R406 and its structural analogs reduce SNCA/α-synuclein levels via autophagic degradation

The presence of neuronal Lewy bodies mainly composed of SNCA/α-synuclein aggregations is a pathological feature of Parkinson disease (PD), whereas reducing SNCA protein levels may slow the progression of this disease. We hypothesized that compounds enhancing SNCA's interaction with MAP1LC3/LC3 May increase its macroautophagic/autophagic degradation. Here, we conducted small molecule microarray (SMM)-based screening to identify such compounds and revealed that the compound R406 could decrease SNCA protein levels in an autophagy-dependent manner. We further validated the proposed mechanism, in which knockdown of essential gene ATG5 for autophagy formation and using the autophagy inhibitor chloroquine (CQ) blocked the effect of R406. Additionally, R406 also reduced the levels of phosphorylated serine 129 of SNCA (p-S129-SNCA) in SNCA preformed fibrils (PFFs)-induced cellular models and rescued neuron degeneration. Importantly, we confirmed that R406 could alleviate PD-relevant disease phenotypes in human SNCA PFFs-induced cellular models and PD patient-derived organoid models. Taken together, we demonstrated the possibility of lowering SNCA levels by enhancing its autophagic degradation by compounds increasing SNCA-LC3 interactions.Abbreviations: ATTEC: autophagy-tethering compounds; BafA1: bafilomycin A₁; BiFC: bimolecular fluorescence complementation; CQ: chloroquine; hMOs: human midbrain organoids; iPSC: induced pluripotent stem cells; MBP: maltose-binding protein; mHTT: mutant huntingtin; OI-RD: oblique-incidence reflectivity difference; PFFs: preformed fibrils; p-S129-SNCA: phosphorylated serine 129 of SNCA; PD: Parkinson disease; ROS: reactive oxygen species; siRNA: small interfering RNA; SMM: small molecule microarray; SNCA: synuclein alpha; SYK: spleen associated tyrosine kinase.