Human astrocytes are resistant to Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis

Caspase-8-mediated inflammation but not apoptosis drives death of retinal ganglion cells and loss of visual function in glaucomaa

Background-

Glaucoma is a complex multifactorial disease where apoptosis and inflammation represent two key pathogenic mechanisms. However, the relative contribution of apoptosis versus inflammation in axon degeneration and death of retinal ganglion cells (RGCs) is not well understood. In glaucoma, caspase-8 is linked to RGC apoptosis, as well as glial activation and neuroinflammation. To uncouple these two pathways and determine the extent to which caspase-8-mediated inflammation and/or apoptosis contributes to the death of RGCs, we used the caspase-8 D387A mutant mouse (Casp8 DA/DA ) in which a point mutation in the auto-cleavage site blocks caspase-8-mediated apoptosis but does not block caspase-8-mediated inflammation.

Methods-

Intracameral injection of magnetic microbeads was used to elevate the intraocular pressure (IOP) in wild-type, Fas deficient Faslpr, and Casp8 DA/DA mice. IOP was monitored by rebound tonometry. Two weeks post microbead injection, retinas were collected for microglia activation analysis. Five weeks post microbead injection, visual acuity and RGC function were assessed by optometer reflex (OMR) and pattern electroretinogram (pERG), respectively. Retina and optic nerves were processed for RGC and axon quantification. Two- and five-weeks post microbead injection, expression of the necrosis marker, RIPK3, was assessed by qPCR.

Results-

Wild-type, Faslpr, and Casp8 DA/DA mice showed similar IOP elevation as compared to saline controls. A significant reduction in both visual acuity and pERG that correlated with a significant loss of RGCs and axons was observed in wild-type but not in Faslpr mice. The Casp8 DA/DA mice displayed a significant reduction in visual acuity and pERG amplitude and loss of RGCs and axons similar to that in wild-type mice. Immunostaining revealed equal numbers of activated microglia, double positive for P2ry12 and IB4, in the retinas from microbead-injected wild-type and Casp8 DA/DA mutant mice. qPCR analysis revealed no induction of RIPK3 in wild-type or Casp8 DA/DA mice at two- or five-weeks post microbead injection.

Conclusions-

Our results demonstrate that caspase-8-mediated extrinsic apoptosis is not involved in the death of RGCs in the microbead-induced mouse model of glaucoma implicating caspase-8-mediated inflammation, but not apoptosis, as the driving force in glaucoma progression. Taken together, these results identify the caspase-8-mediated inflammatory pathway as a potential target for neuroprotection in glaucoma.

Therapeutic Targeting of Glioblastoma and the Interactions with Its Microenvironment

Glioblastoma (GBM) is the most common primary malignant brain tumour, and it confers a dismal prognosis despite intensive multimodal treatments. Whilst historically, research has focussed on the evolution of GBM tumour cells themselves, there is growing recognition of the importance of studying the tumour microenvironment (TME). Improved characterisation of the interaction between GBM cells and the TME has led to a better understanding of therapeutic resistance and the identification of potential targets to block these escape mechanisms. This review describes the network of cells within the TME and proposes treatment strategies for simultaneously targeting GBM cells, the surrounding immune cells, and the crosstalk between them.

Megf10-related engulfment of excitatory postsynapses by astrocytes following severe brain injury

AIMS

To investigate astrocyte-related phagocytosis of synapses in the ipsilateral hippocampus after traumatic brain injury (TBI).

METHODS

We performed controlled cortical impact to simulate TBI in mice. Seven days postinjury, we performed cognitive tests, synapse quantification, and examination of astrocytic phagocytosis in association with Megf10 expression.

RESULTS

During the subacute stage post-TBI, we found a reduction in excitatory postsynaptic materials in the ipsilateral hippocampus, which was consistent with poor performance in the cognitive test. The transcriptome data suggested that robust phagocytosis was responsible for this process. Coincidently, we identified phagocytic astrocytes containing secondary lysosomes that were wrapped around the synapses in the ipsilateral hippocampus. Moreover, a significant increase in the co-location of GFAP and PSD-95 in the CA1 region suggested astrocytic engulfment of excitatory postsynaptic proteins. After examining the reported phagocytic pathways, we found that both the transcription level and protein expression of Megf10 were elevated. Co-immunofluorescence of GFAP and Megf10 demonstrated that the expression of Megf10 was spatially upregulated in astrocytes, exclusively in the CA1 region, and was related to the astrocytic engulfment of PSD-95.

CONCLUSION

Our study elaborated that the Megf10-related astrocytic engulfment of PSD-95 in the CA1 region of the ipsilateral hippocampus aggravated cognitive dysfunction following severe TBI.

Bidirectional Communication Between Microglia and Astrocytes in Neuroinflammation

Neuroinflammation is a common feature of diverse nervous system pathologies. In many instances, it begins at an early stage of the disease, paving the way for further exacerbations. The main drivers of neuroinflammation are brain-resident glial cells, such as microglia and astrocytes. Microglia are the primary responders to any insult to the brain parenchyma, translating the signals into diverse molecules. These molecules derived from microglia can regulate the stimuli-dependent reactivity of astrocytes. Once activated, astrocytes in turn, can control microglia phenotypes. Recent evidence indicates that the crosstalk between these glial cells plays an important role in delaying or accelerating neuroinflammation and overall disease progression. To date, various molecules have been recognized as key mediators of the bidirectional communication between microglia and astrocytes. The current review aims to discuss the novel molecules identified recently, which play a critical role in interglial crosstalk, highlighting their therapeutic potential.

Injury programs shape glioblastoma

Glioblastoma is the most common and aggressive primary brain cancer in adults and is almost universally fatal due to its stark therapeutic resistance. During the past decade, although survival has not substantially improved, major advances have been made in our understanding of the underlying biology. It has become clear that these devastating tumors recapitulate features of neurodevelopmental hierarchies which are influenced by the microenvironment. Emerging evidence also highlights a prominent role for injury responses in steering cellular phenotypes and contributing to tumor heterogeneity. This review highlights how the interplay between injury and neurodevelopmental programs impacts on tumor growth, invasion, and treatment resistance, and discusses potential therapeutic considerations in view of these findings.

Molecular Mechanisms of Neuroimmune Crosstalk in the Pathogenesis of Stroke

Stroke disrupts the homeostatic balance within the brain and is associated with a significant accumulation of necrotic cellular debris, fluid, and peripheral immune cells in the central nervous system (CNS). Additionally, cells, antigens, and other factors exit the brain into the periphery via damaged blood–brain barrier cells, glymphatic transport mechanisms, and lymphatic vessels, which dramatically influence the systemic immune response and lead to complex neuroimmune communication. As a result, the immunological response after stroke is a highly dynamic event that involves communication between multiple organ systems and cell types, with significant consequences on not only the initial stroke tissue injury but long-term recovery in the CNS. In this review, we discuss the complex immunological and physiological interactions that occur after stroke with a focus on how the peripheral immune system and CNS communicate to regulate post-stroke brain homeostasis. First, we discuss the post-stroke immune cascade across different contexts as well as homeostatic regulation within the brain. Then, we focus on the lymphatic vessels surrounding the brain and their ability to coordinate both immune response and fluid homeostasis within the brain after stroke. Finally, we discuss how therapeutic manipulation of peripheral systems may provide new mechanisms to treat stroke injury.

