Objective:

To overcome proteostatic barriers and ameliorate Parkinson disease (PD) pathogenesis, we sought to determine whether knockdown of MTMR5 facilitates alpha-synuclein (asyn) turnover and rescues asyn proteotoxicity.

Background:

PD is a neurodegenerative movement disorder marked by progressive motor and non-motor symptoms that lead to profound disability. Neurodegeneration in PD relates to toxic aggregation of asyn, and mounting evidence shows that asyn can be degraded through the conserved pathway of autophagy. However, multiple aspects of autophagy are impaired in PD, and available methods to modulate autophagy fail to confer clinical benefits in patients because of the intrinsic resistance of neurons to these methods. This resistance stems in part from MTMR5 (myotubularin-related phosphatase 5), a potent autophagy regulator that we previously identified to be selectively enriched in neurons. MTMR5 acts as an autophagy suppressor, and MTMR5 knockdown enhances degradation of multiple autophagy substrates. 

Design/Methods:

To investigate how and to what extent MTMR5 manipulation modifies asyn degradation and cell viability, we established a novel human induced pluripotent stem cell (iPSC)-derived neuron model of PD expressing fluorescently labeled autophagy effectors and asyn. Our PD model combined with super-resolution microscopy enables high-content, non-invasive optical monitoring of asyn degradation by autophagy in human neurons. 

Results:

We found that knockdown of MTMR5 significantly augmented autophagic clearance of not only WT asyn, but also mutant variants of asyn associated with familial PD and that demonstrate enhanced aggregation. We also found that MTMR5 knockdown and pharmacologic stimulation of autophagy mitigated asyn-related neuronal death. We will next employ unbiased, genome-wide CRISPR-based screens to uncover key factors regulating MTMR5 in neurons. 

Conclusions: