Acetylcholine-induced production of platelet-activating factor by human fetal brain cells in culture

Forty Years Since the Structural Elucidation of Platelet-Activating Factor (PAF): Historical, Current, and Future Research Perspectives

In the late 1960s, Barbaro and Zvaifler described a substance that caused antigen induced histamine release from rabbit platelets producing antibodies in passive cutaneous anaphylaxis. Henson described a ‘soluble factor’ released from leukocytes that induced vasoactive amine release in platelets. Later observations by Siraganuan and Osler observed the existence of a diluted substance that had the capacity to cause platelet activation. In 1972, the term platelet-activating factor (PAF) was coined by Benveniste, Henson, and Cochrane. The structure of PAF was later elucidated by Demopoulos, Pinckard, and Hanahan in 1979. These studies introduced the research world to PAF, which is now recognised as a potent phospholipid mediator. Since its introduction to the literature, research on PAF has grown due to interest in its vital cell signalling functions and more sinisterly its role as a pro-inflammatory molecule in several chronic diseases including cardiovascular disease and cancer. As it is forty years since the structural elucidation of PAF, the aim of this review is to provide a historical account of the discovery of PAF and to provide a general overview of current and future perspectives on PAF research in physiology and pathophysiology.

Current Understanding of Platelet-Activating Factor Signaling in Central Nervous System Diseases

Platelet-activating factor (PAF) is a bioactive lipid mediator which serves as a reciprocal messenger between the immune and nervous systems. PAF, a pluripotent inflammatory mediator, is extensively expressed in many cells and tissues and has either beneficial or detrimental effects on the progress of inflammation-related neuropathology. Its wide distribution and various biological functions initiate a cascade of physiological or pathophysiological responses during development or diseases. Current evidence indicates that excess PAF accumulation in CNS diseases exacerbates the inflammatory response and pathological consequences, while application of PAF inhibitors or PAFR antagonists by blocking this signaling pathway significantly reduces inflammation, protects cells, and improves the recovery of neural functions. In this review, we integrate the current findings of PAF signaling in CNS diseases and elucidate topics less appreciated but important on the role of PAF signaling in neurological diseases. We propose that the precise use of PAF inhibitors or PAFR antagonists that target the specific neural cells during the appropriate temporal window may constitute a potential therapy for CNS diseases.

Attenuated Reactive Gliosis and Enhanced Functional Recovery Following Spinal Cord Injury in Null Mutant Mice of Platelet-Activating Factor Receptor

Platelet-activating factor (PAF) is a unique phosphoglycerine that mediates the biological functions of both immune and nervous systems. Excessive PAF plays an important role in neural injury via its specific receptor (PAFR). In this study, we hypothesized that PAF signaling activates reactive gliosis after spinal cord injury (SCI), and blocking the PAF pathway would modify the glia scar formation and promote functional recovery. PAF microinjected into the normal wild-type spinal cord induced a dose-dependent activation of microglia and astrocytes. In the SCI mice, PAFR null mutant mice showed a better functional recovery in grip and rotarod performances than wild-type mice. Although both microglia and astrocytes were activated after SCI in wild-type and PAFR null mutant mice, expressions of IL-6, vimentin, nestin, and GFAP were not significantly elevated in PAFR null mutants. Disruption of PAF signaling inhibited the expressions of proteoglycan CS56 and neurocan (CSPG3). Intriguingly, compared to the wild-type SCI mice, less axonal retraction/dieback at 7 dpi but more NFH-labeled axons at 28 dpi was found in the area adjacent to the epicenter in PAFR null mutant SCI mice. Moreover, treatment with PAFR antagonist Ginkgolide B (GB) at the chronic phase rather than acute phase enhanced the functional recovery in the wild-type SCI mice. These findings suggest that PAF signaling participates in reactive gliosis after SCI, and blocking of this signaling enhances functional recovery and to some extent may promote axon regrowth.

Antidepressant imipramine induces human astrocytes to differentiate into cells with neuronal phenotype

Several recent studies have expanded our conception of the role of astrocytes in neurogenesis, proposing that these cells may contribute to this phenomenon not only as a source of trophic substances, but also as stem cells themselves. We recently observed in vitro that human mature astrocytes can be induced to differentiate into cells with a neuronal phenotype. Antidepressant drugs have been shown to increase neurogenesis in the adult rodent hippocampus. In order to better understand the role of astroglia in antidepressant-induced neurogenesis, primary astrocyte cultures were treated with the antidepressant imipramine. Cell morphology was rapidly modified by treatment. In fact, whereas untreated astrocytes showed large, flat morphology, after a few hours of treatment cells exhibited a round-shaped cell body with long, thin processes. The expression of neuronal markers was analysed by immunocytochemistry, Western Blot and RT-PCR at different treatment times. Results showed an increase in neuronal markers such as neurofilament and neuron-specific enolase (NSE), whereas glial fibrillary acidic protein (GFAP) and nestin expression were not significantly modified by treatment. Similar results were obtained with fluoxetine and venlafaxine. Hes1 mRNA significantly increased after 2 h of treatment, suggesting involvement of this transcription factor in this process. These results confirm the role of astrocytes in neurogenesis and suggest that these cells may represent one of the targets of antidepressants.

Human astrocytes can be induced to differentiate into cells with neuronal phenotype

Several recent studies have proposed that astrocytes may contribute to neurogenesis, not only as a source of trophic substances regulating it, but also as stem cells themselves. In order to better understand these mechanisms, primary astrocyte cultures were established from human fetal brain. After 3-4 weeks in culture, astrocytes (about 95% GFAP+; neurofilament, NF-; neuro-specific enolase, NSE-) were treated with a cocktail of protein kinase activators and FGF-1. After 5 h of treatment, most cells showed morphological changes that increased progressively up to 24-48 h, exhibiting a round cell body with long processes. Immunocytochemistry showed that treatment-induced NF and NSE expression in about 40% of cells. Nestin expression increased after treatment, whereas GFAP immunostaining was not significantly modified. Western blot and RT-PCR confirmed the results. No neuronal electrophysiological properties were observed after treatment, suggesting an incomplete maturation under these experimental conditions. Understanding the regenerative capability and neurogenic potential of astrocytes might be useful in devising therapeutic approaches for a variety of neurological disorders.

Differentiation of human adult CD34+ stem cells into cells with a neural phenotype: role of astrocytes

It has recently been reported that adult hematopoietic stem cells can differentiate into neural cells, opening new frontiers in therapy for neurodegenerative diseases. In this study, adult human hematopoietic stem cells (HSCs) were isolated via magnetic bead sorting, using a specific CD34 antibody and cultured with human astrocyte culture conditioned medium (ACM). In order to evaluate their differentiation into neurons and/or astrocytes, ACM-treated cultures were probed for the expression of several neural markers. We observed morphological modifications and, after 20 days of treatment, cell morphology displayed extending processes. Immunocytochemistry, Western blotting and RT-PCR showed the expression of neuronal markers such as neurofilaments, neuron specific enolase (NSE) and NeuN in ACM-treated HSCs cultured in poly-L-lysine-coated dishes. On the contrary, when the same ACM-treated cells were grown on a plastic substrate, they expressed high levels of glial fibrillary acidic protein (GFAP), with only weak expression of neuronal markers. Nestin, a neural progenitor cell marker, was present in treated cells, regardless of the substrate. These results demonstrate that astrocytes can generate a suitable microenvironment for inducing HSCs to differentiate into neural cells. Therefore, adult bone marrow may represent a readily accessible source of cells for treating neurodegenerative diseases.

