MOBP and HIP1 in multiple system atrophy: New α-synuclein partners in glial cytoplasmic inclusions implicated in the disease pathogenesis

AIMS

Multiple system atrophy (MSA) is a fatal neurodegenerative disease. Similar to Parkinson's disease (PD), MSA is an α-synucleinopathy, and its pathological hallmark consists of glial cytoplasmic inclusions (GCIs) containing α-synuclein (SNCA) in oligodendrocytes. We previously identified consistent changes in myelin-associated oligodendrocyte basic protein (MOBP) and huntingtin interacting protein 1 (HIP1) DNA methylation status in MSA. We hypothesized that if differential DNA methylation at these loci is mechanistically relevant for MSA, it should have downstream consequences on gene regulation.

METHODS

We investigated the relationship between MOBP and HIP1 DNA methylation and mRNA levels in cerebellar white matter from MSA and healthy controls. Additionally, we analysed protein expression using western blotting, immunohistochemistry and proximity ligation assays.

RESULTS

We found decreased MOBP mRNA levels significantly correlated with increased DNA methylation in MSA. For HIP1, we found a distinct relationship between DNA methylation and gene expression levels in MSA compared to healthy controls, suggesting this locus may be subjected to epigenetic remodelling in MSA. Although soluble protein levels for MOBP and HIP1 in cerebellar white matter were not significantly different between MSA cases and controls, we found striking differences between MSA and other neurodegenerative diseases, including PD and Huntington's disease. We also found that MOBP and HIP1 are mislocalized into the GCIs in MSA, where they appear to interact with SNCA.

CONCLUSIONS

This study supports a role for DNA methylation in downregulation of MOBP mRNA in MSA. Most importantly, the identification of MOBP and HIP1 as new constituents of GCIs emphasizes the relevance of these two loci to the pathogenesis of MSA.

Alterations in global DNA methylation and hydroxymethylation are not detected in Alzheimer's disease

AIMS

Genetic factors do not seem to account fully for Alzheimer disease (AD) pathogenesis. There is evidence for the contribution of environmental factors, whose effect may be mediated by epigenetic mechanisms. Epigenetics involves the regulation of gene expression independently of DNA sequence and these epigenetic changes are influenced by age and environmental factors, with DNA methylation being one of the best characterized epigenetic mechanisms. The human genome is predominantly methylated on CpG motifs, which results in gene silencing; however methylation within the body of the gene may mark active transcription. There is evidence suggesting an involvement of environmental factors in the pathogenesis of Alzheimer's disease (AD), which prompted our study examining DNA methylation in this disorder.

METHODS

Using immunohistochemistry with 5-methylcytosine/5-hydroxymethylcytosine antibodies we studied, in comparison with age matched controls, DNA methylation in sporadic and familial AD cases in the entorhinal cortex that exhibits substantial pathology and the cerebellum, which is relatively spared.

RESULTS

Neuronal nuclear labelling with 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) was evident in all cases studied. We did not detect any significant change in the levels of nuclear staining in the AD samples compared to neurologically normal controls. In the entorhinal cortex we also examined global DNA methylation and hydroxymethylation using an enzyme-linked immunosorbent assay (ELISA).

CONCLUSION

No significant differences were found between AD and control cases in global levels of 5mC and 5hmC in the entorhinal cortex using immunohistochemistry and enzyme-linked immunosorbent assays.

Epigenetic mechanisms in Alzheimer's disease

The worldwide increase in life expectancy is leading to an increase in age-dependent diseases, including nonfamilial, sporadic Alzheimer’s disease (AD), which is the subject of this review. The etiology and pathophysiology of the disease is not fully understood, but present observations suggest that, in addition to genetic risk factors, environmental influences may be involved via epigenetic mechanisms. Currently, there is no effective treatment, but there are indications that lifestyle has an impact on the development of the disease. This view is supported by preclinical studies not only showing that human lifestyle-equivalent interventions have a positive effect on cognitive function in animal models of AD, but also indicating the involvement of underlying epigenetic mechanisms. After a brief overview of the most characteristic chromatin modifications, ie, DNA methylation and histone modifications, epigenetic changes associated with aging are considered, given that aging is the most important risk factor for AD. This is followed by a description of some epigenetic alterations recognized in AD. The impact of environmental factors and lifestyle on the epigenome is then considered. Epigenetic treatments with HDAC inhibitors and RNA-based drugs are considered, which – while still in preclinical stages – are promising for potential benefit. It is concluded that while awaiting results from clinical trials in progress, focusing on lifestyle adjustments with an epigenetic background are the best way to prevent/delay the onset of this devastating disease.

