Caspase-Mediated Apoptosis in Neuronal Excitotoxicity Triggered by Nitric Oxide

"NO" Time in Fear Response: Possible Implication of Nitric-Oxide-Related Mechanisms in PTSD

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by persistent fear responses and altered neurotransmitter functioning due to traumatic experiences. Stress predominantly affects glutamate, a neurotransmitter crucial for synaptic plasticity and memory formation. Activation of the N-Methyl-D-Aspartate glutamate receptors (NMDAR) can trigger the formation of a complex comprising postsynaptic density protein-95 (PSD95), the neuronal nitric oxide synthase (nNOS), and its adaptor protein (NOS1AP). This complex is pivotal in activating nNOS and nitric oxide (NO) production, which, in turn, activates downstream pathways that modulate neuronal signaling, including synaptic plasticity/transmission, inflammation, and cell death. The involvement of nNOS and NOS1AP in the susceptibility of PTSD and its comorbidities has been widely shown. Therefore, understanding the interplay between stress, fear, and NO is essential for comprehending the maintenance and progression of PTSD, since NO is involved in fear acquisition and extinction processes. Moreover, NO induces post-translational modifications (PTMs), including S-nitrosylation and nitration, which alter protein function and structure for intracellular signaling. Although evidence suggests that NO influences synaptic plasticity and memory processing, the specific role of PTMs in the pathophysiology of PTSD remains unclear. This review highlights pathways modulated by NO that could be relevant to stress and PTSD.

Identification of the bacterial metabolite aerugine as potential trigger of human dopaminergic neurodegeneration

The causes of nigrostriatal cell death in idiopathic Parkinson's disease are unknown, but exposure to toxic chemicals may play some role. We followed up here on suggestions that bacterial secondary metabolites might be selectively cytotoxic to dopaminergic neurons. Extracts from Streptomyces venezuelae were found to kill human dopaminergic neurons (LUHMES cells). Utilizing this model system as a bioassay, we identified a bacterial metabolite known as aerugine (C10H11NO2S; 2-[4-(hydroxymethyl)-4,5-dihydro-1,3-thiazol-2-yl]phenol) and confirmed this finding by chemical re-synthesis. This 2-hydroxyphenyl-thiazoline compound was previously shown to be a product of a wide-spread biosynthetic cluster also found in the human microbiome and in several pathogens. Aerugine triggered half-maximal dopaminergic neurotoxicity at 3-4 µM. It was less toxic for other neurons (10-20 µM), and non-toxic (at <100 µM) for common human cell lines. Neurotoxicity was completely prevented by several iron chelators, by distinct anti-oxidants and by a caspase inhibitor. In the Caenorhabditis elegans model organism, general survival was not affected by aerugine concentrations up to 100 µM. When transgenic worms, expressing green fluorescent protein only in their dopamine neurons, were exposed to aerugine, specific neurodegeneration was observed. The toxicant also exerted functional dopaminergic toxicity in nematodes as determined by the "basal slowing response" assay. Thus, our research has unveiled a bacterial metabolite with a remarkably selective toxicity toward human dopaminergic neurons in vitro and for the dopaminergic nervous system of Caenorhabditis elegans in vivo. These findings suggest that microbe-derived environmental chemicals should be further investigated for their role in the pathogenesis of Parkinson's disease.

Translational insights into stem cell preconditioning: From molecular mechanisms to preclinical applications

Cell-based therapy (CBT) is a revolutionary approach for curing a variety of degenerative diseases. Stem cell-based regenerative medicine is a novel strategy for treating tissue damages regarding stem cells unique properties such as differentiation potential, paracrine impacts, and self-renewal ability. However, the current cell-based treatments encounter considerable challenges to be translated into clinical practice, including low cell survival, migration, and differentiation rate of transplanted stem cells. The poor stem cell therapy outcomes mainly originate from the unfavorable condition of damaged tissues for transplanted stem cells. The promising method of preconditioning improves cell resistance against the host environment's stress by imposing certain conditions similar to the harsh microenvironment of the damaged tissues on the transplanted stem cells. Various pharmacological, biological, and physical inducers are able to establish preconditioning. In addition to their known pharmacological effects on tissues and cells, these preconditioning agents improve cell biological aspects such as cell survival, proliferation, differentiation, migration, immunomodulation, paracrine impacts, and angiogenesis. This review focuses on different protocols and inducers of preconditioning along with underlying molecular mechanisms of their effects on stem cell behavior. Moreover, preclinical applications of preconditioned stem cells in various damaged organs such as heart, lung, brain, bone, cartilage, liver, and kidney are discussed with prospects of their translation into the clinic.

Therapeutic Potential of Berberine in the Treatment of Glioma: Insights into Its Regulatory Mechanisms

Glioma is known as one of the most common primary intracranial tumors accounting for four-fifths of malignant brain tumors. There are several biological pathways that play a synergistic, pathophysiological role in glioma, including apoptosis, autophagy, oxidative stress, and cell cycle arrest. According to previous rese arches, the drugs used in the treatment of glioma have been associated with significant limitations. Therefore, improved and/or new therapeutic platforms are required. In this regard, multiple flavonoids and alkaloids have been extensively studied in the treatment of glioma. Berberine is a protoberberine alkaloid with wide range of pharmacological activities, applicable to various pathological conditions. Few studies have reported beneficial roles of berberine in glioma. Berberine exerts its pharmacological functions in glioma by controlling different molecular and cellular pathways. We reviewed the existing knowledge supporting the use of berberine in the treatment of glioma and its effects on molecular and cellular mechanisms.

A human stem cell-derived test system for agents modifying neuronal N-methyl-D-aspartate-type glutamate receptor Ca2+-signalling

Methods to assess neuronal receptor functions are needed in toxicology and for drug development. Human-based test systems that allow studies on glutamate signalling are still scarce. To address this issue, we developed and characterized pluripotent stem cell (PSC)-based neural cultures capable of forming a functional network. Starting from a stably proliferating neuroepithelial stem cell (NESC) population, we generate “mixed cortical cultures” (MCC) within 24 days. Characterization by immunocytochemistry, gene expression profiling and functional tests (multi-electrode arrays) showed that MCC contain various functional neurotransmitter receptors, and in particular, the N-methyl-d-aspartate subtype of ionotropic glutamate receptors (NMDA-R). As this important receptor is found neither on conventional neural cell lines nor on most stem cell-derived neurons, we focused here on the characterization of rapid glutamate-triggered Ca²⁺ signalling. Changes of the intracellular free calcium ion concentration ([Ca²⁺]_i) were measured by fluorescent imaging as the main endpoint, and a method to evaluate and quantify signals in hundreds of cells at the same time was developed. We observed responses to glutamate in the low µM range. MCC responded to kainate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and a subpopulation of 50% had functional NMDA-R. The receptor was modulated by Mg²⁺, Zn²⁺ and Pb²⁺ in the expected ways, and various toxicologically relevant agonists (quinolinic acid, ibotenic acid, domoic acid) triggered [Ca²⁺]_i responses in MCC. Antagonists, such as phencyclidine, ketamine and dextromethorphan, were also readily identified. Thus, the MCC developed here may fill an important gap in the panel of test systems available to characterize the effects of chemicals on neurotransmitter receptors.

