Fas/Apo [apoptosis]-1 and associated proteins in the differentiating cerebral cortex: induction of caspase-dependent cell death and activation of NF-kappaB

Potential neurotoxic activity of diverse molecules released by astrocytes

Astrocytes are the main support cells of the central nervous system. They also participate in neuroimmune reactions. In response to pathological and immune stimuli, astrocytes transform to reactive states characterized by increased release of inflammatory mediators. Some of these molecules are neuroprotective and inflammation resolving while others, including reactive oxygen species (ROS), nitric oxide (NO), matrix metalloproteinase (MMP)- 9, L-glutamate, and tumor necrosis factor α (TNF), are well-established toxins known to cause damage to surrounding cells and tissues. We hypothesized that similar to microglia, the brain immune cells, reactive astrocytes can release a broader set of diverse molecules that are potentially neurotoxic. A literature search was conducted to identify such molecules using the following two criteria: 1) evidence of their expression and secretion by astrocytes and 2) direct neurotoxic action. This review describes 14 structurally diverse molecules as less-established astrocyte neurotoxins, including C-X-C motif chemokine ligand (CXCL)10, CXCL12/CXCL12(5-67), FS-7-associated surface antigen ligand (FasL), macrophage inflammatory protein (MIP)- 2α, TNF-related apoptosis inducing ligand (TRAIL), pro-nerve growth factor (proNGF), pro-brain-derived neurotrophic factor (proBDNF), chondroitin sulfate proteoglycans (CSPGs), cathepsin (Cat)B, group IIA secretory phospholipase A₂ (sPLA₂-IIA), amyloid beta peptides (Aβ), high mobility group box (HMGB)1, ceramides, and lipocalin (LCN)2. For some of these molecules, further studies are required to establish either their direct neurotoxic effects or the full spectrum of stimuli that induce their release by astrocytes. Only limited studies with human-derived astrocytes and neurons are available for most of these potential neurotoxins, which is a knowledge gap that should be addressed in the future. We also summarize available evidence of the role these molecules play in select neuropathologies where reactive astrocytes are a key feature. A comprehensive understanding of the full spectrum of neurotoxins released by reactive astrocytes is key to understanding neuroinflammatory diseases characterized by the adverse activation of these cells and may guide the development of novel treatment strategies.

The Absence of Caspase-8 in the Dopaminergic System Leads to Mild Autism-like Behavior

In the last decade, new non-apoptotic roles have been ascribed to apoptotic caspases. This family of proteins plays an important role in the sculpting of the brain in the early stages of development by eliminating excessive and nonfunctional synapses and extra cells. Consequently, impairments in this process can underlie many neurological and mental illnesses. This view is particularly relevant to dopamine because it plays a pleiotropic role in motor control, motivation, and reward processing. In this study, we analyze the effects of the elimination of caspase-8 (CASP8) on the development of catecholaminergic neurons using neurochemical, ultrastructural, and behavioral tests. To do this, we selectively delete the CASP8 gene in cells that express tyrosine hydroxylase with the help of recombination through the Cre-loxP system. Our results show that the number of dopaminergic neurons increases in the substantia nigra. In the striatum, the basal extracellular level of dopamine and potassium-evoked dopamine release decreased significantly in mice lacking CASP8, clearly showing the low dopamine functioning in tissues innervated by this neurotransmitter. This view is supported by electron microscopy analysis of striatal synapses. Interestingly, behavioral analysis demonstrates that mice lacking CASP8 show changes reminiscent of autism spectrum disorders (ASD). Our research reactivates the possible role of dopamine transmission in the pathogenesis of ASD and provides a mild model of autism.

B-Cell Lymphoma 2 (Bcl-2) and Regulation of Apoptosis after Traumatic Brain Injury: A Clinical Perspective

Background and Objectives: The injury burden after head trauma is exacerbated by secondary sequelae, which leads to further neuronal loss. B-cell lymphoma 2 (Bcl-2) is an anti-apoptotic protein and a key modulator of the programmed cell death (PCD) pathways. The current study evaluates the clinical evidence on Bcl-2 and neurological recovery in patients after traumatic brain injury (TBI). Materials and Methods: All studies in English were queried from the National Library of Medicine PubMed database using the following search terms: (B-cell lymphoma 2/Bcl-2/Bcl2) AND (brain injury/head injury/head trauma/traumatic brain injury) AND (human/patient/subject). There were 10 investigations conducted on Bcl-2 and apoptosis in TBI patients, of which 5 analyzed the pericontutional brain tissue obtained from surgical decompression, 4 studied Bcl-2 expression as a biomarker in the cerebrospinal fluid (CSF), and 1 was a prospective randomized trial. Results: Immunohistochemistry (IHC) in 94 adults with severe TBI showed upregulation of Bcl-2 in the pericontusional tissue. Bcl-2 was detected in 36-75% of TBI patients, while it was generally absent in the non-TBI controls, with Bcl-2 expression increased 2.9- to 17-fold in TBI patients. Terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick-end labeling (TUNEL) positivity for cell death was detected in 33-73% of TBI patients. CSF analysis in 113 TBI subjects (90 adults, 23 pediatric patients) showed upregulation of Bcl-2 that peaked on post-injury day 3 and subsequently declined after day 5. Increased Bcl-2 in the peritraumatic tissue, rising CSF Bcl-2 levels, and the variant allele of rs17759659 are associated with improved mortality and better outcomes on the Glasgow Outcome Score (GOS). Conclusions: Bcl-2 is upregulated in the pericontusional brain and CSF in the acute period after TBI. Bcl-2 has a neuroprotective role as a pro-survival protein in experimental models, and increased expression in patients can contribute to improvement in clinical outcomes. Its utility as a biomarker and therapeutic target to block neuronal apoptosis after TBI warrants further evaluation.

Elevated Soluble Fas and FasL in Cerebrospinal Fluid and Serum of Patients With Anti-N-methyl-D-aspartate Receptor Encephalitis

Objective: Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is a severe autoimmune disorder that mainly affects children and young women. The Fas system contains both membrane-bound versions of Fas (mFas) and Fas ligand (mFasL), and soluble versions (sFas and sFasL), which play important roles in apoptosis and regulation of the immune system. Both the levels of sFas and sFasL and the role they play in anti-NMDAR disease pathogenesis remain unclear. Methods: Forty-eight pairs of cerebrospinal fluid (CSF) and serum were collected from patients with anti-NMDAR encephalitis, encephalitis of other causes or peripheral neuropathy. The CSF and serum concentrations of sFas and sFasL were determined with enzyme-linked immunosorbent assay. Results: CSF concentrations of sFas and sFasL were both increased in anti-NMDAR encephalitis patients compared with controls patients. Serum sFas levels were also elevated in anti-NMDAR encephalitis patients relative to controls. sFas and sFasL concentrations in CSF positively correlated with the modified Rankin scale (mRS) both at onset and 6-months follow-up. Conclusion: CSF sFas and sFasL levels were elevated in anti-NMDAR encephalitis patients, and reflect the disease severity of anti-NMDAR encephalitis.

NF-κB regulates caspase-4 expression and sensitizes neuroblastoma cells to Fas-induced apoptosis

Found in neurons and neuroblastoma cells, Fas-induced apoptosis and accompanied activation of NF-κB signaling were thought to be associated with neurodegenerative diseases. However, the detailed functions of NF-κB activation in Fas killing and the effect of NF-κB activation on its downstream events remain unclear. Here, we demonstrated that agonistic Fas antibody induces cell death in a dose-dependent way and NF-κB signaling is activated as well, in neuroblastoma cells SH-EP1. Unexpectedly, NF-κB activation was shown to be pro-apoptotic, as suggested by the reduction of Fas-induced cell death with either a dominant negative form of IκBα (DN-IκBα) or an IκB kinase-specific inhibitor. To our interest, when analyzing downstream events of NF-κB signaling, we found that DN-IκBα only suppressed the expression of caspase-4, but not other caspases. Vice versa, enhancement of NF-κB activity by p65 (RelA) overexpression increased the expression of caspase-4 at both mRNA and protein levels. More directly, results from dual luciferase reporter assay demonstrated the regulation of caspase-4 promoter activity by NF-κB. When caspase-4 activity was blocked by its dominant negative (DN) form, Fas-induced cell death was substantially reduced. Consistently, the cleavage of PARP and caspase-3 induced by Fas was also reduced. In contrast, the cleavage of caspase-8 remained unaffected in caspase-4 DN cells, although caspase-8 inhibitor could rescue Fas-induced cell death. Collectively, these data suggest that caspase-4 activity is required for Fas-induced cell apoptosis and caspase-4 may act upstream of PARP and caspase-3 and downstream of caspase-8. Overall, we demonstrate that NF-κB can mediate Fas-induced apoptosis through caspase-4 protease, indicating that caspase-4 is a new mediator of NF-κB pro-apoptotic pathway in neuroblastoma cells.

