Thermal Cycling Resets the Irreversible Liquid-to-Solid Transition of Peptide Condensates during Aging.

The ability of biomolecular condensates to reversibly dissolve and reform is crucial for maintaining cellular stability and functions. In the context of cell physiology and disease, they can serve as a metastable phase mediating the liquid-to-solid transition of disease proteins or rapidly assemble/disassemble as a mechanism for stress response. However, as metabolic rates decline with aging, the protein-rich condensates persist longer, therefore increasing the propensity of undergoing irreversible liquid-to-solid transitions. Temperature, as a physical stimulus, plays a key role in controlling the condensate formation, dissolution, and material properties. In this study, we explore how the reversibility of short peptide biomolecular condensates (z-FF) can be modulated by a temperature change. Our findings reveal that aged condensates exhibit reduced responsiveness to external temperature stimuli. By using thermal cycling experiments to simulate repeated heat stress, we found that the time taken for irreversible fiber formation could be delayed up to 4.7-fold compared to that of condensates without thermal cycles. We also found that the dissolution rate of condensates progressively slows as they age but remains more stable with thermal cycles. Importantly, our results indicate that continuous cycles of liquid-liquid phase separation and dissolution act as a reset mechanism, preserving the biomolecular condensates from further liquid-to-solid transition. These findings provide valuable insights into how aging impacts condensate behavior and highlight potential strategies to preserve cellular function through controlled phase transitions.