Tau Propagation

Description

Tau propagation refers to the stereotyped spread of tau pathology through the brain following a predictable pattern described by Braak staging: beginning in the locus coeruleus and transentorhinal cortex (Braak I-II), spreading to the hippocampus and limbic system (Braak III-IV), and finally reaching neocortical areas (Braak V-VI). This anatomical progression correlates strongly with clinical symptom severity, making tau spread the best neuropathological predictor of cognitive decline. The mechanisms driving propagation remain actively debated, with prion-like templating, exosomal transmission, and cellular vector models all supported by evidence.

The prion-like model proposes that pathological tau conformers are released from donor neurons, taken up by recipient neurons, and template the misfolding of normal tau in a self-propagating cycle. nSMase2-driven exosomes carry pathological tau across synaptic connections, providing a vesicular mechanism for trans-synaptic spread. The Adult Neurogenesis Theory offers a fundamentally different explanation: migrating neuroblasts from the subgranular zone (SGZ) and ventricular-subventricular zone (V-SVZ) carry hyperphosphorylated 3R-tau as a normal feature of their migratory program, but pathological conditions (chronic Abeta-driven inflammation forcing reactive neurogenesis) escalate this physiological phosphorylation into pathological aggregation. SGZ-derived short-range migration explains hippocampal-dominant LOAD pathology, while V-SVZ-derived aberrant long-range migration explains cortical-dominant EOAD variants.

Tau's cytoskeletal effects are central to its toxicity: pathological tau over-stabilizes F-actin, creates mechanical stress on the nuclear envelope (via the LINC complex), and causes heterochromatin relaxation that reactivates transposable elements. The resulting dsRNA triggers Type I interferon signaling through sterile viral mimicry, linking tau propagation directly to neuroinflammation.

Convergence Nodes

• Cytoskeletal Collapse Node -- Tau-mediated microtubule destabilization and F-actin over-stabilization drive dendritic spine loss
• Transcriptional-Epigenetic Dysregulation Node -- Tau-induced nuclear envelope damage and heterochromatin relaxation activate transposable elements
• Neuroimmune Interface -- Tau-triggered viral mimicry (dsRNA from TEs) activates innate immune responses

Prize Entrants

• Carlo Abbate -- Proposed migrating neuroblasts as cellular vectors of tau propagation; explained Braak staging through neurogenesis niche geography (SGZ for LOAD, V-SVZ for EOAD)
• Bess Frost -- Demonstrated tau-induced F-actin over-stabilization, LINC complex mechanical stress, Lamin B1 depletion, and transposable element reactivation; identified viral mimicry as tau's inflammatory mechanism
• Varghese John -- Identified nSMase2-driven exosomal tau propagation; demonstrated precision targeting of tau PxxP-SH3 interactions as therapeutic strategy

External Scientists

• Marc Diamond -- Prion-like tau templating and conformational strains
• Virginia Lee -- Tau fibril structure and seeding activity
• Michel Goedert -- Tau isoforms and cryo-EM structural characterization
• Bradley Hyman -- In vivo tau spread imaging and network-based propagation
• Karen Duff -- Tau transgenic models and propagation mechanisms
• Heiko Braak -- Defined the anatomical staging system for tau spread

Key Open Questions

• Is tau propagation primarily prion-like (self-templating), exosomal, or mediated by cellular vectors (neuroblast migration)?
• Can anti-tau antibodies effectively intercept tau propagation at the extracellular transfer step, and do clinical trial results support this?
• Does selective disruption of tau-SH3 interactions (John's AxxA6 approach) represent a viable strategy to block pathological tau without disrupting normal function?
• How does the adult neurogenesis model explain tau spread in contexts where adult neurogenesis is limited (neocortex)?