Altered Membrane Fluidity Research Articles

The Wnt1 ligand/Frizzled 3 receptor system plays a regulatory role in the achievement of the 'in vitro' capacitation and subsequent 'in vitro' acrosome exocytosis of porcine spermatozoa.

The aim of this work was to determine the existence of a functional Wnt/β-catenin signaling pathway in boar spermatozoa, which would be linked with the already well-known GSK-3 signaling pathway. This was first confirmed by detecting the presence of the specific Frizzled 3 receptor in these cells. Furthermore, this signaling pathway was activated in boar spermatozoa subjected to 'in vitro' capacitation (IVC) and subsequent progesterone-induced 'in vitro' acrosome exocytosis (IVAE) by incubating cells with separate concentrations of Wnt1 ligand, the Wnt/β-catenin signaling pathway-specific effector. Incubation with the Wnt1 ligand increased the rhythm of the time-dependent reduction in sperm viability during the achievement of both IVC and IVAE. This finding was concomitant with an increase in the percentage of spermatozoa with altered membrane fluidity and permeability determined through both merocyanine-540 and YO-PRO-1 stains. While the Wnt1 ligand did not affect total sperm motility during the achievement of the IVC, it induced a fast and transient increase in the overall motility patterns in spermatozoa subjected to IVAE. This IVAE-linked action was related to a decrease in the percentage of cells with high mitochondrial membrane potential and an increase in the percentage of cells with high intracellular Fluo-3-marked Ca(2+) content. In conclusion, our results suggest that the Wnt1 ligand-modulated Wnt/β-catenin signaling pathway plays a relevant role in the modulation of both IVC and subsequent, progesterone-induced IVAE. Furthermore, our data indicate that the transduction pathways by which the Wnt1 ligand acts on IVC and IVAE are different, and that the Wnt/β-catenin pathway is independent from GSK-3 activity in the achievement of IVC.

Cross matching observations on toxicological and clinical data for the assessment of tolerability and safety of Ginkgo biloba leaf extract.

Ginkgo biloba is one of the most widely used herbal remedies in Europe and the US. It may be purchased in different types of formulations, but most of the clinical studies have been performed with the controlled G. biloba extract EGb761(®). Indications include Alzheimers disease, cardiovascular disease, dementia, memory loss, and cerebral ischemia. The pharmacological modes of action cover antioxidant effects, radical scavenging, inhibition of platelet activating factor, alterations in membrane fluidity (signal transduction), and inhibition of glucocorticoid synthesis. Due to the widespread and long-term use of G. biloba - about a million doses of EGb761(®) are sold per day - tolerability and safety are a crucial issue. Based on broad and long-term clinical use of G. biloba extracts, it is regarded as well tolerated in man. Cross matching, a tool we introduced, combines different fields of knowledge and types of data to a consolidated result. In this article, we combine toxicological and clinical data and utilize other sources of information to assess tolerability and safety of G. biloba. It is well known that because of biological differences between animals and man or even between animal species, animal experiments do not necessarily mimic the effects in humans. Therefore, for adequate risk assessment, the relevance of non-clinical toxicological findings should be correlated with human data. The cross matching of toxicological data and results from clinical studies is possible because many toxicological and clinical studies are available on G. biloba. We give an in depth analysis of the modes of action in animals and describe toxicological studies with regard to metabolism, pharmacokinetics, genotoxicity, as well as carcinogenicity (e.g., the Technical Report TR 578 of the US National Toxicology Program). In addition, 75 clinical trials with high methodological quality are summarized. They included a total of 7115 patients treated with G. biloba. Based on this extensive amount of information, the broad variety of investigations, and their accordance we conclude that G. biloba extract is well tolerated and safe for humans.

