Optogenetics to biomolecular phase separation in neurodegenerative diseases.

Neurodegenerative diseases involve toxic protein aggregation. Recent evidence suggests that biomolecular phase separation, a process in which proteins and nucleic acids form dynamic, liquid-like condensates, plays a key role in this aggregation. Optogenetics, originally developed to control neuronal activity with light, has emerged as a powerful tool to investigate phase separation in living systems. This is achieved by fusing disease-associated proteins to light-sensitive oligomerization domains, enabling researchers to induce or reverse condensate formation with precise spatial and temporal control. This review highlights how optogenetic systems such as OptoDroplet are being used to dissect the mechanisms of neurodegenerative disease. We examine how these tools have been applied in models of neurodegenerative diseases, such as amyotrophic lateral sclerosis, Alzheimer's, Parkinson's, and Huntington's disease. These studies implicate small oligomeric aggregates as key drivers of toxicity and highlight new opportunities for therapeutic screening. Finally, we discuss advances in light-controlled dissolution of condensates and future directions for applying optogenetics to combat neurodegeneration. By enabling precise, dynamic control of protein phase behavior in living systems, optogenetic approaches provide a powerful framework for elucidating disease mechanisms and informing the development of targeted therapies.