AXL kinase-mediated astrocytic phagocytosis modulates outcomes of traumatic brain injury

Background

Complex changes in the brain microenvironment following traumatic brain injury (TBI) can cause neurological impairments for which there are few efficacious therapeutic interventions. The reactivity of astrocytes is one of the keys to microenvironmental changes, such as neuroinflammation, but its role and the molecular mechanisms that underpin it remain unclear.

Methods

Male C57BL/6J mice were subjected to the controlled cortical impact (CCI) to develop a TBI model. The specific ligand of AXL receptor tyrosine kinase (AXL), recombinant mouse growth arrest-specific 6 (rmGas6) was intracerebroventricularly administered, and selective AXL antagonist R428 was intraperitoneally applied at 30 min post-modeling separately. Post-TBI assessments included neurobehavioral assessments, transmission electron microscopy, immunohistochemistry, and western blotting. Real-time polymerase chain reaction (RT-PCR), siRNA transfection, and flow cytometry were performed for mechanism assessments in primary cultured astrocytes.

Results

AXL is upregulated mainly in astrocytes after TBI and promotes astrocytes switching to a phenotype that exhibits the capability of ingesting degenerated neurons or debris. As a result, this astrocytic transformation promotes the limitation of neuroinflammation and recovery of neurological dysfunction. Pharmacological inhibition of AXL in astrocytes significantly decreased astrocytic phagocytosis both in vivo and in primary astrocyte cultures, in contrast to the effect of treatment with the rmGas6. AXL activates the signal transducer and activator of the transcription 1 (STAT1) pathway thereby further upregulating ATP-binding cassette transporter 1 (ABCA1). Moreover, the supernatant from GAS6-depleted BV2 cells induced limited enhancement of astrocytic phagocytosis in vitro.

Conclusion

Our work establishes the role of AXL in the transformation of astrocytes to a phagocytic phenotype via the AXL/STAT1/ABCA1 pathway which contributes to the separation of healthy brain tissue from injury-induced cell debris, further ameliorating neuroinflammation and neurological impairments after TBI. Collectively, our findings provide a potential therapeutic target for TBI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02201-3.

TRAIL Mediates Neuronal Death in AUD: A Link between Neuroinflammation and Neurodegeneration

Although the cause of progressive neurodegeneration is often unclear, neuronal death can occur through several mechanisms. In conditions such as Alzheimer’s or alcohol use disorder (AUD), Toll-like receptor (TLR) induction is observed with neurodegeneration. However, links between TLR activation and neurodegeneration are lacking. We report a role of apoptotic neuronal death in AUD through TLR7-mediated induction of death receptor signaling. In postmortem human cortex, a two-fold increase in apoptotic terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining in neurons was found in AUD versus controls. This occurred with the increased expression of TLR7 and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) death receptors. Binge ethanol treatment in C57BL/6 mice increased TLR7 and induced neuronal apoptosis in cortical regions that was blocked by TLR7 antagonism. Mechanistic studies in primary organotypic brain slice culture (OBSC) found that the inhibition of TLR7 and its endogenous ligand let-7b blocked ethanol-induced neuronal cell death. Both IMQ and ethanol induced the expression of TRAIL and its death receptor. In addition, TRAIL-neutralizing monoclonal antibodies blocked both imiquimod (IMQ) and ethanol induced neuronal death. These findings implicate TRAIL as a mediator of neuronal apoptosis downstream of TLR7 activation. TLR7 and neuronal apoptosis are implicated in other neurodegenerative diseases, including Alzheimer’s disease. Therefore, TRAIL may represent a therapeutic target to slow neurodegeneration in multiple diseases.

Hippocampal TNF-death receptors, caspase cell death cascades, and IL-8 in alcohol use disorder

The relationship between increased neuroimmune gene expression and hippocampal degeneration in alcohol use disorder (AUD) and other mental diseases is poorly understood. We report here that tumor necrosis factor receptor superfamily death receptor 3 (TNFRSF25, DR3) and Fas receptors (Fas) that initiate caspase cell death cascades are increased in AUD hippocampus and following a rat adolescent binge drinking model. Death receptors are known inducers of apoptosis and cell death that recruit death domain (DD) proteins FADD and TRADD and caspases to form death-inducing signaling complexes (DISC). In postmortem human AUD hippocampus, mRNA and IHC protein are increased for the entire death receptor cascade. In AUD hippocampus, ligand-death receptor pairs, i.e., TL1A-DR3 and FasL-Fas, were increased, as well as FADD and TRADD, and active caspase-8, -7, -9, and caspase-3. Further, pNFκB p65, a key neuroimmune transcription factor, and IL-8, a chemokine, were significantly increased. Interestingly, across AUD patients, increases in DR3 and Fas correlated with TRADD, and TRADD with active caspase+IR and IL-8+IR, consistent with coordinated activation of neuronal DISC mediated death cascades and neuroimmune gene induction in AUD. These findings support a role for DR3 and Fas neuroimmune signaling in AUD hippocampal neurodegeneration.

Arsenic trioxide as a novel anti-glioma drug: a review

Arsenic trioxide has shown a strong anti-tumor effect with little toxicity when used in the treatment of acute promyelocytic leukemia (APL). An effect on glioma has also been shown. Its mechanisms include regulation of apoptosis and autophagy; promotion of the intracellular production of reactive oxygen species, causing oxidative damage; and inhibition of tumor stem cells. However, glioma cells and tissues from other sources show different responses to arsenic trioxide. Researchers are working to enhance its efficacy in anti-glioma treatments and reducing any adverse reactions. Here, we review recent research on the efficacy and mechanisms of action of arsenic trioxide in the treatment of gliomas to provide guidance for future studies.

Role of Inflammasomes in HIV-1 and Drug Abuse Mediated Neuroinflammaging

Despite the effectiveness of combined antiretroviral therapy (cART) in suppressing virus replication, chronic inflammation remains one of the cardinal features intersecting HIV-1, cART, drug abuse, and likely contributes to the accelerated neurocognitive decline and aging in people living with HIV-1 (PLWH) that abuse drugs. It is also estimated that ~30–60% of PLWH on cART develop cognitive deficits associated with HIV-1-associated neurocognitive disorders (HAND), with symptomatology ranging from asymptomatic to mild, neurocognitive impairments. Adding further complexity to HAND is the comorbidity of drug abuse in PLWH involving activated immune responses and the release of neurotoxins, which, in turn, mediate neuroinflammation. Premature or accelerated aging is another feature of drug abusing PLWH on cART regimes. Emerging studies implicate the role of HIV-1/HIV-1 proteins, cART, and abused drugs in altering the inflammasome signaling in the central nervous system (CNS) cells. It is thus likely that exposure of these cells to HIV-1/HIV-1 proteins, cART, and/or abused drugs could have synergistic/additive effects on the activation of inflammasomes, in turn, leading to exacerbated neuroinflammation, ultimately resulting in premature aging referred to as “inflammaging” In this review, we summarize the current knowledge of inflammasome activation, neuroinflammation, and aging in central nervous system (CNS) cells such as microglia, astrocytes, and neurons in the context of HIV-1 and drug abuse.

