An issue of concern: unique truncated ORF8 protein variants of SARS-CoV-2

Open reading frame 8 (ORF8) shows one of the highest levels of variability among accessory proteins in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of Coronavirus Disease 2019 (COVID-19). It was previously reported that the ORF8 protein inhibits the presentation of viral antigens by the major histocompatibility complex class I (MHC-I), which interacts with host factors involved in pulmonary inflammation. The ORF8 protein assists SARS-CoV-2 in evading immunity and plays a role in SARS-CoV-2 replication. Among many contributing mutations, Q27STOP, a mutation in the ORF8 protein, defines the B.1.1.7 lineage of SARS-CoV-2, engendering the second wave of COVID-19. In the present study, 47 unique truncated ORF8 proteins (T-ORF8) with the Q27STOP mutations were identified among 49,055 available B.1.1.7 SARS-CoV-2 sequences. The results show that only one of the 47 T-ORF8 variants spread to over 57 geo-locations in North America, and other continents, which include Africa, Asia, Europe and South America. Based on various quantitative features, such as amino acid homology, polar/non-polar sequence homology, Shannon entropy conservation, and other physicochemical properties of all specific 47 T-ORF8 protein variants, nine possible T-ORF8 unique variants were defined. The question as to whether T-ORF8 variants function similarly to the wild type ORF8 is yet to be investigated. A positive response to the question could exacerbate future COVID-19 waves, necessitating severe containment measures.

An issue of concern: unique truncated ORF8 protein variants of SARS-CoV-2

Open reading frame 8 (ORF8) shows one of the highest levels of variability among accessory proteins in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of Coronavirus Disease 2019 (COVID-19). It was previously reported that the ORF8 protein inhibits the presentation of viral antigens by the major histocompatibility complex class I (MHC-I), which interacts with host factors involved in pulmonary inflammation. The ORF8 protein assists SARS-CoV-2 in evading immunity and plays a role in SARS-CoV-2 replication. Among many contributing mutations, Q27STOP, a mutation in the ORF8 protein, defines the B.1.1.7 lineage of SARS-CoV-2, engendering the second wave of COVID-19. In the present study, 47 unique truncated ORF8 proteins (T-ORF8) with the Q27STOP mutations were identified among 49,055 available B.1.1.7 SARS-CoV-2 sequences. The results show that only one of the 47 T-ORF8 variants spread to over 57 geo-locations in North America, and other continents, which include Africa, Asia, Europe and South America. Based on various quantitative features, such as amino acid homology, polar/non-polar sequence homology, Shannon entropy conservation, and other physicochemical properties of all specific 47 T-ORF8 protein variants, nine possible T-ORF8 unique variants were defined. The question as to whether T-ORF8 variants function similarly to the wild type ORF8 is yet to be investigated. A positive response to the question could exacerbate future COVID-19 waves, necessitating severe containment measures.

NPD1-mediated stereoselective regulation of BIRC3 expression through cREL is decisive for neural cell survival

Neuroprotectin D1 (NPD1), a docosahexaenoic acid (DHA)-derived mediator, induces cell survival in uncompensated oxidative stress (OS), neurodegenerations or ischemic stroke. The molecular principles underlying this protection remain unresolved. We report here that, in retinal pigment epithelial cells, NPD1 induces nuclear translocation and cREL synthesis that, in turn, mediates BIRC3 transcription. NPD1 activates NF-κB by an alternate route to canonical signaling, so the opposing effects of TNFR1 and NPD1 on BIRC3 expression are not due to interaction/s between NF-κB pathways. RelB expression follows a similar pattern as BIRC3, indicating that NPD1 also is required to activate cREL-mediated RelB expression. These results suggest that cREL, which follows a periodic pattern augmented by the lipid mediator, regulates a cluster of NPD1-dependent genes after cREL nuclear translocation. BIRC3 silencing prevents NPD1 induction of survival against OS. Moreover, brain NPD1 biosynthesis and selective neuronal BIRC3 abundance are increased by DHA after experimental ischemic stroke followed by remarkable neurological recovery. Thus, NPD1 bioactivity governs key counter-regulatory gene transcription decisive for retinal and brain neural cell integrity when confronted with potential disruptions of homeostasis.

Essential versus accessory aspects of cell death: recommendations of the NCCD 2015

Cells exposed to extreme physicochemical or mechanical stimuli die in an uncontrollable manner, as a result of their immediate structural breakdown. Such an unavoidable variant of cellular demise is generally referred to as ‘accidental cell death' (ACD). In most settings, however, cell death is initiated by a genetically encoded apparatus, correlating with the fact that its course can be altered by pharmacologic or genetic interventions. ‘Regulated cell death' (RCD) can occur as part of physiologic programs or can be activated once adaptive responses to perturbations of the extracellular or intracellular microenvironment fail. The biochemical phenomena that accompany RCD may be harnessed to classify it into a few subtypes, which often (but not always) exhibit stereotyped morphologic features. Nonetheless, efficiently inhibiting the processes that are commonly thought to cause RCD, such as the activation of executioner caspases in the course of apoptosis, does not exert true cytoprotective effects in the mammalian system, but simply alters the kinetics of cellular demise as it shifts its morphologic and biochemical correlates. Conversely, bona fide cytoprotection can be achieved by inhibiting the transduction of lethal signals in the early phases of the process, when adaptive responses are still operational. Thus, the mechanisms that truly execute RCD may be less understood, less inhibitable and perhaps more homogeneous than previously thought. Here, the Nomenclature Committee on Cell Death formulates a set of recommendations to help scientists and researchers to discriminate between essential and accessory aspects of cell death.

Neuroprotectin D1 is synthesized in the cone photoreceptor cell line 661W and elicits protection against light-induced stress

Docosahexaenoic acid (DHA), an omega-3 fatty acid family member, is obtained by diet or synthesized from dietary essential omega-3 linolenic acid and delivered systemically to the choriocapillaris, from where it is taken up by the retinal pigment epithelium (RPE). DHA is then transported to the inner segments of photoreceptors, where it is incorporated in phospholipids during the biogenesis of outer segment disk and plasma membranes. As apical photoreceptor disks are gradually shed and phagocytized by the RPE, DHA is retrieved and recycled back to photoreceptor inner segments for reassembly into new disks. Under uncompensated oxidative stress, the docosanoid neuroprotectin D1 (NPD1), a potent mediator derived from DHA, is formed by the RPE and displays its bioactivity in an autocrine and paracrine fashion. The purpose of this study was to determine whether photoreceptors have the ability to synthesize NPD1, and whether or not this lipid mediator exerts bioactivity on these cells. For this purpose, 661W cells (mouse-derived photoreceptor cells) were used. First we asked whether these cells have the ability to form NPD1 by incubating cells with deuterium (d4)-labeled DHA exposed to dark and bright light treatments, followed by LC-MS/MS-based lipidomic analysis to identify and quantify d4-NPD1. The second question pertains to the potential bioactivity of these lipids. Therefore, cells were incubated with 9-cis-retinal in the presence of bright light that triggers cell damage and death. Following 9-cis-retinal loading, DHA, NPD1, or vehicle were added to the media and the 661W cells maintained either in darkness or under bright light. DHA and NPD1 were then quantified in cells and media. Regardless of lighting conditions, 661W cells acquired DHA from the media and synthesized 4-9 times as much d4-NPD1 under bright light treatment in the absence and presence of 9-cis-retinal compared to cells in darkness. Viability assays of 9-cis-retinal-treated cells demonstrated that 34 % of the cells survived without DHA or NPD1. However, after bright light exposure, DHA protected 23 % above control levels and NPD1 increased protection by 32 %. In conclusion, the photoreceptor cell line 661W has the capability to synthesize NPD1 from DHA when under stress, and, in turn, can be protected from stress-induced apoptosis by DHA or NPD1, indicating that photoreceptors effectively contribute to endogenous protective signaling mediated by NPD1 under stressful conditions.

The docosanoid neuroprotectin D1 induces homeostatic regulation of neuroinflammation and cell survival

The onset of neurodegenerations and nervous system injury both trigger cell signaling perturbations that lead to damage of neuronal circuits and synapic connections, as well as protective signaling that aims to halt disease onset. Here we review recent findings that support the role of the docosanoid mediator neuroprotectin D1 (NPD1) as an early response or sentinel during the initial phase of nervous system damage. NPD1 is derived from docosahexaenoic acid that is selectively concentrated and retained in the nervous system. The protein misfolding triggers the biosynthesis of NPD1 which in turn downregulates pathways that lead to cell death and changes the outcome to cell survival. Proteotoxic stress as a result of protein misfolding is a widespread event in many neurodegenerative diseases. Therefore, mechanisms and mediators such as NPD1 that curtail consequences of these events are of interest as leads in the search for novel preventive and or therapeutic approaches.

