Overexpression of transcription factor BACH1 in fetal Down syndrome brain

CAPE and its synthetic derivative VP961 restore BACH1/NRF2 axis in Down Syndrome

The cells possess several mechanisms to counteract the over-production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), including enzymes such as superoxide dismutase, catalase and glutathione peroxidase. Moreover, an important sensor involved in the anti-oxidant response is KEAP1-NRF2-ARE signaling complex. Under oxidative stress (OS), the transcription factor NRF2 can dissociate from the KEAP1-complex in the cytosol and translocate into the nucleus to promote the transcriptional activation of anti-oxidant genes, such as heme oxygenase 1 and NADPH quinone oxidoreductase. Within this context, the activation of NRF2 response is further regulated by BACH1, a transcription repressor, that compete with the KEAP1-NRF2-ARE complex. In this work, we focused on the role of BACH1/NRF2 ratio in the regulation of the anti-oxidant response, proposing their antithetical relation as a valuable target for a therapeutic strategy to test drugs able to exert neuroprotective effects, notably in aging and neurodegenerative diseases. Among these, Down syndrome (DS) is a complex genetic disorder characterized by BACH1 gene triplication that likely results in the impairment of NRF2 causing increased OS. Our results revealed that BACH1 overexpression alters the BACH1/NRF2 ratio in the nucleus and disturbs the induction of antioxidant response genes ultimately resulting in the accumulation of oxidative damage both in Ts2Cje mice (a mouse model of DS) and human DS lymphoblastoid cell lines (LCLs). Based on this evidence, we tested Caffeic Acid Phenethyl Ester (CAPE) and the synthetic analogue VP961, which have been proven to modulate NRF2 activity. We showed that CAPE and VP961 administration to DS LCLs was able to promote NRF2 nuclear translocation, which resulted in the amelioration of antioxidant response. Overall, our study supports the hypothesis that BACH1 triplication in DS subjects is implicated in the alteration of redox homeostasis and therapeutic strategies to overcome this effect are under investigation in our laboratory.

[Differential expression profile of miRNAs in amniotic fluid exosomes from fetuses with Down syndrome]

OBJECTIVE

To investigate the role of miRNAs in amniotic fluid exosomes in growth and development of fetuses with Down syndrome (DS).

METHODS

Amniotic fluid were collected from 20 fetuses with DS and 20 normal fetuses (control) to extract amniotic exosome miRNA. MicroRNA sequencing technique was used to identify the differentially expressed miRNAs between the two groups, for which gene ontology (GO) and pathway analysis was performed. Three differentially expressed miRNAs with the strongest correlation with DS phenotype were selected for qPCR verification. Dual luciferase reporter assay was used to verify the activity of let-7d-5p for targeted regulation of BACH1.

RESULTS

We identified 15 differentially expressed miRNAs in DS as compared with the control group, among which 7 miRNAs were up-regulated and 8 were down-regulated. Target gene prediction results showed that the differentially expressed miRNAs targeted 17 DS-related genes. GO analysis revealed that the main functions of the target genes involved protein binding, protein transport, ATP binding, transferase activity and synapses. Pathway analysis revealed that the functional pathways were closely related with the development of the nervous system. qPCR results showed that the expression levels of miR-140-3p and let-7d-5p were significantly lower in DS group than in the control group (P < 0.05), as was consistent with miRNA sequencing results; the expression level of miR-4512 was significantly higher in DS group than in control group (P < 0.05), which was contrary to miRNA sequencing results. The results of double luciferase reporter gene assay confirmed that let-7d-5p was capable of targeted regulation of BACH1 expression.

CONCLUSION

Let-7d-5p in amniotic fluid exosomes may promote oxidative stress events in the brain of fetuses with DS by regulating BACH1 expression.

