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S.4.01 Molecular targets identification
S77
Schizophrenia: towards new drug targets
Lectures S.4.01 Molecular targets identification J. Harro1 ° . 1 University of Tartu, Department of Psychology Estonian Centre of Behavioural and Health Sciences, Tartu, Estonia Drugs for schizophrenia are effective in about 50% of patients, so there is an obvious need for novel treatment options. Recent advances in brain imaging have assisted in providing insight into cerebral networks responsible for the positive, negative and cognitive symptom clusters in schizophrenia. In terms of identification of novel drug treatments, these approaches as well as post mortem studies guide our thinking to schizophrenia being a disorder of synaptic connectivity, and suggest looking into every aspect of establishment of neural connections and their maintenance. An alternative, hypothesisfree approach is capitalizing on the strong genetic background of schizophrenia and the high-throughput genomic screening techniques. Genetic investigations including genome-wide association studies have by now delivered a few candidates for schizophrenia risk genes reproducible in follow-up studies, such as DISC1, neuregulin 1, ErbB4, dysbindin, AKT1, NMDA receptor and BDNF [1]. Nevertheless, each of the risk genotypes has a minor effect size and further efforts should be directed to discovering genes causally associated with endophenotypes of schizophrenia. Further, environmental impacts play a major role in the etiopathogenesis of schizophrenia, so models based on simple causality by genotype should rather be replaced with models focusing on the gene × environment effects. The existence of G × E effects and gene-gene interactions also implies that any relevant single gene in reality could have a larger effect than currently estimated. This said, all genes and proteins contributing to development of schizophrenia may not necessarily be successful drug targets. Notwithstanding whether the onset of schizophrenia can be facilitated by a number of genes with rare mutations or by many genes with more common variants acting together, in either case drugs should act rather on the pathways on which effects of these genes are converging, either at individual or population level. Thus, both hypothesis-driven and
exploratory modes of research should be used in parallel, as the former has the potential to miss novel alleys and the latter is prone to both false positive and negative results. Gene expression studies are well positioned to provide clues for implicated pathways and molecular substrates that are key players in these pathways. Major conceptual issues arise in selecting suitable model systems and interpretation of the findings, especially as schizophrenia is a heterogenous disorder. The well-known feature of drugs with antipsychotic action to be anti-dopaminergic suggests that examining of different functional states of the dopaminergic neurotransmission could provide some clues. The similar prevalence of schizophrenia in various populations, and the persistence of that prevalence within populations, suggests that universal, culture-insensitive mechanisms exist that maintain genetic vulnerability, and one could speculate that it is exactly the strong dopaminergic system that provides an evolutionary advantage while enhancing the risks of being vulnerable to G × E effects that can lead to psychosis. The genes and their protein products most strongly associated with schizophrenia regulate dopaminergic, but also glutamateand GABA-ergic neurotransmission [1]. In a genomewide gene expression study, rats with higher dopamine High receptors release and higher proportion of striatal D2 also had differences in several genes of the glutamate and GABA-ergic systems as well as in a number of other genes potentially relevant to schizophrenia; among genes differentially expressed there was a significant overrepresentation of those involved in the neuron development, morphogenesis, and differentiation [2]. An example of a different promising approach would be looking into the long-term effect of clozapine as this drug appears as the most potent anti-schizophrenic agent. Converging evidence from different pathogenetically relevant models can be used to refine the understanding of schizophrenia-related pathways, and identification of gatekeepers such as the dopamine D2 receptor. This should be done with understanding that in order to achieve therapeutic efficacy, it may be necessary for the drug to possess suitable affinities for a number of target molecules. Better understanding of the pathogenesis may come from closer examination of candidate brain regions. For example, inhibitory neurotransmission in dorsolateral prefrontal cortex appears to be impaired in schizophrenia and contribute to cognitive deficits, and lamina and cell
