Platelets from eclampsia patients have reduced membrane microviscosity and lower activities of the signalling enzymes

Dissecting the role of the S1P/S1PR axis in health and disease

Sphingosine-1-phosphate (S1P) is a pleiotropic sphingophospholipid generated from the phosphorylation of sphingosine by sphingosine kinases (SPHKs). S1P has been experimentally demonstrated to modulate an array of cellular processes such as cell proliferation, cell survival, cell invasion, vascular maturation, and angiogenesis by binding with any of the five known G-protein-coupled sphingosine 1 phosphate receptors (S1P1-5) on the cell surface in an autocrine as well as a paracrine manner. Recent studies have shown that the S1P receptors (S1PRs) and SPHKs are the key targets for modulating the pathophysiological consequences of various debilitating diseases, such as cancer, sepsis, rheumatoid arthritis, ulcerative colitis, and other related illnesses. In this article, we recapitulate these novel discoveries relative to the S1P/S1PR axis, necessary for the proper maintenance of health, as well as the induction of tumorigenic, angiogenic, and inflammatory stimuli that are vital for the development of various diseases, and the novel therapeutic tools to modulate these responses in oral biology and medicine.

J. Lysophosphatidic acid as a potential target for treatment and molecular diagnosis of epithelial ovarian cancers

Az ováriumtumorok mortalitása a legmagasabb a nőgyógyászati tumorok között. Ez egyrészt a késői diagnózisnak, másrészt a hatásos terápia hiányának következménye. Az ováriumtumorok karcinogenezise és metasztázisképzése egy komplikált genetikai, molekuláris és biokémiai folyamatsor eredménye. A lizofoszfátsav (LPA) termelésének, receptorstátusának és szignáltranszdukciós útvonalának abnormalitása gyakran megtalálható az ováriumtumorokban, ami azt sejteti, hogy az LPA nagyon fontos szerepet játszik ennek a betegségnek a kialakulásában és patofiziológiájában. Így jogosan feltételezhetjük, hogy az LPA-szignálkaszkád számos célpontot szolgáltat a molekuláris kezelési módok kialakítására és jó példát mutat arra, hogyan lehet új diagnosztikus és terápiás módszereket kialakítani egyes betegségek ellen. Az LPA-t lebontó és termelő enzimcsaládoknak csak a közelmúltban történt felfedezése és a receptorspecifikus molekulák kifejlesztése új fejezetet nyithat e potenciálisan halálos betegség kezelésében. Ebben az összefoglaló tanulmányban ismertetjük, hogy a tumorsejtekben lévő LPA-t lebontó enzimek aktivitása csökkent, és ez hozzájárul a tumor progressziójához. Ugyanezen enzimek mesterségesen létrehozott, fokozott aktivitása csökkenti a tumorsejtek növekedését és elősegíti a fiziológiás viszonyok helyreállását. Bemutatjuk azokat az irodalmi adatokat, amelyek egyértelműen bizonyítják, hogy a lipidfoszfát-foszfatáz enzimek hatásukat a sejten kívüli LPA lebontásával érik el. Minthogy ez a lebontás extracellulárisan történik, ez megmagyarázza a „bystander-effect” előfordulását, amit szintén ismertetünk. Az LPA-lebontás és -termelés enzimjei, illetve az LPA-t kötő receptorok kitűnő célpontok új molekuláris terápia kidolgozására. A különböző LPA-izoformák és más lizofoszfolipidek szintváltozásainak korai detektálása segíthet a tumor korai diagnosztizálásában, illetve később a kezelés hatékonyságának követésében. A közelmúlt jelentős LPA-szignálkaszkáddal kapcsolatos kutatási eredményei azt sejtetik, hogy azok jelentős szerepet fognak játszani ennek a még mindig halálos betegségnek a kezelésében, de további kutatások szükségesek a részletek pontos megértéséhez.

Balance of S1P1 and S1P2 signaling regulates peripheral microvascular permeability in rat cremaster muscle vasculature

Sphingosine-1-phosphate (S1P) regulates various molecular and cellular events in cultured endothelial cells, such as cytoskeletal restructuring, cell-extracellular matrix interactions, and intercellular junction interactions. We utilized the venular leakage model of the cremaster muscle vascular bed in Sprague-Dawley rats to investigate the role of S1P signaling in regulation of microvascular permeability. S1P signaling is mediated by the S1P family of G protein-coupled receptors (S1P(1-5) receptors). S1P(1) and S1P(2) receptors, which transduce stimulatory and inhibitory signaling, respectively, are expressed in the endothelium of the cremaster muscle vasculature. S1P administration alone via the carotid artery was unable to protect against histamine-induced venular leakage of the cremaster muscle vascular bed in Sprague-Dawley rats. However, activation of S1P(1)-mediated signaling by SEW2871 and FTY720, two agonists of S1P(1), significantly inhibited histamine-induced microvascular leakage. Treatment with VPC 23019 to antagonize S1P(1)-regulated signaling greatly potentiated histamine-induced venular leakage. After inhibition of S1P(2) signaling by JTE-013, a specific antagonist of S1P(2), S1P was able to protect microvascular permeability in vivo. Moreover, endothelial tight junctions and barrier function were regulated by S1P(1)- and S1P(2)-mediated signaling in a concerted manner in cultured endothelial cells. These data suggest that the balance between S1P(1) and S1P(2) signaling regulates the homeostasis of microvascular permeability in the peripheral circulation and, thus, may affect total peripheral vascular resistance.

