Identification of neuronal target genes for CCAAT/enhancer binding proteins

Cracking the Code of Neuronal Cell Fate

Transcriptional regulation is fundamental to most biological processes and reverse-engineering programs can be used to decipher the underlying programs. In this review, we describe how genomics is offering a systems biology-based perspective of the intricate and temporally coordinated transcriptional programs that control neuronal apoptosis and survival. In addition to providing a new standpoint in human pathology focused on the regulatory program, cracking the code of neuronal cell fate may offer innovative therapeutic approaches focused on downstream targets and regulatory networks. Similar to computers, where faults often arise from a software bug, neuronal fate may critically depend on its transcription program. Thus, cracking the code of neuronal life or death may help finding a patch for neurodegeneration and cancer.

C/EBPβ Regulates TFAM Expression, Mitochondrial Function and Autophagy in Cellular Models of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that results from the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Since there are only symptomatic treatments available, new cellular and molecular targets involved in the onset and progression of this disease are needed to develop effective treatments. CCAAT/Enhancer Binding Protein β (C/EBPβ) transcription factor levels are altered in patients with a variety of neurodegenerative diseases, suggesting that it may be a good therapeutic target for the treatment of PD. A list of genes involved in PD that can be regulated by C/EBPβ was generated by the combination of genetic and in silico data, the mitochondrial transcription factor A (TFAM) being among them. In this paper, we observed that C/EBPβ overexpression increased TFAM promoter activity. However, downregulation of C/EBPβ in different PD/neuroinflammation cellular models produced an increase in TFAM levels, together with other mitochondrial markers. This led us to propose an accumulation of non-functional mitochondria possibly due to the alteration of their autophagic degradation in the absence of C/EBPβ. Then, we concluded that C/EBPβ is not only involved in harmful processes occurring in PD, such as inflammation, but is also implicated in mitochondrial function and autophagy in PD-like conditions.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

SIRT1 deficiency increases O-GlcNAcylation of tau, mediating synaptic tauopathy

Hyperphosphorylation of the microtubule associated protein tau is associated with several neurodegenerative diseases including Alzheimer's Disease (AD), collectively referred to as tauopathies. However, the mechanisms by which tau is linked to synaptic dysfunction and memory impairment remain unclear. To address this question, we constructed a mouse model with brain-specific deficiency of SIRT1 (SIRT1 flox/Cre + ). Here, we show that increase of site-specific phosphorylation of tau is coupled with the strengthened O-GlcNAcylation of tau triggered by reduced O-GlcNAcase (OGA) and increased O-GlcNAc transferase (OGT) protein level in the brain of SIRT1 flox/Cre+ mice. SIRT1 deletion in mice brain changes the synaptosomal distribution of site-specific phospho-tau. Learning and memory deficiency induced by dendritic spine deficits and synaptic dysfunction are revealed via SIRT1 flox/Cre+ mice. Our results provide evidence for SIRT1 as a potential therapeutic target in clinical tauopathies.

The transcription factor C/EBPβ promotes vascular endothelial growth factor A expression and neural stem cell expansion

The bZIP transcription factor CCAAT enhancer-binding protein β (C/EBPβ) exhibits neurogenic, neuritogenic, and pro-survival effects in the central nervous system. Here, we show that C/EBPβ regulates neural stem cell (NSC) expansion and vascular endothelial growth factor A (VEGF-A) level by acting on a C/EBPβ-responsive element within the Vegf-a promoter. As predicted, C/EBPβ depletion reduced VEGF-A production, NSC number, and average neurosphere size in proliferating cultures. Conversely, deletion of the C/EBPβ repressor CHOP-10 induced C/EBPβ and VEGF-A expression, while stimulating NSC expansion. These data highlight the role of C/EBPβ in regulating VEGF-A production and the growth of NSCs and suggest CHOP-dependent antagonism of C/EBPβ may function as a transcriptional rheostat linking stress-associated cues with stem cell quiescence among other pathological responses affecting the neurogenic niche.

Neuronal C/EBPβ/AEP pathway shortens life span via selective GABAnergic neuronal degeneration by FOXO repression

The age-related cognitive decline of normal aging is exacerbated in neurodegenerative diseases including Alzheimer's disease (AD). However, it remains unclear whether age-related cognitive regulators in AD pathologies contribute to life span. Here, we show that C/EBPβ, an Aβ and inflammatory cytokine-activated transcription factor that promotes AD pathologies via activating asparagine endopeptidase (AEP), mediates longevity in a gene dose-dependent manner in neuronal C/EBPβ transgenic mice. C/EBPβ selectively triggers inhibitory GABAnergic neuronal degeneration by repressing FOXOs and up-regulating AEP, leading to aberrant neural excitation and cognitive dysfunction. Overexpression of CEBP-2 or LGMN-1 (AEP) in Caenorhabditis elegans neurons but not muscle stimulates neural excitation and shortens life span. CEBP-2 or LGMN-1 reduces daf-2 mutant-elongated life span and diminishes daf-16-induced longevity. C/EBPβ and AEP are lower in humans with extended longevity and inversely correlated with REST/FOXO1. These findings demonstrate a conserved mechanism of aging that couples pathological cognitive decline to life span by the neuronal C/EBPβ/AEP pathway.