Emerging potential of cannabidiol in reversing proteinopathies

The aberrant accumulation of disease-specific protein aggregates accompanying cognitive decline is a pathological hallmark of age-associated neurological disorders, also termed as proteinopathies, including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and multiple sclerosis. Along with oxidative stress and neuroinflammation, disruption in protein homeostasis (proteostasis), a network that constitutes protein surveillance system, plays a pivotal role in the pathobiology of these dementia disorders. Cannabidiol (CBD), a non-psychotropic phytocannabinoid of Cannabis sativa, is known for its pleiotropic neuropharmacological effects on the central nervous system, including the ability to abate oxidative stress, neuroinflammation, and protein misfolding. Over the past years, compelling evidence has documented disease-modifying role of CBD in various preclinical and clinical models of neurological disorders, suggesting the potential therapeutic implications of CBD in these disorders. Because of its putative role in the proteostasis network in particular, CBD could be a potent modulator for reversing not only age-associated neurodegeneration but also other protein misfolding disorders. However, the current understanding is insufficient to underpin this proposition. In this review, we discuss the potentiality of CBD as a pharmacological modulator of the proteostasis network, highlighting its neuroprotective and aggregates clearing roles in the neurodegenerative disorders. We anticipate that the current effort will advance our knowledge on the implication of CBD in proteostasis network, opening up a new therapeutic window for aging proteinopathies.

Regulatory effects associated with changes in intracellular potassium level in susceptibility to mitochondrial depolarization and excitotoxicity

Excitotoxicity has been believed to be one of the causes of neurodegenerative diseases such as Alzheimer's disease and Huntington's disease. So far, much research has been done to suppress the neuronal excessive excitations, however, we still have not achieved full control, which may be due to the lack of some factors. As a matter of course, there is an urgent need to clarify all mechanisms that inhibit the onset and progression of neurodegenerative diseases. We found that potassium ion level regulation may be important in the sense that it suppresses mitochondrial depolarization rather than hyperpolarization of cell membrane potential. Minoxidil, an opener of ATP-activated potassium (K_ATP) channels decreased injury with middle cerebral artery occlusion in vivo experiment using TTC staining. In the primary cortical neurons, N-methyl-D-aspartate (NMDA)-induced mitochondrial depolarization was suppressed by minoxidil treatment. Minoxidil inhibited the increase in levels of cleaved caspase 3 and the release of cytochrome c into the cytosol, further reducing potassium ion levels. It was observed decreased potassium levels in neurons by the treatment of minoxidil. Those effects of minoxidil were blocked by glibenclamide. Therefore, it was suggested that minoxidil, via opening of K_ATP channels, reduced intracellular potassium ion level that contribute to mitochondrial depolarization, and suppressed subsequent NMDA-induced mitochondrial depolarization. Our findings suggest that the control of ion levels in neurons could dominate the onset and progression of neurodegenerative diseases.

Development of a neurotoxicity assay that is tuned to detect mitochondrial toxicants

Many neurotoxicants affect energy metabolism in man, but currently available test methods may still fail to predict mito- and neurotoxicity. We addressed this issue using LUHMES cells, i.e., human neuronal precursors that easily differentiate into mature neurons. Within the NeuriTox assay, they have been used to screen for neurotoxicants. Our new approach is based on culturing the cells in either glucose or galactose (Glc-Gal-NeuriTox) as the main carbohydrate source during toxicity testing. Using this Glc-Gal-NeuriTox assay, 52 mitochondrial and non-mitochondrial toxicants were tested. The panel of chemicals comprised 11 inhibitors of mitochondrial respiratory chain complex I (cI), 4 inhibitors of cII, 8 of cIII, and 2 of cIV; 8 toxicants were included as they are assumed to be mitochondrial uncouplers. In galactose, cells became more dependent on mitochondrial function, which made them 2-3 orders of magnitude more sensitive to various mitotoxicants. Moreover, galactose enhanced the specific neurotoxicity (destruction of neurites) compared to a general cytotoxicity (plasma membrane lysis) of the toxicants. The Glc-Gal-NeuriTox assay worked particularly well for inhibitors of cI and cIII, while the toxicity of uncouplers and non-mitochondrial toxicants did not differ significantly upon glucose ↔ galactose exchange. As a secondary assay, we developed a method to quantify the inhibition of all mitochondrial respiratory chain functions/complexes in LUHMES cells. The combination of the Glc-Gal-NeuriTox neurotoxicity screening assay with the mechanistic follow up of target site identification allowed both, a more sensitive detection of neurotoxicants and a sharper definition of the mode of action of mitochondrial toxicants.

Targeting the Blood-Brain Barrier to Prevent Sepsis-Associated Cognitive Impairment

Sepsis is a systemic inflammatory disease resulting from an infection. This disorder affects 750 000 people annually in the United States and has a 62% rehospitalization rate. Septic symptoms range from typical flu-like symptoms (eg, headache, fever) to a multifactorial syndrome known as sepsis-associated encephalopathy (SAE). Patients with SAE exhibit an acute altered mental status and often have higher mortality and morbidity. In addition, many sepsis survivors are also burdened with long-term cognitive impairment. The mechanisms through which sepsis initiates SAE and promotes long-term cognitive impairment in septic survivors are poorly understood. Due to its unique role as an interface between the brain and the periphery, numerous studies support a regulatory role for the blood-brain barrier (BBB) in the progression of acute and chronic brain dysfunction. In this review, we discuss the current body of literature which supports the BBB as a nexus which integrates signals from the brain and the periphery in sepsis. We highlight key insights on the mechanisms that contribute to the BBB's role in sepsis which include neuroinflammation, increased barrier permeability, immune cell infiltration, mitochondrial dysfunction, and a potential barrier role for tissue non-specific alkaline phosphatase (TNAP). Finally, we address current drug treatments (eg, antimicrobials and intravenous immunoglobulins) for sepsis and their potential outcomes on brain function. A comprehensive understanding of these mechanisms may enable clinicians to target specific aspects of BBB function as a therapeutic tool to limit long-term cognitive impairment in sepsis survivors.

