Calcium signals in cell lines derived from the cerebral cortex of normal and trisomy 16 mice

Apolipoprotein E4 heterologous expression, purification under non-denaturing conditions, and effects on neuronal clonal cell lines

The ε4 allele of the apolipoprotein E gene (APOE4) constitutes the main genetic risk factor for late-onset Alzheimer disease (AD). High amounts of pure apolipoprotein E4 (ApoE4), in a rapid and reproducible fashion, could be of value for studying its pathophysiological roles in AD. The aim of the present work was to optimize a preparative method to obtain highly purified recombinant ApoE4 (rApoE4) with full biological activity. rApoE4 was expressed in the E. Coli BL21(D3) strain and a soluble form of the protein was purified by a combination of affinity and size-exclusion chromatography that precluded a denaturation step. The structural integrity and the biochemical activity of the purified rApoE4 were confirmed by circular dichroism and a lipid-binding assay. Several biological parameters affected by rApoE4, such as mitochondrial morphology, mitochondrial membrane potential and reactive oxygen species production were studied in CNh cells, a neuronal cell line, and neurodifferentiation and dendritogenesis were analyzed in the SH-SY5Y neuroblastoma cell line. The improved rApoE4 purification technique reported here enables the production of highly purified protein that retain the structural properties and functional activity of the native protein, as confirmed by tests in two different neuronal cell lines in culture.

Pharmacological Inhibition of p-21 Activated Kinase (PAK) Restores Impaired Neurite Outgrowth and Remodeling in a Cellular Model of Down Syndrome

Down syndrome (DS) is characterized by the trisomy of chromosome 21 and by cognitive deficits that have been related to neuronal morphological alterations in humans, as well as in animal models. The gene encoding for amyloid precursor protein (APP) is present in autosome 21, and its overexpression in DS has been linked to neuronal dysfunction, cognitive deficit, and Alzheimer's disease-like dementia. In particular, the neuronal ability to extend processes and branching is affected. Current evidence suggests that APP could also regulate neurite growth through its role in the actin cytoskeleton, in part by influencing p21-activated kinase (PAK) activity. The latter effect is carried out by an increased abundance of the caspase cleavage-released carboxy-terminal C31 fragment. In this work, using a neuronal cell line named CTb, which derived from the cerebral cortex of a trisomy 16 mouse, an animal model of human DS, we observed an overexpression of APP, elevated caspase activity, augmented cleavage of the C-terminal fragment of APP, and increased PAK1 phosphorylation. Morphometric analyses showed that inhibition of PAK1 activity with FRAX486 increased the average length of the neurites, the number of crossings per Sholl ring, the formation of new processes, and stimulated the loss of processes. Considering our results, we propose that PAK hyperphosphorylation impairs neurite outgrowth and remodeling in the cellular model of DS, and therefore we suggest that PAK1 may be a potential pharmacological target.

RCAN1 Knockdown Reverts Defects in the Number of Calcium-Induced Exocytotic Events in a Cellular Model of Down Syndrome

In humans, Down Syndrome (DS) is a condition caused by partial or full trisomy of chromosome 21. Genes present in the DS critical region can result in excess gene dosage, which at least partially can account for DS phenotype. Although regulator of calcineurin 1 (RCAN1) belongs to this region and its ectopic overexpression in neurons impairs transmitter release, synaptic plasticity, learning and memory, the relative contribution of RCAN1 in a context of DS has yet to be clarified. In the present work, we utilized an in vitro model of DS, the CTb neuronal cell line derived from the brain cortex of a trisomy 16 (Ts16) fetal mouse, which reportedly exhibits acetylcholine release impairments compared to CNh cells (a neuronal cell line established from a normal littermate). We analyzed single exocytotic events by using total internal reflection fluorescence microscopy (TIRFM) and the vesicular acetylcholine transporter fused to the pH-sensitive green fluorescent protein (VAChT-pHluorin) as a reporter. Our analyses showed that, compared with control CNh cells, the trisomic CTb cells overexpress RCAN1, and they display a reduced number of Ca²⁺-induced exocytotic events. Remarkably, RCAN1 knockdown increases the extent of exocytosis at levels comparable to those of CNh cells. These results support a critical contribution of RCAN1 to the exocytosis process in the trisomic condition.

