of DNA-methylation enzymes and, accordingly, downregulated genes involved in neuronal development through epigenetic mechanisms, as demonstrated by methylome analysis. In summary, TNFα showed a dual role on hfNBMs phenotypic plasticity, exerting a negative influence on neurogenesis despite a positive effect on differentiation, through mechanisms that remain to be elucidated. Our results help to clarify the complexity of TNFα effects in human neurons and suggest that manipulation of TNFα signaling could provide a potential therapeutic approach against neurodegenerative disorders.

Nerve growth factor released from collagen scaffolds protects axotomized cholinergic neurons of the basal nucleus of Meynert in organotypic brain slices

BACKGROUND

Alzheimeŕs disease is accompanied by cell death of cholinergic neurons, resulting in cognitive impairment and memory loss. Nerve growth factor (NGF) is the most potent protein to support survival of cholinergic neurons.

NEW METHOD

Organotypic brain slices of the basal nucleus of Meynert (nBM) are a valuable tool to study cell death of axotomized cholinergic neurons, as well as protective effects of NGF added into the medium. The aim of the present study is to use collagen scaffolds crosslinked with polyethyleneglycole and load with NGF to target delivery of NGF to organotypic nBM brain slices.

RESULTS

Collagen scaffolds (visualized by incorporating AlexaFluor 488 antibodies) slowly degraded when applied onto organotypic brain slices within 2 weeks in culture. GFAP reactive astrocytes and Iba1+ microglia became visible around the collagen scaffolds 7days after incubation, showing reactive gliosis. Cholinergic neurons of the nBM survived (201±21, n=8) when incubated with 100ng/ml NGF in the medium compared to NGF-free medium (69±12, n=7). Collagen scaffolds loaded with NGF (1ng/2μl scaffold) significantly rescued cholinergic cell death in the nBM brain slices (175±12, n=10), which was counteracted by an anti-NGF antibody (77±5, n=5).

COMPARISON WITH EXISTING METHODS

The combination of coronal brain slices with biomaterial is a novel and potent tool to selectively study neuroprotective effects.

CONCLUSIONS

Collagen scaffolds loaded with low amounts of a protein/drug of interest can be easily applied directly onto organotypic brain slices, allowing slow targeted release of a protective molecule. Such an approach is highly useful to optimize CollScaff for further in vivo applications.

Hypocretinergic and cholinergic contributions to sleep-wake disturbances in a mouse model of traumatic brain injury

Disorders of sleep and wakefulness occur in the majority of individuals who have experienced traumatic brain injury (TBI), with increased sleep need and excessive daytime sleepiness often reported. Behavioral and pharmacological therapies have limited efficacy, in part, because the etiology of post-TBI sleep disturbances is not well understood. Severity of injuries resulting from head trauma in humans is highly variable, and as a consequence so are their sequelae. Here, we use a controlled laboratory model to investigate the effects of TBI on sleep-wake behavior and on candidate neurotransmitter systems as potential mediators. We focus on hypocretin and melanin-concentrating hormone (MCH), hypothalamic neuropeptides important for regulating sleep and wakefulness, and two potential downstream effectors of hypocretin actions, histamine and acetylcholine. Adult male C57BL/6 mice (n=6-10/group) were implanted with EEG recording electrodes and baseline recordings were obtained. After baseline recordings, controlled cortical impact was used to induce mild or moderate TBI. EEG recordings were obtained from the same animals at 7 and 15 days post-surgery. Separate groups of animals (n=6-8/group) were used to determine effects of TBI on the numbers of hypocretin and MCH-producing neurons in the hypothalamus, histaminergic neurons in the tuberomammillary nucleus, and cholinergic neurons in the basal forebrain. At 15 days post-TBI, wakefulness was decreased and NREM sleep was increased during the dark period in moderately injured animals. There were no differences between groups in REM sleep time, nor were there differences between groups in sleep during the light period. TBI effects on hypocretin and cholinergic neurons were such that more severe injury resulted in fewer cells. Numbers of MCH neurons and histaminergic neurons were not altered under the conditions of this study. Thus, we conclude that moderate TBI in mice reduces wakefulness and increases NREM sleep during the dark period, effects that may be mediated by hypocretin-producing neurons and/or downstream cholinergic effectors in the basal forebrain.