S100b counteracts effects of the neurotoxicant trimethyltin on astrocytes and microglia

Central nervous system degenerative diseases are often characterized by an early, strong reaction of astrocytes and microglia. Both these cell types can play a double role, protecting neurons against degeneration through the synthesis and secretion of trophic factors or inducing degeneration through the secretion of toxic molecules. Therefore, we studied the effects of S100B and trimethyltin (TMT) on human astrocytes and microglia with two glial models, primary cultures of human fetal astrocytes and a microglia cell line. After treatment with 10(-5) M TMT, astrocytes showed morphological alterations associated with an increase in glial fibrillary acidic protein (GFAP) expression and changes in GFAP filament organization. Administration of S100B before TMT treatment prevented TMT-induced changes in morphology and GFAP expression. A decrease in inducible nitric oxide synthase expression was observed in astrocytes treated with TMT, whereas the same treatment induced iNOS expression in microglia. In both cases, S100B prevented TMT-induced changes. Tumor necrosis factor-alpha mRNA expression in astrocytes was not modified by TMT treatment, whereas it was increased in microglia cells. S100B pretreatment blocked the TMT-induced increase in TNF-alpha expression in microglia. To trace the mechanisms involved in S100B activity, the effect of BAY 11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB) activation, and of PD98059, an inhibitor of MEK-ERK1/2, were investigated. Results showed that the protective effects of S100B against TMT toxicity in astrocytes depend on NF-kappaB, but not on ERK1/2 activation. These results might help in understanding the role played by glial cells in brain injury after exposure to chemical neurotoxicants and support the view that S100B may protect brain cells in case of injury. (c) 2005 Wiley-Liss, Inc.

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.

Development of tactile allodynia and thermal hyperalgesia by intrathecally administered platelet-activating factor in mice

Platelet-activating factor (PAF) is a potent inflammatory lipid mediator in peripheral tissues. However, its role in mediation of nociception in central nervous system is unknown. In the present study, whether PAF plays some role in pain transduction in the spinal cord was studied in mice. Intrathecal injection of PAF induced tactile pain, tactile allodynia at as low as 10 fg to 1 pg with a peak response at 100 fg, while lyso-PAF was without effect in the range of doses. Tactile allodynia induced by PAF was blocked by a PAF receptor antagonists, TCV-309, WEB 2086 and BN 50739. The expression of PAF receptor mRNA by RT-PCR was observed in DRG and spinal cord in mice. ATP P2X receptor antagonists, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid and 2',3'-O-(2,4,6-trinitrophenyl)adenosine 5-triphosphate, NMDA receptor antagonist, MK 801 and nitric oxide synthetase inhibitor, 7-nitroindazole blocked the PAF-induced tactile allodynia. PAF-induced tactile allodynia and thermal hyperalgesia disappeared in neonatally capsaicin-treated adult mice, while tactile allodynia but not thermal hyperalgesia induced by intrathecally injected alpha,beta-methylene ATP, a P2X receptor agonist, was capsaicin-insensitive. The present study demonstrated that PAF is a potent inducer of tactile allodynia and thermal hyperalgesia at the level of the spinal cord. PAF-evoked tactile allodynia is suggested to be mediated by ATP and the following NMDA and NO cascade through capsaicin-sensitive fiber, different from exogenously injected alpha,beta-methylene ATP which is insensitive to capsaicin treatment.

Platelet-activating factor receptor modulates respiratory adaptation to long-term intermittent hypoxia in mice

During hypoxia, release of platelet-activating factor (PAF) and activation of its cognate receptor (PAFR) regulate neural transmission and are required for full expression of peak hypoxic ventilatory response (pHVR) but not hypercapnic ventilatory response. However, it is unclear whether PAFR underlie components of long-term ventilatory adaptations to hypoxia. To examine this issue, adult male PAFR(+/+) and PAFR(-/-) mice were exposed to intermittent hypoxia (IH) consisting of 90 s 21% O(2) and 90 s 10% O(2) for 30 days, and normoxic and hypoxic ventilatory patterns were assessed using whole body plethysmography. Starting at day 14 of IH, normoxic ventilation in PAFR(-/-) was reduced significantly compared with PAFR(+/+) mice (P < 0.001), the latter exhibiting a prominent long-term ventilatory facilitation (LTVF). However, IH-exposed PAFR(-/-) mice had markedly enhanced pHVR and hypoxic ventilatory decline that became similar to those of IH-exposed PAFR(+/+) mice. Thus we postulate that PAFR expression and/or function underlies critical components of IH-induced LTVF but does not play a role in the potentiation of the hypoxic ventilatory response after IH exposures.

Dystrophin antisense oligonucleotides decrease expression of nNOS in human neurons

Nitric oxide (NO) plays an important role in the pathogenesis of neurodegenerative disease. It has been shown that neuronal NO synthase (nNOS), the enzyme that constitutively produces NO in brain, is a component of the dystrophin-associated protein complex. The absence of dystrophin causes Duchenne muscular dystrophy. Thus, we attempted to study whether or not a decrease of dystrophin expression would induce a modification in nNOS expression in cultured human neurons. Human fetal neuronal cultures were treated with antisense oligonucleotides against different isoforms of dystrophin and the expression of nNOS tested by RT-PCR and immunocytochemistry. Results showed that nNOS mRNA was significantly decreased by about 35% in neurons treated with brain-specific dystrophin (brain Dp427) antisense, whereas iNOS expression was not affected. Accordingly, a decrease in immunostaining for nNOS was observed in antisense treated neurons compared to controls. Expression of neuronal markers, such as bFGF or synaptophysin, was not affected by the same antisense treatment. Astrocytes were not affected by treatment, as shown by utrophin expression, a dystrophin-like protein that was not modified in pure astrocytic cultures. Thus, we conclude that a decrease of dystrophin in human neurons is associated with a decrease of nNOS expression.

Expression of CD137 and its ligand in human neurons, astrocytes, and microglia: modulation by FGF-2

CD137 (ILA, 4-1BB), a member of the tumor necrosis factor receptor family, and its ligand CD137-L were assayed by RT-PCR and immunocytochemistry in cultured human brain cells. Results demonstrated that both neurons and astrocytes expressed specific RNA for CD137 and its protein, which was found both on the plasma membrane and in the cytoplasm. Surprisingly, microglia, which also expressed CD137 mRNA, showed negative immunostaining. CD137-L-specific RNA was detected only in astrocytes and neurons. When brain cells were treated with fibroblast growth factor-2 (FGF-2), upregulation of CD137 but not of its ligand was observed in neurons and astrocytes. Protein localization was also affected. In microglia, an inhibition of RNA expression was induced by treatment, whereas CD137-L remained negative. Our data are the first demonstration that human brain cells express a protein found thus far in activated immunocompetent cells and epithelia. Moreover, they suggest not only that CD137 and CD137-L might play a role in interaction among human brain cells, but also that FGF-2 might have an immunoregulatory function in brain, modulating interaction of the central nervous system with peripheral immunocompetent cells.