Olfactory receptor coding sequences cause silencing of episomal constructs in multiple cell lines

The mammalian olfactory system consists of sensory neurons with specialized odorant-binding capability accomplished by mutually exclusive odorant receptor (OR) expression. Mutually exclusive OR expression is a complex multi-step process regulated by a number of cis and trans factors, including pan-silencing of all OR genes preceding the robust and stable expression of the one OR selected in each sensory neuron. We transfected two olfactory-placode-derived cell lines modeling immature odorant sensory neurons, as well as the GD25 fibroblast cell line, with episomes containing CMV-driven GFP and TK-driven hygromycin reporter genes. We inserted various coding sequences, along with an IRES, immediately upstream of the GFP gene to produce bicistronic mRNAs driven from the local CMV promoter. We found that the presence of several OR coding sequences resulted in significantly diminished episomal expression of GFP in all three cell lines. These findings suggest that OR coding sequences have intrinsic self-silencing capability that might facilitate mutually exclusive OR expression in olfactory sensory neurons by making it less likely that multiple ORs acquire an above-threshold level of expression at once.

Transcriptional Profiles of Cell Fate Transitions Reveal Early Drivers of Neuronal Apoptosis and Survival

Neuronal apoptosis and survival are regulated at the transcriptional level. To identify key genes and upstream regulators primarily responsible for these processes, we overlayed the temporal transcriptome of cerebellar granule neurons following induction of apoptosis and their rescue by three different neurotrophic factors. We identified a core set of 175 genes showing opposite expression trends at the intersection of apoptosis and survival. Their functional annotations and expression signatures significantly correlated to neurological, psychiatric and oncological disorders. Transcription regulatory network analysis revealed the action of nine upstream transcription factors, converging pro-apoptosis and pro-survival-inducing signals in a highly interconnected functionally and temporally ordered manner. Five of these transcription factors are potential drug targets. Transcriptome-based computational drug repurposing produced a list of drug candidates that may revert the apoptotic core set signature. Besides elucidating early drivers of neuronal apoptosis and survival, our systems biology-based perspective paves the way to innovative pharmacology focused on upstream targets and regulatory networks.

Testis-specific expression pattern of dmrt1 and its putative regulatory region in the sea urchin (Mesocentrotus nudus)

Sea urchin (Mseocentrotus nudus) is an economically important mariculture species in several Asian countries. The growth rate and immunocompetence differ by sex in this species. However, the mechanisms of sex determination in M. nudus have remain unclear. In the present study, we focus on the dmrt1 gene of M. nudus (Mndmrt1) to investigate its dynamic expression pattern during different developmental stages. Real-time quantitative PCR (RT-qPCR) revealed that Mndmrt1 exhibits testis-specific expression and undetectable during the whole embryogenesis. With the development of ontogenetic, Mndmrt1 transcripts are first detected at 9 months post-fertilization (mpf). In addition, both the transcripts and protein of Mndmrt1 gene were specifically expressed in spermatogonia and spermatocytes, indicating that it might be a male germ cells marker in sea urchin. Significantly, the 1441 bp promoter sequence of Mndmrt1 gene was obtained by DNA walking, and one positive regulatory region at -1197/ -968 in the promoter, as well as one negative regulatory region at -1441/ -1198 have been identified by promoter activity analysis. Moreover, two regulatory regions contain multiple putative binding sites for transcription factors, including Sp1, Egr1, Sox5, CEBP, GATA and SRY. These findings suggest that Mndmrt1 may be related to testis differentiation and spermatogenesis in sea urchin and will provide an insight into understanding the regulatory mechanism of the dmrt1 gene.

Gut inflammation triggers C/EBPβ/δ-secretase-dependent gut-to-brain propagation of Aβ and Tau fibrils in Alzheimer's disease

