Trisomic Mice Research Articles

Effects of neonatal neural progenitor cell implantation on adult neuroanatomy and cognition in the Ts65Dn model of Down syndrome.

As much of the aberrant neural development in Down syndrome (DS) occurs postnatally, an early opportunity exists to intervene and influence life-long cognitive development. Recent success using neural progenitor cells (NPC) in models of adult neurodegeneration indicate such therapy may be a viable option in diseases such as DS. Murine NPC (mNPC, C17.2 cell line) or saline were implanted bilaterally into the dorsal hippocampus of postnatal day 2 (PND 2) Ts65Dn pups to explore the feasibility of early postnatal treatment in this mouse model of DS. Disomic littermates provided karyotype controls for trisomic pups. Pups were monitored for developmental milestone achievement, and then underwent adult behavior testing at 14 weeks of age. We found that implanted mNPC survived into adulthood and migrated beyond the implant site in both karyotypes. The implantation of mNPC resulted in a significant increase in the density of dentate granule cells. However, mNPC implantation did not elicit cognitive changes in trisomic mice either neonatally or in adulthood. To the best of our knowledge, these results constitute the first assessment of mNPC as an early intervention on cognitive ability in a DS model.

Mouse models of Down syndrome as a tool to unravel the causes of mental disabilities.

Down syndrome (DS) is the most common genetic cause of mental disability. Based on the homology of Hsa21 and the murine chromosomes Mmu16, Mmu17 and Mmu10, several mouse models of DS have been developed. The most commonly used model, the Ts65Dn mouse, has been widely used to investigate the neural mechanisms underlying the mental disabilities seen in DS individuals. A wide array of neuromorphological alterations appears to compromise cognitive performance in trisomic mice. Enhanced inhibition due to alterations in GABAA-mediated transmission and disturbances in the glutamatergic, noradrenergic and cholinergic systems, among others, has also been demonstrated. DS cognitive dysfunction caused by neurodevelopmental alterations is worsened in later life stages by neurodegenerative processes. A number of pharmacological therapies have been shown to partially restore morphological anomalies concomitantly with cognition in these mice. In conclusion, the use of mouse models is enormously effective in the study of the neurobiological substrates of mental disabilities in DS and in the testing of therapies that rescue these alterations. These studies provide the basis for developing clinical trials in DS individuals and sustain the hope that some of these drugs will be useful in rescuing mental disabilities in DS individuals.

Rescue of Synaptic Failure and Alleviation of Learning and Memory Impairments in a Trisomic Mouse Model of Down Syndrome

Down syndrome (DS) is caused by the triplication of ∼240 protein-coding genes on chromosome 21 and is the most prevalent form of developmental disability. This condition results in abnormalities in many organ systems, as well as in intellectual retardation. Many previous efforts to understand brain dysfunction in DS have indicated that cognitive deficits are coincident with reduced synaptic plasticity and decreased neuronal proliferation. One therapeutic strategy for optimizing the microenvironment for neuronal proliferation and synaptic plasticity in the brain is the use of neurotrophins to restore the homeostasis of the brain biochemical milieu. Here, we show that peripheral administration of Peptide 6, an 11-mer corresponding to an active region of ciliary neurotrophic factor, amino acid residues 146 to 156, can inhibit learning and memory impairments in Ts65Dn mice, a trisomic mouse model of DS. Long-term treatment with Peptide 6 enhanced the pool of neural progenitor cells in the hippocampus and increased levels of synaptic proteins crucial for synaptic plasticity. These findings suggest a therapeutic potential of Peptide 6 in promoting functional neural integration into networks, thereby strengthening biologic substrates of memory processing.

Galantamine improves olfactory learning in the Ts65Dn mouse model of Down syndrome.

Down syndrome (DS) is the most common form of congenital intellectual disability. Although DS involves multiple disturbances in various tissues, there is little doubt that in terms of quality of life cognitive impairment is the most serious facet and there is no effective treatment for this aspect of the syndrome. The Ts65Dn mouse model of DS recapitulates multiple aspects of DS including cognitive impairment. Here the Ts65Dn mouse model of DS was evaluated in an associative learning paradigm based on olfactory cues. In contrast to disomic controls, trisomic mice exhibited significant deficits in olfactory learning. Treatment of trisomic mice with the acetylcholinesterase inhibitor galantamine resulted in a significant improvement in olfactory learning. Collectively, our study indicates that olfactory learning can be a sensitive tool for evaluating deficits in associative learning in mouse models of DS and that galantamine has therapeutic potential for improving cognitive abilities.

Form of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A nonphosphorylated at tyrosine 145 and 147 is enriched in the nuclei of astroglial cells, adult hippocampal progenitors, and some cholinergic axon terminals

Compelling lines of evidence indicate that overexpression of dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) in subjects with trisomy 21 (Down syndrome[DS]) contributes to the abnormal structure and function of the DS brain. In the present study, we used a novel, phospho-dependent antibody recognizing DYRK1A only with nonphosphorylated tyrosine 145 and 147 (DYRK1A Tyr-145/147P(-)), to investigate the expression pattern of this DYRK1A species in trisomic and disomic human and mouse brains. Immunoblotting and dephosphorylation experiments demonstrated higher levels of DYRK1A Tyr-145/147P(-) in postnatal trisomic brains in comparison with controls (by ∼40%) than those of the DYRK1A visualized by three other N- and C-terminally directed antibodies to DYRK1A. By immunofluorescence, the immunoreactivity to DYRK1A Tyr-145/147P(-) was the strongest in the nuclei of astroglial cells, which contrasted with the predominantly neuronal localization of DYRK1A visualized by the three other antibodies to DYRK1A we used. In addition, DYRK1A Tyr-145/147P(-) was enriched in the nuclei of neuronal progenitors and newly born neurons in the adult hippocampal proliferative zone and also occurred in some cholinergic axonal terminals. Our data show a distinctive expression pattern of DYRK1A forms nonphosphorylated at Tyr-145 and Tyr-147 in the brain tissue and suggest that DS subjects may exhibit not only upregulation of total DYRK1A, but also more subtle differences in phosphorylation levels of this kinase in comparison with control individuals.

Altered regulation of tau phosphorylation in a mouse model of down syndrome aging

Down syndrome (DS) results from trisomy of human chromosome 21 (Hsa21) and is associated with an increased risk of Alzheimer's disease (AD). Here, using the unique transchromosomic Tc1 mouse model of DS we investigate the influence of trisomy of Hsa21 on the protein tau, which is hyperphosphorylated in Alzheimer's disease. We show that in old, but not young, Tc1 mice increased phosphorylation of tau occurs at a site suggested to be targeted by the Hsa21 encoded kinase, dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A). We show that DYRK1A is upregulated in young and old Tc1 mice, but that young trisomic mice may be protected from accumulating aberrantly phosphorylated tau. We observe that the key tau kinase, glycogen synthase kinase3-β (GSK-3β) is aberrantly phosphorylated at an inhibitory site in the aged Tc1 brain which may reduce total glycogen synthase kinase3-β activity. It is possible that a similar mechanism may also occur in people with DS.

Neural Stem Cells Reduce Hippocampal Tau and Reelin Accumulation in Aged Ts65Dn down Syndrome Mice

Tau accumulation, in the form of neurofibrillary tangles (NFT), is an early neuropathological characteristic of Alzheimer's disease (AD) and early onset AD frequently seen in Down syndrome (DS). We investigated the presence of tau accumulation in the brains of aging DS mice using the Ts65Dn mouse model. All aged mice appeared to have substantial clusters of extracellular granules that were positive for tau and reelin, but not for amyloid-β or APP. These clusters were found primarily in CA1 of the hippocampus. In addition, the aged trisomic DS mice had a significantly greater accumulation of extracellular tau/reelin granular deposits compared to disomic littermates. These granules were similar to those described by others who also found extracellular proteinous granules in the brains of non-DS mice engineered to model aging and/or AD. When neural stem cells (NSC) were implanted unilaterally into the hippocampus of the Ts65Dn mice, the tau/reelin-positive granules were significantly reduced in both trisomic and disomic mice. Our findings indicate that changes in tau/reelin-positive granules could be used as an index for neuropathological assessment in aging DS and AD. Furthermore, changes in granule density could be used to test the efficacy of novel treatments, such as NSC implantation. Lastly, it is speculated that the unique abilities of NSC to migrate and express growth factors might be a contributing factor to reducing tau/reelin accumulation in aging DS and AD.