Survival signalling in Alzheimer's disease

Significant advancements in our understanding of cell-survival signalling in AD (Alzheimer's disease) stem from recent investigations into the metabolism, trafficking and fate of the essential omega-3 fatty acid DHA (docosahexaenoic acid) (C(22:6), n=3). Brain synaptic terminals and neuronal plasma membranes are highly enriched in DHA, and deficiencies in this polyunsaturated fatty acid are characteristic of AD-affected brain. Oxidative stress, targeting phospholipids containing DHA, and age-related DHA depletion are associated with the progressive erosion of normal cognitive function in AD. Current studies support the idea that DHA itself and novel DHA-derived neural synapse- and membrane-derived lipid messengers have considerable potential to modulate cell survival signalling in stressed cultured neural cell models in vitro and in mammalian models of learning, memory and AD in vivo. Key players in this intrinsic rescue system include the alpha-secretase-processed neurotrophin sAPPalpha [soluble APPalpha (amyloid precursor protein alpha)] peptide, the DHA-derived 10,17S-docosatriene NPD1 (neuroprotectin D1), a tandem brain cytosolic phospholipase A(2) and 15-lipoxygenase enzymatic system that biosynthesizes NPD1, and a small family of anti-apoptotic neuroprotective genes that encode Bcl-2, Bcl-X(L) and Bfl-1 (A1). This paper reviews current ideas regarding DHA and the oxygenated DHA derivative NPD1, intrinsically triggered biolipid neuroprotectants that along with their associated rescue pathways, contribute to life-or-death decisions of brain cells during homoeostasis, aging and neurodegenerative disease.

Regulatory region variability in the human presenilin-2 (PSEN2) gene: potential contribution to the gene activity and risk for AD

We have analyzed the 5'-upstream promoter region of the presenilin 2 gene (PSEN2) for regulatory elements and examined Alzheimer disease (AD) patients and non-demented individuals for polymorphisms in the 5' upstream promoter region of the PSEN2 gene. Direct sequencing analysis detected a common single adenine (A) nucleotide deletion polymorphism in the upstream promoter region of the PSEN2 gene. Examination of cohorts of AD patients and age-matched control individuals revealed no statistically significant differences in the frequency of this polymorphism when compared with the total sample of AD patients and control individuals. However, subgroup and regression analysis suggested that the relatively rare -A/-A genotype increases risk of AD among subjects lacking apolipoprotein E (APOE) epsilon4 and among persons ages 65 years and younger. DNA sequence and DNA-protein binding analysis demonstrated that this mutation negates binding with putative repressor transcription factor (TF), interferon regulatory factor 2 (IRF2), in nuclear extracts prepared from the aged human brain neocortex. However this mutation creates a potential regulatory element, C/EBPbeta, that is responsive to pro-inflammatory (PI) induction. The expression activity assay with luciferase reporter gene into normal human neural progenitor cells in primary culture shows that the mutant PSEN2 regulatory region exhibits a 1.8-fold higher level of basal expression and is sensitive to IL-1beta and Abeta42, but that it is synergistically induced 3.2-fold over the wild-type PSEN2 by [IL-1beta+Abeta42]. These results suggest that under Pl and oxygen stress conditions relatively minor variations in PSEN2 promoter DNA sequence structure can enhance PSEN2 gene expression and that consequently these may play a role in the induction and/or proliferation of a Pl response in AD brain.

Gene expression analyzed by microarrays in HSV-1 latent mouse trigeminal ganglion following heat stress

An understanding of the cellular genes whose expression is altered during HSV reactivation will enable us to better understand host responses and biochemical pathways involved in the process. Furthermore, this knowledge could allow us to develop gene-targeted inhibitors to prevent viral reactivation. Mice latent with HSV-1 strain McKrae and uninfected control mice were subjected to hyperthermic stress (43 degrees C for 10 min) and their trigeminal ganglia (TG) collected 1 h later. Two additional groups included HSV-1 latently infected and uninfected mice not subjected to hyperthermic stress. Poly A+ mRNA was enriched from total mouse TG RNA and reverse transcribed using MMLV RT. Radioactively labeled cDNAs were analyzed by microarray analysis. A stress/toxicology array of 149 mouse genes on a nylon membrane was used. The labeled cDNAs prepared from latently infected, stressed mice demonstrated 3-fold or greater increases in certain mRNA-early response genes (ERGs) compared to cDNAs from uninfected, stressed control mice. The ERG mRNAs that showed increases included two heat shock proteins (HSP60 and HSP40), a basic transcription factor (BTF T62), a DNA repair enzyme, two kinases [MAP kinase and a stress-induced protein kinase (SADK)], an oxidative stress-induced protein, a manganese superoxide dismutase precursor-2 (SOD-2), and cyclooxygenase 2 (COX-2). The gene expression in unstressed, infected TGs was similar to the gene expression in unstressed, uninfected controls. These results suggest that there is a significant difference in the ERG expression profile in latently infected TGs undergoing stress-induced reactivation compared to uninfected TGs.

Differential interaction of platelet-activating factor and NMDA receptor function in hippocampal and dorsal striatal memory processes

The interaction between platelet activating factor (PAF) and NMDA receptor function in hippocampal and dorsal striatal memory processes was examined. In both a hidden and a visible platform water maze task, peripheral post-training injection of MK-801 (0.05 mg/kg) impaired memory. Post-training intrahippocampal infusions of PAF (1.0 microg/0.5 microl) enhanced memory in the hidden platform task, while intradorsal striatal infusion of PAF (1.0 microg/0.5 microl) enhanced memory in the visible platform task. The memory impairing effects of post-training injection of MK-801 was blocked by concurrent intrahippocampal infusion of PAF. In contrast, post-training injection of MK-801 blocked the memory enhancing effects of concurrent intradorsal striatal infusion of PAF. The results suggest that (1) the memory enhancing effects of intracerebral PAF infusion involve an interaction with NMDA receptor function, and (2) the nature of this interaction may represent a differential mechanism mediating the distinct roles of the hippocampus and dorsal striatum in cognitive memory and stimulus-response habit formation, respectively.

Effects of topical unoprostone and latanoprost on acute and recurrent herpetic keratitis in the rabbit

PURPOSE

To determine the effect of the topical ocular hypotensive drug, isopropyl unoprostone, a docosanoid molecule with very weak prostaglandin activity, on herpes keratitis in the rabbit eye.

METHODS

For acute disease, rabbit corneas inoculated with the corticosteroid-sensitive F(MP)E strain of herpes simplex virus type 1 were treated with various combinations of 0.12% isopropyl unoprostone, latanoprost, trifluridine, benzalkonium chloride 0.02%, dexamethasone sodium phosphate, ketorolac tromethamine, or saline solution beginning 1 day after infection. Severity of keratitis was evaluated in a masked manner. For recurrent disease, rabbit corneas infected with McKrae strain herpes simplex virus type 1 were treated with unoprostone or saline solution on postinfection days 25 to 42, and the presence or absence of lesions was recorded.

RESULTS

Eyes treated with unoprostone showed significantly less severe disease than saline-treated or latanoprost-treated eyes during acute infection. Unoprostone-treated and saline-treated eyes showed no significant difference in the frequency of recurrent lesions. Eyes treated with latanoprost and/or dexamethasone, separately or in combination, showed increased severity of acute herpes simplex virus keratitis, whereas benzalkonium chloride 0.02%--treated eyes showed no significant difference, compared with saline treatment. Trifluridine resulted in rapid healing.

CONCLUSIONS

Unoprostone did not increase the severity or recurrence rate of herpes simplex virus keratitis. Unoprostone requires twice-a-day administration, compared with once-a-day for latanoprost, and unoprostone lowers intraocular pressure less than latanoprost. Nevertheless, unoprostone's superior safety profile may make its use advantageous. Benzalkonium chloride alone did not make the keratitis worse.

Diacylglycerol kinase epsilon regulates seizure susceptibility and long-term potentiation through arachidonoyl- inositol lipid signaling

Arachidonoyldiacylglycerol (20:4-DAG) is a second messenger derived from phosphatidylinositol 4,5-bisphosphate and generated by stimulation of glutamate metabotropic receptors linked to G proteins and activation of phospholipase C. 20:4-DAG signaling is terminated by its phosphorylation to phosphatidic acid, catalyzed by diacylglycerol kinase (DGK). We have cloned the murine DGKepsilon gene that showed, when expressed in COS-7 cells, selectivity for 20:4-DAG. The significance of DGKepsilon in synaptic function was investigated in mice with targeted disruption of the DGKepsilon. DGKepsilon(-/-) mice showed a higher resistance to electroconvulsive shock with shorter tonic seizures and faster recovery than DGKepsilon(+/+) mice. The phosphatidylinositol 4,5-bisphosphate-signaling pathway in cerebral cortex was greatly affected, leading to lower accumulation of 20:4-DAG and free 20:4. Also, long-term potentiation was attenuated in perforant path-dentate granular cell synapses. We propose that DGKepsilon contributes to modulate neuronal signaling pathways linked to synaptic activity, neuronal plasticity, and epileptogenesis.

