Mouse Model Of Down Syndrome Research Articles

Altered tongue muscle contractile properties coincide with altered swallow function in the adult Ts65Dn mouse model of down syndrome.

Down syndrome (DS) is a developmental disability associated with difficulties in deglutition. The adult Ts65Dn mouse model of DS has been previously shown to have differences in measures of swallowing compared with euploid controls. However, the putative mechanisms of these differences in swallowing function are unclear. This study tested the hypothesis that the Ts65Dn genotype is associated with atypical measures of tongue muscle contractile properties, coinciding with atypical swallow function. Adult (5-month-old) Ts65Dn (n = 15 female, 14 male) and euploid sibling controls (n = 16 female, 14 male) were evaluated through videofluoroscopy swallow studies (VFSS) to quantify measures of swallowing performance including swallow rate and inter-swallow interval (ISI). After VFSS, retrusive tongue muscle contractile properties, including measures of muscle fatigue, were determined using bilateral hypoglossal nerve stimulation. The Ts65Dn group had significantly slower swallow rates, significantly greater ISI times, significantly slower rates of tongue force development, and significantly greater levels of tongue muscle fatigue, with lower retrusive tongue forces than controls in fatigue conditions. Tongue muscle contractile properties are altered in adult Ts65Dn and coincide with altered swallow function.

Beyond Quiescent and Active: Intermediate Microglial Transcriptomic States in a Mouse Model of Down Syndrome.

Research on microglia in Down syndrome (DS) has shown that microglial activation, increased inflammatory gene expression, and oxidative stress occur at different ages in DS brains. However, most studies resulted in simplistic definitions of microglia as quiescent or active, ignoring potential intermediate states. Indeed, recent work on microglial cells in young DS brains indicated that those evolve through different intermediate activation phenotypes before reaching a fully activated state. Here we used single nucleus RNA sequencing, to examine how trisomy affects microglial states in the Ts65Dn mouse model of DS. Despite no substantial changes in the proportion of glial populations, differential expression analysis revealed cell type-specific gene expression changes, most notably in astroglia, microglia, and oligodendroglia. Focusing on microglia, we identified differential expression of genes associated with different microglial states, including disease-associated microglia (DAMs), activated response microglia (ARMs), and human Alzheimer's disease microglia (HAMs), in trisomic microglia. Furthermore, pseudotime analysis reveals a unique reactivity profile in Ts65Dn microglia, with fewer in a homeostatic state and more in an intermediate aberrantly reactive state than in euploid microglia. This comprehensive understanding of microglial transcriptional dynamics sheds light on potential pathogenetic mechanisms but also possible avenues for therapy for neurodevelopmental disorders.

Reduced REST Expression in Neural Progenitor Cells, Adult Cortex, and Impaired REST Nuclear Translocation in the Prefrontal Cortex of Ts1Cje Mouse Model of Down Syndrome

Reduced REST Expression in Neural Progenitor Cells, Adult Cortex, and Impaired REST Nuclear Translocation in the Prefrontal Cortex of Ts1Cje Mouse Model of Down Syndrome

SARS-CoV-2 Infection Causes Heightened Disease Severity and Mortality in a Mouse Model of Down Syndrome.

Recent epidemiological studies suggest that individuals with Down syndrome are more susceptible to SARS-CoV-2 infection and have higher rates of hospitalization and mortality than the general population. However, the main drivers behind these disparate health outcomes remain unknown. Herein, we performed experimental infections with SARS-CoV-2 in a well-established mouse model of Down syndrome. We observed similar SARS-CoV-2 replication kinetics and dissemination in the primary and secondary organs between mice with and without Down syndrome, suggesting that both groups have similar susceptibilities to SARS-CoV-2 infection. However, Down syndrome mice exhibited more severe disease as defined by clinical features including symptoms, weight loss, pulmonary function, and survival of mice. We found that increased disease severity in Down syndrome mice could not be attributed solely to increased infectivity or a more dramatic pro-inflammatory response to infection. Rather, results from RNA sequencing suggested that differences in the expression of genes from other physiological pathways, such as deficient oxidative phosphorylation, cardiopulmonary dysfunction, and deficient mucociliary clearance in the lungs may also contribute to heightened disease severity and mortality in Down syndrome mice following SARS-CoV-2 infection.

