Lifespan analysis of brain development, gene expression and behavioral phenotypes in the Ts1Cje, Ts65Dn and Dp(16)1/Yey mouse models of Down syndrome

Type I interferon signalling and interferon-responsive microglia in health and disease

Recent evidence suggests that type I interferon (IFN-I) signalling extends beyond its canonical roles in antiviral defence and immunomodulation. Over the past decade, dysregulated IFN-I signalling has been linked to genetic disorders and neurodegenerative diseases, where it may contribute to neurological impairments. Microglia have emerged as key mediators of IFN-I responses in the central nervous system. A distinct transcriptional state responsive to interferons has recently been identified in microglia. The activation of the IFN-I pathway in these cells is now recognised as pivotal in both development and neurodegeneration. This review is divided into two main sections: the first examines the broader role of IFN-I signalling in the central nervous system, particularly its contribution to neurological dysfunction; the second focuses on the specific state of interferon-responsive microglia, exploring its mechanisms and relevance in neurodegenerative conditions. Finally, we discuss how these areas intersect and their implications for both healthy and diseased states.

Beta cell function and global glucose metabolism are impaired in Dp(16)1Yey mouse model of Down syndrome

AIMS

Down syndrome (DS) or trisomy 21 is the most prevalent genetic disorder in the world. In addition to common symptoms such as intellectual disabilities and morphological abnormalities, several comorbidities are associated with DS, including metabolic dysfunction. Obesity and diabetes are more prevalent in people with DS compared with the general population. However, the mechanisms linking obesity/diabetes to DS remain poorly understood. Systematic investigation of metabolic disorders in animal models of DS is scarce.

MATERIALS AND METHODS

We used the Dp(16)1Yey mouse model of DS to evaluate the energy and glucose metabolism in both male and female Dp(16)1Yey mice at 3 and 6 months of age. We assessed the whole-body glucose metabolism by glucose and insulin tolerance tests, and investigated the pancreatic functions in terms of insulin synthesis, ß cell mass and the glucose-induced insulin secretion in vivo.

RESULTS

We show that Dp(16)1Yey mice do not present signs of obesity when they are fed with chow diet. However, these mice are glucose intolerant and insulin resistant, and exhibit dysfunctions of their endocrine pancreas, reflected by decreased insulin content and defective glucose-induced insulin secretion (GIIS) in vivo. The impairment of metabolic parameters is similar between males and females trisomic mice, indicating the absence of metabolic sexual dimorphism in this model.

CONCLUSIONS

Our study suggests that Dp(16)1Yey model is suitable for the assessment of metabolic disorders associated with DS.

JAK inhibition decreases the autoimmune burden in Down syndrome

Background

Individuals with Down syndrome (DS), the genetic condition caused by trisomy 21 (T21), display clear signs of immune dysregulation, including high rates of autoimmunity and severe complications from infections. Although it is well established that T21 causes increased interferon responses and JAK/STAT signaling, elevated autoantibodies, global immune remodeling, and hypercytokinemia, the interplay between these processes, the clinical manifestations of DS, and potential therapeutic interventions remain ill defined.

Methods

We report a comprehensive analysis of immune dysregulation at the clinical, cellular, and molecular level in hundreds of individuals with DS, including autoantibody profiling, cytokine analysis, and deep immune mapping. We also report the interim analysis of a Phase II clinical trial investigating the safety and efficacy of the JAK inhibitor tofacitinib through multiple clinical and molecular endpoints.

Results

We demonstrate multi-organ autoimmunity of pediatric onset concurrent with unexpected autoantibody-phenotype associations in DS. Importantly, constitutive immune remodeling and hypercytokinemia occur from an early age prior to autoimmune diagnoses or autoantibody production. Analysis of the first 10 participants to complete 16 weeks of tofacitinib treatment shows a good safety profile and no serious adverse events. Treatment reduced skin pathology in alopecia areata, psoriasis, and atopic dermatitis, while decreasing interferon scores, cytokine scores, and levels of pathogenic autoantibodies without overt immune suppression.

Conclusions

JAK inhibition is a valid strategy to treat autoimmune conditions in DS. Additional research is needed to define the effects of JAK inhibition on the broader developmental and clinical hallmarks of DS.

Funding

NIAMS, Global Down Syndrome Foundation.

Clinical trial number

NCT04246372.

JAK inhibition decreases the autoimmune burden in Down syndrome

Individuals with Down syndrome (DS), the genetic condition caused by trisomy 21 (T21), display clear signs of immune dysregulation, including high rates of autoimmune disorders and severe complications from infections. Although it is well established that T21 causes increased interferon responses and JAK/STAT signaling, elevated autoantibodies, global immune remodeling, and hypercytokinemia, the interplay between these processes, the clinical manifestations of DS, and potential therapeutic interventions remain ill defined. Here, we report a comprehensive analysis of immune dysregulation at the clinical, cellular, and molecular level in hundreds of individuals with DS. We demonstrate multi-organ autoimmunity of pediatric onset concurrent with unexpected autoantibody-phenotype associations. Importantly, constitutive immune remodeling and hypercytokinemia occur from an early age prior to autoimmune diagnoses or autoantibody production. We then report the interim analysis of a Phase II clinical trial investigating the safety and efficacy of the JAK inhibitor tofacitinib through multiple clinical and molecular endpoints. Analysis of the first 10 participants to complete the 16-week study shows a good safety profile and no serious adverse events. Treatment reduced skin pathology in alopecia areata, psoriasis, and atopic dermatitis, while decreasing interferon scores, cytokine scores, and levels of pathogenic autoantibodies without overt immune suppression. Additional research is needed to define the effects of JAK inhibition on the broader developmental and clinical hallmarks of DS. ClinicalTrials.gov identifier: NCT04246372.

Dissecting the contribution of human chromosome 21 syntenic regions to recognition memory processes in adult and aged mouse models of Down syndrome

Background

Trisomy of human chromosome 21 (Hsa21) results in a constellation of features known as Down syndrome (DS), the most common genetic form of intellectual disability. Hsa21 is orthologous to three regions in the mouse genome on mouse chromosome 16 (Mmu16), Mmu17 and Mmu10. We investigated genotype-phenotype relationships by assessing the contribution of these three regions to memory function and age-dependent cognitive decline, using three mouse models of DS, Dp1Tyb, Dp(17)3Yey, Dp(10)2Yey, that carry an extra copy of the Hsa21-orthologues on Mmu16, Mmu17 and Mmu10, respectively.

Hypothesis

Prior research on cognitive function in DS mouse models has largely focused on models with an extra copy of the Mmu16 region and relatively little is known about the effects of increased copy number on Mmu17 and Mmu10 on cognition and how this interacts with the effects of aging. As aging is is a critical contributor to cognitive and psychiatric changes in DS, we hypothesised that ageing would differentially impact memory function in Dp1Tyb, Dp(17)3Yey, and Dp(10)2Yey, models of DS.

Methods

Young (12-13 months and old (18-20 months mice Dp1Tyb, Dp(17)3Yey and Dp(10)2Yey mice were tested on a battery of object recognition memory test that assessed object novelty detection, novel location detection and associative object-in place memory. Following behavioral testing, hippocampal and frontal cortical tissue was analysed for expression of glutamatergic receptor proteins using standard immunoblot techniques.

Results

Young (12-13 months and old (18-20 months mice Dp1Tyb, Dp(17)3Yey and Dp(10)2Yey mice were tested on a battery of object recognition memory test that assessed object novelty detection, novel location detection and associative object-in place memory. Following behavioral testing, hippocampal and frontal cortical tissue was analysed for expression of glutamatergic receptor proteins using standard immunoblot techniques.

Conclusion

Our results show that distinct Hsa21-orthologous regions contribute differentially to cognitive dysfunction in DS mouse models and that aging interacts with triplication of Hsa21-orthologous genes on Mmu10.

