Caspase signalling controls microglia activation and neurotoxicity

Chronic stress enhances microglia activation and exacerbates death of nigral dopaminergic neurons under conditions of inflammation

Background

Parkinson’s disease is an irreversible neurodegenerative disease linked to progressive movement disorders and is accompanied by an inflammatory reaction that is believed to contribute to its pathogenesis. Since sensitivity to inflammation is not the same in all brain structures, the aim of this work was to test whether physiological conditions as stress could enhance susceptibility to inflammation in the substantia nigra, where death of dopaminergic neurons takes place in Parkinson’s disease.

Methods

To achieve our aim, we induced an inflammatory process in nonstressed and stressed rats (subject to a chronic variate stress) by a single intranigral injection of lipopolysaccharide, a potent proinflammogen. The effect of this treatment was evaluated on inflammatory markers as well as on neuronal and glial populations.

Results

Data showed a synergistic effect between inflammation and stress, thus resulting in higher microglial activation and expression of proinflammatory markers. More important, the higher inflammatory response seen in stressed animals was associated with a higher rate of death of dopaminergic neurons in the substantia nigra, the most characteristic feature seen in Parkinson’s disease. This effect was dependent on glucocorticoids.

Conclusions

Our data demonstrate that stress sensitises midbrain microglia to further inflammatory stimulus. This suggests that stress may be an important risk factor in the degenerative processes and symptoms of Parkinson’s disease.

Delayed, long-term administration of the caspase inhibitor Q-VD-OPh reduced brain injury induced by neonatal hypoxia-ischemia

Apoptosis contributes greatly to the morphological and biochemical features of cell death after neonatal cerebral hypoxia-ischemia (HI), making this mode of cell death a promising therapeutic target. We previously showed that 10 mg/kg of the caspase inhibitor Q-VD-OPh at the onset of and immediately after HI on postnatal day 9 reduced brain infarct volume. In this study, delayed administration of Q-VD-OPh, 12 and 36 h after HI, decreased HI-induced caspase-3 activity (DEVD cleavage) by 23% and diminished the levels of the proinflammatory chemokines CCL2 (MCP-1) and CCL3 (MIP-1α) by 29.3 and 29.1%, respectively, but not the levels of the anti-inflammatory cytokines IL-4 and IL-10. Long-term administration of Q-VD-OPh initiated at 12 h after HI, and continued at 24-hour intervals for 2 weeks, reduced total brain tissue loss by 31.3% from 41.5±3.1 mm3 in the vehicle group to 28.5±3.0 mm3 in the Q-VD-OPh group when evaluated 16 weeks after HI (p=0.004). Q-VD-OPh treatment also ameliorated the loss of sensorimotor function, as evaluated by a cylinder rearing test (Q-VD-OPh: 30.8±4.3% vs. vehicle: 59.7±6.3% in nonimpaired forepaw preference) 3 weeks after HI, and reduced HI-induced hyperactivity, as measured in an open field test (Q-VD-OPh: 4,062±198 cm vs. vehicle: 4,792±205 cm in distance moved) 7 weeks after the insult. However, the functional protection was no longer observed when analyzed again at later time points. The mechanisms underlying the discrepancy between sustained morphological protection and transient functional protection remain to be elucidated.

Tamoxifen use for the management of mania: a review of current preclinical evidence

RATIONALE

Preliminary data on the efficacy of tamoxifen in reducing manic symptoms of bipolar disorder (BD) suggest that this agent may be a potential treatment for the management of this psychiatric disorder. However, the antimanic properties of tamoxifen have not been fully elucidated, hampering the development and/or use of mood-stabilising drugs that may share its same therapeutic mechanisms of action. Notably, we may gain a greater understanding of the neurobiological and therapeutic properties of tamoxifen by using suitable animal models of mania.

OBJECTIVES

Here, we review the preclinical studies that have evaluated the effects of tamoxifen to provide an overview of the current progress in our understanding of its antimanic actions, highlighting the critical role of protein kinase C (PKC) as a therapeutic target for the treatment of BD.

CONCLUSIONS

To date, this field has struggled to make significant progress, and the organisation of an explicit battery of tests is a valuable tool for assessing a number of prominent facets of BD, which may provide a greater understanding of the entire scope of this disease.

Different effects of anesthetic isoflurane on caspase-3 activation and cytosol cytochrome c levels between mice neural progenitor cells and neurons

Commonly used anesthetic isoflurane has been reported to promote Alzheimer’s disease (AD) neuropathogenesis by inducing caspase-3 activation. However, the up-stream mechanisms of isoflurane’s effects remain largely to be determined. Specifically, there is a lack of a good model/system to elucidate the underlying mechanism of the isoflurane-induced caspase-3 activation. We therefore set out to assess and compare the effects of isoflurane on caspase-3 activation in neural progenitor cells (NPCs) and in primary neurons from wild-type (WT) and AD transgenic (Tg) mice. The NPCs and neurons were obtained, cultured and then treated with either 2% isoflurane or under control condition for 6 h. The NPCs or neurons were harvested at the end of the treatment and were subjected to Western blot analysis. Here we showed for the first time that the isoflurane treatment induced caspase-3 activation in neurons, but not in NPCs, from either WT or AD Tg mice. Consistently, the isoflurane treatment increased cytosol levels of cytochrome c, a potential up-stream mechanism of isoflurane-induced caspase-3 activation in the mice neurons, but not NPCs. Finally, the isoflurane treatment induced a greater casapse-3 activation in the neurons, but not the NPCs, from AD Tg mice as compared to the WT mice. These data demonstrated that investigation and comparison of isoflurane’s effects between mice NPCs and neurons would serve as a model/system to determine the underlying mechanism by which isoflurane induces caspase-3 activation. These findings would promote more research to investigate the effects of anesthetics on AD neuropathogenesis and the underlying mechanisms.

Inflammation and programmed cell death in Alzheimer's disease: comparison of the central nervous system and peripheral blood

Although the central nervous system (CNS) has been defined as a privileged site in Alzheimer's disease (AD), periphery can be more than simply witness of events leading to neurodegeneration. The CNS and peripheral blood can mutually communicate through cells and factors trafficking from the circulation into the brain and vice versa. A number of articles have reviewed inflammatory profiles and programmed cell death (PCD) in AD, separately in the CNS and at the peripheral level. This review does not provide an exhaustive account of what has been published on inflammation and PCD in AD. Rather, the aim of this review is to focus on possible linkages between the central and the peripheral compartments during AD progression, by critically analyzing, in a comparative manner, phenomena occurring in the CNS as well as the peripheral blood. In fact, growing evidence suggests that CNS and peripheral inflammation might present common features in the disease. Microarrays and metabolomics revealed that dysfunction of the glycolytic and oxidative pathways is similar in the brain and in the periphery. Moreover, dysregulated autophagosome/lysosomal molecular machinery, both at the CNS and the peripheral level, in AD-related cell damage, has been observed. Possible implications of these observations have been discussed.

Ginsenoside Re rescues methamphetamine-induced oxidative damage, mitochondrial dysfunction, microglial activation, and dopaminergic degeneration by inhibiting the protein kinase Cδ gene

Ginsenoside Re, one of the main constituents of Panax ginseng, possesses novel antioxidant and anti-inflammatory properties. However, the pharmacological mechanism of ginsenoside Re in dopaminergic degeneration remains elusive. We suggested that protein kinase C (PKC) δ mediates methamphetamine (MA)-induced dopaminergic toxicity. Treatment with ginsenoside Re significantly attenuated methamphetamine-induced dopaminergic degeneration in vivo by inhibiting impaired enzymatic antioxidant systems, mitochondrial oxidative stress, mitochondrial translocation of protein kinase Cδ, mitochondrial dysfunction, pro-inflammatory microglial activation, and apoptosis. These protective effects were comparable to those observed with genetic inhibition of PKCδ in PKCδ knockout (-/-) mice and with PKCδ antisense oligonucleotides, and ginsenoside Re did not provide any additional protective effects in the presence of PKCδ inhibition. Our results suggest that PKCδ is a critical target for ginsenoside Re-mediated protective activity in response to dopaminergic degeneration induced by MA.

