Alterations of Audiovisual Integration in Alzheimer's Disease.

Audiovisual integration is a vital information process involved in cognition and is closely correlated with aging and Alzheimer's disease (AD). In this review, we evaluated the altered audiovisual integrative behavioral symptoms in AD. We further analyzed the relationships between AD pathologies and audiovisual integration alterations bidirectionally and suggested the possible mechanisms of audiovisual integration alterations underlying AD, including the imbalance between energy demand and supply, activity-dependent degeneration, disrupted brain networks, and cognitive resource overloading. Then, based on the clinical characteristics including electrophysiological and imaging data related to audiovisual integration, we emphasized the value of audiovisual integration alterations as potential biomarkers for the early diagnosis and progression of AD. We also highlighted that treatments targeted audiovisual integration contributed to widespread pathological improvements in AD animal models and cognitive improvements in AD patients. Moreover, investigation into audiovisual integration alterations in AD also provided new insights and comprehension about sensory information processes.

TREM2 and Microglia Contribute to the Synaptic Plasticity: from Physiology to Pathology.

Synapses are bridges for information transmission in the central nervous system (CNS), and synaptic plasticity is fundamental for the normal function of synapses, contributing substantially to learning and memory. Numerous studies have proven that microglia can participate in the occurrence and progression of neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), by regulating synaptic plasticity. In this review, we summarize the main characteristics of synapses and synaptic plasticity under physiological and pathological conditions. We elaborate the origin and development of microglia and the two well-known microglial signaling pathways that regulate synaptic plasticity. We also highlight the unique role of triggering receptor expressed on myeloid cells 2 (TREM2) in microglia-mediated regulation of synaptic plasticity and its relationship with AD. Finally, we propose four possible ways in which TREM2 is involved in regulating synaptic plasticity. This review will help researchers understand how NDDs develop from the perspective of synaptic plasticity.

TREM2 in the pathogenesis of AD: a lipid metabolism regulator and potential metabolic therapeutic target.

Triggering receptor expressed on myeloid cells 2 (TREM2) is a single-pass transmembrane immune receptor that is mainly expressed on microglia in the brain and macrophages in the periphery. Recent studies have identified TREM2 as a risk factor for Alzheimer's disease (AD). Increasing evidence has shown that TREM2 can affect lipid metabolism both in the central nervous system (CNS) and in the periphery. In the CNS, TREM2 affects the metabolism of cholesterol, myelin, and phospholipids and promotes the transition of microglia into a disease-associated phenotype. In the periphery, TREM2 influences lipid metabolism by regulating the onset and progression of obesity and its complications, such as hypercholesterolemia, atherosclerosis, and nonalcoholic fatty liver disease. All these altered lipid metabolism processes could influence the pathogenesis of AD through several means, including affecting inflammation, insulin resistance, and AD pathologies. Herein, we will discuss a potential pathway that TREM2 mediates lipid metabolism to influence the pathogenesis of AD in both the CNS and periphery. Moreover, we discuss the possibility that TREM2 may be a key factor that links central and peripheral lipid metabolism under disease conditions, including AD. This link may be due to impacts on the integrity of the blood-brain barrier, and we introduce potential pathways by which TREM2 affects the blood-brain barrier. Moreover, we discuss the role of lipids in TREM2-associated treatments for AD. We propose some potential therapies targeting TREM2 and discuss the prospect and limitations of these therapies.

Five Major Psychiatric Disorders and Alzheimer's Disease: A Bidirectional Mendelian Randomization Study.

BACKGROUND: Extensive studies put forward the association between Alzheimer's disease (AD) and psychiatric disorders; however, it remains unclear whether these associations are causal. OBJECTIVE: We aimed to assess the potential causal relationship between major psychiatric disorders and AD. METHODS: A bidirectional two-sample Mendelian randomization (MR) was applied to evaluate potential causality between five psychiatric disorders and AD by selecting the single-nucleotide polymorphisms from the genome-wide association studies as instrumental variables. Inverse-variance weighted (IVW) method was used as the main analyzing approach to estimate possible causal effects, alternative methods including MR-Egger, the MR pleiotropy residual sum and outlier, and leave-one-out analysis method were implemented as sensitivity analyzing approaches to ensure the robustness of results. RESULTS: All forward and reverse MR analyses consistently suggested absent causal relations between psychiatric disorders and AD risk [forward IVW: ORADHD, 1.030, 95% CI, 0.908-1.168, p = 0.674; ORanxiety disorders, 0.904, 95% CI, 0.722-1.131, p = 0.377; ORASD, 0.973, 95% CI, 0.746-1.272, p = 0.846; ORBIP, 1.033, 95% CI, 0.925-1.153, p = 0.564; and ORschizophrenia, 1.039, 95% CI, 0.986-1.095, p = 0.156; reverse IVW: ORADHD, 0.993, 95% CI, 0.954-1.034, p = 0.746; ORanxiety disorders, 1.000, 95% CI, 0.999-1.000, p = 0.898; ORASD, 1.001, 95% CI, 0.962-1.042, p = 0.949; ORBIP, 0.997, 95% CI, 0.966-1.028, p = 0.831; and ORschizophrenia, 1.013, 95% CI, 0.978-1.051, p = 0.466]. CONCLUSION: There is no significant evidence supporting the causal association between the five major psychiatric disorders and AD.

Capgras Syndrome as the Core Manifestation of Early-Onset Alzheimer's Disease.

Capgras syndrome (CS) was usually considered a symptom of a functional disorder in the young, most commonly schizophrenia, or an organic disorder in the elderly. The occurrence of CS among early-onset Alzheimer's disease (EOAD) is extremely rare. We describe a case in which the unrecognition of CS as part of EOAD resulted in a wrong psychiatric diagnosis and inappropriate treatment. This paper aims to acknowledge CS as an early or core manifestation and highlight EOAD as a differential diagnosis of mental disorders in young people, even without a remarkable family history.