S78
Schizophrenia: towards new drug targets
type specific alterations in pre- and postsynaptic aspects of neurotransmission have been examined in sufficient detail to build mechanistic models of schizophreniarelated information processing. Taking into consideration of the developmental course of cytoarchitectonics, gene expression profiling at single cell level can provide insights into molecular cascades possibly involved in cognitive dysfunction. Limitations to the availability of suitable human material can be overcome by further development of animal models that focus on developmental aspects. Given the involvement of developmental and degenerative processes in the onset and chronic course of psychosis, neurotrophic factors and their receptors appear as appealing targets, and the increasing understanding of the neurotrophic mechanism and identification of novel factors is a promising alley. Although little direct evidence exists for epigenetic changes leading to schizophrenia, theoretically psychosisrelated environmental factors may result in pertinent long-lasting epigenetic alterations, particularly when the exposures occur at key developmental changes [3]. There is large potential for drug discovery in revealing the mechanisms of epigenetic regulation of gene expression, and novel molecular targets could be suggested by e.g., epigenetic profiling to reveal genes differentially modified in discordant monozygotic twins. In terms of response to the available antipsychotic medications, schizophrenia is a heterogenous disorder, and thus there is a need for clinical and translational studies that would bring about a better understanding of characteristics of patients, including identification of adequate biomarkers, who do not respond to treatment available currently. Reference(s) [1] Balu, D.T., Coyle, J.T., in press. Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia. Neurosci. Biobehav. Rev. oi:10.1016/j.neubiorev.2010.10.005. [2] Alttoa, A., K˜oiv, K., Hinsley, T.A., Brass, A., Harro, J., 2010. Differential gene expression in a rat model of depression based on persistent differences in exploratory activity. Eur. Neuropsychopharmacol. 20, 288–300. [3] Rutten, B.P.F., Mill, J., 2009. Epigenetic mediation of environmental influences in major psychotic disorders. Schizophrenia Bull. 35, 1045–1056.
Posters P.4.001 Mechanism and behavioural consequences of agonist-induced upregulation of alpha 7 nicotinic acetylcholine receptor levels in the rat brain M.S. Thomsen1 ° , M. El-Sayed1 , D.Z. Christensen1 , J.D. Mikkelsen1 . 1 University Hospital Rigshospitalet, Neurobiology Research Unit, Copenhagen, Denmark Background: The alpha 7 nicotinic acetylcholine receptor (nAChR) is a promising target for the treatment of cognitive deficits in schizophrenia and Alzheimer’s disease. However, the receptor desensitizes rapidly in vitro, which has led to concern regarding its applicability as a clinically relevant drug target. We have recently shown using [125 I]-bungarotoxin (BTX) autoradiography that acute or repeated administration with selective alpha 7 nAChR agonists increases the number of alpha 7 nAChR binding sites in several brain regions, particularly in the prefrontal cortex, whereas no change in binding was observed with the alpha 7 nAChR positive allosteric modulators NS1738 (type I) and PNU120596 (type II) [1]. Type I PAMs increase the amplitude of agonist responses, whereas type II PAMs also decrease agonist-induced desensitization of the receptor. Agonist-induced upregulation may occur either due to activation or desensitization of the alpha 7 nAChR. In addition, upregulation of the alpha 7 nAChR likely affects the behavioural outcome of long-term administration of agonists. Purpose of study: To investigate the mechanism behind and behavioural consequences of alpha 7 nAChR agonistinduced upregulation of the alpha 7 nAChR. Methods: We administered the alpha 7 nAChR agonist A-582941 (10 mg/kg) acutely with or without a type I (XY4093, 1 mg/kg) or II (PNU-120596, 3 mg/kg) alpha 7 nAChR PAM and measured alpha 7 nAChR brain levels in the prefrontal cortex and hippocampus using [125 I]-BTX autoradiography. Additionally, we determined the effect of repeated A-582941 administration on the mRNA levels of several endogenous regulators of alpha 7 nAChR function, i.e. RIC-3 and lynx1 and 2 in the frontal cortex and hippocampus. Finally, we measured the effect of repeated administration of A-582941 in the social discrimination model. Results: The type II PAM PNU-120596, but not the type I PAM XY4083, was able to significantly block A-582941induced upregulation of BTX binding in the prefrontal cortex and hippocampus. Furthermore, A-582941-induced