The BACH1/Nrf2 Axis in Brain in Down Syndrome and Transition to Alzheimer Disease-Like Neuropathology and Dementia

Down syndrome (DS) is the most common genetic cause of intellectual disability that is associated with an increased risk to develop early-onset Alzheimer-like dementia (AD). The brain neuropathological features include alteration of redox homeostasis, mitochondrial deficits, inflammation, accumulation of both amyloid beta-peptide oligomers and senile plaques, as well as aggregated hyperphosphorylated tau protein-containing neurofibrillary tangles, among others. It is worth mentioning that some of the triplicated genes encoded are likely to cause increased oxidative stress (OS) conditions that are also associated with reduced cellular responses. Published studies from our laboratories propose that increased oxidative damage occurs early in life in DS population and contributes to age-dependent neurodegeneration. This is the result of damaged, oxidized proteins that belong to degradative systems, antioxidant defense system, neuronal trafficking. and energy metabolism. This review focuses on a key element that regulates redox homeostasis, the transcription factor Nrf2, which is negatively regulated by BACH1, encoded on chromosome 21. The role of the Nrf2/BACH1 axis in DS is under investigation, and the effects of triplicated BACH1 on the transcriptional regulation of Nrf2 are still unknown. In this review, we discuss the physiological relevance of BACH1/Nrf2 signaling in the brain and how the dysfunction of this system affects the redox homeostasis in DS neurons and how this axis may contribute to the transition of DS into DS with AD neuropathology and dementia. Further, some of the evidence collected in AD regarding the potential contribution of BACH1 to neurodegeneration in DS are also discussed.

Chronic PERK induction promotes Alzheimer-like neuropathology in Down syndrome: Insights for therapeutic intervention

A major challenge in neurobiology is the identification of the mechanisms by which protein misfolding leads to cellular toxicity. Many neurodegenerative disorders, in which aberrant protein conformers aggregate into pathological inclusions, present the chronic activation of the PERK branch of the unfolded protein response. The adaptive effects of the PERK pathway include reduction of translation by transient inhibition of eIF2α and antioxidant protein production via induction of Nrf2 transcription factor. In contrast, PERK prolonged activation leads to sustained reduction in protein synthesis and induction of cell death pathways. To further investigate the role of the PERK pathway in neurodegenerative disorders, we focused on Down syndrome (DS), in which aging confers a high risk of Alzheimer disease (AD). By investigating human DS frontal cortices, we found early and sustained PERK activation associated with the induction of eIF2α and ATF4 downstream signals. We also observed that the Nrf2 response is uncoupled from PERK and its antioxidant effects are repressed in a mechanism implicating the transcription repressor Bach1. The pharmacological inhibition of PERK in DS mice reduced eIF2α-related translational repression and promoted Nrf2 nuclear translocation, favoring the rescue of Nrf2/Bach1 imbalance. The further analysis of peripheral cells from living DS individuals provided strong support of the pathological link between PERK and trisomy 21. Our results suggest that failure to regulate the PERK pathway is a peculiar characteristic of DS pathology and it may represent an essential step to promote cellular dysfunction, which actively contributes in the brain to the early development of AD.

MicroRNA-98-5p ameliorates oxygen-glucose deprivation/reoxygenation (OGD/R)-induced neuronal injury by inhibiting Bach1 and promoting Nrf2/ARE signaling

MicroRNA-98-5p (miR-98-5p) is a stress-related microRNA (miRNA) that plays an important role in regulating cell survival, apoptosis, and oxidative stress in multiple cell types and diseases. However, little is known about the role of miR-98-5p in cerebral ischemia/reperfusion injury. In this study, we investigated the role and mechanism of miR-98-5p in regulating neuronal injury induced by oxygen-glucose deprivation/reoxygenation (OGD/R), an in vitro model of cerebral ischemia/reperfusion injury. We found that miR-98 expression was significantly altered in neurons in response to OGD/R treatment. Functional experiments showed that overexpression of miR-98-5p inhibited OGD/R-induced apoptosis and reactive oxygen species (ROS) production in neurons, whereas inhibition of miR-98-5p showed the opposite effect. Interestingly, bioinformatics analysis predicted that BTB and CNC homology 1 (Bach1) was a potential target gene of miR-98-5p, that was verified by dual-luciferase reporter assay. Moreover, overexpression of miR-98-5p inhibited Bach1 expression while suppression of miR-98-5p promoted Bach1 expression in neurons. Notably, miR-98-5p was shown to regulate the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the activity of the antioxidant response element (ARE). However, overexpression of Bach1 or silencing of Nrf2 significantly abolished the miR-98-5p-mediated neuroprotective effect. Overall, these results demonstrate that miR-98-5p ameliorates OGD/R-induced neuronal injury in vitro through targeting to promote activation of Nrf2/ARE signaling. Our study suggests that miR-98-5p may play a potential role in cerebral ischemia/reperfusion injury and represents a potential therapeutic target for neuroprotection.

