Association of APOE-ε4 and GAP-43-related presynaptic loss with β-amyloid, tau, neurodegeneration, and cognitive decline

APOE ε4 influences the dynamic functional connectivity variability and cognitive performance in Alzheimer's disease

BackgroundApolipoprotein E (APOE) ε4 is the most significant genetic risk factor for sporadic Alzheimer's disease (AD). However, its impact on the dynamic changes in resting-state functional connectivity (FC), particularly concerning network formation, interaction, and dissolution over time, remains largely unexplored in AD.ObjectiveThis study aims to explore the effect of APOE ε4 on dynamic FC (dFC) variability and cognitive performance in AD.MethodsWe analyzed the dFC of AD patients, comparing APOE ε4 carriers (n = 33) with non-carriers (n = 41). The whole-brain dFC was assessed by calculating dynamic fractional amplitude of low-frequency fluctuations (dfALFF) and dynamic regional homogeneity (dReHo). To further explore the relationship between cognitive function and dFC in AD patients, we conducted a correlation analysis. Mediation analysis was also performed to determine whether dFC mediates the link between the APOE ε4 and cognitive decline in AD patients.ResultsAD patients carrying the APOE ε4 exhibited more severe cognitive impairment, along with reduced dReHo and dfALFF in both the left and right posterior cerebellar lobes. In these carriers, the dFC analysis showed lower dFC between the left posterior cerebellar lobe and the left middle temporal gyrus, which was positively correlated with executive function and information processing speed. Additionally, mediation analysis indicated that APOE ε4 influences dFC in this brain region, contributing to executive dysfunction in AD.ConclusionsThese findings offer preliminary evidence that APOE ε4 modulates fluctuating communication within the cerebellar lobe and the dFC between the cerebellar lobe and the temporal gyrus in AD.

Elevated CSF GAP-43 in Mild Cognitive Impairment Linked to Cognitive Impairment Through Increased Amyloid-β Accumulation, with a Shift to Reduced Amyloid-β Accumulation in Alzheimer's Disease

Growth-associated protein 43 (GAP-43), a key regulator of synaptic plasticity, neuronal growth, and memory, has recently been identified as a crucial biomarker for synaptic dysfunction in mild cognitive impairment (MCI) and Alzheimer's disease (AD) dementia. This study aimed to explore the mechanisms underlying GAP-43's role in cognitive impairment by examining the relationship between CSF GAP-43 levels and amyloid-β (Aβ) accumulation in brain regions like the frontal, temporal, and parietal lobes. This study included 332 participants sourced from the Alzheimer's Disease Neuroimaging Initiative (ADNI), categorized into three groups: 93 cognitively normal (CN), 218 with MCI, and 21 with AD dementia. Cognitive status was assessed with ADAS-Cog 13, CSF GAP-43 levels via ELISA, and Aβ accumulation using florbetapir PET imaging and Syngo.PET for SUVr values in key brain regions. The results revealed that CSF GAP-43 levels were highest in the AD dementia group, followed by the MCI group, and lowest in the CN group, with a significant difference (p < 0.001), indicating a link between elevated CSF GAP-43 and cognitive impairment. In MCI group, CSF GAP-43 positively correlated with Aβ accumulation in all regions: Globally (β = 0.362, p < 0.001), frontal (β = 0.388, p < 0.001), temporal (β = 0.382, p < 0.001), and parietal lobes (β = 0.344, p < 0.001). In contrast, the AD dementia group exhibited negative correlations between CSF GAP-43 levels and Aβ accumulation, significantly in the frontal (β =  - 0.513, p = 0.035) and parietal lobes (β =  - 0.513, p = 0.035), suggesting a shift in the CSF GAP-43-Aβ relationship in AD dementia. Mediation analysis, adjusted for age, gender, education, and ApoE ɛ4 status, revealed that elevated CSF GAP-43 is linked to increased cognitive impairment via increasing Aβ accumulation solely in MCI, with significant effects in global (β = 0.0894, CI: [0.0427, 0.1457]), frontal (β = 0.0895, CI: [0.0422, 0.1443]), temporal (β = 0.0941, CI: [0.0466, 0.1522]), and parietal (β = 0.0499, CI: [0.0100, 0.0945]) regions. Thus, elevated CSF GAP-43 may contribute to cognitive impairment by promoting Aβ accumulation in individuals with MCI, while in AD dementia, it may be associated with reduced Aβ accumulation, potentially reflecting a compensatory or disease-stage-dependent effect. This dynamic relationship suggests that GAP-43 could play a dual role in neurodegeneration, influencing Aβ pathology differently across disease stages.

