Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: Challenging the gene dosage effect hypothesis (Part IV)

Triplication of Synaptojanin 1 in Alzheimer's Disease Pathology in Down Syndrome

Down Syndrome (DS), caused by triplication of human chromosome 21 (Hsa21) is the most common form of intellectual disability worldwide. Recent progress in healthcare has resulted in a dramatic increase in the lifespan of individuals with DS. Unfortunately, most will develop Alzheimer's disease like dementia (DS-AD) as they age. Understanding similarities and differences between DSAD and the other forms of the disease - i.e., late-onset AD (LOAD) and autosomal dominant AD (ADAD) - will provide important clues for the treatment of DS-AD. In addition to the APP gene that codes the precursor of the main component of amyloid plaques found in the brain of AD patients, other genes on Hsa21 are likely to contribute to disease initiation and progression. This review focuses on SYNJ1, coding the phosphoinositide phosphatase synaptojanin 1 (SYNJ1). First, we highlight the function of SYNJ1 in the brain. We then summarize the involvement of SYNJ1 in the different forms of AD at the genetic, transcriptomic, proteomic and neuropathology levels in humans. We further examine whether results in humans correlate with what has been described in murine and cellular models of the disease and report possible mechanistic links between SYNJ1 and the progression of the disease. Finally, we propose a set of questions that would further strengthen and clarify the role of SYNJ1 in the different forms of AD.

Meta-analysis of gene expression patterns in Down syndrome highlights significant alterations in mitochondrial and bioenergetic pathways

Individuals with Down syndrome (DS) have an extra copy of chromosome 21. Clinical observations and preclinical studies both suggest that DS is associated with altered bioenergetic pathways. Several studies have reported that differentially expressed genes in DS are located not only on chromosome 21 but also on all other chromosomes. Numerous sets of microarray and RNA-seq data are publicly accessible through the Gene Expression Omnibus. We have conducted a meta-analysis on differentially expressed genes between DS and control subjects. Data deposited before July 1, 2020, were identified by using the search terms "Down syndrome" or "trisomy 21" and "human". Gene expression data were analyzed and normalized for each study. The mixed effect model was used to identify the differentially expressed genes. We conclude that in DS more than 60% of the genes located on chromosome 21 are significantly upregulated and none of them are downregulated. In addition, a significant dysregulation of genes occurs on all other chromosomes as well. Several of the upregulated genes in DS encode for important components of various bioenergetic pathways, for instance PFKL and ACLY. Genes involved in oxidative phosphorylation are mostly downregulated in DS. The gene expression alterations are consistent with the development of significant metabolic disturbances ("pseudohypoxia") in DS cells, which may explain some of the well-known functional defects (ranging from neuronal dysfunction to reduced exercise tolerance) associated with DS.

Upregulation of Mitochondrial Redox Sensitive Proteins in LPS-Treated Stefin B-Deficient Macrophages

Stefin B (cystatin B) is an intracellular inhibitor of cysteine cathepsins and mutations in the stefin B gene, resulting in the development of Unverricht-Lundborg disease, which is a form of myoclonic epilepsy. It was suggested that a key mechanism behind stefin B-mediated disease progression was impaired redox homeostasis. Stefin B-deficient mice were found more sensitive to lipopolysaccharide (LPS)-induced sepsis as a consequence of increased expression of caspase-11 and Nucleotide-binding oligomerization domain, Leucine rich Repeat and Pyrin domain containing (NLRP nflammasome activation and higher levels of mitochondrial reactive oxygen species (ROS). In the present study, we investigated if LPS-triggered oxidative stress affected the protein levels and redox status of redox sensitive proteins-thioredoxin, peroxiredoxins, and superoxide dismutases in macrophages and spleens of LPS-injected mice. LPS challenge was found to result in a marked elevation in mitochondrial peroxiredoxin 3 (Prx3), sulfiredoxin, and superoxide dismutase 2 (Sod2) in stefin B-deficient macrophages and spleens. We determined that sulfiredoxin is targeted to mitochondria after LPS challenge. In conclusion, the upregulation of mitochondrial redox-sensitive proteins Prx3 and Sod2 in stefin B-deficient cells implies a protective role of stefin B in mitochondrial function.

