Membrane Fluidity Characteristics Research Articles

Photosynthetic characteristics and inferred changes in thylakoid membrane fluidity determine bloom succession between Anabaena and Microcystis in eutrophic lakes

Anabaena and Microcystis are common dominant cyanobacterial genera and frequently form blooms in large shallow eutrophic lakes in China. There is usually a quick succession between these two cyanobacterial blooms in early summer; however, there is currently no solid evidence based on photosynthesis and population competition to explain this phenomenon. This study compared the photosynthetic parameters and the indirectly measured thylakoid membrane fluidity characteristics between Anabaena and Microcystis. The results showed that the growth rate, the maximum photochemical efficiency of PSII (F v/F m), and the maximum relative electron transport rate (r ETR max) of Microcystis cultured at 25 °C were significantly lower than those from cells grown at 15 °C, indirectly suggesting a marked limitation of thylakoid membrane fluidity at low temperatures. Chlorophyll fluorescence dynamics also indicated inhibition of NPQ formation and membrane fluidity when Microcystis was cultured at low temperatures; however, this inhibition was not significant for Anabaena. Fourier transition infrared (FT-IR) spectrometry indicated that the thylakoid membrane of Anabaena can maintain homeostasis fluidity through the upregulation of unsaturated fatty acids when exposed to chilling stress. Increasing the temperature significantly promoted the growth rate of Microcystis, while it had little effect on Anabaena. Moreover, photoinhibition of Anabaena was more easily induced by high light, thus accelerating the bloom succession from Anabaena to Microcystis during warm seasons. An activation-energy model was used to deduce that the threshold temperature of bloom succession was 15.4 °C, which would increase to 16.2 °C and decrease to 14.9 °C under conditions of N-limitation and P-limitation.

Abstract 2458: Targeting membrane fluidity as a therapeutic strategy in cancer using BPM 31510

Abstract Cancer cells membranes are relatively more fluid compared to healthy cells. Higher fluidity in cancer cells closely relate to their invasive potential, proliferation, and metastatic ability. Pharmacological modulation of membrane fluidity as a novel therapeutic strategy for potential treatment of cancer is investigated in this study. BPM 31510, a proprietary CoQ10 based liposomal formulation currently in clinical trials affects cell membrane fluidity to influence cancer cell survival. To study the effect of BPM 31510 on biophysical parameters of membrane structure in cancer cells, the CoQ10 concentration in the liposomes was systematically increased and the membrane rigidity (Fluorescence Anisotropy) as function of temperature was measured. A progressive (significant, p<0.05) increase in rigidity of liposomal membranes was observed with increase in CoQ10 concentration to a maxima, after which any further increase in CoQ10 concentration resulted in decreases in membrane rigidity. Interestingly, the local maxima in rigidity matched with the concentration of CoQ10 in BPM 31510 formulation. A spectrum of cell lines including cancer of breast, pancreas, liver, prostate, ovarian cell lines and corresponding healthy non-disease control cell lines including fibroblast, smooth muscles, primary prostate were treated with BPM 31510. For all cell lines, there was a temporal increase in cell membrane rigidity between 0-8 hours following treatment with BPM 31510. The magnitude of increase in membrane rigidity was higher for cells with higher initial membrane fluidity for cancer cells compared to healthy cells. Further, magnitude and rate of this reorganization of cell lipid and protein profile, bioenergetics and metabolic state as a maladaptive response of cells to BPM 31510 correlated with the magnitude of change in cell membrane rigidity. Finally, decrease in cell viability was higher for cells with higher membrane fluidity compared to cells with rigid membrane after 48 hours of treatment of BPM 31510. In in vivo preclinical animal model of cancer, there was a strong correlation between BPM 31510 in-plane rigidity measurements to observed bio-distribution and efficacy. This work provides profound insight into CoQ10 effect on cell membrane dynamics and mechanism of action of BPM 31510. The study provides compelling evidence in support of targeting membrane fluidity characteristics in cancer cells as a novel modality with therapeutic potential in the treatment of cancer. Citation Format: Sumit Garg, Sirisha Dhavala, Katerina Krumova, Vivek K. Vishnudas, Joaquin J. Jimenez, Michael Kiebish, Rangaprasad Sarangarajan, Niven R. Narain. Targeting membrane fluidity as a therapeutic strategy in cancer using BPM 31510. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2458. doi:10.1158/1538-7445.AM2015-2458

