Synergistic Enhancement of ER proteostasis, trafficking, and lysosomes as treatments for Dementia with Lewy bodies and Parkinson’s disease-dementia

Abstract

Dementia with Lewy bodies (DLB), Parkinson’s disease (PD), and PD-Dementia (PDD) are all classified as synucleinopathies due to the accumulation and aggregation of a-synuclein (a-syn) the nervous system. The pathological mechanisms leading to neurodegeneration are not completely understood, however the assembly of a-syn into insoluble fibrils is thought to play key role.

This is supported by the discovery that aggregation-promoting mutations in a-syn lead to early onset PD with Dementia, including the A53T mutation and triplication of the SNCA genomic locus. Furthermore, recent GWAS studies indicate that variants in protein trafficking and lysosomal machinery confer increased risk for developing DLB and PD. Since a-syn is normally degraded by lysosomes, disruption of this pathway is expected to increase a-syn levels and promote conditions for aggregation.

The relationship between dysfunctional lysosomes and synucleinopathies is best described by the discovery that loss of function mutations in lysosomal GBA1, that encodes b-glucocerebrosidase (GCase) represent the strongest genetic risk factor for both PD and DLB with odds ratios of 5.43 and 8.28 respectively. GCase degrades glycosphingolipids (GSLs) in the lysosome, and our previous work showed that GSLs interact and convert a-syn into toxic aggregates in patient-derived iPSC neurons.

Furthermore, our group and others have shown that a-syn inhibits protein maturation of lysosomal hydrolases between the endoplasmic reticulum (ER) and the Golgi, leading to depletion of hydrolases and lysosomal dysfunction. In turn, hydrolases accumulate in the ER and overwhelm the quality control machinery, causing their aggregation into insoluble species.

Our proposal is focused on synergistic improvement of ER folding machinery, protein trafficking, and lysosomal activity. We hypothesize that improving two or all three of these pathways simultaneously will enhance therapeutic benefit compared to each one alone. During the R61 phase, we will use established small molecules to enhance ER chaperones and pharmacological chaperones that directly bind and stabilize GCase in the ER.

These will be combined with trafficking enhancers that promote ER-Golgi SNARE assembly and hydrolase maturation into lysosomes. Finally, we will test the effect of direct GCase allosteric activators combined with both ER proteostasis and trafficking enhancers. We use a combination of patient-derived iPSC-neuron models and mouse models to test our hypotheses in vivo.

Our assay readouts include protein folding in the ER, hydrolase maturation, lysosomal activity, a-syn / tau aggregation, cognitive functions, and neurotoxicity. Our go / no go decisions will be based on whether the combinatorial treatments synergistically improve lysosomal activity, reduction in protein pathology and improve cognition. The R33 phase will be focused on establishing thresholds and duration of activation that are required to activate lysosomes and reduce a-syn, development of blood biomarkers that accurately reflect brain target engagement, and safety assessments for escalating doses in vivo. Our studies may provide the groundwork for future combination therapies for DLB and PD.