Inflammation plays an important role in the pathogenesis of Alzheimer's disease (AD). Some evidence suggests that misfolded protein aggregates found in AD brains may have originated from the gut, but the mechanism underlying this phenomenon is not fully understood. C/EBPβ/δ-secretase signaling in the colon was investigated in a 3xTg AD mouse model in an age-dependent manner. We applied chronic administration of 1% dextran sodium sulfate (DSS) to trigger gut leakage or colonic injection of Aβ or Tau fibrils or AD patient brain lysates in 3xTg mice and combined it with excision/cutting of the gut-brain connecting vagus nerve (vagotomy), in order to explore the role of the gut-brain axis in the development of AD-like pathologies and to monitor C/EBPβ/δ-secretase signaling under those conditions. We found that C/EBPβ/δ-secretase signaling is temporally activated in the gut of AD patients and 3xTg mice, initiating formation of Aβ and Tau fibrils that spread to the brain. DSS treatment promotes gut leakage and facilitates AD-like pathologies in both the gut and the brain of 3xTg mice in a C/EBPβ/δ-secretase-dependent manner. Vagotomy selectively blunts this signaling, attenuates Aβ and Tau pathologies, and restores learning and memory. Aβ or Tau fibrils or AD patient brain lysates injected into the colon propagate from the gut into the brain via the vagus nerve, triggering AD pathology and cognitive dysfunction. The results indicate that inflammation activates C/EBPβ/δ-secretase and initiates AD-associated pathologies in the gut, which are subsequently transmitted to the brain via the vagus nerve.

Dysregulation of miR-15a-5p, miR-497a-5p and miR-511-5p Is Associated with Modulation of BDNF and FKBP5 in Brain Areas of PTSD-Related Susceptible and Resilient Mice

Post-traumatic stress disorder (PTSD) is a neuropsychiatric disorder occurring in susceptible individuals following a traumatic event. Understanding the mechanisms subserving trauma susceptibility/resilience is essential to develop new effective treatments. Increasing evidence suggests that non-coding RNAs, such as microRNAs (miRNAs), may play a prominent role in mediating trauma susceptibility/resilience. In this study, we evaluated the transcriptional expression of two key PTSD-related genes (FKBP5 and BDNF) and the relative targeting miRNAs (miR-15a-5p, miR-497a-5p, miR-511-5p, let-7d-5p) in brain areas of PTSD-related susceptible and resilient mice identified through our recently developed mouse model of PTSD (arousal-based individual screening (AIS) model). We observed lower transcript levels of miR-15a-5p, miR-497a-5p, and miR-511a-5p in the hippocampus and hypothalamus of susceptible mice compared to resilient mice, suggesting that the expression of these miRNAs could discriminate the two different phenotypes of stress-exposed mice. These miRNA variations could contribute, individually or synergically, to the inversely correlated transcript levels of FKBP5 and BDNF. Conversely, in the medial prefrontal cortex, downregulation of miR-15a-5p, miR-511-5p, and let-7d-5p was observed both in susceptible and resilient mice, and not accompanied by changes in their mRNA targets. Furthermore, miRNA expression in the different brain areas correlated to stress-induced behavioral scores (arousal score, avoidance-like score, social memory score and PTSD-like score), suggesting a linear connection between miRNA-based epigenetic modulation and stress-induced phenotypes. Pathway analysis of a miRNA network showed a statistically significant enrichment of molecular processes related to PTSD and stress. In conclusion, our results indicate that PTSD susceptibility/resilience might be shaped by brain-area-dependent modulation of miRNAs targeting FKBP5, BDNF, and other stress-related genes.

Alcohol alters IL-6 Signal Transduction in the CNS of Transgenic Mice with Increased Astrocyte Expression of IL-6

Neuroimmune factors, including the cytokine interleukin-6 (IL-6), are important chemical regulators of central nervous system (CNS) function under both physiological and pathological conditions. Elevated expression of IL-6 occurs in the CNS in a variety of disorders associated with altered CNS function, including excessive alcohol use. Alcohol-induced production of IL-6 has been reported for several CNS regions including the cerebellum. Cerebellar actions of alcohol occur through a variety of mechanisms, but alcohol-induced changes in signal transduction, transcription, and translation are known to play important roles. IL-6 is an activator of signal transduction that regulates gene expression. Thus, alcohol-induced IL-6 production could contribute to cerebellar effects of alcohol by altering gene expression, especially under conditions of chronic alcohol abuse, where IL-6 levels could be habitually elevated. To gain an understanding of the effects of alcohol on IL-6 signal transduction, we studied activation/expression of IL-6 signal transduction partners STAT3 (Signal Transducer and Activator of Transcription), CCAAT-enhancer binding protein (C/EBP) beta, and p42/p44 mitogen-activated protein kinase (MAPK) at the protein level. Cerebella of transgenic mice that express elevated levels of astrocyte produced IL-6 in the CNS were studied. Results show that the both IL-6 and chronic intermittent alcohol exposure/withdrawal affect IL-6 signal transduction partners and that the actions of IL-6 and alcohol interact to alter activation/expression of IL-6 signal transduction partners. The alcohol/IL-6 interactions may contribute to cerebellar actions of alcohol, whereas the effects of IL-6 alone may have relevance to cerebellar changes occurring in CNS disorders associated with elevated levels of IL-6.