Early Chronic Fluoxetine Treatment of Ts65Dn Mice Rescues Synaptic Vesicular Deficits and Prevents Aberrant Proteomic Alterations

Down syndrome (DS) is the most common form of inherited intellectual disability caused by trisomy of chromosome 21, presenting with intellectual impairment, craniofacial abnormalities, cardiac defects, and gastrointestinal disorders. The Ts65Dn mouse model replicates many abnormalities of DS. We hypothesized that investigation of the cerebral cortex of fluoxetine-treated trisomic mice may provide proteomic signatures that identify therapeutic targets for DS. Subcellular fractionation of synaptosomes from cerebral cortices of age- and brain-area-matched samples from fluoxetine-treated vs. water-treated trisomic and euploid male mice were subjected to HPLC-tandem mass spectrometry. Analysis of the data revealed enrichment of trisomic risk genes that participate in regulation of synaptic vesicular traffic, pre-synaptic and post-synaptic development, and mitochondrial energy pathways during early brain development. Proteomic analysis of trisomic synaptic fractions revealed significant downregulation of proteins involved in synaptic vesicular traffic, including vesicular endocytosis (CLTA, CLTB, CLTC), synaptic assembly and maturation (EXOC1, EXOC3, EXOC8), anterograde axonal transport (EXOC1), neurotransmitter transport to PSD (SACM1L), endosomal-lysosomal acidification (ROGDI, DMXL2), and synaptic signaling (NRXN1, HIP1, ITSN1, YWHAG). Additionally, trisomic proteomes revealed upregulation of several trafficking proteins, involved in vesicular exocytosis (Rab5B), synapse elimination (UBE3A), scission of endocytosis (DBN1), transport of ER in dendritic spines (MYO5A), presynaptic activity-dependent bulk endocytosis (FMR1), and NMDA receptor activity (GRIN2A). Chronic fluoxetine treatment of Ts65Dn mice rescued synaptic vesicular abnormalities and prevented abnormal proteomic changes in adult Ts65Dn mice, pointing to therapeutic targets for potential treatment of DS.

Foot Muscle Exercise: A Novel Approach to Improve Motor Functions in Children with Down Syndrome Having Pes Planus - A Randomized Controlled Trial

OBJECTIVE

The study aimed to determine the efficacy of foot muscle exercises in children with DS having pes planus.

METHODS

Forty-seven subjects randomly assigned to foot muscle exercises (study group) or an arch support insole with one-leg balance exercises (control group), thrice weekly intervention for 12-weeks followed by a home program with residual effect assessed after 24-weeks from baseline.

RESULTS

The motor functions were significantly improved in both groups (p = 0.00). A positive residual effect was found in the study group for both parameters. Whilst in the control group it failed to give a positive residual effect for GMFM-88, while PBS yielded positive outcomes. The study group showed significantly better results than the control group in comparison.

CONCLUSION

The novel finding suggests that the foot muscle exercise has the potential to improve motor functions in children with Down syndrome and it can be used as an alternative therapeutic approach to the conventional method.

Pleiotropic effects of trisomy and pharmacologic modulation on structural, functional, molecular, and genetic systems in a Down syndrome mouse model

Down syndrome (DS) is characterized by skeletal and brain structural malformations, cognitive impairment, altered hippocampal metabolite concentration and gene expression imbalance. These alterations were usually investigated separately, and the potential rescuing effects of green tea extracts enriched in epigallocatechin-3-gallate (GTE-EGCG) provided disparate results due to different experimental conditions. We overcame these limitations by conducting the first longitudinal controlled experiment evaluating genotype and GTE-EGCG prenatal chronic treatment effects before and after treatment discontinuation. Our findings revealed that the Ts65Dn mouse model reflected the pleiotropic nature of DS, exhibiting brachycephalic skull, ventriculomegaly, neurodevelopmental delay, hyperactivity, and impaired memory robustness with altered hippocampal metabolite concentration and gene expression. GTE-EGCG treatment modulated most systems simultaneously but did not rescue DS phenotypes. On the contrary, the treatment exacerbated trisomic phenotypes including body weight, tibia microarchitecture, neurodevelopment, adult cognition, and metabolite concentration, not supporting the therapeutic use of GTE-EGCG as a prenatal chronic treatment. Our results highlight the importance of longitudinal experiments assessing the co-modulation of multiple systems throughout development when characterizing preclinical models in complex disorders and evaluating the pleiotropic effects and general safety of pharmacological treatments.

Characterization of Apathy-Like Behaviors in Mouse Models of Down Syndrome

Background

Apathy is a state of decreased interest, lack of initiative, reduced goal-directed activity and blunted emotional responses. Apathy is one of the most common neuropsychiatric symptoms (NPS) in patients with Alzheimer's disease (AD) and is also relatively omnipresent in individuals with Down syndrome (DS). Little is known about the apathy-like behaviors in rodent models of AD and DS.

Objective

This study aimed to characterize apathy-like behaviors with aging in two established DS mouse models: Ts65Dn and Dp16.

Methods

A battery of behavioral tests including nestlet shredding, marble burying, nest building, and burrowing were performed to examine apathy-like behaviors. Individual z-scores for each mouse for each test, and a composite z-score of apathy-like behavior were analyzed for all mice from these behavioral tests.

Results

Analysis of individual test results and composite z-score revealed significant apathy-like behaviors in Ts65Dn mice compared to WT controls. In contrast, Dp16 mice did not exhibit significant apathy-like behaviors.

Conclusions

Our study is the first to characterize apathy-like behaviors in mouse models of DS with aging and highlights the difference between Ts65Dn and Dp16 DS model mice regarding apathy-like manifestations with aging.

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.

Down syndrome is associated with altered frequency and functioning of tracheal multiciliated cells, and response to influenza virus infection

Individuals with Down syndrome (DS) clinically manifest severe respiratory illnesses; however, there is a paucity of data on how DS influences homeostatic physiology of lung airway, and its reactive responses to pulmonary pathogens. We generated well-differentiated ciliated airway epithelia using tracheas from wild-type and Dp(16)1/Yey mice in vitro, and discovered that Dp(16)1/Yey epithelia have significantly lower abundance of ciliated cells, an altered ciliary beating profile, and reduced mucociliary transport. Interestingly, both sets of differentiated epithelia released similar quantities of viral particles after infection with influenza A virus (IAV). However, RNA-sequencing and proteomic analyses revealed an immune hyperreactive phenotype particularly for monocyte-recruiting chemokines in Dp(16)1/Yey epithelia. Importantly, when we challenged mice in vivo with IAV, we observed immune hyper-responsiveness in Dp(16)1/Yey mice, evidenced by higher quantities of lung airway infiltrated monocytes, and elevated levels of pro-inflammatory cytokines in bronchoalveolar lavage fluid. Our findings illuminate mechanisms underlying DS-mediated pathophysiological changes in airway epithelium.

Multidimensional definition of the interferonopathy of Down syndrome and its response to JAK inhibition

Individuals with Down syndrome (DS) display chronic hyperactivation of interferon signaling. However, the clinical impacts of interferon hyperactivity in DS are ill-defined. Here, we describe a multiomics investigation of interferon signaling in hundreds of individuals with DS. Using interferon scores derived from the whole blood transcriptome, we defined the proteomic, immune, metabolic, and clinical features associated with interferon hyperactivity in DS. Interferon hyperactivity associates with a distinct proinflammatory phenotype and dysregulation of major growth signaling and morphogenic pathways. Individuals with the highest interferon activity display the strongest remodeling of the peripheral immune system, including increased cytotoxic T cells, B cell depletion, and monocyte activation. Interferon hyperactivity accompanies key metabolic changes, most prominently dysregulated tryptophan catabolism. High interferon signaling stratifies a subpopulation with elevated rates of congenital heart disease and autoimmunity. Last, a longitudinal case study demonstrated that JAK inhibition normalizes interferon signatures with therapeutic benefit in DS. Together, these results justify the testing of immune-modulatory therapies in DS.

