Serine 133 phosphorylation is not required for hippocampal CREB-mediated transcription and behavior

Dynamic activity changes in transcription factors: Unlocking the mechanisms regulating physiological changes in the brain

Transcription factors (TFs) regulate the establishment and modulation of the transcriptome within cells, thereby playing a crucial role in various aspects of cellular physiology throughout the body. Quantitative measurement of TF activity during the development, function, and dysfunction of the brain is essential for gaining a deeper understanding of the regulatory mechanisms governing gene expression during these processes. Due to their role as regulators of gene expression, assessing and modulating detailed TF activity contributes to the development of practical methods to intervene in these processes, potentially offering more efficient treatments for diseases. Recent methodologies have revealed that TF activity is dynamically regulated within cells and organisms, including the adult brain. This review summarizes the regulatory mechanisms of TF activities and the methodologies used to assess them, emphasizing their importance in both fundamental research and clinical applications.

Targeting tau in Alzheimer's disease: from mechanisms to clinical therapy

ABSTRACT

Alzheimer's disease is the most prevalent neurodegenerative disease affecting older adults. Primary features of Alzheimer's disease include extracellular aggregation of amyloid-β plaques and the accumulation of neurofibrillary tangles, formed by tau protein, in the cells. While there are amyloid-β-targeting therapies for the treatment of Alzheimer's disease, these therapies are costly and exhibit potential negative side effects. Mounting evidence suggests significant involvement of tau protein in Alzheimer's disease-related neurodegeneration. As an important microtubule-associated protein, tau plays an important role in maintaining the stability of neuronal microtubules and promoting axonal growth. In fact, clinical studies have shown that abnormal phosphorylation of tau protein occurs before accumulation of amyloid-β in the brain. Various therapeutic strategies targeting tau protein have begun to emerge, and are considered possible methods to prevent and treat Alzheimer's disease. Specifically, abnormalities in post-translational modifications of the tau protein, including aberrant phosphorylation, ubiquitination, small ubiquitin-like modifier (SUMO)ylation, acetylation, and truncation, contribute to its microtubule dissociation, misfolding, and subcellular missorting. This causes mitochondrial damage, synaptic impairments, gliosis, and neuroinflammation, eventually leading to neurodegeneration and cognitive deficits. This review summarizes the recent findings on the underlying mechanisms of tau protein in the onset and progression of Alzheimer's disease and discusses tau-targeted treatment of Alzheimer's disease.

CREB: A multifaceted transcriptional regulator of neural and immune function in CNS tumors

Cancers of the central nervous system (CNS) are unique with respect to their tumor microenvironment. Such a status is due to immune-privilege and the cellular behaviors within a highly networked, neural-rich milieu. During tumor development in the CNS, neural, immune and cancer cells establish complex cell-to-cell communication networks which mimic physiological functions, including paracrine signaling and synapse-like formations. This crosstalk regulates diverse pathological functions contributing to tumor progression. In the CNS, regulation of physiological and pathological functions relies on various cell signaling and transcription programs. At the core of these events lies the cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), a master transcriptional regulator in the CNS. CREB is a kinase inducible transcription factor which regulates many CNS functions, including neurogenesis, neuronal survival, neuronal activation and long-term memory. Here, we discuss how CREB-regulated mechanisms operating in diverse cell types, which control development and function of the CNS, are co-opted in CNS tumors.

Excitation-transcription coupling, neuronal gene expression and synaptic plasticity

Excitation-transcription coupling (E-TC) links synaptic and cellular activity to nuclear gene transcription. It is generally accepted that E-TC makes a crucial contribution to learning and memory through its role in underpinning long-lasting synaptic enhancement in late-phase long-term potentiation and has more recently been linked to late-phase long-term depression: both processes require de novo gene transcription, mRNA translation and protein synthesis. E-TC begins with the activation of glutamate-gated N-methyl-D-aspartate-type receptors and voltage-gated L-type Ca2+ channels at the membrane and culminates in the activation of transcription factors in the nucleus. These receptors and ion channels mediate E-TC through mechanisms that include long-range signalling from the synapse to the nucleus and local interactions within dendritic spines, among other possibilities. Growing experimental evidence links these E-TC mechanisms to late-phase long-term potentiation and learning and memory. These advances in our understanding of the molecular mechanisms of E-TC mean that future efforts can focus on understanding its mesoscale functions and how it regulates neuronal network activity and behaviour in physiological and pathological conditions.