ApoE4 activates C/EBPβ/δ-secretase with 27-hydroxycholesterol, driving the pathogenesis of Alzheimer's disease

ApoE4, an apolipoprotein implicated in cholesterol transport and amyloid-β (Aβ) metabolism, is a major genetic risk determinant for Alzheimer's Disease (AD) and drives its pathogenesis via Aβ-dependent and -independent pathways. C/EBPβ, a proinflammatory cytokines-activated transcription factor, is upregulated in AD and mediates cytokines and δ-secretase expression. However, how ApoE4 contributes to AD pathogenesis remains incompletely understood. Here we show that ApoE4 and 27-hydroxycholesterol (27-OHC) co-activate C/EBPβ/δ-secretase signaling in neurons, mediating AD pathogenesis, and this effect is dependent on neuronal secreted Aβ and inflammatory cytokines. Inhibition of cholesterol metabolism with lovastatin diminishes neuronal ApoE4's stimulatory effects. Furthermore, ApoE4 and 27-OHC also mediate lysosomal δ-secretase leakage, activation, secretion and endocytosis. Notably, 27-OHC strongly activates C/EBPβ/δ-secretase pathway in human ApoE4-TR mice and triggers AD pathologies and cognitive deficits, which is blocked by C/EBPβ depletion. Hence, our findings demonstrate that ApoE4 and 27-OHC additively trigger AD pathogenesis via activating C/EBPβ/δ-secretase pathway. Lowering cholesterol levels with statins should benefit the ApoE4 AD carriers.

C/EBPβ/δ-secretase signaling mediates Parkinson's disease pathogenesis via regulating transcription and proteolytic cleavage of α-synuclein and MAOB

Parkinson's disease (PD) is characterized by dopaminergic neuronal loss and the presence of intra-neuronal Lewy body (LB) inclusions with aggregated α-synuclein (α-Syn) as the major component. MAOB, a crucial monoamine oxidase for dopamine metabolism, triggers oxidative stress in dopaminergic neurons and α-Syn aggregation. However, the key molecular mechanism that mediates PD pathogenesis remains elusive. Here we show that C/EBPβ acts as an age-dependent transcription factor for both α-Syn and MAOB, and initiates the PD pathologies by upregulating these two pivotal players, in addition to escalating δ-secretase activity to cleave α-Syn and promotes its neurotoxicity. Overexpression of C/EBPβ in human wild-type α-Syn transgenic mice facilitates PD pathologies and elicits motor disorders associated with augmentation of δ-secretase, α-Syn, and MAOB. In contrast, depletion of C/EBPβ from human α-Syn Tg mice abolishes rotenone-elicited PD pathologies and motor impairments via downregulating the expression of these key factors. Hence, our study supports that C/EBPβ/δ-secretase signaling mediates PD pathogenesis via regulating the expression and cleavage of α-Syn and MAOB.

C/EBPβ is a key transcription factor for APOE and preferentially mediates ApoE4 expression in Alzheimer's disease

The apolipoprotein E ε4 (APOE4) allele is a major genetic risk factor for Alzheimer's disease (AD), and its protein product, ApoE4, exerts its deleterious effects mainly by influencing amyloid-β (Aβ) and Tau (neurofibrillary tangles, NFTs) deposition in the brain. However, the molecular mechanism dictating its expression during ageing and in AD remains incompletely clear. Here we show that C/EBPβ acts as a pivotal transcription factor for APOE and mediates its mRNA levels in an age-dependent manner. C/EBPβ binds the promoter of APOE and escalates its expression in the brain. Knockout of C/EBPβ in AD mouse models diminishes ApoE expression and Aβ pathologies, whereas overexpression of C/EBPβ accelerates AD pathologies, which can be attenuated by anti-ApoE monoclonal antibody or deletion of ApoE via its specific shRNA. Remarkably, C/EBPβ selectively promotes more ApoE4 expression versus ApoE3 in human neurons, correlating with higher activation of C/EBPβ in human AD brains with ApoE4/4 compared to ApoE3/3. Therefore, our data support that C/EBPβ is a crucial transcription factor for temporally regulating APOE gene expression, modulating ApoE4's role in AD pathogenesis.

CCAAT/enhancer binding protein δ is a transcriptional repressor of α-synuclein

α-Synuclein is the main component of Lewy bodies, the intracellular protein aggregates representing the histological hallmark of Parkinson's disease. Elevated α-synuclein levels and mutations in SNCA gene are associated with increased risk for Parkinson's disease. Despite this, little is known about the molecular mechanisms regulating SNCA transcription. CCAAT/enhancer binding protein (C/EBP) β and δ are b-zip transcription factors that play distinct roles in neurons and glial cells. C/EBPβ overexpression increases SNCA expression in neuroblastoma cells and putative C/EBPβ and δ binding sites are present in the SNCA genomic region suggesting that these proteins could regulate SNCA transcription. Based on these premises, the goal of this study was to determine if C/EBPβ and δ regulate the expression of SNCA. We first observed that α-synuclein CNS expression was not affected by C/EBPβ deficiency but it was markedly increased in C/EBPδ-deficient mice. This prompted us to characterize further the role of C/EBPδ in SNCA transcription. C/EBPδ absence led to the in vivo increase of α-synuclein in all brain regions analyzed, both at mRNA and protein level, and in primary neuronal cultures. In agreement with this, CEBPD overexpression in neuroblastoma cells and in primary neuronal cultures markedly reduced SNCA expression. ChIP experiments demonstrated C/EBPδ binding to the SNCA genomic region of mice and humans and luciferase experiments showed decreased expression of a reporter gene attributable to C/EBPδ binding to the SNCA promoter. Finally, decreased CEBPD expression was observed in the substantia nigra and in iPSC-derived dopaminergic neurons from Parkinson patients resulting in a significant negative correlation between SNCA and CEBPD levels. This study points to C/EBPδ as an important repressor of SNCA transcription and suggests that reduced C/EBPδ neuronal levels could be a pathogenic factor in Parkinson's disease and other synucleinopathies and C/EBPδ activity a potential pharmacological target for these neurological disorders.