Dissection of a Down syndrome-associated trisomy to separate the gene dosage-dependent and -independent effects of an extra chromosome

As an aneuploidy, trisomy is associated with mammalian embryonic and postnatal abnormalities. Understanding the underlying mechanisms involved in mutant phenotypes is broadly important and may lead to new strategies to treat clinical manifestations in individuals with trisomies, such as trisomy 21 [Down syndrome (DS)]. Although increased gene dosage effects because of a trisomy may account for the mutant phenotypes, there is also the possibility that phenotypic consequences of a trisomy can arise because of the presence of a freely segregating extra chromosome with its own centromere, i.e. a 'free trisomy' independent of gene dosage effects. Presently, there are no reports of attempts to functionally separate these two types of effects in mammals. To fill this gap, here we describe a strategy that employed two new mouse models of DS, Ts65Dn;Df(17)2Yey/+ and Dp(16)1Yey/Df(16)8Yey. Both models carry triplications of the same 103 human chromosome 21 gene orthologs; however, only Ts65Dn;Df(17)2Yey/+ mice carry a free trisomy. Comparison of these models revealed the gene dosage-independent impacts of an extra chromosome at the phenotypic and molecular levels for the first time. They are reflected by impairments of Ts65Dn;Df(17)2Yey/+ males in T-maze tests when compared with Dp(16)1Yey/Df(16)8Yey males. Results from the transcriptomic analysis suggest the extra chromosome plays a major role in trisomy-associated expression alterations of disomic genes beyond gene dosage effects. This model system can now be used to deepen our mechanistic understanding of this common human aneuploidy and obtain new insights into the effects of free trisomies in other human diseases such as cancers.

Triplication of the interferon receptor locus contributes to hallmarks of Down syndrome in a mouse model

Down syndrome (DS), the genetic condition caused by trisomy 21, is characterized by variable cognitive impairment, immune dysregulation, dysmorphogenesis and increased prevalence of diverse co-occurring conditions. The mechanisms by which trisomy 21 causes these effects remain largely unknown. We demonstrate that triplication of the interferon receptor (IFNR) gene cluster on chromosome 21 is necessary for multiple phenotypes in a mouse model of DS. Whole-blood transcriptome analysis demonstrated that IFNR overexpression associates with chronic interferon hyperactivity and inflammation in people with DS. To define the contribution of this locus to DS phenotypes, we used genome editing to correct its copy number in a mouse model of DS, which normalized antiviral responses, prevented heart malformations, ameliorated developmental delays, improved cognition and attenuated craniofacial anomalies. Triplication of the Ifnr locus modulates hallmarks of DS in mice, suggesting that trisomy 21 elicits an interferonopathy potentially amenable to therapeutic intervention.

From neurodevelopment to neurodegeneration: utilizing human stem cell models to gain insight into Down syndrome

Down syndrome (DS), caused by triplication of chromosome 21, is the most frequent aneuploidy observed in the human population and represents the most common genetic form of intellectual disability and early-onset Alzheimer's disease (AD). Individuals with DS exhibit a wide spectrum of clinical presentation, with a number of organs implicated including the neurological, immune, musculoskeletal, cardiac, and gastrointestinal systems. Decades of DS research have illuminated our understanding of the disorder, however many of the features that limit quality of life and independence of individuals with DS, including intellectual disability and early-onset dementia, remain poorly understood. This lack of knowledge of the cellular and molecular mechanisms leading to neurological features of DS has caused significant roadblocks in developing effective therapeutic strategies to improve quality of life for individuals with DS. Recent technological advances in human stem cell culture methods, genome editing approaches, and single-cell transcriptomics have provided paradigm-shifting insights into complex neurological diseases such as DS. Here, we review novel neurological disease modeling approaches, how they have been used to study DS, and what questions might be addressed in the future using these innovative tools.

Developmental Brain Injury and Social Determinants of Health: Opportunities to Combine Preclinical Models for Mechanistic Insights into Recovery

Epidemiological studies show that social determinants of health are among the strongest factors associated with developmental outcomes after prenatal and perinatal brain injuries, even when controlling for the severity of the initial injury. Elevated socioeconomic status and a higher level of parental education correlate with improved neurologic function after premature birth. Conversely, children experiencing early life adversity have worse outcomes after developmental brain injuries. Animal models have provided vital insight into mechanisms perturbed by developmental brain injuries, which have indicated directions for novel therapeutics or interventions. Animal models have also been used to learn how social environments affect brain maturation through enriched environments and early adverse conditions. We recognize animal models cannot fully recapitulate human social circumstances. However, we posit that mechanistic studies combining models of developmental brain injuries and early life social environments will provide insight into pathways important for recovery. Some studies combining enriched environments with neonatal hypoxic injury models have shown improvements in developmental outcomes, but further studies are needed to understand the mechanisms underlying these improvements. By contrast, there have been more limited studies of the effects of adverse conditions on developmental brain injury extent and recovery. Uncovering the biological underpinnings for early life social experiences has translational relevance, enabling the development of novel strategies to improve outcomes through lifelong treatment. With the emergence of new technologies to analyze subtle molecular and behavioral phenotypes, here we discuss the opportunities for combining animal models of developmental brain injury with social construct models to deconvolute the complex interactions between injury, recovery, and social inequity.

Visual discrimination and inhibitory control deficits in mouse models of Down syndrome: A pilot study using rodent touchscreen technology

Several non-verbal cognitive and behavioral tests have been developed to assess learning deficits in humans with Down syndrome (DS). Here we used rodent touchscreen paradigms in adult male mice to investigate visual discrimination (VD) learning and inhibitory control in the Dp(16)1/Yey (C57BL/6J genetic background), Ts65Dn (mixed B6 X C3H genetic background) and Ts1Cje (C57BL/6J genetic background) mouse models of DS. Dp(16)1/Yey and Ts1Cje models did not exhibit motivation or learning deficits during early pre-training, however, Ts1Cje mice showed a significant learning delay after the introduction of the incorrect stimulus (late pre-training), suggesting prefrontal cortex defects in this model. Dp(16)1/Yey and Ts1Cje mice display learning deficits in VD but these deficits were more pronounced in the Dp(16)1/Yey model. Both models also exhibited compulsive behavior and abnormal cortical inhibitory control during Extinction compared to WT littermates. Finally, Ts65Dn mice outperformed WT littermates in pre-training stages by initiating a significantly higher number of trials due to their hyperactive behavior. Both Ts65Dn and WT littermates showed poor performance during late pre-training and were not tested in VD. These studies demonstrate significant learning deficits and compulsive behavior in the Ts1Cje and Dp(16)1/Yey mouse models of DS. They also demonstrate that the mouse genetic background (C57BL/6J vs. mixed B6 X C3H) and the absence of hyperactive behavior are key determinants of successful learning in touchscreen behavioral testing. These data will be used to select the mouse model that best mimics cognitive deficits in humans with DS and evaluate the effects of future therapeutic interventions.

Inverse Comorbidity between Down Syndrome and Solid Tumors: Insights from In Silico Analyses of Down Syndrome Critical Region Genes

An inverse comorbidity has been observed between Down syndrome (DS) and solid tumors such as breast and lung cancers, and it is posited that the overexpression of genes within the Down Syndrome Critical Region (DSCR) of human chromosome 21 may account for this phenomenon. By analyzing publicly available DS mouse model transcriptomics data, we aimed to identify DSCR genes that may protect against human breast and lung cancers. Gene expression analyses with GEPIA2 and UALCAN showed that DSCR genes ETS2 and RCAN1 are significantly downregulated in breast and lung cancers, and their expression levels are higher in triple-negative compared to luminal and HER2-positive breast cancers. KM Plotter showed that low levels of ETS2 and RCAN1 are associated with poor survival outcomes in breast and lung cancers. Correlation analyses using OncoDB revealed that both genes are positively correlated in breast and lung cancers, suggesting that they are co-expressed and perhaps have complementary functions. Functional enrichment analyses using LinkedOmics also demonstrated that ETS2 and RCAN1 expression correlates with T-cell receptor signaling, regulation of immunological synapses, TGF-β signaling, EGFR signaling, IFN-γ signaling, TNF signaling, angiogenesis, and the p53 pathway. Altogether, ETS2 and RCAN1 may be essential for the development of breast and lung cancers. Experimental validation of their biological functions may further unravel their roles in DS and breast and lung cancers.