CREB serine 133 is necessary for spatial cognitive flexibility and long-term potentiation

The transcription factor cAMP response element binding protein (CREB) is widely regarded as orchestrating the genomic response that underpins a range of physiological functions in the central nervous system, including learning and memory. Of the means by which CREB can be regulated, emphasis has been placed on the phosphorylation of a key serine residue, S133, in the CREB protein, which is required for CREB-mediated transcriptional activation in response to a variety of activity-dependent stimuli. Understanding the role of CREB S133 has been complicated by molecular genetic techniques relying on over-expression of either dominant negative or activating transgenes that may distort the physiological role of endogenous CREB. A more elegant recent approach targeting S133 in the endogenous CREB gene has yielded a mouse with constitutive replacement of this residue with alanine (S133A), but has generated results (no behavioural phenotype and no effect on gene transcription) at odds with contemporary views as to the role of CREB S133, and which may reflect compensatory changes associated with the constitutive mutation. To avoid this potential complication, we generated a post-natal and forebrain-specific CREB S133A mutant in which the expression of the mutation was under the control of CaMKIIα promoter. Using male and female mice we show that CREB S133 is necessary for spatial cognitive flexibility, the regulation of basal synaptic transmission, and for the expression of long-term potentiation (LTP) in hippocampal area CA1. These data point to the importance of CREB S133 in neuronal function, synaptic plasticity and cognition in the mammalian brain.

New Insights Into the Pivotal Role of CREB-Regulated Transcription Coactivator 1 in Depression and Comorbid Obesity

Depression and obesity are major public health concerns, and there is mounting evidence that they share etiopathophysiological mechanisms. The neurobiological pathways involved in both mood and energy balance regulation are complex, multifactorial and still incompletely understood. As a coactivator of the pleiotropic transcription factor cAMP response element-binding protein (CREB), CREB-regulated transcription coactivator 1 (CRTC1) has recently emerged as a novel regulator of neuronal plasticity and brain functions, while CRTC1 dysfunction has been associated with neurodegenerative and psychiatric diseases. This review focuses on recent evidence emphasizing the critical role of CRTC1 in the neurobiology of depression and comorbid obesity. We discuss the role of CRTC1 downregulation in mediating chronic stress-induced depressive-like behaviors, and antidepressant response in the light of the previously characterized Crtc1 knockout mouse model of depression. The putative role of CRTC1 in the alteration of brain energy homeostasis observed in depression is also discussed. Finally, we highlight rodent and human studies supporting the critical involvement of CRTC1 in depression-associated obesity.

Key transcription factors mediating cocaine-induced plasticity in the nucleus accumbens

Repeated cocaine use induces coordinated changes in gene expression that drive plasticity in the nucleus accumbens (NAc), an important component of the brain's reward circuitry, and promote the development of maladaptive, addiction-like behaviors. Studies on the molecular basis of cocaine action identify transcription factors, a class of proteins that bind to specific DNA sequences and regulate transcription, as critical mediators of this cocaine-induced plasticity. Early methods to identify and study transcription factors involved in addiction pathophysiology primarily relied on quantifying the expression of candidate genes in bulk brain tissue after chronic cocaine treatment, as well as conventional overexpression and knockdown techniques. More recently, advances in next generation sequencing, bioinformatics, cell-type-specific targeting, and locus-specific neuroepigenomic editing offer a more powerful, unbiased toolbox to identify the most important transcription factors that drive drug-induced plasticity and to causally define their downstream molecular mechanisms. Here, we synthesize the literature on transcription factors mediating cocaine action in the NAc, discuss the advancements and remaining limitations of current experimental approaches, and emphasize recent work leveraging bioinformatic tools and neuroepigenomic editing to study transcription factors involved in cocaine addiction.

