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The impact of Mmu17 non-Hsa21 orthologous genes in the Ts65Dn mouse model of Down syndrome: the “gold standard” refuted

ABSTRACT: Background: Despite successful preclinical treatment studies to improve neurocognition in the Ts65Dn mouse model of Down syndrome (DS), translation to humans has failed. This raises questions about the appropriateness of the Ts65Dn mouse as the “gold standard” for DS research. Here we used the novel Ts66Yah mouse that carries both an extra chromosome and the identical segmental Mmu16 trisomy as Ts65Dn without the Mmu17 non-orthologous region. Methods: Forebrains from embryonic day 18.5 Ts66Yah and Ts65Dn mice, along with euploid littermate controls, were used for gene expression and pathway analyses. Behavioral experiments were performed in neonatal and adult mice. Since male Ts66Yah mice are fertile, parent of origin transmission of the extra chromosome was studied. Results: We mapped 45 protein coding genes to the Ts65Dn Mmu17 non-orthologous, among which 71-82 % are expressed during forebrain development. Several of these genes were uniquely overexpressed in Ts65Dn embryonic forebrain; this produced major differences in dysregulated genes and pathways. Despite these genome-wide differences, the primary Mmu16 trisomic effects were highly conserved in both models, resulting in several commonly dysregulated disomic genes and pathways. Delays in motor development, communication and olfactory spatial memory were present in Ts66Yah but more pronounced in Ts65Dn neonates. Adult Ts66Yah mice showed working memory deficits and sex-specific effects in exploratory behavior and spatial hippocampal memory, while long-term memory was preserved. These deficits were milder when compared to Ts65Dn mice. Conclusions: Our findings suggest that triplication of the non-orthologous Mmu17 genes significantly contributes to the phenotype of the Ts65Dn mouse and may explain why preclinical trials that used this model have unsuccessfully translated to human therapies.

ORGANISM(S): Mus musculus

PROVIDER: GSE222355 | GEO | 2023/01/16

REPOSITORIES: GEO

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Project description:Down syndrome (DS), a genetic condition leading to intellectual disability, is characterized by triplication of human chromosome 21. Neuropathological hallmarks of DS include abnormal central nervous system development that manifests during gestation and extends throughout life. As a result, newborns and adults with DS exhibit cognitive and motor deficits and fail to meet typical developmental and lack independent life skills. A critical outstanding question is how DS-specific prenatal and postnatal phenotypes are recapitulated in different mouse models. To begin answering this question, we developed a life span approach to directly compare differences in embryonic brain development, cellularity, gene expression, neonatal and adult behavior behavior in three cytogenetically distinct mouse models of DS—Ts1Cje, Ts65Dn and Dp16/1Yey (Dp16). In the last two decades multiple therapeutic trials have been attempted to improve cognition in humans with DS but the results of these interventions lacked efficacy despide their succes in the Ts65Dn mouse model of DS. To better understand how phenotypic changes in humans in DS are recapitulated in different mouse models, we copared embryonic brain development and gene expression, perinatal behavior and brain excitatoty/inhibitory cell distribution, and adult behavior and gene expression in the Dp16, Ts65Dn and Ts1Cje mouse models of DS. The objectives of this study were to determine the best model(s) for prenatal and postnatal therapeutic trials and to identify treatment endpoints that can be used to evaluate the fficacy of these therapies prior to human clinical trials. Our data showed that, at embryonic day 15.5, Ts65Dn mice are the most profoundly and consistently affected with respect to somatic growth, brain morphogenesis, and neurogenesis compared to Ts1Cje and Dp16 embryos. However, gene expression results show that both Ts65Dn and Ts1Cje embryonic forebrains have a relatively high number of differentially expressed genes compared to Dp16, with little overlap in gene identities and genomic distribution observed among these models. Additionally, postnatal histological analyses show varying degrees of cell population and brain histogenesis abnormalities among the three strains. Behavioral testing also highlights differences among the models in their ability to meet various developmental milestones. At adulthood, Ts65Dn and Ts1Cje showed hyperactive behavior in the open field test but not Dp16 mice. In the fear conditioning test, all three strains showed lower freezing versus eupploid mice; Dp16 were the most severely affected. In the Morris water maze, Ts65Dn showed significant delays in the hidden platform, probe and reversal trials. Dp16 mice showed milder deficits in the hidden platform trial but severe deficits in reversal. Ts1Cje mice had no spatial memory deficits. In the rotarod test, Dp16 performed poorly in fixed and accelerating speed trials, while Ts1Cje was only abnormal at high speeds. Ts65Dn rotarod performance was unaffected. Compared to euploid, Ts65Dn had a higher number of differentially expressed (DEX) genes in cortex and cerebellum, while Ts1Cje had more DEX genes in hippocampus and cerebellum. Dp16 had the lowest number of DEX genes in all regions analyzed. Pathway analyses highlighted commonly dysregulated pathways, including G-protein signaling, oxidative stress, interferon signaling, glycosylation and disulfide bonds.

Project description:Persons with Down syndrome (DS) exhibit low muscle strength that significantly impairs their physical functioning. The Ts65Dn mouse model of DS also exhibits muscle weakness in vivo and may serve as a useful model to examine potential factors responsible for DS-associated muscle dysfunction. Therefore, the purpose of this experiment was to directly assess skeletal muscle function in the Ts65Dn mouse and to reveal potential mechanisms of DS-associated muscle weakness. Soleus muscles were harvested from anesthetized male Ts65Dn and wild-type (WT) colony controls. In vitro muscle contractile experiments revealed normal force generation of unfatigued Ts65Dn soleus, but a 12% reduction in force was observed in Ts65Dn muscle during recovery following fatiguing contractions compared to WT muscle (p<0.05). Oxidative stress may contribute to DS-related pathologies, including muscle weakness, which may be the result of overexpression of chromosome 21 genes (e.g., copper-zinc superoxide dismutase (SOD1)). SOD1 expression was 25% higher (p<0.05) in Ts65Dn soleus compared to WT muscle but levels of other antioxidant proteins were unchanged. Lipid peroxidation (4-hydroxynoneal) was unaltered in Ts65Dn muscle although protein carbonyls were 20% greater compared to muscle of WT animals (p<0.05). Cytochrome c oxidase expression was reduced 22% in Ts65Dn muscle, suggesting a limitation in mitochondrial function may contribute to post-fatigue muscle weakness. Microarray analysis of Ts65Dn soleus revealed alteration of numerous cellular pathways including: proteolysis, glucose and fat metabolism, neuromuscular transmission, and ATP biosynthesis. In summary, the Ts65Dn mouse displays evidence of muscle dysfunction, and the potential role of mitochondria and oxidative stress warrants further investigation. We used microarrays to gain insight into potential mechanisms of DS-associated skeletal muscle weakness. Soleus muscles were obtained from four male Ts65Dn (DS) mice and four male colony control mice. Animals were apparently healthy and approximately five months old. The muscles were harvested in the basal state under anesthesia induced by sodium pentobarbital at approximately the same time of the day.

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The impact of Mmu17 non-Hsa21 orthologous genes in the Ts65Dn mouse model of Down syndrome: the “gold standard” refuted

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