Platelet-activating factor as a potential retrograde messenger in CA1 hippocampal long-term potentiation

PAFAH1B3 Regulates Papillary Thyroid Carcinoma Cell Proliferation and Metastasis by Affecting the EMT

INTRODUCTION

Thyroid carcinoma (TC) is currently the prevalent type of endocrine malignancy worldwide, having an incidence of around 15.5 per 100,000 people. However, the underlying mechanisms of TC tumorigenesis remain to be further elucidated.

METHODS

Performing the database analyses, Platelet-activating factor acetylhydrolase 1B3 (PAFAH1B3) was found to be dysregulated in several carcinomas and might trigger tumor occurrence as well as the progression of TC. Clinicopathological information of patients from our local validated cohort and The Cancer Genome Atlas (TCGA) cohort also confirmed this hypothesis.

RESULTS

Our present research showed that elevated expression of PAFAH1B3 has a close association with worse behavior in papillary thyroid carcinoma (PTC). We utilized the small interfering RNA to obtain the PAFAH1B3-transfected PTC cell lines, including BCPAP, FTC-133, and TPC-1, and then further examined their biological function in vitro. Furthermore, gene set enrichment analysis suggested that PAFAH1B3 is implicated with epithelial-mesenchymal transition (EMT). Afterward, the western blotting assays aimed at EMT-related proteins were performed.

CONCLUSION

In short, our results revealed that silencing PAFAH1B3 could hinder the capabilities of proliferation, migration, and invasion of PTC cells. Increasing expression of PAFAH1B3 might be of quintessence with lymph node metastasis by triggering EMT in PTC patients.

Ginkgolide B improved postoperative cognitive dysfunction by inhibiting microgliosis-mediated neuroinflammation in the hippocampus of mice

Background

Postoperative cognitive dysfunction (POCD) are a common complication of the central nervous system following surgery and anesthesia. The specific pathogenesis and effective therapeutics of POCD need to be further studied. Ginkgolide B (GB), a platelet-activating factor receptor-specific antagonist, has been suggested to have strong anti-inflammatory effects. Here we tested the effects and mechanism of GB on POCD of aged rats.

Methods

Neurobehavioral tests were used to investigate the effect of GB pretreatment on POCD. The hippocampus were harvested to test the expression of proinflammatory cytokines by ELISA. The expression of the microglial marker ionized calcium-binding adaptor molecule-1 (Iba-1) in the hippocampus was evaluated by western blot assay and immunohistochemistry. A Nissl staining experiment was used to detect the neuronal numbers in the hippocampus.

Results

Surgery might result in the overexpression of platelet activating factor (PAF) in the plasma and hippocampus and might cause hippocampus-dependent memory impairment. GB pretreatment, inhibited the activation of microglia, reduced the levels of IL-1β and TNF-α, decreased the loss of neurons after surgery, and prevented POCD in aged rats.

Conclusion

Our findings suggested that PAF was involved in the development of POCD. Improvement of POCD by PAF antagonist GB was associated with the inhibition of microgliosis-mediated neuroinflammation and neuronal apoptosis in aged rats.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01750-1.

A Review of Oxidative Stress Products and Related Genes in Early Alzheimer's Disease

Oxidative stress is associated with the progression of Alzheimer’s disease (AD). Reactive oxygen species can modify lipids, DNA, RNA, and proteins in the brain. The products of their peroxidation and oxidation are readily detectable at incipient stages of disease. Based on these oxidation products, various biomarker-based strategies have been developed to identify oxidative stress levels in AD. Known oxidative stress-related biomarkers include lipid peroxidation products F2-isoprostanes, as well as malondialdehyde and 4-hydroxynonenal which both conjugate to specific amino acids to modify proteins, and DNA or RNA oxidation products 8-hydroxy-2’-deoxyguanosine (8-OHdG) and 8-hydroxyguanosine (8-OHG), respectively. The inducible enzyme heme oxygenase type 1 (HO-1) is found to be upregulated in response to oxidative stress-related events in the AD brain. While these global biomarkers for oxidative stress are associated with early-stage AD, they generally poorly differentiate from other neurodegenerative disorders that also coincide with oxidative stress. Redox proteomics approaches provided specificity of oxidative stress-associated biomarkers to AD pathology by the identification of oxidatively damaged pathology-specific proteins. In this review, we discuss the potential combined diagnostic value of these reported biomarkers in the context of AD and discuss eight oxidative stress-related mRNA biomarkers in AD that we newly identified using a transcriptomics approach. We review these genes in the context of their reported involvement in oxidative stress regulation and specificity for AD. Further research is warranted to establish the protein levels and their functionalities as well as the molecular mechanisms by which these potential biomarkers are involved in regulation of oxidative stress levels and their potential for determination of oxidative stress and disease status of AD patients.

Molecular mechanism of hippocampal long-term potentiation - Towards multiscale understanding of learning and memory

Long-term potentiation (LTP) of synaptic transmission is considered to be a cellular counterpart of learning and memory. Activation of postsynaptic NMDA type glutamate receptor (NMDA-R) induces trafficking of AMPA type glutamate receptors (AMPA-R) and other proteins to the synapse in sequential fashion. At the same time, the dendritic spine expands for long-term and modulation of actin underlies this (structural LTP or sLTP). How these changes persist despite constant diffusion and turnover of the component proteins have been the central focus of the current LTP research. Signaling triggered by Ca²⁺-influx via NMDA-R triggers kinase including Ca²⁺/calmodulin-dependent protein kinase II (CaMKII). CaMKII can sustain longer-term biochemical signaling by forming a reciprocally-activating kinase-effector complex with its substrate proteins including Tiam1, thereby regulating persistence of the downstream signaling. Furthermore, activated CaMKII can condense at the synapse through the mechanism of liquid-liquid phase separation (LLPS). This increases the binding capacity at the synapse, thereby contributing to the maintenance of enlarged protein complexes. It may also serve as the synapse tag, which captures newly synthesized proteins.

Platelet activating factor in the eye: Physiological roles, diseases and future perspectives

Platelet Activating Factor (PAF) is a known phospholipid mediator of inflammation. Since its first description in 1972, it has emerged as a key regulator of vital cellular signaling functions, as proliferation, cell adhesion, and apoptosis. Evidence suggests that interactions between PAF and its receptor (PAFR) play a critical role in nervous system tissues, including the retina. The retina is a very important constituent of the visual system, along with the cornea, sclera, choroid, iris, and ciliary body, that acts synergistically to provide vision and to maintain optical homeostasis. There is evidence that PAF may regulate a wide range of physiological functions in the visual system tissues, such as eye development, inflammation, epithelial wound healing, and synapsis. Due to their multiple functions, PAF and PAFR also have important pathological and clinical implications in ocular disorders such as Choroidal Neovascularization (CNV), Age Macular Degeneration, (AMD), Diabetic Retinopathy (DR), transplant responses, and pharmacological interactions. Studies with PAFR antagonists have shown promising results such as inhibition of neovascularization and chloroquine-induced retinopathies, as well as reducing inflammation and retinal cell death. Due to the importance of PAFR signaling in the visual system and ophthalmology research, this review aims to provide a general overview of current and future perspectives about PAF in eye biology.

Blocking pro-inflammatory platelet-activating factor receptors and activating cell survival pathways: A novel therapeutic strategy in experimental ischemic stroke

OBJECTIVE

Acute ischemic stroke triggers complex neurovascular, neuroinflammatory, and synaptic alterations. This study explores whether blocking pro-inflammatory platelet-activating factor receptor (PAF-R) plus selected docosanoids after middle cerebral artery occlusion (MCAo) would lead to neurological recovery. The following small molecules were investigated: (a) LAU-0901, a PAF-R antagonist that blocks pro-inflammatory signaling; and (b) derivatives of docosahexaenoic acid (DHA), neuroprotectin D1 (NPD1), and aspirin-triggered NPD1 (AT-NPD1), which activates cell survival pathways and are exert potent anti-inflammatory activity in the brain.

