UAS domain of Ubxd8 and FAF1 polymerizes upon interaction with long-chain unsaturated fatty acids

Ubxd8, a multidomain protein sensor for long-chain unsaturated fatty acids (FAs), plays a crucial role to maintain cellular homeostasis of FAs. Ubxd8 polymerizes upon interaction with long-chain unsaturated FAs, but the molecular mechanism involved in this polymerization remains unclear. Here we report that the UAS domain of Ubxd8 mediates this polymerization. We show that a positively charged surface area in the domain is required for the reaction. Mutations changing the positively charged residues in this area to glutamates prevented long-chain unsaturated FAs from inducing oligomerization of Ubxd8. Consequently, the mutant protein no longer responded to regulation by long-chain unsaturated FAs in cultured cells. Long-chain unsaturated FAs also induced polymerization of Fas-associated factor 1 (FAF1), the only other mammalian protein that contains a UAS domain homologous to that of Ubxd8. These results provide further insights into protein-FA interactions by identifying the UAS domain as a motif interacting with long-chain unsaturated FAs.     

Distinct roles of specific fatty acids in cellular processes: implications for interpreting and reporting experiments

Plasma contains a variety of long-chain fatty acids (FAs), such that about 35% are saturated and 65% are unsaturated. There are countless examples that show how different FAs impart specific and unique effects, or even opposing actions, on cellular function. Despite these differing effects, palmitate (C16:0) is regularly used to represent "FAs" in cell based experiments. Although palmitate can be useful to induce and study stress effects in cultured cells, these effects in isolation are not physiologically relevant to dietary manipulations, obesity, or the consequences of physiological concentrations of FAs. Hence, authors should avoid conclusions that generalize about "FAs" or "saturated FAs" or "high-fat diet" effects if only a single FA was used in the reported experiments.     

The effects of fatty acid composition on cardiac hypertrophy and function in mouse models of diet-induced obesity

High-fat diets (HFDs) are used frequently to study the development of cardiac dysfunction in animal models of obesity and diabetes. However, impairment in systolic function, often reported as declining ejection fraction, may not consistently occur in a given time frame which could be contributable to a variety of factors within the experimental design. One major factor may be the amounts of saturated and unsaturated fatty acids (FAs) that are present in the diet. To determine whether the FA content and composition were critical determinants in the development of cardiac dysfunction in response to high-fat feeding, we fed adult, male mice Western diet (45% fat, 60% saturated), Surwit diet (60% fat, 90% saturated), milk-fat-based diet (60% fat, 60% saturated) or high-fat Western diet (HFWD, 60% fat, 32% saturated) for 12 weeks. We report that neither the amount of total fat nor the ratio of saturated to unsaturated FAs in the diets differentially affects body weight and adiposity in mice. In addition, no evidence of systolic dysfunction is present after 12 weeks. Interestingly, the HFWD, with equal parts saturated, monounsaturated and polyunsaturated FAs, induces mild cardiac hypertrophy and diastolic dysfunction after 12 weeks, which coincides with elevated serum levels of arachidonic acid. Our results suggest that the dietary FA content and composition may be a primary determinant of diastolic, but not systolic, dysfunction in animal models of diet-induced obesity.     

Antibacterial actions of fatty acids and monoglycerides against Helicobacter pylori

The bactericidal potencies of saturated and unsaturated fatty acids (FAs) and monoglycerides (MGs) against Helicobacter pylori were determined following short incubations with freshly harvested cells over a range of pHs. FAs and their derivatives with an equivalent-carbon number of 12 were the most potent: lauric acid had a minimum bactericidal concentration (MBC) at pH 7.4 of 1 mM, myristoleic and linolenic acid were the most potent unsaturated FAs (MBCs of 0.5 mM, pH 7.4), and monolaurin was the most potent MG (MBC 0.5 mM). Potencies of saturated FAs were increased sharply by lowering pH, and a decrease of only 0.5 pH units can cause a change from non-lethal to lethal conditions. Conversely, the bactericidal action of monolaurin was not pH-dependent. The bactericidal potencies of unsaturated FAs increased with degree of unsaturation. When more than one FA or FA plus MGs were present, their combined action was additive. Urea and endogenous urease did not protect H. pylori from the bactericidal action of FAs. These results suggest that H. pylori present in the stomach contents (but not necessarily within the mucus barrier) should be rapidly killed by the millimolar concentrations of FAs and MGs that are produced by pre-intestinal lipase(s) acting on suitable triglycerides such as milk fat.     