Cell death at the cross roads of host-pathogen interaction in Mycobacterium tuberculosis infection

Tuberculosis (TB) continues to be the leading cause of death by any single infectious agent, accounting for around 1.7 million annual deaths globally, despite several interventions and support programs by national and international agencies. With the development of drug resistance in Mycobacterium tuberculosis (M. tb), there has been a paradigm shift in TB research towards host-directed therapy. The potential targets include the interactions between host and bacterial proteins that are crucial for pathogenesis. Hence, collective efforts are being made to understand the molecular details of host-pathogen interaction for possible translation into host-directed therapy. The present review focuses on 'host cell death modalities' of host-pathogen interaction, which play a crucial role in determining the outcome of TB disease progression. Several cell death modalities that occur in response to mycobacterial infection have been identified in human macrophages either as host defences for bacterial clearance or as pathogen strategies for multiplication and dissemination. These cell death modalities include apoptosis, necrosis, pyroptosis, necroptosis, pyronecrosis, NETosis, and autophagy. These processes are highly overlapping with several mycobacterial proteins participating in more than one cell death pathway. Until now, reviews in M. tb and host cell death have discussed either focusing on host evasion strategies, apoptosis, autophagy, and necrosis or describing all these forms with limited discussions of their role in host-pathogen interactions. Here, we present a comprehensive review of various mycobacterial factors modulating host cell death pathways and the cross-talk between them. Besides this, we have discussed the networking of host cell death pathways including the interference of host miRNA during M. tb infection with their respective targets. Through this review, we present the host targets that overlap across several cell death modalities and the technical limitations of methodology in cell death research. Given the compelling need to discover alternative drug target(s), this review identifies these overlapping cell death factors as potential targets for host-directed therapy.

Expression and Purification of Quinine Dihydro Pteridine Reductase from astrocytes and its significance in the astrocyte pathology

Quinine dihydropteridinereductase (QDPR) is involved in the synthesis of tetradihydrobiopteridine (BH4) that serve as cofactor for many aromatic hydroxylases including induced nitric oxide synthase (NOS) leading to NO production. Increased activity of QDPR has been associated with decrease levels of TGF-β, a cytokine that regulates the immune response and that elevated levels of NO has been associated with neurodegenerative diseases. Thus, expression of QDPR in astrocytes is essential to study the pathological changes observed in many neurodegenerative disorders. We have expressed QDPR in astrocytes and generated stably expressing clones that overexpresses QDPR. We further verified the specificity of QDPR expression using immunofluorescence and immunoblotting. To further confirm, we purified QDPR using Ni-NTA column and subjected the purified fraction to immunoblotting using anti-QDPR antibody and identified two major protein products of QDPR resolving at 25 and 17 kDa as reported in the literature. In order to further assess the significance of QDPR expression, we verified the expression of iNOS in QDPR over expressing cells. We show for the first time statistically significant up regulation of iNOS in QDPR overexpressing astrocytes. Increased expression of iNOS associated with astrocyte pathology seen in many neurodegenerative disorders may have implications in autoimmune neurodegenerative disorders.

DNA repair protein APE1 is involved in host response during pneumococcal meningitis and its expression can be modulated by vitamin B6

Background

The production of reactive oxygen species (ROS) during pneumococcal meningitis (PM) leads to severe DNA damage in the neurons and is the major cause of cell death during infection. Hence, the use of antioxidants as adjuvant therapy has been investigated. Previous studies have demonstrated the possible participation of apurinic/apyrimidinic endonuclease (APE1) during PM. The aims of this study were to investigate the APE1 expression in the cortical and hippocampal tissues of infant Wistar rats infected with Streptococcus pneumoniae and its association with cell death and understand the role of vitamin B6 (vitB6) as a protective factor against cell death.

Methods

APE1 expression and oxidative stress markers were analyzed at two-time points, 20 and 24 h post infection (p.i.), in the cortex (CX) and hippocampus (HC) of rats supplemented with vitB6. Statistical analyses were performed by the nonparametric Kruskal–Wallis test using Dunn’s post test.

Results

Our results showed high protein levels of APE1 in CX and HC of infected rats. In the CX, at 20 h p.i., vitB6 supplementation led to the reduction of expression of APE1 and apoptosis-inducing factor, while no significant changes in the transcript levels of caspase-3 were observed. Furthermore, levels of carbonyl content and glutamate in the CX were reduced by vitB6 supplementation at the same time point of 20 h p.i.. Since our data showed a significant effect of vitB6 on the CX at 20 h p.i. rather than that at 24 h p.i., we evaluated the effect of administering a second dose of vitB6 at 18 h p.i. and sacrifice at 24 h p.i.. Reduction in the oxidative stress and APE1 levels were observed, although the latter was not significant. Although the levels of APE1 was not significantly changed in the HC with vitB6 adjuvant therapy, vitB6 supplementation prevented the formation of the truncated form of APE1 (34 kDa) that is associated with apoptosis.

Conclusions

Our data suggest that PM affects APE1 expression, which can be modulated by vitB6. Additionally, vitB6 contributes to the reduction of glutamate and ROS levels. Besides the potential to reduce cell death and oxidative stress during neuroinflammation, vitB6 showed enhanced effect on the CX than on the HC during PM.

Pathological correlations between traumatic brain injury and chronic neurodegenerative diseases

Traumatic brain injury is among the most common causes of death and disability in youth and young adults. In addition to the acute risk of morbidity with moderate to severe injuries, traumatic brain injury is associated with a number of chronic neurological and neuropsychiatric sequelae including neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. However, despite the high incidence of traumatic brain injuries and the established clinical correlation with neurodegeneration, the causative factors linking these processes have not yet been fully elucidated. Apart from removal from activity, few, if any prophylactic treatments against post-traumatic brain injury neurodegeneration exist. Therefore, it is imperative to understand the pathophysiological mechanisms of traumatic brain injury and neurodegeneration in order to identify potential factors that initiate neurodegenerative processes. Oxidative stress, neuroinflammation, and glutamatergic excitotoxicity have previously been implicated in both secondary brain injury and neurodegeneration. In particular, reactive oxygen species appear to be key in mediating molecular insult in neuroinflammation and excitotoxicity. As such, it is likely that post injury oxidative stress is a key mechanism which links traumatic brain injury to increased risk of neurodegeneration. Consequently, reactive oxygen species and their subsequent byproducts may serve as novel fluid markers for identification and monitoring of cellular damage. Furthermore, these reactive species may further serve as a suitable therapeutic target to reduce the risk of post-injury neurodegeneration and provide long term quality of life improvements for those suffering from traumatic brain injury.

Imaging Axonal Degeneration and Repair in Preclinical Animal Models of Multiple Sclerosis

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Over time, this neurologic damage manifests clinically as debilitating motor and cognitive symptoms. Existing MS therapies focus on symptom relief and delay of disease progression through reduction of neuroinflammation. However, long-term strategies to remyelinate, protect, or regenerate axons have remained elusive, posing a challenge to treating progressive forms of MS. Preclinical mouse models and techniques, such as immunohistochemistry, flow cytometry, and genomic and proteomic analysis have provided advances in our understanding of discrete time-points of pathology following disease induction. More recently, in vivo and in situ two-photon (2P) microscopy has made it possible to visualize continuous real-time cellular behavior and structural changes occurring within the CNS during neuropathology. Research utilizing 2P imaging to study axonopathy in neuroinflammatory demyelinating disease has focused on five areas: (1) axonal morphologic changes, (2) organelle transport and health, (3) relationship to inflammation, (4) neuronal excitotoxicity, and (5) regenerative therapies. 2P imaging may also be used to identify novel therapeutic targets via identification and clarification of dynamic cellular and molecular mechanisms of axonal regeneration and remyelination. Here, we review tools that have made 2P accessible for imaging neuropathologies and advances in our understanding of axonal degeneration and repair in preclinical models of demyelinating diseases.

