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CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice and men
Medical Hypotheses (2008) 70, 117–121
http://intl.elsevierhealth.com/journals/mehy
CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice and men Sabine Chourbaji a,*,1, Christiane Brandwein a,1, Daniel Gau b, Martin Depner a, Christina Saam a, Carolina Johansson c, Martin Schalling c, Timo Partonen d, Siegfried Kasper e, Rolf Adolfsson f, ¨nther Schu ¨tz b, Alexandre Urani a, Thomas Lemberger b, Gu Gunter Schumann a, Peter Gass a a
Central Institute of Mental Health Mannheim (ZI), University of Heidelberg, Germany Division of Molecular Biology of the Cell I, German Cancer Research Center (DKFZ), Heidelberg, Germany c Neurogenetics Unit, Department of Molecular Medicine, Karolinska Institute, Stockholm, Sweden d Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki, Finland e Department of General Psychiatry, Vienna University, Vienna, Austria f Department of Clinical Sciences, Division of Psychiatry, University of Umea, Sweden b
Received 28 December 2006; accepted 4 April 2007
Summary Activation of the transcription factor CREB by Ser142 phosphorylation is implicated in synchronizing circadian rhythmicity, which is disturbed in many depressive patients. Hence, one could assume that emotional behaviour and neuroendocrinological markers would be altered in CREBS142A mice, in which serine 142 is replaced by alanine, preventing phosphorylation at this residue. Moreover, associations of CREB Ser142 and seasonal affective disorder (SAD) might be detectable by the analysis of single-nucleotide polymorphisms (SNPs) in the CREB gene close to the Ser142 residue in SAD patients. However, neither CREBS142A mice demonstrate features of depression, nor there is evidence for an association of SAD with the CREB genotypes. Nevertheless, in humans there is an association of a global seasonality score and circadian rhythmicity with the CREB genotypes in healthy control probands, but not SAD patients. This parallels the phenotype of CREBS142A mice, presenting alterations of circadian rhythm and light-induced entrainment. Thus it is reasonable to assume that CREB Ser142 represents a molecular switch in mice and men, which is responsible for the (dys)regulation of circadian rhythms. c 2007 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +49 621 1703 2932; fax: +49 621 1703 2005. E-mail address: [email protected] (S. Chourbaji). 1 Both authors made equal contribution to this paper.
0306-9877/$ - see front matter c 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2007.04.018
118
Background Expression and activity of the transcription factor CREB (cAMP response element-binding protein) have been implicated in the molecular and cellular mechanisms of pathogenesis and therapy of affective disorders (for review see [1,2]). Thus, human postmortem studies demonstrate decreased CREB levels in the temporal lobe of untreated depressed patients, but not in patients under antidepressant therapy [3,4]. In animal models, chronic antidepressant treatment increases both, expression and activation (by phosphorylation) of CREB in the hippocampus [5,6]. Moreover, virus-mediated CREB overexpression in the hippocampus has antidepressant effects in standardized tests for depression-like behaviour such as the forced swim test and the learned helplessness paradigm [7]. CREB is constitutively expressed in all CNS neurons and activated by a variety of cellular signaling pathways that act via cAMP- or Ca2+-activated kinases, or by tyrosine kinases [8]. This activation is achieved by phosphorylation of CREB at least two different serine residues, Ser133 [9] and Ser142 [10], resulting in CRE-mediated transcription of target genes such as brain-derived neurotrophic factor (BDNF). BDNF is mainly effective by activation of a specific receptor: tyrosine receptor kinase B (trkB). Basic and clinical studies indicate that this CREB–BDNF–trkB pathway plays a crucial role in the pathogenesis and therapy of depression [11,12]. While stress compromises the activity of this signaling cascade [13], antidepressant drugs and electroconvulsive therapy activate this pathway [3,5,13–15]. In line with these findings, exogenously administered BDNF has antidepressant effects [16,17]. Recent transgenic animal studies have shown that activation of CREB by Ser142 phosphorylation is an important molecular mechanism for the synchronization of the day-night cycle and the circadian rhythm [18]. Indeed, CREB is involved in light-induced entrainment mechanisms of the circadian clock in the suprachiasmatic nucleus (SCN) and has also been proposed as a molecular interface between various neuronal and endocrine cues that reset this clock [19,20]. This is highly interesting with respect to the postulated role of CREB in affective disorders, because the disruption of biological rhythms is also a hallmark symptom of human depression [1,2]. Thus, patients with severe depressive episodes usually show disturbances of their sleep/wake cycle and/or the circadian regulation of cortisol levels. Vice versa, sleep deprivation and light-therapy are therapeutic measures
Chourbaji et al. that can alleviate a depressive syndrome. In a particular subtype of human depression, the seasonal affective disorder (SAD, winter type [21]), the efficacy of light-treatment as well as the seasonality of the symptoms suggest an involvement of a circadian pacemaker.
