Changes in DNA binding pattern of transcription factor YY1 in neuronal degeneration

Ying Yang 1 engagement in brain pathology

Herein, we discuss data concerning the involvement of transcription factor Yin Yang 1 (YY1) in the development of brain diseases, highlighting mechanisms of its pathological actions. YY1 plays an important role in the developmental and adult pathology of the nervous system. YY1 is essential for neurulation as well as maintenance and differentiation of neuronal progenitor cells and oligodendrocytes regulating both neural and glial tissues of the brain. Lack of a YY1 gene causes many developmental abnormalities and anatomical malformations of the central nervous system (CNS). Once dysregulated, YY1 exerts multiple neuropathological actions being involved in the induction of many brain disorders like stroke, epilepsy, Alzheimer's and Parkinson's diseases, autism spectrum disorder, dystonia, and brain tumors. Better understanding of YY1's dysfunction in the nervous system may lead to the development of novel therapeutic strategies related to YY1's actions.

Discovery of Transcription Factors Novel to Mouse Cerebellar Granule Cell Development Through Laser-Capture Microdissection

Laser-capture microdissection was used to isolate external germinal layer tissue from three developmental periods of mouse cerebellar development: embryonic days 13, 15, and 18. The cerebellar granule cell-enriched mRNA library was generated with next-generation sequencing using the Helicos technology. Our objective was to discover transcriptional regulators that could be important for the development of cerebellar granule cells-the most numerous neuron in the central nervous system. Through differential expression analysis, we have identified 82 differentially expressed transcription factors (TFs) from a total of 1311 differentially expressed genes. In addition, with TF-binding sequence analysis, we have identified 46 TF candidates that could be key regulators responsible for the variation in the granule cell transcriptome between developmental stages. Altogether, we identified 125 potential TFs (82 from differential expression analysis, 46 from motif analysis with 3 overlaps in the two sets). From this gene set, 37 TFs are considered novel due to the lack of previous knowledge about their roles in cerebellar development. The results from transcriptome-wide analyses were validated with existing online databases, qRT-PCR, and in situ hybridization. This study provides an initial insight into the TFs of cerebellar granule cells that might be important for development and provide valuable information for further functional studies on these transcriptional regulators.

Assembly and interrogation of Alzheimer's disease genetic networks reveal novel regulators of progression

Alzheimer's disease (AD) is a complex multifactorial disorder with poorly characterized pathogenesis. Our understanding of this disease would thus benefit from an approach that addresses this complexity by elucidating the regulatory networks that are dysregulated in the neural compartment of AD patients, across distinct brain regions. Here, we use a Systems Biology (SB) approach, which has been highly successful in the dissection of cancer related phenotypes, to reverse engineer the transcriptional regulation layer of human neuronal cells and interrogate it to infer candidate Master Regulators (MRs) responsible for disease progression. Analysis of gene expression profiles from laser-captured neurons from AD and controls subjects, using the Algorithm for the Reconstruction of Accurate Cellular Networks (ARACNe), yielded an interactome consisting of 488,353 transcription-factor/target interactions. Interrogation of this interactome, using the Master Regulator INference algorithm (MARINa), identified an unbiased set of candidate MRs causally responsible for regulating the transcriptional signature of AD progression. Experimental assays in autopsy-derived human brain tissue showed that three of the top candidate MRs (YY1, p300 and ZMYM3) are indeed biochemically and histopathologically dysregulated in AD brains compared to controls. Our results additionally implicate p53 and loss of acetylation homeostasis in the neurodegenerative process. This study suggests that an integrative, SB approach can be applied to AD and other neurodegenerative diseases, and provide significant novel insight on the disease progression.

Transcriptional Response of Polycomb Group Genes to Status Epilepticus in Mice is Modified by Prior Exposure to Epileptic Preconditioning

