BBA - Molecular and Cell Biology of Lipids (v.1841, #4)
Editorial Board (i).
Cyanobacterial monogalactosyldiacylglycerol-synthesis pathway is involved in normal unsaturation of galactolipids and low-temperature adaptation of Synechocystis sp. PCC 6803 by Yuichi Yuzawa; Mie Shimojima; Ryoichi Sato; Naoki Mizusawa; Keiko Ikeda; Mamie Suzuki; Masako Iwai; Koichi Hori; Hajime Wada; Shinji Masuda; Hiroyuki Ohta (475-483).
We characterized certain physiological functions of cyanobacterial monoglucosyldiacylglycerol using a Synechocystis sp. PCC 6803 mutant in which the gene for monoglucosyldiacylglycerol synthase had been disrupted and its function complemented by inclusion of an Arabidopsis monogalactosyldiacylglycerol synthase gene. By using this method, we prepared the first viable monoglucosyldiacylglycerol-deficient mutant of cyanobacterium and found that monoglucosyldiacylglycerol is not essential for its growth and photosynthesis under a set of “normal growth conditions” when monogalactosyldiacylglycerol is adequately supplied by the Arabidopsis monogalactosyldiacylglycerol synthase. The mutant had healthy thylakoid membranes and normal pigment content. The membrane lipid composition of the mutant was similar with that of WT except lack of monoglucosyldiacylglycerol and a slight increase in the level of phosphatidylglycerol at both normal and low temperatures. However, the ratio of unsaturated fatty acids in monogalactosyldiacylglycerol and digalactosyldiacylglycerol was reduced in the mutant compared with WT. Although the growth of the mutant was indistinguishable with that of WT at normal growth temperature, it was markedly retarded at low temperature compared with that of WT. Our data indicated the possibility that cyanobacterial monogalactosyldiacylglycerol-synthesis pathway might be required for the adequate unsaturation level of fatty acids in galactolipids and affect the low-temperature sensitivity.Display Omitted
Keywords: Galactolipid; Monogalactosyldiacylglycerol; Monoglucosyldiacylglycerol; Low temperature; Synechocystis sp. PCC 6803;
TLR2/1 and sphingosine 1-phosphate modulate inflammation, myofibroblast differentiation and cell migration in fibroblasts by Saghi Hamidi; Monika Schäfer-Korting; Günther Weindl (484-494).
Dermal fibroblasts are important regulators of inflammatory and immune responses in the skin. The aim of the present study was to elucidate the interaction between two key players in inflammation, Toll-like receptors (TLRs) and sphingosine 1-phosphate (S1P), in normal human fibroblasts in the context of inflammation, fibrosis and cell migration. We demonstrate that TLR2 ligation strongly enhances the production of the pro-inflammatory cytokines IL-6 and IL-8. S1P significantly induces pro-inflammatory cytokines time- and concentration-dependently via S1P receptor (S1PR)2 and S1PR3. The TLR2/1 agonist Pam3CSK4 and S1P (> 1 μM) or TGF-β markedly upregulate IL-6 and IL-8 secretion. Pam3CSK4 and S1P alone promote myofibroblast differentiation as assessed by significant increases of α-smooth muscle actin and collagen I expression. Importantly, costimulation with S1P (> 1 μM) induces differentiation into myofibroblasts. In contrast, Pam3CSK4 and low S1P concentrations (< 1 μM) accelerate cell migration. These results suggest that TLR2/1 signaling and S1P cooperate in pro-inflammatory cytokine production and myofibroblast differentiation and promote cell migration of skin fibroblasts in a S1P-concentration dependent manner. Our findings provide significant insights into how infectious stimuli or danger signals and sphingolipids contribute to dermal inflammation which may be relevant for skin tissue repair after injury or disease.
Keywords: Toll-like receptor; Sphingosine-1-phosphate; Dermal fibroblast; Cytokine; Myofibroblast;
A potential screening factor for accumulation of cholesteyl ester transfer protein deficiency in East Asia: Schistosoma japonicum by Shinji Yokoyama (495-504).