β2-microglobulin functions as an endogenous NMDAR antagonist to impair synaptic function

Down syndrome (DS) is a neurological disorder with multiple immune-related symptoms; however, crosstalk between the CNS and peripheral immune system remains unexplored. Using parabiosis and plasma infusion, we found that blood-borne factors drive synaptic deficits in DS. Proteomic analysis revealed elevation of β2-microglobulin (B2M), a major histocompatibility complex class I (MHC-I) component, in human DS plasma. Systemic administration of B2M in wild-type mice led to synaptic and memory defects similar to those observed in DS mice. Moreover, genetic ablation of B2m or systemic administration of an anti-B2M antibody counteracts synaptic impairments in DS mice. Mechanistically, we demonstrate that B2M antagonizes NMDA receptor (NMDAR) function through interactions with the GluN1-S2 loop; blocking B2M-NMDAR interactions using competitive peptides restores NMDAR-dependent synaptic function. Our findings identify B2M as an endogenous NMDAR antagonist and reveal a pathophysiological role for circulating B2M in NMDAR dysfunction in DS and related cognitive disorders.

Regional redistribution of CB1 cannabinoid receptors in human foetal brains with Down's syndrome and their functional modifications in Ts65Dn+/+ mice

AIMS

The endocannabinoid system with its type 1 cannabinoid receptor (CB₁ R) expressed in postmitotic neuroblasts is a critical chemotropic guidance module with its actions cascading across neurogenic commitment, neuronal polarisation and synaptogenesis in vertebrates. Here, we present the systematic analysis of regional CB₁ R expression in the developing human brain from gestational week 14 until birth. In parallel, we diagrammed differences in CB₁ R development in Down syndrome foetuses and identified altered CB₁ R signalling.

METHODS

Foetal brains with normal development or with Down's syndrome were analysed using standard immunohistochemistry, digitalised light microscopy and image analysis (NanoZoomer). CB₁ R function was investigated by in vitro neuropharmacology from neonatal Ts65Dn transgenic mice brains carrying an additional copy of ~90 conserved protein-coding gene orthologues of the human chromosome 21.

RESULTS

We detected a meshwork of fine-calibre, often varicose processes between the subventricular and intermediate zones of the cortical plate in the late first trimester, when telencephalic fibre tracts develop. The density of CB₁ Rs gradually decreased during the second and third trimesters in the neocortex. In contrast, CB₁ R density was maintained, or even increased, in the hippocampus. We found the onset of CB₁ R expression being delayed by ≥1 month in age-matched foetal brains with Down's syndrome. In vitro, CB₁ R excitation induced excess microtubule stabilisation and, consequently, reduced neurite outgrowth.

CONCLUSIONS

We suggest that neuroarchitectural impairments in Down's syndrome brains involve the delayed development and errant functions of the endocannabinoid system, with a particular impact on endocannabinoids modulating axonal wiring.

Intranasal Administration of KYCCSRK Peptide Rescues Brain Insulin Signaling Activation and Reduces Alzheimer's Disease-like Neuropathology in a Mouse Model for Down Syndrome

Down syndrome (DS) is the most frequent genetic cause of intellectual disability and is strongly associated with Alzheimer's disease (AD). Brain insulin resistance greatly contributes to AD development in the general population and previous studies from our group showed an early accumulation of insulin resistance markers in DS brain, already in childhood, and even before AD onset. Here we tested the effects promoted in Ts2Cje mice by the intranasal administration of the KYCCSRK peptide known to foster insulin signaling activation by directly interacting and activating the insulin receptor (IR) and the AKT protein. Therefore, the KYCCSRK peptide might represent a promising molecule to overcome insulin resistance. Our results show that KYCCSRK rescued insulin signaling activation, increased mitochondrial complexes levels (OXPHOS) and reduced oxidative stress levels in the brain of Ts2Cje mice. Moreover, we uncovered novel characteristics of the KYCCSRK peptide, including its efficacy in reducing DYRK1A (triplicated in DS) and BACE1 protein levels, which resulted in reduced AD-like neuropathology in Ts2Cje mice. Finally, the peptide elicited neuroprotective effects by ameliorating synaptic plasticity mechanisms that are altered in DS due to the imbalance between inhibitory vs. excitatory currents. Overall, our results represent a step forward in searching for new molecules useful to reduce intellectual disability and counteract AD development in DS.

Ts66Yah, a mouse model of Down syndrome with improved construct and face validity

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21). The understanding of genotype-phenotype relationships, the identification of driver genes and various proofs of concept for therapeutics have benefited from mouse models. The premier model, named Ts(1716)65Dn/J (Ts65Dn), displayed phenotypes related to human DS features. It carries an additional minichromosome with the Mir155 to Zbtb21 region of mouse chromosome 16, homologous to Hsa21, encompassing around 90 genes, fused to the centromeric part of mouse chromosome 17 from Pisd-ps2/Scaf8 to Pde10a, containing 46 genes not related to Hsa21. Here, we report the investigation of a new model, Ts66Yah, generated by CRISPR/Cas9 without the genomic region unrelated to Hsa21 on the minichromosome. As expected, Ts66Yah replicated DS cognitive features. However, certain phenotypes related to increased activity, spatial learning and molecular signatures were changed, suggesting genetic interactions between the Mir155-Zbtb21 and Scaf8-Pde10a intervals. Thus, Ts66Yah mice have stronger construct and face validity than Ts65Dn mice for mimicking consequences of DS genetic overdosage. Furthermore, this study is the first to demonstrate genetic interactions between triplicated regions homologous to Hsa21 and others unrelated to Hsa21. This article has an associated First Person interview with the first author of the paper.

Rescue of deficits by Brwd1 copy number restoration in the Ts65Dn mouse model of Down syndrome

With an incidence of ~1 in 800 births, Down syndrome (DS) is the most common chromosomal condition linked to intellectual disability worldwide. While the genetic basis of DS has been identified as a triplication of chromosome 21 (HSA21), the genes encoded from HSA21 that directly contribute to cognitive deficits remain incompletely understood. Here, we found that the HSA21-encoded chromatin effector, BRWD1, was upregulated in neurons derived from iPS cells from an individual with Down syndrome and brain of trisomic mice. We showed that selective copy number restoration of Brwd1 in trisomic animals rescued deficits in hippocampal LTP, cognition and gene expression. We demonstrated that Brwd1 tightly binds the BAF chromatin remodeling complex, and that increased Brwd1 expression promotes BAF genomic mistargeting. Importantly, Brwd1 renormalization rescued aberrant BAF localization, along with associated changes in chromatin accessibility and gene expression. These findings establish BRWD1 as a key epigenomic mediator of normal neurodevelopment and an important contributor to DS-related phenotypes.

Biphasic cell cycle defect causes impaired neurogenesis in down syndrome

Impaired neurogenesis in Down syndrome (DS) is characterized by reduced neurons, increased glial cells, and delayed cortical lamination. However, the underlying cause for impaired neurogenesis in DS is not clear. Using both human and mouse iPSCs, we demonstrate that DS impaired neurogenesis is due to biphasic cell cycle dysregulation during the generation of neural progenitors from iPSCs named the “neurogenic stage” of neurogenesis. Upon neural induction, DS cells showed reduced proliferation during the early phase followed by increased proliferation in the late phase of the neurogenic stage compared to control cells. While reduced proliferation in the early phase causes reduced neural progenitor pool, increased proliferation in the late phase leads to delayed post mitotic neuron generation in DS. RNAseq analysis of late-phase DS progenitor cells revealed upregulation of S phase-promoting regulators, Notch, Wnt, Interferon pathways, and REST, and downregulation of several genes of the BAF chromatin remodeling complex. NFIB and POU3F4, neurogenic genes activated by the interaction of PAX6 and the BAF complex, were downregulated in DS cells. ChIPseq analysis of late-phase neural progenitors revealed aberrant PAX6 binding with reduced promoter occupancy in DS cells. Together, these data indicate that impaired neurogenesis in DS is due to biphasic cell cycle dysregulation during the neurogenic stage of neurogenesis.

