Nuclear hormone receptor NHR-49 controls fat consumption and fatty acid composition in C. elegans

Mammalian nuclear hormone receptors (NHRs), such as liver X receptor, farnesoid X receptor, and peroxisome proliferator-activated receptors (PPARs), precisely control energy metabolism. Consequently, these receptors are important targets for the treatment of metabolic diseases, including diabetes and obesity. A thorough understanding of NHR fat regulatory networks has been limited, however, by a lack of genetically tractable experimental systems. Here we show that deletion of the Caenorhabditis elegans NHR gene nhr-49 yielded worms with elevated fat content and shortened life span. Employing a quantitative RT-PCR screen, we found that nhr-49 influenced the expression of 13 genes involved in energy metabolism. Indeed, nhr-49 served as a key regulator of fat usage, modulating pathways that control the consumption of fat and maintain a normal balance of fatty acid saturation. We found that the two phenotypes of the nhr-49 knockout were linked to distinct pathways and were separable: The high-fat phenotype was due to reduced expression of enzymes in fatty acid β-oxidation, and the shortened adult life span resulted from impaired expression of a stearoyl-CoA desaturase. Despite its sequence relationship with the mammalian hepatocyte nuclear factor 4 receptor, the biological activities of nhr-49 were most similar to those of the mammalian PPARs, implying an evolutionarily conserved role for NHRs in modulating fat consumption and composition. Our findings in C. elegans provide novel insights into how NHR regulatory networks are coordinated to govern fat metabolism.     

Oscillatory behaviour and unsaturated fatty acid composition of diabetic liver mitochondria

Volume oscillations of liver mitochondria resulting from valinomycin induced K+ transport, may be represented by the equation At/Am = C'.exp(-beta t).sin(omega 1t+ psi) where At is the oscillation amplitude at time t; Am, the maximal amplitude; beta, the damping coefficient, omega 1 the oscillation frequency, and C' and psi, constants. The kinetic parameters beta and omega 1 increased as a function of valinomycin concentration. Measurement of beta and omega 1 for mitochondria from normal rats (A); diabetic rats (B), and normal rats fed corn oil or lard-supplemented diets (C and D, respectively), yielded an increase in beta (P less than 0.05) in B and D as compared with A, and a decrease in omega 1 in B and D as compared with A and C, respectively. Analysis of mitochondrial lipids revealed significant diminution of arachidonic acid and other polyenoic fatty acids in diabetic and lard-fed rats, as compared with normal rats and corn oil-fed rats, respectively. The conclusion is drawn that the abnormal oscillatory behaviour of diabetic liver mitochondria is related to the alteration of the membrane fatty acid composition.     

Altered membrane free unsaturated fatty acid composition in human colorectal cancer tissue

Polyunsaturated free fatty acids (PUFAs) participate in normal functioning of the cell, particularly in control intracellular cell signalling. As nutritional components they compose a human diet with an indirect promoting influence on tumourogenesis. The PUFAs level depends on the functional state of the membrane. This work is focused on changes only of free unsaturated fatty acids amount (AA – arachidonic acid, LA – linoleic acid, ALA – α-linolenic acid, palmitoleic acid (PA) and oleic acid) in cell membranes of colorectal cancer of pT3 stage, G2 grade without metastasis. Qualitative and quantitative composition of free unsaturated fatty acids in the membrane was determined by high-performance liquid chromatography. It was shown that the malignant transformation was accompanied by a decrease in amount of LA and ALA while arachidonic and oleic acids increased. It is of interest that free AA levels are elevated in colon cancer, as AA is the precursor to biologically active eicosanoids.     

Chemosensory regulation of development in C. elegans

The dauer larva is a specialized third-larval stage of Caenorhabditis elegans that is long-lived and resistant to environmental insult. The dauer larva is formed in response to a high external concentration of a constitu-tively secreted pheromone. Response to the dauer-inducing pheromone of C. elegans is a promising genetic model for metazoan chemosensory transduction. More than 20 genes have been identified that are required for normal pheromone response. The functions of these genes include production of the pheromone, exposure of sensory neuron endings to the environment, structural and functional integrity of those sensory endings, and the capacity of sensory neurons to make appropriate output. Genetic evidence suggests that two partially redundant sensory pathways act in concert to control dauer formation. At least two classes of chemosensory neurons, ADF and ASI, are implicated in the pheromone response. On the basis of on these findings, a speculative model for the pheromone response is proposed. In this model, the neurons ADF and ASI are pheromone sensors that repress dauer formation in the absence of pheromone and dere-press dauer formation in response to pheromone. It is currently unclear whether or not the two genetically defined sensory pathways both act in ADF and ASI.     