Desensitization of DMSO‐treated platelets to common agonists via membrane modulation (598.5)

Thrombosis and thromboembolic complications continue to plague mechanical circulatory support devices (MCS). Biochemical pathways involving prostaglandin and ADP are known targets for aspirin and thienopyridines to modulate platelet activation and aggregation, respectively. However, a recent study in our lab has demonstrated the limited ability of these agents to alter shear‐mediated platelet activation. Therefore, this study examines the impact of altering the platelet membrane fluidity by treatment with dimethyl sulfoxide (DMSO) and its inherent effects on platelet activation by standard agonists. DMSO was chosen due to its previously reported antithrombotic properties. Although it was reported that DMSO inhibits platelet activation through cyclooxygenase‐1 inhibition, we believe that the alteration in membrane fluidity also plays a key role in desensitization.Human venous blood was collected from healthy volunteers in citrated buffer with UA‐IRB consent. Platelet rich plasma (PRP) was isolated and treated with DMSO ranging from 0.95%‐60% (v/v). Light transmission aggregometry (LTA) was performed to detect platelet desensitization using arachidonic acid, ADP, collagen, epinephrine, and ristocetin. Platelets were fixed and visualized at the varying DMSO treatments under scanning electron microscopy (SEM).Collagen and epinephrine had limited effect on PRP aggregation ranging from 0.95% to 10% of DMSO. ADP and arachidonic acid showed a clear inhibition at 10% and 5%, respectively. DMSO had no effect on ristocetin‐induced platelet aggregation. SEM of platelets at 5% and 10% showed significant reduction in filopodia.DMSO altered platelet membrane fluidity and desensitized their aggregability from certain common agonists; thus reflecting the role of DMSO in some biochemical pathways that inhibit platelets. Next, we will measure the platelet membrane fluidity using TMA‐DPH and DPH fluorescence anisotropy in the presence of DMSO to further validate our results.

Studying the effect of Dimebon and NT-1505 on microviscosity of mice brain synaptosomal membranes in vivo by EPR spin labeling method

In this work membrane fluidity alterations in synaptosomes, isolated from mice brain tissue, at chronic administration of neuroprotectors Dimebon and NT-1505 in vivo were studied. Membrane microviscosity was measured by electron paramagnetic resonance spin labeling of 2,2,6,6-tetramet-hyl-4-capryloyl-oxylpiperidine-l-oxyl (lipid probe) and 5,6-benzo-2,2,6,6-tetramethyl-1,2,3,4-tetrahydro-gamma-carboline-3-oxyl (near protein probe). It was shown that the neuroprotectors Dimebon and NT-1505 affect a membrane structure. Despite the difference in membrane structures, fluidity of the lipid bilayer in time returned to control values.

Elucidation of Cellular Mechanisms Involved in Experimental Paromomycin Resistance in Leishmania donovani

Leishmania donovani is the causative agent of the potentially fatal disease visceral leishmaniasis (VL). Chemotherapeutic options available to treat VL are limited and often face parasite resistance, inconsistent efficacy, and toxic side effects. Paromomycin (PMM) was recently introduced to treat VL as a monotherapy and in combination therapy. It is vital to understand the mechanisms of PMM resistance to safeguard the drug. In the present study, we utilized experimentally generated PMM-resistant L. donovani to elucidate the mechanisms of resistance and parasite biology. We found increased membrane fluidity accompanied by decreased intracellular drug accumulation in the PMM-resistant parasites. There were marked increases in gene expression of ATP-binding cassette (ABC) transporters (MDR1 and MRPA) and protein phosphatase 2A that evince increased drug efflux. Further, evaluation of parasite tolerance toward host leishmanicidal mechanisms revealed PMM-resistant parasites as being more tolerant to nitrosative stress at the promastigote and amastigote stages. The PMM-resistant parasites also predicted a better survival capacity, as indicated by resistance to complement-mediated lysis and increased stimulation of host interleukin-10 (IL-10) expression. The susceptibilities of PMM-resistant isolates to other antileishmanial agents (sodium antimony gluconate and miltefosine) remained unchanged. The data implicated the roles of altered membrane fluidity, decreased drug accumulation, increased expression of ABC transporters, and greater tolerance of parasites to host defense mechanisms in conferring PMM resistance in Leishmania.

Smokers as blood donors: what do their red blood cell membranes tell us?