Biomarkers of synaptic degeneration in Alzheimer's disease

Synapse has been considered a critical neuronal structure in the procession of Alzheimer's disease (AD), attacked by two pathological molecule aggregates (amyloid-β and phosphorylated tau) in the brain, disturbing synaptic homeostasis before disease manifestation and subsequently causing synaptic degeneration. Recently, evidence has emerged indicating that soluble oligomeric amyloid-β (AβO) and tau exert direct toxicity on synapses, causing synaptic damage. Synaptic degeneration is closely linked to cognitive decline in AD, even in the asymptomatic stages of AD. Therefore, the identification of novel, specific, and sensitive biomarkers involved in synaptic degeneration holds significant promise for early diagnosis of AD, reducing synaptic degeneration and loss, and controlling the progression of AD. Currently, a range of biomarkers in cerebrospinal fluid (CSF), such as synaptosome-associated protein 25 (SNAP-25), synaptotagmin-1, growth-associated protein-43 (GAP-43), and neurogranin (Ng), along with functional brain imaging techniques, can detect variations in synaptic density, offering high sensitivity and specificity for AD diagnosis. However, these methods face challenges, including invasiveness, high cost, and limited accessibility. In contrast, biomarkers found in blood or urine provide a minimally invasive, cost-effective, and more accessible alternative to traditional diagnostic methods. Notably, neuron-derived exosomes in blood, which contain synaptic proteins, show variations in concentration that can serve as indicators of synaptic injury, providing an additional, less invasive approach to AD diagnosis and monitoring.

Pathophysiology characterization of Alzheimer's disease in South China's aging population: for the Greater-Bay-Area Healthy Aging Brain Study (GHABS)

INTRODUCTION

The Guangdong-Hong Kong-Macao Greater-Bay-Area of South China has an 86 million population and faces a significant challenge of Alzheimer's disease (AD). However, the characteristics and prevalence of AD in this area are still unclear due to the rarely available community-based neuroimaging AD cohort.

METHODS

Following the standard protocols of the Alzheimer's Disease Neuroimaging Initiative, the Greater-Bay-Area Healthy Aging Brain Study (GHABS) was initiated in 2021. GHABS participants completed clinical assessments, plasma biomarkers, genotyping, magnetic resonance imaging (MRI), β-amyloid (Aβ) positron emission tomography (PET) imaging, and tau PET imaging. The GHABS cohort focuses on pathophysiology characterization and early AD detection in the Guangdong-Hong Kong-Macao Greater Bay Area. In this study, we analyzed plasma Aβ42/Aβ40 (A), p-Tau181 (T), neurofilament light, and GFAP by Simoa in 470 Chinese older adults, and 301, 195, and 70 had MRI, Aβ PET, and tau PET, respectively. Plasma biomarkers, Aβ PET, tau PET, hippocampal volume, and temporal-metaROI cortical thickness were compared between normal control (NC), subjective cognitive decline (SCD), mild cognitive impairment (MCI), and dementia groups, controlling for age, sex, and APOE-ε4. The prevalence of plasma A/T profiles and Aβ PET positivity were also determined in different diagnostic groups.

RESULTS

The aims, study design, data collection, and potential applications of GHABS are summarized. SCD individuals had significantly higher plasma p-Tau181 and plasma GFAP than the NC individuals. MCI and dementia patients showed more abnormal changes in all the plasma and neuroimaging biomarkers than NC and SCD individuals. The frequencies of plasma A+/T+ (NC; 5.9%, SCD: 8.2%, MCI: 25.3%, dementia: 64.9%) and Aβ PET positivity (NC: 25.6%, SCD: 22.5%, MCI: 47.7%, dementia: 89.3%) were reported.

DISCUSSION

The GHABS cohort may provide helpful guidance toward designing standard AD community cohorts in South China. This study, for the first time, reported the pathophysiology characterization of plasma biomarkers, Aβ PET, tau PET, hippocampal atrophy, and AD-signature cortical thinning, as well as the prevalence of Aβ PET positivity in the Guangdong-Hong Kong-Macao Greater Bay Area of China. These findings provide novel insights into understanding the characteristics of abnormal AD pathological changes in South China's older population.