BBA - Molecular and Cell Biology of Lipids (v.1634, #3)
Editorial Board (ii).
Lipidomics is emerging by Michel Lagarde; Alain Géloën; Michel Record; Dennis Vance; Fritz Spener (61).
Regulation of myocardial triacylglycerol synthesis and metabolism by Tal M. Lewin; Rosalind A. Coleman (63-75).
Studies showing a correlation of excess myocardial triacylglycerol stores with apoptosis, fibrosis, and contractile dysfunction indicate that dysregulation of triacylglycerol metabolism may contribute to cardiac disease. This review covers the regulation of heart triacylglycerol accumulation at the critical control points of fatty acid uptake, enzymes of triacylglycerol synthesis, lipolysis, and lipoprotein secretion. These pathways are discussed in the context of the central role myocardial triacylglycerol plays in cardiac energy metabolism and heart disease.
Keywords: Heart; Fatty acid uptake; Triacylglycerol synthesis; Lipolysis; Lipoprotein;
Reduced atherosclerosis in hormone-sensitive lipase transgenic mice overexpressing cholesterol acceptors by Henry A. Choy; Xu-Ping Wang; Michael C. Schotz (76-85).
Macrophage-specific overexpression of cholesteryl ester hydrolysis in hormone-sensitive lipase transgenic (HSL Tg) female mice paradoxically increases cholesterol esterification and cholesteryl ester accumulation in macrophages, and thus susceptibility to diet-induced atherosclerosis compared to nontransgenic C57BL/6 mice. The current studies suggest that whereas increased cholesterol uptake could contribute to transgenic foam cell formation, there are no differences in cholesterol synthesis and the expression of cholesterol efflux mediators (ABCA1, ABCG1, apoE, PPARγ, and LXRα) compared to wild-type macrophages. HSL Tg macrophages exhibit twofold greater efflux of cholesterol to apoA–I in vitro, suggesting the potential rate-limiting role of cholesteryl ester hydrolysis in efflux. However, macrophage cholesteryl ester levels appear to depend on the relative efficacy of alternate pathways for free cholesterol in either efflux or re-esterification. Thus, increased atherosclerosis in HSL Tg mice appears to be due to the coupling of the efficient re-esterification of excess free cholesterol to its limited removal mediated by the cholesterol acceptors in these mice. The overexpression of cholesterol acceptors in HSL-apoA-IV double-transgenic mice increases plasma HDL levels and decreases diet-induced atherosclerosis compared to HSL Tg mice, with aortic lesions reduced to sizes in nontransgenic littermates. The results in vivo are consistent with the effective efflux from HSL Tg macrophages supplemented with HDL and apoA-I in vitro, and highlight the importance of cholesterol acceptors in inhibiting atherosclerosis caused by imbalances in the cholesteryl ester cycle.
Keywords: Hormone-sensitive lipase; Atherosclerosis; Efflux; Cholesterol acceptor; Macrophage;
Gene structure of pig sterol 12α-hydroxylase (CYP8B1) and expression in fetal liver: comparison with expression of taurochenodeoxycholic acid 6α-hydroxylase (CYP4A21) by Kerstin Lundell; Kjell Wikvall (86-96).
Cholic acid is the major trihydroxy bile acid formed in most mammals. The domestic pig (Sus scrofa) is an exception. The bile of adult pig is devoid of cholic acid whereas hyocholic acid is found in amounts equal to that of cholic acid in humans. The pathway leading to formation of hyocholic acid is believed to be species-specific and to have evolved in the pig to compensate for a nonexistent or deficient cholic acid biosynthesis. However, a high level of cholic acid has recently been found in the bile of fetal pig. Here we describe that a gene encoding the key enzyme in cholic acid biosynthesis, the sterol 12α-hydroxylase (CYP8B1), is in fact present in the pig genome. The deduced amino acid sequence shows 81% identity to the human and rabbit orthologues. CYP8B1 mRNA is expressed at significant levels in fetal pig liver. Both CYP8B1 and the key enzyme in hyocholic acid formation, taurochenodeoxycholic acid 6α-hydroxylase (CYP4A21), were found to be expressed in pig liver in a developmental-dependent but opposite fashion.
Keywords: Cytochrome P450; CYP8B1; CYP4A21; Cholic acid; Hyocholic acid; Pig;
Characterisation of an N-terminal variant of acetyl-CoA carboxylase-α: expression in human tissues and evolutionary aspects by Maureen T. Travers; Amanda J. Vallance; Roger A. Clegg; Ross Thomson; Nigel T. Price; Michael C. Barber (97-106).