Hypothesis (1) According to current concepts, which consider an involvement of CREB in the pathophysiology of depression (as demonstrated by a decrease of CREB in depressive patients, but an upregulation after antidepressive therapy), CREB Ser142 phosphorylation may play a role in the development of specific depressive symptoms in general, or even in the pathogenesis of SAD in particular. This hypothesis is supported by the recent finding of a regulatory effect exerted by this phosphorylation site on the circadian rhythm in mice which carry a point mutation by which serine 142 was replaced by alanine (CREBS142A), thus preventing the phosphorylation of CREB at this residue. (2) An additional validation of the role of CREB should be practicable by the identification of depression-specific markers in subjects with SAD, which demonstrate depressive-like symptoms and changes of their diurnal activity pattern.
Quantifying the hypothesis by murine and human approaches To study the role of Ser142 in affective disorders, mice were examined, carrying a single point mutation by which serine 142 was replaced by alanine (CREBS142A), thus preventing the phosphorylation of CREB at this residue. CREBS142A mice were subjected to a behavioural test battery for locomotion, anxiety, despair, anhedonia, and cognitive abilities. Additionally, their serum corticosterone levels were analyzed as a possible indicator of a depression-like HPA-system dysfunction. For the detection of a potential association of CREB Ser142 and SAD, a genetic analysis of SAD patients and matched controls was performed using two silent single-nucleotide polymorphisms (SNPs) of the human CREB gene (rs2551920 and rs2551921), which are localized upstream and downstream of the human CREB Ser142 phosphorylation site. To correlate the phenotype of CREBS142A mice with symptoms of patients with SAD, this study furthermore aimed to identify a possible association of
CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice SNPs of the CREB gene in SAD and variations of seasonal or diurnal patterns.
Murine approach: CREBS142A mice do not demonstrate depression-like behaviour Mice with a mutation of the CREB Ser142 phosphorylation residue had been regarded as a candidate strain for depression-like behavioural or neuroendocrinological symptoms for several reasons. First, they have a desynchronization of their circadian rhythm [18], a key feature of subgroups of patients suffering from depression, e.g. SAD patients [1,22,23]. Second, CREB is downregulated and/or underactivated in patients with depression [3,4]. Third, CREB induction and activation is induced by antidepressive therapy in mice and men (for review see [1]). However, in the present examination, CREBS142A mice neither show behavioural or neuroendocrinological features of depression when investigated in a test battery for activity, anxiety, despair, anhedonia, and emotional learning nor they demonstrate stress-induced HPA-system abnormalities. The lack of a depression-like phenotype of CREBS142A mice is in line with the behavioural data on other strains of mice with a genetically modified expression of CREB. CREBaD mutant mice, which lack the a and D CREB isoforms leading to a more than 90% reduction of CRE-binding activity in the brain, demonstrate less despair behaviour in the forced swim test and in the tail suspension test than wildtype controls [24]. Mice with decreased CREB activity in the forebrain due to expression of a dominant-negative CREB-mutant polypeptide show reduced depression-like behaviours in the learned-helplessness paradigm [25]. However, despite their lack of depression-like behaviours, CREBaD mutant mice and also mice with a brain-specific lack of all CREB isoforms exhibit increased levels of anxiety when tested in the elevated T-maze and the dark-light box test [26,27]. In summary, despite the obvious role of CREB in the molecular mechanisms of antidepressant therapy, CREB expression and/or function does not seem to be involved in the pathogenesis of depression-like symptoms in mice.