Cholesteryl ester transfer protein (CETP)-deficiency manifests a unique plasma lipoprotein profile without other apparent symptoms. It is highly common in East Asia while rather rare anywhere else. A potential environmental screening factor(s) may therefore contribute to this eccentric distribution, such as its selective advantage against a regional illness, most likely an infectious disease, in relation to plasma lipoproteins. Blood flukes use the host plasma lipoproteins as nutrient sources through the lipoprotein receptor-like systems. Its Asian-specific species, Schistosoma (S) japonicum, which has been endemic in East Asia, takes up cholesteryl ester (CE) from high-density lipoprotein (HDL) for the embryonation of their eggs to miracidia, a critical step of the hepatic pathogenesis of this parasite, but poorly from HDL of CETP-deficiency. CD36-related protein (CD36RP) was cloned from the adults and the eggs of S. japonicum, with 1880-bp encoding 506 amino-acid residues exhibiting the CD36 domains and two transmembrane regions. Its extracellular domain selectively bound human HDL but neither LDL nor CETP-deficiency HDL, and the antibody against the extracellular domain suppressed the selective HDL-CE uptake and embryonation of the eggs. When infected with S. japonicum, wild-type mice developed less hepatic granulomatosis than CETP-transgenic mice by the ectopic egg embryonation. CD36RP is thus a candidate receptor of S. japonicum to facilitate uptake of HDL-CE necessary for egg embryonation. Abnormal HDL caused by CETP-deficiency retards this process and thereby protects the patients from development of hepatic lesions. S. japonicum infection is a potential screening factor for high prevalence of CETP deficiency in East Asia.
Keywords: CETP; CETP deficiency; HDL; Schistosoma; Egg embryonation; Liver;
Characterization of a lysophospholipid acyltransferase involved in membrane remodeling in Candida albicans by Mariam Ayyash; Amal Algahmi; John Gillespie; Peter Oelkers (505-513).
Phospholipid remodeling involves phospholipase activity to remove acyl chains and acyltransferases to replace acyl chains. We here describe the characterization of a lysophospholipid acyltransferase in the opportunistic fungal pathogen, Candida albicans. Expression of this gene, C.a. LPT1, complemented the lysophospholipid acyltransferase defect in Saccharomyces cerevisiae strains lacking the homologous LPT1 gene. In vitro, lysophospholipid acyltransferase activity in these strains showed acyl-CoA substrate specificity, as measured by apparent Vmax/Km ratios, to be linolenoyl-CoA > oleoyl-CoA > linoleoyl-CoA > stearoyl-CoA. To address the physiological importance of C.a. LPT1, homozygous deletion strains were generated. Lysophospholipid acyltransferase activity with amine containing lysophospholipids was dramatically reduced while lysophosphatidylinositol and lysophosphatidic acid esterification was not significantly lowered. However, C.a. LPT1 over-expression yielded an increased amount of lysophosphatidic acyltransferase activity, suggesting a role in de novo phospholipid synthesis. LPT1 deletion strains showed slightly slowed growth in standard liquid media but no phenotype in media containing three antifungals that target sterols. To assess the role of C.a. Lpt1 in phospholipid remodeling, an in vivo, pulse–chase assay utilizing polysorbitan palmitate and mass spectrometry was developed. Cellular phospholipid composition became atypical with the provision of palmitate and gradually returned to the typical distribution when palmitate was removed. Deletion of C.a. LPT1 showed a modest yet significant effect on remodeling under these conditions.
Keywords: Lysophospholipid acyltransferase; Candida albicans; Phospholipid remodeling; Mass spectrometry;
Liquid fructose downregulates Sirt1 expression and activity and impairs the oxidation of fatty acids in rat and human liver cells by Alba Rebollo; Núria Roglans; Miguel Baena; Rosa M. Sánchez; Manel Merlos; Marta Alegret; Juan C. Laguna (514-524).
Fructose ingestion is associated with the production of hepatic steatosis and hypertriglyceridemia. For fructose to attain these effects in rats, simultaneous induction of fatty acid synthesis and inhibition of fatty acid oxidation is required. We aimed to determine the mechanism involved in the inhibition of fatty acid oxidation by fructose and whether this effect occurs also in human liver cells. Female rats were supplemented or not with liquid fructose (10% w/v) for 7 or 14 days; rat (FaO) and human (HepG2) hepatoma cells, and human hepatocytes were incubated with fructose 25 mM for 24 h. The expression and activity of the enzymes and transcription factors relating to fatty acid β-oxidation were evaluated. Fructose inhibited the activity of fatty acid β-oxidation only in livers of 14-day fructose-supplemented rats, as well as the expression and activity of peroxisome proliferator activated receptor α (PPARα). Similar results were observed in FaO and HepG2 cells and human hepatocytes. PPARα downregulation was not due to an osmotic effect or to an increase in protein-phosphatase 2A activity caused by fructose. Rather, it was related to increased content in liver of inactive and acetylated peroxisome proliferator activated receptor gamma coactivator 1α, due to a reduction in sirtuin 1 expression and activity. In conclusion, fructose inhibits liver fatty acid oxidation by reducing PPARα expression and activity, both in rat and human liver cells, by a mechanism involving sirtuin 1 down-regulation.