Organotypic brain slice cultures: A review

In vitro cell cultures are an important tool for obtaining insights into cellular processes in an isolated system and a supplement to in vivo animal experiments. While primary dissociated cultures permit a single homogeneous cell population to be studied, there is a clear need to explore the function of brain cells in a three-dimensional system where the main architecture of the cells is preserved. Thus, organotypic brain slice cultures have proven to be very useful in investigating cellular and molecular processes of the brain in vitro. This review summarizes (1) the historical development of organotypic brain slices focusing on the membrane technology, (2) methodological aspects regarding culturing procedures, age of donors or media, (3) whether the cholinergic neurons serve as a model of neurodegeneration in Alzheimer’s disease, (4) or the nigrostriatal dopaminergic neurons as a model of Parkinson’s disease and (5) how the vascular network can be studied, especially with regard to a synthetic blood–brain barrier. This review will also highlight some limits of the model and give an outlook on future applications.

Effects of acidosis on brain capillary endothelial cells and cholinergic neurons: relevance to vascular dementia and Alzheimer's disease

Alzheimer's disease is a progressive brain disorder which is neuropathologically characterized by an increased number of beta-amyloid plaques, tau pathology and synapse loss. Recent research suggests that vascular pathology may be also important for the development and progression of Alzheimer's disease. It is still unknown whether there is a relation between damage of brain capillary endothelial cells (BCEC) and subsequent cholinergic cell death. The aim of this study was to examine the effects of acidosis on cell death of BCEC and cholinergic neurons in an organotypic brain slice model. We show that BCEC were heavily damaged in medium at pH<6.6. Cholinergic neurons incubated in medium pH 6.0 degenerated within 2-3 days and were not rescued by nerve growth factor (NGF). Lactate did not affect the survival of BCEC or cholinergic neurons. Both BCEC and cholinergic cells were not affected at pH 7.4, 7.0 or 6.6. It is concluded that both endothelial cells and cholinergic neurons have a high capacity to compensate for pH changes. At a certain pH, however, the vascular and neuronal cells show the same vulnerability, indicating that a low pH is deleterious for the cerebral microenvironment. Future studies are necessary to explore whether temporary pH changes could be responsible for cerebrovascular damage and cholinergic cell death. Acidosis may play an important role in the development of vascular dementia and Alzheimer's disease.

The functional tumor necrosis factor-α (308A/G) polymorphism modulates attentional selection in elderly individuals

There has been increasing interest in understanding the role of inflammatory processes for cognitive functions in aging using molecular genetic approaches. Though this has mostly been evaluated in pathological aging, little is known about the relevance for cognitive functions in healthy aging in humans. On the basis of behavioral data and neurophysiological data (event-related potentials and time-frequency decomposition) we show that the A-allele of the functional tumor necrosis factor (TNF)-α -308 A/G polymorphism confers dysfunction in a number of cognitive processes: prolonged attentional selection indexed by a delayed P1/N1 complex, an increased P3a, which is interpreted as an enhanced distractibility by nonrelevant stimuli and compromised response selection mechanisms, as indexed by a reduced frontocentral N2. Time-frequency analyses show that allelic variations further exert their effects by modulating alpha and beta frequency oscillations. On a neurobiological level, these effects might be because of the interaction of TNF-α with glutamatergic neural transmission by which TNF-α is known to boost apoptotic mechanisms in elderly individuals.