MATERIALS AND METHODS

Sprague-Dawley rats received 2 h MCAo and LAU-0901 (30 or 60 mg/kg, 2 h after stroke), NPD1, and AT-NPD1 (333 μg/kg), DHA (5 mg/kg), and their combination were administered intravenous at 3 h after stroke. Behavior testing and ex vivo magnetic resonance imaging were conducted on day 3 or 14 to assess lesion characteristics and lipidomic analysis on day 1. Series 1 (LAU-0901 + NPD1, 14d), Series 2 (LAU-0901 + AT-NPD1, 3d), and Series 3 (LAU-0901 + DHA, 1d).

RESULTS

All combinatory groups improved behavior compared to NPD1, AT-NPD1, or DHA treatments alone. Total lesion volumes were reduced with LAU-0901 + NPD1 by 62% and LAU-0901 + AT-NPD1 by 90% treatments versus vehicle groups. LAU-0901 and LAU-0901 + DHA increased the production of vasoactive lipid mediators (prostaglandins: PGE₂, PGF_{2- α}, 6-keto-PGF_{1- α}, and PGD₂) as well an inflammatory regulating mediator hydroxyoctadecadienoic acid. In contrast, LAU-0901 and LAU-0901 + DHA decreased the production of 12-hydroxyeicosatetraenoic acid, a pro-inflammatory mediator.

CONCLUSION

Combination therapy with LAU-0901 and selected docosanoids is more effective than the single therapy, affording synergistic neuroprotection, with restored pro-homeostatic lipid mediators and improved neurological recovery. Altogether, our findings support the combinatory therapy as the basis for future therapeutics for ischemic stroke.

Plasmalogens, platelet-activating factor and beyond - Ether lipids in signaling and neurodegeneration

Glycerol-based ether lipids including ether phospholipids form a specialized branch of lipids that in mammals require peroxisomes for their biosynthesis. They are major components of biological membranes and one particular subgroup, the plasmalogens, is widely regarded as a cellular antioxidant. Their vast potential to influence signal transduction pathways is less well known. Here, we summarize the literature showing associations with essential signaling cascades for a wide variety of ether lipids, including platelet-activating factor, alkylglycerols, ether-linked lysophosphatidic acid and plasmalogen-derived polyunsaturated fatty acids. The available experimental evidence demonstrates links to several common players like protein kinase C, peroxisome proliferator-activated receptors or mitogen-activated protein kinases. Furthermore, ether lipid levels have repeatedly been connected to some of the most abundant neurological diseases, particularly Alzheimer's disease and more recently also neurodevelopmental disorders like autism. Thus, we critically discuss the potential role of these compounds in the etiology and pathophysiology of these diseases with an emphasis on signaling processes. Finally, we review the emerging interest in plasmalogens as treatment target in neurological diseases, assessing available data and highlighting future perspectives. Although many aspects of ether lipid involvement in cellular signaling identified in vitro still have to be confirmed in vivo, the compiled data show many intriguing properties and contributions of these lipids to health and disease that will trigger further research.

PUFA and their derivatives in neurotransmission and synapses: a new hallmark of synaptopathies

PUFA of the n-3 and n-6 families are present in high concentration in the brain where they are major components of cell membranes. The main forms found in the brain are DHA (22 :6, n-3) and arachidonic acid (20:4, n-6). In the past century, several studies pinpointed that modifications of n-3 and n-6 PUFA levels in the brain through dietary supply or genetic means are linked to the alterations of synaptic function. Yet, synaptopathies emerge as a common characteristic of neurodevelopmental disorders, neuropsychiatric diseases and some neurodegenerative diseases. Understanding the mechanisms of action underlying the activity of PUFA at the level of synapses is thus of high interest. In this frame, dietary supplementation in PUFA aiming at restoring or promoting the optimal function of synapses appears as a promising strategy to treat synaptopathies. This paper reviews the link between dietary PUFA, synapse formation and the role of PUFA and their metabolites in synaptic functions.

Transcriptomic Analysis of Mecp2 Mutant Mice Reveals Differentially Expressed Genes and Altered Mechanisms in Both Blood and Brain

Rett syndrome is a rare neuropsychiatric disorder with a wide symptomatology including impaired communication and movement, cardio-respiratory abnormalities, and seizures. The clinical presentation is typically associated to mutations in the gene coding for the methyl-CpG-binding protein 2 (MECP2), which is a transcription factor. The gene is ubiquitously present in all the cells of the organism with a peak of expression in neurons. For this reason, most of the studies in Rett models have been performed in brain. However, some of the symptoms of Rett are linked to the peripheral expression of MECP2, suggesting that the effects of the mutations affect gene expression levels in tissues other than the brain. We used RNA sequencing in Mecp2 mutant mice and matched controls, to identify common genes and pathways differentially regulated across different tissues. We performed our study in brain and peripheral blood, and we identified differentially expressed genes (DEGs) and pathways in each tissue. Then, we compared the genes and mechanisms identified in each preparation. We found that some genes and molecular pathways that are differentially expressed in brain are also differentially expressed in blood of Mecp2 mutant mice at a symptomatic-but not presymptomatic-stage. This is the case for the gene Ube2v1, linked to ubiquitination system, and Serpin1, involved in complement and coagulation cascades. Analysis of biological functions in the brain shows the enrichment of mechanisms correlated to circadian rhythms, while in the blood are enriched the mechanisms of response to stimulus-including immune response. Some mechanisms are enriched in both preparations, such as lipid metabolism and response to stress. These results suggest that analysis of peripheral blood can reveal ubiquitous altered molecular mechanisms of Rett and have applications in diagnosis and treatments' assessments.

The Mixed-Lineage Kinase Inhibitor URMC-099 Protects Hippocampal Synapses in Experimental Autoimmune Encephalomyelitis

Treatments to stop gray matter degeneration are needed to prevent progressive disability in multiple sclerosis (MS). We tested whether inhibiting mixed-lineage kinases (MLKs), which can drive inflammatory microglial activation and neuronal degeneration, could protect hippocampal synapses in C57BL/6 mice with experimental autoimmune encephalomyelitis (EAE), a disease model that recapitulates the excitatory synaptic injury that occurs widely within the gray matter in MS. URMC-099, a broad spectrum MLK inhibitor with additional activity against leucine-rich repeat kinase 2 (LRRK2) and other kinases, prevented loss of PSD95-positive postsynaptic structures, shifted activated microglia toward a less inflammatory phenotype, and reversed deficits in hippocampal-dependent contextual fear conditioning in EAE mice when administered after the onset of motor symptoms. A narrow spectrum inhibitor designed to be highly selective for MLK3 failed to protect synapses in EAE hippocampi, and could not rescue cultured neurons from trophic deprivation in an in vitro model of MLK-driven neuronal degeneration. These results suggest that URMC-099 may have potential as a neuroprotective treatment in MS and demonstrate that a broad spectrum of inhibition against a combination of MLK and other kinases is more effective in neuroinflammatory disease than selectively targeting a single kinase.