1RBC membrane lipids are rich in polyunsaturated fatty acids; therefore, the exposure to toxins and peroxidants causes hemolysis, as well as loss of membrane stability. 1 In this research, we studied the ultrastructure of RBC membranes of 10 smokers using scanning electron microscopy (SEM) at 1 kV, to determine if this altered membrane fluidity can be visualized. Hundreds of RBCs from the 10 smokers were compared to our RBC database of thousands of micrographs from healthy nonsmoker individuals. Figure A shows a typical healthy nonsmoker’s RBC (scale, 1 mm), while Fig. B shows an RBC from a smoker (scale, 1 mm), and Fig. C is a high machine magnification (100,000 ¥) of the smoker’s RBC membrane (scale, 200 nm). Figure B is a representative RBC of the 10 smokers. RBCs of smokers are smaller and slightly elongated when compared to those of healthy nonsmokers, and membranes form small globular areas, as well as blister-like areas (Fig. C). (No micrograph features were changed and color was added with Adobe Photoshop CS6.) These changes may influence the RBC rheology and confirm the fluidity changes previously noted. These membrane changes are not visible using a traditional light microscope. The membranes of healthy RBCs typically show smooth membrane surfaces. Some researchers believe that there is no fundamental evidence that smokers’ blood does not comply with physiologic quality requirements for transfusion. The altered RBC membrane ultrastructure and fluidity might impact the health of the cell, ultimately impacting the therapeutic benefit to the individual receiving the blood. Therefore, we suggest that there is cause for concern when using blood from smokers for transfusion. Perhaps we must again rethink the use of smokers’ blood in blood donation. ETHICAL APPROVAL DISCLOSURE

Biomechanical Basis of Alzheimer's Disease and Other Protein Misfolding Diseases: Designing a New AFM Probe to Study Amyloid-Mediated Membrane Disorders

Most important biological interactions with its environment occur at interfaces such as a lipid cellular membrane. These interactions are often dynamic and show time-dependent changes in material properties (e.g, viscoelastic properties). A detailed understanding of biomechanical properties at molecular and subcellular level is vital for basic understanding of normal/abnormal biological processes. Indeed, abnormal changes in the mechanics of biological systems are often indicators of pathophysiological states. For example, amyloid beta peptide (Aβ), a protein present in neural plaques formed in Alzheimer's disease and cholesterol are reported to alter cell membrane mechanical properties leading to neuronal degeneration. Atomic force microscopy (AFM) provides an ideal tool to image the structure and examine the mechanics in physiologically relevant medium. We have created a new cantilevered probe for AFM for the study of nano-to-microscale mechanics of biological interfaces. We used it to examine the role of Aβ1-42 insertion in DPPC lipid monolayers and its effect on the viscoelastic properties that underlie altered membrane fluidity. Real-time analysis of mechanical properties of the model membrane monolayer in the presence of Aβ1-42 shows a decrease in the viscosity of the monolayers over time, consistent with increased membrane fluidity. The finding is consistent with changes in membrane permeability due to Aβ-inserted pores.

Disruption of oxidative phosphorylation and synaptic Na+, K+-ATPase activity by pristanic acid in cerebellum of young rats

AimsPeroxisomal biogenesis disorders (PBD) are inherited disorders clinically manifested by neurological symptoms and brain abnormalities, in which the cerebellum is usually involved. Biochemically, patients affected by these neurodegenerative diseases accumulate branched-chain fatty acids, including pristanic acid (Prist) in the brain and other tissues. Main methodsIn the present investigation we studied the in vitro influence of Prist, at doses found in PBD, on oxidative phosphorylation, by measuring the activities of the respiratory chain complexes I–IV and ATP production, as well as on creatine kinase and synaptic Na+, K+-ATPase activities in rat cerebellum. Key findingsPrist significantly decreased complexes I–III (65%), II (40%) and especially II–III (90%) activities, without altering the activities of complex IV of the respiratory chain and creatine kinase. Furthermore, ATP formation and synaptic Na+, K+-ATPase activity were markedly inhibited (80–90%) by Prist. We also observed that this fatty acid altered mitochondrial and synaptic membrane fluidity that may have contributed to its inhibitory effects on the activities of the respiratory chain complexes and Na+, K+-ATPase. SignificanceConsidering the importance of oxidative phosphorylation for mitochondrial homeostasis and of Na+, K+-ATPase for the maintenance of cell membrane potential, the present data indicate that Prist compromises brain bioenergetics and neurotransmission in cerebellum. We postulate that these pathomechanisms may contribute to the cerebellar alterations observed in patients affected by PBD in which Prist is accumulated.

