Elucidating Pathogenic Mechanisms of Early-onset Alzheimer's Disease in Down Syndrome Patients

Symptoms and age of prodromal Alzheimer's disease in Down syndrome: a systematic review and meta-analysis

The diagnostic criteria for adult-onset Alzheimer's disease (AD) in patients with Down syndrome (DS) have not been standardised. This study investigated the specific symptoms of AD in the prodromal stage of DS, the mean age at diagnosis at each stage of dementia, and the relationship between intellectual disability (ID) and dementia. PubMed, Web of Science, and Embase were searched for studies on DS, AD, early-stage disease, initial symptoms, and prodromal dementia registered between January 2012 and January 2022. We also performed a meta-analysis of the differences between the mean age at prodromal symptoms and AD diagnosis and the proportion of mild cognitive impairment in patients with mild and moderately abnormal ID. We selected 14 articles reporting the behavioural and psychological symptoms of dementia (BPSD) and memory- and language-related impairments as early symptoms of AD in patients with DS. The specific symptoms of BPSD were classified into five categories: irritability (agitation), apathy, abnormal behaviour, adaptive functioning, and sleep disturbance. The mean age at the diagnosis of prodromal symptoms and AD dementia was 52.7 and 56.2 years, respectively (mean difference, + 3.11 years; 95% CI 1.82-4.40) in the meta-analysis. The diagnosis of mild dementia tended to correlate with ID severity (odds ratio [OR], 1.38; 95% CI 0.87-2.18). The features of behaviour-variant frontotemporal dementia may be clinically confirmed in diagnosing early symptoms of DS-associated AD (DSAD). Moreover, age-appropriate cognitive assessment is important. Further studies are required to evaluate DSAD using a combination of biomarkers and ID-related data.

Therapeutics for mitochondrial dysfunction-linked diseases in Down syndrome

Genome-wide deregulation contributes to mitochondrial dysfunction and impairment in oxidative phosphorylation (OXPHOS) mechanism resulting in oxidative stress, increased production of reactive oxygen species (ROS) and cell death in individuals with Down syndrome (DS). The cells, which require more energy, such as muscles, brain and heart are greatly affected. Impairment in mitochondrial network has a direct link with patho-mechanism at cellular and systemic levels at the backdrop of generalized metabolic perturbations in individuals with DS. Myriads of clinico-phenotypic features, including intellectual disability, early aging and neurodegeneration, and Alzheimer disease (AD)-related dementia are inevitable in DS-population where mitochondrial dysfunctions play the central role. Collectively, the mitochondrial abnormalities and altered energy metabolism perturbs several signaling pathways, particularly related to neurogenesis, which are directly associated with cognitive development and early onset of AD in individuals with DS. Therefore, therapeutic challenges for amelioration of the mitochondrial defects were perceived to improve the quality of life of the DS population. A number of pharmacologically active natural compounds such as polyphenols, antioxidants and flavonoids have shown convincing outcome for reversal of the dysfunctional mitochondrial network and oxidative metabolism, and improvement in intellectual skill in mouse models of DS and humans with DS.

The Role of a Pathological Interaction between β-amyloid and Mitochondria in the Occurrence and Development of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases in existence. It is characterized by an impaired cognitive function that is due to a progressive loss of neurons in the brain. Extracellular β-amyloid (Aβ) plaques are the main pathological features of the disease. In addition to abnormal protein aggregation, increased mitochondrial fragmentation, altered expression of the genes involved in mitochondrial biogenesis, disruptions in the ER-mitochondria interaction, and mitophagy are observed. Reactive oxygen species are known to affect Aβ expression and aggregation. In turn, oligomeric and aggregated Aβ cause mitochondrial disorders. In this review, we summarize available knowledge about the pathological effects of Aβ on mitochondria and the potential molecular targets associated with proteinopathy and mitochondrial dysfunction for the pharmacological treatment of Alzheimer's disease.

Prenatal NeuN+ neurons of Down syndrome display aberrant integrative DNA methylation and gene expression profiles

Aim: To detect expression quantitative trait methylation (eQTM) loci within the cerebrum of prenatal Down syndrome (DS) and controls. Material & methods: DNA methylation gene expression profiles were acquired from NeuN+ nuclei, obtained from cerebrum sections of DS and controls. Linear regression models were applied to both datasets and were subsequently applied in an integrative analysis model to detect DS-associated eQTM loci. Results & conclusion: Widespread aberrant DNA methylation and gene expression were observed in DS. A substantial number of differentially methylated loci were replicated according to a previously reported study. Subsequent integrative analyses (eQTM) yielded numerous associated DS loci. the authors associated DNA methylation, gene expression and eQTM loci with DS that may underlie particular DS phenotypical characteristics.