Inflammasomes in the CNS

Microglia and macrophages in the CNS contain multimolecular complexes termed inflammasomes. Inflammasomes function as intracellular sensors for infectious agents as well as for host-derived danger signals that are associated with neurological diseases, including meningitis, stroke and Alzheimer's disease. Assembly of an inflammasome activates caspase 1 and, subsequently, the proteolysis and release of the cytokines interleukin-1β and interleukin-18, as well as pyroptotic cell death. Since the discovery of inflammasomes in 2002, there has been burgeoning recognition of their complexities and functions. Here, we review the current understanding of the functions of different inflammasomes in the CNS and their roles in neurological diseases.

Bone marrow-derived mesenchymal stem cells maintain the resting phenotype of microglia and inhibit microglial activation

Many studies have shown that microglia in the activated state may be neurotoxic. It has been proven that uncontrolled or over-activated microglia play an important role in many neurodegenerative disorders. Bone marrow-derived mesenchymal stem cells (BMSCs) have been shown in many animal models to have a therapeutic effect on neural damage. Such a therapeutic effect is attributed to the fact that BMSCs have the ability to differentiate into neurons and to produce trophic factors, but there is little information available in the literature concerning whether BMSCs play a therapeutic role by affecting microglial activity. In this study, we triggered an inflammatory response situation in vitro by stimulating microglia with the bacterial endotoxin lipopolysaccharide (LPS), and then culturing these microglia with BMSC-conditioned medium (BMSC-CM). We found that BMSC-CM significantly inhibited proliferation and secretion of pro-inflammatory factors by activated microglia. Furthermore, we found that the phagocytic capacity of microglia was also inhibited by BMSC-CM. Finally, we investigated whether the induction of apoptosis and the production of nitric oxide (NO) were involved in the inhibition of microglial activation. We found that BMSC-CM significantly induced apoptosis of microglia, while no apoptosis was apparent in the LPS-stimulated microglia. Our study also provides evidence that NO participates in the inhibitory effect of BMSCs. Our experimental results provide evidence that BMSCs have the ability to maintain the resting phenotype of microglia or to control microglial activation through their production of several factors, indicating that BMSCs could be a promising therapeutic tool for treatment of diseases associated with microglial activation.

Dissociation of innate immune responses in microglia infected with Listeria monocytogenes

Microglia, the innate immune cells of the brain, plays a central role in cerebral listeriosis. Here, we present evidence that microglia control Listeria infection differently than macrophages. Infection of primary microglial cultures and murine cell lines with Listeria resulted in a dual function of the two gene expression programmes involved in early and late immune responses in macrophages. Whereas the bacterial gene hly seems responsible for both transcriptional programmes in macrophages, Listeria induces in microglia only the tumor necrosis factor (TNF)-regulated transcriptional programme. Listeria also represses in microglia the late immune response gathered in two clusters, microbial degradation, and interferon (IFN)-inducible genes. The bacterial gene actA was required in microglia to induce TNF-regulated responses and to repress the late response. Isolation of microglial phagosomes revealed a phagosomal environment unable to destroy Listeria. Microglial phagosomes were also defective in several signaling and trafficking components reported as relevant for Listeria innate immune responses. This transcriptional strategy in microglia induced high levels of TNF-α and monocyte chemotactic protein-1 and low production of other neurotoxic compounds such as nitric oxide, hydrogen peroxide, and Type I IFNs. These cytokines and toxic microglial products are also released by primary microglia, and this cytokine and chemokine cocktail display a low potential to trigger neuronal apoptosis. This overall bacterial strategy strongly suggests that microglia limit Listeria inflammation pattern exclusively through TNF-mediated responses to preserve brain integrity.

Preconditioning of microglia by α-synuclein strongly affects the response induced by toll-like receptor (TLR) stimulation

In recent years, it has become accepted that α-synuclein (αSyn) has a key role in the microglia-mediated neuroinflammation, which accompanies the development of Parkinson’s disease and other related disorders, such as Dementia with Lewy Bodies and Alzheimer’s disease. Nevertheless, the cellular and molecular mechanisms underlying its pathological actions, especially in the sporadic forms of the diseases, are not completely understood. Intriguingly, several epidemiological and animal model studies have revealed a link between certain microbial infections and the onset or progression of sporadic forms of these neurodegenerative disorders. In this work, we have characterized the effect of toll-like receptor (TLR) stimulation on primary murine microglial cultures and analysed the impact of priming cells with extracellular wild-type (Wt) αSyn on the subsequent TLR stimulation of cells with a set of TLR ligands. By assaying key interleukins and chemokines we report that specific stimuli, in particular Pam3Csk4 (Pam3) and single-stranded RNA40 (ssRNA), can differentially affect the TLR2/1- and TLR7-mediated responses of microglia when pre-conditioned with αSyn by augmenting IL-6, MCP-1/CCL2 or IP-10/CXCL10 secretion levels. Furthermore, we report a skewing of αSyn-primed microglia stimulated with ssRNA (TLR7) or Pam3 (TLR2/1) towards intermediate but at the same time differential, M1/M2 phenotypes. Finally, we show that the levels and intracellular location of activated caspase-3 protein change significantly in αSyn-primed microglia after stimulation with these particular TLR agonists. Overall, we report a remarkable impact of non-aggregated αSyn pre-sensitization of microglia on TLR-mediated immunity, a phenomenon that could contribute to triggering the onset of sporadic α-synuclein-related neuropathologies.

Minocycline modulates neuroprotective effect of hesperidin against quinolinic acid induced Huntington's disease like symptoms in rats: behavioral, biochemical, cellular and histological evidences

Emerging evidences indicate hesperidin, a citrus flavanone, attenuates neurodegenerative processes and related complications. Besides its anti-oxidant properties, the other probable mechanisms which underpin its neuroprotective potential are still not clear. In light of emerging role of flavonoids in modulating oxidative stress and neuro-inflammation, the study has been designed to explore the possible neuroprotective effect of hesperidin and its combination with minocycline (microglial inhibitor), against quinolinic acid (QA) induced Huntington's disease (HD) like symptoms in rats. Unilateral intrastriatal administration of QA (300 nmol/4 µl) significantly reduced body weight, impaired behavior (locomotor activity, beam balance and memory performance), caused oxidative damage (increased lipid peroxidation, nitrite concentration, depleted super oxide dismutase and reduced glutathione), demonstrated mitochondrial dysfunction (decreased Complex-I, II, III, and IV activities), increased striatal lesion volume and altered the levels of TNF-α, caspase-3 as well as BDNF expression, as compared to sham group. Meanwhile, chronic hesperidin (100mg/kg, p.o.) and minocycline (25mg/kg, p.o.) treatment for 21 days significantly attenuated the behavioral, biochemical and cellular alterations as compared to QA treated (control) animals, whereas hesperidin (50mg/kg, p.o.) treatment was found to be non-significant. However, treatment of hesperidin (50mg/kg) in combination with minocycline (25mg/kg) potentiated their neuroprotective effect, which was significant as compared to their effects per se in QA treated animals. Taken altogether, the results of the present study suggest a possible interplay of microglial modulation and anti-oxidant effect in neuroprotective potential of hesperidin against QA induced HD like symptoms in rats.

SPION-enhanced magnetic resonance imaging of Alzheimer's disease plaques in AβPP/PS-1 transgenic mouse brain

In our program to develop non-invasive magnetic resonance imaging (MRI) methods for the diagnosis of Alzheimer's disease (AD), we have synthesized antibody-conjugated, superparamagnetic iron oxide nanoparticles (SPIONs) for use as an in vivo agent for MRI detection of amyloid-β plaques in AD. Here we report studies in AβPP/PS1 transgenic mice, which demonstrate the ability of novel anti-AβPP conjugated SPIONs to penetrate the blood-brain barrier to act as a contrast agent for MR imaging of plaques. The conspicuity of the plaques increased from an average Z-score of 5.1 ± 0.5 to 8.3 ± 0.2 when the plaque contrast to noise ratio was compared in control AD mice with AD mice treated with SPIONs. The number of MRI-visible plaques per brain increased from 347 ± 45 in the control AD mice, to 668 ± 86 in the SPION treated mice. These results indicated that our SPION enhanced amyloid-β detection method delivers an efficacious, non-invasive MRI detection method in transgenic mice.