NADPH oxidase inhibitor VAS2870 prevents staurosporine-induced cell death in rat astrocytes

Background Astrocytes maintain central nerve system homeostasis and are relatively resistant to cell death. Dysfunction of cell death mechanisms may underlie glioblastoma genesis and resistance to cancer therapy; therefore more detailed understanding of astrocytic death modalities is needed in order to design effective therapy. The purpose of this study was to determine the effect of VAS2870, a pan-NADPH oxidase inhibitor, on staurosporine-induced cell death in astrocytes. Materials and methods Cultured rat astrocytes were treated with staurosporine as activator of cell death. Cell viability, production of reactive oxygen species (ROS), and mitochondrial potential were examined using flow cytometric analysis, while chemiluminescence analysis was performed to assess caspase 3/7 activity and cellular ATP. Results We show here for the first time, that VAS2870 is able to prevent staurosporine-induced cell death. Staurosporine exerts its toxic effect through increased generation of ROS, while VAS2870 reduces the level of ROS. Further, VAS2870 partially restores mitochondrial inner membrane potential and level of ATP in staurosporine treated cells. Conclusions Staurosporine induces cell death in cultured rat astrocytes through oxidative stress. Generation of ROS, mitochondrial membrane potential and energy level are sensitive to VAS2870, which suggests NADPH oxidases as an important effector of cell death. Consequently, NADPH oxidases activation pathway could be an important target to modulate astrocytic death.

Maritoclax Enhances TRAIL-Induced Apoptosis via CHOP-Mediated Upregulation of DR5 and miR-708-Mediated Downregulation of cFLIP

Maritoclax, an active constituent isolated from marine bacteria, has been known to induce Mcl-1 downregulation through proteasomal degradation. In this study, we investigated the sensitizing effect of maritoclax on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human renal carcinoma cells. We found that combined treatment with maritoclax and TRAIL markedly induced apoptosis in renal carcinoma (Caki, ACHN and A498), lung cancer (A549) and hepatocellular carcinoma (SK-Hep1) cells. The upregulation of death receptor 5 (DR5) and downregulation of cellular FLICE-inhibitory protein (cFLIP) were involved in maritoclax plus TRAIL-induced apoptosis. Maritoclax-induced DR5 upregulation was regulated by induction of C/EBP homologous protein (CHOP) expression. Interestingly, maritoclax induced cFLIP downregulation through the increased expression of miR-708. Ectopic expression of cFLIP prevented combined maritoclax and TRAIL-induced apoptosis. Taken together, maritoclax sensitized TRAIL-induced apoptosis through CHOP-mediated DR5 upregulation and miR-708-mediated cFLIP downregulation.

Opioids, gliosis and central immunomodulation

Neuropathic pain is a common health problem that affects millions of people worldwide. Despite being studied extensively, the cellular and molecular events underlying the central immunomodulation and the pathophysiology of neuropathic pain is still controversial. The idea that 'glial cells are merely housekeepers' is incorrect and with respect to initiation and maintenance of neuropathic pain, microglia and astrocytes have important roles to play. Glial cells differentially express opioid receptors and are thought to be functionally modulated by the activation of these receptors. In this review, we discuss evidence for glia-opioid modulation of pain by focusing on the pattern of astrocyte and microglial activation throughout the progress of nerve injury/neuropathic pain. Activation of astrocytes and microglia is a key step in central immunomodulation in terms of releasing pro-inflammatory markers and propagation of a 'central immune response'. Inhibition of astrocytes before and after induction of neuropathic pain has been found to prevent and reverse neuropathic pain, respectively. Moreover, microglial inhibitors have been found to prevent (but not to reverse) neuropathic pain. As they are expressed by glia, opioid receptors are expected to have a role to play in neuropathic pain.

Organelle-Derived Acetyl-CoA Promotes Prostate Cancer Cell Survival, Migration, and Metastasis via Activation of Calmodulin Kinase II

Although emerging evidence suggests a potential role of calcium/calmodulin-dependent kinase II (CaMKII) in prostate cancer, its role in prostate cancer tumorigenesis is largely unknown. Here, we examine whether the acetyl CoA-CaMKII pathway, first described in frog oocytes, promotes prostate cancer tumorigenesis. In human prostate cancer specimens, metastatic prostate cancer expressed higher levels of active CaMKII compared with localized prostate cancer. Correspondingly, basal CaMKII activity was significantly higher in the more tumorigenic PC3 and PC3-mm2 cells relative to the less tumorigenic LNCaP and C4-2B4 cells. Deletion of CaMKII by CRISPR/Cas9 in PC3-mm2 cells abrogated cell survival under low-serum conditions, anchorage-independent growth and cell migration; overexpression of constitutively active CaMKII in C4-2B4 cells promoted these phenotypes. In an animal model of prostate cancer metastasis, genetic ablation of CaMKII reduced PC3-mm2 cell metastasis from the prostate to the lymph nodes. Knockdown of the acetyl-CoA transporter carnitine acetyltransferase abolished CaMKII activation, providing evidence that acetyl-CoA generated from organelles is a major activator of CaMKII. Genetic deletion of the β-oxidation rate-limiting enzyme ACOX family proteins decreased CaMKII activation, whereas overexpression of ACOXI increased CaMKII activation. Overall, our studies identify active CaMKII as a novel connection between organelle β-oxidation and acetyl-CoA transport with cell survival, migration, and prostate cancer metastasis.Significance: This study identifies a cell metabolic pathway that promotes prostate cancer metastasis and suggests prostate cancer may be susceptible to β-oxidation inhibitors. Cancer Res; 78(10); 2490-502. ©2018 AACR.

Presenilin1/γ-secretase protects neurons from glucose deprivation-induced death by regulating miR-212 and PEA15

Reduced cerebral glucose utilization is found in aged individuals and often is an early sign of neurodegeneration. Here, we show that under glucose deprivation (GD) conditions, decreased expression of presenilin 1 (PS1) results in decreased neuronal survival, whereas increased PS1 increases neuronal survival. Inhibition of γ-secretase also decreases neuronal survival under GD conditions, which suggests the PS1/γ-secretase system protects neurons from GD-induced death. We also show that neuronal levels of the survival protein, phosphoprotein enriched in astrocytes at ∼15 kDa (PEA15), and its mRNA are regulated by PS1/γ-secretase. Furthermore, down-regulation of PEA15 decreases neuronal survival under reduced glucose conditions, whereas exogenous PEA15 increases neuronal survival even in the absence of PS1, which indicates that PEA15 promotes neuronal survival under GD conditions. The absence or reduction of PS1, as well as γ-secretase inhibitors, increases neuronal miR-212, which targets PEA15 mRNA. PS1/γ-secretase activates the transcription factor, cAMP response element-binding protein, regulating miR-212, which targets PEA15 mRNA. Taken together, our data show that under conditions of reduced glucose, the PS1/γ-secretase system decreases neuronal losses by suppressing miR-212 and increasing its target survival factor, PEA15. These observations have implications for mechanisms of neuronal death under conditions of reduced glucose and may provide targets for intervention in neurodegenerative disorders.-Huang, Q., Voloudakis, G., Ren, Y., Yoon, Y., Zhang, E., Kajiwara, Y., Shao, Z., Xuan, Z., Lebedev, D., Georgakopoulos, A., Robakis, N. K. Presenilin1/γ-secretase protects neurons from glucose deprivation-induced death by regulating miR-212 and PEA15.