Increased male reproductive success in Ts65Dn “Down syndrome” mice

The Ts65Dn mouse is trisomic for orthologs of about half the genes on Hsa21. A number of phenotypes in these trisomic mice parallel those in humans with trisomy 21 (Down syndrome), including cognitive deficits due to hippocampal malfunction that are sufficiently similar to human that “therapies” developed in Ts65Dn mice are making their way to human clinical trials. However, the impact of the model is limited by availability. Ts65Dn cannot be completely inbred and males are generally considered to be sterile. Females have few, small litters and they exhibit poor care of offspring, frequently abandoning entire litters. Here we report identification and selective breeding of rare fertile males from two working colonies of Ts65Dn mice. Trisomic offspring can be propagated by natural matings or by in vitro fertilization (IVF) to produce large cohorts of closely related siblings. The use of a robust euploid strain as recipients of fertilized embryos in IVF or as the female in natural matings greatly improves husbandry. Extra zygotes cultured to the blastocyst stage were used to create trisomic and euploid embryonic stem (ES) cells from littermates. We developed parameters for cryopreserving sperm from Ts65Dn males and used it to produce trisomic offspring by IVF. Use of cryopreserved sperm provides additional flexibility in the choice of oocyte donors from different genetic backgrounds, facilitating rapid production of complex crosses. This approach greatly increases the power of this important trisomic model to interrogate modifying effects of trisomic or disomic genes that contribute to trisomic phenotypes.

Development of a Mouse Model of DS Megakaryoblastic Leukemia and Identification of the Hsa21 Gene DYRK1A as a Prominent Contributor to DS-AMKL

AbstractAbstract 469Children with Down syndrome (DS) have a 500-fold increased risk of Acute Megakaryoblastic Leukemia (DS-AMKL). In addition to trisomy 21, DS-AMKL blasts harbor somatic mutations in the gene encoding GATA-1, an essential transcriptional regulator of erythroid and megakaryocytic differentiation. In every case, the GATA1 mutations lead to a block in expression of the full-length protein, but allow for the translation of a shortened isoform named GATA-1s, which lacks the N-terminal transcriptional activation domain. Recent studies have shown that mutations in of JAK2, JAK3 and MPL are another feature of AMKL. Whereas the impact on hematopoiesis of individual GATA-1s, JAK2 V617F and MPL W515L mutants is relatively well known, the specific effects of trisomy 21, the initiating event in DS leukemogenesis, remains unclear. Here, we used two different experimental models to identify specific genes on human chromosome 21 (Hsa21) that participate in leukemogenesis: human DS-AMKL cell lines and the Ts1Rhr mouse strain, which is trisomic for only 33 orthologs of Hsa21 genes. Comprehensive analysis of hematopoiesis in progressively more complex mouse models of DS disorders, including Ts1Rhr mice, Ts1Rhr/KI-Gata-1s compound mutant mice, and recipients of Ts1Rhr/KI-Gata-1s hematopoietic progenitors expressing MPL W515L, revealed that the presence of trisomy 21 impacts the phenotype of each genetic background. Ts1Rhr mice develop a progressive myeloproliferative disease with megakaryocytic features while Ts1Rhr/KI-Gata1s double transgenic mice develop thrombocytosis at an earlier age compared to Gata1s mutant or Ts1Rhr mice alone. However neither the Ts1Rhr nor the compound mutant mice develop AMKL. In stark contrast, expression of MPL W515L in Ts1Rhr/KI-Gata1s hematopoietic progenitors led to a rapid lethal megakaryoblastic disorder characterized by profound marrow and splenic fibrosis and the presence of immature megakaryoblasts in lethally irradiated recipients. Of note, transplantation of MPL W515L expressing singly mutant Ts1Rhr or KI-Gata-1s progenitors failed to cause a similar disease. These findings show that three oncogenic events are necessary and sufficient to induce a megakaryoblastic leukemia in recipient mice. In parallel, to identify specific genes on Hsa21 that contribute to AMKL, we performed shRNA screening in DS-AMKL cell lines by knocking down the human orthologs of the 33 genes trisomic in the Ts1Rhr mice. We then evaluated the consequence of knockdown on megakaryocyte proliferation, survival and/or differentiation. This study revealed that altered expression of ERG, DYRK1A, CHAF1B and HLCS affected megakaryocyte growth. Analysis of their expression in human samples suggest that these four genes likely play a role in etiology of DS-AMKL. Moreover expression evaluation of those genes in our in vivo models of 1, 2 or 3 genetic events revealed that ERG, a known megakaryoblastic oncogene, and DYRK1A are the most prominent genes implicated in these megakaryocytic disorders. DYRK1A (dual specificity tyrosine-regulated kinase 1A) has been functionally implicated in many developmental disorders associated with DS and shown to be constitutively phosphorylated/activated in human AMKL cell lines. We found that overexpression of DYRK1A cooperates with Gata1s to lead to a increase in megakaryocyte growth in liquid culture and in colony assays in vitro. In summary, we show that partially trisomic Ts1Rhr mice display progressive defects in the megakaryocytic compartment, that mutagenesis of Gata1 in the Ts1Rhr background exacerbates the Ts1Rhr phenotype, and that addition of an activating mutation of MPL leads to a fulminant megakaryocytic leukemia with myelofibrosis. Moreover, among the 33 genes present in 3 copies in the Ts1Rhr background, we identify DYRK1A as a likely megakaryoblastic oncogene in DS-AMKL. Disclosures:No relevant conflicts of interest to declare.