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.

Deregulation of calcium homeostasis mediates secreted α–synuclein-induced neurotoxicity

α-Synuclein (AS) plays a crucial role in Parkinson's disease pathogenesis. AS is normally secreted from neuronal cells and can thus exert paracrine effects. We have previously demonstrated that naturally secreted AS species, derived from SH-SY5Y cells inducibly overexpressing human wild type AS, can be toxic to recipient neuronal cells. In the current study, we show that application of secreted AS alters membrane fluidity and increases calcium (Ca2+) entry. This influx is reduced on pharmacological inhibition of voltage-operated Ca2+ channels. Although no change in free cytosolic Ca2+ levels is observed, a significantly increased mitochondrial Ca2+ sequestration is found in recipient cells. Application of voltage-operated Ca2+ channel blockers or Ca2+ chelators abolishes AS-mediated toxicity. AS-treated cells exhibit increased calpain activation, and calpain inhibition greatly alleviates the observed toxicity. Collectively, our data suggest that secreted AS exerts toxicity through engagement, at least in part, of the Ca2+ homeostatic machinery. Therefore, manipulating Ca2+ signaling pathways might represent a potential therapeutic strategy for Parkinson's disease.

Study on interaction of bile salts with curcumin and curcumin embedded in dipalmitoyl-sn-glycero-3-phosphocholine liposome

Curcumin, often used as a food spice, is a natural polyphenol that has various medicinal benefits such as anti-cancer, anti-amyloid, anti-oxidant, and anti-inflammatory properties, among others. The interaction between bile salts having physiological significance and curcumin suggests the aggregation of bile salts dramatically alters the absorption and fluorescence parameters of curcumin. The fluorescence emission maximum as well as the intensity can easily detect critical micellar concentration of sodium cholate and sodium deoxycholate respectively to be 16 and 6mM at room temperature. The mechanism of interaction of curcumin with bile salts has been presented at low, intermediate and high bile salt concentrations and depends on temperature. In the presence of bile salts the DPPH scavenging activity was preserved, though less than in the presence of curcumin alone. The effect of submicellar concentration, 5–50μM, of bile salt with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes in solid gel and liquid crystalline phases has been investigated using curcumin as an embedded probe in the membrane. The curcumin based fluorescence probing method indicates even at very low concentration, ∼5μM, incorporation of monomeric bile salt molecules disorders the membrane properties. Expulsion of curcumin from the membrane in the presence of bile salt is ruled out, suggesting wetting of membrane. Alteration of membrane fluidity by bile salts is found to have an opposing effect in the liquid crystalline phase compared to in the solid gel phase, and is sensitive to the nature of bile salt. The permeability in the liquid crystalline phase decreases in the presence of bile salt. The phase transition temperature of the membrane is influenced by bile salt.

Physiological and Transcriptional Responses of Saccharomyces cerevisiae to d -Limonene Show Changes to the Cell Wall but Not to the Plasma Membrane