Caspase-10: a molecular switch from cell-autonomous apoptosis to communal cell death in response to chemotherapeutic drug treatment

The mechanisms of how chemotherapeutic drugs lead to cell cycle checkpoint regulation and DNA damage repair are well understood, but how such signals are transmitted to the cellular apoptosis machinery is less clear. We identified a novel apoptosis-inducing complex, we termed FADDosome, which is driven by ATR-dependent caspase-10 upregulation. During FADDosome-induced apoptosis, cFLIP_L is ubiquitinated by TRAF2, leading to its degradation and subsequent FADD-dependent caspase-8 activation. Cancer cells lacking caspase-10, TRAF2 or ATR switch from this cell-autonomous suicide to a more effective, autocrine/paracrine mode of apoptosis initiated by a different complex, the FLIPosome. It leads to processing of cFLIP_L to cFLIP_p43, TNF-α production and consequently, contrary to the FADDosome, p53-independent apoptosis. Thus, targeting the molecular levers that switch between these mechanisms can increase efficacy of treatment and overcome resistance in cancer cells.

Targetting PED/PEA-15 for diabetes treatment

INTRODUCTION

PED/PEA-15 is an ubiquitously expressed protein, involved in the regulation of proliferation and apoptosis. It is commonly overexpressed in Type 2 Diabetes (T2D) and in different T2D-associated comorbidities, including cancer and certain neurodegenerative disorders. Areas covered: In mice, Ped/Pea-15 overexpression impairs glucose tolerance and, in combination with high fat diets, further promotes insulin resistance and T2D. It also controls β-cell mass, altering caspase-3 activation and the expression of pro- and antiapoptotic genes. These changes are mediated by PED/PEA-15-PLD1 binding. Overexpression of PLD1 D4 domain specifically blocks Ped/Pea-15-PLD1 interaction, reverting the effect of Ped/Pea-15 in vivo. D4α, a D4 N-terminal peptide, is able to displace Ped/Pea-15-PLD1 binding, but features greater stability in vivo compared to the entire D4 peptide. Here, we review early mechanistic studies on PED/PEA-15 relevance in apoptosis before focusing on its role in cancer and T2D. Finally, we describe potential therapeutic opportunities for T2D based on PED/PEA-15 targeting. Expert opinion: T2D is a major problem for public health and economy. Thus, the identification of new molecules with pharmacological activity for T2D represents an urgent need. Further studies with D4α will help to identify smaller pharmacologically active peptides and innovative molecules of potential pharmacological interest for T2D treatment.

Alpha-synuclein stimulation of astrocytes: Potential role for neuroinflammation and neuroprotection

Selective loss of neurons, abnormal protein deposition and neuroinflammation are the common pathological features of neurodegenerative diseases, and these features are closely related to one another. In Parkinson's disease, abnormal aggregation and deposition of α-synuclein is known as a critical event in pathogenesis of the disease, as well as in other related neurodegenerative disorders, such as dementia with Lewy bodies and multiple system atrophy. Increasing evidence suggests that α-synuclein aggregates can activate glial cells to induce neuroinflammation. However, how an inflammatory microenvironment is established and maintained by this protein remains unknown. Findings from our recent study suggest that neuronal α-synuclein can be directly transferred to astrocytes through sequential exocytosis and endocytosis and induce inflammatory responses from astrocytes. Here we discuss potential roles of astrocytes in a cascade of events leading to α-synuclein-induced neuroinflammation.

Didehydro-cortistatin A inhibits HIV-1 Tat mediated neuroinflammation and prevents potentiation of cocaine reward in Tat transgenic mice

HIV-1 Tat protein has been shown to have a crucial role in HIV-1-associated neurocognitive disorders (HAND), which includes a group of syndromes ranging from undetectable neurocognitive impairment to dementia. The abuse of psychostimulants, such as cocaine, by HIV infected individuals, may accelerate and intensify neurological damage. On the other hand, exposure to Tat potentiates cocaine-mediated reward mechanisms, which further promotes HAND. Here, we show that didehydro-Cortistatin A (dCA), an analog of a natural steroidal alkaloid, crosses the blood-brain barrier, cross-neutralizes Tat activity from several HIV-1 clades and decreases Tat uptake by glial cell lines. In addition, dCA potently inhibits Tat mediated dysregulation of IL-1β, TNF-α and MCP-1, key neuroinflammatory signaling proteins. Importantly, using a mouse model where doxycycline induces Tat expression, we demonstrate that dCA reverses the potentiation of cocaine-mediated reward. Our results suggest that adding a Tat inhibitor, such as dCA, to current antiretroviral therapy may reduce HIV-1-related neuropathogenesis.

Intrinsic apoptosis and proinflammatory cytokines regulated in human astrocytes infected with enterovirus 71

Enterovirus 71 (EV71) has emerged as a clinically important neurotropic virus following poliovirus eradication. However, the mechanism of EV71-induced neurological manifestation remains largely unclear. In this study, we showed that human astrocytes were susceptible to EV71 and viral RNA was first detected at 12 h post-infection (p.i.), whilst viral proteins were detected at 36 h p.i. EV71-infected astrocytes underwent apoptosis, in which cytochrome c was released from mitochondria to the cytosol and caspase-9 was activated. Interestingly, caspase-2 and -8 were not cleaved or activated during the infection, whilst a selective inhibitor of caspase-9, Z-LEHD-FMK, blocked the cleavage of caspase-3 and -7, indicating that only the mitochondria-mediated intrinsic apoptotic pathway was activated in EV71-infected astrocytes. EV71 infection also induced proinflammatory cytokines, including IL-6, IL-8, CCL5 and IFN-γ-inducible protein (IP)-10 in astrocytes, which may play a critical role in EV71-induced neuroinflammation and neurological complications. By using inhibitors of mitogen-activated protein kinases (MAPKs), we demonstrated that the induction of the cytokines was mainly regulated by the MAPK p38 signalling pathway as a significant reduction of the cytokines was observed when treated with p38 inhibitors. This study demonstrated that human astrocytes were susceptible to EV71, and the infection led to intrinsic apoptosis and induction of p38-regulated proinflammatory cytokines. These findings further our understanding of the neuropathogenesis in severe cases of EV71 infection.

Protective role of isoflurane pretreatment in rats with focal cerebral ischemia and the underlying molecular mechanism

Inflammation and immunity are important in the pathogenesis of cerebral ischemia. Toll-like receptor 4 (TLR4) is involved in the inflammatory responses of injured brain tissues. Emerging studies have focused on the effect of isoflurane (ISO) pretreatment on cerebral ischemia, however, the association between ISO pretreatment and TLR4 during cerebral ischemia remains to be elucidated. In the present study, the protective role of ISO pretreatment in rats with focal cerebral ischemia reperfusion was investigated and the molecular mechanism was discussed. Using a middle cerebral artery occlusion (MCAO) model, triphenyltetrazolium chloride staining was utilized to measure the infarct volume and brain edema and immunofluorescence staining was used to detect the MCAO-induced TLR4 expression and localization. Western blot analyses were conducted to quantify the protein expression levels of TLR4, myeloid differentiation primary response 88 (MyD88) and nuclear factor (NF)-κB in ischemic brain tissue at different time points. The results demonstrated that, following ISO pretreatment, the neurological deficits, brain edema and cerebral infarct size caused by ischemia/reperfusion were attenuated. The astrocyte and microglial activation in the brain tissue was decreased. In addition, the expression levels of TLR4, MyD88 and NF-κB were decreased. The present study indicated that ISO pretreatment may protect the brain from ischemic damage by downregulating the expression levels of TLR4, MyD88 and NF-κB.

