Nido, G. S. | bioRxiv Science

bioRxiv2019

Dysregulation of histone acetylation and decoupling from transcription in Parkinson disease

Parkinson disease (PD) is a complex neurodegenerative disorder of largely unknown etiology. While several genetic risk factors have been identified, the involvement of epigenetics in the pathophysiology of PD is mostly unaccounted for. We conducted a histone acetylome-wide association study in PD, using brain tissue from two independent cohorts of cases and controls. Immunoblotting revealed increased acetylation at several histone sites in PD, with the most prominent change observed for H3K27, a marker of active promoters and enhancers. Chromatin immunoprecipitation sequencing (ChIP-seq) further indicated that H3K27 hyperacetylation in the PD brain is a genome-wide phenomenon, with a strong predilection for genes implicated in the disease, including SNCA, PARK7, PRKN and MAPT. Integration of the ChIP-seq with transcriptomic data revealed that the correlation between promoter H3K27 acetylation and gene expression is attenuated in PD patients, suggesting that H3K27 acetylation may be decoupled from transcription in the PD brain. Our findings strongly suggest that dysregulation of histone acetylation plays an important role in the pathophysiology of PD and identify novel epigenetic signatures associated with the disease.

genomics↗

bioRxiv2019

Common gene expression signatures in Parkinson’s disease are driven by changes in cell composition

BackgroundThe etiology of Parkinsons disease (PD) is largely unknown. Genome-wide transcriptomic studies in bulk brain tissue have identified several molecular signatures associated with the disease. While these studies have the potential to shed light into the pathogenesis of PD, they are also limited by two major confounders: RNA post mortem degradation and heterogeneous cell type composition of bulk tissue samples. We performed RNA sequencing following ribosomal RNA depletion in the prefrontal cortex of 49 individuals from two independent case-control cohorts. Using cell-type specific markers, we estimated the cell-type composition for each sample and included this in our analysis models to compensate for the variation in cell-type proportions.\n\nResultsRibosomal RNA depletion results in substantially more even transcript coverage, compared to poly(A) capture, in post mortem tissue. Moreover, we show that cell-type composition is a major confounder of differential gene expression analysis in the PD brain. Correcting for cell-type proportions attenuates numerous transcriptomic signatures that have been previously associated with PD, including vesicle trafficking, synaptic transmission, immune and mitochondrial function. Conversely, pathways related to endoplasmic reticulum, lipid oxidation and unfolded protein response are strengthened and surface as the top differential gene expression signatures in the PD prefrontal cortex.\n\nConclusionsDifferential gene expression signatures in PD bulk brain tissue are significantly confounded by underlying differences in cell-type composition. Modeling cell-type heterogeneity is crucial in order to unveil transcriptomic signatures that represent regulatory changes in the PD brain and are, therefore, more likely to be associated with underlying disease mechanisms.

neuroscience↗