Developmentally regulated expression and localization of dystrophin and utrophin in the human fetal brain

Expression of dystrophin and the dystrophin-related protein utrophin has been studied in the human fetal brain both in vivo and in vitro. Results showed that both these proteins were developmentally regulated, even if their expression followed a different pattern. Utrophin was found since very early stages of development, reached a peak between week 15-20 of gestation, declining then, so that at week 32 was barely detectable. The protein was mainly found in neuronal cell bodies, partially associated to the plasma membrane, and in astrocytes cytoplasm. On the contrary, the brain form of dystrophin was first detectable at week 12, increased up to week 15 and then remained stable. Dystrophin localization was similar but not identical to utrophin. In neurons, it was also partially associated with the plasma membrane of cell body and axon hillock. However, the most was concentrated in the cytoplasm and in the processes, where it appeared associated to neurofilaments. Astrocytes were negative for brain dystrophin, but positive for the muscle isoform. Results suggest that utrophin and dystrophin are likely to play a key, though different, role in the immature brain. They help in understanding the basic mechanism(s) underlying cognition defects frequently observed in Duchenne and Becker dystrophic patients.

Production of platelet-activating factor by neuronal cells in the rat brain with cold injury

The production and localization of platelet-activating factor (PAF) in the brain following focal brain injury were examined. Immunofluorescent staining was used to detect PAF in the rat brain with cold-induced local brain injury. After cold injury, immediate-early PAF staining was observed within the cold lesion followed later by immunoreactivity in the ipsilateral white matter. PAF immunoreactivity was also clearly seen both in cortical neurons adjacent to the cold lesion and in the ipsilateral hippocampus which showed delayed neuronal degeneration. The data suggest that PAF synthesis occurs in the neuronal cells in the perilesional area and hippocampus as well as within the cold lesion site during the early stages of cold-induced brain injury. PAF expression may contribute to the onset and progression of further brain damage, such as delayed axotomy and delayed neuronal loss.

Synaptic plasticity in the medial vestibular nuclei: role of glutamate receptors and retrograde messengers in rat brainstem slices

The analysis of cellular-molecular events mediating synaptic plasticity within vestibular nuclei is an attempt to explain the mechanisms underlying vestibular plasticity phenomena. The present review is meant to illustrate the main results, obtained in vitro, on the mechanisms underlying long-term changes in synaptic strength within the medial vestibular nuclei. The synaptic plasticity phenomena taking place at the level of vestibular nuclei could be useful for adapting and consolidating the efficacy of vestibular neuron responsiveness to environmental requirements, as during visuo-vestibular recalibration and vestibular compensation. Following a general introduction on the most salient features of vestibular compensation and visuo-vestibular adaptation, which are two plastic events involving neuronal circuitry within the medial vestibular nuclei, the second and third sections describe the results from rat brainstem slice studies, demonstrating the possibility to induce long-term potentiation and depression in the medial vestibular nuclei, following high frequency stimulation of the primary vestibular afferents. In particular the mechanisms sustaining the induction and expression of vestibular long-term potentiation and depression, such as the role of various glutamate receptors and retrograde messengers have been described. The relevant role of the interaction between the platelet-activating factor, acting as a retrograde messenger, and the presynaptic metabotropic glutamate receptors, in determining the full expression of vestibular long-term potentiation is also underlined. In addition, the mechanisms involved in vestibular long-term potentiation have been compared with those leading to long-term potentiation in the hippocampus to emphasize the most significant differences emerging from vestibular studies. The fourth part, describes recent results demonstrating the essential role of nitric oxide, another retrograde messenger, in the induction of vestibular potentiation. Finally the fifth part suggests the possible functional significance of different action times of the two retrograde messengers and metabotropic glutamate receptors, which are involved in mediating the presynaptic mechanism sustaining vestibular long-term potentiation.

Preparation and crystal structure of the recombinant alpha(1)/alpha(2) catalytic heterodimer of bovine brain platelet-activating factor acetylhydrolase Ib

The intracellular form of mammalian platelet activating factor acetylhydrolase found in brain (PAF-AH Ib) is thought to play a critical role in control in neuronal migration during cortex development. This oligomeric complex consists of a homodimer of the 45 kDa (beta) LIS1 protein, the product of the causative gene for type I lissencephaly, and, depending on the developmental stage and species, one of three possible pairs of two homologous approximately 26 kDa alpha-subunits, which harbor all of the catalytic activity. The exact composition of this complex depends on the expression patterns of the alpha(1) and alpha(2) genes, exhibiting tissue specificity and developmental control. All three possible dimers (alpha(1)/alpha(1), alpha(1)/alpha(2) and alpha(2)/alpha(2)) were identified in tissues. The alpha(1)/alpha(2) heterodimer is thought to play an important role in fetal brain. The structure of the alpha(1)/alpha(1) homodimer was solved earlier in our laboratory at 1.7 A. We report here the preparation of recombinant alpha(1)/alpha(2) heterodimers using a specially constructed bi-cistronic expression vector. The approach may be useful in studies of other systems where pure heterodimers of recombinant proteins are required. The alpha(1)/alpha(2) dimer has been crystallized and its structure was solved at 2.1 A resolution by molecular replacement. These results set the stage for a detailed characterization of the PAF-AH Ib complex.

Reduction of hypoxic-ischemic brain swelling in the neonatal rat with PAF antagonist WEB 2170: lack of long-term protection

Platelet activating factor (PAF) is an inflammatory lipid mediator released by ischemic brain. Our objectives were to use an inhibitor of PAF that does not readily cross the blood-brain barrier, WEB 2170, to study the role of intravascular PAF on brain swelling and subsequent brain atrophy in a neonatal rat model of hypoxic-ischemic brain injury. We injured the right cerebral hemisphere of 7-d-old rats by ligating the right common carotid artery and exposing the rats to 8% oxygen for 2.25 h. Forty-two rats received saline or the PAF antagonist WEB 2170, 1 h before hypoxia. We found that WEB 2170 pretreatment reduced swelling by 64% (p = 0.003). In contrast, treatment immediately after hypoxic-ischemic injury did not reduce swelling. In two additional experiments involving 103 rats, we found that pretreatment or repeated doses of PAF antagonist before and after hypoxic-ischemic injury did not reduce atrophy. We also found that the brain-penetrating PAF antagonist, BN 52021, did not prevent atrophy in our Wistar rat model. In conclusion, we were unable to reduce long-term brain injury with either PAF antagonist. WEB 2170 pretreatment reduced brain swelling by 64% without reducing atrophy. This suggests that although brain swelling may accompany cerebral infarction, it does not contribute to the pathogenesis of infarction and subsequent atrophy in the neonatal rat. The ability to reduce early postischemic brain swelling without reducing atrophy may be particularly unique to the immature animal with a compliant skull.

