Aducanumab binds high molecular weight soluble Aβ oligomers and restores intracellular calcium levels

Alzheimer's disease (AD) is characterized by amyloid-beta (Aβ) accumulation, leading to the formation of neurotoxic soluble oligomers (AβOs) that impair calcium homeostasis in neurons and astrocytes. Aducanumab, a fully human monoclonal antibody targeting aggregated Aβ, has been approved for AD treatment due to its ability to reduce amyloid plaque burden. However, its specificity toward different AβO species and its functional impact on calcium homeostasis remain unclear.

We investigated aducanumab's ability to recognize and immunodeplete low-molecular-weight (LMW) and high-molecular-weight (HMW) AβOs using three Aβ preparations: (1) transgenic conditioned media (TgCM) from cultured Tg2576 neurons, (2) synthetic Aβ42-derived diffusible ligands (ADDLs), and (3) TBS-soluble fractions from aged Tg2576 mouse brain. Size exclusion chromatography and ELISA were used to characterize AβO species. Multiphoton calcium imaging of neuron-astrocyte co-cultures was performed to assess the impact of aducanumab on AβO-induced calcium overload.

Aducanumab preferentially bound and immunodepleted HMW AβOs in ADDLs and the TBS-soluble fraction of Tg2576 mouse brain extracts but did not recognize LMW AβOs in TgCM. In calcium imaging experiments, all three AβO preparations induced calcium overload in neuron-astrocyte co-cultures. Immunodepletion with aducanumab prevented calcium overload in cultures exposed to ADDLs and Tg2576 brain extracts but not in those treated with immunodepleted TgCM, indicating that aducanumab selectively neutralizes HMW AβOs.

Our findings demonstrate that aducanumab specifically targets HMW AβOs, mitigating their neurotoxic effects by restoring intracellular calcium homeostasis. These results provide mechanistic insight into aducanumab's therapeutic action and support its potential role in modifying AD pathology by selectively neutralizing Aβ species.