A human hepatocellular in vitro model to investigate steatosis

The present study was designed to define an experimental model of hepatocellular steatosis with a fat overaccumulation profile in which the metabolic and cytotoxic/apoptotic effects could be separated. This was accomplished by defining the experimental conditions of lipid exposure that lead to significant intracellular fat accumulation in the absence of overt cytotoxicity, therefore allowing to differentiate between cytotoxic and apoptotic effects. Palmitic (C16:0) and oleic (C18:1) acids are the most abundant fatty acids (FFAs) in liver triglycerides in both normal subjects and patients with nonalcoholic fatty liver disease (NAFLD). Therefore, human hepatocytes and HepG2 cells were incubated with a mixture of different proportions of saturated (palmitate) and unsaturated (oleate) FFAs to induce fat-overloading. Similar intracellular levels of lipid accumulation as in the human steatotic liver were achieved. Individual FFAs have a distinct inherent toxic potential. Fat accumulation, cytotoxicity and apoptosis in cells exposed to the FFA mixtures were investigated. The FFA mixture containing a low proportion of palmitic acid (oleate/palmitate, 2:1 ratio) is associated with minor toxic and apoptotic effects, thus representing a cellular model of steatosis that mimics benign chronic steatosis. On the other hand, a high proportion of palmitic acid (oleate/palmitate, 0:3 ratio) might represent a cellular model of steatosis in which saturated FFAs promote an acute harmful effect of fat overaccumulation in the liver. These hepatic cellular models are apparently suitable to experimentally investigate the impact of fat overaccumulation in the liver excluding other factors that could influence hepatocyte behaviour.     

Changes in the content and composition of lipid fatty acids in tobacco leaves and roots at low-temperature hardening

Changes in the fatty acid (FA) composition of leaf and root lipids of heat-loving tobacco (Nicotiana tabacum L., cv. Samsun) plants during low-temperature hardening (8°C for 6 days) were studied. Hardening could improve leaf but not root cold tolerance. As this took place, the relative content of polyunsaturated (18:2n-6 and 18:3n-3) FAs increased and the proportion of saturated and monounsaturated FAs decreased. In contrast, in the roots hardening slightly increased the concentration of saturated FAs (16:0 and 18:0) and reduced the level of unsaturated FAs (18:1n-9, 18:2n-6, and 18:3n-3). At the same time, root lipids contained much C_20–24 FAs, and their content increased during hardening. It was suggested that an increased FA saturation and elevated proportion of C_20–24 FAs in the root lipids resulting in the lower membrane fluidity could be a reason for incapability of heat-loving tobacco plant roots of hardening and plant death at the lowtemperature stress.     

Fatty Acids Regulate Stress Resistance and Virulence Factor Production for Listeria monocytogenes

Fatty acids (FAs) are the major structural component of cellular membranes, which provide a physical and chemical barrier that insulates intracellular reactions from environmental fluctuations. The native composition of membrane FAs establishes the topological and chemical parameters for membrane-associated functions and is therefore modulated diligently by microorganisms especially in response to environmental stresses. However, the consequences of altered FA composition during host-pathogen interactions are poorly understood. The food-borne pathogen Listeria monocytogenes contains mostly saturated branched-chain FAs (BCFAs), which support growth at low pH and low temperature. In this study, we show that anteiso-BCFAs enhance bacterial resistance against phagosomal killing in macrophages. Specifically, BCFAs protect against antimicrobial peptides and peptidoglycan hydrolases, two classes of phagosome antimicrobial defense mechanisms. In addition, the production of the critical virulence factor, listeriolysin O, was compromised by FA modulation, suggesting that FAs play a key role in virulence regulation. In summary, our results emphasize the significance of FA metabolism, not only in bacterial virulence regulation but also in membrane barrier function by providing resistance against host antimicrobial stress.     

