A Small-Molecule TrkB Agonist Promotes Synaptic Resilience Against Aβ and Tau Oligomers and Mitigates Alterations in TrkB-Akt and Fyn Signaling.

BACKGROUND

Pathogenic amyloid-beta and tau oligomers (oAβ, oTau) drive synaptic degeneration and cognitive decline in Alzheimer's disease (AD). Tropomyosin receptor kinase B (TrkB), expressed in neurons and glia, supports synaptic integrity in AD-affected regions. We tested whether PTX-BD4-3, a small-molecule TrkB partial agonist, promotes neuroprotective signaling, reduces degenerative signaling, and prevents synaptic loss in an AD mouse model and hippocampal neurons exposed to oAβ or oTau.

METHODS

Cultured hippocampal neurons were treated with oAβ or oTau ± PTX-BD4-3. Effects on synaptic proteins (±TrkB-blocking antibody), spine density, and Fyn, NR2B, and tau phosphorylation as well as tau oligomerization were assessed. Two cohorts of APPL/S mice, 5 and 12 months of age, received intraperitoneal PTX-BD4-3 or vehicle for 3 months, followed by assessment of synaptic proteins, dendritic spines, TrkB signaling, and Y-maze analysis.

RESULTS

In vitro, PTX-BD4-3 prevented oAβ-induced synaptic marker loss in a TrkB-dependent manner, reduced phosphorylation of Fyn, NR2B, and tau, suppressed oligomeric tau formation, and attenuated oTau-induced spine loss. In APPL/S mice, PTX-BD4-3 mitigated deficient TrkB/Akt signaling, reduced phosphorylation of Fyn and tau, preserved synaptic markers and dendritic spines, and improved Y-maze performance.

CONCLUSIONS

Small-molecule TrkB partial agonists may normalize TrkB signaling and promote synaptic resilience, supporting their potential as AD therapeutics.