The effects of harvesting media on biological characteristics and repair potential of neural stem cells after traumatic brain injury

Various solutions are utilized widely for the isolation, harvesting, sorting, testing and transplantation of neural stem cells (NSCs), whereas the effects of harvesting media on the biological characteristics and repair potential of NSCs remain unclear. To examine some of these effects, NSCs were isolated from cortex of E14.5 mice and exposed to the conventional harvesting media [0.9% saline (Saline), phosphate-buffered saline (PBS) or artificial cerebrospinal fluid (ACSF)] or the proliferation culture medium (PCM) for different durations at 4°C. Treated NSCs were grafted by in situ injection into the lesion sites of traumatic brain injury (TBI) mice. In vitro, harvesting media-exposed NSCs displayed time-dependent reduction of viability and proliferation. S phase entry decreased in harvesting media-exposed cells, which was associated with upregulation of p53 protein and downregulation of cyclin E1 protein. Moreover, harvesting media exposure induced the necrosis and apoptosis of NSCs. The levels of Fas-L, cleaved caspase 3 and 8 were increased, which suggests that the death receptor signaling pathway is involved in the apoptosis of NSCs. In addition, exposure to Saline did not facilitate the neuronal differentiation of NSCs, suggesting that Saline exposure may be disadvantageous for neurogenesis. In vivo, NSC-mediated functional recovery in harvesting media-exposed NSC groups was notably attenuated in comparison with the PCM-exposed NSC group. In conclusion, harvesting media exposure modulates the biological characteristics and repair potential of NSCs after TBI. Our results suggest that insight of the effects of harvesting media exposure on NSCs is critical for developing strategies to assure the successful long-term engraftment of NSCs.

Necrostatin-1 suppresses autophagy and apoptosis in mice traumatic brain injury model

Traumatic brain injury (TBI) results in neuronal apoptosis, autophagic cell death and necroptosis. Necroptosis is a newly discovered caspases-independent programmed necrosis pathway which can be triggered by activation of death receptor. Previous works identified that necrostatin-1 (NEC-1), a specific necroptosis inhibitor, could reduce tissue damage and functional impairment through inhibiting of necroptosis process following TBI. However, the role of NEC-1 on apoptosis and autophagy after TBI is still not very clear. In this study, the amount of TBI-induced neural cell deaths were counted by PI labeling method as previously described. The expression of autophagic pathway associated proteins (Beclin-1, LC3-II, and P62) and apoptotic pathway associated proteins (Bcl-2 and caspase-3) were also respectively assessed by immunoblotting. The data showed that mice pretreated with NEC-1 reduced the amount of PI-positive cells from 12 to 48 h after TBI. Immunoblotting results showed that NEC-1 suppressed TBI-induced Beclin-1 and LC3-II activation which maintained p62 at high level. NEC-1 pretreatment also reversed TBI-induced Bcl-2 expression and caspase-3 activation, as well as the ratio of Beclin-1/Bcl-2. Both 3-MA and NEC-1 suppressed TBI-induced caspase-3 activation and LC3-II formation, Z-VAD only inhibited caspase-3 activation but increased LC3-II expression at 24 h post-TBI. All these results revealed that multiple cell death pathways participated in the development of TBI, and NEC-1 inhibited apoptosis and autophagy simultaneously. These coactions may further explain how can NEC-1 reduce TBI-induced tissue damage and functional deficits and reflect the interrelationship among necrosis, apoptosis and autophagy.

Death receptor signalling in central nervous system inflammation and demyelination

Death receptors (DRs) are members of the tumor necrosis factor receptor (TNF-R) superfamily that are characterised by the presence of a conserved intracellular death domain and are able to trigger a signalling pathway leading to apoptosis. Strong evidence suggests that DRs contribute to the pathology of tissue destructive diseases, including multiple sclerosis (MS), the most common inflammatory demyelinating disease of the central nervous system (CNS). Here, we review the evidence supporting a role for DRs in MS pathology and its implications for the development of therapeutic strategies for MS and other demyelinating pathologies of the CNS.

Cytoarchitectural disruption of the superior colliculus and an enlarged acoustic startle response in the Tuba1a mutant mouse

The Jenna mutant mouse harbours an S140G mutation in Tuba1a that impairs tubulin heterodimer formation resulting in defective neuronal migration during development. The consequence of decreased neuronal motility is a fractured pyramidal cell layer in the hippocampus and wave-like perturbations in the cerebral cortex. Here, we extend our characterisation of this mouse investigating the laminar architecture of the superior colliculus (SC). Our results reveal that the structure of the SC in mutant animals is intact; however, it is significantly thinner with an apparent fusion of the intermediate grey and white layers. Birthdate labelling at E12.5 and E13.5 showed that the S140G mutation impairs the radial migration of neurons in the SC. A quantitative assessment of neuronal number in adulthood reveals a massive reduction in postmitotic neurons in mutant animals, which we attribute to increased apoptotic cell death. Consistent with the role of the SC in modulating sensorimotor gating, and the circuitry that modulates this behaviour, we find that Jenna mutants exhibit an exaggerated acoustic startle response. Our results highlight the importance of Tuba1a for correct neuronal migration and implicate postnatal apoptotic cell death in the pathophysiological mechanisms underlying the tubulinopathies.

Fas activation increases neural progenitor cell survival

Although there is a sizable amount of research focusing on adult neural progenitor cells (NPCs) as a therapeutic approach for many neurodegenerative diseases, including multiple sclerosis, little is known about the pathways that govern NPC survival and apoptosis. Fas, a member of the death receptor superfamily, plays a well-characterized role in the immune system, but its function in neural stem cells remains uncertain. Our study focuses on the effects of Fas on NPC survival in vitro. Activation of Fas by recombinant Fas ligand (FasL) did not induce apoptosis in murine NPCs in culture. In fact, both an increase in the amount of viable cells and a decrease in apoptotic and dying cells were observed with FasL treatment. Our data indicate that FasL-mediated adult NPC neuroprotection is characterized by a reduction in apoptosis, but not increased proliferation. Further investigation of this effect revealed that the antiapoptotic effects of FasL are mediated by the up-regulation of Birc3, an inhibitor of apoptosis protein (IAP). Conversely, the observed effect is not the result of altered caspase activation or FLIP (Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitory protein) up-regulation, which is known to inhibit caspase-8-mediated cell death in T cells. Our data indicate that murine adult NPCs are resistant to FasL-induced cell death. Activation of Fas increased cell survival by decreasing apoptosis through Birc3 up-regulation. These results describe a novel pathway involved in NPC survival.

Interferon-gamma bolsters CD95/Fas-mediated apoptosis of astroglioma cells

In the present study, we investigated the mechanisms of the resistance to CD95-mediated cell death and the effects of interferon-gamma in modulating the susceptibility to CD95-induced apoptosis of human astroglioma cells. We found that interferon-gamma administration sensitized cancer cells to CD95-mediated apoptosis. The mechanism underlying this sensitization appeared to be associated with a framework of cell changes, including up-regulation of death receptor at the cell surface, pro-apoptotic molecule Bax and Bak over-expression and mitochondria hyperpolarization, as is known to be associated with cell sensitization to apoptosis. An involvement of the proteasome activity in the mechanism of sensitization by interferon-gamma was also detected, probably as a result of the differing expression of catalytic proteasome subunits. Taken together, these findings suggest that interferon-gamma could represent a promising candidate for modulating astroglioma cell apoptotic susceptibility.

