Nanoimmunomodulation of the Aβ-STING feedback machinery in microglia for Alzheimer's disease treatment.

Imbalanced production and clearance of amyloid-β (Aβ) is a hallmark pathological feature of Alzheimer's disease (AD). While several monoclonal antibodies targeting Aβ have shown reductions in amyloid burden, their impact on cognitive function remains controversial, with the added risk of inflammatory side effects. Dysregulated stimulator of interferon genes (STING) signaling is implicated in neurodegenerative disorders, yet the biological interaction between this pathway and Aβ, as well as their combined influence on AD progression, is poorly understood. Here, we show that while microglia play a protective role in clearing extracellular Aβ, excessive Aβ engulfment triggers the cytosolic leakage of mitochondrial DNA for cGAS-STING cascade. This creates a negative feedback loop that not only exacerbates neuroinflammation but also impairs further Aβ clearance. To address this, we present a nanomedicine approach termed "Aβ-STING Synergistic ImmunoSilencing Therapy (ASSIST)". ASSIST comprises STING inhibitors encapsulated within a blood-brain barrier (BBB)-permeable polymeric micelle that also serves as an Aβ scavenger. Through a multivalent interaction mechanism, ASSIST efficiently destabilizes Aβ plaques and prevents monomer aggregation, subsequently promoting the engulfment of the dissociated Aβ by microglia rather than neurocytes. Furthermore, the STING signaling induced by excessive Aβ uptake is blocked, reducing inflammation and restoring microglial homeostatic functions involved in Aβ clearance. Intravenous administration of ASSIST significantly reduces Aβ burden and improves cognition in AD mice, with minimal cerebral amyloid angiopathy or microhemorrhages. We provide a proof-of-concept nanoengineering strategy to target the maladaptive immune feedback loop arising from conventional immunotherapy for AD treatment.