Role Of Membrane Fluidity Research Articles

Gene family expansions in Antarctic winged midge as a strategy for adaptation to cold environments

Parochlus steinenii is the only flying insect native to Antarctica. To elucidate the molecular mechanisms underlying its adaptation to cold environments, we conducted comparative genomic analyses of P. steinenii and closely related lineages. In an analysis of gene family evolution, 68 rapidly evolving gene families, involved in the innate immune system, unfolded protein response, DNA packaging, protein folding, and unsaturated fatty acid biosynthesis were detected. Some gene families were P. steinenii-specific and showed phylogenetic instability. Acyl-CoA delta desaturase and heat shock cognate protein 70 (Hsc70) were representative gene families, showing signatures of positive selection with multiple gene duplication events. Acyl-CoA delta desaturases may play pivotal roles in membrane fluidity, and expanded Hsc70 genes may function as chaperones or thermal sensors in cold environments. These findings suggest that multiple gene family expansions contributed to the adaptation of P. steinenii to cold environments.

Preparation of nanoliposomes by microfluidic mixing in herring-bone channel and the role of membrane fluidity in liposomes formation

Introduction of microfluidic mixing technique opens a new door for preparation of the liposomes and lipid-based nanoparticles by on-chip technologies that are applicable in a laboratory and industrial scale. This study demonstrates the role of phospholipid bilayer fragment as the key intermediate in the mechanism of liposome formation by microfluidic mixing in the channel with “herring-bone” geometry used with the instrument NanoAssemblr. The fluidity of the lipid bilayer expressed as fluorescence anisotropy of the probe N,N,N-Trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl) was found to be the basic parameter affecting the final size of formed liposomes prepared by microfluidic mixing of an ethanol solution of lipids and water phase. Both saturated and unsaturated lipids together with various content of cholesterol were used for liposome preparation and it was demonstrated, that an increase in fluidity results in a decrease of liposome size as analyzed by DLS. Gadolinium chelating lipids were used to visualize the fine structure of liposomes and bilayer fragments by CryoTEM. Experimental data and theoretical calculations are in good accordance with the theory of lipid disc micelle vesiculation.

The membrane lipid metabolism in horticultural products suffering chilling injury

AbstractHorticultural commodities suffer chilling injury following exposure to extremely low temperatures, which results in visible symptoms and considerable quality loss. Therefore, it is of significance to understand the mechanism of this physiological disorder and to develop effective strategies to control it. Chilling stress causes alteration in structure and function of the plasma membrane, which is assumed to be the primary event in response to cold stress. During this process, the membrane lipid metabolism plays a pivotal role in membrane fluidity and stability. In this review, we summarized the possible roles of membrane lipid metabolism in the development of chilling injury, having the potential for developing effective strategies to alleviate chilling injury in horticultural products under refrigerated storage in practice.

Involvement of fatty acids in the response to high CO2 and low temperature in harvested strawberries

Fatty acids (FAs) play important roles in membrane fluidity, energy status and the production of specific FA-dependent esters. However, little is known about the modifications in FAs induced by high CO2 that can improve fruit quality and prevent the disorders associated with storage at low temperature. For this purpose, total, free and esterified FAs in neutral and polar lipid fractions were characterized and quantified and their relationship with straight-chain esters was examined in strawberries treated with high doses of CO2 and different times of exposure during early storage at 0 °C. In strawberries stored without added CO2 (T1), storage at 0 °C led to an imbalance in the saturated/unsaturated ratio of polar lipids, mainly due to the decrease in the amount of saturated fatty acids (SFA). In addition, a decrease in the amount of free polyunsaturated fatty acids (PUFA) linked to a prevalence of butanoates and hexanoates esterified to long alcohols was observed. A strong negative correlation (P ≤ 0.01; r ≥ 0.7) between butanoate esters and free PUFA was quantified. In contrast, the application of 2 d 20 kPa CO2 treatment (T2), increased the amount of PUFA from the neutral and polar fractions, with a preference for α-linolenic acid (18:3n3) which results in a rise in the 18:3/18:2 ratio, and which can confer membrane stability and fluidity. Furthermore, our results also showed a strong positive correlation (P ≤ 0.01; r ≥ 0.75) between α-linolenic acid (18:3n3) of polar lipids and some ethyl esters that contribute mostly to the aroma in strawberries. However, 3 d 40 kPa CO2 treatment (T4) depleted the content of FAs from all the lipid fractions in association with deficit ATP levels and an increased lipid peroxidation. These results suggest an active lipid breakdown which could play a causal role in the reported increased leakage of cellular water into intercellular air spaces in stressed-CO2 fruit. Taken together, our results provide new insights into the beneficial effect of 2 d 20 kPa CO2 treatment at 0 °C on the enhancement of PUFA in the polar lipid fraction and on the emission of esters other than ethyl acetate, which could improve membrane fluidity and could contribute to enriching aroma in strawberries.

