The protective paradox: APOE3ch and disease-associated microglia regulating calcium signaling impact the niche in Alzheimer resilience

Abstract

Alzheimer’s disease (AD) resilience refers to the preservation of cognitive function despite substantial neuropathological burden. Among the most informative examples is the APOE3-Christchurch (APOE3ch; R136S) variant, which has been associated with delayed clinical expression of autosomal dominant AD despite extensive amyloid deposition. This review examines APOE3ch as a natural model for investigating protective biology in AD, with particular attention to ApoE–heparan sulfate proteoglycan (HSPG) interactions, tau handling, plaque microenvironment dynamics, disease-associated microglia (DAM), and microglial calcium (Ca²⁺) signaling. Current evidence supports a role for APOE3ch in weakening ApoE–HSPG interactions and modifying tau-related pathological processes. HSPG sulfation patterns also influence tau internalization and proteopathic spread, while TREM2-dependent DAM responses may exert stage-specific protective or harmful effects. Microglial Ca²⁺ signaling, including store-operated calcium entry through Orai/STIM pathways, is increasingly recognized as a key regulator of microglial motility, phagocytosis, cytokine release, and transcriptional programming. However, direct evidence linking APOE3ch-mediated HSPG disruption to altered microglial Ca²⁺ dynamics remains lacking. Therefore, this review proposes the APOE3ch–HSPG–Ca²⁺–DAM axis as a hypothesis-generating framework rather than an established mechanistic pathway. We highlight current evidence, identify inferential gaps, discuss alternative mechanisms of resilience, and outline experimental strategies needed to test whether APOE3ch-associated extracellular remodeling influences microglial Ca²⁺ signaling and protective DAM states. Therapeutic translation will require genotype-sensitive designs, human-relevant models, spatiotemporal resolution, validated biomarkers, and careful safety evaluation.

Keywords

• APOE3-Christchurch (APOE3ch)
• proteoglycans of heparan sulphate
• microglial calcium signaling
• tau propagation
• resilience to Alzheimer’s disease.

Supporting Institution

None

Ethical Statement

There is no need of ethical approval as it is a review article

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