Ethanol transiently suppresses choline-acetyltransferase in basal nucleus of Meynert slices

The cholinergic system plays a major role in learning and cognition and cholinergic neurons appear to be particularly vulnerable to ethanol (EtOH) exposure. There are conflicting results if EtOH directly damages cholinergic neurons. Thus, the aims of the present study were (1) to investigate the effect of different EtOH concentrations on cholinergic neurons in organotypic brain slices of the nucleus basalis of Meynert (nbM) and (2) to study if the most potent cholinotrophic substance nerve growth factor (NGF) or inhibitors of mitogen activated kinase (MAPK) p38- and nitric-oxide synthase (NOS)-pathways may counteract any EtOH effect. Two-week old organotypic rat brain slices of the nbM were exposed to 1–100 mM EtOH for 7 days with or without drugs and the number of choline-acetyltransferase (ChAT)-positive neurons was counted. Our data show that EtOH significantly reduced the number of ChAT-positive neurons with the most potent effect at a concentration of 50 mM EtOH (54 ± 5 neurons per slice, p < 0.001), compared to control slices (120 ± 13 neurons per slice). Inhibition of MAPK p38 (SB 203580, 10 μM) and NOS (L-thiocitrulline, 10 μM) counteracted the EtOH-induced decline of cholinergic neurons and NGF protected cholinergic neurons against the EtOH-induced effect. Withdrawal of EtOH resulted in a reversal of cholinergic neurons to nearly controls. In conclusion, EtOH caused a transient decline of cholinergic neurons, possibly involving MAPK p38- and NOS-pathways suggesting that EtOH does not induce direct cell death, but causes a transient downregulation of the cholinergic key enzyme, possibly reflecting a form of EtOH-associated plasticity.

Age-related neurodegeneration and memory loss in down syndrome

Down syndrome (DS) is a condition where a complete or segmental chromosome 21 trisomy causes variable intellectual disability, and progressive memory loss and neurodegeneration with age. Many research groups have examined development of the brain in DS individuals, but studies on age-related changes should also be considered, with the increased lifespan observed in DS. DS leads to pathological hallmarks of Alzheimer's disease (AD) by 40 or 50 years of age. Progressive age-related memory deficits occurring in both AD and in DS have been connected to degeneration of several neuronal populations, but mechanisms are not fully elucidated. Inflammation and oxidative stress are early events in DS pathology, and focusing on these pathways may lead to development of successful intervention strategies for AD associated with DS. Here we discuss recent findings and potential treatment avenues regarding development of AD neuropathology and memory loss in DS.

Organotypic vibrosections: novel whole sagittal brain cultures

In vitro cell culture models are of enormous importance in neuroscience research and organotypic brain slices are found to be a potent model very close to the in vivo situation. Brain slices can be cultured as single slices or as co-slices. However, there is need to culture whole brain sections, containing the complex functional architecture. The aim of the present study was to develop and characterize whole brain sagittal slice cultures (200μm organotypic vibrosections) from postnatal day 8 rats. We show that sagittal vibrosections can be cultured for several weeks and they maintain survival of cholinergic and dopaminergic neurons, as well as a strong capillary network. Partly long-distance cortico-striatal and cortico-hippocampal nerve fibers were found using Mini-Ruby neurotracing. Dopaminergic nerve fibers extended from the mesencephalon, but in the striato-nigral tract and in the striatum only strong dense varicosities were found. The model also allows to study pathological triggers, such as e.g. hydrogen peroxide markedly increased propidiumiodide-positive nuclei in the hippocampus. In conclusion, our novel model provides an easy potent whole sagittal brain culture system that allows to study cholinergic and dopaminergic neurons together but also in close interaction with all other cells of the brain and with capillaries. It will be a great challenge in future to use this model to re-construct whole pathways. This vibrosection model may partly represent a close adult in vivo situation, which allows to study neurodegeneration and neuroprotection of cholinergic and dopaminergic neurons, which plays an important role in Alzheimer's and Parkinson's disease, respectively.