Investigation of the mechanisms by which the molecular chaperone HSPA2 regulates the expression of sperm surface receptors involved in human sperm-oocyte recognition

A unique characteristic of mammalian spermatozoa is that, upon ejaculation, they are unable to recognize and bind to an ovulated oocyte. These functional attributes are only realized following the cells' ascent of the female reproductive tract whereupon they undergo a myriad of biochemical and biophysical changes collectively referred to as 'capacitation'. We have previously shown that this functional transformation is, in part, engineered by the modification of the sperm surface architecture leading to the assembly and/or presentation of multimeric sperm-oocyte receptor complexes. In this study, we have extended our findings through the characterization of one such complex containing arylsulfatase A (ARSA), sperm adhesion molecule 1 (SPAM1) and the molecular chaperone, heat shock 70kDa protein 2 (HSPA2). Through the application of flow cytometry we revealed that this complex undergoes a capacitation-associated translocation to facilitate the repositioning of ARSA to the apical region of the human sperm head, a location compatible with a role in the mediation of sperm-zona pellucida (ZP) interactions. Conversely, SPAM1 appears to reorient away from the sperm surface, possibly reflecting its primary role in cumulus matrix dispersal preceding sperm-ZP recognition. The dramatic relocation of the complex was completely abolished by incubation of capacitating spermatozoa in exogenous cholesterol or broad spectrum protein kinase A (PKA) and tyrosine kinase inhibitors suggesting that it may be driven by alterations in membrane fluidity characteristics and concurrently by the activation of a capacitation-associated signal transduction pathway. Collectively these data afford novel insights into the sub-cellular localization and potential functions of multimeric protein complexes in human spermatozoa.

119. IDENTIFICATION AND CHARACTERISATION OF SURFACE PROTEIN COMPLEXES IN HUMAN SPERMATOZOA

A unique characteristic of mammalian spermatozoa is that upon ejaculation, they are unable to recognise and bind to an ovulated oocyte. These functional attributes are only realised following the sperms ascent of the female reproductive tract whereupon they undergo a myriad of biochemical and biophysical changes collectively referred to as ‘capacitation’. Since spermatozoa are both transcriptionally and translationally quiescent cells, this functional transformation must be engineered by a combination of post-translational modification and spatial reorganisation of existing sperm proteins. Indeed, evidence from our laboratory suggests that a key attribute of capacitation is the remodeling of the sperm surface architecture leading to the assembly and / or presentation of multimeric sperm-oocyte receptor complex(es). Through the novel application of Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE), we have secured the first direct evidence that human spermatozoa express a number of these protein complexes on their surface. Furthermore, we have demonstrated that a subset of these complexes harbour putative zona adhesion proteins and display strong affinity for solubilised zona pellucidae. In this study, we have extended our findings through the characterisation of one such complex containing arylsulfatase A (ASA), a protein with recognised affinity for sulfated ligands present within the zona pellucida. Through the application of immunohistochemistry and flow cytometry we revealed that ASA undergoes a capacitation-associated translocation to become expressed on the apical region of the human sperm head, a location compatible with a role in the mediation of sperm-zona pellucida interactions. This dramatic relocation was completely abolished by incubation of capacitating spermatozoa in exogenous cholesterol, suggesting that it may be driven in part by alteration in the membrane fluidity characteristics. Our current research is focused on confirming the role of ASA in human sperm-zona pellucida adhesion and elucidating the precise cellular mechanisms that underpin the proteins translocation to the cell surface.