Activation of MT2 receptor ameliorates dendritic abnormalities in Alzheimer's disease via C/EBPα/miR-125b pathway

Impairments of dendritic trees and spines have been found in many neurodegenerative diseases, including Alzheimer's disease (AD), in which the deficits of melatonin signal pathway were reported. Melatonin receptor 2 (MT2) is widely expressed in the hippocampus and mediates the biological functions of melatonin. It is known that melatonin application is protective to dendritic abnormalities in AD. However, whether MT2 is involved in the neuroprotection and the underlying mechanisms are not clear. Here, we first found that MT2 is dramatically reduced in the dendritic compartment upon the insult of oligomer Aβ. MT2 activation prevented the Aβ-induced disruption of dendritic complexity and spine. Importantly, activation of MT2 decreased cAMP, which in turn inactivated transcriptional factor CCAAT/enhancer-binding protein α(C/EBPα) to suppress miR-125b expression and elevate the expression of its target, GluN2A. In addition, miR-125b mimics fully blocked the protective effects of MT2 activation on dendritic trees and spines. Finally, injection of a lentivirus containing a miR-125b sponge into the hippocampus of APP/PS1 mice effectively rescued the dendritic abnormalities and learning/memory impairments. Our data demonstrated that the cAMP-C/EBPα/miR-125b/GluN2A signaling pathway is important to the neuroprotective effects of MT2 activation in Aβ-induced dendritic injuries and learning/memory disorders, providing a novel therapeutic target for the treatment of AD synaptopathy.

C/EBPβ regulates delta-secretase expression and mediates pathogenesis in mouse models of Alzheimer's disease

Delta-secretase cleaves both APP and Tau to mediate the formation of amyloid plaques and neurofibrillary tangle in Alzheimer’s disease (AD). However, how aging contributes to an increase in delta-secretase expression and AD pathologies remains unclear. Here we show that a CCAAT-enhancer-binding protein (C/EBPβ), an inflammation-regulated transcription factor, acts as a key age-dependent effector elevating both delta-secretase (AEP) and inflammatory cytokines expression in mediating pathogenesis in AD mouse models. We find that C/EBPβ regulates delta-secretase transcription and protein levels in an age-dependent manner. Overexpression of C/EBPβ in young 3xTg mice increases delta-secretase and accelerates the pathological features including cognitive dysfunctions, which is abolished by inactive AEP C189S. Conversely, depletion of C/EBPβ from old 3xTg or 5XFAD mice diminishes delta-secretase and reduces AD pathologies, leading to amelioration of cognitive impairment in these AD mouse models. Thus, our findings support that C/EBPβ plays a pivotal role in AD pathogenesis via increasing delta-secretase expression.

Delta-secretase cleaves both APP and Tau, and contributes to Alzheimer’s disease-like pathology. Here the authors show that C/EBPβ, a regulator of inflammation, also regulates transcription of delta-secretase in an age-dependent manner and contributes to Alzheimer’s disease-like pathology in mouse models.

CCAAT/enhancer binding protein β negatively regulates progesterone receptor expression in human glioblastoma cells

Many progesterone (P4) actions are mediated by its intracellular receptor (PR), which has two isoforms (PR-A and PR-B) differentially transcribed from separate promoters of a single gene. In glioblastomas, the most frequent and aggressive brain tumors, PR-B is the predominant isoform. In an in silico analysis we showed putative CCAAT/Enhancer Binding Protein (C/EBP) binding sites at PR-B promoter. We evaluated the role of C/EBPβ in PR-B expression regulation in glioblastoma cell lines, which expressed different ratios of PR and C/EBPβ isoforms (LAP1, LAP2, and LIP). ChIP assays showed a significant basal binding of C/EBPβ, specific protein 1 (Sp1) and estrogen receptor alpha (ERα) to PR-B promoter. C/EBPβ knockdown increased PR-B expression and treatment with estradiol (E2) reduced C/EBPβ binding to the promoter and up-regulated PR-B expression. P4 induced genes were differently regulated when CEBP/β was silenced. These data show that C/EBPβ negatively regulates PR-B expression in glioblastoma cells.