Schizophrenia: towards new drug targets
Lectures S.4.01 Molecular targets identification J. Harro1 ° . 1 University of Tartu, Department of Psychology Estonian Centre of Behavioural and Health Sciences, Tartu, Estonia Drugs for schizophrenia are effective in about 50% of patients, so there is an obvious need for novel treatment options. Recent advances in brain imaging have assisted in providing insight into cerebral networks responsible for the positive, negative and cognitive symptom clusters in schizophrenia. In terms of identification of novel drug treatments, these approaches as well as post mortem studies guide our thinking to schizophrenia being a disorder of synaptic connectivity, and suggest looking into every aspect of establishment of neural connections and their maintenance. An alternative, hypothesisfree approach is capitalizing on the strong genetic background of schizophrenia and the high-throughput genomic screening techniques. Genetic investigations including genome-wide association studies have by now delivered a few candidates for schizophrenia risk genes reproducible in follow-up studies, such as DISC1, neuregulin 1, ErbB4, dysbindin, AKT1, NMDA receptor and BDNF [1]. Nevertheless, each of the risk genotypes has a minor effect size and further efforts should be directed to discovering genes causally associated with endophenotypes of schizophrenia. Further, environmental impacts play a major role in the etiopathogenesis of schizophrenia, so models based on simple causality by genotype should rather be replaced with models focusing on the gene × environment effects. The existence of G × E effects and gene-gene interactions also implies that any relevant single gene in reality could have a larger effect than currently estimated. This said, all genes and proteins contributing to development of schizophrenia may not necessarily be successful drug targets. Notwithstanding whether the onset of schizophrenia can be facilitated by a number of genes with rare mutations or by many genes with more common variants acting together, in either case drugs should act rather on the pathways on which effects of these genes are converging, either at individual or population level. Thus, both hypothesis-driven and
exploratory modes of research should be used in parallel, as the former has the potential to miss novel alleys and the latter is prone to both false positive and negative results. Gene expression studies are well positioned to provide clues for implicated pathways and molecular substrates that are key players in these pathways. Major conceptual issues arise in selecting suitable model systems and interpretation of the findings, especially as schizophrenia is a heterogenous disorder. The well-known feature of drugs with antipsychotic action to be anti-dopaminergic suggests that examining of different functional states of the dopaminergic neurotransmission could provide some clues. The similar prevalence of schizophrenia in various populations, and the persistence of that prevalence within populations, suggests that universal, culture-insensitive mechanisms exist that maintain genetic vulnerability, and one could speculate that it is exactly the strong dopaminergic system that provides an evolutionary advantage while enhancing the risks of being vulnerable to G × E effects that can lead to psychosis. The genes and their protein products most strongly associated with schizophrenia regulate dopaminergic, but also glutamateand GABA-ergic neurotransmission [1]. In a genomewide gene expression study, rats with higher dopamine High receptors release and higher proportion of striatal D2 also had differences in several genes of the glutamate and GABA-ergic systems as well as in a number of other genes potentially relevant to schizophrenia; among genes differentially expressed there was a significant overrepresentation of those involved in the neuron development, morphogenesis, and differentiation [2]. An example of a different promising approach would be looking into the long-term effect of clozapine as this drug appears as the most potent anti-schizophrenic agent. Converging evidence from different pathogenetically relevant models can be used to refine the understanding of schizophrenia-related pathways, and identification of gatekeepers such as the dopamine D2 receptor. This should be done with understanding that in order to achieve therapeutic efficacy, it may be necessary for the drug to possess suitable affinities for a number of target molecules. Better understanding of the pathogenesis may come from closer examination of candidate brain regions. For example, inhibitory neurotransmission in dorsolateral prefrontal cortex appears to be impaired in schizophrenia and contribute to cognitive deficits, and lamina and cell