Human approach: no evidence for an association of SAD with the CREB genotypes With respect to altered expression and phosphorylation levels of CREB described in postmortem studies of depressed patients [3,4], it appeared interesting whether two SNPs, which were in
119
complete LD and were localized in close neighborhood upstream and downstream of the human CREB Ser142 residue, show an association with depressive symptoms of patients with SAD. Analyses of a sample of SAD patients and the same number of matched controls revealed no evidence for an association of SAD with the CREB genotypes assessed. In contrast, the human association approach identified an association of global seasonality score with the CREB genotypes, which was driven mainly by a highly significant association in the matched control sample. Similarly, an association of the CREB genotypes with circadian rhythmicity may only be observed in the control sample. These results support the behavioural findings in CREBS142A mice, which also exhibited a lack of depression-like symptoms, while showing alterations of circadian rhythm and light-induced entrainment [18].
Comparative considerations The latter results provide additional evidence for the validity of our human studies, indicating the presence of a genetic variation close to Ser142, which alters the signaling properties of the CREB1 protein. CREB is known to reset the circadian clock, since light-induced phase shifts are accompanied by rapid phosphorylation of CREB at Ser133 and Ser142 and subsequent CREdependent transcription in the suprachiasmatic nucleus in rodents [18,19,28,29]. Our study provides novel evidence that this may also be relevant for human physiology and behaviour. In addition, our results in humans raise the hypothesis that other disease-specific mechanisms than CREB Ser142 are responsible for alterations in circadian rhythms in depression [1,22]. These mechanisms obviously override the CREB 142mediated effect observed in the healthy control population. To further test this hypothesis, independent studies using larger samples need to be performed. Our hypothesis is in line with the fact that our study did not provide evidence for a role of CREB Ser142 in the pathogenesis of depressive syndromes, neither in mice nor in men. However, depression represents a multifactorial and also a multigenic disease. Therefore it can be assumed, that different genetic factors as well as various psychosocial and environmental variables contribute to this disorder. Thus, it is also conceivable that manipulation of one single genetic function like CREB Ser142 may be necessary but not sufficient to cause a complex syndrome of behavioural alterations.
120 Improved strategies for genetic modeling of depression-like syndromes in animals may, therefore, require a simultaneous targeted dysregulation of several genes involved in the pathogenesis of depression. This approach can be complemented in human models by the identification of behavioural traits, which are thought to be encoded by a limited set of genes. These so-called ‘‘endophenotypes’’ [30,31], may reveal novel insights about the molecular mechanisms underlying circadian rhythmicity as well as specific subgroups of depression, such as SAD. In this respect we have identified a molecular switch in the CREB gene, CREB Ser142, which seems to be responsible for a specific symptom, i.e. the (dys)regulation of circadian rhythms, in mice and men.
Acknowledgements This work was supported by a grant to P.G. from the Deutsche Forschungsgemeinschaft (B3/ SFB636), and to G.S from the State of Baden-Wu ¨rttemberg (‘‘Addictive Behaviour: Improving Healthcare Through Interdisciplinary Research’’, 01EB0110) and the National Genome Research Network Project (‘‘Genetics of Alcoholism’’, FKZ 01GS0117).
References [1] Nestler EJ et al. Neurobiology of depression. Neuron 2002;34(1):13–25. [2] Sulser F. The role of CREB and other transcription factors in the pharmacotherapy and etiology of depression. Ann Med 2002;34(5):348–56. [3] Dowlatshahi D et al. Increased temporal cortex CREB concentrations and antidepressant treatment in major depression. Lancet 1998;352(9142):1754–5. [4] Yamada S et al. Reduced phosphorylation of cyclic AMPresponsive element-binding protein in the postmortem orbitofrontal cortex of patients with major depressive disorder. J Neural Transm 2003;110(6):671–80. [5] Nibuya M, Nestler EJ, Duman RS. Chronic antidepressant administration increases the expression of cAMP response element-binding protein (CREB) in rat hippocampus. J Neurosci 1996;16(7):2365–72. [6] Thome J et al. cAMP response element-mediated gene transcription is upregulated by chronic antidepressant treatment. J Neurosci 2000;20(11):4030–6. [7] Chen AC et al. Expression of the cAMP response element-binding protein (CREB) in hippocampus produces an antidepressant effect. Biol Psychiat 2001;49(9):753–62. [8] Nguyen PV, Woo NH. Regulation of hippocampal synaptic plasticity by cyclic AMP-dependent protein kinases. Prog Neurobiol 2003;71(6):401–37. [9] Montminy M. Transcriptional regulation by cyclic AMP. Annu Rev Biochem 1997;66:807–22.