The lncRNA Snhg11, a new candidate contributing to neurogenesis, plasticity, and memory deficits in Down syndrome.

Down syndrome (DS) stands as the prevalent genetic cause of intellectual disability, yet comprehensive understanding of its cellular and molecular underpinnings remains limited. In this study, we explore the cellular landscape of the hippocampus in a DS mouse model, the Ts65Dn, through single-nuclei transcriptional profiling. Our findings demonstrate that trisomy manifests as a highly specific modification of the transcriptome within distinct cell types. Remarkably, we observed a significant shift in the transcriptomic profile of granule cells in the dentate gyrus (DG) associated with trisomy. We identified the downregulation of a specific small nucleolar RNA host gene, Snhg11, as the primary driver behind this observed shift in the trisomic DG. Notably, reduced levels of Snhg11 in this region were also observed in a distinct DS mouse model, the Dp(16)1Yey, as well as in human postmortem brain tissue, indicating its relevance in Down syndrome. To elucidate the function of this long non-coding RNA (lncRNA), we knocked down Snhg11 in the DG of wild-type mice. Intriguingly, this intervention alone was sufficient to impair synaptic plasticity and adult neurogenesis, resembling the cognitive phenotypes associated with trisomy in the hippocampus. Our study uncovers the functional role of Snhg11 in the DG and underscores the significance of this lncRNA in intellectual disability. Furthermore, our findings highlight the importance of DG in the memory deficits observed in Down syndrome.

Suppression of Sleeping Beauty-induced Gliomagenicity in Ts1Cje Mice, a Model of Down Syndrome.

Individuals with Down syndrome (DS), attributed to triplication of human chromosome 21 (Hsa21), exhibit a reduced incidence of solid tumors. However, the prevalence of glioblastoma among individuals with DS remains a contentious issue in epidemiological studies. Therefore, this study examined the gliomagenicity in Ts1Cje mice, a murine model of DS. We employed the Sleeping Beauty transposon system for the integration of human oncogenes into cells of the subventricular zone of neonatal mice. Notably, Sleeping Beauty-mediated de novo murine gliomagenesis was significantly suppressed in Ts1Cje mice compared to wild-type mice. In glioblastomas of Ts1je mice, we observed an augmented presence of M1-polarized tumor-associated macrophages and microglia, known for their anti-tumor efficacy in the early stage of tumor development. Our findings in a mouse model of DS offer novel perspectives on the diminished gliomagenicity observed in individuals with DS.

Comparative analysis of craniofacial shape in two mouse models of Down syndrome: Ts65Dn and TcMAC21.

Mouse models are central to studying and understanding the genotypic-to-phenotypic outcomes of Down syndrome (DS), a complex condition caused by an extra copy of the long arm of human chromosome 21. The recently developed TcMAC21-a transchromosomic mouse strain with comparable gene dosage to human chromosome 21 (Hsa21)-includes more Hsa21 genes than any other model of DS. Recent studies on TcMAC21 have provided valuable insight into the molecular, physiological, and neuroanatomical aspects of the model. However, relatively little is known about the craniofacial phenotype of TcMAC21 mice, particularly as it compares to the widely studied Ts65Dn model. Here we conducted a quantitative study of the cranial morphology of TcMAC21 and Ts65Dn mice and their respective unaffected littermates. Our comparative data comprise forty three-dimensional cranial measurements taken on micro-computed tomography scans of the heads of TcMAC21 and Ts65Dn mice. Our results show that TcMAC21 exhibit similar patterns of craniofacial change to Ts65Dn. However, the DS-specific morphology is more pronounced in Ts65Dn mice. Specifically, Ts65Dn present with more medio-lateral broadening and retraction of the snout compared to TcMAC21. Our findings reveal the complexity of potential gene interaction in the production of craniofacial phenotypes.

Increased dosage of DYRK1A leads to congenital heart defects in a mouse model of Down syndrome.

