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Women are disproportionately affected by Alzheimer’s disease (AD), yet little is known about sex-specific effects on the development of AD in the Down syndrome (DS) population. DS is caused by a full or partial triplication of chromosome 21, which harbors the amyloid precursor protein (APP) gene, among others. The majority of people with DS in their early- to mid-40s will accumulate sufficient amyloid-beta (A) in their brains along with neurofibrillary tangles for a neuropathological diagnosis of AD, and the triplication of the APP gene is regarded as the main cause. Studies addressing sex differences with age and impact on dementia in people with DS are inconsistent. However, women with DS experience earlier age of onset of menopause, marked by a drop in estrogen, than women without DS. This review focuses on key sex differences observed with age and AD in people with DS and a discussion of possible underlying mechanisms that could be driving or protecting from AD development in DS. Understanding how biological sex influences the brain will lead to development of dedicated therapeutics and interventions to improve the quality of life for people with DS and AD.

Introduction Microglial cells play an important role in the development of Alzheimer's disease (AD). People with Down syndrome (DS) inevitably develop AD neuropathology (DSAD) by 40 years of age. We characterized the distribution of different microglial phenotypes in the brains of people with DS and DSAD. Methods Autopsy tissue from the posterior cingulate cortex (PCC) from people with DS, DSAD, and neurotypical controls was immunostained with the microglial marker Iba1 to assess five microglia morphological types. Results Individuals with DS have more hypertrophic microglial cells in their white matter. In the gray matter, individuals with DSAD had significantly fewer ramified microglia and more dystrophic microglia than controls and the younger individuals with DS. The DSAD group also exhibited more rod‐shaped and amoeboid cells than the AD group. Discussion Individuals with DS and DSAD show a microglial phenotype that distinguishes them from non‐DS controls.

Precise, scalable, and quantitative evaluation of whole slide images is crucial in neuropathology. We release a deep learning model for rapid object detection and precise information on the identification, locality, and counts of cored plaques and cerebral amyloid angiopathy (CAA). We trained this object detector using a repurposed image-tile dataset without any human-drawn bounding boxes. We evaluated the detector on a new manually-annotated dataset of whole slide images (WSIs) from three institutions, four staining procedures, and four human experts. The detector matched the cohort of neuropathology experts, achieving 0.64 (model) vs. 0.64 (cohort) average precision (AP) for cored plaques and 0.75 vs. 0.51 AP for CAAs at a 0.5 IOU threshold. It provided count and locality predictions that approximately correlated with gold-standard human CERAD-like WSI scoring ( p  = 0.07 ± 0.10). The openly-available model can quickly score WSIs in minutes without a GPU on a standard workstation. A deep learning model rapidly identifies locality and counts of cored plaques and cerebral amyloid angiopathy in whole slide images comparably to human experts and without a GPU on a standard workstation.

MicroRNAs play a pivotal role in rapid, dynamic, and spatiotemporal modulation of synaptic functions. Among them, recent emerging evidence highlights that microRNA‐181a (miR‐181a) is particularly abundant in hippocampal neurons and controls the expression of key plasticity‐related proteins at synapses. We have previously demonstrated that miR‐181a was upregulated in the hippocampus of a mouse model of Alzheimer's disease (AD) and correlated with reduced levels of plasticity‐related proteins. Here, we further investigated the underlying mechanisms by which miR‐181a negatively modulated synaptic plasticity and memory. In primary hippocampal cultures, we found that an activity‐dependent upregulation of the microRNA‐regulating protein, translin, correlated with reduction of miR‐181a upon chemical long‐term potentiation (cLTP), which induced upregulation of GluA2, a predicted target for miR‐181a, and other plasticity‐related proteins. Additionally, Aβ treatment inhibited cLTP‐dependent induction of translin and subsequent reduction of miR‐181a, and cotreatment with miR‐181a antagomir effectively reversed the effects elicited by Aβ but did not rescue translin levels, suggesting that the activity‐dependent upregulation of translin was upstream of miR‐181a. In mice, a learning episode markedly decreased miR‐181a in the hippocampus and raised the protein levels of GluA2. Lastly, we observed that inhibition of miR‐181a alleviated memory deficits and increased GluA2 and GluA1 levels, without restoring translin, in the 3xTg‐AD model. Taken together, our results indicate that miR‐181a is a major negative regulator of the cellular events that underlie synaptic plasticity and memory through AMPA receptors, and importantly, Aβ disrupts this process by suppressing translin and leads to synaptic dysfunction and memory impairments in AD. In the hippocampus, neuronal stimulation produces upregulation of translin, reduction of miR‐181a, and an increase in the protein levels of its target GluA2 leading to synaptic plasticity. This plasticity mechanism is impaired by amyloid‐beta (Aβ) toxic species.

Down syndrome (DS) is a form of accelerated aging, and people with DS are highly prone to aging-related conditions that include vascular and neurological disorders. Due to the overexpression of several genes on Chromosome 21, for example genes encoding amyloid precursor protein (APP), superoxide dismutase (SOD), and some of the interferon receptors, those with DS exhibit significant accumulation of amyloid, phospho-tau, oxidative stress, neuronal loss, and neuroinflammation in the brain as they age. In this review, we will summarize the major strides in this research field that have been made in the last few decades, as well as discuss where we are now, and which research areas are considered essential for the field in the future. We examine the scientific history of DS bridging these milestones in research to current efforts in the field. We extrapolate on comorbidities associated with this phenotype and highlight clinical networks in the USA and Europe pursuing clinical research, concluding with funding efforts and recent recommendations to the NIH regarding DS research.