Deletion of Pim kinases elevates the cellular levels of reactive oxygen species and sensitizes to K-Ras-induced cell killing

The Pim protein kinases contribute to transformation by enhancing the activity of oncogenic Myc and Ras, which drives significant metabolic changes during tumorigenesis. In this report, we demonstrate that mouse embryo fibroblasts (MEFs) lacking all three isoforms of Pim protein kinases, triple knockout (TKO), cannot tolerate the expression of activated K-Ras (K-Ras^G12V) and undergo cell death. Transduction of K-Ras^G12V into these cells markedly increased the level of cellular reactive oxygen species (ROS). The addition of N-acetyl cysteine attenuates ROS production and reversed the cytotoxic effects of K-Ras^G12V in the TKO MEFs. The altered cellular redox state caused by the loss of Pim occurred as a result of lower levels of metabolic intermediates in the glycolytic and pentose phosphate pathways as well as abnormal mitochondrial oxidative phosphorylation. TKO MEFs exhibit reduced levels of superoxide dismutase (Sod), glutathione peroxidase 4 (Gpx4) and peroxiredoxin 3 (Prdx3) that render them susceptible to killing by K-Ras^G12V-mediated ROS production. In contrast, the transduction of c-Myc into TKO cells can overcome the lack of Pim protein kinases by regulating cellular metabolism and Sod2. In the absence of the Pim kinases, c-Myc transduction permitted K-Ras^G12V-induced cell growth by decreasing Ras-induced cellular ROS levels. These results demonstrate that the Pim protein kinases play an important role in regulating cellular redox, metabolism and K-Ras-stimulated cell growth.

A role for TRAIL/TRAIL-R2 in radiation-induced apoptosis and radiation-induced bystander response of human neural stem cells

Adult neurons, which are terminally differentiated cells, demonstrate substantial radioresistance. In contrast, human neural stem cells (NSC), which have a significant proliferative capacity, are highly sensitive to ionizing radiation. Cranial irradiation that is widely used for treatment of brain tumors may induce death of NSC and further cause substantial cognitive deficits such as impairing learning and memory. The main goal of our study was to determine a mechanism of NSC radiosensitivity. We observed a constitutive high-level expression of TRAIL-R2 in human NSC. On the other hand, ionizing radiation through generation of reactive oxygen species targeted cell signaling pathways and dramatically changed the pattern of gene expression, including upregulation of TRAIL. A significant increase of endogenous expression and secretion of TRAIL could induce autocrine/paracrine stimulation of the TRAIL-R2-mediated signaling cascade with activation of caspase-3-driven apoptosis. Furthermore, paracrine stimulation could initiate bystander response of non-targeted NSC that is driven by death ligands produced by directly irradiated NSC. Experiments with media transfer from directly irradiated NSC to non-targeted (bystander) NSC confirmed a role of secreted TRAIL for induction of a death signaling cascade in non-targeted NSC. Subsequently, TRAIL production through elimination of bystander TRAIL-R-positive NSC might substantially restrict a final yield of differentiating young neurons. Radiation-induced TRAIL-mediated apoptosis could be partially suppressed by anti-TRAIL antibody added to the cell media. Interestingly, direct gamma-irradiation of SK-N-SH human neuroblastoma cells using clinical doses (2-5 Gy) resulted in low levels of apoptosis in cancer cells that was accompanied however by induction of a strong bystander response in non-targeted NSC. Numerous protective mechanisms were involved in the maintenance of radioresistance of neuroblastoma cells, including constitutive PI3K-AKT over-activation and endogenous synthesis of TGFβ1. Specific blockage of these survival pathways was accompanied by a dramatic increase in radiosensitivity of neuroblastoma cells. Intercellular communication between cancer cells and NSC could potentially be involved in amplification of cancer pathology in the brain.

Physiological functions of TNF family receptor/ligand interactions in hematopoiesis and transplantation

Secretion of ligands of the tumor necrosis factor (TNF) superfamily is a conserved response of parenchymal tissues to injury and inflammation that commonly perpetuates elimination of dysfunctional cellular components by apoptosis. The same signals of tissue injury that induce apoptosis in somatic cells activate stem cells and initiate the process of tissue regeneration as a coupling mechanism of injury and recovery. Hematopoietic stem and progenitor cells upregulate the TNF family receptors under stress conditions and are transduced with trophic signals. The progeny gradually acquires sensitivity to receptor-mediated apoptosis along the differentiation process, which becomes the major mechanism of negative regulation of mature proliferating hematopoietic lineages and immune homeostasis. Receptor/ligand interactions of the TNF family are physiological mechanisms transducing the need for repair, which may be harnessed in pathological conditions and transplantation. Because these interactions are physiological mechanisms of injury, neutralization of these pathways has to be carefully considered in disorders that do not involve intrinsic aberrations of excessive susceptibility to apoptosis.

Increase of zinc finger protein 179 in response to CCAAT/enhancer binding protein delta conferring an antiapoptotic effect in astrocytes of Alzheimer's disease

Reactive astrogliosis is a cellular manifestation of neuroinflammation and occurs in response to all forms and severities of the central nervous system (CNS)'s injury and disease. Both astroglial proliferation and antiapoptotic processes are aspects of astrogliosis. However, the underlying mechanism of this response remains poorly understood. In addition, little is known about why activated astrocytes are more resistant to stress and inflammation. CCAAT/enhancer binding protein delta (CEBPD) is a transcription factor found in activated astrocytes that surround β-amyloid plaques. In this study, we found that astrocytes activation was attenuated in the cortex and hippocampus of APPswe/PS1 E9 (AppTg)/Cebpd (-/-)mice. Furthermore, an increase in apoptotic astrocytes was observed in AppTg/Cebpd (-/-)mice, suggesting that CEBPD plays a functional role in enhancing the antiapoptotic ability of astrocytes. We found that Zinc Finger Protein 179 (ZNF179) was a CEBPD-regulated gene that played an antiapoptotic, but not proliferative, role in astrocytes. The transcriptions of the proapoptotic genes, insulin-like growth factor binding protein 3 (IGFBP3) and BCL2-interacting killer (BIK), were suppressed by ZNF179 via its interaction with the promyelocytic leukemia zinc finger (PLZF) protein in astrocytes. This study provides the first evidence that ZNF179, PLZF, IGFBP3, and BIK contributed to the novel CEBPD-induced antiapoptotic feature of astrocytes.

Identification of death receptors DR4 and DR5 in HTB-12 astrocytoma cell lines and determination of TRAIL sensitivity

Astrocytomas are tumors which arise from astrocytes, cells that form the blood-brain barrier. There are very few drugs that successfully treat brain tumors. In this study, the cytotoxic effects on the HTB-12 astrocytoma cell line by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) were studied. The presence of the TRAIL receptors, Death receptor 4 (DR4) and Death receptor 5 (DR5), were detected in HTB-12 cells by Enzyme-Linked Immunosorbent Assay (ELISA). Cytotoxicity assay by Trypan Blue Exclusion Method showed effective cell killing by TRAIL treatment. Thus, the presence of death receptors and TRAIL efficacy raises the therapeutic potential for this type of brain tumor.