NMDA and AMPA receptors dysregulation in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative condition characterized by cognitive dysfunction and synaptic failure. The current therapeutic approaches are mainly focused on symptomatic treatment and possess limited effectiveness in addressing the pathophysiology of AD. It is known that neurodegeneration is negatively correlated with synaptic plasticity. This negative correlation highlights glutamatergic neurotransmission via N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors and (AMPA) receptors as a critical mediator of synaptic plasticity. Despite this favorable role, extensive extracellular glutamate concentration induces excitotoxicity and neurodegeneration. NMDA receptors containing GluN2A subunits are located at synaptic sites, implicated in the protective pathways. In comparison, GluN2B containing receptors are located mainly at extrasynaptic sites and increase neuronal vulnerability. AMPA receptors are consistently endocytosed and recycled back to the membrane. An increase in the rate of endocytosis has been implicated as a part of AD pathophysiology through inducing long-term depression (LTD) and synaptic disintegration. In the present review, we focused on the mechanisms of glutamatergic system dysregulation in AD, particularly on its interaction with amyloid-beta. We concluded that assigning a specific role to an individual subtype of either NMDA receptors or AMPA receptors might be an oversimplification as they are not static receptors. Therefore, any imbalance between synaptic and extrasynaptic NMDA receptors and a reduced number of surface AMPA receptors will lead to synaptopathy.

Dermal Olfactory Receptor OR51B5 Is Essential for Survival and Collagen Synthesis in Human Dermal Fibroblast (Hs68 Cells)

Skin dermis comprises extracellular matrix components, mainly collagen fibers. A decrease in collagen synthesis caused by several factors, including ultraviolet (UV) irradiation and stress, eventually causes extrinsic skin aging. Olfactory receptors (ORs) were initially considered to be specifically expressed in nasal tissue, but several ORs have been reported to be present in other tissues, and their biological roles have recently received increasing attention. In this study, we aimed to characterize the role of ORs in cell survival and collagen synthesis in dermal fibroblasts. We confirmed that UVB irradiation and dexamethasone exposure significantly decreased cell survival and collagen synthesis in Hs68 dermal fibroblasts. Moreover, we demonstrated that the mRNA expression of 10 ORs detectable in Hs68 cells was significantly downregulated in aged conditions compared with that in normal conditions. Thereafter, by individual knockdown of the 10 candidate ORs, we identified that only OR51B5 knockdown leads to a reduction of cell survival and collagen synthesis. OR51B5 knockdown decreased cAMP levels and dampened the downstream protein kinase A/cAMP-response element binding protein pathway, downregulating the survival- and collagen synthesis-related genes in the dermal fibroblasts. Therefore, OR51B5 may be an interesting candidate that plays a role in cell survival and collagen synthesis.

Dysregulated CRTC1-BDNF signaling pathway in the hippocampus contributes to Aβ oligomer-induced long-term synaptic plasticity and memory impairment

Expression of CREB-regulated transcription coactivator 1 (CRTC1) in the hippocampus is impaired in Alzheimer's disease (AD). However, CRTC1 related mechanisms associated with long-term synaptic plasticity impairment and cognitive decline in the onset of AD are unknown. In this study, electrophysiological recordings indicated that lentivirus-mediated CRTC1 overexpression effectively ameliorates suppression of late-phase long-term potentiation (L-LTP) in rat hippocampal slices treated with oligomeric amyloid β(1-42) peptides (oAβ42) (200 nM). In addition, application of oAβ42 and genetic knockdown of CRTC1 by lentivirus-mediated CRTC1-shRNA inhibit L-LTP, whereas their combination does not further impair L-LTP. Brain-derived neurotrophic factor (BDNF), an important downstream protein confers protection of CRTC1 overexpression against oAβ42-induced L-LTP impairment as shown by administration of K252a (200 nM) and TrkB-FC (20 μg/ml). Furthermore, behavioral and western blotting analyses showed that CRTC1 overexpression reverses oAβ42-induced hippocampal-dependent cognitive deficits, downregulation of CRTC1 and BDNF expression. Notably, CRTC1-shRNA directly elicits cognitive deficits. In summary, these findings show that hippocampal CRTC1 signaling is affected by soluble oAβ, and CRTC1-BDNF pathway is involved in hippocampal L-LTP impairment and memory deficits induced by oAβ42.

In Situ DNA/Protein Interaction Assay to Visualize Transcriptional Factor Activation

The chick embryo chorioallantoic membrane (CAM) represents a powerful in vivo model to study several physiological and pathological processes including inflammation and tumor progression. Nevertheless, the possibility of deepening the molecular processes in the CAM system is biased by the absence/scarcity of chemical and biological reagents, designed explicitly for avian species. This is particularly true for transcriptional factors, proteinaceous molecules that regulate various cellular responses, including proliferation, survival, and differentiation. Here, we propose a detailed antibody-independent protocol to visualize the activation and nuclear translocation of transcriptional factors in cells or in tissues of different animal species. As a proof of concept, DNA/cAMP response element-binding protein (CREB) interaction was characterized on the CAM tissue using oligonucleotides containing the palindromic binding sequence of CREB. Scrambled oligonucleotides were used as controls. In situ DNA/protein interaction protocol is a versatile method that is useful for the study of transcription factors in the cell and tissue of different origins.

