Abnormal APP, cholinergic and cognitive function in Ts65Dn Down's model mice

Shaping down syndrome brain cognitive and molecular changes due to aging using adult animals from the Ts66Yah murine model

Down syndrome (DS) is the most common condition with intellectual disability and is caused by trisomy of Homo sapiens chromosome 21 (HSA21). The increased dosage of genes on HSA21 is associated with early neurodevelopmental changes and subsequently at adult age with the development of Alzheimer-like cognitive decline. However, the molecular mechanisms promoting brain pathology along aging are still missing. The novel Ts66Yah model represents an evolution of the Ts65Dn, used in characterizing the progression of brain degeneration, and it manifest phenotypes closer to human DS condition. In this study we performed a longitudinal analysis (3-9 months) of adult Ts66Yah mice. Our data support the behavioural alterations occurring in Ts66Yah mice at older age with improvement in the detection of spatial memory defects and also a new anxiety-related phenotype. The evaluation of hippocampal molecular pathways in Ts66Yah mice, as effect of age, demonstrate the aberrant regulation of redox balance, proteostasis, stress response, metabolic pathways, programmed cell death and synaptic plasticity. Intriguingly, the genotype-driven changes observed in those pathways occur early promoting altered brain development and the onset of a condition of premature aging. In turn, aging may account for the subsequent hippocampal deterioration that fall in characteristic neuropathological features. Besides, the analysis of sex influence in the alteration of hippocampal mechanisms demonstrate only a mild effect. Overall, data collected in Ts66Yah provide novel and consolidated insights, concerning trisomy-driven processes that contribute to brain pathology in conjunction with aging. This, in turn, aids in bridging the existing gap in comprehending the intricate nature of DS phenotypes.

In and out: Benchmarking in vitro, in vivo, ex vivo, and xenografting approaches for an integrative brain disease modeling pipeline

Human cellular models and their neuronal derivatives have afforded unprecedented advances in elucidating pathogenic mechanisms of neuropsychiatric diseases. Notwithstanding their indispensable contribution, animal models remain the benchmark in neurobiological research. In an attempt to harness the best of both worlds, researchers have increasingly relied on human/animal chimeras by xenografting human cells into the animal brain. Despite the unparalleled potential of xenografting approaches in the study of the human brain, literature resources that systematically examine their significance and advantages are surprisingly lacking. We fill this gap by providing a comprehensive account of brain diseases that were thus far subjected to all three modeling approaches (transgenic rodents, in vitro human lineages, human-animal xenografting) and provide a critical appraisal of the impact of xenografting approaches for advancing our understanding of those diseases and brain development. Next, we give our perspective on integrating xenografting modeling pipeline with recent cutting-edge technological advancements.

Differential Regulation of Neurotrophic Factors During Pathogenic Tau-Aggregation in a Tau Transgenic Mouse Model for Alzheimer's Disease: A Protocol for Double-Labeling mRNA by In Situ Hybridization and Protein Epitopes by Immunohistochemistry

Alzheimer's disease (AD), most tauopathies, and other neurodegenerative diseases are highly associated to impaired neurotrophin regulation and imbalanced neurotrophin transport and distribution. Neurotrophins are crucial for the survival and maintenance of distinct neuronal population therefore their supply is essential for a healthy brain. Tau phosphorylation occurs at different sites of the tau protein and some phospho-epitopes are highly associated to AD (e.g., abnormally phosphorylated tau at Thr212/Ser214). Though the importance of neurotrophins is well known, their analysis in tissue is not trivial and needs careful consideration. Here a detailed protocol is presented, which combines in situ hybridization (ISH) with immunohistochemistry (IHC) to analyze neurotrophin mRNA expression during tau neuropathology and the results were confirmed by immunological methods.With this protocol, it was demonstrated that Brain-Derived Neurotrophic Factor (BDNF) and its receptor Tropomyosin receptor kinase B (TrkB) were significantly decreased in tau-transgenic mice compared to their age-matched littermates. Neurotrophin-3 (NT-3) and its receptor TrkC were not altered with statistical significance, but a tendency for decreased NT-3 and slightly increased TrkC expression was observed in tau transgenic mice. The loss of BDNF-ISH signal was predominantly observed in hippocampus (CA1 and CA3) and cortex (layer II-VI) and verified by BDNF-immunoreactivity. Decreased BDNF and TrkB mRNA was negatively correlated with abnormal tau phosphorylation at Thr212/Ser214 in cortical neurons in transgenic mice. Strikingly, no correlation was observed with age-related phospho-epitopes such as Ser202/Thr205. Interestingly, both, the mRNA and protein levels of Nerve Growth Factor (NGF) were significantly increased in hippocampal neurons in the tau models as demonstrated by ISH, immunofluorescence, and Western Blotting. Here, some co-localization of NGF mRNA and phospho-tau (Thr212/Ser214) was observed but was a rare event. Since there is growing evidence for the relevance of neurotrophic factor distribution in the pathogenesis of neurodegeneration, this technique is a useful tool to investigate the underlying mechanisms and potential therapeutic intervention.

Maternal choline supplementation protects against age-associated cholinergic and GABAergic basal forebrain neuron degeneration in the Ts65Dn mouse model of Down syndrome and Alzheimer's disease

Down syndrome (DS) is a genetic disorder caused by triplication of human chromosome 21. In addition to intellectual disability, DS is defined by a premature aging phenotype and Alzheimer's disease (AD) neuropathology, including septohippocampal circuit vulnerability and degeneration of basal forebrain cholinergic neurons (BFCNs). The Ts65Dn mouse model recapitulates key aspects of DS/AD pathology, namely age-associated atrophy of BFCNs and cognitive decline in septohippocampal-dependent behavioral tasks. We investigated whether maternal choline supplementation (MCS), a well-tolerated treatment modality, protects vulnerable BFCNs from age- and genotype-associated degeneration in trisomic offspring. We also examined the effect of trisomy, and MCS, on GABAergic basal forebrain parvalbumin neurons (BFPNs), an unexplored neuronal population in this DS model. Unbiased stereological analyses of choline acetyltransferase (ChAT)-immunoreactive BFCNs and parvalbumin-immunoreactive BFPNs were conducted using confocal z-stacks of the medial septal nucleus and the vertical limb of the diagonal band (MSN/VDB) in Ts65Dn mice and disomic (2N) littermates at 3-4 and 10-12 months of age. MCS trisomic offspring displayed significant increases in ChAT-immunoreactive neuron number and density compared to unsupplemented counterparts, as well as increases in the area of the MSN/VDB occupied by ChAT-immunoreactive neuropil. MCS also rescued BFPN number and density in Ts65Dn offspring, a novel rescue of a non-cholinergic cell population. Furthermore, MCS prevented age-associated loss of BFCNs and MSN/VDB regional area in 2N offspring, indicating genotype-independent neuroprotective benefits. These findings demonstrate MCS provides neuroprotection of vulnerable BFCNs and non-cholinergic septohippocampal BFPNs, indicating this modality has translational value as an early life therapy for DS, as well as extending benefits to the aging population at large.

Untangle the mystery behind DS-associated AD - Is APP the main protagonist?

Amyloid precursor protein profusion in Trisomy 21, also called Down Syndrome (DS), is rooted in the genetic determination of Alzheimer's disease (AD). With the recent development in patient care, the life expectancy of DS patients has gradually increased, leading to the high prospect of AD development, consequently leading to the development of plaques of amyloid proteins and neurofibrillary tangles made of tau by the fourth decade of the patient leading to dementia. The altered gene expression resulted in cellular dysfunction due to impairment of autophagy, mitochondrial and lysosomal dysfunction, and copy number variation controlled by the additional genes in Trisomy 21. The cognitive impairment and mechanistic insights underlying DS-AD conditions have been reviewed in this article. Some recent findings regarding biomarkers and therapeutics of DS-AD conditions were highlighted in this review.