Leishmania donovani Affects Antigen Presentation of Macrophage by Disrupting Lipid Rafts

Leishmania donovani-infected splenic macrophages and P388D1 (P388D1(I)) failed to activate T cells in response to low dose of exogenous peptide. The membrane fluidity of P388D1(I) was greater than that of the normal counterpart P388D1(N), but could be reduced either by exposing the cell below phase transition point or by loading cholesterol into membrane (L-P388D1(I)), and this was associated with enhanced Ag-presenting ability of P388D1(I). Presentation of endogenous leishmanial Ag, kinetoplastid membrane protein-11, was also defective, but could be corrected by loading cholesterol into membrane. Because membrane rafts are important for Ag presentation at a low peptide dose, raft architecture of P388D1(I) was studied using raft (CD48 and cholera toxin-B) and non-raft (CD71) markers in terms of their colocalization with I-A(d). Binding of anti-CD48 mAb and cholera toxin B subunit decreased significantly in P388D1(I), and consequently, colocalization with I-A(d) was not seen, but this could be restored in L-P388D1(I). Conversely, colocalization between I-A(d) and CD71 remained unaffected regardless of the presence or the absence of intracellular parasites. P388D1(N) and L-P388D1(I), but not P388D1(I), formed peptide-dependent synapse with T cells quite efficiently and this was found to be corroborated with both intracellular Ca2+ mobilization in T cells and IL-2 production. This indicated that intracellular parasites disrupt the membrane rafts, possibly by increasing the membrane fluidity, which could be corrected by making the membrane rigid. This may be a strategy that intracellular L. donovani adopts to evade host immune system.

Lysophospholipids increase ICAM-1 expression in HUVEC through a Gi- and NF-kappaB-dependent mechanism

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S-1-P) are both low molecular weight lysophospholipid (LPL) ligands that are recognized by the Edg family of G protein-coupled receptors. In endothelial cells, these two ligands activate Edg receptors, resulting in cell proliferation and cell migration. The intercellular adhesion molecule-1 (ICAM-1, CD54) is one of many cell adhesion molecules belonging to the immunoglobulin superfamily. This study showed that LPA and S-1-P enhance ICAM-1 expression at both the mRNA and protein levels in human umbilical cord vein endothelial cells (HUVECs). This enhanced ICAM-1 expression in HUVECs was first observed at 2 h postligand treatment. Maximal expression appeared at 8 h postligand treatment, as detected by flow cytometry and Western blotting. Furthermore, the effects of S-1-P on ICAM-1 expression were shown to be concentration dependent. Prior treatment of HUVECs with pertussis toxin, a specific inhibitor of G(i), ammonium pyrrolidinedithiocarbamate and BAY 11-7082, inhibitors of the nuclear factor (NF)-kappaB pathway, or Clostridium difficile toxin B, an inhibitor of Rac, prevented the enhanced effect of LPL-induced ICAM-1 expression. However, pretreatment of HUVECs with exoC3, an inhibitor of Rho, had no effect on S-1-P-enhanced ICAM-1 expression. In a static cell-cell adhesion assay system, pretreatment of LPL enhanced the adhesion between HUVECs and U-937 cells, a human mononucleated cell line. The enhanced adhesion effect could be prevented by preincubation with a functional blocking antibody against human ICAM-1. These results suggest that LPLs released by activated platelets might enhance interactions of leukocytes with the endothelium through a G(i)-, NF-kappaB-, and possibly Rac-dependent mechanism, thus facilitating wound healing and inflammation processes.

Level of sialic acid residues in platelet proteins in diabetes, aging, and Hodgkin's lymphoma: a potential role of free radicals in desialylation

The present study evaluated the levels of sialic acid and carbonylation in platelet proteins from diabetes, old age, and Hodgkin's lymphoma cases and explored the role of free radicals in desialylation. Sialic acid and carbonylation were estimated in platelet suspension obtained from 10 healthy adult control subjects, 20 elderly healthy persons, 20 cases with diabetes, and 10 with Hodgkin's lymphoma. The level of sialic acid residues in platelets was found to be significantly lower and the carbonylation of proteins was higher in old age, diabetes, and lymphoma cases in comparison to controls. The level of carbonylation correlated with desialylation in these cases. In vitro treatment of platelets with free radicals was found to cause desialylation and to increase the carbonyl content. Addition of 2-mercaptoethanol, an antioxidant, significantly attenuated the above effects. The study indicates the possible role of free radicals in desialylation of platelet proteins in the above clinical conditions.

Changes in membrane microenvironment and signal transduction in platelets from NIDDM patients-a pilot study

BACKGROUND

Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by the presence of abnormally active platelets in the circulation, leading to increased incidence of thrombotic complications. In this study, we have attempted to understand the pathophysiology of the platelets in NIDDM.