Flavonoids and cell membrane fluidity

Abstract The membrane fluidity characteristics of multilamellar (MLV) and extruded liposomes prepared with kaempferol (K), kaempferol-3-glucoside (KG), (−)-epigallocatechin (EGC) or (−)-epigallocatechin-3-gallate (EGCG) are presented. Kaempferol caused the highest increase in fluorescence polarisation of DPH in both liposomes (other compounds had not) indicating that K with nK/nLip below 0.2 or 0.1 decreased the membrane fluidity, while at higher molar ratios the membrane fluidity increased. EPR measurements with MLV and spin probes MeFASL(10,3) and MeFASL(2,11) showed a significant decrease in fluidity in the upper part of the membrane for all flavonoids measured, and in the core of the membrane an increase in fluidity for EGCG and EGC. Computer simulation of the EPR spectra showed that the membrane of the MLV used was composed of at least three coexisting domain types with different fluidity and that the order parameter of the most ordered domains is responsible for membrane fluidity alterations.

Membrane fluidity characteristics of human lung cancer

Membrane fluidity of non-cultured lung cancer tissue was studied by electron paramagnetic resonance (EPR). EPR spectra of a lipophilic spin probe in a tissue of resected tumor samples from 51 patients were compared with computer simulated spectra, which were superimpositions of spectra characterizing membrane domains with different fluidity. The membranes of tumor tissues were more fluid, than those of normal lungs; the most fluid domains were enlarged and their order parameter decreased in comparison to normal tissue. An empirical fluidity parameter (H13) was defined as the criterion to correlate EPR and clinical data. The histology of tumor, the quantitative presence of different tumor and non-tumor cells and the pathohisthological stage of the disease had no significant influence on fluidity.

Athermal Alterations in the Structure of the Canalicular Membrane and ATPase Activity Induced by Thermal Levels of Microwave Radiation

Sprague-Dawley rats (200-250 g) were exposed 30 min/day for 4 days to thermogenic levels (rectal temperature increase of 2.2 degrees C) of microwave radiation [2.45 GHz, 80 mW/cm2, continuous-wave mode (CW)] or to a radiant heat source resulting in an equivalent increase in body temperature of 2.2 degrees C. On the fifth day after the 4 days of exposure to microwave radiation, the animals were sacrificed and their livers removed. The canalicular membranes were isolated and evaluated for adenosinetriphosphatase (ATPase) activity, total fatty acid composition and membrane fluidity characteristics. Mg(++)-ATPase activity (Vmax) decreased by 48.5% in the group exposed to microwave radiation, with no significant change in the group exposed to radiant heat. The decrease in Mg(++)-ATPase was partially compensated by a concomitant increase in Na+/K(+)-ATPase activity (170% increase in Vmax over control) in animals exposed to microwave radiation, while no change occurred in the group exposed to radiant heat. This alteration in ATPase activity in the group exposed to microwave radiation is associated with a large decrease in the ratio of saturated to unsaturated fatty acids. Conversely, the group exposed to radiant heat had an increase in the ratio of saturated to unsaturated fatty acids. The most dramatic changes were found in the levels of arachidonic acid. Finally, the electron paramagnetic resonance (EPR) spin label technique used to measure the fluidity of the canalicular membranes of the animals in the three groups (sham, microwave radiation and radiant heat) indicated that the results were different in the three groups, reflecting the changes found in their fatty acid composition. The physiological response to "equivalent" thermal loads in rats is expressed differently for different types of energy sources. Possible mechanisms producing these divergent thermogenic responses are discussed.

Cell lineage in molluscan development.