Alzheimer’s Disease-related Biomarkers in Aging Adults with Down Syndrome: Systematic Review

Background:

Down syndrome (DS) is associated with a high prevalence of cognitive impairment and dementia in middle age and older adults. Given the presence of common neuropathological findings and similar pathogenic mechanisms, dementia in DS is regarded as a form of genetically determined, early-onset AD. The clinical characterization of cognitive decline in persons with DS is a difficult task, due to the presence intellectual disability and pre-existing cognitive impairment. Subtle changes that occur at early stages of the dementing process may not be perceived clinically, given that most cognitive screening tests are not sensitive enough to detect them. Therefore, biological markers will provide support to the diagnosis of DS-related cognitive impairment and dementia, particularly at early stages of this process.

Objective:

To perform a systematic review of the literature on AD-related biomarkers in DS.

Method:

We searched PubMed, Web of Science and Cochrane Library for scientific papers published between 2008 and 2018 using as primary mesh terms ‘Down’, ‘Alzheimer’, ‘biomarker’.

Results:

79 studies were retrieved, and 39 were considered eligible for inclusion in the systematic review: 14 post-mortem studies, 10 neuroimaging, 4 addressing cerebrospinal fluid biomarkers, and 11 on peripheral markers.

Conclusion:

There is consistent growth in the number of publication in this field over the past years. Studies in DS-related dementia tend to incorporate many of the diagnostic technologies that have been more extensively studied and validated in AD. In many instances, the study of CNS and peripheral biomarkers reinforces the presence of AD pathology in DS.

Systematic proteome and proteostasis profiling in human Trisomy 21 fibroblast cells

Down syndrome (DS) is mostly caused by a trisomy of the entire Chromosome 21 (Trisomy 21, T21). Here, we use SWATH mass spectrometry to quantify protein abundance and protein turnover in fibroblasts from a monozygotic twin pair discordant for T21, and to profile protein expression in 11 unrelated DS individuals and matched controls. The integration of the steady-state and turnover proteomic data indicates that protein-specific degradation of members of stoichiometric complexes is a major determinant of T21 gene dosage outcome, both within and between individuals. This effect is not apparent from genomic and transcriptomic data. The data also reveal that T21 results in extensive proteome remodeling, affecting proteins encoded by all chromosomes. Finally, we find broad, organelle-specific post-transcriptional effects such as significant downregulation of the mitochondrial proteome contributing to T21 hallmarks. Overall, we provide a valuable proteomic resource to understand the origin of DS phenotypic manifestations.

Trisomy 21 (T21) is a major cause of Down syndrome but little is known about its impact on the cellular proteome. Here, the authors define the proteome of T21 fibroblasts and its turnover and also map proteomic differences in monozygotic T21-discordant twins, revealing extensive, organelle-specific changes caused by T21.

Congenital heart disease and Down syndrome: various aspects of a confirmed association

BACKGROUND

Congenital heart disease (CHD) is frequently described in patients with Down syndrome (DS) and is the main cause of death in this population during the first two years of life. The spectrum of CHD patterns in DS varies widely worldwide; this variation could be due to sociodemographic, genetic and geographic factors.

METHODS

A six-year retrospective, descriptive study was carried out from December 2008 to October 2014, based on the Paediatric Unit CHD registry of Ibn Rochd University Hospital. Clinical, echocardiographic and outcomes data were collected and sorted according to confirmation of the syndrome.

RESULTS

Among 2 156 patients with CHD, 128 were identified with Down syndrome. The genders were equally represented (gender ratio 1) and the median age at diagnosis was 9.5 months (2 days to 16 years). The median age of mothers at delivery was 39 years (16-47). Of the 186 CHD lesions reported, the most common was atrioventricular septal defect (AVSD, 29%), followed by ventricular septal defect (VSD, 21.5%) and atrial septal defect (ASD, 19.9%). The most common associations of CHD were AVSD + ASD (10%) and VSD + ASD (7.8%). Surgery was the most common modality of treatment (54.3%). The overall mortality rate was 14.1%.

