Reversal of alcohol's effects on neurite extension and on neuronal GAP43/B50, N-myc, and c-myc protein levels by retinoic acid

Expression profiling and Ingenuity biological function analyses of interleukin-6- versus nerve growth factor-stimulated PC12 cells

BACKGROUND

The major goal of the study was to compare the genetic programs utilized by the neuropoietic cytokine Interleukin-6 (IL-6) and the neurotrophin (NT) Nerve Growth Factor (NGF) for neuronal differentiation.

RESULTS

The designer cytokine Hyper-IL-6 in which IL-6 is covalently linked to its soluble receptor s-IL-6R as well as NGF were used to stimulate PC12 cells for 24 hours. Changes in gene expression levels were monitored using Affymetrix GeneChip technology. We found different expression for 130 genes in IL-6- and 102 genes in NGF-treated PC12 cells as compared to unstimulated controls. The gene set shared by both stimuli comprises only 16 genes.A key step is upregulation of growth factors and functionally related external molecules known to play important roles in neuronal differentiation. In particular, IL-6 enhances gene expression of regenerating islet-derived 3 alpha (REG3A; 1084-fold), regenerating islet-derived 3 beta (REG3B/PAPI; 672-fold), growth differentiation factor 15 (GDF15; 80-fold), platelet-derived growth factor alpha (PDGFA; 69-fold), growth hormone releasing hormone (GHRH; 30-fold), adenylate cyclase activating polypeptide (PACAP; 20-fold) and hepatocyte growth factor (HGF; 5-fold). NGF recruits GDF15 (131-fold), transforming growth factor beta 1 (TGFB1; 101-fold) and brain-derived neurotrophic factor (BDNF; 89-fold). Both stimuli activate growth-associated protein 43 (GAP-43) indicating that PC12 cells undergo substantial neuronal differentiation.Moreover, IL-6 activates the transcription factors retinoic acid receptor alpha (RARA; 20-fold) and early growth response 1 (Egr1/Zif268; 3-fold) known to play key roles in neuronal differentiation.Ingenuity biological function analysis revealed that completely different repertoires of molecules are recruited to exert the same biological functions in neuronal differentiation. Major sub-categories include cellular growth and differentiation, cell migration, chemotaxis, cell adhesion, small molecule biochemistry aiming at changing intracellular concentrations of second messengers such as Ca2+ and cAMP as well as expression of enzymes involved in posttranslational modification of proteins.

CONCLUSION

The current data provide novel candidate genes involved in neuronal differentiation, notably for the neuropoietic cytokine IL-6. Our findings may also have impact on the clinical treatment of peripheral nerve injury. Local application of a designer cytokine such as H-IL-6 with drastically enhanced bioactivity in combination with NTs may generate a potent reparative microenvironment.

Developmental neurotoxicity testing in vitro: models for assessing chemical effects on neurite outgrowth

In vitro models may be useful for the rapid toxicological screening of large numbers of chemicals for their potential to produce toxicity. Such screening could facilitate prioritization of resources needed for in vivo toxicity testing towards those chemicals most likely to result in adverse health effects. Cell cultures derived from nervous system tissue have proven to be powerful tools for elucidating cellular and molecular mechanisms of nervous system development and function, and have been used to understand the mechanism of action of neurotoxic chemicals. Recently, it has been suggested that in vitro models could be used to screen for chemical effects on critical cellular events of neurodevelopment, including differentiation and neurite growth. This review examines the use of neuronal cell cultures as an in vitro model of neurite outgrowth. Examples of the cell culture systems that are commonly used to examine the effects of chemicals on neurite outgrowth are provided, along with a description of the methods used to quantify this neurodevelopmental process in vitro. Issues relating to the relevance of the methods and models currently used to assess neurite outgrowth are discussed in the context of hazard identification and chemical screening. To demonstrate the utility of in vitro models of neurite outgrowth for the evaluation of large numbers of chemicals, efforts should be made to: (1) develop a set of reference chemicals that can be used as positive and negative controls for comparing neurite outgrowth between model systems, (2) focus on cell cultures of human origin, with emphasis on the emerging area of neural progenitor cells, and (3) use high-throughput methods to quantify endpoints of neurite outgrowth.

