Specific Lipid Species Research Articles

Towards a Mechanical Model of Skin: Insights into Stratum Corneum Mechanical Properties from Hierarchical Models of Lipid Organisation

ABSTRACTThe stratum corneum (SC), the outermost layer of the skin, provides the body with a physiologically essential barrier to unregulated water loss and the influx of exogenous substances. Furthermore, the 10–20 micron thick SC, composed of overlapping protein-rich corneocytes surrounded by a heterogeneous multilamellar lipid matrix, displays tremendous mechanical cohesion and thermal integrity. To understand the contribution of these components to SC mechanical properties requires building a complete mechanical model of the skin. In this study we focus on modelling the hierarchical microstructure of the lipid phase and its relation to mechanical properties using a combination of atomistic and mesoscale simulations. The modelling approaches are parameterised with experimental data from FT-IR spectroscopy, X-ray scattering and, in the case of the mesoscale simulations, with detailed density profiles derived from atomic models. The atomistic models are used to probe the role of specific lipid species in maintaining the thermal and structural stability of the SC extracellular lipid matrix and to investigate the role of hydrogen bonding networks in SC lipid cohesion. Mesoscale models are used to investigate domain formation and lipid bilayer organisation on length and time scales inaccessible with atomistic models. These coarse grained models display transitions between ordered hexagonal gel phases and fluid phases, reproducing the experimentally observed ordering of the hydrophilic and hydrophobic regions.

Recruiting Protein Kinase in Time for Mitosis

The nuclear lipid cycle and how it is regulated are areas of active investigation (see Irvine ). The generation of specific lipid species in the nucleus may play a key role in recruiting and activating lipid-dependent enzymes such as members of the protein kinase C (PKC) family. Deacon et al . suggest that the formation of the tetraunsaturated diacylglycerol species, 1-stearoyl, 2-arachidonyl glycerol (SAG), may be a key element for the localization and activation of PKC βII, a classical PKC isoform that is regulated by calcium and diacylgycerol. PKC βII translocated to the nucleus during the G 2 to M phase of the cell cycle and was presumably activated by its association with the membrane. Furthermore, the concentration of SAG was selectively increased in the nuclei of cells at G 2 -M. SAG activated PKC βII and PKC α in vitro. Thus, the localized increase in nuclear SAG may be sufficient to recruit and activate specific PKC isoforms during the G 2 -M phase of the cell cycle. R. Irvine, Nuclear lipid signaling. Science's STKE (2000), http://stke.sciencemag.org/cgi/content/full/OC_sigtrans;2000/48/re1 [Abstract] [Full Text] E. M. Deacon, T. R. Pettitt, P. Webb, T. Cross, H. Chahal, M. J. O. Wakelan, J. M. Lord, Generation of duacylglycerol molecular species through the cell cycle: a role for 1-stearoyl, 2-arachidonyl glycerol in the activation of nuclear protein kinase C-βII at G2/M. J. Cell Sci. 115 , 983-989 (2002). [Online Journal]

Recruiting Protein Kinase in Time for Mitosis

The nuclear lipid cycle and how it is regulated are areas of active investigation (see Irvine). The generation of specific lipid species in the nucleus may play a key role in recruiting and activating lipid-dependent enzymes such as members of the protein kinase C (PKC) family. Deacon et al. suggest that the formation of the tetraunsaturated diacylglycerol species, 1-stearoyl, 2-arachidonyl glycerol (SAG), may be a key element for the localization and activation of PKC βII, a classical PKC isoform that is regulated by calcium and diacylgycerol. PKC βII translocated to the nucleus during the G2 to M phase of the cell cycle and was presumably activated by its association with the membrane. Furthermore, the concentration of SAG was selectively increased in the nuclei of cells at G2-M. SAG activated PKC βII and PKC α in vitro. Thus, the localized increase in nuclear SAG may be sufficient to recruit and activate specific PKC isoforms during the G2-M phase of the cell cycle.R. Irvine, Nuclear lipid signaling. Science's STKE (2000), http://stke.sciencemag.org/cgi/content/full/OC_sigtrans;2000/48/re1 [Abstract] [Full Text]E. M. Deacon, T. R. Pettitt, P. Webb, T. Cross, H. Chahal, M. J. O. Wakelan, J. M. Lord, Generation of duacylglycerol molecular species through the cell cycle: a role for 1-stearoyl, 2-arachidonyl glycerol in the activation of nuclear protein kinase C-βII at G2/M. J. Cell Sci. 115, 983-989 (2002). [Online Journal]

Phenotypic changes associated with deletion and overexpression of a stage-regulated gene family in Leishmania.