Protective effect of memantine against Doxorubicin toxicity in primary neuronal cell cultures: influence a development stage

One of the serious unwanted effects of the anthracycline anticancer drug doxorubicin (Dox, adriamycin) is its neurotoxicity, which can be evoked by the activation of extracellular (FAS/CD95/Apo-1) pathway of apoptosis in cells. Since memantine, a clinically used N-methyl-D: -aspartic acid (NMDA) receptor antagonist, shows antiapoptotic action in several models of neuronal cell damage, in this study we evaluated the effect of memantine on the cell death induced by Dox in primary neuronal cell cultures. First, we investigated the effect of different concentrations of Dox (0.1-5 microM) on mouse neocortical, hippocampal, striatal, and cerebellar neurons on 7- and 12-day in vitro (DIV). The 7 DIV neuronal cell cultures were more prone to Dox-induced cell death than 12 DIV cultures. The cerebellar neurons were the most resistant to Dox-induced apoptosis in comparison to neuronal cell cultures derived from the forebrain. Memantine (0.1-2 microM) attenuated the Dox-evoked lactate dehydrogenase release in 7 DIV neuronal cell cultures with no significant effect on 12 DIV cultures. The ameliorating effect of memantine on Dox-mediated cell death was also confirmed by an increase in cell viability measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. There was no effect of memantine on Dox-induced caspase-8 and -3 activity and Dox-evoked decrease in mitochondrial potential, although attenuation in the number of cells with apoptotic DNA fragmentation was observed. We also showed that the antiapoptotic effect of memantine in our model was NMDA receptor-independent, since two other antagonists of this receptor, MK-801 and AP-5, did not attenuate Dox-induced cell death. Furthermore, memantine did not influence the Dox-evoked increase in cytoplasmic Ca2+ level. The obtained data suggest developmental regulation of both, the Dox-mediated neurotoxicity and efficacy of memantine in alleviating the Dox-induced cell damage in neuronal cell cultures. Moreover, this neuroprotective effect of memantine seems not to be dependent on caspase-3 activity and on the antagonistic action on NMDA receptor.

A critical role for Fas/CD-95 dependent signaling pathways in the pathogenesis of hyperoxia-induced brain injury

OBJECTIVE

Prematurely born infants are at risk for development of neurocognitive impairment in later life. Oxygen treatment has been recently identified as a trigger of neuronal and oligodendrocyte apoptosis in the developing rodent brain. We investigated the role of the Fas death receptor pathway in oxygen-triggered developmental brain injury.

METHODS

Six-day-old Wistar rats were exposed to 80% oxygen for various periods (2, 6, 12, 24, 48, and 72 hours), and mice deficient in either Fas (B6.MRL-Tnfrsf6(lpr)) or Fas ligand (B6Smn.C3-Fasl(gld)) and control mice (C57BL/6J) were exposed to 80% oxygen for 24 hours. Polymerase chain reaction, Western blotting, and caspase activity assays of thalamus and cortex tissue were performed.

RESULTS

Fas and Fas ligand messenger RNA and protein were upregulated. Furthermore, hyperoxia resulted in induction of downstream signaling events of Fas, such as Fas-associated death domain (FADD), the long and short form of FADD-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (FLIP-L, FLIP-S), and cleavage of caspase-8 and caspase-3. Injection of a selective caspase-8 inhibitor (TRP801, 1mg/kg) at the beginning of hyperoxia blocked subsequent caspase-3 cleavage in this model. B6.MRL-Tnfrsf6(lpr) mice were protected against oxygen-mediated injury, confirming Fas involvement in hyperoxia-induced cell death. Mice deficient in Fas ligand did not differ from control animals in the amount of cell death.

INTERPRETATION

We conclude that neonatal hyperoxia triggers Fas receptor and its downstream signaling events in a Fas ligand-independent fashion. Lack of functional Fas receptors and selective pharmacological inhibition of caspase-8 prevents activation of caspase-3 and provides significant neuroprotection.

Modeling the impact of alcohol on cortical development in a dish: strategies from mapping neural stem cell fate

During the second trimester period, neuroepithelial stem cells give birth to millions of new neuroblasts, which migrate away from their germinal zones to populate the developing brain and terminally differentiate into neurons. During this period, large numbers of cells are also eliminated by programmed cell death. Therefore, the second trimester constitutes an important critical period for neuronal proliferation, migration, differentiation and apoptosis. Substantial evidence indicates that teratogens like ethanol can interfere with neuronal maturation. However, there is a paucity of good model systems to study early, second trimester events. In vivo models are inherently interpretatively complex because cell proliferation, migration, differentiation, and death mechanisms occur concurrently in regions like the cerebral cortex. This temporal overlap of multiple developmental critical periods makes it difficult to evaluate the relative vulnerability of any individual critical period. Our laboratory has elected to utilize fetal rodent cerebral cortical-derived neurosphere cultures as an experimental model of the second-trimester ventricular neuroepithelium. This model has enabled us to use flow cytometric approaches to identify neuroepithelial stem cell and progenitor sub-populations and to show that ethanol accelerates the maturation of neural stem cells. We have also developed a simplified mitogen-withdrawal/matrix-adhesion paradigm to model the exit of neuroepithelial cells from the ventricular zone towards the subventricular zone and cortical plate, and their maturation into multipolar neurons. We can treat neurosphere cultures with ethanol to mimic exposure during the period of neuroepithelial proliferation and by using the step-wise maturation model, ask questions about the impact of prior ethanol exposure on the subsequent maturation of neurons as they migrate and undergo terminal differentiation. The combination of neurosphere culture and stepwise maturation models will enable us to dissect out the contributions of specific developmental critical periods to the overall teratology of a drug of abuse like ethanol.

Increased serum sFas and TNFalpha following isolated severe head injury in males

OBJECTIVES

Severe traumatic brain injury (TBI) is associated with a 30-70% mortality rate. Nevertheless, controversy has been raised concerning the prognostic value of biomarkers following severe TBI. Therefore, our aim was to determine whether sFas or TNFalpha serum levels correlate with primary outcome following isolated severe TBI.

METHODS

Seventeen consecutive male patients, victims of isolated severe TBI (Glasgow Coma Scale score 3-8) and a control group consisting of 6 healthy male volunteers were enrolled in this prospective study. Clinical outcome variables of severe TBI comprised: survival, time for intensive care unit (ICU) discharge, and neurological assessment by Glasgow Outcome Scale at ICU discharge. Venous blood samples were taken at admission in the ICU. Serum sFas and TNFalpha concentrations were measured by ELISA assays.

RESULTS

At admission in the ICU (mean time 10.2 h after injury), mean sFas and TNFalpha concentrations were significantly increased in the TBI (0.105 and 24.275 rhog/l, respectively) compared with the control group (0.047 and 15.475 rhog/l, respectively). However, no significant correlation was found between higher serum sFas or TNFalpha concentrations and fatal outcome.

CONCLUSIONS

Increased serum sFas and TNFalpha levels following isolated severe TBI did not predict fatal outcome.

Negative autoregulation by FAS mediates robust fetal erythropoiesis

Tissue development is regulated by signaling networks that control developmental rate and determine ultimate tissue mass. Here we present a novel computational algorithm used to identify regulatory feedback and feedforward interactions between progenitors in developing erythroid tissue. The algorithm makes use of dynamic measurements of red cell progenitors between embryonic days 12 and 15 in the mouse. It selects for intercellular interactions that reproduce the erythroid developmental process and endow it with robustness to external perturbations. This analysis predicts that negative autoregulatory interactions arise between early erythroblasts of similar maturation stage. By studying embryos mutant for the death receptor FAS, or for its ligand, FASL, and by measuring the rate of FAS-mediated apoptosis in vivo, we show that FAS and FASL are pivotal negative regulators of fetal erythropoiesis, in the manner predicted by the computational model. We suggest that apoptosis in erythroid development mediates robust homeostasis regulating the number of red blood cells reaching maturity.

Lifeguard/neuronal membrane protein 35 regulates Fas ligand-mediated apoptosis in neurons via microdomain recruitment

Fas ligand (FasL)-receptor system plays an essential role in regulating cell death in the developing nervous system, and it has been implicated in neurodegenerative and inflammatory responses in the CNS. Lifeguard (LFG) is a protein highly expressed in the hippocampus and the cerebellum, and it shows a particularly interesting regulation by being up-regulated during postnatal development and in the adult. We show that over-expression of LFG protected cortical neurons from FasL-induced apoptosis and decreased caspase-activation. Reduction of endogenous LFG expression by small interfering RNA sensitized cerebellar granular neurons to FasL-induced cell death and caspase-8 activation, and also increased sensitivity of cortical neurons. In differentiated cerebellar granular neurons, protection from FasL-induced cell death could be attributed exclusively to LFG and appears to be independent of FLICE inhibitor protein. Thus, LFG is an endogenous inhibitor of FasL-mediated neuronal death and it mediates the FasL resistance of CNS differentiated neurons. Finally, we also demonstrate that LFG is detected in lipid rafts microdomains, where it may interact with Fas receptor and regulate FasL-activated signaling pathways.