Presenilin-2 (PS2) expression up-regulation in a model of retinopathy of prematurity and pathoangiogenesis

Presenilin-2 (PS2; AD4), a regulator of intercellular signaling during CNS development and cell fate determination, appears to be involved in pathogenic processing of beta-amyloid precursor protein (betaAPP) into potentially neurotoxic beta-amyloid (Abeta) peptides. The PS2 gene promoter contains multiple DNA binding sites for the relatively rare hypoxia-inducible transcription factor HIF-1, suggesting that PS2 expression may be a sensitive indicator of decreased oxygen availability. We have used a cycled hypoxia/hyperoxia (10-50% O2) protocol followed by normoxia (20% O2) as a retinal model of retinopathy of prematurity to induce neovascularization (NV) in rat pups. Retinal cell nuclear extracts from pups undergoing hypoxia exhibited a dramatic increase in HIF-1-DNA binding, followed by a delayed (2-7 day) elevation of PS2 RNA message and protein. PS2 gene activation during hypoxia may direct cellular fate towards pathoangiogenesis and intercellular PS2-mediated signaling dysfunction.

Attenuated LTP in hippocampal dentate gyrus neurons of mice deficient in the PAF receptor

Platelet-activating factor (PAF), a bioactive lipid (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) derived from phospholipase A(2) and other pathways, has been implicated in neural plasticity and memory formation. Long-term potentiation (LTP) can be induced by the application of PAF and blocked by a PAF receptor (PAF-R) inhibitor in the hippocampal CA1 and dentate gyrus. To further investigate the role of PAF in synaptic plasticity, we compared LTP in dentate granule cells from hippocampal slices of adult mice deficient in the PAF-R and their age-matched wild-type littermates. Whole cell patch-clamp recordings were made in the current-clamp mode. LTP in the perforant path was induced by a high-frequency stimulation (HFS) and defined as >20% increase above baseline of the amplitude of excitatory postsynaptic potentials (EPSPs) from 26 to 30 min after HFS. HFS-induced enhancement of the EPSP amplitude was attenuated in cells from the PAF-R-deficient mice (163 +/- 14%, mean +/- SE; n = 32) when compared with that in wild-type mice (219 +/- 17%, n = 32). The incidence of LTP induction was also lower in the cells from the deficient mice (72%, 23 of 32 cells) than in the wild-type mice (91%, 29 of 32 cells). Using paired-pulse facilitation as a synaptic pathway discrimination, it appeared that there were differences in LTP magnitudes in the lateral perforant path but not in the medial perforant path between the two groups. BN52021 (5 microM), a PAF synaptosomal receptor antagonist, reduced LTP in the lateral path in the wild-type mice. However, neither BN52021, nor BN50730 (5 microM), a microsomal PAF-R antagonist, reduced LTP in the lateral perforant path in the receptor-deficient mice. These data provide evidence that PAF-R-deficient mice are a useful model to study LTP in the dentate gyrus and support the notion that PAF actively participates in hippocampal synaptic plasticity.

Alterations in lipid and calcium metabolism associated with seizure activity in the postischemic brain

Transient ischemia is known to lead to a long-lasting depression of cerebral metabolic rate and blood flow and to an attenuated metabolic and circulatory response to physiological stimuli. However, the corresponding responses to induced seizures are retained, demonstrating preserved metabolic and circulatory capacity. The objective of the present study was to explore how a preceding period of ischemia (15 min) alters the release of free fatty acids (FFAs) and diacylglycerides (DAGs), the formation of cyclic nucleotides, and the influx/efflux of Ca(2+), following intense neuronal stimulation. For that purpose, seizure activity was induced with bicuculline for 30 s or 5 min at 6 h after the ischemia. Extracellular Ca(2+) concentration (Ca(2+)(e)) was recorded, and the tissue was frozen in situ for measurements of levels of FFAs, DAGs, and cyclic nucleotides. Six hours after ischemia, the FFA concentrations were normalized, but there was a lowering of the content of 20:4 in the DAG fraction. Cyclic AMP levels returned to normal values, but cyclic GMP content was reduced. Seizures induced in postischemic animals showed similar changes in Ca(2+)(e), as well as in levels of FFAs, DAGs, and cyclic nucleotides, as did seizures induced in nonischemic control animals, with the exception of an attenuated rise in 20:4 content in the DAG fraction. We conclude that, at least in the neocortex, seizure-induced phospholipid hydrolysis and cyclic cAMP/cyclic GMP formation are not altered by a preceding period of ischemia, nor is there a change in the influx/efflux of Ca(2+) during seizure discharge or in associated spreading depression.

Modulation of early response gene expression by prostaglandins in cultured rat retinal pigment epithelium cells

PURPOSE

To explore the role of prostaglandins (PGs) as modulators of retinal pigment epithelium (RPE) rod outer segment (ROS)-phagocytosis and ROS-phagocytosis-induced gene expression.

METHODS

RPE cells in primary cell culture were pre-incubated with PGE( 2), PGD(2), PGF(2)alpha, PGJ(2), 15-deoxy-Delta( 12,14)-PGJ(2) or U-46619 (stable analog of thromboxane A(2)), and fed with a suspension of ROS. Expression of zif-268 and tis-1 mRNA was determined by Northern blotting. DNA-binding activity of TIS-1 protein was assessed by electrophoretic mobility shift assay. Concentration of PGE (2) and PGD (2) in the tissue culture medium was measured by enzyme immuno-assay. Phagocytis-tosis was quantified by counting of double-immunostained bound and ingested ROS.

RESULTS

PGE 2, the most potent of PGs, strongly elevated both basal and ROS-phagocytosis-induced levels of tis-1 mRNA, while significantly inhibiting both basal and phagocytosis-induced expression of zif-268 mRNA. PGD(2), PGJ(2) and 15-deoxy-Delta(12,14)-PGJ( 2) elevated ROS-phagocytosis-induced, but not basal, expression of tis-1 mRNA expression. PGF(2alpha) super-induced both phagocytosis-induced and basal tis-1 mRNA expression. U-46619 and carbaprostacyclin had no effect on expression of tis-1 mRNA. PGE(2) was the only PG to affect zif-268 expression. Exogenous PGE(2), PGD( 2) and PGF(2alpha), when added to the medium at 1-microM concentrations, significantly inhibited ingestion of ROS, with PGE(2) being the most potent PG affecting ROS-phagocytosis.

CONCLUSIONS

PGs act as selective regulators of phagocytosis-induced transcription factor gene expression in RPE cells, as well as of ROS-phagocytosis itself. This modulation may help to ensure specificity in the differential activation of target genes by ROS-phagocytosis receptor-mediated signal transduction in RPE cells.

Neuroinflammatory signaling upregulation in Alzheimer's disease

Alzheimer's disease (AD) is a progressive, neurodestructive process of the human neocortex, characterized by the deterioration of memory and higher cognitive function. A progressive and irreversible brain disorder, AD is characterized by three major pathogenic episodes involving (a) an aberrant processing and deposition of beta-amyloid precursor protein (betaAPP) to form neurotoxic beta-amyloid (betaA) peptides and an aggregated insoluble polymer of betaA that forms the senile plaque, (b) the establishment of intraneuronal neuritic tau pathology yielding widespread deposits of agyrophilic neurofibrillary tangles (NFT) and (c) the initiation and proliferation of a brain-specific inflammatory response. These three seemingly disperse attributes of AD etiopathogenesis are linked by the fact that proinflammatory microglia, reactive astrocytes and their associated cytokines and chemokines are associated with the biology of the microtubule associated protein tau, betaA speciation and aggregation. Missense mutations in the presenilin genes PS1 and PS2, implicated in early onset familial AD, cause abnormal betaAPP processing with resultant overproduction of betaA42 and related neurotoxic peptides. Specific betaA fragments such as betaA42 can further potentiate proinflammatory mechanisms. Expression of the inducible oxidoreductase cyclooxygenase-2 and cytosolic phospholipase A2 (cPLA2) are strongly activated during cerebral ischemia and trauma, epilepsy and AD, indicating the induction of proinflammatory gene pathways as a response to brain injury. Neurotoxic metals such as aluminum and zinc, both implicated in AD etiopathogenesis, and arachidonic acid, a major metabolite of brain cPLA2 activity, each polymerize hyperphosphorylated tau to form NFT-like bundles. Further, epidemiological and longitudinal studies have identified a reduced risk for AD in patients (<70 yrs) previously treated with non-steroidal anti-inflammatory drugs for non-CNS afflictions that include arthritis. This review will focus on the interrelationships between the mechanisms of PS1, PS2 and betaAPP gene expression, tau and betaA deposition and the induction, regulation and proliferation in AD of the neuroinflammatory response. Novel therapeutic interventions in AD are discussed.