ABSTRACT Alzheimer's disease (AD) is a complex neurodegenerative proteinopathy in which Aβ and tau misfold and aggregate into entities that structurally unsettle native proteins, mimicking a prion‐like or “seeding” process. These Aβ and tau “seeds” can arrange in different conformations or strains that might display distinct pathogenic properties. Furthermore, recent evidence suggests that microglia play a key role in the amyloidogenic event and can modulate the propagation and aggregation processes. Here, we employed histological and molecular approaches to determine whether seeds from human AD brains compared to those from transgenic mice (3xTg‐AD) are more prone to induce Aβ and tau aggregates in vivo, as well as potential differences in the microglial response to the plaque pathology. Brain homogenates were injected into the hippocampus of 3xTg‐AD mice and hAβ‐KI mice and examined at 18–20 months of age. The seeds from the human AD brain induced more aggressive amyloid pathology compared to seeds from aged 3xTg‐AD mice. However, the AD seeds from aged transgenic mice triggered more tau pathology. Interestingly, such mice seeds impaired microglial clustering around plaques, leading to more severe neuritic pathology. Furthermore, the human AD seeds injected into the hippocampus of hAβ‐KI mice were not able to induce plaque formation. These results suggest that multiple variables such as the AD seed, recipient model, and time are critical factors that can modulate the amyloid pathology onset and progression. Thus, more profound understanding of these factors will provide key insight into how amyloid and tau pathology progresses in AD. This study shows that human and mouse brains contain a different pool of strains that differentially affect the formation of Aβ and tau aggregates. Moreover, the murine seeds trigger an unresponsiveness microglial state, which causes the loss of plaque microglial coverage and affects the formation of amyloid plaques, leading to more severe neuritic pathology. The findings provide insights into the differences between mouse and human Aβ and tau strains and their impact on disease progression.

Alzheimer's disease (AD) is conceptualized as a synaptic failure disorder in which loss of glutamatergic synapses is a major driver of cognitive decline. Thus, novel therapeutic strategies aimed at regenerating synapses may represent a promising approach to mitigate cognitive deficits in AD patients. At present, no disease-modifying drugs exist for AD, and approved therapies are palliative at best, lacking in the ability to reverse the synaptic failure. Here, we tested the efficacy of a novel synaptogenic small molecule, SPG302 — a 3rd-generation benzothiazole derivative that increases the density of axospinous glutamatergic synapses — in 3xTg-AD mice. Daily dosing of 3xTg-AD mice with SPG302 at 3 and 30 mg/kg (i.p.) for 4 weeks restored hippocampal synaptic density and improved cognitive function in hippocampal-dependent tasks. Mushroom and stubby spine profiles were increased by SPG302, and associated with enhanced expression of key postsynaptic proteins — including postsynaptic density protein 95 (PSD95), drebrin, and amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) — and increased colocalization of PSD95 with synaptophysin. Notably, SPG302 proved efficacious in this model without modifying Aβ and tau pathology. Thus, our study provides preclinical support for the idea that compounds capable of restoring synaptic density offer a viable strategy to reverse cognitive decline in AD.

Diabetes mellitus (DM) is one of the most devastating diseases that currently affects the aging population. Recent evidence indicates that DM is a risk factor for many brain disorders, due to its direct effects on cognition. New findings have shown that the microtubule‐associated protein tau is pathologically processed in DM; however, it remains unknown whether pathological tau modifications play a central role in the cognitive deficits associated with DM. To address this question, we used a gain‐of‐function and loss‐of‐function approach to modulate tau levels in type 1 diabetes (T1DM) and type 2 diabetes (T2DM) mouse models. Our study demonstrates that tau differentially contributes to cognitive and synaptic deficits induced by DM. On one hand, overexpressing wild‐type human tau further exacerbates cognitive and synaptic impairments induced by T1DM, as human tau mice treated under T1DM conditions show robust deficits in learning and memory processes. On the other hand, neither a reduction nor increase in tau levels affects cognition in T2DM mice. Together, these results shine new light onto the different molecular mechanisms that underlie the cognitive and synaptic impairments associated with T1DM and T2DM.

The current issue of the Journal of Clinical Medicine (JCM) contains a collection of papers depicting different aspects of aging with DS, from biological pathways involved in age-related conditions to the impact of lifestyle, or novel interventions that can reduce the effects of aging on the brain in people with DS. In Hendrix et al.’s (2021) [4] paper, the Longitudinal Investigation for Enhancing Down Syndrome Research (LIFE-DSR) Study reported early findings from a natural history study of adults with DS in the USA. [...]the research group from Cambridge University in the UK included an interesting review focused on the clinical and neuropathological features of sporadic and genetic forms of AD (Félez et al., 2021) [13], in which they compared the clinical and pathological aspects of genetic versus sporadic AD, focusing on DSAD and autosomal dominant Alzheimer’s disease (ADAD), compared with the more common late-onset form of the disease. Funding This research was funded by an NIH/NIA grant (R01AG061566) and a Bright Focus Foundation grant (CA2018010) to A.-C.G.; NIH grants (P01AG014449 and P01AG017617) to M.J.A. Conflicts of Interest The authors declare no conflict of interest.