A rare TMEM175 mutation drives Parkinson’s disease pathology by disrupting proton gating and lysosomal acidification

Transmembrane protein 175 (TMEM175), implicated in Parkinson's disease (PD) risk, has been variably proposed to function as a background K+ "leak" channel or a proton-activated proton channel in lysosomes. Here, we identified the rare TMEM175 variant p.L275R in a patient with early onset PD. Electrophysiological analyses revealed that TMEM175-L275R mutant proteins retain normal lysosomal expression and K+ "leak" activity, but specifically lose proton- and agonist-dependent activation gating. In skin fibroblasts isolated from the patient with PD harboring the monoallelic p.L275R mutation (TMEM175+/L275R), and in derived induced pluripotent stem cells and induced dopaminergic neurons, lysosomal H+ flux, acidification, and degradation were impaired. These lysosomal defects were corrected upon genome editing to produce the isogenic WT allele (+/+Cor), but appeared when the mutant allele was introduced onto a WT background (+/L275RMut). Pathological α-synuclein aggregation was facilitated in patient-derived (+/L275R) and mutation-introduced (+/L275RMut) neurons. Consistent with these genetic findings, pharmacological activation of TMEM175 with small-molecule agonists restored lysosomal functions and reduced α-synuclein aggregation in TMEM175+/L275R neurons. In in-vivo studies, equivalent-site-mutation knock-in mice demonstrated synucleinopathy and PD-like motor phenotypes. Collectively, our work provides genetic and pharmacological evidence that severe loss-of-function mutations may contribute causally to the onset age and pathogenesis of PD and identifies lysosomal proton channels and transporters as potential therapeutic targets for PD intervention.