Therapeutic Advantages of Dual Targeting of PPAR-δ and PPAR-γ in an Experimental Model of Sporadic Alzheimer's Disease

Background:

Alzheimer’s disease (AD) is associated with progressive impairments in brain responsiveness to insulin and insulin-like growth factor (IGF). Although deficiencies in brain insulin and IGF could be ameliorated with trophic factors such as insulin, impairments in receptor expression, binding, and tyrosine kinase activation require alternative strategies. Peroxisome proliferator-activated receptor (PPAR) agonists target genes downstream of insulin/IGF stimulation. Furthermore, their anti-oxidant and anti-inflammatory effects address other pathologies contributing to neurodegeneration.

Objectives:

The goal of this research was to examine effects of dual delivery of L165, 041 (PPAR-δ) and F-L-Leu (PPAR-γ) agonists for remediating in the early stages of neurodegeneration.

Model:

Experiments were conducted using frontal lobe slice cultures from an intracerebral Streptozotocin (i.c. STZ) rat model of AD.

Results:

PPAR-δ+ PPAR-γ agonist treatments increased indices of neuronal and myelin maturation, and mitochondrial proliferation and function, and decreased neuroinflammation, AβPP-Aβ, neurotoxicity, ubiquitin, and nitrosative stress, but failed to restore choline acetyl transferase expression and adversely increased HNE(lipid peroxidation) and acetylcholinesterase, which would have further increased stress and reduced cholinergic function in the STZ brain cultures.

Conclusion:

PPAR-δ + PPAR-γ agonist treatments have substantial positive early therapeutic targeting effects on AD-associated molecular and biochemical brain pathologies. However, additional or alternative strategies may be needed to optimize disease remediation during the initial phases of treatment.

Enzymatic Responses to Alcohol and Tobacco Nicotine-Derived Nitrosamine Ketone Exposures in Long Evans Rat Livers

BACKGROUND

Chronic feeding plus binge administration of ethanol causes very high blood alcohol concentrations. However, its co-administration with tobacco Nicotine-Derived Nitrosamine Ketone (NNK) results in somewhat lower blood alcohol levels, suggesting that NNK and therefore smoking, alters alcohol metabolism in the liver. To explore this hypothesis, we examined effects of ethanol and/or NNK exposures on the expression and activity levels of enzymes that regulate their metabolism in liver.

METHODS

This study utilized a 4-way model in which Long Evans rats were fed liquid diets containing 0% or 26% ethanol for 8 weeks, and respectively i.p injected with saline or 2 g/kg of ethanol 3 times/week during Weeks 7 and 8. The control and ethanol-exposed groups were each sub-divided and further i.p treated with 2 mg/kg of NNK or saline (3×/week) in Weeks 3-8. ADH, catalase and ALDH activities were measured using commercial kits. CYP450 mRNA levels (17 isoforms) were measured by qRT-PCR analysis.

RESULTS

Ethanol significantly increased hepatic ADH but not catalase or ALDH activity. NNK had no effect on ADH, ALDH, or catalase, but when combined with ethanol, it increased ADH activity above the levels measured in all other groups. Ethanol increased CYP2C7, while NNK increased CYP2B1 and CYP4A1mRNA levels relative to control. In contrast, dual ethanol + NNK exposures inhibited CYP2B1 and CYP4A1 expression relative to NNK. Conclusion: Dual exposures to ethanol and NNK increase hepatic ethanol metabolism, and ethanol and/or NNK exposures alter the expression of CYP450 isoforms that are utilized in NNK and fatty acid metabolism.

Leptin levels are reduced by intravenous ghrelin administration and correlated with cue-induced alcohol craving

Increasing evidence supports the role of appetite-regulating pathways, including ghrelin and leptin, in alcoholism. This study tested the hypothesis that intravenous exogenous ghrelin administration acutely decreases endogenous serum leptin levels, and that changes in leptin levels negatively correlate with alcohol craving. This was a double-blind, placebo-controlled human laboratory study. Non-treatment-seeking, alcohol-dependent, heavy drinkers (n=45) were randomized to receive intravenous ghrelin or placebo, followed by a cue-reactivity procedure, during which participants were exposed to neutral (juice) and alcohol trial cues. There was a main effect for intravenous ghrelin administration, compared with placebo, in reducing serum leptin levels (P<0.01). Post hoc analysis showed significant differences in serum leptin levels at the alcohol trial (P<0.05) that persisted at the end of the experiment (P<0.05). By contrast, there were no significant differences in serum leptin levels at the juice trial (P=not significant (NS)). The change of serum leptin level at the alcohol trial correlated with the increase in alcohol urge (P<0.05), whereas urge to drink juice was not correlated with the leptin change at the juice trial (P=NS). These findings provide preliminary evidence of ghrelin-leptin cross-talk in alcoholic individuals and suggest that their relationship may have a role in alcohol craving.

Dose effect of gestational ethanol exposure on placentation and fetal growth

INTRODUCTION

Prenatal ethanol exposure compromises fetal growth by impairing placentation. Invasive trophoblastic cells, which mediate placentation, express the insulin-IGF regulated gene, aspartyl-asparaginyl β-hydroxylase (ASPH), which has a critical role in cell motility and invasion. The aims of this study were to characterize effects of ethanol on trophoblastic cell motility, and assess ethanol dose-dependent impairments in placentation and fetal development.

METHODS

Pregnant Long Evans dams were fed with isocaloric liquid diets containing 0%, 8%, 18% or 37% ethanol (caloric content) from gestation day (GD) 6 to GD18. Fetal development, placental morphology, density of invasive trophoblasts at the mesometrial triangle, as well as placental and mesometrial ASPH and Notch-1 protein expression were evaluated. Directional motility of control and ethanol-exposed HTR-8/SVneo cells was assessed by ATP Luminescence-Based assay.

RESULTS

Severity of fetal growth impairment correlated with increasing doses of ethanol. Ethanol exposure produced dose-dependent alterations in branching morphogenesis at the labyrinthine zone, and inhibited physiological transformation of maternal arteries. ASPH and Notch-1 protein expression levels were reduced, corresponding with impairments in placentation.

DISCUSSION

Prenatal ethanol exposure compromises fetal growth and placentation in a dose-responsive manner. Ethanol's adverse effects on placental development are mediated by: (1) altered branching morphogenesis in labyrinthine zone; (2) suppression of invasive trophoblastic precursor cells; and (3) inhibition of trophoblastic cell adhesion and motility, corresponding with reduced ASPH and Notch-1 protein expression.

Precision-cut slice culture method for rat placenta

Primary trophoblasts, placental explants, and cell line cultures are commonly used to investigate placental development, physiology, and pathology, particularly in relation to pregnancy outcomes. Organotypic slice cultures are increasingly used in other systems because they maintain the normal three-dimensional tissue architecture and have all cell types represented. Herein, we demonstrate the utility of the precision-cut placental slice culture model for studying trophoblastic diseases.

Impaired placentation in fetal alcohol syndrome

Intrauterine growth restriction (IUGR) is one of the key features of fetal alcohol syndrome (FAS), and IUGR can be mediated by impaired placentation. Insulin-like growth factors (IGF) regulate placentation due to stimulatory effects on extravillous trophoblasts, which are highly motile and invasive. Previous studies demonstrated that extravillous trophoblasts express high levels of aspartyl-(asparaginyl) beta-hydroxylase (AAH), a gene that is regulated by IGF and has a critical role in cell motility and invasion. The present study examines the hypothesis that ethanol impaired placentation is associated with inhibition of AAH expression in trophoblasts. Pregnant Long Evans rats were fed isocaloric liquid diets containing 0% or 37% ethanol by caloric content. Placentas harvested on gestation day 16 were used for histopathological, mRNA, and protein studies to examine AAH expression in relation to the integrity of placentation and ethanol exposure. Chronic ethanol feeding prevented or impaired the physiological conversion of uterine vessels required for expansion of maternal circulation into placenta, a crucial process for adequate placentation. Real-time quantitative RT-PCR analysis demonstrated significant reductions in IRS-1, IRS-2, and significant increases in IGF-II and IGF-II receptor mRNA levels in ethanol-exposed placentas. These abnormalities were associated with significantly reduced levels of AAH expression in trophoblastic cells, particularly within the mesometrial triangle (deep placental bed) as demonstrated by real time quantitative RT-PCR, Western blot analysis, ELISA, and immunohistochemical staining. Ethanol-impaired placentation is associated with inhibition of AAH expression in trophoblasts. This effect of chronic gestational exposure to ethanol may contribute to IUGR in FAS.