The role of free fatty acids in mitochondrial energetic metabolism in winter wheat seedlings

The effect of fatty acids (FAs) (C12–C24) on the functioning of winter wheat (Triticum aestivum L.) mitochondria was studied. Such fatty acids as C12:0, C16:0, and C18:0 and unsaturated FAs, such as C18:1 (n-9 cis), C18:1 (n-12 cis), C18:2 (n-9, 12), (18:3, n-3), and C22:1 (n-9 cis) caused efficient uncoupling of oxidative phosphorylation in mitochondria, i.e., an increase in the nonphosphorylating respiration rate and a decrease in the respiratory control value. It was established that C16:0 had the strongest uncoupling effect among all saturated FAs, and C18:3, among unsaturated FAs. The uncoupling effect of saturated FAs is provided by the ADP/ATP-antiporter, while plant uncoupling proteins play an important role in the uncoupling effect of unsaturated FAs. In addition, unsaturated, as well as saturated FAs might serve as oxidative substrates for mitochondria. It was concluded that the role of FAs in energetic metabolism of winter wheat seedlings consisted of uncoupling of oxidative phosphorylation and of serving as substrates for oxidation.     

Membrane phase behavior of Escherichia coli during desiccation, rehydration, and growth recovery

The membrane lipid bilayer is one of the primary cellular components affected by variations in hydration level, which cause changes in lipid packing that may have detrimental effects on cell viability. In this study, Fourier transform infrared (FTIR) spectroscopy was used to quantify changes in the membrane phase behavior, as identified by membrane phase transition temperature (T_m), of Escherichia coli during desiccation and rehydration. Extensive cell desiccation (1 week at 20%-40% RH) resulted in an increase in T_m from 8.4 ± 1.7 °C (in undried control samples) to 16.5 ± 1.3 °C. Fatty acid methyl ester analysis (FAME) on desiccated samples showed an increase in the percent composition of saturated fatty acids (FAs) and a decrease in unsaturated FAs in comparison to undried control samples. However, rehydration of E. coli resulted in a gradual regression in T_m, which began approximately 1 day after initial rehydration and plateaued at 12.5 ± 1.8 °C after approximately 2 days of rehydration. FAME analysis during progressive rehydration revealed an increase in the membrane percent composition of unsaturated FAs and a decrease in saturated FAs. Cell recovery analysis during rehydration supported the previous findings that showed that E. coli enter a viable but non-culturable (VBNC) state during desiccation and recover following prolonged rehydration. In addition, we found that the delay period of approximately 1 day of rehydration prior to membrane reconfiguration (i.e. decrease in T_m and increase in membrane percent composition of unsaturated FAs) also preceded cell recovery. These results suggest that changes in membrane structure and state related to greater membrane fluidity may be associated with cell proliferation capabilities.     

Seasonal characteristics of surface water fulvic acids from Lake Biwa and Lake Tankai in Japan

Seasonal characteristics of surface water fulvic acids (FAs) isolated from Japanese clear-water lakes were investigated. Qualitative changes in Lake Biwa and Lake Tankai FAs were determined and compared. Although the relative molecular weights determined by high-performance size-exclusion chromatography did not change remarkably, the elemental compositions, E₆₀₀^1% E_{600}^{1\% } values and ¹H- and ¹³C-NMR spectral properties varied with the season. Both the H/C and N/C ratios for Lake Biwa FAs tended to be higher than those for Lake Tankai FAs, but O/C ratios were lower and decreased from spring to winter. The E₆₀₀^1% E_{600}^{1\% } values suggested that Lake Biwa FAs contained lower levels of unsaturated structures than Lake Tankai FAs, and the amounts of these structures increased in winter. The ¹H and ¹³C NMR spectra indicated that Lake Biwa FAs are richer in saturated aliphatic chains, especially in spring. Overall, Lake Biwa FAs exhibited clearer seasonal changes in these characteristics than Lake Tankai FAs, suggesting that the seasonal variation may depend on changes in aquatic microbial activities.     