Properties and regulation of microsomal PAF-synthesizing enzymes in rat brain cortex

Platelet-activating factor (PAF) is a phospholipid mediator of long-term potentiation, synaptic plasticity and memory formation as well as of the development of brain damage. In brain, PAF is synthesized by two distinct pathways but their relative contribution to its productions, in various physiological and pathological conditions, is not established. We have further investigated on the properties of the two enzymes that catalyze the last step of the de novo or remodeling pathways in rat brain microsomes, PAF-synthesizing phosphocholinetransferase (PAF-PCT) and lysoPAF acetyltransferase (lysoPAF-AT), respectively. The latter enzyme is fully active at microM Ca2+ concentration, inhibited by MgATP and activated by phosphorylation. Because the reversibility of the reaction catalyzed by PAF-PCT, its direction depends on the ratio [CDP-choline]/[CMP], which is related to the energy charge of the cell. These and other properties indicate that the de novo pathway should mainly contribute to PAF synthesis for maintaining its basal levels under physiological conditions. The remodeling pathway should be more involved in the production of PAF during ischemia. During reperfusion, the overproduction of PAF should be the result of the concomitant activation of both pathways.

Interaction between neurone and microglia mediated by platelet-activating factor

BACKGROUND

Platelet-activating factor (PAF) is a potent phospholipid mediator that plays various roles in neuronal function and brain development. The production and release of PAF in the brain has also been reported under various pathological conditions. However, neither the cell types and mechanism responsible for the synthesis of PAF nor its target cells have been fully identified.

RESULTS

Using primary culture cells derived from rat brain and a very sensitive assay method for PAF, we found that PAF was synthesized in neurones following stimulation with glutamic acid. PAF synthesis required activation of NMDA receptors and subsequent elevation of intracellular calcium ions. Microglia, which express functional PAF receptors to a high level, showed a marked chemotactic response to PAF. This chemotaxis is a receptor-mediated process, as microglia from PAF-receptor-deficient mice did not show such a response. The activation of a pertussis-toxin-sensitive G-protein and mitogen-activated protein kinase presumably plays a role in intracellular signalling leading to chemotaxis.

CONCLUSIONS

Considering the cytoprotective and cytotoxic roles of microglia, PAF functions as a key messenger in neurone-microglial interactions.

Role of fibroblast growth factor-2 in human brain: a focus on development

Trophic factors have gained a great degree of attention as regulators of neural cells proliferation and differentiation as well as of brain maturation. Very little is known, however, about their effects on human immature nervous system. In this paper, data on expression of fibroblast-growth factor-2 and its receptors are reviewed and discussed in the light of its possible role in human brain development.

Platelet activating factor is elevated in cerebral spinal fluid and plasma of patients with relapsing-remitting multiple sclerosis

Platelet-activating factor (PAF) is a phospholipid mediator of inflammation with a wide range of biological activities, including the alteration of barrier function of endothelium. A biological assay combined with high pressure liquid chromatography-tandem mass spectrometry showed that plasma and cerebral spinal fluid (CSF) PAF levels in 20 patients with relapsing/remitting or secondary progressive multiple sclerosis (MS) studied by magnetic resonance imaging (MRI) were significantly higher than in healthy controls (plasma: 3.29+/-4.52 vs. 0.48+/-0.36 ng/ml, p < 0.002; CSF: 4.95+/-6.22 ng/ml vs. 0.01+/-0.04 ng/ml, p < 0.0001). Values were also significantly higher in relapsing/remitting than in secondary progressive (plasma: 5.10+/-4.97 vs. 0.52+/-0.85 ng/ml, p < 0.005; CSF: 8.59+/-6.39 vs. 0.55+/-0.68 ng/ml, p < 0.002). It was also found that both plasma (R2: 0.65) and CSF (R2:0.72) levels were correlated with the MRI number of gadolinium enhancing lesions, which are markers of blood-brain barrier (BBB) injury, whereas their peaks were not correlated with the MRI number of white matter lesions, nor with the expanded disability status score (EDSS) according to Kurtze [Kurtze, J.F., 1983. Rating neurological impairment in multiple sclerosis: an expanded disability scale (EDSS). Neurology 33, 1444-1452]. Both plasma and CSF in patients with relapsing/remitting MS and marked gadolinium enhancement contained the two major molecular species of PAF: 1-0-hexadecyl- (C16:O) and 1-0-octadecyl-sn-glycero-3-phosphocholine (C18:O). The ratio of the two molecular species was different in the two biological fluids, being PAF C18:0 more abundant in CSF and PAF C16:0 in plasma, indicating a different cellular origin of PAF or different enzymatic processing. These findings suggest that PAF is a significant mediator of BBB injury in the early stages of MS, rather than a marker of its progression and severity.

Modulation of hypoxic ventilatory response by systemic platelet-activating factor receptor antagonist in the rat

Platelet activating factor (PAF) has recently emerged as an important modulator of neuronal excitability by enhancing synaptic glutamate release. Since PAF receptors (PAFR) are ubiquitously distributed in the brain, we hypothesized that PAF may play a role in respiratory control. To examine this issue, hypoxic (10% O2 for 15 min, n = 14) and hypercapnic (5% CO2 for 30 min, n = 6) challenges were performed in chronically-instrumented, unrestrained adult rats following administration of the pre-synaptic PAFR antagonist BN52021 (i.p. 20 mg/kg in 0.5 ml) or vehicle (Veh). In normoxia, BN52021 elicited VT decreases and corresponding f increases such that minute ventilation (VE) was unaffected. During hypercapnia, peak VE increased similarly after both treatments (103+/-18% in BN52021 vs. 94+/-19% in Veh, p-NS). In contrast, significant reductions in the peak hypoxic VE response occurred after BN52021 (42+/-10% vs. 104+/-18% in Veh, P<0.002). BN52021 increased normoxic arterial blood pressure and decreased heart rate. However, hypoxia-induced chronotropic responses were attenuated and depressor responses were enhanced by BN52021. We further examined protein kinase C (PKC) translocation patterns during acute hypoxia after systemic BN52021 administration. Activation of PKC beta and delta was blocked by BN52021, PKC gamma was attenuated, with no effects on PKC alpha, epsilon, theta, iota, mu, and zeta. We conclude that systemic administration of a PAFR antagonist attenuates cardioventilatory recruitment to hypoxia and selectively attenuates activation of PKC in the rat brainstem. We speculate that enhanced regional PAF production and release during hypoxic conditions may contribute important excitatory inputs and signal transduction pathways within neuronal structures underlying cardiovascular and respiratory control.