Cholinergic Senescence in the Ts65Dn Mouse Model for Down Syndrome

Down syndrome (DS) induces a variable phenotype including intellectual disabilities and early development of Alzheimer’s disease (AD). Moreover, individuals with DS display accelerated aging that affects diverse organs, among them the brain. The Ts65Dn mouse is the most widely used model to study DS. Progressive loss of cholinergic neurons is one of the hallmarks of AD present in DS and in the Ts65Dn model. In this study, we quantify the number of cholinergic neurons in control and Ts65Dn mice, observing a general reduction in their number with age but in particular, a greater loss in old Ts65Dn mice. Increased expression of the m1 muscarinic receptor in the hippocampus counteracts this loss. Cholinergic neurons in the Ts65Dn mice display overexpression of the early expression gene c-fos and an increase in the expression of β-galactosidase, a marker of senescence. A possible mechanism for senescence induction could be phosphorylation of the transcription factor FOXO1 and its retention in the cytoplasm, which we are able to confirm in the Ts65Dn model. In our study, using Ts65Dn mice, we observe increased cholinergic activity, which induces a process of early senescence that culminates in the loss of these neurons.

Rodent Modeling of Alzheimer's Disease in Down Syndrome: In vivo and ex vivo Approaches

There are an estimated 6 million people with Down syndrome (DS) worldwide. In developed countries, the vast majority of these individuals will develop Alzheimer's disease neuropathology characterized by the accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles within the brain, which leads to the early onset of dementia (AD-DS) and reduced life-expectancy. The mean age of onset of clinical dementia is ~55 years and by the age of 80, approaching 100% of individuals with DS will have a dementia diagnosis. DS is caused by trisomy of chromosome 21 (Hsa21) thus an additional copy of a gene(s) on the chromosome must cause the development of AD neuropathology and dementia. Indeed, triplication of the gene APP which encodes the amyloid precursor protein is sufficient and necessary for early onset AD (EOAD), both in people who have and do not have DS. However, triplication of other genes on Hsa21 leads to profound differences in neurodevelopment resulting in intellectual disability, elevated incidence of epilepsy and perturbations to the immune system. This different biology may impact on how AD neuropathology and dementia develops in people who have DS. Indeed, genes on Hsa21 other than APP when in three-copies can modulate AD-pathogenesis in mouse preclinical models. Understanding this biology better is critical to inform drug selection for AD prevention and therapy trials for people who have DS. Here we will review rodent preclinical models of AD-DS and how these can be used for both in vivo and ex vivo (cultured cells and organotypic slice cultures) studies to understand the mechanisms that contribute to the early development of AD in people who have DS and test the utility of treatments to prevent or delay the development of disease.

Analysis of multi-omics data on the relationship between epigenetic changes and nervous system disorders caused by exposure to environmentally harmful substances

Environmentally hazardous substances and exposure to these can cause various diseases. Volatile organic compounds can easily evaporate into the atmosphere, thereby exerting toxic effects through either the skin or respiratory tract exposures. Toluene, a neurotoxin, has been widely used in various industries. However, it has a detrimental effect on the nervous system (such as hallucinations or memory impairment), while data on the mechanism underlaying its harmful effects remain limited. Therefore, this study investigates the effect of toluene on the nervous system via epigenetic and genetic changes of toluene-exposed individuals. We identified significant epigenetic changes and confirmed that the affected abnormally expressed genes negatively influenced the nervous system. In particular, we confirmed that the miR-15 family, upregulated by toluene, downregulated ABL2, which could affect the R as signaling pathway resulting in neuronal structural abnormalities. Our study suggests that miR-15a-5p, miR-15b-5p, miR-16-5p, miR-301a-3p, and lncRNA NEAT1 may represent effective epigenomic markers associated with neurodegenerative diseases caused by toluene.

Temporal and brain region-specific elevations of soluble Amyloid-β40-42 in the Ts65Dn mouse model of Down syndrome and Alzheimer's disease

Down syndrome (DS) is a leading cause of intellectual disability that also results in hallmark Alzheimer's disease (AD) pathologies such as amyloid beta (Aβ) plaques and hyperphosphorylated tau. The Ts65Dn mouse model is commonly used to study DS, as trisomic Ts65Dn mice carry 2/3 of the triplicated gene homologues as occur in human DS. The Ts65Dn strain also allows investigation of mechanisms common to DS and AD pathology, with many of these triplicated genes implicated in AD; for example, trisomic Ts65Dn mice overproduce amyloid precursor protein (APP), which is then processed into soluble Aβ_40-42 fragments. Notably, Ts65Dn mice show alterations to the basal forebrain, which parallels the loss of function in this region observed in DS and AD patients early on in disease progression. However, a complete picture of soluble Aβ_40-42 accumulation in a region-, age-, and sex-specific manner has not yet been characterized in the Ts65Dn model. Here, we show that trisomic mice accumulate soluble Aβ_40-42 in the basal forebrain, frontal cortex, hippocampus, and cerebellum in an age-specific manner, with elevation in the frontal cortex and hippocampus as early as 4 months of age. Furthermore, we detected sex differences in accumulation of Aβ_40-42 within the basal forebrain, with females having significantly higher Aβ_40-42 at 7-8 months of age. Lastly, we show that APP expression in the basal forebrain and hippocampus inversely correlates with Aβ_40-42  levels. This spatial and temporal characterization of soluble Aβ_40-42 in the Ts65Dn model allows for further exploration of the role soluble Aβ plays in the progression of other AD-like pathologies in these key brain regions.

The Nerve Growth Factor Metabolic Pathway Dysregulation as Cause of Alzheimer's Cholinergic Atrophy

The cause of the loss of basal forebrain cholinergic neurons (BFCNs) and their terminal synapses in the cerebral cortex and hippocampus in Alzheimer's disease (AD) has provoked a decades-long controversy. The cholinergic phenotype of this neuronal system, involved in numerous cognitive mechanisms, is tightly dependent on the target-derived nerve growth factor (NGF). Consequently, the loss of BFCNs cholinergic phenotype in AD was initially suspected to be due to an NGF trophic failure. However, in AD there is a normal NGF synthesis and abundance of the NGF precursor (proNGF), therefore the NGF trophic failure hypothesis for the atrophy of BCNs was abandoned. In this review, we discuss the history of NGF-dependency of BFCNs and the atrophy of these neurons in Alzheimer's disease (AD). Further to it, we propose that trophic factor failure explains the BFCNs atrophy in AD. We discuss evidence of the occurrence of a brain NGF metabolic pathway, the dysregulation of which, in AD explains the severe deficiency of NGF trophic support for the maintenance of BFCNs cholinergic phenotype. Finally, we revise recent evidence that the NGF metabolic dysregulation in AD pathology starts at preclinical stages. We also propose that the alteration of NGF metabolism-related markers in body fluids might assist in the AD preclinical diagnosis.

Dyrk1a from Gene Function in Development and Physiology to Dosage Correction across Life Span in Down Syndrome

Down syndrome is the main cause of intellectual disabilities with a large set of comorbidities from developmental origins but also that appeared across life span. Investigation of the genetic overdosage found in Down syndrome, due to the trisomy of human chromosome 21, has pointed to one main driver gene, the Dual-specificity tyrosine-regulated kinase 1A (Dyrk1a). Dyrk1a is a murine homolog of the drosophila minibrain gene. It has been found to be involved in many biological processes during development and in adulthood. Further analysis showed its haploinsufficiency in mental retardation disease 7 and its involvement in Alzheimer's disease. DYRK1A plays a role in major developmental steps of brain development, controlling the proliferation of neural progenitors, the migration of neurons, their dendritogenesis and the function of the synapse. Several strategies targeting the overdosage of DYRK1A in DS with specific kinase inhibitors have showed promising evidence that DS cognitive conditions can be alleviated. Nevertheless, providing conditions for proper temporal treatment and to tackle the neurodevelopmental and the neurodegenerative aspects of DS across life span is still an open question.