Targeting CREB in Cancer Therapy: A Key Candidate or One of Many? An Update

Simple Summary

Only 5% of all drug-related targets currently move from preclinical to clinical in cancer, and just some of them achieve patient’s bedside. Among others, intratumor heterogeneity and preclinical cancer model limitations actually represent the main reasons for this failure. Cyclic-AMP response element-binding protein (CREB) has been defined as a proto-oncogene in different tumor types, being involved in maintenance and progression. Due to its relevance in tumor pathophysiology, many CREB inhibitor compounds have been developed and tested over the years. Herein, we examine the current state-of-the-art of both CREB and CREB inhibitors in cancer, retracing some of the most significant findings of the last years. While the scientific statement confers on CREB a proactive role in cancer, its therapeutic potential is still stuck at laboratory bench. Therefore, pursuing every concrete result to achieve CREB inhibition in clinical might give chance and future to cancer patients worldwide.

Abstract

Intratumor heterogeneity (ITH) is considered the major disorienting factor in cancer treatment. As a result of stochastic genetic and epigenetic alterations, the appearance of a branched evolutionary shape confers tumor plasticity, causing relapse and unfavorable clinical prognosis. The growing evidence in cancer discovery presents to us “the great paradox” consisting of countless potential targets constantly discovered and a small number of candidates being effective in human patients. Among these, cyclic-AMP response element-binding protein (CREB) has been proposed as proto-oncogene supporting tumor initiation, progression and metastasis. Overexpression and hyperactivation of CREB are frequently observed in cancer, whereas genetic and pharmacological CREB downregulation affects proliferation and apoptosis. Notably, the present review is designed to investigate the feasibility of targeting CREB in cancer therapy. In particular, starting with the latest CREB evidence in cancer pathophysiology, we evaluate the advancement state of CREB inhibitor design, including the histone lysine demethylases JMJD3/UTX inhibitor GSKJ4 that we newly identified as a promising CREB modulator in leukemia cells. Moreover, an accurate analysis of strengths and weaknesses is also conducted to figure out whether CREB can actually represent a therapeutic candidate or just one of the innumerable preclinical cancer targets.

Epigenetic Regulation as a Basis for Long-Term Changes in the Nervous System: In Search of Specificity Mechanisms

Abstract

Adaptive long-term changes in the functioning of nervous system (plasticity, memory) are not written in the genome, but are directly associated with the changes in expression of many genes comprising epigenetic regulation. Summarizing the known data regarding the role of epigenetics in regulation of plasticity and memory, we would like to highlight several key aspects. (i) Different chromatin remodeling complexes and DNA methyltransferases can be organized into high-order multiprotein repressor complexes that are cooperatively acting as the “molecular brake pads”, selectively restricting transcriptional activity of specific genes at rest. (ii) Relevant physiological stimuli induce a cascade of biochemical events in the activated neurons resulting in translocation of different signaling molecules (protein kinases, NO-containing complexes) to the nucleus. (iii) Stimulus-specific nitrosylation and phosphorylation of different epigenetic factors is linked to a decrease in their enzymatic activity or changes in intracellular localization that results in temporary destabilization of the repressor complexes. (iv) Removing “molecular brakes” opens a “critical time window” for global and local epigenetic changes, triggering specific transcriptional programs and modulation of synaptic connections efficiency. It can be assumed that the reversible post-translational histone modifications serve as the basis of plastic changes in the neural network. On the other hand, DNA methylation and methylation-dependent 3D chromatin organization can serve a stable molecular basis for long-term maintenance of plastic changes and memory.