Bach1 overexpression in Down syndrome correlates with the alteration of the HO-1/BVR-a system: insights for transition to Alzheimer's disease

Bach1, among the genes encoded on chromosome 21, is a transcription repressor, which binds to antioxidant response elements of DNA thus inhibiting the transcription of specific genes involved in the cell stress response including heme oxygenase-1 (HO-1). HO-1 and its partner, biliverdin reductase-A (BVR-A), are upregulated in response to oxidative stress in order to protect cells against further damage. Since oxidative stress is an early event in Down syndrome (DS) and might contribute to the development of multiple deleterious DS phenotypes, including Alzheimer's disease (AD) pathology, we investigated the status of the Bach1/HO-1/BVR-A axis in DS and its possible implications for the development of AD. In the present study, we showed increased total Bach1 protein levels in the brain of all DS cases coupled with reduced induction of brain HO-1. Furthermore, increased oxidative stress could, on one hand, overcome the inhibitory effects of Bach1 and, on the other hand, promote BVR-A impairment. Our data show that the development of AD in DS subjects is characterized by (i) increased Bach1 total and poly-ubiquitination; (ii) increased HO-1 protein levels; and (iii) increased nitration of BVR-A followed by reduced activity. To corroborate our findings, we analyzed Bach1, HO-1, and BVR-A status in the Ts65Dn mouse model at 3 (young) and 15 (old) months of age. The above data support the hypothesis that the dysregulation of HO-1/BVR-A system contributes to the early increase of oxidative stress in DS and provide potential mechanistic paths involved in the neurodegenerative process and AD development.

Defective thymic progenitor development and mature T-cell responses in a mouse model for Down syndrome

In addition to archetypal cognitive defects, Down syndrome (DS) is characterized by altered lymphocyte development and function, including premature thymic involution and increased incidence of infections. However, the potential mechanisms for these changes have not been fully elucidated. The current study used the Ts65Dn mouse model of DS to assess deficiencies in T-cell development and possible molecular alterations. Ts65Dn mice exhibited premature thymic involution and a threefold to fourfold decrease in the number and proportion of immature, double-negative thymocyte progenitors. In addition, there were twofold fewer double-positive and CD4 single-positive thymocytes in Ts65Dn thymuses. Reflecting this deficient thymic function, there were fewer naive T cells in the spleen and polyclonal stimulation of peripheral T cells exhibited a marked reduction in proliferation, suggesting a senescent phenotype. In contrast, B-cell progenitors were unchanged in the bone marrow of Ts65Dn mice, but in the spleen, there were decreased transitional and follicular B cells and these cells proliferated less upon antigen receptor stimulus but not in response to lipopolysaccharide. As a potential mechanism for diminished thymic function, immature thymocyte populations expressed diminished levels of the cytokine receptor interleukin-7Rα, which was associated with decreased proliferation and increased apoptosis. Increased oxidative stress and inhibition of the Notch pathway were identified as possible mediators of decreased interleukin-7Rα expression in Ts65Dn mice. The data suggest that immature thymocyte defects underlie immune dysfunction in DS and that increased oxidative stress and reduced cytokine signalling may alter lymphocyte development in Ts65Dn mice.

Down syndrome: the brain in trisomic mode

Down syndrome is the most common form of intellectual disability and results from one of the most complex genetic perturbations that is compatible with survival, trisomy 21. The study of brain dysfunction in this disorder has largely been based on a gene discovery approach, but we are now moving into an era of functional genome exploration, in which the effects of individual genes are being studied alongside the effects of deregulated non-coding genetic elements and epigenetic influences. Also, new data from functional neuroimaging studies are challenging our views of the cognitive phenotypes associated with Down syndrome and their pathophysiological correlates. These advances hold promise for the development of treatments for intellectual disability.