Brain-Derived Neurotrophic Factor Signaling in the Pathophysiology of Alzheimer's Disease: Beneficial Effects of Flavonoids for Neuroprotection

The function of the brain-derived neurotrophic factor (BDNF) via activation through its high-affinity receptor Tropomyosin receptor kinase B (TrkB) has a pivotal role in cell differentiation, cell survival, synaptic plasticity, and both embryonic and adult neurogenesis in central nervous system neurons. A number of studies have demonstrated the possible involvement of altered expression and action of the BDNF/TrkB signaling in the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD). In this review, we introduce an essential role of the BDNF and its downstream signaling in neural function. We also review the current evidence on the deregulated the BDNF signaling in the pathophysiology of AD at gene, mRNA, and protein levels. Further, we discuss a potential usefulness of small compounds, including flavonoids, which can stimulate BDNF-related signaling as a BDNF-targeting therapy.

Bexarotene Impairs Cognition and Produces Hypothyroidism in a Mouse Model of Down Syndrome and Alzheimer's Disease

All individuals with Down syndrome (DS) eventually develop Alzheimer's disease (AD) neuropathology, including neurodegeneration, increases in β-amyloid (Aβ) expression, and aggregation and neurofibrillary tangles, between the third and fourth decade of their lives. There is currently no effective treatment to prevent AD neuropathology and the associated cognitive degeneration in DS patients. Due to evidence that the accumulation of Aβ aggregates in the brain produces the neurodegenerative cascade characteristic of AD, many strategies which promote the clearance of Aβ peptides have been assessed as potential therapeutics for this disease. Bexarotene, a member of a subclass of retinoids that selectively activates retinoid receptors, modulates several pathways essential for cognitive performance and Aβ clearance. Consequently, bexarotene might be a good candidate to treat AD-associated neuropathology. However, the effects of bexarotene treatment in AD remain controversial. In the present study, we aimed to elucidate whether chronic bexarotene treatment administered to the most commonly used murine model of DS, the Ts65Dn (TS) mouse could reduce Aβ expression in their brains and improve their cognitive abilities. Chronic administration of bexarotene to aged TS mice and their CO littermates for 9 weeks diminished the reference, working, and spatial learning and memory of TS mice, and the spatial memory of CO mice in the Morris water maze. This treatment also produced marked hypoactivity in the plus maze, open field, and hole board tests in TS mice, and in the open field and hole board tests in CO mice. Administration of bexarotene reduced the expression of Aβ1-40, but not of Aβ1-42, in the hippocampi of TS mice. Finally, bexarotene increased Thyroid-stimulating hormone levels in TS mice and reduced Thyroid-stimulating hormone levels in CO mice, while animals of both karyotypes displayed reduced thyroxine levels after bexarotene administration. The bexarotene-induced hypothyroidism could be responsible for the hypoactivity of TS and CO mice and their diminished performance in the Morris water maze. Together, these results do not provide support for the use of bexarotene as a potential treatment of AD neuropathology in the DS population.

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.

Ultrastructural and dynamic studies of the endosomal compartment in Down syndrome

Enlarged early endosomes have been visualized in Alzheimer's disease (AD) and Down syndrome (DS) using conventional confocal microscopy at a resolution corresponding to endosomal size (hundreds of nm). In order to overtake the diffraction limit, we used super-resolution structured illumination microscopy (SR-SIM) and transmission electron microscopies (TEM) to analyze the early endosomal compartment in DS.By immunofluorescence and confocal microscopy, we confirmed that the volume of Early Endosome Antigen 1 (EEA1)-positive puncta was 13-19% larger in fibroblasts and iPSC-derived neurons from individuals with DS, and in basal forebrain cholinergic neurons (BFCN) of the Ts65Dn mice modelling DS. However, EEA1-positive structures imaged by TEM or SR-SIM after chemical fixation had a normal size but appeared clustered. In order to disentangle these discrepancies, we imaged optimally preserved High Pressure Freezing (HPF)-vitrified DS fibroblasts by TEM and found that early endosomes were 75% denser but remained normal-sized.RNA sequencing of DS and euploid fibroblasts revealed a subgroup of differentially-expressed genes related to cargo sorting at multivesicular bodies (MVBs). We thus studied the dynamics of endocytosis, recycling and MVB-dependent degradation in DS fibroblasts. We found no change in endocytosis, increased recycling and delayed degradation, suggesting a "traffic jam" in the endosomal compartment.Finally, we show that the phosphoinositide PI (3) P, involved in early endosome fusion, is decreased in DS fibroblasts, unveiling a new mechanism for endosomal dysfunctions in DS and a target for pharmacotherapy.

Cilostazol, a Phosphodiesterase 3 Inhibitor, Moderately Attenuates Behaviors Depending on Sex in the Ts65Dn Mouse Model of Down Syndrome

People with Down syndrome, which is a trisomy of chromosome 21, exhibit intellectual disability from infancy and neuropathology similar to Alzheimer’s disease, such as amyloid plaques, from an early age. Recently, we showed that cilostazol, a selective inhibitor of phosphodiesterase (PDE) 3, promotes the clearance of amyloid β and rescues cognitive deficits in a mouse model of Alzheimer’s disease. The objective of the present study was to examine whether cilostazol improves behaviors in the most widely used animal model of Down syndrome, i.e., Ts65Dn mice. Mice were supplemented with cilostazol from the fetal period until young adulthood. Supplementation significantly ameliorated novel-object recognition in Ts65Dn females and partially ameliorated sensorimotor function as determined by the rotarod test in Ts65Dn females and hyperactive locomotion in Ts65Dn males. Cilostazol supplementation significantly shortened swimming distance in Ts65Dn males in the Morris water maze test, suggesting that the drug improved cognitive function, although it did not shorten swimming duration, which was due to decreased swimming speed. Thus, this study suggests that early supplementation with cilostazol partially rescues behavioral abnormalities seen in Down syndrome and indicates that the effects are sex-dependent.

Using mouse models to understand Alzheimer's disease mechanisms in the context of trisomy of chromosome 21

People who have Down syndrome are at significantly elevated risk of developing early onset Alzheimer's disease that causes dementia (AD-DS). Here we review recent progress in modeling the development of AD-DS in mouse models. These studies provide insight into mechanisms underlying Alzheimer's disease and generate new clinical research questions. In addition, they suggest potential new targets for disease prevention therapies.

Translational validity and implications of pharmacotherapies in preclinical models of Down syndrome

Neurodevelopmental disorders are challenging to study in the laboratory, and despite a large investment, few novel treatments have been developed in the last decade. While animal models have been valuable in elucidating disease mechanisms and in providing insights into the function of specific genes, the predictive validity of preclinical models to test potential therapies has been questioned. In the last two decades, diverse new murine models of Down syndrome (DS) have been developed and numerous studies have demonstrated neurobiological alterations that could be responsible for the cognitive and behavioral phenotypes found in this syndrome. In many cases, similar alterations were found in murine models and in individuals with DS, although several phenotypes shown in animals have yet not been confirmed in the human condition. Some of the neurobiological alterations observed in mice have been proposed to account for their changes in cognition and behavior, and have received special attention because of being putative therapeutic targets. Those include increased oxidative stress, altered neurogenesis, overexpression of the Dyrk1A gene, GABA-mediated overinhibition and Alzheimer's disease-related neurodegeneration. Subsequently, different laboratories have tested the efficacy of pharmacotherapies targeting these alterations. Unfortunately, animal models are limited in their ability to mimic the extremely complex process of human neurodevelopment and neuropathology. Therefore, the safety and efficacy identified in animal studies are not always translated to humans, and most of the drugs tested have not demonstrated any positive effect or very limited efficacy in clinical trials. Despite their limitations, though, animal trials give us extremely valuable information for developing and testing drugs for human use that cannot be obtained from molecular or cellular experiments alone. This chapter reviews some of these therapeutic approaches and discusses some reasons that could account for the discrepancy between the findings in mouse models of DS and in humans, including: (i) the incomplete resemble of the genetic alterations of available mouse models of DS and human trisomy 21, (ii) the lack of evidence that some of the phenotypic alterations found in mice (e.g., GABA-mediated overinhibition, and alterations in adult neurogenesis) are also present in DS individuals, and (iii) the inaccuracy and/or inadequacy of the methods used in clinical trials to detect changes in the cognitive and behavioral functions of people with DS. Despite the shortcomings of animal models, animal experimentation remains an invaluable tool in developing drugs. Thus, we will also discuss how to increase predictive validity of mouse models.