Embryonic cerebral cortical progenitors are resistant to apoptosis, but increase expression of suicide receptor DISC-complex genes and suppress autophagy following ethanol exposure

BACKGROUND

In utero exposure to ethanol can result in severe fetal brain defects. Previous studies showed that ethanol induces apoptosis in differentiated cortical neurons. However, we know little about ethanol's effects on proliferating embryonic cortical progenitors. This study investigated the impact of ethanol exposure on the Fas/Apo-1/CD95 suicide receptor pathway, and on the survival of proliferating cortical neuroepithelial progenitors.

METHODS

Murine embryonic-derived primary cortical neuroepithelial cells were maintained as neurosphere cultures and exposed to a dose range of ethanol for periods ranging from 1 to 5 days. Programmed cell death was measured by 4 independent means (Annexin-V staining, caspase activation, DNA fragmentation, and autophagic vacuole formation). Surface Fas/Apo-1 suicide receptor expression was measured by flow cytometry. Expression of Fas/Apo-1-associated DISC-complex genes was measured by quantitative polymerase chain reaction.

RESULTS

Ethanol exposure did not substantially increase apoptosis, necrosis, or surface Fas/Apo-1 expression. Moreover, ethanol significantly decreased caspase activation and autophagic activity. Finally, ethanol exposure induced mRNA expression of genes that constitute the death receptor complex.

CONCLUSIONS

This study provides surprising evidence that ethanol does not induce either programmed cell death or necrosis of immature progenitors during neurogenesis, although ethanol may render neural progenitors susceptible to future apoptotic insults. Furthermore, our novel observation that ethanol suppresses autophagy is consistent with a hypothesis that ethanol promotes premature neural progenitor maturation. Taken together with our previous data regarding the role of the Fas/Apo-1 receptor in neural development, we conclude that ethanol disrupts basic proliferation and differentiation machinery rather than initiating cell death per se.

Ethanol regulates angiogenic cytokines during neural development: evidence from an in vitro model of mitogen-withdrawal-induced cerebral cortical neuroepithelial differentiation

BACKGROUND

Heavy alcohol consumption during pregnancy can cause significant mental retardation and brain damage. We recently showed that ethanol depletes reserve cerebral cortical stem cell capacity. Moreover, proliferating neuroepithelial cells exposed to ethanol were resistant to subsequent retinoic acid-induced differentiation. Emerging evidence suggests that cytokines play a crucial growth-promoting role in the developing neural tube.

METHODS

We cultured murine cortical neurosphere cultures in control or ethanol-supplemented mitogenic medium, to mimic alcohol exposure during the period of neuroepithelial proliferation. Cultures were then treated with a step-wise mitogen-withdrawal, integrin-activation model to mimic subsequent phases of neuronal migration and early differentiation. We examined the impact of alcohol exposure during neurogenesis on the secretion of inflammatory and growth-promoting cytokines.

RESULTS

Cortical neurosphere cultures exhibit increasingly complex differentiation phenotypes in response to step-wise mitogen-withdrawal and laminin exposure. Some inflammation-modulating cytokines were secreted independent of differentiation state. However, chemotactic cytokines were specifically secreted at high levels, as a function of differentiation stage. monocyte chemotactic protein-1, vascular endothelial growth factor-A, and interleukin (IL)-10 were coordinately decreased during differentiation compared with neuroepithelial proliferation, while granulocyte macrophage-colony stimulating factor (GM-CSF) was induced during differentiation, compared with the neuroepithelial proliferation period. Ethanol exposure during the period of neuroepithelial proliferation prevented the early differentiation-induced increase in GM-CSF while inducing differentiation-associated increase in IL-12 secretion.

CONCLUSION

Embryonic cerebral cortical neuroepithelial-derived precursors secrete high levels of several angiogenic and neural-growth-promoting cytokines as they differentiate into neurons. Our data collectively suggest that ethanol exposure during the period of neuroepithelial proliferation significantly disrupts cytokine signals that are required for the support of emerging neurovascular networks, and the maintenance of neural stem cell beds.

Effects of opiate drugs on Fas-associated protein with death domain (FADD) and effector caspases in the rat brain: regulation by the ERK1/2 MAP kinase pathway

This study was designed to assess the effects of opiate treatment on the expression of Fas-associated protein with death domain (FADD) in the rat brain. FADD is involved in the transmission of Fas-death signals that have been suggested to contribute to the development of opiate tolerance and addiction. Acute treatments with high doses of sufentanil and morphine (mu-agonists), SNC-80 (delta-agonist), and U50488H (kappa-agonist) induced significant decreases (30-60%) in FADD immunodensity in the cerebral cortex, through specific opioid receptor mechanisms (effects antagonized by naloxone, naltrindole, or nor-binaltorphimine). The cannabinoid CB1 receptor agonist WIN 55,212-2 did not alter FADD content in the brain. Chronic (5 days) morphine (10-100 mg/kg), SNC-80 (10 mg/kg), or U50488H (10 mg/kg) was associated with the induction of tachyphylaxis to the acute effects. In morphine- and SNC-80-tolerant rats, antagonist-precipitated (2 h) or spontaneous withdrawal (24-48 h) induced a new and sustained inhibition of FADD (13-50%). None of these treatments altered the densities of caspases 8/3 (including the active cleaved forms) in the brain. Pretreatment of rats with SL 327 (a selective MEK1/2 inhibitor that blocks ERK activation) fully prevented the reduction of FADD content induced by SNC-80 in the cerebral cortex (43%) and corpus striatum (29%), demonstrating the direct involvement of ERK1/2 signaling in the regulation of FADD by the opiate agonist. The results indicate that mu- and delta-opioid receptors have a prominent role in the modulation of FADD (opposite to that of Fas) shortly after initiating treatment. Opiate drugs (and specifically the delta-agonists) could promote survival signals in the brain through inhibition of FADD, which in turn is dependent on the activation of the antiapoptotic ERK1/2 signaling pathway.

Nell-1 induces acrania-like cranioskeletal deformities during mouse embryonic development

We previously reported NELL-1 as a novel molecule overexpressed during premature cranial suture closure in patients with craniosynostosis (CS). Nell-1 overexpression also results in premature suture closure/craniosynostosis in newborn transgenic mice. On a cellular level, increased levels of Nell-1 induce osteoblast differentiation and apoptosis. In this report, mice over-expressing Nell-1 were examined during embryonic development as well as shortly after birth for further analysis of craniofacial defects including neural tube defects (NTDs). The results demonstrated that overexpression of Nell-1 could induce acrania at relatively late gestation stage (E15.5) in mouse embryos, through massive apoptosis in calvarial osteoblasts and neural cells. The induced apoptosis was associated with an increase in Fas and Fas-L production. In addition, transgenic E15.5 and newborn transgenic mice with the CS phenotype displayed distortion of the chondrocranium associated with premature hypertrophy and increased apoptosis of chondrocytes. These findings were also verified in vitro with primary chondrocytes transduced with AdNell-1. In conclusion, Nell-1 overexpression can induce craniofacial anomalies associated with neural tube defects during embryonic development and may involve mechanisms of massive apoptosis associated with the Fas/Fas-L signaling pathway. NELL-1: used when describing the human gene; NELL-1: used when describing the human protein; Nell-1: used when describing the rodent gene; Nell-1: used when describing the rodent protein.