Tiny Toes to Tau Tangles: Down's Syndrome and Its Association With Alzheimer's Disease

Down’s syndrome (DS) is a common genetic condition caused by the trisomy of chromosome 21, which leads to the development of many multisystemic complications, early-onset Alzheimer’s disease (AD) being one of its most common complications. In this article, we have performed an intensive literature review that established a strong relationship between AD and DS. These two conditions are clubbed pathologically, clinically, and diagnostically to understand the association between AD and DS. This article focuses on understanding the impact of AD on a DS patient on both clinical and pathological levels and exploring some advanced treatment modalities. It has also emphasized the importance of early screening and diagnosis for AD in this group of patients to prevent AD development. Regular monitoring, early diagnosis, and a proper treatment plan can slow the AD occurrence in DS patients.

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.

Elevated soluble amyloid beta protofibrils in Down syndrome and Alzheimer's disease

Down syndrome (DS) is caused by trisomy of chromosome 21, which leads to a propensity to develop amyloid β (Aβ) brain pathology in early adulthood followed later by cognitive and behavioral deterioration. Characterization of the Aβ pathology is important to better understand the clinical deterioration of DS individuals and to identify interventive strategies. Brain samples from people with DS and Alzheimer's disease (AD), as well as non-demented controls (NDC), were analyzed with respect to different Aβ species. Immunohistochemical staining using antibodies towards Aβ was also performed. Elevated levels of soluble Aβ protofibrils and insoluble Aβx-40 and Aβx-42 in formic acid brain extracts, and elevated immunohistochemical staining of Aβ deposits were demonstrated with the antibody BAN2401 (lecanemab) in DS and AD compared with NDC. These data and the promising data in a large phase 2 CE clinical trial with lecanemab suggest that lecanemab may have the potential to preserve cognitive capacity in DS. Lecanemab is currently in a phase 3 CE clinical trial.

The novel DYRK1A inhibitor KVN93 regulates cognitive function, amyloid-beta pathology, and neuroinflammation

Regulating amyloid beta (Aβ) pathology and neuroinflammatory responses holds promise for the treatment of Alzheimer's disease (AD) and other neurodegenerative and/or neuroinflammation-related diseases. In this study, the effects of KVN93, an inhibitor of dual-specificity tyrosine phosphorylation-regulated kinase-1A (DYRK1A), on cognitive function and Aβ plaque levels and the underlying mechanism of action were evaluated in 5x FAD mice (a mouse model of AD). KVN93 treatment significantly improved long-term memory by enhancing dendritic synaptic function. In addition, KVN93 significantly reduced Aβ plaque levels in 5x FAD mice by regulating levels of the Aβ degradation enzymes neprilysin (NEP) and insulin-degrading enzyme (IDE). Moreover, Aβ-induced microglial and astrocyte activation were significantly suppressed in the KVN-treated 5xFAD mice. KVN93 altered neuroinflammation induced by LPS in microglial cells but not primary astrocytes by regulating TLR4/AKT/STAT3 signaling, and in wild-type mice injected with LPS, KVN93 treatment reduced microglial and astrocyte activation. Overall, these results suggest that the novel DYRK1A inhibitor KVN93 is a potential therapeutic drug for regulating cognitive/synaptic function, Aβ plaque load, and neuroinflammatory responses in the brain.

miR-194 Accelerates Apoptosis of Aβ1⁻42-Transduced Hippocampal Neurons by Inhibiting Nrn1 and Decreasing PI3K/Akt Signaling Pathway Activity

This article explores the mechanism of miR-194 on the proliferation and apoptosis of Aβ_1–42-transduced hippocampal neurons. Aβ_1–42-transduced hippocampal neuron model was established by inducing hippocampal neurons with Aβ_1–42. MTT assay and flow cytometry were used to detect the viability and apoptosis of hippocampal neurons, respectively. qRT-PCR was used to detect changes in miR-194 and Nrn1 expression after Aβ_1–42 induction. Aβ_1–42-transduced hippocampal neurons were transfected with miR-194 mimics and/or Nrn1 overexpression vectors. Their viability and neurite length were detected by MTT assay and immunofluorescence, respectively. Western blot was used to detect protein expression. Aβ_1–42 inhibited Aβ_1–42-transduced hippocampal neuron activity and promoted their apoptosis in a dose-dependent manner. miR-194 was upregulated and Nrn1 was downregulated in Aβ_1–42-transduced hippocampal neurons (p < 0.05). Compared with the model group, Aβ_1–42-transduced hippocampal neurons of the miR-194 mimic group had much lower activity, average longest neurite length, Nrn1, p-AkT, and Bcl-2 protein expression and had much higher Bax, Caspase-3, and Cleaved Caspase-3 protein expression. Compared with the model group, Aβ_1–42-transduced hippocampal neurons of the LV-Nrn1 group had much higher activity, average longest neurite length, Nrn1, p-AkT, and Bcl-2 protein expression and had much lower Bax, Caspase-3, and Cleaved Caspase-3 protein expression. Nrn1 is a target gene of miR-194. miR-194 inhibited apoptosis of Aβ_1–42-transduced hippocampal neurons by inhibiting Nrn1 and decreasing PI3K/AkT signaling pathway activity.