Knockdown of TNFAIP1 prevents di-(2-ethylhexyl) phthalate-induced neurotoxicity by activating CREB pathway

Di-(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer. It has neurotoxicity and exposure to it causes impairment of neurodevelopment, behavior and cognition. However, the molecular mechanisms responsible for the DEHP-induced neurotoxicity are not yet clearly defined. Tumor necrosis factor-induced protein 1 (TNFAIP1) was first discovered in umbilical vein endothelial cells and was further found to be important in the progress of Alzheimer's disease. Herein we explore the mechanism of TNFAIP1 in DEHP-induced neurotoxicity with the involvement of cyclic AMP response elements binding protein (CREB) signaling pathway in a mouse neuroblastoma cell line (N2a cells). We found that exposure to DEHP induced apoptosis and downregulated the expression of brain-derived neurotrophic factor (BDNF), synaptic proteins PSD 95 and synapsin-1 while upregulated the expression of TNFAIP1 and decreased the levels of phosphorylated Akt, CaMK Ⅳ, catalytic subunits of PKA and CREB in CREB signaling pathway. Knockdown of TNFAIP1 using TNFAIP1 small interfering RNA (siRNA) expression vector prevented DEHP from inhibiting CREB pathway, thus reduced apoptosis and restored expression of BDNF, PSD 95 and synapsin-1. Our data indicate that downregulation of TNFAIP1 prevents DEHP-induced neurotoxicity via activating CREB pathway. Therefore, TNFAIP1 is a potential target for relieving the DEHP-induced neurotoxicity and related neurological disorders.

A neuroscientist's guide to transgenic mice and other genetic tools

The past decade has produced an explosion in the number and variety of genetic tools available to neuroscientists, resulting in an unprecedented ability to precisely manipulate the genome and epigenome in behaving animals. However, no single resource exists that describes all of the tools available to neuroscientists. Here, we review the genetic, transgenic, and viral techniques that are currently available to probe the complex relationship between genes and cognition. Topics covered include types of traditional transgenic mouse models (knockout, knock-in, reporter lines), inducible systems (Cre-loxP, Tet-On, Tet-Off) and cell- and circuit-specific systems (TetTag, TRAP, DIO-DREADD). Additionally, we provide details on virus-mediated and siRNA/shRNA approaches, as well as a comprehensive discussion of the myriad manipulations that can be made using the CRISPR-Cas9 system, including single base pair editing and spatially- and temporally-regulated gene-specific transcriptional control. Collectively, this review will serve as a guide to assist neuroscientists in identifying and choosing the appropriate genetic tools available to study the complex relationship between the brain and behavior.

Non-canonical activation of CREB mediates neuroprotection in a Caenorhabditis elegans model of excitotoxic necrosis

Excitotoxicity, caused by exaggerated neuronal stimulation by Glutamate (Glu), is a major cause of neurodegeneration in brain ischemia. While we know that neurodegeneration is triggered by overstimulation of Glu-receptors (GluRs), the subsequent mechanisms that lead to cellular demise remain controversial. Surprisingly, signaling downstream of GluRs can also activate neuroprotective pathways. The strongest evidence involves activation of the transcription factor cAMP response element-binding protein (CREB), widely recognized for its importance in synaptic plasticity. Canonical views describe CREB as a phosphorylation-triggered transcription factor, where transcriptional activation involves CREB phosphorylation and association with CREB-binding protein. However, given CREB's ubiquitous cross-tissue expression, the multitude of cascades leading to CREB phosphorylation, and its ability to regulate thousands of genes, it remains unclear how CREB exerts closely tailored, differential neuroprotective responses in excitotoxicity. A non-canonical, alternative cascade for activation of CREB-mediated transcription involves the CREB co-factor cAMP-regulated transcriptional co-activator (CRTC), and may be independent of CREB phosphorylation. To identify cascades that activate CREB in excitotoxicity we used a Caenorhabditis elegans model of neurodegeneration by excitotoxic necrosis. We demonstrated that CREB's neuroprotective effect was conserved, and seemed most effective in neurons with moderate Glu exposure. We found that factors mediating canonical CREB activation were not involved. Instead, phosphorylation-independent CREB activation in nematode excitotoxic necrosis hinged on CRTC. CREB-mediated transcription that depends on CRTC, but not on CREB phosphorylation, might lead to expression of a specific subset of neuroprotective genes. Elucidating conserved mechanisms of excitotoxicity-specific CREB activation can help us focus on core neuroprotective programs in excitotoxicity. Cover Image for this issue: doi: 10.1111/jnc.14494.