Chronic gestational exposure to ethanol causes insulin and IGF resistance and impairs acetylcholine homeostasis in the brain

In fetal alcohol syndrome (FAS), cerebellar hypoplasia is associated with impaired insulin-stimulated survival signaling. This study characterizes ethanol dose-effects on cerebellar development, expression of genes required for insulin and insulin-like growth factor (IGF) signaling, and the upstream mechanisms and downstream consequences of impaired signaling in relation to acetylcholine (ACh) homeostasis. Pregnant Long Evans rats were fed isocaloric liquid diets containing 0%, 2%, 4.5%, 6.5%, or 9.25% ethanol from gestation day 6. Ethanol caused dose-dependent increases in severity of cerebellar hypoplasia, neuronal loss, proliferation of astrocytes and microglia, and DNA damage. Ethanol also reduced insulin, IGF-I, and IGF-II receptor binding, insulin and IGF-I receptor tyrosine kinase activities, ATP, membrane cholesterol, and choline acetyltransferase (ChAT) expression. In vitro studies linked membrane cholesterol depletion to impaired insulin receptor binding and insulin-stimulated ChAT. In conclusion, cerebellar hypoplasia in FAS is mediated by insulin/IGF resistance with attendant impairments in energy production and ACh homeostasis.

Ethanol inhibits insulin expression and actions in the developing brain

Ethanol-induced cerebellar hypoplasia is associated with inhibition of insulin-stimulated survival signaling. The present work explores the mechanisms of impaired insulin signaling in a rat model of fetal alcohol syndrome. Real-time quantitative RT-PCR demonstrated reduced expression of the insulin gene in cerebella of ethanol-exposed pups. Although receptor expression was unaffected, insulin and insulin-like growth factor (IGF-I) receptor tyrosine kinase (RTK) activities were reduced by ethanol exposure, and these abnormalities were associated with increased PTP1b activity. In addition, glucose transporter molecule expression and steady-state levels of ATP were reduced in ethanol-exposed cerebellar tissue. Cultured cerebellar granule neurons from ethanol-exposed pups had reduced expression of genes encoding insulin, IGF-II, and the IGF-I and IGF-II receptors, and impaired insulin- and IGF-I-stimulated glucose uptake and ATP production. The results demonstrate that ethanol inhibits insulin-mediated actions in the developing brain by reducing local insulin production and insulin RTK activation, leading to inhibition of glucose transport and ATP production.

Neuronal thread protein regulation and interaction with microtubule-associated proteins in SH-Sy5y neuronal cells

In Alzheimer's disease (AD), neuronal thread protein (NTP) accumulates in cortical neurons and colocalizes with phospho- tau-immunoreactive cytoskeletal lesions that correlate with dementia. To generate additional information about the potential role of NTP in AD, we characterized its expression and regulation in human SH-Sy5y neuronal cells. Quantitative real-time reverse transcription-polymerase chain reactin and Western blot analysis demonstrated prominent insulin, moderate insulin-like growth factor, type 1 (IGF-1) and minimal nerve growth factor stimulation of NTP expression. In addition, NTP protein was more stable and it progressively accumulated in cells that were stimulated with insulin for 24 or 48 h. Metabolic labeling and phospho-amino acid analysis demonstrated phosphorylation of NTP on Serine residues, 30-60 min after insulin or IGF-1 stimulation, when glycogen synthase kinase 3beta (GSK-3beta) activity would no longer have been suppressed. Kinase inhibitor and in vitro phosphorylation studies demonstrated a role for GSK-3beta in the positive regulation of NTP expression and phosphorylation. Coimmunoprecipitation studies demonstrated physical interactions between NTP and tau or microtubule-associated protein 1b (MAP-1b), and ubiquitin immunoreactivity in NTP immunoprecipitates. In summary, these studies showed that (i) NTP expression is regulated at the level of transcription by insulin and IGF-1 stimulation; (ii) NTP is phosphorylated by GSK-3beta; (iii) NTP can physically interact with tau and MAP-1b and (iv) NTP-MAP complexes are ubiquitinated. The results suggest a functional role for NTP in relation to the turnover or processing of neuronal cytoskeletal proteins, attributes that may be modulated by insulin/IGF-1-mediated signaling.

Chronic gestational exposure to ethanol impairs insulin-stimulated survival and mitochondrial function in cerebellar neurons

Chronic gestational exposure to ethanol has profound adverse effects on brain development. In this regard, studies using in vitro models of ethanol exposure demonstrated impaired insulin signaling mechanisms associated with increased apoptosis and reduced mitochondrial function in neuronal cells. To determine the relevance of these findings to fetal alcohol syndrome, we examined mechanisms of insulin-stimulated neuronal survival and mitochondrial function using a rat model of chronic gestational exposure to ethanol. In ethanol-exposed pups, the cerebellar hemispheres were hypoplastic and exhibited increased apoptosis. Isolated cerebellar neurons were cultured to selectively evaluate insulin responsiveness. Gestational exposure to ethanol inhibited insulin-stimulated neuronal viability, mitochondrial function, Calcein AM retention (membrane integrity), and GAPDH expression, and increased dihydrorosamine fluorescence (oxidative stress) and pro-apoptosis gene expression (p53, Fas-receptor, and Fas-ligand). In addition, neuronal cultures generated from ethanol-exposed pups had reduced levels of insulin-stimulated Akt, GSK-3beta, and BAD phosphorylation, and increased levels of non-phosphorylated (activated) GSK-3beta and BAD protein expression. The aggregate results suggest that insulin-stimulated central nervous system neuronal survival mechanisms are significantly impaired by chronic gestational exposure to ethanol, and that the abnormalities in insulin signaling mechanisms persist in the early postnatal period, which is critical for brain development.

Ethanol impairs insulin-stimulated mitochondrial function in cerebellar granule neurons

Ethanol impairs insulin-stimulated survival and mitochondrial function in immature proliferating neuronal cells due to marked inhibition of downstream signaling through P13 kinase. The present study demonstrates that, in contrast to immature neuronal cells, the major adverse effect of chronic ethanol exposure (50 mM) in post-mitotic rat cerebellar granule neurons is to inhibit insulin-stimulated mitochondrial function (MTT activity, MitoTracker Red fluorescence, and cytochrome oxidase immunoreactivity). Ethanol-impaired mitochondrial function was associated with increased expression of the p53 and CD95 pro-apoptosis genes, reduced Calcein AM retention (a measure of membrane integrity), increased SYTOX Green and propidium iodide uptake (indices of membrane permeability), and increased oxidant production (dihydrorosamine fluorescence and H2O2 generation). The findings of reduced membrane integrity and mitochondrial function in short-term (24 h) ethanol-exposed neurons indicate that these adverse effects of ethanol can develop rapidly and do not require chronic neurotoxic injury. A role for caspase activation as a mediator of impaired mitochondrial function was demonstrated by the partial rescue observed in cells that were pre-treated with broad-spectrum caspase inhibitors. Finally, we obtained evidence that the inhibitory effects of ethanol on mitochondrial function and membrane integrity were greater in insulin-stimulated compared with nerve growth factor-stimulated cultures. These observations suggest that activation of insulin-independent signaling pathways, or the use of insulin sensitizer agents that enhance insulin signaling may help preserve viability and function in neurons injured by gestational exposure to ethanol.

Neurodegeneration changes in primary central nervous system neurons transfected with the Alzheimer-associated neuronal thread protein gene

The AD7c-NTP gene is over-expressed in brains with Alzheimer's disease (AD), and increased levels of the corresponding protein are detectable in cortical neurons, brain tissue extracts, cerebrospinal fluid, and urine beginning early in the course of AD neurodegeneration. In the present study, we utilized a novel method to transfect post-mitotic primary neuronal cell cultures, and demonstrated that over-expression of the AD7c-NTP gene causes cell death and neuritic sprouting, two prominent abnormalities associated with AD. These results provide further evidence that aberrantly increased AD7c-NTP expression may have a role in AD-type neurodegeneration. In addition, we demonstrate that primary post-mitotic neurons can be efficiently transfected with conventional recombinant plasmid DNA to evaluate the effects of gene over-expression in relevant in vitro models.

Alzheimer-associated neuronal thread protein-induced apoptosis and impaired mitochondrial function in human central nervous system-derived neuronal cells

In Alzheimer Disease (AD), dementia is due to cell loss and impaired synaptic function. The cell loss is mediated by increased apoptosis, predisposition to apoptosis, and impaired mitochondrial function. Previous studies demonstrated that the AD7c-NTP neuronal thread protein gene is over-expressed in AD beginning early in the course of disease, and that in AD, AD7c-NTP protein accumulation in neurons co-localizes with phospho-tau-immunoreactivity. To determine the potential contribution of AD7c-NTP over-expression to cell loss in AD, we utilized an inducible mammalian expression system to regulate AD7c-NTP gene expression in human CNS-derived neuronal cells by stimulation with isopropyl-1-beta-D-thiogalactopyranoside (IPTG). IPTG induction of AD7c-NTP gene expression resulted in increased cell death mediated by apoptosis, impaired mitochondrial function, and increased cellular levels of the p53 and CD95 pro-apoptosis gene products as occur in AD. In addition, over-expression of AD7c-NTP was associated with increased levels of phospho-tau, but not amyloid-beta immunoreactivity. These results suggest that AD7c-NTP over-expression may have a direct role in mediating some of the important cell death cascades associated with AD neurodegeneration, and further establish a link between AD7c-NTP overexpression and the accumulation of phospho-tau in preapoptotic CNS neuronal cells.