A Simplified Paradigm of Late Gestation Transient Prenatal Hypoxia to Investigate Functional and Structural Outcomes from a Developmental Hypoxic Insult

Late-gestation transient intrauterine hypoxia is a common cause of birth injury. It can lead to long-term neurodevelopmental disabilities even in the absence of gross anatomic injury. Currently, postnatal models of hypoxia-ischemia are most commonly used to study the effect of oxygen deprivation in the fetal brain. These models, however, are unable to take into account placental factors that influence the response to hypoxia, exhibit levels of cell death not seen in many human patients, and are unable to model preterm hypoxia. To address this gap in research, we have developed a protocol to induce transient hypoxia in fetal mice. A pregnant dam at gestational day 17.5 is placed into a hypoxia chamber. Over 30 min, the inspired oxygen is titrated from 21% (ambient air) to 5%. The dam remains in the chamber for up to 8 h, after which fetal brains can be collected or pups delivered for postnatal studies. This protocol recapitulates phenotypes seen in human patients exposed to transient in utero hypoxia and is readily reproducible by researchers. Graphical abstract.

Brain circuit pathology in Down syndrome: from neurons to neural networks

Down syndrome (DS), a genetic pathology caused by triplication of chromosome 21, is characterized by brain hypotrophy and impairment of cognition starting from infancy. While studies in mouse models of DS have elucidated the major neuroanatomical and neurochemical defects of DS, comparatively fewer investigations have focused on the electrophysiology of the DS brain. Electrical activity is at the basis of brain functioning. Therefore, knowledge of the way in which brain circuits operate in DS is fundamental to understand the causes of behavioral impairment and devise targeted interventions. This review summarizes the state of the art regarding the electrical properties of the DS brain, starting from individual neurons and culminating in signal processing in whole neuronal networks. The reported evidence derives from mouse models of DS and from brain tissues and neurons derived from individuals with DS. EEG data recorded in individuals with DS are also provided as a key tool to understand the impact of brain circuit alterations on global brain activity.

Chr21 protein-protein interactions: enrichment in proteins involved in intellectual disability, autism, and late-onset Alzheimer's disease

Down syndrome (DS) is caused by human chromosome 21 (HSA21) trisomy. It is characterized by a poorly understood intellectual disability (ID). We studied two mouse models of DS, one with an extra copy of the <i>Dyrk1A</i> gene (189N3) and the other with an extra copy of the mouse Chr16 syntenic region (Dp(16)1Yey). RNA-seq analysis of the transcripts deregulated in the embryonic hippocampus revealed an enrichment in genes associated with chromatin for the 189N3 model, and synapses for the Dp(16)1Yey model. A large-scale yeast two-hybrid screen (82 different screens, including 72 HSA21 baits and 10 rebounds) of a human brain library containing at least 10⁷ independent fragments identified 1,949 novel protein-protein interactions. The direct interactors of HSA21 baits and rebounds were significantly enriched in ID-related genes (<i>P</i>-value &lt; 2.29 × 10^-8). Proximity ligation assays showed that some of the proteins encoded by HSA21 were located at the dendritic spine postsynaptic density, in a protein network at the dendritic spine postsynapse. We located HSA21 DYRK1A and DSCAM, mutations of which increase the risk of autism spectrum disorder (ASD) 20-fold, in this postsynaptic network. We found that an intracellular domain of DSCAM bound either DLGs, which are multimeric scaffolds comprising receptors, ion channels and associated signaling proteins, or DYRK1A. The DYRK1A-DSCAM interaction domain is conserved in <i>Drosophila</i> and humans. The postsynaptic network was found to be enriched in proteins associated with ARC-related synaptic plasticity, ASD, and late-onset Alzheimer's disease. These results highlight links between DS and brain diseases with a complex genetic basis.

Neurodevelopment in Down syndrome: Concordance in humans and models

Great strides have been made over the past 30 years in understanding the neurodevelopmental changes underlying the intellectual disability (ID) in Down syndrome (DS). Detailed studies of human tissue coupled with findings from rodent and induced pluripotent stem cells (iPSCs) model systems have uncovered the changes in neurogenesis, synaptic connectivity, and myelination that drive the anatomical and physiological changes resulting in the disability. However, there remain significant conflicting data between human studies and the models. To fully understand the development of ID in DS, these inconsistencies need to be reconciled. Here, we review the well documented neurodevelopmental phenotypes found in individuals with DS and examine the degree to which widely used models recapitulate these phenotypes. Resolving these areas of discord will further research on the molecular underpinnings and identify potential treatments to improve the independence and quality of life of people with DS.

Multimodal in vivo Imaging of the Integrated Postnatal Development of Brain and Skull and Its Co-modulation With Neurodevelopment in a Down Syndrome Mouse Model

The brain and skeletal systems are intimately integrated during development through common molecular pathways. This is evidenced by genetic disorders where brain and skull dysmorphologies are associated. However, the mechanisms underlying neural and skeletal interactions are poorly understood. Using the Ts65Dn mouse model of Down syndrome (DS) as a case example, we performed the first longitudinal assessment of brain, skull and neurobehavioral development to determine alterations in the coordinated morphogenesis of brain and skull. We optimized a multimodal protocol combining in vivo micro-computed tomography (μCT) and magnetic resonance imaging (μMRI) with morphometric analyses and neurodevelopmental tests to longitudinally monitor the different systems' development trajectories during the first postnatal weeks. We also explored the impact of a perinatal treatment with green tea extracts enriched in epigallocatechin-3-gallate (GTE-EGCG), which can modulate cognition, brain and craniofacial development in DS. Our analyses quantified alterations associated with DS, with skull dysmorphologies appearing before brain anomalies, reduced integration and delayed acquisition of neurodevelopmental traits. Perinatal GTE-EGCG induced disparate effects and disrupted the magnitude of integration and covariation patterns between brain and skull. Our results exemplify how a longitudinal research approach evaluating the development of multiple systems can reveal the effect of morphological integration modulating the response of pathological phenotypes to treatment, furthering our understanding of complex genetic disorders.

Genes Associated with Disturbed Cerebral Neurogenesis in the Embryonic Brain of Mouse Models of Down Syndrome

Down syndrome (DS), also known as trisomy 21, is the most frequent genetic cause of intellectual disability. Although the mechanism remains unknown, delayed brain development is assumed to be involved in DS intellectual disability. Analyses with human with DS and mouse models have shown that defects in embryonic cortical neurogenesis may lead to delayed brain development. Cre-loxP-mediated chromosomal engineering has allowed the generation of a variety of mouse models carrying various partial Mmu16 segments. These mouse models are useful for determining genotype–phenotype correlations and identifying dosage-sensitive genes involved in the impaired neurogenesis. In this review, we summarize several candidate genes and pathways that have been linked to defective cortical neurogenesis in DS.

Comprehensive phenotypic analysis of the Dp1Tyb mouse strain reveals a broad range of Down syndrome-related phenotypes

Down syndrome (DS), trisomy 21, results in many complex phenotypes including cognitive deficits, heart defects and craniofacial alterations. Phenotypes arise from an extra copy of human chromosome 21 (Hsa21) genes. However, these dosage-sensitive causative genes remain unknown. Animal models enable identification of genes and pathological mechanisms. The Dp1Tyb mouse model of DS has an extra copy of 63% of Hsa21-orthologous mouse genes. In order to establish whether this model recapitulates DS phenotypes, we comprehensively phenotyped Dp1Tyb mice using 28 tests of different physiological systems and found that 468 out of 1800 parameters were significantly altered. We show that Dp1Tyb mice have wide-ranging DS-like phenotypes, including aberrant erythropoiesis and megakaryopoiesis, reduced bone density, craniofacial changes, altered cardiac function, a pre-diabetic state, and deficits in memory, locomotion, hearing and sleep. Thus, Dp1Tyb mice are an excellent model for investigating complex DS phenotype-genotype relationships for this common disorder.

