Differential autophagy cargo engagement in amyloid-β-induced neuronal toxicity.

Neurodegenerative diseases are characterized by progressive neuronal loss and the accumulation of misfolded proteins. In Alzheimer's disease, several pathogenic protein species, including amyloid precursor protein, amyloid beta, tau, phosphorylated tau, and alpha-synuclein, are known substrates of macroautophagy. However, the extent to which macroautophagy selectively engages these proteins for degradation under conditions of proteotoxic stress remains poorly understood. Here, the contribution of specifically macroautophagy to the degradation of amyloid precursor protein, amyloid beta, tau, phosphorylated tau, and alpha-synuclein was investigated using an amyloid precursor protein overexpression model. Mouse neuroblastoma N2A cells stably expressing the human Swedish amyloid precursor protein mutation were treated with butyric acid for 24 and 48 h to produce increasing proteotoxicity and molecular pathology. Autophagic flux was assessed using bafilomycin A1 and protein abundance quantified by western blotting. Confocal microscopy and colocalization analysis was performed to examine intracellular protein localization and recruitment to the autophagy compartment. Amyloid precursor protein overexpression and autophagosome/lysosome fusion inhibition elicited distinct protein-specific responses, with phosphorylated tau showing highest accumulation and autophagic recruitment. In contrast, tau and amyloid precursor protein exhibited moderate increases, while alpha-synuclein and amyloid beta showed differential and limited responses upon macroautophagy inhibition. Collectively, these findings suggest that the autophagy molecular machinery does not engage uniformly with Alzheimer's disease-associated proteins but may be characterized by a highly differential cargo engagement under amyloid precursor protein-driven proteotoxic stress. Phosphorylated tau emerged as the earliest and most prominent protein to be target to the autophagy compartment, highlighting its potential importance in disease progression and therapeutic intervention.