Objective: The SYNJ1 homozygous mutation (p.Arg258Gln) leads to juvenile Parkinsonism (PARK20). SYNJ1 plays an important role in synaptic vesicle cycling, and regulating autophagic flux. We generated an in vitro model of PARK20 using small molecule induced dopaminergic neurons (iDA) from SYNJ1 p.Arg258Gln patient derived and control induced pluripotent stem cells (IPSCs), to investigate the disease molecular mechanisms.

Background: Our lab and others have identified a SYNJ1 homozygous mutation (p.Arg258Gln) segregating with disease in consanguineous families with Parkinsonism, dystonia, and cognitive deterioration. The mutation impairs the Sac1 domain phosphatase activity of SYNJ1 protein in vitro. Another homozygous mutation within the Sac1 domain (p.Arg459Pro), as well as compound heterozygous mutations have been recently described as a cause of autosomal recessive juvenile Parkinsonism Strikingly, mutations in the SYNJ1 gene that result in complete loss of SYNJ1 expression lead to more severe phenotypes, including early onset refractory seizures and juvenile lethality, suggesting a phenotype-genotype correlation. Although mechanistic insight is lacking, these studies point towards a strong link between SYNJ1 mutations and neurodegeneration.

Methods: Patient derived SYNJ1 p.Arg258Gln and control induced pluripotent stem cells (IPSCs) were exposed to small molecules and differentiated for 4 weeks to induced dopaminergic (iDA) neurons. After 4 weeks, iDA neurons were exposed to starvation and control conditions and probed for markers of autophagy (i.e. LC3B, WIPI2) and synaptic vesicle recycling pathways (i.e. clathrin, endophilin) by immunocytochemistry and Western blotting techniques. Expression levels were quantified using FIJI software.

Results: Tyrosine Hydroxylase expressing neurons could be detected after 4 weeks of small molecule treatment both in control and patient cell lines. Immunohistochemistry analysis showed increased expression levels of the autophagy marker WIPI2 in patient derived iDA neurons as compared to control neurons before and after starvation.

Conclusions: Our preliminary data indicate that the SYNJ1 p.Arg258Gln mutation affects the autophagy pathway as indicated by increased levels of WIPI2 expression in patient derived iDA neurons. Further research is needed to clarify the role of SYNJ1 in the autophagy and synaptic vesicle cycling pathway.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-neuronal-model-of-park20-synj1-mutation-using-patient-derived-ipscs/