Knockdown of Myo-Inositol Transporter SMIT1 Normalizes Cholinergic and Glutamatergic Function in an Immortalized Cell Line Established from the Cerebral Cortex of a Trisomy 16 Fetal Mouse, an Animal Model of Human Trisomy 21 (Down Syndrome)

The Na⁺/myo-inositol cotransporter (SMIT1) is overexpressed in human Down syndrome (DS) and in trisomy 16 fetal mice (Ts16), an animal model of the human condition. SMIT1 overexpression determines increased levels of intracellular myo-inositol, a precursor of phophoinositide synthesis. SMIT1 is overexpressed in CTb cells, an immortalized cell line established from the cerebral cortex of a Ts16 mouse fetus. CTb cells exhibit impaired cytosolic Ca²⁺ signals in response to glutamatergic and cholinergic stimuli (increased amplitude and delayed time-dependent kinetics in the decay post-stimulation), compared to our CNh cell line, derived from the cerebral cortex of a euploid animal. Considering the role of myo-inositol in intracellular signaling, we normalized SMIT1 expression in CTb cells using specific mRNA antisenses. Forty-eight hours post-transfection, SMIT1 levels in CTb cells reached values comparable to those of CNh cells. At this time, decay kinetics of Ca²⁺ signals induced by either glutamate, nicotine, or muscarine were accelerated in transfected CTb cells, to values similar to those of CNh cells. The amplitude of glutamate-induced cytosolic Ca²⁺ signals in CTb cells was also normalized. The results suggest that SMIT1 overexpression contributes to abnormal cholinergic and glutamatergic Ca²⁺ signals in the trisomic condition, and knockdown of DS-related genes in our Ts16-derived cell line could constitute a relevant tool to study DS-related neuronal dysfunction.

Restrained Phosphatidylcholine Synthesis in a Cellular Model of Down's Syndrome is Associated with the Overexpression of Dyrk1A

Aberrant formation of the cerebral cortex could be attributed to the lack of suitable substrates that direct the migration of neurons. Previous work carried out at our laboratory has shown that oleic acid is a neurotrophic factor. In order to characterize the effect of oleic acid in a cellular model of Down's syndrome (DS), here, we used immortalized cell lines derived from the cortex of trisomy Ts16 and euploid mice. We report that in the plasma membrane of euploid cells, an increase in phosphatidylcholine concentrations occurs in the presence of oleic acid. However, in trisomic cells, oleic acid failed to increase phosphatidylcholine incorporation into the plasma membrane. Gene expression analysis of trisomic cells revealed that the phosphatidylcholine biosynthetic pathway was deregulated. Taken together, these results suggest that the overdose of specific genes in trisomic lines delays differentiation in the presence of oleic acid. The dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1A (DYRK1A) gene is located on human chromosome 21. DYRK1A contributes to intellectual disability and the early onset of Alzheimer's disease in DS patients. Here, we explored the potential role of Dyrk1A in the reduction of phosphatidylcholine concentrations in trisomic cells in the presence of oleic acid. The downregulation of Dyrk1A by small interfering RNA (siRNA) in trisomic cells returned phosphatidylcholine concentrations up to similar levels to those of euploid cells in the presence of oleic acid. Thus, our results highlight the role of Dyrk1A in brain development through the modulation of phosphatidylcholine location, levels and synthesis.

GABAergic hyperinnervation of dentate granule cells in the Ts65Dn mouse model of down syndrome: Exploring the role of App

It has been suggested that increased GABAergic innervation in the hippocampus plays a significant role in cognitive dysfunction in Down syndrome (DS). Bolstering this notion, are studies linking hyper-innervation of the dentate gyrus (DG) by GABAergic terminals to failure in LTP induction in the Ts65Dn mouse model of DS. Here, we used extensive morphometrical methods to assess the status of GABAergic interneurons in the DG of young and old Ts65Dn mice and their 2N controls. We detected an age-dependent increase in GABAergic innervation of dentate granule cells (DGCs) in Ts65Dn mice. The primary source of GABAergic terminals to DGCs somata is basket cells (BCs). For this reason, we assessed the status of these cells and found a significant increase in the number of BCs in Ts65Dn mice compared with controls. Then we aimed to identify the gene/s whose overexpression could be linked to increased number of BCs in Ts65Dn and found that deleting the third copy of App gene in Ts65Dn mice led to normalization of the number of BCs in these mice. Our data suggest that App overexpression plays a major role in the pathophysiology of GABAergic hyperinnervation of the DG in Ts65Dn mice. © 2016 Wiley Periodicals, Inc.

