Massa, Nashali

Abstract INTRODUCTION Neurodegenerative diseases often involve overlapping alpha‐synuclein (asyn), amyloid beta, and tau proteinopathies, yet the mechanisms, impact, and directionality of their interactions remain unclear. METHODS We induced brain‐wide neuronal asyn/tau pathologies via viral expression of wild‐type asyn, mutant asyn E46K , mutant tau A152T , or both asyn E46K /tau A152T in adult amyloidosis knock‐in mice and controls, either post‐plaque deposition (6 months old) or pre‐plaque (3 months old). Open‐field behavior was assessed baseline and 3 and 6 months post‐transduction, followed by neuropathology and neuroinflammation analyses. RESULTS Post‐plaque induction in amyloid mice increased asyn/tau total and phosphorylated levels and exacerbated amyloid‐related hyperlocomotion/anxiety. Pre‐plaque induction produced robust phosphorylated pathologies irrespective of amyloid, while causing similar amyloid‐dependent behavioral synergy. Tau pathology drove LGALS3 + inflammatory glial responses in white‐matter fibers. DISCUSSION Amyloid context gates vulnerability, with certain synergies manifesting across stages. White‐matter gliosis is a novel mechanism of tau A152T risk. Together, our data argue for the development of stage‐aware, multitarget interventions and biomarkers.

Aducanumab, an anti-amyloid immunotherapy for Alzheimer’s disease, efficiently reduces Aβ, though its plaque clearance mechanisms, long-term effects, and effects of discontinuation are not fully understood. We assessed the effect of aducanumab treatment and withdrawal on Aβ, neuritic dystrophy, astrocytes, and microglia in the APP/PS1 amyloid mouse model. We found that reductions in amyloid and neuritic dystrophy during acute treatment were accompanied by microglial and astrocytic activation, and microglial recruitment to plaques and adoption of an aducanumab-specific pro-phagocytic and pro-degradation transcriptomic signature, indicating a role for microglia in aducanumab-mediated Aβ clearance. Reductions in Aβ and dystrophy were sustained 15 but not 30 wk after discontinuation, and reaccumulation of plaques coincided with loss of the microglial aducanumab signature and failure of microglia to reactivate. This suggests that despite the initial benefit from treatment, microglia are unable to respond later to restrain plaque reaccumulation, making further studies on the effect of amyloid-directed immunotherapy withdrawal crucial for assessing long-term safety and efficacy.