Axon Regeneration Is Regulated by Ets-C/EBP Transcription Complexes Generated by Activation of the cAMP/Ca2+ Signaling Pathways

The ability of specific neurons to regenerate their axons after injury is governed by cell-intrinsic regeneration pathways. In Caenorhabditis elegans, the JNK and p38 MAPK pathways are important for axon regeneration. Axonal injury induces expression of the svh-2 gene encoding a receptor tyrosine kinase, stimulation of which by the SVH-1 growth factor leads to activation of the JNK pathway. Here, we identify ETS-4 and CEBP-1, related to mammalian Ets and C/EBP, respectively, as transcriptional activators of svh-2 expression following axon injury. ETS-4 and CEBP-1 function downstream of the cAMP and Ca2+-p38 MAPK pathways, respectively. We show that PKA-dependent phosphorylation of ETS-4 promotes its complex formation with CEBP-1. Furthermore, activation of both cAMP and Ca2+ signaling is required for activation of svh-2 expression. Thus, the cAMP/Ca2+ signaling pathways cooperatively activate the JNK pathway, which then promotes axon regeneration.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

An evolving view of epigenetic complexity in the brain

Recent scientific advances have revolutionized our understanding of classical epigenetic mechanisms and the broader landscape of molecular interactions and cellular functions that are inextricably linked to these processes. Our current view of epigenetics includes an increasing appreciation for the dynamic nature of DNA methylation, active mechanisms for DNA demethylation, differential functions of 5-methylcytosine and its oxidized derivatives, the intricate regulatory logic of histone post-translational modifications, the incorporation of histone variants into chromatin, nucleosome occupancy and dynamics, and direct links between cellular signalling pathways and the actions of chromatin 'reader', 'writer' and 'eraser' molecules. We also have an increasing awareness of the seemingly ubiquitous roles played by diverse classes of selectively expressed non-coding RNAs in transcriptional, post-transcriptional, post-translational and local and higher order chromatin modulatory processes. These perspectives are still evolving with novel insights continuing to emerge rapidly (e.g. those related to epigenetic regulation of mobile genetic elements, epigenetic mechanisms in mitochondria, roles in nuclear architecture and 'RNA epigenetics'). The precise functions of these epigenetic factors/phenomena are largely unknown. However, it is unequivocal that they serve as key mediators of brain complexity and flexibility, including neural development and aging, cellular differentiation, homeostasis, stress responses, and synaptic and neural network connectivity and plasticity.

Increased astrocyte expression of IL-6 or CCL2 in transgenic mice alters levels of hippocampal and cerebellar proteins

Emerging research has identified that neuroimmune factors are produced by cells of the central nervous system (CNS) and play critical roles as regulators of CNS function, directors of neurodevelopment and responders to pathological processes. A wide range of neuroimmune factors are produced by CNS cells, primarily the glial cells, but the role of specific neuroimmune factors and their glial cell sources in CNS biology and pathology have yet to be fully elucidated. We have used transgenic mice that express elevated levels of a specific neuroimmune factor, the cytokine IL-6 or the chemokine CCL2, through genetic modification of astrocyte expression to identify targets of astrocyte produced IL-6 or CCL2 at the protein level. We found that in non-transgenic mice constitutive expression of IL-6 and CCL2 occurs in the two CNS regions studied, the hippocampus and cerebellum, as measured by ELISA. In the CCL2 transgenic mice elevated levels of CCL2 were evident in the hippocampus and cerebellum, whereas in the IL-6 transgenic mice, elevated levels of IL-6 were only evident in the cerebellum. Western blot analysis of the cellular and synaptic proteins in the hippocampus and cerebellum of the transgenic mice showed that the elevated levels of CCL2 or IL-6 resulted in alterations in the levels of specific proteins and that these actions differed for the two neuroimmune factors and for the two brain regions. These results are consistent with cell specific profiles of action for IL-6 and CCL2, actions that may be an important aspect of their respective roles in CNS physiology and pathophysiology.

The neurobiology of tetrahydrobiopterin biosynthesis: a model for regulation of GTP cyclohydrolase I gene transcription within nigrostriatal dopamine neurons