Maternal Choline Supplementation Alters Basal Forebrain Cholinergic Neuron Gene Expression in the Ts65Dn Mouse Model of Down Syndrome

Down syndrome (DS), trisomy 21, is marked by intellectual disability and a premature aging profile including degeneration of the basal forebrain cholinergic neuron (BFCN) projection system, similar to Alzheimer's disease (AD). Although data indicate that perinatal maternal choline supplementation (MCS) alters the structure and function of these neurons in the Ts65Dn mouse model of DS and AD (Ts), whether MCS affects the molecular profile of vulnerable BFCNs remains unknown. We investigated the genetic signature of BFCNs obtained from Ts and disomic (2N) offspring of Ts65Dn dams maintained on a MCS diet (Ts+, 2N+) or a choline normal diet (ND) from mating until weaning, then maintained on ND until 4.4-7.5 months of age. Brains were then collected and prepared for choline acetyltransferase (ChAT) immunohistochemistry and laser capture microdissection followed by RNA extraction and custom-designed microarray analysis. Findings revealed upregulation of select transcripts in classes of genes related to the cytoskeleton (Tubb4b), AD (Cav1), cell death (Bcl2), presynaptic (Syngr1), immediate early (Fosb, Arc), G protein signaling (Gabarap, Rgs10), and cholinergic neurotransmission (Chrnb3) in Ts compared to 2N mice, which were normalized with MCS. Moreover, significant downregulation was seen in select transcripts associated with the cytoskeleton (Dync1h1), intracellular signaling (Itpka, Gng3, and Mlst8), and cell death (Ccng1) in Ts compared to 2N mice that was normalized with MCS. This study provides insight into genotype-dependent differences and the effects of MCS at the molecular level within a key vulnerable cell type in DS and AD.

Hydroxyurea Improves Spatial Memory and Cognitive Plasticity in Mice and Has a Mild Effect on These Parameters in a Down Syndrome Mouse Model

Down syndrome (DS), a genetic disorder caused by partial or complete triplication of chromosome 21, is the most common genetic cause of intellectual disability. DS mouse models and cell lines display defects in cellular adaptive stress responses including autophagy, unfolded protein response, and mitochondrial bioenergetics. We tested the ability of hydroxyurea (HU), an FDA-approved pharmacological agent that activates adaptive cellular stress response pathways, to improve the cognitive function of Ts65Dn mice. The chronic HU treatment started at a stage when early mild cognitive deficits are present in this model (∼3 months of age) and continued until a stage of advanced cognitive deficits in untreated mice (∼5–6 months of age). The HU effects on cognitive performance were analyzed using a battery of water maze tasks designed to detect changes in different types of memory with sensitivity wide enough to detect deficits as well as improvements in spatial memory. The most common characteristic of cognitive deficits observed in trisomic mice at 5–6 months of age was their inability to rapidly acquire new information for long-term storage, a feature akin to episodic-like memory. On the background of severe cognitive impairments in untreated trisomic mice, HU-treatment produced mild but significant benefits in Ts65Dn by improving memory acquisition and short-term retention of spatial information. In control mice, HU treatment facilitated memory retention in constant (reference memory) as well as time-variant conditions (episodic-like memory) implicating a robust nootropic effect. This was the first proof-of-concept study of HU treatment in a DS model, and indicates that further studies are warranted to assess a window to optimize timing and dosage of the treatment in this pre-clinical phase. Findings of this study indicate that HU has potential for improving memory retention and cognitive flexibility that can be harnessed for the amelioration of cognitive deficits in normal aging and in cognitive decline (dementia) related to DS and other neurodegenerative diseases.

Restoring microglial and astroglial homeostasis using DNA immunization in a Down Syndrome mouse model

Down Syndrome (DS), the most common cause of genetic intellectual disability, is characterized by over-expression of the APP and DYRK1A genes, located on the triplicated chromosome 21. This chromosomal abnormality leads to a cognitive decline mediated by Amyloid-β (Aβ) overproduction and tau hyper-phosphorylation as early as the age of 40. In this study, we used the Ts65Dn mouse model of DS to evaluate the beneficial effect of a DNA vaccination against the Aβ1-11 fragment, in ameliorating Aβ-related neuropathology and rescue of cognitive and behavioral abilities. Anti-Aβ1-11 vaccination induced antibody production and facilitated clearance of soluble oligomers and small extracellular inclusions of Aβ from the hippocampus and cortex of Ts65Dn mice. This was correlated with reduced neurodegeneration and restoration of the homeostatic phenotype of microglial and astroglial cells. Vaccinated Ts65Dn mice performed better in spatial-learning tasks, exhibited reduced motor hyperactivity typical for this strain, and restored short-term memory abilities. Our findings support the hypothesis that DS individuals may benefit from active immunotherapy against Aβ from a young age by slowing the progression of dementia.

Intranasal rapamycin ameliorates Alzheimer-like cognitive decline in a mouse model of Down syndrome

Background

Down syndrome (DS) individuals, by the age of 40s, are at increased risk to develop Alzheimer-like dementia, with deposition in brain of senile plaques and neurofibrillary tangles. Our laboratory recently demonstrated the disturbance of PI3K/AKT/mTOR axis in DS brain, prior and after the development of Alzheimer Disease (AD). The aberrant modulation of the mTOR signalling in DS and AD age-related cognitive decline affects crucial neuronal pathways, including insulin signaling and autophagy, involved in pathology onset and progression. Within this context, the therapeutic use of mTOR-inhibitors may prevent/attenuate the neurodegenerative phenomena. By our work we aimed to rescue mTOR signalling in DS mice by a novel rapamycin intranasal administration protocol (InRapa) that maximizes brain delivery and reduce systemic side effects.

Methods

Ts65Dn mice were administered with InRapa for 12 weeks, starting at 6 months of age demonstrating, at the end of the treatment by radial arms maze and novel object recognition testing, rescued cognition.

Results

The analysis of mTOR signalling, after InRapa, demonstrated in Ts65Dn mice hippocampus the inhibition of mTOR (reduced to physiological levels), which led, through the rescue of autophagy and insulin signalling, to reduced APP levels, APP processing and APP metabolites production, as well as, to reduced tau hyperphosphorylation. In addition, a reduction of oxidative stress markers was also observed.

Discussion

These findings demonstrate that chronic InRapa administration is able to exert a neuroprotective effect on Ts65Dn hippocampus by reducing AD pathological hallmarks and by restoring protein homeostasis, thus ultimately resulting in improved cognition. Results are discussed in term of a potential novel targeted therapeutic approach to reduce cognitive decline and AD-like neuropathology in DS individuals.

Anti-IL17 treatment ameliorates Down syndrome phenotypes in mice

Down syndrome (DS) is characterized by structural and functional anomalies that are present prenatally and that lead to intellectual disabilities. Later in life, the cognitive abilities of DS individuals progressively deteriorate due to the development of Alzheimer's disease (AD)-associated neuropathology (i.e., β-amyloid (Aβ) plaques, neurofibrillary tangles (NFTs), neurodegeneration, synaptic pathology, neuroinflammation and increased oxidative stress). Increasing evidence has shown that among these pathological processes, neuroinflammation plays a predominant role in AD etiopathology. In AD mouse models, increased neuroinflammation appears earlier than Aβ plaques and NFTs, and in DS and AD models, neuroinflammation exacerbates the levels of soluble and insoluble Aβ species, favoring neurodegeneration. The Ts65Dn (TS) mouse, the most commonly used murine model of DS, recapitulates many alterations present in both DS and AD individuals, including enhanced neuroinflammation. In this study, we observed an altered neuroinflammatory milieu in the hippocampus of the TS mouse model. Pro-inflammatory mediators that were elevated in the hippocampus of this model included pro-inflammatory cytokine IL17A, which has a fundamental role in mediating brain damage in neuroinflammatory processes. Here, we analyzed the ability of an anti-IL17A antibody to reduce the neuropathological alterations that are present in TS mice during early neurodevelopmental stages (i.e., hippocampal neurogenesis and hypocellularity) or that are aggravated in later-life stages (i.e., cognitive abilities, cholinergic neuronal loss and increased cellular senescence, APP expression, Aβ peptide expression and neuroinflammation). Administration of anti-IL17 for 5 months, starting at the age of 7 months, partially improved the cognitive abilities of the TS mice, reduced the expression of several pro-inflammatory cytokines and the density of activated microglia and normalized the APP and Aβ_1-42 levels in the hippocampi of the TS mice. These results suggest that IL17-mediated neuroinflammation is involved in several AD phenotypes in TS mice and provide a new therapeutic target to reduce these pathological characteristics.