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21). DS is a gene dosage disorder that results in multiple phenotypes including congenital heart defects. This clinically important cardiac pathology is the result of a third copy of one or more of the approximately 230 genes on Hsa21, but the identity of the causative dosage-sensitive genes and hence mechanisms underlying this cardiac pathology remain unclear. Here, we show that hearts from human fetuses with DS and embryonic hearts from the Dp1Tyb mouse model of DS show reduced expression of mitochondrial respiration genes and cell proliferation genes. Using systematic genetic mapping, we determined that three copies of the dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1a) gene, encoding a serine/threonine protein kinase, are associated with congenital heart disease pathology. In embryos from Dp1Tyb mice, reducing Dyrk1a gene copy number from three to two reversed defects in cellular proliferation and mitochondrial respiration in cardiomyocytes and rescued heart septation defects. Increased dosage of DYRK1A protein resulted in impairment of mitochondrial function and congenital heart disease pathology in mice with DS, suggesting that DYRK1A may be a useful therapeutic target for treating this common human condition.

EGCG-like non-competitive inhibitor of DYRK1A rescues cognitive defect in a down syndrome model

Overexpression of the chromosome 21 DYRK1A gene induces morphological defects and cognitive impairments in individuals with Down syndrome (DS) and in DS mice models. Aging neurons of specific brain regions of patients with Alzheimer's disease, DS and Pick's disease have increased DYRK1A immunoreactivity suggesting a possible association of DYRK1A with neurofibrillary tangle pathology. Epigallocatechin-3-gallate (EGCG) displays appreciable inhibition of DYRK1A activity and, contrary to all other published inhibitors, EGCG is a non-competitive inhibitor of DYRK1A. Prenatal exposure to green tea polyphenols containing EGCG protects from brain defects induced by overexpression of DYRK1A.In order to produce more robust and possibly more active analogues of the natural compound EGCG, here we synthetized new EGCG-like molecules with several structural modifications to the EGCG skeleton. We replaced the ester boun of EGCG with a more resistant amide bond. We also replaced the oxygen ring by a methylene group. And finally, we positioned a nitrogen atom within this ring. The selected compound was shown to maintain the non-competitive property of EGCG and to correct biochemical and behavioral defects present in a DS mouse model. In addition it showed high stability and specificity.

Lamivudine modulates the expression of neurological impairment-related genes and LINE-1 retrotransposons in brain tissues of a Down syndrome mouse model.

Elevated activity of retrotransposons is increasingly recognized to be implicated in a wide range of neurodegenerative and neurodevelopmental diseases, including Down syndrome (DS), which is the most common chromosomal condition causing intellectual disability globally. Previous research by our group has revealed that treatment with lamivudine, a reverse transcriptase inhibitor, improved neurobehavioral phenotypes and completely rescued hippocampal-dependent recognition memory in a DS mouse model, Ts65Dn. We hypothesized that retrotransposition rates would increase in the Ts65Dn mouse model, and lamivudine could block retrotransposons. We analyzed the differentially expressed long interspersed element-1 (LINE-1 or L1) mapping on MMU16 and 17, and showed for the first time that retrotransposition could be associated with Ts65Dn's pathology, as misregulation of L1 was found in brain tissues associated with trisomy. In the cerebral cortex, 6 out of 26 upregulated L1s in trisomic treated mice were located in the telomeric region of MMU16 near Ttc3, Kcnj6, and Dscam genes. In the hippocampus, one upregulated L1 element in trisomic treated mice was located near the Fgd4 gene on MMU16. Moreover, two downregulated L1s rescued after treatment with lamivudine were located in the intronic region of Nrxn1 (MMU17) and Snhg14 (MMU7), implicated in a variety of neurodegenerative disorders. To gain further insight into the mechanism of this improvement, we here analyzed the gene expression profile in the hippocampus and cerebral cortex of trisomic mice treated and no-treated with lamivudine compared to their wild-type littermates. We found that treatment with lamivudine rescued the expression of 24% of trisomic genes in the cortex (located on mouse chromosome (MMU) 16 and 17) and 15% in the hippocampus (located in the human chromosome 21 orthologous regions), with important DS candidate genes such as App and Ets2, rescued in both regions.