Sleep/Wake Disruption in a Mouse Model of BLOC-1 Deficiency

Mice lacking a functional Biogenesis of Lysosome-related Organelles Complex 1 (BLOC-1), such as those of the pallid line, display cognitive and behavioural impairments reminiscent of those presented by individuals with intellectual and developmental disabilities. Although disturbances in the sleep/wake cycle are commonly lamented by these individuals, the underlying mechanisms, including the possible role of the circadian timing system, are still unknown. In this paper, we have explored sleep/circadian malfunctions and underlying mechanisms in BLOC-1-deficient pallid mice. These mutants exhibited less sleep behaviour in the beginning of the resting phase than wild-type mice with a more broken sleeping pattern in normal light-dark conditions. Furthermore, the strength of the activity rhythms in the mutants were reduced with significantly more fragmentation and lower precision than in age-matched controls. These symptoms were accompanied by an abnormal preference for the open arm in the elevated plus maze in the day and poor performance in the novel object recognition at night. At the level of the central circadian clock (the suprachiasmatic nucleus, SCN), loss of BLOC-1 caused subtle morphological changes including a larger SCN and increased expression of the relative levels of the clock gene Per2 product during the day but did not affect the neuronal activity rhythms. In the hippocampus, the pallid mice presented with anomalies in the cytoarchitecture of the Dentate Gyrus granule cells, but not in CA1 pyramidal neurones, along with altered PER2 protein levels as well as reduced pCREB/tCREB ratio during the day. Our findings suggest that lack of BLOC-1 in mice disrupts the sleep/wake cycle and performance in behavioural tests associated with specific alterations in cytoarchitecture and protein expression.

Selective Depletion of CREB in Serotonergic Neurons Affects the Upregulation of Brain-Derived Neurotrophic Factor Evoked by Chronic Fluoxetine Treatment

Neurotrophic factors are regarded as crucial regulatory components in neuronal plasticity and are postulated to play an important role in depression pathology. The abundant expression of brain-derived neurotrophic factor (BDNF) in various brain structures seems to be of particular interest in this context, as downregulation of BDNF is postulated to be correlated with depression and its upregulation is often observed after chronic treatment with common antidepressants. It is well-known that BDNF expression is regulated by cyclic AMP response element-binding protein (CREB). In our previous study using mice lacking CREB in serotonergic neurons (Creb1^TPH2CreERT2 mice), we showed that selective CREB ablation in these particular neuronal populations is crucial for drug-resistant phenotypes in the tail suspension test observed after fluoxetine administration in Creb1^TPH2CreERT2 mice. The aim of this study was to investigate the molecular changes in the expression of neurotrophins in Creb1^TPH2CreERT2 mice after chronic fluoxetine treatment, restricted to the brain structures implicated in depression pathology with profound serotonergic innervation including the prefrontal cortex (PFC) and hippocampus. Here, we show for the first time that BDNF upregulation observed after fluoxetine in the hippocampus or PFC might be dependent on the transcription factor CREB residing, not within these particular structures targeted by serotonergic projections, but exclusively in serotonergic neurons. This observation may shed new light on the neurotrophic hypothesis of depression, where the effects of BDNF observed after antidepressants in the hippocampus and other brain structures were rather thought to be regulated by CREB residing within the same brain structures. Overall, these results provide further evidence for the pivotal role of CREB in serotonergic neurons in maintaining mechanisms of antidepressant drug action by regulation of BDNF levels.

The Phosphorylation of CREB at Serine 133 Is a Key Event for Circadian Clock Timing and Entrainment in the Suprachiasmatic Nucleus

Within the suprachiasmatic nucleus (SCN)-the locus of the master circadian clock- transcriptional regulation via the CREB/CRE pathway is implicated in the functioning of the molecular clock timing process, and is a key conduit through which photic input entrains the oscillator. One event driving CRE-mediated transcription is the phosphorylation of CREB at serine 133 (Ser¹³³). Indeed, numerous reporter gene assays have shown that an alanine point mutation in Ser¹³³ reduces CREB-mediated transcription. Here, we sought to examine the contribution of Ser¹³³ phosphorylation to the functional role of CREB in SCN clock physiology in vivo. To this end, we used a CREB knock-in mouse strain, in which Ser¹³³ was mutated to alanine (S/A CREB). Under a standard 12 h light-dark cycle, S/A CREB mice exhibited a marked alteration in clock-regulated wheel running activity. Relative to WT mice, S/A CREB mice had highly fragmented bouts of locomotor activity during the night phase, elevated daytime activity, and a delayed phase angle of entrainment. Further, under free-running conditions, S/A CREB mice had a significantly longer tau than WT mice and reduced activity amplitude. In S/A CREB mice, light-evoked clock entrainment, using both Aschoff type 1 and 6 h "jet lag" paradigms, was markedly reduced relative to WT mice. S/A CREB mice exhibited attenuated transcriptional drive, as assessed by examining both clock-gated and light-evoked gene expression. Finally, SCN slice culture imaging detected a marked disruption in cellular clock phase synchrony following a phase-resetting stimulus in S/A CREB mice. Together, these data indicate that signaling through CREB phosphorylation at Ser¹³³ is critical for the functional fidelity of both SCN timing and entrainment.