CLIF, a novel cycle-like factor, regulates the circadian oscillation of plasminogen activator inhibitor-1 gene expression

The onset of myocardial infarction occurs frequently in the early morning, and it may partly result from circadian variation of fibrinolytic activity. Plasminogen activator inhibitor-1 activity shows a circadian oscillation and may account for the morning onset of myocardial infarction. However, the molecular mechanisms regulating this circadian oscillation remain unknown. Recent evidence indicates that basic helix-loop-helix (bHLH)/PAS domain transcription factors play a crucial role in controlling the biological clock that controls circadian rhythm. We isolated a novel bHLH/PAS protein, cycle-like factor (CLIF) from human umbilical vein endothelial cells. CLIF shares high homology with Drosophila CYCLE, one of the essential transcriptional regulators of circadian rhythm. CLIF is expressed in endothelial cells and neurons in the brain, including the suprachiasmatic nucleus, the center of the circadian clock. In endothelial cells, CLIF forms a heterodimer with CLOCK and up-regulates the PAI-1 gene through E-box sites. Furthermore, Period2 and Cryptochrome1, whose expression show a circadian oscillation in peripheral tissues, inhibit the PAI-1 promoter activation by the CLOCK:CLIF heterodimer. These results suggest that CLIF regulates the circadian oscillation of PAI-1 gene expression in endothelial cells. In addition, the results potentially provide a molecular basis for the morning onset of myocardial infarction.

Oxygen free radical injury is sufficient to cause some Alzheimer-type molecular abnormalities in human CNS neuronal cells

Cell loss and neuritic/cytoskeletal lesions represent two of the major categories of dementia-associated structural abnormalities in Alzheimer's disease (AD). Cell loss is ultimately mediated by apoptosis and mitochondrial DNA damage due to enhanced sensitivity to oxidative stress, but the mechanism responsible for the neuritic/cytoskeletal lesions including the abnormal proliferation of cortical neurites is not known. This study examines the potential role of oxygen free radical injury as a factor contributing to both cell death and neuritic sprouting cascades in AD. PNET2 human neuronal cells were treated with H2O2 (8 micro M to 88 micro M) for 24 hours and then analyzed for viability, DNA damage, and pro-apoptosis, survival, and sprouting gene expression and signaling. H2O2-treatment resulted in dose-dependent increases in cell death due to genomic and mitochondrial DNA damage associated with increased levels of 8-OHdG and the p53 and CD95 pro-apoptosis genes, reduced levels of the Bcl-2 survival gene, activation of JNK and p38 stress kinases, and inhibition of PI3 kinase survival signaling. However, the H2O2-treated cells also manifested increased expression of growth and sprouting molecules, including GAP-43, nitric oxide synthase 3, neuronal thread protein (NTP; approximately 17 kD and approximately 21 kD forms), proliferating cell nuclear antigen, and phospho-Erk MAPK, and normal levels of the AD-associated approximately 41 kD NTP species, cyclin dependent kinase 5 (cdk-5), and phospho-tau. In addition, the H2O2-treated cells had increased levels of p25, the catalytically active and stable cleavage product of p35, which regulates cdk-5 activity. Previous studies demonstrated p25 accumulation in AD brains and p25-induced hyperphosphorylation of tau and neuronal apoptosis. The findings herein suggest that oxygen free radical injury in human CNS neuronal cells is sufficient to cause some but not all of the pro-death and pro-sprouting molecular abnormalities that occur in AD.

Partial rescue of ethanol-induced neuronal apoptosis by growth factor activation of phosphoinositol-3-kinase

BACKGROUND

Ethanol inhibition of insulin signaling pathways may contribute to impaired central nervous system (CNS) development in the fetal alcohol syndrome and brain atrophy associated with alcoholic neurodegeneration. Previous studies demonstrated ethanol inhibition of insulin-stimulated growth in PNET2 CNS-derived proliferative (immature) neuronal cells. We now provide evidence that the growth-inhibitory effect of ethanol in insulin-stimulated PNET2 cells is partly due to apoptosis.

METHODS

Control and ethanol-treated PNET2 cells were stimulated with insulin and analyzed for viability, apoptosis, activation of pro-apoptosis and survival gene expression and signaling pathways, and evidence of caspase activation.

RESULTS

Ethanol-treated PNET2 neuronal cells exhibited increased apoptosis mediated by increased levels of p53 and phospho-amino-terminal c-jun kinase (phospho-JNK), and reduced levels of Bcl-2, phosphoinositol 3-kinase (PI3 K), and intact (approximately 116 kD) poly (ADP ribose) polymerase (PARP), a deoxyribonucleic acid repair enzyme and important substrate for caspase 3. Partial rescue from ethanol-induced neuronal cell death was effected by culturing the cells in medium that contained 2% fetal calf serum instead of insulin, or insulin plus either insulin-like growth factor type 1 or nerve growth factor. The resulting enhanced viability was associated with reduced levels of p53 and phospho-JNK and increased levels of PI3 K and intact PARP.

CONCLUSIONS

The findings suggest that ethanol-induced apoptosis of insulin-stimulated neuronal cells can be reduced by activating PI3 K and inhibiting pro-apoptosis gene expression and intracellular signaling through non-insulin-dependent pathways.

Oxidative stress and hypoxia-like injury cause Alzheimer-type molecular abnormalities in central nervous system neurons

Neuronal loss and neuritic/cytoskeletal lesions (synaptic disconnection and proliferation of dystrophic neurites) represent major dementia-associated abnormalities in Alzheimer's disease (AD). This study examined the role of oxidative stress as a factor contributing to both the cell death and neuritic degeneration cascades in AD. Primary neuron cultures were treated with H2O2 (9-90 microM) or desferrioxamine (2-25 microM) for 24 h and then analyzed for viability, mitochondrial mass, mitochondrial function, and pro-apoptosis and sprouting gene expression. H2O2 treatment causes free-radical injury and desferrioxamine causes hypoxia-type injury without free radical generation. The H2O2-treated cells exhibited sustained viability but neurite retraction, impaired mitochondrial function, increased levels of the pro-apoptosis gene product CD95/Fas, reduced expression of N2J1-immunoreactive neuronal thread protein and synaptophysin, and reduced distribution of mitochondria in neuritic processes. Desferrioxamine treatment resulted in dose-dependent neuronal loss associated with impaired mitochondrial function, proliferation of neurites, and reduced expression of GAP-43, which has a role in path-finding during neurite outgrowth. The results suggest that oxidative stress can cause neurodegeneration associated with enhanced susceptibility to apoptosis due to activation of pro-apoptosis genes, neurite retraction (synaptic disconnection), and impaired transport of mitochondria to cell processes where they are likely required for synaptic function. In contrast, hypoxia-type injury causes neuronal loss with proliferation of neurites (sprouting), impaired mitochondrial function, and reduced expression of molecules required to form and maintain synaptic connections. Since similar abnormalities occur in AD, both oxidative stress and hypoxic injury can contribute to AD neurodegeneration.

Mitochondrial DNA damage as a mechanism of cell loss in Alzheimer's disease

Aging is associated with impaired mitochondrial function caused by accumulation of oxygen free radical-induced mitochondrial (Mt) DNA mutations. One prevailing theory is that age-associated diseases, including Alzheimer's disease (AD), may be precipitated, propagated, or caused by impaired mitochondrial function. To investigate the role of MtDNA relative to genomic (Gn) DNA damage in AD, temporal lobe samples from postmortem AD (n = 37) and control (n = 25) brains were analyzed for MtDNA and GnDNA fragmentation, mitochondrial protein and cytochrome oxidase expression, MitoTracker Green fluorescence (to assess mitochondrial mass/abundance), and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG) immunoreactivity. Brains with AD had more extensive nicking and fragmentation of both MtDNA and GnDNA as demonstrated by agarose gel electrophoresis, end-labeling, and the in situ terminal deoxynucleotide transferase end-labeling (TUNEL) assay, and only the brains with AD had detectable 8-OHdG immunoreactivity in cortical neurons. Increased MtDNA damage in AD was associated with reduced MtDNA content, as demonstrated by semiquantitative PCR analysis and reduced levels of Mt protein and cytochrome oxidase expression by Western blot analysis or immunohistochemical staining with image analysis. The finding of reduced MitoTracker Green fluorescence in AD brains provided additional evidence that reduced Mt mass/abundance occurs with AD neurodegeneration. The presence of increased MtDNA and GnDNA damage in AD suggest dual cell death cascades in AD. Impaired mitochondrial function caused by MtDNA damage may render brain cells in AD more susceptible to oxidative injury and thereby provide a mechanism by which systemic or environmental factors could influence the course of disease.