Spermatogonial depletion and a spermatogenesis defect in the Dp(16)1Yey mouse model of Down syndrome

In brief Little is known about the mechanism responsible for male infertility in Down syndrome. Duplication of Mmu16 chromosome (an orthologue of Hsa21, bearing Dyrk1A) in Dp(16)1Yey mice is responsible for impaired spermatogenesis through spermatogonial depletion and hypogonadotropic hypogonadism. Abstract Down syndrome (DS), or trisomy 21, is the most common chromosomal disorder in humans. Men with DS are infertile. The DYRK1A gene on Hsa21 is involved in several features of DS. Overexpression of the homolog dyrk1A disrupts primordial germ cell migration in zebrafish, and overexpression of Dyrk1A impairs gonadotropic axis function and the early stages of spermatogenesis in the mouse. Other genes on Hsa21 might be involved in the pathogenesis of infertility in DS. We investigated the Dp(16)1Yey mouse model of DS, which features segmental duplication of chromosome Mmu16 (orthologous to a large part of Hsa21 and carrying Dyrk1A and 112 other genes). Using an immunohistochemical assay for the spermatogonial marker STRA8, we observed spermatogonial depletion in the Dp(16)1Yey mouse. This was correlated with low mRNA expression of GFRα1 (a marker of the self-renewal stem cell pool) in an RT-qPCR assay and low protein expression of PLZF (a marker of differentiating stem cells) in a slot-blot assay. Spermatogenesis was present but impaired, with a low sperm count, low protamine-1 expression, a low testis weight, and a low seminiferous tubule diameter. Low circulating luteinizing hormone and follicle-stimulating hormone levels and an elevated testis anti-Müllerian hormone level (as measured in ELISAs) revealed the presence of hypogonadotropic hypogonadism. The Dp(16)1Yey mouse model of DS recapitulates observations made in zebrafish and mice overexpressing DYRK1A homologs. The presence of an excess of Mmu16 material perturbs spermatogenesis and the gonadotropic axis. More generally, DYRK1A’s role in human infertility (outside DS) remains to be characterized.

GM‐CSF Treatment Increases the Number of Purkinje Cells in a Mouse Model of Down Syndrome

AbstractBackgroundDown syndrome (DS), the most common chromosomal disorder that is a genetic cause of intellectual disability (ID), is characterized by mild‐to‐severe cognitive deficits and several neurological and brain anatomical abnormalities in people with DS and in animal models of DS. Among them, a marked reduction in the volume of the cerebellum has been reported in fetuses, newborns, and adults with DS, and in mouse models of DS. It has been well documented that children and adults with DS display motor deficits consistent with cerebellar abnormalities. Growing evidence suggests that the cerebellum is involved in the processing of cognitive functions. Reduced size of the cerebellum may be one of the underlying causes of cognitive deficits in DS. However, the cellular functions of the cerebellum remain poorly understood in people with DS. The beneficial effects of treatment with the hematopoietic growth factor granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) in animal models of DS, Alzheimer’s disease (AD), normal aging, and clinical trials of AD subjects suggest that it may serve as a potential therapeutic for these disorders. Our recent published data showed that treatment with GM‐CSF rescues the cognitive impairments and improves hippocampal pathology in Dp16 mice. To elucidate cerebellum‐associated cellular functions, we investigated purkinje cell pathology in aged male Dp16 mice after treatment with GM‐CSF compared to saline‐injected mice.MethodWe injected 12‐ to 14‐month‐old male Dp16 male mice subcutaneously with GM‐CSF (5 mg/day; 5 days/week) or with saline (200 ml) for 24 injections total over 29 days. On day 29, the brains were fixed, and tissues were processed for immunohistochemistry.ResultWe observed a reduced number of parvalbumin‐positive purkinje cells and loss of arborization in the cerebellum of male Dp16 mice compared to wild‐type littermates. Treatment with GM‐CSF significantly increased the number of parvalbumin‐positive purkinje cells and partially restored dendritic arborization in the cerebellum of Dp16 mice compared to saline‐injected mice.ConclusionOur results suggest that treatment with GM‐CSF improves cellular abnormalities by increasing the number of purkinje cells in the cerebellum of Dp16 mice. Taken together with our previous results, these findings provide further evidence that GM‐CSF/sargramostim may have therapeutic benefits in people with DS.