Recommendations from the INHAND Apoptosis/Necrosis Working Group

Historically, there has been confusion relating to the diagnostic nomenclature for individual cell death. Toxicologic pathologists have generally used the terms "single cell necrosis" and "apoptosis" interchangeably. Increased research on the mechanisms of cell death in recent years has led to the understanding that apoptosis and necrosis involve different cellular pathways and that these differences can have important implications when considering overall mechanisms of toxicity, and, for these reasons, the separate terms of apoptosis and necrosis should be used whenever differentiation is possible. However, it is also recognized that differentiation of the precise pathway of cell death may not be important, necessary, or possible in routine toxicity studies and so a more general term to indicate cell death is warranted in these situations. Morphological distinction between these two forms of cell death can sometimes be straightforward but can also be challenging. This article provides a brief discussion of the cellular mechanisms and morphological features of apoptosis and necrosis as well as guidance on when the pathologist should use these terms. It provides recommended nomenclature along with diagnostic criteria (in hematoxylin and eosin [H&E]-stained sections) for the most common forms of cell death (apoptosis and necrosis). This document is intended to serve as current guidance for the nomenclature of cell death for the International Harmonization of Nomenclature and Diagnostic Criteria Organ Working Groups and the toxicologic pathology community at large. The specific recommendations are:Use necrosis and apoptosis as separate diagnostic terms.Use modifiers to denote the distribution of necrosis (e.g., necrosis, single cell; necrosis, focal; necrosis, diffuse; etc.).Use the combined term apoptosis/single cell necrosis whenThere is no requirement or need to split the processes, orWhen the nature of cell death cannot be determined with certainty, orWhen both processes are present together. The diagnosis should be based primarily on the morphological features in H&E-stained sections. When needed, additional, special techniques to identify and characterize apoptosis can also be used.

The protective effect of melatonin on neural stem cell against LPS-induced inflammation

Stem cell therapy for tissue regeneration has several limitations in the fact that transplanted cells could not survive for a long time. For solving these limitations, many studies have focused on the antioxidants to increase survival rate of neural stem cells (NSCs). Melatonin, an antioxidant synthesized in the pineal gland, plays multiple roles in various physiological mechanisms. Melatonin exerts neuroprotective effects in the central nervous system. To determine the effect of melatonin on NSCs which is in LPS-induced inflammatory stress state, we first investigated nitric oxide (NO) production and cytotoxicity using Griess reagent assays, LDH assay, and neurosphere counting. Also, we investigated the effect of melatonin on NSCs by measuring the mRNA levels of SOX2, TLX, and FGFR-2. In addition, western blot analyses were performed to examine the activation of PI3K/Akt/Nrf2 signaling in LPS-treated NSCs. In the present study, we suggested that melatonin inhibits NO production and protects NSCs against LPS-induced inflammatory stress. In addition, melatonin promoted the expression of SOX2 and activated the PI3K/Akt/Nrf2 signaling under LPS-induced inflammation condition. Based on our results, we conclude that melatonin may be an important factor for the survival and proliferation of NSCs in neuroinflammatory diseases.

Regulation of apoptosis and innate immune stimuli in inflammation-induced preterm labor

An innate immune response is required for successful implantation and placentation. This is regulated, in part, by the a2 isoform of V-ATPase (a2V) and the concurrent infiltration of M1 (inflammatory) and M2 (anti-inflammatory) macrophages to the uterus and placenta. The objective of the present study was to identify the role of a2V during inflammation-induced preterm labor in mice and its relationship to the regulation of apoptosis and innate immune responses. Using a mouse model of infection-induced preterm delivery, gestational tissues were collected 8 h after intrauterine inoculation on day 14.5 of pregnancy with either saline or peptidoglycan (PGN; a TLR 2 agonist) and polyinosinic-polycytidylic acid [poly(I:C); a TLR3 agonist], modeling Gram-positive bacterial and viral infections, respectively. Expression of a2V decreased significantly in the placenta, uterus, and fetal membranes during PGN+poly(I:C)-induced preterm labor. Expression of inducible NO synthase was significantly upregulated in PGN+poly(I:C)-treated placenta and uterus. PGN+poly(I:C) treatment disturbed adherens junction proteins and increased apoptotic cell death via an extrinsic pathway of apoptosis among uterine decidual cells and spongiotrophoblasts. F4/80(+) macrophages were increased and polarization was skewed in PGN+poly(I:C)-treated uterus toward double-positive CD11c(+) (M1) and CD206(+) (M2) cells, which are critical for the clearance of dying cells and rapid resolution of inflammation. Expression of Nlrp3 and activation of caspase-1 were increased in PGN+poly(I:C)-treated uterus, which could induce pyroptosis. These results suggest that the double hit of PGN+poly(I:C) induces preterm labor via reduction of a2V expression and simultaneous activation of apoptosis and inflammatory processes.

Selective vulnerability of synaptic signaling and metabolism to nitrosative stress

SIGNIFICANCE

Nitric oxide (NO) plays diverse physiological roles in the central nervous system, where it modulates neuronal communication, regulates blood flow, and contributes to the innate immune responses. In a number of brain pathologies, the excessive production of NO also leads to the formation of reactive and toxic intermediates generically termed reactive nitrogen species (RNS). RNS cause irreversible or poorly reversible damage to brain cells.

RECENT ADVANCES

Recent work in the field focused on the ability of NO and RNS to yield protein modifications, including the S-nitrosation of cysteine residues, which, in many instances, impact cellular functions and viability.

CRITICAL ISSUES

The vast majority of neuropathological studies focus on the loss of cell viability, but nitrosative stress may also strongly impair the functions of neuronal processes: axonal projections and dendritic trees. The functional integrity of axons and dendrites critically depends on local metabolism and effective delivery of metabolic enzymes and organelles. Here, we summarize the existing literature describing the effects of nitrosative stress on the major pathways of energetic metabolism: glycolysis, tricarboxylic acid cycle, and mitochondrial respiration, with the emphasis on modifications of protein thiols.

FUTURE DIRECTIONS

We propose that axons and dendrites are highly vulnerable to nitrosative stress because of their low glycolytic capacity and high dependence on timely delivery of metabolic enzymes and organelles from the cell body. Thus, supplementation with the end products of glycolysis, pyruvate or lactate, may help preserve metabolism in distal neuronal processes and protect or restore synaptic function in the ailing brain.

Nitric oxide: considerations for the treatment of ischemic stroke

Some 40 years ago it was recognized by Furchgott and colleagues that the endothelium releases a vasodilator, endothelium-derived relaxing factor (EDRF). Later on, several groups identified EDRF to be a gas, nitric oxide (NO). Since then, NO was identified as one of the most versatile and unique molecules in animal and human biology. Nitric oxide mediates a plethora of physiological functions, for example, maintenance of vascular tone and inflammation. Apart from these physiological functions, NO is also involved in the pathophysiology of various disorders, specifically those in which regulation of blood flow and inflammation has a key role. The aim of the current review is to summarize the role of NO in cerebral ischemia, the most common cause of stroke.