Molecular abnormalities of the brain in Down syndrome: relevance to Alzheimer's neurodegeneration

Down syndrome is caused by over-expression of genes located within a segment of chromosome 21, termed the Down locus. Down syndrome is associated with developmental abnormalities of the central nervous system that result in mental retardation and age-dependent Alzheimer-type neurodegeneration. Some of the neurodegenerative lesions, including A beta amyloid deposition, apoptotic cell death, and aberrant dendritic arborization, are in part due to constitutively increased expression of genes that encode the amyloid precursor protein, superoxide dismutase I, and S100-beta, and located within the Down locus. However, neurodegeneration in Down syndrome is also associated with aberrant expression of genes that are not linked to the Down locus, including the growth associated protein, GAP-43, nitric oxide synthase 3, neuronal thread protein, and pro-apoptosis genes such as p53, Bax, and interleukin-1 beta-converting enzyme. Increased expression of these non-Down locus genes correlates with proliferation of dystrophic neurites and apoptotic cell death, two important correlates of cognitive impairment in Alzheimer's disease. This article reviews the functional importance of abnormal gene expression in relation to Alzheimer-type neurodegeneration in brains of individuals with Down syndrome.

Role of aberrant nitric oxide synthase-3 expression in cerebrovascular degeneration and vascular-mediated injury in Alzheimer's disease

Nitric oxide (NO) is an important signaling molecule that is generated through the catalytic activity of nitric oxide synthase (NOS). In the brain, NO mediates neuronal survival, synaptic plasticity, vascular smooth muscle relaxation, and endothelial cell permeability. Previous studies demonstrated aberrant expression of the NOS-III gene in neurons and glial cells in brains with Alzheimer's disease (AD). Since NOS-III is also expressed in vascular cells, and cerebrovascular disease (CVD) frequently complicates the pathology of AD, we investigated the role of NOS-III in relation to CVD in AD. Vasculopathy in AD + CVD was characterized by thickening and hyalinization of the media of small and medium-size vessels, variable degrees of beta-amyloid (A beta) deposition, and increased apoptosis of vascular smooth muscle and endothelial cells, particularly involving white matter vessels. These abnormalities were correlated with reduced levels of NOS-III expression in cerebral vessels. Double-labeling studies demonstrated that the low levels of cerebrovascular NOS-III were associated with increased levels of the pro-apoptosis gene product, p53 in smooth muscle and endothelial cells, suggesting a role for altered NOS-III expression in AD-associated vascular degeneration. Constitutively reduced cerebrovascular NOS-III expression and NO production could also lead to cerebral hypoperfusion due to impaired vasodilation responses, and diminished capacity to remove respiratory waste products and toxins from the extracellular space due to reduced capillary permeability. The role for phosphodiesterases as modulators of NOS activity is discussed, as these molecules represent potential therapeutic targets given their cell type and cyclic nucleotide specificities of action.

Aberrant expression of nitric oxide synthase III in Alzheimer's disease: relevance to cerebral vasculopathy and neurodegeneration

Alzheimer's disease (AD) has heterogeneous pathology, in part due to the large subset of cases (AD+CVD) with superimposed vascular lesions that are sufficient in number and distribution to accelerate the clinical course of dementia. Brains with AD+CVD have lower densities of neurofibrillary tangles and A beta-amyloid diffuse plaques, and increased numbers of cerebral vessels exhibiting p53-associated apoptosis relative to brains with uncomplicated AD. AD and AD+CVD both exhibit altered expression of the nitric oxide synthase 3 (NOS-III) gene; however, in AD+CVD, reduced NOS-III expression in cerebral vessels is associated with an increased frequency of vascular lesions, vascular smooth muscle cell apoptosis, and A beta-amyloid plaques. In contrast, experimental and spontaneous focal acute and subacute cerebral infarcts are associated with increased NOS-III expression in perifocal neurons, glial cells, cerebrovascular smooth muscle and endothelial cells, and diffuse A beta-amyloid plaque formation. This suggests that ischemic injury and oxidative stress can precipitate NOS-III-mediated cell loss and neurodegeneration. A role for aging-associated impaired mitochondrial function as a contributing factor in AD and CVD is suggested by the reduced levels of mitochondrial protein observed in AD and AD+CVD cortical neurons and vascular smooth muscle and endothelial cells. The aggregate findings suggest that cell loss and neurodegeneration may be mediated by somewhat distinct but overlapping mechanisms in AD and AD+CVD.

Overexpression of human aspartyl (asparaginyl) beta-hydroxylase is associated with malignant transformation

The human aspartyl (asparaginyl) beta-hydroxylase (HAAH) is a highly conserved enzyme that hydroxylates epidermal growth factor-like domains in transformation-associated proteins. We previously reported overexpression of the HAAH gene in human hepatocellular carcinomas and cholangiocarcinomas (L. Lavaissiere et al., J. Clin. Investig., 98: 1313-1323, 1996). In the present study, we determined whether HAAH protein overexpression was linked to cellular proliferation or malignant transformation of bile ducts by using a human disease and rat model of bile duct proliferation. In addition, the transforming properties of the AAH genes were assessed by transient and stable transfection of NIH-3T3 cells with human and murine wild-type as well as mutant cDNA constructs that lacked hydroxylation activity. Cellular characteristics of the malignant phenotype were assessed by formation of transformed foci, growth in soft agar, and tumor development in nude mice. We found that HAAH gene expression was undetectable during bile duct proliferation in both human disease and rat models as compared with cholangiocarcinoma. Overexpression of HAAH in NIH-3T3 cells was associated with generation of a malignant phenotype, and enzymatic activity was required for cellular transformation. These findings suggest that overexpression of HAAH is linked to cellular transformation of biliary epithelial cells.

Differential effects of ethanol on insulin-signaling through the insulin receptor substrate-1

Insulin stimulation increases cell proliferation and energy metabolism by activating the insulin receptor substrate I (IRS-1)-signaling pathways. This downstream signaling is mediated by interactions of specific tyrosyl phosphorylated (PY) IRS-1 motifs with SH2-containing molecules such as growth-factor receptor-bound protein 2 (Grb2) and Syp. Ethanol inhibits insulin-stimulated tyrosyl phosphorylation of IRS-1 and DNA synthesis. This study explores the roles of the Grb2- and Syp-binding motifs of IRS-1 in relation to the inhibitory effects of ethanol on insulin-stimulated DNA synthesis, proliferating cell nuclear antigen (PCNA) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression, and activation of mitogen-activated protein kinase (MAPK), which is known to be essential for cell proliferation. NIH3T3 cells were stably transfected with wild-type IRS-1, or IRS-1 mutated at the Grb2 (IRS-1deltaGrb2), Syp (IRS-1deltaSyp), or Grb2 and Syp (IRS-1deltaGrb2deltaSyp)- binding sites. Cells transfected with IRS-1 had increased levels of DNA synthesis, PCNA, GAPDH, and activated MAPK. The IRS-1deltaGrb2 transfectants were highly responsive to insulin stimulation, achieving levels of GAPDH, PCNA, and activated MAPK that were higher than control. In contrast, the IRS-1deltaSyp and IRS-1deltaGrb2deltaSyp transfectants had reduced levels of DNA synthesis, PCNA, and activated MAPK. Ethanol exposure decreased insulin-stimulated DNA synthesis, PCNA, GAPDH, and activated MAPK levels in all clones, but the wild-type IRS-1 transfectants were relatively resistant, and the IRS-1deltaGrb2 transfectants were extraordinarily sensitive to these inhibitory effects of ethanol. The findings suggest that insulin-stimulated DNA synthesis and PCNA expression are mediated through the Syp-binding domain, whereas GAPDH expression and MAPK activation are modulated through both the Grb2 and Syp motifs of IRS-1. In addition, ethanol exposure may preferentially inhibit downstream signaling that requires interaction between Syp and PY-IRS-1.