Higher Lipophilic Index Indicates Higher Risk of Coronary Heart Disease in Postmenopausal Women

Fatty acids (FAs) are essential components of cell membranes and play an integral role in membrane fluidity. The lipophilic index [LI, defined as the sum of the products between FA levels and melting points (°C), divided by the total amount of FA: [Formula: see text]] is thought to reflect membrane and lipoprotein fluidity and may be associated with the risk of coronary heart disease (CHD). Therefore, we examined the associations of dietary and plasma phospholipid (PL) LI with CHD risk among postmenopausal women. We determined dietary LI for the cohort with completed baseline food frequency questionnaires and free of prevalent cardiovascular diseases in the Women's Health Initiative (WHI) observational study (N=85,563). We additionally determined plasma PL LI in a matched case-control study (N=2428) nested within the WHI observational cohort study. Cox proportional hazard regression and multivariable conditional logistic regression were used to calculate HRs/ORs for CHD risk between quartiles of LI after adjusting for potential sources of confounding and selection bias. Higher dietary LI in the cohort study and plasma PL LI in the case-control study were significantly associated with increased risk of CHD: HR=1.18 (95% CI 1.07-1.31, P for trend <0.01) and OR=1.76 (95% CI 1.33-2.33, P for trend <0.01) comparing extreme quartiles and adjusting for potential confounders. These associations still persisted after adjusting for the polyunsaturated to saturated fat ratio. Our study indicated that higher LI based on either dietary or plasma measurements, representing higher FA lipophilicity, was associated with elevated risk of CHD among postmenopausal women.

Membrane fluidity is a driving force for recoverin myristoyl immobilization in zwitterionic lipids

Recoverin is the only protein for which the phenomenon of calcium-myristoyl switch has been demonstrated without ambiguity. It is located in rod disk membranes where the highest content in polyunsaturated lipid acyl chains can be found. However, although essential to better understand the inactivation of the phototransduction process, the role of membrane fluidity on recoverin recruitment is unclear. We have therefore investigated the immobilization of the recoverin myristoyl moiety in the presence of phosphocholine bilayers using 2H solid-state NMR spectroscopy. Several lipids with different acyl chains were selected to investigate model membranes characterized by different fluidity. Immobilization of the recoverin myristoyl moiety was successfully observed but only in the presence of calcium and in specific lipid disordered states, showing that an optimal fluidity is required for recoverin immobilization.

Abstract MP38: Plasma Lipophilic Index and Risk of Coronary Heart Disease in Postmenopausal Women

Introduction: Fatty acids (FAs) are essential components of cell membranes and play an integral role in membrane fluidity. The lipophilic index (LI, defined as the sum of the products between FA percentage and melting points (°C) of each FA, divided by the total percentage of FAs) is a novel index that captures the overall FA profile and reflects lipoprotein fluidity. Limited studies have evaluated the relationship between plasma LI and CHD risk, and none has assessed this association among postmenopausal women. Hypothesis: Higher plasma LI is associated with increased CHD risk among postmenopausal women. Methods: In a nested case-control study in Women’s Health Initiative Observational Study, we measured levels of plasma phospholipid FAs, expressed as molar percentage (mol%), in 1214 matched CHD cases (including myocardial infarction and coronary death) and controls. Multivariate conditional logistic regression was used to calculate ORs for CHD risk between each quartiles (based on controls) of LI after adjusting for confounders. Results: The mean age of the women was 67.8±6.8 years, average BMI was 27.6±6.0, 89.5% were White, 6.6% were current smokers, 41.2% were hypertensive, and 15.2% had dyslipidemia. The median plasma LI among cases and controls were 22.5 and 22.1, respectively. Palmitic acid (16:0) and stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2), and docosahexaenoic acid (22:6) were the most common saturated, monounsaturated, n-6 and n-3 polyunsaturated FAs, respectively. The association between quartiles of LI and CHD risk are shown in Table below. After multivariate adjustment in the parsimonious model, plasma LI was significantly associated with an increased risk of CHD: OR=1.61 (95% CI 1.25-2.07, P for trend&lt;0.01) comparing extreme quartiles. This association was attenuated to 1.57 (1.22 - 2.03, P for trend&lt;0.01) in the fully adjusted model. Conclusion: Our study indicated that higher plasma LI, which represents lower FA fluidity, was associated with higher risk of CHD among postmenopausal women.