Context Fear Conditioning in Down Syndrome Mouse Models: Effects of Trisomic Gene Content, Age, Sex and Genetic Background

Down syndrome (DS), trisomy of the long arm of human chromosome 21 (Hsa21), is the most common genetic cause of intellectual disability (ID). Currently, there are no effective pharmacotherapies. The success of clinical trials to improve cognition depends in part on the design of preclinical evaluations in mouse models. To broaden understanding of the common limitations of experiments in learning and memory, we report performance in context fear conditioning (CFC) in three mouse models of DS, the Dp(16)1Yey, Dp(17)1Yey and Dp(10)1Yey (abbreviated Dp16, Dp17 and Dp10), separately trisomic for the human Hsa21 orthologs mapping to mouse chromosomes 16, 17 and 10, respectively. We examined female and male mice of the three lines on the standard C57BL/6J background at 3 months of age and Dp17 and Dp10 at 18 months of age. We also examined female and male mice of Dp17 and Dp10 at 3 months of age as F1 hybrids obtained from a cross with the DBA/2J background. Results indicate that genotype, sex, age and genetic background affect CFC performance. These data support the need to use both female and male mice, trisomy of sets of all Hsa21 orthologs, and additional ages and genetic backgrounds to improve the reliability of preclinical evaluations of drugs for ID in DS.

Building the Future Therapies for Down Syndrome: The Third International Conference of the T21 Research Society

Research focused on Down syndrome has increased in the last several years to advance understanding of the consequences of trisomy 21 (T21) on molecular and cellular processes and, ultimately, on individuals with Down syndrome. The Trisomy 21 Research Society (T21RS) is the premier scientific organization for researchers and clinicians studying Down syndrome. The Third International Conference of T21RS, held June 6-9, 2019, in Barcelona, Spain, brought together 429 scientists, families, and industry representatives to share the latest discoveries on underlying cellular and molecular mechanisms of T21, define cognitive and behavioral challenges and better understand comorbidities associated with Down syndrome, including Alzheimer's disease and leukemia. Presentation of cutting-edge results in neuroscience, neurology, model systems, psychology, cancer, biomarkers and molecular and phar-ma-cological therapeutic approaches demonstrate the compelling interest and continuing advancement in all aspects of understanding and ameliorating conditions associated with T21.

Coat Color-Facilitated Efficient Generation and Analysis of a Mouse Model of Down Syndrome Triplicated for All Human Chromosome 21 Orthologous Regions

Down syndrome (DS) is one of the most complex genetic disorders in humans and a leading genetic cause of developmental delays and intellectual disabilities. The mouse remains an essential model organism in DS research because human chromosome 21 (Hsa21) is orthologously conserved with three regions in the mouse genome. Recent studies have revealed complex interactions among different triplicated genomic regions and Hsa21 gene orthologs that underlie major DS phenotypes. Because we do not know conclusively which triplicated genes are indispensable in such interactions for a specific phenotype, it is desirable that all evolutionarily conserved Hsa21 gene orthologs are triplicated in a complete model. For this reason, the Dp(10)1Yey/+;Dp(16)1Yey/+;Dp(17)1Yey/+ mouse is the most complete model of DS to reflect gene dosage effects because it is the only mutant triplicated for all Hsa21 orthologous regions. Recently, several groups have expressed concerns that efforts needed to generate the triple compound model would be so overwhelming that it may be impractical to take advantage of its unique strength. To alleviate these concerns, we developed a strategy to drastically improve the efficiency of generating the triple compound model with the aid of a targeted coat color, and the results confirmed that the mutant mice generated via this approach exhibited cognitive deficits.

Multi-influential genetic interactions alter behaviour and cognition through six main biological cascades in Down syndrome mouse models

Down syndrome (DS) is the most common genetic form of intellectual disability caused by the presence of an additional copy of human chromosome 21 (Hsa21). To provide novel insights into genotype–phenotype correlations, we used standardized behavioural tests, magnetic resonance imaging and hippocampal gene expression to screen several DS mouse models for the mouse chromosome 16 region homologous to Hsa21. First, we unravelled several genetic interactions between different regions of chromosome 16 and how they contribute significantly to altering the outcome of the phenotypes in brain cognition, function and structure. Then, in-depth analysis of misregulated expressed genes involved in synaptic dysfunction highlighted six biological cascades centred around DYRK1A, GSK3β, NPY, SNARE, RHOA and NPAS4. Finally, we provide a novel vision of the existing altered gene–gene crosstalk and molecular mechanisms targeting specific hubs in DS models that should become central to better understanding of DS and improving the development of therapies.

Insulin resistance, oxidative stress and mitochondrial defects in Ts65dn mice brain: A harmful synergistic path in down syndrome

Dysregulation of brain insulin signaling with reduced downstream neuronal survival and plasticity mechanisms are fundamental abnormalities observed in Alzheimer disease (AD). This phenomenon, known as brain insulin resistance, is associated with poor cognitive performance and is driven by the inhibition of IRS1. Since Down syndrome (DS) and AD neuropathology share many common features, we investigated metabolic aspects of neurodegeneration in DS and whether they contribute to early onset AD in DS. We evaluated levels and activation of proteins belonging to the insulin signaling pathway (IR, IRS1, BVR-A, MAPK, PTEN, Akt, GSK3β, PKCζ, AS160, GLUT4) in the frontal cortex of Ts65dn (DS model) (n = 5-6/group) and euploid mice (n = 6/group) at different ages (1, 3, 9 and 18 months). Furthermore, we analyzed whether changes of brain insulin signaling were associated with alterations of: (i) proteins regulating brain energy metabolism (mitochondrial complexes, hexokinase-II, Sirt1); (ii) oxidative stress (OS) markers (iii) APP cleavage; and (iv) proteins mediating synaptic plasticity mechanisms (PSD95, syntaxin-1 and BDNF). Ts65dn mice showed an overall impairment of the above-mentioned pathways, mainly characterized by defects of proteins activation state. Such alterations start early in life (at 1 month, during brain maturation). In particular, accumulation of inhibited IRS1, together with the uncoupling among the proteins downstream from IRS1 (brain insulin resistance), characterize Ts65dn mice. Furthermore, reduced levels of mitochondrial complexes and Sirt1, as well as increased indices of OS also were observed. These alterations precede the accumulation of APP-C99 in Ts65dn mice. Tellingly, oxidative stress levels were negatively associated with IR, IRS1 and AS160 activation as well as mitochondrial complexes levels in Ts65dn mice, suggesting a role for oxidative stress in the observed alterations. We propose that a close link exists among brain insulin resistance, mitochondrial defects and OS that contributes to brain dysfunctions observed in DS, likely favoring the development of AD in DS.

From the lab to the people: major challenges in the biological treatment of Down syndrome

Down syndrome (DS) refers to a genetic condition due to the triplication of human chromosome 21. It is the most frequent autosomal trisomy. In recent years, experimental work has been conducted with the aim of removing or silencing the extra chromosome 21 (C21) in cells and normalizing genetic expression. This paper examines the feasibility of the move from laboratory studies to biologically treating “bone and flesh” people with DS. A chromosome or a gene therapy for humans is fraught with practical and ethical difficulties. To prevent DS completely, genome editing would have to be performed early on embryos in the womb. New in vitro findings point toward the possibility of epigenetic silencing the extra C21 in later embryonic or fetal life, or even postnatally for some aspects of neurogenesis. These possibilities are far beyond what is possible or allowed today. Another approach is through epigenetic regulation of the overexpression of particular genes in C21. Research with mouse modeling of DS is yielding promising results. Human applications have barely begun and are questioned on ethical grounds.