Keywords: PPARα; Steatosis; Triglyceride; ChREBP;
Regulation of autophagy and mitophagy by nutrient availability and acetylation by Bradley R. Webster; Iain Scott; Javier Traba; Kim Han; Michael N. Sack (525-534).
Normal cellular function is dependent on a number of highly regulated homeostatic mechanisms, which act in concert to maintain conditions suitable for life. During periods of nutritional deficit, cells initiate a number of recycling programs which break down complex intracellular structures, thus allowing them to utilize the energy stored within. These recycling systems, broadly named “autophagy”, enable the cell to maintain the flow of nutritional substrates until they can be replenished from external sources. Recent research has shown that a number of regulatory components of the autophagy program are controlled by lysine acetylation. Lysine acetylation is a reversible post-translational modification that can alter the activity of enzymes in a number of cellular compartments. Strikingly, the main substrate for this modification is a product of cellular energy metabolism: acetyl-CoA. This suggests a direct and intricate link between fuel metabolites and the systems which regulate nutritional homeostasis. In this review, we examine how acetylation regulates the systems that control cellular autophagy, and how global protein acetylation status may act as a trigger for recycling of cellular components in a nutrient-dependent fashion. In particular, we focus on how acetylation may control the degradation and turnover of mitochondria, the major source of fuel-derived acetyl-CoA.
Keywords: Acetylation; Sirt3; GCN5L1; Mitophagy; Autophagy;
Bovine lactoferrin binds oleic acid to form an anti-tumor complex similar to HAMLET by Bing Fang; Ming Zhang; Mai Tian; Lu Jiang; Hui Yuan Guo; Fa Zheng Ren (535-543).
α-Lactalbumin (α-LA) can bind oleic acid (OA) to form HAMLET-like complexes, which exhibited highly selective anti-tumor activity in vitro and in vivo. Considering the structural similarity to α-LA, we conjectured that lactoferrin (LF) could also bind OA to obtain a complex with anti-tumor activity. In this study, LF–OA was prepared and its activity and structural changes were compared with α-LA–OA. The anti-tumor activity was evaluated by methylene blue assay, while the apoptosis mechanism was analyzed using flow cytometry and Western blot. Structural changes of LF–OA were measured by fluorescence spectroscopy and circular dichroism. The interactions of OA with LF and α-LA were evaluated by isothermal titration calorimetry (ITC). LF–OA was obtained by heat-treatment at pH 8.0 with LD50 of 4.88, 4.95 and 4.62 μM for HepG2, HT29, and MCF-7 cells, respectively, all of which were 10 times higher than those of α-LA–OA. Similar to HAMLET, LF–OA induced apoptosis in tumor cells through both death receptor- and mitochondrial-mediated pathways. Exposure of tryptophan residues and the hydrophobic regions as well as the loss of tertiary structure were observed in LF–OA. Besides these similarities, LF showed different secondary structure changes when compared with α-LA, with a decrease of α-helix and β-turn and an increase of β-sheet and random coil. ITC results showed that there was a higher binding number of OA to LF than to α-LA, while both of the proteins interacted with OA through van der Waals forces and hydrogen bonds. This study provides a theoretical basis for further exploration of protein–OA complexes.
Keywords: Lactoferrin; Oleic acid; HAMLET; Anti-tumor; Apoptosis; Isothermal titration calorimetry;
Choline kinase alpha expression during RA-induced neuronal differentiation: Role of C/EBPβ by Pablo Domizi; Chieko Aoyama; Claudia Banchio (544-551).