Cystatin C prevents neuronal loss and behavioral deficits via the endosomal pathway in a mouse model of down syndrome

Cystatin C (CysC) plays diverse protective roles under conditions of neuronal challenge. We investigated whether CysC protects from trisomy-induced pathologies in a mouse model of Down syndrome (DS), the most common cause of developmental cognitive and behavioral impairments in humans. We have previously shown that the segmental trisomy mouse model, Ts[Rb(12.1716)]2Cje (Ts2) has DS-like neuronal and behavioral deficiencies. The current study reveals that transgene-mediated low levels of human CysC overexpression has a preventive effect on numerous neuropathologies in the brains of Ts2 mice, including reducing early and late endosome enlargement in cortical neurons and decreasing loss of basal forebrain cholinergic neurons (BFCNs). Consistent with these cellular benefits, behavioral dysfunctions were also prevented, including deficits in nesting behavior and spatial memory. We determined that the CysC-induced neuroprotective mechanism involves activation of the phosphotidylinositol kinase (PI3K)/AKT pathway. Activating this pathway leads to enhanced clearance of accumulated endosomal substrates, protecting cells from DS-mediated dysfunctions in the endosomal system and, for BFCNs, from neurodegeneration. Our findings suggest that modulation of the PI3/AKT pathway offers novel therapeutic interventions for patients with DS.

CA1 pyramidal neuron gene expression mosaics in the Ts65Dn murine model of Down syndrome and Alzheimer's disease following maternal choline supplementation

Although there are changes in gene expression and alterations in neuronal density and afferent inputs in the forebrain of trisomic mouse models of Down syndrome (DS) and Alzheimer's disease (AD), there is a lack of systematic assessments of gene expression and encoded proteins within individual vulnerable cell populations, precluding translational investigations at the molecular and cellular level. Further, no effective treatment exists to combat intellectual disability and basal forebrain cholinergic neurodegeneration seen in DS. To further our understanding of gene expression changes before and following cholinergic degeneration in a well-established mouse model of DS/AD, the Ts65Dn mouse, we assessed RNA expression levels from CA1 pyramidal neurons at two adult ages (∼6 months of age and ∼11 months of age) in both Ts65Dn and their normal disomic (2N) littermates. We further examined a therapeutic intervention, maternal choline supplementation (MCS), which has been previously shown to lessen dysfunction in spatial cognition and attention, and have protective effects on the survival of basal forebrain cholinergic neurons in the Ts65Dn mouse model. Results indicate that MCS normalized expression of several genes in key gene ontology categories, including synaptic plasticity, calcium signaling, and AD-associated neurodegeneration related to amyloid-beta peptide (Aβ) clearance. Specifically, normalized expression levels were found for endothelin converting enzyme-2 (Ece2), insulin degrading enzyme (Ide), Dyrk1a, and calcium/calmodulin-dependent protein kinase II (Camk2a), among other relevant genes. Single population expression profiling of vulnerable CA1 pyramidal neurons indicates that MCS is a viable therapeutic for long-term reprogramming of key transcripts involved in neuronal signaling that are dysregulated in the trisomic mouse brain which have translational potential for DS and AD.

mTOR in Down syndrome: Role in Aß and tau neuropathology and transition to Alzheimer disease-like dementia

The mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase involved in the regulation of protein synthesis and degradation, longevity and cytoskeletal formation. The mTOR pathway represents a key growth and survival pathway involved in several diseases such as cancer, obesity, cardiovascular disease and neurodegenerative diseases. Numerous studies linked the alterations of mTOR pathway to age-dependent cognitive decline, pathogenesis of Alzheimer disease (AD) and AD-like dementia in Down syndrome (DS). DS is the most frequent chromosomal abnormality that causes intellectual disability. The neuropathology of AD in DS is complex and involves impaired mitochondrial function, defects in neurogenesis, increased oxidative stress, altered proteostasis and autophagy networks as a result of triplication of chromosome 21(chr 21). The chr21 gene products are considered a principal neuropathogenic moiety in DS. Several genes involved respectively in the formation of senile plaques and neurofibrillary tangles (NFT), two main pathological hallmarks of AD, are mapped on chr21. Further, in subjects with DS the activation of mTOR signaling contributes to Aβ generation and the formation of NFT. This review discusses recent research highlighting the complex role of mTOR associated with the presence of two hallmarks of AD pathology, senile plaques (composed mostly of fibrillar Aß peptides), and NFT (composed mostly of hyperphosphorylated tau protein). Oxidative stress, associated with chr21-related Aβ and mitochondrial alterations, may significantly contribute to this linkage of mTOR to AD-like neuropathology in DS.

Normalizing the gene dosage of Dyrk1A in a mouse model of Down syndrome rescues several Alzheimer's disease phenotypes

The intellectual disability that characterizes Down syndrome (DS) is primarily caused by prenatal changes in central nervous system growth and differentiation. However, in later life stages, the cognitive abilities of DS individuals progressively decline due to accelerated aging and the development of Alzheimer's disease (AD) neuropathology. The AD neuropathology in DS has been related to the overexpression of several genes encoded by Hsa21 including DYRK1A (dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A), which encodes a protein kinase that performs crucial functions in the regulation of multiple signaling pathways that contribute to normal brain development and adult brain physiology. Studies performed in vitro and in vivo in animal models overexpressing this gene have demonstrated that the DYRK1A gene also plays a crucial role in several neurodegenerative processes found in DS. The Ts65Dn (TS) mouse bears a partial triplication of several Hsa21 orthologous genes, including Dyrk1A, and replicates many DS-like abnormalities, including age-dependent cognitive decline, cholinergic neuron degeneration, increased levels of APP and Aβ, and tau hyperphosphorylation. To use a more direct approach to evaluate the role of the gene dosage of Dyrk1A on the neurodegenerative profile of this model, TS mice were crossed with Dyrk1A KO mice to obtain mice with a triplication of a segment of Mmu16 that includes this gene, mice that are trisomic for the same genes but only carry two copies of Dyrk1A, euploid mice with a normal Dyrk1A dosage, and CO animals with a single copy of Dyrk1A. Normalizing the gene dosage of Dyrk1A in the TS mouse rescued the density of senescent cells in the cingulate cortex, hippocampus and septum, prevented cholinergic neuron degeneration, and reduced App expression in the hippocampus, Aβ load in the cortex and hippocampus, the expression of phosphorylated tau at the Ser202 residue in the hippocampus and cerebellum and the levels of total tau in the cortex, hippocampus and cerebellum. Thus, the present study provides further support for the role of the Dyrk1A gene in several AD-like phenotypes found in TS mice and indicates that this gene could be a therapeutic target to treat AD in DS.

