Altered Fatty Acid Composition of Dopaminergic Neurons Expressing α-Synuclein and Human Brains with α-Synucleinopathies

Abstract

␣-Synuclein (␣S) is an abundant neuronal protein that accumulates in insoluble inclusions in Parkinson's disease (PD) and the related disorder, dementia with Lewy bodies (DLB).A central question about the role of ␣S in the pathogenesis of PD and DLB concerns how this normally soluble protein assembles into insoluble aggregates associated with neuronal dysfunction. We recently detected highly soluble oligomers of ␣S in normal brain supernatants and observed their augmentation in PD and DLB brains. Further, we found that polyunsaturated fatty acids (PUFAs) enhanced ␣S oligomerization in intact mesencephalic neuronal cells. We now report the presence of elevated PUFA levels in PD and DLB brain soluble fractions. Higher PUFA levels were also detected in the supernatants and high-speed membrane fractions of neuronal cells over-expressing wild-type or PD-causing mutant ␣S. This increased PUFA content in the membrane fraction was accompanied by increased membrane fluidity in the ␣S overexpressing neurons. In accord, membrane fluidity and the levels of certain PUFAs were decreased in the brains of mice genetically deleted of ␣S. Together with our earlier observations, these results suggest that ␣S-PUFA interactions help regulate neuronal PUFA levels as well as the oligomerization state of ␣S, both normally and in human synucleinopathies.␣-Synuclein (␣S), 1 a 140-residue protein implicated in both familial and sporadic Parkinson's disease (PD), occurs principally as a cytoplasmic polypeptide in neurons and is localized in part to presynaptic terminals (1). In general, brain ␣S is highly soluble, and purified recombinant ␣S is reported to have a disordered random coil structure in solution (2). A wide array of factors has been found to induce the aggregation of ␣S under experimental conditions. These include PD-causing missense mutations in ␣S (3-5), mitochondrial inhibitors and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (6, 7), proteosome inhibitors (8, 9), heavy metals (10, 11), oxidative stress (12, 13), ␣S phosphorylation (14), and fatty acids, whether within phospholipids (15) or as free fatty acids (16). Interestingly, some of the factors that can induce ␣S aggregation experimentally have been found to be associated with PD, e.g. ␣S mutations, mitochondrial complex I dysfunction, proteosomal dysfunction, and oxidative stress. Other factors, including free fatty acid composition, have not been comprehensively studied in the brains of patients with PD and other synucleinopathies.We recently obtained evidence that ␣S can directly bind fatty acids (17) and can form highly soluble oligomers in response to the treatment of cultured neurons with polyunsaturated fatty acids (PUFA) (16). Further, we observed a pool of soluble ␣S oligomers that is detectable only after biochemical treatments that remove fatty acids and other lipids (16, 17). These highly soluble, lipid-associated oligomers were detected in mesencephalic neuronal (MES) cells expressing human ␣S, in the brains of normal and human ␣S transgenic mice, an...

Acyl-CoA Synthetase Activity Links Wild-Type but Not Mutant α-Synuclein to Brain Arachidonate Metabolism

“…These results are consistent with those observed for uptake of 16:0 into brains lacking α-synuclein (29) and with its affect on 20:4n-6 and 16:0 uptake and metabolism in primary astrocytes (11). Brain cytosolic, unesterified polyunsaturated fatty acid mass is reduced when α-synuclein is absent (88), suggesting a connection between α-synuclein expression and polyunsaturated fatty acids. The observed reduction in targeting to the organic fraction is accounted by reduced incorporation coefficients for 20:4n-6 into individual brain phospholipids in Snca -/-mice.…”

Severe Alterations in Lipid Composition of Frontal Cortex Lipid Rafts from Parkinson’s Disease and Incidental Parkinson’s Disease

“…Our results are well in agreement with previous data published for frontal cortex in PD pathology (20,54) and indicate increased levels of peroxidable fatty acids. These results demonstrate that, while in whole cortical tissues from PD brains, there are increased levels of LCPUFAs (particularly DHA), their presence in lipid rafts was dramatically reduced.…”

Alpha-Synuclein Interactions with Membranes

“…Indeed, elevated PUFA levels have been detected in the soluble fractions of PD and Lewy bodies dementia brains. The levels of saturated and monounsaturated fatty acids did not change in these PD brains or in cells overexpressing -synuclein, which indicated thatsynuclein is involved specifically in the maintenance of PUFA levels (Sharon et al, 2003b). Using binding assays, it has been demonstrated that -synuclein binds saturably and with high affinity to detergent-resistant membranes, to lipid rafts, in permeabilized HeLa cells, and in the presence of synaptosomal membranes from transgenic mice expressing humansynuclein.…”