Posiphen'S Pharmacokinetics and Mechanism-of-action in Mildly Cognitive Impaired Patients

Posiphen® is in clinical development as an oral treatment for Alzheimer's disease (AD). In cell cultures, normal, transgenic and trisomic mice Posiphen reduces the rate of synthesis of amyloid-β precursor protein (APP) and, thereby, lowers levels of Aβ and potentially other toxic peptides generated from APP processing. We decided to conduct a trial in mild cognitive impaired (MCI) patients to confirm this mechanism of action (reduced rate of APP synthesis) in humans and correlate it with the pharmacokinetics of the drug and its metabolites in CSF and plasma. In order to avoid potential inter-subject variability we decided to use subjects as their own controls and measure CSF and plasma levels for 12 hours both prior to and following Posiphen dosing of 10 days. 5 MCI patients received Posiphen at 240 mg/ day for 10 days (4x60 mg was found in a multiple dose safety study to be well tolerated in elderly healthy volunteers). Serial CSF samples were collected via indwelling lumbar catheter for 12 hours one day before the start of dosing and immediately after the last dose. Plasma samples were taken at the same sampling times. CSF and plasma/serum samples were analyzed for pK: Posiphen and the primary metabolites: N1-norPositphen, N8-norPosiphen, N1, N8-norPosiphen pD 1: soluble α and βAPP, Aβ 40/42, AChEI/BChEI pD 2: Tau/phospho-Tau, C-terminal fragment/C31 and other potential AD associated markers. pD 3: α-synuclein The patients tolerated the procedure well and we have preliminary data indicating that Posiphen reduces circulating APP levels, consistent with the inhibition of APP synthesis as a key mechanism of action of Posiphen in humans. We also have data showing that the activity of Posiphen is prolonged by some of its metabolites. We are in the process of measuring a number of other markers and will report all the data at ICAD. Posiphen in MCI patients reduced APP levels making it a promising drug to modify the course of AD.

Down's syndrome-like cardiac developmental defects in embryos of the transchromosomic Tc1 mouse

AimsCardiac malformations are prevalent in trisomies of human chromosome 21 [Down's syndrome (DS)], affecting normal chamber separation in the developing heart. Efforts to understand the aetiology of these defects have been severely hampered by the absence of an accurate mouse model. Such models have proved challenging to establish because synteny with human chromosome Hsa21 is distributed across three mouse chromosomes. None of those engineered so far accurately models the full range of DS cardiac phenotypes, in particular the profound disruptions resulting from atrioventricular septal defects (AVSDs). Here, we present analysis of the cardiac malformations exhibited by embryos of the transchromosomic mouse line Tc(Hsa21)1TybEmcf (Tc1) which contains more than 90% of chromosome Hsa21 in addition to the normal diploid mouse genome.Methods and resultsUsing high-resolution episcopic microscopy and three-dimensional (3D) modelling, we show that Tc1 embryos exhibit many of the cardiac defects found in DS, including balanced AVSD with single and separate valvar orifices, membranous and muscular ventricular septal defects along with outflow tract and valve leaflet abnormalities. Frequencies of cardiac malformations (ranging from 38 to 55%) are dependent on strain background. In contrast, no comparable cardiac defects were detected in embryos of the more limited mouse trisomy model, Dp(16Cbr1-ORF9)1Rhr (Ts1Rhr), indicating that trisomy of the region syntenic to the Down's syndrome critical region, including the candidate genes DSCAM and DYRK1A, is insufficient to yield DS cardiac abnormalities.ConclusionThe Tc1 mouse line provides a suitable model for studying the underlying genetic causes of the DS AVSD cardiac phenotype.