Control of life-or-death decisions by RIP1 kinase

RIP1 kinase, a multifunctional protein that contains an N-terminal Ser/Thr kinase and a C-terminal death domain, has emerged as a key regulatory molecule involved in regulating both cell death and cell survival. When the proinflammatory cytokine TNFα stimulates its receptor, TNFR1, RIP1 regulates whether the cell lives by activating NF-κB or dies by apoptosis or necroptosis, two distinct pathways of programmed cell death that may be activated to eliminate unwanted cells. The kinase domain of RIP1 is involved in regulating necroptosis, and the death domain regulates RIP1 recruitment to the intracellular domain of TNFR1. The intermediate domain of RIP1 activates NF-κB and also interacts with RIP3 kinase, a downstream mediator of RIP1 in the execution of necroptosis. This review focuses on the functional roles of RIP1 in regulating multiple cellular mechanisms, the dynamic regulation of RIP1, and the physiological and pathological roles of RIP1 kinase in human health and disease.

A shift to organismal stress resistance in programmed cell death mutants

Animals have many ways of protecting themselves against stress; for example, they can induce animal-wide, stress-protective pathways and they can kill damaged cells via apoptosis. We have discovered an unexpected regulatory relationship between these two types of stress responses. We find that C. elegans mutations blocking the normal course of programmed cell death and clearance confer animal-wide resistance to a specific set of environmental stressors; namely, ER, heat and osmotic stress. Remarkably, this pattern of stress resistance is induced by mutations that affect cell death in different ways, including ced-3 (cell death defective) mutations, which block programmed cell death, ced-1 and ced-2 mutations, which prevent the engulfment of dying cells, and progranulin (pgrn-1) mutations, which accelerate the clearance of apoptotic cells. Stress resistance conferred by ced and pgrn-1 mutations is not additive and these mutants share altered patterns of gene expression, suggesting that they may act within the same pathway to achieve stress resistance. Together, our findings demonstrate that programmed cell death effectors influence the degree to which C. elegans tolerates environmental stress. While the mechanism is not entirely clear, it is intriguing that animals lacking the ability to efficiently and correctly remove dying cells should switch to a more global animal-wide system of stress resistance.

As an animal interacts with its environment, it invariably encounters stressful conditions such as extreme temperatures, drought, UV exposure and harmful xenobiotics. Since the ability to respond appropriately to stressful stimuli is paramount to survival, organisms have developed sophisticated stress response programs. Some stressful conditions cause damaged cells to commit suicide (undergo apoptosis), whereas others cause the entire organism to develop mechanisms to resist environmental stress. Studying the small roundworm C. elegans, we find that these two responses are somehow linked: perturbing the mechanisms that allow cells to undergo apoptosis changes the whole animal's response to environmental stress. In fact, perturbing the apoptosis machinery in any way—through mutations that prevent apoptosis altogether, or through mutations that either slow or accelerate the clearance of dying cells—causes the animal to become more stress resistant. Together our findings raise the possibility that the animal may have a way of detecting defects in the normal programmed cell death pathway, and that in response it induces a new program that protects itself from a harsh environment.

Caspase-3 and RasGAP: a stress-sensing survival/demise switch

The final decision on cell fate, survival versus cell death, relies on complex and tightly regulated checkpoint mechanisms. The caspase-3 protease is a predominant player in the execution of apoptosis. However, recent progress has shown that this protease paradoxically can also protect cells from death. Here, we discuss the underappreciated, protective, and prosurvival role of caspase-3 and detail the evidence showing that caspase-3, through differential processing of p120 Ras GTPase-activating protein (RasGAP), can modulate a given set of proteins to generate, depending on the intensity of the input signals, opposite outcomes (survival vs death).

Tumor necrosis factor α antagonism improves neurological recovery in murine intracerebral hemorrhage

Background

Intracerebral hemorrhage (ICH) is a devastating stroke subtype characterized by a prominent neuroinflammatory response. Antagonism of pro-inflammatory cytokines by specific antibodies represents a compelling therapeutic strategy to improve neurological outcome in patients after ICH. To test this hypothesis, the tumor necrosis factor alpha (TNF-α) antibody CNTO5048 was administered to mice after ICH induction, and histological and functional endpoints were assessed.

Methods

Using 10 to 12-week-old C57BL/6J male mice, ICH was induced by collagenase injection into the left basal ganglia. Brain TNF-α concentration, microglia activation/macrophage recruitment, hematoma volume, cerebral edema, and rotorod latency were assessed in mice treated with the TNF-α antibody, CNTO5048, or vehicle.

Results

After ICH induction, mice treated with CNTO5048 demonstrated reduction in microglial activation/macrophage recruitment compared to vehicle-treated animals, as assessed by unbiased stereology (P = 0.049). This reduction in F4/80-positive cells was associated with a reduction in cleaved caspase-3 (P = 0.046) and cerebral edema (P = 0.026) despite similar hematoma volumes, when compared to mice treated with vehicle control. Treatment with CNTO5048 after ICH induction was associated with a reduction in functional deficit when compared to mice treated with vehicle control, as assessed by rotorod latencies (P = 0.024).

Conclusions

Post-injury treatment with the TNF-α antibody CNTO5048 results in less neuroinflammation and improved functional outcomes in a murine model of ICH.

Selective detection and inhibition of active caspase-3 in cells with optimized peptides

Caspases are a family of cysteine-aspartyl proteases that are well recognized for their essential roles in apoptosis and inflammation. Recently, caspases have also been linked to the promotion of other biologically important phenomena, such as cellular differentiation and proliferation. Dysregulation of the multifaceted and indispensable activities of caspases has been globally linked to several diseases, including cancer and neurodegenerative disorders; however, the specific caspase members responsible for these diseases have yet to be assigned. Activity-based probes (ABPs) and peptide-based inhibitors are instrumental in the detection and control of protease activity and serve as alternative methods to genetic approaches. Such molecules aid in the interrogation of specific proteases within cellular and animal models as well as help elucidate aberrant proteolytic function correlated to disease phenotypes. No ABPs or inhibitors have been discovered that specifically target one of the eleven human caspases in a cellular context. Therefore, ascribing distinct contributions to an individual caspase activity within naturally occurring biological systems is not possible. Herein, we describe a peptide series optimized for the selective detection and inhibition of active caspase-3 in cells. These compounds exhibit low nanomolar potency against caspase-3 with >120-fold selectivity over caspase-7 which shares 77% active site identity. Our ability to individually target wild-type active caspase-3 for detection and cell permeable inhibition is a valuable proof-of-concept methodology that can be readily employed to probe the significance of caspase-3 in apoptosis, neurological disorders, cardiovascular diseases, and sepsis.

Inhibition of microglia activation as a phenotypic assay in early drug discovery

Complex biological processes such as inflammation, cell death, migration, proliferation, and the release of biologically active molecules can be used as outcomes in phenotypic assays during early stages of drug discovery. Although target-based approaches have been widely used over the past decades, a disproportionate number of first-in-class drugs have been identified using phenotypic screening. This review details phenotypic assays based on inhibition of microglial activation and their utility in primary and secondary screening, target validation, and pathway elucidation. The role of microglia, both in normal as well as in pathological conditions such as chronic neurodegenerative diseases, is reviewed. Methodologies to assess microglia activation in vitro are discussed in detail, and classes of therapeutic drugs known to decrease the proinflammatory and cytotoxic responses of activated microglia are appraised, including inhibitors of glutaminase, cystine/glutamate antiporter, nuclear factor κB, and mitogen-activated protein kinases.