Mini-ruby is rapidly taken up by neurons and astrocytes in organotypic brain slices

Cholinergic neurons are intensively studied, because they degenerate in Alzheimer's disease. Although neurotracer techniques are widely used to study axonal transport, guidance, regeneration or sprouting it is not clear if cholinergic neurons can be stained by tracer techniques and studied in brain slices. The aim of the present study was to evaluate the characteristics of the neurotracer Mini-ruby in organotypic brain slices of the basal nucleus of Meynert (nBM), focusing on cholinergic neurons. Mini-ruby is a biotinylated dextran amine and is taken up very fast by a variety of cells. When 2-week old nerve growth factor-incubated brain slices of the nBM were treated with Mini-ruby crystals for 1 h, only a few (2-3%) cholinergic neurons were clearly labeled as shown by co-localization with choline acetyltransferase. The staining was found in neuN-positive neurons and microtubule associated protein-2 (MAP-2)-positive nerve fibers. A very rapid dynamic change was observed in these labeled varicosities within seconds. However, Mini-ruby was taken up also by many glutamine synthethase-positive astrocytes. At the site of Mini-ruby application an intense CD11b-positive microglial staining was evident. In conclusion, neurons and astrocytes in organotypic brain slices can be labeled very fast with the fluorescent dye Mini-ruby which undergoes dynamic processes.

Differential effects of short- and long-term hyperhomocysteinaemia on cholinergic neurons, spatial memory and microbleedings in vivo in rats

Hyperhomocysteinaemia (HHcy) has been identified as a cardiovascular risk factor for neurodegenerative brain diseases. The aim of the present study was to investigate the effects of short (5 months) or long (15 months) HHcy in Sprague–Dawley rats in vivo. Short- and long-term HHcy differentially affected spatial memory as tested in a partially baited eight-arm radial maze. HHcy significantly reduced the number of choline acetyltransferase (ChAT)-positive neurons in the basal nucleus of Meynert and ChAT-positive axons in the cortex only after short-term but not long-term treatment, while acetylcholine levels in the cortex were decreased at both time points. Nerve growth factor (NGF) was significantly enhanced in the cortex only after 15 months of HHcy. HHcy did not affect cortical levels of amyloid precursor protein, beta-amyloid(1-42), tau and phospho-tau181 and several inflammatory markers, as well as vascular RECA-1 and laminin density. However, HHcy induced cortical microbleedings, as illustrated by intensive anti-rat IgG-positive spots in the cortex. In order to study the regulation of the key enzyme ChAT, organotypic rat brain slices were incubated with homocysteine, which induced a decline of ChAT that was counteracted by NGF treatment. In conclusion, our data demonstrate that chronic short- and long-term HHcy differentially caused memory impairment, cholinergic dysfunction, NGF expression and vascular microbleedings.

Involvement of interleukin-1 in lipopolysaccaride-induced microglial activation and learning and memory deficits

We have developed an animal model of learning and memory impairment associated with activation of microglia in the mouse brain. Injection of lipopolysaccharide into the CA1 region of the mouse hippocampus resulted in an increased production of inflammatory cytokines, such as interleukin-1β. Immunostaining for interleukin-1β revealed an increase in the signal at 6 hr after lipopolysaccharide injection. Immunopositive cells for interleukin-1β were colocalized with those immunopositive for CD11b. When subacute lipopolysaccharide treatment (20 μg/2 μl/injection, bilaterally for 5 consecutive days) was performed, long-term activation of microglia and learning and memory deficits as evaluated using a step-through passive avoidance test were observed in the wild-type mice. Gene expression of the N-methyl-D-aspartate receptor NR1 and NR2A subunits was also decreased by the lipopolysaccharide treatment. In contrast, activation of microglia and the associated behavioral deficits were not observed in mice lacking interleukin-1α and -1β following the subacute lipopolysaccharide treatment, together with little change in the gene expression of NR1 and NR2A subunits. However, the subacute lipopolysaccharide treatment produced almost similar changes in those parameters in the tumor necrosis factor-α knockout mice as in the wild-type animals. The injection of interleukin-1β neutralizing antibody with lipopolysaccharide for 5 consecutive days resulted in the improvement of lipopolysaccharide-induced learning and memory deficits. These findings suggest that the expression of interleukin-1 plays an important role in lipopolysaccharide-induced activation of microglia and the associated functional deficits in learning and memory.

