PCYT1A Regulates Phosphatidylcholine Homeostasis from the Inner Nuclear Membrane in Response to Membrane Stored Curvature Elastic Stress.

Cell and organelle membranes consist of a complex mixture of phospholipids (PLs) that determine their size, shape, and function. Phosphatidylcholine (PC) is the most abundant phospholipid in eukaryotic membranes, yet how cells sense and regulate its levels in vivo remains unclear. Here we show that PCYT1A, the rate-limiting enzyme of PC synthesis, is intranuclear and re-locates to the nuclear membrane in response to the need for membrane PL synthesis in yeast, fly, and mammalian cells. By aligning imaging with lipidomic analysis and data-driven modeling, we demonstrate that yeast PCYT1A membrane association correlates with membrane stored curvature elastic stress estimates. Furthermore, this process occurs inside the nucleus, although nuclear localization signal mutants can compensate for the loss of endogenous PCYT1A in yeast and in fly photoreceptors. These data suggest an ancient mechanism by which nucleoplasmic PCYT1A senses surface PL packing defects on the inner nuclear membrane to control PC homeostasis

The sphingosine 1‐phosphate analogue, FTY720, modulates the lipidomic signature of the mouse hippocampus

The small‐molecule drug, FTY720 (fingolimod), is a synthetic sphingosine 1‐phosphate (S1P) analogue currently used to treat relapsing–remitting multiple sclerosis in both adults and children. FTY720 can cross the blood–brain barrier (BBB) and, over time, accumulate in lipid‐rich areas of the central nervous system (CNS) by incorporating into phospholipid membranes. FTY720 has been shown to enhance cell membrane fluidity, which can modulate the functions of glial cells and neuronal populations involved in regulating behaviour. Moreover, direct modulation of S1P receptor‐mediated lipid signalling by FTY720 can impact homeostatic CNS physiology, including neurotransmitter release probability, the biophysical properties of synaptic membranes, ion channel and transmembrane receptor kinetics, and synaptic plasticity mechanisms. The aim of this study was to investigate how chronic FTY720 treatment alters the lipid composition of CNS tissue in adolescent mice at a key stage of brain maturation. We focused on the hippocampus, a brain region known to be important for learning, memory, and the processing of sensory and emotional stimuli. Using mass spectrometry‐based lipidomics, we discovered that FTY720 increases the fatty acid chain length of hydroxy‐phosphatidylcholine (PCOH) lipids in the mouse hippocampus. It also decreases PCOH monounsaturated fatty acids (MUFAs) and increases PCOH polyunsaturated fatty acids (PUFAs). A total of 99 lipid species were up‐regulated in the mouse hippocampus following 3 weeks of oral FTY720 exposure, whereas only 3 lipid species were down‐regulated. FTY720 also modulated anxiety‐like behaviours in young mice but did not affect spatial learning or memory formation. Our study presents a comprehensive overview of the lipid classes and lipid species that are altered in the hippocampus following chronic FTY720 exposure and provides novel insight into cellular and molecular mechanisms that may underlie the therapeutic or adverse effects of FTY720 in the central nervous system

Effect of membrane lipids on phosphofructokinase from Bacillus stearothermophilus using a novel 33P radiochemical assay

Phosphofructokinase (PFK-1), a major regulatory enzyme of glycolysis, catalyses the phosphorylation of d-fructose 6-phosphate by ATP to yield d-fructose 1,6-bisphosphate. Mammalian PFK-1 is known to bind to biomembranes with a regulatory effect on enzyme activity (Karadsheh and Uyeda, 1977). We have conducted a study into whether PFK-1 activity depends on membrane lipid composition and whether this enzyme is regulated via membrane stored curvature elastic stress, in an analogous manner to CTP:phosphocholine cytidylytransferase (CCT) (Attard et al., 2000 G.S. Attard, R.H. Templer, W.S. Smith, A.N. Hunt and S. Jackowski, PNAS 97 (16) (2000), p. 9032. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (82)[Attard et al., 2000] and [Attard et al., 2006]). As part of this investigation, we developed a novel 33P radiochemical assay for PFK-1. The assay combines the benefits of a previously available 32P assay (Sola-Penna et al., 2002), with the advantage of a markedly smaller decay energy. Kinetic studies yielded comparable results to both the spectrophotometric and 32P radiochemical assays, confirming the reliability of the method. The effect of vesicles composed of dioleoyl phosphatidylcholine (DOPC) and oleic acid (OA) on PFK-1 from Bacillus stearothermophilus was studied. OA was found to increase catalytic activity twofold and threefold compared to DOPC and no lipid present, respectively. While these results suggest that stored curvature elastic energy may play a role in modulating enzyme activity, they are significantly different from the results obtained with CCT. Therefore, interesting questions arise about the fundamental mechanisms that underlie the effect of membrane lipid composition on PFK-1 activity