Exposure of the brain to brief, non-harmful seizures can activate protective mechanisms that temporarily generate a damage-refractory state. This process, termed epileptic tolerance, is associated with large-scale down-regulation of gene expression. Polycomb group (PcG) proteins are master controllers of gene silencing during development that are re-activated by injury to the brain. Here, we explored the transcriptional response of genes associated with polycomb repressive complex (PRC) 1 (Ring1A, Ring1B, and Bmi1) and PRC2 (Ezh1, Ezh2, and Suz12), as well as additional transcriptional regulators Sirt1, Yy1, and Yy2, in a mouse model of status epilepticus (SE). Findings were contrasted to changes after SE in mice previously given brief seizures to evoke tolerance. Real-time quantitative PCR showed SE prompted an early (1 h) increase in expression of several genes in PRC1 and PRC2 in the hippocampus, followed by down-regulation of many of the same genes at later times points (4, 8, and 24 h). Spatio-temporal differences were found among PRC2 genes in epileptic tolerance, including increased expression of Ezh2, Suz12, and Yy2 relative to the normal injury response to SE. In contrast, PRC1 complex genes including Ring 1B and Bmi1 displayed differential down-regulation in epileptic tolerance. The present study characterizes PcG gene expression following SE and shows prior seizure exposure produces select changes to PRC1 and PRC2 composition that may influence differential gene expression in epileptic tolerance.

Yin Yang 1 is a repressor of glutamate transporter EAAT2, and it mediates manganese-induced decrease of EAAT2 expression in astrocytes

Impairment of astrocytic glutamate transporter (GLT-1; EAAT2) function is associated with multiple neurodegenerative diseases, including Parkinson's disease (PD) and manganism, the latter being induced by chronic exposure to high levels of manganese (Mn). Mn decreases EAAT2 promoter activity and mRNA and protein levels, but the molecular mechanism of Mn-induced EAAT2 repression at the transcriptional level has yet to be elucidated. We reveal that transcription factor Yin Yang 1 (YY1) is critical in repressing EAAT2 and mediates the effects of negative regulators, such as Mn and tumor necrosis factor alpha (TNF-α), on EAAT2. YY1 overexpression in astrocytes reduced EAAT2 promoter activity, while YY1 knockdown or mutation of the YY1 consensus site of the EAAT2 promoter increased its promoter activity and attenuated the Mn-induced repression of EAAT2. Mn increased YY1 promoter activity and mRNA and protein levels via NF-κB activation. This led to increased YY1 binding to the EAAT2 promoter region. Epigenetically, histone deacetylase (HDAC) classes I and II served as corepressors of YY1, and, accordingly, HDAC inhibitors increased EAAT2 promoter activity and reversed the Mn-induced repression of EAAT2 promoter activity. Taken together, our findings suggest that YY1, with HDACs as corepressors, is a critical negative transcriptional regulator of EAAT2 and mediates Mn-induced EAAT2 repression.

Yin yang 1 directly regulates the transcription of RE-1 silencing transcription factor

The RE-1 silencing transcription factor (REST) is a master transcription factor that plays a critical role in embryo development, especially during the process of neurogenesis and neural plasticity. However, the mechanism of REST gene transcription regulation is still an open question. Here, by combining bioinformatics analysis and experimental studies, we report that the transcription factor Yin Yang 1 (YY1) bound to a conserved YY1 binding site in the promoter of the mouse REST gene and positively regulated activity of this promoter in SH-SY5Y cells. Furthermore, analysis of microarray data revealed a significant correlation between the expression of YY1 and REST genes. Overall, this study suggests that YY1 directly regulates expression of the REST gene.

The Yin and Yang of YY1 in the nervous system

The transcription factor Yin Yang 1 (YY1) is a multifunctional protein that can activate or repress gene expression depending on the cellular context. YY1 is ubiquitously expressed and highly conserved between species. However, its role varies in diverse cell types and includes proliferation, differentiation, and apoptosis. This review will focus on the function of YY1 in the nervous system including its role in neural development, neuronal function, developmental myelination, and neurological disease. The multiple functions of YY1 in distinct cell types are reviewed and the possible mechanisms underlying the cell specificity for these functions are discussed.

Glutamate‐dependent transcriptional regulation of GLAST/EAAT1: a role for YY1

Glutamate is the major excitatory transmitter in the vertebrate brain and its extracellular levels are tightly regulated to prevent excitotoxic effects. The Na(+)-dependent glutamate/aspartate transporter GLAST/EAAT1 is regulated in the short and in the long term by glutamate. A receptors-independent change in its membrane translocation rate, accounts for an acute modulation in GLAST/EAAT1 transport. In contrast, activation of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate subtype of glutamate receptors represses the transcription of the chick glast gene. A glutamate responsive element has been mapped to the promoter region of this gene containing a bonafide binding site for the transcription factor Ying-Yang 1. Using cultured chick cerebellar Bergmann glia cells, glutamate elicited a time and dose-dependent increase in Ying-Yang 1 DNA binding consistent with the negative response generated in a reporter gene construct controlled for Ying-Yang 1. Over-expression of this transcription factor leads to a substantial reduction in GLAST/EAAT1 transporter uptake and an important decrease in mRNA levels, all associated with the transcriptional repression of the chick glast promoter activity. These results provide evidence for an involvement of Ying-Yang 1 in the transcriptional response to glutamate in glial cells and favor the notion of a relevant role of this factor in GLAST/EAAT1 transcriptional control.