Chourbaji et al. [10] Mayr BM, Canettieri G, Montminy MR. Distinct effects of cAMP and mitogenic signals on CREB-binding protein recruitment impart specificity to target gene activation via CREB. Proc Natl Acad Sci USA 2001;98(19): 10936–41. [11] Altar CA. Neurotrophins and depression. Trend Pharmacol Sci 1999;20(2):59–61. [12] Urani A et al. The neurotrophin hypothesis of depression revisited by transgenic mice. Clin Neurosci Res 2003;3: 263–9. [13] Nibuya M, Morinobu S, Duman RS. Regulation of BDNF and trkB mRNA in rat brain by chronic electroconvulsive seizure and antidepressant drug treatments. J Neurosci 1995;15(11):7539–47. [14] Chen B et al. Increased hippocampal BDNF immunoreactivity in subjects treated with antidepressant medication. Biol Psychiatr 2001;50(4):260–5. [15] Koch JM et al. Changes in CREB-phosphorylation during recovery from major depression. J Psychiatr Res 2002;36(6):369–75. [16] Siuciak JA et al. Antidepressant-like effect of brainderived neurotrophic factor (BDNF). Pharmacol Biochem Behav 1997;56(1):131–7. [17] Shirayama Y et al. Brain-derived neurotrophic factor produces antidepressant effects in behavioural models of depression. J Neurosci 2002;22(8):3251–61. [18] Gau D et al. Phosphorylation of CREB Ser142 regulates light-induced phase shifts of the circadian clock. Neuron 2002;34(2):245–53. [19] Ding JM et al. Resetting the biological clock: mediation of nocturnal CREB phosphorylation via light, glutamate, and nitric oxide. J Neurosci 1997;17(2):667–75. [20] von Gall C et al. CREB in the mouse SCN: a molecular interface coding the phase-adjusting stimuli light, glutamate, PACAP, and melatonin for clockwork access. J Neurosci 1998;18(24):10389–97. [21] Koorengevel KM et al. Sleep in seasonal affective disorder patients in forced desynchrony: an explorative study. J Sleep Res 2002;11(4):347–56. [22] Bunney WE, Bunney BG. Molecular clock genes in man and lower animals: possible implications for circadian abnormalities in depression. Neuropsychopharmacology 2000;22(4):335–45. [23] Steeves TD et al. Molecular cloning and characterization of the human CLOCK gene: expression in the suprachiasmatic nuclei. Genomics 1999;57(2):189–200. [24] Conti AC et al. cAMP response element-binding protein is essential for the upregulation of brain-derived neurotrophic factor transcription, but not the behavioural or endocrine responses to antidepressant drugs. J Neurosci 2002;22(8):3262–8. [25] Newton SS et al. Inhibition of cAMP response elementbinding protein or dynorphin in the nucleus accumbens produces an antidepressant-like effect. J Neurosci 2002;22(24):10883–90. [26] Graves L et al. Behavioural analysis of CREB alpha delta mutation on a B6/129 F1 hybrid background. Hippocampus 2002;12(1):18–26. [27] Valverde O et al. Modulation of anxiety-like behaviour and morphine dependence in creb-deficient mice. Neuropsychopharmacology 2004. [28] Obrietan K et al. Circadian regulation of cAMP response element-mediated gene expression in the suprachiasmatic nuclei. J Biol Chem 1999;274(25):17748–56. [29] Ginty DD et al. Regulation of CREB phosphorylation in the suprachiasmatic nucleus by light and a circadian clock. Science 1993;260(5105):238–41.
CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice [30] Gottesman II, Gould TD. The endophenotype concept in psychiatry: etymology and strategic intentions. Am J Psychiat 2003;160(4):636–45.
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[31] Cryan JF, Mombereau C. In search of a depressed mouse: utility of models for studying depression-related behaviour in genetically modified mice. Mol Psychiat 2004;9(4):326–57.