Photoreceptor phagocytosis selectively activates PPARgamma expression in retinal pigment epithelial cells

Phagocytosis of tips of rod outer segments (ROS) by retinal pigment epithelial (RPE) cells is vitally important for maintaining structural and functional integrity of the retina. We previously reported that receptor-mediated specific phagocytosis of ROS induces expression of early response genes coding for transcription factors. Here we study the expression of peroxisome proliferator-activated receptors (PPAR) -alpha, -delta (beta) and -gamma during ROS phagocytosis of rat RPE cells in primary cell culture, using competitive quantitative RT-PCR. During phagocytosis of ROS (but not of latex particles) by RPE cells, RT-PCR revealed a transient increase in PPARgamma mRNA expression, that peaked at 4-6 hr. We sequenced and described two alternatively spliced variants of rat PPARgamma: rPPARgamma1a and rPPARgamma1b. Both of these, along with the recently described rPPARgamma2 were induced by ROS phagocytosis. PPARalpha and PPARdelta mRNA expression was also detected in RPE cells, but the level of expression did not change during ROS phagocytosis. All-trans-retinoic acid and prostaglandin E(2) (PGE(2)) selectively potentiated both basal and ROS-phagocytosis-induced PPARgamma expression. All-trans-retinoic acid had the opposite inhibitory effect on PPARalpha and PPARdelta expression. Cycloheximide had a dual action on PPARgamma expression in RPE cells: it enhanced expression under basal conditions but repressed expression induced by ROS phagocytosis. It also stimulated expression of PPARalpha but had no effect on PPARdelta. Selective activation of PPARgamma may play an important role in regulating the expression of target genes that are involved in lipid and fatty acid metabolism in the photoreceptor renewal process.

Cortical impact injury in rats promotes a rapid and sustained increase in polyunsaturated free fatty acids and diacylglycerols

Neurotrauma activates the release of membrane phospholipid-derived second messengers, such as free arachidonic acid (20:4n-6, AA) and diacylglycerols (DAGs). In the present study, we analyze the effect of cortical impact injury of low-grade severity applied to the rat frontal right sensory-motor cortex (FRC) on the accumulation of free fatty acids (FFAs) and DAGs in eight brain areas 30 min and 24 hours after the insult. At these times, accumulation of FFAs and DAGs occurred mainly in the damaged FRC. The cerebellum was the only other brain area that displayed a significant accumulation of DAGs by day one post-injury. By 30 min, accumulation of free AA in the FRC displayed the greatest relative increase (300% over sham value), followed by free docosahexaenoic acid (22:6n-3, DHA, 150%), while both 20:4-DAGs and 22:6-DAGs were increased 100% over sham values. At day one, free 22:6 and 22:6-DAGs showed the greatest increase (590% and 230%, respectively). These results suggest that TBI elicits the hydrolysis of phospholipids enriched in excitable membranes, targeting early on 20:4-phospholipids (by 30 min post- trauma) and followed 24 hours later by preferential hydrolysis of DHA-phospholipids. These lipid metabolic changes may contribute to the initiation and maturation of neuronal and fiber track degeneration observed following cortical impact injury.

Induction of cyclooxygenase-2 gene expression in retinal pigment epithelium cells by photoreceptor rod outer segment phagocytosis and growth factors

Retinal pigment epithelium (RPE) cells in culture display selective induction of certain early response transcription factors at the onset of photoreceptor rod outer segment (ROS)-specific phagocytosis (Ershov et al., 1996a). Moreover, this response is modulated by prostaglandins. The purpose of this study is to examine the expression of the key enzymes in prostaglandin synthesis: cyclooxygenase-1 (COX-1, constitutive) and cyclooxygenase-2 (COX-2, inducible), during phagocytosis of ROS by RPE cells. Rat RPE cells in primary cell culture were fed with a suspension of freshly isolated rat ROS. COX-1 and COX-2 mRNA expression was studied by quantitative competitive reverse transcriptase-polymerase chain reaction (RT-PCR). During phagocytosis of ROS by RPE cells, RT-PCR revealed an increase in mRNA expression of COX-2, but not of COX-1. COX-2 was also induced by the phospholipid growth factor lyso-phosphatidic acid (LPA) and by the peptide growth factors platelet derived growth factor (PDGF), basic fibroblast growth factor (FGF), and transforming growth factor (TGFbeta), but not nerve growth factor (NGF). Induction of COX-2 by ROS phagocytosis and growth factors through the modulation of prostanoid synthesis may play an important role in the regulation of cell functions associated with photoreceptor cell renewal.

Interleukin-1 beta activates expression of cyclooxygenase-2 and inducible nitric oxide synthase in primary hippocampal neuronal culture: platelet-activating factor as a preferential mediator of cyclooxygenase-2 expression

Interleukin-1 beta (IL-1beta) is an inflammatory cytokine whose expression is elevated in brain during seizures, ischemia, and injury. Expression of IL-1beta and its receptor can also be observed in normal brain. Platelet-activating factor (PAF) is also a dual mediator that promotes neuronal plasticity responses as well as inflammation. We have determined the role of PAF in the regulation of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) genes by IL-1beta in rat primary hippocampal cultures. As assessed by reverse transcriptase/polymerase chain reaction (RT/PCR), recombinant mouse IL-1beta (1 nM) led to an induction of COX-2 mRNA which peaked at 2 hours, declined to baseline levels by 4 hours, began to rise again by 6 hours, and remained elevated at 24 hours post-treatment. iNOS mRNA was also induced, but unlike COX-2, its abundance peaked at 4 hours and decreased by 6 hours to a plateau lasting through 24 hours. Pretreatment with PAF antagonist BN50730 blocked induction of COX-2 mRNA by 2-hour IL-1beta treatment, and 2-hour treatment with the PAF analog mcPAF mimicked the effects of IL-1beta on COX-2 mRNA levels. Following injury, synaptic plasticity changes may be affected by IL-1beta-PAF-COX-2 neuronal signaling.

Platelet-activating factor inhibits ionotropic GABA receptor activity in cultured hippocampal neurons

Platelet-activating factor (PAF), one of the most potent bioactive lipids, has been implicated in modulating long-term potentiation (LTP) and neurotoxicity. In the CNS, glutamate and GABA are the major excitatory and inhibitory neurotransmitters, respectively. Previous work has focused on the effects of PAF on glutamatergic receptor responses. The purpose of the present study was to investigate the possible actions of PAF on ionotropic GABA receptor responses in primary cultured hippocampal neurons using the whole-cell and single channel patch clamp techniques. Extracellular application of PAF induced a reduction of the GABA gated Cl- current in a majority of cells (29 of 44 cells), while it caused an enhancement in 10 of 44 cells. A similar heterogeneous modulation of PAF on the GABA receptor activities was also observed in outside-out patch recordings. Moreover, the cell-attached single channel recordings showed that PAF decreased the GABA channel activity. Therefore, PAF may modulate synaptic activity by inhibiting GABA receptor channels. During seizures and neural injury, when enhanced synthesis of this lipid mediator takes place, the actions of PAF on inhibitory GABA receptors may contribute to synaptic dysfunction.

Secretory phospholipase A2 potentiates glutamate-induced rat striatal neuronal cell death in vivo

The secretory phospholipases A2 (sPLA2) OS2 (10, 20 and 50 pmol) or OS1, (50 pmol) purified from taipan snake Oxyuranus scutellatus scutellatus venom, and the excitatory amino acid glutamate (Glu) (2.5 and 5.0 micromol) were injected into the right striatum of male Wistar rats. Injection of 10 and 20 pmol OS2 caused no neurological abnormalities or tissue damage. OS2 (50 pmol) caused apathy and circling towards the injection side. Histology revealed an infarct at the injection site. Injection of 50 pmol OS1 showed very little or no signs of neurotoxicity. Injection of 2.5 micromol Glu caused no tissue damage or neurological abnormality. After injection of 5.0 micromol Glu, the animals initially circled towards the side of injection, and gradually developed generalized clonic convulsions. These animals showed a well demarcated striatal infarct. When non-toxic concentrations of 20 pmol OS2 and 2.5 micromol Glu were co-injected, a synergistic neurotoxicity was observed. Extensive histological damage occurred in the entire right hemisphere, and in several rats comprising part of the contralateral hemisphere. These animals were apathetic in the immediate hours following injection, with circling towards the side of injection in the following days. Thus, OS2 greatly potentiates glutamate excitoxicity in vivo.

