The Abundance of PE 18:2 is Increased in Parkinson’s Disease Patient Brain Tissue and DJ-1 Knockout Zebrafish Disease Models

Parkinson’s Disease (PD) is an age-related neurodegenerative disorder associated with both motor and non-motor symptoms. It is characterized by depletion of dopamine-producing neurons in the substantia nigra and the presence of aggregated protein-rich filaments within the brain, referred to as Lewy bodies. The brain, by dry weight, consists of about 50% lipids that can interact with proteins and other lipids. In environments characterized by elevated levels of oxidative stress and reactive oxygen species, such as in PD, lipids are readily oxidized, generating toxic oxidation products. Dysfunctional lipid metabolism in PD is implicated in inflammation, mitochondrial dysfunction, lipid peroxidation and oxidative stress, which are hallmarks of the disease. This thesis hypothesized a link between PD development and lipids through their metabolism and oxidation, and that this would be manifested in the brain tissue of affected individuals and PD zebrafish models. Protocols for lipid extraction and brain sampling were also evaluated. PD-related phospholipid alterations were assessed in grey and white matter from the brains of a healthy individual and a sporadic PD patient, as well as from the brains of four months old wild-type (WT) and DJ-1 knockout (KO) zebrafish. The DJ-1 KO zebrafish line functioned as a PD model as it lacks the gene encoding the neuroprotective protein DJ-1, a mutation related to autosomal recessive PD. The lipids were extracted using a modified Bligh & Dyer extraction approach, and their phospholipid and fatty acid profiles were analysed using 31P NMR and untargeted UPLC-HRMS/MS, respectively. Western blotting was also used to assess oxidative stress levels by examination of DJ-1 and oxidized DJ-1 expression levels, due to the role of DJ-1 as a cellular stress-sensor. Reduced levels of DJ-1 were detected, along with noteworthy increases in abundances of PC plasmalogens, sphingomyelin, PE 18:2 (linoleic acid), and PS 22:5 (DPA). Altogether, the findings suggest the presence of elevated oxidative stress levels and a potential counteracting defence mechanism to said oxidative stress, primarily due to the neuroprotective and anti-inflammatory properties exhibited by these compounds. Deviations in the phospholipid profile of the sporadic PD brain compared to those reported in the literature, combined with the observed up- and downregulations of phospholipids and fatty acids, highlights the dysregulated lipid metabolism typically reported in PD. However, larger sample sizes are needed to draw reliable conclusions. Future experiments could focus on developing methods for the detection of lyso-phospholipids and oxidized lipids, to provide insight into phospholipid degradation and related signalling pathways implicated in PD. In future experiments, it is recommended to use age-matched human samples, minimize variations in post-mortem interval times of the harvested tissue, and avoid freeze-thaw cycles and long-term storage of lipid samples to minimize their lipid degradation.

Masteroppgåve i molekylærbiologi

MOL399

MAMN-MOL