Neuroprotective effects of diallyl sulfide against transient focal cerebral ischemia via anti-apoptosis in rats

OBJECTIVES

Diallyl sulfide (DAS) is the main organosulfur component of garlic and it is known for multiple pharmacological actions. Recent studies have demonstrated that DAS has neuroprotective effects against ischemia/reperfusion injury. While some of the possible mechanisms behind this protection have been explored, its ability to inhibit apoptosis has yet to be fully explained. In the present study, the effects of DAS on focal cerebral ischemia in rats were tested and its anti-apoptotic action was explored.

METHODS

To examine the protective effects of DAS, focal cerebral ischemia/reperfusion was induced in rats by transient middle cerebral artery occlusion for 2 hours followed by reperfusion for 24 hours. The animals received DAS in quantities of 100, 150, and 200 mg/kg (intraperitoneal; every day), for 7 days before transient middle cerebral artery occlusion. The neurological score and infarct volume were measured at 24 hours after the end of reperfusion. Apoptotic cells were counted by terminal dUTP nick end labeling staining and apoptotic mechanisms were studied by fluorescence immunohistochemistry staining and western blot analysis.

RESULTS

For animals with induced ischemia/reperfusion, those pretreated with 200 mg/kg DAS showed an infarct volume (22.36 ± 0.67%) significantly lower than that of the non-treated ischemia/reperfusion group (38.23 ± 0.72%), and the percentage of terminal dUTP nick-end labeling-positive cells (23.46 ± 1.02%) of the DAS-pretreated group was also significantly decreased compared to non-treated (36.41 ± 1.58%). Fluorescence immunohistochemistry staining and western blot analysis indicated that DAS reduced caspase-3 expression and increased Bcl-2 expression.

CONCLUSION

These results suggest that the mechanism by which DAS protects the brain from ischemia/reperfusion injury is related to its anti-apoptotic effects in part.

GFAP-independent inflammatory competence and trophic functions of astrocytes generated from murine embryonic stem cells

The directed generation of pure astrocyte cultures from pluripotent stem cells has proven difficult. Generation of defined pluripotent-stem-cell derived astrocytes would allow new approaches to the investigation of plasticity and heterogeneity of astrocytes. We here describe a two-step differentiation scheme resulting in the generation of murine embryonic stem cell (mESC) derived astrocytes (MEDA), as characterized by the upregulation of 19 astrocyte-associated mRNAs, and positive staining of most cells for GFAP (glial fibrillary acidic protein), aquaporin-4 or glutamine synthetase. The MEDA cultures could be cryopreserved, and they neither contained neuronal, nor microglial cells. They also did not react to the microglial stimulus lipopolysaccharide, while inflammatory activation by a complete cytokine mix (CCM) or its individual components (TNF-α, IL1-β, IFN-γ) was readily observed. MEDA, stimulated by CCM, became susceptible to CD95 ligand-induced apoptosis and produced NO and IL-6. This was preceded by NF-kB activation, and up-regulation of relevant mRNAs. Also GFAP-negative astrocytes were fully inflammation-competent. Neurotrophic support by MEDA was found to be independent of GFAP expression. In summary, we described here the generation and functional characterization of microglia-free murine astrocytes, displaying phenotypic heterogeneity as is commonly observed in brain astrocytes.

Evidence for cellular injury in the midbrain of rats following chronic constriction injury of the sciatic nerve

Complex behavioural disabilities, as well as pain, characterise neuropathic pain conditions for which clinical treatment is sought. In rats, chronic constriction injury (CCI) of the sciatic nerve evokes, allodynia and hyperalgesia as well as three distinct patterns of disability, characterised by changes in social and sleep-wake behaviours: (i) Pain & Disability; (ii) Pain & Transient Disability and (iii) Pain alone. Importantly, the degree of allodynia and hyperalgesia is identical for each of these groups. Social-interactions and sleep-wake behaviours are regulated by neural networks, which converge on the periaqueductal grey (PAG). Rats with Pain & Disability show astrocyte activation restricted to the lateral and ventrolateral PAG. Reactive astrocytes are a hallmark of cell death (apoptosis and necrosis). Quantitative real-time RT-PCR for the mRNAs encoding Bax, Bcl-2, heat shock protein 60 (HSP60), mitogen activated kinase kinase (MEK2) and iNOS was performed on the dorsal midbrains of individual, disability characterised rats, extending our earlier Gene-Chip data, showing a select up-regulation of Bax and MEK2 mRNA, and a down-regulation of HSP60 mRNA, in Pain & Disability rats. The anatomical location of TUNEL and cleaved-caspase-3 immunoreactive profiles in the midbrain was also identified. Rats with Pain & Disability showed: (i) pro-apoptotic ratios of Bax:Bcl-2 mRNAs; (ii) decreased HSP60 mRNA; (iii) increased iNOS and MEK2 mRNAs; (iv) TUNEL-positive profiles in the lateral and ventrolateral PAG; and (v) caspase-3 immunoreactive neurons in the mesencephalic nucleus of the trigeminal nerve. Cell death in these specific midbrain regions may underlie the disabilities characterising this subgroup of nerve-injured rats.

Engulfment of cerebral apoptotic bodies controls the course of prion disease in a mouse strain-dependent manner

Progressive accumulation of PrP(Sc), a hallmark of prion diseases, occurs when conversion of PrP(C) into PrP(Sc) is faster than PrP(Sc) clearance. Engulfment of apoptotic bodies by phagocytes is mediated by Mfge8 (milk fat globule epidermal growth factor 8). In this study, we show that brain Mfge8 is primarily produced by astrocytes. Mfge8 ablation induced accelerated prion disease and reduced clearance of cerebellar apoptotic bodies in vivo, as well as excessive PrP(Sc) accumulation and increased prion titers in prion-infected C57BL/6 × 129Sv mice and organotypic cerebellar slices derived therefrom. These phenotypes correlated with the presence of 129Sv genomic markers in hybrid mice and were not observed in inbred C57BL/6 Mfge8(-/-) mice, suggesting the existence of additional strain-specific genetic modifiers. Because Mfge8 receptors are expressed by microglia and depletion of microglia increases PrP(Sc) accumulation in organotypic cerebellar slices, we conclude that engulfment of apoptotic bodies by microglia may be an important pathway of prion clearance controlled by astrocyte-borne Mfge8.

Transnitrosylation of XIAP regulates caspase-dependent neuronal cell death

X-linked inhibitor of apoptosis (XIAP) is a potent antagonist of caspase apoptotic activity. XIAP also functions as an E3 ubiquitin ligase, targeting caspases for degradation. However, molecular pathways controlling XIAP activities remain unclear. Here, we report that nitric oxide (NO) reacts with XIAP by S-nitrosylating its RING domain (forming SNO-XIAP), thereby inhibiting E3 ligase and antiapoptotic activity. NO-mediated neurotoxicity and caspase activation have been linked to several neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases. We find significant SNO-XIAP formation in brains of patients with these diseases, implicating this reaction in the etiology of neuronal damage. Conversely, S-nitrosylation of caspases is known to inhibit apoptotic activity. Unexpectedly, we find that SNO-caspase transnitrosylates (transfers its NO group) to XIAP, forming SNO-XIAP, and thus promotes cell injury and death. These findings provide insights into the regulation of caspase activation in neurodegenerative disorders mediated, at least in part, by nitrosative stress.