Platelet-activating factor modulates cardiorespiratory responses in the conscious rat

Platelet-activating factor receptor (PAFR) activation is associated with increases in neuronal excitability. We hypothesized that PAF may play a role in cardiorespiratory control. Ventilatory responses to microinjection of a long-acting PAF analog (mc-PAF, 1 microg in 1 microl) within the dorsocaudal brain stem were measured in unrestrained adult rats. mc-PAF elicited significant minute ventilation (VE) enhancements that were primarily due to tidal volume increases and were accompanied by respiratory alkalosis, heart rate increase, and reduction of arterial blood pressure. Such cardiovascular and respiratory effects did not occur after administration of either vehicle or the inactive analog lyso-PAF. The effect was blocked when animals were coadministered the presynaptic PAFR antagonist BN-52021 or recombinant PAF acetyl hydrolase. To determine the relative contribution of PAF to hypercapnic and hypoxic ventilation, microinjections were performed in additional animals with either vehicle (CO, 1 microl) or with 5 microg in 1 microl of BN-52021. Hypercapnic challenges with 5% CO2 were unaffected by BN-52021. In contrast, although 10% O2 breathing increased VE from 120.4 +/- 7.5 to 204.6 +/- 11.4 ml/min in CO, after BN-52021, VE increased only from 118.7 +/- 6.9 to 137.3 +/- 8. 9 ml/min (CO vs. BN-52021, P < 0.001). We conclude that PAFR activation in the dorsocaudal brain stem exerts significant cardioventilatory effects during normoxia and appears to play an important modulatory role in the VE response to hypoxia in conscious rats.

Effects of CDP-choline administration on brain striatum platelet-activating factor in aging rats

Cytidine 5'-diphosphocholine (CDP-choline) is a precursor in platelet-activating factor (PAF) biosynthesis and it is used in the treatment of diseases of the central nervous system. PAF levels in the striatum of aged (19 months) rats were 67% lower than those found in young (2 months) animals. Chronic treatment of aged rats with CDP-choline (500 mg/kg per day) reduced these PAF levels by more than 65% with respect to those of untreated aged rats after 8 days of treatment. PAF subsequently stabilized at these low levels as treatment continued. These results suggest that some effects of CDP-choline could be mediated by changes in brain PAF levels.

Systematic screening of the LDL-PLA2 gene for polymorphic variants and case-control analysis in schizophrenia

Systematic scans of the genome using microsatellite markers have identified chromosome 6p21.1 as a putative locus for schizophrenia in multiply affected families. There is also evidence from a series of studies for a role of abnormal phospholipid metabolism in schizophrenia. In light of these findings, and the role of platelet activating factor in neurotransmission and neurodevelopment, we have examined the LDL-PLA2 (plasma PAF acetylhydrolase, PAF-AH) gene, a serine dependent phospholipase that has been mapped by hybrid mapping to chromosome 6p21.1, as a positional candidate gene for schizophrenia. The gene was systematically screened using SSCP/HD analysis for polymorphisms associated with the disease. Four polymorphic variants were found within the gene and studied in a group of 200 schizophrenic patients and 100 controls. The variant in exon 7 (Iso195Thr) was found to be weakly associated with schizophrenia (p = 0.04) and the variant in exon 11 (Val379Ala) almost reached significance (p = 0.057). After correcting for multiple testing no significant associations were detected. Haplotype analysis combining pairs of polymorphisms also provided no evidence for association of this gene with schizophrenia in our sample of patients.

PAF analogues capable of inhibiting PAF acetylhydrolase activity suppress migration of isolated rat cerebellar granule cells

Intracellular platelet-activating factor (PAF) acetylhydrolase in the bovine brain is a heterotrimeric enzyme composed of alpha1, alpha2 and beta subunits. The trimeric enzyme may be involved in neural cell migration, since the human homolog of the non-catalytic beta subunit is a product of the LIS-1 gene which is a causative gene for Miller-Dieker syndrome. Miller-Dieker syndrome is a form of lissencephaly that is characterized by widespread agyria of the brain and defects of neuronal cell migration. In the present study, we attempted to determine whether the catalytic activity of either the alpha1 or alpha2 subunit is required for the regulation of granule cell migration. Granule cells prepared from rat cerebellum at postnatal day 0 express all three subunit proteins (alpha1, alpha2 and beta) as determined by western blotting. Granule cell migration, which was observed in vitro on a layer coated with laminin, was effectively blocked by PAF analogs which showed PAF receptor-antagonistic activity (CV-6209 and CV-3988) and PAF receptor-agonistic activity (carbamoyl PAF). These PAF analogs also inhibited the activity of bovine brain PAF acetylhydrolase. Cell migration was restored when the inhibitors were removed by washing the treated cells with buffer, indicating that the inhibitory effect of PAF analogs is reversible. Structurally-unrelated PAF antagonists (SM-12502, TCV-309 and YM-264), none of which showed any appreciable inhibitory activity against PAF acetylhydrolase, did not block granule cell migration under the same conditions. It is suggested that the catalytic activity of PAF acetylhydrolase may play a crucial role in neural cell migration.

Activities of enzymes involved in the metabolism of platelet-activating factor in neural cell cultures during proliferation and differentiation

Platelet-Activating Factor (PAF) is a potent lipid mediator involved in physiological and pathological events in the nervous tissue where it can be synthesized by two distinct pathways. The last reaction of the de novo pathway utilizes CDPcholine and alkylacetylglycerol and is catalyzed by a specific phosphocholinetransferase (PAF-PCT) whereas the remodelling pathway ends with the reaction catalyzed by lyso-PAF acetyltransferase (lyso-PAF AcT) utilizing lyso-PAF, a product of phospholipase A2 activity, and acetyl-CoA. The levels of PAF in the nervous tissue are also regulated by PAF acetylhydrolase that inactivates this mediator. We have studied the activities of these enzymes during cell proliferation and differentiation in two experimental models: 1) neuronal and glial primary cell cultures from chick embryo and 2) LA-N-1 neuroblastoma cells induced to differentiate by retinoic acid (RA). In undifferentiated neuronal cells from 8-days chick embryos the activity of PAF-PCT was much higher than that of lyso-PAF AcT but it decreased during the period of cellular proliferation up to the arrest of mitosis (day 1-3). During this period no significant changes of lyso-PAF AcT activity was observed. Both enzyme activities increased during the period of neuronal maturation and the formation of cellular contacts and synaptic-like junctions. The activity of PAF acetylhydrolase was unchanged during the development of the neuronal cultures. PAF-PCT activity did not change during the development of chick embryo glial cultures but lyso-PAF AcT activity increased up to the 12th day. RA treatment of LA-N-1 cell culture in proliferation decreased PAF-PCT activity and had no significant effect on lyso-PAF AcT and PAF acetylhydrolase indicating that the synthesis of PAF by the enzyme catalyzing the last step of the de novo pathway is inhibited when the LA-N-1 cells are induced to differentiate. These data suggest that: 1) in chick embryo primary cultures, both pathways are potentially able to contribute to PAF synthesis during development of neuronal cells particularly when they form synaptic-like junctions whereas, during development of glial cells, only the remodelling pathway might be particularly active on synthesizing PAF; 2) in LA-N-1 neuroblastoma cells PAF-synthesizing enzymes coexist and, when cells start to differentiate the contribution of the de novo pathway to PAF biosynthesis might be reduced.