Activation of GSK-3β and caspase-3 occurs in Nigral dopamine neurons during the development of apoptosis activated by a striatal injection of 6-hydroxydopamine

The 6-Hydroxydopamine (6-OHDA) rat model of Parkinson's disease is essential for a better understanding of the pathological processes underlying the human disease and for the evaluation of promising therapeutic interventions. This work evaluated whether a single striatal injection of 6-OHDA causes progressive apoptosis of dopamine (DA) neurons and activation of glycogen synthase kinase 3β (GSK-3β) and caspase-3 in the substantia nigra compacta (SNc). The loss of DA neurons was shown by three neuron markers; tyrosine hydroxylase (TH), NeuN, and β-III tubulin. Apoptosis activation was determined using Apostain and immunostaining against cleaved caspase-3 and GSK-3β pY216. We also explored the possibility that cleaved caspase-3 is produced by microglia and astrocytes. Our results showed that the 6-OHDA caused loss of nigral TH(+) cells, progressing mainly in rostrocaudal and lateromedial directions. In the neostriatum, a severe loss of TH(+) terminals occurred from day 3 after lesion. The disappearance of TH(+) cells was associated with a decrease in NeuN and β-III tubulin immunoreactivity and an increase in Apostain, cleaved caspase-3, and GSK-3β pY216 in the SNc. Apostain immunoreactivity was observed from days 3 to 21 postlesion. Increased levels of caspase-3 immunoreactivity in TH(+) cells were detected from days 1 to 15, and the levels then decreased to day 30 postlesion. The cleaved caspase-3 also collocated with microglia and astrocytes indicating its participation in glial activation. Our results suggest that caspase-3 and GSK-3β pY216 activation might participate in the DA cell death and that the active caspase-3 might also participate in the neuroinflammation caused by the striatal 6-OHDA injection.

Microglial P2Y12 deficiency/inhibition protects against brain ischemia

Objective

Microglia are among the first immune cells to respond to ischemic insults. Triggering of this inflammatory response may involve the microglial purinergic GPCR, P2Y₁₂, activation via extracellular release of nucleotides from injured cells. It is also the inhibitory target of the widely used antiplatelet drug, clopidogrel. Thus, inhibiting this GPCR in microglia should inhibit microglial mediated neurotoxicity following ischemic brain injury.

Methods

Experimental cerebral ischemia was induced, in vitro with oxygen-glucose deprivation (OGD), or in vivo via bilateral common carotid artery occlusion (BCCAO). Genetic knock-down in vitro via siRNA, or in vivo P2Y₁₂ transgenic mice (P2Y₁₂−/− or P2Y₁₂+/−), or in vivo treatment with clopidogrel, were used to manipulate the receptor. Neuron death, microglial activation, and microglial migration were assessed.

Results

The addition of microglia to neuron-astrocyte cultures increases neurotoxicity following OGD, which is mitigated by microglial P2Y₁₂ deficiency (P<0.05). Wildtype microglia form clusters around these neurons following injury, which is also prevented in P2Y₁₂ deficient microglia (P<0.01). P2Y₁₂ knock-out microglia migrated less than WT controls in response to OGD-conditioned neuronal supernatant. P2Y₁₂ (+/−) or clopidogrel treated mice subjected to global cerebral ischemia suffered less neuronal injury (P<0.01, P<0.001) compared to wild-type littermates or placebo treated controls. There were also fewer microglia surrounding areas of injury, and less activation of the pro-inflammatory transcription factor, nuclear factor Kappa B (NFkB).

Interpretation

P2Y₁₂ participates in ischemia related inflammation by mediating microglial migration and potentiation of neurotoxicity. These data also suggest an additional anti-inflammatory, neuroprotective benefit of clopidogrel.

Dysfunctional brain-bone marrow communication: a paradigm shift in the pathophysiology of hypertension

It is widely accepted that the pathophysiology of hypertension involves autonomic nervous system dysfunction, as well as a multitude of immune responses. However, the close interplay of these systems in the development and establishment of high blood pressure and its associated pathophysiology remains elusive and is the subject of extensive investigation. It has been proposed that an imbalance of the neuro-immune systems is a result of an enhancement of the "proinflammatory sympathetic" arm in conjunction with dampening of the "anti-inflammatory parasympathetic" arm of the autonomic nervous system. In addition to the neuronal modulation of the immune system, it is proposed that key inflammatory responses are relayed back to the central nervous system and alter the neuronal communication to the periphery. The overall objective of this review is to critically discuss recent advances in the understanding of autonomic immune modulation, and propose a unifying hypothesis underlying the mechanisms leading to the development and maintenance of hypertension, with particular emphasis on the bone marrow, as it is a crucial meeting point for neural, immune, and vascular networks.

The histone H4 lysine 16 acetyltransferase hMOF regulates the outcome of autophagy

Autophagy is an evolutionarily conserved catabolic process involved in several physiological and pathological processes. Although primarily cytoprotective, autophagy can also contribute to cell death; it is thus important to understand what distinguishes the life or death decision in autophagic cells. Here we report that induction of autophagy is coupled to reduction of histone H4 lysine 16 acetylation (H4K16ac) through downregulation of the histone acetyltransferase hMOF (also called KAT8 or MYST1), and demonstrate that this histone modification regulates the outcome of autophagy. At a genome-wide level, we find that H4K16 deacetylation is associated predominantly with the downregulation of autophagy-related genes. Antagonizing H4K16ac downregulation upon autophagy induction results in the promotion of cell death. Our findings establish that alteration in a specific histone post-translational modification during autophagy affects the transcriptional regulation of autophagy-related genes and initiates a regulatory feedback loop, which serves as a key determinant of survival versus death responses upon autophagy induction.

Caspase blockade induces RIP3-mediated programmed necrosis in Toll-like receptor-activated microglia

Microglia are the resident immune cells in the central nervous system and key players against pathogens and injury. However, persistent microglial activation often exacerbates pathological damage and has been implicated in many neurological diseases. Despite their pivotal physiological and pathophysiological roles, how the survival and death of activated microglia is regulated remains poorly understood. We report here that microglia activated through Toll-like receptors (TLRs) undergo RIP1/RIP3-dependent programmed necrosis (necroptosis) when exposed to the pan caspase inhibitor zVAD-fmk. Although zVAD-fmk and the caspase-8 inhibitor IETD-fmk had no effect on unstimulated primary microglia, they markedly sensitized microglia to TLR1/2,3,4,7/8 ligands or TNF treatment, triggering programmed necrosis that was completely blocked by R1P1 kinase inhibitor necrostatin-1. Interestingly, necroptosis induced by TLR ligands and zVAD was restricted to microglial cells and was not observed in astrocytes, neurons or oligodendrocytes even though they are known to express certain TLRs. Deletion of genes encoding TNF or TNFR1 failed to prevent lipopolysaccharide- and poly(I:C)-induced microglial necroptosis, unveiling a TNF-independent programmed necrosis pathway in TLR3- and TLR4-activated microglia. Microglia from mice lacking functional TRIF were fully protected against TLR3/4 activation and zVAD-fmk-induced necrosis, and genetic deletion of rip3 also prevented microglia necroptosis. Activation of c-jun N-terminal kinase and generation of specific reactive oxygen species were downstream signaling events required for microglial cell death execution. Taken together, this study reveals a robust RIP3-dependent necroptosis signaling pathway in TLR-activated microglia upon caspase blockade and suggests that TLR signaling and programmed cell death pathways are closely linked in microglia, which could contribute to neuropathology and neuroinflammation when dysregulated.