Utilization of the novel adeno‐associated virus PHP.eB serotype to modulate Intersectin 1 expression in the Ts65Dn mouse model of Down syndrome

AbstractBackgroundDown Syndrome (DS) and Alzheimer’s disease (AD) include cholinergic neurodegeneration which parallels cognitive decline. Triplicated genes in DS are thought to play a role in basal forebrain cholinergic neuron (BFCN) pathology; one avenue to assess triplicated genes’ role is to normalize their expression in DS mouse models by stereotaxic injection of adeno‐associated viruses (AAVs) carrying silencing constructs such as single hairpin mRNA (shRNA). However, stereotaxic surgeries have drawbacks particularly when targeting areas lying deep within the brain. The introduction of the AAV‐PHP.eB serotype, which can cross the blood‐brain‐barrier when introduced into peripheral vasculature, has been shown to vary in efficiency depending on mouse background. Here, we investigated tropism of the AAV‐PHP.eB serotype in the Ts65Dn mouse, the most commonly used DS mouse model. We then used AAV‐PHP.eB to assess our ability to globally modulate expression of intersectin 1 (ITSN1), a protein triplicated in DS that may relate to BFCN dysfunction and memory impairments.MethodsWe retro‐orbitally injected N = 16 4‐4.5 month‐old male mice, (C57Bl, Ts65Dn trisomic and normosomic) with AAV‐PHP.eB‐CamKII‐GFP‐scrmble‐shRNA, to assess tropism and optimize virus concentration (2, 5, and 10µL). Four weeks post injection we imaged for GFP expression in 50µm coronal sections. To knock down ITSN1 globally, we injected N = 58 Ts65Dn mice (3 months, balanced by sex, genotype, virus) with either 5μl AAV‐PHP.eB‐U6‐scrmble‐GFP (control) or AAV‐PHP.eB‐U6‐shITSN1‐GFP (ITSN1); mice were behaviorally tested at 7 months and euthanized at 8 months followed by tissue collection.ResultsMice injected with AAV‐PHP.eB‐CamKII‐GFP‐scrmble‐shRNA showed GFP expression 4 weeks following injection, with robust expression visible with 5µL virus. Mice subsequently injected with control and ITSN1 AAVs showed significant effects of ITSN1 knockdown, including increased tremors, increased latency in the radial arm water maze – suggesting impaired spatial reference learning and memory – decreased brain weight, and altered weight change.ConclusionThe AAV‐PHP.eB serotype shows successful CNS tropism in the Ts65Dn mouse model, with 5µL of AAV providing the best efficiency throughout key brain regions affected in DS and AD. Furthermore, the AAV‐PHP.eB serotype can be used to modulate expression of genes triplicated in DS to investigate their mechanistic role in neurodegeneration both molecularly and behaviorally.

Unlocking cognition with pulsatile GnRH in Down Syndrome: implications for Alzheimer’s disease

AbstractBackgroundThere is currently no viable treatment for the cognitive and olfactory deficits of Trisomy 21 and Alzheimer’s disease.MethodPhysiological characterization and epigenetic, cellular, chemogenetic, and pharmacological interventions in male and female Ts65Dn mice (P9‐P360), a mouse model of Down syndrome, and 12‐month‐old THY::TAU22 male mice, a mouse model of Alzheimer’s disease, and their wild‐type littermates. Seven men with Down syndrome (20‐50 years of age) were enrolled in an open‐label pilot study to assess the effect of 6‐month pulsatile GnRH therapy on cognitive and olfactory function.ResultWe show in Ts65Dn mice that olfactory and cognitive neurological symptoms are closely related to a post‐pubertal decrease in hypothalamic and extra‐hypothalamic expression of a master molecule controlling reproduction ‐ gonadotropin‐releasing hormone (GnRH) ‐ and appear to be linked to an imbalance in a microRNA‐gene network known to regulate the maturation of GnRH neurons as well as to an alteration in hippocampal synaptic transmission. Restoring physiological GnRH levels abolishes olfactory and cognitive deficits in Ts65Dn and THY::TAU22 mice, while pulsatile GnRH treatment improves cognition and brain connectivity in adult T21 patients.ConclusionWe have discovered that GnRH plays a crucial role in olfaction and cognition, and pulsatile GnRH treatment holds promise for improving cognitive deficits in patients with Down syndrome. Such treatment could potentially also be beneficial for mobilizing cognitive reserve in pathological brain aging such as that found in Alzheimer’s disease.