Overexpressed Down Syndrome Cell Adhesion Molecule (DSCAM) Deregulates P21-Activated Kinase (PAK) Activity in an In Vitro Neuronal Model of Down Syndrome: Consequences on Cell Process Formation and Extension

In humans, Down syndrome (DS) is caused by the presence of an extra copy of autosome 21. The most striking finding in DS patients is intellectual disability and the onset of Alzheimer's disease (AD)-like neuropathology in adulthood. Gene overdose is most likely to underlie both developmental impairments, as well as altered neuronal function in DS. Lately, the disruption of cellular signaling and regulatory pathways has been implicated in DS pathophysiology, and many of such pathways may represent common targets for diverse DS-related genes, which could in turn represent attractive therapeutical targets. In this regard, one DS-related gene Down Syndrome Cell Adhesion Molecule (DSCAM), has important functions in neuronal proliferation, maturation, and synaptogenesis. p21-associated kinases (PAKs) appear as a most interesting possibility for study, as DSCAM is known to regulate the PAKs pathway. Hence, in DS, overexpressed DSCAM could deregulate PAKs activity and affect signaling pathways that regulate synaptic plasticity such as dendritic spine dynamics and axon guidance and growth. In the present work, we used an immortalized cell line derived from the cerebral cortex of an animal model of DS such as the trisomy 16 (Ts16) fetal mouse (named CTb), and a similar cell line established from a normal littermate (named CNh), to study the effect of DSCAM in the PAKs pathway. The present study shows that DSCAM is overexpressed in CTb cells by approximately twofold, compared to CNh cells. Congruently, PAK1, as well as its downstream effectors LIMK and cofilin, stay phosphorylated for longer periods after DSCAM activation in the CTb cells, leading to an altered actin dynamics, expressed as an increased basal F/G ratio and reduced neurite growth, in the trisomic condition. The present work presents the correlation between DSCAM gene overexpression and a dysregulation of the PAK pathway, resulting in altered morphological parameters of neuronal plasticity in the trisomic cell line, namely decreased number and length of processes.

Overexpression of DYRK1A inhibits choline acetyltransferase induction by oleic acid in cellular models of Down syndrome

Histological brain studies of individuals with DS have revealed an aberrant formation of the cerebral cortex. Previous work from our laboratory has shown that oleic acid acts as a neurotrophic factor and induces neuronal differentiation. In order to characterize the effects of oleic acid in a cellular model of DS, immortalized cell lines derived from the cortex of trisomy Ts16 (CTb) and normal mice (CNh) were incubated in the absence or presence of oleic acid. Oleic acid increased choline acetyltransferase expression (ChAT), a marker of cholinergic differentiation in CNh cells. However, in trisomic cells (CTb line) oleic acid failed to increase ChAT expression. These results suggest that the overdose of specific genes in trisomic lines delays differentiation in the presence of oleic acid by inhibiting acetylcholine production mediated by ChAT. The dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1A (DYRK1A) gene is located on human chromosome 21 and encodes a proline-directed protein kinase. It has been proposed that DYRK1A plays a prominent role in several biological functions, leading to mental retardation in DS patients. Here we explored the potential role of DYRK1A in the modulation of ChAT expression in trisomic cells and in the signaling pathways of oleic acid. Down-regulation of DYRK1A by siRNA in trisomic CTb cells rescued ChAT expression up to levels similar to those of normal cells in the presence of oleic acid. In agreement with these results, oleic acid was unable to increase ChAT expression in neuronal cultures of transgenic mice overexpressing DYRK1A. In summary, our results highlight the role played by DYRK1A in brain development through the control of ChAT expression. In addition, the overexpression of DYRK1A in DS models prevented the neurotrophic effect of oleic acid, a fact that may account for mental retardation in DS patients.