Astrogliopathy and oligodendrogliopathy are early events in CNS demyelination

We examined the phenotypic composition of cells and the underlying mechanisms of demyelination following injection of lipopolysaccharide (LPS) into the corpus callosum of rats. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed fragmented DNA, which co-localized with oligodendrocytes in areas of demyelination following intracerebral injection with LPS. Immunostaining showed the presence of caspase 3 in cells which expressed the oligodendrocyte markers, suggesting activation of the apoptotic pathway. Commensurate reduction in glial fibrillary acid protein (GFAP)+/ gap junction protein connexin43+ (Cx43) cells, was also seen in the corpus callosum prior to histochemical evidence of demyelination. Expression of mRNA for proinflammatory cytokines was maximal 3 day postinjection, at a time when the numbers of TUNEL positive cells in the corpus callosum were declining and the total number of CD68+ cells peaked at day 14 postinjection. Our studies suggest that death of oligodendrocytes is an early event in LPS model of demyelination. We believe that the innate immune model of oligodendrocyte death will be useful in the development of neuroprotective agents capable of rescuing oligodendrocytes from apoptosis.

Minocycline treatment and bone marrow mononuclear cell transplantation after endothelin-1 induced striatal ischemia

We explored whether the modulation of microglia activation with minocycline is beneficial to the therapeutic actions of bone marrow mononuclear cells (BMMCs) transplanted after experimental stroke. Male Wistar adult rats were divided in four experimental groups: ischemic control saline treated (G1, N = 6), ischemic minocycline treated (G2, N = 5), ischemic BMMC treated (G3, N = 5), and ischemic minocycline/BMMC treated (G4, N = 6). There was a significant reduction in the number of ED1+ cells in G3 animals (51.31 ± 2.41, P < 0.05), but this effect was more prominent following concomitant treatment with minocycline (G4 = 29.78 ± 1.56). There was conspicuous neuronal preservation in the brains of G4 animals (87.97 ± 4.27) compared with control group (G1 = 47.61 ± 2.25, P < 0.05). The behavioral tests showed better functional recovery in animals of G2, G3, and G4, compared with G1 and baseline (P < 0.05). The results suggest that a proper modulation of microglia activity may contribute to a more permissive ischemic environment contributing to increased neuroprotection and functional recovery following striatal ischemia.

Role of mTOR, Bad, and Survivin in RasGAP Fragment N-Mediated Cell Protection

Partial cleavage of p120 RasGAP by caspase-3 in stressed cells generates an N-terminal fragment, called fragment N, which activates an anti-apoptotic Akt-dependent survival response. Akt regulates several effectors but which of these mediate fragment N-dependent cell protection has not been defined yet. Here we have investigated the role of mTORC1, Bad, and survivin in the capacity of fragment N to protect cells from apoptosis. Neither rapamycin, an inhibitor of mTORC1, nor silencing of raptor, a subunit of the mTORC1 complex, altered the ability of fragment N from inhibiting cisplatin- and Fas ligand-induced death. Cells lacking Bad, despite displaying a stronger resistance to apoptosis, were still protected by fragment N against cisplatin-induced death. Fragment N was also able to protect cells from Fas ligand-induced death in conditions where Bad plays no role in apoptosis regulation. Fragment N expression in cells did neither modulate survivin mRNA nor its protein expression. Moreover, the expression of cytoplasmic survivin, known to exert anti-apoptotic actions in cells, still occurred in UV-B-irradiated epidermis of mouse expressing a caspase-3-resistant RasGAP mutant that cannot produce fragment N. Additionally, survivin function in cell cycle progression was not affected by fragment N. These results indicate that, taken individually, mTOR, Bad, or Survivin are not required for fragment N to protect cells from cell death. We conclude that downstream targets of Akt other than mTORC1, Bad, or survivin mediate fragment N-induced protection or that several Akt effectors can compensate for each other to induce the pro-survival fragment N-dependent response.

Microglia and interleukin-1β in ischemic retinopathy elicit microvascular degeneration through neuronal semaphorin-3A

OBJECTIVE

Proinflammatory cytokines contribute to the development of retinal vasculopathies. However, the role of these factors and the mechanisms by which they elicit their effects in retina are not known. We investigated whether activated microglia during early stages of ischemic retinopathy produces excessive interleukin-1β (IL-1β), which elicits retinal microvascular degeneration not directly but rather by triggering the release of the proapoptotic/repulsive factor semaphorin-3A (Sema3A) from neurons.

APPROACH AND RESULTS

Sprague Dawley rats subjected to retinopathy induced by hyperoxia (80% O2; O2-induced retinopathy) exhibited retinal vaso-obliteration associated with microglial activation, NLRP3 upregulation, and IL-1β and Sema3A release; IL-1β was mostly generated by microglia. Intraperitoneal administration of IL-1 receptor antagonists (Kineret, or rytvela [101.10]) decreased these effects and enhanced retinal revascularization; knockdown of Sema3A resulted in microvessel preservation and, conversely, administration of IL-1β caused vaso-obliteration. In vitro, IL-1β derived from activated primary microglial cells, cultured under hyperoxia, stimulated the release of Sema3A in retinal ganglion cells-5, which in turn induced apoptosis of microvascular endothelium; antagonism of IL-1 receptor decreased microglial activation and on retinal ganglion cells-5 abolished the release of Sema3A inhibiting ensuing endothelial cell apoptosis. IL-1β was not directly cytotoxic to endothelial cells.

CONCLUSIONS

Our findings suggest that in the early stages of O2-induced retinopathy, retinal microglia are activated to produce IL-1β, which sustains the activation of microglia and induces microvascular injury through the release of Sema3A from adjacent neurons. Interference with IL-1 receptor or Sema3A actions preserves the microvascular bed in ischemic retinopathies and, consequently, decreases ensued pathological preretinal neovascularization.

Microchannel acoustophoresis does not impact survival or function of microglia, leukocytes or tumor cells

BACKGROUND

The use of acoustic forces to manipulate particles or cells at the microfluidic scale (i.e. acoustophoresis), enables non-contact, label-free separation based on intrinsic cell properties such as size, density and compressibility. Acoustophoresis holds great promise as a cell separation technique in several research and clinical areas. However, it has been suggested that the force acting upon cells undergoing acoustophoresis may impact cell viability, proliferation or cell function via subtle phenotypic changes. If this were the case, it would suggest that the acoustophoresis method would be a less useful tool for many cell analysis applications as well as for cell therapy.

METHODS

We investigate, for the first time, several key aspects of cellular changes following acoustophoretic processing. We used two settings of ultrasonic actuation, one that is used for cell sorting (10 Vpp operating voltage) and one that is close to the maximum of what the system can generate (20 Vpp). We used microglial cells and assessed cell viability and proliferation, as well as the inflammatory response that is indicative of more subtle changes in cellular phenotype. Furthermore, we adapted a similar methodology to monitor the response of human prostate cancer cells to acoustophoretic processing. Lastly, we analyzed the respiratory properties of human leukocytes and thrombocytes to explore if acoustophoretic processing has adverse effects.

RESULTS

BV2 microglia were unaltered after acoustophoretic processing as measured by apoptosis and cell turnover assays as well as inflammatory cytokine response up to 48 h following acoustophoresis. Similarly, we found that acoustophoretic processing neither affected the cell viability of prostate cancer cells nor altered their prostate-specific antigen secretion following androgen receptor activation. Finally, human thrombocytes and leukocytes displayed unaltered mitochondrial respiratory function and integrity after acoustophoretic processing.

CONCLUSION

We conclude that microchannel acoustophoresis can be used for effective continuous flow-based cell separation without affecting cell viability, proliferation, mitochondrial respiration or inflammatory status.

The brain's best friend: microglial neurotoxicity revisited

One long standing aspect of microglia biology was never questioned; their involvement in brain disease. Based on morphological changes (retracted processes and amoeboid shape) that inevitably occur in these cells in case of damage in the central nervous system, microglia in the diseased brain were called “activated.” Because “activated” microglia were always found in direct neighborhood to dead or dying neuron, and since it is known now for more than 20 years that cultured microglia release numerous factors that are able to kill neurons, microglia “activation” was often seen as a neurotoxic process. From an evolutionary point of view, however, it is difficult to understand why an important, mostly post-mitotic and highly vulnerable organ like the brain would host numerous potential killers. This review is aimed to critically reconsider the term microglia neurotoxicity and to discuss experimental problems around microglia biology, that often have led to the conclusion that microglia are neurotoxic cells.