Epigenetic mechanisms in Alzheimer's disease: progress but much to do

The interesting review from Mastroeni and colleagues highlights recent progress on epigenetic analysis of Alzheimer's disease, but it also illustrates how much we still need to do.

Interleukin-1beta interferes with signal transduction induced by neurotrophin-3 in cortical neurons

It was previously observed that IL-1beta interferes with BDNF-induced TrkB-mediated signal transduction and protection of cortical neurons from apoptosis evoked by deprivation from trophic support [Tong L., Balazs R., Soiampornkul R., Thangnipon W., Cotman C.W., 2007. Interleukin-1beta impairs brain derived neurotrophic factor-induced signal transduction. Neurobiol. Aging]. Here we investigated whether the effect of the cytokine on neurotrophin signaling is more general. The influence of IL-1beta on NT-3 signaling was therefore studied under conditions when NT-3 primarily activated the TrkC receptor. The cytokine reduced NT-3-induced activation of MAPK/ERK and Akt, but did not interfere with Trk receptor autophosphorylation. IL-1beta reduced tyrosine phosphorylation of the docking proteins, IRS-1 and Shc, which convey receptor activation to the downstream protein kinase cascades. These are the steps that are also inhibited by IL-1beta in BDNF-induced signal transduction. The functional consequences of the effect of IL-1beta on NT-3 signaling were severe, as NT-3 protection of the trophic support-deprived cortical neurons was abrogated. In view of the role in the maintenance and plasticity of neurons of ERK, Akt and CREB, which are activated by neurotrophins, elevated IL-1beta levels in the brain in Alzheimer's disease and other neurodegenerative diseases might contribute to the decline in cognitive functions before the pathological signs of the disease develop.

Interleukin-1 beta impairs brain derived neurotrophic factor-induced signal transduction

The expression of IL-1 is elevated in the CNS in diverse neurodegenerative disorders, including Alzheimer's disease. The hypothesis was tested that IL-1 beta renders neurons vulnerable to degeneration by interfering with BDNF-induced neuroprotection. In trophic support-deprived neurons, IL-1 beta compromised the PI3-K/Akt pathway-mediated protection by BDNF and suppressed Akt activation. The effect was specific as in addition to Akt, the activation of MAPK/ERK, but not PLC gamma, was decreased. Activation of CREB, a target of these signaling pathways, was severely depressed by IL-1 beta. As the cytokine did not influence TrkB receptor and PLC gamma activation, IL-1 beta might have interfered with BDNF signaling at the docking step conveying activation to the PI3-K/Akt and Ras/MAPK pathways. Indeed, IL-1 beta suppressed the activation of the respective scaffolding proteins IRS-1 and Shc; this effect might involve ceramide generation. IL-1-induced interference with BDNF neuroprotection and signal transduction was corrected, in part, by ceramide production inhibitors and mimicked by the cell-permeable C2-ceramide. These results suggest that IL-1 beta places neurons at risk by interfering with BDNF signaling involving a ceramide-associated mechanism.

Trophic effect of glutamate

During development, Glu receptors and N-methyl-D-aspartate receptors in particular initiate a cascade of signal transduction events and gene expression changes primarily involving Ca(2+) ion-mediated signaling induced by activation of either Ca(2+) ion-permeable receptor channels or voltage-sensitive Ca(2+) ion channels. The consecutive activation of major protein kinase signaling pathways, such as Ras-MAPK/ERK and PI3-K-Akt, contributes to regulation of gene expression through the activation of key transcription factors, such as CREB, SRF, MEF-2, NF-kappaB. Metabotropic Glu receptors can also engage these signaling pathways and this may be mediated, in part, by transactivating receptor tyrosine kinases. Indirect effects of Glu receptor stimulation are due to the production and release of neurotrophic factors, such as brain derived neurotrophic factor and also involve glia-neuronal interaction through Glu-induced release of trophic factors from glia. The trophic effect of Glu receptor activation is developmental stage-dependent and may play an important role in determining the selective survival of neurons that made proper connections. During this sensitive developmental period interference with Glu receptor function may lead to widespread neuronal loss. However, NMDA receptor blockade-induced neurodegeneration can also occur in the adult brain. Depending on the stimulus strength, Glu receptors mediate biphasic effects. In addition to synaptic transmission, physiological stimulation of Glu receptors can mediate trophic effects and promote neuronal plasticity. Excessive stimulation is neurotoxic. Attention must, therefore, be paid to these features, when therapeutic manipulation of excitatory amino acid receptors is considered in the clinical setting.