Role of tau protein in neuronal damage in Alzheimer's disease and Down syndrome

Neurodegenerative disorders constitute a growing concern worldwide. Their incidence has increased steadily, in particular among the elderly, a high-risk population that is becoming an important segment of society. Neurodegenerative mechanisms underlie many ailments such as Parkinson's disease, Huntington's disease, Alzheimer's disease (AD) and Down syndrome (DS, trisomy 21). Interestingly, there is increasing evidence suggesting that many such diseases share pathogenic mechanisms at the cellular and subcellular levels. These include altered protein misfolding, impaired autophagy, mitochondrial dysfunction, membrane damage, and altered axonal transport. Regarding AD and DS, the first common link comes from observations that DS patients undergo AD-like pathology early in adulthood. Also, the gene encoding for the amyloid precursor protein is present in human autosome 21 and in murine chromosome 16, an animal model of DS. Important functions related to preservation of normal neuronal architecture are impaired in both conditions. In particular, the stable assembly of microtubules, which is critical for the cytoskeleton, is impaired in AD and DS. In this process, tau protein plays a pivotal role in controlling microtubule stability. Abnormal tau expression and hyperphosphorylation are common features in both conditions, yet the mechanisms leading to these phenomena remain obscure. In the present report we review possible common mechanisms that may alter tau expression and function, in particular in relation to the effect of certain overexpressed DS-related genes, using cellular models of human DS. The latter contributes to the identification of possible therapeutic targets that could aid in the treatment of both AD and DS.

The in vivo Down syndrome genomic library in mouse

Mouse models are key elements to better understand the genotype-phenotype relationship and the physiopathology of Down syndrome (DS). Even though the mouse will never recapitulate the whole spectrum of intellectual disabilities observed in the DS, mouse models have been developed over the recent decades and have been used extensively to identify homologous genes or entire regions homologous to the human chromosome 21 (Hsa21) that are necessary or sufficient to induce DS cognitive features. In this chapter, we review the principal mouse DS models which have been selected and engineered over the years either for large genomic regions or for a few or a single gene of interest. Their analyses highlight the complexity of the genetic interactions that are involved in DS cognitive phenotypes and also strengthen the hypothesis on the multigenic nature of DS. This review also addresses future research challenges relative to the making of new models and their combination to go further in the characterization of candidates and modifier of the DS features.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

To date many aspects of neurons and glia biology remain elusive, due in part to the cellular and molecular complexity of the brain. In recent decades, cell models from different brain areas have been established and proven invaluable toward understanding this complexity. In the field of steroid hormone neurobiology, an important question is: what is the profile of steroid hormone receptor expression in these specific cell lines? Currently, a clear summary of such receptor profiling is lacking. For this reason, we summarized in this review the expression of estrogen, progesterone, and androgen receptors in several widely used cell lines (glial and neuronal) derived from the forebrain and midbrain, based on our own data and that from the literature. Such information will aid in the selection of specific cell lines used to test hypotheses related to the biology of estrogens, progestins, and/or androgens.

Altered voltage dependent calcium currents in a neuronal cell line derived from the cerebral cortex of a trisomy 16 fetal mouse, an animal model of Down syndrome

Human Down syndrome (DS) is determined by the trisomy of autosome 21 and is expressed by multiple abnormalities, being mental retardation the most striking feature. The condition results in altered electrical membrane properties (EMPs) of fetal neurons, which are qualitatively identical to those of trisomy 16 fetal mice (Ts16), an animal model of the human condition. Ts16 hippocampal cultured neurons reportedly exhibit increased voltage-dependent calcium currents (I (Ca)) amplitude. Since Ts16 animals are unviable, we have established immortalized cell lines from the cerebral cortex of Ts16 (named CTb) and normal littermates (named CNh). Using the whole-cell patch-clamp technique, we have now studied I (Ca) in CTb and CNh cells. Current activation occurs at -40 mV in both cell lines (V (holding) = -80 mV). Trisomic cells exhibited a 2.4 fold increase in the maximal Ca(2+) current density compared to normal cells (CNh = -6.3 ± 0.77 pA/pF, n = 18; CTb = -16.4 ± 2.423 pA/pF; P < 0.01, n = 13). Time dependent kinetics for activation and inactivation did not differ between the two cell types. However, steady state inactivation studies revealed a 15 mV shift toward more depolarized potentials in the trisomic condition, suggesting that altered voltage dependence of inactivation may underlie the increased current density. Further, the total charge movement across the membrane is increased in CTb cells, in agreement with that expected by the potential sensitivity shift. These results indicate that CTb cells present altered Ca(2+) currents, similar to those of Ts16 primary cultured central neurons. The CTb cell line represents a model for studying DS-related impairments of EMPs.