Dual Role of CREB in The Regulation of VSMC Proliferation: Mode of Activation Determines Pro- or Anti-Mitogenic Function

Vascular smooth muscle cell (VSMC) proliferation has been implicated in the development of restenosis after angioplasty, vein graft intimal thickening and atherogenesis. We investigated the mechanisms underlying positive and negative regulation of VSMC proliferation by the transcription factor cyclic AMP response element binding protein (CREB). Incubation with the cAMP elevating stimuli, adenosine, prostacyclin mimetics or low levels of forksolin activated CREB without changing CREB phosphorylation on serine-133 but induced nuclear translocation of the CREB co-factors CRTC-2 and CRTC-3. Overexpression of CRTC-2 or -3 significantly increased CREB activity and inhibited VSMC proliferation, whereas CRTC-2/3 silencing inhibited CREB activity and reversed the anti-mitogenic effects of adenosine A2B receptor agonists. By contrast, stimulation with serum or PDGF_BB significantly increased CREB activity, dependent on increased CREB phosphorylation at serine-133 but not on CRTC-2/3 activation. CREB silencing significantly inhibited basal and PDGF induced proliferation. These data demonstrate that cAMP activation of CREB, which is CRTC2/3 dependent and serine-133 independent, is anti-mitogenic. Growth factor activation of CREB, which is serine-133-dependent and CRTC2/3 independent, is pro-mitogenic. Hence, CREB plays a dual role in the regulation of VSMC proliferation with the mode of activation determining its pro- or anti-mitogenic function.

CRTC1 mediates preferential transcription at neuronal activity-regulated CRE/TATA promoters

Gene expression mediated by the transcription factor cAMP-responsive element-binding protein (CREB) is essential for a wide range of brain processes. The transcriptional coactivartor CREB-regulated transcription coactivator-1 (CRTC1) is required for efficient induction of CREB target genes during neuronal activity. However, the mechanisms regulating induction of specific CREB/CRTC1-dependent genes during neuronal activity remain largely unclear. Here, we investigated the molecular mechanisms regulating activity-dependent gene transcription upon activation of the CREB/CRTC1 signaling pathway in neurons. Depolarization and cAMP signals induce preferential transcription of activity-dependent genes containing promoters with proximal CRE/TATA sequences, such as c-fos, Dusp1, Nr4a1, Nr4a2 and Ptgs2, but not genes with proximal CRE/TATA-less promoters (e.g. Nr4a3, Presenilin-1 and Presenilin-2). Notably, biochemical and chromatin immunoprecipitation analyses reveal constitutive binding of CREB to target gene promoters in the absence of neuronal activity, whereas recruitment of CRTC1 to proximal CRE/TATA promoters depends on neuronal activity. Neuronal activity induces rapid CRTC1 dephosphorylation, nuclear translocation and binding to endogenous CREB. These results indicate that neuronal activity induces a preferential binding of CRTC1 to the transcriptional complex in CRE/TATA-containing promoters to engage activity-dependent transcription in neurons.

Acute Stress Enhances Epigenetic Modifications But Does Not Affect the Constitutive Binding of pCREB to Immediate-Early Gene Promoters in the Rat Hippocampus