The phospholipase A2 pathway controls a synaptic cholesterol ester cycle and synapse damage

The cellular prion protein (PrP^C) acts as a scaffold protein that organises signalling complexes. In synaptosomes, the aggregation of PrP^C by amyloid-β (Aβ) oligomers attracts and activates cytoplasmic phospholipase A₂ (cPLA₂), leading to synapse degeneration. The signalling platform is dependent on cholesterol released from cholesterol esters by cholesterol ester hydrolases (CEHs). The activation of cPLA₂ requires cholesterol released from cholesterol esters by cholesterol ester hydrolases (CEHs), enzymes dependent upon platelet activating factor (PAF) released by activated cPLA₂ This demonstrates a positive feedback system in which activated cPLA₂ increased cholesterol concentrations, which in turn facilitated cPLA₂ activation. PAF was also required for the incorporation of the tyrosine kinase Fyn and cyclooxygenase (COX)-2 into Aβ-PrP^C-cPLA₂ complexes. As a failure to deactivate signalling complexes can lead to pathology, the mechanisms involved in their dispersal were studied. PAF facilitated the incorporation of acyl-coenzyme A:cholesterol acyltransferase (ACAT)-1 into Aβ-PrP^C-cPLA₂-COX-2-Fyn complexes. The esterification of cholesterol reduced cholesterol concentrations, causing dispersal of Aβ-PrP^C-cPLA₂-COX-2-Fyn complexes and the cessation of signalling. This study identifies PAF as a key mediator regulating the cholesterol ester cycle, activation of cPLA₂ and COX-2 within synapses, and synapse damage.

Homozygous Expression of Mutant ELOVL4 Leads to Seizures and Death in a Novel Animal Model of Very Long-Chain Fatty Acid Deficiency

Lipids are essential components of the nervous system. However, the functions of very long-chain fatty acids (VLC-FA; ≥ 28 carbons) in the brain are unknown. The enzyme ELOngation of Very Long-chain fatty acids-4 (ELOVL4) catalyzes the rate-limiting step in the biosynthesis of VLC-FA (Agbaga et al., Proc Natl Acad Sci USA 105(35): 12843-12848, 2008; Logan et al., J Lipid Res 55(4): 698-708, 2014), which we identified in the brain as saturated fatty acids (VLC-SFA). Homozygous mutations in ELOVL4 cause severe neuropathology in humans (Ozaki et al., JAMA Neurol 72(7): 797-805, 2015; Mir et al., BMC Med Genet 15: 25, 2014; Cadieux-Dion et al., JAMA Neurol 71(4): 470-475, 2014; Bourassa et al., JAMA Neurol 72(8): 942-943, 2015; Aldahmesh et al., Am J Hum Genet 89(6): 745-750, 2011) and are post-natal lethal in mice (Cameron et al., Int J Biol Sci 3(2): 111-119, 2007; Li et al., Int J Biol Sci 3(2): 120-128, 2007; McMahon et al., Molecular Vision 13: 258-272, 2007; Vasireddy et al., Hum Mol Genet 16(5): 471-482, 2007) from dehydration due to loss of VLC-SFA that comprise the skin permeability barrier. Double transgenic mice with homozygous knock-in of the Stargardt-like macular dystrophy (STDG3; 797-801_AACTT) mutation of Elovl4 with skin-specific rescue of wild-type Elovl4 expression (S ⁺ Elovl4 ^mut/mut mice) develop seizures by P19 and die by P21. Electrophysiological analyses of hippocampal slices showed aberrant epileptogenic activity in S ⁺ Elovl4 ^mut/mut mice. FM1-43 dye release studies showed that synapses made by cultured hippocampal neurons from S ⁺ Elovl4 ^mut/mut mice exhibited accelerated synaptic release kinetics. Supplementation of VLC-SFA to cultured hippocampal neurons from mutant mice rescued defective synaptic release to wild-type rates. Together, these studies establish a critical, novel role for ELOVL4 and its VLC-SFA products in regulating synaptic release kinetics and epileptogenesis. Future studies aimed at understanding the molecular mechanisms by which VLC-SFA regulate synaptic function may provide new targets for improved seizure therapies.

From peroxisomal disorders to common neurodegenerative diseases - the role of ether phospholipids in the nervous system

The emerging diverse roles of ether (phospho)lipids in nervous system development and function in health and disease are currently attracting growing interest. Plasmalogens, a subgroup of ether lipids, are important membrane components involved in vesicle fusion and membrane raft composition. They store polyunsaturated fatty acids and may serve as antioxidants. Ether lipid metabolites act as precursors for the formation of glycosyl-phosphatidyl-inositol anchors; others, like platelet-activating factor, are implicated in signaling functions. Consolidating the available information, we attempt to provide molecular explanations for the dramatic neurological phenotype in ether lipid-deficient human patients and mice by linking individual functional properties of ether lipids with pathological features. Furthermore, recent publications have identified altered ether lipid levels in the context of many acquired neurological disorders including Alzheimer's disease (AD) and autism. Finally, current efforts to restore ether lipids in peroxisomal disorders as well as AD are critically reviewed.

Platelet Activating Factor Enhances Synaptic Vesicle Exocytosis Via PKC, Elevated Intracellular Calcium, and Modulation of Synapsin 1 Dynamics and Phosphorylation

Platelet activating factor (PAF) is an inflammatory phospholipid signaling molecule implicated in synaptic plasticity, learning and memory and neurotoxicity during neuroinflammation. However, little is known about the intracellular mechanisms mediating PAF’s physiological or pathological effects on synaptic facilitation. We show here that PAF receptors are localized at the synapse. Using fluorescent reporters of presynaptic activity we show that a non-hydrolysable analog of PAF (cPAF) enhances synaptic vesicle release from individual presynaptic boutons by increasing the size or release of the readily releasable pool and the exocytosis rate of the total recycling pool. cPAF also activates previously silent boutons resulting in vesicle release from a larger number of terminals. The underlying mechanism involves elevated calcium within presynaptic boutons and protein kinase C activation. Furthermore, cPAF increases synapsin I phosphorylation at sites 1 and 3, and increases dispersion of synapsin I from the presynaptic compartment during stimulation, freeing synaptic vesicles for subsequent release. These findings provide a conceptual framework for how PAF, regardless of its cellular origin, can modulate synapses during normal and pathologic synaptic activity.

Emerging Trends in Retrograde Signaling

Retrograde signaling is defined as the signaling events leading from the plastids to the nucleus in plants and across the chemical synapse, from the postsynaptic neuron to the presynaptic neuron in animals. The discovery of various retrograde messengers has opened many avenues and clouds of thoughts as to the role of retrograde signaling. They have been implicated particularly in long-term potentiation (LTP) and synaptic plasticity. But the basic assumptions about retrograde signaling have not been studied upon for many years. This review focuses on established facts and hypothesis put forward in retrograde signaling.

Lipidomic mass spectrometry and its application in neuroscience

Central and peripheral nervous systems are lipid rich tissues. Lipids, in the context of lipid-protein complexes, surround neurons and provide electrical insulation for transmission of signals allowing neurons to remain embedded within a conducting environment. Lipids play a key role in vesicle formation and fusion in synapses. They provide means of rapid signaling, cell motility and migration for astrocytes and other cell types that surround and play supporting roles neurons. Unlike many other signaling molecules, lipids are capable of multiple signaling events based on the different fragments generated from a single precursor during each event. Lipidomics, until recently suffered from two major disadvantages: (1) level of expertise required an overwhelming amount of chemical detail to correctly identify a vast number of different lipids which could be close in their chemical reactivity; and (2) high amount of purified compounds needed by analytical techniques to determine their structures. Advances in mass spectrometry have enabled overcoming these two limitations. Mass spectrometry offers a great degree of simplicity in identification and quantification of lipids directly extracted from complex biological mixtures. Mass spectrometers can be regarded to as mass analyzers. There are those that separate and analyze the product ion fragments in space (spatial) and those which separate product ions in time in the same space (temporal). Databases and standardized instrument parameters have further aided the capabilities of the spatial instruments while recent advances in bioinformatics have made the identification and quantification possible using temporal instruments.