CONCLUSION

Our study confirmed that the profile and type of CHD in DS in the Moroccan setting exhibited slight differences in the distribution of these CHDs compared with European neighbours and other Western countries. Further studies are needed to determine which variables have an impact on these differences.

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.

Dissecting Alzheimer disease in Down syndrome using mouse models

Down syndrome (DS) is a common genetic condition caused by the presence of three copies of chromosome 21 (trisomy 21). This greatly increases the risk of Alzheimer disease (AD), but although virtually all people with DS have AD neuropathology by 40 years of age, not all develop dementia. To dissect the genetic contribution of trisomy 21 to DS phenotypes including those relevant to AD, a range of DS mouse models has been generated which are trisomic for chromosome segments syntenic to human chromosome 21. Here, we consider key characteristics of human AD in DS (AD-DS), and our current state of knowledge on related phenotypes in AD and DS mouse models. We go on to review important features needed in future models of AD-DS, to understand this type of dementia and so highlight pathogenic mechanisms relevant to all populations at risk of AD.

Down's-syndrome-related kinase Dyrk1A modulates the p120-catenin-Kaiso trajectory of the Wnt signaling pathway

The Wnt pathways contribute to many processes in cancer and development, with β-catenin being a key canonical component. p120-catenin, which is structurally similar to β-catenin, regulates the expression of certain Wnt target genes, relieving repression conferred by the POZ- and zinc-finger-domain-containing transcription factor Kaiso. We have identified the kinase Dyrk1A as a component of the p120-catenin-Kaiso trajectory of the Wnt pathway. Using rescue and other approaches in Xenopus laevis embryos and mammalian cells, we found that Dyrk1A positively and selectively modulates p120-catenin protein levels, thus having an impact on p120-catenin and Kaiso (and canonical Wnt) gene targets such as siamois and wnt11. The Dyrk1A gene resides within the Down's syndrome critical region, which is amplified in Down's syndrome. A consensus Dyrk phosphorylation site in p120-catenin was identified, with a mutant mimicking phosphorylation exhibiting the predicted enhanced capacity to promote endogenous Wnt-11 and Siamois expression, and gastrulation defects. In summary, we report the biochemical and functional relationship of Dyrk1A with the p120-catenin-Kaiso signaling trajectory, with a linkage to canonical Wnt target genes. Conceivably, this work might also prove relevant to understanding the contribution of Dyrk1A dosage imbalance in Down's syndrome.

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.

Molecular and cellular mechanisms elucidating neurocognitive basis of functional impairments associated with intellectual disability in Down syndrome

Down syndrome, the most common genetic cause of intellectual disability, is associated with brain disorders due to chromosome 21 gene overdosage. Molecular and cellular mechanisms involved in the neuromorphological alterations and cognitive impairments are reported herein in a global model. Recent advances in Down syndrome research have lead to the identification of altered molecular pathways involved in intellectual disability, such as Calcineurin/NFATs pathways, that are of crucial importance in understanding the molecular basis of intellectual disability pathogenesis in this syndrome. Potential treatments in mouse models of Down syndrome, including antagonists of NMDA or GABA(A) receptors, and microRNAs provide new avenues to develop treatments of intellectual disability. Nevertheless, understanding the links between molecular pathways and treatment strategies in human beings requires further research.

Mutations in phosphoinositide metabolizing enzymes and human disease

Phosphoinositides are implicated in the regulation of a wide variety of cellular functions. Their importance in cellular and organismal physiology is underscored by the growing number of human diseases linked to perturbation of kinases and phosphatases that catalyze interconversion from one phosphoinositide to another. Many such enzymes are attractive targets for therapeutic interventions. Here, we review diseases linked to inheritable or somatic mutations of these enzymes.

Aneuploidy: cells losing their balance

A change in chromosome number that is not the exact multiple of the haploid karyotype is known as aneuploidy. This condition interferes with growth and development of an organism and is a common characteristic of solid tumors. Here, we review the history of studies on aneuploidy and summarize some of its major characteristics. We will then discuss the molecular basis for the defects caused by aneuploidy and end with speculations as to whether and how aneuploidy, despite its deleterious effects on organismal and cellular fitness, contributes to tumorigenesis.