Postnatal environmental or experiential amelioration of neurobehavioral effects of perinatal alcohol exposure in rats

Fetal alcohol spectrum disorders (FASDs) in children are characterized by life-long compromises in learning, memory, and adaptive responses. To date, there are no clinical remedies for the treatment of global fetal alcohol effects, although interventions for specific outcomes are available. Here we review basic research in animal models of perinatal alcohol exposure to assess the potential of global environmental manipulations to ameliorate the neurobehavioral effects associated with FASD. Enhancement of the postnatal environment via neonatal handling, environmental enrichment, or rehabilitative or "therapeutic" motor training, can improve behavioral performance and ameliorate or even eliminate some deficits in perinatal alcohol-exposed rats and mice. While neuroanatomical changes associated with the behavioral improvements have been reported in some models, there generally appears to be a persistent impairment in neuronal plasticity. Such research suggests that it may be possible to manage the postnatal environment or experience of children with FASDs to improve function. It is, however, necessary to consider the difficulties in translating findings from research in animals to the clinic, school or home because sex-, postnatal age- and species-specific differences are critical factors in how specific environments may influence brain development. Continued study of the potential ameliorative effects of neonatal handling, environmental enrichment, and rehabilitative training as "therapies" in animal models will remain a valuable source of information for eventually devising treatments for children with FASDs.

Molecular characterization of a transport vesicle protein Neurensin-2, a homologue of Neurensin-1, expressed in neural cells

We have isolated and characterized a novel cDNA encoding a small neuronal membrane protein showing high sequence homology to Neuro-p24/Neurensin-1, a protein containing a microtubule-associated domain at the carboxyl-terminus and exclusively localized to small vesicles of neurons. The newly identified Neurensin-2 constitutes two-membrane spanning domains but not the microtubule-binding domain, with a molecular mass of 28 kDa. Neurensin-2 mRNA is expressed only in brain, whereas the protein expressed in various neurons including those of the thalamus/hypothalamus and hippocampus, of postnatally developing mice. While the levels of Neurensin-1 mRNA and protein in retinoic acid-exposed mouse neuroblastoma Neuro2a cells increased, those of Neurensin-2 mRNA and protein remained unchanged. When the Neurensin-2 cDNA was transfected into Neuro2a cells, Neurensin-2 was expressed in small vesicles including lysosomes in the perinuclear region. On the cotransfection of Neurensin-1 and -2 cDNA into Neuro2a cells, Neurensin-2 was mainly found in small vesicles of the cell body and Neurensin-1 in those of growth cones. In nerve growth factor-stimulated PC12 cells, the intracellular localization of these proteins also differed. Furthermore, immunochemical staining of mouse brain revealed that Neurensin-1 and -2 had a similar distribution in many regions such as the Diagonal band, hippocampus, amygdaloid nucleus, and habenula nucleus, but differed in the intracellular localization as follows: Neurensin-1 was found mainly in neuritic processes, while Neurensin-2 was found in cell bodies. Thus, both Neurensin-1, and -2 are localized in small vesicles in neural cells, but their localizations of the vesicles are not always the same by each other, suggesting that they are under separate regulation.

Prenatal alcohol exposure delays the development of the cortical barrel field in neonatal rats

In-utero alcohol exposure produces sensorimotor developmental abnormalities that often persist into adulthood. The rodent cortical barrel field associated with the representation of the body surface was used as our model system to examine the effect of prenatal alcohol exposure (PAE) on early somatosensory cortical development. In this study, pregnant female rats were intragastrically gavaged daily with high doses of alcohol (6 gm/kg body weight) throughout the first 20 days of pregnancy. Blood alcohol levels were measured in the pregnant dams on gestational days 13 (G13) and G20. The ethanol treated group (EtOH) was compared to the normal control chowfed (CF) group, nutritionally matched pairfed (PF) group, and cross-foster (XF) group. Cortical barrel development was examined in pups across all treatment groups from G25, corresponding to postnatal day 2 (P2), to G32 corresponding to P9. The EtOH and control group pups were weighed, anesthetized, and perfused. Brains were removed and weighed with, and without cerebellum and olfactory bulbs, and neocortex was removed and weighed. Cortices were then flattened, sectioned tangentially, and stained with a metabolic marker, cytochrome oxidase (CO) to reveal the barrel field. Progression of barrel development was distinguished into three categories: (a) absent, (b) cloudy barrel-like pattern, and (c) well-formed barrels with intervening septae. The major findings are: (1) PAE delayed barrel field development by one or more days, (2) the barrel field first appeared as a cloudy pattern that gave way on subsequent days to an adult-like pattern with clearly demarcated intervening septal regions, (3) the barrel field developed differentially in a lateral-to-medial gradient in both alcohol and control groups, (4) PAE delayed birth by one or more days in 53% of the pups, (5) regardless of whether pups were born on G23 (normal expected birth date for non-alcohol controls) or as in the case for the alcohol-delayed pups born as late as G27, the barrel field was never present at birth suggesting the importance of postnatal experience on barrel field development, and (6) PAE did not disrupt the normal barrel field pattern, although both total body and brain weights were compromised. These findings suggest that PAE delays the development of the somatosensory cortex (SI); such delays may interfere with timing and formation of cortical circuits. It is unknown whether other nuclei along the somatosensory pathway undergo similar delays in development or if PAE selectively disrupts cortical circuitry.