Effects of cholesterol and its 24S-OH and 25-OH oxysterols on choline acetyltransferase-positive neurons in brain slices

In Alzheimer's disease (AD) neurons expressing the enzyme choline acetyltransferase (ChAT) degenerate and a loss of cholinergic activity directly correlates with cognitive decline. Recent studies have suggested that cholesterol plays a role in AD. The aim of the present study was to explore if cholesterol and its oxysterols, 24S-hydroxycholesterol (24S-OH Chol) and 25-hydroxycholesterol (25-OH Chol), affect ChAT-positive neurons in organotypic brain slices of the basal nucleus of Meynert (nBM). We showed that slices expressed approximately 140 ChAT-positive neurons/slice after 2 weeks when incubated with nerve growth factor (NGF). This number markedly decreased when incubated without NGF to approximately 20 neurons/slice. Cholesterol and 24S-OH Chol delayed this decrease in ChAT-positive neurons. In contrast, 25-OH Chol induced a decline in ChAT-positive neurons in 2-week-old slices within 4 days. The effects of cholesterol and its oxysterols were exhibited in a dose- and time-dependent way. Our results show that cholesterol and 24S-OH Chol delays the decrease in ChAT-positive neurons, while 25-OH Chol rapidly decreases ChAT expression, suggesting differential mechanisms on ChAT expression in cholinergic nBM neurons.

Effect of rimonabant, the cannabinoid CB1 receptor antagonist, on peripheral nerve in streptozotocin-induced diabetic rat

The aim of this study is to investigate the effect of rimonabant, which has antiatherosclerotic and antiinflammatory properties, on peripheral neuropathy in a diabetic rat. Diabetic rat models were induced by treatment with streptozotocin and then either normal or diabetic rats were treated with an oral dose of 10mg/kg/day rimonabant or placebo for 24 weeks. We quantified the densities of intraepidermal (PGP9.5+) nerve fiber and total skin (RECA-1+) capillary length. We also measured the current perception threshold, as defined by the intensity of sine-wave stimulus, skin blood flow after treadmill running and TNF-alpha level in spinal cord tissue or plasma. After 24 weeks, rimonabant reduced the body weight and food intake in both diabetic and normal rats, but it had no effect on blood sugar levels. In addition, rimonabant treatment significantly improved the decreased intraepidermal nerve fiber density (5.53+/-0.12 vs. 4.36+/-0.27/mm, P<0.05) and alleviated the increased current perception threshold in rimonabant-treated versus control diabetic rats. These responses were closely associated with the attenuation of skin capillary loss (1.98+/-0.07 vs. 1.67+/-0.10 mm/mm(2), P<0.05), increase in skin blood flow (14.93+/-1.08 vs. 12.07+/-0.87 TPU, P<0.05) and reduction in TNF-alpha level in tissue (70.10+/-4.99 vs. 91.18+/-3.34 pg/mg, P<0.05) in rimonabant-treated diabetic rats compared with placebo. These findings suggest that rimonabant can be beneficial for treatment of diabetic peripheral neuropathy, possibly due to its potential role in micro- and macrovessel protection and its anti-inflammatory properties.