Selective retinal pigment epithelial cell lipid metabolism and remodeling conserves photoreceptor docosahexaenoic acid following phagocytosis

Retinal pigment epithelial cells (RPE) actively retrieve and recycle docosahexaenoic acid (DHA, 22:6n-3) from phagosomal phospholipids back to photoreceptor cells. Here we studied the fate of DHA in primary culture rat RPE cells after feeding with a suspension of rod outer segments (ROS) for 4 hr. Phospholipids (PLs), triacylglycerols (TAG), and free fatty acids were isolated from cells and media by thin layer chromatography (TLC), and their acyl groups quantified by gas liquid chromatography (GLC). In RPE cells, DHA-PLs increased 3. 5-fold by 4 hr, decreasing thereafter to 1.6-fold above basal by 24 hr. In contrast, 18:1-PLs were decreased by 13%-18% below RPE basal values by 8-24 hr, respectively. DHA-TAG showed the highest increase (21-fold) by 8 hr. Free DHA displayed a small increase in the cells with a preferential release and accumulation into the media by 24 hr. These results show that in rat RPE cells, photoreceptor cell DHA is transiently incorporated into TAG prior to its release and uptake into 18:1-PLs. These metabolic pathways and remodeling may be critical in the conservation of this essential, photoreceptor cell fatty acid.

Neuroprotection by pigment epithelial-derived factor against glutamate toxicity in developing primary hippocampal neurons

Pigment epithelial-derived factor (PEDF) has been shown to be a survival factor for cerebellar granule neurons. Here we investigated the ability of PEDF to enhance the survival of hippocampal neurons in culture, and to protect these neurons against acute glutamate toxicity. Hippocampal neurons prepared from 1- to 3-day postnatal rat brain were cultured for either 7 or 14 days in vitro (DIV). At 14 DIV, neurons were only slightly protected (13% +/- 4%) against 50 microM glutamate toxicity when treated with 1 microg/ml of PEDF for 3 successive days before glutamate exposure as measured by lactate dehydrogenase (LDH) release. In comparison, basic fibroblast growth factor (bFGF) at 10 ng/ml for the same treatment period protected 58% +/- 8% of the neurons against glutamate. Using quantitative image analysis of digitized micrographs, we found that the average size of neurons in young, developing hippocampal cultures (7 DIV), was greatly decreased by treatment with 50 microM glutamate. Treatment for up to 5 successive days with 1 microg/ml of PEDF before glutamate addition dramatically increased the average hippocampal neuron soma size, compared to cells treated with glutamate alone. Thus, PEDF may promote the growth of hippocampal neurons, and, if added to developing hippocampal neurons, can also protect these cells from subsequent injury, such as the excitotoxicity of glutamate.

The interleukin-1 type 2 receptor gene displays immediate early gene responsiveness in glucocorticoid-stimulated human epidermal keratinocytes

Human epidermal keratinocytes (HEKs) in primary culture (P2-P4) were used to study glucocorticoid (GC)-mediated transcription of the genes encoding the constitutively expressed interleukin-1 type 1 receptor (IL-1R1) and the inducible interleukin-1 type 2 receptor (IL-1R2). Utilizing Northern dot blot analysis and a quantitative reverse transcription-polymerase chain reaction protocol for IL-1R1 and IL-1R2, dexamethasone and, in particular, the budesonide epimer R were shown to effectively and rapidly induce transcription from the IL-IR2 gene when compared with IL-1R1 or beta-actin RNA message levels in the same sample. Southern blot analysis of newly generated IL-1R2 reverse transcription-polymerase chain reaction products using end-labeled IL-1R2 intron probes suggested that GC enhancement of IL-1R2 expression was regulated primarily at the level of de novo transcription. GC-induced IL-1R2 gene transcription displayed features characteristic of a classical immediate early gene response, including a signal transduction function, a relatively low basal abundance, a rapid, transient induction, cycloheximide superinduction, actinomycin D suppression, and a rapid decay of IL-1R2 RNA message. Parallel time course kinetic analysis of IL-1R2 RNA message levels with Western immunoblotting revealed tight coupling of de novo IL-IR2 gene transcription with translation of the IL-1R2 RNA message; a newly synthesized ( approximately 46-kDa) IL-1R2 protein was detected in the HEK growth medium as early as 1 h after budesonide epimer R treatment. These data indicate that different GC compounds can variably up-regulate the IL-1R2 response in HEKs through transcription-mediated mechanisms and, for the first time, suggest that a gene encoding a soluble cytokine receptor can respond like an immediate early gene.

Glutamate receptor signaling interplay modulates stress-sensitive mitogen-activated protein kinases and neuronal cell death

Glutamate receptors modulate multiple signaling pathways, several of which involve mitogen-activated protein (MAP) kinases, with subsequent physiological or pathological consequences. Here we report that stimulation of the N-methyl-D-aspartate (NMDA) receptor, using platelet-activating factor (PAF) as a messenger, activates MAP kinases, including c-Jun NH2-terminal kinase, p38, and extracellular signal-regulated kinase, in primary cultures of hippocampal neurons. Activation of the metabotropic glutamate receptor (mGluR) blocks this NMDA-signaling through PAF and MAP kinases, and the resultant cell death. Recombinant PAF-acetylhydrolase degrades PAF generated by NMDA-receptor activation; the hetrazepine BN50730 (an intracellular PAF receptor antagonist) also inhibits both NMDA-stimulated MAP kinases and neuronal cell death. The finding that the NMDA receptor-PAF-MAP kinase signaling pathway is attenuated by mGluR activation highlights the exquisite interplay between glutamate receptors in the decision making process between neuronal survival and death.

The neuromessenger platelet-activating factor in plasticity and neurodegeneration

Synaptic activation leads to the formation of arachidonic acid, platelet-activating factor (PAF, 1-O-alkyl-2-acyl-sn-3-phosphocholine) and other lipid messengers. PAF is a potent bioactive phospholipid in synaptic plasticity. PAF enhances presynaptic glutamate release, is a retrograde messenger in long-term potentiation and enhances memory formation. PAF also couples synaptic events with gene expression by stimulating a FOS/JUN/AP-1 transcriptional signaling system, as well as transcription of COX-2 (inducible prostaglandin synthase). Since the COX-2 gene is also involved in synaptic plasticity, the PAF-COX-2 pathway may have physiological significance. Seizures, ischemia and other forms of brain injury promote phospholipase A2 (PLA2) overactivation, resulting in the accumulation of bioactive lipids at the synapse. PAF, under these pathological conditions, behaves as a neuronal injury messenger by at least two mechanisms: (a) enhancing glutamate release; and, (b) by sustained augmentation of COX-2 transcription. These events link PAF with neurodegeneration. The upstream intracellular pathways of signal transduction involved in neuronal or photoreceptor cell apoptosis are not well understood and involve stress sensitive kinases. PAF is a transcriptional activator of the COX-2 gene. BN 50730, a potent intracellular PAF antagonist, blocks COX-2 induction. COX-2 transcription and protein expression are upregulated in the hippocampus in kainic acid induced epileptogenesis. There is a selectively elevated induction of COX-2 (72-fold) by kainic acid preceding neuronal cell death. BN 50730 administered by i.c.v. injection blocks seizure-induced COX-2 induction. Overall, PAF is a dual modulator of neural function and becomes an endogenous neurotoxin when over produced.

Selective changes in protein kinase C (PKC) isoform expression in rabbit corneal epithelium during wound healing. Inhibition of corneal epithelial repair by PKCalpha antisense

Protein kinase C (PKC) isoforms display different sensitivities to modulators, tissue specificities and subcellular localizations. PKCalpha increases during rabbit corneal epithelial wound healing. Here we report differential expression of PKC isoforms in the cornea of rabbits at 1, 2, 4 and 8 days during re-epithelization. Cytosolic, membrane and detergent-insoluble fractions from epithelium were analysed by Western blot using monoclonal antibodies against the different PKC isoforms. We have identified PKCalpha, gamma, epsilon, mu and iota. PKCalpha and gamma were expressed only in the cytosolic fraction, with the expression of PKCalpha markedly increasing 4 days after injury. Corneas cultured in the presence of rabbit-specific PKCalpha antisense showed a greater than 50% inhibition of wound closure, compared to controls. The PKCepsilon and mu were expressed in the soluble, as well as in the membrane fraction. Additionally, 12% of PKCmu was found attached to the detergent insoluble fraction. The expression of the membrane-bound PKCepsilon and mu isoforms decreased between 1 and 2 days following injury. Only 10% of the PKCiota expressed in corneal epithelium was membrane bound, but between 4 and 8 days after de-epithelization, the expression in this fraction increased three-fold. Our results suggest that changes in the expression and distribution within the various fractions of selective isoforms of PKC after injury could be involved in events leading to wound healing and that PKCalpha is a key modulator in rabbit corneal wound repair.