The LmcDNA16 locus of Leishmania major contains three highly related genes HASPA1, HASPA2 and HASPB, encoding hydrophilic, acylated surface proteins and a tandem pair of unrelated sequences, SHERP1 and SHERP2, coding for a small, hydrophilic protein that localizes to the endoplasmic reticulum and outer mitochondrial membrane. Differential regulation of these genes results in expression of a subset of the HASP proteins and SHERP only in infective stage parasites. To assess the contribution of these molecules to parasite virulence, the diploid LmcDNA16 gene locus has been removed by targeted gene deletion. Homozygous null mutants have precise deletions of both alleles and exhibit no HASP or SHERP expression. They are at least as virulent as wild-type parasites in macrophage invasion and intracellular survival assays, both in vitro and in vivo. Conversely, null mutants engineered to overexpress the entire LmcDNA16 gene locus are unable to survive within the intramacrophage environment despite their differentiation into infective metacyclic parasites. Both null and overexpressing null parasites show increased sensitivity to complement-mediated lysis, suggesting perturbation of their surface architecture. Avirulence in overexpressing parasites correlates with selective depletion of a specific lipid species, decreased expression of the major surface glycoprotein GP63, but no significant downregulation of the glycoconjugate lipophosphoglycan.

Electrospray ionization mass spectrometry analysis of changes in phospholipids in RBL-2H3 mastocytoma cells during degranulation

Biological membranes contain an extraordinary diversity of lipids. Phospholipids function as major structural elements of cellular membranes, and analysis of changes in the highly heterogeneous mixtures of lipids found in eukaryotic cells is central to understanding the complex functions in which lipids participate. Phospholipase-catalyzed hydrolysis of phospholipids often follows cell surface receptor activation. Recently, we demonstrated that granule fusion is initiated by addition of exogenous, nonmammalian phospholipases to permeabilized mast cells. To pursue this finding, we use positive and negative mode Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) to measure changes in the glycerophospholipid composition of total lipid extracts of intact and permeabilized RBL-2H3 (mucosal mast cell line) cells. The low energy of the electrospray ionization results in efficient production of molecular ions of phospholipids uncomplicated by further fragmentation, and changes were observed that eluded conventional detection methods. From these analyses we have spectrally resolved more than 130 glycerophospholipids and determined changes initiated by introduction of exogenous phospholipase C, phospholipase D, or phospholipase A2. These exogenous phospholipases have a preference for phosphatidylcholine with long polyunsaturated alkyl chains as substrates and, when added to permeabilized mast cells, produce multiple species of mono- and polyunsaturated diacylglycerols, phosphatidic acids, and lysophosphatidylcholines, respectively. The patterns of changes of these lipids provide an extraordinarily rich source of data for evaluating the effects of specific lipid species generated during cellular processes, such as exocytosis.

Oligodendrocyte-substratum adhesion activates the synthesis of specific lipid species involved in cell signaling.

Ovine oligodendrocytes (OLGs) undergo biochemical and morphological changes following attachment to polylysine. Autoradiographs of two-dimensional thin-layer chromatograms of [14C]Gal-labeled OLG cultures revealed that attachment of OLGs to a polylysine substratum and their subsequent morphological differentiation is accompanied by an increased synthesis of multiple forms of galactosylceramide, sulfogalactosylceramide, and both sulfogalactosyl- and galactosyl-diglycerides, together with an array of complex sialoglycosphingolipids, predominantly GM2 ganglioside. As previously reported, overall lipid synthesis measured by [14C]acetate incorporation into glycerophosphatides, sphingomyelin, and neutral lipids also increased dramatically for up to 60 days (last time point examined) following OLG-substratum adhesion, reflecting membrane growth. Attachment was associated with a rapid augmentation in the synthesis of ethanolamine plasmalogen from 12 to 27% within 24 hr to reach a 35% plateau at 30 days and remain constant thereafter. In contrast, the plasmalogen content of phosphatidylcholine remained constant at 3-5%. This rapid increase in lipid synthesis (especially in the ethanolamine plasmalogen content following attachment) closely paralleled increased diacylglycerol (DAG) production and protein kinase C-dependent phosphorylation of both myelin basic protein and 2',3'-cyclic nucleotide phosphohydrolase. Labeling studies indicated that the major source of [3H]arachidonate-labeled DAG following attachment was from phosphatidylinositol turnover (and to a lesser extent phosphatidylcholine) rather than polyphosphoinositides or plasmalogens. Enhanced lipid synthesis is not only required for the production of membranes in these myelin-producing cells but is also a source of second messengers required in the posttranslational modification of key myelin and cellular proteins.

Glycopeptidolipids from Mycobacterium fortuitum: a variant in the structure of C-mycoside

Strains from the Mycobacterium fortuitum complex contain surface species-specific lipids allowing their precise identification. In M. fortuitum biovar. peregrinum two major glycopeptidolipids, of the C-mycoside type, were characterized by a combination of chemical analyses, NMR, and FAB mass spectrometry. Important information was obtained by mass spectrometry both on their molecular weight and on the peptide and saccharide sequences without any derivatization. The basic structure of the two compounds was shown to be [formula: see text] The disaccharide part linked O-glycosidically to alaninol was either 3,4-di-O-methyl-alpha-L-rhamnopyranosyl (1----2) 3,4-di-O-methyl-alpha-L-rhamnopyranoside (mycoside I) or 3-O-methyl-alpha-L-rhamnopyranosyl (1----2) 3,4-di-O-methyl-alpha-L-rhamnopyranoside (mycoside II). This is an unusual structure of a C-mycoside since neither 6-deoxytalose nor its derivatives are present. Moreover, the oligosaccharide part is linked to the alaninol residue instead of the allo-threonine.