Experimental allergic encephalomyelitis: dissociation of neurological symptoms from lipid alterations in brain

Fifty years of biophysics in Argentina

In 1972, a group of young Argentinean scientists nucleated in the so-called Membrane Club constituted the Biophysical Society of Argentina (SAB). Over the years, this Society has grown and embraced new areas of research and emerging technologies. In this commentary, we provide an overview of the early stages of biophysics development in Argentina and highlight some of the notable achievements made during the past five decades. The SAB Annual Meetings have been a platform for intense scientific discussions, and the Society has fostered numerous international connections, becoming a hallmark of SAB activities over these 50 years. Initially centered on membrane biophysics, SAB focus has since expanded to encompass diverse fields such as molecular, cellular, and systems biophysics.

CNS myelin structural modification induced in vitro by phospholipases A2

Myelin is the self-stacked membrane surrounding axons; it is also the target of several pathological and/or neurodegenerative processes like multiple sclerosis. These processes involve, among others, the hydrolytic attack by phospholipases. In this work we describe the changes in isolated myelin structure after treatment with several secreted PLA2 (sPLA2), by using small angle x-ray scattering (SAXS) measurements. It was observed that myelin treated with all the tested sPLA2s (from cobra and bee venoms and from pig pancreas) preserved the lamellar structure but displayed an enlarged separation between membranes in certain zones. Additionally, the peak due to membrane asymmetry was clearly enhanced. The coherence length was also lower than the non-treated myelin, indicating increased disorder. These SAXS results were complemented by Langmuir film experiments to follow myelin monolayer hydrolysis at the air/water interface by a decrease in electric surface potential at different surface pressures. All enzymes produced hydrolysis with no major qualitative difference between the isoforms tested.

Composition-driven surface domain structuring mediated by sphingolipids and membrane-active proteins. Above the nano- but under the micro-scale: mesoscopic biochemical/structural cross-talk in biomembranes

Biomembranes contain a wide variety of lipids and proteins within an essentially two-dimensional structure. The coexistence of such a large number of molecular species causes local tensions that frequently relax into a phase or compositional immiscibility along the lateral and transverse planes of the interface. As a consequence, a substantial microheterogeneity of the surface topography develops and that depends not only on the lipid-protein composition, but also on the lateral and transverse tensions generated as a consequence of molecular interactions. The presence of proteins, and immiscibility among lipids, constitute major perturbing factors for the membrane sculpturing both in terms of its surface topography and dynamics. In this work, we will summarize some recent evidences for the involvement of membrane-associated, both extrinsic and amphitropic, proteins as well as membrane-active phosphohydrolytic enzymes and sphingolipids in driving lateral segregation of phase domains thus determining long-range surface topography.

Biophysics of sphingolipids II. Glycosphingolipids: An assortment of multiple structural information transducers at the membrane surface

Glycosphingolipids are ubiquitous components of animal cell membranes. They are constituted by the basic structure of ceramide with its hydroxyl group linked to single carbohydrates or oligosaccharide chains of different complexity. The combination of the properties of their hydrocarbon moiety with those derived from the variety and complexity of their hydrophilic polar head groups confers to these lipids an extraordinary capacity for molecular-to-supramolecular transduction across the lateral/transverse planes in biomembranes and beyond. In our opinion, most of the advances made over the last decade on the biophysical behavior of glycosphingolipids can be organized into three related aspects of increasing structural complexity: (1) intrinsic codes: local molecular interactions of glycosphingolipids translated into structural self-organization. (2) Surface topography: projection of molecular shape and miscibility of glycosphingolipids into formation of coexisting membrane domains. (3) Beyond the membrane interface: glycosphingolipid as modulators of structural topology, bilayer recombination and surface biocatalysis.