Monoterpenes can, upon hydrogenation, be used as light-fraction components of sustainable aviation fuels. Fermentative production of monoterpenes in engineered microorganisms, such as Saccharomyces cerevisiae, has gained attention as a potential route to deliver these next-generation fuels from renewable biomass. However, end product toxicity presents a formidable problem for microbial synthesis. Due to their hydrophobicity, monoterpene inhibition has long been attributed to membrane interference, but the molecular mechanism remains largely unsolved. In order to gain a better understanding of the mode of action, we analyzed the composition and structural integrity of the cell envelope as well as the transcriptional response of yeast cells treated with an inhibitory amount of d-limonene (107 mg/liter). We found no alterations in membrane fluidity, structural membrane integrity, or fatty acid composition after the solvent challenge. A 4-fold increase in the mean fluorescence intensity per cell (using calcofluor white stain) and increased sensitivity to cell wall-degrading enzymes demonstrated that limonene disrupts cell wall properties. Global transcript measurements confirmed the membrane integrity observations by showing no upregulation of ergosterol or fatty acid biosynthesis pathways, which are commonly overexpressed in yeast to reinforce membrane rigidity during ethanol exposure. Limonene shock did cause a compensatory response to cell wall damage through overexpression of several genes (ROM1, RLM1, PIR3, CTT1, YGP1, MLP1, PST1, and CWP1) involved with the cell wall integrity signaling pathway. This is the first report demonstrating that cell wall, rather than plasma membrane, deterioration is the main source of monoterpene inhibition. We show that limonene can alter the structure and function of the cell wall, which has a clear effect on cytokinesis.

Rapid cortisol signaling in response to acute stress involves changes in plasma membrane order in rainbow trout liver

The activation of genomic signaling in response to stressor-mediated cortisol elevation has been studied extensively in teleosts. However, very little is known about the rapid signaling events elicited by this steroid. We tested the hypothesis that cortisol modulates key stress-related signaling pathways in response to an acute stressor in fish liver. To this end, we investigated the effect of an acute stressor on biophysical properties of plasma membrane and on stressor-related protein phosphorylation in rainbow trout (Oncorhynchus mykiss) liver. A role for cortisol in modulating the acute cellular stress response was ascertained by blocking the stressor-induced elevation of this steroid by metyrapone. The acute stressor exposure increased plasma cortisol levels and liver membrane fluidity (measured by anisotropy of 1,6-diphenyl-1,3,5-hexatriene), but these responses were abolished by metyrapone. Atomic force microscopy further confirmed biophysical alterations in liver plasma membrane in response to stress, including changes in membrane domain topography. The changes in membrane order did not correspond to any changes in membrane fatty acid components after stress, suggesting that changes in membrane structure may be associated with cortisol incorporation into the lipid bilayer. Plasma cortisol elevation poststress correlated positively with activation of intracellular stress signaling pathways, including increased phosphorylation of extracellular signal-related kinases as well as several putative PKA and PKC but not Akt substrate proteins. Together, our results indicate that stressor-induced elevation of plasma cortisol level is associated with alterations in plasma membrane fluidity and rapid activation of stress-related signaling pathways in trout liver.

The Lipid Composition and Physical Properties of the Yeast Vacuole Affect the Hemifusion–Fusion Transition

Yeast vacuole fusion requires the formation of SNARE bundles between membranes. Although the function of vacuolar SNAREs is controlled in part by regulatory lipids, the exact role of the membrane in regulating fusion remains unclear. Because SNAREs are membrane-anchored and transmit the force required for fusion to the bilayer, we hypothesized that the lipid composition and curvature of the membrane aid in controlling fusion. Here, we examined the effect of altering membrane fluidity and curvature on the functionality of fusion-incompetent SNARE mutants that are thought to generate insufficient force to trigger the hemifusion-fusion transition. The hemifusion-fusion transition was inhibited by disrupting the 3Q:1R stoichiometry of SNARE bundles with the mutant SNARE Vam7p(Q283R) . Similarly, replacing the transmembrane domain of the syntaxin homolog Vam3p with a lipid anchor allowed hemifusion, but not content mixing. Hemifusion-stalled reactions containing either of the SNARE mutants were stimulated to fuse with chlorpromazine, an amphipathic molecule that alters membrane fluidity and curvature. The activity of mutant SNAREs was also rescued by the overexpression of SNAREs, thus multiplying the force transferred to the membrane. Thus, we conclude that either increasing membrane fluidity, or multiplying SNARE-generated energy restored the fusogenicity of mutant SNAREs that are stalled at hemifusion. We also found that regulatory lipids differentially modulated the complex formation of wild-type SNAREs. Together, these data indicate that the physical properties and the lipid composition of the membrane affect the function of SNAREs in promoting the hemifusion-fusion transition.