Structural and functional heterogeneity of nuclear bodies

The nuclear body is a cellular structure that appears to be involved in the pathogenesis of acute promyelocytic leukemia and viral infection. In addition, the nuclear body is a target of autoantibodies in patients with the autoimmune disease primary biliary cirrhosis. Although the precise function of the nuclear body in normal cellular biology is unknown, this structure may have a role in the regulation of gene transcription. In a previous investigation, we identified a leukocyte-specific, gamma interferon (IFN-gamma)-inducible autoantigen designated Sp140. The objectives of the present study were to investigate the cellular location of Sp140 with respect to the nuclear-body components PML and Sp100 and to examine the potential role of Sp140 in the regulation of gene transcription. We used adenovirus-mediated gene transfer to express Sp140 in human cells and observed that the protein colocalized with PML and Sp100 in resting cells and associated with structures containing PML during mitosis. In cells infected with the adenovirus expressing Sp140 and incubated with IFN-gamma, the number of PML-Sp100 nuclear bodies per cell increased but immunoreactive Sp140 was not evenly distributed among the nuclear bodies. Sp140 associated with a subset of IFN-gamma-induced PML-Sp100 nuclear bodies. To examine the potential effect of Sp140 on gene transcription, a plasmid encoding Sp140 fused to the DNA-binding domain of GAL4 was cotransfected into COS cells with a chloramphenicol acetyltransferase (CAT) reporter gene containing five GAL4-binding sites and a simian virus 40 enhancer region. The GAL4-Sp140 fusion protein increased the expression of the reporter gene. In contrast, Sp100 fused to the GAL4 DNA-binding domain inhibited CAT activity in transfected mammalian cells. The results of this study demonstrate that Sp140 associates with a subset of PML-Sp100 nuclear bodies in IFN-gamma-treated cells and that Sp140 may activate gene transcription. Taken together, these observations suggest that the nuclear bodies within a cell may be heterogeneous with respect to both composition and function.

Differential effects of ethanol on insulin-signaling through the insulin receptor substrate-1

Insulin stimulation increases cell proliferation and energy metabolism by activating the insulin receptor substrate I (IRS-1)-signaling pathways. This downstream signaling is mediated by interactions of specific tyrosyl phosphorylated (PY) IRS-1 motifs with SH2-containing molecules such as growth-factor receptor-bound protein 2 (Grb2) and Syp. Ethanol inhibits insulin-stimulated tyrosyl phosphorylation of IRS-1 and DNA synthesis. This study explores the roles of the Grb2- and Syp-binding motifs of IRS-1 in relation to the inhibitory effects of ethanol on insulin-stimulated DNA synthesis, proliferating cell nuclear antigen (PCNA) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression, and activation of mitogen-activated protein kinase (MAPK), which is known to be essential for cell proliferation. NIH3T3 cells were stably transfected with wild-type IRS-1, or IRS-1 mutated at the Grb2 (IRS-1deltaGrb2), Syp (IRS-1deltaSyp), or Grb2 and Syp (IRS-1deltaGrb2deltaSyp)- binding sites. Cells transfected with IRS-1 had increased levels of DNA synthesis, PCNA, GAPDH, and activated MAPK. The IRS-1deltaGrb2 transfectants were highly responsive to insulin stimulation, achieving levels of GAPDH, PCNA, and activated MAPK that were higher than control. In contrast, the IRS-1deltaSyp and IRS-1deltaGrb2deltaSyp transfectants had reduced levels of DNA synthesis, PCNA, and activated MAPK. Ethanol exposure decreased insulin-stimulated DNA synthesis, PCNA, GAPDH, and activated MAPK levels in all clones, but the wild-type IRS-1 transfectants were relatively resistant, and the IRS-1deltaGrb2 transfectants were extraordinarily sensitive to these inhibitory effects of ethanol. The findings suggest that insulin-stimulated DNA synthesis and PCNA expression are mediated through the Syp-binding domain, whereas GAPDH expression and MAPK activation are modulated through both the Grb2 and Syp motifs of IRS-1. In addition, ethanol exposure may preferentially inhibit downstream signaling that requires interaction between Syp and PY-IRS-1.

Properties of monoclonal antibodies directed against hepatitis B virus polymerase protein

Hepadnavirus polymerases are multifunctional enzymes that play critical roles during the viral life cycle but have been difficult to study due to a lack of a well-defined panel of monoclonal antibodies (MAbs). We have used recombinant human hepatitis B virus (HBV) polymerase (Pol) expressed in and purified from baculovirus-infected insect cells to generate a panel of six MAbs directed against HBV Pol protein. Such MAbs were subsequently characterized with respect to their isotypes and functions in analytical and preparative assays. Using these MAbs as probes together with various deletion mutants of Pol expressed in insect cells, we mapped the B-cell epitopes of Pol recognized by these MAbs to amino acids (aa) 8 to 20 and 20 to 30 in the terminal protein (TP) region of Pol, to aa 225 to 250 in the spacer region, and to aa 800 to 832 in the RNase H domain. Confocal microscopy and immunocytochemical studies using various Pol-specific MAbs revealed that the protein itself appears to be exclusively localized to the cytoplasm. Finally, MAbs specific for the TP domain, but not MAbs specific for the spacer or RNase H regions of Pol, appeared to inhibit Pol function in the in vitro priming assay, suggesting that antibody-mediated interference with TP may now be assessed in the context of HBV replication.

Neuritic sprouting with aberrant expression of the nitric oxide synthase III gene in neurodegenerative diseases

Neuronal loss, synaptic disconnection and neuritic sprouting correlate with dementia in Alzheimer's disease (AD). Nitric oxide (NO) is an important synaptic plasticity molecule generated by nitric oxide synthase (NOS) oxidation of a guanidino nitrogen of L-arginine. Experimentally, the NOS III gene is modulated with neuritic sprouting. In a previous study, NOS III expression was found to be abnormal in cortical neurons, white matter glial cells, and dystrophic neurites in AD and Down syndrome brains. The present study demonstrates the same abnormalities in neuronal and glial NOS III expression with massive proliferation of NOS III-immunoreactive neurites and glial cell processes in other neurodegenerative diseases including: diffuse Lewy body disease, Pick's disease, progressive supranuclear palsy, amyotrophic lateral sclerosis, multiple system atrophy, and Parkinson's disease. However, each disease, including AD, was distinguished by the selective alterations in NOS III expression and sprouting in structures marred by neurodegeneration. Double label immunohistochemical staining studies demonstrated nitrotyrosine and NOS III co-localized in only rare neurons and neuritic sprouts, suggesting that peroxynitrite formation and nitration of growth cone proteins may not be important consequences of NOS III enzyme accumulation. The results suggest that aberrant NOS III expression and NOS III-associated neuritic sprouting in the CNS are major abnormalities common to several important neurodegenerative diseases.

Adenovirus-mediated gene transfer of cGMP-dependent protein kinase increases the sensitivity of cultured vascular smooth muscle cells to the antiproliferative and pro-apoptotic effects of nitric oxide/cGMP

Studies in vitro have underestimated the importance of cGMP-dependent protein kinase (PKG) in the modulation of vascular smooth muscle cell (SMC) proliferation and apoptosis in vivo. This is attributable, in part, to a rapid decline in PKG levels as vascular SMC are passaged in culture. We used a recombinant adenovirus encoding PKG (Ad.PKG) to augment kinase activity in cultured rat pulmonary artery SMC (RPaSMC). Incubation of Ad. PKG-infected RPaSMC (multiplicity of infection = 200) with 8-Br-cGMP decreased serum-stimulated DNA synthesis by 85% and cell proliferation at day 5 by 74%. The effect of 8-Br-cGMP on DNA synthesis in Ad.PKG-infected RPaSMC was blocked by KT5823 (PKG inhibitor), but not by KT5720 (cAMP-dependent protein kinase inhibitor). A nitric oxide (NO) donor compound, S-nitrosoglutathione, at concentrations as low as 100 nM, inhibited DNA synthesis in Ad. PKG-infected RPaSMC, but not in uninfected cells or in cells infected with a control adenovirus. In addition, 8-Br-cGMP and S-nitrosoglutathione induced apoptosis in serum-deprived RPaSMC infected with Ad.PKG, but not in uninfected cells or in cells infected with a control adenovirus. These results demonstrate that modulation of PKG levels in vascular SMC can alter the sensitivity of these cells to NO and cGMP. Moreover, these observations suggest an important role for PKG in the regulation of vascular SMC proliferation and apoptosis by NO and cGMP.

Ethanol inhibition of insulin signaling in hepatocellular carcinoma cells

Chronic ethanol toxicity impairs liver regeneration, inhibits DNA synthesis, and mutes cellular responses to growth factor stimulation. Previous studies demonstrated that the adverse effects of ethanol are mediated by inhibition of tyrosyl phosphorylation of the insulin receptor and the insulin receptor substrate-type 1 (IRS-1). However, overexpression of IRS-1 leads to increased DNA synthesis and cellular transformation due to constitutive activation of mitogen-activated protein (MAP) kinase. The present study examines the effects of ethanol on insulin signaling through IRS-1 in FOCUS hepatocellular carcinoma cells, which overexpress IRS-1, to determine whether such cells were resistant to the inhibitory effects of ethanol. The results demonstrated that ethanol treatment (100 mM) caused 30 to 50% reductions in the levels of insulin-stimulated tyrosyl phosphorylation of the insulin receptor beta-subunit, tyrosyl phosphorylation of IRS-1, phosphorylation of Erk2, association of phosphatidylinositol-3 kinase with tyrosyl-phosphorylated IRS-1, and MAP kinase and phosphatidylinositol-3 kinase activities. In contrast, ethanol treatment had no effect on epidermal growth factor-stimulated tyrosyl phosphorylation of Shc. Corresponding with the pronounced inhibition of MAP kinase, ethanol treatment resulted in 30 to 50% reductions in the expression levels of two important insulin-responsive genes: glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and proliferating cell nuclear antigen (PCNA). The findings suggest that, in FOCUS hepatocellular carcinoma cells, which overexpress IRS-1, ethanol treatment substantially inhibits IRS-1 and MAP kinase signaling and growth-associated gene expression, but has no effect on Shc phosphorylation, which activates p21ras through an IRS-1 independent pathway.