The Folch-Lees proteolipid induces phase coexistence and transverse reorganization of lateral domains in myelin monolayers

Solvent solubilized myelin membranes spread as monomolecular layers at the air-water interface show a heterogeneous pattern at all surface pressures. In order to asses the role of myelin protein and lipid components in the surface structuring we compared the topography, as seen by Brewster angle microscopy (BAM) and epifluorescence microscopy, of monolayers made from mixtures containing all myelin lipids (except gangliosides) and variable proportions of Folch-Lees proteolipid protein (PLP, the major protein component of myelin). The presence of the single PLP, in the absence of the other myelin proteins, can reproduce the surface pattern of the whole myelin extract films in a concentration-dependant manner. Moreover, a threshold mole fraction of PLP is necessary to induce the lipid-protein component reorganization leading to the appearance of a rigid (gray) phase, acting as a surface skeleton, at low surface pressures and of fractal clusters at high surface pressures. The average size of those clusters is also dependent on the PLP content in the monolayer and on the time elapsed from the moment of film spreading, as they apparently result from an irreversible lateral aggregation process. The transverse rearrangement of the monolayer occurring under compression was different in films with the highest and lowest PLP mole fractions tested.

Concerted modulation by myelin basic protein and sulfatide of the activity of phospholipase A2 against phospholipid monolayers

The effect of myelin basic protein (MBP) on the activity of phospholipase A2 (PLA2, EC 3.1.1.4) against monolayers of dilauroylphosphatidylcholine (dlPC) or dilauroylphosphatidic acid (dlPA) containing different proportions of sulfatide (Sulf) and galactocerebroside (GalCer) was investigated. MBP was introduced into the interface by direct spreading as an initial constitutive component of the lipid-protein film or by adsorption and penetration from the subphase into the preformed lipid monolayers. The effect of MBP on PLA2 activity depends on the type of phospholipid and on the proportion of MBP at the interface. At a low mole fraction of MBP, homogeneously mixed lipid-protein monolayers are formed, and the PLA2 activity against dlPC is only slightly modified while the degradation of dlPA is markedly inhibited. This is probably due to favorable charge-charge interactions between dlPA and MBP that interfere with the enzyme action. The PLA2 activity against either phospholipid is increased when the mole fraction of MBP exceeds the proportion at which immiscible surface domains are formed. GalCer has little effect on the modulation by MBP of the phospholipase activity. The effect of Sulf depends on its proportions in relation to MBP. The individual effects of both components balance each other, and a finely tuned modulation is regulated by the interactions of MBP with Sulf or with the phospholipid.

Passive transfer of experimental autoimmune encephalomyelitis in Wistar rats: dissociation of clinical symptoms and biochemical alterations

We have used passive transfer of myelin-reactive lymphocytes in the Wistar rat model of experimental autoimmune encephalomyelitis (EAE) to investigate the nature of the central nervous system immunopathological alterations induced by these cells. Mononuclear cells from lymph nodes or spleen from sick myelin/complete Freund's adjuvant-immunized donors did not transfer clinical disease. However, depending on the previous treatment of the transferred cells, recipients develop central nervous system biochemical and histological alterations. Fresh cells from lymph nodes immediately transferred after procurement from the sick EAE donor rat were capable of inducing the most significant diminution in the content of myelin basic protein, sulfatides, and 2',3'-cyclic nucleotide-3'-phosphohydrolase activity, with concomitant inflammatory infiltrations of white matter, principally in spinal cord and cerebellar lobules. Similar alterations were observed when animals were injected with spleen mononuclear cells activated in the presence of a nonspecific mitogen as concanavalin A. However, antigen-specific activated spleen cells generated by culturing in the presence of bovine myelin induced alterations to a lesser degree. Results point to a dissociation of the clinical disease from the central nervous system biochemical and histopathological lesions occurring in the EAE-transferred Wistar rats and indicate that these alterations in EAE are induced principally by T cells activated in vivo rather than by cells activated in vitro by myelin antigens. Therefore, these findings suggest a possible participation of lymphocytes unlike the encephalitogenic T cells in the induction of the described alterations and provide a useful model to explore further the subclinical responses to this experimental disease.

Molecular interactions of the major myelin glycosphingolipids and myelin basic protein in model membranes

The molecular organization, interactions, phase state and membrane-membrane interactions of model membranes containing cerebroside (GalCer), sulfatide (Sulf) and myelin basic protein (MBP) were investigated. Sulf shows a larger cross-sectional area than GalCer, in keeping with the lateral electrostatic repulsions in the negatively charged polar head group. The interactions of GalCer with different phospholipids are similar while those with Sulf depend on the phosphoryl choline moiety in the phospholipid. MBP induces a decrease of the phase transition temperature in both lipids but with Sulf this occurs at lower proportions of MBP. In mixtures of Sulf with phosphatidylcholine MBP induces phase separation among Sulf-rich and PC-rich domains. Extensive apposition of bilayers containing Sulf is induced by MBP while GalCer interferes with this process. Few membrane interactions proceed to bilayer merging or whole bilayer fusion and the glycosphingolipids help preserve the membrane integrity.