The immediate early genes (IEGs) c-Fos and Egr-1 are rapidly and transiently induced in sparse neurons within the hippocampus after exposure to an acute stressor. The induction of these genes is a critical part of the molecular mechanisms underlying successful behavioral adaptation to stress. Our previous work has shown that transcriptional activation of c-Fos and Egr-1 in the hippocampus requires formation of a dual histone mark within their promoter regions, the phosphorylation of serine 10 and acetylation of lysine 9/14 of histone H3. In the present study, using chromatin immuno-precipitation (ChIP), we found that an increase in the formation of H3K9ac-S10p occurs within the c-Fos and Egr-1 promoters after FS stress in vivo and that these histone modifications were located to promoter regions containing cAMP Responsive Elements (CREs), but not in neighboring regions containing only Serum Responsive Elements (SREs). Surprisingly, however, subsequent ChIP analyses showed no changes in the binding of pCREB or CREB-binding protein (CBP) to the CREs after FS. In fact, pCREB binding to the c-Fos and Egr-1 promoters was already highly enriched under baseline conditions and did not increase further after stress. We suggest that constitutive pCREB binding may keep c-Fos and Egr-1 in a poised state for activation. Possibly, the formation of H3K9ac-S10p in the vicinity of CRE sites may participate in unblocking transcriptional elongation through recruitment of additional epigenetic factors.

Emerging Roles of CREB-Regulated Transcription Coactivators in Brain Physiology and Pathology

The brain has the ability to sense, coordinate, and respond to environmental changes through biological processes involving activity-dependent gene expression. cAMP-response element binding protein (CREB)-regulated transcription coactivators (CRTCs) have recently emerged as novel transcriptional regulators of essential biological functions, while their deregulation is linked to age-related human diseases. In the brain, CRTCs are unique signaling factors that act as sensors and integrators of hormonal, metabolic, and neural signals contributing to brain plasticity and brain-body communication. In this review, we focus on the regulatory mechanisms and functions of CRTCs in brain metabolism, lifespan, circadian rhythm, and synaptic mechanisms underlying memory and emotion. We also discuss how CRTCs deregulation in cognitive and emotional disorders may provide the basis for potential clinical and therapeutic applications in neurodegenerative and psychiatric diseases.

Genome-Wide Temporal Expression Profiling in Caenorhabditis elegans Identifies a Core Gene Set Related to Long-Term Memory

The identification of genes related to encoding, storage, and retrieval of memories is a major interest in neuroscience. In the current study, we analyzed the temporal gene expression changes in a neuronal mRNA pool during an olfactory long-term associative memory (LTAM) in Caenorhabditis elegans hermaphrodites. Here, we identified a core set of 712 (538 upregulated and 174 downregulated) genes that follows three distinct temporal peaks demonstrating multiple gene regulation waves in LTAM. Compared with the previously published positive LTAM gene set (Lakhina et al., 2015), 50% of the identified upregulated genes here overlap with the previous dataset, possibly representing stimulus-independent memory-related genes. On the other hand, the remaining genes were not previously identified in positive associative memory and may specifically regulate aversive LTAM. Our results suggest a multistep gene activation process during the formation and retrieval of long-term memory and define general memory-implicated genes as well as conditioning-type-dependent gene sets.SIGNIFICANCE STATEMENT The identification of genes regulating different steps of memory is of major interest in neuroscience. Identification of common memory genes across different learning paradigms and the temporal activation of the genes are poorly studied. Here, we investigated the temporal aspects of Caenorhabditis elegans gene expression changes using aversive olfactory associative long-term memory (LTAM) and identified three major gene activation waves. Like in previous studies, aversive LTAM is also CREB dependent, and CREB activity is necessary immediately after training. Finally, we define a list of memory paradigm-independent core gene sets as well as conditioning-dependent genes.

CREB overexpression in dorsal CA1 ameliorates long-term memory deficits in aged rats

The molecular mechanisms underlying age-related cognitive deficits are not yet fully elucidated. In aged animals, a decrease in the intrinsic excitability of CA1 pyramidal neurons is believed to contribute to age-related cognitive impairments. Increasing activity of the transcription factor cAMP response element-binding protein (CREB) in young adult rodents facilitates cognition, and increases intrinsic excitability. However, it has yet to be tested if increasing CREB expression also ameliorates age-related behavioral and biophysical deficits. To test this hypothesis, we virally overexpressed CREB in CA1 of dorsal hippocampus. Rats received CREB or control virus, before undergoing water maze training. CREB overexpression in aged animals ameliorated the long-term memory deficits observed in control animals. Concurrently, cells overexpressing CREB in aged animals had reduced post-burst afterhyperpolarizations, indicative of increased intrinsic excitability. These results identify CREB modulation as a potential therapy to treat age-related cognitive decline.

DOI:http://dx.doi.org/10.7554/eLife.19358.001