Subtle Roles of Down Syndrome Cell Adhesion Molecules in Embryonic Forebrain Development and Neuronal Migration

Down Syndrome (DS) Cell Adhesion Molecules (DSCAMs) are transmembrane proteins of the immunoglobulin superfamily. Human DSCAM is located within the DS critical region of chromosome 21 (duplicated in Down Syndrome patients), and mutations or copy-number variations of this gene have also been associated to Fragile X syndrome, intellectual disability, autism, and bipolar disorder. The DSCAM paralogue DSCAM-like 1 (DSCAML1) maps to chromosome 11q23, implicated in the development of Jacobsen and Tourette syndromes. Additionally, a spontaneous mouse DSCAM deletion leads to motor coordination defects and seizures. Previous research has revealed roles for DSCAMs in several neurodevelopmental processes, including synaptogenesis, dendritic self-avoidance, cell sorting, axon growth and branching. However, their functions in embryonic mammalian forebrain development have yet to be completely elucidated. In this study, we revealed highly dynamic spatiotemporal patterns of Dscam and Dscaml1 expression in definite cortical layers of the embryonic mouse brain, as well as in structures and ganglionic eminence-derived neural populations within the embryonic subpallium. However, an in-depth histological analysis of cortical development, ventral forebrain morphogenesis, cortical interneuron migration, and cortical-subcortical connectivity formation processes in Dscam and Dscaml1 knockout mice (Dscam del17 and Dscaml1 GT ) at several embryonic stages indicated that constitutive loss of Dscam and Dscaml1 does not affect these developmental events in a significant manner. Given that several Dscam- and Dscaml1-linked neurodevelopmental disorders are associated to chromosomal region duplication events, we furthermore sought to examine the neurodevelopmental effects of Dscam and Dscaml1 gain of function (GOF). In vitro, ex vivo, and in vivo GOF negatively impacted neural migration processes important to cortical development, and affected the morphology of maturing neurons. Overall, these findings contribute to existing knowledge on the molecular etiology of human neurodevelopmental disorders by elucidating how dosage variations of genes encoding adhesive cues can disrupt cell-cell or cell-environment interactions crucial for neuronal migration.

Mitigating Cognitive Deficits in Down Syndrome by Managing Microglia Activation

In this issue of Neuron, the comprehensive and multidisciplinary results from Pinto et al. (2020) point to novel and widespread microglial dysfunction in Down syndrome that results in impaired cognitive ability. A common pharmaceutical (acetaminophen) is shown to offset these effects in mouse models.

Network analysis of Down syndrome and SARS-CoV-2 identifies risk and protective factors for COVID-19

SARS-CoV-2 infection has spread uncontrollably worldwide while it remains unknown how vulnerable populations, such as Down syndrome (DS) individuals are affected by the COVID-19 pandemic. Individuals with DS have more risk of infections with respiratory complications and present signs of auto-inflammation. They also present with multiple comorbidities that are associated with poorer COVID-19 prognosis in the general population. All this might place DS individuals at higher risk of SARS-CoV-2 infection or poorer clinical outcomes. In order to get insight into the interplay between DS genes and SARS-cov2 infection and pathogenesis we identified the genes associated with the molecular pathways involved in COVID-19 and the host proteins interacting with viral proteins from SARS-CoV-2. We then analyzed the overlaps of these genes with HSA21 genes, HSA21 interactors and other genes consistently differentially expressed in DS (using public transcriptomic datasets) and created a DS-SARS-CoV-2 network. We detected COVID-19 protective and risk factors among HSA21 genes and interactors and/or DS deregulated genes that might affect the susceptibility of individuals with DS both at the infection stage and in the progression to acute respiratory distress syndrome. Our analysis suggests that at the infection stage DS individuals might be more susceptible to infection due to triplication of TMPRSS2, that primes the viral S protein for entry in the host cells. However, as the anti-viral interferon I signaling is also upregulated in DS, this might increase the initial anti-viral response, inhibiting viral genome release, viral replication and viral assembly. In the second pro-inflammatory immunopathogenic phase of the infection, the prognosis for DS patients might worsen due to upregulation of inflammatory genes that might favor the typical cytokine storm of COVID-19. We also detected strong downregulation of the NLRP3 gene, critical for maintenance of homeostasis against pathogenic infections, possibly leading to bacterial infection complications.

Decrease in the T-box1 gene expression in embryonic brain and adult hippocampus of down syndrome mouse models

Down syndrome (DS, Trisomy 21) is the most common genetic cause of delayed fetal brain development and postnatal intellectual disability. Although delayed fetal brain development might be involved in intellectual disability, no evidence of an association between these abnormal phenotypes has been shown. To identify molecules differentially expressed in both the prenatal forebrain and adult hippocampus of Ts1Cje mice, a mouse model of DS, we employed a transcriptomic analysis. In the present study, we conducted transcriptomic profiling of the hippocampus of adult Ts1Cje mice and compared the results with the previously obtained transcriptomic profile of the prenatal forebrain at embryonic day 14.5. Results showed that the Tbx1 mRNA expression was decreased at both life stages. In addition, the decreased expression of Tbx1 mRNA was confirmed in other DS mouse models, Dp(16)1Yey/+ and Ts1Rhr mice, which carry longer and shorter trisomic regions, respectively. Taken together, these findings suggest that Tbx1 may link the delayed fetal brain development and intellectual disability in DS.

JAK1 Inhibition Blocks Lethal Immune Hypersensitivity in a Mouse Model of Down Syndrome

Individuals with Down syndrome (DS; trisomy 21) display hyperactivation of interferon (IFN) signaling and chronic inflammation, which could potentially be explained by the extra copy of four IFN receptor (IFNR) genes encoded on chromosome 21. However, the clinical effects of IFN hyperactivity in DS remain undefined. Here, we report that a commonly used mouse model of DS overexpresses IFNR genes and shows hypersensitivity to IFN ligands in diverse immune cell types. When treated repeatedly with a TLR3 agonist to induce chronic inflammation, these animals overexpress key IFN-stimulated genes, induce cytokine production, exhibit liver pathology, and undergo rapid weight loss. Importantly, the lethal immune hypersensitivity and cytokine production and the ensuing pathology are ameliorated by JAK1 inhibition. These results indicate that individuals with DS may experience harmful hyperinflammation upon IFN-inducing immune stimuli, as observed during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, pointing to JAK1 inhibition as a strategy to restore immune homeostasis in DS.

Apigenin as a Candidate Prenatal Treatment for Trisomy 21: Effects in Human Amniocytes and the Ts1Cje Mouse Model

Human fetuses with trisomy 21 (T21) have atypical brain development that is apparent sonographically in the second trimester. We hypothesize that by analyzing and integrating dysregulated gene expression and pathways common to humans with Down syndrome (DS) and mouse models we can discover novel targets for prenatal therapy. Here, we tested the safety and efficacy of apigenin, identified with this approach, in both human amniocytes from fetuses with T21 and in the Ts1Cje mouse model. In vitro, T21 cells cultured with apigenin had significantly reduced oxidative stress and improved antioxidant defense response. In vivo, apigenin treatment mixed with chow was administered prenatally to the dams and fed to the pups over their lifetimes. There was no significant increase in birth defects or pup deaths resulting from prenatal apigenin treatment. Apigenin significantly improved several developmental milestones and spatial olfactory memory in Ts1Cje neonates. In addition, we noted sex-specific effects on exploratory behavior and long-term hippocampal memory in adult mice, and males showed significantly more improvement than females. We demonstrated that the therapeutic effects of apigenin are pleiotropic, resulting in decreased oxidative stress, activation of pro-proliferative and pro-neurogenic genes (KI67, Nestin, Sox2, and PAX6), reduction of the pro-inflammatory cytokines INFG, IL1A, and IL12P70 through the inhibition of NFκB signaling, increase of the anti-inflammatory cytokines IL10 and IL12P40, and increased expression of the angiogenic and neurotrophic factors VEGFA and IL7. These studies provide proof of principle that apigenin has multiple therapeutic targets in preclinical models of DS.

ViceCT and whiceCT for simultaneous high-resolution visualization of craniofacial, brain and ventricular anatomy from micro-computed tomography

Up to 40% of congenital diseases present disturbances of brain and craniofacial development resulting in simultaneous alterations of both systems. Currently, the best available method to preclinically visualize the brain and the bones simultaneously is to co-register micro-magnetic resonance (µMR) and micro-computed tomography (µCT) scans of the same specimen. However, this requires expertise and access to both imaging techniques, dedicated software and post-processing knowhow. To provide a more affordable, reliable and accessible alternative, recent research has focused on optimizing a contrast-enhanced µCT protocol using iodine as contrast agent that delivers brain and bone images from a single scan. However, the available methods still cannot provide the complete visualization of both the brain and whole craniofacial complex. In this study, we have established an optimized protocol to diffuse the contrast into the brain that allows visualizing the brain parenchyma and the complete craniofacial structure in a single ex vivo µCT scan (whiceCT). In addition, we have developed a new technique that allows visualizing the brain ventricles using a bilateral stereotactic injection of iodine-based contrast (viceCT). Finally, we have tested both techniques in a mouse model of Down syndrome, as it is a neurodevelopmental disorder with craniofacial, brain and ventricle defects. The combined use of viceCT and whiceCT provides a complete visualization of the brain and bones with intact craniofacial structure of an adult mouse ex vivo using a single imaging modality.

