Explorative Combined Lipid and Transcriptomic Profiling of Substantia Nigra and Putamen in Parkinson's Disease

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons from the substantia nigra (SN) that project to the dorsal striatum (caudate-putamen). To better understand the molecular mechanisms underlying PD, we performed combined lipid profiling and RNA sequencing of SN and putamen samples from PD patients and age-matched controls. SN lipid analysis pointed to a neuroinflammatory component and included elevated levels of the endosomal lipid Bis (Monoacylglycero)Phosphate 42:8, while two of the three depleted putamen lipids were saturated sphingomyelin species. Remarkably, we observed gender-related differences in the SN and putamen lipid profiles. Transcriptome analysis revealed that the top-enriched pathways among the 354 differentially expressed genes (DEGs) in the SN were "protein folding" and "neurotransmitter transport", and among the 261 DEGs from putamen "synapse organization". Furthermore, we identified pathways, e.g., "glutamate signaling", and genes, encoding, e.g., an angiotensin receptor subtype or a proprotein convertase, that have not been previously linked to PD. The identification of 33 genes that were common among the SN and putamen DEGs, which included the α-synuclein paralog β-synuclein, may contribute to the understanding of general PD mechanisms. Thus, our proof-of-concept data highlights new genes, pathways and lipids that have not been explored before in the context of PD.