A mouse embryonic stem cell bank for inducible overexpression of human chromosome 21 genes

BackgroundDosage imbalance is responsible for several genetic diseases, among which Down syndrome is caused by the trisomy of human chromosome 21.ResultsTo elucidate the extent to which the dosage imbalance of specific human chromosome 21 genes perturb distinct molecular pathways, we developed the first mouse embryonic stem (ES) cell bank of human chromosome 21 genes. The human chromosome 21-mouse ES cell bank includes, in triplicate clones, 32 human chromosome 21 genes, which can be overexpressed in an inducible manner. Each clone was transcriptionally profiled in inducing versus non-inducing conditions. Analysis of the transcriptional response yielded results that were consistent with the perturbed gene's known function. Comparison between mouse ES cells containing the whole human chromosome 21 (trisomic mouse ES cells) and mouse ES cells overexpressing single human chromosome 21 genes allowed us to evaluate the contribution of single genes to the trisomic mouse ES cell transcriptome. In addition, for the clones overexpressing the Runx1 gene, we compared the transcriptome changes with the corresponding protein changes by mass spectroscopy analysis.ConclusionsWe determined that only a subset of genes produces a strong transcriptional response when overexpressed in mouse ES cells and that this effect can be predicted taking into account the basal gene expression level and the protein secondary structure. We showed that the human chromosome 21-mouse ES cell bank is an important resource, which may be instrumental towards a better understanding of Down syndrome and other human aneuploidy disorders.

Abstract B28: Trisomy suppress tumorgenesis in the NP-cis tumor model

Abstract Down syndrome results from trisomy for human chromosome 21 (chr21). People with DS have an increased risk of getting leukemia, but the likelihood of solid tumors might be reduced by contribution of several genes. We showed that trisomy in Ts65Dn “Down syndrome” mice reduces tumor number in the ApcMin model of intestinal cancer and that tumor number is inversely proportional to copy number of the Ets2 gene [Sussan TE, Nature 451, 73–75]. The current study provides evidence for additional dosage sensitive tumor repressor gene(s) in the cancer model, NP-cis. These mice carry a single copy of both the tightly linked Nf1 and p53 genes in cis. Tumors form by LOH. When NP-cis mice were crossed with Ts65Dn, trisomic offspring survived significantly longer than euploid. In contrast to the intestinal adenoma finding, introduction of a null allele of Ets2 in either trisomic or euploid mice (resulting in 2 or one copies of Ets2, respectively) had no effect on survival. This result demonstrates further dosage effects of genes trisomic in these mice and in Down syndrome. The lack of Ets2 effect in the NP-cis model is consistent with a protective mechanism that involves up-regulation of p53 by Ets2, thereby sensitizing trisomic cells to p53-mediated apoptosis. This mechanism would not work in NP-cis since tumors form due to loss of p53. In this regard, in vitro analysis of fibroblast cell lines from several genotypes showed that trisomic cells expressing more Ets2 than euploid were more sensitive to induction of apoptosis by camptothecin and showed a higher frequency of senescence. Other genes, like Endostatin, a cleavage product of Col18a1, and Rcan1 have been shown to inhibit angiogenesis in adosage dependent manner in xenograft models of tumor growth [Zorick TS, EJHG 9, 811-4, Baek KH, Nature 459, 1126-30]. In contrast to results from xenografted tumors, endogenous tumors formed in trisomic, NP-cis mice showed no reduction in angiogenesis. Our findings indicate that multiple mechanisms involving other genes trisomic in Ts65Dn mice likely contribute to reduced tumor incidence in Down syndrome. Citation Information: Cancer Res 2009;69(23 Suppl):B28.