Rotenone induces cell death of cholinergic neurons in an organotypic co-culture brain slice model

In Alzheimer and Parkinson's disease cell death of cholinergic and dopaminergic neurons are characteristic hallmarks, respectively. It is well established that rotenone, an inhibitor of complex I of the electron transport chain, induces cell death of dopaminergic neurons, however, not much is known on the effects of rotenone on cholinergic neurons. The aim of the present study was to evaluate the effects of rotenone on cholinergic neurons in an organotypic in vitro brain co-slice model. When co-cultures were treated with 10 μM rotenone for 24 h a significantly decreased number of cholinergic neurons was found in the basal nucleus of Meynert but not in the dorsal striatum. This cell death exhibited apoptotic DAPI-positive malformed nuclei and enhanced TUNEL-positive cells. In summary, inhibition of complex I of the electron transport chain may play a role in neurodegeneration of cholinergic neurons.

The pro-apoptotic substance thapsigargin selectively stimulates re-growth of brain capillaries

Thapsigargin is a pro-apoptotic chemical, which has been shown to be useful to study cell death of cholinergic or dopaminergic neurons, or cells, which degenerate in Alzheimer's disease or Parkinson's disease, respectively. The aim of the present work was to study the effects of thapsigargin in the well established organotypic brain co-slice model composed of the basal nucleus of Meynert (nBM), ventral mesencephalon (vMes), dorsal striatum (dStr) and parietal cortex (Ctx). Cholinergic acetyltransferase-positive neurons in the nBM and dStr and dopaminergic tyrosine hydroxylase-positive neurons in the vMes survived, when cultured for 4 weeks with nerve growth factor and glial cell line-derived neurotrophic factor. Nerve fibers of cholinergic nBM neurons grew into the cortex and dopaminergic nerve fibers sprouted into dopamine D2 receptor-positive dStr. The whole co-slice contained a dense laminin-positive capillary network. Treatment of co-cultures with 3 microM thapsigargin for 24 hr significantly decreased the number of cholinergic neurons and dopaminergic neurons. This cell death displayed apoptotic DAPI-positive malformed nuclei and enhanced TUNEL-positive cells. Thapsigargin selectively stimulated the laminin-positive capillary growth between the nBM and Ctx. In conclusion, the induced cell death of cholinergic and dopaminergic neurons may be accompanied by enhanced angiogenic activity.

Tumor necrosis factor alpha stimulates NMDA receptor activity in mouse cortical neurons resulting in ERK-dependent death

Multiple cytokines are secreted in the brain during pro-inflammatory conditions and likely affect neuron survival. Previously, we demonstrated that glutamate and tumor necrosis factor alpha (TNFalpha) kill neurons via activation of the N-methyl-d-aspartate (NMDA) and TNFalpha receptors, respectively. This report continues characterizing the signaling cross-talk pathway initiated during this inflammation-related mechanism of death. Stimulation of mouse cortical neuron cultures with TNFalpha results in a transient increase in NMDA receptor-dependent calcium influx that is additive with NMDA stimulation and inhibited by pre-treatment with the NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid, or the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione. Pre-treatment with N-type calcium channel antagonist, omega-conotoxin, or the voltage-gated sodium channel antagonist, tetrodotoxin, also prevents the TNFalpha-stimulated calcium influx. Combined TNFalpha and NMDA stimulation results in a transient increase in activity of extracellular signal-regulated kinases (ERKs) and c-Jun N-terminal kinases (JNKs). Specific inhibition of ERKs but not JNKs is protective against TNFalpha and NMDA-dependent death. Death is mediated via the low-affinity TNFalpha receptor, TNFRII, as agonist antibodies for TNFRII but not TNFRI stimulate NMDA receptor-dependent calcium influx and death. These data demonstrate how microglial pro-inflammatory secretions including TNFalpha can acutely facilitate glutamate-dependent neuron death.