Cell lineage specification in molluscs is brought about by two mechanism: the segregation of morphogenetic plasms and inductive cell interactions. The evidence for the existence of morphogenetic plasms is largely circumstantial, but in one species, Bithynia, such a plasm has been identified in the polar lobe that forms at first cleavage. Inductive cell interactions are thought to be a prerequisite for the development of a large number of tissues and organs. The most extensively studied example is the specification of the mesodermal stem cell in Lymnaea and Patella, which occurs between 5th and 6th cleavage through an interaction between one macromere and a large number of micromeres. Both segregation and induction are tuned to the animal-vegetal polarity of the egg, at least during early development. This polarity probably arises during oogenesis and is manifest in regional differentiations of the surface architecture of the egg, in the distribution of inner membrane particles in the plasma membrane, in membrane fluidity characteristics, in ionic conductance properties of the plasma membrane, etc. All these phenomena have in common that they represent properties of the egg surface, suggesting that the polarity of the egg is somehow imprinted into the plasma membrane and the cortex of the egg during oogenesis.

Ischemia/reperfusion-induced changes in membrane fluidity characteristics of brain capillary endothelial cells and its prevention by liposomal-incorporated superoxide dismutase

The effect of global cerebral ischemia and reperfusion on cerebral capillary endothelial cell membrane fluidity was examined using electron paramagnetic resonance techniques following 8 minutes of global ischemia and 15 minutes of blood reperfusion. The luminal surface of the cerebral vasculature was perfused with a series of doxyl stearic acid reporters (5-, 12-, 16-doxyl stearic acid) which differ in the site of attachment of the nitroxide free radical on the fatty acid chain. Each doxyl stearic acid reports on membrane fluidity characteristics from different depths within the membrane. Ischemia/reperfusion produced a membrane ordering that was markedly dependent on intramembrane location, and was consistent with changes previously associated with lipid peroxidation. The effect of ischemia/reperfusion on membrane fluidity was maximal in the membrane environment reported by 12-doxyl stearic acid (12-DS). The utilization of a liposomal system was shown to enhance superoxide dismutase delivery to cerebral tissues as well as attenuating the change in membrane order seen following reperfusion-induced lipid peroxidation.

Regulation of glycolipid synthesis during differentiation of clonal murine muscle cells

The two clonal murine muscle cell lines G7 and G8, originally derived from the M114 line, represent unique models for comparative studies of myogenesis. Glycolipid synthesis was examined during differentiation using [3H]-galactose and [3H]-glucosamine as precursors. Upon G7 contact glucosylceramide labeling increased and nLcOse5Cer labeling stopped. During membrane fusion, glucosylceramide labeling stopped and lactosylceramide became the major synthetic product. G8 cells presented a different pattern, with increased labeling of GbOse3Cer during myogenesis. The major ganglioside synthesized by both myoblasts was GM3, and more complex structures were observed following completion of myotube formation. Total glycopeptide labeling increased when G8 myoblasts fused and remained elevated in myotubes, whereas no differences during fusion of G7 cells were noted. Upon comparison of the two clonal lines, the only consistent observation was a significant increase in the synthesis of total gangliosides and neutral glycolipid during cell contact and membrane fusion (p less than 0.02). The results suggest that changes in the synthesis of specific glycolipid structures during myogenesis are unique to each muscle cell line examined. However, transient increases in synthesis of total myoblast gangliosides and neutral glycolipids may be a more general phenomenon, possibly by curbing proliferation or by altering myoblast membrane fluidity characteristics during differentiation.

Lipid composition of a psychrophilic, a mesophilic and a thermophilic Mucor species

Total lipid composition of the psychrophile Mucor psychrophilus , the mesophile M. hiemalis and the thermophile M. pusillus differed little. However, there were marked differences in their phospholipids, especially those extracted from membranes. Although the three species had little ability to amend levels of membrane phospholipid saturation with changing temperature, membrane phospholipid unsaturation decreased from psychrophile to mesophile to thermophile. In addition, M. pusillus membrane phospholipids were composed of significantly longer chain lengths. These differences are discussed in relation to membrane fluidity characteristics which affect membrane themostability and the activity of membrane-associated processes.