Reassessment of teratogenic risk from antenatal ultrasound

AbstractScience has shown that risk of cavitation and hyperthermia following prenatal ultrasound exposure is relatively negligible provided intensity, frequency, duration of exposure, and total numbers of exposures are safely limited. However, noncavitational mechanisms have been poorly studied and occur within what are currently considered “safe” levels of exposure. To date, the teratogenic capacity of noncavitational effectors are largely unknown, although studies have shown that different forms of ultrasound-induced hydraulic forces and pressures can alter membrane fluidity, proliferation, and expression of inflammatory and repair markers. Loose regulations, poor end user training, and unreliable ultrasound equipment may also increase the likelihood of cavitation and hyperthermia during prenatal exposure with prolonged durations and increased intensities. The literature suggests a need for tighter regulations on the use of ultrasound and further studies into its teratogenicity.

Membrane Physical Properties Influence Transmembrane Helix Formation

ThepHLIPpeptidehasthreestates:(I)solubleinaqueousbuffer,(II)bound to the bilayer surface at neutral pH, and (III) inserted as atransmembrane (TM) helix at acidic pH. The membrane insertion ofpHLIP at low pH can be used to target the acidic tissues character-istic of different diseases, such as cancer. We find that the α-helixcontent of state II depends on lipid acyl chain length but notcholesterol, suggesting the helicity of the bound state may be con-trolled by the bilayer elastic bending modulus. Experiments withthe P20G variant show the proline residue in pHLIP reduces theα-helix content of both states II and III. We also observe that themembrane insertion pKa is influencedbymembranephysicalprop-erties, following a biphasic pattern similar to the membrane thick-ness optima observed for the function of eukaryotic membraneproteins. Because tumor cells exhibit altered membrane fluidity,we suggest this might influence pHLIP tumor targeting. We useda cell insertion assay to determine the pKa in live cells, observingthat the properties in liposomes held in the more complex plasmamembrane. Our results show that the formation of a TM helix ismodulated by both the conformational propensities of the peptideand the physical properties of the bilayer. These results suggest aphysical role for helix-membrane interactions in optimizing thefunction of more complex TM proteins.

The protective effect of a 17 °C holding time on boar sperm plasma membrane fluidity after exposure to 5 °C

The holding time (HT) is the period during which an ejaculate, either in a raw or diluted state, is held at 17°C before further processing for cold-storage. In boars, the HT positively influences select sperm quality parameters of semen cooled from 15 to 5°C, a range in temperature during which plasma membrane remodeling occurs. Objective insight into the effect of HT on plasma membrane organization remains unknown. Therefore, the present work sought to elucidate if HT contributes to minimizing alterations in boar sperm plasma membrane fluidity at the initial step of the cooling process in a cryopreservation practice (holding at 5°C) and in relation with select sperm quality parameters. Nineteen ejaculates from five boars were collected and processed according to different treatments: T1) Fresh diluted semen, 0h at 17°C; T2) Fresh diluted semen, 24h at 17°C (HT); T3) Sperm from T1 in a lactose-egg yolk (LEY) extender, 3h at 5°C; T4) Sperm from T2 in LEY, 3h at 5°C; T5) Sperm from T1 in LEY, 24h at 5°C; T6) Sperm from T2 in LEY, 24h at 5°C. Sperm motility was assessed using CASA, and sperm plasma membrane integrity and fluidity were evaluated by flow cytometry with dual labeling (M540/YO-PRO®-1). Results demonstrated that the lack of exposure to a HT (T5) results in reduced sample motility compared to those having a HT (T6), with sperm exposed to HT exhibiting less plasma membrane fluidity. Collectively, these results provide empirical evidence that incorporation of a HT in semen processing protects boar sperm against cold injury through maintenance of lipid architecture of the plasma membrane.