Fatty acid profiles and desaturase-encoding genes are different in thermo- and psychrotolerant strains of the Bacillus cereus Group.

BackgroundThe Bacillus cereus Group consists of closely-related bacteria, including pathogenic or harmless strains, and whose species can be positioned along the seven phylogenetic groups of Guinebretière et al. (I–VII). They exhibit different growth-temperature ranges, through thermotolerant to psychrotolerant thermotypes. Among these, B. cytotoxicus is an atypical thermotolerant and food-poisoning agent affiliated to group VII whose thermotolerance contrasts with the mesophilic and psychrotolerant thermotypes associated to the remaining groups I–VI. To understand the role of fatty acid (FA) composition in these variable thermotypes (i.e. growth behavior vs temperatures), we report specific features differentiating the FA pattern of B. cytotoxicus (group VII) from its counterparts (groups I–VI).FindingsThe FA pattern of thermotolerant group VII (B. cytotoxicus) displayed several specific features. Most notably, we identified a high ratio of the branched-chain FAs iso-C15/iso-C13 (i15/i13) and the absence of the unsaturated FA (UFA) C16:1(5) consistent with the absence of ∆5 desaturase DesA. Conversely, phylogenetic groups II–VI were characterized by lower i15/i13 ratios and variable proportions of C16:1(5) depending on thermotype, and presence of the DesA desaturase. In mesophilic group I, thermotype seemed to be related to an atypically high amount of C16:1(10) that may involve ∆10 desaturase DesB.ConclusionThe levels of i15/i13 ratio, C16:1(5) and C16:1(10) UFAs were related to growth temperature variations recorded between thermotypes and/or phylogenetic groups. These FA are likely to play a role in membrane fluidity and may account for the differences in temperature tolerance observed in B. cereus Group strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-015-1288-4) contains supplementary material, which is available to authorized users.

Genetic Engineering of Membrane Lipid Composition in E. Coli

Understanding the functional basis for cell membrane composition is a challenge because of the scarcity of available tools for modulating lipid composition in vivo. Here I introduce a synthetic biology approach for studying the effects of lipid composition in the model bacterium Escherichia coli. This approach involves knocking out lipid synthesis genes from the chromosome, thus freeing them from endogenous regulation pathways, and reintroducing them under the control of plasmid-based titratable expression promoters. Using this strategy, I have developed a set of strains in which several parameters of lipid composition - acyl unsaturation and cyclopropane content, cardiolipin levels - can be systematically modulated by varying the concentration of inducer in the culture. In the case of acyl unsaturation, this has allowed me to directly test the phenotypic effects of varying membrane fluidity, which is otherwise homeostatically maintained via transcriptional regulation of unsaturated fatty acid synthesis. These experiments suggest a novel role for membrane fluidity as a physical regulator of central metabolism.

NK cell phenotypic and functional heterogeneities and molecular mechanisms of cytotoxicity.

