mTOR and STING Modulation Restores Hydrolase Activities and Decreases Alpha-Synuclein Pathology in the Cells from the Patients with GBA1-Associated Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by dopaminergic neuron loss and pathological accumulation of alpha-synuclein. Aberrant activation of the mechanistic target of rapamycin (mTOR) and of the stimulator of interferon genes (STING) signaling pathways are increasingly recognized as central contributors to PD pathogenesis. The GBA1 variants are the most common genetic risk factor for PD. However, currently there are no disease-modifying therapies for treatment of the GBA1-associated PD (GBA1-PD). Here, we investigated the effects of selective inhibitors of mTOR (Torin 1) and STING (H-151) on the pathway activity, autophagy, lysosomal function, including hydrolase activity, and lysosphingolipid levels, in the peripheral blood monocyte cells-derived macrophages (PBMC-derived macrophages) and induced pluripotent stem cell (iPSC)-derived dopaminergic neurons from the patients with GBA1-PD. Consistent with our previous findings of the reduced glucocerebrosidase (GCase) activity, substrate accumulation, and impaired autophagy, the cells derived from the GBA1-PD patients exhibited marked activation of both mTOR and STING signaling. mTOR inhibition increased number and size of lysosomes and reduced the level of monomeric alpha-synuclein, consistent with the enhanced TFEB-mediated lysosomal biogenesis. In contrast, STING inhibition broadly attenuated the disease-associated phenotypes, reducing levels of oligomeric and phosphorylated alpha-synuclein (Ser129), lysosphingolipid accumulation, and Ras-related protein Rab-10 (Rab10) phosphorylation (Thr73), while also decreasing TFEB phosphorylation, which is consistent with TFEB activation and restoration of lysosomal trafficking via the LRRK2-dependent mechanism. Together, these findings identify mTOR and STING as central regulators of lysosomal functioning and GCase activity in the GBA1-PD, acting through the distinct but partially overlapping mechanisms. Targeting these pathways could, therefore, provide a strategy to restore lysosomal homeostasis and autophagic flux, either alone or in combination with other therapeutic approaches, and to mitigate the alpha-synuclein pathology in GBA1-PD.