Identification of rare X-linked neuroligin variants by massively parallel sequencing in males with autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is highly heritable, but the genetic risk factors for it remain largely unknown. Although structural variants with large effect sizes may explain up to 15% ASD, genome-wide association studies have failed to uncover common single nucleotide variants with large effects on phenotype. The focus within ASD genetics is now shifting to the examination of rare sequence variants of modest effect, which is most often achieved via exome selection and sequencing. This strategy has indeed identified some rare candidate variants; however, the approach does not capture the full spectrum of genetic variation that might contribute to the phenotype.

METHODS

We surveyed two loci with known rare variants that contribute to ASD, the X-linked neuroligin genes by performing massively parallel Illumina sequencing of the coding and noncoding regions from these genes in males from families with multiplex autism. We annotated all variant sites and functionally tested a subset to identify other rare mutations contributing to ASD susceptibility.

RESULTS

We found seven rare variants at evolutionary conserved sites in our study population. Functional analyses of the three 3' UTR variants did not show statistically significant effects on the expression of NLGN3 and NLGN4X. In addition, we identified two NLGN3 intronic variants located within conserved transcription factor binding sites that could potentially affect gene regulation.

CONCLUSIONS

These data demonstrate the power of massively parallel, targeted sequencing studies of affected individuals for identifying rare, potentially disease-contributing variation. However, they also point out the challenges and limitations of current methods of direct functional testing of rare variants and the difficulties of identifying alleles with modest effects.

Regulation of APC development, immune response, and autoimmunity by Bach1/HO-1 pathway in mice

APCs are essential for innate and adaptive immunity as well as self-immune tolerance. Here, we show that the Cap'n'collar member Bach1 regulates the generation of APCs, specifically macrophages and dendritic cells, in mice. The impaired APC development in Bach1(-/-) mice was accompanied by defects in downstream T-cell responses and partial protection from experimental autoimmune encephalomyelitis. Genomewide analyses identified a panel of Bach1 target genes and ablation of the direct Bach1 target gene HO-1 exacerbated the impaired APC development observed in Bach1(-/-) mice. This was attributed to the impaired ability of HO-1(-/-)Bach1(-/-) double mutants to produce upstream APC progenitor cells, including common myeloid progenitor (CMP)-Flk2(+). By contrast, we observed an increase in hematopoietic stem-progenitor cells (HSPCs) in these mice, suggesting a developmental block in the progression of HSPCs to CMP-Flk2(+) and subsequently APCs.

Genomic determinants in the phenotypic variability of Down syndrome

Down syndrome caused by trisomy 21 is a collection of phenotypes with variable expressivity and penetrance. The significant advances in exploring the human genome now provide the tools to better understand the contribution of trisomy 21 in the different manifestations of Down syndrome, and the functional links between the genome variability and the phenotypic variability.

Trisomy 21 and Down syndrome: a short review

Even though the molecular mechanisms underlying the Down syndrome (DS) phenotypes remain obscure, the characterization of the genes and conserved non-genic sequences of HSA21 together with large-scale gene expression studies in DS tissues are enhancing our understanding of this complex disorder. Also, mouse models of DS provide invaluable tools to correlate genes or chromosome segments to specific phenotypes. Here we discuss the possible contribution of HSA21 genes to DS and data from global gene expression studies of trisomic samples.

Mass-spectrometrical analysis of proteins encoded on chromosome 21 in human fetal brain

Overexpression of chromosome 21 genes is directly or indirectly responsible for the Down syndrome phenotype. In order to analyse chromosome 21 gene products (Chr21Ps), we extracted proteins from fetal human brain cortex and applied an ultracentrifugal and chromatographic prefractionation principle followed by two-dimensional gel electrophoresis (2-DE) and mass-spectrometrical analysis using high-throughput automated MALDI-TOF/TOF. Nine Chr21Ps were identified: pyridoxal kinase; superoxide dismutase [Cu/Zn] 1; carbonyl reductase 1; ES1 protein homolog, mitochondrial [Precursor]; cystathionine-beta-synthetase; T-complex protein 1, theta subunit; cystatin B; 6-phosphofructokinase; glycinamide ribonucleotide synthetase. Mass-spectrometric characterisation of Chr21Ps following separation in 2-DE gels is a useful tool for the analysis of these structures in brain, independent of antibody availability and specificity.