Effect of dystrophin antisense oligonucleotides on cultured human neurons

Antisense oligonucleotides offer the potential to block the expression of specific molecules within the cell, thus providing a useful tool in cell function studies. In this paper, we tested the possibility to block dystrophin expression in in vitro cultured neurons with antisense oligonucleotides administration. Human fetal neuronal cultures were treated with different doses of antisense oligonucleotides against dystrophin, the protein coded by the Duchenne muscular dystrophy gene. Results showed that labelled oligonucleotides rapidly accumulated into cultured neurons, but were discarded 15-24 h after treatment. However, no effects could be observed until 3-4 days after treatment, when immunocytochemical staining for dystrophin was significantly decreased in treated neurons. This result was confirmed by polymerase chain reaction assay which showed a significantly lower expression of the dystrophin specific mRNA. Electron microscope observations confirmed that neurons were affected. Large inclusions or packed granules were detectable in their cytoplasm and in terminal endings. Neuronal nuclear membrane was sometimes shredded, so that nuclear shape was altered. These phenomena were dose-dependent, further substantiating the hypothesis of a specific effect of antisense treatment. This interpretation was supported by the absence of alterations when cultures were treated with mismatch or non specific antisenses. Since the function of dystrophin is still unknown, these data might help in understanding the role played by this protein in the developing brain.

Platelet-activating factor in the CNS

Platelet-activating factor (PAF) is a phospholipid synthesized in a variety of cells throughout the body. Platelet-activating factor has been identified in the CNS and has a number of diverse physiological and pathological functions. It has been shown to be a modulator of many CNS processes, ranging from long-term potentiation (LTP) to neuronal differentiation. Excessive levels of PAF appear to play an important role in neuronal cell injury, such as that resulting from ischaemia, inflammation, human immunodeficiency syndrome (HIV) and meningitis. The beneficial effects of PAF receptor antagonists are many and give rise to possible therapeutic strategies for neurotrauma.

Platelet-activating factor: a case for its role in CNS function and brain injury

In the past 10 years evidence has been accumulating on the synthesis, distribution, regulation and function of platelet-activating factor (PAF) and related phospholipids in the brain. Clearly, much needs to be done to establish specific biological functions for PAF in the brain and in particular its role in disease processes. The cellular elements responsible for PAF synthesis and release in vivo is not yet clear nor has it been established whether PAF has a role in chronic pathological conditions. Hopefully, this 'decade of the brain' will lead us to better insights on these issues.

Alkylglycerophosphate acetyltransferase and lyso platelet activating factor acetyltransferase, two key enzymes in the synthesis of platelet activating factor, are found in neuronal nuclei isolated from cerebral cortex

Neuronal nuclear fractions (N1) isolated from cerebral cortices of 15-day-old rabbits were enriched in two acetyltransferases involved in biosynthetic pathways leading to platelet activating factor (PAF). Alkylglycerophosphate (AGP) acetyltransferase of the de novo biosynthetic path had specific activities in fraction N1 which were 3-times those of the microsomal fraction (P3D) from cerebral cortex. Lyso PAF acetyltransferase of the remodelling path had specific activities in N1 which were 16-times those of P3D and 51-times those of the homogenate. The maximum specific activity observed for the N1 AGP acetyltransferase was 1.4-times the corresponding N1 lyso PAF acetyltransferase value. The pH optimum for the N1 AGP acetyltransferase was within the alkaline range (pH 8-9), while the N1 lyso PAF acetyltransferase showed a much broader pH optimal range which extended over the neutral and physiological pH values. Both acetyltransferases were inhibited by MgATP (0.125-1 mM) or oleoyl CoA (2-10 microM). However, the N1 AGP acetyltransferase could be distinguished from the N1 lyso PAF acetyltransferase by a greater sensitivity to MgATP inhibition. When NaF was not present in the assays, less of the product of N1 AGP acetyltransferase was recovered, likely indicating a hydrolysis of the acetylated AGP. When the AGP and lyso PAF substrates were combined in acetyltransferase assays, the two N1 acetylations appeared to proceed independently. The enrichment of the acetyltransferases, and particularly the lyso PAF acetyltransferase, within the neuronal nuclear fraction is of particular interest with respect to the intracellular effects of PAF which are considered to be involved in nuclear signalling mechanisms.

Predominant expression of platelet-activating factor receptor in the rat brain microglia

Cellular localization of platelet-activating factor (PAF) receptor in the rat brain was determined by (1) in situ hybridization, (2) Northern blot analysis in primary cell cultures of neurons, microglia, astrocytes, and fibroblasts, and (3) Ca2+ imaging in hippocampal culture. In situ hybridization revealed that the PAF receptor mRNA is expressed intensely in microglia and moderately in neurons. Northern blot analysis revealed that PAF receptor mRNA is the most abundant in microglia. In primary hippocampal cultures, PAF elevated intracellular Ca2+ concentration in microglia and also in neurons, but to a lesser extent. These results suggest predominant presence of PAF receptor in microglia. Cultured microglia also expressed cPLA2 mRNA the most intensely. PAF-activated microglia released arachidonic acid in a Ca(2+)-dependent manner and without conversion to its derivatives. We propose that microglia as well as neurons contribute to PAF-related events in the CNS by releasing arachidonic acid.

The neuroprotective properties of the Ginkgo biloba leaf: a review of the possible relationship to platelet-activating factor (PAF)

Ginkgo biloba (Ginkgoaceae) is an ancient Chinese tree which has been cultivated and held sacred for its health-promoting properties. There is substantial experimental evidence to support the view that Ginkgo biloba extracts have neuroprotective properties under conditions such as hypoxia/ischemia, seizure activity and peripheral nerve damage. Research on the biochemical effects of Ginkgo biloba extracts is still at a very early stage. One of the components of Ginkgo biloba, ginkgolide B, is a potent platelet-activating factor (PAF) antagonist. Although the terpene fraction of Ginkgo biloba, which contains the ginkgolides, may contribute to the neuroprotective properties of the Ginkgo biloba leaf, it is also likely that the flavonoid fraction, containing free radical scavengers, is important in this respect. Taken together, the evidence suggests that Ginkgo biloba extracts are worthy of further investigation as potential neuroprotectant agents.

Cloning and expression of a cDNA encoding the beta-subunit (30-kDa subunit) of bovine brain platelet-activating factor acetylhydrolase

Bovine brain platelet-activating factor (PAF) acetylhydrolase isoform Ib is a heterotrimeric enzyme. Its gamma-subunit (which, formerly, we called the 29-kDa subunit) acts as a catalytic subunit, whereas the alpha-subunit (45 kDa) is the bovine homolog of the product of human LIS-1, the causative gene of Miller-Dieker lissencephaly, indicating that this intracellular PAF acetylhydrolase plays a key role in brain development. In the current study, we cloned the cDNA for the beta-subunit (30 kDa) of bovine brain PAF acetylhydrolase Ib. The predicted 229-amino acid sequence was homologous (63.2% identity) to that of the gamma-subunit, especially (86% identity) in the catalytic and PAF receptor homologous domains. The recombinant beta-protein produced in Escherichia coli showed significant PAF acetylhydrolase activity. A mutant protein, in which Ser48, which corresponds to the active serine residue of the gamma-subunit, was replaced with cysteine showed no enzymatic activity, suggesting Ser48 is the active serine residue. Although the beta- and gamma-subunits form a heterocomplex in the native enzyme, both recombinant beta- and gamma-proteins exist as a homodimer. The purified recombinant beta-protein was labeled readily with [1,3-H]diisopropyl fluorophosphate, whereas the beta-subunit in the native complex was only labeled with higher concentrations of [1,3-3H]diisopropyl fluorophosphate to a lesser extent than the gamma-subunit. Combined with our previous data, the present study demonstrated that bovine brain PAF acetylhydrolase Ib is a unique enzyme possessing two catalytic subunits and another, possibly regulatory, subunit.