P53- and CD95-associated apoptosis in neurodegenerative diseases

Apoptosis is likely to be an important mechanism of cell loss in neurodegenerative diseases, but the signaling cascades activated before DNA fragmentation have not yet been determined. p53 or CD95 gene up-regulation precedes apoptosis in many cell types, and a potential role for these molecules in apoptosis of neurons and glial cells has already been demonstrated in Alzheimer's disease (AD). To determine whether apoptosis in other neurodegenerative diseases is mediated by similar mechanisms, p53 and CD95 expression were examined in postmortem central nervous system tissues from patients with diffuse Lewy body disease (DLBD), Pick's disease (PkD), progressive supranuclear palsy (PSP), multiple system atrophy (MSA), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Down's syndrome plus Alzheimer's disease (DN+AD). Quantitative immunoblot analysis demonstrated higher temporal lobe levels of p53 and CD95 proteins in DLBD, PkD, and DN+AD, and higher temporal lobe levels of CD95 only in MSA and PSP relative to PD and aged controls (for all, p < 0.01). In histologic sections, increased p53 immunoreactivity was localized in neuronal and glial cell nuclei, neuronal perikarya, and dystrophic neuritic and glial cell processes in the frontal (Area 1 1) and temporal (Area 21) lobes in DLBD, PkD, and DN+AD, the motor cortex and spinal ventral horns in ALS, and the striatum and midbrain in DLBD, MSA, PD, and PSP. Increased CD95 expression and nuclear DNA fragmentation were present in the same cell types and structures that manifested increased nuclear p53 immunoreactivity. The results suggest that p53- or CD95-associated apoptosis may be a common mechanism of cell loss in several important neurodegenerative diseases. In addition, the presence of abundant p53-immunoreactive neurites and glial cell processes appears to be a novel feature of neurodegeneration shared by these distinct diseases.

Cyclic-GMP-binding, cyclic-GMP-specific phosphodiesterase (PDE5) gene expression is regulated during rat pulmonary development

Increased nitric oxide (NO) production plays a critical role in the mammalian pulmonary vascular adaptation to extrauterine life. NO activates soluble guanylate cyclase, increasing intracellular cGMP concentrations, thereby inducing relaxation of vascular smooth muscle. cGMP is inactivated by cyclic nucleotide phosphodiesterases (PDEs). One PDE isozyme, PDE5, specifically hydrolyzes cGMP, is abundant in lung tissues, and modifies the pulmonary vasodilatory response to exogenous NO. To investigate the regulation of PDE5 gene expression during pulmonary development, PDE5 mRNA levels, as well as cGMP-metabolizing PDE enzyme activity, were measured in the lungs of perinatal and adult rats. RNA blot hybridization revealed that PDE5 mRNA was detectable in fetal lung tissue as early as 18.5 d of the 22-d term gestation and reached maximal levels in neonatal lungs. mRNA levels in adult rat lungs were 3-4-fold less than the levels measured in lungs of 1- and 8-d-old rats. Pulmonary cGMP hydrolytic activity in 1-d-old animals was 30-fold greater than the cGMP hydrolytic activity of adult rat lungs. Zaprinast, a specific PDE5 antagonist, inhibited 52 and 56% of cGMP hydrolytic activity in lungs of 1- and 8-d-old rats, respectively, but only 18% of the activity in adult lungs. In situ hybridization revealed that PDE5 mRNA transcripts were present in the vascular smooth muscle cells of neonatal and adult lungs. PDE5 mRNA was also detected in the alveolar walls of neonatal rat lungs. These results demonstrate that the gene encoding PDE5 is abundantly expressed in the lungs of perinatal rats, and is available to participate in the mammalian pulmonary vascular transition to extrauterine life. Extravascular PDE5 gene expression in neonatal lungs suggests a potentially important nonvascular role for this enzyme during pulmonary development.

Correlates of p53- and Fas (CD95)-mediated apoptosis in Alzheimer's disease

Apoptosis may be an important mechanism of cell loss in Alzheimer's disease (AD). Experimentally, apoptosis is preceded by nuclear accumulation of p53, and increased expression of Fas (CD95) antigen. In the present study, quantitative Western blot analysis of postmortem frontal and temporal lobe tissue demonstrated significantly higher mean levels of p53 and Fas in AD relative to age-matched controls. Immunohistochemical staining and in situ apoptosis assays demonstrated increased p53 and Fas expression and DNA fragmentation in overlapping populations of cortical neurons, and cortical and white matter glial cells distributed in regions damaged by neurodegeneration. Double-label immunohistochemical staining studies revealed p53 immunoreactivity in: 1) cortical neurons without tau-immunoreactive neurofibrillary tangles; 2) numerous, but not all tau-immunoreactive neuropil neurites and white matter axons; 3) dystrophic fibrils surrounding amyloid-beta-immunoreactive plaques; and 4) glial cells characterized as A2B5+ protoplasmic astrocytes or oligodendrocytes. The prominent distribution of dystrophic p53-immunoreactive processes around amyloid-beta-containing plaques suggests that amyloid deposits are associated with local neuritic degeneration. In addition, the results suggest that many tau-immunoreactive neuritic processes originate from degenerating (p53) as well as regenerating neurons. Finally, apoptosis of glial cells (A2B5+) required to maintain the functional integrity of axons and dendrites may represent an important pathogenic mechanism of axonal loss and synaptic disconnection in AD.

Neuronal thread protein gene modulation with cerebral infarction

Neuronal thread proteins (NTP) are a family of phosphoproteins expressed during neuritic sprouting. The 15 to 18 kD NTP cluster is associated with development and neuronal differentiation, whereas the 21 kD and 39 to 42 kD species are overexpressed in Alzheimer's disease, correlating with neurodegenerative sprouting and synaptic disconnection. Empirical observations suggested that NTP might also be modulated with central nervous system injury and stroke. In this study of both human and experimental (rat) focal cerebral infarcts, in situ hybridization and immunocytochemical staining revealed NTP gene expression up-regulated in perifocal neurons. These findings were confirmed by quantitative Northern and Western blot analyses. Moreover, Western blot analysis demonstrated selectively increased expression of the 15 to 18 kD NTP species during the acute, subacute, and healing phases of cerebral infarction in both humans and experimental animals, corresponding with the expected period of neuronal repair. These results suggest an additional role for the 15 to 18 kD NTP species in neuritic sprouting required for neuronal regeneration after injury in the mature central nervous system.

Pulmonary soluble guanylate cyclase, a nitric oxide receptor, is increased during the perinatal period

Nitric oxide (NO) has an important role in the pulmonary vasodilatation associated with the transition from fetal to neonatal life. NO activates pulmonary soluble guanylate cyclase (sGC), an obligate heterodimer composed of alpha1- and beta1-subunits, increasing synthesis of guanosine 3',5'-cyclic monophosphate (cGMP) and leading to vasodilation. In this study, regulation of sGC subunit expression during pulmonary development was examined. RNA blot hybridization revealed abundant alpha1- and beta1-subunit mRNA in lungs of late-gestation fetal and neonatal Sprague-Dawley rats, with markedly reduced levels detected in adult lungs. Pulmonary sGC enzyme activity in the presence of 1 mM sodium nitroprusside, a NO-donor compound, was approximately sevenfold greater in 1- and 8-day-old rats than in adult rats (P < 0.03). With the use of immunoblot techniques, pulmonary alpha1-subunit concentrations closely correlated with mRNA levels. With in situ hybridization, alpha1- and beta1-subunit mRNAs were readily detected in pulmonary vascular and bronchial smooth muscle cells as well as alveolar and serosal epithelial cells in lungs of 1-day-old rats. In adult lungs, sGC subunit mRNAs were present at low levels and were found nearly exclusively in bronchial and vascular smooth muscle cells. These results demonstrate that abundant pulmonary sGC is available to respond to the increased NO produced during the perinatal period. High-level expression of sGC subunit genes outside the vasculature of lungs of 1-day-old rats suggests an important role for NO-cGMP signal transduction in the perinatal regulation of pulmonary epithelial function and bronchial tone.