Mitochondrial fragmentation and neuronal cell death in response to the Bcl-2/Bcl-x(L)/Bcl-w antagonist ABT-737

Inhibition of pro-survival Bcl-2 family proteins by BH3-only proteins is a key initial step leading to apoptotic cell death. In neurons, investigating cell death pathways is often hampered by the multi-factorial nature of the stress stimuli employed. Here we investigate the action of ABT-737, a small molecule inhibitor which specifically targets the BH3-protein binding domain of pro-survival Bcl-2, Bcl-X(L) and Bcl-w. ABT-737 produced a time- and concentration-dependent neuronal cell death which displayed the classical hallmarks of apoptosis. Cell death was maximal by around 4 h ABT-737 treatment, and the effect of ABT-737 could be delayed by the broad spectrum caspase inhibitor zVADfmk. Examining, using real-time confocal microscopy, the molecular basis for the onset of response demonstrated recruitment of pro-apoptotic Bax to specific mitochondrial foci, followed by mitochondrial fragmentation. Treatment of neurons with ABT-737 also produced cleavage of Bid, a BH3-only protein known to be a caspase substrate. Interestingly, cleaved Bid translocated to mitochondria but did not colocalise with Bax foci. zVADfmk inhibited Bid cleavage and slowed the rate of fragmentation, suggesting a role for cleaved Bid in the amplification of the apoptotic response. siRNA-mediated knockdown of Bax significantly inhibited ABT-737 induced cell death, whereas knockdown of the BH3-only proteins Bid or Bim had no effect. ABT-737 therefore appears to be a useful tool with which to examine neuronal apoptotic pathways. Our data suggests that caspase-dependent cleavage of Bid may be a downstream amplification event which enhances the rate of mitochondrial fragmentation.

Alteration of the nuclear pore complex in Ca(2+)-mediated cell death

Cell death requires coordinated intracellular signalling before disassembly of cell architecture by degradative enzymes. Although the death signalling cascades that involve the mitochondria, the ER and the plasma membrane have been extensively characterized, only a handful of studies have examined the functional and structural alterations of the nuclear pore complex (NPC) during neuronal death. Here, we show that during excitotoxic neuronal degeneration calpains redistributed across the nuclear envelope and mediated the degradation of NPC components causing altered permeability of the nuclear membrane. In primary dissociated neurons, simultaneous recording of cytosolic [Ca(2+)] and localization of fluorescent proteins showed that the onset of Ca(2+) overload signalled a progressive increase in the diffusion of small reporter molecules across the nuclear envelope. Later, calpain-mediated changes in nuclear pore permeability allowed accumulation of large proteins in the nucleus. Further, in a model of excitotoxic neuronal degeneration in Caenorhabditis elegans, we found similar nuclear changes and redistribution of fluorescent probes across the nuclear membrane in dying neurons. Our findings strongly suggest that increased leakiness of the nuclear barrier affects nucleocytoplasmic transport, alters the localization of proteins across the nuclear envelope and it is likely to be involved in Ca(2+)-dependent cell death, including ischemic neuronal demise.

Biochemical and cellular toxicology of peroxynitrite: implications in cell death and autoimmune phenomenon

Reactive nitrogen species include nitric oxide (.NO), peroxynitrite (ONOO(-)) and nitrogen dioxide radical (NO2*). Peroxynitrite is a reactive oxidant, produced from nitric oxide (*NO) and superoxide anion (O(2*-), that reacts with a variety of biological macromolecules. It is produced in the body in response to physiological stress and environmental toxins. It is a potent trigger of oxidative protein and DNA damage-including DNA strand breakage and base modification. It activates the nuclear enzyme poly-ADP ribose polymerase (PARP) resulting in energy depletion and apoptosis/necrosis of cells. Peroxynitrite generation is a crucial pathological mechanism in stroke, diabetes, inflammation, neurodegeneration, cancer, etc. Peroxynitrite modified DNA may also lead to the generation of autoantibodies in various autoimmune disorders such as systemic lupus erythematosus (SLE). In chronic inflammatory diseases, peroxynitrite formed by phagocytic cells may cause damage to DNA, generating neoepitopes leading to the production of autoantibodies. Hence, understanding the pathophysiology of peroxynitrite could lead to important therapeutic interventions.

Identification of candidate drugs for the treatment of ALS

A consortium of investigators interested in neurodegenerative diseases collaborated to screen 1040 drugs in multiple neurodegenerative disease assays. One model of amyotrophic lateral sclerosis (ALS) pathogenesis in particular incorporated glutamate exposure in enriched primary rat motor neuron cultures. In this model 78 compounds decreased motor neuron death caused by 100 microM glutamate. Almost all these pharmacological agents act at one or more of the following cellular targets: 1) protein synthesis inhibition; 2) Cox inhibition; 3) regulation of anion flux; 4) modulation of GABA receptors; 5) antioxidant, and 6) cell cycle inhibition. The most prevalent mode of action was the regulation of intracellular calcium. These data extend the understanding of motor neuron degeneration and identify a number of cellular targets for the improvement of combined therapies for neurodegenerative disease.

The complexity of neurobiological processes in acute ischemic stroke

There is an urgent need for improved diagnostics and therapeutics for acute ischemic stroke. This is the focus of numerous research projects involving in vitro studies, animal models and clinical trials, all of which are based on current knowledge of disease mechanisms underlying acute focal cerebral ischemia. Insight in the chain of events occurring during acute ischemic injury is essential for understanding current and future diagnostic and therapeutic approaches. In this review, we summarize the actual knowledge on the pathophysiology of acute ischemic stroke. We focus on the ischemic cascade, which is a complex series of neurochemical processes that are unleashed by transient or permanent focal cerebral ischemia and involves cellular bioenergetic failure, excitotoxicity, oxidative stress, blood-brain barrier dysfunction, microvascular injury, hemostatic activation, post-ischemic inflammation and finally cell death of neurons, glial and endothelial cells.

N-methyl-D-aspartate receptors mediate the phosphorylation and desensitization of muscarinic receptors in cerebellar granule neurons

Changes in synaptic strength mediated by ionotropic glutamate N-methyl-d-asparate (NMDA) receptors is generally considered to be the molecular mechanism underlying memory and learning. NMDA receptors themselves are subject to regulation through signaling pathways that are activated by G-protein-coupled receptors (GPCRs). In this study we investigate the ability of NMDA receptors to regulate the signaling of GPCRs by focusing on the G_q/11-coupled M₃-muscarinic receptor expressed endogenously in mouse cerebellar granule neurons. We show that NMDA receptor activation results in the phosphorylation and desensitization of M₃-muscarinic receptors through a mechanism dependent on NMDA-mediated calcium influx and the activity of calcium-calmodulin-dependent protein kinase II. Our study reveals a complex pattern of regulation where GPCRs (M₃-muscarinic) and NMDA receptors can feedback on each other in a process that is likely to influence the threshold value of signaling networks involved in synaptic plasticity.