Beta-amyloid peptide at sublethal concentrations downregulates brain-derived neurotrophic factor functions in cultured cortical neurons

The accumulation of beta-amyloid (Abeta) is one of the etiological factors in Alzheimer's disease (AD). It has been assumed that the underlying mechanism involves a critical role of Abeta-induced neurodegeneration. However, low levels of Abeta, such as will accumulate during the course of the disease, may interfere with neuronal function via mechanisms other than those involving neurodegeneration. We have been testing, therefore, the hypothesis that Abeta at levels insufficient to cause degeneration (sublethal) may interfere with critical signal transduction processes. In cultured cortical neurons Abeta at sublethal concentrations interferes with the brain-derived neurotrophic factor (BDNF)-induced activation of the Ras-mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) and phosphatidylinositol 3-kinase (PI3-K)/Akt pathways. The effect of sublethal Abeta(1-42) on BDNF signaling results in the suppression of the activation of critical transcription factor cAMP response element-binding protein and Elk-1 and cAMP response element-mediated and serum response element-mediated transcription. The site of interference with the Ras/ERK and PI3-K/Akt signaling is downstream of the TrkB receptor and involves docking proteins insulin receptor substrate-1 and Shc, which convey receptor activation to the downstream effectors. The functional consequences of Abeta interference with signaling are robust, causing increased vulnerability of neurons, abrogating BDNF protection against DNA damage- and trophic deprivation-induced apoptosis. These new findings suggest that Abeta engenders a dysfunctional encoding state in neurons and may initiate and/or contribute to cognitive deficit at an early stage of AD before or along with neuronal degeneration.

Physical activity elicits sustained activation of the cyclic AMP response element-binding protein and mitogen-activated protein kinase in the rat hippocampus

To elucidate molecular mechanisms involved in physical activity-induced beneficial effects on brain function, we studied in rats the influence of voluntary running on the activation in the hippocampus of cyclic AMP response element-binding protein (CREB) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK). These are signaling molecules that play critical roles in synaptic plasticity, including learning and memory. Exercise resulted in an increase in the level of the activated transcription factor, CREB phosphorylated at Ser-133. The amount of the activated transcription factor about doubled already after 1 night of running and remained elevated for at least a week, although control levels were restored after 1 month of exercise. In addition, binding activity in nuclear extracts to cyclic AMP response element (CRE) motif containing oligonucleotides increased significantly in the hippocampus after 3 nights of exercise, although the total amount of the immunochemically identified CREB remained unaltered. Electrophoretic mobility supershift assays indicated that the increased binding was due to the recruitment of members of this transcription factor family, in addition to the CREB proper. Voluntary running also resulted in an increase in the level of phosphorylated MAPK (both p42 and p44). The time-courses of the increases in the level of the phosphorylated protein kinase and the activated transcription factor were different. In comparison with the activated CREB, the increase in the phosphorylated MAPK was delayed, but lasted longer, being detectable even after 1 month of exercise. These observations are consistent with the view that the relatively long-lasting activation of these signaling molecules participates in the regulation of genes, such as the neurotrophin genes, and contributes to the beneficial effects of physical exercise on brain function.

Effects of exercise on gene-expression profile in the rat hippocampus

Exercise has beneficial effects on brain function, including the promotion of plasticity and the enhancement of learning and memory performance. Previously we found that exercise increases the expression of certain neurotrophic factors including brain derived neurotrophic factor in the rat hippocampus. To further explore the molecular mechanisms underlying these changes, we used high-density oligonucleotide microarrays containing probe sets representing approximately 5000 genes to analyze the level of gene transcripts in the hippocampus of rats voluntary running for 3 weeks in comparison with sedentary animals. An improved statistical approach for the analysis of DNA microarray data, Cyber-T, was utilized in data analysis. Here we show that exercise leads to changes in the level of a large number of gene transcripts, many of which are known to be associated with neuronal activity, synaptic structure, and neuronal plasticity. Our data indicate that exercise elicits a differential gene expression pattern with significant changes in genes of relevance for brain function.