mRNA encoding a variant acetyl-CoA carboxylase (ACC)-α isozyme, transcribed from a downstream promoter, PIII, was detected in human tissues. Such exon 5A-containing transcripts (E5A-mRNA) encode ACC-α with a distinct N-terminus, with 15/17 residues identical to those encoded by the ovine mRNA. In the current study we used antisera directed against the E5A N-terminus to verify that ovine E5A translates are present in tissues consistent with the distribution of E5A-mRNA. The presence of E5A alters the context of adjacent regulatory phosphorylation sites in E6, which may indicate altered regulation of activity for this isozyme. Sequences with high identity to the proximal promoter of PIII and E5A are present in the mouse and rat ACC-α genes, however, the coding region of E5A is not conserved, and E5A transcripts are not detected in tissues. Thus E5A must have been present in a common ancestor of rodents, primates, and ruminants, and has become nonfunctional in the former. A minor human PIII-derived mRNA containing an additional 111-bp sequence encoded by a downstream exon, E5B, was also detected. E5B encodes an in-frame stop-codon such that the E5A open-reading frame is terminated, however, ACC-α translation may be re-initiated from a downstream AUG in E6, potentially generating an isozyme lacking the N-terminal phosphorylation sites. Transcription of human ACC-α from at least three promoters and the potential to generate ACC-α isozymes with differential susceptibilities to phosphorylation indicate that the regulation of fatty acid synthesis in human tissues is likely to be complex.
Keywords: Acetyl-CoA carboxylase; Fat synthesis; Brain; Phosphorylation; Transcription;
A novel lipopeptide, an inhibitor of bacterial adhesion, from the thermophilic and halotolerant subsurface Bacillus licheniformis strain 603 by Stanislav G Batrakov; Tatiana A Rodionova; Stanislav E Esipov; Nikita B Polyakov; Vladimir I Sheichenko; Nina V Shekhovtsova; Sergey M Lukin; Nikolai S Panikov; Yuri A Nikolaev (107-115).
A new Bacillus licheniformis strain, 603, isolated from a mixture of drilling fluid and subsurface thermal water, has been found to produce a cyclic lipopeptide which is released into cultural medium as well as present in cells as the major lipid constituent (57% of the total cell lipids extractable with 2:1 chloroform–methanol). The quantitative ratio of the extracellular and intracellular lipopeptide has been estimated as 23:10. The metabolite represents a heptapeptide, l-Asp→l-Leu→l-Leu→l-Val→l-Val→l-Glu→l-Leu, N-acylated to the N-terminal amino acid, l-Asp, by a 3-hydroxy fatty acid (from 13:0 to 17:0 with n-, iso-, and anteiso-chains), the 3-OH group of which is esterified by the C-terminal amino acid, l-Leu. The chemical structure of the lipopeptide has been established by means of infrared (IR), 1H- and 13C-nuclear magnetic resonance (NMR) spectroscopy, electrospray ionisation (ESI) mass spectrometry (MS), including secondary ion mass spectrometry, along with chemical and enzymatic degradation. Although a diversity of similar metabolites synthesised by various B. licheniformis strains are presently known, such a structure has not been reported thus far. Added to the growth medium of strain 603 at the concentration of 1.6 μg/ml, the lipopeptide prevents adhesion of cells to a glass surface. Also, it exhibits a considerable growth-inhibiting activity against Corynebacterium variabilis and a much lower activity against Acinetobacter sp.
Keywords: Lipopeptide; Adhesion; Bacillus licheniformis;
Micelle formation of sodium chenodeoxycholate and solubilization into the micelles: comparison with other unconjugated bile salts by Ryoko Ninomiya; Keisuke Matsuoka; Yoshikiyo Moroi (116-125).
Micellization of sodium chenodeoxycholate (NaCDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle at 288.2, 298.2, 308.2, and 318.2 K. They were compared with those of three other unconjugated bile salts; sodium cholate (NaC), sodium deoxycholate (NaDC), and sodium ursodeoxycholate (NaUDC). The I 1/I 3 ratio of pyrene fluorescence and the solubility dependence of solution pH were employed to determine the CMC values. As the results, a certain concentration range for the CMC and a stepwise molecular aggregation for micellization were found reasonable. Using a stepwise association model of the bile salt anions, the mean aggregation number (n̄) of NaCDC micelles was found to increase with the total anion concentration, while the n̄ values decreased with increasing temperature; 9.1, 8.1, 7.4, and 6.3 at 288.2, 298.2, 308.2, and 318.2 K, respectively, at 50 mmol dm−3. The results from four unconjugated bile salts indicate that the number, location, and orientation of hydroxyl groups in the steroid nucleus are quite important for growth of the micelles. Activity of the counterion (Na+) was determined by a sodium ion selective electrode in order to confirm the low counterion binding to micelles. The solubilized amount of cholesterol into the aqueous bile salt solutions increased in the order of NaUDC<NaC<NaCDC<NaDC. The first stepwise association or solubilization constants (K̄ 1) between a cholesterol monomer and a vacant micelle were evaluated at different bile salt concentrations. The constants were also determined for polycyclic aromatic compounds (benzene, naphthalene, anthracene, and pyrene). The corresponding ΔG 0 value was most negative for cholesterol among the solubilizates studied, which indicated that cholesterol was thermodynamically stabilized most by solubilization into the bile salt micelles.
Keywords: Micellization; Solubilization; Sodium chenodeoxycholate; Unconjugated bile salt; Cholesterol;