Platelet activating factors in depression and coronary artery disease: a potential biomarker related to inflammatory mechanisms and neurodegeneration

The persistence of a depressive episode in coronary artery disease (CAD) patients not only heightens the risk of acute ischemic events, but it is also associated with accelerated cognitive decline. Antidepressant interventions for depression in CAD have only modest effects and novel approaches are limited by a poor understanding of etiological mechanisms. This review proposes that the platelet activating factor (PAF) family of lipids might be associated with the persistence of a depressive episode and related neurodegenerative pathology in CAD due to their association with leading etiological mechanisms for depression in CAD such as inflammation, oxidative and nitrosative stress, vascular endothelial dysfunction, and platelet reactivity. The evidence implicating PAFs in CAD, vascular pathology, and neurodegenerative processes is also presented. We also propose future directions for the investigation of PAFs as mediators of persistent depression. In summary, PAFs are implicated in leading mechanisms associated with depression in CAD. PAFs may therefore be associated with the persistence of depression in CAD and related to neurodegenerative and cognitive sequelae.

Developmental dynamics of PAFAH1B subunits during mouse brain development

Platelet-activating factor (PAF) mediates an array of biological processes in the mammalian central nervous system as a bioactive lipid messenger in synaptic function and dysfunction (plasticity, memory, and neurodegeneration). The intracellular enzyme that deacetylates the PAF (PAFAH1B) is composed of a tetramer of two catalytic subunits, ALPHA1 (PAFAH1B3) and ALPHA2 (PAFAH1B2), and a regulatory dimer of LIS1 (PAFAH1B1). We have investigated the mouse PAFAH1B subunit genes during brain development in normal mice and in mice with a hypomorphic allele for Lis1 (Lis1/sLis1; Cahana et al. [2001] Proc Natl Acad Sci U S A 98:6429-6434). We have analyzed quantitatively (by means of real-time polymerase chain reaction) and qualitatively (by in situ hybridization techniques) the amounts and expression patterns of their transcription in developing and postnatal brain, focusing mainly on differences in two laminated encephalic regions, the forebrain (telencephalon) and hindbrain (cerebellum) separately. The results revealed significant differences in cDNA content between these two brain subdivisions but, more importantly, between the LIS1 complex subunits. In addition, we found significant spatial differences in gene expression patterns. Comparison of results obtained with Lis1/sLis1 analysis also revealed significant temporal and spatial differences in Alpha1 and Lis1 expression levels. Thus, small changes in the amount of the Lis1 gene may differentially regulate expression of Alpha1 and Alpha2, depending on the brain region, which suggests different roles for each LIS1 complex subunit during neural differentiation and neural migration.

The pharmacology of neuroplasticity induced by non-invasive brain stimulation: building models for the clinical use of CNS active drugs

The term neuroplasticity encompasses structural and functional modifications of neuronal connectivity. Abnormal neuroplasticity is involved in various neuropsychiatric diseases, such as dystonia, epilepsy, migraine, Alzheimer's disease, fronto-temporal degeneration, schizophrenia, and post cerebral stroke. Drugs affecting neuroplasticity are increasingly used as therapeutics in these conditions. Neuroplasticity was first discovered and explored in animal experimentation. However, non-invasive brain stimulation (NIBS) has enabled researchers recently to induce and study similar processes in the intact human brain. Plasticity induced by NIBS can be modulated by pharmacological interventions, targeting ion channels, or neurotransmitters. Importantly, abnormalities of plasticity as studied by NIBS are directly related to clinical symptoms in neuropsychiatric diseases. Therefore, a core theme of this review is the hypothesis that NIBS-induced plasticity can explore and potentially predict the therapeutic efficacy of CNS-acting drugs in neuropsychiatric diseases. We will (a) review the basics of neuroplasticity, as explored in animal experimentation, and relate these to our knowledge about neuroplasticity induced in humans by NIBS techniques. We will then (b) discuss pharmacological modulation of plasticity in animals and humans. Finally, we will (c) review abnormalities of plasticity in neuropsychiatric diseases, and discuss how the combination of NIBS with pharmacological intervention may improve our understanding of the pathophysiology of abnormal plasticity in these diseases and their purposeful pharmacological treatment.

Presynaptic LTP and LTD of excitatory and inhibitory synapses

Ubiquitous forms of long-term potentiation (LTP) and depression (LTD) are caused by enduring increases or decreases in neurotransmitter release. Such forms or presynaptic plasticity are equally observed at excitatory and inhibitory synapses and the list of locations expressing presynaptic LTP and LTD continues to grow. In addition to the mechanistically distinct forms of postsynaptic plasticity, presynaptic plasticity offers a powerful means to modify neural circuits. A wide range of induction mechanisms has been identified, some of which occur entirely in the presynaptic terminal, whereas others require retrograde signaling from the postsynaptic to presynaptic terminals. In spite of this diversity of induction mechanisms, some common induction rules can be identified across synapses. Although the precise molecular mechanism underlying long-term changes in transmitter release in most cases remains unclear, increasing evidence indicates that presynaptic LTP and LTD can occur in vivo and likely mediate some forms of learning.

Superior Neuroprotective Efficacy of LAU-0901, a Novel Platelet-Activating Factor Antagonist, in Experimental Stroke

Platelet-activating factor (PAF) accumulates during cerebral ischemia, and inhibition of this process plays a critical role in neuronal survival. Recently, we demonstrated that LAU-0901, a novel PAF receptor antagonist, is neuroprotective in experimental stroke. We used magnetic resonance imaging in conjunction with behavior and immunohistopathology to expand our understanding of this novel therapeutic approach. Sprague–Dawley rats received 2 h middle cerebral artery occlusion (MCAo) and were treated with LAU-0901 (60 mg/kg) or vehicle 2 h from MCAo onset. Behavioral function, T2-weighted imaging (T2WI), and apparent diffusion coefficients were performed on days 1, 3, and 7 after MCAo. Infarct volume and number of GFAP, ED-1, and NeuN-positive cells were conducted on day 7. Behavioral deficit was significantly improved by LAU-0901 treatment compared to vehicle on days 1, 3, and 7. Total lesion volumes computed from T2WI were significantly reduced by LAU-0901 on days 1, 3, and 7 (by 83%, 90%, and 96%, respectively), which was consistent with decreased edema formation. Histopathology revealed that LAU-0901 treatment resulted in significant reduction of cortical and subcortical infarct volumes, attenuated microglial infiltration, and promoted astrocytic and neuronal survival. These findings suggest LAU-0901 is a promising neuroprotectant and provide the basis for future therapeutics in patients suffering ischemic stroke.

Platelet-activating factor receptor antagonism targets neuroinflammation in experimental epilepsy

PURPOSE

Temporal lobe epilepsy is associated with the inflammatory process related to the basic mechanisms that lead to seizure susceptibility and brain damage. Platelet-activating factor (PAF), a potent, short-lived phospholipid mediator of inflammation, participates in physiologic signaling in the brain. However, after seizures, PAF accumulates in the brain and activates intracellular signaling related with inflammation-mediated excitotoxicity and hippocampal hyperexcitability. The objective of this study is to evaluate the effect of PAF antagonism on hippocampal hyperexcitability, seizure susceptibility, and neuroprotection using the kindling paradigm and pilocarpine-induced seizure damage models.

METHODS

The PAF antagonist, LAU-0901 (60 mg/kg, i.p.), or vehicle, was administrated each day of kindling or daily during the 4 weeks after status epilepticus (SE). We analyzed seizure severity, electrical activity, cellular damage, and inflammation in the hippocampi of both treated groups.

KEY FINDINGS

LAU-0901 limits the progression of kindling and attenuates seizure susceptibility 1 week after the kindling procedure. In addition, under the seizure-damage conditions studied here, we observed that LAU-0901 induces hippocampal neuroprotection and limits somatostatin interneuronal cell loss and inflammation.

SIGNIFICANCE

Our results indicate that modulation of PAF overactivity attenuates seizure susceptibility, hippocampal hyperexcitability, and neuroinflammation.

