Objective: To identify key molecular perturbations affecting medium spiny neuron functions and their role in the clinical symptoms of Parkinson’s disease (PD).

Background: The degeneration of dopaminergic neurons in the substantia nigra is a hallmark of PD, leading to dysfunction of the striatum, which receives innervation from dopaminergic afferents. Striatal dysfunction manifests as motor and non-motor symptoms of PD. To identify the molecular mechanisms underlying symptom manifestation, we investigated transcriptomic alterations in the PD striatum. We previously reported changes in RNA levels in the striatum that were associated with PD symptoms¹. In neurons, RNA splicing is additionally an important regulatory mechanism to alter the protein diversity from a limited genome. Here, we delve into the effects of RNA splicing that lead to protein variations and functional consequences in PD.

Method: We conducted RNA-sequencing on post-mortem striatum (caudate and putamen) obtained from  unaffected controls (n=35) and PD (n=25) patients. Medium spiny neurons were isolated by fluorescence-activated nuclear sorting. RNA binding protein-mediated targeting was identified by high-throughput sequencing of RNA after cross-linking and immunoprecipitation.  We utilized Limma for differential gene expression analysis and Multivariate Analysis of Transcript Splicing to examine alternative splicing events. Significant changes in gene expression were defined by a log2 fold change ≥ 0.5 and q-value < 0.05, while significant splicing events were determined by a difference in absolute percent spliced in  > 10% and q-value < 0.05.

Results: In addition to changes in gene expression we have previously reported, RNAs were differentially spliced in the striatum in PD. Splicing aberrations notably impacted neuronal RNAs. We demonstrate that altered RNA splicing contribute to changes in glutamate and dopaminergic signaling in the medium spiny neurons. These altered splicing events impact direct and indirect pathway signaling, thereby contributing to the clinical symptoms of PD.  Using high-throughput sequencing after crosslinking and immunoprecipitation, we further identify the neuronal RNA binding proteins that modulate these splice events in PD.

Conclusion: RNA regulation plays a pivotal role in altering RNA diversity and thereby protein diversity in neurons. Altered splicing significantly impacts the striatal medium spiny neurons, ultimately contributing to the clinical symptoms of PD.

References: 1. Irmady K, Hale CR, Qadri R, Fak J, Simelane S, Carroll T, Przedborski S, Darnell RB. Blood transcriptomic signatures associated with molecular changes in the brain and clinical outcomes in Parkinson’s disease. Nat Commun. 2023 Jul 5;14(1):3956. Available from: http://dx.doi.org/10.1038/s41467-023-39652-6 PMCID: PMC10322907

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MDS Abstracts - https://www.mdsabstracts.org/abstract/role-of-rna-splicing-in-parkinsons-disease/