Natural killer (NK) cells were discovered four decades ago, independently, by the Kiessling and Herberman groups. Since then, significant advances have accrued regarding the functional and molecular properties of NK cells as well as their clinical relevance. The important feature of NK cells is their inability to kill normal cells, while they are highly cytotoxic for infected or transformed cells. This discrimination has been largely resolved by the discovery of both activating and inhibitory receptors on NK cells and corresponding ligands on target cells. This review focuses briefly on several issues related to NK cells: (1) the phenotypic properties of NK cells, (2) the heterogeneity of NK cell activities, (3) the determination of three major NK subsets (Free, Binder, and Killer), (4) the maturation and activation of NK subsets, (5) the response of NK cells to various cytokines, (6) the target-induced inactivation and cell death of NK cells, (7) the multiple mechanisms of cell-mediated cytotoxicity, (8) the characterization of NK cytotoxic factors (NKCF), and (9) the role of membrane fluidity in cytotoxicity. These subjects are described chronologically beginning shortly after the discovery of NK cells as a result of Ron Herberman's leadership, and I am gratefully indebted to him.

The effect of alcohols on red blood cell mechanical properties and membrane fluidity depends on their molecular size.

The role of membrane fluidity in determining red blood cell (RBC) deformability has been suggested by a number of studies. The present investigation evaluated alterations of RBC membrane fluidity, deformability and stability in the presence of four linear alcohols (methanol, ethanol, propanol and butanol) using ektacytometry and electron paramagnetic resonance (EPR) spectroscopy. All alcohols had a biphasic effect on deformability such that it increased then decreased with increasing concentration; the critical concentration for reversal was an inverse function of molecular size. EPR results showed biphasic changes of near-surface fluidity (i.e., increase then decrease) and a decreased fluidity of the lipid core; rank order of effectiveness was butanol > propanol > ethanol > methanol, with a significant correlation between near-surface fluidity and deformability (r = 0.697; p<0.01). The presence of alcohol enhanced the impairment of RBC deformability caused by subjecting cells to 100 Pa shear stress for 300 s, with significant differences from control being observed at higher concentrations of all four alcohols. The level of hemolysis was dependent on molecular size and concentration, whereas echinocytic shape transformation (i.e., biconcave disc to crenated morphology) was observed only for ethanol and propanol. These results are in accordance with available data obtained on model membranes. They document the presence of mechanical links between RBC deformability and near-surface membrane fluidity, chain length-dependence of the ability of alcohols to alter RBC mechanical behavior, and the biphasic response of RBC deformability and near-surface membrane fluidity to increasing alcohol concentrations.

Optimizing conditions for treating goat semen with cholesterol-loaded cyclodextrins prior to freezing to improve cryosurvival

The fertility of goat sperm is highly variable and new methods for improving sperm cryosurvival are needed. Cholesterol plays important roles in membrane fluidity, cold shock sensitivity and cryodamage, and treating sperm from cold-shock sensitive species with cholesterol-loaded cyclodextrins (CLC) prior to cryopreservation enhances sperm cryosurvival. The aim of this study was to develop a CLC-treatment to optimize goat sperm cryopreservation. A total of 45 ejaculates coming from eleven adult Murciano-Granadina bucks were used and three experiments were conducted to determine: (1) the optimal CLC concentration to treat goat sperm; (2) the optimal time to treat the sperm (before or after seminal plasma removal); and (3) optimal freezing diluent (either of two Tris-citrate diluents containing 2% or 20% egg yolk and 4% glycerol or a skim milk diluent with 7% glycerol) to cryopreserve goat sperm. Goat sperm cryosurvival rates were greatest when they were treated with 1mg CLC/120×106sperm prior to freezing. The benefit was also greatest if the sperm were treated with CLC after seminal plasma removal. Finally, CLC treatment improved sperm cryosurvival rates for sperm frozen in all three diluents, however, CLC treatment was most effective for sperm frozen in egg-yolk diluents. In conclusion, treating goat sperm, with CLC prior to cryopreservation, improved sperm cryosurvival rates. In addition, CLC treatment was effective for all freezing diluents tested, making this technology practical for the industry using current cryopreservation techniques. Nevertheless, additional studies should be conducted to determine how CLC might affect sperm functionality and fertilizing ability.

Anti-inflammatory/anti-amyloidogenic effects of plasmalogens in lipopolysaccharide-induced neuroinflammation in adult mice

BackgroundNeuroinflammation involves the activation of glial cells in neurodegenerative diseases such as Alzheimer’s disease (AD). Plasmalogens (Pls) are glycerophospholipids constituting cellular membranes and play significant roles in membrane fluidity and cellular processes such as vesicular fusion and signal transduction.MethodsIn this study the preventive effects of Pls on systemic lipopolysaccharide (LPS)-induced neuroinflammation were investigated using immunohistochemistry, real-time PCR methods and analysis of brain glycerophospholipid levels in adult mice.ResultsIntraperitoneal (i.p.) injections of LPS (250 μg/kg) for seven days resulted in increases in the number of Iba-1-positive microglia and glial fibrillary acidic protein (GFAP)-positive astrocytes in the prefrontal cortex (PFC) and hippocampus accompanied by the enhanced expression of IL-1β and TNF-α mRNAs. In addition, β-amyloid (Aβ3–16)-positive neurons appeared in the PFC and hippocampus of LPS-injected animals. The co-administration of Pls (i.p., 20 mg/kg) after daily LPS injections significantly attenuated both the activation of glial cells and the accumulation of Aβ proteins. Finally, the amount of Pls in the PFC and hippocampus decreased following the LPS injections and this reduction was suppressed by co-treatment with Pls.ConclusionsThese findings suggest that Pls have anti-neuroinflammatory and anti-amyloidogenic effects, thereby indicating the preventive or therapeutic application of Pls against AD.

Effects of plasmalogens on systemic lipopolysaccharide‐induced glial activation and β‐amyloid accumulation in adult mice

Neuroinflammation essentially involves an activation of glial cells as the cause/effect of neurodegenerative diseases such as Alzheimer's disease (AD). Plasmalogens (Pls) are glycerophospholipids constituting cellular membranes and play significant roles in membrane fluidity and cellular processes like vesicular fusion and signal transduction. Intraperitoneal (i.p.) injection of lipopolysaccharide (LPS, 250 μg/kg) for 7 days resulted in the morphological changes and increase in number of Iba-1(+) microglia showing neuroinflammation in the adult mouse hippocampus. The LPS-induced activation of glial cells was significantly attenuated by i.p. pretreatment with Pls dissolved in corn oil. In addition, systemic injection of LPS induced Aβ(1-16) (+) neurons in the hippocampus were also abolished by application of Pls. Finally, contents of Pls in the hippocampus decreased after LPS injection, and the reduction was suppressed by administration of Pls. These findings suggest an antiamyloidogenic effect of Pls, implicating a possible therapeutic application of Pls against AD.

Synthesis and production of unsaturated and polyunsaturated fatty acids in yeast: current state and perspectives

Recently, many genes involved in the formation of unsaturated and polyunsaturated fatty acids (PUFAs) were isolated. In most cases, their activities were confirmed by expressing them in the well-studied model organism Saccharomyces cerevisiae because its fatty acid compositions are very simple and it does not contain PUFAs. Taking advantage of its genetic tractability and increasing wealth of accessible data, many groups are attempting to produce various useful fatty acids in the model yeasts, mainly in S. cerevisiae. This review describes typical such examples including a very recent study on the expression of a fatty acid hydroxylase gene in fission yeast Schizosaccharomyces pombe. Furthermore, the impact of the genetically engineered alteration of fatty acid composition on the stress tolerance is presented because unsaturated fatty acids have crucial roles in membrane fluidity and signaling processes. Lastly, recent attempts at increasing lipid content in S. cerevisiae are discussed.

Vascular endothelial wound closure under shear stress: role of membrane fluidity and flow-sensitive ion channels

Sufficiently rapid healing of vascular endothelium following injury is essential for preventing further pathological complications. Recent work suggests that fluid dynamic shear stress regulates endothelial cell (EC) wound closure. Changes in membrane fluidity and activation of flow-sensitive ion channels are among the most rapid endothelial responses to flow and are thought to play an important role in EC responsiveness to shear stress. The goal of the present study was to probe the role of these responses in bovine aortic EC (BAEC) wound closure under shear stress. BAEC monolayers were mechanically wounded and subsequently subjected to either "high" (19 dyn/cm(2)) or "low" (3 dyn/cm(2)) levels of steady shear stress. Image analysis was used to quantify cell migration and spreading under both flow and static control conditions. Our results demonstrate that, under static conditions, BAECs along both wound edges migrate at similar velocities to cover the wounded area. Low shear stress leads to significantly lower BAEC migration velocities, whereas high shear stress results in cells along the upstream edge of the wound migrating significantly more rapidly than those downstream. The data also show that reducing BAEC membrane fluidity by enriching the cell membrane with exogenous cholesterol significantly slows down both cell spreading and migration under flow and hence retards wound closure. Blocking flow-sensitive K and Cl channels reduces cell spreading under flow but has no impact on cell migration. These findings provide evidence that membrane fluidity and flow-sensitive ion channels play distinct roles in regulating EC wound closure under flow.