Modelling of the development and response to amyloid‐β accumulation in the context of trisomy21 in the rodent brain

AbstractBackgroundIndividuals who have Down syndrome (DS), a genetic condition caused by having three copies of chromosome 21, frequently develop early‐onset Alzheimer’s disease (AD). This is caused by the additional copy of the APP gene, located on chromosome 21, which leads to a raised abundance of amyloid‐β. However, significant evidence demonstrates that the additional copy of other genes on the chromosome modifies the accumulation and response to amyloid‐β. Here we present a series of rodent preclinical models of AD‐DS, which we use to investigate this biology and can be used to test potential therapeutic approaches.MethodsWe previously crossed mouse models of DS with the AppNL‐F model of amyloid‐β accumulation; demonstrating that three copies of a region of chromosome 21 containing 38 genes is sufficient to reduce the accumulation of amyloid‐β. Here we present new data from a cross of the Dp1Tyb DS mouse model with an App gene knock‐out (to normalise the number of copies of this gene) and novel DS‐AD rodent models in which the endogenous App gene has been partially humanized (Dup(Rno11)‐APP‐H3 and Ts68Yah) compared with DS model controls (Dup(Rno11) and Ts66Yah). Brain material from these models at a range of ages was analyzed by western blot, biochemical fractionation and MSD assay, and immunohistology to study APP processing and amyloid‐β accumulation. We used MSD assay and immunofluorescence to study the response to accumulating amyloid‐β with a focus on the response of microglia, neuroinflammation and break‐down of the blood‐brain barrier.ResultsOur data indicate that three copies of App contribute to altered microglia biology in the Dp1Tyb mouse model of DS and that partial humanization of the App gene in DS rodent models leads to alterations in the processing of APP, and results in raised levels of human amyloid‐β in the brain.ConclusionThese new model systems of DS‐AD amyloid‐β biology can be used to better understand the early development of AD in people who have DS and to test the safety and efficacy of new therapies for this important group of individuals who are at extremely high risk of developing early onset dementia.

Electrophysiological effects of mitochondria‐derived extracellular vesicles: implications for memory dysfunction in neurodegenerative disorders

AbstractBackgroundMitovesicles are a newly identified subtype of small extracellular vesicles (EVs) of mitochondrial origin. We recently developed a method to separate mitovesicles from other EVs after their isolation from the extracellular space of murine and human brain tissues. This method permits the study of the roles of mitovesicles in physiology and disease.Given their origin, we hypothesized that mitochondrial dysfunction, a hallmark of both Alzheimer’s disease (AD) and Down syndrome (DS), could induce alterations in mitovesicles, thus perturbing brain homeostasis and contributing to propagation of pathology. Therefore, we studied mitovesicle components and functionality after their isolation from the brain of a mouse model of DS (hereafter Ts2) as compared to diploid (2N) controls, as well as from frontal cortices of individuals with DS as compared to their age‐matched 2N controls.MethodBrain mitovesicles were isolated and analyzed by Western blotting, electron microscopy, nanotrack analysis, and monoamine neurotransmitter degradation assay as recently described (D’Acunzo, et al., 2022, PMID: 35962195). Coronal hippocampal slices from wild‐type mice were perfused with different subtypes of brain EVs, pretreated or not with clorgiline and pargyline (1 μM each), irreversible inhibitors of the monoamine oxidases type A and B (MAO‐A and MAO‐B), respectively. Long‐term potentiation (LTP) was induced at the level of the Schaeffer collateral fibers through a theta‐burst stimulation (Fà, et al., 2014, PMID: 24643165).ResultMitovesicle number is higher in brains of DS individuals and of Ts2 mice and contain a higher MAO‐B protein amount and enzymatic activity as compared to diploid controls, suggesting a potential mitovesicle‐dependent impairment of neuroamine homeostasis in DS. In agreement with that, Ts2 (but not 2N) mitovesicles stimulated a decreased LTP in recipient hippocampal slices as compared to vehicle control (Fig. 1; mtVs: mitovesicles). This biological activity was abolished when MAO‐B (but not MAO‐A) was blocked. The other EV subtypes of both genotypes, microvesicles and exosomes, did not trigger an effect on LTP. DS changes were found to be sex independent.ConclusionPathogenic mitovesicles are previously undescribed active players of the brain extracellular milieu by regulating LTP via MAO‐B, and potentially contribute to memory formation deficiencies typically found in AD and DS.

