Changes in sphingomyelin level affect alpha-synuclein and ABCA5 expression

The pathological hallmark of Parkinson's disease (PD) is the presence of aggregated α-synuclein associated with lipids. Substantial evidence now exists to indicate that α-synuclein binds and interacts with regions of membranes that are enriched in lipids (lipid rafts). Lipids are transported around the brain by a group of proteins called ATP-Binding Cassette subfamily A (ABCA) transporters and in recent years there has been mounting evidence indicating that ABCA transporters regulate a number of neurodegenerative disease processes. Only recently a genome-wide association study reported that ABCA5 was genetically associated with a reduced risk for PD. However, very little is known about the role of lipids and ABCA5 in the pathological process of PD. In this study we investigate the impact of the lipid-raft lipid sphingomyelin on α-synuclein and ABCA5 expression. We also investigate in which primary human brain cells ABCA5 is expressed and whether the expression of ABCA5 is altered in PD brain. When SK-N-SH neuronal cells were treated with sphingomyelin the expression of both α-synuclein and ABCA5 was significantly increased, indicating sphingomyelin as a potential substrate for the ABCA5 transporter. ABCA5 was strongly expressed in neurons and moderately in microglia, with only weak expression observed in astrocytes and oligodendrocytes. The expression of ABCA5 was significantly elevated in PD brains compared to age- and gender-matched control brains, possibly as a protective response to the disease. These data provide new evidence indicating that lipid is important for α-synuclein pathology in PD.