Aberrant expression of the constitutive endothelial nitric oxide synthase gene in Alzheimer disease

Neuritic pathology is a major neuroanatomical correlate of dementia in Alzheimer disease (AD). Nitric oxide (NO) is linked to neuritic growth and synaptic plasticity. Expression of one of the enzymes responsible for NO synthesis, the constitutive endothelial NO synthase (ceNOS), was investigated in brains of AD and Down syndrome patients using RNase protection assays, in situ hybridization, and immunocytochemistry. In end-stage AD, ceNOS expression was reduced in cortical neurons, and the enzyme was aberrantly translocated to membranes of proliferated swollen or collapsed neuritic processes. In addition, ceNOS expression was strikingly increased in glial cells characterized mainly as protoplasmic (Type 2) astrocytes, which are responsible for maintaining the structural and functional integrity of cell processes in the CNS. In Down syndrome, similar abnormalities emerged by the third decade, preceding the cognitive decline and establishment of CERAD criteria for AD, indicating that aberrant ceNOS expression occurs early in the course of neurodegeneration. The results suggest that aberrant ceNOS translocation and gene regulation may have important roles in the pathogenesis of AD neuritic pathology.

Identification and characterization of a leukocyte-specific component of the nuclear body

The nuclear body (NB) is a cellular organelle that is involved in the pathogenesis of acute promyelocytic leukemia and viral infection. The NB is also a target of antibodies in the serum of patients with the autoimmune disease primary biliary cirrhosis. In this study, serum from a patient with primary biliary cirrhosis was used to identify a cDNA encoding a novel component of the NB, a 140-kDa protein designated Sp140. The predicted amino acid sequence of the amino-terminal portion of Sp140 was similar to Sp100, a previously identified NB protein. The carboxyl portion of Sp140 contained a zinc-finger domain and a bromodomain, motifs that are present in proteins regulating gene transcription. High levels of Sp140 mRNA were detected in human spleen and peripheral blood leukocytes, but not other human tissues. The level of SP140 mRNA in myeloid precursor cell lines HL60 and NB4 markedly increased in response to chemically induced cellular differentiation. Immunohistochemical techniques were used to demonstrate that SP140 localized to the NB in differentiated HL60 and NB4 cells. The location of Sp140 in the NB, and expression of this gene in cells involved in host defense, suggest that Sp140 may be involved in the pathogenesis of acute promyelocytic leukemia and viral infection.

Modulation of neuronal thread protein expression with neuritic sprouting: relevance to Alzheimer's disease

Widespread proliferation of dystrophic neurites in the cerebral cortex represents an important neuroanatomical correlate of dementia in Alzheimer's disease (AD). Increased CNS expression of the 21-kDa neuronal thread protein (NTP) species is also correlated with dementia in AD. Pilot in vitro experiments provided evidence that high-level NTP expression might be linked to neuritic growth. The present study examines retinoic acid (RA) modulation of NTP expression during neurite outgrowth and neuronal differentiation in SH-Sy5y neuroblastoma and PNET2 CNS-derived cells. In both cell lines, RA-induced neuronal differentiation resulted in increased synthesis, expression, and phosphorylation of several NTP species, with high steady-state levels and stepwise hyper-phosphorylation of 21-kDa NTP molecules. With neurite outgrowth, NTP molecules were translocated from the perikarya to long, slender, unbranched cell processes (axons) and growth cones. RA-mediated changes in NTP expression were independent of DNA synthesis. The findings suggest that high-level expression of 21-kDa, and closely related phosphorylated NTP molecules correlates with neuritic growth. Therefore, over-expression of 21-kDa NTP molecules in AD probably reflects the widespread cortical neuritic sprouting associated with dementia. In view of the rapid phosphorylation and cell process translocation of NTP that occurs during neurite outgrowth in vitro, the accumulation of NTP in AD cortical neuronal perikarya suggests a further problem related to post-translational processing and transport of NTP molecules in AD neurodegeneration.

Developmental patterns of neuronal thread protein gene expression in Down syndrome

Neuronal thread proteins (NTP) are a group of immunologically related molecules expressed in brain and neuroectodermal tumor cell lines. NTP gene expression is up-regulated and NTP molecules accumulate in Alzheimer's disease (AD) brains, pathological states associated with regenerative neuritic sprouting, and during brain development. To investigate the role of NTP over-expression in AD, we examined NTP immunoreactivity in brains from differently aged individuals with Down syndrome, since patients with Down syndrome nearly always develop AD neuropathology and dementia. Using SMI monoclonal antibodies to neurofilament protein, we detected age-associated increases in neurofilament immunoreactive (SMI-positive) neurites in Layers I and II of the cerebral cortex beginning at 1 year of age, followed by SMI-positive neurofibrillary tangles beginning at age 5 years, and then SMI-positive plaques beginning in the third decade. Increased NTP immunoreactivity in Down syndrome brains began in the second decade, prior to establishment of widespread AD neurodegeneration (Down syndrome + AD), and at an age when low-level or absent NTP expression was observed in control brains. Analysis of SDS and Triton X-100-treated histological sections and tissue extracts demonstrated that a largely insoluble, denaturation-resistant form of NTP accumulates in both Down syndrome + AD and AD brains. The findings provide further evidence that abnormal NTP expression and accumulation in brain may be an early marker of AD neurodegeneration in Down syndrome.

Aberrant GAP-43 gene expression in Alzheimer's disease

GAP-43 is a growth-associated phosphoprotein expressed at high levels in neurons during development, axonal regeneration, and neuritic sprouting. GAP-43 gene expression in mature neurons is probably functionally important for the structural remodeling of synapses as required for learning and establishing new memory. The widespread aberrant neuritic growth accompanied by impaired synaptic plasticity in Alzheimer's disease (AD) suggests that abnormal GAP-43 gene expression may contribute to the cascade of neurodegeneration. In the present study, end-stage AD brains exhibited reduced neuronal expression but increased glial cell levels of GAP-43 mRNA and protein. Glial cell localization of GAP-43 gene expression was confirmed by in situ hybridization of cerebral tissue, Northern blot analysis of microdissected cerebral white matter, and independent analysis of astrocytoma cell lines and primary malignant astrocytomas. In addition, in AD, GAP-43 immunoreactivity was translocated from the cytosol to membranes of swollen neuritic (dendritic) and glial cell processes throughout cerebral cortex and white matter. Downregulated and aberrant neuronal GAP-43 gene expression appears to reflect an important molecular lesion that precedes and progresses with the widespread synaptic disconnection and dementia in AD. At the same time, the presence of similar neuronal abnormalities in Pick's disease, diffuse Lewy body disease, Parkinson's disease, and Down syndrome suggests common mechanisms in the respective cascades of neurodegeneration. Finally, the finding of aberrantly increased glial cell GAP-43 gene expression in AD exposes a previously unrecognized neurodegenerative change that may account for the axonal loss and white matter atrophy detected early in the course of disease.

Ethanol inhibits insulin receptor substrate-1 tyrosine phosphorylation and insulin-stimulated neuronal thread protein gene expression

Neuronal thread proteins (NTPs) are molecules that accumulate in the brains of patients with Alzheimer's disease, and may play a key role in both normal and neurodegenerative neuritic sprouting. In this investigation we determined whether NTP expression is up-regulated by insulin, an important neurotrophic factor that stimulates differentiation-associated neurite outgrowth, and studied the effects of ethanol, a known inhibitor of growth factor receptor tyrosine phosphorylation, on NTP expression and insulin-mediated signal transduction cascade in neuronal [primitive neuroectodermal tumour cell line 2; (PNET2)] cells. PNET2 cells were treated with 50 m-units/ml insulin in the presence or absence of 100 mM ethanol for 0.2-96 h, and cell proliferation and expression of NTP molecules were investigated by metabolic labelling, immunoprecipitation and immunohistochemical staining. Insulin stimulation resulted in an immediate increase in the levels of three (38, 18 and 15 kDa) of five NTP species (the others were of 26 and 21 kDa), followed by a decline in expression within 120 min; however, studies performed up to 96 h of culture demonstrated up-regulation by insulin of all five NTP species. Ethanol either abolished or severely muted the short- and long-term insulin-mediated upregulation of NTP expression, and substantially reduced insulin-mediated neuronal differentiation. The effects of ethanol on NTP gene expression were associated with impaired insulin-mediated tyrosine phosphorylation of both the insulin receptor beta subunit and the insulin receptor substrate-1 (IRS-1), resulting in decreased association of phosphatidylinositol 3-kinase with IRS-1. The findings suggest that ethanol may inhibit NTP expression associated with central nervous system neuronal differentiation by uncoupling the IRS-1-mediated insulin signal transduction pathway.