Time course of biochemical and immunohistological alterations during experimental allergic encephalomyelitis

A comprehensive biochemical, immunological and histological study was undertaken during different stages of experimental allergic encephalomyelitis (EAE). Wistar rats with EAE induced by sensitization with bovine myelin showed a maximum decrease of body weight 14-16 days post-inoculation (dpi), coincident with the appearance of the paralysis symptom (acute period). Quantitation of some brain components indicated a temporal dissociation among the alterations observed. The higher diminution of myelin basic protein (MBP) occurred at 6 dpi and then increased to reach 21 dpi, a normal value. Also, the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase was reduced by 40% with respect to control animals only at 6 dpi. The total lipid content was normal; however, among the individual lipids, sulfatides were principally degraded during the acute stage but the amount of cerebrosides was decreased during the recovery period (29-40 dpi). Free cholesterol was similar in both groups of animals, whereas cholesterol esters were detected in EAE animals from 14 to 40 dpi. Central nervous system meningeal and parenchymal infiltration with mononuclear cells was recognized principally at 14 dpi, but some of cells were still present at 40 dpi. Deposits of immunoglobulins in the infiltrated regions as well as in spinal cord motor neurons were observed among 14-29 dpi. Total circulating antibodies to MBP began to increase at 14 dpi, reaching a plateau at 21 dpi and then maintaining this value until 40 dpi. However, the population of anti-MBP antibodies that also recognizes the neuronal protein synapsin was only present at 14 dpi. The present results suggest that the neurological symptoms can be related to some early changes in the myelin membrane followed by alterations involving neuronal structures. The existence of immunological factors against some epitopes in MBP that also recognize a synaptosomal protein might account, at least in part, for the axonal damage and disruption of the normal interneuronal activity in EAE and lead together with the alterations in some specific myelin constituents and the concomitant CNS inflammatory process to the observed hindlimb paralysis.

Experimental autoimmune encephalomyelitis: antigen-induced inhibition of biochemical and immunohistological alterations

A comprehensive biochemical, immunological, and histological study was undertaken during suppression of experimental autoimmune encephalomyelitis (EAE) induced by antigen-specific inhibition of the immune response. Pretreatment of Wistar rats by intraperitoneal administration of low doses of saline-soluble bovine myelin or myelin basic protein (MBP) but not with ovalbumin suppresses the appearance of the clinical symptoms of EAE induced by sensitization with bovine myelin in complete Freund's adjuvant. Analysis of the central nervous system (CNS) of animals pretreated with MBP or whole myelin shows inhibition of the diminution of MBP and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) activity observed in the EAE animals or in rats pretreated with ovalbumin. With respect to the CNS lipid content, these suppressive treatments abolish the increase in esterified cholesterol and partially revert the diminution in the content of cerebrosides and total cholesterol characteristic of the acute stage of the disease. Concomitantly, meningeal and parenchymal infiltration with mononuclear cells and deposits of immunoglobulins in the infiltrated regions as well as in spinal cord motor neurons were reduced. Analysis of the humoral response to myelin antigens shows that all EAE as well as treated animals developed antibodies to MBP and other myelin proteins. However, a higher incidence and level of these antibodies was observed in nontreated EAE animals and MBP- and ovalbumin-treated rats, while rats treated with total bovine myelin showed a highly reduced humoral response. The present results indicate that intraperitoneal treatment with soluble forms of myelin antigens, concomitant with the suppression of the clinical symptoms of the disease, markedly reduces the biochemical and histological alterations occurring in EAE animals and produces changes in the autoimmune humoral response.