Recent progress in phospholipase A₂ research: from cells to animals to humans

Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.

GABAergic activities control spike timing- and frequency-dependent long-term depression at hippocampal excitatory synapses

GABAergic interneuronal network activities in the hippocampus control a variety of neural functions, including learning and memory, by regulating θ and γ oscillations. How these GABAergic activities at pre- and postsynaptic sites of hippocampal CA1 pyramidal cells differentially contribute to synaptic function and plasticity during their repetitive pre- and postsynaptic spiking at θ and γ oscillations is largely unknown. We show here that activities mediated by postsynaptic GABA_ARs and presynaptic GABA_BRs determine, respectively, the spike timing- and frequency-dependence of activity-induced synaptic modifications at Schaffer collateral-CA1 excitatory synapses. We demonstrate that both feedforward and feedback GABA_AR-mediated inhibition in the postsynaptic cell controls the spike timing-dependent long-term depression of excitatory inputs (“e-LTD”) at the θ frequency. We also show that feedback postsynaptic inhibition specifically causes e-LTD of inputs that induce small postsynaptic currents (<70 pA) with LTP-timing, thus enforcing the requirement of cooperativity for induction of long-term potentiation at excitatory inputs (“e-LTP”). Furthermore, under spike-timing protocols that induce e-LTP and e-LTD at excitatory synapses, we observed parallel induction of LTP and LTD at inhibitory inputs (“i-LTP” and “i-LTD”) to the same postsynaptic cells. Finally, we show that presynaptic GABA_BR-mediated inhibition plays a major role in the induction of frequency-dependent e-LTD at α and β frequencies. These observations demonstrate the critical influence of GABAergic interneuronal network activities in regulating the spike timing- and frequency-dependences of long-term synaptic modifications in the hippocampus.

PAF-AH Catalytic Subunits Modulate the Wnt Pathway in Developing GABAergic Neurons

Platelet-activating factor acetylhydrolase 1B (PAF-AH) inactivates the potent phospholipid platelet-activating factor (PAF) and is composed of two catalytic subunits (α1 and α2) and a dimeric regulatory subunit, LIS1. The function of the catalytic subunits in brain development remains unknown. Here we examined their effects on proliferation in the ganglionic eminences and tangential migration. In α1 and α2 catalytic subunits knockout mice we noticed an increase in the size of the ganglionic eminences resulting from increased proliferation of GABAergic neurons. Our results indicate that the catalytic subunits act as negative regulators of the Wnt signaling pathway. Overexpression of each of the PAF-AH catalytic subunits reduced the amount of nuclear beta-catenin and provoked a shift of this protein from the nucleus to the cytoplasm. In the double mutant mice, Wnt signaling increased in the ganglionic eminences and in the dorsal part of the cerebral cortex. In situ hybridization revealed increased and expanded expression of a downstream target of the Wnt pathway (Cyclin D1), and of upstream Wnt components (Tcf4, Tcf3 and Wnt7B). Furthermore, the interneurons in the cerebral cortex were more numerous and in a more advanced position. Transplantation assays revealed a non-cell autonomous component to this phenotype, which may be explained in part by increased and expanded expression of Sdf1 and Netrin-1. Our findings strongly suggest that PAF-AH catalytic subunits modulate the Wnt pathway in restricted areas of the developing cerebral cortex. We hypothesize that modulation of the Wnt pathway is the evolutionary conserved activity of the PAF-AH catalytic subunits.

H2O2 and PAF mediate Abeta1-42-induced Ca2+ dyshomeostasis that is blocked by EGb761

Calcium (Ca2+) dyshomeostasis may be of pivotal importance in mediating the neurotoxic action of amyloid beta peptide (Abeta), but the mechanism whereby Abeta disrupts Ca2+ homeostasis remains unclear. Using hippocampal neuronal cultures, the present study investigated possible mechanisms underlying Ca2+ dyshomeostasis induced by the oligomeric form of Abeta1-42 and two possible mediators of its toxicity, hydrogen peroxide (H2O2) and platelet-activating factor (PAF). It was found that, both H2O2 and PAF were able to reproduce each of the events induced by oligomeric Abeta1-42, including (a) Ca2+ influx via N-methyl-D-aspartic acid (NMDA) receptors, (b) enhancement of Ca2+ response to NMDA via activation of protein kinase C (PKC), (c) the increase of extracellular concentrations of glutamate and (d) the increase in cytosolic free Ca2+ ([Ca2+]i). Moreover, each of these events could be blocked by Ginkgo biloba extract EGb761, a free radical scavenger with PAF antagonism, and by quercetin, a constituent with well-established free radical scavenging property. In contrast, ginkgolide B, another constituent of EGb761 with well-established PAF-antagonizing activity protected the neurons against Ca2+ dyshomeostasis induced by Abeta1-42 and PAF, but not by H2O2. These results suggested the possibility that Abeta1-42-induced Ca2+ dyshomeostasis might be mediated by formation of toxic mediators such as H2O2 and PAF. Therefore, increased production of toxic mediators such as H2O2 and PAF in the brain may be critical in the pathological mechanism of neurodegenerative diseases, particularly Alzheimer's disease (AD), and may serve as major therapeutic targets for these diseases.

Platelet-activating factor-induced synaptic facilitation is associated with increased calcium/calmodulin-dependent protein kinase II, protein kinase C and extracellular signal-regulated kinase activities in the rat hippocampal CA1 region

Platelet-activating factor (PAF) is an important inflammatory lipid mediator affecting neural plasticity. In the present study, we demonstrated how PAF affects synaptic efficacy through activation of protein kinases in the rat hippocampal CA1 region. In cultured hippocampal neurons, 10 to 1000 nM PAF stimulated autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) and phosphorylation of synapsin I and myristoylated alanine-rich protein kinase C substrate (MARCKS). In hippocampal CA1 slices, field excitatory postsynaptic potentials (fEPSPs) induced by stimulation of the Schaffer collateral/commissural pathways were significantly increased 10-50 min after exposure to 100 to 1000 nM PAF. Immunoblotting analysis showed that 100 nM PAF treatment for 10 or 50 min significantly and persistently increased CaMKII autophosphorylation in the hippocampal CA1 region. Increased protein kinase Calpha (PKCalpha) autophosphorylation was also seen at the same time point after PAF exposure. By contrast, extracellular signal-regulated kinase (ERK) phosphorylation was slightly but significantly increased at 10 min after PAF exposure. Consistent with increased CaMKII autophosphorylation, AMPA-type glutamate receptor subunit 1 (GluR1) (Ser-831) phosphorylation as a CaMKII postsynaptic substrate significantly increased after 10 or 50 min of treatment, whereas synapsin I (Ser-603) phosphorylation as a presynaptic substrate increased at 10 min in the hippocampal CA1 region. Phosphorylation of MARCKS (Ser-152/156) and NMDA receptor subunit 1 (NR1) (Ser-896) as PKCalpha substrates also significantly increased after 10 min but had not further increased by 50 min in the CA1 region. Increased of fEPSPs induced by PAF treatment completely and/or partly inhibited by KN93 and/or U0126 treatment. These results suggest that PAF induces synaptic facilitation through activation of CaMKII, PKC and ERK in the hippocampal CA1 region.