Nonparticipation of nuclear factor kappa B (NFkappaB) in the signaling cascade of c-Jun N-terminal kinase (JNK)- and p38 mitogen-activated protein kinase (p38MAPK)-dependent tumor necrosis factor alpha (TNFalpha) induction in lipopolysaccharide (LPS)-stimulated microglia

The molecular mechanism of cytotoxic cytokine tumor necrosis factor alpha (TNFalpha) induction in microglia remains to be clarified. We have previously reported that p38 mitogen-activated protein kinase (p38MAPK) is an important signaling molecule for the induction of TNFalpha in lipopolysaccharide (LPS)-stimulated microglia. Recently, we have shown that c-Jun N-terminal kinase (JNK) is associated with the induction of TNFalpha. Furthermore, using an NFkappaB inhibitor (SN50), we discovered that activation of nuclear factor kappaB (NFkappaB) may also be linked to TNFalpha induction. We therefore examined the relationship between NFkappaB and the two MAPKs (p38MAPK and JNK) in the signaling cascade of TNFalpha induction in LPS-stimulated microglia. NFkappaB inhibitor SN50 decreased the induction of TNFalpha under the suppressed NFkappaB activation. However, SN50 was found to prevent the activation of MKK3/6-p38MAPK and MKK4-JNK pathways. On the other hand, the other NFkappaB inhibitor ammonium pyrrolidine dithiocarbamate (APDC) neither prevented the activation of p38MAPK and JNK nor inhibited TNFalpha induction in LPS-stimulated microglia, although it was confirmed to serve as an NFkappaB inhibitor. These results suggest that both MKK3/6-p38MAPK and MKK4-JNK pathways are important signaling cascades leading to the induction of TNFalpha in LPS-stimulated microglia, but that NFkappaB itself is not required for this induction.

Oxidative stress and inflammation in Parkinson's disease: is there a causal link?

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a dramatic loss of dopaminergic neurons in the substantia nigra (SN). Among the many pathogenic mechanisms thought to contribute to the demise of these cells, dopamine-dependent oxidative stress has classically taken center stage due to extensive experimental evidence showing that dopamine-derived reactive oxygen species and oxidized dopamine metabolites are toxic to nigral neurons. In recent years, however, the involvement of neuro-inflammatory processes in nigral degeneration has gained increasing attention. Not only have activated microglia and increased levels of inflammatory mediators been detected in the striatum of deceased PD patients, but a large body of animal studies points to a contributory role of inflammation in dopaminergic cell loss. Recently, postmortem examination of human subjects exposed to the parkinsonism-inducing toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), revealed the presence of activated microglia decades after drug exposure, suggesting that even a brief pathogenic insult can induce an ongoing inflammatory response. Perhaps not surprisingly, non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the risk of developing PD. In the past few years, various pathways have come to light that could link dopamine-dependent oxidative stress and microglial activation, finally ascribing a pathogenic trigger to the chronic inflammatory response characteristic of PD.

Inhibition of inflammatory cytokine secretion from mouse microglia cells by DHMEQ, an NF-κB inhibitor

Activation of microglia has been implicated in various neurodegenerative disorders, and thus the inhibition of microglial activity may suppress these disorders. Earlier we designed and synthesized an NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ) that showed anti-inflammatory and anti-tumor activities in vivo. In the present research, we studied whether DHMEQ would inhibit the activation of mouse microglial cells. DHMEQ inhibited lipopolysaccharide (LPS)-induced activation of NF-kappaB in an electrophoresis mobility shift assay. It also inhibited LPS-induced secretions of TNF-alpha and IL-6 from mouse microglial cell line 6-1 cells.