Protein expression of BACE1, BACE2 and APP in Down syndrome brains

Down syndrome (DS) is the most common human chromosomal abnormality caused by an extra copy of chromosome 21. The phenotype of DS is thought to result from overexpression of a gene or genes located on the triplicated chromosome or chromosome region. Several reports have shown that the neuropathology of DS comprises developmental abnormalities and Alzheimer-like lesions such as senile plaques. A key component of senile plaques is amyloid beta-peptide which is generated from the amyloid precursor protein (APP) by sequential action of beta-secretases (BACE1 and BACE2) and gamma-secretase. While BACE1 maps to chromosome 11, APP and BACE2 are located on chromosome 21. To challenge the gene dosage effect and gain insight into the expressional relation between beta-secretases and APP in DS brain, we evaluated protein expression levels of BACE1, BACE2 and APP in fetal and adult DS brain compared to controls. In fetal brain, protein expression levels of BACE2 and APP were comparable between DS and controls. BACE1 was increased, but did not reach statistical significance. In adult brain, BACE1 and BACE2 were comparable between DS and controls, but APP was significantly increased. We conclude that APP overexpression seems to be absent during the development of DS brain up to 18-19 weeks of gestational age. However, its overexpression in adult DS brain could lead to disturbance of normal function of APP contributing to neurodegeneration. Comparable expression of BACE1 and BACE2 speaks against the hypothesis that increased beta-secretase results in (or even underlies) increased production of amyloidogenic A beta fragments. Furthermore, current data indicate that the DS phenotype cannot be fully explained by simple gene dosage effect.

New cerebellar phenotypes in YAC transgenic mouse in vivo library of human Down syndrome critical region-1

Down syndrome (DS) is the most frequent genetic cause of mental retardation (MR) associated with neurological alterations. To allow a genetic dissection of DS phenotype, we studied eight transgenic mouse lines carrying YACs containing human DNA fragments covering DS critical region (DCR-1), as an in vivo library. Herein, we found an increased brain size in the 152F7-mice containing DYRK1A gene. We also identified a new cerebellar alteration in two independent lines carrying 230E8-YAC. These mice showed significant elongation of the cerebellar antero-posterior axis (p<0.001), determined by increased length of rostral folia of the vermis (lobule II-V, p<0.0001; lobule VI, p<0.001). In addition, we identified a major neurological defect in culmen and declivus lobules in the 230E8-mice. We analyzed P30, P12, and P9 stages and detected high significant increased lengths of anterior lobules (II-VI) of 230E8-mice at P30 and P12 (lobule II-V, p<0.0001; lobule VI, p<0.05), but not at P9, indicating that this new phenotype appears between P9 and P12. Interestingly, 230E8-mice also present increased cortical cell density and mild learning defects. 230E8-YAC contains seven genes, some of which could be potentially responsible for this phenotype. Between them, we proposed DOPEY2 as potential candidate gene for these cerebellar alterations considering its high expression in the brain and that its homologous genes in yeast, Caenorhabditis elegans and Drosophila are involved in morphogenesis, suggesting a conserved role of DOPEY2 as a patterning gene.

Altered expression of mitochondrial and extracellular matrix genes in the heart of human fetuses with chromosome 21 trisomy

BACKGROUND

The Down syndrome phenotype has been attributed to overexpression of chromosome 21 (Hsa21) genes. However, the expression profile of Hsa21 genes in trisomic human subjects as well as their effects on genes located on different chromosomes are largely unknown. Using oligonucleotide microarrays we compared the gene expression profiles of hearts of human fetuses with and without Hsa21 trisomy.

RESULTS

Approximately half of the 15,000 genes examined (87 of the 168 genes on Hsa21) were expressed in the heart at 18-22 weeks of gestation. Hsa21 gene expression was globally upregulated 1.5 fold in trisomic samples. However, not all genes were equally dysregulated and 25 genes were not upregulated at all. Genes located on other chromosomes were also significantly dysregulated. Functional class scoring and gene set enrichment analyses of 473 genes, differentially expressed between trisomic and non-trisomic hearts, revealed downregulation of genes encoding mitochondrial enzymes and upregulation of genes encoding extracellular matrix proteins. There were no significant differences between trisomic fetuses with and without heart defects.