A Novel Transgenic Mouse Model of Down Syndrome Acute Lymphoblastic Leukemia Identifies Targetable Vulnerabilities

Background: Children with Down syndrome (DS) have a 10-fold increased risk of developing B-cell acute lymphoblastic leukemia (B-ALL), and they have poorer survival due to increased relapses and treatment-related mortality (TRM). Targeted therapies for DS-ALL are needed to improve anti-leukemic efficacy and reduce the risk of TRM. Mouse models and cell lines recapitulating DS-ALL are lacking, and may aid in identifying new targets for DS-ALL. Methods: We used the Dp(16)1Yey (Dp16) mouse model of DS, which has a triplication of ~115 human chromosome 21 (Hsa21) orthologues. We introduced Kras G12D and Pax5 heterozygosity, both driven in B cells by CD19-Cre, in Dp16 and non-DS wild-type (WT) mice. We performed RNA-Sequencing (RNA-Seq) and gene set enrichment analysis (GSEA) to identify differentially regulated signaling pathways in Dp16 and WT B-ALL blasts. We cultured B-ALL blasts from mice to generate immortal cell lines. We tested the chemosensitivity of Dp16 and WT B-ALL cell lines with 35 agents with known efficacy in hematologic malignancies, and with 481 anti-cancer compounds used in the Cancer Therapeutics Response Portal project, to screen for drugs effective in DS-ALL. We screened top candidate drugs in DS-ALL and non-DS ALL patient samples in vitro, and tested FK866 and cucurbitacin I in vivo in mice xenografted with a DS-ALL patient sample. Results: Kras G12D.Pax5 +/- mice developed B-ALL with complete penetrance, with significantly shorter median survival in the Dp16 versus WT background (Figure 1A; 80 versus 114 days, p<0.0001). GSEA demonstrated upregulation of DNA repair signaling pathways in Dp16 B-ALL, recapitulating a signature observed in human DS-ALL. Growth of Dp16 and WT B-ALL cell lines, and DS-ALL and non-DS ALL patient samples, was inhibited at low nanomolar concentrations by novel therapies targeting NAMPT, DNA damage responses, autophagy, and JAK and PI3K/mTOR signaling. In mice xenografted with a DS-ALL patient sample, the NAMPT inhibitor FK866 significantly reduced the leukemic burden compared to vehicle (Figure 1B; 14.6% vs 22.4% after 4 weeks of treatment, p<0.005). The effect of FK866 was also significant after weeks 2 and 3 of treatment. Conclusions: We have generated the first de novo mouse model and cell lines recapitulating DS-ALL, which we have employed in drug screens to identify novel therapeutic approaches. These studies suggest promising candidates for further study in DS-ALL and other high-risk ALL subtypes to reduce toxicity and improve outcomes.