Silencing of decoy receptor 3 (DcR3) expression by siRNA in pancreatic carcinoma cells induces Fas ligand-mediated apoptosis in vitro and in vivo

Decoy receptor 3 (DcR3) is abundantly expressed in human tumors and protects cells from a wide range of apoptotic stimuli. In this study, we demonstrate that DcR3 is overexpressed in pancreatic carcinoma cells, and that the pancreatic carcinoma cell lines, Panc-1 and SW1990, are resistant to Fas ligand (FasL)-mediated apoptosis. To further define the function of DcR3 in cell growth and apoptosis, we used small interfering RNA (siRNA) to knockdown the expression of the DcR3 gene in Panc-1 and SW1990 cells. Our results revealed that the silencing of DcR3 expression enhanced the inhibitory effects of FasL and reduced the capabiltiy of the cells for proliferation and colony formation in vitro. In addition, the downregulation of DcR3 modulated the cell apoptotic regulators, Fas-associated death domain (FADD), caspase‑3 and caspase‑8, thus triggering cell apoptosis. Furthermore, the knockdown of DcR3 inhibited the growth of Panc-1 tumor xenografts. Taken together, our findings indicate that DcR3 is important in cancer progression and may be a used as a potential therapeutic target for the gene therapy of pancreatic carcinoma.

Resistance to TRAIL in non-transformed cells is due to multiple redundant pathways

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine and a selective inducer of apoptosis in a range of tumour cells, but not in normal, untransformed cells. A large number of chemotherapeutics as well as biological agents are being tested for their potential to sensitise resistant tumour cells to TRAIL as a means to broaden the range of tumours treatable with TRAIL. However, because of the incomplete understanding of the mechanism(s) underlying TRAIL resistance in non-malignant cells, it is unpredictable whether the effect of these sensitisers will be restricted to tumour cells or they would also sensitise non-transformed cells causing unwanted toxicity. In this study, we carried out a systematic analysis of the mechanisms driving TRAIL resistance in non-transformed cells. We found that cellular FLICE-like inhibitory protein, anti-apoptotic B-cell lymphoma 2 proteins, and X-linked inhibitor of apoptosis protein were independently able to provide resistance to TRAIL. Deficiency of only one of these proteins was not sufficient to elicit TRAIL sensitivity, demonstrating that in non-transformed cells multiple pathways control TRAIL resistance and they act in a redundant manner. This is contrary to the resistance mechanisms found in tumour cell types, many of them tend to rely on a single mechanism of resistance. Supporting this notion we found that 76% of TRAIL-resistant cell lines (13 out of 17) expressed only one of the above-identified anti-apoptotic proteins at a high level (≥1.2-fold higher than the mean expression across all cell lines). Furthermore, inhibition or knockdown of the single overexpressed protein in these tumour cells was sufficient to trigger TRAIL sensitivity. Therefore, the redundancy in resistance pathways in non-transformed cells may offer a safe therapeutic window for TRAIL-based combination therapies where selective sensitisation of the tumour to TRAIL can be achieved by targeting the single non-redundant resistance pathway.

Proteome analysis of post-transplantation recovery mechanisms of an EAE model of multiple sclerosis treated with embryonic stem cell-derived neural precursors

Multiple sclerosis (MS) is a chronic inflammatory and progressive disorder of the central nervous system (CNS), which ultimately causes demyelination and subsequent axonal injury. Experimental autoimmune encephalomyelitis (EAE) is a well-characterized animal model to study the etiology and pathogenesis of MS. This model can also be used to investigate various therapeutic approaches for MS. Herein; we have treated a score 3 EAE mouse model with an embryonic stem cell-derived neural precursor. Clinical analysis showed recovery of the EAE model of MS following transplantation. We analyzed the proteome of spinal cords of healthy and EAE samples before and after transplantation. Proteome analysis revealed that expressions of 86 spinal cord protein spots changed in the EAE or transplanted mouse compared to controls. Mass spectrometry resulted in identification of 72 proteins. Of these, the amounts of 27 differentially expressed proteins in EAE samples returned to sham levels after transplantation, suggesting a possible correlation between changes at the proteome level and clinical signs of EAE in transplanted mice. The recovered proteins belonged to various functional groups that included disturbances in ionic and neurotransmitter release, apoptosis, iron hemostasis, and signal transduction. Our results provided a proteomic view of the molecular mechanisms of EAE recovery after stem cell transplantation.

BIOLOGICAL SIGNIFICANCE

In this study, we applied proteomics to analyze the changes in proteome pattern of EAE mouse model after embryonic stem cell-derived neural precursor transplantation. Our proteome results clearly showed that the expression levels of several differentially expressed proteins in EAE samples returned to sham levels after transplantation, which suggested a possible correlation between changes at the proteome level and decreased clinical signs of EAE in transplanted mice. These results will serve as a basis to address new questions and design new experiments to elucidate the biology of EAE and recovery after transplantation. A thorough understanding of stem cell-mediated therapeutic mechanisms might result in the development of more efficacious therapies for MS than are currently available.

Quantitative proteomics for identifying biomarkers for Rabies

INTRODUCTION

Rabies is a fatal acute viral disease of the central nervous system, which is a serious public health problem in Asian and African countries. Based on the clinical presentation, rabies can be classified into encephalitic (furious) or paralytic (numb) rabies. Early diagnosis of this disease is particularly important as rabies is invariably fatal if adequate post exposure prophylaxis is not administered immediately following the bite.

METHODS

In this study, we carried out a quantitative proteomic analysis of the human brain tissue from cases of encephalitic and paralytic rabies along with normal human brain tissues using an 8-plex isobaric tags for relative and absolute quantification (iTRAQ) strategy.

RESULTS AND CONCLUSION

We identified 402 proteins, of which a number of proteins were differentially expressed between encephalitic and paralytic rabies, including several novel proteins. The differentially expressed molecules included karyopherin alpha 4 (KPNA4), which was overexpressed only in paralytic rabies, calcium calmodulin dependent kinase 2 alpha (CAMK2A), which was upregulated in paralytic rabies group and glutamate ammonia ligase (GLUL), which was overexpressed in paralytic as well as encephalitic rabies. We validated two of the upregulated molecules, GLUL and CAMK2A, by dot blot assays and further validated CAMK2A by immunohistochemistry. These molecules need to be further investigated in body fluids such as cerebrospinal fluid in a larger cohort of rabies cases to determine their potential use as antemortem diagnostic biomarkers in rabies. This is the first study to systematically profile clinical subtypes of human rabies using an iTRAQ quantitative proteomics approach.

Staurosporine induces different cell death forms in cultured rat astrocytes

Background

Astroglial cells are frequently involved in malignant transformation. Besides apoptosis, necroptosis, a different form of regulated cell death, seems to be related with glioblastoma genesis, proliferation, angiogenesis and invasion. In the present work we elucidated mechanisms of necroptosis in cultured astrocytes, and compared them with apoptosis, caused by staurosporine.

Materials and methods

Cultured rat cortical astrocytes were used for a cell death studies. Cell death was induced by different concentrations of staurosporine, and modified by inhibitors of apoptosis (z-vad-fmk) and necroptosis (nec-1). Different forms of a cell death were detected using flow cytometry.

Results

We showed that staurosporine, depending on concentration, induces both, apoptosis as well as necroptosis. Treatment with 10⁻⁷ M staurosporine increased apoptosis of astrocytes after the regeneration in a staurosporine free medium. When caspases were inhibited, apoptosis was attenuated, while necroptosis was slightly increased. Treatment with 10⁻⁶ M staurosporine induced necroptosis that occurred after the regeneration of astrocytes in a staurosporine free medium, as well as without regeneration period. Necroptosis was significantly attenuated by nec-1 which inhibits RIP1 kinase. On the other hand, the inhibition of caspases had no effect on necroptosis. Furthermore, staurosporine activated RIP1 kinase increased the production of reactive oxygen species, while an antioxidant BHA significantly attenuated necroptosis.

Conclusion

Staurosporine can induce apoptosis and/or necroptosis in cultured astrocytes via different signalling pathways. Distinction between different forms of cell death is crucial in the studies of therapy-induced necroptosis.