METHODS

Platelet aggregation was induced by thrombin receptor-activating peptide or epinephrine. Membrane fluidity was derived from the steady-state fluorescence anisotropy of diphenylhexatriene incorporated in the membrane. The phosphotyrosine content of the platelet proteins was probed using specific monoclonal antibodies. The extent of calpain activity was assessed from the proteolysis of calpain substrates.

RESULTS

Aggregation was significantly enhanced (p<0.001) in the platelets obtained from the cases of NIDDM. Anisotropy measurements reflected a significant increase in the microviscosity of platelet membranes from 3.315 (+/-0.103) in the control to 4.153 (+/-0.119) in NIDDM. Proteins of relative mobilities of 131, 100, 47 and 38 kDa were found to remain phosphorylated on tyrosine in the resting platelets obtained from NIDDM patients, while they were not phosphorylated in the control counterparts. This was associated with heightened activity of the calcium-dependent thiol protease, calpain, in NIDDM.

CONCLUSIONS

Taken together, these data indicated significant changes in the signaling mechanism in the platelets obtained from NIDDM, which could lead to platelet hyperactivity in this disease.

Evidence for a physiological role for membrane rafts in human platelets

We have investigated raft formation in human platelets in response to cell activation. Lipid phase separation and domain formation were detected using the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (diI-C(18)) that preferentially partitions into gel-like lipid domains. We showed that when human platelets are activated by cold and physiological agonists, rafts coalesce into visible aggregates. These events were disrupted by depletion of membrane cholesterol. Using Fourier transform infrared spectroscopy (FTIR), we measured a thermal phase transition at around 30 degrees C in intact platelets, which we have assigned as the liquid-ordered to the liquid-disordered phase transition of rafts. Phase separation of the phospholipid and the sphingomyelin-enriched rafts could be observed as two phase transitions at around 15 and 30 degrees C, respectively. The higher transition, assigned to the rafts, was greatly enhanced with removal of membrane cholesterol. Detergent-resistant membranes (DRMs) were enriched in cholesterol (50%) and sphingomyelin (20%). The multi-functional platelet receptor CD36 selectively partitioned into DRMs, whereas the GPI-linked protein CD55 and the major platelet integrin alpha(IIb)beta(3a) did not, which suggests that the clustering of proteins within rafts is a regulated process dependent on specific lipid protein interactions. We suggest that raft aggregation is a dynamic, reversible physiological event triggered by cell activation.

Altered membrane fluidity and signal transduction in the platelets from patients of thrombotic stroke

Several earlier studies have implicated platelet activation with the pathogenesis of thrombotic stroke. In this report we have studied the changes in membrane physical microenvironment and signal transduction in the platelets obtained from the patients with thrombotic stroke. Aggregation induced by the synthetic agonist thrombin receptor-activating peptide was significantly enhanced (p < 0.001) in the platelets obtained from the patients. Steady-state fluorescence anisotropy measurements using diphenylhexatriene reflected a significant increase in membrane microviscosity from 3.315 (+/- 0.103) in the control to 4.600 (+/- 0.119) in the stroke. Proteins of relative mobilities of 131, 100, 47 and 38 kDa were found to remain phosphorylated on tyrosine in the resting platelets obtained from thrombotic stroke patients while they were not phosphorylated in the control counter-parts. Besides, calpain, a calcium dependent thiol protease present in the platelets, was found to remain active in this disease as reflected from the proteolysis of calpain substrates. Taken together, these data indicated abnormal circulating platelets in the patients ofthrombotic stroke. which could contribute to the etiopathogenesis of this disease.

Macrophage heterogeneity, antigen presentation, and membrane fluidity: implications in visceral Leishmaniasis

Morphological and functional heterogeneity of the splenic macrophage (M phi) population was studied in Leishmania donovani (LD) infected BALB/c mice. On a discontinuous percoll gradient two distinct M phi populations were separated. They differed significantly in size as evident from Scanning Electron Microscopy (SEM). Morphologically, the bigger M phi (LM) showed surface projections, whereas the smaller M phi (SM) was round. As regards the antigen-presenting abilities, the LM of infected animals showed defective antigen-presenting abilities at a later stage of the disease, i.e. 6 months post infection ((6)I-LM) but not earlier, whereas the SM population remained functionally intact throughout the course of the infection. Further, the (6)I-LM showed a much enhanced Ad status as compared to their controls. Interestingly, both the (6)I-LM and the control set showed a comparable level of binding of a known A(d) restricted peptide. Despite the presence of sufficient A(d) molecules and the ability to bind the appropriate peptide, (6)I-LM were unable to stimulate peptide specific T-cell hybridoma. Further, the (6)I-LM showed an increase in membrane fluidity and distorted morphology with membrane fissure and blebs as evident from SEM. It is possible that an increase in the membrane fluidity may lead to the defective antigen-presenting ability of (6)I-LM. Thus, the LD infection functionally keep the (6)I-LM out of antigen presentation and this may contribute to the defective cell mediated immune response in leishmaniasis.