Cortical cells reveal APP as a new player in the regulation of GABAergic neurotransmission

The amyloid precursor protein (APP) modulates synaptic activity, resulting from the fine tuning of excitatory and inhibitory neurotransmission. GABAergic inhibitory neurotransmission is affected by modifications in intracellular chloride concentrations regulated by Na+-K+-2Cl- cotransporter 1 (NKCC1) and neuronal K+-Cl- cotransporter 2 (KCC2), allowing entrance and efflux of chloride, respectively. Modifications in NKCC1 and KCC2 expression during maturation of cortical cells induce a shift in GABAergic signaling. Here, we demonstrated that APP affects this GABA shift. Expression of APP in cortical cells decreased the expression of KCC2, without modifying NKCC1, eliciting a less inhibitory GABA response. Downregulation of KCC2 expression by APP was independent of the APP intracellular domain, but correlated with decreased expression of upstream stimulating factor 1 (USF1), a potent regulator of Slc12a5 gene expression (encoding KCC2). KCC2 was also downregulated in vivo following APP expression in neonatal mouse brain. These results argue for a key role of APP in the regulation of GABAergic neurotransmission.

Maternal choline supplementation in a mouse model of Down syndrome: Effects on attention and nucleus basalis/substantia innominata neuron morphology in adult offspring

The Ts65Dn mouse model of Down syndrome (DS) and Alzheimer's disease (AD) exhibits cognitive impairment and degeneration of basal forebrain cholinergic neurons (BFCNs). Our prior studies demonstrated that maternal choline supplementation (MCS) improves attention and spatial cognition in Ts65Dn offspring, normalizes hippocampal neurogenesis, and lessens BFCN degeneration in the medial septal nucleus (MSN). Here we determined whether (i) BFCN degeneration contributes to attentional dysfunction, and (ii) whether the attentional benefits of perinatal MCS are due to changes in BFCN morphology. Ts65Dn dams were fed either a choline-supplemented or standard diet during pregnancy and lactation. Ts65Dn and disomic (2N) control offspring were tested as adults (12-17months of age) on a series of operant attention tasks, followed by morphometric assessment of BFCNs. Ts65Dn mice demonstrated impaired learning and attention relative to 2N mice, and MCS significantly improved these functions in both genotypes. We also found, for the first time, that the number of BFCNs in the nucleus basalis of Meynert/substantia innominata (NBM/SI) was significantly increased in Ts65Dn mice relative to controls. In contrast, the number of BFCNs in the MSN was significantly decreased. Another novel finding was that the volume of BFCNs in both basal forebrain regions was significantly larger in Ts65Dn mice. MCS did not normalize any of these morphological abnormalities in the NBM/SI or MSN. Finally, correlational analysis revealed that attentional performance was inversely associated with BFCN volume, and positively associated with BFCN density. These results support the lifelong attentional benefits of MCS for Ts65Dn and 2N offspring and have profound implications for translation to human DS and pathology attenuation in AD.

Trans-acting epigenetic effects of chromosomal aneuploidies: lessons from Down syndrome and mouse models

An important line of postgenomic research seeks to understand how genetic factors can influence epigenetic patterning. Here we review epigenetic effects of chromosomal aneuploidies, focusing on findings in Down syndrome (DS, trisomy 21). Recent work in human DS and mouse models has shown that the extra chromosome 21 acts in trans to produce epigenetic changes, including differential CpG methylation (DS-DM), in specific sets of downstream target genes, mostly on other chromosomes. Mechanistic hypotheses emerging from these data include roles of chromosome 21-linked methylation pathway genes (DNMT3L and others) and transcription factor genes (RUNX1, OLIG2, GABPA, ERG and ETS2) in shaping the patterns of DS-DM. The findings may have broader implications for trans-acting epigenetic effects of chromosomal and subchromosomal aneuploidies in other human developmental and neuropsychiatric disorders, and in cancers.

Attentional function and basal forebrain cholinergic neuron morphology during aging in the Ts65Dn mouse model of Down syndrome

Individuals with Down syndrome (DS) exhibit intellectual disability and develop Alzheimer's disease-like neuropathology during the third decade of life. The Ts65Dn mouse model of DS exhibits key features of both disorders, including impairments in learning, attention and memory, as well as atrophy of basal forebrain cholinergic neurons (BFCNs). The present study evaluated attentional function in relation to BFCN morphology in young (3 months) and middle-aged (12 months) Ts65Dn mice and disomic (2N) controls. Ts65Dn mice exhibited attentional dysfunction at both ages, with greater impairment in older trisomics. Density of BFCNs was significantly lower for Ts65Dn mice independent of age, which may contribute to attentional dysfunction since BFCN density was positively associated with performance on an attention task. BFCN volume decreased with age in 2N but not Ts65Dn mice. Paradoxically, BFCN volume was greater in older trisomic mice, suggestive of a compensatory response. In sum, attentional dysfunction occurred in both young and middle-aged Ts65Dn mice, which may in part reflect reduced density and/or phenotypic alterations in BFCNs.

Effects of Maternal Choline Supplementation on the Septohippocampal Cholinergic System in the Ts65Dn Mouse Model of Down Syndrome

Down syndrome (DS), caused by trisomy of chromosome 21, is marked by intellectual disability (ID) and early onset of Alzheimer's disease (AD) neuropathology including hippocampal cholinergic projection system degeneration. Here we determined the effects of age and maternal choline supplementation (MCS) on hippocampal cholinergic deficits in Ts65Dn mice compared to 2N mice sacrificed at 6-8 and 14-18 months of age. Ts65Dn mice and disomic (2N) littermates sacrificed at ages 6-8 and 14-18 mos were used for an aging study and Ts65Dn and 2N mice derived from Ts65Dn dams were maintained on either a choline-supplemented or a choline-controlled diet (conception to weaning) and examined at 14-18 mos for MCS studies. In the latter, mice were behaviorally tested on the radial arm Morris water maze (RAWM) and hippocampal tissue was examined for intensity of choline acetyltransferase (ChAT) immunoreactivity. Hippocampal ChAT activity was evaluated in a separate cohort. ChAT-positive fiber innervation was significantly higher in the hippocampus and dentate gyrus in Ts65Dn mice compared with 2N mice, independent of age or maternal diet. Similarly, hippocampal ChAT activity was significantly elevated in Ts65Dn mice compared to 2N mice, independent of maternal diet. A significant increase with age was seen in hippocampal cholinergic innervation of 2N mice, but not Ts65Dn mice. Degree of ChAT intensity correlated negatively with spatial memory ability in unsupplemented 2N and Ts65Dn mice, but positively in MCS 2N mice. The increased innervation produced by MCS appears to improve hippocampal function, making this a therapy that may be exploited for future translational approaches in human DS.

New Perspectives for the Rescue of Cognitive Disability in Down Syndrome

Down syndrome (DS) is a relatively common genetic condition caused by the triplication of human chromosome 21. No therapies currently exist for the rescue of neurocognitive impairment in DS. This review presents exciting findings showing that it is possible to restore brain development and cognitive performance in mouse models of DS with therapies that can also apply to humans. This knowledge provides a potential breakthrough for the prevention of intellectual disability in DS.

Principal Component Analysis of the Effects of Environmental Enrichment and (-)-epigallocatechin-3-gallate on Age-Associated Learning Deficits in a Mouse Model of Down Syndrome

Down syndrome (DS) individuals present increased risk for Alzheimer's disease (AD) neuropathology and AD-type dementia. Here, we investigated the use of green tea extracts containing (-)-epigallocatechin-3-gallate (EGCG), as co-adjuvant to enhance the effects of environmental enrichment (EE) in Ts65Dn mice, a segmental trisomy model of DS that partially mimics DS/AD pathology, at the age of initiation of cognitive decline. Classical repeated measures ANOVA showed that combined EE-EGCG treatment was more efficient than EE or EGCG alone to improve specific spatial learning related variables. Using principal component analysis (PCA) we found that several spatial learning parameters contributed similarly to a first PC and explained a large proportion of the variance among groups, thus representing a composite learning measure. This PC1 revealed that EGCG or EE alone had no significant effect. However, combined EE-EGCG significantly ameliorated learning alterations of middle age Ts65Dn mice. Interestingly, PCA revealed an increased variability along learning sessions with good and poor learners in Ts65Dn, and this stratification did not disappear upon treatments. Our results suggest that combining EE and EGCG represents a viable therapeutic approach for amelioration of age-related cognitive decline in DS, although its efficacy may vary across individuals.