Targeting caspase-3 as dual therapeutic benefits by RNAi facilitating brain-targeted nanoparticles in a rat model of Parkinson's disease

The activation of caspase-3 is an important hallmark in Parkinson’s disease. It could induce neuron death by apoptosis and microglia activation by inflammation. As a result, inhibition the activation of caspase-3 would exert synergistic dual effect in brain in order to prevent the progress of Parkinson’s disease. Silencing caspase-3 genes by RNA interference could inhibit the activation of caspase-3. We developed a brain-targeted gene delivery system based on non-viral gene vector, dendrigraft poly-L-lysines. A rabies virus glycoprotein peptide with 29 amino-acid linked to dendrigraft poly-L-lysines could render gene vectors the ability to get across the blood brain barrier by specific receptor mediated transcytosis. The resultant brain-targeted vector was complexed with caspase-3 short hairpin RNA coding plasmid DNA, yielding nanoparticles. In vivo imaging analysis indicated the targeted nanoparticles could accumulate in brain more efficiently than non-targeted ones. A multiple dosing regimen by weekly intravenous administration of the nanoparticles could reduce activated casapse-3 levels, significantly improve locomotor activity and rescue dopaminergic neuronal loss and in Parkinson’s disease rats’ brain. These results indicated the rabies virus glycoprotein peptide modified brain-targeted nanoparticles were promising gene delivery system for RNA interference to achieve anti-apoptotic and anti-inflammation synergistic therapeutic effects by down-regulation the expression and activation of caspase-3.

Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

The role of neuroinflammation and the adaptive immune system in PD (Parkinson's disease) has been the subject of intense investigation in recent years, both in animal models of parkinsonism and in post-mortem PD brains. However, how these processes relate to and modulate α-syn (α-synuclein) pathology and microglia activation is still poorly understood. Specifically, how the peripheral immune system interacts, regulates and/or is induced by neuroinflammatory processes taking place during PD is still undetermined. We present herein a comprehensive review of the features and impact that neuroinflamation has on neurodegeneration in different animal models of nigral cell death, how this neuroinflammation relates to microglia activation and the way microglia respond to α-syn in vivo. We also discuss a possible role for the peripheral immune system in animal models of parkinsonism, how these findings relate to the state of microglia activation observed in these animal models and how these findings compare with what has been observed in humans with PD. Together, the available data points to the need for development of dual therapeutic strategies that modulate microglia activation to change not only the way microglia interact with the peripheral immune system, but also to modulate the manner in which microglia respond to encounters with α-syn. Lastly, we discuss the immune-modulatory strategies currently under investigation in animal models of parkinsonism and the degree to which one might expect their outcomes to translate faithfully to a clinical setting.

Neuroprotective effects of Lycium barbarum polysaccharides in lipopolysaccharide-induced BV2 microglial cells

Polysaccharides extracted from Lycium barbarum (LBPs) possess a wide variety of biological activities. However, their neuroprotective effects have not yet been fully elucidated. The aim of the present study was to investigate the inhibitory effects of LBPs on the production of lipopolysaccharide (LPS)‑induced proinflammatory mediators in BV2 microglia. BV2 mouse microglial cells were cultured and an MTT assay was performed to determine whether LBPs had an effect on the apoptosis of LPS-stimulated BV2 cells. Our data showed that LPS induced the activation of nuclear factor‑κB (NF‑κB) and its upstream protein caspase 3, upregulated the expression of an additional apoptosis‑inducing factor, heat shock protein 60 (HSP60), in BV2 microglial cells and increased the release of TNF-α and HSP60 in the culture media. Following treatment with LBPs, the activated NF‑κB and caspase 3 were significantly suppressed. Furthermore, the enhanced expression of HSP60 was reduced and the LPS-induced release of TNF-α and HSP60 were inhibited. These results suggest that LBPs may have therapeutic potential for the treatment of neurodegenerative diseases that are accompanied by microglial activation.

Sevoflurane anesthesia in pregnant mice induces neurotoxicity in fetal and offspring mice

BACKGROUND

Each year, over 75,000 pregnant women in the United States undergo anesthesia care. The authors set out to assess the effects of the anesthetic sevoflurane on neurotoxicity in pregnant mice and on learning and memory in fetal and offspring mice.

METHODS

Pregnant mice (gestational day 14) and mouse primary neurons were treated with 2.5% sevoflurane for 2 h and 4.1% sevoflurane for 6 h, respectively. Brain tissues of both fetal and offspring mice (P31) and the primary neurons were harvested and subjected to Western blot and immunohistochemistry to assess interleukin-6, the synaptic markers postsynaptic density-95 and synaptophysin, and caspase-3 levels. Separately, learning and memory function in the offspring mice was determined in the Morris water maze.

RESULTS

Sevoflurane anesthesia in pregnant mice induced caspase-3 activation, increased interleukin-6 levels (256 ± 50.98% [mean ± SD] vs. 100 ± 54.12%, P = 0.026), and reduced postsynaptic density-95 (61 ± 13.53% vs. 100 ± 10.08%, P = 0.036) and synaptophysin levels in fetal and offspring mice. The sevoflurane anesthesia impaired learning and memory in offspring mice at P31. Moreover, interleukin-6 antibody mitigated the sevoflurane-induced reduction in postsynaptic density-95 levels in the neurons. Finally, environmental enrichment attenuated the sevoflurane-induced increases in interleukin-6 levels, reductions of synapse markers, and learning and memory impairment.

CONCLUSIONS

These results suggest that sevoflurane may induce detrimental effects in fetal and offspring mice, which can be mitigated by environmental enrichment. These findings should promote more studies to determine the neurotoxicity of anesthesia in the developing brain.

Protein kinase C, an elusive therapeutic target?

Protein kinase C (PKC) has been a tantalizing target for drug discovery ever since it was first identified as the receptor for the tumour promoter phorbol ester in 1982. Although initial therapeutic efforts focused on cancer, additional indications--including diabetic complications, heart failure, myocardial infarction, pain and bipolar disorder--were targeted as researchers developed a better understanding of the roles of eight conventional and novel PKC isozymes in health and disease. Unfortunately, both academic and pharmaceutical efforts have yet to result in the approval of a single new drug that specifically targets PKC. Why does PKC remain an elusive drug target? This Review provides a short account of some of the efforts, challenges and opportunities in developing PKC modulators to address unmet clinical needs.

Glibenclamide enhances neurogenesis and improves long-term functional recovery after transient focal cerebral ischemia

Glibenclamide is neuroprotective against cerebral ischemia in rats. We studied whether glibenclamide enhances long-term brain repair and improves behavioral recovery after stroke. Adult male Wistar rats were subjected to transient middle cerebral artery occlusion (MCAO) for 90 minutes. A low dose of glibenclamide (total 0.6 μg) was administered intravenously 6, 12, and 24 hours after reperfusion. We assessed behavioral outcome during a 30-day follow-up and animals were perfused for histological evaluation. In vitro specific binding of glibenclamide to microglia increased after pro-inflammatory stimuli. In vivo glibenclamide was associated with increased migration of doublecortin-positive cells in the striatum toward the ischemic lesion 72 hours after MCAO, and reactive microglia expressed sulfonylurea receptor 1 (SUR1) and Kir6.2 in the medial striatum. One month after MCAO, glibenclamide was also associated with increased number of NeuN-positive and 5-bromo-2-deoxyuridine-positive neurons in the cortex and hippocampus, and enhanced angiogenesis in the hippocampus. Consequently, glibenclamide-treated MCAO rats showed improved performance in the limb-placing test on postoperative days 22 to 29, and in the cylinder and water-maze test on postoperative day 29. Therefore, acute blockade of SUR1 by glibenclamide enhanced long-term brain repair in MCAO rats, which was associated with improved behavioral outcome.