CONCLUSION

We conclude that dosage-dependent upregulation of Hsa21 genes causes dysregulation of the genes responsible for mitochondrial function and for the extracellular matrix organization in the fetal heart of trisomic subjects. These alterations might be harbingers of the heart defects associated with Hsa21 trisomy, which could be based on elusive mechanisms involving genetic variability, environmental factors and/or stochastic events.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

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.

NOR Expression increases in interphase lymphocytes of Down syndrome babies/children as AgNORs surface, according to the mitogen concentration in the culture medium

The extra chromosome 21 of Down syndrome (DS) or trisomy 21 patients contains an average of 40 extra copies of rRNA genes and the in vivo/in vitro regulation of the activity of these genes is not fully understood. The objective of this work was to compare the NORs expression pattern in interphase lymphocytes of DS patients with regular trisomy 21 and control individuals according to phytohemagglutinin (PHA) concentration (0.37, 0.75, 1.48 and 2.21 ml) per 100 ml of medium. Because the AgNOR staining is an indicator of the active rRNA genes, comparison of the image analysis values of the AgNOR area in 72 h cultivated lymphocytes for each concentration of PHA between DS patients (N=30) and controls (N=24) provided a plausible conclusion on the regulation of the extra rRNA genes in DS lymphocytes. The nucleolus organizer regions area/total nuclear area (NORa/TNa) was calculated using an in-house computer program. Fifty consecutive interphases per PHA concentration were analysed for each individual, for determination of the NORa/TNa. In contrast to healthy controls, NORa/TNa of lymphocytes from DS patient babies/children (0-8 years old) increased gradually in parallel with the PHA concentration in the culture medium: 10.44+/-1.72% for 0.37 ml of PHA, 11.74+/-1.93% for 0.75 ml of PHA, 13.25+/-2.03% for 1.48 ml of PHA and 13.43+/-2.08% for 2.21 ml of PHA per 100 ml of medium. Contrary to control cells (in which the NORa/TNa ratio according to PHA concentration in the culture medium remains constant), DS interphase lymphocytes in culture do not down-regulate their NOR expression. These results obtained from interphase NORs are consistent with the previous results obtained by evaluating the mean of AgNOR+ chromosome number in metaphase cells, also in relation to the mitogen concentration in the culture medium.

Age-dependent decreases in mitogen-stimulation level and RNA content in peripheral blood mononuclear cells of down syndrome patients

OBJECTIVE

The aim of the present study was to determine whether or not the phytohemagglutinin (PHA)-activated proliferation and average RNA content in peripheral blood mononuclear cells (PBMC) of Down syndrome (DS) patients change with age.

METHOD

Stimulated portion of PBMC and total RNA levels in these cells after 72 h of PHA stimulation from 38 DS patients were compared with 28 age-matched healthy controls using flow cytometric measurement.

RESULTS

Decreased ratio of PBMC from DS patients undergoes mitogenic stimulation with age (r = -0.84, P = 0.000). This decrease is not observed in the cells of control individuals (r = 0.03, P = 0.869). Stimulated PBMC in infants with DS have higher level of RNA contents compared to controls (Z = 2.227, P = 0.026). While RNA content in mitogen-stimulated PBMC of DS decreased progressively and significantly with age (r = -0.70, P = 0.000), no significant age-related change in RNA content was found among the cells of healthy individuals in the range of 0-27 year old (r = 0.275, P = 0.157, P > 0.05).

CONCLUSION

Age-dependent decreases in mitogen-activated proliferation ratio and average RNA content of PBMC from DS patients appear as regular events. These results may contribute to the explanation of the immune deficiency seen in DS patients since the PHA-stimulated cells are principally T-lymphocytes. This is the first report on the decrease in PHA-stimulated proliferation ratio (stimulability) and RNA level in PBMC of DS patients in relation to age.