Neuronal differentiation is a complex process characterized by a halt in proliferation and extension of neurites from the cell body. This process is accompanied by changes in gene expression that mediate the redirection leading to neurite formation and function. Acceleration of membrane phospholipids synthesis is associated with neurite elongation, and phosphatidylcholine (PtdCho) is the major membrane phospholipid in mammalian cells. The transcription of two genes in particular encoding key enzymes in the CDP–choline pathway for PtdCho biosynthesis are stimulated; the Chka gene for choline kinase (CK) alpha isoform and the Pcyt1a gene for the CTP:phosphocholine cytidylyltransferase (CCT) alpha isoform. We report that the stimulation of CKα expression during retinoic acid (RA) induced differentiation depends on a promoter region that contains two CCAAT/Enhancer-binding Protein-β (C/EBPβ) sites. We demonstrate that during neuronal differentiation of Neuro-2a cells, RA induces Chka expression by a mechanism that involves ERK1/2 activation which triggers C/EBPβ expression. Elevated levels of C/EBPβ bind to the Chka proximal promoter (Box1) inducing CKα expression. In addition we identified a downstream sequence named Box2 which together with Box1 is required for the promoter to reach the full induction. This is the first elucidation of the mechanism by which the expression of Chka is coordinately regulated during neuronal differentiation.
Keywords: Chka gene promoter; Phosphatidylcholine; Neuritogenesis; Transcriptional regulation; C/EBPβ;
Silencing diacylglycerol kinase-theta expression reduces steroid hormone biosynthesis and cholesterol metabolism in human adrenocortical cells by Kai Cai; Natasha C. Lucki; Marion B. Sewer (552-562).
Diacylglycerol kinase theta (DGKθ) plays a pivotal role in regulating adrenocortical steroidogenesis by synthesizing the ligand for the nuclear receptor steroidogenic factor 1 (SF1). In response to activation of the cAMP signaling cascade nuclear DGK activity is rapidly increased, facilitating PA-mediated, SF1-dependent transcription of genes required for cortisol and dehydroepiandrosterone (DHEA) biosynthesis. Based on our previous work identifying DGKθ as the enzyme that produces the agonist for SF1, we generated a tetracycline-inducible H295R stable cell line to express a short hairpin RNA (shRNA) against DGKθ and characterized the effect of silencing DGKθ on adrenocortical gene expression. Genome-wide DNA microarray analysis revealed that silencing DGKθ expression alters the expression of multiple genes, including steroidogenic genes, nuclear receptors and genes involved in sphingolipid, phospholipid and cholesterol metabolism. Interestingly, the expression of sterol regulatory element binding proteins (SREBPs) was also suppressed. Consistent with the suppression of SREBPs, we observed a down-regulation of multiple SREBP target genes, including 3-hydroxy-3-methylglutary coenzyme A reductase (HMG-CoA red) and CYP51, concomitant with a decrease in cellular cholesterol. DGKθ knockdown cells exhibited a reduced capacity to metabolize PA, with a down-regulation of lipin and phospholipase D (PLD) isoforms. In contrast, suppression of DGKθ increased the expression of several genes in the sphingolipid metabolic pathway, including acid ceramidase (ASAH1) and sphingosine kinases (SPHK). In summary, these data demonstrate that DGKθ plays an important role in steroid hormone production in human adrenocortical cells.Display Omitted
Keywords: Diacylglycerol kinase theta; Phosphatidic acid; Cortisol; Adrenal cortex; cAMP;
A role for the human peroxisomal half-transporter ABCD3 in the oxidation of dicarboxylic acids by Carlo W.T. van Roermund; Lodewijk IJlst; Tom Wagemans; Ronald J.A. Wanders; Hans R. Waterham (563-568).
