Role of Ddx56 gene associated with early-onset Parkinson disease in maintaining neural development and protecting against dopaminergic neuron apoptosis in zebrafish

To investigate the role of Ddx56 and Galnt13 associated with the pathogenesis of early-onset Parkinson disease (PD) in maintaining survival of dopaminergic (DA) neurons during early development of zebrafish.

In situ hybridization and qPCR were used to detect the temporal expression and tissue-specific distribution of Ddx56 and Galnt13 in AB zebrafish, and the changes in expressions of PD- and DA neuron-associated genes following Ddx56 or Galnt13 knockdown were detected. In SH-SY5Y cells, effects of Ddx56 knockdown and overexpression on cell apoptosis were analyzed using flow cytometry. RNA-seq technique was used to investigate the changes in gene expression profiles following Ddx56 knockdown to explore the role of Ddx56 in early development of the nervous system.

Both Ddx56 and Galnt13 were extensively expressed in early zebrafish embryos. Ddx56 was highly expressed predominantly in the brain and testis, and Galnt13 in the brain and eye of the zebrafish. Ddx56 knockdown resulted in significant changes in expressions of the PD-related genes Sncga, Sncgb, Polg, Pink1, Parkin, Lrrk2, Gba, and Sncb, while Galnt13 knockdown affected the expressions of Sncgb, Syn2b, and Lrrk2. Ddx56 knockdown caused a significant increase of apoptosis in SH-SY5Y cells and differential expressions of an array of genes, which were enriched mainly in the immune system, energy metabolism, protein translation, and signal transduction; no fewer than 20 genes in the ribosome pathway and the metabolic pathway each, in particular, showed differential expressions following Ddx56 knockdown. These differentially expressed genes were significantly associated with neurodegenerative diseases, and their alterations resulted in changes in the level of oxidative phosphorylation.

Ddx56 is highly expressed in the brain during early development of zebrafish. Ddx56 knockdown causes changes in PD- and DA-associated genes and induces apoptosis of DA neurons, suggesting its potential as a biomarker for early diagnosis of PD.