Enzymes of platelet activating factor synthesis in brain

In this review, evidence is summarized for the production of PAF in brain, in response to stimulation associated with pathology. As well, there is a growing literature on the duality of actions of this lipid autocoid upon nervous tissue, indicated by extracellular and intracellular actions and binding sites for PAF in brain. The metabolic routes to PAF can be divided into the de novo and remodelling pathways of synthesis. The de novo route consists of 1-alkyl glycerophosphate acetyltransferase, and the subsequent actions of distinct phosphohydrolase and cholinephosphotransferase activities. This acetyltransferase can be activated by phosphorylation, and inhibited by MgATP and fatty acyl CoA thioesters, inhibitions which have particular relevance to brain ischemia. There is also evidence that the cholinephosphotransferase is controlled by phosphorylation, and regulated by levels of CDP-choline. The remodelling pathway to PAF relies upon the actions of phospholipase A2 or CoA-independent transacylases to generate the 1-alkyl glycerophosphorylcholine, as substrate for a distinct acetyltransferase. Following stimulation, rising intracellular calcium may trigger arachidonate selective cytosolic phospholipase activity which leads to increased PAF synthesis. The 1-alkyl glycerophosphocholine acetyltransferase activity is quite small in brain in comparison with the de novo acetyltransferase activity, and is also controlled by phosphorylation. Evidence has been presented for the actions of both pathways in brain, in response to biologically relevant stimulation pertinent to the disease state.

Human microglia cultures: a powerful model to study their origin and immunoreactive capacity

In this paper, we report that pure cultures of human microglia were obtained from long-term astrocytic cultures of human fetal brain. After five to six months and repeated cell passages, macrophage-like cells started to spontaneously form in vitro, so that in two to three weeks the whole culture was populated by them. These cells were grown up to over 50 passages in culture and analyzed for morphology, specific marker positivity, growth rate and major histocompatibility complex (MHC) antigen expression with or without gamma-interferon (IFN) stimulation. We found that, regardless of embryonic age of original cultures (10-15 weeks of gestation), cultures showed a remarkable homogeneity and purity and over 90 stained for typical microglial markers. Under basal conditions, two cell subpopulations similar to those described in vivo, we observed: the reactive 'ameboid' type and the resting 'ramified' one, the latter increasing with time in vitro and cell passages. Both cell subpopulations were capable of active phagocytosis and of high-rate proliferation. They spontaneously expressed low levels of MHC class II antigens, but were negative for MHC class I. Stimulation with gamma-interferon lymphokine upregulated the MHC class II expression as well as the MHC class I heavy chain form in ameboid, 'reactive' cells but not in the ramified ones. We also found that beta 2 microglobulin, already expressed in basal conditions, was dissociated from HLA A-B-C molecules in lymphokine-stimulated cells at early passages. The physiological significance of these data, as well as the possible correlation with in vivo ontogenetic modifications, are also discussed.

Modulation of signal transduction in rat synaptoneurosomes by platelet activating factor

The potential involvement of platelet activating factor (PAF, 1-O-alkyl 2-O-acetyl-sn-glycero-3-phosphocholine) in aggravation of ischemic brain injury has been recently postulated. Reported evidences in support of this thesis include increases of brain PAF concentration during ischemia and the neuroprotective effect exerted by PAF antagonists. In this article, we demonstrate that several PAF-mediated biochemical responses in synaptoneurosomes in vitro resemble these observed previously in ischemic brain and are widely acknowledged as the potentially causal factors in this pathology. In synaptoneurosomes prepared from rat hippocampus, 10 nM PAF caused an observable elevation of intracellular calcium as measured by fluorescence Fura-2A probe. A similar elevation of synaptoneurosomal [Ca2+]i was evoked by 1 mM glutamate treatment. As an effect of calcium entry after PAF application, a translocation of protein kinase C (PKC) toward plasma membranes was demonstrated by 3H-labeled phorbol-binding method. It was followed by an increase of 50 kDa proteolytic fragment of the enzyme (PKM) recognized on Western blots with anti-PKC antibody. Incubation of synaptoneurosomes in the presence of calcium chelators abolished these effects of PAF and significantly decreased the content of PKC in the membranes. Furthermore, PAF treatment markedly attenuated the receptor- and postreceptor-activated cAMP accumulation in synaptoneurosomes. The decrease of cAMP level seems to be secondary to the PAF-induced calcium entry with subsequent activation of cAMP-specific phosphodiesterase, since it was completely blocked by IBMX, a potent inhibitor of this enzyme. Our observations indicate that PAF in a concentration found in ischemic brain can elevate [Ca2+]i and potentiate calcium-dependent intracellular signalling in synaptoneurosomes in vitro, including PKC translocation/activation and proteolysis, followed by IBMX-sensitive inhibition of cAMP production. The relative contribution of these events to ischemic brain injury is currently under extensive investigation.

Platelet-activating factor production by human fetal microglia. Effect of lipopolysaccharides and tumor necrosis factor-alpha

Since platelet-activating factor (PAF) exerts neurotoxic effects on brain cells, we explored the possibility of PAF production by human fetal microglial cells in vitro. PAF content in pure cultures was assayed and characterized in basic conditions, and after stimulation with growth factors and cytokines. Results showed that microglia cells synthesized PAF when challenged with tumor necrosis factor-alpha and lipopolysaccharides, whereas other molecules, such as gamma-interferon or basic fibroblast growth factor, were ineffective. The induced PAF production was concentration- and time-dependent. These results are in line with the hypothesis that microglia can start a cascade of events leading to tissue damage, thus playing a central role in the pathogenesis of several central nervous system diseases.

Miller-Dieker lissencephaly gene encodes a subunit of brain platelet-activating factor acetylhydrolase [corrected]

Platelet-activating factor (PAF) is involved in a variety of biological and pathological processes and PAF acetylhydrolase, which inactivates PAF by removing the acetyl group at the sn-2 position, is widely distributed in plasma and tissue cytosols. One isoform of PAF acetylhydrolase present in bovine brain cortex is a heterotrimer comprising subunits with relative molecular masses of 45K, 30K and 29K (ref. 4). We have now isolated the complementary DNA for the 45K subunit. Sequence analysis revealed a striking identity (99%) of the subunit with a protein encoded by the causative gene (LIS-1) for Miller-Dieker lissencephaly, a human brain malformation manifested by a smooth cerebral surface and abnormal neuronal migration. This indicates that the LIS-1 gene product is a human homologue of the 45K subunit of intracellular PAF acetylhydrolase. Our results raise the possibility that PAF and PAF acetylhydrolase are important in the formation of the brain cortex during differentiation and development.