Beta -amyloid-(1-42) impairs activity-dependent cAMP-response element-binding protein signaling in neurons at concentrations in which cell survival Is not compromised

Cognitive impairment is a major feature of Alzheimer's disease and is accompanied by beta-amyloid (Abeta) deposition. Transgenic animal models that overexpress Abeta exhibit learning and memory impairments, but neuronal degeneration is not a consistent characteristic. We report that levels of Abeta-(1-42), which do not compromise the survival of cortical neurons, may indeed interfere with functions critical for neuronal plasticity. Pretreatment with Abeta-(1-42), at sublethal concentrations, resulted in a suppression of cAMP-response element-binding protein (CREB) phosphorylation, induced by exposure to either 30 mm KCl or 10 microm N-methyl-d-aspartate. The effects of Abeta-(1-42) seem to involve mechanisms unrelated to degenerative changes, since Abeta-(25-35), a toxic fragment of Abeta, at sublethal concentrations did not interfere with activity-dependent CREB phosphorylation. Furthermore, caspase inhibitors failed to counteract the Abeta-(1-42)-evoked suppression of CREB activation. Abeta-(1-42) also interfered with events downstream of activated CREB. The Abeta-(1-42) treatment suppressed the activation of the cAMP response element-containing brain-derived neurotrophic factor (BDNF) exon III promoter and the expression of BDNF exon IIII mRNA induced by neuronal depolarization. In view of the critical role of CREB and BDNF in neuronal plasticity, including learning and memory, the observations indicate a novel pathway through which Abeta may interfere with neuronal functions and contribute to cognitive deficit in Alzheimer's disease before the stage of massive neuronal degeneration.

Differential effects of learning and recall of a spatial task on phosphoinositide hydrolysis induced by the metabotropic glutamate receptor agonist 1S,3R-ACPD (1S,3R-1-amino-cyclopentane-1,3-discarboxylic acid) in the hippocampus and the prefrontal cortex of rats

Phosphoinositide (PI) hydrolysis, stimulated by 1S,3R-1-amino-cyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), an agonist of metabotropic glutamate receptors (mGluRs), was measured in hippocampal and prefrontal cortical slices obtained from rats which had been trained for 8 days in a Morris water maze and had learned an allocentric spatial task. Brain slices were pre-labeled with myo-3H-inositol and 1S,3R-ACPD (100 microM) stimulation was assessed by measuring the accumulation of [3H]inositol phosphates ([3H]IPs) in the presence of Li+. Measurements conducted 24 h following the last training session revealed no differences in 1S,3R-ACPD-stimulated formation of [3H]IPs, either in the hippocampus or in the prefrontal cortex. However, a diminished response to mGluRs stimulation was detected in the hippocampus of animals re-trained after an 11-day interval. The decrease was not evident in the prefrontal cortex. These data indicate a differential involvement of the hippocampus and the prefrontal cortex in the processing of spatial information and correspond to the functional differences attributed to these areas.

Somatostatin receptors are expressed by immature cerebellar granule cells: evidence for a direct inhibitory effect of somatostatin on neuroblast activity

Somatostatin and somatostatin receptors are transiently expressed in the immature rat cerebellar cortex but virtually undetectable in the cerebellum of adults. Although somatostatin binding sites have been visualized during the postnatal period in the external granule cell layer, the type of cell that expresses somatostatin receptors has never been identified; thus, the potential function of somatostatin in the developing cerebellum remains unknown. In the present study, we have taken advantage of the possibility of obtaining a culture preparation that is greatly enriched in immature cerebellar granule cells to investigate the presence of somatostatin receptors and the effect of somatostatin on intracellular messengers on cerebellar neuroblasts in primary culture. Autoradiographic labeling revealed the occurrence of a high density of binding sites for radioiodinated Tyr-[D-Trp8]somatostatin-(1-14) on 1-day-old cultured immature granule cells. Saturation and competition studies showed the existence of a single class of high-affinity binding sites (Kd = 0.133 +/- 0.013 nM, Bmax = 3038 +/- 217 sites per cell). Somatostatin induced a dose-dependent inhibition of forskolin-evoked cAMP formation (ED50 = 10 nM), and this effect was prevented by preincubation of cultured immature granule cells with pertussis toxin. Somatostatin also caused a marked reduction of intracellular calcium concentration. These results show the presence of functionally active somatostatin receptors on immature granule cells. Our data suggest the possible involvement of somatostatin in the regulation of proliferation and/or migration of neuroblasts during the development of the cerebellar cortex.

