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Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and behavioral changes, driven by the accumulation of misfolded proteins, synaptic dysfunction, and chronic neuroinflammation in the brain. It is the most common cause of dementia, accounting for an estimated 60–70% of cases worldwide.¹

Overview of Alzheimer's disease pathology

AD develops over decades, with molecular and cellular changes preceding clinical symptoms by 15–20 years. The disease is defined neuropathologically by two hallmark lesions: extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. These lesions are accompanied by synapse loss, neuronal death, glial activation, and progressive brain atrophy, particularly in the hippocampus and cortex.²

While AD was historically framed around the amyloid cascade hypothesis, the current consensus recognizes a more integrated model. Aβ accumulation, tau pathology, neuroinflammation, vascular dysfunction, and impaired proteostasis act together and reinforce one another  to drive neurodegeneration. Genetic risk factors such as APOE, alongside aging and lifestyle factors, modulate susceptibility and disease trajectory.³

Genetic and risk factors

AD is broadly classified into early-onset familial AD (<5% of cases), driven by autosomal-dominant mutations in APP, PSEN1, or PSEN2, and late-onset sporadic AD, which represents the vast majority of cases. The APOE ε4 allele is the strongest common genetic risk factor for late-onset disease, influencing Aβ clearance, lipid metabolism, and neuroinflammatory responses.⁴

Additional risk factors include aging, cardiovascular and metabolic conditions, traumatic brain injury, and lifestyle factors such as sleep, diet, and cognitive engagement. These contributors converge on shared mechanisms, such as vascular health, neuroinflammation, and proteostasis, that shape individual disease trajectories.

What are the core pathological drivers of Alzheimer's disease?

The three central pathological axes of AD (amyloid-β, tau, and neuroinflammation) are deeply interconnected. Aβ accumulation is thought to act as an upstream trigger, tau pathology correlates most strongly with cognitive decline, and neuroinflammation amplifies and sustains neuronal injury throughout the disease course.

Amyloid-β pathology

Aβ peptides are generated through sequential cleavage of the amyloid precursor protein (APP) by β- and γ-secretases. Imbalance between Aβ production and clearance promotes oligomerization and plaque deposition, disrupting synaptic function and triggering downstream toxicity.

Tau pathology

Tau is a microtubule-associated protein that, under pathological conditions, becomes hyperphosphorylated, detaches from microtubules, and aggregates into neurofibrillary tangles. Tau pathology spreads in a stereotyped, trans-synaptic manner and closely tracks with neurodegeneration and cognitive symptoms.

Neuroinflammation

Microglia and astrocytes respond to Aβ and tau by adopting reactive states that initially aim to clear pathological proteins but, when sustained, contribute to synapse loss and neuronal damage. Genetic evidence implicating innate immune genes (eg TREM2, CD33) underscores neuroinflammation as a core disease mechanism rather than a secondary response.

How do core Alzheimer's mechanisms interact to drive neurodegeneration?

Aβ, tau, and neuroinflammation form a self-reinforcing pathological loop. Aβ oligomers can promote tau hyperphosphorylation and activate microglia, while reactive glia release cytokines that exacerbate both Aβ and tau pathology. Tau aggregates, in turn, propagate trans-synaptically and disrupt neuronal circuits, leading to network dysfunction and atrophy.⁵

Synaptic loss is the strongest correlate of cognitive decline in AD. It reflects the convergence of multiple insults: impaired proteostasis, mitochondrial dysfunction, oxidative stress, and disrupted neurotransmission. Vascular contributions, including blood–brain barrier breakdown and reduced cerebral perfusion, further compound neuronal vulnerability, particularly in late-onset AD.⁶

Fluid biomarkers in Alzheimer's disease

Fluid biomarkers have transformed AD research and clinical evaluation by enabling detection of pathology long before symptom onset. Measurable in cerebrospinal fluid (CSF) and, increasingly, blood, these biomarkers reflect the underlying molecular changes of the disease and support the ATN framework (Amyloid, Tau, Neurodegeneration).⁷

Key Alzheimer's disease biomarkers

Plasma-based assays, particularly p-tau217 and the Aβ42/Aβ40 ratio, have shown strong concordance with PET imaging and CSF measures, opening the door to scalable, minimally invasive detection. These markers are now central to patient stratification, clinical trial enrollment, and monitoring of disease-modifying therapies.⁸

Why is tissue imaging important in Alzheimer's disease research?

Tissue imaging remains essential for characterizing the spatial distribution, cellular context, and co-localization of AD pathologies. Unlike fluid biomarkers, which provide a global readout, immunohistochemistry (IHC), immunofluorescence (IF), and multiplexed imaging reveal how plaques, tangles, and glial responses are organized within neuroanatomical circuits.

High-resolution and multiplex imaging approaches allow simultaneous visualization of Aβ plaques, tau aggregates, microglial and astrocytic markers, synaptic proteins, and vascular components within the same tissue section. This is critical for understanding disease staging, regional vulnerability, and the cellular microenvironments that shape disease progression.⁹

Frequently asked questions

Alzheimer’s disease resources

We also collaborate with leading researchers and institutions worldwide to develop clear, cutting-edge pathways and guides. Whether you're investigating tau protein abnormalities, amyloid-beta pathways, or exploring new therapeutic targets, here are the products and resources to accelerate your research.

References

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5. Busche MA, Hyman BT. Synergy between amyloid-β and tau in Alzheimer's disease. Nat Neurosci. 2020;23(10):1183–1193.
6. Iadecola C. The neurovascular unit coming of age: a journey through neurovascular coupling in health and disease. Neuron. 2017;96(1):17–42.
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8. Hansson O, Edelmayer RM, Boxer AL, et al. The Alzheimer's Association appropriate use recommendations for blood biomarkers in Alzheimer's disease. Alzheimers Dement. 2022;18(12):2669–2686.
9. Serrano-Pozo A, Frosch MP, Masliah E, Hyman BT. Neuropathological alterations in Alzheimer disease. Cold Spring Harb Perspect Med. 2011;1(1):a006189.