Neocortical neuronal production and maturation defects in the TcMAC21 mouse model of Down syndrome

Down syndrome (DS) results from trisomy of human chromosome 21 (HSA21), and DS research has been conducted by the use of mouse models. We previously generated a humanized mouse model of DS, TcMAC21, which carries the long arm of HSA21. These mice exhibit learning and memory deficits, and may reproduce neurodevelopmental alterations observed in humans with DS. Here, we performed histologic studies of the TcMAC21 forebrain from embryonic to adult stages. The TcMAC21 neocortex showed reduced proliferation of neural progenitors and delayed neurogenesis. These abnormalities were associated with a smaller number of projection neurons and interneurons. Further, (phospho-)proteomic analysis of adult TcMAC21 cortex revealed alterations in the phosphorylation levels of a series of synaptic proteins. The TcMAC21 mouse model shows similar brain development abnormalities as DS, and will be a valuable model to investigate prenatal and postnatal causes of intellectual disability in humans with DS.

Increased lethality of respiratory infection by Streptococcus pneumoniae in the Dp16 mouse model of Down syndrome.

We sought to investigate whether the Dp16 mouse model of Down syndrome (DS) is more susceptible to severe and lethal respiratory tract infection by Streptococcus pneumoniae. We infected controls and Dp16 mice with Streptococcus pneumoniae and measured survival rates. We compared cytokine production by primary lung cell cultures exposed to Streptococcus pneumoniae. We examined lung protein expression for interferon signaling related pathways. We characterized the histopathology and quantified the extent of bronchus-associated lymphoid tissue. Finally, we examined mouse tissues for the presence of oligomeric tau protein. We found that the Dp16 mouse model of DS displayed significantly higher susceptibility to lethal respiratory infection with Streptococcus pneumoniae compared to control mice. Lung cells cultured from Dp16 mice displayed unique secreted cytokine profiles compared to control mice. The Dp16 mouse lungs were characterized by profound lobar pneumonia with massive diffuse consolidation involving nearly the entire lobe. Marked red hepatization was noted, and Dp16 mice lungs contained numerous bronchus-associated lymphoid tissues that were highly follicularized. Compared to uninfected mice, both control mice and Dp16 mice infected with Streptococcus pneumoniae showed evidence of oligomeric tau aggregates. Increased susceptibility to severe respiratory tract infection with Streptococcus pneumoniae in Dp16 mice closely phenocopies infection in individuals with DS. The increase does not appear to be linked to overexpression of mouse interferon genes syntenic to human chromosome 21.

Investigating brain alterations in the Dp1Tyb mouse model of Down syndrome

Down syndrome (DS) is one of the most common birth defects and the most prevalent genetic form of intellectual disability. DS arises from trisomy of chromosome 21, but its molecular and pathological consequences are not fully understood. In this study, we compared Dp1Tyb mice, a DS model, against their wild-type (WT) littermates of both sexes to investigate the impact of DS-related genetic abnormalities on the brain phenotype.We performed in vivo whole brain magnetic resonance imaging (MRI) and hippocampal 1H magnetic resonance spectroscopy (MRS) on the animals at 3 months of age. Subsequently, ex vivo MRI scans and histological analyses were conducted post-mortem. Our findings unveiled the following neuroanatomical and biochemical alterations in the Dp1Tyb brains: a smaller surface area and a rounder shape compared to WT brains, with DS males also presenting smaller global brain volume compared with the counterpart WT. Regional volumetric analysis revealed significant changes in 26 out of 72 examined brain regions, including the medial prefrontal cortex and dorsal hippocampus. These alterations were consistently observed in both in vivo and ex vivo imaging data. Additionally, high-resolution ex vivo imaging enabled us to investigate cerebellar layers and hippocampal subregions, revealing selective areas of decrease and remodelling in these structures.An analysis of hippocampal metabolites revealed an elevation in glutamine and the glutamine/glutamate ratio in the Dp1Tyb mice compared to controls, suggesting a possible imbalance in the excitation/inhibition ratio. This was accompanied by the decreased levels of taurine. Histological analysis revealed fewer neurons in the hippocampal CA3 and DG layers, along with an increase in astrocytes and microglia. These findings recapitulate multiple neuroanatomical and biochemical features associated with DS, enriching our understanding of the potential connection between chromosome 21 trisomy and the resultant phenotype.