Peroxisomes play a major role in human cellular lipid metabolism, including fatty acid β-oxidation. Free fatty acids (FFAs) can enter peroxisomes through passive diffusion or by means of ATP binding cassette (ABC) transporters, including HsABCD1 (ALDP, adrenoleukodystrophy protein), HsABCD2 (ALDRP) and HsABCD3 (PMP70). The physiological functions of the different peroxisomal half-ABCD transporters have not been fully determined yet, but there are clear indications that both HsABCD1 and HsABCD2 are required for the breakdown of fatty acids in peroxisomes. Here we report that the phenotype of the pxa1/pxa2Δ yeast mutant, i.e. impaired oxidation of oleic acid, cannot only be partially rescued by HsABCD1, HsABCD2, but also by HsABCD3, which indicates that each peroxisomal half-transporter can function as homodimer. Fatty acid oxidation measurements using various fatty acids revealed that although the substrate specificities of HsABCD1, HsABCD2 and HsABCD3 are overlapping, they have distinctive preferences. Indeed, most hydrophobic C24:0 and C26:0 fatty acids are preferentially transported by HsABCD1, C22:0 and C22:6 by HsABCD2 and most hydrophilic substrates like long-chain unsaturated-, long branched-chain- and long-chain dicarboxylic fatty acids by HsABCD3. All these fatty acids are most likely transported as CoA esters. We postulate a role for human ABCD3 in the oxidation of dicarboxylic acids and a role in buffering fatty acids that are overflowing from the mitochondrial β-oxidation system.Display Omitted
Keywords: Peroxisomes; Fatty acid oxidation; ABC transporter; Fatty acid transport; ABCD3; Dicarboxylic acid;
Upregulation of endogenous farnesyl diphosphate synthase overcomes the inhibitory effect of bisphosphonate on protein prenylation in Hela cells by Subhajit Das; Peter A. Edwards; Julie C. Crockett; Michael J. Rogers (569-573).
Nitrogen-containing bisphosphonates (N-BPs) such as zoledronic acid (ZOL) are the gold standard treatment for diseases of excessive bone resorption. N-BPs inactivate osteoclasts via inhibition of farnesyl diphosphate synthase (FPPS), thereby preventing the prenylation of essential small GTPases. Not all patients respond to N-BP therapy to the same extent, and some patients, for example with tumour-associated bone disease or Paget's disease, appear to develop resistance to N-BPs. The extent to which upregulation of FPPS might contribute to these phenomena is not clear. Using quantitative PCR and western blot analysis we show that levels of FPPS mRNA and protein can be upregulated in HeLa cells by culturing in lipoprotein deficient serum (LDS) or by over-expression of SREBP-1a. Upregulated, endogenous FPPS was predominantly localised to the cytosol and did not co-localise with peroxisomal or mitochondrial markers. Upregulation of endogenous FPPS conferred resistance to the inhibitory effect of low concentrations of ZOL on the prenylation of the small GTPase Rap1a. These observations suggest that an increase in the expression of endogenous FPPS could confer at least partial resistance to the pharmacological effect of N-BP drugs such as ZOL in vivo.
Keywords: Bisphosphonate; Osteoporosis; Farnesyl diphosphate synthase; SREBP; Prenylation; Osteoclast;
Recombinant PNPLA3 protein shows triglyceride hydrolase activity and its I148M mutation results in loss of function by Piero Pingitore; Carlo Pirazzi; Rosellina M. Mancina; Benedetta M. Motta; Cesare Indiveri; Arturo Pujia; Tiziana Montalcini; Kristina Hedfalk; Stefano Romeo (574-580).
The patatin-like phospholipase domain containing 3 (PNPLA3, also called adiponutrin, ADPN) is a membrane-bound protein highly expressed in the liver. The genetic variant I148M (rs738409) was found to be associated with progression of chronic liver disease. We aimed to establish a protein purification protocol in a yeast system (Pichia pastoris) and to examine the human PNPLA3 enzymatic activity, substrate specificity and the I148M mutation effect. hPNPLA3 148I wild type and 148M mutant cDNA were cloned into P. pastoris expression vectors. Yeast cells were grown in 3 L fermentors. PNPLA3 protein was purified from membrane fractions by Ni-affinity chromatography. Enzymatic activity was assessed using radiolabeled substrates. Both 148I wild type and 148M mutant proteins are localized to the membrane. The wild type protein shows a predominant lipase activity with mild lysophosphatidic acid acyl transferase activity (LPAAT) and the I148M mutation results in a loss of function of both these activities. Our data show that PNPLA3 has a predominant lipase activity and I148M mutation results in a loss of function.
Keywords: Patatin-like phospholipase domain containing 3 (PNPLA3); Adiponutrin (ADPN); rs738409 (I148M); Pichia pastoris; Triglyceride hydrolase activity; Lysophosphatidic acid acyltransferase activity;
Kinetic and structural characterization of triacylglycerol lipases possessing phospholipase A1 activity by Ahmed Aloulou; Fakher Frikha; Alexandre Noiriel; Madiha Bou Ali; Abdelkarim Abousalham (581-587).