Mechanism of the apparent regulation of Escherichia coli unsaturated fatty acid synthesis by exogenous oleic acid.

Starvation of strains of Escherichia coli which are glycerol auxotrophs and are also defective in beta oxidation results in the accumulation of large amounts of free fatty acid (Cronan, J. E., Jr., Weisberg, L. W., and Allen, R. G. (1975) J. Biol. Chem. 250, 5835-5840). We now report that addition of exogenous oleic acid to these cultures results in no decrease in the synthesis of the unsaturated acids of the free fatty acid fraction although a 40 to 60% decrease of [14C]acetate incorporation into phospholipid unsaturated acyl moieties occurs under these conditions. This result indicates that the decreased synthesis of phospholipid unsaturated acyl moieties observed by others during oleic acid supplementation can be attributed to competition between exogenous and endogenously synthesized unsaturated fatty acids rather than a curtailment of unsaturated fatty acid synthesis per se.     

DNA supercoiling and thermal regulation of unsaturated fatty acid synthesis in Bacillus subtilis

Bacillus subtilis growing at 37° C synthesizes, almost exclusively, saturated fatty acids. However, when a culture growing at 37°C is transferred to 20°C, the synthesis of unsaturated fatty acids is induced. The addition of the DNA gyrase inhibitor novobiocin specifically prevented the induction of unsaturated fatty acid synthesis at 20° C. Furthermore, it was determined that plasmid DNA isolated from cells growing at 20°C was significantly more negatively supercoiled than the equivalent DNA isolated from cells growing at 37°C. The overall results agree with the hypothesis that an increase in DNA supercoiling associated with a temperature downshift could regulate the unsaturated fatty acids synthesis in B. subtilis.     

The influence of dietary essential fatty acids on uterine C20 and C22 fatty acid composition.

The effect of dietary fatty acids on uterine fatty acid composition was studied in rats fed control diet or semi-synthetic diet supplemented with 1.5 microliter/g/day evening primrose oil (EPO) or fish oil (FO). Diet-related changes in uterine lipid were detected within 21 days. Changes of 2- to 20-fold were detected in the uterine n-6 and n-3 essential fatty acids (EFA) and in certain saturated and monounsaturated fatty acids. The FO diet was associated with higher uterine C20 and C22 n-3, and the EPO diet, with higher uterine n-6 fatty acid. High uterine C18:2 n-6 was detected in neutral lipid (NL) of rats fed high concentrations of this fatty acid, but there was little evidence of selective incorporation or retention of C18:2 n-6 by uterine NL. The incorporation of EFA into uterine phospholipids (PL) was greater than NL EFA incorporation, and uterine PL n-3/n-6 ratios showed greater diet dependence. Tissue/diet fatty acid ratios in NL and PL also indicated preferential incorporation/synthesis of C16:1 n-9, and C16:0, and there was greater incorporation of C12:0 and C14:0 into uteri of rats fed EPO and FO. Replacement of 50-60% of arachidonate with n-3 EFA in uterine PL may inhibit n-6 EFA metabolism necessary for uterine function at parturition.     

A novel unsaturated fatty acid hydratase toward C16 to C22 fatty acids from Lactobacillus acidophilus

Hydroxy FAs, one of the gut microbial metabolites of PUFAs, have attracted much attention because of their various bioactivities. The purpose of this study was to identify lactic acid bacteria with the ability to convert linoleic acid (LA) to hydroxy FAs. A screening process revealed that a gut bacterium, Lactobacillus acidophilus NTV001, converts LA mainly into 13-hydroxy-cis-9-octadecenoic acid and resulted in the identification of the hydratase responsible, fatty acid hydratase 1 (FA-HY1). Recombinant FA-HY1 was purified, and its enzymatic characteristics were investigated. FA-HY1 could convert not only C18 PUFAs but also C20 and C22 PUFAs. C18 PUFAs with a cis carbon-carbon double bond at the Δ12 position were converted into the corresponding 13-hydroxy FAs. Arachidonic acid and DHA were converted into the corresponding 15-hydroxy FA and 14-hydroxy FA, respectively. To the best of our knowledge, this is the first report of a bacterial FA hydratase that can convert C20 and C22 PUFAs into the corresponding hydroxy FAs. These novel hydroxy FAs produced by using FA-HY1 should contribute to elucidating the bioactivities of hydroxy FAs.     