Cloning and expression analysis of YY1AP-related protein in the rat brain

YY1AP-related protein (YARP) is a structural homolog of YY1AP, a transcriptional coactivator of the multifunctional transcription factor YY1. We cloned a rat YARP cDNA that encoded a 2256 amino acid protein with 93% homology to the human counterpart. Northern blots revealed significant expression of the YARP gene in the rat brain. In situ hybridization demonstrated its expression in neurons throughout the brain, including pyramidal cells in the cerebral cortex and hippocampus and granule cells in the dentate gyrus. YARP was coexpressed with YY1 in these same neuronal cells. However, there was no evidence of YARP expression in glia. In the developing rat brain, the level of YARP mRNA ( approximately 10 kb) peaked at embryonic day 18 and promptly declined thereafter to reach the steady-state level found in adulthood, by 14 days after birth. These results suggest that YARP functions at a late stage of neurogenesis during perinatal development of the rat brain, as well as in mature neurons.

Transcriptional and translational regulation of BACE1 expression--implications for Alzheimer's disease

The proteolytical processing of the amyloid precursor protein (APP) gives rise to beta-amyloid peptides, which accumulate in brains of Alzheimer's disease (AD) patients. Different soluble or insoluble higher molecular weight forms of beta-amyloid peptides have been postulated to trigger a complex pathological cascade that may cause synaptic dysfunction, inflammatory processes, neuronal loss, cognitive impairment, and finally the onset of the disease. The generation of beta-amyloid peptides requires the proteolytical cleavage of APP by an aspartyl protease named beta-site APP-cleaving enzyme 1 (BACE1). The expression and enzymatic activity of BACE1 are increased in brains of AD patients. Here we discuss the importance of a number of recently identified transcription factors as well as post-transcriptional modifications and activation of intracellular signaling molecules for the regulation of BACE1 expression in brain. Importantly, some of these factors are known to be involved in the inflammatory and chronic stress responses of the brain, which are compromised during aging. Moreover, recent evidence indicates that beneficial effects of non-steriodal anti-inflammatory drugs on the progression of AD are mediated--at least in part--by effects on the peroxisome proliferator-activated receptor-gamma response element present in the BACE1 promoter. The identification of the cell type-specific expression and activation of NF-kappaB, Sp1 and YY1 transcription factors may provide a basis to specifically interfere with BACE1 expression and, thereby, to lower the concentrations of beta-amyloid peptides, which may prevent neuronal cell loss and cognitive decline in AD patients.

The transcription factor Yin Yang 1 is an activator of BACE1 expression

The beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is a prerequisite for the generation of beta-amyloid peptides, the principle constituents of senile plaques in the brains of patients with Alzheimer's disease (AD). BACE1 expression and enzymatic activity are increased in the AD brain, but the regulatory mechanisms of BACE1 expression are largely unknown. Here we show that Yin Yang 1 (YY1), a highly conserved and multifunctional transcription factor, binds to its putative recognition sequence within the BACE1 promoter and stimulates BACE1 promoter activity in rat pheochromocytoma 12 (PC12) cells, rat primary neurones and astrocytes. In rat brain YY1 and BACE1 are widely expressed by neurons, but there was only a minor proportion of neurones that co-expressed YY1 and BACE1, suggesting that YY1 is not required for constitutive neuronal BACE1 expression. Resting astrocytes in the untreated rat brain did not display either YY1 or BACE1 immunoreactivity. When chronically activated, however, astrocytes expressed both YY1 and BACE1 proteins, indicating that YY1 is important for the stimulated BACE1 expression by reactive astrocytes. This is further emphasized by the expression of YY1 and BACE1 by reactive astrocytes in proximity to beta-amyloid plaques in the AD brain. Our observations suggest that interfering with expression, translocation or binding of YY1 to its BACE1 promoter-specific sequence may have therapeutic potential for treating patients with AD.