Design and screening of a glial cell-specific, cell penetrating peptide for therapeutic applications in multiple sclerosis

Multiple Sclerosis (MS) is an autoimmune, neurodegenerative disease of the central nervous system (CNS) characterized by demyelination through glial cell loss. Current and proposed therapeutic strategies to arrest demyelination and/or promote further remyelination include: (i) modulation of the host immune system; and/or (ii) transplantation of myelinating/stem or progenitor cells to the circulation or sites of injury. However, significant drawbacks are inherent with both approaches. Cell penetrating peptides (CPP) are short amino acid sequences with an intrinsic ability to translocate across plasma membranes, and theoretically represent an attractive vector for delivery of therapeutic peptides or nanoparticles to glia to promote cell survival or remyelination. The CPPs described to date are commonly non-selective in the cell types they transduce, limiting their therapeutic application in vivo. Here, we describe a theoretical framework for design of a novel CPP sequence that selectively transduces human glial cells (excluding non-glial cell types), and conduct preliminary screens of purified, recombinant CPPs with immature and matured human oligodendrocytes and astrocytes, and two non-glial cell types. A candidate peptide, termed TD2.2, consistently transduced glial cells, was significantly more effective at transducing immature oligodendrocytes than matured progeny, and was virtually incapable of transducing two non-glial cell types: (i) human neural cells and (ii) human dermal fibroblasts. Time-lapse confocal microscopy confirms trafficking of TD2.2 (fused to EGFP) to mature oligodendrocytes 3-6 hours after protein application in vitro. We propose selectivity of TD2.2 for glial cells represents a new therapeutic strategy for the treatment of glial-related disease, such as MS.

Neuroimmune crosstalk in the central nervous system and its significance for neurological diseases

The central nervous system (CNS) is now known to actively communicate with the immune system to control immune responses both centrally and peripherally. Within the CNS, while studies on glial cells, especially microglia, have highlighted the importance of this cell type in innate immune responses of the CNS, the immune regulatory functions of other cell types, especially neurons, are largely unknown. How neuroimmune cross-talk is homeostatically maintained in neurodevelopment and adult plasticity is even more elusive. Inspiringly, accumulating evidence suggests that neurons may also actively participate in immune responses by controlling glial cells and infiltrated T cells. The potential clinical application of this knowledge warrants a deeper understanding of the mutual interactions between neurons and other types of cells during neurological and immunological processes within the CNS, which will help advance diagnosis, prevention, and intervention of various neurological diseases. The aim of this review is to address the immune function of both glial cells and neurons, and the roles they play in regulating inflammatory processes and maintaining homeostasis of the CNS.

An astrocyte-specific proteomic approach to inflammatory responses in experimental rat glaucoma

PURPOSE

To delineate astrocyte-mediated inflammatory processes in glaucoma, we analyzed proteomic responses of retinal astrocytes in an experimental rat model using a cell-specific approach.

METHODS

IOP elevation was induced in rats by hypertonic saline injections into episcleral veins. Enriched samples of astrocytes were isolated through the immunomagnetic cell selection process established originally for retinal ganglion cell (RGC) sampling. Ocular hypertensive and control samples were collected by pooling from rat eyes matched for the cumulative IOP exposure. Protein expression was analyzed complementarily by quantitative two-dimensional capillary liquid chromatography and linear ion trap mass spectrometry (LC-MS/MS) followed by quantitative Western blot analysis and retinal tissue immunolabeling using specific antibodies to selected proteins.

RESULTS

Following validation of enriched astrocyte samples, LC-MS/MS analysis resulted in the identification of over 2000 proteins with high confidence. Bioinformatic comparison analysis of the high-throughput MS/MS data along with the findings of immunoblotting and immunohistochemistry supported distinct responses of ocular hypertensive astrocytes during the experimental paradigm, which exhibited predominantly cellular activation and immune/inflammatory responses as opposed to activation of cell death signaling in ocular hypertensive RGCs. Inflammatory responses of astrocytes in experimental glaucoma included up-regulation of a number of immune mediators/regulators linked to TNF-α/TNFR signaling, nuclear factor kappa-B (NF-κB) activation, autophagy regulation, and inflammasome assembly.

CONCLUSIONS

These findings validate an astrocyte-specific approach to quantitatively identify proteomic alterations in experimental glaucoma, and highlight many immune mediators/regulators characteristic of the inflammatory responses of ocular hypertensive astrocytes. By dissecting the complexity of prior data obtained from whole tissue, this pioneering approach should enable astrocyte responses to be defined and new treatments targeting astrocytes to be developed.

Engulfing astrocytes protect neurons from contact-induced apoptosis following injury

Clearing of dead cells is a fundamental process to limit tissue damage following brain injury. Engulfment has classically been believed to be performed by professional phagocytes, but recent data show that non-professional phagocytes are highly involved in the removal of cell corpses in various situations. The role of astrocytes in cell clearance following trauma has however not been studied in detail. We have found that astrocytes actively collect and engulf whole dead cells in an in vitro model of brain injury and thereby protect healthy neurons from bystander cell death. Time-lapse experiments showed that migrating neurons that come in contact with free-floating cell corpses induced apoptosis, while neurons that migrate through groups of dead cells, garnered by astrocytes, remain unaffected. Furthermore, apoptotic cells are present within astrocytes in the mouse brain following traumatic brain injury (TBI), indicating a possible role for astrocytes in engulfment of apoptotic cells in vivo. qRT-PCR analysis showed that members of both ced pathways and Megf8 are expressed in the cell culture, indicating their possible involvement in astrocytic engulfment. Moreover, addition of dead cells had a positive effect on the protein expression of MEGF10, an ortholog to CED1, known to initiate phagocytosis by binding to phosphatidylserine. Although cultured astrocytes have an immense capacity for engulfment, seemingly without adverse effects, the ingested material is stored rather than degraded. This finding might explain the multinuclear astrocytes that are found at the lesion site in patients with various brain disorders.

CaMKII-γ mediates phosphorylation of BAD at Ser170 to regulate cytokine-dependent survival and proliferation

Phosphorylation of the BH3 (Bcl-2 homology domain 3)-only protein BAD (Bcl-2/Bcl-X(L)-antagonist, causing cell death) can either directly disrupt its association with the pro-survival proteins Bcl-X(L) and/or Bcl-2, or cause association of BAD with 14-3-3 proteins. In the present study, we further characterize phosphorylation of BAD at Ser170, a unique site with unclear function. We provide further evidence that mutation of Ser170 to a phospho-mimetic aspartic acid residue (S170D) can have a profound inhibitory effect on the pro-apoptosis function of BAD. Furthermore, mutated BAD with an alanine substitution inhibited cell proliferation, slowing progression specifically through S-phase. We identify the kinase responsible for phosphorylation at this site as CaMKII-γ (γ isoform of Ca2+/calmodulin-dependent kinase II), but not the other three isoforms of CaMKII, revealing an extraordinary specificity among these closely related kinases. Furthermore, cytokine treatment increased BAD-Ser170-directed CaMKII-γ activity and phosphorylation of CaMKII-γ at an activating site, and CaMKII activity directed to the BAD-Ser170 site was elevated during S-phase. Treating cells with a selective inhibitor of CaMKII caused apoptosis in cells expressing BAD, but not in cells expressing the BAD-S170D mutant. The present study provides support for BAD-Ser170 phosphorylation playing a key role not only in regulating BAD's pro-apoptotic activity, but also in cell proliferation.