Available online at www.sciencedirect.com
http://intl.elsevierhealth.com/journals/mehy
CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice and men Sabine Chourbaji a,*,1, Christiane Brandwein a,1, Daniel Gau b, Martin Depner a, Christina Saam a, Carolina Johansson c, Martin Schalling c, Timo Partonen d, Siegfried Kasper e, Rolf Adolfsson f, ¨nther Schu ¨tz b, Alexandre Urani a, Thomas Lemberger b, Gu Gunter Schumann a, Peter Gass a a
Central Institute of Mental Health Mannheim (ZI), University of Heidelberg, Germany Division of Molecular Biology of the Cell I, German Cancer Research Center (DKFZ), Heidelberg, Germany c Neurogenetics Unit, Department of Molecular Medicine, Karolinska Institute, Stockholm, Sweden d Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki, Finland e Department of General Psychiatry, Vienna University, Vienna, Austria f Department of Clinical Sciences, Division of Psychiatry, University of Umea, Sweden b
Received 28 December 2006; accepted 4 April 2007
Summary Activation of the transcription factor CREB by Ser142 phosphorylation is implicated in synchronizing circadian rhythmicity, which is disturbed in many depressive patients. Hence, one could assume that emotional behaviour and neuroendocrinological markers would be altered in CREBS142A mice, in which serine 142 is replaced by alanine, preventing phosphorylation at this residue. Moreover, associations of CREB Ser142 and seasonal affective disorder (SAD) might be detectable by the analysis of single-nucleotide polymorphisms (SNPs) in the CREB gene close to the Ser142 residue in SAD patients. However, neither CREBS142A mice demonstrate features of depression, nor there is evidence for an association of SAD with the CREB genotypes. Nevertheless, in humans there is an association of a global seasonality score and circadian rhythmicity with the CREB genotypes in healthy control probands, but not SAD patients. This parallels the phenotype of CREBS142A mice, presenting alterations of circadian rhythm and light-induced entrainment. Thus it is reasonable to assume that CREB Ser142 represents a molecular switch in mice and men, which is responsible for the (dys)regulation of circadian rhythms. c 2007 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +49 621 1703 2932; fax: +49 621 1703 2005. E-mail address: [email protected] (S. Chourbaji). 1 Both authors made equal contribution to this paper.
0306-9877/$ - see front matter c 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2007.04.018
118
Background Expression and activity of the transcription factor CREB (cAMP response element-binding protein) have been implicated in the molecular and cellular mechanisms of pathogenesis and therapy of affective disorders (for review see [1,2]). Thus, human postmortem studies demonstrate decreased CREB levels in the temporal lobe of untreated depressed patients, but not in patients under antidepressant therapy [3,4]. In animal models, chronic antidepressant treatment increases both, expression and activation (by phosphorylation) of CREB in the hippocampus [5,6]. Moreover, virus-mediated CREB overexpression in the hippocampus has antidepressant effects in standardized tests for depression-like behaviour such as the forced swim test and the learned helplessness paradigm [7]. CREB is constitutively expressed in all CNS neurons and activated by a variety of cellular signaling pathways that act via cAMP- or Ca2+-activated kinases, or by tyrosine kinases [8]. This activation is achieved by phosphorylation of CREB at least two different serine residues, Ser133 [9] and Ser142 [10], resulting in CRE-mediated transcription of target genes such as brain-derived neurotrophic factor (BDNF). BDNF is mainly effective by activation of a specific receptor: tyrosine receptor kinase B (trkB). Basic and clinical studies indicate that this CREB–BDNF–trkB pathway plays a crucial role in the pathogenesis and therapy of depression [11,12]. While stress compromises the activity of this signaling cascade [13], antidepressant drugs and electroconvulsive therapy activate this pathway [3,5,13–15]. In line with these findings, exogenously administered BDNF has antidepressant effects [16,17]. Recent transgenic animal studies have shown that activation of CREB by Ser142 phosphorylation is an important molecular mechanism for the synchronization of the day-night cycle and the circadian rhythm [18]. Indeed, CREB is involved in light-induced entrainment mechanisms of the circadian clock in the suprachiasmatic nucleus (SCN) and has also been proposed as a molecular interface between various neuronal and endocrine cues that reset this clock [19,20]. This is highly interesting with respect to the postulated role of CREB in affective disorders, because the disruption of biological rhythms is also a hallmark symptom of human depression [1,2]. Thus, patients with severe depressive episodes usually show disturbances of their sleep/wake cycle and/or the circadian regulation of cortisol levels. Vice versa, sleep deprivation and light-therapy are therapeutic measures
Chourbaji et al. that can alleviate a depressive syndrome. In a particular subtype of human depression, the seasonal affective disorder (SAD, winter type [21]), the efficacy of light-treatment as well as the seasonality of the symptoms suggest an involvement of a circadian pacemaker.