Stimulus-coupled release of amino acids from cerebellar granule cells in culture

Cerebellar cultures greatly enriched in excitatory granule neurons were depolarized by exposure to either elevated K+ or veratrine. Stimulation of the release of not only Glu, but also of certain amino acids, including Gly, Ala and Ser, was observed. The effect was specific, as depolarization did not induce the release of all the estimated amino acids or of lactate dehydrogenase. In comparison with the characteristics of the evoked release of Glu, those of the responsive neutral amino acids were similar in terms of Ca2+-dependence, but differences were also noted. Thus, upon stimulation, the relative rise was smaller than for Glu and the degree of depolarization causing maximal release was lower. The questions of whether stimulus-coupled release of the non-transmitter amino acids from granule cells may play a neuromodulatory role in the cerebellum is discussed.

Effect of calcium agonists and antagonists on cerebellar granule cells

In cerebellar cultures, comprising predominantly granule neurones, dihydropyridine (DHP) Ca2+ agonists were potent stimulators of voltage-sensitive 45Ca2+ uptake. Their effect was maximal in partially depolarized cells; at 15 mM K+e half maximal stimulation occurred at about 5 X 10(-8) M BAY K 8644 and 10(-7) M (+)-(S)-202791. Organic Ca2+ antagonists were effective inhibitors of voltage-sensitive calcium entry into granule cells: the order of potency in blocking uptake induced by sub-maximal concentration of K+ and BAY K 8644 was nifedipine greater than (-)-202791 greater than D600. BAY K 8644 also stimulated the release of glutamate, the transmitter of the granule cells, from depolarized cells. Granule cells are therefore a class of neurones whose responsiveness to organic Ca2+ effectors is similar to that of cardiac and smooth muscle. The discrepant findings on the effect of calcium effectors in various preparations of nervous tissues may thus reflect a differential distribution of voltage-sensitive Ca2+ channels in different neuronal cell types.

The effect of a neuron-specific antiserum, BPM, on the in vitro development of cerebellar granule cells

Anti-BPM is a neuron-specific antiserum which specifically recognizes the D2 cell adhesion molecule in crossed immunoelectrophoresis of Triton X-100-solubilized brain extracts. Here the effect of this antiserum on the in vitro development of cerebellar neuronal cultures is described. The initial adhesion of cells and neurite outgrowth were not influenced by immunoglobulin fractions of anti-BPM. However, after 5 days in vitro the cultures had become completely disorganized, with the majority of cells being dead at immunoglobulin concentrations greater than 0.5 mg/ml culture medium. This effect was seen only with immunoglobulins and their F(ab')2 fragments, the F(ab') fragments being without effect. The addition of anti-BPM to 8-day-old cultures resulted in a more rapid and pronounced rate of cell death. In many instances this was preceded by a rapid "destabilization" of culture organization. The cytotoxic effect of anti-BPM was neuron specific and the small numbers of astrocytes and fibroblasts found in the cultures were unaffected by prolonged exposure to this serum.

The effects of thyroid hormone on differentiation and neurofilament expression in rat brain aggregating cultures

The effects of thyroid hormone on neural development in vitro were studied using rat fetal forebrain aggregating cultures. They were examined morphologically after growth for 21 days in medium containing fetal calf serum (S+), in a chemically defined medium (S-), or in serum-free medium containing 30 nM triiodothyronine (T3). Aggregates grown in S+ showed certain morphological differences compared to those grown in the absence of serum: a glia limitans was present in the former, but not the latter, which were further characterized by a marginal zone rich in fibres and containing few cells. Immunocytochemistry using a monoclonal antibody against neurofilaments showed that immunostaining was most pronounced in aggregates grown in T3 (especially in the marginal zone) and weakest in those grown in S+. Quantitative estimation using an immunoadsorbent assay confirmed that T3 medium increased the amount of neurofilament protein in the aggregates, consistent with the view that thyroid hormone promotes neural development in vitro.