S78
Schizophrenia: towards new drug targets
type specific alterations in pre- and postsynaptic aspects of neurotransmission have been examined in sufficient detail to build mechanistic models of schizophreniarelated information processing. Taking into consideration of the developmental course of cytoarchitectonics, gene expression profiling at single cell level can provide insights into molecular cascades possibly involved in cognitive dysfunction. Limitations to the availability of suitable human material can be overcome by further development of animal models that focus on developmental aspects. Given the involvement of developmental and degenerative processes in the onset and chronic course of psychosis, neurotrophic factors and their receptors appear as appealing targets, and the increasing understanding of the neurotrophic mechanism and identification of novel factors is a promising alley. Although little direct evidence exists for epigenetic changes leading to schizophrenia, theoretically psychosisrelated environmental factors may result in pertinent long-lasting epigenetic alterations, particularly when the exposures occur at key developmental changes [3]. There is large potential for drug discovery in revealing the mechanisms of epigenetic regulation of gene expression, and novel molecular targets could be suggested by e.g., epigenetic profiling to reveal genes differentially modified in discordant monozygotic twins. In terms of response to the available antipsychotic medications, schizophrenia is a heterogenous disorder, and thus there is a need for clinical and translational studies that would bring about a better understanding of characteristics of patients, including identification of adequate biomarkers, who do not respond to treatment available currently. Reference(s) [1] Balu, D.T., Coyle, J.T., in press. Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia. Neurosci. Biobehav. Rev. oi:10.1016/j.neubiorev.2010.10.005. [2] Alttoa, A., K˜oiv, K., Hinsley, T.A., Brass, A., Harro, J., 2010. Differential gene expression in a rat model of depression based on persistent differences in exploratory activity. Eur. Neuropsychopharmacol. 20, 288–300. [3] Rutten, B.P.F., Mill, J., 2009. Epigenetic mediation of environmental influences in major psychotic disorders. Schizophrenia Bull. 35, 1045–1056.
Posters P.4.001 Mechanism and behavioural consequences of agonist-induced upregulation of alpha 7 nicotinic acetylcholine receptor levels in the rat brain M.S. Thomsen1 ° , M. El-Sayed1 , D.Z. Christensen1 , J.D. Mikkelsen1 . 1 University Hospital Rigshospitalet, Neurobiology Research Unit, Copenhagen, Denmark Background: The alpha 7 nicotinic acetylcholine receptor (nAChR) is a promising target for the treatment of cognitive deficits in schizophrenia and Alzheimer’s disease. However, the receptor desensitizes rapidly in vitro, which has led to concern regarding its applicability as a clinically relevant drug target. We have recently shown using [125 I]-bungarotoxin (BTX) autoradiography that acute or repeated administration with selective alpha 7 nAChR agonists increases the number of alpha 7 nAChR binding sites in several brain regions, particularly in the prefrontal cortex, whereas no change in binding was observed with the alpha 7 nAChR positive allosteric modulators NS1738 (type I) and PNU120596 (type II) [1]. Type I PAMs increase the amplitude of agonist responses, whereas type II PAMs also decrease agonist-induced desensitization of the receptor. Agonist-induced upregulation may occur either due to activation or desensitization of the alpha 7 nAChR. In addition, upregulation of the alpha 7 nAChR likely affects the behavioural outcome of long-term administration of agonists. Purpose of study: To investigate the mechanism behind and behavioural consequences of alpha 7 nAChR agonistinduced upregulation of the alpha 7 nAChR. Methods: We administered the alpha 7 nAChR agonist A-582941 (10 mg/kg) acutely with or without a type I (XY4093, 1 mg/kg) or II (PNU-120596, 3 mg/kg) alpha 7 nAChR PAM and measured alpha 7 nAChR brain levels in the prefrontal cortex and hippocampus using [125 I]-BTX autoradiography. Additionally, we determined the effect of repeated A-582941 administration on the mRNA levels of several endogenous regulators of alpha 7 nAChR function, i.e. RIC-3 and lynx1 and 2 in the frontal cortex and hippocampus. Finally, we measured the effect of repeated administration of A-582941 in the social discrimination model. Results: The type II PAM PNU-120596, but not the type I PAM XY4083, was able to significantly block A-582941induced upregulation of BTX binding in the prefrontal cortex and hippocampus. Furthermore, A-582941-induced