Partial BACE1 reduction in a Down syndrome mouse model blocks Alzheimer-related endosomal anomalies and cholinergic neurodegeneration: role of APP-CTF

β-amyloid precursor protein (APP) and amyloid beta peptide (Aβ) are strongly implicated in Alzheimer's disease (AD) pathogenesis, although recent evidence has linked APP-βCTF generated by BACE1 (β-APP cleaving enzyme 1) to the development of endocytic abnormalities and cholinergic neurodegeneration in early AD. We show that partial BACE1 genetic reduction prevents these AD-related pathological features in the Ts2 mouse model of Down syndrome. Partially reducing BACE1 by deleting one BACE1 allele blocked development of age-related endosome enlargement in the medial septal nucleus, cerebral cortex, and hippocampus and loss of choline acetyltransferase (ChAT)-positive medial septal nucleus neurons. BACE1 reduction normalized APP-βCTF elevation but did not alter Aβ40 and Aβ42 peptide levels in brain, supporting a critical role in vivo for APP-βCTF in the development of these abnormalities. Although ameliorative effects of BACE1 inhibition on β-amyloidosis and synaptic proteins levels have been previously noted in AD mouse models, our results highlight the additional potential value of BACE1 modulation in therapeutic targeting of endocytic dysfunction and cholinergic neurodegeneration in Down syndrome and AD.

Dissecting Alzheimer disease in Down syndrome using mouse models

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

A genetic cause of Alzheimer disease: mechanistic insights from Down syndrome

Down syndrome, which arises in individuals carrying an extra copy of chromosome 21, is associated with a greatly increased risk of early-onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP)--an Alzheimer disease risk factor--although the possession of extra copies of other chromosome 21 genes may also play a part. Further study of the mechanisms underlying the development of Alzheimer disease in people with Down syndrome could provide insights into the mechanisms that cause dementia in the general population.

Pain perception in people with Down syndrome: a synthesis of clinical and experimental research

People with an intellectual disability experience both acute and chronic pain with at least the same frequency as the general population. However, considerably less is known about the pain perception of people with Down syndrome. In this review paper, we evaluated the available clinical and experimental evidence. Some experimental studies of acute pain have indicated that pain threshold was higher than normal but only when using a reaction time method to measure pain sensitivity. However, when reaction time is not part of the calculation of the pain threshold, pain sensitivity in people with Down syndrome is in fact lower than normal (more sensitive to pain). Clinical studies of chronic pain have shown that people with an intellectual disability experience chronic pain and within that population, people with Down syndrome also experience chronic pain, but the precise prevalence of chronic pain in Down syndrome has yet to be established. Taken together, the literature suggests that people with Down syndrome experience pain, both acute and chronic, with at least the same frequency as the rest of the population. Furthermore, the evidence suggests that although acute pain expression appears to be delayed, once pain is registered, there appears to be a magnified pain response. We conclude by proposing an agenda for future research in this area.

Sleep-like behavior and 24-h rhythm disruption in the Tc1 mouse model of Down syndrome

Down syndrome is a common disorder associated with intellectual disability in humans. Among a variety of severe health problems, patients with Down syndrome exhibit disrupted sleep and abnormal 24-h rest/activity patterns. The transchromosomic mouse model of Down syndrome, Tc1, is a trans-species mouse model for Down syndrome, carrying most of human chromosome 21 in addition to the normal complement of mouse chromosomes and expresses many of the phenotypes characteristic of Down syndrome. To date, however, sleep and circadian rhythms have not been characterized in Tc1 mice. Using both circadian wheel-running analysis and video-based sleep scoring, we showed that these mice exhibited fragmented patterns of sleep-like behaviour during the light phase of a 12:12-h light/dark (LD) cycle with an extended period of continuous wakefulness at the beginning of the dark phase. Moreover, an acute light pulse during night-time was less effective in inducing sleep-like behaviour in Tc1 animals than in wild-type controls. In wheel-running analysis, free running in constant light (LL) or constant darkness (DD) showed no changes in the circadian period of Tc1 animals although they did express subtle behavioural differences including a reduction in total distance travelled on the wheel and differences in the acrophase of activity in LD and in DD. Our data confirm that Tc1 mice express sleep-related phenotypes that are comparable with those seen in Down syndrome patients with moderate disruptions in rest/activity patterns and hyperactive episodes, while circadian period under constant lighting conditions is essentially unaffected.

Evidence of altered age-related brain cytoarchitecture in mouse models of down syndrome: a diffusional kurtosis imaging study

Mouse models of Down syndrome (DS) exhibit abnormal brain developmental and neurodegenerative changes similar to those seen in individuals with DS. Although DS mice have been well characterized cognitively and morphologically there are no prior reports utilizing diffusion MRI. In this study we investigated the ability of diffusional kurtosis imaging (DKI) to detect the progressive developmental and neurodegenerative changes in the Ts65Dn (TS) DS mouse model. TS mice displayed higher diffusional kurtosis (DK) in the frontal cortex (FC) compared to normal mice at 2months of age. At 5months of age, TS mice had lower radial kurtosis in the striatum (ST), which persisted in the 8-month-old mice. The TS mice exhibited lower DK metrics values in the dorsal hippocampus (HD) at all ages, and the group difference in this region was larger at 8-months. Regression analysis showed that normal mice had a significant age-related increase in DK metrics in FC, ST and HD. On the contrary, the TS mice lacked significant age-related increase in DK metrics in FC and ST. Although preliminary, these results demonstrate that DK metrics can detect TS brain developmental and neurodegenerative abnormalities.

Expression profile analysis of vulnerable CA1 pyramidal neurons in young-Middle-Aged Ts65Dn mice

Down syndrome (DS) is the most prevalent cause of intellectual disability (ID). Individuals with DS show a variety of cognitive deficits, most notably in hippocampal learning and memory, and display pathological hallmarks of Alzheimer's disease (AD), with neurodegeneration of cholinergic basal forebrain (CBF) neurons. Elucidation of the molecular and cellular underpinnings of neuropathology has been assessed via gene expression analysis in a relevant animal model, termed the Ts65Dn mouse. The Ts65Dn mouse is a segmental trisomy model of DS that mimics DS/AD pathology, notably age-related cognitive dysfunction and degeneration of basal forebrain cholinergic neurons (BFCNs). To determine expression level changes, molecular fingerprinting of cornu ammonis 1 (CA1) pyramidal neurons was performed in adult (4-9 month-old) Ts65Dn mice, at the initiation of BFCN degeneration. To quantitate transcriptomic changes during this early time period, laser capture microdissection (LCM), terminal continuation (TC) RNA amplification, custom-designed microarray analysis, and subsequent validation of individual transcripts by qPCR and protein analysis via immunoblotting was performed. The results indicate significant alterations within CA1 pyramidal neurons of Ts65Dn mice compared with normal disomic (2N) littermates, notably in the downregulation of neurotrophins and their cognate neurotrophin receptors among other classes of transcripts relevant to neurodegeneration. The results of this single-population gene expression analysis at the time of septohippocampal deficits in a trisomic mouse model shed light on a vulnerable circuit that may cause the AD-like pathology invariably seen in DS that could help to identify mechanisms of degeneration, and provide novel gene targets for therapeutic interventions. J. Comp. Neurol. 523:61-74, 2015. © 2014 Wiley Periodicals, Inc.

Prediction of miRNA-mRNA associations in Alzheimer's disease mice using network topology

BACKGROUND

Little is known about the relationship between miRNA and mRNA expression in Alzheimer's disease (AD) at early- or late-symptomatic stages. Sequence-based target prediction algorithms and anti-correlation profiles have been applied to predict miRNA targets using omics data, but this approach often leads to false positive predictions. Here, we applied the joint profiling analysis of mRNA and miRNA expression levels to Tg6799 AD model mice at 4 and 8 months of age using a network topology-based method. We constructed gene regulatory networks and used the PageRank algorithm to predict significant interactions between miRNA and mRNA.