The effect of lipids on the enzymatic activity of 6-phosphofructo-1-kinase from B. stearothermophilus

6-Phosphofructo-1-kinase (PFK-1), a major regulatory enzyme in the glycolysis pathway, is a cytoplasmic enzyme with complicated allosteric kinetics. Here we investigate the effects of lipids on the activity of PFK from Bacillus stearothermophilus (BsPFK), to determine whether BsPFK shares any of the membrane binding or lipid binding properties reported for some mammalian PFKs. Our results show that large unilamellar vesicles (LUVs) composed of either the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or of 1:1 (mole ratio) DOPC and the fatty acid, oleic acid (OA), cause a three-fold increase in Vmax, depending on the lipid concentration and vesicle composition, but no change in Km. Further studies show lipids do not reverse the allosteric inhibitory effects of phosphoenolpyruvate (PEP) on BsPFK. SDS/PAGE studies do not show significant binding of the BsPFK tetramer to the surface of the phospholipid vesicles, suggesting that modulation of catalytic activity is due to binding of lipid monomers. By simulating the kinetics of BsPFK interaction with vesicles and lipid monomers we conclude that the change in BsPFK catalytic activity with respect to lipid concentration is consistent with monomer abstraction from vesicles rather than direct uptake of lipid monomers from solution

Mammalian phospholipid homeostasis: evidence that membrane curvature elastic stress drives homeoviscous adaptation in vivo

Several theories of phospholipid homeostasis have postulated that cellsregulate the molecular composition of their bilayer membranes, such that acommon biophysical membrane parameter is under homeostatic control.Two commonly cited theories are the intrinsic curvature hypothesis, whichstates that cells control membrane curvature elastic stress, and the theory ofhomeoviscous adaptation, which postulates cells control acyl chain packingorder (membrane order). In this paper, we present evidence from datadrivenmodelling studies that these two theories correlate in vivo.We estimatethe curvature elastic stress of mammalian cells to be 4-7 10212 N, a valuehigh enough to suggest that in mammalian cells the preservation of membraneorder arises through a mechanism where membrane curvature elastic stressis controlled. These results emerge from analysing the molecular contributionof individual phospholipids to both membrane order and curvature elasticstress in nearly 500 cellular compositionally diverse lipidomes. Our modelsuggests that the de novo synthesis of lipids is the dominant mechanism bywhich cells control curvature elastic stress and hence membrane orderin vivo. These results also suggest that cells can increase membrane curvatureelastic stress disproportionately to membrane order by incorporatingpolyunsaturated fatty acids into lipids

Partitioning of ssRNA molecules between preformed monolithic H(II) liquid crystalline phases of lipids and supernatant isotropic phases

The interaction of nucleic acids with the nanoarchitectures formed by lipidic systems is a new area of research that may offer insights into the functioning of genetic materials in vivo. Here we report that ssRNA has a strong preference to reside in isotropic solution rather than in inverse hexagonal (HII) liquid crystalline phases. This is in contrast to dsDNA, which becomes localized in the pores of the HII phase. The RNA that does associate with the external surfaces of the HII phase appears to form an accretion layer, tens of molecules thick, but this layer still allows the transcription of dsDNA that resides within the pores of the phase.<br/