Role for Membrane Fluidity in Ethanol-Induced Oxidative Stress of Primary Rat Hepatocytes

The relationship between bulk membrane fluidizing effect of ethanol and its toxicity due to oxidative stress is still unknown. To elucidate this issue, membrane fluidity of primary rat hepatocytes was studied by measuring order parameter after inhibition of ethanol-induced oxidative stress. We showed that pretreating cells with either 4-methyl-pyrazole (to inhibit ethanol metabolism), thiourea [a reactive oxygen species (ROS) scavenger], or vitamin E (a free radical chain-breaking antioxidant) prevented the ethanol-induced increase in membrane fluidity, thus suggesting that ethanol metabolism and ROS formation were involved in this elevation. The effects of membrane stabilizing agents (ursodeoxycholic acid or ganglioside GM1), shown to prevent fluidification, next pointed to a role for this increase in membrane fluidity in the development of ethanol-induced oxidative stress. Indeed, ROS production, lipid peroxidation, and cell death were all inhibited by these agents. In contrast, the fluidizing compounds Tween 20 or 2-(2-methoxyethoxy) ethyl 8-(cis-2-n-octylcyclopropyl) octanoate, which increased the membrane fluidizing effect of ethanol, enhanced the related oxidative stress. Using electron paramagnetic resonance to determine low molecular weight iron, we finally demonstrated that membrane fluidity influence proceeded through an increase in low molecular weight iron to enhance oxidative stress. In conclusion, the present findings clearly highlight the pivotal role of membrane fluidity in ethanol-induced oxidative stress and the potential therapeutic effect of membrane stabilizing compounds.

Cholesterol and the activity of bacterial toxins

Cholesterol may affect the activity of microbial toxins in a direct, specific way, or it may exert indirect effects because of its role in membrane fluidity, membrane line tension, and in the stabilization of rafts in the cytoplasmic membrane. The thiol-activated toxins of gram-positive bacteria, and the cytolysin of Vibrio cholerae are presented as examples of specific toxin-cholesterol interaction. Several mechanisms of indirect effects of cholesterol are discussed using examples such as Staphylococcus aureusα-hemolysin, aerolysin, and diphtheria toxin.

Cholesterol and the activity of bacterial toxins

Cholesterol may affect the activity of microbial toxins in a direct, specific way, or it may exert indirect effects because of its role in membrane fluidity, membrane line tension, and in the stabilization of rafts in the cytoplasmic membrane. The thiol-activated toxins of gram-positive bacteria, and the cytolysin of Vibrio cholerae are presented as examples of specific toxin–cholesterol interaction. Several mechanisms of indirect effects of cholesterol are discussed using examples such as Staphylococcus aureus α-hemolysin, aerolysin, and diphtheria toxin.

The fatty acid content and composition of spinal cord and brain of rabbits receiving intrathecal ketamine

AbstractThe present study investigates the effects of intrathecal ketamine on the concentration and composition of fatty acids in blood-brain barrier (BBB) tissues of New Zealand male rabbits. Ketamine is a drug that produces analgesia following intrathecal injection. It is very well known that fatty acids (FAs) play an important role in membrane fluidity of BBB tissues, which control the transportation of substances into brain. The total cellular fatty acids in brain and three spinal cord sections (cervical, thoracic, lumbar) of rabbits with or without drug administration were determined by gas chromatography using the Sherlock software (Microbial ID, Newark, DE) with the eukary database of fatty acid methyl ester (FAME) profiles for eukaryotic cells (Sherlock version 4.0). The fatty acid profiles of three different spinal cord sections were quite similar, but different than those of brain tissues. There were 23–25 fatty acids in spinal cord sections and 11 in the brain tissues of control animals compare...