Hypothesis (1) According to current concepts, which consider an involvement of CREB in the pathophysiology of depression (as demonstrated by a decrease of CREB in depressive patients, but an upregulation after antidepressive therapy), CREB Ser142 phosphorylation may play a role in the development of specific depressive symptoms in general, or even in the pathogenesis of SAD in particular. This hypothesis is supported by the recent finding of a regulatory effect exerted by this phosphorylation site on the circadian rhythm in mice which carry a point mutation by which serine 142 was replaced by alanine (CREBS142A), thus preventing the phosphorylation of CREB at this residue. (2) An additional validation of the role of CREB should be practicable by the identification of depression-specific markers in subjects with SAD, which demonstrate depressive-like symptoms and changes of their diurnal activity pattern.
Quantifying the hypothesis by murine and human approaches To study the role of Ser142 in affective disorders, mice were examined, carrying a single point mutation by which serine 142 was replaced by alanine (CREBS142A), thus preventing the phosphorylation of CREB at this residue. CREBS142A mice were subjected to a behavioural test battery for locomotion, anxiety, despair, anhedonia, and cognitive abilities. Additionally, their serum corticosterone levels were analyzed as a possible indicator of a depression-like HPA-system dysfunction. For the detection of a potential association of CREB Ser142 and SAD, a genetic analysis of SAD patients and matched controls was performed using two silent single-nucleotide polymorphisms (SNPs) of the human CREB gene (rs2551920 and rs2551921), which are localized upstream and downstream of the human CREB Ser142 phosphorylation site. To correlate the phenotype of CREBS142A mice with symptoms of patients with SAD, this study furthermore aimed to identify a possible association of
CREB-regulated diurnal activity patterns are not indicative for depression-like symptoms in mice SNPs of the CREB gene in SAD and variations of seasonal or diurnal patterns.
Murine approach: CREBS142A mice do not demonstrate depression-like behaviour Mice with a mutation of the CREB Ser142 phosphorylation residue had been regarded as a candidate strain for depression-like behavioural or neuroendocrinological symptoms for several reasons. First, they have a desynchronization of their circadian rhythm [18], a key feature of subgroups of patients suffering from depression, e.g. SAD patients [1,22,23]. Second, CREB is downregulated and/or underactivated in patients with depression [3,4]. Third, CREB induction and activation is induced by antidepressive therapy in mice and men (for review see [1]). However, in the present examination, CREBS142A mice neither show behavioural or neuroendocrinological features of depression when investigated in a test battery for activity, anxiety, despair, anhedonia, and emotional learning nor they demonstrate stress-induced HPA-system abnormalities. The lack of a depression-like phenotype of CREBS142A mice is in line with the behavioural data on other strains of mice with a genetically modified expression of CREB. CREBaD mutant mice, which lack the a and D CREB isoforms leading to a more than 90% reduction of CRE-binding activity in the brain, demonstrate less despair behaviour in the forced swim test and in the tail suspension test than wildtype controls [24]. Mice with decreased CREB activity in the forebrain due to expression of a dominant-negative CREB-mutant polypeptide show reduced depression-like behaviours in the learned-helplessness paradigm [25]. However, despite their lack of depression-like behaviours, CREBaD mutant mice and also mice with a brain-specific lack of all CREB isoforms exhibit increased levels of anxiety when tested in the elevated T-maze and the dark-light box test [26,27]. In summary, despite the obvious role of CREB in the molecular mechanisms of antidepressant therapy, CREB expression and/or function does not seem to be involved in the pathogenesis of depression-like symptoms in mice.