Higher NORs-expression in lymphocyte of trisomy 21 babies/children: In vivo evaluation

Extra chromosome 21 of Down syndrome (DS) or trisomy 21 patients contains an average of 40 extra copies of rRNA genes and the in vivo regulation of these genes is not known. The objective of this work is to compare the NORs expression in interphase nuclei in non-stimulated lymphocytes of DS patients and healthy controls. Because the AgNOR staining is the indicator of the active rRNA genes, comparison of the image analysis values of AgNORs area between DS's and healthy controls' interphase lymphocytes is considered to be sufficient to evaluate the level of rDNA activities in the two groups. The Nucleolus Organizer Regions area/Total Nuclear area (NORa/TNa) was calculated using a computer program designed by us. 100 consecutive NORa/TNa per individual were evaluated. We report that 24 DS children's peripheral lymphocytes show significantly higher NORa/TNa mean value (6.32 +/- 1.77%) than that of the 20 healthy controls' cells (5.31 +/- 1.34%) (2-tailed Mann-Whitney U test, z = 19.4, P = 0.000). The same is true for the nucleolus (AgNOR spot) number per nucleus. The mean value of nucleoli number per nucleus in DS lymphocytes was significantly higher than that of the controls: z = 14.6, P = 0.000. In conclusion, extra rRNA genes on the chromosome 21 are not down-regulated in DS patients' lymphocytes. Rather, extra NORs expressions in 'in vivo' condition contribute to the increase of AgNORs area and AgNOR spots number per nucleus. This is the first work on the comparison of NORs activities in resting (non-stimulated) interphase lymphocytes between DS and healthy controls.

Gene expression analysis of cultured amniotic fluid cell with Down syndrome by DNA microarray

Complete or partial triplication of human chromosome 21 results in Down syndrome (DS). To analyze differential gene expressions in amniotic fluid (AF) cells of DS, we used a DNA microarray system to analyze 102 genes, which included 24 genes on chromosome 21, 28 genes related to the function of brain and muscle, 36 genes related to apoptosis, 4 genes related to extracellular matrix, 8 genes related to other molecular function and 2 house-keeping genes. AF cells were collected from 12 pregnancies at 16-18 weeks of gestation in DS (n=6) and normal (n=6) subjects. Our DNA microarray experiments showed that the expressions of 11 genes were altered by at least 2-folds in DS, as follows. Ten genes, COL6A1, CASP5, AKT2, JUN, PYGM, BNIP1, OSF-2, PRSS7, COL3A1, and MBLL were down-regulated and GSTT1 was only up-regulated. The differential expressions of GSTT1 and COL3A1 were further confirmed by semi-quantitative RT-PCR for each sample. The gene dosage hypothesis on chromosome 21 may explain the neurological and other symptoms of DS. However, our results showed that only two genes (COL6A1 and PRSS7), among 24 genes on chromosome 21, were down-regulated in the AF cells of DS. Our data may provide the basis for a more systematic identification of biological markers of fetal DS, thus leading to an improved understanding of pathogenesis for fetal DS.

NOR expression increases on metaphase chromosomes of down syndrome lymphocytes in concordance with mitogen concentration in culture medium

BACKGROUND

Regulation of nucleolus organizer region (NOR) expression in trisomy 21 (Down syndrome [DS]) cells is not fully explained. This work compared NOR expression on metaphase chromosomes in gradiently stimulated lymphocytes from DS patients with those from healthy controls.

METHOD

Conventional peripheral blood culture (72 h) and chromosomal preparation procedures were used except that blood samples from each individual were cultivated in the same but gradiently increasing concentrations (0.37, 0.75, 1.48, and 2.21 ml) of phytohemagglutinin (PHA) per 100 ml of medium. One hundred consecutive metaphases per concentration were analyzed for scoring the means of the active NORs bearing chromosomes (AgNOR+ chromosome) per individual and per concentration.

RESULTS

In contrast to healthy controls (n=24), AgNOR+ chromosomal number in lymphocytes from 30 DS patients increased in concordance to the gradient of PHA concentration in the culture medium.

