Identification of the Palmitoyltransferase for Glucocerebrosidase Trafficking Receptor LIMP2 and Restoration of GBA1 Function in Parkinson Disease and Lewy Body Dementia. - “Synucleinopathies” are a group of neurodegenerative disorders characterized by aggregations of the protein alpha-synuclein (αS). These include Parkinson disease (PD), Parkinson disease dementia (PDD), and Dementia with Lewy bodies (DLB). Such synucleinopathies are increasing rapidly in prevalence, yet a disease modifying treatment does not exist, and recent efforts have not been fruitful. This important problem calls for novel approaches. Recent work by the PI suggests that modulating palmitoylation, modification of the proteins by the fatty acid palmitate, may have potential as a new and unexplored space for therapeutic development. This is because palmitoylation is essential for vesicle and protein trafficking, processes which are disrupted by pathological αS. Thus, the PI has demonstrated that inhibition of the depalmitoylase acyl protein thioesterase-1 (APT1), which increases palmitoylation of its substrates, mitigates αS cellular pathologies including αS inclusions, toxicity, and phosphorylation at serine 129, a marker of disease. Further, treatment of PD/DLB model mice with a pharmacologic APT1 inhibitor, ML348, restores αS homeostasis and alleviates their PD/DLB-like motor and dementia phenotypes. To understand the substrates which mediate these beneficial effects, we recently identified in an unbiased manner the lysosome membrane protein 2 (LIMP2) as a major neuronal APT1 substrate which was not previously known to be palmitoylated. Remarkably, LIMP2 is the trafficking receptor for glucocerebrosidase (GCase), a lysosomal enzyme encoded by the GBA1 gene and the most common genetic risk factor for PD/DLB. This remarkable concordance between our work on palmitoylation and a lysosomal trafficking pathway central to PD/DLB strongly supports the idea that palmitoylation an important player in PD/DLB pathophysiology. In accord, our preliminary data show that LIMP2 restores GCase activity and αS homeostasis in a palmitoylation-dependent manner. In this proposal, we take the next step in assessing the therapeutic potential of this approach by identifying the ZDHHC family palmitoyltransferase (PAT) for LIMP2 in order to enhance LIMP2 palmitoylation in GBA1 mutant patient-derived neurons. Such an approach may have advantages over APT1 depalmitoylase inhibition, given the multiple substrates of APT1 and possible off-target effects. We then determine if the ZDHHC for LIMP2 can rescue various GBA-PD/DLB related phenotypes in patient-derived neurons, including GCase activity, αS levels, and αS homeostasis. Additionally, we characterize the physiologic function of LIMP2 palmitoylation using LIMP2 CRISPR knockout iPSC derived neurons. This proposal is a crucial step in our long-term goal of developing innovative, palmitoylation-based treatments for PD, PDD, and DLB. To that end, they pursue research priorities pertaining to the Alzheimer’s disease related dementias (ADRD), specifically Parkinson disease dementia and Dementia with Lewy bodies.