Urea enhances the nerve growth factor-induced neuroprotective effect on cholinergic neurons in organotypic rat brain slices

Cholinergic neurons degenerate in Alzheimer's disease and dementia and neuroprotective substances are of high interest to counteract this cell death. The aim of the present study was to test the effect of urea and the nitric oxide synthetase inhibitor l-thiocitrulline on the survival of cholinergic neurons. Organotypic brain slices of the basal nucleus of Meynert were cultured for 2 weeks in the presence of 1-100 microM urea with or without NGF or other growth factors or with or without 1-10 microM of the NOS inhibitor L-thiocitrulline. A high number of cholinergic neurons survived in the presence of 0.1-100 ng/ml NGF. Urea or L-thiocitrulline alone did not exhibit neuroprotective activity; however, when brain slices were incubated with urea or L-thiocitrulline together with NGF there was a significant potentiating survival effect. Incubation of brain slices with NGF + urea + L-thiocitrulline did not further enhance the number of cholinergic neurons. NGF as well as urea did not stimulate expression of the enzyme choline acetyltransferase pointing to survival promoting effects. Urea did not modulate the NGF binding in PC12 cells indicating that this effect was indirect. It is concluded that urea may play a role as an indirect survival promoting molecule possibly involving the nitric oxide pathway.

Regulation of cytokine-induced neuron death by ovarian hormones: involvement of antiapoptotic protein expression and c-JUN N-terminal kinase-mediated proapoptotic signaling

Mechanisms underlying the divergent effects of ovarian hormones on neuron death induced by TNFalpha were investigated in differentiated PC12 cells (dPC12). dPC12 cells were exposed to 17beta-estradiol (E, 1.0 nm), progesterone (P, 100 nm), or a combination of both hormones for 0-72 h before treatment with TNFalpha (0-150 ng) to induce cell death. Cells undergoing apoptosis were identified by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling assay and fluorescence-activated cell sorting after 18 h. Cell death induced by TNFalpha was decreased 89% after E treatment and increased 2-fold after P treatment compared with cells treated with TNFalpha alone. Treatment with E for 24 h before TNFalpha exposure was required for maximum neuroprotection, whereas P-enhanced death was maximal after a 30-min P treatment. TNFalpha induced a 3-fold increased activity of c-JUN-N-terminal kinase (JNK) 1 in d PC12 cells within 20 min that could be increased 5- to 8-fold by P together with TNFalpha. A peptide inhibitor of JNK1 abrogated P enhancement of TNFalpha-mediated dPC12 death but had only a minimal effect on cell death by TNFalpha alone. Inhibition of caspase-8 activation reduced death induced by TNFalpha alone but was much less effective for P+TNF. P alone did not activate caspase-8. E increased estrogen receptor alpha (ERalpha) and Bcl-xL expression and all but abolished TNFalpha receptor 1 (TNFR1) expression. P decreased ERalpha and Bcl-xL expression and doubled TNFR1 expression. These data suggest that P regulates apoptosis or survival through augmentation of JNK signaling and altered TNFR1 expression, whereas E mainly affects the expression of BCL-xL, TNFR1, and ERalpha.

Brain capillaries and cholinergic neurons persist in organotypic brain slices in the absence of blood flow

Angiogenesis plays an important role during development of the brain and under pathological conditions. The aim of the present study was to observe interaction of brain capillaries and cholinergic neurons in organotypic brain slices. Immunohistochemistry was used to visualize brain capillary-like structures (RECA-1 antigen) and cholinergic neurons (choline acetyltransferase). Under normal culture conditions, a very low number of brain capillaries was found in 2- and 4-week-old cortex brain slices. Treatment of slices with acidic medium (pH 6) or hyperthermia (42 degrees C) markedly enhanced the number of brain capillaries. Incubation with 10 ng/mL vascular endothelial growth factor only enhanced angiogenesis in more developed slices. Cholinergic neurons survived in slices of the basal nucleus of Meynert; however, hyperthermia but not acidosis markedly decreased their number. In coslices of the basal nucleus of Meynert and cortex (pretreated with acidic medium), a high number of RECA-1-positive capillaries and cholinergic neurons persisted and displayed strong nerve fibre growth of cholinergic fibres into the cortex. In conclusion, we have demonstrated that RECA-1-positive capillaries and cholinergic neurons can be studied in slice cultures in the absence of blood perfusion, and that this model could provide a system to study mechanisms involved in vascular dementia.