Detection of genes for ordinal traits in nuclear families and a unified approach for association studies

There is growing interest in genomewide association analysis using single-nucleotide polymorphisms (SNPs), because traditional linkage studies are not as powerful in identifying genes for common, complex diseases. Tests for linkage disequilibrium have been developed for binary and quantitative traits. However, since many human conditions and diseases are measured in an ordinal scale, methods need to be developed to investigate the association of genes and ordinal traits. Thus, in the current report we propose and derive a score test statistic that identifies genes that are associated with ordinal traits when gametic disequilibrium between a marker and trait loci exists. Through simulation, the performance of this new test is examined for both ordinal traits and quantitative traits. The proposed statistic not only accommodates and is more powerful for ordinal traits, but also has similar power to that of existing tests when the trait is quantitative. Therefore, our proposed statistic has the potential to serve as a unified approach to identifying genes that are associated with any trait, regardless of how the trait is measured. We further demonstrated the advantage of our test by revealing a significant association (P = 0.00067) between alcohol dependence and a SNP in the growth-associated protein 43.

Differential effect of retinoic acid and triiodothyronine on the age-related hypo-expression of neurogranin in rat

Given the important role of retinoids and thyroid hormone for optimal brain functioning and the tenuous relationship between retinoic acid (RA) and triiodothyronine (T3) signalings, we compared the effects of RA or T3 administrations on RA and T3 nuclear receptors (RAR, RXR and TR) and on their target genes, neuromodulin (GAP43) and neurogranin (RC3) in 24-month-old rats. Quantitative real time PCR and western blot analysis allowed us to verify that retinoid and thyroid signalings and GAP43 and RC3 expression are affected by age. By in situ hybridization we observed a decreased expression of RC3 in hippocampus, striatum and cerebral cortex. RARbeta, RXRbeta/gamma and GAP43 were up-regulated by RA as well as T3 treatment. The abundance of TRalpha/beta mRNA and RC3 expression were only increased by T3 administration in the whole brain. This up-regulator effect of T3 on RC3 was only observed in the striatum. During aging, T3 become a limiting factor alone able to correct the age-related concomitant hypo-activation of retinoid and thyroid signalings and alterations of synaptic plasticity.

Prenatal alcohol exposure alters the size, but not the pattern, of the whisker representation in neonatal rat barrel cortex

Maternal alcohol exposure results in a variety of neurodevelopmental abnormalities that include cognitive and sensorimotor dysfunctions that often persist into adulthood. Many reports of central nervous system disturbances associated within a clinical diagnosis of fetal alcohol syndrome point toward disturbances in central information processing. In this study, we used the rat barrel field cortex as a model system to examine the effects of prenatal alcohol exposure (PAE) on the organization and size of the large whisker representation in layer IV of the posteromedial barrel subfield (PMBSF) in somatosensory cortex. Pregnant rats (Sprague-Dawley) were intragastrically gavaged daily with alcohol doses (6 gm/kg body weight) from gestational day 1 to day 20 in a chronic binge pattern which produced blood alcohol levels ranging between 260 mg/dl and 324 mg/dl. Chow-fed (CF), pair-fed (PF), and cross-foster (XF) groups served as normal, nutritionally matched, and maternal controls, respectively, for the ethanol-exposed (EtOH) treatment group. All pups were examined on gestational day 32 corresponding approximately to postnatal day 9. EtOH and control group pups were weighed, anesthetized, and perfused. Brains were removed and weighed, with and without cerebellum and olfactory bulbs, and the neocortex was removed and weighed. Cortices were then flattened, sectioned tangentially, and stained with a metabolic marker-cytochrome oxidase-to reveal the barrel field. A subset of 27 cortical barrels, associated with the representation of the large whisker pad, was selected to examine in detail. The major results were: (i) the total barrel field area comprising the PMBSF was significantly reduced in EtOH (by 17%) and XF (by 16%) pups compared with CF pups, (ii) the sizes of individual barrels within the PMBSF were also significantly reduced in EtOH (16%) and XF (18%) pups, (iii) the septal region between barrels was also significantly reduced in EtOH (18%) and XF (12%) pups, (iv) anteriorly located barrels underwent greater reduction in size relative to the posteriorly located barrels, (v) body weights were also significantly reduced in EtOH (21%) and XF (27%) pups, (vi) total brain weight [with and without (forebrain) cerebellum/olfactory bulbs] and cortical weights were also significantly reduced in EtOH (total brain weight 15%, forebrain weight 16%, cortical weight 15%) and XF (18%, 19%, 20%) pups, and in contrast (vi) neither the overall barrel field pattern nor the pattern of individual barrels in the PMBSF was altered. These findings suggest that PAE reduces body and brain weight as well as the central cortical representation of the whisker pad, while leaving the overall barrel field pattern unperturbed. While these results might appear to support a miniaturization hypothesis (smaller PMBSF, smaller brain, smaller body weight), PAE also shows regional vulnerability within the PMBSF whereby anteriorly located barrels are most affected.

