Exploring the role of protein farnesylation in the regulation of SNARE protein ykt6 in synucleinopathy models

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Abstract Synucleinopathies, such as Parkinson's disease (PD), are a group of incurable neurodegenerative diseases characterized by the accumulation of aggregated alpha-synuclein (a-syn). Disturbances in protein trafficking and cellular degradation pathways, such as lysosomes, have been implicated in the pathogenesis of these disorders. The strongest genetic risk factors for PD are loss-of-function mutations in lysosomal glucocerebrosidase (GCase), that degrades glucosylceramide (GluCer). Our previous work showed that loss of GCase activity and GluCer accumulation directly induces a-syn aggregation and cell death in neurons. This indicates that lysosomal dysfunction plays an important role in PD pathogenesis, and that enhancing lysosomal function may reduce a- syn aggregation. We also showed that a-syn, when aggregated at the cell body of neurons, inhibits the trafficking of lysosomal hydrolases between the endoplasmic reticulum (ER) and the Golgi, thereby reducing lysosomal function. Therefore, methods to enhance ER-Golgi trafficking may improve lysosomal hydrolase targeting and function, and enhance the clearance of pathological a-syn aggregates. However no therapeutic targets exist that are capable of enhancing trafficking or lysosomal activity. We propose to explore the mechanism of a potential novel therapeutic target called ykt6 that functions as a Soluble NSF Attachment protein REceptor (SNARE) to enhance protein trafficking between the ER and the Golgi, therefore improving the maturation of lysosomal enzymes and hydrolase activity. Previous work has shown that cognate SNARE binding of ykt6 is regulated by farnesylation, and we will examine how farnesylation of ykt6 influences its ability to control ER-Golgi trafficking using PD patient-derived neurons from induced pluripotent stem cell (iPSC) models and isogenic corrected controls. Preliminary data indicate that inhibiting the farnesylation of ykt6 enhances the trafficking of lysosomal hydrolases and improves lysosomal function. Furthermore, pharmacological inhibition of farnesyltransferase using a brain-penetrant, clinically validated small-molecule inhibitor can reduce pathological, insoluble a-syn in cell lines in a ykt6-dependent manner. We propose to examine how the farnesyl-mediated regulatory mechanism of ykt6 function is related to its ability to enhance lysosomal function and reduce pathological a-syn. As these studies are exploratory, they are aimed to assess the future potential of ykt6 as a therapeutic target for the synucleinopathies by focusing on the mechanism that regulates its ER-Golgi trafficking activity. We expect these studies to lead to novel hypothesis for regulation of ER-Golgi trafficking and lysosomal activity, and possibly other vesicular trafficking pathways in the cell, that may be examined in future proposals. There are currently no known methods to enhance hydrolase trafficking and lysosomal function, and our studies may help to validate ykt6 as a druggable target to enhance these processes and reduce pathological forms of a-syn. Our studies may be rapidly translated into therapies since farnesyltransferase inhibitors are well-developed in the clinic as cancer therapies, leading to the possibility of repurposing these agents for the treatment of PD.