Lung disease and brain development

With the technical progress made in fetal and neonatal intensive care, perinatal mortality has decreased by 25% over the last decade and has expanded the surviving premature population. Prematurity drastically changes the environment of the developing organism. Striking evidence from a number of disciplines has focused attention on the interplay between the developing organism and the circumstances in which it finds itself. The environmental event during a sensitive period in development, induces injury and/or biological adaptations that lead to altered differentiation of tissues. The organism can express specific adaptive responses to its environment which include short-term changes in physiology as well as long-term adjustments. This review addresses these short-term as well as longer-term changes occurring in lung and brain tissue and illustrates how these changes can be studied using advanced imaging techniques such as magnetic resonance imaging

Fas/CD95/APO-1 can function as a death receptor for neuronal cells in vitro and in vivo and is upregulated following cerebral hypoxic-ischemic injury to the developing rat brain

Fas/CD95/Apo-1 is a cell surface receptor that transduces apoptotic death signals following activation and has been implicated in triggering apoptosis in infected or damaged cells in disease states. Apoptosis is a major mechanism of neuronal loss following hypoxic-ischemic injury to the developing brain, although the role of Fas in this process has not been studied in detail. In the present study, we have investigated the expression and function of Fas in neuronal cells in vitro and in vivo. Fas was found to be expressed in the 14 day old rat brain, with strongest expression in the cortex, hippocampus and cerebellum. Cross-linking of Fas induced neuronal apoptosis both in neuronal PC12 cells in culture and following intracerebral injection in vivo, indicating that neuronal Fas was functional as a death receptor. This death was shown to be caspase dependent in primary neuronal cultures and was blocked by the selective caspase 8 inhibitor IETD. Finally, cerebral hypoxia-ischemia resulted in a strong lateralised upregulation of Fas in the hippocampus, that peaked six to twelve hours after the insult and was greater on the side of injury. These results suggest that Fas may be involved in neuronal apoptosis following hypoxic-ischemic injury to the developing brain.

Control of neuronal branching by the death receptor CD95 (Fas/Apo-1)

The CD95 (Apo-1/Fas)/CD95 ligand (CD95L) system is best characterized as a trigger of apoptosis. Nevertheless, despite broad expression of CD95L and CD95 in the developing brain, absence of functional CD95 (lpr mice) or CD95L (gld mice) does not alter neuronal numbers. Here, we report that in embryonic hippocampal and cortical neurons in vivo and in vitro CD95L does not induce apoptosis. Triggering of CD95 in cultured immature neurons substantially increases neurite branches by promoting their formation. The branching increase occurs in a caspase-independent and death domain-dependent manner and is paralleled by an increase in the nonphosphorylated form of Tau. Most importantly, lpr and gld mutants exhibit a reduced number of dendritic branches in vivo at the time when synapse formation takes place. These data reveal a novel function for the CD95 system and add to the picture of guidance molecules in the developing brain.

Suppression of Fas-FasL coexpression by erythropoietin mediates erythroblast expansion during the erythropoietic stress response in vivo

Erythropoietin (Epo) is the principal regulator of the erythropoietic response to hypoxic stress, through its receptor, EpoR. The EpoR signals mediating the stress response are largely unknown, and the spectrum of progenitors that are stress responsive is not fully defined. Here, we used flow cytometry to identify stress-responsive Ter119+CD71highFSChigh early erythroblast subsets in vivo. In the mouse spleen, an erythropoietic reserve organ, early erythroblasts were present at lower frequencies and were undergoing higher rates of apoptosis than equivalent cells in bone marrow. A high proportion of splenic early erythroblasts coexpressed the death receptor Fas, and its ligand, FasL. Fas-positive early erythroblasts were significantly more likely to coexpress annexin V than equivalent, Fas-negative cells, suggesting that Fas mediates early erythroblast apoptosis in vivo. We examined several mouse models of erythropoietic stress, including erythrocytosis and beta-thalassemia. We found a dramatic increase in the frequency of splenic early erythroblasts that correlated with down-regulation of Fas and FasL from their cell surface. Further, a single injection of Epo specifically suppressed early erythroblast Fas and FasL mRNA and cell-surface expression. Therefore, Fas and FasL are negative regulators of erythropoiesis. Epo-mediated suppression of erythroblast Fas and FasL is a novel stress response pathway that facilitates erythroblast expansion in vivo.

Peripheral lipopolysaccharide induces apoptosis in the murine olfactory bulb

The olfactory bulb (OB) is one of the few structures in the adult mammalian CNS that contains a continuous supply of newly generated neurons in the subventricular zone. Therefore, the balance between the supply of new cells and apoptosis in the OB might determine olfactory function. Lipopolysaccharide-induced tumor necrosis factor (TNF)-alpha triggers the apoptotic cascade mediated by the TNF/TNF receptor (TNFR) pathway. The present study therefore examines the effect of the propagated innate immune reaction triggered by peripheral lipopolysaccharide on the OB of C3H/HeN mice. Within 2 h of an intraperitoneal injection of lipopolysaccharide, mRNA expression levels of the genes encoding IkappaB, TNF-alpha, and TNFR type 1 in the mouse OB were significantly enhanced. Double immunofluorescence microscopy confirmed that almost all TNF-alpha-immunopositive cells in the OB of the TNF-injected mice were located in the subependymal zone and that they overlapped cells immunostained with antibody against glial fibrillary acidic protein, but not with the antibody against F4/80, an antigenic marker of microglia. The number of TUNEL-positive cells identified exclusively in the granule cell layer was significantly increased in mice injected with lipopolysaccharide and sacrificed at 24 h thereafter. These results suggest that peripheral lipopolysaccharide causes disequilibrium between the supply and disappearance of the cells in the OB, which might lead to olfactory dysfunction.

Maturational changes in neuromodulation of central pathways underlying hypoxic ventilatory response

The neuromodulator systems mediating the central component of the hypoxic ventilatory response (HVR) during development are complex and diverse. The early component of the HVR is mediated through N-methyl-D-aspartate (NMDA) glutamate receptors in the caudal brainstem. The intracellular downstream signal transductions of the NMDA receptors involve protein kinase C (PKC), neuronal nitric oxide synthase (nNOS) and tyrosine kinase (TK). Activation of NMDA receptors will also lead to activation of the early gene transcription factors including AP-1 (c-fos, c-jun) and NF-kappaB which may play a role in modulation of the subsequent response to hypoxia. NMDA receptors in the caudal brainstem play a critical role in the development of the HVR and increasing dependency on NMDA receptors emerges over time. Similarly, hypoxia-induced PKC, NOS and c-Fos activation in the caudal brainstem is relatively weak in the immature animals, but this activation increases with age and the strength of the response appears to increase concomitantly with the appearance of NMDA expression. Several neurotransmitters including adenosine, gamma-aminobutyric acid (GABA), serotonin and opioids are involved in the late component of the HVR. In addition, the late phase of the HVR is mediated in part through platelet-derived growth factor (PDGF)-beta receptors. PDGF-beta receptor activation is an important contributor of the hypoxic ventilatory depression at all postnatal ages, but its role is more critical in the developing animals. Maturation of these neuromodulators, especially the NMDA and PDGF-beta receptors-mediated pathways, occurs primarily during the early postnatal period. Perturbation of these developmental processes may result in short-term or sustained alterations to the HVR and may also affect neuronal survival during hypoxia.

NF-κB in the Survival and Plasticity of Neurons

The transcription factor nuclear factor kappa-B (NF-kappaB) is involved in regulating responses of neurons to activation of several different signaling pathways in a variety of physiological and pathological settings. During development of the nervous system NF-kappaB is activated in growing neurons by neurotrophic factors and can induce the expression of genes involved in cell differentiation and survival. In the mature nervous system NF-kappaB is activated in synapses in response to excitatory synaptic transmission and may play a pivotal role in processes such as learning and memory. NF-kappaB is activated in neurons and glial cells in acute neurodegenerative conditions such as stroke and traumatic injury, as well as in chronic neurodegenerative conditions such as Alzheimer's disease. Activation of NF-kappaB in neurons can promote their survival by inducing the expression of genes encoding anti-apoptotic proteins such as Bcl-2 and the antioxidant enzyme Mn-superoxide dismutase. On the other hand, by inducing the production and release of inflammatory cytokines, reactive oxygen molecules and excitotoxins, activation of NF-kappaB in microglia and astrocytes may contribute to neuronal degeneration. Emerging findings suggest roles for NF-kappaB as a mediator of effects of behavioral and dietary factors on neuronal plasticity. NF-kappaB provides an attractive target for the development of novel therapeutic approaches for a range of neurological disorders.