Increased NR2A expression and prolonged decay of NMDA-induced calcium transient in cerebellum of TgDyrk1A mice, a mouse model of Down syndrome

Transgenic mice overexpressing Dyrk1A (TgDyrk1A), a Down syndrome (DS) candidate gene, exhibit motor and cognitive alterations similar to those observed in DS individuals. To gain new insights into the molecular consequences of Dyrk1A overexpression underlying TgDyrk1A and possibly DS motor phenotypes, microarray studies were performed. Transcriptome analysis showed an upregulation of the NR2A subunit of the NMDA type of glutamate receptors in TgDyrk1A cerebellum. NR2A protein overexpression was also detected in TgDyrk1A cerebellar homogenates, in the synaptosome-enriched fraction and in TgDyrk1A primary cerebellar granular neuronal cultures (CGNs). In TgDyrk1A synaptosomes, calcium-imaging experiments showed a higher calcium uptake after NMDA stimulation. Similarly, NMDA administration promoted longer calcium transients in TgDyrk1A CGNs. Taken together, these results show that NMDA-induced calcium rise is altered in TgDyrk1A cerebellar neurons and indicate that calcium signaling is dysregulated in TgDyrk1A mice cerebella. These findings suggest that DYRK1A overexpression might contribute to the dysbalance in the excitatory transmission found in the cerebellum of DS individuals and DS mouse models.

Cell Lines as In Vitro Models for Drug Screening and Toxicity Studies

Cell culture is highly desirable, as it provides systems for ready, direct access and evaluation of tissues. The use of tissue culture is a valuable tool to study problems of clinical relevance, especially those related to diseases, screening, and studies of cell toxicity mechanisms. Ready access to the cells provides the possibility for easy studies of cellular mechanisms that may suggest new potential drug targets and, in the case of pathological-derived tissue, it has an interesting application in the evaluation of therapeutic agents that potentially may treat the dysfunction. However, special considerations must be addressed to establish stable in vitro function. In primary culture, these factors are primarily linked to greater demands of tissue to adequately survive and develop differentiated conditions in vitro. Additional requirements include the use of special substrates (collagen, laminin, extracellular matrix preparations, etc.), growth factors and soluble media supplements, some of which can be quite complex in their composition. These demands, along with difficulties in obtaining adequate tissue amounts, have prompted interest in developing immortalized cell lines which can provide unlimited tissue amounts. However, cell lines tend to exhibit problems in stability and/or viability, though they serve as a feasible alternative, especially regarding new potential applications in cell transplant therapy. In this regard, stem cells may also be a source for the generation of various cell types in vitro. This review will address aspects of cell culture system application, with focus on immortalized cell lines, in studying cell function and dysfunction with the primary aim being to identify cell targets for drug screening.

Effect of the knockdown of amyloid precursor protein on intracellular calcium increases in a neuronal cell line derived from the cerebral cortex of a trisomy 16 mouse

Murine trisomy 16 (Ts16) is a useful model to study the deleterious effect of aneuploidy in neural pathophysiology. The CTb cell line derived from the cerebral cortex of a Ts16 mouse overexpresses the amyloid precursor protein (APP) and exhibits altered intracellular Ca(2+) homeostasis. In the present work, we induced knockdown of APP by transfecting specific mRNA antisense sequences into CTb cells. Forty-eight hours after transfection, the APP expression was knocked down by 40%, reaching levels comparable to those of the cortical line CNh, derived from a normal animal. Calcium measurements showed that the APP knockdown decreased intracellular Ca(2+) basal levels and accelerated the kinetics of the decay of Ca(2+) responses induced by glutamatergic agonists, nicotine, depolarization or ionomycin, to levels similar to those previously reported for CNh cells. The present results suggest that APP overexpression plays an important role on the altered intracellular Ca(2+) homeostasis in the trisomic cells.

The cholinergic system in Down's syndrome

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain. Alterations of the transmission communicators are accompanied by reduction of the cortical activity, which is associated with a learning and memory deficit. Down's syndrome is a pathological condition characterized by a high number of abnormalities that involve the brain. The cholinergic system is involved in alterations of the neurological system such as severe learning difficulties. To explain these alterations, important results are obtained from studies about murine trisomy 16 (animal model of Down's syndrome). The results obtained provide useful elements in the improvement of knowledge about the neurological and neurotransmissional alterations that are responsible for the neurobiological characteristics of Down's syndrome. These data potentially justify, in these patients, the therapeutic use of drugs that are principally administered to improve the severe learning difficulties of people with Alzheimer's disease, and suggest a trend which generates a hypothesis worthy of further exploration.

