Substrate specificity,plasma membrane localization,and lipid modification of the aldehyde dehydrogenase ALDH3B1

The accumulation of reactive aldehydes is implicated in the development of several disorders. Aldehyde dehydrogenases (ALDHs) detoxify aldehydes by oxidizing them to the corresponding carboxylic acids. Among the 19 human ALDHs, ALDH3A2 is the only known ALDH that catalyzes the oxidation of long-chain fatty aldehydes including C16 aldehydes (hexadecanal and trans-2-hexadecenal) generated through sphingolipid metabolism. In the present study, we have identified that ALDH3B1 is also active in vitro toward C16 aldehydes and demonstrated that overexpression of ALDH3B1 restores the sphingolipid metabolism in the ALDH3A2-deficient cells. In addition, we have determined that ALDH3B1 is localized in the plasma membrane through its C-terminal dual lipidation (palmitoylation and prenylation) and shown that the prenylation is required particularly for the activity toward hexadecanal. Since knockdown of ALDH3B1 does not cause further impairment of the sphingolipid metabolism in the ALDH3A2-deficient cells, the likely physiological function of ALDH3B1 is to oxidize lipid-derived aldehydes generated in the plasma membrane and not to be involved in the sphingolipid metabolism in the endoplasmic reticulum.     

Plasmalogen deficiency in cerebral adrenoleukodystrophy and its modulation by lovastatin

In cerebral adrenoleukodystrophy (cALD), an accumulation of very long chain fatty acids stems from a defect of the peroxisomal ALD protein (ALDP) and results in the loss of myelin/oligodendrocytes, induction of inflammatory disease and mental deterioration. In brain white matter of cALD patients, we observed not only increased levels of very long chain fatty acid but also reduced levels of plasmenylethanolamine (PlsEtn) and increased levels of reactive oxygen species (ROS). The loss of PlsEtn was greatest in the plaque area and lesser but significant at histologically normal-looking areas of the cALD brain. The reduction in PlsEtn was related to oxidative stress, as supported by increased levels of reactive lipid aldehydes (4-hydroxynonenal and acrolein) and deleterious oxidized proteins (protein carbonyl) in all areas of the cALD brain. This inverse relationship between the levels of PlsEtn and reactive oxygen species (ROS) was further supported in an in vitro study using gene-silencing for dihydroxyacetone phosphate-acyl transferase, a key enzyme for PlsEtn biosynthesis. Levels of PlsEtn were also found decreased in vitro following gene-silencing for the ALDP/ALD-related protein. Furthermore, low levels of PlsEtn were detected in brain white matter of ALDP knock out (KO) mice. A treatment of ALDP KO mice with lovastatin increased PlsEtn levels in the brain. Further, in an in vitro study, lovastatin treatment of rat C6 glial cells increased PlsEtn biosynthesis and reduced the cytokine-induced ROS accumulation. In summary, this study reports that altered metabolism of PlsEtn and ROS in cALD may be corrected by lovastatin treatment.     

Very-long-chain polyunsaturated fatty acids accumulate in phosphatidylcholine of fibroblasts from patients with Zellweger syndrome and acyl-CoA oxidase1 deficiency

Peroxisomes are subcellular organelles that function in multiple anabolic and catabolic processes, including β-oxidation of very-long-chain fatty acids (VLCFA) and biosynthesis of ether phospholipids. Peroxisomal disorders caused by defects in peroxisome biogenesis or peroxisomal β-oxidation manifest as severe neural disorders of the central nervous system. Abnormal peroxisomal metabolism is thought to be responsible for the clinical symptoms of these diseases, but their molecular pathogenesis remains to be elucidated. We performed lipidomic analysis to identify aberrant metabolites in fibroblasts from patients with Zellweger syndrome (ZS), acyl-CoA oxidase1 (AOx) deficiency, D-bifunctional protein (D-BP) and X-linked adrenoleukodystrophy (X-ALD), as well as in peroxisome-deficient Chinese hamster ovary cell mutants. In cells deficient in peroxisomal biogenesis, plasmenylethanolamine was remarkably reduced and phosphatidylethanolamine was increased. Marked accumulation of very-long-chain saturated fatty acid and monounsaturated fatty acids in phosphatidylcholine was observed in all mutant cells. Very-long-chain polyunsaturated fatty acid (VLC-PUFA) levels were significantly elevated, whilst phospholipids containing docosahexaenoic acid (DHA, C22:6n-3) were reduced in fibroblasts from patients with ZS, AOx deficiency, and D-BP deficiency, but not in fibroblasts from an X-ALD patient. Because patients with AOx deficiency suffer from more severe symptoms than those with X-ALD, accumulation of VLC-PUFA and/or reduction of DHA may be associated with the severity of peroxisomal diseases.     

缩醛磷脂提取和制备的实验研究

通过将新鲜猪心切块、绞碎,制成组织匀浆后,再经一系列过程包括总脂的提取、从总脂提取物中制取磷脂酰乙醇胺、碱水解进一步纯化缩醛磷脂酰乙醇胺以及对获得的缩醛磷脂酰乙醇胺制剂鉴定其纯度。通过Ｉｏｄｉｎｅ ｄｉｓａｐｐｅａｒａｎｃｅ法测出缩醛磷脂酰乙醇胺制剂中的含量为１５．３５ｍｍｏｌ／Ｌ,通过Ｂａｒｔｅｌｌ法测出缩醛磷脂酰乙醇胺制剂中无机磷含量为１６．１０ｍｍｏｌ／Ｌ。因此,获得缩醛磷脂酰乙醇胺制剂的纯     

Very long-chain fatty acid accumulation causes lipotoxic response via 5-lipoxygenase in cerebral adrenoleukodystrophy

Abstract Childhood adrenoleukodystrophy (cALD) is a metabolic disorder in which very long-chain fatty acids (VLCFA) accumulate due to ALD protein gene defects, ultimately leading to lipotoxicity-induced neuroinflammatory demyelinating disease. Therefore, we examined VLCFA-mediated alterations in the metabolism of lipoxidative enzymes and inflammatory mediators in the cALD brain. 5-Lipoxygenase (5-LOX)-derived leukotrienes were significantly elevated in all the areas of white matter in the cALD brain. Unlike cyclooxygenase-2 expression, which was moderately high only in the plaque area, expression of 5-LOX and cytosolic phospholipase A2 was prominent in all the areas. This lipoxidative burden in the cALD brain was further shown by reduced levels of glutathione and enhanced expression of heat shock protein-70/manganese superoxide dismutase. These pathological observations were confirmed through in vitro mechanistic investigation. After increasing VLCFA through silencing Abcd1+Abcd2 in mouse primary astrocytes, enhanced expression of 5-LOX was observed, and this increased expression was blocked by treatment with monoenoic fatty acids. These results link the previously observed accumulation of VLCFA in cALD to the 5-LOX enzyme pathway. A similar increase in 5-LOX expression in astrocytes was also detected following treatment with exogenous VLCFA (C26:0). In sum, through 5-LOX activation, VLCFA accumulation causes a lipotoxic response consistent with cALD brain pathology.