Human approach: no evidence for an association of SAD with the CREB genotypes With respect to altered expression and phosphorylation levels of CREB described in postmortem studies of depressed patients [3,4], it appeared interesting whether two SNPs, which were in
119
complete LD and were localized in close neighborhood upstream and downstream of the human CREB Ser142 residue, show an association with depressive symptoms of patients with SAD. Analyses of a sample of SAD patients and the same number of matched controls revealed no evidence for an association of SAD with the CREB genotypes assessed. In contrast, the human association approach identified an association of global seasonality score with the CREB genotypes, which was driven mainly by a highly significant association in the matched control sample. Similarly, an association of the CREB genotypes with circadian rhythmicity may only be observed in the control sample. These results support the behavioural findings in CREBS142A mice, which also exhibited a lack of depression-like symptoms, while showing alterations of circadian rhythm and light-induced entrainment [18].
Comparative considerations The latter results provide additional evidence for the validity of our human studies, indicating the presence of a genetic variation close to Ser142, which alters the signaling properties of the CREB1 protein. CREB is known to reset the circadian clock, since light-induced phase shifts are accompanied by rapid phosphorylation of CREB at Ser133 and Ser142 and subsequent CREdependent transcription in the suprachiasmatic nucleus in rodents [18,19,28,29]. Our study provides novel evidence that this may also be relevant for human physiology and behaviour. In addition, our results in humans raise the hypothesis that other disease-specific mechanisms than CREB Ser142 are responsible for alterations in circadian rhythms in depression [1,22]. These mechanisms obviously override the CREB 142mediated effect observed in the healthy control population. To further test this hypothesis, independent studies using larger samples need to be performed. Our hypothesis is in line with the fact that our study did not provide evidence for a role of CREB Ser142 in the pathogenesis of depressive syndromes, neither in mice nor in men. However, depression represents a multifactorial and also a multigenic disease. Therefore it can be assumed, that different genetic factors as well as various psychosocial and environmental variables contribute to this disorder. Thus, it is also conceivable that manipulation of one single genetic function like CREB Ser142 may be necessary but not sufficient to cause a complex syndrome of behavioural alterations.
120 Improved strategies for genetic modeling of depression-like syndromes in animals may, therefore, require a simultaneous targeted dysregulation of several genes involved in the pathogenesis of depression. This approach can be complemented in human models by the identification of behavioural traits, which are thought to be encoded by a limited set of genes. These so-called ‘‘endophenotypes’’ [30,31], may reveal novel insights about the molecular mechanisms underlying circadian rhythmicity as well as specific subgroups of depression, such as SAD. In this respect we have identified a molecular switch in the CREB gene, CREB Ser142, which seems to be responsible for a specific symptom, i.e. the (dys)regulation of circadian rhythms, in mice and men.
Acknowledgements This work was supported by a grant to P.G. from the Deutsche Forschungsgemeinschaft (B3/ SFB636), and to G.S from the State of Baden-Wu ¨rttemberg (‘‘Addictive Behaviour: Improving Healthcare Through Interdisciplinary Research’’, 01EB0110) and the National Genome Research Network Project (‘‘Genetics of Alcoholism’’, FKZ 01GS0117).
References [1] Nestler EJ et al. Neurobiology of depression. Neuron 2002;34(1):13–25. [2] Sulser F. The role of CREB and other transcription factors in the pharmacotherapy and etiology of depression. Ann Med 2002;34(5):348–56. [3] Dowlatshahi D et al. Increased temporal cortex CREB concentrations and antidepressant treatment in major depression. Lancet 1998;352(9142):1754–5. [4] Yamada S et al. Reduced phosphorylation of cyclic AMPresponsive element-binding protein in the postmortem orbitofrontal cortex of patients with major depressive disorder. J Neural Transm 2003;110(6):671–80. [5] Nibuya M, Nestler EJ, Duman RS. Chronic antidepressant administration increases the expression of cAMP response element-binding protein (CREB) in rat hippocampus. J Neurosci 1996;16(7):2365–72. [6] Thome J et al. cAMP response element-mediated gene transcription is upregulated by chronic antidepressant treatment. J Neurosci 2000;20(11):4030–6. [7] Chen AC et al. Expression of the cAMP response element-binding protein (CREB) in hippocampus produces an antidepressant effect. Biol Psychiat 2001;49(9):753–62. [8] Nguyen PV, Woo NH. Regulation of hippocampal synaptic plasticity by cyclic AMP-dependent protein kinases. Prog Neurobiol 2003;71(6):401–37. [9] Montminy M. Transcriptional regulation by cyclic AMP. Annu Rev Biochem 1997;66:807–22.
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