Effects of posttraining intrahippocampal injections of platelet-activating factor and PAF antagonists on memory

The present experiments examined the effects of posttraining intrahippocampal injections of the degradative enzyme-resistant methylcarbamyl analog of the bioactive phospholipid platelet-activating factor (mc-PAF) and the platelet-activating factor (PAF) receptor antagonists BN52021 and BN 50730 on memory in male Long-Evans rats trained in a hidden platform version of the Morris water maze. Following an eight-trial training session, rats received a unilateral intrahippocampal injection of mc-PAF (0.5, 1.0, or 2.0 microgram/0.5 microliter), lyso-PAF (1.0 microgram/0.5 microliter), the cell surface PAF receptor antagonist BN 52021 (0.25, 0.5, or 1.0 micrigram/0.5 microliter/, the intracellular PAF receptor antagonist BN 50730 (2.0, 5.0, or 10.0 microgram/0.5 microliter), or vehicle (50% DMSO in 0.9% saline; 0.5 microliter). On a retention test conducted 24 h after training, the escape latencies of rats administered mc-PAF (1.0 or 2.0 microgram) were significantly lower than those of the vehicle-injected controls, demonstrating a memory-enhancing effect of mc-PAF. Injections of lyso-PAF, a structurally similar metabolite of PAF, had no influence on memory, indicating that the memory-enhancing effect of mc-PAF is not caused by membrane perturbation by the phospholipid. The retention test escape latencies of rats administered BN 52021 (0.5 microgram) and BN 50730 (5.0 or 10 microgram) were significantly higher than those of the controls, indicating a memory impairing effect of both PAF antagonists. When mc-PAF, BN 52021, or BN 50730 was administered 2 h posttraining, no effect on retention was observed, indicating a time-dependent effect of the neuroactive substances on memory storage. The findings suggest a role for endogenous PAF in hippocampal-dependent memory processes.

Strong nuclear factor-kappaB-DNA binding parallels cyclooxygenase-2 gene transcription in aging and in sporadic Alzheimer's disease superior temporal lobe neocortex

Cyclooxygenase-2 (COX-2; EC 1.14.99.1) RNA message abundance in 25 control and Consortium to Establish a Registry for Alzheimer's Disease (CERAD)-confirmed sporadic Alzheimer's disease (AD) brains is remarkably heterogeneous when compared with 55 other AD brain RNA message levels that were previously characterized (Lukiw and Bazan: J Neurosci Res 50:937-945, 1997). Examination of nuclear protein extracts (NPXTs) that were derived from control and AD-affected brain neocortical nuclei (n = 20; age range, 60-82 years; postmortem interval, 0.5-6.5 hours) by using gel shift, gel supershift, and cold oligonucleotide competition assay revealed a highly significant relationship between the extent of inflammatory transcription factor, nuclear factor (NF)-kappaB: DNA binding and the abundance of the COX-2 RNA signal (P < 0.0001; analysis of variance). No strong correlation with AP-1-DNA binding was noted (P > 0.045). These data are the first linking inflammation-related transcription factor NF-KB-DNA binding to up-regulation of transcription from a key inflammatory gene, COX-2, in both normally aging brain and in AD-affected neocortex. Systematic deletion of NF-KB-DNA binding sites in human COX-2 promoter constructs attenuates COX-2 transcriptional induction by mediators of inflammation. Strong NF-kappaB-DNA binding has been reported previously to temporally precede COX-2 gene transcription in human epithelial (A549), hamster B-cell (HIT-T15), human endothelial (HUVEC), human lymphoblast (IM9), human fibroblast (IMR90), rat glioma/mouse neuroblastoma (NG108-15), human keratinocyte (NHEK), mouse fibroblast (NIH 3T3), rat neuroblastoma (SH-SY5Y) cell lines and in mouse and rat brain hippocampus, indicating a highly conserved inflammatory signaling pathway that is common to diverse species and cell types. The mouse, rat, and human COX-2 immediate promoters, despite 7.5 x 10(7) years of DNA sequence divergence, each retain multiple recognition sites specific for NF-kappaB-DNA binding. These data suggest that basic gene induction mechanisms, which have been conserved over long periods of evolution, that increase NF-kappaB-DNA binds ing may be fundamental in driving transcription from inflammation-related genes, such as COX-2, that operate in stressed tissues, in normally aging cell lines, and in neurodegenerative disorders that include AD brain.

Strong nuclear factor-kappaB-DNA binding parallels cyclooxygenase-2 gene transcription in aging and in sporadic Alzheimer's disease superior temporal lobe neocortex

Cyclooxygenase-2 (COX-2; EC 1.14.99.1) RNA message abundance in 25 control and Consortium to Establish a Registry for Alzheimer's Disease (CERAD)-confirmed sporadic Alzheimer's disease (AD) brains is remarkably heterogeneous when compared with 55 other AD brain RNA message levels that were previously characterized (Lukiw and Bazan: J Neurosci Res 50:937-945, 1997). Examination of nuclear protein extracts (NPXTs) that were derived from control and AD-affected brain neocortical nuclei (n = 20; age range, 60-82 years; postmortem interval, 0.5-6.5 hours) by using gel shift, gel supershift, and cold oligonucleotide competition assay revealed a highly significant relationship between the extent of inflammatory transcription factor, nuclear factor (NF)-kappaB: DNA binding and the abundance of the COX-2 RNA signal (P < 0.0001; analysis of variance). No strong correlation with AP-1-DNA binding was noted (P > 0.045). These data are the first linking inflammation-related transcription factor NF-KB-DNA binding to up-regulation of transcription from a key inflammatory gene, COX-2, in both normally aging brain and in AD-affected neocortex. Systematic deletion of NF-KB-DNA binding sites in human COX-2 promoter constructs attenuates COX-2 transcriptional induction by mediators of inflammation. Strong NF-kappaB-DNA binding has been reported previously to temporally precede COX-2 gene transcription in human epithelial (A549), hamster B-cell (HIT-T15), human endothelial (HUVEC), human lymphoblast (IM9), human fibroblast (IMR90), rat glioma/mouse neuroblastoma (NG108-15), human keratinocyte (NHEK), mouse fibroblast (NIH 3T3), rat neuroblastoma (SH-SY5Y) cell lines and in mouse and rat brain hippocampus, indicating a highly conserved inflammatory signaling pathway that is common to diverse species and cell types. The mouse, rat, and human COX-2 immediate promoters, despite 7.5 x 10(7) years of DNA sequence divergence, each retain multiple recognition sites specific for NF-kappaB-DNA binding. These data suggest that basic gene induction mechanisms, which have been conserved over long periods of evolution, that increase NF-kappaB-DNA binds ing may be fundamental in driving transcription from inflammation-related genes, such as COX-2, that operate in stressed tissues, in normally aging cell lines, and in neurodegenerative disorders that include AD brain.

Recombinant plasma-type platelet-activating factor acetylhydrolase attenuates NMDA-induced hippocampal neuronal apoptosis

The bioactive lipid platelet-activating factor (PAF) accumulates in brain during injury, seizures and ischemia and may, in addition, be significant in AIDS dementia and in other neurodegenerative diseases. We have used plasma-type recombinant PAF acetylhydrolase (rPAF-AH) to test the hypothesis that PAF accumulation is involved in early events leading to neuronal apoptosis during excitotoxic neuronal injury. Neuronal cultures were labeled with FITC-12-dUTP (TUNEL technique) and propidium iodide, digitized using fluorescence microscopy and a chilled 3CCD color camera, and analyzed with 2D graphics analysis software. N-methyl-D-aspartate (NMDA) (50 microM, 2 hr) induced a 2.5-fold increase in apoptosis of hippocampal neurons compared with controls when analyzed 24 hr after NMDA treatment. Hippocampal neurons receiving rPAF-AH (20 microg/ml) before, during, and after NMDA treatment demonstrated a concentration-dependent neuroprotective effect which resulted in 47% and 30% neuroprotection against 50 and 100 microM NMDA, respectively. The noncompetitive NMDA receptor antagonist MK-801(300 nM) completely inhibited apoptosis caused by NMDA. The neuroprotective effect of rPAF-AH against NMDA-induced apoptosis was confirmed using as additional criteria, histone release, electron microscopy, and DNA laddering. Neuroprotection elicited by rPAF-AH demonstrates that PAF is an injury mediator in NMDA-induced neuronal apoptosis and that the recombinant protein is potentially useful as a therapeutic approach.