Immunohistochemical analysis of the early ontogeny of the neuropeptide Y system in rat brain

The distribution of neuropeptide Y in the developing rat brain was studied with immunocytochemistry, using the peroxidase-antiperoxidase method. Immunoreactive perikarya were first seen on embryonic day 13 and staining of fibres appeared from embryonic day 15 onwards: perikaryal staining was generally more intense prenatally than after birth. Areas rich in neuropeptide Y immunostaining included the monoaminergic regions of the brain stem from embryonic day 13 (especially the lateral reticular nucleus and the medullary reticular formation), the dorsal mesencephalon (with spots of immunoreactivity in the outer subventricular zone at embryonic days 13 or 14 and many cells and fibres in the inferior colliculus from embryonic days 16-20) and the olfactory tubercle/ventral striatum from embryonic day 15 until birth. The period of development of cortical neurones extended from embryonic day 19 until postnatal day 21. A hitherto unreported feature unique to neuropeptide Y was the presence in certain parts of the cerebral cortex of transient cells at the base of the cortical plate bearing radial processes which transverse its width. They were present from embryonic day 17 until postnatal day 4 and were maximally developed at embryonic days 20 or 21, contributing at this age a substantial fibre projection through the immature corpus callosum. The abundance of neuropeptide Y in the prenatal rat brain suggests it may play an important role in development.

Altered composition of polyunsaturated fatty acyl groups in phosphoglycerides of Down's syndrome fetal brain

We have observed recently that in vitro lipoperoxidation is enhanced in Down's syndrome brain homogenates of prenatal age. As this may relate to the composition of polyunsaturated acyl groups (PUFA) in phospholipids, we have examined the PUFA of ethanolamine and serine phosphoglycerides (EPG and SPG), which are particularly rich in PUFA, in the same series of cerebral cortex specimens of Down's syndrome and age-matched control fetuses. Although the total percentages of PUFA in the two phosphoglycerides were not altered, compared with controls the ratio of PUFA of the (n-3) series to those of the (n-6) series was very significantly elevated in Down's syndrome, from 0.32 to 0.55 in EPG and from 0.60 to 0.97 in SPG. In particular, docosahexaenoyl, 22:6(n-3), groups were uniformly increased in Down's syndrome compared with controls by 54% and 33% in EPG and SPG, respectively, while arachidonoyl, 20:4(n-6), groups were decreased by 16% and 30%, respectively. Similar changes occur during normal development, but the (n-3) to (n-6) ratio of PUFA in these phosphoglycerides of Down's syndrome at the fifth month of gestation resembled that of normal human cerebral grey matter at term. However, other developmental indices related to PUFA composition were not significantly affected. It seems therefore that in the developing Down's syndrome brain there may be a distortion of the normal transformations of essential fatty acids and of their incorporation into phosphoglycerides. The disproportion between docosahexaenoyl and arachidonoyl groups in membrane phosphoglycerides during prenatal development in Down's syndrome may also result in disturbances of the proper functioning, and the ontogenetic integration, of membrane enzymes and transport processes.

Survival, morphology and adhesion properties of cerebellar interneurones cultured in chemically defined and serum-supplemented medium

Cultures obtained from early postnatal rat cerebellum, grown in either chemically defined or in serum-supplemented medium containing 25 mM K+, contained predominantly (greater than 90%) small interneurones, mostly granule cells, with good and comparable viability (assessed by the retention of preloaded 51Cr). Neuronal survival was prolonged in the chemically defined medium, nerve cells living up to two weeks longer than in serum-supplemented medium, although the proportion of non-neuronal cells was not greatly increased. In the serum-supplemented medium neurones became organised into clumps connected by thick, fasciculated bundles of neurites by about one week in vitro. In comparison, in the chemically defined medium aggregation of neurones and fasciculation of neurites was markedly reduced even after 4 weeks in culture. The possible relationship between the organisation of neurones and the nature of the substratum, chemical factors in the medium as well as the surface properties of the cells is discussed.