The pancreatic lipase gene family displays various substrate selectivities for triglycerides and phospholipids. The structural basis for this difference in substrate specificity has not been definitively established. Based on a kinetic comparative study between various pancreatic lipase family members, we showed here that porcine pancreatic lipase (PPL), which was so far classified as “classical lipase”, was able to hydrolyze phosphatidylcholine (PC). Amino acid sequence alignments revealed that Val260 residue in PPL lid could be critical for the interaction with lipid substrate. Molecular dynamics was applied to investigate PC binding modes within the catalytic cavity of PPL and human pancreatic lipase (HPL), aiming to explain the difference of specificity of these enzymes towards phospholipids. Results showed that with HPL, the oxyanion hole was not able to accommodate the PC molecule, suggesting that no activity could be obtained. With PPL, the formation of a large pocket involving Val260 allowed the PC molecule to come near the catalytic residues, suggesting that it could be hydrolyzed. One more interesting finding is that human pancreatic lipase related protein 2 could hydrolyze phospholipids through its PLA1 and PLA2 activities. Overall, our study shed the light on new structural features of the phospholipase activity of pancreatic lipase family members.
Keywords: Human pancreatic lipase; Human pancreatic lipase related protein 2; Porcine pancreatic lipase; Phospholipase A1; Activity; Regioselectivity;
Adipose triglyceride lipase activity is inhibited by long-chain acyl-coenzyme A by Harald M. Nagy; Margret Paar; Christoph Heier; Tarek Moustafa; Peter Hofer; Guenter Haemmerle; Achim Lass; Rudolf Zechner; Monika Oberer; Robert Zimmermann (588-594).
Adipose triglyceride lipase (ATGL) is required for efficient mobilization of triglyceride (TG) stores in adipose tissue and non-adipose tissues. Therefore, ATGL strongly determines the availability of fatty acids for metabolic reactions. ATGL activity is regulated by a complex network of lipolytic and anti-lipolytic hormones. These signals control enzyme expression and the interaction of ATGL with the regulatory proteins CGI-58 and G0S2. Up to date, it was unknown whether ATGL activity is also controlled by lipid intermediates generated during lipolysis. Here we show that ATGL activity is inhibited by long-chain acyl-CoAs in a non-competitive manner, similar as previously shown for hormone-sensitive lipase (HSL), the rate-limiting enzyme for diglyceride breakdown in adipose tissue. ATGL activity is only marginally inhibited by medium-chain acyl-CoAs, diglycerides, monoglycerides, and free fatty acids. Immunoprecipitation assays revealed that acyl-CoAs do not disrupt the protein–protein interaction of ATGL and its co-activator CGI-58. Furthermore, inhibition of ATGL is independent of the presence of CGI-58 and occurs directly at the N-terminal patatin-like phospholipase domain of the enzyme. In conclusion, our results suggest that inhibition of the major lipolytic enzymes ATGL and HSL by long-chain acyl-CoAs could represent an effective feedback mechanism controlling lipolysis and protecting cells from lipotoxic concentrations of fatty acids and fatty acid-derived lipid metabolites.Display Omitted
Keywords: Adipose triglyceride lipase; Hormone-sensitive lipase; Lipolysis; Regulation; acyl-CoA;
MAM (mitochondria-associated membranes) in mammalian cells: Lipids and beyond by Jean E. Vance (595-609).
One mechanism by which communication between the endoplasmic reticulum (ER) and mitochondria is achieved is by close juxtaposition between these organelles via mitochondria-associated membranes (MAM). The MAM consist of a region of the ER that is enriched in several lipid biosynthetic enzyme activities and becomes reversibly tethered to mitochondria. Specific proteins are localized, sometimes transiently, in the MAM. Several of these proteins have been implicated in tethering the MAM to mitochondria. In mammalian cells, formation of these contact sites between MAM and mitochondria appears to be required for key cellular events including the transport of calcium from the ER to mitochondria, the import of phosphatidylserine into mitochondria from the ER for decarboxylation to phosphatidylethanolamine, the formation of autophagosomes, regulation of the morphology, dynamics and functions of mitochondria, and cell survival. This review focuses on the functions proposed for MAM in mediating these events in mammalian cells. In light of the apparent involvement of MAM in multiple fundamental cellular processes, recent studies indicate that impaired contact between MAM and mitochondria might underlie the pathology of several human neurodegenerative diseases, including Alzheimer's disease. Moreover, MAM has been implicated in modulating glucose homeostasis and insulin resistance, as well as in some viral infections.