Impaired Plasticity at Specific Subset of Striatal Synapses in the Ts65Dn Mouse Model of Down Syndrome

Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation. There is limited insight into the biological basis for the cognitive and motor deficits in DS. Because the striatum plays a key role in the regulation and learning of voluntary movements and in cognitive processes, our study was aimed at investigating striatal synaptic transmission and plasticity in a well-accepted genetic model of DS. Electrophysiological recordings were performed in a corticostriatal slice preparation from trisomic (Ts65Dn) and wild-type mice. Synaptic properties and plasticity, long-term potentiation (LTP) and long-term depression (LTD), were investigated. The basal electrophysiological properties of striatal principal spiny neurons and cholinergic interneurons were spared in the Ts65Dn mouse model of DS. Striatal principal spiny neurons from Ts65Dn mice maintained their ability to undergo LTP and LTD. Conversely, LTP was lost in striatal cholinergic interneurons of Ts65Dn mice. The loss of LTP in striatal cholinergic interneurons of Ts65Dn mice was accompanied by a severe impairment of endogenous cholinergic signaling within the striatum. The intrastriatal cholinergic system that was thought to be spared in DS is functionally altered in the Ts65Dn genetic model of DS. Altered cholinergic transmission might play a critical role in the pathophysiology of motor and cognitive deficits in DS, leading to an abnormal processing of neuronal inputs within the basal ganglia. Targeting striatal cholinergic transmission might represent a new therapeutic strategy in DS.

Complex contributions of Ets2 to craniofacial and thymus phenotypes of trisomic “Down syndrome” mice

Ts65Dn mice have segmental trisomy for orthologs of about half of the genes on human chromosome 21, including Ets2. These mice develop anomalies of the cranial skeleton and thymus that parallel those in Down syndrome. Overexpression of the Ets2 transcription factor gene was posited to be sufficient to produce these craniofacial and thymus deficits in transgenic mice that constitutively overexpress a processed Ets2 transcript under a promiscuous promoter [Sumarsono et al. (1996); Nature 379:534-537; Wolvetang et al. (2003); Hum Mol Genet 12:247-255]. Evaluation of trisomic mice with varying copy numbers of a properly regulated Ets2 gene indicated increased dosage of Ets2 was not sufficient to produce effects on thymus and most of the cranial anomalies seen in Ts65Dn mice. However, mesoderm-derived cranial skeletal elements are significantly more affected in Ts65Dn, Ets2(+/-) mice compared to Ts65Dn littermates suggesting a differential interaction of Ets2-related processes with mesoderm-derived and neural crest-derived formative tissues. Our results support the growing evidence for interactions among multiple genes contributing to developmental perturbations resulting in variation in complex Down syndrome phenotypes.

Age‐dependent dysregulation of brain amyloid precursor protein in the Ts65Dn Down syndrome mouse model

Individuals with Down syndrome develop beta-amyloid deposition characteristic of early-onset Alzheimer's disease (AD) in mid-life, presumably because of an extra copy of the chromosome 21-located amyloid precursor protein (App) gene. App mRNA and APP metabolite levels were assessed in the brains of Ts65Dn mice, a mouse model of Down syndrome, using quantitative PCR, western blot analysis, immunoprecipitation, and ELISAs. In spite of the additional App gene copy, App mRNA, APP holoprotein, and all APP metabolite levels in the brains of 4-month-old trisomic mice were not increased compared with the levels seen in diploid littermate controls. However starting at 10 months of age, brain APP levels were increased proportional to the App gene dosage imbalance reflecting increased App message levels in Ts65Dn mice. Similar to APP levels, soluble amino-terminal fragments of APP (sAPPalpha and sAPPbeta) were increased in Ts65Dn mice compared with diploid mice at 12 months but not at 4 months of age. Brain levels of both Abeta40 and Abeta42 were not increased in Ts65Dn mice compared with diploid mice at all ages examined. Therefore, multiple mechanisms contribute to the regulation towards diploid levels of APP metabolites in the Ts65Dn mouse brain.

Down syndrome--recent progress and future prospects

Down syndrome (DS) is caused by trisomy of chromosome 21 (Hsa21) and is associated with a number of deleterious phenotypes, including learning disability, heart defects, early-onset Alzheimer's disease and childhood leukaemia. Individuals with DS are affected by these phenotypes to a variable extent; understanding the cause of this variation is a key challenge. Here, we review recent research progress in DS, both in patients and relevant animal models. In particular, we highlight exciting advances in therapy to improve cognitive function in people with DS and the significant developments in understanding the gene content of Hsa21. Moreover, we discuss future research directions in light of new technologies. In particular, the use of chromosome engineering to generate new trisomic mouse models and large-scale studies of genotype–phenotype relationships in patients are likely to significantly contribute to the future understanding of DS.