Effect of thyroid hormone and serum on the development of Na+, K+-adenosine triphosphatase and associated ion fluxes in cultures from rat brain

The effect of culture conditions, serum supplementation or chemically defined medium and the influence of thyroid hormone were studied on the development of the Na+, K+-adenosine triphosphatase (Na+,K+-ATPase) and on the intracellular content of K+ and Na+ ions in cultures which either were greatly enriched in a neuronal cell type, the cerebellar granule cells, or contained a mixed population of cells (brain reaggregates). Foetal rat brain reaggregates displayed lower Na+,K+-ATPase activity when cultured in chemically defined medium than in the presence of serum. Supplementation of the serum-free medium with thyroid hormone resulted in a rise in the Na+,K+-ATPase activity and [3H]ouabain binding to levels similar to those found in the cultures grown in the serum-containing medium. Thyroid hormone had no significant effect on the Mg2+-ATPase activity and on the intracellular content of Na+ and K+ ions. In the granule cell-enriched cerebellar surface cultures the Na+,K+-ATPase activity was lower when the cells were grown in chemically defined medium compared with the serum-containing medium, and the intracellular Na+ to K+ ratio was higher. Thyroid hormone had no effect on the Na+,K+-ATPase activity, [3H]ouabain binding or Mg2+-ATPase activity. The hormone also failed to influence ATPase activities in cerebellar astrocytes maintained in chemically defined medium. Although thyroid hormone had no effect on the Na+,K+-ATPase activity of cultured cerebellar granule cells, treatment with the hormone resulted in a decrease in the ratio of intracellular Na+ to K+ ion content. The effect of the hormone on the Na+,K+-pump activity in live cells was therefore tested by estimating ouabain-sensitive 86Rb uptake. This was regulated as in other cell types, by the rate of Na+ entry: the Na+-ionophore monensin trebled the rate of 86Rb uptake, which was also increased (+30-100%) by 10% foetal calf serum, the maximal response being obtained by about 20 min exposure to serum. The effect was completely blocked by the Na+/H+ exchange inhibitor amiloride. The factor(s) in the serum responsible for the regulation of the Na+,K+-pump were, however, not the thyroid hormones, which failed to affect 86Rb uptake. On the basis of comparing thyroid hormone effects on the different cultures studied it was concluded that not every type of neural cell is target of the hormone action during development.

Cell surface proteins of cerebellar interneurones and astrocytes cultured in chemically defined and serum-supplemented media

Lactoperoxidase catalysed 125I-iodination of cerebellar interneurone enriched cultures grown in serum-supplemented or in serum-free, chemically defined medium was studied. It was observed that the differences in the adhesion properties of nerve cells under these conditions are accompanied by differences both in the degree of 125I-iodination of the proteins on the plasma membrane of nerve cells and in the profile of the labelled polypeptides resolved by SDS-polyacrylamide gel electrophoresis. The relative labelling of the major 125I-iodinated polypeptides changed with time in both types of cultures, suggesting that alterations in the overall organisation of the neuronal plasma membrane occur during the development of the cells under both culture conditions. The developmental changes affecting the D2 protein (which is nerve cell specific in these cultures) were significantly retarded in the neuronal cultures grown in the serum-free medium compared with those grown in the serum-containing medium: the increase in D2 content was reduced by 7 DIV and the maturational change in the molecular form of D2 was retarded significantly during the whole cultivation period. The degree of surface 125I-iodination of cerebellar astrocytes in culture was only a fraction (7-20% depending on cultivation time and conditions) of that of the neuronal cultures and the labelled polypeptide profiles obtained from the two types of cultures were markedly different. In comparison with cultures in the serum-supplemented medium, astrocytes under the serum-free conditions showed only minor and transient differences in the profile of surface 125I-iodinated proteins, although the morphology of the cells was markedly different.

Changes in the expression of a neuronal surface protein during development of cerebellar neurones in vivo and in culture

The expression of the neurone-specific D2 protein changes both quantitatively and qualitatively during development in vivo and in cultures of cerebellar nerve cells. The total D2 content per unit protein shows a two-fold increase in vivo from birth to postnatal day 6, after which it declines progressively to about 50% of the maximal value. This increase can be accounted for by an immature form of the protein anodic D2 being preferentially expressed at the early stages of cerebellar development. After postnatal day 9 this form gradually switches to a mature form cathodic D2. This switch can be mimicked by neuraminidase treatment, suggesting a developmental loss of sialic acid from the D2 protein. In freshly isolated cells the total D2 content per unit protein is only 30% of that in the corresponding intact tissue from 8-day-old cerebella, but it increases rapidly during the first 8 days of culture to levels similar to those of the equivalent age in vivo. The switch from anodic D2 to cathodic D2 also occurs at a faster rate in culture, probably reflecting the culture conditions that favour differentiation. The changes in the expression of D2 during development of cerebellar nerve cells in culture suggest that anodic D2 is preferentially expressed on nerve cells that are proliferating, migrating, or in the initial stages of differentiation, whereas cathodic D2 is associated with differentiated neurones. The transition between the two forms appears to occur during the formation of interneuronal contacts.

