TMEM106B deficiency exacerbates α-synuclein aggregation in Parkinson's disease.

Parkinson's disease is an age-related neurodegenerative disease that is characterized by the deposition of α-synuclein aggregates in the brain. Nevertheless, the molecular mechanisms that regulate α-synuclein aggregation have not yet been identified fully. TMEM106B is a lysosomal transmembrane protein that has been reported to be associated with brain ageing and neurodegenerative diseases, including Parkinson's disease. Here we show that TMEM106B is reduced in the brains of patients with Parkinson's disease. Knockout of Tmem106b increases the formation of α-synuclein aggregates in primary neurons and mouse brains. TMEM106B deficiency results in impaired lysosomal acidification, lipid metabolism disorders and lipid droplet deposition in neurons. Interestingly, lipid droplets promote α-synuclein aggregation, resulting in the formation of α-synuclein fibrils with enhanced seeding activity and neurotoxicity in comparison to α-synuclein fibrils formed in the absence of lipid droplets. TMEM106B deficiency also leads to retardation of α-synuclein degradation by reducing the enzymatic activity of the lysosomal protease cathepsin D. Taken together, these results indicate that TMEM106B deficiency contributes to Parkinson's disease pathogenesis by accelerating α-synuclein aggregation and halting α-synuclein degradation.