Excitable membranes, lipid messengers, and immediate-early genes. Alteration of signal transduction in neuromodulation and neurotrauma

The physical nature of neuronal cells, particularly in the functional and morphological segregation of synapse, soma, and dendrites, imparts special importance on the integrity of their cell membranes for the localization of function, generation of intrinsic second messengers, and plasticity required for adaptation and repair. The component phospholipids of neural membranes are important sources of bioactive mediators that participate in such diverse phenomena as memory formation and cellular damage following trauma. A common role for PAF in these processes is established through the suppressive effects of its antagonists. Furthermore, being both an extracellular and intracellular agonist of phospholipase activation, in addition to being a product of phospholipase activity, PAF assumes a centralized role in the cellular metabolism following neural stimulation. The linkage of PAF to neural immediate-early gene expression, both in vitro and in vivo, suggests that its effects are initiating to long-term formative and reparative processes. Such a common link between destructive and plastic responses provides an important view of cellular and tissue maintenance in the nervous system.

Protein kinase C activator phorbol 12, 13-dibutyrate inhibits platelet activating factor-stimulated Ca2+ mobilization and phosphoinositide turnover in neurohybrid NG108-15 cells

The protein kinase C (PKC) activator, phorbol 12, 13-dibutyrate (PDBu) dose-dependently inhibited platelet-activating factor (PAF)-induced [Ca2+]i elevation and inositol monophosphate (IP1) accumulation in neurohybrid NG108-15 cells with IC50 values of 162 nM and 35 nM, respectively. Pretreatment of NG108-15 cells with PKC inhibitor H-7 partially prevented the inhibitory effect of PDBu on PAF-induced [Ca2+]i elevation as well as PI metabolism in NG108-15 cells. Pretreatment of the cells with pertussis toxin (PTX) resulted in a dose-dependent inhibition of PAF-induced IP1 and IP3 accumulation but only slightly affected PAF-induced [Ca2+]i elevation in NG108-15 cells. The results reveal that PAF receptor-mediated Ca2+ mobilization and PI metabolism in NG108-15 cells are regulated by PKC while a PTX-sensitive G protein is coupled to PAF receptor for inducing activation of phospholipase C.

Platelet-activating factor (PAF) receptor in rat brain: PAF mobilizes intracellular Ca2+ in hippocampal neurons

Platelet-activating factor (PAF), an alkylether phospholipid, is produced in the brain when it is subjected to various stimuli. Using a Xenopus oocyte expression system, we obtained evidence for functional PAF receptor mRNA expression in rat brain. The presence of the PAF receptor was confirmed and shown to be quite ubiquitous in the CNS by RNA blot and radioligand binding studies. To investigate the neuronal functions of PAF, intracellular Ca2+ increase elicited by nanomolar PAF application was analyzed in cultured rat hippocampal cells. Fractions of NMDA-responsive cells and non-NMDA-responsive cells were shown to respond to PAF, suggesting a potential role for PAF in the Ca2+ signaling pathway in the hippocampus.

Immunocompetent cell markers in human fetal astrocytes and neurons in culture

During the past few years, evidence has accumulated that interaction with peripheral immune cells as well as immunoregulatory functions in the central nervous system (CNS) can be played by several types of brain resident cells. Since very little information is available in man, however, we investigated the presence of markers so far considered typical of immunocompetent cells in in vitro cultures of human fetal brain. Immunocytochemistry at the light, scanning, and transmission electron microscopic levels revealed positivity for a very restricted range of macrophage antigens in astrocytes, which, however, were incapable of phagocytosis. In particular, expression of the major histocompatibility complex-class II antigen HLA-DR was observed in the cytoplasm and on the cell surface of GFA-P+ astrocytes and increased with time in culture and cell passages. Among the T-lymphocyte markers tested, Thy.1 and CD4 were positive. Both neurons and astrocytes carried Thy.1 from early cell passages. Noteworthy was the presence of CD4, which serves as the receptor for AIDS virus, in neurons from the first 2 weeks, whereas astrocytes became positive after only 4-6 weeks. Even if most staining was in the cytoplasm, some was exposed on cell surface. Astrocytes were found positive for the B-lymphocyte marker CD21, the cellular receptor for Epstein-Barr virus, whereas CD24 was detected in both neurons and astrocytes. Both antigens are related to B-cell proliferation. Results are in favour of the hypothesis of human brain cells being actively involved in CNS immunological events.

Correlation between P19 presence and MHC class II expression in human fetal astroglial cells cocultured with HTLV-I donor cells

The possibility of a direct infection of human brain by HTLV-I, has been studied using an in vitro model. Human fetal astroglial cells were cocultivated with irradiated HTLV-I donor cell line MT-2, and assayed for the presence of HTLV-I core protein p19 after 1 week. Fifty-six per cent of GFAP positive astrocytes showed the viral core protein p19 and increased expression of Class II MHC antigens. Electron microscopy of astroglial cells exposed to HTLV-I revealed the presence of vacuoli-like structures containing viral core protein p19. Cell intermediate filament cytoskeleton was also disorganized. Even if this study does not provide direct evidence for virus replication inside astroglial cells, all these findings suggest that HTLV-I can indeed enter the cell and exert a cytopathic effect. Therefore the results of the present study are consistent with the hypothesis that astroglial cells could be involved in demyelination processes occurring in the HTLV-I associated neurological disorders, such as human associated myelopathy and tropical spastic paraparesis.

Dystrophin immunoreactivity in normal and Duchenne human fetal neurons in culture

Dystrophin, the protein product defective in Duchenne muscular dystrophy (DMD), is present in all types of muscle and in the brain. The function of the protein is unknown and its role in the brain is unclear, although 30% of DMD patients show nonprogressive mental retardation. We have therefore studied the localisation of dystrophin in cultures of normal and DMD human fetal neurons using antibodies raised to different regions of the protein. Dystrophin immunoreactivity was demonstrated in the soma and axon hillock of normal neurons and appeared to be associated with the inner part of the cell membrane, although some intracellular staining was also observed. Positive dystrophin staining was present only in cells with fully developed neuronal features, although not all the neurons were positive. Glial cells were always negative for the antigen. Immunostaining with antibodies to the brain spectrins indicate that the dystrophin antibodies did not crossreact with these proteins. The possibility of cross-reactivity with other proteins is discussed. Studies of cells cultured from a DMD fetus also showed specific dystrophin immunostaining in neurons, although the muscle was generally negative for dystrophin. However, the localisation of dystrophin immunostaining and that of the brain spectrins and neurofilaments appeared abnormal, as did the overall morphology of the cells. This suggests that dystrophin may play a role during brain development and dystrophin deficiency results in abnormal neuronal features. This would be consistent with the nonprogressive nature of the mental retardation observed in DMD patients.