Influence of cellular fatty acid composition on the response ofSaccharomyces cerevisiaeto hydrostatic pressure stress

High hydrostatic pressure (HHP) interferes with cellular membrane structure. The orientation of lipid molecules is changed, especially in the vicinity of proteins, leading to decreased membrane fluidity. Adaptation to HHP requires increased membrane fluidity, often achieved through a rise in the proportion of unsaturated fatty acids. In this work, a desaturase-deficient Saccharomyces cerevisiae mutant strain (OLE1 gene deletion) was grown in media supplemented with fatty acids differing in size and number of unsaturations and submitted to pressure up to 200 MPa for 30 min. Desaturase-deficient yeast supplemented with palmitoleic acid demonstrated increased sensitivity to pressure compared to cells supplemented with oleic acid or a proportionate mixture of both acids. In contrast, yeast cells grown with linoleic and linolenic acids were more piezoresistant than cells treated with oleic acid. Furthermore, growth with palmitoleic acid led to higher levels of lipid peroxidation. Intracellular trehalose during HHP treatment increased cell tolerance to pressure. However, when trehalose remained extracellular cells were sensitised to pressure. Therefore, fatty acid composition and trehalose content might play a role in the protection of the cell membrane from oxidative damage produced by HHP, confirming that alteration in cell membrane fluidity is correlated with pressure resistance in yeast.

Membrane physical properties influence transmembrane helix formation

The pHLIP peptide has three states: (I) soluble in aqueous buffer, (II) bound to the bilayer surface at neutral pH, and (III) inserted as a transmembrane (TM) helix at acidic pH. The membrane insertion of pHLIP at low pH can be used to target the acidic tissues characteristic of different diseases, such as cancer. We find that the α-helix content of state II depends on lipid acyl chain length but not cholesterol, suggesting the helicity of the bound state may be controlled by the bilayer elastic bending modulus. Experiments with the P20G variant show the proline residue in pHLIP reduces the α-helix content of both states II and III. We also observe that the membrane insertion pKa is influenced by membrane physical properties, following a biphasic pattern similar to the membrane thickness optima observed for the function of eukaryotic membrane proteins. Because tumor cells exhibit altered membrane fluidity, we suggest this might influence pHLIP tumor targeting. We used a cell insertion assay to determine the pKa in live cells, observing that the properties in liposomes held in the more complex plasma membrane. Our results show that the formation of a TM helix is modulated by both the conformational propensities of the peptide and the physical properties of the bilayer. These results suggest a physical role for helix-membrane interactions in optimizing the function of more complex TM proteins.

Progestin modulates the lipid profile and sensitivity of breast cancer cells to docetaxel

Progestins induce lipid accumulation in progesterone receptor (PR)-positive breast cancer cells. We speculated that progestin-induced alterations in lipid biology confer resistance to chemotherapy. To examine the biology of lipid loaded breast cancer cells, we used a model of progestin-induced lipid synthesis. T47D (PR-positive) and MDA-MB-231 (PR-negative) cell lines were used to study progestin response. Oil red O staining of T47D cells treated with progestin showed lipid droplet formation was PR dependent, glucose dependent and reduced sensitivity to docetaxel. This protection was not observed in PR-negative MDA-MB-231 cells. Progestin treatment induced stearoyl CoA desaturase-1 (SCD-1) enzyme expression and chemical inhibition of SCD-1 diminished lipid droplets and cell viability, suggesting the importance of lipid stores in cancer cell survival. Gas chromatography/mass spectroscopy analysis of phospholipids from progestin-treated T47D cells revealed an increase in unsaturated fatty acids, with oleic acid as most abundant. Cells surviving docetaxel treatment also contained more oleic acid in phospholipids, suggesting altered membrane fluidity as a potential mechanism of chemoresistance mediated in part by SCD-1. Lastly, intact docetaxel molecules were present within progestin induced lipid droplets, suggesting a protective quenching effect of intracellular lipid droplets. Our studies suggest the metabolic adaptations produced by progestin provide novel metabolic targets for future combinatorial therapies for progestin-responsive breast cancers.