Rethinking neurodegeneration through a co-proteinopathy lens.

Neurodegenerative diseases have long been considered distinct proteinopathies: amyloid-β and tau in Alzheimer's disease, α-synuclein in Parkinson's disease, and TDP-43 in amyotrophic lateral sclerosis. This single-protein paradigm has guided therapeutic development for decades; yet clinical outcomes remain modest. Mounting evidence, however, reveals that protein aggregates rarely occur in isolation; instead, they coexist, colocalise, and modulate each other's pathogenicity. Here, we propose a co-proteinopathy framework that views neurodegeneration as an interactive network of misfolded proteins rather than as isolated disorders. Adopting this framework demands multiplexed quantification of protein aggregates and disease models that better reflect the biological complexity of human neurodegeneration. The co-proteinopathy perspective offers a more realistic foundation for next-generation approaches to neurodegeneration research and treatment.