Does fire drive fatty acid composition in seed coats of physically dormant species?

• Seed dormancy is the key driver regulating seed germination, hence is fundamental to the seedling recruitment life-history stage and population persistence. However, despite the importance of physical dormancy (PY) in timing post-fire germination, the mechanism driving dormancy-break within seed coats remains surprisingly unclear. We suggest that seed coat chemistry may play an important role in controlling dormancy in species with PY. In particular, seed coat fatty acids (FAs) are hydrophobic, and have melting points within the range of seed dormancy-breaking temperatures. Furthermore, melting points of saturated FAs increase with increasing carbon chain length. We investigated whether fire could influence seed coat FA profiles and discuss their potential influence on dormancy mechanisms.
• Seed coat FAs of 25 species within the Faboideae, from fire-prone and fire-free ecosystems, were identified and quantified through GC–MS. Fatty acid profiles were interpreted in the context of species habitat and interspecific variation.
• Fatty acid compositions were distinct between species from fire-prone and fire-free habitats. Fire-prone species tended to have longer saturated FA chains, a lower ratio of saturated to unsaturated FA, and a slightly higher relative amount of FAs compared to fire-free species.
• The specific FA composition of seed coats of fire-prone species indicated a potential role of FAs in dormancy mechanisms. Overall, the distinct FA composition between fire-prone and fire-free species suggests that chemistry of the seed coat may be under selection pressure in fire-prone ecosystems.

     

On the Physiological Role of Anaerobically Synthesized Lipids in <Emphasis Type="Italic">Oryza sativa</Emphasis> Seedlings

The objective of this work was to elucidate a possible adaptive role of lipid biosynthesis and unsaturated fatty acids (FAs), esterified to lipids, as terminal acceptors of electrons, alternative to molecular oxygen, in the shoots of rice seedlings (Oryza sativa L.) under conditions of strict anoxia. Biosynthesis of lipids and their accumulation, as well as the reduction of double bonds in unsaturated FAs, were studied by electron microscopic observation of the accumulation of lipid bodies in the cytoplasm and by the biochemical analysis of FAs in shoot lipids before and after anaerobic incubation of the shoots. The experiments were carried out with intact coleoptiles after 5 and 8 days of anaerobic germination of seeds (primary anoxia) and with detached shoots, preliminarily grown in air and then subjected to anoxia in the presence of 2% glucose for 48 h (secondary anoxia). In these experiments, lipid bodies did not accumulate in the cytoplasm under anoxic conditions. Lipid bodies appeared only during 48-h anaerobic incubation of detached coleoptiles in the absence of exogenous glucose, when mitochondria degraded. There was no change either in the double bond index of FAs, or in the qualitative and quantitative composition of FAs during shoot anaerobic incubation. We conclude that neither lipids synthesized under anaerobic conditions nor esterified unsaturated FAs are involved in plant adaptation to anaerobiosis as terminal acceptors of electrons, alternative to molecular oxygen. Lipid biosynthesis under anoxic conditions, which was demonstrated for anoxia-tolerant seedlings of Oryza sativa and Echinochloa phyllopogon in experiments with radioactive precursors, ¹⁴C-acetate and ³H-glycerol, is only the manifestation of a turnover of saturated FAs and various classes of lipids, which stabilizes cell membranes under adverse conditions of strict anoxia.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 540–548.Original Russian Text Copyright © 2005 by Generosova, Vartapetian.     

