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

Abstract

Because α-synuclein (Snca) has a role in brain lipid metabolism, we determined the impact that the loss of α-synuclein had on brain arachidonic acid (20:4n-6) metabolism in vivo using Snca -/-mice. We measured [1-14 C]20:4n-6 incorporation and turnover kinetics in brain phospholipids using an established steady-state kinetic model. Liver was used as a negative control and no changes were observed between groups. In Snca -/-brains, there was a marked reduction in 20:4n-6-CoA mass and in microsomal acyl-CoA synthetases (Acsl) activity toward 20:4n-6. Microsomal Acsl activity was completely restored after the addition of exogenous wt mouse or human α-synuclein, but not by A30P, E46K, and A53T forms of α-synuclein. Acsl and acyl-CoA hydrolase expression was not different between groups. The incorporation and turnover of 20:4n-6 into brain phospholipid pools was markedly reduced. The dilution coefficient lambda, which indicates 20:4n-6 recycling between the acyl-CoA pool and brain phospholipids, was increased 3.3-fold, indicating more 20:4n-6 was entering the 20:4n-6-CoA pool from the plasma relative to that being recycled from the phospholipids. This is consistent with the reduction in Acsl activity observed in the Snca -/-mice. Using titration microcalorimetry, we determined that α-synuclein bound free 20:4n-6 (K d of 3.7 μM), but did not bind 20:4n-6-CoA. These data suggest α-synuclein is involved in substrate presentation to Acsl rather than product removal. In summary, our data demonstrate that α-synuclein has a major role in brain 20:4n-6 metabolism through its modulation of endoplasmic reticulum localized acyl-CoA synthetase activity, although mutants forms of α-synuclein fail to restore this activity. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript α-Synuclein is a 140 amino acid soluble protein that is highly expressed in the central nervous system (1,2) and is abundant in presynaptic terminals of neurons (1,(3)(4)(5). α-Synuclein is also found in other regions of neurons, in astrocytes, and in oligodendroglia (6-11). Overexpression of and mutations in α-synuclein are associated with early onset Parkinson's disease (12)(13)(14)(15) and other neurodegenerative diseases (16)(17)(18)(19)(20). Despite this association with neurodegenerative diseases, the physiological function of this protein remains unclear.Several lines of evidence suggest that α-synuclein can influence brain lipid metabolism. It has structural similarities to class A2 apolipoproteins (21,22) and to fatty acid binding proteins (23), suggesting that α-synuclein may alter intracellular lipid trafficking, the regulation of lipid metabolism, and may act to stabilize lipid membranes. α-Synuclein binds to small phospholipid vesicles (22,24,25) and to brain vesicles (26). Consistent with this binding, the lack of α-synuclein decreases the resting/reserve pool of synaptic vesicles (27,28). Although the direct binding of fatty acids is controversial (23,29), recent studies indicate a strong potential for an important ...

Brain prostaglandin formation is increased by α-synuclein gene-ablation during global ischemia

“…In addition, Parkinsonism is associated with a maintained presence of reactive microglia [30;35;49]. Importantly, mutant forms of Snca, that are associated with familial forms of Parkinsonism [25;38;54], do not restore 20:4n-6-CoA synthetase activity in Snca ablation which we show is critical for 20:4n-6 recycling [15]. Collectively, this suggests a link between the functions of Snca and neuroinflammation associated with Parkinsonism.…”

“…Snca facilitates palmitic acid and arachidonic acid (20:4n-6) uptake in astrocytes [9] and in brain [14;15], although it has no affect on docosahexaenoic acid (22:6n-3) uptake both in astrocytes and brain [9;16], indicating a fatty acid selective affect. More importantly, we have recently demonstrated a functional interaction of Snca with microsomal acyl-CoA synthetases in brain, accounting for the profound reduction in 20:4n-6 incorporation and turnover in phospholipids in Snca -/-mice [15]. Conversely, 22:6n-3 incorporation and turnover is increased in these mice as a result of metabolic compensation for the decrease in 20:4n-6 brain metabolism [16].…”

α-Synuclein Expression Modulates Microglial Activation Phenotype

“…In addition, our recent work suggested that ␣-synuclein expression also modulates PLA 2 (phospholipase A 2 )-dependent signaling events. We have linked ␣-synuclein to 20:4n-6 metabolism via its impact on endoplasmic reticulum localized acyl-CoA synthetases (Golovko et al, 2006). Mutant forms of ␣-synuclein (A30P, E46K, A53T) fail to modulate acyl-CoA synthetase activity, suggesting potential derangement of arachidonic acid metabolism and eicosanoiddependent signaling in the brain (Golovko et al, 2006).…”

“…It is found in presynaptic terminals of neurons (Maroteaux et al, 1988;McLean et al, 2000), but also in other regions of neurons as well as within astrocytes and oligodendroglia (Richter-Landsberg et al, 2000;Mori et al, 2002). ␣-Synuclein binds a variety of proteins (Jenco et al, 1998;Peng et al, 2005) and lipid vesicles , and is involved in lipid metabolism (Cabin et al, 2002;Castagnet et al, 2005;Golovko et al, 2005Golovko et al, , 2006. Absence of ␣-synuclein expression is associated with striatal dysfunction (Abeliovich et al, 2000).…”

Mode of action of mood stabilizers: is the arachidonic acid cascade a common target?

“…brain phospholipids and, after correcting for the specific activity of the appropriate acyl-CoA pool, turnover rates and half-lives of individual fatty acids in brain phospholipids. This method has been used to determine fatty acid turnover rates for the brain, 70 liver 32 and heart. 71 Quantitative autoradiography also allows one to determine incorporation coefficients for unesterified fatty acids from plasma into brain phospholipids within specific brain regions.…”