Expression of neurogranin and neuromodulin is affected in the striatum of vitamin A-deprived rats

Our previous data showed that vitamin A deficiency (VAD) induces, in whole brain, a reduced amount of mRNA for brain retinoic acid (RA) and triiodothyronine (T3) nuclear receptors (i.e., RAR, RXR, and TR, respectively), which is accompanied by reduced amounts of mRNA and protein of neurogranin (RC3, a neuronal protein involved in synaptic plasticity) as well as selective behavioral impairment. Given the important role of retinoids for optimal brain functioning, the effects of vitamin A depletion and subsequent administration of RA or T3 on the mRNA levels of RA and T3 nuclear receptors and on two target genes' (RC3 and neuromodulin or GAP43) mRNA and protein levels were examined in the hippocampus, striatum, and cerebral cortex. A quantitative real-time polymerase chain reaction (PCR), in situ hybridization, and Western blot analysis demonstrated that the striatal region is the brain site where both RA and T3 signaling pathways are most affected by VAD. Indeed, rats fed a vitamin A-free diet for 10 weeks exhibited decreased expression of RAR, RXR, TR, RC3, and GAP43 in the striatum. The administration of T3 to these vitamin A-deprived rats reversed the reduction in mRNA levels of RA and T3 nuclear receptors and in mRNA and protein levels of target genes in this region. These data suggest that modifications that appear preferentially in the striatum, a region highly sensitive to vitamin A bioavailability, may contribute to neurobiological alterations and the spatial learning impairment that occurs in vitamin A-deprived animals.

Interaction of ethanol with retinol and retinoic acid in RAR beta and GAP-43 expression

Fetal ethanol exposure has many detrimental effects on neural development, which possibly occurs through ethanol-induced disruption of the function of vitamin A. In LAN-5 neuroblastoma cells, retinol (10(-6) M) and retinoic acid (RA; 10(-5)-10(-6) M) increased RAR beta mRNA expression. Ethanol downregulated RAR beta levels, even in the presence of retinol. RAR beta mRNA expression was decreased by ethanol in the presence of 10(-6) M RA, but not 10(-5) M RA. With cycloheximide (CX), RA still stimulated RAR beta mRNA, but the effect of ethanol was abolished. The mRNA expression of GAP-43, an important factor in neural development, increased with 10(-6) M retinol and 10(-5)-10(-9) M RA. Ethanol decreased GAP-43 mRNA expression in the presence or absence of retinol. Ethanol was without effect on GAP-43 mRNA at 10(-5) M RA, but did lower the levels at 10(-6) and 10(-7) M RA. CX prevented the effects of both RA and ethanol on GAP-43 mRNA. These studies provide support for the hypothesis that retinoid function is altered by ethanol.

Amelioration of fetal alcohol-related neurodevelopmental disorders in rats: exploring pharmacological and environmental treatments

Fetal alcohol syndrome (FAS) and alcohol-related neurodevelopmental disorders (ARNDs) in children are characterized by life-long compromises in learning, memory, and adaptive responses. Until the advent of effective prevention measures, it will remain necessary to seek ways to treat the life-long neurobehavioral consequences of prenatal alcohol exposure. To date, there are no clinical remedies to recommend for either specific or global fetal alcohol effects. This article reviews our basic research in animal models that assesses the potential of global environmental manipulations or specific psychopharmacological treatments to ameliorate the neurobehavioral effects of prenatal exposure to alcohol. Postweaning environmental enrichment can improve behavioral performance and ameliorate or even eliminate deficits in prenatal alcohol-exposed rats, although there is persistent impairment in neuronal plasticity, as indicated by the failure of hippocampal pyramidal cells to increase dendrite spine density. Behavioral and neural responses to CNS stimulants differ in rats exposed prenatally to alcohol, although it is not clear that these shifts in dose-response curves would predict benefit to children. Although the present results may sound a note of optimism for the development of effective treatment strategies for children with FAS or ARNDs, it is important to consider that application of these findings in rodents may not be straightforward. We also need to know the critical features of specific environments that influence brain development, and the limits of pharmacotherapy, as well as critical periods of exposure. Continued study of the beneficial, ameliorative effects of environmental enrichment, rehabilitative training, and of pharmacological therapies in animal models, will remain a valuable source of information for eventually devising treatments specific for children with FAS and ARNDs.