Keywords: Autophagy; Endoplasmic reticulum; Mitochondria; Lipid transport; Apoptosis; Neurodegeneration;
Very-long-chain polyunsaturated fatty acids accumulate in phosphatidylcholine of fibroblasts from patients with Zellweger syndrome and acyl-CoA oxidase1 deficiency by Yuichi Abe; Masanori Honsho; Hiroki Nakanishi; Ryo Taguchi; Yukio Fujiki (610-619).
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.
Keywords: Peroxisome; Zellweger syndrome; X-ALD; Peroxisomal β-oxidation; Very-long-chain fatty acid; Lipidomics;
Properties of apolipoprotein E derived peptide modulate their lipid-binding capacity and influence their anti-inflammatory function by Sunil A. Nankar; Abhay H. Pande (620-629).
Apolipoprotein-derived peptides are promising candidates for the treatment of various inflammatory conditions. The beneficial effects of these peptides are based on multiple mechanisms; prominent among them being high-affinity binding to pro-inflammatory oxidized phospholipids (Ox-PLs) and facilitating their sequestration/metabolism/clearance in the body. This indicates that peptides which can bind exclusively to Ox-PLs without recognizing normal, non-oxidized phospholipids (non-Ox-PLs) will be more potent anti-inflammatory agent than that of the peptides that bind to both Ox-PLs and non-Ox-PLs. In order to develop such Ox-PL-specific peptides, the knowledge about the properties (molecular determinants) of peptides that govern their Ox-PL preference is a must. In this study we have synthesized eleven peptides corresponding to the conserved regions of human apolipoprotein E and compared their biochemical properties, lipid-binding specificities, and anti-inflammatory properties. Our results show that these peptides exhibit considerably different specificities towards non-Ox-PL and different species of Ox-PLs. Some of these peptides bind exclusively to the Ox-PLs and inhibit the pro-inflammatory function of Ox-PLs in human blood. Biochemical characterization revealed that the peptides possess substantially different properties. Our results suggest that physicochemical properties of peptides play an important role in their lipid-binding specificity.
Keywords: Apolipoprotein-derived peptide; Inflammation; qRT-PCR; Ox-PAPC; ELISA; Circular dichroism;
Coenzyme Q supplementation or over-expression of the yeast Coq8 putative kinase stabilizes multi-subunit Coq polypeptide complexes in yeast coq null mutants by Cuiwen H. He; Letian X. Xie; Christopher M. Allan; UyenPhuong C. Tran; Catherine F. Clarke (630-644).
Coenzyme Q biosynthesis in yeast requires a multi-subunit Coq polypeptide complex. Deletion of any one of the COQ genes leads to respiratory deficiency and decreased levels of the Coq4, Coq6, Coq7, and Coq9 polypeptides, suggesting that their association in a high molecular mass complex is required for stability. Over-expression of the putative Coq8 kinase in certain coq null mutants restores steady-state levels of the sensitive Coq polypeptides and promotes the synthesis of late-stage Q-intermediates. Here we show that over-expression of Coq8 in yeast coq null mutants profoundly affects the association of several of the Coq polypeptides in high molecular mass complexes, as assayed by separation of digitonin extracts of mitochondria by two-dimensional blue-native/SDS PAGE. The Coq4 polypeptide persists at high molecular mass with over-expression of Coq8 in coq3, coq5, coq6, coq7, coq9, and coq10 mutants, indicating that Coq4 is a central organizer of the Coq complex. Supplementation with exogenous Q6 increased the steady-state levels of Coq4, Coq7, and Coq9, and several other mitochondrial polypeptides in select coq null mutants, and also promoted the formation of late-stage Q-intermediates. Q supplementation may stabilize this complex by interacting with one or more of the Coq polypeptides. The stabilizing effects of exogenously added Q6 or over-expression of Coq8 depend on Coq1 and Coq2 production of a polyisoprenyl intermediate. Based on the observed interdependence of the Coq polypeptides, the effect of exogenous Q6, and the requirement for an endogenously produced polyisoprenyl intermediate, we propose a new model for the Q-biosynthetic complex, termed the CoQ-synthome.Display Omitted
Keywords: Coenzyme Q supplementation; Mitochondrial metabolism; Protein complex; Q-biosynthetic intermediate; Saccharomyces cerevisiae; Ubiquinone;