Human adult olfactory neuroepithelial derived progenitors retain telomerase activity and lack apoptotic activity

Olfactory epithelium (OE) contains a population of progenitors responsible for its life-long regenerative capacity. Procedures for the isolation of these progenitors have been established [F.J. Roisen, K.M. Klueber, C.L. Lu, L.M. Hatcher, A. Dozier, C.B. Shields, Adult human olfactory stem cells, Brain Res., 890 (2001) 11-12.] and over 40 patient-specific cell lines from adult postmortem OE and endoscopic biopsy from patients undergoing nasal sinus surgery have been obtained. As these cells emerged in primary cultures, they formed neurospheres (NSFCs). The purpose of the present study was to further characterize these adult human olfactory-derived progenitors. Subcultures of the NSFCs have been passaged nearly 200 times, with a mitotic cycle of 18-20 h. Telomerase activity remains in stem cells; therefore, ELISA was employed to determine the telomerase activity of different lines and passages. Since progenitors undergo low levels of apoptosis, the levels of apoptosis were also examined in these populations. The levels of telomerase and apoptotic activity in 12 NSFC lines remained relatively constant irrespective of donor age, culture duration, or sex. To further study the apoptotic characteristics of the NSFCs, nine different caspases (cysteine proteases) known to be critical in apoptosis were evaluated using gene-microarrays comparing cells from a single line at passages 14, 88, and 183. No increases were found in caspase activity in all passages studied. ELISA confirmed the absence of caspase activity over the entire range of passages. This study further suggests that NSFCs can be obtained and used from patients, irrespective of age, sex, or time in culture without altered viability expanding the potential utility of these cells for autologous transplantation and possible diagnostic testing.

Low soluble Fas (sFas) and sFas ligand (sFasL) content in breast milk after preterm as opposed to term delivery

AIM

Various mechanisms of innate immunity and gastrointestinal integrity are potentially affected by soluble Fas (sFas) and sFas ligand (sFasL). Assuming that sFas and sFasL in milk reflect cellular events during lactogenesis, we aimed to assess the impact of premature parturition and duration of lactation on the concentrations of sFas and sFasL in human milk.

PATIENTS AND METHODS

The content of the soluble form of the cell surface receptor Fas (sFas) and its natural ligand (sFasL) was measured in human breast milk of 44 healthy mothers after preterm (<35 wk, n=21) and term (>37 wk, n=23) delivery. Milk was furthermore classified as immature breast milk (days 4-7 of lactation) or mature breast milk (days 35-45 of lactation). Breast milk (2-3 ml) was sampled 5 min after the start of breastfeeding by manual expression or milk pump, and stored at -20 degrees C until analysis by an ELISA.

RESULTS

sFas and sFasL concentrations were lower in immature milk after preterm compared to term delivery (sFas: 1.71; 1.38-2.47 ng/ml vs 3.03; 2.02-4.30 ng/ml, p < 0.001; sFasL: 0.13; 0.07-0.21 ng/ml vs 0.29; 0.15-0.60 ng/ml, p < 0.001 [median +/- interquartile range]). Mature milk samples, taken 1 mo later from both gestational groups, did not differ in sFas/sFasL content. Soluble Fas was positively correlated with sFasL in the same sample of immature (p < 0.001) and mature human milk (p < 0.05). A positive correlation was found between sFas and sFasL in immature and mature milk samples of the same mother (p < 0.01). The body mass index of the mothers and duration of pregnancy were positively correlated with the sFas and sFasL content in immature milk (p < 0.05 and p < 0.01, respectively) but not in mature milk.

CONCLUSION

Preterm newborn infants fed with breast milk have a lower intake of sFas and sFasL compared to term neonates. Our results demonstrate that preterm delivery affects breast milk composition.

Inhibition of IκBα phosphorylation prevents glutamate-induced NF-κB activation and neuronal cell death

NF-kappaB is a nuclear transcription factor involved in the control of fundamental cellular functions including regulation of cell survival. We investigated NF-kappaB activation induced by two opposing modulators of cell viability: IL-1beta and glutamate. We found that IL-1beta activated p50, p65 and c-Rel subunits of NF-kappaB, while glutamate activated only p50 and p65 proteins. Cell stimulation by glutamate, correlated with expression of the pro-apoptotic genes Caspase-3, Caspase-2L and Bax. Conversely, IL-1beta induced the expression of the short anti-apoptotic isoform of Caspase-2. Finally, we analysed the effect of the inhibition of IkappaBalpha degradation on glutamate-induced toxicity by using BAY 11-7082, a selective inhibitor of IkappaBalpha phosphorylation. Our results suggest that BAY 11-7082 preserves neuron viability from the glutamate-mediated injury.

Neonatal mice lacking functional Fas death receptors are resistant to hypoxic-ischemic brain injury

Neonatal hypoxia-ischemia (HI) upregulates Fas death receptor expression in the brain, and alterations in expression and activity of Fas signaling intermediates occur in neonatal brain injury. B6.MRL-Tnfrsf6(lpr) mice lacking functional Fas death receptors are protected from HI brain damage in cortex, striatum, and thalamus compared to wild-type mice. Expression of Fas death receptor and active caspases increase in the cortex after HI. In wild-type mice, the hippocampus is most severely injured, and the hippocampus is the only region not protected in the B6.MRL-Tnfrsf6(lpr) mice. The selective vulnerability of the hippocampus to injury correlates with (1) lower basal expression of [Fas-associated death-domain-like IL-1beta-converting enzyme]-inhibitory protein (FLIP), (2) increased degradation of spectrin to its 145 or 150 kDa breakdown product, and (3) a higher percentage of non-apoptotic cell death following neonatal HI. We conclude that Fas signaling via both extrinsic and intrinsic caspase cascades causes brain injury following neonatal HI in a region-dependent manner. Basal levels of endogenous decoy proteins may modulate the response to Fas death receptor signaling and provide a novel approach to understanding mechanisms of neonatal brain injury.

Involvement of p53 and Fas/CD95 in murine neural progenitor cell response to ionizing irradiation

We investigated the role of tumor suppressor p53 and Fas (CD95/APO-1), a member of the tumor necrosis factor receptor family, in neural progenitors response to gamma-irradiation exposure. Telencephalic cells were obtained from wild-type C57Bl/6, or p53-/- or fas-/-, 15-day-old mouse embryos. They were cultured in conditions allowing neural progenitors to form proliferating clusters (neurospheres). A 2 Gy gamma-irradiation induced a G1 cell cycle arrest and triggered apoptosis in wild-type neural progenitor cultures in correlation with an enhanced expression of p53 and of its downstream target p21(WAF1), both of them acquiring a nuclear localization. These effects did not occur in p53-/- neural progenitors demonstrating the central role played by p53 in their response to ionizing radiation. Furthermore, the monoclonal antibody Jo2 directed against Fas induced apoptosis of wild type but not of fas-/- neural progenitors, indicating the existence of a functional Fas signaling pathway in neural progenitors. Ionizing radiation induced an increase of Fas membrane expression related to a p53-dependent increase of fas mRNA expression in wild-type neural progenitors. Moreover, fas-/- neural progenitors exhibited delayed radiation-induced apoptosis compared to wild-type cells. Therefore, these findings establish a role for Fas/CD95 related to p53 in the response of neural progenitors to gamma-radiation exposure. Similar mechanisms could be triggered in neural progenitors in case of different stresses during brain development or in the course of various diseases affecting the adult brain.

The death receptor antagonist FAIM promotes neurite outgrowth by a mechanism that depends on ERK and NF-kapp B signaling

Fas apoptosis inhibitory molecule (FAIM) is a protein identified as an antagonist of Fas-induced cell death. We show that FAIM overexpression fails to rescue neurons from trophic factor deprivation, but exerts a marked neurite growth–promoting action in different neuronal systems. Whereas FAIM overexpression greatly enhanced neurite outgrowth from PC12 cells and sympathetic neurons grown with nerve growth factor (NGF), reduction of endogenous FAIM levels by RNAi decreased neurite outgrowth in these cells. FAIM overexpression promoted NF-κB activation, and blocking this activation by using a super-repressor IκBα or by carrying out experiments using cortical neurons from mice that lack the p65 NF-κB subunit prevented FAIM-induced neurite outgrowth. The effect of FAIM on neurite outgrowth was also blocked by inhibition of the Ras–ERK pathway. Finally, we show that FAIM interacts with both Trk and p75 neurotrophin receptor NGF receptors in a ligand-dependent manner. These results reveal a new function of FAIM in promoting neurite outgrowth by a mechanism involving activation of the Ras–ERK pathway and NF-κB.