Simultaneous analysis of multiple gene expression patterns as a function of development, injury or senescence

Concurrent changes in expression of eight genes were examined following cryogenic rat brain injury. Cortical RNA levels were catalogued at time 0, and at 1 h and 1 week following injury. The genes include thymidine kinase (TK), c-fos, renin, myelin basic protein (MBP), proteolipid protein (PLP), glial fibrillary acidic protein (GFAP), insulin-like growth factor-1 (IGF-1), and somatostatin. All demonstrate increased expression following injury. Renin and c-fos exhibit detectable changes as early as 1 h post-injury.

Strong nuclear factor-kappaB-DNA binding parallels cyclooxygenase-2 gene transcription in aging and in sporadic Alzheimer's disease superior temporal lobe neocortex

Cyclooxygenase-2 (COX-2; EC 1.14.99.1) RNA message abundance in 25 control and Consortium to Establish a Registry for Alzheimer's Disease (CERAD)-confirmed sporadic Alzheimer's disease (AD) brains is remarkably heterogeneous when compared with 55 other AD brain RNA message levels that were previously characterized (Lukiw and Bazan: J Neurosci Res 50:937-945, 1997). Examination of nuclear protein extracts (NPXTs) that were derived from control and AD-affected brain neocortical nuclei (n = 20; age range, 60-82 years; postmortem interval, 0.5-6.5 hours) by using gel shift, gel supershift, and cold oligonucleotide competition assay revealed a highly significant relationship between the extent of inflammatory transcription factor, nuclear factor (NF)-kappaB: DNA binding and the abundance of the COX-2 RNA signal (P < 0.0001; analysis of variance). No strong correlation with AP-1-DNA binding was noted (P > 0.045). These data are the first linking inflammation-related transcription factor NF-KB-DNA binding to up-regulation of transcription from a key inflammatory gene, COX-2, in both normally aging brain and in AD-affected neocortex. Systematic deletion of NF-KB-DNA binding sites in human COX-2 promoter constructs attenuates COX-2 transcriptional induction by mediators of inflammation. Strong NF-kappaB-DNA binding has been reported previously to temporally precede COX-2 gene transcription in human epithelial (A549), hamster B-cell (HIT-T15), human endothelial (HUVEC), human lymphoblast (IM9), human fibroblast (IMR90), rat glioma/mouse neuroblastoma (NG108-15), human keratinocyte (NHEK), mouse fibroblast (NIH 3T3), rat neuroblastoma (SH-SY5Y) cell lines and in mouse and rat brain hippocampus, indicating a highly conserved inflammatory signaling pathway that is common to diverse species and cell types. The mouse, rat, and human COX-2 immediate promoters, despite 7.5 x 10(7) years of DNA sequence divergence, each retain multiple recognition sites specific for NF-kappaB-DNA binding. These data suggest that basic gene induction mechanisms, which have been conserved over long periods of evolution, that increase NF-kappaB-DNA binds ing may be fundamental in driving transcription from inflammation-related genes, such as COX-2, that operate in stressed tissues, in normally aging cell lines, and in neurodegenerative disorders that include AD brain.

Dominant expression of rat prostanoid DP receptor mRNA in leptomeninges, inner segments of photoreceptor cells, iris epithelium, and ciliary processes

Prostaglandin (PG) D2 is one of the major prostanoids in the mammalian brain and eye tissues. Its function is mediated by the prostanoid DP receptor, which is specific for PGD2 among the various prostanoids. In this study, we cloned the full-length cDNA for the rat DP receptor and used it for detection of DP receptor mRNA in various rat tissues. Northern blotting and RT-PCR analyses revealed that this DP receptor was expressed most intensely in the eye tissues, moderately in the leptomeninges and oviduct, and weakly in the epididymis. The tissue distribution profile of the mRNA for the rat DP receptor is overlapped with those of hematopoietic and lipocalin-type PGD synthases. Among rat eye tissues, the expression was the highest in the iris. In situ hybridization and in situ RT-PCR revealed DP receptor mRNA to be localized in the epithelium of the iris and ciliary body and in photoreceptor cells of the retina, suggesting the involvement of the receptor in the physiological regulation of intraocular pressure and the vision process. In the brain, DP receptor mRNA was dominantly expressed in the leptomeninges and was not detected in the brain parenchyma including the ventral rostral forebrain, the surface area of which is reportedly involved in sleep induction by PGD2.

Platelet-activating factor is a downstream messenger of kainate-induced activation of mitogen-activated protein kinases in primary hippocampal neurons

Excitatory amino acids transduce physiological and pathological signals to neurons. Similarly, the neuroactive lipid platelet-activating factor (PAF) has been implicated in modulating long-term potentiation and neuronal survival. Excitatory amino acids and PAF have been shown to increase mitogen-activated protein (MAP) kinases in different cell types. Here, we have investigated the similarities and differences between PAF and kainate in activating MAP kinases in primary hippocampal neurons in vitro. Extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 kinases were activated by kainate or PAF in hippocampal neurons. This activation was blocked by the receptor antagonists CNQX and BN 50730 for kainate and PAF, respectively. The PAF receptor antagonist BN 50730 also blocked kainate activation. CNQX had no effect on PAF activation of the kinases, indicating that PAF is downstream of kainate activation. Coapplication of submaximal concentrations of PAF and kainate resulted in a less than additive activation, suggesting similar routes of activation by the two agonists. Both CNQX and BN 50730 blocked kainate-induced neurotoxicity. These results indicate that PAF and kainate activate similar kinase pathways. Therefore, PAF acts downstream of the kainate subtype of glutamate receptors, and when excessive receptor activation takes place, this bioactive lipid may contribute to neuronal cell death.

Run-on gene transcription in human neocortical nuclei. Inhibition by nanomolar aluminum and implications for neurodegenerative disease

The incorporation of [alpha-32P]-uridine triphosphate into DNA transcription products was examined in short post-mortem interval (PMI) human brain neocortical nuclei (n, 22; PMI, 0.5-24 h) using run-on-gene transcription. Reverse Northern dot-blot hybridization of newly synthesized RNA against either total cDNA or Alu repetitive DNA indicated that human brain neocortical nuclei of up to 4-h PMI were efficient in incorporating radiolabel into new transcription products, after which there was a graded decline in de novo RNA biosynthetic capacity. To test the effects of 0-3000 nM concentrations of ambient aluminum on RNA polymerase I (RNAP I) and RNA polymerase II (RNAP II) transcription, dot blots containing 0.5, 1.0, 2.0, and 5.0 micrograms of DNA for (1) the human-specific Alu repetitive element (2) the neurofilament light (NFL) chain, and (3) glial fibrillary acidic protein (GFAP) were Northern hybridized against newly synthesized radiolabeled total RNA. These DNAs represent heterogeneous nuclear RNA (hnRNA), neuronal-, and glial-specific markers, respectively. We report here a dose-dependent repression in the biosynthetic capabilities of brain RNAP II in the range of 50-100 nM aluminum, deficits similar to those previously described using a rabbit neocortical nuclei transcription system and at concentrations that have been reported in Alzheimer's disease (AD) euchromatin. Transcription from RNAP II and the neuron-specific NFL gene in the presence of aluminum was found to be particularly affected. These findings support the hypothesis that brain gene transcription in the presence of trace amounts of ambient aluminum impairs mammalian brain DNA to adequately read out genetic information.

KID-1, a protein kinase induced by depolarization in brain

Membrane depolarization leads to changes in gene expression that modulate neuronal plasticity. Using representational difference analysis, we have identified a previously undiscovered cDNA, KID-1 (kinase induced by depolarization), that is induced by membrane depolarization or forskolin, but not by neurotrophins or growth factors, in PC12 pheochromocytoma cells. KID-1 is an immediate early gene that shares a high degree of sequence similarity with the family of PIM-1 serine/threonine protein kinases. Recombinant KID-1 fusion protein is able to catalyze both histone phosphorylation and autophosphorylation. KID-1 mRNA is present in a number of unstimulated tissues, including brain. In response to kainic acid and electroconvulsive shock-induced seizures, KID-1 is induced in specific regions of the hippocampus and cortex.