Neuronal dysfunction in Down syndrome: contribution of neuronal models in cell culture

Down syndrome (DS) in humans, or trisomy of autosome 21, represents the hyperdiploidy that most frequently survives gestation, reaching an incidence of 1 in 700 live births. The condition is associated with multisystemic anomalies, including those affecting the central nervous system (CNS), determining a characteristic mental retardation. At a neuronal level, our group and others have shown that the condition determines marked alterations of action potential and ionic current kinetics, which may underlie abnormal processing of information by the CNS. Since the use of human tissue presents both practical and ethical problems, animal models of the human condition have been sought. Murine trisomy 16 (Ts16) is a model of the human condition, due to the great homology between human autosome 21 and murine 16. Both conditions share the same alterations of electrical membrane properties. However, the murine Ts16 condition is unviable (animals die in utero), thus limiting the quantity of tissue procurable. To overcome this obstacle, we have established immortal cell lines from normal and Ts16 mice with a method developed by our group that allows the stable in vitro immortalization of mammalian tissue, yielding cell lines which retain the characteristics of the originating cells. Cell lines derived from cerebral cortex, hippocampus, spinal cord and dorsal root ganglion of Ts16 animals show alterations of intracellular Ca2+ signals in response to several neurotransmitters (glutamate, acetylcholine, and GABA). Gene overdose most likely underlies these alterations in cell function, and the identification of the relative contribution of DS associated genes on such specific neuronal dysfunction should be investigated. This could enlighten our understanding on the contribution of these genes in DS, and identify new therapeutic targets.

Knockdown of amyloid precursor protein normalizes cholinergic function in a cell line derived from the cerebral cortex of a trisomy 16 mouse: An animal model of down syndrome

We have generated immortal neuronal cell lines from normal and trisomy 16 (Ts16) mice, a model for Down syndrome (DS). Ts16 lines overexpress DS-related genes (App, amyloid precursor protein; Sod1, Cu/Zn superoxide dismutase) and show altered cholinergic function (reduced choline uptake, ChAT expression and fractional choline release after stimulation). As previous evidence has related amyloid to cholinergic dysfunction, we reduced APP expression using specific mRNA antisense sequences in our neuronal cell line named CTb, derived from Ts16 cerebral cortex, compared to a cell line derived from a normal animal, named CNh. After transfection, Western blot studies showed APP expression knockdown in CTb cells of 36% (24 hr), 40.4% (48 hr), and 50.2% (72 hr) compared to CNh. Under these reduced APP levels, we studied 3H-choline uptake in CTb and CNh cells. CTb, as reported previously, expressed reduced choline uptake compared to CNh cells (75%, 90%, and 69% reduction at 1, 2, and 5 min incubation, respectively). At 72 hr of APP knockdown, choline uptake levels were essentially similar in both cell types. Further, fractional release of 3H-choline in response to glutamate, nicotine, and depolarization with KCl showed a progressive increase after APP knockdown, reaching values similar to those of CNh after 72 hr of transfection. The results suggest that APP overexpression in CTb cells contributes to impaired cholinergic function, and that gene knockdown in CTb cells is a relevant tool to study DS-related dysfunction.

Monoamine transporter inhibitors and norepinephrine reduce dopamine-dependent iron toxicity in cells derived from the substantia nigra

The role of dopamine in iron uptake into catecholaminergic neurons, and dopamine oxidation to aminochrome and its one-electron reduction in iron-mediated neurotoxicity, was studied in RCSN-3 cells, which express both tyrosine hydroxylase and monoamine transporters. The mean +/- SD uptake of 100 microm 59FeCl3 in RCSN-3 cells was 25 +/- 4 pmol per min per mg, which increased to 28 +/- 8 pmol per min per mg when complexed with dopamine (Fe(III)-dopamine). This uptake was inhibited by 2 microm nomifensine (43%p < 0.05), 100 microm imipramine (62%p < 0.01), 30 microm reboxetine (71%p < 0.01) and 2 mm dopamine (84%p < 0.01). The uptake of 59Fe-dopamine complex was Na+, Cl- and temperature dependent. No toxic effects in RCSN-3 cells were observed when the cells were incubated with 100 microm FeCl3 alone or complexed with dopamine. However, 100 microm Fe(III)-dopamine in the presence of 100 microm dicoumarol, an inhibitor of DT-diaphorase, induced toxicity (44% cell death; p < 0.001), which was inhibited by 2 microm nomifensine, 30 microm reboxetine and 2 mm norepinephrine. The neuroprotective action of norepinephrine can be explained by (1) its ability to form complexes with Fe3+, (2) the uptake of Fe-norepinephrine complex via the norepinephrine transporter and (3) lack of toxicity of the Fe-norepinephrine complex even when DT-diaphorase is inhibited. These results support the proposed neuroprotective role of DT-diaphorase and norepinephrine.