Activation of Fas receptor is required for the increased formation of the disialoganglioside GD3 in cultured cerebellar granule cells committed to apoptotic death

Apoptosis was induced in cultured cerebellar granule cells by lowering extracellular K+ concentrations (usually from 25 to 10 mM). The apoptotic phenotype was preceded by an early and transient increase in the intracellular levels of the disialoganglioside, GD3, which behaves as a putative pro-apoptotic factor. We examined whether activation of Fas receptor mediates the increase in GD3 formation in granule cells committed to die. Degenerating granule cells showed increased expression of both Fas receptor and its ligand (Fas-L), at times that coincided with the increase in GD3 levels and the induction of GD3 synthase mRNA. Addition of neutralizing anti-Fas-L antibodies reduced the extent of 'low-K+'-induced apoptosis and abolished the increase in GD3 levels and GD3 synthase mRNA. Similar reductions were observed in cultures prepared from gld or lpr mice, which harbor loss-of-function mutations of Fas-L and Fas receptor, respectively. In addition, exogenous application of soluble Fas-L further enhanced both the increase in GD3 formation and cell death in cultured granule cells switched from 25 into 10 mM K+. We conclude that activation of Fas receptor is entirely responsible for the increase in GD3 levels and contributes to the development of apoptosis by trophic deprivation in cultured cerebellar granule cells.

Voltage-gated K+ current: a marker for apoptosis in differentiating neuronal progenitor cells?

We investigated apoptosis during early stages of in vitro differentiation of neuronal precursors generated by embryonic day 14 (E14) mouse striata stem cells. Differentiation was in conditions of suboptimal growth factor supply. Apoptosis reached 10-15% of cells and affected proliferating as well as postmitotic cells, including TUJ1-positive cells. Inhibition of apoptosis led to an increased proportion of TUJ1-positive cells generated by stem cells. K(+) current was reported to be related to apoptosis. Outward K(+) currents were present in differentiating neuronal precursors that were consistent with delayed rectifier and transient A-type currents. The amplitude of the delayed rectifier current varied during the first 4 days of stem cell differentiation. Current amplitude was greatly increased in the presence of staurosporine but reduced at elevated extracellular K(+) concentration. In addition, the amplitude of the current was significantly diminished by inhibiting several caspases, but not caspase 8. In Bax knock-out transgenic neuronal precursors, K(+) current was not decreased after the first day but at later stages of cell differentiation. At this early stage, apoptosis of proliferating cells and of TUJ1-positive cells was not reduced by the absence of Bax, but was by caspase 9 inhibition. Thus, activation of a delayed rectifier K(+) current in differentiating stem cells is related to apoptosis. Recordings of this current revealed that apoptosis at early stages of neuronal differentiation occurred in two phases that did not exhibit similar dependence on the proapoptotic protein Bax and that probably used different pathways.

Lyssavirus matrix protein induces apoptosis by a TRAIL-dependent mechanism involving caspase-8 activation

Lyssaviruses, which are members of the Rhabdoviridae family, induce apoptosis, which plays an important role in the neuropathogenesis of rabies. However, the mechanisms by which these viruses mediate neuronal apoptosis have not been elucidated. Here we demonstrate that the early induction of apoptosis in a model of lyssavirus-infected neuroblastoma cells involves a TRAIL-dependent pathway requiring the activation of caspase-8 but not of caspase-9 or caspase-10. The activation of caspase-8 results in the activation of caspase-3 and caspase-6, as shown by an increase in the cleavage of the specific caspase substrate in lyssavirus-infected cells. However, neither caspase-1 nor caspase-2 activity was detected during the early phase of infection. Lyssavirus-mediated cell death involves an interaction between TRAIL receptors and TRAIL, as demonstrated by experiments using neutralizing antibodies and soluble decoy TRAIL-R1/R2 receptors. We also demonstrated that the decapsidation and replication of lyssavirus are essential for inducing apoptosis, as supported by UV inactivation, cycloheximide treatment, and the use of bafilomycin A1 to inhibit endosomal acidification. Transfection of cells with the matrix protein induced apoptosis using pathways similar to those described in the context of viral infection. Furthermore, our data suggest that the matrix protein of lyssaviruses plays a major role in the early induction of TRAIL-mediated apoptosis by the release of a soluble, active form of TRAIL. In our model, Fas ligand (CD95L) appears to play a limited role in lyssavirus-mediated neuroblastoma cell death. Similarly, tumor necrosis factor alpha does not appear to play an important role.

c-FLIP-L recombinant adeno-associated virus vector infection prevents Fas-mediated but not nerve growth factor withdrawal-mediated cell death in PC12 cells

Fas is a cell surface death receptor that may play an important role in regulating cell death in neuronal cell types by activation of caspase 8. Cellular FLICE inhibitory protein-long (c-FLIP-L) is an endogenous inhibitor of the activation of caspase 8 by Fas. The current study addresses the role of c-FLIP-L in regulation of cell death in PC12 cells induced by nerve growth factor (NGF) withdrawal and Fas antibody, which acts as a Fas ligand and activates the Fas receptor. A recombinant adeno-associated virus (rAAV) vector that expresses c-FLIP-L was constructed. PC12 cells infected with the c-FLIP-L rAAV were resistant to apoptosis induced by treatment with Fas antibody compared to cells infected with enhanced green fluorescent protein (EGFP) expressing rAAV. Overexpression of c-FLIP-L rAAV inhibited cleavage of caspase 8 induced by Fas antibody treatment. In contrast, treatment with the c-FLIP-L rAAV did not protect PC12 cells from cell death induced by NGF withdrawal. In conclusion, overexpression of c-FLIP-L rAAV inhibits Fas antibody-mediated cell death, but not NGF withdrawal-mediated cell death in PC12 cells.

Differential regulation of the mitochondrial and death receptor pathways in neural stem cells

Despite an increasing interest in neural stem cell (NSC) research, relatively little is known about the biochemical regulation of cell death pathways in these cells. We demonstrate here, using murine-derived multipotent C17.2 NSCs, that cells undergo mitochondria-mediated cell death in response to apoptotic stimuli such as oxidative stress induced by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ). In particular, treated cells exhibited apoptotic features, including Bax translocation, cytochrome c release, activation of caspase-9 and -3, chromatin condensation and DNA fragmentation. Although C17.2 cells possess the Fas receptor and express procaspase-8, agonistic Fas mAb treatment failed to induce apoptosis. Fas treatment activated the extracellular signal-regulated protein kinase (ERK) pathway, which may have an antiapoptotic as well as a growth stimulating role. Combined, our findings indicate that while NSCs are sensitive to cytotoxic stimuli that involve an engagement of mitochondria, Fas treatment does not induce death and may have an alternative role.

Expression of ICAM-1, TNF-alpha, NF kappa B, and MAP kinase in tubers of the tuberous sclerosis complex

Individuals affected with tuberous sclerosis complex (TSC) develop cortical tubers characterized by disorganized cytoarchitecture and morphologically abnormal cell types, such as dysplastic neurons (DNs) and giant cells (GCs). As part of ongoing cDNA array analysis to study the molecular pathogenesis of tuber formation, we detected increased expression of intercellular adhesion molecule-1 (ICAM-1) mRNA, a cell adhesion molecule (CAM) that functions in cytokine signaling, in tubers. Western and immunohistochemical analyses revealed that ICAM-1 protein was selectively expressed in tubers, but was only minimally expressed in control cortex, adjacent nontuberal cortex, or in non-TSC focal cortical dysplasia. Increased expression of ICAM-1 was found in mice in which the Tsc1 gene was conditionally inactivated in astrocytes. Expression of molecules involved in ICAM-1 activation and cytokine signaling were increased in tubers, including tumor necrosis factor alpha (TNF-alpha), mitogen activated protein kinase (MAPK), and nuclear factor kappa B (NF-kappaB). Numerous CD68-immunoreactive macrophages were observed clustered around GCs further supporting an inflammatory response in tubers. Expression of caspase 8 and Fas support cytokine activation and detection of TUNEL reactivity suggests ongoing cell death in tubers. Specific alterations in ICAM-1, TNF-alpha, NF-kappaB1, and MAPK expression coupled with the detection of numerous CD68-immunoreactive macrophages suggests activation of proinflammatory cytokine signaling pathways in tubers that may culminate in cell death.