Insulin-induced differentiation and modulation of neuronal thread protein expression in primitive neuroectodermal tumor cells is linked to phosphorylation of insulin receptor substrate-1

Neuronal thread proteins (NTPs) are a family of developmentally regulated molecules expressed in central nervous system (CNS) neurons and primitive neuroectodermal tumor (PNET) cell lines. NTP gene expression is modulated with DNA synthesis, neuritic sprouting, and neuronal differentiation. The present study explores the mechanism of insulin modulation of NTP gene expression during neuronal differentiation using PNET cell lines of CNS origin. PNET2 cells underwent neuronal differentiation with neurite outgrowth coupled with transient up-regulation of several species of NTP. In contrast, PNET1 cells failed to differentiate in response to insulin stimulation, although insulin receptors were more abundant than in PNET2 cells. Analysis of the insulin-mediated signal transduction pathway demonstrated that the lack of insulin responsiveness in PNET1 cells was primarily caused by impaired insulin-mediated tyrosyl phosphorylation of the insulin receptor substrate-1 (IRS-1). Correspondingly, the association between phosphatidyl-inositol 3 (PI3) kinase and phosphorylated IRS-1 was reduced in PNET1 compared with PNET2 cells. In contrast, the levels of IRS-1 protein were similar in PNET1 and PNET2 cells, and expression of the insulin receptor beta subunit (Ir beta) and insulin-mediated tyrosyl phosphorylation of the Ir beta were greater in PNET1 than PNET2 cells. The findings suggest that insulin effected neuronal differentiation and modulation of NTP gene expression in PNET cells utilizes a signal transduction cascade that requires tyrosyl phosphorylation of IRS-1.

Regional and maturation-associated expression of endothelin 2 in rat gastrointestinal tract

Endothelin 2 (ET2), also referred to as vasoactive intestinal contractor peptide, is a member of a family of vasoactive peptides. ET2 is a potent constrictor of intestinal smooth muscle, and the mRNA that encodes it has been detected in murine intestinal extracts. To further investigate the potential physiological roles of ET2, we characterized the cellular distribution of ET2 gene expression in adult rat gastrointestinal tract. Using an RNAse protection assay, an overall proximal to distal gradient of increasing ET2 gene expression was observed from stomach to colon. In situ hybridization studies confirmed this finding and demonstrated ET2 mRNA localized in lamina propria stromal cells. Moreover, ET2 gene expression in stromal cells increased from crypt to villous tip. The results demonstrate that ET2 is produced by stromal cells in villi throughout the intestine. Increased ET2 gene expression at the villous tip is associated with more mature overlying epithelial cells, suggesting a possible role for this vasoactive peptide in intestinal epithelial differentiation or secretory activity.

Modulation of p36 gene expression in human neuronal cells

p36 is a calcium/lipid-binding phosphoprotein that is expressed at high levels in proliferating and transformed cells, and at low levels in terminally differentiated cells, such as CNS neurons. The calcium-dependent binding to membrane phospholipids, and its capacity to interact with intermediate filament proteins suggest that p36 may be involved in the transduction of extracellular signals. The present work examines p36 gene expression in the mature CNS, primary primitive neuroectodermal tumors (PNETs), and transformed PNET cell lines. p36 immunoreactivity was not observed in normal adult human brain, but low levels of the protein were detected by Western blot analysis. Following acute anoxic cerebral injury, the mean levels of p36 protein were elevated two-fold, and injured neurons exhibited increased p36 immunoreactivity. This phenomenon was likely to have been mediated by post-transcriptional mechanisms since there was no corresponding change in the level p36 mRNA. p36 immunoreactivity was detected in 8 of 9 primary PNETs, and in 3 of 3 neurofilament-expressing PNET cell lines. The levels of p36 protein in PNET cell lines were 5-fold higher than in adult human brain tissue. Although p36 gene expression was generally high in proliferating PNET cells, the levels of p36 mRNA and protein were not strictly correlated with DNA synthesis. Instead, p36 gene expression was modulated in both proliferating and non-proliferating PNET cell cultures by treatment with 50 mIU/ml of insulin, 100 mM ethanol, or 5 microM retinoic acid. The frequent discordances observed experimentally and in vivo between p36 mRNA and p36 protein expression suggest that the steady-state levels of p36 protein in neuronal cells may be regulated primarily by post-transcriptional mechanisms.

Diagnostic utility of quantitating neurofilament-immunoreactive Alzheimer's disease lesions

The diagnosis of Alzheimer's disease (AD) neurodegeneration is based on histopathological detection of paired helical filament-associated lesions. Silver stains are routinely used but the results are fraught with intra- and interinstitutional variability. This study employed monoclonal antibodies to middle and high molecular weight neurofilament subunits in an immunohistochemical assay to assess the extent of paired helical filament-associated lesions in brains with AD, Down's syndrome plus AD lesions (AD+DN), Parkinson's disease dementia (PD), AD+PD, and normal aging changes. The densities of neurofilament-immunoreactive (NFI) cortical neurofibrillary tangles and plaques were significantly higher in AD and AD+DN than in PD and aged control brains (p < 0.001), and NFI neurofibrillary tangles and plaques were more abundant in AD and AD+DN compared with AD+PD and PD, yet all patients with AD, AD+PD, or PD died with end-stage dementia. In contrast, the densities of NFI dystrophic neurites (primarily dendrites) in cortical Layer 2 were similar among the AD, AD+DN, AD+PD, and PD groups, and all were significantly higher than control (p < 0.005). Stepwise multivariate regression analysis demonstrated significant correlations between AD diagnosis and high densities of NFI neurofibrillary tangles and plaques (p < 0.001) and between end-stage AD-type dementia and high densities of NFI dystrophic neurites (p < 0.001). This study demonstrates that the histopathological lesions correlated with AD dementia can be readily detected and quantified by immunostaining with monoclonal antibodies to phosphorylated and non-phosphorylated neurofilaments. Moreover, the findings suggest that NFI neurite pathology may be an important feature contributing to the clinically manifested AD-type dementia in individuals with Parkinson's disease.

Characterization of thread proteins expressed in neuroectodermal tumors

Neuronal thread protein is a novel 21-kDa protein that accumulates in brains with Alzheimer's disease and exhibits developmentally associated changes in the level of expression. Recently, we discovered that primary human primitive neuroectodermal tumor (PNETs), malignant astrocytomas, and several human PNET and glioblastoma cell lines also express thread protein immunoreactivity. However, in addition to the 21-kDa species, there are approximately 17- and approximately 14-kDa thread protein-immunoreactive molecules expressed in both PNET and glioblastoma cell lines and a fourth approximately 8-kDa thread protein detected in glioblastoma cell lines. Metabolic labeling studies demonstrated that the 21-kDa thread proteins are phosphorylated, whereas the approximately 17-, approximately 14-, and approximately 8-kDa thread proteins are not. Glycosylated residues were not detected in either the PNET- or glioblastoma-derived thread proteins. Using a panel of monoclonal antibodies, we observed differences between PNET and glioblastoma cells suggesting that the thread proteins expressed in neuronal and glial cells are distinct. The levels of thread protein immunoreactivity in both PNET and glial cells were highest during the log phase of cell growth and lowest in serum-starved, nonproliferating cultures. The findings suggest that there are several distinct neuronal and glial derived thread proteins expressed in the central nervous system and that their levels of expression may be modulated with cell growth.

Neuronal thread protein over-expression in brains with Alzheimer's disease lesions

Neuronal thread protein (NTP) is a recently characterized molecule that is over-expressed in brains with Alzheimer's disease (AD) lesions. The present study encompasses a detailed analysis of NTP expression in AD compared with other neurodegenerative diseases and aged controls. Using a specific monoclonal antibody, NTP immunoreactivity was evaluated in 309 paraffin-embedded sections from 8 different regions of the frontal, parietal, and temporal lobes of 73 brains with AD, AD + Down's syndrome (DN), AD + Parkinson's disease (PD), PD dementia (PDD), aged controls, and disease controls with Huntington's disease, multi-infarct dementia, or schizophrenia. In 250 adjacent blocks of snap-frozen unfixed tissue the concentration of NTP (ng/mg of protein) was measured using a 3-site forward sandwich monoclonal antibody based immunoradiometric assay (M-IRMA). Immunohistochemical studies demonstrated that brains with AD, AD + PD, and AD + DN contained significantly higher densities of NTP immunoreactive neurons and more frequent immunostaining of neuropil and white matter fibers compared with PDD and aged controls (both P < 0.001) which had few or no AD lesions. In addition, the overall mean concentrations of NTP in AD, AD + PD, and AD + DN were significantly higher than in PDD and aged controls (P < 0.005). Greater degrees of NTP immunoreactivity and higher concentrations of the protein in cerebral tissue were significantly correlated with AD diagnosis and abundant neurofibrillary tangles (P < 0.005). The findings suggest that NTP over-expression may serve as a marker for the type of neuronal degeneration that occurs in AD.