Cellular immune crossreactivity between myelin basic protein and synapsin in rats with experimental allergic encephalomyelitis

We previously demonstrated that antibodies against myelin basic protein (MBP) obtained from animals with experimental allergic encephalomyelitis (EAE), induced with MBP and purified by affinity chromatography, have the property to recognize a neuronal protein, synapsin Ia and Ib. To investigate whether this crossreactivity also occurs at the cellular level, we purified spleen and lymph node mononuclear cells from rats sensitized with MBP or synapsin using polystyrene plates coated with the respective antigen. We observed that animals injected with MBP have T lymphocytes that bind both antigens. Using the same system, each purified cell population was confronted again to the studied antigens. The anti-MBP cells recognized once more epitopes of MBP and about 40% of them also recognized synapsin. On the other hand, cells that first were attached to synapsin, in the second exposure to antigens bound to MBP and synapsin in similar amounts. Double immunofluorescent labeling of the mononuclear cells isolated from animals injected with bovine myelin or MBP showed that the same lymphocyte was able to recognize MBP as well as synapsin. In both experimental systems the quantitative results were similar indicating that in bovine myelin- or MBP-sensitized animals practically all the cells that recognize synapsin are anti-MBP cells, and of the total cells raised against MBP, around 40% of them show this crossreactivity. On the contrary, animals injected with synapsin have cells that bind to this protein but not to MBP indicating that the described crossreactivity, as observed at humoral level, is only in one way.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical changes in central nervous system membranes in chronic-relapsing experimental allergic encephalomyelitis

Biochemical studies of myelin fractions were undertaken on Lewis rats during various time-points in the development of chronic-relapsing experimental allergic encephalomyelitis (CR-EAE). Lipid and protein composition of myelin fractions obtained by sucrose density gradient centrifugation at 10, 19, 24, and 66 d postinduction (pi) were determined by high-performance thin-layer chromatography (HPTLC) and sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS PAGE), respectively. When comparing the myelin fractions of CR-EAE affected animals with those of controls, main differences were observed at 10 d pi. These changes were particularly evident in the light myelin fraction, where a decrease in the percentage of phosphatidylethanolamine and small basic protein relative to the total lipids and proteins of the fraction were observed. At 19 and 24 d pi no biochemical differences were present in both fractions. At 66 d pi, differences in the lipid composition were observed again only in the light myelin fraction. These findings suggest that the light myelin fraction is the most sensitive, particularly at the early stages of the disease, and must play a key role in demyelinating processes.

Identification as synapsin of a synaptosomal protein immunoreacting with anti-myelin basic protein antiserum

Rat brain proteins able to react with anti-myelin basic protein antiserum, raised under conditions to induce experimental allergic encephalomyelitis in rabbits, were examined by immunoblot methods after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Apart from the four forms of myelin basic protein present in rat brain, the antiserum detected other proteins of higher molecular weight. Subcellular fractionation shows that these high-molecular-weight proteins are relatively concentrated in a synaptosome-enriched fraction compared to a myelin fraction. A major protein fraction immunorelated to myelin basic protein migrated in the gels as a doublet with apparent molecular weights of approximately 80K and 86K; these proteins were tentatively identified as synapsin Ia and Ib. A purified synapsin preparation analyzed by immunoblot after two-dimensional gel electrophoresis also reacted with anti-myelin basic protein antisera. When the serum was purified by affinity chromatography on a myelin basic protein-conjugated Sepharose column the nonadsorbed material lost this activity whereas the eluted antibodies reacted with myelin basic protein and synapsin. In addition, sequence amino acid comparison of decapeptides showed some homology between these two proteins. A possible implication of immunological agents against myelin basic protein cross-reacting with extra-myelin proteins in the process of experimental allergic encephalomyelitis is considered.

Molecular interactions and thermotropic behavior of glycosphingolipids in model membrane systems

The oligosaccharide chain of glycosphingolipids (GSLs) has a marked influence on their thermotropic behavior, intermolecular packing and surface electrical potential. The transition temperature and enthalpy of GSLs decrease proportionally to the complexity of the polar head group and show a linear dependence with the intermolecular spacings. Interactions occurring among GSLs and phospholipids induce changes of the molecular area and surface potential that depend on the type of GSLs. Increasing proportions of phospholipids perturb the thermodynamic properties of the GSLs up to a point where phase separated phospholipid domains separate out but no phase separation of pure GSLs occurs. Heterogeneous equilibria among different structures occur for some systems. Large changes of the molecular free energy, eccentricity, asymmetry ratio and phase state of the GSLs-containing structure can be triggered by small changes of the molecular parameters, lipid composition and lateral surface pressure. The thermotropic behavior of GSLs is considerably perturbed by myelin basic protein. Phase separation occurs depending on the amount of protein and type of GSLs. The protein induces a decrease of the lipid molecular area, the more so the more complex the oligosaccharide chain in the GSLs. These membrane systems can not be described only on the basis of the individual properties of the molecules involved in a simple causal manner. Still scarcely explored long range thermodynamic, geometric and field effects that belong simultaneously to the intervening molecules, to the morphological properties of the structure involved and to the aqueous environment, are important determinants of their behavior.