Longitudinal neuroanatomical and behavioral analyses show phenotypic drift and variability in the Ts65Dn mouse model of Down syndrome

Mouse models of Down syndrome (DS) have been invaluable tools for advancing knowledge of the underlying mechanisms of intellectual disability in people with DS. The Ts(1716)65Dn (Ts65Dn) mouse is one of the most commonly used models as it recapitulates many of the phenotypes seen in individuals with DS, including neuroanatomical changes and impaired learning and memory. In this study, we use rigorous metrics to evaluate multiple cohorts of Ts65Dn ranging from 2014 to the present, including a stock of animals recovered from embryos frozen within ten generations after the colony was first created in 2010. Through quantification of prenatal and postnatal brain development and several behavioral tasks, our results provide a comprehensive comparison of Ts65Dn across time and show a significant amount of variability both across cohorts as well as within cohorts. The inconsistent phenotypes in Ts65Dn mice highlight specific cautions and caveats for use of this model. We outline important steps for ensuring responsible use of Ts65Dn in future research.This article has an associated First Person interview with the first author of the paper.

A multi-level developmental approach to exploring individual differences in Down syndrome: genes, brain, behaviour, and environment

In this article, we focus on the causes of individual differences in Down syndrome (DS), exemplifying the multi-level, multi-method, lifespan developmental approach advocated by Karmiloff-Smith (1998, 2009, 2012, 2016). We evaluate the possibility of linking variations in infant and child development with variations in the (elevated) risk for Alzheimer's disease (AD) in adults with DS. We review the theoretical basis for this argument, considering genetics, epigenetics, brain, behaviour and environment. In studies 1 and 2, we focus on variation in language development. We utilise data from the MacArthur-Bates Communicative Development Inventories (CDI; Fenson et al., 2007), and Mullen Scales of Early Learning (MSEL) receptive and productive language subscales (Mullen, 1995) from 84 infants and children with DS (mean age 2;3, range 0;7 to 5;3). As expected, there was developmental delay in both receptive and expressive vocabulary and wide individual differences. Study 1 examined the influence of an environmental measure (socio-economic status as measured by parental occupation) on the observed variability. SES did not predict a reliable amount of the variation. Study 2 examined the predictive power of a specific genetic measure (apolipoprotein APOE genotype) which modulates risk for AD in adulthood. There was no reliable effect of APOE genotype, though weak evidence that development was faster for the genotype conferring greater AD risk (ε4 carriers), consistent with recent observations in infant attention (D'Souza, Mason et al., 2020). Study 3 considered the concerted effect of the DS genotype on early brain development. We describe new magnetic resonance imaging methods for measuring prenatal and neonatal brain structure in DS (e.g., volumes of supratentorial brain, cortex, cerebellar volume; Patkee et al., 2019). We establish the methodological viability of linking differences in early brain structure to measures of infant cognitive development, measured by the MSEL, as a potential early marker of clinical relevance. Five case studies are presented as proof of concept, but these are as yet too few to discern a pattern.

Behavioral Phenotyping for Down Syndrome in Mice

Down syndrome (DS) is the most frequent genetic cause of intellectual disability, characterized by alterations in different behavioral symptom domains: neurodevelopment, motor behavior, and cognition. As mouse models have the potential to generate data regarding the neurological basis for the specific behavioral profile of DS, and may indicate pharmacological treatments with the potential to affect their behavioral phenotype, it is important to be able to assess disease-relevant behavioral traits in animal models in order to provide biological plausibility to the potential findings. The field is at a juncture that requires assessments that may effectively translate the findings acquired in mouse models to humans with DS. In this article, behavioral tests are described that are relevant to the domains affected in DS. A neurodevelopmental behavioral screen, the balance beam test, and the Multivariate Concentric Square Field test to assess multiple behavioral phenotypes and locomotion are described, discussing the ways to merge these findings to more fully understand cognitive strengths and weaknesses in this population. New directions for approaches to cognitive assessment in mice and humans are discussed. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Preweaning neurodevelopmental battery Basic Protocol 2: Balance beam Basic Protocol 3: Multivariate concentric square field test (MCSF).

Alterations of specific cortical GABAergic circuits underlie abnormal network activity in a mouse model of Down syndrome

Down syndrome (DS) results in various degrees of cognitive deficits. In DS mouse models, recovery of behavioral and neurophysiological deficits using GABA_AR antagonists led to hypothesize an excessive activity of inhibitory circuits in this condition. Nonetheless, whether over-inhibition is present in DS and whether this is due to specific alterations of distinct GABAergic circuits is unknown. In the prefrontal cortex of Ts65Dn mice (a well-established DS model), we found that the dendritic synaptic inhibitory loop formed by somatostatin-positive Martinotti cells (MCs) and pyramidal neurons (PNs) was strongly enhanced, with no alteration in their excitability. Conversely, perisomatic inhibition from parvalbumin-positive (PV) interneurons was unaltered, but PV cells of DS mice lost their classical fast-spiking phenotype and exhibited increased excitability. These microcircuit alterations resulted in reduced pyramidal-neuron firing and increased phase locking to cognitive-relevant network oscillations in vivo. These results define important synaptic and circuit mechanisms underlying cognitive dysfunctions in DS.

Down syndrome is a genetic disorder caused by the presence of a third copy of chromosome 21. Affected individuals show delayed growth, characteristic facial features, altered brain development; with mild to severe intellectual disability. The exact mechanisms underlying the intellectual disability in Down syndrome are unclear, although studies in mice have provided clues. Drugs that reduce the inhibitory activity in the brain improve cognition in a mouse model of Down syndrome. This suggests that excessive inhibitory activity may contribute to the cognitive impairments.

Many different neural circuits generate inhibitory activity in the brain. These circuits contain cells called interneurons. Sub-types of interneurons act via different mechanisms to reduce the activity of neurons. Identifying the interneurons that are affected in Down syndrome would thus improve our understanding of the brain basis of the disorder.

Zorrilla de San Martin et al. compared mice with Down syndrome to unaffected control mice. The results revealed an increased activity in two types of inhibitory brain circuits in Down syndrome. The first contains interneurons called Martinotti cells. These help the brain to combine inputs from different sources. The second contains interneurons called parvalbumin-positive basket cells. These help different areas of the brain to synchronize their activity, which in turn makes it easier for those areas to exchange information.

By mapping the changes in inhibitory circuits in Down syndrome, Zorrilla de San Martin et al. have provided new insights into the biological basis of the disorder. Future studies should examine whether targeting specific circuits with pharmacological treatments could ultimately help reduce the associated impairments.

Attitudes Toward Hypothetical Uses of Gene-Editing Technologies in Parents of People with Autosomal Aneuploidies

Researchers are exploring the use of gene-editing technologies to prevent and/or treat genetic conditions in humans. Stakeholder views, including those of patient and family populations, are important in the ongoing bioethical discussion. We conducted 27 semi-structured interviews with parents of people with trisomy 21 (T21; N = 10), trisomy 18 (T18; N = 8), and trisomy 13 (T13; N = 9)-conditions not previously studied in regard to attitudes toward hypothetical gene editing. While many discussions focus on the morality of gene editing, parents in our study focused on quality of life and concerns about changing their children's identity. All participants prioritized ameliorating life-threatening health issues when those were present; many also emphasized increasing their children's communication and cognitive ability. These results suggest that patient populations with the lived experience of genetic conditions have unique concerns that may differ from broader discourse.