Budesonide epimer R or dexamethasone selectively inhibit platelet-activating factor-induced or interleukin 1beta-induced DNA binding activity of cis-acting transcription factors and cyclooxygenase-2 gene expression in human epidermal keratinocytes

To further understand the molecular mechanism of glucocorticoid action on gene expression, DNA-binding activities of the cis-acting transcription factors activator protein 1 (AP1), AP2, Egr1 (zif268), NF-kappaB, the signal transducers and activators of transcription proteins gamma interferon activation site (GAS), Sis-inducible element, and the TATA binding protein transcription factor II D (TFIID) were examined in human epidermal keratinocytes. The cytokine interleukin 1beta (IL-1beta) and platelet-activating factor (PAF), both potent mediators of inflammation, were used as triggers for gene expression. Budesonide epimer R (BUDeR) and dexamethasone (DEX) were studied as potential antagonists. BUDeR or DEX before IL-1beta- or PAF-mediated gene induction elicited strong inhibition of AP1-, GAS-, and in particular NF-kappaB-DNA binding (P < 0.001, ANOVA). Only small effects were noted on AP2, Egr1 (zif268), and Sis-inducible element-DNA binding (P > 0.05). No significant effect was noted on the basal transcription factor TFIID recognition of TATA-containing core promoter sequences (P > 0.68). To test the hypothesis that changing cis-acting transcription factor binding activity may be involved in inflammatory-response related gene transcription, RNA message abundance for human cyclooxygenase (COX)-1 and -2 (E.C.1.14.99.1) was assessed in parallel by using reverse transcription-PCR. Although the COX-1 gene was found to be expressed at constitutively low levels, the TATA-containing COX-2 gene, which contains AP1-like, GAS, and NF-kappaB DNA-binding sites in its immediate promoter, was found to be strongly induced by IL-1beta or PAF (P < 0.001). BUDeR and DEX both suppressed COX-2 RNA message generation; however, no correlation was associated with TFIID-DNA binding. These results suggest that on stimulation by mediators of inflammation, although the basal transcription machinery remains intact, modulation of cis-activating transcription factor AP1, GAS, and NF-kappaB-DNA binding by the glucocorticoids BUDeR and DEX play important regulatory roles in the extent of specific promoter activation and hence the expression of key genes involved in the inflammatory response.

Temporal changes in gene expression following cryogenic rat brain injury

Expression of 18 genes was examined at 8 different time points between 1 h and 28 days following cryogenic rat brain injury. The genes include thymidine kinase (TK), p53 tumor suppressor, c-fos, renin, myelin basic protein (MBP), proteolipid protein (PLP), transferrin, transferrin receptor, platelet-derived growth factor A (PDGF A), platelet-derived growth factor B (PDGF B), platelet-derived growth factor receptor alpha (PDGF alpha receptor), platelet-derived growth factor receptor beta (PDGF beta receptor), glial fibrillary acidic protein (GFAP), transforming growth factor-beta 1 (TGF-beta 1), basic fibroblast growth factor (bFGF), fibroblast growth factor receptor-1 (FGF-R1), insulin-like growth factor-1 (IGF-1), and somatostatin. Time courses of gene expression were determined for RNAs derived from hippocampus and cortex. Genes were divided into categories based upon those in which statistically significant changes in expression were first observed at or before 24 h (early genes) and those in which changes were first observed at or after 72 h (late genes). In the present model, many genes demonstrate elevated RNA levels in the cortex prior to hippocampus, following injury. RNAs transcribed from late genes tend to be elevated concurrently in cortex and hippocampus.

Localization of lipocalin-type prostaglandin D synthase (beta-trace) in iris, ciliary body, and eye fluids

PURPOSE

Prostaglandin (PG) D synthase is present in neural tissues and cerebrospinal fluid (beta-trace). This enzyme belongs to the lipocalin family which consists of transporter proteins for lipophilic substances in the extracellular space. PGD synthase is found in retinal pigment epithelium, from where it is secreted into the interphotoreceptor matrix. The authors have undertaken the localization of this unique enzyme within the tissues and spaces of the anterior segment of the eye.

METHODS

Iris, ciliary body, lens, and aqueous and vitreous humors were collected from adult rats and mice. PGD synthase activity was determined, and the protein was quantified by Western blot analysis and localized immunohistochemically. Finally, in situ hybridization was performed to localize PGD synthase mRNA.

RESULTS

PGD synthase was most abundant in the aqueous and vitreous humors. It was less abundant in tissue cytosolic fractions; these fractions had almost 10-fold as much as their corresponding membrane-bound fractions. Lens tissue had the lowest amount observed. PGD synthase was localized to the epithelial cells of the iris and the ciliary body and to the adjacent extracellular chambers, but PGD synthase mRNA was found only within the epithelial cells. Several glycosylated forms of PGD synthase were also detected.

CONCLUSIONS

PGD synthase was synthesized within the epithelial cells of the iris and the ciliary body and was then secreted into the aqueous and vitreous humors, where it accumulated as an active enzyme.

Cyclooxygenase 2 RNA message abundance, stability, and hypervariability in sporadic Alzheimer neocortex

Long-term treatment by nonsteroidal anti-inflammatory drugs has been shown to decrease the incidence of Alzheimer's disease (AD). Both platelet-activating factor and interleukin-1beta, potent mediators of the inflammatory and immune response, strongly induce transcription of the cyclooxygenase-2 (COX-2) gene in brain cells. Using Northern and RT-PCR analysis, we have determined in 15 control and 10 sporadic AD human neocortical samples (age range, 60-82 yr; postmortem interval [PMI] range, 0.7-16.0 hr) the levels of COX-2 RNA in relation to the constitutively expressed COX-1 and beta-actin RNA message levels. Our results indicate that in short PMI brain, COX-1 and COX-2 transcripts are relatively low abundance RNA messages, ranging from a mean of 6.8% of the beta-actin signal in controls to 8.5% of the beta-actin signal in AD-affected brain. A large variation in the signal intensity for COX-2 RNA was noted in both control and AD; although there was a trend for higher COX-2 RNA message abundance in AD neocortex to +11.5% of that of controls, it did not reach statistical significance (ANOVA = 0.45). Several human tissues, including heart, skeletal muscle, lung, kidney, and spinal cord, displayed 4.6- and 2.8-kb COX-2 RNA message isoforms; however, the 4.6-kb COX-2 RNA predominated in the hippocampus and association neocortex. COX-2 RNA message was found to be degraded at similar rates in both control and AD tissues, and a strong positive correlation between the PMI and the intensity of the COX-2 RNA signal was noted (ANOVA = 0.006). Linear regression analysis indicated that the 4.6-kb COX-2 RNA is an unstable short-lived RNA species with a half-life of not more than 3.5 hr, a feature characteristic of immediate early gene transcripts. Individual hypervariability in COX-2 RNA message abundance may reflect various degrees of expression of AD-related inflammatory processes.

Platelet-activating factor induces cyclooxygenase-2 gene expression in corneal epithelium. Requirement of calcium in the signal transduction pathway

PURPOSE

To investigate the effect of the inflammatory mediator platelet-activating factor (PAF) in the induction of the inducible prostaglandin H synthase-cyclooxygenase-2 (COX-2) gene expression in corneal epithelium.

METHODS

Rabbit corneas were incubated in organ culture with or without carbamyl PAF (cPAF, 100 nM). The effects of PAF antagonist BN50730 (10 microM), protein synthesis inhibitor cycloheximide (CHX; 30 micrograms/ml), RNA synthesis inhibitor actinomycin D (50 micrograms/ml), and tumor promoter phorbol ester (TPA); (100 nM) were tested. Total RNA for corneal epithelium was analyzed by Northern blot analysis using mouse COX-2 cDNA fragments labeled with 32P as probes. Western blots were performed using mouse monoclonal antibodies. Primary cultures of rabbit corneal epithelium were loaded with the fluorescent dye fluo-3 AM and changes in intracellular calcium concentration [Ca2+]i were analyzed by laser scanning confocal microscopy.

RESULTS

Platelet-activating factor induction of COX-2 expression was detectable by Northern blot analysis at 2 hours, peaked at 4 hours, and remained increased for as long as 8 hours. At 16 hours, there was a marked increase in COX-2 expression. The effect was abolished by the PAF antagonist. TPA also induced COX-2 gene expression. Neither PAF-nor TPA-induced expression was inhibited by CHX. In a Ca(2+)-free medium, there was a 50% inhibition of COX-2 gene induction by PAF. The calcium ionophore A23187 also caused an increase in expression of COX-2 messenger RNA; this did not occur in Ca(2+)-free medium. Confocal microscopy imaging showed that after the addition of PAF, there was a transient increase in [Ca2+]i in corneal epithelial cells that peaked between 30 and 60 seconds. The increase was inhibited in the presence of BN50730 or in a Ca(2+)-free medium. A23187 also caused a transient increase in [Ca2+]i that was not altered in cells previously treated with PAF or BN50730.

CONCLUSIONS

PAF may enhance prostaglandin synthesis in the corneal epithelium by increasing COX-2 gene expression. This increase is by means of transcriptional activation of the gene and results in increased COX-2 protein formation. Influx of Ca2+ due to PAF stimulation is required to induce the COX-2 gene. A PAF antagonist abolishes all PAF effects and could be of therapeutic value by modulating ocular inflammation at the level of COX-2 gene expression.