Phospholipase A2 (PLA2) is the name for the class of lipolytic enzymes that hydrolyze the acyl group from the sn-2 position of glycerophospholipids, generating free fatty acids and lysophospholipids. The products of the PLA2-catalyzed reaction can potentially act as second messengers themselves, or be further metabolized to eicosanoids, platelet-activating factor, and lysophosphatidic acid. All of these are recognized as bioactive lipids that can potentially alter many ongoing cellular processes. The presence of PLA2 in the central nervous system, accompanied by the relatively large quantity of potential substrate, poses an interesting dilemma as to the role PLAS has during both physiologic and pathologic states. Several different PLA2 enzymes exist in brain, some of which have been partially characterized. They are classified into two subtypes, Ca 2~-dependentand Ca2-independent, based on their catalytic dependence on Ca~.Under physiologic conditions, PLA 2 may be involved in phospholipid turnover, membrane remodeling, exocytosis, detoxification of phospholipid peroxides, and rieurotransmitter release. However, under pathological situations, increased PLA2 activity may result in the loss of essential membrane glycerophospholipids, resulting in altered membrane permeability, ion homeostasis, increased free fatty acid release, and the accumulation of lipid peroxides. These processes, along with loss of ATP, may be responsible for the loss of membrane phospholipid and subsequent neuronal injury found in ischemia, spinal cord injury, and other neurodegenerative diseases. This review outlines the current knowledge of the PLA2 found in the central nervous system and attempts to define the role of PLA2 during both physiologic and pathologic conditions.

Both (Li 1 ) and valproic acid (VPA) are effective in treating bipolar disorder, but the pathway by which either works, and whether it is common to both drugs, is not agreed upon. We recently reported, using an in vivo fatty acid model, that Li 1 reduces the turnover rate of the second messenger arachidonic acid (AA) by 80% in brain phospholipids of the awake rat, without changing turnover rates of docosahexaenoic or palmitic acid. Reduced AA turnover was accompanied by down-regulation of gene expression and protein levels of an AA-speci®c cytosolic phospholipase A 2 (cPLA 2 ). To see if VPA had the same effect on AA turnover, we used our in vivo fatty acid model in rats chronically administered VPA (200 mg/ kg, i.p. for 30 days). Like Li 1 , VPA treatment signi®cantly decreased AA turnover within brain phospholipids (by 28± 33%), although it had no effect on cPLA 2 protein levels. Thus, both mood stabilizers, Li 1 and VPA have a common action in reducing AA turnover in brain phospholipids, albeit by different mechanisms.

(type VI) were unaffected by lithium. These and prior results indicate that lithium targets a part of the AA cascade that involves cPLA 2 and COX-2. This effect may contribute to lithium's therapeutic action in bipolar disorder.

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 ...

Sodium valproate, a mood stabilizer, when chronically administered to rats (200 mg/kg i.p. daily for 30 days) significantly reduced the brain protein levels of cyclooxygenase (COX)-1 and COX-2, without altering the mRNA levels of these enzymes. COX activity was decreased, as were the brain concentrations of 11-dehydrothromboxane B 2 and prostaglandin E 2 (PGE 2 ), metabolites of arachidonic acid (AA) produced via COX. In contrast, the brain protein level of 5-lipoxygenase and the concentration of its AA metabolite leukotriene B 4 were unchanged. In view of published evidence that lithium chloride administered chronically to rats, like chronic valproate, reduces AA turnover within brain phospholipids, and that lithium post-transcriptionally down-regulates COX-2 but not COX-1 protein level and enzyme activity, these observations suggest that mood stabilizers generally modulate the release and recycling of AA within brain phospholipids, and the conversion of AA via COX-2 to PGE 2 and related eicosanoids. If targeting this part of the 'AA cascade' accounts for their therapeutic action, non-steroidal antiinflammatory drugs or selective COX-2 inhibitors might prove effective in bipolar disorder.