TRAIL promotes membrane blebbing, detachment and migration of cells displaying a dysfunctional intrinsic pathway of apoptosis

Recently, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) has been shown to be a potential candidate for cancer therapy. TRAIL induces apoptosis in various cancer cells but not in normal tissues. Here we show that HCT116 and SW480 cells with a deficient mitochondrial apoptotic pathway were resistant to TRAIL-induced apoptosis, whereas HCT116 and SW480 cells with a functional mitochondrial apoptotic pathway underwent apoptosis upon exposure to TRAIL. Surprisingly, TRAIL induced phenotypic changes in cells with a dysfunctional mitochondrial apoptotic pathway, including membrane blebbing and a transient loss of adhesion properties to the substratum. Accordingly, TRAIL stimulated the ability of these cells to migrate. This behavior was the consequence of a transient TRAIL-induced ROCK1 cleavage. In addition, we report that Bax-deficient HCT116 cells exposed to TRAIL for a prolonged period lost their sensitivity to TRAIL as a result of downregulation of TRAIL receptor expression, and became resistant to combination of TRAIL and other drugs such as MG-132 and bortezomib. These findings may have important consequences for TRAIL anti-cancer therapy.

Caspases playing in the field of neuroinflammation: old and new players

Neuroinflammation is a complex immune response against the harmful effects of diverse stimuli within the central nervous system. Caspases are a family of intracellular cysteine proteases that mediate proteolytic events indispensable for transduction of signaling pathway-controlling biological phenomena such as apoptosis and inflammation. To date, 14 players have been identified in mammals. For many years, caspases were simply divided into 'apoptotic' and 'proinflammatory' caspases and this classification remains useful to some extent. However, increasing evidence indicates that many of these so-called apoptotic caspases also exert nonapoptotic functions. In addition, the role of certain members of the supposed inflammatory caspases in the inflammatory process per se has also been discussed. In this review, we highlight the role for 'apoptotic' and 'proinflammatory' caspases in the regulation of the inflammation response with a special focus on the central nervous system.

Essential roles of mitochondrial depolarization in neuron loss through microglial activation and attraction toward neurons

As life spans increased, neurodegenerative disorders that affect aging populations have also increased. Progressive neuronal loss in specific brain regions is the most common cause of neurodegenerative disease; however, key determinants mediating neuron loss are not fully understood. Using a model of mitochondrial membrane potential (ΔΨm) loss, we found only 25% cell loss in SH-SY5Y (SH) neuronal mono-cultures, but interestingly, 85% neuronal loss occurred when neurons were co-cultured with BV2 microglia. SH neurons overexpressing uncoupling protein 2 exhibited an increase in neuron-microglia interactions, which represent an early step in microglial phagocytosis of neurons. This result indicates that ΔΨm loss in SH neurons is an important contributor to recruitment of BV2 microglia. Notably, we show that ΔΨm loss in BV2 microglia plays a crucial role in microglial activation and phagocytosis of damaged SH neurons. Thus, our study demonstrates that ΔΨm loss in both neurons and microglia is a critical determinant of neuron loss. These findings also offer new insights into neuroimmunological and bioenergetical aspects of neurodegenerative disease.

Caspase inhibitors protect neurons by enabling selective necroptosis of inflamed microglia

Microglia are resident brain macrophages, which can cause neuronal loss when activated in infectious, ischemic, traumatic, and neurodegenerative diseases. Caspase-8 has both prodeath and prosurvival roles, mediating apoptosis and/or preventing RIPK1-mediated necroptosis depending on cell type and stimulus. We found that inflammatory stimuli (LPS, lipoteichoic acid, or TNF-α) caused an increase in caspase-8 IETDase activity in primary rat microglia without inducing apoptosis. Inhibition of caspase-8 with either Z-VAD-fmk or IETD-fmk resulted in necrosis of activated microglia. Inhibition of caspases with Z-VAD-fmk did not kill non-activated microglia, or astrocytes and neurons in any condition. Necrostatin-1, a specific inhibitor of RIPK1, prevented microglial caspase inhibition-induced death, indicating death was by necroptosis. In mixed cerebellar cultures of primary neurons, astrocytes, and microglia, LPS induced neuronal loss that was prevented by inhibition of caspase-8 (resulting in microglial necroptosis), and neuronal death was restored by rescue of microglia with necrostatin-1. We conclude that the activation of caspase-8 in inflamed microglia prevents their death by necroptosis, and thus, caspase-8 inhibitors may protect neurons in the inflamed brain by selectively killing activated microglia.

Ghrelin is neuroprotective in Parkinson's disease: molecular mechanisms of metabolic neuroprotection

Ghrelin is a circulating orexigenic signal that rises with prolonged fasting and falls postprandially. Ghrelin regulates energy homeostasis by stimulating appetite and body weight; however, it also has many nonmetabolic functions including enhanced learning and memory, anxiolytic effects as well as being neuroprotective. In Parkinson's disease, ghrelin enhances dopaminergic survival via reduced microglial and caspase activation and improved mitochondrial function. As mitochondrial dysfunction contributes to Parkinson's disease, any agent that enhances mitochondrial function could be a potential therapeutic target. We propose that ghrelin provides neuroprotective effects via AMPK (5' adenosine monophosphate-activated protein kinase) activation and enhanced mitophagy (removal of damaged mitochondria) to ultimately enhance mitochondrial bioenergetics. AMPK activation shifts energy balance from a negative to a neutral state and has a role in regulating mitochondrial biogenesis and reducing reactive oxygen species production. Mitophagy is important in Parkinson's disease because damaged mitochondria produce reactive oxygen species resulting in damage to intracellular proteins, lipids and DNA predisposing them to neurodegeneration. Many genetic mutations linked to Parkinson's disease are due to abnormal mitochondrial function and mitophagy, for example LRRK2, PINK1 and Parkin. An interaction between ghrelin and these classic Parkinson's disease markers has not been observed, however by enhancing mitochondrial function, ghrelin or AMPK is a potential therapeutic target for slowing the progression of Parkinson's disease symptoms, both motor and nonmotor.

Reciprocal interactions of mouse bone marrow-derived mesenchymal stem cells and BV2 microglia after lipopolysaccharide stimulation

Introduction

Mesenchymal stem cells (MSCs) are immunosuppressive, but we lack an understanding of how these adult stem cells are in turn affected by immune cells and the surrounding tissue environment. As MSCs have stromal functions and exhibit great plasticity, the influence of an inflamed microenvironment on their responses is important to determine. MSCs downregulate microglial inflammatory responses, and here we describe the mutual effects of coculturing mouse bone marrow MSCs with BV2 microglia in a lipopolysaccharide (LPS) inflammatory paradigm.

Methods

Mouse MSCs were cultured from femoral and tibial bone marrow aspirates and characterized. MSCs were cocultured with BV2 microglia at four seeding-density ratios (1:0.2, 1:0.1, 1:0.02, and 1:0.01 (BV2/MSC)), and stimulated with 1 μg/ml LPS. In certain assays, MSCs were separated from BV2 cells with a cell-culture insert to determine the influence of soluble factors on downstream responses. Inflammatory mediators including nitric oxide (NO), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and chemokine (C-C motif) ligand 2 (CCL2) were measured in cocultures, and MSC and BV2 chemotactic ability determined by migration assays.

Results

We demonstrated MSCs to increase expression of NO and IL-6 and decrease TNF-α in LPS-treated cocultures. These effects are differentially mediated by soluble factors and cell-to-cell contact. In response to an LPS stimulus, MSCs display distinct behaviors, including expressing IL-6 and very high levels of the chemokine CCL2. Microglia increase their migration almost fourfold in the presence of LPS, and interestingly, MSCs provide an equal impetus for microglia locomotion. MSCs do not migrate toward LPS but migrate toward microglia, with their chemotaxis increasing when microglia are activated. Similarly, MSCs do not produce NO when exposed to LPS, but secrete large amounts when exposed to soluble factors from activated microglia. This demonstrates that certain phenotypic changes of MSCs are governed by inflammatory microglia, and not by the inflammatory stimulus. Nonetheless, LPS appears to "prime" the NO-secretory effects of MSCs, as prior treatment with LPS triggers a bigger NO response from MSCs after exposure to microglial soluble factors.