Changes in the fatty acid composition of symbiotic dinoflagellates from the hermatypic coral <Emphasis Type="Italic">Echinopora lamellosa</Emphasis> during adaptation to the irradiance level

The composition of fatty acids (FAs) of symbiotic dinoflagellates isolated from the hermatypic coral Echinoporal lamellosa adapted to the irradiance of 95, 30, 8, and 2% PAR was studied. Polar lipids and triacylglycerols (TAG) differed between them in FA composition. Polar lipids were enriched in unsaturated FAs, whereas TAG, in saturated FAs. Light exerted a substantial influence on the FA composition in both polar lipids and TAG. The elevation of irradiance resulted in the accumulation of 16:0 acid in both lipid groups and 16:1(n-7) acid in TAG. It seems likely that de novo synthesis of 16:0 acid occurred actively in the cells of symbiotic dinoflagellates in high light. Since these processes are energy-consuming ones, they utilize excessive energy. When light intensity declined, 18:4(n-3) and 20:5(n-3) acids accumulated in polar lipids, which was accompanied by the increase in the content of chlorophyll a in the cells of zooxanthellae, whereas the levels of 22:6(n-3) and 20:4(n-6) acids reduced. Although the relative content of particular FAs varied substantially in dependence of irradiance, the balance between the sum of saturated and unsaturated FAs changed insignificantly. We concluded that the role of photoadaptation could not be limited only to changes in the degree of lipid unsaturation and membrane fluidity. It is supposed that light-induced changes in the FA composition reflect the interrelation between photosynthesis and FA biosynthesis.     

Fatty-acid preference changes during development in Drosophila melanogaster

Fatty-acids (FAs) are required in the diet of many animals throughout their life. However, the mechanisms involved in the perception of and preferences for dietary saturated and unsaturated FAs (SFAs and UFAs, respectively) remain poorly explored, especially in insects. Using the model species Drosophila melanogaster, we measured the responses of wild-type larvae and adults to pure SFAs (14, 16, and 18 carbons) and UFAs (C18 with 1, 2, or 3 double-bonds). Individual and group behavioral tests revealed different preferences in larvae and adults. Larvae preferred UFAs whereas SFAs tended to induce both a strong aversion and a persistent aggregation behavior. Adults generally preferred SFAs, and laid more eggs and had a longer life span when ingesting these substances as compared to UFAs. Our data suggest that insects can discriminate long-chain dietary FAs. The developmental change in preference shown by this species might reflect functional variation in use of FAs or stage-specific nutritional requirements, and may be fundamental for insect use of these major dietary components.     

Effects of dietary fatty acids on the respiratory and cardiovascular physiology of fish

In animals, the composition of fatty acids (FAs) in body pools reflects dietary intake. This paper reviews evidence that the manipulation of tissue lipids of farmed fish, by feeding them different natural oils, can have significant effects on their respiratory and cardiovascular physiology. Sturgeon and eels with tissue lipids rich in highly unsaturated FAs of the n-3 series (n-3HUFAs, accumulated from dietary menhaden oil) had significantly lower metabolic rates than fish with tissues rich in saturated FAs (SFAs, from coconut oil), although they grew equally well. In sturgeon, the difference in metabolism influenced tolerance of hypoxia. Degrees of hypoxia that depressed oxygen uptake and spontaneous activity in fish rich in SFAs had no such effects on fish rich in n-3HUFAs. In the isolated sturgeon heart working in vitro, reduced oxygen supply depressed the performance of hearts with lipids rich in SFAs but not that of hearts rich in n-3HUFAs. In salmon fed diets with graded mixtures of menhaden and canola oils, there was no relationship between tissue n-3HUFA content (from menhaden oil) and any measured aspect of swimming performance, but a linear relationship between maximum sustainable swimming speed and muscle oleic acid levels (from canola oil). Such exploratory studies indicate that an animal's responses to its environment may be profoundly affected by the oils and FAs it consumes in its diet.     