BackgroundLong-term acetate supplementation reduces neuroglial activation and cholinergic cell loss in a rat model of lipopolysaccharide-induced neuroinflammation. Additionally, a single dose of glyceryl triacetate, used to induce acetate supplementation, increases histone H3 and H4 acetylation and inhibits histone deacetylase activity and histone deacetylase-2 expression in normal rat brain. Here, we propose that the therapeutic effect of acetate in reducing neuroglial activation is due to a reversal of lipopolysaccharide-induced changes in histone acetylation and pro-inflammatory cytokine expression.MethodsIn this study, we examined the effect of a 28-day-dosing regimen of glyceryl triacetate, to induce acetate supplementation, on brain histone acetylation and interleukin-1β expression in a rat model of lipopolysaccharide-induced neuroinflammation. The effect was analyzed using Western blot analysis, quantitative real-time polymerase chain reaction and enzymic histone deacetylase and histone acetyltransferase assays. Statistical analysis was performed using one-way analysis of variance, parametric or nonparametric when appropriate, followed by Tukey's or Dunn's post-hoc test, respectively.ResultsWe found that long-term acetate supplementation increased the proportion of brain histone H3 acetylated at lysine 9 (H3K9), histone H4 acetylated at lysine 8 and histone H4 acetylated at lysine 16. However, unlike a single dose of glyceryl triacetate, long-term treatment increased histone acetyltransferase activity and had no effect on histone deacetylase activity, with variable effects on brain histone deacetylase class I and II expression. In agreement with this hypothesis, neuroinflammation reduced the proportion of brain H3K9 acetylation by 50%, which was effectively reversed with acetate supplementation. Further, in rats subjected to lipopolysaccharide-induced neuroinflammation, the pro-inflammatory cytokine interleukin-1β protein and mRNA levels were increased by 1.3- and 10-fold, respectively, and acetate supplementation reduced this expression to control levels.ConclusionBased on these results, we conclude that dietary acetate supplementation attenuates neuroglial activation by effectively reducing pro-inflammatory cytokine expression by a mechanism that may involve a distinct site-specific pattern of histone acetylation and histone deacetylase expression in the brain.

Acetate supplementation increases brain, heart, and liver acetyl-CoA levels and reduces lipopolysaccharide-induced neuroinflammation. Because intracellular acetyl-CoA can be used to alter histone acetylation-state, using Western blot analysis, we measured the temporal effect that acetate supplementation had on brain and liver histone acetylation following a single oral dose of glyceryl triacetate (6 g/kg). In parallel experiments, we measured the effect that acetate supplementation had on histone deacetylase (HDAC) and histone acetyltransferase (HAT) enzymic activities and the expression levels of HDAC class I and II enzymes using Western blot analysis. We found that acetate supplementation increased the acetylation-state of brain histone H4 at lysine 8 at 2 and 4 h, histone H4 at lysine 16 at 4 and 24 h, and histone H3 at lysine 9 at 4 h following treatment. No changes in other forms of brain or liver H3 and H4 acetylation-state were found at any post-treatment times measured. Enzymic HAT and HDAC assays on brain extracts showed that acetate supplementation had no effect on HAT activity, but significantly inhibited by 2-fold HDAC activity at 2 and 4 h post-treatment. Western blot analysis demonstrated that HDAC 2 levels were decreased at 4 h following treatment. Based on these results, we conclude that acetyl-CoA derived from acetate supplementation increases brain histone acetylation-state by reducing HDAC activity and expression.

The mechanism by which chronic lithium exerts its therapeutic effect in brains of bipolar patients is not known. One possibility, suggested by our demonstration in the rat brain, is that chronic lithium inhibits turnover of arachidonic acid (AA) by reducing the activity of an AA-specific phospholipase A2 (PLA2). To test this further, mRNA levels of two AA-specific PLA2s, cytosolic PLA2 (cPLA2) type IV and intracellular PLA2 (iPLA2) type VIII, and protein level of cPLA2 were quantified in the brain of rats given lithium for 6 weeks. Chronic lithium markedly reduced brain mRNA and protein level of cPLA2, but had no effect on mRNA level of iPLA2. These results suggest that the final common path effect of chronic lithium administration is to reduce turnover of AA in brain by down-regulating cPLA2.