Alcohol reduces neurofilament protein levels in primary cultured hippocampal neurons

High concentrations of alcohol (> or = 1.8%) were shown previously to impair health and viability of cultured hippocampal neurons. Because neurofilament proteins are essential for neuronal process outgrowth and differentiation, the effects of alcohol on these proteins were determined in the neuronal processes of primary cultured gestational day 18 rat hippocampal neurons. At the relatively lower concentrations used in the present study, alcohol caused a concentration-dependent reduction (< or = 47%) in 68 and 200 kDa neurofilament proteins (p < 0.05). Alcohol caused a 32% downward trend in 160 kDa neurofilament protein levels. Alcohol up to 1% (72-h exposure) produced no obvious alterations in neurite extension or explant morphology, and there were no visual signs of cell death. The sensitive MTT dye reduction assay showed no biochemical evidence of decreased cell viability at < or = 0.5% alcohol. The 32-47% reductions in neurofilament protein levels in vitro may hold implications for later hippocampal neuronal differentiation events in animals prenatally exposed to alcohol.

Transcriptional regulation of tracheo-bronchial mucin (TBM) gene by ethanol

The epithelia of the respiratory tract are protected by a mucin glycoprotein. The expression of mucin changes when epithelia come in contact with toxic agents such as ethanol. Previously, we have identified and characterized the expression of a tracheo-bronchial mucin (TBM) gene. In the present study, we observed that ethanol regulates TBM expression at the transcription level. Ethanol enhanced the expression of TBM mRNA in a dose- and time-dependent manner in HBE1 cells. At 100 mM concentration (a concentration reported to be present in alcoholics), ethanol induced an eight-fold increase in TBM transcription as determined by reporter gene expression analysis.

What research with animals is telling us about alcohol-related neurodevelopmental disorder

The substantial advances in understanding fetal alcohol syndrome over the past 20 years were made in large part because of research with animals. This review illustrates recent progress in animal research by focusing primarily on the central nervous system effects of prenatal alcohol exposure. Current findings suggest further progress in understanding consequences, risk factors, mechanisms, prevention and treatment will depend on continued research with animals.

Exposure of embryonic cells to alcohol: contrasting effects during preimplantation and postimplantation development

Alcohol is a known teratogen that causes a broad variety of developmental anomalies, including fetal growth retardation, craniofacial anomalies, and neurological disorders. The etiology of this multiple defect syndrome, known as fetal alcohol syndrome, has been studied in animal models that reproduce many of the attributes of the human disease. These studies show that ethanol is most teratogenic during organogenesis and development of the nervous system. The molecular basis of fetal alcohol effects has been further investigated using embryo and cell culture systems. Recent studies show that signal transduction pathways controlling cell proliferation are perturbed during ethanol exposure. Ethanol can induce the release of intracellular calcium stores, which stimulates the cell cycle, and it also up-regulates the expression of myc proteins associated with cell proliferation. Increased proliferation is advantageous during the preimplantation period, but ethanol interference with terminal differentiation events within developing tissues during organogenesis may underlie alcohol teratogenicity.

Alcohol inhibits neurite extension and increases N-myc and c-myc proteins

Alcohol teratogenesis may be due, in part, to inhibition of neuronal differentiation by alcohol. Because decreases in the N-myc and c-myc proteins are believed to be linked causally to neuronal differentiation, we hypothesized that alcohol would increase N-myc and c-myc proteins in undifferentiated neuronal cells and would oppose the decreases in these two proteins that normally precede differentiation. In undifferentiated LA-N-5 cultured human neuroblastoma cells, alcohol increased N-myc protein levels (178% vs. control cells) and c-myc levels (222% of control). Retinoic acid decreased N-myc and c-myc and induced neurite outgrowth (a differentiation marker). Alcohol prevented retinoic acid-elicited decreases in both myc isoforms and prevented neurite outgrowth. A significant 100% increase in c-myc and an upward trend (48%) in N-myc were observed in CA1 pyramidal neurons of the dorsal hippocampus in mouse fetuses exposed prenatally to alcohol. These data suggest that increases in N-myc and c-myc protein levels are associated with inhibition of neurite extension by alcohol.