Aging is associated with the deterioration of various biological processes including disrupted proteostasis and impaired macroautophagy/autophagy. Biomolecules can undergo liquid-liquid phase separation (LLPS) to form biomolecular condensates that exert specific biological functions. Trr1 (thioredoxin reductase 1) is a pivotal enzyme in the thioredoxin antioxidant system. Deletion of TRR1 results in impaired autophagy; however, the underlying mechanism is largely unexplored. In this study, we explored whether LLPS of Trr1 affected autophagy. Trr1 formed dynamic LLPS condensates during replicative aging in yeast. Phase separation of Trr1 occurred in response to endoplasmic reticulum (ER) stress generated by cellular aging, rather than to oxidative stress. Furthermore, Trr1 condensates participated at the phagophore assembly site during endoplasmic reticulophagy and promoted autophagosome development by affecting lipidation of the Atg8 protein. Additionally, maintaining the liquid-like dynamic nature of Trr1 condensates was essential for cellular fitness. Our findings revealed an unconventional role of Trr1 through LLPS in aging. The function of phase-separated condensates of Trr1 in mitigating aging-associated ER stress offers insights into the mechanisms underlying healthy cellular aging. These findings highlight a potential target for developing interventions to combat aging and associated diseases.Abbreviations: Atg: autophagy related; DTT: dithiothreitol; ER: endoplasmic reticulum; ERAD: endoplasmic reticulum-associated degradation; ERphagy: endoplasmic reticulophagy; FRAP: fluorescence recovery after photobleaching; GFP: green fluorescent protein; LLPS: liquid-liquid phase separation; PAS: phagophore assembly site; PLDs: prion-like domains; RFP: red fluorescent protein; RLS: replicative lifespan; Trr1: thioredoxin reductase 1; Trx: thioredoxin; UPR: unfolded protein response; IDRs: intrinsically disordered regions.
