ABSTRACT
The eye is continuously under oxidative stress due to high metabolic activity and reactive oxygen species generated by daily light exposure. The redox-sensitive protein DJ-1 has proven to be essential in order to protect retina and retinal pigment epithelium (RPE) from oxidative-stress-induced degeneration. Here, we analyzed the specific role of Müller cell DJ-1 in the adult zebrafish retina by re-establishing Müller-cell-specific DJ-1 expression in a DJ-1 knockout retina. Loss of DJ-1 resulted in an age-dependent retinal degeneration, including loss of cells in the ganglion cell layer, retinal thinning, photoreceptor disorganization and RPE cell dysfunction. The degenerative phenotype induced by the absence of DJ-1 was inhibited by solely expressing DJ-1 in Müller cells. The protective effect was dependent upon the cysteine-106 residue of DJ-1, which has been shown to be an oxidative sensor of DJ-1. In a label-free proteomics analysis of isolated retinas, we identified proteins differentially expressed after DJ-1 knockout, but with restored levels after Müller cell DJ-1 re-insertion. Our data show that Müller cell DJ-1 has a major role in protecting the retina from age-dependent oxidative stress.
ABSTRACT
DJ-1 is a protein with a wide range of functions importantly related to redox regulation in the cell. In humans, dysfunction of the PARK7 gene is associated with neurodegeneration and Parkinson's disease. Our objective was to establish a novel DJ-1 knockout zebrafish line and to identify early brain proteome changes, which could be linked to later pathology. The CRISPR-Cas9 method was used to target exon 1 of the park7-/- gene to produce a transgenic DJ-1-deficient zebrafish model of Parkinson's disease. Label-free mass spectrometry was employed to identify altered protein expression in the DJ-1 null brain of early adult animals. The park7-/- line appears to develop normally at young adult and larval stages. With aging however, DJ-1 null fish exhibit lower tyrosine hydroxylase levels, respiratory failure in skeletal muscle, and lower body mass which is especially prevalent among male fish. By proteomic analysis of early adult brains, we determined that less than 5% of the 4091 identified proteins were influenced by the lack of DJ-1. The dysregulated proteins were mainly proteins known to be involved in mitochondrial metabolism, mitophagy, stress response, redox regulation, and inflammation. This dysregulation in protein networks of our novel DJ-1-deficient zebrafish model occurs in the early adult stage preceding a Parkinson's disease-related phenotype and the reduction of tyrosine hydroxylase level. The identified protein changes provide new mechanistic background for DJ-1 function. The experimental power of zebrafish makes this model a highly valuable tool to understand and modulate cellular signaling leading to neurodegeneration.
