Hypothesis

Neuronal activity hubs in the human connectome release exosomes enriched with oligomeric Aβ that act as cross‑seeds for tau aggregation, thereby creating a hub‑centric acceleration of tau spread that exceeds predictions from structural connectivity alone.

Mechanistic Rationale

Recent network‑epidemic models show tau‑PET variance explained by connectivity seeding, yet regions with high Aβ burden accumulate more tau than connectivity predicts 1. Aβ deposits appear simultaneously across cortex following sigmoidal kinetics 2, challenging staged cascade views. At the microscale, minimal two‑parameter models distinguish autonomous aggregation from cell‑to‑cell triggering over ~100 µm, identifying propagation as dominant after a threshold 3. Exosome‑mediated transfer of oligomeric Aβ from AD brains drives neuron‑to‑neuron spread and toxicity, and blocking exosome formation/uptake reduces oligomer dissemination 4. Vibrational imaging shows plaque evolution from short antiparallel β‑sheets (oligomer‑rich) to parallel β‑sheet‑rich cores 5, indicating that exosomal Aβ oligomers precede fibrillar plaque formation. Adaptive ODE models integrating Aβ‑p‑tau interactions reveal limited cognitive benefit from targeting p‑tau alone, underscoring the need to address upstream seeding mechanisms 6.

Testable Predictions

1. In vivo imaging of exosome flux (e.g., CD63‑GFP reporter) in transgenic AD mice will show significantly higher exosome release rates in high‑degree connectome hubs compared with low‑degree regions during early Aβ accumulation.
2. Pharmacological inhibition of exosome uptake (using heparin or GW4869) will reduce tau‑PET signal preferentially in hub regions, producing a greater relative decrease in hub‑vs‑non‑hub tau burden than a global reduction in tau load.
3. Chemogenetic activation of neuronal hubs (e.g., hM3Dq DREADDs) in Aβ‑low mice will increase exosomal Aβ oligomer content and accelerate tau seeding, whereas hub inhibition will blunt tau spread despite comparable Aβ levels.
4. Longitudinal PET‑MRI studies in humans will reveal that baseline hub exosome‑related MRI signatures (e.g., increased extracellular vesicle‑associated contrast) predict faster future tau accumulation in those hubs, independent of baseline Aβ burden.

Potential Falsification

If exosome blockade yields uniform tau reduction across all brain regions, or if hub‑specific exosome flux does not correlate with subsequent tau accumulation, the hub‑centric seeding mechanism would be falsified. Similarly, if chemogenetic manipulation of hub activity fails to alter exosomal Aβ levels or tau spread, the proposed activity‑exosome link would be unsupported.

Implications

Validating this hypothesis would shift therapeutic focus from broad anti‑tau or anti‑Aβ strategies to modulators of neuronal activity‑driven exosome release and uptake, potentially offering a precision‑medicine approach that targets the network nodes most responsible for driving tau pathology.