Gene-dosage effect on chromosome 21 transcriptome in trisomy 21: implication in Down syndrome cognitive disorders

In the era of human functional genomics, the chromosome 21 has represented a prototype for pioneering global biotechnologies. Its relatively low gene content enabled studying Down syndrome at the chromosomal scale, for which the last years have seen intense research activity aiming at genotype-phenotype correlations. The global gene-dose dependent upregulation of gene expression seen in the context of trisomy and preliminary functional annotation of chromosome 21 genes points towards candidate genes and molecular pathways potentially associated with the cognitive defects observed in Down syndrome.

Extravasation of plasma proteins can confound interpretation of proteomic studies of brain: A lesson from apo A-I in mesial temporal lobe epilepsy

Apolipoprotein A-I (apo A-I), a major component of high density lipoproteins, has been shown to be involved in lipid metabolism, cholesterol homeostasis and degeneration/regeneration of brain tissues and was proposed as a useful marker for the extent and severity of CNS injury. We searched for aberrant protein expression in hippocampus from patients with mesial temporal lobe epilepsy (MTLE) by an analytical method based on two-dimensional gel electrophoresis coupled with mass spectrometry (MALDI-TOF/TOF) and unambiguously identified 2 spots as apolipoprotein A-I forms in brain of MTLE patients with 7.5-fold increased levels (controls: 0.046 +/- 0.046; MTLE patients: 0.343 +/- 0.154, mean +/- SD, P = 0.003). Western blot analysis confirmed increased apo A-I levels in MTLE. Immunohistochemistry detected staining for apo A-I extracellularly in perivasal brain parenchyma, neuropil and areas with increased glial fibrillary acidic protein (GFAP) expression as well as some pyramidal neurons and subpial astrocytes. These findings indicate that the increase of apo A-I in MTLE was possibly not reflecting a pathogenetic role but was rather due to extravasates, bleedings or increase of microvascular endothelial cells known to synthesize apo A-I. Care has to be taken when protein expressional findings are to be interpreted in the presence of plasma proteins, including apo A-I, thus clearly representing a confounding factor.

Aberrant protein expression of transcription factors BACH1 and ERG, both encoded on chromosome 21, in brains of patients with Down syndrome and Alzheimer’s disease

Down syndrome (DS; trisomy 21) is a genetic disorder associated with early mental retardation and patients inevitably develop Alzheimer's disease (AD)-like neuropathological changes. The molecular defects underlying the DS-phenotype may be due to overexpression of genes encoded on chromosome 21. This so-called gene dosage hypothesis is still controversial and demands systematic work on protein expression. A series of transcription factors (TF) are encoded on chromosome 21 and are considered to play a pathogenetic role in DS. We therefore decided to study brain expression of TF encoded on chromosome 21 in patients with DS and AD compared to controls: Frontal cortex of 6 male DS patients, 6 male patients with AD and 6 male controls were used for the experiments. Immunoblotting was used to determine protein levels of TF BACH1, ERG, SIM2 and RUNX1. SIM2 and RUNX1 were comparable between groups, while BACH1 was significantly reduced in DS, and ERG was increased in DS and AD as compared to controls. These findings may indicate that DS pathogenesis cannot be simply explained by the gene dosage effect hypothesis and that results of ERG expression in DS were paralleling those in AD probably reflecting a common pathogenetic mechanism possibly explaining why all DS patients develop AD like neuropathology from the fourth decade. We conclude that TF derangement is not only due to the process of neurodegeneration and propose that TFs BACH1 and ERG play a role for the development of AD-like neuropathology in DS and pathogenesis of AD per se and the manifold increase of ERG in both disorders may form a pivotal pathogenetic link.