LAU-0901, a novel platelet-activating factor receptor antagonist, confers enduring neuroprotection in experimental focal cerebral ischemia in the rat

LAU-0901, a novel platelet-activating factor (PAF) receptor antagonist, is highly neuroprotective in a rodent model of cerebral ischemia. This study was conducted to establish whether the neuroprotection induced by LAU-0901 persists with chronic survival. Male Sprague-Dawley rats were anesthetized with isoflurane and subjected to 2 h of temporary middle cerebral artery occlusion (MCAo) induced by means of a poly-L-lisine-coated intraluminal nylon suture. Animals were treated with either LAU-0901 (60 mg/kg) or vehicle (45% cyclodextran) administered i.p. at 2 h from onset of MCAo. They received neurobehavioral examinations during MCAo (60 min) and then at 1, 2, 3, 7, 14, 21 and 28 days followed by histopathology at 30 days. LAU-0901 significantly improved the behavior compared to the vehicle group, beginning on day 1 (by 29%, p=0.00007) and persisting throughout a 30-day survival period (42%, p=0.0001). Compared with vehicle treatment, LAU-0901 treatment significantly increased volume of non-infarcted brain tissue loss relative to the unlesioned hemisphere (16.3 +/- 4.6% vs. 46.0 +/- 10.3%, respectively). These results establish that LAU-0901 confers enduring ischemic neuroprotection.

LAU-0901, a novel platelet-activating factor antagonist, is highly neuroprotective in cerebral ischemia

Platelet-activating factor (PAF) is a bioactive phospholipid that accumulates during ischemia-reperfusion and is involved in the activation of platelets, neutrophils, and pro-inflammatory signaling. PAF has been suggested to enhance brain ischemia-reperfusion damage. LAU-0901, a novel PAF receptor antagonist, was examined in models of focal cerebral ischemia in rats and mice. Sprague-Dawley rats were anesthetized and received 2-hour middle cerebral artery occlusion (MCAo) by intraluminal suture. LAU-0901 (30, 60, 90 mg/kg; n=9-11) or vehicle (n=11) was administered i.p. at 2 h after onset of MCAo. The neurological status was evaluated at 60 min, and on days 1, 2, 3 and 7 after MCAo. In the dose-response study in mice, C57BL/6 mice were anesthetized and received 1 h MCAo by intraluminal suture. LAU-0901 (15, 30, 60 mg/kg; n=7-9) or vehicle (n=8) was given i.p. at 1 h after onset of MCAo. Local cerebral blood flow (LCBF) was measured at 1, 2, 4, and 6 h after MCAo in mice. LAU-0901 treated rats showed improved neurological score throughout the 7-day survival period. LAU-0901 treatment (30, 60 and 90 mg/kg) reduced total corrected infarct volume compared to vehicle rats by 76, 88 and 90%, respectively. Mice treated with LAU-0901 (30 and 60 mg/kg) reduced total infarction by 29% and 66%, respectively. LCBF was improved by treatment with LAU-0901 (30 mg/kg) by 77% of baseline at 6 h. In conclusion, we demonstrate for the first time that LAU-0901 improves behavioral scores, LCBF and reduces infarct volume after focal cerebral ischemia in rats and mice. Thus, this PAF receptor antagonist exhibits potent and sustained neuroprotection that may be of value for the design of stroke therapies.

Phospholipases A(2) in the genome of the sea anemone Nematostella vectensis

The genome of the sea anemone Nematostella vectensis (Nv) (Cnidaria, Anthozoa) was sequenced recently (Putnam et al., Science 317: 86, 2007). In the current study, 22 proteins of Nv were identified as putative phospholipases A(2) (PLA(2)) that showed up to 40-50% sequence identity with secreted or intracellular PLA(2)s including those of humans. Nv1-Nv6 PLA(2)s have identity with secreted human group (G)IB and GIIA PLA(2)s and PLA(2)s of the sea anemones Adamsia carciniopados and Urticina crassicornis. Nv7 and Nv8 PLA(2)s have identity with human and bee venom GIII PLA(2)s and Nv9 PLA(2) with GXIIA PLA(2). Nv10-Nv13 PLA(2)s show identity with GIX PLA(2) of Conus magus and bacterial PLA(2)s but no significant identity with any human PLA(2). Nv14 has identity with intracellular GIV PLA(2), Nv15 with GVII PLA(2), Nv16 and Nv17 with GVIII PLA(2), Nv18-Nv20 with GVI PLA(2), and Nv21 and Nv22 with patatin, respectively. The observations indicate that the cnidarian phospholipasome contains a rich array of orthologs of most types of animal PLA(2)s, and that many of the PLA(2)-driven vital functions prevail in these ancient metazoans. Cnidarian PLA(2)s may be considered as evolutionary precursors of PLA(2)s of higher animals.

Ginkgolides protect against amyloid-beta1-42-mediated synapse damage in vitro

Background

The early stages of Alzheimer's disease (AD) are closely associated with the production of the Aβ_1–42 peptide, loss of synapses and gradual cognitive decline. Since some epidemiological studies showed that EGb 761, an extract from the leaves of the Ginkgo biloba tree, had a beneficial effect on mild forms of AD, the effects of some of the major components of the EGb 761 extract (ginkgolides A and B, myricetin and quercetin) on synapse damage in response to Aβ_1–42 were examined.

Results

The addition of Aβ_1–42 to cortical or hippocampal neurons reduced the amounts of cell associated synaptophysin, a pre-synaptic membrane protein that is essential for neurotransmission, indicating synapse damage. The effects of Aβ_1–42 on synapses were apparent at concentrations approximately 100 fold less than that required to kill neurons; the synaptophysin content of neuronal cultures was reduced by 50% by 50 nM Aβ_1–42. Pre-treatment of cortical or hippocampal neuronal cultures with ginkgolides A or B, but not with myrecitin or quercetin, protected against Aβ_1–42-induced loss of synaptophysin. This protective effect was achieved with nanomolar concentrations of ginkgolides. Previous studies indicated that the ginkgolides are platelet-activating factor (PAF) receptor antagonists and here we show that Aβ_1–42-induced loss of synaptophysin from neuronal cultures was also reduced by pre-treatment with other PAF antagonists (Hexa-PAF and CV6209). PAF, but not lyso-PAF, mimicked the effects Aβ_1–42 and caused a dose-dependent reduction in the synaptophysin content of neurons. This effect of PAF was greatly reduced by pre-treatment with ginkgolide B. In contrast, ginkgolide B did not affect the loss of synaptophysin in neurons incubated with prostaglandin E₂.

Conclusion

Pre-treatment with ginkgolides A or B protects neurons against Aβ_1–42-induced synapse damage. These ginkgolides also reduced the effects of PAF, but not those of prostaglandin E₂, on the synaptophysin content of neuronal cultures, results consistent with prior reports that ginkgolides act as PAF receptor antagonists. Such observations suggest that the ginkgolides are active components of Ginkgo biloba preparations and may protect against the synapse damage and the cognitive loss seen during the early stages of AD.

A neuroscientist's guide to lipidomics

Nerve cells mould the lipid fabric of their membranes to ease vesicle fusion, regulate ion fluxes and create specialized microenvironments that contribute to cellular communication. The chemical diversity of membrane lipids controls protein traffic, facilitates recognition between cells and leads to the production of hundreds of molecules that carry information both within and across cells. With so many roles, it is no wonder that lipids make up half of the human brain in dry weight. The objective of neural lipidomics is to understand how these molecules work together; this difficult task will greatly benefit from technical advances that might enable the testing of emerging hypotheses.