Staurosporine induces apoptosis and necroptosis in cultured rat astrocytes

Apoptosis and necroptosis are highly regulated, interconnected forms of a cell death. The distinction between them is critical, because necroptosis may cause significant cell loss and local inflammation, whereas apoptosis is essential for tissue homeostasis. The same stimulus can induce both apoptosis and necroptosis. Both forms of a cell death were detected in various pathologies, including pathologies in the central nervous system. Astrocytes are a large, heterogeneous cell population in the central nervous system, with many supportive, developmental functions. Although their demise may seriously impair normal functions of the central nervous system, it is still poorly understood. In this study, apoptosis and necroptosis were induced in cultured rat astrocytes by staurosporine. When a low concentration (10(-7) M) of staurosporine was applied, a significantly increased proportion of early apoptotic cells was detected after regeneration in a staurosporine free medium. The proportion of necroptotic cells was already increased without regeneration after 3 hours of exposure to staurosporine. When a higher (10(-6) M) concentration of staurosporine was applied, further significantly increased necroptosis was detected after regeneration in a staurosporine free medium. Necroptosis was significantly reduced when RIP1 kinase was inhibited by necrostatin-1, whereas inhibition of caspases with z-vad-fmk, an irreversible pan-caspase inhibitor, did not prevent necroptosis. This report of necroptosis induced by staurosporine represents a simple approach for the in vitro induction and detection of apoptosis and necroptosis.

Ferulic acid prevents the cerebral ischemic injury-induced decreases of astrocytic phosphoprotein PEA-15 and its two phosphorylated forms

Ferulic acid protects neuronal cells against focal cerebral ischemic injury through its anti-oxidative and anti-inflammatory effects. Phosphoprotein enriched in astrocytes 15 (PEA-15) is known to modulate various cellular processes including cell proliferation, apoptosis, and survival. This study was investigated whether ferulic acid can regulate the levels of PEA-15 and its two phosphorylated forms (Ser 104 and Ser 116) in a cerebral ischemic injury model and in neuronal cells exposed to glutamate. A middle cerebral artery occlusion (MCAO) was performed to induce focal cerebral ischemic injury. Adult male rats were immediately treated with vehicle or ferulic acid (100 mg/kg) at the beginning of the MCAO, and then cerebral cortices were collected 24h after MCAO. The decrease in PEA-15 level after ischemic injury was detected using a proteomic approach. Ferulic acid administration prevented the ischemic injury-induced decrease of PEA-15 level. Moreover, Western blot analysis clearly confirmed that ferulic acid attenuates the ischemic injury-induced decreases in PEA-15, phospho-PEA-15 (Ser 104), and phospho-PEA-15 (Ser 116) levels. Glutamate exposure induced significant reductions in the levels of PEA-15 and the two phospho-PEA-15 (Ser 104 and Ser 116) in cultured hippocampal neuron, while pretreatment with ferulic acid prevented the glutamate toxicity-induced decreases in these proteins levels. The decrease of phospho-PEA-15 protein level indicates that the anti-apoptotic function of PEA-15 was being inhibited. Thus, these results suggest that ferulic acid protects neuronal cells against ischemic injury by maintenance of phospho-PEA-15 protein levels.

A20 ubiquitin ligase-mediated polyubiquitination of RIP1 inhibits caspase-8 cleavage and TRAIL-induced apoptosis in glioblastoma

The TNF-related apoptosis-inducing ligand (TRAIL) apoptotic pathway has emerged as a therapeutic target for the treatment of cancer. However, clinical trials have proven that the vast majority of human cancers are resistant to TRAIL apoptotic pathway-targeted therapies. We show that A20-mediated ubiquitination inhibits caspase-8 cleavage and TRAIL-induced apoptosis in glioblastoma through 2 signaling complexes. A20 is highly expressed in glioblastomas and, together with the death receptor 5 and receptor-interacting protein 1, forms a plasma membrane-bound preligand assembly complex under physiologic conditions. Treatment with TRAIL leads to the recruitment of caspase-8 to the plasma membrane-bound preligand assembly complex for the assembly of a death-inducing signaling complex. In the death-inducing signaling complex, the C-terminal zinc finger (Znf) domain of the A20 ubiquitin ligase mediates receptor-interacting protein 1 polyubiquitination through lysine-63-linked polyubiquitin chains, which bind to the caspase-8 protease domain and inhibit caspase-8 dimerization, cleavage, and the initiation of TRAIL-induced apoptosis in glioblastoma-derived cell lines and tumor-initiating cells.

SIGNIFICANCE

These results identify A20 E3 ligase as a therapeutic target whose inhibition can overcome TNF-related apoptosis-inducing ligand resistance in glioblastoma and thus have an impact on ongoing clinical trials of TNF-related apoptosis-inducing ligand-targeted combination cancer therapies.

Targeted mutation of Fas ligand gene attenuates brain inflammation in experimental stroke

Inflammation is an important contributing mechanism in ischemic brain injury. The current study elucidates a previously unexplored role of Fas ligand (FasL) in post-stroke inflammatory responses that is independent of its well-known effect in triggering apoptosis. Focal cerebral ischemia was induced for 2 h by right middle cerebral artery occlusion (MCAO) in FasL mutant (gld) and wild-type mice. FasL mutation profoundly reduced brain damage and improved neurological performance from 6 to 72 h after ischemic stroke. The production of inflammatory cytokines in the brain was attenuated in gld mice after ischemia in the absence of dramatic change in inflammatory cell apoptosis. FasL mutation attenuated the recruitment of peripheral inflammatory cells (neutrophil) and inhibited the activation of residential glial cells (microglia and astrocyte). FasL mutation reduced CD8(+) T cells and turned the Th1/Th2 balance towards Th2 in the brain and peripheral blood after cerebral ischemia. In contrast to cerebral ischemia, the molecular and cellular inflammatory changes induced by intracerebroventricular injection of lipopolysaccharide (LPS) were also attenuated in gld mice. Moreover, the soluble FasL (sFasL) and phospho-SAPK/JNK were decreased in gld mice, suggesting that the inflammatory role of FasL in experimental stroke might relate to sFasL and the c-Jun N-terminal kinase (JNK) signaling pathway. Taken together, our data suggest a novel role of FasL in the damaging inflammatory responses associated with cerebral ischemia. Neutralization of FasL may be a novel therapeutic strategy to suppress post-stroke inflammation and improve the long-term outcomes of stroke.

Does calcium contribute to the CD95 signaling pathway?

Death receptors play a crucial role in immune surveillance and cellular homeostasis, two processes circumvented by tumor cells. CD95 (also termed Fas or APO1) is a transmembrane receptor, which belongs to the tumor necrosis factor receptor superfamily, and induces a potent apoptotic signal. Initial steps of the CD95 signal take place through protein/protein interactions that bring zymogens such as caspase-8 and caspase-10 closer. Aggregation of these procaspases leads to their autoprocessing, to the release of activated caspases in the cytosol, which causes a caspase cascade, and to the transmission of the apoptotic signal. In parallel, CD95 engagement drives an increase in the intracellular calcium concentration (Ca(2+))i whose origin and functions remain controversial. Although Ca(2+) ions play a central role in apoptosis/necrosis induction, recent studies have highlighted a protective role of Ca(2+) in death receptor signaling. In the light of these findings, we discuss the role of Ca(2+) ions as modulators of CD95 signaling.