Protective effect of quercetin against ICV colchicine-induced cognitive dysfunctions and oxidative damage in rats

Intracerebroventricular (i.c.v.) administration of colchicine, a microtubule-disrupting agent, causes cognitive dysfunction and oxidative stress. The present study was designed to investigate the protective effects of quercetin against colchicine-induced memory impairment and oxidative damage in rats. An i.c.v. cannula was implanted in the lateral ventricle of male Wistar rats. Colchicine was administered at dose of 15 microg/rat. Morris water maze and plus-maze performance tests were used to assess memory tasks. Various biochemical parameters such as lipid peroxidation, reduced glutathione, nitrite level, acetylcholinesterase and proteins were also assessed. Central administration of colchicine (15 microg/rat) showed poor retention of memory. Chronic treatment with quercetin (20 and 40 mg/kg, p.o.) twice daily for a period of 25 days beginning 4 days prior to colchicine injection significantly improved the colchicine-induced cognitive impairment. Biochemical analysis revealed that i.c.v. colchicine injection significantly increased lipid peroxidation, nitrite and depleted reduced glutathione activity in the brains of rats. Chronic administration of quercetin significantly attenuated elevated lipid peroxidation and restored the depleted reduced glutathione, acetylcholinesterase activity and nitrite activity. The results of the present study clearly indicated that quercetin has a neuroprotective effect against colchicine-induced cognitive dysfunctions and oxidative damage. This article was published online on 3 November 2008. An error was subsequently identified. This notice is included in the online and print version to indicate that both have been corrected.

Measurement of cellular beta-site of APP cleaving enzyme 1 activity and its modulation in neuronal assay systems

Amyloid-beta peptide (Abeta), a putatively causative agent of Alzheimer's disease (AD), is proteolytically derived from beta-amyloid precursor protein (APP). Here we describe cellular assays to detect the activity of the key protease beta-site of APP cleaving enzyme 1 (BACE1) based on an artificial reporter construct containing the BACE1 cleavage site of APP. These methods allow identification of inhibitors and indirect modulators of BACE1. In primary neuronal cultures transfected with human APP constructs (huAPP), Abeta production was modified by BACE1 inhibitors similarly to the production of endogenous murine Abeta in wild-type cells and to that of different transgenic neurons. To further improve the assay, we substituted the extracellular domain of APP by secreted alkaline phosphatase (SEAP). SEAP was easily quantified in the cell culture supernatants after cleavage of SEAP-APP by BACE1 or alpha-secretases. To render the assay specific for BACE1, the alpha-secretase cleavage site of SEAP-APP was eliminated either by site-directed mutagenesis or by substituting the transmembrane part of APP by the membrane domain of the erythropoietin receptor (EpoR). The pharmacology of these constructs was characterized in detail in HEK293 cells (human embryonic kidney cell line), and the SEAP-APP-EpoR construct was also introduced into primary murine neurons and there allowed specific measurement of BACE1 activity.

Nitric oxide, C-type natriuretic peptide and cGMP as regulators of endochondral ossification

Coordinated proliferation and differentiation of growth plate chondrocytes is required for endochondral bone growth, but the mechanisms and pathways that control these processes are not completely understood. Recent data demonstrate important roles for nitric oxide (NO) and C-type natriuretic peptide (CNP) in the regulation of cartilage development. Both NO and CNP stimulate the synthesis of cGMP and thus the activation of common downstream pathways. One of these downstream mediators, cGMP-dependent kinase II (cGKII), has itself been shown to be essential for normal endochondral bone formation. This review summarizes our knowledge of the roles and mechanisms of NO, CNP and cGKII signaling in cartilage and endochondral bone development.

Prolonged exposures of cerebellar granule neurons to S-nitroso-N-acetylpenicillamine (SNAP) induce neuronal damage independently of peroxynitrite

Nitric oxide (NO) induces cell proliferation or cell death, depending on the cell type involved, the isoform of nitric oxide synthase activated, and its cellular localisation. In neurons, the damaging effect of NO is usually attributed to the highly toxic peroxynitrite, formed by its reaction with superoxide. Peroxynitrite induces DNA damage and consequently the activation of poly (ADP-ribose) polymerase (PARP). This study set out to examine the contribution of peroxynitrite to the damage induced in cerebellar granule neurons (CGNs) by treatment with the NO donor S-nitroso-N-acetylpenicillamine (SNAP), for short (6 h) or prolonged (24 h) exposures. The Alamar blue assay was used to quantify CGN viability, which was also assessed by morphological examination. SNAP (10 microM-1 mM) induced a concentration- and time-dependent reduction of CGN viability, with associated damage to cell bodies and neurite processes evident following 100 microM SNAP treatments. Damage from 6 h exposures was prevented by the presence of haemoglobin (a NO scavenger), uric acid (a peroxynitrite scavenger), melatonin (a non-specific antioxidant), and by cyclosporin A (a permeability transition pore blocker). It was reduced by the PARP-1 inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-isoquinolinone (DPQ), whilst superoxide dismutase (SOD) potentiated the effects. Following 24 h exposure to SNAP, damage was only partially blocked by haemoglobin, melatonin, cyclosporin A and DPQ, but was not affected by uric acid or SOD. The data suggest that short exposure to NO induces neuronal damage through peroxynitrite produced by its interaction with superoxide, whereas a longer exposure to NO can induce damage partly by a mechanism which is independent of peroxynitrite formation.

The role of the complement cascade in endotoxin-induced septic encephalopathy

The complement system normally eliminates bacteria and has a protective effect. However, in an inflammatory setting such as sepsis, an exaggerated or insufficient activation of this cascade can have deleterious effect through the activation of glial cells, secretion of proinflammatory cytokines and generation of other toxic products. The aim of the present study was to investigate the role of the complement cascade in septic encephalopathy, through the passive injection of endotoxin/lipopolysaccharide (LPS) into mice overexpressing the potent complement inhibitor, CR1-related y (Crry-tg). Increased gliosis occurred in brains of endotoxemic mice. Concomitant with this, there was a significant rise in mRNA expression of GFAP, CD45 and proinflammatory molecules, TLR4, TNF-alpha and NO, in these brains. Consistent with the capacity of these inflammatory mediators, there was increased apoptosis as determined by DNA fragmentation and TUNEL staining on LPS treatment, which occurred through the Akt pathway. In addition, there was increased water content in brain, similar to cerebral edema observed in sepsis. Relative to wild-type mice, complement-inhibited mice had an attenuated inflammatory response, decreased edema and reduced apoptosis. Therefore, we demonstrate for the first time that the complement cascade appears to be one of the key players that cause brain pathology in an endotoxemic setting and therefore is a viable therapeutic target.