Novel mechanisms and approaches in the study of neurodegeneration and neuroprotection. a review

Cellular mechanisms involved in neurodegeneration and neuroprotection are continuing to be explored, and this paper focuses on some novel discoveries that give further insight into these processes. Oligodendrocytes and activated astroglia are likely generators of the pro-inflammatory cytokines, such as the tumor necrosis factor family and interleukin family, and these glial support cells express adhesion receptors (e.g., VCAM) and release intercellular adhesion molecules (ICAM) that have a major role in neuronal apoptosis. Even brief exposure to some substances, in ontogeny and sometimes in adulthood, can have lasting effects on behaviors because of their prominent toxicity (e.g., NMDA receptor antagonists) or because they sensitize receptors (e.g., dopamine D2 agonists), possibly permanently, and thereby alter behavior for the lifespan. Cell cycle genes which may be derived from microglia, are the most-recent entry into the neuroprotection schema. Neuroprotection afforded by some common substances (e.g., melatonin) and uncommon substances [e.g., nicotine, green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG), trolox], ordinarily thought to be simple radical scavengers, now are thought to invoke previously unsuspected cellular mechanisms in the process of neuroprotection. Although Alzheimer's disease (AD) has features of a continuous spectrum of neural and functional decline, in vivo PET imaging and and functional magnetic resonance imaging, indicate that AD can be staged into an early phase treatable by inhibitors of beta and gamma secretase; and a late phase which may be more amenable to treatment by drugs that prevent or reverse tau phosphorylation. Neural transplantation, thought to be the last hope for neurally injured patients (e.g., Parkinsonians), may be displaced by non-neural tissue transplants (e.g., human umbilical cord blood; Sertoli cells) which seem to provide similar neurotrophic support and improved behavior - without posing the major ethical dilemma of removing tissue from aborted fetuses. The objective of this paper is to invite added research into the newly discovered (or postulated) novel mechanisms; and to stimulate discovery of additional mechanisms attending neurodegeneration and neuroprotection.

Corticosterone down-regulates dopamine D4 receptor in a mouse cerebral cortex neuronal cell line

We have previously reported that restraint stress applied to the gestant mother results in long-lasting effects in the offspring that show an increase in the number of dopamine D2-type receptors in limbic areas on the adult rat brain cortex. Evidence that stress during pregnancy results in activation of the hypothalamic-pituitary-adrenal (HPA) axis has been extensively demonstrated. Therefore, high levels of corticosterone secreted in response to stress by the gestant mother might be one of the predisposing factors for the changes observed in dopamine receptors in the adult rat brain. In this study we addressed the question whether corticosterone would directly up-regulate D2-type receptors in vitro. We have investigated the effect of different concentrations of corticosterone on D4 dopamine receptor in immortalized cell lines from cerebral cortex of normal mouse fetuses, detected by immunocytochemistry employing polyclonal antibodies generated against synthetic peptides homologous to an extracellular domain of D4 receptor. The results show that corticosterone in vitro decreases the number of dopamine D4 receptors, suggesting that the increase of D2-type receptors in adult rats following prenatal stress is not related to a direct action of corticosterone on receptor expression.

Establishment and characterization of immortalized neuronal cell lines derived from the spinal cord of normal and trisomy 16 fetal mice, an animal model of Down syndrome

We report the establishment of continuously growing cell lines from spinal cords of normal and trisomy 16 fetal mice. We show that both cell lines, named M4b (derived from a normal animal) and MTh (trisomic) possess neurological markers by immunohistochemistry (neuron specific enolase, synaptophysin, microtubule associated protein-2 [MAP-2], and choline acetyltransferase) and lack glial traits (glial fibrillary acidic protein and S100). MTh cells were shown to overexpress mRNA of Cu/Zn superoxide dismutase, whose gene is present in autosome 16. We also studied intracellular Ca2+ signals ([Ca2+]i) induced by different agonists in Indo-1 loaded cells. Basal [Ca2+]i was significantly higher in MTh cells compared to M4b cells. Glutamate (200 microM) and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACDP) (100 microM) induced rapid, transient increases in [Ca2+]i in M4b and MTh cells, indicating the presence of glutamatergic metabotropic receptors. N-methyl-D-aspartate (NMDA) and kainate, but not alpha-amino-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), produced [Ca2+)]i rises in both cell types. MTh cells exhibited faster time-dependent decay phase kinetics in glutamate-induced responses compared to M4b cells. Nicotine induced a transient increase in [Ca2+]i in M4b and MTh cells, with significantly greater amplitudes in the latter compared to the former. Further, both cell types responded to noradrenaline. Finally, we examined cholinergic function in both cell lines and found no significant differences in the [3H]-choline uptake, but fractional acetylcholine release induced by either K+, glutamate or nicotine was significantly higher in MTh cells. These results show that M4b and MTh cells have neuronal characteristics and the MTh line shows differences which could be related to neuronal pathophysiology in Down's syndrome.