Biochemical changes in central nervous system membranes in experimental allergic encephalomyelitis

Biochemical and morphological studies of myelin subfractions were undertaken on Lewis rats during the early stage of the development of experimental allergic encephalomyelitis (EAE). Myelin subfractions, obtained by sucrose density gradient centrifugation at 10 days post-induction, were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and assayed for 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity. Aliquots were processed for electron microscopic analysis. When comparing the myelin subfractions of EAE-affected animals with those of controls, differences were observed only in the light fractions, i.e., a decrease in the specific activity of CNPase and in the percentage of basic proteins relative to the total proteins of the fraction. This decrease was also evident in the basic protein/proteolipid protein ratio which is frequently used in the literature. In addition, electron microscopic observations demonstrated strong differences in the morphology of the same fraction. These findings suggest that the light fraction is the most sensitive in the early stages of the disease and must play a key role in demyelinating processes.

Chemical analysis of organotypic cultures of mouse spinal cord in normal, demyelinative, and nondemyelinative conditions

Several biochemical parameters were analyzed in cultured embryonic mouse spinal cord during various stages of normal myelinogenesis or demyelination. In cultures demyelinated by exposure to anti-whole CNS tissue serum plus complement, the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37) was decreased 70%, whereas in cultures that did not show morphological changes with complement-inactivated anti-CNS serum or anti-myelin basic protein serum, the activity was 30% lower than in control cultures. The lipid composition of these cultures was quantitated by means of high-performance thin-layer chromatography densitometry technique. Cultures with normal nutrient medium alone or with the addition of 5% normal rabbit serum plus 10% guinea pig serum had 30% of the total lipid content of that present in newborn mouse spinal cord of the corresponding age. There were, however, relatively more lysophospholipids, cholesterol esters, triglycerides, and free fatty acids and less phosphatidylethanolamine and galactolipids in cultures as compared with normal spinal cord. Explants demyelinated by exposure to anti-CNS serum plus complement demonstrated principally a 70% decrease in the content of galactolipids with respect to normal cultures. When complement was inactivated, total lipids increased 42% (with increases of 40-70% in individual lipids). Inclusion of anti-myelin basic protein serum plus complement in the medium produced no significant changes in the lipid composition of the cultures.

Central nervous system lipid alterations in rats with experimental allergic encephalomyelitis and its suppression by immunosuppressive drugs

Rats with experimental allergic encephalomyelitis (EAE) induced with myelin or spinal cord show decreases in the content of sulphatides and cerebrosides and increases in the level of esterified cholesterol in the CNS. In this work it is shown that brain sulphatide changes can be obtained by injection of mixtures containing glycosphingolipids. Alterations in the content of cerebrosides occur when the injection mixture contains cerebrosides. The alterations of sulphatides and cholesterol ester induced by injection of spinal cord could be suppressed by treatment with immunosuppressive drugs (dexamethasone, cyclophosphamide and 6-mercaptopurine) able to prevent clinical signs of EAE.

Membrane instability induced by purified myelin components. Its possible relevance to experimental allergic encephalomyelitis

The fusogenic properties of purified myelin components in a system employing chicken erythrocytes were studied. Sulphatides, myelin basic protein and the apoprotein of Folch-Lees proteolipid were capable of individually inducing membrane fusion in the presence of Ca2+. By contrast, cerebrosides or a mixture of sulphatides and myelin basic protein (molar ratio 19 : 1) did not show such effect. The fusogenic ability of sulphatide was correlated to its behaviour in mixed monolayers with phospholipids at the air-water interface. Mixed films of sulphatides with phosphatidylcholine or sphingomyelin but not with phosphatidylethanolamine showed reductions of molecular packing and surface potential similar to those found for other fusogenic compounds. The effects of myelin components described could be of importance in the membrane instability and vesicular disruption of myelin occurring in demyelinative disorders.