Fas ligand/Fas system in the brain: regulator of immune and apoptotic responses

Apoptosis, also known as programmed cell death, is the major type of cell death involved in normal development, regeneration, proliferation and pathologic degeneration in the central nervous system (CNS). The apoptotic process can be divided further into two pathways depending on the involvement of mitochondria and related biochemical cascades. The internal pathway of apoptosis is initiated by a variety of cytotoxic stimuli and mediated by the release of cytochrome c and subsequent activation of downstream caspases. The external pathway is mainly triggered by ligation of death receptors such as Fas, tumor necrosis factor (TNF)-related apoptosis inducing ligand-R1 (TRAIL-R1), TRAIL-R2 and TNFRp55, and mediated by direct activation of upstream caspases. The Fas-FasL system has been known as a prototypic inducer of extrinsic cell death responsible for cell-mediated cytotoxicity, peripheral immune regulation, immune privilege and "counterattack" of malignant tumor cells against the host immune system. Fas and FasL are expressed in the normal CNS, and expression increases in inflamed and degenerated brains. Like other specialized tissues such as the eye and testis, the Fas-FasL system is thought to be involved in immune suppressed status in the CNS. Expression of Fas and FasL is significantly elevated in a variety of the neurologic disorders, suggesting the possibility that this system may play roles in degenerative and inflammatory responses in the CNS. Therefore, the FasL-Fas system should be considered as a double-edged sword in the CNS: maintaining the immune suppressed status in normal brain and inducing neuronal cell death and inflammation in a variety of neurologic disorders.

Fas ligation induces IL-1beta-dependent maturation and IL-1beta-independent survival of dendritic cells: different roles of ERK and NF-kappaB signaling pathways

The mechanisms that underpin the intriguing capacity of Fas ligation on dendritic cells (DCs) to induce maturation and activation, rather than apoptosis, remain unclear. In the present study we confirm that Fas signaling induces both phenotypic and functional maturation of murine DCs, and we demonstrate that phenotypic maturation is associated with phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, activation of caspase-1, and secretion of interleukin-beta (IL-1beta). Specific inhibition of ERK1/2 diminished Fas ligation-induced caspase-1 activation, IL-1beta secretion, and ensuing up-regulation of developmental markers, whereas treatment with neutralizing anti-IL-1beta antibody abrogated phenotypic and functional maturation, indicating that IL-1beta mediates Fas ligation-induced DC maturation in an autocrine manner. NF-kappaB activation was responsible for maintaining DC viability after Fas ligation. Inhibiting NF-kappaB did not affect either IL-1beta secretion or phenotypic maturation but rather sensitized DCs to Fas-mediated apoptosis. In conclusion, positive signals originating from Fas are transduced through at least 2 different intracellular pathways in DCs, promoting not only survival but also an increase in maturation that correlates with increased antigen-presentation capability.

Defined inflammatory states in astrocyte cultures: correlation with susceptibility towards CD95-driven apoptosis

A complete cytokine mix (CCM) or its individual components tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) were used to switch resting murine astrocytes to reactive states. The transformation process was characterized by differential up-regulation of interleukin-6 (IL-6), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthetase (iNOS) mRNA and protein and a subsequent release of prostaglandin E2, nitric oxide (NO) and IL-6. Both CD95L and anti-CD95 antibodies triggered caspase activation followed by apoptotic death in fully pro-inflammatory astrocytes, whereas resting cells were totally resistant. Two other death-inducing ligands, TNF and TNF-related apoptosis-inducing ligand (TRAIL) did not induce apoptosis in reactive astrocytes. The switch in astrocyte sensitivity was accompanied by up-regulation of caspase-8 and CD95 as well as the capacity to recruit Fas-associated death domain (FADD) to the activated death receptor complex. Neither CD95-mediated death, nor other inflammatory parameters were affected by inhibition of iNOS or COX, respectively. Accordingly, IFN-gamma was absolutely essential for up-regulation of iNOS, but not for the switch in apoptosis sensitivity. In contrast, p38 kinase activity was identified as an important controller of both the inflammatory reaction and apoptosis both in astrocytes stimulated with CCM and in glia exposed to TNF and IL-1 only.

Changes in peptidyl-prolyl cis/trans isomerase activity and FK506 binding protein expression following neuroprotection by FK506 in the ischemic rat brain

FK506 is an immunosuppressant also showing neuroprotection following cerebral ischemia. FK506 binds to intracellular proteins (FKBP) which have a wide range of functions but have in common the peptidyl-prolyl cis/trans isomerase activity. Following transient focal ischemia, we have analyzed the expression of FKBP12, 52 and 65 and the total FKBP enzyme activity. Furthermore, we have investigated the effect of FK506 on signal transduction in neurons and perfusion changes in the infarct area. After 90 min of transient middle cerebral artery occlusion in male rats the expression of FKBP12, 52 and 65 was analyzed by Western blot in FK506-treated and control animals and the peptidyl-prolyl cis/trans isomerase activity was determined. Magnetic resonance imaging was used to measure tissue perfusion, development of vasogenic edema and infarct size. To investigate the neuronal stress signal cascade, activating transcription factor 2 (ATF-2), Fas-ligand (Fas-L) and c-Jun expression and phosphorylation were analyzed by immunohistochemistry. FK506 decreased the cerebral infarct volume by 53% and reduced the cytotoxic edema. The total FKBP enzymatic activity in the infarct area was increased and blocked dose dependently by FK506. FKBP expression was selectively up-regulated by cerebral ischemia. FK506 treatment does not influence the expression patterns. c-Jun phosphorylation in neurons of the peri-infarct area and Fas-L expression was reduced by FK506 treatment whereas ATF-2 expression was preserved. Cerebral ischemic damage to the brain was reduced by FK506. It was shown for the first time that neuroprotection by FK506 also included the suppression of the cerebral peptidyl-prolyl cis/trans isomerase activity of FKBP in vivo whereas the expression levels of FKBP12, 52 and 65 following ischemia changed slightly and FK506 treatment does not suppress the expression patterns. However, changes of FKBP enzymatic activity result in suppression of the stress cell body response in the peri-infarct area as observed by suppression of c-Jun phosphorylation and Fas-L expression.

Tissue inhibitor of metalloproteinases-3 and matrix metalloproteinase-3 regulate neuronal sensitivity to doxorubicin-induced apoptosis

Metalloproteinase activity at the cell surface influences cellular sensitivity to extrinsic death vs. survival signals in a variety of cell types, through proteolytic shedding of cell surface signalling molecules. Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a unique natural metalloproteinase inhibitor that plays a pro-apoptotic role through its ability to inhibit metalloproteinases that proteolytically cleave death receptors and their ligands from the cell surface. To study the convergence of metalloproteinase activity and death receptor signalling in neurons, we established an in vitro model of neuronal apoptosis utilizing the chemotherapeutic drug, doxorubicin (Dox). Primary cultures established from embryonic rat cerebral cortices displayed robust and selective neuronal apoptosis in response to Dox, an effect that was dependent on the activation of the death receptor, Fas. We demonstrate that both TIMP-3 and matrix metalloproteinase-3 (MMP-3) are constitutively expressed by primary cortical neurons in culture, and selectively modulated Fas-mediated neuronal apoptosis induced by Dox. Metalloproteinase inhibition by TIMP-3 was found to be necessary for Dox-induced neuronal death, whereas addition of active MMP-3 markedly attenuated apoptosis and diminished Fas-Fas ligand interaction at the cell surface. These observations implicate a physiological role for the balance of TIMP-3 and MMP-3 activity at the neuronal surface in regulating death receptor sensitivity. The convergence of metalloproteinase activity and death receptor signalling at the cell surface may influence neuronal cell death vs. survival decisions.

Expression of a functional Fas death receptor by human foetal motoneurons

The expression of the apoptosis inducer Fas (CD95/APO-1) surface receptor by human foetal neurons was investigated in vitro and ex vivo. Immunofluorescence studies of brain and spinal cord cells in primary cultures and of cryosections obtained from 9- and 10-week-old human foetuses, respectively, showed that all Fas-expressing cells were motoneurons (5.3 and 4.2% of the neurons in brain or spinal cord cultures, respectively) on the basis of morphology, reactivity with the monoclonal antibody SMI-32, a mostly motoneuronal marker and acetylcholine esterase expression. Fas was undetectable on the other cell types in culture. The ability of Fas to induce apoptosis of cultured cells from both tissues was determined by using the terminal transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) method combined with the same double-staining procedure. Under basal culture conditions, about 9% of cells, all glial fibrillary acidic protein-expressing astrocytes, were apoptotic. After a 48-h incubation with Fas ligand, mean 28.5% of brain motoneurons and 29.4% of spinal motoneurons underwent apoptosis, with an inhibition by Z-IETD-FMK, a caspase-8 inhibitor. Hence, Fas appears to be functional through a caspase-8-dependent pathway in a subpopulation of human foetal motoneurons.