Platelet-activating factor contributes to the induction of long-term potentiation in the rat somatosensory cortex in vitro

The contribution of platelet-activating factor (PAF) to the induction of neocortical LTP was examined in rat brain slices containing the primary somatosensory cortex (SI). Field potentials evoked by single pulse stimulation in cortical layer IV were recorded from layer II/III. In control experiments, tetanic high frequency stimulation (HFS) resulted in input-specific, NMDA receptor-dependent LTP (21.1+/-3.2%; mean+/-SEM; n=15; P<0.001). BN-52021 (5 microM), an antagonist at the extracellular PAF receptor, weakened the HFS-induced LTP to 12.4+/-2.7% (n=11; P<0.05). In contrast, HFS-induced LTP was significantly enhanced to 29.4+/-2.3% (n=11; P<0.05) when brain slices were superfused with ACSF containing the PAF receptor-agonist C-PAF (1.5 microM). The difference between LTP weakened by BN-52021 and LTP enhanced by C-PAF was highly significant (P<0.0005). These results suggest a physiological contribution of PAF to the induction of LTP in neocortical area SI. This contribution of PAF is mediated by an action at extracellular receptor sites.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

Synaptic activity becomes excitotoxic in neurons exposed to elevated levels of platelet-activating factor

Neurologic impairment in HIV-1-associated dementia (HAD) and other neuroinflammatory diseases correlates with injury to dendrites and synapses, but how such injury occurs is not known. We hypothesized that neuroinflammation makes dendrites susceptible to excitotoxic injury following synaptic activity. We report that platelet-activating factor, an inflammatory phospholipid that mediates synaptic plasticity and neurotoxicity and is dramatically elevated in the brain during HAD, promotes dendrite injury following elevated synaptic activity and can replicate HIV-1-associated dendritic pathology. In hippocampal slices exposed to a stable platelet-activating factor analogue, tetanic stimulation that normally induces long-term synaptic potentiation instead promoted development of calcium- and caspase-dependent dendritic beading. Chemical preconditioning with diazoxide, a mitochondrial ATP-sensitive potassium channel agonist, prevented dendritic beading and restored long-term potentiation. In contrast to models invoking excessive glutamate release, these results suggest that physiologic synaptic activity may trigger excitotoxic dendritic injury during chronic neuroinflammation. Furthermore, preconditioning may represent a novel therapeutic strategy for preventing excitotoxic injury while preserving physiologic plasticity.

Variations in genes regulating neuronal migration predict reduced prefrontal cognition in schizophrenia and bipolar subjects from mediterranean Spain: A preliminary study

Both neural development and prefrontal cortex function are known to be abnormal in schizophrenia and bipolar disorder. In order to test the hypothesis that these features may be related with genes that regulate neuronal migration, we analyzed two genomic regions: the lissencephaly critical region (chromosome 17p) encompassing the LIS1 gene and which is involved in human lissencephaly; and the genes related to the platelet-activating-factor, functionally related to LIS1, in 52 schizophrenic patients, 36 bipolar I patients and 65 normal control subjects. In addition, all patients and the 25 control subjects completed a neuropsychological battery. Thirteen (14.8%) patients showed genetic variations in either two markers related with lissencephaly or in the platelet-activating-factor receptor gene. These patients performed significantly worse in the Wisconsin Card Sorting Test-Perseverative Errors in comparison with patients with no lissencephaly critical region/platelet-activating-factor receptor variations. The presence of lissencephaly critical region/platelet-activating-factor receptor variations was parametrically related to perseverative errors, and this accounted for 17% of the variance (P = 0.0001). Finally, logistic regression showed that poor Wisconsin Card Sorting Test-Perseverative Errors performance was the only predictor of belonging to the positive lissencephaly critical region/platelet-activating-factor receptor group. These preliminary findings suggest that the variations in genes involved in neuronal migration predict the severity of the prefrontal cognitive deficits in both disorders.

Lipid signaling: sleep, synaptic plasticity, and neuroprotection

Increasing evidence indicates that bioactive lipids participate in the regulation of synaptic function and dysfunction. We have demonstrated that signaling mediated by platelet-activating factor (PAF) and cyclooxygenase (COX)-2-synthesized PGE2 is involved in synaptic plasticity, memory, and neuronal protection [Clark GD, Happel LT, Zorumski CF, Bazan NG. Enhancement of hippocampal excitatory synaptic transmission by platelet-activating factor. Neuron 1992; 9:1211; Kato K, Clark GD, Bazan NG, Zorumski CF. Platelet-activating factor as a potential retrograde messenger in CA1 hippocampal long-term potentiation. Nature 1994; 367:175; Izquierdo I, Fin C, Schmitz PK, et al. Memory enhancement by intrahippocampal, intraamygdala or intraentorhinal infusion of platelet-activating factor measured in an inhibitory avoidance. Proc Natl Acad Sci USA 1995; 92:5047; Chen C, Magee CJ, Bazan NG. Cyclooxygenase-2 regulates prostaglandin E2 signaling in hippocampal long-term synaptic plasticity. J Neurophysiol 2002; 87:2851]. Recently, we found that prolonged continuous wakefulness (primarily rapid eye movement (REM)-sleep deprivation, SD) causes impairments in hippocampal long-term synaptic plasticity and hippocampus-dependent memory formation [McDermott CM, LaHoste GJ, Chen C, Musto A, Bazan NG, Magee JC. Sleep deprivation causes behavioral, synaptic, and membrane excitability alterations in hippocampal neurons. J Neurosci 2003; 23:9687]. To explore the mechanisms underlying SD-induced impairments, we have studied several bioactive lipids in the hippocampus following SD. It appears that SD causes increases in prostaglandin D2 (PGD2) and 2-arachidonylglycerol (2-AG), and a decrease in PGE2, suggesting that these lipid messengers participate in memory consolidation during REM sleep. We have also explored the formation of endogenous neuroprotective lipids. Toward this aim, we have used ischemia-reperfusion damage and LC-PDA-ESI-MS-MS-based lipidomic analysis and identified docosanoids derived from synaptic phospholipid-enriched docosahexaenoic acid. Some of the docosanoids exert potent neuroprotective bioactivity [Marcheselli VL, Hong S, Lukiw WJ, et al. Novel docosanoids inhibit brain ischemia-reperfusion-mediated leukocyte infiltration and pro-inflammatory gene expression. J Biol Chem 2003; 278:43807; Mukherjee PK, Marcheselli VL, Serhan CN, Bazan, NG. Neuroprotectin D1: A docosahexaenoic acid-derived docosatriene protects human retinal pigment epithelial cells from oxidative stress. Proc Nat Acad Sci USA 2004; 101:8491). Taken together, these observations that signaling lipids participate in synaptic plasticity, cognition, and survival indicate that lipid signaling is closely associated with several functions (e.g; learning and memory, sleep, and experimental stroke) and pathologic events. Alterations in endogenous signaling lipids or their receptors resulting from drug abuse lead to changes in synaptic circuitry and induce profound effects on these important functions. In the present article, we will briefly review bioactive lipids involved in sleep, synaptic transmission and plasticity, and neuroprotection, focusing mainly on our experimental studies and how these signaling molecules are related to functions and implicated in some neurologic disorders.

Terpene trilactones from Gingko biloba: from ancient times to the 21st century

Ginkgolides were always close to my heart. I continue to be strongly attracted to Ginkgo biloba, the ginkgolides and bilobalide. Starting in 1963, I became fascinated by these molecules while working on their isolation and structure elucidation in Sendai. Presumably, due to the ginkgolide studies, I received an invitation to join the faculty at Columbia University. After almost three decades of not touching the ginkgolide project, we have unexpectedly resumed the studies, at this time because of their enigmatic biological effects. This account is a reflection on earlier studies, as well as an outline of our current work.