RESULTS

In total, 8 cluster modules were predicted by the transcriptome data for co-expression networks of AD pathology. In total, 54 miRNAs were identified as being differentially expressed in AD. Among these, 50 significant miRNA-mRNA interactions were predicted by integrating sequence target prediction, expression analysis, and the PageRank algorithm. We identified a set of miRNA-mRNA interactions that were changed in the hippocampus of Tg6799 AD model mice. We determined the expression levels of several candidate genes and miRNA. For functional validation in primary cultured neurons from Tg6799 mice (MT) and littermate (LM) controls, the overexpression of ARRDC3 enhanced PPP1R3C expression. ARRDC3 overexpression showed the tendency to decrease the expression of miR139-5p and miR3470a in both LM and MT primary cells. Pathological environment created by Aβ treatment increased the gene expression of PPP1R3C and Sfpq but did not significantly alter the expression of miR139-5p or miR3470a. Aβ treatment increased the promoter activity of ARRDC3 gene in LM primary cells but not in MT primary cells.

CONCLUSIONS

Our results demonstrate AD-specific changes in the miRNA regulatory system as well as the relationship between the expression levels of miRNAs and their targets in the hippocampus of Tg6799 mice. These data help further our understanding of the function and mechanism of various miRNAs and their target genes in the molecular pathology of AD.

Maternal choline supplementation improves spatial mapping and increases basal forebrain cholinergic neuron number and size in aged Ts65Dn mice

Down syndrome (DS) is marked by intellectual disability (ID) and early-onset of Alzheimer's disease (AD) neuropathology, including basal forebrain cholinergic neuron (BFCN) degeneration. The present study tested the hypothesis that maternal choline supplementation (MCS) improves spatial mapping and protects against BFCN degeneration in the Ts65Dn mouse model of DS and AD. During pregnancy and lactation, dams were assigned to either a choline sufficient (1.1g/kg choline chloride) or choline supplemented (5.0g/kg choline chloride) diet. Between 13 and 17months of age, offspring were tested in the radial arm water maze (RAWM) to examine spatial mapping followed by unbiased quantitative morphometry of BFCNs. Spatial mapping was significantly impaired in unsupplemented Ts65Dn mice relative to normal disomic (2N) littermates. Additionally, a significantly lower number and density of medial septum (MS) hippocampal projection BFCNs was also found in unsupplemented Ts65Dn mice. Notably, MCS significantly improved spatial mapping and increased number, density, and size of MS BFCNs in Ts65Dn offspring. Moreover, the density and number of MS BFCNs correlated significantly with spatial memory proficiency, providing support for a functional relationship between these behavioral and morphometric effects of MCS for trisomic offspring. Thus, increasing maternal choline intake during pregnancy may represent a safe and effective treatment approach for expectant mothers carrying a DS fetus, as well as a possible means of BFCN neuroprotection during aging for the population at large.

Maternal choline supplementation differentially alters the basal forebrain cholinergic system of young-adult Ts65Dn and disomic mice

Down syndrome (DS), trisomy 21, is a multifaceted condition marked by intellectual disability and early presentation of Alzheimer's disease (AD) neuropathological lesions including degeneration of the basal forebrain cholinergic neuron (BFCN) system. Although DS is diagnosable during gestation, there is no treatment option for expectant mothers or DS individuals. Using the Ts65Dn mouse model of DS that displays age-related degeneration of the BFCN system, we investigated the effects of maternal choline supplementation on the BFCN system in adult Ts65Dn mice and disomic (2N) littermates at 4.3-7.5 months of age. Ts65Dn dams were maintained on a choline-supplemented diet (5.1 g/kg choline chloride) or a control, unsupplemented diet with adequate amounts of choline (1 g/kg choline chloride) from conception until weaning of offspring; post weaning, offspring were fed the control diet. Mice were transcardially perfused with paraformaldehyde, and brains were sectioned and immunolabeled for choline acetyltransferase (ChAT) or p75-neurotrophin receptor (p75(NTR) ). BFCN number and size, the area of the regions, and the intensity of hippocampal labeling were determined. Ts65Dn-unsupplemented mice displayed region- and immunolabel-dependent increased BFCN number, larger areas, smaller BFCNs, and overall increased hippocampal ChAT intensity compared with 2N unsupplemented mice. These effects were partially normalized by maternal choline supplementation. Taken together, the results suggest a developmental imbalance in the Ts65Dn BFCN system. Early maternal-diet choline supplementation attenuates some of the genotype-dependent alterations in the BFCN system, suggesting this naturally occurring nutrient as a treatment option for pregnant mothers with knowledge that their offspring is trisomy 21.

Age-dependent effects of valproic acid in Alzheimer's disease (AD) mice are associated with nerve growth factor (NGF) regulation

Alzheimer's disease (AD) is a progressive neurodegenerative disease that causes cognitive impairment. Major pathophysiological AD characteristics include numerous senile plaque, neurofibrillary tangles, and neuronal loss in the specific regions of patients' brains. In this study, we aimed to understand disease stage-dependent regulation of histone modification for the expression of specific markers in plasma and the hippocampus of in vivo AD model. Since the control of histone acetylation/deacetylation has been studied as one of major epigenetic regulatory mechanisms for specific gene expression, we detected the effects of histone deacetylase (HDAC) inhibitor on marker expression and neuroprotection in in vivo AD model mice. We determined the effects of valproic acid (VPA, HDAC inhibitor), on the levels of cytokines, secreted form of APP (sAPP), nerve growth factor (NGF), and cognitive function in Tg6799 AD mice in three different disease stages (1month: pre-symptomatic; 5months: early symptomatic; and 10months: late-symptomatic stages). VPA decreased the mRNA levels of nuclear factor kappaB (NF-κB) and IL-1ß in the plasma of Tg6799 mice compared to vehicle control at 10months of age. VPA increased the protein levels of NGF in the hippocampus of Tg6799 mice at 5 and 10months of age. In addition, VPA decreased escape latencies of Tg6799 mice at 5 and 10months of age in Morris water maze assessment. Taken together, HDAC inhibition is a promising therapeutic target for AD and it needs to be considered in an age-dependent and/or stage-dependent manner.

Nerve growth factor metabolic dysfunction in Down's syndrome brains

Basal forebrain cholinergic neurons play a key role in cognition. This neuronal system is highly dependent on NGF for its synaptic integrity and the phenotypic maintenance of its cell bodies. Basal forebrain cholinergic neurons progressively degenerate in Alzheimer's disease and Down's syndrome, and their atrophy contributes to the manifestation of dementia. Paradoxically, in Alzheimer's disease brains, the synthesis of NGF is not affected and there is abundance of the NGF precursor, proNGF. We have shown that this phenomenon is the result of a deficit in NGF's extracellular metabolism that compromises proNGF maturation and exacerbates its subsequent degradation. We hypothesized that a similar imbalance should be present in Down's syndrome. Using a combination of quantitative reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting and zymography, we investigated signs of NGF metabolic dysfunction in post-mortem brains from the temporal (n = 14), frontal (n = 34) and parietal (n = 20) cortex obtained from subjects with Down's syndrome and age-matched controls (age range 31-68 years). We further examined primary cultures of human foetal Down's syndrome cortex (17-21 gestational age weeks) and brains from Ts65Dn mice (12-22 months), a widely used animal model of Down's syndrome. We report a significant increase in proNGF levels in human and mouse Down's syndrome brains, with a concomitant reduction in the levels of plasminogen and tissue plasminogen activator messenger RNA as well as an increment in neuroserpin expression; enzymes that partake in proNGF maturation. Human Down's syndrome brains also exhibited elevated zymogenic activity of MMP9, the major NGF-degrading protease. Our results indicate a failure in NGF precursor maturation in Down's syndrome brains and a likely enhanced proteolytic degradation of NGF, changes which can compromise the trophic support of basal forebrain cholinergic neurons. The alterations in proNGF and MMP9 were also present in cultures of Down's syndrome foetal cortex; suggesting that this trophic compromise may be amenable to rescue, before frank dementia onset. Our study thus provides a novel paradigm for cholinergic neuroprotection in Alzheimer's disease and Down's syndrome.