Widespread impairment of cell proliferation in the neonate Ts65Dn mouse, a model for Down syndrome

Among the many pathological aspects of Down syndrome, brain hypoplasia and mental retardation have been recently ascribed to defective proliferation of neural precursors during central nervous system development. By analogy, other features of Down syndrome, such as heart defects, gastrointestinal abnormalities, craniofacial dystrophy and reduced growth rate could be related, at least in theory, to similar proliferation impairment in peripheral tissues. In order to test this hypothesis, we evaluated cell proliferation in peripheral tissues of the Ts65Dn mouse, one of the animal models most commonly used to investigate Down syndrome. In fibroblast cultures from neonatal Ts65Dn mice, we found that cell proliferation was notably impaired. While length of the cell cycle was similar in fibroblasts from Ts65Dn and control mice, the number of actively proliferating cells was significantly smaller in Ts65Dn mice. Moreover, fibroblasts from Ts65Dn animals exhibited limited population-doubling capacity, decreased proliferative lifespan and premature senescence. Analysis of cell proliferation in the skin of neonates, in vivo, showed that in Ts65Dn mice, cell proliferation was significantly reduced compared to control mice. Our results suggest that defective proliferation may be a generalized feature of trisomic mice. In view of the genetic and phenotypic similarities between Ts65Dn mice and individuals with Down syndrome, proliferation impairment in various organs may also occur in subjects with Down syndrome. Thus, perturbation of a basic developmental function, cell proliferation, may be a critical determinant that contributes to the many aspects of pathology of this condition.

Increased expression of β-catenin in brain microvessels of a segmentally trisomic (Ts65Dn) mouse model of Down syndrome

We examined the distribution of beta-catenin and endogenous blood serum albumin at the ultrastructural level in blood microvessels (capillaries) from brains of control and trisomic Ts65Dn mice. Morphological examination revealed an increased immunolabeling for beta-catenin in endothelial substructures of the capillary network, such as intercellular junctions, cytoplasm, and nuclei. These immunosignals were significantly increased in all endothelial substructures from trisomic mice. These changes, however, did not affect the blood-brain barrier function of the entire microvascular network, because the increased uptake of albumin by endothelial cells and the eventual escape of this protein (microleakage) into the perivascular neuropil were noted only in a few capillary profiles. Nevertheless, these findings suggest the involvement of some segments of the microvascular network in the brain pathology associated with DS.

Prevention of Developmental Delays in a Down Syndrome Mouse Model

To estimate whether prenatal treatment with neuroprotective peptides prevents the developmental delay and the glial deficit in the Ts65Dn mouse model for Down syndrome and to explore the peptides' effects on achievement of normal development. Pregnant Ts65Dn females were randomly assigned to NAPVSIPQ+SALLRSIPA or control and were treated by investigators blinded to treatment and genotype on gestational days 8-12. Offspring were tested from postnatal day 5 to 21 for motor and sensory milestones with standardized tests by operators blinded to the pup's treatment and genotype. The pup's genotype was determined after completion of all tests. Activity-dependent neurotrophic factor, glial fibrillary acidic protein, and vasoactive intestinal peptide expression were determined using real-time polymerase chain reaction. Trisomic mice achieved milestones with a significant delay in four of five motor and sensory milestones. Trisomic mice that were prenatally exposed to NAPVSIPQ+SALLRSIPA achieved developmental milestones at the same time as the controls in three of four motor and one of four sensory milestones (P<.01). Euploid pups prenatally treated with NAPVSIPQ+SALLRSIPA achieved developmental milestones significantly earlier than the euploid pups prenatally treated with placebo. Activity-dependent neurotrophic factor expression was significantly downregulated in the Ts65Dn brains compared with the controls, prenatal treatment with NAPVSIPQ+ SALLRSIPA prevented the activity-dependent neurotrophic factor decrease in the Ts65Dn brains, and the expression was not different from the controls. The glial marker glial fibrillary acidic protein demonstrated the known glial deficit in the Ts65Dn mice, and treatment with NAPVSIPQ+ SALLRSIPA prevented its downregulation. Lastly, vasoactive intestinal peptide levels were increased in the trisomic brains, whereas treatment with NAPVSIPQ+SALLRSIPA did not prevent its upregulation. Prenatal treatment with NAPVSIPQ and SALLRSIPA prevented developmental delay and the glial deficit in Down syndrome. These findings highlight a possibility for the prevention of developmental sequelae in Down syndrome and suggest a potential intervention during pregnancy that may improve the outcome.