Within the brain, the reduced pteridine cofactor 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) is absolutely required for the synthesis of the monoamine (MA) neurotransmitters dopamine (DA), norepinephrine, epinephrine (E), and serotonin (5-HT), the novel gaseous neurotransmitter nitric oxide and the production of yet to be identified 1-O-alkylglycerol-derived lipids. GTP cyclohydrolase I (GTPCH) catalyzes the first and limiting step in the BH4 biosynthetic pathway, which is now thought to involve up to eight different proteins supporting six alternate de novo and two alternate salvage pathways. Gene expression analysis across different regions of the human brain shows the abundance of transcripts coding for all eight of these proteins to be highly correlated with each other and to be enriched within human MA neurons. The potential for multiple routes for BH4 synthesis therefore exists within the human brain. GTPCH expression is particularly heterogeneous across different populations of human and rodent MA-containing neurons, with low expression levels and therefore BH4 being a characteristic of nigrostriatal DA (NSDA) neurons. Basic knowledge of how GCH1 gene transcription is controlled within NSDA neurons may explain the distinctive susceptibility of these neurons to human genetic mutations that result in BH4 deficiency. A model for cyclic adenosine monophosphate-dependent GCH1 transcription is described that involves a unique combination of DNA regulatory sequences and transcription factors. This model proposes that low levels of GCH1 transcription within NSDA neurons are driven by their distinctive physiology, suggesting that pharmacological manipulation of GCH1 gene transcription can be used to modify BH4 levels and therefore DA synthesis in the basal ganglia.

Role of transcription factors in peripheral nerve regeneration

Following axotomy, the activation of multiple intracellular signaling cascades causes the expression of a cocktail of regeneration-associated transcription factors which interact with each other to determine the fate of the injured neurons. The nerve injury response is channeled through manifold and parallel pathways, integrating diverse inputs, and controlling a complex transcriptional output. Transcription factors form a vital link in the chain of regeneration, converting injury-induced stress signals into downstream protein expression via gene regulation. They can regulate the intrinsic ability of axons to grow, by controlling expression of whole cassettes of gene targets. In this review, we have investigated the functional roles of a number of different transcription factors - c-Jun, activating transcription factor 3, cAMP response element binding protein, signal transducer, and activator of transcription-3, CCAAT/enhancer binding proteins β and δ, Oct-6, Sox11, p53, nuclear factor kappa-light-chain-enhancer of activated B cell, and ELK3 - in peripheral nerve regeneration. Studies involving use of conditional mutants, microarrays, promoter region mapping, and different injury paradigms, have enabled us to understand their distinct as well as overlapping roles in achieving anatomical and functional regeneration after peripheral nerve injury.

Identification of the role of C/EBP in neurite regeneration following microarray analysis of a L. stagnalis CNS injury model

Background

Neuronal regeneration in the adult mammalian central nervous system (CNS) is severely compromised due to the presence of extrinsic inhibitory signals and a reduced intrinsic regenerative capacity. In contrast, the CNS of adult Lymnaea stagnalis (L. stagnalis), a freshwater pond snail, is capable of spontaneous regeneration following neuronal injury. Thus, L. stagnalis has served as an animal model to study the cellular mechanisms underlying neuronal regeneration. However, the usage of this model has been limited due to insufficient molecular tools. We have recently conducted a partial neuronal transcriptome sequencing project and reported over 10,000 EST sequences which allowed us to develop and perform a large-scale high throughput microarray analysis.

Results

To identify genes that are involved in the robust regenerative capacity observed in L. stagnalis, we designed the first gene chip covering ~15, 000 L. stagnalis CNS EST sequences. We conducted microarray analysis to compare the gene expression profiles of sham-operated (control) and crush-operated (regenerative model) central ganglia of adult L. stagnalis. The expression levels of 348 genes were found to be significantly altered (p < 0.05) following nerve injury. From this pool, 67 sequences showed a greater than 2-fold change: 42 of which were up-regulated and 25 down-regulated. Our qPCR analysis confirmed that CCAAT enhancer binding protein (C/EBP) was up-regulated following nerve injury in a time-dependent manner. In order to test the role of C/EBP in regeneration, C/EBP siRNA was applied following axotomy of cultured Lymnaea PeA neurons. Knockdown of C/EBP following axotomy prevented extension of the distal, proximal and intact neurites. In vivo knockdown of C/EBP postponed recovery of locomotory activity following nerve crush. Taken together, our data suggest both somatic and local effects of C/EBP are involved in neuronal regeneration.

Conclusions

This is the first high-throughput microarray study in L. stagnalis, a model of axonal regeneration following CNS injury. We reported that 348 genes were regulated following central nerve injury in adult L. stagnalis and provided the first evidence for the involvement of local C/EBP in neuronal regeneration. Our study demonstrates the usefulness of the large-scale gene profiling approach in this invertebrate model to study the molecular mechanisms underlying the intrinsic regenerative capacity of adult CNS neurons.

Neuroadaptive changes in cerebellar neurons induced by chronic exposure to IL-6

IL-6 is an important signaling molecule in the CNS. CNS neurons express IL-6 receptors and their signal transduction molecules, consistent with a role for IL-6 in neuronal physiology. Research indicates that IL-6 levels are low in the normal brain but can be significantly elevated in CNS injury and disease. Relatively little is known about how the elevated levels of IL-6 affect neurons. In the current study we show that under conditions of chronic exposure, IL-6 induces alterations in the level of protein expression in developing CNS cells. Such changes may play a role in the altered CNS function observed in CNS conditions associated with elevated levels of IL-6 in the CNS.