Lipid signaling in neural plasticity, brain repair, and neuroprotection

The extensive networking of the cells of the nervous system results in large cell membrane surface areas. We now know that neuronal membranes contain phospholipid pools that are the reservoirs for the synthesis of specific lipid messengers on neuronal stimulation or injury. These messengers in turn participate in signaling cascades that can either promote neuronal injury or neuroprotection. Prostaglandins are synthesized as a result of cyclooxygenase activity. In the first step of the arachidonic acid cascade, the short-lived precursor, prostaglandin H2, is synthesized. Additional steps in the cascade result in the synthesis of an array of prostaglandins, which participate in numerous physiological and neurological processes. Our laboratory recently reported that the membrane polyunsaturated fatty acid, docosahexaenoic acid, is the precursor of oxygenation products now known as the docosanoids, some of which are powerful counter-proinflammatory mediators. The mediator 10,17S-docosatriene (neuroprotectin D1, NPD1) counteracts leukocyte infiltration, NF-kappa activation, and proinflammatory gene expression in brain ischemia-reperfusion and is an apoptostatic mediator, potently counteracting oxidative stress-triggered apoptotic DNA damage in retinal pigment epithelial cells. NPD1 also upregulates the anti-apoptotic proteins Bcl-2 and Bcl-xL and decreases pro-apoptotic Bax and Bad expression. Another biologically active messenger derived from membrane phospholipids in response to synaptic activity is platelet-activating factor (PAF). The tight regulation of the balance between synthesis (via phospholipases) and degradation (via acetylhydrolases) of PAF modulates the functions of this lipid messenger. Under pathological conditions, this balance is tipped, and PAF becomes a proinflammatory mediator and neurotoxic agent. The newly discovered docosahexaenoic acid signaling pathways, as well as other lipid messengers related to synaptic activation, may lead to the clarification of clinical issues relevant to stroke, age-related macular degeneration, spinal cord injury, Alzheimer's disease, and other diseases that include neuroinflammatory components.

Platelet-activating factor enhances the expression of nerve growth factor in normal human astrocytes under hypoxia

Nerve growth factor (NGF) is required for the survival of neurons. We have addressed the effect of platelet-activating factor (PAF), one of the mediators of ischemic injury of the brain, on NGF expression in astrocytes. Normal human astrocytes in culture were stimulated with PAF, and levels of NGF mRNA and protein were analyzed by reverse transcription-polymerase chain reaction (RT-PCR), real-time quantitative PCR and enzyme-linked immunosorbent assay (ELISA). PAF increased the expressions of NGF mRNA and protein in astrocytes in time- and concentration-dependent manners. After 48-h stimulation, 10 nmol/L PAF increased the levels of NGF protein in astrocyte-conditioned medium by 1.4-fold. The PAF-induced stimulation of NGF expression was further enhanced (2.1-fold of the control) in the cells under hypoxic culture condition. BN52021 (Ginkgolide B), an antagonist for PAF binding sites, suppressed the effect of PAF. We conclude that PAF enhances NGF gene expression in human astrocytes, and the PAF-induced increase in the expression of NGF under hypoxia may benefit the protection of the nervous tissue by promoting neuronal survival.

Preparation of a tritiated ginkgolide

Ginkgolide B, a constituent of the tree Ginkgo biloba, was radiolabeled with the beta-emitter tritium ([(3)H]) in two steps from ginkgolide C. First, a triflate precursor was prepared utilizing the selective reactivity of 7-OH in ginkgolide C; the triflate was then reduced with sodium borotritide to yield tritiated ginkgolide B ([(3)H]GB) in good yield and high specific activity. The tritiated ginkgolide will be an important tool for studying neuromodulatory properties of ginkgolides.

Platelet-activating factor receptor and respiratory and metabolic responses to hypoxia and hypercapnia

Activation of the platelet-activating factor receptor (PAFR) regulates neural transmission. A PAFR blocker reduced the peak hypoxic (pHVR) but not hypercapnic ventilatory (HCVR) responses in rats [Am. J. Physiol. 275 (1998) R604]. To further examine the role of PAFR in respiratory control, genotype-verified PAFR -/- and PAFR +/+ adult male mice underwent hypoxic and hypercapnic challenges. HCVR was similar in the two groups (p-NS). However, pHVR was significantly reduced in PAFR -/- mice (38 +/- 13% baseline [S.D.]) compared to PAFR +/+ mice (78 +/- 16% baseline; P < 0.001, ANOVA), with reduced tidal volume recruitments during pHVR. In addition, hypoxic ventilatory depression was attenuated in PAFR -/- mice (P < 0.01), and was primarily due to attenuation of the time-dependent decreases in oxygen consumption during sustained hypoxia (P < 0.01). Thus, PAFR expression/function modulates components of the acute ventilatory and metabolic adaptations to hypoxia but not to hypercapnia. Imbalances in PAFR activity may lead to maladaptive regulation of the tightly controlled metabolic-ventilatory relationships during hypoxia.

Interplay among platelet-activating factor, oxidative stress, and group I metabotropic glutamate receptors modulates neuronal survival

Platelet-activating factor (PAF) is a potent phospholipid messenger in the nervous system that participates in synaptic plasticity and in pathologic processes, including neurodegeneration. Oxidative stress plays important roles in neuronal cell death. To define the interaction between PAF and oxidative radicals in neuronal death, we studied the effects of PAF in the presence of oxidative radicals in primary neurons in culture. Exogenous PAF (50 microM) caused PAF receptor-independent injury to neurons. A nonneurotoxic PAF concentration (500 nM) potentiated neuronal death caused by hydrogen peroxide as determined by lactate dehydrogenase (LDH) assay, Hoechst staining, and TUNEL analysis, but it did not potentiate neuronal death caused by menadione, a superoxide donor, or by the nitric oxide donors 3-morpholino-sydnonimine (SIN-1) and sodium nitroprusside (SNP). This potentiation of the hydrogen peroxide effect was selectively blocked by a PAF membrane-receptor antagonist, BN52021 (5 microM). The neurotoxic effect of PAF and hydrogen peroxide was also completely blocked by ebselen and partially decreased by pretreatment with (S)-3,5-dihydroxyphenylglycine (DHPG), a group I metabotropic glutamate receptor (mGluR) agonist. This study suggests that PAF-receptor antagonists may be useful for neuroprotection. A similar effect might also be obtained with group I mGluR agonists, probably by way of a different underlying mechanism.

Involvement of the NMDA receptor/nitric oxide signal pathway in platelet-activating factor-induced neurotoxicity

Platelet-activating factor (PAF), a bioactive phospholipid implicated in neuronal excitotoxic death, augments the presynaptic release of glutamate. Excessive activation of postsynaptic glutamate receptors and subsequent downstream signals leads to excitotoxicity. The present study proposed that the NMDA receptor/nitric oxide (NO) signal pathway might be involved in PAF-induced neurotoxicity. After the cultured neurons were exposed to PAF for 24 h the percentage of neuronal death increased in a dose-dependent manner. The PAF effects were significantly prevented not only by BN52021, a PAF antagonist, but also by MK-801, an NMDA antagonist, and L-NAME, an NO synthase (NOS) inhibitor. Moreover, the increases in NOS activity and neuronal NOS expression induced by chronic exposure of the cultured neurons to PAF were dramatically blocked by BN52021 and MK-801, respectively. Our findings suggest that the NMDA receptor/NO signaling pathway might contribute to the pathological mechanism of cell death triggered via PAF receptor activation.

Platelet-activating factor receptor-deficient mice are protected from experimental sleep apnea-induced learning deficits

Intermittent hypoxia (IH) during sleep, a hallmark of sleep apnea, is associated with neurobehavioral impairments, regional neurodegeneration and increased oxidative stress and inflammation in rodents. Platelet-activating factor (PAF) is an important mediator of both normal neural plasticity and brain injury. We report that mice deficient in the cell surface receptor for PAF (PAFR-/-), a bioactive mediator of oxidative stress and inflammation, are protected from the spatial reference learning deficits associated with IH. Furthermore, PAFR-/- exhibit attenuated elevations in inflammatory signaling (cyclo-oxygenase-2 and inducible nitric oxide synthase activities), degradation of the ubiquitin-proteasome pathway and apoptosis observed in wild-type littermates (PAFR+/+) exposed to IH. Collectively, these findings indicate that inflammatory signaling and neurobehavioral impairments induced by IH are mediated through PAF receptors.