The Characterization of the PARK10 Gene USP24 in Autophagy and Mitophagy

Abstract

Parkinson’s disease (PD) is the second most common neurodegenerative disease in the world and there is currently no cure, just treatments to mask symptoms. PD results in loss or damage to dopaminergic (DA) neurons within the substantia nigra pars compacta. Autophagy, a lysosome-dependent degradation pathway, is essential for neuronal survival. Dysregulation of this pathway has been linked to several neurodegenerative diseases. Defects in autophagy and mitochondrial specific autophagy (mitophagy) have been implicated in PD. The goal of this project was to characterize the function of the deubiquitinating enzyme (DUB) ubiquitin-specific peptidase 24 (USP24) in autophagy as well as in mitophagy. USP24 is located on chromosome 1p of the PARK10 locus that has been associated with late-onset PD. As a DUB USP24 is responsible for removing ubiquitin chains from target substrates, thus altering their stability and function. The precise role of USP24 in PD is not yet known. My data demonstrate that USP24 is a negative regulator of autophagy that is downstream of MTROC1 and acts via the class III PtdIns3K and ULK1 complexes. Specifically, USP24 negatively regulates ubiquitination levels and stability of the ULK1 protein, thus decreasing autophagy flux. I have also shown that USP24 is able to regulate autophagy in induced pluripotent stem cells (iPSC)-derived DA neurons with no adverse effects. In fact, knockdown of USP24 led to increased neurite length in aged iPSC-DA neurons, suggesting a potential neuroprotective effect. Furthermore, in addition to ULK1, USP24 may regulate levels of the PD-associated Parkin protein. Recruitment of Parkin to the outer mitochondrial membrane is necessary for initiation of mitophagy. My data demonstrate that similarly to ULK1, stability of Parkin is increased following USP24 knockdown, suggesting that USP24 may negatively regulate Parkin-dependent mitophagy. Together, my data provide a better understanding of USP24 function in regulation of autophagy, mitophagy and PD. In addition, the data suggest that USP24 could be a possible new therapeutic target for PD.