Genetic instability of C. elegans comes naturally

There have been many attempts to measure the genome-wide mutation rate for spontaneous mutations, using measurements of traits in inbred lines in which mutations have accumulated. However, these are likely to miss many small-effect mutations that are important for evolutionary processes. Recently, the genome-wide spontaneous mutation rate in inbred lines of Caenorhabditis elegans was estimated, using DNA sequencing. The results imply that the mutation rate is surprisingly high, and that insertion-deletion mutations are unexpectedly common. Phenotypic assays of the same lines detected only a small proportion of mutations that were predicted to have evolutionarily significant fitness effects.     

Chromatin regulation during C. elegans germline development

Recent studies in Caenorhabditis elegans implicate PcG- and NuRD-like chromatin regulators in the establishment and maintenance of germline-soma distinctions. Somatic cells appear to utilize NuRD-related nucleosome-remodeling factors to overwrite germline-specific chromatin states that are specified through PcG-like activities. The germline, in turn, may rely on an asymmetrically inherited inhibitor to prevent chromatin reorganization that would otherwise erase pluripotency.     

Sucrose-mediated regulation of fatty acid composition in asexual embryos of Theobroma cacao

Asexual embryos of Theobroma cacao L. cultured in vitro grew to a size and fresh weight equal to mature zygotic embryos in vivo when cultured in liquid medium on a rollodrum apparatus. Changes in the fatty acid composition in the asexual embryos, similar to those which occur in the zygotic embryo during normal maturation, were stimulated as the sucrose concentration in the medium was increased to an optimum at 27% sucrose (w/v). As the sucrose concentration increased, there was a shift in the fatty acid composition from predominantly polyunsaturated to saturated and monounsaturated fatty acids characterized by an increase in the mole percents of stearic (18:0) and oleic (18:1) acids and a decrease in the mole percents of linoleic (18:2) and linolenic acids (18:3).     

Genetic analysis of a population of Tribolium. V. Viability of the unsaturated fatty acid sensitive mutant.

The viability pattern of the unsaturated fatty acid sensitive mutant (cos/cos) of Tribolium castaneum was examined with reference to the normal genotype from egg hatching through adult emergence. The beetles were cultured on diets with 0, 3, or 5% corn oil in growth chambers maintained at 33 +/- 1 degree C and either 42 +/- 6% or 75 +/- 3% relative humidity. The pattern of the mutant was altered during the larval stage and was dependent on both the concentration of dietary fatty acid and the relative humidity of the culture chamber. Values of the viability component of fitness were assigned to the cos/cos, +/-/cos and +/-/+/- genotypes for multiple environments based on the number of eggs surviving to pupation. In large, random mating populations segregating at this locus, a stable genetic polymorphism is forecast. Predicted rates of change of allele frequency are dependent upon the culture conditions.     

马尾藻中产不饱和脂肪酸真菌的分离及其脂肪酸组成分析

【背景】随着从鱼类、农作物原料中提取不饱和脂肪酸的成本越来越高,寻找特殊且成本低的提取原料迫在眉睫。海洋环境的特殊性造就了丰富而特有的微生物资源,成为获取产不饱和脂肪酸的新策略。【目的】从湛江徐闻马尾藻中分离筛选产油脂真菌,并对其脂代谢产物进行气相色谱分析(GC)。【方法】通过利用选择性培养基及苏丹黑染色方法从马尾藻中筛选高产油脂真菌,对目标菌进行形态特征、培养特征及ITS序列鉴定,利用GC技术对三氯甲烷-甲醇提取的油脂进行组成成分分析与含油量测定。【结果】共筛选到7株产油脂真菌,其中菌株A17脂肪颗粒大且密集,是一株高产菌株,经形态与基因水平鉴定,确定菌株A17为变红镰孢菌(Fusarium incarnatum)。提取的油脂占细胞干重的24.75%,并且不饱和脂肪酸占总油脂的60.76%,其中油酸与亚油酸分别为32.80%和26.20%。【结论】该研究可为开发马尾藻中产油脂菌株提供理论依据。