A dorsal root ganglia cell line derived from trisomy 16 fetal mice, a model for Down syndrome

We have established two immortalized cell lines from dorsal root ganglia of normal (G4b) and trisomy 16 mice (GT1), a model for Down syndrome. By immunohistochemistry, both cell lines exhibit neuronal traits and lack glial markers. GTl cells exhibited greater [3H]choline uptake than G4b cells. K+ and nicotine-mediated acetylcholine release was greater in GT1 cells. Basal intracellular Ca2+ concentration ([Ca2+]i) was significantly lower in GTl cells. More GTl cells responded to neurotransmitters with a transient [Ca2+]i increase compared to G4b cells, but both cell types showed similar amplitudes of [Ca2+]i responses. The results show that both cell lines retain neuronal characteristics and respond to specific neurotransmitter stimuli. Altered GT1 cell responses could be related to neuronal pathophysiology in Down's syndrome.

Evidence for an interferon-related inflammatory reaction in the trisomy 16 mouse brain leading to caspase-1-mediated neuronal apoptosis

The trisomy of human chromosome 21 (Down syndrome) is the leading genetic cause of learning difficulties in children, and predisposes this population to the early onset of the neurodegeneration of Alzheimer's disease. Down syndrome is associated with increased interferon (IFN) sensitivity resulting in unexpectedly high levels of IFN inducible gene products including Fas, complement factor C3, and neuronal HLA I which could result in a damaging inflammatory reaction in the brain. Consistent with this possibility, we report here that the trisomy 16 mouse fetus has significantly increased whole brain IFN-gamma and Fas receptor immunoreactivity and that cultured whole brain trisomy 16 mouse neurons have increased basal levels of caspase 1 activity and altered homeostasis of intracellular calcium and pH. The trisomic neurons also showed a heightened sensitivity to the increase in both Fas receptor levels and caspase 1 activity we observed when IFN-gamma was added to the neuron culture media. Because of the autoregulatory nature of IFN activity, and the IFN inducing capability of caspase-1-activated cytokine activity, our data argue in favor of the possibility of an interferon-mediated, self-perpetuating, inflammatory response in the trisomy brain that could subserve the loss of neuron viability seen in this trisomy 16 mouse model for Down syndrome.

Impaired cholinergic function in cell lines derived from the cerebral cortex of normal and trisomy 16 mice

Murine trisomy 16 is an animal model of human Down's syndrome. We have successfully established permanently growing cell lines from the cerebral cortex of normal and trisomy 16 foetal mice using an original procedure. These lines, named CNh (derived from a normal animal) and CTb (derived from a trisomic foetus), express neuronal markers. Considering that Down's syndrome exhibits cholinergic deficits, we examined cholinergic function in these lines, using incorporation of [3H]-choline and fractional release studies. After 1, 3 and 5 min of [3H]-choline incubation, CTb cell uptake was lower by approximately 50% compared to controls. Hemicholinium-3 significantly reduced the incorporation of [3H]-choline in both CNh and CTb cells at high concentration (10 microM), suggesting high-affinity choline transport. However, CTb cells exhibited greater sensitivity to the blocker. For fractional release experiments, the cells were stimulated by K+ depolarization, glutamate or nicotine. When depolarized, CTb cells showed a 68% reduction in fractional release of [3H]-acetylcholine compared to CNh cell line, and a 45% reduction when stimulated by nicotine. Interestingly, glutamate induced similar levels of release in both cell types. The results indicate the existence of cholinergic dysfunction in CTb cells when compared to CNh, similar to that reported for primary cultures of trisomy 16 brain tissue (Fiedler et al. 1994, Brain Res., 658, 27-32). Thus, the CTb cell line may serve as a model for the study of Down's syndrome pathophysiology.