Bioinformatic profiling of the transcriptional response of adult rat cardiomyocytes to distinct fatty acids

Diabetes mellitus, obesity, and dyslipidemia increase risk for cardiovascular disease, and expose the heart to high plasma fatty acid (FA) levels. Recent studies suggest that distinct FA species are cardiotoxic (e.g., palmitate), while others are cardioprotective (e.g., oleate), although the molecular mechanisms mediating these observations are unclear. The purpose of the present study was to investigate the differential effects of distinct FA species (varying carbon length and degree of saturation) on adult rat cardiomyocyte (ARC) gene expression. ARCs were initially challenged with 0.4 mM octanoate (8:0), palmitate (16:0), stearate (18:0), oleate (18:1), or linoleate (18:2) for 24 h. Microarray analysis revealed differential regulation of gene expression by the distinct FAs; the order regarding the number of genes whose expression was influenced by a specific FA was octanoate (1,188) > stearate (740) > palmitate (590) > oleate (83) > linoleate (65). In general, cardioprotective FAs (e.g., oleate) increased expression of genes promoting FA oxidation to a greater extent than cardiotoxic FAs (e.g., palmitate), whereas the latter induced markers of endoplasmic reticulum and oxidative stress. Subsequent RT-PCR analysis revealed distinct time- and concentration-dependent effects of these FA species, in a gene-specific manner. For example, stearate- and palmitate-mediated ucp3 induction tended to be transient (i.e., initial high induction, followed by subsequent repression), whereas oleate-mediated induction was sustained. These findings may provide insight into why diets high in unsaturated FAs (e.g., oleate) are cardioprotective, whereas diets rich in saturated FAs (e.g., palmitate) are not.     

A new strain of Butyrivibrio fibrisolvens that has high ability to isomerize linoleic acid to conjugated linoleic acid

A new strain of Butyrivibrio fibrisolvens (TH1) that has high potential to produce conjugated linoleic acid (CLA) was isolated. Strain TH1 had higher LA isomerase (LA-I) activity, and was much more tolerant to linoleic acid (LA) than other strains examined. However, high CLA reductase (CLA-R) activity resulted in the temporary accumulation of CLA and subsequent conversion to trans-vaccenic acid (t-VA). When LA was added to growing TH1 cultures in a solution with dimethylsulfoxide (LA/DMSO), CLA produced was greater than when LA was added in a mixture with bovine serum albumin (BSA). The number of viable cells decreased upon addition of LA/DMSO, but then increased as the CLA decreased upon its conversion to t-VA. This result suggests that B. fibrisolvens can resume growing by the removal of CLA from the cells. Most CLA was released from B. fibrisolvens cells by gentle washing with BSA, suggesting that CLA bound to the cells might be removed in the rumen and large intestine. Thus, CLA production by B. fibrisolvens in the digestive tract could be increased by a reduction in CLA-R activity without accompanying an overall decrease in the cell number of B. fibrisolvens. Fatty acids (FAs) with 18 carbon backbone inducted LA-I activity, whereas unsaturated FAs induced CLA-R activity, suggesting that FAs stimulate the synthesis of LA-I and CLA-R. Providing a diet with a low ratio of unsaturated to saturated FAs may favor CLA production.     

EFFECTS OF VARIATION IN TEMPERATURE. II. ON THE FATTY ACID COMPOSITION OF EIGHT SPECIES OF MARINE PHYTOPLANKTON1

Eight species of marine phytoplankton showed significant variation in the relative amount of some fatty acids (FAs) in response to variation in temperature. Large changes in relative amounts of certain FAs occurred as a result of a 15° C change in growth temperature. For example, 14:0 increased from ?4% of total FAs at 10° C to > 20% at 25° C for Chaetoceros simplex and Isochrysis aff. galbana but decreased for Phaeodactylum tricornutum. The percentage of the polyunsaturated fatty acid (PUFA) 16:ω1 was consistently greater at 10° C than at 25° C, and the converse was usually true for 16: 4ω3. Calculated over all eight species, there was a modest but significant inverse relationship between the percentage of PUFAs and temperature. Only for Thalassiosira pseudonana was the percentage of either of the PUFAs and nutritionally essential fatty acids (EFAs) also an inverse function of temperature. For T. pseudonana, the percentage of the EFA 22:6ω3 decreased linearly with increasing temperature over the range from 10 to 25° C. For three species, the ratio of unsaturated/saturated FAs was correlated with growth rate when growth rate was controlled by variation in irradiance and temperature. Only for Thalassiosira pseudonana was the ratio of unsaturated/saturated FAs also an inverse function of temperature alone.