CONCLUSION

DS lymphocytes do not downregulate their NOR expression in the limit of control cells. This in vitro result may serve as a clue for the explanation of the DS phenotype due to the wasted energy in producing unnecessary rRNA transcripts and AgNOR proteins in utero during organogenesis. These results also indicate that precautions must be used in routine work of NOR evaluation/interpretation in DS lymphocytes.

Flow cytometric comparison of RNA content in peripheral blood mononuclear cells of down syndrome patients and control individuals

OBJECTIVE

Trisomy 21 or Down syndrome (DS) is the most common genetic cause of mental retardation associated with the immunologic and other known defects. Extra chromosome 21 of DS patients contains an average of 40 extra copies of rRNA genes and the in vivo regulation of these genes' activity is not known. Because over 80% of total cellular RNA is rRNA, the measurement of total cellular RNA provides information on rRNA content. The aim of this work was to determine whether or not the additional chromosome 21 causes any increase in total cellular RNA content in mononuclear cells from peripheral blood (PBMNCs) of these patients and whether or not this content is modified with age.

METHOD

PBMNCs of 48 patients with DS and 48 healthy controls were studied. RNA content of isolated PBMNCs was evaluated by flow cytometric measurements.

RESULTS

Average RNA content of younger DS patients' cells was significantly higher than that of healthy controls (P=0.003). Furthermore, the RNA content decreased significantly with increasing age of DS patients (r=-0.377, P=0.008) in the range of 0-26 year old, whereas no significant relationship was found between age and PBMNCs' RNA content of healthy controls in the same range of ages.

CONCLUSION

RNA content of PBMNCs from DS patients decreases rapidly with age. This is the first work on the age-dependent decrease of the RNA content in PBMNCs of DS patients.

Dosage-dependent over-expression of genes in the trisomic region of Ts1Cje mouse model for Down syndrome

Down syndrome (DS) is the most common chromosomally caused form of mental retardation and is caused by trisomy of chromosome 21. The over-expression of genes located on the trisomic region has been assumed to be responsible for the phenotypic abnormalities of DS, but this hypothesis has not been confirmed fully and the very existence of gene dosage effects has been called into question. We have therefore investigated global gene expression profiles in Ts1Cje, a mouse model for DS that displays learning deficits and has a segmental trisomy of chromosome 16 orthologous to a segment of human chromosome 21 spanning from Sod1 to Znf295. DNA microarray analyses of six Ts1Cje and six normal littermate (2N) mouse brains at postnatal day 0 with probe sets representing approximately 11,300 genes revealed that the number of expressed genes and their identities in Ts1Cje mice were almost same in 2N mice. Notably, the expression levels of most genes in the trisomic region were increased approximately 1.5-fold, and the top 24 most consistently over-expressed genes in the Ts1Cje mice were all located in the trisomic region. In contrast, the expression levels of genes on other chromosomes or the euploid region of chromosome 16 were largely the same (1.0-fold) in Ts1Cje and 2N mice. These results indicate that the genes in the trisomic region of Ts1Cje are over-expressed in a dosage-dependent manner and are implicated in the molecular pathogenesis of DS.

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.

Transcription factor REST dependent proteins are comparable between Down Syndrome and control brains: challenging a hypothesis

Impairment of the RE-1-silencing transcription factor (REST) and REST-dependent genes in Down Syndrome (DS) neuronal progenitor cells and neurospheres has been published recently. As dysregulation of this system has been shown at the RNA level and considering the long and unpredictable way from RNA to proteins, and as it is the proteins that do the function in brain, we decided to test this hypothesis at the protein level. Cortex of brains of patients with Down Syndrome at the early second trimester were used. REST-dependent structures as synapsin I, brain derived neurotrophic factor BDNF and neuronal growth-associated protein SCG10 were determined at the protein level using immunoblotting. Proteins were comparably expressed in fetal Down syndrome and control brains. Even when normalized versus housekeeping genes (glyceraldehyde-6-phosphate-dehydrogenease) and a marker for neuronal density (neuron-specific enolase) DS results were resembling controls. Therefore, we cannot confirm the REST-hypothesis by our studies in the 18/19th week of gestation at the protein level in brain and taking into account that the hypothesis was based upon studies in progenitor cells.