Superoxide dismutase, glutathione peroxidase and lipoperoxidation in Down's syndrome fetal brain

Certain aspects of the metabolism of oxygen derivatives were investigated in the cerebral cortex from Down's syndrome (trisomy 21) fetuses. In comparison with controls of similar gestational age, the specific activity of the cytosolic Cu/Zn-dependent superoxide dismutase (SOD-I) was significantly elevated by 60 +/- 5%. This is consistent with a gene dosage effect, as the gene coding for SOD-I is on chromosome 21. In order to determine whether the increase in SOD-I activity is associated with an adaptive rise in glutathione peroxidase (GSHPx), as has been observed in other tissues, the activity of this enzyme was also estimated but was found not to be altered in the Down's syndrome brain. In addition, in vitro lipoperoxidation, estimated by the formation of malondialdehyde (MDA) on incubation of homogenates fortified with ascorbate and Fe2+, was significantly elevated (36 +/- 4%) in cerebral cortex of the Down's syndrome fetuses. The concentration of total combined polyunsaturated fatty acids (PUFA) was not significantly altered in the tissue, although there is evidence for differences in the composition of certain phospholipids. It is proposed that, on account of the evidence for a potential perturbation of oxygen free radical metabolism (notably an increased SOD-I activity not compensated by a rise in GSHPx) and for enhanced in vitro peroxidizability of PUFA, there may be increased lipoperoxidative damage in the Down's syndrome brain prenatally.

Observations on rat cerebellar cells in vitro: influence of substratum, potassium concentration and relationship between neurones and astrocytes

We present data on the effect of elevated concentrations of K+ ions (25 mM) and polylysine (PLL) coating of the substratum on the in vitro survival and behaviour of cells derived from 8-day-old rat cerebellum. The cells were grown in Eagle's basal medium in the presence of 10% foetal calf serum and cytosine arabinoside (10 microM), as a mitotic inhibitor. The most conspicuous effect of the high potassium was to facilitate the relatively long survival of the nerve cells, whereas PLL influenced the nerve cell attachment and thereby the size of the aggregates formed in the cultures. When cells were grown in high [K+] on PLL-coated dishes (standard conditions) over 70% of the plated cells survived beyond 7 DIV, and about 95% of the cells were small interneurones, tentatively identified as predominantly granule cells. The most numerous non-neuronal cells were glial fibrillary acid protein (GFA) positive astrocytes. The beneficial effect of high potassium on nerve cell survival was most prominent after 7 DIV, when it is known that transmission-associated neurochemical functions are just becoming detectable under the standard conditions. Initially (at 3 DIV) under all the tested conditions, and throughout the experimental period under the standard conditions, the dominant type of GFA-positive cells was the process bearing 'differentiated' astrocyte. When the conditions resulted in a great decrease in nerve cell numbers, on the other hand, flat astroblast-like cells became the most abundant cells in this class. Neurones grown on polylysine in the presence of 25 mM potassium extended neurites as early as 6 h after plating, and with longer culture times, an extensive network of fibres of neuronal origin was generated. Neurites did not seem to follow the processes of GFA-positive astrocytes in the cultures. Although there was a limited tendency for neuronal cell bodies to be positioned around astrocytes at 1 DIV, this became less marked with time, and no preferential association between astrocytes and neurones could be detected in the cultures later than 2 DIV.

Do drugs acting on the nervous system affect cell proliferation in the developing brain

Drugs which alter the balance of neurotransmitter activity may, while failing to cause gross structural malformations of the brain, produce long-lasting functional disturbances if given when the brain is developing. Subtle anatomical changes may underlie such disturbances; reserpine has been shown to interfere with cell proliferation in the brain of suckling rats, and long-term alterations in behaviour reported after treatment with reserpine may be related to this effect of the drug. Neurotransmitters, apart from their conventional role, may also function as neurohumours and be involved in the regulation of cell proliferation in the nervous system. Thus drugs influencing central neurotransmitter activity, such as phenothiazines and adrenergic agonists and antagonists, which in clinical practice are often given to pregnant mothers, may affect the developing brain through mechanisms similar to those reported for reserpine. More experimental information is needed about the influence of such drugs on cell proliferation in the brain, and about their "behavioural teratogenicity".