Oxidative stress and apoptosis: impact on cancer therapy

It is well established that some chemotherapeutic agents and radiation therapy generate reactive oxygen species (ROS) in patients during cancer therapy. Free radicals, particularly ROS have been proposed as common mediators for apoptosis. Recent studies have demonstrated that the mode of cell death depends on the severity of the oxidative damage. This review will address some of the current paradigms of oxidative stress, and antioxidants on apoptosis, and discuss the potential mechanisms by which oxidants can regulate apoptotic pathways. It will also review new developments in eliminating cancer cells by selectively inducing apoptosis.

Glycogen synthase kinase 3beta inhibition reduces the development of nonseptic shock induced by zymosan in mice

Glycogen synthase kinase 3 has recently been identified as a ubiquitous serine-threonine protein kinase that participates in a multitude of cellular processes and plays an important role in the pathophysiology of a number of diseases. In the present study, we have investigated the effects of 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), a glycogen synthase kinase 3beta inhibitor, on the development of nonseptic shock caused by zymosan (dose, 500 mg/kg i.p. suspension in saline) in mice. Organ failure and systemic inflammation in mice was assessed 18 h after administration of zymosan and/or TDZD-8; another group of mice was monitored for 12 days (for clinical score and mortality). Treatment of mice with TDZD-8 (dose, 10 mg/kg i.p., 1 and 6 h after zymosan administration) attenuated the peritoneal exudation and the migration of polymorphonuclear cells caused by zymosan. TDZD-8 also attenuated the lung, liver, and pancreatic injury, the renal dysfunction caused by zymosan, and the increase in myeloperoxidase activity caused by zymosan in the lung and in the intestine. Immunohistochemical analysis for inducible nitric oxide synthase, nitrotyrosine, poly(ADP-ribose), CD30, CD30 ligand, and Fas ligand revealed positive staining in lung and intestinal tissues obtained from zymosan-injected mice. The degree of staining for inducible nitric oxide synthase, nitrotyrosine, poly(ADP-ribose), CD30, CD30 ligand, and Fas ligand were markedly reduced in tissue sections obtained from zymosan-injected mice that had received TDZD-8. This study provides the first evidence that TDZD-8 attenuates the degree of zymosan-induced, nonseptic shock in mice.

Absence of functional alternative complement pathway alleviates lupus cerebritis

The complement inhibitor, Crry, which blocks both the classical and alternative pathways, alleviates CNS disease in the lupus model, MRL/MpJ-Tnfrsf6lpr (MRL/lpr) mice. To understand the role of the alternative pathway, we studied mice deficient in a key alternative pathway protein, complement factor B (fB). Immune deposits (IgG and C3) were reduced in the brains of MRL/lpr fB-deficient (fB-/-MRL/lpr) compared to fB-sufficient (MRL/lpr) mice, indicating reduced complement activation. Reduced neutrophil infiltration (22% of MRL/lpr mice) and apoptosis (caspase-3 activity was reduced to 33% of MRL/lpr mice) in these mice indicates that the absence of the alternative pathway was neuroprotective. Furthermore, expression of phospho (p)-Akt (0.16+/-0.02 vs. 0.35+/-0.13, p<0.03) was increased, while expression of p-PTEN (0.40+/-0.06 vs. 0.11+/-0.07, p<0.05) was decreased in fB-/-MRL/lpr mice compared to their MRL/lpr counterparts. The expression of fibronectin, laminin and collagen IV was significantly decreased in fB-/-MRL/lpr mice compared to MRL/lpr mice, indicating that in the lupus setting, tissue integrity was maintained in the absence of the alternative pathway. Absence of fB reduced behavioral alterations in MRL/lpr mice. Our results suggest that in lupus, the alternative pathway may be the key mechanism through which complement activation occurs in brain, and therefore it might serve as a therapeutic target for lupus cerebritis.

Inhibition of tyrosine kinase-mediated cellular signalling by Tyrphostins AG126 and AG556 modulates secondary damage in experimental spinal cord trauma

Protein tyrosine kinases help to regulate the expression of many genes, which play an important role in the pathophysiology of a number of diseases. Here we investigate the effects of the tyrosine kinase inhibitors, AG126 and AG556 on the degree of experimental spinal cord trauma induced by the application of vascular clips to the dura via a four-level T4-T8 laminectomy. Spinal cord injury in mice resulted in severe trauma characterized by oedema, neutrophil infiltration, production of a range of inflammatory mediators, tissue damage, and apoptosis. Treatment of the mice with AG126 and AG556 significantly reduced the degree of (1) spinal cord inflammation and tissue injury (histological score), (2) neutrophil infiltration (myeloperoxidase activity), (3) iNOS, nitrotyrosine, and PARP expression and (4) apoptosis (TUNEL staining and Bax and Bcl-2 expression). In a separate set of experiments, AG126 and AG556 significantly ameliorated the recovery of limb function (evaluated by motor recovery score). This study provides an experimental evidence that (1) prevention of the activation of protein tyrosine kinases reduces the development of inflammation and tissue injury associated with spinal cord trauma, and (2) inhibition of the activity of certain tyrosine kinases may represent a novel approach for the therapy of spinal cord trauma.

Phosphorylation and regulation of a G protein-coupled receptor by protein kinase CK2

We demonstrate a role for protein kinase casein kinase 2 (CK2) in the phosphorylation and regulation of the M₃-muscarinic receptor in transfected cells and cerebellar granule neurons. On agonist occupation, specific subsets of receptor phosphoacceptor sites (which include the SASSDEED motif in the third intracellular loop) are phosphorylated by CK2. Receptor phosphorylation mediated by CK2 specifically regulates receptor coupling to the Jun-kinase pathway. Importantly, other phosphorylation-dependent receptor processes are regulated by kinases distinct from CK2. We conclude that G protein–coupled receptors (GPCRs) can be phosphorylated in an agonist-dependent fashion by protein kinases from a diverse range of kinase families, not just the GPCR kinases, and that receptor phosphorylation by a defined kinase determines a specific signalling outcome. Furthermore, we demonstrate that the M₃-muscarinic receptor can be differentially phosphorylated in different cell types, indicating that phosphorylation is a flexible regulatory process where the sites that are phosphorylated, and hence the signalling outcome, are dependent on the cell type in which the receptor is expressed.

Apoptosis-inducing factor: A matter of neuron life and death

The mitochondrial flavoprotein apoptosis-inducing factor (AIF) is the main mediator of caspase-independent apoptosis-like programmed cell death. Upon pathological permeabilization of the outer mitochondrial membrane, AIF is translocated to the nucleus, where it participates in chromatin condensation and is associated to large-scale DNA fragmentation. Heavy down-regulation of AIF expression in mutant mice or reduced AIF expression achieved with small interfering RNA (siRNA) provides neuroprotection against acute neurodegenerative insults. Paradoxically, in addition to its pro-apoptotic function, AIF likely plays an anti-apoptotic role by regulating the production of reactive oxygen species (ROS) via its putative oxidoreductase and peroxide scavenging activities. In this review, we discuss accumulating evidence linking AIF to both acute and chronic neurodegenerative processes by emphasising mechanisms underlying the dual roles apparently played by AIF in these processes.