Expression analysis of prestin and selected transcription factors in newborn rats

Transcription factors (TFs) have a central role to play in regulating gene expression. To analyze the co-expression patterns of selected TFs with the motor protein prestin of the outer hair cells, we applied an real-time PCR approach combining several kinds of information: (i) expression changes during postnatal development, (ii) expression changes by exposure of organotypic cultures of the organ of Corti to factors which significantly affect prestin expression [thyroid hormone (T4), retinoic acid (RA), butyric acid (BA), increased KCl concentration] and (iii) changes along the apical-basal gradient. We found that the mRNA levels of the TF Brn-3c (Pou4f3), a member of the POU family, are significantly associated with the regulation of prestin during postnatal development and in cultures supplemented with T4 (0.5 μM), BA (0.5-2.0 mM), and high KCl (50 mM) concentration. The mRNA level of the constitutively active TF C/ebpb (CCAAT/enhancer binding protein beta) correlates positively with the prestin expression during postnatal development and in cultures exposed to T4 and RA (50-100 μM). The mRNA levels of the calcium-dependent TF CaRF correlates significantly with the prestin expression in cultures exposed to T4 and high KCl concentration. The observed coexpression patterns may suggest that the TFs Brn-3c, C/ebpb, and Carf contribute to regulating the expression of prestin under the investigated conditions.

Bioluminescence imaging of the brain response to acute inflammation in living C/EBP reporter mice

The transcription factor CCAAT enhancer binding protein (C/EBP) is a key regulator of inflammation and immune responses, and recent studies suggest it is involved in inflammatory processes in the nervous system. We generated a transgenic reporter mouse model, carrying the luciferase (luc) gene under the transcriptional control of C/EBP, for visualising C/EBP activity in vivo. Real-time bioluminescence imaging reflecting C/EBP activity was performed in an acute inflammation model, after systemic administration of lipopolysaccharides (LPS), in C/EBP-luc mice. A striking activity of C/EBP was imaged predominantly in the brain of living C/EBP-luc mice in response to LPS, showing for the first time in vivo that C/EBP mediates the brain response to inflammation. Furthermore, dexamethasone, a potent anti-inflammatory agent, diminished the LPS-induced C/EBP activity demonstrating the physiological regulation of bioluminescence intensity in the brain of C/EBP-luc mice. Our results implicate that C/EBP reporter mice have the potential to be a valuable tool for studies on the mechanisms of brain inflammation in vivo and for the noninvasive preclinical evaluation of therapeutic agents targeting neuroinflammatory diseases.

Genome-wide gene expression and promoter binding analysis identifies NFIL3 as a repressor of C/EBP target genes in neuronal outgrowth

NFIL3 (nuclear factor IL-3 regulated) is a multifunctional transcription factor implicated in a wide range of physiological processes, including cellular survival, circadian gene expression and natural killer cell development. We recently demonstrated that NFIL3 acts as a repressor of CREB-induced gene expression underlying the regeneration of axotomized DRG sensory neurons. In this study we performed chromatin immunoprecipitation assays combined with microarray technology (ChIP-chip) to reveal direct NFIL3 and CREB target genes in an in vitro cell model for regenerating DRG neurons. We identified 505 promoter regions bound by NFIL3 and 924 promoter regions bound by CREB. Based on promoter analysis of NFIL3-bound genes, we were able to redefine the NFIL3 consensus-binding motif. Histone H3 acetylation profiling and gene expression microarray analysis subsequently indicated that a large fraction (>60%) of NFIL3 target genes were transcriptionally silent, whereas CREB target genes in general were transcriptionally active. Only a small subset of NFIL3 target genes also bound CREB. Computational analysis indicated that a substantial number of NFIL3 target genes share a C/EBP (CCAAT/Enhancer Binding Protein) DNA binding motif. ChIP analysis confirmed binding of C/EBPs to NFIL3 target genes, and knockdown of C/EBPα, C/EBPβ and C/EBPδ, but not C/EBPγ, significantly reduced neurite outgrowth in vitro. Together, our findings show that NFIL3 is a general feed-forward repressor of basic leucine zipper transcription factors that control neurite outgrowth.

ChIP-chip analysis of neurexins and other candidate genes for addiction and neuropsychiatric disorders

Several addiction susceptibility genes have been mapped by linkage and genomewide association. However, functional alleles associated with disease risk have not been identified, with a few possible exceptions. In addition, little is known about the cis- and trans-acting factors involved in regulating their expression. To address these issues, we used a ChIP-chip approach to identify regulatory elements in fetal-brain- targeting genes implicated in addiction and other neuropsychiatric conditions. Our data point to a number of putative regulatory elements, several of which, we show, are functionally significant. Many established or putative regulatory elements map near-disease-associated SNPs. These regions would be of interest to survey for patient-specific functional variants involved in disease susceptibility.