Project description:Loss-of-function mutations in the parkin gene can cause early onset Parkinson’s disease, a movement disorder resulting from the selective degeneration of dopaminergic neurons in the basal ganglia. Analogously, movement deficits and loss of a subset of dopaminergic neurons are observed in Drosophila melanogaster homozygous for null mutations in parkin. Parkin is an E3 ubiquitin ligase that functions with the mitochondrial localized serine/threonine kinase PINK1 in a pathway required to maintain mitochondrial integrity. We previously established that the PINK1/Parkin pathway functions in Drosophila dopaminergic and cholinergic neurons to maintain mitochondrial membrane potential. However, the mechanisms through which the PINK/Parkin pathway selectively impacts dopaminergic neuron survival remains unclear, as do the mechanisms that lead to the selective vulnerability of dopaminergic neurons in Parkinson’s disease. Because the transcriptome of a cell determines its identity we hypothesized that knowledge of the transcriptional alterations that occur in dopaminergic neurons isolated from parkin null Drosophila would provide insight into the mystery of selective vulnerability in Parkinson's disease. Results: To test our hypothesis we measured the transcriptome of dopaminergic and cholinergic neurons isolated from isogenic heterozygous and homozygous parkin null mutants using a novel flow cytometry-based method we developed. Computational analysis and experimental confirmation demonstrate that our method allows for the successful expression analysis of defined neural subsets from the Drosophila brain. In addition, our dataset implicates iron handling and dopamine signaling as being significantly dysregulated in parkin null dopaminergic neurons. Conclusions: Our flow cytometry-based method allows for the isolation and microarray analysis of neuronal subsets from the adult Drosophila brain. Our microarray analyses implicate iron handling and dopamine metabolism as contributing factors in the etiology of parkin-associated early onset Parkinson’s disease. Here we provide a novel dataset that may serve as a foundation for subsequent functional analyses of the pathways underlying neuronal selective vulnerability in Parkinson's disease.

Project description:Purpose: The E3 ubiquitin ligase Parkin is a well-characterized regulator of mitochondrial autophagy (mitophagy); however, it is becoming increasingly appreciated to perform additional roles in various compartments of the cell. Our laboratory confirmed the presence of Parkin in the nucleus of various tissues (biochemical fractionations) and cell types (immunofluorescent imaging). Hypoxia-induced nuclear translocation of Parkin occured independent of the mitophagy regulator PINK1, and Parkinson's disease-associated mutants were restricted from the nuclueus. Accordingly, we inserted a nuclear localization sequence (NLS) at the n-terminus of Parkin and overexpressed both NLS Parkin and the wild-type protein in HeLa cells cultured at normoxia and hypoxia. Next-generation RNA-sequencing (RNA-seq) was used to determine the effect of nuclear Parkin on cellular transcription. Methods: mCherry-tagged NLS and wild-type Parkin were overexpressed in HeLa cells. Differential expression analyses were performed on Parkin vs. mCherry control cells and NLS Parkin vs. mCherry control cells at normoxia and following 12hr of hypoxia (n=3/group/condition). Paired-end sequencing was performed using the HiSeq4000. FastQC v0.11.3 was used for quality control, Trimmomatic v0.36 was used to trim reads which were aligned to the human genome (GRCh37.p13) using the STAR aligner v2.5.3a. Read quantification was performed with RSEM v 1.3.0 and the Gencode release 19. The R BioConductor packages edgeR and limma were used to implement the limma-voom method for differential expression analysis. Results: During normoxia, Parkin had no effect on basal transcription; however, overexpression of NLS Parkin was associated with 168 differentially expressed genes (DEGs: fold-change </= 1.5, FDR < 0.05) relative to mCherry control cells. Following hypoxia, the transcriptome associated with the overexpression of wild-type Parkin more closely resembled that of NLS Parkin. Along these lines, Parkin overexpression during hypoxia coincided with a total of 158 DEGs, 37% of which were shared with NLS Parkin. Overlapping and shared DEGs among Parkin and NLS Parkin were implicated in cellular metabolism, HIF1 signaling and survival. Our follow up co-immunoprecipitation and real-time quantitative PCR studies demonstrated that Parkin interacts with the Estrogen Related Receptor Alpha (ERRa) to promote the induction of its downstream target genes. Conclusions: Nuclear translocation of Parkin is a novel means by which this cytoprotective protein contributes to cellular homeostasis and especially critical during hypoxia.

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