Conclusions

These effects demonstrate the multifaceted and reciprocal interactions of MSCs and microglia within an inflammatory milieu.

Cell-cell communication induces random spikes of spontaneous calcium oscillations in multi-BV-2 microglial cells

As the first and main form of active immune defense in the central nervous system, microglial cells usually exhibit complicated intracellular calcium (Ca²⁺) activity that can regulate the downstream components of signaling cascades. In the present work, spontaneous oscillations of the cytosolic calcium concentration ([Ca²⁺]c) in multi-BV-2 microglial cells were observed by video microscopy. These cells exhibited random spikes of Ca²⁺ oscillations. Cross-correlation analysis of the temporal dependence of the oscillations indicated the existence of cell-cell communication mediated by extracellular messengers. Numerical simulations based on a simple mathematical model suggested that these communications could induce random spikes of spontaneous Ca oscillations in the multi-cell system. Short-time imaging analysis of random spikes in different regions of a single cell showed that spontaneous Ca²⁺ oscillations resulted from Ca²⁺ wave generated by other cells as well as from calcium elevation inside the cell. Taken together, our data demonstrate that cell-cell communication existed between the BV-2 microglial cells in vitro and further resulted in the random spikes of spontaneous Ca²⁺ oscillations.

Microglia: scapegoat, saboteur, or something else?

Microglia are resident immune cells in the brain and spinal cord. These cells provide immune surveillance and are mobilized in response to disparate diseases and injuries. Although microglial activation is often considered neurotoxic, microglia are essential defenders against many neurodegenerative diseases. It also seems increasingly likely that microglial dysfunction can underlie certain neurological diseases without an obvious immune component.

Involvement of early growth response-2 (Egr-2) in lipopolysaccharide-induced neuroinflammation

Early growth response-2 (Egr-2) protein is a transcription factor, which belongs to Egr family which involve in modulating the peripheral immune response, by means of the induction of differentiation of lymphocyte precursors, activation of T and B cells. Egr-2 plays essential roles in peripheral nerve myelination, adipogenesis, tissue repair and fibrosis, immune tolerance; however, its regulation and role in central nervous system (CNS) remain poorly understood. In contrast to Egr-1, which has been extensively investigated, the regulation and function of Egr-2 remains less well characterized. To elaborate whether Egr-2 was involved in CNS injury, we performed a neuroinflammatory model by lipopolysaccharide (LPS) lateral ventral injection in adult rats. Egr-2 expression was strongly induced in active glia cells (astrocytes and microglias) in inflamed brain cortex. In vitro studies indicated that the upregulation of Egr-2 may be involved in the subsequent glia cellular activation following LPS exposure; and knock down of Egr-2 in primary mixed glial cultures (MGC) by siRNA showed that Egr-2 promoted the synthesis of TNF-α. Collectively, these results suggested Egr-2 may be important in host defense in CNS immune response, which might provide a potential target to the treatment of neuroinflammation.

Targeting Nrf2-mediated gene transcription by extremely potent synthetic triterpenoids attenuate dopaminergic neurotoxicity in the MPTP mouse model of Parkinson's disease

Although the etiology of Parkinson's disease (PD) remains unclear, ample empirical evidence suggests that oxidative stress is a major player in the development of PD and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. Nuclear factor E2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that upregulates a battery of antioxidant response element (ARE)-driven antioxidative and cytoprotective genes that defend against oxidative stress.

AIMS

We evaluated whether the strategy of activation of Nrf2 and its downstream network of cytoprotective genes with small molecule synthetic triterpenoids (TP) attenuate MPTP-induced PD in mice.

RESULTS

We show that synthetic TP are thus far the most potent and direct activators of the Nrf2 pathway using a novel Neh2-luciferase reporter. They upregulate several cytoprotective genes, including those involved in glutathione biosynthesis in vitro. Oral administration of TP that were structurally modified to penetrate the brain-induced messenger RNA and protein levels for a battery of Nrf2-dependent cytoprotective genes reduced MPTP-induced oxidative stress and inflammation, and ameliorated dopaminergic neurotoxicity in mice. The neuroprotective effect of these TP against MPTP neurotoxicity was dependent on Nrf2, since treatment with TP in Nrf2 knockout mice failed to block against MPTP neurotoxicity and induce Nrf2-dependent cytoprotective genes.

INNOVATION

Extremely potent synthetic TP that are direct activators of the Nrf2 pathway block dopaminergic neurodegeneration in the MPTP mouse model of PD.

CONCLUSION

Our results indicate that activation of Nrf2/antioxidant response element (ARE) signaling by synthetic TP is directly associated with their neuroprotective effects against MPTP neurotoxicity and suggest that targeting the Nrf2/ARE pathway is a promising approach for therapeutic intervention in PD.

Quantification of active caspase-3 and active caspase-8 in microglia cells

During microglia activation the levels of active caspase-3, caspase-7 and caspase-8 are increased, which leads to the transcription of proinflammatory cytokines and factors. As such, the induction of caspase activity in microglia can be used as a marker for activation. The use of sensitive and quantitative techniques has made it possible to reproducibly detect these low levels of active caspases. This chapter outlines the materials and methodology for three different ways to detect caspase activation in microglia.

Myelin Basic Protein-primed T Helper 2 Cells Suppress Microglial Activation via AlphaVBeta3 Integrin: Implications for Multiple Sclerosis

Multiple sclerosis (MS) is the most common autoimmune demyelinating disease in human and T helper type 2 (Th2) cells have been shown to be beneficial for this disease. However, mechanisms by which Th2 cells ameliorate disease in MS are poorly understood. Microglial activation plays an important role in the pathogenesis of MS and other neurodegenerative disorders. Here, we delineate that Th2 cells are capable of suppressing microglial activation via cell-to-cell contact. After polarization of MBP-primed Th1 cells to Th2 by gemfibrozil and other drugs, we observed that MBP-primed Th2 cells dose dependently inhibited the production of interleukin-1β (IL-1β) and nitric oxide (NO) in LPS-stimulated microglia via cell-to-cell contact. Similarly, Th2 cells also suppressed the microglial inflammatory response in the presence of different pathological stimuli of Alzheimer’s disease (AD), Parkinson’s disease (PD), and HIV associated dementia (HAD). Interestingly, Th2 cells expressed higher levels of alphaV (αV) and beta3 (β3) integrins as compared to Th1 cells, and functional blocking antibodies against αV and β3 integrins impaired the ability of Th2 cells to suppress microglial activation. Furthermore, we demonstrate that microglia expressed the beta subunit of PDGF receptor (PDGFRβ) and that neutralization of PDGFRβ abrogated the ability of Th2 cells to suppress microglial inflammation. Activation of microglial cAMP response element-binding (CREB) by Th2 cells, suppression of CREB activation by neutralization of either αV and β3 integrins on Th2 cells or PDGFRβ on microglia, abrogation of anti-inflammatory activity of Th2 cells by siRNA knockdown of microglial CREB, highlights the importance of αVβ3 and PDGFRβ in guiding the anti-inflammatory activity of Th2 cells via activation of CREB, which may be responsible for beneficial effect of Th2 cells in MS and other related disorders.

Cell culturing of human and murine microglia cell lines

Despite the fact that microglia cells were first described almost a century ago, microglia-derived immortalized cell lines have only been established in the last two decades. One should be aware of their limitations but also of their advantages. Cell lines offer a potentially powerful tool to investigate some functional aspects of microglia. Cell culturing of human and murine microglia cell lines will be described in this chapter. It includes a presentation of equipment needed, cell culture medium and supplements, cell culture monitoring, and a protocol describing the steps for subculturing of microglia cell lines.