RETREG1 and Parkinson disease: The major findings are: (1) MSCs enhance ER-αSyn clearance and restore ER and cellular function by inducing FAM134B-mediated selective ER-phagy; (2) MSC-enhanced ER-phagy exhibits neuroprotective effects in a PD model with nigral injection of AAV-ER-αSyn; and (3) MSCs regulate ER-phagy through the transcription factor NR4A1.